Quote:
Originally Posted by niky
Aren't planetary gears simply... one gear?
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Hello niky,
I saw MPGranger's post, and I didn't think it really addressed your question.
I'm assuming you know what a planetary gearset is, and you've seen or studied them for aircraft or toys or something. So yes, a single planetary gearset presents one gear ratio.
But for something like an automatic transmission, in general using planetary gears you need one planetary system for 2 ratios, plus you need an additonal planetary set as a reverser. So for a 6 speed transmission you need 4 gearsets.
Matthieu Rihn developed the "
ravigneaux" gearset using 2 sun gears, 2 ring gears and 1 planet carrier. By using clutches and brake bands, you can have 2 planetary gearsets produce 3 forward ratios and reverse.
However, the planetary CVTs that vskid3 was referring to is the electrically controlled "
power-split device" used in the Prius and other hybrids. It is based on the 1970s
U.S patents 3,566,717 and 3,732,751.
-mort