Shift assist system for an outboard motor

[0002] 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, the entire contents of which is hereby expressly incorporated by reference.

[0003] 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.

[0004] 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.

[0005] 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.

[0006] 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.

[0007] 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.

[0008] 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.

[0009] 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 force-detecting switch.

[0010] 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'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.

[0011] 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:

[0012] 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

[0013] 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

[0014] FIG. 3 is a schematic drawing illustrating the shift assist control system.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] The engine 12 further has an ignition system comprising spark plugs 40 and a triggering system (not shown).

[0023] 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.

[0024] 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.

[0025] The engine 12 also typically includes a cooling system, a lubrication system and other systems, mechanisms or devices other than the systems described above.

[0026] 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.

[0027] 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 a 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.

[0028] 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 the 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.

[0029] 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.

[0030] An electrical current A3 traveling through an easily accessible connector 76 is made up of two currents, A1, A2 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 A1 is designated as the current that travels through the shifting force-detecting switch 70 and the current A2 is designated as the current that travels through the parallel resistor circuit 72.

[0031] 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 A1 equals zero, and the ECU 48 detects a current A3 equal to the current flow A2 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.

[0032] 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.

[0033] If the ECU measured current A3 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.

[0034] If the ECU measured current A3 is equal to the current A1 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 in 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 76 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.

[0035] In operation, during a high shifting force gear disengaging state, the shifting force-detecting switch 70 is closed, and the ECU measured current A3 equals the current A1 traveling through the shifting force-detecting switch 70. When the ECU 48 recognizes the current A3 equals the current A1 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.

[0036] Normal Operation Before and After Shifting

[0037] 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 A2 through resistor 72. So long as the voltage of battery 49 does not drop below its normal voltage, current A2 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.

[0038] Normal Operation During Shifting

[0039] 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 A3 to ECU 48 is equal to a current flow A1 which is greater than N. Since the current A3 to ECU 48 is now greater than the steady-state current N (A2) 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 to the shifter mechanism, switch 70 is opened. The current to the ECU is once again equal to the N current value A2. This reduction in current N is detected by ECU 8 which automatically returns the engine RPM to its normal rotational velocity.

[0040] 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.

[0041] Switch 70 Fails Closed Circuit

[0042] If force detecting unit 74 fails in a closed circuit mode, the ECU detects the increased current flow A1. 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.

[0043] Open Circuit Failure

[0044] 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.

[0045] Battery Voltage Drops Below a Predetermined Value

[0046] 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 the resistor may 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.

[0047] The monitored current parameters A1, A2, and A3 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.

[0048] 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.