Abstract:
A shift fork restrictor operably disposed in a transfer case for the purpose of allowing the shift motor to transfer energy to the currently existing double wound spring, where the energy is stored until the shift motor sensor indicates that the motor is in the proper range location. When the motor is in the proper range location, the stored energy in the spring is released by the shift fork restrictor releasing the cam allowing for maximum torque and speed to be provided through the secondary rail, cam, and shift fork to complete the requested range shift. This configuration can be used to, among other things, select a high or low range in the transfer case, as well as couple the input and output shafts together, which have different gear ratios.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U.S. Provisional Application No. 60/762,680, filed Jan. 27, 2006. The disclosure of the above applications is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to a shift restrictor apparatus for a transfer case.  
       BACKGROUND OF THE INVENTION  
       [0003]     This invention relates generally to the operation of two-speed transfer cases and more specifically to the shift from high to low range. It is known in the automobile industry that most vehicles that use either four-wheel-drive or all-wheel-drive systems are equipped with some sort of device for transferring power to the front wheels, usually this device is a transfer case, or something similar.  
         [0004]     Current designs of the transfer case involve the use of a planetary gear set to obtain different gear ratios between the input shaft and output shaft of the transfer case. To change gear ratios, a shift system having a spring loaded shift device is used for completing delayed gear shifts once the input and output shafts are synchronized. Although the current spring loaded shift design is adequate, there exists a need for improvement of the design and advancement of the art. Current problems existing in the design include a “clunk” noise that can occur when the range shift is performed if the input and output shafts are not properly synchronized, resulting in a delay in the shift. The present invention will allow for a faster shift once the input and output shafts are synchronized to reduce any undesirable shift noise or delay.  
       SUMMARY OF THE INVENTION  
       [0005]     A shift fork restrictor operably disposed in a transfer case for the purpose of allowing the shift motor to transfer energy to the currently existing double wound spring, where the energy is stored until the shift motor sensor indicates that the motor is in the proper range location. When the motor is in the proper range location, the stored energy in the spring is released by the shift fork restrictor releasing the cam allowing for maximum torque and speed to be provided through the secondary rail, cam, and shift fork to complete the requested range shift. This configuration can be used to, among other things, select a high or low range in the transfer case, as well as couple the input and output shafts together, which have different gear ratios.  
         [0006]     Another improvement to the current design that the present invention provides will be the use of sensors that can detect the position of the dog clutch. The dog clutch is the device that, depending upon its position along the output shaft, will provide either a direct drive, or a reduced speed gear ratio. Current designs of the transfer case use the position of a bidirectional motor, which is the device that controls the shift, to detect where the position of the dog clutch is located. Because of possible lag in the shift, the position of the bidirectional motor may not always give the correct position of the dog clutch. The use of sensors in the transfer case positioned in such a fashion to locate the exact position of the dog clutch will allow for the present invention to permit the shift to take place at the exact time necessary so no lag, or disturbing “clunk” noise, occurs.  
         [0007]     Therefore, it is an object of this invention to provide an improved shift system in a transfer case.  
         [0008]     It is a further object of this invention to provide a maximum speed shift from high to low range in the transfer case, and vise versa.  
         [0009]     It is yet a further object of this invention to provide a shift fork restrictor that is adapted for use with a cam and shift fork assembly in a transfer case.  
         [0010]     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0012]      FIG. 1  is a cross-section of a transfer case incorporating the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0013]     The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.  
         [0014]     Referring to  FIG. 1 , a transfer case that has the present invention is shown at  10 . The transfer case  10  includes a casing  18  which includes various supports, bearing surfaces, threaded openings, and other various features that serve the purpose of receiving other components of the transfer case. Among the other components is a gear reduction set  16  that is driven by the input shaft  12  and is coupled with the output shaft  14 . The input shaft  12  has a plurality of teeth that are splined with the teeth on the internal surface of the sun gear  20 . The sun gear  20  also has a plurality of teeth on its external surface that are in mesh with the planetary gears  22 . The planetary gears  22  are rotatably received on stub shafts  28 , which are mounted onto carrier  24 . The ring gear  26  has a plurality of teeth that are directed inward and are in alignment with the sun gear  20 . The planetary gears  22 , in addition to being in mesh with the sun gear  20 , are also in mesh with the ring gear  26 . The carrier  24  has a plurality of teeth that are directed inwardly toward the dog clutch  30 , and can selectively mate with a plurality of teeth on the external surface of the dog clutch  30 . The dog clutch  30  also has a plurality of teeth that are splined to and is received about the output shaft  14 . The dog clutch  30  rotates with the output shaft  14 , but also may slide axially. The teeth on the internal surface of the dog clutch  30  are also complementary with the teeth on the input shaft  12 .  
         [0015]     The dog clutch  30  can be axially translated between three positions along the output shaft  14 . The first is a forward position wherein the internal teeth of the dog clutch  30  are coupled with the teeth of the input shaft  12  and the output shaft  14 , providing a direct or one-to-one ratio between the input shaft  12  and output shaft  14 . In this position, the dog clutch  30  is not coupled to gear reduction set  16 , therefore, gear reduction set  16  is not involved in transmitting torque through the transfer case  10 . When the dog clutch  30  is axially translated into a position fully to the rear, the internal teeth of the carrier  24  are received upon the external teeth of the dog clutch  30 , which is received about the output shaft  14 . The input shaft  12  drives the sun gear  20 , which is in mesh with the planetary gears  22 . As the planetary gears  22  are driven by the sun gear  20 , they also rotate the carrier  24 , which in turn rotates the dog clutch  30 , which then rotates the output shaft  14 . This configuration causes the speed of the output shaft  14  to be reduced compared to the input shaft  12 , normally at a ratio of 2:1 or 4:1. The third position of the dog clutch  30  is a neutral position, between the forward, or direct drive position, and the rearward, or reduced speed position. In this position, the input shaft  12  is not connected to the output shaft  14  in any fashion, and no power is transferred between them.  
         [0016]     The location of the dog clutch  30  is controlled by a bidirectional motor  32  through the use of a worm gear assembly  36  and a shift fork and cam assembly  34 . The shift fork and cam assembly  34  is made of several components, comprising of a drive shaft  38 , a spring assembly  40  which is wrapped around the drive shaft  38 , cylindrical cam  42 , cam follower  44 , shift fork  46 , shift rail  48 , and shift fork restrictor  50 . The bidirectional motor  32  rotates drive shaft  38  through the worm gear assembly  36 . The drive shaft  38  is supported in the casing  18  so that it may rotate freely when commanded to by the bidirectional motor  32 . The spring assembly  40  couples the drive shaft  38  and the cam  42 ; the cam  42  is connected to the spring through an arm  54  that extends axially from the cam  42  into the spring assembly  40 . The drive shaft  38  contains an arm  56  on the forward end that is also connected to the spring assembly  40 . The spring assembly  40  acts as an elastic coupler between the drive shaft  38  and the cam  42 , compensating for any lag when the bidirectional motor  32  is actuated, allowing the bidirectional motor  32  to reach its proper location. When a shift is requested, the internal teeth of the dog clutch  30  may not always be lined up with the teeth on the input shaft  12 ; conversely, the external teeth of the dog clutch  30  may also not been lined up with the inward teeth of the carrier  24 . When the shift fork restrictor  50  is not engaged, it restricts movement of the cam  42 . The drive shaft  38  is still allowed to rotate, and upon doing so, stores potential energy in the spring assembly. When the shift fork restrictor  50  is actuated, it releases the cam  42 , thereby releasing the potential energy stored in the cam  42 . The releasing of this energy allows for a maximum speed shift. Since the drive shaft  38  can be rotated in both directions, a faster shift can be achieved for shifting from low to high range, as well as high to low range. The cylindrical cam  42  defines a helical surface  58  that extends about the cam  42  approximately 270°. The cam follower  44  is received by the cam  42 , and is coupled with, as well as axially translates the shift fork  46 . The shift fork  46  is mounted to the shift rail  48 , which is secured to the casing  18 . The shift fork  46  engages the periphery of the dog clutch  30  and when the cam  42  rotates, the shift fork  46  is moved along the shift rail  48  axially and therefore locates the dog clutch  30  into one of the aforementioned positions.  
         [0017]     Also included in the transfer case is an electromagnetic clutch assembly  60 , comprising a circular drive member  66 , a circular driven member  64 , apply plate  62 , an electromagnetic coil  68 , and clutch pack  70 . Circular driven member  64  can freely rotate about the output shaft  14 , and is directly secured to rotor  72 . The rotor  72  possesses a U-shaped cross-section that surrounds the magnetic coil  68  on three sides. Both the circular drive member  66 , and the circular driven member  64  both include a plurality of opposed recesses  74 , which receive load transferring balls  76 . The opposed recesses  74  function as a ramp or cam that will push apart circular drive member  66 , and circular driven member  64  when relative motion between them occurs. Circular drive member  66  and apply plate  62  are both splined to output shaft  14 .  
         [0018]     Upon activation of the electromagnetic coil  68 , frictional contact occurs between surfaces  80  and  82 . When the secondary output shaft  84  is rotating at a different speed than output shaft  14 , frictional torque transfers load from the output shaft  14  through the circular drive member  66 , through the load transferring balls  76 , and through the circular driven member  64 . This results in the load transferring balls  76  riding up in their respective recesses, displacing circular drive member  66  away from circular driven member  64  axially along the drive shaft  14 . The circular drive member  66  then translates an apply plate  62  which in turn compresses clutch pack  70 .  
         [0019]     It should also be noted that those skilled in the are will recognized that activation of the clutch pack  70  can be accomplished by other means than through the use of electromagnetic coil  68 . Clutch pack  70  could also be engaged through the use of hydraulic fluid, or pressurized air.  
         [0020]     The clutch pack  70  is composed of a plurality of discs, interleaved with one another. The friction discs  96  are splined to the clutch hub  92 , and the steel discs  94  are splined to the housing  78 .  
         [0021]     The clutch housing  78  is not splined to the output shaft  14 , and can rotate freely. The housing  78  is coupled to drive sprocket  86 , which is also free to rotate about the output shaft  14 . Upon engagement of the clutch pack  70 , torque from the output shaft  14  is transferred through the clutch hub  92 , through the clutch pack  70 , through the housing  78 , through the drive sprocket  86 , then through chain  88 , through driven sprocket  90 , and finally, through secondary output shaft  84 .  
         [0022]     It should be appreciated by those skilled in the art that the clutch pack  70  can be engaged by means other than the use of the electromagnetic coil  68 . Hydraulic fluid or pressurized air could also be used to actuate the clutch pack, and produce the same result.  
         [0023]     Also incorporated in the transfer case are two Hall Effect sensors  52 . A first Hall Effect sensor  52  is disposed in proximate sensing relationship with collar of the dog clutch  30 , when it is in the one-to-one, or direct-drive, position. A second Hall Effect sensor  52  is in proximate sensing relationship to the dog clutch  30  when it is in the reduced speed position. The Hall Effect sensors  52  directly locate the position of the dog clutch  30 , which eliminates the need for detecting the position of the dog clutch  30  by use of the bidirectional motor  32 .  
         [0024]     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.