Abstract:
A marine propulsion system that utilizes a transmission shift sequence to control shifting of the propulsion system transmission between forward and reverse gears. The marine propulsion system includes a controller that executes the transmission shift sequence using engine speed and transmission fluid pressure signals to determine the timing of various steps in the shift sequence. The controller is connected to a shift actuator for the transmission and to an engine speed throttle to thereby control transmission shifting and engine speed as a part of the transmission shift sequence. By monitoring engine speed and transmission fluid pressure, and by controlling transmission shifting and engine speed settings, the transmission shift sequence can provide the operator with the ability to carry out quick shifts that will neither stall the engine nor damage the transmission clutch.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application claims the benefit of the priority of U.S. Provisional Application Ser. No. 60/480,429, filed Jun. 20, 2003, the entire contents of which are hereby incorporated by reference. 

   TECHNICAL FIELD 
   The present invention relates to a method and apparatus for controlling transmission shifts in a marine propulsion system. 
   BACKGROUND OF THE INVENTION 
   Marine vessels in use today use marine propulsion systems that typically include the following sub-systems: an engine to provide power, a transmission to transfer drive power to a propeller, and a control system to provide control of engine speed and transmission engagement. An operator or pilot of the vessel nominally has control of the engine speed and transmission shifting through one or more operator controls. Using these operator controls, the transmission can be shifted between forward and reverse, usually through a neutral (transmission disengaged) position, and the engine speed can be set as desired by the operator. 
   Engine stalling is a problem sometimes encountered when operating a marine vessel, and often this occurs when the vessel is moving in one direction at high speed and the operator suddenly shifts the transmission into the opposite gear. The stall is the result of the linear momentum of the vessel moving through the water which imparts a drag load on the propeller that tends to keep the propeller, transmission, and engine rotating in the same direction. Reversing the transmission under these circumstances, however, places a sudden increased load on the engine because of the drag load on the propeller. As a result, the engine is often unable to overcome the sudden increased load and, therefore, the engine stalls. 
   Another problem can arise when a pilot attempts to avoid the engine stalling problem. Faced with a potential engine stall, a pilot will often “race” the engine prior to shifting it into the reverse gear. Racing the engine, however, can lead to transmission clutch damage caused by excessive engine speed prior to full engagement of the transmission clutch to the engine. To avoid damage to the transmission, marine transmission manufacturers recommend maximum acceptable engine speeds (typically 1,000 RPM) for all transmission shifts including neutral to forward or reverse, and forward or reverse through neutral to the opposite gear. Exceeding the maximum acceptable engine speed during a shift tends to result in excessive clutch temperatures and possibly clutch failure. 
   Attempts to alleviate the above problems usually involve using electronic controls, or “blind timers”, to delay the time between shifting the transmission and increasing of the speed of the engine to allow the transmission clutch to fully engage the engine and propeller driveshaft. This method is only effective under specific conditions, such as where the drag load on the propeller decreases by a sufficient amount during the time delay such that the engine can overcome the sudden increased load without stalling. In some instances, however, this method may be ineffective because the shift is not delayed long enough and the engine stalls, or because the delay is too long resulting in an unnecessarily long shift delay. 
   SUMMARY OF THE INVENTION 
   In accordance with one aspect of the present invention, there is provided a method of controlling a marine vessel transmission to shift the transmission from an initial gear position to an opposite gear position. A request to shift the transmission from the initial gear position into the opposite gear position is received, engine speed and transmission fluid pressure is measured, and a transmission shift sequence is carried out using the measured engine speed and transmission fluid pressure. 
   In accordance with another aspect of the invention, there is provided a control system for controlling a marine engine and marine transmission. The control system includes a control module having a controller, a transmission fluid pressure sensor coupled to the controller to provide a transmission fluid pressure signal, and an engine speed sensor coupled to the controller to provide an engine speed signal. The controller is operable to control shifting of the transmission between forward and reverse gears using the engine speed signal and transmission fluid pressure signal. 
   In accordance with a further aspect of the invention, there is provided a marine propulsion system including an engine, a transmission coupled to the engine by a clutch to permit selective engagement and disengagement with the engine, and a propulsion unit coupled to the transmission. A controller is provided in communication with the engine and the transmission. An operator input device includes a position sensor that is coupled to the controller to permit an operator to input a transmission shift request. The transmission further includes a transmission shift actuator coupled to the controller to receive shift commands from the controller, and also includes a transmission fluid pressure sensor coupled to the controller. The engine includes an engine speed actuator coupled to the controller to receive speed commands from the controller, and further includes an engine speed sensor coupled to the controller. In response to receiving a transmission shift request from the operator input device, the controller determines one or more shift commands using signals from the sensors and sends the shift command(s) to the transmission shift actuator to thereby provide a controlled shifting of the transmission in a manner that reduces wear to the clutch and avoids engine stalls. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred exemplary embodiments of the invention will hereinafter be described in conjunction with the appended drawings, wherein like designations denote like elements, and wherein: 
       FIG. 1  is a block diagram of a marine propulsion system; 
       FIG. 2  is a flow and state diagram showing an algorithm for a marine transmission shift from forward to reverse, or vice-versa; and 
       FIG. 3  is a graphical representation of a transmission shift including time vs. commanded engine speed, actual engine speed, and transmission fluid pressure. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  illustrates a block diagram of a marine propulsion system  10  according to an embodiment of the present invention. The marine propulsion system  10  generally resides within a marine vessel (not shown) and includes the following main elements: a prime mover (engine)  12  for powering the vessel, a propulsion unit  14  for propelling the vessel, a marine transmission  16  for converting the output of the engine  12  into an input to the propulsion unit  14 , a throttle control lever  18  or other manual input device used by the pilot to control transmission shifting and engine speed, and a control module  20  for controlling the engine  12  and transmission  16  in response to the manual input from the pilot. 
   The engine  12  is mounted to the vessel as is well-known in the art and, as used herein, the term “engine” means an internal combustion engine, a turbine engine, electric motor, and the like. For example, an internal combustion engine provides rotational power from a crankshaft (not shown) that rotates at the speed or revolution rate (RPM) of the engine  12 . The engine  12  can include an electronically controlled actuator or throttle  22  such as by a throttle servo, and also includes a speed sensor  24  for measuring the rotational speed of the crankshaft or output shaft. The speed sensor  24  generates an output engine speed signal that is provided to the control module  20 . 
   The propulsion unit  14  is mounted to the vessel as is well-known in the art and may encompass a simple drive shaft and propeller  26 , or a more elaborate device such as an sterndrive unit made by OMC, Mercury Marine, and the like. 
   The marine transmission  16  is also mounted to the vessel and is connected between the propulsion unit  14  and engine  12 . As is well-known in the art, the marine transmission  16  is coupled to both the propulsion unit  14  and the engine  12 , but can be selectively engaged and disengaged from the engine  12  using any of a variety of clutch or other coupling mechanisms. For example, the marine transmission can utilize a transmission clutch  28  that engages a flywheel  30  mounted to the output shaft of the engine  12 . Separate forward and reverse clutches can be used. Alternatively, it can use a fluid coupling, such as a torque converter. As used herein, the term “clutch” includes all of these as well as other suitable coupling mechanisms. 
   The marine transmission  16  is a variable speed device that includes forward, neutral, and reverse gear settings. The clutch  28  used in the transmission is activated using transmission oil as is well known, and can include a solenoid-operated actuator or valve  32  or other device to provide electronic control of the transmission oil pressure for purposes of shifting. The solenoid receives a control signal from the control module  20  and adjusts the valve  32  accordingly to control the transmission fluid to either engage or disengage the transmission clutch  28 , and/or to engage or disengage low or high gearsets (not shown). The transmission  16  includes a transmission fluid pressure sensor  34  for measuring the fluid pressure within the transmission  16 . This sensor  34  generates a transmission fluid pressure signal that is provided to the control module  20 . 
   The throttle control lever  18  or other manual input device is typically mounted within a cockpit (not shown) of the marine vessel and is provided to convert a speed and/or directional request from a marine vessel operator to an electronic signal. The input device can be, for example, a combined transmission and engine throttle control lever  18  mounted on a control console  36 . The control lever mechanism  18  can include a transducer or position sensor  38  for generating and outputting to the control module  20  a suitable direction signal that is representative of the angular position of the operator control lever  18 . 
   The control module  20  monitors various marine propulsion system parameters by receiving inputs of engine speed, transmission fluid pressure, and operator requests for speed and direction via the throttle control lever  18 . In the illustrated embodiment, the control module  20  includes a controller  40 , a memory  42 , and interface electronics  44 . A variety of other control module circuit designs and configurations can be used in lieu of that shown. The interface electronics  44  may conform to protocols such as RS-232, parallel, small computer system interface, and universal serial bus, etc. Moreover, the interface electronics  44  can include circuits or software for developing the drive signals needed to actuate the engine throttle  24  and transmission shift solenoid  32 , etc. The memory  42  can be RAM, ROM, EPROM, and the like, and can be a separate component or integrated into the controller  40  itself. The controller  40  is configured to provide control logic that provides the functionality for the marine propulsion system. In this respect, the controller  40  may comprise a microprocessor, a micro-controller, an application specific integrated circuit, and the like. The controller  40  is interfaced with the memory  42  which provides storage of the computer software that provides the functionality of the marine propulsion system  10  and that may be executed by the controller  40 . The memory  42  may also be configured to provide a temporary storage area for data received by the marine propulsion system  10  from the sensors  24 ,  34 ,  38  or even from a separate host device, such as a computer, server, workstation, and the like (not shown). 
   The controller  40  includes an input module  46  which can simply be data inputs for receiving the commanded throttle and/or transmission shift signal from the operator, as well as the engine speed signal from the engine  12  and the transmission pressure signal from the marine transmission  16 . The controller  40  also includes an analysis module  48  which can be a software module or routine that is a part of the main control program that is executed by the controller  40  and that determines the appropriate transmission shifting and engine speed control signals that are to be sent to the transmission  16  and engine  12 , respectively. For example, based on the direction signal, the controller  40  outputs a control signal to the engine throttle servo  22  so as to position the engine throttle  22  in a position that is proportional to the operator control lever  18  position. The controller  40  further includes an output module  50  which can be various data outputs connected to the interface electronics  44  that supply the control signals to the engine  12  and transmission  16 . 
   Referring now primarily to  FIG. 2  in addition to  FIGS. 1 and 3 , a method  200  of controlling the marine propulsion system  10  is provided according to an embodiment of the present invention. During regular operation of the marine vessel, the controller  40  receives requested gear shifts and/or throttle changes from the operator and generates the appropriate control signals for the transmission  16  and/or engine throttle  22 . When the controller  40  receives a request from the operator to shift the transmission  16  into an opposite gear (e.g., forward to reverse or vice-a-versa), the controller  40  carries out the transmission shift sequence of  FIG. 2 . Detection of this shift request and the carrying out of the transmission shift sequence can be done using the analysis module routine of the controller software. For the illustrated embodiment,  FIG. 3  depicts an exemplary graph  300  of commanded engine speed v C , actual engine speed v A , and transmission fluid pressure P T  values versus time that results from the transmission shift sequence of  FIG. 2 . 
   The transmission shift sequence is carried out by the software control program in the controller  40 . This process can be carried out upon a transmission shift to an opposite gear, or can also be done each time a shift from neutral into forward or reverse gear is requested. The process involves the following steps. 
   ENGINE SPEED DRAG DOWN  210 . First, the controller  40  commands the engine throttle  22  to idle (e.g., 550 RPM) from its current speed setting and maintains the current (or initial) transmission gear position. This command is represented graphically in  FIG. 3  by plot v C , between points  302  and  304 . This command reduces the engine speed v A  as quickly as possible without stalling the engine  12  and to a point where a shift may occur without damage to the clutch  28  or other transmission parts. Before proceeding to the next step, the controller  40  waits until the engine speed v A  falls below point  306  which represents a predetermined “Maximum Engine Speed To Shift”, such as 800 RPM. 
   TRANSMISSION PRESSURE DRAG DOWN  220 . After the engine speed v A  has dropped below the “Maximum Engine Speed To Shift” value, the controller  40  commands the transmission  16  to reverse the initial gear position, from forward to reverse, or vice-versa. In effect, this command enables the transmission fluid pressure P T  to drop quickly and is represented between points  308  and  310  of plot P T  of  FIG. 3 . Before proceeding to the next step, the controller  40  waits for disengagement of the transmission  16  out of the initial gear position by waiting until the transmission fluid pressure P T  falls below a predetermined maximum gear “Disengage Limit”, such as 200 PSI. The Disengage Limit is represented graphically in  FIG. 3  by point  312 . This delay ensures complete disengagement of the transmission clutch from the engine  12  to prevent clutch  28  burn up. 
   NEUTRAL WAIT  230 . Once the transmission fluid pressure P T  has fallen below the “Disengage Limit”, the controller  40  overrides the previous command to reverse gear position and now commands the transmission  16  to the neutral gear position. The controller  40  also commands the engine speed to a “Set Speed” value, such as 900 RPM. This command is represented graphically in  FIG. 3  by points  314  and  316  of plot v C . As represented between points  318  and  320  of plot v A  in  FIG. 3 , this command permits the engine speed Va to rise quickly to the “Set Speed” value, which is high enough to enable engagement of the transmission  16  into an opposite gear position, without loading and stalling the engine  12 . Note that the transmission  16  has not yet completely reversed from the initial gear position all the way through neutral and actually into the opposite gear position. In other words, the Neutral Wait step  230  interrupts the reverse gear command to prevent damage to the transmission  16  and engine  12 . Before proceeding to the next step, the controller  40  waits for the engine speed v A  to reach “Set Speed” at point  320 . Thereafter, the engine speed v A  peaks at point  322  and drops back toward the commanded “Set Speed” value. 
   WAIT FOR GEAR ENGAGE  240 . Next, the controller  40  maintains the commanded engine speed v C  at “Set Speed” and commands the transmission  16  to the reverse gear position. Accordingly, the transmission  16  moves from neutral to the gear setting that is opposite of the initial gear setting, and the transmission clutch  28  engages the engine  12 . This clutch engagement is represented graphically in  FIG. 3  by the rapid rise in transmission fluid pressure P T  beginning at point  326  and by the concurrent rapid drop in actual engine speed v A  beginning at point  324 , after which the engine speed v A  bottoms out at point  328 , but thereafter begins recovery due to the continued application of the “Set Speed” command. But, before proceeding to the next step, the controller  40  waits until the transmission fluid pressure P T  increases above a predetermined “Engage Limit”, such as 250 PSI, which is graphically represented at point  330  of  FIG. 3 . This indicates that the transmission clutch  28  has fully engaged the engine  12  and that the engine speed can be increased without damaging the transmission  16 . 
   WAIT FOR ENGINE SPEED RECOVERY  250 . Engagement of the clutch  28  in the opposite gear from the initial gear setting places a load on the engine  12  that will slow the engine speed v A , perhaps even below idle. Accordingly, the commanded engine speed v C  is held at “Set Speed” while the controller  40  waits until the actual engine speed v A  climbs back toward “Set Speed” and actually reaches an “Exit Speed”, such as 650 RPM, which is represented by point  332  of  FIG. 3 . The “Exit Speed” is the speed at which the engine  12  is deemed to have recovered from the load placed thereon by the transmission clutch engagement. As depicted by points  334  and  336  on plot v C  of  FIG. 3 , once the engine  12  has recovered to the “Exit Speed” setpoint, the controller  40  resumes normal operation  260  commanding the engine speed to that set by the marine vessel operator and, in effect, relinquishing speed control back to the operator. For example, the commanded engine speed v C  can default to the idle speed as depicted by point  336  of  FIG. 3 . Following the command, the engine speed v A  peaks at point  338  and drops toward the commanded idle speed. From this point on, the marine vessel operator can increase or decrease engine speed at will, until another reverse gear request is made wherein the method  200  repeats. 
   Accordingly, the present invention helps alleviate many problems in the prior art including excessive shift time, engine stalls, and transmission damage. To protect the transmission  16 , the controller  40  limits engine speed to less than the “Maximum Engine Speed To Shift” until the transmission pressure P T  reaches the “Engage Limit”. This indicates that the transmission clutch  28  has effectively coupled the propulsion unit  14  to the engine  12  and that the engine speed may now be increased without damaging the transmission  16 . To achieve a minimum shift time, and still avoid engine stalling under a high speed high load transmission shift, the controller  40  compares several inputs (including requested direction, engine speed, and transmission fluid pressure) against several optimum predetermined setpoints. One of ordinary skill in the art will recognize that the various setpoints may vary from application to application and may be dictated by manufacturers of one or more of the engine, marine transmission, marine vessel, etc. 
   The method  200  described herein can be implemented via a computer program and the various setpoints may be stored in memory as individual data points or in a look-up table or the like. The computer program may exist in a variety of forms both active and inactive. For example, the computer program can exist as software program(s) comprised of program instructions in source code, object code, executable code or other formats; firmware program(s); or hardware description language (HDL) files. Any of the above can be embodied on a computer readable medium, which include storage devices and signals, in compressed or uncompressed form. Exemplary computer readable storage devices include conventional computer system RAM (random access memory), ROM (read only memory), EPROM (erasable, programmable ROM), EEPROM (electrically erasable, programmable ROM), and magnetic or optical disks or tapes. 
   It will thus be apparent that there has been provided in accordance with the present invention a control method and apparatus for a marine propulsion system that achieves the aims and advantages specified herein. It will of course be understood that the foregoing description is of preferred exemplary embodiments of the invention and that the invention is not limited to the specific embodiments shown. Various changes and modifications will become apparent to those skilled in the art and all such variations and modifications are intended to come within the scope of the appended claims. 
   As used in this specification and appended claims, the terms “for example” and “such as,” and the verbs “comprising,” “having,” “including,” and their other verb forms, when used in conjunction with a listing of one or more components or other items, are each to be construed as open-ended, meaning that the listing is not to be considered as excluding other, additional components or items. Other terms are to be construed using their broadest reasonable meaning unless they are used in a context that necessarily requires a different interpretation.