GB2184784A - Locking arrangement for an actuator - Google Patents

Abstract

A lock arrangement for capturing an axially movable member such as the output rod of a linear stroke actuator. The exemplary embodiment consists of a vehicle door actuator. The actuator output rod passes through a lock housing attached to an actuator mounting bracket. Within the housing the output member passes between a pair of pawls which are arranged to pivot in one direction only to allow a collar fixed to the member to pass between them in said one direction. The pawls engage the collar and capture the member preventing its return movement until released. The housing consists of two sections which can be separated slightly to allow the pawls to slide radially outwards and thereby to release the collar. The actuator cylinder is coupled to one of the housing sections and has a limited lost motion relative to the mounting bracket so that when the actuator is energised for release the lock housing sections are separated to free the pawls. <IMAGE>

Description

SPECIFICATION Locking Arrangement for an Actuator The invention concerns an automatic locking arrangement for an actuator, and is particularly concerned with a lock or latch for a linear stroke actuator.

Actuators of the linear stroke type are found, inter alia, in public transport vehicles to operate the doors. To prevent a door being opened, deliberately or otherwise, while the vehicle is in motion the doors are latched closed. It is well known to use a pin and hook type of latch for this function.

However, the space requirement for latches and associated operating linkages can be an embarrassement since space envelopes allocated for door operating equipments are frequently minimal. Further, wear of latch hook and pin may lead to a less than positive lock action, liable to release should manual or other shock loading be applied in the "opening" direction.

The present invention seeks to provide a compact and fully housed latch or lock arrangement for this type of actuator, integral with the actuator and which will in normal service automatically and positively latch the door upon closing so that it cannot be opened by hand but, yet, is automatically released when power is re-applied to the actuator to open the door. There is further provided a manual release for releasing the door in the event of power failure or emergency.

According to the present invention there is provided a locking arrangement for an axially movable member comprising first means carried by the member, second means located in the relatively fixed housing and which cooperates with the first means to form a positive mechanical lock, the second means comprising at least one pawl pivotally mounted in the housing to allow the first means and the member to pass in one direction, and to engage with the first means upon a small return movement to capture the member.

The invention will now be described, by way of example only, with reference to a particular embodiment illustrated in the accompanying drawings, in which: Fig. 1 shows a sectional view through part of a vehicle door actuator, Fig. 2 shows a perspective view of the latch pawls, and Fig. 3 shows a side view, partly cut away, of a section of actuator rod and its locking collar, fixed relative to and effectively part of the actuator rod.

Referring now to the drawings there is shown in Fig.

1 the piston rod or "head" end of a vehicle door actuator and its mounting brackets with a part view of the actuator "tail" end supported by a pin slideably mounted in a fixed bracket 21. A spring abutting the fixed bracket 21 urges the actuator, via pin mounting 20, to the right as drawn, so that the head end housing 7 firmly abuts the main mounting bracket. The actuator cylinder end cap is indicated at 1 and through this there emerges an actuator rod 2 which is connected to a sliding piston inside the actuator cylinder but not shown in the drawing. The valve and porting arrangements for pneumatic pressure to operate the actuator form no part of the present invention and are not depicted in the drawings.

The end cap 1 is attached to a mounting bracket 3 through an intermediate housing 4. Cap 1 is rigidly secured to the housing 4 and this is, in turn, attached to the bracket 3 by means of a lost motion arrangement comprising bolts 5 which pass through the brackets 3 into the housing 4 and have captive spacer bushes 6 trapped between counterbores in the face of the housing 4 and under the bolt heads 5a. The bushes 6 locate the housing to prevent rotation relative to the bracket 3, but permit the housing 4 to move a pre-determined distance "A" relative to the bracket 3, towards the left in the plane of the drawing.

The housing 4 comprises an outer housing 7, which is fixed to the cap 1 and attached to the bracket 3 by the lost motion mounting of bolts 5, and an inner concentric member 8 which acts as a latch pawl carrier. The member 8 is effectively an integral part of bracket 3 and comprises a cylindrical member formed with an annular shoulder 9 towards one end, leaving a short length of cylinder 10 protrudii ig to form a spigot which is pressed into an aperture formed in a flanged part of the bracket 3 till the shoulder 9 abuts the bracket.

Behind the shoulder 9 adjacent to its exposed face there are formed in the surface of the cylinder two diametrically opposed apertures which, viewed along a direction transverse to the axis of the cylinder, have the form of two quadrants of a circle.

Into each of these apertures is fitted a pawl 11, shown in more detail in Fig. 2. Each pawl consists of a central region 11 a flanked by two legs 11b and 11 c.

Each pawl 11 is fitted into one of the quadrant sectioned apertures with its central portion 11a resting in the aperture and the legs 11 b, 1 1c extending around the outside of the cylindrical member 8. The faces 11 d, remote from the observer as drawn, are flat and have partial countersinks 11 e similar to the partial countersinks 1 1f on the faces in view. Chamfered face 1 1g at its intersection with chordal flat 11 h on each pawl forms a fulcrum x-x about which each pawl may rotate, guided by the quadrantal recesses in member 8.

With the cylindrical member 8 in place in the outer housing 7 the pawls 11 are retained in position by control pins 12 located in crossbores in the outer housing. These pins 12 are formed in their central region with two stepped faces, one affording clearance with the shoulder 9, the other facing the chordal flat 11 h on the pawl 11 so as to prevent radially outward movement of the pawl. The "riser" face between the step faces has a very small clearance with the exposed face of shoulder 9.

The pawls 11 are thus constrained against the movement outwardly or to the right as drawn by the right angle formed by the face of shoulder 9 and the underside of pins 12 as shown in Fig. 1. In this position the pawls 11 are able to rock in one direction, towards the left in Fig. 1,so as to permit a member having a dimension slightly greater than the dimension of the aperture defined between the two pawl members to be admitted into the interior of the housing 4, but cannot move to permit the member to be withdrawn.

The pawls 11 are biased towards the position shown in Fig. 1 by a thrust ring 13 which is urged by a thrust spring 14to bear against the distal ends of fhe pawl legs Ilb and Ilc.

As previously mentioned the housing assembly 4 has a limited lost motion relative to bracket 3, as provided by spaces 6. The bolts 5 are carried by the outer housing 7, which is therefore able to move relative to bracket 3, while the inner member 8 is fixed relative to bracket 3 by its spigot 10. If the lost motion "A" is taken up, the outer housing 7 moves towards the left, in Fig. 1, and carries with it the control pins 12. As the pins 12 move away from the shoulder 9 on the inner member 8 a space is created immediately adjacent the shoulder 9 and above the pawls 11. If the piston rod then urges the conical face 15a of collar 15 against the countersunk lock faces of pawls 11 the collar tends to push the pawls radially outwards into the spaces appearing between the steps of pins 12 and the shoulder 9.The faces of pawl 11 are chamfered so that when the outer housing 7 returns towards the right the edges between the inner steps and the "risers" on pins 12 bear against angled faces of the pawls 11 to create a radially inward force which returns the pawls slidingly on the exposed face of shoulder 9 to their former position in the pawl carrier member 8.

The pawls 11 define between them an aperture having an inscribed circle the centre of which lies on the axis of actuator rod 2. The minimum dimension of this aperture is slightly greater than the diameter of the actuator rod 2 so that it will pass unimpeded between the pawls. The collar 15, shown partly sectioned in Fig. 3, is fitted to the actuator rod in a position such that as the actuator rod 2 reaches one end of its travel the collar 15 lies within the housing 7. It is arranged that this position corresponds to the closed position of a door connected to the actuator rod, when the collar 15 is marginally inwardly clear of pawls 11.

Just as the door reaches the closed position the conical face 15b of collar 15 abuts the pawls 11 which pivot, or rock, towards the left admitting the collar into the housing. The thrust ring 13 then returns the pawls to their former position so that the pawls will engage the collar 15 and act positively to latch the actuator rod 2 in that position.

When the pneumatic pressure is admitted to the actuator cylinder to drive the actuator rod towards the right of Fig. 1, and thereby to open a door, a reactive force is produced between the actuator end cap and the bracket 3. This reactive force has the effect of compressing spring 19, thus taking up the lost motion between housing 4 and bracket 3, as the housing 4 and end cap 1 temporarily move towards the left in the drawing. This movement provides the pawls 11 with an additional freedom of movement.

Under the action of collar 15 the pawls 11 move radially outwards relative to the housing thus releasing the collar 15 so that the actuator rod is freed to move towards the right.

However, without the reactive force between end cap 1 and bracket 3 the pawls remain positively engaged with the collar 15 in the event of any movement of the actuator rod towards the right in the drawing, thus the door remains shut. Therefore, the door can only be opened by the application of pneumatic pressure in the actuator cylinder under normal service conditions.

In the event of pneumatic power failure or other emergency it is necessary to be able to open the door or doors manually. This, because of the positively safe mechanical lock provided by the device described, is impossible without forcible destruction of the mechanism unless an alternative release means is provided. Further, should the emergency not involve pneumatic failure, air pressure maintained in the "closed" mode in normal service would also resist manual effort to open the door.

There is provided, therefore, a cam device operated by special key or other suitable means.

When actuated, a first portion of this device (not shown) operates valves and/or electrical switches (not shown) as appropriate to isolate a particular door set from the vehicle system and exhaust any residual air pressure from the actuator. A second portion of the device may for example only comprise a cam 17 (Fig. 1 ) cooperating with a tappet end carrier 20 attached to the actuator tail end.

Rotation of the cam (clockwise as drawn) urges the actuator to the left as drawn via pushrod 18 and pin carrier 19 so taking up lost motion "A" and releasing pawls 11 for manual opening of the door. The cam device is detented (not shown) to maintain any one of three positions, i.e. "normal service", "isolate" or "unlock".

Fig. 4 illustrates the reaction forces on one pawl. It will be seen that there is no turning moment on a pawl, any force applied to extend the piston rod being reacted directly by members 8 and thence the fixed main mounting bracket 3, the pawl being effectively wedged in the right angled space defined by the face of shoulder 9 and step surface of pin 12.

The provision of at least two pawls located diametrically opposite in member 8 ensures balance in the forces resisting extension of the piston rod.

Claims (14)

1. A positive mechanical locking arrangement for an axially movable member comprising first means carried by the member, second means located in a relatively fixed housing to cooperate with the first means to form the lock, the second means including a pawl pivotally mounted in the housing to allow the first means and the member to pass in one direction, and to engage with the first means upon a return movement to capture the member.

2. A locking arrangement as claimed in claim 1 including two pawls located on opposite sides of an aperture to receive the axially movable member, and both pawls engage the said first means carried by the member.

3. A locking arrangement as claimed in claim 1 or claim 2 wherein the housing comprises two parts relatively movable from a first relative position to a second position so as to provide an additional freedom of movement to the second means to release the lock elements and to permit said return movement of the axial member.

4. A locking arrangement as claimed in claim 3 wherein the two parts of a housing are biased towards the first position.

5. A locking arrangement for an axially movable member substantially as described with reference to the accompanying drawings.

Amendments to the Claims have been filed, and have the following effect: Claims 4 & 5 above have been deleted or textually amended.

New or textually amended claims have been filed as follows:

4. A locking arrangement as claimed in claim 3 wherein the additional freedom of movement of the second means is movement in a direction perpendicular to the direction of movement of the axially movable member.

5. A locking arrangement as claimed in claim 3 or claim 4 wherein the said freedom of movement is provided by a lost motion arrangement.

6. A locking arrangement as claimed in claim 5 wherein the said two parts of the lock housing are coupled together by the lost motion arrangement

7. A locking arrangement as claimed in claim 6 wherein the lost motion arrangement further includes bias means which urges the two parts of the housing towards the said first position.

8. An actuator having a axially movable output member including a locking arrangement as claimed in any preceding claim arranged to capture the output member whereby to lock the actuator.

9. An actuator as claimed in claim 8 wherein the locking arrangement is disposed to capture the actuator output member towards an extreme position of its movement.

10. An actuator as claimed in claim 9 wherein the first means carried by the axially movable member comprises a collar fixed to the said actuator output rod.

11. An actuator as claimed in any one of claims 8 to 10 including a locking arrangement in accordance with claim 3 to 7 wherein in the means for providing the lost motion the first part of the lock housing is fixed relative to an actuator mounting bracket and the second part of the housing is movable with respect to the bracket.

12. An actuator as claimed in claim 11 wherein the second part of the housing is carried by or is part of the actuator such that the lost motion movement is caused to be taken up by a reaction force generated by energisation of the actuator in the locked position.

13. A locking arrangement substantially as described with reference to the accompanying drawings.

14. An actuator including a locking arrangement substantially as described with reference to the accompanying drawings.