Posted by Steve Pardoe on August 17, 2006, 9:57 pm
> Sorry to top-post but I just wanted to compliment you on your excellent,
> comprehensive reply to Steve's question. Scroll no further.
>>I apologize if my message is a little curt... IE just went and ate my
>> longer and much thought out response. (GRR!) Hopefully I get it all
>> right this second time around.
<snip>
Agreed, very comprehensive and thanks for taking the trouble to post again.
It's contrary to anecdotal evidence from respected consumer organisations
and road test magazines in the UK, which have consistently stated (but
without numerical evidence) that the mileage achieved by typical drivers is
significantly worse than the 66 mpg (Imp) headline figure I've seen claimed
for the Prius. Perhaps it's to do with the kinds of journeys we typically
make over here.
Steve (signing off)
Posted by Carpe Diem on August 18, 2006, 3:27 am
> Agreed, very comprehensive and thanks for taking the trouble to post
> again.
> It's contrary to anecdotal evidence from respected consumer organisations
> and road test magazines in the UK, which have consistently stated (but
> without numerical evidence) that the mileage achieved by typical drivers
> is significantly worse than the 66 mpg (Imp) headline figure I've seen
> claimed for the Prius. Perhaps it's to do with the kinds of journeys we
> typically make over here.
> Steve (signing off)
See also :
http://test.nepsecure.co.uk/ADMIN/PropMotorsPlatform/newportal/motoringnews/fullstory.asp?siteid=&storyid0
Posted by mrv@kluge.net on August 18, 2006, 1:22 pm
Steve Pardoe wrote:
> It's contrary to anecdotal evidence from respected consumer organisations
> and road test magazines in the UK,
Based on what I've been reading on
http://autos.groups.yahoo.com/group/Prius-UK/ , I didn't think that
there were any "respected" organizations/magazines, only entertainment
avenues.
Posted by =?iso-8859-1?Q?mark=5Fdigital= on August 15, 2006, 5:33 pm
>> 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
I went from Pittsfield MA and then onto MA Pike, drove 62 mph, and got 63.9
mpg.
Posted by NeoPhyte_Rep on August 15, 2006, 9:23 pm
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.
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> comprehensive reply to Steve's question. Scroll no further.
>>I apologize if my message is a little curt... IE just went and ate my
>> longer and much thought out response. (GRR!) Hopefully I get it all
>> right this second time around.