Chapter 22 Hybrid Drive Systems 433
to engage that gear position and to control the hybrid power
control module. The hybrid ECU sends signals to a power split-
ter in the transmission, which connects and disconnects the gas
engine and electric motor through a series of gears.
When the gas pedal of a hybrid is pressed, a pedal-
position sensor sends a signal to the hybrid drive ECU. The
hybrid ECU has in memory whether to drive in all-electric
mode (slow acceleration), start the internal combustion
engine (rapid acceleration), or use a combination of inter-
nal combustion engine and electric drive.
The hybrid drive ECU is designed to keep the HV bat-
tery pack operating at the optimum temperature and state
of charge. By keeping the HV battery pack at optimum tem-
perature and charge, the hybrid drive ECU increases battery
service life and fuel economy. The hybrid drive ECU must
also control the power control module and motor-generator.
It helps use battery power effi ciently and to properly recharge
the HV battery pack through regenerative braking when the
HV battery pack is partially drained.
The hybrid drive ECU interfaces with the HV battery
pack, power control module, motor-generator, and engine
ECU to keep all components working together in synergy.
Battery Relays and Contactors
Battery relays and contactors are used to control the
fl ow of electricity between the battery pack and the power
control module. As shown in Figure 22-25, when the ignition
key is off and battery relays are open, the large high-current
Figure 22-25. Note how the battery relays operate the large electrical contactors. The relays and contactors work in conjunction to
disconnect battery pack energy from the electric drive train. Note that the VOM shows no voltage to the power control module until
the relays close the contactors.
0.0
+ –
+
–
3
3
1
2
5
4
+ –
+
–
Volts
DC
Electric
Motor-
Generator
Power
Control
Module
Ground
Fault
Monitor
Contactor
Relays Closed
(Relays Off)
12-Volt
Battery
Volts
DC
274
Electric
Motor-
Generator
Power
Control
Module
Contactor
Relays Closed
(Relays On)
12-Volt
Battery
HV Battery
HV Battery
3-Phase AC DC Voltage
High Voltage Safety System—Vehicle Shut Off (Ready off)
High Voltage Safety System—Vehicle On and Operational (Ready on)
Contactor
Open
Contactor
Closed
Ground
Fault
Monitor