GB2183751A

GB2183751A - A gear box

Info

Publication number: GB2183751A
Application number: GB08528331A
Authority: GB
Inventors: Kenneth William Ridley Smale
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-11-18
Filing date: 1985-11-18
Publication date: 1987-06-10
Also published as: GB8528331D0

Abstract

A gear box comprises rotatably mounted primary and secondary shafts 2 and 4 respectively, a plurality of primary gears 26, 28 and 30 rotatably mounted on the tubular primary shaft 2 and complementary secondary gears 68, 70 and 72 engaged therewith to form gear pairs and fixedly mounted on the secondary shaft. Any one of the gear pairs can be selected to provide driving engagement between the primary and secondary shafts 2 and 4 by engagement of a primary gear such as 26 with the primary shaft, such engagement being achieved by lugs 56, 58 or 60 which can radially extend from the primary shaft 2 to engage in a complementary slot 33, 35, 37 in any one of the primary gears. The lugs are carried by a gear change member 44 which is longitudinally displaceably received in the primary shaft 2; selection of gear pair is achieved by longitudinal displacement of the gear change member 44 which brings any one of these lugs 56, 58 or 60 into alignment with one of the primary gears 26, 28 or 30 with which it engages. <IMAGE>

Description

SPECIFICATION A gear box Technical Field and Background Art This invention relates to a gear box, and particularly to a gear box capable of providing a discrete range of mechanical advantages between its input and output shafts. A problem encountered with gear boxes of this type is the difficulty of providing means to change the mechanical advantages provided by the gear box while the gear box is operating. Such means in existing gear boxes tend to be mechanically complex and therefore expensive and relatively heavy.

It is an object of the present invention to alleviate the aforementioned disadvantages of the prior art.

STATEMENT OF INVENTION AND ADVAN TAGES According to the present invention there is provided a gear box comprising rotatably mounted primary and secondary shafts, a plurality of primary gears rotatably mounted on the primary shaft, each in driving engagement with a respective one of a plurality of secondary gears fixedly mounted on the secondary shaft, and selecting means capable of selectively engaging any one of the primary gears with the primary shaft.

It is envisaged that the primary and secondary shafts are rotatably mounted parallel to each other. The primary gears are rotatably mounted on the primary shaft by bearing means which enable them to rotate freely about the shaft when not engaged therewith by the selecting means. A plurality of secondary gears, equal in number to the number of primary gears, are fixedly mounted on the secondary shaft and each primary gear is in driving engagement with one of the secondary gears to form a plurality of gear sets. Preferably each gear set will provide a different mechanical advantage between the shafts, from each of the other gear sets, to provide a discrete range of drive ratios between the shafts.

When the selecting means is operated to place one of the primary gears in driving engagement with the primary shaft, a.particular gear set (of which the selected primary gear is a component) is selected, and hence a transmission is provided between primary and secondary shafts.

The selector means will preferably be operated by a mechanical linkage, although it should be realised that an hydraulic or electromechanical linkage could be employed. In a preferred form of selector means the primary shaft is of tubular construction. An elongate cylindrical gear change member is linearly slidable in the primary shaft but is engaged with the primary shaft to rotate therewith. The gear change member is equipped with a plurality of lug means which are biased radially away from the longitudinal axis of the gear change member. When mounted inside the primary shaft the lug means of the gear change member are constrained to remain flush with the surface of that member by the interior surface of the primary shaft.A plurality of slots are provided in the primary shaft, through which one only at a lime, the lug means may extend when the gear change member is linearly displaced within the primary shaft, to bring one of the lug means into alignment with one of the slots. When the lug means extends it engages one of the primary gears, by for example engaging in a slot in the gear. Since only one of the lug means may be extended at a time the gear change member may be readily moved to engage any one of the primary gears.

In an alternative form of the invention the lug means may be actuated by a cam slide inside the primary shaft.

Preferably linear motion of the gear change member is achieved by means of a stirrup which engages the ends of the gear change member extending from the primary shaft by way of thrust bearings.

Drive input to the gear box is preferably provided by way of the primary shaft, and drive output is provided by the secondary shaft. However it should realised that the gear box can be operated with the secondary shaft as the drive input and primary shaft as output when on light load. A reverse gear may be easily provided in the gear box, by constructing one of the range of gear sets with an intermediate third gear between the primary and secondary gears.

DRAWINGS Embodiments of a gear box constructed in accordance with the present invention will now be described, by way of example only, with reference to the accompanying illustrative drawings in which: Figure 1 is a sectional view through a gear box.

Figure 2 is a view of the section AA on Fig.

1.

Figure 3 is a sectional view though a second embodiment of the invention showing part of a primary shaft and gear change member with lugs displaceable radially by a cam slide.

Figure 4 shows a sectional view of the embodiment of Fig. 3 on the line l-l.

DETAILED DESCRIPTION OF DRAWINGS The embodiment of the gear box shown in Fig. 1 has a primary shaft 2 and secondary shaft 4. The primary shaft 2 and secondary shaft 4 are elongate, cylindrical and rotatably mounted parallel to each other in a hollow housing 6. Ends 8 and 12 of the primary and secondary shafts 2 and 4 respectively extend through one end wall part 16 of the housing 6, and ends 10 and 14 of the primary and secondary shafts 2 and 4 respectively extend through an opposite end wall part 18, of the housing 6.

The primary shaft 2 is tubular and is provided with three slots 20, 22 and 24 which extend through the tube wall of the primary shaft 2 and are spaced at intervals along the length of the primary shaft 2 within the housing.

Three annular primary gears 26, 28 and 30 have different external diameters and are rotatably mounted on the primary shaft 2 so that the circular appertures 32, 34 and 36 at the centres of the gears and through which the primary shaft 2 passes, overlap the slots 20, 22 and 24 respectively. The primary gears 26, 28 and 30 are rotatably mounted on the primary shaft by means of annular bearings 38, 40 and 42 respectively. The annular bearings 38, 40 and 42 also prevent axial displacement of the primary gears along the shaft. Each of the of primary gears 26, 28 and 30 has a longitudinally aligned slot 33, 35 and 37 cut radially into a circular apperture 32, 34 and 36 respectively. At one point in the primary gears rotation about the primary shaft the slot will be coextensive with the slots 20, 22 or 24.

An elongate cylindrical gear change member 44 is slidably inserted into primary shaft 2.

First and second ends 46 and 48 of the gear change member 44 extend from open ends 8 and 10 respectively of the primary shaft 2 and are capable of longitudinal but not rotational displacement relative to the primary shaft 2.

The gear change member 44 may be prevented from rotational displacement relative to the primary shaft 2, by means of splines (not shown) on its surface capable of engaging complementary splines on the interior surface of the primary shaft 2. Axially aligned slots 50, 52 and 54 are cut radially into the cylindrical gear change member, to extend from the its to part way through the gear change member. The slots 50, 52 and 54 are spaced at intervals along the length of the gear change member 44 so that longitudinal motion of the gear change member 44 relative to the primary shaft 2 is capable of bringing one of the slots 50, 52 or 54 into alignment with one only of the slots 20, 22 or 24 respectively so that the aligned slots are coextensive.

Lugs 56, 58 and 60 are slidably mounted in the slots 50, 52 and 54 respectively and resiliently biased by means of compression springs 62, 64 and 66 respectively, radially away from the longitudinal axis of the gear change member 44. Thus, if as shown in Fig.

1 the gear change member is displaced longitudinally to bring the slot 50 into alignment with the slot 20, the lug 56 will be moved radially away form the longitudinal axis of the gear change member to project into the slot 20. Rotation of the primary gear 26 about the primary shaft 2 will eventually bring the slot 50 into alignment with the slot 20 and the lug 56 therein and the lug 56 will extend into the slot 50 thereby drivably engaging the primary gear 26 with the primary shaft 2 and gear change member 44. However, the longitudinal distance between the slots 50, 52 and 54 in the gear change member 44 and the longitudinal distance between the slots 20, 22 and 24 in the primary shaft is so arranged that only one primary gear at a time may be drivable engaged with the primary shaft 2 and gear change member 44, by lugs 56, 58 or 60.

The primary gears 26, 28 and 30 are in driving engagement with the seconary gears 68, 70 and 72 respectively which are mounted on and in driving engagement with the secondary shaft 4. These secondary gears 68, 70 and 72 have diameters complementary to those of the primary gears 26, 28 and 30 so that the shafts are parallel.

Longitudinal motion of the gear change member 44 can be achieved by means of a stirrup 74 mounted entirely outside the housing 6. This strirrup 74 comprises two parallel coextensive elongate members 76 and 78 which are substantially perpendicular to and extend from the ends 46 and 48 respectively of the gear change member 44. The members 76 and 78 are rigidly linked at their ends remote from the gear change member by a link member 80. The ends of the members 76 and 78 are coupled to the ends 46 and 48 of the gear change member 44 by means of thrust bearing 82 and 84 respectively. Thrust bearing 82 and 84 permit free rotation of the gear change member, while allowing a longitudinal force to be applied to and move the gear change member.

Power is transmitted to the gear box from the prime mover at end 48 of the primary shaft preferably by a clutch. The inertia of the primary shaft is small compared to that of the secondary shaft which is connected to the load. Thus shock of lock in the lugs is minimal. The operation of the gear box will be described for the case where the primary shaft 2 is rotated by an external motor, and the secondary shaft 4 provides the power output from the gear box. It will however be realised that the power input to the gear box may be via the secondary shaft 4 while power output can be from the primary shaft 2.

Initially the gear change member 44 will be moved longitudinally in the primary shaft 2 so that its end 46 is as remote from the end wall part 16 of the housing as posible. In this position none of the slots 50, 52 or 54 in the gear change member 44 are in alignment with the slots 20, 22 or 24 of the primary shaft.

The lugs 56, 58 and 60 will therefore be withdrawn into the gear change member, so that the primary shaft will not be in driving engagement with any of the primary gears.

Thus the gear box is effectively in neutral and there is no transmission of rotary motion from the primary to the secondary shaft. To provide transmission of rotary motion from the primary shaft 2 to the secondary shaft 4 the end 46 of the gear change member 44 is moved towards the wall part 16 of the housing 6. This causes the slot 50 in the gear change member to come into alignment with the slot 20 in the primary drive shaft 2; and as previously described and shown in Figs. 1 and 2 the lug 56 will engage the primary gear 26. The primary gear 26 is thus caused to rotate by the primary shaft 2 and in turn causes rotation of the secondary gear 68 and thereby the secondary shaft 4. The gears 26 and 68 provide a first mechanical advantage in the gear box.The primary gears 28 and 30 will be caused to rotate at different speeds by their engagement with the secondary gears 70 and 72 respectively, but none of this rotary motion is transmitted to the primary shaft 2 since they are not in driving engagement with it.

The second pair of gears 28 and 70 may be selected to provide a different mechanical advantage to the first pair 26 and 68 by moving the end 46 of the gear change member further towards the end wall part 16. This motion causes the slot 50 to progressively move out of alignment with the slot 20. The part of the lugs 56, 58 and 60 which extend from the gear change member 44 to engage in slots 20, 22 or 24 in the primary shaft 2 and slots 33, 35 or 37 in the primary gears, is contoured to slope towards each end of the gear change member. Because this part of the lugs is contoured the progressive misalignment of the slots forces and extended lug to withdraw into its slot in the gear change member.

Hence the misalignment of the slots 20 and 50 causes disengagement of the gear 26. As the end 46 of the gear change member 44 is moved still further towards the end wall 16 the slots 52 and 22 come into alignment, and the lug 58 engages primary gear 28. In this position rotary motion is transmitted through the primary gear 28 engaging with the primary shaft 2 and secondary gears 70, while the primary gears 26 and 30 rotate about primary shaft 2.

The third pair of gears 30 and 72 can be engaged by moving the end 46 of the primary gear change member 44 even further towards the end wall 16. This motion maintains slots 20 and 50 out of alignment while slots 22 and 52 are moved out of alignment and slots 24 and 54 are moved into alignment. Thus the lugs 56 and 58 will be withdrawn into the gear change member 44 disengaging primary gears 26 and 28, and the lug 60 will engage with the primary gear 30.

The second embodiment of the invention illustrated in Figs. 3 and 4, has lugs 100 operable by a cam slide, but is otherwise substantially identical to the embodiment described in Figs. 1 and 2.

As for the embodiment described above, there is an elongate tubular primary shaft 106 having a short axially aligned elongate slot 110 cut in it. A primary gear 104 is mounted on the primary shaft 106 to overlap the slot 110; the gear 104 is capable of rotating freely about the primary shaft 106.

An elongate cylindrical gear change member 108 is slidably inserted into the primary shaft 106, wherein it is constrained to rotate with the primary shaft 106 by means of interengaging splines (not shown). The gear change member 108 has a channel; 122 cut transversely across it in which rests a lug 100, so that the lug 100 can be displaced axially with the gear change member 108.

Cut into the interior wall surface of the primary shaft 106 are two axially extending grooves 114, each groove being positioned approximately ninety degrees to either side of the slot 110 around the internal circumference of the primary shaft. In a region 124 adjacent the slot 110 the grooves 114 are cut closer to the slot 110 while in regions 126 remote from the slot the grooves 114 are circumferentially further away from the slot 110.

The lug 100 has two rods 116 and 118 which each extend laterally to either side of the lug 100 to engage in the grooves 114.

The rod 116, is rigidly mounted on the lug 100; the rod 118 is mounted in a slot 128 which extends radially in the lug 100. A compression spring 120 engages the rod 118 in slot 128 to bias the rod towards one end of the slot 120.

The operation of this embodiment of the gear box is the same as that described for the embodiments of Figs. 1 and 2. Thus to select and engage the gear 104, the gear change member 106 is displaced axially to bring the lug 100 into alignment with the slot 110. As the lug 100 is brought into alignment with the slot 110 the engagement of rods 116 and 118 in the grooves 114 causes the lug 100 to be displaced radially through the slot 110 to engage the gear 104. This is because the grooves 114 are cut closer towards the slot 110 in the region 124.

To disengage the gear 104 it is only necessary to move the gear change member 108 to misalign the lug 100 and slot 110. As the movement of the gear change member takes place the lug 100 is withdrawn into the primary shaft 106, by the engagement of the rods 116 and 118 in grooves 114.

Although this second embodiment of the invention is described as having only one gear it will be readily appreciated by those skilled in the art that as for the previously described embodiments as many gear sets as are desired may be used.

The gear box described above has only three different ratios, however it will be real ised by those skilled in the art that additional gear ratios may be added simply by adding extra pairs of primary and secondary gears to the shafts, and extra engaging lugs on the gear change means as necessary.

The gear box may be provided with a reverse gear, by incorporating a gear set having an intermediate gear between the primary and secondary gears of the gear set. The embodiment of the invention described above enables the construction of a gear box having a relatively simple, inexpensive and a light weight gear change means to alleviate the disadvantages of the prior art as previously described.

Claims

1. A gear box comprising rotatably mounted primary and secondary shafts, a plurality of primary gears rotatably mounted on the primary shaft, each in driving engagement with a respective one of a plurality of secondary gears fixedly mounted on the secondary shaft, and selecting means capable of selectively engaging any one of the primary gears with the primary shaft.

2. A gear box according to claim 1 wherein the primary shaft comprises an axially extending elongate chamber in which is received an elongate gear change member longitudinally displaceable within said chamber but relatively non-rotatable with respect to the said primary shaft; longitudinal displacement of said gear change member being arranged to actuate gear engaging means and thereby selectively engage a selected one of said primary gears.

3. A gear box according to claim 2 wherein the gear engaging means comprises a lug provided on the gear change member, which lug is radially displaceable through one or more apertures in said primary shaft to engage a selected gear by engagement in a corresponding radially extending slot in said selected gear.

4. A gear box according to claim 3 wherein said lug is radially displaceable in response to longitudinal correspondence of the lug to an aperture, to engage a primary gear, by resilient biassing means operating between the lug and said gear change member; and is radially displaceable to disengage said gear in response to longitudinal mis-alignment with the aperture, by abutment of a wedge shaped part of the lug with the edges of the aperture which urges the lug to withdraw into the primary shaft.

5. A gear box according to claim 3 wherein an element of the lug is slidably engaged in a longitudinally extending can track which is formed in the surface of the chamber and is arranged to radially displace the lug to engage and disengage the gears in response to longitudinal displacement of the gear change member.

6. A gear box according to claim 5 wherein resilient biassing means operates between the cam track engaging element and the lug to resiliently bias the lug in the direction of radial displacement.

7. A gear box according to any one of the preceding claims wherein a plurality of longitudinally spaced lugs are carried by the gear change member and the longitudinal spacings of the lugs and said gears and apertures are such that only one gear at a time can be engaged.

8. A gear box according to any one of the preceding claims wherein an end of said gear change member projects from the chamber and a linkage is secured to the end to be relatively rotatable but not longitudinally displaceable with respect to the gear change member so that longitudinal displacement of the linkage effects longitudinal displacement placement of the gear change member.

9. A gear box according to any one of the preceding claims wherein a reverse gear is provided by the engagement of an intermediate gear between a one of the primary gears and of the secondary gears.

10. A gear box according to claim 1, substantially as herein described with reference to the accompanying illustrative drawings.