434 Auto Electricity and Electronics
Figure 22-26. Power splitter can be used to change the power fl ow
and rotating speeds inside a hybrid transaxle or transmission.
Gas Engine
Motor-Generator 1
Motor-Generator 2
Sun Gear
(Generator)
Planetary
Carrier
(Engine)
Pinion
Gear
Ring Gear
(Motor/Output
Axle)
Reduction
Gear Unit
Connected
to the Final
Drive
contactors are also open and no battery voltage or current
can fl ow to the power control module and motor-generator.
However, when the ignition key is turned to run, the
ECU energizes the battery relays. The relays close and send
current to the large contactor coils, which pull the contactor
lugs closed. High voltage and high current can then fl ow
through the contactor lugs to the power control module.
Hybrid Power Splitter
A hybrid power splitter is planetary gearset used to con-
trol the engagement of the motor-generators with the transaxle
or transmission output gears, chains, belts, and shafts. The
hybrid power splitter and transaxle is under computer control
using the hybrid ECU, engine ECU, brake ECU, battery ECU,
power control module, and most vehicle sensors.
When the driver moves the gear shift selector in the
passenger compartment, an electric signal is sent from the
gear shift sensor to the main computer or hybrid ECU. The
hybrid ECU then energizes or shuts off specifi c solenoids
in the transaxle. In this way, the shift lever position sensor
can apply or release friction bands or clutches to hold or
release members of the power splitter.
Hybrid transmission solenoids are used to control the
power split device. By holding or releasing different parts
of the power splitter, the planetary gearset(s) and the fl ow
of torque through both the gas-engine and electric drive
systems can be controlled.
For example, a hybrid transmission can obtain a gear
reduction for the motor-generator armature and a torque
increase out of the motor-generator by holding the sun gear
while driving the ring gear. When power turns the ring gear,
the planet gears “walk” (rotate) around the locked sun gear.
The planet gears move in the same direction as the ring
gear, but not as fast. As a result, more torque is applied to
the output member (planetary carrier) and output shaft.
Gear reduction can be produced in the planetary
gearset by turning the sun gear and holding the ring gear.
A planetary gearset can also reverse output direction. The
input shaft drives the sun gear. The carrier is held, and the
ring gear turns the output shaft. In this way, the power split-
ter can control the fl ow of torque through the transmission
while also maintaining proper motor speed for transmis-
sion output speed. When a motor-generator is operating as
a generator, it can transfer the drive line torque into the
motor-generator armature when braking or coasting.
As shown in Figure 22-26, the engine crankshaft is con-
nected to a shaft running through the front motor-generator and
into the planetary gearset. The planet carrier is splined to the
engine crankshaft. The ring gear is connected to the front motor-
generator armature. The rear motor-generator is connected to
the front motor-generator and to a reduction gear mechanism.
By electro-hydraulically holding and releasing different
parts of the hybrid power splitter, a compact, strong means
of allowing power fl ow through both the motor-generators
and conventional drive train can be achieved.
Hybrid Dash Display
A combination meter or cluster in the dash of a hybrid
displays many variables pertaining to the performance and
condition of the gasoline engine and electric drive system.
The combination meter contains the speedometer odom-
eter, fuel gauge, engine gauges, hybrid power display, and
the hybrid drive ready light, as well as several warning
lights. One design is shown in Figure 22-27.
A hybrid power display in the combination meter
informs the driver of the hybrid drive operating conditions.
Many hybrid displays indicate when the electric “assist”
is working, how electrical energy is being used, and how
much energy remains in the battery pack. The power dis-
play often reads in kilowatts (kW) of power output from
the HV battery pack. This display helps the driver utilize
and recapture as much energy as possible while driving.
The idea is to use as much regenerative braking energy as
possible while using as little gasoline or diesel fuel as pos-
sible. A hybrid power display allows the driver to know:
❑ When to coast downhill, using little or no energy.
❑ How fast to accelerate to use more electrical energy
and less gas engine power.
❑ How hard to apply the brakes when stopping with-
out engaging the hydraulic friction pads/shoes on the
rotors or drums.