Rain sensor using low harmonic content signals

• US 6,634,225 B1
• Filed: 12/17/2001
• Issued: 10/21/2003
• Est. Priority Date: 06/18/1999
• Status: Expired due to Term

• Current Assignee: Valeo Auto-Electric Wischer und Motoren GmbH (Valeo SE)
• Original Assignee: Valeo Auto-Electric Wischer und Motoren GmbH (Valeo SE)
• Inventors: Reime, Gerd
• Primary Examiner(s): Lefkowitz, Edward
• Assistant Examiner(s): Ellington, Alandra
• Application Number:
  US10/019,085
• Time in Patent Office: 673 Days
• Field of Search: 731/701.7, 737/18, 737/15, 731/94, 731/702.1, 731/701.6, 738/63, 219/522, 219/203, 219/543, 318/483, 318/587, 318/130
• US Class Current: 73/170.17
• CPC Class Codes: B60S 1/0822 characterized by the arrangement or type of detection means
• CPC Class Codes: B60S 1/0837 with a particular arrangement of the optical elements

Abstract

A rain sensor to detect humidity drops inside an area on a transparent window has at least one transmitting element to emit optical rays into the window and has at least one receiving element to receive at least one part of the emitted optical rays where the intensity of the optical rays received is dependent on the number of humidity drops in the area of the window observed by the rain sensor. So that interference from the rain sensor with radio broadcasts is effectively reduced and, if possible even completely prevented, the rain sensor has a generator to generate an electrical signal which has a lower harmonic content than square-wave signals, preferably a sine-wave electrical signal to power each transmitting element of the rain sensor.

Claims

1. A rain sensor for detecting humidity drops within an area on a transparent window, the rain sensor comprising:

at least one transmitting element for emitting optical rays into the window;

at least one receiving element for receiving at least one part of the optical rays emitted, wherein the intensity of the optical rays received is dependent on the number of humidity drops in the area of the window observed by the rain sensor; and

means for generating an electrical signal having a lower harmonic content than a square-wave signal, the generating means supplying the electrical signal to the at least one transmitting element of the rain sensor.

2. The rain sensor in accordance with claim 1, wherein the rain sensor has a plurality of transmitting elements, each of the plurality of transmitting elements grouped in one of two signal paths, and wherein the rain sensor further comprises:

a comparator to compare the intensity of the optical rays from each signal path received by the at least one receiving element.

3. The rain sensor in accordance with claim 2, wherein the electrical signal is a sine-wave electrical signal, the rain sensor further comprising:

a voltage divider to divide the sine-wave electrical signal into two sine-wave electrical signals to power respective transmitting elements of the two signal paths.

4. The rain sensor in accordance with claim 3, further comprising:

a first controller to regulate the amplitude of the individual sine-wave electrical signals so that there is no difference in level between the output signals of the two signal paths.

5. The rain sensor in accordance with claim 4, wherein the first controller is a PID controller.

6. The rain sensor in accordance with claim 3, wherein the voltage divider includes means for shifting the phases of each of the two sine-wave electrical signals by 180 degrees.

7. The rain sensor in accordance with claim 4, further comprising:

a second controller to jointly regulate both amplitudes of the sine-wave electrical signals so that at least one of the electrical signals always has a specifiable maximum amplitude.

8. The rain sensor in accordance with claim 7 wherein a control loop with the second controller is superposed on a control loop with the first controller.

9. The rain sensor in accordance with claim 2 further comprising:

a window discriminator to detect deviations in the output signal from the comparator from a constant value and to put out a matching output signal from the rain sensor.

10. The rain sensor in accordance with claim 8, further comprising:

a synchronous demodulator associated with each of the at least one receiving elements, each synchronous demodulator dividing the signal received by each receiving element into two differential signals, where each of the signals includes specific half waves of the received signal.

11. The rain sensor in accordance with claim 10, further comprising:

integrators to integrate the differential signals upward.

12. The rain sensor in accordance with claim 1, wherein the at least one receiving element is one centrally-located receiving element and the at least one transmitting element includes eight transmitting elements grouped into two signal paths and positioned around the one centrally-located receiving element at a specific radius.

13. The rain sensor in accordance with claim 1, wherein each of the at least one transmitting element is a luminescent diode.

14. The rain sensor in accordance with claim 1, wherein each of the at least one receiving element is a luminescent diode.

15. The rain sensor in accordance with claim 1 wherein the optical rays are infrared rays.

16. The rain sensor in accordance with claim 10, wherein the synchronous demodulator comprises two transistors operable in response to a sine-wave switching voltage.

17. A method of operating a rain sensor to detect humidity drops within an area on a transparent window, the method comprising the steps of:

emitting optical rays into the window using at least one transmitting element emits optical rays;

receiving at least one part of the emitted optical rays using at least one receiving element, wherein the intensity of the received optical rays is dependent on the number of humidity drops in the area of the window observed by the rain sensor; and

supplying power to the at least one transmitting element using an electrical signal having a lower harmonic content than a square-wave signal.

18. The method in accordance with claim 17, wherein the step of supplying power further comprises the step of supplying power to the at least one transmitting element of the rain sensor using a sine-wave electrical signal.

19. The method in accordance with claim 17 wherein each signal in the rain sensor has a lower harmonic content than a square-wave signal.

20. The method in accordance with claim 19, wherein each signal in the rain sensor is a sine-wave signal.

21. A rain sensor for a transparent window, comprising:

a transmitting element for emitting optical rays into the window;

a receiving element for receiving optical rays reflected from the window;

means for generating an electrical signal and supplying the electrical signal to the transmitting element, the electrical signal having a lower harmonic content than a square-wave signal; and

processing circuitry for receiving signals from the receiving element and for determining an amount of humidity drops on the window.