JPS6461900A - Ultrasonic wave-system vehicle sensor - Google Patents

Abstract

PURPOSE:To eliminate a misoperation by a human being and to eliminate the effect of high-order reflection by sensing a vehicle in the combination of a vehicle reflection wave and a road reflection wave. CONSTITUTION:When the vehicle is out of a vehicle sensible area R, the gain of a second gain variable amplifying circuit 18 is at a second level during a vehicle gate period, and at a first level (the first level>the second level) during the period other than the vehicle gate. Thus, the road reflection wave S2 of 16L, which is an eight-times of a threshold 2L, is inputted to a threshold circuit 20. Next, when the vehicle enters up to the 1/2 of an area T, the level during the period of the vehicle gate of the circuit 18 is at the second level, and the gain level during the period of the road gate is at the first level. Consequently, the gain level of the road reflection wave becomes 8L, and that of the vehicle reflection wave becomes 4L. Next when the vehicle enters upto the 7/8 of the area R, the gain level of the road reflection wave becomes 2L, and that of the vehicle reflection wave becomes 7L, and the condition immediately before the vehicle sensing is obtained, and next, both the gain levels become 1L and 14L, and the value immediately after the vehicle sensing is obtained.