GB2469064A

GB2469064A - Unidirectional drive assembly

Info

Publication number: GB2469064A
Application number: GB0905539A
Authority: GB
Inventors: William Hardy
Original assignee: Individual
Current assignee: Individual
Priority date: 2009-03-31
Filing date: 2009-03-31
Publication date: 2010-10-06
Also published as: GB0905539D0

Abstract

A ratchet unidirectional drive assembly, e.g, for wave power generation, comprises a drive assembly with coaxial input and output shafts 12, 16 that are interconnected by a first freewheel 15 that couples rotation of the input shaft 12 to the output shaft 16 in a first direction. Rotation in an opposed second direction is not transmitted to the output shaft 16 through that freewheel 15. An intermediate assembly 20 is arranged parallel to the drive assembly and has first and second intermediate shafts 21, 22 interconnected by a second freewheel 24. A first drive train, e.g. a sprocket and chain mechanism 26, 27, 28, couples the rotation of the input shaft 12 to the first intermediate shaft 21 in the same direction and a second drive train 29, 30 couples the output shaft 16 to the second intermediate shaft 22, in an opposite direction. Rotation of the input shaft 12 in either the first or second direction causes rotation of the output shaft 16 only in the first direction.

Description

RATCHET MECHANSIM

This invention relates to a ratchet mechanism, and in particular to a ratchet mechanism to convert bidirectional rotation of an input shaft into unidirectional rotation of an output shaft.

There are many circumstances that require a mechanism that converts bidirectional rotation (ie rotation in either direction about a common axis) of an input shaft into unidirectional rotation of an output shaft. For example, a power generator using wave energy may require an output shaft to turn in only one direction to generate electricity, and this can be powered by bidirectional rotation from an input shaft that rotates one way as the waves rise and the other as they fall. Alternatively, the present invention could be used on a winch when rotation of a crank in two directions moves the winch in only a single direction, so only half the number of crank actions are required, as compared to using a one-way ratchet.

Therefore, according to the present invention there is provided a ratchet mechanism to convert bidirectional motion of an input shaft into unidirectional motion of an output shaft the ratchet mechanism comprising: -a drive assembly having coaxial input and output shafts, the input and output shafts being interconnected at adjacent ends by a first freewheel, the other end of the input shaft being adapted for bidirectional rotation by an external force, and the other end of the output shaft being connectable to an object to be driven, whereby the free wheel couples the rotation of the input shaft to the output shaft in a first direction only so that rotation of the input shaft in that first direction causes the first freewheel to engage and drive the output shaft in that same direction, but when the input shaft is rotated in an opposed second direction, the first freewheel does not transmit that rotation to the output shaft; -an intermediate assembly, arranged substantially parallel to the drive assembly and comprising coaxial first and second intermediate shafts interconnected at adjacent ends by a second freewheel, whereby the second freewheel couples the rotation of the first intermediate shaft to the second intermediate shaft only in a second direction such that rotation of the first intermediate shaft in the second direction causes the second intermediate shaft to rotate in that direction, but rotation in the opposed first direction, is not transmitted by the second freewheel to the second intermediate shaft; -a first drive train that couples the rotation of the input shaft to the first intermediate shaft, whereby rotation of the input shaft in either the first or second direction causes rotation of the first intermediate shaft in the same direction; and -a second drive train that couples the output shaft to the second intermediate shaft, whereby rotation of the second intermediate shaft in one direction causes the output shaft to rotate in an opposite direction; -wherein rotation of the input shaft in either the first or second direction causes the rotation of the output shaft only in the first direction.

The ratchet mechanism of this invention can be made in any size according to intended use. The other end of the input shaft (ie the force input end) could be connected to a lever or handle for manual operation, or it could be adapted to couple to any sort of drive means. For example this could be in the form of a wheel, either for manual or mechanical operation. The unidirectional rotation of the output shaft can be used for any suitable purpose, and it could be coupled to external devices such as a gear or pulley system.

To prevent debris from getting into the ratchet mechanism and causing damage, it is preferred that the drive assembly and the intermediate assembly are enclosed in a housing, with only the outer free ends of the input shaft and output shaft being external of the housing.

The first drive train could comprise any means that suitably couples rotational movement. This may be as simple as a drive belt attached between pulley wheels mounted to the input shaft and the first intermediate shaft.

However, in a preferred embodiment the first drive train is a sprocket and chain mechanism, as these will not slip. The second drive train could also comprise any means that suitably couples and reverses the rotational movement of the output shaft to the second intermediate shaft. Preferably it comprises two interlocking cogs, one attached to each of the output shaft and second intermediate shaft Any freewheel suitable for use on coaxial shafts could be used depending on the size and intended use of the ratchet mechanism. In one embodiment the first and second freewheels are sprag clutches, or alternatively and just as preferably the first and second freewheels have a pawl and ratchet mechanism, such as that found on a bicycle wheel.

So that is may be better understood, one embodiment of the present invention will now be described in detail, but by way of example only, with reference to the following drawings in which: Figure 1 shows a perspective view of a ratchet mechanism according to the present invention showing rotation of the handle in a first direction; Figure 2 shows a perspective view of the ratchet mechanism of Figure 1 showing rotation of the handle in a second direction; Figure 3 shows a side view of the ratchet mechanism of Figures 1 and 2; Figure 4 shows a cross sectional view of the first and second freewheels when rotated in the first direction; and Figure 5 shows a cross sectional view of the first and second freewheels of Figure 1 when rotated in the second direction.

With reference to all of the Figures, there is shown a ratchet mechanism generally indicated 10 the components parts of which are generally enclosed within a housing 11. The ratchet mechanism comprises a drive assembly, generally indicated 12, which comprises a rotationally mounted input shaft 13, one end of which is connected to a lever 14, and the other end is linked to a first freewheel, generally indicated 15. The lever 14 can be used to rotate the input shaft 13 in either direction.

An output shaft 16 is mounted, co-axially with the input shaft, and is connected at one end to the first freewheel 15. The other end 17 extends out of the housing. The other end 17 of the output shaft can be connected to another mechanism requiring unidirectional rotational drive.

Arranged substantially parallel to the drive assembly 12 within the housing is an intermediate assembly, generally indicated 20. The intermediate assembly 20 comprises coaxial first intermediate shaft 21 and second intermediate shaft 22. Both the intermediate shafts are mounted for rotation about a major axis. The first intermediate shaft is mounted at one end in a bearing 23 in the housing 11. The other end is coupled to a second freewheel 24. The second intermediate shaft 22 is also coupled to the second freewheel 24, and is mounted at the other end in a bearing 25 in the housing 11 so that it may rotate about a major longitudinal axis. The first intermediate shaft 21 is in this embodiment arranged substantially parallel to the input shaft 13 of the drive assembly 12 and the second intermediate shaft 22 is therefore also arranged substantially parallel to the output shaft 16 of the drive assembly 12.

As shown more clearly in Figures 1 to 3, the input shaft 13 and first intermediate shaft 21 are rotational interconnected by a first drive train. This comprises a first sprocket 26 mounted on the input shaft 13 and a second sprocket 27, of identical diameter to the first sprocket 26, mounted on the first intermediate shaft 21, and a chain 28 that passes around and engages with both sprockets. Rotation of the input shaft 13 in one direction causes the first intermediate shaft 21 to rotate in the same direction.

As is clearly shown in Figures 1 to 3, the output shaft 16 of the drive assembly 12 and the second intermediate shaft 22 of the intermediate assembly 20 are also rotationally interconnected. A pair of interlocking cogs 29 and 30, which are of identical diameter, are mounted on the two shafts.

Rotation of the second intermediate shaft 22in one direction causes the output shaft 16 to rotate in the opposite direction at the same speed. The cogs 29, 30 and the sprockets 26, 27 are appropriately sized to ensure the speed of rotation of the output shaft are the same regardless of the rotational direction of input.

If the cogs, sprockets and freewheels are appropriately configured the input rotation speed will match the output rotational speed, but gearing could also be employed to alter the speed.

Figures 4 and 5, show a cross section through the first and second freewheels 15, 24. Identical reference numerals will be used for each as they are essentially identical, though the first freewheel 15 is a mirror-image of the second freewheel 24. The first and second freewheels 15, 24 each comprise a housing 31 to which the input shaft 13 or first intermediate shaft 21 are respectively connected. Mounted within the housing 31 is a ratchet 32 and pawl 33 mechanism. Each ratchet 32 is connected to the output shaft 16 or the second intermediate shaft 22 of the intermediate assembly 20. The pawls 33 engage with the teeth of the respective ratchet 32 to prevent different relative rotation in one direction.

The first freewheel 15 is arranged so that the pawls 33 engage with the teeth of the ratchet 32 when the input shaft 13 is rotated in a first direction, driving the output shaft 16 in the same, first direction, but to disengage when the input shaft 13 is rotated in the second direction.

The second freewheel 24 is arranged so that the pawls 33 engage with the teeth of the ratchet 32 when the first intermediate shaft 21 is rotated in the second direction, driving the second intermediate shaft 22 in the same, second direction, but to disengage when the first intermediate shaft 21 is rotated in the first direction.

In use, the mechanism of the present invention converts rotation of the input shaft 13 in either direction into unidirectional motion of the output shaft 16.

As shown in Figures 1 and 4, rotation of the handle 14 in the first direction (as shown by arrows 40) rotates the input shaft 13 in this direction. Rotation in this direction causes the pawls 33 of the first freewheel 15 to engage with the teeth of the ratchet 32 in the first freewheel 15, 50 that the output shaft 16 also rotates in the first direction 40. The first intermediate shaft 21 is also driven to rotate in the first direction 40 by the drive train 26,27,28. The second freewheel 24 is disengaged so the second intermediate shaft 22 is not driven to rotate by the first intermediate shaft. However it is linked to the output shaft 16 and rotates in a second direction, as indicated by arrows 41.

As shown in Figures 2 and 5, rotation of the handle 14 in the second direction (arrow 41) rotates the input shaft 13 in this direction. Rotation in this second direction causes the pawls 33 of the first freewheel 15 to disengage from the teeth of the ratchet 32 therein.

The first intermediate shaft 21 is also driven to rotate in the second direction 41 by the drive train 26,27,28. The pawls 33 of the second freewheel 24 engage with the teeth of the ratchet 32 in that second freewheel 24, and the second intermediate shaft 22 is thereby driven to rotate in the second direction 41. The second intermediate shaft 22 then drives the output shaft 16, through interlocking cogs 29,30 to rotate in the first direction 40.

Claims

CLAIMS1. A ratchet mechanism to convert bidirectional motion of an input shaft into unidirectional motion of an output shaft the ratchet mechanism comprising: -a drive assembly having coaxial input and output shafts, the input and output shafts being interconnected at adjacent ends by a first freewheel, the other end of the input shaft being adapted for bidirectional rotation by an external force, and the other end of the output shaft being connectable to an object to be driven, whereby the free wheel couples the rotation of the input shaft to the output shaft in a first direction only so that rotation of the input shaft in that first direction causes the first freewheel to engage and drive the output shaft in that same direction, but when the input shaft is rotated in an opposed second direction, the first freewheel does not transmit that rotation to the output shaft; -an intermediate assembly, arranged substantially parallel to the drive assembly and comprising coaxial first and second intermediate shafts interconnected at adjacent ends by a second freewheel, whereby the second freewheel couples the rotation of the first intermediate shaft to the second intermediate shaft only in a second direction such that rotation of the first intermediate shaft in the second direction causes the second intermediate shaft to rotate in that direction, but rotation in the opposed first direction, is not transmitted by the second freewheel to the second intermediate shaft; -a first drive train that couples the rotation of the input shaft to the first intermediate shaft, whereby rotation of the input shaft in either the first or second direction causes rotation of the first intermediate shaft in the same direction; and -a second drive train that couples the output shaft to the second intermediate shaft, whereby rotation of the second intermediate shaft in one direction causes the output shaft to rotate in an opposite direction; -wherein rotation of the input shaft in either the first or second direction causes the rotation of the output shaft only in the first direction.
2. A ratchet mechanism as claimed in claim 1, wherein the first drive train is a sprocket and chain mechanism.
3. A ratchet mechanism as claimed in any of the preceding claims, wherein the drive assembly and the intermediate assembly are enclosed in a housing.
4. A ratchet mechanism as claimed in claim 3, wherein the other end of the input shaft and the other end of the output shaft are external of the housing.
5. A ratchet mechanism as claimed in any of the preceding claims, wherein the first and second freewheels are sprag clutches.
6. A ratchet mechanism as claimed in any of claims 1 to 4, wherein the first and second freewheels have a pawl and ratchet mechanism.
7. A ratchet mechanism as claimed in claim 1 and as substantially herein described with reference to and as illustrated in the accompanying drawings.