----- Original Message ---- From: Edmund Storms
> So, taking your numbers, they use the same size engine as in a Prius. The > only difference is the way they couple the engine power to the wheels. The > question is, Is this method more efficient and lighter than the way Toyota > does the job? It appears to be better for two well-known reasons. First - electric motors give highest torque at 0 rpm and with gas engines it is usually over 2000 rpm, and consequently gas engines are inefficient in accelerating from a stop. Prius' present electric motor is too small to make a difference there. Secondly, gas engines are more efficient when run at a fixed rpm, and the genset permits this -- and GM has gone one more step by making the torque curve and power curve overlap at the fixed engine speed which saves the most fuel; Prius can't do that without an infinitely variable transmission. These may come out soom however. Then it will get down to cost. Plus GM has coupled their electric motor to some kind of special transmission for high speed. As for only ~35 kW from the ICE genset possibly being enough, or not -- when admittedly this is too little power for use with a normal drivetrain and transmission - this may also get back to the genset delivering the full amount of power- at all times regardless of the speed of the vehicle. Perhaps the genset requirement can be less than suspected with this kind of large electric motor as the main feature. IOW the electric motor plus batteries make it seems like you have 3 times more power when you need it on hills - that your genset can put out. When we we talking about this subject a year ago, before the Volt was even firmed up - it seemed that a good choice for the backup ICE would be the Wankel -- which is not normally though of as being "green" primarily because it is especially sensitive to having a "preferred rotational speed" (and it is a high speed) where it becomes efficient, when otherwise it is notably inefficient except in that narrow range. This is apparently due to the seals working best when they are compressed at high rpm. It is a gas guzzler when it must operate over a wide range of speeds, however, and this has limited it sales. It appears from the blip below that Mazda is about ready to introduce a Volt clone with said Wankel driving the genset -- and this makes sense due to the reduced weight and high rpm capability. Plus of all engine designs, the Wankel is the one which runs especially well on hydrogen - and so long as it can be a fixed speed only implementation - well - this could be part of the reason Mazda is choosing it over their 4-cylinder to compete with the Volt. http://www.autocar.co.uk/News/NewsArticle.aspx?AR=234607
