Abstract:
A switch device for rotating and stopping a DC motor includes a first switch element having two moving contacts, two normally open NO contacts and two normally closed NC contacts, a second switch element having one or two normally closed NC contacts, and an operating element. The operating element serves to connect the two moving contacts individually to input terminals of the DC motor, the two NO contacts to a voltage source line at a higher voltage, and each of the two NC contacts of the first switch element to another voltage source line at a lower voltage such as the ground potential, each through the NC contact, or one of the two NC contacts, of the second switch element. The NC contact of the second switch element is maintained in an open condition during a period from when either one of the NO contacts begins to change from a closed condition to an open condition until the corresponding NC contact of the first switch element finishes changing from an open condition to a closed condition.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a switch device for starting and stopping the rotation of a DC electric motor for opening and closing a window of a motor vehicle such as an automobile or for a similar purpose and more particularly to such a switch device for a DC electric motor operating at a high source voltage (such as 42V). 
     Automobiles currently make use of a 14V electrical system with source voltage of 12V. Since an increased number of electronic devices are being carried on automobiles, however, a 14V system is sometimes hardly capable of supplying sufficient power. As a result of global discussions in consortia representing both universities and industries in view of this problem, a consensus has been obtained from the point of view of safety to human bodies to adopt a voltage system that is three times higher, or a 42V system with source voltage of 36V. Examples of electrical equipment to be operated in a 42V electrical system include DC motors contained in a door for opening and closing a window (or so-called DC motors for operating a power window). 
       FIGS. 10A and 10B  are respectively a structural diagram and a circuit diagram of a prior art switch device  1  for rotating (both in positive and negative directions) and stopping such a DC motor  2  for operating a power window. Such a switch device may typically be installed inside the elbow rest attached to the front or back seat of the vehicle or inside a door.  FIGS. 10A and 10B  show the switch device  1  when the DC motor  2  is stopped, that is, when a knob  3  therefor is not being operated. In what follows, this condition is referred to as the neutral condition. 
     The knob  3  is attached to a case  4  on a door such that it can be tilted by a specified angle both in clockwise and counter-clockwise directions, as shown in  FIG. 10A . If the knob  3  is rotated in the clockwise direction, the window is closed (to be in the UP condition). If the knob  3  is rotated in the counter-clockwise direction, the window is opened (to be in the DOWN condition). If the force applied on the knob  3  is released, or if the finger is lifted therefrom, the knob  3  returns to its neutral position by the operations of a spring  5  and a plunger  6  buried inside the knob  3  and thereafter remains in this neutral condition. 
     The knob  3  has a downward protrusion  7  which is at a position as shown in  FIG. 10A  when the knob  3  is in the neutral position but swings to the left when the knob  3  is in the UP condition as shown in  FIG. 12A  and to the right when the knob  3  is in the DOWN condition (not shown in drawing). 
     Provided inside the case  4  is a switch unit  9  mounted to a printed circuit board  8  so as to function as a two-circuit two-contact switch of a momentary type.  FIG. 11  shows an external view of this switch unit  9 , comprising a housing  10 , two common terminals  11  and  12  coming out of one side surface of the housing  10 , one normally open terminal  13  coming out of the other side surface of the housing  10  and two normally closed terminals  14  and  15  coming out of the bottom surface of the housing  10 . These terminals  11 – 15  are soldered to specified conductor circuits on the printed circuit board  8  so as to be connected to a power source line (or the +B line)  17 , a grounding line  18  and the DC motor  2 , as shown in  FIG. 10B . 
     As shown in  FIG. 10B , the switch unit  9  includes two switch mechanisms A and B adapted to operate mutually exclusively according to the position of a slider  28  on the upper surface of the switch unit  9 . In the above, to be switched mutually exclusively means opening only the normally closed (NC) contact of either one of the switch mechanisms A and B, or closing only the normally open (NO) contact of that switch mechanism. 
     Explained more in detail, when the slider  28  is in the neutral condition, as shown in  FIG. 10A , it is in the closed condition between the moving contact  19  and the NC contact  23  of the first switch mechanism A and between the moving contact  20  and the NC contact  24  of the second switch mechanism B. In this position, the NO contacts  21  and  22  of both switch mechanisms A and B are in open condition and the NC contacts  23  and  24  of both switch mechanisms A and B are in closed condition, as their names (NO and NC) indicate. If the slider  28  is moved to the left as indicated by arrow L in  FIG. 11  to be in the UP condition, the closed condition between the moving contact  20  and the NC contact  24  of the second switch mechanism B is maintained but the NC contact  23  of the first switch mechanism A is released from the closed condition and a new closed condition is established between the moving contact  19  and the NO contact  21 . Likewise, if the slider  28  is moved to the right as indicated by arrow R in  FIG. 11  to be in the DOWN condition, the closed condition between the moving contact  19  and the NC contact  23  of the first switch mechanism A is maintained but the NC contact  24  of the second switch mechanism B is released from the closed condition and a new closed condition is established between the moving contact  20  and the NO contact  22 . 
     The switching operations as described above are made possible by the movement of the slider  28  as well as by the designed shape of the bottom surface of the slider  28 .  FIGS. 11C and 11D  are sectional views of the slider  28  taken respectively along lines  11 C— 11 C and  11 D and  11 D of  FIG. 11B .  FIG. 11C  shows that the right-hand half of the slider  28  is made thicker and  FIG. 11D  shows that the left-hand half of the slider  28  is made thicker. As will be explained below, the switching mechanisms A and B are switched in a mutually exclusive manner according to the positional relationship between these thickly made portions of the slider  28 . It is to be noted that only one of the common terminals  11  and  12  and one of the normally closed terminals  14  and  15  are visible in  FIG. 10A  because the others of the common terminals and the normally closed terminals are hidden behind the front ones. 
     As explained above, the switch unit  9  described above functions as a two-circuit two-contact switch of a momentary type. This comes about because the moving contacts  19  and  20 , the NO contacts  21  and  22  and the NC contacts  23  and  24  are connected respectively to the common terminals  11  and  12 , the normally open terminal  13  and the normally closed terminals  14  and  15  such that the switching of contacts in two circuits (that is, the switching between the NO contact  21  and the NC contact  23  by the moving contact  19  and the switching between the NO contact  22  and the NC contact  24  by the moving contact  20 ) can be effected in a mutually exclusive manner. 
     The moving contacts  19  and  20  are attached at the tips of a mobile pieces  25  and  26  each in the form of a metallic spring plate, and these mobile pieces  25  and  26  are biased downwardly with reference to  FIG. 10A  by means of push buttons  27 A (for the first switch mechanism A) and  27 B (for the second switch mechanism B). These push buttons  27 A and  27 B are in contact with the bottom surface of the slider  28  and are individually pushed downward if the slider  28  is moved to the left as shown in  FIG. 12A  according to the contour (or the position of the thick portions) of the slider  28 . The slider  28  has an upward protrusion  29  that engages with the tip of the downward protrusion  7  of the knob  3  and slides in the left-right direction according to the movement of the knob  3  into the UP and DOWN conditions. 
     In other words, as the knob  13  of this switch device  1  is raised into the UP condition, the slider  28  slides to the left and the push button  27 A in contact with its thick portion along line  11 C— 11 C is pushed downward, thereby establishing an open condition between the moving contact  19  and the NC contact  23  of the first switch mechanism A while maintaining a closed condition between the moving contact  19  and the NO contact  21 . 
     If the finger is released from the knob  3  to set it in its neutral condition, the slider  28  slides to the right to return to its original position, causing the push button  27 A to move upward and the moving contact  19  and the NC contact  23  of the first switch mechanism A to be in the closed condition. 
     If the knob  3  is pushed down to set it in the DOWN condition, the slider  28  slides to the right and the push button  27 B in contact with its thick portion along line  11 D— 11 D is pushed downward, thereby establishing an open condition between the moving contact  20  and the NC contact  24  of the second switch mechanism B while maintaining a closed condition between the moving contact  20  and the NO contact  22 . If the finger is released from the knob  3  thereafter to set it in its neutral condition, the slider  28  slides to the left to its original position, causing the push button  27 B to move upward and the moving contact  20  and the NC contact  24  of the second switch mechanism B to be in the closed condition. 
     When the knob  3  is in the neutral condition, the contacts of the first and second switch mechanisms A and B are in conditions as shown in  FIG. 10B , that is, the moving contact  19  and the NC contact  23  of the first switch mechanism A are in the closed condition and the moving contact  20  and the NC contact  24  of the second switch mechanism B are in the closed condition. Under this condition, the DC motor  2  is not connected to the +B line  17  and hence the DC motor  2  does not rotate. 
     When the knob  3  is in the UP condition, the contacts of the first and second switch mechanisms A and B are in conditions as shown in  FIG. 12B , that is, the moving contact  19  and the NO contact  21  of the first mechanism A are in the closed condition and the moving contact  20  and the NC contact  24  of the second switch mechanism B are in the closed condition. Under this condition, a closed circuit is formed from the +B line  17  to the DC motor  2  to the grounding line  18 , and the DC motor  2  rotates in the direction of closing the window. 
     If the knob  3  is in the DOWN condition, although not shown, the moving contact  19  and the NC contact  23  of the first switch mechanism A are closed and the moving contact  20  and the NO contact  22  of the second switch mechanism B are closed. Under this condition, a closed circuit is formed from the grounding line  18  to the DC motor  2  to the +B line  17 , and the DC motor  2  rotates in the direction of opening the window. 
     Although an example has been explained wherein the rotation of a DC motor is controlled by a single switch unit, there are also switch devices, depending on the kind of automobiles, allowing the window on the rider&#39;s side or the back windows to be controlled from the driver&#39;s seat.  FIG. 13  shows a circuit structure for such a switch device, structured as a combination of a switch unit  9  for the driver and another switch unit  9 ′ for the rider such that the DC motor  2  for the window on the rider&#39;s side can be rotated or stopped not only by the rider but also by the driver. 
     Although an example was described above wherein a single terminal is assigned to each of the moving contacts  19  and  20  and the NC contacts  23  and  24  (that is, the common terminals  11  and  12  and the normally closed terminals  14  and  15 ) and a single normally open terminal  13  is assigned to both NO contacts  21  and  22  such that there are altogether five terminals, there are examples of other types such as shown in  FIG. 14 . The example shown in  FIG. 14  is characterized wherein contacts connected to the grounding line  18  (the NC contacts  23  and  24  of the first and second switch mechanisms A and B) are connected together inside the unit and then pulled out from a single terminal  15   a  to be connected to the grounding line  18  such that there are altogether four terminals. Alternatively, two switch mechanisms each with one circuit may be used. In such a case, there are six terminals altogether. 
     Examples of prior art switch system described above with reference to  FIGS. 10–14  may all be used without any trouble as long as they are used with a conventional 14V electrical system. If such a prior art switch system is used with a 42V electrical system, however, an overly strong current will flow between a specified pair of contacts at the return time from the UP condition to the neutral condition or from the DOWN condition to the neutral condition, thereby damaging these contacts. 
       FIG. 15  shows how such a damage may come about,  FIG. 15A  showing the switch device in the UP condition,  FIG. 15B  showing it at a moment immediately before its return to the neutral condition, and  FIG. 15C  showing when the switch device has returned to the neutral condition. They are different from the diagrams explaining the prior art operations in that a higher voltage (the source voltage of a 42V electrical system being 36V) is being applied to the +B line  17 . 
     When the mechanism is in the UP condition as shown in  FIG. 15A , the NO contact  21  and the moving contact  19  of the first switch mechanism A are in the closed condition and the moving contact  20  and the NC contact  24  of the second switch mechanism B are similarly in the closed condition. As a result, a closed circuit is formed from the +B line  17  to the DC motor  2  to the grounding line  18  and the DC motor  2  rotates in the direction of closing the window. When the driver&#39;s finger is released from the knob  3 , the NO contact  21  and the moving contact  19  of the first switch mechanism A are released from their closed condition and the moving contact  19  begins to move towards the NC contact  23  while generating small arc discharges between the NO contact  21  within an allowable range until finally the moving contact  19  and the NC contact  23  of the first switch mechanism A come to be in the closed condition as shown in  FIG. 15C . The source voltage then ceases to be supplied to the DC motor  2  and the rotation of the DC motor  2  stops. 
     In the case of a prior art switch device, the contact gap is as small as about 0.5 mm and hence cannot support an arc discharge voltage of about 42V. Thus, the moving contact  19  is in the condition of having a voltage of several volts applied thereto when it becomes connected to the NC contact  23 . By experiments carried out by the present inventors, it was discovered that a large current of over 100A will flow from the moving contact  19  to the grounding line  18  through the NC contact  23  over a very short period of time such as about 0.5 ms (as indicated by a thick arrow  31  in  FIG. 15C  and that this results in a large discharge (indicated by numeral  32 ) between the NO contact  21  and the NC contact  23 , thereby damaging or destroying the moving contact  19  and the NC contact  23 . 
     Since this phenomenon will impede the popular acceptance of 42V electrical systems, its elimination has been a technical problem to be solved as quickly as possible. 
     In general, the gap between contacts is made wider as the applied voltage is increased in order to prevent arc discharges. If the gap is increased to about 4 mm, the arc discharge voltage may be accordingly increased and the moving contact  19  can be connected to the NC contact  23  while no voltage is applied thereon. If the gap is thus increased, however, the switch unit as a whole becomes large and may be inconvenient for being used on a vehicle. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of this invention to provide a switch device which will not cause the switch unit to become large when applied to a 42V electrical system, while being able to prevent damages to the contacts and causing no increase in the time lag in switching between contacts. 
     A switch device according to a first embodiment of this invention for rotating and stopping a DC motor may be characterized as comprising a first switch element, a second switch element and an operating element, the first switch element having two moving contacts, two normally open NO contacts and two normally closed NC contacts, the second switch element having at least one (say, one or two) normally closed NC contact, and the operating element serving to make connections in specified manners such as connecting the two moving contacts of the first switch element individually to input terminals of the DC motor, connecting the two NO contacts to a voltage source line (“the higher voltage source line), and connecting each of the two NC contacts of the first switch element to another voltage source line (“the lower voltage source line”) at a lower voltage than the higher voltage source line each through one of the at least one NC contact of the second switch element. The operating element further serves to maintain the aforementioned at least one NC contact of the second switch element in an open condition during a period from when the NO contacts begin to change from a closed condition to an open condition until the NC contacts of the first switch element finish changing from an open condition to a closed condition. 
     With a switch device thus structured, the DC motor stops its rotation if the two NC contacts of the first switch element are set in the closed condition because the lower voltage of the lower source line (say, at the ground voltage) is then applied to both of the input terminals of the DC motor through these two NC contacts of the first switch element and the NC contact or contacts of the second switch element. If either one of the two NC contacts of the first switch element alone is set in the closed condition, the DC motor rotates because while the lower voltage source line is connected to one of the input terminals of the DC motor through this closed NC contact of the first switch element and the NC contact of the second switch element (if the second switch element has only one NC contact) or the corresponding one of the NC contacts of the second switch element (if the second switch element has two NC contacts) connected to the closed NC contact of the first switch element, the higher voltage source line is connected to the other of the input terminals of the DC motor through the closed one of the two NO contacts of the first switch element. 
     If the closed one of the two NO contacts of the first switch element is returned to its normally open condition while the DC motor is rotating as explained above, the DC motor stops its rotation. In this situation, during the period from the starting moment when the closed NO contact of the first switch element begins to be opened until the corresponding NC contact completes its change from the open condition to the closed position, the corresponding NC contact of the second switch element is maintained in the open condition such that the current route between the NC contacts of the first switch element and the lower voltage source line and hence no large instantaneous current can be generated and damage to the contacts of the first switch element can be prevented. 
     A switch device according to a second embodiment of the invention is similar to the one according to the first embodiment described above except that the operating element serves to connect the two NC contacts of the first switch element to the lower voltage source line and each of the two NO contacts of the first switch element to the higher voltage source through the NC contact or one of the NC contacts of the second switch element. Moreover, before either one of the NO contacts of the first switch element changes from a closed condition to an open condition, the operating element allows the normally closed NC contact of the second switch element connected to the opened NO contact to be in an open condition. 
     With a switch device thus structured, the DC motor stops its rotation if the two NC contacts of the first switch element are set in the closed condition because the lower voltage source line is then connected to both of the input terminals of the DC motor through these two NC contacts of the first switch element. If either one of the two NC contacts of the first switch element alone is set in the closed condition, the DC motor rotates because while the lower voltage source line is connected to one of the input terminals of the DC motor through this closed NC contact of the first switch element, the higher voltage source line is connected to the other of the input terminals of the DC motor through the closed one of the two NO contacts of the first switch element and the NC contact of the second switch element (if the second switch element has only one NC contact) or the corresponding one of the NC contacts of the second switch element (if the second switch element has two NC contacts) connected to the closed NC contact of the first switch element. 
     If the closed one of the two NO contacts of the first switch element is returned to its normally open condition while the DC motor is rotating as explained above, the DC motor stops its rotation. In this situation, before the closed one of the NO contacts of the first switch element changes from a closed condition to an open condition, the corresponding NC contact of the second switch element is allowed (say, by a manual operation) to be in an open condition such that the current route between the NO contacts of the first switch element and the higher voltage source line and hence no large instantaneous current can be generated and damage to the contacts of the first switch element can be prevented. 
     A switch device according to a third embodiment of this invention may be characterized also as comprising a first switch element, a second element and an operating element. The first element has two normally open NO contacts and the second switch element has two normally closed NC contacts. The operating element serves to connect the two input terminals of a DC motor to the higher voltage line each through a corresponding one of the two NO contacts of the first switch element and the two input terminals of the DC motor to the lower voltage source line through a corresponding one of the two NC contacts of the second switch element. Before either one of the NO contacts of the first switch element changes from an open condition to a closed condition, the operating element allows the NC contact of the second switch element connected to the closed NO contact to be in an open condition. 
     With a switch device thus structured, the DC motor stops its rotation if the two NO contacts of the first switch element are set in the open condition and the two NC contacts of the second switch element are set in the closed condition because the lower voltage source line is then connected to both of the input terminals of the DC motor through the two NC contacts of the second switch element. If either one of the two NO contacts of the first switch element alone is set in the closed condition and the NC contact of the second switch element connected to the corresponding NC contact is opened, the DC motor rotates because while the lower voltage source line is connected to one of the input terminals of the DC motor through these closed contacts, the higher voltage source line is connected to the other of the input terminals of the DC motor. 
     If the closed one of the two NO contacts of the first switch element is returned to its normally open condition while the DC motor is rotating as explained above and the corresponding NC contact of the second switch element is returned to its closed condition, the DC motor stops its rotation. In this situation, before the closed one of the NO contacts of the first switch element changes from a closed condition to an open condition, the corresponding NC contact of the second switch element is allowed to be returned to the closed condition such that the NO contacts of the first switch element can support a sufficiently large voltage for an arc discharge and the generation of a large instantaneous current can be prevented although the NC contact connected to this NO contact of the first switch element becomes closed and hence damage to the contacts of the first switch element can be prevented. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a structural diagram of a switch device embodying this invention. 
         FIG. 2  is a plan view of a slider as the operating element of the switch device of  FIG. 1 . 
         FIG. 3  is a diagram for showing the operation of one of switch groups. 
         FIGS. 4A ,  4 B,  4 C and  4 D, together referred to as  FIG. 4 , are circuit diagrams of a system for rotating in both positive and negative directions and stopping a DC motor for opening and closing a window by incorporating the switch device of  FIG. 1 . 
         FIGS. 5–8  are circuit diagrams of various embodiments of this invention. 
         FIG. 9  is an external view of an embodiment wherein the first and second switch elements are formed as separate units. 
         FIGS. 10A and 10B , together referred to as  FIG. 10 , are respectively a structural diagram and a circuit diagram of a prior art switch device when it is in the neutral condition. 
         FIGS. 11A ,  11 B,  11 C and  11 D, together referred to as  FIG. 11 , are respectively an external view of the switch unit of  FIG. 10 , a plan view of its slider, a sectional view taken along line  11 C— 11 C of  FIG. 11B  and a sectional view taken along line  11 D— 11 D of  FIG. 11B . 
         FIGS. 12A and 12B , together referred to as  FIG. 12  are respectively a structural diagram and a circuit diagram of the prior art switch device of  FIG. 10  when it is in the UP condition. 
         FIG. 13  is a circuit diagram of another prior art switch device. 
         FIG. 14  is a circuit diagram of still another prior art switch device having a total of four terminals. 
         FIGS. 15A ,  15 B and  15 C, together referred to as  FIG. 15 , are circuit diagrams for explaining how contacts of a switch device may be damaged. 
     
    
    
     Throughout herein, components that are equivalent or at least similar may be indicated by the same symbols and may not necessarily be explained or described in a repetitious manner. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention is described next by way of examples.  FIG. 1  shows a switch device  40  according to a first embodiment of this invention, which may be roughly characterized as comprising two switch elements (the first switch element  41  and the second switch element  42 ) and an operating element  43  for carrying out the switching operations of these two switch elements  41  and  42 . 
     Next, each of these elements will be described individually. The first switch element  41  is comprised of six fixed electrodes  41   a – 41   f  each made of a planar metallic conductor inserted inside a molded base (not shown) or formed as a thin film and two mobile members  41   g  and  41   h . The metallic material for these six fixed electrodes has a high electrical conductivity and is strong against wears such as copper, bronze and alloys of copper and iron. These six fixed electrodes are arranged in two group of three each, the first group consisting of electrodes  41   a ,  41   b  and  41   c  and the second group consisting of electrodes  41   d ,  41   e  and  41   f . The two groups of fixed electrodes are arranged parallel to each other, as shown in  FIG. 1 . 
     Let D 41   a , D 41   b , D 41   c , D 41   d , D 41   e  and D 41   f  denote respectively the surface areas of the fixed electrodes  41   a ,  41   b ,  41   c ,  41   d ,  41   e  and  41   f . Then, they are related as follows: D 41   a =D 41   d , D 41   b =D 41   e  and D 41   c =D 41   f . The fixed electrodes  41   a ,  41   b  and  41   c  of the first group are arranged in this order in the direction shown by line  44  from right to left with reference to  FIG. 1 . The fixed electrodes  41   d ,  41   e  and  41   f  of the second group are arranged in this order along the same line from left to right with reference to  FIG. 1 . The separation L 1   a  between the fixed electrodes  41   a  and  41   b  is greater than the separation L 2   a  between the fixed electrodes  41   b  and  41   c . Similarly, the separation L 1   b  (=L 1   a ) between the fixed electrodes  41   d  and  41   e  is greater than the separation L 2   b  (=L 2   a ) between the fixed electrodes  41   e  and  41   f.    
     The mobile members  41   g  and  41   h  are shaped so as to be slidable in the direction of the line  44  respectively over the first and second groups of the fixed electrodes  41   a – 41   c  and  41   d – 41   f . For example, each may have two curved downward protrusions (the mobile member  41   g  having protrusions  41   g   1  and  41   g   2 , and the mobile member  41   h  having protrusions  41   h   1  and  41   h   2 ). Each may be made of a metallic material such as copper, bronze and alloys of copper and iron with a high electrical conductivity and strong against frictional wears. 
     The mobile members  41   g  and  41   h  are downwardly biased by means respectively of springs  41   i  and  41   j  such that their protrusions are pressed respectively against the fixed electrodes  41   a – 41   c  and  41   d – 41   f  of the first and second groups. The separation between the two protrusions on each of the mobile members  41   g  and  41   h  is so set as to be greater than L 1   a  (=L 1   b ). Explained for the mobile member  41   g  (because the other mobile member  41   h  is similar), for example, the separation between its protrusions  41   g   1  and  41   g   2  is determined such that they can contact only the fixed electrodes  41   a  and  41   b  of the first group to connect their metallic conductors and also only the fixed electrodes  41   b  and  41   c  of the first group to connect their metallic conductors. 
     It may be reminded at this point that these mobile members  41   g  and  41   h  need not be made entirely of a metallic material of a high conductivity and strong against frictional wears. What is essential is that each be capable of moving in the direction of the line  44  so as to contact only the fixed electrodes  41   a  and  41   b  of the first group (in the case of mobile member  41   g ) to connect their metallic conductors and also only the fixed electrodes  41   b  and  41   c  to connect their metallic conductors. Thus, it is sufficient for this purpose if the two protrusions on each of the mobile members  41   g  and  41   h  are made of a friction-resistant metallic material with a high conductivity either entirely or on the contacting surfaces and if these two protrusions are electrically connected. 
     The two mobile members  41   g  and  41   h  are adapted to move to left and right in the direction of the line  44  while remaining parallel to each other as shown in  FIG. 1  by the operation of the aforementioned operating element  43 . 
     With the first switch element  41  thus structured as explained above, if its two mobile members  41   g  and  41   g  are in their neutral positions as shown in  FIG. 1 , the protrusions  41   g   1  and  41   g   2  of the mobile member  41   g  contact the fixed electrodes  41   b  and  41   c  of the first group to connect their conductors together in a closed condition and the protrusions  41   h   1  and  41   h   2  of the other mobile member  41   h  contact the fixed electrodes  41   e  and  41   f  to connect their conductors together in a closed condition. In other words, the fixed electrodes  41   a  and  41   b  of the first group and the fixed electrodes  41   d  and  41   e  of the second group can be kept in an open condition with respect to each other. 
     If the mobile member  41   g  is moved from the neutral position to right with reference to  FIG. 1 , its protrusions  41   g   1  and  41   g   2  come to contact the fixed electrodes  41   a  and  41   b  of the first group to connect their conductors in a closed condition. In this situation, the fixed electrodes  41   b  and  41   c  are switched into an open condition. At the same time, the other mobile member  41   h  is caused to move from its neutral position to right with reference to  FIG. 1  but its protrusions  41   h    1  and  41   h   2  keep the fixed electrodes  41   f  and  41   e  of the second group in the closed condition. 
     Similarly, when the mobile member  41   h  is moved from its neutral position to left with reference to  FIG. 1 , its protrusions  41   h   1  and  41   h   2  come to contact the fixed electrodes  41   d  and  41   e  of the second group to connect their conductors in a closed condition. In this situation, the fixed electrodes  41   e  and  41   f  of the second group are switched into an open condition. At the same time, the other mobile member  41   g  is caused to move from its neutral position to left with reference to  FIG. 1  but its protrusions  41   g   1  and  41   g   2  keep the fixed electrodes  41   c  and  41   b  of the first group in the closed condition. 
     Circle portion C of  FIG. 1  shows the circuit structure of the first switch element  41 . In this circuit diagram, the mobile members  41   g  and  41   h  and the fixed electrodes  41   b  and  41   e  correspond to the two moving contacts described above in the Background section. The fixed electrodes  41   a  and  41   d  correspond to the NO contacts and the fixed electrodes  41   c  and  41   f  correspond to the NC contacts. 
     When the mobile members  41   g  and  41   h  are in their neutral positions as shown in  FIG. 1 , the NC contacts ( 41   c  and  41   f ) are in the closed condition. If the mobile member  41   g  moves from its neutral position to right along the line  44 , the NC contact  41   c  is released from its closed condition and the NO contact  41   a  comes to be in the closed condition. If the other mobile member  41   h  moves to left from its neutral position along the line  44 , the NC contact  41   f  is released from its closed condition and the NO contact  41   d  comes to be in the closed condition. 
     In summary, this first switch element  41  functions like a switch of a two-circuit, four-contact type. If the centering positions of the mobile members  41   g  and  41   h  is adjusted to the aforementioned neutral positions shown in Table 1 by means of the operating element  43  to be described below, two ( 41   c  and  41   f ) of the four fixed electrodes  41   a ,  41   c ,  41   d  and  41   f  on both sides of this neutral position become the NC contacts and the remaining two ( 41   a  and  41   d ) become the NO contacts. 
     The second switch element  42  is formed on the same base board (not shown) on which is formed the first switch element  41  by mounting thereon two switch mechanisms of the same structure to be described below. 
     Explained more in detail, the second switch element  42  is comprised of U-shaped members  42   a  and  42   b  set on the aforementioned base board, mobile members  42   c  and  42   d  each in the form of a metallic plate spring and having one end supported by a corresponding one of the U-shaped members  42   a  and  42   b , moving contacts  42   e  and  42   f  attached to the other ends of the mobile members  42   c  and  42   d , reverse L-shaped members  42   g  and  42   h  set on the base board and fixed contacts  42   i  and  42   j  set on the downwardly facing end parts of the reverse L-shaped members  42   g  and  42   h.    
     The metallic plate spring-like mobile members  42   c  and  42   d  have cutout portions  42   k  and  42   m  which are bent so as to contact the U-shaped members  42   a  and  42   b . The elastic returning force of these cutout portions  42   k  and  42   m  is utilized so as to normally keep the moving contacts  42   e  and  42   f  on the other ends in contact with the fixed contacts  42   i  and  42   j  in closed conditions. Thus, the fixed contacts  42   i  and  42   j  function as normally closed (NC) contacts. 
     If a downward external force in excess of the elastic returning force of the cutout portions  42   k  and  42   m  is applied to the mobile members  42   c  or  42   d  through a corresponding one of push buttons  42   n  and  42   p  which are individually provided, the tip portions of the mobile members  42   c  and  42   d  move downward and the closed conditions between the moving contacts  42   e  and  42   f  and the fixed contacts  42   i  and  42   j  are released and open conditions are set between these contacts. 
     Circle portion D of  FIG. 1  shows the circuit structure of the second switch element  42 . In this circuit diagram, the two moving contacts  42   e  and  42   f  are in closed condition respectively with the fixed contacts (NC contacts)  42   i  and  42   j . If a downward external force is applied to the mobile member  42   c , the closed condition between the moving contact  42   e  and the fixed contact (NC contact)  42   i  is released and they come to be in the open condition. Similarly, if a downward external force is applied to the other mobile member  42   d , the closed condition between the moving contact  42   f  and the fixed contact (NC contact)  42   j  is released and they come to be in the open condition. 
     In summary, this second switch element  42  functions like a switch of the two-circuit, two-contact type, having a pair of NC contacts ( 42   i  and  42   j ). 
     The aforementioned operating element  43  is indicated by broken lines in  FIG. 1  for the convenience of disclosure and is characterized as having the following four functions: (1) the function of maintaining the first and second switch elements  41  and  42  in the neutral positions as shown in  FIG. 1  if there is no input from the operator (such as the operation on the knob  13  to the UP or DOWN condition as explained above); (2) the function of returning the first and second switch elements  41  and  42  to their neutral positions as soon as an input operation by the operator is released; (3) the function of moving one of the mobile members (such as the member  41   h ) of the first switch element  41  from the neutral position along the line  44  in one direction (such as to left with reference to  FIG. 1 ) and setting one of the NC contacts (such as the fixed contact  42   j ) of the second switch element  42  in the open condition in response to an operation of the operator (such as the UP operation); and (4) the function of moving the other of the mobile members (such as the member 41 g) of the first switch element  41  from the neutral position along the line  44  in the other direction (such as to right with reference to  FIG. 1 ) and setting the other of the NC contacts (such as the fixed contact  42   i ) of the second switch element  42 . 
       FIGS. 2 and 3  illustrate these functions of the operating element  43 . As shown in  FIG. 2 , the operating element  43  includes an operating means  43   a , which is structured similarly to the slider  28  described above with reference to  FIGS. 10–12  and slides to left or right with reference to  FIG. 1  along the line  44  as the knob  3  (also described above with reference to  FIGS. 10 and 12 ) is moved from the UP condition to the neutral condition to the DOWN condition or from the DOWN condition to the neutral condition to the UP condition. 
     As the operating means  43   a  is moved in one direction (such as to left with reference to  FIG. 1 ) along the line  44 , one of the mobile members of the first switch element  41  (say, for example, the mobile member  41   h ) is moved from its neutral position along the line  44  to left with reference to  FIG. 1  such that the fixed electrodes  41   d  and  41   e  come to be in the closed condition and the other NC contact of the second switch element  42  (say, for example, the fixed contact  42   j ) comes to be in the open condition. 
     If the operating means  43   a  slides further to left, the fixed contact  42   j  comes to be in the closed condition and the function of driving the DC motor for opening the window is established. In other words, it may be said that these participating contacts  41   h ,  41   d ,  41   e  and  41   j  together form a motor driving switch group for the UP condition (or the UP switch group). 
     If the operating means  43   a  is moved in the opposite direction (that is, to right with reference to  FIG. 1 ) along the line  44 , the other of the mobile members of the first switch element  41  (that is, the mobile member  41   g ) moves from its neutral position along the line to right such that the fixed electrodes  41   a  and  41   b  come to be in the closed condition and the other NC contact of the second switch element  42  (that is, the fixed contact  42   i ) comes to be in the open condition. 
     If the operating means  43   a  slides further to right, the fixed contact  42   i  comes to be in the closed condition and the function of driving the DC motor for closing the window is established. In other words, it may be said that these participating contacts  41   g ,  41   a ,  41   b  and  41   i  together form a motor driving switch group for the DOWN condition (or the DOWN switch group). 
     For the convenience of description, operations of the UP switch group (as one of the switch groups defined above) are explained with reference to  FIG. 3  wherein “X—X” and “Y—Y” indicate the sectional views taken respectively along the lines X—X and Y—Y shown in  FIG. 2 . Step 1 indicates the initial position in the neutral condition wherein the mobile member  41   h  of the first switch element  41  is located between the fixed electrodes  41   e  and  41   f  respectively at the center and on the right-hand side, keeping them in the closed condition. The push button  42   p  of the second switch element  42  is engaged in one of the indentations on the bottom surface of the operating means  43   a  and is in the raised condition. The metallic plate spring-like mobile member  42   d  is not bent downward and the moving contact  42   f  at the tip of this mobile member  42   d  is in the closed condition with the fixed contact  42   j.    
     Immediately after the operating means  43   a  begins to move to left from the condition of Step 1 to approach the UP condition (Step 2), the mobile member  41   h  of the first switch element  41  remains at the position in Step 1, keeping the fixed electrodes  41   e  and  41   f  in the closed condition but the push button  42   p  of the second switch element  42  is out of the indentation on the bottom surface of the operating means  43   a  and contacts the thick portion of the operating means  43   a . Since the push button  42   p  is thus being pressed downward, the mobile member  42   d  is bent downward and the closed condition between the moving contact  42   f  and the fixed contact  42   j  is released and they are now in the open condition. 
     As the UP condition progresses (Step 3), the mobile member  41   h  of the first switch element  41  is between the fixed electrodes  41   d  and  41   e  respectively on the right-hand side and at the center and keeps them in the closed condition while the fixed electrodes  41   e  and  41   f  are in the open condition. Since the push button  42   p  of the second switch element  42  is still at the thick portion of the operating means  43   a  and the mobile member  42   d  remains bent downward, the moving contact  42   f  at the tip of this mobile member  42   d  remains in the open condition with the fixed contact  42   j.    
     As the UP condition progresses still further (Step 4), the mobile member  41   h  of the first switch element  41  continues to be between the fixed electrodes  41   d  and  41   e  to keep them in the closed condition. The push button  42   p  of the second switch element  42  engages in the other indentation on the bottom surface of the operating means  43   a  and is in the raised position. The mobile member  42   d  returns to its horizontal position such that the moving contact  42   f  at the tip of this mobile member  42   d  is in the closed condition with the fixed contact  42   j.    
     Operations from the neutral condition to the DOWN condition is similar to those from the neutral condition to the UP condition described above and may be described by making the following replacements of symbols in the description of the operations from the neutral condition to the UP condition given above:  41   h → 41   g ,  41   d → 41   a ,  41   e → 41   b ,  41   f → 41   c ,  42   d → 42   c ,  42   j → 42   i ,  42   f → 42   e  and  42   p → 42   n.    
     There are shown in  FIG. 4  (comprised of  FIGS. 4A ,  4 B,  4 C and  4 D) circuit diagrams of a system for rotating (in both positive and negative directions) and stopping a DC motor for opening and closing an automobile window by incorporating the switch device  40  embodying this invention. In  FIG. 4 , the +B line  17  serves as the power (voltage) source on the positive electrode side (or the +B line of the electrical system for a vehicle) and the grounding line  18  serves as the power (voltage) source on the negative electrode side (or the grounding line for the system) but they are distinguishable from prior art systems wherein the voltage applied through the +B line  17  is higher (say, a source voltage of 36V for a 42V electrical system) than that in the case of a 14V electrical system. 
       FIG. 4A  shows the circuit when the system is in the DOWN condition,  FIG. 4D  shows the moment when the system has returned from the DOWN condition to the neutral condition and  FIGS. 4B and 4C  show the system at moments in between. When the system is in the DOWN condition, each of the contacts of the first and second switch elements  41  and  42  is in the condition of Step 4 shown in  FIG. 3 , that is, the mobile member  41   g  and the NO contact  41   a  of the first switch element  41  are in the closed condition, the mobile member  41   h  and the NC contact  41   f  are in the closed condition and the two NC contacts  42   i  and  42   j  of the second switch element  42  are in the closed condition. Thus, the voltage (such as +42V) of the +B line  17  is applied to one input terminal of the DC motor  2  while the ground voltage (0V) of the grounding line  18  is applied to the other input terminal of the DC motor  2 , causing the DC motor  2  to rotate in the direction of opening the window. 
     If the system is released from the DOWN condition described above (say, by releasing the finger from the knob  3  referenced above), the circuit comes to appear as shown in  FIG. 4B , that is, the two NC contacts  42   i  and  42   j  of the second switch element  42  comes to be in the open condition while the contacts of the first switch element  41  remain in the same conditions as before such that the DC motor  2  becomes disconnected from the grounding line  18 . 
     Next, the condition as shown in  FIG. 4C  is reached wherein the closed condition between the mobile member 41 g and the NO contact  41   a  of the first switch element  41  is released and the mobile member  41   g  and the NC contact  41   c  come to be in the closed condition while the two NC contacts  42   i  and  42   j  of the second switch element remain in the open condition. Finally as the condition as shown in  FIG. 4D  is reached thereafter, the two NC contacts  42   i  and  42   j  of the second switch element  42  come to be in the closed condition and the both input terminals of the DC motor  2  become connected to the grounding line  18  such that the rotation of the DC motor  2  is stopped. 
     As explained above, the problem with prior art technology was that a large current flows through contacts when the DC motor is switched from the UP condition to the neutral condition or from the DOWN condition back to the neutral condition by switching contacts and that damages are frequently caused to the contacts due to such a large current flowing therethrough. According to the embodiment of the invention described above, the second switch element  42  is set in the open condition such that the flow route of such a large current is broken before or simultaneously as contacts of the first switch element  41  are switched. Thus, a large current is prevented from flowing through the contacts and damages thereto can be averted. Although two NC contacts are employed and this tends to increase the width, the switch device  40  need not be made larger to any significant degree and the response characteristics are not adversely affected since the contact gaps need not be increased. Since the second switch element  42  is realized with two NC contacts, furthermore, the space for the NO contacts may be utilized for increasing the contact gaps. 
     Although an embodiment has been described wherein the second switch element  42  was of the two-circuit, two-contact type, this may be realized with a one-circuit, one contact type, as shown in  FIG. 5 . The circuit shown in  FIG. 5  is different from the one described above wherein the two NC contacts  41   c  and  41   f  of the first switch element are joined together within the switch and connected together through a single NC contact ( 42   i  or  42   j ) to the grounding line  18 . 
     As a second example, a second switch element  42  of a two-circuit, two-contact type may be connected to the side of the positive voltage source, as shown in  FIG. 6 . The circuit shown in  FIG. 6  is different wherein the mobile member  42   e  and NC contact  42   i  of the second switch element  42  are inserted between the NO contact  41   a  of the first switch element  41  and the +B line  17  and the other mobile member  42   f  and the other NC contact  42   j  of the second switch element  42  are inserted between the other NO contact  41   d  of the first switch element and the +B line  17 . 
     The second switch element  42  of  FIG. 6  may be formed as a one-circuit, one contact type, as shown in  FIG. 7 . The circuit shown in  FIG. 7  is different wherein the two NC contacts  41   c  and  41   f  of the first switch element  41  are joined together within the switch and connected together through a single NC contact ( 42   i  or  42   j ) to the +B line  17 . 
     When either of the circuits as shown in  FIGS. 6 and 7  is used, the NC contact  42   i  or  42   j  is set in the open condition before either of the NO contacts  41   a  and  41   d  of the first switch element  41  is switched from the closed condition to the open condition. Since the route for a large current is thereby broken such that damages to the contacts in the first switch element  41  can be prevented and there is no need to increase the contact gaps, the size of the switch device does not increase and its response characteristics are not adversely affected. 
     As a further variation, the first switch element  41  may be of a four-circuit, four-contact type, as shown in  FIG. 8 . The circuit shown in  FIG. 8  is different wherein the two NC contacts  41   c  and  41   f  of the first switch element  41  are dispensed with and wherein the input terminals of the DC motor  2  are made selectively connectable to the +B line  17  through the two NO contacts  41   a  and  41   d  of the first switch element  41  and to the grounding line  18  through the two NC contacts  42   i  and  42   j  of the second switch unit  42 . In order to prevent damages to the NO contacts  41   a  and  41   d  of the first switch element  41 , the NC contacts  42   i  and  42   j  of the second switch element  42  connected to these NO contacts may be set in the open condition. 
     In all of the variations described above, the first and second switch elements  41  and  42  were represented as forming a single unit together but this is not intended to limit the scope of this invention.  FIG. 9  shows an example of this invention having a first unit  51  containing the first switch element  41  and a second unit containing the second switch element  42 , arranged next to each other. Numeral  50  indicates a knob, which is an equivalent of the knob  3  described above with reference to  FIGS. 10 and 12 , provided with two indentations  50   a  and  50   b  adapted to engage switch operating parts of the first and second units  51  and  52 , respectively (a protrusion  51   b  on a slider  51   b  of the first unit  51  and a protrusion  52   a  for the operation of the second unit  52 ). 
     As should be clear from the description of the embodiments of the invention, the route of the instantaneous flow of a large current can be broken by opening the contacts of the second switch element at an appropriate timing such that damages to the contacts in the first switch element can be prevented. Thus, the inconvenience of prior art technology when a high source voltage such as a 42V electrical system is used on a vehicle can be eliminated. Since the new technology according to this invention does not required any increase in the contact gaps, the switch unit does not become large and the response characteristics are not adversely affected.