High Pitch Noise

Its probably inverter noise from regenerative braking. I can hear it in my Gen 2 Prius. It is probably the highest pitched noise that the Prius makes.

 

I was out driving today and my passenger commented on the same noise. I said I did not know what it was but the radio can drown it out. Great minds think alike?

 

I went up to Lake Tahoe yesterday. On the way back is a steep grade which I coasted down with cruise control set. The engine was making an extremely high pitched sound. Louder then the revs of the ICE while climbing up. The only way to get rid of it was to apply the gas to kick in the ICE. Battery was 100% charged (first time I've ever seen that since buying the car), MPG was pegged at 100MPG and the displayed showed the batteries in "charging" mode. Was this the inverter? If so, will this cause any damage? I tried different modes (PWR, Normal, etc) to no avail.

 

Forgive me if this has been covered before but why the heck would the ICE be running at all if you going downhill (unless it was charging battery and or the heater was needed)? Not to mention max RPMs? That makes no sense to me.

Peter

 

I think it is done to allow some "engine" braking like on a conventional power system. If the battery can't take anymore charge or is taking too many amps the generator can't brake the car any longer. My 2005 did it on my 3200 feet downhill drive every day. My 2010 does it to hold my cruise control setting down a hill which is a nice feature that I hadn't expected.

 

My 2005 didn't hold cruise, it would just go faster down hill. The ICE usually kicked in before the battery was full, I assume there was some kind of current limit. I like the cruise holding the speed but probably be more fuel efficent if I just let it go faster

 

I think I get it now... the ICE is "spinning" but not actually combusting fuel thus the air compressor simile. Now I am tracking.
Peter

 

We get the weirdest trolls on PC.

 

Correct. To slow down the car (being cruise control limiting speed increase or applying brakes), the Prius will :

• Generate current from the motor to charge the battery, kinetic energy will be converted to electricity then to chemical energy in the battery;
• If the battery is full, this can no longer happen (it would overcharge the battery, shortening its lifespan). The car will make the engine pump air to transform kinetic energy to heat. The engine probably gets less wear from it than the friction breaks would and is build to disperse heat (water pump, radiator). You can force the car to do this immediately by putting into B-mode (regenerative braking will still happen along with engine compression).

Friction brakes (that we usually call “the brakesâ€) are only used on the Prius under a certain speed (something around 10MPH) or if you press hardly on the brake pedal in emergency (and the 2010 Prius now gives you four wheel disks brakes).

 

My son has a new 2010 Prius that is very quiet and doesn't have the high pitched noise - although the cars are the same even to the dollar amount we paid.

The whine you believe comes from the inverter in my new 2010 Prius is incrediblly annoying, especially at the highest pitch.

Can anything be done besides wearing ear plugs, of course?

Thanks in advance.

 

Well, at the risk of being obvious, if one car does it and the other doesn't, on the same stretch of road, it sounds like maybe a trip to the dealer is in order.

 

You can try aging. Loosing high-pitch hearing is probably the best and most affordable solution.

 

Friction brakes must be used anytime the braking need exceeds the regeneration capacity. This limit is easily exceeded with moderate braking at street speed, and light braking at highway speed.

I believe the regeneration limit is 27 kW. Hard braking at highway speed would be around 500 kW.