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Take a regular manual transmission and engine and replace the clutch with a planetary gear set with the trans connected to the planets and the engine connected to the sun gear. Gear it in such a way so that if the ring is held stationary it will act as a direct drive system 1:1. Now attach a low HP
permanent magnet electric motor to the ring gear which has a standard brake to lock its motion.
The basic setup enables the electric motor act as an electric clutch which isn’t original, but that fact that the system uses a reversible electric gearmotor generator adds some possibilities that seems to be outside the standard parallel hybrid design.
The design of the gearmotor and associated brake should be such that the max torque exceeds the max torque of the engine and its RPM band only needs to be as great as the engine band between normal shifts.
Now to shift into first gear from a stand still the motor spins in reverse to negate the engine RPM, the gears are engaged, then the motor switches into generator mode to accelerate the car till the brake can be applied. Then the engine is brought up to peak torque RPM and the motor spins in the standard direction to raise the car half way to the next gear, then the motor counter spins to release the torque on the trans and the gear is released. The motor then spins to match the correct input RPM for the next gear and the process repeats as the motor first acts as a generator then a motor while the engine stays at its most efficient RPM.
HP and Torque for a 45HP Harley
http://www.calsci.c...nfo/Horsepower.html
[MisterQED, Jul 05 2008]
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//the engine is brought up to peak torque RPM and the motor spins in the standard direction to raise the car half way to the next gear// at that point though, wouldn't the electric gearmotor be required to match the real engine's RPM *and* torque? The gearmotor combo would therefore have to be able to supply the same power (HP) as the primary engine. The idea may still have some merit, but not with a "low" HP electric motor. |
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The motor is connected in a differential fashion, so the RPMs are additive as long as the torques match. If the torques don't match one motor will slow down. So the electric motor just needs to be geared down so that it will have enough torque to match the engine, then it can add it's RPM to the RPM of the engine. |
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It's going to add a fair bit of mass and bulk to the transmission assembly - might work better on a railway locomotive. Do the math: |
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Assume the IC powerplant has an output of 50 BHP (not unreasonable). That's 50*725 = 36kW. Allowing for your gearing, assume the motor/generator can be as small as 20kW. That's still fairly bulky, and will need cooling. Add the drive and control electronics (with big heatsinks, and more forced-draught cooling for low speeds - you can use air ram cooling at higher speeds) and bulk may be more of a problem than weight.
There will also be some losses in the reduction geartrain between the motor/generator and the CVT. |
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This one probably falls into the category of "practical, but uneconomic". |
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Hold on, I'm trying to work thru the numbers for a Harley which isn't a car engine but it's the first one I found full charts for and it should be reasonably respective of small car engines. I'm thinking you could use a much smaller electric motor than the 20kW mentioned I was originally thinking more like 5kW. |
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Gearing the motor down doesn't help - it reduces the torque the motor needs to produce, but increases the speed which it must run at. The power requirement doesn't change as it is set by the rest of the system. |
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In other words, if you gear the motor down so that it produces enough torque, then the RPMs it can add become small. How small, of course, depends on the motor. |
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Correct, but this system only needs to add enough RPM to get half way to the next shift, so for the Harley where you want to keep in the peak torque, you'd probably shift up when you hit 5000 and drop it to 3000, I'd only need an electric motor with a 1000 RPM range and a torque above 80ft/lbs across that range. So I think you can get an electric motor that will do 20ft/lbs to 4000 RPM, I can drop it to 80ft/lbs to 1000 RPM and be good. I can then leave the engine at 4000 RPM producing 80ft/lbs of torque and do the rest with the trans. So I think that puts the motor at around a quarter the HP of the engine. The HP requirements of the motor are dependent on both the engine HP and shift distances. |
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// puts the motor at around a quarter the HP of the engine // |
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Revisiting the math, you might just get away with the motor being 30-35% of the primary power unit, but not less; the installation losses rise and the efficiency drops with motor size.
However, a small, high-revving low-torque motor, highly geared, would have the merit of low inertia and being able to change the applied torque quickly. |
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If you flip it inside out, put the break and motor into the rotating part, then when locked, the assembly would just act as a shaft. Thus there would be no transmission losses through it other than a couple of bearings. |
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The snag here though, is there would be much more rotating mass which may hamper acceleration somewhat. |
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Good for a family car but less so for something designed to ZOOM about. |
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It would be hard to beat the simplicity of a lockable diff. |
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//If you flip it inside out, put the break and motor into the rotating part, then when locked, the assembly would just act as a shaft. Thus there would be no transmission losses through it other than a couple of bearings.// That is the way it is designed. The idea is to keep the efficiency of a standard trans an only use electric motor to push the total RPM up to the next shift point. My goal was to allow longer shifts, but definitely to leave natural shift points at the common speeds 15, 35, 55 mph in US, but adjustable for locality by the gearing in the rear. |
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In that way most of the time the motor is not moving and the brake is applied leaving the motor at it's peak efficiency pushing the car down the road unassisted. The key is for a gas engine to always be running at full throttle and geared to produce just the amount of torque at the rear wheel needed to push the car. |
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The computer controlled shifts remove the need for syncros so more gears could be placed in the same trans. |
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Here's an invention for you - paragraph breaks. |
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