Probably because it doesn't power the car? I know the Gen 2 Prius' MG1 has a power output of 10kW vs. 50kW for the MG2.
According to the media preview materials packet from the February press event in Yountville, CA, MG1 is 56HP(42kW). Wayne
42 kW sounds like an awful lot for any MG1 in any generation. I understood more like 10 - 15 depending on how much heat you can pull out of it at the same time. Well, if/when the right power is determined, you'd have to divide that by maximum RPM [maybe minus some fudge-factor to guess the maximum power point] to determine torque. . Is there some larger purpose for which this figure is needed? . _H*
Most of the documentation I have seen rates MG1 @ 30KW with MG2 being 50KW. Since the battery output is rated at 20KW (Gen II) this is consistent for the scenario where MG2 is being fed from MG1 plus the battery. (Full acceleration) 50KW = 30KW + 20KW. These are short term ratings - I wouldn't think they could do that for more than a few minutes. kevin
My math for the best balance is... Gen2: 50kW(MG2) - 25kW(battery) = 25kw(MG1) Gen3: 60kW(MG2) - 27kW(battery) = 33kW(MG1) Ken@Japan
I also saw the 42kW number at following page. Green Car Congress: Toyota Previews Generation III 2010 Prius Hybrid However, I'm doubtful about the number. As Hobbit pointed out, the 42kW is too much for the 60kW MG2. If the MG1 supplied 42kW to MG2, the 27kW max battery power has to be calmed down to 18kW on the full use of 60kW MG2 power. Otherwise, the MG2 will be overheated or melted down. Ken@Japan
Conversion of power from AC to DC, through the DC parts, and back to AC, is not 100%. In addition, the rating is when used as a motor, not the output power when used as a generator, which is controllable, and proportional to the electrical resistance presented - the resistance to motion increases as the electrical resistance increases, though power output is also dependent on the speed of rotation. Further, power ratings are given by the heat dissipated and are averages. Exceeding the power rating for short periods might not be a problem. (Power is rate of change of energy and temperature is energy, excess power would indicate a greater rate of change of energy than the cooling can handle long-term but whether that is a problem depends on the starting temperature.) Possibly all we've established is that MG1 might be slightly overspecified. It may be that Gen 3's MG1 is rated higher than we expected to help it cope with the 60mph EV speed of the plug-in, which appears to have the same components as the regular hybrid (certainly the listed specifications are the same).
Assuming MG1 is 42kW: 42kW = 56 hp (Torque x RPM ) / 5050 = hp Torque x RPM = hp x 5050 Torque = (hp x 5050) / RPM Torque = (56 x 5050) / 10,000 Torque = 28 lbs-ft This calculation assumes the peak power is at max RPM. For electric motors, it is not the case. Electric motor's torque at max RPM is lowest. So 28 lbs-ft should be minimum.
My simple math does not count any conversion losses. During the EV mode, the MG1 do nothing. It just does free spinning. I've heard that the Gen2 plug-in prototype Prius uses the same MG1 and MG2 as the regular Prius, and the max EV speed is 100km/h. TOYOTA: News Releases Anyway, the max torque of the ICE is 105 lbs-ft and the MG1 receives 29.4 lbs-ft (28% of the ICE torque:mechanical loss is not considered) max. Ken@Japan
