The present invention relates to distance measuring equipment for a car, and in particular to distance measuring equipment for a car with optical measuring means to measure a distance between an observing car and a forward or backward obstacle or object.
The following systems have required distance measuring equipment (DME) for measuring a distance between an observing car in which a measuring operator rides and a forward or backward obstacle on the basis of the time elapsed from the time of the emission of laser light to the time of the reception of the laser light reflected by the obstacle, by optical measuring means such as a laser radar:
(1) Systems for warning of a collision such as a rear-end collision by the detection of a relative speed and distance between an observing car and a forward obstacle (car);
(2) Systems for automatically operating a brake in order to prevent a collision such as a rear-end collision by the detection of a relative speed and distance between an observing car and a forward obstacle (car);
(3) Systems for automatically operating a steering gear or a brake in order to prevent a collision such as a rear-end collision by the detection of a relative speed, distance, position between an observing car and a forward obstacle (car), and a road condition.
The optical measuring means used for such distance measuring equipment comprises one provided outside a car and the other provided within a car. In the former, raindrops in case of rain or dust adheres to the surface of a lens, so that the interruption or diffusion of the input/output light occurs, causing the detecting range thereof to be narrowed or distorted. This also brings about mismeasurements leading to the deterioration in performance. Also, since the optical measuring means per se is exposed to raindrops or dust, its mechanical or electrical performance is easily deteriorated, resulting in a short life.
Thus, the latter optical measuring means provided within a car is preferrable to the former one provided outside a car.
However, in this case, raindrops or dust which adheres to a protective glass (front or rear glass) for a car must to be removed from the glass.
Such prior art equipment is disclosed in Japanese Utility Model Application Laid-open Nos. 60-76280 and 60-109064. The former prior art is provided with a washing nozzle and a wiper in a window for the emission of laser light and a window for the reception of the light reflected from the obstacle. The latter prior art actuates a washing unit subsequent to a predetermined operation of light emission of a laser unit.
However, since such prior art equipment starts to operate the wiper manually, it is disadvantageous in that it is troublesome to an operator and it is not adequate for such a system that automatically operates the distance measuring equipment.
It is also diadvantageous that the wiper disturbs the laser light of the optical measuring means so that without any modification, some errors will arise in the measured data.