Fluid pressure actuators

Abstract

 A fluid pressure actuator has a cylinder (2) comprising a rectilinearly displaceable piston (10) that acts on a drive member (40) to rotate the drive member during a first, greater part of the stroke of the piston and then moves the drive member rectilinearly for the remaining part of the stroke. The rotation is generated by a spiral cam mechanism (26, 42). Further cam means (48, 52,48) restrain linear displacement of the drive member during the first part of the stroke but permit its rotation to a predetermined angular position and thereafter said further cam means restrain said rotation but permit said linear displacement by the piston. Cushioning means (70, 84) are provided whereby the end of the rotational movement preceding the linear movement are cushioned, but not the linear movement.

Description

[0001] This invention relates to fluid pressure actuators. It is particularly concerned, although not necessarily exclusively so, with such actuators for use in door operating mechanisms and with door operating mechanisms incorporating fluid pressure actuators.

[0002] For commercial road vehicles such as coaches and buses, a form of passenger access door that is being used increasingly is the plug door, which comprises a leaf door mounted on a mechanism that keeps the leaf generally parallel to the door frame. The mechanism also displaces the leaf transversly to the door frame to engage sealing means around the frame in the final stage of the closing movement and it is conveniently in the form of a pivoting linkage. To secure the door firmly in its closed position, locating elements mounted on the door leaf and frame are interengaged by a final small lifting movement of the door leaf when it reaches a closed sealing position, so that it is then held rigidly.

[0003] A fluid pressure actuator for a door-operating mechanism of this kind is shown in GB 2014231A. The actuator comprises a vertical fluid pressure cylinder, with a piston rod projecting upwards into a tubular rotary column on which pivot levers of the door leaf are fixed. The cylinder piston is held against rotation and on the upper end of its rod there is a helical driver that causes the column to rotate as the piston rises, thereby closing the door. A limit of rotation is reached when the door leaf closes against its frame and a remaining small movement of the piston lifts the column and the door leaf with it to engage the locating elements. This sequence of operations assumes that the cylinder pressure force for pivoting the door leaf closed will be considerably less than that required to lift it, and conversely that the closed door leaf will drop freely to disengage the locating elements while the opening torque is acting on it. There is a danger, however, that the proper sequence of events will be disturbed if these conditions should change, e.g. if due to obstruction of the door the resistance to the pivoting closing movement increases substantially, of if due to friction the door tends to stick in its raised position when it is to be opened.

[0004] According to one aspect of the present invention, there is provided an actuator having a pressure fluid cylinder comprising a chamber and a piston axially slidable therein, a drive member displaceable by the relative movement between the piston and chamber, means permitting rotational movement of the drive member but restraining axial movement thereof over the greater part of the stroke of the piston, and over the remaining part of the piston stroke, rotational movement of the drive member being restrained and axial movement being permitted.

[0005] According to another aspect of the invention, there is provided an actuator having a fluid pressure cylinder comprising a chamber and a piston axially slidable therein, the piston being connected to a drive member to rotate the drive member and to displace the member in the direction of its rotary axis, the connection between the piston and the drive member comprising first cam means for said rotation of the member and further cam means between the piston and the drive member comprising an element restraining said linear displacement during a part of the stroke of the piston relative to the chamber and until a predetermined position of relative rotation has been reached, and permitting said linear displacement during a remaining part of the piston stroke.

[0006] Said further cam means may comprise a circumferential guide concentric to the axis of rotation of the drive member with which a follower engages to permit only rotary movement between the follower and guide, and an axial guide projecting from the circumferential guide for co-operation with the follower when the follower has been brought into registration therewith by said rotary movement, the drive member being thereby freed to move axially with the piston while being constrained against rotary movement.

[0007] Conveniently, said axial guide provides a limiting stop for the linear movement of the drive member.

[0008] The first and further cam means may conveniently comprise guides, in particular slots, in the drive member. In a preferred arrangement both said cam means are disposed axially beyond the pressure cylinder.

[0009] An embodiment of the invention that will be described by way of example with reference to the accompanying drawings, in which:

Fig. 1 is an axial section of an actuator according to the invention,

Fig. 2 is a side view of the actuator in the direction II,

Fig. 3 is a side view of the drive tube of the actuator, and

Fig. 4 is a transverse sectional view illustrating the porting to the lower end of the pressure cylinder of the actuator.

[0010] The actuator comprises a fluid pressure cylinder 2 comprising an enclosed chamber formed by a tubular body 4 clamped between upper and lower end plates 6, 8 respectively, and a piston 10 which includes a head 12 closely fitting the inner wall of the body 4 and a piston rod 14 projecting through a sealed bore 16 in the upper end plate 6. An outer tube 18 clamped between the upper end plate and a top plate 20, coaxial with the cylinder 2, is held fixed by a dowel 22. The clamping force between the top end plate 20 and the lower end plate 8 for the outer tube 18 and the cylinder body 4 is obtained by screwed tie rods 24 that extend between the top end plate and the lower end plate. An outer cover 25 is also held between the end plates 6, 20 to enclose the outer tube.

[0011] The projecting end of the piston rod carries a cross-pin 26 with inner and outer pairs of bushes 28, 30 respectively disposed symmetrically on it. The outer tube 18 has a pair of diametrically opposed axial slots 32 along most of its length in which the outer pair of bushes 30 are slidably engaged, and the piston 10 is thereby prevented from rotating.

[0012] A drive tube 40 is disposed concentrically within the outer tube and has a pair of diametrically opposed helical slots 42 slidably engaged by the inner pair of bushes 28. The tube is rotatably supported on its lower ends on a thrust bearing 44 and it projects through a bush 46 in the top plate 20 to be supported laterally thereby. In the position shown in Figure 1, a circumferential recess 48 in the tube is disposed in the bore in direct registration with a pair of diametrically opposed passages 50 in the top plate in each of which a ball 52 retained by a plug 54 projects into the recess. Axial movement of the drive tube is thus prevented although the balls 52 allow it to rotate on its axis.

[0013] Porting 60, 62 is provided in the upper and lower end plates for the supply of compressed air to the cylinder 2 on one side or the other of the piston, so reciprocating it in the cylinder. During this movement, the slots 32 in the outer tube 18 holding the cross-pin 26 prevent rotation of the piston. At the same time, while restrained by the balls 52 in its recess 48 the drive tube cannot move axially. The axial movement of the piston therefore results in a rotary movement of the drive tube through the engagement of the cross-pin 26 in the helical slots 42. The axial movement of the piston from its bottom position shown in Fig. 1 to near the top of its stroke this rotates the drive tube through the angular extent of the slots 42, in this case 155⁰.

[0014] At two diametrically opposite positions in the circumferential recess 48 there are axially downward extensions 58 of the recess and the drive tube is so disposed that these come into registration with the balls 52 as the rising cross-pin comes to the top of the helical slots.

[0015] In the remaining upwards movement of the piston to its full stroke the drive tube is raised bodily with it, the recess extensions.engaging the balls and thereby permitting this vertical movement while preventing any further rotary movement of the drive tube.

[0016] When the movement of the piston is reversed, the recess extensions 58 still prevent rotary movement so that initially the drive tube is lowered axially with the piston until the balls 52 are once more in alignment with the circumferential recess 48. Only at this stage is the drive tube freed rotationally to enable the cross-pin to run down its helical slots and so rotate the drive tube. Immediately the recess extensions move out of alignment with the balls, vertical movement of the drive tube is again prevented. The sequence of rotary and linear displacements is thus always maintained while the piston itself performs a single linear stroke between its end limits.

[0017] As mentioned above, the actuator is intended to be used to drive a plug door operating mechanism (not illustrated). The mechanism maintains the door leaf generally parallel to the door frame while the leaf is displaced to and from its closed position, the displacement during the first stage of the opening movement and the final stage of the closing movement being transverse to the door opening, to and from the closed position in which the door leaf engages sealing means around the door frame and lies substantially flush with the side of the vehicle. The rotary drive provided by the actuator generates such a movement in a known manner through a parallel linkage, the drive conveniently being transmitted through a pivot shaft (not shown) disposed at one side of the door frame with its axis substantially vertical and parallel to an adjacent side edge of the door. To connect with the shaft, the drive tube 40 has at its upper end a pair of dogs 64 with which a complementary lower end connection (not shown) of the door pivot shaft engages. The pivot shaft extends over at least a substantial part of the height of the door and has a number of corresponding links fixed to it so as to distribute the forces from the driving torque more evenly on the door leaf.

[0018] In use in such an arrangement, the illustrated position of the actuator in Fig. 1 represents the open position of the door and to close the door the actuator is operated by admitting pressure air through the bottom connection below the piston and venting the space above it. The closed position of the door is reached substantially as the cross-pin 26 reaches the upper end of the slots 42 in the drive tube. The pressure cylinder piston has still to complete its stroke, and as already described, the drive tube then cannot rotate and is only free to move upwards. In this final vertical movement it is lifted through a distance of about 10mm, and anti-rattle locators (not shown) are engaged between the door frame and the door leaf. Such locators preferably take the form of male and female wedge members on the door leaf and its frame respectively, the apex line of the door frame member being in a plane parallel to the door opening and being inclined upwardly towards the door leaf, the members on the door leaf having a complementary form.

[0019] There may be a number of such locators at both sides of the door to hold the door leaf firmly against any movement when it is closed and the vehicle is travelling.

[0020] When the door is to be opened or closed, it is desirable to prevent too violent a movement, especially in the initial opening movement when the weight of the door leaf acts to accelerate the movement and also in the final stages of the closing movement when there is a risk of hitting anyone entering or leaving.

[0021] The actuator is therefore provided with means for cushioning the movement at the end of the piston stroke, comprising respective seals 70, 72 in the upper and lower plates 6, 8. In the descending movement of the piston, a larger diameter portion 74 on the end of the piston rod 14 engages the seal 72 as the piston nears the end of its stroke. This seals off the space 76 through which a main passage 78 from the port 62 communicates with the cylinder. In the remaining movement of the piston, the fluid in the main cylinder space below the piston end can only escape through a bleed orifice 80.

[0022] The port 60 in the upper plate is connected to the interior of the cylinder in a manner similar to the port 62, and its bleed orifice 82 is also shown in Fig. 1. When the piston rises, a sealing sleeve 84 on the piston rod has a larger diameter portion spaced above the piston head which engages with the seal 70 to close off the main passage from the port 60 to the main cylinder space above the piston head, so that the fluid in that space can only escape through the bleed orifice 82. In this case, however, the larger diameter portion of the sleeve 84 passes through the seal 70 before the piston has reached its top limit position, so that in the last part of the piston movement, fluid can escape freely from the space above the piston head and the cushioning back-pressure is thus removed. It is arranged that, during the rise of the piston, the cushioning has effect on the final pivoting closing movement of the door leaf. The release of the cushioning back-pressure coincides with the lifting of the door leaf after its pivoting movement has been completed, so that the full pressure force of the actuator is applied to lock the door leaf in its anti-rattle locators as soon as the door has closed.

[0023] The seals 70, 72 are each formed with a thin- walled annular lip inclined towards the piston head. When the piston head moves away from either end position, therefore, the pressure fluid admitted behind the adjacent seal 70 or 72 can easily deform the inclined lip so that from the start of the movement away from the end position the presure fluid acts on the main area of the piston head and the acceleration of the piston is not limited by the rate of flow through the adjacent bleed valve.

[0024] It is also possible to utilise the rise and fall movement at the end of the actuator stroke to operate microswitches or other sensing devices, whether to indicate the door position or to initiate other activities. Thus, there is shown a spool valve 88 fixed to a bracket 90 for engagement with the door and positioned so as to be switched when the lifting movement of the door leaf has been completed, to actuate door locks.

[0025] It will be understood that the actuator and the other features of the door operating mechanism described above can be modified in many ways within the scope of the invention, and that the actuator can itself be employed for other operating mechanisms.

Claims

1. An actuator having a pressure fluid cylinder (2) comprising a chamber in which a piston (10) is axially slidable, a drive member (40) displaceable by the relative movement between the piston and the chamber, characterised in that means (48, 52, 58) are provided permitting rotational movement of the drive member but restraining axial movement thereof over the greater part of the stroke of the piston, and over the remaining part of the stroke of the piston rotational movement of the drive member being restrained and axial movement being permitted.

2. An actuator having a pressure fluid cylinder (2) comprising a chamber in which a piston (10) is axially slidable, the piston being connected to a drive member (40) to rotate the drive member and also to displace the member linearly in the direction of its rotary axis, characterised in that the connection between the piston and the drive member comprises first cam means (26, 42) for said rotation of the member by the piston, and further cam means (48, 52, 58) between the piston and the drive member restraining said linear displacement during a part'of the stroke of the piston relative to the chamber and until a predetermined position of relative rotation has been reached, and permitting said linear displacement during a remaining part of the piston stroke.

3. An actuator according to claim 2 wherein said further cam means comprises a circumferential guide (48) concentric to the axis of rotation of the drive member with which a follower (52) engages to permit only rotary movement between the follower and the guide.

4. An actuator according to claim 3 wherein an axial guide (58) projects from the circumferential guide for co-operation with the follower (52) when the follower has been brought into registration therewith by said rotary movement, the drive member (40) being thereby freed to move axially with the piston while being constrained against rotary movement.

5. An actuator according to claim 4 wherein said axial guide provides a limiting stop for the linear displacement of the drive member.

6. An actuator according to any one of claims 2 to 5 wherein the first and/or the further cam means comprise guides, such as slots (42, 48, 58), in the drive member.

7. An actuator according to any one of claims 2 to 6 wherein said cam means (26, 42 and 48, 52, 58) are disposed axially beyond the fluid cylinder (2).

8. An actuator according to any one of the preceding claims wherein cushioning means (70, 82, 84) are provided for the piston operable to retard the piston movement during rotational movement of the drive member immediately preceding said axial movement but being rendered inoperative when the piston enters the remaining part of its stroke causing said axial movement.

9. An actuator according to claim 8 wherein the cushioning means comprise a seal member (70) surrounding rod (14) of the piston and a sealing sleeve (84) forming an annular protuberance on the piston rod at a spacing from head (12) of the piston, said protuberance cooperating with the seal member to seal off a main fluid conduit from the space above the piston head whereby to produce a cushioning effect, and the protuberance passing beyond the seal member in a final part of the piston stroke whereby the fluid path through said main conduit is restored and the cushioning effect removed.

10. A plug door and frame having an actuator according to any one of the preceding claims, wherein the rotational movement of the drive member opens and closes the door and the axial movement of the drive member engages and disengages anti-rattle locators while the door is in its closed position, each said locator comprising male and female wedge members on the door and its frame respectively, the wedge of the door frame member having an apex line in a plane parallel to the door opening and said line being inclined upwardly towards the door and the wedge of the door member having a complementary form.

Drawing