[Dave]

I just received my 2005 Prius two weeks ago. I thought that the car ran on batteries up to 15 mph. Mine seems to turn on the ICE earlier than that. Is there any way to gage if the car is running properly and can the point that the ICE turns on be modified? Is it safe to change the profile? And can this be done by software or hardware?

 

[DanMan32]

It's actually closer to 7 MPH under normal acceleration. But it does depend on how fast you accelerate, and if you are going uphill or downhill.

When it does start though, you are using both ICE and MG2, with MG1 and possibly (probably?) the battery powering MG2.

Sometimes I do wonder if we would actually get a little better performance in MPG VS. torque if it did wait until it reached 15 MPH.

Now that I think of it, yes MG2 could provide the torque to go as high as 15 MPH and higher, but it needs enough electric power to do it. The battery can't quite deliver the needed power. MG1 provides much of that needed power, and it gets its energy from ICE.

Also remember, whatever you take out of the battery, you have to put back in, with losses. Only 2 ways to recharge the battery: ICE through MG1, and regen with MG2.

Best not to second guess Toyota and the computer they designed. It really is quite efficient.

 

[efusco]

I just received my 2005 Prius two weeks ago. I thought that the car ran on batteries up to 15 mph. Mine seems to turn on the ICE earlier than that. Is there any way to gage if the car is running properly and can the point that the ICE turns on be modified? Is it safe to change the profile? And can this be done by software or hardware?

You have a serious misunderstanding of how the hybrid synergy drive system works.

The electric power is inefficient as the sole source of power from a stop. Although it is possible to nurse the electric only mode up to even 41mph, there is no point what so ever in doing so and it's very very difficult to do b/c the car is programmed to use the ICE to accomplish acceleration. It might be better to think of the electric motor as a booster for the ICE. You will see electric only power from time to time both when starting from a dead stop and in motion it is not, in itself, an objective to be attained, but rather a phase in the operation of the hybrid system as a whole.

 

[Canadian Prius]

Although it is possible to nurse the electric only mode up to even 41mph, there is no point what so ever in doing so and it's very very difficult to do b/c the car is programmed to use the ICE to accomplish acceleration. It might be better to think of the electric motor as a booster for the ICE. You will see electric only power from time to time both when starting from a dead stop and in motion it is not, in itself, an objective to be attained, but rather a phase in the operation of the hybrid system as a whole.

Yes, I think this is the right way to look at it, but it takes a while for a Prius owner to get to this way of thinking. From what I see here, most Prius drivers would be most content if the ICE never turned on! At the same time, everyone knows the car can't work that way.

I believe that the most efficient use of the battery only mode is to encourage the car to use the ICE for hard work, and the battery for easy work. Acceleration is hard work. You would drain the battery in no time if you used it exclusively to get up to speed. This is best done by the ICE. On the other hand, maintaining speed is relatively easy work. As you travel down a windy, slightly hilly road at 40 mph, you can go for miles and miles on battery power alone. After a drive like this, you will see your MPG is extremely high. And, you will notice that you regenerated lots of power over the drive. Using the ICE exclusively on the same drive would use lots of gas because the ICE, while under light load, burns far more gas relative to the work it performs.

Another example of this is when you wait at a long light on a cold day with the heater on. The ICE runs to warm up the car and run the heating system, and you sit there and watch your MPG reading dismally plummet.

 

[zinzindorff9]

There really has got to be a reason Toyota gives you a phone number to call if you foollisly run out of gas along with the admonishment to not attempt even a short drive seeking fuel on battery alone. They may be warranted for 150,000 miles but that may be negated by the attempt to drive eight miles battery alone!

 

[Canadian Prius]

There really has got to be a reason Toyota gives you a phone number to call if you foollisly run out of gas along with the admonishment to not attempt even a short drive seeking fuel on battery alone. They may be warranted for 150,000 miles but that may be negated by the attempt to drive eight miles battery alone!

Yes, they have a really good reason for that - the car is not designed to run on battery alone. They make this very clear.

Could you point to the reference where running out of gas voids the warranty? I hadn't heard about this. Now I understand your concerns. That's really a shocker!

 

[zinzindorff9]

Sorry, the post does give the impression that I was concerned about the warranty. I don't see how that could be proven regardless but my intent was that the batteries are warranted for 150.000 miles and I believe that is if common sense is used. I don't believe the engineers of these cars meant in any way that they were to be driven on battery power alone. I would skip any form of EV button and let the "ECM" do it's job.

 

[DanMan32]

I think the main issue of the warning to not run out of gas is so that you don't damage the HV battery by draining it often. Without gas, the car can't charge the battery when it gets below 2 bars. Yes, it will shut down before it is actually depleted, but you don't want to do that frequently.

 

[nevesis]

HSD "transmission"

Also, keep in mind that this car has no "transmission" in the traditional sense of the term. There is no changing of the gear ratios - whatsoever. The car is always in "high gear". It's like getting onto a 10-speed bycicle on it's highest gear.

The engine alone cannot get the car rolling from stop. There simply is not enough torque. This is why traditional cars have transmissions, and lower gears - to provide more torque at a lower speed. However, the HDS also has at its disposal the MG2 generator-motor. Luckily for us (and the success of HSD), MG2 is most efficient at lower speeds. Therefore, the MG2 motor is what does most of the work propelling the car from standstill.

The planetary gears, or power split device, is hard-coded to deliver the power at a fixed rate. It cannot change. There are three variables - ICE, MG1, and the drivetrain (which is MG2 and the wheels). I don't have the formulas in front of me, but approx 75% of the engine's toque is delivered to the drivetrain. From stop, this wouldn't get you far. But approx 25% of the torque is driving MG1; and since the car is not moving, all the power is channeled to MG1. This generates electricity. This electricity is used to power MG2 to propel the car. And once it starts running, power is also being delivered directly from the engine via the power split device as well, supplementing MG2.

Whenever one of the variables is zero (engine stopped, or car not moving) - then the math through the power split device is quite simple. This is why the engine can never run when moving faster than 42MPH. This would cause the MG1 motor-generator to spin faster than is spec'd to do so. Even in "neutral", rolling down a hill with the engine off - MG1 will spin. The transmission is always engaged, and never changes ratios.

So, while there may always be arguments as far as which is the best power source to use and when, just keep in mind that the power distribution is fixed, and follows very specific rules. Even in the case of "Electric Only" mode, MG2 supplies the power, directly to the drivetrain. However, the power split device is still engaged, and still spins - usually the MG1 motor. (It can be set to spin freely, not supplying or wasting energy). Spinning the motor is less efficient, and is done only when necessary - not supplying fuel to the cylinders saves fuel, but still requires energy from the system (acting as an engine brake) - but usually at those speeds, the engine is running, powering the drivetrain, and generating electricity for either storage, or supplemental power to MG2.

 

[zinzindorff9]

This is a great expanation of what goes "on", Sort of negates any need or use of the "EV" button to being more than a demonstration "toy"

 

[richard schumacher]

I don't see how that could be proven regardless

If by "it" you mean "ran out of gas", the computer records it if it happens. I agree that the EV button is mostly a gimmick.

 

[Jim Biggs]

I don't quite understand

"This is why the engine can never run when moving faster than 42MPH"
I assume you mean MG1?
Thanks,
Jim

 

[ken1784]

Re: I don't quite understand

"This is why the engine can never run when moving faster than 42MPH"
I assume you mean...
"This is why the engine needs to be run when moving faster than 42MPH"

"just keep in mind that the power distribution is fixed"
I assume you mean...
"just keep in mind that the TORQUE distribution is fixed"
(power = TORQUE X revolution)

Regards,
[email protected]

 

[Jim Biggs]

Faster than 44 MPH

Ken,
Thanks for the clarification.
Jim

 

[Canadian Prius]

These posts are about the heart of the Prius.

In these posts you are showing how the practical application of dedication to efficiency has revealed itself through the genius of engineering in a practical world. i.e. using what we have available in the most efficient method.

In particular, the marriage of the characteristics of high torque at low revs electric motors to supplement the gas engine where it is least efficient in torque, while using its best and most efficient characteristics.

A billion dollars was spent by Toyota working this out, and ensuring the result would be robust and durable.

How many other solutions of this kind is our technology capable of, given the determination toward the right goals? Can six to fifteen billion people eventually sustainably live within the resources of our planet, without upsetting its equilibrium? If so, Toyota is pointing the way.

 

[nevesis]

Sorry, yes, I got a little backwards there a few times. I shouldn't post so late. But understanding better how it works makes things clearer as to how ans why things are.

In anything were to be changed, I for one would like to get rid of some of those "features" making the Prius feel like a standard car such as automatic "creep" (the car moves forward just by releasing the brake and applying no accelerator pressure), and "drag" (automatic application of braking power by letting up completely on the accelerator pedal). I know some people would freak out and reject the car without them, but I for one would embrace such a change for a truly unique and new type of vechicle.

Anyway, as for the EV mode - yes, it is mostly a gimmic. I consider it to be a "geek toy". You can show off how silent you are, or navigate a parking lot silently. For the most part, it is possible to do this without the EV button, but that gives you better control. I barely ever use it - just when I want to "show off" - and when I move my car from a far spot to a closer one in the parking lot at work - no need for the engine to start for such an incredibly short trip (which sometimes I even do completely in reverse).

 

[Canadian Prius]

I for one would like to get rid of ... automatic "creep" (the car moves forward just by releasing the brake and applying no accelerator pressure), and "drag" (automatic application of braking power by letting up completely on the accelerator pedal).

The 'creep' feature is for drivers who can't start off up a hill without falling back a foot or two. I don't need it myself, but I think I would be glad the Prius in front of me has it so they wouldn't hit me as they try to start up the hill.

The 'drag' feature is a convenient way of gathering extra charging for the battery without making the car act in an unfamiliar way. If you want to 'disable' it, you can touch the accellerator very lightly, and the car will coast as if in neutral. Personally, I like the extra charge to the battery, and this feature keeps my Prius in the same coasting speed range as the other cars going in a line down a long hill. Without it, I would have to use the brakes for the same amount of drag that the other cars have through normal engine braking. Also, out of consideration for other drivers, I prefer not to brake going downhill unless it is really necessary. That it, I don't like to see the car in front of me constantly making small adjustments to his speed with the brakes while going down hill. It suggests he is a poor, uncertain driver, and it forces me to adjust my speed the same way.

Having said that, I would like to see a 'configuration' panel on the Prius. Then the driver could set the car the way he prefers to drive it, with as much control as he likes over EV, drag, creep, ICE on/off priorities, etc. This could be exercised through coded usage of existing controls, such as the cruise control lever. Here I anticipate and agree with the standard cautions that the Prius is designed to be best run by the computer. However we are the drivers of the vehicle, and even if the computer can do things 'best', I don't agree that we shouldn't have the option of doing things differently, if sometimes a little less well, if that's what we want. And of course, there are numerous cases where we can see things the computer can't, and we could add to efficiency by acting on them.

One minor example of where we could improve on efficiency is where the Prius, when fully warmed up, will sometimes continue to run the ICE as it desends a long hill. Even if it is burning very little gas, I would like to flick it into EV mode (not installed in Canada). Another 'configuration' control I would adjust is the use of the heater. On cold days when it requires a full blowing fan, turning it on will start the ICE when otherwise it would be off. In my case, I would set the heater to automatically turn off if the conditions are such that the ICE would turn off without it, (and then on again when the ICE starts up for other reasons). I know from doing this manually that the car would stay plenty warm. I also know that this would save a considerable amount of gas.

 

[zinzindorff9]

My guess would be that the "big sell" of this car is it's fuel economy and that Toyota has set all systems up primarily with this in mind. Changing even one thing would probably cost in consumption figures. We've even been told that with only the addition of "mud flaps" we would decrease long interstate milage figures.

 

[ehurtley]

Emissions first, then economy.

My guess would be that the "big sell" of this car is it's fuel economy and that Toyota has set all systems up primarily with this in mind. Changing even one thing would probably cost in consumption figures. We've even been told that with only the addition of "mud flaps" we would decrease long interstate milage figures.

Actually, from most of the Toyota technical literature, the big engineering point was low EMISSIONS, not fuel economy. i.e. It was designed to get the lowest possible emissions, then tuned for fuel economy. This explains why the engine runs to heat up the exhaust system when you first start it. If all was for economy, it wouldn't bother, since it doesn't do anything to increase economy.

The Honda Insight is a good example of a vehicle designed first-and-foremost for fuel economy.

 

[Canadian Prius]

Re: Emissions first, then economy.

Actually, from most of the Toyota technical literature, the big engineering point was low EMISSIONS, not fuel economy.

Yes, this is true. The Prius gets 2 - 3 times better mileage than the average car, but 90% fewer emissions. It is a 'green' car, with emphasis on sustainable, non-polluting principles in every stage of its manufacture and operation.