range extending cars ?

[bluebear]

OK here we go. How do range extending cars work, cars like the Chevrolet volt and fisker karma. pure electric cars go only so far then need a complete re charge. OK i understand that. Range extending cars have batteries and a engine in the front that acts as a generator is what i under stand. But do you still need to plug it in at night. Could you use it as a "normal" car. IE just keep topping up the fuel tank. or must you plug the thing in aswell. could you drive from to edinburgh to London or do you need to stop of and recharge the batteries and top up with fuel. Never been quite sure how these things work.

[Mr Gear]

bluebear said:

OK here we go. How do range extending cars work, cars like the Chevrolet volt and fisker karma. pure electric cars go only so far then need a complete re charge. OK i understand that. Range extending cars have batteries and a engine in the front that acts as a generator is what i under stand. But do you still need to plug it in at night. Could you use it as a "normal" car. IE just keep topping up the fuel tank. or must you plug the thing in aswell. could you drive from to edinburgh to London or do you need to stop of and recharge the batteries and top up with fuel. Never been quite sure how these things work.

You don't NEED to plug it in, but you can, and the more you charge it up, the less petrol it will have to burn.

HTH.

[kambites]

Indeed. There's no need to plug it in, but it would be rather stupid not to - electricity is a fair bit cheaper than petrol.

[bluebear]

if the technology is so fuel efficient, why has it taken so long to come up with what seems like a simple idea

[kambites]

bluebear said:

if the technology is so fuel efficient, why has it taken so long to come up with what seems like a simple idea

It's heavy and expensive and takes up a lot of space in the car. Plus you need very strong noise and vibration isolation to be able to produce an acceptable car with an engine that, when running, is operating constantly at peak efficiency.

[Mr Gear]

bluebear said:

if the technology is so fuel efficient, why has it taken so long to come up with what seems like a simple idea

It's actually a horrible engineering compromise. All the cost of an electric car, with all the complexity of an internal combustion car.

It gets results though, and it's testament to GM's investment in the project that these cars are available at a sensible price at all.

[bluebear]

so what sort of combined cycle figures are these cars returning without a charge in the batteries. as i suspect how most will be run. lots of figures on how many miles you are getting with a full charge ! but not many if any on if you are running with no charge. example if your on a two day business trip and parking in multi storeys with no access to charging. is it going to make more sense to take the wife's diesel picasso

[Mr Gear]

bluebear said:

so what sort of combined cycle figures are these cars returning without a charge in the batteries. as i suspect how most will be run. lots of figures on how many miles you are getting with a full charge ! but not many if any on if you are running with no charge. example if your on a two day business trip and parking in multi storeys with no access to charging. is it going to make more sense to take the wife's diesel picasso

They only really make sense if you mainly make shortish urban journeys but don't want to hire a car for occasionally going further afield. If you drive huge miles every day, then forget it.

[bluebear]

So is this really any better technology than a Prius. I'm i right in thinking its not the technological leap i thought it was. Are we still waiting for the big one, hydrogen powered cars ?

[williamp]

There seems to be con fusion here between range extender cars and pure EV. The former does have a combustion engine as well. This acts as a generator abd does not power the wheels directly but charges up batteries which are then used to power the wheels via eelctric motors.

The idea has been around for almost as long as the car- well over 100 years ago you could buy pure EV, hybrid, range extender or petrlolium.

There are downsides: the extra weight, and the problems of marrying the two together.

But there are several advantages: they can often be driven on pure electric for a short while- useful when some Cities are talking about banning combustion engines/ taxing them hugely

With hub-mounted electric motors, you can have max torque at 0rpm to each wheel- can you imagine a land rover with that- it really would be unstoppable off-road

The petrol/diesel engine can be small and frugal, and can run at its optimum (not across a broad rev range). It can slo be a jet engine- see the Jaguar concept car, which uses an effecient jet turbine to charge the batteries.

In fact, for a good summary of whats possible, have a look at their green limo concept:

http://www.mira.co.uk/Case_Studies/documents/Limo%...

I've been in it, and you cannot tell when the engine stops/starts, and having that range/low emissions whilst still having the luxury, aircon etc is a good step forward in my opinion. It wont be for every car, but it really is good for those vehicles on long journeys

[thinfourth2]

bluebear said:

So is this really any better technology than a Prius. I'm i right in thinking its not the technological leap i thought it was. Are we still waiting for the big one, hydrogen powered cars ?

Think of it as buy an electric car and you get a fossil fuelled car thrown in for free.

If you do 90% short journeys under 20 miles and you plug it in overnight then you need never fill it up with petrol so it would get bonkers MPG

If you do long journeys like everyone one here who has a 300 mile commute and never plug it in as that would make you a gay hippy then it will probably get pretty piss poor mpg

As all cars you choose your car for what you intend to use it for.

I won't replace my land rover with a lotus elise not because a lotus elise is crap it just can't do what a land rover can do.


But to complicate things the prius is going to get a bigger battery pack and come in a plug-in version so you use less fuel and more electricity but it works in a completely different way to the volt.

[kambites]

bluebear said:

So is this really any better technology than a Prius. I'm i right in thinking its not the technological leap i thought it was. Are we still waiting for the big one, hydrogen powered cars ?

The point is, for most people most of the time, it's just an electric car - you plug it in every evening, drive your ten miles to work and back, and never have to run the ICE. Think of it as an electric car that wont leave you stranded if you try to drive too far.

In terms of motorway efficiency when running entirely on internally generated energy, it should still be better than a conventional car because the engine can run at peak efficiency all the time and the extra weight means little at constant speed. It wont be orders of magnitude better than a normal car, though. A normal car might manage 30% efficiency on the motorway, a range extender electric car could possibly manage 40%? Something like that.

Edited by kambites on Tuesday 6th September 19:06

[thinfourth2]

Using the same engine I would of thought the range extender would be less efficient

Anyway watch the whiny wet liberal drive a vauxhall ampera

http://www.youtube.com/watch?v=3emYdFEWyJ8

[bluebear]

did the top gear monkeys not have a go at this !

[anonymous-user]

Basically, it's a bodge, to allow a car that has massively limited range to be slightly more practical in the real world. The issue is one of "round trip energy conversion efficiency". If you have to start the IC engine, then the absolute best thing is to just couple it mechanically to the wheels as you have a very high drive train efficiency. if you use an IC engine to drive the wheels via:IC - generator - power electronics - battery - power electronics - traction motor - wheels, you stuggle to get a round trip efficiency above 50% due to all the power conversion steps. Hence a "range extended" electric vehicle is actually lower efficiency during "range extended" operation than a conventional IC mechanical transmission system. The hope is that if you use the car under conditions that allow you to mostly just use plugin battery energy, then overall, the cars energy consumption will be lower. (so getting a range extended car, then sitting on the Mway at 90 is competely pointless ! )

[anonymous-user]

williamp said:

With hub-mounted electric motors, you can have max torque at 0rpm to each wheel- can you imagine a land rover with that- it really would be unstoppable off-road

No, it would be crap! Have a look behind the engine on a std landrover, at the large lump of alluminium with lots of wizzy gears in it for a clue as to why directly coupled hub motors are hopeless !!

(300Nm @ crank x low 1st x final drive ratio is a VERY large number indeed)


(and as an aside, in a practical electric motor you can't actually have peak torque at zero speed for 2 major reasons: 1) as the motor is stationary, only 1 electrical phase is being used, this results in rapid overheating of that phase and a high temperature gradient resulting often in winding insulation breakdown (bad) and 2) for the same reason, the power electonics will only be using 2 legs of it's H bridge power silicon, again, very bad from a thermal point of view.)

The practical advantage of an electric "crawl" is better used in something like a Freelander, which does not have a low range transmission, (due to cost/co2 reasons). here, an ultra controlable, electric creep mode would be really usefull both offroad and for things like trailer hitching operations etc ;-)

[bluebear]

Max_Torque said:

williamp said:

With hub-mounted electric motors, you can have max torque at 0rpm to each wheel- can you imagine a land rover with that- it really would be unstoppable off-road

No, it would be crap! Have a look behind the engine on a std landrover, at the large lump of alluminium with lots of wizzy gears in it for a clue as to why directly coupled hub motors are hopeless !!

(300Nm @ crank x low 1st x final drive ratio is a VERY large number indeed)


(and as an aside, in a practical electric motor you can't actually have peak torque at zero speed for 2 major reasons: 1) as the motor is stationary, only 1 electrical phase is being used, this results in rapid overheating of that phase and a high temperature gradient resulting often in winding insulation breakdown (bad) and 2) for the same reason, the power electonics will only be using 2 legs of it's H bridge power silicon, again, very bad from a thermal point of view.)

The practical advantage of an electric "crawl" is better used in something like a Freelander, which does not have a low range transmission, (due to cost/co2 reasons). here, an ultra controlable, electric creep mode would be really usefull both offroad and for things like trailer hitching operations etc ;-)

SAY WHAT !!!!!!!!!!!!!!

Edited by bluebear on Wednesday 7th September 14:34

[anonymous-user]

anonymous said:

[redacted]

Theoretically yes, but i will leave you to sort out the practical embodiment of a design of hub motor that can deliver both 12,000Nm @ 4.7mph AND 120bhp @ 85mph. Gears are very underated ! ;-)

(then get same hub motor to cope with high G and vibrational loadings, not take up the same space as the brake system, be completely sealed yet still able to cool itself, and keep the unsprung mass to a minimum to maintain ride and handling. If it were easy, someone would have done it by now...........)

[thinfourth2]

Max_Torque said:

Basically, it's a bodge, to allow a car that has massively limited range to be slightly more practical in the real world.

This real world being the one where everyone drives 100 miles to work and back

Where as in fantasy land most folk have a commute of less then 20 miles

[thinfourth2]

bluebear said:

did the top gear monkeys not have a go at this !

Yep thats a range extended electric car

But i feel the real ones might be a bit better