GB2066364A - Actuator - Google Patents

Abstract

A pressurised fluid linear or semi- rotary actuator 4c, 4d, 4e or 4f is provided with a free-floating piston P or vane which separates two distinct pressurised fluid supply lines opening into the actuator working chamber. In the piston and cylinder actuator shown, pressure in both the supply lines causes the free piston P to occupy a central position, but if one of the supply lines fails, the free piston P moves into contact either with the closed end of the cylinder or with the working piston 3, whereupon the actuator continues to function with a single source of pressurised fluid. The four actuators 4c, 4d, 4e, and 4f are disposed in opposed pairs to turn a tiller arm 2 of a ship's steering gear when a diametrically opposite pair is pressurised and the other diametrically opposite pair is allowed to exhaust. Separate hydraulic circuits connect two pumps 5a, 5b to respective opposite sides of the free piston P of each actuator. Braking systems employing actuators of the piston-and-cylinder type are also described. <IMAGE>

Description

SPECIFICATION Actuator This invention relates to an actuator and to a pressurised fluid system incorporating a plurality of such actuators, preferred examples of such systems being an hydraulic steering gear for a large ship, or an hydraulic vessel braking system.

In recent years there has been an increasing effort to improve the safety of vehicle braking systems, for example by the introduction of dual braking circuits, while the need for a more reliable hydraulic steering gear for large ships has been underlined by at least one disaster to a supertanker attributable to a failure of its steering and is recognised by Protocols and Regulations made under the International Convention for the Safety of Life at Sea, calling as recently as 1978 for improvements in the safety and performance of the hydraulic steering systems of tankers in excess of 10,000 tons displacement.

A principal object of the invention is to provide an actuator which, when incorporated in a pressurised fluid system, will provide an increased measure of safety and one which, moreover, may be incorporated in a ship's steering gear with the minimum of modification and using almost all of the conventional equipment so that adaptation of existing systems can be carried out with the minimum of expense as well as the provision of new systems.

In accordance with the invention there is provided a pressurised fluid actuator comprising a chamber and means defining opposite end walls of the chamber relatively movable in response to variation of fluid pressure in the chamber, wherein two supply lines for pressurised fluid open into the chamber in spaced relation between said end wall defining means and there extends across the chamber to be movable therein between said end wall defining means an element having a normal position intermediate and forming a barrier between said supply line openings, said barrier element being movable toward one of said end wall defining means to close one of the said supply line openings in response to a pressure difference across said barrier element caused by a reduction of pressure in said one supply line relative to the other.

In one embodiment of the invention the chamber is a cylinder, at least one of said end wall defining means comprising a working piston reciprocable in the cylinder in response to a variation of the total fluid pressure in the cylinder and said barrier element comprising a free piston reciprocable in the cylinder toward or away from said working piston in response to a pressure difference in the cylinder across said free piston. In this arrangement the other end wall defining means is either a closed end of the cylinder or a second working piston reciprocable in the cylinder.

In another embodiment of the invention the chamber is an arcuate chamber of a rotary actuator, and said end wall defining means are respectively a stator vane and a rotor vane of said actuator, said barrier element being a free vane interposed between said rotor and stator vanes.

The actuator may be included in an hydraulic vehicle braking system, or in an hydraulic steering gear system for a ship.

Each said pressurised fluid supply line is preferably in communication with a reservoir for hydraulic fluid adapted to provide the required supplement to the vaiume of fluid in the said other fluid supply line when said barrier element moves to close said one supply line, and means preferably is provided for maintaining hydraulic fluid in the reservoir under pressure.

A preferred hydraulic steering gear for a large ship comprises four actuators of the piston-andcylinder type disposed in opposed pairs to control a common tiller arm, and two pumps adapted selectively to supply pressurised fluid to actuators which are diametrically opposite across the rotary axis of the tiller arm while fluid is vented from the other two actuators, each pump being selectively connectable with one of said diametrically opposite pairs of actuators by a respective supply line opening to each cylinder on a respective side of the normal position of the free piston therein.

Preferred embodiments of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 illustrates a first embodiment of a ship's hydraulic steering gear, Figure 2 illustrates a second embodiment of a ship's hydraulic steering gear, Figure 3 illustrates an hydraulic braking system for a vehicle, and Figures 4 and 5 are views similar to Figure 3 of modified hydraulic braking systems for vehicles.

In the system illustrated in Figure 1, four hydraulic rams 4C, 4D, 4E and 4F rotate a rudder stock 1 to any desired position by moving a tiller arm 2 using a mechanism known as Rapsons slide or variations of this mechanism. The hydraulic power is supplied by two hydraulic pumps 5A and 5B usually known as Helleshaw or Janney pumps, which have variable rate of flow and direction of flow and are driven by electric motors. The direction and rate of oil flow is controlled by the position of a control rod 13 which is attached to the middle of a free-floating lever 12 known as a "hunting lever". One end of this lever is attached to a remote control piston 11 which is operated from the navigation bridge of the ship by remote control means (not shown). The other end of the lever 12 is attached through a link to a point on the radius of the rudder stock.

If the remote control lever 11 is moved to the right as viewed in Figure 1, this will result in the lever 12 pivoting about its lower end and cause movement of the pump control rod 13 to the right also. This will start oil flow from the cylinders of rams 4C and 4F and into the cylinders 4D and 4E and result in anti-clockwise rotation of the rudder.

This will cause the lower end of lever 12 attached to the rudder stock to move to the left. This movement results in lever 12 returning to its mid position and control rod 13 moves left until it reaches its original neutral position. Oil flow then ceases and rudder movement stops. It can thus be seen that the angle taken up by the rudder is directly dependent on the position and movement of remote control piston 11. In case of failure of the remote control system, a local hand steering system (not shown) may be connected up and used.

Other equipment in the system includes: a) Oil feed pumps 6A and 6B which are driven by the same electric motors driving the hydraulic pumps 5A and 5B and supply low pressure oil under constant pressure through non-return feed check valves 14 to both hydraulic systems thus ensuring that the oil is under a minimum pressure and topping up any oil lost from leakage, b) Automatic isolating valves 5A which function to shut off and isolate one hydraulic pump when not in use and prevent back flow or oil between a working pump and an idle pump, c) Manual isolating valves 8 serving to shut off two rams out of the four should this become necessary due to partial failure of the hydraulic or mechanical systems, d) Relief valves 7F which allow excess oil delivered from feed pumps 6 to flow back to an oil storage tank and keep the system under pressure, and e) Relief valves 7C which will allow exchange of oil between the cylinders in case of high abnormal pressure which may result from action of rough seas on the rudder or by collision of the rudder with an external object.

It may be seen that should such a movement occur, this will cause movement of the rudder stock 1 and the lower point of lever 12 will be displaced. This caused the rod 13 to be displaced resulting in oil flow which will restore the rudder to its former position.

When both hydraulic pumps 5A and 5B are in operation, the reate of oil flow as determined by the position of the pump control rods 1 3 is double that when only one of the pumps 5A or 5B is in operation. This results in a quicker movement of the rudder with two pumps in use and is normally the case when the ship is manoeuvring in close waters such as when entering or leaving harbours.

In the open sea quick rudder movements are not necessary and one pump is shut off.

The above is a description of the hydraulic steering gear as current in use. The weakness of the presently used system having only the features so far described lies in the fact that there is only one common hydraulic system and should major failure of this system occur - such as failure of a major hydraulic pipe coupiing the ship will be left without means of working the rudder which can be brought quickly into use.

In accordance with the present invention a free floating piston P is inserted in the cylinder of each hydraulic ram 4. The hydraulic circuit is altered so that two entirely separated supply systems are incorporated, one system connected to one of the hydraulic pumps 5A and the other to 5B. Pump 5B supplies the portion of each cylinder between the free floating pistons P and the cylinder end.

The hydraulic pump 5A and its entirely separate hydraulic system supplies the portion of each hydraulic cyclinder between P and the piston 3 in said cylinder.

When both pumps 5A and 5B are in operation each piston P occupies a middle position between the main piston 3 and the cylinder end. Operatiqn of the control piston 11 to the right will result in oil being pumped from cylinder 4C and 4F to 4D and 4E, the two circuits complementing each other to produce rapid movement of the rudder anti-clockwise, and movement of piston 11 to the left will have converse effect to rotate the rudder stock 1 clockwise.

If pump 5B is switched off with the rudder at midships, the solenoid operated valves SB will move downwards draining oil out of the spaces between the free floating pistons P and the cylinder ends. This will cause the pistons P to move towards the cylinder ends until they come into mechanical contact therewith. The drainage of oil is made through orifices 1 6 which are inserted to reduce the rate of oil flow and movement of piston P when one pump is shut off.

As the pistons P move towards the cylinder ends, the space between each main piston 3 and the associated piston P is increased and oil must be fed in sufficient quantity from the pump 6 through the feed valves 14. This sudden surge of oil flow will require a very large capacity of pump 6 and to reduce this hydraulic accumulators 1 5 are fitted.

These will be low pressure large capacity accumulators which will take care of sudden large demands for low pressure oil to be fed to the system.

Once the pistons P have reached the end positions where they are in contact with the cylinder ends they will stay in that position and operation of the steering gear will be by oil flow from pumps 5A to the portion of each hydraulic cylinder adjacent to the pistons 3 therein.

Conversely, if pump 5A is shut off the free floating pistons P come to rest against the main pistons 3 and operation of the main pistons 3 is by pump 5B filling the space between each cylinder end cover and the associated free piston P.

It may thus be seen that the system of Figure 1 has the following features distinguishing it from systems currently in use: 1) The hydraulic cylinders 4 are divided into two distinct and separate pressure chambers by the free floating pistons P.

2) With both hydraulic pumps 5A and 5B in operation the free floating pistons P will lie at a mid position between the main pistons 3 and the cylinder ends. Oil flow of both pumps from two cylinders to diametrically opposite cylinder will result in angular movement of the rudder. With two pumps on, the oil flows from and to the two pumps will complement each other producing rapid movement of the rudder.

3) Any one pump 5A or 5B may be shut off under open sea conditions. When this is done the free floating pistons will occupy a position against the cylinder ends or against the main pistons 3 depending on which pump is shut off. The speed of angular movement of the rudder is dependent on the rate of flow through one pump only and is half that when two pumps are in use.

4) The torque produced on the rudder is dependent only on the difference in hydraulic pressure between two opposite pairs of cylinders and is not altered or reduced by shutting off one pump.

5) Complete failure of any one pressurised hydraulic fluid supply lines will not reduce the available rudder torque in any way and the other separate system will continue to function.

A possible disadvantage of the system illustrated in Figure 1 lies in the fact that normal operation is temporarily disrupted during transient conditions when the two hydraulic pumps are being started, switched off or changed over.

Operational sequences that will occur on board ship to offset this disadvantage are described below together with descriptions of changes during transient conditions.

A) Leaving port - Start up both pumps 5A and 5B one after another. Work rudder hard over to port and then hard over to starboard. This will centre the free pistons P and operation will continue as above described.

B) On reaching the open sea after dropping the harbour pilot, with rudder amidships, switch off one pump, either 5A or 5B. No rudder movement should normally be made during the few seconds that it will take for the free pistons P to reach their end positions. Should a movement be necessary the differential pressure caused by hydraulic pump 5A or 5B will assist to move the free pistons P over faster but no rudder movement will result until the pistons P have reached their end positions.

C) On arrival at a port from the open sea, with initially one pump 5A or 5B in use, switch on the other pump and put the rudder hard over to each side port and starboard, after which the pistons P will attain their mid position and normal conditions will prevail.

If movement of the rudder is necessary after starting the second pump but before manoeuvring the rudder to centre the free pistons P the necessary excess oil will be obtained temporarily from the hydraulic accumulators 1 5 and pumps 6.

At sea with one pump in use, failure or stoppage of this pump will cause the other pump to start automatically.

D) To meet such a situation, the capacity of each hydraulic accumulator should be made equal to or slightly larger than the total displacement volume of two main pistons 3. A margin of safety in excess of this required capacity will be provided by the oil feed pumps 6.

If the main defect of the system lies in the temporary disruption of rudder movement which will occur during operation B when both pumps were initially running and one pump is switched off, and operation D when failure of one pump and start up of the other pump occur, it should be noted that of these operations B will not normally be a problem. Shut down of one pump after leaving a port may be done selectively under safe conditions with adequate sea room. Abnormal change over of pumps in operation D will occur in case of emergency and under such conditions unavoidable temporary disruption is considered allowable, such as when electric power failure occurs and emergency generators are started up.

Regardless of the above-mentioned defect the invention will result in less chance of complete failure of steering power in ships.

The above description relates to hydraulic ram operated steering gear for ships, but the invention may equally be applied to other types of hydraulic steering gear. Figure 2 shows the adoption of the same principle in a "vane" type hydraulic steering gear. Here the tiller arm 2 and pistons 3 in the ram type system of Figure 1 correspond to radial rotor arms 2 which are fixed to the rudder stock 1. The segments between the arms 2 and the fixed casing 3 serve as arcuate hydraulic chambers in the same way as the cylinders 4 of the ram type system. Instead of free pistons P free floating vanes VS are arranged to separate each of the hydraulic quadrant chambers into two compartments. The working principles of this system are the same as for the hydraulic ram piston type.

With two pumps running the free floating vanes VS will occupy a middle position between the rotor arms 2 and the edges of casing 3 serving as stators. With one pump shut off the vanes VS will occupy positions adjacent to the rotor arms 2 or to edges of casing 3.

The same principles may be applied to the brakes of a car or other vehicle.

Figure 3 shows the application of the same principle of having free floating pistons inside actuating cylinders and separating two separate hydraulic circuits or a car braking system.

The master brake cylinders 1 A and 1 B are actuated together by the driver's foot. The brake cylinders are shown as drum brakes C and D for the front wheels and the rear brakes are disc type E and F. Two types of brakes are selected by way of illustration to show that the system may be used for both disc and drum type brakes.

A free floating piston P is inserted in each brake actuating cylinder. The hydraulic master cylinder 1 A works one side of each actuating cylinder by applying hydraulic pressure and cylinder 1 B the other side of such actuating cylinder, both master cylinders working together and supplementing each other. The magnitude of the movement of the pistons of the brake actuating cylinders C, D, E and F depends entirely on the amount of depression of the driver's foot.

If there is a complete failure of the hydraulic circuit associated with master cylinder 1 A then the free piston P will travel towards one side of the actuating cylinders. Several movements of the master cylinder B will be required to completely fill the actuating cylinders after which they will continue to function by the action of the driver's foot on cylinder B only. When this occurs the free floating pistons P will move to one side of the actuating cylinders. The hydraulic fluid in cylinder B must be supplemented from the fluid reservoir tank 7B through feed valves 8. Several strokes of the brake may be required to drive the free floating pistons P to one side.

Alternatively, the fluid reservoirs 7B and 7A may be kept under pressure say from a power booster pump such as is used for supplementing the required force exerted from the foot of the driver. With such an arrangement, depression of the brake pedal a few strokes in case of failure of one brake hydraulic system will not be required.

Although only hydraulic systems have been described by way of example it will be apparent that the invention is equally applicable to a pneumatic actuator or system incorporating the same.

Claims (9)

1. A pressurised fluid actuator comprising a chamber and means defining opposite end walls of the chamber relatively movable in response to variations of fluid pressure in the chamber, wherein two supply lines for pressurised fluid open into the chamber in spaced relation between said end wall defining means and there extends across the chamber to be movable therein between said end wall defining means an element having a normal position intermediate and forming a barrier between said supply line openings, said barrier element being movable toward one of said end wall defining means to close one of said supply line openings in response to a pressure difference across said barrier element caused by a reduction of pressure in said one supply line relative to the other.

2. An actuator as claimed in claim 1, wherein the chamber is a cylinder, at least one of said end wall defining means comprises a working piston reciprocable in the cylinder in response to a variation of the total fluid pressure in the cylinder and said barrier element comprises a free piston reciprocable in the cylinder toward or away from said working piston in response to a pressure difference in the cylinder across said free piston.

3. An actuator as claimed in claim 2, wherein the other end wall defining means is a closed end of the cylinder.

4. An actuator as claimed in claim 2, wherein the other end wall defining means is a second working piston reciprocable in the cylinder.

5. An actuator as claimed in claim 1, wherein the chamber is an arcuate chamber of a rotary actuator, wherein said end wall defining means are respectively a stator vane and a rotor vane of said actuator and said barrier element is a free vane interposed between said rotor and stator vanes.

6. An actuator as claimed in any one of the preceding claims when included in an hydraulic vehicle braking system.

7. An actuator as claimed in any one of claims 1 to 5 when included in an hydraulic steering gear system for a ship.

8. A system as claimed in claim 6 or claim 7, wherein each pressurised fluid supply line is in communication with a reservoir for hydraulic fluid adapted to provide the required supplement to the volume of fluid in the said other fluid supply line when said barrier element moves to close said one supply line.

9. A pressurised fluid steering gear system for a ship substantially as herein described with reference to and as shown in Figure 1 or Figure 2 of the accompanying drawings.

9. A system as claimed in claim 8, wherein means is provided for maintaining hydraulic fluid in the reservoir under pressure.

10. A system as claimed in claim 7, or claim 8 or claim 9 when appendant to claim 7, and comprising four actuators, each as claimed in any one of claims 1 to 4, disposed in opposed pairs to control a common tiller arm, and two pumps adapted selectively to supply pressurised fluid to actuators which are diametrically opposite across the rotary axis of the tiller arm while fluid is vented from the other two actuators, each pump being selectively connectable with one of said diametrically opposite pairs of actuators by a respective supply line opening to each cylinder on a respective side of the normal position of the free piston therein.

11. A pressurised fluid actuator substantially as herein described with reference to and as shown in any one of Figures 1 to 5 of the accompanying drawings.

12. An hydraulic vehicle braking system substantially as herein described with reference to and as shown in Figure 3, Figure 4 or Figure 5 of the accompanying drawings.

13. An hydraulic steering gear system for a ship substantially as herein described with reference to and as shown in Figure 1 or Figure 2 of the accompanying drawings.

New claims or amendments to claims filed on 18th Aug. 80.

Superseded claims: 1 to 1 3.

New or amended claims:

1. A pressurised-fluid operated steering gear system for a ship, said system comprising four pressurised-fluid actuators disposed in opposed pairs to control a common tiller arm, and two pumps adapted selectively to supply pressurised fluid to actuators which are diametrically opposite across the rotary axis of the tiller arm while fluid is vented from the other two actuators, each said actuator comprising a chamber and means defining opposite end wails of the chamber relatively movable in response to variations of fluid pressure in the chamber, two supply lines for pressurised fluid opening into the chamber in spaced relation between said end wall defining means and respectively connected to the pumps and there being provided to extend across the chamber to be movable therein between said end wall defining means an element having a normal position intermediate and forming a barrier between said supply line openings, said barrier element being movable toward one of said end wall defining means to close one of said supply line openings in response to a pressure difference across said barrier element caused by a reduction of pressure in said one supply line relative to the other, each pump being selectively connectable with one of said diametrically opposite pairs of actuators by a respective pair of said supply lines opening to the associated chamber on a respective side of the normal position of said barrier element therein.

2. A steering gear system as claimed in claim 1, wherein each chamber is a cylinder, at least one of said end wall defining means comprises a working piston reciprocable in the cylinder in response to a variation of the total fluid pressure in the cylinder and said barrier element comprises a free piston reciprocable in the cylinder toward or away from said working piston in response to a pressure difference in the cylinder across said free piston.

3. A steering gear system as claimed in claim 2, wherein the other end wall defining means is a closed end of the cylinder.

4. A steering gear system as claimed in claim 2, wherein the other end wall defining means is a second working piston reciprocable in the cylinder.

5. A steering gear system as claimed in claim 1, wherein each chamber is an arcuate chamber of a rotary actuator, wherein said end wall defining means are respectively a stator vane and a rotor vane of said actuator and said barrier element is a free vane interposed between said rotor and stator vanes.

6. A steering gear system as claimed in any one of claims 1-5, wherein each pressurised fluid supply line is in communication with a reservoir for pressurised fluid adapted to provide the required supplement to the volume of fluid in the said other fluid supply line when said barrier element moves to close said one supply line.

7. A steering gear system as claimed in claim 6, wherein means is provided for maintaining fluid in the reservoir under pressure.

8. A steering gear system as claimed in any one of the preceding claims, wherein the pressurised fluid is hydraulic fluid.