Theoretically fully active suspension is the nirvana of the motoring world.
A true active suspension has double-acting hydraulic actuators instead of springs and dampers. As tyres meets bumps, the wheel's acceleration and vertical load is transmitted to a computer which calculates the required wheel velocity and displacement and sends control signal to the actuator.
As this dialogue is conducted hundreds of times a second, the wheel accurately follows the contour of road and bumps, protecting the body structure against unwanted forces.
When riding on a bump, Active suspension, Hydractive suspension and Adaptive damping react very differently.
Adaptive damping :
Hydractive suspension :
Active suspension :
As you can see, active suspension is a perfect concept. Theoretically it could absorb all the shock while maintaining the car body totally stable. Lotus that put it into reality.
Lotus started researching active suspension in 1981, originally intended to equip its Formula One racing cars. The active F1 ran in Brazil and Long Beach '83 in the hands of Nigel Mansell. Despite lacking competitiveness in other areas, It proved that active suspension could withstand hard use at 180 mph and 3 g lateral acceleration. The development team went back to drawing board and did more tests to improve the software. It was not raced again until 1987, when the Honda powered 99T won 3 races in the hands of Ayrton Senna.
However, the active suspension did not offer sufficient advantage in F1 racing. Theoretically, it could raise cornering speed considerably. ("Cornering at 200mph" used to be Team Lotus's slogan when defending this technology.) But on the down side, its hydraulic pump consumed horsepower. we don't have the exact figure, but years later Lotus told us the active suspension in its Excel development car consumed 4 - 4.5 hp on smooth road and up to 9 hp on rough roads. Worst of all, Team Lotus did not get the specially developed tyres needed to extract its potential. As the active suspension reduced tyre's slip angle, the tyres generated insufficient heat to attain the necessary working temperature, and as a result always ran cold.
Just after the F1 debut in the 1983 season, Lotus Engineering started developing the active suspension technology for production car use. It used the Esprit as the development platform. Like the racing car, the hardware - hydraulic actuators - came from aerospace industry, where active suspension was used in advanced jet engines. According to the engineers involved, the most crucial part was the software rather than hardware. They had to road test for a lot of hours to acquire the necessary data in order to write the program.
The first 2 generations were spring less, but the Mk III and Mk IV system, which were equipped in the Excel development cars, had springs as back up in case the active system broke. The software was gradually improved.
British magazine Fastlane tested them twice, once in the '87 Mk III and then in the Mk IV two years later. In the latter it reported significant improvement in ride quality and body control. It also expressed optimistically that the system would go into mass production within a few years, probably under the name Volvo, Chevrolet or Mercedes-Benz, as they all had been consulting Lotus.
This did not come true. The main reasons, are likely to be cost, and reliability. The only successful application was still in motor racing - between 1992 and 1994, F1 championship were dominated by the active Williams and Benetton. As F1 was at the stage of running Turbo power with a surfeit of BHP the losses presumably were not a problem.
Meanwhile, The DTM series also saw active suspension's superiority in Mercedes C-class and Opel Calibra, it was too superior, the FIA banned it.
The last time Active suspension reared its head was in 1995 (?), when Lotus showed the Esprit SDIII development car. After that, the automotive world seems to have forgotten about Active suspension.
Which is a shame because if you look at all the suspension designs out there you will see how they, all compromise something in some way. The compromise is almost always caused by body roll, and so far active suspension is the only way to eliminate body roll whilst, actually having suspension which can deal with bumps proficiently.
Why, well :
Assuming, that the active system is set to give zero roll then it is
becomes very interesting to follow through the implications for the cars
geometric roll centers.
If we have no roll then the roll axis becomes irrelevant, as does the need to have suspension layouts that try to keep the outside wheels upright under cornering roll, rather than under all conditions.
Active suspension could mean a return to parallel equal length wishbones or perhaps even , the cheaper trailing or leading arm systems.
These designs suffer because of changes in roll centre positions, and the associated camber angle varying with the roll angle of the body, but if the body does not roll ????????