Automotive Electronics for Mechanical Engineering

Automotive Electronics

1. SYLLABUS UNIT IV: VEHICLE MOTION CONTROL AND AUTOMOTIVE DIAGNOSTICS Cruise control system, Digital cruise control, Timing light, Engine analyzer, On- board and off- board diagnostics, Expert systems. Stepper motor based actuator, Cruise control electronics, Vacuum – antilock braking system,Electronic suspension system Electronic steering control, Computer- based instrumentation system, Sampling and Input and output signal conversion, Fuel quantity measurement, Coolant temperature measurement, Oil pressure measurement, Vehicle speed measurement, Display devices, Trip- Information- Computer

2. Cruise Control System What is cruise control system The purpose of a cruise control system is to accurately maintain a speed set by the driver without any outside intervention by controlling the throttle- accelerator pedal linkage. The earliest variants of cruise control were actually in use even before the creation of automobiles. The inventor and mechanical engineer James Watt developed a version as early as the 17th century, which allowed steam engines to maintain a constant speed up and down inclines. Cruise control as we know it today was invented in the late 1940s, when the idea of using an electrically- controlled device that could manipulate road speeds and adjust the throttle accordingly was conceived.

3. Cruise Control System How does cruise control work? The cruise control system controls the speed of your car the same way you do – by adjusting the throttle (accelerator) position. However, cruise control engages the throttle valve by a cable connected to an actuator, rather than by pressing a pedal. The throttle valve controls the power and speed of the engine by limiting how much air it takes in (since it’s an internal combustion engine). The driver can set the cruise control with the cruise switches, which usually consist of ON, OFF, RESUME, SET/ACCEL and COAST. These are commonly located on the steering wheel or on the windshield wiper or turn signal stalk. The SET/ACCEL knob sets the speed of the car. One tap will accelerate it by 30km/hr mph, two by 31km/hr and so on. Tapping the knob in the opposite direction will decelerate the vehicle. As a safety feature, the cruise control system will disengage as soon as you hit the brake pedal.

4. Cruise Control System Figure: Block Diagram of Cruise Control System

5. Adaptive Cruise Control System Adaptive cruise control (ACC) is an active safety system that automatically controls the acceleration and braking of a vehicle. It is activated through a button on the steering wheel and cancelled by driver’s braking and/or another button. Figure: Adaptive Cruise Control

6. Adaptive Cruise Control How does adaptive cruise control work? By monitoring other vehicles and objects on the road, adaptive cruise control enables a safe and comfortable driving experience. It does so by helping the driver keep a steady vehicle speed at a given moment. The driver can set their preference regarding certain factors, such as the distance to the car in front, driving mode – for example, economical, sporty or comfortable – and others. Together with information about speed limits, road curvature, accidents data and more, these choices influence the automatically selected speed. Cruise control has come a long way from its early days in its quest to assist drivers on the road. When first introduced, it was only found in luxury car models due to its high production cost. As less expensive sensors reached the market, adaptive cruise control is steadily becoming a standard feature in new vehicles today.

7. Adaptive Cruise Control Figure: Block Diagram:- Adaptive Cruise Control System

8. On-Board Vs Off-Board Diagnosis The state of the motion or rest of the car becomes primarily important. Also, the diagnostics parameters change when the vehicle is moving and when it is at rest in a garage. In order to cover both these scenarios, off- board and on- board vehicle diagnostics have been introduced. The typical vehicle diagnostics feature checks the state of functions performed by the subsystems, sensors and other such components. The errors reported by all these components are recorded in the error memory in the form of DTCs (Diagnostic Trouble Codes). While on- board vehicle diagnostics protocols like OBD/OBD2 are tasked primarily with emission related diagnosis, off- board vehicle diagnostics (UDS, KWP etc.) handle the diagnostics related to every other vehicle ECU (Electronic Control Unit).

9. On-Board Vs Off-Board Diagnostics What’s the Functional Scope of On- board Diagnostics System On- board vehicle diagnostics (OBD2) comes into the picture when the vehicle is moving. The tests are being conducted while the vehicle is on the road. The test results can be seen on the vehicle’s dashboard in the form of MIL (Malfunction indicator light) or an OBD tester tool. The data that the OBD makes accessible is related to: Emission Control System Engine and Transmission ECUs (powertrain) OBD2 was mandatory for all the cars that were manufactured in the USA after the year 1996. This was essentially done to keep the emissions level of the vehicles in check. Every parameter related to the vehicle emission such as info from oxygen sensors and the fuel injectors etc. is checked. In case of any malfunction, an MIL (malfunction indicator light) is triggered to warn the vehicle owner.

10. On-Board Vs Off-Board Diagnostics The error that triggers the MIL is also stored in the automotive ECU which can later be retrieved by the tester tool at the garage. This error code helps the technicians to pin- point the emission issue and rectify it. The technician sends the PIDs and gets the response corresponding to that PID. The technician can then zero in on the specific issue that is causing the trouble. These tester tools perform generic tests that are similar for most vehicles.

11. On-Board Vs Off-Board Diagnostics What’s the Functional Scope of Off- board Diagnostics System Off- board vehicle diagnostics takes care of the diagnostics of every other vehicle ECU function other than emission. There are several protocol standards defined for off- board diagnostics, however, Unified Diagnostics Services (UDS) is the most popular diagnostic protocol. The diagnostics manager of the UDS protocol stores every issue as fault codes called Diagnostics Trouble Code (DTC). When a vehicle is running, the off- board diagnostics is also active. However, the contrast with on- board diagnostics lies in the reporting part.

12. On-Board Vs Off-Board Diagnostics In case of OBD, the fault is communicated to the information cluster by triggering the Malfunction indicator light. Whereas, in the off- board diagnostics, no such instant reporting is carried out. The issue is stored in the EEPROM part of the vehicle ECU for retrieval at the service garage using a vehicle diagnostic testing tool. The scope of off- board diagnostics (UDS) is not limited to just storing the diagnostic trouble codes (DTCs). It is capable of offering services such as vehicle ECU reprogramming, remote routine activation, writing data on the automotive Electronic Control Unit and even more.

13. Modern Automotive Instrumentation The evolution of instrumentation in automobiles has been influenced by electronic technological advances in much the same way as the engine control system. Of particular importance has been the advent of the microprocessor,solid- state display devices, and solid- state sensors. Figure: General Instrumentation System

14. Modern Automotive Instrumentation In electronic instrumentation, a sensor is required to convert any nonelectrical signal to an equivalent voltage or current. Electronic signal processing is then performed on the sensor output to produce an electrical signal that is capable of driving the display device. The display device is read by the vehicle driver. If a quantity to be measured is already in electrical form (e.g. the battery charging current), then this signal can be used directly and no sensor is required. In contemporary automotive instrumentation, a microcomputer (or related digital subsystem) performs all signal- processing operations for several measurements. The primary motivation for computer- based instrumentation is the great flexibility offered in the design of the instrument panel.

15. Modern Automotive Instrumentation Figure: Computer Based Instrumentation System

16. Modern Automotive Instrumentation All measurements from the various sensors and switches are processed in a special- purpose digital computer, i.e. the instrumentation computer. The processed signals are routed to the appropriate display or warning message. It is common practice in modern automotive instrumentation to integrate the display or warning in a single module that may include both solid- state alphanumeric display, lamps for illuminating specific messages, and traditional electromechanical indicators. For convenience, this display system will be termed the instrument panel (IP).

17. Modern Automotive Instrumentation The inputs to the instrumentation computer include sensors (or switches) for measuring (or sensing) various vehicle variables as well as diagnostic inputs from the other critical electronic subsystems. The vehicle status sensors may include any of the following: 1 2 3 4 5 6 7 8 9 fuel quantity fuel pump pressure fuel flow rate vehicle speed oil pressure oil quantity coolant temperature outside ambient temperature windshield washer fluid quantity 10 brake fluid quantity

18. Modern Automotive Instrumentation The input may include switches for determining gear selector position, brake activation, and detecting open doors and trunk, as well as IP selection switches for multifunction displays that permit the driver to select from various display modes or measurement units. Modern instrumentation systems is to receive diagnostic information from certain subsystems and to display appropriate warning messages to the driver. The powertrain control system, for example, continuously performs self- diagnosis operation. If a problem has been detected, a fault code is set indicating the nature and location of the fault. This code is transmitted to the instrumentation system via a powertrain digital data line (PDDL). This code is interpreted in the instrumentation computer and a “Check Engine” warning message is displayed.

19. Input-Output Signal Conversion A typical instrumentation computer is an integrated subsystem that is designed to accept all of these input formats. A typical system is designed with a separate input from each sensor or switch. An example of an analog input is the fuel quantity sensor, which can be a potentiometer attached to a float Figure: Digital Instrumentation System

20. What is ADC? ADC (Analog to Digital Converter) is an electronic device that converts a continuous analog input signal to discrete digital numbers . Analog Real world signals that contain noise Continuous in time Digital Discrete in time and value Binary digits that contain values or 1

21. Why is AD C Important? ☐ All microcontrollers store information using digital logic Compress information to digital form for efficient storage Medium for storing digital data is more robust Digital data transfer is more efficient Digital data is easily reproducible Provides a link between real- world signals and data storage ☐ ☐ ☐ ☐ ☐

22. How ADC Works 2 Stages: Sampling Sample- Hold Circuit Aliasing Quantizing and Encoding Resolution Binary output

23. Sampling ☐ Reduction of a continuous signal to a discrete signal Achieved through sampling and holding circuit Switch ON – sampling of signal (time to charge capacitor w/ V in ) Switch OFF - voltage stored in capacitor (hold operation) Must hold sampled value constant for digital conversion ☐ ☐ ☐ ☐ Response of Sample and Hold Circuit Simple Sample and Hold Circuit

24. Sampling ☐ Sampling rate depends on clock frequency Use Nyquist Criterion Increasing sampling rate increases accuracy of conversion Possibility of aliasing ☐ ☐ ☐ f s T s  1 Sampling Period: Nyquist Criterion: f s  2  f max Sampling Signal: T w

25. Aliasing ☐ High and low frequency samples are indistinguishable Results in improper conversion of the input signal Usually exists when Nyquist Criterion is violated Can exist even when: f s  2  f max Prevented through the use of Low- Pass (Anti- aliasing) Filters ☐ ☐ ☐ ☐

26. Quantizing and Encoding ☐ Approximates a continuous range of values and replaces it with a binary number Error is introduced between input voltage and output binary representation Error depends on the resolution of the ADC ☐ ☐

27. Resolution resolution  V range /(2 n  1) Example: V range  7.0 V n  3 1 V  7 V /(2 3  1) V range =Input Voltage Range n= # bits of ADC Resolution Qerror   resolution / 2   .5 V

28. Resolution ☐ Increase in resolution improves the accuracy of the conversion Minimum voltage step recognized by ADC Analog Signal Digitized Signal- High Resolution Digitized Signal- Low Resolution

29. Flash A/D Converter Successive Approximation A/D Converter Example of Successive Approximation Dual Slope A/D Converter Delta – Sigma A/D Converter Types of A/D Converters

30. FLASH A/D CONVERTER 3 Bit Digital Output Resolution 2 3 - 1 = 7 Comparators

31. What is a DAC? 33 DAC 100101 … A digital-to-analog converter (DAC) takes a digital code as its input and produces an analog voltage or current as its output. This analog output is proportional to the digital input.

32. Digital to Analog Conversion (DAC) 34 Digital to Analog conversion involves transforming the computer’s binary output in 0’s and 1’s (1’s typically = 5.0 volts) into an analog representation of the binary data DAC : n digital inputs for digital encoding analog input for Vmax analog output a DAC Vmax x0 x1 Xn-1 … a General Concept:

33. Digital to Analog Conversion (DAC) 35 Applications for Digital to Analog Converters: Voltage controlled Amplifier digital input, External Reference Voltage as control Digitally operated attenuator External Reference Voltage as input, digital control Programmable Filters Digitally controlled cutoff frequencies Circuit Components

34. Digital to Analog Conversion (DAC) 36 Applications for Digital to Analog Converters: Motor Controllers Cruise Control Valve Control Motor Control

35. Digital to Analog Conversion (DAC) 37 Types of DAC Many types of DACs available Binary Weighted Resistor R-2R Ladder Multiplier DAC Non-Multiplier DAC Among them Weighted & R-2R are commonly used.

36. Digital to Analog Converter(DAC) Utilizes A Inverting Weighted Op-amp Circuit. Weighted Resistors Are Used To Distinguish Each Bit From The Most Significant To The Least Significant 38 Binary Weighted Resistor R f 2R R V o -V REF LSB 4R 8R MSB General Concept:

37. Digital to Analog Converter(DAC) 39 Binary Representation V REF Least Significant Bit Most Significant Bit CLEARED SET ( 1 1 1 1 ) 2 = ( 15 ) 10 Binary Weighted Resistor

38. Digital to Analog Converter(DAC) 40 MSB LSB LSB MSB Output Voltage Analysis

39. Input-Output Signal Conversion The analog inputs must all be converted to digital format using an analog-to- digital (A/D) converter a quantity x being measured uses an analog sensor with output voltage V ( x ) . The instrumentation computer causes a sample of V to be taken at time t k via a sample and hold(SH) circuit. The sampled voltage v o ( t k ) is, then, converted to a digital input v k by the A/D converter and is input to the CPU in digital format. The digital inputs are already in the desired format. The conversion process requires an amount of time that depends primarily on the A/D converter. After the conversion is complete, the digital output generated by the A/D converter is the closest possible approximation to the equivalent analog voltage, using an M- bit binary number (where M is chosen by the designer and could, for example, be between 6 and 32).

40. Input-Output Signal Conversion The A/D converter then sends a signal to the computer by changing the logic state on a separate lead (labeled EOC,indicating end of conversion) that is connected to the computer. The output voltage of each analog sensor for which the computer performs signal processing must be converted in this way. Once the conversion and any required digital signal processing are complete, the digital output is transferred to a register in the computer. If the output is to drive a digital display, this output can be used directly. However, if an analog display is used, the binary number must be converted to the appropriate analog signal by using a digital-to-analog (D/A) converter.

41. Input-Output Signal Conversion A typical D/A converter used to transform digital computer output to an analog signal is shown below ] Figure: Digital Input Analog Output

42. Input-Output Conversion The N digital output leads transfer the results of the signal processing to a D/A converter. When the transfer is complete, the computer sends a signal to the D/A converter to start converting. The D/A output generates a voltage that is proportional to the binary number in the computer output. The D/A conversion often includes a zero- order hold circuit (ZOH). A low- pass filter (which could be as simple as a capacitor) is often connected across the D/A output to smooth the analog output between samples. The sampling of the sensor output, A/D conversion, digital signal processing, and D/A conversion normally take place during the time slot allotted for the measurement of the variable in a sampling time sequence (although time delays are possible)

43. Advantages of Computer Based Instrumentation One of the major advantages of computer- based instrumentation is its great flexibility. To change from the instrumentation for one vehicle or one model to another often requires only a change of computer program. This change can often be implemented by replacing one ROM with another. The program is permanently stored in a ROM that is typically packaged in a single integrated circuit package. Another benefit of microcomputer- based electronic automotive instrumentation is its improved performance compared with conventional instrumentation.

44. Advantages of Computer Based Instrumentation The traditional electro- mechanical fuel gauge system has errors that are associated with 1 Nonlinearities in the mechanical and geometrical characteristics of the tank relative to the sender unit The instrument voltage regulator The display dynamic response 2 3 The electronic instrumentation system eliminates the error that results from imperfect voltage regulation. In general, the electronic fuel quantity measurement maintains calibration over essentially the entire range of automotive operating conditions. It significantly improves the display accuracy by replacing the electro- mechanical galvanometer display with an all- electronic digital display.

45. Fuel Quantity Measurement During a measurement of fuel quantity, the MUX switch functionally connects the computer input to the fuel quantity sensor. This sensor output is converted to digital format and then sent to the computer for signal processing. Figure: Fuel Quantity Management System

46. Fuel Quantity Measurement Figure: Fuel Quantity Sensor Configuration

47. Fuel Quantity Measurement A potentiometer was introduced as a sensor for measuring throttle angular position. It also has application in certain fuel- measuring instrumentation. A constant current passes through the sensor potentiometer, since it is connected directly across the regulated voltage source. The potentiometer is used as a voltage divider so that the voltage at the wiper arm is related to the float position, which is determined by fuel level.

48. Fuel Quantity Measurement The sensor output voltage is not directly proportional to fuel quantity in gallons because of the complex shape of the fuel tank. The computer memory contains the functional relationship between sensor voltage and fuel quantity for the particular fuel tank used on the vehicle. The computer reads the binary number from the A/D converter that corresponds to sensor voltage and uses it to address a particular memory location. Another binary number corresponding to the actual fuel quantity in gallons for that sensor voltage is stored in that memory location. The computer then uses the number from memory to generate the appropriate display signal (either analog or digital, depending on display type) and sends that signal via DEMUX to the display.

49. Coolant Temperature Measurement The measurement of this quantity is different from that of fuel quantity because usually it is not important for the driver to know the actual temperature at all times. For safe operation of the engine, the driver only needs to know that the coolant temperature is less than a critical value. The coolant temperature sensor used in most cars is a solid-state sensor called a thermistor. Where it was shown that the resistance of this sensor decreases with increasing temperature.

50. Coolant Temperature Measurement Figure: Coolant Temperature Measurement System

51. Coolant Temperature Measurement Figure: Coolant Temperature Sensor Unit

52. Coolant Temperature Measurement The sensor output voltage is sampled during the appropriate time slot and is sampled (S) converted to a binary number equivalent by the A/D converter. The computer compares this binary number to the one stored in memory that corresponds to the high- temperature limit. If the coolant temperature exceeds the limit, an output signal is generated that activates the warning indicator. If the limit is not exceeded, the output signal is not generated and the warning message is not activated. A proportional display of actual temperature can be used if the memory contains a cross- reference table between sensor output voltage and the corresponding temperature.