Chapter 6 Answers to Review Questions

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Chapter 6 Answers to Review Questions


Short Answer Essays

1. A CVT uses an electromagnetic clutch to transfer torque from the engine to the transmission. Its operation is controlled by a clutch control unit. The clutch control unit switches current to energize and de-energize the electromagnetic clutch in response to inputs from various sensors. These sensors include a brake switch, accelerator pedal switches, and an inhibitor switch. The brake switch de-energizes the clutch when the vehicle is slowing or coming to a stop. The control unit uses inputs from the accelerator pedal switches to vary the amount of current to the clutch and to signal ratio changes to the adjustable pulleys inside the transmission. The inhibitor switch prevents clutch engagement when the gear selector is in the P or N position. When the electromagnetic clutch is energized, engine torque is transferred to the transmission’s input shaft and the drive pulley. At the end of the transmission’s input shaft is the transmission’s oil pump; therefore the clutch control unit has indirect control of the oil pressure in the transmission. Pressure from the pump is used to control the sheaves of both the drive and driven pulleys. Line pressure is controlled by a three-way solenoid in the transmission valve body.

2. Rotary flow is in the direction of impeller rotation and results from the paddle action of the impeller vanes against the fluid. Vortex oil flow is the fluid flow circulating between the impeller and turbine as the fluid moves from the impeller to the turbine and back to the impeller.

3. A typical torque converter consists of three elements sealed in a single housing: the impeller, the turbine, and the stator. The impeller is the drive member of the unit, and its fins are attached directly to the converter cover. The turbine is the converter's output member and is coupled to the transmission's input shaft. The turbine is driven by the fluid flow from the impeller and always turns at its own speed. The stator is the reaction member of the converter. This assembly is about one-half the diameter of the impeller or turbine and is positioned between the impeller and turbine.

4. Automatic transmission pumps are driven by the engine's crankshaft through the torque converter housing. The pumps in all rear-wheel drive and some front-wheel drive transmissions are driven externally by the torque converter's drive hub. The hub has two slots or flats machined in it, which fit into the pump drive. As the converter rotates, the pump is driven directly by the hub. Many front-wheel drive transaxles use a hex-shaped or splined shaft fitted in the center of the converter cover to drive the pump. This system is called an internal drive.

5. Stall occurs when the turbine is held stationary and the impeller is spinning. Stall speed is the fastest speed an engine can reach while the turbine is at stall.

6. Modulating the TCC solenoid allows for smooth clutch engagement and disengagement. It also allows for partial engagement.

7. Slippage in a torque converter results from a loss of energy, and most of these losses are in the generation of frictional heat. Heat is produced as the fluid hits and pushes its internal members. To maintain the efficiency that it has, the fluid must be cooled. The transmission's pump continually delivers ATF into the torque converter through a hollow shaft in the center of the torque converter assembly. The fluid is circulated through the converter and exits past the turbine through the turbine shaft. From there, the fluid is directed to an external oil cooler and back to the transmission's oil pan. This cooling circuit ensures that the fluid flowing into the converter is cooled, thereby maintaining the converter's normal efficiency.

8. A converter clutch disc is splined to the turbine so that it can drive the turbine when the friction material is forced against the torque converter's cover. All converter clutch assemblies are fitted with a damper assembly that directs the power flow through a group of coil springs. The damper springs are either located at the center of the disc or grouped around the outer edge of the disc. These springs are designed to absorb the normal torsional vibrations of an engine, which vary with changes in speed and load.

9. The stator receives the fluid thrown off by the turbine and redirects the fluid so that it re-enters the impeller in the same direction as crankshaft rotation. The redirection of the fluid by the stator not only prevents a torque loss, but also provides for a multiplication of torque. The stator is mounted on a one-way clutch that allows the stator to rotate in one direction only. The stator locks in the opposite direction of turbine rotation. The fluid leaving the turbine must pass through the stator blades before reaching the impeller. In passing through the stator, the direction of fluid flow is reversed by the curvature of the stator blades. The fluid now moves in a direction that aids in the rotation of the impeller. The impeller accelerates the movement of the fluid and it now leaves with nearly twice the energy and exerts a greater force on the turbine. This action results in a torque multiplication.

10. The velocity of the vortex flow is the sum of the impeller produced velocity plus the velocity of the fluid returning from the turbine and stator.


1. Fluid, torque converter, flexplate

2. Higher, faster, more

3. Housing, impeller, turbine

4. Zero, partial, half, full, cycling

5. Light emitting diode (LED), PM generator

6. 90, torque multiplication

7. Impeller, turbine, stator, piston, clutch plate, thrust washers, roller bearings

8. Gear, rotor, vane, vane

9. Rotor, body, clutch cover, silicone fluid

10. Vortex, high, low

Multiple Choice

1. C

2. A

3. C

4. D

5. B

6. A

7. C

8. C

9. B

10. A


ASE-Style Review Questions

1. C

2. D

3. A

4. D

5. B

6. C

7. B

8. D

9. C

10. C

ASE Challenge Questions

1. C

2. C

3. A

4. A

5. B

Instructor’s Guide to Accompany Today’s Technician: Automatic Transmissions & Transaxles 3E

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