GB1593570A - Mechanical drives for generating linear displacement - Google Patents

Abstract

The screw spindle mechanism is used to produce linear relative displacements of two bodies. It has a single-start screw (6) which is guided in axially displaceable fashion in a mechanism housing (1). A spindle nut (3) with a self-locking action in relation to the screw (6) is mounted in rotatable and axially non-displaceable fashion in the mechanism housing (1). Secured on the spindle nut (3) is a bevel gear (3a) which meshes with a bevel gear (7a) of a drive shaft (7) mounted in the mechanism housing (1). The drive shaft (7) and the screw (6) run perpendicularly to one another and their axes intersect. Compared to screw mechanisms with a worm-type transmission gear mechanism, this screw mechanism permits a considerably higher feed rate of the screw, a higher efficiency and a more favourable spatial configuration. Further shafts (8) can be coupled to the spindle nut in the same way as the drive shaft (7), via bevel gears (8a), and these shafts can transmit the driving power to similar screw mechanisms without additional direction-changing mechanisms. <IMAGE>

Description

(54) MECHANICAL DRIVES FOR GENERATING LINEAR DISPLACEMENT (71) We, PFAFF-SILBERBLAU HEBEZEUGFABRIK GmbH, a joint stock company organised under the laws of the Federal Republic of Germany, of Industriestrasse, 8901 Derching, West Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to mechanical drives for generating linear relative displacement between two bodies.

One kind of such drive utilises a singlethread screw spindle capable of being axially displaced within a housing and a spindle nut rotatably located within the housing but incapable of being displaced axially. The spindle nut is provided at its periphery with a gear and is self-locking with respect to the screw spindle. A drive shaft is located in the housing and is provided with a driving element in mesh with the spindle nut gear, the axis of the shaft being at right angles to the axis of the screw spindle.

Drives of this type, the spindle nut of which is provided with a wormgear and is driven by a driving worm located in the housing and rotated by motor or manually, have been known for a long time and are used for raising and lowering loads or for pushing, pulling or displacing heavy block loads or as drives for dams, sluice gates, large gates, screw jacks or similar devices. As distinct from hydraulic drives of comparable power which are likewise used for such purposes they offer the advantage that several drives can easily be coupled with one another in a synchronous manner without any impairment of such synchronous operation if the individual drives are unevenly loaded, in addition to which the strokes can be accurately adjusted and even the heaviest loads can be retained at a given level for an indefinite period of time. Since single-thread screw spindles possess the advantageous charac teristic bf being self-locking special locking devices to present reversal of the loaded spindle are not necessary.

However, single-thread spindles driven by worm gear are subject to the disadvantage that at normal driving speeds the spindle cannot be raised or advanced at higher rates than about 2.7 m/min and that owing to their low efficiency motorised drives of this type can only be operated for short periods of time.

These disadvantages have been overcome in various ways. Thus when higher lifting speeds were required with identical loads, overdimensioned screw spindle drives were in some instances installed, but this solution is very uneconomical in terms of cost, spatial requirements and technical effort. Another solution consists in reducing the number of wormgear teeth. But owing to heavy wear during operation this solution is restricted to individual cases and is not of general application.

A further solution described in US-PS 3 178 958 and DE-AS 1 222 219, respectively, consists in providing friction-reducing circulating balls between the screw spindle and the spindle nut, the self-locking action being transferred to the worm gearing, or in providing the screw spindle with a solid nut arranged in tandem with the spindle nut which carries the recirculating balls.

Although this solution leads to a noticeable improvement of the gear efficiency the lifting rate cannot be increased by more than 70% since the ball circulating spindle can openly be made with one thread and only with a certain pitch. Besides, such ball circulating screw spindle drives are uneconomical in view of both their manufacturing costs and their spatial requirements.

A further relatively simple and cheap solution has been described in DE-GbmS 69 50 395 and consists in the screw spindle and the corresponding spindle nut being multithreaded, the gearing consisting again of a worm drive. Since with normal dimensioning and normal combination of materials multithread screw spindles are not self-locking it is necessary with these drives to transfer the self-locking action to the wormgearing, which leads to reductions in lifting rate or to the use of brake motors, which again is bound to lead to undesirable increases in costs or additional spatial requirements.

Worm gearing such as are used with all known screw spindle drives, are subject to the general disadvantage that the driving shaft, the axis of which is at right angles to the screw spindle axis, must be spaced from, but close to, the axis of the screw spindle. As a result it is necessary for the drive to have minimum spatial dimensions and if several such screw spindle drives are connected so as to constitute a multiple drive, such an arrangement is subject to the limitation that the various drives must be so arranged with respect to one another that the axes of their drive shafts are located along a straight line.

In many cases this presents no difficulties but there are also cases (for instance, fourcolumn lifting platforms) in which the driving power must be transmitted diagonally from one drive to the next drive. With known drives it is in such cases always essential to provide special intermediate couplings (bevel gear drives, angular drives, crown wheel drives or crossed helical drives) enabling mechanical transmission of the driving power in a diagonal direction, this has an unfavourable effect on the costs, efficiency and spatial requirements of the entire system.

The invention is, accordingly, intended to solve the problem of improving mechanical drives of the general type initially described in such a way as to increase their lifting and advancing rates and improve their efficiency while retaining the basically simple design of such drives; they also offer the advantage that if several such drives are combined in a multiple arrangement there is a greater freedom as regards mechanical transmission from one drive to the next, and of the driving power supplied by a prime mover without any requirement for intermediate couplings.

According to the invention a mechanical drive for generating linear relative displacement between two bodies comprises a threaded screw spindle capable of being axially displaced within a housing, a spindle nut in mesh therewith rotatably located within the housing but incapable of axial displacement and self-locking with respect to the screw spindle, the nut being provided with peripheral gear teeth, and a plurality of drive shafts located within the housing each provided with a driving element in mesh with the gear teeth of the nut, the axes of the shafts lying at right angles to the axis of the screw spindle, wherein the gear teeth on the nut are in the form of a bevel gear or the equivalent and the driving elements mounted on the driving shaft are cooperating gears in mesh with the said gear teeth.

The gear ratio of the gearing between driving element and the nut is preferably between 1.5:1 and 3.5:1.

By comparison with drives of known type a drive according to the invention offers the advantage that the lift or advance rate can be considerably increased and the efficiency of the drive improved while at the same time retaining a basically very simple design and the advantageous self-locking action of a single-thread screw spindle. In addition, it is possible to achieve a more advantageous spatial arrangement of the drive since with bevel gearing the axes of the gear shafts intersect.

The invention also offers the advantage that since there are a plurality of drive shafts any drive shaft which is additional to a first drive shaft can serve either to increase the power of the drive or elso to transmit the power introduced by the first drive shaft to other drives.

In one embodiment of the invention two bevel gear shafts can be arranged coaxial on opposite sides of the screw spindle. This arrangement results in a very compact gearbox of simple design.

In another embodiment of the invention there are two or more bevel gear shafts, the axes of these shafts lying in a plane at right angles to the axis of the screw spindle, and the said shaft axes may include between themselves different or preferably identical angles. This embodiment can be applied in various versions entailing multiple arrangements of such drives.

The invention is now described in detail with reference to the attached drawing which shows a preferred embodiment of a drive in accordance with the invention, with by way of example two or four symmetrically arranged bevel gear shafts.

A nut 3 is located within a housing 1 of a gearbox and a cover 2 encloses the housing at one side. The nut 3 is rotatably supported in anti-friction bearings 4, 5 and is incapable of axial displacement. The inner thread of nut 3 engages the outer thread of a non-rotatable screw spindle 6 so that the latter is axially displaced if nut 3 is rotated. Screw spindle 6 passes through a guide ring 2a in an axially displaceable manner, guide ring 2a being screwed into housing cover 2, and also projects into a sleeve la secured to housing 1, only part of the sleeve being shown in the drawmg.

Nut 3 carries a bevel gear 3a, and the screw spindle 6 passes in a axially displaceable manner through the hub of the bevel gear.

With the embodiment shown in the drawing the bevel gear 3a constitutes an intermediate component by means of which nut 3 is guided within the inner race of an anti-friction bearing 5.

In housing 1 two bevel gear shafts 7 and 8 are each located in anti-friction bearings 9 and 10, respectively, and axes of these shafts being in a plane which intersects the axis of the screw spindle 6 at right angles. The bevel gear shafts 7 and 8 carry bevel gears 7a and 8a, respectively, which engages the bevel gear 3a of nut 3. One or both of shafts 7 and 8 can be drive shafts coupled to a manual or motor drive. Alternatively one of the two shafts 7 and 8 can be a driven shaft enabling the driving power introduced into the drive to be transmitted to another point. In this case the bevel gear 3a of nut 3 constitutes an intermediate gear through which the driving power is reversed from bevel gear 7a to the other bevel gear 8a or vice versa, and accordingly from one shaft to the other shaft.

The drive can of course possess only a single bevel gear shaft 7 or 8 (this design is not shown) where driving power is to be introduced into the drive from only one prime mover and where transmission of the driving power to a further drive is not necessary.

According to a further embodiment not shown in the drawing, two bevel gear shafts 7 and 8 can be located in the housing with the axes of the shafts lying in a plane intersecting the axis of screw spindle 6 at a right angle and they include a right angle between themselves. Such an embodiment is particularly suitable for applications in which the driving power introduced through one shaft has to be transmitted by means of the second shaft at an angle of 90O to a further drive. The axes of the two shafts can of course also include any other angle.

Lastly, a further embodiment of the above drive (also not shown in the drawing) provides for three, four or more bevel gear shafts 7, 8 etc. to be located in housing 1, their arrangement in respect of screw spindle 6 being axially symmetrical, and the axes of these shafl:s being situated in a plane intersecting the axes of the screw spindle at a right angle and the shafts preferably include identical angles between themselves in each case.

Such an embodiment enables the driving power introduced into the drive through one of the shafts to be transmitted to an appropriate number of further drives in an appropriate arrangement.

The bevel gear 3a may be integral with the spindle nut 3 (this is not shown in the drawing). Similarly, each of the bevel gears 7a, 8a etc. can be integral with the appropriate bevel gear shafts 7, 8 etc.

The arrangement of the above bevel gearing is not limited to drives with single-thread screw spindles and can in certain cases be usefully employed in conjunction with multi-thread screw spindles.

Instead of bevel gearings, equivalent transmission components such as angle gears or crown gears can be used provided that they enable the required gear ratios and efficiencies to be achieved.

WHAT WE CLAIM IS: 1. A mechanical drive for generating linear relative displacement between two Poodles comprising a threaded screw spindle axially displaceable within a housing, spindle nut in mesh therewith rotatably located within the housing but incapable of axial displacement and self-locking with respect to the screw spindle, the nut being provided with peripheral gear teeth, and a plurality of drive shafts located within the housing each provided with a driving element in mesh with the gear teeth on the nut, the axes of the drive shafts lying at right angles to the axis of the screw spindle, wherein the gear teeth on the nut are in the form of a bevel gear or the equivalent and the driving elements mounted on the drive shafts are cooperating gears in mesh with the said gear teeth.

2. The mechanical drive in accordance with claim 1, characterised in that the gear ratio of the gearing between the driving element and the nut is between 1.5:1 and 3.5:1.

3. The mechanical drive in accordance with claim 1 or 2, characterised in that the said driving elements are also in the form of bevel gears or the equivalent.

4. The mechanical drive in accordance with any one of the preceding claims characterised in that two drive shafts are provided which are coaxially arranged at opposite sides of the screw spindle.

5. The mechanical drive in accordance with claim 3 and comprising two or more shafts the bevel gears of which engage the spindle nut gear, characterised in that the axes of these shafts are located in a common plane at right angles to the axis of the screw spindle.

6. The mechanical drive in accordance with claim 5, characterised in that the angles between the axes of the shafts are identical.

7. The mechanical drive as claimed in any one of the preceding claims in which the screw spindle has a single thread.

8. mechanical drive for generating linear relative displacement substantially as described with reference to the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. gear 3a of nut 3. One or both of shafts 7 and 8 can be drive shafts coupled to a manual or motor drive. Alternatively one of the two shafts 7 and 8 can be a driven shaft enabling the driving power introduced into the drive to be transmitted to another point. In this case the bevel gear 3a of nut 3 constitutes an intermediate gear through which the driving power is reversed from bevel gear 7a to the other bevel gear 8a or vice versa, and accordingly from one shaft to the other shaft. The drive can of course possess only a single bevel gear shaft 7 or 8 (this design is not shown) where driving power is to be introduced into the drive from only one prime mover and where transmission of the driving power to a further drive is not necessary. According to a further embodiment not shown in the drawing, two bevel gear shafts 7 and 8 can be located in the housing with the axes of the shafts lying in a plane intersecting the axis of screw spindle 6 at a right angle and they include a right angle between themselves. Such an embodiment is particularly suitable for applications in which the driving power introduced through one shaft has to be transmitted by means of the second shaft at an angle of 90O to a further drive. The axes of the two shafts can of course also include any other angle. Lastly, a further embodiment of the above drive (also not shown in the drawing) provides for three, four or more bevel gear shafts 7, 8 etc. to be located in housing 1, their arrangement in respect of screw spindle 6 being axially symmetrical, and the axes of these shafl:s being situated in a plane intersecting the axes of the screw spindle at a right angle and the shafts preferably include identical angles between themselves in each case. Such an embodiment enables the driving power introduced into the drive through one of the shafts to be transmitted to an appropriate number of further drives in an appropriate arrangement. The bevel gear 3a may be integral with the spindle nut 3 (this is not shown in the drawing). Similarly, each of the bevel gears 7a, 8a etc. can be integral with the appropriate bevel gear shafts 7, 8 etc. The arrangement of the above bevel gearing is not limited to drives with single-thread screw spindles and can in certain cases be usefully employed in conjunction with multi-thread screw spindles. Instead of bevel gearings, equivalent transmission components such as angle gears or crown gears can be used provided that they enable the required gear ratios and efficiencies to be achieved. WHAT WE CLAIM IS:

1. A mechanical drive for generating linear relative displacement between two Poodles comprising a threaded screw spindle axially displaceable within a housing, spindle nut in mesh therewith rotatably located within the housing but incapable of axial displacement and self-locking with respect to the screw spindle, the nut being provided with peripheral gear teeth, and a plurality of drive shafts located within the housing each provided with a driving element in mesh with the gear teeth on the nut, the axes of the drive shafts lying at right angles to the axis of the screw spindle, wherein the gear teeth on the nut are in the form of a bevel gear or the equivalent and the driving elements mounted on the drive shafts are cooperating gears in mesh with the said gear teeth.

2. The mechanical drive in accordance with claim 1, characterised in that the gear ratio of the gearing between the driving element and the nut is between 1.5:1 and 3.5:1.

3. The mechanical drive in accordance with claim 1 or 2, characterised in that the said driving elements are also in the form of bevel gears or the equivalent.

4. The mechanical drive in accordance with any one of the preceding claims characterised in that two drive shafts are provided which are coaxially arranged at opposite sides of the screw spindle.

5. The mechanical drive in accordance with claim 3 and comprising two or more shafts the bevel gears of which engage the spindle nut gear, characterised in that the axes of these shafts are located in a common plane at right angles to the axis of the screw spindle.

6. The mechanical drive in accordance with claim 5, characterised in that the angles between the axes of the shafts are identical.

7. The mechanical drive as claimed in any one of the preceding claims in which the screw spindle has a single thread.

8. ss mechanical drive for generating linear relative displacement substantially as described with reference to the accompanying drawing.