Just bought an 07. Engine Loud when accelerating

<div class='quotetop'>QUOTE(smoothburn @ Jun 7 2007, 08:34 PM) [snapback]457704[/snapback]</div>

Yup, all cars with continuously variable transmissions have that "transmission slipping" sound/feeling.


I'm not sure I would agree about it being noisy but the sensation and sounds are a little different than normal.

 

Yes, it's normal. The engine is sending power to the wheels and to MG2 which is generating power for MG1 and the battery may be supplying power to MG1 too. The Energy screen shows what is happening. The HSD system is highly tuned to provide the best efficiency possible consistent with your demand for acceleration (how floored you have the pedal).

Contrary to what wyounger implied, the Prius CVT can not slip, it's all gears locked in a fixed ratio. There's a drive train dampener which is sort of a fixed clutch that is always engaged, designed to modify any shocks from the ICE, but there's nothing in the gear box to slip. Cone-and-belt CVTs can and do slip.

 

What about going downhill using the braking gear? I have had my 2007 for a few weeks now, I love it. I do notice however that going down a 4 mile grade using the braking gear that once the battery is fully charged and I'm just coasting down hill that the generator seems quite loud. If I accelerate the noise disapates until I let off the gas again. Is this expected behavior?

Jim

 

If you are using B gear, it provides engine braking by adjusting the ICE valve timing. Going down that long hill is the exact right time to use B, but once the battery is fully charged and no more energy is going to it, the ICE and friction brakes are doing all the work to slow your descent. The ICE very normally gets loud then.

 

Hi Smoothburn,

Yes, that is normal. Its actually an advantage. Other cars cannot rev the engine high, because the gearing of the transmission limits how high the engine can go at low RPM, and its expensive to put more than about 4 gears in an automatic transmission. If you had like a 10 speed automatic transmission, and floored the throttle, it would switch to a gear with a very high ratio, and the engine would rev right up into a hi power condition. Remember, power is proportional to torque times rpm. With a DOHC engine, torque is pretty flat, so the hgher the RPM, the higher the power. The problem is getting all that high speed power into a car that is just starting off.

This is how a 110 HP Prius can accellerate similar to a the same size car with a 145 hp engine and standard automatic transmission. Not having to pause while gears are shifted helps too. Additional torque from the battery power helps too.