All,
Lately, when I press the gas from a stop, the engine revs but response seems really slow - the same feeling of a clutch slipping. This is 2005 Prius II.

Is this my imagination, or has anyone else had a problem with the transmission? Thanks.

Mike

 

I have only experienced this during severe cold weather -15 to 45 degrees. I simply let the car sit for about five minutes at these times, to truly warm up all the fluids, and that stopped it. Not sure what could be causing it a warmer temps...

 

You are experiencing normal Prius CVT behavior (specifically Prius CVT). Engine RPM is not directly related to ground speed or acceleration. In addition, there is no possibility of slippage in the Prius because all components of the drive train are always locked together and engaged, even in neutral. There are no clutches, no torque converters, and no fluid couplings.

There are plenty of web sites out there that explain how the Power-Split Device works, how the components of the electric drive system interact with the engine and so forth, and of course plenty of posts here and other Prius bulletin boards. The only reason I do not try to explain here in detail is due to the complexity of the subject. In short and oversimplified terms, the power-split device is a planetary gear pack which integrates the 3 motive sources of the vehicle together. Those motive sources include 2 motor/generators (MG1; smaller, low torque and high rpm and MG2; larger, high torque, lower RPM). They are motor/generators because the computer system will alternate their purpose based upon numerous conditions from braking to high speed driving, low speed driving, acceleration, etc.

The sensation you are feeling is probably related to the computer system telling the ICE (engine) to run faster to allow for both forward motion and increased generation capacity. I notice this sensation when climbing hills at highway speeds and increased torque is necessary. Since the ICE provides so little torque relative to MG2, the onboard logic might actual use the ICE to spin MG1 creating power which is then consumed by MG2 to provide massive torque.

I do not agree with letting the car sit to "warm-up". This is highly inefficient and will tank your fuel economy even more than normal cold weather driving. The oiling system inside the electric drive section of the car is a low pressure drip and slosh system. Unlike an auto tranny where fluid is essential to shifting and drive, in this system, transmission fluid is for lubrication purposes only.

 

Thanks for the background, guys. That explained a lot and eliminated some suspicions (mechanical slipping, transmission fluid). However, since I only noticed this recently, I have one more thing to check out. This roughly correlates to when I installed the aftermarket EV-only module. Maybe it's messin' with the computer even when it's off and the battery is full. I'll pull it out and see if anything feels differently.

Mike

 

I seriously doubt that an aftermarket EV switch is at fault here. All Prii come from the factory with the same logic and control system. The EV switch you installed did nothing more than access a part of the car's existing programming which is already there but not accessible in stock North American market vehicles.

If you have EV mode engeged and floor the accelerator from a stoplight I believe you will hear the car chime or beep twice and the ICE will fire up and off you go. In addition, if you drive around in EV mode to the point that the battery needs charging the vehicle will disable EV mode and return to normal driving and will actively work to charge the battery to a more acceptable level. The car has safeguards on top of safeguards for protecting battery state of charge to prolong the battery's life. It is highly unlikley that activating EV mode with any aftermarket kit has had any effect on your vehicle's performance.

But don't let EV mode convince you that you are saving loads of gas. Remember, the electric power you are using comes from predominantly one place, the ICE and to a lesser extent regenerative braking. Pushing EV mode to its limits often times hurts Prius fuel economy because the car is compeled by programming to recharge the battery if it starts approaching the lower SOC limits. You might find yourself idiling/charging at a stop light after extended use of EV mode. That probably eats up any gains you might have had when using EV mode.

Have fun.

 

I've experienced this same slippage in several Priuses in the past; the easiest way to reproduce it is to come to a stop, then, just after you reach below 7mph, hit the gas. I've experienced it plenty of times and that's not the only scenario I've had it happen, but it's the easiest way to hit it if you're curious.

I'd guess given the mechanics of the Prius that it's obviously not real "slippage" like you imagine in a typical automatic (with sheering transmission fluid), but rather one or more engines is spinning in the wrong direction, and the "slip" you feel - the delay in getting any accelleration - is the engine(s) getting everything turning back the way it should again.

 

Hi Mike,

Do you have some way to setup a small, digital camera and record this behavior and one that works? Many digitial cameras have the ability to record a 60-90 second mpeg and documenting the behavior would be very helpful.

Do use a tripod so once you trigger the camera and point it so you can get both the 'Consumption' and MPG display.

Alternatively, if post everyone who has seen this, post how you reproduce it. A clear set of instructions is the key.

Bob Wilson

 

I'm not certain you can get any extra info from the dash - there's no tachometer or anything like the new Lexus (which is very cool to see in there by the way).

Instructions:
1) Drive until the gas engine kicks in.
2) Brake moderately (not lightly like a hypermiler would do, but not a sudden stop either)
3) When the speedometer hits the single digits, hit the gas moderately (again not lightly like a hypermiler)
You can feel the engine get a bit confused. In some cases you'll actually brake a bit harder for a second when you hit the gas, then startup slowly. In other cases you'll just notice no acceleration for a second or 2, then things start moving forward.

The delay I admit has always worried me just a little, since it might be right when I need to get out of trouble. Knock on wood.

 

Cold (first 5 minutes) or warm?

Bob Wilson

 

Hm, interesting question. I've really never considered it before. It actually happened to me last night within the first 5 minutes of driving, but it was closer to the end of that 5 minutes. Perhaps cold - but I'll keep that part in mind as I drive the next few times and if it happens, let you know how far after the car start it was.