Device and method for operating a rain detector

• US 6,331,819 B1
• Filed: 02/02/2000
• Issued: 12/18/2001
• Est. Priority Date: 09/13/1997
• Status: Expired due to Fees

• Current Assignee: Robert Bosch GmbH
• Original Assignee: Robert Bosch GmbH
• Inventors: Hog, Norbert
• Primary Examiner(s): Lee, Benjamin C.
• Assistant Examiner(s): TANG, SON M
• Application Number:
  US09/463,934
• Time in Patent Office: 685 Days
• Field of Search: 340/604, 340/619, 340/602, 340/601, 340/603
• US Class Current: 340/604
• CPC Class Codes: B60S 1/0818 including control systems responsive to external conditions, e.g. by detection of moisture, dirt or the like
• CPC Class Codes: B60S 1/0833 Optical rain sensor

Abstract

An apparatus and a method for operating an optoelectronic rain sensor for detecting the wetting of a window (14) with moisture for wetting-dependent triggering of a system, in particular a windshield wiper system for motor vehicles, is proposed in which the component of the ambient beam (18) of the sensor signal (22) in a first interval is virtually eliminated and therefore need no longer be taken into account in the ensuing detection of the sensor signal (22) in a second interval relevant to triggering of the windshield wiper system. The apparatus includes first means (26, 40, 42), which in the first interval detect the sensor signal (22) and ascertain an interfering light signal (44) corresponding to the ambient beam (18), the latter signal being delivered to a regulator (50), which as a function of the interfering light signal (44) regulates compensation means (30) disposed in the current circuit of the receiver (16), and second means (26, 60, 62), which in the second interval, directly following the first, detect the sensor signal (22) and ascertain a useful light signal (64) corresponding substantially to the transmitter beam (12).

Claims

1. An apparatus for operating a rain sensor for detecting a wetting of a window with moisture for wetting-dependent triggering of a windshield wiper system for motor vehicles, the apparatus comprising a transmitter which outputs a transmitter beam into a window at a first point;

a receiver which detects a beam outcoupled from the window at a second point and as a function of a radiation intensity detected outputs a sensor signal;

an amplifier device which receives said sensor signal and has a downstream evaluation assembly that triggers the system, with the beam having a transmitter beam component as a function of moisture on the window and/or an ambient beam component;

first means which in a first interval for detecting the ambient beam component with said transmitter switched off detect the sensor signal amplified in said amplifier device and from this signal ascertain an interfering light signal corresponding to the ambient beam;

a regulator to which the later signal is delivered and which drives a compensation means disposed in a current circuit of said receiver to regulate the interfering light signal to a desired value; and

second means which in a second interval directly following the first interval, responsive to the transmitter beam component and the ambient beam with said transmitter switched on, to detect the amplified sensor signal which is influenced by said compensation means and from which the amplified sensor signal ascertains a useful light signal corresponding substantially to a beam of said transmitter.

2. An apparatus as defined in claim 1, wherein said regulator is formed to regulate the interfering light signal to a desired value which has a low level of zero volts.

3. An apparatus as defined in claim 1, wherein said amplifier device has a current-controlled input, said compensation means including a controlled current source.

4. An apparatus as defined in claim 1, wherein said amplifier device has a controlled current sink.

5. An apparatus as defined in claim 1, wherein said amplifier device has a current-control input, said compensation means including a regulatable resistance in form of a controllable MOSFET.

6. An apparatus as defined in claim 1, wherein said first means and said second means include sample and hold elements.

7. An apparatus as defined in claim 1, wherein said first means is formed so as to furnish said regulator with a continuous signal over said first interval.

8. An apparatus as defined in claim 1, wherein said second means is formed so as to furnish said evaluation assembly with a continuous signal for evaluation over said second interval.

9. An apparatus as defined in claim 7, wherein said second means is formed so as to furnish said evaluation assembly with a continuous signal for evaluation over said second interval.

10. An apparatus as defined in claim 1, wherein said first and second means are formed so that a duration of said first and second interval is 5 milliseconds and 1 millisecond respectively.

11. A method of operating a rain sensor for detecting a wetting of a window with moisture for wetting-dependent triggering of a windshield wiper system for motor vehicles, comprising the steps of outputting a transmitter beam by a transmitter into the window at a first point;

detecting a beam out coupled from the window at a second point by a receiver;

as a function of a radiation intensity detected, outputting a sensor signal to an amplifier device and to a downstream evaluation assembly;

providing a beam with a transmitter beam component as a function of moisture of the window, and an ambient beam component;

in a first interval for detecting the ambient beam with the transmitter switched off, amplifying the sensor signal in the amplifier device and delivering the amplified sensor signal to first means;

ascertaining by the first means an interfering light signal corresponding to the ambient beam;

regulating said interfering signal to a desired value by means of a regulator responsive to the first means to a drive a compensation means disposed in a current circuit of the receiver; and

in a second interval directly following the first interval for detecting the transmitter beam and the ambient beam with the transmitter switched on, delivering the amplified sensor signal to said second means by which from the amplified sensor signal a useful light signal corresponding substantially to the transmitter beam is ascertained.