Patent Publication Number: US-6220905-B1

Title: Tilt-trim subsystem for marine propulsion systems

Description:
BACKGROUND OF THE INVENTION 
     The invention relates generally to marine propulsion systems and, more particularly, to outboard motors including propulsion units which are steerable in a generally horizontal plane and tiltable in a generally vertical plane. 
     The invention also relates to tilt/trim subsystems for power tilting/trimming of propulsion units between a lower normal running position in which the propeller is submerged in water, and a tilted or raised position in which the propeller is located for above-the-water accessibility. 
     Relatively small vessels, such as motor boats or the like, generally use a tilt-trim subsystem. Known tilt-trim subsystems typically comprise a tilt cylinder unit for swinging a swivel bracket through a relatively large angle to lift the lower portion of the outboard motor above the water level or, conversely, lower the outboard motor below the water level. Such subsystems may further comprise a distinct trim cylinder unit for angularly moving the swivel bracket through a relatively small angle to trim the outboard motor while the lower portion thereof is being submerged. One desirable characteristic of a tilt-trim subsystem would be to provide a slower rate of rotation during trimming to retain the propulsion unit in water for a longer interval during movement thereof through a predetermined angular trim range and thereafter to more rapidly elevate the propulsion unit from the water so as to reach a full tilt-up position. Unfortunately, previous tilt-trim subsystems, as suggested above, may require use of distinct tilt and trim cylinder units or have required use of fairly complex mechanical structures to somewhat meet the tilt-trim requirements of the propulsion unit. Thus, it would be desirable to provide a single cylinder/piston subassembly that would allow to meet the trim-tilt requirements of the propulsion unit. It would be further desirable for that subassembly to provide a relatively slower rate of rotation during trimming, as compared to the rate of rotation used to reach a fully tilt-up position. The tilt-trim subsystem should allow for a low-cost and uncomplicated mechanical installation capable of being installed in kit form and capable of being serviced without requiring substantial time and expenditures. 
     BRIEF SUMMARY OF THE INVENTION 
     Generally speaking the present invention fulfills the foregoing needs by providing a tilt-trim subsystem for a boat propulsion system. The propulsion system may include a stern bracket mounted on a transom of the boat. A swivel bracket is pivotally supported relative to the stern bracket for rotation about a generally horizontal axis. The subsystem may include a tilt and trim assembly having at least one cam pivotally supported by the stern bracket. The cam is configured to impart a relatively slow rate of rotation to the swivel bracket, at least when there is driving contact between the cam and the swivel bracket within a predetermined angular range for trimming, as compared to a rate of rotation within a predetermined angular range for tilting. 
     The present invention further fulfills the foregoing needs by providing a marine propulsion system having a stern bracket mounted on a transom of the boat. A swivel bracket is pivotally supported relative to the stern bracket for rotation about a generally horizontal axis. The propulsion system further includes a tilt and trim assembly having at least one cam pivotally supported by the stern bracket. The cam is configured to impart a relatively slow rate of rotation to the swivel bracket, at least when there is driving contact between the cam and the swivel bracket within a predetermined angular range for trimming, as compared to a rate of rotation within a predetermined angular range for tilting. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features and advantages of the present invention will become apparent from the following detailed description of the invention when read with the accompanying drawings in which: 
     FIG. 1 is a side elevational view of an exemplary outboard motor incorporating a prior art tilt/trim subsystem; 
     FIG. 2 illustrates an isometric view of an exemplary embodiment of the tilt/trim subsystem of the present invention; and 
     FIG. 3 is made up of three respective side elevational views that collectively illustrate exemplary details regarding the operation of the tilt/trim subsystem of FIG.  2   
    
    
     Before explaining one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The invention may be capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting. 
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 illustrates an exemplary prior art marine propulsion system in the form of an outboard motor  11  having a standard propulsion unit  13  including, at the lower end thereof, a rotatably mounted propeller  15  driven by a propeller shaft  17  to develop thrust to propel a boat  25  in a desired direction. The outboard motor  11  also includes means  21  for pivotally mounting the propulsion unit  13  for pivotal movement in both the horizontal and vertical planes relative to a transom  23  of the boat  25 , to provide for steering movement of the propulsion unit  13  in the horizontal plane, and to provide for movement in the vertical plane of the propulsion unit  13  between a lowermost position with the propeller  15  fully submerged in water for driving propulsion and a raised position affording above-water accessibility to the propeller  15 . 
     The means  21  for pivotally mounting the propulsion unit  13  includes a transom bracket means  31  adapted to be fixedly mounted on the transom  23  of the boat  25 . The means  21  for pivotally mounting the propulsion unit  13  also includes a stern bracket  41  having an upper end  43 , as well as first or upper pivot means  45  located rearwardly of the boat transom  23  and connecting the upper end  43  of the stern bracket  41  to the transom bracket means  31  for pivotal movement of the stern bracket  41  about a first or upper pivot axis  47  which is horizontal when the transom bracket means  31  is boat mounted. The means  21  for pivotally mounting the propulsion unit  13  further includes a swivel bracket  51 , together with a lower or second pivot means  53  connecting the swivel bracket  51  to the stern bracket  41  at a point below the first pivot means  45  for pivotal movement of the swivel bracket  51  relative to the stern bracket  41  about a second or lower pivot axis  55  which is parallel to the first or upper pivot axis  47 . 
     The outboard motor  11  also includes means for displacing the swivel bracket  51  and connected propulsion unit  13  about the lower horizontal pivot axis  55  and about the upper horizontal pivot axis  47 . As seen in FIG. 1, such means comprises one or more tilt hydraulic cylinder-piston subassemblies  65 . One end  69  is pivotally connected to the transom bracket means  31  and the other end  70  is pivotally connected to the stern bracket  41 . In addition, the means for pivotally displacing the swivel bracket  51  and connected propulsion unit  13  includes one or more trim cylinder-piston subassemblies  71 . One end  75  is pivotally connected, by any suitable means, to the stern bracket  41 , and the other end  76  is pivotally connected, by any suitable means, to the swivel bracket  51 . Thus, as suggested above, typical presently available outboard arrangements generally comprise distinct trim and tilt piston/cylinder subassemblies for pivoting the propulsion unit. In particular, the trim subassembly when actuated allows for trimming the engine by changing its angle position relative to the transom of the boat. The tilt subassembly when actuated allows to further change the angle to the full tilt up position. 
     FIG. 2 illustrates an exemplary embodiment of a tilt-trim subsystem  100  embodying features of the present invention. As shown in FIG. 2, tilt-trim subsystem  100  includes at least one cam  102  extending from one end of a cam support stud  104  supported by the stern bracket  41 . Cam support stud  104  is pivotally mounted between respective side walls  106  (one of which is seen in FIG. 2) of the stern bracket  41  by means of respective pivot studs  108 . It will be appreciated that, depending on the size of the load to be driven, another cam  103  could similarly extend from the respective opposite end of cam support stud  104  so as to provide more symmetrical load distribution. It will be further appreciated that cams  102  and  103  together with cam support stud  104  may comprise a unitized body, such as may be achieved using well-understood casting techniques. Alternatively, each of cams  103  and  103  could constitute an individual part that could be respectively affixed to cam support stud  104  using bolts or any other means for mechanically affixing two components to one another. 
     A cylinder/piston subassembly  110  that may be actuated in response to a pressurized fluid, such as hydraulic or pneumatic fluid, is pivotally supported onto support stud  104  by means of a lower pivot pin  112 . Pivot pin  112  also extends into generally arcuated slots  114  configured in the side walls of stern bracket  41 . It will be appreciated that the respective ends of slots  114  allow for limiting the rotation of cam support stud  104  and consequently the rotation of cam  102 . The opposite end of cylinder/piston subassembly  110  is pivotally mounted to swivel bracket  51  by means of an upper pivot pin  116 . Swivel bracket  51  further includes rollers or bearings  118  that slidably ride on the surface of cam  102  at least when there is driving contact between the cam and the swivel bracket preferably within a predetermined angular range for trimming. It will now be appreciated by those skilled in the art that the curvature of the surface of the cam that contacts bearings  118  may be chosen using well-understood mechanical design techniques to impart a relatively slow rate of rotation to the swivel bracket, as compared to the rate of rotation that may be directly imparted by the piston within a predetermined angular range for tilting. As suggested above, this is a desirable feature being that a slower rate of rotation during trimming is desirable to retain the propulsion unit  13  (FIG. 1) in water for a longer interval during movement thereof through the predetermined angular trim range and thereafter to more rapidly elevate the propulsion unit  13  from the water so as to reach a full tilt-up position. 
     FIGS. 3A-3C collectively allow for illustrating respective operational details of the tilt-trim subassembly shown in FIG.  2 . As shown in FIG. 3A, with the piston of subassembly  110  substantially retracted, the bearing  118  may be located at the upper portion of the cam surface that would drive swivel bracket  51  through the predetermined trim positions. FIG. 3B shows the piston of subassembly  110  upon reaching a partially extended position. In this case, the cam  102  has rotated through the predetermined angular range for trimming that may extend between the initial position illustrated in FIG.  3 A and the intermediate position of FIG.  3 B and the bearing  118  is about to lift up from the lower end of the cam driving surface. FIG. 3C shows the piston in a fully extended position so as to provide a full tilt-up to the propulsion unit. As suggested above, it will be appreciated that the use of the cam  102  and associated components allow for a slower rate of travel in the trim range and a faster rate of travel in the tilt range using a single cylinder/piston subassembly. This allows for an even more reliable and less costly propulsion system design that may be readily incorporated in new boat models or retrofitted in existing models as part of a replacement kit. 
     While the preferred embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions will occur to those of skill in the art without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.