01-13-2008, 03:35 PM
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Active Enthusiast
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Real Name: Pete Berry
Hybrids: '06 Highlander 4Wi Standard, 34,000 mi
Posts: 59
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Re: How much max power really goes to the rear wheels?
Quote:
Originally Posted by Don R
"MG1 and MG2 can be considered an electric torque converter. MG2 has copious torque at low RPMs where the engine is weak on torque. Thus under heavy acceleration, the engine is allowed to spin up in RPMs quickly, generating power in MG1 which immediately converts into high levels of low RPM torque from MG2 to get the vehicle moving quickly and more efficiently than a conventional hydraulic torque converter. In this mode, the engine is trading its horsepower for MG2's torque. MG1 and MG2 also play the role of continuously variable transmission as they directly control the engine RPM for optimal efficiency at all speeds and power demands without the need for shifting gears and clutches found in a conventional transmission.
Keep in mind that whenever the vehicle is being powered forward under engine power, both MG1 and MG2 are always energized and double-converting power. Neither motor can take a break while the engine is providing power, as the gearset will then freewheel and power will cease flowing to the wheels.
When the vehicle is cruising at speed under light engine power, a different more efficient operating mode engages that is not described in the diagrams I provided. Rather than MG1 generating power and MG2 immediately supplying it back to the planetary gear set, the reverse occurs. MG2 generates power and MG1 immediately supplies it back as mechanical torque. Since MG2 has an extra gear reduction of 2.478 to 1 in its connection with the engine than MG1, it needs to generate less power to oppose the engine torque during steady state cruising. This reduces the amount of double power conversion taking place (mechanical -> electrical -> mechanical) for higher efficiency operation at a steady cruise.
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Thanks again for your detailed explanations; I think I finally have the big picture down now. One final question: how efficient are the new motor-generator designs in the various mechanical<--->electrical conversions taking place? My 70% figure must have come from much older AC genset designs.
Pete
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