GB2040246A - Steering apparatus - Google Patents

Abstract

A fluid actuated steering apparatus for a ship, comprising first and second fluid pumps (16, 17), associated first and second piston and cylinder assemblies (10, 11) for actuating a tiller (38) of the ship, means (40, 54, 55) for automatically isolating said first fluid pump (16) and first piston and cylinder assembly (10) from the second fluid pump (17) and second piston and cylinder assembly (11) in the event of fluid leakage and to deactivate or leave in a deactivated condition that one of the pumps (16, 17) corresponding to the isolated portion of the steering apparatus in which the fluid leak is located. The means can be a float valve 40 sensitive to fluid level in reservoirs 18, 19 and connected to actuate pilot valves 54, 54 respectively which can each operate one of isolating valves 30, 31. <IMAGE>

Description

SPECIFICATION Steering apparatus The invention relates to steering apparatus for use in ships and particularly concerns hydraulically actuated steering apparatus incorporating an automatic failsafe system.

Hydraulic steering apparatus for ships normally have duplicated pump units and either two or four double acting cylinders. Either one of the pump units is capable of fulfilling the required duty with the other as stand by. It is possible however to operate both pump units simultaneously to give rapid steering for example when manoeuvering in harbours.

Because of this latter requirement and the desirability of keeping the hydraulic pressure balanced between the working cylinders the pumps and cylinders are connected in parallel so that corresponding sides of both cylinders are always in hydraulic communication and both pumps can act together. Thus although there are two separate steering arrangements, each on its own capable of steering the ship, the two steering gears are not isolated from one another and if failure, for example as a result of fluid leakage, occurs in one it is likely to affect the other so that the whole steering apparatus becomes inoperative.

Usually valves are fitted to the steering apparatus as a whole to enable the portion of the steering apparatus in which the failure occurs to be isolated so that steering may be continued in the other half at reduced power.

This however involves the manual operation of several valves in the correct sequence after identifying the source of the failure and as some time may have elapsed before the ship's staff is aware of the failure, all the hydraulic fluid could be lost and the pumps seized through lack of lubrication, the ship's rudder being consequently out of control.

It is an aim of the present invention to provide steering apparatus, for use in a ship, which overcomes the aforementioned disadvantages.

With the above aim in mind the present invention provides a fluid actuated steering apparatus for a ship, comprising first and second fluid pumps, associated respective first and second piston and cylinder assemblies for actuating a rudder of the ship, means for detecting fluid leakage, and means for automatically isolating said first fluid pump and first piston and cylinder assembly from said second fluid pump and second piston and cylinder assembly in the event of fluid leakage and to deactivate, or leave in a deactivated condition, that one of said first and second pumps corresponding to the isolated portion of the steering apparatus in which the fluid leak is located.

Advantageously in the case where the piston and cylinder assemblies are double-acting, the means for automatically isolating the pump and piston and cylinder assemblies is also operative to open valves to establish fluid communication between both sides of the cylinder in the isolated portion of the steering apparatus in which the fluid leak is located. Preferably said means is also operative to activate or leave activated that one of said first and second pumps corresponding to the isolated portion of the steering gear in which the fluid leak is not located.

The invention will hereinafter be further described by way of example with reference to the accompanying drawings in which: Figure 1 is a schematic diagram showing a conventional ship's steering apparatus comprising two double-acting piston and cylinder assemblies.

Figure 2 is a schematic diagram showing a first embodiment of a ship's steering gear apparatus in accordance with the present invention: Figure 3 is a schematic diagram showing in detail the Float switch system of the steering apparatus of Figure 2; Figure 4 is a schematic drawing of a second embodiment of a ship's steering apparatus in accordance with the present invention and comprising four double-acting piston and cylinder arrangements; and Figure 5 is a diagram of an electric control circuit for the steering apparatus of Figure 4.

Referring firstly to Figure 1, the known steering apparatus comprises a symmetrical arrangement in halves. Each half has a respective one of double acting piston and cylinder arrangements 10 and 11, a respective one of hydraulic pumps 12 and 13 and a respective one of solenoid operated spool valves 14 and 15. Each pump is driven by a respective one of electric motors 16 and 17 to pump hydraulic fluid from a respective one of fluid reservoir 18 and 19. A fluid line 20 connects valve 14 to one side of the piston and cylinder assembly 10 and one side of the piston and cylinder assembly 11. A line 21 connects the other side of the assembly to valve 14. Corresponding lines 22 and 23 are provided. Each line is provided with a respective one of pressure relief valves 24, 25,26 and 27.Lines 21 and 22 are connected by a line 28 whilst lines 20 and 23 are connected by a line 29. Manually operable isolating valves 30 and 31 serve to close lines 28 and 29 bypass ports 32 and 33 are disposed on opposite sides of the valves 30 and 31, and connect lines 29 and 28. Normally valves 30 and 31 are open. If we assume that pump 12 is in operation whilst pump 13 is off then according to which of the two extreme positions spool valve 14 is placed in the tiller 38 will be pivoted clockwise or anticlockwise. It will be understood that the fluid delivered by pump 12 acts on both pistons and cylinder assemblies though in opposite directions. If a fluid leak should occur in lines 21 or 23 the fluid level in reservoir 18 will fall and may result in pump 12 seizing. If the fluid leakage is detected early enough then the valve 30 may be closed to isolate the halves of the system.If however the fluid leakage occurs above in lines 20 or 22 (as seen in Figure 1)then it will be necessaryto switch pump 12 off, switch pump 13 on and close valve 31 instead of valve 30. It will readily be appreciated that the danger of permanent damage occuring is very great following a leak in the hydraulic system, and that it is far from desirable to have to rely on human perception of a failure, and consequent manual remedial action being taken.

A hydraulically actuated steering apparatus in accordance with the present invention is illustrated in Figure 2 and incorporates means for automatically taking remedial action. Parts corresponding to the steering apparatus of Figure 1 are given the same reference numerals. In addition, fluid reservoirs 18-19 have a float 40 in a cylinder 41. Two Proximity switches 42 and 43 activated by a probe 44 on the piston rod 45 activate the solenoids of pivot spool valves 54 and 55 (Figure 2). When the oil level falls.

From Figure 3 it will be seen that spool valve 30 has two working positions and is controlled by solenoid operated pilot valve 55. Similarly spool valve 31 is controlled by solenoid operated pilot valve 54. The pilot pressure to energise valves 30 and 31 is supplied by pumps 12 or 13 through lines 56 and 57 respectively, maintained under pressure by relief valves 58 and 59.

To describe the operation of the steering apparatus of Figures 2 and 3 it will be assumed that pump 12 is operating and that pump 13 is off. Valves 30 and 31 are open. To pivot rod tiller 38 in an anticlockwise sense valve 14 is moved to the left so that fluid is supplied to appropriate (and opposite) sides of the cylinders of assemblies 10 and 11. To pivot the rod tiller 38 clockwise the spool of valve 14 is moved up as seen in Figure 2. Fluid displaced from those sides of the cylinder of the assemblies 10 and 11 in which the volume is decreasing is returned to reservoir 18 so that the fluid level in the reservoir remains constant unless there is a fluid leakage in the hydraulic circuit. If such a leakage occurs however, then the fluid level in reservoir 18 will begin to fall and proximity switch 42 will close and energise the solenoid of pilot valve 54.This valve will then connect line 56 to the servo piston of valve 31 causing it to close lines 28 and 29 to maintain the integrity of lines 20 and 22 and to connect lines 21 and 23 through bypass port 33 in valve 31.

As a consequence if the fluid leakage has occurred in any part of the hydraulic circuit connected to lines 21 and 23 (as seen in Figure 2) the fluid level in reservoir 18 will remain constant, not dropping any further and steering is maintained by the action of the lower chambers of the pisfon and cylinder assemblies 10 and 11. The upper assembly acting passively. Activation of switch 42 will also activate an alarm (audible and/or visual) to signal fluid leakage, and steps may be taken to remedy the fault.

If, however, the fluid leakage has occurred at a point in the hydraulic circuit connected directly to lines 20 and 22 then the fluid level in reservoir 18 will continue to fall and proximity switch 43 will also be actuated, consequently energising solenoid 50 of valve 55 and at the same time de-energising solenoid 49 of valve 54. Thus valve 31 is opened and valve 30 is closed maintaining the integrity of lines 21 and 23 and connecting lines 20 and 22 through bypass port 32 in valve 30. Simultaneously electric motor 16 is switched off, and electric motor 17 is switched on to drive pump 13 (which may be a fixed or variable delivery pump) and steering is maintained by the action of the upper chambers of the piston and cylinder assembly 10 and 11 under the action of fluid supplied under pressure by pump 13.

If a failure occurs, resulting in fluid leakage, initially whilst pump 13 is operating then a similar sequence of events occurs. Firstly proximity switch 42 is actuated to activate solenoid 50 thereby operating valves 46 and 30. If fluid level in reservoir 19 continues to fall proximity switch 43 is actuated thereby activating solenoid 49 and deactivating solenoid 50, whilst at the same time electric motor 17 is switched off and electric motor 16 is switched on to drive pump 12, which again may be a fixed or a variable delivery pump.

In the above example only two isolating valves 30 and 31 have been described and illustrated. In practice however it could be advantageous to have four isolating valves operated by pilots valves 54 and 55 and cylinder thus giving two additional valves in case of valve failure in the first two. In the event of failure of the system manual override would advantageously be provided for the actuation of valves 30 and 31. Similarly in Figure 4 valve 78 is controlled by a solenoid valve 81 operative to connect fluid line 82 of valve 78 to the output of pump 71. Both valves 77 and 78 are provided with manual override in case of servo mechanism failure. In the same manner in the embodiment of Figure 2, the hydraulic fluid reservoirs 73 and 74 are provided with a float switch 83.

System can be tested by manually depressing float.

Figure 5 is an electrical control circuitforthe apparatus of Figures 1 and 2, working together with the float switch, Figure 3 to provide automatic isolation of two sides of the steering apparatus in the event of fluid leakage together with alarm actuation.

Supply voltage from each of the two pump motor starters is led through terminals 87 and 88 and from an independent source through terminal 103.

Terminal 87 is connected through isolating switch 106 and terminal 89 of the tripple pole switch 93 to the lower live terminal of solenoid operated switch 91 which is spring operated to the lower position when de-energised (normal position) this connects the supply to the starting circuit of pump motor 69 through terminal 104 of isolating switch 106 (Figure 4).

Terminal 88 is similarly connected.through isolating switch 106 and terminal 90 of the tripple pole switch 93 which is spring operated to the lower position when de-energised. (Normal position) this connects the supply to the starting circuit of pump motor 70 through terminal 105 or isolating switch 106 (Figure 4).

Terminals 101 are connected to the normally open proximity switch 42 (Figure 3) and terminals 102 are connected to the normally open proximity switch 43 (Figure 3).

Solenoid operated switch 98 is spring operated to the raised position when de-energised. (Normal position) Solenoid operated switch 100 is spring operated to the open position when de-energised. (Normal position).

Terminals 99 are connected to visual and audible alarms in the wheelhouse and engine room.

The isolating switch 106 is shown in the 'on' position in Figure 5. When in the 'off' position, terminals 87 and 104, and 88 and 105 are respectively connected, allowing normal operation of the pumps starters and motors with automatic device isolators.

Single motor operation If it is desired to operate on, say, motor 69 then switch 93 is moved to the left to engage contacts 89, 95 and 97 thus providing a secondary parallel path for the supply from terminal 87 through contact 89, upper contacts of solenoid switch 98 and through contact 95 bypassing switch 91 to motor 69.

Similarly if it is desired to operate on motor 70 then switch 93 is moved to the right to engage contacts 90, 94 and 96 thus providing a secondary parallel path for the supply from terminal 88 through 89, upper contacts of solenoid switch 98 and through contact 94 bypassing switch 92 to motor 70.

Double motor operation If it is desired to operate both motors then it is immaterial to which side the switch 93 is moved. As long as one pump has a secondary parallel path for its supply.

The operation of the steering apparatus of Figure 4 and control circuit of Figure Swill now be described.

Referring firstly to Figure 4 the steering apparatus will normally be operated underthe action of one pump, say pump 71 (motor 69). Solenoid valves 77 and 78 will be in the positions shown so that all four piston and cylinder assemblies 60,61, 62 and 63 are actuated by fluid from pump 71. With valve 75 in the extreme right position (as seen in Figure 4) it will be apparent that the piston and cylinder assemblies are actuated to turn tiller 68 in a clockwise sense whilst when valve 75 is moved to the extreme left position tiller 68 will be moved anti clockwise. Of course, both pumps may be generated together, valves 75 and 76 are moved in synchronism, to double the speed.

If only pump 71 (motor 69) is being used and leakage occurs the level of hydraulic fluid in reservoirs 73 and 86 will fall and proximity switch 42 triggered by the falling float 40 (Figure 3) will close.

Reference to Figure 5 will show that this energises valve 100 which on closing will conduct the supply to alarm terminals 99 and solenoids of switches 91 and 99 this will open the lower contacts of the latter and close the upper contacts. The triple pole switch 93 will be in the left hand position engaging contacts 89, 95 and 97, providing a secondary path to motor 69 bypassing switch 91. It also connects the supply to solenoid operated pilot valve 81 which directs hydraulic fluid to operate valve 78 which will close off the side of the circuit associated with pump 71 to maintain its integrity and bypass the other side. If the fault is in this latter side then the oil level in the reservoirs 73 and 86 will remain constant, not dropping any further and steering is maintained by the action of the left hand piston and cylinder assemblies 60 and 61.The right hand assemblies acting passively. The alarm will have signalled fluid leakage, and stops may be taken to remedy the fault.

If however, the leakage has occurred at a point in the hydraulic circuit connected to the side including pump 71 then the fluid level in the reservoirs 73 and 86 will continue to fall and proximity switch 43 will close, and energise the solenoid of switch 98 opening the upper contacts and cutting off the supply to motor 69 and the solenoid of pilot valve 81 which will then allow valve 78 to return to the open position, simultaneously the making of the lower contact of switch 98 will feed the supply through contact 97 of switch 93 to energise the solenoid operated pilot valve 79 which directs hydraulic fluid to operate valve 77 which will close off the side of the circuit associated with pump 72 to maintain its integrity and bypass the other side.Steering is maintained by the action of the right hand piston and cylinder assemblies 62 and 63 under the action of fluid supplied under pressure from pump 72.

If a failure occurs, resulting in fluid leakage initially whilst pump 72 is operating then a similar sequence of events occurs. Switch 93 is in the right hand position. Firstly proximity switch 42 is closed to activate the solenoids of pilot valve 79 and direct hydraulic fluid under pressure to operate valve 77. If the fluid level continues to fall then proximity switch 43 closes, de-activating solenoid 79 and cutting off the supply is connected to drive motor 69 and energise solenoid of pilot valve 81.

When both pumps are running loss of fluid in the reservoir will close proximity switch 42 and switch 100 thus connecting the supply to the solenoids of switches 91 and 92 thereby disconnecting the direct supply to both motors and leaving only one motor running on the secondary parallel circuit led through the 3 pole switch 93. With only one motor operating the sequences already described will be applicable.

The steering gears described are of the type using fixed delivery pumps and solenoid operated contol valves but the system can be also applied to steering gears with variable delivery pumps.

It will readily be appreciated that the present invention provides distinct advantages. Damage to the pumps is avoided as they are not allowed to run dry. Furthermore, repairs can be carried out while maintaining course and speed without any loss of control.

Claims (6)

1. Afluid actuated steering apparatus for a ship, comprising first and second fluid pumps, associated respective first and second piston and cylinder assemblies for actuating a tiller of the ship, means for detecting fluid leakage, and means for automatically isolating said first fluid pump and first piston and cylinder assembly from said second fluid pump and second piston and cylinder assembly in the event of fluid leakage and to deactivate, or leave in a deactivated condition, that one of the pumps corresponding to the isolated portion of the steering apparatus in which the fluid leak is located.

2. Apparatus as claimed in claim 1, wherein the piston and cylinder assemblies are double-acting, the means for automatically isolating the pump and piston and cylinder assemblies is also operative to open valves to establish fluid communication between both sides of the cylinder in the isolated portion of the steering apparatus in which the fluid leak is located.

3. Apparatus as claimed in claim 2, wherein said means is also operative to activate or leave activated that one of the first and second pumps corresponding to the isolated portion of the steering gear in which the fluid leak is not located.

4. Apparatus as claimed in claim 1, 2 or 3, wherein said means includes a float switch capable of sensing the level of fluid in a fluid reservoir for the system and operative to isolate one portion of the steering gear in the event of a drop in fluid pressure.

5. Apparatus as claimed in claim 4, wherein the float switch has a second operating level, below the aforesaid first, which is operative to isolate a second portion of the steering gear and activate the first portion should fluid level continue to fall due to the leak being in the second portion.

6. A fluid actuated steering apparatus for a ship substantially as hereinbefore described with reference to and as illustrated in Figures 2 to 5 of the accompanying drawings.