PSD Functioning

If you have really listened to what the man had to say around the 6:00 mark you would have heard him saying loud and clear that the ring plate applies constant pressure to keep the "clutch disc" always applied. In other words the "clutch" is never disengaged.

 

So called cluch is the torque limiter between ICE and PSD in reality. There is not and active part to disengage the clutch.

 

Toyota calls that the torque dampener. It's not a clutch.

Edit: More correctly the "Transaxle Damper" from Toyota Technical Training / Toyota Hybrid System Diagnosis / Hybrid Vehicle Control Systems Section 4-5.

"A coil spring damper with low torsion characteristics transmits the drive force from the engine. Also, a torque fluctuation absorbing mechanism that uses a dry-type single-plate friction material is used."

"On the '04 and later Prius the spring rate characteristics of the coil spring have been reduced further to improve its vibration absorption performance. Also, the shape of the flywheel has been optimized for weight reduction."

 

This is the Volt's torque damper along with 3 additional clutches.

 

Yes, it definitely follows the same equations that it follows.

Yes, the three power supplying devices (ICE, MG1, and MG2) are all always connected to the PSD. No, because the PSD is a planetary gear set, at slow to moderate speeds the ICE does not have to turn, but can turn to supply extra power if/when needed.

No, the torque damper (or clutch if you want to cal it that) does not disengage.

Call it what you want, but it does not disengage the ICE from the PSD. It is a damper to reduce vibration and shock loads on the trans-axle.

 

Thanks. The video is especially helpful. That is amazingly clever and elegantly simple for what it does.

 

What happens when we shift from Drive to Neutral if the gears are all connected the same? I am guessing

• Input from gas pedal is ignored
• MG2 free spins (no current going in or out)
• Engine idles or stops or free spins depending on warm up stage and vehicle speed
• MG1 is driven according to MG2 RPM and engine RPM in order to cancel out whatever torque coming from the engine such that there is no net torque on the Ring Gear
• Input from brake pedal only drives mechanical brake

Make sense?

 

Correct.

 

This is a little complex don t you think?

 

There is no AC compressor clutch. The compressor is electric (and sealed) just like a home AC or refrigerator. It gets power from the inverter box and has it's own integrated variable frequency drive module.

 

Absolutely.

Volt:


Prius Gen2 (left) and Gen3 (right):

 

Nope, sorry -- wrong on that one too.

Tom

 

99% of mechanics would call the "Transmission Input Damper" a clutch if you brought it to them and asked what it is. Typical clutch with friction disc, flywheel, pressure plate etc. It transmits power from the engine to the drivetrain, definition of a clutch. The amount of slippage is controlled by the pressure plate, definition of a clutch. It allows the crankshaft to rotate independently from the output shaft via slippage, clutch. The "Torque Control Clutch" (SAE terminology) is called a "Transmission Input Damper" by Toyota. It's still a very typical friction disc with pressure plate, therefore it's a clutch.

And what's your fancy name for the clutch in the AC compressor? Even though Toyota calls it a clutch in their repair manual several times?

 

This clearly never happens in the Prius. So therefore people were incline to provide a correction. However, yes you are correct that it is a clutch, even though it does not "disconnect" anything.

In my line of work, I would call it a torque limiter before calling in a clutch, only because most people commonly think of clutches as engaging or disengaging something. But a torque limiter is a clutch, just not the garden variety one.

It's just semantics, but sometimes it makes a difference. Kinda like foot-pound and pound-foot, which I lazily use interchangeably, even though they're different.

I think only the original/classic Prius used a belt driven AC compressor, so I believe it would use a clutch to connect to the engine.

 

Cut 'n paste typo.

 

You are absolutely correct that the transmission input damper contains a permanently engaged friction clutch. In that respect the Prius does contain a single clutch. However, no knowledgeable person would consider the transmission input damper a clutch in the control sense of the word, which is how "clutch" is normally used in the automotive world. The damper is a safety device which allows slippage in extreme conditions. Generally automotive engineers avoid calling this a clutch to eliminate the confusion found in this thread.

If it had one, I would call it a clutch. The current Prius uses a hermetically sealed variable speed electrically driven AC compressor. By using a controllable electric motor to drive the AC compressor, the Prius does not need a belt drive from the engine. This eliminates the need for a clutch, allows for siting flexibility, and makes for a more efficient system. It's really slick.

The original Gen I Prius had a normal AC compressor. That one had a standard clutch.

Tom

 

evpv what is happening wiith you anyway? I suggest you should stop obsessing over the fact that PSD is clutchless. Get over it.Though If you cannot live with that, should you visit a car dealer and look for more clutches in a brand new Prius. Rumors say that there is a clutch behind every button on the dashboard too! :flypig:

 

You can certainly call it a clutch if you want, and technically you would be correct. The problem is when you use such a generic term you confuse people, including yourself, into thinking that it can be disengaged. A clutch is a mechanical device which provides for the transmission of power (and therefore usually motion) from one component (the driving member) to another (the driven member). However, most people think of a clutch as something that can be disengaged. A Torque Limiter is specific type of clutch that in this case cannot be disengaged.

 

So brakes are clutches also. Yes, Prius has four of those.

 

To be fair, the Volt picture includes the differential, while the Prius pictures don't.