A PROJECT REPORT ONAUTOCLUTCH FOR AUTOMOBILE Submitted in partial fulfilment of the requirements For the award of B.TECH ENGINEERING IN ____________________________________ ENGINEERING SUBMITTED BY -------------------- (--------------) --------------------- (---------------) --------------------- (---------------) DEPARTMENT OF _______________________ ENGINEERING __________COLLEGE OF ENGINEERING AFFILIATED TO ___________ UNIVERSITY 1 CERTIFICATE This is to certify that the dissertation work entitled “AUTOCLUTCH FOR AUTOMOBILE” is the work done by _______________________________________________submitted in partial fulfilment for the award of ‘DIPLOMA IN ENGINEERING’ in __________________________Engineering from______________ SCHOOL of Engineering affiliated to _________ University, ________________ ____________ (Head of the department,______) (Assistant Professor) 2 ACKNOWLEDGEMENT The satisfaction and euphoria that accompany the successful completion of any task would be incomplete without the mentioning of the people whose constant guidance and encouragement made it possible. We take pleasure in presenting before you, our project, which is result of studied blend of both research and knowledge. We express our earnest gratitude to our internal guide, Assistant Professor ______________, Department of __________, our project guide _____________________, for his constant support, encouragement and guidance. We are grateful for his cooperation and his valuable suggestions. Finally, we express our gratitude to all other members who are involved either directly or indirectly for the completion of this project. 3 DECLARATION We, the undersigned, declare that the project entitled ‘AUTOCLUTCH FOR AUTOMOBILE’, being submitted in partial fulfilment for the award of B-tech in Engineering in _________________________Engineering, affiliated to _________ University, is the work carried out by us. __________ _________ _________ __________ _________ _________ 4 ABSTRACT Our main focus in this project is to design a small auto-clutch for automobile system or for a car system. In this project we have to studied the automatic clutch mechanism in vehicles. The fabrication part of it has been considered with almost case for its simplicity and economy, such that this can be accommodated as one of the essential tools on automobile garages. With automatic clutch system for car you can convert a manual car to semi-automatic at the touch of button. This automatically activates the clutch pedal movement in a completely controlled system. Then the car will be driven by using just the brake and accelerator. Features of using this type of system is changing gear without using your foot to operate the clutch and more fuel economical then an automatic. Auto-clutch comprises of two units first is elaborate electronic control and the second is electric motor. 5 Twist the key. Auto transmissions use something called a torque converter. Sure. but the practice is quite harassing within the clogged confines of the city. So what exactly is an automatic gearbox? Well. making that rev needle dance within the power band. Now this function of shifting gears automatically can be achieved via various means. The flexibility of a CVT allows it to be tuned for better fuel economy or performance. A DCT or a dual-clutch transmission is an advanced version of a semi-automatic system that utilizes two separate clutches for odd and even gear sets. The system is capable of shifting gears more quickly than conventional automatic transmission. an automatic gearbox can change gear ratios on its own as the vehicle moves without the driver having to shift gears manually. 6 . SemiAutomatic transmissions. The simple alternative to those irritating manual shifts is to go with a car with an auto tranny. and hence has application in cars where driving pleasure and quick shifting response cannot be compromised. Finally. Automatic Transmissions differ in operation to CVTs or semi-automatics. So what exactly is this auto transmission? Is there any substantial difference between various types of auto transmissions available today? Which cars come with the option of an Auto ‘box and what are the associated advantages and disadvantages? Let’s try and find the answers to some of these questions. and DCTs (Dual Clutch Transmissions). instead of clutch to manage the relation between engine speeds and transmission gears. This system allows the driver to override auto shifts manually if he so desires. This system costs substantially more than your usual automatic transmissions. which is controlled through electro-hydraulic means. these transmissions are divided in four basic categories – Automatic transmissions. and not a torque converter. you would love to use that shifter as you steer your baby around a set of twisties. On the other hand. put the selector in D and you won’t have to touch the gear shifter or depress the clutch lever before you reach your destination. Based on the method applied to shift the gears automatically. a semi-automatic transmission facilitates the shift in gear ratios through a clutch-like setup. a CVT uses a belt or some other means of torque transmission to allow an infinite number of gear ratios between two fixed highest and lowest ratios. CVTs (Continuously Variable Transmissions).INTRODUCTION Automatic transmission cars are getting increasingly popular within the urban-scape as crammed streets make shifting gears an undesirable job. although the final shifting is still taken care of by the hydraulics. however. From the Santro. Here’s a list of some of the mainstream cars that are available with the option of an automatic transmission. to the i10. but such advanced systems are available only in premium cars and are very expensive. there are some disadvantages as well. and sometimes it takes much longer than you would like to shift a gear higher or lower. The Engine Control Unit. Apart from slow response. Of late. or the ECU. Modern transmissions have come very close. even Maruti has shown intent to offer auto transmission as an option in its cars. only Hyundai offers an auto transmission option across its model range.000 to 1 lakh more expensive than their manual transmission counterparts. auto transmissions are also known be less fuel efficient than their manual counterparts. Mainstream car companies in India are yet to take the automatic option seriously. are expensive. auto transmission variant are Rs 50. especially VW’s DSG have managed to go around the problem of slow response. every small car from the company comes equipped with an automatic transmission option. auto transmissions cars are not as responsive as their manual transmission counterparts. To start with. • • • • • • • • • • Maruti Suzuki A-Star Hyundai Santro Xing Hyundai i10 Hyundai i20 Hyundai Verna Honda City Honda Civic Skoda Laura Chevrolet Cruze VW Jetta 7 . The company launched the AT variant of its A-star a few months back. which is the brain of a car.While auto transmissions bring along great convenience. and are even better than manual transmissions in response time. The shifts are not as quick. This reduces driving pleasure and the overtaking capabilities of the car to an extent. isn’t in most cases as intelligent as the human brain to derive the best fuel efficiency and performance from the engine. to the i20. Advanced DCTs. Of all the volumes players that we have in the Indian car market. even in the case of small cars. Such systems. Also. Auto-clutch is mainly comprised of two units. automatic clutch system. The engagement of the clutch is then simulated using the acquired model. the usability of auto transmission actually cuts across genders and age groups. car automatic clutch. Considered an option only for the females in India. In traffic when releasing the brake pedal car creeps forward like an automatic. AUTOMATIC CLUTCH Automatic clutch. especially for the urban market. brake pedal. Then the car can be driven by using just the brake and accelerator. Based on this analysis a control strategy is suggested and the designed control law is implemented. After all. It can be available in any types of car and the car can be driven by using just the brake and accelerator This is an intelligent electronically controlled mechanism which enables the driver to select the gears simply by pressing the button on the gear level and shifting. particularly in traffic situations. This automatically activate the clutch pedal movement in a completely controlled system. who doesn’t want to add a bit of convenience to his drive… In this report the dynamic behaviour of an automotive clutch is analyzed using dynamical models. The first elaborate electronic control unit controls the second compact electric motor. its popularity will increase as awareness spreads and traffic scenario becomes even more annoying.There is ample evidence that more and more car companies are realizing the need of presenting an auto option in their cars. Although an auto transmission is not as popular in India as in the more developed nations. The electric motor is mechanically connected to the clutch to the clutch pedal with a cable. Auto-clutch takes the fatigue away from having to operate the clutch pedal continuously. The accelerator pedal. The auto clutch converts the manual car into semi-automatic by pressing a button. auto clutch system for car which is mainly developed to match hectic traffic condition suitable to all kind of cars. hand brake and 8 . 1 Automatic clutch NEED FOR AUTOMATION: Automation can be achieved through computers. pneumatics. robotics etc. pneumatic form an attractive medium for low cost automation Automation plays an important role in automobile. FIGURE 1. The entire system is installed in the interior compartment of the car.road speed are monitored for signals which result in automatic activation of the system. of these sources. hydraulics. The automobile vehicle is being atomized for the following reasons. Nowadays almost all the automobile vehicle is being atomized in order to product the human being. 9 . freeing the driver from having to shift gears manually.-To achieve high safety -To reduce man power -To increase the efficiency of the vehicle -To reduce the work load -To reduce the vehicle accident -To reduce the fatigue of works -To high responsibility -Less maintenance cost BLOCK DIAGRAM AUTOMATIC TRANSMISSION An automatic transmission (also called automatic gearbox) is a type of motor vehicle transmission that can automatically change gear ratios as the vehicle moves. Most automatic transmissions have a defined 10 . often via paddle shifters. with the option being an automated transmission such as a conventional automatic. by using the transmission's computer to change gear. AUTOMATIC TRANSMISSION MODE In order to select the transmission operating mode. Some machines with limited speed ranges or fixed engine speeds. In order to select modes. the driver must push a button in (called the shift lock button) or pull the 11 . but controls the clutch through electro-hydraulic means. such as some forklifts and lawn mowers. In contrast. The ability to shift gears manually. can also be found on certain automated transmissions. there are also other types of automated transmissions such as a continuously variable transmission (CVT) and semi-automatic transmissions. A conventional manual transmission is frequently the base equipment in a car. A semi-automatic retains a clutch like a manual transmission. semi-automatic. automatic transmissions differ significantly in internal operation and driver's feel from semi-automatics and CVTs. An automatic uses a torque converter instead of a clutch to manage the connection between the transmission gearing and the engine. except that most automatic selectors on the floor do not move in the same type of pattern as a manual lever. Similar but larger devices are also used for heavy-duty commercial and industrial vehicles and equipment. semi-automatics and CVTs. most automatic levers only move vertically). the driver moves a selection lever located either on the steering column or on the floor (as with a manual on the floor. that free the driver from having to shift gears manually. or to manually select specific gear ratios. Besides automatics.set of gear ranges. if for example the driver were redlining the engine. only use a torque converter to provide a variable gearing of the engine to the wheels. or CVT. a CVT uses a belt or other torque transmission scheme to allow an "infinite" number of gear ratios instead of a fixed number of gear ratios. Despite superficial similarity to other transmissions. often with a parking pawl feature that locks the output shaft of the transmission stroke face. freeing up space on the central console. Automatic transmissions have various modes depending on the model and make of the transmission. A hand brake should also prevent the car from moving if a worn selector accidentally drops into reverse gear while idling. and therefore the vehicle from moving. but the vehicle's driven wheels may still rotate individually (because of the differential). or similar. or clockwise). Such a pattern led to a number of deaths and injuries owing to driver error causing unintentional gear selection. For this reason. as well as the non-driven road wheels may still rotate freely. top to bottom. because parking on an incline with the transmission in park without the parking brake engaged will cause undue stress on the parking pin. Some vehicles position selector buttons for each mode on the cockpit instead. restricting the vehicle from moving in any direction.handle (only on column mounted shifters) out. 12 . Some of the common modes include: Park (P) This selection mechanically locks the output shaft of transmission. This also increases the life of the transmission and the park pin mechanism. Prior to this. quadrant-selected automatic transmissions often used a P-N-D-L-R layout. it is recommended to use the hand brake (parking brake) because this actually locks (in most cases) the wheels and prevents them from moving. as well as the danger of having a selector (when worn) jump into Reverse from Low gear during engine braking manoeuvres. A parking pawl prevents the transmission from rotating. Vehicles conforming to US Government standards must have the modes ordered P-R-N-D-L (left to right. completing the circuit (when the key is turned to the start 13 . Buses in Hong Kong (Kowloon Motor Bus) do not have Parking mode (P). so use of both the parking brake and the transmission park lock provides the greatest security against unintended movement on slopes. In many modern cars and trucks. A car should be allowed to come to a complete stop before setting the transmission into park to prevent damage. Advice is given in some owner's manuals that if the vehicle is parked on a steep slope using the park lock only. which must be placed in neutral with the air-operated parking brakes set. The Park position is omitted on buses/coaches (and some road tractors) with automatic transmission (on which a parking pawl is not practical). It is typical of front-wheel-drive vehicles for the parking brake to lock the rear (non-driving) wheels. the other being Neutral (N) (Buses in Hong Kong mentioned above has to be in Neutral mode (N) ONLY before the engine can be started). This is typically achieved via a normally open inhibitor switch (sometimes called a "neutral safety switch") wired in series with the starter motor engagement circuit.It should be noted that locking the transmission output shaft with park does not definitively lock the driving wheels. Usually. and will rotate in the opposite direction to the more heavily loaded non-slipping wheel. it may not be possible to release the park lock (move the selector lever out of P). instead. Most automobiles require P or N to be set on the selector lever before the engine can be started. they are using a single lever to prevent the whole bus from moving. If one driving wheel has little vertical load it will tend to slip. Park (P) is one of only two selections in which the car's engine can be started. Another vehicle may be required to push the stuck vehicle uphill slightly to remove the loading on the park lock pawl. which is closed when P or N is selected. Only a parking brake can be relied upon to positively lock both of the parking-braked wheels. the driver must have the foot brake applied before the transmission can be taken out of park. which could damage the transmission. electronically engaged by a switch on the brake pedal. Some modern automatic transmissions have a safety mechanism in place. depress the shift lock button (or move the shift lever toward the driver in a column shifter. permitting the vehicle to be driven backward. Not coming to a complete stop may cause severe damage to the transmission. Some electronic transmissions prevent or delay engagement of reverse gear altogether while the car is moving. Some shifters with a shift button allow the driver to freely move the shifter from R to N or D. effectively disconnecting the transmission from the driven wheels. the driver cannot shift back to R without depressing the shift button. such a mechanism may consist of a solenoid-controlled physical barrier on either side of the Reverse position. To select reverse in most transmissions. Therefore. the brake pedal needs to be depressed in order to allow the selection of reverse. or move the shifter sideways along a notched channel in a console shifter) and select reverse. and operates a switch to turn on the backup lights for improved visibility (the switch may also activate a beeper on delivery trucks or other large vehicles to warn other drivers and nearby pedestrians of the driver's reverse movement). allowing the vehicle to coast freely under its own 14 . Reverse (R) This engages reverse gear within the transmission. which does. to some extent.position). Neutral / No gear (N) This disengages all gear trains within the transmission. along with any other safety devices which may be present on newer cars (such as a foot-brake application). However. especially at high speeds. prevent (but not completely avoid) inadvertently putting the car in reverse when the vehicle is moving forward. the driver must come to a complete stop. or simply moving the shifter to N or D without actually depressing the button. to prevent accidental shifting. as the transmission's lubrication pump is driven by non-idle engine RPMs. The number of gear ratios within the transmission depends on the model. This is the only other selection in which the vehicle's engine may be started. but keep the remaining available gears continuously engaged to the engine for use of compression braking. allowing the vehicle to move forward and accelerate through its range of gears. Similarly. In these transmissions. though. Drive (D) This position allows the transmission to engage the full range of available forward gear ratios. Drive (D) locks the automatic overdrive off. Other vehicles with this selector (example light trucks) will not only disable up-shift to the overdrive gear. 'OD'. Manufacturers understand emergency situations and list limitations of towing a vehicle in neutral (usually not to exceed 55 mph and 50 miles). Verify the behaviour of this switch and consider the benefits of 15 . Six-speed automatic transmissions are probably the most common offering in cars and trucks. OD (Overdrive) in these cars is engaged under steady speeds or low acceleration at approximately 35–45 mph (56–72 km/h). the transmission will automatically downshift. Under hard acceleration or below 35–45 mph (56–72 km/h). Coasting in idle down long grades (where law permits) should be avoided. or a boxed [D] or the absence of an illuminated 'O/D OFF') This mode is used in some transmissions to allow early computer-controlled transmissions to engage the automatic overdrive.weight and gain momentum without the motive force from the engine. but they initially ranged from three to four and five speeds. but is identical otherwise. Overdrive ('D'. emergency towing with an automatic transmission in neutral should be a last resort. Chrysler models with a three-speed automatic since the late 1980s have called this gear 3 while using the traditional names For Drive and Low. as well as climbing or going down hills in winter. This can be used to climb or going down. First (1 or L [Low]) This mode locks the transmission in first gear only. This gear is also recommended while towing a trailer. Some vehicles will automatically shift up out of third gear in this mode if a certain revolutions per minute (RPM) range is reached in order to prevent engine damage. and use of this position enables this with an automatic transmission. Some vehicles will automatically shift up out of second gear in this mode if a certain RPM range is reached in order to prevent engine damage. Kia. Oldsmobile has called second gear as the 'Super' range — which was first used on their 4-speed Hydramatic transmissions. although the use of this term continued until the early 1980s when GM's Turbo Hydramatic automatic transmissions were standardized by all of their divisions years after the 4-speed Hydramatic was discontinued. or sometimes locks the transmission in third gear. Some vehicles will automatically shift up out of first gear in this mode if a certain RPM range is reached in order to prevent engine damage. like second. Third (3) This mode limits the transmission to the first three gear ratios. can be 16 .reduced friction brake use when city driving where speeds typically do not necessitate the overdrive gear. Second (2 or S) This mode limits the transmission to the first two gear ratios. and Honda models.hill. This can be used to drive in adverse conditions such as snow and ice. It is usually recommended to use second gear for starting on snow and ice. Although traditionally considered second gear. there are other names used. it will not change to any other gear range. This. or locks the transmission in second gear on Ford. In older vehicles. such as city driving.). D2 and D1 These modes are found on older Ford transmissions (C6. such as city driving. 17 . Acura. According to the manual. this mode is used commonly for highway use (as stated in the manual). dependent on the manufacturer and model. whereas in D2 the car starts in second gear and up-shifts to third. Volkswagen and Pontiac four-speed automatics and only uses the first three gear ratios. As well as the above modes there are also other modes. D4 This mode is also found in Honda and Acura four or five-speed automatics. and only uses the first four gear ratios. for towing. it is used for stop-and-go traffic. all three gears are used. According to the manual. and uses all five forward gears.used during the winter season. or for downhill driving to increase the engine braking effect. D3 or 3 This mode is found in Honda. Some examples include: D5 In Hondas and Acuras equipped with five-speed automatic transmissions. it is used for stop-and-go traffic. In D1. etc. or ice. and M This is for the Manual mode selection of gears in certain automatics.S or Sport This is commonly described as Sport mode. being the same as the 2 position on a Chrysler. or slippery roads like dirt. This would have been recommended for use on steep grades. 18 . Journey. locking the transmission into first gear. and therefore enhances the performance of the vehicle. Corolla. or ice. Some early GMs equipped with HYDRA-MATIC transmissions used (S) to indicate Second gear. maximising the effects of engine braking. This would have been recommended for use on steep grades. + −. being the same as the 2 position on a Chrysler. and limited to speeds under 15 mph. Mazda products such as the Mazda 3. This mode will also down-change much higher up the rev range compared to "D" mode. except that the up-shifts change much higher up the engine's rev range. Hyundai has a Norm/Power switch next to the gearshift for this purpose on the Tiburon. It operates in an identical manner as "D" mode. and Pontiac G6. This mode will have a detrimental effect on fuel economy. as well as Toyota's Camry. Mazda6. and the CX-7. This has the effect on maximising all the available engine output. particularly during acceleration. such as Porsche's Tiptronic and Honda's StepTronic. and limited to speeds under 40 mph. (L) was used in some early GMs to indicate (L)ow gear. or slippery roads like dirt. shifting between only first and second gears. The M feature can also be foundin Chrysler and General Motors products such as the Dodge Magnum. and a set of planetary gear sets to provide a range of gear ratios. but it has the same effect in slowing the car without using the brakes. GM called this "HR" ("hill retarder") and "GR" ("grade retarder") in the 1950s. It is not the same as downshifting in a non-hybrid car. this mode lets the engine do compression braking. the driver can shift up and down at will by toggling the (console mounted) shift lever similar to a semi-automatic transmission. In non-hybrid cars. Mitsubishi and some Audi models (Audi TT). also known as engine braking. and is Second Gear Start after 1990. this mode converts the electric motor into a generator for the battery (Regenerative Braking). instead of the brakes slowing it down. On Ford. using a fluid coupling or torque converter. The engine holds the car back. a winter mode can be engaged so that second gear is selected instead of first when pulling away from stationary. then taking your foot off the accelerator while selecting D once the car is moving. meanwhile do not have the M. Instead of engaging the brakes. On GM cars. to reduce the likelihood of loss of traction due to wheel spin on snow or ice. and Honda automatics. Brake (B) A mode selectable on some Toyota models. the engine in a non-hybrid car switches to a lower gear and slows down the spinning tires..Fortuner. which is separated from the rest of the shift modes. BMW and General Motors Europe models. Mercedes-Benz. the same is true for some Peugeot products like Peugeot 206. This mode may be engaged either through a selector/position or by actually changing the gears (e.g. this feature can be accessed by moving the gear selector to 2 to start. typically when encountering a steep downhill. Winter (W) In some Volvo. 19 . this was D2 in the 1950s. Meanwhile. Kia. For hybrid cars. and instead have the + and -. HYDRAULIC AUTOMATIC TRANSMISSION The predominant form of automatic transmission is hydraulically operated. Previa and Innova. tipping the gear-down paddles mounted near the driver's fingers on the steering wheel). A torque converter differs from a fluid coupling. These clutches are actuated by the valve body (see below). thereby transmitting torque and producing gear reductions or overdrive ratios. which is needed for transmission components to operate.Parts and operation A hydraulic automatic transmission consists of the following parts: Torque converter: A type of fluid coupling. 20 . while allowing another member to rotate. It takes the place of a mechanical clutch. the pump is typically a gear pump mounted between the torque converter and the planetary gear set. in effect using the leftover force of it to enhance torque multiplication. The stator captures the kinetic energy of the transmission fluid. so the pump provides pressure whenever the engine is running and there is enough transmission fluid. allowing push-starting. Planetary gear-set: A compound epi-cyclic planetary gear set. providing two or more gear ratios. Early automatic transmissions also had a rear pump. It draws transmission fluid from a sump and pressurizes it. increasing breakaway acceleration. one of two types of clutches or bands are used to hold a particular member of the planetary gear set motionless. whose bands and clutches are actuated by hydraulic servos controlled by the valve body. and by altering the shapes of the vanes inside the coupling in such a way as to curve the fluid's path into the stator. (Not part of some manufacturer’s transmissions during some eras. hydraulically connecting the engine to the transmission. Clutches and bands: to effect gear changes. Honda being but one). which in turn is bolted to the engine's flywheel. without stalling. Pump: Not to be confused with the impeller inside the torque converter. This is accomplished with a third member in the coupling assembly known as the stator. allowing the transmission to stay in gear and the engine to remain running while the vehicle is stationary. The input for the pump is connected to the torque converter housing. in that it provides a variable amount of torque multiplication at low engine speeds. the GM Turbo-Hydrometrics incorporated this. this component of the transmission provides lubrication. it transmits torque only in one direction. Valve body: hydraulic control centre that receives pressurized fluid from the main pump operated by the fluid coupling/torque converter. a type of device known as a sprig or roller clutch is used for routine up-shifts/downshifts. the ATF is one of the few parts of the automatic transmission that needs routine service as the vehicle ages. Bands are used for braking. free-wheeling or "overrunning" in the other. Bands are not applied when drive/overdrive range is selected. and operate on the planetary drum's circumference. and a hydraulic medium to convey mechanical power (for the operation of the transmission). in many modern automatic transmissions. corrosion prevention. the valves are controlled by electro-mechanical servos which are controlled by the electronic engine control unit (ECU) or a separate transmission control unit (TCU. and releasing automatically when the next gear's sprig clutch assumes the torque transfer. Hydraulic & lubricating oil: called automatic transmission fluid (ATF). check balls and servo pistons. The advantage of this type of clutch is that it eliminates the sensitivity of timing a simultaneous clutch release/apply on two planetaries. the difference between the pressures changes. The valves use the pump pressure and the pressure from a centrifugal governor on the output side (as well as hydraulic signals from the range selector valves and the throttle valve or modulator) to control which ratio is selected on the gear set. Operating much as a ratchet. also known as transmission control module (TCM). causing different sets of valves to open and close. Principally. the torque being transmitted by the sprig clutches instead. However. simply "taking up" the drive train load when actuated. 21 . thereby controlling the operation of the planetary gearset to select the optimum gear ratio for the current operating conditions. and processed to provide properties that promote smooth power transmission and increase service life.their sequence controlled by the transmission's internal programming. Primarily made from refined petroleum. as the vehicle and engine change speed. The hydraulic pressure controlled by these valves drives the various clutch and brake band actuators. The pressure coming from this pump is regulated and used to run a network of spring-loaded valves. such as low range or reverse. The bands come into play for manually selected gears. which uses fluid pressure to determine the correct shifting patterns and operate the various automatic clutch mechanisms. Thus the manual transmission requires very little engine power to function. Energy efficiency Hydraulic automatic transmissions are almost always less energy efficient than manual transmissions due mainly to viscous and pumping losses. originally made hydraulic automatic transmissions much more complicated (and expensive) to build and repair than manual transmissions. and whether or not the elimination of spool down/accelerator lift off represent a significant enough gain to counter the slightly higher power consumption of the automatic transmission itself. both in the torque converter and the hydraulic actuators. Turbo-boost is normally lost between gear changes in a manual whereas in an automatic the accelerator pedal can remain fully depressed. sport-utility vehicle. Manual transmissions use a mechanical clutch to transmit torque. luxury. In most cars (except US family. and minivan models) they have usually been extra-cost options for this reason.The multitude of parts. Manual transmissions also avoid the power requirement of the hydraulic control system. This however is still largely dependent upon the number and optimal spacing of gear ratios for each unit. 22 . A relatively small amount of energy is required to pressurize the hydraulic control system. thus avoiding the primary source of loss in an automatic transmission. rather than a torque converter. by relying on the human muscle power of the vehicle operator to disengage the clutch and actuate the gear levers. The on-road acceleration of an automatic transmission can occasionally exceed that of an otherwise identical vehicle equipped with a manual transmission in turbo-charged diesel applications. along with the complex design of the valve body. Mass manufacturing and decades of improvement have reduced this cost gap. and the mental power of the operator to make appropriate gear ratio selections. with the main power consumption due to drag from the gear train being immersed in the lubricating oil of the gearbox. one shaft is driven by a motor and the other drives a drill chuck. 2) Gradual engagement:The clutch should engage gradually to avoid sudden jerks. torque produced and finally the use of the whole device. different kinds of clutches are used. The clutch connects the two shafts so that they may be locked together and spin at the same speed (engaged). Clutches are useful in devices that have two rotating shafts. Depending on the orientation. linear clutches are also possible. While typically the motions involved are rotary. Requirement of a clutch: 1) Torque transmission: The clutch should be able to transmit maximum torque of the engine. In the simplest application. The clutch connects the two shafts so that they can either be locked together and spin at the same speed (engaged). In these devices.. 23 . which employs different configurations and different principles in various models available. clutches control whether automobiles transmit engine power to the wheels). which can be engaged and disengaged. speeds. In a torque-controlled drill. Let us take an instance where one shaft is driven by a motor and the other drives a drill chuck. or unlocked and spinning at different speeds (disengaged). In the following lines. In these devices. one shaft is typically attached to a motor or other power unit (the driving member) while the other shaft (the driven member) provides output power for work. for instance.CLUTCH Clutch is a mechanism for transmitting rotation. material. and the other shaft drives another device. we have provided the different kinds of clutches that are available. electric screwdrivers limit how much torque is transmitted through use of a clutch.g. clutches connect and disconnect two rotating shafts (drive shafts or line shafts). one shaft is typically driven by a motor or pulley. or be decoupled and spin at different speeds (disengaged). The clutch in itself is a mechanism. locked together but spinning at different speeds (slipping). Clutches are used whenever the transmission of power or motion must be controlled either in amount or over time (e. This is particularly required in the case of high speed engine clutches. 7) Free pedal play: The clutch should have free pedal play in order to reduce effective clamping load on the carbon thrust bearing and wear on it. 5) Vibrating damping: The clutch should have suitable mechanism to damp vibrations and to eliminate noise produced during the power transmission. 6) Size:The clutch should be as small as possible in size so that it will occupy minimum space. PRINCIPLES OF OPERATIONS: 24 .3) Heat dissipation: The clutch should be able to dissipate large amount of heat which is generated during the clutch operation due to friction. 8) Easy in operation: The clutch should be easy to operate requiring as little exertionas possible on the part of the driver. 9) Lightness:The driven member of the clutch should be made as light as possible so that it will not continue to rotate for any length of time after the clutch has been disengaged. 4 ) Dynamic balancing:The clutch should be dynamically balanced. The flywheel bolted to a cover which carries a pressure plate or a driving disc. 1. 25 . Driving member 2. When two friction surfaces are brought in contact with each other and pressed they are united due to the friction between them if now one is revolved the other will also be revolved. One surface is considered as a driving member the other as a driven member. The driving members consist of a flywheel mounted on the engine crankshaft. The clutch housing and the cover provided with openings dissipate the heat generated by the friction during the clutch operation.Clutch works on the principle of friction. pressure applied on them and co-efficient of friction of the surface material. The two surfaces can be separated and brought into contact when required. This is the principle on which the clutch operates. The friction between the two surfaces depends upon the area of the surfaces. Operating member DRIVING MEMBER: The driving members consist of a flywheel mounted on the engine crankshaft. Thus the entire assembly of the flywheel and the cover rotates all the time. When the driven member is separated from the driving member it does not rotate. The driving member is kept rotating. Driven member 3. MAIN PARTS OF CLUTCH: The main parts of clutch are divided into three groups. the pressure springs and releasing levers. when the driven member is brought in contact with the driving member it also rotates. When it is gripped between the flywheel and the pressure plate. It is free to slide lengthwise on the splines of the clutch shaft. It carries friction materials on both of its surfaces. The driven member consists of the disc or plate. it rotates the clutch shaft through the splines. called the clutch plate.Flywheel couple with clutch DRIVEN MEMBER: The driven member consists of a disc or plate. Flywheel couple with clutch 26 . called the clutch plate. OPERATING MEMBERS: The operating members consist of a foot pedal. release or throw-out bearing. The operating members consist of a foot pedal. linkage. release or throw out bearing. release levers and springs. Bearing and spring 27 . Pedal. linkage. release levers and the springs necessary to insure the proper operation of the clutch. you'll learn why you need a clutch. how the clutch in your car works and find out some interesting. and the other shaft drives another device. places where clutches can be found. 28 . In a drill. In fact. chain saws have a centrifugal clutch and even some yo-yos have a clutch. And it turns out that folks with automatic transmission cars have clutches. too.Main Parts Of Single Plate Clutch WORKING OF CLUTCH: If you drive a manual transmission car. In this article. you may be surprised to find out that it has more than one clutch. one of the shafts is typically driven by a motor or pulley. there are clutches in many things you probably see or use every day: Many cordless drills have a clutch. and perhaps surprising. In these devices. Clutches are useful in devices that have two rotating shafts. it helps to know a little bit about friction.for instance. Friction is caused by the peaks and valleys that are part of every surface -. one shaft is driven by a motor and the other drives a drill chuck. which is a measure of how hard it is to slide one object over another. To understand how a clutch works. you need a clutch because the engine spins all the time. or be decoupled and spin at different speeds. the wheels need to be disconnected from the engine somehow. 29 . the harder it is to slide the object. In order for a car to stop without killing the engine. but the car's wheels do not. In a car. The clutch allows us to smoothly engage a spinning engine to a nonspinning transmission by controlling the slippage between them. You can learn more about friction in How Brakes Work.even very smooth surfaces still have microscopic peaks and valleys. The larger these peaks and valleys are. The clutch connects the two shafts so that they can either be locked together and spin at the same speed. reverse action takes place: the driven plate is again forced against the flywheel by the pressure plate.because of the force exerted by the pressure springs. When the clutch pedal is released. thus allowing it to move away from the Clutch Driven Plate. This causes the Pressure Plate to compress the Pressure Springs. thus achieving vehicle movement. through pedal movement. without turning the transmission. Any further increase in pressure will cause the clutch plate and the transmission shaft to turn along with the flywheel. OPERATION OF THE CLUTCH When the clutch pedal is depressed. The pressure plate will keep on compressing the facings of the driven plate until the friction created becomes equal to the resistance of the vehicle. which being connected to the clutch release levers. 30 . This action releases the pressure on the Driven Plate and Flywheel. the clutch release bearing presses on the clutch release lever plate. We'll look at how these parts work together in the next section. forces these levers forward.A clutch works because of friction between a clutch plate and a flywheel. the flywheel is now free to turn independently. The clutch lets the driver control power flow between the engine and the transmission or transaxle. Clutch Release Mechanism 31 . you must first become familiar with the parts and their function. Before understanding the operation of a clutch. This information is very useful when learning to diagnose and repair the clutch assembly.Single Plate Clutch CLUTCH CONSTRUCTION: The clutch is the first drive train component powered by the engine crankshaft. A clutch release mechanism allows the operator to operate the clutch. Movement of the clutch pedal creates hydraulic pressure in the master cylinder. hydraulic lines. The slave cylinder then moves the clutch fork. cable. Generally. It has three basic parts. or A hydraulic clutch release mechanism (fig. it consists of the clutch pedal assembly. 4-5) uses a simple hydraulic circuit to transfer clutch pedal action to the clutch fork. which actuates the slave cylinder. either mechanical linkage. and a slave cylinder. CLUTCH CABLE MECHANISM Clutch Fork 32 .master cylinder. Release Bearing The release bearing. 33 . A rubber boot fits over the clutch fork. There are two types of pressure plates. oil. enclosing the clutch assembly. and other debris from entering the clutch housing. The clutch disc fits between the flywheel and the pressure plate. The clutch fork sticks through a square hole in the bell housing and mounts on a pivot. When the clutch fork is moved by the release mechanism. is a ball bearing and collar assembly. It bolts to the rear of the engine. The pressure plate is a spring-loaded device that can either engage or disengage the clutch disc and the flywheel. The release bearing is a sealed unit pack with a lubricant. It can be made of aluminium. water. magnesium. The lower front of the housing has a metal cover that can be removed for fly-wheel ring gear inspection or when the engine must be separated from the clutch assembly. This boot is designed to keep road dirt. transfers motion from the release mechanism to the release bearing and pressure plate. also called a clutch arm or release arm. or cast iron. with the manual transmission bolted to the back of the housing. It reduces friction between the pressure plate levers and the release fork. Then fork movement in either direction slides the release bearing along the transmission hub sleeve. It slides on a hub sleeve extending out from the front of the manual transmission or transaxle. The release bearing snaps over the end of the clutch fork. it PRIES on the release bearing to disengage the clutch.The clutch fork.the coil spring type and the diaphragm type. Small spring clips hold the bearing on the fork. A hole is provided in the side of the housing for the clutch fork. It bolts to the flywheel. Pressure Plate Clutch Housing The clutch housing is also called the bell housing. also called the throw-out bearing. rocks. round disc of spring steel. The release levers are hinged inside the pressure plate to pry on and move the pressure plate face away from the clutch disc and flywheel. Diaphragm pressure plate (fig. and the pressure plate face. the pressure plate moves back and forth inside the clutch cover. Small clip-type springs fit around the release levers to keep them rattling when fully released. the release levers. Holes around the outer edge of the cover are for bolting the pressure plate to the flywheel. 34 . flat ring that contacts the clutch disc during clutch engagement.Coil spring pressure plate: It uses small coil springs similar to valve springs (fig. The face of the pressure plate is a large. The backside of the pressure plate has pockets for the coil springs and brackets for hinging the release levers. The pressure plate cover fits over the springs. 4-7) uses a single diaphragm spring instead of coil springs. During clutch action. The spring is bent or dished and has pie-shaped segments running from the outer edge to the centre. The diaphragm spring is mounted in the pressure plate with the outer edge touching the back of the pressure plate face. 4-6). The outer rim of the diaphragm is secured to the pressure plate and is pivoted on rings (pivot rings) approximately 1 inch from the outer edge. Its main purpose is to hold the assembly together.This type of pressure plate functions similar to that of the coil spring type. The diaphragm spring is a large. DIAPHRAGM PRESSURE PLATE OPERATION 35 . it prevents jerky motion of the vehicle. the power flows from the engine to the rear wheels through the transmission system and the vehicle moves. the power is not transmitted to the rear wheels and the vehicles stops while the engine is still running. The clutch is kept engaged when the vehicle is moving. when shifting the gears. The clutch also permits the gradual taking up of the load. When properly operated. When the clutch is disengaged. Some clutches are operated by hydraulic means. TYPES OF CLUTCHES: The clutches used in motor vehicles are almost very similar in construction and operation. The wet clutch operates in a batch of oil. when stopping the vehicle and when idling the engine. The clutch is disengaged when starting the engine. The drive plate clutch operates dry without using oil. There are some differences in the details of a linkage as well as in the pressure plate assemblies. 36 . Most design of the clutches use number of coil springs but some uses a diaphragm or conical type springs.Functions of a clutch are as follows: When the clutch is engaged. Different types of clutches are as follows: 1. The purpose of friction clutches is to connect a moving member to another that is moving at a different speed or stationary. Friction clutch a) Single plate clutch b) Multi plate clutch 1) Wet 2) Dry c) Cone clutch 1) External 2) Internal 2. Positive clutch – Dog and spline clutch 6. Vacuum clutch 9. Centrifugal clutch 3 Semi-centrifugal clutch 4 Conical spring clutch or diaphragm clutch (a) Tapered finger type (b) Crown spring type 5. Electro-magnetic clutch 8. 37 . Over running clutch or free wheeled unit. Hydraulic clutch 7. FRICTION CLUTCH The vast majority of clutches ultimately rely on frictional forces for their operation. and/or to transmit power. Usually as little slippage (difference in speeds) as possible between the two members are desired. often to synchronise the speeds. the release bearing can be known as a thrust bearing (as per the image above). Push/Pull Friction disk clutches generally are classified as push type or pull type depending on the location of the pressure plate fulcrum points. In this instance. including asbestos in the past. They are fully compressed and no longer in use once the main damper springs take up drive. which reduce driveline vibration. In a pull type clutch. Modern clutches typically use a compound organic resin with copper wire facing or a ceramic material. pre-dampers may be used to reduce gear rattle at idle by changing the natural frequency of the disc.Materials Various materials have been used for the disc friction facings. In automotive applications. The opposite is true with a push type. the release bearing is pushed into the clutch disengaging the vehicle drive. the action of pressing the pedal pulls the release bearing. In addition to the damped disc centres. though the harder ceramic materials increase flywheel and pressure plate wear. A typical coefficient of friction used on a friction disc surface is 0. Dampers A clutch damper is a device that softens the response of the clutch engagement/disengagement. Ceramic materials are typically used in heavy applications such as racing or heavy-duty hauling. this is often provided by a mechanism in the clutch disc centres. These weaker springs are compressed solely by the radial vibrations of an idling engine. pulling on the diaphragm spring and disengaging the vehicle drive.25 for ceramic.35 for organic and 0. Load 38 . 39 . however. Wet and dry clutch A 'wet clutch' is immersed in a cooling lubricating fluid. A 'dry clutch'. For example drive straps are now commonly employed to transfer torque as well as lift the pressure plate upon disengagement of vehicle drive. The two parts of the clutch are designed such that one will push the other. Without slippage. Manufacturing Modern clutch development focuses its attention on the simplification of the overall assembly and/or manufacturing method. heat treatment is crucial. causing both to rotate at the same speed and will never slip. A synchromesh arrangement ensures smooth engagement by matching the shaft speeds before the dog clutch is allowed to engage.Mercedes truck examples: A clamp load of 33 kN is normal for a single plate 430. Bursts speeds are typically around 5. is not bathed in fluid. With regard to the manufacture of diaphragm springs. tend to lose some energy to the liquid. Laser welding is becoming more common as a method of attaching the drive plate to the disc ring with the laser typically being between 2-3KW and a feed rate 1m/minute. Dog clutches are used inside manual automotive transmissions to lock different gears to the rotating input and output shafts. dog clutches are not affected by wear in the same way that friction clutches are. stacking multiple clutch disks can compensate for the lower coefficient of friction and so eliminate slippage under power when fully engaged. Wet clutches. which also keeps the surfaces clean and gives smoother performance and longer life. Dog clutches are used where slip is undesirable and/or the clutch is not used to control torque. The 400 Twin application offers a clamp load of a mere 23 kN. DOG CLUTCH A dog clutch is a type of clutch that couples two rotating shafts or other rotating components not by friction but by interference.000 rpm with the weakest point being the facing rivet. Since the surfaces of a wet clutch can be slippery (as with a motorcycle clutch bathed in engine oil). as the name implies. Centrifugal clutches are often used in mopeds. This is because the clutch doesn't have to be pushed in all the way and the gears will be changed quicker. with the driving shaft nested inside the driven shaft. chainsaws. the cone clutch uses two conical surfaces to transmit torque by friction. They are usually now confined to very specialist transmissions in racing. and mini bikes. instead of mating two spinning disks. The cone clutch transfers a higher torque than plate or disk clutches of the same size due to the wedging action and increased surface area. Centrifugal clutch A centrifugal clutch is a clutch that uses centrifugal force to connect two concentric shafts. or in extreme off-road vehicles.Cone clutch A cone clutch serves the same purpose as a disk or plate clutch. Engine power is transmitted via a set of vee-belts that are slack when the engine is idling. It has been used in automobile transmissions as an alternative to a mechanical clutch. rallying. Cone clutches are generally now only used in low peripheral speed applications although they were once common in automobiles and other combustion engine transmissions. lawnmowers. It also has widespread application in marine and industrial machine drives. Wrap-spring clutches 40 . go-karts. Belt clutch Used on agricultural equipment and some piston-engine-driven helicopters. where variable speed operation and/or controlled start-up without shock loading of the power transmission system is essential. Fluid coupling A fluid coupling is a hydrodynamic device used to transmit rotating mechanical power. but by means of a ten-sioner pulley can be tightened to increase friction between the belts and the sheaves. although they are common in power boats. However. in case of automobiles going down the hill.These have a helical spring wound with square-cross-section wire. They are known to have common problems associated with hydraulic couplings. and are a bit unsteady in transmitting torque. An example of such a situation can be when a cyclist stops peddling and cruises. Electromagnetic clutch Electromagnetic clutches operate electrically. you cannot take your feet off the gas pedal. If you do so. this device allows a rotating shaft to "slip" or disengage when higher than normal resistance is encountered on a machine. This is why they used to be referred to as electro-mechanical clutches. 41 . Rotating the driving member the other way makes the spring wrap itself tightly around the driving surface and the clutch locks up. The spring fits closely around a cylindrical driving member. coupling is hydrodynamic. However. They work as an alternative to mechanical clutches. If the driving member rotates in the direction that would unwind the spring the spring expands minutely and slips although with some drag. Hydraulic clutch The driving and driven members are not in physical contact. the coupling is hydrodynamic and the shafts are not actually in contact. If a stone or something else is encountered by the grass mower. the whole engine system can be damaged. it stops immediately and does not hamper the blades. its other end is unattached. but transmit torque mechanically. Overrunning Clutch Also known as the freewheel mechanisms. In simple form the spring is fastened at one end to the driven member. Safety Clutch Also known as the torque limiter. when the driven shaft rotates faster than the driveshaft. An example of a safety clutch is the one mounted on the driving shaft of a large grass mower. In a hydraulic clutch system. as there is no free wheel system. this type of clutch disengage the driveshaft from the driven shaft. of the coil and the friction between the steel of the armature and the steel of the clutch rotor. This field (flux) overcomes an air gap between the clutch rotor and the armature. the north and south pole is created by a coil shell and a wound coil. Copper (sometimes aluminium) magnet wire. in the rotor and armature. what occurs is a leaping of the flux path. pulls the armature in contact with the rotor face. if the clutch is required to have an extended time to speed or slip time. the electromagnetic lines of flux have to pass into the rotor. For example. In theory. that is not possible to do. a magnetic circuit is created. 42 . such as automotive requirements. is used to create the coil. if the armature is designed properly and has similar banana slots. but different types of material can also be used to change the coefficient of friction (torque for special applications). a low coefficient friction material can be used and if a clutch is required to have a slightly higher torque (mostly for low rpm applications). a magnetic field is created in the coil. Obviously. This is important in applications where size and weight are critical. when power is applied. By having more points of contact. The double or trip flux refers to the number of north/south flux paths. and in turn. In an electromagnetic clutch. The coil shell is made with carbon steel that has a combination of good strength and good magnetic properties. which is held in shell either by a bobbin or by some type of epoxy/adhesive. friction material is used between the poles. is what causes the rotational motion to start. attract and pull the armature in contact with it to complete clutch engagement. This means that. if there were 2 sets of poles at the same diameter. This magnetic attraction. But by using a double flux design. In a clutch. Mobile clutches of other specialty electromagnetic clutches can use a double or triple flux rotor. there are magnetic flux losses because of the bridges between the banana slots. which goes north south. The torque comes from the magnetic attraction. The material is mainly used to help decrease the wear rate. and by using a triple flux design. which is being controlled by the strength of the magnetic field. a high coefficient friction material can be used. a 40%-90% in torque can be achieved. so the points of contact have to be at a smaller inner diameter. the torque can be greatly increased.CONSTRUCTION A horseshoe magnet has a north and south pole. Most industrial clutches use what is called a single flux. a 30%-50% increase in torque. If a piece of carbon steel contacts both poles. the torque would double in a clutch. For many industrial clutches. north south. can be achieved. Also. two pole design. The frictional contact. In a clutch. Slipping between the rotor face and the armature face continues until the input and output speed is the same (100% lockup). One or more springs hold the armature away from the rotor at a predetermined air gap. Within this.) The flux (magnetic attraction) pulls the armature in contact with the rotor (the armature is connected to the component that requires the acceleration). many mobile clutches are exposed to outside elements. good magnetic traction could not occur between the faces. friction material is used between the poles on the face of the rotor. and hub (output) . Some people look at electromagnetic clutches and mistakenly assume that. since the friction material is flush with the steel that the clutch has already worn down but this is not the case. Disengagement is very simple. The actual time for this is quite short. and their cost is more sensitive. Engagement time There are actually two engagement times to consider in an electromagnetic clutch. This friction material is flush with the steel on the rotor.To help increase life in applications. so by not having friction material. Also. WORKING OF ELECTROMAGNETIC CLUTCH The clutch has four main parts: field. since if the friction material was not flush. as the armature and the output start to accelerate. (The rotor is normally connected to the part that is always moving in the machine. Once the field starts to degrade. agriculture. armature. it eliminates the possibility of swelling (reduced torque). The first one is the amount of ampere turns in a coil. Clutches used in most mobile applications. The first one is the time that it takes for a coil to develop a magnetic field. strong enough to pull in an armature. construction equipment) do not use friction material. flux falls rapidly and the armature separates. Their cycle requirements tend to be lower than industrial clutches. that can happen when friction material absorbs moisture. When voltage is applied the stationary magnetic field generates the lines of flux that pass into the rotor. there are two factors to consider. rotor. (automotive. The second one is air 43 . which will determine the strength of a magnetic field. between 1/200th of a second and 1 second. this is important because a new machine that has accurate timing can eventually see a “drift” in its accuracy as the machine gets older.gap. where registration is important. but the key to sizing a clutch is calculating how much inertial is reflected back to the clutch or brake. Once it is known how much inertia is present for the clutch to start then the torque can be calculated and the appropriate size of clutch can be chosen. To do this. The friction material varies in composition depending on many considerations such as whether the clutch is "dry" or "wet".. Major types by application Vehicular (general) There are different designs of vehicle clutch but most are based on one or more friction discs pressed tightly together or against a flywheel using springs. Clutches found in 44 . engineers use the formula: T = (wk2 × ΔN) / (308 × t) Where T = required torque in lb-ft. Magnetic lines of flux diminish quickly in the air. this is what the end-user is most concerned with. ΔN = change in the rotational speed in rpm. This is referred to as “time to speed”. Most CAD systems can automatically calculate component inertia. and t = time during which the acceleration or deceleration must take place. in registration of a machine. Even in a normal cycle application. WK2 = total inertia in lb-ft2. which is the space between the armature and the rotor. Friction discs once contained asbestos but this has been largely eliminated. It involves calculating the amount of inertia that the clutch needs to accelerate. There are also online sites that can help confirm how much torque is required to accelerate a given amount of inertia over a specific time. even the difference of 10 to 15 milliseconds can make a difference. Air gap is an important consideration especially with a fixed armature design because as the unit wears over many cycles of engagement the armature and the rotor will create a larger air gap which will change the engagement time of the clutch. In high cycle applications. In reality. The second factor in figuring out response time of a clutch is actually much more important than the magnet wire or the air gap. jerky start. engine mountings being flexible by design. Automobile powertrain This plastic pilot shaft guide tool is used to align the clutch disk as the spring-loaded pressure plate is installed. such remote means of actuation are necessary to eliminate the effect of vibrations and slight engine movement. 45 . depending on type. With a rigid mechanical linkage. the engine spins the input shaft of the transmission. The transmission's drive splines and pilot shaft have a complementary shape. On older cars the clutch might be operated by a mechanical linkage. Engaging the clutch abruptly when the engine is turning at high speed causes a harsh. raising the engine speed too high while engaging the clutch causes excessive clutch plate wear." The default state of the clutch is engaged . A number of such devices fit various makes and models of drivetrains. This kind of start is necessary and desirable in drag racing and other competitions. However. Even though the clutch may physically be located very close to the pedal. However. The spring pressure is released when the clutch pedal is depressed thus either pushing or pulling the diaphragm of the pressure plate. these have a "grabby" action generally considered unsuitable for passenger cars.that is the connection between engine and gearbox is always "on" unless the driver presses the pedal and disengages it. In a modern car with a manual transmission the clutch is operated by the leftmost pedal using a hydraulic or cable connection from the pedal to the clutch mechanism. where speed is more important than comfort. but no power is transmitted to the wheels. smooth engagement would be nearimpossible because engine movement inevitably occurs as the drive is "taken up. If the engine is running with clutch engaged and the transmission in neutral.heavy duty applications such as trucks and competition cars use ceramic plates that have a greatly increased friction coefficient. the gearbox input shaft is free to change its speed as the internal ratio is changed. as disengaging it is required to change gear. at a fixed speed ratio. and Chevrolet Corvette (since 1997). then the wheels. Any resulting difference in speed between the engine and gearbox is evened out as the clutch slips slightly during reengagement. there is no torque transmitted through it. Porsche 924. Clutches in typical cars are mounted directly to the face of the engine's flywheel. The propeller shaft between front and rear rotates continuously as long as the engine is running. thus less friction between gears and their engagement dogs. even if the clutch is disengaged or the transmission is in neutral. Some racing clutches use small multi-plate disk packs that are not part of the flywheel. combined with the rear axle to form a transaxle. sought a more even weight distribution between front and back by placing the weight of the transmission at the rear of the car. Both clutch and flywheel are enclosed in a conical bellhousing. Although the gearbox does not stop rotating during a gear change. Motorcycles A basket clutch 46 . A few cars.The clutch is located between the engine and the gearbox. and so both always rotate together. With the clutch disengaged. as this already provides a convenient large diameter steel disk that can act as one driving plate of the clutch. which (in a rearwheel drive car) usually forms the main mounting for the gearbox. notably the Alfa Romeo Alfetta. The output shaft of the gearbox is permanently connected to the final drive. On motorcycles the clutch is operated by a hand lever on the left handlebar. which lets the fan spin at about 20% to 30% of the shaft speed. which. When the temperature is low. Racing motorcycles often use slipper clutches to eliminate the effects of engine braking. Other clutches—such as for an air conditioning compressor—electronically engage clutches using magnetic force to couple the driving member to the driven member. Some plates have lugs on their inner diameters that lock them to the engine crankshaft. while pulling the lever back towards the rider disengages the clutch plates through cable or hydraulic actuation. Other plates have lugs on their outer diameters that lock them to a basket that turns the transmission input shaft. When "tripped". it unwinds and opens the valve. If the trip mechanism is operated when the clutch would otherwise disengage the clutch remains engaged. The driving and driven members are separated by a silicone-based fluid and a valve controlled by a bimetallic spring. No pressure on the lever means that the clutch plates are engaged (driving). As the temperature of the spring rises. For example. it locks up solidly (typically in a few to tens of milliseconds) and rotates the driven member just one full turn. a belt-driven engine cooling fan may have a heat-activated clutch. Specialty clutches and applications Single-revolution clutch When inactive it is disengaged and the driven member is stationary. allowing the rider to shift gears or coast. being applied only to the rear wheel. Variants include half-revolution (and other fractional-revolution) 47 . Automobile non-powertrain Cars use clutches in places other than the drive train. These clutches are usually made up of a stack of alternating plain steel and friction plates. can cause instability. the spring winds and closes the valve. allowing fluid past the valve.Motorcycles typically employ a wet clutch with the clutch riding in the same oil as the transmission. makes the fan spin at about 60% to 90% of shaft speed. A set of coil springs or a diaphragm spring plate force the plates together when the clutch is engaged. Load torque tightened the wrap so it did not slip once engaged. Typically. They were also found in motor-driven mechanical calculators. including the Teletype Model 28 and its successors. When the clutch was to disengage power was disconnected from the electromagnet and the pawl moved close to the sleeve. an electromagnet attracted the pawl away from the sleeve. cycling for tens. as well as electric typewriters. but the wrap was so effective that the lubricant did not defeat the grip. Basically the spring was kept expanded (details below) and mostly out of contact with the driving sleeve. the Marchant had several of them. These were an essential part of printing telegraphs such as tele-printer page printers. this kept the spring expanded to minimize contact with the driving cylinder. The sleeve had a projecting tooth. but nevertheless close to it. Cascaded-pawl single-revolution clutches These superseded wrap-spring single-revolution clutches in page printers. If the pawl were held away from the sleeve the clutch would continue to drive the load without slipping. They are also used in farm machinery and industry. Considering that the drive motors in some of these (such as tele-printers for news wire services) ran 24 hours a day for years the spring could not be allowed to stay in close contact with the driving cylinder. maybe hundreds of millions of cycles without need of maintenance other than occasional lubrication with recommended oil. When the sleeve's tooth contacted the pawl the sleeve and the load's inertiaun wrapped the spring to disengage the clutch. Together with the restraint at the other end of the spring created by the trip pawl and sleeve tooth. The other end of the spring was fastened to a thick disc attached to the driven member. A spring-loaded pawl pressed against the sleeve and kept it from rotating. These clutches had long operating lives.types. The other end of the spring was attached to the driven member inside which the drive shaft could rotate freely. The wrap spring's torque rotated the sleeve. To engage the clutch. One end of the spring was attached to a sleeve surrounding the spring. These clutches were lubricated with conventional oil. such as teleprinters. these were a variety of dog clutch. Single-revolution clutches in tele-printers were of this type. notably the IBM Selectric. The wrap spring's torque kept the sleeve's tooth pressing against the pawl. like a ratchet tooth. using the same design 48 . which permitted the spring to contract and wrap tightly around the driving sleeve. wear would be excessive. When the clutch locked up the driven mechanism coasted and its inertia rotated the disc until a tooth on it engaged a pawl that kept it from reversing. If the lever engaged the pawl. part of the clock's gear train. including the pre-World War II Hammond manual-start clocks. The spring did not rotate. The first pawl had a projection that engaged a trip lever. The inertia of the rotor going backwards engaged the clutch and wound the spring. the clutch was disengaged. Coupled to the rotor by one (or possibly two) stages of reduction gearing was a wrap-spring clutch-brake. Many different types of synchronous clock motors were used. which in turn kept the third one engaged. their behaviour was chaotic and they were equally likely to start rotating in the wrong direction. creating the cascaded lockup just described.principles. it restarted the motor in the correct direction. but also had some spring action. a mounting surface for the pressure plate. Some designs had no explicit spring as such—but were simply compliant mechanisms. Some types of self-starting synchronous motors always started when power was applied. 49 . Inside the hollow disc-shaped housing were two or three freely floating pawls arranged so that when the clutch was tripped. the other was free. the IBM Selectric typewriter had several of them. the load torque on the first pawl to engage created force to keep the second pawl engaged. but in detail. but if the trip lever engaged the clutch would quickly unlock. The clutch-brake locked up when rotated backwards. The clutch did not slip once locked up. a mounting for the starter driven gear. Kickback clutch-brakes These mechanisms were found in some types of synchronous-motor-driven electric clocks. As it unwound. the flywheel is a factor in engine balance. These were typically disc-shaped assemblies mounted on the drive shaft. As the clutch rotated it would stay locked up if the trip lever were out of the way. The mechanism was lubricated and wear did not present a problem. and on some engines. This sequence happened quite fast. One end was fixed. As well. When the trip lever moved out of the way the first pawl engaged. on the order of milliseconds. It rode freely but closely on the rotating member. CLUTCH COMPONENTS: 1) FLYWHEEL: The flywheel provides a friction surface for the clutch disc. Used flywheels can be re-surfaced. The amount of material removed from the face can affect which clutch release bearing should be used. This is attached to a splined hub that the transmission input gear protrudes into.005 (five thousandths) of an inch.The condition of the friction surface of the flywheel is important for proper clutch function. It has a friction material riveted to each side of a wavy spring (called a marcel). This is the "driven" part of the clutch. Though not a composite part of the clutch flywheel is what the clutch derives power from and delivers it to the gear box. This should be done by grinding rather than lathe turning as less material is removed. The surface should be smooth and free of burned spots and surface cracks. Face runout should not exceed . 50 . A flywheel should always be checked for runout on the engine it will be used on. 2) CLUTCH DISC: A clutch disc consists of springs between the hub and the disc to absorb the shock when the clutch is engaged. The organic is best for all around use. release finger. The metallic is preferred by some for severe duty applications but requires high spring pressures and is hard on the flywheel and pressure plate friction surfaces. anti-rattle clip. 51 . Avoid solid hub clutches and clutches without marcel as they will always chatter when used in vehicles with a rear differential mounted on springs (as opposed to a transaxle design). eye bolt & a fulcrum pin. 3) PRESSURE PLATE: As the name defines a pressure plate is present to reduce pressure when the power transfer occurs it consists of coil springs. strut. These are organic and metallic.There are basically two types of friction material used for clutch lining. 4) CLUTCH COVER: The clutch cover is used to cover the entire clutch assembly. 5) HUB AND RELEASE FORK: The hub is where the power from the fly wheel is transferred to the gear box and the release fork releases the clutch from engaged position once the transmission is complete.001 and . pre-lubed bushing rather than an actual bearing. but by far. this is a porous bronze.002 total. It pilots the end of the transmission input gear in the crankshaft. The bronze bushing type should be a press fit in the crankshaft bore. 6) PILOT BUSHING In most cases. as it is often called. It must be installed carefully. A few applications still use an actual bearing and others use a needle roller type bearing. You cannot use a roller bearing on a transmission shaft originally designed for a bronze bushing due to different type of heat treatment on the shafts. the most common type is bronze.003 clearance on the transmission shaft when installed. The pilot bushing is seldom thought of as a part of the clutch system but it is one of the most vital parts of the system. The pilot bushing is only functional when the clutch is disengaged but it is a factor in input gear alignment at ALL times. it can cause serious clutch problems or transmission failure. 52 . If it is worn or not running "true". Pilot bushing bore runout should always be checked with a dial indicator and should be within . It should have between . its tubular snout is the surface on which the throw out bearing rides on its way into to depress the springs of the pressure plate. However. vary considerably with the particular engine. Thirdly. This first is as its name implies. Conversions often require special and modified retainers to achieve compatibility. The second is to provide a register on which the bell housing must centre. The carriers.7) CLUTCH RELEASE BEARING As its name implies. in some cases. 53 . improper linkage adjustment or riding the clutch with your foot when driving can wear the bearing prematurely. It is often referred toas a "throw-out" bearing. They come on a number of different style carriers.Because the release bearing only works when the clutch is being released it usually lasts quite a long time. This fact is important and will be discussed further when we get to the part about setting up the clutch linkage. this is the bearing that releases the clutch. 8) TRANSMISSION FRONT BEARING RETAINER This great device has three critical functions. Normally there should be a minimum of 1/16" clearance between the face of the bearing and the three release fingers or diaphragm spring of the pressure plate when the clutch is engaged. This is feature is sometimes overlooked with expensive consequences. These two diagrams include every parts of the clutch. 54 . ADVANTAGES 1) 2) 3) 4) 5) 6) 7) It requires simple maintenance cares. Replacement of parts is easy. Easy to handle Low cost automation project Repairing is easy. The safety system for automobile. because of the main parts are screwed. 2) Air tank is required for this operation. Checking and cleaning are easy. DISADVANTAGES 1) Initial cost is high. CONCLUSION 55 . 56 .