1. Chapter 7: Classroom and shop manuals
Automatic Transmission

2. Hydraulic Circuits and Controls
Classroom Manual
Hydraulic Circuits and Controls

3. Hydraulic Circuits and Controls
Classroom Manual
Hydraulic Circuits and Controls

4. Describe the basic types of valves used in automatic transmissions.
Objectives
Describe design and operation of hydraulic controls used in modern transmissions.
Describe the basic types of valves used in automatic transmissions.
Describe various configurations of a spool valve and explain how it can be used to open and close various hydraulic circuits.
Explain the role and operation of the pressure control solenoid (PC solenoid) assembly.

5. Describe how fluid flow and pressure can be controlled by a solenoid.
Objectives (cont’d)
Describe how fluid flow and pressure can be controlled by a solenoid.
Explain why load sensing devices are necessary for automatic transmission efficiency.
Identify the various pressures in the transmission and explain their purpose
Describe the purpose of a transmission’s valve body.

6. Transmissions shift according to engine load and vehicle speed
Introduction
Transmissions shift according to engine load and vehicle speed
Transmissions shift by holding and driving different members of a planetary gear set
Using servos, bands, and one-way clutches
These are applied by hydraulic pressure routed by the valve body

7. Two or more main parts including a separate and/or transfer plate
Valve Bodies
Directs fluid pressure to the apply devices that hold and drive the planetary members
Three types of valves
Disc (poppet)
Check ball
Spool valves
Two or more main parts including a separate and/or transfer plate

8. Valve Bodies (cont’d)

9. Multiple-Part Valve Bodies
Found in many Chryslers
The valve body assembly is comprised of the main valve body, regulator valve body, servo body, top accumulator body, and accumulator body, all assembled together as a single assembly.
GM also has a multiple-part valve body that is attached to the TCM in the oil pan, along with the input and output shaft speed sensors and the transmission range switch

10. Slow down hydraulic apply pressures
Orifices
Slow down hydraulic apply pressures
Can be part of the separator plate under the valve body

11. Orifices (cont’d)

12. Check valves can be used to redirect fluid flow

13. Check Valves (cont’d)
Check valves can be used to redirect fluid flow

14. Check Valves (cont’d)
Click on graphic above to animate

15. Normally a flat disc with stem to guide valve’s operation
Poppet Valve
Normally a flat disc with stem to guide valve’s operation
Often used to prevent back flow

16. Poppet Valve (cont’d)

17. Open or close a fluid passage
Check Balls
Commonly used to redirect fluid flow or to stop it from back flowing to the reservoir
Open or close a fluid passage

18. Check Balls (cont’d)

19. Used to control hydraulic pressures in the valve body
Spool Valves
Used to control hydraulic pressures in the valve body
As the valve moves, it covers and uncovers hydraulic passages

20. Spool Valves
Click on box above to play video

21. Spool Valves (cont’d)

22. Spool Valve Operation
Click on graphic above to animate

23. Spool valve that can have several lands and reaction areas
Relay Values
Spool valve that can have several lands and reaction areas
Controls direction of fluid flow and does not control pressure

24. Relay Valves

25. Direct line pressure to apply devices
Shift Valves
Direct line pressure to apply devices
Acted on one side by governor pressure
Acted on other side by throttle pressure
When valve moves the transmission shifts
Late model transmissions use shift solenoids

26. Valve directs fluid to components when drive range is selected
Manual Valve
Spool valve operated manually within valve body by gear selector linkage
Valve directs fluid to components when drive range is selected

27. Pressures
Mainline
Regulated pressure from the pump

28. Shifting
The TCM can activate a shift solenoid to signal the transmission shift valve to move and apply the clutches
Signal pressures control the direction of the line pressure to the appropriate apply device by their action on shift valves
May use a speed sensor to help the TCM decide when to activate a shift solenoid

29. Pressure Control Valves
Control line pressures and pressures used to control or signal shift points
Shift pressure control solenoids can regulate the shift pressure for a particular shift
Pressure regulator valves
Pressure relief

30. Pressure Regulator Valve
To prevent stalling caused by increased pressure in the transmission, pressure regulator valve is used
Allows pump to produce enough pressure for transmission to function
Resulting pressure is called line pressure

31. Pressure Regulator Valve (cont’d)

32. Electronic Pressure Controls
The hydraulic pressure is controlled by an electronic pressure control (EPC) solenoid
which is controlled by the TCM
The shift pressure control solenoids can alter the pressure to a particular clutch pack to compensate for wear and to make sure the shift happens at the particular time and pressure conditions

33. Electronic Pressure Controls (cont’d)
Pressure Switches
Are used to let the TCM know if there is hydraulic pressure at a particular hydraulic circuit

34. Electronic Shift Timing Controls
Modern transmissions use electronic sensors to determine:
Engine load
Temperature
Throttle position
Gear selector position and vehicle speed
Picking the optimum shift speed and quality

35. Electronic Shift Timing Controls (cont’d)
Vehicle Speed Sensors
Used to determine shift points
Load Sensors
Shift timing also depends on engine load
Engine load is sensed electronically by the MAP and TPS

36. Can be traced like electrical diagrams
Oil Circuits
Can be traced like electrical diagrams
Individual circuit tracing can help in diagnosis
They determine how these circuits work and what components are doing

37. Typical Shifting Controls in a Late-Model Transmission
Oil Circuits (cont’d)
Typical Shifting Controls in a Late-Model Transmission
Uses clutch-to-clutch shifting
Fluid Flow before the Shift
Is mainline pressure
Clutch Pressure Control Solenoid
Normally open allowing fluid to pass

38. Clutch Transmission Fluid Pressure Switch
Oil Circuits (cont’d)
Clutch Transmission Fluid Pressure Switch
Monitors if fluid pressure is present at the clutch apply circuit
Shifting Control Valves and Solenoids
The TCM commands the shift solenoid valve open. Under pressure the shift valve opens, it then applies pressure to the clutch pack

39. General Hydraulic System Service
Shop Manual
General Hydraulic System Service

40. Remove and install the valve body from common transmissions
Objectives
Remove and install the valve body from common transmissions
Check valve body mating surfaces
Inspect and measure valve body bores, springs, sleeves, retainers, brackets, check balls, and screens
Inspect and replace valve body spacers and gaskets
Check and/or adjust valve body bolt torque

41. Refer to service manual for specific instructions for removal
Valve Body Removal
Refer to service manual for specific instructions for removal
If valve body is removed without removing the transmission:
Always use new gaskets and seals
Torque the valve body bolts
Carefully note the position of parts
Watch for springs and check balls that might fall out during removal

42. Valve Body Removal (cont’d)

43. Keep parts well organized Carefully clean each part
Valve Body Service
Keep parts well organized
This is mandatory
Carefully clean each part
Dry with compressed air and reassemble
Do not use heavy sandpaper on valves
Polish with a fine abrasive only

44. Valve Body Service (cont’d)
Check Valve to Bore Tolerances
Reassembly
After the valve body has been cleaned, it should be allowed to air dry
Once dried, it should be soaked in clean ATF
Torque valve body bolts

45. Summary
Automatic transmission receives power from engine through the torque converter
Gear ratios are selected according to engine load and vehicle speed
Valve body directs fluid pressure through the transmission to shift gears
Check, poppet, orifices, and spool valves are used to control hydraulic pressure
Relief valves allow or prevent pressure until a particular pressure is reached

46. Spool valves are flow directing valves
Summary (cont’d)
Spool valves are flow directing valves
Mainline pressure is the source of all pressures in the transmission
A PM generator
Electronic device that uses a magnetic pickup on the transaxle housing and a trigger wheel on the output shaft
Engine load can be monitored electronically through the MAP and TP sensor