GB2062135A

GB2062135A - Reversible transmission devices

Info

Publication number: GB2062135A
Application number: GB7937746A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1979-10-31
Filing date: 1979-10-31
Publication date: 1981-05-20

Abstract

A reversible transmission device includes an input shaft (2) and an output shaft (3) disposed in spaced parallel relation to the input shaft (2). A drive gear (6) fixed to the input shaft is in constant mesh with a driven gear (8) rotatable on the output shaft, and a drive sprocket (7) fixed to the input shaft continuously drives, via a chain (9), a driven sprocket (10) rotatable on the output shaft. A clutch mechanism (11, 12) is operable to couple the driven gear (8) to the output shaft to rotate the latter in one direction relative to the input shaft, or alternatively to couple the driven sprocket (10) to the output shaft to reverse the direction of rotation of the latter. The device may be employed in a power boat. <IMAGE>

Description

SPECIFICATION Improvements in reversible transmission devices.

The present invention relates to a reversible transmission device which includes a rotatable input member, an output member rotatable by the input member, and means operable selectively to change the direction of rotation of the output member with respect to the input member. Such a device will hereinafter be referred to as a "device of the type specified".

In a simple device of the type specified, for example a reversible gearbox in which the input and output members are rotatable about parallel spaced axes, input and output gears coupled respectively to the input and output members are arranged so as to mesh, either directly with each other, or with an intermediate reversing gear. The input and output members will rotate in opposite directions when the input and output gears directly mesh, and will rotate in the same direction when the input and output gear mesh with the intermediate gear. The requirement for an intermediate gear, which rotates about an axis parallel to but displaced from the axes of the input and output gears, complicates and increases the bulk of the gearbox.

It is an object of the present invention to provide a reversible transmission device or gearbox which eliminates the necessity for an intermediate reversing gear or equivalent, and the disadvantages associated therewith.

In its broadest aspect, the present invention provides a reversible transmjssion device of the type specified, wherein the input and output members are rotatably drivingly interconnectable,.

selectively, via a train of gears, or via a flexible endless drive element, such as a chain or belt, mounted on and drivingly cooperating with sprockets or the like rotatable about axes common to the gears of the train.

From another aspect, the present invention provides a reversible transmission device of the type specified, wherein the input member, a first gear and a sprocket or the like, are rotatable about a first common axis, and the output member, a second gear and a second sprocket or the like, are rotatable about a second common axis disposed in fixed spaced parallel relation to the first common axis, the first and second gears being in constant driving connection, and the first and second sprockets being in constant driving connection via a flexible endless drive element, such as a chain or belt, passing around the first and second sprockets, the output member being rotatable by the input member selectively via the first and second gears, or via the first and second sprockets and associated flexible drive element.

The sprockets may be toothed or otherwise configured to cooperate with an internally toothed or otherwise configured single or multiplex chain.

Alternatively, the sprockets may comprise rollers, or pulleys which are grooved or otherwise configured to cooperate respectively with a flat belt, or a V-section or otherwise configured single or multiplex belt.

Preferably, the gear and sprocket associated with one of the input and output members are permanently coupled to that member so as to rotate therewith, whilst the gear and sprocket associated with the other of the input and output members are rotatable relative to that member, clutch means being provided to selectively couple the latter gear or sprocket to that member so as to rotate therewith.

The transmission device or gearbox may be a change-ratio device, for example a step-up or step-down device. In this event, it is preferable that the gear and sprocket associated with the lower speed or stepped-down member be provided with the clutch means.

In order that the invention may be more readily understood, reference will now be made to the accompanying drawing in which: Figure 1 is a diagrammatic vertical axial section through a reversible gearbox embodying the invention; and Figure 2 is a diagrammatic layout of the gears, sprockets and chain incorporated in the gearbox of Figure 1.

Referring to Figure 1 , the reversible gearbox comprises a casing 1 in which an input shaft 2 and output shaft 3 are rotatable about parallel, spaced axes. The shafts are journalled, for example in roller bearings 4 and ball bearings 5.

Secured, for example keyed or splined, to the input shaft 2 is a drive gear 6 and a drive sprocket 7. The drive gear 6 is in constant direct mesh with a driven gear 8 rotatable mounted on the output shaft 3, and the drive sprocket 7 is coupled by an endless chain 9 to a driven sprocket 10 also rotatably mounted on the output shaft. The gears 6 and 8 may be straight cut spur gears, and the sprockets 7 and 10 may have generally straight cut teeth which cooperate with an internally toothed metal chain, for example of the type supplied under the trade name "HIVO" by The Morse Chain Co. Ltd.

A clutch mechanism is provided to selectively lock either the driven gear 8 or the driven sprocket 10 against rotation relative to the output shaft 3.

In this embodiment, the clutch mechanism comprises a face dog 11 which is keyed or splined at 12 to the output shaft, whereby the face dog is axially slidable on, but non-rotatably secured to, the output shaft. The face dog 11 has projections on or recesses in its opposite axially directed side faces (not shown) which are releasably and drivingly cooperable with corresponding recesses in or projections on the adjacent axially directed side faces of the gear 8 and sprocket 10. The dog 11 is axially displaceable from the "neutral" position shown, to the left or right as viewed in Figure 1, into driving engagement respectively with the gear 8 or sprocket 10, from outside the casing 1 , via an appropriate linkage 13, 14.

When the input shaft 2 is rotated with the face dog 11 positioned as shown in Figure 1, the driven gear 8 will be rotated on the output shaft 3 by the drive gear 6 in a direction opposite to that of the drive shaft 2, the driven sprocket 10 will be rotated on the output shaft 3 by the drive sprocket 7, via the chain 9, in the same direction as the input shaft. Thus, when the dog 11 is displaced to the left to couple the gear 8 to the output shaft 3, the output shaft will be rotated in a direction opposite to that of the input shaft. When the dog 11 displaced to the right to couple the sprocket 10 to the output shaft, the output shaft will rotate in the same direction as the input shaft.

In the illustrated embodiment, the relative diameters of the drive and driven gears are selected to produce a speed reduction or stepdown in the rotation of the output shaft relative to the input shaft, and the diameters of the drive and driven sprockets are selected to produce the same step-down ratio. However, this is not essential, and the gearbox is preferabiy so designed that the pairs of gears and pairs of sprockets may be replaced by other matched pairs to facilitate ratio changes in one or both directions of rotation of the output shaft.The clutch mechanism is preferably associated with the shaft which rotates at the lower speed, i.e. the output shaft in the illustrated embodiment, and if the gearbox is intended to be a step-up gearbox, then the clutch mechanism is preferably associated with the lower speed input shaft, either by design, or by reversing the roles of the input and output shafts.

Lubrication of the various components may be achieved by partially filling the casing 1 with lubricating oil, into which the gear 8 and/or sprocket 10 and chain 9 dip. If required, pressure lubrication of the components and in particular of the chain and sprocket teeth may be provided.

This may advantageously be achieved by internally shaping the casing 1 in the region of the gear 8 to cooperate with the latter, so that the gear 8 functions as a gear pump, and feeds the oil to the required locations, under pressure, via appropriate galleries.

From the foregoing, it will be seen that there is provided a particularly compact reversible gearbox. For example, a gearbox capable to transmitting 200 horsepower or more may have a casing which, as viewed in Figure 1, has an overall axial length of the order of 5 inches, the spacing between the axes of the input and output shafts, being of the order of 4 inches.

The maximum power which can be transmitted by the gearbox is dictated by the axial lengths of the gears and sprockets so that the powercarrying capacity of the gearbox can be changed by changing the latter axial lengths, without changing the diameters of the gears and/or sprockets, and therefore without changing the inter-axial spacing of the input and output shafts.

However, gearboxes embodying the invention may be readily designed to have a range of inter-axial spacings depending upon requirements.

Since cylindrical, parallel-toothed spur gears are employed for the gears 6 and 8, and the sprockets 7 and 10 are also parallel-toothed, problems associated with axial thrust, end float and mesh adjustment of, for example bevel or skew-gear drives, are eliminated, and the power absorption is minimised.

The gearbox possesses the advantages of relative simplicity in production, assembly, setting-up, and replacement of the gears and sprockets. The casing 1, which may be cast, machined or otherwise formed from conventionally employed materials, for example from a light metal alloy of aluminium or magnesium, requires accurate machining only in so far as the location of the bearings for the input and output shafts are concerned. The individual gears, sprockets, chain, bearings, oil seals and shafts may be of conventional design and materials.

Gearboxes embodying the invention have numerous applications where it is required to reversibly couple a drive motor to a final drive device, particularly where the centerline of the motor output shaft and the centerline of the final drive device input shaft are not coaxial. The gearboxes are particularly suitable for use in the transmission systems of marine vessels where, for example, it is desired to couple an inboardmounted internal combustion engine to a propeller shaft, or a stern or outboard drive unit, such as that forming the subject of my British Patent No.

1,529,459. Not only does the gearbox provide the necessary forward-neutral-reverse facility in the transmission, but it also drops the engine output drive line to a position adjacent the bottom of the hull in alignment with the input drive line of the outboard drive unit.

The gearboxes may be employed to particular advantage in multi-engined, multi-propellor power boats where it is advantageous and/or essential to contra-rotate the propellors to counteract propellor torque and preserve straight-line stability of the vessel at high speed. This may be readily achieved by utilising an individual gearbox between each engine and its associated propellor or outboard drive unit, the contra-rotation being achieved by driving one propellor via the gears.6 and 8 of its associated gearbox, and the other propellor via the sprockets 7 and 10 and chain 9 of its associated gearbox.

It will be understood that various modifications may be made without departing from the scope of the present invention. For example, the drive and driven gears may have teeth configurations other than straight cut. The sprocket and chain arrangement may employ a roller chain instead of an internally toothed chain, or may be replaced by an equivalent friction drive, such as a grooved sprocket (pulley) and drive belt (V-belt) arrangement.

Whilst the driven gear and sprocket are selectively clutched and declutched by means of a slidable clutch dog in the illustrated embodiment, other types of clutch mechanisms may be employed, for example a multiple plate clutch.

The invention may be applied to a gearbox in which the input and output shafts are coaxial. In this case, an input shaft will, for example, have a drive gear meshing with a driven gear fixed to a second shaft spaced from and parallel to the input shaft. The second shaft will carry a gear and sprocket, equivalent to the gear 6 and sprocket 7, which drive, respectively, a gear and sprocket equivalent to the gear 8 and sprocket 10, selectively couplable to the output shaft, as described with reference to this illustrated embodiment.

Claims

1. A reversible transmission device which includes a rotatable input member, an output member rotatable by the input member, and means operable selectively to change the direction of rotation of the output member with respect to the input member, wherein the input and output members are rotatably drivingly interconnectable, selectively, via a train of constant mesh gears, or via a chain, belt or other flexible endless drive element mounted on and constantly drivingly cooperating with sprockets, pulleys or other drive element-mounting members rotatable about axes common to the gears of the train.

2. A reversible transmission device which includes a rotatable input member, an output member rotatable by the input member, and means operable selectively to change the direction of rotation of the output member with respect to the input member, wherein the input member, a first gear, and a first sprocket, pulley or other flexible endless drive element-mounting member, are rotatable about a first common axis, and the output member, a second gear, and a second sprocket, pulley or other flexible endless drive element-mounting member, are rotatable about a second common axis disposed in fixed spaced parallel relation to the first common axis, the first and second gears being in constant driving connection, and the first and second mounting members being in constant driving connection via a chain, belt or other flexible endless drive element passing around the first and second mounting members, the output member being rotatable by the input member, selectively, via the first and second gears, or via the first and second mounting members and associated drive element.

3. A reversible transmission device as claimed in claim 1 or 2, wherein the mounting members comprise sprockets which are toothed or otherwise configured to cooperate with an internally toothed or otherwise configured single or multiplex chain which comprises the drive element.

4. A reversible transmission device as claimed in claim 1 or 2, wherein the mounting members comprise rollers or pulleys which are grooved or otherwise configured to cooperate respectively with a flat belt, or a V-section or otherwise configured single or multiplex belt which comprises the drive element.

5. A reversible transmission device as claimed in any preceding claim, wherein the gear and mounting member associated with one of the input and output members are permanently coupled to that one member so as to rotate therewith, whilst the gear and mounting member associated with the other of the input and output members are rotatable relative to that other member, clutch means being provided to selectively couple the latter gear or mounting member to that other member so as to rotate therewith.

6. A reversible transmission device as claimed in claim 5 which comprises a change-ratio device, wherein the first and second gears have mutually different diameters, and/or the first and second mounting members have mutually different diameters, the larger diameter gear and/or mounting member being provided with the clutch means.

7. A reversible transmission device substantially as hereinbefore described with reference to the accompanying drawings.

8. A power boat including an inboard-mounted internal combustion engine, a stern or outboard drive unit or propellor shaft, and a reversible transmission device as claimed in any preceding claim coupling the engine to the drive unit or propellor shaft.

9. A power boat as claimed in claim 8, wherein the reversible transmission device is oriented with the axis of the output member below the axis of the input member.