DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] Turning now to the drawings and initially to FIG. 1, a boat 12 incorporates a power steering assist system 10 (hereafter simply “power steering system”) constructed in accordance with a preferred embodiment of the present invention. The boat 12 includes a hull 14 having a bow 16 and a stern 18, an outboard motor 20 mounted on the stern 18, and a cowling or dash 22 extending laterally across the hull 14 near the bow 16. As is conventional, the motor 20 is mounted on the boat 12 by a pivoting mount assembly (not shown) that permits the motor 20 to be pivoted about a vertical axis to cause a rudder formed on or by the motor 20 to steer the boat 12. The motor 20 could alternatively be a non-pivoting inboard or outboard motor, and the boat 12 could be steered by one or more rudders movable separately from the motor 20.

[0028] Referring now to FIGS. 1-2, the steering system 10 for the boat 12 includes a tiller arm 24 coupled to the motor 20 and forming the boat's steered mechanism, a helm 26 including a steering wheel 28 serving as the boat's steering mechanism, a pressure source 30, and a steering cylinder assembly 32. The present embodiment contains no mechanical linkage connecting the helm 26 to the steering cylinder assembly 32. Both assemblies 26 and 32 are pressurized by a single power source. The helm 26 is mounted through the dash 22 and is actuated by the steering wheel 28. The steering cylinder assembly 32 is actuated by the helm 26 to move the tiller arm 24 and pivot the motor 20 on its mount under power supplied by the pressure source 30. In order to minimize the size and weight of the components that are mounted behind the dash 22, the steering cylinder assembly 32 is located remote from the helm 26, possibly adjacent the motor 20 as illustrated, or on the motor, so as to be connectable directly to the tiller arm 24. Alternatively, the steering cylinder assembly 32 could be mounted at some other location on the boat 12 and connected to the tiller arm 24 by a push-pull cable or the like. Multiple steering cylinders could be provided in a multiple engine watercraft and connected to the helm 26 in a parallel fashion. The helm 26 is connected to the pressure source 30 by a high pressure line 34 and a return line 36. It is also connected to the steering cylinder assembly 32 by the high pressure line 34 and a slave line 38.

[0029] The fluid pressure source 30 could comprise any structure or assembly capable of generating hydraulic pressure and of transmitting it to the helm 26 and the steering cylinder assembly 32. It also can be located virtually anywhere on the boat 12. In the illustrated embodiment, the fluid pressure source 30 includes a pump 40 and a reservoir 42, best seen in the assembly illustrated in FIG. 2. The pump 40 has an inlet 44 connected to an outlet of the reservoir 42 and has an outlet 46 connected to or, as in the illustrated embodiment, forming the pressurized outlet of the pump assembly 30. An accumulator (not shown) could be provided between the pump outlet 44 and the helm 26, if desired. The reservoir 42 has an inlet 48 connected to or, as in the illustrated embodiment, forming the unpressurized inlet of the pressure source 30.

[0030] Referring to FIGS. 2, 4, 5, and 6 the steering cylinder assembly 32 comprises a hydraulically actuated, unbalanced steering cylinder assembly operatively coupled to the helm 26, the pump outlet 44, and the tiller arm 24. “Unbalanced” as used herein means that the cylinder assembly's piston has different effective surface areas on opposite sides thereof such that equal fluid pressures on both sides of the piston generate an intensification effect on the side of the piston having a greater effective surface area and drive the piston to move towards the side of the cylinder facing the side of the piston having a smaller effective surface area. The steering cylinder assembly 32 includes a steering cylinder 50, a steering piston 52 mounted in the steering cylinder to form first and second chambers 54, 56 on opposite sides of the steering piston 52, and a rod 57 connected to the steering piston 52. A first port 58 opens into the first chamber 54 for connection to the high pressure line 34 in a check valve 59. A second port 60 opens into the second chamber 56 for connecting to the metering line 38. The steering cylinder 50 of this embodiment is stationary and is mounted on the stem 18 of the hull 14 by a suitable bracket 62. The rod 57 extends axially through a rod end 64 of the steering cylinder 50 (disposed opposite a cylinder end 66) and terminates at a free end that is coupled to the tiller arm 24. The unbalanced condition of the assembly 32 therefore is created by virtue of the attachment of the rod 57 to the steering piston 52 and the consequent reduction in piston surface area exposed to fluid pressure in the first chamber 54. Alternatively, the rod 57 could extend completely through the steering cylinder 50 and could be affixed to a stationary support, in which case the steering cylinder 50 would be coupled to the tiller arm 24 and would reciprocate relative to the stationary piston 52. In this case, the unbalanced condition of the assembly 32 would be achieved by other measures, e.g., by making one end of the steering rod 57 diametrically smaller than the other.

[0031] Referring to FIG. 3, the helm 26 is mounted through the dash 22. It includes the steering wheel 28, a steering shaft 68 extending forwardly from the dash 22, and a helm casing 70 located behind the dash 22. The helm casing 70 is relatively compact, having a body 72 and a cap 74 screwed onto the front end of the body 72. The back end of the cap 74 is mounted on the front surface of the dash 22 by bolts 76. The body 72 is cylindrical, having a rear axial end 78 (FIG. 5), a front axial end 80, and an outer radial periphery 82. It is very narrow, having a diameter of no more than 3¼″. The body 72 also is relatively short, having a total length of no more than about 3″ to 3½″. The entire helm casing 70, including the body 72 and the cap 74, is no longer than 6″ to 7″. Mounting behind the dash 22 is facilitated by the fact that the helm casing 70 has only a limited number of fittings (three in the preferred embodiment), and all of those fittings extend from the relatively easily-accessible rear axial end 80 of the helm casing 70. The helm 26 therefore is considerably smaller than the helm disclosed in the '279 patent and easier to mount to the dash. It is also considerably lighter, weighing 6 to 7 pounds less than the commercial version of the helm disclosed in the '279 patent. The helm cylinder also need not be formed from a casting.

[0032] The hydraulic circuitry contained within the pressure source 30, the helm 26, and the steering cylinder assembly 32 will now be described with reference to FIG. 4. The helm casing 70 has a high pressure port 84 connected to the high pressure line 34, a metering port 86 connected to the metering line 38, and a return port 88 connected to the return line 36. Located within the helm casing 70 (FIG. 3) are a valve body 90 having a control valve assembly, a metering device 92, and a relief valve assembly including a relief valve 186, a pilot-operated valve 188, and a make-up valve 196. A control chamber 100 is formed in helm casing 70 (FIG. 3) between the metering device 92 and the valve body 90.

[0033] The control valve assembly includes first and second normally closed two-way/two-position valves. Still referring to FIG. 4, the first valve is a supply valve 102 having an inlet port 104 coupled to the high pressure port 84 and having an output port 106 coupled to the control chamber 100. The second valve is a return valve 108 having an inlet port 110 coupled to the control chamber 100 and an outlet port 112 connected to the return port 88 via the valves 186 and 196. Both valves 102 and 108 are coupled to a common actuator 114 (preferably one acted upon by the steering shaft 68 (FIG. 3)), such that movement of the actuator in a first direction opens one of the valves 102 or 108 while leaving the other valve closed, and movement of the actuator in a second direction opens the other valve 108 or 102 while leaving the one valve closed. A suitable actuator is described below in conjunction with FIG. 5.

[0034] It can thus be seen that the first chamber 54 of the steering cylinder 50 will always be at a pressure P1 that is the same pressure as the pump outlet pressure. The control chamber 100 of the helm casing 70 (FIG. 3) and the second chamber 56 of the steering cylinder 50 will all be at a second pressure P2 when no load is applied to the rod 57. The pressure P2 will, depending upon the operational state of the valve assembly and the direction of load applied to rod 57, vary from a low of essentially 0 psi relative to the atmosphere to a high of P1 (typically on the order of 1000 psi).

[0035] Referring now to FIG. 5, the physical structure of a helm assembly incorporating the hydraulics of FIG. 4 can be seen to include a helm casing 70 that supports, from rear to front end, the steering shaft 68, the valve actuator 114, the valve body 90, and the metering device 92. The steering shaft 68 protrudes outwardly from an opening 120 in the rear end 78 of the casing 70. The valve actuator 114 and valve body 90 are housed in an interior chamber 122 of the casing 70. The front end 80 of the helm casing 70 is formed from a casing 200 of the metering device 92, which is attached to the remainder of the helm casing 70 by bolts 126. The valve body 90 is coupled to a rotary input (not shown) of the metering device 92 so that the metering element and valve body rotate together as a unit.

[0036] Referring to FIGS. 5 and 6, the steering shaft 68 is sealed to the opening 120 via an O-ring seal 128. The front end of the steering shaft 68 is stepped to present a rectangular protrusion 130. An actuator pin 134 extends forwardly from the protrusion 130 and into the valve actuator 114. As best seen in FIG. 6, the actuator pin 134 is located eccentrically on the protrusion 130 so as to revolve about the axis of rotation of the steering shaft 68 upon steering shaft rotation, thereby driving the actuator 114 to move radially relative to the valve body 90 when the steering shaft 68 rotates relative to the valve body 90.

[0037] Referring to FIGS. 5 and 7, the valve body 90 comprises a tubular metal structure having a body portion 136, a rear end 138, and a front shaft portion 140. The body portion 136 is sealed against an inner surface of the helm casing 70 by O-rings 139 to form (1) a vent chamber 142 in front of the valve body 90 and (2) the control chamber 100 between the valve body 90 and the metering device 92. The rear end cap 138 is rotatably bound in the helm casing 70 by a thrust bearing 144. The thrust bearing 144 bears the load imposed on the system by pressure in the control chamber 100. The end cap 138 also has a rectangular central opening 146 formed in it that receives the protrusion 130 on the end of the steering shaft 68 in a manner that permits limited relative rotational movement between the protrusion 130 and the periphery of the opening 146. Finally, the shaft portion 140 extends forwardly from the front end of the body portion 136 and is connected to the metering device 92 such that the valve body 90 and the operated component (metering element 202) of the metering device 92 rotate as a unit. Still referring to FIG. 5, the supply and return valves 102 and 108 are housed in cross-bores formed in the rear end of the body portion 136 of the valve body 90. The valves 102 and 108 cooperate with supply and vent passages 148 and 150 in the body portion 136 so as to permit a control passage 152 in the body portion 136 to be selectively connected the high pressure port 84 and to the vent chamber 142 by suitable switching of the valves 102 and 108. Specifically, the supply passage 148 has an helm coupled to the high pressure port 84 of the valve casing 70 by an inlet passage 154 extending through the metering device 92 and has an outlet coupled to the inlet 104 of the supply valve 102. The vent passage 150 has an inlet communicating with the outlet 112 of the return valve 108 and an outlet opening into the vent chamber 142. The control passage 152 extends axially from the control chamber 100 to the valve assembly in fluid communication with the outlet 106 of the supply valve 102 and the inlet 110 of the return valve 108.

[0038] Still referring to FIG. 5, the supply valve 102 seats toward one end of the supply passage 148. It includes a ball-type valve element biased towards its seat by a spring 156. Conversely, the return valve 108 seats towards the other side of the vent passage 150. It also includes a ball valve element biased toward its seat by a spring 158.

[0039] The valve actuator 114 is coupled to the steering shaft 68 so as to move radially through a limited stroke with respect to the valve body 90 upon relative rotational movement between the steering shaft 68 and the valve body 90. Specifically, with reference to FIGS. 5 and 7, the valve actuator 114 comprises a shaft 160 mounted in the rear end of the body portion 136 of the valve body 90. A slot 162 is cut in the center of the shaft 160 for receiving the actuator pin 134. In addition, first and second actuator support tabs 164 and 166 are bolted to opposed peripheral surfaces of the shaft 160 and extend forwardly from the front end of the shaft 160. First and second actuator pins 168 and 170 are threaded into bores in the respective tabs 164 and 166. The bases of the pins 168 and 170 are spaced from one another by a distance that is greater than the diameter of the valve body 90, thereby forming a radial clearance between each of the bases and the outer periphery of the valve body 90 when the valves 102 and 108 are closed. This arrangement permits adjustment of the at-rest clearance of the actuator pins 168 and 170 and the stroke of the pins. Hence, when the valve actuator 114 moves radially relative to the valve body 90 in a first direction, the pin 168 engages the ball-type valve element forming the supply valve 102 to open the supply valve (compare FIG. 5 to FIG. 8). Similarly, when the valve actuator 114 moves relative to the valve body in the second direction, the pin 170 engages the ball-type valve element forming the return valve 108 to open the return valve (compare FIG. 5 and FIG. 9).

[0040] Still referring to FIG. 5, the vent chamber 142 is connected to the return port 88 in the valve casing by a drain passage 180 extending generally axially through the outer portion of the helm casing 70. The drain passage 180 includes first and second branches 182 and 184 having first and second valves 186 and 188 mounted therein. Each of the valves 186 and 188 is biased into its closed position by a respective return spring 190, 192. The valve 186 is a spring-loaded relief valve. The valve 188 is a pilot actuated valve that normally held in its open position by fluid pressure in a branch 194 of the inlet passage 154 so as to permit unrestricted flow into the branch 184 of the drain passage 180 from the vent chamber 142. However, upon pump failure, the valve 188 closes under the force of the biasing spring 192 so as to isolate the vent chamber 142 from the drain passage 180, whereupon the vent chamber 142 drains to the reservoir 42 only when the pressure therein rises to a pressure high enough to overcome the biasing force of the spring 190 and open the relief valve 186. Finally, make-up fluid for manual operation is provided via a spring loaded check valve 196 located in a make-up passage 198 extending from the drain passage 180 to the control chamber 100.

[0041] The metering device 92 may comprise any commercially available metering pump. Still referring to FIG. 5, a suitable metering device includes a stationary annular casing 200 forming the rear end of the helm casing 70 and a central rotatable metering element 202 coupled to the shaft portion 140 of the valve body 90. A first port 204 of the metering element 202 opens into the control chamber 100. Passages 206 and 208 are formed axially through the casing 200 for receiving tubular extensions of the inlet passage 154 and drain passage 180, respectively. The metering element 202 typically (but not necessarily) will comprise a so-called metering gear. Depending on the operational status of the system, the metering device 92 may operate as a valve (controlling fluid flow between the control chamber 100 and the metering port 86) or as a pump (pumping fluid to or from the metering port 86). A metering device having these characteristics is available, e.g., from Eaton Corporation, under the brand name Char-Lynn.

[0042] The operation of the power assist steering system will now be described with the assumption that the components are in the position illustrated in FIG. 5 and the steering wheel 28 and steering shaft 68 are stationary. The valve actuator 114 is balanced with respect to the valve body 90 at this time, and both the supply and return valves 102 and 108 are closed to block flow into or out of the control chamber 100. Initial rotation of the steering shaft 68 in either direction drives the valve actuator 114 to move radially relative to the valve body 90 until one of the actuator pins opens the associated valve. Hence, counterclockwise rotation of the steering shaft 68 drives the actuator pin 168 to the position illustrated in FIG. 8 to open the supply valve 102. Pressurized fluid from the first chamber 54 in the steering cylinder 52 and the pump 40 flows through the high pressure port 84 of the helm casing, through the supply passage 148, through the open supply valve 102, and into the control chamber 100. Fluid in the control chamber 100 then flows through the metering device 92 and into the second chamber 56 of the steering cylinder 32, thereby driving the piston 52 of the steering cylinder 32 to move to the right as illustrated in FIG. 8. Fluid flow through the metering device 92 drives the metering gear 202 to rotate, thereby driving the valve body 90 to rotate counterclockwise. When the operator stops turning the steering shaft 68, the metering element 202 of the metering device 92 will continue to rotate for a brief time, thereby continuing to turn the valve body 90 relative to the valve actuator 114 until the supply valve 102 is reseated to terminate fluid flow through the metering device 92 from the control chamber and, accordingly, to terminate steering cylinder piston movement.

[0043] Conversely, when the steering shaft 68 is rotated clockwise, the valve actuator pin 170 opens the return valve 108 as seen in FIG. 9. Fluid is therefore free to flow from the second chamber 56 of the steering cylinder 32, through the metering port 86 of the helm casing 70, through the metering device 92, through the control chamber 100, through the return valve 108, and into the vent chamber 142. Because the pilot operated valve 188 is open at this time under pilot pressure in the supply passage branch 194, fluid in the vent chamber 142 is free to flow through the valve 188 and the second branch 184 of the vent passage, out of the return port 88, and to the reservoir 42. The pressure differential across the piston 52 resulting from fluid flow from the second chamber 56 in the steering cylinder 32 drives the steering piston 52 to the left at this time to alter the steering angle of the watercraft. Fluid flow through the metering device 92 under these conditions also drives the metering element 202 to drive the valve body 90 to rotate the valve body in the same direction as the steering shaft 68, i.e., clockwise. When steering shaft rotation ceases, the metering element 202 will continue to rotate for a brief period of time until the valve body 90 moves relative to the actuator 114 sufficiently to reseat the return valve 108. At this time, fluid flow out of the second chamber 56 of the steering cylinder 32 terminates, arresting further movement of the steering piston 52.

[0044] In the event of pressure source failure, the relief valve assembly operates to permit the helm 26 to be operated manually. Specifically, if the steering shaft 68 is rotated clockwise under these conditions, the actuator pin 170 will open the return valve 108 as discussed above. Continued steering shaft rotation will cause the rectangular protrusion 130 on the end of the steering shaft 68 to contact the periphery of the opening 146 in the rear end cap 138, at which point the steering shaft 68 will drive the valve body 90 to rotate. The valve body will, in turn, drive the metering element 202 to rotate. The metering device 92 now acts as a pump and draws fluid out of the second chamber 56 of the steering cylinder 32 and into the control chamber 100. Fluid in the control chamber 100 then flows through the return valve 108 and into the vent chamber 142. However, because the inlet passage 154 is now unpressurized, the valve 188 is closed, and fluid flow out of the vent chamber 142 is blocked until the pressure therein rises to a level that sufficiently high to unseat the relief valve 186. When the fluid pressure in the vent chamber 142 reaches this level, the supply valve 102 also opens to allow fluid flow past the supply valve 102, backwards through the supply passage 148, out of the high pressure port 84, and into the first chamber 54 of the steering cylinder 32. The resultant pressure differential across the piston 52 drives the piston to the left. Because of the volume differential between the first and second chambers 54 and 56 of the steering cylinder 32, and because the volume of the second chamber 56 is larger than the volume of the first chamber 54, the first chamber 54 is incapable of receiving all of the fluid flowing out of the second chamber 56. The excess fluid instead flows past the relief valve 186 and back to the reservoir 42 through the drain passage 180.

[0045] Conversely, if the pump 40 fails and the steering shaft 68 is rotated counterclockwise, steering shaft rotation serves to first open the supply valve 102 and then drive the valve body 90 to rotate counterclockwise to drive the metering element 202 to rotate counterclockwise. Counterclockwise rotation of the metering element 202 pumps fluid from the control chamber 100 to the second chamber 56 of the steering cylinder 32. Simultaneously, fluid will be forced out of the first chamber 54 of the steering cylinder 32, through the high pressure port 84, the inlet and supply passages 154 and 148, the open supply valve 102, and into the control chamber 100. The resulting pressure differential drives the steering cylinder piston 52 to the right to effect a steering operation in the opposite direction. Because volume of the first chamber 54 of the steering cylinder 32 is smaller than the volume of the second chamber 56, a negative pressure is generated in the control chamber 100 during this process. That negative pressure lifts the valve 196 off its seat to permit make-up fluid to be drawn into the control chamber 100 from the reservoir 42, the drain passage 180, and the make-up passage 198.

[0046] Many changes and modifications could be made to the invention without departing from the spirit thereof. Some of these changes are discussed above. Other changes will become apparent from the appended claims.