Steve Pardoe <steveSP@AMpardoes.com> wrote:
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As we move down the road, the engine is only used when we exceed about 15 mph or the traction battery needs a charge. If there is a down slope and the engine is not yet running, the potential energy will be used either to increase speed or recharge the traction battery or both, recovering a portion of the energy used to climb the hill. It is not necessary to apply the brakes for this to occur. It is merely necessary to request less speed increase than the hill can provide. A gasoline only vehicle would still be consuming gasoline on this same route. The last two cars I've owned (one petrol / gasoline, one diesel) consume no fuel at all on the over-run (but I agree they are not conserving any energy while slowing down).
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When we reach a controlled intersection and come to a complete stop, the gasoline engine is turned off. All ancillary devices are run off the traction battery. Again, we aren't consuming gasoline to go nowhere.
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Yes, although a diesel engine consumes a remarkably small amount when idling compared with a gasoline engine, since it can run very much leaner.
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There is one other Prius operational mode not yet discussed called
Electric Vehicle (EV) or "stealth mode." At speeds below 42 mph, the
vehicle can operate on just the electric motor with the engine off. The
distance increases significantly at speeds below 30 mph. For example,
the last 1-2 miles into work or returning home, I take streets with
25-30 mph limits. This last mile is run with almost no gas consumption
unless I have to react to other traffic. This includes 2-4 m. rises,
which can be taken at 10 mph without the engine.
This EV mode is a unique to the stock Toyota and Ford hybrid systems.
Some models of Prius in Europe and Japan come with the EV button and in
the USA, there is an after market kit to fit an EV button. So, are any
other vehicles able to climb 2-4 m. without turning on the engine?
My 03 Prius has one well documented EV mode, reverse. In fact, even
cold, the engine can not run when I back out of my driveway. The reason
has to do with the planetary gears and engine. I can also climb steep
hills in reverse.
It is possible to use the EV capability to considerably extend the
"glide" part of "pulse and glide" driving. What this means is the speed
decay is countered by the EV so the hybrid vehicle 'glides' further than
an engine-off non-hybrid. For example, two vehicles starting at 40 mph
start a glide down to 30 mph. The non-hybrid will go about 1/2 mile
before reaching 30 mph and having to start the engine to speed back to
40 mph. The hybrid vehicle can stretch that energy-off glide to nearly a
mile using a small amount of electrical power. The pulse back to 40 mph
quickly add that energy back and you're back in glide again. But in the
meanwhile, the hybrid has gone a considerably further distance.
Hybrids are also designed for frequent engine off and on operation. This
means the start-engine fuel burn is extremely low and efficient. There
is no Bendix gear that has to reach out and engaged the flywheel but
effectively a directly connected motor that engages electronicly. This
minimizes starting friction losses and engine wear. Unlike traditional
12 VDC starter motors drawing a hundred or more amps, the hybrid motors
are 200-270 VAC motors drawing a few tens of amps. This lower current
minimizes the resistance losses and heat suffered by ordinary starter
motors.
Bob Wilson
Question about MPG
Linear Mode
