Chassis integrated load cells : Installation in spring seat on Scania tandem boogies

The thesis presented in this report has been made on behalf of Scania and their basic frame design department with the subject to solve an implementation of a weight sensing system in the chassis. The system is supposed to be implemented in the seat springs, and the reason for this is that all the force will have to go through the weight sensing transducers. With all the force going through the transducers the weight sensing system will not be sensitive for the differences in tolerances from manufacturing. The transducers could be pre-calibrated to avoid a calibration of the whole vehicle after it’s completed from the manufacturing line. Weight sensing systems is today a reality in trucks with air springs. Complete systems is also sold in the big aftermarket for trucks. None of Scanias competitors have a solution for this as of today. The thesis was from start limited to only process the BT-301S bogie. A system will likely be easy to adapt to the other bogies with small modifications. Through the thesis possible problems are illuminated to understand the function and make a properly working weight sensing system. In the present bogie system the main problem for a proper function is the frictional forces that appears in the surface between the spring and the spring seat. In the report a proposition with a rubber part between the spring and the spring seat is introduced, with the idea to get around the known problems with the frictional forces. The rubber itself does produce a reaction force when deformed, but the forces could through simulation be known, and hence compensated for. A rubber part under the spring would result in a contact surface much higher than today. A new spring, or a new version of the spring, will be needed for this solution to work. For the work to come, Scania need to decide what precision the weight sensing system need. But smaller decisions like the size and stiffness for the rubber part will also be needed. This thesis has only dealt with the bogie, but in a close future, the front axles need to be done. Much can likely be carried over from this thesis for that. A weight sensing might be possible to implement, but with what precision at uneven ground? Most likely will the variation in load on the transducers be too much. An approximation for the precision with a total span of 7% is realistic