GB2125897A

GB2125897A - Pneumatic door closing apparatus

Info

Publication number: GB2125897A
Application number: GB8317259A
Authority: GB
Inventors: John Lewis Hall
Original assignee: PETERS PLC Ltd; PLC PETERS Ltd
Current assignee: PETERS PLC Ltd; PLC PETERS Ltd
Priority date: 1982-06-24
Filing date: 1983-06-24
Publication date: 1984-03-14
Also published as: GB8317259D0

Abstract

A double-acting piston-cylinder arrangement for actuating the door has an effective area on one side of the piston (15) at least three times greater than the effective area (20) on the other side. For opening of the door, pneumatic control valve (22) connects a pressure source (21) to both sides of the piston, whilst for closure and holding of the door, the pressure source (21) is connected to the said other side-of the piston. Rapid opening with a more gentle closing action is thereby provided. Preferably the smaller-area piston chamber is choked (25) during opening, the chamber acting as an air spring for gradual deceleration of the door. <IMAGE>

Description

SPECIFICATION Pneumatic door The present invention relates to pneumatically operated door arrangements and actuators therefor. It is of particular use in the case of railway carriage vestibule doors, although having many other applications.

In one form of known arrangement of this type operation of the door is effected by a doubleacting pneumatic piston-cylinder unit, in which air under pressure is supplied to one side of the piston (the other side being vented to exhaust) to open or close the door. In the closed position, no air pressure is applied, the door being held in position by other means such as a magnetic latch.

Such arrangements require relatively complex control systems. The opening force must be relatively large for rapid opening, and the (equal) closing force needs the provision of safety switches to avoid injury to persons passing through the doorway. The door can also be difficult to open manually if pressure is maintained in the event of a fault. A three position control valve is required to switch between the three states, requiring, in turn, limit switches to sense when the closed position is reached. Also the piston-cylinder unit requires internal cushioning valves to slow it down at the end of its stroke. Magnetic retaining latches can often be unreliable, which is particularly inconvenient in the case of a railway vehicle where failure to latch the door successfully in the closed position can result in the door running back and forth when the vehicle is negotiating curves.When control is by an electrical sensor such as a pressure sensitive foot-pad, the relatively violent application of pneumatic power requires electrical "debounce" circuitry to avoid "chatter" of the pneumatic system when intermittent electrical contact is made within the pad.

According to the present invention there is provided a pneumatic door actuator comprising a double acting piston cylinder arrangement with a ratio between the effective area on a first side of the piston and the effective area on the second side of at least three to one, and pneumatic control means having two states in the first of which a pressure source is connected to both sides of the piston for opening of the door and in the second of which the pressure source is connected to the second side of the piston and the first side is vented, for closure and holding of the door.

The area ratio may be higher e.g. 4:1, 6:1, 10:1 or even more.

Preferably, in the first state, the pressure source is connected to the second side of the piston via a choke which is bypassed when the control means is in its second state.

In a preferred arrangement, the piston of the unit has a head portion of a diameter to fit the bore of the cylinder and a hollow tubular skirt portion extending through sealing means at one end of the cylinder and an elongate connecting rod extends within the skirt portion and is resiliently or pivotably secured at one end to the head portion of the piston and secured at the other end to the door. One embodiment of the invention will now be described by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective drawing of a sliding door arrangement; and Figure 2 shows in more detail the actuator of the arrangement of Figure 1 with its associated pneumatic and electrical control system.

Referring to Figure 1, a single-leaf sliding door arrangement comprises a door leaf 1, mounted by wheels 2 running on a rail 3 forming part of an extruded support member 4: double-leaf arrangements are, of course equally possible. The door is intended as a vestibule door for a railway carriage and is automatically operable from its normal, closed position to its open position by a pressure sensitive foot pad 5 which operates a pneumatic actuator, piston-cylinder unit 6, to operate the door via a piston rod 7.

The actuator 6, along with its associated pneumatic circuit, is shown in more detail in Figure 2.

It comprises an elongate cylinder 10 with a closed end 11 having an air inlet 1 2 to the righthand chamber 13 of the unit. The cylinder 10 accommodates an elongate piston 1 4. The piston 14 has a head 15 of a diameter to suit the bore of the cylinder 10, which carries a seal 31. The head 1 5 is attached to a relatively long, hollow, thinwalled tubular section 1 6, of smaller diameter, which extends through the left-hand end 1 7 of the cylinder: seals 1 8 are provided at this point.A further pneumatic connection 1 9 is provided to the left-hand chamber of the unit The effective piston area acted upon by air pressure in the left-hand chamber (viz. the annular area 20) is appreciably (at least a factor of 3) less than that in the right-hand chamber (i.e. the bore area of the cylinder). For example, for a 40 mm bore, the hollow piston section might be 35 mm diameter.

The air supply, from a pressure source 21 is controlled by a two-position spool valve 22, operated by a solenoid 30 controlled by the foot pad switch 5. In its first (non-actuated) position, as shown, the valve 22 applies pressure from the air supply 21 via the connection 1 9 to the lefthand piston chamber: connection 1 2 is vented to atmosphere. By virtue of the smaller effective area of the left-hand side of the piston, a relatively small force is applied by the piston to move the door to, and hold it in, its closed position.

Typically, for a 40 kg door with 2 kgf friction, this force may be 3 kgf. This relatively small force is sufficient to close the door, although closure of the door is not rapid. The slow closure and low maximum closing force have the advantage that, in the event of a person obstructing the door, there is no danger of injury due either to the momentum of the door or to the closure force, so that obstacle detection can be dispensed with.

Moreover, in the event of tread mat failure, the door can be opened manually against the closing force:, for the figures given above, this would require a force of 5 kgf. The closing velocity may be limited by a choke 23 in the exhaust line. So that manual opening is not impeded, a one-way valve 24 connects the inlet 1 2 to atmosphere if pressure in the chamber 13 falls below atmospheric.

To open the door, the tread mat 5, or other operating system, produces an electrical signal to actuate the solenoid 30 and hence operate the spool valve 22 to its second position in which full air pressure is applied to the right-hand chamber.

The left-hand chamber is permanently connected to the compressed air supply. However, during opening the direct connection is disconnected, the chamber remaining connected to the air supply via a relatively small-orifice choke 25. The piston thus moves to the left, to open the door.

The initial pressure in the left-hand chamber is that of the supply, but because of the area difference, the restraining force exerted on the piston is substantially less than that supplied by the right-hand chamber, in this case one quarter, and hence a relatively large force (e.g. 9 kgf) is available to accelerate the door upon opening. Air from the left-hand chamber is displaced into the air supply through the choke 25, the chamber acting as an air spring, so that the initial fast movement is not restricted but an increasingly large restraining force is exerted as the air is compressed (owing to the pressure of the choke 25) so as to decelerate the door gradually towards the end of its opening movement. When the operating signal is released, the valve 22 reverts to its original position and air bleeds away from the right-hand chamber and the door closes again, after a short delay.

The relatively low closing force, and this "automatic" cushioning effect, obviate the requirement for cushioning valves within the cylinder, and for the "debounce" circuitry referred to above. Since the system has only two states (power open/low power close and hold) rather than three states (power open/power close/relax), a single two-position valve taking its signal directly from the floor mat can be employed, and limit switches to sense the closed position are not needed: separate magnetic/mechanical locking arrangements are also rendered unnecessary.

Referring again to Figure 2, a further feature of the arrangement shown is that the connecting rod 6 is of elongate form and extends through the hollow thin-walled section 1 6 of the piston where it is resiliently secured within the piston head by a rubber mounting 26. This arrangement is selfaligning in that it allows a degree of lateral movement at the door end of the piston rod to accomodate misalignment and vibration, without exerting excessive lateral forces on the piston skirt and, more particularly the seals 18, 31. Also, because the tubular part of the piston rod carries no door thrust forces it substantially eliminates buckling forces and the ensuing side loads on the piston and rod seals which normally occur when an actuator is extended. This reduces wear, and friction, facilitating manual operation.

Claims

1. A pneumatic door actuator comprising a double acting piston cylinder arrangement with a ratio between the effective area on a first side of the piston and the effective area on the second side of at least three to one, and pneumatic control means having two states in the first of which a pressure source is connected to both sides of the piston for opening of the door and in the second of which the pressure source is connected to the second side of the piston and the first side is vented, for closure and holding of the door.

2. An actuator according to claim 1 in which the area ratio is at least 4:1.

3. An actuator according to claim 1 in which the area ratio is at least 6:1.

4. An actuator according to claim 1 in which the area ratio is at least 1 0:1.

5. An actuator according to any of claims 1 to 4 in which, in the first state, the pressure source is connected to the second side of the piston via a choke which is bypassed when the control means is in its second state.

6. An actuator according to any one of the preceding claims in which the piston of the unit has a head portion of a diameter to fit the bore of the cylinder and a hollow tubular skirt portion extending through sealing means at one end of the cylinder, and an elongate connecting rod extends within the skirt portion and is resiliently or pivotably secured at one end to the head portion of the piston and secured at the other end to the door.

7. A pneumatic door actuator substantially as herein described with reference to the accompanying drawings.