Engine control device of ship propeller

Abstract

To provide an engine control device of a ship propeller capable of reducing the decrease of ship speed and of improving navigation amenity when the ship speed suddenly decreases during the ship sailing.SOLUTION: An engine control device 21 to control the prime mover 8 of an outboard engine 6 comprises a driving control unit 24 for driving the engine 8 so that the engine 8 generates the driving torque according to the operation amount of the operation lever 32 of a remote control 31, a rotation speed determination unit 26 for determining whether or not the deceleration of rotation speed of the engine 8 is the deceleration reference value or more, and a torque enhancement processing unit 29 for performing torque enhancement processing to increase the driving torque generated by the engine 8 to a value greater than the driving torque corresponding to the operation mount by the operation lever 32, when the deceleration of rotation speed of the engine 8 is equal to or greater than the deceleration reference value as the determined result by the rotation speed determination unit 26.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a motor control device for a boat propulsion unit that propels a boat. [Background technology]

[0002] A boat propulsion unit has a prime mover as a power source for rotating a propeller. An engine (internal combustion engine) or a motor (electric motor) is typically used as the prime mover for a boat propulsion unit. The boat propulsion unit can be operated by an operating device such as a remote control. The operating device has an operating lever, and the boat operator can change the direction and magnitude of the propulsive force generated by the boat propulsion unit by operating the operating lever. For example, when the boat operator moves the operating lever forward, the boat propulsion unit generates a propulsive force in a direction that moves the boat forward, and the greater the forward operation of the operating lever, the greater the propulsive force.

[0003] The propulsive force generated by a marine propulsion unit increases as the drive torque (rotational torque) generated by the prime mover of the marine propulsion unit increases. A prime mover control device is provided between the operating device and the prime mover, and controls the increase or decrease of the drive torque generated by the prime mover in accordance with the amount of operation of the operating lever.

[0004] Furthermore, Japanese Patent Laid-Open Publication No. 2003-176743 (Patent Document 1) describes a jet propulsion boat to which an engine rotation control device is applied. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-176743 Summary of the Invention [Problem to be solved by the invention]

[0006] When the operator moves the control lever forward by a large amount, the engine of the boat propulsion unit generates a driving torque corresponding to the amount of operation of the control lever, and the boat propulsion unit generates a large thrust that moves the boat forward, increasing the boat speed, and as a result, the boat enters a sailing state.

[0007] When a ship is sailing, it may run up onto a wave and jump above the water. When the ship hits the water, the waterline of the ship's hull rises, and the water resistance on the hull or the propeller of the ship's propulsion unit increases sharply. As a result, the ship's speed decreases suddenly and significantly. Another example of a sudden decrease in ship speed is when a ship hits a high wave head-on and the waterline at the bow rises. A sudden decrease in ship speed can cause a large forward force to be exerted on the operator or passengers, reducing the comfort of the journey. Therefore, when a ship's speed suddenly decreases due to a ship hitting the water or colliding with a wave while sailing, it is desirable to minimize the decrease in ship speed and prevent the operator or passengers from being pushed forward, thereby improving the comfort of the journey.

[0008] Japanese Patent Application Laid-Open Publication No. 2003-176743 discloses that engine overspeed can occur when a jet propulsion boat traveling at high speed on the water surface jumps and lands on water after jumping due to engine load fluctuations. The publication also describes "rotation suppression control," which involves suppressing engine rotation using well-known techniques such as cutting or reducing fuel supply, leaning the mixture, retarding ignition timing, and thinning out ignition. The publication also describes preventing overspeed by initiating rotation suppression control when the engine rotation speed exceeds a first threshold while increasing, and then terminating the rotation suppression control when the engine rotation speed falls below a second threshold while decreasing. The publication also describes that, in the overspeed prevention process, the second threshold is set higher than the first threshold, thereby minimizing the drop in rotation speed after the rotation suppression control ends. The publication also describes that, after the rotation suppression control ends during the overspeed prevention process, the engine switches to normal operation.

[0009] The over-rev prevention process described in the publication is thought to minimize the decline in engine speed by terminating the rotation suppression control earlier after the rotation speed starts to decrease due to the rotation suppression control. However, as described in paragraph 0021 of the publication, this over-rev prevention process switches the engine to normal operation after the rotation suppression control ends. Even if the rotation suppression control is terminated earlier, simply switching the engine to normal operation after the rotation suppression control ends may not be effective in reducing the decline in engine speed. Therefore, the over-rev prevention process described in JP 2003-176743 A may not sufficiently minimize the decrease in boat speed when the boat speed suddenly decreases due to the boat landing on water or collision with waves while sailing. As a result, it may not be possible to prevent the operator or passengers from being pushed forward, which may result in a lack of comfort during the journey.

[0010] The present invention has been made in consideration of problems such as those described above, and an object of the present invention is to provide a motor control device for a marine propulsion unit that can reduce the amount of reduction in marine speed when the marine speed suddenly decreases while the marine vessel is sailing, thereby improving the comfort of the sailing. [Means for solving the problem]

[0011] In order to solve the above problems, the present invention provides a prime mover control device for a marine propulsion unit that controls the prime mover of a marine propulsion unit having a propeller and a prime mover that rotates the propeller, and is characterized by comprising: a drive control unit that drives the prime mover so that the prime mover generates a drive torque that corresponds to the amount of operation of an operating device that operates the marine propulsion unit; a rotation speed determination unit that determines whether the deceleration of the rotation speed of the prime mover or the propeller is equal to or greater than a predetermined deceleration reference value; and a torque enhancement processing unit that performs torque enhancement processing to increase the drive torque generated by the prime mover beyond the drive torque that corresponds to the amount of operation of the operating device as a result of the determination by the rotation speed determination unit. [Effects of the Invention]

[0012] According to the present invention, when the vessel speed suddenly decreases while the vessel is sailing, the amount of decrease in vessel speed can be reduced, thereby improving the comfort of the vessel during sailing. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1A is an external view showing a vessel equipped with a vessel propulsion system including an engine control device according to an embodiment of the present invention, and FIG. 1B is an explanatory diagram showing the vessel in a jumping state. [Figure 2] 1 is a block diagram showing a marine vessel propulsion system including a prime mover control device according to an embodiment of the present invention; [Figure 3] FIG. 1 is an explanatory diagram showing a remote control device. [Figure 4] 4 is a flowchart showing a process for suppressing a sudden decrease in boat speed in the motor control device according to the embodiment of the present invention. [Figure 5]4 is a timing chart showing an example of the required torque, boat speed, engine rotation speed, etc. when a boat speed sudden decrease suppression process is performed in the engine control device according to the embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] A prime mover control device for a marine propulsion unit according to an embodiment of the present invention is a device for controlling a prime mover of a marine propulsion unit having a propeller and a prime mover for rotating the propeller. The prime mover control device of this embodiment includes a drive control unit, a rotation speed determination unit, and a torque boost processing unit.

[0015] The drive control unit drives the prime mover so that the prime mover generates a drive torque corresponding to the amount of operation of an operating device that operates the vessel propulsion unit. For example, if the operating device has an operating lever, the drive control unit drives the prime mover so that the drive torque generated by the prime mover increases the greater the amount of operation of the operating lever, for example, forward. As a result, when the operator increases the amount of operation of the operating lever forward, the drive torque generated by the prime mover increases. If the load applied to the prime mover and the load applied to the propeller are constant, as the drive torque generated by the prime mover increases, the rotation speed of the prime mover increases, the rotation speed of the propeller increases, and the thrust generated by the vessel propulsion unit increases. If the water resistance and other factors acting on the vessel hull are constant, as the thrust generated by the vessel propulsion unit increases, the vessel speed increases.

[0016] The rotation speed determination unit determines whether the deceleration of the rotation speed of the prime mover is equal to or greater than a predetermined deceleration reference value. By determining whether the deceleration of the rotation speed of the prime mover is equal to or greater than the deceleration reference value, it is possible to recognize whether the rotation speed of the prime mover has suddenly decreased.

[0017] Furthermore, if the load on the propeller (e.g., water resistance) increases suddenly, the propeller rotation speed decreases suddenly, and accordingly, the prime mover rotation speed also decreases suddenly. If the rotation speeds of the propeller and prime mover also decrease suddenly, the thrust generated by the vessel propulsion unit also decreases suddenly, and the vessel speed also decreases suddenly. If the resistance of water on the hull also increases suddenly, the vessel speed also decreases suddenly. If the vessel speed also decreases suddenly, the load on the propeller (e.g., water resistance) also increases suddenly, causing the propeller rotation speed to decrease suddenly, and therefore the prime mover rotation speed also decreases suddenly. In this way, if the load on the propeller increases suddenly and the prime mover rotation speed decreases suddenly, the vessel speed also decreases suddenly, and if the load on the hull also increases suddenly and the vessel speed also decreases suddenly, the prime mover rotation speed also decreases suddenly. Therefore, by determining whether the engine rotation speed has suddenly decreased, it is possible to determine whether the vessel speed has suddenly decreased. That is, by determining whether the deceleration of the rotational speed of the prime mover is equal to or greater than the deceleration reference value, it is possible to recognize whether the boat speed has suddenly decreased.

[0018] The torque boosting processing unit performs torque boosting processing when the rotation speed determination unit determines that the deceleration of the rotation speed of the prime mover or propeller is equal to or greater than the deceleration reference value, i.e., when the boat speed suddenly decreases. Torque boosting processing is processing that increases the drive torque generated by the prime mover to a value greater than the drive torque corresponding to the amount of operation of the operating device. By increasing the drive torque generated by the prime mover through torque boosting processing, the rotation speeds of the prime mover and propeller can be increased, the propulsive force generated by the boat propulsion unit can be increased, and the degree of sudden decreases in boat speed can be reduced. Specifically, the amount of decrease in boat speed when the boat speed suddenly decreases can be reduced.

[0019] According to the engine control device of this embodiment, when a sudden decrease in boat speed occurs while the boat is sailing, for example, due to the boat jumping and landing on water or the boat hitting a high wave head-on, the motor control device recognizes the sudden decrease in boat speed and immediately performs torque boosting processing to reduce the amount of decrease in boat speed during such a sudden decrease. Therefore, when the boat hits water or collides with a wave while sailing, it is possible to prevent the boat operator or passengers from being pushed forward by a large force. This improves the comfort of the boat when sailing compared to conventional technology. [Example]

[0020] (ship) Fig. 1(A) shows a boat 1 provided with a boat propulsion system 5 including a motor control device 21 according to an embodiment of the present invention. Fig. 1(B) shows the boat 1 jumping while sailing.

[0021] The vessel 1 is, for example, a small vessel as shown in Fig. 1(A), and specifically, is a leisure boat, fishing boat, sports boat, cruiser, fishing boat, etc. Note that the present invention is not limited to such small vessels, but can also be applied to medium-sized or large vessels.

[0022] An outboard motor 6 is provided at the rear of the hull 2 ​​of the boat 1. The outboard motor 6 is one form of boat propulsion device. The prime mover control device 21 of this embodiment is a device that controls the prime mover 8 of the outboard motor 6, but the prime mover control device of the present invention can also be applied to control the prime mover of other types of boat propulsion devices, such as an inboard-outboard motor or an inboard motor.

[0023] (Marine Propulsion Systems) Fig. 2 shows the configuration of a boat propulsion system 5. The boat propulsion system 5 is a system that propels the boat 1 and is provided on the boat 1. As shown in Fig. 2, the boat propulsion system 5 includes an outboard motor 6, a remote control device (remote control) 31, and a boat speed sensor 33. The outboard motor 6 also includes a propeller 7, a prime mover 8, a rotation detection unit 10, and a prime mover control device 21. The prime mover control device 21 may be provided outside the outboard motor 6, for example, in the hull 2 ​​of the boat 1.

[0024] The propeller 7 is a device that generates a propulsive force for the boat 1 by rotating. The prime mover 8 is a power source that rotates the propeller 7. The prime mover 8 can be a motor (electric motor), an engine (internal combustion engine), or a hybrid power unit that combines a motor and an engine. Here, an example is given in which a motor is used as the prime mover 8. For example, the prime mover 8 is an AC motor, and more specifically, a three-phase synchronous motor. Although not shown in detail, a power transmission mechanism 9 (e.g., a drive shaft, a gear mechanism, a propeller shaft, etc.) that transmits the power of the prime mover 8 to the propeller 7 is provided between the prime mover 8 and the propeller 7. Although not shown in detail, the hull 2 ​​or the outboard motor 6 is provided with a battery that supplies power to the prime mover 8.

[0025] Rotation detection unit 10 is a device that detects the angle or angular velocity of the rotor of prime mover 8 and the rotation speed n of prime mover 8. Rotation detection unit 10 outputs a detection signal that indicates the angle or angular velocity of the rotor of prime mover 8 to subordinate control unit 22. Rotation detection unit 10 also outputs a detection signal that indicates the rotation speed n of prime mover 8 to host control unit 23. Note that, for example, a configuration may be adopted in which a rotation detection unit that detects only the angle of the rotor of prime mover 8 is provided, subordinate control unit 22 calculates the angular velocity of prime mover 8 based on the detection signal from the rotation detection unit, and host control unit 23 calculates the rotation speed of prime mover 8 based on the detection signal from the rotation detection unit. Furthermore, if prime mover 8 is an engine, a device that detects the angle, angular velocity, or rotation speed of the engine's crankshaft can be used as rotation detection unit 10.

[0026] The remote control 31 is a device for operating the outboard motor 6. As shown in Fig. 3, the remote control 31 has an operation lever 32 that allows the operator to input operations. As shown in Fig. 2, the remote control 31 outputs an operation signal p that indicates the tilt direction (operation direction) and tilt angle (operation amount) of the operation lever 32 to the higher-level control unit 23.

[0027] The boat speed sensor 33 is a device that detects the speed (boat speed s) of the boat 1. The boat speed sensor 33 outputs a detection signal indicating the boat speed s to the upper control unit 23.

[0028] (Motor control device) The prime mover control device 21 is a device that controls the prime mover 8. In this embodiment, the prime mover control device 21 employs torque-based control as a higher-level control method for the prime mover 8, and vector control as a lower-level control method for the prime mover 8. As shown in FIG. 2, the prime mover control device 21 has a lower-level control unit 22 and a higher-level control unit 23. The prime mover control device 21 is configured such that the higher-level control unit 23 controls the lower-level control unit 22, which in turn controls the prime mover 8 according to the control of the higher-level control unit 23. The higher-level control unit 23 has an arithmetic processing unit, a storage device, etc. The lower-level control unit 22 has a vector control circuit, a PWM (Pulse Width Modulation) inverter circuit, etc.

[0029] If the prime mover 8 is an engine, the subordinate control unit 22 has circuits that control, for example, a fuel injection device, a throttle device, spark plugs, etc. provided in the engine, as well as a shift device provided in the outboard motor. The shift device controls a gear mechanism in the power transmission mechanism 9 that transmits the power of the prime mover 8 to the propeller 7, and switches between forward and reverse rotation of the propeller according to the rotation of the engine.

[0030] The host control unit 23 functions as a drive control unit 24 and a boat speed sudden decrease suppression control unit 25 by executing a computer program stored in a storage device that the host control unit 23 has, for example.

[0031] (Drive control unit) The drive control unit 24 controls the drive of the prime mover 8 in response to the operation of the operating lever 32 of the remote control 31. Specifically, the drive control unit 24 drives the prime mover 8 so that the rotation direction of the rotor of the prime mover 8 corresponds to the tilt direction (operation direction) of the operating lever 32, and so that the drive torque generated by the prime mover 8 corresponds to the tilt angle (operation amount) of the operating lever 32.

[0032] More specifically, in FIG. 3 , when moving the boat 1 forward, the boat operator tilts the operation lever 32 forward to the forward position. When moving the boat 1 astern, the boat operator tilts the operation lever 32 rearward to the reverse position. When stopping the boat 1, the boat operator places the operation lever 32 in the neutral position. As shown in FIG. 2 , the remote control 31 outputs an operation signal p indicating the tilt direction and tilt angle of the operation lever 32 to the upper control unit 23. The drive control unit 24 determines a rotation direction instruction j based on the tilt direction of the operation lever 32 indicated by the operation signal p. Specifically, when the tilt direction of the operation lever 32 indicated by the operation signal p is forward, the drive control unit 24 sets the rotation direction instruction j to an instruction to change the rotation direction of the prime mover 8 in one direction, and when the tilt direction of the operation lever 32 indicated by the operation signal p is backward, the drive control unit 24 sets the rotation direction instruction j to an instruction to change the rotation direction of the prime mover 8 in the other direction. The drive control unit 24 also determines the required torque r based on the tilt angle of the operating lever 32 indicated by the operation signal p. The drive control unit 24 increases the required torque r as the tilt angle of the operating lever 32 indicated by the operation signal p increases. The drive control unit 24 then outputs a command signal indicating the rotation direction instruction j and the required torque r to the subordinate control unit 22.

[0033] The lower-level control unit 22 drives the prime mover 8 based on the command signal output from the drive control unit 24 and the angle or angular velocity of the rotor of the prime mover 8 output from the rotation detection unit 10. Specifically, the lower-level control unit 22 drives the prime mover 8 so that the rotation direction of the rotor of the prime mover 8 coincides with the rotation direction indicated by the rotation direction command j and the drive torque generated by the prime mover 8 corresponds to the required torque r. The drive torque generated by the prime mover 8 increases as the required torque r increases.

[0034] Through the control of the drive control unit 24 and the subordinate control unit 22 as described above, the rotor of the prime mover 8 rotates in a direction corresponding to the tilt direction of the operating lever 32, and the driving torque generated by the prime mover 8 corresponds to the tilt angle of the operating lever 32. For example, when the operator tilts the operating lever 32 forward to the forward position, the propeller rotates forward, generating a propulsive force that moves the boat 1 forward; further, the greater the forward tilt angle of the operating lever 32, the greater the propulsive force that moves the boat 1 forward.

[0035] In addition, when the prime mover 8 is an engine, the lower control unit 22 controls the shift device so that the rotation direction of the propeller 7 is the rotation direction indicated by the rotation direction instruction j, and drives the engine so that the driving torque generated by the prime mover 8 is a driving torque corresponding to the required torque r.

[0036] (Ship speed sudden decrease suppression control unit) The sudden vessel speed decrease suppression control unit 25 recognizes a sudden decrease in vessel speed while the vessel is sailing that is not caused by operation of the operating lever 32, and when it recognizes such a sudden decrease in vessel speed, it intervenes in the drive control of the prime mover 8 by the drive control unit 24 to increase the drive torque generated by the prime mover 8 and perform control to reduce the amount of vessel speed decrease when the vessel speed suddenly decreases. The sudden vessel speed decrease suppression control unit 25 has a rotation speed determination unit 26, a vessel speed determination unit 27, a required torque determination unit 28, and a torque enhancement processing unit 29. The rotation speed determination unit 26 determines whether the deceleration d of the rotation speed of the prime mover 8 is equal to or greater than a predetermined deceleration reference value Dth. The vessel speed determination unit 27 determines whether the speed of the vessel 1 (vessel speed s) is equal to or greater than a predetermined vessel speed reference value Sth. The required torque determination unit 28 determines whether the required torque r is equal to or greater than a predetermined required torque reference value Rth. The required torque determination unit 28 also determines whether the increase rate w of the required torque r is equal to or greater than a predetermined required torque increase rate reference value Wth. The required torque determination unit 28 is a specific example of a "first required torque determination unit" and a "second required torque determination unit." The torque boost processing unit 29 performs torque boost processing. The torque boost processing is processing for increasing the driving torque generated by the prime mover 8 to a value higher than the driving torque corresponding to the tilt angle of the operating lever 32.

[0037] (Sudden decrease in ship speed suppression processing) 4 shows the sudden vessel speed decrease suppression process performed by the sudden vessel speed decrease suppression control unit 25. The sudden vessel speed decrease suppression process is repeatedly executed while the vessel propulsion system 5 is in operation. The sudden vessel speed decrease suppression process is a process that recognizes a sudden decrease in vessel speed while the vessel is sailing that is not caused by operation of the operating lever 32, and increases the drive torque generated by the prime mover 8 when such a sudden decrease in vessel speed is recognized. The sudden vessel speed decrease suppression process is performed for the purpose of suppressing a sudden large decrease in vessel speed while the vessel 1 is sailing, even though the vessel operator has not performed an operation to slow down the vessel 1, such as when the vessel 1 jumps and hits water or when the vessel 1 hits a high wave head-on.

[0038] As shown in Fig. 4, the sudden vessel speed decrease suppression process includes a sudden vessel speed decrease determination process (steps ST1 to ST4) and a torque increase process (steps ST5 to ST9). The sudden vessel speed decrease determination process is a process for determining whether or not the vessel speed has suddenly decreased while the vessel 1 is sailing, without being caused by operation of the operation lever 32. The torque increase process is a process for increasing the drive torque generated by the prime mover 8 to a value greater than the drive torque corresponding to the tilt angle of the operation lever 32. The sudden vessel speed decrease suppression process is generally configured to first perform a sudden vessel speed decrease determination process, and if the result of the sudden vessel speed decrease determination process shows that the vessel speed has suddenly decreased while the vessel 1 is sailing, without being caused by operation of the operation lever 32, then perform a torque increase process to increase the drive torque generated by the prime mover 8.

[0039] The sudden vessel speed decrease suppression process will now be described in detail. In Figure 4, the sudden vessel speed decrease suppression control unit 25 first performs sudden vessel speed decrease determination process. In the sudden vessel speed decrease determination process, the vessel speed determination unit 27 first determines whether the current vessel speed s is equal to or greater than the vessel speed reference value Sth based on the detection signal output from the vessel speed sensor 33 (step ST1).

[0040] A sudden and large decrease in vessel speed occurs, for example, when the vessel 1 jumps and hits water, or when the vessel 1 hits a high wave head-on. The vessel 1 jumping or colliding with a wave is more likely to occur when the vessel 1 is at a high vessel speed than when the vessel 1 is at a low vessel speed. In other words, a sudden and large decrease in vessel speed is more likely to occur when the vessel 1 is at a high vessel speed. By determining whether the vessel speed s is equal to or greater than the vessel speed reference value Sth, it is possible to recognize situations in which a sudden and large decrease in vessel speed is likely to occur. This makes it possible to prevent the torque boosting process from being performed in situations in which a sudden and large decrease in vessel speed is unlikely to occur. In other words, since performing the torque boosting process in situations in which a sudden and large decrease in vessel speed is unlikely to occur often does not provide any useful effect, it is possible to prevent such meaningless torque boosting process from being frequently performed. The vessel speed reference value Sth is set to a vessel speed at which a sudden and large decrease in vessel speed is likely to occur, such as a vessel speed at which the vessel 1 jumps or collides with a wave. Such a vessel speed can be determined, for example, by experiment or simulation.

[0041] If the current boat speed s is equal to or greater than the boat speed reference value Sth, the required torque determination unit 28 then determines whether the required torque r currently being output from the drive control unit 24 to the lower control unit 22 is equal to or greater than the required torque reference value Rth (step ST2).

[0042] When the required torque is large, the driving torque generated by the prime mover 8 increases, and the boat speed increases. As described above, when the boat speed is high, a sudden and large decrease in boat speed is likely to occur. By determining whether the required torque r is equal to or greater than the required torque reference value Rth, it is possible to recognize situations in which a sudden and large decrease in boat speed is likely to occur. This makes it possible to prevent torque boosting processing from being performed in situations in which a sudden and large decrease in boat speed is unlikely to occur. The required torque reference value Rth is set to a required torque that makes a sudden and large decrease in boat speed more likely to occur, such as a required torque that makes it more likely that the boat 1 will jump or that the boat 1 will collide with a wave. Such a required torque can be determined, for example, by experiment or simulation.

[0043] If the required torque r currently output from the drive control unit 24 to the low-level control unit 22 is equal to or greater than the required torque reference value Rth, the required torque determination unit 28 then calculates the current increase rate w of the required torque r per unit time and determines whether the increase rate w is equal to or greater than the required torque increase rate reference value Wth (step ST3). The increase rate w is positive when the required torque r increases, and negative when the required torque r decreases. In this embodiment, the required torque increase rate reference value Wth is set to 0.

[0044] In the vessel sudden deceleration suppression process in this embodiment, the torque increase process is not performed when the vessel speed suddenly decreases due to the vessel helmsman operating the control lever 32 to decelerate the vessel 1. The determination of whether the increase rate w of the required torque r per unit time is equal to or greater than the required torque increase rate reference value Wth is performed for the purpose of recognizing whether the vessel helmsman is operating to decelerate the vessel 1 while the vessel helmsman is sailing. When the vessel helmsman is sailing, the control lever 32 is tilted forward and in the forward position. In this state, when the vessel helmsman decelerates the vessel 1, the vessel helmsman operates the control lever 32 in a direction approaching the neutral position. This reduces the required torque, reduces the drive torque generated by the prime mover 8, and decelerates the vessel 1. In this way, when the vessel helmsman operates to decelerate the vessel 1, the required torque decreases, and the increase rate of the required torque becomes a value smaller than 0. Therefore, by setting the required torque increase rate reference value Wth to 0 and determining whether the increase rate w of the required torque r per unit time is equal to or greater than the required torque increase rate reference value Wth, it is possible to recognize whether the vessel helmsman is operating to decelerate the vessel 1 while the vessel 1 is sailing. By not performing torque increase processing when the vessel speed is suddenly reduced as a result of the vessel helmsman operating the operating lever 32 to decelerate the vessel 1, it is possible to prevent the deceleration of the vessel 1 in response to the vessel 1 deceleration operation from becoming sluggish.

[0045] The required torque increase rate reference value Wth may be set to a predetermined small negative value. That is, whether the vessel helmsman operates the control lever 32 to suddenly and significantly decelerate the vessel 1 or whether the vessel helmsman operates the control lever 32 to slowly or gently decelerate the vessel 1, the increase rate of the required torque per unit time is less than 0. Therefore, if the increase rate of the required torque is set to 0, the torque boosting process will not be executed even if the vessel speed suddenly decreases while the vessel helmsman operates the control lever 32 to slowly or gently decelerate the vessel 1. However, since the operation of slowly or gently decelerating the vessel 1 does not result in a sudden decrease in vessel speed, even if the torque boosting process is permitted while the vessel helmsman operates the control lever 32 to slowly or gently decelerate the vessel 1, the torque boosting process will rarely actually be executed. On the other hand, while the vessel helmsman is slowly or gently decelerating the vessel 1, for example, if the vessel 1 jumps and lands on water or if the vessel collides head-on with a high wave, the vessel speed may suddenly and significantly decrease. In order to prevent such a sudden and large decrease in vessel speed, it is preferable to allow the execution of the torque boosting process while the vessel helmsman is operating to slightly or gently decelerate the vessel 1. Therefore, the increase rate of the required torque when the vessel helmsman is operating the control lever 32 to slightly or gently decelerate the vessel 1 may be obtained by experiment or simulation (this increase rate will be a small negative value), and this increase rate may be set as the required torque increase rate reference value Wth.

[0046] If the current increase rate w of the required torque r per unit time is equal to or greater than the required torque increase rate reference value Wth, the rotation speed determination unit 26 then calculates the deceleration d of the current rotation speed of the prime mover 8 based on the detection signal output from the rotation detection unit 10 to the upper control unit 23, and determines whether the deceleration d is equal to or greater than the deceleration reference value Dth (step ST4).

[0047] By determining whether the deceleration d of the rotational speed of the prime mover 8 is equal to or greater than the deceleration reference value Dth, it is possible to recognize whether the rotational speed of the prime mover 8 has suddenly decreased. Furthermore, if the load on the propeller 7 (for example, water resistance) suddenly increases, the rotational speed of the propeller 7 suddenly decreases, and accordingly, the rotational speed of the prime mover 8 also suddenly decreases. Then, if the rotational speeds of the propeller 7 and the prime mover 8 suddenly decrease, the thrust generated by the outboard motor 6 suddenly decreases, and the boat speed suddenly decreases. Furthermore, if the water resistance or the like applied to the hull 2 ​​suddenly increases, the boat speed suddenly decreases. Then, if the boat speed suddenly decreases, the load on the propeller 7 (for example, water resistance) suddenly increases, and the rotational speed of the propeller 7 suddenly decreases, and accordingly, the rotational speed of the prime mover 8 also suddenly decreases. In this way, a sudden increase in the load on the propeller 7 causes a sudden decrease in the rotation speed of the prime mover 8, resulting in a sudden decrease in the boat speed, and a sudden increase in the load on the hull 2 ​​causes a sudden decrease in the boat speed, resulting in a sudden decrease in the rotation speed of the prime mover 8. Therefore, whether or not the boat speed has suddenly decreased can be determined by determining whether or not the rotation speed of the prime mover 8 has suddenly decreased. In other words, whether or not the boat speed has suddenly decreased can be determined by determining whether or not the deceleration d of the rotation speed of the prime mover 8 is equal to or greater than the deceleration reference value Dth.

[0048] The sudden vessel speed reduction suppression process recognizes a sudden decrease in vessel speed while the vessel 1 is sailing due to, for example, the vessel 1 landing on water or the vessel 1 colliding with a wave, and when such a sudden decrease in vessel speed is recognized, increases the drive torque generated by the engine 8 to reduce the amount of decrease in vessel speed, thereby aiming to suppress a sudden and large decrease in vessel speed. To achieve this, it is necessary to recognize a sudden decrease in vessel speed and execute torque increase processing before the vessel speed decreases significantly due to, for example, the vessel 1 landing on water or the vessel 1 colliding with a wave. Therefore, the sudden vessel speed reduction suppression process recognizes a sudden decrease in vessel speed when the vessel speed begins to decelerate due to, for example, the vessel 1 landing on water or the vessel 1 colliding with a wave, or in other words, the start of a sudden decrease in vessel speed. Specifically, the deceleration of the rotational speed of the engine 8 is the amount or rate of decrease in the rotational speed of the engine 8 per unit time. In the vessel sudden deceleration suppression process, the unit time for calculating the deceleration d of the rotational speed of the engine 8 is set to a time that is significantly shorter than the time from when the vessel speed starts to decrease due to the vessel 1 landing on water or the vessel 1 colliding with waves until the vessel speed decreases significantly (until the amount of decrease in vessel speed reaches its maximum). For example, the unit time for calculating the deceleration d of the rotational speed of the engine 8 is set to, for example, approximately 0.05 to 0.1 seconds. This makes it possible to recognize a sudden decrease in vessel speed in an extremely short time, or in other words, instantly, after the vessel speed starts to decrease due to the vessel 1 landing on water or the vessel 1 colliding with waves, that is, to recognize the start of a sudden decrease in vessel speed. Furthermore, the deceleration reference value Dth is set to the deceleration of the rotational speed of the engine 8 at the start of a sudden decrease in vessel speed due to the vessel 1 landing on water or the vessel 1 colliding with waves, etc. Such a deceleration can be determined, for example, by experiment or simulation.

[0049] In the process of determining whether the ship speed is rapidly decreasing, the following determinations are made in this order: whether the ship speed s is equal to or greater than the ship speed reference value Sth; whether the required torque r is equal to or greater than the required torque reference value Rth; whether the increase rate w of the required torque r is equal to or greater than the required torque increase rate reference value Wth; and whether the deceleration d of the rotation speed of the prime mover 8 is equal to or greater than the deceleration reference value Dth; however, the order of these determinations can be reversed.

[0050] If the current boat speed s is not equal to or greater than the boat speed reference value Sth, the required torque r currently output from the drive control unit 24 is not equal to or greater than the required torque reference value Rth, the current increase rate w of the required torque r per unit time is not equal to or greater than the required torque increase rate reference value Wth, or the current deceleration d of the rotational speed of the prime mover 8 is not equal to or greater than the deceleration reference value Dth, the boat speed sudden decrease determination process is executed again. On the other hand, if the current boat speed s is equal to or greater than the boat speed reference value Sth, the required torque r currently output from the drive control unit 24 is equal to or greater than the required torque reference value Rth, the current increase rate w of the required torque r per unit time is equal to or greater than the required torque increase rate reference value Wth, and the current deceleration d of the rotational speed of the prime mover 8 is equal to or greater than the deceleration reference value Dth, the torque boosting processor 29 starts the torque boosting process.

[0051] In the torque boosting process, the torque boosting processor 29 first determines the boost torque ra according to the current deceleration d of the rotation speed of the prime mover 8 (step ST5). Specifically, the torque boosting processor 29 increases the boost torque ra as the current deceleration d of the rotation speed of the prime mover 8 increases.

[0052] Next, the torque boosting processing unit 29 stores the current required torque r as the basic required torque rb in the storage device of the higher-level control unit 23 (step ST6).

[0053] Next, the torque boosting processing unit 29 increases the required torque r by adding the boosted torque ra to the current required torque r (step ST7). As a result, the required torque r increases by an amount equivalent to the boosted torque ra, even though the operator has not increased the tilt angle of the control lever 32 while the boat 1 is sailing. The increased required torque r is output as a command signal from the drive control unit 24 to the subordinate control unit 22, thereby increasing the drive torque generated by the prime mover 8. Furthermore, the increase in the drive torque generated by the prime mover 8 increases as the deceleration d of the current rotation speed of the prime mover 8 increases.

[0054] Next, the torque boosting processor 29 gradually reduces the required torque r, which was increased in step ST7, until it becomes equal to or less than the basic required torque rb. Specifically, the torque boosting processor 29 reads the basic required torque rb stored in the storage device of the upper control unit 23, and repeatedly reduces the required torque r by a unit amount until the required torque r, which was increased in step ST7, becomes equal to or less than the basic required torque rb (steps ST8 and ST9). As a result, the required torque r gradually decreases even though the operator is not gradually decreasing the tilt angle of the operating lever 32. Furthermore, because the required torque r is continuously output from the drive control unit 24 to the lower control unit 22, the drive torque generated by the prime mover 8 gradually decreases in response to the gradual decrease in the required torque r.

[0055] When the required torque r becomes equal to or less than the basic required torque rb, the process of gradually reducing the required torque r ends. The basic required torque rb is equal to the required torque r immediately before the boost torque ra is added to the required torque r. Therefore, the required torque r at the time when the process of gradually reducing the required torque r ends is approximately equal to the required torque r immediately before the boost torque ra is added to the required torque r. Then, the process returns to step ST1.

[0056] Fig. 5 shows an example of the required torque r, the vessel speed s, and the rotation speed n of the prime mover 8 when the vessel speed sudden decrease suppression process is performed. In addition, in order to show the behavior of the vessel 1, a graph showing the change in the position of the waterline of the vessel 1 is added at the top of Fig. 5.

[0057] In Fig. 5, while the boat 1 is sailing, it jumps over a wave, for example, at time t1, and lands on water at time t2. Immediately after the boat 1 lands on water at time t2, a sudden decrease in boat speed is recognized instantaneously by the boat speed sudden decrease determination process, and then the torque increase process is instantaneously started and terminated at time t3. From time t0 to time t4 in Fig. 5, the operating lever 32 is not operated at all; that is, the operating lever 32 is in the forward position, and the tilt angle of the operating lever 32 does not change.

[0058] To explain in more detail, at time t1 in Figure 5, the boat 1 jumps, causing the propeller 7 of the outboard motor 6 to rise above the water surface, reducing the load (water resistance) on the propeller 7 and significantly increasing the rotation speed n of the prime mover 8.

[0059] After that, at time t2, the jumped vessel 1 lands on the water. As can be seen from the fact that the waterline position at time t2 is higher than the waterline position K when the vessel 1 is normally sailing, the vessel 1 is deeper underwater when it lands on the water than when it is normally sailing. Therefore, at time t2, the water resistance acting on the hull 2 ​​and propeller 7 increases sharply, and as a result, the vessel speed s and the rotation speed n of the prime mover 8 both decrease sharply at the same time.

[0060] Furthermore, at time t2, i.e., the time when the boat 1 lands on water, the boat speed s is equal to or greater than the boat speed reference value Sth, the required torque r is equal to or greater than the required torque reference value Rth, the increase rate w of the required torque r is equal to or greater than the required torque increase rate reference value Wth (=0), and the deceleration d of the rotation speed n of the prime mover 8 is equal to or greater than the deceleration reference value Dth. As a result, immediately after time t2, i.e., immediately after the boat 1 lands on water, a sudden decrease in boat speed is recognized by the boat speed sudden decrease determination process, and then, the torque augmentation process is instantaneously started. Then, the torque augmentation process increases the required torque r by an amount equivalent to the augmentation torque ra. As a result, immediately after the boat 1 lands on water, the drive torque generated by the prime mover 8 increases, and the propulsive force generated by the outboard motor 6 increases. As a result, the amount of decrease in boat speed when the boat 1 suddenly decreases due to lands on water is reduced.

[0061] In the graph of vessel speed s in Figure 5, solid line Ls1 shows the change in vessel speed s when torque augmentation processing is performed, and dashed line Lb1 shows the change in vessel speed s when torque augmentation processing is not performed. As can be seen from solid line Ls1 and dashed line Lb1, when torque augmentation processing is performed, the amount of vessel speed reduction when vessel speed suddenly decreases due to vessel 1 hitting water is smaller than when torque augmentation processing is not performed. Furthermore, when torque augmentation processing is performed, the vessel speed rebound (the phenomenon in which vessel speed repeatedly decreases and increases) after the vessel speed suddenly decreases due to vessel 1 hitting water is smaller than when torque augmentation processing is not performed. Note that vessel speed rebound does not occur in Figure 5.

[0062] Furthermore, in the graph of the rotation speed n of the prime mover 8 in Figure 5, the solid line Ls2 shows the change in the rotation speed n of the prime mover 8 when the torque boosting process is executed, and the dashed line Lb2 shows the change in the rotation speed n of the prime mover 8 when the torque boosting process is not executed. As can be seen from the solid line Ls2 and the dashed line Lb2, when the torque boosting process is executed, the amount of decrease in the rotation speed of the prime mover 8 when the vessel speed suddenly decreases due to the vessel 1 hitting water is smaller than when the torque boosting process is not executed. Furthermore, when the torque boosting process is executed, the fluctuation in the rotation speed of the prime mover 8 after the vessel speed suddenly decreases due to the vessel 1 hitting water is smaller than when the torque boosting process is not executed. Note that in Figure 5, there is no fluctuation in the rotation speed after the vessel speed suddenly decreases.

[0063] As described above, the engine control device 21 according to the embodiment of the present invention instantly recognizes a sudden decrease in boat speed through the boat speed sudden decrease determination process immediately after the boat 1 lands on water, and then instantly performs torque increase process. This reduces the amount of boat speed decrease when the boat 1 suddenly decreases in boat speed due to the boat 1 landing on water, and also reduces the rebound of boat speed after the boat 1 suddenly decreases in boat speed due to the boat 1 landing on water. This prevents the boat operator or passengers from being pushed forward when the boat 1 lands on water, and also prevents the boat operator or passengers from being subjected to large vibrations in the fore-and-aft direction. This improves the comfort of the boat. Similarly, the engine control device 21 also reduces the amount of boat speed decrease when the boat 1 suddenly decreases in boat speed due to hitting a high wave head-on while sailing, and also reduces the rebound of boat speed, thereby improving the comfort of the boat.

[0064] Furthermore, in the torque boosting process in the boat speed sudden decrease suppression process of the motor control device 21, the boost torque ra is determined according to the deceleration d of the rotational speed of the motor 8 at time t2. Specifically, the greater the deceleration d of the rotational speed of the motor 8 at time t2, the greater the boost torque ra. As a result, the greater the deceleration d of the rotational speed of the motor 8 at time t2, the greater the increase in the drive torque generated by the motor 8. In this way, the increase in the drive torque generated by the motor 8 by the torque boosting process, i.e., the increase in the propulsive force generated by the outboard motor 6, can be made to be approximately balanced with the decrease in boat speed caused by the boat 1 landing on water or the boat 1 colliding with a wave, for example. Therefore, even when the boat 1 jumps very high and hits water, or when the boat 1 hits a high wave head-on, the decrease in boat speed during a sudden decrease in boat speed can be reliably reduced. In addition, when the boat 1 makes a low jump and lands on the water, or when the boat 1 lightly hits a high wave head-on, the torque boosting process prevents the propulsive force generated by the outboard motor 6 from becoming excessively large, causing the boat speed to suddenly decrease and then increase significantly, causing the boat 1 to vibrate back and forth.

[0065] Immediately after time t2 in Figure 5, the required torque r increases by an amount equivalent to the increased torque ra due to the torque increase process, and then the required torque r gradually decreases due to the torque increase process. Then, at time t3, the magnitude of the required torque r becomes approximately equal to the magnitude of the required torque r at time t2 (the required torque r immediately before the increase). Also, at time t3, the torque increase process ends. Then, after time t3, the required torque r, the drive torque generated by the prime mover 8, and the propulsive force generated by the outboard motor 6 correspond to the tilt angle of the operating lever 32 at that time.

[0066] In this way, according to the prime mover control device 21 of the embodiment of the present invention, immediately after the boat 1 lands on water or collides with a wave, the required torque r is instantaneously increased by the torque boosting process, and then the required torque r is gradually reduced, thereby preventing sudden changes in the required torque r, the driving torque generated by the motor 8, and the propulsive force generated by the outboard motor 6 at the end of the torque boosting process, and preventing the boat 1 from vibrating back and forth due to such sudden changes at the end of the torque boosting process.

[0067] As described above, the prime mover control device 21 of the embodiment of the present invention increases the propulsive force generated by the outboard motor 6 when the boat speed suddenly decreases while the boat 1 is sailing, for example, when the boat 1 jumps onto the water or hits a high wave head-on. This reduces the amount of decrease in boat speed when the boat suddenly decreases. Therefore, when the boat 1 hits the water or collides with a wave, it is possible to prevent the operator or passengers from being pushed forward by a large force, thereby improving the comfort of the boat during sailing.

[0068] Furthermore, according to the prime mover control device 21 of the embodiment of the present invention, by combining a determination of whether the vessel speed s is equal to or greater than the vessel speed reference value Sth, a determination of whether the required torque r is equal to or greater than the required torque reference value Rth, and a determination of whether the deceleration d of the rotation speed of the prime mover 8 is equal to or greater than the deceleration reference value Dth, it is possible to accurately recognize a sudden decrease in vessel speed due to the vessel 1 landing on water or the vessel 1 colliding with a wave, etc. Furthermore, according to the prime mover control device 21 of the embodiment of the present invention, by adding a determination of whether the increase rate w of the required torque r is equal to or greater than the required torque increase rate reference value Wth to these determinations, it is possible to prevent the torque boosting process from being executed when the vessel speed is suddenly decreased due to the operation of the control lever 32 by the vessel operator. Therefore, it is possible to prevent the deceleration of the vessel 1 in response to the deceleration operation of the vessel 1 from becoming sluggish, and good maneuverability of the vessel 1 can be ensured.

[0069] In the above embodiment, the process for determining whether the ship speed is suddenly reduced is described as an example of determining whether the deceleration d of the rotation speed of the prime mover 8 is equal to or greater than the deceleration reference value Dth of the rotation speed of the prime mover 8. However, the present invention is not limited to this, and it may be determined whether the deceleration of the rotation speed of the propeller 7 is equal to or greater than the deceleration reference value of the rotation speed of the propeller 7.

[0070] In addition, in the above embodiment, the sudden boat speed reduction determination process is exemplified by the cases where (1) a determination is made as to whether the boat speed s is equal to or greater than the boat speed reference value Sth, (2) a determination is made as to whether the required torque r is equal to or greater than the required torque reference value Rth, (3) a determination is made as to whether the increase rate w of the required torque r is equal to or greater than the required torque increase rate reference value Wth, and (4) a determination is made as to whether the deceleration d of the rotation speed of the prime mover 8 is equal to or greater than the deceleration reference value Dth, but the present invention is not limited to this. In the sudden boat speed reduction determination process, for example, of these determinations (1) to (4), only determinations (1), (3), and (4) may be made, or only determinations (2), (3), and (4) may be made. Furthermore, when there is a clear difference between the deceleration of the rotation speed of the prime mover 8 caused by the vessel 1 landing on water or the like when traveling at high speed and the deceleration of the rotation speed of the prime mover 8 caused by the vessel 1 landing on water or the like when traveling at low speed, it is possible to accurately predict, based on the deceleration of the rotation speed of the prime mover 8, that the vessel speed will suddenly decrease significantly when traveling at high speed due to the vessel 1 landing on water or the like. In such cases, the vessel speed sudden decrease determination process may only perform the determinations (3) and (4). Furthermore, when it is more important to prevent a sudden deceleration of the vessel 1 due to a sudden and large deceleration operation than to have the vessel 1 decelerate more slowly in response to the deceleration operation of the vessel 1, the vessel speed sudden decrease determination process may not perform the determination of (3). In other words, the torque boosting process may be performed even when the vessel speed suddenly decreases due to the vessel helmsman's deceleration operation of the vessel 1.

[0071] Furthermore, in the torque boosting process of the above embodiment, the boost torque ra is changed according to the deceleration d of the rotation speed of the prime mover 8, but the boost torque ra may be set to a predetermined fixed value regardless of the deceleration d of the rotation speed of the prime mover 8.

[0072] Furthermore, in the torque boosting process of the above embodiment, the required torque r is increased and then gradually reduced, but if the longitudinal vibration of the vessel 1 at the end of the torque boosting process is not a significant problem, the required torque r does not need to be gradually reduced.

[0073] Furthermore, in the above embodiment, the required torque functions as a command value for controlling the drive torque generated by the prime mover 8, but if the prime mover 8 is an engine and torque-based control is not adopted as the engine control method, the required torque may be replaced with a command value for controlling the throttle opening of a throttle device provided in the engine, etc.

[0074] Furthermore, the present invention can be modified as appropriate within the scope that does not contradict the gist or concept of the invention that can be read from the claims and the entire specification, and a motor control device for a marine propulsion unit that involves such modifications is also included in the technical concept of the present invention. [Explanation of symbols]

[0075] 1 ship 6 Outboard motors (marine propulsion units) 7 propellers 8 Prime Mover 21 Prime mover control device 22 Lower control section 23 Upper control section 24 Drive control unit 25. Ship speed sudden decrease suppression control unit 26 Rotation speed determination unit 27 Ship speed judgment section 28 Required torque determination unit 29 Torque boosting processing section 31 Remote control device (operating device) 32 Operating lever

Claims

1. A motor control device for a marine vessel propulsion device that controls a motor of the marine vessel propulsion device having a propeller and a motor that rotates the propeller, a drive control unit that drives the prime mover so that the prime mover generates a drive torque corresponding to an operation amount of an operation device that operates the marine vessel propulsion machine; a rotation speed determination unit that determines whether the deceleration of the rotation speed of the prime mover or the propeller is equal to or greater than a predetermined deceleration reference value; and a torque boosting processing unit that performs torque boosting processing to increase the drive torque generated by the prime mover beyond the drive torque corresponding to the amount of operation of the operating device when the deceleration of the rotation speed is equal to or greater than the deceleration reference value as a result of the determination by the rotation speed determination unit.

2. a vessel speed determination unit that determines whether the speed of the vessel provided with the vessel propulsion device is equal to or greater than a predetermined vessel speed reference value; 2. The prime mover control device for a vessel propulsion device according to claim 1, wherein the torque boosting processing unit performs the torque boosting processing when the rotation speed determination unit determines that the deceleration of the rotation speed is equal to or greater than the deceleration reference value, and when the vessel speed determination unit determines that the vessel speed is equal to or greater than the vessel speed reference value.

3. a first required torque determination unit that determines whether a required torque corresponding to an operation amount of the operating device is equal to or greater than a predetermined required torque reference value; the drive control unit drives the prime mover so that the prime mover generates a drive torque corresponding to the required torque, 2. The prime mover control device for a marine propulsion device according to claim 1, wherein the torque boosting processing unit performs the torque boosting processing when the rotation speed determination unit determines that the deceleration of the rotation speed is equal to or greater than the deceleration reference value, and when the first required torque determination unit determines that the required torque is equal to or greater than the required torque reference value.

4. a second required torque determination unit that determines whether an increase rate of the required torque corresponding to the operation amount of the operating device is equal to or greater than a predetermined required torque increase rate reference value; the drive control unit drives the prime mover so that the prime mover generates a drive torque corresponding to the required torque, 2. The prime mover control device for a marine propulsion device according to claim 1, wherein the torque boosting processing unit performs the torque boosting processing when the rotation speed determination unit determines that the deceleration of the rotation speed is equal to or greater than the deceleration reference value and the second required torque determination unit determines that the increase rate of the required torque is equal to or greater than the required torque increase rate reference value.

5. 2. The prime mover control device for a marine propulsion device according to claim 1, wherein the torque boosting processing unit increases the amount of increase in the drive torque generated by the prime mover as the deceleration of the rotation speed increases.

6. the torque boosting processing unit adds a boost torque to the driving torque of the prime mover according to the operation amount of the operating device in the torque boosting process, 2. The motor control device for a marine propulsion device according to claim 1, wherein the torque boosting processing unit increases the boosted torque as the deceleration of the rotational speed increases.

7. 2. The prime mover control device for a marine propulsion device according to claim 1, wherein the torque boosting processing unit, in the torque boosting process, adds a boosting torque to the drive torque of the prime mover that corresponds to the amount of operation of the operating device, and then gradually reduces the drive torque of the prime mover.

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