Method and apparatus for controlling a propulsive force of a marine vessel

1. A propulsive force controlling apparatus for controlling a propulsion system that is attached to a hull of a marine vessel and includes a motor and a propulsive force generating member which receives a torque from the motor to generate a propulsive force, the propulsive force controlling apparatus comprising:

a clutch mechanism which operates only in either a coupling state which permits transmission of the torque from the motor to the propulsive force generating member with virtually no slippage and a decoupling state which prohibits the transmission of the torque from the motor to the propulsive force generating member;

a clutch actuator which actuates the clutch mechanism;

a target propulsive force acquiring section which acquires a target propulsive force to be generated by the propulsion system, the target propulsive force acquiring section includes a target rotational speed acquiring section which acquires a target rotational speed of the motor; and

a clutch controlling section including a rotational speed comparing section which compares the target rotational speed acquired by the target rotational speed acquiring section with a predetermined lower limit to judge whether to perform an intermittent coupling control operation to intermittently maintain the clutch mechanism in the coupling state, and which performs the intermittent coupling control operation if the target rotational speed is lower than the lower limit.

2. A propulsive force controlling apparatus as set forth in claim 1 , wherein the clutch controlling section includes:

a coupling duration calculating section which calculates a duration of the coupling state in a predetermined control period according to the target propulsive force acquired by the target propulsive force acquiring section; and

an intermittent coupling controlling section which maintains the clutch mechanism in the coupling state for the duration calculated by the coupling duration calculating section, and maintains the clutch mechanism in the decoupling state for the rest of the control period for switching the clutch mechanism alternately between the coupling state and the decoupling state.

3. A propulsive force controlling apparatus as set forth in claim 2 , further comprising a motor controlling section which drives the motor at a predetermined reference rotational speed if the comparison result provided by the target rotational speed comparing section indicates that the target rotational speed is lower than the lower limit, wherein

the coupling duration calculating section calculates the duration of the coupling state of the clutch mechanism so as to provide a propulsive force that is equivalent to a propulsive force to be generated by driving the motor at the target rotational speed, if the comparison result provided by the target rotational speed comparing section indicates that the target rotational speed is lower than the lower limit.

4. A propulsive force controlling apparatus as set forth in claim 3 , wherein the coupling duration calculating section calculates the duration of the coupling state of the clutch mechanism from the following expression:

s =( Na/Nb )· S

wherein s is the duration of the coupling state, Na is the target rotational speed, Nb is the reference rotational speed, and S is the control period.

5. A propulsive force controlling apparatus as set forth in claim 3 , wherein the reference rotational speed is equal to the lower limit.

6. A propulsive force controlling apparatus as set forth in claim 1 , wherein

the marine vessel includes a plurality of propulsion systems attached to the hull, and

the clutch controlling section controls clutch actuators provided in the respective propulsion systems so that clutch mechanisms provided in the respective propulsion systems are switched between the coupling state and the decoupling state in synchronization with each other during the intermittent coupling control operation for intermittently maintaining the clutch mechanisms in the coupling state.

7. A propulsive force controlling apparatus as set forth in claim 1 , further comprising a motor state judging section which judges whether the motor is active or inactive, wherein

the clutch controlling section interrupts the intermittent coupling control operation of the clutch mechanism if the motor state judging section determines that the motor, is inactive during the intermittent coupling control operation, and restarts the intermittent coupling control operation when the motor state judging section thereafter determines that the motor is active.

8. A propulsive force controlling apparatus as set forth in claim 7 , wherein

the marine vessel includes a plurality of propulsion systems attached to the hull,

the motor state judging section judges whether motors provided in the respective propulsion systems are each active or inactive, and

the clutch controlling section interrupts the intermittent coupling control operation of all clutch mechanisms provided in the respective propulsion systems if the motor state judging section determines that at least one of the motors is inactive during the intermittent coupling control operation of the clutch mechanisms.

9. A propulsive force controlling apparatus as set forth in claim 7 , further comprising a restart controlling section which restarts the motor that has been judged to be inactive by the motor state judging section.

10. A propulsive force controlling apparatus as set forth in claim 1 , wherein the clutch mechanism can be switched among a forward drive coupling state in which the torque is transmitted from the motor to the propulsive force generating member so as to move the hull forward, a rearward drive coupling state in which the torque is transmitted from the motor to the propulsive force generating member so as to move the hull rearward, and the decoupling state which prohibits the transmission of the torque from the motor to the propulsive force generating member.

11. A marine vessel maneuvering supporting system for supporting maneuvering of a marine vessel having a hull and a propulsion system attached to the hull, the propulsion system including a motor and a propulsive force generating member which receives a torque from the motor to generate a propulsive force, the marine vessel maneuvering supporting system comprising:

a clutch mechanism which operates only in either a coupling state which permits transmission of the torque from the motor to the propulsive force generating member with virtually no slippage and a decoupling state which prohibits the transmission of the torque from the motor to the propulsive force generating member;

a clutch actuator which actuates the clutch mechanism;

a target propulsive force inputting section for inputting a target propulsive force to be generated by the propulsion system; and

a propulsive force controlling apparatus which controls the propulsion system on the basis of the target propulsive force input from the target propulsive force inputting section, the propulsive force controlling apparatus including:

a target propulsive force acquiring section which acquires the target propulsive force input from the target propulsive force inputting section, the target propulsive force acquiring section includes a target rotational speed acquiring section which acquires a target rotational speed of the motor; and

a clutch controlling section including a rotational speed comparing section which compares the target rotational speed acquired by the target rotational speed acquiring section with a predetermined lower limit to judge whether to perform an intermittent coupling control operation to intermittently maintain the clutch mechanism in the coupling state and which performs the intermittent coupling control operation if the target rotational speed is lower than the lower limit.

12. A marine vessel comprising:

a hull;

a propulsion system attached to the hull and including a motor, a propulsive force generating member which receives a torque from the motor to generate a propulsive force, a clutch mechanism which operates only in either a coupling state which permits transmission of the torque from the motor to the propulsive force generating member with virtually no slippage and a decoupling state which prohibits the transmission of the torque from the motor to the propulsive force generating member, and a clutch actuator which actuates the clutch mechanism;

a target propulsive force inputting section for inputting a target propulsive force to be generated by the propulsion system; and

a propulsive force controlling apparatus which controls the propulsion system on the basis of the target propulsive force input from the target propulsive force inputting section, the propulsive force controlling apparatus including:

a target propulsive force acquiring section which acquires the target propulsive force input from the target propulsive force inputting section, the target propulsive forceacquiring section includes a target rotational speed acquiring section which acquires a target rotational speed of the motor; and

a clutch controlling section including a rotational speed comparing section which compares the target rotational speed acquired by the target rotational speed acquiring section with a predetermined lower limit to judge whether to perform an intermittent coupling control operation to intermittently maintain the clutch mechanism in the coupling state, and which performs the intermittent coupling control operation if the target rotational speed is lower than the lower limit.

13. A propulsive force controlling method for controlling a propulsion system attached to a hull of a marine vessel and including a motor, a propulsive force generating member which receives a torque from the motor to generate a propulsive force, a clutch mechanism which operates only in either a coupling state which permits transmission of the torque from the motor to the propulsive force generating member with virtually no slippage and a decoupling state which prohibits the transmission of the torque from the motor to the propulsive force generating member, and a clutch actuator which actuates the clutch mechanism, the method comprising the steps of:

acquiring a target propulsive force to be generated by the propulsion system;

the target propulsive force acquiring step includes the step of acquiring a target rotational speed of the motor;

comparing the acquired target rotational speed with a predetermined lower limit to judge whether to perform an intermittent coupling control operation to intermittently maintain the clutch mechanism in the coupling state; and

performing the intermittent coupling control operation if the target rotational speed is lower than the lower limit.