Patent Publication Number: US-8118626-B2

Title: Outboard motor control apparatus

Description:
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 (&#39;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. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects and advantages of the invention will be more apparent from the following description and drawings in which: 
         FIG. 1  is an overall schematic view of an outboard motor control apparatus including a boat (hull) according to an embodiment of the invention; 
         FIG. 2  is an enlarged sectional side view partially showing the outboard motor shown in  FIG. 1 ; 
         FIG. 3  is an enlarged side view of the outboard motor shown in  FIG. 1 ; 
         FIG. 4  is an enlarged sectional view showing a region around a torque converter shown in  FIG. 2 ; 
         FIG. 5  is a hydraulic circuit diagram schematically showing the torque converter, a hydraulic pump and other components shown in  FIG. 2 ; and 
         FIG. 6  is a flowchart showing the control of an electronic control unit shown in  FIG. 1 . 
     
    
    
     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. 1  is an overall schematic view of an outboard motor control apparatus including a boat (hull) according to an embodiment of the invention.  FIG. 2  is an enlarged sectional side view partially showing the outboard motor shown in  FIG. 1  and  FIG. 3  is an enlarged side view of the outboard motor. 
     In  FIGS. 1 to 3 , a symbol  10  indicates an outboard motor. As illustrated, the outboard motor  10  is clamped (fastened) to the stern or transom of a boat (hull)  12 . 
     As shown in  FIG. 2 , the outboard motor  10  is fastened to the boat  12  through a swivel case  14 , tilting shaft  16  and stern brackets  18 . The outboard motor  10  is equipped with a mount frame  20  and shaft  22 . The shaft  22  is housed in the swivel case  14  to be rotatable about the vertical axis such that the outboard motor  10  can be rotated about the vertical axis relative to the boat  12 . The mount frame  20  is fixed at its upper end and lower end to a frame (not shown) constituting a main body of the outboard motor  10 . 
     An electric steering motor (actuator)  24  for operating the shaft  22  and a power tilt-trim unit  26  for regulating a tilt angle and trim angle of the outboard motor  10  are installed near the swivel case  14 . A rotational output of the steering motor  24  is transmitted to the shaft  22  via a speed reduction gear mechanism  28  and the mount frame  20 , whereby the outboard motor  10  is steered about the shaft  22  as a steering axis to the right and left directions (steered about the vertical axis). 
     The power tilt-trim unit  26  integrally comprises a hydraulic cylinder  26   a  for adjusting the tilt angle and a hydraulic cylinder  26   b  for adjusting the trim angle. When the hydraulic cylinders  26   a ,  26   b  are extended and contracted, the swivel case  14  is rotated about the tilting shaft  16  as a rotational axis, thereby tiling up/down and trimming up/down the outboard motor  10 . 
     An internal combustion engine (hereinafter referred to as the “engine”)  30  is disposed in the upper portion of the outboard motor  10 . The engine  30  comprises a spark-ignition, water-cooling gasoline engine with a displacement of 2,200 cc. The engine  30  is located above the water surface and covered by an engine cover  32 . 
     An intake pipe  34  of the engine  30  is connected to a throttle body  36 . The throttle body  36  has a throttle valve  38  installed therein and an electric throttle motor (actuator)  40  for opening and closing the throttle valve  38  is integrally disposed thereto. 
     The output shaft of the throttle motor  40  is connected to the throttle valve  38  via a speed reduction gear mechanism (not shown). The throttle motor  40  is operated to open and close the throttle valve  38 , thereby regulating the flow rate of the air sucked in the engine  30  to control the engine speed. 
     The outboard motor  10  further comprises a drive shaft (vertical shaft)  42  installed parallel to the vertical axis to be rotatably supported, a torque converter  44  interposed between the engine  30  and drive shaft  42 , a hydraulic pump  46  that is attached to the drive shaft  42  and pumps operating oil to a lubricated portion of the engine  30 , the torque converter  44  and the like, and a reservoir  50  for reserving the operating oil. 
     The upper end of the drive shaft  42  is connected to a crankshaft  52  of the engine  30  through the torque converter  44  and the lower end thereof is connected via a shift mechanism  54  with a propeller shaft  56  supported to be rotatable about the horizontal axis. One end of the propeller shaft  56  is attached with a propeller  60 . Thus the drive shaft  42  connects the engine  30  with the propeller  60 . 
       FIG. 4  is an enlarged sectional view showing a region around the torque converter  44  shown in  FIG. 2 . 
     As shown in  FIG. 4 , the torque converter  44  includes a pump impeller  44   a  connected to the crankshaft  52  through a drive plate  62 , a turbine runner  44   b  that is installed to face the pump impeller  44   a  to receive/discharge the operating oil and connected to the drive shaft  42 , a stator  44   c  installed between the pump impeller  44   a  and turbine runner  44   b , a lockup clutch  44   d  and other components. 
       FIG. 5  is a hydraulic circuit diagram schematically showing the torque converter  44 , hydraulic pump  46 , etc. 
     The hydraulic pump  46  driven by the engine  30  pumps up the operating oil in the reservoir  50  and forwards it to a first oil passage  64   a . The pressurized operating oil forwarded to the first oil passage  64   a  is supplied to the lubricated portion of the engine  30  or the like and then returns to the reservoir  50  through a second oil passage  64   b.    
     The first oil passage  64   a  is provided with a third oil passage  64   c  connecting the first oil passage  64   a  with an intake hole of the hydraulic pump  46 . The third oil passage  64   c  is interposed with a relief valve  66  that opens when the pressure of the operating oil to be supplied to the engine  30  is at or above a defined value and closes when it is below the defined value. 
     A fourth oil passage  64   d  for circulating the operating oil to be supplied to the torque converter  44  is connected to the first oil passage  64   a  at a point between a discharge hole of the hydraulic pump  46  and a branch point of the first and third oil passages  64   a ,  64   c . A fifth oil passage  64   e  for circulating the operating oil returning from the torque converter  44  to the hydraulic pump  46  is connected to the third oil passage  64   c  at a location downstream of the relief valve  66 . The fourth and fifth oil passages  64   d ,  64   e  are installed with a lockup control valve  70  for controlling the operation of the lockup clutch  44   d.    
     The lockup control valve  70  is a solenoid valve. The output of the valve  70  is connected to a piston chamber  44   d   1  of the lockup clutch  44   d  of the torque converter  44 , and also connected to a chamber (rear chamber)  44   d   2  disposed in the rear of the piston chamber  44   d   1 . The lockup control valve  70  switches the oil passage upon being magnetized/demagnetized, thereby controlling the ON/OFF state (engagement/release) of the lockup clutch  44   d.    
     Specifically, when the lockup control valve  70  is magnetized, the operating oil is supplied to the piston chamber  44   d   1  and discharged from the rear chamber  44   d   2  so as to make the lockup clutch  44   d  ON (engaged), and when the valve  70  is demagnetized (the status in  FIG. 5 ; initial condition), the operating oil is supplied to the rear chamber  44   d   2  and discharged from the piston chamber  44   d   1  so as to make the lockup clutch  44   d  OFF (released). Since the details of the aforementioned torque converter  44  is disclosed in &#39;498, further explanation is omitted here. 
     The explanation of  FIG. 2  will be resumed. The shift mechanism  54  comprises a forward bevel gear  54   a  and reverse bevel gear  54   b  which are connected to the drive shaft  42  to be rotated, a clutch  54   c  which can engage the propeller shaft  56  with either one of the forward bevel gear  54   a  and reverse bevel gear  54   b , and other components. 
     The interior of the engine cover  32  is disposed with an electric shift motor (actuator)  72  that drives the shift mechanism  54 . The output shaft of the shift motor  72  can be connected via a speed reduction gear mechanism (not shown) with the upper end of a shift rod  54   d  of the shift mechanism  54 . When the shift motor  72  is operated, its output appropriately displaces the shift rod  54   d  and a shift slider  54   e  to move the clutch  54   c  to 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 shaft  42  is transmitted via the shift mechanism  54  to the propeller shaft  56  to rotate the propeller  60  in one of the directions making the boat  12  move forward or rearward. The outboard motor  10  is equipped with a power source (not shown) such as a battery or the like attached to the engine  30  to supply operating power to the motors  24 ,  40 ,  72 , etc. 
     As shown in  FIG. 3 , a throttle opening sensor  74  is installed near the throttle valve  38  and produces an output or signal indicative of opening of the throttle valve  38 , i.e., throttle opening TH. An absolute pressure sensor (manifold absolute pressure detector)  76  is installed in the intake pipe  34  on downstream of the throttle valve  38  and produces an output or signal proportional to the manifold absolute pressure (absolute pressure) Pb. 
     A shift position sensor  80  installed near the shift rod  54   d  produces an output or signal corresponding to a shift position (neutral, forward or reverse) and a neutral switch  84  also installed near the shift rod  54   d  produces an ON signal when the shift position is neutral and an OFF signal when it is forward or reverse. 
     A crank angle sensor  84  is installed near the crankshaft  52  of the engine  30  and produces a pulse signal at every predetermined crank angle. A drive shaft rotation speed sensor  86  is installed near the drive shaft  42  and produces an output or signal indicative of rotation speed of the drive shaft  42 . 
     The outputs of the foregoing sensors and switch are sent to an electronic control unit (ECU)  90  disposed in the outboard motor  10 . The ECU  90  which has a microcomputer including a CPU, ROM, RAM and other devices is installed in the engine cover  32  of the outboard motor  10 . 
     As shown in  FIG. 1 , a steering wheel  94  is installed near a cockpit (the operator&#39;s seat)  92  of the boat  12  to be manipulated or rotated by the operator. A steering angle sensor  96  installed near a shaft (not shown) of the steering wheel  94  produces an output or signal corresponding to the steering angle applied or inputted by the operator through the steering wheel  94 . 
     A remote control box  100  provided near the cockpit  92  is equipped with a shift/throttle lever  102  installed to be manipulated by the operator. Upon the manipulation, the lever  102  can 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 sensor  104  is installed in the remote control box  100  and produces an output or signal corresponding to a position of the lever  102 . The outputs of the steering angle sensor  96  and lever position sensor  104  are also sent to the ECU  90 . 
     Based on the inputted outputs, the ECU  90  controls the operations of the motors and ON/OFF state of the lockup clutch  44   d  of the torque converter  44 . 
       FIG. 6  is a flowchart showing the control of the ECU  90 . The illustrated program is executed by the ECU  90  at predetermined interval, e.g., 100 milliseconds. 
     The program begins in S 10 , in which it is determined whether the shift position is neutral. This determination is made by checking as to whether the neutral switch  82  outputs the ON signal. When the result in S 10  is negative, i.e., it is determined to be in gear, the program proceeds to S 12 , in which the throttle opening TH is detected or calculated from the output of the throttle opening sensor  74  and to S 14 , 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 S 16 , in which it is determined whether the throttle valve  38  is operated in the closing direction, i.e., the boat  12  is 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 valve  38  is determined to be operated in the closing direction (the boat  12  is in the decelerating condition) and when the change amount DTH is 0 or a positive value, the throttle valve  38  is determined to be operated to stop or in the opening direction (the boat  12  is operated to cruise at a constant speed or accelerate). 
     When the result in S 16  is negative, the program proceeds to S 18 , in which it is determined whether a bit of an acceleration completed determination flag of the torque converter  44  (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 S 18  in the first program loop is generally affirmative and the program proceeds to S 20 , in which it is determined whether a bit of an amplification determination flag of the torque converter  44  (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 engine  30  is amplified through the torque converter  44  and transmitted to the drive shaft  42  (i.e., where the operation of the outboard motor  10  is in a range (torque amplification range) that the torque is to be amplified by the torque converter  44  to accelerate the boat  12 ) is established, and reset to 0 when the output torque of the engine  30  is not amplified (i.e., the operation of the outboard motor  10  is out of the torque amplification range). 
     Since the initial value of a bit of the amplification determination flag is also 0, the result in S 20  in the first program loop is generally affirmative and the program proceeds to S 22 , in which it is determined whether the throttle valve  38  is operated in the opening direction, i.e., the boat  12  is 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) DTHref 1  and, when the change amount DTH is equal to or greater than the predetermined value DTHref 1 , the throttle valve  38  is determined to be operated in the opening direction (the boat  12  is in the accelerating condition). The first throttle predetermined value DTHref 1  is set to a value (e.g., 0.5 degree) enabling to determine whether the boat  12  is in the accelerating condition. 
     When the result in S 22  is negative, i.e., when the boat  12  is 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 S 24 , in which the torque converter  44  is controlled with a lockup-OFF mode. The operation in the lockup-OFF mode is to demagnetize the lockup control valve  70  and make the lockup clutch  44   d  of the torque converter  44  OFF. As a result, the output torque of the engine  30  is amplified through the torque converter  44  and transmitted to the drive shaft  42 , thereby improving acceleration performance. 
     Next, in S 26 , 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 motor  10  is in a condition that the output torque of the engine  30  is amplified by the torque converter  44  to accelerate the boat  12 , the result in S 20  in the next and subsequent loops is negative and the program proceeds to S 28 . 
     In S 28 , an input rotation speed NIN and output rotation speed NOUT of the torque converter  44  are detected or calculated. Since the input side of the torque converter  44  is connected to the crankshaft  52  of the engine  30 , 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 sensor  84 . The output rotation speed NOUT is detected from the output of the drive shaft rotation speed sensor  86 . 
     The program proceeds to S 30 , in which a speed ratio e of the torque converter  44  is 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 ratio  e =(Output rotation speed NOUT)/(Input rotation speed NIN)
 
     The program proceeds to S 32 , in which it is determined whether the torque amplification range of the torque converter  44  has 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 S 32  is affirmative, the program proceeds to S 34 , 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 S 36 , in which it is determined whether the speed of the boat  12  remains 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 boat  12  remains 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 S 36  is affirmative, the program proceeds to S 38 , in which the torque converter  44  is controlled with the lockup-ON mode. The operation of the lockup-ON mode is to magnetize the lockup control valve  70  and make the lockup clutch  44   d  ON. Since this establishes the direct connection between the crankshaft  52  of the engine  30  and the drive shaft  42 , slippage of the torque converter  44  can be prevented so that the speed of the boat  12  reaches 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 clutch  44   d  of the torque converter  44  is made ON. After the step of S 38 , in S 40 , a bit of the torque converter amplification determination flag is reset to 0 and in S 42 , 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 converter  44  is completed and the lockup clutch  44   d  is made ON, and in the other cases, reset to 0, as described later. 
     When the result in S 32  or S 36  is negative, since it means that the torque amplification range of the torque converter  44  does not end (or is not saturated), or that the speed of the boat  12  is not stable at the maximum speed or thereabout, the steps of S 38  to S 42  are skipped and the program is terminated. 
     When a bit of the acceleration completed determination flag is set to 1 in S 42 , the result in S 18  in the next and subsequent loops is negative and the program proceeds to S 44  onward. In S 44 , based on the output of the absolute pressure sensor  76 , the manifold absolute pressure Pb of the intake pipe  34  is detected or calculated and in S 46 , 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 engine  30  has changed. 
     To be specific, in the case where, for example, the boat  12  climbs up and goes over a relatively big wave with the lockup clutch  44   d  positioned ON, the wave influences the resistance of water flow acting on the boat  12  to increase. It results in the decrease of the engine speed and the insufficiency (decrease) of the output torque of the engine  30 , 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 engine  30  due to the influence of a wave is detected or estimated based on change of load of the engine  30 . When the output torque insufficiency is detected, the lockup clutch  44   d  is made OFF to amplify the output torque through the torque converter  44  so as to compensate for the insufficiency. 
     Specifically, in S 46 , when the change amount DTH is less than a second throttle predetermined value DTHref 2  (e.g., 0.5 degree) and the manifold absolute pressure Pb is decreased by a first predetermined value Pbref 1  or 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 Pbref 1  on 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 Pbref 1  or 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 DTHref 2  is set to a value enabling to determine whether the change of the throttle opening TH is relatively small and the first predetermined value Pbref 1  is 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 S 46  that 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 S 48 , in which the torque converter  44  is controlled with the lockup-OFF mode to make the lockup clutch  44   d  OFF. 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 S 50 , 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 S 46  after the lockup clutch  44   d  is made OFF in S 48  in a previous program loop, the determination as to the change in the load of the engine  30  is made again. The explanation thereon will be made in detail. After the boat  12  has gone over a big wave, the increased resistance of water flow acting on the boat  12  decreases and it results in the increase of the engine speed. Since the insufficient condition of the output torque of the engine  30  ends accordingly, it is not necessary to amplify the output torque by the torque converter  44   d . Further, at this time, if the lockup clutch  44   d  remains OFF, it causes slippage of the torque converter  44  and the maximum speed may not be maintained. 
     Therefore, in this embodiment, the end of the insufficient condition of the output torque of the engine  30  is detected or estimated based on the change in the engine load and when it is detected that the insufficient condition has ended, the lockup clutch  44   d  is made ON again to prevent slippage of the torque converter  44 , thereby reliably maintaining the maximum speed of the boat  12 . 
     Specifically, in S 46 , when the change amount DTH of the throttle opening TH is less than the second throttle predetermined value DTHref 2  and the manifold absolute pressure Pb is increased by a second predetermined value Pbref 2  or 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 Pbref 2  on the positive side, it is determined that the engine load has changed in the decreasing direction because the boat  12  has gone over a wave and the insufficient condition of the output torque of the engine  30  has ended. 
     More specifically, when the manifold absolute pressure Pb is increased by the second predetermined value Pbref 2  or 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 Pbref 2  is 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 S 46 , the engine load is determined to have changed in the decreasing direction, the program proceeds to S 52 , in which the torque converter  44  is controlled with the lockup-ON mode to make the lockup clutch  44   d  ON again. Owing to this configuration, slippage of the torque converter  44  after the boat  12  has gone over a wave can be prevented, thereby reliably maintaining the maximum speed. After the processing of S 52 , in S 54 , a bit of the torque converter amplification determination flag is reset to 0 and the program is terminated. 
     When the result in S 10  is affirmative, i.e., when the shift position is neutral, the program proceeds to S 56 , in which the torque converter  44  is controlled with the lockup-ON mode, to S 58 , in which a bit of the torque converter amplification determination flag is reset to 0 and then to S 60 , in which a bit of the torque converter acceleration completed determination flag is reset to 0. 
     When the result in S 16  is affirmative, i.e., when the boat  12  is in the decelerating condition, the program proceeds to S 62 , in which the torque converter  44  is controlled with the lockup-OFF mode, to S 64 , in which a bit of the amplification determination flag is set to 1, to S 66 , 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 ( 44   d ) and interposed between the engine and the drive shaft, comprising: a speed ratio calculator (ECU  90 , S 28 , S 30 ) 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 sensor  76 , ECU  90 , S 44 ) that detects manifold absolute pressure (Pb) of the engine; and a clutch controller (ECU  90 , S 32 , S 38 , S 46 , S 48 ) 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 (Pbref 1 ) or more. 
     Thus, when the manifold absolute pressure Pb is decreased by the first predetermined value Pbref 1  or more, it is determined that, since the boat  12  is climbing up and going over a relatively big wave, the resistance of water flow acting on the boat  12  increases due to the influence of the wave, resulting in the insufficiency of the output torque of the engine  30 , and based on the determination, the lockup clutch  44   d  is made OFF (i.e., the output torque of the engine  30  is amplified through the torque converter  44 ). With this, even when the resistance of water flow acting on the boat  12  increases due to the influence of a wave, the insufficiency of the output torque is compensated through amplification by the torque converter  44  and it makes possible to prevent the boat speed from decreasing, thereby maintaining the maximum speed. 
     Further, since the lockup clutch  44   d  is 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 clutch  44   d  is made ON upon the completion of acceleration, speed performance can be enhanced. Further, slippage of the torque converter  44  can be prevented by making the lockup clutch  44   d  ON, 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 (Pbref 2 ) 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 Pbref 2  or more, it is determined that, since the boat  12  has gone over a wave, the increased resistance of water flow acting on the boat  12  has decreased and the insufficient condition of the output torque of the engine  30  has ended, and based on the determination, the lockup clutch  44   d  is made ON again (S 46 , S 52 ). With this, it becomes possible to prevent loss in transmittance caused by slippage of the torque converter  44  after the boat  12  has 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 sensor  74 , ECU  90 , S 14 ) 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 DTHref 2 ) and the detected manifold absolute pressure is decreased by the first predetermined value or more after the lockup clutch is made ON (S 46 , S 52 ). With this, in addition to the above effects, it becomes possible to detect the insufficiency of the output torque of the engine  30  due 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 sensor  74 , ECU  90 , S 14 ) 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 DTHref 2 ) and the detected manifold absolute pressure has been increased by the second predetermined value or more after the lockup clutch is made OFF (S 46 , S 48 ). 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 engine  30 , 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 (Pbref 1 ) 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 (Pbref 2 ) 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 Pbref 1 , Pbref 2 , displacement of the engine  30  and 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.