Patent Publication Number: US-9422047-B1

Title: Systems and methods for facilitating shift changes in marine propulsion devices

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims the benefit of and priority to U.S. Provisional Patent Application Ser. No. 61/782,485, filed Mar. 14, 2013, which is incorporated herein by reference in entirety. 
    
    
     FIELD 
     The present disclosure relates to marine propulsion devices, and more particularly to systems and methods for facilitating shift changes in marine propulsion devices. 
     BACKGROUND 
     The following US Patents and Applications provide background information and are incorporated herein by reference in entirety. 
     U.S. Pat. No. 4,753,618 discloses a shift cable assembly for a marine drive that includes a shift plate, a shift lever pivotally mounted on the plate, and a switch actuating arm pivotally mounted on the plate between a first neutral position and a second switch actuating position. A control cable and drive cable interconnect the shift lever and switching actuating arm with a remote control and clutch and gear assembly for the marine drive so that shifting of the remote control by a boat operator moves the cables to pivot the shift lever and switch actuating arm which in turn actuates a shift interrupter switch mounted on the plate to momentarily interrupt ignition of the drive unit to permit easier shifting into forward, neutral and reverse gears. A spring biases the arm into its neutral position and the arm includes an improved mounting for retaining the spring in its proper location on the arm. 
     U.S. Pat. No. 4,952,181 discloses a shift cable assembly for a marine drive having a clutch and gear assembly, including a remote control for selectively positioning the clutch and gear assembly into forward, neutral and reverse, a control cable connecting the remote control to a shift lever pivotally mounted on a shift plate, a drive cable connecting the shift lever on the shift plate to the clutch and gear assembly, and a spring guide assembly with compression springs biased to a loaded condition by movement of the remote control from neutral to forward and also biased to a loaded condition by movement of the remote control from neutral to reverse. The bias minimizes chatter of the clutch and gear assembly upon shifting into gear, and aids shifting out of gear and minimizes slow shifting out of gear and returns the remote control to neutral, all with minimum backlash of the cables. The spring guide assembly includes an outer tube mounted to the shift plate, and a spring biased plunger axially reciprocal in the outer tube and mounted at its outer end to the shift lever. 
     U.S. Pat. No. 4,986,776 discloses a shift speed equalizer in a marine transmission in a marine drive subject to a decrease in engine speed upon shifting from neutral to a forward or reverse gear due to a high propeller pitch or the like, such as in bass boat applications, and subject to an increase in engine speed upon shifting back to neutral. The shift from neutral to forward or reverse is sensed, and engine speed is increased in response thereto, to compensate the decrease in engine speed due to shifting. The return shift back to neutral is sensed, and engine speed is decreased in response thereto, to compensate the increase in engine speed due to shifting. Engine speed is increased by advancing engine spark ignition timing, and engine speed is decreased by retarding or returning engine ignition timing to its initial setting. Particular methodology and structure is disclosed, including modifications to an existing shift plate and to an existing guide block to enable the noted functions, and including the addition of an auxiliary circuit to existing ignition circuitry enabling the desired altering of engine ignition timing to keep engine speed from dropping when shifting into forward or reverse. 
     U.S. Pat. No. 6,273,771 discloses a control system for a marine vessel that incorporates a marine propulsion system that can be attached to a marine vessel and connected in signal communication with a serial communication bus and a controller. A plurality of input devices and output devices are also connected in signal communication with the communication bus and a bus access manager, such as a CAN Kingdom network, is connected in signal communication with the controller to regulate the incorporation of additional devices to the plurality of devices in signal communication with the bus whereby the controller is connected in signal communication with each of the plurality of devices on the communication bus. The input and output devices can each transmit messages to the serial communication bus for receipt by other devices. 
     U.S. Pat. No. 6,544,083 discloses a gear shift mechanism in which a cam structure comprises a protrusion that is shaped to extend into a channel formed in a cam follower structure. The cam follower structure can be provided with first and second channels that allow the protrusion of the cam to be extended into either which accommodates both port and starboard shifting mechanisms. The cam surface formed on the protrusion of the cam moves in contact with a selected cam follower surface formed in the selected one of two alternative channels to cause the cam follower to move axially and to cause a clutch member to engage with either a first or second drive gear. 
     U.S. Pat. No. 6,929,518 discloses a shifting apparatus for a marine propulsion device that incorporates a magneto-elastic elastic sensor which responds to torque exerted on the shift shaft of the gear shift mechanism. The torque on the shift shaft induces stress which changes the magnetic characteristics of the shift shaft material and, in turn, allows the magneto-elastic sensor to provide appropriate output signals representative of the torque exerted on the shift shaft. This allows a microprocessor to respond to the onset of a shifting procedure rather than having to wait for actual physical movement of the components of the shifting device. 
     U.S. Pat. No. 6,942,530 discloses an engine control strategy for a marine propulsion system that selects a desired idle speed for use during a shift event based on boat speed and engine temperature. In order to change the engine operating speed to the desired idle speed during the shift event, ignition timing is altered and the status of an idle air control valve is changed. These changes to the ignition timing and the idle air control valve are made in order to achieve the desired engine idle speed during the shift event. The idle speed during the shift event is selected so that the impact shock and resulting noise of the shift event can be decreased without causing the engine to stall. 
     U.S. Pat. No. 7,214,164 discloses shift operation control system for an outboard motor, which is capable of reducing a load that is acting on a shift operation lever during a shift operation and a shock occurring during the shift operation, to thereby facilitate the shift operation. The shift operation by the shift operation lever is continuously detected by a shift position detector, and when an early stage of the shift operation from the forward position to the neutral position or from the reverse position to the neutral position is detected and at the same time the engine speed at the detection is not less than a predetermined value, engine output reduction control is carried out, and when the shift position detector detects that the shift position has been switched to the neutral position, the engine output reduction control is canceled. 
     U.S. patent application Ser. No. 13/462,570 discloses systems and methods for controlling shift in a marine propulsion device. A shift sensor outputs a position signal representing a current position of a shift linkage. A control circuit is programmed to identify an impending shift change when the position signal reaches a first threshold and an actual shift change when the position signal reaches a second threshold. The control circuit is programmed to enact one or more shift interrupt control strategies that facilitate the actual shift change when the position signal reaches the first threshold, and to actively modify the first threshold as a change in operation of the marine propulsion device occurs. 
     U.S. patent application Ser. No. 13/760,870 discloses a system and method for diagnosing a fault state of a shift linkage in a marine propulsion device. A control lever is movable towards at least one of a maximum reverse position and a maximum forward position. A shift linkage couples the control lever to a transmission, wherein movement of the control lever causes movement of the shift linkage that enacts a shift change in the transmission. A shift sensor outputs a position signal representing a current position of the shift linkage. A control circuit diagnoses a fault state of the shift linkage when after the shift change the position signal that is output by the shift sensor is outside of at least one range of position signals that is stored in the control circuit. 
     U.S. patent application Ser. No. 14/144,135 discloses methods and systems for facilitating shift changes in a marine propulsion device having an internal combustion engine and a shift linkage that operatively connects a shift control lever to a transmission for effecting shift changes amongst a reverse gear, a neutral gear and a forward gear. A position sensor senses position of the shift linkage. A speed sensor senses speed of the engine. A control circuit compares the speed of the engine to a stored engine speed and modifies, based upon the position of the shift linkage when the speed of the engine reaches the stored engine speed, a neutral state threshold that determines when the control circuit ceases reducing the speed of the engine to facilitate a shift change. 
     SUMMARY 
     This Summary is provided to introduce a selection of concepts that are further described herein below in the Detailed Description. This Summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter. 
     In certain examples, methods are for facilitating shift changes in a marine propulsion device. The marine propulsion device has an internal combustion engine and a shift linkage that operatively connects a shift lever to a transmission for effecting the shift changes amongst a reverse gear, a neutral gear and a forward gear. The method comprises: determining that a reduction in speed of the engine is necessary to facilitate a shift change; sensing a current speed of the engine; comparing the current speed of the engine to a stored threshold speed; and waiting to invoke the reduction in speed of the engine if the current speed of the engine is above the stored threshold speed. 
     In certain other examples, systems are for facilitating shift changes in a marine propulsion device. The systems comprise an internal combustion engine; a shift linkage that operatively connects a shift lever to a transmission for effecting shift changes amongst a reverse gear, a neutral gear and a forward gear; a speed sensor that senses current speed of the engine; and a control circuit that controls the engine to provide a reduction in speed of the engine to facilitate a shift change. The control circuit compares the current speed of the engine to a stored threshold speed and waits to invoke a reduction in speed of the engine until the current speed of the engine reaches the stored threshold speed. 
     In certain other examples, methods for facilitating shift changes in a marine propulsion device comprise moving the shift lever towards the neutral gear from one of the reverse gear and the forward gear; indicating to a control circuit that a reduction in speed of the engine is necessary to facilitate a shift change; sensing a current speed of the engine; comparing, with the control circuit, the current speed of the engine to a stored threshold speed; waiting to invoke said reduction in speed of the engine if the current speed of the engine is above the stored threshold speed; and thereafter if the shift change has not yet occurred, invoking the reduction in speed of the engine once the current speed of the engine reaches the stored threshold speed. 
     Various other aspects and exemplary combinations for these examples are further described herein below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Examples of methods and systems for facilitating shift changes in marine propulsion devices are described with reference to the following figures. The same numbers are used throughout the figures to reference like features and components. 
         FIG. 1  is a schematic depiction of a shift control system for a marine propulsion device. 
         FIG. 2  is a state flow diagram depicting states of a shift control system for a marine propulsion device. 
         FIG. 3  is a graph depicting sensed movement of a shift linkage during a shift event. 
         FIG. 4  is a graph depicting sensed movement of a shift linkage and a throttle linkage during a shift event. 
         FIG. 5  is a graph depicting change in speed of an engine over time wherein a shift lever is moved from forward gear into neutral gear. 
         FIG. 6  is a flow chart depicting steps in one example of a method of controlling shift in a marine propulsion device. 
         FIG. 7  is a flow chart depicting steps in another example of a method of controlling shift in a marine propulsion device. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     In the present description, certain terms have been used for brevity, clearness and understanding. No unnecessary limitations are to be inferred therefrom beyond the requirement of the prior art because such terms are used for descriptive purposes only and are intended to be broadly construed. The different methods and systems described herein may be used alone or in combination with other methods and systems. Various equivalents, alternatives, and modifications are possible within the scope of the appended claims. 
       FIG. 1  depicts an exemplary shift control system  10  for a marine propulsion device  12  on a marine vessel  13 . In the examples shown and described herein below, the marine propulsion device  12  is an outboard motor however the concepts of the present disclosure are not limited for use with outboard motors and can be implemented with other types of marine propulsion devices, such as inboard motors, sterndrives, hybrid electric marine propulsion systems, pod drives and/or the like. In the examples shown and described, the marine propulsion device  12  has an internal combustion engine  14  that causes rotation of a drive shaft  16  to thereby cause rotation of a propeller shaft  18 . A propeller  20  is connected to and rotates with the propeller shaft  18  to propel the marine vessel  13  to which the marine propulsion device  12  is connected. The direction of rotation of propeller shaft  18  and propeller  20  is changeable by a transmission  22  having a clutch, which in the example shown is a conventional dog clutch; however many other types of clutches can instead or also be employed. As is conventional, the transmission  22  is actuated between forward gear, neutral gear and reverse gear by a shift rod  24 . 
     The system  10  also includes a remote control  25  having an operator control lever  26 , which in the example of  FIG. 1  is a combination shift/throttle lever that is pivotally movable between a reverse wide open throttle position  26   a , a reverse detent position (zero throttle)  26   b , a neutral position  26   c , a forward detent position (zero throttle)  26   d  and a forward wide open throttle position  26   e , as is conventional. The remote control  25  typically is located remote from the marine propulsion device  12 , for example at the helm of the marine vessel  13 . The shift/throttle lever  26  is operably connected to a mechanical shift linkage  28  and a mechanical throttle linkage  29 , such that pivoting movement of the shift/throttle lever  26  causes corresponding movement of the shift linkage  28  and such that pivoting movement of the shift/throttle lever  26  causes corresponding movement of the throttle linkage  29 . Portions  28   a  of the shift linkage  28  are typically located at the remote control  25  and other portions  28   b  of the shift linkage  28  are located at the engine  14 . Similarly, portions  29   a  of the throttle linkage  29  are typically located at the remote control  25  and other portions  29   b  of the throttle linkage  29  are located at the engine  14 . The shift linkage  28  also includes a shift link  30  that translates movement of the shift/throttle lever  26  to the marine propulsion device  12 , and ultimately to the shift rod  24 , for causing a shift event (i.e. a change in gear) in the transmission  22 . The shift link  30  can be for example a cable, rod, and/or the like. The throttle linkage  29  includes a throttle link  32  that translates movement of the shift/throttle lever  26  to the engine  14  of the marine propulsion device  12 , and ultimately to change the position of a throttle valve  34  of the engine  14 . The throttle link  32  can be for example a cable, rod, and/or the like. 
     The system  10  also includes a control circuit  36  that is programmable and includes a computer processor  38 , software  39 , a memory (i.e. computer storage)  40  and an input/output (interface) device  41 . The processor  38  loads and executes the software  39  from the memory  30 . When executed, software  39  controls the system  10  to operate as described herein in further detail below. The processor  38  can comprise a microprocessor and other circuitry that retrieves and executes software  39  from memory  40 . Processor  38  can be implemented within a single device but can also be distributed across multiple processing devices or sub-systems that cooperate in executing program instructions. Examples include general purpose central processing units, application specific processors, and logic devices, as well as any other type of processing device, combinations of processing devices, and/or variations thereof. 
     Thus, the control circuit  36  can be located anywhere in the system  10  and/or located remote from the system  10  and can communicate with various components of the marine vessel  13  via wired and/or wireless links, as will be explained further herein below. The control circuit  36  can have one or more microprocessors that are located together or remote from each other in the system  10  or remote from the system  10 . The system  10  can include more than one control circuit  36 . For example, the system  10  can have a control circuit  36  located at or near the shift/throttle lever  26  and can also have a control circuit  36  located at or near the marine propulsion device  12 . Each control circuit  36  can have one or more control sections. 
     The memory  40  can include any storage media readable by processor  38 , and capable of storing software  39 . The memory  40  can include volatile and non-volatile, removable and non-removable media implemented in any method or technology for storage of information, such as computer readable instructions, data structures, program modules, or other data. Memory  40  can be implemented as a single storage device but may also be implemented across multiple storage devices or sub-systems. Memory  40  can further include additional elements, such as a controller, capable of communicating with the processor  38 . Examples of storage media include random access memory, read-only memory, magnetic discs, optical discs, flash memory disks, virtual and non-virtual memory, magnetic sets, magnetic tape, magnetic disc storage or other magnetic storage devices, or any other medium which can be used to store the desired information and that may be accessed by an instruction execution system, as well as any combination of variation thereof, or any other type of storage media. In some implementations, the storage media can be a non-transitory storage media. 
     The input/output device  41  can include any one of a variety of conventional computer input/output interfaces for receiving electrical signals for input to the processor  38  and for sending electrical signals from the processor  38  to various components of the system  10 . 
     The control circuit  36 , via the input/output device  41 , communicates with components of the marine propulsion device  12  via a communication link  50 , which can be a wired or wireless link. As explained further herein below, the control circuit  36  is capable of monitoring and controlling operational characteristics of the marine propulsion device  12  by sending and/or receiving control signals via the link  50 . Although the link  50  is shown as a single link, the term “link” can encompass one or a plurality of links that are each connected to one of more of the components of the system  10 . 
     A throttle valve  34  is provided on the engine  14  and a throttle valve position sensor (throttle sensor)  46  senses the position of the throttle valve  34 , which is movable between open and closed positions. The type of throttle sensor  46  can vary. In this example, the throttle sensor  46  generates and provides electrical signals to the control circuit  36  via the link  50  indicating the current position of the throttle valve  34 , for example in terms of a percent opening of the throttle valve  34 , with 100% open being a fully open position of the throttle valve  34  and 0% open being a fully closed position of the throttle valve  34 . One example of a throttle sensor  46  can be a wiper-type sensor, which can be located on the body of the throttle valve  34  and is commercially available from Cooper Auto or Walbro. 
     A shift sensor  48  senses a current position of the shift linkage  28  and provides this information to the control circuit  36  via the link  50 . The control circuit  36  communicates with the shift sensor  48  via the link  50 , which can be a wired or wireless link. The type of shift sensor  48  can vary. In this example, the shift sensor  48  includes a potentiometer and an electronic converter, such as an analog to digital converter that outputs discrete analog to digital (ADC) counts that each represents a position of the shift linkage  28 . Such potentiometer and electronic converter combinations are known in the art and commercially available for example from CTS Corporation. 
     An engine speed sensor  53  is provided on the engine  14  and senses speed (e.g. rotations per minute [RPM]) of the engine  14 . The type and location of engine speed sensor  53  can vary and in one example is a Hall Effect or variable reluctance VR sensor located near the encoder ring of the engine  14 . Such an engine speed sensor  53  is known in the art and commercially available for example from CTS Corporation or Delphi. 
     An inertial switch  55  is provided on the operator shift/throttle lever  26 , optionally being connected to the shift linkage  28 . The inertial switch being actuated based upon a resistance on the shift linkage. The type and location of the inertial switch  55  can vary and in one example is a potentiometer, which is commercially available for example from CTS Corporation. 
     As mentioned herein above, the control circuit  36  is configured to monitor and control operational characteristics of the marine propulsion device  12  by sending and/or receiving control signals via the link  50 .  FIG. 2  is a stateflow diagram depicting several different operational modes or “control states” of the control circuit  36 . In each control state, the control circuit  36  follows a protocol, as will be explained further herein below, to obtain a desired functional/operational output from the marine propulsion device  12  that is commensurate with operator inputs to the shift/throttle lever  26 . In this example, the control circuit  36  is programmed to control the speed of the engine  14  based upon a current position of the shift/throttle lever  26  about its pivot axis. More specifically, as the shift/throttle lever  26  is pivoted, the shift sensor  48  outputs discrete ADC counts to the control circuit  36  based upon the position of the shift linkage  28 . Each ADC count corresponds to a position of the shift/throttle lever  26  with respect to its pivot access. As will be explained further herein below, the control circuit  36  compares the current ADC count to a threshold and then controls that the engine  14  of the marine propulsion device  12  act according to a certain control state based upon the comparison, to thereby facilitate easier shifting by the marine propulsion device  12 . 
     As described in the incorporated U.S. Pat. No. 6,942,530, shifting from one gear position to another gear position (such as from neutral gear to forward gear) can often result in significant impact noise and/or impact shock to the marine propulsion device, and particularly its drive components. This noise and/or shock results from the impact that occurs between moving parts of the clutch, for example. The amount of noise and/or shock is often proportional to the speed of the engine  14 . The faster the speed of the engine  14 , the more noise and/or shock, and vice versa. Shifting from one gear position to another gear position (such as from forward gear to neutral gear) can often cause a significant load to be placed on the shift mechanism. The faster the speed of the engine  14 , the more load on the shift mechanism, and vice versa. During a shift event, it can therefore be desirable to briefly reduce the speed of the engine  14  in order to facilitate a shift event having less noise and/or shock and/or a shift event encountering reduced load. The speed of the engine  14  can be reduced by the control circuit  36  implementing one of several known “shift interrupt control strategies”, several of which are disclosed in the above referenced U.S. Pat. No. 6,942,530, which are described in the context of reducing noise and/or shock. These shift interrupt control strategies can also be used to reduce the load. Shift interrupt control strategies can include for example controlling the engine  14  by varying spark ignition, varying engine torque profile, interrupting ignition, reducing engine torque, varying throttle valve position, interrupting engine ignition circuit, cutting fuel, opening the idle air control valve. The means by which these operational characteristics are implemented are well within the skill in the art. Implementing any one of these shift interrupt control strategies can cause the speed of the engine  14  to slow, thus decreasing the torque provided to the drive train, including the noted clutch. 
     The control circuit  36  is programmed to select and enact a shift interrupt control strategy (which briefly lowers the speed of the engine) when the position signal provided by the shift sensor  48  reaches a stored threshold. As explained in the above-referenced U.S. patent application Ser. Nos. 13/760,870; 13/760,870; and 14/144,135; advantageously, the control circuit  36  also can be programmed to actively modify one or more stored thresholds as a change in operation of the marine propulsion device  12  occurs, such as for example a change in a position of the throttle valve  34 , as sensed by the throttle sensor  46 . 
     As explained herein above, the control circuit  36  is programmed to compare the current position signal (here an ADC count) outputted by the shift sensor  48  to a threshold. When the position signal reaches the threshold, the control circuit  36  enacts a new control state. It should be understood that the control circuit  36  can follow generally the same protocol during a shift from neutral gear to reverse gear as it does during a shift from neutral gear to forward gear. Also, the control circuit  36  can follow generally the same protocol during a shift from reverse gear to neutral gear as it does during a shift from forward gear to neutral gear. As such, for discussion purposes and for brevity, an exemplary control circuit  36  protocol during a shift from neutral gear to forward gear, and back to neutral gear is discussed herein below with reference to  FIGS. 2-4 . 
     Referring to  FIG. 2 , the control circuit  36  is programmed with a threshold indicating a change from a Neutral State  60  to a Neutral-to-Forward State  66  in which the control circuit  36  can optionally be programmed to enact one or more shift interrupt control strategies, as defined herein above. The control circuit  36  can also be programmed with another threshold indicating a change from Neutral-to-Forward State  66  to Forward State  62 , at which point the control circuit  36  can optionally be programmed to stop enacting the noted shift interrupt control strategies. The control circuit  36  is further programmed with another threshold indicating a change from the Forward State  62  to a Forward-to-Neutral State  68  during which state the control circuit  36  is programmed to enact one or more of the noted shift interrupt control strategies. The value of the threshold indicating a change from Forward State  62  to Forward-to-Neutral State  68  can be different than the value of the threshold indicating a change from Neutral-to-Forward State  66  to Forward State  62 . The control circuit  36  is programmed with another threshold indicating a change from Forward-to-Neutral State  68  to the Neutral State  60 , wherein the control circuit  36  is programmed to stop enacting the noted shift interrupt control strategies. As discussed above, this same type of protocol can apply in reverse, i.e. when a shift request is entered at the shift/throttle lever  26  for neutral to reverse shift and thereafter for reverse to neutral shift, wherein the control circuit  36  is programmed to employ a Neutral-to-Reverse State  70 , Reverse State  64 , and Reverse-to-Neutral State  72 . 
     The system  10  is a mechanical system wherein manual inputs from the operator directly actuate the shift event. Thus the control circuit  36  has an observational role relative to the actual shifting event because the shifting event is largely controlled by mechanical connections in the marine propulsion device  12 , including among other things the connections between the shift/throttle lever  26 , throttle linkage  29 , shift linkage  28 , shift rod  24 , and clutch. However the control circuit  36  can control characteristics of the engine  14  based upon the sensed operator inputs to the shift/throttle lever  26  and more specifically based upon sensed movements of the shift linkage  28 , for example. In this example, mechanical tolerances and connections between the noted shift/throttle lever  26 , shift linkage  28  (including portions  28   a ,  28   b  and shift link  30 ) will vary for each marine propulsion device  12 . Because of this variability, the noted thresholds that are programmed in the control circuit  36  at the time the system  10  is initially configured, which thresholds typically represent common or estimated positions of the shift linkage  28  at which a shift event most likely occurs, will not necessarily accurately reflect such a result in every system. The difference between the thresholds that are programmed when the system  10  is initially configured and the actual positions at which changes in shift states occur can vary. For example, the position of the shift linkage  28 , will not always accurately and/or precisely predict and/or represent the position at which an actual shift event occurs at the transmission  22 . Each system will have slightly different physical characteristics, which causes the correlation between the position of the shift/throttle lever  26  and actuation of the clutch to vary and be unpredictable at the time of initial configuration of the system  10 . 
       FIG. 3  graphically depicts the above-described concepts in an exemplary shift linkage  28 . The vertical axis V 1  designates a range of analog to digital counts (ADC). The horizontal axis H designates a range of angular position of the shift/throttle lever  26  with respect to a vertical or neutral N position. Dashed line  80  designates the angle of the shift/throttle lever  26  at which a shift event actually occurs. In this example, the angle is twenty degrees. Solid line  81  designates the shift position signal (ADC) output by the shift sensor  48  as the shift/throttle lever  26  is pivoted about its axis. In this example, the shift position signal is 840 ADC when the actual shift event occurs at the noted twenty degrees. Dashed horizontal line  85  represents an ADC count at which the shift linkage  28  stops moving. Dashed horizontal line  87  designates the position signal (here, 840 ADC) output by the shift sensor  48  when the actual shift event occurs. The line  81  thus has a first portion  82  that shows the shift position signal (ADC) up until when the actual shift event occurs at twenty degrees. The line  81  also has a second portion  83  that shows changes in the shift position signal (ADC) after the actual shift event occurs. Second portion  83  thus illustrates additional movement of the shift linkage  28  after the actual shift event has occurred. This is movement is lost or wasted motion in the mechanical system. More particularly, the second portion  83  illustrates lost motion in the shift linkage  28  (including the associated shift link  30 ) that occurs during movement of the shift/throttle lever  26  from the forward detent position  26   d  to the forward wide open throttle position  26   e . This motion of the shift linkage  28  does not impact or otherwise accurately predict the timing of the actual shift event. The slope and magnitude of second portion  83  will vary depending upon the particular marine propulsion device and depending upon the particular thresholds that are selected, for example when the system  10  is configured and the particular physical characteristics of the shift linkage  28 . 
     Like  FIG. 3 .  FIG. 4  depicts the shift position signal (solid line  81 ) that is output by the shift sensor  48 . Line  84 ,  FIG. 4 , depicts the percent opening of the throttle valve  34  of the engine  14  during the movement of the shift/throttle lever  26 . Vertical axis V 2  indicates the percent opening of throttle valve  34 . Once the actual shift event occurs at twenty degree lever position, the throttle valve  34  gradually opens from a closed throttle valve position at  91  to a fully open throttle valve position at  93 . 
     Through research and development efforts, the present inventors have recognized that employing shift interrupt control strategies—such as varying spark ignition, varying engine torque profile, interrupting ignition, reducing engine torque, varying throttle valve position, interrupting engine ignition circuit, cutting fuel, opening the idle air control valve, etc.—at high engine speeds can be potentially harmful to the engine  14  and can also negatively affect the way in which the engine  14  ramps down to idle speed, thus causing instability and a potential for stalling when the shift/throttle lever  26  is quickly moved from forward or reverse gear to neutral gear. In addition, the inventors have found that, typically, the higher the engine speed, the less effective the shift interrupt control strategies. 
     Thus, advantageously, according to certain methods and systems of the present disclosure, implementation of the noted shift interrupt control strategies is delayed by the control circuit  36  until after the engine  14  achieves a “threshold speed” stored in the memory  40 . The amount of the “threshold speed” can vary depending upon the particular system and in certain examples can be an amount that is calibrated based upon operational history and/or other characteristics of the system. 
     In one example, the noted threshold speed is a stored speed at which the control circuit  36  is programmed to begin controlling (i.e. ramping) speed of the engine  14  down to an idle set point speed at which the engine  14  is maintained in neutral gear. With reference to  FIG. 5 , Line A depicts speed (RPM) of the engine over time. Line B depicts an idle set point speed (RPM) that is stored in the control circuit  36 . At time T 1 , the speed of the engine  14  begins to rapidly decrease because of an operator rapidly moving the lever  26  from the forward wide open throttle position  26   f  to the neutral position  26   c . Rapid movement of the shift/throttle lever  26  into the neutral position  26   c  moves the throttle linkage  29 , which causes the throttle valve  34  to rapidly close, which in turn throttles the engine  14  and causes the speed of the engine  14  to rapidly decrease in the manner shown. This is sometimes referred to in the art as a “throttle chop”. At a later time T 2 , in order to prevent stalling of the engine  14 , the control circuit  36  is programmed to control an idle air control valve  51  on the engine  14  in a manner that transitions (i.e. ramps) the speed of the engine  14  down to the noted idle control set point speed, shown at C, without stalling or damage to the engine  14 . Movement of the shift/throttle lever  26  at time T 1  also causes movement of the shift linkage  28 , which in some examples is sensed by the shift sensor  48  and communicated to the control circuit  36  via the link  50 . As explained herein above, once the shift linkage  28  reaches the stored position threshold for the Forward-to-Neutral State  68 , the control circuit  36  is programmed to determine that a shift interrupt control strategy is necessary to better facilitate a shift change from forward gear to neutral gear. In other examples, movement of the shift/throttle lever  26  at time T actuates the shift interrupt switch  55 , which indicates to the control circuit  36  via link  57  that the shift interrupt control strategy is necessary to better facilitate the shift change from forward gear to neutral gear. 
     However in this example, contrary to the prior art, instead of immediately enacting the one or more shift interrupt control strategies once the position threshold of the Forward-to-Neutral State  68  is reached and/or the inertial switch  55  is actuated, the control circuit  36  is programmed to first compare the current speed of the engine  14  to a stored threshold speed in the memory  40 . The control circuit  36  is programmed to wait to invoke the shift interrupt control strategies until the current speed of the engine  14  reaches the stored threshold speed. Once the current speed of the engine  14  reaches the stored threshold speed, the control circuit  36  is programmed to invoke the shift interrupt control strategies so as to reduce the speed of the engine  14  and facilitate the shift change. Preferably, the control circuit  36  is programmed to only enact the reduction in speed of the engine  14  if the shift change has not occurred already. That is, the control circuit  36  can be programmed to first determine whether the shift change has already occurred (based upon the position of the shift linkage  28  provided by the shift sensor  48  and position thresholds stored in the memory  40 ). If the stored threshold speed is reached and the shift change has not already occurred, the control circuit  36  can be programmed to enact the shift interrupt control strategies. 
     The present disclosure thus provides a system  10  for facilitating shift changes in a marine propulsion device  12 . The system can comprise the engine  14 ; the shift linkage  28  that operatively connects a shift/throttle lever  26  to a transmission  22  for effecting shift changes amongst a reverse gear R, a neutral gear N, and a forward gear F; a speed sensor  51  that senses current speed of the engine  14 ; and the control circuit  36  that controls the engine  14  to provide a reduction in speed of the engine to facilitate a shift change. The control circuit  36  can be programmed to compare the current speed of the engine  14  to a stored threshold speed and wait to invoke a reduction in speed of the engine  14  until the current speed of the engine  14  reaches the stored threshold speed. 
     In certain examples, the control circuit  36  is programmed to invoke the reduction in speed of the engine  14  once the current speed of the engine  14  reaches the stored threshold speed and only if the shift change has not yet occurred. The reduction in speed of the engine  14  is invoked by employing one or more shift interrupt control strategies which can include for example controlling the engine  14  by varying the spark ignition, varying engine torque profile, interrupting ignition, reducing engine torque, varying throttle valve position, interrupting engine ignition circuit, cutting fuel, and opening an idle air control valve  15 , and/or the like. The shift sensor  48  senses a current position of the shift linkage  28  and the control circuit  36  determines that the reduction in speed of the engine  14  is necessary once the current position of the shift linkage  28  reaches a stored position threshold. The throttle sensor  46  senses position of a throttle valve  34  on the engine  14  and the control circuit  36  further determines that the reduction in speed of the engine  14  is necessary once the throttle valve  34  closes by a stored amount. In other examples, an inertial switch  55  is actuated based upon a resistance from the shift linkage  28 . The control circuit  36  determines that the reduction in speed of the engine  14  is necessary based upon actuation of the inertial switch  55 . The stored threshold speed can include an idle entry threshold speed whereupon the control circuit  36  controls (ramps) speed of the engine  14  down to a stored idle set point speed by for example controlling the idle air control valve  51  and/or timing of spark in the engine  14 , and/or the like. 
     Referring to  FIG. 6 , one example of a method of facilitating shift changes in the marine propulsion device  12  according to the present disclosure is provided. At step  100 , the control circuit  36  determines that a reduction in speed of the engine  14  is necessary to facilitate a shift change. The control circuit  36  can make this determination based upon the position of the shift linkage  28 , as communicated by the shift sensor  48 , the position of the throttle valve  34 , as communicated by the throttle sensor  46 , and/or actuation of an inertial switch  55 , as communicated by the link  57 . At step  102 , the speed sensor  53  senses the current speed of the engine  14  and communicates this information to the control circuit  36  via the link  50 . At step  104 , the control circuit  36  compares the current speed of the engine  14  to the stored threshold speed—which in certain examples can be a speed at which the control circuit  36  controls speed of the engine  14  down to the idle speed—to determine whether the current speed of the engine  14  has reached the stored threshold speed. If no, the method returns to step  102 . If yes, at step  106 , the control circuit  36  determines whether an actual shift change has occurred in the transmission  22 . As discussed above, this can be accomplished by the control circuit  36  monitoring the position of the shift linkage  28  via the shift sensor  48 . If yes, at step  108 , the control circuit  36  aborts enactment of the reduction in speed of the engine  14  via shift interrupt control strategies since the shift change has already occurred. If no, at step  110 , the control circuit  36  controls the engine  14  to invoke the reduction in speed of the engine  14  via one or more of the noted shift interrupt control strategies. 
       FIG. 7  depicts another example of a method of facilitating shift changes in a marine propulsion device  12 . At step  200 , the throttle sensor  46  senses the position of the throttle valve  34  on the engine  14 . At step  202 , the control circuit  36  determines whether the throttle valve  34  is closed by a stored amount (e.g. a stored % throttle opening amount). The current position of the throttle valve  34  is communicated to the control circuit  36  by the throttle sensor  46  via the link  50 . The value of the stored amount (% throttle opening amount) can change and can be a calibrated amount. If no, the method returns to step  200 . If yes, at step  204 , the shift sensor  48  senses position of the shift linkage  28  and communicates same to the control circuit  36  via the link  50 . At step  206 , the control circuit  36  determines whether the shift linkage  28  has reached a stored position threshold, such as for example the above-noted threshold indicating movement from the forward to neutral state  68  to the neutral state  60 . If no, the method returns to step  204 . If yes, at step  208 , the control circuit  36  determines that a reduction in speed of the engine  14  is necessary to facilitate a shift change. At step  210 , the speed sensor  53  senses current speed of the engine  14  and communicates this information to the control circuit  36  via the link  50 . At step  212 , the control circuit  36  determines whether the speed of the engine  14  has reached a stored threshold speed. If no, the control circuit returns to step  210 . If yes, at step  214 , the control circuit  36  determines whether an actual shift change has occurred. If yes, at step  216 , the control circuit  36  does not enact the shift interrupt control strategies because the shift change has already occurred. If no, at step  218 , the control circuit  36  invokes the shift interrupt control strategies to reduce the speed of the engine  14  and facilitate the shift change. 
     The present disclosure thus provides a method of facilitating shift changes in the marine propulsion device  12  having the engine  14  and the shift linkage  28  that operatively connects the shift/throttle lever  26  to the transmission  22  for effecting shift changes amongst the reverse gear R, neutral gear N and forward gear F. The method can comprise (a) determining that a reduction in speed of the engine  14  is necessary to facilitate a shift change; (b) sensing a current speed of the engine  14 ; (c) comparing the current speed of the engine  14  to a stored threshold speed; and (d) waiting to invoke the reduction in speed of the engine  14  if the current speed of the engine  14  is above the stored threshold speed. The method can further comprise (e) invoking the reduction in speed of the engine  14  once the current speed of the engine  14  reaches the stored threshold speed; and (f) invoking the reduction in speed of the engine only if the shift change has not yet occurred. In certain examples, the control circuit  36  can determine that the reduction in speed of engine is necessary by sensing a position of the shift linkage  28  and determining that the reduction in speed of the engine  14  is necessary once the current position of the shift linkage  28  reaches a stored position threshold, and further sensing position of a throttle valve  34  on the engine  14  and determining that the reduction in speed of the engine  14  is necessary once the throttle valve  34  closes by a stored amount. In certain other examples, the step of determining that a reduction in speed of the engine  14  is necessary to facilitate a shift change can be accomplished by monitoring actuation of the inertial switch  55  that is connected to the shift linkage  28  and is actuated based upon a resistance of the shift linkage  28 . The stored threshold speed can be an idle entry threshold speed whereupon speed of the engine  14  is ramped down to a stored idle set point speed. Ramping of the speed of the engine  14  down to the stored idle set point can be accomplished by controlling at least one of an idle air control valve  51  and/or timing of spark in the engine  14 , and/or the like. 
     The examples described in  FIGS. 6 and 7  refer to a shift action from forward gear to neutral gear. However, it will be understood by those having ordinary skilled in the art that the concepts of the present disclosure are equally applicable to a shift event from reverse gear to neutral gear. 
     In the above description, certain terms have been used for brevity, clarity, and understanding. No unnecessary limitations are to be inferred therefrom beyond the requirement of the prior art because such terms are used for descriptive purposes and are intended to be broadly construed. The different systems and method steps described herein may be used alone or in combination with other systems and methods. It is to be expected that various equivalents, alternatives and modifications are possible within the scope of the appended claims. Each limitation in the appended claims is intended to invoke interpretation under 35 U.S.C. §112(f), only if the terms “means for” or “step for” are explicitly recited in the respective limitation.