WIPER SPEED CONTROL SYSTEM FOR AN AUTOMOTIVE WINDSHIELD WIPER

Abstract: A wiper speed control system for an automotive wiper controls the operational speed of a wiper in accordance with rain conditions. The control system includes a rain sensor (30) detecting rain conditions to produce . an analog signal having an amplitude depending upon the detected rain conditions. The analog sensor signal is converted into a digital pulse signal by a converter (12) for application to a digital circuit system. A control signal is produced by digitally processing the pulse signal. The control signal is applied to a wiper driver circuit to adjust the operational speed or timing in accordance with the control signal.

Description: The invention relates to an intermittent timing control system for an automotive windshield wiper as indicated in the precharacterizing part of claim 1. In such a prior art control system (FUNKSCHAU 1978, Heft 19, Page 104) as a rain sensor a raindrop impact sensor is provided having a surface exposed to an air stream travelling over the vehicle. This sensor generates electric pulses by changing an electric field provided at the capacitive sensor arrangement. The electric pulses corresponding to impacts of raindrops are amplified by a pulse amplifier and extended by a pulse extension means in order to directly control a relay switching the wiper drive motor. It is the object of the invention to provide a wiper speed control system which satisfactorily and successfully avoids the influence of external conditions on detection of rain conditions. In accordance with the invention this object is solved by the features as claimed in the characterizing part of claim 1. By means of the mechanical vibrator which is secured to a piezoelectric element a sensor signal is generated having an amplitude and frequency corresponding to the magnitude and frequency of vibration of said one surface of the vibrator which is exposed outwardly of said vehicle so that raindrops directly collide with said one surface. As a result the sensor signal is not influenced by external conditions which are independent of the rain conditions to be detected. A wiper speed control system according to one embodiment of the invention includes a control circuit which can convert an analog rain sensor signal into a pulse signal suitable for digital processing. In practice, the pulses of the pulse signals are counted and compared with a predetermined threshold value to produce a driver signal when the counter value becomes equal to the predetermined threshold value. By controlling the wiper operation according to the digitally processed rain condition data, the influence on detection of the rain conditions due to external conditions can be satisfactorily and successfully avoided. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will he understood more fully from the detailed description give below and from the accompanying drawings of the preferred embodiment of the invention, which, however, should not be taken to limit the invention to the specific embodiment but for explanation and understanding only. In the drawings: Fig. 1 is a schematic block diagram of the preferred embodiment of a wiper speed control system according to the present invention; Fig. 2 is a sectional view of a rain sensor employed in the wiper speed control system of Fig. 1; Fig. 3 is schematic block diagram of a modification of the wiper speed control system of Fig. 1; Fig. 4 is a diagram illustrating location of a rain sensor on a vehicle with regard to dynamic air pressure; Fig. 5 is a diagram of application of the rain sensor to the wiper speed control system of Fig. 3; and Fig. 6 illustrates the vibration frequency spectrum acting on the rain sensor. DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, particularly to Fig. 1, a wiper speed control system of the preferred embodiment of the present invention generally comprises a rain sensor 10 which detect rain conditions and produces a sensor signal having a value indicative of the detected rain conditions. The rain sensor 10 is connected to a pulse signal generator 12 which is adapted to shape the sensor signal and to output a signal in the form of a train of pulses. The pulse train produced by the pulse signal generator 12 has a frequency corresponding to the sensor signal value and so indicating the detected rain conditions. The pulse train is fed to a counter 14. The counter 14 counts the pulses of the pulse train and produces a counter signal whenever the counter value reaches a predetermined value. The counter signal is fed to a driver circuit 16 including a driver motor 18 to drive a wiper mechanism 20. As shown in Fig. 2, the rain sensor 10 comprises a vibration sensor having a sensor surface 102 inclined essentially parallel to the windshield 23 of a vehicle. The sensor surface 102 is formed on a vibrator panel 104 secured in a sensor housing 106 in turn rigidly secured to a cowl top panel 22 near the windshield 23. A piezoelectric element 108 is secured to the inner surface of the vibrator panel 104 for vibration therewith. In this design, the rain sensor 10 detects vibrations produced by impact of rain drops on the sensor surface. That is, when rain falls, rain drops impinge on the sensor surface. Shock applied to the sensor surface and the vibrator panel 104 varies depending on the size of the colliding rain drop, its speed at impact and frequency of occurence of its collision. Therefore, the magnitude of vibration caused by impact of rain drops varies depending upon the size of the colliding rain drop, the collision speed and frequency of occurence of its collision. The piezoelectric element 108 vibrates with the vibrator panel and produces a sensor signal having a value corresponding to the magnitude of vibration. In summary, the sensor signal produced by the rain sensor in the manner set forth above is an analog signal, the output voltage of which varies in dependence upon the vibration amplitude of the vibrator panel and, in turn, in dependence upon the rain conditions. The pulse signal generator 12 converts the analog signal into a pulse train suitable for digital processing for the purpose of wiper speed control. The counter 14 is a digital counter for counting the pulses from the pulse signal generator 12 and internally compares the counter value with a predetermined threshold value to produce a counter signal when the counter value becomes equal to the threshold value. When the wipers have been manually selected to operate intermittently, the counter signal can serve as a driver signal activating the driver circuit to operate the wiper mechanism 20. In this case, the timing of occurrences of the counter signal corresponds to the interval between successive wiper operations, the frequency of which varies in dependence upon rain conditions. However, according to the shown embodiment it is also possible to control the wiper operational speed depending upon the detected rain conditions, even in low- or high-speed continuous operation modes. In this case, wiper speed control may be performed by adjusting the voltage to be applied to the driver motor 18 in accordance with the frequency of occurrence of the counter signal. Fig. 3 shows a modification of the foregoing preferred embodiment of wiper speed control system according to the present invention. In this modification, a rain sensor 30 is associated with the pulse signal generator 12. As in the foregoing preferred embodiment, the rain sensor 30 produces an analog sensor signal having a value indicative of the rain conditions. The pulse signal generator 12 converts the analog sensor signal into a pulse train having a frequency corresponding to the sensor signal value. The pulse signal generator 12 is connected to a counter 32. The counter 32 is also connected to an oscillator 34 which is adapted to output a pulse train with a constant frequency. The counter 32 counts the pulses from both the pulse signal generator 12 and the oscillator 34 and produces a counter signal when the counter value, which represents the total number of pulses from the pulse signal generator and the oscillator 34, become equal to the predetermined threshold. As shown in Figs. 4 and 5, the rain sensor 30 is mounted on the cowl top panel 22 of the vehicle body at a point subject to positive pressure from the air stream, as indicated by hatched area in Fig. 4. If the rain sensor 30 is mounted on the vehicle body at a point subject to negative dynamic air pressure, the air pressure may adversely influence detection of rain conditions, since the angle of incidence of the rain will be affected by the influence of the air pressure. The sensor surface 302 of the rain sensor 30 is inclined at a given angle with respect to the horizontal plane such that the rear edge is higher than the front edge. The angle of inclination of the sensor surface with respect to horizontal plane is empirically selected to fall within the range of from 5° to 25°. Normally, rain drop speed is approximately 1 m/sec. to 15 m/sec. In this normal rain condition, the selected inclination angle of the sensor surface, i.e. 5° to 25° is satisfactory for detecting rain condition under usual vehicle speed. Preferably, the rain sensor would be provided with a sensor surface which can be variably inclined in dependence upon the rain drop speed. Dynamic air pressure reflecting vehicle speed may be used as a detecting parameter to control the inclination angle of the sensor surface. As in the foregoing embodiment, the rain sensor 30 includes a vibrator panel 304 with a sensor surface 302 exposed by a sensor housing 306. The vibrator panel 304 engages the sensor housing 306 only at its circumferential edge so that it can vibrate in response to impact of rain drops on the sensor surface. A piezoelectric element 308 is secured to the vibrator panel 304 via an electrode 310 formed therebetween. Another electrode 312 is formed on the opposite surface of the piezoelectric element 308. The electrodes 310 and 312 are electrically connected to an amplifier 316. The amplifier 316 is connected to the wiper speed control circuit, including the pulse signal generator 12, the counter 32 and the oscillator 34, to supply the sensor signal thereto. The natural or natural resonate frequency of the vibrator panel 304 is chosen to fall in the range of 10 KHz to 25 KHZ. This specific natural frequency of the vibrator panel is experimentarily selected to avoid the influence of vibrations created by the vehicle horn or other equipment or engine vibrations. Fig. 6 shows the vibration frequency spectrum created by vehicle horn and received by the rain sensor. As will be appreciated from Fig. 6, the maximum frequency of vibration created by the vehicle horn is approximately 9 KHz. Therefore, by selecting the natural frequency of the vibrator panel 304 in the given range, i.e., 10 KHz to 25 KHz, the influence of the vehicle horn upon detection of the rain conditions can be satisfactorily avoided. The maximum natural frequency of the vibrator panel 304 is selected in view of the amplitude of the sensor signal. To achieve a natural resonant frequency of the vibrator panel 304 beyond 25 KHz, the vibrator panel has to be adequately thick in relation to the area of the sensor surface. In this case, the amplitude of vibration produced by impact of rain drops onto the sensor surface will be too low to be used in the wiper control system. That is, by setting the natural frequency of the vibrator panel so high, the sensivity to rain will be lowered, thereby degrading the response characteristics of the wiper control system. In this modification, since the counter signal is produced when the total number of pulses from both the pulse signal generator and the oscillator reaches the predetermined threshold, the wiper mechanism can be driven at the longest interval in intermittent operational mode or at the lowest speed in continuous operational mode, as defined by pulse period of the pulse train from the oscillator. As a result, the wiper mechanism will continue to operate even when the vehicle passes through a tunnel in which rain drop cannot be detected. This will be advantageous for providing clear vision for the driver. It should be noted that the sensor surface subjected to rain should be larger than 100 mm² in area in accordance with experimental results. In experimental tests, it was found that a rain drop impinging on a plane surface usually expands to an area of approximately 100 mm². It is necessary to provide a sensor surface sufficiently large to receive the full volume of rain water upon impact in order to detect the rain conditions. Otherwise, a plurality of rain sensors, each of which has a sensor surface area of less than 100 mm², can be used so that the total contiguous area of the sensor surface exceeds 100 mm². As set forth above, according to the present invention, an analog sensor signal is converted into a pulse train so that the influence of errors in the circuit element characteristics, temperature conditions and so forth can be avoided.

Claims: An intermittent timing control system for a wiper system of a vehicle, comprising: a rain sensor (30) for monitoring rain condition to produce a rain condition indicative sensor signal, said sensor (30) being mounted on a point on a body of said vehicle subject to positive pressure from an air stream travelling over said vehicle, a control signal generator means (12,32,34) for generating a wiper control signal on the basis of said sensor signal having an amplitude and frequency corresponding to the impact of raindrops, and a wiper driver motor (18) responsive to the control signal for driving a windshield wiper (20) at variable intervals in an intermittent mode of operation characterized in that said rain sensor (30) having mechanical vibrator (304) adapted to vibrate at an amplitude and frequency depending upon the rate of rain, said vibrator (304) having one surface (302) exposed outwardly of said vehicle so that raindrops directly collide with said one surface (302) for causing vibration of said vibrator (304), and said vibrator (304) is secured to a piezoelectric element (308) producing said sensor signal having an amplitude and frequency corresponding to the magnitude and frequency of vibration of said one surface (302); and said means (12,32,34) is responsive to the magnitude and frequency of said sensor signal for deriving an intermittent timing signal for wiper intermittent operated based on the sensor signal value. The control system as set forth in claim 1 wherein said one surface (302) of said rain sensor (30) has an area greater than 100 mm². The control system as set forth in claim 1 or 2 wherein said one surface (302) of said rain sensor (30) is inclined at an angle relative to the horizontal. The control system as set forth in claim 3 wherein said angle is in the range of 5 degrees to 25 degrees. The control system as set forth in claim 4 wherein said angle is variable in dependence on raindrop speed. The control system as set forth in any of claims 1 to 5, wherein said one surface (302) is mounted on a cowl top panel (22) of said vehicle.

Inventors: SHIRAISHI, YASUHIRO
Applicants: NISSAN MOTOR CO., LTD.
Application year: 1983
Main classification: B60S1
IPC codes: B60S1