Prius Traction Control Complaints on the Rise

Once we reach age 50+, at least for many of us, we really should not be considered "layman" insofar as driving a car is concerned.

"..resurgence....RWD..."

"..Not because of better handling for the layman in slippery conditions.."

Agreed.

Many "layman" never even encounter seriously adverse roadbed conditions. Plus for those of us that do they generally exist only a small portion of the year. So for the clear majority the FWD vs RWD decision is a non-issue. And nowadays with VSC and TDC (Traction for Directional Control) along with tire studs the issue rarely comes up.

But I'll stick with: leave the entire front traction coefficient allocated to directional control and the "driving" forces at the rear.

 

If I remember, I'll try that on the ride home tonight and get back to you on the RPM. Remember this is drive-by-wire, there's no cable from the accelerator pedal to the fuel injection system. The CPU can decide what RPM the engine should run at to meet what it thinks your intentions are. Most of the time the intentions are pretty clear, but if you have both the brake and gas down all the way, I'm not sure what the engineering management decided to do in that case, but it's not wide-open-throttle.

 

There is nothing I can ad with regards to your revision. I've never performed this action on a slick surface like ice so I don't know what would happen. I have tried this on a drag race track and there was zero tirespin and other than instant forward motion nothing else changed. My 0-60' time did not seem to change.

 

Not sure the test requires a slippery surface. The post "implies" that the ICE revs well above idle prior to brake release.

 

Here is where a little knowledge is a dangerous thing. Correlation does not necessarily imply causation.

Up to the early 70s gasoline and steel were cheap, there were no cafe standards, and RWD ruled because there were advantages in handling.

Then came oil price spikes, imported econoboxes, and cafe standards. FWD weighs less and has fuel economy advantages for similar costing, similar interior sized vehicles. Air bags and crumple zones also made the cars safer but more expensive to repair. Torque steer is still a problem with FWD, and this is being worked on. The better handling in snow was a nice benefit with the change to smaller more fuel efficient cars, but it is not why automakers did it. The best handling cars are still rear wheel drive.

 

The post would be correct then. The engine is not at idle speed when performing this action. From the sound of it I would expect it to be over 3,000rpm. Because we are not working with a standard transmission, releasing the brake at this rpm will not result in a tire spinning fury like it would on a non-hybrid equipped with a manual transmission. Everything is much more subdued. I've never looked at the scan gauge to verify the RPM but it is definitely well above idle.

 

Do you realize that might mean Sike's incident was completely valid.

If, for some reason, the engine ECU did not know the Prius was already in motion the system would DRIVE the car even with the brakes fully applied.

"..Everything is much more subdued.."

Probably not.

These is no torque converter and the operation of the PSD is about as close to a manual transmission as one can get, no "slippage" in the drive train. So it seems to me that at ~3000 RPM the Prius would must definitely LURCH forward when you release the brake due to the dethottling delay plus the mechanical inertia of the ICE and the MGs.

 

No, I'm not sure it would. Could you please explain thoroughly how you think this would happen?

In the mean time I just went outside and captured video with my phone to show you how this works and how it is safe. I'm uploading from my phone to my laptop for editing.

 

In summary: with the gas pedal at WOT and with the brakes fully applied the Prius ICE will still rise well above idle....~3,000 RPM.

Let's assume, something, whatever, even a floor mat trapped gas pedal, was causing the Sike's Prius to be UA. If the engine/transaxle ECU had no roadspeed input signal the brakes would have NO EFFECT. Frictional braking would work, as it clearly did, but the HSD system would sustain the ICE RPM at a high level, DRIVING the front wheels, not go into regen mode.

 

Yes, it's SAFE, but only as long as the engine/transaxle ECU can reliably detect, sense, that the car is motionless.

 

Ok, thanks for the explanation. The only hitch with that idea is that the brakes will still stop the car even if the car is in motion.

The video I made for you will be up in a few moments.

 

Front wheel drive was not originally less expensive, nor was it as durable as rear wheel drive. It was hard to build a cheap, durable transaxel, which is the real reason front wheel drive wasn't common in the old days.

Rear wheel drive remains popular in performance cars because of handling, but that's not the whole story. There is also the expectation that performance cars will have rear wheel drive, which makes it hard to market anything else. A similar thing happed with multi-engined aircraft when Cessna introduced the Skymaster. The Skymaster had twin engines, located in-line at the front and rear of the aircraft. It was a far superior arraignment over conventional twin-engined aircraft with the engines on the wings. The problem was that it wasn't sexy. Any serious multi-engined pilot wanted to demonstrate his manhood by flying a "real" multi-engined plane, not a Cessna "Mix Master". It didn't help that the Skymaster had fixed gear, but still, it was a good product that suffered from a weak image.

The same is true with performance cars. Part of the package is mystique. Performance drivers want to wear driving gloves and drive rear wheel drive cars. If performance were really the overarching issue, they would drive all wheel drive cars, as demonstrated by the now banned all wheel drive race cars.

Never underestimate the power of image and customer expectations.

Tom

 

I thought it had already been well proven, accepted, that with a FWD car the brakes cannot overcome both the engine drive torque AND the vehicle inertia if already moving at, say, 60+

That appears to be why Saylor could not regain control of the Camry.

 

Completely false. We have enough factual evidence to this up. I even stated above that I have done this at approx. 100mph. I performed the same emergency stop in the video I am uploading but at much lower speeds since this is a residential area.

 

That seems like pure speculation. Do you have examples of similar FWD cars being more expensive than similar RWD peers. FWD did have durability problems and handling problems. Many of these have been solved. It is harder to dial in good steering feel when those same wheels are powering the car.

RWD cars are built with RWD because they handle better and people perceive they handle better. That seems to be a good story. Ford is trying to put steering systems in place that compensate for torque steer in the focus. VW has done a good job on steering feel, but let us face it, a vw does not handle as well as a rwd bmw. If they cost the same to build and had the same fuel economy, ford and vw would be building more rwd cars and not trying so hard to compensate for the short comings. I'm not sure what you can say about your little story. The skymaster was around before I could fly, but it had pretty questionable design. I don't think you can learn lessons from a failure if there are multiple reasons for that failure.

Or they may actually want the car to perform. The Japanese engineers of the vitz/yaris freely talk about the rolly polly handling. This is fine in a car of that class, but you wouldn't say the vitz or prius handling would be acceptable in a sporty car let alone a sports or luxury car.

for your reading pleasure about what makes a great handling car. Note this does not mean it will handle great on snow or on a mountain trail ;-)
http://www.caranddriver.com/reviews...merica_for_less_than_100_000-comparison_tests

 

The Cessna Skymaster...

Early problems were that the rear engine would "die" during taxi and an inattentive pilot would attempt a takeoff without knowing an engine was out. Solved by adding a warning light.

Second problem was the lack of efficiency of the rear engine due to the fusilage "shadow".

By the time I came along, was able to afford one, the Skymaster had retractable gear and I seem to remember a P-337...

I wasn't at all bothered by the "manly" issue, just attracted by the simpler licensing/insurance/flying aspects.

But ended up buying a T-210.

But I don't think RWD vehicles really have a "weak" image.

"..If performance were.. all wheel drive cars.."

Which "AWD" ? There are literally a myriad of choices out there in the marketplace today.

My preference will always be R/awd...

But the VC in my '01 R/awd Porsche C4 isn't really ever robust enough to say I have "AWD". Same with our '01 F/awd RX300, practically non-existent VC, relies on TC (along with INSTANT engine dethrottling) for F/R torque distribution. Our '92 R/awd Ford Aerostar is our go-to vehicle when the going gets slippery.

The Honda/Acura SH-AWD seems to be the best of the best insofar as sideways engine mount is concerned. The Porsche (base, V6) Cayenne or the 4Runner for R/awd.

 

Engine WOT, ROARING at 100MPH, FWD, (NOT-Prius***) and you had enough braking to bring it down to a stop in a reasonable distance..?

Hard to swallow.

*** In a normally operating prius at highway speeds the Prius' HSD would NOT "drive" the front wheels with the brake applied. My statement involved the WOT engine actually DRIVING the front wheels.

 

So you are creating hypothetical scenarios instead of what is actually occurring in simulations? If so I cannot help you there. I don't like thought experiments that cannot be backup up with real experiments.

 

This at least shows how the force charge mode works and does not induce tirespin.

 

Both in the Saylor incident, with Mrs. Smith, and even with Sikes, the indications are that even with full/hard braking the engine (ICE/HSD) continued to DRIVE the front wheels so hard that the braking could not overcome the inertia and the DRIVE enough to even slow the vehicle, let alone bring it to a stop.

But of course a properly operating Prius will NOT continue to drive the front wheels when the car is in motion and braking is used.