The invention concerns a method of controlling the resilience of variable vibration suppressors in a semi-active chassis with variable valves. The structure of a semi-active chassis is explicable in terms of an oscillator comprising two masses--a non-resiliently supported "wheel mass" consisting of the wheels and their bearings and, resting thereon, a "body mass" consisting of the vehicle's participating superstructure. The two masses are separated by a system of springs and dashpots. A chassis of this type attains two contradictory objectives. The wheels of a vehicle in motion over a to-some-extent necessarily uneven roadway will transmit vibrations to the body. The vibrating wheels and body will be detrimental to the passengers' comfort and safety. The purpose of the chassis is accordingly to guide the wheels as straight as possible over the roadway, to maintain as much resilience as possible between the wheels and the ground, and to compensate for motions of the axle deriving from irregularities in the roadway in order to increase the passengers' comfort. Varying the resilience of the suspension in accordance with excitation on the part of the roadway will result in extensive absorption of the vibrations and ensure a safe ride.
A known principle for varying the resilience of a suspension system is the skyhook algorithm. When the difference between the speed of the body and that of the axis opposes the body's vertical speed, the resilience is kept soft. When that difference is the same as the body speed, or when the resilience opposes the body speed, the resilience is hardened.
A principle for varying the resilience of a vibration suppressor with variable valves in accordance with irregularities in the roadway is known form German OS 4 015 972. The resilience is varied in accordance with this principle, Huang's algorithm, by closing a bypass when the product of the body acceleration and the difference between the speed of the body mass and that of the wheel mass is greater than zero and opening it when the produce is less than zero.
These procedures very satisfactorily ensure compliance with the demands for safety and comfort in the event of once-only roadway excitation by extensively absorbing any vibrations that occur. To maintain consistency, however, the resilience must be constantly varied between soft and hard, leading to annoying knocks in conjunction with periodic roadway excitation and having a negative effect on the passengers' perception of the drive.