Skyhook theory

The Skyhook theory is an idea that states that an object can maintain a stable posture if it is traveling suspended by an imaginary straight line (Skyhook). The theory forms the basis of Active suspension.

Theory

Fig. 1

Fig. 2

Fig. 3

A vehicle contacts the ground through the spring and damper in a normal spring damper suspension, as in Fig. 1. To achieve the same sustainability in the Skyhook theory, the vehicle must contact the ground through the spring, and the imaginary line with the damper, as in Fig. 2. Theoretically, in a case where the coefficient of the damper reaches an infinite value, the vehicle will be in a state where it is completely fixed to the imaginary line, thus the vehicle will not shake. There is actually no such thing as an imaginary line, so instead, the actuator will be operated where it will agree with the skyhook theory. The imaginary line (acceleration = 0) is calculated based on the value provided by an acceleration sensor installed on the top of the vehicle (Fig. 3). Since the dynamical elements are only made up of the linear spring and the linear damper, no complicated calculations are necessary.

References

• Cost-Effective Skyhook Control for Semiactive Vehicle Suspension Applications
• FUNDAMENTAL PERFORMANCE OF A HYDRAULICALLY ACTUATED FRICTION DAMPER FOR SEISMIC ISOLATION SYSTEM BASED ON THE SKYHOOK THEORY