Are the wheels on 2010 Prius alwaus driven by Electric Motor?

1. Learn about the PSD.
2. Yes same power throttle wide open in all modes.

 

The ICE is not directly connected to the wheels, and needs MG1 to provide resistance, so it will push MG2 and the wheels mechanically. As I understand it, it normally sends 28% of the power to MG1 to generate electricity and 72% mecanically to MG2 and the tires.

If MG1 does not need to charge the HV Battery, it's electrical power is also sent to MG2.

A simulation of Prius's Planetary Gear

"Are the wheels on 2010 Prius always driven by Electric Motor?" For any given speed, MG2 and the wheels are directly linked. This is true even if MG2 is not being used as an electric motor. MG1 and the ICE can vary speeds without altering the vehicle speed, both can be 'off' if MG2 is doing all the work. (the ICE is at 0 RPM when off, MG1 is freewheeling at any RPM when off)

So any of MG2, the ICE, or MG1 may be providing mechanical power to the wheels, together or alone. (I doubt MG1 can work alone, but there are modes where it provides mechanical power)

 

Technically it depends on your definition of "driven". Prius requires MG resistance to transfer power to the wheels, so in some respect, that is "driven" as the MG resistance is created by power through its' windings. But most people would consider the answer to be "no". The car will and does move with no assist from the MGs (other than the above resistance - which can be from power generated by the ICE and not taken from the battery).

 

I have seen those numbers about 72% mechanical / 28% electrical, but given the variability of the system, I can only assume that that is the ratio when providing "peak" hp. Anyone know?

The reason I say this is because at 0mph (dead stop), only MG2 provides power to the wheels - therefore 100% of ICE torque/power goes to electrical generation via MG1.

And at certain combinations of wheel speed and engine RPM, where MG1 = 0rpm, 100% of ICE torque/power could theoretically go to the wheels mechanically. (e.g.: ICE rpm 2000, speed 47mph, MG1=0rpm. OR ICE rpm 1500, speed 35mph, MG1=0rpm.)

 

The term "resistance" is misleading. MG1 must actually turn its input to the PSD against the force of the ICE in order for power from the ICE to flow to MG2, and from there to the drive train which is directly connected to MG2. Other than during braking there is no time at which either MG is configured to "resist" motion.

Also, stating that the ICE can drive the wheels without power from either MG is just wrong. Sure, the power can come from the ICE - so what? All the power comes from the ICE at some point. No matter where the power is coming from, at least MG1 must be actively driven in order for any power from the ICE to reach the wheels. The only power source that can drive the wheels directly without another power input is MG2.

 

I'm going to rephrase what the others have said, but in a simple fashion. If you want technical details, go to the link about the PSD (Power Split Device).

Here it is in a nutshell:

1) The Prius has two Motor-Generators, MG1 and MG2. They are called motor-generators because they serve as both electric motors *and* as generators. They can do either, depending on whether you put electricity into them or take it out.

2) The Prius has one Internal Combustion Engine (ICE), which is a gas engine like that on any normal car. It has some nifty features to make it more efficient, but that's not relevant to this discussion.

3) The two MGs and the ICE are always coupled to each other and to the drive wheels. This is done through gearing. There is no clutch or transmission in the normal sense.

4) MG2 can directly drive the wheels without any help from MG1 or the ICE.

5) The ICE can directly drive the wheels, but only if MG1 provides some resistance. Otherwise MG1 will freewheel.

6) The ICE can also indirectly power the drive wheels by spinning MG1 as a generator and sending this power to MG2 which works as a motor to spin the drive wheels. When doing this, some of the power from the ICE is also mechanically coupled to the drive wheels.

7) In addition to being used as a generator, MG1 also serves as the starter motor for the ICE.

So what does this really mean? Normally some of the power from the ICE goes mechanically to the drive wheels and some of the power goes from the ICE to MG1 to MG2 as electricity. At lower effective gear ratios, a greater percentage of the power is sent along the electrical path from MG1 to MG2.

When lightly loaded, the Prius may also run without the ICE. In this case power comes from the battery and goes to MG2 to turn the drive wheels.

Tom

 

This post is wrong. The intention is good, but the poster has become confused in the details. There are two issues above divided into two paragraphs. I'll number them 1 and 2:

1) The term "resistance" is not misleading. The most common operation of MG1 is to work as a generator, where it is indeed resisting the motion of the ICE. In this mode, the ICE supplies torque to the drive wheels and torque to MG1. By resisting the torque from the ICE, MG1 balances the torque supplied to the drive wheels. Without this balance the ring and planet gears would freewheel. The resistance of MG1 generates electrical power which goes to either the HV battery, MG2, or both.

The is also the heretical mode where MG1 works as a motor powered by MG2. Of course MG1 also works as a motor when starting the ICE.

2) The ICE can indeed power the drive wheels without power from the MGs. In this direct drive mode, MG1 is locked in place to counter the torque going to the drive wheels, but since MG1 is not moving there is no power contribution.

Tom

 

Not to be picky but...

The exact wording should be that the ICE appy 72% of its torque to the wheels/MG2 and 28% to MG1. Power can be split (by the Power Split Device) in any proportion between the two. As an example, when the car is stopped and the ICE is running to recharge the battery, 72% of the torque is still applied to the wheels and only 28% to the generator but as the wheels are stopped, all the power goes to the generator.

So:
1. The 72/28% torque split is fixed.
2. The power split can be any, as decided by the computer control systems.

 

Also note that if a MG is being "locked" or providing resistance it is absorbing power from the system. It takes current to do that. Voltage times current is power. It just doesn't take a -lot- of power. I'd bet it's more efficient than a cone type continuously variable transmission.

 

Your post could be interpreted as saying there's some mechanical lock preventing MG1 from rotating. There isn't. It's all done with electromagnetic forces from current flow, either powering the field coils or resisting the production of current in the coils. The only physical lock that prevents any part of the transmission rotating is the parking pawl, which applies to the outside of the ring gear, physically preventing MG2 from rotating when in Park.

The car cannot move off from a stop under engine power alone, assuming MG1 does not rotate. The engine would have to be able to produce torque from a standstill, which it can't, it would simply stall. Conventional cars have limited slip systems (torque converter or slippable clutch) which allow the engine to rev higher than the speed imposed by the road speed, divided by the selected gear ratio, to avoid stalling. The Prius has a torque damper similar to a clutch but it's not intended for slipping in the sense used in manual transmissions.

Even if it could move off, the engine still produces relatively little torque. Conventional transmissions use gear ratios (either a limited number of fixed ratios, or a belt-and-cone system that effectively varies the ratios) to multiply up the torque from the engine, so the torque at the differential is typically quite high. The Prius transmission doesn't have any selectable torque-multiplying ratios.

To move away, it uses the high torque of MG2 which can deliver about four times the torque that the engine delivers at peak (Gen 2). Gen 3's inherent MG2 motor torque is lower than Gen 2, but has a multiplying ratio between the motor and the PSD, delivering greater torque at the PSD than Gen 2. Electric motors can deliver practically their maximum torque output from rest, they will not stall.

 

The terminology gets tricky in this situation. From the control perspective, locking MG1 requires field current, which indeed consume electrical power. However, from the standpoint of the transmission of power, a locked MG1 consumes nor supplies any power, since its speed is zero. It is kind of like the power used to lock the brake bands in place for a normal automatic transmission.

The net result is that locking MG1 takes a bit of energy, but it does nothing with that energy other than make heat. It is a loss.

Tom

 

I read the above post and marvel that Toyota has devised such a system. I do not understand it, nor do I understand the diagrams I have seen, but I do understand that it is an engineering marvel.

On another thread, I read that Toyota's genius, was energy management. It really is remarkable that such a vehicle can be built for the general public, that it is so comfortable. easy to drive, reliable, that uses such a small battery, and is fuel efficient. Sure, future vehicles promise to do better, and I certainly hope they do, but I have one of these wonderful machines in my garage ... now!

 

Just to help me complete the picture... how is the ICE able to idle in park? Is it physically disconnected from the PSD or does it spin the outer ring but somehow does not spin MG2? Hmm I guess it would have to spin the ring so MG1 can recharge the traction battery. ??

 

The brakes are applied, keeping MG2 (the wheels) stopped. MG1 spins with energy from the battery, forcing the ICE to turn, then ignition is applied to the ICE. With the ICE then spinning and generating energy, MG1 will not simply spin freely, but will usually apply a electromagnetic counter-torque on the ICE, generating current to charge the battery. It will only "idle" to heat the ICE in the first moments, until the catalytic converter is hot enough to chunk through exhaust gases.

The latter is correct. MG2 and the wheels are attached together. To answer your question, there is no clutch (and also no mechanical torque converter). Everything is achieved through a balance between the rotations of MG2 (the wheels), MG1 and the ICE. If one turns and one is stopped, the last one needs to also rotate.

 

OK, this is starting to sink in. So while MG1 is starting the ICE (outer ring spinning, inner ring stationary, if the ICE is having a little trouble catching, this is likely the cause of occasional rough starts because there is little to no play in the gears and it is fighting MG1.
The more I figure this thing out the more amazing the physics become. Thanks for the information.

 

The ring gear is physically locked by the parking pawl (well, there's a little free play). The engine is connected to the planet carrier - when the planet carrier rotates the planet gears are pushed against the stationary ring gear. Because it can't move, the planet gears turn in the opposite direction. Because the planet gears are rotating, the sun gear (connected to MG1) is pushed in the opposite direction to the planet gears, i.e. in the same direction as the planet carrier. Therefore MG1 is pushed around so it charges the battery.

One of the complexities is that both MG1 and MG2 can act as either motor or generator at any time, though they never perform the same role at the same time. Regen braking is normally done by taking power off MG2 as a generator, and when driving MG1 is normally a generator and MG2 a motor, but there is the 'heretical' mode where MG1 is a motor and MG2 a generator.

Graham's original Prius site (frames) has a good What's Going On As I Drive page. He wrote it for Gen 1, so some information is a little out-of-date, but the geometry of the PSD is the same across all three generations. Gen 3 has a different final drive ratio and wheel+tyre diameter to the earlier cars so the ratio of MG2 speed to road speed is wrong.

 

As explained in the post above, you've got things reversed. It is:
1. Motor-generator1 (MG1) is the sun gear, in the center. It is usually used as a generator.
2. The ICE is the planet carrier, in the middle
3. MG2 is the ring gear, at the outside. It is attached to the wheel through a gear reduction box (upgrading torque to the wheels). MG2 is used as a motor to move the car, and as a generator when using regenerative breaking.

 

You are right, I had it backwards... thinking MG2 was at the center instead of MG1. Thanks again.

 

That's not a good scenario which is why Prius accelerate with HV battery first. Depending on how hard I press the accelerator, I can accelerate on HV battery up to 7-15mph while keeping up with cars around me.