Gearbox assembly and its worm shaft assembly

Abstract

The present invention relates to a gearbox assembly, which includes: a housing; a first shaft assembly, the first shaft assembly including a worm transmission and being supported by a first supporting assembly relative to the housing; and a second shaft assembly, the second shaft assembly including a worm gear transmission, the worm gear transmission also being supported by a second supporting assembly relative to the housing, the worm gear transmission being engaged with the worm of the worm transmission to allow torque to be transmitted between the two shaft assemblies, and is characterized in that the first shaft assembly includes an elongated shaft carrying the worm transmission and a split-type claw drive mechanism, the claw drive mechanism being fastened to one end of the elongated shaft by the first supporting assembly, so that torque is transmitted between the elongated shaft and the claw drive mechanism during use.

Description

Technical Field

[0001] The present invention relates to improvements in gearbox assemblies, and more particularly to a gearbox assembly for an electric power steering assembly. The present invention also relates to a worm shaft assembly incorporated in the gearbox, and to an electric power steering system including the gearbox assembly. Background Art

[0002] It is known to provide a gearbox assembly having a housing that positions and protects a worm-type gear transmission assembly. The transmission assembly includes a first shaft assembly and a second shaft assembly. The first shaft assembly includes a worm transmission in the form of a screw extending along the length of the shaft, the worm transmission being supported relative to the housing by at least one annular support assembly; the second shaft assembly includes a load-bearing worm gear transmission, which is also supported relative to the housing by at least one support assembly. The two shafts are axially offset and arranged perpendicular to each other so that the teeth on the periphery of the worm gear transmission engage with the worm of the worm transmission. Rotation of the worm gear transmission will cause rotation of the worm transmission, and vice versa. This allows torque to be transmitted between the two shafts. One shaft can define the input of the gearbox assembly and the other shaft can define the output of the gearbox assembly.

[0003] Worm and worm gear assemblies are particularly well-suited for applications requiring a simple, compact mechanism with a high transmission ratio. By appropriately selecting the gear tooth design, worm gear assemblies can provide minimal backlash and low friction in both transmission directions. These characteristics are crucial for electric power steering assemblies, where a motor applies auxiliary torque to a portion of the steering mechanism via a gearbox to assist the driver in turning the steering wheel. Any backlash can create an undesirable sensation for the driver through the steering wheel. The 90-degree offset between input and output allows the drive motor to be conveniently positioned next to the steering shaft.

[0004] In order to connect an electric motor to the input shaft of a gearbox assembly, it is known to provide a dog drive mechanism as part of a worm shaft. This dog drive mechanism may include a set of dog teeth that engage with a similar dog drive mechanism fixed to the motor. FIG3 shows a prior art worm shaft having a set of four dog teeth at one end. As can be seen, the dog teeth are mounted on a radially protruding annular carrier that has a relatively large diameter compared to the worm shaft. Providing dog teeth to transmit driving force from one rotating component to another without the possibility of slippage is well known in the field of gearbox design, particularly in the field of gearboxes for electric power steering systems.

[0005] The applicant has realised that, due to the large radius of the annular carrier, it is very wasteful to manufacture such a shaft from metal bar stock. This makes the part relatively expensive to produce and, in the case of a single metal part, makes the shaft relatively heavy. Summary of the Invention

[0006] According to a first aspect of the present invention, there is provided a gearbox assembly, comprising a gearbox assembly comprising: a housing; a first shaft assembly, the first shaft assembly including a worm drive and supported relative to the housing by a first bearing assembly; and a second shaft assembly, the second shaft assembly including a worm gear drive, the worm gear drive also supported relative to the housing by a second bearing assembly, the worm gear drive engaging with a worm of the worm gear drive to allow torque to be transferred between the two shaft assemblies.

[0007] It is characterized in that the first shaft assembly includes an elongated shaft carrying the worm gear transmission device and a split claw drive mechanism, and the claw drive mechanism is fastened to one end of the elongated shaft through the first supporting assembly, so that torque is transmitted between the elongated shaft and the claw drive mechanism during use.

[0008] The dog drive mechanism may include two or more dog teeth radially offset from the axis of the elongated shaft to engage corresponding dog teeth of an external drive mechanism. This external mechanism may be a complementary dog ​​drive mechanism fixed to the output shaft of the electric motor, the dogs of the two dog drive mechanisms interlocking to transmit the rotational motion of the motor to the first shaft assembly.

[0009] The first shaft assembly may include a connection arrangement for securing the elongate shaft of the first shaft assembly to the jaw drive mechanism, the connection arrangement including a first bearing assembly.

[0010] The connection device may further include a biasing mechanism that positions the first bearing assembly around a portion of the jaw drive mechanism and applies an axial thrust load to the jaw drive mechanism through the bearing assembly.

[0011] The connecting means may be separate from the jaw drive mechanism and the elongate shaft and may take the form of a collar.

[0012] Alternatively, the connection means may be an integral part of the jaw drive mechanism that interacts with a member on the elongate shaft.

[0013] The jaw drive mechanism may therefore be a snap-fit ​​member that snaps onto the elongated shaft, and the support assembly is a snap-fit ​​member that snaps onto the outside of the jaw drive mechanism, wherein the support assembly, when in place, prevents the jaw drive mechanism from disengaging from the elongated shaft, thereby locking the jaw drive mechanism in place.

[0014] The engagement can be achieved by providing a portion of the claw driving mechanism with elastic force.

[0015] The jaw drive mechanism may include a fixing portion that fits around an end portion of the elongated shaft, the fixing portion including inwardly facing splines that engage corresponding outwardly facing splines provided on the end of the shaft. The fixing portion may be separate from the provided connection means.

[0016] The fixed portion may define a cylindrical portion of the jaw driver having an inner diameter substantially matching the outer diameter of the elongate shaft.

[0017] The first bearing assembly may include an annular bearing assembly having an annular inner race, an annular outer race, and a bearing element located between the two races, wherein the inner race is a press fit or interference fit to the outer surface of the cylindrical portion of the jaw drive mechanism. The inner race presses the splines of the jaw drive mechanism into engagement with the splines of the shaft, which in turn prevents the jaw drive mechanism from rotating relative to the shaft.

[0018] The cylindrical portion may have a continuous wall extending around the end portion of the shaft. However, skilled artisans will appreciate that the cylindrical portion may define a discontinuous wall and may include a cut-away area that exposes the shaft surface. For example, the cylindrical portion may form a set of axially extending elongated fingers spaced about the circumference of the end portion of the elongated shaft and between the first bearing assembly and the end portion of the shaft.

[0019] The inner race of the first bearing assembly may bear against a shoulder provided on the jaw drive mechanism that reacts the thrust load from the bearing assembly.

[0020] The biasing means of the coupling may comprise a corrugated ring, or a star washer, or a conical coil spring acting between the elongate shaft and the inner race of the bearing assembly to retain the bearing assembly in position about the cylindrical portion of the jaw drive mechanism.

[0021] When the biasing means is integrally formed with the jaw drive mechanism, the fixed portion may comprise a plurality of axially extending tabs having splines formed on their inner faces which engage with the splines on the elongated shaft. The tabs may be spaced around the splined portion of the elongated shaft.

[0022] The biasing means may comprise at least one further tab having a raised or hooked portion along its length or at its free end which engages with a member on the elongate shaft.

[0023] The support assembly may secure the biasing device in engagement with the elongated shaft when in the use position such that the biasing device prevents axial movement of the pawl mechanism relative to the elongated shaft.

[0024] The jaw drive mechanism may comprise a one-piece component having a radial disc-shaped portion at one end from which two or more jaw teeth project from one face and a plurality of elongated resilient tabs extending away from an opposite face, at least one of the tabs comprising an outwardly facing rib at a free end, the rib retaining the bearing assembly against the disc-shaped portion and an inwardly facing tang engaging a recess in the elongated shaft. This resilient tab, along with the rib and tang, may form the connecting means of the assembly.

[0025] The disc-shaped portion may have a central opening that receives the end portion of the elongated shaft. The disc-shaped portion may abut against a circumferential shoulder formed on the end of the elongated shaft to limit the distance the jaw drive mechanism can be pushed onto the shaft.

[0026] At least one locating tab may be provided, extending from the same face of the disc as the resilient tab, the locating tab being provided with one or more splines on an inner face thereof which are complementary to and engage with the splines on the elongated shaft. This engagement allows the jaw drive mechanism to transmit torque to the elongated shaft.

[0027] There may be at least two spring tabs and two positioning tabs, the positioning tabs and spring tabs alternating around the circumference of the elongated shaft.

[0028] In an alternative embodiment to a one-piece component, the jaw drive mechanism may include two separate half-sleeves that fit together to surround the end portion of the elongated shaft and form a cylindrical portion and a shoulder, the two half-sleeves being fixed in place on the elongated shaft by the first support assembly and the biasing device.

[0029] The jaw drive mechanism may include a biasing device that engages a recess in the outer circumferential surface of the end of the elongated shaft to prevent the half-sleeve from moving axially relative to the elongated shaft. The first bearing assembly retains the engaged portion in this recess and prevents it from jumping out radially under load.

[0030] The recess may comprise a groove which may extend around the entire circumference of the shaft.

[0031] In the alternative, the shaft may carry a radial projection in the inner surface of the jaw drive mechanism which projects into the recess, engages the shaft to provide the axial retention function.The radial projection may comprise an annular rib formed on an end portion of the elongate shaft.

[0032] The first shaft assembly may comprise an input of the gearbox assembly and the second shaft assembly may comprise an output of the gearbox assembly.

[0033] The elongated shaft may comprise a metal component or a metal alloy.

[0034] The jaw mechanism may comprise a molded plastic component or an additively manufactured (AM) part.

[0035] According to a second aspect, the present invention provides a worm shaft assembly for a worm gearbox assembly,

[0036] The worm shaft assembly includes an elongated shaft carrying a worm gear transmission device, and a split claw drive mechanism fastened to one end of the elongated shaft, wherein the elongated shaft and the split claw drive mechanism are fixed together by a support assembly, and the support assembly prevents relative axial movement and rotational movement between the elongated shaft and the split claw drive mechanism, so that torque is transmitted between the elongated shaft and the claw drive member during use. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Several embodiments of the present invention will now be described, by way of example only, with reference to and as illustrated in the accompanying drawings, in which:

[0038] Figure 1 is a perspective view of a housing of a worm gearbox assembly;

[0039] Figure 2 is a cross-sectional view of a general transmission assembly located within a housing;

[0040] 3( a ) and 3 ( b ) are perspective views of a one-piece metal worm shaft assembly for a worm gearbox of the prior art;

[0041] 4( a ) and 4 ( b ) are perspective views of a first embodiment of a worm shaft assembly of a gearbox assembly according to the present invention;

[0042] 5( a ) and 5 ( b ) are cross-sectional views corresponding to FIG. 4( a ) and 4 ( b ).

[0043] Figure 6 is an enlarged cross-sectional view of a portion of the worm shaft assembly of Figures 4 and 5, illustrating the connection of the split jaw drive mechanism to the end of the worm shaft;

[0044] 7( a ) and 7 ( b ) are perspective and corresponding cross-sectional views of the elongated shaft before it is assembled to the gearbox assembly;

[0045] 8( a ) and 8 ( b ) are perspective views of a pair of half shells of the jaw drive mechanism, and FIG. 8 ( c ) is a cross-sectional view of the half shells;

[0046] Figure 9(a) to Figure 9(c) are different views of the crimped gasket of the assembly of the first embodiment;

[0047] Figure 10(a) to Figure 10(e) The main steps to be performed to assemble the worm shaft assembly of the first embodiment are shown;

[0048] Figures 11(a) and 11(b) illustrate a second embodiment of a worm shaft assembly assembled and during assembly;

[0049] Figure 12 is a perspective view of a split ring for retaining a jaw drive mechanism of a second embodiment;

[0050] 13( a ) and 13 ( b ) illustrate a third embodiment of a worm shaft assembly assembled and during assembly;

[0051] Figure 14 is a perspective view of a conical coil spring for retaining a pawl drive mechanism of a second embodiment;

[0052] FIG15 is a view of another embodiment in which the shaft shown in FIG15(a) is overmolded with a portion forming a jaw drive mechanism shown in FIG15(b); and

[0053] 16(a) and 16(b) are perspective views of the jaw drive mechanism of FIG. 15 removed from the shaft to reveal the internal splines.

[0054] Figure 17 and Figure 18 is a perspective view of one half shell of a pair of half shells of a pawl drive mechanism in another embodiment of the present invention;

[0055] Figure 19 shows how the two half-shells are fastened to the elongated shaft by means of a bearing assembly;

[0056] Figure 20 and Figure 21 is a perspective view of an alternative one-piece jaw drive mechanism in a still further embodiment of the present invention; and

[0057] Figure 22 Shown is how a one-piece jaw drive mechanism is secured to an elongated shaft via a bearing assembly. DETAILED DESCRIPTION

[0058] like Figure 1 As shown, the gearbox assembly 1 includes a housing 10 that houses a transmission assembly, wherein a drive mechanism is fixed to the end of an input shaft 11 of the transmission assembly protruding from one face of the housing, and the end of an output shaft 12 of the transmission assembly protrudes from the other face at 90 degrees to the input shaft.

[0059] Figure 2 The internal components of gearbox assembly 1 are shown in cross-section. A first shaft assembly 13 includes an elongated input shaft 11 carrying a worm gear 14. Elongated shaft 11 is supported relative to the housing by two bearing assemblies 15 and 16, each positioned proximate opposite ends of shaft 11. Bearing assemblies 15 and 16 are retained in seats formed in the inner wall of the housing. Each bearing assembly comprises a set of annular bearings positioned between an inner annular race and an outer annular race.

[0060] The second shaft assembly 17 includes a second shaft 18 carrying a worm gear 19. This second shaft is also supported at each end relative to the housing by bearing assemblies (not shown), which are located in seats in the inner wall of the housing. The axis of rotation of the second shaft 18 is offset from the axis of rotation of the first shaft 11 and is perpendicular thereto.

[0061] The teeth of the worm gear 19 engage with the worm gear 14 to allow torque to be transmitted between the two shafts.

[0062] The first shaft 11 is shown in Figure 7 with all other components removed and in cross-section in Figure 8. The first shaft comprises an elongated metal shaft with a worm drive 14 cut into the outer surface midway along the shaft. A set of axial splines 21 are formed at one end, and inside these splines is an annular groove 22 terminating in a shoulder 23 facing the splines across the groove.

[0063] At one end of the first shaft assembly is a split jaw drive mechanism 24 which forms the input to the gearbox assembly 1 (at Figure 1 (as can be seen in the figure). This jaw drive mechanism is a molded plastic component that, in this embodiment, comprises two half-shells 25. The elongated first shaft 11 and the split jaw drive mechanism 24 are secured together by one of the support assemblies 16 to prevent relative axial and rotational movement between the elongated first shaft and the jaw drive mechanism, allowing torque to be transmitted between the elongated shaft 11 and the jaw drive mechanism 24 during use. Notably, the jaw drive mechanism has a larger diameter than the elongated shaft.

[0064] The two half shells 25 of the plastic claw drive mechanism are identical, and Figure 8(a) to Figure 8(c)One of the half-shells is shown in detail. Each shell has a partially cylindrical portion 26 including a set of inwardly extending splines 27, and a partially disc-shaped shoulder portion 28 extending radially outward from the end face of the partially cylindrical portion 26. This defines two faces: one facing the partially cylindrical portion and defining the shoulder, and another facing away from the partially cylindrical portion 26, carrying two dog teeth 29. When the two half-shells 25 are placed together onto the end of an elongated shaft 11, they form a complete cylinder that surrounds the splined portion of the shaft and the radially extending disc that forms the shoulder.

[0065] As shown, the two half-shells are identical, but this is not required for the present invention. The two half-shells 25 can be placed around the ends of the elongated shaft 11 so that the splines 27 of the half-shells engage with the corresponding splines 21 on the elongated shaft 11. An inwardly extending ring 30 on the end of the cylindrical portion furthest from the shoulder engages with a correspondingly shaped groove in the shaft adjacent to the splines. This prevents the jaw drive mechanism 24 from being pulled axially away from the end of the shaft.

[0066] To hold the two half-shells 25 together, the annular support assembly 16 is positioned on the cylindrical portion 26 and the bellows ring 40 is positioned in the groove that receives the inwardly extending ring, with the resilient fingers 41 of the bellows ring applying a thrust on the support and, in turn, on the shoulder of the jaw drive mechanism. A suitable bellows ring is shown in FIG9 . Figure 6 The position of the corrugated ring 40 is best shown in the cross-sectional view of the worm shaft assembly.

[0067] Figure 10(a) to Figure 10(e) Shown are steps that may be performed during assembly of a worm shaft assembly.

[0068] Step A—Place the two half shells 25 onto the ends of the elongated shaft 11 so that the internal splines 27 engage the splines of the elongated shaft 11 and the inwardly facing rings 30 engage in the grooves of the shaft.

[0069] Step B—Pressing the annular bearing assembly 16 onto the shaft 11 from the end furthest from the half-shell 25 towards the half-shell 25 .

[0070] Step C - Bring the bearing assembly 16 against the shoulders of the two half-shells 25, wherein the inner race of the bearing assembly is interference fit with the outer surface of the cylindrical portion 26 of the two half-shells 25. This squeezes the plastic splines of the half-shells 25 onto the metal splines of the shaft 11.

[0071] Step D - Thread the bellows ring 40 onto the shaft 11 from the end furthest from the support assembly 16, and finally

[0072] Step E—snapping the bellows ring 40 into the groove 22 on the shaft and applying a thrust to the inner race of the bearing assembly 16 , this thrust being reacted by the shoulder of the half-shell 25 .

[0073] Figure 11 and Figure 12 A second embodiment of the present invention is shown. This second embodiment has the same components as the first embodiment, except that a steel split ring 50 is used instead of a corrugated ring. This split ring 50 engages in a groove in the shaft to apply the required thrust to the bearing assembly 16.

[0074] In Figures 13 and Figure 14 In another alternative embodiment shown, a conical coil spring 60 is provided as an alternative to the corrugated ring. The smallest coil of the spring engages a groove in the shaft, while the largest coil acts on the support assembly. The spring remains compressed to generate the required thrust on the support assembly.

[0075] FIG16 shows a completely different embodiment. In this embodiment, the shaft 11 is the same as in the other embodiments, but a single-piece jaw drive mechanism 70 is provided by overmolding a plastic component onto the end of the shaft 11. The shaft can be the same as in the previous embodiment. The overmolded jaw drive mechanism 70 is similar to the two half-shells in that it engages the grooves 22 and splines of the shaft 11 and has a radial ring that forms a bearing surface for the jaw teeth.

[0076] In the overmolded arrangement, the support assembly 16 is pressed onto the outside of the cylindrical portion of the overmolding 70 in the same manner as the two half shells and may be held in place by the bellows 40, split washer 50 or conical spring 60 in the same manner as the previous embodiments of the invention.

[0077] Figure 17 and Figure 18 An alternative embodiment is shown that eliminates the need for a bellows ring by utilizing a resilient member of the jaw drive mechanism. Similar to the embodiment of FIG8 , a jaw drive mechanism 80 is provided that includes two jaw half-shells 85 that together form the jaw mechanism. Similar to the previous two embodiments, these jaw half-shells are secured to an elongated shaft 90 using splines on the inside of the shells that engage with splines on the ends of the elongated shaft. The bearing assembly is then press-fitted around the shells.

[0078] Each shell has an axially extending tab in the form of a mostly cylindrical portion 86 that defines a tab including a set of inwardly extending splines 87, and a partially disc-shaped shoulder portion 88 that extends radially outward from the end face of the partially cylindrical portion 86. This defines two faces, one facing the tab and defining the shoulder, and the other facing away from the tab, carrying two dog teeth 89. When the two half-shells 85 are placed together onto the end of an elongated shaft 90, they form a cylindrical body that surrounds the splined portion of the shaft and a radially extending disc that forms the shoulder.

[0079] Each half-shell also carries two narrower tabs 91 extending along respective sides of the tab. These narrower tabs are resilient and have outward-facing hooks 92 at one end. The spacing between hooks 92 and the facing surfaces of shoulder portion 88 is selected to be slightly smaller than the width of the inner race of the support assembly, so that the support assembly can be snapped into this spacing by deflecting the narrower tabs. Simultaneously, this deforms the ends of the narrower tabs to form inward-facing tangs 93 that press into grooves in the elongated shaft. These tangs cooperate with the shoulder of the disc to prevent axial movement of the half-shells relative to the elongated shaft.

[0080] Figure 20 and Figure 21 A still further alternative embodiment is presented which also eliminates the need for a bellows ring by using a resilient member of the jaw drive mechanism. Figure 17 and Figure 18 The embodiment shown functions similarly, but rather than two half shells, the jaw mechanism is formed as a one-piece component 100. Figure 17 and Figure 18 Narrow, resilient tabs 101 with outwardly extending hooks, operating in the same manner as the tabs on the half shells, allow the inner race of the support to snap into place and simultaneously apply a radially inward force that presses the ends of the tabs into the grooves of the elongated shaft. Another set of locating tabs 103, each having a spline 104 on its inner face, engages with the splines on the elongated shaft to transmit torque. The shaft and support can be connected with Figure 17 and Figure 18 The same is used in the embodiments of FIG.

Claims

1. A gearbox assembly, comprising: case; a first shaft assembly including a worm drive and supported relative to the housing by a first bearing assembly; and a second shaft assembly including a worm gear also supported relative to the housing by a second bearing assembly, the worm gear engaging a worm of the worm gear to allow torque to be transferred between the first and second shaft assemblies, 18. The swiftly and minutely adjusting device for a wood-planer working table as claimed in claim 1, wherein said linking rod and said adjusting base are pivotally connected to each other with a bolt, and said bolt has a round shank to contact with said linking rod.

2. The gearbox assembly according to claim 1, wherein: The pawl drive mechanism includes two or more pawl teeth radially offset from the axis of the elongated shaft to engage corresponding pawl teeth of an external drive mechanism.

3. The gearbox assembly according to claim 1, wherein: The first shaft assembly includes a connection arrangement for securing the shaft assembly to the jaw drive mechanism, and wherein the connection arrangement includes the first bearing assembly.

4. The gearbox assembly according to claim 3, wherein: The connection arrangement includes a biasing mechanism that positions the first bearing assembly about a portion of the jaw drive mechanism and applies an axial thrust load to the jaw drive mechanism through the bearing assembly.

5. The gearbox assembly according to claim 4, wherein: The connecting device is a collar that is separate from the jaw drive mechanism.

6. The gearbox assembly according to claim 4, wherein: The connection means is an integral part of the jaw drive mechanism that interacts with a member on the elongate shaft.

7. The gearbox assembly according to claim 6, wherein: The jaw drive mechanism is a snap-fit ​​member that snaps onto the shaft, and the support assembly is a snap-fit ​​member that snaps onto the outside of the jaw drive mechanism, wherein the support assembly, when in place, prevents the jaw drive mechanism from disengaging from the elongated shaft, thereby locking the jaw drive mechanism in place.

8. The gearbox assembly according to any one of claims 1 to 7, wherein: The pawl drive mechanism comprises a one-piece component having a radial disc-shaped portion at one end from which two or more pawl teeth project from one face and a plurality of elongated resilient tabs extending away from an opposite face, at least one of the tabs comprising an outwardly facing rib at a free end portion and an inwardly facing tang, the outwardly facing rib retaining the bearing assembly against the radial disc-shaped portion and the inwardly facing tang engaging a recess in the elongated shaft.

9. The gearbox assembly according to claim 4, wherein: The jaw drive mechanism includes two separate sleeve halves that fit together to surround the end portion of the elongated shaft and form a cylindrical portion and a shoulder, the two sleeve halves being secured in position on the elongated shaft by the first bearing assembly and the biasing mechanism.

10. The gearbox assembly according to claim 9, wherein: The jaw drive mechanism includes a biasing device that engages a recess in the outer circumferential surface of the end of the elongated shaft to prevent the sleeve half from moving axially relative to the elongated shaft.

11. A worm shaft assembly for a worm gearbox assembly, The worm shaft assembly comprises: An elongated shaft carrying a worm gear; and a split jaw drive mechanism fastened to one end of the elongated shaft, wherein the elongated shaft and the split jaw drive mechanism are fixed together by an inner race of a supporting assembly, the inner race of the supporting assembly being located on the split jaw drive mechanism, wherein the split jaw drive mechanism includes a fixing portion, the fixing portion being assembled around the end portion of the elongated shaft, the fixing portion including an inwardly facing spline, the spline engaging with a corresponding outwardly facing spline provided on the end portion of the elongated shaft, the inwardly extending ring on the end of the split jaw drive mechanism engaging with a correspondingly formed groove in the elongated shaft to prevent relative axial and rotational movement between the elongated shaft and the split jaw drive mechanism, so that torque is transmitted between the elongated shaft and the split jaw drive mechanism during use.

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