Electric Cars and Solar Power Kills babies.

[ravingdave]

The reason the exhaust valve opens early is specific power. You throw away energy to get more cycles per second.

Of course you know that.

If the engine is designed for constant speed it can be optimized to throw away less energy. The other problem that ties into that is fixed valve timing. The difficulty with electrical valves is their power. Even that is getting technical solutions.

Yeah, I knew that. The IC engine was built originally to be a convenient power plant in an era of cheap fuels. They sacrificed efficiency to improve performance as the most important thing in most of the engines history was a lot of power in a small package.

Fixed valve timing is only a problem with an engine that revs and derevs. Run it at a fixed speed, and fixed valve timing becomes an asset!


David

[MSimon]

I have no personal experience with an Atkinson (or Miller) cycle engine, and what I know of them is entirely theoretical. However if what you say is true, the problem still goes away when you simply drive a generator with it. Constant rpm, constant load, there won't be any issues of revving and derevving an engine

Even if revving was a problem you can keep the engine unloaded until it reaches speed. Just cut back on rotor current.

BTW the trouble with wheel motors is unsprung weight. That would be my guess as to the reason development has been so slow. Not to mention heat from the brakes.

Motors at each wheel mounted on the chassis may be the way to go for now.

[ravingdave]

I have no personal experience with an Atkinson (or Miller) cycle engine, and what I know of them is entirely theoretical. However if what you say is true, the problem still goes away when you simply drive a generator with it. Constant rpm, constant load, there won't be any issues of revving and derevving an engine

Even if revving was a problem you can keep the engine unloaded until it reaches speed. Just cut back on rotor current.

BTW the trouble with wheel motors is unsprung weight. That would be my guess as to the reason development has been so slow. Not to mention heat from the brakes.

Motors at each wheel mounted on the chassis may be the way to go for now.

A friend and I were discussing this just last friday. I speculated about using the existing front wheel drive design with a couple of CV joints coupled to wheel motors to solve the problem.

Yeah, the inertia of a wheel motor would be problematic when you hit a serious pot hole. Perhaps if we willing to toss out the rotor and caliper (relying instead on just electrical breaking) we might find sufficient weight savings to make it the equal of the existing wheel weight.


David

[MSimon]

I have no personal experience with an Atkinson (or Miller) cycle engine, and what I know of them is entirely theoretical. However if what you say is true, the problem still goes away when you simply drive a generator with it. Constant rpm, constant load, there won't be any issues of revving and derevving an engine

Even if revving was a problem you can keep the engine unloaded until it reaches speed. Just cut back on rotor current.

BTW the trouble with wheel motors is unsprung weight. That would be my guess as to the reason development has been so slow. Not to mention heat from the brakes.

Motors at each wheel mounted on the chassis may be the way to go for now.

A friend and I were discussing this just last friday. I speculated about using the existing front wheel drive design with a couple of CV joints coupled to wheel motors to solve the problem.

Yeah, the inertia of a wheel motor would be problematic when you hit a serious pot hole. Perhaps if we willing to toss out the rotor and caliper (relying instead on just electrical breaking) we might find sufficient weight savings to make it the equal of the existing wheel weight.

David

The deal is you would need a completely new design with wheel motors. That is tough. Motors on the chassis is an incremental improvement. And you still need fully functional brakes as a backup. And "motor" brakes only work as long as the rotors are moving at relatively high speed. Without wheel brakes you need to feed a motor current to generate holding torque. What a waste.

BTW don't call them CV joints. Call them by their proper name. U joints.

[chrismb]

Motors at each wheel mounted on the chassis may be the way to go for now.

Again, been done. I've been involved with a couple of University projects to this end.

The problem is safety. If one motor were to fail while you were under power, so you'd get tremendous torque steer. Sticking the output of a motor through a conventional diff avoids this safety risk.

What is required is just like the SR-71 (which also produces an immediately fatal yaw if one engine stalls) - you have to shut the whole system down immediately as soon as one part looses power. But the SR-71 has 1,000's of feet to re-manoeuvre, whereas if you're on a busy freeway it could be immediately fatal.

In one cae, the project vehicle's software was modified so that it deliberately caused differential torque, which was then hooked up to a joystick. The whole vehicle could be driven in that way, no mechanical connection to the front wheels (such is the power of the steering action of un-matched motors). This applies to fixed (rear) axles aswell, you still get vehicle yaw.

[MSimon]

FWIW I have (had? who knows how it changed) a couple of lines of code (a fix) flying in the SR-71.

[ravingdave]

Even if revving was a problem you can keep the engine unloaded until it reaches speed. Just cut back on rotor current.

BTW the trouble with wheel motors is unsprung weight. That would be my guess as to the reason development has been so slow. Not to mention heat from the brakes.

Motors at each wheel mounted on the chassis may be the way to go for now.

A friend and I were discussing this just last friday. I speculated about using the existing front wheel drive design with a couple of CV joints coupled to wheel motors to solve the problem.

Yeah, the inertia of a wheel motor would be problematic when you hit a serious pot hole. Perhaps if we willing to toss out the rotor and caliper (relying instead on just electrical breaking) we might find sufficient weight savings to make it the equal of the existing wheel weight.

David

The deal is you would need a completely new design with wheel motors. That is tough. Motors on the chassis is an incremental improvement. And you still need fully functional brakes as a backup. And "motor" brakes only work as long as the rotors are moving at relatively high speed. Without wheel brakes you need to feed a motor current to generate holding torque. What a waste.

BTW don't call them CV joints. Call them by their proper name. U joints.

A Constant Velocity joint is now referred to as a Universal Joint ?

Why was *I* not informed !


No, seriously, i've replaced dozens of CV joints. If I told them U-Joint at the parts store they'd think I was an idiot. A CV joint is actually a misnomer. There are TWO CV joints in a typical front wheel drive shaft. One right at the wheel, and the other right next to the output shaft of the trans-axle. So when you are asking for a "CV Joint" you are actually getting two of them.

A CV joint is necessary because we use the front wheels to steer with. A U-Joint is perfectly fine for small angles of deflection on the two rotating shafts, but as the angle approaches acute, the load shaft increases and decreases it's velocity causing a massively varying load reflecting back to the driving source.
It ends up stressing all the components from the driving one to the load and including the U-Joint which is the first thing that breaks.

A CV joint is made with variable tracks in it that allow ball bearings to couple the inside joint with the outside joints. The Tracks allow variations in shaft angle to apply greater and lesser moments on the joint depending on whether the ball bearing (which couples the force) are on the inside or outside of the angle.(between the two shafts.)


I've taken them apart, re-lubed them, replaced the bellows grease seals, and installed them in slews of different vehicles. (it's a hobby. I like fixing stuff. )

If I am misusing the term, it is an exceedingly common mistake.



As for the Motor holding current, it might be very minimal. Most wheel motor designs i've seen are geared for torque, so a very slow wheel rotation might result in a much faster rotor rotation. The comparison of the driving current to the holding current is probably 100 to 1, and we can always use the back wheels with regular hydraulic breaks.

Dunno. Just speculating.




David

[ravingdave]

Motors at each wheel mounted on the chassis may be the way to go for now.

Again, been done. I've been involved with a couple of University projects to this end.

The problem is safety. If one motor were to fail while you were under power, so you'd get tremendous torque steer. Sticking the output of a motor through a conventional diff avoids this safety risk.

What is required is just like the SR-71 (which also produces an immediately fatal yaw if one engine stalls) - you have to shut the whole system down immediately as soon as one part looses power. But the SR-71 has 1,000's of feet to re-manoeuvre, whereas if you're on a busy freeway it could be immediately fatal.

In one cae, the project vehicle's software was modified so that it deliberately caused differential torque, which was then hooked up to a joystick. The whole vehicle could be driven in that way, no mechanical connection to the front wheels (such is the power of the steering action of un-matched motors). This applies to fixed (rear) axles aswell, you still get vehicle yaw.

I must admit, I hadn't thought of a wheel motor locking up as being a safety issue, but it is probably the most likely type of failure to occur that would cause a wheel lockup.

How about a radian wrench coupling with a friction clutch for reverse ? (how much torque do you need going in reverse ?)

I think perhaps a pawl and tooth lockup system might work.

You can pull both of these parts out of many automatic transmissions. If I was cobbling together a project car, i'd probably do it this way. It would save the hassle of having to design one from scratch, then figuring out if you haven't made any mistakes.


How about a sacrificial coupling, like a mechanical version of a fusable link ? Hmm, might be problematic if you made it too weak.


There's probably a solution. Given the benefits of all wheel drive electric, (or even two wheel drive) surely some relatively simple solution could be found.



David

[chrismb]

Vehicles with in-hub motors are already quite common, just not on the road. Most of the enormous dumper trucks in quarries are in-hub designs with diesel-electric drive systems. So at the moment, 'road going' sized-vehicles of such a diesel-electric design are in military use. There's a six-wheeler that's made here in the UK. In-hub motors provide, obviously, huge flexibility for 6x6 off-road vehicles and a big reduction in all up weight of transmission systems.

They're normally linked up through epicyclic gears within the hub to form a single assembly that down-gears the motor output.

As the reliability can be improved and relied on, there is more hope that such systems will be seen on road. There is already talk of getting the legislation changed to permit steer-by-wire systems, so why not in-hub systems and some suitable means to mitigate the risks will evolve once the safety analyses and FMEAs are done.

[MSimon]

No, seriously, i've replaced dozens of CV joints. If I told them U-Joint at the parts store they'd think I was an idiot. A CV joint is actually a misnomer. There are TWO CV joints in a typical front wheel drive shaft. One right at the wheel, and the other right next to the output shaft of the trans-axle. So when you are asking for a "CV Joint" you are actually getting two of them.

Just like a drive shaft with two U joints. I replaced more than a few in my time. CV joint seems so prissy.

[TallDave]

1) But you don't want to buy another car for the other 10%. Example: shortly after graduating I had to drive most of the way across IL (about 700 miles in all, I think) to take the CPA exam. I could not have done that in an electric car.

2)Of course, many people who live in the city don't own cars at all. Electrics have to fit into a fairly specialized niche where you don't need power or distance, but it's too far to bike or walk.

1) It depends on three things, the price of petrol, the price of electricity and the capital cost of the vehicle. With the way the capital costs of vehicles are going with the tata ($1000) and the like, it may not be long before a vehicle will have a similar cost to 1 or 2 year's worth of fuel consumption. If that happens then you may well prefer to have two vehicles, one for short range commutes that runs on cheap electricity and one for the occassional long range commute which runs on more expensive oil. In terms of efficiency this makes more sense that a plug-in hybrid since the electric vehicle isn't lugging around the unecessary load of a petrol engine and the petrol vehicle doesn't lug around the unnecessary load of the battery.

2) Not just distances that are too far to bike or walk but also loads. I'm prepared to bike 10 miles, but not while carrying my weekly shopping!

1. One large complex tool will almost always be better than two large complex tools. You have to put it somewhere, maintain it, etc. And they won't get much cheaper in the West, with all the safety requirements -- Nanos are great for Third World countries, but in the West the airbags alone cost more than that.

It's also worth noting something that a lot of people don't seem to realize: even after every last drop of extracted oil runs out, we will probably transition to an alcohol economy rather than give up the ICE. This will be expensive in the short run, esp. to food prices, but I doubt gas will stay over $5-7/gal for long once biofuels get a running start.

2. Actually, that just depends on how serious you are about biking. In China it's fairly common to have a three-wheeled bike for groceries. Most Westerners are too fashionable for such things.

[jmc]

1. One large complex tool will almost always be better than two large complex tools. You have to put it somewhere, maintain it, etc. And they won't get much cheaper in the West, with all the safety requirements -- Nanos are great for Third World countries, but in the West the airbags alone cost more than that.

It's also worth noting something that a lot of people don't seem to realize: even after every last drop of extracted oil runs out, we will probably transition to an alcohol economy rather than give up the ICE. This will be expensive in the short run, esp. to food prices, but I doubt gas will stay over $5-7/gal for long once biofuels get a running start.

2. Actually, that just depends on how serious you are about biking. In China it's fairly common to have a three-wheeled bike for groceries. Most Westerners are too fashionable for such things.

1. Depends How much garage space you have, it also depends whether maintainence costs scale with age or usage (i.e. will they go down dramatically if it is stored in an appropriate environment without being run frequently). Regarding cheapness, I don't think you should underestimate the power of the learning curve. I'm sure we'll find a happy medium between cost and safety, if India can do it so can we!

I've heard that the land area required for crops to power every vehicle in Britain is the size of all the agricultural land in Britain. Learning curves work with technology, but you can't create land out of thin air, although I'm sure it would be possible with fission or fusion reactors to synthetically make ethanol ort methanol someday, which would be good.

2. I sometimes use bikes for my groceries, but only for trips less than two miles. If I wanted to travel ten miles to buy a computer, I'd rather use an EV!

[MSimon]

1. Depends How much garage space you have, it also depends whether maintainence costs scale with age or usage (i.e. will they go down dramatically if it is stored in an appropriate environment without being run frequently). Regarding cheapness, I don't think you should underestimate the power of the learning curve. I'm sure we'll find a happy medium between cost and safety, if India can do it so can we!

We already know what the trade off is. Seat belts. They produce 95% of the safety at a cost of $10 per. For another $500 per we can get another 5% (roughly) of safety. Oh yeah. Exploding gas bags don't work without seat belts.

I leave the math as an exercise for the reader.

Let me add. The market didn't decide. The government did. Go figure.

[IntLibber]

The problem with greater fuel efficiency is that people drive more - actual total consumption stays constant or rises.

Jevons paradox.

Depends, there is a time lag on this. The US reduced energy consumption by a huge amount in the bad old Reagan years, it took a decade for oil prices to come down and people to start building muscle cars again.

The proper means to adjust consumer usage permanently is to have a gas tax that is variable with gas prices so as to maintain a constant consumer price. If people don't see a price benefit from lower consumption they will continue to drive economically.

[MSimon]

The problem with greater fuel efficiency is that people drive more - actual total consumption stays constant or rises.

Jevons paradox.

Depends, there is a time lag on this. The US reduced energy consumption by a huge amount in the bad old Reagan years, it took a decade for oil prices to come down and people to start building muscle cars again.

The proper means to adjust consumer usage permanently is to have a gas tax that is variable with gas prices so as to maintain a constant consumer price. If people don't see a price benefit from lower consumption they will continue to drive economically.

But that just reduces economic efficiency because the government will piss the money away buying votes or spend it on crony capitalism.

The best price is determined by supply and demand.

If gasoline is cheap it should be burned until there is a better economic alternative.

100 million people spread around the country can make a better decision on the trade offs than 535 people in Washington bought and paid for by various interests. Always remember:

We have the best government money can buy.