Toyota Suspends Sales of Recalled Vehicle

Yes. Only momentary acceleration, however. No accidents.

Once it happened on the freeway in the fast lane and put the fear of God in me. The other two times I was coming up on a stop sign. So three momentary events in 10k miles. All three times it was brief but definitely noticeable. The freeway event felt slightly longer, maybe because of the high speed (~75mph).

Since I have a lot of experience with cars over years and years of mechanical and restoration work, and in my career I work with advanced electronics, I don't feel that I would have any problem controlling even the most advanced car. Basically, by turning off the cruise control and a/c systems, and by rapidly toggling controls, I was able to almost immediately kick my 2010 Prius Gen. III out of its acceleration state on the freeway. The slow speed events were brief and stopped spontaneously.

I worry about other drivers, though. And, I worry about the potential for a more severe lockup where things like the joystick (gearshift) cease to provide input. (Ever been on a desktop system that crashed but the mouse still moves?)

I know it's painful to admit that this great and wonderfully advanced car might have a problem. The richly synchronized command-and-control systems inside the Prius are a technical marvel, in fact. Unfortunately, it obviously is financially damaging to recount stories that might impact resale values. And, it's a sensitive subject for someone who loves their car.

So, disappointingly, most of Toyota's behavior on this matter has been a snow job, including the exclusion of the Prius in recalls. The excellent reporting of Ralph Vartabadian and Ken Bensinger of the L.A. Times brought this issue into the clear, bright light of day. NEWS FLASH -- It's not the floor mats, folks. Pressing a gas pedal is a pretty basic movement, and hard to get wrong. In my case, and probably in most others, this definitely wasn't the situation.

Toyota's recall is the reflection of the transparency and dedication of reporters pursuing this matter. Ignoring the Prius is a matter of containment and damage control. It's hard to argue that a problem like this in the world's most technically advanced and forward-thinking production car is not a product of computer electronics. They really do not know or understand the root cause of most of the acceleration problems. I don't blame them: It must be tough to troubleshoot, debug and test the complex web of systems that run these things.

-- a1

 

> tough to troubleshoot, debug and test the complex web of systems

Agreed. Particularly when it is almost unreproducible.

 

Our '06 Prius must have a "smart throttle".

Recently, I went out on the free way and at 60 mph floored the throttle and pushed on the brake pedal at the same time. The acceleration was immediately cut and the car began to slow dramatically to a stop. When I released the brake the accelreation returned untill I again applied the brake. The brake application with this car cuts acceleration immediately.

I presume this is why the Prius is not part of this latest recall.

I use two floor mats on the driver's side in the winter time to collect the extra road crud off my boots and have never noticed any possibility of mat/accelerator interferance.

 

I have no idea whether the braking and acceleration control systems on the Prius are independednt, or integral to one another. But this much I know - for fact (ie this is one of the first things they teach you in any advanced/performance driving schools) - there is no engine made that can "over power" a cars brakes. The brakes are THE most powerful thing on a car. So, if they are indpendedent systems, then both would have to simultaneously fail (ie, both braking and acceleration). IMO, such an event where both systems failed at the same time would be EXTREMELY unlikely to happen. If braking and acceleration is controlled by one system, and that system fails, then I can see where such a thing could happen.

But let me be clear - If the brakes are functioning correctly, and you floor the gas peddle, your car will come to a stop. This is FACT. It will not accelerate out of control. Just not possible if the brakes are working correctly.

So without dismissing this as "driver error" (as what Audi did), my logic would say to look for some common control of the brakes and acceleration mechanisms. If there is NO common link between the two mechanisms, then I would conclude the lack of the driver's ability to control acceleration lies someplace other than with the car.

 

If you want to look at an example of software design problems, the Therac-25 machine is a classic example that is used in software engineering courses. It was used for radiation therapy and due to a software bug, hit some patients with approximately 100 times the intended dose and some patients died as a result of radiation poisoning. The bug was due to a race condition that did not appear in testing as it took the operator using the interface at a speed that only occurred as operators became proficient in the use of the machine.

 

Very informative expanation by Mike Dimmick of the UK (over on the Tech side). As you can see from Mike's description of how the brakes on the Prius work, it's pretty complicated and a lot of "fail-safe" mechanisms are built in. I will assume everything said is accurate, but don't know for sure -


"When you press the brake pedal, hydraulic fluid is moved in a piston just as in a regular car. However, in normal use, that piston doesn't then move fluid in the brake cylinders. Instead the pressure change is monitored by a pressure sensor connected to the Skid Control ECU. (The fluid enters a device called the Stroke Simulator, which provides the same sort of feel you expect from the brake cylinders.)

From there, the Skid Control ECU works out how much braking force you want, and asks the Hybrid Vehicle ECU to provide up to that amount through regeneration. The HV ECU replies saying how much it can provide. The Skid Control ECU then makes up the difference, if any, by controlling valves from a high-pressure reserve (the Brake Accumulator) to the brake cylinders, which increase the pressure in the brake cylinders, and other valves from the cylinders to the fluid reserve tank, which reduce the pressure.

The rear wheels are always braked with friction brakes as regeneration only operates on the front wheels (the motors are only connected to the front wheels).

If the wheels lose traction, the Skid Control ECU asks the HV ECU to stop providing regeneration and it modulates the pressure on the wheel cylinders to try to keep the wheels just on the verge of locking up. This is ABS.

There is a variable resistor - like a classic volume control on an amplifier - which monitors how fast you press the brake pedal. If you press the brake pedal quickly, it skips asking for regeneration (the HV ECU can't react quickly) and just applies the brakes. It also applies more force than you asked for - this is called Brake Assist - as it's known that drivers frequently don't brake hard enough in emergencies.

If there's a problem with regeneration, the HV ECU will report no braking effort and the Skid Control ECU does it all with the friction brakes. If the Skid Control ECU doesn't see a response from the HV ECU it assumes no regen is available and does all braking with friction brakes.

If there's a problem with the electronically-controlled braking system, the Gen 2 opened and closed valves to isolate the Stroke Simulator and send the fluid moved by the driver's foot directly to the front brakes only, with no power assistance. There are actually two pistons in the Master Cylinder, both of which are pressed by the rod that the brake pedal connects to, which gives two independent brake lines. One connects to the front left wheel and the other to the front right.

Gen 3 (2010 Prius) improves on this by using the accumulator as a booster and sending fluid from one Master Cylinder piston to the front wheels, the other to the rear. I believe it can keep electronic control of one pair and use driver's effort for the other.

Hopefully this fail-safe mode is never needed, but some people here have experienced it."

 

Yes, cruise control was on in the freeway incident. I probably was going for the pass. But that doesn't explain the slow speed situations.

I've reached the limit of the accumulator boost on rare occasions and/or exhausted vacuum in any power booster, which caused a loss of power assist. In that situation it does take some force to get good braking response. This, by the way, had nothing to do with the acceleration incidents. But it would be bad to have them both occur simultaneously!

 

I just read on MSNBC that CTS Corporation provided the accelerator potentiometers for the Toyota assembly lines that will be shut down in the US. I think a different manufacturer supplies the Prius since it is built in Japan.

CTS Corp., Automotive - Pedal Module Products & Specifications

 

Denso supplies accelerator pedals for all the non recalled models as well as all Japanese production. The Camry Hybrid built in Georgetown has a Denso pedal assembly as well as 25%-30% of Camry gas models built there.