Abstract:
An electromagnetic switch of an engine starter includes a pair of stationary contacts connectable to a starter motor, a movable contact disposed at a first distance from the pair of stationary contacts; a rod having one end that slidably supports the movable contact via an insulating member and a stopper that restricts axial movement of said movable contact, an electromagnetic coil unit that includes a plunger, a stator core, a spring that urges the movable contact against the stopper and an exciting coil which moves the rod by the plunger a second distance when excited, and an inclination rectifying member, disposed near the stationary contacts, for providing a rectifying surface disposed at a third distance from the movable contact to abut the movable contact when one of the stationary contacts wears to a preset degree. There is the following relationship between the first, second and third distances: the second distance&gt;the third distance&gt;the first distance.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   The present application is based on and claims priority from Japanese Patent Application 2003-337999, filed Sep. 29, 2003, the contents of which are incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an electromagnetic switch of an engine starter to be mounted in a vehicle. 
   2. Description of the Related Art 
   An engine starter for a vehicle usually includes an electromagnetic switch that turns on or off a power circuit for supplying electric power to a starter motor. JP-A-2003-35241 or U.S. 2002/0145494, a counter part of application, discloses such an electromagnetic switch, which includes a pair of bolt-like external terminals each having stationary contact at its inner end, a rod carrying a movable contact at its one end, a cylindrical exciting coil, a stationary care disposed inside the cylindrical exciting coil at one end thereof, a plunder disposed inside the cylindrical exciting coil at the other end thereof and coup springs disposed around the rod to exert spring force on the plunger. There movable contact us supported by the rod via an insulating member. When the exciting coup of the above electromagnetic switch is energized, the stationary core is magnetized to pull the plunder. As the plunger moves, the movable contact of the rod is brought in contact with the stationary contacts, so that the stationary contacts are electrically connected to close the power circuit. 
   If the exciting coil is deenergized thereafter, the plunger and the rod are pushed back by the coil springs, so that the movable contact leaves the stationary contacts to open the power circuit. 
   When the movable contact leaves the stationary contacts, an electric arc or a spark is generated and may cause damage or wear on the movable and stationary contacts. The wear of the stationary contacts, especially the wear of the positive side stationary contact is larger than others. Therefore, there arises a difference in height between the positive stationary contact and the negative stationary contact. Accordingly, the movable contact inclines when it contacts the stationary contacts, so that an offset load may be applied to the insulating member that is disposed between the movable contact and the rod. If the movable contact inclines much, the offset load may increase to a degree to break the insulating member. This problem may arise in case a vehicle is equipped with a system of engine-stopping-at-idling-operation (hereinafter referred to as the idling stop system), which stops an engine of a vehicle each time the vehicle temporarily stops at a traffic light or the like. 
   SUMMARY OF THE INVENTION 
   Therefore, the present invention is to provide an improved electromagnetic switch of an engine starter that can prevent the moving contact from inclining. 
   According to a main feature of the invention, an electromagnetic switch of an engine starter includes a pair of stationary contacts connectable to a starter motor, a movable contact disposed at a distance L2 from the pair of stationary contacts, a rod having one end that slidably supports the movable contact via an insulating member and a stopper that restricts axial movement of the movable contact, an electromagnetic coil unit that includes a plunger that moves the rod, a stator core, a spring that urges the movable contact against the stopper and an exciting coil that moves the plunger toward the stator core and moves the rod by a distance L 1  in an axial direction when excited, and an inclination rectifying member, disposed near at least one of the stationary contacts, for providing a rectifying surface at a distance L 3  from the movable contact to abut the movable contact when the same one of the stationary contact wears to a preset degree. In the above electromagnetic switch, the distances L 1 , L 2  and L 3  have the following relationship: L 1 &gt;L 3 &gt;L 2 . 
   According to another feature of the invention, the above electromagnetic switch further includes a resinous contact cover that accommodates the pair of stationary contacts and the movable contact therein, and the rectifying member is integrated with the contact cover. 
   According to another feature of the invention of the above electromagnetic switch, the rod is fixed to the plunger so that the rod and the plunger can move together. However, the rod may be linked with the plunger so that the rod and the plunger can move together after the plunger moves by a predetermined distance. 
   According to another feature of the invention, the above electromagnetic switch may further includes a sensor that provides a warning signal when the movable contact inclines to a predetermined degree. The sensor may be a pressure sensor or a temperature sensor that is disposed at a portion between the movable contact and the rectifying member. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects, features and characteristics of the present invention as well as the functions of related parts of the present invention will become clear from a study of the following detailed description, the appended claims and the drawings. In the drawings: 
       FIG. 1  is a cross-sectional longitudinal side view of an electromagnetic switch according to the first embodiment of the invention when the movable and stationary contacts thereof are opened; 
       FIG. 2  illustrates a power circuit and a starter motor on which the electromagnetic switch is mounted; 
       FIGS. 3A ,  3 B,  3 C,  3 D and  3 E illustrates variations of an inclination rectifying member that surrounds one of the stationary contacts; 
       FIG. 4  is a cross-sectional longitudinal side view of the electromagnetic switch according to the first embodiment when the movable and stationary contacts are closed; and 
       FIG. 5  is a cross-sectional longitudinal side view of the electromagnetic switch according to the second embodiment when the movable and stationary contacts are opened; 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   An electromagnetic switch according to the first embodiment of the invention that is to be mounted on a starter motor  2 , which is shown in  FIG. 2 , will be described with reference to  FIGS. 1-4 . 
   As shown in  FIG. 1 , the electromagnetic switch  1  has a pair of external electric terminals  3 ,  4 , a pair of stationary contacts  5   a ,  5   b  each of which is integrated with one of the external electric terminals  3 ,  4 , a movable contact  6 , disposed opposite the stationary contacts  5   a ,  5   b , a rod  8  which carries the movable contact  6  at one end via an insulating member  7 , an electromagnetic coil unit  9  that pushes the rod  8  when energized and others. 
   As shown in  FIG. 2 , the terminal  3  is connected to the positive terminal of a battery  11  via a battery cable  10 , and the terminal  4  is connected to the starter motor  2  via a motor lead wire  12 . Accordingly, the stationary contact  5   a  becomes positive, and the stationary contact  5   b  becomes negative when the terminals  3  and  4  are respectively connected to the battery  10  and the starter motor  2 . Both terminals  3  and  4  are fixed to a bottom of a cylindrical resinous contact cover  13 , which is fixed to the electromagnetic coil unit  9 . 
   The movable contact  6  is a conductive disk plate that has a center hole. The movable contact  6  is carried by the one end of the rod  8  via the insulating member  7 . The insulating member  7  is comprised of a flanged cylindrical member  7   a  inserted in the center hole of the movable contact  6  and a ring member  7   b  that covers the central portion of the movable contact  6  on the side thereof confronting the stationary contacts  3 ,  4 . 
   The rod  8  has an annular groove at the one end and a stopper or a circlip  16  that is fitted to the annular groove. The stopper  16  and the insulation member  7  fix the movable contact  6  in the axial direction. A contact spring  17  is disposed on the periphery of the rod  8  at the side of the movable contact behind the stopper  16  to urge the movable contact  6  via the insulating member  7  toward the stopper  16 . 
   The electromagnetic coil unit  9  includes a plunger  15 , an exciting coil  19 , a stationary magnetic path member disposed around the exciting coil  19 . The plunger  15  is disposed within the exciting coil  19  and has a cavity at its central portion, to which the other end of the rod  8  is force-fitted so that the rod can move together with the plunger  15 . The stationary magnetic path member includes a cup-like cylindrical frame  22 , a ground disk plate  23 , a cylindrical stator core  24  and a bracket plate  25 . The stationary magnetic path member provides a magnetic path to conduct magnetic flux generated by the exciting coil  19 . 
   The electromagnetic switch  1  is designed, when the exciting coil  19  is not energized, so that a rod-moving distance L 1  between plunger  15  and the stator core  24  is larger than a contact distance L 2  between the movable contact  6  and the stationary contacts  5   a ,  5   b , that is L 1 &gt;L 2 . 
   The resinous contact cover  13  has a cylindrical outer member  13   a , a cylindrical inner wall member  13   b  and an inclination rectifying member  14  that is integrally formed on an axial end of the inner wall member  13   b.    
   The rectifying member  14  is an insulating member disposed within a reach of the movable contact  6  inside the contact cover  13 . The rectifying member  14  projects in the axial direction of the contact cover  13  from the inner wall  13   b  along the inner side of the stationary contacts  5   a ,  5   b  to surround an end portion of the rod  8 . In other words, the rectifying member  14  is disposed inside the contact cover  13  between the axis line of the rod  8  and the stationary contacts  5   a ,  5   b  so that the inner axial end surface of the rectifying member  14  comes radially inner side of the stationary contacts  5   a ,  5   b  and comes axially at a distance L 3  from the surface of the movable contact  6 , with L 3  being the following relationship: L 1 &gt;L 3 &gt;L 2 . The rectifying member  14  is formed to abut or surround the stationary contact  5   a , or  5   b , which may be square, rectangular or round, as shown in  FIGS. 3A-3E . 
   The exciting coil  19  includes a pulling coil  19   a , a holding coil  19   b , a sleeve  20  and a bobbin  21  that accommodates the pulling coil  19   a  and the holding coil  19   b  in two layers. The sleeve  20  is disposed between the bobbin  21  and the plunger  15 . The cylindrical frame  22  accommodates the exciting coil  19 . 
   The ground disk plate  23  has a center hole to which an end of the stator core  24  is fitted to magnetically connect to the ground disk plate  23 . The cylindrical frame has an open end to which the outer periphery of the ground disk plate  23  is clamped and a bottom end to which the bracket plate  25  is fixed. The bracket plate  25  is to be fixed to a starter body, which is not shown. 
   The plunger  15 , which is a movable magnetic core that composes a part of a magnetic circuit, is disposed inside the cylindrical sleeve  20  to confront the stator core  24  and urged by a return spring  26  in the direction opposite to the stator core  24 . The plunger  15  is pulled by the stator core  24  and sticks to the same when the exciting coil  19  is energized to magnetize the stator core  24 . On the other hand, the plunger  15  is pushed by the return spring  26  in the direction opposite to the stator core  24  when the exciting coil  19  is deenergized. 
   Therefore, when the plunger  15  is pulled together with the rod  8 , the movable contact  6  contacts the pair of stationary contacts  5   a ,  5   b  before the rod  8  stops or the plunger  15  abuts the stator core  24 , as long as the electromagnetic switch  19  is new. In other words, the rod  8  keeps moving after the movable contact  6  contacts the stationary contacts  5   a ,  5   b , so that the movable contact  6  starts compressing the contact spring  17  and moves back relative to the rod  8 . Therefore, the contact spring  15  absorbs or relieves the impacting shock of the movable contact  6 , and the reaction force of the contact spring  15  is applied to the stationary contact  5   a ,  5   b  as contact pressure. 
   The electromagnetic switch  1  operates as follows. 
   When the starter switch  18  is turned on, the exciting coil  19  is energized to magnetize the stator core  24  and the plunger  15 , so that the plunger  15  is pulled by the stator core  24 . Consequently, the rod  8  moves right in  FIG. 1 , and the movable contact  6  contacts the pair of the stationary contacts  5   a ,  5   b . Thereafter, the rod  8  further moves right so that the contact spring  17  can accumulate a reaction force until the plunger  15  abuts the end surface of the stator core  24 . This reaction force provides a contact pressure between the movable contact  6  and the pair of stationary contacts  5   a ,  5   b , so that the stationary contact  5   a  and the stationary contact  5   b  are connected to close the power circuit of the starter motor  2 . As a result, starting current is supplied from the battery  11  to the starter motor  2 . 
   When an engine has started, the starter switch  18  is turned off to cut the current supplied to the exciting coil  19 . Accordingly, the pulling force exerted between the stator core  24  and the plunger  15  disappears, so that the plunger  15  is returned by the return spring  26 . Consequently, the rod  8  moves left in  FIG. 1 , so that the movable contact  6  leaves the pair of stationary contacts  5   a ,  5   b . As a result, the power circuit of the starter motor  2  is opened, and the electric supply of the starter motor  2  stops. 
   After the above operation is repeated many times, the positive side stationary contact  5   a  wears more than the negative side contact  5   b , so that the movable contact  6  may incline when it contacts the pair of stationary contacts  5   a ,  5   b . However, when the positive side contact  5   a  wears and its height (axial length) decreases to a preset level, the movable contact  6  abuts the rectifying member  14  disposed near the positive side contact  5   a , as shown in FIG.  4 . Therefore, further inclination of the movable contact  6  can be prevented. 
   Even if the stationary contact  5   a  wears out, the final distance L 4  between the movable contact  6  and the stationary contact  5   a  will not become longer than L 3 . Therefore, the moving distance of the rod  8 , which is the rod-moving distance L 1 , is always longer than L 4 . That is, the rod  8  moves by the rod-moving distance L 1  when the exciting coil  19  is energized, the movable contact  6  moves backward relative to the rod  8  by a distance ΔL=L 1 −L 4 . Therefore, a reaction force is accumulated by the contact spring  17 , so that the contact pressure between the movable contact  6  and the pair of stationary contacts can be always provided. 
   When electric supply to the exciting coil  19  is stopped, the plunger  15  and the rod  8  are pushed back. The movable contact  6  leaves the stationary contacts  5   a ,  5   b  after the rod  8  has moved back by the distance Δ L when the stopper or circlip  16  collides with the insulation ring member  7   b . This impacting shock is effective for the movable contact  6  to leave the stationary contacts  5   a ,  5   b . Thus, even if the positive side contact  5   a  has worn away to be as high as the rectifying member  14 , the movable contact  6  can surely leave the stationary contact  5   a  whenever the starting switch  18  is turned off. 
   The rectifying member  14 , which is unitary formed with the contact cover  13 , can be separately provided. 
   An electromagnetic switch  1  according to the second embodiment of the invention will be described with reference to FIG.  5 . 
   Although the plunger  15  has a cavity at its central portion, the left end of the rod  8  is disposed at a distance L 5  right from the plunger  15  and is not fixed to the plunger  15  as in the first embodiment. Therefore, the rod does not move together with the plunger  15  until the plunger  15  is driven to move right by a distance L 5 . That is, the rod  8  moves a rod-moving distance L 1  while the plunger moves a plunger-moving distance Lp that is L 5  longer than L 1 . This embodiment has another spring  27  that pushes the rod  8  against the right end thereof when the exciting coil  19  is deenergized. The rectifying member  14  is provided in the same manner as the first embodiment. 
   An inclination sensor may be disposed at the surface of the rectifying member  14 . The inclination sensor may be comprised of a pressure sensor such as a piezoelectric sensor. When the stationary contact  5   a  wears, the movable contact  6  abuts the pressure sensor, which provides a warning signal. 
   The inclination sensor may be comprised of a temperature sensor that senses heat generated at the movable contact  6 . As the stationary contact  5   a  wears more, the gap between the stopper  16  and the insulation ring member  7   b  becomes smaller. This decreases the reaction force of the contact spring  17  and increases the electric resistance of contact between the movable contact  6  and the stationary contacts  5   a ,  5   b , resulting in that Joule heat increases to rise temperature of the movable contact  6 . Thus, the warning signal is provided by the temperature sensor. 
   In the foregoing description of the present invention, the invention has been disclosed with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made to the specific embodiments of the present invention without departing from the scope of the invention as set forth in the appended claims. Accordingly, the description of the present invention is to be regarded in an illustrative, rather than a restrictive, sense.