Practical Limit on Gear Ratios for Automotive Application

[TheSwener]

Hi All,

I am doing some early thinking for a light (~60hp) EV application, trying to understand what the options are for reduction gearing and I could use some help!

- We would like to achieve ~8:1 reduction between the motor shaft and the axle. Is this possible with a single stage helical or spiral bevel setup? Any higher?

- My understanding is that a hypoid could handle this, but would the added expense and efficiency loss make a 2-stage helical reduction the better option?

- What happens if we try to transfer power backwards through a hypoid (i.e. regen braking)? Will it work at all, poorly?

- I have heard that gearing through perpendicular shafts is inherently less efficient than parallel - is that true?

Any advice/professional opinions on the limits of each option and which would have the lowest total cost would be incredibly helpful, thanks!


Rob

 

[tbuelna]

TheSwener,

If you can keep your gear shafts parallel, that is probably a good start. The housings and bearings are usually more compact,lower cost, and are easier to assemble with parallel shafts.

You could theoretically get an 8:1 reduction with either a single stage spiral bevel or helical/spur mesh, assuming you have the room. But you'll have to do a trade study of each, taking into account power, speed, torque, PLV, volume, etc.

Spiral bevels and hypoids have excellent torque capacity, but they also tend to have slightly lower efficiency due to some inherent contact sliding. Spiral bevels and hypoids can drive in both directions, assuming their bearing mounting is designed properly. But the meshes also would have less capacity in one driving direction, due to the shape of the tooth flanks.

Hope that helps.
Terry

 

[MikeHalloran]

OR, you could use someone else's production axle assembly, with say a 3:1 reduction and a differential built in, and drive it with a 2.6:1-ish reduction of your own, which you could do with commercial spur gears or a timing belt.



Mike Halloran
Pembroke Pines, FL, USA

 

[TheSwener]

Hi guys, and thanks for the input. It sounds like there is no obvious choice (as usual)...

Which companies would be best to talk to for help with this kind of work? I'm in NorCal, but local isn't necessary.


Cheers,

Rob

 

[TVP]

For hypoid systems, Dana or AAM are the largest automotive suppliers. Magna Powertrain is another North American option. Saab and AAM recently announced a JV for hybrid and EV applications, but there isn't a dedicated website yet, so you can contact Saab Engineering.

http://www.dana.com/wps/wcm/connect/Dext/dana/markets/light+vehicle/drivetrain/drivetrain+systems

http://www.magnapowertrain.com/xchg/en/102-2308/powertrain_systems/Products+&+Services

http://www.aam.com/index.php?s=29

http://www.saabengineering.com/engineering/powertrain/