Removable gear drive for mechanical jack

[0002] This application claims priority from U.S. Provisional Application No. 60/336,151 filed on Nov. 15, 2001.

[0003] I. Field of The Invention

[0004] This invention relates to a mechanical jack for raising and lowering an object such as a trailer and, in particular, to a gear drive for the jack which can be readily assembled within the jack tube and, if necessary disassembled for repair or replacement.

[0005] II. Description of the Prior Art

[0006] Mechanical jacks are convenient devices for raising and lowering a portion of a vehicle such as the tongue or forward portion of a trailer. The forward portion may need to be raised or lowered to level the trailer or to position the trailer coupler for connection to the towing vehicle. Typical jacks include telescoping sections, the extension and retraction of which is controlled by an axial screw extending through the housing and drivably engaging a screw nut. Rotation of the screw within the jack may be controlled directly by a crank or through a gear assembly drivably connecting the crank to the screw. Rotation of the crank in one direction rotates the screw causing expansion of the jack sections as the screw nut travels along the screw. Conversely, rotation of the crank in the opposite direction causes contraction of the jack sections as the screw nut travels along the screw in the opposite direction.

[0007] The gear drive for the jack includes a first beveled gear mounted to the crankshaft and a second cooperating gear mounted to the axial screw such that rotation of the crank is transmitted to the screw. The cooperation of the components within the jack tube creates difficulty in assembly particularly for components which need to be secured within these limited spaces. In some prior known assemblies the beveled gear would have to be fastened to the crankshaft once assembled within the jack tube. This fastening also reduced the ability to disassemble the gear drive.

[0008] The present invention overcomes the disadvantages of the prior known jack assemblies by providing a gear drive which is readily assembled within the jack tube yet has sufficient durability for heavy-duty applications.

[0009] The gear drive assembly of the present invention facilitates insertion and assembly of the gear drive components within the limited space of a jack tube without the need for precision insertion of small components such as drive pins. The gear drive assembly is mounted within an upper end of a jack tube and is drivably connected to an axial jack screw extending through the tube. The gear drive assembly of the present invention is driven by a side crank requiring that the rotational motion be transmitted at a right angle. The crank is connected to a crankshaft extending laterally through the jack tube and supported by opposite walls of the tube. The crankshaft includes an intermediate portion having a hexagonal configuration although any non-circular configuration may be employed.

[0010] The crankshaft is supported in the opposite walls of the jack tube by bushings which receive the circular end portions of the crankshaft such that the shaft will rotate in the fixed bushings. A first bushing is inserted into the wall of the jack tube from the interior of the tube while the second bushing is inserted into the opposite wall from the exterior to secure the entire drive assembly. A first beveled gear is mounted to the hexagonal portion of the crankshaft. Rotation of the crankshaft is therefore transmitted to the first gear through the hexagonal portion of the shaft. The hexagonal portion has a diameter of the circular end portions and the inner diameter of the bushings thereby preventing the hexagonal portion from moving into the bushings.

[0011] The first gear drivably engages a second beveled gear axially aligned with the jack screw whereby rotation of the second gear is transmitted directly to the screw. The second gear is carried on a removable plate extending across the jack tube and connected directly to the jack screw. With the second beveled gear mounted to the screw, the first bushing is inserted into the tube wall from the interior of the jack tube and the first gear is positioned in driving engagement with the second gear with its throughbore aligned with the bushing. The crankshaft is then inserted transversely through the jack tube and the aligned bushing and gear until the hexagonal intermediate portion of the gear is received within the first gear and engages the bushing. The exterior bushing is placed over the end of the crankshaft and fastened to the jack tube to secure the gear drive assembly.

[0012] Other objects, features and advantages of the invention will be apparent from the following detailed description taken in connection with the accompanying drawing.

[0013] The present invention will be more fully understood by reference to the following detailed description of a preferred embodiment of the present invention when read in conjunction with the accompanying drawing, in which like reference characters refer to like parts throughout the views and in which:

[0014] FIG. 1 is a perspective view of a jack embodying the gear drive assembly of the present invention;

[0015] FIG. 2 is an enlarged perspective view of an upper end of the jack showing the gear drive assembly;

[0016] FIG. 3 is a side view thereof;

[0017] FIG. 4 is an exploded view of the gear drive assembly;

[0018] FIG. 5 is a perspective view of the first gear of the drive assembly; and

[0019] FIG. 6 is an end view of the first gear.

[0020] Referring first to FIG. 1, there is shown a jack assembly 10 selectively extendable and contractible to raise and lower a structure 12 such as a portion of a recreational vehicle. The recreational vehicle may need to be raised or lowered for leveling or to facilitate attachment to a towing vehicle. The jack assembly 10 generally includes a lower jack tube 14 telescopically received within an upper jack tube 16. A ground engaging footpad 18 may be attached to the lower tube 14 while the upper tube 16 is secured to the structure 12 in a well known manner. In accordance with the present invention, an external crank 20 is used to operate the jack 10 to raise and lower the structure 12 as desired.

[0021] The crank 20 is operatively connected to a gear drive assembly 22 embodying the present invention which is drivably connected to a jack screw 24 extending axially through the tubes 14,16. The jack screw 24 extends through and is threadably connected to a screw nut 26 secured to the lower tube 14. Rotation of the jack screw 24 in a first direction will drive the screw nut 26 downwardly to telescopically expand the jack assembly 10 and rotation of the jack screw 24 in an opposite second direction will draw the screw nut 26 upwardly along the screw 24 to telescopically contract the jack assembly.

[0022] Referring now to FIGS. 2 through 6, the gear drives assembly 22 of the present invention is designed to transmit rotation of the crank 20 to the jack screw 24 for telescopic operation of the jack 10. The crank 20 is connected to a crankshaft 30 which extends transversely through the upper jack tube 16. The crankshaft 30 includes cylindrical end portions 32 and an intermediate portion 34 which has a non-circular cross-sectional configuration. In a preferred embodiment of the present invention, the non-circular intermediate portion 34 is hexagonal and has a diameter greater than the diameter of the end portions 32. However, any non-circular configuration may be employed as a drive segment for the crankshaft 30. The ends 32 of the crankshaft 30 are rotatably supported within the tube 16 by first bushing 36 and second bushing 38. Each of the bushings 36,38 have a hub 40 with a throughbore 42 corresponding to the diameter of the end portions 32 of the crankshaft 30. The hubs 40 have an external diameter corresponding to apertures 44 formed in opposite walls of the tube 16 so as to be supported within the apertures 44. A flange 46 limits the extent the bushings 36,38 extend through the respective aperture 44.

[0023] The first bushing 36 is mounted from the interior of the tube 16 and includes an anti-rotation lobe 48 which will prevent the interior bushing 36 from spinning within the aperture 44. The second bushing 38 is secured to the tube 16 using fasteners 50 passing through the flange 46 to engage the tube 16. The larger diameter of the intermediate hexagonal portion 34 prevents the intermediate portion 34 from traveling into the bushings 36,38. However, to prevent wear on the hex portion 34 as it rotates against the bushings 36,38 thrust washers 52 are inserted at the ends of the hex portion 34.

[0024] Drivably mounted to the intermediate portion 34 of the crankshaft 30 is a first drive gear 54. As is well known, the gear 54 is beveled with a plurality of gear teeth 56 and an axial throughbore 58 for receiving the crankshaft 30. In accordance with the present invention, the configuration of the throughbore 58 matches the cross-sectional configuration of the non-circular intermediate portion 34 of the crankshaft. In this manner, rotation of the crankshaft 30 is transmitted directly to the first gear 54 and it is not necessary to fasten the gear 54 to the crankshaft 30 as is required in other drive systems. As is best shown in FIGS. 5 and 6, the hexagonal throughbore 58 has a plurality of relief cavities 60 formed at the corners of the bore 58. The cavities 60 are intended to reduce stress on the corners or tips of the hexagonal shaft portion 34 and concentrate the rotational force against the flat surfaces 62 of the bore 58 within the gear 54.

[0025] The first gear 54 drivably engages a second gear 64 which is directly axially connected to the jack screw 24. The second gear 64 is also beveled with a plurality of gear teeth 66 which interact with the gear teeth 56. The second gear 64 is supported at a right angle to the first gear 54 on a removable platform 68 which extends through the jack tube 16. The platform 68 is inserted transversely through the tube 16 through opposing slots 70.

[0026] The gear drive assembly 22 of the present invention facilitates simple assembly within the jack assembly 10 and, if necessary, disassembly for repair or replacement of components. The first interior bushing 36 is inserted into the corresponding aperture 44 in the tube wall 16 and the lobe 48 aligned to prevent rotation. One end 32 of the crankshaft 30 is fed through the opposing aperture 44 and the first gear 54 then thrust washer 52 are slid over the end 32 of the shaft 30 as that same end is fed through the throughbore 42 of the interior bushing 36. The crankshaft 30 will travel through the tube 16 until the intermediate portion 34 engages the thrust washer 52 and the thrust washer 52 engages the bushing 36 preventing further lateral movement. The other thrust washer 52 and the exterior bushing 38 can then be slid over the end of the crankshaft 30 until the washer 52 engages the hex portion 34 of the shaft 30 and the flange 46 of the exterior bushing 38 engages the wall of the jack tube 16. With the hub 40 in the aperture 44, the fasteners 50 can be used to secure the exterior bushing 38 to the jack tube 16. The crankshaft 30 and first gear 54 will essentially be captured between the bushings 36 and 38. Furthermore, the input or first gear 54 is positionally captured between the bushing 36 in one direction and interference with the drive or second gear 64 in the other direction.

[0027] Once the crank 20 is attached to one or both of the end portions 32 of the crankshaft 30, rotation of the crank 20 will rotate the crankshaft 30 thereby rotatably driving the first gear 54. Rotation of the first gear 54 is transmitted to the second gear 64 and the jack screw 24 to extend or contract the jack assembly.

[0028] The foregoing detailed description has been given for clearness of understanding only and no unnecessary limitations should be understood therefrom as some modifications will be obvious to those skilled in the art without departing from the scope and spirit of the appended claims.