Electric car drive
Electric car drive
(OP)
Good day,
We wish to get into electric car drives. Actually, we want to have a brushless DC machine for each of the car wheels.
(so that's 4 DC machines per car)
We know this is a knew way of doing it, that no-one's ever tried before, and so it'll be risky. -but it will make for smaller size since the motors are in the wheels.
We'll use a battery for power.
We will have coils around the stator of each wheel and simply switch current in and out of them as the wheel turns. We will have to sense the rotary position of the wheel so that we know when to switch current through which coil.
We will also need to know the actual and demanded rotary speed of the wheel so that we know whether to pulse the coils with a greater or lesser duty cycle.
We will also have to sense coil current so that we don't run the iron into saturation and so that we don't melt the coils.
Also, we'll switch current into each of the coils using a four transistor H-bridge...the reason for this being that it will allow "regen"...where during braking the wheel acts like a generator and puts power back into the battery.
We know that we need four quadrant operation since we want to be able to go... 1. forwards,... 2. backwards, and be able to do... regen going both.... 3. forwards, -and.... 4. backwards...making for 4 quadrant operation.
...It all sounds deceptively simple.
We believe that just to check that our theory works.....we should start with just a little model car, with very small wheels, probably just 4 inch diameter wheels to start with.
We will need to control the coil currents well because what if one wheel hits a skid patch?....or when the car turns a corner and the inner wheels are supposed to go slower than the outer but with the same torque?
If we get this small model working, -will it be straightforward to scale up to the full car size?
....people tell me that with higher power power-systems, all sorts of transient electrical effects come into play and things start going wrong badly and unpredictably.
Is this true?
Also, what kind of power would we need for the four motors for an electric car that could up to do say 80 miles per hour? (one motor for each of the four wheels)
We wish to get into electric car drives. Actually, we want to have a brushless DC machine for each of the car wheels.
(so that's 4 DC machines per car)
We know this is a knew way of doing it, that no-one's ever tried before, and so it'll be risky. -but it will make for smaller size since the motors are in the wheels.
We'll use a battery for power.
We will have coils around the stator of each wheel and simply switch current in and out of them as the wheel turns. We will have to sense the rotary position of the wheel so that we know when to switch current through which coil.
We will also need to know the actual and demanded rotary speed of the wheel so that we know whether to pulse the coils with a greater or lesser duty cycle.
We will also have to sense coil current so that we don't run the iron into saturation and so that we don't melt the coils.
Also, we'll switch current into each of the coils using a four transistor H-bridge...the reason for this being that it will allow "regen"...where during braking the wheel acts like a generator and puts power back into the battery.
We know that we need four quadrant operation since we want to be able to go... 1. forwards,... 2. backwards, and be able to do... regen going both.... 3. forwards, -and.... 4. backwards...making for 4 quadrant operation.
...It all sounds deceptively simple.
We believe that just to check that our theory works.....we should start with just a little model car, with very small wheels, probably just 4 inch diameter wheels to start with.
We will need to control the coil currents well because what if one wheel hits a skid patch?....or when the car turns a corner and the inner wheels are supposed to go slower than the outer but with the same torque?
If we get this small model working, -will it be straightforward to scale up to the full car size?
....people tell me that with higher power power-systems, all sorts of transient electrical effects come into play and things start going wrong badly and unpredictably.
Is this true?
Also, what kind of power would we need for the four motors for an electric car that could up to do say 80 miles per hour? (one motor for each of the four wheels)





RE: Electric car drive
No. It is not at all new. And there are several govermental and commercial projects under way. Plus some actual cars. Google to find out about a few dozens of projects.
The one-motor-per-wheel structure has proven less suitable. Even the motor structure is not new - BLDC is one name for such a motor. And there are several others.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Electric car drive
" . . . the Lohner-Porsche features a chassis and body made of wood and one internal-pole motor on each of the front-wheel hubs."
http:/
RE: Electric car drive
But first you should read about "unsprung weight in automobiles". Any weight on a vehicle's wheels is 'unsprung'. Unsprung is bad. Adding heavy motors there is generally not good. This is why Corvettes had the brake disk rotors brought inboard so they could be 'sprung'.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Electric car drive
Figure out all your drag losses to figure out how much power is needed to go 80mph. Figure out the power to climb a certain angle of hill or the power to get a set level of acceleration too while you're at it.
Actually, that was Jaguar.
RE: Electric car drive
Ah well, thanks for the correction.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Electric car drive
Doesn't mean it wasn't some type of hybrid or after market kit based on a 'Vette IRS but it seems to me that the Jag IRS is the most commonly copied setup. Don't ask me which Jag though. I somewhat expect the C5/C6 Vette suspension to become more popular in the future though - all aluminum double A-arm all around.
RE: Electric car drive
LionelHutz thankyou for the correct term of these motors.
We are working on the principle that with a multi-poled stator and rotor, the "next stator pole along" should have its coil pulse to make it attract the rotor coil, and the stator pole that's just passed should at that point have its coil pulsed with current in such a direction as to repel the rotor pole.
-But we don't want to suddenly switch from north to south poles...we want to do it sinusoidally....sinusoidally bringing the "next stator coil" to attractivity so it runs smooth.....so we will vary our pulse length and do so sinusoidally.
So we see the use of the 4 IGBT bridge ...it allows switching of the current direction to give north or south pole and attract or repel the rotor pole as required.
We will seek some hardened ferrite for the wheel as iron would have too much eddy current loss at the high switching frequency. -Train track 'wipers' are hard enough ferrite.
In order to re-generate, we must ensure that the stator coils experience a changing magnetic field....so therefore the rotor must have some magnetic field generating capability...either by permanent magnets or by electro type.
"Overall, I consider the motor per wheel idea overly complicated"
....but we believe we can make this work well.
RE: Electric car drive
having the motors in the wheels frees up room elsewhere and cuts down weight...important as a battery will run out quick with a heavy car.
If you dont have the motors in the wheels, then you end up with a differential driving the wheel shaft from an electric motor.....and if the motor is mounted low enough to get the differential mounting/connection right, then you havnt got enough room to put the circuitry etc around the rotor.....and if you raise it...you need two differentials.
Thats why putting a motor in each wheel is the way to go with electric cars.
RE: Electric car drive
RE: Electric car drive
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Electric car drive
Bill
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"Why not the best?"
Jimmy Carter
RE: Electric car drive
RE: Electric car drive
Did some of you have a chance to see a WABCO haulpak once (mining hauling workhorse)? You'd be amazed that the drive is a motor on each rear wheel! The diesel engine-generator provides electric power with electronics control for speed, braking etc.
The technology is way back in the '80s!
RE: Electric car drive
RE: Electric car drive
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Electric car drive
I think you are refering to the "Segway" critter.
For "state of the art" in electric cars one might want to google Tesla and ignore all the fine contributions that the engineer/scientist made....
Me, I'm thinking of a minibike frame, an old generator from a 1956 Ford, chain drive and one halfway good battery charger. The trick is to motor down to the local Starbuck's for a coffee, then plug it in and recharge (and steal the power from the coffee place). Oh, forgot to mention, a good long extension cord........
Cheers,
Rich S.
RE: Electric car drive
http://www
The D7E is in the 60,000-pound (27 000-kilogram) weight range and is powered by a Cat® C9 engine producing 235 horsepower (175 kilowatts). Compared to the Caterpillar® D7R Series II, the D7E will deliver 25 percent more material moved per gallon of fuel, 10 percent greater productivity and 10 percent lower lifetime operating costs.
Diesel-electric without significant storage is not technically a hybrid scheme, though, is it?
Itsmoked suggested adding batteries to an electric drive diesel truck.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Electric car drive
From the Tesla website, i notice that they "appear" to have mounted the electric motor around the rear wheel axle.
Tesla dont give details of the type of motor/drive, but i suspect some kind of Brushless DC motor.
The Tesla looks excellent and all the best to them.
Of course I would opt for having a motor on each wheel as it's space saving and lighter. Also, spreading the power out amongst the 4 wheels cuts down the power density.
-Though with the 4 wheel-motors, we need to conform to waross's comments and not think about doing it with synchronous motors......getting each of the 4 wheels to give exactly the same torque at the same time would be terrible.
So we will use induction motors, such that there can be a "slip" and such that the rotating field in each of the wheels don't have to be entirely synchronous with each other.
I have often looked at the sparks seen under subway trains at night and realised that these are caused due to the fact that the drives in the bogeys are not absolutely synchronized and some bogeys are driving their wheel set harder than others, causing spin and sparks.
But thank goodness for the Tesla, as it looks the best of the current electric car range....and we all need efficient electric cars very badly.
RE: Electric car drive
" the sparks seen under subway trains at night and realised that these are caused due to the fact that the drives in the bogeys are not absolutely synchronized "
You are as far from truth as can be here.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Electric car drive
Komatsu has 100s of similar diesel electric trucks in use here in the oil sands and coal mines. 930E, 830E etc with GE wheel motors. Some owners perceive better peformance and reliability compared with the mechanical trucks, and CAT is now building a 360 ton truck equivalent to their 797 with electric drive; apparently to be exhibited at MinExpo in September.
RE: Electric car drive
Yet one more company that has beaten you to the punch.
http://www.e-traction.com/
Yeah, or maybe the third-rail paddle is making intermittent contact with third-rail. Let's see, DC voltage, thousands of amps, a whole lot of inductance. Nah, no way that could cause a spark.
RE: Electric car drive
Mitsubishi had a nice demonstrator using wheel motors, but have recently gone for the more conventional alternative.
http://ww
I'm in two minds. if you have a ground-up redesign then outboard wheel motors seem very attractive for a small car. At the same time I don't like sticking expensive fragile bits out at the corners where they'll hit kerbs and potholes.
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Electric car drive
In Louisiana, they wouldn't survive ten miles.
Mike Halloran
Pembroke Pines, FL, USA
RE: Electric car drive
http://www.evworld.com/article.cfm?storyid=525
htt
RE: Electric car drive
It is not about motors surviving. It is more about driver and car surviving when you get into a sharp curve. Perhaps with some monor bumps. Unsprung mass is no good in such a situation. Why do you think there are test traces where manueverbility is tested? Why do you think there are lawsuits about car accidents caused by unstable cars?
Wheel motors work in mining equipment simply because they are not driven like cars.
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Electric car drive
Jaguar had them on their IRS system. As far as I know Corvette did not. Jaguar rear ends ere very popular Hot Rodders as they had a modular independent relatively robust rear end.
Citroen had a inboard font disk brake system on their D series from about 1955.
Regards
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RE: Electric car drive
http://ww
RE: Electric car drive
As already mentioned, iIt was done in 1900 by Porsche.
Not previously mentioned, in 1901, Porsche developed and successfully raced a racing version and also developed a 4 wheel drive version. 108 years ago ind of establishes "prior art".
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RE: Electric car drive
Interesting note about the Mini - there are blocks under the wheels. Did they forget the emergency brake?
Actually, I should take back what I posted about it not working in practice. There are some powerful magnets available that can be used to make high power/weight motors that could be light enough to work. As far as the electronics - processing power is advancing to the point is is possible on that side. So, yes, it's possible.