GB2213886A

GB2213886A - Coiled spring clutch mechanism

Info

Publication number: GB2213886A
Application number: GB8900190A
Authority: GB
Inventors: Michael John Sykes; John Claughton Knight
Original assignee: SEAFARER NAVIGATION INTERNATIO
Current assignee: SEAFARER NAVIGATION INTERNATIO
Priority date: 1988-01-05
Filing date: 1989-01-05
Publication date: 1989-08-23
Also published as: GB8800138D0; GB8900190D0

Abstract

A clutch mechanism comprises a coiled spring (32) having an outwardly projecting or inwardly projecting detent at each end, a spring locating member (28) on which the spring is coiled for outwardly projecting detents and within which the spring is coiled for inwardly projecting detents, and force-applying means (38, 41) engageable with the detents in such a manner as to be able to apply a substantially tangential force to either of the detents in either circumferential direction, thereby to engage and disengage the drive between the spring (32) and the spring locating member (28). The force-applying means preferably comprises a pair of diametrically opposed, relatively rotatable, substantially semi-cylindrical sleeves (38, 41) defining opposed gaps in which the spring detents are located. The mechanism is located in an electrical drive with the capacity for manual override and may be modified (Fig 3) to transfer torque by expansion of the coiled spring. <IMAGE>

Description

CLUTCH MECHANISM SPECIFICATION This invention relates to clutch mechanisms, and is particularly concerned with bi-directfonal clutch mechanisms. Although the clutch mechanism of the present invention can be incorporated into a wide variety of devices, machines and apparatus, it is particularly appropriate for incorporation into an autopilot.

It is an object of the present invention to provide a bi-directional clutch mechanism for use anywhere where one wishes to have electrical drive under normal operating circumstances but with the capacity for manual override.

In accordance with the present invention there is provided a bi-directional clutch mechanism comprising a coiled spring having an outwardly projecting detent at each end thereof, a spring locating member on which the spring is coiled, and force-applying means radially outwardly of the spring and engageable with said detents in such manner as to be able to apply a substantially tangential force to either of the detents in either circumferential direction, thereby to engage and disengage the drive between the spring and the spring locating member.

Also in accordance with the present invention there is provided a bi-directional clutch mechanism comprising a coiled spring having an inwardly projecting detent at each end thereof, a spring locating member within which the spring is coiled, and force-applying means radially inwardly of the spring and engageable with said detents in such manner as to be able to apply a substantially tangential force to either of the detents in either circumferential direction, thereby to engage and disengage the drive between the spring and the spring locating member.

Preferably, the spring is a cylindrical, parallelturn coil spring.

Preferably, the force-applying means comprises a pair of diametrically opposed, relatively rotatable1 substantially semi-cylindrical sleeves of equal radius having a circumferential length such as to be able to provide a pair of diametrically opposed gaps therebetween in which the spring detents are located.

In order that the invention may be fully understood, two embodiments of clutch mechanism in accordance with the invention will now be described by way of example and with reference to the acconpanyin drawings, in which: Fig. 1 is a sectional view through a first embodiment of clutch mechanism, taken along the line I I of Fig. 2; Fig. 2 is a sectional view through the first embodiment of clutch mechanism, taken along the line II-II of Fig. 1 and with the motor and outer casing removed; Fig. 3 illustrates how the clutch mechanism may be modified according to a second embodiment; and, Fig. 4 is an end view of the spring of the mechanism of Fig. 3.

The clutch mechanism of the present invention may be embodied in various machines and pieces of apparatus where one wishes to engage and disengage the drive, but is described hereinafter, as an illustration, as a clutch for an autopilot. The device comprises an outer casing 10 fitted with a backplate 12. A motor is indicated generally at 14 in Fig. 1 and is mounted on a flange plate 16 which is an extension from a fixed cylindrical sleeve 18. Rotatable within the fixed sleeve 18 is a generally cylindrical inner sleeve 19.

The motor 14 has an output shaft on which is mounted a small gearwheel 20 which is in meshing engagement with a main gearwheel 22. The main gearwheel 22 is coaxial with the main longitudinal axis of the clutch mechanism and with the output stub shaft 24 of the device. The main gearwheel 22 is bolted from the outside by bolts 25 to a spring locating member 28. The spring locating member 28 has a radially extending annular portion 29 and a cylindrical longitudinally inwardly extending boss 30. The inner sleeve 19 is bolted to the spring locating member 28 by radial bolts 31 to be rotatable therewith. Mounted on the cylindrical boss 30 of the spring locating member 23 is a wrap spring 32. The spring 32 is preferably a parallel-turn spring of square cross-section. A split bush 33 of low-friction plastics material such as "Tufnol" is positioned between the spring 32 and the boss 30.The split bush 33 is in two diametrically opposed halves. The spring 32 is provided with a radially outwardly projecting tang 34a, 34b at each end. Each tong is curved, as shown in Fig. 2, but with the directions of curvature being opposite for the respective tongs.

The output stub shaft 24 is fixedly connected to a stub shaft locator 36. The stub shaft locator 36 is rotatable within the inner sleeve 19 and comprises a cylindrical shell portion 37 which is integral with a substantially semi-cylindrical shell portion 38. This semi-cylindrical shell portion 38 overlies the spring 32.

Also mounted within the inner sleeve 19 is a centre spigot indicated generally at 39. This centre spigot 39 has a cylindrical sleeve portion 40 which is soused within the stub shaft locator 36 and has an integral substantially semi-cylindrical shell portion 41 which is positioned to overlie the spring 32. When the central spigot 39 is positioned within the mechanism the semi-cylindrical shell portion 41 thereof is diametrically opposed to the semi-cylindrical shell portion 38 of the stub shaft locator 36. As shown most clearly in Fig. 2, there is a gap at each side of the mechanism between the two semi-cylindrical shell portions 38, 41, in which the tangs 34a, 34b of the spring 32 are positioned.The longitudinally extending ends of the spigot shell portion 41 are rounded to match the curvature of the spring tangs 34a,34b. The ends of the shell portion 38 are flat. As there is the capacity for movement of the semi-cylindrical shell portion 41 of the spigot 39 relative to the semicylindrical portion 38 of the stub shaft locator 36, relative rotational movement in one sense will cause one of the two tangs 34a or 34b to be grippe between the facing surfaces of the two semi-cylindrical shell portions and the other tang to be freed from engagement, and vice versa for relative rotational movement in the other sense.With this mechanism it is thus possible to apply tangential forces to the tangs of the spring 32 which cause the spring either to be held wrapped tightly onto the boss 30 of the spring locating member 28 or alternatively to expand the spring outwardly from the boss 30 to permit slip to occur between the spring and the boss 30, aided by the low-friction split bush 33.

In operation, in the manual mode, the drive takes place through the central spigot 36. In the automatic mode, the drive is effected by way of the main gearwheel 22, via the spring locating member 28 to which it is bolted. As this spring locating member 28 rotates it attempts to tighten the spring 32 onto the shaft, thus providing the drive.

In order to achieve manual override, by holding an associated steering wheel, the spring 32 will release the shaft, permitting drive through the central spigot.

Secured to the stub shaft locator 36 is a disc 42 which is rotatable with the stub shaft locator 36.

This disc is preferably a coded disc operating as a rotatable slave element and cooperating with sensors mounted on sensor plates 44 carried by the outer casing 10. The disc 42 is provided with for example three circular tracks from which one can determine the direction of rotation of the disc, the angle through which the disc has rotated, and the initial angular setting of the disc for example. The disc 42 may be of the type described in K patent application GB 21 89663A.

Figs. 3 and 4 illustrate how the clutch mechanism of Figs. 1 and 2 may be modified to provide what is essentially the inverse arrangement. Whereas in the embodiment shown in Figs. 1 and 2 the spring 32 is wrapped around a cylindrical sleeve, i.e. boss 30, in the modified arrangement shown in Figs. 3 and 4 the spring, here indicated at 50, is positioned within a surrounding cylindrical sleeve, here indicated at 52.

The clutch mechanism thus comprises a cylindrical parallel coiled spring 50 of several turns, left hand or right hand, with a free outside diameter which is normally greater than the inside diameter of the cylindrical sleeve or housing 52 which contains it.

When the spring 50 is located within the cylindrical sleeve 52 which is of smaller internal diameter than the outside diameter of the spring, the spring 50 is under a radial load, i.e. the spring 50 is reduced in diameter and is under radial tension.

The spring 50 is provided with a radially inwardly directed tang 54 at each end, only one of the tangs being shown in Figs. 3 and 4. When a tangential force is exerted against the tang 54 at one end of the sprIng in the direction indicated by the arrow a in Fig. 4, this causes the diameter of the spring to be reduced, thus reducing the frictional drag between the spring and the surrounding sleeve, with the result that the spring 50 will slip within the sleeve 52 and become free to rotate within the sleeve. Conversely, if the tangential force is applied to the tang at the same end in the direction indicated by the arrow b in Fig.4, the spring will be urged to expand and to increase its diameter, thus increasing the friction between the spring and the surrounding sleeve and providing a rotational drive to the sleeve 52.

When a tangential force is applied to the tang at the opposite end of the spring 50, in either circumferential direction, the same results will be achieved but in the opposite sense. The clutch mechanism is thus bi-directional.

To reduce problems of wear, the internal surface of the cylindrical sleeve or housing 52 which is in contact with the spring 50 is preferably lined with a suitable low-friction material, preferably a plastics material, in order to provide smoother operation.

The construction of the rest of the clutch mechanism associated with the spring 50 and sleeve 52 is similar to that shown in Figs. 1 and 2, except that the force-applying members, equivalent to the shell portions 38 and 41, will be located within the spring instead of around it. Although the clutch mechanism of the present invention is particularly suitable for use in an autopilot, it should be understood that it can be used elsewhere where one requires electrical drive with manual override.

Claims

CLAIMS:

1. A bi-directional clutch mechanism comprising a coiled spring having an outwardly projecting detent at each end thereof, a spring locating member on which the spring is coiled, and force-applying means radially outwardly of the spring and engageable with said detents in such manner as to be able to apply a substantially tangential force to either of the detents ; either circumferential direction, thereby to engage and disengage the drive between the spring and the spring locating member.

2. A bi-directional clutch mechanism comprising a coiled spring having an inwardly projecting detent at each end thereof, a spring locating member within which the spring is coiled, and force-applying means raaaily inwardly of the spring and engageable wit;n said etents in such manner as to be able to apply a substantially tangential force to either of the detents in either circumterential {direction thereby to engage and disengage the drive between the spring and the spring locating member.

3. A clutch mechanism as claimed in claim 1 or 2, in which the spring is a cylinarical, parallel-tarn coil spring.

4. A clutch mechanism as claimed in any preceding claim, in which the force-applying means comprises a pair of diametrically opposea, relatively rotatable, substantially semi-cylindrical sleeves of equal radius having a circumferential length such as to be able to provide a pair of diametrically opposed gaps therebetween in which the spring detents are located.

5. A clutch mechanism as claimed in claim 4, in which one of said substantially semi-cylindrical sleeves is mounted for rotation with an output shaft, and the other of said substantially semi-cylindrical sleeves is arranged to be rotatable from an input to the clutch mechanism.

6. A clutch mechanism as claimed in any preceding claim, which includes driving gearwheel means connected for joint rotation with the spring locating member, and motor means arranged to drive said gearwheel means.

7. A clutch mechanism as claimed in any preceding claim, which includes a rotatable output shaft, a slave element rotatable with the output shaft, and sensor means positioned to detect and determine rotation of the slave element.

8. A clutch mechanism as claimed in claim 7, in which the slave element is a disc provided with three coded circular tracks, and in which the sensor means is adapted to sense the coding and to provide an output indicative of the direction of rotation of the disc, the angle through which the disc has rotated and the initial angular setting of the disc.

9. A bi-directional clutch mechanism substantially as hereinbefore described with reference to the accompanying drawings.

10. An autopilot comprising a bi-directional clutch mechanism as claimed in any preceding claim.