Re: It's official. Manual transmissions are making a comeback.


That has a drawing of a "conventional" (Honda-like) CVT that made me think the article was all wrong. It's a paragraph or two later that it explains the Toyota PSD, but even then the picture is wrong. It looks like the MG1 and CE are slaved on a single shaft.

<http://home.earthlink.net/~graham1/MyToyotaPrius/Understanding/PowerSplitDevice.htm
That made interesting reading. Doesn't cover all of the operation, but I can fill in the rest... MG1 must be the "starter motor". MG2 supplies regen braking. But I think I understand it now... The oddities are compromises. It all makes sense.
The Honda Charge/Assist displays what I expect it to display. When I floor the gas pedal, the assist goes full, and stays there. Because the IMA has a power peak at 4000 RPM, I would really expect the bar graph to drop off some above 4000 engine RPM, but maybe that's literary license for the masses, who wouldn't want the graph to reduce while demand is full.
In the Escape, flooring it gives near full assist for a little bit, then swings to charge. That confused me, but it is clearer now. That only happens at higher speeds. (I actually went out and drove the Escape to test my new thoughts.) It is because MG2 is tied to the wheels, and has a peak power at some road speed. I might guess that it's 47mph, where the EPA highway test runs ;-) It is above thirty, and less than sixty. At about 10mph, going up a steep hill, flooring it leaves it at full assist, like I would expect, for the duration of my little test run.
The Escape ICE seems to go to about 4,000 RPM under almost any enthusiastic "gas pedal" position. The MG2 speed would change exactly as the road speed changed, with good power up to a road speed that I could calculate if I went back to Graham's page. The MG1 RPM would change inversely as the road speed increased if the engine stayed at 4,000 RPM.
I don't see how it relates to the "combined HP" being less than additive between the MG2 and the ICE. The MG2 maximum would be related to road speed. The ICE could be held at its maximum HP, and the RPM of that has little to do with the RPM of MG2. The MG1 output would be lower as ICE went higher, so there would eventually be some electrical starvation as the batteries depleted, but it seems that you should be able to see maximum MG2 horsepower added to the maximum ICE horsepower, at least for a few seconds, and maybe only at one particular road speed.
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Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8,-122.5
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Yep - forget about that site. It's pretty messed up. It also describes the SHS as having two 67 hp motors, while MG1 is about half that capacity.

MG2, and regen braking is almost exclusively MG2. Reverse is MG2 all the way. When driving, MG1 is primarily responsible for controlling the engine load (virtual gear ratio), and it is in that role it operates as a generator.

MG1 to MG2. That part limits the power of the system because the power can only be counted once. For example, if you have a 100 hp engine and a 50 hp motor, but at full power 20 hp of the motor output comes from the engine through MG1 (rather than from the battery) the total is only 130 hp.
Mike
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I had heard that. But at stall, that's 94 HP, isn't it? I've heard of people getting stuck in potholes, because they couldn't move forward and didn't have the power to move backward. I was trying to decide how I could test for that.

I've heard that this power arrangement, where MG1 is draining power during highest power demand, is due in part to the battery not having enough of an amperage rating to drive MG2 at full power, but I wonder about that. Maybe it just isn't efficeient to run at full power from the batteries for very long, due to the total amp-hours available, and a balance has been found that is more efficient.
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Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8,-122.5
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As with all cars, it's zero hp at stall (any force times zero distance). However, the full electric torque is available. The torque is considerable - 295 ft-lb compared with the rated 82 ft-lb from the engine - so the stories of getting stuck in potholes are urban legend. (But note the torques aren't directly comparable because of the effect of the power split device... the electric provides something like 2/3 of the torque at the wheels.) At any rate, I can attest from our 40K miles experience with a 2002 model it just isn't a problem.

that the hybrid computer gets the command from the accelerator and brake pedals to go so much or stop so much, and it calls on the engine or batteries to make it happen according to the hybrid computer's programing. For example, in the earlier generation if more than 9 KW was needed the engine would fire up. In the current generation it is some slightly higher figure I don't remember.
As far as the generation by MG1, it is easiest to think of it as the way it provides the prescribed load to the engine. That's how the "ECVT" does it thing.
It certainly illustrates why the "ECVT" can't be replaced by a manual transmission. The engine is a resource of the hybrid computer and is only under the most indirect control of the driver... about the way your heart rate is under your control. I can floor the accelerator with the shifter in "park" and hold it there. The engine gradually revs, reaching a peak of 2250 rpm in a couple of minutes. Imagine trying to shift that arrangement.
Mike
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I have an Escape, so the "2002 model" caught me off guard there. The getting stuck part is being written as first hand in the Edmunds forum.
It is said that applying throttle slowly doesn't work, because of overload sensing. I have gotten "stuck" in a small ditch on my property. I seemed stuck, but I had read the posting, so I got "more aggressive" with the throttle. I might go try it again, with a normally cautious application of power, and see if the motor gives up.

I had toyed with the lack of response, but hadn't held it there...
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Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8,-122.5
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older Toyota Hybrid System (THS), like in our 2002 Prius, the hybrid computer handles wheel spin in an unsophisticated version of traction control. In snow for example, we just push the throttle down somewhat and the system does a sort of slow ABS in reverse, cutting power for perhaps 1/2 second when it detects wheel spin. It works well for slippery starts and slippery hills. Apparently the Synergy Hybrid System (SHS) Toyota has made since 2004 MY (and licensed to Ford for the Escape) responds by shutting down power completely at ordinary throttle settings, leaving the driver sitting until the throttle is either released or floored. I'm told the behavior at full throttle is what I'm used to at any throttle setting. I don't think I'd like the new way, and I don't know why Toyota changed the hybrid computer program. I'd think having the accelerator floored when finally getting to good road surface could be unsettling.
What surprises me is that the hybrid computer could be programmed for the most intelligent way of handling wheel spin. The computer tightly controls the MG2 speed; why isn't it programmed to calculate the friction it encounters and adjust to the best torque for the conditions? It could even be programmed to rock safely out of a hole, something that is forbidden to the driver in the Prius (and many modern cars - my daughter's '93 Accord expressly forbids it too.) It would require a special "gear" (selection on the shifter - there are no gears anyway) and some lines of code but it would be a boon. It could be far more effective than even the most experienced driver, because it could control torque instantaneously and map the friction contour of the hole as it worked. Maybe someday....
Mike
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