Electric motor engaged while at a stoplight

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by 8AA, Mar 20, 2005.

  1. 8AA

    8AA Active Member

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    From time to time while I am sitting at a stoplight, I'll glance over at the Energy Monitor and see that the electric motor is engaged. I'll press on the brake pedal a little bit more and the energy flow will turn off. I wonder how many Prius owners are sitting at lights thinking that they are holding their cars stationary with their hydraulic brakes, when actually the electric motor is contributing as well.
     
  2. paprius4030

    paprius4030 My first Prius

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    I've noticed this also. I always thought that it was just the screen and pushing harder on the break tripped some micro switch somewhere to get the scrren to react. Is it really the electric motor engaged?
     
  3. peart75

    peart75 New Member

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    yes, you must press firmly to turn off the electric motor.

    -drew
     
  4. prius04

    prius04 New Member

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    In all cars with an automatic transmission if you don't put your foot on the brake it will creep forward.

    With the Prius, when the gas engine shuts off, there would be no such creep from the electric drive, at least not naturally. Electric motors don't idle, thus no creep.

    But everyone knows that the Prius WILL creep at stop lights, even when the gas engine is off. That's because Toyota added that creep with software. They did this to make the Prius respond more like a regular car, after all, American's can only handle so much change. :D :D

    So what you see is the evidence of this feature on the screen. If you press harder, like Drew said above, you can shut off this creep. Let up a little and the creep comes back.

    There was another thread awhile ago about whether this creep feature could be shut off completely. I don't know how that thread ended up.
     
  5. Sufferin' Prius Envy

    Sufferin' Prius Envy Platinum Member

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    This built-in “creep†is there to prevent you from rolling backwards if you are stopped on an uphill incline.

    If it weren’t there, you would be rolling backwards in the amount of time it takes you to step from the brake to the accelerator pedal.

    Just press the brake harder.
     
  6. prius04

    prius04 New Member

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    <div class='quotetop'>QUOTE(Sufferin' Prius Envy\";p=\"74168)</div>
    What about the millions that drive manual transmissions? It may take some skill to prevent the car from going backwards, it is far from all that difficult with a little practice.

    And whatever the reason, the creep was "designed in" and is not "natural" for an electric motor.

    IMHO, Toyota had other options to prevent that backward slide on hills. They picked "creep". It simply seems to me that they could have picked a "soft lock" of some kind, instead they picked "creep".
    Whatever.
     
  7. Sufferin' Prius Envy

    Sufferin' Prius Envy Platinum Member

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    <div class='quotetop'>QUOTE(prius04\";p=\"74182)</div>
    That is the reason the percentage of cars sold in San Francisco with manual transmission is nil. :eek:

    “Creep†is an excellent solution, unless you want to drive a car that feels like a golf cart!

    Prior to the brakes being fully disengaged the electric motor provides forward torque . . . just like you would expect to feel in an old style car.

    Within certain design limitations, electric motors providing instantaneous torque without revolutions is very “natural.†I’m sure the Toyota design engineers took that into consideration when designing this highly critical component.

    Per 2005 Owner’s Manual, page 139:
    “(g) Vehicle driving characteristics . . . Creeping.
    In order to hold the vehicle properly on an incline and for better accelerator pedal operation at starting, your vehicle is designed like a typical automatic transmission vehicle which tends to move without depressing the accelerator pedal . . .â€


    P.S. Never buy a used car with manual transmission from a San Franciscan!

    Just step harder on the brakes folks!
     
  8. jayman

    jayman Senior Member

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    <div class='quotetop'>QUOTE(prius04\";p=\"74182)</div>
    Well, actually, it is *perfectly* natural for a multi-phase electric motor to provide almost instantaneous torque at rest. If you carefully control the applied frequency and voltage, you can create a natural "creep" that does the motor no harm at all.

    I have a lot of industrial process control experience with high HP three phase electric motors up to 4,000 VAC. I'll try to keep this as simple as possible.

    Imagine an electromagnet: the wound coil possesses the properties of resistance, inductance, and capacitance. The inductance is what provides the torque or force, and when first energized produces tremendous inrush and back EMF.

    You can design a circuit with suitable components - a capacitor and a diode are simple examples - that will allow the inrush for maximum force, then limit the current to prevent burning out the electromagnet.

    A modern 3 phase electric motor with precision rotor/stator works like a parallel arrangement of electromagnets, except instead of pulling/pushing a rod the excitation turns a shaft. The motor has maximum power - and maximum power consumption - when first energized, especially if the rotor shaft is jammed or otherwise hard to turn.

    This is refereed to as Locked Rotor torque. If you use something like an AEMC Phase Analyzer or Power Quality Analyzer, you will notice the immediate peak amp surge which is LRA (Locked Rotor Amp). If you graph the peak inrush current wrt time, within 1 cycle you've peaked and fallen off to around 71%.

    With no overcurrent protection, and no automatic monitoring of stator temperature, the motor will quickly burn out. With modern controls, you can carefully tailor the motor input voltage and frequency to provide almost full LR torque with minimal heating. This is the function of the VFD (Variable Frequency Drive).

    With a VFD, you must specify a motor rated for VFD duty. This will ensure the winding insulation is of better quality otherwise you may experience Corona due to the rapid frequency shifts causing voltage spikes within the stator. The rapid frequency shifts and resultant voltage spikes will break down the regular winding insulation.

    In an application like a screw conveyor auger that transports material from a silo into a process area, the motor will usually be running at 20-30% of it's maximum rated speed. In something like a centrifugal pump pumping a liquid or a slurry, the duty cycle may rapidly change from 10-99%.

    In the above applications, the VFD not only monitors the voltage and amp draw, it also accepts 3 thermistor inputs, one from each phase of the stator. If a thermistor indicates an overheat approaching, the VFD can ramp the frequency down or even stop the motor to cool things off.

    Rest assured the Toyota engineers are *not* sacrificing long-term durability by taking advantage of this natural property of a 3 phase motor. They appear to carefully monitor the current, voltage, and motor temps.
     
  9. jayman

    jayman Senior Member

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    <div class='quotetop'>QUOTE(Sufferin' Prius Envy\";p=\"74195)</div>
    Patrick:

    Yeah, I bet!

    The grinding of a release bearing or scraping of metal on a flywheel never ceases to make me cringe.

    The only sound worse than that is when somebody attempts to shift into R without shifting into 3rd first. Hint: you stop the mainshaft turning so you don't grind gears going into reverse.
     
  10. john1701a

    john1701a Prius Guru

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    > What about the millions that drive manual transmissions?

    Some of them bought a manual for the sole benefit of saving gas... which is no longer necessary. That's why my first vehicle was a manual. And I am sure glad Prius eliminates that need.

    > It may take some skill to prevent the car from going backwards, it is far from all that difficult with a little practice.

    Any interface that requires greater attention from the driver is an obvious safety compromise. Having driven 60,000 miles with my manual, I can easily say the extra hand & foot requirements in addition to the higher level of awareness is genuine problem. If you don't pay attention, the vehicle rolls backward, or worse stalls. That's really bad.

    By the way, whenever I came to a stop at an intersection, I waited for the light to turn green with my foot on the brake only. I left the car out of gear. That ability does not exist in the manual hybrid from Honda. In order for the autostop to shut off the engine, you must have the clutch fully depressed.

    Long story short, the appeal of manuals is changing.
     
  11. DanMan32

    DanMan32 Senior Member

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    I believe the creep is controlled by the brake light switch, which can be adjusted if you want it more sensitive.
    Check at night if your center brake light is lit when you think you should not be in creep mode but you are.
     
  12. KMO

    KMO Member

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    I don't believe it is, Dan. As far as I've seen, my brake lights come on with the lightest of touches to the brakes - not even enough to stop it creeping forward. You have to press somewhat firmer to stop, and further still to lose the yellow battery arrows.
     
  13. Dr.Jay

    Dr.Jay New Member

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    For what it's worth, Toyota added the 'Creep' (mentioned somewhere on their site) so the Prius would have the 'feel' of a normal car when stopped in traffic.
    i.e. lift your foot off the brake and the car will slowly move forward. . .no need to step on gas.
    With a 'normal' car, if you don't press the brake hard enough, you hear the brakes making a strange 'Jumping?' noise.
    With the Prius, the motor is engaged but the car is not moving.
    As mentioned. . .just press brake harder.
     
  14. 8AA

    8AA Active Member

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    Thank you for all the suggestions to press the brake pedal harder, however, that was not the reason for the original post. I fully realize that pressing harder on the brakes will turn off the yellow arrows. What I was wondering was how many people might be sitting at stoplights unaware that the electric motor was engaged. It is quite easy to apply just enough pressure to keep the car from creeping forward, but not quite enough to disengage the electric motor. This is just an observation/warning for those drivers who use a screen other than the Energy Monitor for their primary display.
     
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