Measuring and testing – Testing of shock absorbing device – In situ vehicle suspension
Patent
1996-12-13
2000-12-19
Dombroske, George
Measuring and testing
Testing of shock absorbing device
In situ vehicle suspension
73 1206, 731181, 73 1109, G01M 1704
Patent
active
06161419&
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for determining the characteristics of the shock-absorbers installed in a motor vehicle. According to this process, the vehicle is run up a ramp and onto a support surface which is then removed suddenly so that the vehicle drops onto a base. The vertical distance between the base and the support surface corresponds to the residual wheel-rebound-clearance imposed by the design of the vehicle concerned. When the vehicle hits the base, the curve of the wheel-contact force exerted on the base is determined.
This process is described in EP Patent 2 269 81 [sic]. Using this process to test the condition of the running gear of a motor vehicle, it is already possible, by suitable curve-analysis of the results representing the wheel-force on the base, to produce, among other things, findings regarding the damping characteristics of the suspension joints of a motor vehicle, the quality of the shock-absorbers, and the hardness of the vehicle's springs. However, an evaluation of a vehicle's vibration-behaviour based on the graphs obtained when measuring the wheel-contact forces on the base provides no absolute characteristic-data values for the vehicle at the time of testing, because the effects of tyre-pressure, vehicle-loading, and the type of tyre fitted cannot be taken into account.
The aim of the present invention is to develop a process whereby the characteristics of a shock-absorber fitted to a motor vehicle can be determined without having to detach the shock-absorber, irrespective of such variables as the tyre-pressure, type of tyre, vehicle-load, etc. In other words, the aim of the invention is to provide a process whereby all those forces which, in the known process, codetermine the vibration-behaviour of the vehicle once it hits the base, can be eliminated; and whereby the actual values for the damping constants and spring-stiffness--i.e. the current condition of the shock-absorber--can be computed from the measured values.
This aim is achieved as follows, according to the invention: for the wheel contact force, are introduced into the known differential equations for damped vibrations, and computed--said characteristic data being: the body and wheel masses, spring-stiffness, and damping constants.
The advantage of the process according to the invention, compared with the prior-art processes, is that the result obtained with the process according to the invention is independent of the tyre-pressure, type of tyre, or loading of the tested vehicle, and gives the actual values valid at the time of testing.
By determining the overall vibration-behaviour of the body and of one wheel in each case, it is possible to obtain not only a damping-value, but also the damping-characteristic of the shock-absorber, divided into tension and compression regions. A further advantage of the new process is that the total testing-time is very short, and both wheels of a wheel-axis can be tested simultaneously after the shock-producing impact. As well as the characteristic curve for the shock-absorber, the stiffness of the vehicle's springs and the effective masses can also be determined.
The possibility of obtaining all the data needed to evaluate the condition of the vehicle by means of a single, brief measuring operation, makes the process suitable for: industry (for end-of-production-line checking and running-gear analysis); and be compared with the required values.
Preferably the vibration-behaviour of the vehicle-body and of each wheel of the wheel-axis being tested can be determined by measuring the displacement of the translational vibrations of the body and wheel, for each side of the wheel-axis being tested; such displacement-measurement is performed either by individually determining the vibration-amplitudes of the body relative to the base and the vibration-amplitudes of the wheel relative to the base, or by determining the amplitude-difference between these two vibrations. It may be preferred, however, to determine the curve of the vibration by measuring the velocity of the motion
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Dombroske George
Snap-on Technologies, Inc.
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