Assessing the reliability of testing methods used for fluid telescopic shock absorbers in cars

Shock absorbers in modern cars have asymmetric damping characteristics corrected by overflow valves. Their indicator diagrams are far from being elliptical. Defective shock absorbers may lead to excessive amplitudes in vibration accelerations, excessive car body rolls, both lateral and longitudinal, excessive braking distance and destruction of the car components or road surface. The paper discusses methods of testing shock absorbers mounted or removed from the car. Advantages and disadvantages of the methods are used as bas is for the assessment. It is pointed out that the methods should not assume linear characteristics of springs and damping elements. Testing methods can be divided as follows: - those referring to shock absorbers removed from the car, - those referring to shock absorbers mounted in the car. Methods used for testing shock absorbers removed from the car are those performed on indicator test rigs provided with mechanical-electric or electrohydraulic extortion system. Such test rigs have measuring devices to enable recording of indicator diagrams relative to the absorber damping force in function of piston stroke with deflection and reflection. Among a variety of testing methods, those requiring no removal are by far preferred by Vehicle Control Stations or diagnostic lines. The methods can be divided asfollows: -free vibration type, -forced vibration type.