What part of HSD is vulnerable to loss of traction requiring Traction Control

The gearing in the PSD can be damaged. Likewise transients can produce voltage spikes which could damage the electronics. On the other hand, voltage spikes are fairly easy to protect against.

Tom

 

The Prius has loads of torque available at 0RPM because of the electric motor. It would be bad to spin the wheels too fast because if they suddenly caught traction, it could rip the gears.

 

Shock (or impact) loading of the differential gears. Both in the Torque Split device and the normal differential in the final drive gears.

That's my final answer.

 

You can also shock load a conventional open rear axle. Have one wheel on dry pavement, the other wheel on a stretch of glare ice. Floor it, the wheel on ice will spin like crazy

Eventually you will get to dry pavement and there will be a huge shock load on the side gears and case itself. Sometimes it will go bang

 

And that's a bad thing.

 

Cause people don't understand physics. :madgrin:

 

I've always thought the first thing they are protecting against is:
You come to a stop and the engine shuts down.
You try to take off and the wheel/s slip, over-reving MG2, throwing the windings all over the place.

This is because it takes a few seconds to start up the engine, but 1/2 sec. to reach destructive RPMs with MG2 with no or very little friction from the wheels. With the engine running, even at idle, you have to reach very high RPM before damage can occur in MG2, and that takes more time to reach so the HSD can compensate by raising engine RPM.

The second thing they are protecting you (well, your HSD) from is:
You try to take off and the wheels spin up, then hit a dry patch. This shocks the drivetrain, possibly stripping gears etc.

So all this brings up a point I've been harping locally on. As you can see from my location <- (over there) I live in "winter country". We have ice/snow on the roads for at least six months of the year (though intermittently). I have found the Prius to be very easy to drive in these conditions, and the reason is it won't let you slip the tires much. Slipping the tires will polish up the ice/snow reducing whatever marginal traction you may have. -Any- vehicle with lots of power, or with a "quick" accelerator is very hard to drive in snow/ice because they tend to start out slipping the wheels (manufacturers often set up the accelerator so it comes on quickly because this makes a vehicle -appear- to be powerful and consumers like that).

 

Because if the TC is too sensitive (My '04 Prius did NOT have "real" TC but a drivetrain protection algorithm - my '07 FJ has "real" TC) then the vehicle remains motionless

I learned to drive in winter conditions. I knew I had a problem when my brand new '04 Prius came to a stop at the intersection of Waverly and Bishop and refused to move. I almost got nailed by a semi

I tried various studless winter tires, they all helped but glare ice was still a problem. I then slapped on a set of aggressive studded Goodyear Nordic winter tires, that cured almost all of my '04 Prius TC issues

When I sold the Prius, the guy who bought the car didn't want the winter tires. "We have all season tires now." I sold the studded winter tires to a guy who bought a new '07 Corolla.

Kind of funny how the next winter that guy who bought my Prius called me, whining about how "dangerous" the car was on snow and ice. Well, I had tried to warn him, so tough s***

My FJ is like that. It has a very strong V6 and gearing to match it well. It also has "real" TC

Normally, my FJ is RWD. If a rear wheel slips, the disk brake is applied to that wheel. If excessive wheel spin is detected the engine power is reduced

One test my FJ will easily pass - even with "all season" tires - is if the right side of the vehicle is on glare ice and the left side of the vehicle is on dry pavement.

Light turns green, step on gas, Brake is applied to right rear wheel, you hear clicking noises from the electric brake booster. FJ smoothly drives away, leaving other vehicles behind it struggling on the icy patch

Now combine "real" TC with factory studded Nokian SUV winter tires, and you have an unstoppable machine

 

Because most people push on the accelerator when the wheels start to spin (making it worse) when the correct response is to let up on the gas. It's a lot like ABS brakes. The ABS eases up on the brakes to keep them from locking up even if the driver jams on the brakes.

 

I would imagine if anything it's the chain that is unique in the Prius drivetrain over a conventional car. The power split device and diff aren't that different fundamentally from other transmission components. The chain carries a lot of torque at a lower r/min.

-Iain

 

The original poster has a 2010 Prius, which doesn't have a chain in the transaxle. It was replaced with regular spur gears.

 

Has the gear ratio changed much between gen 2 and gen 3 Prius? In gen 2 it is the MG1 that tends to over-rev, not the MG2.

 

Thanks for the correction. It is MG1.

 

Prius is definitely the best car i've driven in snow. Bear in mind 99% of cars here are FWD, Manual box, light weight and with 4 cylinders. "Burning through" the snow doesn't work, and my county has one snow plough. one.

Prius is brilliant, because gently easing off the brake it applies a teeny tiny amount of torque, the wheels don't slip, you build momentum, and then you can accelerate. trying to manually apply that tiny amount of torque with a manual box is almost impossible - if you're on a hill, you're just plain fucked.

 

Are you claiming the brakes are used actively in the Prius' TC ?

 

Voltage spikes and transients are definitely NOT easy to protect against. There's no instantaneous off switch.

 

It's curious why Toyota chose the bicycle chain in the first place.

 

No, not at all. with your foot sat on the brake, completely stationary, the car does not move. As you slowly release the brake, the car starts trying to creep (like an automatic) but because the torque being applied is electronically controlled you can use a very very small amount. Even on packed snow that i could not hope to walk on, the prius gets moving. Compared to a manual box, where you have to set your revs so the engine doesn't stall and then try to apply a minimal amount of clutch so you don't spin the wheels, which is very very difficult, especially on a hill!

If you do decide to floor it, the car's TC did what i expected and cut power to a level that would get you moving but not slip, it did really well.