Petrol head (me) vs electric car engineer (mate)
Discussion
So picture this. Me and a mate at a meal with our better halfs just about to tuck into my main course as he tells me about the company he works for now and how they are pioneering electric car technology. So far so good. Then he goes on to say how they use regular petrol cars as a basis and swap out the engine and fuel tank for batteries and an electric engine!
So I calmly put down my fork and say why on earth do that? One of the major benefits of an eletric car in my mind is you get four wheel drive benefits by having a motor on each wheel, without all the hassle petrol cars have, ie non of this complexity with gears, diffs and transmission loss etc.. Plus the ability to accelerate individual wheels and not just brake them must be a stability control plus?
Cue total rant by mate how I know crap all about cars and that would never work ya de da and there way is THE way forward.
Decided this was not the occasion to talk shop and dropped it, my food was good :-)
So what do the PH crowd think (leaving aside the general hate for electric) Would it work by design and if it did would it give the electrics the edge over traditional cars for handling or am I just clueless?
So I calmly put down my fork and say why on earth do that? One of the major benefits of an eletric car in my mind is you get four wheel drive benefits by having a motor on each wheel, without all the hassle petrol cars have, ie non of this complexity with gears, diffs and transmission loss etc.. Plus the ability to accelerate individual wheels and not just brake them must be a stability control plus?
Cue total rant by mate how I know crap all about cars and that would never work ya de da and there way is THE way forward.
Decided this was not the occasion to talk shop and dropped it, my food was good :-)
So what do the PH crowd think (leaving aside the general hate for electric) Would it work by design and if it did would it give the electrics the edge over traditional cars for handling or am I just clueless?
If we're hypothesising you can make an electric engine to fit perfectly that has all the range, power and lower running costs associated with electric cars what is the issue?
The only thing I would question is it's economic viability.
The only thing I would question is it's economic viability.
Edited by Prof Prolapse on Wednesday 16th March 12:46
It could work, but I don't think you'd ever bother on a road car. The advantages of 4WD on a road car (talking about normal cars, not performance cars) are insignificant in most conditions and you're adding a fair bit of weight and complexity for the sake of having it.
FWD makes most sense for a pure electric car, IMHO.
I also don't understand where the idea that electric cars don't need a gearbox comes from. If you want any kind of performance, they need one for the same reason that an ICE powered car needs one.
FWD makes most sense for a pure electric car, IMHO.
I also don't understand where the idea that electric cars don't need a gearbox comes from. If you want any kind of performance, they need one for the same reason that an ICE powered car needs one.
If battery technology overcomes the energy density problems we have currently I reckon electric cars could be something of a revelation. Even if they never quite get down to the weight of an IC-engined powertain, the fact is you have far more freedom where you put that weight in an electric car.
I've only driven one fully electric car - a very ordinary urban runaround - but the handling was far better than it had any right to be. The engineers at the company attributed this to the fact the batteries were mounted on the floor of the passenger compartment. It gets the weight low down and central, so with no real sacrifice you can acheive the sort of CofG position you normally only get with sports cars.
I've only driven one fully electric car - a very ordinary urban runaround - but the handling was far better than it had any right to be. The engineers at the company attributed this to the fact the batteries were mounted on the floor of the passenger compartment. It gets the weight low down and central, so with no real sacrifice you can acheive the sort of CofG position you normally only get with sports cars.
kambites said:
I also don't understand where the idea that electric cars don't need a gearbox comes from. If you want any kind of performance, they need one for the same reason that an ICE powered car needs one.
Because of the torque curve from an electric motor. We didn't run a gearbox on our electric formula student car and that was nigh on as fast as our petrol car.
Non-electric cars cause war and people die, electric is the only option.
Apparently.
http://parkers.posterous.com/libya-the-internal-co...
Apparently.
http://parkers.posterous.com/libya-the-internal-co...
deveng said:
Because of the torque curve from an electric motor.
What about it? It's typically fairly flat, as is a petrol engine. Yes, peak torque generally starts to fall pretty much from 0rpm, but no where near fast enough to give you constant power at the wheels.Edited by kambites on Wednesday 16th March 13:05
kambites said:
I think the big problem with hub-motors, is the amount of unsprung weight. Much more sensible to have them motors at the other end of half-shafts, even if you have one per wheel.
need help with that one,s urely its better to have equal weight on each corner vs typical car with heavy end at the front causing nose heavy handling?. The half drive shaft idea might work two at the fron two at the back. Still on corners can't see how it helps.kambites said:
I also don't understand where the idea that electric cars don't need a gearbox comes from. If you want any kind of performance, they need one for the same reason that an ICE powered car needs one.
That's not entirely true. If you have a machine with constant peak power and sufficient peak torque, why bother with a gearbox? They may not exist completely in this state currently, but its not impossible. Motors have a much wider operating capability than IC engines - the best example being they don't need to idle.stargazer30 said:
need help with that one,s urely its better to have equal weight on each corner vs typical car with heavy end at the front causing nose heavy handling?. The half drive shaft idea might work two at the fron two at the back. Still on corners can't see how it helps.
You don't know what unsprung weight means? I'm not sure that my knowledge of physics is up to explaining it in detail, but basically the smaller the ratio of unsprung weight (that on the wheel end of the spring) to sprung weight (that on the car end), the better the suspension can keep the wheels in contact with the road because the wheel has less inertia for the spring to overcome.On the weight distribution front, whilst you're right that you want somewhere near equal weight on all four wheels (especially on a 4WD car), the actual location of the weight and consequent polar moment on inertia is also important. You want the weight in the middle of the car, not at the ends.
Edited by kambites on Wednesday 16th March 13:15
M Powered said:
That's not entirely true. If you have a machine with constant peak power and sufficient peak torque, why bother with a gearbox?
Agreed. But current electric motors aren't really much closer to this than internal combustion engines. I'd have thought that a CVT would be the obvious choice for an electric car. Edited by kambites on Wednesday 16th March 13:18
kambites said:
stargazer30 said:
need help with that one,s urely its better to have equal weight on each corner vs typical car with heavy end at the front causing nose heavy handling?. The half drive shaft idea might work two at the fron two at the back. Still on corners can't see how it helps.
You don't know what unsprung weight means? I'm not sure that my knowledge of physics is up to explaining it in detail, but basically the smaller the ratio of unsprung weight (that on the wheel end of the spring) to sprung weight (that on the car end), the better the suspension can keep the wheels in contact with the road because the wheel has less inertia for the spring to overcome.kambites said:
I think the big problem with hub-motors, is the amount of unsprung weight. Much more sensible to have them motors at the other end of half-shafts, even if you have one per wheel.
Exactly this. At the moment, hub-based motors promote terrible unsprung-weight handling issues. Remote mounted 4WD motors is plausible but one of the reasons why electric cars struggle to get a foothold is cost. Reusing as much of the current tech as possible makes a lot of sense at this stage.kambites said:
I think the big problem with hub-motors, is the amount of unsprung weight. Much more sensible to have them motors at the other end of half-shafts, even if you have one per wheel.
Actually the biggest problem is making them produce enough torque to be able to pull away on anything other than Norfolk spec flatness.And the durability issues of having the thing pounding away with the road.
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