ECCVT system.

I've never felt anything like that with ours, but perceptions can vary. Ask to drive another Prius, just to test the feel.

Tom

 

Yeah, this doesn't sound right. The drivetrain on mine is smooth as silk unless the ICE is switching on or off. The only other time I feel any surging is when it's running at a fast idle in park. It makes me wonder if one of the other systems is screwed up, like maybe one of the hydraulic brakes applying and disengaging for no reason.

 

<div class='quotetop'>QUOTE(BrooksWW @ Jan 31 2007, 07:15 PM) [snapback]383523[/snapback]</div>

Hi Brooks,

Are you talking about the speed surging, or the engine? If the engine is surging, that is normal. The speed stays within a mph, but the engine and HSD systems is constantly changing to control that speed. The engine will surge when allot of power is needed, and then the electric regenration will kick in when the car needs to pull energy out (like going downhill, or being dragged by a truck's aerodynamic wake) to maintain speed.

For example your on a slight downhill at 60 mph, and the car is in electric mode. The road then slopes up. In response the engine will come on and supply allot of power to the front wheels. There may also be an extra burst of electric power as the engine throttles up. The torque reaction of the front wheel drive axles will cause the car to raise up a little bit in the front. Then as you crest the hill onto a level surface the engine powers way back. The cruise control has a very fast reaction time primarily because it has motors. The motors are very quick reacting. It will vary the power requirement as fast as road loads on the car require, and it will use full throttle power from the engine and batteries if needed to maintain the set speed.

Sudden application of full power can cause the nose of the car to move around a little, too. Is this what you are talking about?

 

I have some doubts about this... I wonder if you really feel it or if it is the sound and visual changes that make you THINK you feel it. I don't mean to be dismissive to you, but consider that if it changed 1 MPH in 1 second (and you say you don't see the speedo change so its less than that), than that is about 1/22g (less than one twentieth the force of gravity), which would be a very slight change indeed, probably not detectable in the bumpy environment of a car on a road.

Can you try cruising as a passenger, with earplugs and blindfold on (or just block the MFD and speedo displays), and see if you can still feel it?

 

<div class='quotetop'>QUOTE(KTPhil @ Feb 1 2007, 12:19 PM) [snapback]384056[/snapback]</div>

First time I read this I thought you were saying that the driver should wear earplugs and a blindfold to see if he can sense the surging....

WOKE me right up! and read it again...

Phew.... thank G-d we don't have drivers doing that kind of testing.... can you imagine... :blink:

 

Well, judging by the "driving" behavior by some I wonder if there are those conducting this experiment from the driver's seat...

 

I too have noticed this, normally on the highway when I'm trying to maintain speed. For some reason the car gets into a funk and does tend to surge a little. It's not smooth as silk in this case, and it is somewhat distracting. My parents 97 Camry XLE is a lot smoother in this regard.

I tend to be a somewhat aggressive driver at times, especially on the freeway, and the thing that bothers me the most about this car is the huge lag between coasting and acceleration. When I change lanes and press down on the gas somewhat hard to get out of the way of the guy behind me, the car hesitates. I got honked at the other day because of that.

Dave

 

I got in trouble with a certain now-absent poster when I suggested that there is a lag, so proceed at your peril!

I noticed it when coasting at about 10-15mph (approaching a right-turn onramp), then mashing the pedal (to go up the ramp to the freeway). I could count 1-2 before there was significant acceleration. It is not a total lack of accel, because the electric motor tries its best and is so smooth you don't feel it much. But the lag before the gas engine really kicks in (which gives you the real oomph up the onramp) is noticable, and I've been tailgated after not accelerating fast enough up the ramp. Theories included the change in direction of one of the MGs and the time to rev and fire the gas engine--never settled before it got ugly...

 

I guess the only answer to the lag thing is "don't do that." Maybe not the ideal answer, but smooth transitions are the best practice in any vehicle. It could be that I'm not bothered by this since I came from a manual transmission, and whatever HSD is doing in a "power NOW" scenario can't take any longer than double-clutching to rev-match a couple gears down in the rare instance that it was necessary. (Alas, that was fun.)

The only thing I've noticed is that the Prius seems to go into a different mode immediately after a burst of hard acceleration. I needed to step on it today and for several minutes after it refused to shut the engine down, as if it was trying to be ready for my next aggressive move. No warp stealth, no glide for at least four miles. There could be something going on in the ECU that tries to complement the driving style, rewarding conservative driving with an efficient profile and aggressive driving with a more responsive profile.

With respect to the original topic, Hobbit finally finished a writeup describing his observations of HSD behavior at steady-state. He, too, mentioned something about particular conditions where MG1 kept transitioning back and forth. I wonder we could use that data to reproduce the behavior that started this thread? Here's the page if anyone is up for some fairly technical reading:

http://techno-fandom.org/~hobbit/cars/heat...results-03.html

 

how long ago did you buy it? go back and insist they let you drive another car or they buy yours back.

 

My two cents on my experiences in my plain-Jane '06:

* I have never noticed a surge while maintaining a speed on level ground.

* I have noticed a surge while cruise control is on and I'm going up a hill. (Which is a 'duh' because obviously you need more power to maintain the same speed. But I just thought I'd throw that in.)

* I have never had a delay in acceleration while already in motion. (Changing lanes, passing idiots, etc. is always safe and easy.) I've many a time gone even from deceleration to a rapid acceleration without a flinch. (The joys of congested interstate driving.)

* I have had many a stutter in acceleration from a complete stop, as if the computer can't decide if I really mean it that I want to floor it and juggles through a couple of profiles over a second or two until it finally gets it right.

So when push comes to shove, know what your car can do, know what it can't do, and don't drive like an arse if you know your car can't (or even may just occasionally hesitate to) do what you want it to. Drive safe. Know your car. Drive within its abilities.

For example, I never peel out from a stop sign to nearly cut off oncoming traffic because I know my Prius will occasionally stutter through the first two seconds of acceleration from a stop and I'd really love to not be rear-ended just because I'm feeling impatient and my car decides to act goofy.

 

My hesitation lag is repeatable, and happens when approaching a tight turn and ensuing steep on-ramp at low speed (maybe 20 mph). The conditions to create the lag are:
- coasting at a low enough speed and state of charge that the ICE shuts down for a few seconds (so the ICE is at rest).
- stomping the pedal after making the turn when on the steep ramp.

I think the cause is that it spends a second or so in pure electric mode until the ICE is started and spun up to an rpm that allows it to contribute a significant amount of power. While the electric motor has high torque from zero speed, once underway it contributes less and less as speeds are increased. The ICE produces more and more power as rpms increase (up to redline).

I think this lag situation is happening because this road condition is asking for high power at a speed that is too high for the motor, and too low/soon for the stopped ICE.

Mid-speed electric-only acceleration is not neck-snapping! Remember, for those with an EV switch, asking for too much power kicks you out of EV mode, and this is why.

I have been able to eliminate the lag by selecting B-range when coasting as I approach the ramp. This means the ICE is already spinning when I floor it, so it doesn't have to be restarted and then spun up before producing power.

In those conditions (being tailgated while coasting but soon needing a burst of acceleration), I use B until I am accelerating. As suggested above, I take this just as part of the performance personality of the car and it has become habit.

 

<div class='quotetop'>QUOTE(efusco @ Jan 31 2007, 12:13 PM) [snapback]383330[/snapback]</div>

"B" is wonderful if you live on a mountain like I do. I slip it into "B" on the way down and it holds very near 25 mph until I get to the bottom. You are right about "B" for flat roads, though...