GB2037382A

GB2037382A - Power Transmission Device

Info

Publication number: GB2037382A
Application number: GB7941287A
Authority: GB
Original assignee: De la Rue Crosfield Ltd
Current assignee: De la Rue Crosfield Ltd
Priority date: 1978-12-08
Filing date: 1979-11-29
Publication date: 1980-07-09

Abstract

The object of the invention is to produce a power transmission device of simple construction in which no selectively operable movable components are required to render effective either of the desired gear ratios and which does not use externally powered clutches or brakes. This is achieved by means of a gear box which, when its driving shaft is rotated in one direction, operates at one gear ratio; and, when its driving shaft is rotated in the opposite direction operates at a different gear ratio. The output shaft rotates in the same direction in each case. A motor M drives an input pinion 6 which meshes with two pinions 11 and 8 connected through respective oppositely acting one-way clutches 10, 12 to shafts 13 and 7. Rotation of the shaft 5 in direction C causes output shaft 7 to rotate at one speed in direction A. Rotation of shaft 5 in direction B produces rotation of the shaft 7 at a different speed but in the same direction. <IMAGE>

Description

SPECIFICATION Power Transmission Device This invention relates to power transmission devices of the type having a driven power input shaft, a power output shaft and an intermediary means including one or more gear trains capable of mechanically coupling together said two shafts so as to provide either of two aiternative gear ratios.

An example of a known device capable of fulfilling the above function comprises a gear-box in which respective input and output gears are selectively coupled together by means of axially engageable gears disposed on a gearbox layshaft. A further example comprises a constantmesh type gearbox which may be, for example, of the planetary or epicyclic type and include selectively engageable brake means to arrest either of two rotary assemblies.

Furthermore, it is known to provide a gearbox in which either of two gear ratios may be attained by selectively operable clutches which may be of the mechanical or of the electro-magnetic type.

Analogous gear-box devices are also known in which belt drives, for example of the internally notched type, replace gear systems.

All of the above-mentioned prior art examples of dual-ratio power transmission devices are necessariiy complicated and generally require movable mechanical components, which are selectively operated to provide either of the two desired gear ratios.

It is the prime object of the present invention to provide a power transmission device of the above-mentioned type which is, a) of simple construction, b) which eliminates the need for selectively operable movable components to render effective either of the desired gear ratios, and c) which does not necessitate the use of externally powered clutches or braking devices.

According to the present invention a dual-ratio power transmission device having an input shaft driven by a reversible power unit and a unidirectional output shaft comprises a first gear train having a first overall gear ratio adapted to drive said output shaft from said input shaft in the same direction of rotation, a second gear train having a second overall gear ratio different from said first ratio, adapted to drive said output shaft from said input shaft in an opposite direction of rotation, and a one-way clutch means disposed in each of said gear trains, said clutches being arranged in an opposite manner so that when said input shaft is driven in a clockwise direction said first gear train is operative and when it is driven in an anti-clockwise direction said second gear train is operative.

Preferably the input shaft is provided with a fixedly mounted gear, which serves as an input gear for each of said gear trains.

Preferably, the first gear train comprises an output gear which is adapted to mesh with said input gear, is loosely mounted to said output shaft and contains a one-way clutch.

Preferably the second gear train includes a layshaft carrying a first gear adapted to mesh with said input gear and a second gear adapted to mesh with a gear mounted upon said output shaft. The one-way clutch may be contained in either of the lay-shaft gears or the associated output shaft gear.

The one-way clutches may be of any convenient type. For example, they may be of the pawl and ratchet type, or more preferably, of the wedge ramp and roller or ball type.

In the accompanying drawing is shown a partly cut-away perspective view of a two-ratio gearbox embodying the invention.

The framework of the gearbox comprises a pair of drilled frame plates 1 and 2 spacially connected together in parallel relationship by four pillars 3 and associated screws 4.

Symbol 5 indicates one end of an armature shaft of a reversible electric motor M, said shaft 5 constituting the power input shaft of the gear box.

The shaft 5 passes through the frame plate 1 and carries a fixedly mounted gear box input pinion 6.

The output of the gear box comprises a shaft 7 disposed in parallel relationship to the input shaft 5 and which is adapted to be driven in the direction indicated by the arrow A.

Disposed between the frame plates is the output shaft 7 which is provided with a freely mounted gear-wheel 8 and a fixedly mounted gear-wheel 9. The centre of the gear-wheel 8 is provided with a one-way clutch 10 which serves to transmit power to the shaft 7 only when the input pinion 6 is driven in the direction indicated by the arrow B. In the specific example, the pinion 6 and the gear-wheel 8 collectively provide a reduction ratio of 1.7:1.

The input pinion 6 also meshes with a freely mounted gear-wheel 11, the hub portion of which contains a second one-way clutch 12, disposed on a gear-box lay-shaft 13. The latter clutch is arranged in an opposite sense to the clutch 10 and serves to transmit power to the shaft 13 only when the input pinion 6 is driven in the direction indicated by the arrow C. Fixedly mounted to layshaft 13 is a pinion 14 which meshes with the gear-wheel 9. The compound gear train thus described provides an overall reduction ratio of 20:1.

It will thus be seen that if the gear-box is used in conjunction with a reversible electric motor M having a running speed of 1400 RPM, two alternative uni-directional output speeds 823.5 or 70 RPM may be attained simply by selecting the direction of rotation of the motor, The clutch 12 may alternatively be provided in the gear-wheel 9 instead of in the gear-wheel 11 (which of course must be disposed in opposite sense to the clutch 10), to reduce wear in the lay-shaft bearings when the gearbox is providing the higher output speed.

Whilst the described example includes only a single- lay-shaft it is obvious that more complex systems may be provided for one or both gear trains to enable very high speed reduction ratios to be attained. However, it is essential to ensure that complementary input/output directions of rotation are effected in the two trains, and which may be achieved by the provision of an odd and even number of gear axles in the respective gear trains.

One application of this gear-box is described in our co-pending Patent Application No. 47671/78 in which the gear-box is employed in a sheet counting apparatus.

Claims

1. A duai-ratio power tansmission device having an input shaft driven by a reversible power unit and a unidirectional output shaft comprising a first gear train having a first overall gear ratio adapted to drive said output shaft from said input shaft in the same direction of rotation, a second gear train having a second overall gear ratio different from said first ratio, adapted to drive said output shaft from said input shaft in an opposite direction of rotation, and a one-way clutch means disposed in each of said gear trains, said clutches being arranged in an opposite manner so that when said input shaft is driven in a clockwise direction said first gear train is operative and when it is driven in an anti-clockwise direction said second gear train is operative.

2. A power transmission device according to claim 1 in which said input shaft is provided with a fixedly mounted gear, which serves as an input gear for each of said gear trains.

3. A power transmission device according to claim 2 and in which the first gear train comprises an output gear which is adapted to mesh with said input gear, is loosely mounted to said output shaft and contains a one-way clutch

4. A power transmission device according to any of claims 1 to 3 and in which the second gear train includes a layshaft carrying a first gear adapted to mesh with said input gear and a second gear adapted to mesh with a gear mounted upon said output shaft.

5. A power transmission device according to claim 4 and in which the one-way clutch is contained in either of the lay-shaft gears or in the associated output shaft gear.

6. A power transmission device according to any preceding claim and in which the clutches are of the pawl and ratchet type.

7. A power transmission device according to any of claims 1 to 5 and in which the clutches are of the wedge ramp and roller or ball type.

8. A power transmission device substantially as hereinbefore described and as illustrated in the accompanying drawing.