Two-poster rig plays a very important role in accelerated durability evaluation in a motorcycle industry, similar to what a four-poster rig does in a car industry. The rig simulates the exact road conditions in the vertical direction through tire coupling by applying feedback control on displacement. On account of its ability to simulate to the exact customer usage conditions, it reproduces the failures realistically as it happens on the field. However, as complete vehicle is required for testing on the rig, the testing happens mostly in the advanced stages of product development. Any failures beyond the concept stage have a huge impact on the development time and cost and the same should be avoided. Therefore, in this paper, a virtual testing methodology is proposed, based on which potential failures on the vehicles can be captured at the concept design stage itself.
An ADAMS model of a motorcycle was created. In the model, frame, footrest, swing arm etc, were modeled as flexible bodies. The rubber elements in the vehicle like rear suspension eyelet rubber, swing arm rubber etc. were measured and modeled as well. Road load data acquisition was done on a rough road and the same was simulated on a two-poster rig. To validate the model, the motorcycle was tested in the lab using the simulated road load on two-poster rig. Satisfactory virtual to physical validation results were achieved. After model validation, the motorcycle model was integrated with a tire coupled virtual test rig to form a virtual testing system.
Different iterations were conducted using the virtual testing system. Front and rear wheel hub acceleration and shock displacement signals were used as control signals for tire coupled virtual testing. A Comparison was done on physical and virtual acceleration, potentiometer & strain signals. The results indicate that there is a fairly good match for acceleration signals between the tire coupled virtual test system and the two-poster rig.
To better understand the limitations of a two-poster system, the same motorcycle model was integrated with a hub-coupled system to form a hub-coupled virtual test system. Front and rear wheel hub vertical accelerations, fork bending moment, swing arm pivot joint longitudinal force, front and rear shock displacements were used for hub coupled virtual testing. On comparison with the road, a definite improvement was seen in the results. In general, it was observed that virtual testing with a hub-coupled system has better acceleration and strain correlation results than a tire-coupled system.
Also, a comparison study was conducted to find out the difference between virtual testing using tire coupled and hub coupled motorcycle virtual testing systems. The results showed that tire- coupled system could only reproduce vertical signals accurately, which is what a two-poster rig does. The hub-coupled system can reproduce vertical and longitudinal signals accurately, a combination of which is what is seen on the road. As a result, damage associated with longitudinal loads for components such as front fork can be reproduced more accurately by using a hub-coupled testing system.