Active suspension

Posted On December 9th, 2019

The suspension of a modern car is a compromise between handling, stability and comfort. A stiffer suspension provides minimal roll, which means better handling and stability. The soft suspension is characterized by a smooth ride, but when maneuvering it leads to a buildup of the car, a deterioration in handling and stability. Therefore, many car manufacturers are developing and implementing various active suspension designs on their cars.

The term “ active ” means a suspension whose parameters can change during operation. The electronic control system as part of the active suspension allows you to change parameters automatically. Active suspension designs can be divided into suspension elements, the parameters of which vary:

Pendant element
Variable parameter
Shock absorber
  • degree of damping;
  • suspension stiffness
Elastic element
  • suspension stiffness;
  • body height
Anti-roll bar
  • stabilizer stiffness
  • lever length;
  • toe-in

A number of active suspension designs use effects on several elements.

The most widely used active suspension designs are shock absorbers with an adjustable degree of damping. This type of active suspension has its own established name – adaptive suspension . Such a suspension is also called a semi-active suspension because its design does not use additional drives.

When adjusting the damping ability of the shock absorber, two approaches are implemented: the use of electromagnetic valves in the shock absorber rack and the use of special magnetic rheological fluid to fill the shock absorber. Electronics allows you to adjust the degree of damping individually for each shock absorber, which achieves various characteristics of suspension stiffness (high degree of damping – rigid suspension, low degree of damping – soft suspension). Known adaptive suspension designs are:

  • Adaptive Chassis Control, DCC (Volkswagen);
  • Adaptive Damping System, ADS (Mercedes-Benz);
  • Adaptive Variable Suspension, AVS (Toyota);
  • Continuous Damping Control, CDS (Opel);
  • Electronic Damper Control, EDC (BMW).

Active suspension with adjustable elastic elements is more versatile, as allows you to maintain a certain body height and suspension stiffness. On the other hand, such a suspension has a more complex structure (a separate drive is used to regulate the elastic elements), and therefore its cost is much higher. Traditional springs, as well as pneumatic and hydropneumatic elastic elements, are used as an elastic element in the active suspension.

In Mercedes-Benz’s Active Body Control, ABC suspension, the spring stiffness is changed by a hydraulic drive that delivers oil to the shock absorber strut under high pressure. A spring-mounted coaxially with the shock absorber is affected by the hydraulic fluid of the hydraulic cylinder.

The hydraulic cylinders of the shock absorber struts are controlled by an electronic system that includes 13 different sensors (body position, longitudinal, lateral and vertical acceleration, pressure), a control unit and actuators – electromagnetic valves. The ABC system almost completely eliminates body roll under various driving conditions (turning, accelerating, braking), and also adjusts the body’s height position (lowers the car by 11 mm at speeds above 60 km / h).

The pneumatic resilient element is the basis of air suspension. It provides adjustment of the height of the body relative to the surface of the road. The pressure in the pneumatic elastic elements is created using a pneumatic actuator that includes an electric motor with a compressor. To change the stiffness of the suspension, shock absorbers with an adjustable degree of damping are used. This approach is implemented in the Mercedes-Benz Airmatic Dual Control air suspension, which uses the adaptive Adaptive Damping System.

Hydropneumatic elastic elements are used in a hydropneumatic suspension, which allows you to change the stiffness and height of the body depending on driving conditions and the wishes of the driver. The suspension is operated by a high-pressure hydraulic drive. The hydraulic system is controlled by solenoid valves. The modern design of the hydropneumatic suspension is the third-generation Hydractive system, which is installed on Citroёn cars.

A separate group consists of active suspension designs, in which the stiffness of the anti-roll bar changes. When the movement is straight, the anti-roll bar is turned off, due to which the suspension moves increase, bumps are processed better and thereby high smoothness and comfort of movement are achieved. When turning or a sharp change in the direction of movement, the stiffness of the stabilizers increases in proportion to the acting forces, and the body rolls are prevented. Known designs for active suspension stabilization are:

  • BMW Dynamic Drive
  • Kinetic Dynamic Suspension System, KDSS from Toyota.

Hyundai offers one of the most interesting active suspension designs on its vehicles. The Active Geometry Control Suspension (AGCS) system allows you to change the length of the suspension arms, thereby changing the toe of the rear wheels. An electric drive is used to change the length of the lever. With rectilinear movement and maneuvering at low speed, the system sets the minimum convergence. Turning at high speed, actively changing from row to row is accompanied by an increase in the convergence of the rear wheels. The car gets extra stability and better handling. The AGCS system interacts with the stability control system.


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