Development of automobile wheel speed sensor using the injection molding by lifting the insert parts

Abstract

If a long period has passed after plastic wheel speed sensors were assembled into an automobile, the sensing error may occur when the outer holes of speed sensor crack and water enter through the crack. This not only may put the automobile into the danger of malfunctioning, but the driver may at the psychologically very anxious situation. To resolve this problem, an injection molding method that can remove the outer holes of the plastic wheel speed sensor was developed, and the developed injection molding process was numerically simulated. In the newly developed forming methodology, the pins for securing the wheel speed sensor within the cavity are forced to be removed while the forming process is completed so that the outer pin holes disappear. But, in the conventional methodology, the pins for securing the wheel speed sensor are kept without being removed until the forming process is completed so that the outer pin holes remain. Besides, a real injection mold was manufactured and the comparative study of injection molding process between real conduction and numerical simulation was performed. The filling length in actual molding was about 1.5 mm longer than the length of the simulation. This was a relatively good match since it corresponds to 5% of the major reference length. And, for the real molded wheel speed sensors, the performance tests such as the dimension precision, insulation resistance, X-ray scan and thermal shock test were made. In particular, any damage did not occur at the interior and exterior of the sensor during the 600 cycle thermal shock test. Furthermore, all the performance test results satisfied the regulated standards. Thus, the validity of the developed new injection molding method was justified.