Engine RPM oscillates/surges between 0 and ~1300 at ~0.3 Hz?

Discussion in 'Gen 2 Prius Technical Discussion' started by 2009Prius, Jan 18, 2011.

  1. 2009Prius

    2009Prius A Wimpy DIYer

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    I noticed something strange about the engine RPM in two separate trips today:
    (Note: the graphs are wide and may be shrunk by the web page but can be shown in full size separately if you click on each graph)
    [​IMG]

    [​IMG]

    As shown in the graphs the RPM oscillates between 0 and ~1300 at ~0.3 Hz. In both times when it occurred I had to do a "pulse" (as in pulse and glide) to come out of the strange state. When it occurred the second time I turned down the radio to listen to the sound of the engine to make sure it was indeed revving and not just a bug in my PriiDash(TM) software. Internally the RPM is reported by one of the ECUs at about 14 Hz. The graphs are plotted at 1 Hz but also keep track of min and max during each 1 second period. I do have the raw data saved so a high resolution graph can be generated if interested.

    It was snowing and both times I was going slightly down hill. Before it happened the second time I noticed the traction control warning lighted up briefly, but it was off and no other warning lights were on during the time period of the strange RPM oscillation.

    Could this be the traction control going out of control (in its effort to rev up the ICE to prevent the MGs from over-revving)? :rolleyes:

    Anyone seen this before?
     
  2. bisco

    bisco cookie crumbler

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    was it indeed revving audibly?
     
  3. uart

    uart Senior Member

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    That certainly does look odd 2009Prius. Can you tell us roughly what speed you were going and what was the SOC on the traction battery at the time.
     
  4. pEEf

    pEEf Engineer - EV nut

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    I have seen this pattern during "limp-home" mode, when the HV ECU decides to lock out the battery. It's always accompanied with a DTC's and lots of lights.

    You can cause it simply by unplugging the battery ECU in the rear.
     
  5. donee

    donee New Member

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    Hi 2009...,

    Its seems unlikely the engine was going was 0 RPM, then 1300 RPM, then 0 RPM and so on every 2 or 3 seconds. The mass of the rotating components precludes such a change in RPM that rapidly.

    This like something like a loose connection, or a missed interupt in the computer logging program, or corrupted data in a packet. Where the 0 RPM occurs when the connection is open, or an interupt was missed, and the RPM was not logged, or the RPM value in the data packet was corrupted/miswrote.
     
  6. 2009Prius

    2009Prius A Wimpy DIYer

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    Yes the sound of the engine matches the up and down of the RPM reading.

    Here are graphs with more parameters plotted:
    [​IMG]

    [​IMG]

    Thanks! Though as you can see in the updated graph above there does not seem to be anything out of ordinary about the HV battery: SOC, temperatures, max charging and discharging currents all seem OK.

    The ECU may be reporting "target" as opposed to "actual" RPM. Do note that I heard the engine sound going up and down in sync with the read RPM values. So I think this is real phenomenon, not data/program error.

    To all: any other ideas welcome! :)
     
  7. pEEf

    pEEf Engineer - EV nut

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    Yeah, I tested my car by unplugging my BMS (Battery ECU) from the CAN bus. The engine immediately cranks and then revs like you mention. It is also accompanied by the Radiator fans running on high, even though the engine temp is @ less than 60 degrees F.

    So you have no DTC's, correct?

    I wonder if this could be a sticky throttle body?

    What frame are you reading RPM from? 3C8? (348 is target)
     
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  8. 2009Prius

    2009Prius A Wimpy DIYer

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    I don't know whether there is any DTC or not. I haven't tried to read any yet. At least there is no warning light and the car runs fine. I will see if I can read it.

    When the weather gets warm I can check the throttle.

    RPM is from 3C8. So that's the actual I suppose?
     
  9. pEEf

    pEEf Engineer - EV nut

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    The lack of a red triangle tells me there is no serious DTC, though it wouldn't hurt to check.

    3C8 indeed contains RPM reported from the ECM.
     
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  10. 2009Prius

    2009Prius A Wimpy DIYer

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    Thanks! Is it just a matter of sending "03" and see what's coming back or is there some more steps to check for all DTCs thoroughly?
     
  11. planetaire

    planetaire Plug in 20 kWh 85 km/h or > 208km range

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    Hi 2009Prius

    Your graph look like one i published two years ago:

    [​IMG]

    In this graph you can see:
    -accelerator pedal in yellow (multiply by 20; max 50%)
    -speed in green (max 23mph (35 km/h), in ligne 394)
    -Rpm in blue (pid 3c8) (max 1300rpm)
    -Injection in red (pid 520, a slow one)

    Duration 45sec.

    Initial Ice temp was 72°C (161°F)

    This appened when i was just starting and the traction control detect slipery condition at a very low speed on a muddy road. When this appened the accel pedal was at 50% so the Engine goes on.
    In line 170 you can see that the speed seems increasing from 5 to 10 km/h (3 to 6mph). But in fact it was only the front whell speed not the car speed.

    After these 45 seconds everithing was back to normal.

    :)
     
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  12. 2009Prius

    2009Prius A Wimpy DIYer

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    Thank you so much for the independent (and much earlier) confirmation that it is indeed the traction control going out of control! :) I will still try to read DTCs just for the fun of it but I am quite certain now it is just one of the peculiar behavior of our Prius cars. Thanks again! :)
     
  13. 2009Prius

    2009Prius A Wimpy DIYer

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    Update: I went back to the raw data and plotted the speed of the four wheels - sure enough there was a large mismatch between the front the rear wheels that would trigger traction control in each of the two occasions:

    [​IMG]

    [​IMG]

    The weird thing was that the RPM oscillation starts at a time long after the speed mismatch has diminished (i.e. traction control off). I saw the same thing on the dash lights: the traction control warning light went on, then off, and some time after that the RPM started to go up and down repeatedly while no warning lights were on.

    Another funny thing is that the vehicle speed reported at 3CA is very jagged compared to the wheel speeds. I will change the speed reading to the average of the two rear wheels from now on.
     
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