Abstract:
Described herein is a compliant plunger for a latching solenoid. The compliant plunger prevents disengagement of the solenoid when the solenoid is subjected to incidental axial movement. The compliant plunger takes advantage of a compressible compliance device to absorb the incidental axial movement.

Description:
FIELD OF THE INVENTION 
     The present invention relates to methods and systems for securing a latching actuator. The actuator is secured by a complaint plunger designed to aid in maintaining the engagement of the actuator. In certain embodiments, the invention relates to actuators for use in power take-off units or vehicular drivetrain systems, such as differentials, axle disconnect systems, or power transfer units. In a specific embodiment, the invention relates to an actuator for use in an axle disconnect system. 
     BACKGROUND OF THE INVENTION 
     In the automotive industry, actuators are used for a number of purposes, including in vehicular systems such as power take-off units and drivetrain systems such as differentials, axle disconnect systems, or power transfer units. As just one example, typical all-wheel drive systems for vehicles push torque through a torque coupling to the secondary axle to provide enhancements in performance, handling and mobility. These systems require that the secondary axle, and the rest of the driveline, be continually rotating at road speed, which reduces the overall efficiency of the vehicle, and reduces fuel economy. 
     Secondary axle disconnects are available and they permit the secondary axle and prop shaft to stop rotating. These disconnect systems increase vehicle efficiency, but the current systems also require power to both engage and disengage the output and/or remain engaged or disengaged. The latter situation may require constant power to the system, which reduces overall system efficiency, or may require the use of permanent magnets. 
     As is known in the art, the actuator converts electrical current into mechanical force. The flow of electrical current into the actuator creates a magnetic field that moves a metal armature which, via additional mechanical elements, results in a change in the engagement/disengagement status of the particular drivetrain or other vehicular system, such as the axle disconnect system described briefly above. 
     Traditionally, when the actuator was energized, the armature would be drawn towards the solenoid as a result of the magnetic field generated, engaging the axle disconnect system. If it was desirable to keep the system engaged, either current would have to be continually applied or permanent magnets would have to be included in the design of the actuator so that the armature would stay in the engaged position. For obvious reasons, it is not desirable to have a solenoid draw significant power when holding the system engaged (or disengaged). 
     Latching solenoids can also accomplish maintained engagement with a permanent magnet in the system. Use of permanent magnets has undesirable consequences such as temperature demagnetization and shock demagnetization. In addition, depending on the material, permanent magnets can be costly, difficult to fasten, and can be fragile. 
     In a previous invention, filed as U.S. Prov. Appln. Ser. No. 62/023,944 filed Jul. 13, 2014, and PCT Appln. No. PCT/US15/40195 filed Jul. 13, 2015, both of which are hereby incorporated herein to the full extent permitted by law, an actuator was described that takes advantage of the residual magnetism in the coil housing that remains even after power to the solenoid has been shut off. The previous invention uses this residual magnetism to keep the actuator in an engaged position without a continual power draw. 
     However, in any of the given situations described above, a latching solenoid is unable to tolerate any incidental movement of the plunger. Incidental movement can cause the solenoid to become fully disengaged and will result in a loss of engagement of the system. The latching solenoid would need to be reactivated to correct the accidental disengagement. The invention described herein allows for the plunger to remain engaged while allowing for unintended force to be absorbed before causing disengagement. The particulars of the plungers of the invention can be tuned to suit the application requirements. 
     SUMMARY OF THE INVENTION 
     The disclosure herein describes an actuator with an electromagnetic coil comprising copper windings disposed in an overmold, a housing at least partially surrounding the coil, a slide ring radially inward from the housing, wherein the slide ring is in sliding engagement with the housing, and wherein the slide ring has a radially inward projecting arm. The actuator also can have a divot in a radially inward surface of the slide ring, a thrust washer radially inward from the slide ring, a groove in a radially outward surface of the thrust washer, a retaining device disposed in both the divot and the groove, and a compliance device, wherein the compliance device is in contact with and axially in line with the thrust washer and wherein the compliance device is in contact with and axially in line with the arm of the slide ring. 
     Axle disconnect systems using the actuator are also described, as are methods of maintaining latching of the actuator by using the actuator described herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above, as well as other advantages of the present invention, will become readily apparent to those skilled in the art from the following detailed description when considered in the light of the accompanying drawings in which: 
         FIG. 1  is a schematic in cross-section of an actuator with a compliant plunger in accordance with an embodiment of the invention. 
         FIG. 2  shows a schematic cross sectional view of an axle disconnect system with an embodiment of an actuator in accordance with the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     It is to be understood that the invention may assume various alternative orientations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific assemblies, articles and features illustrated in the attached drawings, and described in the following specification are simply exemplary embodiments of the inventive concepts. Hence, specific dimensions, directions, or other physical characteristics relating to the embodiments disclosed are not to be considered as limiting, unless expressly stated otherwise. Also, although they may not be, like elements in various embodiments may be commonly referred to with like reference numerals within this section of the application. 
     For use in this description only, the terms actuator and solenoid can be used interchangeably. 
     Turning now to  FIG. 1 , is an actuator  10  in accordance with one embodiment of the invention. The actuator will include an electromagnetic coil  12  formed of copper windings  14  in an overmold  16 . The coil  12  is disposed in a housing  18 . The housing  18  can be unitary or can include a separate cover  20 . The housing  18  may be of a generally U-shape or generally a J-shape. In the particular embodiment shown, not intended to be limiting, the housing  18  is J-shaped, with an outer wall  22 , a side wall  24  and an inner wall  26 . The inner wall  26  is separated from the overmold  16 , thereby creating a space  28 . 
     Also part of the actuator  10  is a secondary housing piece  30 . The secondary housing piece  30  has three portions: a first end portion  32 , a middle portion  34 , and a second end portion  36 . The middle portion  34  has a protrusion  38  that extends past the outer face  40  of the secondary housing piece  30  away from interior of the coil  12 . The second end portion  36  of the secondary housing piece  30  is formed as a finger-like projection that fits into the space  28  between the inner wall  26  of the coil housing  18  and the overmold  16 . 
     A slide ring  42  is located between the coil housing  16  and a shift collar  22 . More particularly, the slide ring  42  is located radially inward from the inner wall  26  of the coil housing  18  and is in direct contact therewith. The slide ring  42  is also in contact with the secondary housing piece  30 . A first end  44  of the slide ring  42  has a catch  46  that projects radially outward from the slide ring  42 . The catch  46  abuts the face  40  of the secondary housing piece  30 . The slide ring  42  also has a body portion  48 . The body portion  48  has at least one divot  50  on its inward radial surface  52 . An arm  54  extends radially inward from the slide ring  42 . A first side  56  of the inwardly extending arm  54  is located axially adjacent a first side  58  of a compliant element  60 . 
     The slide ring  42  is adapted for selective axial movement. The slide ring  42  is constructed of a metallic material that is susceptible to magnetic forces, such as steel. 
     The compliant mechanism  60  abuts the arm  54  of the slide ring  42  on a first axial side  58 , and on a second axial side  62 , opposite the first axial side  58 , abuts a thrust washer  64 . The outer radial surface  66  of thrust washer  64  has a groove  68  of width D 1  disposed therein. The thrust washer  64  is disposed in a recess  70  defined by a shift collar  72 . 
     The compliant mechanism  60  can be a spring, rubber, or other compressible material. It will have a spring rate of K. K will vary depending on the exact materials and overall design. The thrust washer  64  is made from a wear resistant material, such as, but not limited to, plastic, epoxy or other polymer. 
     The shift collar  72  is located directly radially inward from the slide ring  42  and directly radially outward from an output shaft (not shown), and has a first portion  74  and a second portion  76 . The first and second portions  74 ,  76  are unitary and one-piece with one another. More particularly, the first portion  74  is located directly radially inward from the slide ring  42  and extends radially outward parallel to the radially inwardly extending arm  54  of the slide ring  42 . The first portion  74  of the shift collar  72  has a first set of axially extending teeth  78 . 
     The second portion  76  is located radially inward from the first portion  74 , and extends in an axial direction parallel with the output shaft (not shown). The second portion  76  defines a first set of axially extending splines  80 . The splines  80  are integrally formed and unitary with the shift collar  72  and allow for axial movement along the output shaft (not shown). 
     In addition, at least a portion of a retaining device  82  with width D 2  is disposed within the groove  68  of the thrust washer  64 . The width D 2  of the retaining device  82  is less than the width D 1  of the groove  68 . The difference in widths allows for some ‘play’ in between the retaining device  82  and the thrust washer  64 . The retaining device  82  will also be at least partially disposed in divot  50  in the slide ring  42 . 
     In preferred embodiments, the retaining device  82  is an ID/OD retaining device that is well-known in the mechanical arts and widely commercially available. 
       FIG. 2  shows the actuator of  FIG. 1  in an environment typical of an axle disconnect system  100 . The system has two modes of operation. In a first mode of operation as depicted in  FIG. 2 , the shift collar  72  and output gear  110  are not connected or rotating together, but sometimes it is desired that they be connected so that they rotate together. When this mode is to be used, electricity is sent to the coil  12  and the coiled wires  14  create a magnetic flux. In other words, the current in the coil  14  causes the coil housing  18  to become magnetized. The sum of the coil flux and the housing magnetism causes the slide ring  42  to move in an axial direction. The force generated by the movement of the slide ring  42  is greater than the sum of the spring force generated by return springs  112  and friction force of the slide ring  42 . Within a few milliseconds of the coil  12  being energized, the magnetic flux contributes to the magnetic slide ring  42  moving in the axial direction. The slide ring  42  axially moves the compliant device  60  and retaining device  82 , which in turn axially moves the shift collar  72  pushing the shift collar  72  into engagement with the output gear  110 . 
     As the first mode is being engaged, teeth  78  on the shift collar  72  are not engaged with the output gear  110 ; a gap separates the teeth on the shift collar  72  and the output gear  110 . However, as the shift collar  72  is moved, the gap separating the two closes. In a short amount of time, on the order of milliseconds, the gap is closed and the teeth  78  on the shift collar  72  engage with the output gear  110 . Upon engagement the shift collar  72  is rotationally fixed to the output gear  110 . The rotation from the shift collar  72  is transferred through the output gear  110  to the output shaft  114 . 
     The design is engineered specifically for the a particular application by adjusting the spring rate K of the compliance device  60  and the amount of axial travel the actuator  10  is required to tolerate. The design is engineered so that peak force generated from the compliance device  60  is less than the minimum holding force generated by the actuator  10 . In the event of an axial force being applied to the shift collar  72 , the shift collar  72  will move towards the actuator  10 . This movement will then push on the thrust washer  64 , compressing the compliance device  60 . The compliance device  60  will continue to compress until the axial travel of the thrust washer  64  is reduced to zero. After the axial force event is over, the compliance device  60  and thrust washer  64  will push the shift collar  72  back into position. 
     Although this actuator  10  is shown, various embodiments are contemplated to be within the scope of the invention, including actuators with differently shaped covers, armatures and housings. The way the slide ring and housing interact can vary, as can how the slide ring and cover interact upon engagement. The actuator  10  shown is just one of many possibilities. One important aspect of the invention is that the actuator be able to stay engaged, or latched, even when an axial force is applied to the solenoid. Such a force can be the result of vibrations or other physical forces stemming from movement of the parts surrounding the actuator or the vehicle itself. 
     As noted previously, the axle disconnect system described above is just one example of many systems in which the current invention can be used. Variations in axle disconnect systems might include different shapes of coil housing  16 , or the addition or subtraction of other elements in the system. 
     Also, it can be appreciated that one embodiment of the system described and depicted herein is for an axle connect/disconnect system. However, the device described herein is not limited to just axles. Instead, the device can be applied to other devices, equipment and methods known in the automotive arts including, but not limited to, power take off units, differentials, and power transfer units. Several examples of systems that can be used with actuators of the invention can be found in U.S. patent application Ser. No. 14/606,066, hereby incorporated herein to the full extent permitted by law, which discusses several axle disconnect and power take-off unit systems, all of which could be used with actuators containing compliant plungers as described herein. 
     In accordance with the provisions of the patent statutes, the present invention has been described in what is considered to represent its preferred embodiments. However, it should be noted that the invention can be practiced otherwise than as specifically illustrated and described without departing from its spirit or scope.