Hydraulic Pump & Motor 1

[spacewrench]

I am looking into using a hydraulic drive system in an electric motorcycle. My reason for doing this is that most braking force on a bike is in the front wheel, so that's the place to recover energy in a regenerative system. However, because of the way the front wheel must move, it's difficult to have a mechanical linkage to a generator (leaving aside the possibility of an electric hub motor, which I believe is heavier than a hydraulic motor of similar spec).

So, I'll need a hydraulic device that can be both driven as a motor (for going) and that can produce pressure as a pump (for stopping). (A similar device, run backwards, will be connected to the electric motor/generator.) My question is, what types of hydraulic pumps/motors have good characteristics when run "backwards?" I've found some motors on surpluscenter.com that say "can be run as pumps;" is there a particular type of motor or pump that works better one way, or about the same either way?

Thanks!

 

[BrianPetersen]

You might want to look into the two-wheel-drive system that Yamaha was playing around with on dual-purpose bikes a few years ago. I believe they ran the Paris/Dakar rally with such a bike. It did indeed use hyraulic drive to the front wheel. It's reported to have had a few interesting torque-steer effects, but that's another matter. Point is, it can be done and has been done. I don't know how efficient it is ... my experience with industrial hydraulics would suggest that it is not very.

Gear pumps generally have no issue running forwards, backwards, or with either side pressurized or not.

 

[spacewrench]

Thanks, I know that Yamaha was experimenting with 2WD on the road racers (those engines make more power than you can put down through the rear tire, so this was a way to use more of it). They had a hydraulic system to the front wheel, too.

I may end up putting together a test system, just to see how (in)efficient it is. If it's much worse than chain, then it probably won't recover enough via regeneration to make up for the expense, weight, etc.

 

[IceStationZebra]

You don't need to put together a system to estimate its efficiency. Gear pumps are only 75-90% volumetrically efficient. Piston pumps have better efficiency but are heavier for a given displacement.

ISZ

 

[spacewrench]

Gear pumps are only 75-90% volumetrically efficient.

That doesn't sound so good...even assuming 90%, I'd be at 81% overall for going electric->hydraulic pump->hydraulic motor. The motor itself is probably no better than 95% or so. I suppose I'll have to go with chain and only the regen I get off the rear wheel.

 

[BrianPetersen]

I think 81% is optimistic. 60% is probably realistic.

 

[GregLocock]

You might be interested to learn that typical electric regen systems, such as the Prius, are ony about 60% efficient when you consider the round trip braking->battery->traction.

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[spacewrench]

<i>only about 60% efficient...</i>

That's lower than I'd expected, but still, I don't want to choose a primary drive system that's down on efficiency, just so that I can have better regen. Maybe I can come up with a front-wheel system that <i>only</i> operates during braking (to drive the electric motor in generating mode). If it's got very low drag when not engaged, it might work.

Thanks for the help, everyone!

 

[GregLocock]

Good point, I agree, that sounds very difficult.

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.