Stupid Transmission question

[coastalcruiser]

This may be pertinent to just the Bolt, or to all EVs. Does the Bolt have any sort of traditional transmission? I mean, does the car shift gears like a conventional auto, or does the drive ratio between the offset gearing and the axles always remain the same? In that case I'd assume as vehicle speed increases, the electric motor revs proportionality increase.

Carla

 

[evguy]

I looked around and all I could find was this from Chevy's press release back in January:

Single Motor Drive Unit
Like most EVs on the road, the Bolt EV’s drive system uses a single high capacity electric motor to propel the car. But it’s the smooth, powerful and quiet motor design, gear configuration and shift-by-wire system that separates it from the pack.

The engineering team designed the Bolt EV’s electric motor with an offset gear and shaft configuration tailored to meet efficiency and performance targets – most notably more than an estimated 200 miles of range. The motor is capable of producing up to 266 lb.-ft. (360 Nm) of torque and 200 hp (150 kW) of motoring power. Combined with a 7.05:1 final drive ratio, it helps propel the Bolt EV from 0-60 mph in less than seven seconds.

Power delivery is controlled by Chevrolet’s first Electronic Precision Shift system. This shift and park-by-wire system sends electronic signals to the Bolt EV’s drive unit to manage precise feel and delivery of power and torque, based on drive mode selection and accelerator inputs. A by-wire shifter requires less packaging space than a traditional mechanical shifter, resulting in more interior space and improved interior layout.

From what I can interpret, the electric motor is hooked to a gearbox that gears it 7.05 to 1 (every 7.05 times the electric motor rotates, the tires rotate 1 time). That's the only indication of gearing, which makes me think there is no transmission - the speed is fully controlled by the electric motor.

 

[DucRider]

The Bolt will have one speed as with most (all?) production EV's. Conversions (Porsche's, Beetles, etc) usually utilize the existing trans, but 1st gear is useless and rarely are they actually shifted.

Tesla played with a 2-speed transmission when developing the Model S, but decided the extra weight and complexity were not worth it. We may see 2 speed transmissions (seamless?) in the future, but the current consensus seems to be that for all but the heaviest vehicles (think trucks, buses) the advantages of a single speed outweigh the benefits of multi-speed gearboxes.

Details on the Bolt motor/reduction gearing can be found here:
http://insideevs.com/deep-dive-chevrolet-bolt-battery-pack-motor-and-more/

Edit: This applies to BEV's - PHEV's all utilize multi-speed transmissions and a cost effective approach is to replace the torque converter with the electric drive unit. Mercedes (and BMW?) does this on their Plug-ins.

 

[coastalcruiser]

Thanx evguy and gary. It's making sense now. the electric motor just spins faster and faster as the wheels turn faster and faster.

And apparently the top speed of the car is hit before the motor spins so fast the magnets start flying out of the motor and poke through the hood. How convenient.

c

 

[WetEV]

Tesla played with a 2-speed transmission when developing the Model S, but decided the extra weight and complexity were not worth it.

Yes, Tesla played with a 2-speed transmission, but for the Roadster, their first model, before the Model S. The first few Roadsters shipped with a 2-speed transmission locked into high gear, and were retrofitted with single speed transmissions later.