[Prz]

I know many people purchased the EV Mode enabler already, but I'm more interested in a switch that will turn off all electricity generation for freeway driving. I'd like the transmission to lock the gears so that all the power is driven to the wheels. Like the EV mode where the engine will turn on as the battery level lessens, the transmission gears could slip a little to run the generator like it currently does.

I don't know how much slipage current takes place, so this could be moot. However, I think mechanical power is much more critical then electrical power when driving on the freeway.

Chime in with any thoughts...

 

[Bob Allen]

This is a very bad idea. The electric motor is an integral part of the power plant. When you accelerate to pass other cars or merge onto the freeway, the electric engine provides the initial torque required because the gasoline engine in the Prius is not efficient at providing start up torque. You stated that "mechanial power" is more desireable at freeway speeds than electrical power. Actually, the Prius system uses both the electric motor and the gasoline engine to provide mechanical power to the wheels, so I don't understand your distinction here.

Assuming you could do it, shutting off all electrical regeneration would, in short order, shut down the electric motor by allowing the battery charge to drop below operating levels. The gasoline engine, alone, is not sufficient to provide you with enough power to operate safely on the freeway. There have been accounts of people making it to gas stations on electrical power alone, but this too is a bad idea because the battery needs the regenerative charge from the gasoline engine. They are a pair and you can't split them up.

I don't think you understand the "transmission" in the Prius. There aren't gears in the sense that your old car had, say, five gears. Prius uses a planetary gear system that allows either or both gasoline and electric engines to operate; the computer determines the optimum use of each based on the load being put on the car and the charge in the battery. So, there isn't anything to lock up. When you start up a conventional car, the lower gears and the engine take the stress of moving the two tons of car from a stop to forward motion. This is the hardest strain on the gears and the engine. The Prius uses the electric motor to do that both because the motor is ideal for low rpm/high torque situations and because electric motors are direct drive and don't need gearboxes to translate piston rpms to wheel rpms. The gasoline engine in the Prius is allowed to operate within its optimum rpm range and with a minimum of start and stop stresses imposed on it. That's the inherent beauty of this system: each power plant operates in its optimum efficiency range. Why mess with it?

Toyota got it right and you most likely won't be able to tweak the system for any added hidden efficiencies without voiding your warranty and possibly ruining your car.
Bob

 

[RSnyder]

Your Prius comes standard with a switch that will disconnect all electrical activity. It's called N mode

Of course it has the disadvantage that Neutral in any car has, namely you can't get power from the engine to the wheels. Anyway, there are no mechanical clutches or locks in the Prius transmission. It's mechanically an incredibly simple device, topographically equivalent to a simple differential. (Not a posi).

 

[Daniel]

There is no slippage in the Prius because everything is connected by gears that are always engaged. How this can be done is mind-bogglingly elegant. Find a link to Graham's Prius Page for detailed explanations with diagrams and animated gifs.

Due to the nature of the planetary power-split device, a fixed proportion of the torque of the ICE always goes to MG1 to generate electricity, which the computer can send to the battery or to MG2 to help power the wheels. But because of the physics of the device, the faster the car is moving, the less power is shunted via MG1. Thus, at highway speeds, most of the power is going directly from the ICE to the wheels, just as you want it to be. At low speeds, where a conventional car is inefficient and lugs, the Prius ICE runs at efficient RPMS, sending power to MG1 then to MG2 and then to the wheels.

Believe it or not (and the numbers don't lie) the HSD is the most efficient way to drive a gasoline-powered car today. Only the Insight gets higher mileage, and that's because it is so much lighter in weight. If you did tell the car not to charge or draw from the battery at highway speeds, you'd actually reduce its efficiency, because even on the highway, the load-balancing effect improves overall efficiency.

 

[AgentElrond]

I think I'll take the Drew Carey approach and give everyone 1000 points each for good info. Of course, the points don't matter... :wink:

 

[ehurtley]

I think I'll take the Drew Carey approach and give everyone 1000 points each for good info. Of course, the points don't matter... :wink:

THE POINTS DON'T MATTER!?!?!?!?!?! Blasphemy! How else do they decide who does the closing credits?! :wink:

 

[AgentElrond]

How else do they decide who does the closing credits?! :wink:

Seems to be whoever gave Drew the most grief during the show.

 

[RSnyder]

In an attempt to deepen Daniel's understanding of the Prius and bore the rest of you, I'll comment on the following snippet from his well stated post.

. . . a fixed proportion of the torque of the ICE always goes to MG1 to generate electricity . . .

Daniel, you need to separate the concepts of torque and power. The generation of electricity requires power, but power depends on the product of torque and angular velocity, both of which are signed numbers. It turns out that when cruising at highway speeds, the torque and angular velocity have opposite signs from the engine to MG1 (i.e. MG1 is spinning backward w.r.t the direction of engine spin). Thus MG1 is providing power to the PSD (it's acting like a motor, not a generator). Since the engine is also providing power to the PSD and there's only one other place for it to go, ALL power from the engine (and from MG1) goes to the shaft attached to MG2 and the wheels. MG2 may choose to absorb some of this power (act as a generator), contribute even more power (act as a motor), or on rare occasion, do nothing.

Once upon a time, Graham called this "heretical mode" since nobody wanted to believe MG1 acted as a motor during cruising. Now that it's generally accepted (proved by the miniscanner), it's mostly refered to as "overdrive" since that's exactly what it is (engine spining slower than output shaft of transmission).

It's an incredibly efficient mode because only a relatively small amount of electric power is involved. I suspect it's more efficient that sending the engine power through the additional gear meshes and other efficiency sappers of a conventional automatic transmission. Just another reason why the Prius transmission is genius!

 

[richard schumacher]

There is no slippage in the Prius because everything is connected by gears that are always engaged. How this can be done is mind-bogglingly elegant. Find a link to Graham's Prius Page for detailed explanations with diagrams and animated gifs.

That would be http://home.earthlink.net/~graham1/MyTo ... Frames.htm

Follow "Understanding the Prius".

 

[statultra]

inspection mode

there is a mode called inspection mode which allows the gasoline engine to run all the time, but it says in the book " may damage transaxle if driven in this mode"

sounds cool , maybe not!

 

[CaPriusLover]

richard schumacher, Thanks for the link!!!!

 

[Daniel]

Richard:
If both MG1 and MG2 are acting as motors at highway speed, then how come I still see electricy flowing sometimes to the battery, and sometimes out of it? For there to be battery charging going on, mustn't MG1 be acting as a generator? Or does it go into and out of "heretical mode" somehow as needed?

Agreed that the whole system is elegant and efficient. And that my understanding of it is superficial at best. A layman's partial understanding of the info on Graham's web site.

And, yes, I do understand the difference between torque and power, which is why there can be a fixed split of torque between the wheels and MG1 and yet a decreasing proportion of power going to MG1 as vehicle speed increases. That, also, I read on Graham's web site.

 

[RSnyder]

If both MG1 and MG2 are acting as motors at highway speed, then how come I still see electricy flowing sometimes to the battery, and sometimes out of it? For there to be battery charging going on, mustn't MG1 be acting as a generator? Or does it go into and out of "heretical mode" somehow as needed?

Sometimes both MG1 and MG2 act as motors at highway speed. Obviously not during the times that you observe energy flow into the battery. During those times, if you're cruising, MG1 is acting as a motor and MG2 is acting as a generator. Some of the power from MG2 flows back to MG1 to enable it to be a motor, while the rest goes back to recharge the battery. This is actually a pretty common case during highway cruising. The current levels are relatively low compared to what MG2 is capable of generating (for instance during regenerative braking). Something like 5 amps vs. 50 amps. So it's not really going into and out of heretical mode (MG1 acts as a motor all the time during overdrive cruising), but MG2 switches back and forth between motoring and generating. You see the arrows reverse when it does this.

There's a fairly big "dead zone" around the engine speed that would result in MG1 having zero spin. That's why when you ask for more power (to pass, or go uphill for example), the engine speed suddenly jumps much higher (gets much louder). MG1 is switching from a motor spinning backward to a generator being spun forward (where the direction of engine spin is considered forward).

 

[CaPriusLover]

Between reading this thread and going to Grahams site, I have a hole new respect for this care and the engineers who designed it.

The reinvented most of the car, with the exception of the basic with the ICM works!!

 

[Daniel]

... Sometimes both MG1 and MG2 act as motors at highway speed. Obviously not during the times that you observe energy flow into the battery. During those times, if you're cruising, MG1 is acting as a motor and MG2 is acting as a generator. Some of the power from MG2 flows back to MG1 to enable it to be a motor, while the rest goes back to recharge the battery...

So MG2, which normally helps drive the wheels when you go, and slow them when you brake, can act against them while you want to go, to provide electricity so that MG1, which normally is a generator, can become a motor? I have a hard time conceptualizing this. I think at this point I need to spend some more time on Graham's Prius page.

 

[richard schumacher]

richard schumacher, Thanks for the link!!!!

Yer welcome, but all credit belongs to Graham for his marvellously clear and thorough description of the mechanism and operating principles.

One thing that adds to confusion is that the Multi-Function Display in the Prius shows only one motor/generator, and not the two that are actually present.

 

[RSnyder]

I think at this point I need to spend some more time on Graham's Prius page.

If I might suggest clicking "Understanding your Prius", then "The Power Split Device" and considering the red line on the nomograph about 2/3 down the page. It actually works to think of the line as a bar with up to three forces on it. The ICE is providing power, thus pushing up on the red line. This needs to be counterbalanced on both ends since it's steady state and the line isn't moving. The physical drag on the wheels represent a force pushing down on the right side (trying to slow down the spin value on the right side). MG1 also needs to push down. Since it's in the negative spin range, this means trying to spin faster, which means it must act as a motor.

The nomograph is pretty cool since it's drawn so that the relative distances invoke leverage representing the mechanical advantage MG1 has over the ICE.

 

[Daniel]

I've been spending some time on Graham's page. I read about the nomograph (and printed it out for easy reference) and re-read the bit about heretical mode, which I had read before but it had not stuck with me. I do think I understand it a bit better.

So I know that either motor/generator can be a motor in either direction. Apparently either one can also be a generator in either direction. What has to be done to determine which it is? Is it just a matter of whether there is a voltage or a resistance applied across the terminals?

 

[RSnyder]

Motor/generator control is a pretty involved subject. The howstuffworks site can help a lot, as can Graham's site. But conservation of energy makes it fairly easy to understand the strategy. Basically, if the battery is connected to the terminals in a manner that causes electromagnets to pull/push the rotor in the direction it's moving, the m/g acts as a motor and the battery sees a drop in voltage across its terminals causing it to lose energy. This balances the rotational energy being created by the motor. If, instead, the battery is connected such that the electromagnets pull/push the rotor in the direction opposite to it's spin, the m/g acts as a generator and the battery sees an increase in voltage across its terminals causing it to gain energy. This balances the rotational energy being removed by the generator. In both cases "balances" is used loosely. Some energy is always lost to heat/friction/vibration to keep the world's supply of entropy rising.

To go back to the nomograph briefly, if the m/g tries to push it's point on the bar away from zero, it's acting as a motor and requires electrical energy (from the battery or the other m/g). If it tries to push it's point on the bar toward zero, it's acting as a generator of electrical energy. However, near the zero RPM point it's not able to act as a generator because the induced electric fields from the rotor passing the fixed windings are too small. It's also somewhat inefficient as a motor since relatively large amount of energy is lost to heating the windings. So the computers try to stay away from zero if possible.

 

[Daniel]

Thanks for all that, Robert. I think I grasp the general idea.