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May 6, 2005
Motorcycles Gain Traction with New 2WD System
The world's first two-wheel drive production motorcycle roars to life, thanks to a groundbreaking 2WD system that uses hydraulics to deliver power to the front wheel when the rear wheel slips. And the system can be installed on almost any bike:
Öhlins Racing AB of Sweden, part of the Yamaha group, has developed a revolutionary two-wheel drive system, which is featured on the Yamaha WR450F 2-TRAC--the world's first two-wheel drive production motorcycle. Considered a technological breakthrough for the motorcycle industry, the reliable, compact and relatively inexpensive 2WD system can be installed on nearly any bike without any significant modification to the frame or front forks, bolstering traction, stability and performance on- and off-road. The company hopes the system will have the same impact as 4WD rally cars.
The 2WD system relies on hydraulic components from Rexroth Sweden, a unit of Bosch Rexroth in Germany. It utilizes a piston pump and matching fixed displacement motor to automatically apply power to the front wheel when the rear wheel starts to slip, increasing and decreasing the amount of traction delivered based on the amount of spin at the rear.
The system has already been fitted to over 300 production bikes by Yamaha Italy, with a similar number anticipated this year. Additionally, other motorcycle manufacturers have expressed interest in the Yamaha-patented innovation.
Development work on the 2WD system was carried out at the Öhlins Research Center, under the direction of Lars Jansson, R&D manager for future projects. He explains that they chose hydraulic transmission because it retains the standard bike layout and allows the use of proven components. Unlike a car, where it is easy and efficient to fit a mechanical drive from the side of the wheel hub, Jansson points out that a motorcycle is essentially two-dimensional and requires complicated mechanical transmission to drive the front wheel, necessitating overly complex and awkwardly styled front suspension members and frame elements.
By choosing hydraulics, the development team was able to fit the pump neatly ahead of the rear suspension, below the carburetor and above the bike's gearbox. The hydraulic pump is chain-driven by the gear output shaft so the speed of its rotation is directly proportional to that of the back wheel. The corresponding hydraulic motor is mounted in the machine's front hub and powers the front wheel by means of a reduction gear unit, produced by Öhlins. The pump and motor are linked mainly by a reinforced flexible hydraulic hose with steel tubes used for concealed sections. Normal engine oil is used to cope with high temperatures.
The entire system is delivered pre-assembled, complete with hydraulic fluid and pressure tested, ready for fitting.
The pump and motor are tuned to rotate at the same rate, creating a system that is simple and self-regulating. When the bike transfers more power to the ground under acceleration, the back wheel rotates more quickly than the front, due to deformation of the rear tire; this slight difference in rotation speed causes the pump to supply more pressure, therefore transferring traction to the front wheel, through the geared hydraulic motor. The more the back wheel spins, such as on wet and slippery surfaces or when negotiating curves, the greater the power transferred to the front wheel. The pump's pressure relief valve also prevents dangerously high pressure in the system.
The front wheel actually transmits relatively little power, typically around 5%, but by utilizing some of the drive wasted by rear wheel spin, the hydrostatic system boosts overall transmission efficiency. This results in increased stability at high speeds, better traction--especially in sand, mud and snow--and improved corner exit speed and handling. On the road, it improves traction, predictability around corners and straight-line acceleration out of bends.
"The bigger and heavier the bike and the more inexperienced the rider, the more you benefit from 2WD," says Jansson. "An experienced rider will think he's down on power, because he cannot spin the rear wheel as normal or do power slides, but timed on a race course he'll be much quicker than before."
In fact, the top speed of a Yamaha WR450F 2-TRAC on a sandy track is around 10% higher than its conventional counterpart, thanks to improved traction. Öhlins Research also tested a powerful road bike and found that lap times in wet conditions were 5 seconds faster over a 1-minute, 20-second circuit.
Says Jansson, "At the moment, 2WD is a limited volume market, although if customer attitudes change and competition regulations are modified to accept it, the system would have a major impact on off-road events and road racing... as well as everyday motorcycling. Essentially, there are no drawbacks."
Source:
Rexroth Hydraulics Help Power Unique 2WD Bike
Bosch Rexroth Corp. Press Release, March 15, 2005
www.boschrexroth.com
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27 CommentsThe text of this article talks about the ease of mounting this unit. It discusses mounting for carbureted models. Is this unit equally easy to mount for EFI models? I am thinking specifically about something like a VTX 1800 or the like.
May 5, 2005 11:00 AMSounds great. Where can I purchase one of this systems?
Best Rgds.
May 5, 2005 11:07 AMI thnk that this is not the first 2wd production motorcycle. Remember the Rokon?
It may, however, be the first 2wd system installable on various motorcycles.
Looks really useful for choppers with radical rakes as the long wheelbase can put the front on highly different ground than the rear wheel.;)
This not the first 2 wheel drive motorcycle; ROKON has been manufacturing 2WD motorcycles for many years; I have one that was made in the 1960's sitting in my barn.
May 5, 2005 11:10 AMGee, the Rokon has had 2WD for the last 40 years.
May 5, 2005 11:11 AMThis is not the first "production 2-wheel drive motorcycle". It misses by about 40 years. The ROKON company has been making 2-wheel drive motorcycles since the mid-60s. They are still in business. Several thousand units have been produced, many of which are still in service. This would seem to qualify as being "in production". A new unit with a 4-cycle engine costs about $5000.
ROKONs are a special-purpose machine designed for extremely rough off-road environments. Among other capabilities, they will easily cross a 14-inch diameter log from a standing start. Some models also float in water, although not while under power. However their top speed is about about 20 mph for an older 2-cycle unit, or 30 mph for a new 4-cycle unit. So they are not really suited for highway use, and aren't intended for competition.
May 5, 2005 11:12 AMThis is nice, but not first. The folks at Rokon are still building 2 wheel drive motorcycles, and have been for over 30 years.
I am not even sure if they were first, they are just the most noteworthy.
I have watched large farm spray rigs run on hydraulic, wheel driven, motors for years and wondered why you couldn't do that with a motorcycle. Yamaha has designed this system as an add on and this is a great first step. The next step would be to eliminate the transmission all together and let the hydraulic pump act as both transmission and power delivery. This should save weight and make the selection of gear ranges infinitely tunable. This would also give more options to designer in mounting the power unit because it no longer needs to be in line with the rear sprocket or the direction of power delivery. Who says a bike has to be driven by a chain, belt or shaft? What a great development!
May 5, 2005 11:57 AMThis would be the perfect time to say "my bad!"
You readers are right that the Yamaha WR450F 2-TRAC is NOT the world's first two-wheel drive production motorcycle. I forgot to add "of its kind."
Meaning it is "the first 2WD production motorcycle of its kind." In short, it's unique but certainly not a first.
Katrina Arabe, the humbled writer of this post
May 5, 2005 12:02 PMHydraulic motors are not mechanically efficient, although they can be made powerful. Hydraulic motors on bikes represent another major peoblem too: If it leaks going down the road, the rider could suffer a fatal accident due to hydraulic fluid on the road beneath the wheels. Belts, chains and shafts are more power efficient than hydraulics, and hydraulics can't support the same kinds of rotational speed because of the physical limitations inherent in fluid dynamics of pumps and motors used in these systems. I am not ready to have slippery fluid under extreme pressures inside the wheel hubs of any bike I will ever ride because of the safety factor.
Ed
May 5, 2005 12:17 PMInteresting idea,
That I also had years ago. I discounted it because I am mainly a trail rider and it is important to be able to get the front wheel off the ground at times. I have to wonder if this has been considered in design with the 95/5 power distribution ratio. Maybe a front wheel power bypass initiated by a hard upward handlebar pull would make it user friendly and allow more flexibility if wheel stands are an issue. I wouldn't worry about Fluid leakage unless I was riding on the street by the way.
Send me a sample, I would be more then happy to demo and give feedback. ;)
This is pretty exciting to me.. not as a two-wheel drive, but as a replacement for belt or chain for traditional rear-wheel drive.
Hydraulic drive would allow for extreme design flexibility. Could you picture a scoot with the seat positioned BELOW the rear axle center line?
How 'bout designing a direct replacement for a softail 5 speed? The unit would completely replace the transmission, and utilize the original belt or chain primary. Bolt it in and forget it! No more chain stretch/wear issues, no more belt rub/alignment/wear issues!
Call me first!
May 6, 2005 10:44 AMEd,
I think you're right about hydraulic power not being efficient, although it can transmit tremendous force. It is not really suitable for high-speed systems. It appears this new system is "part time", only sending force to the front wheel when the rear wheel is starting to slip. It also might be limited in the amount of power that it is able to send to the front.
One of the reasons ROKON has survived for 40 years is its simplicity. (KISS principal) Perhaps I'm descending into trivia, but: The power to the front wheel is sent through a shaft running lengthwise under the tank. There is a wrapped-spring one-way clutch on the shaft that allows for any difference in speed between the front and rear wheels. A constant velocity joint under the steering head allows power to be transmitted to the front wheel and still allow the wheel to turn sideways. A right angle miter-box sends power to a chain which drives the front wheel.
It is a simple system that uses mostly go-kart and off-the-shelf industrial parts. A really skilled person with machining and welding skills could build one by themselves.
The real genius (but also weakness) of the ROKON system is that no suspension is used, so there is no necessity to have a drive system which compensates for motion of the wheels. The chain sprockets have a constant center-to-center distance. Instead, the enormous 3 psi tires take up most of the vertical motion. The system soaks up bumps and works reasonably well at 10 mph. But this "hard-tail" (and "hard-front") suspension would probably be dangerous at highway speeds.
why do a lot of people ask so mean things?
September 27, 2007 12:59 PM
