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Re: corrected...
Posted by Reality (more from Reality) on Thu, 14 Jun 2012 19:07:26
In Reply to: Re: corrected..., Snowmobile , Thu, 14 Jun 2012 13:26:38
Regenerative braking can only recover a very small percentage of the total kinetic energy of the vehicle, because:

1. Regenerative braking is not operative at very low vehicle speed; conventional brake pads have to be used in order to make the vehicle stop;

2. Regenerative braking is only available on driven wheels;

3. In braking where the braking performance is crucial, the braking force is matched to the maximum that the wheel contact patch can generate, which is many times the output of the typical drive train. In a hybrid, the electric motor/generator is only sized to be a small fraction of the total drive train output.

Counting on regenerative braking to provide the entire braking force is a little like using "engine braking" only without ever using the brakes. Not exactly practical if you don't want to be a serial murderer.

I was sloppy in the sample. The typical high traffic vs. no traffic driving is the not the mad driver making up the lost stop time, but instead the 30min of 1200rpm (360000Rev) becomes a one-hour drive like I initially mentioned before I gave the wrong time segments. That one hour will consist of 30min of idling at 800rpm, 28min of 1200rpm 30mph driving, and 2min of 3000rpm accelearation. The heavy traffic does not allow for high speed driving. Total engine rotation is 63600Rev, or about 75% more gas consumption for a trip that takes twice as long in time. That's the difference between 30mpg smooth highway driving vs. 18mpg stuck in city traffic. The long idling is what kills the gas mileage, and something that the hybrids help the most (cutting out 24000revs in this example).

posted by 75.67.1...
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