Prius Generations

John, I just went to your web site and looked at the PSD digrams. How cool!!! What an elegant bit of engineering! Thanks for the wealth of info you provide for us new owners.

 

Dang, the one thing I was looking for on the chart was mpg. A little effort is required to adjust for the EPA methodology changes, but everything else on the chart is engineered to achieve those mpg numbers.

 

I am confused by John's table. In much of the previous narratives the Traction Motor has been designated as MG2, with MG1 being the smaller motor/generator supplying electrical power to drive MG2, in addition to providing torque for starting the ICE.
It also provides resistive torque under heavy acceleration to MG2 and the ICE.
If the Traction Motor (TM) in the G3 Prius is providing lower torque levels than the G2 variant, the only explanation must be that the PSD gearing and final drive ratios have changed. That would also require a change to the TM maximum RPM (higher?) too, would it not?

 

To remove the North American-centric nature of the chart you could include that outside NA the stock tyre width is 195mm but like you say John, you want to keep it simple. It's a good job.

Could you include 3 more lines?
Total interior space in cubic feet or litres
Luggage space in cubic feet or litres
Passenger space in cubic feet or litres
These are areas where there have been constant improvement and if your not carrying anything or anyone in a Prius it's just an ornament.

 

Hi John,
Thank you for the table.
I had an opportunity to see a preliminary Toyota shop manual and I would like to comment some...

* max MG2 rpm is 13,500rpm.
(I believe we heard the max MG1 rpm is 13,500 at PCD, but Chief told us wrong information, maybe.)

The shop manual says battery power is increased from 25kW to 27kW. I believe the MG1 kW is ...
* MG1 kW is 60kW(motor)-27kW(battery)=33kW
(The Iconic MG1 kW is 50kW(motor)-25kW(battery)=25kW)

Anyway, my dealer told me the final shop manual will be available by mid March.
I'll try to update these information then.

Ken@Japan

 

Gears.

Gear ratios reduce revolutions and increase torque, or vice versa.

Let's say we have a pair of gears with 30 teeth on the drive gear and 60 teeth on the driven gear, a ratio of 1:2. For every revolution of the drive gear, the driven gear moves half a revolution: we have to turn the drive gear twice to get one revolution of the driven gear.

Say the torque is (arbitrarily) 100Nm. Say our drive gear is 20cm (0.2m) across. Torque is force multiplied by distance, so at the teeth, the force is the torque divided by the distance, so here it would be 1,000N (because we're looking at the radius, not the diameter). Our driven gear is twice as big to accommodate all the teeth: therefore the torque is 1,000 x 0.2m = 200Nm.

If I recall correctly, from a diagram I saw here, the Camry Hybrid setup has MG2 driving the sun gear of the second planetary set, while the ring is coupled to the first planetary set and the final reduction gear - the planet carrier is fixed. I'm not sure how that works out in terms of ratios.

Frankly the motor manufacturers might as well not quote half the stats they do, as they're effectively meaningless - they're basically playing [ame="http://en.wikipedia.org/wiki/Top_Trumps"]Top Trumps[/ame] with each other. The important statistic is how much force is actually applied to the road, which is a function of the engine output torque at the current engine speed, and the selected gear ratio.

MG2 may well max out at 13,500 rpm, but if the final drive ratio is the same as the earlier cars, that would be a top speed of something like 200mph. Clearly that's not right! Again, the division of the gear ratio corrects this.

 

Speed Reduction Unit in the Camry hybrid multiplied MG2 torque by 2.48 times. We'll have to see if that's the same for 3G Prius.

Dual stage would add a third PSD and two clutches. I am still not clear (due to conflicting info) if 3G Prius will have dual stage. So far we have only seen the dual stage in the Lexus RWD performance hybrids.

 

Hi Ken,

Please tell us more!

Hi Evan,

Please note that we also were given the torque ratings and other data, printed in the Media Information DVD jacket.

 

18kws of extra power manages a better 0-60 time of 0.3secs. A result of all that loss in torque?

 

I believe the 2 stage refered to is the final drive reduction is 2 stage, that is there is a primary and secondary gear reduction. There are no clutches or changable ratios. I don't know if the chain drive in the iconic Prius was a reduction ratio or just a way to get the drive out from between the 2 motors?
I could be wrong, I was wrong once before ...

 

Looking at Art's transaxle teardown, the chain drive in a classic Prius looks like it was 1:1. It couples the PSD ring gear to the main reduction gear, which drives the differential.

If I recall correctly the repackaging of the new transaxle means no more chain drive, which hopefully will reduce the slack and therefore the distance rolled when the car is put in Park.

It doesn't really matter how the drive gets there, but there is an additional ratio between MG2 and the wheels that wasn't there before, so the reduction in actual motor torque is multiplied back up with no change (or even possibly an improvement) in torque at the wheel. It may be that the change means greater torque across a wider rev range compared to the Iconic Prius.

 

I reduce the roll distance in park by using the park brake, works great.
I wonder what the overall final drive reduction is compared to the Iconic, because MG1 spins faster it can be geared lower yet still maintain the same or lower engine revs. Yep, this might more than make up for the overall torque reduction.

 

Not less torque at the drive wheels, just less torque at MG2. MG2 is more powerful on the 2010, but develops the power at higher RPMs, requiring gearing. MG2 is also smaller and lighter.

We were told 9.8 seconds at the show in Detroit.

This is still somewhat fuzzy. Attempts to clarify have been inconclusive. I wish Prius Team would come up and give us a conclusive answer.

Tom