51 replies to this topic

[Nathan]

The titled could probably have been worded better, my apologies.

I'm curious if there is a present or future advantage to doing away with the standard gearbox, driveshaft (if applicable) and differential and replacing these with an electric generator and a electric motor for each drive wheel?

Thanks.

Edited by Nathan, 23 November 2009 - 02:48.

[Canuck]

Yes.

[cheapracer]

Maybe

[Nathan]

I would imagine this would have weight benefit with AWDs.

For a sports car, would you be able to get a generator and motor combo that would weigh no more than a gearbox and differential? How much of an efficiency difference would there be? Would a motor on each wheel create the ideal differential?

[Greg Locock]

Last bit first, yes obviously you'd have the potential for the best active differential/traction control/abs around.

Weight wise, no I don't think you could quite do it at the moment. Efficiency would be pretty good. Cost would be a lot, for the electronics as much as the motors.

[DaveW]

The concept offers huge potential for lateral dynamics & traction control, regenerative braking, more efficient "1st stage" power coversion etc., but some (e.g. J. Edlund) are convinced increased weight, decreased transmission efficiency and "2nd stage" conversion losses will always outweigh the potential advantages. J. outlined his thoughts here (e.g. post 66). It is certainly true that shipping electrons around a vehicle always weighs more than anticipated.

[mariner]

I think that is pretty much what the last GM hydrogen car had in terms of transmission. If you think of the fuel cell as the engine the electricity from that was fed to a pancake motor on each wheel so full variable wheel torque control existed. GM seem to have move away from that on the Volt but the system exists.
Weight is clearly a problem with wheel motors but when you look at the GM fuel cell car's pancake motors next to big ventilated discs on each wheel you can straight away see that the holy grail would be a combined electric motor rotor/disc where the stator surrounds the disc with caliper(s) fitted in as well. Then about half the weight of the wheel motor is eliminated. I suspec the practical problems are nerly impossible due to the risk of heat soak in the rotor melting the windings etc. but it would be a big step forward I think for wheel motors.

[John Brundage]

The DMA bus in Boston MA. uses similar technology. The DMA is a 60' dual mode articulated bus that can run on either a catenary or in diesel mode. When in diesel mode, the engine runs a genset. There is a traction motor at the rear axle and another at the middle axle. Instead of a traction motor at the wheel, the design on the bus utilizes a driveshaft and a ZF axle at the rear and middle. Brakes are regen as well as the normal air brake system.

[GeorgeTheCar]

With 5% loss at each stage of a gear train and electric's advantage of 100% torque at 0 RPM it is clear to see why heavy movers, trains, dump trucks have been diesel electrics for years.

Cars are a completely different deal. Fuel savings from regenerative braking is a huge part of the advantage but that won;t be maximized until there is regenerative braking at each corner. Wheel motor/gen sets will take serious design efforts to get effective and light enough but bring it on!

4 wheel drive, 4 wheel anti-lock brakes, traction control!

[cheapracer]

As someone who actually works in an electric car factory there are some things that opens one's eyes the first being weight of any electric motor or cousins (you wouldn't believe how much those 1/2 watt electric scooter motor wheels weigh) and the very sad site of many returned batteries with no home to go to. If I remember I will get a snap of that reality.

While I'm not a big admirer of fancy unsprung weight figures I can't imagine 'heavy as' electric wheel motors for cars can be easy to give a good ride - Greg?

[GeorgeTheCar]

Cheapracer

Might you enlighten us on the corner weight of a wheel motor vs a conventional setup. (Wheel, tires, brake, axle, etc)

[desmo]

Wouldn't it make better sense to mount the heavy motors/generators inboard as sprung weight and transmit the torques through halfshafts? I assume you'll need conventional friction brakes in any realistic case.

[Greg Locock]

That's the nicest way to do it, but you've just cost yourself 250 bucks in halfshafts etc, and lost a huge packaging advantage. But your expensive motors won't get wiped out when you kerb the wheel.

So far as adding mass to the wheel, somebody kindly posted the results of that experiment here a while back. It was different to what I'd expected.

Mitsubishi have a record setting EV with a motor at each corner.

[cheapracer]

Cheapracer

Might you enlighten us on the corner weight of a wheel motor vs a conventional setup. (Wheel, tires, brake, axle, etc)

Having never weighed or held a wheel motor appropriate for the circumstance we are talking about no, sorry I can not.

The 3kw and 5kw motors at the factory weigh 33 and 70 kgs respectively though so we can imagine.

[Wuzak]

PML Flightlink claim 25kg for their 120kW motor in wheel drive

http://www.pmlflight...hipa_drive.html

These are used in the Lightning electric car, and were demonstrated in a Mini a while back.

[zac510]

Could an electric motor cope with the shock and vibration of being mounted on the upright too?

[mariner]

I am no expert of any kind on electric motors or electric rail locomotives but I do know that the motors on many electric and diesel electric locos are linked to the axle which absorbs some very nasty high frequency vibrations from the track. There have been two general approaches , the so called " axle hung" and various forms of cushioned drive.

Axle hung is mostly what it says, the motor frome is pivoted on the bogie and the other end is on the axle. so a simple gearing with good gear alignment. The downside is poor ride and it beats up the track. works up to 70 mph or so though.

The flexible drives get 100% of motor weight off the axle at the cost of a complex drive ( quill shafts or similar) which drives up maintianance. You probably will not be surprised to hear that US railroads usually used the cheap and rugged axle hung whereas the french go for the complex sprung system!

In reality it is top speed that is the decider, as the speeds go from 40/70 mph in US freight operstions to 180 mph on a TGV the track forces rise to unacceptable levels so it is better to spend on complex drives than rebuild the track more often.

[gordmac]

Been some thought on electric hillclimb cars but I don't know what has happened. There was supposed to be a single seater designed by Martin Ogilvie out this year. From memory Martin intended to use a motor per wheel structurally mounted in the car driving via shafts.
http://www.greenmoto...88,1,14752.html

[J. Edlund]

Wouldn't it make better sense to mount the heavy motors/generators inboard as sprung weight and transmit the torques through halfshafts? I assume you'll need conventional friction brakes in any realistic case.

If we look at practical electric and serial hybrid vehicles, this is how they do it. A single traction motor at the rear or at the front with a reduction gearbox and a differential which use conventional driveshafts is the common solution. Basically the motor unit replaces the differential in a conventional car. This solution is actually cheaper, lighter and more efficient than using separate motors for the wheels. The use of a reduction gear allows a higher speed low torque motors to be used and since the motor or motors are placed in the chassi rather than in the wheel hubs the environment is easier on the motors.

Of course, there are applications of wheel motors too since they offer packaging advantages which can be useful in certain applications. Below is an example of such an application. Six air cooled 45 kW synchronous motors provide a total of 270 kW, and up to 540 kW during short periods of time. Two 200 kW diesel engines connected to two alternators supply the electricity. The traction motors are rated at 160 Nm and operate at speeds up to 9000 rpm. The torque output of the motor is multiplied by a planetary gearing inside the hub. Since the motors are completly individual this allows a great degree of freedom in terms of control, but it also means that if the traction is lost at one or several wheels the torque excess can't be transfered to a wheel with better traction.

[onelung]

Electric drive: what a great idea!
Acknowledgement to Georgano

[Lee Nicolle]

To me the best way would be mount the motors inboard and drive the wheels with a conventional driveshaft.But then it is heavy to have four motors so probably more practical to mount the bigger single motor and drive the wheels in the traditional way.
But ofcourse until electric cars can generate enough power to run theirself they will always be a trendy inefficient toy wth limited usefullness.
I love the Greenies who waffle on about rechargeable cars being clean and green. They are probably dirtier than an efficient petrol engine by the power generated at the Power station.And ofcourse have no range or much accelaration.
And the batterys are an ecological drama too.

[Wuzak]

To me the best way would be mount the motors inboard and drive the wheels with a conventional driveshaft.But then it is heavy to have four motors so probably more practical to mount the bigger single motor and drive the wheels in the traditional way.
But ofcourse until electric cars can generate enough power to run theirself they will always be a trendy inefficient toy wth limited usefullness.
I love the Greenies who waffle on about rechargeable cars being clean and green. They are probably dirtier than an efficient petrol engine by the power generated at the Power station.And ofcourse have no range or much accelaration.
And the batterys are an ecological drama too.

I have seen reports that suggest that even when using power from coal fired power stations electric cars produce less emissions.

[Greg Locock]

I have seen reports that suggest that even when using power from coal fired power stations electric cars produce less emissions.

Just about possible if you are burning best quality anthracite.

[gruntguru]

Just about possible if you are burning best quality anthracite.

And that's just CO2, noxious emissions will be much lower.

[Greg Locock]

And that's just CO2, noxious emissions will be much lower.

No power station in the world burns best quality anthracite.

[Fat Boy]

No power station in the world burns best quality anthracite.

Apparently, you have confused the goal of global emissions control. The goal is the appearance of action, not the actual action itself. If the actual action is detrimental to the environment while at the same time allowing the champions of such action to appear environmentally conscious, then it is deemed a successful endeavor. Get with the times, Greg.

Edited by Fat Boy, 21 December 2009 - 03:29.

[gruntguru]

No power station in the world burns best quality anthracite.

What about budget anthracite?

[Wuzak]

No power station in the world burns best quality anthracite.

I guess you'd be worse off using Victorian power.....

Not as much a problem here is Tassie, but we have been buying power from the national grid since our dams have been low.

Anyway, emissions (CO2) of various fuels from http://en.wikipedia....m_various_fuels

Fuel name					   CO2 emitted	   CO2 emitted	
							 (lbs/10^6 Btu)	   (g/10^66 J)
Natural gas							  17			 50.30 
Liquefied petroleum gas				 139			 59.76 
Propane								 139			 59.76 
Aviation gasoline					   153			 65.78 
Automobile gasoline					 156			 67.07 
Kerosene								159			 68.36 
Fuel oil								161			 69.22 
Tires/tire derived fuel				 189			 81.26 
Wood and wood waste					 195			 83.83 
Coal (bituminous)					   205			 88.13 
Coal (subbituminous)					213			 91.57 
Coal (lignite)						  215			 92.43 
Petroleum coke						  225			 96.73 
Coal (anthracite)					   227			 97.59

I guess you were talking about the other types of emissions from coal, such as sulphur dioxide?

[gruntguru]

we have been buying power from the national grid since our dams have been low.

Climate change?

[Wuzak]

Climate change?

No, don't think so. We've had some goo drains in the right areas this year to raise the levels of the dams.

I think this has been a problem for years.

[Greg Locock]

Wuzak, the Ozzie takeover of this board is nearly complete.

The gain in emissions comes for the better efficincy of the elctric car, say if you take the Volt it uses about 200 Wh per mile (40 miles on 50% of its 16 kWh battery), on electric, or 50 mpUSg on dead dinosaurs.

So the raw energy usage per mile is 0.7 MJ on electric, or 2.7 MJ/mi on gas. So if the electric car is 100% efficient (it isn't) then the IC engine is about 25%. Close enough to reasonable.

To counterbalance that, getting dinojuice from the well into the tank is about 85% efficient. Getting that power from a coal mine to the battery is about 35% efficinet.

And, finally you need to know the CO2 emissions per MJ of calorific value for each fuel. For good quality coal that is about 90g/MJ, so we get 90 g*.7/.35 ~180 g/mi

For gas the number is 73g/MJ (I had to work that out it may be wrong), so the CO2 emissions per mile are 73g*2.7/.85~ 232 g/mi

Bugger, thought it would have been closer. Interesting how far they are from various publicized figures.

[gruntguru]

And, finally you need to know the CO2 emissions per MJ of calorific value for each fuel. For good quality coal that is about 90g/MJ, so we get 90 g*.7/.35 ~180 g/mi

For gas the number is 73g/MJ (I had to work that out it may be wrong), so the CO2 emissions per mile are 73g*2.7/.85~ 232 g/mi

Bugger, thought it would have been closer. Interesting how far they are from various publicized figures.

23% CO2 reduction? - not too far from this: (Source Wikipedia)

"Contrary to widespread belief, according to Department of Energy research conducted at Pacific National Laboratory, 84% of existing vehicles could be switched over to plug-in hybrids without requiring any new grid infrastructure.^[29] In terms of transportation, the net result would be a 27% reduction in carbon dioxide emissions, a slight reduction in nitrous oxide emissions, an increase in particulate matter emissions, the same sulfur dioxide emissions, and the near elimination of carbon monoxide and volatile organic compound emissions. The emissions would be displaced away from street level and have correspondingly less effect on human health."

Of course this is based on 84% fleet conversion and a mix of electricity generation sources (not just combustion of best quality anthracite).

[Greg Locock]

The interesting number in that lot is the efficincy of the engine.

They are running the engine at a few setpoints (five from memory), and never at idle, so 25% is a fair bit off the pace set by Prius or a German diesel, 37-42%. Prius never drops below 30% except when idling, when operating on its peak efficiency curve., as it does.

The tradeoff analysis is quite interesting - if most of your customers use the battery mostly, then it is not worth fitting an ultra efficient engine, it is just ballast.

[NeilR]

Actually with a change in legislation we could get a small shift away from cars to bikes. I watched a MTB rider with a 1kw front hub motor get away from the lights and he was ahead of the cars for the first 30 yards. Having a chat to some of the blokes who do this was surprising: Cruise speed no pedalling was 30-35kph, 45kph with pedalling and range was 50km no pedalling - some are working on regenerative braking as well. I was told a recumbent version is on the way. Curiously these things require a motorbike lic in Australia.

[desmo]

I like the idea of electrically assisted bicycles as everyday transportation but can you imagine your typical morbidly obese American who can barely waddle across a Wal-Mart and can't even imagine any form of transport that doesn't involve first climbing up into a small building on wheels with a sofa to sit on trying to cope with it?

[Greg Locock]

I like the idea of electrically assisted bicycles as everyday transportation but can you imagine your typical morbidly obese American who can barely waddle across a Wal-Mart and can't even imagine any form of transport that doesn't involve first climbing up into a small building on wheels with a sofa to sit on trying to cope with it?

Honda make a small efficient wheel motor for bikes. They were very surprised to find that the main market was little old ladies. They like the idea of cycling, but can't cope with hills (OK, no i don't knwo why gears don't work) . The electric assist sorts that out.

[desmo]

I'm actually not too surprised that older folk would find the idea attractive. The waddling fat, must drive some ridiculous rolling apartment building with a cellphone in one hand and a four dollar 1000 calorie coffee in the other generation are actually mostly the younger ones.

Gears work to achieve mechanical advantage on a bicycle but on a hill where the slope and the rider's power output combined means slowing down to near walking speeds- not a rare thing on a bike unless you are an actual athlete- it becomes probably more efficient just walking than trying to maintain balance and ride at the same time. Bicycles are almost magic on flats and downhills, but on uphills they are mostly just unwelcome, unwieldy dead weight no matter the gear ratios. A motor to assist, even if only up hills, will make cycling much more attractive to real people I'd guess.

[Fat Boy]

but on uphills they are mostly just unwelcome, unwieldy dead weight no matter the gear ratios. A motor to assist, even if only up hills, will make cycling much more attractive to real people I'd guess.

When the road points up, that's when the fun starts.

Older, waddly types can ride tricycles. After a while, they won't be so waddly. If you're under 70, then 2 wheels is fine. To me, most of the answers to the emissions issues are absurd. The bicycle, however, makes a hell of a lot of sense on a number of fronts. Getting people to use them isn't easy, getting people driving cars to treat cyclists like something other than a speedbump is also not without problems. Getting stores to make life easy on cyclists is a bit of a trick as well. Solve some of those issues, and we've finally found something I can nod 'yes' to.

Greg, one thing you missed in your pollution analysis is the batteries in the electric car. Those are an immeasurable bigger problem than CO2 (regardless of what those flying their private jets to Copenhagen might say).

[imaginesix]

Riding uphill also gives the feeling of getting very little return for one's effort, which is discouraging.

I expect electric-assist bicycles to become the household standard within my lifetime. Considering how readily people will spend thousands of dollars today for very small gains in efficiency, as well as the increased focus on energy conservation in the future, the electric assist bike should start to sell itself.

[NeilR]

perhaps, I already do a 24km commute on my bike. It takes around 10min more than public transport. Where electric assist would come in handy would be say an inner suburban delivery bike etc.

[Tony Matthews]

...getting people driving cars to treat cyclists like something other than a speedbump is also not without problems.

I agree with all of your post, but it would also help if cyclists obeyed the basic rules of the road.

[Fat Boy]

I agree with all of your post, but it would also help if cyclists obeyed the basic rules of the road.

This is a good point, but to a large extent not in play when it comes to accidents. The most common car/bike accident is the cyclist on the correct side of the road pedaling along and the motorist drifting into the bike lane or onto the shoulder because of not paying attention. Dead cyclist and a bent bumper....who pays for that one?

Often when obeying the basic rules of the road, cyclist are blamed for not doing so. Bikes have the same right-of-way as cars in most states on city streets (not freeways, of course). It's OK for them to ride 2-by-2 and take some of the road. That is legal. It may inconvenience the motorist, but it's completely legal. Yes, the car may have to slow for several seconds before passing. They accept it in Holland.

The biggest law foul by cyclist is rolling through stop signs. In many states, bikes are allowed to slow to a walking pace to check for a clear intersection and then continue without actually stopping. This varies widely, so it may or may not apply. What you see as illegal may be fine. Regardless, they shouldn't affect the flow of auto traffic, but they often do.

Being on a bike doesn't mean that you're automatically in the right. No question. What it does absolutely guarantee is that when there is a collision, you'll get the worst end of it. Sometimes everyone seems to forget this.

[Fat Boy]

Riding uphill also gives the feeling of getting very little return for one's effort, which is discouraging.

It's called paying the gravity god. He always pays you back. The head-wind god can be a real bastard, though.

[Tony Matthews]

Being on a bike doesn't mean that you're automatically in the right. No question. What it does absolutely guarantee is that when there is a collision, you'll get the worst end of it. Sometimes everyone seems to forget this.

I could equally have said 'if everyone obeyed the basic rules of the road', and of course you are right to say that in a collision between car - and especially, truck - the cyclist will come off worst, but I see more acts of recklessness, law-breaking and sheer stupidity by cyclists than other road users. I speak as a motorist, cyclist, some-time biker and pedestrian. Actually, I have realised that pedestrians are pretty close in the stupidity stakes, but as they are moving more slowly they cause less havoc.

The nearest I have come to serious personal injury was when walking across a large city intersection, cars having stopped at red, pedestrian lights green for me, only to have a cyclist ride through at high speed between two lanes of cars, only my cat-like relexes saving us both. Believe me, if I had been able to apprehend him he would not have been able to ride for some time!

A bit nearer to the thread, I wonder if electric assist will make cyclists a bigger danger to themselves and others, or the fact that losing momentum is not such a pain, it might encourage a slightly more responsible riding style.

[Tony Matthews]

The head-wind god can be a real bastard, though.

The tail-wind god is more benign, and often in waiting.

[dosco]

The head-wind god can be a real bastard, though.

The omnidirectional headwind was my <sarcasm> favorite </sarcasm>. Especially in the summer, when it felt like a hairdryer. Oh yeah, baybee.

[imaginesix]

It's called paying the gravity god. He always pays you back. The head-wind god can be a real bastard, though.

I meant to add that.

Though to be fair the gravity God never pays back in full, precisely because the wind God always takes his cut.

Oh, and the payback is always more short-lived than the initial expenditure.

Edited by imaginesix, 22 December 2009 - 18:31.

[Wuzak]

I recently did some calcs to see what sort of would be required to drive my Falcon (EL). The aim was to get somewhere near factory performance, including matching the 180km/h (limited) top speed.

My first though was to have direct drive - convert to IRS and have the motor next to the back axle connected to the diff. Then the possibility would be to have a small range extender in place of the six, plus, of couse, batteries.

Checked on a DIY electric car forums to see how they were doing theirs. Most had DC motors operating through the original gearbox.

I found a few motors which would give either the top speed or the acceleration, but not both.

I did find a Siemens motor which would match the performance requirements, if my calcs were correct.

The motor in question had a peak performance of 430Nm constant until it reached maximum power of 200kW (approximately 4400rpm), which it held until 6500rpm. The power then dropped to 150kW at the maximum rpm of 10,000.

Gearing for absolute maximum speed gave estimated values for acceleration of 0-100km/h in 8.6s, 80-120km/h in 4s and a top speed of just over 210km/h.

Gearing for a maximum speed of 180km/h gave 0-100km/h in 7.3s and 80-120km/h in 3.8s.

I figure about 44kW/58hp for a 120km/h cruise.

All assuming that my calcs are correct (which they probably aren't!).

Being a 3 phase AC motor the Siemens is undoubtedly more expensive than a backyarder could afford, whilst the unavailaibility of suitable controllers rated to 200kW would also be a stumbling block.

Range would be short, except when using the range extender. I understand that GM is experiencing problems with the Volt in this area.

[Fat Boy]

The omnidirectional headwind was my <sarcasm> favorite </sarcasm>. Especially in the summer, when it felt like a hairdryer. Oh yeah, baybee.

....and if you ever get the sensation that, "Hey, there must be no wind today" then it's 20mph or so at your back, idiot.

[J. Edlund]

I recently did some calcs to see what sort of would be required to drive my Falcon (EL). The aim was to get somewhere near factory performance, including matching the 180km/h (limited) top speed.

My first though was to have direct drive - convert to IRS and have the motor next to the back axle connected to the diff. Then the possibility would be to have a small range extender in place of the six, plus, of couse, batteries.

Checked on a DIY electric car forums to see how they were doing theirs. Most had DC motors operating through the original gearbox.

I found a few motors which would give either the top speed or the acceleration, but not both.

I did find a Siemens motor which would match the performance requirements, if my calcs were correct.

The motor in question had a peak performance of 430Nm constant until it reached maximum power of 200kW (approximately 4400rpm), which it held until 6500rpm. The power then dropped to 150kW at the maximum rpm of 10,000.

Gearing for absolute maximum speed gave estimated values for acceleration of 0-100km/h in 8.6s, 80-120km/h in 4s and a top speed of just over 210km/h.

Gearing for a maximum speed of 180km/h gave 0-100km/h in 7.3s and 80-120km/h in 3.8s.

I figure about 44kW/58hp for a 120km/h cruise.

All assuming that my calcs are correct (which they probably aren't!).

Being a 3 phase AC motor the Siemens is undoubtedly more expensive than a backyarder could afford, whilst the unavailaibility of suitable controllers rated to 200kW would also be a stumbling block.

Range would be short, except when using the range extender. I understand that GM is experiencing problems with the Volt in this area.

Electric motors are rated quite different from combustion engines when it comes to the power output. Typically they are rated with their maximum continuous output, the maximum output the motor can give in continuous operation before the temperature starts to run out of control. For short durations, such as accelerations, they can typically handle much higher power outputs, often several times the maximum continuous output. In such a situation it becomes more of a question what the battery and the power controller can handle.

A123Systems for instance have batteries with power densities close to 5 kW/kg these days. So to provide 200 kW, the battery needs to be at least 40 kg, but with about 5.2 kWh the batteries won't give such a good range. Double the size of the pack and we're at about 10.5 kWh, enough for probably 50 km, and around 400 kW. That should provide a good acceleration even if the motor can't handle that sort of power for any longer duration.