When the vehicle is brought to a stop, the control sys-
tem again moves various valves to lower the gear ratios to
match vehicle speed and engine load. The control system
releases the converter lockup clutch as the vehicle
approaches the completely stopped position.
In Reverse, the manual valve sends pressure to the
proper holding members. They apply and hold the plane-
tary gears to place the transmission in Reverse. Power goes
through the impeller, turbine, and input shaft to the plane-
tary gears. The planetary gears reverse the direction of
rotation before delivering power to the output shaft.
Hybrid Vehicle Drivetrain Operation
Hybrid vehicles use more than one source of energy
for propulsion. A hybrid gas-electric vehicle uses both an
internal combustion engine and an electric motor-generator.
The motor-generator is installed between the engine and
the transmission or transaxle. Some vehicles have two
motor-generators. Depending on driving conditions and
the type of hybrid, the vehicle can be moved by the engine
only, the motor-generator only, or both the engine and the
motor-generator.
Figure 1-40 shows a motor-generator installed in a
transmission case. A stationary field winding is attached to
the engine block and a rotor is attached to the engine
crankshaft. A large, high-voltage battery is installed in the
vehicle body. An electronic control system operates the
motor-generator for maximum efficiency. The motor-gener-
ator can crank the engine, eliminating the need for starter
and flywheel gears. When the internal combustion engine
is running, the motor-generator can produce electricity to
recharge the hybrid's batteries and power its electrical
circuits. Some hybrid vehicles do not have a reverse gear, and
the motor-generator runs in reverse to back up the vehicle. An
overrunning clutch keeps the engine from turning backward
when the vehicle is in reverse.
The two major classes of hybrid vehicles are full
hybrids and mild hybrids. The motor-generator on a full
hybrid moves the vehicle as long as the battery is charged
above a certain preset level. If the battery charge falls
below this level, the engine starts and propels the vehicle
while recharging the battery.
On a mild hybrid, the engine moves the vehicle.
During operation, the mild hybrid's engine shuts off during
coasting, braking, and complete stops. When the driver
presses the accelerator pedal, the motor-generator restarts
the engine. When the engine starts, it begins turning the
motor-generator, which then functions as an alternator to
recharge the vehicle's battery.
30 Automatic Transmissions and Transaxles
Parking gear
Planetary output gear
Parking pawl
Free Lock
Figure 1-36. The parking gear linkage is attached to the transmission/transaxle shifter linkage. Moving the linkage causes the park-
ing pawl to engage the parking gear on the output shaft. (Subaru)
Carburetor
lever
Valve
assembly
TV link
TV cable
Throttle lever and
bracket assembly
Cable adjuster
Figure 1-37. On many older vehicles, throttle linkage was used
to control shift speeds and transmission pressures.The linkage
was connected between the carburetor or throttle body and a
throttle valve in the transmission. Increased throttle opening
caused the throttle valve to increase pressures in the trans-
mission and to delay the upshift. (General Motors)