Drive systems for ship propulsion

Abstract

This system allows for proper control of engine speed while minimizing the supply of excessive fuel or electricity, thereby contributing to energy conservation during navigation and ultimately reducing fuel costs. [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 rotational speed n1 of the engine 11 to a predetermined target rotational speed n2. When the difference e between the rotational speed n1 and the target rotational speed n2 of the engine 11 becomes greater than or equal to a predetermined value T, the control unit 14 reduces the rate at which the rotational speed n1 increases from its previous value.

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 rotational speed 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. Further, the control of the rotational speed at this time is performed by proportional control such as PID control, which corrects the rotational speed command value based on a value proportional to the difference between the actual rotational speed (actual rotational speed) of the diesel engine and the target rotational speed (for example, refer to 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 main engine's rotational speed may drop significantly. In such cases, the main engine's control unit will send a command to the governor to increase the fuel supply amount using the aforementioned PID control in order to quickly restore the reduced rotational speed, thus supplying an amount of fuel commensurate with the significant drop in rotational speed. 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 rotational speed will increase 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 frequency using the frequency value just before the drop 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 electricity supplied to the motor will be wasted.

[0006] In light of the above circumstances, this specification aims to address the technical challenge of enabling proper control of the engine speed and, consequently, the ship'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 problems are solved by the ship propulsion drive device according to the present invention. Specifically, this ship propulsion drive device comprises a ship propulsion engine mounted on a ship and a control unit that controls the rotational speed of the engine to a predetermined target rotational speed, wherein the control unit is characterized in that, when the difference between the rotational speed of the engine and the target rotational speed exceeds a predetermined value, it reduces the rate at which the rotational speed increases from the value immediately before the difference reaches the predetermined value.

[0008] As described above, in the ship propulsion drive system according to the present invention, when the rotational speed of the engine mounted on the ship drops significantly due to headwinds or other resistance, the system anticipates that an excess of energy will be supplied in advance and controls the rotational speed by lowering the rate of increase in rotational speed from the value just before the difference reaches a predetermined value. By lowering the rate of increase in rotational speed from the value just before, it is possible to suppress the sudden increase in energy supply that conventionally occurred immediately after the rotational speed dropped. As a result, the amount of energy consumed by the engine is reduced, so that the situation in which some of the energy supplied to the engine is wasted is avoided, and it becomes possible to improve fuel efficiency and, consequently, reduce energy costs. Of course, when the difference drops to below the predetermined value, such as when the ship is freed from resistance such as headwinds or other resistance, the rotational speed can be quickly recovered by returning to the value just before the rate of increase in rotational speed was lowered, so that the ship can sail at a generally constant speed over a long period of time, such as during a voyage.

[0009] Furthermore, the ship propulsion drive device according to the present invention may also be equipped with a rotational speed measuring unit for measuring the rotational speed of the prime mover. In this case, the control unit controls the rotational speed in proportion to the difference between the rotational speed measured by the rotational speed measuring unit and the target rotational speed. If the difference between the rotational speed and the target rotational speed exceeds a predetermined value, the control unit may control the rotational speed by lowering the coefficient of the difference from the value immediately before the difference exceeded the predetermined value.

[0010] Thus, if the control unit controls the rotational speed in proportion to the difference between the engine's rotational speed measured by the rotational speed measurement unit and the target rotational speed, the rate of increase in rotational speed can be reduced simply by lowering the coefficient of the difference from the previous value, provided that the difference between the rotational speed and the target rotational speed exceeds a predetermined value. Therefore, it is possible to easily reduce the rate of increase in rotational speed without actually performing control that feeds back the rate of increase in rotational speed. As a result, the situation in which the amount of fuel supplied increases in proportion to the decrease in rotational speed 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 some of the fuel supplied to the combustion chamber is wasted, thereby improving fuel efficiency and, consequently, reducing fuel costs.

[0011] Furthermore, in the ship propulsion drive system according to the present invention, the prime mover is an electric motor, and the control unit is configured to control the frequency of the electric motor. The control unit may control the frequency such that, when the difference exceeds a predetermined value, the target rotational speed becomes smaller than the previous value.

[0012] If the prime mover is an electric motor and the control unit is configured to control the frequency of the motor, the rate at which the rotational speed increases can also be reduced by controlling the frequency so that the target rotational speed becomes smaller than the previous value, provided that the difference between the rotational speed and the target rotational speed exceeds a predetermined value. Therefore, even in this case, it is possible to easily reduce the rate at which the rotational speed increases without actually performing control that feeds back the rate at which the rotational speed increases. This avoids a situation where the amount of power supplied increases in proportion to the decrease in rotational speed, thus suppressing the increase in power supply compared to conventional methods. Therefore, it is possible to avoid a situation where some of the power supplied to the electric motor is wasted, thereby improving fuel efficiency and ultimately reducing power generation costs.

[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. Here, when the control unit performs proportional control of the rotational speed, if the difference exceeds a predetermined value and the state detection unit detects that the ship is going up a wave, the control unit may perform proportional control of the rotational speed while going up a wave with the difference coefficient lowered from the value immediately before the difference exceeded the predetermined value. Alternatively, when the control unit controls the frequency of the electric motor, if the difference exceeds a predetermined value and the state detection unit detects that the ship is going up a wave, the control unit may control the frequency while going up a wave with the target rotational speed lowered from the value immediately before the difference exceeded the predetermined value.

[0014] By providing a state 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 where the difference exceeds a predetermined value, in particular, an increase in rotational speed commensurate with the increase in fuel supply cannot be expected. Therefore, during such situations (while going up the waves), by performing proportional control of the rotational speed with the difference coefficient lowered from the value just before the difference exceeds a predetermined value, it is possible to suppress unnecessary fuel consumption more reliably and effectively. Similarly, when the prime mover is an electric motor, while going up the waves, by controlling the frequency with the target rotational speed lowered from the value just before the difference exceeds a predetermined value, it is possible to suppress unnecessary power consumption more reliably and effectively.

[0015] Furthermore, in the ship propulsion drive system according to the present invention, when controlling the rotational speed with a reduced differential coefficient while the ship is going up a wave, proportional control of the rotational speed may be performed by reducing the differential coefficient within a range in which the ship can continue to move forward. Similarly, when the prime mover is an electric motor and the control unit controls the frequency of the electric motor, the rotational speed may be controlled by reducing the frequency within a range in which the ship can continue to move forward.

[0016] When sailing up waves, lowering the differential coefficient increases the fuel-saving effect. However, lowering the differential coefficient too much can require a significant amount of time to recover the engine speed (and consequently the ship's speed), or in the worst case, the ship may stop, leading to a decrease in fuel efficiency. The same problem can occur when the engine is an electric motor. In light of this, it is preferable to set the lower limit of the differential coefficient within a range that allows the ship to continue moving forward, and moreover, so as not to fall below a predetermined minimum cruising speed (corresponding to the engine speed). When the engine is an electric motor, it is also preferable to set the lower limit of the frequency within a range that allows the ship to continue moving forward.

[0017] Furthermore, in the ship propulsion drive system according to the present invention, when controlling the rotational speed with a reduced difference coefficient 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, control the rotational speed while the ship is going down a wave with the difference coefficient increased from the value immediately before it was detected that the ship was going down a wave. Similarly, when the prime mover is an electric motor and the control unit controls the frequency of the electric motor, when it detects that the ship is going down a wave using the state detection unit, the control unit may control the frequency so that the target rotational speed increases from the value immediately before it was detected that the ship was going down 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 rotational speed of the main engine (prime motor) 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 while sailing down a wave, the difference coefficient is increased from the value just before detecting that the ship is sailing down a wave, and proportional control of the rotational speed is performed, so that the rotational 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. When the control unit controls the frequency of the electric motor as the prime motor, while sailing down a wave, the frequency is controlled so that the target rotational speed is higher than the value just before detecting that the ship is sailing down a wave, so that the rotational speed can be efficiently and quickly returned to the value before sailing up a wave, so that it is 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 then execute rotational speed control appropriate for 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.

[0023] Further, in the marine propulsion drive device according to the present invention, when the difference is less than a predetermined value, the control unit may perform proportional control of the rotational speed with respect to a constant target rotational speed while keeping the coefficient of the difference constant. Alternatively, when the prime mover is an electric motor and the control unit controls the frequency of the electric motor, the control unit may control the frequency so that the frequency becomes constant when the difference is less than a predetermined value.

[0024] By performing control in this manner, stable rotational speed control can be achieved during normal navigation (when sailing without receiving large resistance). As a result, the total amount of fuel or electric power required for the voyage can be estimated with high accuracy, so that further improvement in fuel efficiency can be achieved by reducing the fuel or power source loaded on the ship as much as possible. [Effects of the Invention]

[0025] As described above, according to the marine propulsion drive device of the present invention, it is possible to appropriately control the rotational speed of the prime mover and thus the speed of the ship while preventing excessive supply of fuel or electric power as much as possible, so that energy saving during navigation and thus suppression of fuel costs can be achieved. [Brief Description of the Drawings]

[0026] [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 a 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 coefficient of the difference when control is performed based on the control method shown in Figure 2. [Figure 5] (a) is a diagram conceptually showing a state where the ship is climbing a wave, and (b) is a diagram conceptually showing a state where the ship is descending a wave. [Figure 6]This is a schematic diagram of a ship propulsion drive device according to a second embodiment of the present invention. [Figure 7] Figure 6 is a flowchart illustrating the essential aspects of a speed control method using a ship propulsion drive system. [Figure 8] This graph shows the variation in rotational speed when controlled according to the control method shown in Figure 7. [Modes for carrying out the invention]

[0027] 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.

[0028] 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 prime mover 11. Specifically, this ship propulsion drive unit 10 mainly comprises a prime mover 11, a rotation speed measuring unit 12 for measuring the actual rotation speed n1 of the prime mover 11, a governor 13 for adjusting the amount of fuel supplied to the prime mover 11, and a rotation speed control unit 14 for controlling the rotation speed n1 by operating the governor 13 based on the measured rotation speed n1. Here, the rotation speed control unit 14 corresponds to the control unit according to the present invention. In this embodiment, the ship propulsion drive unit 10 further comprises a state detection unit 15 for detecting the state of the ship 1 in relation to waves. After describing the details of each element of the ship propulsion drive unit 10, the details of the speed control method of the ship propulsion drive unit 10 will be described below.

[0029] 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 (not shown) attached to the tip of the drive shaft 11a, which serves as the rotating shaft. 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.

[0030] The rotational speed measurement unit 12 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 drive shaft 11a of the prime mover 11 at predetermined time intervals. The applicable measurement means are arbitrary, and known means can be used.

[0031] The data regarding the rotational speed n1 of the prime mover 11, measured by the rotational speed measurement unit 12, is transmitted to the rotational speed control unit 14.

[0032] The state detection unit 15 is for detecting the state of the ship 1 in relation to the wave W (see Figure 5). 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 12). 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 15 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.

[0033] The data regarding the state of the ship 1 in relation to the wave W detected by the state detection unit 15 is transmitted to the rotation speed control unit 14, similar to the data regarding the rotation speed n1.

[0034] The rotational speed control unit 14 controls the rotational speed n1 of the prime mover 11 by operating the governor 13. Specifically, it 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 13. The governor 13 that the rotational speed control unit 14 operates on can be any known type of governor, such as a mechanical governor, a hydraulic governor, or an electric governor, as long as proportional control (electronic control) of the rotational speed n1 through the operation of the governor 13, as described later, is possible.

[0035] The rotational speed control unit 14 is configured to perform proportional control of the rotational speed n1 based on the difference e between the rotational speed n1 of the prime mover 11 measured by the rotational speed measurement unit 12 and a preset target rotational speed n2 of the prime mover 11. More specifically, the rotational speed control unit 14 has two or more different control modes, and is configured to perform proportional control of the rotational speed n1 by selectively selecting and using one of these two or more control modes depending on the value of the difference e.

[0036] Specifically, if the difference e between rotational speed n1 and target rotational speed n2 (here, e = n2 - n1) is less than a predetermined positive value (hereinafter referred to as threshold T), the rotational speed control unit 14 is configured to maintain the coefficient of the difference e at a predetermined value (here, the first set value K1) and to perform proportional control of rotational speed n1 with respect to a constant target rotational speed n2 (first control mode).

[0037] On the other hand, if the difference e between the rotational speed n1 and the target rotational speed n2 exceeds a threshold T, the rotational speed control unit 14 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 set value K1 in this case), that is, with the coefficient of the difference e set to a second set value K2 which is a predetermined amount smaller than the first set value K1 (second control mode).

[0038] In this embodiment, in addition to when the difference e becomes greater than or equal to the threshold T, when the state detection unit 15 detects that the ship 1 is going up the wave W (see Figure 5(a)), the rotation speed control unit 14 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.

[0039] Furthermore, in this embodiment, when the state detection unit 15 detects that the ship 1 is sailing down waves W (see Figure 5(b)), the rotational speed control unit 14 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 (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).

[0040] 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 13. 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 13.

[0041] Below, an example of a method for controlling the rotational speed of the ship propulsion drive unit 10 with the above configuration will be explained, mainly based on Figures 2 to 5.

[0042] Figure 2 shows a flowchart illustrating an example of a rotational speed control method for a ship propulsion drive unit 10. As shown in this flowchart, when the ship 1 is in motion, the rotational speed control unit 14 receives data on the rotational speed n1 of the prime mover 11 measured by the rotational speed measurement unit 12, 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).

[0043] Then, if the calculated difference e is determined to be less than or equal to the threshold T, the rotational speed control unit 14 further determines whether the ship 1 is sailing downstream of 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 15 at the same time (step S3 in Figure 2). For example, if the state detection unit 15 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 rotational speed control unit 14 determines that the ship 1 is sailing upstream of the wave W when the tilt angle θ exceeds a predetermined positive value (see Figure 5(a)). Alternatively, if the tilt angle θ falls below a predetermined negative value, the rotational speed control unit 14 determines that the ship 1 is sailing downstream of the wave W (see Figure 5(b)).

[0044] Then, if it is determined that the ship 1 is not going down the waves W based on the above criteria, the rotational speed control unit 14 performs proportional control of the rotational speed n1 with respect to a constant target rotational speed n2, with the coefficient of the difference e set to the first set value K1 (see step S4 in Figure 2 and period P1 in Figure 4, respectively). In this case, it is estimated that the ship 1 is not experiencing significant resistance from waves W, wind, ocean currents, etc., so during periods when the waves W are not very large, the processing is performed in the order of steps S1 to S4 above based on the rotational speed n1 and attitude data of the ship 1 measured at predetermined time intervals, and proportional control of the rotational speed n1 with the coefficient of the difference e set to the first set value K1 is continuously performed. In this case, the rotational speed n1 of the prime mover 11 is maintained within a very narrow range centered on the target rotational speed n2 (see period P1 in Figure 3).

[0045] 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 as the load acting on the prime mover 11 increases. In such a situation, if the rotational speed control unit 14 determines that the value of the difference e calculated in step S2 is greater than or equal to the threshold T, it 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 15 at the same time (step S5 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 15 exceeds a predetermined positive value, it is determined that the ship 1 is going up the waves W (see Figure 5(a)).

[0046] Then, if the engine speed control unit 14 determines, based on the above criteria, that the vessel 1 is not going up the wave W, it performs proportional control of the rotation speed n1 under the first set value K1 (step S4). On the other hand, if the engine speed control unit 14 determines, based on the above criteria, that the vessel 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 rotation speed n1 with respect to a constant target rotation speed n2 (see step S6 in Figure 2 and period P2 in Figure 4, respectively).

[0047] In this case, the second setting value K2 can, in principle, be set arbitrarily. On the other hand, at the point when proportional control of rotational speed n1 is performed with the coefficient of 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 viewpoint, 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 a preset 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. 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).

[0048] The proportional control described above (proportional control of rotational speed n1 with the coefficient of difference e as the second setpoint K2) continues until it is determined that the value of difference e, calculated at predetermined time intervals after the start of the control, is less than the threshold T, or until it is determined that the wave W is not being raised.

[0049] On the other hand, if it is determined that the difference e is less than the threshold T, the rotational speed control unit 14 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 15 (step S3 in Figure 2). If it is determined that the vessel 1 is going down the wave W based on the above criteria, the rotational speed control unit 14 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 S7 in Figure 2 and period P3 in Figure 4, respectively).

[0050] 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 preferable 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.

[0051] The proportional control described above (proportional control of rotational speed n1 with the coefficient of difference e set to the third set value K3) 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 descending.

[0052] 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 10 of this embodiment, proportional control is performed by 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 value of difference e is greater than or equal to the threshold T, and after the wave W has decreased in size to such that the value of difference e is less than the threshold T, the system returns to proportional control with the coefficient of difference e constant (first set value K1) (steps S1 to S4 in Figure 2 are repeatedly performed).

[0053] As described above, in the ship propulsion drive device 10 according to this embodiment, when the rotational speed n1 of the prime mover 11 mounted on the ship 1 drops significantly due to waves W, the coefficient of the difference e is lowered by a predetermined amount from the previous value (first setting value K1) and proportional control of the rotational speed n1 is performed, anticipating that an excess of fuel will be supplied in advance. This reduces 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 amount of fuel supplied increases by the amount the rotational speed n1 drops is avoided, and the increase in the amount of fuel supplied is suppressed compared to conventional methods. Therefore, it is possible to avoid the situation in which some 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.

[0054] Furthermore, in this embodiment, a state detection unit 15 is provided to detect the state of the vessel 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 15 detects that the vessel 1 is going up the wave W, proportional control of the rotation speed n1 is performed while the vessel is going up the wave W with the coefficient of the difference e lowered from the previous value K1. 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 rotation speed n1 commensurate with the increase in fuel supply cannot be expected. Therefore, during such a situation (while going up the wave W), proportional control of the rotation speed n1 is performed with the coefficient of the difference e lowered from the previous value, the first set value K1, to the second set value K2, making it possible to suppress unnecessary fuel consumption more reliably and effectively.

[0055] Furthermore, in this embodiment, while the ship 1 is going up a large wave W, the rotational speed n1 is controlled with the coefficient of difference e reduced. Additionally, when the state detection unit 15 detects that the ship 1 is going down the wave W, the rotational speed n1 is controlled while the ship is going down the wave W with the coefficient of difference e set to a larger value than the previous value (in this case, the third set value K3). 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 controlling the rotational speed n1 with the coefficient of difference e increased 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 fuel reduction effect.

[0056] Next, the contents of the ship propulsion drive device according to the second embodiment of the present invention will be described based on the drawings.

[0057] Figure 6 shows a schematic configuration diagram of a ship propulsion drive unit 20 according to a second embodiment of the present invention. As shown in Figure 6, 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 mainly comprises a prime mover 21, a rotation speed measuring unit 22 for measuring the actual rotation speed n1 of the prime mover 21, a power supply device 23 for supplying power to the prime mover 21, and a rotation speed control unit 24 for controlling the rotation speed n1 based on the measured rotation speed n1. Here, the rotation speed control unit 24 corresponds to the control unit according to the present invention. In this embodiment, the ship propulsion drive unit 20 further comprises a state detection unit 25 for detecting the state of the ship 1 in relation to waves. 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. Since the rotation speed measurement unit 22 and the state detection unit 25 are substantially the same as the rotation speed measurement unit 12 and the state detection unit 15 of the first embodiment, a detailed explanation will be omitted.

[0058] In this embodiment, the prime mover 21 is an electric motor, and it is capable of providing thrust to the ship 1 by rotating a propeller 26 attached to the tip of the drive shaft 21a, which serves as the rotating shaft. In this embodiment, the propeller 26 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 26 (pitch) is fixed at a constant distance. In this illustrated example, the ship propulsion drive system 20 is shown as being composed of two prime movers (electric motors) 21, but the ship propulsion drive system 20 may be composed of one or three or more prime movers (electric motors) 21.

[0059] The power supply device 23 is capable of supplying a predetermined amount of power to the prime mover 21, and in this embodiment, it comprises a generator 27 and a ship propulsion drive device 28 for driving the generator 27. In this embodiment, the power supply device 23 is disposed between the generator 27 and the prime mover 21 and further comprises a switchboard 29 for distributing the power generated by the generator 27 to the prime mover 21.

[0060] The generator 27 is electrically connected to the prime mover 21. This allows the electricity generated by the generator 27 to be supplied to the prime mover 21. The number of generators 27 is, in principle, arbitrary, and it is possible to install a number of generators 27 other than the number shown in Figure 6 (3).

[0061] The ship's propulsion drive unit 28 is for driving the generator 27, and in this embodiment, it is composed of an internal combustion engine such as a diesel engine. The number of ship's propulsion drive units 28 is, in principle, arbitrary, and in this embodiment, the same number as the generator 27 (3 units) of ship's propulsion drive units 28 are installed.

[0062] It should be noted that the configuration of the power supply device 23 described above (generator 27, ship propulsion drive device 28) 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.

[0063] The rotational speed control unit 24 controls the rotational speed n1 of the prime mover 21, and specifically controls the frequency of the generator 27 that supplies power to the prime mover 21, which is an electric motor. In this case, the rotational speed control unit 24 can be configured as a so-called inverter. In this embodiment, one rotational speed control unit 24 is provided for each prime mover 21, and the frequency of the power supplied from the generator 27 to each prime mover 21 via the distribution board 29, and thus the rotational speed n1, are controlled for each unit.

[0064] The rotational speed control unit 24 is configured to control the rotational speed n1 to a predetermined target rotational speed n2 according to the difference e between the rotational speed n1 of the prime mover 21 measured by the rotational speed measurement unit 22 and a preset target rotational speed n2 of the prime mover 21. More specifically, the rotational speed control unit 24 is configured to be able to set two or more different target rotational speeds n2 (n21, n22…), and is configured to control the rotational speed n1 by setting one of the two or more preset target rotational speeds n21, n22… as the target rotational speed n2 according to the difference e.

[0065] Specifically, if the difference e between rotational speed n1 and target rotational speed n2 is less than a predetermined positive threshold T, the rotational speed control unit 24 is configured to control the frequency of the generator 27 so that the target rotational speed n2 of the prime mover 21 becomes the first target rotational speed n21 (first control mode). That is, during normal navigation, the rotational speed control unit 24 controls the rotational speed n1 of the prime mover 21 to the first target rotational speed n21, and controls the rotational speed n1 of the prime mover 21 to the first target rotational speed n21 as long as the actual rotational speed n1 does not deviate significantly from the first target rotational speed n21 (the difference e is less than the threshold T).

[0066] On the other hand, if the difference e between rotational speed n1 and target rotational speed n2 (first target rotational speed n21) is greater than or equal to a threshold T, the rotational speed control unit 24 is configured to control rotational speed n1 by lowering the target rotational speed n2 by a predetermined amount from the previous value (in this case, the first target rotational speed n21), that is, by setting the target rotational speed n2 to a second target rotational speed n22 which is a predetermined amount smaller than the first target rotational speed n21 (second control mode). In this case, since the rotational speed n1 of the prime mover 21 is proportional to the frequency of the generator 27, the rotational speed control unit 24 can control the frequency of the generator 27 to (second target rotational speed n22) / (first target rotational speed n21) × (frequency of the generator 27 when the first target rotational speed n21) thereby controlling the rotational speed n1 of the prime mover 21 to the second target rotational speed n22.

[0067] 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 5(a)), the rotation speed control unit 24 is configured to control the rotation speed n1 with the target rotation speed n2 reduced by a predetermined amount from the value immediately before detecting that the ship was going up the wave W (the target rotation speed n2 is set to the second target rotation speed n22). Further details will be described later.

[0068] Furthermore, in this embodiment, when the state detection unit 25 detects that the ship 1 is sailing down waves W (see Figure 5(b)), the rotational speed control unit 24 is configured to control the rotational speed n1 by raising the target rotational speed n2 by a predetermined amount from the previous value (here, for example, the second target rotational speed n22), that is, by setting the target rotational speed n2 to a third target rotational speed n23, which is a predetermined amount greater than the second target rotational speed n22 (third control mode). In this case, since the rotational speed n1 of the prime mover 21 is proportional to the frequency of the generator 27, the rotational speed control unit 24 can control the frequency of the generator 27 to (third target rotational speed n23) / (second target rotational speed n22) × (frequency of the generator 27 when the second target rotational speed n22) to control the rotational speed n1 of the prime mover 21 to the third target rotational speed n23.

[0069] Below, an example of a method for controlling the rotational speed of the ship propulsion drive unit 20 with the above configuration will be explained, mainly based on Figures 6 to 8.

[0070] Figure 7 shows a flowchart illustrating an example of a rotational speed control method for a ship propulsion drive unit 20. As shown in this flowchart, when the ship 1 is in motion, the rotational speed control unit 24 receives data on the rotational speed n1 of the prime mover 21 measured by the rotational speed measurement unit 22. The unit then calculates the difference e between the received rotational speed n1 and a preset target rotational speed n2 (in this case, the first target rotational speed n21) (step S11 in Figure 7), and determines whether this difference e is greater than or equal to a threshold T (step S12 in Figure 7).

[0071] Then, if the calculated difference e is determined to be not greater than or equal to the threshold T, i.e., less than the threshold T, the rotation speed control unit 24 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 25 at the same time (step S13 in Figure 7). For example, if the state detection unit 25 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 rotation speed control unit 24 determines that the ship 1 is going up the wave W if the tilt angle θ exceeds a predetermined positive value (see Figure 5(a)). Alternatively, if the tilt angle θ falls below a predetermined negative value, the rotation speed control unit 24 determines that the ship 1 is going down the wave W (see Figure 5(b)).

[0072] Then, if it is determined that the ship 1 is not going down the waves W based on the above criteria, the rotational speed control unit 24 controls the rotational speed n1 while controlling the frequency of the generator 27 so that the target rotational speed n2 becomes the first target rotational speed n21 (see step S14 in Figure 7 and period P1 in Figure 8, respectively). In this case, it is estimated that the ship 1 is not experiencing significant resistance from waves W, wind, ocean currents, etc., so during periods when the waves W are not very large, the processing is carried out in the order of steps S11 to S14 above based on the rotational speed n1 and attitude data of the ship 1 measured at predetermined time intervals, and as a result, rotational speed n1 is continuously controlled so that the target rotational speed n2 becomes the first target rotational speed n21. In this case, the rotational speed n1 of the prime mover 21 is maintained within a very narrow range centered on the first target rotational speed n21 (see period P1 in Figure 8).

[0073] 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 load acting on the prime mover 21 increases. In such a situation, if the rotational speed control unit 24 determines that the value of the difference e calculated in step S12 is greater than or equal to the threshold T, it 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 S15 in Figure 7). For example, if the tilt angle θ of the ship 1 with respect to the horizontal attitude detected by the state detection unit 25 exceeds a predetermined positive value, it is determined that the ship 1 is going up the waves W (see Figure 5(a)).

[0074] If the ship 1 is determined not to be going up the wave W based on the above criteria, the rotational speed control unit 24 controls the rotational speed n1 by controlling the frequency of the generator 27 so that the target rotational speed n2 becomes the first target rotational speed n21 (step S14). On the other hand, if the ship 1 is determined to be going up the wave W based on the above criteria, the rotational speed control unit 24 controls the rotational speed n1 by controlling the frequency of the generator 27 so that the target rotational speed n2 is reduced from the previous value, the first target rotational speed n21, to the second target rotational speed n22 (see step S16 in Figure 7 and period P2 in Figure 8, respectively).

[0075] In this case, the second target rotational speed n22 can, in principle, be set arbitrarily. On the other hand, at the point when controlling rotational speed n1 with the target rotational speed n2 reduced to the second target rotational speed n22, it is presumed that the ship 1 is going up a large wave W, making it difficult for rotational speed n1 to increase. Alternatively, it is presumed that, due to the large resistance caused by the wave W, rotational speed n1 will further decrease even after control of rotational speed n1 is started with the second target rotational speed n22 set. From this viewpoint, it is preferable to set the magnitude of the second target rotational speed n22 within a range in which the ship 1 can continue to move forward, preferably within a range that does not fall below a preset minimum cruising speed (corresponding rotational speed), and more preferably within a range that does not fall below the rotational speed n1 at the time control under the second target rotational speed n22 is started. Figure 8 illustrates the case where the magnitude of the second target rotational speed n22 is set so that the rotational speed n1 at the time control under the second target rotational speed n22 is maintained or slightly increased (see period P2 in Figure 8).

[0076] The control described above (control of rotational speed n1 with the target rotational speed n2 as the second target rotational speed n22) continues until it is determined that the difference e calculated at predetermined time intervals after the start of the control is less than the threshold T, or until it is determined that the wave W is not being raised.

[0077] On the other hand, if the difference e is determined to be less than the threshold T, the rotational speed control unit 24 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 25 (step S13 in Figure 7). If the rotational speed control unit 24 determines that the vessel 1 is going down the wave W based on the above criteria, the rotational speed control unit 24 controls the rotational speed n1 by controlling the frequency of the generator 27, raising the target rotational speed n2 from the second target rotational speed n22, which is the value immediately before detecting that the vessel 1 was going down the wave W, to the third target rotational speed n23 (see step S17 in Figure 7 and period P3 in Figure 8, respectively).

[0078] In this case, the third target rotational speed n23 can, in principle, be set arbitrarily. For example, it can be set to a value that is smaller than the first target rotational speed n21 and larger than the second target rotational speed n22. On the other hand, when controlling rotational speed n1 with the target rotational speed n2 set to the third target rotational speed n23, it is presumed that the ship 1 is going down the wave W, and that the rotational speed n1 is likely to increase. From this perspective, for example, it is preferable to set the rotational speed corresponding to the continuous maximum output of the prime mover 21 as the upper limit, and set the third target rotational speed n23 to a value greater than the first target rotational speed n21, within the range that does not exceed this upper limit.

[0079] The control described above (control of rotational speed n1 with target rotational speed n2 as the third target rotational speed n23) 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 wave W is not descending.

[0080] 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, control is performed to switch the target rotation speed n2 between the second target rotation speed n22 and the third target rotation speed n23 when the ship begins to receive waves W (head waves) of a size such that the difference e is greater than or equal to the threshold T (steps S13 and S17 in Figure 7 are repeatedly performed), and after the wave W has become small enough that the difference e is less than the threshold T, the control returns to setting the target rotation speed n2 to the first target rotation speed n21 (period P1 in Figure 8).

[0081] As described above, in the ship propulsion drive system 20 according to this embodiment, when the prime mover 21 is an electric motor and the rotational speed control unit 24 is configured to control the frequency of the prime mover 21, the frequency is controlled so that the target rotational speed n2 becomes smaller than the previous value, provided that the difference e between the rotational speed n1 and the target rotational speed n2 is greater than or equal to a threshold T. Therefore, the rate of increase of the rotational speed n1 can be reduced immediately after detecting that the difference e is greater than or equal to a threshold T. Thus, it is possible to easily reduce the rate of increase of the rotational speed n1 without actually performing control that feeds back the rate of increase of the rotational speed n1. As a result, the situation in which the amount of power supplied from the power supply device 23 increases in proportion to the decrease in rotational speed n1 is avoided, and the increase in the amount of power supplied 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 21 is wasted, thereby improving fuel efficiency and, consequently, reducing power generation costs.

[0082] Although the first and second 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.

[0083] For example, in the first embodiment, when passing through a sea area where the rotation speed n1 drops significantly due to large waves W, the coefficient of difference e is alternately switched between a second setting value K2, which is smaller than the coefficient of difference e used during normal navigation (first setting value K1), and a third setting value K3, which is larger than the first setting value K1, to perform proportional control of the rotation speed n1 (see Figure 4). However, the control mode by the rotation speed control unit 14 is of course not limited to this. For example, although not shown in the figure, if the ship 1 is sailing in a horizontal or near-horizontal attitude for a predetermined period immediately after going up a wave W, proportional control can be performed by switching the coefficient of difference e based on the flow shown in Figure 2, so that when going down the same wave W after going up it, for example, the coefficient is switched from the second setting value K2 to the first setting value K1, and then to the third setting value K3. Furthermore, if the vessel 1 is sailing in a horizontal or near-horizontal position for a predetermined period immediately after descending a wave W, proportional control can be performed by switching the coefficient of difference e based on the flow shown in Figure 2. For example, when sailing up the next wave W after sailing down one wave W, the coefficient can be switched from the third set value K3 to the first set value K1, and then to the second set value K2. Similarly, in the second embodiment, although not shown in the figure, if the vessel 1 is sailing in a horizontal or near-horizontal position for a predetermined period immediately after sailing up a wave W, control can be performed by switching the target rotation speed n2 from the second target rotation speed n22 to the first target rotation speed n21, and then to the third target rotation speed n23 when sailing down the same wave W after sailing up the wave W, based on the flow shown in Figure 7. Furthermore, if the vessel 1 is sailing in a horizontal or near-horizontal position for a predetermined period immediately after descending wave W, control can be performed to switch the target rotation speed n2 from the third target rotation speed n23 to the first target rotation speed n21, and then to the second target rotation speed n22, based on the flow shown in Figure 7, when ascending the next wave W after descending wave W.

[0084] Furthermore, in the first embodiment, a case was illustrated in which proportional control of the rotational speed n1 is performed based on the current difference e value and the state of the vessel 1. However, of course, the ship propulsion drive device according to the present invention can also control the rotational speed in ways other than those illustrated. For example, a means for calculating the height of the wave W at the position of the vessel 1 may be provided based on information acquired by the state detection unit 15 (e.g., vertical acceleration of the bow of the vessel 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 rotational speed control unit 14 calculates the height of the wave W that the vessel 1 is climbing (e.g., the maximum height) based on the information acquired by the state detection unit 15, it estimates the height of the next wave W (e.g., it estimates that the next wave W will also be of a similar height). In this case, when the vessel 1 actually begins to climb the next wave W, before detecting (measuring) that the rotational speed n1 has actually decreased significantly, the coefficient of the difference e may be lowered in advance to reduce the rate of increase of the rotational speed n1 from the previous value. This makes it possible to further reduce fuel waste and further reduce fuel costs. Similarly, in the second embodiment, if the rotation speed control unit 24 estimates that the next wave W will be of a similar height, it may lower the target rotation speed in advance to reduce the rate of increase of rotation speed n1 from the previous value, before detecting (measuring) that the rotation speed n1 has actually decreased significantly when the ship 1 begins to ascend the next wave W. Furthermore, when estimating the height of the next wave W as described above, the rate of decrease in the rate of increase of rotation speed n1 may be varied depending on the estimated height of wave W. That is, if it is estimated that a relatively high wave W is coming, the rate of increase of rotation speed n1 may be reduced significantly, and if it is estimated that a relatively low wave W is coming, the rate of increase of rotation speed n1 may be reduced only slightly.

[0085] Furthermore, in the first embodiment, an example was given in which proportional control of the rotation speed n1 is performed with the coefficient of the difference e lowered from the previous value when the value of the difference e is greater than or equal to the threshold T and the state detection unit 15 determines that the ship 1 is going up a wave W, but of course, it is not limited to this. For example, although not shown in the figure, the coefficient of the difference e may be lowered from the previous value and subsequent proportional control may be performed based solely on whether or not the value of the difference e is greater than or equal to the threshold T. Similarly in the second embodiment, the target rotation speed n2 may be lowered from the previous value and subsequent control may be performed based solely on whether or not the value of the difference e is greater than or equal to the threshold T. In this case, possible events include large headwinds W or transverse waves, 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 load on the main engines 11 and 21). Therefore, by controlling the rotational speed n1 by lowering the coefficient of difference e or the target rotational speed n2 from the previous value as described above, it becomes 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.

[0086] Furthermore, in the first embodiment, the control mode shown in Figure 2 is merely an example. The control mode by the rotational speed control unit 14 is arbitrary, as long as the coefficient of the difference e between rotational speed n1 and target rotational speed n2 can be reduced from the previous value when the difference e is greater than or equal to a threshold T, thereby enabling proportional control of rotational speed n1. In the second embodiment as well, the control mode shown in Figure 7 is merely an example, and the control mode by the rotational speed control unit 24 is arbitrary, as long as the target rotational speed n2 can be reduced from the previous value when the difference e is greater than or equal to a threshold T, thereby enabling control of rotational speed n1. Moreover, the control mode by the ship propulsion drive device according to the present invention is arbitrary, as long as the rate of increase of rotational speed n1 is reduced from the previous value when the difference e between the rotational speed n1 and target rotational speed n2 of the prime movers 11 and 21 is greater than or equal to a threshold T. [Explanation of Symbols]

[0087] 1 ship 10,20 Drive systems for ship propulsion 11,21 Engine 11a, 21a Drive shaft 12,22 Rotational speed measurement unit 13 Governors 14,24 Speed ​​control unit 15,25 State detection unit 23 Power supply equipment 26 propellers 27 Generators 28. Drive systems for ship propulsion (for driving generators) 29 Switchboard e difference K1 First setting value K2 Second setting value K3 Third setting value n1 rotation speed n2 Target rotational speed n21 First target rotational speed n22 Second target rotational speed n23 Third target rotation speed T threshold W wave θ Tilt angle

Claims

1. A prime mover installed on a ship for ship propulsion, A control unit that controls the rotational speed of the prime mover to a predetermined target rotational speed, In a ship propulsion drive system equipped with, The control unit is characterized in that, when the difference between the rotational speed of the prime mover and the target rotational speed exceeds a predetermined value, it reduces the rate at which the rotational speed increases from the previous value.

2. The system further includes a rotation speed measuring unit for measuring the rotation speed of the prime mover, The control unit performs proportional control of the rotational speed based on the difference between the rotational speed measured by the rotational speed measurement unit and the target rotational speed, and The ship propulsion drive device according to claim 1, wherein the control unit, when the difference becomes greater than or equal to the predetermined value, reduces the coefficient of the difference from the previous value to perform proportional control of the rotational speed.

3. The prime mover is an electric motor, and the control unit is configured to control the frequency of the electric motor. The ship propulsion drive device according to claim 1, wherein the control unit controls the frequency such that the target rotation speed becomes smaller than the previous value when the difference becomes greater than or equal to a predetermined value.

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 2, wherein the control unit, when the difference exceeds a predetermined value and the state detection unit detects that the ship is going up a wave, performs proportional control of the rotational speed while the ship is going up a wave, with the coefficient of the difference reduced from the value immediately before the difference exceeded the predetermined value.

5. 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 3, wherein the control unit controls the frequency while the ship is going up a wave, such that the target rotation speed is lower than the value immediately before the difference exceeded the predetermined value, when the difference exceeds a predetermined value and the state detection unit detects that the ship is going up a wave.

6. 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 increases the coefficient of the difference from the value immediately before detecting that the ship is going down a wave and performs proportional control of the rotation speed while the ship is going down a wave.

7. The ship propulsion drive device according to claim 5, wherein the control unit, when it detects that the ship is going down a wave by the state detection unit, controls the frequency so that the target rotation speed increases from the value immediately before it was detected that the ship was going down a wave while it was going down a wave.

Images