Drive systems for ship propulsion

Abstract

The aim is to prevent excessive fuel or electricity supply while appropriately controlling the ship's speed, thereby saving energy and reducing costs during navigation. [Solution] This ship propulsion drive system 10 comprises a ship propulsion engine 11 mounted on a ship 1 and a control unit 14 that controls the speed of the engine 11. The control unit 14 reduces the output of the engine 11 when an external load of a predetermined magnitude or greater acts on the main shaft 11a of the engine 11.

Description

Technical Field

[0001] The present invention relates to a marine vessel propulsion drive device, and more particularly to a technique for achieving speed control of a marine vessel by controlling the output of a prime mover for marine vessel propulsion.

Background Art

[0002] For example, the rotational speed of a diesel engine mounted on a marine vessel as a prime mover (main engine) for marine vessel propulsion is controlled to a constant value by controlling a governor that adjusts the amount of fuel supplied to the diesel engine. It is known that the speed of a marine vessel is generally proportional to the rotational speed of the prime mover serving as the main engine. Therefore, by controlling the rotational speed of the prime mover to a constant value as described above, the speed of the marine vessel can be controlled to a predetermined value (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Incidentally, for large vessels such as tankers, the amount of fuel consumed during long voyages is enormous, and it is easy to imagine that fuel costs will be enormous. Therefore, in these types of vessels, it is crucial to reduce fuel costs by minimizing wasteful fuel consumption. For example, when a ship encounters significant resistance during navigation due to large waves from the front, strong headwinds, or strong currents, the rotational speed of the main engine may drop sharply, causing a significant decrease in the ship's speed. In such cases, the main engine control unit will send a command to increase the output of the main engine in order to quickly restore the ship's speed, and an amount of fuel corresponding to the increase in output will be supplied. However, supplying excessive fuel leads to the consumption of wasted fuel that does not contribute to combustion, and not only is it unlikely that the speed will be restored in proportion to the amount of fuel supplied, but there is a high risk of wasting fuel.

[0005] The problems described above are not limited to engines that use fuel as an energy source; they can also occur when, for example, an electric motor that uses electricity as an energy source is used as the prime mover (main engine) for ship propulsion. When this type of electric motor is driven by electricity supplied from a generator, the control unit controls the rotational speed of the motor by controlling the frequency of the generator. Therefore, if the rotational speed of the motor drops sharply due to the ship experiencing significant resistance from waves, the motor's control unit will continue to control the generator's frequency using the frequency value just before the drop in rotational speed as the command value. However, when experiencing significant resistance from waves, an increase in rotational speed commensurate with the command value cannot be expected, and there is a high risk that much of the supplied electricity will be wasted.

[0006] In light of the above circumstances, this specification aims to address the technical challenge of enabling appropriate control of a vessel's speed while preventing excessive fuel or electricity supply as much as possible, thereby achieving energy conservation and cost reduction during navigation. [Means for solving the problem]

[0007] The aforementioned problem is solved by the ship propulsion drive device according to the present invention. Specifically, this ship propulsion drive device comprises a ship propulsion prime mover mounted on a ship and a control unit that controls the output of the prime mover, wherein the control unit reduces the output of the prime mover when an external load of a predetermined magnitude or greater acts on the main shaft of the prime mover.

[0008] Thus, in the ship propulsion drive system according to the present invention, when an external load exceeding a predetermined size acts on the main shaft of the prime mover due to headwinds or other resistance, it is anticipated that energy supplied to the prime mover will be wasted. In conventional control systems, the output of the prime mover is increased to quickly recover the significantly reduced speed. However, in the present invention, the output of the prime mover is deliberately reduced. By reducing the output of the prime mover in this way, the sudden increase in energy supply that occurred immediately after a significant decrease in the ship's speed can be suppressed. As a result, the amount of energy consumed by the prime mover is reduced, thus avoiding the situation where some of the energy supplied to the prime mover is wasted, and improving fuel efficiency and, consequently, reducing energy costs. Of course, when the external load acting on the main shaft of the prime mover decreases to below a predetermined size, such as when the ship is freed from resistance such as headwinds or other resistance, the output can be returned to its original size to quickly recover the ship's speed. Therefore, when viewed over a long period such as a voyage, it is possible to sail the ship at a generally constant speed.

[0009] Furthermore, the ship propulsion drive system according to the present invention may further include an electric motor configured to provide rotational driving force to the main shaft of the prime mover. In this case, the control unit may reduce the output of the prime mover by reducing the output of the electric motor when an external load of a predetermined size or larger is applied to the main shaft.

[0010] Thus, when a ship's propulsion system includes, in addition to the main engine, an electric motor configured to provide rotational driving force to the main shaft of the main engine, the final output of the main engine is the sum of the output of the main engine itself and the output of the electric motor that provides rotational driving force to the main shaft of the main engine. Normally, in electric motors capable of assisting this type of main engine, the frequency is controlled to be constant, so the output assisting the main engine is also controlled to a constant magnitude. In this respect, the present invention reduces the output (assist force) from the electric motor to the main shaft, which was conventionally constant, when an external load exceeding a predetermined magnitude acts on the main shaft of the main engine due to headwinds or other factors. This reduces the final output of the main engine, thus preventing or suppressing, as much as possible, the wasteful consumption of electrical energy supplied to the electric motor immediately after a significant decrease in the ship's speed. Therefore, this configuration makes it possible to improve fuel efficiency and, consequently, reduce power generation costs. Of course, it is also possible to further reduce the final output of the main engine by reducing the output of the electric motor and the output of the main engine itself.

[0011] Furthermore, in the ship propulsion drive system according to the present invention, the prime mover has a propeller with a variable blade angle on the main shaft, and the control unit may reduce the output of the prime mover by reducing the blade angle of the propeller when an external load of a predetermined size or more acts on the main shaft.

[0012] Typically, a propeller is mounted on the main shaft of a ship's propulsion engine to generate thrust. These propellers are broadly classified into two types: fixed-pitch propellers (FPP), where the angle of the propeller blades (wing angle) is fixed, meaning the thrust distance per revolution (pitch) is fixed to a constant size; and variable-pitch propellers (CPP), where the wing angle is variable, meaning the pitch can be changed. In the case of a variable-pitch propeller, the relationship between rotational speed and output changes depending on the size of the wing angle. For example, the larger the wing angle, the greater the corresponding output at the same rotational speed, increasing the ship's speed. Conversely, the smaller the wing angle, the less the corresponding output at the same rotational speed, decreasing the ship's speed. In this configuration, when an external load exceeding a predetermined size acts on the main shaft, the propeller's wing angle is reduced to decrease the engine's output, making it easy and accurate to adjust the engine's output in a downward direction. This avoids a situation where the amount of fuel or electricity supplied increases in proportion to the decrease in the ship's speed, thus suppressing the increase in fuel or electricity supply compared to conventional systems. Therefore, it becomes possible to avoid situations where some of the fuel or electricity supplied to the prime mover is wasted, thereby improving fuel efficiency and ultimately reducing fuel costs. Of course, by reducing the wing angle and lowering the rotational speed of the prime mover, it is also possible to further reduce the final output of the prime mover.

[0013] Furthermore, the ship propulsion drive system according to the present invention may further include a state detection unit for detecting the state of the ship in relation to waves. In this case, if an external load of a predetermined magnitude or greater is acting on the main shaft and the state detection unit detects that the ship is going up a wave, the control unit may maintain a state in which the output of the prime mover is reduced compared to the magnitude immediately before the detection of going up a wave while the ship is going up a wave.

[0014] By providing a condition detection unit that detects the state of the ship in relation to waves, it is possible to detect when the ship is being affected by waves (especially headwinds) and is going up the waves. When going up large waves, especially when an external load of a certain size or larger is acting on the main shaft, an increase in rotational speed commensurate with the increase in fuel supply cannot be expected. Therefore, during such conditions (while going up the waves), maintaining the output of the prime mover at a reduced level compared to the level just before detecting that the ship is going up the waves makes it possible to more reliably and effectively reduce wasted fuel consumption. Similarly, when an electric motor is also provided to assist the output of the prime mover, maintaining the output of the electric motor at a reduced level compared to the level just before detecting that the ship is going up the waves makes it possible to more reliably and effectively reduce wasted power consumption.

[0015] Furthermore, in the ship propulsion drive system according to the present invention, when control is performed to maintain a state in which the output of the prime mover is reduced while the ship is going up a wave, the state in which the output of the prime mover is reduced may be maintained within a range in which the ship can continue to move forward.

[0016] When sailing up a wave, reducing the engine's output can increase fuel savings. However, reducing the output too much can require a significant amount of time to recover the engine's output (and consequently the ship's speed), or in the worst case, the ship may stop, leading to a decrease in fuel efficiency. In light of this, it is preferable to set the lower limit of the engine's output (and the corresponding lower limit of its rotational speed) within a range that allows the ship to continue moving forward, and moreover, so as not to fall below a predetermined minimum cruising speed (and the corresponding rotational speed).

[0017] Furthermore, in the ship propulsion drive system according to the present invention, when performing control to maintain a state in which the output of the prime mover is reduced while the ship is going up a wave, the control unit may, when it detects that the ship is going down a wave using the state detection unit, maintain a state in which the output of the prime mover is increased compared to the magnitude while going up a wave while the ship is going down a wave.

[0018] When a ship is sailing down a wave, it is easier to increase the output of the main engine (prime motor) and, consequently, the ship's speed, compared to sailing up a wave, and even compared to normal sailing (when not sailing up or down a wave). This configuration was made in consideration of this point, and by maintaining a state in which the prime motor's output is increased compared to when sailing up a wave while sailing down a wave, the prime motor's output and, consequently, the ship's speed can be efficiently and quickly returned to the value before sailing up a wave. Therefore, it is possible to improve fuel efficiency while enjoying a good fuel reduction effect. Even when an electric motor is further equipped to assist the prime motor's output, by maintaining a state in which the electric motor's output is increased compared to when sailing up a wave while sailing down a wave, the prime motor's output and, consequently, the ship's speed can be efficiently and quickly returned to the value before sailing up a wave, making it possible to improve fuel efficiency while enjoying a good power reduction effect.

[0019] Furthermore, if the ship propulsion drive system according to the present invention further includes a state detection unit, the state detection unit may be composed of a state detection device that detects the attitude of the ship.

[0020] By configuring the state detection unit in this way, it is possible to determine the tilt of the ship, reliably determine whether the ship is going upwind or downwind, and execute output control appropriate to each state.

[0021] Alternatively, if the ship propulsion drive device according to the present invention further includes a state detection unit, the state detection unit may be composed of an acceleration detection device that detects the vertical acceleration of the bow side of the ship.

[0022] By configuring the state detection unit in this way, it is possible to reliably determine whether the ship is going up or down a wave. Furthermore, by evaluating the magnitude of acceleration, the wave size can be determined as early as possible, making it possible to quickly switch to a control mode appropriate for each state. [Effects of the Invention]

[0023] As described above, according to the marine propulsion drive device of the present invention, it is possible to appropriately control the rotational speed while preventing the supply of excess fuel or electric power as much as possible, so that energy saving during navigation and consequently suppression of fuel costs can be achieved. [BRIEF DESCRIPTION OF THE DRAWINGS]

[0024] [Figure 1] This is a schematic configuration diagram of the marine propulsion drive device according to the first embodiment of the present invention. [Figure 2] This is a flowchart related to the main part of the speed control method using the marine propulsion drive device shown in Figure 1. [Figure 3] This is a graph showing the variation mode of the rotational speed when control is performed based on the control method shown in Figure 2. [Figure 4] This is a graph showing the variation mode of the difference coefficient when control is performed based on the control method shown in Figure 2. [Figure 5] This is a graph showing the variation mode of the output of the prime mover when control is performed based on the control method shown in Figure 2, at (a) the transition from period P1 to period P2, and (b) the transition from period P2 to period P3. [Figure 6] (a) is a diagram conceptually showing a state where the vessel is climbing a wave, and (b) is a diagram conceptually showing a state where the vessel is descending a wave. [Figure 7] This is a schematic configuration diagram of the marine propulsion drive device according to the second embodiment of the present invention. [Figure 8] This is a flowchart related to the main part of the speed control method using the marine propulsion drive device shown in Figure 7. [Figure 9] This is a graph showing the variation mode of the output when control is performed based on the control method shown in Figure 8. [Figure 10] This is a schematic configuration diagram of the marine propulsion drive device according to the third embodiment of the present invention. [Figure 11] This is a flowchart related to the main part of the speed control method using the marine propulsion drive device shown in Figure 10. [Modes for carrying out the invention]

[0025] The contents of the ship propulsion drive device according to the first embodiment of the present invention will be described below with reference to the drawings.

[0026] Figure 1 shows a schematic configuration diagram of a ship propulsion drive unit 10 according to the first embodiment of the present invention. As shown in Figure 1, this ship propulsion drive unit 10 is used as the main engine for ship propulsion mounted on a ship 1 and is equipped with a speed control system for the ship 1. Specifically, this ship propulsion drive unit 10 comprises a prime mover 11, a control unit 12 for controlling the output A of the prime mover 11, an electric motor 13 configured to apply rotational driving force to the main shaft 11a of the prime mover 11, and a power supply device 14 for supplying power to the electric motor 13. In this embodiment, the ship propulsion drive unit 10 further comprises a rotation speed measuring unit 15 for measuring the actual rotation speed n1 of the prime mover 11, a governor 16 for adjusting the amount of fuel supplied to the prime mover 11, and a state detection unit 17 for detecting the state of the ship 1 in relation to waves. The details of each element of the ship propulsion drive unit 10 will be described below, followed by a detailed explanation of the speed control method of the ship propulsion drive unit 10.

[0027] In this embodiment, the prime mover 11 is a combustion engine such as a diesel engine, and it can provide thrust to the ship 1 by rotating a propeller 18 attached to the tip of the main shaft 11a, which serves as the rotating axis. In this embodiment, the propeller 18 is a propeller of the type with a fixed blade angle (a so-called fixed-pitch propeller), and the amount of thrust per rotation of the propeller 18 is fixed at a certain distance. In this illustrated example, the ship propulsion drive system 10 is shown as being composed of one prime mover 11, but the ship propulsion drive system 10 may be composed of two or more prime movers 11.

[0028] The electric motor 13 is connected to the main shaft 11a (main shaft) of the prime mover 11, for example, as shown in Figure 1. In this case, the rotational drive shaft of the electric motor 13 is made rotatable together with the main shaft 11a of the prime mover 11. The rotational speed and output A2 of the electric motor 13 can be controlled separately and independently by the control unit 12, which will be described later.

[0029] Note that the power transmission configuration of the electric motor 13 to the main shaft 11a is not limited to that shown in Figure 1. For example, although not shown in the figure, the electric motor 13 may be connected to the main shaft 11a of the prime mover 11 via a reduction gear. In this case, it is not necessary for the rotational speed n1 of the prime mover 11 and the rotational speed of the electric motor 13 to match, and their rotational speeds can be set independently of each other.

[0030] The power supply device 14 is capable of supplying power to the electric motor 13, and for example, although not shown in the diagram, it consists of a generator and a prime mover to drive the generator. Of course, the above-described configuration of the power supply device 14 is just one example. For example, although not shown in the diagram, the power supply device 14 may also be configured with energy storage devices such as batteries or capacitors.

[0031] The rotational speed measurement unit 15 is capable of directly or indirectly measuring the rotational speed n1 of the prime mover 11. In this embodiment, it is configured to measure the rotational speed n1 of the main shaft 11a of the prime mover 11 at predetermined time intervals. The applicable measurement means are arbitrary, and known means can be used.

[0032] The data regarding the rotational speed n1 of the prime mover 11, measured by the rotational speed measurement unit 15, is transmitted to the control unit 12.

[0033] The state detection unit 17 is for detecting the state of the ship 1 in relation to the wave W (see Figure 6). In this embodiment, for example, it is composed of an attitude detection device that detects the attitude of the ship 1 at predetermined time intervals (and, for example, at the same timing as the rotation speed measurement unit 15). The detection means is arbitrary as long as it can detect the state of the ship 1 in relation to the wave W (whether it is going up the wave W or down the wave W). For example, although not shown in the figure, the state detection unit 17 may be configured with an acceleration detection device that detects the vertical acceleration of the bow side of the ship 1, in addition to or instead of the attitude detection device.

[0034] The data regarding the state of the ship 1 in relation to the wave W detected by the state detection unit 17 is transmitted to the control unit 12, similar to the data regarding the rotation speed n1.

[0035] The control unit 12 is configured to control the drive of the prime mover 11 and also to control the drive of the electric motor 13. The details of each drive control mode are described below.

[0036] The control unit 12 is configured to control the output A of the prime mover 11 (more precisely, the standalone output A1 of the prime mover 11) by operating the governor 16 to control the rotational speed n1 of the prime mover 11. Specifically, the control unit 12 controls the rotational speed n1 of the prime mover 11 by adjusting the amount of fuel supplied to the prime mover 11 through the governor 16. As long as proportional control (electronic control) of the rotational speed n1 through the operation of the governor 16, as described later, is possible, known types of governors such as mechanical governors, hydraulic governors, and electric governors can be used as the governor 16 that the control unit 12 operates.

[0037] Furthermore, the control unit 12 has two or more different control modes for controlling the rotational speed n1 of the prime mover 11, and is configured to selectively select one of the two or more control modes according to the magnitude of the external load acting on the spindle 11a of the prime mover 11 to perform proportional control of the rotational speed n1. In this embodiment, the control unit 12 evaluates the magnitude of the external load acting on the spindle 11a based on the magnitude of the difference e (here, e = n2 - n1) between the rotational speed n1 of the prime mover 11 measured by the rotational speed measurement unit 15 and the target rotational speed n2 of the prime mover 11, which is set in advance. If the difference e is less than a predetermined positive value (hereinafter referred to as threshold T), the control unit 12 considers that the external load acting on the spindle 11a is less than the predetermined magnitude, and is configured to perform proportional control of the rotational speed n1 with respect to a constant target rotational speed n2 while maintaining the coefficient of the difference e at a predetermined value (here, the first set value K1) (first control mode).

[0038] On the other hand, if the difference e between the rotational speed n1 and the target rotational speed n2 is greater than or equal to a threshold T, the control unit 12 considers that the external load acting on the spindle 11a is greater than or equal to a predetermined magnitude, and is configured to perform proportional control of the rotational speed n1 with respect to a constant target rotational speed n2, with the coefficient of the difference e reduced by a predetermined amount from the previous value (for example, the first setting value K1), that is, with the coefficient of the difference e set to a second setting value K2 which is a predetermined amount smaller than the first setting value K1 (second control mode).

[0039] In this embodiment, in addition to when the difference e becomes greater than or equal to the threshold T, when the state detection unit 17 detects that the ship 1 is going up the wave W (see Figure 6(a)), the control unit 12 is configured to perform proportional control of the rotation speed n1 with the coefficient of the difference e reduced by a predetermined amount from the value immediately before detecting that the ship was going up the wave W (the coefficient of the difference e is set to the second set value K2). Further details will be described later.

[0040] Furthermore, in this embodiment, when the state detection unit 17 detects that the ship 1 is going down the wave W (see Figure 6(b)), the control unit 12 is configured to perform proportional control of the rotational speed n1 with respect to a constant target rotational speed n2, with the coefficient of difference e increased by a predetermined amount from the previous value (here, for example, the second setting value K2), that is, with the coefficient of difference e set to a third setting value K3 which is a predetermined amount larger than the second setting value K2 (third control mode).

[0041] Furthermore, proportional control in each control mode controls the rotational speed n1 toward the target rotational speed n2 by using a manipulated variable proportional to the difference e as a command value to the governor 16. Of course, it is also possible to control the rotational speed n1 toward the target rotational speed n2 by using a manipulated variable calculated from an equation that further includes not only a linear term of the difference e, but also a time integral term of the difference e, or both a time integral term and a time derivative term of the difference e, as a command value to the governor 16.

[0042] Secondly, the control unit 12 is configured to control the rotational speed, i.e., frequency, of the electric motor 13, as well as the output A2 (in watts [W]) of the electric motor 13. Regarding the rotational speed of the electric motor 13, the control unit 12 controls the frequency of the electric motor 13 to a predetermined magnitude so that it matches as closely as possible with the rotational speed n1 of the prime mover 11.

[0043] On the other hand, the control unit 12 has two or more different control modes with respect to the output A2 of the electric motor 13, and is configured to selectively select one of the two or more control modes according to the magnitude of the external load acting on the rotational drive shaft of the electric motor 13 through the main shaft 11a of the prime mover 11 to control the output A2.

[0044] More specifically, the control unit 12 evaluates the magnitude of the external load acting on the main shaft 11a based on the magnitude of the difference e between the rotational speed n1 of the prime mover 11 measured by the rotational speed measurement unit 15 and the preset target rotational speed n2 of the prime mover 11. If the difference e is less than a preset threshold T, the control unit 12 is configured to maintain the output A2 of the electric motor 13 at a predetermined magnitude (in this case, for example, the first set value A21 as the output set value during normal operation) as the external load acting on the main shaft 11a being less than a predetermined magnitude (first control mode).

[0045] On the other hand, if the difference e between the rotational speed n1 and the target rotational speed n2 becomes greater than or equal to a threshold T, the control unit 12 considers that the external load acting on the spindle 11a is greater than or equal to a predetermined magnitude, and is configured to maintain the output A2 of the electric motor 13 at a second setpoint A22, which is a predetermined amount smaller than the first setpoint A21, by a predetermined amount (second control mode).

[0046] In this embodiment, in addition to when the difference e becomes greater than or equal to the threshold T, when the state detection unit 17 detects that the ship 1 is going up the wave W (see Figure 6(a)), the control unit 12 is configured to maintain the output A2 of the electric motor 13 at a predetermined level, lowered by a predetermined amount from the value immediately before detecting that the ship was going up the wave W (the output A2 is set to the second set value A22). Further details will be described later.

[0047] Furthermore, in this embodiment, when the state detection unit 17 detects that the ship 1 is sailing down waves W (see Figure 6(b)), the control unit 12 is configured to maintain the output A2 of the electric motor 13 at a predetermined level, increased by a predetermined amount from the previous value (for example, the second setting value A22), that is, at a third setting value A23, which is a predetermined amount greater than the second setting value A22 (third control mode).

[0048] Below, an example of a speed control method for the ship propulsion drive unit 10 with the above configuration will be explained, mainly based on Figures 2 to 6.

[0049] Figure 2 shows a flowchart illustrating an example of a method for controlling the speed of a ship 1 using a ship propulsion drive unit 10. As shown in this flowchart, when the ship 1 is in motion, the control unit 12 receives data on the rotational speed n1 of the prime mover 11 measured by the rotational speed measurement unit 15, calculates the difference e between the rotational speed n1 related to the received data and a preset target rotational speed n2 (step S1 in Figure 2), and determines whether the value of this difference e is greater than or equal to a threshold T (step S2 in Figure 2).

[0050] Then, if the calculated difference e is determined to be less than or equal to the threshold T, the control unit 12 further determines whether the ship 1 is going down the wave W based on the data regarding the state of the ship 1 with respect to the wave W detected by the state detection unit 17 at the same time (step S3 in Figure 2). For example, if the state detection unit 17 is capable of detecting the tilt angle θ with respect to the horizontal direction as a positive value when the bow side is positioned higher than the stern side, the control unit 12 determines that the ship 1 is going up the wave W if the tilt angle θ exceeds a predetermined positive value (see Figure 6(a)). Alternatively, if the tilt angle θ falls below a predetermined negative value, the control unit 12 determines that the ship 1 is going down the wave W (see Figure 6(b)).

[0051] Then, if the control unit 12 determines, based on the above criteria, that the ship 1 is not sailing down waves W, the control unit 12 performs proportional control of the rotational speed n1 to a constant target rotational speed n2 with the coefficient of difference e set to the first set value K1 for the prime mover 11 (see step S4 in Figure 2 and period P1 in Figure 4, respectively). The control unit 12 also controls the electric motor 13 to maintain its output A2 at the first set value A21 (step S5 in Figure 2). In this case, it is presumed that the ship 1 is not experiencing significant resistance from waves W, wind, ocean currents, etc. Therefore, during periods when the waves W are not very large, the processing is performed in the order of steps S1 to S5 above based on the data related to the rotational speed n1 and the attitude of the ship 1 measured at predetermined time intervals. As a result, proportional control of the rotational speed n1 with the coefficient of difference e set to the first set value K1 is continuously performed, and the output A2 of the electric motor 13 is maintained at the first set value A21. In this case, the output A of the prime mover 11 is maintained at a magnitude equal to the sum of the output of the prime mover 11 alone (single output A11) and the output A2 of the electric motor 13 (here, the first set value A21) (see the output at rotational speed n1 in Figure 5(a)).

[0052] On the other hand, when the waves W acting on the ship 1 reach a certain size, the value of the difference e calculated in step S1 also begins to increase in accordance with the increase in the external load acting on the prime mover 11. In such a situation, if the control unit 12 determines that the value of the difference e calculated in step S2 is greater than or equal to the threshold T, the control unit 12 further determines whether the ship 1 is going up the waves W based on the data regarding the state of the ship 1 with respect to the waves W detected by the state detection unit 17 at the same time (step S6 in Figure 2). For example, if the tilt angle θ of the ship 1 with respect to the horizontal attitude detected by the state detection unit 17 exceeds a predetermined positive value, it is determined that the ship 1 is going up the waves W (see Figure 6(a)).

[0053] If the control unit 12 determines, based on the above criteria, that the ship 1 is not going up the wave W, it performs proportional control of the rotational speed n1 of the prime mover 11 under the first setpoint K1 (step S4) and controls the output A2 of the electric motor 13 to the first setpoint A21 (step S5). On the other hand, if the control unit 12 determines, based on the above criteria, that the ship 1 is going up the wave W, it lowers the coefficient of the difference e from the previous value, the first setpoint K1, to the second setpoint K2, and performs proportional control of the rotational speed n1 with respect to a constant target rotational speed n2 (see step S7 in Figure 2 and period P2 in Figure 4, respectively). The control unit 12 also lowers the output A2 of the electric motor 13 from the previous value, the first setpoint A21, to the second setpoint A22 (see step S8 in Figure 2 and Figure 5(a)). Through the above control, the individual output A1 of the prime mover 11 remains substantially the same or slightly increased compared to the value A11 immediately before the change in control mode. On the other hand, the output A2 of the electric motor 13 may decrease significantly compared to the value A21 immediately before the control mode is changed (see Figure 5(a) for both). Therefore, the output A of the prime mover 11 decreases compared to immediately before the control mode is changed.

[0054] In this case, the second setting value K2 can, in principle, be set arbitrarily. On the other hand, when proportional control of the rotational speed n1 is performed with the coefficient of the difference e reduced to the second setting value K2, it is presumed that the ship 1 is going up a large wave W, making it difficult for the rotational speed n1 to increase. Alternatively, it is presumed that the rotational speed n1 will further decrease even after proportional control under the second setting value K2 is started due to the large resistance caused by the wave W. From this perspective, it is preferable to set the magnitude of the second setting value K2 within a range in which the ship 1 can continue to move forward, preferably within a range that does not fall below the predetermined minimum cruising speed (corresponding rotational speed), and more preferably within a range that does not fall below the rotational speed n1 at the time proportional control under the second setting value K2 is started. The same applies to the modified output of the electric motor 13 (second setting value A22). Figure 3 illustrates the case where the magnitude of the second setting value K2 is set so that the rotational speed n1 at the time proportional control under the second setting value K2 is started is maintained or slightly increased (see period P2 in Figure 3).

[0055] The control described above (proportional control of rotational speed n1 with the coefficient of difference e set to the second set value K2, and control of the output A2 of the electric motor 13 with the second set value A22) continues after the start of the control until it is determined that the value of difference e, which is calculated at predetermined time intervals, is less than the threshold T, or until it is determined that the wave W is not being raised.

[0056] On the other hand, if the difference e is determined to be less than the threshold T, the control unit 12 determines whether or not the vessel 1 is going down the wave W based on the data regarding the state of the vessel 1 with respect to the wave W detected by the state detection unit 17 (step S3 in Figure 2). If the control unit 12 determines that the vessel 1 is going down the wave W based on the above criteria, it raises the coefficient of the difference e from the second set value K2, which is the value immediately before it was detected that the vessel 1 was going down the wave W, to the third set value K3, and performs proportional control of the rotational speed n1 with respect to a constant target rotational speed n2 (see step S9 in Figure 2 and period P3 in Figure 4, respectively). The control unit 12 also raises the output A2 of the motor 13 from the second set value A22, which is the value immediately before it was detected, to the third set value A23 (see step S10 in Figure 2 and Figure 5(b)). As a result of the above control, both the individual output A1 (A13) of the prime mover 11 and the output A2 (third setpoint A23) of the electric motor 13 increase compared to the values ​​A12 and A22 immediately before the control mode was changed (see Figure 5(b)).

[0057] In this case, the third setting value K3 can, in principle, be set arbitrarily. For example, it can be set to a value smaller than the first setting value K1 and larger than the second setting value K2. On the other hand, when proportional control of the rotational speed n1 is performed with the coefficient of the difference e set to the third setting value K3, it is presumed that the ship 1 is going down the wave W, and the rotational speed n1 is likely to increase. From this perspective, for example, it is best to set the rotational speed corresponding to the continuous maximum output of the prime mover 11 as the upper limit, and set the third setting value K3 to a value larger than the first setting value K1, within the range that does not exceed this upper limit. The same applies to the output A2 of the electric motor 13, where the third setting value A23 can, in principle, be set arbitrarily. Here, considering that the ship 1 is going down the wave W and the rotational speed n1 is likely to increase when the output A2 of the electric motor 13 is set to the third setting value A23, it is best to set the third setting value A23 to a value larger than the first setting value A21, within the range that does not exceed the maximum output of the electric motor 13. In this embodiment, the first setting value A21 is set to a value corresponding to the maximum output of the electric motor 13, and the third setting value A23 is set to the same value as the first setting value A21 (see Figures 5(a) and 5(b)).

[0058] The control described above (proportional control of rotational speed n1 with the coefficient of difference e set to the third setting value K3, and control of the output A2 of the electric motor 13 with the third setting value A23) continues after the start of the control until it is determined that the value of difference e calculated at predetermined time intervals is greater than or equal to the threshold T, or until it is determined that the wave W is not falling.

[0059] The series of control mode switching operations described above are repeatedly performed until the ship passes through an area with large waves W. Specifically, according to the ship propulsion drive device 10 of this embodiment, proportional control of the rotational speed n1 is performed, switching the coefficient of difference e between the second set value K2 and the third set value K3, from the moment the ship begins to receive waves W (head waves) of a size such that the difference e value is greater than or equal to the threshold T. At the same time, output control of the motor 13 is performed, switching the output A2 of the motor 13 between the second set value A22 and the third set value A23. Furthermore, from the point when the wave W has decreased in size to such that the difference e value is less than the threshold T, the control returns to proportional control with the coefficient of difference e constant (first set value K1) and output control with the output A2 of the motor 13 constant (first set value A21) (steps S1 to S5 in Figure 2 are repeatedly performed).

[0060] As described above, the ship propulsion drive system 10 according to this embodiment is further equipped with an electric motor 13 that is configured to provide rotational driving force as an assist force to the main shaft 11a of the prime mover 11, in addition to the prime mover 11 which is the main engine. Furthermore, when the difference e between the measured rotational speed n1 of the prime mover 11 and the target rotational speed n2 exceeds a threshold T, it is considered that an external load of a predetermined magnitude or greater is acting on the main shaft 11a of the prime mover 11, and the output A2 (assist force) to the main shaft 11a by the electric motor 13, which was conventionally constant, is reduced to decrease the final output A of the prime mover 11. As a result, it is possible to prevent or suppress as much as possible the wasteful consumption of electrical energy supplied to the electric motor 13 immediately after the speed of the ship 1 has decreased significantly. Accordingly, this configuration makes it possible to improve fuel efficiency and, consequently, reduce power generation costs.

[0061] Furthermore, in this embodiment, the magnitude of the external load acting on the spindle 11a is evaluated by the magnitude of the difference e between the rotational speed n1 of the prime mover 11 measured by the rotational speed measurement unit 15 and the preset target rotational speed n2 of the prime mover 11. If this difference e exceeds a preset threshold T, it is considered that an external load of a predetermined magnitude or greater has acted on the spindle 11a, and the coefficient of the difference e is reduced by a predetermined amount from the previous value (first setting value K1) to perform proportional control of the rotational speed n1, thereby reducing the rate at which the rotational speed n1 increases from the previous value (first setting value K1). By performing proportional control with the coefficient of the difference e changed to a value smaller than the previous value (second setting value K2), the situation in which the fuel supply amount increases by the amount that the rotational speed n1 decreases is avoided, and the increase in fuel supply amount is suppressed compared to the conventional method. Therefore, it is possible to avoid the situation in which a portion of the fuel supplied to the combustion chamber is wasted, and to reduce fuel costs. Of course, if the difference e drops below the threshold T, for example, by passing through an area experiencing large waves W, the rotational speed n1 can be quickly restored by returning the coefficient of the difference e to the value just before it was lowered (first set value K1). Therefore, when viewed over a longer span than the load fluctuation span described above, it becomes possible to navigate the ship 1 at a constant rotational speed n1 and thus at a constant speed.

[0062] Furthermore, in this embodiment, a state detection unit 17 is provided to detect the state of the ship 1 in relation to the wave W. When the difference e becomes greater than or equal to a threshold T and the state detection unit 17 detects that the ship 1 is going up the wave W, the output A2 of the motor 13 is kept lower than the previous value A21 while going up the wave W. In particular, when going up large waves W such that the difference e is greater than or equal to a threshold T, an increase in rotational speed n1 commensurate with the increase in power supply cannot be expected. Therefore, during such a situation (while going up the wave W), by lowering the output A2 from the previous value, the first set value A21, to the second set value A22, it is possible to suppress the consumption of wasted energy more reliably and effectively.

[0063] Furthermore, in this embodiment, while the ship 1 is going up a large wave W, the rotational speed n1 is controlled with a reduced coefficient of difference e. When the state detection unit 17 detects that the ship 1 is going down the wave W, the output A2 of the motor 13 is maintained at a value greater than the previous value (in this case, the third set value A23) while going down the wave W. When the ship 1 is going down the wave W, it is easier to increase the rotational speed n1 of the prime mover 11, not only compared to when it is going up the wave W, but also compared to normal navigation (when navigating in an area where it does not encounter large waves W). Therefore, as described above, by increasing the output A2 of the motor 13 from the previous value while going down the wave W, the rotational speed n1 can be efficiently and quickly returned to the value before riding up the wave W (target rotational speed n2). Thus, it is possible to improve fuel efficiency while enjoying a good power reduction effect.

[0064] Next, the contents of the ship propulsion drive device according to the second embodiment of the present invention will be described based on Figures 7 to 9.

[0065] Figure 7 shows a schematic configuration diagram of a ship propulsion drive unit 20 according to the second embodiment of the present invention. As shown in Figure 7, this ship propulsion drive unit 20 is used as the main engine for ship propulsion mounted on a ship 1 and is equipped with a speed control system for the prime mover 21. Specifically, this ship propulsion drive unit 20 comprises a prime mover 21, a control unit 22 for controlling the output A of the prime mover 21, a rotation speed measurement unit 23, a governor 24, and a state detection unit 25. After describing the details of each element of the ship propulsion drive unit 20, the details of the speed control method of the ship propulsion drive unit 20 will be described below. Note that the rotation speed measurement unit 23, the governor 24, and the state detection unit 25 are substantially the same as the rotation speed measurement unit 15, the governor 16, and the state detection unit 17 of the first embodiment, so a detailed explanation will be omitted.

[0066] In this embodiment, the prime mover 21 is a combustion engine such as a diesel engine, and it can provide thrust to the ship 1 by rotating a propeller 26 attached to the tip of the main shaft 21a, which serves as the rotation axis. In this embodiment, the propeller 26 is a type of propeller (a so-called variable pitch propeller) configured to allow the blade angle to be changed, and the amount of thrust per rotation of the propeller 26 can be appropriately changed by the control unit 22. The structure for enabling the blade angle of the propeller 26 is arbitrary; for example, each propeller blade 26a can be configured to rotate around an axis Y perpendicular to the main shaft 21a. In this case, each propeller blade 26a may be driven separately and independently, or all propeller blades 26a may be driven in conjunction with each other.

[0067] The control unit 22 is configured to control the drive of the main shaft 21a of the prime mover 21, as well as the drive of the propeller blades 26a provided on the main shaft 21a.

[0068] First, regarding the drive control of the spindle 21a, the control unit 22 is configured to control the output A of the prime mover 21 by operating the governor 24 to control the rotational speed n1 of the spindle 21a of the prime mover 21. Specifically, the control unit 22 controls the rotational speed n1 of the prime mover 21 by adjusting the amount of fuel supplied to the prime mover 21 through the governor 24.

[0069] Furthermore, the control unit 22 has two or more different control modes for controlling the rotational speed n1 of the prime mover 21, and is configured to selectively select one of the two or more control modes according to the magnitude of the external load acting on the main shaft 21a of the prime mover 21 to perform proportional control of the rotational speed n1. Details of each control mode are the same as in the first embodiment, so they will not be explained in this embodiment.

[0070] Next, regarding the drive control of the propeller blades 26a, the control unit 22 electrically controls the drive mechanism of the propeller blades 26a (not shown) to change the attitude (blade angle) of each propeller blade 26a relative to the main shaft 21a. This control of the changeable blade angle d can be performed separately and independently from the control of the rotational speed n1 of the main shaft 21a.

[0071] On the other hand, the control unit 22 has two or more different control modes with respect to the blade angle d, and is configured to control the blade angle d by selectively selecting one of the two or more control modes according to the magnitude of the external load acting on the main shaft 21a of the prime mover 21.

[0072] More specifically, the control unit 22 evaluates the magnitude of the external load acting on the main shaft 21a based on the magnitude of the difference e between the rotational speed n1 of the prime mover 21 measured by the rotational speed measurement unit 23 and a preset target rotational speed n2 of the prime mover 21. If the difference e is less than a preset threshold T, the control unit 22 is configured to maintain the blade angle d at a predetermined size (in this case, for example, the first set angle d1 as a set value during normal navigation) as the external load acting on the main shaft 21a being less than a predetermined size (first control mode).

[0073] On the other hand, if the difference e between the rotational speed n1 and the target rotational speed n2 becomes greater than or equal to a threshold T, the control unit 22 considers that the external load acting on the main shaft 21a is greater than or equal to a predetermined magnitude and is configured to reduce the blade angle d by a predetermined amount from the previous value (in this case, for example, the first set angle d1), that is, to change the blade angle d to a second set angle d2 which is smaller by a predetermined amount than the first set angle d1 (second control mode).

[0074] In this embodiment, in addition to when the difference e becomes greater than or equal to the threshold T, when the state detection unit 25 detects that the ship 1 is going up the wave W (see Figure 6(a)), the control unit 22 is configured to maintain the blade angle d at a state where it is reduced by a predetermined amount from the value immediately before detecting that the ship is going up the wave W (the blade angle d is set to the second set angle d2). Further details will be described later.

[0075] Furthermore, in this embodiment, when the state detection unit 25 detects that the ship 1 is going down the wave W (see Figure 6(b)), the control unit 22 is configured to maintain the blade angle d in a state where it has been raised by a predetermined amount from the previous value (here, for example, the second setting angle d2), that is, the blade angle d is set to a third setting angle d3 which is a predetermined amount larger than the second setting angle d2 (third control mode).

[0076] Below, an example of a speed control method for the ship propulsion drive unit 20 with the above configuration will be explained, mainly based on Figures 8 and 9.

[0077] Figure 8 shows a flowchart illustrating an example of a method for controlling the speed of a ship 1 using a ship propulsion drive unit 10. As shown in this flowchart, when the ship 1 is in motion, the control unit 22 receives data on the rotational speed n1 of the prime mover 21 measured by the rotational speed measurement unit 23, calculates the difference e between the rotational speed n1 related to the received data and a preset target rotational speed n2 (step S11 in Figure 8), and determines whether the value of this difference e is greater than or equal to a threshold T (step S12 in Figure 8).

[0078] Then, if the calculated difference e is determined to be not equal to or less than the threshold T, i.e., less than the threshold T, the control unit 22 further determines whether or not the ship 1 is going down the wave W, based on the data regarding the state of the ship 1 with respect to the wave W detected by the state detection unit 25 at the same time (step S13 in Figure 8).

[0079] If the control unit 22 determines that the ship 1 is not sailing down wave W, it controls the prime mover 21 proportionally to a constant target rotational speed n2, with the coefficient of difference e set to a first set value K1 (see step S14 in Figure 8 and period P1 in Figure 4, respectively). The control unit 22 also controls the drive of each propeller blade 26a on the main shaft 21a of the prime mover 21 so that the blade angle d of the propeller 26 becomes the first set angle d1 (step S15 in Figure 8). In this case, it is presumed that the ship 1 is not subjected to significant resistance from waves W, wind, ocean currents, etc. Therefore, during periods when the waves W are not very large, the processing is performed in the order of steps S11 to S15 described above based on the rotation speed n1 and attitude data of the ship 1 measured at predetermined time intervals. As a result, proportional control of the rotation speed n1 is continuously performed with the coefficient of the difference e as the first set value K1, and the blade angle d of the propeller 26 is maintained at a predetermined value (first set angle d1).

[0080] In this type of prime mover 21, there is a predetermined proportional relationship between the power of the rotational speed n1 (usually the cube) and the output A, and it is known that this relationship varies with the blade angle d. In other words, once the blade angle d is uniquely determined, the output curve L showing the relationship between output A and rotational speed n1 is uniquely determined according to the magnitude of this blade angle d. Therefore, as described above, when the blade angle d is set to the first set angle d1, the output Aa of the prime mover 21 becomes a value corresponding to the rotational speed n1 (in this case, the target rotational speed n2) on the first output curve L1 corresponding to the first set angle d1 (see Figure 9).

[0081] On the other hand, when the waves W acting on the ship 1 reach a certain size, the value of the difference e calculated in step S11 also begins to increase as the external load acting on the main shaft 21a of the prime mover 21 increases. In such a situation, if the control unit 22 determines that the value of the difference e calculated in step S12 is greater than or equal to the threshold T, the control unit 22 further determines whether the ship 1 is going up the waves W based on the data regarding the state of the ship 1 with respect to the waves W detected by the state detection unit 25 at the same time (step S16 in Figure 8).

[0082] If the control unit 22 determines that the ship 1 is not going up the wave W, it performs proportional control of the rotational speed n1 of the prime mover 21 under a first set value K1 (step S14) and maintains the blade angle d of the propeller 26 at the first set angle d1 (step S15). On the other hand, if the control unit 22 determines that the ship 1 is going up the wave W, it lowers the coefficient of the difference e from the previous value, the first set value K1, to the second set value K2, and performs proportional control of the rotational speed n1 with respect to a constant target rotational speed n2 (see step S17 in Figure 8 and period P2 in Figure 4, respectively). The control unit 22 also lowers the blade angle d of the propeller 26 from the previous value, the first set angle d1, to the second set angle d2 (see step S18 in Figure 8). As a result of the above control, the output curve L of the prime mover 21 shown in Figure 9 shifts downward to the right (from the first output curve L1 to the second output curve L2). Considering that the rotational speed n1 hardly changes before and after changing the control mode, the output A decreases immediately after changing from the first control mode to the second control mode (arrow Z1 in Figure 9).

[0083] In this case, the second setting angle d2 can, in principle, be set arbitrarily. On the other hand, when changing from the first control mode to the second control mode, if the vessel 1 is going up a large wave W and the rotation speed n1 is difficult to increase or may even decrease, it is preferable to set the size of the second setting angle d2 within a range in which the vessel 1 can continue to move forward, preferably within a range that does not fall below a preset minimum cruising speed (corresponding rotation speed).

[0084] The control described above (proportional control of rotational speed n1 with the coefficient of difference e set to the second set value K2, and control to reduce the blade angle d to the second set angle d2) continues until the value of difference e, calculated at predetermined time intervals after the start of the control, is determined to be less than the threshold T, or until it is determined that the blade is not moving up the wave W.

[0085] On the other hand, if the difference e is determined to be less than the threshold T, the control unit 22 determines whether the ship 1 is going down the wave W based on the data regarding the state of the ship 1 with respect to the wave W detected by the state detection unit 25 (step S13 in Figure 8). If the control unit 22 determines that the ship 1 is going down the wave W, it raises the coefficient of the difference e from the second set value K2, which is the value immediately before detecting that the ship was going down the wave W, to the third set value K3, and performs proportional control of the rotation speed n1 with respect to a constant target rotation speed n2 (see step S19 in Figure 8 and period P3 in Figure 4, respectively). The control unit 22 also raises the blade angle d of the propeller 26 from the second set angle d2, which is the value immediately before, to the third set angle d3 (see step S20 in Figure 8). As a result of the above control, the output curve L of the prime mover 21 shown in Figure 9 shifts to the upper left (from the second output curve L2 to the third output curve L3). Considering that there is no change in the increasing trend of rotational speed n1 before and after changing the control mode, the output A increases immediately after changing from the second control mode to the third control mode (arrow Z2 in Figure 9).

[0086] In this case, the third setting angle d3 can, in principle, be set arbitrarily. For example, it can be set to a value smaller than the first setting angle d1 and larger than the second setting angle d2. On the other hand, when changing from the second control mode to the third control mode, considering that the ship 1 is going down the wave W and the rotational speed n1 is likely to increase, it is advisable to set the rotational speed corresponding to the continuous maximum output of the prime mover 21 as the upper limit, and to set the third setting angle d3 to a value larger than the first setting angle d1, within the range that does not exceed this upper limit.

[0087] The control described above (proportional control of rotational speed n1 with the coefficient of difference e set to the third set value K3, and control of the blade angle d of the propeller 26 with the third set angle d3) continues after the start of the control until it is determined that the value of difference e calculated at predetermined time intervals is greater than or equal to the threshold T, or until it is determined that the wave W is not being moved downwards.

[0088] The series of control mode switching operations described above are repeatedly performed until the ship passes through an area with large waves W. That is, according to the ship propulsion drive device 20 of this embodiment, proportional control of the rotational speed n1 is performed, switching the coefficient of difference e between the second set value K2 and the third set value K3, when the ship begins to receive waves W (head waves) of a size such that the difference e value is greater than or equal to the threshold T, and control is performed to switch the blade angle d of the propeller 26 between the second set angle d2 and the third set angle d3. Furthermore, after the wave W has decreased in size to a size such that the difference e value is less than the threshold T, the control returns to proportional control with the coefficient of difference e constant (first set value K1) and output control with the blade angle d of the propeller 26 set to the size during normal navigation (in this case, the first set angle d1) (steps S11 to S15 in Figure 8 are repeatedly performed).

[0089] As described above, in the ship propulsion drive system 20 according to this embodiment, when the difference e between the measured rotational speed n1 of the prime mover 21 and the target rotational speed n2 exceeds a threshold T, it is considered that an external load of a predetermined magnitude or greater is acting on the main shaft 21a of the prime mover 21, and the blade angle d of the propeller 26 provided on the main shaft 21a is reduced to decrease the output A of the prime mover 21. This makes it possible to easily and accurately adjust the output A of the prime mover 21 in a direction that decreases. As a result, the situation in which fuel increases in proportion to the decrease in the speed of the ship 1 is avoided, and the increase in fuel supply can be suppressed more than in the conventional method. Therefore, it is possible to avoid the situation in which a portion of the fuel supplied to the prime mover 21 is wasted, thereby improving fuel efficiency and, consequently, reducing fuel costs.

[0090] Figure 10 shows a schematic configuration diagram of a ship propulsion drive unit 30 according to the third embodiment of the present invention. As shown in Figure 10, this ship propulsion drive unit 30 is equipped with a speed control system for a prime mover 31 used as the main engine for ship propulsion mounted on a ship 1. Specifically, this ship propulsion drive unit 30 comprises a prime mover 31, a control unit 32 capable of controlling the drive of the prime mover 31, a power supply device 33 capable of supplying power to the prime mover 31, a rotation speed measurement unit 34, and a state detection unit 35. After describing the details of each element of the ship propulsion drive unit 30, the details of the speed control method of the ship propulsion drive unit 30 will be described below. Note that the rotation speed measurement unit 34 and the state detection unit 35 are substantially the same as the rotation speed measurement unit 15 and the state detection unit 17 of the first embodiment, so a detailed explanation will be omitted.

[0091] In this embodiment, the prime mover 31 is an electric motor, and it is capable of providing thrust to the ship 1 by rotating a propeller 36 attached to the tip of the main shaft 31a, which serves as the rotational drive shaft. In this embodiment, the propeller 36 is a type of propeller (a so-called variable pitch propeller) configured to allow the blade angle to be changed, and the amount of thrust per revolution of the propeller 36 can be appropriately changed by the control unit 32. The structure for enabling the blade angle of the propeller 36 is arbitrary; for example, each propeller blade 36a can be configured to rotate around an axis Y perpendicular to the main shaft 31a.

[0092] The power supply device 33 is capable of supplying a predetermined amount of power to the prime mover 31, and in this embodiment, it comprises a generator 37 and a prime mover 38 for driving the generator 37. In this embodiment, the power supply device 33 is further equipped with a switchboard 39 disposed between the generator 37 and the prime mover 31 for distributing the power generated by the generator 37 to the prime mover 31.

[0093] The generator 37 is electrically connected to the prime mover 31. This allows the power generated by the generator 37 to be supplied to the prime mover 31. In this embodiment, the frequency of the power generated by the generator 37 becomes the rotational speed n1 of the prime mover 31. Therefore, by controlling the frequency of the power generated by the generator 37 with a control unit (not shown), the rotational speed n1 of the prime mover 31 can be set to any value (for example, target rotational speed n2). The number of generators 37 is, in principle, arbitrary, and it is possible to install a number of generators 37 other than the number shown in Figure 10 (3).

[0094] The prime mover 38 is for driving the generator 37, and in this embodiment, it is composed of an internal combustion engine such as a diesel engine. The number of prime movers 38 is, in principle, arbitrary, and in this embodiment, the same number of prime movers 38 as the generator 37 (3 units) are installed.

[0095] It should be noted that the configuration of the power supply device 33 described above (generator 37, prime mover 38) is merely one example. Of course, other power generation devices, as well as energy storage devices such as batteries and capacitors, can also be used.

[0096] The control unit 32 is configured to control the drive of the propeller blades 36a mounted on the main shaft 31a. Specifically, the control unit 22 electrically controls the drive mechanism of the propeller blades 36a (not shown) to change the attitude (blade angle) of each propeller blade 36a relative to the main shaft 31a.

[0097] On the other hand, the control unit 32 has two or more different control modes with respect to the blade angle d, and is configured to selectively select one of the two or more control modes according to the magnitude of the external load acting on the main shaft 31a of the prime mover 31 to control the blade angle d. The details of each control mode are the same as in the second embodiment, so they will not be explained in this embodiment.

[0098] Below, an example of a speed control method for the ship propulsion drive unit 30 with the above configuration will be explained, mainly based on Figure 11.

[0099] Figure 11 shows a flowchart illustrating an example of a method for controlling the speed of a ship 1 using a ship propulsion drive unit 30. As shown in this flowchart, when the ship 1 is in motion, the control unit 32 receives data on the rotational speed n1 of the prime mover 31 measured by the rotational speed measurement unit 34, calculates the difference e between the rotational speed n1 related to the received data and a preset target rotational speed n2 (step S21 in Figure 11), and determines whether the value of this difference e is greater than or equal to a threshold T (step S22 in Figure 11).

[0100] Then, if the calculated difference e is determined to be not equal to or less than the threshold T, i.e., less than the threshold T, the control unit 32 further determines whether or not the ship 1 is going down the wave W, based on the data regarding the state of the ship 1 with respect to the wave W detected by the state detection unit 35 at the same time (step S23 in Figure 11).

[0101] If the control unit 32 determines that the ship 1 is not sailing down waves W, it controls the drive of each propeller blade 36a on the main shaft 31a of the prime mover 31 so that the blade angle d of the propeller 36 becomes the first set angle d1 (step S24 in Figure 11). In this case, it is presumed that the ship 1 is not experiencing significant resistance from waves W, wind, ocean currents, etc. Therefore, during periods when the waves W are not very large, the processing is performed in the order of steps S21 to S24 described above based on the rotational speed n1 and attitude data of the ship 1 measured at predetermined time intervals, and as a result, the blade angle d of the propeller 26 is maintained at a predetermined value (first set angle d1).

[0102] When the control unit 32 adopts the control mode described above (first control mode), the output Aa of the prime mover 21 becomes a value corresponding to the rotational speed n1 (in this case, the target rotational speed n2) on the first output curve L1 corresponding to the first set angle d1 (see Figure 9).

[0103] Furthermore, frequency-controlled power is continuously supplied to the prime mover 31 from the power supply device 33 so that the rotational speed n1 of the prime mover 31 is always at the target rotational speed n2.

[0104] On the other hand, when the waves W acting on the ship 1 reach a certain size, the value of the difference e calculated in step S21 also begins to increase as the external load acting on the main shaft 31a of the prime mover 31 increases. In such a situation, if the control unit 32 determines that the value of the difference e calculated in step S22 is greater than or equal to the threshold T, the control unit 32 further determines whether the ship 1 is going up the waves W based on the data regarding the state of the ship 1 with respect to the waves W detected by the state detection unit 35 at the same time (step S25 in Figure 11).

[0105] If the control unit 32 determines that the ship 1 is not going up the wave W, it maintains the blade angle d of the propeller 36 at the first set angle d1 (step S24). On the other hand, if the control unit 32 determines that the ship 1 is going up the wave W, it lowers the blade angle d of the propeller 36 from the previous value, the first set angle d1, to the second set angle d2 (see step S26 in Figure 11). Due to the above control, the output curve L of the prime mover 31 shifts downward to the right as shown in Figure 9 (shifting from the first output curve L1 to the second output curve L2). Considering that the rotational speed n1 hardly changes before and after changing the control mode, the output A decreases immediately after changing from the first control mode to the second control mode (arrow Z1 in Figure 9).

[0106] The control described above (control to reduce the wing angle d to the second set angle d2) continues until the value of the difference e calculated at predetermined time intervals after the start of the control is determined to be less than the threshold T, or until it is determined that the aircraft is not rising up the wave W.

[0107] On the other hand, if the difference e is determined to be less than the threshold T, the control unit 32 determines whether the ship 1 is going down the wave W based on the data regarding the state of the ship 1 with respect to the wave W detected by the state detection unit 35 (step S23 in Figure 11). If the control unit 32 determines that the ship 1 is going down the wave W, it raises the blade angle d of the propeller 36 from the previous value, the second setting angle d2, to the third setting angle d3 (see step S27 in Figure 11). Due to the above control, the output curve L of the prime mover 31 shifts upward and to the left as shown in Figure 9 (shifting from the second output curve L2 to the third output curve L3), so immediately after changing from the second control mode to the third control mode, the output A increases (arrow Z2 in Figure 9).

[0108] The control described above (control to set the blade angle d of the propeller 36 to the third set angle d3) continues until it is determined that the difference e calculated at predetermined time intervals after the start of the control is greater than or equal to the threshold T, or until it is determined that the vehicle is not descending wave W.

[0109] The series of control mode switching operations described above are repeatedly performed until the ship passes through an area with large waves W. In other words, according to the ship propulsion drive device 30 of this embodiment, control is performed to switch the blade angle d of the propeller 26 between the second setting angle d2 and the third setting angle d3 when the ship begins to receive waves W (head waves) of a size such that the difference e value is greater than or equal to the threshold T. After the wave W has decreased to a size such that the difference e value is less than the threshold T, the output control returns to the size of the blade angle d of the propeller 36 during normal navigation (in this case, the first setting angle d1) (steps S21 to S24 in Figure 11 are repeatedly performed).

[0110] As described above, in the ship propulsion drive system 30 according to this embodiment, when the difference e between the measured rotational speed n1 of the prime mover 31 and the target rotational speed n2 exceeds a threshold T, it is considered that an external load of a predetermined magnitude or greater is acting on the main shaft 31a of the prime mover 31, and the blade angle d of the propeller 36 provided on the main shaft 31a is reduced to decrease the output A of the prime mover 31. This makes it possible to easily and accurately adjust the output A of the prime mover 31 in a decreasing direction. As a result, the situation in which power consumption increases in proportion to the decrease in the speed of the ship 1 is avoided, and the increase in power supply can be suppressed more than in the conventional system. Therefore, it is possible to avoid the situation in which a portion of the power supplied to the prime mover 31 is wasted, thereby improving fuel efficiency and, consequently, reducing power generation costs.

[0111] Although the first, second, and third embodiments of the present invention have been described above, the ship propulsion drive device according to the present invention may also adopt configurations other than those described above, without departing from the spirit of the invention.

[0112] For example, in the first embodiment, an example was given in which the output A of the prime mover 11 is controlled based on the current difference e value and the state of the ship 1. However, of course, the ship propulsion drive device according to the present invention can also control the output in ways other than those illustrated. For example, a means for calculating the height of the wave W at the position of the ship 1 may be provided based on information acquired by the state detection unit 17 (for example, the vertical acceleration of the bow of the ship 1, GPS position information, etc.). This means for calculating the height of the wave W can be provided, for example, as software capable of executing a predetermined program. In this case, when the control unit 12 calculates the height of the wave W that the ship 1 is climbing (for example, the maximum height) based on the information acquired by the state detection unit 17, it estimates the height of the next wave W (for example, it estimates that the next wave W will also be of a similar height). In this case, when the ship 1 actually starts to climb the next wave W, the output A2 of the motor 13 may be reduced in advance from the previous value to decrease the output A of the prime mover 11, before detecting (measuring) that the rotational speed n1 has actually decreased significantly. This further suppresses the wasteful consumption of electrical energy, making it possible to further improve fuel efficiency and, consequently, further reduce power generation costs. Similarly, in the second and third embodiments, if the control unit 22 estimates that the next wave W will be of a similar height, it may, before detecting (measuring) that the rotational speed n1 has actually decreased significantly when the ship 1 begins to ascend the next wave W, reduce the blade angle d of the propeller 26(36) of the main shaft 21a(31a) from the previous value to reduce the output A of the prime mover 21(31). Furthermore, when estimating the height of the next wave W as described above, the rate of reduction of the output A may be varied depending on the estimated height of the wave W. That is, if it is estimated that a relatively high wave W is coming, in the first embodiment, the output A2 of the electric motor 13 may be reduced significantly from the previous value in advance, and if it is estimated that a relatively low wave W is coming, the output A2 may be reduced only slightly in advance. Furthermore, in the second and third embodiments, if it is estimated that relatively high waves W are coming, the blade angle d of the propeller 26(36) on the main shaft 21a(31a) may be reduced significantly in advance, and if it is estimated that relatively low waves W are coming, the blade angle d may be reduced significantly in advance.

[0113] Furthermore, in the first embodiment, an example was given in which, when the value of difference e is greater than or equal to a threshold T, and the state detection unit 17 determines that the ship 1 is going up a wave W, the output A2 of the electric motor 13 is reduced from the previous value to reduce the output A of the prime mover 11. However, this is by no means limited to this. For example, although not shown in the figures, the output A2 of the electric motor 13 may be raised or lowered based solely on whether the value of difference e is greater than or equal to a threshold T. Similarly, in the second and third embodiments, the blade angle d of the propeller 26(36) of the main shaft 21a(31a) may be reduced from the previous value based solely on whether the value of difference e is greater than or equal to a threshold T, and subsequent control may be performed. In this case, possible scenarios include large headwinds W or crosswinds, strong headwinds, or ocean currents in the opposite direction to the direction of travel accompanied by large swells. In any case, these events (sea conditions) increase the resistance experienced by the ship 1 (and consequently the external load on the main shafts 11a, 21a, and 31a of the prime movers 11, 21, and 31). Therefore, as described above, by reducing the output A2 of the electric motor 13 or the blade angle d from the previous value and controlling the output A of the prime movers 11, 21, and 31, it is possible to suppress the supply of unnecessary fuel or electricity that does not contribute to combustion, thereby effectively reducing fuel costs or power generation costs.

[0114] Furthermore, in the first and second embodiments, a case was described in which, when the difference e between rotational speed n1 and target rotational speed n2 becomes greater than or equal to a threshold T, the coefficient of the difference e is reduced from the previous value to perform proportional control of rotational speed n1. However, the control mode by the control units 12, 22, and 32 is arbitrary, as long as the output A2 of the motor 13 or the blade angle d is reduced from the previous value to decrease the output A of the prime movers 21 and 31. In other words, when proportionally controlling the rotational speed n1 of the prime movers 11 and 21 with respect to the target rotational speed n2, the coefficient of the difference e may always be fixed to a constant value.

[0115] Furthermore, the above explanation illustrates a case where, if the difference e between the rotational speed n1 of the prime mover 11(21,31) measured by the rotational speed measurement unit 15(23,34) and the target rotational speed n2 becomes greater than or equal to a predetermined magnitude (threshold T), it is considered that an external load of a predetermined magnitude or greater has been applied to the main spindle 11a(21a,31a) of the prime mover 11(21,31), and control is performed to reduce the output. However, this is by no means limited to this example. Any detection means and judgment criteria can be used as long as it is possible to determine that an external load of a predetermined magnitude or greater has been applied to the main spindle 11a(21a,31a). [Explanation of Symbols]

[0116] 1 ship 10, 20, 30 Drive systems for ship propulsion 11, 21, 31 Engine 11a,21a,31a Main shaft 12,22,32 Control Unit 13 Electric motor 14 Power supply device (electric motor) 15, 23, 34 Rotation speed measurement unit 16,24 Governor 17, 25, 35 State detection unit 18, 26, 36 propellers 26a, 36a Propeller blades 33 Power supply equipment 37 Generators 38. Prime mover (generator) 39 Switchboard A, Aa Output (Prime Motor) A1, A11, A12, A13 Single output (prime mover) A2 output (motor) A21, A22, A23 Setting values d Wing angle d1, d2, d3 Setting angles (wing angles) e difference K1, K2, K3 settings (difference coefficients) L1,L2,L3 output curve n1 rotation speed n2 Target rotational speed P1,P2,P3 period T threshold W wave θ Tilt angle

Claims

1. A prime mover installed on a ship for ship propulsion, A control unit for controlling the speed of the prime mover, In a ship propulsion drive system equipped with, The control unit is characterized in that it reduces the output of the prime mover when an external load of a predetermined magnitude or greater acts on the main shaft of the prime mover, thereby providing a propulsion system for ships.

2. The motor further comprises an electric motor configured to provide rotational driving force to the main shaft of the prime mover, The ship propulsion drive device according to claim 1, wherein the control unit reduces the output of the prime mover by lowering the output of the electric motor when an external load of a predetermined size or greater acts on the main shaft.

3. The prime mover has a propeller with a variable blade angle mounted on the main shaft, The ship propulsion drive device according to claim 1, wherein the control unit reduces the output of the prime mover by reducing the blade angle of the propeller when an external load of a predetermined size or greater acts on the main shaft.

4. The vessel is further provided with a state detection unit that detects the state of the vessel in relation to waves, The ship propulsion drive device according to claim 1, wherein the control unit maintains a state in which the output of the prime mover is reduced compared to the magnitude immediately before the detection of the ship climbing a wave, when an external load of a predetermined magnitude or greater is applied to the main shaft and the state detection unit detects that the ship is climbing a wave, while the ship is climbing a wave.

5. The ship propulsion drive device according to claim 4, wherein, when the state detection unit detects that the ship is going down a wave, the control unit maintains a state in which the output of the prime mover is increased compared to the magnitude of the wave while the ship is going up a wave.

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