Abstract:
A method of disengaging an axle disconnect system including providing an actuator having a coil ( 214 ) at least partially surrounded by a housing ( 220 ), an armature ( 216 ) located within the housing and the coil, where the armature is capable of actuating between a first and second position, and at least one of the housing and the armature is part of a magnetic circuit. Applying a current to the coil and actuating the armature from the first position to the second position. Developing an uninterrupted magnetic flux through the magnetic circuit and stopping application of the current to the coil. Permitting the magnetic flux through the magnetic circuit to continue in its uninterrupted state and maintain the armature in the second position. Applying an alternating current, having decreasing amplitude over time, to the coil to dissipate the magnetic flux through the magnetic circuit.

Description:
BACKGROUND 
       [0001]    All-wheel drive capable vehicles have many advantages over vehicles having a driveline connected to only a single axle. Specifically, all-wheel drive capable vehicles have increased traction and enhanced drivability over similar vehicles that are driven using only a single axle. 
         [0002]    However, traditional all-wheel drive vehicles are disadvantaged by requiring continuous rotation of a second drive axle, and other portions of the driveline, at road speed, even when the all-wheel drive functionality is not beneficial. Consequently, traditional all-wheel drive vehicles tend to have reduced fuel, and overall, efficiency when compared to vehicles having only a single drive axle. 
         [0003]    All-wheel drive vehicles incorporating a secondary driveline disconnect feature are being developed. In such vehicles, when a control system detects that all-wheel drive functionality is not required, the control system disconnects the second drive axle (and other associated driveline components) to place the driveline into a single axle drive mode. Once the second drive axle is disconnected, there is no transfer of torque to the second drive axle. As a result, speed-dependent losses associated with the second drive axle (and other associated driveline components) are eliminated by allowing the second drive axle (and other associated driveline components) to remain in an idle condition. 
         [0004]    Secondary driveline disconnect systems may utilize an electromagnetic actuator to perform an engagement and a disengagement of the secondary driveline. Remanent magnetization may be utilized to place the electromagnetic actuator in a stable state without the application of current thereto. However, removing the remanent magnetization in a consistent and predictable manner using conventional methods may be affected by many operational variables, such as but not limited to, temperature, manufacturing tolerances, and part variation. 
         [0005]    The disclosure herein describes a method and system for consistently and efficiently connecting and disconnecting an electromagnetic actuator. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0006]    The accompanying drawings, incorporated herein as part of the specification, illustrate the presently disclosed subject matter, and with the description, serve to explain the principles of the disclosed subject matter and to enable a person skilled in the pertinent art to make and use the disclosed subject matter. 
           [0007]      FIG. 1  is a schematic diagram of a portion of a portion of an automobile driveline having primary and secondary wheel sets according to an embodiment of the presently disclosed subject matter; 
           [0008]      FIG. 2  is a cross-section of a portion of an electromagnetic rapid disconnect apparatus according to an embodiment of the presently disclosed subject matter; 
           [0009]      FIG. 3  is a graph of a decaying sine-wave having exponentially decreasing amplitude according to an embodiment of the presently disclosed subject matter; 
           [0010]      FIG. 4  is a graph of a series of hysteresis curves illustrating a degaussing process according to an embodiment of the presently disclosed subject matter; 
           [0011]      FIG. 5  is a schematic diagram of a circuit according to an embodiment of the presently disclosed subject matter; 
           [0012]      FIG. 6  is perspective view cross-section of a portion of an electromagnetic rapid disconnect apparatus according to an embodiment of the presently disclosed subject matter; 
           [0013]      FIG. 7  is a cross-section of the electromagnetic rapid disconnect apparatus according to  FIG. 6 . 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0014]    It is to be understood that the presently disclosed subject matter may assume various alternative orientations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific devices, assemblies, systems and processes illustrated in the attached drawings, and described in the following specification are simply exemplary embodiments of the inventive concepts defined herein. 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 described herein may be commonly referred to with like reference numerals within this section of the application. 
         [0015]    Certain embodiments of a driveline disconnect system  200  are utilized with an all-wheel-drive (“AWD”) driveline assembly. However, the driveline disconnect apparatus  200  is not limited to use with the driveline assemblies described herein. The driveline disconnect apparatus  200  may be utilized with, but is not limited to, driveline assemblies of other shapes, sizes, orientations, and designs in automobiles and manufacturing equipment. 
         [0016]      FIG. 1  illustrates an embodiment of the presently disclosed subject matter wherein a vehicle  100  includes a driveline  102  having all-wheel drive functionality. The driveline  102  comprises a power source  104 , a final drive unit  106 , and a rear drive unit  108 . The driveline  102  further includes a driveline disconnect system  200 . 
         [0017]    As illustrated in  FIG. 2 , in an embodiment, the driveline disconnect system  200  comprises a control unit  202 , an electromagnetic actuator  204 , a clutch fork  206 , and a dog-clutch  208 . The control unit  202  is in communication with the electromagnetic actuator  204 . The electromagnetic actuator  204  is driveably connected to the clutch fork  206 , which is drivingly connected with the dog-clutch  208 . 
         [0018]    The control unit  202  may execute a series of instructions in response to a command by a vehicle operator, data received from a vehicle controller (not shown), or data received from at least one sensor, or a combination thereof. It is understood that the series of instructions executed by the control unit  202  may be stored on a portion of the control unit  202  or on a device (not shown) in communication with the control unit  202 . The control unit  202  is in communication with the electromagnetic actuator  204  to place the electromagnetic actuator  204  into the engaged position and to perform a degaussing of the electromagnetic actuator  204 . 
         [0019]    The electromagnetic actuator  204  comprises a housing  220 , a coil  214 , an armature  216 , and a biasing member  218 . In response to a current from the control unit  202  supplied to the coil  214 , the coil  214  is energized, creating a magnetic field. The magnetic field causes the armature  216  to actuate and compress the biasing member  218 . The clutch fork  206  is also driven by the movement of the armature  216 , and the clutch fork  206  actuates the dog-clutch  208 . The dog-clutch  208  then becomes drivingly engaged with the driving part  210  and the driven part  212 . When the current from the control unit  202  to the coil  214  is interrupted, the dog-clutch  208  remains drivingly engaged because of the residual magnetism of the armature  216 . 
         [0020]    In addition to the actuation sequence described above, the electromagnetic actuator  204  uses a remanent field to maintain the engaged position of the electromagnetic actuator  204 . The remanent field facilitates maintaining the electromagnetic actuator  204  in the engaged position without application of electrical current by the control unit  202 . The remanent field may be generated in the coil  214  or in any ferrous portion of the electromagnetic actuator  204 . In addition to using a remanent field to maintain the engaged position of the electromagnetic actuator  204 , the electromagnetic actuator  204  may also incorporate the use of permanent magnets to maintain the engaged position of the electromagnetic actuator  204 . It is to be understood that such principles may also be applied to a variation of the present subject matter in which a remanent field facilitates maintaining an electromagnetic actuator in a disengaged position without application of electrical current. 
         [0021]    In an embodiment, to disengage the dog-clutch  208 , or aid therein, the remanent field is dissipated. Upon dissipation of the remanent field, the armature  216  is capable of axial movement, and the biasing member  218  drives the armature  216  to a disengaged position. In response to the actuation of the armature  216 , the dog-clutch  208  becomes drivingly disengaged from the driving part  210  and the driven part  212 . 
         [0022]    The control unit  202  dissipates the remanent field by performing a degaussing process on the coil  214  or the ferrous portion of the electromagnetic actuator  204  in which the remanent field resides. The degaussing process at least partially dissipates the remanent field from the electromagnetic actuator  204  by applying an alternating current, having decreasing amplitude, to the coil  214 . An example of the alternating current utilized in a degaussing process is shown in  FIG. 3 . The alternating current illustrated in  FIG. 3  is an exponentially decaying sine-wave. Application of an alternating current having decreasing amplitude to the coil  214  causes the remanent field of the electromagnetic actuator  204  to experience successively smaller hysteresis curves. An example of a family of hysteresis curves characteristic of the dissipation of the remanent field is illustrated in  FIG. 4 . In  FIG. 4 , the notation “B R ” represents flux density, the notation “H C ” represents coercivtiy, and the notation “T” denotes the unit of measurement the tesla. During the degaussing process the remanent field is dissipated at least until the biasing member  218  is able to overcome the force(s) of the magnetic field of the electromagnetic actuator  204  and drive the armature  216  to a disengaged position. The degaussing process applied to the electromagnetic actuator  204  provides a robust and efficient procedure to disengage the dog-clutch  208 . 
         [0023]    The control unit  202  can perform the degaussing process in one of a plurality of ways. As non-limiting examples, the control unit  202  may perform the degaussing process using a digital control or an analog circuit. The digital control may comprise, but is not limited to, a 555 timer IC. The control unit  202  may comprise a circuit having a digital current source inverter. 
         [0024]    A circuit  500  that may be utilized by the control unit  202  to perform the degaussing process described herein supra is illustrated in  FIG. 5 . In an embodiment, the circuit  500  may form a portion of the control unit  202  or may be integrated into a portion of the electromagnetic actuator  204 . In other embodiments, the circuit  500  may be configured in other arrangements that may perform the degaussing process. In an embodiment, the circuit  500  comprises a capacitor  502 , a power supply  504 , a resistor  506 , a first switch  510 , a second switch  512 , a diode  514 , and the coil  214 . The circuit  500  supplies a current to the electromagnetic actuator  204  when the second switch  512  is closed to a first point  520 , and the first switch  510  is closed. The electromagnetic actuator  204  remains engaged when the circuit  500  first switch  510  is opened, and no current is supplied to the coil  214 . The circuit  500  dissipates the remanent field of the electromagnetic actuator  204  via the degaussing process by closing the second switch  512  to a second point  522  while the first switch  510  is opened; the capacitor  502 , starting at a voltage of the power supply  204 , then applies a decaying alternating current to the coil  214 . 
         [0025]    In another embodiment, any circuit comprising the ability to engage the electromagnetic actuator  204  via controlling a current through the coil  214 , hold the electromagnetic actuator  204  in a state of engagement without the application of current to the coil  214 , and apply a current to the coil  214  that causes the degaussing process, may be utilized by the control unit  202 . Additionally, together in another embodiment, or in separate embodiments, the circuit  500  may be modified to use a different mechanism to charge the capacitor  502 , add a switch in series with the resistor  506  for charging the capacitor  502 , and use a digitally controlled charging circuit that includes a power electronics topology. Furthermore, the first switch  510  may comprise a high frequency switch. 
         [0026]    As illustrated in  FIGS. 6 and 7 , in an embodiment, the electromagnetic actuator  304  comprises a housing assembly  319  including a substantially annular housing  320  and an annular housing plate  321 . The annular housing  320  may be a unitary module comprising, but not limited to, a U-shaped or a J-shaped cross-section. The housing  320  includes an annular exterior wall  322  and an annular interior wall  324  connected via a discoid base  326 , the base  326  having a bore therethrough defined by the interior wall  324 . A coil assembly  314  is disposed in the interior of the housing  320 , the housing  320  interior being defined by the exterior wall  322 , the interior wall  324 , and the base  326 . The housing  320  exterior wall  322  also defines an aperture  328  that permits an electrical coupling  380  between the coil assembly  314  and a control unit (not depicted). 
         [0027]    The coil assembly  314  comprises multiple wire windings and a potting material, together having a substantially annular geometry. A radial protrusion  318  is disposed on an interior surface  315  of the coil assembly  314 . The protrusion  318  comprises a first surface  318 A and a second surface  318 B. When the electromagnetic actuator  304  is assembled, the second surface  318 B is substantially contiguous with or touching an end surface  324 A of the housing  320  interior wall  324 . The protrusion  318  projects inward from the coil assembly  314  interior surface  315  such that a third surface  318 C of the protrusion  318  is substantially level with the plane of the interior surface  324 B of the housing  320  interior wall  324 . 
         [0028]    An annular sleeve  330  is disposed on, and concentric with, the interior surface  315  of the coil assembly  314 . A first surface  330 A of the sleeve  330  is disposed substantially tangential to the first surface  318 A of the coil assembly protrusion  318 . In addition, the annular sleeve  330  comprises a thickness between its outer diameter and inner diameter which is less than the distance which the protrusion  318  projects radially-inward from the coil assembly  314  interior surface  315 . 
         [0029]    Furthermore, a generally annular and cylindrical armature  340  is slideably disposed on the interior surface  324 B of the housing  320  and the third surface  318 C of the coil assembly  314  projection  318 . The armature  340  comprises an outward-radial projection  342  having a first surface  342 A, a second surface  342 B, and a third surface  342 C. The third surface  342 C of the armature projection  342  is slideably disposed against the inner diameter of the sleeve  330 . The armature  340  also comprises an inward-radial projection  344  having a first surface  344 A. Situated axially adjacent the first surface  344 A is an annular bushing  346  concentrically disposed inside the armature  340 . A magnetic circuit may be formed by at least one of the housing assembly  319 , the housing  320 , and the armature  340  when a current is applied to the coil assembly  314 . 
         [0030]    A first clutch module  350  is also positioned concentrically within the armature  340 . The first clutch module  350  illustrated in  FIG. 6  comprises a substantially cylindrical geometry, however, the clutch module  350  may comprise other shapes including, but not limited to, rectangular, discoid, and conical geometries. A surface  352  of the first clutch module  350  is located axially-adjacent to the bushing  346 . The first clutch module  350  is rotatable and capable of axial actuation. The first clutch module  350  further comprises a first portion  354  and a second portion  356 . The first portion  354  comprises inwardly extending radial splines  358  drivingly engaged with splines on a differential half-shaft (not depicted). The second portion  356  of the first clutch module  350  comprises a set of clutch teeth  366 . The second portion  356  of the first clutch module  350  also comprises an annular groove  360  in which is located a biasing member  362 . The biasing member  362  may comprise, but is not limited to, a wave spring. A first end  362 A of the biasing member  362  abuts and is axially-adjacent to a snap ring  364 . The snap ring  364  is axially fixed, and operatively connected to a second clutch module  368 . 
         [0031]    When the electromagnetic actuator  304  is engaged, the first clutch module  350  clutch teeth  366  mesh with a set of clutch teeth  370  on the second clutch module  368 . Additionally, when the first clutch module  350  engages the second clutch module  368 , the biasing member  362  is compressed between the first clutch module  350  and the snap ring  364 . The second clutch module  368  is axially fixed and comprises a first portion  368 A and a second portion  368 B, the second portion  368 B comprising the clutch teeth  370 . The first portion  368 A comprises outwardly extending radial splines  372  drivingly engaged with splines (not depicted) on a half-shaft (not depicted) which is driveably connected to a wheel (not depicted). The second clutch module  368  is substantially axially-fixed relative to a housing of, for example, a front drive unit (not depicted) or a power transfer unit via an annular bushing  374  concentrically disposed on an exterior surface of the second portion  368 B of the second clutch module  368 . The second clutch module  368  illustrated in  FIG. 6  comprises a substantially cylindrical geometry, however, the clutch module  368  may comprise other shapes including, but not limited to, rectangular, discoid, and conical geometries. 
         [0032]    The first clutch module  350  may comprise, but is not limited to, a unitary module, or an apparatus including the first portion  354  comprising a separable component having a means for driving engagement with the differential half shaft, and the second portion  356  comprising a separable component having a means of driving engagement with the second clutch module  368 . The second clutch module  368  may also comprise, but is not limited to, a unitary module, or an apparatus including the first portion  368 A comprising a separable component having a means for driving engagement with the half shaft, and the second portion  368 B comprising a separable component having a means of driving engagement with the first clutch module  350 . 
         [0033]    When current from the control unit is directed to the coil  314 , thereby engaging the electromagnetic actuator  304 , the armature  340  actuates and axially drives the first clutch module  350 , compressing the biasing member  362  until the armature  340  projection  340  first surface  342 A abuts the interior surface of the housing plate  321  and the first clutch module  350  clutch teeth  366  mesh with the clutch teeth  370  on the second clutch module  368 . When the clutch teeth  366  and  370  are engaged, the flow of current to the coil  314  is stopped; the armature  340  remains in the engaged position with projection  340  first surface  342 A disposed axially adjacent to the inner surface of the housing plate  321  such that there is no, or only a minimal, magnetic air gap therebetween, and the remanent field of the electromagnetic actuator  304  maintains the clutch engagement. 
         [0034]    The control unit dissipates the remanent field by performing a degaussing process on the electromagnetic actuator  304  in which the remanent field resides. The degaussing process at least partially dissipates the remanent field from the electromagnetic actuator  304  by applying an alternating current, having decreasing amplitude over time, to the coil  314 . An example of the alternating current and the hysteresis curves caused thereby in a degaussing process are described above and illustrated in  FIGS. 3 and 4 . The degaussing process dissipates the remanent field at least until the biasing member  362  overcomes the force(s) of the remanent field and drives the armature  340  to a disengaged position, thereby disengaging the clutch teeth  366  and  370 . 
         [0035]    A module is defined here as an isolatable element that has a defined interface with other elements, unless otherwise indicated. Residual magnetism, remanent field, remanence, and uninterrupted magnetic flux may be commonly interchanged herein and define the same characteristic or occurrence, unless otherwise indicated. 
         [0036]    While various embodiments of the presently disclosed subject matter have been described above, it should be understood that they have been lo presented by way of example, and not limitation. It will be apparent to persons skilled in the relevant art(s) that the disclosed subject matter may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The embodiments described above are therefore to be considered in all respects as illustrative—not restrictive.