Electric motor engaged while at a stoplight

[8AA]

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.

[paprius4030]

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?

[peart75]

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

-drew

[prius04]

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.

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.

[Sufferin' Prius Envy]

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.

[prius04]

<div class='quotetop'>QUOTE(Sufferin' Prius Envy\";p=\"74168)</div>

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.[/b]

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.

[Sufferin' Prius Envy]

<div class='quotetop'>QUOTE(prius04\";p=\"74182)</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.[/b]

That is the reason the percentage of cars sold in San Francisco with manual transmission is nil.

“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 . . .”

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

Just step harder on the brakes folks!

[jayman]

<div class='quotetop'>QUOTE(prius04\";p=\"74182)</div>

And whatever the reason, the creep was \"designed in\" and is not \"natural\" for an electric motor.[/b]

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.

[jayman]

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

P.S. Never buy a used car with manual transmission from a San Franciscan![/b]

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.

[john1701a]

> 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.