Screw jack

Abstract

 A rotating worm screw jack has a worm (2) which meshes with a worm wheel (4) and a screw (9) drivingly secured to and rotatable with the worm wheel (4). The screw (9) is drivingly secured to the worm wheel (4) by an external thread (11) on the screw (9) meshing with an internal thread (12) of the worm wheel (4) and a locking member (15) is provided for preventing relative rotation there between.

Description

[0001] This invention relates to screw-jacks and more particularly to rotating worm screw jacks.

[0002] A known rotating worm screw jack, shown partially sectioned in Fig. 1 of the accompanying drawings, includes a housing 1 in which is a worm 2 mounted on a shaft 3, the shaft 3 being supported within the housing 1 by bearings (not shown). The worm 2 engages concave external worm threads of a worm wheel 4 which is supported between upper and lower thrust bearings 5, 6 respectively comprising ball elements caged in any suitable manner. The thrust bearings 5 and 6 are restrained within annular recesses in a housing cap 7 and a base portion 8 of the housing 1 respectively, the housing cap 7 being threadably engaged with an opening in the top of the housing 1. Extending perpendicularly to both the axis of the worm 2 and the worm wheel 4 is a screw 9 to which the worm wheel is keyed by a square sectioned key 10 having a longitudinal axis extending parallel to the longitudinal axis of the screw 9. The screw 9 has screw threaded portions 11 and 12 at the extremities thereof, the remaining portions of the screw 9 being plane. A section of the screw 9 between the threaded portions 11 and 12 and above (as viewed in Fig. 1) the key 10 is a plane section 13 having a diameter which is larger than the major diameter of the screw threaded portion 11 and which is mounted on an upper shoulder 14 of the worm wheel 4. A lock-nut 15 is secured to the threaded portion 12 and abuts a lower shoulder 16 of the worm wheel 4 so that by means of the lock nut bearing on the shoulder 16 and the section 13 bearing on the shoulder 14 of the worm wheel the screw is held in a predetermined longitudinal position relative to the worm wheel 4. A sealing sleeve 17 is located intermediate the housing cap 7 and the section 13 of the screw by a grub screw 18 and a circular aperture in the base portion 8 of the housing 1 is closed by a plug 19. The worm and worm wheel are lubricated by a grease nipple 20 located on the side of the housing 1.

[0003] In operation rotation of the worm 2 rotates the worm wheel 4 and since the worm wheel 4 is keyed to the screw 9 so the screw 9 rotates in the same direction as the worm wheel. For transmitting directional movement to a load a travelling nut 21 is provided to co-operatively engage with the threaded portion 11 of the screw, the travelling nut 21 having four aqui-spaced holes 22 for fixing to a load (not shown) to be raised or lowered. Since the travelling nut 21 is secured to the load it does not rotate and hence upon rotation of the screw 9 so the travelling nut moves up or down depending upon the direction of rotation of the screw.

[0004] Such rotating worm screw jacks may be of the upright type as shown in Fig. 1 or of the inverted type in which the screw protrudes through the opening closed by the plug 19 and the screw threaded portion 11 and travelling nut 21 are below the portion 8 of the housing.

[0005] Rotating worm screw jacks of the forementioned types tend to be complex to manufacture due to the numerous machining operations that are required on the screw 9 and it is an object of the present invention to provide a rotating worm screw jack of simpler construction.

[0006] According to this invention a rotating worm screw jack includes a worm meshing with a worm wheel and a screw drivingly secured to and rotatable with said worm wheel, said screw having an external thread meshing with an internal thread of the worm wheel and means for preventing relative rotation therebetween.

[0007] Preferably the means for preventing the relative rotation comprises at least one dowel pin inserted parallel to the longitudinal axis of said screw and into both the worm wheel and the nut.

[0008] Conveniently, the screw extends through the worm wheel to be substantially flush therewith at the side of the worm wheel, in operation, remote from a load and at least one dowel pin is inserted parallel to the longitudinal axis of said screw and into the confluenae of the major diameters of the meshing threads.

[0009] Advantageously the at least one dowel pin is or are secured in position by, for example, adhesive.

[0010] The invention will now be described by way of example with reference to Fig. 2 of the accompanying drawings in which like references to those in Fig. 1 are denoted by like reference numerals and the representation is again shown partially in section.

[0011] The rotated worm screw jack shown in Fig. 2 is of the upright type although like the prior art screw jack described with reference to Fig. 1, the present invention is also applicable to inverted rotated worm screw jacks.

[0012] The majority of components in Fig. 2 have been described but the screw 9 of the present invention is threaded throughout its entire length and the external thread of the screw meshing with an internal thread of the worm wheel 4 and the lower end of the screw remote from the load is arranged to be substantially flush with the lower side of the worm wheel. Relative rotation between the worm wheel 4 and screw 9 is prevented by two dowel pins 30, only one of which is shown for clarity. The dowel pins 30 are substantially parallel to the longitudinal axis of the screw and are inserted at the confluence of the major diameters of the meshing threads of the worm wheel 4 and screw 9. So as to prevent loosening of the dowel pins 30 they are secured in position by any suitable means such as an adhesive known under the trade name as Loctite.

[0013] It will thus be seen that by utilization of the present invention fewer components are used since the securement of the screw 9 in relation to the worm wheel 4 is provided by meshing threads on the screw 9 and the worm wheel 4 rather than the shoulders 14 and 16 on the worm wheel and the section 13 and locknut 15 of the rotating worm screw jack shown in Fig. 1. Furthermore, the complex machining operations of the screw 9 are avoided since a convenient piece of screw can be used. It has also been calculated that the safety factor of the jack is substantially increased for comparable physical sizes of rotating worm screw jacks. of the jack is substantially increased for comparable physical sizes of rotating worm screw jacks.

Claims

1. A rotating worm screw jack including a worm meshing with a worm wheel and a screw drivingly secured to and rotatable with said worm wheel, characterised in that the screw (9) has an external thread meshing with an internal thread of the worm wheel (4) and a member (e.g. 30) is provided for preventing relative rotation therebetween.

2. A rotating worm screw jack as claimed in claim 1 characterised in that the member is an adhesive.

3. A rotating worm screw jack as claim in claim 2 characterised in that there is also provided at least one dowel pin (30) inserted parallel to the longitudinal axis of the screw (9) and into both the worm wheel (4) and the screw (9) to assist in preventing relative rotation therebetween.

4. A rotating worm screw jack as claimed in any preceding claim characterised in that the screw extends through the worm wheel to be substantially flush therewith at the side of the worm wheel, in operation, remote from a load and at least one dowel pin is inserted parallel to the longitudinal axis of said screw and into the confluence of the major diameters of the meshing threads.

5. A rotating worm screw jack as claimed in claim 3 or 4 characterised in that at least one dowel pin is inserted parallel to the longitudinal axis of said screw and into both the worm wheel and the screw to assist in preventing relative rotation therebetween.

Drawing