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Written by Kacey Green
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Wednesday, 06 September 2006 |
Technology Review reports : 9/1
GM and partners vow to beat Toyota with mechanical engineering.
When it comes to hybrid vehicles, electronics and batteries tend to get the most attention. But it is elegant mechanical engineering that established Toyota as the market leader in hybrids. Now General Motors, DaimlerChrysler, and BMW are applying mechanical engineering to catch up. The three manufacturers have joined forces to develop transmission technology that could beat Toyota's system--at least on the highway.
Toyota's patents for their hybrid vehicle focus on the control systems and sophisticated transmission used to shift and share power among the engine, electric motors, and wheels. "There's a lot of mechanics in the system," says David Hermance, executive engineer for environmental engineering at Toyota's Gardena, CA, Technical Center. "Even if you make significant improvements on the electrical side, if you don't do a good job on the mechanical side you don't get as much efficiency, and you're looking to improve efficiency every place you can."
I don't see how this "Two-Mode" system can be more eloquent than Toyota's Power Split Device, PSD (planetary gear-set that functions as the transmission and power transfer device in THS, THS II and HSD systems). In Toyota's PSD you don't have to worry about transmission failures because the unit is permanently engaged, so it doesn't wear out in the same way as an automatic or "Two-Mode" transmission would. The article mentions having the electrical system never shut off is a drag on the system. The electrical system can essentially freewheel and with it always being at the ready you can change hundreds of times per second the power flow such that you get more efficiency by not having to go through a shift operation every time you hit a slight downhill or uphill...
Compare the complexity of the GM "Two Mode" system shown above, to the Toyota PSD shown here:  lets not forget this is the same hybrid transmission that is used by Ford and Nissan, Ford makes their own hybrid components with Toyota patents and Nissan buys their hybrid components from Toyota. Look at the size benefit here, the electric motors don't get downsized either because the space savings already give you space for larger electric motors. With the Toyota hybrids four wheel drive is handled by a dedicated electric motor on the front or rear axle, this way there are no losses from a drive shaft for a feature that isn't used as often. (Studies show most 4x4 owners rarely use this feature.) GM is targeting a savings around 10% less than Toyota already gets today. (If Toyota gets 40% today GMs Target is 30%, I can't find the exact numbers)
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Last Updated ( Sunday, 26 August 2007 )
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