Why does Prius run the ICE at low mpg?

It's all demand-based. Hopefully this is enough of the software
picture for you: the hybrid system always seeks a 60% SoC, unless
it is being called upon to handle other conditions such as electric-
only propulsion or absorbing energy via regen. Whether or not the
engine comes on is all calculated via balancing measured SoC versus
where the driver's foot is. Lower SoC, lower accel-pedal threshold
for when the engine is started. That, in fact, is one of the simpler
things that the software does!
.
_H*

 

One other small point, ukr2, is that the ICE always runs as efficiently as possible. The HSD let's the ICE run at an appropriate RPM; energy not needed for propulsion, either directly or by spinning one motor as a generator to provide electicity for the other motor, is sent to the HV battery. The ICE never lugs at low speed as it might in a conventional car.

And sometimes the ICE will start just to warm itself and the catalytic converter. You might want to think of the Prius as first and foremost a low emissions car. It accomplishes this by producing the fuel efficiency most people associate with the Prius.

 

Hi All,

In the summer, at low speeds, the Prius will use the battery in the slow stop-and-go traffic to a much accelleration. In the winter, while the engine may be warmed up, that does not mean the battery is. In the recent heavy snow commuting, I found the car would hang in electric mode readily toward the end of the trip. Technically, I think this is due to the available power from the battery versus temp. The battery ECU may report to the hybrid ECU the available battery power, estimated from battery temp and SOC. If demand exceeds battery power, then the engine is assigned the bulk of the power duty. Of course, at lower temps, the power required to flex the cold rubber in the tires is allot more too. The hybrid system can directly measure the needed wheel torque by the MG2 current. So, if the MG2 current exceeds what the battery can deliver, the engine comes on, supplying the missing current, and or reducing the amount of current required.

Additionally, in cold weather there is the 35 mph coast engine shut-off routine. Once the engine is running, it wants to keep running until the car is at low power greater than 35 mph operation. Then it will shut off, and small accelleration will bring the battery on-line. One can access this, by lifting throttle for a few seconds when one is above 35 mph, and then bringing the throttle back up slowly. At which point one can cruise along in electric down at speeds below 35 mph if traffic conditions dictate. Once the temp is up above 50 F (?) or so, this changes too, and the car will drop the engine quickly. It might be sensing engine coolant temp to do this, or just enviormental temp. Not sure.

 

I have noticed recently that my Prius is far more likely to shut the ICE down at stops if I have the climate control turned off. I live in town, and when I make short trips, I will keep the climate control off as long as it isn't brutally cold in the car.

Harry

 

So... how do I get one of these EV buttons? =)

 

<div class='quotetop'>QUOTE(efusco @ Feb 14 2007, 07:04 PM) [snapback]390631[/snapback]</div>

Evan -

I know that you know this - I just wanted to point out to others that it is only in this situation that the ICE is more efficient than using the battery power (only in the situation where the ICE has to recharge the batteries). Taking this one line out of context can give folks the wrong impression. An electric motor is quite a bit more efficient than any gasoline ICE can ever hope to be. The problem here, of course, is that the PRIUS requires gasoline to run the EV part of the program.

 

Hi ukr2,

If you would like to see the best overall mileage number, please try to avoid using the battery power.
http://hybridcars.about.com/od/ownership/a/pulseandglide.htm

Ken@Japan

 

ukr2-

Every driving situation is unique. If you can use battery power for traction, and then recharge that battery mostly through regen, then you're doing GREAT. If, in stead, the battery is rechared through extra load on the ICE, then you are losing ground.

The best solution is to toss the gas engine altogether and get into a real EV... You know - once they're for sale again.

 

<div class='quotetop'>QUOTE(Bill Merchant @ Feb 14 2007, 10:48 PM) [snapback]390729[/snapback]</div>

Actually the Prius does its best to "lug" the engine at low speed.

It even uses the energy recirculate mode (described in another post by Bob Wilson) to intentionally lower the engine speed when the engine is producing too much power for a given road-speed. The Prius normally runs the ICE at almost full throttle whenever it is above 1200RPM and controls engine output by changing the engine speed - not by changing the throttle position.

kevin

 

<div class='quotetop'>QUOTE(kevin17 @ Mar 5 2007, 07:56 PM) [snapback]400633[/snapback]</div>

This is a brilliant way to describe ICE power management. Ordinarily, this approach to engine power management would be unstable. As the ICE rpm increased, the power would increase and the rpm increase even faster. But the ability to moderate MG1 torque to keep the rpm at a 'commanded speed' prevents power run-away, speed up or stalling from too little rpm.

Thanks,
Bob Wilson

 

actually the EV switch is handy for a lot of things. case in point (doesnt apply on the shift ive had for nearly two years but in the old days...

i work at a place that employees about 400 people in a complex that employees 3,000 people for a dozen different agencies. we have 75 parking spaces in the lot next to the building and two overflow parking areas that are either 150 or about 500 feet away. now i am into exercise, walking and all that crap...but in Western Wa where rain is frequent, not to mention an average of 3 trips a day out to my car for something or another, parking next to the building is a highly sought after position. considering the 50 different shifts and start times, the parking lot constantly has traffic coming and going.

i used to work later in the morning and was forced to park in the overflow lot. i would move next to the building at my earliest convenience and EV mode was perfect for the 500 ft trip.

 

It's too bad that I can't get the EV button on my '02 Prius. There are plenty of times where my ICE is running and it's not really doing anything useful, ie running but not using any power. It'd be a real help during the winter when I could just shut off the ICE at stoplights. It would still help during the summer, but not as much since the warm-up period is shorter.

BTW, since blocking the grill helps decrease the warm-up period, why don't they offer some type of feature like that on every car? Something along the lines of blocking the grill, or radiator, until everything warms up enough, then press a button, or have it done automatically, that removes the blockage so everything runs like it should. Wouldn't that, in effect, increase the MPG on pretty much every car that is driven today?