PSD Functioning

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This may help you understand the PSD Toyota Prius - Power Split Device

 

The PSD is a simple planetary gear set with fixed gear ratios. Because of this the torque split is also fixed. The power ratio is varied by controlling the speed of the various parts: Power is work per unit time; work is force times distance; for a given torque, faster equals more distance for a given time, so more power.

Tom

 

So I read that the three devices are always connected. So does that mean that the IC engine is always connected and thus the electric must turn it in addition to pushing the car forward when the gas engine is off?

If it does ever disconnect, how is that done? I did not see any part to do that in the breakdown on some of the sites of the PSD. OTOH a dealer mechanic indicated the IC engine could be disconnected when not in use but he did not mention the mechanism.

Ray

 

It has a clutch to disconnect it when needed.

 

This is patently wrong. There is no clutch anywhere in a Prius.

MG1, MG2, and the ICE are always connected. MG2 is also directly tied to the drive wheels, so it turns when the wheels turn.

At lower speeds the ICE does not need to turn when it is not in use. It remains connected to the PSD, but MG1 spins backward to keep the ICE from needing to move. This technique is elegant and works well up to the RPM limit of MG1. Eventually, at speeds in the mid 40s, MG1's speed is limited to avoid damage. If you limit the speed of MG1 while increasing the speed of the wheels and MG2, the only option is for the ICE to start turning, which it does. It costs a little energy to freewheel the engine, but it avoids clutches, synchronization, and all of the associated complexity.

Tom

 

We are talking about Prius PSD, not the Volt. Volt has 3 clutches.

PSD stands for Power Split Device which is basically a planetary gearset. Splitting power from the gas engine is well known. What is not so well known is that it is also a Power Blending Device (PBD). The same hardware is able to blend the power from the gas engine with the electricity motor.

PSD used as PBD is more pronounced in Prius PHV with the bigger PHV battery.

 

Call it what you want, but it disengages the ICE from the PSD.

 

See 8:40

 

It looks like a clutch, it can slip like a clutch, but there is nothing there to engage or disengage it. I think it is just a safety device to prevent damage to the transmission if the engine backfires. Maybe it could be called a torque limiter.

 

Warning: I am not an automobile mechanic or an expert on planetary gears. I'll agree that it looks a lot like a clutch plate in an assembly, but I believe you are wrong to say it disengages the ICE from the PSD. In fact, the ICE is integral to the PSD because there is no mechanism to separate the ICE crank from the PSD. The difference is that the ICE doesn't connect directly to MG2, so it doesn't ever actually drive the front wheels. The ICE's output powers MG1, one way or the other, and assists MG2 in turning the chain that drives the wheels. (Whew! Sounds a bit like a conductor explaining what drives the little engine that could.)

That sounds about right to me. I think there is no way for the pressure plate to let go and allow the clutch plate to move. It is all part of the flywheel assembly, I think, and appears to be a torque dampening device, if anything.

(Where are those engineers who really know how this thing works?)

 

The instructor in the video calls it a clutch a couple of times, see the 6:00 mark. Seems like a waste to have a clutch disc and flywheel if it doesn't do anything.

Some Prius clutch discs for sale:

Prius Clutch Disc Search

The AC compressor has a clutch, so there is at least one clutch on a Prius.

 

I don't think that is correct. The ICE drives the planetary gears, so it can directly drive the wheels. See the video around the 6:00 mark.

 

According to the paper from Argonne, it's a torque-limiting clutch. RobH and a priori are correct; there's to way to disengage the clutch, it's always connected, and will only slip to protect the system.

So, if you pay attention to any of the other parts of that video, you'll notice that it is quite possible for the ICE to run when the wheels don't move, or the ICE to be stopped while the wheels are moving, or the ICE to be spinning but not use any gas when moving at a high speed; and no clutch is used for this. Disconnecting the engine from the wheels is accomplished electronically by using the motors in combination with a fancy set of gears.

 

i would call it a shock absorbing plate. clutches can actually spin. this plate never goes out of rotation from the inputs and outputs it's attached to. it will only shift back and forth so abrupt stops from the ICE and changes between regen and assist are not as intrusive to the driver. it also probably limits wear on the whole system.

 

the ICE does not directly power the front wheels. MG2 is technically the only thing that sends power directly to the wheels. the ICE relies on MG1 to work. they both rely on MG2 to determine the final speed while MG1 determines the load on the ICE... so the ICE is last in the list of things although it's definitely #1 when it comes to power source as all power comes from gas... unless you're always driving down hill..

 

The clutch in the Prius is a safety devise. It’s always engaged
as told in the video above. With the ECVT transmission there is no
need for a clutch. It’s for protection of parts only. So, there is no
engage and disengage. It’s always engaged.

 

That's the Transmission Input Damper, according to the diagram on page EM-89 of the 2006 service manual. It limits the torque that the engine can deliver to the transaxle - basically it starts to slip if the torque exceeds a threshold level, but below that level, the plates are locked and the input shaft revolves at the same speed as the engine's flywheel.

I note that you stole that image from ArtsAutomotive.com. The paragraph immediately above the image reads:

"There is a sort of clutch-like damper assembly between the engine and transaxle, but it only provides a little damping, no actual clutch like action."

Source: Prius 1st gen - Replacing Transaxle

I name thee troll.

 

For God sake!
Maybe you want to make up some of your own , but Prius PSD does not have clutches.