Automotive Electronics

AutomotiveElectronics Faculty: Sankar Dasiga Why this course? • KPIT is one of the reasons only!! (Opportunities exist in many Automotive OEMs, tier 1 / 2 and service companies) • It is a true domain of application of many courses / topics - + Controls + Signal Processing + Microcontrollers + Embedded Systems + CCN + Programming in C etc • Use of Electronics in Automobiles is ever increasing so much so, the present day Automobiles are equally electronic systems as being mechanical systems!!  Electronics is used in the Engine Control (MPFI), Safety (Airbag System), Passenger Comfort (Controlling the Air-conditioning), Passenger Entertainment (Multimedia Player), Driver Assistance (Parking Assistance, Navigation, Google Maps) etc  Now there is a push world over on advanced Automotive applications like Collision Avoidance, Detection of Pedestrian crossing, Vehicle to Vehicle Communication, Driverless Riding etc  In addition Electronics is used in Diagnostics like – checking of level of Engine, Brake etc oils / fluids etc Why this course? • Automotives are not cars alone .. Nowadays we have lot of electronics in Two-wheelers, and Buses, and, more has to happen in vehicles like Goods Transport Vehicles (Tempos, Trucks etc), JCB etc • Electric vehicles is another area which is fast evolving Meaning lot more still to come and more opportunities!!! • It’s a demanding domain with several “Standards” / “Guidelines”  Automotive Standards - for the Hardware  Guidelines such as MISHRA for the Software As such, if someone has the exposure to and experience of working with the Automotive Standards / Guidelines, he / she can easily work on the development of systems for the domains – military, space, consumer etc • Several tools are used at various stages of development of Automotives Electronic Systems; as such knowing about and understanding them is a significant advantage!!  Besides there are innumerable topic specific white papers and material Books etc from the vendors / players in the domain available on the net. Also available on the net are several youtube videos 1. William Ribbens, “Understanding Automotive Electronics”, 6th Edition, Elsevier 2. Tom Denton: "Advanced Automotive Diagnosis”, 2nd Edition, Elsevier, 2006 • References 1. Ronald K Jurgen: "Automotive Electronics Handbook, 2nd Edition, McGraw-Hill, 1999 2. James D Halderman: -Automotive electricity and Electronics", PHI Publication 3. Terence Rybak. Mark Stefika: Automotive Electromagnetic Compatibility (EMC), Springer. 2004 4. Allan Bonnick.: “Automotive Computer Controlled Systems” Diagnostic Tools and Techniques". Elsevier Science, 2001 5. Uwe Kieneke and Lars Nielsen: Automotive Control Systems Engine, Driveline and Vehicle, 2nd Edition Springer Verlag, 2005 6. David Alciatore, Michael Histand: "Introduction to Mechatronics and Measurement Systems (SIE) TMH, 2007 7. Iqbal Husain: "Electric and Hybrid Vehicles: Design fundamentals” CRC Press, 2003. 8. G. Meyer, J. Valldorf and W. Gessner: "Advanced Microsystems for Automotive Applications”, Springer. 2009 9. Tracy Martin: “How to Diagnose and Repair Automotive Electrical Systems" Motor Books/MBl Publishing Company. 2005. 10. Mehrdad Ebsani. Ali Emadi, Yimin Gao: - “Modern electronic. Hybrid Electric and Fuel Cell Vehicles: Fundamentals. Theory and Design". 2nd CRC Press. 2009 11. Marc Herniter: “Introduction to Model Based System Design – Rose Hulman Institute of Technology Trends in Automotive CAR Technology TRAFFIC DRIVER SKILLS > 1891 mechanical system very low very high technical skills > 1920 + pneumatic systems low high technical skills + hydraulic systems low driving skills > 1950 + electric systems increasing good technical skills increasing driving skills > 1980 + electronic systems congestion low technical skills + optronic systems starts high driving skills > 2010 + nanoelectronics congested very low technical skills + biotronic systems optimization decreasing driving skills starts > 2040 + robotics maximal and no technical skills + nanotechnology optimized no driving skills Unit 1 Major Players General Generics General Tools & Semicon’s OEM’s Tier1’s Software Services Top Automotive OEMs • OEM: Original Equipment Manufacturer. Though some in the automotive industry have taken to referring to car companies themselves as OEMs, the term relates to any company that manufactures parts for use in new vehicles. • Some of the Top Automotive OEMs are: Toyota, Volkswagen, General Motors, Hyundai, Ford, Nissan, Fiat / Chrysler, Honda, Suzuki, Peugoet Automotive Supply Chain Market Drivers for Auto Industry Government International trade Suppliers • TREAD Act • Exchange rate • Global presence • Disposal/ •Trade acts/ tariff • Emerge of low • reconciliation cost destination •Safety and environmental • Increasing Tiers legislations Technology Competition OEM • Telematics • Competing on cost / features • Consolidation • Hybrid fuel • Collaborative • Globalized • Overcapacity design • Distributed operation • High FG inventory •Trade union Customer Market • Technology • Sluggish growth adoption differs • Weak economic outlook • Variety • Globalization Supply Chain Vs Value Chain Supply Chain Vs Value Chain Evolution of Automotive Electronics • The dawn of automotive electronics came in the early 1970s, when the only electronics in a car were the radio, the alternator (diodes) and the voltage regulator that controlled the alternator. The last 30 years have seen rapid technological innovations in automotive electronics, driven primarily by advancement in semiconductors and related software that controls the systems 1. 1970’s: Introduction of electronics for engine controls 2. 1980’s: Anti-lock braking introduced 3. Early 1990’s: Airbags become standard 4. Late 1990’s: Rapid expansion of body electronics – seat motors (body computers), instrument panel lighting, auto locking systems and keyless entry 5. Early 2000’s to date: infotainment, including sophisticated audio and video; signals sent via satellite (such as the OnStar System); GPS and mapping capabilities; satellite radio 6. Late 2000’s : Steer-by-wire, wireless connectivity 7. Trends 2020 – Connected Cars and Autonomous vehicles Automotive Electronics Today… Exchangeability and Reuse – Supply Chain Evolution of Safety Systems Some Challenges in Automotive Electronics Industry 1. Standardization – Hardware as well as Software 2. Availability of hardware components • Automotive technology cycles exceeding those for semiconductor industry • Redesign with new components requires extensive validation 3. Service personnel not qualified for electronics or software based systems 4. Embedded systems with mostly hard real-time requirements • Drive train -> order of 100μs • Chassis -> order of ms • Body-> order of 10..100ms Electronics controls used in various car systems today Factors influencing Automotive Electronic Systems Automobile: 1. increasingly more product variations within a car family, 2. manufacturers offering full range of vehicle type spectrum 3. design cycle time and resources decreasing 4. leading manufacturers competing for technology leadership and quality Mechatronic Systems: 1. innovative functionality realized through interaction of formerly autonomous units resulting in highly complex distributed system architecture 2. only few strong suppliers capable of designing future systems 3. personnel and financial project resources becoming scarce 4. sourcing decisions dominated by financial factors (cost) 1 3/13/ © KPIT Technologies 9 2018 Limited Vehicle Domains Body electronics: Central vehicle functions such as Infotainment: Functions for access management systems information, entertainment and and anti-theft devices communication - instrument actuation of windows, panel, audio system, antenna tailgates, seats, and wipers, tuner, video module, navigation or cabin air management system, telephone etc.), including the central HMI (Human Machine Chassis and driver Interface) assistance: Functions enabling safe vehicle Powertrain: All functions dynamics, such as ABS controlling the generation of driving power and its conversion Passive safety: Functions for into propulsion: Digital engine collision detection and control, gear control, fuel pump, injury mitigation such as onboard diagnostics seat belt pre-tensioners, airbags, pyrotechnic roll- over bars etc 2 3/13/ © KPIT Technologies 0 2018 Limited Why Systems Engineering Approach Automotive development unquestionably has its roots in traditional engineering, and the prevailing culture in development centers is dominated by “car guys” OEMs introduced systems engineering as a sustainable approach to developing reliable E/E systems as part of the PDP. The International Council on Systems Engineering (INCOSE) defines System Engineering as an interdisciplinary means to enable the realization of successful systems by 2 3/13/ © KPIT Technologies 1 2018 Limited Classical V-Model of Development 2 3/13/ © KPIT Technologies 2 2018 Limited Example : Engine Control 2 3/13/ © KPIT Technologies 3 2018 Limited Automotive Systems Systems of an Automobile Systems of an Automobile Rear Wheel Drive Rear Wheel Drive Front Wheel Drive The Engine Major Components of the Engine Role of Electronics Engine Block Cylinder Head The Piston Piston Connection to Crank Shaft Valve Operating Mechanism Valve Operating Mechanism 4-stroke / cycle SI Engine Intake Stroke Compression Stroke Power Stroke Exhaust stroke Power Pulse from a 4-cylinder Engine Engine Control Engine Control Ignition System Ignition System Ignition System Circuits • Primary Circuit • Secondary Circuit – (Low Voltage) – (High Voltage) • Ignition Switch • Coil Secondary • Resistor Winding • Coil Primary • Coil Wire Winding • Distributor Cap & • Ignition Module Rotor • Pick-up Assembly • Plug Wires • Spark Plugs Coil Ignition Circuit Distributor Ignition Timing • Ignition is timed – So it occurs just before piston reaches top of compression stroke • Ignition timing variation – Computer determines best ignition timing setting • Advanced or retarded in response to engine speed and load changes, altitude, and engine temperature – Intake manifold vacuum senses engine load Ignition Timing (cont'd.) • Computer systems continuously adjust spark timing to optimize power and emissions • Some functions were not possible with mechanical distributors – Throttle position sensor determines throttle position – MAP sensor determines intake manifold pressure – Primary trigger interprets engine speed – Coolant temperature sensor allows adjustments for changes in engine temperature Automobile Drivertrain System Transmission Differential Differential Suspension System Suspension System Shock Absorber Shock Absorber Assembly Shock Absorber Assembly Brakes Disk Brake System Disk Brake System Disk Brake System Steering System Steering System Steering System Steering Mechanism Automotive Steering System Power Steering System Power Steering System Power Steering System Electric Steering: an Example Electric Propulsion • An alternative to the Internal Combustion (IC) engine as an automotive power plant is electric propulsion • The necessary electric energy required was supplied by storage batteries. • Issue; the energy density (i.e., the energy per unit weight) of storage cells has been and continues to be significantly less than gasoline or diesel fuel • On the other hand, the exhaust emissions coming from an electrically powered car are (theoretically) zero, making this type of car very attractive • The efficiency of electric propulsion is improved by raising the operating voltage from the present-day 14-volt systems (i.e., using 12-volt-rated batteries) to 42-volt systems – there will be two separate electrical buses, one at 14 volts and the other at 42 volts. The 14-volt bus will be tied to a single 12-volt (nominal) battery. The 42-volt electrical bus will be tied to three 12-volt batteries connected in series – The 14-volt bus will supply power to those components and subsystems that are found in present-day vehicles including, for example, all lighting systems and electronic control systems. The 42-volt bus will be associated with the electric drive system Hybrid Vehicle System • An attractive option for electrically powered cars is a combination of a gasoline-fueled engine with an electric propulsion system • The hybrid vehicle is capable of operation in three modes in which power comes from: (a) the engine only; (b) the electric motor only; and (c) the combined engine and electric motor • To achieve these modes of operation, the engine and electric motor must be coupled to the drivetrain • The electric motor in this configuration is the generator / alternator for electric power as well as the motor for the electric propulsion. Under mode (a), the motor rotates freely and neither produces nor absorbs any power. In modes (b) and (c), the motor receives electric power from an electronic control system and delivers the required power to the drivetrain. • Although many electric motor types have the potential to provide the mechanical power in a hybrid vehicle, the brushless d-c motor is preferred Hybrid Vehicle System • The engine and motor are coupled to the drivetrain via a power-splitting device capable of controlling the power split between IC engine and electric motor. • The relative power from the IC engine and the electric motor is adjusted to give optimum performance during normal driving Note: A transaxle performs both the gear-changing function of a transmission and the power- splitting ability of an axle differential in one integrated unit Electronic Control Unit (ECU) • In automotive electronics, ECU is a generic term for any system or subsystems in a motor vehicle embedded system that controls one or more of the electrical systems An electronic control unit An ECU is made up of (ECU) is a embedded hardware and software electronic device, basically (firmware) a digital computer The most important of The software (firmware) is The hardware is made up of these components is a a set of lower-level codes various electronic microcontroller chip along that runs in the components on a PCB with an EPROM or a Flash microcontroller memory chip Components of ECU ECU Internal Blocks ECUs and Vehicle Internal Systems Customer/Supplier Relationships V-Model of Development Core Process for Electronic Systems and Software Development Analysis of User Requirements • The objective of this process is to define the logical system architecture based on the project-relevant user requirements • Logical system architecture includes – definition of the function network – the function interfaces – the communication among the functions of electronic systems and software Analysis of the Logical System Architecture • The logical system architecture is the basis for the specification of the actual technical system architecture • The analysis of technical implementation alternatives is based on a unified logical system architecture and is supported by a variety of methods of the participating engineering disciplines • The technical system architecture also includes a definition of all functions or sub functions that will be implemented by means of software • This definition is also called software requirements Analysis of Software Requirements and Specification of Software Architecture • The software requirements thus defined are analyzed in the next step, and the software architecture is specified • That is, the software system boundaries and interfaces are defined, with software components, software layers, and operating modes Specification of software components • This step is followed by the specification of software components • The procedure initially assumes an “ideal-world” environment • This means that this step ignores any implementation details, such as the implementation in integer arithmetic Design, Implementation, and Tests of Software Components • In the design phase, the previously ignored real- world aspects are subject to scrutiny • At this point, all details affecting the implementation must be defined • The resulting design decisions govern the implementation of software components • At the end of this step, software components are tested Integration of Software Components and Software Integration Tests • When the development of the software components is completed—frequently done by applying the principle of division of labor—and components have passed the subsequent tests, integration can begin • After integration of the components into a software system, a software integration test concludes this step Integration of System Components and System Integration Tests • In the next step, the software must be installed on the ECU hardware to provide the respective ECU with functional capabilities • The ECUs then must be integrated with the other electronic system components such as setpoint generators, sensors, and actuators • In a subsequent system integration test, the interaction of all systems with the plant is evaluated Calibration • The calibration of the ECU software functions comprises their parameterization • Parameter settings may be supplied by the software in the form of characteristic values, characteristic curves, and characteristic maps System Test and Acceptance Test • A system test focusing on the logical system architecture can be performed, with an acceptance test that concentrates on user requirements Different Types of ECU • ECM – Engine Control module • EBCM – Electronic Brake control module • PCM – Powertrain control module • VCM – Vehicle control module • BCM – Body control module Other Electronic Control Systems Key Design Considerations for ECUs • Numerous interfaces with sensors and actuators are located primarily on the engine or transmission • ECUs are installed close to the components they control • The operating conditions for these ECUs tend to be harsh in many cases • ECUs are exposed to an extended temperature range, humidity, and vibration ECUs for various Automotive Systems • Various Systems are discussed based on : – User interfaces and setpoint generators – Sensors and actuators – Software functions – Installation space – Model variants and scalability Airbag System www.infineon.com Electric Power Steering (EPS) www.infineon.com Redundancy!! • Safety critical systems are built with fault tolerance- with many of its essential information would be derived from more than one sensor and, handled by more than the bare necessity hardware (path as well as components) • For Eg., a brake-by-wire system has three main types of redundancy: 1. Redundant sensors in safety critical components such as the brake pedal. 2. Redundant copies of some signals that are of particular safety importance such as displacement and force measurements of the brake pedal copied by multiple processors in the pedal interface unit. 3. Redundant hardware to perform important processing tasks such as multiple processors for the electronic control unit (ECU) • Another example of safety critical system is Steer-by-Wire brake-by-wire system Note: Brake calipers squeeze the brake pads against the surface of the brake rotor to slow or stop the vehicle. Brake calipersare essential to your car's ability to stop and are arguably one of the most important automobile brak e parts. Most carstoday have disc brakes, at least for the front wheels Tools Used in Automotive System Development • Several tools are used at different stages / phases in the development of automotive systems – to handle complexities (Several Components / Features / Versions, Multiple Teams / Functions / Sites, Variants, enforce standards (automotive standards – for safety etc) • Some of the examples – Project Management (Eg., MS Project) – Supply Chain Management (ERPs such as SAP) – Requirements Management (Eg., Doors) – System Modeling (tools for SysML) – Modeling and Simulation (Eg., MatLab) – Software Configuration Management (Eg., ClearCase) – Software Development - IDEs such as Keil with plug-ins for i) enforcing coding standards such as Mishra, ii) simulation and debugging, iii) emulation of the hardware – Test Benches, Test Cases and Tracking of Issues / Bugs (Eg., Jira, Bugzilla) • Besides innumerable templates and word processing tools are used for documentation • Further, several templates are used for reviews (such as documents, code, test results) are employed Unit 2 System!! System Approach Electronic Systems Transducer, Sensor and Actuator • Transducer A device that converts a signal from one physical form to a corresponding signal having a different physical form – Physical form: mechanical, thermal, magnetic, electric, optical, chemical... – Transducers are ENERGY CONVERTERS or MODIFIERS • Sensor: an input transducer (i.e., a microphone) • Actuator: an output transducer (i.e., a loudspeaker A System with Sensors and Actuators Measurement • The process of comparing an unknown quantity with a standard of the same quantity (measuring length) or standards of two or more related quantities (measuring velocity) Types of Sensors • Active vs. Passive – Does sensor draw energy from the signal ? • Digital vs. Analog – Is the signal discrete or continuous? – Digital sensors • The signal produced or reflected by the sensor is binary – Analog sensors • The signal produced by the sensor is continuous and proportional to the measurand • Null and deflection methods • The signal produces some physical (deflection) effect closely related to the measured quantity • Input – Output configuration – The signal produced by the sensor is counteracted to minimize the deflection – That opposing effect necessary to maintain a zero deflection should be proportional to the signal of the measurand Calibration • A sensor or instrument is calibrated by applying a number of KNOWN physical inputs and recording the response of the system Sensor Characteristics • Static characteristics The properties of the system after all transient effects have settled to their final or steady state – Accuracy – Discrimination – Precision – Errors – Drift – Sensitivity – Linearity – Hysteresis (backslash) • Dynamic Characteristics The properties of the system transient response to an input – Zero order systems – First order systems – Second order systems Sensor Fundamentals • Range – Every sensor is designed to work over a specified range – The design ranges are usually fixed, and if exceeded, result in permanent damage to or destruction of a sensor • Sensitivity – Sensitivity of a sensor is defined as the change in output of the sensor per unit change in the parameter being measured – The factor may be constant over the range of the sensor (linear), or it may vary (nonlinear). • Resolution – Resolution is defined as the smallest change that can be detected by a sensor • Response – The time taken by a sensor to approach its true output when subjected to a step input is sometimes referred to as its response time. Sensor Fundamentals • Linearity – The most convenient sensor to use is one with a linear transfer function. That is an output that is directly proportional to input over its entire range, so that the slope of a graph of output versus input describes a straight line. • Hysteresis – Hysteresis refers to the characteristic that a transducer has in being unable to repeat faithfully, in the opposite direction of operation, the data that have been recorded in one direction • Full Scale Output – Full scale output (FSO) is the algebraic difference between the electrical output signals measured with maximum input stimulus and the lowest input stimulus applied. This must include all deviations from the ideal transfer function • Accuracy – A very important characteristic of a sensor is accuracy which really means inaccuracy. Inaccuracy is measured as a ratio of the highest deviation of a value represented by the sensor to the ideal value. It may be represented in terms of measured value Accuracy and Errors • Systematic errors • Result from a variety of factors • Interfering or modifying variables (i.e., temperature) • Drift (i.e., changes in chemical structure or mechanical stresses) • The measurement process changes the measurand (i.e., loading errors) • The transmission process changes the signal (i.e., attenuation) • Human observers (i.e., parallax errors) • Systematic errors can be corrected with COMPENSATION methods (i.e., feedback, filtering) Accuracy and Errors • Random errors – Also called NOISE: a signal that carries no information – True random errors (white noise) follow a Gaussian distribution – Sources of randomness: – Repeatability of the measurand itself (i.e., height of a rough surface) – Environmental noise (i.e., background noise picked by a microphone) – Transmission noise (i.e., 60Hz hum) – Signal to noise ratio (SNR) should be >>1 – With knowledge of the signal characteristics it may be possible to interpret a signal with a low SNR (i.e., understanding speech in a loud environment Signal Conditioning Signal conditioning means manipulating an analog signal in such a way that it meets the requirements of the next stage for further processing Key signal conditioning technologies provide distinct enhancements to both the performance and accuracy of data acquisition systems. Signal Conditioning Techniques • Amplification – Amplifiers increase voltage level to better match the analog-to-digital converter (ADC) range, thus increasing the measurement resolution and sensitivity. In addition, using external signal conditioners located closer to the signal source, or transducer, improves the measurement signal-to-noise ratio by magnifying the voltage level before it is affected by environmental noise • Attenuation – Attenuation, the opposite of amplification, is necessary when voltages to be digitized are beyond the ADC range. This form of signal conditioning decreases the input signal amplitude so that the conditioned signal is within ADC range. Attenuation is typically necessary when measuring voltages that are more than 10 V • Isolation – Isolated signal conditioning devices pass the signal from its source to the measurement device without a physical connection by using transformer, optical, or capacitive coupling techniques. In addition to breaking ground loops, isolation blocks high-voltage surges and rejects high common-mode voltage and thus protects both the operators and expensive measurement equipment. Signal Conditioning Techniques • Filtering – Filters reject unwanted noise within a certain frequency range. Oftentimes, low pass filters are used to block out high-frequency noise in electrical measurements, such as 60 Hz power. Another common use for filtering is to prevent aliasing from high-frequency signals. This can be done by using an antialiasing filter to attenuate signals above the Nyquist frequency. • Excitation – Excitation is required for many types of transducers. For example, strain gauges, accelerometers thermistors, and resistance temperature detectors (RTDs) require external voltage or current excitation Signal Conditioning Techniques • Linearization – Linearization is necessary when sensors produce voltage signals that are not linearly related to the physical measurement. Linearization is the process of interpreting the signal from the sensor and can be done either with signal conditioning or through software. Thermocouples are the classic example of a sensor that requires linearization Automotive Sensors & Actuators • Automotive manufacturers are continuously increasing the use of electronics systems to- – improve vehicle performance – Safety – passenger comfort. • Sensors and actuators integrated with automotive control computers help optimize vehicle performance while improving reliability and durability. Sensor- Input Microcontroller Actuator- Output A Generic (Automotive) DAS MEASURED ELECTRICAL VOLTAGE SERIAL QUANTITY OUTPUT OR PARALLEL SIGNAL SENSOR CONDITIONING A/D CPU Selection Criteria • What is to be measured • Magnitude, range, dynamics of measured quantity • Required resolution, accuracy • Cost • Environment • Interface Requirements: – Output quantity (voltage, current, resistance,…) – Sensitivity – Signal conditioning – A/D requirements (#bits, data rate) Typical Electronic Engine Control System MAF - Mass (Air) Flow sensor TPS – Throttle Position Sensor EGO – Exhaust Gas Oxygen EGR - exhaust gas recirculation Thermistors • Commonly used for temperature measurement on vehicles • They are made out of semiconductor materials such as cobalt or nickel oxides • Change in temperature causes change in resistance of the thermistor • Most of the thermistors are of the negative temperature coefficient (NTC) type • Resistance range – Several Kilo Ohms at 0oC to a few hundred Ohms at 100o C. Thus it can be more sensitive. Thermistors • Important factors for accurate measurements: – Supply must be constant – Current through the thermistor should be negligible ( I.e. No heating effect) • These devices are commonly used as sensors for- – Air intake – Battery – Engine and transmission temperature – Air conditioning and internal/external environmental temperature – Oil and gas temperatures. Temperature Sensor • Application Engine management • Function Registration of temperature of coolants, fuel and air • Installation Engine block, coolant circuit, air-intake tract • Sensing principle NTC technology (hot conductor, negative temperature coefficient) • Technical data – Temperature range: -40°C...+150°C – Time constant: 5 s...44 s (depending on type) – Accuracy: ± 0.8 K at 100°C ±1.5 K at 20°C Thermocouples • When two dissimilar metals are joined together, the thermocouple junction is formed • Among the two junctions used, one of the junctions is kept at a constant known temperature where as the other at the temperature to be measured • Ex: 70% platinum & 30% rhodium alloy known as B Type , Has a range of 0 15000C • Used for measuring Exhaust Gas and turbocharger temperatures in a Magnetic Sensors-Variable Reluctance (VR) Sensors • Used mainly for speed and position measurements of rotating members. (Ex: crank shaft speed and position sensing) • The variable reluctance sensor is an electro- magnetic device consisting of a permanent magnet surrounded by a winding of wire • The sensor is used in conjunction with a ferrous target that either has notches or teeth • Rotation of the target wheel near the tip of the sensor changes the magnetic flux, creating an analog voltage signal in the sensor coil • Though the voltage may vary depending on the speed of rotating member, the frequency is used for measurement Variable Reluctance (VR) Sensors • A common method of converting this signal into a useful signal for interfacing with other digital circuit is by using a Schmitt trigger circuit • Another method is by using a quenched oscillator circuit as shown in the figure. This circuit has good resistance to interference Magnetic Reluctance Crankshaft Position Sensor • One of the engine sensor configurations that measures crankshaft position directly (using magnetic phenomena) This sensor consists of a permanent magnet with a coil of wire wound around it. A steel disk that is mounted on the crankshaft (usually in front of the engine) has tabs that pass between the pole pieces of this magnet. The passage of each tab can correspond to the position of a cylinder on its power stroke. This sensor is of the magnetic reluctance type and is based on the concept of a magnetic circuit. A magnetic circuit is a closed path through a magnetic material (e.g., iron, cobalt, Hall Effect Transducers Principle: • If a certain type of crystal is carrying a current in a transverse magnetic field, then a voltage will be produced at right angles to the supply current • The magnitude of the voltage is proportional to the supply current and to the magnetic field strength • With proper design, the output of this device is a square wave • The principle is used in distributors and also to detect the current flowing on a cable Hall Effect Transducers • These sensors are mainly used for sensing larger change in position – Example: The throttle position sensor, which is a potentiometer • It is supplied with a stable 5 Volts DC • The wiper is driven by the throttle shaft. Thus , the voltage from the wiper contact will be proportional to the throttle position • In many cases,throttle potentiometer is used to indicate the rate of change of throttle position. This information is used in implementing acceleration enrichment or over- run fuel cut-off Work-in-Progress Where do we find electronics in a car