Why don't car makers make direct drive electric hybrids?

[redfalconf35]

As a former engineer, I sometimes preoccupy my mind with questions of engineering, and the one question I have the hardest time answering is why car makers make their hybrid cars so dadgum complicated.

It seems pretty simple to me. Small internal combustion engine (designed and controlled to provide enough energy at very high fuel efficiency) connected to a battery that is connected to one or more electric motors that directly drive the wheels. No bulky transmission, no giant high performance engine, no squeezing the battery between the seats.

Of course, the answer is likely one of three things:
1) the battery isn't able to keep up with the energy demands;
2) the electric motors aren't able to keep up with the energy demands; or
3) doing it this way is so heavy that you lose any gains in efficiency.

Does anybody know better why car makers are sticking with the more complicated hybrid systems?

 

[bberg100]

Your idea has worked well with locomotives, without batteries, for almost 100 years. Now they are starting to insert batteries in-line and not having to surge the engine so much.

 

[Zipslack]

I like the idea of a small Honda generator under the hood with 4 motors/CV axles to drive the wheels.

 

[Slash McCoy]

I have experimented with electric drive and repowered my boat to electric. I have built and commuted with electric bikes. I have taken a hard look at what it takes to build an electric car. Just establishing my bonafides.

The problem with direct drive is the motors. It is difficult to design a motor that works well when directly driving a wheel at low speeds. If you look at your own car and measure or calculate the circumference, then divide that into a normal city driving speed or even a normal moderate highway speed, you will see that you are working with a very low wheel RPM. OTOH you are looking at a very high power needed to push the car. The obvious answer, apartt from a reduction gear, Or a LOT of wheels each driven by its own motor, is a larger diameter motor with more poles. Unfortunately, directly driving a wheel requires a motor smaller in diameter than the wheel. So there is a limitation. The power that the motor can convert is limited by the size wire in the windings. The bouncing and jarring of the wheel plays havoc with a motor. Motors of practical size and weight and power output work best at speeds much higher than wheel rotational speed. Soin most successful electric or hybrid cars, a central motor, reduction/transmission, and differential are in the drive line and they power one or more wheels just like a conventional car.

Lots of guys tinker with electric cars in their garages and start out with a lot of obvious ideas that in reality nobody has figured out how to make them work properly yet. Do feel free to join the crowd. You just might get lucky or get that flash of inspiration.

 

[redfalconf35]

It is difficult to design a motor that works well when directly driving a wheel at low speeds.

Fascinating! I could've thought for a year about this and never realized that would be an issue.

I wish i had the time, money, and garage necessary to tinker with EVs. Maybe someday.

 

[OldSaw]

Fascinating! I could've thought for a year about this and never realized that would be an issue.

I wish i had the time, money, and garage necessary to tinker with EVs. Maybe someday.

...or you can just go get a Leaf. That's what I did. All electric, all the time.

We have a hybrid household, one gas car and one electric. Works for us.

 

[redfalconf35]

I can't really make myself like all-electric. Until I can swap a battery with a fresh one at a gas station in 1.5 minutes, I can't really justify electric. I ended up with a fusion hybrid and love it.

 

[Andy77]

I can't really make myself like all-electric. Until I can swap a battery with a fresh one at a gas station in 1.5 minutes, I can't really justify electric. I ended up with a fusion hybrid and love it.

This is the tipping point for a mass exodus from gasoline to electric cars- infrastructure. We have a friend who had to park her car at our home and get ride to the airport because her Leaf won't make the round trip.

If the public (and our Leaf driving friend) could count on being able to swap batteries on every street corner like we can rely on gas stations the distance limitations of electric vehicles become a non issue.

It took many decades for gas stations to become ubiquitous. My money's on electric vehicle "refilling" stations taking less time.

 

[OldSaw]

This is the tipping point for a mass exodus from gasoline to electric cars- infrastructure. We have a friend who had to park her car at our home and get ride to the airport because her Leaf won't make the round trip.

If the public (and our Leaf driving friend) could count on being able to swap batteries on every street corner like we can rely on gas stations the distance limitations of electric vehicles become a non issue.

It took many decades for gas stations to become ubiquitous. My money's on electric vehicle "refilling" stations taking less time.

My Leaf is equipped with a rapid charging circuit, (which I haven't used). In large metropolitan areas, they have charging stations that will charge from zero to 80% in about 30 minutes. That is the future that I see. Charging will continue to get better and it won't take much longer than getting a tank of gasoline. Plug your car in, go inside, use restroom, buy snacks, hit the road.

 

[imatabor]

This is the tipping point for a mass exodus from gasoline to electric cars- infrastructure. We have a friend who had to park her car at our home and get ride to the airport because her Leaf won't make the round trip.

If the public (and our Leaf driving friend) could count on being able to swap batteries on every street corner like we can rely on gas stations the distance limitations of electric vehicles become a non issue.

It took many decades for gas stations to become ubiquitous. My money's on electric vehicle "refilling" stations taking less time.

What about us rural guys? 45 miles to the nearest city, rough dirt roads, sub zero conditions most of our 8 months of winter and several feet of snow. Maybe I just have some misconceptions about electric vehicles but I can't imagine one being practical here.

 

[redfalconf35]

45 miles to the nearest city, rough dirt roads, sub zero conditions most of our 8 months of winter and several feet of snow.

This is why the utopian self-driving all-electric car vision of the future is more fantasy than reality. There will always be a place for petroleum based engines. Petroleum has such a high energy density in comparison to lithium ion batteries, that it'll never make sense to go 100% electric for everybody. It's even a stretch to apply to people in the outer suburbs sometimes.

That's why I think increasingly efficient hybrids are a more likely future. Greatly increased economy and all the benefits of an ICE. Heck, some enterprising company could probably rig up some modular thing that let you slide in an extra battery pack for EV commuting, an ICE for longer trips and more rugged surroundings, or some exotic fuel cell for the fun of it. With a serial hybrid, anything that generates electricity would work.

 

[Andy77]

What about us rural guys? 45 miles to the nearest city, rough dirt roads, sub zero conditions most of our 8 months of winter and several feet of snow. Maybe I just have some misconceptions about electric vehicles but I can't imagine one being practical here.

I'm hardly an expert- and a rural transportation situation is very different in many many ways from suburban/urban. But Teslas get 200-265 miles per charge. If that becomes standard I could imagine electric vehicles working for most people.

But this is all "future thinking." Imatabor, I don't think anyone expects you to trade your truck in for a Nissan Leaf any time soon!!

 

[imatabor]

Imatabor, I don't think anyone expects you to trade your truck in for a Nissan Leaf any time soon!!

 

[vacman]

As far as the size of the motor limited by the wheel size, reverse the normal motor to a fixed armature and a spinning field. Mount the wheel and the tire directly to the field. This does nothing to keep the motor from being damaged by ruts in the roads, however, and it still creates limitations to the motor size. Remember though, you need a lot of current to charge one of these electric cars and our electric grid is not designed to handle that much current, plus the fact that the power plants use fossil fuels, so where's the ultimate savings? I would prefer a small 3 or 4 cylinder diesel turbocharged engine. I do take trips of 700 miles + at a time, so electric is definitely out for me. Google Elio Motors and see what one guy is hoping to release within the year.

 

[Slash McCoy]

As far as the size of the motor limited by the wheel size, reverse the normal motor to a fixed armature and a spinning field. Mount the wheel and the tire directly to the field. This does nothing to keep the motor from being damaged by ruts in the roads, however, and it still creates limitations to the motor size. Remember though, you need a lot of current to charge one of these electric cars and our electric grid is not designed to handle that much current, plus the fact that the power plants use fossil fuels, so where's the ultimate savings? I would prefer a small 3 or 4 cylinder diesel turbocharged engine. I do take trips of 700 miles + at a time, so electric is definitely out for me. Google Elio Motors and see what one guy is hoping to release within the year.

You are describing a hub motor, I think. They are actually common for ebikes, scooters, motorcycles, etc and work okayish in that application. I used front wheel three phase Brushless DC (PMAC) hub motors on my ebikes. For a car you still need a motor with a diameter bigger than the wheel, due to limitations posed by wire sizes, current, etc vehicle mass and inertia, speed requirements, etc. Higher voltage helps, as this reduces the current needed to get work done. That is why higher performance electric cars are all 144v up to about 320v. I believe the Teslas are in the neighborhood of 280v, but I wont swear to that without googling it. The problem with higher voltage is it pushes the RPM range upward, making a car even less likely to work well without a reduction gear.

Unfortunately Elio has been making promises for so long that I am afraid it is just vaporware. I really had hopes for that quirky 3 wheeler to make a big market splash. It did, and still does, seem like a good idea.

For long road trips, the infernal combustion engine will be king for a long time to come, maybe forever. Where electric really shines is short to midrange commuting, errand running, stuff like that. If we can get solar cell efficiency up to around 40%, or triple the energy density of storage devices, then we might have a real game changer. Oh, and the cost has to be competitive with fossil fuel cars.

 

[Slash McCoy]

I like the idea of a small Honda generator under the hood with 4 motors/CV axles to drive the wheels.

Oh, a small generator won't get the job done. With perfectly efficient conversion of energy, 746 watts is one horsepower. So a 2k honda generator in a perfect universe is good for about what... 2.8HP? What such a generator COULD do is run continuously even when parked, and recharge the batteries, as well as extend the range a bit while driving. For most cars you would want a generator of around 15kw to 20kw, I think, in order to drive indefinitely. Something about the size of... <drum roll> a very small car engine.

 

[Macfrommichigan]

Way back when I was in grad school one of my profs said that in the early 1900s electric cars were superior to the internal combustion engine, but gas powered vehicles won out because they were sexy in a macho way-- and that if we had continued with electric cars, battery and motor development would have advanced at a much quicker pace. Maybe so.

 

[Slash McCoy]

Way back when I was in grad school one of my profs said that in the early 1900s electric cars were superior to the internal combustion engine, but gas powered vehicles won out because they were sexy in a macho way-- and that if we had continued with electric cars, battery and motor development would have advanced at a much quicker pace. Maybe so.

To a large degree that is correct. The early electric cars from 1905 through about 1915 were marketed toward women. It was felt that the lack of exhaust, and the gentler, quieter ride were more suitable for the fairer sex. As a consequence, most electric cars of that era had a lot of overhead clearance inside, to allow for large hats and coiffures. Gasoline cars were for men. Getting out to hand crank the engine, after checking oil and doing other dirty but necessary tasks, was seen as manly endeavor. Women got in their electric flivvers, turned a knob, and silently whirred away down the street, safely above the mud and dust that characterized streets in the day.

Do a quick google for the General Motors EV-1, and while you're at it, watch "Who Killed the Electric Car?", a documentary on the same. GM is sitting on the patents for what was, in its day, a revolutionary battery, whose performance rivals todays state of the art LiFePO4 batteries, with a lower risk of fire or explosion. Death By Patent.

Interestingly, the most durable electric car batteries ever invented, were Nickel/Iron Alkaline batteries called Edison Cells, and now, 100 years later, many of them are still in use. Edison Cells of course were simply too long-lived for anyone to make a profit selling them, so they nearly suffered Death By Patent, too, but now they are made in China and recently a company called Iron Edison has begun making them in the U.S.

You can make a direct connection with the shaving world. It is tough to make a product, like a straight razor, that lasts a couple hundred years, and see a lot of growth. Or even a DE razor that lasts 100 years and uses replaceable blades that can be had for 10 cents apiece and last a week. If a product is too good, too reliable, nobody wants to make it. A somewhat flawed version that needs constant repair and upgrade is better for our corporate world.

 

[Macfrommichigan]

Slash, eloquent analysis. Thank you!

 

[6Cuda6]

Direct drive motors do exist and they work quite well at LOW speed.....problem is our average speed for cars is about 40mph which is beyond the direct drive efficiency range.

As for limiting factors with electric its the batteries....although they are improving by leeps and bounds we just dont have the capacity to charge speed we need ....yet. Also we dont have a good enough life cycle meaning that the batteries only last about 7 years then needing replacement.

Although i think its a viable alternative to fosil fuel vehicles its by no means environmentaly friendly....after all we still need to charge the thing and most of our electricity comes from coal fired hydro plants....lets not forget also that if even 50% of all vehicles where electric our electric grids in the cities couldnt support it.....dont even get me started on the tax losses from not buying gasoline and the increased cost of hydro do to consuption.