A hydraulic system for control of a marine drive unit

Abstract

A marine drive unit has a hydraulic system. The hydraulic system includes a hydraulic tilt actuator operable to move a propeller arrangement of the drive unit from a position in water to a position above water, and a hydraulic steering actuator operable to adjust an azimuth thrust angle of the propeller arrangement. The hydraulic system has a first hydraulic pump connected via a hydraulic valve arrangement to the tilt actuator and to the steering actuator. The hydraulic system is arranged to prioritize control of the steering actuator over control of the tilt actuator by the hydraulic valve arrangement.

Description

TECHNICAL FIELD

[0001] This disclosure relates generally to marine drive units. In particular aspects, the disclosure relates to hydraulic systems for trim, tilt and steering of one or more marine drive units. Aspects of the disclosure can be advantageously applied in electrically powered leisure craft and smaller commercial vessels. Although the disclosure may be described with respect to a particular marine vessel type, the disclosure is not restricted to any particular type of boat or ship.BACKGROUND

[0002] Marine vessels such as leisure craft and smaller commercial vessels can be powered by one or more propeller arrangements. The propeller arrangements are driven by respective power sources, such as combustion engines and / or electrical machines, and supported by drive units that extend down into the water, normally from the transom of the boat or from the bottom of the hull. A drive unit can often be both steered and trimmed in use, where steering of the drive unit relates to adjusting a thrust angle of the propeller arrangement in the azimuth plane, and trimming relates to adjustment of the elevation thrust angle of the thrust. Some drive units can also be tilted in order to move the propeller arrangement out of the water.

[0003] It is desired to provide efficient actuator systems for trim, tilt and steering of a marine drive unit.SUMMARY

[0004] It is an objective of the present disclosure to provide improved marine drive units and hydraulic systems for marine drive units. According to aspects of the disclosure, there is presented a marine drive unit comprising a hydraulic system. The hydraulic system in turn comprises a hydraulic tilt actuator operable to move a propeller arrangement of the drive unit from a position in water to a position above water, and also a hydraulic steering actuator operable to adjust an azimuth thrust angle of the propeller arrangement. The hydraulic system comprises a first hydraulic pump connected via a hydraulic valve arrangement to the tilt actuator and to the steering actuator, where the hydraulic system is arranged to prioritize control of the steering actuator over control of the tilt actuator by the hydraulic valve arrangement. The disclosed hydraulic system may seek to provide a more cost efficient drive unit at least in part since a single pump is used to power both steering and tilt actuators. The disclosed hydraulic system may also seek to provide a more spatially efficient drive unit at least in part since a single pump is used to power both steering and tilt actuators. The steering actuator is, however, given priority over the tilt actuator, which can be achieved in several different ways. It is an advantage that the steering and tilt actuators share the same pump, since these two actuators are not necessary to use simultaneously, at least not at full actuator loads.

[0005] According to a first example the valve arrangement comprises a hydraulic selector valve arranged to be controlled by a control unit of the marine drive unit to prioritize control of the steering actuator over control of the tilt actuator. In other words, the control unit is configured to select the steering actuator in case both steering actuation and tilt actuation is desired. The selector valve is a low complexity hydraulic solution which can be electronically controlled by the control unit in a straight-forward manner to connect the steering actuator to the pump when steering is desired, i.e., to prioritize the steering actuator over the tilt actuator. The selector valve is preferably also arranged to default to a state where the steering actuator is connected to the first hydraulic pump in case of malfunction, i.e., in case of power outage or malfunction in the control unit.

[0006] According to a second example the valve arrangement comprises a hydraulic priority valve arranged to prioritize control of the steering actuator over control of the tilt actuator. This way the tilt actuator function cannot negatively affect the steering function even if there is a malfunction in the system since the steering function will receive the requested hydraulic pressure and flow at all times. The tilt actuator will only be possible to operate when the steering actuator requests allow sufficient margin for also operating the tilt actuator. The hydraulic priority valve is preferably arranged to default to a state where the steering actuator is connected to the first hydraulic pump in case of malfunction.

[0007] According to some aspects, the hydraulic system is configurable in a nominal mode of operation and in a de-rated mode of operation, where the hydraulic system is arranged to decrease a maximum hydraulic flow of at least the steering actuator when in the de-rated mode of operation. The de-rated mode of operation is suitable for use-cases where the full performance of the steering actuator is not required, such as when the drive unit is partially up-tilted for reduced draught. The hydraulic system may also be arranged to decrease a maximum hydraulic flow of the tilt actuator when in the de-rated mode of operation.

[0008] The hydraulic system optionally comprises a second hydraulic pump connected to a hydraulic trim actuator of the drive unit, where the trim actuator is operable to adjust an elevation thrust angle of the propeller arrangement. The trim actuator, if present, is advantageously operated in simultaneously with the steering actuator, hence a separate pump is preferred. A more advanced hydraulic valve capable of distributing hydraulic flow in priority between steering actuator, trim actuator and tilt actuator is often not as cost efficient as using a second hydraulic pump for the trim function. This more advanced hydraulic valve would also require a larger pump which adds to the spatial footprint of the hydraulic system.

[0009] The flow rate and flow direction of the hydraulic steering actuator and of the hydraulic trim actuator are preferably independently controllable.

[0010] An operating pressure of the first hydraulic pump may be different than an operating pressure of the second hydraulic pump, allowing the first hydraulic pump specification and the second hydraulic pump specification to be optimized separately, which is an advantage.

[0011] The tilt actuator may be operable to rotate the propeller arrangement about a first pivot axis and the trim actuator may be operable to rotate the propeller arrangement about a second pivot axis that is spatially offset from the first pivot axis. This offset between the two pivot axes allows for the propeller arrangement to be operated at reduced draught in an efficient manner.

[0012] The marine drive unit may, according to some aspects, be arranged to decrease a hydraulic flow of the first hydraulic pump and / or of the second hydraulic pump below a respective nominal hydraulic flow when both the steering actuator and the trim actuator are used simultaneously. This reduces a peak power consumption of the hydraulic system, which is an advantage. The decrease in hydraulic flow can be triggered by the control unit, or by a hydraulic connection between the two systems.

[0013] The disclosed aspects, examples (including any preferred examples), and / or accompanying claims may be suitably combined with each other as would be apparent to anyone of ordinary skill in the art. Additional features and advantages are disclosed in the following description, claims, and drawings, and in part will be readily apparent therefrom to those skilled in the art or recognized by practicing the disclosure as described herein.BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Examples are described in more detail below with reference to the appended drawings.

[0015] FIG. 1 illustrates an example transom-mounted marine drive unit.

[0016] FIG. 2 shows an example marine drive unit in nominal operating position.

[0017] FIG. 3 shows an example drive unit in an up-tilted position.

[0018] FIG. 4 schematically illustrates an example hydraulic system in a marine drive unit.

[0019] FIG. 5 schematically illustrates components of an example hydraulic system.DETAILED DESCRIPTION

[0020] The detailed description set forth below provides information and examples of the disclosed technology with sufficient detail to enable those skilled in the art to practice the disclosure.

[0021] FIG. 1 shows a marine vessel 100 with a transom-mounted drive unit 110. The drive unit 110 supports a propeller arrangement 115 which provides thrust that propels and also steers the vessel 100. As mentioned above, a marine vessel may generally comprise one or more drive units, that support one or more propeller arrangements. A set of reference axes x, y, z will be used herein to describe various geometrical relationships. A rotation about an axis i will generally be denoted by ωi, as indicated in FIG. 1.

[0022] The drive unit 110 is connected to a main power source 140 which powers the propeller arrangement 115. The main power source 140 may be a combustion engine or an electric machine. Hybrid power sources comprising a mix of combustion engine and electric machine are also possible. It is appreciated that the power source may be integrally formed with the drive unit 110 or be spatially separated from the drive unit 110.

[0023] The drive unit 110 also comprises a hydraulic system 130 for controlling at least steering and tilt of the drive unit 110, and preferably also trim of the drive unit. FIG. 2 illustrates an example drive unit 110 in a nominal operating position 200 where the propeller arrangement 115 is positioned under the water surface and operable to propel the vessel 100. Drive unit steering relates to adjustment of the azimuth angle ωz of the propeller thrust Tx, while drive unit trim relates to adjustment of the elevation thrust angle ωy,Tx of the propeller thrust Tx. The propeller axle 210 is at least approximately parallel with the horizontal plane in the nominal operating position.

[0024] FIG. 3 illustrates an example drive unit 110 in an up-tilted position 300, where the drive unit 110 has been pivoted by the tilt actuator such as to move 310 the propeller arrangement 115 to a position above water, where the propeller axle 210 has a significant angle relative to the horizontal plane, such as 50-90 degrees. Tilting of the drive unit 110 involves a rotation about a lateral axis just like the trim rotation, but it is different from a rotation by the trim actuator since it is a much larger rotation which moves the propeller arrangement 115 out from the water and into a storage position above water where, e.g., less biofouling occurs. In the examples illustrated in FIGS. 2-4, the tilt actuator is operable to rotate the drive unit 110 about a first pivot axis y1 while the trim actuator is operable to rotate the drive unit 110 about a second pivot axis y2 that is spatially offset from the first pivot axis y1. This offset between trim and tilt axes allows the drive unit 110 to be operated at reduced draught, by uptilting the drive unit by the tilt actuator and at the same time trimming the elevation thrust angle ωy,Tx of the propeller thrust Tx to be more parallel to the horizontal plane.

[0025] Another difference between the operation of the trim actuator and the operation of the tilt actuator is that the tilt actuator is operable to change the elevation thrust angle ωy,Tx of the propeller axle 210 by more than 30 degrees, or even more than 50 degrees, while the trim actuator seldom has a range of more than 20-30 degrees around a nominal orientation of the propeller axle 210.

[0026] The hydraulic system 130 and the power source 140 of the drive unit 110 are controlled by a control unit 120. The control unit 120 may include a microprocessor, microcontroller, programmable digital signal processor or another programmable device. The control unit 120 may also, or instead, include an application specific integrated circuit, a programmable gate array or programmable array logic, a programmable logic device, or a digital signal processor. Where the control unit includes a programmable device such as the microprocessor, microcontroller or programmable digital signal processor mentioned above, the processor may further include computer executable code that controls operation of the programmable device.

[0027] FIG. 4 and FIG. 5 illustrate aspects of an example marine drive unit 110 comprising a hydraulic system 130. The dashed line components in FIG. 5 are optional. The hydraulic system 130 comprises a hydraulic tilt actuator 450 operable to move 310 a propeller arrangement 115 of the drive unit 110 from a position in water 200 to a position 300 above water as exemplified in FIG. 3, and a hydraulic steering actuator 430 operable to adjust an azimuth thrust angle ωz of the propeller arrangement 115, as indicated in FIG. 2. The hydraulic system 130 comprises a first hydraulic pump 410 connected via a hydraulic valve arrangement 510 to the tilt actuator 450 and to the steering actuator 430. The hydraulic system 130 is arranged to prioritize control of the steering actuator 430 over control of the tilt actuator 450 by the hydraulic valve arrangement 510, which means that hydraulic flow is delivered firstly to the steering actuator according to its requirements. It has been realized that the steering function of the drive unit will not be used at the same time as the tilt function that moves the propeller out of the water, at least not at full load. Hence, to provide a more cost efficient design that is also more spatially efficient, a single pump can be used to power the steering actuator when the propeller arrangement is in the water and the drive unit is active, and the tilt actuator when the steering actuator is not used or is used at low load. This way the pump specifications in terms of maximum hydraulic flow and pressure can be relaxed, and in most cases be dimensioned to support only the hydraulic steering actuator. The hydraulic system is preferably set up so that it defaults to the steering actuator in case of malfunction, i.e., if the priority function fails for some reason.

[0028] The prioritization of the steering actuator over the tilt actuator can be achieved in some different ways. The valve arrangement 510 can for instance be implemented as a hydraulic selector valve arranged to be controlled by a control unit 120 of the marine drive unit 110 to prioritize control of the steering actuator 430 over control of the tilt actuator 450. The control unit electrically controls the selector valve to connect the steering actuator to the first hydraulic pump when steering is desired, and the tilt actuator when steering is not required, in which case the steering function is inactivated. The hydraulic system is preferably set up so that it defaults to the steering actuator in case of malfunction. Hydraulic selector valves with a default configuration are known in the art and will therefore not be discussed in more detail herein.

[0029] The valve arrangement 510 may also be implemented as a hydraulic priority valve arranged to prioritize control of the steering actuator 430 over control of the tilt actuator 450. A hydraulic priority valve, sometimes also called a priority flow control valve, is a valve designed to always provide flow to the main priority flow path (in this case the steering actuator), and only then supply the excess flow to the secondary line (in this case the tilt actuator). Hydraulic priority valves are generally known and will therefore not be discussed in more detail herein.

[0030] The hydraulic system 130 preferably also comprises a second hydraulic pump 420 connected to a hydraulic trim actuator 440 of the drive unit 110. The trim actuator is operable to adjust an elevation thrust angle ωy,Tx of the propeller arrangement 115 as indicated in FIG. 3. It is an advantage that the trim actuator is independent from the steering actuator, since the two must be possible to control simultaneously. Further advantages are obtained if the tilt actuator 450 is operable to rotate the drive unit 110 about a first pivot axis y1 and the trim actuator 440 is operable to rotate the drive unit 110 about a second pivot axis y2 spatially offset from the first pivot axis y1, as illustrated in the drawings. This allows the position of the propeller arrangement 115 to be adjusted in order to operate the drive unit at reduced draught.

[0031] According to some aspects, there is a back-up connection 520 between the second hydraulic pump 420 and the steering actuator 430. This back-up connection 520 is schematically illustrated in FIG. 5. The back-up connection 520 is arranged to divert hydraulic flow to the steering actuator 430 in case of malfunction by the first hydraulic pump 410. Several different implementations are possible for the back-up connection 520, such as a selector valve arrangement controlled by the control unit 120 and a hydraulic priority valve that prioritizes the steering actuator 430 over the trim actuator. The back-up connection 520 can also be implemented as a cross-over valve arrangement that switches the connections from the output ports of the hydraulic pumps 410, 420, such that the second pump 420 can be selected for powering the tilt and steering actuators 430, 450 and such that the first pump 410 can be selected for powering the trim actuator 440.

[0032] Some of the example hydraulic systems discussed herein are configurable in a nominal mode of operation and in a de-rated mode of operation, where the hydraulic system 130 is arranged to decrease a maximum hydraulic flow of at least the steering actuator 430 when in the de-rated mode of operation. An example application of the de-rated mode of operation is, for instance, when the tilt actuator and the trim actuators have been operated jointly to move the propeller arrangement 115 to a position of reduced draught. Since both the steering actuator and the tilt actuator will be used in this mode, a de-rating may be required. Still, the steering actuator will be given priority over the tilt actuator. According to some aspects the hydraulic system 130 is also arranged to decrease a maximum hydraulic flow of the tilt actuator 450 when in the de-rated mode of operation.

[0033] Moreover, the valve arrangement 510 comprises a hydraulic priority valve arranged to prioritize control of the steering actuator 430 over control of the tilt actuator 450, where the hydraulic system 130 is configurable in a nominal mode of operation and in a de-rated mode of operation, where the hydraulic system 130 is arranged to decrease a maximum hydraulic flow of the steering actuator 430 when in the de-rated mode of operation. Hereby the operational domain of the drive unit 110 is extended to enable use in cases where both steering and tilt functions need to be operational at the same time.

[0034] An operating pressure of the first hydraulic pump 410 may be configured differently from an operating pressure of the second hydraulic pump 420. Also, in many cases it is a requirement that the flow rate and flow direction of the hydraulic steering actuator 430 and of the hydraulic trim actuator 440 are independently controllable.

[0035] Both the first and second hydraulic pump draws power in use, and the total peak current may become significant in some cases. To reduce peak power consumption of the hydraulic system comprising both the first and the second hydraulic pumps, the hydraulic flow of the first hydraulic pump 410 and / or the second hydraulic pump 420 can be decreased below a respective nominal hydraulic flow when both the steering actuator 430 and the trim actuator 440 are used simultaneously. This can, e.g., be controlled from the control unit 120.

[0036] Certain aspects and variants of the disclosure are set forth in the following examples numbered consecutive below.

[0037] Example 1: A marine drive unit (110) comprising a hydraulic system (130), the hydraulic system (130) comprising a hydraulic tilt actuator (450) operable to move (310) a propeller arrangement (115) of the drive unit (110) from a position in water (200) to a position (300) above water, and a hydraulic steering actuator (430) operable to adjust an azimuth thrust angle (ωz) of the propeller arrangement (115),

[0038] the hydraulic system (130) comprising a first hydraulic pump (410) connected via a hydraulic valve arrangement (510) to the tilt actuator (450) and to the steering actuator (430),

[0039] where the hydraulic system (130) is arranged to prioritize control of the steering actuator (430) over control of the tilt actuator (450) by the hydraulic valve arrangement (510).

[0040] Example 2: The marine drive unit (110) according to example 1, where the valve arrangement (510) comprises a hydraulic selector valve arranged to be controlled by a control unit (120) of the marine drive unit (110) to prioritize control of the steering actuator (430) over control of the tilt actuator (450).

[0041] Example 3: The marine drive unit (110) according to example 2, where the hydraulic selector valve is arranged to default to a state where the steering actuator (430) is connected to the first hydraulic pump in case of malfunction.

[0042] Example 4: The marine drive unit (110) according to example 1 or 2, where the valve arrangement (510) comprises a hydraulic priority valve arranged to prioritize control of the steering actuator (430) over control of the tilt actuator (450).

[0043] Example 5: The marine drive unit (110) according to example 4, where the hydraulic system (130) is configurable in a nominal mode of operation and in a de-rated mode of operation, where the hydraulic system (130) is arranged to decrease a maximum hydraulic flow of the steering actuator (430) when in the de-rated mode of operation.

[0044] Example 6: The marine drive unit (110) according to example 5, where the hydraulic system (130) is arranged to decrease a maximum hydraulic flow of the tilt actuator (450) when in the de-rated mode of operation.

[0045] Example 7: The marine drive unit (110) according to example 5 or 6, where the de-rated mode of operation is associated with a reduced draught of the propeller arrangement (115).

[0046] Example 8: The marine drive unit (110) according to any previous examples, where the hydraulic system (130) further comprises a second hydraulic pump (420) connected to a hydraulic trim actuator (440) of the drive unit (110), where the trim actuator is operable to adjust an elevation thrust angle (ωy,Tx) of the propeller arrangement (115).

[0047] Example 9: The marine drive unit (110) according to example 8, where the tilt actuator (450) is operable to rotate the drive unit (110) about a first pivot axis (y1) and where the trim actuator (440) is operable to rotate the drive unit (110) about a second pivot axis (y2) spatially offset from the first pivot axis (y1).

[0048] Example 10: The marine drive unit (110) according to example 9, where an operating pressure of the first hydraulic pump (410) is different compared to an operating pressure of the second hydraulic pump (420).

[0049] Example 11: The marine drive unit (110) according to any of examples 8-10, arranged to decrease a hydraulic flow of the first hydraulic pump (410) and / or of the second hydraulic pump (420) below a respective nominal hydraulic flow when both the steering actuator (430) and the trim actuator (440) are used simultaneously.

[0050] Example 12: The marine drive unit (110) according to any of examples 8-11, where the flow rate and flow direction of the hydraulic steering actuator (430) and of the hydraulic trim actuator (440) are independently controllable.

[0051] Examples 13: The marine drive unit (110) according to any of examples 8-12, comprising a controllable back-up connection (520) between the second hydraulic pump (420) and the steering actuator (430) operable to power the steering actuator (430) in case of malfunction by the first hydraulic pump (410).

[0052] Example 14: The marine drive unit (110) according to any previous example, comprising an electric machine (140) arranged to power the propeller arrangement (115).

[0053] Example 15: The marine drive unit (110) according to any previous example, where the propeller arrangement (115) comprises one or more propellers.

[0054] Example 16: The marine drive unit (110) according to example 15, wherein the one or more propellers are configured to push the marine vessel in a forward motion of the marine vessel.

[0055] Example 17: The marine drive unit (110) according to example 15, wherein the one or more propellers are configured to pull the marine vessel in a forward motion of the marine vessel.

[0056] Example 18: The marine drive unit (110) according to any of the examples 15-17, wherein the propeller arrangement (115) comprises a first propeller and a second propeller.

[0057] Example 19: The marine drive unit (110) according to example 18, wherein the first propeller is arranged to be counter-rotating compared to the second propeller.

[0058] Example 20: The marine drive unit (110) according to any of the examples 15-19, wherein the one or more propellers comprises an angle of thrust.

[0059] Example 21: The marine drive unit (110) according to example 9, where the first pivot axis has a first pivot joint and the second pivot axis has a second pivot joint, a connecting arm is arranged between the first pivot joint and the second pivot joint.

[0060] Example 22: A marine vessel (100) comprising a drive unit (110) according to any previous example.

[0061] Example 23: A method for securing steering of a marine drive unit (110) according to any of the examples 1-21, comprising

[0062] providing a hydraulic system (130), the hydraulic system (130) comprising a hydraulic tilt actuator (450) operable to move (310) a propeller arrangement (115) of the drive unit (110) from a position in water (200) to a position (300) above water, and a hydraulic steering actuator (430) operable to adjust an azimuth thrust angle (ωz) of the propeller arrangement (115), the hydraulic system (130) comprising a first hydraulic pump (410) connected via a hydraulic valve arrangement (510) to the tilt actuator (450) and to the steering actuator (430),

[0063] controlling the hydraulic system (130) to prioritize control of the steering actuator (430) over control of the tilt actuator (450) by the hydraulic valve arrangement (510).

[0064] Example 24: The method according to example 23, further comprising providing a hydraulic selector valve,

[0065] arranging the hydraulic selector valve to be controlled by a control unit (120) of the marine drive unit (110) to prioritize control of the steering actuator (430) over control of the tilt actuator (450).

[0066] Example 25: The method according to example 24, further comprising arranging the hydraulic selector valve to default to a state where the steering actuator (430) is connected to the first hydraulic pump in case of malfunction.

[0067] Example 26: The method according to example 23 or 24, further comprising arranging a hydraulic priority valve to prioritize control of the steering actuator (430) over control of the tilt actuator (450).

[0068] Example 27: The method according to example 26, whereby configuring the hydraulic system (130) in a nominal mode of operation and in a de-rated mode of operation, arranging the hydraulic system (130) to decrease a maximum hydraulic flow of the steering actuator (430) when in the de-rated mode of operation.

[0069] Example 28: The method according to example 27, further comprising arranging the hydraulic system (130) to decrease a maximum hydraulic flow of the tilt actuator (450) when in the de-rated mode of operation.

[0070] Example 29: The method according to example 27 or 28, where the de-rated mode of operation is associated with a reduced draught of the propeller arrangement (115).

[0071] The terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a,”“an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items. It will be further understood that the terms “comprises,”“comprising,”“includes,” and / or “including” when used herein specify the presence of stated features, integers, actions, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, actions, steps, operations, elements, components, and / or groups thereof.

[0072] It will be understood that, although the terms first, second, etc., may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element without departing from the scope of the present disclosure.

[0073] Relative terms such as “below” or “above” or “upper” or “lower” or “horizontal” or “vertical” may be used herein to describe a relationship of one element to another element as illustrated in the Figures. It will be understood that these terms and those discussed above are intended to encompass different orientations of the device in addition to the orientation depicted in the Figures. It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element, or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present.

[0074] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having a meaning consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0075] It is to be understood that the present disclosure is not limited to the aspects described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the present disclosure and appended claims. In the drawings and specification, there have been disclosed aspects for purposes of illustration only and not for purposes of limitation, the scope of the disclosure being set forth in the following claims.

Claims

1. A marine drive unit comprising a hydraulic system, the hydraulic system comprising a hydraulic tilt actuator operable to move a propeller arrangement of the drive unit from a position in water to a position above water, and a hydraulic steering actuator operable to adjust an azimuth thrust angle of the propeller arrangement,the hydraulic system comprising a first hydraulic pump connected via a hydraulic valve arrangement to the tilt actuator and to the steering actuator,the hydraulic system further comprises a second hydraulic pump connected to a hydraulic trim actuator of the drive unit, where the trim actuator is operable to adjust an elevation thrust angle of the propeller arrangement,where the hydraulic system is arranged to prioritize control of the steering actuator over control of the tilt actuator by the hydraulic valve arrangement,where the valve arrangement comprises a hydraulic priority valve arranged to prioritize control of the steering actuator over control of the tilt actuator,where the hydraulic system is arranged to decrease a hydraulic flow of the first hydraulic pump and / or of the second hydraulic pump below a respective nominal hydraulic flow when both the steering actuator and the trim actuator are used simultaneously.

2. The marine drive unit according to claim 1, where the valve arrangement comprises a hydraulic selector valve arranged to be controlled by a control unit of the marine drive unit to prioritize control of the steering actuator over control of the tilt actuator.

3. The marine drive unit according to claim 2, where the hydraulic selector valve is arranged to default to a state where the steering actuator is connected to the first hydraulic pump in case of malfunction.

4. (canceled)5. The marine drive unit according to claim 1, where the hydraulic system is configurable in a nominal mode of operation and in a de-rated mode of operation, where the hydraulic system is arranged to decrease a maximum hydraulic flow of the steering actuator when in the de-rated mode of operation.

6. The marine drive unit according to claim 5, where the hydraulic system is arranged to decrease a maximum hydraulic flow of the tilt actuator when in the de-rated mode of operation.

7. The marine drive unit according to claim 5, where the de-rated mode of operation is associated with a reduced draught of the propeller arrangement.

8. (canceled)9. The marine drive unit according to claim 1, where the tilt actuator is operable to rotate the drive unit about a first pivot axis and where the trim actuator is operable to rotate the drive unit about a second pivot axis spatially offset from the first pivot axis.

10. The marine drive unit according to claim 9, where an operating pressure of the first hydraulic pump is different compared to an operating pressure of the second hydraulic pump.

11. (canceled)12. The marine drive unit according to claim 1, where the flow rate and flow direction of the hydraulic steering actuator and of the hydraulic trim actuator are independently controllable.

13. The marine drive unit according to claim 1, comprising a controllable back-up connection between the second hydraulic pump and the steering actuator operable to power the steering actuator in case of malfunction by the first hydraulic pump.

14. The marine drive unit according to previous claim 1, comprising an electric machine arranged to power the propeller arrangement.

15. A marine vessel comprising a drive unit according to claim 1.

16. A method for securing steering of a marine drive unit according to claim 1, comprisingproviding a hydraulic system, the hydraulic system comprising a hydraulic tilt actuator operable to move a propeller arrangement of the drive unit from a position in water to a position above water, and a hydraulic steering actuator operable to adjust an azimuth thrust angle of the propeller arrangement, the hydraulic system comprising a first hydraulic pump connected via a hydraulic valve arrangement to the tilt actuator and to the steering actuator,the hydraulic system further comprises a second hydraulic pump connected to a hydraulic trim actuator of the drive unit, where the trim actuator is operable to adjust an elevation thrust angle of the propeller arrangement,controlling the hydraulic system to prioritize control of the steering actuator over control of the tilt actuator by the hydraulic valve arrangement,arranging a hydraulic priority valve to prioritize control of the steering actuator over control of the tilt actuator,decreasing a hydraulic flow of the first hydraulic pump and / or of the second hydraulic pump below a respective nominal hydraulic flow when both the steering actuator and the trim actuator are used simultaneously.

17. The method according to claim 16, further comprising providing a hydraulic selector valve,arranging the hydraulic selector valve to be controlled by a control unit of the marine drive unit to prioritize control of the steering actuator over control of the tilt actuator.

18. The method according to claim 17, further comprising arranging the hydraulic selector valve to default to a state where the steering actuator is connected to the first hydraulic pump in case of malfunction.

19. The method according to any of claims 16, whereby configuring the hydraulic system in a nominal mode of operation and in a de-rated mode of operation, arranging the hydraulic system to decrease a maximum hydraulic flow of the steering actuator when in the de-rated mode of operation.

20. The method according to claim 19, further comprising arranging the hydraulic system to decrease a maximum hydraulic flow of the tilt actuator when in the de-rated mode of operation.

21. The method according to claim 19, where the de-rated mode of operation is associated with a reduced draught of the propeller arrangement.

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