Patent US 5,263,006

A device for detecting the presence of a vehicle by means of an ultrasonic device has an ultrasonic sensor (22) associated with an electronic transmitting and receiving circuit (28, 30). The sensor (22) emits periodic pulses whose reflections are received and evaluated by the circuit (28, 30). A positive presence signal is emitted if reflections are present. To ensure that a positive presence signal is always obtained irrespective of the shape of the vehicle and of the part of vehicle which has just been identified, the ultrasonic device has a central sensor (22) and two external sensors (26, 28) situated equidistant from the latter and at the maximum possible distance apart. The external sensors (25, 26) are connected identically and operated on a par with each other. Either the central sensor (22) is connected as the receiving sensor and the external sensors (24, 26) as the emitting or vice versa.