|
 The Deltabox frame would continue to be a leader on the GP scene while undergoing a number of changes like the
structure of the main tube (reinforcing studs added inside the squared cross-section tube), optimizing of alloy types and rigidity balance, etc. The next big turning point in this frame's design would
come in 1993 model YZR500, called the OWF2.
"In an effort to achieve a dramatic improvement in the rigidity of the frame for the OWF2 of '93, we switched to extruded aluminium parts. Extruded
aluminium is made by a process of heating up the aluminium stock to an appropriate temperature and then forcing it through a die to produce tube stock of the desired shape. Because the extrusion process
enables more complex shapes than the type of panel stock we had been using and also a higher degree of precision in shape and dimensions, we believed it would be advantageous for improving rigidity.
"When we saw the test results, it in fact gave us much higher rigidity figures than we had ever hoped for. It was a machine with this new frame that Wayne Rainey rode to three consecutive 500cc
titles. Studying the motion of the machine in actual racing, however, we observed that there was not a good harmony between the torsion characteristics of the frame itself and the functioning range of
the suspension. And, we were not getting good feedback about the handling character at super-high speeds. This was part of the reason the Rainey used an ROC Yamaha frame from the eighth round of that
year's series," says Mr. Masahiko Nakajima, who was an engineer of OWF2.
Having learned these lessons, the next spec, the OWF9, once again returned to the previous panel-stock frame. This was a
period when the focus of Yamaha's frame design turned to the problem of how to best use the torsion characteristics of an aluminium frame to contribute to handling performance.
The aluminium
Deltabox frame technology was eventually fed back to Yamaha's production supersport models and as is well known today, it went on to have a decisive influence on the world standard for production
supersport bikes by all the makers.
 In 1990, Wayne Rainey and John Kocinski brought Yamaha double championship title in the 500 and 250 classes. In '91 Kocinski also moved up to the 500cc class
and the YZR500 and this was also the year that the OWD3 spec YZR500 adopted a full-fledged computerised electronic suspension (CES) for the first time. The machine mounting the CES suspension jointly
developed with Ohlins would be the one Rainey rode to his second consecutive title in '91.
The system consisted of (1) a stroke sensor, (2) a control unit and (3) the shock absorber. The
stroke sensor was positioned on a parallel axis with the shock absorber to measure the volume and speed of its stroke. In the system, the stroke volume and speed data is sent to the control unit where
it is filtered through a pre-programmed map to render an electronic current that is then sent to the shock absorber to drive a solenoid valve that precisely regulates the flow of hydraulic fluid to
provide exactly the right amount of cushioning force on both the compression and rebound strokes. The advantage of this system was that it enabled precise setting of the desired damping force in the
stroke in accordance with course conditions and/or rider preference simply by rewriting the memory in the control unit's microcomputer from an external terminal.
"We had begun doing tests with a
CES rear suspension from 1989, but '91 was the first year we used it for the whole GP season. What you could call the "active" suspensions on automobiles were not advantageous for motorcycles because of
the complicated parts like the hydraulic fluid pump, the system weight and the space it requires. So, we developed a system that built the damping force control function into the shock absorber itself.
By then connecting this to an electronic control unit, the CES system we developed became in effect a passive system that achieved the same effect as an active system. We also provided a fingertip
switch that enable the rider to switch between three or so different control maps," explains Mr. Nakajima.
Although the system was not mounted on later YZR500s, the know-how gained from the
development of the CES system would contribute to the later versions of Yamaha's suspensions. The Monocross suspension that began with considerations about interference with the intake system and
chassis material balances would evolve to concerns for rising-rate effect, maturation of the bottom-link format and finally electronic control.
With Wayne Rainey's successive titles in 1990 and
'91, Yamaha won both the GP500 manufacturer and rider titles two consecutive years. At the same time, however, the number of machines competing in 500cc Grands Prix was decreasing steadily, and some
were even beginning to worry about whether or not the championships would survive.
In answer to this need to stimulate the GP race scene, Yamaha announced in September of '91 that it
would provide its YZR500 engine to any of the prominent constructors in Europe at the time that wished to use it. Actual sales began in '92 was a part of Yamaha's efforts to promote the sport of
motorcycle racing. In fact, Europe had a long tradition of GP teams that used engines by the makers mounted on frames built by the constructors to produce competition machines. It was Yamaha's belief
that the racing scene would be stimulated by the presence of new teams using machines constructed in Europe according to this tradition.
 The release of technology in the form of these engine
sales brought a big change to GP racing. A full two-thirds of the machines on the starting grid for the 500cc class on March 29 in the '92 GP series' opening round at Suzuka were powered by the Yamaha
YZR500 engine and the number of machines was larger. Riding the '92 spec OWEO (YZR500) were Rainey, John Kocinski, Juan Garriga, Miguel Duhamel, Niall Mackenzie, Kevin Magee and Norihiko Fujiwara, while
Randy Mamola and Eddie Laycock competed on 1990 model OWC1s fitted with ’92-spec motors. In addition, 14 other riders competed on Harris Yamaha and ROC Yamaha machines.
"We considered working to
stimulate the 500cc class to a mission just as important to us as winning the title. The European constructor machines from Harris and ROC mounting Yamaha engines gave many more riders a chance to
compete in the GP and made the races more exciting and competitive," says Mr. Shyuji Sakurada who was a chief of this project. Along with the challenge of winning the GP, Yamaha was equally eager to
promote the sport itself.
During this period, Yamaha released vital machine technologies to ROC and Harris. Perhaps never before in the history of the GP had a factory provided constructors with
design blueprints and full instructions on the full details of maintenance and setting methods like this. And, the base machine to which this information applied was the OWC1 that Rainey had won the
title with in 1990.
Using made-in-Europe aluminium stock, the constructors built their own brand bikes with chassis equivalent to the YZR500 (OWC1) to enter in the GP. Between 1992 and '94 ROC
Yamaha and Harris Yamaha placed fifth and sixth in the constructors championship ranking. It was not only due to the competitiveness of their Yamaha engines but also a measure of the all-round qualities
of the machines, ranging from set-up to serviceability. The fact that such competitive machines could be built without special aluminium alloys but just commercially available aluminium stock was also a
statement about the basic soundness of the Yamaha chassis designs. Beyond the successive championship titles won by Yamaha in these years (1990 to 1992 by Rainey), we also see an important aspect of the
Yamaha corporate philosophy in its willingness to release technical information for the sake of the sport.
Chronology  OW20 (1973-74) - Yamaha's first 500cc factory machine
The OW20 was Yamaha's first
factory machine built to compete in the GP 500cc class. This machine mounted a liquid-cooled two-stroke parallel-four piston reed valve engine on a chromium molybdenum steel frame with disc brakes front
and rear. It debuted at the opening round of the 1973 series in April, the French GP and Jarno Saarinen piloted it to a debut win.
The following year, 1974, it became even more
competitive with the adoption of the Monocross suspension. Giacomo Agostini signed with Yamaha for the first time and competed with teammate Tevo Lansivuori. Agostini won rounds three and six and
Lansivuori won round eight of the series. This, combined with the points earned by other Yamaha riders gave Yamaha its first manufacturers title in the 500cc class.
 OW23 (1974-75)- Developed
specifically for Grands Prix
Debuting at the Belgian GP of 1974, this was Yamaha's first machine developed specifically for the 500cc class. It is the machine that Giacomo Agostini would ride to win
the GP500 title in '75, giving Yamaha its first individual championship in its third year of GP500 competition. Compared to the OW20 which had been developed jointly with the 700cc machine for Daytona
competition with cylinder bored down to 500cc, the OW23 was considerably lighter and more compact in both engine and chassis and had a shorter wheelbase as well.
As a feature to reduce setup
time, it also adopted a cassette type transmission. It was the same type as the on the MZ and MV Agusta, with the main shaft, drive shaft and shifter assembly as one unit that that was extractable on
the opposite side from the sprocket, but it also featured detail maturation and improved reliability. This cassette transmission would become the base unit for those used eventually on the TZ250
production racer and the production TZR250SPR. Also the new muffler shape that would be called a stepped taper type featured a gentle trumpet shape in the defuser portion and a bowl shape at the rear
portion of the expansion chamber that served to improve max. power output and torque in post-peak range. The square-type rear arm was another defining feature. The following year, 1976, Yamaha did not
compete with a factory team in the GP, but Johnny Cecotto rode the OW23 to a second-place finish in the series opener.
 OW35 (1977)- New engine with revised bore and stroke
The 1977 model
YZR500 (OW35) was the factory machine Yamaha returned to 500cc competition with after a one-year hiatus. The piston reed valve intake that had been used on the OW20 and OW23 was replaced by a piston
valve system. Also, the cylinder pitch, which had been kept as small as possible on the OW23 for the sake of compactness, was increased (92 to 115) in order to allow more design freedom for the
scavenging port. With this, the bore x stroke changed from the former 54 x 54 to a high-revving type 56 x 50.6 and a power jet type carburettor was adopted. Revisions were also made to the chassis to
optimize aerodynamics with the rider's form figured into the equation. Riding this machine, Steve Baker mounted the podium six times to finish the '77 season ranked in second place.
 OW35K:
Roberts' title winner
OW35K (1977-78) - Roberts rides the YPVS model to his first title
Taking the 1977 GP model OW35 as its base, the OW35K adopted Yamaha's new YPVS (Yamaha Power Valve System)
technology for the first time. By making possible variable exhaust timing, this revolutionary device helped remove torque valleys from the engine's power development characteristics and thus led to
dramatic shortening of lap times. This YPVS had first been used in GP competition secretly from the Finnish GP in '77. Johnny Cecotto rode this machine to wins at the Finnish GP and the Czechoslovakia
GP to finish the season fourth, while Kenny Roberts won four of the series' 11 rounds to win his first of what would be three consecutive 500cc titles.
|
