Actually, this is the HSD-II system found on the gen 2 Prius and all newer Toyota and Lexus hybrids. The second gearset is just used to raise the gear ratio between the torque motor and the wheels and has one of the three gears fixed. That is, it is just a gearing for the second electric motor to make it more efficient, used more like planetary gears are typically used.

-- Alan

 

Hi

In the high-end GS450H they do have a changeable gear-ratio:

From the Lexus web-site:
"The car has one last trick, a two-stage variable gearset that basically — although nothing is basic in this car — acts like a two-speed transfer case between the big electric motor and the driveline, multiplying torque at low speeds (equivalent to a 3.9:1 rear-gear ratio) and reducing engine rpm at high speeds (1.9:1)."

I expect this is mainly to improve performance and the top-speed. The Camry put a fixed ratio between MG2 and the transaxle to increase the motor power to 110KW from the 50KW in Prius, increasing the max rotational rate of the motor to 12,500 RPM.

In the HSD design the top speed is limited by (among other things) the output voltage of MG2 causing the main DC rail to reach the design limit (500V in Prius, 650V in others) - having a variable ratio extends that limit.

kevin

 

Thanks! That is very cool.

I traded my GS300 in on the Camry Hybrid, in part, because I did not like the new GS design (many reasons, but performance was not one of them!). My GS sure did have great performance, but this hybrid has a higher fun quotient! Never thought a car could make driving for FE fun, but it sure does.

-- Alan

 

The smart fortwo cdi was rated at about 70 US MPG in the EU cycle overall up to last model year, and it is an absolute brick of a shape...mind you the Polo is a fair bit quicker than the smart, so losing 10 MPG for that and two extra seats is not a bad thing. The next generaton one will be interesting to see.....both the soft hybrid (basically stop/start) and cdi....

Mine is averaging overall the same 3.8 L/100 km (~62 MPG US) that Transport Canada estimates for highway fuel economy, despite (recent) wider wheels/tires and a basically carefree (FE-wise) driving approach.

We won't be seeing this Polo in North America anytime soon.....