Car-development engineers are invariably discontented with the status quo. That’s especially true in ride-and-handling development, where twin-tube shock absorbers—more accurately called suspension dampers—are now under scrutiny. These 100-plus-year-old devices are finally prime candidates for replacement by more sophisticated hardware.
Twin-tube dampers are inexpensive to manufacture, serviceable for tens of thousands of miles, and entirely suitable for mainstream use. That said, they’re susceptible to wear, which deteriorates their performance over time, and they lack the tuning flexibility offered by newer damper designs.
Enter Multimatic, a Canadian enterprise that strives to be every car company’s problem solver. This suspension-systems and composite-body specialist is currently Ford’s ally for constructing its GT supercar. In addition, Multimatic’s Motorsports division has a lengthy history of designing, engineering, constructing, and campaigning race cars for top-series competition around the globe.
In 2010, Multimatic applied for a patent on an innovative suspension damper. Code named DSSV, for Dynamic Suspensions Spool Valve, this design initially proved its merit by helping Newman-Haas Racing win seven of the 19 races and the driver’s championship in the 2002 CART series. DSSV hardware became mandatory equipment in five other major racing series between 2006 and 2015. Red Bull Racing used them to win four consecutive Formula 1 titles (2010–2013) and nearly half of this year’s Le Mans 24 Hours competitors swear by DSSV dampers.
The size and shape of the spool-valve windows determine damping characteristics.
Conventional dampers use multiple thin discs covering ports in the piston moving up and down within a tube containing hydraulic oil to generate the forces that control body and wheel motion. The flexibility tuned into these discs—and the size and shape of the ports they cover—determines how fluid flows between the chambers above and below the piston. The greater the flow restriction, the higher the damping force.
While that principle is sound, problems arise with mileage. The steel disc material is subject to fatigue, which diminishes its strength and stiffness. Bits of debris from the damper seals, piston, and shaft become trapped between the disc layers, altering their damping qualities. Anyone who has owned a high-mileage car with clapped-out shocks knows that the term “handling” no longer describes its dynamic behavior.
The other shortcoming with conventional dampers is that they can’t be tuned to cover the full scope of road driving, track lapping, and off-pavement excursions that ambitious manufacturers are striving to cover.
Multimatic’s DSSV dampers retain basic components such as a sealed tube filled with hydraulic oil and a piston that moves within that tube in sync with suspension motion. The difference is that the thin discs are replaced with a pair of hollow cylindrical sleeves nested concentrically within each other and held apart by a coil spring. Suspension motion forces damper oil inside the sleeve cavity. When that internal pressure is sufficient to overcome the spring force, one sleeve moves slightly with respect to the other, uncovering apertures, which allow oil to move to the opposite side of the piston. One sleeve valve regulates compression damping; another controls rebound damping.
The coil springs inside this pair of spool valves resist motion of the inner portion, helping control the magnitude of damping force produced.
The beauty of this arrangement is that the sleeve valve components are not susceptible to wear or fatigue. The stiffness of the coil spring and its preload and the shape of the apertures facilitate three distinct damping curves. A linear “curve” provides damping forces directly proportional to the velocity of the suspension movement. Progressive damping characteristics mean that the force rises gradually with suspension velocity. Digressive damping is a steep initial rise in damping followed by the force curve leveling off at some specific suspension-travel velocity. Multimatic has software called SpecFinder that allows ride-and-handling engineers to quickly and easily pick spool valves that deliver the damping curves they desire.
What proof do we have that DSSV works as touted? At Car and Driver’s 2014 Virginia International Raceway Lightning Lap event, the Chevrolet Camaro Z/28 and its standard Multimatic DSSV dampers bested a Porsche Cayman S, a Jaguar F-type R coupe, and a BMW M4 in its class. In Turn 1, it cornered at 1.16 g, matching a Porsche 918 spyder as the grippiest car we’ve experienced in that bend to date. We went on to extol: “Holding the fear pedal to the floor is necessary to discover the genius of the Z/28, which is that nothing scary happens. The curbing, the bumps, the speed, and the violent transitions don’t affect the Camaro’s trajectory one micrometer.” We also crested the hill at the top of the climbing esses at 118.5 mph, an all-time Lightning Lap record at that time. As compression began going into the following left-hander, the Z/28’s suspension was so capable that the challenge was resisting excessive use of the brakes. While the astute damping characteristics were at the heart of this Chevy’s track prowess, credit must be shared with the overall suspension tuning and the Z/28’s humongous Pirelli P Zero Trofeo R tires.
Camaro lessons learned, Chevrolet partnered with Multimatic a second time for the 2017 off-road-rated Colorado ZR2 mid-size pickup. Here, DSSV technology has moved forward another step with what Multimatic calls Position Sensitive Damping (PSD) to provide specific damping characteristics in different areas of the suspension’s travel. Combining three spool valves with a remote nitrogen-charged fluid reservoir [see top animation] allowed engineers to tune the ZR2’s dampers for optimum performance both on-road and in severe off-road use. The added reservoir supports longer wheel travel and increases the amount of working fluid to resist overheating. The extra spool valve provides the damping needed to control extremes of wheel movement during high-impact compression cycles.
Chevrolet and Multimatic used two approaches to meet their performance targets. First, a computer-aided-engineering model of the DSSV damper was created using ADAMS (Automated Dynamic Analysis of Mechanical Systems) software. This step occurred well before the first running Colorado ZR2 was constructed. After the dampers and the entire vehicle were validated in virtual form, on- and off-road test driving of prototypes began. This included desert runs, rock crawling, high-speed trail drives, paved-road evaluations, and stints on Multimatic’s four-post shaker rig.
This analysis helped reach ambitious goals. One was minimizing the ZR2’s frame weight while keeping peak loads below the acceptable limit by tuning the dampers to absorb more impact energy. Other aims were to reduce the peak vertical movement of the ZR2’s center of gravity by 40 percent and the driver’s hip upward displacement by 50 percent with damper tuning. Combining DSSV with PSD lowered the peak vertical force at the front tires by an impressive 35 percent while traversing a challenging “whoops” road profile at General Motors’ Milford Proving Ground.
We’re looking forward to sampling the Colorado ZR2 alongside Ford’s larger F-150 Raptor at an appropriately difficult off-road venue, such as Mexico’s Baja 1000 course. Unfortunately, Multimatic has no plans to sell DSSV dampers in the aftermarket except for replacement parts engineered for the Camaro Z/28. They’ll work on any sixth-generation Camaro, so anyone owning a 2016 or newer Chevrolet pony car can upgrade to at least partial Z/28 specs through GM’s service parts organization.
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