From the November 2017 issue
Scant bits of technology trickle down from racing to street cars anymore. Multimatic’s Dynamic Suspensions Spool Valve dampers are one of the few. The Canadian supplier’s dampers first appeared in the 2002 CART series, then migrated to Formula 1, and now populate about half the Le Mans starting grid. Aston Martin’s limited-edition One-77 was the first production car fitted with DSSV dampers and Chevrolet’s fifth-generation Camaro Z/28 followed in 2014. With their blend of street comfort and track-ready attitude, DSSV dampers are like shampoo and conditioner in one. Currently you can find them in the Ford GT, the Mercedes-AMG GT, and the Chevy Camaro ZL1 1LE and Colorado ZR2. Their simplicity is a thing of engineering beauty, so we uglied one up by cutting it in half with a band saw.
Conventional dampers set compression and rebound forces by controlling the flow of fluid through orifices with stacks of flexible shims. Spool valves (001) dynamically vary damping force by controlling fluid flow through precisely shaped ports using a spring-loaded shuttle. Each DSSV damper contains two spool valves, one for compression and one for rebound.
Windows: There are six ports, or windows (002), on each street-car valve. Racing applications get fewer. The shape of the port helps define the damper’s baseline force-velocity curve—how much damping force is generated based on the vertical speed of wheel movements. The narrow end of each opening establishes the low-speed damping. Multimatic has eight window shapes in production, but the possibilities are nearly infinite. The window shape is one of the first things locked in the tuning process. When cutting the ports into the spool valves, Multimatic leaves the edges rough. The resulting turbulent flow smooths out the damper’s action.
Shuttle: The shuttle (003) is the metaphorical shutter that opens and closes the window to fluid flow. It looks like a piston with holes in its crown and is supported by a spring that compresses under the force of vertical wheel movement. The faster the movement, the more the window opens to let the damper’s fluid pass through the valve. It is both passive and elegant. The initial position of the shuttle relative to the window is also a tunable element.
Pin: The force that moves the shuttle acts through a cuplike pin (004) in the center of the shuttle. A larger-diameter pin reduces the gradient of the force-velocity curve.
Valve Spring: A stiffer spring requires more force (greater speed) to open the window. In some cases, the springs (005) are preloaded with shims.
Bleed Paths: Small orifices (006) with one-way check valves allow fluid to bypass the compression spool valve during rebound and vice versa.
This damper from a Chevrolet Camaro ZL1 1LE differs from most DSSV applications in that it is an inverted strut, meaning the damper’s piston moves in the body as opposed to the body moving around the piston.
This results in increased stiffness. The ball joint at the top (007) allows the wheel camber to be changed with just a few bolts.
Old Dog, New Trick
Sliding spool valves are commonplace in the hydraulic systems of machinery such as tractors and bulldozers. The valve body of a modern automatic transmission uses them. So they’re nothing new; Multimatic is simply the first to use spool valves in a damper.
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