Vehicle Computer Systems Chapter 34

1. Vehicle Computer SystemsChapter 34 DSL 131

2. OBJECTIVES • Understand the language of computerized truck engine management systems. • Describe the circuit layout of an electronically managed truck engine. • Identify the differences between partial authority and full authority electronic engine management. • Outline the stages of a computer processing cycle. • Describe the data retention media used in vehicle ECMs. • Describe the role played by the various memory components in a truck ECM. • Identify the command and monitoring input circuits on a vehicle electronic system. • Define the principles of operation of thermistors, variable capacitance sensors, Hall-effect sensors, potentiometers, induction pulse generators, and piezoresistive sensors.

3. OBJECTIVES (Cont.) • Describe how an ECM processes inputs and uses programmed data to generate outputs. • Identify current computer-controlled engines by OEM and engine series. • Define the role played by the injector driver unit in a typical full authority engine management system. • Differentiate between customer and proprietary data reprogramming and identify the levels of access passwords used. • Describe the processes used to reprogram a truck engine ECM with proprietary data.

4. INTRODUCTION • Most highway truck and, increasingly, bus and off-highway equipment use computers to manage engine and other onboard system functions. • They are cybernetically controlled. • Cybernetics is the science of computer control systems. • The technician is required to troubleshoot system problems and reprogram parameters (values), in most cases, using software loaded to personal computers (PCs), laptops, or handheld units. • Onboard vehicle computers are referred to as engine/electronic control modules (ECM) or electronic/engine control units (ECU).

5. Engine Controller • An ECM is a modular housing containing a microprocessor, data retention media and (usually) an output or switching apparatus. • It is the engine controller. • Is normally (but not necessarily) mounted on the engine. • Electronics now control many chassis systems besides the engine and are interconnected by a data bus. • The bus is the information highway which interconnects the various electronic controls on the vehicle. • Multiple devices communicating on a single bus is called multiplexing.

6. Multiplexing • Multiplexing allows computers to share information with each other over a serial data line that goes to each controller. • Reduces the amount of wiring needed • Reduces drivers needed for the computer • Reduces load across the sensors • Enhances diagnostics

7. Definition •  multiple signal transmission: the sending of two or more signals along one communication channel

8. An Example At Home • Cable TV • Many input Sources • Internet Service • Video – On-Demand. • Audio • One Cable • Many output functions. • Stereo • Computer • DVR • Telephone

9. Home Example SCI FI ESPN TV CBS STEREO CABLE TV PROVIDER HOME DECODER ABC COMPUTER On-Demand DVR INTERNET MUSIC

10. IN A CAR • Door Controls • R/F Window • L/F Window • R/R Window • L/R Window • Mirror (4 Channels) • Door Locks

11. In a Car R/F WINDOW L/F WINDOW L/F DOOR PROCESSOR MAIN DOOR CONTROL PROCESSOR L/ MIRROR L/RWINDOW LOCK R/R WINDOW R/F WINDOW R/F DOOR PROCESSOR L/ MIRROR R/ MIRROR R/ MIRROR DOOR CONTROL PROCESSOR LOCK R/R WINDOW R/R WINDOW R/R DOOR PROCESSOR R/R DOOR PROCESSOR LOCK LOCK DOOR CONTROL PROCESSOR DOOR CONTROL PROCESSOR

12. DATA PROCESSING • Stages of the information processing cycle include the following: • Input • Voltage signal from an input device. May be a sensor or a switch. • Processing • Compare input info to programmed instructions. • Storage • Program instructions. • Some input signals. • Output • Send control commands to output devices.

13. Data Input • Simply raw information. • Comes from monitoring sensors such as: • Crankshaft Position Sensor • Throttle position Sensor • Engine coolant temperature sensor. • May be either analog or digital. • Analog signals must be digitized before the computer can process the information.

14. Data Processing • A central processing unit (CPU) contains a control unit that executes program instructions. • Random Access Memory (RAM) is data that is electyronically stored in the ECM. • This data can be accessed at high speed. • RAM , often known as main memory. • Is lost if power is cut. • Read Only Memory (ROM) contains the basic operating characteristics and permanent instruction for the computer. • Is retained even when power is turned off. • Output drivers are transistors that switch controlled circuits on and off. • Ie. Operate injector units.

15. Outputs. • The results of processing operations must be converted into action by switching units and actuators. • The output devices are called drivers. • The injector driver would be one of the primary outputs to be switched. • ECM commands are converted to a signal that will determine the pulse width of the injector.

16. J-STANDARDS • The “J” standard is surface vehicle recommended practice. • Dictates the hardware and software rules for multiplexing data exchange between modules. • Two primary data buses are used on current trucks. They are referred to as: • SAE J1587/1708 • First generation for multiplexing. • J1587 = Software rules • J1708 = Hardware rules. • SAE J1939 • Standards that include both software and hardware protocols on a high speed bus • Controller Area Network 2.0 (CAN 2.0)

17. DATA RETENTION IN VEHICLE ECMs • Data may be retained (stored) optically, magnetically or electronically. • Random-Access Memory • Temporary information, lost if power is interrupted. • Volatile • Determines power of system. • Loaded by system at startup. • NV-RAM (Non-Volatile RAM) • Keeps data until battery is disconnected or system reset. • Example = radio station presets • Read-Only Memory • Permanently Stored Information • All the basic information for initial engine operation.

18. DATA RETENTION IN VEHICLE ECM’s • PROM-programmable read-only memory • Magnetically retained data. • May be removable or reprogrammable. • Qualify a system to a specific vehicle. • EEPROM-electrically erasable PROM • Stays active during power interruptions, but can be replaced in the event of updates. • Can be reprogrammed (flashed) without R&R. • May be used to store customer preferences (ie. LS or VS governor control).

19. DATA RETENTION IN VEHICLE ECMs (Cont.) • Flash Memory • Magnetically retained, non-volatile, solid state memory. • Used for portable data storage (thumb drives and memory chips in cameras and audio players). • Form of EEPROM • Proprietary Data EEPROM • May be downloaded from factory server to a pc, then used to reprogram an ECM.

20. INPUT CIRCUIT • ECM inputs can be divided into sensor inputs and switched inputs. • Inputs to the ECM can be divided into: • Monitoring • Command

21. SENSORS • Anything that signals input data to a computer system can be described as a sensor. • Sensors may be: • Simple switches that an operator toggles open or closed to ground a reference voltage • modulate a reference voltage • powered up either by V-Ref or require power-up outside of the V-Ref circuit.

22. SENSORS • Thermisters • Used as temperature sensors

23. SENSORS • Engine Oil Pressure Sensor of the Variable Capacitance Type • Three wire sensors (V-Ref). • Pressure acts on a ceramic disk moving it closer to, or away from a steel disk changing its capacitance.

24. SENSORS • Accelerator Position Sensor of the Potentiometer Type

25. TECH TIP • When a sensor logs an active fault code, try disconnecting the sensor and observing whether the fault mode indicator (FMI) changes. • It there is no change, it suggests that the fault lies in the wiring circuit. • If the FMI changes, it would suggest that the problem lies in the sensor.

26. Signal-Generating Sensors • Hall-effect sensors generate a digital signal as timing windows or vanes on a rotating disc pass through a magnetic field. • In a rotary Hall-effect sensor, the rotating disc is known as a pulse wheel or tone wheel.

27. Signal-Generating Sensors • Camshaft Position Sensorof the Hall-Effect Type

28. Signal-Generating Sensors • Williams Electronic Foot-Pedal Assembly (EFPA) • Uses a hall type sensor. • Eliminates the mechanical wear of a potentiometer.

29. Signal-Generating Sensors • Induction Pulse Generator. • Creates an AC signal voltage.

30. Signal-Generating Sensors • Galvanic Sensors: • O2 or oxygen sensors. • Also called lamda sensors. • Used to sample the exhaust stream and determine the oxygen content. • Used primarily in SI engines to maintain a “stoichiometric” fuel air ratio. • Used in diesels converted to LNG or NG to monitor catalyst function.

31. Signal-Generating Sensors • Negatively charged oxygen ions are drawn to the thimble where they collect on both the inner and outer surfaces.

32. Signal-Generating Sensors • A difference in oxygen content between the atmosphere and the exhaust gases enables an O2S sensor to generate voltage.

33. Signal-Generating Sensors • The oxygen sensor provides a quick response at the stoichiometric air–fuel ratio of 14.7:1.

34. SIGNAL-GENERATING SENSORS • NOx Sensors • Introduced in 2007 • Used in most post-2010 engines.

35. MASS AIRFLOW SENSOR TYPESHOT WIRE SENSOR • The hot wire sensor uses a heated wire to sense the mass airflow instead of the hot film. • The hot wire sensor uses a temperature-sensing resistor (thermistor) to measure the temperature of the air entering the sensor. • The energy expended to keep the wire at 70 deg C above the incoming air determines the mass of air flowing through the sensor. • May include a “burn off” circuit to keep the sensing wire clean.

36. MAF Sensors • Critical flow venture (CFV), pressure differential MAF Sensor. • Measures the pressure differentials at the inlet and outlet of a venture to calculate the mass airflow.

37. MAF Sensors • Vortex airflow sensor. • AKA “Karman vortex flow sensors”. • Uses a triangle-shaped rod to create vortexes as the air flows through the sensor. • The electronics in the sensor itself converts these vortexes to a digital square wave signal.

38. Water-in-Fuel Sensor (WIF) • Uses the change in conductivity (dielectric properties) due to the presence of water in the fuel. • When the threshold is met, a service alert is sent to drain the fuel/water separator.

39. Switches • Switches complement the sensor circuit and can usually be classified as command inputs. • Switches may be electromechanical or “smart;” that is, they use “messages” rather than analog voltage values to signal a change in status. • Switches can be subdivided into three groups: • Switches grounding a reference signal (V-Ref) • Manual switches • Smart switches

40. Switches • Switches grounding a reference signal. • Example • Coolant level switch • Switch normally grounds through the coolant, but loses its ground when the fluid level drops below the sensor.

41. Switches • Manual Switches • Control electrical circuit activity. • Used by operator to control vehicle functions. • Examples • Ignition key • Engine retarder mode • Cruise control.

42. Switches • Smart Switches • Smart switches use digital signals to indicate a change in status. • May be automatically generated by a change in status condition . • May be generated by a mechanical action such as an operator toggling a switch. • Review chapter 37 for more detail.

43. ECMs AND THE PROCESSING CYCLE • A diesel engine management ECM has four basic functions: • Regulating reference voltage (V-Ref) • Input conditioning, amplification, and ADC • Processing • Managing output drivers • ECM is the generic term for the unit housing the engine management electronics. • Illustration: Navistar DT466E seen from the left side. The location of the ECM and some sensors is shown.

44. ECM Input Signal Conditioning and Data Retention • Weak signals may need to be amplified. • Analog signals may need to be converted to a digital signal.

45. Processing Cycle • Processing in the ECM involves: • Scanning the programmed fuel map data (ROM + PROM+EEPROM). • Monitoring engine and chassis sensors. (VSS, ECT etc.) • Monitoring command inputs (TPS, Cruise etc.) • Plotting actual fuel delivery. Bosch ECM Used on a NavistarMaxxforce Series Engine

46. Processing Speeds • ECM processing occurs at different frequencies classified as foreground and background computations. • Less important data like engine oil temp may be computed at a slower pace in the background. • High priority operations like TPS signals would be processed in the foreground. A Volvo ECM

47. Processing Cycle • ECM outputs are switching functions. • Generally driven at chassis voltage. • May be spiked to higher values to drive specific actuators. Simplified example of the processing cycle of an International Trucks HEUI, Three-Module (3-box) Controller System

48. ECMs AND THE PROCESSING CYCLE • ECMs may be located anywhere on chassis • Engine management ECMs are often mounted on the engine close to devices monitored and switched. • Special cooling and vibration control may be required (cooling via fuel etc.) • May be mounted under the dash. • This reduces vibration etc. but requires more/longer wiring.

49. ECMs AND THE PROCESSING CYCLE (Cont.) • The following are examples of some OEM acronyms used to refer to engine and fuel system controllers: • EEC: Electronic engine control • EECU: Electronic engine control unit • ECI: Electronically controlled injection • ECU: Electronic control unit • FIC: Fuel injection control module • MCM: Motor control module • PCM: Powertrain control module • PLD: German acronym for ECM (Mercedes-Benz)

50. OUTPUT CIRCUIT • The switching apparatus used with each electronic management system is what truly differentiates one system from another. • At the time of this writing, full authority engine management systems use EUIs, hydraulically-actuated electronic unit injectors (HEUIs), EUPs, and common rail (CR) actuators that characterize each OEM system.