New Owner! Hey, what's with the speed lunges?

Looper, I picked up my prius last Wednesday. Drove about 150 miles home on the highway and it drove beautifully. When I got off the highway, I had to drive down a small incline/hill and when applying the brake to stop, I felt the car lunge. It was quite an odd feeling. The car stopped perfectly but for a split second, it felt like the car was going to accelerate. I don't know if the car was switching from electric to gas or vice versa or if it was something with my braking on a hill. I went down the hill again today, was extremely conscious of my braking, and it did not do it. I think I have about 180 miles on the car now, so it not at all broken in.

Perhaps an experienced prius driver can give us more information.

 

I've noticed the same thing on my month old Prius too..
When engaging the cruise on a slight upward incline there is a slight delay as it engaged and the car accelerates to compensate for the little drop in speed when going up the incline. I got used to it..

Also when going down a hill with cruise control on.. as I depress the brake and the cruise diengages there is a slight acceleration, it's as if the car free wheels for a second before the brakes apply. I got used to that too..

 

i'm thinking it's pretty much a normal scenerio...if i remember, we had that for a while...but as time goes on and the miles pile up...it smoothes out...ours no longer lunges or surges...we just came off our 3rd 6000mile trip over the last 4 years and had absolutely no problems whatsoever...we have about 96000miles overall with a lifetime mpg of 49mpg +/-

 

Hmmmm....OK, can the OP please provide some additional information about what's happening on the MFD, what was the speed, and what the driver was doing during these "lunges"?

I'll be one of the first to say that feeling of entering a glide (even if you don't know what that is, you can still get into that operational state) feels a bit odd (as the regen braking "disengages" it feels like the car is going to accelerate, but the feeling is only momentary.) "Glides" are indicated by no arrows on the MFD if your speed is 41 mph or less.

Entering "warp-stealth" (a high speed glide, i.e., speed greater than 41 mph, but characterized by only yellow arrows on the MFD) doesn't seem to have the same feeling associated with it.

If you're talking about speeds of 41 mph or less and there are no arrows on the MFD, then you're likely feeling a glide.

Without more information, it's really hard to say anything more.

 

I don't remember any lunging, but I picked my Prius up with about 190 miles on it already. The car has always made smooth transitions which I attribute to the CVT.

Just a note: some dealers tell buyers to avoid cruise control during the break-in period (~500 miles). There some interesting threads on the break-in period and procedures which might help you.

 

The only thing I can think of that fits the OP's description is the low-speed transition from regen braking to the physical brakes. On the fairly rare occasion, I have felt this happen. At low speeds (around 7 mph) you may feel an un-nerving "surge" as you apply the brakes. It feels as though the car is not going to stop, but that it will continue going on.

Across the 12 months I've had my Prius, I think I recall having this happen about 3 times. The first time, though, I was a bit spooked.

If this doesn't describe your scenario, please try to give some better description of what you were doing when you felt this "lunge."

 

There are three separate issues being discussed in this thread:

1) Transition from regenerative braking to friction braking - This happens at about 7 mph, and can feel like a slight loss of braking or even a lunge to a new Prius driver. Keep pressing the brake and all will be well.

2) Traction control activation during regenerative braking - Regenerative braking works by making electricity from the front wheels. If the front wheels loose traction over a bump or slippery spot, the traction control system senses it and switches to full hydraulic friction brakes. The short transition scares the bejezus out of new drivers, especially those that tailgate or wait too long before braking. Once again, just keep pressing the brake pedal and everything will work properly.

3) Speed surges while driving - I believe this is what the OP is describing. There are a couple of things going on with this phenomenon. First, the Prius uses a lot of drive-by-wire technology, and the coupling between the driver's foot and the speed of the car feels a little different than with normal cars. It's easy to induce oscillation when making small adjustments with your foot. The second issue involves the complex interaction of the ICE and electric motors. Varying amounts of power are extracted from the engine and motors as your Prius cruises down the highway. The control system does a good job hiding this from the driver, but there is a lot of juggling going on all of the time. On occasion, this juggling will be noticeable, usually feeling like the car is hunting for the proper speed. It isn't very pronounced, but a sensitive driver can feel it when it happens.

Tom

 

Thanks, Tom. I forgot about your #3. That really is more of an oscillation, as I recall, and I've only felt it once. As I recall, it happens right around the 41 mph transition. That's not a great place to be (in terms of MPGs), so I tend to stay away from that speed.

 

A priori makes a good point. At around 41 mph the Prius is in a transition zone. Below that speed the engine can shut down and stop as needed. Above that speed the engine can be unpowered, but it will still spin. As you go back and forth through that speed, the engine may alternately spin up an stop. Try to avoid doing that.

Tom