What did we learn from the Chief Engineer?

"Two-Speed" seems to be the most appropriate label I've encountered for the design/behavior. It avoids the craziness associated with Two-Mode while indicating that there is a second something available.

Anyone hear of an official identifier?

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I believe it is a fixed planetary gear. I suppose it could be a two-speed planetary gear, but then you need brake bands or clutches, and you start down the path to GM's dual-mode system.

Tom

 

I love you too.

 

Hi all,
Let me clarify about reduction gears.

The NHW10/NHW11/NHW20 Priuses have low-speed/high-torque MG2 and the ring gear is driven by the MG2 directly, no reduction gear.

The RX400h/Highlander/Camry have high-speed/low-torque MG2 and the ring gear is driven by the MG2 through reduction gear (single stage).

The GS450h/LS600h/2010 Prius are designed to cover wide range of speed more efficiently, then the ring gear is now driven by the MG2 through two-stage reduction gear.

TOYOTA: Company > Technology

Ken@Japan

 

The HSDII for the TCH has a second planetary gear set for MG2 speed reduction. The ratio is 2.6:1 and single speed only.

I believe the G3 uses the same system.

 

Japanese press clearly says 2010 Prius has two-stage reduction gear.
2010 Prius at Detroit show

Ken@Japan

 

Thank you Ken.
Can you provide for a better link where a nice diagram of the GS450h/LS600h system is found? Anyone?
I would like to understand what are the connections, what spins with what, and that page that Ken provided at Toyota does not show that.

P.S. - Ken I have sent you a private message some days ago, can you please check it? Thanks.

 

Interesting, Ken. Thank you for the information. This begs several other questions:

1) How is gearing shifted between the two ratios?

2) Will we be able to detect the shift, as in some sort of shift shock?

3) Will the shifting mechanism reduce the overall reliability of the HSD?

I can take a guess, and that's all this is:

1) I imagine they are using a planetary gear system where one section freewheels or is locked depending on the ratio.

2) Shift shock should be minimal, since we are dealing with a fast electric motor, but I'm going to guess that we will be able to detect it. If we can't feel it, then they might be using some sort of smooth braking system on the planetary gear; perhaps an electromechanical lock.

3) More parts, more mechanical things to break. I don't suppose it's a big hit, given Toyota's track record, but added complexity always concerns me. That's one of the things I like about the original HSD - it's so darned simple.

Tom

 

A two-stage reduction doesn't mean that you will switch between two ratios.

• A single-stage reduction uses 1 set of gears (2 total) to achieve the required reduction ratio.
• A two-stage reduction uses 2 sets of gears (4 total) to achieve the same reduction ratio.
• A three-stage reduction uses 3 sets of gears (6 total) to achieve the same reduction ratio.

There is no limits to the number of stages

Why would you want to use two-stage instead of a single stage to get the same reduction ratio? Size. Every additional stage reduces the size of the gears so you can achieve the same reduction ratio within a smaller package. You can also use different stage reductions to change harmonic frequencies to get them to cancel out instead of resonate.

In Bedrock's PDF from the Compound Gear Unit to the Final Driven Gear is a two-stage reduction.

The transmission company that I worked for used a two stage reduction from our motor gear to the final gear for packaging reasons. The downside is number of parts, complexity, and cost.

This is a two-stage reduction from a segway:

EDIT: If this was a one stage reduction the shaft with the 68 and 17 tooth gears would disappear and the 91 tooth gear would need to be a 360 tooth gear.

 

Two stage is different from two speed. Two stages means the final ratio is archived by using two gear reduction sets cascades together.

 

The PHEV Li version will be in fleet use (by the hundreds) in 2009. There was no word that I heard about retail timing. We also heard that there is no (Toyota sanctioned) way to upgrade the 2010 production car to the later Li PHEV versin.

 

Thanks for that clarification. I mixed up stages and speeds. This makes a lot more sense.

Tom

 

So it seems to me that the final drive system is still two-stage, as it is in the current 2004 - 2008 Prius; does that mean that the silent chain step from MG2 is retained, for weight reduction reasons? The gearing ratio between the higher RPM MG2 motor is probably increased to provide the enhanced 0 - 60mph acceleration, since the larger (1.8L) ICE torque curve at low speed is probably not much better than the smaller 1.5L ICE in the current Prius.

This is a lot of guessing on my part; I'm sure those with more info can correct and enlighten me!

 

The question I got to ask was about grill-blocking. I suggested the Prius seemed to have excess cooling capacity, particularly for some climates at certain times of the year. I asked if there was any thought given to thermostat-controlled louvers on the air intakes, which would lower the aerodynamic drag and improve the cabin heating and the mileage. I got the impression he'd love to be able to do something like that, but cost considerations pretty much ruled it out.

 

Bummer. I CAN NOT believe it would cost more to make thermostatically controlled louvers than to stick a sun/moon roof on it. No concerns about water leakage, no 'tight tolerance' for windage when closed. No 'pop up / slide back' design and motor issues. No lost head room

The 'deciders' at Toyota just have not yet been convinced there are a LOT of people who could benefit from such a system. Do they know how many people are strapping pipe insulation over the lower grill and stuffing it into the upper grill?? Probably a good number of the 'special invitees' at the show. I suspect I could foam the entire engine compartment tonight (other than engine air intake) and not have it over heat tomorrow, it is supposed to be -17F.