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1、Suspension performance testingThe suspension system, while not absolutely essential to the operation of a motor vehicle, makes a big difference in the amount of pleasure experienced while driving. Essentially, it acts as a bridge between the occupants of the vehicle and the road they ride on. The te
2、rm suspension refers to the ability of this bridge to suspend a vehicles frame, body and powertrain above the wheels. Like the Golden Gate Bridge hovering over San Francisco Bay, it separates the two and keeps them apart. To remove this suspension would be like taking a cool dive from the Golden Gat
3、e: you might survive the fall, but the impact would leave you sore for weeks. Think of a skateboard. It has direct contact with the road. You feel every brick, crack, crevice and bump. Its almost a visceral experience. As the wheels growl across the pavement, picking up a bump here, a crack there, t
4、he vibration travels up your legs and settles in your gut. You could almost admit you were having fun, if you didnt feel like you were gonna toss your tacos at any second. This is what your car would feel like without a suspension system.In the interests of road safety, it is logical to include in p
5、eriodic roadworthiness tests an inspection of vehicle suspension performance. The results of tests with a prototype machine are presented and a specification proposed for a valid suspension test.Demonstrations organized by the European Shock Absorbers Manufacturers Association ( EuSAMA) in many coun
6、tries have drawn attention to the importance of correctly functioning shock absorbers. In the United Kingdom it is anticipate that the Department of the Environment will include a specific shock absorber check in the MOT Test with effect from January 1977.Of the machines currently available for test
7、ing shock absorbers without removing them from the vehicle, there is no real consensus of opinion concerning their validity to evaluate suspension safety objectively. But it is felt that possible more stringent legislation on European periodic vehicle tests in the future will demand a form of object
8、ive testing on equipment that is incapable of erroneous interpretation.Since its formation in 1971 EuSAMA has realized the imnportance of the problem, and initially charged its technical sub-committee with the task of examining and analyzing the various test machines then available. Two basic types
9、of machine were offered at that time for diagnosing faulty shock absorbers. These were:Machines which lift up the wheels on an axle by about 100 mm and then let them drop. The subsequent displacements of the body on each side are recorded and the results compared with preset values for the particula
10、r vehicle and the suspension position, front or rear. Such a machine simulates a step input and records the subsequent body movements (see Fig 1).Machines which measure wheel movements induced by the exitation of the suspension through a frequency scan from above resonance frequency to zero, applied
11、 by means of a spring-supported platform under the tyre. Results are recorded in the form of wheel displacement against time. While passing through the wheel bounce resonant frequency the maximum amplitude is obtained and this is compared with preset values for the particular vehicle and the suspens
12、ion position front or rear (see Fig 2).A third machine, introduced later, measures phase shift induced by the excitation of the suspension at a constant frequency and stroke, applied by means of a vibrating platform under the tyre. The phase shift between the moment of excitation and the force-react
13、ion is recorded and the result is compared with preset values for the particular vehicle and suspension position (see Fig 3).These systems have three fundamental drawbacks:A: The actual damping is compared with the original damping the limit being a certain degradation in comparison with the origina
14、l performance. The original performance, however, can already be marginal.B: The problems of limit setting, namely by whom should the limits be set and what are the criteria they should about? At present there is hardly any relation between set limits and acceptable performance in practice.C: The pr
15、actical problem of various limits for different vehicle types and their suspensions. This requires comprehensive reference manuals that need continuously updating.Despite these fundamental drawbacks, examples of the ? widely used test machines were put through their paces by the Automotive Engineers
16、 Laboratory of the University of Ghent, as well as by several EuSAMA members. As expected, the first conclusion is that no test method which does not include dismantling the shock absorbers from the vehicle is able to furnish information concerning the shock absorber alone, and it is in fact the whole of the vehicle suspension system that is tested. This can be considered as a positive aspect of testing, since the whole of the suspension should be
