The rebound damping fluid flow is controlled by this rod with a reverse needle valve at the end. The rod screws up and down in the valve body. This covers or exposes more or less of the fluid passage in the center spindle/valve body and this allows more or less fluid flow through the valve and thus more or less rebound damping. The rod passes through a hole in the shock shaft and up to the purple rebound adjuster knob at the top of the shaft.
This is the shock piston, it is attached to the end of shock rod. On the compression side of the piston or the back side we have this one-way valve disc and a star shaped washer spring. This and the rectangular orifices in the piston control some of the compression damping, the non adjustable part of it. The amount of force generated here is dependent on the hole size in the pistons and the tension of the star washer. These are the calibration factors. The compression valve in the piston is important as it affects the pressure balance of the shock between the body of the shock and the remote reservoir. Too much pressure going to the remote reservoir can cause valve cavitation and make the adjustable part of the damping curve difficult to calibrate. Too little and the adjustable part of the curve might not have enough influence on the shape of the damping curve for good user tunability.
This is the rebound side of the piston, it affects the fixed and non adjustable high speed part of the rebound damping curve. It uses the smaller inner holes of the piston, the washer like check valve and the coil spring that holds it closed to affect the rebound damping characteristics. These are all tuning factors. The smaller valve and the longer travel coil spring are what increases the valves hysteresis. The smaller valve must move further to activate which takes more time.
The final rebound calibration point is found in the piston bottom nut. This holds the rebound center spindle/valve body and the piston to the shock rod. It has orifices in it to bleed flow passing through the center spindle/ valve body. It has a one way check valve in it as this helps make the compression and rebound circuits more discrete so the adjustments will have less bleed through. The street KW shocks, like a Variant 3 don’t have this check valve.
The above rebound valve, piston assembly is the new fast acting low hysteresis EXR valve technology. As you can see it looks completely different.
8 comments
I’m going to have to do some napkin drawings after I’ve had enough coffee; I’m not saying anything against them, but some of the ways KW do things are very different than I’m used to.
The low speed is much like any other shock, via a needle valve. The high-speed short travel fast response valves are certainly different than your traditional deflecting disc, poppet or spool valves.
The execution of the needle valve is a lot different though even if it works similarly.
The high speed blowoff stuff reminds me a bit of the Penske regressive valve in terms of how the closing shim moves (not the port shape interaction, just the shim moving straight with a spring preload vs deflecting); I’d expect kind of a sharper divide between high speed adjustments and low speed on that vs the conventional style of high speed adjustment… like the shim stack varying preload is going to open more and more with flow while KW’s should, once the pressure hits whatever value, open a lot more area all at once. KW’s method seems like it’d be more sensitive to manufacturing tolerances on the bellville setup but obviously they have it working.
This stuff really is fascinating to me – I mean it’s all “a pressure sensitive valve that changes its open area” but the number of ways to do that is huge.
Yeah it’s more of a reverse needle.
Does KW have a prevalved set of shocks that would work on my Subaru Legacy that I could order for our local timed rally cross events in Sonoma Calif? My Legacy has 1032 whp and 888 ft lbs of torque and currently weighs 2550 lbs with me in the seat.
KW ERX shocks are from their Motorsports line and are made to order. They could certainly build you a set of shocks. Man, tell us more about your car, that seems worthy of a MotoIQ feature!
Any interest in building a mono shock for flat track motorcycle racing? 92 RWHP, 750 cc, 325 pounds, spec tire. Currently using Penske.
Ohlins might have an application using through-shaft solid piston technology.