Chapter 10b: Electronic Systems

1. Chapter 10b: Electronic Systems BAE 599 - Lecture 10 Part B

2. Electronic Systems Manufacturers are turn to electronics for enhanced vehicle functionality, productivity, and performance. While specialists are employed to design these systems, vehicle designers must have a basic understanding of these systems to take full advantage of evolving technologies.

3. Electronic Control Units (ECU) ECU, when combined with sensors and actuators, make up modern electronic control systems. ECU are composed of microcontrollers, input/output interfaces, input power conditioning, connectors, and an enclosure. ECU�s accept digital and analog inputs, provide typically digital outputs, and have limited computing capabilities.

4. ECUs Continued Typically employ EEPROM or Flash memory. ECUs of today do not process control cycles faster than 1 ms (debatable). Signal conditioning is required to convert signals to the input range of the mcontroller for A/D conversion (8, 10 or 12 bit).

5. Digital Input Interface is usually needed. Pull up resistor can be used to convert switch closures to digital input. Input signal must usually be in the 0-5 V range. Arcing at switch closure causes �bounce.�

6. Fig. 10.16 Switch Closure for Digital Input

7. Digital Output Digital outputs are utilized to drive vales, actuators, or indicators. Low-side driver circuits are often employed. Metal Oxide Semiconductor Field-Effective Transistors (MOSFET) are utilized as switches. MOSFETs become conductive when a 5 V signal is applied.

8. Fig. 10.17 Low-Side Solenoid Circuit

9. Pulse Width Modulation (PWM) PWM is a method of communicating a proportional rate in digital form. Essentially PWM is a variable duty-cycle. Frequency of cycle is set high enough so the pulses are averaged by the system being controlled, and do not show up in the response.

10. Fig. 10.18 Pulse-Width Modulation

11. H-Bridge DC Motor Control Circuit used for bi-directional control of electric motors. Circuit is typically driven via PWM. �Switches control motor direction of rotation.

12. Fig. 10.19 H-Bridge DC Motor Control

13. Sensors Critical to embedded control systems. Typical sensor output is analog voltage, frequency, or a digital signal. Voltage or current analog sensors produce a signal that is proportional to the parameter being sensed. Sensors are usually powered externally, and require a third wire for the signal.

14. Table 10.7 Common Sensors for Off-Road Vehicles

15. Sensors Voltage drop in conductors can effect sensor accuracy, and therefore current based signals are often preferred. With voltage based sensors bridge configuration are often utilized to compensate for changes in resistance (temperature related). Double ended output is often preferred to single ended (common ground).

16. Fig. 10.20 Sensor Bridge (Double Ended Output)

17. Smart Sensors and Actuators Sensors are combined with mcontrollers to produce digital information that is communicated to the ECU. Reverse process occurs with actuators.

18. Controller Area Networks Allows component to component communications (hitch can talk to transmission). Communications enables system optimization. Cost of adding communications is small when compared with other vehicle costs.

19. Fig. 10.21 Encoded Data

20. Priority Networks Multiplex wiring has evolved to support communications between ECUs � a two-wire communications bus. Data is assembled into messages to facilitate communications between ECUs. Protocol embedded in ECUs requires continual checking of the bus to avoid new transmissions while the bus is being used.

21. Examples Chrysler Collision Detection protocol used on Deere 7000 series tractors facilitated communications between five ECUs (1992). New Holland deployed CAN-based network in the Genesis tractor (1994) with 4 ECUs. CAN developed by Bosch. Caterpillar utilized the SAE J1587 data link on the Challenger 75 and 85 tractors (1993). Flexi-Coil utilized a SAE 1708-based network on their air-seeder with up to 18 ECUs.

22. Examples Continued Ag-Chem Equipment Company patents network-based control of product application in 1995. LBS (DIN 9684) introduced in Europe in the early 1990s. LBS is the basis of the Fendt Vario tractor introduced in the late 1990s.

23. Fig. 10.22 Multiplexed Wiring

24. ISO 11783/SAE J1939/DIN 9684 Need for standardization becomes evident as the use of communications networks grow. SAE J1939 developed to support component level communications for on and off-road applications. DIN 9684 was developed to support implement communications to tractor-mounted displays.

25. ISO 11783/SAE J1939/DIN 9684 ISO 11783 evolves to support comprehensive standardized networks for tractor and implement systems. Part of ISO 11783 are derived from SAE J1939 and DIN 9684.

26. ISO 11783/SAE J1939 Both standards formalized multiplexing wiring based n the CAN version 2 protocol. This protocol uses a prioritized arbitration process to allow messages access to the bus. When two messages are sent at the same time their identifiers are imposed bit serially onto the bus.

27. ISO 11783/SAE J1939 Bus must be designed to allow the dominant bits to overwhelm the recessive bits when both messages are sent at the same time. There is no response when both ECU send the same bits. However, when one ECU sends a dominant bit while the other sends a recessive bit, the latter must sense the difference and stop transmitting.

28. ISO 11783/SAE J1939 The latter ECU will try to resend the lower priority message at time when the bus is free. This strategy allows more dominant identifiers (lower numerical values) to have a higher priority. ISO 11783 provides for communication where multiple ECU�s share a common bus with message access based on priority.

29. ISO 11783 Overview Standard written to support tractor/implement and self-propelled agricultural equipment. Several busses are identified: Tractor, Implement, and Implement Sub-Network. Busses are interconnected via ECU�s that serve as bridges.

30. ISO 11783 Overview Part 9 describes the characteristics of the tractor ECU. Part 6 describes the Virtual Terminal. Part 10 describes the task controller and management computer gateway.

31. ISO 11783 Overview Standardized communications are defined between the task controller and implement, and between the task controller interface and the management computer applications software. The interface between management computer and task controller is not standardized.

32. Fig. 10.23 Schematic of ISO 11783 Network

33. ISO 11783 Overview Network provides for the communications of messages between any of the components in Fig. 10.23. Some messages are defined with repetition rates of 100 Hz, utilizing up to 5% of the bus capacity. Maximum average bus use rates are targeted at 35%.

34. ISO 11783 Overview Tractor ECU filters messages going to and from the implement bus � to avoid overloading of either bus. Support for precision farming is provided in the implement bus, and for tractor/implement interaction. Network supports simultaneous proprietary communications.

35. Wiring and Connectors � Physical Layer Twisted quad cabling was developed specifically for ISO 11783. 125 K bits/s was the highest possible data transfer rate without shielding. 250 K bits/s shielded twisted pair was available from SAE J 1939. Deere proposed 250 K bits/s with twisted pair (no shielding) with carefully selected voltage slope and current control. Proven design was accepted and became Part 2 of standard.

36. Wiring and Connectors � Physical Layer Four wires enclosed in a jacket CAN_H CAN_L TCB_PWR TCB_RTN Terminating Bias Circuit (TCB) are includes in the cabling at all points � not connected to ECUs. Terminators are required for the TCB circuit.

37. Fig. 10.24 Twisted Quad Network Cabling

38. Wiring and Connectors � Physical Layer Termination of the bus at both ends is a requirement. Unhooking the implement from the tractor poses a problem � which has been solved by the development of a special self-terminating connector. Part 2 specifies three standard connectors: bus breakaway, diagnostics, and in-cab connectors.

39. Wiring and Connectors � Physical Layer Bus topology restrictions 40 m single segment length 0.1 m minimum length between ECUs �T� configurations of the bus should be avoided � must use serpentine approach. �T� are permitted when connected length is less than 0.6 m. Limit of 30 ECUs per single segment bus with maximum of 254 ECUs for interconnected segments.

40. Fig. 10.25 Connector use in ISO 11783

41. Message Structure ISO 11783 is based on the CAN 2.0b 29-bit protocol developed by Bosch (1991). Message frame consists of identifier and data fields. Undetected error rates are approximated as 4.7x10-11 times the error rate

42. Fig. 10.26 CAN Frame Components

43. Message Structure Two types of Protocol Data Units (PDU) exist. Least significant 8 bits define a source address � physical address of unit sending message. Most significant 3 bits are independent priority bits. Type 1 PDU permits the inclusion of the ECU address of the destination of the message.

44. Message Structure Remainder of 29 bit identifier is utilized to identifier the parameter group contained in the data field. Addresses of ECU must be unique. CAN messages can be composed of multiple data frames � two types Initial frame is sent announcing the format of the remaining data frames. Connection mode message sent to a specific destination that controls the flow of subsequent data.

45. Fig. 10.27 CAN Frame Identifiers

46. The Network Layer A bridge must be used to interconnect bus segments. Repeaters cannot be used to interconnect segments! ISO 11783 defines filtering capabilities for network interconnections. Traffic partitioning performed by network interconnection devices controls bus loading.

47. The Network Layer Segment to segment interconnections are limited to one.

48. Addressing, NAMEing and Initialization ISO 11783 Part 5 provides requirements for a unique NAME to be associated with each ECU. Each 64-bit name within the system must be unique. Upper 32-bits is a unique name, lower 32-bits is a manufacturer specific code. Manufacturer codes must be obtained from the ISO 11783 Workgroup.

49. Fig. 10.28 ISO 11783 NAMEing Structure

50. Addressing, NAMEing and Initialization Initially, an address (8-bit) was included to allow peer to peer communication. Self-configuring ECUs were introduced when the ISO 11783 Workgroup came to the realization that 254 unique addresses would not support all possible ECU types (e.g., transmission, engine, steering, hitch, etc.).

51. Addressing, NAMEing and Initialization Some ECUs have a fixed address, requiring arbitration for the self-configuring units (NAME of self-configuring ECU contains a self-configuring bit to insure ECU with fixed addresses win arbitration).

52. Virtual Terminals Virtual Terminals (VT) display information to users, and allows them to input information to the system. VTs are to be slaves to ECUs, and ECUs are blind as to which ECU is using the VT. From the user�s perspective the VT can be utilized to display information from one or more ECU, simultaneously.

53. Virtual Terminals VTs support downloading of masks for different user displays, alarms, and soft key functions. Data can be formatted and displayed on the screen, and similarly, operator supplied data can be input to the screen. VTs support both graphic and text display. Graphic functions for line drawings, dials, and bars are supported along with the ability to input bit-mapped graphics.

54. Fig. 10.29 Schematic of Virtual Terminal Panel

55. Task Controlling ISO 11783 supports task-control applications. Tasks are contained within individual ECUs. Tasks can be loaded into the controller from the management computer prior to field operations. Three modes of tasks are supported: time-based, distance-based, and position based.

56. Task Controlling Typical applications include the development or prescriptions for the management of inputs to crop production systems. Messages were created as Part 7 of ISO 11783 to allow tasks to be passed from controllers to implements, and from implements to controllers. Identifiers contain the values in the R, G, and PDU fields to identify the data fields in the process data message.

57. Task Controlling The message contains both source and destination addresses so that it can be sent to a particular ECU. A single process variable is sent in the 4-byte process data field. The data selector indicates the data format of the variable, the type, a modifier, and qualification regarding the variable.

58. Task Controlling Data type indicates if the process variable is an actual value or set point, and whether the message is a response or request. The count number field specifies a particular element within an implement (roe or bin), or all elements of the implement. The data dictionary specifies the process variable that is a function of the implement.

59. Fig. 10.30 Process Data Message

60. Task Controlling The process data message allow controller to send commands and query implements regarding set point and actual operating points. The same message can be used by implements to current set points and actual operating points.

61. Tractor and Tractor ECU Messages ISO 11783 Part 7 specifies standard tractor messages that are available for use by the implement (Table 10.8). Most of these messages are sent repetitively and at fixed rates. Others messages are sent upon request (e.g., time, date, etc.). ISO 11783 Part 9 specifies the requirements for tractor and implement networks.

62. Table 10.8 Part 7 Basic Messages

63. Tractor and Tractor ECU Messages Tractor are classified with regard to their network capabilities: Class 1 � basic information and lighting Class 2 � adds more complete speed draft information Class 3 � adds ability of implement to control hitch, PTO and hydraulic valves

64. Table 10.9 Message Requirements for Tractor Classes

65. Messages on the Tractor Bus An extensive set of tractor bus messages is identified in ISO 11783 Part 8. These are essentially the same as those outlined in SAE J1939-71. Tractor-Forage Harvester: Utility can be demonstrated through the use of the Electronic Engine Control Message #1 (containing torque) by the implement to select a new tractor transmission gear ration to maximize tractor-implement performance.

66. Diagnostics Currently (?), ISO 11783 does not define diagnostics. ISO 11783 defines a standard diagnostics connector (SAE J1939). VT can be used to retrieve and display information for diagnostic purposes. Initial diagnostics support through proprietary tools.

67. Design Strategies for ISO 11783 Locate ECU where inputs and outputs are concentrated. Minimize the number of wires crossing critical boundaries. Connect sensors and actuators to the nearest ECU. Locate ECUs such that closed-loop control is not performed over the network.

68. Design Strategies for ISO 11783 Condition and scale sensor and actuator signals at the module to which they are connected. Transmit information over network in engineering units. Make no assumption about hardware or operator interface connected to ECUs.

69. Design Strategies for ISO 11783 Broadcast data at a fixed rate. Do not incorporate emerging standards until they are well defined.

70. Fault Management ISO 11783 Part 2 identifies many of the potential failures associated with bus wiring. If bus transmission errors are detected at a rate of 10/s, users should experience 10,000 h of operation between undetected errors. ISO 11783 Part 2 defines ECU operation requirements during power dropout � ECU should retain their data and operate normally after 10 ms power drop-out.

71. Fault Management Measures should be designed into ECU software for reasonable machine operation after a communications failure.

72. System Environmental Concerns Climatic conditions (temperature, moisture, and dust) Chemical conditions (fertilizer, pesticides, fuels, and lubricants). Mechanical conditions (vibration, shock, and impact) Electrical conditions (steady-state, transient, electrostatic, and electromagnetic)

73. Table 10.10 Supply Voltages per ASABE EPP 455

74. Electromagnetic Compatibility Electromagnetic compatibility (EMC) encompasses issues of radio frequency electronic emissions as well as susceptibilities. ASABE EEP 455 specifies critical FCC regulations and SAE recommendations. Communications busses built to ISO 11783 have been shown to meet EMC requirements in the U.S. and Europe.

75. Homework Set No. 10 Do problems 10.8 and 10.9 at the end of Chapter 10 for next Thursday.