| 摘要 |
PURPOSE:To enable safe driving by expanding an obstacle detection area only for a specific time right after a vehicle has an attitude for backward movement. CONSTITUTION:When the gear of the vehicle is placed in reverse mode, a timer circuit 27 supplies electric power to a warning device through a power switch 28 and also outputs a signal for driving a gain varying circuit 29 for a specific time at the same time. Here, the circuit 29 increases the gain of an amplifying circuit 20 while the circuit 27 is in operation to expand the detection area of an obstacle by a transmitter receiver 18. A reflected wave within the timer time (t) in a reflected wave from the obstacle becomes sufficiently large and the output waveform of the circuit 20 exceeds the threshold value of a level detecting circuit 22 to drive a switching circuit 25 through an integration circuit 23 and an FF circuit 24, thereby operating a display device 26. An obstacle entering a normal detection area is detected after the time (t). Thus, the rear warning function of backward movement is improved and safe driving is performed.
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