I think you have all the questions and concerns about gears that many of us have.
You can just jump in based on the experience of others or you can do the math and get a good idea what will happen. Some of the EV books discuss this and there are web sites that help, search for "ev calculations". The original ICE car was designed and optimized by a large group of engineers. The ICE engine has a narrow power band (range of RPM's) where torque and RPM are available to move the vehicle. To better match that power band to the road, the transmission changes the Torque and RPM delivered to the wheels. First gear reduces the RPM to the wheels and increases torque to accelerate, as vehicles speed increases more RPM are needed and less torque is needed and that requires a different gear. The series wound DC motor used in most conversions have a different Torque and RPM characteristics. They have very high torque at low RPM. As the RPM pick up the torque drops and the range of usable RPM is much larger the equivalent of 3 gears with an ICE. The question is which gear will be best. In my conversion I have chosen a 67 KW peak (30 KW continuous) AC motor. It has much less low speed torque than the DC motor and more high speed torque. The torque produced by AC is constant over the full range of RPM from zero. With the constant torque I will need to maintain my transmission and I expect to use first and third gears. If I could use a larger motor and batteries, like in a eBox 120 kW peak, 50 kW continuous, no gear changes would be needed. David Kerzel -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Katie Robinson Sent: Sunday, August 17, 2008 2:26 PM To: FLEAA Mailing List Subject: [FLEAA] Transmissions and meet idea When doing an EV conversion is it better to have a transmission that is geared towards (ICE) performance, or efficiency? I ask because I know EVs can do fine in only 1 gear, and I would hate to be missing that best gear ratio. Perhaps it depends on the rest of the components, and what the goal of the conversion is? Also, I was thinking it would be a good idea to do tire pressure checks at our meetings. They do them the the Milwaukee Hybrid Group meets, which I got a taste of when I went to HybridFest last year. It's a great way to remember to check your tires every month. I would guess, at Coastal Tire and Auto at least, we'd have air to pump up those who are low. -Katie _______________________________________________ Florida EAA mailing list [email protected] http://www.floridaeaa.org _______________________________________________ Florida EAA mailing list [email protected] http://www.floridaeaa.org
