Jones Beene wrote:
It appears to be better for two well-known reasons. First - electric motors give highest torque at 0 rpm and with gas engines it is usually over 2000 rpm, and consequently gas engines are inefficient in accelerating from a stop. Prius' present electric motor is too small to make a difference there.
That is way wrong. From 0 to 30 mph, the Prius accelerates faster than a high performance Volvo sedan or BMW. (I have driven all three.) On a short highway merge such as the Washington Beltway, from a standing start to highway speed, you can really feel the electric motor kicking in. It is as fast as the Volvo.
Secondly, gas engines are more efficient when run at a fixed rpm, and the genset permits this . . .
So does the Prius transmission.
Plus GM has coupled their electric motor to some kind of special transmission for high speed.
The Prius transmission is radically different from previous ones and it is incredibly efficient. I have read that it is unlikely anything better could be designed with today's technology. The motor is couples directly to the drivetrain with little loss. I doubt you could make something as efficient going from ICE to battery to electric motor.
As for only ~35 kW from the ICE genset possibly being enough, or not -- when admittedly this is too little power for use with a normal drivetrain and transmission - this may also get back to the genset delivering the full amount of power- at all times regardless of the speed of the vehicle. Perhaps the genset requirement can be less than suspected with this kind of large electric motor as the main feature. IOW the electric motor plus batteries make it seems like you have 3 times more power when you need it on hills - that your genset can put out.
Ed's point -- and mine -- is that you cannot count on having the electric motor plus batteries on hills. The moment the batteries drain, you are in serious trouble. I mean life-threatening trouble. Where Ed lives the hills are very steep, and 10 or 20 miles long in places. You have to have an ICE capable of carrying the entire load up the steepest hill at maximum speed. (In a Prius, the maximum speed is 106 miles an hour as I recall. The computer will not let it go faster. The tires are not rated for higher speeds.)
When the Prius battery drains going uphill, the car does not stop or slow down a bit, because it is all computer regulated -- there is no mechanical connection from the accelerator pedal to the gasoline supply throttle as far as I know. It is fly-by-wire. The computer screen on the dashboard shows that the battery is drained, and the engine immediately starts to make much more noise. Acceleration becomes more sluggish.
The Prius gas pedal has a peculiar quality that I described in my book. When you first shift the transmission into drive, which is also an imaginary fly-by-wire operation, and you take your foot off the brake, the car begins to creep forward like a car with an automatic transmission. You do not need to press the gas pedal. Of course this is purely the way it is programmed. They could just as easily make the car stand stock still until you press the gas pedal. There is no danger the car will roll backwards the way it does with a manual transmission. However, people are used to cars creeping forward, so they made this one emulate an automatic transmission. In my book, chapter 7, I described this:
"New technology often imitates older forms, even when it would work better if it did not. . . . With ingenuity and extra effort, the limitations of the old [are] imposed on the new."
I read about an absurd version this with automobile transmissions. In the Atlanta Journal-Constitution in 2006, they described a continuously variable transmission (CVT) with no discrete gears, like the Prius one. Quote: While very efficient -- the engine always operates in the sweet spot -- the CVT car does not offer the customary jolt as it accelerates. "They feel like they do not shift," says Brauer of Edmunds.com. "It disturbs people." Designers are even trying to develop a CVT with an artificial shift tilt to make it more acceptable to drivers, Whitsitt says. There was no need to have a "clunk." I expect it will cause mechanical troubles and reduce efficiency. When you drive a Prius it takes about five minutes to get used to the CVT and the fact that it does not "clunk." I hate to think of these engineers wasting their time making the machine work less well.
- Jed
