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1990 Chevy Corvette ZR-1 Prototype - Back To The Future

Ahead Of Its Time, The Active Suspension ZR-1 Prototype

Brendan Moran Jan 1, 2009
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Beginning with Lotus's original architecture, the GM engineers developed a program for a Delco computer that would hydraulically control all four struts to actively level the body through corners and undulating surfaces, as well as maximize load distribution and vehicle dynamics. To do so, the computer would have to enter speed, tire load, steering, throttle, and several other inputs into a complex algorithm that would dictate where the belt-driven hydraulic pump would deliver its fluid. Understeer, oversteer, or neutral handling could be coerced with just a few keystrokes by the engineers. After being given the green light, Active Suspension was installed on the assembly line by the crew at Bowling Green, KY into 25 pre-production ZR-1s for testing. In doing so, one of the problems encountered was that the actuators had to be so responsive to make the system work that it conflicted with the accelerometers in the wheels on some cars. Some sort of preview sensor or transducer, Turner said, would have easily solved this problem. Unfortunately that sort of technology didn't surface until 10 years later, just before Jack retired. The system was not without other problems such as electronic interference, noise isolation, and packaging. However, these problems were merely bumps in the road.

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In 1988, GM committed over $27 million to designing the most advanced suspension ever built on a production car, according to the former project manager Jack Turner. If his team, Lotus, and several outside contractors had anything to say about it, the 1990 Corvette ZR-1 was to be the first time Active Suspension was ever used on a production vehicle. The ZR-1 was already shaping up to be a quantum leap in production car design, bringing race car technology to the street in a market flooded with anemic two-doors masquerading as sports cars. Active Handling would have put the ZR-1 way over the top, and previously had only been used by a handful of race teams such as Lotus. However, even the talented engineers at Lotus had trouble making the "smart" suspension viable with the professional race team's ample budget. GM had quite a challenge ahead of them.

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The biggest issues with the Active Suspension program, and why it never made it to production, were cost and durability. Between the Eaton hydraulic pump and Moog actuators alone, cost was skyrocketing on what was already going to be the most expensive Corvette ever made. Total cost per vehicle was easily $35,000 according to Turner, since mass-producing some of the parts (ordinarily used for aircraft applications) was becoming difficult, to say nothing of what it would cost to service the vehicles and train technicians on how to do so. Durability was also a concern with a system that needed to maintain 3,000psi of fluid pressure to operate. Friction and corrosion were two unknowns upon designing the system, and friction in particular became problematic on the actuators and displacement transducers. Heat was a major concern that they hoped to alleviate with hood and side vents, as well as hydraulic oil coolers with large intake scoops on the front fascia to direct the air. Another problem was that the sensitivity calibration proved inconsistent car to car using the current hardware, which would have been a nightmare in the first production run of 200-let alone a year or two later.

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Despite its shortcomings, the ZR-1's Active Suspension was successful in helping to usher in a new wave of technological breakthroughs in automotive design. By the mid-'90s it was becoming quite clear that designers and engineers were starting to think way outside the box...or inside if you are talking about the PCM and other control modules. Though some might call Active Suspension a failure, it did help the engineers learn quite a bit about hydraulics, PCMs, and adjustable suspensions. In fact, this program gave way to Active Handling in '96, in which the very same GM engineers were applying their newly found knowledge. Conversely, Active Handling uses the very same inputs and sensors to detect an understeer or oversteer situation and then applies the ABS system to correct. As the result, it is actually a passive system in comparison, and a safeguard to prevent the driver from losing control.

When Magnetic Selective Ride Control came out on the '03 Corvette it was apparent that GM had finally perfected a more active system that actually incorporated PCM-adjusted damping rates, similar to Active Suspension, using the same inputs and sensors. Except unlike the C4's hydraulic system, the C5's F55 suspension used a more powerful PCM and "Magneto-Rheological" fluid contained in traditional shock absorbers. The synthetic oil permeates millions of tiny iron balls, which changes viscosity based upon the electric current that feeds it. The desired goal, though, was the same-a flatter ride and more responsive handling. As we near the seventh generation Corvette, we can only wonder what the latest evolution of this technology holds for us.

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The controls for Active Suspension, seen here in front of the shifter. Between the A.S. gadgets and the ZR-1's valet key, this was ultra high-tech for the late '80s! ----->

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