| 摘要 |
PURPOSE:To obtain a raindrop sensor which has high detection sensitivity of a raindrop and never malfunction by setting the natural oscillation frequency of a diaphragm within a 10-25KHz range oscillating by the collosion of the raindrop. CONSTITUTION:A piezoelectric element 6 having electrodes 5 and 5' on both surfaces is stuck to the reverse surface 3b of the diaphragm 3 with an adhesive, etc., and the electrodes 5 and 5' of the piezoelectric element 6 are connected to an amplifier 8 through lead lines 7 and 7'. The thickness and the size of the diaphragm 3 are set to hold its natural oscillation frequency within the 10- 25KHz range. A lower limit, i.e. 10KHz natural oscillation frequency is for preventing malfunction due to unnecessary oscillation propagating through a vehicle body and the upper-limit natural oscillation frequency of the diaphragm 3 for securing the proper thickness and the area of the diaphragm is set to 25KHz. The detection signal of the raindrop sensor 2 after being amplified by an amplifier 8 is supplied to a control circuit 9, which discriminates the rainfall from the level, the frequency, etc., of the detection signal to drive a wiper motor 10 on the basis of the control output of an intermittence time and the operation speed of the wiper. |
