Top Speed when out of gas??

<div class='quotetop'>QUOTE(wwhalenc @ Nov 9 2007, 09:44 PM) [snapback]537509[/snapback]</div>

Hi Wwhalenc,

MG1 only propels the car in what is called "herectical" mode which is at higher speeds with the engine also running. With the engine off, and not turning MG2 which is three times the size propels the car at low speeds. It can accellerate and run the car up to 34 mph with the engine not turning over. But due to the small battery, the system only allows very slow accelleration before it will start the engine. Unless you have a battery SOC (State of Charge) which is much too high (like after coasting down a long hill), then the computer will let you give allot of pedal and the engine wont come on, say 10 seconds to 34 mph .

If you accellerate up to 40 mph with the engine, the computer will let MG2 keep the car moving along at that speed while it shuts off and stops the engine for extended periods. A max of 2 miles on level terrain can be travelled this way.

MG2 can cruise the car and pump the engine at 1100 RPM up to about 64 mph. But as the engine pumping wastes energy, and the battery is quite small compared to what might be in an EV, the computer only lets it do this on very level terrain for a moment, or longer down hill.

The PHEV Prius is said to be able to cruise on all electric with the engine off at 60 mph. Details of the power sharing device and engine rpms are not released for those yet.

Check out this website for some interesting animation and demo where you can adjust sliders on the various motors and the engine: http://eahart.com/prius/psd/

 

<div class='quotetop'>QUOTE(wwhalenc @ Nov 9 2007, 09:26 PM) [snapback]537526[/snapback]</div>

The previous answer explains EV mode during normal operation, but not when the car runs out of gas, which is waht you were wondering about. There's a different strategy for that. Try to find top speed after you've run out of gas, and the HV ECU will shut down pretty quickly.

 

0.

 

<div class='quotetop'>QUOTE(wwhalenc @ Nov 9 2007, 07:44 PM) [snapback]537509[/snapback]</div>

The prius manually says you should not try to run the car with fuel empty. Then again it says you can't tow with the prius and they sell after market trailer hitches specifically designed for the prius....

 

Toyota don't sell after market hitches... some other company does.

If you had unlimited amounts of energy and an unlimited battery, you can probably propel the prius to its maximum speed if the control system was disabled. It'll take alot of energy though...

 

No, that is highly unlikely. Since the engine is between motor 1 and motor 2. You can't use motor 1 (the smaller motor) to power the car with the engine off. Thus motor 2 is on its own.

Now, permanent magnet motors are also generators. (Thus you can have regenerative brakes...) The faster the motor is spinning the more voltage it generates. This is referred to as back emf. The motor controller must have a higher voltage than the back emf voltage to continue to power the motor... Otherwise the controller/battery becomes a deterant to the motor spinning, or in other words regenerative braking...

The other problem is to the faster you go, the more torque you need to maintain a certain speed. Thus you need more current (amps) to power the motor and controller. Now you need more voltage to over come the back emf. Thus you need both more current and voltage = more power ^ 2. (Power = volts X amps.) This will verry quickly become more than what the motor controller can handle.

Also more current = more heat generated = more heat dissipation needed from the motor. Since permanent magnet brushless motors have their field coils (electro magnets) in the stator, they don't have motion to cool them. Thus they also need cooling which may not be designed for additional stresses.

The conclusion, is that when something is engineered to perform certain tasks, going above specifications is a surefire way to shorten its life expectancy. It's like over clocking a computer. Done without consideration, it WILL fry your system... same goes with the prius motor.

 

I can reliably state that the answer is 52 MPH. Unfortunately, I can say that due to recent experience. And it only did it for about 3/4 mile (just long enough to get off the freeway and to a safe place to stop.)

 

This sounds pretty reasonable. Although the motor is spec'd at 50kW, the battery/inverter is only spec'd at ~23kW (as I recall). Thats only ~32 HP which is not going to push a ~3000 lb car all that fast. Under certain conditions the rest of the power comes from the gas motor turning mg 1 pushing mg 2 up towards 50kW. I think this is the freeway mode the PHEVers run in. Battery is almost always high SOC, so HV controller directs power from battery and from MG1 to MG2 resulting in very nice highway mpg numbers.

Are you sure about that? I was under the impression that this was a risky thing to do specifically because the HV controller will happily let you drive around until your HV battery is completely flat. Now you have no battery power with which to restart the gas engine after you refill and have a very big problem (that even your dealer cannot solve, they have to call in help from corporate). There is even a section in the Toyota hybrid tech training manual that shows you how to pull the fuel pump relay (I think it was) to simulate this condition in order to experience what a fuel out condition looks like, and feel what its like to drive around on electric only. There are big cautions next to this to not run the battery down too far, and on how to reset all the errors you will have generated.

I believe this is why the new gen 3 (04+) Prius went to a lower system voltage 201 down from 280? but added a 500V boost converter to the inverter. I assume this allows effective power output at much higher RPMs than the previous design. MG2 is oil cooled, so probably does pretty well even under load. Of course you are right, there are practical limits to everything. The real bottleneck seems to be the inverter in terms of real high speed full EV operation. Cranking up the batteries will allow longer cruising, but the inverter can't put any more power to the motor. Designing a new inverter is _way_ more complicated than throwing a big battery and BMS in the trunk, which is already complicated

Rob

 

If the car sends a no fuel code and a low SOC code the HV ecm will shut down the HV batteries to prevent them from running down too far. This is called safe mode. The codes must be cleared and then the car will start right up with the remaining charge in the HV battery. The car is too smart to let you kill it. The dire warnings about bringing the HV charger from region are apparently overstated.

Please don't ask how I know this. It was embarrassing enough to tell the story the first time.

 

Thanks for sharing, I was not aware of that!

Rob

 

I can confirm that, as of today, if the system wants to it can easily run at 70mph with ICE non operational either due to no sparks or no fuel or both (I'm not sure which)

I believe it operates MG1 and MG2 to keep you going and turns the ICE at whatever speed it needs to compensate.

It can maintain speed or gradually decelerate but wont accelerate (maybe unless downhill), possibly to conserve battery as long as possible