Chapter 6 Answers to Review Questions
CLASSROOM MANUAL, PAGES 192-194
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
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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.
Fill-in-the-Blanks
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
Instructor’s Guide to Accompany Today’s Technician: Automatic Transmissions & Transaxles 3E
40
9. B
10. A
SHOP MANUAL, PAGES 286-288
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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