Simulation of CamDrum for Shock Absorbers

Abstract: Simulation can play an important role when aiming to streamline extensive and time-consuming tests. It has the potential to save time, money and energy. One of the testing methods used to test shock absorbers (SA), is accelerated life testing using a rolling road, CamDrum. It is therefore of great interest to examine the possibilities to streamline this testing method. This master thesis is conducted in co-operation with Öhlins Racing AB and the Machine Design department at KTH. The thesis project aims to look into the following: How can the use of simulation software aid in streamlining the test sequence used for shock absorbers in CamDrum? What limitations is there when simulating the CamDrum method using the selected simulation software? The goal was to develop an adequate model according to specified requirements, to facilitate early testing of new ideas and parameter changes. The delimitations includes, that the project only focuses the test-rig for MTB shock absorbers, the parts of the test-rig are assumed to be rigid and the simulation of the shock absorber is out of scope, since the aim of this thesis is to simulate the test-rig. To succeed with the project, a background research was conducted to gain knowledge about shock absorbers, test method and equipment, dynamics and useful software. The simulation model was verified against data obtained from tests. The tests were performed using the CamDrum with two different MTB shock absorbers and a stiff rod. The aim was to log and verify the change in position for the test-rig, shock absorbers and wheel. In addition the forces acting on the shock absorbers was investigated using strain gauges attached to the test-rig. The mean deviation in % for configuration 70-30-30 [mm] bump: SA MTBM1899, A4: 11.6% - 23.2%. SA MTB1691, A4: 15.8% - 28.1%. Stiff rod, A3: 0.9% - 4.9%, A5: 2.0% - 5.1%. SA Force, 16.1% - 24.0%. The deviation between the simulation and the test environment increases with the velocity. The use of stiff rod verifies the model against the CamDrum regarding the displacement. The resulting force from the use of strain gauges verifies the simulation models force regarding the shape. The Amesim model has the potential to be of great aid when designing tests.