Transmission Slipping

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Just bought an 07. Engine Loud when accelerating, Engine sounds like it's reving high...slipping

 

Think of the ICE as a constant-torque device -- always producing
around 75-85 newton-meters. Almost like keeping your foot at a
constant, fairly high throttle setting in a manual transmission but
then having an infinite selection of gears to throw it into to
control RPM. Up hills, your RPM would climb, right? And on the
flat you'd need to bring really low to just tool along at a steady
speed. That's pretty much how Prius throttle-control and the
relationship to the transaxle works, except at various boundary
conditions.
.
_H*

 

<div class='quotetop'>QUOTE(jon2223 @ Oct 20 2007, 05:38 PM) [snapback]528258[/snapback]</div>

HMMM.....was going to say its your driving method/pedal method and not used to the Prius CVT feel and sound because my 07 is kind of like that in that if I punch it a little hard it will over rev much more than a usual auto before it really gets going but its gets going really quick. I'm very pleased with this car's acceleration. But your 2005 does not have that problem? Thats not good. I would let the dealer look at the 07 and at least check the trans fluid level. Its free. They might not do it cause there lazy and will discount whatever you say so I would lie and say you smelled burnt auto trans fluid smell now & again. Good luck and post follow-up please.

 

<div class='quotetop'>QUOTE(jon2223 @ Oct 21 2007, 03:25 AM) [snapback]528387[/snapback]</div>

I also have the '07 Touring purchased in Feb. and I think I have felt the same thing you are. It seems that if I hit a hill going at, say 55, there is a lag time and loss of speed, even with increased pressure on the pedal, before the car responds. I have so far attributed this to my inexperience in how much acceleration to apply and when to apply it. I find that if I enter the same situation at 65 mph the car responds far better. I recently got a Scangauge and am watching the RPMs in these situations. I very seldom will floor it. What I have learned to do is to anticipate the upcoming hill and give it a little pressure just prior in order to maintain speed, then either back off just a little on the down side to maintain the speed if the road is flat, or maintain the increased RPM if another hill is approaching. Am I making any sense? I guess what I'm saying is it is not a problem with the car, but a matter of my learning how to better use what it is capable of doing. Since getting the Scangauge, I can see visually when I am being too easy on the accelerator. If I'm going along at a low RPM, or with ICE off, it takes longer for the engine to respond to my request for more power. I find the Scangauge II really helpful in this situation, and you might consider getting one to help you out. For me it was well worth the money spent. But I'm still learning and I hope what I'm describing makes some sense to you.

 

*Horsepower* is all about how fast you lift the weight, by
definition. Power is torque * RPM. If you want an assload of power
on tap to get up a hill fast, you're going to have to wind it up.
If, on the other hand, you'd like to keep the drivetrain on an even
keel and in its most efficient range, you'll wind up adopting a
method in which you push a *little* harder as you hit a hill but
not be at all bothered if you slow down a bit on the way up. You'll
make it up on the backside, but in a way that again doesn't let the
system become inefficient. That returns the best fuel economy, and
there's nothing wrong with the "rollercoaster" aspect -- trucks do
it mile after mile every day.
.
_H*

 

<div class='quotetop'>QUOTE(jon2223 @ Oct 20 2007, 04:38 PM) [snapback]528258[/snapback]</div>

If I remember correctly, the touring model has larger diameter tires than the standard model, 16" versus 15". This would require a little more torque, 1/15 = ~6.6% to sustain the same motive force. Going up a hill would be one of those peak torque situations.

An interesting experiment would be to see if 14" wheels could fit on a Touring Prius. This should give an increase in effective torque over stock Touring wheels, 2/16= ~12.5%, due to the shorter moment arm. Such a car should be pretty quick in acceleration, beat the 10 seconds to 60 mph, and scoot up hills quite nicely.

What sort of battery level were you seeing? Was the AC on at the time? I believe that under maximum acceleration the NHW11 ICE will disengage the compressor and add extra horsepower to the available battery power. This would give the impression of a sudden boost in power.

Bob Wilson

 

<div class='quotetop'>QUOTE(jon2223 @ Oct 21 2007, 03:25 AM) [snapback]528387[/snapback]</div>

I just realized after reading this post I have never driven up a hill since I bought this car. Not one hill...not even a small hill...I miss Vermont. Sorry..never mind me.

 

<div class='quotetop'>QUOTE(bwilson4web @ Oct 21 2007, 09:29 AM) [snapback]528423[/snapback]</div>

Not necessarily. It's the overall diameter of the mounted tire that matters, not the diameter of the wheel. With a given vehicle type, larger wheels are usually accompanied by lower profile tires, so the overall diameter comes out the same. I don't know if this is the case with the Prius touring model.

Tom

 

<div class='quotetop'>QUOTE(qbee42 @ Oct 21 2007, 11:22 AM) [snapback]528493[/snapback]</div>

According to this tire size calculator, the standard Prius tires rotate 850.3 revolutions per mile and the Touring Prius tires rotate 851.0 revs per mile. The difference of less than one tenth of one percent is insignificant.

 

<div class='quotetop'>QUOTE(qbee42 @ Oct 21 2007, 11:22 AM) [snapback]528493[/snapback]</div>

From a physics standpoint I dont think that would be entirely true. Wouldn't you expect to need more torque to rotate an object who's mass has moved farther away from it's axis point? For example; a 15" wheel has more of it's mass closer to the hub and because the 15" tire has a greater sidewall height so it's mass is more spread out and closer to the hub. A 17" wheel would have it's mass spread out farther from the hub and the tire itself is much more concentrated (shorter sidewall height) and it is farther from the hub.

I'm not great at physics but wouldn't this apply?

 

<div class='quotetop'>QUOTE(F8L @ Oct 21 2007, 04:36 PM) [snapback]528528[/snapback]</div>

What you are referring to is an object's radius of gyration, which is another measurement similar to center of gravity, center of effort, and so on. The radius of gyration is the distance for which the rotational characteristics of an object would be the same if the object's mass were replaced with a hoop of the same mass at that distance.

As for it's effects in relation to a tire and driving torque, the following apply:

1) The object's mass and radius of gyration are only related to torque when changing the angular velocity of the object. There is no steady state effect, other than that associated with frictional losses. In other words, it takes more torque to get a larger mass or larger radius of gyration spinning, but you get that back when you slow it down.

2) The tire and wheel's radius of gyration is not directly related to the size of the wheel or tire profile. It's the total distribution of mass of both the tire and the wheel. The type of wheel, material, size, tire profile, tire materials, and tire weight all contribute to the mass and radius of gyration.

There are other effects related to mass and radius of gyration, such as gyroscopic effects and unsprung weight. While these influence driving characteristics, they are not directly related to the torque.

Tom

 

<div class='quotetop'>QUOTE(IsrAmeriPrius @ Oct 21 2007, 02:43 PM) [snapback]528513[/snapback]</div>

Good point! I had not included the 'profile' height.

Bob Wilson

 

Hmm, the touring option may affect this... but the bigger point is that the "slipping clutch" feeling is completely normal in all Prius. Unlike conventional cars the engine RPMs are not directly related to the car's speed. The engine winds up as needed to provide the power called for. Don't be afraid to hold the pedal on the floor when passing or going uphill: the engine may roar, but it cannot harm itself.

 

<div class='quotetop'>QUOTE(jon2223 @ Oct 21 2007, 02:25 AM) [snapback]528387[/snapback]</div>

Does this happen when you have the cruise control engaged or only when you are driving without it?


<div class='quotetop'>QUOTE(Neicy @ Oct 21 2007, 06:12 AM) [snapback]528409[/snapback]</div>

Same question for you, Neicy: Does this also happen when you have cruise control engaged?