Bi-Directional Washer Pump Robust Design Development 2002-01-0561
Washer pumps feed the washer fluid to enable the vehicle wiper system to effectively clean the windshield. Today's bi-directional washer pumps are increasingly complex. These pumps must feed both front and rear wiper systems and be able to deliver a variety of washer fluid types. Increasingly tight system power constraints make pump efficiency critical. The consequence of lower efficiency would be a larger motor, which would reduce profit potential or makes the product altogether non-competitive.
In developing an optimal washer pump, performance cannot be easily estimated through simulation. Initial research and brainstorming identified at least eight critical parameters. At three levels per variable, evaluating alternate fluids, and incorporating replicates, the number of samples can grow to over twenty thousand. To add to data complexity, washer pump optimal performance is not based on a single point estimate. Performance is based on maximizing the entire pressure - flow rate curve. Adding to the challenges is the very strong influence from motor-to-motor variation.
A robust design approach was selected as an efficient means to evaluate multiple design parameters while also taking into consideration motor-to-motor variation. Our approach was to optimize energy conversion efficiency, focusing on fluid pressure - flow rate performance curves. Using a dynamic characteristic signal-to-noise ratio, we were able to determine the optimal design factors for maximizing performance. Instead of thousands of units otherwise required, we were able to effectively determine an optimal design using only thirty-six parts for both low and high viscosity conditions. This resulted in a high performing, cost effective washer pump.