Help me understand what I'm hearing

Discussion in 'Gen 2 Prius Main Forum' started by sas0611, Apr 4, 2008.

  1. sas0611

    sas0611 Member

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    I know this is probably a normal sound of the prius hybrid system but maybe someone could explain what it is and when to expect it.

    Yesterday was the first day I actually drove my new prius in center city conditions. Before that it was pretty much suburban usage. I also didn't have any radio or climate control on so I was able to hear everything the car was doing.

    When creeping along in traffic the car would repeatedly emit a sound that I can best describe as a very tame whirling/ratchet sound starting a a higher RPM /pitch and slowing to lower RPM/pitch. When it occurs, it lasts for about 1.5 seconds at most. It wasn't loud and with the radio on or road noise I don't think I'd have heard it before. Since I was on pretty smooth streets and running a low speeds I did hear it and have to assume it was always doing it to some lesser degree but now in stop and go situations it was occuring more frequently and in the quiet... will you get the picture.

    Watching the power flow screen it seemed to correspond with the times when I applied the brakes while the traction motor was delivering power to the wheels. The state switched to recharging the battery when I applied the brakes obviously.

    I am assuming that this was regenerative noises that are normal but since braking didn't always cause this sound I was just wondering if in fact it is normal, what exactly is the system doing, and what algorithm or situation elicits it. When the energy flow screen already had the battery recharging and I applied the brakes the sound didn't occur. I think it was just during the state changes from delivering power from traction motor to delivering recharge to battery but I am just guessing.

    Thanks in advance for the explanations and hopefully the reassurances.
     
  2. qbee42

    qbee42 My other car is a boat

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    Whirring sounds, like those on a subway, are the traction motor. The ratcheting sound is the brake accumulator pump. The power brakes on the Prius use an electric pump for pressure, and this pump runs every few applications of the brakes. The ratcheting sound will come from somewhere forward of the driver's footwell.

    Tom
     
  3. David Beale

    David Beale Senior Member

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    Probably the brake booster pump, which is electric.

    Read the owners manual. There are two facing pages that deal with sounds you will hear. What they say basically is that -any- sound you hear is normal. ;)
    I found this part of the manual the best part. Humor in an owners manual! Who would have thought!

    Also listen for the coolant transfer pump when you shut the car off. If you listen closely you can also actually hear the engine stop and start. And you can hear the inverter high pitch squeal. I haven't yet heard the A/C electric pump, but I'll bet some have.
     
  4. prius729

    prius729 New Member

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    I can't recall ever hearing something like this. Only thing that comes to mind, similar to your discription, is after shutting down the car I hear whirring noises coming from the front of the car. Which is normal, according to the manual.
     
  5. hobbit

    hobbit Senior Member

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    In this case, from the description, most likely the brake pressure
    accumulator pump that runs periodically to top up the >2000 psi
    fluid reserve.
    .
    _H*
     
  6. sas0611

    sas0611 Member

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    Thank you to all who have taken the time to reply to my post. I'm glad I found this site. I've learned so much from other owners here and it has helped me to better understand my new vehicle.
     
  7. hill

    hill High Fiber Member

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    As stated above, theres no vacume pump for brakes, so an electric 'whir' happens when the system recharges itself.
     
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