Hydraulic steering arrangement for a thruster of a marine vessel

Abstract

A novel design of a hydraulic steering arrangement for a thruster of a marine vessel is specifically designed for thrusters intended to operate in an arctic environment where ice is present. To meet the arctic demands the steering arrangement is provided with a cross-over safety block arranged close to the hydraulic steering motor for absorbing the torque subjected to the thruster by ice for instance.

Claims

1. A hydraulic steering arrangement for a thruster of a marine vessel, the steering arrangement comprising: a hydraulic oil tank arranged in flow communication with at least one hydraulic motor used for steering the thruster via at least one hydraulic pump, the at least one hydraulic motor having ports for a hydraulic oil; a control valve block; a counterbalance block, the counterbalance block includes a safety valve; and a cross-over safety block, the cross-over safety block connected to, and in fluid communication with, the counterbalance block by hydraulic pipe portions, the cross-over safety block connected to, and in fluid communication with, ports of the at least one hydraulic motor by cross-over oil passages, the cross-over oil passages dimensioned for higher volumetric flows than the hydraulic pipe portions.

2. The hydraulic steering arrangement as recited in claim 1, wherein the cross-over safety block is arranged on the at least one hydraulic motor at an upper end of the thruster.

3. The hydraulic steering arrangement as recited in claim 1, wherein the cross-over safety block comprises at least one pressure relief valve connected by means of the cross-over oil passages to the ports of the at least one hydraulic motor.

4. The hydraulic steering arrangement as recited in claim 3, wherein the cross-over safety block comprises two pressure relief valves connected by means of the cross-over oil passages to the ports of the at least one hydraulic motor.

5. The hydraulic steering arrangement as recited in claim 1, wherein the cross-over safety block comprises two pressure relief valves connected by means of the cross-over oil passages to the ports of the at least one hydraulic motor.

6. The hydraulic steering arrangement as recited in claim 1, wherein the cross-over safety block comprises one pressure relief valve connected via four check valves and by means of the cross-over oil passages to the ports of the at least one hydraulic motor.

7. The hydraulic steering arrangement as recited in claim 1, wherein the cross-over oil passages have a first flow capacity and the hydraulic pipe portions have a second flow capacity, the first flow capacity being at least 5 to 10 times the second flow capacity for maintaining pipe pressure within acceptable limits.

8. The thruster of a marine vessel as recited in claim 1, wherein the safety valve of the counterbalance block comprises two pressure relief valves.

9. The thruster of a marine vessel as recited in claim 1, wherein the safety valve of the counterbalance block comprises one pressure relief valve connected via four check valves.

10. A thruster of a marine vessel, the thruster comprising: a propeller unit, a substantially vertical housing and a steering arrangement; the vertical housing being arranged rotatable by means of bearings within a support frame, the steering arrangement having a hydraulic oil tank in fluid communication with at least one hydraulic motor used for steering the thruster via at least one hydraulic pump, a control valve block, a counterbalance block, and a cross-over safety block, the at least one hydraulic motor being attached to the support frame and having ports for a hydraulic oil the counterbalance block includes a safety valve, the cross-over safety block connected to, and in fluid communication with, the counterbalance block by hydraulic pipe portions, the cross-over safety block connected to, and in fluid communication with, the ports of the at least one hydraulic motor by of cross-over oil passages, the cross-over oil passages dimensioned for higher volumetric flows than the hydraulic pipe portions.

11. The thruster of a marine vessel as recited in claim 10, wherein the cross-over safety block is arranged on the at least one hydraulic motor at an upper end of the thruster.

12. The thruster of a marine vessel as recited in claim 10, wherein the cross-over safety block comprises at least one pressure relief valve connected by means of the cross-over oil passages to the ports of the at least one hydraulic motor.

13. The thruster of a marine vessel as recited in claim 10, wherein the cross-over safety block comprises two pressure relief valves connected by means of the cross-over oil passages to the ports of the at least one hydraulic motor.

14. The thruster of a marine vessel as recited in claim 10, wherein the cross-over safety block comprises one pressure relief valve connected via four check valves and by means of the cross-over oil passages to the ports of the at least one hydraulic motor.

15. The thruster of a marine vessel as recited in claim 10, wherein the cross-over oil passages have a first flow capacity and the hydraulic pipe portions have a second flow capacity, the first flow capacity being at least 5 to 10 times the second flow capacity for maintaining pipe pressure within acceptable limits.

16. The thruster of a marine vessel as recited in claim 10, wherein the safety valve of the counterbalance block comprises two pressure relief valves.

17. The thruster of a marine vessel as recited in claim 1, wherein the safety valve of the counterbalance block comprises one pressure relief valve connected via four check valves.

Description

BRIEF DESCRIPTION OF DRAWING

(1) In the following, the hydraulic steering arrangement of a thruster is explained in more detail with reference to the accompanying Figures, of which

(2) FIG. 1 illustrates schematically a prior art thruster with its steering arrangement,

(3) FIG. 2 illustrates schematically a prior art steering arrangement of a thruster,

(4) FIG. 3 illustrates schematically a first preferred embodiment of the steering arrangement of the present invention,

(5) FIG. 4 illustrates schematically a second preferred embodiment of the steering arrangement of the present invention,

(6) FIG. 5 illustrates schematically a third preferred embodiment of the steering arrangement of the present invention,

(7) FIG. 6 illustrates schematically a fourth preferred embodiment of the steering arrangement of the present invention, and

(8) FIG. 7 illustrates schematically a fifth preferred embodiment of the steering arrangement of the present invention.

DETAILED DESCRIPTION OF DRAWINGS

(9) FIG. 1 illustrates a state-of-the-art thruster 1, which is here understood as a steerable propulsion device arranged mainly beneath the hull (not shown) of a marine vessel. The thruster 1 is formed of a propeller unit 2 (rotatable/steerable round a vertical axis) beneath the hull and a substantially vertical housing 3. The vertical housing 3 extends up into the hull of the marine vessel through an opening 4 in the bottom of the hull. The upper end of the vertical housing 3 is arranged rotatable by means of bearings within a round support frame 5 that is attached to the hull bottom such that it fills the opening 4. The upper end of the vertical housing 3 is provided with a first gear wheel 6, which communicates with one or more smaller second gear wheels 7 each rotated by a hydraulic steering motor 8 attached to the support frame 5. Normally several hydraulic motors will be present for redundancy and sizing reasons. The first and second gear wheels, 6 and 7, respectively, form the mechanical components of a gear transmission azimuth steering arrangement. The vertical housing 3 of the thruster 1 is in itself rotatable by means of the hydraulic steering motor/s 8. The drive of the propeller 9 is arranged through the hollow interior of the vertical housing 3. Thus the drive of the propeller is mechanical with drive shafts 10, 10 and angular gears 11, 11. However, the hydraulic steering arrangement of the invention may be used with hydraulic or electric drives, too.

(10) FIG. 2 illustrates schematically the hydraulic instrumentation of a prior art steering arrangement of a thruster 1. The major difference when compared to the steering arrangement of the earlier discussed JP document is the safety and counterbalance block 30, which is arranged between the thruster control block 20 and the hydraulic motor 8 turning the thruster 1. Thus the control block 20 performs essentially the same functions as the proportional valve in the JP document.

(11) The control block 20 of the thruster 1 comprises a proportional directional valve 22 (4 ports, 3 positions) Depending on the flows and pressures applied the operation of the valve may be performed with pilot operated valves. The hydraulic steering arrangement has at least one hydraulic pump 26 for pressurizing the oil stored in the hydraulic oil tank 28. Normally the number of hydraulic pumps 26 is at least two, for instance for safety and redundancy purposes. In such a case, one pump may be capable of fulfilling the need of oil of all the consumers, or both pumps may be used simultaneously. In non-steering conditions the proportional valve (and the optional pilot valves) is in neutral position blocking oil flow through the valves, whereby the oil pressure created by the pump/s 26 acts on the valves only. When the direction of the thruster 1 needs to be changed the proportional valve is moved to the desired direction. Now a flow communication from the pump/s 26 towards the steering motor 8 is opened resulting in rotation of the steering motor 8 and turning of the thruster 1. The oil flow returning from the steering motor 8 flows through the proportional directional valve 22 back to the oil tank 28. When the desired azimuth angle of the thruster 1 is reached the proportional directional valve 22 is then returned to its neutral position. As a result it is blocking the oil flow from the pump/s 26 to the steering motor 8. This function locks the steering angle of the thruster (assuming negligible leakage from the hydraulic motor).

(12) The safety and counterbalance block 30 includes a safety valve arrangement 32 and two, i.e. a first and a second, counterbalance valve arrangements 40 and 40. The purpose of the safety valve arrangement 32 is to open a flow path from one port of the hydraulic steering motor 8 to the other port thereof in such a case that the motor 8, for some reason, starts acting as a pump and raises pressure in one of its ports. The safety valve arrangement 32 is formed of four check valves 34, 34 and 36, 36 and a safety or pressure relief valve 38. When the motor 8 acts as a pump and creates an oil pressure exceeding the predetermined opening pressure of the safety valve 38 one of the first two check valves 34 and 34 i.e. one of the two check valves 34 and 34 (depending in which direction the motor is rotated) in the flow paths between the hydraulic motor 8 and the safety valve 38 opens and as a result, the oil flows through the safety valve 38, passes one of the second check valves 36 and 36 and enters the pipe of the hydraulic motor 8 prevailing at a lower pressure, i.e. the one acting as the inlet pipe of the hydraulic motor.

(13) The first and second counterbalance valve arrangement 40 and 40 have been coupled farther away than the safety valve arrangement 38 to the hydraulic pipes 50 and 52 connected to the ports of the hydraulic steering motor 8. The first counterbalance valve arrangement 40 includes a check valve 42 and a pilot-operated pressure relief valve 44 and the second counterbalance valve arrangement 40 includes a check valve 46 and a pilot-operated pressure relief valve 48. The purpose of the counterbalance valve arrangements 40 and 40 is to lock the steering i.e. maintain the thruster 1 in the direction it has been turned by the hydraulic steering motor/s 8 controlled by the proportional directional valve 22. In other words, the counterbalance valve arrangements 40 and 40 take the pressure load, if the hydraulic motor 8 starts to act as a pump, whereby the proportional directional valve 22 is not subjected to any pressure load from the direction of the hydraulic motor 8.

(14) At a steering phase the counterbalance valve arrangements 40 and 40 function as follows assuming that a first pipe portion 50 and a second pipe portion 50, allows oil flow to the motor and pipe 52 takes care of the return flow. The first valve arrangement 40 positioned at the inlet pipe 50 of the steering motor/s 8 allows the pressurized oil to flow via the check valve 42 to the inlet port/s of the steering motor/s 8 with a minimal pressure loss. In the second valve arrangement 40 the pressure of the returning oil at the first outlet pipe portion 52 of the steering motor/s 8 affects the pilot-operated pressure relief valve 48 and opens it, assisted by the pilot pressure from the pressure pipe 50 between the proportional directional valve 22 and the pilot-operated pressure relief valve 44. Thus the returning oil has a certain counterpressure, i.e. a pressure loss takes place in the second counterbalance valve arrangement 40.

(15) When the desired thruster direction, i.e. angular position is reached, and the steering action thus ceased the thruster is maintained at its desired direction. As explained already above, the proportional directional valve 22 is moved to its neutral position whereby no flow through the proportional valve 22 takes place from the supply side to the hydraulic motor side. However, due to the presence of the counterbalance valve arrangements it is not the proportional directional valve 22 that prevents the steering motor from rotating, as is the case in the steering arrangement of the above cited Japanese reference, but the counterbalance valve arrangements 40 and 40. In this case the steering motor/s 8 is/are subjected to no internal load. However, the thruster 1 may be subjected to external loads from the sea or any objects therein, whereby the thruster 1 acts on the steering motor/s 8 through the steering gear transmission (discussed in connection with FIG. 1) and tries to rotate such. In practice this means that the motor/s 8 start/s acting as pump/s. The motor/s 8 create/s oil pressure that acts on both the safety valve 38 and one of the pilot-operated pressure relief valves 44, 48. As long as the hydraulic motor/s 8 has/have no internal leakage the thruster 1 is not able to turn until the pressure the steering motor/s 8 has/have succeeded in creating in front of the safety valve 38 exceeds its predetermined opening value. When the value is exceeded the pressurized oil flows from the outlet port/s of the steering motor/s 8 to the inlet port/s thereof via two check valves and the safety valve 38. Thus the opening pressure of the safety valve 38 is lower than that of the pilot-operated pressure relief valves 44, 48. It should be noted that the pilot pressure of the pilot-operated pressure relief valves 44, 48 is negligible (the proportional directional valve 22 being in neutral position).

(16) In FIG. 3 the hydraulic steering arrangement of a thruster 1 in accordance with a preferred embodiment of the present invention is illustrated. The hydraulic steering arrangement consists of four main parts, which are physically grouped together, i.e. a hydraulic powerblock 60, a counterbalance block 70, a cross-over safety block 80, and the hydraulic steering motor 8. The general construction and function of the hydraulic powerblock 60, the counterbalance block 70 and the hydraulic steering motor 8 are known before and have been discussed in more detail above in connection with FIG. 2.

(17) The hydraulic powerpack 60, thus, contains hydraulic pumps 26, an oil tank 28, and the control block (discussed in connection with FIG. 2) including a proportional directional valve 22 as its main component. The proportional directional valve 22 may optionally be operated by means of at least one proportional directional solenoid valve 24. The two pumps 26 shown in FIGS. 2 and 3 may be sized as two times 50% of the required flow or as two times 100%, which means that just one pump will be active and the other pump is redundant. However, if considered worthwhile the number of hydraulic pumps of the hydraulic steering arrangement may exceed two. The function of the hydraulic powerpack 60 is to supply oil to the hydraulic steering motors 8. Depending on the position of the proportional directional valve 22, a certain flow is supplied by the hydraulic powerpack 60. The required load pressure is automatically generated (the means not shown) up to the safety pressure setting of the powerpack 60.

(18) The counterbalance block 70 contains the counterbalance valves, i.e. the pilot-operated pressure relief valves 44 and 48, the check valves 42 and 46 in cooperation therewith, the pressure relief valve, i.e. the safety valve 38 with its check valves (34, 34, 36 and 36) and the cavitation protection system 76 utilizing check valve 36 or check valve 36.

(19) The counterbalance block 70 has three functions. The main function is accomplished by the counterbalance valves, i.e. the pilot-operated pressure relief valves 44 and 48 and the check valves 42 and 46 in cooperation therewith. For instance, a path to the hydraulic motor/s 8 is arranged via a check valve 42 i.e. with a low pressure drop. However, the return path back to the proportional directional valve 22 is arranged via a pilot-operated pressure relief valve 48, i.e. with a large pressure drop. In fact, the counterbalance block 70 shown in FIG. 3 has two pilot-operated pressure relief valves 44 and 48. The valves are for all hydraulic steering motors 8 together. In other words, one counterbalance block is used for one thruster, i.e. controlling oil flows to all steering motors of a thruster. As another option, it would also be possible to arrange a counterbalance block for a certain number of steering motors. For instance for a thruster using six steering motors one might have two or three counterbalance blocks, each serving three or two steering motors. A relatively high pressure is needed to open the return path via the pilot-operated pressure relief valve 44 or, in the above example, via the pilot-operated pressure relief valve 48. The pressure that opens the return path is the combination of the load pressure (pressure of the returning oil) and the pressure in the forward path (flowing from pilot-operated pressure relief valve 44 towards the steering motors 8), which is called the pilot pressure. If the purpose is to rotate the hydraulic motors 8, then the pilot pressure will be considerable high, as well as the load pressure and consequently, the counterbalance valve, i.e. the pilot-operated pressure relief valve 48 in the return oil path will open. If the purpose is to hold the hydraulic steering motors 8 in place, i.e. not rotate the thruster 1, then the pilot pressure will be low because there is an open connection through the proportional directional valve 22 to the oil tank 28 when the proportional directional valve 22 is in centre i.e. neutral position. In that case, only the load pressure is present to open the pilot-operated pressure relief valves 44 and 48. To be able to open the pilot-operated pressure relief valves 44 and 48 the load pressure should be significantly higher as it should suffice without the help of the pilot pressure. This concept is used to maintain the angular positions of the hydraulic steering motors 8. This function is also required by the classification society, which requires that in case of failure in the powerpack 60, the thruster 1 must maintain its position.

(20) Another function of the counterbalance block 70 is the pressure relief in case of too high pressure prevailing in one of the pipe portions 50 or 52 coming from the steering motor 8. A certain pressure makes the pressure relief valve, i.e. the safety valve 38 open so that oil may flow to the oil tank 28 or to the other pipe portion 52 or 50.

(21) The third main part is the hydraulic steering motor 8, which is connected to the gear transmission and mounted on the support frame (as shown in FIG. 1). Normally several hydraulic steering motors 8 will be present for redundancy and sizing reasons. The three parts 60, 70 and 8 are connected by oil pipes. Normally, after the counterbalance block 70, the oil pipes will have several pipe portions to the hydraulic motors 8, i.e. there is one counterbalance block 70 for one thruster 1. The hydraulic powerpack 60 and the counterbalance block 70 are not necessarily mounted on the thruster 1; preferably they are arranged at a distance thereof. The hydraulic steering motors 8 convert the oil flow to a rotational velocity of a shaft.

(22) The hydraulic powerpack 60 and the counterbalance block 70 are sized to handle the flow corresponding to a desired thruster steering speed of around 2 rpm (hydraulic motors 8 will naturally rotate faster because of the steering gear transmission). Since the thruster steering speed may be imposed by an ice block or some other solid object and this speed may be much higher than the design steering speed, the steering arrangement of the present invention has been provided with a cross-over safety block 80. The safety block 80 comprises pressure relief valves 82 and 84, which are preferably arranged as close to the steering motor 8 as practically possible. In other words, the cross-over safety block 80 is preferably attached to the hydraulic motor 8. In case one safety block 80 is coupled to several hydraulic motors the safety block is preferably arranged so that the cross-over oil passage lengths between the motors and the block are minimized. The pressure relief valves 82 and 84 are sized to handle a much larger flow than the corresponding pressure relief valves 38, 44 and 48 in the counterbalance block 70. The main reason for this kind of sizing is the goal to keep the hydraulic oil pressure at an acceptable level in the entire hydraulic arrangement, and to prevent pressure pulses and their negative effects in the hydraulic steering arrangement.

(23) The cross-over safety block 80 comprises further two cross-over oil passage 54 and 56, which are connected at their one ends to the ports of the hydraulic motor 8 and at their opposite ends to the pressure relief valves 82 and 84. The cross-over oil passage 54 and 56 have a diameter allowing high volumetric flows from the hydraulic motor 8 to the pressure relief valves 82 and 84 and from these valves back to the motor 8. The dimensioning of the cross-over oil passage 54 and 56 is to be based on a significant higher flow capacity, 5- to 10-fold compared to the hydraulic pipe portions 50 and 52 branching from the cross-over oil passage 54 and 56 and connecting the cross-over safety block 80 to the counterbalance block 70. Thus the hydraulic pipe portions 50 and 52 may be dimensioned as in prior art hydraulic steering arrangements. The higher flow capacity of the cross-over oil passage 54 and 56 ensure that the pressure in said cross-over oil passage is maintained within acceptable limits.

(24) The cross-over safety block 80 functions as follows: Once the hydraulic steering arrangement, normally due to ice or some other solid object tending to turn the thruster 1, is subjected to an unacceptable load whereby the hydraulic steering motors 8 are driven and rotated by the load, i.e. the hydraulic steering motors 8 start operating as pumps, one of the cross-over safety valves, for instance pressure relief valve 82, opens. Thus, the flow generated by the hydraulic steering motors 8 goes through one of the cross-over safety valves 82 and 84. The obtainable steering speeds, when the hydraulic motors 8 are driven mechanically, i.e. by the thruster 1, are easily higher than the steering speeds, which are normally imposed by the hydraulic motors 8. It has been estimated that such a speed may easily be 5-fold, and sometimes even 10-fold compared to ordinary steering speed. Thus both the pressure relief valves 82 and 84 as well as the cross-over oil passage 54 and 56 of the cross-over safety block 80 are dimensioned to 5-fold, preferably to 10-fold volumetric flows compared to pipes 50 and 52 leading from the cross-over safety block 80 to the counterbalance block 70, for instance.

(25) The safety valve 38 in the counterbalance valve block 70 is optional. The flow capacity required during ice contact of the complete hydraulic system is increased by adding the valve. The setting of the valves should be slightly higher than that of the cross over safety valves 82 and 84 on the steering motors. The sizing of the cross-over safety valves i.e. the pressure relief valves 82 and 84 close to the hydraulic motors 8 and the optional safety valve 38 in the counterbalance block is made in such a way that the pressure increase within the hydraulic steering arrangement is restricted to a limited value.

(26) Given the pressure settings on the pressure relief valves 82 and 84 the hydraulic motors 8 need to generate a significant pressure to be able to open one of the valves and thus to enable the oil flow through the valve. A beneficial result is that the hydraulic motors 8 need to be rotated by a significant load moment to enable the rotation. The hydraulic motors still generate a torque opposing the external ice load. The hydraulic motors 8 act, thus, as brakes. As a consequence the azimuth rotation speed of the arrangement is, to a certain degree, limited.

(27) In FIG. 4 the hydraulic steering arrangement of a thruster in accordance with a second preferred embodiment of the present invention is illustrated. In this embodiment the design of the cross-over safety valve block 80 has been changed compared to the embodiment discussed in FIG. 3. Otherwise the second embodiment corresponds to the first one, i.e. the one illustrated in FIG. 3. Here, the cross-over safety valve block 80 comprises only one safety valve 86, and four check valves 88 by means of which the pressurized oil from the hydraulic motor 8 is directed to the safety valve 86, and from the safety valve 86 back to the hydraulic motor 8 irrespective of the direction of rotation of the hydraulic motor 8.

(28) In FIG. 5 the hydraulic steering arrangement of a thruster in accordance with a third preferred embodiment of the present invention is illustrated. The steering arrangement of this embodiment is shown to be similar with the second embodiment of the present invention discussed in FIG. 4. The basic idea in this embodiment is that the counterbalance valve block 70 does not any more need the safety valve 38 (shown in FIG. 3, present also in the embodiment of FIG. 4), as the safety valve 86 is arranged in a safety valve block 80 of its own close to the hydraulic motor 8.

(29) In FIG. 6 the hydraulic steering arrangement of a thruster in accordance with a fourth preferred embodiment of the present invention is illustrated. The steering arrangement of this embodiment is shown to be similar to the first embodiment discussed in FIG. 3. The basic idea in this embodiment is that the counterbalance valve block 70 does not any more need the safety valve 38 (shown in FIG. 3), as the two safety valves 82 and 84 in FIG. 3 are arranged in a safety valve block 80 of its own close to the hydraulic motor 8.

(30) In FIG. 7 the hydraulic steering arrangement of a thruster in accordance with a fifth preferred embodiment of the present invention is illustrated. Here it has been shown how a number of hydraulic motors 8 arranged for turning a thruster have been provided with a single cross over safety valve block 80 comprising two safety valves 82 and 84. Thus there may be one or more hydraulic motors 8 per safety valve block 80. Naturally, the safety valve block 80 may also be constructed as shown in FIG. 5, i.e. with only one safety valve and a number of check valves. Also, the check valve of the counterbalance block may be taken out, as taught by FIGS. 5 and 6.

(31) It should be understood that the above is only an exemplary description of a novel and inventive hydraulic steering arrangement of a thruster and a method of arrangement. It should be understood that the above description discusses only a few preferred embodiments of the present invention without any purpose to limit the invention to the discussed embodiments and their details only. Thus the above specification should not be understood as limiting the invention by any means but the entire scope of the invention is defined by the appended claims only. From the above description it should be understood that separate features of the invention may be used in connection with other separate features even if such a combination has not been specifically shown in the description or in the drawings.