Environmental Engineering Reference
In-Depth Information
When cabin climate control burden is regulated as part of the economy testing,
the electrical burden will be increased appropriately. Table 3.7 illustrates average
and peak values for various vehicle systems.
Table 3.7 Vehicle electrical loads
Feature
Average load (W)
Peak load (W)
Headlamps
120
-
Engine management
240
240
Electromechanical valves (V6 engine)
800
3,000
Engine coolant pump
80
300
Engine cooling fan
300
800
Electric assist power steering
100
1,500
Electrohydraulic brakes
300
1,000
Heated windshield
-
2,000
After market audio systems*
500
1,500
*Added woofers and amplifiers are rated 500 W rms and 1,500 W peak
3.6.3 Grade holding and creep
Idle-stop hybrid functionality requires some means to sense and hold the vehicle
position on a grade. Early idle-stop hybrid implementations utilized vehicle tilt
detectors to sense a grade and apply brakes. Others such as the Aisen Warner
Navimatic transmission use global positioning satellite elevation information to
sense grades and engage the neutral idle grade holding function. All automatic
transmissions provide creep function so that the vehicle does not roll back when
stopped on a grade.
Power split hybrid propulsion systems use a brake on the planetary gear set
ring gear to hold a grade. A CVT transmission, for example, would also use a brake
to lock the driveline when stopped.
3.6.4 Neutral idle
In a conventional automatic transmission the engine must work against the torque
converter when the vehicle is stopped. This is a high slip condition on the torque
converter that consumes fuel during vehicle stopped events. In a hybrid vehicle
with automatic transmission a separate, electrically driven oil pump is necessary to
pressurize the torque converter when the engine is off so that immediately fol-
lowing a warm restart the vehicle is ready to launch. If the torque converter is not
properly conditioned upon restart and launch, there will be a lag as the engine input
power fills and pressurizes the torque converter. In a neutral idle transmission the
input clutch is controlled in slip mode so that the engine does not work against the
torque converter. Moreover, the fact that the input clutch is allowed to slip in a
controlled manner means that normal automatic transmission creep is maintained
and driveability does not suffer.
