Pressure operated door actuator

Abstract

 A pneumatic door actuator in which an actuator rod (5) is driven by a piston (1) working within a cylinder (2), opposite ends (3, 4) of which are selectively pressurised and vented to provide motive effort for the piston (1). If a a closing door is temporarily obstructed the pressure in the vented end (3) of the cylinder (2) may drop sufficiently to cause the door to be slammed shut when the obstruction is removed. The appropriate cylinder end (3) is thus vented through a valve (14) which is unseated when the difference between the pressure remaining in the cylinder and the exhaust port vent (11) exceeds a predetermined level. When this pressure difference falls the valve (14) closes trapping the remaining pressure so that it acts as a cushion when piston movement is resumed.

Description

[0001] The invention relates to a pressure operated door actuator.

[0002] Pneumatic and hydraulic pressure operated actuators are used extensively to open and close vehicle doors. Pressures on opposite sides of a actuator piston are varied by means of control valves to move the piston which is connected to a door mechanism. Due to the interplay of pressures caused by these control valves in known actuator arrangements if a door is obstructed during a closing movement and excessive pressure drop - occurs on one side of the piston there is an inherent tendency for the door to slam when the obstruction is removed.

[0003] The object of the present invention is to provide an arrangement which obviates this tendency for a pressure operated door actuator to slam shut a door following release from a temporary obstruction.

[0004] According to the present invention there is provided a pressure operated door actuator comprising a piston and cylinder arrangement in which piston movement is determined by pressure difference between opposite ends of the cylinder, valve means leading from a port to one end of the cylinder to admit pressure for a door opening stroke and to exhaust pressure for a door closing stroke and, means for halting exhaustion of pressure in the event of piston movement ceasing due to obstruction of a closing door.

[0005] Preferably the means for halting exhaustion of pressure comprises means for reseating the valve means, and in one embodiment there is provided valve lifting means responsive to excess cylinder pressure over port pressure to unseat said valve means during the exhaust stroke and to reseat the valve means if said excess falls below a predetermined value. The value of said excess pressure may be determined by a spring.

[0006] The invention and how it may be carried into effect will now be described, by way of example only, by reference to the embodiment illustrated accompanied in the accompanying drawings in which:

Fig. 1 shows a sectional view of a pneumatic door actuator, and

Fig. 2 shows a sectional view of an anti-slam mechanism for actuator of Fig. 1.

[0007] Referring now to Fig. 1 the pneumatic door actuator comprises a piston 1 reciprocally slidable in a cylinder 2. Either end of the cylinder is closed by an end cap 3 and 4 which includes ports for admitting or exhausting pressure from the respective end of the cylinder 2. The motion of the piston 1 is transmitted to the door (not shown) by means of a piston rod 5 which extends through and is slidably mounted within the end cap 4. In Fig. 1 the piston 1 is shown in the door closed position; to open the door pressure is admitted to the left hand end of cylinder 2 through valve means in end cap 3 while the right hand end of the cylinder 2 is vented through the valve means in end cap 4. The piston 1 therefore travels towards the right carrying with it piston rod 5. The door is closed by an opposite sequence of events in which the left hand end of the cylinder is vented through the valve in end cap 3 and pressure is admitted to the right hand end of the cylinder 2 through the valve means and end cap 4 thus, causing the piston 1 to now move leftwards, in the drawing, again carrying with it piston rod 5.

[0008] In a conventional door actuator should the door, which is connected to piston rod 5, be obstructed in its motion the piston 1 will be temporarily halted in its travel along the cylinder but, the left hand end of the cylinder will remain vented and thus subject to continuing decrease in pressure, whilst the right hand end of the cylinder will remain connected to a source of actuator pressure. The result will be a greater than usual pressure difference between opposite sides of piston 1 so that when the obstruction is removed from the door piston 1 will accelerate to a greater than normal closing speed tending to slam shut the door.

[0009] The anti-slam mechanism of Fig. 2 is housed within the end cap 3 at the,left hand end of cylinder 2 in Fig. 1. The arrangement comprises a pressure inlet/exhaust port 10 connected via a passageway 11 to a chamber 12 which is closed at one end by a piston 13 and at its other by a ball valve generally indicated by reference 14. The valve means 14 communicates via a further chamber 15 and a duct 16 to the left hand end of the cylinder 2 through a port 17 drilled in the face of end cap 3.

[0010] The ball valve 14 comprises a ball valve member 20 which is urged against a valve seat 21 by a bias spring 22. The piston 13 has a limited degree of axial movement within the chamber 12 and is normally biassed towards the right by a further spring 23. The piston carries a leftward extending probe 24 which acts as a valve lifting means to unseat the ball valve member 20 of ball valve 14 when piston 13 is towards the left hand end of its movement. The right hand end of piston 13 also carries a member 25 which extends through end cap 3 for a short distance into cylinder 2 for abutment by a further probe 26 carried on the piston 1.

[0011] In operation of the illustrated door actuator to open the door compressed air is admitted through inlet/exhaust port 10 to chamber 12 and, as pressure acts on the valve member 20 of ball valve 14 it is lifted against the bias spring 22 to-allow compressed into chamber 15 and via duct 16 and port 17 into the left hand end of cylinder 2. At the same time the right hand end of cylinder 2 is vented via the valve means in end cap 4, therefore the piston 1 commences a rightward movement.

[0012] To close the door compressed air is admitted to the right hand end of cylinder 2 via the valve means in end cap 4 whilst the port 10 is vented. In this condition the chamber 12 is also vented but the valve member 20 of ball valve 14 is seated sealing off the chamber 15, duct 16 and left hand end of cylinder 2. The pressure retained in this end of cylinder 2 however, will exert a force on the piston 13 moving it against its spring 23 so that the probe 24 will mechanically lift the valve member 20 from its seat allowing venting from the cylinder to proceed. Providing that the pressure on the vented side of cylinder 2 does not fall to the pressure determined by the piston spring 23 then the ball valve 14 will remain open and the closing stroke will continue.

[0013] Should the door be obstructed and halted in its movement then piston 1 will also cease to move and pressure on the vented side of cylinder 2 will continue to fall until the spring 23 overcomes the pressure on the piston 13 moving it rightwards in chamber 12 to release ball valve member 20 permitting it to reseat. As a result pressure in the left hand end of cylinder 2 will be retained for as long as movement of piston 1 is prevented.

[0014] When the obstruction is removed and piston 1 resumes its leftward motion the consequent pressure increase now overcomes spring 23 and piston 13 re-opens ball valve 14 to resume exhaustion of pressure. The retained pressure in the cylinder acts to reduce the closing force on the door and, excess speed of the released door causes an increase in cylinder pressure at the vented end which, appearing as a back pressure valve assisting spring 23, tends to close the ball valve 14 until equilibrium has been restored. The actuator then continues operation as normal until all pressure is exhausted.

[0015] Towards the end of the door closing stroke the probe 24 of piston 13 will tend to permit valve member 20 to reseat before cylinder pressure is completely exhausted. Therefore, a probe 26 carried by piston 1 is arranged to abut extension member 25 of piston 13 towards the end of the stroke thereby mechanically holding ball valve 14 open to permit remaining pressure on that side of the piston 1 to leak away.

[0016] The embodiment illustrated is also provided with a damping valve 27 which is resiliently mounted on the piston 1 so that at an intermediate stage of the movement it comes to rest against the face of end cap 3 and closes port 17 leading to duct 16 by which route exhausting pressure escapes into chamber 15 leading to ball valve 14. To permit a continued but damped movement an alternative path of smaller cross-section is provided via an axial port 28 drilled in the extension 25 of the piston 13 into a section 29 of the chamber 12 formed by an annular recess 29 in the piston 13, a peripheral port 30 in the wall of section 28 and, through an adjustable cushioning valve 31 and a further duct 32 into the chamber 15. Thus, when the damping valve 27 closes off the main duct 16 air pressure continues to escape via this auxiliary route, thereby providing a damped, i.e. slowed, final phase of movement.

Claims

1. A pressure operated door actuator comprising a piston (1) and cylinder (2) arrangement in which piston movement is determined by pressure difference between opposite ends of the cylinder (2), valve means leading from a port (10) to one end of the cylinder (2) to admit pressure for a door opening stroke and to exhaust pressure for a door closing stroke and, means (14) for halting exhaustion of pressure in the event of piston movement ceasing due to obstruction of a closing door.

2. A door actuator according to Claim 1 wherein the means (14) for halting exhaustion of pressure comprises means (22) for reseating the valve means (14).

3. A door actuator according to Claim 1 or 2 including valve lifting means (13) responsive to excess cylinder pressure over port pressure to unseat said valve means (14) for the exhaust stroke and to reseat the valve means (14) if said excess falls below a predetermined valve.

4. A door actuator according to Claim 3 wherein the piston (1) interacts with the valve lifting means (13) in a final phase of an exhaust stroke to unseat said valve means (14). to complete exhaustion of cylinder pressure.

5. A door actuator according to Claim 3 or 4 wherein the valve lifting means (13) comprises a piston-like arrangement (13, 24, 28, 29) housed in . one end (3) of the cylinder.

6. A door actuator according to Claim 3, 3 or 5 wherein the level of excess pressure is determined by spring (23) force.

7. A door actuator according to any preceding claim wherein the valve lifting means (13) is operated by abutment (28) with the piston towards the end of a closing movement to completely exhaust the pressure.

Drawing