Chapter 7Hydraulic Circuits and Controls
Upon completion and review of this chapter, the student should be able to:
Classroom Manual Objectives· Describe the design and operation of the hydraulic controls and valves used in modern transmissions and transaxles.
· Describe the basic types of valves used in automatic transmissions.
· Describe the 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 following components of the transmission control system: pressure regulation valve, throttle valve, governor assembly, manual valve, shift valves, and kickdown assembly.
· Describe the operation of the main pressure regulator valve.
· Describe how fluid pressure can be controlled by a solenoid.
· Describe the different designs of a governor and explain the operation of each type.
· Explain why load-sensing devices are necessary for automatic transmission efficiency.
· Identify the various pressures in the transmission and explain their purpose in the total functioning of the transmission.
· Describe the purpose of a transmission’s valve body.
· Trace through the oil circuit for a transmission and describe where the fluid flows in each transmission range. / Shop Manual 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.
· Inspect and replace governor cover and seals.
· Inspect, adjust, repair, and replace governor sleeve, valve, weights, springs, retainers, and gear.
Overview
This chapter in both manuals discusses hydraulic systems and apply devices. They include the theory and service of the various valves used in today’s transmissions.
Reading Assignments
Classroom Manual, pages 195-245
Shop Manual, pages 297-316
Terms to Know
Ball-type valveCarburetor cleaner
Hybrid valve
Lands
Manual shaft
Manual valve
Needle check valve
Oil circuit / Orifice
Poppet valve
Pressure-regulating valve
Reaction area
Relay valve
Relief valve
Separator plate
Shift valve / Solenoid/pressure switch
Spool valve
Throttle valve
Transfer plate
Transmission fluid pressure switch
Two-way check valve
Valley
Lecture Outline and Notes
I. Objectives
Review the chapter’s objectives.
II. Introduction
Discuss the power flow through the transmission.
III. Control Devices
A. Discuss the need for a transmission check valve.
B. Describe how relief valves control pressure.
C. Describe the need for small openings to control fluid.
D. Describe spool valves and how they are used.
E. Describe how control valves direct the flow of fluid.
F. Describe relay valves and their operation.
IV. Valve Bodies
A. Theory
1. Discuss the purpose of the valve body.
2. Describe the three types of valves found in a valve body.
3. List and describe the main parts of a valve body.
B. Valve Body Removal
1. Discuss the precautions to take when removing a valve body.
2. Describe and demonstrate how to keep check balls in check.
3. Describe and demonstrate how to keep the various valve body bolts in
order so that reassembly is done correctly.
4. Describe how to disassemble the valve body.
C. Valve Body Service
1. Describe the reassembly procedure.
2. Describe the general inspection of the valves.
3. Discuss the use of hazardous cleaning agents.
4. Discuss the importance of checking gasket placement.
5. Discuss torquing the valve body bolts.
V. Valves
A. Pressure Regulator Valves
1. Describe how the pressure regulator works.
2. Discuss the valve’s primary purposes.
B. Shift Valves
1. Describe shift valves and their operation.
2. Describe how the manual spool valve works.
3. Discuss the need for a kickdown valve and how it works.
VI. Pressures
A. Mainline Pressure
1. Describe mainline pressure.
2. Discuss the generation of mainline pressure.
3. Describe the use of mainline pressure within the hydraulic circuits of a
transmission.
4. Explain the purpose and operation of the pressure regulator valve.
B. Throttle Pressure
1. Define throttle pressure.
2. Discuss the purpose of throttle pressure.
3. Explain how throttle pressure is controlled.
4. Describe the relationship of throttle pressure to mainline pressure and
boost pressure.
C. Governor Pressure
1. Define governor pressure.
2. Explain how governor pressure is generated and controlled.
3. Describe the relationship of governor pressure to throttle pressure.
4. Discuss how throttle and governor pressures control shifting.
VII. Governors
A. Theory and Purpose
1. Describe how the governor works to achieve proper shifting.
2. Discuss vehicle speed sensors and how they work to replace a
governor in today’s transmissions.
B. Governor Service
1. Describe disassembly of the governor.
2. Describe the reassembly procedure.
3. Explain the necessity of correctly placing weights and valves.
VIII. Load Sensors
A. Describe the operation of a vacuum modulator.
B. Describe how the throttle linkage works to balance the load.
C. Discuss the MAP sensor and its possible use as a load sensor
D. Discuss shift timing and its purpose.
IX. Electronic Pressure Controls
A. Describe the use of electronics to control pressure.
B. Discuss solenoid-operated valves.
C. Compare older types of valves to electronic control valves.
X. Oil Circuits
Discuss the flow of fluids through the circuits in the transmission and the valve body.
XI. Summary
Review the material covered, emphasizing the main points and key words.
Chapter 7 Answers to Review Questions
CLASSROOM MANUAL, PAGES 246-248
Short Answer Essays
1. All fluids conform to the shape of their container. Pascal determined that force applied to liquid creates pressure, or the transmission of force through the liquid. Liquids have no shape of their own; they acquire the shape of the container they are put in. Liquids are basically incompressible. The pressure applied to a liquid in a sealed container is transmitted equally in all directions and to all areas of the system and acts with equal force on all areas. When a pressure is applied to a confined liquid, the pressure of the liquid is the same everywhere within the hydraulic system.
2. The basic types of valves used in automatic transmissions are ball, poppet, or needle check valves and relief valves, orifices, and spool valves.
3. Check valves are used to hold fluid in cylinders and to prevent fluid from returning to the reservoir. A check valve opens when fluid is flowing and closes when the flow stops. The valve also closes when fluid pressure is applied to the outlet side of the valve. Check valves can also serve as a one-way valve and the direction of the fluid flow controls and operates the check valve.
4. The transmission’s pump provides a flow of fluid to the mainline circuit. This flow is limited by engine speed and the pressure regulator valve. Mainline pressure is developed by the pressure regulator valve when it blocks or resists the flow of fluid.
5. The separator and transfer plates are designed to seal off some of the passages, and they contain some openings that help to control and direct fluid flow through specific passages.
6. Mainline pressure is a regulated pump pressure that is the source of all other pressures in the transmission. Governor pressure is a regulated hydraulic pressure that varies with vehicle speed. Throttle pressure is a regulated pressure that varies with engine load or throttle position.
7. The three common designs of governors are shaft-mounted, gear-driven with check balls, and gear-driven with a spool valve.
8. Shift valves control the upshifting and downshifting of the transmission by controlling the flow of fluid to the apply devices that engage the different gears.
9. Shifting electronically allows for shifting at more optimum times than does shifting by hydraulics and is based on inputs to a control computer from various sensors, such as engine temperature, engine speed, engine load, vehicle speed, throttle position, and gear selector position.
10. A ball-type check valve without a return spring can be used as a two-way check valve. This type of valve is used where hydraulic pressure from two different sources is to be sent to the same outlet port. When hydraulic pressure on one side of the valve is stronger than the pressure on the other side of the valve, the ball moves to the weaker side and closes that port. The ball will toggle between the ports in response to differing pressures. Both ports are open at the same time unless the pressures on both sides of the ball are equal. Normally, if the pressures were equal, the ball would be centered and would block off the outlet port.
Fill-in-the-Blanks
1. Ball-type check valves
2. Pressure-regulating, flow-directing
3. Increased, increased, heavy loads
4. Regulator, exhaust
5. High, low
6. Manual
7. Lands, hydraulic passages, reaction area, lands
8. Valve body, separator plate, transfer plate
9. Mainline, throttle, governor
10. Shaft, gear, check balls, gear, spool valve
Multiple Choice
1. C
2. A
3. A
4. C
5. A
6. C
7. C
8. C
9. C
10. C
SHOP MANUAL, PAGES 317-318
ASE-Style Review Questions
1. B
2. D
3. A
4. C
5. B
6. B
7. D
8. C
9. C
10. A
ASE Challenge Questions
1. D
2. B
3. A
4. C
5. A
Instructor’s Guide to Accompany Today’s Technician: Automatic Transmissions & Transaxles 3E 51