Traction Control

This is what I find the most annoying with my '07. With any other car I've ever owned, I could rock it gently and get out. The intersections in our area don't get the amount of attention they really need and I have been forced to roll through some of them so I won't get stopped dead in my tracks by the overly enthusiastic TC. Also, I was recently making a left turn with oncoming traffic at a more than safe distance away when, I encountered a very small patch of slush/snow with only one of the front wheels and the car nearly stopped dead leaving my side exposed to the now dangerously close car. This same situation would NOT have happened on any other car I have owned. Instead of braking the spinning tire and allowing the other tire to continue pulling the car along, Toyota stupidly chose to kill all movement. I think this could turn out dangerous and possibly deadly. Just because this is the way the Prius TC behaves or was designed to act doesn't make it right or acceptable. Toyota screwed up and they need to re-think it. Other than this, I'm really happy with the car so far.

 

The rotation speed differential sensing is between the front and rear wheels. Rear wheel rotation is used as the reference. As for braking, my experience differs from yours. I have experienced the traction control on braking that you describe, but I have never experienced any loss of braking action. The switch from regenerative braking to friction braking is obvious, but does not hinder the braking action in any way, assuming the driver continues to press the brake pedal. All that happens is that I feel a little slip, the traction control light flashes, and the brakes work as they would on any normal car. That is why I can not support your assertion that the brake design is defective. Of course I have no way of knowing how the brakes work on your Prius, so I can only work from my own experience. Perhaps there is an adjustment that controls the transition from regenerative to friction.

Tom

 

Sorry, I thought you were asking if any of us had "solved" our TC issues by using winter tires. In my case, the answer is *yes* under most conditions. But as I stated, once the car bogs down, that's it. The front wheels refuse to turn

 

This is interesting in that a lot of folks have reported the overly-aggressive TC had been "fixed" for 06 and beyond.

I'm looking at an 08 but really don't like the idea of getting a car that has the same issues as my 04.

I somehow doubt the dealer would like it if I purposely got the 08 Prius stuck during a test drive, just to see if it is capable of rocking itself out

 

Well, what I have sounds similar to what you describe, except that I definitely can't say that it's just a little slip or that it doesn't hinder the braking action. It feels pretty significant to me, and long (in the sense that as you're approaching a car braking in front of you, and your brakes don't seem to be working, even a short period of time can seem quite long!).

 

I have become accustomed to the traction control and if you accelerate in a controlled manner it's fine once you get used to it.
I have never engaged the ABS in the Prius although I have in my work car(Holden Commodore).

Traction control feels worse than it is because the loss of power is sudden but short in duration, the acceleration at low speed between traction control is excellent up to 25km/h and above that the traction control is not a problem.

I can squeal the inside front tyre right through the turn when making a right turn and not have the traction control engage and cut power. Just throttle control and watching for man hole covers.

 

I have never been able to squeal the tires, even accidently. My Trac wont allow it

 

So has the problem been fixed in the 08's. I'm still not clear???

 

So, it seems to me, that the solution would be for an option that turns off traction control and the electric motor keeping the ICE running. The option could auto disable at 10mph.

 

So I take it that no changes have been made to the traction control system since the 04 model was introduced?

 

Some say yes, some say no. Most have reported for +2006 the Trac is much less sensitive. I can't confirm that as I have not had a chance to drive another Prius but my own

Of course, you also have those who claim [Sarcasm Mode ON] their Prius will charge through 6 ft of snow and ice on bald factory tires [Sarcasm Mode OFF] so it's difficult to determine who is right and who is perhaps wrong

 

I can't say if the traction control has changed or not, as I haven't driven a 2004/2005 car. I can say in my 2007 with Nokian WR tires, the traction control does trip frequently, but it has never been a problem for me. If it's really icy, it usually gets the car moving after two or three tries. I just relax and let it do its' thing. Nobody honks, nobody else gets in a huff. I usually pull away from all other vehicles, probably because the automatic control runs the tires closer to slip than the drivers of other vehicles can. It certainly isn't me, as I just hold the throttle down a bit and don't compensate.

You DO NOT want to disable traction control. The motor (MG2) can overspin MG1 on ice -before- you can react. My own guess is this would only happen when the ICE is shut down.

One possible "fix" would be to allow a condition, either automatic or manual via a switch, that would allow the system to hold the wheel speed at some fixed rate, for "crawling" through slippery stuff, such as mud or slush. But the Prius is not a 4WD, AWD, or off road vehicle, so this probably wasn't even considered in the design phase.

 

This option is not possible. The electric motors are an integral part of the Hybrid Synergy Drive (HSD) system. There is a lot of information on this forum about how the HSD works, and it's well worth reading for anyone with any interest in technology. Boiling it down to the case at hand, without the electric motors, running the ICE on the Prius will make the gears spin but little torque will be transmitted to the wheels. The planet gears and sun gear and MG1 will spin, but the ring gear and drive train will just sit there.

Tom

 

I think part of this issue is one of perception. We all have a well developed sense of what a car should feel like. This car is one like no other that has ever been seen. Toyota has done an awful lot to make it feel and act like a "normal" car, but the illusion is not perfect.

There are a number of cases where this becomes apparent. For example, as a previous stick driver, I naturally associate engine RPMs with speed. It really throws me off from time to time that the Prius RPMs having nothing whatsoever to do with how fast you're going. Sometimes I'll be convinced that I'm speeding up or slowing down and find that just the opposite is true. When the car makes a normal transition from electronic braking to mechanical there is a brief period where there is a little less braking. Since slowing down less feels like accelerating, you get the claims of unexpected acceleration during braking. I think that what happens when you hit a pot hole is you may be tripping the "panic braking" mode. In this case I as I understand the car quickly switches from electric to mechanical braking regardless of speed, and kicks in the brake booster. There is a momentary feeling like your brakes went out, and the associated "oh my god my brakes went out and I'm going to die" feeling and then the car stops just like its supposed to.

The TC one is a little trickier. I've yet to be in a situation on levelish ground where the car would not drive it self (albeit) slowly out of a slippy situation. I agree on steep icy hills it could be problematic, but then again there are a lot of cars that would have a problem in these conditions. Just because another vehicle would let you spin the wheels doesn't mean it would drive up the hill My parents live on a big snowy hill, so they drive subarus. TC isn't supposed to turn your car into a 4wd, its supposed to prevent wheel spin. The TC system on a 4wd is a very different beast. It is designed to be part of the electro-mechanical system that keeps you moving forward in tough conditions. I wish my Prius could go everywhere my Land Rover can, so I could sell the gas guzzling, oil leaking, noisy, smelly but somehow loveable POS :lol: I agree though, it would be nice if they applied more of that learning back to the cars.

I can understand why some would think that the car is doing something unsafe, because it does do some things that feel to us like they would be unsafe based on our perception of what other cars do and feel like. I can see how having the TC kick in when making a close left turn could be actually dangerous. On the other hand, making a left turn without plenty of space when there is any snow/slush/ice on the ground probably isn't very safe in any vehicle. I made one such turn this morning and hit a pot hole, kicking TC in. It was kind of scary, but it was a turn I knew I really shouldn't have gone for. Even so the car picked back up in plenty of time as I floored it, but I freely admit it did scare the hell out of me. I've made a similar close turn in my WRX before and blew the launch (anyone who's driven a WRX knows what i mean, there is 0 power below 2500 rpm). Ultimately I shouldn't have gone for either turn, the car had very little to do with how unsafe the situation was. There are certainly cars in existence with superior handling and traction, but there are certainly many worse as well. That doesn't make the Prius the modern day Corvair.

I don't think the tire issue can be underestimated. Bear in mind that basically by definition low resistance = less traction. The stock tires will almost certainly have less traction than what you are probably used. For many parts of the country this is not really an issue given the limited power of the vehicle. For some parts of the country in some seasons they're probably not ideal.

Just my 2c.

rob

 

This post is spot on. It includes a lot of points that I have felt like making, but haven't taken the time to do. Thanks for the good posting.

Tom

 

as for the tire issues, I am driving on the stock oem goodyears. I live in Northeast Ohio and I find that they perform pretty good in really bad conditions, I tend to only notice issues with them when you have wet road / dry tires or wet tires / dry road (ie go through a puddle and the rest of the pavement is dry or light drizzle to make the road damp but your tires don't really pick up any water so the tires aren't wet)
Anyway mine is a 2007 and I think the TC / and the ABS is amazing especially when in comparison to my wife's 2001 Beetle which has just absolutely horrible TC and even worse ABS brakes.

 

While this -has- been true in the past, it seems the Nokian WR, at least, has turned this on its' head. I saw no decrease in mileage when I put them on, but I did see a very large increase in traction.
Technology marches on!

 

Re: Traction Control and VSC

I do not live in a cold (snowy) climate, however I am an aircraft engineer and the braking system on the prius is comparable (if not better) than the systems recently developed for the new Airbus A380. Also the Australian Prius has Eurpoean suspension, 4 wheel discs and is fitted with Michelin tyres standard.

The systems are designed to stop the car as quickly as the environment you are in allows and VSC if fitted is working in with TC/ABS to keep your car on the correct line through a corner.

Here we have many bad dirt roads (many corrugations) and I have taken my Prius on these roads and have attempted (under controlled conditions) to force these systems to operate, in the effort to "feel" what it is like so I can recognise the effect when it activates to save my life.

The VSC amazingly was very hard to activate and I had to very deliberately over steer into corners and it was extremely effective at applying the right ratio of braking to the correct wheels and even some steering input could be felt.

As for the TC/ABS with a full emergency brake application the car declerated very quickly with hardly any sliding. When it hit a rut I think the VSC combined with it to assist in keeping the car straight. The TC comes into it's own when accelerating away from a stop and on the dirt it appeared to apply just the right amount of thrust if I did not use full throttle. If I slammed the throttle down it was jerking the power on and off with slip, however it eventually pulled away at about the same overall rate.

I found out that if you loose all electrics, they have placed a Backup Power Supply Unit (capacitor) bank near the 12v Battery to provide power for the Brake System Control Units functions.

When it has finally discharged (emergency over) 2 solenoids relax and allow manual hydraulic braking to the front wheels to get you home.

What an unbelievably advanced system.

Just a note that the Airbus brake system electronics is worth Millions.

 

Re: Traction Control and VSC

My 2004 Prius clearly does *not* work like that. If it senses wheelspin on acceleration, all power is cut.

The first year I had my Prius, I quickly found out the limitations of the Trac. Some co-workers wanted to spend a few days at a tourist camp for relaxation/fishing, etc. I suspect what they really wanted to do was escape nagging wives and bawling children, but what do I know I'm happily single

The tourist camp is about 3 hours east of Winnipeg, in NW Ontario. The topography has many rolling hills and bare rock. Once off the highway, the gravel road had a few steep hills to climb.

It was impossible to get a running start, as there was a steep curve before the hill. The co-worker with the Lexus RX330 had no trouble whatsoever. My Prius stopped around half way up the hill and refused to budge. There was zero wheelspin, it just stopped

The co-worker in the VW Golf tdi had to stop behind me, then drive around. He had minor wheelspin when he let the clutch out to go around, but also had no trouble

I backed down and tried a few times, with no luck. Didn't matter if I floored it or used gentle pedal pressure. Finally we used the emergency towing eyebolt and the co-worker with the Lexus pulled me up

On ice the first winter with "all season" tires, when the light turned green, the car refused to budge. Then the light turns red and you have oncoming traffic bearing down on you, honking their horns using a rather famous middle digit gesture

Other cars around me appeared to have little difficulty and were moving with minor wheelspin. Again, it didn't matter if I used gentle pedal pressure, or as some here have suggested, floor it

Note: if one is raised in a winter driving environment, one is taught to pretend there is an egg between the gas pedal and your foot. In any conventional car, SUV, or truck, flooring the pedal on snow/ice is incredibly dangerous

I always use dedicated winter tires in winter driving, and when they finally arrived, they made a huge difference. The studless winter tires still didn't help too much on ice. I finally put on studded Goodyear Nordic winter tires from Canadian Tire, this is the same as the Goodyear Ultra Grip 500 sold in Europe

With the studded tires, I'm fine on ice and the car is very decent in winter conditions driving on slippery ice and snow under 3-4 inches deep. Last winter we had a blizzard at the hobby farm, and I got the PRius stuck in some rutted drifted snow by the highway. Once again, the tires refused to turn

With recent logging activity on the gravel sideroad to my hobby farm, I no longer drive the Prius out there at all. It's just not worth the risk.

I recently purchased a TOyota FJ Cruiser, and it also has VSC and Trac. The Trac works on the rear wheels in 2wd, and on all the wheels in 4wd. If it senses wheelspin on one of the rear wheels, the brake is applied to that wheel. Compared to my Prius, the FJ Trac simply works. Period

What I find difficult to understand is how Toyota engineers could engineer the FJ Trac to be so unobstrusive - and to work so well - and with at least my Prius, to conspire against you in bad conditions.

WIth the studless Toyo Open Country winter tires on my FJ, I don't even have to use 4wd. It will happily push drifted snow with the front bumper, the Trac working to find the rear wheel with the most traction. When it does finally bog down, the rear wheels still turn

 

You should always use your brain's built-in accelerometers to orient yourself under any acceleration, rather than taking any sort of 'cues' from the vehicle. And this goes for any vehicle, even aircraft.