GB2076088A - Rotary drive mechanism - Google Patents

Abstract

A rotary drive mechanism comprises an input drive pinion 20 for driving an output spindle 12 through the agency of a coupling which prevents the pinion 20 being driven from the output spindle 12. The coupling comprises a detent arrangement 46 which is operable to prevent rotation of the input pinion 20 except when rotational drive is imparted via the pinion itself, in which case the detent 46 is released from a toothed disc of the pinion 20 by means of a cam disc 24 moving a follower 40 connected to the detent 46. The cam disc 24 is formed with a recess 48 into which a correspondingly shaped projection (not shown) of the toothed disc of the pinion is disposed with lost motion. Initial movement of the cam disc lifts the follower 40 when taking up the lost motion. <IMAGE>

Description

SPECIFICATION Drive mechanism This invention relates to a rotary drive mechanism of the kind in which the coupling between an input and an output of the mechanism allows drive transmission in one direction, i.e. from input to output, but resists drive transmission in the opposite direction, i.e. from output to input.

Drive mechanisms of this kind are especially useful in devices where the output is connected to an adjustable component whose position of adjustment is varied by means of the input and where the component may be subjected to loads which tend to drive the mechanism in reverse, i.e.

from output to input. The fact that the drive mechanism resists transmission of drive from output to input enables the mechanism to maintain the component in a selected position of adjustment when under load.

One common expedient for providing the resistance to reverse drive transmission is to employ some form of spring loading. This has the drawback that the spring resistance may be experienced at the input end especially where the input drive is effected by means of a user operable rotary knob or the like. In such arrangements, any attempt to reduce the spring resistance in order to reduce the effort needed at the input end inevitably reduces the resistance to reverse drive transmission.

The object of the present invention is to provide an improved drive mechanism of the kind first mentioned.

According to the present invention we provide a drive mechanism comprising an input member, an output member and a rotary drive train between said members'which allows the transmission of drive from the input member to the output member but resists transmission of drive in the opposite direction, characterised in that said drive train includes a rotary element and means engageable with said rotary element to resist rotation thereof, said means being automatically disabled or at least partially disabled in response to rotation of said input member whereby the resistance to rotation is at least substantially reduced.

According to a preferred feature of the invention, said drive train includes a second rotary element and means providing a lost motion coupling between said first and second rotary elements, the first element being connected to said input member through the agency of said second member whereby, with the rotationresisting means disabled, the first element can only rotate with the second element and hence the input member after said lost motion has been taken up by relative rotation between said first and second elements, the rotation-resisting means being movable to the disabled position by a control member cooperable with the second element during said relative rotation between the first and second elements.

The rotation-resisting means may comprise detent means in the form of for example a plurality of recesses provided in and spaced angularly about the axis of said first rotary element, a detent projection movable between recess-engaged and recess-disengaged positions and means biasing said projection towards the recess-engaged position. The second element is conveniently provided with a cam track extending about its axis of rotation and said control member is cooperable with the cam track and linked to said detent projection in such a way that, during said relative rotation between said elements, the control member displaces said projection into the disengaged position and, during continued rotation of said elements after the lost motion has been taken up, maintains said projection in the disengaged position as the recesses move past the projection.

In the preferred embodiment, said detent projection is provided adjacent one end of an arm which is mounted for pivotal movement in such a way that the detent projection bears against a peripheral portion of said first element provided with said recesses. The cam track preferably has a smoothly undulating profile including a number of crests ( with dies therebetween) whose angular spacing corresponds to said recesses, and the control member is conveniently in the form of a second pivotally movable arm provided with a follower projection which is urged against said cam track, the follower and the detent arms being coupled together in such a way that, as the follower projection rides up the cam track to a crest, the consequent deflection of the follower arm is translated into deflection of the detent arm to disengage the detent projection.

In the preferred embodiment, said detent and follower arms are in the form of flexural elements which are rigidly anchored adjacent one end thereof so as to be deflectable in a pivotal manner.

The inherent flexibility of said arms serves to spring bias the detent and follower projections into engagement with said recesses and the cam track respectively. In a particularly advantageous embodiment, the detent and follower arms are constituted by a common flexural element, the longitudinal halves of which are provided with said detent and follower projections respectively.

The lost motion means between the first and second elements may comprise a non-circular recess in one element and a non-circular boss or the like on the other element engaged in said noncircular recess, the configurations of the recess and boss being such that a limited degree of angular movement is permitted between said elements before the recess and boss make drive transmitting contact.

One example of the present invention is shown in the accompanying drawings to which reference is now made. In the drawings: Figure 1 is a side view of the drive mechanism; Figure 2 is a view of the mechanism seen from the opposite sides: and Figure 3 is a sectional view taken in the direction 1-1 in Figure 1.

The purpose of the mechanism is to rotatably drive a spindle 10 journalled for rotation about an axis 1 2 by a pair of spaced apart side plates 14, 1 6. The mechanism comprises a sector gear 1 8 rotatably fast with the spindle 10 and a pinion 20 which is mounted for rotation about an axis 22.

The pinion 20 is rotatable by means of a suitable drive input such as a user operable knob (not shown) connected to the pinion by means of a coupling arrangement which allows drive transmission from the input to the spindle 10 but resists drive transmission from the spindle 10 to the input.

In the illustrated embodiment, the one way coupling arrangement comprises a pair of members 24, 26 which are co-axial with the pinion 20. The member 24 is adapted for connection to the drive input, in this case a user operable knob which has a non-circular recess for reception of a complementary non-circular boss 28 on the member 24. The member 26 is shown as being formed integrally with the pinion 20. As will become apparent, a limited degree of relative angular movement between the members 24 and 26 is necessary and whilst various possibilities can be adopted to achieve this, in the illustrated embodiment the members 24, 26 have interengaging formations, e.g. recess 30 and boss 32, which are shaped so that the recess 30 can turn about the boss 32 through a limited angle before the member 24 begins to transmit drive to the member 26.

The member 24 has an undulating or sinuous periphery consisting of a number of uniformly spaced V-shaped formations 34 which may extend over the entire or part only of the periphery of member 24. A follower 36 is cooperable with the periphery of the member 24 and is in the form of a blade spring securely anchored at one end thereof to a stud 38 and formed with a lateral projection 40 adjacent its other end for engagement with member 24. It will be understood that as the member 24 rotates the follower 36 moves inwardly and outwardly relative the axis 22 as indicated by the solid and broken outlines in Figure 2.

The member 26 also has a profiled periphery which forms a number of uniformly spaced pockets 42, the pitch of which corresponds to that of the V-shaped formations 34. A detent 44 is cooperable with the profile of member 26 and comprises a lateral projection 46 for reception in the pockets 42, the shape of the projection 46 and the pockets 42 being such that the detent positively prevents rotation of the member 26 when its projection 46 is engaged in a pocket 42.

The detent 44 is in the form of a blade spring securely anchored at one end to the stud 38.

An abutment 48 is provided adjacent the stud 38 to form a fulcrum about which the follower 36 and the detent 44 can flex. The follower 36 and detent 44 are coupled together in such a way that the detent 44 is displaced outwardly with the follower 36 as the latter rides up each of the formations 34. In this way, the detent projection 46 is drawn out of the pocket 42 as indicated in broken outline in Figure 1 To this end, the follower and the detent may be constituted by the longitudinal halves of a single blade spring, one half being formed with the projection 40 and the other half being formed with the projection 46.

However, in some circumstances, it may be desirable for the detent and follower to have differing degrees of resilience and in this event (and other circumstances) it may be desirable for them to be separate but coupled together so that the projection 46 is held outwardly as the follower 36 rides over the crests of the formations 34.

From the foregoing, it will be seen that the drive mechanism provides substantial resistance to reverse drive transmission, i.e. from the spindle 10 to the rotary handle, the resistance being provided by engagement of the detent projection 46 in one of the pockets 42. When the angular position of the spindle is to be adjusted however via the input, the only resistance is that Drovided bv the spring 36 as the projection 38 rides up and down the cam track formed by the V-shaped formations 34.

During initial turning of the input knob, only the member 24 rotates because the member 26 is maintained stationary by the detent and by virtue of the lost motion between the members 24 and 26. By the time this lost motion has been taken up, the projection 38 will have reached the crest of the first formation 34 and consequentiy the detent 46 will have been disengaged from the first pocket 42. The member 26 is therefore free to rotate with the member 24 and the detent is held disabled during continued rotation either by engagement with the peripheral portions extending between adjacent pockets 42 or, when the detent is in registry with one of the pockets, by virtue of the fact that at that instant the follower 40 will be engaged with a crest of one of the formations 34 thereby holding the detent disabled.When rotation of the knob is discontinued, the detent is free to engage with the pocket 42 once again, if necessary after a small degree of rotation of the member 26 has taken place relative to the member 24.

The members 24 and 26 may be manufactured as plastics mouldings or die castings and, if desired, the pinion 20 may be integrally formed with the member 26, as shown. The characteristics of the mechanism may be readily varied by using members 24, 26 of differing sizes.

The drive mechanism disclosed above is capable of various applications involving adjustment of one component relative to another. One application is in a seat lumbar adjuster of the form disclosed in our prior patent application No. 7930378, the disclosure of which is incorporated herein by reference. Thus, for example, the spindle 10 of the drive mechanism may be connected to, or constitute the spindle 28 shown in the embodiment illustrated in the prior application. Various other applications of the drive mechanism are envisaged; for example, the drive mechanism may be used in a seat reclining hinge for adjusting the backrest hinge plate relative to the seat cushion plate.

Although, in the illustrated embodiment the rotation-resisting means is in the form of a detent other possibilites are envisaged. For example, the rotation-resisting means may comprise a springloaded member bearing against a rotary part of the drive train so that the resistance to rotation is dependent on the pressure with which the springloaded member bears against the rotary part. In this event, the pressure exerted by the springloaded member on the rotary part may either be removed entirely or reduced to some extend in respect to rotation of the input. This may be achieved for example by pulling the spring-loaded member at least partly away from the rotary part in a similar fashion to that employed in the illustrated embodiment. Because the initial rotation of the input is effective to take up lost motion and disable the rotation resisting means, the user does not experience the spring force exerted by the rotation-resisting means because it is disabled or at least partly disabled while the input member is being used to transmit drive through the drive train to the output.

Claims (13)

1. A drive mechanism comprising an input member, an output member and a rotary drive train between said members which allows the transmission of drive from the input member to the output member but resists transmission of drive in the opposite direction, characterised in that said drive train includes a rotary element and means engageable with said rotary element to resist rotation thereof, said means being automatically disabled or at least partially disabled in response to rotation of said input member whereby the resistance to rotation is at least substantially reduced.

2. A mechanism as claimed in Claim 1 in which said drive train includes a second rotary element and means providing a lost motion coupling between said first and second rotary elements, the first element being connected to said input member through the agency of said second member whereby, with the rotation-resisting means disabled, the first element can only rotate with the second element and hence the input member after said lost motion has been taken up by relative rotation between said first and second elements.

3. A mechanism as claimed in Claim 2 in which the rotation resisting means is movable to the disabled position by a control member cooperable with the second element during said relative rotation between the first and second elements.

4. A mechanism as claimed in any one of Claims 1 to 3 in which the rotation resisting means comprises detent means in the form of a plurality of recesses provided in and spaced angularly about the axis of said first rotary element, a detent projection movable between recess-engaged and recess-disengaged positions and means biasing said projection towards the recess-engaged position.

5. A mechanism as claimed in Claim 3 or Claim 4 when appendent to Claim 3 in which the second element is provided with a cam track extending about its axis of rotation and said control member is cooperable with the cam track linked to said detent projection in such a way that, during said relative rotation between said elements, the control member displaces said projection into the disengaged position and, during continued rotation of said elements after the lost motion has been taken up, maintains said projection in the disengaged position as the recesses move past the projection.

6. A mechanism as claimed in Claim 5 in which the cam track has a smoothly undulating profile including a number of crests whose angular spacing corresponds to said recesses.

7. A mechanism as claimed in any one of Claims 4 to 6 in which said detent projection is provided adjacent one end of an arm which is mounted for pivotal movement in such a way that the detent projection bears against a peripheral portion of said first element provided with said recesses.

8. A mechanism as claimed in Claim 5, 6 or 7 in which the control member is in the form of a second pivotally movable arm provided with a follower projection which is urged against said cam track, the follower and the detent arms being coupled together in such a way that, as the follower projection rides up the came track to a crest, the consequent deflection of the follower arm is translated into deflection of the detent arm to disengage the detent projection.

9. A mechanism as claimed in Claim 8 in which said detent and follower arms are in the form of flexural elements which are rigidly anchored adjacent one end thereof so as to be deflectable in a pivotal manner.

10. A mechanism as claimed in Claim 9 in which the detent and follower arms are constituted by a common flexural element, the longitudinal halves of which are provided with said detent and follower projections respectively.

11. A mechanism as claimed in Claim 2 or any one of Claims 3 to 10 when appendent to Claim 2 in which the lost motion means between the first and second elements comprises a non-circular recess in one element and a non-circular boss or the like on the other element engaged in said noncircular recess, the configurations of the recess and boss being such that a limited degree of angular movement is permitted between said elements before the recess and boss make drive transmitting contact.

12. A drive mechnism substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.

13. A hinge structure comprising first and second parts hingedly connected to each other and incorporating a drive mechanism as claimed in any one of Claims 1 to 12 for effecting hinging of one part relative to the other.