Cycle News - Archive Issues - 1980's

By Mark Karlya, Photos courtesy of Hydraunc Engineering, Inc. TaJce a casual glance at the bike in the large photos.Jwt a basic Yamaha YZ2JOH, right? Now, take a closer look. See those side cases? See those hoses to the rear wheel? See any chain or spocket OT braJce? E:ctemaUy, it is quite evident that there is no chain, shaft OT even belt to popel the motOTc'ycle. This, ladies and gentlemen, is a hydTastatic drive bike, an idea that Roger South has been working on for sU: years. A motoCTosser in the state of Washington, Roger raced fOT about eight years, graduating through the ranks to AMA amateur E:cpert and rode as a CMC Pro for two years befOTe other things began to talee priority a couple ofyears ago. During his racing stint, Roger also became involved in hydraulics and has been employed in the Seattle area in this field for about sU: years. "I've done primarily hydraulic design and fabrication WOTk, manufacturing custom one-oj-a-kind power units and hydraulic machinery. " He recognized the poblems in getting around a motoCToss course on a bike un'th a narrow powerband and believed he could blend his two interests to come up un'th a solution. After much theory, conceptualizing and work on his own, though, he ran short offunds and put the poject on hold. A bout a year ago, Hydrualic Engineering in Kent, WA employed Roger as one of their engineers. ACCOTding to him, the c0l:ny "specializes in cwtom system design engineering and fabrication of one-o -a-kind hydraulic equipment. We do total design WOTk - mechanical, electrica and hydraulic - pototype work, that sort ofthing. " The company's thrwt got Roger to thinking more about his idea ofa hydTastatic drive motorcycle, and with his employer's permission, he began to finish what he had started. He took a new Yamaha YZ2JOH in the middle ofJanuary and in about two months, poduced the WOT/cing model pictured here. The concept is intriguing so we asked him to explain things in a bl~ more detail. How did the concept of a hydrutatic drive motorcycle come about? Well, it was something that I've played with for the last six years. Actually; it's what got me interested in hydraulics in the first place. I could see the advantages of a fluid power transmission. A DT-I MX was the bike I had to race with at the time, you know, lots of ponies in a very narrow powerband and zero suspension. Not the greatest way to get around a motocross track. The problem is to match a narrow powerband with five or six gears; this requires an expert rider with lighten• -rI mg ,,::..exes. The ideal solution would be an infinitel variable transmission that could Y • automaucally modulate and compen._.. d cis sate for t h e vancu power eman required to negotiate a motocrall course. I knew if engineered correctly, a hydra. static fluid drive system could do all of these things and possible more. Has anyone ebe done anything like this before? To my knowledge only one of the Japanese factories did any work along the same lines about four years-ago. As far as I know they haven't carried development any further. Now, in layman's terms, could you explain what your design is and how it worlu? Well, primarily the biggest difference consists of replacing the clutch, all six gear clusters, countershaft sprocket, rear chain, rear sprocket and associated chain tensioning devices with a variable displacement closed loop piston pump driven by the engine and a hydraulic wbeel motor hub assembly. Also, a control package is included as part of the p~ton pump. The system works by sensing engine rpm internally; rising engine speed will send a control signal to move the pump's cam plate on stroke. Hydraulic pressure to the rear wheel or load signal is :also fed into the control pack· age. When enough horsepower is avail· able to accelerate, the pump goes on stroke causing forward movement. If the cycle should encounter a sudden load, say a hill or deep $andy corner, the pump automatically compensates for the change, allowing the engine to stay ahead of the horsepower demand. What is the difference between hydralIt:ltic and hydraulic drives? A hydraulic drive is simply a means of transmitting power through fluid components, a pump and motor of any type. There is no means of changing ratios, displacement versus speed, that sort of thing. A hydrastatic transmission, on the other hand, offers variable volume in both pumps and in some systems, a variable displacement motor, as well as a true transmission. That is basically how it:aU worlu? What we accomplish with this system is to take raw horsepower occurring at any rpm and by tuning the hydraulics, program a smooth, colUtant accelera· tion curve. By using these adjustments, this system can compensate for rider weight, track conditions and optimize available horsepower tractability. . Have you ru~ mto any problema 10 far ~n your bike? . We ve had some. faJiures, ~o doubt about that. All rmnor stuff: like t~ler. lanikceshaand types of matenals, things e t t. B . U th h . Uta en, you aye your. va,nable dISplacement p~~ lDSlde w~ the normal trlInlnllM'OIl would be,and It pumps 01 out through a . '1 h hi h th th h b oee w ,c en goes to e rear u that you ve ~tom manuf~~red. Is ~e~ an addiuonal motor tnslde that u .. Yeah, that motor IS an mtegral part of the ~,ub; it's a hydrauli~ wheel motor. That s why our motor IS so .co~p~ct. How does tha.t work? A Ip~D1ng vane or something? No, it is a piston-type motor, and that is about all I can tell you without giving away too many secrets. What sort of efficiency docs this have? Approximately 89% from the engine to the rear wheel because we eliminate so many conventional drive train parts, like the clutch, gears, chain, sprockets, etc. We simplify the possi· bilities of efficiency loss. Do you think there would be any problems using this idea on a 125 or adapting it to an Open bike, on the other hand? Actually, this system would be ideal for a 125 because of their even narrow· er powerbands, plus :all the split-second shifting required. On an Open class bike, tractability and elimination of the chain would be the obvious advantages. HaTe you ridden the bike? What is it like to ride? It is very smooth and progressive. It is a little bit strange because acceleration isn't totally)inked with engine rpm. The engine starts to come on the pipe and the bike accelerates in one constant drone, no plateau or flat spots. Would it be kind of like the old R.okon? . The Rokon was a torque converter automatic transmission type; the engine would come up on the powerband and shift up in rpm agam and sh1ft and so_ on. Our bike produces a constant torque at a relatively steady rpm. I noticed from the photoe that there is no rear brake fitted. We employ what is known as the r, .-4 00 0) .-4 (Clockwise from top) The custom hub houMa Ita own hydreulc: motor. The hydrBuIIcs C8f'I be progremmed. An 01 cooler .. UMd. The entire tr8I.m'n'Dn .. replaced with • pump. HOMS on both sides of the awtno-m C8rFY 01. dynamic braking system. When de· celeration is called for, by simply turning the throttle off, the available pressure to hold the pump on stroke decreases. As this happens, the oil coming from the rear wheel is throttled. During braking, forward momentum causes ~e rear (hub) motor to actually pump oil back into the variable pump. As the pump approached neutral or centered position, the oil tries to motor the variable pump against the engine. At this point, the engine is nothing more than an air pump being throttled by the carburetor slide. A big advantage of this type system is there is no mechanical lock-up ofthe rear suspension during braking, in addition to the dynamic effects. What was normally the clutch lever is now connected to the stroking mechanism. By applying this lever the pump can be brought to center manually for pinpoint braking. Like an emergency brake? More like a manual override to the automatic braking system which, by the way, can :also be programmed to tune the deceleration curve to adjust for rider skill and traction conditions. How does that compare to a normal rear brake? As I already mentioned, there is no mechanical triangular effect to cause suspension lock-up going into comers, allowing you to float over everybody else's stutter humps. Also, without any friction bind, the rear tire remains in contact with the ground better. That makes the throttle a critical part of the bike then? There are no foot controls, only the front brake, clutch-type lever and throttle. Engine speed dictates accel· eration and the lack of engine speed controls deceleration so the throttle does play an important part of our control package. What about lOme of that other plumbing I see in the photol? Coming out of the bottom of the front down tube, there is a 9CMlegree elbow and steel braided line. That line carries the oil extracted from the loop for cooling purposes. The oil goes up the down tube, then into the two aluminum finned coolers. After the coolers, the hydraulic fluid reenters the frame. Approximately how much oil does this system hold? About two and a half gallons. I know a lot of people would want to have a lot of ground clearance, and that's what I was asking about that bottom line. That tube is stricdy a function of packaging. We just happened to put it there; it can easily go somewhere else. It's never been a problem to us. Are there any plans to make this lile a production itemr Our business is not building motor· cycles; this project was undertaken to promote hydraulic equipment and our company. We plan to campaign it in competition to a limited degree. Do you think that this would have an easy application to one of the major manufacturc:n if they wanted to? Oh, I know with their full technology and manufacturing capability, it would be very easy to bring this from the stage we have it now, because we have advanced it to a pre-production prototype stage. It would be very easy for .a large manufacturing company to simply bring it into production. How much longer do you think until the package is complete and ready to race? I would say in a month to six weelu we would have something. It could be ac· celerated, it. mainly depends on other people's attitudes. Like I said, we are a small company. What we are looking for nbw are sponsors to help us defray some of the cost. The hydraulic sector, hose manufacturers, maybe oil com· panies, hydraulic equipment manufacturers, and possibly motorcycle corpora-' tions might want to develop this for their own ,Products. Any parocular reason why you choee the 250 YZ? Because it was a good competitive motorcycle that had good handling characteristics and had exactly the problem ·that we knew we had a cure for - a fairly narrow peak. power· band. •

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