Isolators perform a crucial role in the operation and performance of damped structures such as, for example, motor vehicles. By limiting the transmission of mechanical energy between vehicle components, isolators affect vehicle handling, increase component life by reducing vibrations, and improve the ride performance experienced by vehicle occupants.
Isolators are used in various locations throughout an automotive vehicle, including suspension shock absorbers, engine mounts, body mounts, and exhaust hangers. Tires may also be considered isolators in that they affect how road surface roughness is transmitted to the vehicle body. Hydraulic isolators use a fluid to dissipate mechanical energy. Elastomeric isolators use a resilient solid to dissipate mechanical energy. The stiffness and damping coefficients for an elastomeric isolator tends to be independent of frequency while coefficients for hydraulic isolators tend to be frequency dependent.
Noise, vibration and harshness (NVH) issues are critical to the acceptance of a vehicle by consumers. Isolators are a key component in NVH design. In NVH design, the type, sizing and placement of isolators are important. Vibration analysis of total vehicles requires a large, complex finite element model and long computation time. Therefore, NVH engineers have traditionally depended heavily on test data and results of simple model analysis. Prior design methodologies generally required multiple design-and-test cycles before a satisfactory result was achieved.
One difficulty with current techniques for vehicle isolator design using modeling is the inability to consider all isolators in the system simultaneously. Also, in order to achieve relevant results, all six degrees of freedom must be considered for each isolator.
Another difficulty with current techniques for vehicle isolator design using modeling is the complexity of the vehicle model. One solution in previous techniques is to use quarter or half vehicle models. Partial models are not effective for simulating complex road inputs and do not fully model all isolators. Another solution is to treat each vehicle component as a rigid element. Such models produce approximate solutions that may lack necessary accuracy.
Still another difficulty with current techniques for vehicle isolator design using modeling is the representation of forcing functions. System stimuli may come from external sources, in particular excitation of tires by road surface roughness. For best simulation results, each tire should be capable of providing an independent input. System stimuli may also come from internal sources such as the engine, transmission, and exhaust systems.
A further difficulty with current techniques for vehicle isolator design using modeling is an inability to handle multiple isolator types, such as elastomeric isolators and hydraulic isolators, in the same design application.
A system and method is required for analyzing and determining the design variable values for a plurality of isolators. The ability to utilize a full system model, capable of incorporating rigid and flexible components, is needed. Excitation from multiple external and internal sources should be accommodated. Different types of isolators within the same model should be supported. Design iterations should be processed without human intervention until an optimal design is produced.