<div class='quotetop'>QUOTE(Russ Yost\";p=\"96309)</div> Russ: Well, no, not really. It has to do with how the planetary gear sets and their shafts relate to the sun carrier gear. The planetary gears will just spin. The problem is that any attempt to post a diagram or to explain it in this forum will only produce more confusion. Once you see a demonstration sun/planetary gear set, and play with it a bit (How do you think budding engineers or mechanics learn? They have to take things apart to "play" with them), it should become easy to understand. Clearly this is one obvious case where "book" learning is woefully inadequate. You really do have to see the sun/planetary in action, to see why one can turn when the other doesn't or free-runs. The URL that Frank posted is a useful learning tool, as you can play with the sliders to see how the motion of the carrier shaft, the planetary gears, and the sun gear relate to each other. Jay
<div class='quotetop'>QUOTE(Frank Hudon\";p=\"96304)</div> Frank: I bet that wasn't very often. With decent maintenance a sun/planetary appears to last forever. They're actual gears, no chain stretch or belt slipping or any of that. Only a manufacturing defect appears to kill them early. It appears the 4L80E used in some 2000-2003 GM 3/4 and 1 ton trucks (Not the Allison 5 speed, the 4 speed 4L80E used with the 6.0 V8) had a defect where the teeth would fracture off the planetary ring. The truck would come to a stop rather quickly. It wouldn't matter how often you serviced the automatic, it will fail without warning. Jay
Sorry guys, but assuming that MG1 is not actively controlling the power transfer, if enough power is being fed in from the ring gear, it could push the planetary gear carrier. It all depends who is applying the most force to counteract the spin attempted by the ring gear: the ICE or MG1. I agree, MG1 is most likely to give, but ICE could still turn spontaneously.
If anybody is curious, Oak Ridge National Laboratory took apart a 2004 Prius and did a lot of investigation on the Hybrid Synergy Drive system. This document is 602 KB and is in pdf, so you'll need the free Adobe Acrobat reader to view it.
Oh, forgot to mention they discuss the actual power splitter Acrobat pages 17-21. There is also an ORNL document on thermal management in the Prius motor/generator, but at 9.2 MB it's too large to upload. The forum refuses it.
<div class='quotetop'>QUOTE(\"DanMan32\";p=\"96430\")</div> the ratio of reduction thru the planets is probably very near the max torque that MG1 can absorb from the ring gear. I say near as I've not got one apart to count teeth and see what the reduction amounts to. Also there is no published Kwh for MG1 so it's going to be an estimate on the amount of power it's capable of absorbing. As a guess if MG2 is 50hp and the reduction is say 3-1 MG1 should be about 17hp. Normal vehicle starter hp is in the range of 3-5 hp. The planets would much rather spin on their shafts at less than maximum power.
<div class='quotetop'>QUOTE(Frank Hudon\";p=\"97315)</div> Hi Frank: You won't have to, as the engineers at Oak Ridge National Labs already did. I guess they got bored building weapons of mass destruction. According to the file I posted, which is in Adobe Acrobat pdf format, the information is on P.17, actual document page 9. If you need the Acrobat Reader, it's free. You can download it from: http://www.adobe.com/reader I think you will find the ORNL evaluation fascinating, especially the much larger 9.2 MB thermal analysis of the motor and generator. Anyhoo, here are the number of teeth in the Prius planetary gearset: Ring Gear: 78 Sun Gear: 30 Pinion Gear: 23 Figure 2.6 on Acrobat page 19 (Document page 11) clearly illustrates the relationship of the sun/planetary gears: Jay
