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

And for 2010, traction control is much less aggressive. This could be a coincidence, or it could be that getting rid of the chain reduces the need for protection.

MG2 has a fixed ratio connection with the drive wheels. There isn't really a risk of over-speed with MG2, unless you also have over-speed with the tires.

You don't want an instantaneous off switch: that's what causes spikes. They key is to keep the electrons flowing, and for that semiconductors are plenty fast. Generally we use snubbing diodes, freewheel diodes, and metal oxide varistors to do the job.

Tom

 

Chains have been used by other transaxle manufacturers for years, such as at least gm and ford.

 

In the small percentage of gen2 HSDs that have had problems, I have never heard of a chain failure. I don't believe that the chain was a weak point of the mechanical design. Eliminating the chain reduced mechanical losses, size and weight of the HSD.

JeffD

 

OK we have a theory that changes to the hsd made it more robust so there is less need for an overly aggressive traction control, vsc, or what ever the electric nannies are. Part of this improvement may have been removal of the chain.

I don't really understand what the mg/electronics issue is, only that it has been brought up as a reason why the TRAC needs to protect the drive train. Its hard for me to believe that MG2 would fail when a wheel catches. It would just slow down. MG1 seems are more likely culprit, but again, I would expect that you could build it beefy enough to handle the stresses. I also agree that rapid changes to voltages and currents can be taken care of with elecrical hard ware. The question is does the prius have this hardware.

But that is a question, do we not have failures because of the aggressive "traction control". I don't think the chain is really the reason. Is the HSD in our gen IIIs strong enough to give us an off switch to the traction control? After all this discussion I'm beginning to think that the software might have been put in place to protect some weaknesses in gen II, and toyota just doesn't give us an off switch because switches cost money.

 

Do you have a reason to believe that brakes are not used actively in Prius TC?

So far as I am aware selective application of brakes to transfer power away from wheels that rotate much faster than others because they have lost traction is what defines Traction Control. I.e.: Without it you don't have TC.

This is pretty much how Toyota describes TC here. Traction Control – Truck Safety. They also mention reduction of engine power which makes sense because in this situation, excessive power is likely to break traction at the other driven wheel(s) and may perhaps cause other problems.

 

actually traction control is defined as reducing wheelspin. In some of the earliest (and less costly) versions, this was (and may still be) accomplished via power reduction: be it changing the timing, fuel delivery, or throttle position. Brake application is a second (more complex/expensive) iteration. I don't know what the prius uses though...

 

Prior to the Gen III, none of the Prius have selective brake application traction control, only power modulation. Anecdotal evidence, and some Toyota statements, indicate that this is also true with the Gen III. Until we see positive confirmation that this has changed, it seems likely that the Prius only modulates power without applying any brakes.

Tom

 

Overspeed is not the only source of concern.

Exactly.

Yes, but the diodes are not field replaceable parts, are they ?

 

Do you have the torque-throttle graph for the Prius ?

Clutches are excellent at smoothly transferring torque from the engine to wheels.
The Prius' TC can't match that.

 

Diodes, not fuses. If the diodes act like fuses, someone doesn't know how to design snubbing arrays.

Tom

 

Yes,diodes. Voltage spikes are a major cause of failure.

... or doesn't know how to protect an HSD from damaging electrical transients.

 

OK guys, how about agreeing that yes there are ways to make the car electrically robust enough to handle a spinning wheel getting traction. I'm going to stay out of the implementation discussion.

Given that it can be done, and I think we all agree that it can, what is being done. Do we know what electronics are in the prius to protect the motors, inverters, and batteries? If we did then we can reasonably debate whether they need the additional protection of TRAC and VSC.

 

That's a good question. All motor control circuits contain some method of dissipating the transient spikes that occur during normal operation. Undoubtedly the Prius has those. The big question comes down to unintended transients, and this is where the engineers and marking people have to make compromises. Most engineers want to design for the worst case, but that usually isn't cost effective, so they end up designing for the likely ones, fully understanding that freak conditions will cause failures.

I don't have the schematics for the drive system, so I can't offer any analysis. Even with schematics, we wouldn't know the dielectric characteristics of the motor windings, so there would still be a lot of guesswork.

Tom

 

Simple, when releasing brake, MG2 applies what is called "crawl", a 600W power to the wheels, forward (D) or reverse (R).
I wonder your clutch is even more smooth than that.

 

Nope. But i am not talking about the throttle, i am talking about the power/torque with the creep feature while you're touching the brake. It's that creep feature that allows you to start rolling before you go anywhere near the "throttle"

When was the last time you tried to get a manual, 3000lb car rolling, up a hill with two inches of compacted ice/snow with the revs set at 1,000 to stop is stalling? Ever? I am not even talking about traction control, i am talking about it's ability to apply very small very controlled power so the DRIVER can maintain the traction as the surface permits.

 

A lot of people confuse power with torque.

How well does the Prius' TCS control torque ?

 

Let me put this way, I don't feel that I'm confusing power with torque. I know the difference very well. I brought a value of power sent to MG2 when in crawl mode from a stop, simple.

About the second answer, I'm willing to learn, so I don't know the answer. Never the TCS performed in my car.
From MPOV, if it performed perfectly, it was not discussed as it is.

 

I'll try again. I AM NOT TALKING ABOUT THE TC SYSTEM. I am talking about driving away very slowly in a controlled manner on ice/snow.

 

I liked the answer "throwing the windings all over the place" as why you don't want to bypass traction control.
I guess that the Prius has enough torque to twist the axles in half if the power weren't controlled. All car manufacturers make compromises or design for various reasons (cost, weight, complexity), and can't over-design components for every situation. Has anyone disconnected the TC and tried a pair of slicks on the front of their Prius? You know, "drag racing"! Probably a very bad idea. My brother was twisting VW axles in half with his turbocharged motor... I could do wheelies in my VW, but I didn't make the kind of HP and torque he did!

I think people's skill levels are all over the place. Turning off TC would not help most people. I drove a twin turbo Mazda RX-7 R1 all over the mountains around Taos, NM with high-performance all season tires. It had a limited slip diff.
You learn how to slip the clutch and use the power judiciously. OTOH, I enjoyed "drifting" it on snowy roads.

People can talk all they want about tires and how snow this and studded that will let a Prius climb a mountain, but what do you do when you are caught in a snowstorm with the OEM tires? I wanted some momentum to help me up my driveway and I got next to nothing; then it just seemed to quit trying. That was unacceptable to me. As I said in another, related thread, I have driven crappy FWD, non-TC cars up our drive when others could not. To not be able to claw my way up the drive in the Prius was a bummer.
Thankfully, my STi snow tires fit right on my v five. Just had to go get 12 X 1.5 thread pitch lug nuts.

 

Yes the TC appears not to transfer torque from the spinning wheel to the opposite wheel. That is what happeed to me , the spinning whell sits there spinning slowly while the opposite wheel never moves.