Transmissions

[steve.sagerian]

I understand that we don't want to convert a vehicle with a automatic transmission due to its poor efficiency. Is the reason we want a manual transmission is to simplify the controller electronics for reverse, parking, and neutral  ? It seems like one of the biggest benefits of an EV motor is the ability to shed the old ICE and its transmission. Is this a trade off until better, safer and cheaper controllers come along?
THanks!

Steve

[rich.carroll]

Automatic transmissions control their shifting by a combination of electronics, mechanical linkage, and hydraulic pressures within the valve body.  This is difficult to over ride when converting to an electric motor.  Automatics are preprogrammed by their manufacturer to shift at certain points depending on the load to the engine (uphill or not) accelerator position, vehicle speed, and engine rpm.  All of these shift points were carefully selected, based on a motor with very specific torque peaks and a specific horsepower band. The torque converter is an integral part of the system, and the torque converter is factored into every calculation.

Electric motors do not need a torque converter, they develop high torque at few PRM's.  Electric motors are fairly insensitive to their speed, but do have a "sweet spot" that is about 4000-5000 RPM in many, but variations in manufacturing can change this.  Many EV drivers prefer to have a manual transmission so they can leave the trans in second or third or fourth for most driving.  (I say second, because my car has a three-speed stick)  The favorite gear of most EV drivers is not a direct drive. (unless, or course, you rebuild the differential with a 4:56 ratio or wilder.)

A few folks have built vehicles without a transmission, but this usually does not allow the safety of being able to disconnect the power from the drive wheels in an emergency situation.  Without a transmission, reverse is not a problem, the motor can be electrically reversed.  Most vehicles need to have a working emergency or parking brake.  This takes the place of "park."  We do not recommend building a vehicle without a neutral or a means of disconnecting the power from the drive wheels.

[todd.dore]

While I'm not enough of an expert on the nuances of ATs and MTs, and why MTs are better for EVs, I appreciate Rich's clear and easily understandable explanation.

From my experience, it is a far easier adventure to start with a donor vehicle that is manual than to try to swap one out. 

We did finally get the MT to work in Electric Bug (many thanks to those that helped, esp. Jim Dawson).  And I can say that for an EV with a clutchless MT where you use perhaps 2 gears and a reverse, this is probably the most simple setup there is.

[steve.sagerian]

If I have a manual transmission ICE and I take it out of gear and let off the gas, the vehicle will coast and slow down. I can apply the brake to slow down if needed.  Is it so (similarly) that if I have an electric vehicle without any transmission, if I let off the throttle will the power to the motor will go to zero and I can also coast and apply the brake? Is that a true assumption?
Is the issue with safety more along the lines that if I let off the throttle and the pot box linkage fails,I could have power still going to the motor without any way to turn it off?

thanks

[michael.henry]

 Yes, power disconnect in a direct drive vehicle is a must. Probably any EV.
I set up a linkage to a large Anderson connector from the clutch pedal. Step on the pedal and main power is interrupted.
                                      Mike

[steve.sagerian]

Mike,
thanks for the response. Can you point me to this "Anderson connector".

Steve