Abstract
Recently, the increasingly strict safety and emission regulations in the automotive industry drove the interest towards automatic length compensating devices, e.g., hydraulic lash adjusters (lower emission) and slack adjuster in brake systems (faster brake response). These devices have two crucial requirements: (a) be stiff during high load, while (b) be flexible in the released state to compensate for environmental effects such as wear and temperature difference. This study aims to use the advantageous properties of shear thickening fluids to develop a less complicated, cost-efficient design. The proposed design is modeled by a system of ordinary differential equations in which the effect of the non-Newtonian fluid flow is taken into account with a novel, simplified, semi-analytical flow rate-pressure drop relationship suitable for handling arbitrary rheology. The adjuster’s dimensions are determined with a multi-objective genetic algorithm based on the coupled solid-fluid mechanical model for six different shear thickening rheologies. The accuracy of the simplified flow model is verified by means of steady-state and transient CFD simulations for the optimal candidates. We have found that the dominating parameters of such devices are (a) the shear thickening region of the fluid rheology and (b) the gap sizes, while the piston diameters and the zero viscosity or the critical shear rate of the fluid have less effect. Based on the results, we give guidelines to design similar-length compensating devices.
Highlights
1.1 MotivationHeavy-duty vehicles include a number of wear parts whose wear must be compensated for the vehicle’s whole lifetime
The governing equations comprise a six-degree-of-freedom system of ordinary differential equations (ODEs)
The effect of the shear thickening rheology is derived from the simplified Navier-Stokes equation, and the obtained p(Q) functions are substituted into the ODEs for 6 different rheologies
Summary
Heavy-duty vehicles include a number of wear parts (e.g., brake pads, clutch disks) whose wear must be compensated for the vehicle’s whole lifetime. This work seeks for a solution to compensate the wear in pneumatic clutch actuators to increase the automatic transmission system’s reliability and performance. The proper adjustment of transmission systems are currently essential for driver comfort, environmental protection, and autonomous driving The appropriate transmission system can adapt the gear shifting to the actual vehicle load and road conditions, which cause significant fuel savings. To achieve the optimal settings, the gear shifting process of the vehicles must be fully automated. The traditional manual clutch systems are nowadays automated using an electro-pneumatic actuator to substitute manual force
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