Specifically for the mountain-biking crowd who could use the extra traction, or for people who bike a lot in the snow.
Instead of driving a chain, the pedals would drive a variable displacement hydraulic pump. Displacement (swash plate angle) would be controlled via wire by a control similar to a standard bicycle gear selector - only it would be on the frame and not the handlebars, and be infinitely variable. From the pump, the oil would pass through a flow divider and from there to motors on the front and rear axles. Oil flow and return to the front wheel motor would pass through hydraulic slip rings in the fork hinge, allowing complete 360 degree rotation of the front forks. As well, by means of a bypass valve (a second control on the frame), oil return could be used to charge an accumulator. I see this as being potentially useful when cycling downhill, as you could charge the system while coasting downhill, and then use that energy on demand for a power assist up the next incline. Brakes would not be in the form of pads (i.e. physical friction on the wheel), but rather as a variable flow restrictor in the oil return - controlled by brake handles as per a normal bicycle. By not having the brake pads, you gain clearance around the wheel/tire, allowing the use of tire chains for traction in the mud and snow.
The problems are:
Friction. I would have to use a low viscosity oil which maintains its performance when cold, and I would have to size all of the oil lines appropriately to keep things moving without undue resistance. This worsens the second problem:
Weight. Obviously, you still have to keep the bike as light as possible. I don’t know if you can get off-the-shelf hydraulic components which are lightweight aluminium - it may require custom machining. In any case, even with the lightweight components, this will still be significantly heavier than a standard mountain bike. That, I guess, is the price to be paid for two wheel drive and one of the coolest looking (even if it doesn’t perform to expectations) bikes around.
Think it’ll fly? (No, not the bike - the project…)
Now we ALL have an idea for a two-wheel drive bicycle…
That’s a fascinating idea! I would think the weight of the oil itself would be a hindrance also. And since pedaling is your pump, it seems unlikely that human power would be enough to really be practical, unless it was EXTREMELY efficient (no energy loss.) But I’m a gut-feeling kind of engineer and might be totally wrong.
Gut says your drive will lose more in efficiency than is gained in traction, but I could be wrong. I recall seeing a 2wd system for a bike using a cable drive coming off the rear hub looping up along the top tube and down to the front hub. It was an aftermarket add-on type deal. The mb mag I saw it in said there was a noticeable gain in a few situations where the front wheel would pull one out of trouble, but that the whole bike felt so much more sluggish than it did without the 2wd that it wasn’t worth it. Course, cable drive would involve a frightening amount of friction, so perhaps the hydraulic design would work better.
The main problem however is the lack of power, humans can produce up to around 400 Watts, but not for long, less than half that continuously for most of us and perhaps 250 Watts for the very fit.
Any losses will be significant, especially in cycling as stamina is a key part of it.
I like the idea of the regenerative brakes, the accumulator could be part of the frame tubes and would probably be useful in downhilling, though the way the stored energy is released would be the main issue, along with wether or not the governing body of the sport would accept it.
When you lose that much traction forward motion is virtually halted, it is generally more useful to pick up the bike and run, and this is what you see in cross country racing.
I think you’d have to build something and try it out, there might be issues with steering geometry, overall balance of the machine, it is possible that having a little bit of drive on the front wheel might help the front end to track better when riding along sunken trails or in vehicle tracks on rough terrain.
I dunno, you will have some scepticism from the traditionalists but if you can demonstrate some useful properties of such a system then the mountain biking crowd will take it up, cost is not as much an issue with them as you might think, I have known folk pay over $1000 for just one front wheel, and well over $4000 for the complete bike.
This was Preston Tucker’s original idea for his car. Unfortunately, he couldn’t get it working and other companies have tried to get it to work in automobile applications (it’s being used in industrial machinery, IIRC) and have all failed due to lack of funding. Tesla also had a similar idea that he was never able to develop, so you’re merely the latest in a long list of folks that have tried to do something similar.
That doesn’t mean you won’t be able to do it, of couse, just means that you’ll have to be smarter than they’ve been. My advice would be to use as many off-the-shelf components as you possibly can. Having things specially machined isn’t cheap (you could, however, find a school and either take a machining class or get them to make it for you, generally the cost is little more than the price of materials) and is, IMHO, unnecessary in a “proof of concept” vehicle.
As for a source for the lightweight hydraulic parts you need, I’d suggest looking at car customization sites as many of those guys use such things (or pneumatic equivliant, which could be adapted to hydraulics fairly easily, I believe) in their cars. You could probably adapt that stuff well enough for it to prove your idea, then you can worry about getting investors.
I know two-wheel drive has been done, but not hydraulically. One thing I didn’t mention in the original post, is that the two-wheel drive would be on-demand only (by means of a directional spool valve), so you wouldn’t have to pedal against the full resistance of the system unless you wanted 2WD. In fact (thinking about this as I type) you could implement automatic traction control, engaging or disengaging the forward motor according to wheel velocity. THAT would sound good in the brochure…
