1. Your Instructor today is
Electronic Automatic
Transmissions
Your Instructor today is
(Your name)

2. Objectives
• Identify the Allison and Caterpillar families of electronically controlled, on-highway automatic transmissions. • Describe the operating principles of first-generation, Allison partial authority transmissions. • Describe the modular design used by the current family of Allison WTs.

3. (Objectives cont.)
• Outline how Allison WT and Caterpillar CX transmissions use full authority management electronics to effect shifting and communicate with other vehicle electronic systems. • Identify some of the service and repair advantages of the modular construction of the Allison WT.

4. (Objectives cont.)
• Identify the components used in a Caterpillar CX and note the differences between six- and eight-speed models. • Describe how the electronic control modules on both Allison and Caterpillar electronic transmissions master the operation of the transmission. • Define the terms pulse width modulation, primary modulation, and secondary modulation.

5. (Objectives cont.)
• Describe how base versions of both Allison and Caterpillar transmissions use three interconnected planetary gearsets to stage gearing to provide six forward ranges, reverse, and neutral. • Outline the differences between Caterpillar CX six- and eight-speed transmissions.

6. (Objectives cont.)
• Describe the integral driveline retarder components and operating principles used in electronic automatic transmissions.
• Outline the function of the dropbox option in one Allison WT model.
• Describe the role of the electrohydraulic controls used in Allison and Caterpillar electronic automatic transmissions.

7. (Objectives cont.)
• Identify the electronic components used in electronic automatic transmissions and classify them as input circuit, processing, and output circuit components. • Describe how electronic automatic transmissions interface with the SAE J1939 data bus to optimize vehicle performance. • Describe how the WT clutches are controlled.

8. (Objectives cont.)
• Outline the torque paths through the WT in each range selected. • Describe how diagnostic codes are logged in the Allison WT ECU and the manner in which they are displayed. • Perform some basic diagnostic troubleshooting on Allison and Caterpillar electronic transmissions.

9. (Objectives cont.)
• Calibrate a Caterpillar CX transmission. • Describe the operation of a Voith transmission.

10. INTRODUCTION
• Allison CEC partial authority transmissions • Allison WT full authority • Caterpillar CX full authority transmissions

11. HISTORY
Allison has optioned computerized management of its automatic transmissions since These controls have become more comprehensive over the years. The first versions of electronically controlled Allison transmissions were known as Allison Transmission Electronic Controls (ATEC); this evolved into Commercial Electronic Control (CEC).

12. Shop Talk
The term full authority is borrowed from the way we categorize engines. In the early days of engine management electronics, the term partial authority was used to describe a hydromechanical system that was adapted for electronic management: This description fits an Allison CEC transmission perfectly

13. A full authority engine was one that was designed from the blueprint to be managed by electronics. Again, if we use these terms to categorize transmissions, full authority perfectly describes the WT and CX transmissions.

14. APPLICATION AND RECON
Fully automatic transmissions have a higher unit cost compared to standard and automated transmissions. This higher unit cost, rather than being inappropriate for the application, means that they are less likely to be found in general highway truck applications.

15. ADVANTAGES
A major advantage of the automatic transmission is the fact that a lower level of driver skill is required and much less driver fatigue is generated. Using a fully automatic transmission in a continuous stop/start operation such as picking garbage up is kinder not only to the driver but also to the vehicle drivetrain. Because fully automatic transmissions are driven through a fluid coupling or torque converter, some forgiveness is applied to any form of driveline shock load.

16. CEC TRANSMISSIONS

17. CEC ELECTRONIC CONTROL UNIT (ECU)

18. Placement and Power Requirements
The technician should know that a minimum of 10V is required to operate the unit; 16V continuous and 19V intermittent are the maximum voltages to which the unit should ever be subjected. This means that great care should be exercised when blast charging, that is, using a generator to start a truck with dead batteries.

19. PROM CHIPS

20. THROTTLE POSITION SENSOR (TPS)

21. TPS Operation

22. Throttle position sensor initial adjustment.

23. PRESSURE SWITCHES

24. Three different types of oil pressure switches
• Lube pressure switch—normally open • Low oil level/pressure (fluidic type) sensor (see Figure 21–8 and note operation) • Fluid oil level sensor—normally closed

25. Fluidic Oil Pressure Sensor

26. CEC ELECTROHYDRAULIC VALVE BODIES
ECU commands are converted to action by the electrohydraulic valve body. This action sequence could be described as electronic-over-electric- over hydraulic in CEC transmissions. The transmission hydraulic circuits and valves are controlled by a series of solenoids that are switched by the ECU.

27. Solenoids

28. OVERVIEW OF CEC ELECTRO HYDRAULIC VALVE BODY

29. Solenoid Designations
Each solenoid receives a constant flow of main pressure. It also is given a letter designation. Solenoids A, B, C, and D are latching solenoids that replace the conventional shift signal valves. Solenoids are all directly switched by the ECU. The following examples are for a CEC five-speed transmission.

30. Shop Talk
An Allison CEC transmission, although electronically controlled, is still a hydromechanical device. As such, the importance of correct transmission fluid level cannot be emphasized enough. If the fluid level is low, the converter and clutches will not receive enough fluid. If the fluid level is high, the fluid will aerate and the transmission will overheat.

31. WT MODULAR CONSTRUCTION
The full authority Allison WT family of transmissions has been around for a generation. The family can be subdivided as follows: • 1000/2000 series: light-duty truck • 3000/4000 series: medium- and heavy-duty truck • 5000/6000 series: heavy-duty off-highway

32. MODULAR CONSTRUCTION

33. WT IDENTIFICATION

36. WT INPUT MODULES

38. TRANSFER GEAR OR DROPBOX MODULE

40. WTEC ELECTRONICS
Electronic management of the WT is known as WTEC. The system is similar to the earlier CEC with some of the refinements that might be expected in a more advanced version of the system. Most notable is the ability to multiplex to the chassis data bus and better programmability to suit specific vehicle applications. First-generation versions of WT (WTEC I and II) could be networked to J1587.

41. Current WTEC transmissions are designed to network to the J1939 bus with a MID 130 address. WTEC can broadcast range-inhibit, check transmission light data, and send range status to the data bus for display onto the appropriate dash displays.

42. Shift Selectors

43. Vehicle Interface Module (VIM)

44. Speed Sensors

45. Adaptive Logic
The significant improvement in WT shift logic in comparison with CEC is accounted for by replacing hard parameter processing outcomes with soft logic processing, better called adaptive logic.

46. Autodetect
The Allison WTEC ECU also has an auto detect feature. Autodetect works a little like Windows “plug-and-play.” The autodetect mode is active in the system for the first 30 seconds of the first 24 to 49 engine starts (dependent on the component or sensor being detected).

48. Shop Talk
TPSs that output a pulse width modulation (PWM) signal (variable capacitance type or current Caterpillar) are not autodetected and must be programmed to WTEC using Allison software or the diagnostic data reader (DDR).

49. WT OUTPUT CIRCUIT

50. Normally Closed (NC) Solenoids

51. Normally Open (NO) Solenoids

52. Pulse Width Modulation (PWM)
WT solenoids are controlled by pulse width modulated (PWM) signals from the ECM. A PWM signal can be divided into primary modulation, which controls the amount of on time, and secondary or submodulation, which controls the current flow. The WT ECU controls the transmission clutch apply-and-release characteristics by varying the primary and secondary modulation signals to the control solenoids.

53. Primary Modulation

54. Shop Talk
In a general sense, the WT electronic management circuit is no different from that used to manage most of today’s engines. It consists of input, processing, and output circuits. It must also interact with other chassis electronic systems to optimize vehicle performance.

55. WT Digital Display (DD)
The data that appears on DD is controlled by the ECU. In other words, it does not display data directly as a result of mechanically pushing buttons or moving the shift lever.

56. Serial Communications Interface (SCI)
SCI is the data bus portal that permits WTEC to interact with the chassis data bus. This optimizes transmission operation with that of the rest of the powertrain and chassis systems. The SCI occupies the MID 130 address on the data bus. It is, therefore, both an input and an output mechanism in the WT electronic circuit. Current Allison transmission electronics are ISO 9141 compliant.

57. THE WTEC DIAGNOSTIC TOOLS
The Allison electronic service tools (EST) required to read and reprogram WTEC electronics are the NEXIQ DDR and the Allison diagnostic optimized connection (DOC) software used with PC- or PDA-based ESTs.

58. Shop Talk
In a general sense, the WT electronic management circuit is no different from that used to manage most of today’s engines. It consists of input, processing, and output circuits. It must also interact with other chassis electronic systems to optimize vehicle performance.

59. Shop Talk
Learning hydraulic circuit and torque powerflows helps visualize transmission operation so they are a key to achieving a proper understanding of Allison transmission operation. For the Allison specialist tech, knowing the hydraulic circuit factors and torque powerflows are essential to diagnose performance problems.

60. HYDRAULIC CIRCUITS
The following sequence of schematics shows the hydraulic circuits in a WT. Although you may need some help in guiding your way through a circuit the first time, you will get used to this layout in no time.

61. WT hydraulic schematic—neutral.

62. WT hydraulic schematic—first range.

63. WT hydraulic schematic—second range.

64. WT hydraulic schematic—third range.

65. WT hydraulic schematic—fourth range.

66. WT hydraulic schematic—fifth range.

67. WT hydraulic schematic—sixth range.

68. WT hydraulic schematic—reverse.

69. Neutral powerflow.

70. First range powerflow.

71. Second range powerflow.

72. Third range powerflow.

73. Fourth range powerflow.

74. Fifth range powerflow.

75. Sixth range powerflow.

76. Reverse range powerflow.

77. TROUBLESHOOTING WTS
WT electronics are equipped with an extensive self-diagnostic capability. Fault codes are used to isolate the nature, source, and severity of a problem in the electronic circuit. To effectively troubleshoot WTs, the Allison WT troubleshooting manuals should always be used. The following section outlines some of the diagnostic techniques recommended by Allison.

78. Shop Talk
The off-going and oncoming ratio test can detect clutch slippage almost immediately. This provides a considerable advantage to the technician when troubleshooting WTs. WT electronics can command a hold in the previous range to protect the transmission when severe clutch slippage warrants this failure strategy.

79. In former generations of electronic automatics, by the time the driver complained of a slippage problem, significant transmission damage had already occurred: this was a major problem in Allison CEC transmissions.

80. DNS Light
Whenever WT electronics sense a condition that could damage the transmission, transmission electronics, or the vehicle drivetrain, shifting is restricted and the DNS light is illuminated.

81. Shop Talk
The DNS light is not necessarily illuminated every time a diagnostic code is logged.

82. ACCESSING DIAGNOSTIC CODES

85. CAUTION:
Always use the appropriate Allison troubleshooting procedure and never make any assumptions based on a previous WT problem.

86. CATERPILLAR CX TRUCK TRANSMISSIONS
Caterpillar introduced its CX family of transmissions in This full authority electronically controlled automatic transmission is based on a design used for a number of years in Caterpillar off-highway 725-series articulated trucks.

87. CX CONSTRUCTION

88. CX MAIN PRESSURE AND TAP LOCATIONS

89. CX Adjustments

90. SHIFT PAD

91. CX transmission Hall effect fluid level sensor.

92. CX ELECTRONICS

93. Cat ECPCs
The ECPCs are ECU switched solenoids. Each ECPC is identical (same part numbers) and can be swapped around when performing hydraulic troubleshooting. When PWM actuated, the ECPCs route main pressure (350 psi [2,400 kPa]) to engage clutches that hold planetary members. There are two phases to ECPC activation: Current spike during actuation, current drop-off at full clutch engagement.

97. CX Hydraulics Troubleshooting

98. The tap locations on a CX31

100. CX CALIBRATION
Shift quality in CX transmissions is unusually smooth. This is due to precise powershift trim that optimizes shift quality. This precise trim is “learned” through initial calibration after which it is continually updated using adaptive logic. Calibration should be undertaken:

101. Calibration Procedure
To calibrate a CX transmission, the vehicle must be driven through an extensive road test while the technician/driver responds to prompts from the electronic technician (ET).

102. CX EXTERNAL COMPONENT LOCATION

103. VOITH DIWA electronically controlled automatic transmission

104. SUMMARY
• Allison CEC transmission is an older partial authority electronic management system that adapts a hydromechanical Allison transmission to computerized monitoring and controls. • Primary input signals to CEC electronics are the shift signal, TPS signal, and road speed data.

105. Summary (cont.)
• Three types of ECUs are used to manage the CEC electronics: Splashproof, Sealed Standard, and Sealed Plus II. • An electrohydraulic valve body is used to convert the results of ECU logic into hydromechanical outcomes.

106. Summary (cont.)
• The WT uses a modular design and full authority management electronics to effect shifting and communicate with the chassis data bus. • WT modules may be removed from the transmission and be serviced or replaced as separate units.

107. Summary (cont.)
• WT modules may be grouped into input, gearbox, and output categories. • The WT input modules are the torque converter module, the converter housing module, and the front support/charging pump module.

108. Summary (cont.)
• The WT gearbox modules are the rotating clutch module, the main housing module, the P1 planetary module, the P2 planetary module, and the main shaft module. • The WT output modules are the rear cover module, output retarder module, or the transfer gear/dropbox module (depending on the model).

109. Summary (cont.)
• The electronic control module is a computer that masters the operation of the transmission. • All electronic automatic transmissions use interconnected planetary gearsets to provide multiple stages of gearing, depending on the range selected.

110. Summary (cont.)
• WT and CX transmissions option integral driveline retarders. These can supplement vehicle service brake applications. These function similarly to a torque converter driven in reverse. • One WT model is available with a dropbox or transfer gear for four-wheel-drive vehicles.

111. Summary (cont.)
• The electrohydraulic control module in a WT houses the solenoids, sensors, valves, and regulators required to effect the results of ECU processing into outcomes. • SAE J1939–compatible hardware and software give WT and CX transmissions full multiplexing capability.

112. Summary (cont.)
• The programming of WTs determines the actual number of ranges available in a chassis. • In both WT and CX transmissions, the clutches are controlled by solenoids PWM switched by the ECM.

113. Summary (cont.)
• The term primary modulation is used by Allison to describe the amount of time a solenoid is energized. Secondary modulation describes the current flow through a solenoid during energization. • Understanding the powerflows through WT and CX transmissions can be a useful diagnostic tool.

114. Summary (cont.)
• Codes logged into ECU memory can be classified as active or historic (inactive). • Codes are usually displayed in the order in which they are logged with the most recent displayed first. In cases in which one code can produce more severe consequences, this code is displayed first.

115. Summary (cont.)
• Caterpillar CX transmissions use an external hydraulic circuit and pressure taps to troubleshoot the system. • CX clutch control is effected by PWM-actuated ECPCs. ECU driver current to the ECPCs is spiked on actuation and dropped off after the clutch is engaged.

116. Summary (cont.)
• Final shift quality in CX transmissions is trimmed by adaptive logic in an ET-managed, road test procedure. • The Voith DIWA automatic transmission is used in transit bus applications and features a counter-rotating torque converter that doubles as a driveline retarder.

117. Any Questions ?
Thank You !