Secrets of F1 suspension: active and FRIC

With Formula 1 weighing up lifting the ban on active suspension, which was outlawed ahead of the 1994 season, it's worth revisiting the concept.

CRAIG SCARBOROUGH explains the efforts teams have gone to replicate active suspension's effects within the current regulations, and the potential benefits its return could offer.

WHY ACTIVE SUSPENSION COULD COME BACK

Using powered electro-hydraulics to control suspension has been a panacea for the chassis designer for many years. Effectively, it allows complete control of the suspension's response via software, rather than by mechanical means.

There have been three eras of active suspension, from Lotus's first trials in the 1980s to Williams's reactive project, before the technology was resurrected by Adrian Newey at Williams, which led to what is commonly known as the active era in the early '90s.

Active suspension first appeared in a grand prix on Nigel Mansell's Lotus in the 1983 Long Beach race © LAT

The ban for 1994 was largely in response to the proliferation of driver aids, such as traction control and ABS brakes. But active suspension was not so much a driver aid as an engineer aid.

Suspension since 1994 has been bound by regulations that demand the set-up only responds to changes in wheel load. So no powered systems or electronics are allowed.

Developing purely mechanical systems to provide the non-linear compliance required for the key suspension characteristics - heave, roll and individual wheel movement - has required massive investment and huge complexity at each end of the car.

Therefore, each end may have some or all of the following: spring, damper, inerter and bump rubber for each of the three elements, such that the engineer may have as many as 32 different compliance parameters for the car!

The further level of interlinking only compounds that complexity.

It has long been argued that, given the advent of the FIA standard ECU (SECU) and software, active suspension's reintroduction would be a positive move for cost control without the fear of driver aids creeping back in.

This year's introduction of rear brake-by-wire supports this argument, as the risk of anti-lock braking or traction control being a function of electronic brake control has been eliminated by the FIA's control of the ECU and diligence in software inspection.

The current inboard suspension set-up is complicated, with torsion bars, dampers, inerters, anti-roll bars, third springs, roll dampers and bump rubbers.

An active suspension set-up simply has a hydraulic actuator attached to each push or pullrod. Each of these is controlled by the hydraulic pressure being metered by a servo valve.

By 1993, active suspension was mandatory for success - and Williams mastered it best © LAT

Hydraulic fluid is delivered to the servo valves by the pump driven off the engine and the valves opened by electronic control from the FIA SECU. Each of the actuators used in coordination with these can replicate every aspect of the car's current suspension through software algorithms.

The current development process for suspension is; design, simulate, build, rig test and track test. With active suspension, it would be to code the software and send the results straight into the simulator for assessment.

This technology was first pioneered in F1 with the advent of active suspension. Since then it has become commonplace for controlling many of the car's systems, from throttles to gearshifts. Adding this extra level of control system is well known and relatively cheap technology.

With the simple electro/hydraulic control, the key aspect of active suspension's return will be the rule book restricting what is considered normal suspension control to merely mimic current mechanical suspension - and not allow extreme suspension control used to exploit aerodynamics.

FRIC EXPLAINED

In the late 1980s and '90s, as underfloor aerodynamics grew ever more important, controlling ride height also became critical.

Teams started to link the front suspension to the rear to keep the floor attitude to the track constant. This eventually spawned active suspension, but after the 1994 ban this solution fell into disuse.

It was revived by Lotus (then Renault) in 2008, then subsequently Mercedes. Now nearly every team has an interlinked suspension, often termed FRIC (front/rear interconnected), set-up of some kind.

Renault began using FRIC in 2008 © XPB

With the key aim of controlling the relative ride height between the front and rear axles, a relatively simple hydraulic set-up is used. By using the movement of one end of the car to support the other end, you can have positive effects such as preventing dive under braking.

On each end of the car, the pull or pushrods operate rockers that in turn have a double-acting hydraulic cylinder mounted in between them. Within each of these cylinders, a piston moves with the suspension to compress one of the chambers.

Each chamber either side of the cylinder is linked with pipework to the corresponding cylinder at the other end of the car. Along the way, these pipes pass through a valve system to tune the suspension's response to movement of the cylinders.

This system does not use any form of electronics or powered hydraulics so it's completely passive. To use anything other than this would be illegal under the post-1994 regulations.

By varying the size of the cylinders and the valving, it's possible not just to control dive and squat, but also to drop the rear ride height at speed. This effectively reduces the rear-wing angle for less drag on the straights.

If the cylinders on each of the car split into two, such that each wheel operates its own cylinder, then the system can be set up to incorporate roll control into the linked system. With this, the attitude known as warp, where the car is both rolling and diving at the same time, can be tuned.

Having these further levels of complexity in the suspension set-up absorbs huge amounts of teams' time spent setting up the car.

Although a team's simulation facilities ease this somewhat, there is a large amount of extra resource required to introduce and develop these mechanical systems.

This week's AUTOSPORT magazine features more on the push for active suspension's F1 return, including drivers' and engineers' memories of the 1980s systems