Abstract:
An axle disconnect system for drive axles that utilizes an engagement spring, an electric motor and a slidable gear. The motor is connected to the slidable gear which moves along threads thereby engaging or disengaging clutch teeth on a first side gear which selectively engages a second side gear. The engagement spring is located between a bearing and the first side gear wherein when engagement is desired, but blocked by misalignment of the teeth, the engagement spring can apply a load to allow for engagement once alignment of the teeth is achieved. The use of a second engagement spring allows for the disengagement of the system when disengagement is typically blocked due to high driveline torques without having to reapply current to the motor

Description:
RELATED APPLICATIONS 
       [0001]    The present application claims priority to and the benefit from Provisional U.S. patent application Ser. No. 62/266,946 filed on Dec. 14, 2015. The content of the above-noted patent application is hereby expressly incorporated by reference into the detailed description of the present application. 
     
    
     FIELD 
       [0002]    The present disclosure relates to a system for connecting and disconnecting axles within a vehicle and, more particularly, to an axle disconnect system for an auxiliary drive axle system of a four-wheel drive motor vehicle. 
       BACKGROUND 
       [0003]    Four-wheel drive (or all-wheel) vehicles which are operable in either a two-wheel drive mode or four-wheel drive mode are well-known in the prior art. Typically, four-wheel drive capable vehicles include a transfer case, a rear drive shaft, a front drive shaft and an axle disconnect system. The transfer case is configured to divide power between the rear and front drive shafts when the four-wheel drive mode is engaged. 
         [0004]    Axle disconnect systems for front and rear axle assemblies are well-known and various assemblies or mechanisms have been proposed. These disconnect systems allow for increased fuel economy by selectively disconnecting driveline rotating parts when four-wheel drive is not engaged. Although suitable disconnect mechanisms have been developed, there is a need for systems that allow for rapid and frequent engagements and disengagements under high driveline drag conditions without increasing the mass, weight and packaging for the systems and, thus, the cost of the system. 
       SUMMARY 
       [0005]    The present disclosure provides for an improved axle disconnect system which allows for engagement and disengagement under high driveline drag conditions. 
         [0006]    In one aspect, the axle disconnect system for drive axles of a motor vehicle includes an engagement spring having two axial ends, a power source, a stationary axle housing having a threaded portion on a radially inner surface thereof, a slidable gear drivingly connected to the power source having a radially inner surface and a radially outer surface with a set of threads thereon, a first side gear drivingly connected to a first axle half shaft and the slidable gear having two axial ends and a radially outer surface, a second side gear having teeth on one end thereof and drivingly connected to a second axle half shaft, and a bearing positioned between the radially outer surface of the first side gear and the radially inner surface of the slidable gear. The threads of the stationary axle mate with the threads on the slidable gear. The first side gear has teeth one end thereof that selectively engage with the teeth of the second side gear. The engagement spring is positioned on the radially outer surface of the first side gear having one axial end surface connected to the bearing and the other axial end surface connected to the first side gear. The slidable gear slides along the threads to preload the engagement spring when the teeth of the first and second side gears are not in alignment. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The above, as well as other advantages of the present embodiments, 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: 
           [0008]      FIG. 1  is a schematic view of vehicle drivetrain as including a preferred embodiment of the axle disconnect system; 
           [0009]      FIG. 2  is a partial section of a preferred embodiment of the axle disconnect system; 
           [0010]      FIG. 3A  is a partial section of another preferred embodiment of the axle disconnect system; and 
           [0011]      FIG. 3B  is a partial section of an additional preferred embodiment of the axle disconnect system showing the use of an additional engagement spring. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0012]    It is to be understood that the embodiments 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 in 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. In addition, 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. 
         [0013]    Referring now to the drawings and more particularly to  FIG. 1 , there is shown a schematic diagram of a four-wheel or all-wheel drive drivetrain of a motor vehicle  100  including an axle disconnect system  115 . The schematic shows a primarily rear wheel driven vehicle; however, the axle disconnect system  115  can also be used on a primarily front wheel driven vehicle or other driveline assemblies and arrangements. 
         [0014]    As shown in  FIG. 1 , in one embodiment, the vehicle  100  includes a power source  110 , a transmission  113  and a transfer case  114  mounted on a vehicle chassis (not shown). The power source  110  includes, but is not limited to, an internal combustion engine and is drivingly coupled to the transmission  113 . The transfer case  114  is mounted behind the transmission  113 . The transfer case  114  is drivingly connected to a front differential assembly  111  by a front drive shaft  119  and to a rear differential assembly  112  by a rear drive shaft  116 . The engine  110  and transmission  113  are conventional and well-known components. 
         [0015]    Inside the transfer case  114 , drive torque originating from the transmission  113  is divided between the rear  116  and front  119  drive shafts. In one case, referred to as “all-wheel drive,” drive torque is provided to both drive shafts  119 ,  116 . In another case, referred to as “two-wheel drive,” drive torque is provided only to one drive shaft,  119  or  116 . Each of the drive shafts  119 ,  116  used with the transfer case  114  are rotatably supported within the transfer case  114  by appropriate support means, such as ball bearing assemblies or the like and the openings through which the drive shafts  119 ,  116  enter or exit the transfer case  114  are provided with appropriate seal assemblies 
         [0016]    The transfer case  114  typically includes an input shaft, a main output shaft and an auxiliary output shaft. The main output shaft is drive connected to the input shaft by a clutch or the like in the transfer case  114  and customarily offset from the transfer case. The clutch is actuated by a suitable selector mechanism controlled by the vehicle operator. The internal details of the transfer case  114  and details of a selector are not shown because these are conventional and well-known components. 
         [0017]    The front differential assembly  111  includes a differential gear arrangement. The differential gear arrangement can include a pinion gear, a ring gear and differential side gears; however, other differential gear arrangements are possible. A first front wheel  120  is connected to the front differential assembly  111  by a front drive axle  126 . The axle disconnect system  115  is drivingly connected to the front differential assembly  111  by a first front drive half axle  171   a.  A second front wheel  121  is connected to the disconnect system  115  by a second front drive half axle  171   b.    
         [0018]    The rear differential assembly  112  is connected to the transfer case  114  by the rear drive shaft  116 . The rear differential assembly  112  includes a differential gear arrangement. The differential gear arrangement can include a pinion gear, a ring gear and differential side gears; however, other differential gear arrangements are possible. 
         [0019]    Primary rear wheels  122 ,  123  are drivingly connected to the rear differential assembly  112  by rear shafts  117 ,  118  respectively. The secondary wheels  120 ,  121  are undriven wheels except that they are connected to the power source  110  when in “all-wheel drive” is operating. The secondary wheels  120 ,  121  are selectively driven when the disconnect system  115  connects the first front half axle  171   a  and the second front drive half axle  171   b.    
         [0020]    As shown in  FIG. 1 , the disconnect system  115  is integrated with the front drive assembly, but can be a separate assembly. 
         [0021]      FIG. 2  illustrates a detailed section view of one preferred embodiment of the axle disconnect system  115  including a power source  130  with an output shaft  131  drivingly connected to a drive gear  132 . The power source  130  may be a high speed-low torque power source including, but not limited to, a brushed direct current electric motor. 
         [0022]    The drive gear  132  has teeth formed on one end thereof that mesh with teeth  134   c  formed on the end of a slidable gear  134 . By selecting the outer diameter of the gears  132 ,  134 , and/or the number of teeth on each gear  132 ,  134 , the drive ratio of the gear set can be selected. In addition, additional gears (not depicted) may be operatively connected between the power source  130  and gear  134  to obtain a desired speed reduction ratio or enable specific position of the power source  130 . In one embodiment the drive gear ratio between the drive gear  132  and the slidable gear  134  is greater than 1. 
         [0023]    The slidable gear  134  has a radially extending portion  134   a  and an axially extending portion  134   b.  The radially extending portion  134   a  has a set of teeth  134   c  on the radially outer end thereof that meshes with the teeth on the drive gear  132 . 
         [0024]    The axially extending portion  134   b  has a radially inner surface  136   a  and a radially outer surface  136   b.  The surfaces  136   a,    136   b  are parallel to one another. The radially outer surface  136   b  includes a plurality of threads  135   a  formed thereon. 
         [0025]    A stationary axle housing  137  has a radially inner surface  137   b  and a radially outer surface  137   a.  The radially inner surface  137   b  has threads  135   b  formed thereon that mesh with threads  135   a  of the slidable gear  134 . The stationary axle housing  137  can be of one-piece or multi-piece construction. The power source  130  is positioned outside the stationary axle housing  137  with the output shaft  131  extending therethrough to connect with the drive gear  132 . 
         [0026]    A bearing  138  including an outer  138   a  and inner  138   b  raceway is coupled to the axially extending portion  134   b  of the slidable gear  134  on the outer raceway  138   a  and coupled to a first side gear  139  on the inner raceway  138   b.    
         [0027]    The first side gear  139  is positioned radially inward from the slidable gear  134 . The first side gear  139  has an axially extending portion  139   b  and a radially extending portion  139   a.  The axially extending portion  139   b  has longitudinally extending splines  144  formed on a radially inner surface  148  thereof that mate with a set of splines  176  formed on an outer surface  173  of the first front drive half axle shaft  171   a.  The radially extending portion  139   a  has clutch teeth  140  formed on one end thereof in the axial direction. The clutch teeth  140  mesh with clutch teeth  142  formed on an end of a second side gear  143 . 
         [0028]    An engagement spring  161  is positioned between bearing inner raceway  138   b  and the radially extending portion  139   a  of the first side gear  139  in the axial direction. The engagement spring  161  can be, but is not limited to, a compression coil spring. The engagement spring  161  can have two axial ends  161   a,    161   b.  One axial end  161   a  is in connected to an outer surface of the inner raceway  138   b  and the other axial end  161   b  is connected to an outer surface the radially extending portion  139   a.    
         [0029]    The second side gear  143  has a radial outer surface  143   a  and inner surface  143   b  with a set of longitudinally extending splines  145  formed on the inner surface  143   b.  Splines  145  mesh with a set of splines  175  formed on an outer surface  174  of the second front drive half axle shaft  171   b.  As depicted in  FIG. 2 , the splines  145  are formed on an axially extending portion of the second side gear  143 . The axially extending outer surface  143   a  of second side gear  143  is connected to an inner raceway  146   a  of a bearing  146 . Bearing  146  has an outer raceway  146   b  coupled to a stationary axle housing  137   c.    
         [0030]    The stationary axle housing  137 ,  137   a,    137   b,    137   c  houses slidable gear  134 , the first side gear  139  and second side gear  143 . The shape of the stationary axle housing  137 ,  137   a,    137   b,    137   c  can vary as the shape of the gears  134 ,  139 ,  143  vary allowing the disconnect system  115  to have a small footprint. 
         [0031]      FIG. 3A  depicts another preferred embodiment of an axle disconnect system  215  including a power source  230  with an output shaft  231  drivingly connected to a drive gear  232 . The power source  230  may be a high speed-low torque power source including, but not limited to, a brushed direct current electric motor. 
         [0032]    The drive gear  232  has teeth formed on one end thereof that mesh with teeth  234   c  formed on the end of a slidable gear  234 . By selecting the outer diameter of the gears  232 ,  234 , and/or the number of teeth on each gear  232 ,  234 , the drive ratio of the gear set can be selected. In addition, additional gears (not depicted) may be operatively connected between the power source  230  and gear  234  to obtain a desired speed reduction ratio/ or enable specific position of the power source  230 . 
         [0033]    The slidable gear  234  has a radially extending portion  234   a  and an axially extending portion  234   b.  The radially extending portion  234   a  has a set of teeth  234   c  on the radially outer end thereof that meshes with the teeth  232   c  on the drive gear  232 . 
         [0034]    The axially extending portion  234   b  has a radially inner surface  236   a  and a radially outer surface  236   b.  The surfaces  236   a,    236   b  are parallel to one another. The radially outer surface  236   b  includes a plurality of threads  235   a  formed thereon. 
         [0035]    A stationary axle housing  237  has a radially inner surface  237   b  and a radially outer surface  237   a.  The radially inner surface  237   b  has threads  235   b  formed thereon that mesh with threads  235   a  of the slidable gear  234 . The stationary axle housing  237  can be of one-piece or multi-piece construction. The power source  230  is positioned axially and radially outside the stationary axle housing  237  with the output shaft  231  extending therethrough to connect with the drive gear  232 . As depicted in  FIG. 3A , threads  235   a  can be positioned on any portion of the outer radially inner surface  237   b  of the stationary axle housing  237  parallel to an axially extending portion of a first side gear  239 . 
         [0036]    A bearing  238  including an outer  238   a  and inner  238   b  raceway is coupled to the axially extending portion  234   b  of the slidable gear  234  on the outer raceway  238   a  and coupled to the first side gear  239  on the inner raceway  238   b.    
         [0037]    The first side gear  239  is positioned radially inward from the slidable gear  234 . The first side gear  239  includes the axially extending portion  239   b  and a radially extending portion  239   a.  The axially extending portion  239   b  has longitudinally extending splines  244  formed on a radially inner surface  248  thereof that mate with a set of splines  176  formed on an outer surface  173  of the first front drive half axle shaft  171   a.  The radially extending portion  239   a  has clutch teeth  240  formed on one end thereof in the axial direction. The clutch teeth  240  mesh with clutch teeth  242  formed on an end of a second side gear  243 . 
         [0038]    An engagement spring  261  is positioned between bearing inner raceway  238   b  and the radially extending portion  239   a  in the axial direction. The engagement spring  261  can be, but is not limited to, a compression coil spring. The engagement spring  261  can have two axial ends  261   a,    261   b.  One axial end  261   a  is connected to an outer surface of the inner raceway  238   b  and the other axial end  261   b  is connected to an outer surface of the radially extending portion  239   a.    
         [0039]    The second side gear  243  has a radial outer surface  243   a  and inner surface  243   b  with a set of longitudinally extending splines  245  formed on the inner surface  243   b.  Splines  245  mesh with a set of splines  175  formed on an outer surface  174  of the second front drive half axle shaft  171   b.  As depicted in  FIG. 3A , the splines  245  are formed on an axially extending portion of the second side gear  243 . The axially extending outer surface  243   a  of second side gear  243  is connected to an inner raceway  246   a  of a bearing  146 . Bearing  246  has an outer raceway  246   b  coupled to a stationary axle housing  237   c.    
         [0040]    The stationary axle housing  237 ,  237   a,    237   b,    237   c  houses the slidable gear  234 , the first side gear  239  and second side gear  243 . The shape of the stationary axle housing  237 ,  237   a,    237   b,    237   c  can vary as the shape of the gears  234 ,  239 ,  243  vary allowing the disconnect system  215  to have a small footprint. 
         [0041]    The motor  130 ,  230  when energized by a current or other means, rotates gears  132 ,  134 ,  232 ,  234  and slidable gear  134 ,  234  moves axially forward and backwards along stationary axle housing  137 ,  237  via the threads  135   a,    135   b,    235   a,    235   b  driving side gear  139 ,  239  toward and away from the second side gear  143 ,  243 . 
         [0042]    When the first side gear  139 ,  239  is moved axially toward the second side gear  143 ,  243  the clutch teeth  140 ,  142 ,  240 ,  242  can align and engage and the second side gear  143 ,  243  drives the second front drive half axle shaft  171   b  through splines  145 ,  245 ,  175  connecting the first front drive half axle shaft  171   a  and the second front drive half axle shaft  171   b.    
         [0043]    In some cases, when the first side gear  139 ,  239  is moved axially toward the second side gear  143 ,  243 , the teeth  140 ,  142 ,  240 ,  242  will be misaligned, or blocked. When this occurs the slidable gear  134 ,  234  continues to exert a force on the first side gear  139 ,  239  and the engagement spring  161 ,  261  is compressed and preloaded. When the teeth  140 ,  142 ,  240 ,  242  are properly aligned, the engagement spring  161 ,  261  urges the teeth  140 ,  142 ,  240 ,  242  into meshed engagement by releasing its an axial load on the teeth  140 ,  142 ,  240 ,  242  without requiring the motor  130 ,  230  to apply additional force. 
         [0044]    In another embodiment, as shown in  FIG. 3B , the axle disconnect system  215  can include a second engagement spring  263 . The second engagement spring  263  can be, but is not limited to, a compression coil spring. The second engagement spring  263  is positioned on the opposite side of bearing  238  than that of engagement spring  261  in the axial direction. The second engagement spring  263  can have two axial ends  263   a,    263   b.  One axial end  263   a  is connected to an outer surface of the inner raceway  238   b  and the other axial end  263   b  is connected to the end of the axially extending portion  239   b  of side gear  239 . 
         [0045]    In between the bearing  238  and the second engagement spring  263  is a shoulder spacer  283 . In between the second engagement spring  263  and the axially extending portion  239   b  of side gear  239  is a retaining ring  284 . The retaining ring  284  can be a snap ring. When the axle disconnect system  215  is engaged and disengagement is desired, the second engagement spring  263  allows disengagement by allowing the slidable gear  234  to move along the threads  235  despite a driveline torque that without the second engagement spring  263  may be too high to pull the clutch teeth  240 ,  242  out of engagement. The use of the second engagement spring allows for the disengagement of the system  215  when disengagement of the clutch teeth  240 ,  242  is typically blocked due to high driveline torques without having to reenergize the power source  230 . 
         [0046]    The shoulder spacer  283  prevents the second engagement spring  263  from loading the first engagement spring  261  when moving from a disengaged to an engaged position. The second engagement spring  263  should have a lower spring constant than the first engagement spring  261  to prevent the second engagement spring  263  to prevent the second engagement spring  263  from applying a biasing force greater than the biasing force of the first engagement spring  261 . 
         [0047]    In accordance with the provisions of the patent statutes, the present disclosure 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.