Outboard motor control apparatus

In an apparatus for controlling operation of an outboard motor mounted on a boat and having a torque converter equipped with a lockup clutch, it is configured to calculate a speed ratio of the torque converter based on an input rotation speed and output rotation speed of the torque converter, detect manifold absolute pressure of the engine, control the lockup clutch to ON when the calculated speed ratio has been equal to or greater than a reference value, and control the lockup clutch to OFF when the manifold absolute pressure has been decreased by a first predetermined value or more. With this, it becomes possible to prevent the boat speed from decreasing even when the resistance of water flow acting on the boat increases due to the influence of a wave etc., thereby maintaining the maximum speed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an outboard motor control apparatus, particularly to an apparatus for controlling an outboard motor having a torque converter.

2. Description of the Related Art

In recent years, there is proposed an outboard motor having a torque converter interposed between an internal combustion engine and drive shaft to amplify output torque of the engine and then transmit it to the drive shaft for enhancing acceleration performance, etc., as taught, for example, by Japanese Laid-Open Patent Application No. 2007-315498 ('498). In this conventional technique, the torque converter includes a lockup clutch.

SUMMARY OF THE INVENTION

The outboard motor having the torque converter as in the reference is configured so that the lockup clutch is made ON (engaged) upon completion of the acceleration to prevent loss in transmittance of the engine output caused by slippage of the torque converter, thereby making the boat speed reach the maximum speed.

In the case where a boat equipped with such the outboard motor climbs up and goes over a relatively big wave with the lockup clutch positioned ON, the wave influences the resistance of water flow acting on the boat to increase. It results in the insufficiency of the output torque of the engine, whereby the boat speed may decrease. It is disadvantageous that the maximum speed can not be maintained.

An object of this invention is therefore to overcome the foregoing drawback by providing an apparatus for controlling an outboard motor having a torque converter, which apparatus can prevent the boat speed from decreasing even when the resistance of water flow acting on the boat increases due to the influence of a wave or the like, thereby maintaining the maximum speed.

In order to achieve the object, this invention provides in its first aspect an apparatus for controlling operation of an outboard motor mounted on a stern of a boat and having an internal combustion engine to power a propeller, a drive shaft connecting the engine and the propeller, and a torque converter equipped with a lockup clutch and interposed between the engine and the drive shaft, comprising: a speed ratio calculator that calculates a speed ratio of the torque converter based on an input rotation speed and output rotation speed of the torque converter; a manifold absolute pressure detector that detects manifold absolute pressure of the engine; and a clutch controller that controls the lockup clutch to ON when the calculated speed ratio has been equal to or greater than a reference value, and controls the lockup clutch to OFF when the detected manifold absolute pressure has been decreased by a first predetermined value or more.

In order to achieve the object, this invention provides in its second aspect a method of controlling operation of an outboard motor mounted on a stern of a boat and having an internal combustion engine to power a propeller, a drive shaft connecting the engine and the propeller, and a torque converter equipped with a lockup clutch and interposed between the engine and the drive shaft, comprising steps of: calculating a speed ratio of the torque converter based on an input rotation speed and output rotation speed of the torque converter; detecting manifold absolute pressure of the engine; and controlling the lockup clutch to ON when the calculated speed ratio has been equal to or greater than a reference value, and controlling the lockup clutch to OFF when the detected manifold absolute pressure has been decreased by a first predetermined value or more.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred embodiment of an outboard motor control apparatus according to the invention will now be explained with reference to the attached drawings.

FIG. 1is an overall schematic view of an outboard motor control apparatus including a boat (hull) according to an embodiment of the invention.FIG. 2is an enlarged sectional side view partially showing the outboard motor shown inFIG. 1andFIG. 3is an enlarged side view of the outboard motor.

InFIGS. 1 to 3, a symbol10indicates an outboard motor. As illustrated, the outboard motor10is clamped (fastened) to the stern or transom of a boat (hull)12.

As shown inFIG. 2, the outboard motor10is fastened to the boat12through a swivel case14, tilting shaft16and stern brackets18. The outboard motor10is equipped with a mount frame20and shaft22. The shaft22is housed in the swivel case14to be rotatable about the vertical axis such that the outboard motor10can be rotated about the vertical axis relative to the boat12. The mount frame20is fixed at its upper end and lower end to a frame (not shown) constituting a main body of the outboard motor10.

An electric steering motor (actuator)24for operating the shaft22and a power tilt-trim unit26for regulating a tilt angle and trim angle of the outboard motor10are installed near the swivel case14. A rotational output of the steering motor24is transmitted to the shaft22via a speed reduction gear mechanism28and the mount frame20, whereby the outboard motor10is steered about the shaft22as a steering axis to the right and left directions (steered about the vertical axis).

The power tilt-trim unit26integrally comprises a hydraulic cylinder26afor adjusting the tilt angle and a hydraulic cylinder26bfor adjusting the trim angle. When the hydraulic cylinders26a,26bare extended and contracted, the swivel case14is rotated about the tilting shaft16as a rotational axis, thereby tiling up/down and trimming up/down the outboard motor10.

An internal combustion engine (hereinafter referred to as the “engine”)30is disposed in the upper portion of the outboard motor10. The engine30comprises a spark-ignition, water-cooling gasoline engine with a displacement of 2,200 cc. The engine30is located above the water surface and covered by an engine cover32.

An intake pipe34of the engine30is connected to a throttle body36. The throttle body36has a throttle valve38installed therein and an electric throttle motor (actuator)40for opening and closing the throttle valve38is integrally disposed thereto.

The output shaft of the throttle motor40is connected to the throttle valve38via a speed reduction gear mechanism (not shown). The throttle motor40is operated to open and close the throttle valve38, thereby regulating the flow rate of the air sucked in the engine30to control the engine speed.

The outboard motor10further comprises a drive shaft (vertical shaft)42installed parallel to the vertical axis to be rotatably supported, a torque converter44interposed between the engine30and drive shaft42, a hydraulic pump46that is attached to the drive shaft42and pumps operating oil to a lubricated portion of the engine30, the torque converter44and the like, and a reservoir50for reserving the operating oil.

The upper end of the drive shaft42is connected to a crankshaft52of the engine30through the torque converter44and the lower end thereof is connected via a shift mechanism54with a propeller shaft56supported to be rotatable about the horizontal axis. One end of the propeller shaft56is attached with a propeller60. Thus the drive shaft42connects the engine30with the propeller60.

FIG. 4is an enlarged sectional view showing a region around the torque converter44shown inFIG. 2.

As shown inFIG. 4, the torque converter44includes a pump impeller44aconnected to the crankshaft52through a drive plate62, a turbine runner44bthat is installed to face the pump impeller44ato receive/discharge the operating oil and connected to the drive shaft42, a stator44cinstalled between the pump impeller44aand turbine runner44b, a lockup clutch44dand other components.

FIG. 5is a hydraulic circuit diagram schematically showing the torque converter44, hydraulic pump46, etc.

The hydraulic pump46driven by the engine30pumps up the operating oil in the reservoir50and forwards it to a first oil passage64a. The pressurized operating oil forwarded to the first oil passage64ais supplied to the lubricated portion of the engine30or the like and then returns to the reservoir50through a second oil passage64b.

The first oil passage64ais provided with a third oil passage64cconnecting the first oil passage64awith an intake hole of the hydraulic pump46. The third oil passage64cis interposed with a relief valve66that opens when the pressure of the operating oil to be supplied to the engine30is at or above a defined value and closes when it is below the defined value.

A fourth oil passage64dfor circulating the operating oil to be supplied to the torque converter44is connected to the first oil passage64aat a point between a discharge hole of the hydraulic pump46and a branch point of the first and third oil passages64a,64c. A fifth oil passage64efor circulating the operating oil returning from the torque converter44to the hydraulic pump46is connected to the third oil passage64cat a location downstream of the relief valve66. The fourth and fifth oil passages64d,64eare installed with a lockup control valve70for controlling the operation of the lockup clutch44d.

The lockup control valve70is a solenoid valve. The output of the valve70is connected to a piston chamber44d1of the lockup clutch44dof the torque converter44, and also connected to a chamber (rear chamber)44d2disposed in the rear of the piston chamber44d1. The lockup control valve70switches the oil passage upon being magnetized/demagnetized, thereby controlling the ON/OFF state (engagement/release) of the lockup clutch44d.

Specifically, when the lockup control valve70is magnetized, the operating oil is supplied to the piston chamber44d1and discharged from the rear chamber44d2so as to make the lockup clutch44dON (engaged), and when the valve70is demagnetized (the status inFIG. 5; initial condition), the operating oil is supplied to the rear chamber44d2and discharged from the piston chamber44d1so as to make the lockup clutch44dOFF (released). Since the details of the aforementioned torque converter44is disclosed in '498, further explanation is omitted here.

The explanation ofFIG. 2will be resumed. The shift mechanism54comprises a forward bevel gear54aand reverse bevel gear54bwhich are connected to the drive shaft42to be rotated, a clutch54cwhich can engage the propeller shaft56with either one of the forward bevel gear54aand reverse bevel gear54b, and other components.

The interior of the engine cover32is disposed with an electric shift motor (actuator)72that drives the shift mechanism54. The output shaft of the shift motor72can be connected via a speed reduction gear mechanism (not shown) with the upper end of a shift rod54dof the shift mechanism54. When the shift motor72is operated, its output appropriately displaces the shift rod54dand a shift slider54eto move the clutch54cto change the shift position among a forward position, reverse position and neutral position.

When the shift position is forward or reverse, the rotational output of the drive shaft42is transmitted via the shift mechanism54to the propeller shaft56to rotate the propeller60in one of the directions making the boat12move forward or rearward. The outboard motor10is equipped with a power source (not shown) such as a battery or the like attached to the engine30to supply operating power to the motors24,40,72, etc.

As shown inFIG. 3, a throttle opening sensor74is installed near the throttle valve38and produces an output or signal indicative of opening of the throttle valve38, i.e., throttle opening TH. An absolute pressure sensor (manifold absolute pressure detector)76is installed in the intake pipe34on downstream of the throttle valve38and produces an output or signal proportional to the manifold absolute pressure (absolute pressure) Pb.

A shift position sensor80installed near the shift rod54dproduces an output or signal corresponding to a shift position (neutral, forward or reverse) and a neutral switch84also installed near the shift rod54dproduces an ON signal when the shift position is neutral and an OFF signal when it is forward or reverse.

A crank angle sensor84is installed near the crankshaft52of the engine30and produces a pulse signal at every predetermined crank angle. A drive shaft rotation speed sensor86is installed near the drive shaft42and produces an output or signal indicative of rotation speed of the drive shaft42.

The outputs of the foregoing sensors and switch are sent to an electronic control unit (ECU)90disposed in the outboard motor10. The ECU90which has a microcomputer including a CPU, ROM, RAM and other devices is installed in the engine cover32of the outboard motor10.

As shown inFIG. 1, a steering wheel94is installed near a cockpit (the operator's seat)92of the boat12to be manipulated or rotated by the operator. A steering angle sensor96installed near a shaft (not shown) of the steering wheel94produces an output or signal corresponding to the steering angle applied or inputted by the operator through the steering wheel94.

A remote control box100provided near the cockpit92is equipped with a shift/throttle lever102installed to be manipulated by the operator. Upon the manipulation, the lever102can be swung in the front-back direction from the initial position and is used by the operator to input a shift position change command and engine speed regulation command. A lever position sensor104is installed in the remote control box100and produces an output or signal corresponding to a position of the lever102. The outputs of the steering angle sensor96and lever position sensor104are also sent to the ECU90.

Based on the inputted outputs, the ECU90controls the operations of the motors and ON/OFF state of the lockup clutch44dof the torque converter44.

FIG. 6is a flowchart showing the control of the ECU90. The illustrated program is executed by the ECU90at predetermined interval, e.g., 100 milliseconds.

The program begins in S10, in which it is determined whether the shift position is neutral. This determination is made by checking as to whether the neutral switch82outputs the ON signal. When the result in S10is negative, i.e., it is determined to be in gear, the program proceeds to S12, in which the throttle opening TH is detected or calculated from the output of the throttle opening sensor74and to S14, in which a change amount (variation) DTH of the detected throttle opening TH per a unit time (e.g., 500 milliseconds) is calculated.

The program proceeds to S16, in which it is determined whether the throttle valve38is operated in the closing direction, i.e., the boat12is in a condition to be decelerated (hereinafter called “decelerating condition”). This determination is made by checking as to whether the change amount DTH of the throttle opening TH is less than 0 degree. Specifically, when the change amount DTH is a negative value, the throttle valve38is determined to be operated in the closing direction (the boat12is in the decelerating condition) and when the change amount DTH is 0 or a positive value, the throttle valve38is determined to be operated to stop or in the opening direction (the boat12is operated to cruise at a constant speed or accelerate).

When the result in S16is negative, the program proceeds to S18, in which it is determined whether a bit of an acceleration completed determination flag of the torque converter44(torque converter acceleration completed determination flag; explained later) is 0. Since the initial value of a bit of this flag is 0, the result in S18in the first program loop is generally affirmative and the program proceeds to S20, in which it is determined whether a bit of an amplification determination flag of the torque converter44(torque converter amplification determination flag) is 0.

As explained below, a bit of the amplification determination flag is set to 1 when a condition where the output torque of the engine30is amplified through the torque converter44and transmitted to the drive shaft42(i.e., where the operation of the outboard motor10is in a range (torque amplification range) that the torque is to be amplified by the torque converter44to accelerate the boat12) is established, and reset to 0 when the output torque of the engine30is not amplified (i.e., the operation of the outboard motor10is out of the torque amplification range).

Since the initial value of a bit of the amplification determination flag is also 0, the result in S20in the first program loop is generally affirmative and the program proceeds to S22, in which it is determined whether the throttle valve38is operated in the opening direction, i.e., the boat12is in a condition to be accelerated (hereinafter called “accelerating condition”). Specifically, the calculated change amount DTH of the throttle opening TH is compared with a first throttle predetermined value (threshold value) DTHref1and, when the change amount DTH is equal to or greater than the predetermined value DTHref1, the throttle valve38is determined to be operated in the opening direction (the boat12is in the accelerating condition). The first throttle predetermined value DTHref1is set to a value (e.g., 0.5 degree) enabling to determine whether the boat12is in the accelerating condition.

When the result in S22is negative, i.e., when the boat12is determined to be neither decelerated nor accelerated but is operated to cruise at a constant speed, the remaining steps are skipped and when the result is affirmative, the program proceeds to S24, in which the torque converter44is controlled with a lockup-OFF mode. The operation in the lockup-OFF mode is to demagnetize the lockup control valve70and make the lockup clutch44dof the torque converter44OFF. As a result, the output torque of the engine30is amplified through the torque converter44and transmitted to the drive shaft42, thereby improving acceleration performance.

Next, in S26, a bit of the torque converter amplification determination flag is set to 1 and the present program loop is terminated. When the bit of this flag is set to 1, since it means that the outboard motor10is in a condition that the output torque of the engine30is amplified by the torque converter44to accelerate the boat12, the result in S20in the next and subsequent loops is negative and the program proceeds to S28.

In S28, an input rotation speed NIN and output rotation speed NOUT of the torque converter44are detected or calculated. Since the input side of the torque converter44is connected to the crankshaft52of the engine30, the input rotation speed NIN is identical with the engine speed and therefore can be detected by counting the output pulses of the crank angle sensor84. The output rotation speed NOUT is detected from the output of the drive shaft rotation speed sensor86.

The program proceeds to S30, in which a speed ratio e of the torque converter44is calculated based on the input rotation speed NIN and output rotation speed NOUT. The speed ratio e is obtained by dividing the output rotation speed NOUT by the input rotation speed NIN as shown in the following equation.
Speed ratioe=(Output rotation speed NOUT)/(Input rotation speed NIN)

The program proceeds to S32, in which it is determined whether the torque amplification range of the torque converter44has ended, precisely, whether the torque amplification range (acceleration range) has been saturated and the acceleration has been completed. Specifically, the calculated speed ratio e is compared with a reference value (threshold value) eref and when the speed ratio e is equal to or greater than the reference value eref, it is determined that the torque amplification range has ended. The reference value eref is set to a value (e.g., 0.7) enabling to determine whether the torque amplification range has ended.

When the result in S32is affirmative, the program proceeds to S34, in which a change amount DNIN of the input rotation speed NIN (i.e., a change amount (variation) of the engine speed) is calculated. The change amount DNIN is obtained by subtracting the input rotation speed NIN detected in the present program loop from that detected in the previous program loop.

The program proceeds to S36, in which it is determined whether the speed of the boat12remains stable at the maximum speed or thereabout after the acceleration is completed. This determination is made by comparing an absolute value of the calculated change amount DNIN with a prescribed value (threshold value) DNINref. When the absolute value is equal to or less than the prescribed value DNINref, it is determined that the boat speed is stable at the maximum value or thereabout. The prescribed value DNINref is set to a value (e.g., 500 rpm) enabling to determine whether the speed of the boat12remains stable at about the maximum value after the acceleration is completed, in other words, the change amount DNIN is relatively small.

When the result in S36is affirmative, the program proceeds to S38, in which the torque converter44is controlled with the lockup-ON mode. The operation of the lockup-ON mode is to magnetize the lockup control valve70and make the lockup clutch44dON. Since this establishes the direct connection between the crankshaft52of the engine30and the drive shaft42, slippage of the torque converter44can be prevented so that the speed of the boat12reaches the maximum speed (in a range of the engine performance), thereby improving speed performance.

Thus, when the speed ratio e is equal to or greater than the reference value eref and the absolute value of the change amount DNIN is equal to or less than the prescribed value DNINref, the lockup clutch44dof the torque converter44is made ON. After the step of S38, in S40, a bit of the torque converter amplification determination flag is reset to 0 and in S42, a bit of the torque converter acceleration completed determination flag is set to 1. As is clear from above, the acceleration completed determination flag is set to 1 when the acceleration through torque amplification by the torque converter44is completed and the lockup clutch44dis made ON, and in the other cases, reset to 0, as described later.

When the result in S32or S36is negative, since it means that the torque amplification range of the torque converter44does not end (or is not saturated), or that the speed of the boat12is not stable at the maximum speed or thereabout, the steps of S38to S42are skipped and the program is terminated.

When a bit of the acceleration completed determination flag is set to 1 in S42, the result in S18in the next and subsequent loops is negative and the program proceeds to S44onward. In S44, based on the output of the absolute pressure sensor76, the manifold absolute pressure Pb of the intake pipe34is detected or calculated and in S46, based on the detected manifold absolute pressure Pb and the change amount DTH of the throttle opening TH, it is determined whether load of the engine30has changed.

To be specific, in the case where, for example, the boat12climbs up and goes over a relatively big wave with the lockup clutch44dpositioned ON, the wave influences the resistance of water flow acting on the boat12to increase. It results in the decrease of the engine speed and the insufficiency (decrease) of the output torque of the engine30, whereby the boat speed may decrease, as mentioned above. It is disadvantageous that the maximum speed can not be maintained.

Therefore, in this embodiment, the insufficiency of the output torque of the engine30due to the influence of a wave is detected or estimated based on change of load of the engine30. When the output torque insufficiency is detected, the lockup clutch44dis made OFF to amplify the output torque through the torque converter44so as to compensate for the insufficiency.

Specifically, in S46, when the change amount DTH is less than a second throttle predetermined value DTHref2(e.g., 0.5 degree) and the manifold absolute pressure Pb is decreased by a first predetermined value Pbref1or more within a predetermined time period (e.g., 500 milliseconds), i.e., when a change amount (variation) of the manifold absolute pressure Pb per a unit time is equal to or greater than the first predetermined value Pbref1on the negative side, it is determined that the engine load has changed in the increasing direction due to the influence of a wave and the output torque is insufficient.

More specifically, when the manifold absolute pressure Pb is decreased by the first predetermined value Pbref1or more despite the fact that the throttle opening TH hardly changes, it is estimated that the engine load has changed due to the influence of a wave. The second throttle predetermined value DTHref2is set to a value enabling to determine whether the change of the throttle opening TH is relatively small and the first predetermined value Pbref1is set to a value (e.g., 10 kPa) enabling to determine whether the engine load has changed due to the influence of a wave.

When it is determined in S46that there is no change or small change in the engine load, the remaining steps are skipped and when the load is determined to have changed in the increasing direction, the program proceeds to S48, in which the torque converter44is controlled with the lockup-OFF mode to make the lockup clutch44dOFF. As a result, the insufficiency of the output torque due to the influence of a wave is compensated through amplification. With this, it becomes possible to prevent the boat speed from decreasing, thereby maintaining the maximum speed.

The program proceeds to S50, in which a bit of the torque converter amplification determination flag is set to 1 and the program is terminated.

When the program proceeds to S46after the lockup clutch44dis made OFF in S48in a previous program loop, the determination as to the change in the load of the engine30is made again. The explanation thereon will be made in detail. After the boat12has gone over a big wave, the increased resistance of water flow acting on the boat12decreases and it results in the increase of the engine speed. Since the insufficient condition of the output torque of the engine30ends accordingly, it is not necessary to amplify the output torque by the torque converter44d. Further, at this time, if the lockup clutch44dremains OFF, it causes slippage of the torque converter44and the maximum speed may not be maintained.

Therefore, in this embodiment, the end of the insufficient condition of the output torque of the engine30is detected or estimated based on the change in the engine load and when it is detected that the insufficient condition has ended, the lockup clutch44dis made ON again to prevent slippage of the torque converter44, thereby reliably maintaining the maximum speed of the boat12.

Specifically, in S46, when the change amount DTH of the throttle opening TH is less than the second throttle predetermined value DTHref2and the manifold absolute pressure Pb is increased by a second predetermined value Pbref2or more within a predetermined time period (e.g., 500 milliseconds), i.e., when the change amount (variation) of the manifold absolute pressure Pb per a unit time is equal to or greater than the second predetermined value Pbref2on the positive side, it is determined that the engine load has changed in the decreasing direction because the boat12has gone over a wave and the insufficient condition of the output torque of the engine30has ended.

More specifically, when the manifold absolute pressure Pb is increased by the second predetermined value Pbref2or more despite the fact that the throttle opening TH hardly changes, it is estimated that the engine load has changed because there is no longer any influence of a wave. The second predetermined value Pbref2is set to a value (e.g., 10 kPa) enabling to determine whether the engine load has changed because there is no longer any influence of a wave.

When, in S46, the engine load is determined to have changed in the decreasing direction, the program proceeds to S52, in which the torque converter44is controlled with the lockup-ON mode to make the lockup clutch44dON again. Owing to this configuration, slippage of the torque converter44after the boat12has gone over a wave can be prevented, thereby reliably maintaining the maximum speed. After the processing of S52, in S54, a bit of the torque converter amplification determination flag is reset to 0 and the program is terminated.

When the result in S10is affirmative, i.e., when the shift position is neutral, the program proceeds to S56, in which the torque converter44is controlled with the lockup-ON mode, to S58, in which a bit of the torque converter amplification determination flag is reset to 0 and then to S60, in which a bit of the torque converter acceleration completed determination flag is reset to 0.

When the result in S16is affirmative, i.e., when the boat12is in the decelerating condition, the program proceeds to S62, in which the torque converter44is controlled with the lockup-OFF mode, to S64, in which a bit of the amplification determination flag is set to 1, to S66, in which a bit of the acceleration completed determination flag is reset to 0 and then the program is terminated.

As stated above, the embodiment is configured to have an apparatus for and a method of controlling operation of an outboard motor (10) mounted on a stern of a boat (12) and having an internal combustion engine (30) to power a propeller (60), a drive shaft (42) connecting the engine and the propeller, and a torque converter (44) equipped with a lockup clutch (44d) and interposed between the engine and the drive shaft, comprising: a speed ratio calculator (ECU90, S28, S30) that calculates a speed ratio (e) of the torque converter based on an input rotation speed (NIN) and output rotation speed (NOUT) of the torque converter; a manifold absolute pressure detector (absolute pressure sensor76, ECU90, S44) that detects manifold absolute pressure (Pb) of the engine; and a clutch controller (ECU90, S32, S38, S46, S48) that controls the lockup clutch to ON when the calculated speed ratio has been equal to or greater than a reference value (eref), and controls the lockup clutch to OFF when the detected manifold absolute pressure has been decreased by a first predetermined value (Pbref1) or more.

Thus, when the manifold absolute pressure Pb is decreased by the first predetermined value Pbref1or more, it is determined that, since the boat12is climbing up and going over a relatively big wave, the resistance of water flow acting on the boat12increases due to the influence of the wave, resulting in the insufficiency of the output torque of the engine30, and based on the determination, the lockup clutch44dis made OFF (i.e., the output torque of the engine30is amplified through the torque converter44). With this, even when the resistance of water flow acting on the boat12increases due to the influence of a wave, the insufficiency of the output torque is compensated through amplification by the torque converter44and it makes possible to prevent the boat speed from decreasing, thereby maintaining the maximum speed.

Further, since the lockup clutch44dis made ON when the calculated speed ratio e has been equal to or greater than the reference value eref, it becomes possible to accurately detect a time point when the acceleration is completed, and since the lockup clutch44dis made ON upon the completion of acceleration, speed performance can be enhanced. Further, slippage of the torque converter44can be prevented by making the lockup clutch44dON, thereby avoiding fuel efficiency from deteriorating.

In the apparatus and method, the clutch controller controls the lockup clutch to ON again when the detected manifold absolute pressure has been increased by a second predetermined value (Pbref2) or more after the lockup clutch is made OFF. In other words, when the manifold absolute pressure Pb is increased by the second predetermined value Pbref2or more, it is determined that, since the boat12has gone over a wave, the increased resistance of water flow acting on the boat12has decreased and the insufficient condition of the output torque of the engine30has ended, and based on the determination, the lockup clutch44dis made ON again (S46, S52). With this, it becomes possible to prevent loss in transmittance caused by slippage of the torque converter44after the boat12has gone over a wave, thereby further reliably maintaining the maximum speed.

The apparatus and method further includes a throttle opening change amount detector (throttle opening sensor74, ECU90, S14) that detects a change amount (DTH) of throttle opening (TH) of a throttle valve (38) of the engine, and the clutch controller controls the lockup clutch to OFF when the detected change amount of the throttle opening has been less than a throttle predetermined value (second throttle predetermined value DTHref2) and the detected manifold absolute pressure is decreased by the first predetermined value or more after the lockup clutch is made ON (S46, S52). With this, in addition to the above effects, it becomes possible to detect the insufficiency of the output torque of the engine30due to the influence of a wave, thereby making the lockup clutch OFF at the further appropriate timing.

The apparatus and method further includes a throttle opening change amount detector (throttle opening sensor74, ECU90, S14) that detects a change amount of throttle opening of a throttle valve of the engine, and the clutch controller controls the lockup clutch to ON again when the detected change amount of the throttle opening has been less than a throttle predetermined value (second throttle predetermined value DTHref2) and the detected manifold absolute pressure has been increased by the second predetermined value or more after the lockup clutch is made OFF (S46, S48). With this, in addition to the above effects, it becomes possible to accurately detect the end of the insufficient condition of the output torque of the engine30, thereby making the lockup clutch ON at the further appropriate timing.

In the apparatus and method, the reference value (eref) is a value that enables to determine that acceleration of the boat through torque amplification by the torque converter is completed.

In the apparatus and method, the first predetermined value (Pbref1) is a value that enables to determine that load of the engine has changed due to influence of a wave.

In the apparatus and method, the second predetermined value (Pbref2) is a value that enables to determine that load of the engine has changed because there is no longer any influence of a wave.

It should be noted that, although the reference value eref, first and second predetermined values Pbref1, Pbref2, displacement of the engine30and other values are indicated with specific values in the foregoing, they are only examples and not limited thereto.

Japanese Patent Application No. 2009-101154 filed on Apr. 17, 2009 is incorporated by reference herein in its entirety.

While the invention has thus been shown and described with reference to specific embodiments, it should be noted that the invention is in no way limited to the details of the described arrangements; changes and modifications may be made without departing from the scope of the appended claims.