Does the 2010 drive system work backwards?

At the 2010 Pius event last Sunday, Toyota had glass case with the current generation power split device and a 2010 power split device. One main difference is that the current version uses a drive chain connecting two main shafts, and in the 2010 version - a pair of gears connects the shafts. Great idea as this elliminates another moving part (the chain, and all of its' bits and pieces). Ok, so when two shafts are connected by a drive chain (or belt), both shafts rotate in the same directions. When a pair of gears mesh, the shafts rotate in the opposite direction. Having said all of that, A) is there another set of new gears that reverses the drive gear set direction? or b) Does the 2010 power split device now run backwards compared to the current generation 2004-2009 Prius?, or C) does the Prius drive very fast in reverse, but only up to about 25 mph going forward? or D) is there something else going on??? (I don't think the answer is C because the 2010 I drove worked just fine going forward.)

Keith

Hi Tech Guy,

Doesn't the Gen II Prius have an additional shaft (not shown in your picture) ? And its the transfer from the chain driven shaft to the additional shaft that reverses the direction. I seem to remember comments about that in one of the National Labs papers that it was extra gearing loss.

With the 2010 configuration the extra gearing loss only applies to the MG2 to axle path, rather than both MG2 and the Engine's path to the Axle, as with the Gen II Prius.

.

The answer is A).

Ken@Japan

nice picture thx a lot

I believe it is more correct that the final output gear count before the differential has gone down by one. The left, NHW20 chain drives a gear that turns the second gear that drives the differential. The Right unit doesn't have the chain power takeoff gear.

Something I just noticed is the smaller width of the 2010 final gear compared to the older NHW20. The width of a gear is normally an indication of the torque. This suggests the differential, power takeoff gear has a larger diameter and does more of the rpm reduction.

Not shown is the extra gearing in the power split device (PSD) needed to handle the higher MG1/MG2 rpm. Depending upon how one counts the planetary, spider gears, the number of gear stages is roughly the same because the PSD now has two gear stages.

I am really looking forward to the 2010 SAE paper!

Bob Wilson

Any idea when the SAE paper you referred to will be out, Bob, and what it will contain?

Looks like the SAE paper will show up in April, per this reference: Green Car Congress: Toyota Previews Generation III 2010 Prius Hybrid

Hi Bob Wilson,

They look the same width to me. The gear that drives the differential is the smaller diameter gear on the most forward of the shafts in the picture. The Gen II drive train is more forward in the picture.

Hi Bob,
Have you ever seen following ORNL paper about Camry Hybrid?
Information Bridge: DOE Scientific and Technical Information - Sponsored by OSTI

The transaxle is shown at page-37(48 of pdf) and below.
The reduction gear structure can be seen on page-42.
The 2010 Prius gear structure would be similar to the Camry's.

Ken@Japan

Good reference, thank-you Ken. If the new G3 Prius does share the same transaxle gear-set with the Camry, it appears from the analysis in the reference paper that the MG2 max. torque level gets multiplied up in the transaxle by the speed reduction gear ratio of 2.478, which would increase the the final drive torque to 2.478 x 153 = 379 ft-lbs. That is over 28% higher than for the G2 model Prius, hence the livelier 0-60 mph acceleration, assuming the final drive ratios result in a similar top speed.

Prius Team provided the SRU ratio to be 2.636.

MG2 torque after the SRU would be 153 x 2.636 = 403 lbs-ft torque, making it 37% increase over the Iconic model. The final gear ratio for the 2010 is 3.267 so you are looking at 1,316 lbs-ft at the wheel.

For the Iconic model, MG2 torque with 295 lbs-ft and 4.113 final gear ratio makes it 1,213 lbs-ft at the wheel.

The 2010 Prius' MG2 has 8.5% more torque at the wheels. Remember, when the gas engine on, you'll also have 72% of it's torque at the wheel as well.

The Iconic's ICE outputs 82 lbs-ft of torque. 72% of it is 59 lbs-ft. The 2010's ICE outputs 105 lbs-ft and 72% is 76 lbs-ft.

Overall ICE+MG2 torque output at the wheels for the Iconic and 2010 are as follow:

Iconic: (59 + 295) x 4.113 = 1,456 lbs-ft
2010: (76 + 403) x 3.267 = 1,565 lbs-ft (7.5% increase)

P.S: There is a slight change in the wheel diameter and 110 lbs weight increase in the 2010 Prius that we need to take account.

Your numbers may well be correct.
But what are the tooth counts on the SRU planetary unit that give the 2.636 torque multiplication factor?.

The planetary PSD carrying the ICE and MG1 appears to be identical to the G2 Prius with the internal ring gear of 78 teeth, 4 planet carrier gear teeth of 23 count and a sun gear of 30 teeth, giving sun-to-ring ratio of 2.6 (78/23 x 23/30).

I believe that is 20% of the existing ~92-93% efficiency. We really need the absolute transmission efficiency to understand the drive train loss. In absolute terms, I think we're looking at ~1-2% transmission efficiency gains, which is terrific considering what we see with the 'honorable competition.'

Bob Wilson

As Yoshi-san pointed out I corrected my calculation. My prior calculation did not take of the final drive ratio of the ICE torque. Corrected value:

Iconic: (59 + 295) x 4.113 = 1,456 lbs-ft
2010: (76 + 403) x 3.267 = 1,565 lbs-ft (7.5% increase)

usbseawold2000,

These are the exact same number that you provided above, in posts #12 and #16. What is the correction. or am I missing something?

I corrected the post #12 also. You can see the mistake in the quote of post #14.

It is interesting to see the difference (26%) in the final drive ratio. 2010 PSD ring gear will be spinning 26% slower than the Iconic model.

So, if the planetary SRU for MG2 delivers a speed reduction of 2.636, the number of ring gear teeth must have increased by one (to 58) and the number on the sun gear decreased by one (to 22). The carrier pinion teeth remain at the same at 18, when compared to the Camry SRU.

Interesting... if they kept the PSD and SRU with the same number of teeth, it should be cheaper to manufacture just one instead of two different specs.