Hybrid Electric Vehicle (Hev) Overview; Cooling System - freightliner BUSINESS CLASS M2 Driver Manual

Hybrid Electric Vehicle
Hybrid Electric Vehicle (HEV)
Overview
A hybrid electric vehicle (HEV) has both a diesel en-
gine and an electric motor. Engine torque is aug-
mented with electrical torque. The electric motor is
powered by batteries, which are charged by regen-
erative braking and, on vehicles equipped with the
ePTO option, the diesel engine.
The batteries cannot move the vehicle for long dis-
tances at highway speeds. In the event of a diesel
engine failure, drive the vehicle to a safe location as
quickly as possible.
Eaton Corporation developed and supplies the hybrid
electric system for Freightliner Trucks. The primary
system components are the hybrid drive unit (or
"HDU", which includes the electric generator/motor
and automated transmission), power electronics car-
rier (PEC), and the motor inverter/controller. Electric
power take-off (ePTO) and auxiliary power generator
(APG) components are optional on the HEV system.
Freightliner Trucks designed the stand-alone liquid
cooling system required to support the operation of
Eaton's HEV system. Its primary system components
are the electric water pump, reservoir/expansion
tank, radiator, electric radiator fan, and coolant
plumbing.
Body builders will develop the components for the
PTO, the PTO plumbing, and a safety switch to pre-
vent the diesel engine from starting when the hood is
open.
Regenerative Braking
Regenerative braking reduces vehicle speed by con-
verting some of the vehicle's kinetic energy into elec-
tric energy to charge the hybrid system's batteries.
When the accelerator pedal is at idle while coasting,
or the service brake is depressed to slow the vehicle,
the hybrid system charges the batteries.
The regeneration will feel as if the brake is being
lightly applied when you remove your foot from the
accelerator pedal. The full power of the service brake
is always available to the driver, and regenerative
braking is automatically shut off during an ABS (an-
tilock brake) event.
The Eaton Hybrid Control Unit will automatically shut
off regenerative braking when the batteries are fully
charged.
15.1
High-Voltage Safety Features
The HEV has high-voltage cables and a service
switch on the PEC.
High-voltage cables are covered in orange insulation
and conduit. Each high-voltage component is tagged
with a warning or danger label.
IMPORTANT: The service switch on the PEC
should only be used for an emergency shut-
down, or when the service manual or trouble-
shooting guide calls for work on the high-voltage
system. The service manual and troubleshooting
guide for the hybrid electric system are available
from www.roadranger.com.
The red service switch is located next to the high-
voltage cable connections at one end of the PEC.
Pushing in the red service switch will shut down the
engine. The hybrid system will be disabled, and the
high-voltage batteries in the PEC, though still live,
are isolated in the PEC.
NOTE: The PEC may be mounted in an area
with limited access.
For information on emergency shutdowns, see
"Emergencies" in this chapter.

Cooling System

The HEV requires a liquid cooling system for the
HDU, inverter, DC/DC Converter (if ePTO equipped),
and APG (if equipped). The HEV's cooling system is
separate from the engine cooling system.
For coolant, use a mixture of 50 percent ethylene
glycol and 50 percent water.
Electric Power Take-Off (ePTO)
The Electric Power Take-Off (ePTO) option provides
standard hydraulic functions without continuous die-
sel engine operation. The PTO drive power is pro-
vided by the hybrid motor and hybrid batteries. When
the hybrid batteries deplete, the diesel engine auto-
matically starts to recharge them and provide PTO
drive power. Once the batteries are fully charged, the
engine shuts down automatically. Vehicles with the
ePTO option are designed with a safety switch to
ensure the diesel engine does not start when the
hood is open.
A DC/DC converter is required for ePTO applications
to convert high-voltage DC to 12-volt DC.