Abstract:
A shifting mechanism and method of using the shift mechanism is described. The shifting mechanism has a shift fork. Flanges are connected to a portion of the shift fork. Pin apertures in the flanges receive pins therein. The pins are connected to a block, which receives a screw gear therein. The screw gear is connected to a shift motor.

Description:
RELATED APPLICATIONS 
       [0001]    This continuation application claims priority to and the benefit of U.S. patent application Ser. No. 14/160,849 filed on Jan. 22, 2014 which claims priority to and the benefit of U.S. Patent Application Ser. No. 61/759,750 filed on Feb. 1, 2013, both of which are incorporated by reference in their entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    Four wheel drive for vehicles can be advantageous in certain circumstances, like when additional traction is needed because of surface conditions, or during cornering or acceleration. Driving all four of the wheels and their associated components, however, is not often required during most driving conditions and it results in increased fuel consumption. 
         [0003]    It is preferable that two of the four wheels be selectively engaged only when required at least to avoid the increase in fuel consumption. It is known to directly drive two wheels of a vehicle and then to use a power take off unit to selectively drive the other two wheels. Typically, a shift fork and a sliding clutch, among other components, are used to selectively engage and disengage the rear wheels at the power take off unit. 
         [0004]    One embodiment of a prior art shift fork  10  and sliding clutch  12  is depicted in  FIG. 1 . The shift fork  10  is moved in the axial direction by a linear push rod or piston  14 . The shift fork  10  is connected to the sliding clutch  12 . The sliding clutch  12  slides on, and rotates with, a source of rotation. In the depicted in embodiment, the sliding clutch  12  is mounted for axial movement on a ring gear  16 . The ring gear  16  is driven by a shaft  18 . 
         [0005]    The clutch  12  has a set of teeth  20  on one of its side surfaces. The shift fork  10  selectively moves the sliding clutch  12 , and its teeth  20 , axially into and out of engagement with a set of teeth  22  on an adjacent shaft  24 . The shaft  24  is connected to a drive shaft  26 , such as an axle half shaft. As shown in the figures, the adjacent shaft  24  is concentric about the drive shaft  26 . 
         [0006]    The above-described system has a number of drawbacks. First, it requires a large amount of space for the sliding clutch  12  to be translated in the axial direction. Second, it requires a relatively large and powerful device to move the entire fork  10  and the entire clutch  12 . Third, because the clutch  12  is moved, the shift fork  10  and other components must be robust, and thus heavy, to withstand the repeated loading and unloading. Fourth, the response time for the clutch  12  to be engaged or disengaged is slow often because of the large amount of time needed for the shift fork  10  to axially move the clutch  12  adequately for engagement or disengagement with the adjacent set of teeth  22 . 
       SUMMARY OF THE INVENTION 
       [0007]    A shifting mechanism and method of using the shifting mechanism are described. The shifting mechanism has a shift fork with a lower arm, an upright portion and an upper arm. An upper flange and a lower flange located on an outer surface of the upright portion. A first pin aperture is located in the upper flange and a second pin aperture is located in the lower flange. A first block pin is located within the first pin aperture and a second block pin is located within the second pin aperture. A block is provided on which the first block pin and the second block pin are attached. The block has internal threads. A screw gear is engaged with the block internal threads and the screw gear is connected to a shift motor. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0008]    The above 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: 
           [0009]      FIG. 1  is one embodiment of a prior art shift mechanism; 
           [0010]      FIG. 2  is a schematic of a vehicle driveline; 
           [0011]      FIG. 3  is a side view of one embodiment of the invention; 
           [0012]      FIG. 4  is a perspective view of the invention of  FIG. 3 ; 
           [0013]      FIG. 5  is a top view of the invention of  FIG. 3 ; 
           [0014]      FIG. 6  is a detail view of the invention of  FIG. 3 ; 
           [0015]      FIG. 7  is a partial cross-section side view of another embodiment; and 
           [0016]      FIG. 8  is a perspective view of the embodiment of  FIG. 7   
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]    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 devices and processes illustrated in the attached drawings, and described in the following specification are simply exemplary embodiments of the inventive concepts defined in the appended claims. Hence, specific dimensions, directions or other physical characteristics relating to the embodiments disclosed are not to be considered as limiting, unless the claims expressly state otherwise. 
         [0018]      FIG. 2  schematically depicts a drivetrain  28  of an all-wheel drive (AWD) or four-wheel-drive (4WD) motor vehicle. The AWD drivetrain  28  comprises a pair of front drive wheels  30  and  32 , a pair of rear drive wheels  34  and  36  and a front-wheel-drive (FWD) transaxle unit  38 . The FWD transaxle unit  38  is operatively connected to a prime mover  40 , such as an internal combustion engine, electric motor, etc. 
         [0019]    The FWD transaxle unit  38  is a drive setup in which a power transmission  42 , a final drive, and a front differential assembly  44  are combined into a single unit connected directly to the prime mover  40 ; these components do not have to be in a single unit. The FWD transaxles are commonly used in front wheel drive motor vehicles. The power transmission  42  is commonly known in the art as a mechanical unit containing a manual or automatic change-speed gear system and associated actuating machinery. An output from the power transmission  42  is connected to the front differential assembly  44  through the final drive. The front differential assembly  44  is drivingly connected to right-hand and left-hand front output axle shafts  46  and  48 , respectively. In turn, the output axle shafts  46  and  48  drive the front wheels  30  and  32 , through suitable coupling means, such as constant-velocity joints (not shown). 
         [0020]    As illustrated, the FWD transaxle unit  38  further includes an integrated torque-coupling device  50  and power take-off unit (PTU)  52 . The torque-coupling device  50  is provided for selectively restricting differential rotation of the front differential assembly  44 , i.e. of the output axle shafts  46  and  48 , and the PTU  52  is adapted for use in a full-time AWD system and is operable to transfer drive torque from the prime mover  40  and the power transmission  42  at a predetermined distribution ratio to the rear wheels  34 ,  36  of a rear drive axle  54  through a propeller shaft  56 , a rear differential assembly  58  and rear axle shafts  60  and  62 . 
         [0021]    Although, the preferred embodiment of the present invention is described with the reference to the front-wheel-drive transaxle unit, it will be appreciated that the present invention is equally applicable to a rear-wheel-drive transaxle unit. The components described below may also be adapted to any other known power take off units for vehicles or other machinery. 
         [0022]      FIGS. 3-6  depict one embodiment of a PTU  52 . An input shaft  64 , rotationally driven by the transmission  42 , is depicted. The input shaft  64  drives a pinion gear (not shown), which is in meshed engagement with a ring gear (not shown). In a preferred embodiment, the ring and pinion gears are in a hypoid arrangement, but other connections between the ring and pinion gears are permissible. The pinion gear and ring gear are located within a power-take-off unit housing  66 . 
         [0023]    The ring gear is connected to a power take off output shaft  68 . The power take off output shaft  68  is oriented substantially transversely to the input shaft  64  in the depicted embodiment. The ring and pinion gears transfer rotational power coming from the input shaft  64 , which is aligned along a first axis  70 , to the power take off output shaft  68 , which is perpendicular to the input shaft  64 , and aligned along a second axis  72 . 
         [0024]    A shift motor  74  is located within the power take off housing  66 . The motor  74  may be an electric motor, but pneumatic, hydraulic, mechanical and/or magnetic sources may also be used. In the depicted embodiment, an electric motor is provided and oriented along an axis  76 . The motor axis  76  is perpendicular to the input shaft axis  70  and power take off output shaft axis  72 . The motor  74  may also be located outside of the power take off housing  66 . 
         [0025]    An output shaft  78 , connected to the motor  74 , extends through an output end of the motor  74 . The shaft  78  is aligned with the motor axis  76 . A gear  80  is secured to the shaft  78  for rotation therewith. 
         [0026]    The motor  74  may be adapted to turn in both a clockwise and a counterclockwise direction. A controller (not shown) signals the motor  74  when to turn and in what direction the motor  74  should turn in. The controller may be such an electronic controller connected to the motor  74 . 
         [0027]    The motor gear  80  is part of a reduction gear system  82  that also comprises a first intermediate gear  84 . The motor gear  80  is in meshed engagement with the first intermediate gear  84 . 
         [0028]    The first intermediate gear  84  may be larger in diameter than the motor gear  80 . The increased diameter size of the first intermediate gear  84  compared with the motor gear  80  results in a reduction in the revolutions per minute of the first intermediate gear  84  compared with the motor gear  80 . 
         [0029]    The first intermediate gear  84  is mounted for rotation within the power take off housing  66 . The first intermediate gear  84  rotates about an axis  86  that is parallel to the axis  76  of the motor  74 . 
         [0030]    The reduction gear system  82  also comprises a second intermediate gear  88 . The second intermediate gear  88  rotates about the same axis  86  as the first intermediate gear  84 . The second intermediate gear  88  may be located above the first intermediate gear  84 . The first and second intermediate gears  84 ,  88  may be mounted to one another or they may be separate. If the gears  84 ,  88  are separate a means for one to drive the other is preferred. 
         [0031]    The second intermediate gear  88  may have an outer diameter that is reduced compared to the first intermediate gear  84 . Therefore, the number of revolutions per minute of the second intermediate gear  88  compared with the first intermediate gear  84  is increased. 
         [0032]    The gear reduction system  82  may be comprised of greater or fewer gears than depicted in the figure, and of the gears selected, the sizes and number or type of teeth may vary from what is shown. 
         [0033]    A lever arm  90  is provided with a first end portion  92  and a second end portion  94 . The first end portion  92  terminates in an edge  96 . Preferably, the edge  96  is curvilinear; most preferably, it is arc-shaped. The width of the edge  96  may be greater than the diameter of the second intermediate gear  88 , as shown in the Figures. The width of the edge  96  may be less than, equal to or greater than the diameter of the first intermediate gear  84 . The thickness of the edge  96  may be approximately that of the second intermediate gear  88 . 
         [0034]    A plurality of teeth  98  may define the lever arm edge  96 . The teeth  98  are directly engaged with teeth  100  on the second intermediate gear  88 . 
         [0035]    The lever arm first end portion  92  extends to the second end portion  94  in a bar-like fashion. The second end portion  94  is unitary, one-piece and integrally formed with a shift fork  102 . The shift-fork  102  comprises a C-shaped portion  104  where one of the legs of the C is elongated and comprises the lever arm. 
         [0036]    The shift fork  102  thus comprises the lever arm as a lower leg  106 , an upwardly extending portion  108  and an upper leg  110  all of which are unitary, one-piece and integrally formed with one another. The shift fork  102  also comprises an inner hemispherical surface  112 , which partially defines the C-shape  104  of the fork  102 . 
         [0037]    While terms like “upper,” “lower,” and “upwardly” are used with certain elements above, these terms are not intended to be limiting since the shift fork  102  can be located in any orientation. The terms are merely used for clarification of the shift fork elements depicted in one orientation in the figures. 
         [0038]    At least one shift fork peg is provided in the shift fork  102 . Preferably, two shift fork pegs are utilized. A first peg  114  is located in the upper leg  110  of the shift fork  102  and a second peg  116  is located in the lower leg  106  of the shift fork  102 . The pegs  114 ,  116  are preferably axially aligned with one another, as shown in  FIG. 3 . 
         [0039]    The pegs  114 ,  116  extend through the shift fork  102  and into a groove  118  of a clutch collar  120 . The groove  118  may be circumferential, or only partially circumferential, about the collar  120 . Preferably, the inner hemispherical surface  112  of the shift fork  102  is complimentary to an outer surface  122  of the clutch collar  120 . The outer surface  122  defines the groove  118 . Thus, it can be appreciated that, at least partially, the shift fork  102  is externally concentric with the clutch collar  120 . 
         [0040]    Internally concentric with the clutch collar is a hub structure  124  that locates the collar  120  on to the power take off shaft  68 . The hub structure  124  permits the collar  120  to selectively move axially along the power take off shaft  68 . The hub structure  124  may be comprised of a splined connection between the hub structure  124  and the shaft  68 , or the structure may be comprised of smooth engagement surfaces between the hub structure  124  and the shaft  68  that permit the collar  120  to move along the shaft  68 . 
         [0041]    The clutch collar  120  is connected to a synchronizer (not shown). Synchronizers are used for matching, or synchronizing, the rotation of two parts that might rotating at different rates, or where one part is rotating and the other is not. 
         [0042]    In one embodiment, the synchronizer may be such as a cone synchronizer. A cone synchronizer generally comprises two parts: a selectively rotatable cone-shaped structure, such as a ring, and a complimentary shaped structure. The cone structure may be moved selectively into and out of engagement with the complimentary shaped structure, or vice versa. 
         [0043]    It can be appreciated that, for example, if the cone structure is rotating and the complimentary structure is not, as the cone structure is introduced into the complimentary structure, the complimentary structure begins to rotate. As the cone structure is introduced more and more into the complimentary structure, the complimentary structure begins to rotate closer to the speed of the cone structure. If the rotation of the complimentary structure is to be reduced, the cone structure is gradually withdrawn in the same fashion. 
         [0044]    The clutch collar  120  may be connected to either the cone structure or the complimentary shaped structure. Thus, it can be appreciated that the clutch collar  120  and the power take off shaft  68  can be selectively engaged and disengaged from the power take off unit  52  for engagement and disengagement of drive for the rear wheels. 
         [0045]    The vehicle on which the power take off unit  52  is located has various sensors, programmed software and computers (not shown) to determine when the power take off unit  52  should transfer power to the rear drive wheels  34 ,  36 . In some cases, the operator of the vehicle may make the determination when the rear wheels  34 ,  36  should be engaged so that vehicle operates in four wheel drive. 
         [0046]    Engaging the rear wheels  34 ,  36  begins with the shift motor  74  receiving a signal to rotate the motor gear  80 . The gear  80  rotates causing the first and second intermediate gears  84 ,  88  to also rotate. The second intermediate gear  88  drives through the arc-shaped toothed surface of the lever arm  90 . The lever arm  90  pivots in response to the movement of the second intermediate gear  88 . The lever arm  90  pivots about a pivot axis  126  located through the arm  90 . The pivot axis  126  is parallel to the motor axis  76  and transverse to the input shaft axis  72  and the second axis  76 . 
         [0047]    The lever arm edge  96  moves along an arc  128  as best seen in  FIGS. 5 and 6 . The lever arm pivot point/axis  126  can also be more clearly appreciated in  FIG. 5 . 
         [0048]    The pivot action of the lever arm  90  and the shift fork  10  axially slides the clutch collar  120  to engage the synchronizer. Rotation transfers through the synchronizer resulting in the rotation of the power take off output shaft  68 . 
         [0049]    Disconnecting the drive to the rear wheels  34 ,  36  begins with the shift motor  74  receiving a signal to rotate in the opposite direction. The motor gear  80  rotates in the second direction, which rotates the first and second intermediate gears  84 ,  88 . The second intermediate gear  88  drives back across the arc-shaped toothed edge  92  of the lever arm  90 . The clutch collar  120  pivots about the pivot axis away from the synchronizer, thus disengaging the drive. 
         [0050]    Based on the foregoing, it can be appreciated that the amount of space required to accommodate the lever arm  90 , the clutch collar  120  and the movement of both is reduced compared with prior art designs. Additionally, it can be appreciated that because the entire clutch collar  120  does not have to be axially moved, but just a portion has to be pivoted, that the size of the motor required to do the moving can be reduced. Further, the lever arm  90  provides a mechanical advantage that the prior art designs did not have to move the clutch collar  120 . The motor  74 , and the other components, may therefore be smaller and lighter weight than the prior designs. Lastly, because the lever arm  90  accentuates the movement received by the reduction gears  84 ,  88 , the clutch collar  120  is moved relatively quickly into and out of position resulting a fast clutch engagement and disengagement. 
         [0051]      FIGS. 7 and 8  depict an alternative embodiment wherein the shift motor  74 ′ is oriented parallel and planar with the power take off output shaft  68 ′. The shift motor  74 ′ drives a screw-type gear  130  that extends axially with the shift motor  74 ′. The screw-type gear  130  extends through a block  132 . 
         [0052]    The block  132  has internal threads complementary to the gear  130 . The combined screw-type gear  130  and threaded block  132  create a worm gear. The complementary threads of the worm gear effectively lock together when the motor  74 ′ stops turning. This has the advantage of holding the gear  130  with respect to the block  132  in a fixed position, thus the shift fork  102 ′ is also locked in position. 
         [0053]    The block  132  is connected to shift fork  102 ′. In the depicted embodiment, the block  132  has at least one pin extending transversely to the motor axis. Preferably, two pins  134 ,  136 , which are axially aligned with one another, are located within flanges  138  on the shift fork  102 ′. The pins are connected to the block. The flanges  138  extend from an outer surface  140  of the shift fork  102 ′. There may be an upper flange and a lower flange. The upper and lower flanges  138  extend opposite the lower arm and the upper arm but the flanges  138  are parallel the arms and the flanges  138  are parallel one another. 
         [0054]    The flanges  138  define pin apertures  142  for receiving the block pins  134 ,  136  therein. There may be a first pin aperture and a second pin aperture in the first and second flanges, respectively. Preferably, the first pin aperture is aligned with the second pin aperture. The block pins  134 ,  136  are free to rotate within the pin apertures  142 . The block pins  134 ,  136  extend opposite one another from the block. The shift fork  102 ′ utilizes the pins  134  described above to connect with the clutch collar  120 ′. 
         [0055]    It can be appreciated that upon rotation of the screw-type gear  130  in a first direction, the block  132  is moved away from the motor  74 ′. The clutch  120  follows the block  132  resulting in the collar  120 ′ moving away from the synchronizer. The synchronizer is thus disengaged. The collar  120 ′ pivots about a pivot point  144 , which is opposite the flanges  138 . The arc  146  traveled by the flanges  138  can be appreciated by  FIG. 7 . Upon rotation of the screw-type gear  130  in a second opposite direction, the block  132  is moved toward the motor  74 . The clutch collar  120 ′ follows the block  132  resulting in the collar  120 ′ moving toward the synchronizer. The synchronizer is thus engaged. The flanges  138  travel along the same arc  128  and pivot about the same pivot point  144 . 
         [0056]    The connection of the block  132  and collar  120 ′ creates a lever arm, thus providing a mechanical advantage for moving the clutch collar  120 ′. The mechanical advantage provided by the lever arm means that the motor  74 ′ does not have to be as large to move the clutch collar  120 ′ compared with prior art designs. The space reduction means that the entire system can be located in a smaller envelope. The space reduction and small motor translate to lighter weight. Lastly, because the lever arm accentuates the movement received by motor  74 ′, the clutch collar  120 ′ is moved relatively quickly into and out of position resulting a fast clutch engagement and disengagement. 
         [0057]    In accordance with the provisions of the patent statutes, the principles and modes of operation of this invention have been described and illustrated in its preferred embodiments. However, it must be understood that the invention may be practiced otherwise than specifically explained and illustrated without departing from its spirit or scope.