Abstract
The increasing interest in cascading NVH targets down to subsystem specification requires suitable benchmarking and production monitoring processes to be available. Consequently there is a requirement for processes that can identify the performance requirements of a single suspension unit, on an absolute scale, under true operating conditions. This paper describes one such methodology, developed at MIRA, to calculate the force transmissibility to the body through a single suspension unit. This process, based on a novel combination of laboratory and road based data, can be used to calculate the dynamic forces applied to the body under normal operational conditions by a single unit.
The method calculates the force transmissibility of a suspension system from transfer functions and point inertances measured in the laboratory. Combining this transmissibility with the hub forces, experienced under normal operating conditions, provides an estimate of the forces applied to the body. The forces applied to the wheel hub can be either measured directly or derived from hub acceleration data.
A validation exercise was performed to identify the limitations of the method, showing the force calculation to be accurate above 50 Hz. This paper also compares traditional Transfer Path Analysis techniques with the new methodology. To illustrate the application of the methodology, the forces at the body connection points were obtained for two C/D class vehicles with very different refinement characteristics.
This method can be applied for suspension target setting; targets can be derived for suspension units by defining the appropriate level of input forces from the suspension unit into the body and the force transmissibility will characterise a particular suspension design.