. . . The power split hybrid approach is similar to single-mode hybrids that create two paths for applying torque to the wheels from a gasoline powered internal combustion engine and a battery powered motor. However, instead of a generator and a traction motor used in single-mode hybrids, the two-mode Electric Variable Transmission (EVT) hybrid has an electric variator that uses two 60-kW motors, one that operates in low speed range and one that operates in the high speed range.. As explained by Peter Savagian, engineering director for Hybrid Power Systems at General Motors, planetary gears split the engine power and can multiply all torque.
Clutches activate the EVT modes and fixed gear ratios. With fixed gears ratios, the motors do not have to carry engine power. The results are improved fuel consumption in real world driving with increased continuous duty operation for towing and increased speed range for high-speed driving. . . .
This article has more details about the 2-mode transmission and a couple of videos. One shows the motors in operation and the other shows a moving cutaway of the internal parts. BTW, 60-KW is ~80hp. Included in the article was this system sketch:
Interesting although I wonder why the first clutch is needed. The planetary gear between the ICE and first motor makes sense but the clutch doesn't. Otherwise, the rest looks good to me.
It might be there to atenuate the torque spikes caused by the ICE. It may also suppress some of the vibrations before they reach a tight running planetary gearset. This could be a mandatory design feature/compromize for larger engine platforms - which this appears to be the case.
It might be there to atenuate the torque spikes caused by the ICE. It may also suppress some of the vibrations before they reach a tight running planetary gearset. This could be a mandatory design feature/compromize for larger engine platforms - which this appears to be the case.
The Prius has a permanent clutch called a "torque limiter" that is a clutch-plate bolted to the flywheel holding a clutch disk. The disk still has the rotational springs but otherwise, is a fixed part of the drive train. There have been reports of the torque limiter wearing out in Europe where higher speeds are more commonly found.
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Re: GM's 2-Mode 2008 Hybrid
Did you see the description of the 2-mode presented by GM/BMW/DC earlier. From their schematics it appears that they see their main benefits as being that they have a larger flow of mechanical energy ( ICE+traditional transmission ) than the Toyota model which has a larger flow of electrical energy.
The fact that they can use an existing mechanical coupling which is durable enought for large vehicles and heavy towing with an electrical alternative at times of low load gives them a benefit in large SUV's and trucks. The THS being primarily, in their view, electrical power is not durable enough for heavy duty applications.
The three 2-moders further go on to point out that their system is 'scalable' to any vehicle since the motors are part of an existing mechanical transmission. This is where they say that migrating the system to the Aura or Malibu or even down to the Cobalt or G5 is easily done.
Much of what is already part of the current hybrid systems will also be part of the 2-mode package; regenerative braking, engine off during coasting and stopping. Although I don't think that they will be able to charge their battery packs during continuous operation such as a long highway drive ( no PSD ). I have to look further into this though.
It does look like an interesting development. My main question is while it is 'scalable' to smaller vehicles will the basically mechanical coupling ( ICE==>mechanical tranny ) be as efficient as the THS II ( or THS III )?
It may be that GM/DC/BMW have staked out the heavy vehicle segment.
Toyota has staked out the midsized vehicle segment.
Honda has staked out the small vehicle segment.
All of this is subject to sudden new technological developments now hidden in some corporate fortress lab.
Lifetime fuel usage: 2.1 GPC at 90,000 miles & counting
GM's 2-Mode 2008 Hybrid
