How is the ICE Cupled to the PSD?

<div class='quotetop'>QUOTE(OutOfHere @ Sep 22 2007, 09:38 PM) [snapback]516391[/snapback]</div>

Bolted to the ICE flywheel is a torque limiting device that looks like a clutch plate but it is fixed, never open. The plate has some small springs, just like a regular clutch plate, but these help moderate the power pulses. Under high power conditions, the torque limiting device can slip, like a clutch plate, to limit how much torque goes to the PSD.

From the torque limiting device, the ICE power passes via a shaft that is welded to the PSD, gear carrier. This planetary gear carrier holds the spider gears between the center sun gear and the outer ring gear. The sun gear is connected to MG1 and MG1 provides the counter torque for the engine power. When MG1 has no power applied, it rotates freely and no ICE torque or power is transfered to the ring gear.

The power from the ring gear passes via a chain to the rest of the gears and to the differential and wheel shafts.

Bob Wilson

 

Here's a real neat "PSD simulator" that lets you see the rotational speeds of the various components (sun gear, planetary gears, ring gear, planetary gear carrier, etc.) under various conditions: http://www.wind.sannet.ne.jp/m_matsu/prius...index_i18n.html

It's great for visualizing what's moving, how fast, and when. Cool stuff. B)

Yep, the planetary gear carrier remains stationary when the ICE isn't running (so while the planetary gears remain in their respective positions, they still spin in-place to transmit rotation between the ring gear and sun gear). Very ingenious in its elegant simplicity.

This slideshow at the University of Michigan says it was TRW that developed the PSD concept and Toyota developed its practical application by putting it in a hybrid car: http://www.engin.umd.umich.edu/vi/w4_works.../Miller_W04.pdf

It is indeed way cool!

 

Is there any sort of "brake" to prevent the ICE or electric motor from turning when they're off? E.g., if you're in stealth mode is the ICE held still?

 

<div class='quotetop'>QUOTE(alanh @ Sep 23 2007, 12:54 AM) [snapback]516459[/snapback]</div>

When the engine is stopped, it looks like there is a brief power pulse to MG1 to de-spin the engine. Testing with "N"-"D"-"N" reveals a slight shudder if the ICE comes to a stop on its own. Once stopped, compression drag is enough to keep the ICE from spinning.

When considering the possibility of making an EV Prius, one excellent approach is to weld-up the ICE shaft so MG1 and MG2 can be used to power the wheels. For details about one effort:
http://www.99mpg.com/ProjectCars/evinsight/

Bob Wilson

 

<div class='quotetop'>QUOTE(bwilson4web @ Sep 23 2007, 08:58 AM) [snapback]516512[/snapback]</div>

Just to clarify Bobs excellent description, the "brief power pulse" is actually there to stop the ICE in one position only. If it misses, you can feel it retry. I've felt mine try as many as three times (car is still new, so I surmise it's more difficult to get to one position due to engine stiffness).

 

<div class='quotetop'>QUOTE(David Beale @ Sep 23 2007, 12:44 PM) [snapback]516528[/snapback]</div>

Interesting! Does anyone know WHY it the HSD designers want the ICE stopped in the same position all the time?