with a gas engine driving a generator, with electronic distribution to four electric motors, one for each wheel.
What it won’t have:
A large battery as with a hybrid. The trade off is no regeneration.
No central transmission, transfer case or differentials. Even “locking” wheels can be done electronically.
No physical damage from mis-matched wheel sizes.
Put the motors inboard with jointed shafts to minimize un-sprung weight.
Ya listening Mr. Musk?
How does it turn? Each motor would have to increase or reduce speed every time the steering wheel went the slightest bit off center, wouldn’t it? Or encountered a road irregularity.
“Each motor would have to increase or reduce speed…”
Most electric motors deliver torque proportional to input current; speed is flexible.
An engine-generator-motor drive train is not as efficient as an engine-mechanical one is, i.e., inherently lower mpgs.
Wouldn’t a diesel-fired engine running a generator be a better choice than gasoline?
I think that’s a pretty good idea circuitsmith . I can’t think of a reason why it wouldn’t work. You get all wheel drive with no problems with differentials. I suppose you still need some form of CV joint on the front drive axels, unless you are proposing to eliminate the drive axels too, and just install the motor right on the wheel hub. Seems like that would simplify suspension issues. Definitely worth considering.
I would ditch the gas engine and would go with a small - maybe around 600 cc - purpose built diesel engine with 2 or 3 cylinders. It would be set to run at a set rpm for high efficiency to charge batteries and power the electric motors if the stored electricity is low.
I can’t help think about how that would work on an icy road with a crown in the center. The least little slip sends you to the ditch.
If you want to duplicate the acceleration of a given gas engine, say with 200 HP, wouldn’t your gas engine need to have 200 HP to drive the 4 electric motors?
If not, why?
@GeorgeSanJose, my idea was to have four short drive axles, one to each motor (located inboard).
Locating the motors at the wheels would greatly increase unsprung mass: the motors would have to move with road irregularities.
Reducing unsprung mass improves suspension performance.
Of course a diesel could be used. That’s really a separate issue, as are the size of the engine and vehicle.
@insightful, I would argue that an electric genset will be ~75-80% efficient.
Higher than a hydraulic torque converter.
Even a transmission + differential + transfer case is no more than 90%.
OTOH you have essentially a CVT that can optimize engine speed vs load more quickly and smoothly than any mechanical transmission.
@Bing, it should perform better on ice than a mechanical system because the electronic control of individual wheel speeds and torque will be faster and more precise.
@JoeMario, yes all the power to the wheels (plus losses) come from the engine.
It’s a hybrid minus the battery storage.
Put in a battery and the engine can be much smaller and you get regenerative braking. Electronics to control all of that is cheap. you only need high horsepower during acceleration. During cruising the requirement is much lower.
I’ve often wondered why the auto industry has not gone in this direction, also.
Perhaps the electric motors could be light enough so that they could be connected directly to the wheels and eliminate the CV joints.
“Put in a battery and the engine can be smaller and you get regenerative braking.”
That’s current hybrid technology. Not everyone wants a hybrid.
Batteries are still big and heavy compared to combustible fuel; they also wear out and are pretty expensive.
Regeneration is a mixed bag.
“Put in a battery and the engine can be smaller and you get regenerative braking.”
I don’t see any downside. The battery can be sized so that it’s weight is equal to that gained by moving to a smaller engine. Fuel economy goes way up. Battery life is equal to engine life.
This would be a hybrid perhaps, but not typical, as the engine would have no direct connection to the drive wheels.
Batteries will not shrink. They need to be as large as the public will bear price and weight-wise to provide decent range. The Volt is only up to about 50 miles range for 2016, and Toyota is far below that. A diesel would be nice if price were no object, but the plug-in hybrids are already too expensive. Adding a more expensive engine will just make them even less interesting from a price perspective.
No@ circut,its very doable,the really big things do it all the time,I would love to have a front drive ,electric rear drive hybrid,it would answear a lot of questions and the battery life doesnt seem to be much of an issue now anyway,with many Prius owners getting over 200K from the battery pack in the city a hybrid really shines(actually its best cycle)though for the buck on the highway its hard to justify the added expense over the bottom end economy cars.
Thomas Edison developed a battery cell over a hundred years ago that for all practical purposes had Heirloom quality,but the caveat was the weight,strangely enough were weight isnt much of an issue(heavy trucks battery drive works fairly good,There was a Class eight RIG In LA ,powered by an APU and a large battery pack(worked very well thank you)
But there are some things I just dont think battery power is suitable for,I cant see heavy earthmovers for the most part being anything but conventional(there are a few exceptions or were)Lets try to save the reasonable cost oil for that.Some switch engines now run on 4 or so small gen sets,I dont know the details,but they are setup tp really have impressive gains in efficiency.California is hard hit by Tier 4 regulations,so expect some novel ideas to come from there
How about using 4 in hub electric motors? No drive axles just wires running to the wheels…
Probably cheaper with 1 motor and an AWD system.
I would argue that an electric genset will be ~75-80% efficient. Higher than a hydraulic torque converter.
All modern torque converters run locked up most of the time (basically, 100% efficient). Otherwise, I agree with your efficiency numbers, which proves my case.
OK, in my “gee whiz” bag…what about a parallel-series hybrid Class 8 truck, utilizing a small, light, gas turbine generator? You’d have a much lighter power plant, lose the twin driveshafts (each axle driven by a motor), lose the transmissions…and all of that saved Tare can go to payload. Storage batteries just large enough to “average” the power output of the turbine, letting it run at constant RPM/load.
Just a few thoughts on the idea. Electric drivetrains must be made from lots iron. Electric motors don’t work without magnetic material. They also use copious quantities of heavy copper because the resistance is lower than aluminum both for the motor and the generator. That adds weight over the aluminum used in drivetrain housings and supports. Circuit recognized that weight in the original post by suggesting inboard mounting.
The main reason this isn’t the preferred drivetrain is because the losses are greater than a mechanical system. The engine efficiency is a bit better because of more constant speed and load. Everything else stinks. I’ll be generous on these numbers. A/C Generator efficiency can be as high as 90%, the motor controllers/wiring can be 92%, the A/C motors themselves will vary quite a bit because they are the prime movers, say 90% average. You also have half-shafts, CV joints and wheel bearings with another 1-2 % loss. Multiply them all together gives you 73% total efficiency. That is less than the 85% mechanical driveline efficiency and you can’t get that back from the engine.
If you add re-gen, now you need AC/DC invertors (90% efficiency, each way) and batteries (96% efficiency for Li-Ion) PLUS the regen efficiencies from the motors, maybe 75% at best, so you lose half of the re-gen energy. But half is better than none so it is worth the cost an weight to carry the batteries and invertors. That’s what locomotives figured out was the best path but they didn’t have the mechanical transmission as an alternative.
Supercar builders add the hybrid part as part of their AWD systems. Mid-engine, gas powered cars with an electric regen-FWD boost motor added to the front of the car for AWD-hybrid-go-real-fast supercar speed with the gas-saving benefits of hybrid technology. Seems silly on a supercar but many are doing it.