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In a test bench for automotive shock absorbers the angular velocity of the "scotch yoke" mechanism must be constant, but the load (resulting from shock forces) varies in function of the speed, resulting in fluctuations in the speed along the course of the test, in function of the frequency variator response time controlling the electric motor. Employing a closed loop control system for the automotive shock absorber tests will result in tests with better quality at higher speeds and loads, thus enabling a better representation of the shock absorber condition. The paper presents the state of the art and research in development that is linked to closed loop control mechanisms. It is developed a control system which allows maintaining a constant test speed, independent of the load reaction to a range of shock absorber tested, as a function of resultant load. The mathematical modeling of the problem is presented, quantifying the magnitudes involved.

Automotive shock absorbers are key elements in the dynamic behavior of vehicles. Their degradation is slow, gradual and progressive, so that the driver of the vehicle eventually gets used to the decrease of the damper's performance without noticing it. This article describes how a test bench was developed based on existing market models, however having as its main goal the low cost of production. The Crankshaft and Scotch Yoke mechanisms were studied in an analog way and simulated in CAD software. After this analysis the Scotch Yoke system was chosen because its motion describes a perfect sine function. To drive the system it was used a 5HP electric motor, and a frequency inverter to control the motor's speed with capability of 7.33A, allowing the device to have the ability to test not only production line vehicles but also competition dumpers.