Abstract:
A low-cost leak sensor that prevents leakage current from flowing between electrodes when moisture is deposited. A leak sensor is formed on an insulating substrate. The leak sensor has a through hole having a pair of opposed walls with a predetermined space. The opposed walls are provided with conducting films. On the opening of the through hole in the insulating substrate, a pair of lands are connected electrically with the pair of conducting films. A pair of wiring patterns are connected electrically with the pair of lands on the insulating substrate.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a leak sensing switch for detecting a leakage current and an insulating substrate having a leak sensing switch. 
     Power window apparatuses are used to automatically open and close the window glass panels of side doors or the like of vehicles. The window glass panels are elevated or lowered when a driver operates an up switch or a down switch of the power window apparatus. However, if the power window apparatus is immersed in water, a drive circuit for the drive motors of the power window apparatus tends to malfunction, failing to energize the drive motors. To solve the above problem, th drive circuit of the power window apparatus is provided with a leak sensing switch for detecting a leakage current. When the leak sensing switch detects a leakage current at the time the power window apparatus is immersed in water, the drive circuit becomes operational based on the detection of the leakage current. 
     FIG. 5 is a schematic plan view of a first conventional leak sensing switch  50 . A pair of pattern wirings  52   a ,  52   b  extend parallel to each other on a circuit board  51 , and first and second branch wirings  53   a ,  53   b  extending perpendicularly to the pattern wirings are disposed between the pattern wirings. Electrodes  54   a ,  54   b  produced by soldering are disposed respectivelyon the first and second branch wirings  53   a ,  53   b . The electrodes  54   a ,  54   b  have a given length  11 , and are spaced from each other by a predetermined gap g 1 . When the leak sensing switch  50  is immersed in water, a leakage current flows between the electrodes  54   a ,  54   b , thus detecting the immersion in water. 
     FIG. 6 is schematic plan view of a second conventional leak sensing switch  55 . A pair of pattern wirings  57   a ,  57   b  extend in series and is spaced from each other in a predetermined space on a circuit board  56 , a C-shaped first electrode support  58   a  connected to the pattern wiring  57   a  and a circular second electrode support  58   b  connected to the pattern wiring  57   b  disposed between the pattern wirings  57   a ,  57   b . The first electrode support  58   a  is spaced from the second electrode support  58   b  by a predetermined gap g 2  and is disposed to surround the second electrode support  58   b . Electrodes  59   a ,  59   b  produced by soldering are disposed respectively on the first and second electrode supports  58   a ,  58   b.    
     FIG. 7 is a schematic perspective view of a third conventional leak sensing switch  60 . A base  62  of synthetic resin having insulating properties is disposed on a circuit board  61 , and a pair of parallel electrode pins  63   a ,  63   b  are disposed on the base  62 . The electrode pins  63   a ,  63   b  are electrically connected to a wiring pattern, not shown. The electrode pins  63   a ,  63   b  have a given length  13 , and are spaced from each other bya predetermined gap g 3 . 
     When the difference between the temperature within the power window apparatus and the temperature outside the power window apparatus increases, moisture tends to be condensed in the power window apparatus, disadvantageously. 
     With the leak sensing switches  50 ,  55  shown in FIGS. 5 and 6, when water droplets are produced between the electrodes  54   a ,  54   b  and between the electrodes  59   a ,  59   b  due to dew condensation, a leakage current may flow between the electrodes  54   a ,  54   b  and between the electrodes  59   a ,  59   b  and may be detected even though the power window apparatus is not immersed in water. 
     With the leak sensing switch  60  shown in FIG. 7, however, since the electrode pins  63   a ,  63   b  are not disposed on a plane, the possibility of a leakage current flowing between the electrodes  63   a ,  63   b  due to dew condensation is low. However, the cost of manufacture of the leak sensing switch is increased because its production needs a manual process for the worker to insert the electrode pins  63   a ,  63   b  into the base  52 . 
     BRIEF SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a leak sensing switch which prevents a leakage current from flowing between electrodes due to dew condensation and manufacturing cost from increasing. 
     According to a first aspect of the present invention, there is provided a leak sensing switch formed on an insulating substrate. The leak sensing switch is formed on an insulating substrate and has a through hole defined in the insulating substrate and having a pair of inner side surfaces opposing each other across a predetermined space. A pair of conducting films are disposed respectively on the inner side surfaces. A pair of lands electrically connected to the conducting films, respectively are disposed on peripheral edges of the opening of the through hole in the insulating substrate. A pair of wiring patterns electrically connected to the pair of lands, respectively, are disposed on the insulating substrate. 
     According to a second aspect of the present invention, there is provided an insulating substrate having a leak sensing switch disposed thereon. The leak sensing switch is formed on an insulating substrate and has a through hole defined in the insulating substrate and having a pair of inner side surfaces opposing each other across a predetermined space. A pair of conducting films are formed respectively on the inner side surfaces. A pair of lands electrically connected to a pair of conducting films, respectively are disposed on peripheral edges of the opening of the through hole in the insulating substrate. A pair of wiring patters electrically connected to the pair of lands, respectively, are disposed on the insulating substrate. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a schematic block diagram of a power window apparatus according to an embodiment of the present invention; 
     FIG. 2 is a schematic perspective view of a leak sensing switch according to an embodiment of the present invention; 
     FIG. 3 is a schematic plan view of the leak sensing switch shown in FIG. 2; 
     FIG. 4 is a schematic cross-sectional view of the leak sensing switch shown in FIG. 2; 
     FIG. 5 is a schematic plan view of a first conventional leak sensing switch; 
     FIG. 6 is a schematic plan view of a second conventional leak sensing switch; and 
     FIG. 7 is a schematic plan view of a third conventional leak sensing switch. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     A leak sensing switch mounted in a power window apparatus according to an embodiment of the present invention will be described below with reference to FIGS. 1 through 4. 
     FIG. 1 is a schematic block diagram of a power window apparatus  11 . 
     The power window apparatus  11  has an electronic control unit (ECU)  12 , a drive circuit  13 , and a drive motor  14 . 
     The ECU  12  has input terminals to which connected a switch group  15  including a down switch, an up switch, and an automatic switch. The ECU  12  has an output terminal connected to the drive circuit  13 . The drive motor  14  for elevating or lowering a window glass panel of a vehicle, not shown, is connected to the drive circuit  13 . The drive motor  14  preferably comprises a DC motor. 
     Each of the down and up switches comprises a double-click tumbler switch. When a down knob or an up knob of the switch is pressed one click, it supplies a down signal or an up signal to the ECU  12 . In resposne to the down signal or the up signal, the ECU  12  supplies a drive signal to the drive circuit  13  which energizes the drive motor  14  to lower or elevate the window glass panel. When the down knob or the up knob of the switch is pressed two clicks, it supplies the down signal or the up signal and also an automatic signal to the ECU  12 . In response to the automatic signal, the ECU  12  supplies a drive signal to the drive circuit  13  which energizes the drive motor  14  until the window glass panel reaches a fully closed position or a fully open position. A leak sensing switch  16  is connected to the drive circuit  13 . The leak sensing switch  16  detects a leakage current when the power window apparatus  11  is immersed in water. 
     As shown in FIG. 2, the leak sensing switch  16  is disposed on a circuit board  17  of the drive circuit  13 . The circuit board  17  is disposed in a location free from exposure to rainwater, such as a passenger compartment, an engine compartment, a trunk, or the like of a vehicle. A first pattern wiring  18   a  and a second pattern wiring  18   b  spaced a predetermined distance from each other are disposed in line with each other on the circuit board  17 . The first and second pattern wirings  18   a ,  18   b  are electrically connected to other wiring patterns (not shown). The pattern wirings  18   a ,  18   b  have opposite ends on which semicircular lands  19   a ,  19   b  are formed. The lands  19   a ,  19   b  have respective linear edges (chordal edges) disposed in opposing relation to each other. The linear edges of the lands  19   a ,  19   b  lie parallel to each other. The pattern wirings  19   a ,  19   b  and the lands  19   a ,  19   b  are formed of plated copper films on the circuit board  17 . The lands  19   a ,  19   b  are electrically connected to the pattern wirings  19   a ,  19   b , respectively. 
     A through hole  20  is formed in the circuit board  17  between the lands  19   a ,  19   b . As shown in FIG. 3, the through hole  20  has an I-shaped (slender) opening having opposing surfaces  21   a ,  21   b  parallel to each other. The through hole  20  has a length L 1  greater than the diameter D of the lands  19   a ,  19   b . The opposing surfaces  21   a ,  21   b  have a length L 2  which is also greater than the diameter D. 
     As shown in FIG. 4, first and second electrodes  22   a ,  22   b  are formed in the through hole  20 . The first and second electrodes  22   a ,  22   b  comprise plated copper films extending from upper surfaces of the lands  19   a ,  19   b  over the opposing surfaces  21   a ,  21   b  to cover a part of the back surfaces of the circuit board  17 . The first and second electrodes  22   a ,  22   b  are disposed fully o the opposing surfaces  21   a ,  21   b . The first and second electrodes  22   a ,  22   b  are electrically connected to the lands  19   a ,  19   b . The first and second electrodes  22   a ,  22   b  are formed as follows: First, as indicated by the two-dot-and-dash lines in FIG. 3, a through hole  20  having an oblong shape is for in the circuit board  17 , and then a plated copper film is deposited on the entire inner surface of the through hole  20 . Thereafter, wide holes  20   a ,  20   b  are defined in the circuit board  17  at the opposite ends of through hole  20 , and the first and second electrodes  22   a ,  22   b  are formed only on the opposing surfaces  21   a ,  21   b.    
     A predetermined gap G is present between the electrodes  22   a ,  22   b . The gap G and the through hole length L 1  are set at values large enough provide an insulating distance between the first and second electrodes  22   a ,  22   b  and allow a leakage current to flow between the first and second electrodes  22   a ,  22   b  when the power window apparatus is immersed in water. 
     The through hole  20 , the lands  19   a ,  19   b , and the electrodes  22   a ,  22   b  are formed at the same time that wiring patterns of the drive circuit  13 , other lands, and other through holes for inserting component terminals, not shown, are formed. 
     Operation of the leak sensing switch  16  will be described below. 
     When the power window apparatus  11  is not immersed in water, but moisture is condensed in the power window apparatus  11  due to the difference between the temperature within the power window apparatus  11  and the temperature outside the power window apparatus  11 , water droplets are deposited on the first and second electrodes  22   a ,  22   b  of the leak sensing switch  16 . At this time, since the electrodes  22   a ,  22   b  do not lie on the same plane, and are spaced apart by the gap G across the through hole  20 , the water droplets flow down the electrodes  22   a ,  22   b  or remain retained on the electrodes  22   a ,  22   b . Therefore, no leak current flows between the electrodes  22   a ,  22   b  through the water droplets. 
     When the power window apparatus  11  is immersed in an electrolytic liquid such as rainwater, water enters the through hole  20  in the leak sensing switch  16 , causing a leakage current to flow between the first and second electrodes  22   a ,  22   b . Since the opening area of the through hole  20  is relatively large, the water surely finds its way into the through hole  20 . Furthermore, because the first and second electrodes  22   a ,  22   b  face each other and are disposed fully over the entire opposing surfaces  21   a ,  21   b , the leakage current flows effectively between the first and second electrodes  22   a ,  22   b , so that the immersion of the power window apparatus  11  in water can reliably be detected. When the leakage current flows between the electrodes  22   a ,  22   b , the drive circuit  13  does not malfunction based on the detection of the leakage current, and keeps the drive motor  14  operable. 
     The leak sensing switch  16  according to the present embodiment offers the following advantages: 
     (1) Since the first and second electrodes  22   a ,  22   b  are formed in the through hole  20  so as to oppose each other across the predetermined space, no leakage current flows between the electrodes  22   a ,  22   b  even when moisture is condensed in the power window apparatus  11 . 
     (2) The manufacturing cost of the power window apparatus  11  is not increased because the through hole  20 , the first and second electrodes  22   a ,  22   b , and the lands  19   a ,  19   b  are formed in the same process as wiring patterns of the drive circuit  13 , other lands, and other through holes. 
     (3) Since the opening area of the through hole  20  is relatively large, water surely enters the through hole  20 , allowing a leakage current to be detected reliably. 
     (4) As the first and second electrodes  22   a ,  22   b  are disposed parallel to each other, the distance between them is kept constant, allowing a leakage current to be detected reliably. 
     (5) The length L 2  of the opposing surface  21   a ,  21   b  is greater than the diameter D of the lands  19   a ,  19   b , and the electrodes  22   a ,  22   b  are disposed fully over the opposing surfaces  21   a ,  21   b . Consequently, the are for detecting a leakage current when the power window apparatus  11  is immersed in water is relatively large, allowing a leakage current to be detected reliably. 
     The above embodiment may be modified as follows: 
     (a) The through hole  20  may be formed in a circular shape as well as in an oblong shape. 
     (b) The width of the first and second electrodes  22   a ,  22   b  may be the same as or smaller than the diameter D of the lands  19   a ,  19   b.    
     (c) The first and second electrodes  22   a ,  22   b  may be formed only on the opposing surfaces  21   a ,  21   b . In this case, the first and second electrodes  22   a ,  22   b  need to be electrically connected to the lands  19   a ,  19   b.    
     (d) The leak sensing switch  16  may be provided in not only the drive circuit  13  of the power window apparatus  11 , but also other drive circuits. 
     (e) The leak sensing switch  16  may be used in other devices where the circuit board  17  is liable to be immersed in another electrolytic solution. 
     (f) A circuit board having the leak sensing switch  16  may be provided separately from the circuit board of the drive circuit  13 .