Active suspension

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Active suspension is a term that is mostly used in motorsport. In the automotive industry, this is more precisely referred to as active suspension (alternatively active chassis ). An actuator completely or partially supplies the forces that are otherwise passively generated by springs or dampers. The aim is to reduce the otherwise unavoidable rolling and pitching movements of the body when cornering ( roll stabilization ) or when braking or accelerating. In addition, the distance between the vehicle and the road is regulated. These functions consume energy, which usually has to be made available hydraulically and sometimes also electrically. This is to be distinguished from semi-active suspensions, in which it is possible to switch between different characteristics of the spring or damper elements (cf. hydractive suspension , magnetorheological shock absorbers ).

A first insert found the active suspension in the formula 1 , where a computer-controlled electronics in the suspension to improve the aerodynamics of the vehicle contributed during the period of the seasons 1987-1993. At the end of 1993 it was banned by the FIA .

From 2008 to 2014, the purely hydraulically controlled FRIC system was used in Formula 1 . FRIC is an acronym for Front and Rear Inter-Connected. In 2014, FRIC was classified by the FIA ​​in Formula 1 as a movable aerodynamic aid and therefore illegal. FRIC is currently used in the FIA World Endurance Championship ( WEC).

history

The development of the active suspension was started by Lotus chief engineer Colin Chapman as early as 1981/1982. The active wheel suspension was first used for racing in 1987 at Lotus Cars in the 99T model . At the same time, Williams also developed an active wheel suspension in the FW11B . However, the active suspension was still immature and the software could not make optimal use of the potential of this invention because it was not yet able to fully process the information. Nevertheless, the Lotus 99T with the Ayrton Senna won the races in Monaco and the USA ( Detroit ). Nelson Piquet won the race in Italy in a Williams Honda . In 1988 development continued unabated, especially at Williams and Lotus; however, the technique proved to be too complex and was discontinued until further notice, until it was resumed by Williams at the end of the 1991 season . The breakthrough came in the 1992 season ; Nigel Mansell was the superior driver world champion in the Williams FW14B , the Williams team secured the constructors' title. The technology that gave the Williams team an enormous advantage was adopted and further developed by other teams at the beginning of the 1993 season . Alain Prost won the second title for a Williams with active suspension this year.

Mode of action

All information important for the functioning of the system (e.g. driving speed, accelerations, spring travel, ...) is recorded by sensors . The on-board computer uses this to calculate the force required on each wheel. Different actuators are used depending on the application, energy consumption and other criteria. With spring base adjustment z. B. the force is applied hydraulically with a cylinder in series with a spring. This is necessary because each actuating system only has a limited capacity. Higher-frequency excitations that can no longer be actively controlled are kept away from the structure. In addition to the mechanical components, the mode of operation depends heavily on the software, so that the know-how and imagination of the engineers are required here.

Active suspension in motorsport

Since the aerodynamics of racing cars are very sensitive to changes in the pitch angle and ground clearance, the position of the vehicle is set regardless of the external conditions (driving speed, tank content, ...) in such a way that the aerodynamic attachments have a favorable flow and the ground clearance is as constant as possible. By distributing the wheel load differences between the front and rear axles, understeer / oversteer in bends and traction when accelerating out of bends can be improved.

Active suspension in road traffic

In 1983 the first electronically controlled semi-active wheel suspension for steel suspension and in 1986 for air suspension made its debut in the Toyota Soarer : Toyota Electronic Modulated Suspension (TEMS, current name: Adaptive Variable Suspension).

In March 1989, when the Mercedes-Benz SL R129 was presented, the ADS (Adaptive Damping System) system was offered as an option. This involved a partially hydraulic wheel suspension with level control for both the front and rear axles. The optimal damping was continuously electronically calculated for each wheel on the basis of parameters from wheel acceleration sensors and the vehicle's longitudinal and lateral acceleration sensors and adjusted in four stages. In addition, the vehicle was lowered by 20 mm at speeds above 120 km / h and the ground clearance could be increased by 40 mm at the push of a button at speeds below 40 km / h.

In 1989, the Toyota Celica (and 1991 Toyota Soarer / Lexus SC ) introduced a computerized hydraulic Toyota Active Control suspension that no stabilizers required and the shaky balances. According to Toyota, this was the world's first fully active suspension. (Mercedes-Benz introduced a similar system in 1999: Active Body Control )

In 1991, Nissan introduced a hydraulic, electronically controlled active suspension in the Cima and Infiniti Q45 : Full Active Suspension.

Citroën introduced in 1995 in the Citroen Xantia an active chassis stabilization (AFS) one. The Xantia Activa was the (technical) top model of the Xantia series from Citroën. The presentation was at the end of 1994, and a little more than 18,000 units were built between spring 1995 and autumn 2001.

In addition to Hydractive II, the Activa also had the so-called Active Chassis Stabilization (AFS), in the French SC.CAR = Systems Citroën de Contrôle Actif du Roulis , which was the first active anti-roll bar to be offered in series in the automotive industry. With this system, the lateral inclination is reduced to a minimum (−0.2 ° to 1 °) through mechanical control with hydraulic cylinders that act on the anti-roll bars. According to the manufacturer, this technology enables lateral accelerations of up to 1.2 g with optimally grippy road surfaces  and still offers above-average suspension comfort and thus safe road holding. Compared to the standard models, the Activa has seats with reinforced side bolsters, which are also pneumatically adjustable in the first series (X1). This guarantees more lateral support.

Operation of AFS / SC.CAR: Both cross stabilizers (mm front 28, rear 25 mm diameter) are diagonally opposite (front-left and rear-right) via a differential - hydraulic cylinder connected to the check rails.

These cylinders are connected to a control valve which is actuated directly by the front wishbones using push rods via a spring-lever mechanism. Any roll moment that occurs (lateral inclination) acts in the opposite direction on the wishbones - one wheel compresses, the other rebounds. As a result, the control valve - the inclination corrector - is pulled / pushed out of its rest position (straight-ahead position) by the push rods in one direction, whereby it sets a pressure in the hydraulic cylinders proportional to the roll moment.

This changes the length of the hydraulic cylinders and counteracts the tension in the anti-roll bar. They "push" the body back into the horizontal position against the roll moment acting on the anti-roll bars, which enables cornering of up to 0.6  g lateral acceleration with a lateral inclination of −0.2 to 0.5 °. From a lateral acceleration of 0.6  g the actuating cylinders come to their stop, from here the Xantia Activa leans up to 1 ° into the curve until it reaches the curve limit area, which corresponds to the value of a good sports car with a correspondingly tight set-up.

Since this active roll stabilizer works independently of the Hydractive II chassis, its spring deflection is almost completely retained even in extreme cornering and thus ensures a significantly better road holding in these situations than conventional wheel suspensions can. When driving straight ahead, a solenoid valve is actuated via the control unit of the hydractive suspension, which switches an additional spring ball into the hydraulic control circuit of the actuating cylinder. As a result, on the one hand, the rigidity of the hard-tuned stabilizer rods is "virtually" reduced by the gas filling of the spring ball in order to reduce copying movements and thus increase comfort. In addition, its storage effect has a dampening effect on the control loop, so that when driving straight ahead, no undesired control oscillations occur due to brief actuation of the inclination corrector caused by the suspension.

In 1999 Mercedes-Benz introduced an active suspension system in the CL under the name Active Body Control , in which the degrees of freedom of movement for lifting, pitching and rolling were actively influenced. With additional hydraulic forces on each wheel, rolling and pitching movements when cornering or when accelerating longitudinally are largely avoided, without the driving comfort on uneven road surfaces suffering. This enables both very good driving behavior and high driving comfort.

Other models from Mercedes-Benz (Adaptive Damping System ADS), Porsche (Porsche Active Suspension Management PASM), Audi (adaptive air suspension), BMW (EDC), Opel (FlexRide) and Renault have technologies that do not all have degrees of body clearance regulated: Continuous Damping Control .

Further developments rely on electronic control units that record the driving condition via sensors and control actuators ( active stabilizers ) accordingly. For example BMW ( Dynamic Drive : active stabilizers, alternative names: Adaptive Drive, Active Roll Stabilization ARS) or Porsche PDCC.

The Bose company develops an active suspension based on a linear motor. The static wheel load is carried here by a passive spring.

Web links

Commons : Active Suspension  - Collection of pictures, videos and audio files

Individual evidence

  1. Christopher Hilton: Nigel Mansell. The fighter and his triumph (1992) ISBN 978-3-908007-49-4 , p. 187
  2. ^ Automotive paperback. Bosch 2003, pp. 758–759 ( limited preview in Google book search)
  3. ^ A 75-Year History through Data> Automotive Business> Products, Technology> Technical Development> Chassis . Toyota. 2012. Retrieved January 5, 2015.
  4. https://www.sae.org/publications/technical-papers/content/840341/
  5. Toyota Soarer UZZ32 . UZZ32. November 2, 2014. Retrieved January 18, 2015.
  6. ^ A 75-Year History through Data> Automotive Business> Products, Technology> Technical Development> Chassis . Toyota. 2012. Retrieved January 5, 2015.
  7. ^ Development of an electronic control system for active suspension - IEEE Conference Publication . Retrieved July 20, 2018.
  8. https://www.jstage.jst.go.jp/article/isfp1989/1993/2/1993_2_99/_pdf
  9. http://papers.sae.org/901747/ Society of Automotive Engineers: Development of the Full Active Suspension by Nissan
  10. Active Bose chassis: Spiegel Online