Such control would not take large amounts of electrical power to operate. It wouldn't be much different from current ABS systems in design. Current ABS systems already have enough authority to override braking pressure independently for each wheel. It isn't rocket science to get them applying the same force.
Christian.
If you short out the generator, it will stop having a braking effect, although it might explode.
However, the energy transfer rate required for emergency braking is (or should be) well above what the motor should cope with. This is because making it capable of the full emergency braking load would make the motor much larger and heavier than is required in normal conditions. Emergency braking is so rare, that no energy saving advantage would flow from it. It would be lighter, cheaper and probably more energy efficient to install an auxilliary mechanical braking system and have a motor size optimised for the likely acceleration and braking loads met in normal service.
Christian.
For EM braking (not for the flywheel one) it needn't 'run out', the electricity can be dumped into a dummy load, or even, if the motor/gennys can handle it, shorted out completely.
From that new description, all they have to do is apply no force to the driven wheels via normal brakes whilst the regenerative braking is meeting the requested deceleration.
Sounds like a description of normal ABS...
LOL, you're half right. The 'breaking' effect would be the absolute maximum that could be acheived by the genny, it would be equivalent to a load equal to the impedance of the windings. It would do its little best to stop the car and would probably spontaneously combust. I wasn't quite serious..
You're spot on here, there is no (energy) advantage to harvesting the power from emergency braking.
I suppose there could conceivably be an advantage in maximising the load on the genny with the aim of assisting the mechanical brakes. Probably not though, it couldn't compete with the braking force of a well designed system
In article , snipped-for-privacy@nospam.yahooxxxx.co.uk says... Therefore, and for additional safety and low speed reasons, you also need a
thatw as one of the two ways I understood it, but wasn't too sure.
I would think that with shorted windings, the actual retardation would be lower than maximum. Lots of amps (to blow up the genny), but no volts, so the actual power developed (and hence braking force) will be much lower. What does get generated will just be dissipated in the motor windings, which will be completely unable to take it.
Maximum braking power would happen when the load impedence matched that of the generator, although this would not be anywhere near the maximum generating efficiency and might still cause damage.
Christian.
Depends what you mean by performance. Clearly it is useless for track work or sustained wide throttle work.
Most people just want a bit more response in the 1000-3000 rpm bracket. In normal road driving, there are always long periods of low demand to give time for charging.
"Christian McArdle" wrote
The volts are developed on the non zero resistance windings. I don't think there are any practical superconductor generators.
So design it to cope.
No. Maximum power in the system occurs when the generator is shorted. Maximum power transfer into a load is when the load matches the source.
I know this sounds very radical, but how about the electricity being used by the vehicle to power the brake lights?
(:-)
No....ok....i'll get my coat.......
Graham
On Tue, 31 Aug 2004 16:31:08 +0100, "Dave Plowman (News)" wrote (more or less):
Except that unless you're on a constant-speed cruise at high speed, it's entirely relevant.
A lot of performance is only used to accelerate sharply, rather than maintaining a constant high speed.
Sod's law says not when you really need it.
Ever driven a car with vacuum windscreen wipers? Even with a reservoir tank, they always gave out when you were overtaking something up a hill with a truck coming in the opposite direction...
It's not a new idea - merely a flawed one. But people often think they've re-invented the wheel.
So you carry around a load of surplus weight just for the odd occasion?
And remember, a battery can't be charged as quickly as it can be discharged. And if it could be, you'd use more energy in doing this than just having a large enough engine in the first place.
Yes- it is possible to get batteries that are designed for repeated "deep" cycle charge/discharge in very short spaces of time. There is at least one UK company working on an all-electric bus system with induction-loop charging in the bus stops.
Hopefully, the magnetic field generated by the induction loop will, as a fringe benefit, trap cyclists...
A service bus does predictable journeys with predictable load, and has a long life so capital cost may not matter as much as running costs. They don't tend to be taken to Brighton at the weekend, or France on holiday with four times the 'normal' load . Same as milk floats, really
Few private cars have such predictable use - unless you use one purely for the same commute every day. Which is why electric cars of any description are a total waste of time for most.
Fortunately not though this is not equivalent. An engine usually has enough power to maintain headway though it may not provide acceleration. After you have done the necessary 2 or 3 seconds of acceleration and 30 seconds, say, are left in the battery, it doesn't look like a particularly serious issue.
Many ideas are only flawed because the technology doesn't exist. An all electric car isn't a bad idea as such - just still hopelessly impractical.
On Wed, 01 Sep 2004 21:53:23 +0100, "Dave Plowman (News)" wrote (more or less):
Just as you do with a big engine...
While true, it's not really relevant surely? Unless you're flooring the accelerator more often than not.
It will only become truly practical when they develop a battery that will give about the same range and performance as we're used to with a normal car, and can be recharged about as quickly as filling a tank. And at a comparable price. Or, of course, some form of fuel cell.
I'll not hold my breath waiting.
On Thu, 2 Sep 2004 17:48:09 +0100, DavidR wrote (in message ):
And also not the environmental panacea some proponents would like us to believe, ditto Hydrogen, also put forward as a 'zero emmisions' power source. Funny, some people never suggest just where the electrical energy or hydrogen would come from in the first place !
Simon
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