Abstract
Shock absorbers are a fundamental element of the suspension system of a motor vehicle. Their degradation could cause a significant variation of the dynamic behaviour of the vehicle. A worn out damper could reduce the tire-road contact which can lead to an increase in stopping distance. Similarly, lateral stability may be compromised due to uncontrolled rolling movements. Finally, the effects that may occur in the comfort of the occupants should be highlighted. Excessive vibration inside the car could lead to premature fatigue and lack of attention while driving.
It is desirable to have a method that allows us to know the state of wear of this component in order to decide when it must be replaced before the defect may cause an accident.
In this paper, we examine the influence of oil degradation in the performance of a vehicle hydraulic shock absorber, so that an objective criterion can be established to determine the point at which it must be replaced.
Through infrared spectroscopy, the infrared absorption spectrum (IR) of the shock oil in different stages of wear has been analysed in order to establish a correlation between the IR absorption index and the loss of the shock absorber performances.
This study is based on the experimental results obtained in a damper test rig where the damper behaviour charts have been measured along with the working cycles of the component.
From previous work, the authors have been able to establish an objective criterion based on the minimum allowable damping coefficient that allows us to know if the damper is within the safety limits from a vehicle stability point of view. This work has allowed us to relate this value to the infrared absorption (IR) index measured in oil dampers under wearing conditions in order to establish a reference of IR value rate that determines the time at which the shock absorber must be replaced.
Keywords: Infrared Spectroscopy, Shock Absorber, Damping coefficient, Suspension System.