Rolls's Crazy Engine Idea No. 22: Cvt Via Electrically Coupled Generator And Motor.

[Rolls]

So the concept of CVTs is pretty cool, constantly varying gearbox giving the perfect ratio at all times, also means the engine can be designed to operate in a very small rpm range for optimum performance/efficiency. The current CVTs fall over due to low torque limits and losing energy via heat due to the bands slipping.

The concept is to make this CVT out of an electrically linked generator and motor. Eg the engine drives a generator and the generator powers a motor to drive the wheels except there is no intermediate batteries or such, the coils for the generator are linked directly to the coils for the motor.

Ignoring the issues of how one would control such device (eg final ratio to control engine rpm) generally how efficient are generators and motors, what kind of losses could we expect to see? how do they compare to those of a traditional gearbox? Also how heavy would the coils be to successfully transmit say 200kw of power?

Here is a picture if you can't visualise what I am talking about.

No doubt weight, efficiency etc would make it pointless, but is the concept sound?

Discuss.

Edited September 14, 2011 by Rolls

[HR32GTS 4DOOR]

No doubt you would be able to make it work i think, If you get two little electric motors and connect the terminals together, then spin one of the motors the other one will spin. Same concept really so I bet you could get it to work. Also I'm wondering if the power losses due to resistance in the wires and coils would be less than the losses of a trans. and you could get hub motors for even less mechanical losses, but they are shithouse for power. Pretty crazy idea Rolls.....

[Bond]

Diesel locomotive does exactly this but not sure why this is in Forced induction.

[Rolls]

Diesel locomotive does exactly this but not sure why this is in Forced induction.

Because my concept uses a turbocharged engine

[GTSBoy]

Diesel locomotive does exactly this but not sure why this is in Forced induction.

This. Hundred year old idea is hundred years old.

[Rolls]

This. Hundred year old idea is hundred years old.

I'm talking about using it to create a CVT and comparing it to a traditional transmission weight and efficiency wise, the reason diesel-electric trains use them is entirely different.

Edited September 14, 2011 by Rolls

[KiwiRS4T]

I am sure such a system is in use in one or more cars somewhere but don't have time to look it up. You effectively don't need a gearbox because of the massive instant torque of an electric motor.

[Lithium]

Rolls, seems we think similar - you've been spouting ideas I've pondered in the last decade or so and (in most cases unfortunately) then abandoned due to finding out they either exist, are impractical, or just aren't actually sound as I research and learn more.

Keep it up! Sooner or later you may find you come across something that hasn't been hit on, or even something that has been hit on, used, and forgotten about due to various reasons but turns out to be a good idea again - if nothing else, having a brain is pointless if you aren't exercising it

[ARTZ]

i still dont understand how you broke a camshaft...

[GTSBoy]

the reason diesel-electric trains use them is entirely different.

Not really. The reason is basically the same. How to run a big engine with limited rev range in an efficient manner whilst being able to operate the vehicle over a wide speed range.

Same problem.

[89CAL]

You gain quite alot of torque using an electric drive motor (depending on the reduction etc) but this is also were your problem lies. The motors are still geared (assuming your still going to use one or more final drives) to achieve speed or torque or a mixture. So you won't be achieving the same as a CVT which is always changing ratios.

I can go touch a design that is exactally what you are describing right now (Komatsu 730E dump truck) and i can also tell you it will carry a he'll of a lot of dirt but only do 60km/h

If you knew the equipment you need to get it to work pepperly then you'd realize it's not as easy as plugging a motor into a generator and away you go (not that you were thinking that)

For example, our trucks use several contactors, IGBT's capacitors etc to make them work. Not to mention all the resistors for retarding (wouldn't be necessary on a car) as well

This also generates quite a bit of heat which is another problem with storage of components and cooling

Your idea is fair enough, I think Lexus even use a similar system on one of there cars, but I think it's a solution better left for trucks/trains. Some of the parts are expensive when they go wrong and you don't get all the same benefits of a true CVT

Edited September 14, 2011 by 89CAL

[GTScotT]

This one is fairly simple. You cannot create or destroy energy, first law of physics.

It means you need an engine making in excess of 200kw driving the generator to drive the electric motor if you want it to produce 200kw. Or you need pre charged battery cells with 200kw per hour of energy stored in them.

Then you have to consider losses in energy, remember that heat is loss in energy. So if your electric motor will produce heat, it will lose some of your said energy.

Someone else has recently thought of a new cvt model that uses reduction gears of some sort.. With a tension on them. I saw it on the ABC but wasnt sure how it worked, Maybe a slide gearset.

Anyway, like I explained to my dad (LOL here we go) cant make or create energy. He thought he could get a 12v engine to run off a car battery and spin an alternator/generator. Enabling him to keep the car battery charged and create excess power. What he ended up with was a very expensive fish pond set that needs its car battery changed every 24-48 hours.

[The Dan]

Love the idea. I think it would work....but you'd have to ask the question of why the car companies have not done it yet? There has to be SOME reason why it won't be economical

[Bond]

This would probably be easier using a good variable speed drive Hydraulic setup.

[Birds]

This one is fairly simple. You cannot create or destroy energy, first law of physics.

It means you need an engine making in excess of 200kw driving the generator to drive the electric motor if you want it to produce 200kw. Or you need pre charged battery cells with 200kw per hour of energy stored in them.

Then you have to consider losses in energy, remember that heat is loss in energy. So if your electric motor will produce heat, it will lose some of your said energy.

Someone else has recently thought of a new cvt model that uses reduction gears of some sort.. With a tension on them. I saw it on the ABC but wasnt sure how it worked, Maybe a slide gearset.

Anyway, like I explained to my dad (LOL here we go) cant make or create energy. He thought he could get a 12v engine to run off a car battery and spin an alternator/generator. Enabling him to keep the car battery charged and create excess power. What he ended up with was a very expensive fish pond set that needs its car battery changed every 24-48 hours.

[Rolls]

Rolls, seems we think similar - you've been spouting ideas I've pondered in the last decade or so and (in most cases unfortunately) then abandoned due to finding out they either exist, are impractical, or just aren't actually sound as I research and learn more.

Hehe I get bored easily and always think about shit like this, I remember when I was ~15 and thought of the radial engine, turns out someone invented it in WW2 put it in planes and it failed dismally.

This one is fairly simple. You cannot create or destroy energy, first law of physics.

It means you need an engine making in excess of 200kw driving the generator to drive the electric motor if you want it to produce 200kw. Or you need pre charged battery cells with 200kw per hour of energy stored in them.

Yep, the goal is that you can run the motor at peak power at all times and as the speed changes the 'ratio' changes. I am not sure how you would control the load on the motor to limit rpm, but with the electric motor half you don't need a ratio, it just creates peak torque at all times. This is how it would act like a CVT, always at peak power rpm, electric motor delivers what ever 'power' it is generating at all speeds.

magnets

f**kING MAGNETS HOW DO THEY WORK?

Edited September 15, 2011 by Rolls

[Bond]

Yep, the goal is that you can run the motor at peak power at all times and as the speed changes the 'ratio' changes. I am not sure how you would control the load on the motor to limit rpm, but with the electric motor half you don't need a ratio, it just creates peak torque at all times.

Variable speed hydraulic drives do EXACTLY this. We use them at work on our pit pumps. The diesel engines are set at their most efficient or max power rpm and then we just adjust the flow according.

I am not sure how you would control the load on the motor to limit rpm

You don't control the load.....you just control the rpm using a governor or in this case your right foot.

[Rolls]

You don't control the load.....you just control the rpm using a governor or in this case your right foot.

Lets say peak power was at 5k and you wanted to generate this peak power so had full throttle, what would stop the motor revving to say 6k? That is what I am trying to understand.

Edited September 15, 2011 by Rolls

[GTSBoy]

Alright, to talk about how the actual device would work, and what the losses could/would be....

The output motor would have to be either an AC motor with a variable frequency variable voltage drive or a DC motor with some sort of pulse width modulation and possibly variable voltage control. This would all be under the control of a computer which would change the output characteristics to suit the speed and the load.

The input generator would be either an AC unit or a DC unit, depending on what makes the most sense given the choice of the motor - or maybe some clever electrical guy can tell us that there's only one sensible combination of the two units. Regardless, the generator is the dumbest part of the whole system because all it does it turn flywheel power into electrons.

The engine would probably have to be completely under the control of the same computer that's running the output electric motor. The driver would simply input a throttle position, being the main 0-100% load signal, and the computer would then run the engine to make enough power from the generator to do what it needs to do at the output motor. I'd suggest that the engine would be best run at or near peak torque revs most of the time, unless they have an operating point that provides significantly better efficiency and still provides enough torque for cruising and lighter load accelaration. And the engine would be able to be revved up to peak power for when the driver is asking for more than the engine can give at peak torque. Sacrificing fuel efficiency but extending the performance range to replicate what petrol/diesel engine drivers are accustomed to.

So, you'd hope that the engine would be able to be run in a significantly more fuel efficient manner than a normal transmission allows, thus saving some %. But you then have a generator, some sort of inverter/PWM arrangement and an electric motor to act as a transmission. The rotating electrical devices would have efficiency over 90% - but the absolute number at any time will likely depend on speed and load. So you might give away 15% overall efficiency across those two devices. The electrical efficiency of the inverter/PWM controls in the middle are something of an unknown. You'd hope that they would be >95%, but anything's possible. So I'd think you might give away up to 20% in total across the transmission. This is possibly more than the REAL power losses across a normal gearbox. You'd hope that the ECVT would have better than 20% losses, but I can see how it might not be much better. So with the possible fuel savings by running the engine better, you might be down to <15% losses compared to existing transmissions, which might put it into the same overall ballpark as existing stuff.

Now, having gone through all that stuff, if the whole purpose of all that expensive electronics and rotating equipment is just to do a CVT, I'm sure you could get much better efficiency just using a fully hydraulic transmission. Just run the pump off the engine, some tricky control system and hydraulic motors at each wheel (or inboard of each wheel to save unsprung weight), and you'd probably be much better off.

cheers

[Rolls]

Just run the pump off the engine, some tricky control system and hydraulic motors at each wheel (or inboard of each wheel to save unsprung weight), and you'd probably be much better off.

This is another idea I had, using essentially a massive fluid torque converter as the gearbox and change the gear ratio based on how the fluid dynamics work. I get the impression these systems are very lossy and a lot of energy is lost as heat though.

WIth the motor and generator combination, could you not just use an AC -> AC motor? There are no inverters, regulators, nothing needed, you could literally just wire them directly together removing a point of inefficiency.

Edited September 15, 2011 by Rolls