The invention relates to an optical sensor having the characteristics recited in the preamble to claim 1.
Windshield wiper systems for windshields of motor vehicles are known in which control of the windshield wipers is effected not only via a manually actuatable lever on the steering column but in addition via an optical rain sensor. The optical rain sensor includes a light source, whose electromagnetic radiation is reflected differently by the windshield depending on the film of moisture on the windshield. The proportion reflected, i.e., the reflected portion, is detected by means of a photo element, so that an output signal of the rain sensor can be furnished that corresponds to the film of moisture. These output signals can be evaluated and used to control the windshield wipers in such a way that both turning on the windshield wiper system and a wiper speed can be varied as a function of a detected wetting of a windshield.
Systems for automatically turning on a light system in the motor vehicle are also known. By measuring an output signal of a photo element, a conclusion is drawn about ambient brightness of the motor vehicle, and as a function thereof, the vehicle lights are turned on without anyaction on the part of a driver.
The optical sensor according to the invention, having the characteristics recited in claim 1, has the advantage in particular of furnishing a combined sensor for controlling the vehicle equipment that is important to a driver and improves his vision. Along with a rain sensor for controlling a windshield wiper system, a sensor for detecting outdoor brightness is integrated with the optical sensor, so that as a function of the measured ambient brightness, a light system can be turned on and off, and as a function of wetting of the windshield by precipitation, the windshield wiper system can automatically be triggered.
In a preferred feature of the invention, from the detected view-affecting parameters, namely essentially precipitation in the form of rain, fog or snow, as well as the ambient brightness, a combined control of the windshield wiper system and the light system can be achieved. For instance in heavy rain, on the one hand, it may be appropriate to turn on not only the windshield wipers but also the vehicle headlights. When it is dark, on the other hand, because of the greatly increased risk of glare from headlights of oncoming vehicles, however, it is even more important than during the day to keep the windshield free of wetness at all times. It is therefore appropriate when it is dark to provide for increased sensitivity of the windshield wiper controller to even slight degrees of wetting of the windshield. A switchover of the rain sensor sensitivity for triggering the windshield wiper system can be preferably varied by means of a signal formed by an ambient light sensor.
A combination of a rain sensor and an outdoor light sensor in one common optical sensor furthermore has the advantage of considerable simplification of its installation and assembly, which moreover means a cost reduction. By mounting all the electronic and optoelectronic components on a common printed circuit board, preferably using the SMD (surface mounted device) technique, very compact sensors can be made that can also be installed without difficulty in the vehicle. Such an optical sensor can thus be equally compact as known rain sensors, and like them, it can be mounted for instance behind an inside rear view mirror, on the inside of the windshield.
In a preferred feature of the invention, along with a brightness sensor for ambient light, which furnishes a signal that is largely affected by daylight and correspondingly has a relatively wide and preferably upward-oriented opening cone for incident light, at least one additional remote sensor is provided, which has a narrow opening cone preferably pointing forward in the direction of travel. As a result, this remote sensor is capable, with relatively high reliability, of detecting tunnel entrances or underpasses and thus of furnishing an early signal for turning on the vehicle lighting.
The focusing of the incident light can be done advantageously by means of an optical waveguide that at the same time functions as a base plate for the sensor housing. Such an optical waveguide may for instance be made from a plastic such as PMMA (polymethyl methacrylate) by injection molding, and then optical structures such as focusing lenses can be incorporated in the molding process in a simple way.
The connection with the windshield can be realized either by means of a frame on the window and a sensor housing clipped into the frame, or in a very simple way by means of a double-sided self-adhesive transparent film.
In a further preferred feature, additional control functions can be implemented, such as turning on fog headlights. By means of a suitably sensitive rain sensor, this sensor can detect the droplet size and can thus distinguish whether the wetting of the window is due to rain, fog, or snow. In heavy fog or in snow, along with the windshield wipers the fog headlights and/or the fog taillights can be turned on as well, thus further increasing driving safety. In fog, for instance, precipitation comprising superfine droplets on the windshield can be detected by the rain sensor. By suitable design of software for evaluating the rain sensor signals, the turning on of individual components of the light system (fog lights, fog taillights) can then be tripped.
In a preferred feature of the invention, it is provided that both the receiver of the rain sensor and at least one of the receivers of the ambient brightness sensor and/or of the remote sensor are formed by a common photo element. As a result, the expense for optoelectronic components to be used for the combined rain sensor and outdoor light sensor of the motor vehicle can be reduced. The receiver can thus take on a dual function for furnishing trigger signals for both the windshield wiper system and for the light system of the motor vehicle. In particular, it is preferred if an optical waveguide of the optical sensor has structures that take on corresponding focusing of the electromagnetic waves to be sensed onto the common photo element. Thus, by simple means, both the ambient brightness and the wetting of the windshield can be sensed.
In a further preferred feature of the invention, it is provided that the transmitting diode of the rain sensor can be triggered in clocked fashion. As a result, the common receiver can associate the received signals with either the rain sensor function or the automatic light control function of the optical sensor, in accordance with a duty cycle of the clocked triggering.
Further preferred features of the invention will become apparent from the other characteristics recited in the dependent claims.