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Author Topic: New Volvo  (Read 8672 times)
stephen
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« on: September 07, 2007, 11:06:29 AM »

Well it looks like Volvo have launched its new plug in and go car. It does 62 miles per 3 hour charge then swaps to petrol.
The advantage is that it plugs into a 3 pin socket.
its out in 2010

Stephen
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KenB
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« Reply #1 on: September 07, 2007, 11:38:37 AM »

Stephen, List,

Well at least one European manufacturer has put their head above the parapet, and is combining a high efficiency diesel, with a good sized battery in a series hybrid configuration.

This means that the wheels are driven solely by electric motor(s)  and there is no mechanical connection between engine and wheels.

The series hybrid was deemed to be less overall efficient than the parallel hybrid, and used unfamiliar parts for most auto manufacturers - ie.  electric propulsion and no conventional transmission system.

It also has slightly greater complexity than the parallel hybrid because you need both an engine mounted generator/alternator and an electric motor drivetrain.

However it means that the diesel engine can be downsized in power, so that it supplies just the average power required for propulsion, with the peak power being supplied from the battery pack.

This means that they probably only need a 15kW diesel, rather than a 55kW diesel.

It also means that the diesel could run at constant speed and constant power output, as it is completely dissociated from the traction power - however I suspect that Volvo have opted to oversize the diesel from the bare minimum, so that it can provide a boost where needed.

It's all heading in the right direction, but the proof of the concept will be sales of affordable Volvo C30 hybrids in 2010, and the efficiency of the overall system reflected in the fuel consumption and electrical energy consumption figures - remembering that  in the UK and most of Europe, the bulk of our electricity is still supplied from coal and gas fired power stations at a 35 to 49% efficiency.

Other European manufacturers are also working on diesel hybrids,  2010 should be an interesting year.   However they could have done all this years ago, instead we had 10 years of "half baked" petrol fuelled hybrids, and other turkeys like the Lexus, GM and Ford (US) hybrids.



Ken

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kristen
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« Reply #2 on: September 07, 2007, 12:13:00 PM »

Does this mean that the diesel engine only generated electricity to charge the battery?

If so isn't that less efficient than driving the wheels directly?

(Sorry if I'm being thick!)

Kristen
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KenB
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« Reply #3 on: September 07, 2007, 02:30:39 PM »

Kristen, List,

In the series hybrid, the diesel engine only drives a generator or alternator. This provides power for  charging the batteries, but if the generator had enough power output it could contribute electrical power to the electric motor.

Series hybrids are often quoted as being less efficient than parallel hybrids - where the diesel engine also connects to the roadwheels via some sort of mechanical gearbox.

If your generator is 90% efficient, and your electric motor is 90% efficient, then in a series arrangement, these efficiencies are compounded meaning that only 81% of your diesel power reaches the road wheels.

IMHO - the best thing to do with a diesel is take it out of the car and put it in your shed where at least it can do some good ;-)



Ken
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wyleu
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« Reply #4 on: September 07, 2007, 03:59:36 PM »

If your car wheels were to be continually driven directly by the engine you would have to turn the engine off at traffic lights. Stupid remark of course but it has a lot to do with what goes on. The gearbox does the job of converting the relatively small efficient band of power of a car engine in to the wide range of speed ( including backwards) we need to do all the exciting things we do with cars. ( 83 mph apparently for J Clarkson, who was only lent the car honest your honour). You really only use gearboxes on small engines, in the railway world, apart from a couple of mavericks and small shunters, the diesel engine does very little other than drive a big generator which then powers the electric motors driving the wheels. The reasons for this are manifold. The level of control that can be derived from an electric system is much wider, particularly at very low speeds, where the enormous forces needed to get engines going are nicely matched by the electric motors characteristics. The other element is efficiency, the losses in a big gear box, not to say the considerable complexities of maintenance, means that the diesel engine can run in it's most efficient part of the curve when pwering rather than the frantic gear changing that would be required. The penalty is of course weight, and this is quite considerable, but in the railway world this is useful from the breaking perspective so it's not all bad.

For hybrid cars the weight issue is probably one of the largest concerns, not so much the weight of the generator/alternator which will be considerably less than the gear box that is replaced, but the batteries. However the level of control that can be produced from electrical management is streets ahead of the deisel engines control, plus the braking system can be employed to recharge the batteries rather than jut wearing out the brake blocks as happens with conventional cars.

There will be journeys that are more optimally done in a hybrid, some that best suit electric and others that are best matched to a pure diesel, unfortunately Ford or Volvo have sold us on a particular driving experience which they will now have to match with alternative technologies, and the appropriate large investments, which until Government stumps up the cash for R&D they will probably find reasons to postpone.
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kristen
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« Reply #5 on: September 08, 2007, 12:27:11 AM »

Very useful, thanks.

So can the electricity-generating-diesel-engine be a lot smaller than one that drives a car directly?

And can the electric engine actually be 4 small engines, one at each wheel?

And overall could that use less engine-bay space, allowing for more luggage space? or perhaps meaning that batteries take up no more space than the present engine bay (particularly if they were tucked into the space between the engine and bulkhead of the engine bay)

Kristen
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KenB
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« Reply #6 on: September 08, 2007, 08:00:05 AM »

Kristen, List,

In theory the diesel can be made to provide only the average power needed by the vehicle, with the peak power coming from the batteries.

A car doing 60mph on the level only needs about 15hp to propel it, but to accelerate up a a hill you might need 60hp.

If the diesel engine in the Volvo were rated at 20 to 25hp, then this would allow motorway driving at 70mph or so, and keep the battery topped up.  The smaller diesel engine could be only 2 or 3 cylinders and about 1000cc displacement rather than the more usual 1900cc +.

When you want to accelerate, the battery supplies the boost power to the electric motor.  It would  be easy to get 100hp from an electric motor - if you only need that sort of power for a minute or so. Then the power is reduced and the motor is allowed to cool down.

Individual wheel motors are a possibility, but on the grounds of cost and complexity, Volvo is likely to be using just 1 motor driving either the front wheels or rear wheels through a reduction gear and differential.

Ken

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kristen
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« Reply #7 on: September 08, 2007, 10:17:18 AM »

Thanks Ken, that's filled in a blank part of my brain.  Hope it stays there!
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MrMoosehead
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« Reply #8 on: September 12, 2007, 08:18:43 AM »

Someone (i forget who) recently stripped out a (BMW) mini and refitted it with batteries, 4 individual electric motors on the wheels and most importantly dual redundancy regenerative braking systems.
Why waste all that lovely kinetic energy through heat in the brake pads, when you can put it back in the battery...
Smiley

And another thing - why are all 'eco-cars' designed by geeks with no sense of style? No wonder they don't catch on. And why are they always two seaters? No good for the school run.

A.

IANAE, SWKWBAIAM
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KenB
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« Reply #9 on: September 12, 2007, 09:22:15 AM »

Mr. Moosehead, List,

This seems like a lot of unnecessary complication for a conversion of an existing vehicle.

We fitted regenerative braking to our AVT 100 in 1994,  purely to improve the drive-ability for the average driver - energy return to the battery was <10% on typical urban/city driving.

4 motors will add unnecessary unsprung weight to the suspension system.  Why not just do what every car converter does and graft a single traction motor onto the end of the gearbox bell-housing?

Whilst the purist will argue that an electric vehicle does not need a gearbox, you would be amazed the improvement in overall electric motor efficiency that can be achieved by using a conventional gearbox.  A motor trying to accelerate a car against a single high gear ratio, is very wasteful of energy.  A conventional gearbox also makes the vehicle "more familiar" for the average punter to drive.

Regenerative braking is not all its cracked up to be. It returns perhaps 10% of the energy back into the battery, but it does improve the feel of the car when decelerating - again makes it feel more like IC engine braking.

Re-inventing dual redundancy regenerative braking is a waste of effort, when all vehicles have a perfectly reliable and trusted hydraulic/friction braking system that has be standard for decades.  Regenerative braking can and will work alongside hydraulic braking - but cannot be trusted to bring the car to an absolute standstill in an emergency situation.

It sounds like whoever built this prototype has too much budget and their head in the clouds - way too obsessed with "re-inventing the wheel"- is it any wonder why we never see practical, everyday electric vehicle designs reaching manufacture.





Ken

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MrMoosehead
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« Reply #10 on: September 12, 2007, 12:11:03 PM »

See, told you I Am Not An Expert and Someone Who Knows Will Be Along In A Minute...

  Grin
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Ivan
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« Reply #11 on: September 13, 2007, 01:18:10 PM »

I agree a single large motor is probably the best choice, however, I think perhaps the choice of 4 small motors may be due to:

They had access to 4 small motors perhaps designed for alternative purpose, whereas one large one is more than likely specifically made for electric vehicles.

Lower current in the wiring to each motor, than for a single large motor - perhaps easier?

Better traction in slippery conditions due to 4-wheel drive (is this going to be an issue with electric vehicles?!)


The unsprung weight issue probably won't bother most electric vehicle drivers!!!

There is a lot of 'reinventing the wheel' in the electric car market.

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MrMoosehead
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« Reply #12 on: September 13, 2007, 04:12:56 PM »

Here's a couple of links:
http://www.treehugger.com/files/2006/08/the_hybrid_mini.php
http://www.worldcarfans.com/2060724.006/pml-builds-640hp-electric-mini
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