Slight “Sudden Acceleration” in the Prius II in slow speed turns?

xcel · #1 08-22-2006, 08:08 PM

Hi All:

___While speaking with the Cherney’s at the Milwaukee Hybrid Group meet last weekend; they both mentioned something that I would call strange which has happened in their 2005 Prius II more then once while turning corners at slower speeds …

___What they described was a slight acceleration while going around corners and both have felt the sensation of acceleration with their right foot completely off the accelerator at different times. I thought maybe they were up around 41 mph on an on/off ramp like scenario and the ICE was brought to life as the injectors lit off after fuel cut with accelerator input but this is not what they described. This sudden but slight acceleration appears to happen at much lower speeds (10 - 15 mph) and not all the time but just once every few weeks or so. They asked if I had ever heard of such a thing happening in other Prius II's and I said I had not but would look into it for them.

___Looking over some of the Prius groups, IIHS and NHTSA reports, and general net searches did not really yield anything other then 2 instances and one was where a Prius II’s CC appeared to lock the Prius II into a WOT mode. The driver used the brakes to bring it to a stand still and then Powered it down but that is not what the Cherney’s are describing here.

___Has anyone ever heard of or possibly have a link to a similar description, discussion, or possibly TSB about a similar situation wrt to the Prius II? What they described to me does not sound dangerous given the slower speeds and just a hint of acceleration but a simple and slight acceleration when none was expected would concern me as not being normal as it has them …

___Again, this has been felt by both and/or one or the other alone in the car more then once if that helps clarify that it appears to be a very real scenario … They will be reporting the incidents to the Toyota dealership on their next service but I was just wondering if anyone else has ever heard of such a thing and maybe we can help them out beforehand?

___Good Luck

___Wayne

TonyPSchaefer · #2 08-22-2006, 09:34 PM

I can't think of a situation in which I can recall experiencing this but I will certianly be paying more attention in the future.

Perhaps on topic, perhaps off: there are times when I'm coming to a stop with my foot lightly on the brake and I feel as though the car lurches. It's sometimes to the point that I have to hit the brake harder which makes for a jerkier stop and the occational "?" glance from the passenger.

xcel · #3 08-22-2006, 10:08 PM

Hi Tony:

___Could it be something like the Prius II’s tranny creep coming in a little earlier or at a higher speed then expected from what you have experienced? Maybe that is what is going on given your description?

___Good Luck

___Wayne

CitrusInsighter · #4 08-22-2006, 10:32 PM

I have never experienced anything like the Cherneys mentioned, but I often feel a bit of a lurch as I am gently coming to a stop. It feels as if regen braking has stopped and you really have to push harder to get the friction brakes egaged and come to a complete abrupt stop.
If you use heavy pressure throughout your stop, the lurch is almost unnoticeable.

brick · #5 08-23-2006, 06:50 AM

In Tony's great description of entering a Glide in the Prius-II, he mentioned that it could almost be mistaken for acceleration as you exit regen and enter the free coast. Could it be that they are crossing a threshold at low speeds, perhaps depending on other factors, where regen cuts out even with the driver's foot completely off the accelerator? Now that I read up the thread, that's pretty much what CitrusInsighter is describing.

I guess it would be a little much to ask someone to check what the energy monitor's arrows are doing at the moment they think the car is about to accelerate out of control?

FireEngineer · #6 08-23-2006, 02:42 PM

Brick you are correct, Justin is finding the regen kick off at the 7 MPH threshold.

And the Cherney's problem could be exactly the same. The speedometer and the MFD both have a hysteresis between what they show and what is happening. And that hysteresis is not the same bewteen the two.

So as the car turns the speedometer may show 10-15 MPH but is likely less if they are decelerating into the turn. The MFD may show ICE on or show stealth power but the car could have been transitioning to glide due to less demand for power or transitioning to friction brakes only since the speed may have hit the magic number of 7 MPH, hence the feeling of going faster.

So they are feeling the actual condition of the speed and hybrid system but see something different on the MFD and speedometer. This is a common question/complaint by Prius owners on other boards. Only time it usually scares people is when they have cars infront of them at a traffic light and the car goes to friction braking the car lets go of regen and gives that "speed-up" sensation.

Wayne M

xcel · #7 08-23-2006, 03:47 PM

Hi Wayne, Tim, and Justin:

___Thanks for the differing responses as this my indeed be what they are experiencing. I know the transition you are speaking of but never felt it as acceleration, just a transition. Although they are not members here that I now of, I will make sure they receive the link and hopefully it gives them the explanation they were looking for …

___If not, I will try and get a hold of them by phone directly for even more clarification.

___Good Luck and thanks again to you all.

___Wayne

Gerbil · #8 08-25-2006, 06:57 AM

Thanks to all for your thoughts on the subject of the Prius lurching while stoping. I think Tony S's theory is what we are talking about, if it is normal, I guess we will have to deal with it. We will moiitor it more closely to see what is actually going on.

Thanks Wayne for putting the question out, and we are members now.

TonyPSchaefer · #9 08-25-2006, 07:47 AM

"Gerbil"?

Cute and cirious at the same time.
And how will we know which one posted so that we know which internal voice to use?

phoebeisis · #10 08-25-2006, 01:02 PM

I haven't really noticed it, but I wonder if you could get a little jolt if the ICE kicked on in response to their AC needing more current than the battery was programed to give at that state of charge.It was summertime when it happened.
Still, I suspect I would feel more of a little jerk than actual acceleration.Oh well,Charlie
PS -Everyone has noticed the little jerk you get in a normal car when the AC comes on, and the RPMS go up.At full blow with the ac on ,the Pilot does 15 mph-no ac it is more like 7 mph.