Patent Publication Number: US-6213822-B1

Title: Tilt and trim unit for marine drive

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a marine propulsion unit for a watercraft, and more particularly to a tilt and trim unit for a marine propulsion unit. 
     2. Description of the Related Art 
     Outboard motors with four-cycle engines have grown in popularity in recent years, due in part to environmental concerns associated with two-cycle outboard motors. The application of four-cycle engines in outboard motors, however, has raised some challenges, especially with large horse power engines. A four-cycle engine will weigh more than a two-cycle engine that produces a comparable horsepower to that of the four-cycle engine. The additional weight creates problems for the conventional hydraulic tilt and trim units used with the outboard motor. 
     A tilt and trim unit commonly operates between components of a clamping assembly to adjust the trim and tilt position of the outboard motor. In particular, the tilt and trim unit usually includes an extendable hydraulic cylinder, piston assembly that operates between a clamping bracket and a swivel bracket of the clamping assembly, which typically supports an outboard motor on a watercraft. The clamping bracket is attached to the watercraft and the swivel bracket supports the outboard motor. A pivot pin connects together the swivel and clamping brackets. Extension of a rod of the cylinder causes the swivel bracket to pivot about the axis of the pivot pin, relative to the stationary clamping bracket, to raise or lower the outboard drive. This assembly prevents the outboard motor from popping up when operating in reverse, while permitting the outboard motor to pop up when it strikes an underwater object as it travels forward. 
     Manually operated tilt and trim units usually include a bypass passage that interconnects chambers of the cylinder which the piston separates. A valve assembly is located within the passage to regulate flow through the passage. When the valve assembly is opened, the outboard motor can be manually tilted up without having to act against the resistance of the hydraulic cylinder. U.S. Pat. No. 4,784,625 entitled “Tilt Lock Mechanism For Marine Propulsion Device,” illustrates an exemplary arrangement of the valve assembly and bypass passage of a tilt and trim unit. The tilt lock mechanism disclosed in the &#39;625 patent includes a separate accumulator chamber that communicates with the two chambers of the hydraulic cylinder. Check valves normally restrict flow between the cylinder chambers and the accumulator chamber. An actuating mechanism selectively opens one of the check valves or the other to permit manual movement of the outboard motor, either up or down, without working against the hydraulic cylinder. 
     FIG. 1 illustrates another prior construction of a hydraulic cylinder, piston assembly  20 , in cross-section. The prior cylinder  20  includes a piston  22  that slides within a bore  24  of the cylinder  20 . The piston  22  divides the bore  24  into upper and lower fluid chambers  26 ,  28 . 
     A piston rod  30  is attached to the piston  22  and extends beyond one end of the cylinder  20 , through the upper chamber  26 . The outer end of the piston rod  30  includes a trunnion  32  that is pivotally attached to an associated swivel bracket. The cylinder body  20  also includes a lower trunnion  34  that is pivotally connected to the associated clamping bracket. 
     A passage  36  extends generally parallel and next to the cylinder bore  24 , on one side of the cylinder  20 , and connects together the upper and lower fluid chambers  26 ,  28 . A manual valve  38  operates within the passage  36  to control the flow of working fluid through the passage  36 . When the valve  38  is open, the upper and lower fluid chambers  26 ,  28  communicate with each other through the passage  36 , and the piston  22  can be easily slid within the bore  24 . The outboard motor thus can be raised and lowered, unencumbered by the hydraulic cylinder assembly  20 . When the valve  38  is closed, however, the hydraulic cylinder assembly  20  locks the outboard motor in the established tilt or trim position. An actuator  39  is used to open and close the valve  38 . 
     As seen in FIG. 1, the cylinder assembly  20  also includes an accumulation chamber  40  arranged on one side of the cylinder bore  24 . The accumulation chamber  40  communicates with the lower fluid chamber  28  of the cylinder  20  to compensate for the volumetric differences between the upper and lower fluid chambers  26 ,  28 . That is, because the piston rod  30  extends through the upper chamber  26 , and thus reduces the volume in the upper chamber  26 , less fluid will be displaced from the upper chamber  26  than is required to make up the volume in the lower chamber  28  as the piston  22  moves upwardly. The accumulation chamber  40  directly communicates with the lower fluid chamber  28  to compensate for this volumetric difference between the fluid chambers  26 ,  28 . The accumulation chamber  40  is arranged on a side of the cylinder bore  24  opposite of the passage  36  and the manual valve  38 . 
     Another prior cylinder assembly for a tilt locking mechanism is illustrated in U.S. Pat. No. 5,368,509, issued Nov. 29, 1994, and entitled “Tilt Lock System For Outboard Motor.” The construction of this assembly is generally similar to the cylinder assembly construction illustrated in FIG. 1, but with a multi-position valve located on the same side of the cylinder as the accumulation chamber and interposed between these components of the cylinder assembly. 
     The constructions of both tilt and trim units, illustrated in FIG.  1  and disclosed in the &#39;509 patent, result in a wide assembly. The swivel and clamping consequently must be wide and reinforced to accommodate the hydraulic cylinder assembly. The increased weight of the new four-cycle outboard motors further exacerbates this problem, requiring additional reinforcement of the brackets. Such reinforcing increases the size and weight of the brackets, as well as increases the manufacturing cost. 
     An additional prior construction of a hydraulic cylinder assembly  50  is illustrated in FIG. 2, which depicts the cylinder assembly in cross-section. In this cylinder assembly  50 , an accumulation chamber  52  is integrated into an upper fluid chamber  54  above a port  56  that communicates with the upper fluid chamber  54 . FIG. 2 illustrates the position of a piston  58  and piston rod  60  in a fully retracted position. Under this condition, a volume of working fluid F 1  remains above the piston  58  with a volume of inert compressible gas F 2  residing above the working fluid F 1  to form the accumulation chamber  52  above the upper fluid chamber  54 . 
     The width of the tilt and trim unit illustrated in FIG. 2 is less than the width of the unit illustrated in FIG. 1; however, the length of the unit increases as a result of the location of the accumulation chamber above the piston. In order for the unit to fit between the clamping and swivel brackets with the outboard motor in a fully trimmed down position, the size of the accumulation chamber must be reduced. A smaller accumulation chamber consequently reduces the diameter size of the piston. And a smaller size piston reduces the amount of weight the hydraulic unit can support so that the unit cannot be used with heavy outboard motors. 
     In addition, both the cylinder assembly designs illustrated in FIGS. 1 and 2 are difficult to adjust, especially when supporting a heavy motor. In both prior designs, the manual valve is opened to tilt up the outboard motor. If the person adjusting the trim position wants to close the valve once the outboard motor has been raised to the desired position, the user cannot simply let go of the outboard motor as it will immediately lower (i.e., trim or tilt down) under its own weight. The person thus must hold the heavy outboard motor while leaning over the transom of the watercraft to close the valve. This operation is difficult and awkward for one person to perform alone. 
     SUMMARY OF THE INVENTION 
     A need therefore exists for a compact tilt and trim unit of a minimal width which is capable of supporting heavier outboard motors and which eases manually trimming and tilting up of the outboard motor. 
     One aspect of the present invention thus involves a compact tilt and trim unit. The tilt and trim unit comprises an actuator including a first variable volume fluid chamber and a second variable volume fluid chamber. A piston, which moves along a stroke axis of the actuator, separates the first and second fluid chambers. The chambers communicate with each other through a valve mechanism. A sub-chamber is connected to the first fluid chamber. The sub-chamber and the valve mechanism are arranged next to the actuator on the same side of the actuator stroke axis and directly above one another. In one mode, the valve mechanism is arranged next to the second fluid chamber, and the sub-chamber is arranged next to the first fluid chamber below the valve mechanism. This construction produces a compact arrangement without sacrificing the size of the sub-chamber. 
     Another aspect of the invention involves a tilt and trim unit for a marine drive comprising a cylinder. The cylinder includes a first variable-volume fluid chamber and a second variable-volume fluid chamber separated by a movable piston. A sub-chamber freely communicates with the first fluid chamber and communicates with the second fluid chamber through a valve mechanism. The sub-chamber includes a volume of working fluid and a volume of compressible fluid occupying a space above the working fluid. Both the first and second chambers of the cylinder communicate with the sub-chamber at a point below an interface surface between working fluid and the compressible fluid. In one mode, a conduit, which extends generally parallel to an axis of the cylinder, extends through a portion of the space occupied by the compressible fluid and connects the second fluid chamber to the sub-chamber at a point below the interface surface. 
     In accordance with another aspect of the present invention, a tilt and trim unit includes an improved valve assembly that eases manual trim and tilt up of an associated marine drive. The tilt and trim unit also includes a cylinder having a first variable-volume fluid chamber and a second variable-volume fluid chamber, which are separated by a movable piston. The first and second fluid chambers communicate with each other through a passage. The valve assembly is positioned within the passage to establish at least a plurality of flow conditions through the passage. The valve assembly includes first and second valves, each valve including a valve seat and a valve element biased against the corresponding valve seat. The valves of the assembly are positioned such that a common biasing member acts upon the valve elements. The valves are also arranged such that the first valve inhibits fluid flow through the passage in a first flow direction which is opposite to a second flow direction inhibited by the second valve. 
     In a preferred mode, the valve assembly additionally comprises a valve actuator. The valve actuator includes a first rotational cam member that cooperates with the valve element of the first valve to move the valve element between an open position and a closed position. The valve actuator also includes a second rotational cam member that cooperates with the valve element of the second valve to move the valve element between an open position and a closed position. The first cam member and the second cam member preferably are arranged to establish three flow conditions through the passage: (1) a closed flow condition in which the valve elements of both valves are simultaneously in the closed position; (2) a one-way flow condition in which the valve element of one valve is open and the valve-element of the other valve is closed; and (3) an open flow condition in which the valve elements of both valves are simultaneously in the open position. 
     Further aspects, features, and advantages of the present invention will become apparent from the detailed description of the preferred embodiments which follows. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     As noted above, FIGS. 1 and 2 illustrate prior tilt and trim units used with small size outboard motors. These figures are provided in order to assist the reader&#39;s understanding of the prior art and for the reader to better appreciate the aspects, features, and advantages associated with the present invention. 
     FIGS. 3 through 8 illustrate a preferred embodiment of the present tilt and trim system. The above-mentioned and other features of the invention will now be described with reference to this embodiment, which are intended to illustrate, but not to limit, the present invention. The following further describes the figures of this embodiment. 
     FIG. 3 is a side elevational view of an outboard motor supported on a transom of a watercraft by a tilt and trim system configured in accordance with the preferred embodiment of the present invention. 
     FIG. 4 is a front elevational view of the tilt and trim system of FIG. 3 as viewed in the direction of arrow A. 
     FIG. 5 is cross-sectional view of a cylinder assembly of the tilt and trim system of FIG. 3, and illustrates a main cylinder, a sub-cylinder and a manually controlled valve assembly of the cylinder assembly. 
     FIG. 6A schematically illustrates a first cam member and associated components of the valve assembly of FIG. 5 in a closed state. FIG. 6B schematically illustrates a second cam member and associated components of the valve assembly of FIG. 5 in the closed state. And FIG. 6C is an enlarged, partial sectional view of the valve assembly of FIG. 5, taken normal to the first and second cam members, with the valve assembly in the closed state. 
     FIG. 7A schematically illustrates the first cam member and associated components of the valve assembly of FIG. 5 in a one-way state. FIG. 7B schematically illustrates the second cam member and associated components of the valve assembly of FIG. 5 in the one-way state. And FIG. 7C is an enlarged, partial sectional view of the valve assembly of FIG. 5, taken normal to the first and second cam members, with the valve assembly in the one-way state. 
     FIG. 8A schematically illustrates the first cam member and associated components of the valve assembly of FIG. 5 in an open state. FIG. 8B schematically illustrates the second cam member and associated components of the valve assembly of FIG. 5 in the open state. And FIG. 8C is an enlarged, partial sectional view of the valve assembly of FIG. 5, taken normal to the first and second cam members, with the valve assembly in the open state. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 3 illustrates an exemplary outboard motor  100  which incorporates a tilt and trim unit  102  configured in accordance with the present invention. Because the present tilt and trim unit has particular utility with an outboard motor, the following describes the tilt and trim unit in connection with such an outboard motor; however, the depiction of the invention in conjunction with an outboard motor is merely exemplary. Those skilled in the art will readily appreciate that the present tilt and trim adjustment system can be readily adapted for use with other types and sizes of marine drives. 
     In the illustrated embodiment, the tilt and trim unit  102  operates between the outboard motor  100  and a transom  104  of an associated watercraft. An exemplary outboard motor  100  is illustrated in FIG. 3, and the following will initially describe the outboard motor in order to provide the reader with an understanding of the illustrated environment of use. 
     The outboard motor  100  has a power head  106  which desirably includes an internal combustion engine. The internal combustion engine can have any number of cylinders and cylinder arrangements, and can operate on a variety of known combustion principles (e.g., on a two-stroke or a four-stroke principle). 
     A protective cowling assembly  108  surrounds the engine. The cowling assembly  108  includes a lower tray  110  and a top cowling  112 . The tray  110  and the cowling  112  together define a compartment which houses the engine with the lower tray  110  encircling a lower portion of the engine. 
     The engine is mounted conventionally with its output shaft (i.e., a crankshaft) rotating about a generally vertical axis. The crankshaft drives a drive shaft, as known in the art. The drive shaft depends from the power head  106  of the outboard motor  100 . 
     A drive shaft housing  114  extends downwardly from the lower tray and terminates in a lower unit  116 . The drive shaft extends through the drive shaft housing  114  and is suitably journaled therein for rotation about the vertical axis. 
     The drive shaft continues into the lower unit  116  to drive a propulsion shaft through a transmission. The propulsion shaft drives a propulsion device  118  which the lower unit  116  supports. 
     In the illustrated embodiment, the propulsion device  118  comprises a propeller. The propulsion device, however, can take the form of a dual, counter-rotating propeller system, a hydrodynamic jet, or like propulsion device. 
     A coupling assembly  120  supports the outboard motor  100  on the watercraft transom  104  so as to position the propulsion device  118  in a submerged position with the watercraft resting on the surface of a body of water. The coupling assembly  120  is principally formed between a clamp bracket  122 , a swivel bracket  124 , a steering shaft  126 , and a pivot pin  128 . 
     The steering shaft  126  is affixed to the drive shaft housing  114  through upper and lower brackets. An elastic isolator connects each bracket to the drive shaft housing  114  (or to a section of the outboard motor connected to the drive shaft housing, e.g., an exhaust guide located beneath the engine). The elastic isolators permit some relative movement between the drive shaft housing  114  and the steering shaft  126  and contain damping mechanisms for damping engine vibrations transmitted from the drive shaft housing  114  to the steering shaft  126 . 
     The steering shaft  126  is rotatably journaled for steering movement about a steering axis within the swivel bracket  124 . A steering actuator  130  is attached to an upper end of the steering shaft  126  to steer the outboard motor  100 , in a known manner. Movement of the actuator  130  rotates the steering shaft  126 , as well as the drive shaft housing  114  which is connected through the upper and lower brackets about the steering axis. 
     The swivel bracket  124  includes a cylindrical housing through which the steering shaft  126  extends. A plurality of bearing assemblies journal the steering shaft  126  within the cylindrical housing. And as understood from FIG. 4, the swivel bracket  124  includes a pair of bracket arms  127  that are positioned in front of the cylindrical housing and project toward the clamping bracket  122 . 
     The swivel bracket  124  also includes a pair of lugs which project forward toward the watercraft transom  104 . Each lug includes a coupling hole at its front end. The coupling holes are aligned with each other along a common pivot axis. 
     As seen in FIG. 3, the clamping bracket  122  is affixed in a conventional manner to the transom  104 . The clamping bracket  122  includes a support plate. The support plate abuts the outer surface of the transom  104  when the clamping bracket  122  is attached to the watercraft. 
     A pair of flanges  129  project toward the outboard motor  100  from the sides of the support plate, as seen in FIG.  3 . The flanges  129  are spaced apart from each other by a sufficient distance to receive the swivel bracket  124  between the flanges. The flanges  129  also shield the space between the support plate and the cylindrical housing of the swivel bracket  124  to protect the inner components of the tilt and trim adjustment system  102 , as appreciated from FIGS. 3 and 4. 
     The pivot pin  128  completes the hinge coupling between the clamping bracket  122  and the swivel bracket  124 . The pivot pin  128  extends through the aligned coupling holes of the clamping bracket and the swivel bracket lugs and is fixed to the clamping bracket. The inner surfaces of the coupling holes through the swivel bracket lugs act as bearing surfaces as the swivel bracket  124  rotates about the pivot pin  128 . The outboard motor  100  thus can be pivoted about the pivot axis defined by the pivot pin  128 , through a continuous range of trim positions. In addition, the pivotal connection permits the outboard motor  100  to be trimmed up or down, as well as to be tilted up and out of the water for storage or transport, as known in the art. 
     The tilt and trim unit  102  operates between the clamping bracket  122  and the swivel bracket  124  to lock a manually established tilt or trim position of the outboard motor  100 . While the present embodiment is described in the context of a hydraulic system, other types of working fluids (e.g., air, nitrogen) can also be used. 
     The tilt and trim unit  102  will now be described with additional reference to FIGS. 3 through 8. In order to describe the present system, a coordinate system is provided that includes a longitudinal axis X, a lateral axis Y, and a vertical axis Z. With the outboard motor positioned on a watercraft when afloat, the longitudinal axis X extends generally in the direction from bow to stem and parallel to the surface of the body of water in which the watercraft is floating, the lateral axis Y extends normal to the longitudinal axis and parallel to the water surface, and the vertical axis Z extends normal to both the longitudinal and lateral axes, as best understood from FIGS. 3 and 4. 
     With reference principally to FIG. 5, the tilt and trim unit  102  includes a cylinder housing assembly  132  comprised of a main cylinder part  134  that defines a cylinder bore  136  extending in a generally vertical direction. The cylinder housing  134  is provided with a trunnion  138  having a bore that is adapted to receive a pivot pin  140  (FIG. 4) that passes between the sides of the swivel bracket  124  so as to pivotally connect the cylinder housing  132  to the swivel bracket  124 . 
     A piston assembly  142  include a piston  144  that is slidably supported within the cylinder bore  136  and defines an upper chamber  146  and a lower chamber  148 , both of which are filled with hydraulic fluid. A piston rod  150  is affixed to the piston  144  and extends through a closure plug  152  fixed in the lower end of the cylinder housing  132  for closing the cylinder bore  136 . The projecting end of the piston rod  150  is provided with a trunnion  154  that receives a pivot pin  156  (FIG. 4) for pivotal connection to the clamping bracket  122 . 
     A floating piston  158  of the piston assembly  142  is positioned in the upper chamber  146  and defines a further intermediate chamber  160  below the floating piston  158 . The floating piston  158  normally engages the piston  144  in an abutting manner, and controls the upward position of the piston  144 . The intermediate chamber  160  is also filled with hydraulic fluid. 
     An absorber valve, indicated generally by the reference numeral  162 , is provided in the piston  144  for permitting flow from the lower chamber  148  to the intermediate chamber  160  when an underwater obstacle is struck with sufficient force. The absorber valve  162 , however, requires sufficient force to open it so that it will not permit the outboard motor  100  to pop up when traveling in reverse. The absorber valve  162  is comprised of a passageway that extends from the lower chamber  148  and which is normally closed by a ball type valve  164  that is held in its closed position by means of a coil compression spring. The compression spring sets the pressure at which the absorber valve  162  will open. 
     A return valve, indicated generally by the reference numeral  166 , is provided for permitting fluid flow from the intermediate chamber  160  back to the lower chamber  148  when the underwater obstacle is cleared. The return valve  166  is comprised of a passageway in the piston  144  in which a ball type check valve is positioned. The passageway extends between the lower and intermediate chambers  148 ,  160 . A light return spring (not shown) holds the ball valve in its closed position but is adapted to open under relatively low pressures as exerted by the weight of the outboard motor  100  once the underwater obstacle is cleared. As understood from FIG. 3, a center of gravity of the outboard motor  100  is disposed rearwardly of the horizontal tilt axis defined by the pivot pin  128  so that the weight of the outboard motor  100  will tend to cause it to move downwardly. 
     Because the piston rod  150  extends in the lower chamber  148  and thus displaces some of the fluid from it, there will be less fluid displaced from the lower chamber  148  than is required to make up the volume in the upper chamber  146  as the piston  142  moves downward. To compensate for this change in fluid volume, an accumulator assembly, indicated generally by the reference numeral  168 , is formed integrally with the cylinder housing  132 . The accumulator assembly  168  comprises a sub-chamber  170  in which hydraulic fluid is positioned. In addition, a pressurized inert gas G, such as, for example, nitrogen, is charged in the chamber  170  over the working fluid W. If desired, adequate pressure may be stored in the sub-chamber  170  so as to provide some lift assistance during tilt up operation, as will become apparent. And, as illustrated in FIG. 5, an interface surface S is defined between the compressible gas G and the working fluid W. 
     An opening  172  is formed on the lower side of the cylinder housing  132  and opens into the sub-chamber  170 . A plug  174  seals the opening  172  closed and defines a lower wall of the sub-chamber  170 . 
     A bypass, which is generally designated by reference numeral  176 , is provided for selectively bypassing the shock absorbing mechanism  162  of the tilt and trim unit  102  to permit manual movement of the outboard motor  100 . In the illustrated embodiment, the sub-chamber  170  forms a portion of this bypass. The balance of the bypass is formed by a lower passage  178 , a conduit  180 , a valve assembly  182  and an upper passage  184 , as understood from FIG.  5 . 
     The lower passage  178  links the sub-chamber  170  with the lower fluid chamber  148  of the cylinder. In the illustrated embodiment, the lower passage  178  extends from a point near a lower wall of the lower chamber  148  to a point in the sub-chamber  170  just above the sealing plug  174 . 
     A valve assembly  182  lies within the cylinder assembly  132  above the sub-chamber  170 . One side of the valve assembly  182  communicates with the upper chamber  146  through the upper passage  184 . The upper passage  184  desirably opens into the upper chamber  146  at a point near an upper end of the chamber. And as seen in FIG. 5, the floating piston  158  has a narrowed width to provide a fluid passage around the piston  158  within the upper chamber  146 . 
     The other side of the valve  182  communicates with the sub-chamber  170  through the conduit  180 . In the illustrated embodiment, the conduit  180  is formed in part by a stand pipe  186  that is arranged generally parallel to a stroke axis of the cylinder (i.e., parallel to an axis of the piston rod  150 ); however, the conduit  180  can have other orientations, as well as be integrally formed within the housing  132  of the cylinder assembly. The conduit  180 , however, desirably communicates with the sub-chamber  170  at a point below the interface surface S regardless of the position of the piston assembly  142  within the cylinder bore  136 . For instance, as illustrated in FIG. 5, a lower end of the stand pipe  186  terminates below the interface surface S even when the piston assembly  142  is moved to its uppermost position with the piston rod  150  fully retracted. This arrangement ensures that the conduit  180  always draws working fluid W, and not the compressible gas G. 
     As understood from FIG. 5, the stand pipe  186  is connected to an upper receptacle  188  through the lower opening  172  on the cylinder housing  132 . This arrangement eases assembly and simplifies fabrication because the stand pipe  186  need not be integrally formed with the cylinder housing  132 . The upper receptacle  188  is integrally formed in the cylinder housing  132  at the upper end of the sub-chamber  170 , and communicates with a passage  190 . The passage  190  and the stand pipe  186  together define the conduit  180  in the illustrated embodiment. 
     The valve assembly  182  operates between the upper passage  184  and an upper section of the conduit  180  (e.g., the passage  190 ). In the illustrated embodiment, the valve assembly  182  includes two ports: an upper port and a lower port. The upper port communicates with the upper passage  184 , while the lower port communicates with the conduit  180 . These ports are formed within a valve housing  192 . 
     In the embodiment illustrated in FIG. 5, valve housing  192  generally has a cylindrical plug-like shape and is fit into a corresponding recess formed in the cylinder housing  132 . The housing  192  defines a central bore in which a rotatable actuator shaft  194  rotates. The valve housing  132  also defines an internal passage that links the upper and lower ports. 
     A pair of valves  194 ,  196  are arranged to control fluid flow through the internal passage. The valves  194 ,  196  are arranged in series with one valve  194  constructed to prevent fluid flow in a direction from the upper chamber  146  to the lower chamber  148 , and the other valve  196  constructed to prevent fluid flow in the opposite direction. For this purpose, each valve  194 ,  196  desirably is a one-way valve, and includes a valve element  198  and a corresponding valve seat  200 . A common biasing member  202  urges each valve element  198  against the corresponding valve seat  200  to close the valve  194 ,  196 . The valve seats  200  oppose each other with the valve elements  198  generally positioned between the valve seats  200  and the biasing element  202  interposed between the valve elements  198  in the valve assembly  182 . 
     In the illustrated embodiment, each valve  194 ,  196  comprises a ball type check valve that includes a movable ball valve element  198 . A compression spring  202 , which functions as the biasing member, is arranged between the ball valve elements  198  of the valves  194 ,  196  and biases each ball valve element  198  against the corresponding valve seat  200 . Other types of valve and valve elements, however, can also be used. 
     The valve assembly  182  also includes a valve actuator  204  formed in part by the actuator shaft  194 . The actuator shaft  194  supports first and second cam members  206 ,  208  of the valve actuator  204 , which each interact with one of the ball valve elements  198  as appreciated from FIG.  5 . The first cam member  206  is fixed to the actuator shaft  194  to rotate with the shaft  194 , while the second cam member  208  is rotatable supported by the actuator shaft  194 , as will described in more detail below. 
     With reference to FIG. 6A, the first cam member  206  generally has a circular disc-like shape with a hole  210  that receives a portion of the corresponding ball valve element  198 . The cam member  206  also includes a recess  212  of a given arc length that extends into body of the cam member  206  toward its center. 
     FIG. 6B illustrates the construction of the second cam member  208 . Like the first cam member  206 , the second cam member  208  also has a circular disc-like with a hole  214  that receives a portion of the other ball valve element  198 . The cam member  208  also includes a recess  216  of a given arc length that extends into the body of the cam member  208  toward its center. The arc length of the recess  216  of the second cam member  208 , however, is less than the arc length of the first cam member recess  212 . 
     In the illustrated embodiment, as best seen in FIG. 5, the first cam member  206  includes a hub  218  with a bore that receives an end of the actuator shaft  194 . The hub  218  also supports second cam member  208  at a location spaced from the first cam member disc. Both diameters of the first and second cam members  206 ,  208  are generally equal to a diameter of the bore of the cylinder housing  132  in which the valve assembly  182  is mounted. 
     A lost motion coupling, generally designated by reference numeral  220  in FIG. 6B, operates between the first and second cam members  206 ,  208  such that the first cam member  206  can rotate relative to the second cam member  208  over a first rotational range. The coupling  220 , however, causes the first and second cam members  206 ,  208  to rotate together over a second rotational range. 
     In the illustrated embodiment, the lost motion coupling  220  is formed by a projection  222  on the first cam member which fits within an opening  224  in the second cam member  208 . The projection  222  extends from an inner surface of the first cam member  206 . The projection  222  includes an abutment edge  226  and a relief  228 . 
     The opening  224  of the second cam member  208  is sized to receive the projection  222  of the first cam member  206 . The opening  224  is larger than the projection  222  to permit relative movement between the first and second cam members  206 ,  208 . An edge of the opening provides a contact surface  230  against which the abutment edge  226  of the projection  222  acts. 
     A biasing element  232  is arranged between the first and second cam members  206 ,  208  so as to bias the abutment edge  226  of the projection  222  toward the contact surface  230  of the second cam member  208 . In the illustrated embodiment, the biasing member  232  is a compression spring arranged between the projection  222  and a side of the opening  224  that is generally opposite of the contact surface  230 . The compression spring  232  fits within the relief  228  of the projection  222  and onto a spindle element  234  that projects into the opening  224  from the corresponding side. The biasing element, however, can take other forms, such as, for example, but without limitation, a torsion spring operating between the first and second cam members or between the second cam member and the actuator shaft. 
     With the projection  222  of the first cam member  206  positioned within the opening  224  of the second cam member  208 , the recesses  212 ,  216  of the cam members  206 ,  208  generally overlap as viewed in the lateral direction. A stop element  236  is positioned within the recesses  212 ,  216  of the first and second cam members  206 ,  208  to limit the rotational movement of the cam members  206 ,  208 , and thus the actuator shaft  194 . In the illustrated embodiment, the stop element  236  comprises a cylindrical pin that extends generally parallel to the actuator shaft  194 ; however, other types of stops can also be used. 
     When assembled, as understood from FIGS. 5 and 6C, the first and second cam members  206 ,  208  lie generally parallel to each other and generally normal to the supporting actuator shaft  194 . The ball valve elements  198  are contained within the corresponding holes  210 ,  214  in the cam members  206 ,  208  and are biased against the corresponding valve seat  200  by the compression spring  202 . The compression spring  202  extends between the ball valve elements  198 , through the space between the cam members  206 ,  208 . 
     As best understood from FIGS. 3 and 4, a lever  238  is connected to the actuator shaft  194  to operate the valve  182 . The lever  238  projects to one side of the tilt and trim unit  102 , desirably beyond one side of the swivel bracket  124 . In this position, the lever  238  can easily be rotated by a person to move the valve  182  between the plurality of valve positions described below. 
     With reference to FIG. 5, a biasing element  240  is arranged within the lower fluid chamber  148  and rests at a position against the end wall of the chamber  148 . In the illustrated embodiment, the biasing element  240  generally has a disc-like shape, and can be configured like a belleville spring. The vertical dimension of the spring  240  desirably matches the vertical dimension of the port at the end of the lower passage  178 . The spring  240  functions to urge the piston  142  away from the lower wall when the piston  142  moves from a position abutting the lower wall (i.e., from a fully extended, bottomed position). 
     The valve assembly  182  desirably has three operational states: a closed state; a one-way state; and an open state. FIGS. 6 through 8 illustrate these states which will now be described in connection with the operation of the valve assembly. 
     With initial reference to FIGS. 6A through 6C, the components of the valve assembly  182  are illustrated in a closed position. As seen in FIGS. 6A and 6B, both cam members  206 ,  208  contact the stop element  23  as as to prevent further rotation (e.g., rotation in the counter-clockwise direction in the illustrated embodiment). In this position, the projection  222  of the first cam member  206  compresses the spring  232  against the opening wall of the second cam member  208 . The biasing member  202  also forces the ball valve elements  198  to seat within the corresponding valve seat  200 . The biasing element  202  is sufficiently stiff to inhibit the valves  194 ,  196  from opening even under the force of full throttle; however, it is understood that the spring constant could be selected to prevent automatic movement under some operating conditions. 
     FIGS. 7A through 7C illustrates the components of the valve assembly  182  in a position corresponding to the one-way state. Rotation of the actuator shaft  194  in a clockwise direction moves the first cam member  206  relative to the stop  236 , as seen in FIG.  7 A. The second cam member  208 , however, does not follow this movement, as understood from FIG.  7 B. That is, the first cam member  206  rotates relative to the second cam member  208  as the valve  182  is moved from the closed position to the one-way position. The projection  222  moves through the larger opening  224  of the second cam member  208  with the spring  232  expanding with this movement. Once this position is reached, the abutment edge  226  of the first cam member  206  contacts the contact surface  230  of the second cam member  208 , with the spring  232  urging these corresponding elements to remain in contact. 
     As seen in FIGS. 7A and 7C, the first cam member  206  moves the corresponding ball valve element  198  to an unseated position, thereby opening the corresponding valve seat  200  of the second valve  196 . The port to the upper fluid chamber  146  thus is opened. The biasing element  202 , however, urges the other ball valve element  198  of the first valve  194  against the corresponding valve seat  200  so as to continue to function as a one-way valve to prevent fluid flow from the upper fluid chamber  146  to the sub-chamber  170 . 
     With the valve assembly  182  in this state, a person can raise the outboard motor  100  with little encumbrance from the tilt and trim unit  102 . Because the effective length of the biasing element  202  is increased, less spring force biases the one ball valve  194  closed. Thus, by manually pivoting the outboard motor  100  to raise the lower unit, the piston assembly  142  moves downward to extend the piston rod  150 . This action forces fluid from the lower chamber  148  and draws fluid into the upper chamber  146 . The one-way valve  194  easily opens with the reduced spring force under this condition, and working fluid flow through the other valve  196 , which is opened by the first cam member  206 , into the upper chamber. 
     FIGS. 8A through 8C illustrate the valve components in an open state. Further clockwise rotation of the actuator shaft  194  from the one-way position toward the open position rotates the first and second cam members  206 ,  208  together. Under the force of the spring  232 , the second cam member  208  follows the movement of the first cam member  206 . The stop  136  contacts the edges of the aligned recesses  212 ,  216  of the first and second cam members  206 ,  208  to establish the open position. The stop  236  prevents further rotation of the cam members  206 ,  208  in the clockwise direction. 
     As seen in FIGS. 8A and 8C, the first cam member  206  moves the corresponding ball valve element  196  to further away from the corresponding valve seat  200  to hold the valve  196  open. The port to the upper fluid chamber  146  thus remains open. And as seen in FIGS. 8B and 8C, the second cam member  208  moves the corresponding ball valve element  198  to a position unseating the ball valve element  198  from its respective valve seat  200  of the first valve  194 . The internal passage within the valve assembly  182  thus is opened to allow free communication between the upper chamber  146  and the sub-chamber  170 , and thus between the upper and lower chambers  146 ,  148 . With the valve assembly  182  in this state, a person can freely raise or lower the outboard motor  100  with minimal affect from the tilt and trim unit  102 . 
     To move the valve  182  in the opposite direction, the actuator shaft  194  rotates in a counter-clockwise direction. The second cam member  208  follows the first cam member  206  between the open position to the one-way position because the spring  232  urges the second cam member  208  to follow the first cam member  206 . Once in the one-way position, as seen in FIG. 7B, the stop  236  prevents further counter-clockwise rotation of the second cam member. The first cam member  206  can rotate further, however, due to the lost motion coupling  220  between the cam members  206 ,  208 . As the first cam member  206  rotates in the counter-clockwise direction, the spring  232  between the cam members  206 ,  208  is compressed with the projection  22  moving within the opening  224  of the second cam member  208 . The stop  236  prevents further counter-clockwise rotation of the first cam member  206  once the closed position is reached. In both the closed and one-way positions, the cam members  206 ,  208  hold the corresponding ball valve elements  198  in the above described positions. 
     This valve design thus eases manual tilt up of the outboard motor. The person raising the lower unit of the outboard motor can initially position the valve assembly in the one-way position to allow the person to release the outboard motor once a desired tilt or trim position has been established. The person can then move the valve to the closed position to hold the outboard motor in the desired position. 
     The configuration of the cylinder assembly additionally integrated this improved valve design into a compact package. The arrangement of the sub-chamber and valve assembly in series with the valve assembly positioned above the sub-chamber also aids this purpose. The alignment of the sub-chamber directly beneath the valve assembly, with these components generally parallel to the cylinder, also contributes to the overall small size of the tilt and trim unit. The tilt and trim unit consequently can fit between the swivel and clamping brackets without requiring reinforcement of the arms of these brackets. 
     Although this invention has been described in terms of a certain preferred embodiment, other embodiments apparent to those of ordinary skill in the art are also within the scope of this invention. Accordingly, the scope of the invention is intended to be defined only by the claims that follow.