Abstract:
A forced return solenoid that includes an electrical winding configured to create an electromagnetic field when electrical current flows through the winding, an electrical terminal configured to be connected to a source of electrical energy, and a moveable contact plate configured to be moved into contact with the electrical terminal. Embodiment of the forced return solenoid include a plunger configured to move axially in response to the electromagnetic field generated by the electrical winding. Movement of the plunger in one direction causes the moveable contact plate to connect with the electrical terminal. Movement of the plunger in the opposite direction causes an impact intended to break the connection between the moveable contact plate and the electrical terminal. Embodiments of the forced return solenoid further include a return spring configured to move the plunger in the second direction, wherein the impact means comprises a removable snap ring affixed to the plunger.

Description:
FIELD OF THE INVENTION 
     This invention generally relates to electrical components for a vehicle, and, more specifically, to starter motors used in the ignition system of a vehicle. 
     BACKGROUND OF THE INVENTION 
     Generally, internal combustion engines require the pistons to be moving before ignition can commence. Typically, this means that the engine must be set in motion by some external force before the engine can power itself via combustion of fuel. Most vehicles employ an electric starter to set the engine in motion, thereby allowing ignition to take place. 
     An electric starter motor is often used to crank internal combustion engines prior to ignition. Typically, the electric starter consists of three main assemblies: 1) the solenoid switch that ensures axial movement of the plunger within the electrical coils of the switch, and, therefore, the subsequent engagement and disengagement of a pinion into a ring gear through an engagement lever, and also establishing and breaking of the electrical contacts, which enables transmission of electric energy from the battery to the electric motor part of the starter; 2) a DC electric motor, which transform electrical power into the mechanical rotating power that is required to crank the internal combustion engine; and 3) a mechanical transmitter which consists of a reduction gear, clutch, and a pinion, and is used to transmit the rotating power from the electrical motor to the internal combustion engine. 
     A typical starter for a vehicle may include a DC electric motor with a solenoid switch that is activated upon the closing of an ignition switch. When a driver turns an ignition key or presses a start button that closes the ignition switch, an electrical current is supplied from the battery to the solenoid windings. Typically, this causes a drive pinion on the starter driveshaft to mesh with a ring gear on the flywheel of the engine. The solenoid assembly, which has an electrical winding, electrical terminals, and high-current contacts, acts to close the high-current contacts for the starter&#39;s DC electric motor after the drive pinion engages the ring gear, thus connecting the battery to the electric motor and causing the electric motor to turn. The meshing of the pinion to the flywheel ring gear means that the rotating DC electric motor causes the vehicle engine to rotate as well. Generally, after the engine starts, the ignition switch opens, and a return spring in the solenoid assembly pulls the pinion gear away from the ring gear, and the starter&#39;s electric motor stops. 
     Occasionally, the switching of the starter motor current on and off results in a partial welding or fusing of the high-current contacts and the electrical terminals due to electrical arcing between the high-current contacts and the contact plate. Typically, the solenoid assembly return spring has enough force to mechanically break this partial fusing of contact and terminal. However, occasionally, the return spring force is insufficient, and the solenoid&#39;s high-current contacts can become welded in the closed position to a contact plate. This causes the starter&#39;s DC electric motor to maintain its connection to the vehicle battery even after the engine is running, and the starter will remain energized after the vehicle operator has released the ignition switch. Consequently, the starter motor will continue to run even after the vehicle engine is running on its own and the pinion has disengaged from the ring gear. As a result of the welded contact plate and terminals, it is possible that the starter motor could continue to run after the engine is turned off. In this case, the continuous usage of electrical energy by the starter motor may cause the battery&#39;s charge to be depleted prematurely. In any case, continuous operation of the starter motor caused by welded contact plate and terminals, will likely result in the overheating and premature failure of the starter motor, leading to increased maintenance costs for the vehicle owner and a potential for premature replacement of the affected components. 
     It would therefore be desirable to have a solenoid assembly with a mechanism for reducing the likelihood of high-current contact plate becoming welded to the electrical terminals. Embodiments of the invention provide such a solenoid assembly. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein. 
     BRIEF SUMMARY OF THE INVENTION 
     In one aspect, embodiments of the invention provide a forced return solenoid that includes an electrical winding configured to create an electromagnetic field when electrical current flows through the winding, an electrical terminal configured to be connected to a source of electrical energy, and a moveable contact plate configured to be moved into contact with the electrical terminal. Embodiments of the forced return solenoid include a plunger configured to move axially in response to the electromagnetic field generated by the electrical winding. Movement of the plunger in one direction causes the moveable contact plate to connect with the electrical terminal. Movement of the plunger in the opposite direction causes an impact intended to break the connection between the moveable contact plate and the electrical terminal. Some embodiments of the forced return solenoid further include a return spring configured to move the plunger in the second direction, wherein the plunger impacts the moveable contact via a removable snap ring affixed to the plunger. 
     In another aspect, embodiments of the invention provide a method of operating a solenoid assembly used in a vehicle starting system. In an embodiment of the invention, this method includes the steps of mechanically biasing a moveable contact plate away from an electrical terminal such that the moveable contact plate and electrical terminal are physically separated. In this embodiment, the method further includes and mechanically biasing a moveable plunger away from the moveable contact plate such that the moveable plunger and the moveable contact plate are physically separated. Some embodiments of the method further include the steps of generating an electromagnetic field configured to overcome the bias on the moveable contact plate, and to overcome the bias on the moveable plunger in order to bring the moveable contact plate into contact with the electrical terminal, and attaching a removable snap ring to the moveable plunger. In an embodiment of the invention, the removable snap ring is configured to transfer kinetic energy from the moveable plunger to the moveable contact plate. 
     Other aspects, objectives and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention and, together with the description, serve to explain the principles of the invention. In the drawings: 
         FIGS. 1A and 1B  are cross-sectional views of a starter system incorporating a forced return solenoid assembly, constructed in accordance with an embodiment of the invention; and 
         FIG. 2  is a cross-sectional view of the forced return solenoid assembly shown in  FIG. 1 ; 
         FIG. 3  is a cross-sectional view of the forced return solenoid assembly shown in  FIG. 2 , showing the movement of the plunger and contact plate after the solenoid winding has been energized; and 
         FIG. 4  is a cross-sectional view of the forced return solenoid assembly shown in  FIG. 2  showing the electric contact plate partially fused to the electrical terminals. 
     
    
    
     While the invention will be described in connection with certain preferred embodiments, there is no intent to limit it to those embodiments. On the contrary, the intent is to cover all alternatives, modifications and equivalents as included within the spirit and scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1A and 1B  illustrate a cross-sectional view of a starter system  100  incorporating a forced return solenoid assembly  105 , constructed in accordance with an embodiment of the invention. In operation, starter motor system  100  works to start the internal combustion engine (not shown), of a vehicle for example, using a DC electric motor  101  that is connected through a reduction gear (not shown) with gear shaft  102 . In this embodiment, the gear shaft  102  includes a slipping clutch and pinion  103 . The DC motor  101  is mounted on a front drive end bracket  104  on which is mounted to the forced return solenoid assembly  105 . A plunger  106  is configured to move axially within a housing  111  of the forced return solenoid assembly  105 . The axial movement of the plunger is  106  is transferred to the slipping clutch and pinion  103  through an engagement lever  107 . A central portion of the engagement lever  107  is coupled to a pin  119 , such that the engagement lever  107  is configured to rotate around the pin  119 . Movement of the plunger  106  in one direction causes movement of the slipping clutch and pinion  103 , via the engagement lever  107 , in the opposite direction. For example, movement of the plunger  106  to the left causes the engagement lever  107  to move the slipping clutch and pinion  103  to the right. Conversely, movement of the plunger  106  to the right causes the engagement lever  107  to move the slipping clutch and pinion  103  to the left towards the engine ring gear  109 . 
     In an embodiment of the invention, the operator triggers the command to crank the internal combustion engine using an ignition key. In this way, power is supplied to electrical terminal  115  when the driver turns the ignition key. The current runs to the pull-in and hold-in winding  114  of the forced return solenoid assembly  105 , which results in the generation of an electromagnetic field within the pull-in and hold-in winding  114 . 
       FIG. 2  is a cross-sectional view of the forced return solenoid assembly  105  shown in  FIGS. 1A and 1B . The forced return solenoid assembly  105  includes a housing  111 , which is also the carrying body of the forced return solenoid assembly  105 . Within the housing  111  of the solenoid assembly  105  there is the solenoid coil, also known as the pull-in and hold-in winding  114 . The plunger  106  has a plunger handle  113  whose reciprocal movement, in turn, moves the slipping clutch and pinion  103  (shown in  FIG. 1A ) via the engagement lever  107  (shown in  FIG. 1A ). The plunger  106  is free to move axially within the cylindrical space inside the pull-in and hold-in winding  114 . 
     In an embodiment of the invention, a cylindrical rod  112  is disposed in a central opening  126  within the plunger  106 . The cylindrical rod  112  has a longitudinal axis that coincides with a longitudinal axis  125  of the solenoid assembly  105 . A side plate  123 , disposed within the housing  111 , and abuts an electrical contact plate  116 . The side plate  123  has a central opening  128  to accommodate the cylindrical rod  112 . The electrical contact plate  116  has an opening  129  to accommodate the cylindrical rod  112 , and abuts a flange  134  on the cylindrical rod  112 . In an alternate embodiment, the flange  134  is a lock washer, nut or similar device attached to the cylindrical rod  112 . As will be shown below, the presence of the attached flange  134  allows for compression of a second coil spring  118 , when the plunger  106  moves toward the electrical terminals  115 . 
     When the pull-in and hold-in winding  114  is not energized, the side plate  123  is normally separated from the plunger  106 . In this embodiment, a first coil spring  110  is assembled onto the cylindrical rod  112  between the plunger  106  and the side plate  123 . In at least one embodiment of the invention, the first coil spring  110  extends from a stopping ring  121 , affixed to the cylindrical rod  112 , to the side plate  123 . The second coil spring  118  is positioned at one end of the cylindrical rod  112  between the cylindrical rod  112  and the terminal cover  124  at the end of the housing  111  that holds the electrical terminals  115 . One end of the second coil spring  118  abuts the flange  134  on the cylindrical rod  112 . The terminal cover  124  is configured to protect the contact and terminal area against the ingress of water and solid impurities that might degrade the performance of the solenoid assembly  105 . A third coil spring  120  is positioned along the cylindrical rod  112  and acts as a contact reserve, and, as such, is configured to ensure good contact between the electrical contact plate  116  and the electrical terminal  115  in case of shifting tolerances related to the assembly process, or in case of contact wear. In contrast, the first coil spring  110  is configured to separate, or bias, the plunger  106  away from the side plate  123 , and the second coil spring  118  is configured to separate, or bias, the electrical contact plate  116  and the cylindrical rod  112  away from the electrical terminals  115 . 
       FIG. 3  illustrates a cross-sectional view of the forced return solenoid assembly  105  showing the movement of the plunger  106  and electrical contact plate  116  after the pull-in and hold-in winding  114  has been energized. In operation, the forced return solenoid assembly  105  is energized by electrical current supplied to the pull-in and hold-in winding  114 . The plunger  106  is made of a ferromagnetic material such that the electromagnetic forces generated by the pull-in and hold-in winding  114  will cause the plunger  106  to move axially within the winding  114 . Referring to  FIG. 1B , energizing the pull-in and hold-in winding  114  moves the plunger  106  to the right. As a result, the engagement lever  107  moves to the left bringing the slipping clutch and pinion  103  into contact with the engine&#39;s ring gear  109  (shown in  FIG. 1B ). As shown in  FIG. 2 , when the plunger  106  moves to the right, it compresses the first coil spring  110 , the second coil spring  118 , and the third coil spring  120 . The electromagnetic forces generated by the pull-in and hold-in winding  114  must be stronger than the opposing force of the first coil spring  110 , second coil spring  118 , and third coil spring  120  to bring the plunger  106  into contact with the side plate  123 . In at least one embodiment, the opening  126  (shown in  FIG. 2 ) in the plunger  106  includes an angled portion  130  configured to align with an angled portion  132  of the side plate  123 . 
     If the electromagnetic forces generated by the pull-in and hold-in winding  114  are sufficient, the plunger  106  will cause the cylindrical rod  112  and electrical contact plate  116  to move to the right, compressing the first coil spring  110 . At the same time, the movement of the cylindrical rod  112  and the attached flange  134  toward the electrical terminals  115  compresses the second coil spring  118 . Eventually, the movement of the plunger  106  brings the electrical contact plate  116  into contact with the electrical terminals  115 . When the slipping clutch and pinion  103  (shown in  FIG. 1B ) is in contact with the engine&#39;s ring gear  109  (shown in  FIG. 1B ), the electrical contact plate  116  is also in contact with the electrical terminals  115 . The electrical current flows to the DC electric motor  101  (shown in  FIG. 1A ), which causes the motor  101  to rotate. As a result, the torque from the rotating DC electric motor  101  is transmitted to the internal combustion engine (not shown). 
     When the vehicle operator releases the ignition key, the pull-in and hold-in winding  114  is no longer energized and, consequently, there is no electromagnetic force to hold the plunger  106  in contact with the side plate  123  of the forced return solenoid assembly  105 . As a result, only the forces generated by the first and second coil springs  110 ,  118  act on the plunger  106  and electrical contact plate  116  via the cylindrical rod  112 , and, under normal circumstances, cause the plunger  106  and electrical contact plate  116  to move back to their initial position before the pull-in and hold-in winding  114  was energized. Normally, the movement of the plunger  106  back to its initial position moves the engagement lever  107  causing the slipping clutch and pinion  103  to disengage from the engine&#39;s ring gear  109  (shown in  FIG. 1A ), and, at the same time, breaks the connection between the electrical contact plate  116  and the electrical terminals  115 . 
     However, in some cases, electrical arcing between the electrical contact plate  116  and the electrical terminals  115  may result in localized spots of molten metal at the site of the arcing. This, in turn, may cause the contact plate  116  to partially fuse with the electrical terminals  115 .  FIG. 4  provides a cross-sectional view of the forced return solenoid assembly  105  showing the electric contact plate partially fused to the electrical terminals. In such a case, the force of the second coil spring  118  may not be sufficient to separate the electrical contact plate  116  from the electrical terminals  115 . 
     To address this problem, the plunger  106  includes a groove  136  into which a snap ring  122  is inserted. The snap ring  122  is configured such that its inner diameter protrudes into the opening  126  (shown in  FIG. 2 ) in the plunger  106 . As can be seen in the illustration of  FIG. 2 , the cylindrical rod  112  has the stopping ring  121  attached near an end of the cylindrical rod  112 . In an embodiment of the invention, a first lock washer  117  is used to retain the stopping ring  121  from sliding off the end of the cylindrical rod  112 . A second lock washer  127  on the other side (opposite the first lock washer  117 ) of the stopping ring  121  is used to keep the stopping ring  121  from sliding further down the cylindrical rod  112 . The outer diameter of the stopping ring  121  is only slightly smaller than the diameter of the opening  126  in the plunger  106 , such that axial movement of the plunger  106  in response to electromagnetic forces within the pull-in and hold-in winding  114  is not hindered by the stopping ring  121 . In the embodiment shown in  FIG. 2 , there is only a small amount of clearance between the plunger  106  and the stopping ring  121 . However, the outer diameter of the stopping ring  121  is larger than the inner diameter of the snap ring  122 . 
     As can be seen in  FIG. 2 , the forced return solenoid assembly  105  is assembled such that the stopping ring  121  is to the left of the plunger groove  136  and snap ring  122 . As such, the plunger  106  and snap ring  122  can move to the right towards the side plate  123  without the snap ring  122  impacting any part of the assembly. In those cases where the plunger  106  moves the cylindrical rod  112  and electrical contact plate  116  to the right until the electrical contact plate  116  contact the electrical terminals  115 , and electrical arcing causes the electrical contact plate  116  and electrical terminals  115  to become partially fused in the manner described above, the contact plate  116  and cylindrical rod  112  will remain to the right of their initial position, even after the pull-in and hold-in winding  114  is de-energized and the plunger  106  starts to move to the left back to its initial position. 
     Referring again to  FIG. 4 , if the force from the second coil spring  118  is insufficient to separate the electrical contact plate  116  and electrical terminals  115 , the force of the first coil spring  110  will still cause the plunger  106  to move to the left. As the spring force accelerates the plunger  106  to the left, at some point the snap ring  122  in the plunger  106  impacts the stopping ring  121  on the cylindrical rod  112  with enough force to separate the electrical contact plate  116  and electrical terminals  115 . The kinetic energy from moving plunger  106  is transferred via the snap ring  122  to the stopping ring  121 , cylindrical rod  112 , and electrical contact plate  116 , thus breaking the partial weld. In this manner, the combination of the snap ring  122  in plunger groove  136  and the stopping ring  121  attached to the cylindrical rod  112  provides a mechanism to break the partial fusing of the electrical contact plate  116  and electrical terminals  115 . 
     An additional effect of the impact of the snap ring  122  and stopping ring  121  is that the force of the first coil spring  110  is added to the second coil spring  118 . At that moment, there are at least three forces that are working to release or break the welded contact: the force of the first coil spring  110 , the force of the second coil spring  118 , and the kinetic energy from the plunger  106 . Further, if the engine starts, there is an additional force working to break the weld. That force is supplied through the helix spline  138 . In an embodiment of the invention, the helix spline  138  is coupled to one end of a drive assembly  140 . The other end of the drive assembly is coupled to the slipping clutch and pinion  103 . The force of the rotating slipping clutch and pinion  103  is transferred through the helix spline  138  to the electrical contact plate  116  via the plunger  106 . When the engine is rotating faster than the starter motor  101  (shown in  FIG. 1 ), the drive assembly  140  and helix spline  138  are configured to move to the right and out of contact with the ring gear  109 . The movement of the drive assembly  140  and helix spline  138  to the right causes the engagement lever  107  to move the plunger  106  to the left, thus adding kinetic energy in a manner that would tend to separate an electrical contact plate  116  welded to electrical terminals  115 . This additional force delivered to the plunger  106  through the helix spline  138  only occurs when the engine has been successfully started. 
     If the electrical contact plate  116  is welded to the electrical terminals  115 , and the engine does not start, the slipping clutch and pinion  103  will oscillate back and forth due to the varying rotational speeds of the engine as it attempts to start. Because of the oscillating speed of the slipping clutch and pinion  103 , there is also oscillating of the force, and it appears as slight impacting on the electrical contact plate  116  via a force placed on the plunger  106  by the pivoting engagement lever  107 . 
     All references, including publications, patent applications, and patents cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein. 
     The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) is to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. 
     Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.