Question by al mond: In a hybrid vehicle like the Toyota Prius, couldn’t the electric motor be used to replace the transmission?
Couldn’t the electric motor part of the hybrid vehicle be used strictly for getting up to speed before connecting to the gasoline engine. The gas engine might then be run at a constant speed with greater gas engine efficiency. Maybe even not have a conventional transmission system at all, but use the electric motor in its place.
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Best answer:

Answer by SlightlyDusty
Things could get scary with a direct drive to the wheels at 3000-6000 rpm

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4 Responses

  1. a transmission is the “gear box” connected to the motor in your engine. it is the piece that transfers spinning motor shaft and connects it to the drive shaft which makes the wheels spin.

    to answer your question, not exactly.
    alot of cars these days have an electric motor that goes up to, say – 15 mph, then the engine takes over.
    but if you removed the transmission system the car wouldn’t move, and the engine would be obsolete. if you have an engine running at a constant speed you wouldn’t be able to exceed about 20mph. electric motors just arent powerful enough

  2. you need some way to transmit power to the wheels. you cannot use an electric motor to as a transmission , it does not work that way. This is why these vehicles are heavy, it takes battery power to run the electric motors. and fuel to power a transmission. without gas, you dont need the engine, but electricity in batteries is limited. Until the battery advances a lot more than it is at present, you only have short distance electric cars, that need to be charged up regularly to go 50 miles or so a day. Battery technology has made some advancements but there are still chemical coumpounds that have far too much explosive power for them to be approved for use on the street on a daily basis.

  3. Umm… In the Prius, which is a series-parallel “full” hybrid the motor-generators (there are 2) DO replace the transmission. MG2 is direct coupled to the final drive, hence the wheels and to the ring gear of the PSD which is a simple planetary gear set, MG1 is connected to the sun gear, and the engine is connected to the planet carrier.

    28% of the engine’s torque always goes to MG1, From there the electricity can be sent to MG2 or to the HV battery, the other 72% of the torque goes directly to the wheels. The hybrid vehicle ECU controls the speed and direction difference between the 2 motor-generators by feeding power from one to the other to control the effective gear ratio. At low speeds MG1 spins faster than MG2 to act as low gear, at highway speeds MG1 spins backwards which slows down the engine and acts as an overdrive.

    Note that torque is split at a fixed 28/72% but power isn’t since power is torque multiplied by RPM, AKA if the wheels are still (stopped) 100% of the power goes to MG1, if MG1 were theoretically still (which never happens with the car moving) 100% goes to the wheels.

    In assist “mild” hybrids like those from Honda the motor-generator is separate from the transmission.

  4. Strictly speaking, there is no transmission in the Prius, just like Wondering says. The engine in the Prius is connected to the motors by a simple planetary gear system similar to a differential. The gear ratio remains the same but the engine and two motors spin at varying speeds. This means that the gas engine’s RPMs are not tightly coupled to vehicle speed allowing it to run at a more constant speed. In addition, it can shut off during periods of low power demand. Here is a site that goes into detail about how the Prius works.
    Click on the “Understanding your Prius” link. Although this site only covers the first generation Prius, the principles remain the same, only the numbers are different in the later models.

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