Transmission shift fork

Abstract

The disclosed transmission shift fork has improved contact areas that engage a gear that is shifted into and out of engagement with the drive train. As a result of the improved contact areas the gear and the shift fork have a more stable alignment that reduces wear during shifting and avoids uneven wear of the parts. The shift fork has an elongated pin that is positioned inside of a biasing spring. The pin has a length that is greater than the length of a compressed biasing spring, which contributes to increased stability and reduced wear from linear movement.

Claims

What is claimed is: 1 . A vehicle transmission shift fork for engaging a transfer gear, the shift fork comprising: a hub with a midsection that supports dependent arms that define an interior cavity of a predetermined diameter that complements an interior diameter associated with a circumferential channel encircling a predetermined transfer gear; each dependent arm has an end contact portion of a predetermined size that is complementarily to the circumferential channel; wherein the hub midsection and the dependent arms are centered about a common plane; and, wherein a combination of the complementary fit between the contact portions and a predetermined transfer gear's circumferential channel maintains the combination centered about the common plane. 2 . The shift fork of claim 1 wherein the hub includes a tubular projection and a shaft that are aligned along a longitudinal axis. 3 . The shift fork of claim 2 wherein the longitudinal axis is perpendicular to the common plane about which the hub midsection and the dependent arms are centered. 4 . The shift fork of claim 1 wherein the end portions of the dependent arms include wear surfaces. 5 . The shift fork of claim 4 wherein the wear surfaces have parallel outer faces that are separated by an inner face. 6 . The shift fork of claim 5 wherein the inner face is perpendicular to the parallel outer faces. 7 . The shift fork of claim 5 wherein the parallel outer faces that are separated by a distance that is substantially equal to a width associated with a circumferential channel encircling a predetermined transfer gear. 8 . The shift fork of claim 7 wherein the inner face of the end portions are spaced apart by a distance substantially equal to the predetermined diameter that complements an interior diameter associated with a circumferential channel encircling a predetermined transfer gear. 9 . The shift fork of claim 1 further comprising a hub having: a tubular projection; a shaft with a predetermined length; and a compression spring with a compressed length that is less than the predetermined length of the shaft. 10 . The shift fork of claim 9 wherein the wear surfaces have parallel outer faces that are separated by an inner face. 11 . The shift fork of claim 10 wherein the inner face is perpendicular to the parallel outer faces. 12 . The shift fork of claim 11 wherein the parallel outer faces that are separated by a distance that is substantially equal to a width associated with a circumferential channel encircling a predetermined transfer gear. 13 . The shift fork of claim 12 wherein the inner face of the end portions are spaced apart by a distance substantially equal to the predetermined diameter that complements an interior diameter associated with a circumferential channel encircling a predetermined transfer gear. 14 . A vehicle transmission shift fork for engaging a transfer gear, the shift fork comprising: a hub that includes a face with a dependent shaft that extends along a longitudinal axis that is perpendicular to the hub face; a midsection that has is joined to the hub and combines with dependent arms to form an arched cavity; each of the dependent arms has an end portion with a wear pad that is sized to fit within a predetermined bearing collar channel that is defined by a circular base and opposed circular flanges that are spaced apart by the base; each wear pad has first and second opposed faces that contact the circular flanges and inner face that contacts the circular base. 15 . A vehicle transmission shift fork for engaging a transfer gear, the shift fork comprising: a hub a with a midsection that supports dependent arms that define an interior cavity with a predetermined diameter that complements a circumferential channel encircling a predetermined transfer gear, and the hub midsection and dependent arms are centered about a common plane; each dependent arm has a free end with a contact portion of a predetermined size that is complementary to a portion of the circumferential channel; and, wherein a combination of the contact portions and a circumferential channel encircling a predetermined transfer gear maintains the shift fork and transfer gear centered about the common plane.
FIELD OF INVENTION [0001] The present invention relates generally to distributing power from the engine through the drive train to the vehicle's wheels. More particularly, the invention relates to movable shift forks that are located in the drive train to enable an operator to select different drive train configurations. Most particularly, the invention relates to shift forks associated with the selection between two and four wheel drive. BACKGROUND [0002] Transmission shift forks have been common in transmissions and drive trains for some time. More recently, vehicles that can selectively be shifted between drive trains that engage two or four wheel drive are becoming increasingly popular. In many applications, the shift fork is the part of the drive assembly that is moved to engage or disengage a coupling between an input gear and an output gear. When the vehicle is in two wheel drive, the shift fork is positioned for disengagement and, conversely, when the shift fork is positioned for engagement the vehicle is in four wheel drive. [0003] Known prior art shift forks of the type this invention concerns have suffered from two deficiencies. One deficiency has been wear on the fork or the surfaces OF THE dependent arm due to the continuous contact between the fork and the spinning coupling gear that is shifted by the fork. Another problem area has been wear and breakage of the fork's pilot pin which guides linear movement of the fork. [0004] With respect to the first deficiency, there have been attempts to add wear pads to the surfaces of the fork that contact the gear flanges that define the outer edges of the race within which the fork rest when it engages the gear. However, this attempt has not been successful as did not alleviate the misalignment between the fork and the gear. This misalignment ultimately led to wear on the shaft or pin on which the fork rest for liner movement to effect the desired engagement. With respect to the defect in the shaft or pin, the inventors are not aware of any prior art attempt to address this problem. [0005] The objects of the present invention are to provide a shift fork with improved pilot pin and contact wear surfaces. SUMMARY [0006] The present solution provides a shift fork with improved contact areas for engaging the gear that is shifted into and out of engagement. As a result of the improved contact areas the gear and the shift fork have a more stable horizontal alignment that reduces wear and avoids uneven wear of the parts. In addition to the improved contact areas, the shift fork also has an elongated pin that is positioned inside of a biasing spring and has a length that is greater than the length of the biasing spring when it is in a compressed condition. BRIEF DESCRIPTION OF THE DRAWING(S) [0007] FIG. 1 is a perspective view of the shift fork according to the invention; [0008] FIG. 2 is a perspective view of the shift fork of FIG. 1 form the other side; [0009] FIG. 3 is a plan view of the shift fork in engagement with a shift gear; FIG. 4 is a side elevation of an engaged shift fork and shift gear; [0010] FIG. 5 is a section along the line 5 - 5 in FIG. 4 ; [0011] FIG. 6 is an illustration of the gear and a shift fork according to the invention in a transfer case with a biasing spring positioned about the pin of the shift fork; [0012] FIG. 7 illustrates the relationship between the pin and biasing spring of the invention during compression within a transfer case; and, [0013] FIG. 8 illustrates the relationship between the pin and the biasing spring of the prior art during compression within a transfer case. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) [0014] With reference to the perspective view of one side of the shift fork in FIG. 1 , the shift fork 2 has a hub 10 that includes face 12 , midsection 13 , and a pilot pin or shaft 14 that is generally perpendicular to and centered on the horizontal face 12 . The shaft 14 extends along the longitudinal axis “A.” Depending from the midsection 13 is a torso 20 with dependent arms 22 and 24 . The arms 22 and 24 extend outwardly from the torso 20 in an arched or semi-circular fashion that defines an interior opening between them. Each arm has a free end that terminates in a contact portion or wear pad 26 . The wear pads 26 have parallel faces 28 and 30 , see FIGS. 1 and 2 , a planar inner face 32 that extends between faces 28 and 30 and is perpendicular to them. The outer face 34 of the wear pads 26 extends between faces 28 and 30 and is somewhat arcuate. The [0015] With reference to FIGS. 1 and 2 , the torso 20 has a central wear pad 40 . The wear pad 40 has different faces on either side of the torso 20 . On the side of torso 20 with the shaft 14 , the wear pad 40 has two parts 42 on either side of a lubrication channel that extends from the surfaces 43 into the face 12 just beneath the shaft 14 . The lower faces 43 of the parts 42 are in the same plane 44 as the rest of the wear pad 40 . On the opposite side of torso 20 , there is a wear pad 46 with a continuous surface, see FIG. 2 . The wear pads 26 and 40 have a width 36 that is selected to complement the transfer gear as is explained later. [0016] Also with reference to the side shown in FIG. 2 , there is a tubular projection 50 which is configured in accordance with an original equipment shift fork so it fits the pre-existing environment. [0017] With reference to FIGS. 3 and 5 , there is illustrated a combination of the present shift fork 10 with an existing transfer gear 58 . The wear pads 26 and 40 have planar surfaces, 32 and 44 respectively, that form tangents to the inner circumference 62 of a circumferential channel 60 having an outer circumference 64 . The circumferential channel 60 has outer walls 70 that define a predetermined width to the channel 60 . The width of the channel 60 associated with a given transfer gear will determine the width 36 of the wear pads 26 and 40 . The channel and wear pads are dimensioned so that lubricant flows between them and the gear rotates freely; however, it will be understood that this is a close tolerance that just accommodates the viscosity of the lubricant in the transmission case. [0018] With reference to FIG. 4 , there is a side view of combination of FIG. 3 . It can be seen from FIG. 4 that the fit between the wear pads, 26 and 40 , with the channel, 60 , of the transfer gear, 58 , maintains hub 10 , torso 20 , arms 22 and 24 and transfer gear 58 centered about a common plane, “P”, that is perpendicular to longitudinal axis “A”. [0019] FIG. 6 illustrates the combination of a shift fork, 10 , according to the present invention and a transfer gear, 58 , in fragmentary transmission housing. When the fork 10 is located within the transmission housing, it is surrounded by a compression spring 70 . As shown in FIG. 6 , the compression spring is in a relaxed state. When the shift fork 10 is moved linearly to a condition where the spring 70 is compressed, the pin 14 extends beyond the beyond the end of the compressed spring. This relationship between the pin and spring in the compressed state differs from the prior art because the prior art pin does not extend beyond the end of the compressed spring, but the current pilot pin 14 is provided with a greater length. This increased length means that the present pilot pin 14 extends beyond the compressed spring and stabilizes the pin 14 during linear movement. This additional stability combines with the existing tubular projection 50 to maintain a centralized orientation about common plan “P” see FIG. 4 . This centralized orientation reduces known prior art problem of the shift fork slanting and contributing to misalignment problems. [0020] FIG. 7 is a fragmentary illustration of the pin and compressed spring of the present invention in a transmission housing and FIG. 8 is a fragmentary illustration of a prior art pin and compressed spring in transmission housing.

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