Posted by Horse's Ass on August 15, 2006, 10:30 pm
You and Bill are wasting your time. He isn't paying attention.
> Steve Pardoe wrote:
>>> Steve Pardoe wrote:
>>>> There are two caveats. The first is that in normal driving (not in
>>>> stop-start traffic) how much time do you actually spend pressing the
>>>> brake pedal?
>>> Point of clarification:
>>>
>>> The Prius does not wait for the application of the brake to begin the
>>> regeneration cycle. I've seen the display indicate regeneration at 50
>>> miles per hour when the conditions are adequate.
>>
>> What? If the Prius is charging its battery while the engine is running,
>> but you're not applying the brakes, that's got to be generation, not
>> regeneration.
>>
>>> This is why steady driving is a good thing. If the electronics detects
>>> a request for 50 steady mph and there is a down slope of as little 2%,
>>> the controller may turn off the engine, turn on the motor, and may even
>>> begin regeneration.
>>
>> Again, if the (electric) motor is turned on, it's hard to see where the
>> regenerative energy is coming from! Either the car is slowing and
>> converting some of the energy (which in a conventional car would be lost
>> as heat from the brakes) into battery charge, or it's drawing power from
>> the battery to run its electric motor. It can't be doing both at the same
>> time.
>>
>>> If the down slope is even more severe, but does not require braking to
>>> control the speed of the Prius, the electronics will still take
>>> advantage of the situation.
>>
>> I presume this refers to cruise control 'braking' the car?
>>
>>>> Not much, as a proportion of a journey, unless you are a driver with
>>>> exceptionally poor anticipation. This is evidenced by the very low
>>>> capacity of the Prius battery pack, only able to power the car for a
>>>> few seconds at full output, which in turn explains why Toyota provided
>>>> no facility to charge it from the mains. There's no point.
>>>>
>>>> Second, lugging the additional mass of the battery pack, electric motor
>>>> / generator set, power and temperature control units, etc around all
>>>> the time has an impact on economy.
>>>>
>>> Your second point is offset somewhat by the continual running of a
>>> non-hybrid to support the ancillary requirements. The Prius
>>> air-conditioning is run off the traction battery, thus allowing complete
>>> shutoff of the engine at any complete stop. Given that some of our
>>> intersections require minutes of stopped cross traffic, that can be a
>>> major savings.
>>
>> But surely no _net_ saving at all, since all the charge taken from the
>> battery during rest has to be replaced by energy from the gasoline engine
>> at some point (unless you believe in perpetual motion)?
>>
>>> Probably the reason we don't have hybrid diesels for the U.S. is the
>>> high sulfur content of the petroleum we receive from our sources as
>>> opposed to the lower concentration in the supplies sent to Europe. There
>>> is a new requirement to lower that content at the refinery that should
>>> lead us to diesel hybrids as the best of both technologies.
>>
>> Plus of course the fact that until recently gasoline in the US has been
>> so cheap and plentiful that there's been no incentive to look for
>> alternatives.
>>
>>> In fact, I hope someone takes a close look at a serial hybrid (the Prius
>>> is a parallel hybrid in that both sources directly drive the wheels). A
>>> constant rotation diesel can be more efficient than a variable speed
>>> diesel. It would seem a diesel that charges a battery or capacitor
>>> that runs the motor would be the ultimate combination. And then, if we
>>> plug it in for the first twenty or forty miles of power requirements, we
>>> may have the best energy balance compromise.
>>
>> Yes, though it will always be more efficient to use the internal
>> combustion engine (gasoline or diesel) directly, rather than using it to
>> drive a generator to charge a battery to drive an electric motor to drive
>> the transmission, since you have significant conversion losses at every
>> stage. As I understand, it the main advantage of the battery in the Prius
>> is that it boosts short-term acceleration (especially in the urban cycle)
>> without a corresponding increase in instantaneous power demand (and hence
>> emissions) from the IC engine. Energy recovery from regenerative braking
>> is a bonus, but only of secondary importance.
>>
>> Good debate, thanks for your input.
>> SP
> Let me try this again. Obviously I haven't communicated the complexity of
> the control model implemented in the Prius' computers.
> When you get into the Prius and turn on the system, all ancillary devices
> are initially run off the traction battery. If this were a gasoline only
> vehicle, we would immediately begin consuming gasoline and get no miles
> credited for it.
> The Prius' gasoline engine is turned on briefly to warm the catalytic
> converter. This does not get us any miles, either, but if we haven't
> wasted any time getting into motion, the converter will be warmed up by
> the same engine heat used to move the car.
> 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.
> 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.
> It is my feeling that using an idling gasoline engine to run ancillary
> devices and never recovering any energy used to climb hills is what costs
> the gasoline engine only vehicle the mileage that the Prius delivers. The
> Prius is a better overall compromise of a design. It is the total of
> small changes that gains the Prius significant mileage improvement. What
> the Toyota engineers have done is make it far more probable that a turning
> gasoline engine is causing the wheels to turn, thus improving the miles
> for each gallon it consumes.
Posted by Steve Pardoe on August 16, 2006, 2:03 pm
<snip>
> Let me try this again. Obviously I haven't communicated the complexity
> of the control model implemented in the Prius' computers.
Sorry...
> When you get into the Prius and turn on the system, all ancillary
> devices are initially run off the traction battery. If this were a
> gasoline only vehicle, we would immediately begin consuming gasoline and
> get no miles credited for it.
Sure.
> The Prius' gasoline engine is turned on briefly to warm the catalytic
> converter. This does not get us any miles, either, but if we haven't
> wasted any time getting into motion, the converter will be warmed up by
> the same engine heat used to move the car.
With you so far.
> 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).
> 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.
Yes, although a diesel engine consumes a remarkably small amount when idling
compared with a gasoline engine, since it can run very much leaner.
> It is my feeling that using an idling gasoline engine to run ancillary
> devices and never recovering any energy used to climb hills is what
> costs the gasoline engine only vehicle the mileage that the Prius
> delivers. The Prius is a better overall compromise of a design.
I think it's fair to say that whether or not a gasoline / electric hybrid
such as the Prius is "a better overall compromise of a design" depends on
what kind of driving you mainly do. If you mainly drive in the city and
spend a lot of time stopped at intersections, it makes good sense. Several
European manufacturers make city cars with a stop-start system with a
conventional engine. On a long steady journey with little opportunity to
regenerate, the savings must be very slight, if any, compared with the same
car without the 'hybrid' bit (but for the sake of argument still using the
very efficient Atkinson-cycle engine and planetary transmission), and so
under such conditions there's no reason why the car should be any better
than a diesel, which was my original question.
> It is
> the total of small changes that gains the Prius significant mileage
> improvement. What the Toyota engineers have done is make it far more
> probable that a turning gasoline engine is causing the wheels to turn,
> thus improving the miles for each gallon it consumes.
Well made point, and all credit to them, and indeed to the far-sighted
customers who care enough about all this to buy and run a Prius. Iadmire
them, especially since I now understand that diesel isn't a viable
alternative in much of the USA. However, as in my first post, I was really
more interested in a straightforward user-based mpg comparison.
Thanks anyway,
Steve
Posted by Bill on August 16, 2006, 3:57 pm
> If you mainly drive in the city and
> spend a lot of time stopped at intersections, it makes good sense.
> Several
> European manufacturers make city cars with a stop-start system with a
> conventional engine. On a long steady journey with little opportunity to
> regenerate, the savings must be very slight, if any, compared with the
> same
> car without the 'hybrid' bit (but for the sake of argument still using the
> very efficient Atkinson-cycle engine and planetary transmission), and so
> under such conditions there's no reason why the car should be any better
> than a diesel, which was my original question.
Again, which vehicle are you comparing the Prius to? Until you compare EPA
mileage figures, this is speculation.
>However, as in my first post, I was really more interested in a
>straightforward user-based mpg comparison.
Which user? I presume that would be you. We are back to my earlier
suggestion that you rent a Prius to compare with the mystery vehicle to
which you constantly allude.
Posted by Bob Wilson on August 17, 2006, 9:39 am
> > 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).
>
> > 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.
>
> Yes, although a diesel engine consumes a remarkably small amount when idling
> compared with a gasoline engine, since it can run very much leaner.
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
Posted by richard schumacher on August 16, 2006, 3:22 pm
> > The Prius does not wait for the application of the brake to begin the
> > regeneration cycle. I've seen the display indicate regeneration at 50
> > miles per hour when the conditions are adequate.
>
> What? If the Prius is charging its battery while the engine is running, but
> you're not applying the brakes, that's got to be generation, not
> regeneration.
He meant that, when you're coasting, the motors/generators are taking
energy from the wheels and putting it back into the battery. One does
not have to be using the brakes to be regenerating.
> > Your second point is offset somewhat by the continual running of a
> > non-hybrid to support the ancillary requirements. The Prius
> > air-conditioning is run off the traction battery, thus allowing complete
> > shutoff of the engine at any complete stop. Given that some of our
> > intersections require minutes of stopped cross traffic, that can be a
> > major savings.
>
> But surely no _net_ saving at all, since all the charge taken from the
> battery during rest has to be replaced by energy from the gasoline engine at
> some point (unless you believe in perpetual motion)?
It's a net savings because when the engine runs to recharge the battery
it does so in its most efficient operating range, which produces much
more power than is needed to run the A/C and other accessories. When
the engine is off is obviously uses no fuel at all. Overall, even with
the conversion losses, it's more fuel efficient to run the engine
intermittently.
> Yes, though it will always be more efficient to use the internal combustion
> engine (gasoline or diesel) directly, rather than using it to drive a
> generator to charge a battery to drive an electric motor to drive the
> transmission, since you have significant conversion losses at every stage.
> As I understand, it the main advantage of the battery in the Prius is that
> it boosts short-term acceleration (especially in the urban cycle) without a
> corresponding increase in instantaneous power demand (and hence emissions)
> from the IC engine. Energy recovery from regenerative braking is a bonus,
> but only of secondary importance.
The beauty of Toyota's HSD system is that it can use a variable fraction
of the engine's output with a direct mechanical connection, and allows
sizing the engine to something much less than the maximum power
requirement.
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>>> Steve Pardoe wrote:
>>>> There are two caveats. The first is that in normal driving (not in
>>>> stop-start traffic) how much time do you actually spend pressing the
>>>> brake pedal?
>>> Point of clarification:
>>>
>>> The Prius does not wait for the application of the brake to begin the
>>> regeneration cycle. I've seen the display indicate regeneration at 50
>>> miles per hour when the conditions are adequate.
>>
>> What? If the Prius is charging its battery while the engine is running,
>> but you're not applying the brakes, that's got to be generation, not
>> regeneration.
>>
>>> This is why steady driving is a good thing. If the electronics detects
>>> a request for 50 steady mph and there is a down slope of as little 2%,
>>> the controller may turn off the engine, turn on the motor, and may even
>>> begin regeneration.
>>
>> Again, if the (electric) motor is turned on, it's hard to see where the
>> regenerative energy is coming from! Either the car is slowing and
>> converting some of the energy (which in a conventional car would be lost
>> as heat from the brakes) into battery charge, or it's drawing power from
>> the battery to run its electric motor. It can't be doing both at the same
>> time.
>>
>>> If the down slope is even more severe, but does not require braking to
>>> control the speed of the Prius, the electronics will still take
>>> advantage of the situation.
>>
>> I presume this refers to cruise control 'braking' the car?
>>
>>>> Not much, as a proportion of a journey, unless you are a driver with
>>>> exceptionally poor anticipation. This is evidenced by the very low
>>>> capacity of the Prius battery pack, only able to power the car for a
>>>> few seconds at full output, which in turn explains why Toyota provided
>>>> no facility to charge it from the mains. There's no point.
>>>>
>>>> Second, lugging the additional mass of the battery pack, electric motor
>>>> / generator set, power and temperature control units, etc around all
>>>> the time has an impact on economy.
>>>>
>>> Your second point is offset somewhat by the continual running of a
>>> non-hybrid to support the ancillary requirements. The Prius
>>> air-conditioning is run off the traction battery, thus allowing complete
>>> shutoff of the engine at any complete stop. Given that some of our
>>> intersections require minutes of stopped cross traffic, that can be a
>>> major savings.
>>
>> But surely no _net_ saving at all, since all the charge taken from the
>> battery during rest has to be replaced by energy from the gasoline engine
>> at some point (unless you believe in perpetual motion)?
>>
>>> Probably the reason we don't have hybrid diesels for the U.S. is the
>>> high sulfur content of the petroleum we receive from our sources as
>>> opposed to the lower concentration in the supplies sent to Europe. There
>>> is a new requirement to lower that content at the refinery that should
>>> lead us to diesel hybrids as the best of both technologies.
>>
>> Plus of course the fact that until recently gasoline in the US has been
>> so cheap and plentiful that there's been no incentive to look for
>> alternatives.
>>
>>> In fact, I hope someone takes a close look at a serial hybrid (the Prius
>>> is a parallel hybrid in that both sources directly drive the wheels). A
>>> constant rotation diesel can be more efficient than a variable speed
>>> diesel. It would seem a diesel that charges a battery or capacitor
>>> that runs the motor would be the ultimate combination. And then, if we
>>> plug it in for the first twenty or forty miles of power requirements, we
>>> may have the best energy balance compromise.
>>
>> Yes, though it will always be more efficient to use the internal
>> combustion engine (gasoline or diesel) directly, rather than using it to
>> drive a generator to charge a battery to drive an electric motor to drive
>> the transmission, since you have significant conversion losses at every
>> stage. As I understand, it the main advantage of the battery in the Prius
>> is that it boosts short-term acceleration (especially in the urban cycle)
>> without a corresponding increase in instantaneous power demand (and hence
>> emissions) from the IC engine. Energy recovery from regenerative braking
>> is a bonus, but only of secondary importance.
>>
>> Good debate, thanks for your input.
>> SP
> Let me try this again. Obviously I haven't communicated the complexity of
> the control model implemented in the Prius' computers.
> When you get into the Prius and turn on the system, all ancillary devices
> are initially run off the traction battery. If this were a gasoline only
> vehicle, we would immediately begin consuming gasoline and get no miles
> credited for it.
> The Prius' gasoline engine is turned on briefly to warm the catalytic
> converter. This does not get us any miles, either, but if we haven't
> wasted any time getting into motion, the converter will be warmed up by
> the same engine heat used to move the car.
> 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.
> 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.
> It is my feeling that using an idling gasoline engine to run ancillary
> devices and never recovering any energy used to climb hills is what costs
> the gasoline engine only vehicle the mileage that the Prius delivers. The
> Prius is a better overall compromise of a design. It is the total of
> small changes that gains the Prius significant mileage improvement. What
> the Toyota engineers have done is make it far more probable that a turning
> gasoline engine is causing the wheels to turn, thus improving the miles
> for each gallon it consumes.