OBJECTIVES

2. OBJECTIVES After studying Chapter 6, the reader should be able to: • Discuss hydraulic principles. • Describe how a hydraulic system operates. • Identify the parts of a transmission hydraulic system and explain their purpose. • Explain the requirements for a transmission hydraulic system. • Identify the requirements for automatic transmission fluid and the differences between fluids.

3. INTRODUCTION • The automatic transmission’s hydraulic system has several important functions . • It must be able to: • Apply the clutches and bands and therefore control the transmission power flow, • Transmit sufficient force and motion to completely apply the control units to prevent slippage, • Maintain fluid flow through the torque converter for its proper operation, • Maintain fluid flow to lubricate and cool the moving parts of the gear train.

4. FIGURE 6-1 A hydraulic diagram for a four-speed transmission with electronic controls. Diagrams are used to determine the relationship of the components. They are often color-coded to help locate the circuits. (Courtesy of Chrysler Corporation) INTRODUCTION

5. HYDRAULIC PRINCIPLES • Hydraulics, often called fluid power, is a method of transmitting motion and/or force. • Hydraulics is based on the fact that liquids can flow easily through complicated paths, but they cannot be compressed. • All the components in a hydraulic system are connected so that fluid pressure can be transmitted and allowed to work.

6. FIGURE 6-2 Fluid pressure is transmitted undiminished in all directions. Note that the pressure is equal throughout the system. HYDRAULIC PRINCIPLES

7. FIGURE 6-3 Fluids flow freely and will assume the shape of their container (a), yet they are virtually noncompressible (b). HYDRAULIC PRINCIPLES

8. FIGURE 6-4 A 100-lb force applied on an input piston that has an area of 1 in. will produce a fluid pressure of 100 psi. HYDRAULIC PRINCIPLES • Pressure is defined as the amount of force applied to a given area.

9. FIGURE 6-5 System pressure can be determined by dividing the input force (50 lb) by the area of the input piston (0.5 in2). Output force can be determined by multiplying the area of the output piston (2 in2) by the fluid pressure (100 psi). HYDRAULIC PRINCIPLES

10. HYDRAULIC PRINCIPLES • When discussing hydraulic pistons and computing fluid pressures and forces, it is important to use the area of the piston and not the diameter. • The area of a piston or any circle can be determined using this formula: • πr2 or π (0.785d2)

11. FIGURE 6-6 A simple memory triangle will help you remember the commonly used hydraulic formulas. HYDRAULIC PRINCIPLES

12. FIGURE 6-7 The basic components of a simple hydraulic system. SIMPLE HYDRAULIC SYSTEMS • Many hydraulic systems use an engine- or motor-driven pump to produce fluid movement. • These systems normally consist of the pump, a fluid intake system usually equipped with a filter, a fluid supply (sump), control valves, and the actuators that provide the system output.

13. FIGURE 6-8 In many transmissions, the oil pump is at the front of the transmission and is driven by the torque converter hub. (Courtesy of Chrysler Corporation) BASIC AUTOMATIC TRANSMISSION HYDRAULICS • In most automatic transmissions, the pump is built into the front or engine end of the transmission and is driven by the back of the torque converter.

14. FIGURE 6-9 This pump assembly (20) is attached to the valve body (51) and channel plate (280). The pump is driven by the oil pump drive shaft (340). (Courtesy of Slauson Transmission Parts, www.slauson.com) BASIC AUTOMATIC TRANSMISSION HYDRAULICS

15. FIGURE 6-10 A pressure regulator valve. When fluid pressure acting on the right end of the valve exceeds spring tension, the valve will move to the left and open the passage back to the pump inlet. (Courtesy of Chryster Corporation). BASIC AUTOMATIC TRANSMISSION HYDRAULICS

16. FIGURE 6-11 This valve body has two sections that contain 11 sets of valves. BASIC AUTOMATIC TRANSMISSION HYDRAULICS

17. FIGURE 6-11 (CONTINUED) This valve body has two sections that contain 11 sets of valves. BASIC AUTOMATIC TRANSMISSION HYDRAULICS

18. FIGURE 6-12 The manual valve is connected to the gear shift lever so movement of the lever will slide the valve along its bore. (Courtesy of Nissan North America, Inc.) BASIC AUTOMATIC TRANSMISSION HYDRAULICS

19. FIGURE 6-13 A typical shift valve has a spring to move the valve to a downshift position; throttle pressure works with this spring. When governor pressure gets high enough, the valve will move to an upshift position. BASIC AUTOMATIC TRANSMISSION HYDRAULICS

20. FIGURE 6-14 Operation of the valve controls fluid flow to the actuator. It can block operation (a), cause apply (b), or cause release (c). BASIC AUTOMATIC TRANSMISSION HYDRAULICS

21. FIGURE 6-15 An internal-external gear pump (a), gerotor pump (b), and vane pump (c). PRODUCING FLUID FLOW AND PRESSURE • Three common types of rotary pumps are used to produce the fluid flow and resulting pressure in an automatic transmission. • They are the internal-external gear with crescent (crescent or gear) pump, the gerotor (rotor) pump, and the vane pump.

22. FIGURE 6-15 (CONTINUED) An internal-external gear pump (a), gerotor pump (b), and vane pump (c). PRODUCING FLUID FLOW AND PRESSURE

23. FIGURE 6-16 As a pump rotates, a low pressure/vacuum is created as the pumping members move apart in one area, and atmospheric pressure will force fluid into this area. Pressure is created where the pumping members move together. PRODUCING FLUID FLOW AND PRESSURE

24. FIGURE 6-17 A variable displacement vane pump in maximum and minimum output positions. The slide is moved to the high-output position by the spring moving the slide. Decreased pressure comes from the pressure regulator valve. (Reprinted with permission of General Motors) PRODUCING FLUID FLOW AND PRESSURE

25. FIGURE 6-18 This transmission uses a dual-stage, external gear pump. Both stages are used at low engine speeds to produce enough fluid for the transmission’s needs. At higher engine speeds, the secondary stage is vented. (Courtesy of Chrysler Corporation) PRODUCING FLUID FLOW AND PRESSURE

26. PROVIDING CLEAN FLUID • A filter is located at the pump inlet to trap dirt, metal, and any other foreign particles that might cause wear in the pump, bearings, bushings, and gear train or cause sticking of the various valves. • Three types of filters are used: • Surface • Depth • Paper

27. FIGURE 6-19 Two filters: a surface/screen filter (a) and a depth/felt filter (b and c). PROVIDING CLEAN FLUID

28. FIGURE 6-20 A surface filter traps particles that are too big to pass through the openings in the screen. (Courtesy of SPX Filtran) PROVIDING CLEAN FLUID

29. FIGURE 6-21 The surface area of a surface filter is reduced somewhat by the material that makes up the screen. The size of the screen openings determines how small of a particle can be filtered. PROVIDING CLEAN FLUID

30. FIGURE 6-22 A depth filter is a group of woven fibers of a certain thickness. Foreign particles are trapped at different levels as they try to flow through. (Courtesy of SPX Filtran) PROVIDING CLEAN FLUID

31. FIGURE 6-23 Comparison of the filtering ability of four types of filters. (Courtesy of SPX Filtran) PROVIDING CLEAN FLUID

32. FIGURE 6-24 General Motors transaxles have two fluid reservoirs. One is the lower pan, and one is the valve body cover. The thermostatic element closes when the fluid heats up to raise the fluid level in the upper pan. (Reprinted with permission of General Motors) PROVIDING CLEAN FLUID

33. CONTROLLING FLUID FLOW • The fluid flow from the pressure regulator valve to the manual valve and into the control circuit is called mainline, line, or control pressure. • Flow to and from a transmission hydraulic actuator is controlled by one or more valves. • Spool valves sliding in a round bore are used for this purpose. • A spool valve gets its name from its resemblance to a spool used for thread

34. FIGURE 6-25 A spool valve resembles a spool for thread (top). FIGURE 6-26 A spool valve and its bore. Note the names of the various parts. (Courtesy of Chrysler Corporation) CONTROLLING FLUID FLOW

35. FIGURE 6-27 The sleeve allows the larger primary regulator valve to enter its part of the bore and also provides the bore for the smaller No. 1 and No.2 plungers. (Courtesy of Toyota Motor Sales USA, Inc.) CONTROLLING FLUID FLOW

36. FIGURE 6-29 Fluid pressure acting on the surface area of the valve face can move the valve along the bore. FIGURE 6-28 When a valve moves in its bore, the side passages are opened or closed to control fluid flow. (Courtesy of Chrysler Corporation) CONTROLLING FLUID FLOW

37. FIGURE 6-30 The governor valve produces a fluid pressure that is proportional to the speed of the vehicle. (Courtesy of Nissan North America, Inc.) FIGURE 6-31 Ideally, governor pressure increases with speed so the pressure in psi matches the speed in mph. There should be about 40 psi at 40 mph. CONTROLLING FLUID FLOW

38. FIGURE 6-32 A vacuum-operated throttle valve uses a vacuum modulator to produce an engine-load-sensitive signal at the transmission (a). A mechanical-controlled throttle valve (in this case a cable) transfers an engineload- sensitive signal through mechanical linkage (b). (Reprinted with permission of General Motors) CONTROLLING FLUID FLOW

39. FIGURE 6-33 This kickdown valve is controlled by the electric solenoid and is closed when there is no electrical signal (a). The valve opens when the solenoid is energized (b). (Courtesy of Nissan North America, Inc.) CONTROLLING FLUID FLOW

40. FIGURE 6-34 A check valve is opened by fluid flow in one direction (left) and closes when the fluid tries to flow in the other direction. FIGURE 6-35 When fluid flows through this shuttle valve from port B to port C, the check ball moves over to close port A (left). Fluid flow from port A will close port B (right). CONTROLLING FLUID FLOW

41. FIGURE 6-36 A pressure relief valve (a). When fluid pressure acting on the area of the ball exceeds the spring force, the ball will move off of its seat and allow excess pressure to escape (b). CONTROLLING FLUID FLOW

42. FIGURE 6-37 This valve spool has four possible hydraulic reaction faces. The areas are calculated like those of any other circular surface using the formula πr2. CONTROLLING FLUID FLOW • Valve Hydraulic Forces • Think of a valve as a hydraulic actuator. • The hydraulic force exerted by a valve is simply the valve land area multiplied by fluid pressure. • The valve area is determined using the formula for the area of a circle, πr2.

43. CONTROLLING FLUID PRESSURE • Fluid pressure in an automatic transmission is controlled by a variable pressure regulator valve. • Fluid pressure must be high enough to apply a clutch or band tightly enough to prevent slippage. • Excessive fluid pressure will produce heat and fluid foaming as well as more drag on the engine. • Remember that fluid horsepower is a product of pressure and flow.

44. CONTROLLING FLUID PRESSURE • In most transmissions, the pressure regulator valve is positioned close to the outlet of the pump. • This valve is usually arranged so fluid pressure is at one end and a spring is at the other end. • An additional passage from the pump enters the valve at one valley, and a passage leading back to the pump inlet is located at an adjacent valley

45. FIGURE 6-38 When fluid pressure at the right end of the regulator valve gets high enough, the valve will move toward the left and allow excess pressure to return to the pump suction passage. (Courtesy of Chrysler Corporation) CONTROLLING FLUID PRESSURE

46. SEALING FLUID PRESSURE • The fluid passages run throughout the valve body, transmission case, shafts, and tubes of the transmission. • Remember that fluid transmits pressure equally through a passage, regardless of its size or shape. • The many passages in the valve body and the transmission case look like a bunch of worm tracks (a nickname used by transmission rebuilders.

47. FIGURE 6-39 This valve body uses upper (at bottom) and lower sections (at top) that are separated by the separator plate. Note how the separator plate can restrict a passage so it becomes a port or orifice for flow into the other section. (Courtesy of Chrysler Corporation) SEALING FLUID PRESSURE

48. FIGURE 6-40 This intermediate shaft has fluid passages to transfer lubricating oil to the planetary gearsets. (Courtesy of Chrysler Corporation) SEALING FLUID PRESSURE

49. FIGURE 6-41 Static seals prevent fluid from passing between two stationary surfaces. Dynamic seals keep fluid from passing through when one of the surfaces is moving. (Courtesy of Toyota Motor Sales USA, Inc.) SEALING FLUID PRESSURE

50. FIGURE 6-42 The sealing member of a metal-clad lip seal makes a dynamic seal with the rotating shaft while the metal case forms a static seal with the transmission case. (Courtesy of Chrysler Corporation) SEALING FLUID PRESSURE