Environmental Engineering Reference
In-Depth Information
Gear shift ratio coverage =
AT
5
5.5
6.7
Europe EC
1,900 kg sedan
Japan 10-15
1,900 kg sedan
US combined
2,900 kg SUV
4
4.5
5
5.5
6
6.5
7
G src
Figure 3.15 Driveline matching impact due to various drive cycles
3.4.4 Dynamics of acceleration/deceleration
Hybrid propulsion systems offer a further advantage over CVs in that vehicle
launch and decelerations can remain smooth even with the engine off. Electric-only
launch is characteristic of Toyota's THS hybrid systems. Vehicles with automatic
transmissions in stop-go traffic retain smooth launch feel because the torque con-
verter holds the driveline in a 'wound-up' state. Then, when the brake pedal is
released there is no driveline dead band to cause a clunk. If the driveline is allowed
to relax at a stop and then the propulsion power re-applied, there will be an interval
of wind-up prior to wheel revolution and a consequent unpleasant feel. M/G pre-
sence can be used to advantage in such circumstances.
There is now concern with PHEV and BEV during charging that RESS voltage
isolation levels may require some form of isolation, such as use of rubber bushing
in the propeller shaft. Such added compliance will have direct impact on driveline
dynamics during acceleration and deceleration with introduction of a dead band
being one specific consequence if improperly designed. There is also concern with
the voltage ripple introduced during charging that ripple currents will flow in the
chassis via motor winding to case capacitance, inverter headsink to chassis capa-
citance and other parasitic paths that can present a shock hazard. This concern is
currently under investigation.
3.4.5 Wide open throttle launch
It was shown in Chapter 2 in reference to the Honda Civic that the integrated motor
assist (IMA) system can be used to advantage to augment engine torque by as much
as 66% during vehicle launch. The Civic, with its downsized engine, maintains
good launch feel at WOT because of the added torque. Conventional vehicles
equipped with automatic transmissions enjoy smooth launch, especially under
WOT, since the torque converter has a multiplying effect on driveline torque. This
effect diminishes within 2 s, a short time interval, but sufficient to make a lasting
impression of vehicle character on the driver. With hybrid M/Gs in non-automatic
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