Abstract:
A shift assist system for an outboard motor regulates the torque of the engine to ensure proper effortless shifting. The system recognizes open circuit or short circuit faults and nevertheless enables the torque of the engine to be reduced to facilitate easy gear selection.

Description:
PRIORITY INFORMATION  
       [0001]    This application is based on and claims priority to Japanese Patent Application No. 2000-361067, filed Nov. 28, 2000 and to the Provisional Application No. 60/322192, filed Sep. 13, 2001, (Attorney Docket No. FS.17312US0PR) the entire contents of which is hereby expressly incorporated by reference. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates generally to a shift assist control arrangement for an engine, and more particularly to an improved shift assist control arrangement for a split-bank, multicylinder engine.  
         DESCRIPTION OF THE RELATED ART  
         [0003]    In many forms of marine propulsion systems, the powering internal combustion engine drives a propulsion device through a transmission. Conventionally, the transmissions utilized for this purpose are bevel gear forward, neutral, reverse transmissions shifted by means of dog clutches. These transmissions have the advantage of being able to transmit large amounts of power while maintaining a relatively small and compact assembly. However, this type of transmission has problems in that the engagement of the dog clutches can be difficult at times. This is particularly true if the engine is running at a high speed or developing a large amount of power at the time the shift is attempted.  
           [0004]    It has, therefore, been the practice to provide a variety of shift assisting mechanisms which will automatically reduce the speed of the engine when high shifting forces are encountered. For example, Japanese Patent No. 2759475 and U.S. Pat. No. 6,098,591 disclose shift assist arrangements.  
         SUMMARY OF THE INVENTION  
         [0005]    This invention relates to an improved engine control system and method and more particularly to an improved control system and method for engines and particularly to drive transmissions incorporating shift assists. The preferred embodiments of the invention provide an improved shift assist system for a watercraft and particularly for watercraft with an outboard motor.  
           [0006]    In accordance with one aspect of a preferred embodiment of the shift assist control system of this invention, the shift force detecting unit includes a shift force detection switch and a neutral switch connected to a shift mechanism. The shift mechanism is connected to a dog clutch in the transmission unit. The force detecting unit relays information to the electronic control unit, and engine torque is then lowered depending on the value of the current traveling through the force detecting unit. A significant feature of the preferred embodiments of this invention is that the shift assist system is not adversely affected by abnormal control circuit faults including a short circuit or an open circuit failure of the shift control system.  
           [0007]    In accordance with another aspect of a preferred embodiment of the invention, operation of the operator controlled shifting is detected to effect a change in transmission ratio and reduce the torque of the engine in response to a sensed operation of the operator controlled shifting.  
           [0008]    A further aspect of a preferred embodiment of the invention is a shift assist control system including an electronic control unit that responds to both normal shifting of the engine and abnormal conditions produced by either an electrical disconnect with the shift force-detecting switch or a short circuit in the fire-detecting switch.  
           [0009]    Another aspect of a preferred embodiment of the invention is a shift assist system which normally supplies a current of known value to the engine&#39;s electronic control unit. However, during a shift that requires an excessive force or an abnormal condition of circuit disconnect or short-circuit, this current value is changed and this change in current value is detected by the electronic control unit to automatically reduce the speed of the engine.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    The foregoing features, aspects, and advantages of the present invention will now be described with reference to the drawings of a preferred embodiment that is intended to illustrate and not to limit the invention. The drawings comprise three figures in which:  
         [0011]    [0011]FIG. 1 is a side elevational view of an outboard motor configured in accordance with a preferred embodiment of the present invention, with an associated watercraft partially shown in section; and  
         [0012]    [0012]FIG. 2 is a top view of an outboard motor configured in accordance with a preferred embodiment of the present invention, with various parts shown in phantom; and  
         [0013]    [0013]FIG. 3 is a schematic drawing illustrating the shift assist control system. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
     THE OVERALL CONSTRUCTION  
       [0014]    [0014]FIG. 1 illustrates an overall construction of an outboard motor  10  that employs an internal combustion engine  12  configured in accordance with certain features, aspects and advantages of the present invention. The engine  12  has particular utility in the context of a marine drive, such as, for example the outboard motor  30 , and thus is described in the context of an outboard motor. The engine  12 , however, can be used with other types of marine drives (i.e., inboard motors, inboard/outboard motors, etc.) and also with certain land vehicles, which include lawnmowers, motorcycles, go carts, all terrain vehicles, and the like. Furthermore, the engine  12  can be used as a stationary engine for some applications that will become apparent to those of ordinary skill in the art.  
         [0015]    In the illustrated arrangement, the outboard motor  10  generally comprises a drive unit  14  and a bracket assembly  16 . The bracket assembly  16  supports the drive unit  14  on a transom  18  of an associated watercraft  20  and places a marine propulsion device (e.g., a propeller) in a submerged position with the watercraft  20  resting relative to a surface  22  of a body of water.  
         [0016]    The illustrated drive unit  14  comprises a power head  24 , a driveshaft housing  26 , and a lower unit  28 . The power head  24  is disposed atop the driveshaft housing  26  and includes an internal combustion engine  12 .  
         [0017]    The engine  12  in the illustrated embodiment operates on a four-cycle combustion principle. This type of engine, however, merely exemplifies one type of engine on which various aspects and features of the present invention can be suitably used. A typical engine has two cylinder banks, which extend separately of each other. However, engines having other numbers of cylinders, other cylinder arrangements (in-line, opposing, etc.), and operating on other combustion principles (e.g., crankcase compression two-stroke or rotary) also can advantageously employ various features, aspects and advantages of the present invention. In addition, the engine can be formed with separate cylinder bodies rather than a number of cylinder bores formed in a cylinder block. Regardless of the particular construction, the preferred engine embodiment comprises an engine body that includes at least one cylinder bore.  
         [0018]    A crankshaft  28  extends generally vertically through a cylinder block  30  and can be journaled for rotation about a rotational axis  32  by several bearing blocks. Connecting rods (not shown) couple the crankshaft  28  with the respective pistons (not shown) in any suitable manner. Thus, the reciprocal movement of the pistons (not shown) rotates the crankshaft  28 .  
         [0019]    As shown in FIG. 1, the cylinder block  30  is preferably located at the forwardmost position of the engine  12 . A cylinder head assembly  34  is disposed rearward from the cylinder block  30 . Generally, the cylinder block  30  (or individual cylinder bodies) and the cylinder head assembly  34  together define the engine  12 .  
         [0020]    With reference now to FIG. 2, the engine  12  preferably has an indirect, port or intake passage fuel injection system. The fuel injection system preferably comprises at least two fuel injectors  36  with one fuel injector allotted for each one of the respective cylinders. The fuel injectors  36  preferably are mounted on throttle bodies  38 .  
         [0021]    The engine  12  further has an ignition system comprising spark plugs  40  and a triggering system (not shown).  
         [0022]    Each fuel injector  36  preferably has an injection nozzle directed downstream within associated intake passages  42 , which are downstream of the throttle bodies  38 . The fuel injectors  36  spray fuel  44  into the intake passages  42  where the fuel is met and atomized with incoming induction air  46 .  
         [0023]    As shown in FIG. 3, an electronic control unit (ECU)  48  receives power from a battery  49  and is coupled to an engine speed sensor  51  responsive to the rotational velocity of crankshaft  28 . The ECU  48  controls both the initiation timing and the duration of the fuel injection cycle of the fuel injectors  36  so that the nozzles spray a proper amount of fuel each combustion cycle. The ECU  48  also controls the ignition timing of the sparks plugs  40  in order to correctly facilitate the ignition of the air-fuel mixture.  
         [0024]    The engine  12  also typically includes a cooling system, a lubrication system and other systems, mechanisms or devices other than the systems described above.  
         [0025]    As shown in FIG. 1, the driveshaft housing  26  depends from the power head  24  to support a driveshaft  50  which is coupled with the crankshaft  28  and extends generally vertically through the driveshaft housing  26 . The driveshaft  50  is journaled for rotation and is driven by the crankshaft  28 .  
         [0026]    The drive unit  14  depends from the driveshaft housing  26  and supports a transmission unit  52  that is driven by the driveshaft  50 . The transmission unit  52  extends generally horizontally through the lower unit  64  and is operated by a shift mechanism  54 . A propulsion device is attached to the transmission unit  52 . In the illustrated arrangement, the propulsion device is a propeller  56  that is in communication with the transmission unit  52 . The propulsion device, however, can take the form of a dual counter-rotating system, a hydrodynamic jet, or any of a number of other suitable propulsion devices.  
       THE SHIFT ASSIST CONTROL SYSTEM  
       [0027]    With reference now to FIG. 3, a schematic drawing illustrating the shift assist control system is shown. Within a power transmission unit  58  are various shifting components in order to shift the transmission unit  52 . A shift actuating unit  60  includes an operating coupling  62  which translates the operators shift request to a shifting mechanism  54 . The shifting mechanism  54  moves a dog clutch  66  in a direction dependent on whether forward or reverse gear is selected. A neutral detection switch  68  senses when the shift mechanism  54  is in neutral e.g. when neither forward or reverse gear is chosen and the engine  12  is allowed to run while letting the propeller  56  stand idle.  
         [0028]    Attached to the shift mechanism  54  is a shifting force-detecting switch  70  combined within an abnormality detecting parallel resistor circuit  72  making up a shifting force detection unit  74 . The shifting force detection unit  74  determines the amount of force required to move the dog clutch  66  when engaging or disengaging the dog clutch  66  from forward or reverse gear. An easily accessible connector  76  communicates a signal between the shifting force detection unit  74  and the ECU  48 .  
         [0029]    An electrical current A 3  traveling through an easily accessible connector  76  is made up of two currents, A 1 , A 2  and allows the ECU to correctly determine if engine speed should be reduced in order to protect the dog clutch  66  and assist in easier shifting. The current A 1  is designated as the current that travels through the shifting force-detecting switch  70  and the current A 2  is designated as the current that travels through the parallel resistor circuit  72 .  
         [0030]    During normal driving operation, the dog clutch  66  is engaged in either forward or reverse gear. When forward or reverse is engaged the neutral detection switch  68  and the shifting force detection switch  70  are open, the current A 1  equals zero, and the ECU  48  detects a current A 3  equal to the current flow A 2  traveling through the parallel resistor circuit  72 . In another arrangement a high shifting force gear engaging state may be realized and the engine speed is reduced by various means including ignition and/or fuel injection timing or cutoff or through the operation of the air bypass valve  78 . By reducing the engine speed, an assisted engaging shift operation can be easily performed.  
         [0031]    It is conceivable due to the normal vibrations and operation of a watercraft that a short circuit or an open circuit fault may present itself. The present invention is designed to detect such errors and still provide adequate shifting assistance.  
         [0032]    If the ECU measured current A 3  equals zero it is determined that an open circuit is present within or between the shifting force detection unit  74  and the ECU  48 . An alarm  80  is activated and the ECU  48  lowers the engine speed in order to provide a smooth shifting environment. Alarm  80  may be either or both an audible alarm and a visual alarm such as a flashing electrical lamp.  
         [0033]    If the ECU measured current A 3  is equal to the current A 1  traveling through the shifting force-detecting switch  70  for a predetermined amount of time greater than the normal shifting time of “X”, it is determined that a short circuit is present within or between the shifting force detection unit  74  and the ECU  48 . The alarm  80  is activated and the ECU  48  lowers the engine speed in order to provide a smooth shifting environment. If a disturbance is shifting capability is noticed by the operator the connector  76  can always be disconnected in order to produce an open circuit between the shifting force detection unit  74  and the ECU  48 . Although disconnecting the connector  74  will reduce engine performance, it allows a “limp home” mode and lets the transmission  52  be easily shifted in order to continue to operate the watercraft  20  safely.  
       Operation of the Shift Control System  
       [0034]    In operation, during a high shifting force gear disengaging state, the shifting force-detecting switch  70  is closed, and the ECU measured current A 3  equals the current A 1  traveling through the shifting force-detecting switch  70 . When the ECU  48  recognizes the current A 3  equals the current A 1  for a predetermined amount of time less than “X”, a high shifting force gear disengaging state is realized. The engine speed is then reduced by various means including ignition and/or fuel injection timing or cutoff or through the operation of an air bypass valve  78 . By reducing the engine speed, an assisted disengaging shift operation can be easily performed. The shift control system shown in FIGS. 2 and 3 operates under “normal” and “abnormal” conditions described below to provide significant improvement in the state-of-the-art of shift assist control systems.  
       NORMAL CONDITIONS  
     Normal Operation Before and After Shifting  
       [0035]    Force detecting switch  70  is normally open circuit, i.e., under normal operating conditions it is only closed during shifting that requires excessive operator force. Accordingly, the only current flowing in circuit  72  is current A 2  through resistor  72 . So long as the voltage of battery  49  does not drop below its normal voltage, current A 2  will remain substantially constant at a value N. The current detector circuitry within the ECU responds to currents above or below this normal value of N current flow. Thus, the ECU will not operate to automatically reduce engine speed or sound the alarm  80  when the current has the normal value of N.  
       Normal Operation During Shifting  
       [0036]    Normal operation includes excessive operator force that is necessarily applied during a shift sequence by virtue of the dog clutch mechanism. When the operator is required to exert a force on the shift lever greater than a predetermined value, the resistor  72  is shorted by the closure of switch  70 . As a result, the current flow A 3  to ECU  48  is equal to a current flow A 1  which is greater than N. Since the current A 3  to ECU  48  is now greater than the steady-state current N (A 2 ) when switch  70  is open, the current detector within ECU  48  detects this change and automatically reduces the engine RPM to assist this shifting operation by reducing the frictional force generated by the engagement of the dog clutch. Advantageously, the reduction in RPM occurs within approximately 0.5 seconds. As soon as the operator reduces the force applied o the shifter mechanism, switch  70  is opened. The current to the ECU is once again equal to the N current value A 2 . This reduction in current N is detected by ECU  8  which automatically returns the engine RPM to its normal rotational velocity.  
         [0037]    A shift requiring excessive force requires this relatively short period of time X. Accordingly, the automatic timer within the ECU does not sound the alarm during a normal “excessive force” shift of the engine.  
       ABNORMAL CONDITIONS  
     Switch  70  Fails Closed Circuit  
       [0038]    If force detecting unit  74  fails in a closed circuit mode, the ECU detects the increased current flow A 1 . When this current flows longer than X, the period of time preset by the automatic timer within the ECU circuit, the ECU actuates alarm  80  notifying the operator of the abnormal condition. If the operator is unable to shut off the alarm, the operator can disconnect the connector  76  resulting in zero current flow. This condition is described below. In any event, a short circuit of unit  74  results in a reduced engine RPM so that the operation can easily shift the dog clutch mechanism and run the engine in a reduced power mode.  
       Open Circuit Failure  
       [0039]    When a line disconnection occurs between the shift force detection unit  74  and the ECU  48 , zero current  43  will flow to the ECU  48 . This change in current value is detected by the ECU current detection circuitry and the engine RPM is automatically reduced. This non-intentional fluctuation of the engine  12  will be felt by the operator who can either fix the connection or operate in a “limp home” condition with an engine operating, but at a reduced RPM. Shifting of the dog clutch does not present any problem because of the reduced power of the engine. Further, the ECU circuit advantageously differentiates between a line-disconnection and a short-circuit within unit  74  by changing the flashing interval of the visual lamp of alarm  80 .  
       Battery Voltage Drops Below a Predetermined Value  
       [0040]    The voltage of battery will fall below a predetermined value if the battery is failing or the electrical changing system is not operating to change the battery. In one embodiment of the invention, the ECU detects both a zero current flow caused by an electrical disconnect and a current flow greater than zero but less than N. This lower current value is produced by battery  49  being in a low voltage state. As a result, the voltage across resistor be reduced. As in the line-disconnect mode described above, this reduced current can be detected within the ECU and the operator is immediately notified of this problem. Advantageously, alarm  80  includes a flashing light which is energized to advise the operator of a low voltage condition.  
         [0041]    The monitored current parameters A 1 , A 2 , and A 3  thereby enable the ECU  48  to accurately assess when shifting assistance is required and when a fault is present within the shift assist control system, which increases transmission shifting response, overall performance, improves reliability, and provides accurate driving response and efficiency.  
         [0042]    Thus, from the foregoing description it should be readily apparent that the described construction is very effective in providing an improved shift assist system insuring good shifting operation regardless of open circuit or shorted shift control electrical connections. Of course, the foregoing description is that of a preferred embodiment of the invention and various changes and modifications may be made without departing from the spirit and scope of the invention, as defined by the appended claims.