Typically the velocity dependent hydraulic damper characterization is done using a sinusoidal input to the damper. Damping force vs. displacement and velocity plots are used to represent the damping behaviour. It was observed that the dampers exhibit equal damping characteristics using this conventional method, shows a significant difference in ride comfort levels of the vehicle. This behaviour primarily arises due to the variation in response of the damper with the excitation frequency. On actual riding conditions, apart from harmonic loads, the suspension experiences impact loads that affect the damping generation characteristics. So the damper also needs to be characterized with variation of frequency ranging from 0.5 Hz to 25 Hz. Due to the limitations of damper stroke and input frequency, complete characterization of damper is not possible with sinusoidal input test rig.
In this paper, a new test rig is conceptualized and developed to characterize the damper behaviour closer to on-road riding conditions. The principle of this rig is to apply an impact force on the damper (shock absorber) with a free falling mass. During the experiment, a Linear Variable Differential Transducer is used to measure displacement of the shock absorber. Two damper designs that show equal damping in conventional method are tested using the developed test rig. The results show a significant difference in damping behaviour and response especially in extension/rebound stroke. With these two different damper designs, a vehicle level ride comfort test has been conducted and observed that the displacement behaviour of these dampers are matching with results of new test rig. Hence, the test method that is developed is useful to characterize the dampers and also increase the scope to improve ride comfort. The damper can be characterized more precisely, with the information obtained from this test method along with the conventional test method.