OBJECTIVES

2. OBJECTIVES After studying Chapter 7, the reader should be able to: • Explain how an automatic transmission hydraulic system operates. • List the valves used in an automatic transmission. • Describe the operation of the valves in an automatic transmission. • Describe how vehicle speed and load affect automatic shifts. • Follow an upshift or downshift sequence through a hydraulic schematic.

3. INTRODUCTION • The hydraulic system enables an automatic transmission to operate automatically. • The basic function of the hydraulic control system is to: • Schedule shifts to optimize engine performance, • Provide the best gear ratio for the driving conditions, • Safely shift into reverse when requested • Provide driver control of the operating ranges, • Provide engine braking to help control vehicle speed on downgrades, • Lock or unlock the torque converter clutch.

4. FIGURE 7-1 This electronic transmission valve body (a) has only five valves. Four solenoids in the solenoid assembly (b) control shifts and torque converter clutch (TCC) apply and release. (Courtesy of Chrysler Corporation) INTRODUCTION

5. FIGURE 7-1 (CONTINUED) This electronic transmission valve body (a) has only five valves. Four solenoids in the solenoid assembly (b) control shifts and torque converter clutch (TCC) apply and release. (Courtesy of Chrysler Corporation) INTRODUCTION

6. FIGURE 7-2 The valve body is mounted to the bottom of the main case of transmissions and some transaxles (a). It is also mounted at the end or top of some transaxles (b). (Reprinted with permission of General Motors) INTRODUCTION

7. FIGURE 7-3 The switch valve (a) will shift the fluid flow from circuit 1 to circuit 2 when the controlling pressure increases. This regulator valve has two servo valves (TV boost, and D2 and rev. boost) (b), which cause a pressure increase when the throttle is opened or when the transmission is shifted into D2 or reverse. This regulator valve (c) controls supply pressure to become mainline pressure. INTRODUCTION

8. TABLE 7-1 Hydraulic System Subcircuits INTRODUCTION

9. PRESSURE DEVELOPMENT AND CONTROL • As soon as the engine starts, the torque converter hub drives the transmission pump to produce fluid flow. • Pressure is created by resistance to fluid flow. • This pressure is called: • Line • Mainline • Supply • Control pressure

10. FIGURE 7-4 Many pressure regulator valves have three positions. (a) The spring has moved the valve to the bottom of the bore. (b) Line pressure is moving the valve upward, opening the passage to the torque converter (circle). (c) Increased line pressure has moved the valve upward to where it can release pressure to the pump inlet (circle). Note that boost pressure in either of the two upper ports can cause a pressure increase. PRESSURE DEVELOPMENT AND CONTROL

11. FIGURE 7-5 The pressure regulator of this variable displacement vane pump can send fluid pressure to the DECREASE passage. This pressure will move the pump slide to the right and reduce pump output. (Reprinted with permission of General Motors) PRESSURE DEVELOPMENT AND CONTROL

12. FIGURE 7-6 This manual valve is arranged so it dumps line pressure to the sump in park (circle). This reduces line pressure to below 30 psi. (Courtesy of Chrysler Corporation) PRESSURE DEVELOPMENT AND CONTROL

13. FIGURE 7-7 Some pressure regulators use an adjusting screw that allows adjustment of line pressure. Others use a shim/spacer to allow an adjustment. PRESSURE DEVELOPMENT AND CONTROL

14. FIGURE 7-8 Hydraulic pressure moves this regulator valve to the left against spring tension. Pressure in the manual valve circuit will work against hydraulic pressure to increase/boost line pressure. Pressure in the overdrive clutch circuit will reduce/cut back line pressure. (Courtesy of Chrysler Corporation) PRESSURE DEVELOPMENT AND CONTROL

15. FIGURE 7-9 Fluid from the manual valve reverse circuit acts on the primary regulator valve to increase line pressure in reverse. (Courtesy of Toyota Motor Sales USA, Inc.) PRESSURE DEVELOPMENT AND CONTROL

16. TORQUE CONVERTER, OIL COOLER, AND LUBRICATION CIRCUIT • As soon as the supply circuit begins to develop pressure, the regulator valve moves slightly and opens a passage to the torque converter. • This fluid flow serves several purposes: • It ensures that the torque converter is filled so it can transmit torque from the engine to the transmission’s input shaft. • It helps control converter fluid temperature. • It provides lubrication for the moving parts inside the transmission

17. FIGURE 7-10 The converter and cooler feed circuit begins at the pressure regulator, goes through the converter and cooler, and then into the lube passages. Note that the cooler and the lines connecting it to the transmission are outside of the transmission. (Courtesy of Chrysler Corporation) TORQUE CONVERTER, OIL COOLER, AND LUBRICATION CIRCUIT

18. TORQUE CONVERTER, OIL COOLER, AND LUBRICATION CIRCUIT • Torque Converter Pressure Control • Torque Converter Clutch Control • Cooler Flow • Lubrication Flow

19. FIGURE 7-11 When the engine is not running, the regulator valve spring moves the T/C control valve to the right, blocking the cooler passage and reducing the chance of converter drain down. Note the bypass valve that will open if the cooler becomes plugged. (Courtesy of Chrysler Corporation) TORQUE CONVERTER, OIL COOLER, AND LUBRICATION CIRCUIT

20. FIGURE 7-12 With the torque converter clutch (TCC) released, fluid enters this converter through the input shaft. It leaves through the area between the input shaft and the stator support. (Courtesy of Chrysler Corporation) TORQUE CONVERTER, OIL COOLER, AND LUBRICATION CIRCUIT

21. FIGURE 7-13 This TCC is controlled by a valve that is controlled by a solenoid that is controlled by the power train control module (PCM). When the solenoid is energized (right), the valve moves to the left, and this applies the TCC. TORQUE CONVERTER, OIL COOLER, AND LUBRICATION CIRCUIT

22. FIGURE 7-14 The lock-up valve and fail-safe valve control the switch valve. This in turn controls fluid flow through the converter and therefore converter lock-up. (Courtesy of Chrysler Corporation) TORQUE CONVERTER, OIL COOLER, AND LUBRICATION CIRCUIT

23. FIGURE 7-15 The transmission cooler is normally mounted in the colder, outlet tank of the radiator. Steel lines are normally used to connect the transmission to the cooler. (Courtesy of Chrysler Corporation) TORQUE CONVERTER, OIL COOLER, AND LUBRICATION CIRCUIT

24. FIGURE 7-16 This cooler has a large, flat passage from its inlet to its outlet (a). The screenlike turbulator is shown (b). TORQUE CONVERTER, OIL COOLER, AND LUBRICATION CIRCUIT

25. FIGURE 7-17 Cold fluid tends to stick to the walls of a plain tube cooler (top). The turbulator causes fluid turbulence to promote mixing so all of the fluid cools (bottom). TORQUE CONVERTER, OIL COOLER, AND LUBRICATION CIRCUIT

26. FIGURE 7-18 An auxiliary filter can be installed in one of the cooler lines to help trap contaminants (a). The cutaway view shows the internal magnet and folded paper filter element (b). (Courtesy of SPX Filtran) TORQUE CONVERTER, OIL COOLER, AND LUBRICATION CIRCUIT

27. FIGURE 7-19 An auxiliary cooler is mounted so the fluid flows through it and then through the standard cooler in the radiator. (Courtesy of Chrysler Corporation) TORQUE CONVERTER, OIL COOLER, AND LUBRICATION CIRCUIT

28. FIGURE 7-20 Transmission lube passages. Note how the passage leads to gears and bushings. (Courtesy of Toyota Motor Sales USA, Inc.) TORQUE CONVERTER, OIL COOLER, AND LUBRICATION CIRCUIT

29. FIGURE 7-21 This planet carrier burned out from lack of lubrication; note the excess clearance and dark coloration at the planet gear shafts. TORQUE CONVERTER, OIL COOLER, AND LUBRICATION CIRCUIT

30. THROTTLE PRESSURE • A circuit carrying a throttle pressure signal is always available while the engine is running in most transmissions. • Throttle valves are pressure-regulating valves, and they provide a pressure signal that is proportionate to the load on the engine

31. FIGURE 7-22 The throttle valve produces a pressure signal that is directly related to throttle opening or engine load. This pressure signal is used to control line pressure so that line pressure increases as the throttle is opened. THROTTLE PRESSURE

32. FIGURE 7-23 In this hydraulically controlled transmission, the shift valves are positioned by a spring and hydraulic pressures from the throttle valve and governor. (Courtesy of Chrysler Corporation) THROTTLE PRESSURE

33. FIGURE 7-24 Application speed of this front band is controlled by the accumulator stroke rate, and this is controlled by the shuttle valve and the 1–2 shift control valve. (Courtesy of Chrysler Corporation) THROTTLE PRESSURE • The transmission control system uses throttle pressure to reprogram or reschedule several areas of operation: • Shift quality • Shift timing • Shift feel • Torque converter clutch control

34. FIGURE 7-25 This mechanical throttle valve is operated by a cable that is connected to the engine throttle body and accelerator pedal. (Courtesy of Chrysler Corporation) THROTTLE PRESSURE

35. FIGURE 7-26 At wide-open throttle, the kickdown valve pushes the throttle valve to the end of the bore. At this position, TV pressure is equal to line pressure in both the TV and kickdown passages. (Courtesy of Chrysler Corporation) THROTTLE PRESSURE • Mechanical Throttle Valves • Vacuum Throttle Valves • Wide-Open Throttle Kickdown Valve

36. FIGURE 7-27 With high manifold vacuum, the modulator diaphragm and modulator valve are to the left, and modulator pressure is low. When manifold vacuum drops, the spring moves the diaphragm toward the right, and modulator pressure will increase. Note the bellows used in this modulator. (Reprinted with permission of General Motors) THROTTLE PRESSURE

37. FIGURE 7-28 Vacuum modulators have different diameters, which change the relative strength of the modulator. THROTTLE PRESSURE

38. FIGURE 7-29 Manifold vacuum varies with load. Cruising at light load produces about 15 to 20 in. Hg. A high load produces zero vacuum,0 in. Hg. (Courtesy of Nissan North America, Inc.) THROTTLE PRESSURE

39. FIGURE 7-30 The manual valve is moved by the shift lever and held in position by the detent lever (cam). MANUAL VALUE • The manual valve controls the fluid flow to the band servos, clutch apply pistons, and the shift valves for the various forward and reverse gears. • This valve is also called a selector valve.

40. FIGURE 7-31 The manual valve is in drive and the transmission is in first gear. Fluid is being sent to the rear clutch, accumulator, 1–2 shift valve, throttle valve, and governor. (Courtesy of Chrysler Corporation) MANUAL VALUE

41. GOVERNOR VALVE • The transmission will begin transferring power and rotating the output shaft when the selector lever is moved to drive, intermediate, or low. • When the output shaft starts turning, the governor spins with it. • The governor is either shaft mounted (attached directly onto the output shaft) or case mounted (driven by a gear on the output shaft).

42. FIGURE 7-32 A case-mounted governor is driven by a gear on the output shaft. It provides a pressure signal relative to vehicle speed. (Reprinted with permission of General Motors) GOVERNOR VALVE

43. FIGURE 7-33 The ideal governor pressure signal increases in exact proportion to vehicle speed, but a simple governor produces a signal that is too low at intermediate speeds or too high at higher speeds. The pressure signal from a two-stage governor comes closer to matching vehicle speed. GOVERNOR VALVE

44. GOVERNOR VALVE • Governor valve assemblies are manufactured in four basic styles. • Two are shaft mounted, and two are case mounted: • Shaft mounted with the weight(s) opposing the valve • Shaft mounted with a primary and secondary valve • Case mounted with a pair of primary and secondary weights • Case-mounted bleed-off system

45. FIGURE 7-34 As the vehicle speeds up, centrifugal force acting on the governor weight tries to move the weight and valve toward the right to increase governor pressure. This is opposed by governor pressure at the valve, which tries to move the valve toward the left and reduce governor pressure. (Courtesy of Chrysler Corporation) GOVERNOR VALVE

46. FIGURE 7-35 This two-stage, shaft-mounted governor uses both a primary and secondary valve. (Courtesy of Chrysler Corporation) GOVERNOR VALVE

47. FIGURE 7-36 Centrifugal force will cause the two weights to move outward. This pushes the two balls against their seats, reducing the amount of exhaust and increasing governor pressure. (Reprinted with permission of General Motors) GOVERNOR VALVE

48. FIGURE 7-37 Centrifugal force produces an upward force on the valve that will increase governor pressure if the valve moves. Governor pressure at the top of the valve opposes this action. The governor valve is positioned between these two forces. (Reprinted with permission of General Motors) GOVERNOR VALVE

49. SHIFT VALVES • An upshift or downshift occurs when the shift valves move. • Shift valves are balanced between the governor pressure trying to move the valve to cause an upshift and the spring plus throttle pressure trying to resist an upshift.

50. FIGURE 7-38 Governor pressure can move this 1–2 shift valve from the downshift position (left) to the upshift position. SHIFT VALVES