Rotary dampers: the upcoming trend or an exotic screen door closer?
By John Olsen, Contributing Writer
So what’s up with Suzuki? This relatively quiet company, known for its occasional flashes of brilliance followed by long periods of technical sleepiness, appears to have become a technological Godzilla. Recent examples include the dominant redesign of their GSXR-750 and its little brother, the GSXR-600. And perhaps most amazing of all, the TL-1000S with its inverted forks and fuel injection. This Ducati 916 clone delivers, at least on paper, most of the cutting edge technology of the much-vaunted 916, but at 9 / 16th the cost.
One technological feature that could help Suzuki compete with the all-conqueror Ducatis is the new rotary damper. Suzuki chose to separate the spring and damping functions for this bike. Why open up a seemingly new path – a path that might be littered with unknown landmines? Why not stick to the well-understood benefits of the universal rear suspension on today’s sports bikes – the single shock absorber rear end actuated by a linkage? After all, the status quo is not bad.
One obvious answer lies in a central problem in modern motorcycle design: packaging. The latest school of racing bike design requires that much of a bike’s weight be carried by the front tire and for a short wheelbase that operates at a steep steering angle for quick handling. Get enough weight on the front tire and you get several vital benefits: The bike can accelerate harder without wheeling, which allows for directional corrections when accelerating. In addition, the greater the weight of the front tire, the harder it can be turned without exceeding reasonable slip angles. A longer wheelbase increases the turning radius of the bike, which means that a greater lean angle is needed to maintain speed through turns. Additionally, cyclist inputs or bike responses to bumps occur more slowly.
A 90-degree longitudinal V-twin, like the TL, any Ducati twin, or the Honda VTR1000, presents a packaging challenge. Tilt the engine forward and you experience clearance issues between the front wheel and the radiator. Tilt it back and the rear cylinder takes up valuable volume that could be used for the battery and electrical system, or the shock absorber. The result is that 90-degree V-twin sports bikes tend to the long side, with the TL and 916 the shortest at 55.7 and 55.6 inches, respectively, and the VTR and 900SS at 56. 3 and 56.4. The VTR tries to minimize the wheelbase penalty by using twin side radiators, allowing the engine to approach the front tire as far as fork travel and fork flex allows.
Suzuki achieves relatively forward weight and a moderately short wheelbase thanks to a clever engine and head design (the cam drives and the arrangement of the cams in the heads are specifically designed to allow the engine to live closer to the wheel. before). In addition, the placement of various objects in the space where Ducatis and Honda place their rear shocks allows for a tighter cut set.
So where does the shock go? Suzuki, together with Kayaba, opted for a solution that has already been used in large numbers – the hydraulic lever-type rotary shock absorber. While many people will credit Suzuki with inventing this design, a similar concept shock absorber, the Houdaille, has been used on vehicles ranging from sports cars to trucks since the early days of damped suspension.
Suzuki’s rotary damper gives them a few advantages in addition to a shorter wheelbase. One is heat dissipation. Perhaps the main enemy of any shock absorber design is heat build-up. Damping is simply the conversion of some of the mechanical energy generated by the motorcycle bouncing off its springs into thermal energy. Since hydraulic fluids and rubber seals cannot work at high temperatures, this heat must be dissipated, otherwise the shock absorber will malfunction.
The TL’s aluminum shock body has more mass than a tubular shock, and that mass by itself will absorb heat from the damping fluid until it is as hot as the fluid. In fact, early testers report that the shock stays cool to the touch, even during hard track sessions, which you can’t claim for typical tube shock design.
The relative movement between the moving parts of this shock absorber consists, of course, in rotation. Two good things happen with the rotational rather than telescoping motion: the rotary joints between the shock body and the shaft are easy to seal and clean, and you can use bearings rather than rings between the two parts. . Both changes make it likely that there will be reduced friction in the TL’s shock absorber, which has no exposed sliding surfaces. In contrast, conventional tubular shocks have a potentially dirty shaft that slides in and out of a joint, and these shocks are subjected to side loads from the bushing. The two sources of friction increase the force required to move the suspension.
However, rotary shocks still use sliding joints to separate the working volumes inside the shock. Two rubber-tipped metal vanes mounted on the rotor seal against the inside diameter of the damper body, trapping damping fluid between them and two other vanes attached to the inside diameter of the damper body. These vanes, in turn, should seal against the outer surface of the rotor. As the oil is compressed by the two rotor blades, it passes through the ports to the expansion or compression valve and the stack of washers. The damping ports and valves work exactly the same as in a conventional damper. A small pressurized gas chamber in front of the rotor is only there to compensate for the thermal expansion of the oil as it heats up, as there is no rod volume to accommodate like on a telescopic damper .
It is in the sealing that hides a potential dark side of the rotary hydraulic damper. Any leakage means loss of damping, as is the case with any hydraulic shock. All vane seals must seal a rectangular area, and this is harder than the annular area that a typical telescopic shock seal faces. Why? The rectangular area between the rotor and the shock body has sharp angles that want to warp or bend, especially when movement is in both directions. It is likely that the precision of assembly required to ensure that the vanes are perfectly sealed is what prompted Suzuki and Kayaba to declare the damper unusable. Since the sizes and volumes of the working chambers are not limited by the size of the inside diameter of a coil spring. , the TL shock absorber can pump a lot of oil. This high flow rate could be used to facilitate fine and precise damping adjustments than with the more stringent tube damper design. Indeed, the damping adjustment screws (compression on one side, rebound on the other) are fairly easy to access, no remote mechanism is necessary.
As the shock absorber is actuated by its own linkage, it can be configured for a different speed increase than the spring. For example, it would be possible to design the linkage so that the spring gets stronger and the damper weaker as the suspension reaches the full rebound stroke, or vice versa. This example is patently silly, but split binding offers unique (and potentially confusing) tuning options if a serious tuner is willing and able to design and build new bindings.
Suzuki gave the TL shock absorber a fairly fixed rate linkage so that the force of the shock stays fairly consistent with the stroke, while the spring has a progressive or increasing rate design.
The biggest drawback to the rotary damping concept may well be the complete lack of a fallback position. Think about it: if you don’t like the Kayaba or Showa shock in your traditional damper bike, there are a number of alternative shocks you can choose from from reputable aftermarket sellers. If you don’t like the TL’s rotating unit, you go up the stream without a shock – at least until the aftermarket starts producing shocks for the TL.
Suzuki took risks with this design, but for good reason. We hope the limb turns out to be solid, as the rotating design has some obvious advantages and helps make Suzuki’s TL the mind-blowing bike it is.