Patent Publication Number: US-9889913-B1

Title: Marine power steering system

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Patent Application Ser. No. 62/132,627, filed Mar. 13, 2015 and entitled Flow Control Valve for Marine Power Steering System, the contents of which are hereby incorporated by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     I. Field of the Invention 
     The invention relates to marine power steering systems and, more particularly, to a hydraulically-actuated marine power steering system providing pressurized hydraulic fluid for the system. The invention additionally relates to an actuator for such a system that limits flow during at least initial and closing phases of actuator operation so that the steering rate is less than maximum. The invention additionally relates to improved valving for the actuator of the system. 
     II. Description of Related Art 
     Typically, marine power steering systems for outboard motors and stern drives utilize an extendible and contractible steering ram or rod connected to the boat transom and to the propulsion unit. Extension and contraction of the piston ram causes the propulsion unit to pivot and steer the boat. Such units require a rather large hydraulic pump since rather large volumes of hydraulic fluid are required if the steering is moved rapidly from one side to the other. Two such systems are in use today. One of the systems uses a continuous running electric powered pump which requires a high output electrical charging system to keep the system&#39;s battery charged. Most engines in the marketplace do not possess an adequate charging system, which limits the use of such a system. The second system uses an electrically-powered pressure amplifier that is placed between a standard hydraulic helm and a steering cylinder on the engine. The pressure amplifier turns on and off every time a steering input is generated. The power requirement of this system is not as severe as one having a continuously running pump, but it is significant. 
     Both systems have a limited maximum volume output. In a rapid steering situation, the volume of fluid needed to steer the engine exceeds the maximum volume output of the power supply. The effect of power steering thus can be lost. 
     To help counter this effect, helms have been designed to increase the number of steering wheel turns required to steer the engine from one side to the other. A traditional “three turn system” requiring three steering wheel revolutions to maximize the helm&#39;s steering angle now requires four or five turns. The requirement for additional turns makes it more difficult for the operator to overun the output of the power supply. However, system responsiveness is degraded, hindering docking or other precise maneuvers. 
     More recently, systems have been introduced that use an accumulator to store pressurized hydraulic fluid, permitting the use of smaller pumps requiring less power. Such a system is disclosed in U.S. Pat. No. 5,241,894 (the &#39;894 patent). The system disclosed in the &#39;894 patent includes a pump that provides pressurized hydraulic fluid from a reservoir and a control system to selectively place the pump in an operative or inoperative mode. The hydraulic system is also provided with a valve that selectively provides pressurized hydraulic fluid to a double acting hydraulic cylinder to cause extension or retraction of the piston ram in the cylinder. 
     The system disclosed in the &#39;894 patent works well but has some drawbacks. 
     For example, internal “extend” and “retract” valves, located in the barrel of the hydraulic cylinder, control fluid flow into and out of the respective ends of the hydraulic cylinder to extend and retract the cylinder ram and, thus, steer the engine to in one direction or the other. Traditional valves have relatively linear flow characteristics such that the “flow area” or minimum cross sectional area of the flow path surrounding the valve at any point in the valve&#39;s opening stroke and that thus fluid flow rate through each valve at a given pressure increases linearly throughout at least most of the operating stroke of the valve. As a result, ram motion is relatively rapid, even for relative small inputs. This can result in “chatter” at low steering inputs occurring when the valve repeatedly opens and close as ram extension or retraction speed exceeds the steering input speed. 
     The need therefore exists to provide improved control of a marine power steering system actuator at relatively small inputs. 
     Another problem associated with the system disclosed in the &#39;894 patent and commercial version of that system is that its valving is relatively difficult to assemble or replace because it is located in the barrel of the hydraulic cylinder as opposed to in the actuator block. It also must be manufactured to close tolerances and is relatively difficult to seal. 
     Thus, there remains room for improvement. 
     SUMMARY OF THE INVENTION 
     In accordance with an aspect of the invention, a power steering system for a marine steering system includes at least one flow limiting valve that, through a substantial portion of a stroke thereof, limits fluid flow rates through the valve to a relatively low value during the early phases of valve opening, limiting the rate of extension or retraction of the ram out of or into the barrel of the system&#39;s hydraulic cylinder. 
     The flow limiting valve may be configured such the flow rate through the flow limiting valve valves remains at a relatively low and generally constant value through a substantial portion of the operating stroke thereof and thereafter increases progressively, possibly non-linearly, during at least another substantial portion of the operating stroke. 
     The flow limiting valve may have a body that is located within the bore when the valve is closed and that has a first portion of greater diameter than the remainder of the body. An annular gap, formed between the surface of the bore and the first portion of the body, defines a flow path through the valve of small cross-sectional area. The flow limiting valve may additionally have an upstream metering portion that extends axially and radially inwardly into the bore from the first portion and that extends radially inwardly, creating a flow path through the valve that increases progressively in cross sectional area with continued valve movement. 
     The flow limiting valve may be an extend valve which, when actuated, causes the ram of the system&#39;s cylinder to extend from the barrel at a rate that is dependent on a magnitude of extend valve movement from its closed position. The system may additionally include another flow limiting valve forming a retract valve which, when actuated, causes the ram to retract into the barrel at a rate that is dependent on a magnitude of retract valve movement from its closed position. 
     In accordance with another aspect of the invention, a method of operating a marine power steering system may include imposing manual steering forces on an actuator, the actuator being mounted on a ram of a piston and cylinder assembly and being movable through an actuator stroke. In response to the imposition of the manual forces on the actuator, a flow limiting valve may open to permit fluid to flow within the piston and cylinder assembly at a generally constant, lower than maximum, flow rate through at least an initial portion of the actuating stroke of the actuator, thereby causing the ram to move relative to the barrel at a reduced rate. 
     The fluid flow rate through the flow limiting valve may increase from zero to a low value, then remain at the low valve during a first subsequent portion of the actuator stroke, and then increases to a high value during a second subsequent portion of the actuator stroke. The fluid flow rate through the valve may then increase progressively and non-linearly during the second subsequent portion of the actuating stroke. 
     The imposition of manual forces in a first direction may actuate an extend valve to cause the ram to extend from the barrel at a rate that is dependent on a magnitude of actuator movement, and imposition of manual forces in a second direction may actuate a retract valve to cause the ram to retract into the barrel at a rate that is dependent on a magnitude of actuator movement. 
     In accordance with yet another aspect of the invention, a power steering system for a marine steering system includes a hydraulic cylinder having a barrel and a ram that moves into and out of one end of the barrel, an actuator block that is mounted on an outer end of the ram, an actuator, and valving. The actuator is mounted on the actuator block. The actuator is configured to move on the actuator block upon the transmission of steering command forces thereto. The valving is located within the actuator block and is configured to control the flow of hydraulic fluid to and from the hydraulic cylinder to cause the ram to extend into the barrel and retract from the barrel. 
     The valving may comprise ball-type extend and retract check valves located in the actuator block. The valves may be located on opposite sides of an axial centerline of the ram, in which case the actuator may include a rocker assembly that rocks is responsive to actuator movement to actuate the extend and retract valves. The rocker assembly may include first and second rocker arms, each of which is associated with a respective one of the extend valve the retract valve. 
     These and other features and advantages of the invention will become apparent to those skilled in the art from the following detailed description and the accompanying drawings. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof; and the invention includes all such modifications 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Preferred exemplary embodiments of the invention are illustrated in the accompanying drawings, in which like reference numerals represent like parts throughout, and in which: 
         FIG. 1  schematically illustrates a marine power steering system constructed in accordance with an embodiment of the invention and mounted on the transom of a boat; 
         FIG. 2A  is a cross-sectional elevation view of an actuator assembly of the marine power steering system of  FIG. 1 , showing the actuating assembly in a neutral position thereof; 
         FIG. 2B  corresponds to  FIG. 2A  and illustrates the actuator assembly in a first actuated position thereof; 
         FIG. 3  is a detail view of an extend valve of the actuator assembly of  FIGS. 2A and 2B  and showing the valve in a partially open state thereof; 
         FIG. 4  is a fragmentary detail view of the portion of the extend valve designated  4 - 4  in  FIG. 3  and showing the valve in the partially open state thereof; 
         FIG. 5  is a family of curves comparing flow characteristics of one of the valves of the marine power steering system of  FIGS. 1-4  to a prior art valve; 
         FIG. 6  is a sectional side elevation view of an actuator assembly constructed in accordance with a second embodiment of the invention and illustrating the actuator assembly in a neutral state thereof; 
         FIG. 7  is a sectional end elevation view taken along the line  7 - 7  in  FIG. 6 ; and 
         FIG. 8  is a fragmentary sectional side elevation view of the actuator assembly of  FIGS. 6 and 7 , showing the assembly in an actuated state thereof. 
     
    
    
     DETAILED DESCRIPTION 
     Turning now to the drawings and initially to  FIG. 1 , a cable steering system having a power steering system constructed in accordance with the present invention is illustrated. The system is shown in conjunction with an outboard motor  51  shown as being mounted on the transom  54  of a boat by transom mounts  56 . As is typical, a stationary swivel mount  58  is mounted on the exterior surface of the transom  54  by the transom mounts  56 . The motor  51  is supported on a pivot shaft  60  located behind the transom  54  and can tilt about a horizontal axis by moving about a horizontal engine tilt tube  67 . Shaft  60  is rotatably supported on the swivel mount  58  and is driven to rotate about a generally vertical axis by a steering arm  62 . The steering arm  62  is driven by the cable steering system  50  and/or the power steering system  52 . Steering commands are generated by a steering mechanism  64  such as a steering wheel coupled indirectly to the steering arm  62  by a cable  66 , a steering ram  68 , and a steering link  69 . The steering system  50  thus can be considered a “cable steering system,” though the invention is also applicable to systems actuated by linkages and devices other than cables and can be used with marine propulsion systems other than outboard motors. 
     Still referring to  FIG. 1 , the power steering system  52  includes a power source  70  and an actuator assembly comprising a hydraulic cylinder or steering cylinder  72  and an actuator block  74 . The power source  70  is mounted in the boat. It typically comprises an integrated pump/reservoir having a pressurized fluid outlet  76  coupled to the outlet of an internal pump and an unpressurized inlet  78  that opens into the reservoir. The outlet  76  delivers hydraulic fluid to the cylinder  72  via a supply hose  80 , and the inlet  78  receives fluid via a return hose  82  coupled to a port  84  on the actuator block  74 . 
     Referring to  FIGS. 1-2B , the hydraulic cylinder  72  includes a barrel  90  and a ram  92 . The barrel  90  is fixedly mounted on the swivel mount  58  by a bracket assembly  86 . The barrel includes a cylindrical body that is open at its outer end and closed at its inner end by a cap  94  ( FIGS. 2A and 2B ). Ram  92  extends from and retracts into the barrel  90  under the flow of hydraulic fluid to and from the hydraulic cylinder  72 . The ram  92  is hollow. A piston assembly  100  is provided at the inner end of the ram  92  and houses a valve assembly  102 . The actuating rod  96  has an inner end portion  104 , an intermediate valve entrapment surface  106 , and an outer end  107  extending outwardly from the ram  92  and an opening in the actuator block  74 . A nut  210  is threaded onto the innermost end  107  of actuating rod  96 . 
     The actuator block  74  will now be described with reference to  FIGS. 2A-2B . The actuator block  74  includes a generally cylindrical body  110  having a boss  112  facing the hydraulic cylinder  72 . A yoke  114  is provided on the body  110  at a location above the boss  112  for connection to the steering link  69 . A cavity  116  opens into the body  110  from above, and a bore  118  extends axially inwardly from the cavity  116  and through the boss  112 . The bore  118  is internally threaded so as to permit the body  110  to be mounted on threaded end  120  of the ram  92  so that the actuator block  74  translates with the ram  92 . The cavity  116  has an upper opening  122  and is connected to a lower opening  124  in the body  110  via a vertical passage  126 . The lower opening  124  is in fluid communication with the return hose  82  and the reservoir. An actuator, which in this embodiment comprises a control stem  130 , is mounted in the cavity  116  so as to be pivotable within cavity  116  about a pivot axis defined by a pin  132 . Pin  132  extends through control stem  130  and into a collar  134  mounted in the upper portion end of the cavity  116 . The lower end of the control stem  130  terminates in a ball  136  which is received in a socket  138  in the outer end of the actuating rod  96 . The upper end of the control stem  130  protrudes from the body  110  and terminates in a yoke  140  that receives the end of the steering ram  68 . Movement of the steering ram  68  in the direction of arrow  142  in  FIG. 2A  causes the control stem  130  to pivot about the pin  132  to drive the actuating rod  96  into or out of the ram  92  to actuate the valve assembly  102 , causing the ram  92  to move into or out of the barrel  90 . 
     Still referring to  FIGS. 2A and 2B , piston assembly  100  generally includes an outer nipple  150  threaded into the ram  92 , a central body portion  152 , and an inner end cap  154 . The central and outer portions are sealed in the barrel  90  by respective seals  148  and  149 . The body portion  152  of the piston assembly  100  has a central cavity  156  that houses the valve assembly  102 . Body portion  152  includes a circumferential groove  158  at its outer axial end that forms an inner end of a chamber  144 . Chamber  144  surrounds a portion of the ram  92  is connected to an inlet port (not shown) receiving pressurized fluid from the source  70  and hose  80  of  FIG. 1 . A series of passages, two of which are shown at  160  and  162 , connect groove  158  to a central passage or groove  164 . Central passage  164  also selectively communicates with the central cavity  156  in the body portion  152  as described in more detail below. Axial passages  166  and  168  extend through the end cap  154  from cavity  156  and open onto a control chamber  146  formed between the inner end of the piston assembly  100  and the barrel end cap  94 . 
     Still referring to  FIGS. 2A and 2B , the valve assembly  102  is selectively adjustable to 1) isolate the control chamber  146  from the power source and the reservoir, thus maintaining the ram  92  stationary, 2) connect the control chamber  146  to the high pressure outlet of the pressure source while isolating chamber  146  from the reservoir, thus causing the ram  92  to extend, and 3) connect the control chamber  146  to the reservoir while isolating chamber  146  from the high pressure outlet of the pressure source, thus causing the ram  92  to retract. Valve assembly  102  includes a normally closed extend valve  200  that is openable to cause the ram extension, and a normally closed retract valve  202  that is openable to cause ram retraction. The extend valve  200  is slidably disposed in the inner end of a bore  205  formed in outer nipple  150  of piston assembly  100 . The extend valve  200  has, amongst other features described below, a projection  204  at its outer or upstream end that extends through and projects axially outwardly from the inner end of the nipple  150  of the piston assembly  100 . Projection  204  also is sealed to the nipple  150  via a seal  151 . The above-described groove  164  is formed in projection  204 . Retract valve  202  similarly includes, amongst other features, a portion  206  at its inner or downstream end that is slidably received within a bore  208  formed in piston end cap  154 . An outer axial end portion of the retract valve  202  surrounds the inner axial end portion of the extend valve  200  and is sealed to the extend valve  200  by a seal  207 . Extend valve  200  and retract valve  202  are each formed with an axial internal passage that receives the inner end portion  104  of the actuating rod  96 . 
     A spring  212  bears against facing surfaces  214 ,  216  formed on the extend valve  200  and the retract valve  202 , respectively. The spring  212  urges the extend valve  200  into sealing engagement with a seat  220  formed at the inner opening of the bore  205  provided at the outer axial end of the body portion  152 . The spring  212  also urges the retract valve  202  into sealing engagement with a seat  218  provided at the inner end of the bore  208  in the piston end cap  154 . An annular groove or chamber  222  is provided in the projecting portion  206  of retract valve  202 . A pair of radial passages  224 ,  226  connects the groove  222  to and annular chamber  228  surrounding the actuating rod  98 . The annular chamber  228  extends the length of the actuating rod and opens into cavity  116  and, ultimately, to the reservoir. By the action of spring  212  urging the extend and retract valves  200  and  202  into sealing engagement with the seats  218 ,  220 , the grooves  164  and  222  are fluidically isolated from the central cavity  156  when the extend and retract valves  200  and  202  are closed, isolating cavity  156  from both the pressure source and the reservoir. 
     Each of the extend and retract valves  200  and  202  is designed to control flow therethrough so that, at a given system pressure, the flow rate of fluid through the valve is limited to a relatively low and generally constant value through an initial portion of the valve stroke to restrict the rate of ram extension and retraction and prevent valve chatter. The flow rate then increases non-linearly during additional opening movement of the valve. 
     The extend and retract valves  200  and  202  are essentially mirror images of one another. Referring to  FIGS. 3 and 4 , the extend valve  200  thus will be described, it being understood that the description applies generally equally to the retract valve  202 . Extend valve  200  is slidably disposed in the bore  205 . When viewed in the direction of fluid flow through the bore  205 , it also includes a head  248 , a sealing surface  250  extending upstream from the head  248 , and a valve body  251  extending upstream from the sealing surface. The spring  212  abuts against the head  248 . The sealing surface  250  extends radially inwardly and axially outwardly from the head  248  to and beyond a location at which it seals against the seat  220  when the valve  200  is closed. The sealing surface  250  terminates in a relatively smaller diameter surface portion  252  of the body  251 . 
     Another surface portion  254  of the body extends axially outwardly and radially in the direction of fluid flow from portion  252  at an angle of; for example, 27° from the radial to a maximum diameter portion  256  that may be of negligible axial length. The diameter of portion  256  is the maximum effective diameter of the valve  200 . Maximum diameter portion  256  defines the maximum effective diameter of the valve  200  because an annular gap between the maximum diameter portion  256  and the bore  205  defines a flow path of minimum diameter through the valve  200 . Discounting the effects that the sealing surface  250  has on fluid flow through the valve  200  in the early phases of valve opening, the “effective flow area” of the valve  200 , defined as the cross sectional area of the gap between the bore  205  and the widest portion of the valve body  251  remaining in the bore  205  at any given point in the opening stroke of the valve  200 , is at minimum at this location. Upstream beyond portion  256 , a curved metering portion  258  of the body  251  extends radially inwardly to an undercut portion  257  on the valve  200  that forms the inner surface of the groove  164 . The metering portion  258  may have a radius of for example, 0.250 and extend through an axial length of about 0.1″ to 0.2″. Due to the curvature of this portion  258 , the effective flow are of the valve  200  increases progressively and non-linearly, i.e., at an accelerating pace, when the effective flow area of the valve  200  is governed by metering portion  258 . 
     In operation, actuation of the extend valve  200  by leftward or inward movement of the actuating rod  96  moves valve  200  off its seat  220  to permit fluid to flow through the passage  164 , past valve seat  220 , and into cavity  156 , causing the ram  92  to extend from the barrel  90  as will be described in greater detail below. The manner in which that flow depends on the magnitude of valve opening will now be described on a comparative basis with a prior art valve. The curves  300  and  302  in  FIG. 5  plot valve stroke from a closed position vs. flow area for a prior art extend valve and for an extend valve constructed in accordance with this embodiment of the invention, respectively. The prior art valve is characterized by a valve body that is inclined linearly downwardly and outwardly from the base of the sealing surface so that the effective area of the valve increases linearly throughout the valve opening stroke. Referring to the curve  300  in  FIG. 5 , the effective flow area and thus the flow rate at a given pressure increase fairly rapidly so that the effective flow area is 0.004 in 2  after only 0.02″ of valve stroke and is 0.06 in 2  after only 0.03″ of valve stroke. This equates to relatively rapid ram extension even at small magnitudes of operator input and could lead to undesirable valve chatter. Valve chatter can occur if the ram momentarily moves faster than the input, causing the valve to reseat, which reduces fluid flow though the valve and slows the rate of ram extension then reopens, causing in a rapid or “jerky” movement of the ram. There are many factors involved that can cause this to happen. 
     During operation of the valve  200 , however, the effective flow area of the valve and thus the fluid flow rate through the valve are limited significantly during the early phases of valve opening due to the influence of the maximum diameter portion  256  of body  251  on fluid flow through the valve  200 . The curve  302  indicates that the effective flow area increases to about 0.0015 in 2  after the valve  200  opens and remains at that level until the trailing edge of the portion  256  clears the seat  220  at the end of a first subsequent portion of the valve&#39;s stroke. That portion is about 0.03″ in this embodiment. Comparing point  304  in curve  300  to point  306  in curve  302 , the effective flow area of the valve  200 , is only about ⅓ that of a prior art system at this level of steering input. The possibility of valve chatter therefore is greatly reduced. As the valve  200  opens further in a second subsequent portion of the valve&#39;s stroke, the effective flow area begins to increase because of the decreasing diameter of the curved metering portion  258 . The ram  92  thereafter extends faster due to increased fluid flow through the valve  200 , with the fluid flow and the rate of ram extension increasing progressively with progressive valve movement and a resultant increase in the effective flow area. The effective flow rate through the valve  200  and thus the ram extension rate surpasses that of the prior art valve at point  310  where the curves  300  and  302  intersect and, then continues to increase. 
     As mentioned above, the same valve design is used for the retract valve  202 . When closed, the retract valve  202  isolates the chamber  146  from an end of groove  222 , thus preventing fluid flow through the passages  224 ,  226 ,  228 , out of the port  124 , and to the reservoir. When the retract valve  202  is open, chamber  146  is connected to the groove  222 , permitting fluid to flow through the groove and passages  222 ,  224 , and  226 , out of the port  124 , and to the reservoir at a rate that depends on the magnitude of valve opening which, in turn, depends on the magnitude of actuating stem stroke, thus causing the ram  92  to retract into the barrel  90 . 
     In operation of the system as a whole, when no steering forces are imposed on the central stem  130  so that it remains in its position as shown in  FIG. 2A , the extend and retract valves  200  and  202  are closed, preventing movement of the ram  92  relative to barrel  90 . To extend ram  92 , yoke  140  is moved rightwardly by operation of steering ram  68  so as to cause clockwise pivoting of control stem  130  about pin  132 , as shown in  FIG. 2B . This movement of control stem  130  causes leftward movement of actuating rod  96  within ram  92 . When this occurs, an abutment face  97  on the actuating rod  96  engages the outer axial end of the projecting portion  204  of extend valve  200 . Continued actuating rod motion results in inward movement of extend valve  200  against the force of spring  212 , moving the sealing surface  250  of extend valve  200  out of engagement with seat  220 . Pressurized fluid flows from high pressure chamber  144  and through the extend valve  200  at rate that is dependent on the extent of valve opening. Pressurized fluid then flows from cavity  156 , through passages  166  and  168 , and into chamber  146 , driving the piston assembly  100  to the right as seen in  FIG. 2B  to extend the ram  92 . This extension of ram  92  causes rightward movement actuation of block  74 , and thus the steering link  69 , so as to pivot engine  58  through arm  62  ( FIG. 1 ). This movement is slow during small actuating arm strokes and is faster during larger strokes. 
     When the desired steering effect has been attained by extension of the ram  92 , the operator ceases turning the steering wheel, thereby resulting in movement of control stem  130  to its neutral position as shown in  FIG. 2A . This moves abutment face  97  of the actuating rod  96  out of engagement with the rightward end of extend valve projecting portion  204 , and spring  212  then returns extend valve  200  to its closed position, thereby cutting off communication of chamber  144  with cavity  156  and chamber  146 . The position of ram  92  thus is maintained relative to barrel  90 , maintaining the desired angular position of the motor relative to the boat. 
     When it is desired to turn the motor in the opposite direction, the operator turns the steering wheel so as to actuate steering cable  66  to cause the steering ram  68  to drive the control stem  130  to pivot counterclockwise about pin  132 . When in this position, control stem  130  causes rightward movement of actuating rod  96 . Such movement causes the nut  210  on the actuating rod  96  to drive the retract valve  202  against the bias of spring  212 , opening the retract valve  202 . Fluid then flows from chamber  146 , through passages  166  and  168  and chamber  156 , through retract valve  202 , into groove  222 , through passages  224  and  226 , into and through annular chamber  228 , and out of the port  124  to the reservoir. Fluid pressure in chamber  144  then drives the piston assembly  100  to the left to retract the ram  92 . As with the extend valve  200 , fluid flows through the retract valve  202  at a rate that is dependent upon the extent of retract valve opening. This retraction of ram  92  results in rotation of engine  58  at a rate that is slow for low steering inputs and faster for high steering inputs. 
     When the desired position of the engine is attained, the operator stops turning the steering wheel to remove actuation forces from the control stem  130 . Accordingly, spring  212  once again biases retract valve  202  to its closed position, thereby insolating chamber  146  from the reservoir and maintaining ram  92  in its existing position. 
     Turning now to  FIGS. 6-8 , an actuator assembly  352  is constructed in accordance with another embodiment of the invention in which the valve assembly is contained within the actuator block  374  as opposed to being contained within the piston and cylinder assembly  372 . The actuator assembly  352  is designed to be mounted on a transom of a boat in at least generally the same manner as the actuator assembly of  FIGS. 1-4  and to be connected to a steering link  69  and a steering ram  68  as described above in connection with the first embodiment Inlet and outlet ports are connected to the high-pressure outlet of the power source and to the reservoir, also as described above in connection with the first embodiment. 
     Also, as in the first embodiment, the actuator assembly  352  includes a stationary barrel  390  and a ram  392  that is movable linearly into and out of the barrel  390 . The barrel  390  includes a cylindrical body  410  and a fixed inner endcap  412 . The ram  392  of this embodiment includes a stepped piston  400  having an inner end portion  414  of increased diameter and an outer end portion  416  of reduced diameter. The inner end portion  414  of piston  400  is sealed to the interior of the barrel body  410  by a seal  418 . The outer end portion  416  of piston  400  is threaded onto an inner end of the ram  392 , which is sealed to the interior of barrel body  410  by a seal  419 . Chambers  422  and  424  are formed on opposite sides of inner end portion  414  of the piston  400 . A hollow tube  426  extends axially through the ram  392 . Tube  426  presents an internal passage  428  having an inner end communicating with the chamber  422  and outer end that opens into a control chamber  520  formed in the actuator block as detailed below. The inner end portion of the tube  426  is sealed to the piston  400  by an O-ring  430 . The outer end portion of the tube  426  is sealed to an internal surface of the actuator block  374  by another O-ring  431 . 
     The chamber  424  is an annular chamber formed between the outer surface of the reduced diameter portion  416  of the piston  400  and the inner radial surface of the barrel  390 . This chamber  424  communicates with the high-pressure inlet via a supply passage  427 . Radial passages  429  and  430  connect chamber  424  to an annular passage  432  surrounding the tube  426 . The outlet of the annular passage  432  opens into the valve assembly as discussed below. 
     Still referring  FIGS. 6 and 7 , the actuator block  374  includes an actuator body  450  and an actuator in the form of an actuating lever  452  pivotally mounted on an outer surface of the actuator body  450 . The actuating lever  452  extends beyond the actuator body  450  and has a yoke  454  for connection to the steering ram  68 . A tab  456  is also provided on the body  450 . Tab  456  presents a yoke  458  for connection to the steering link  69 . The body  450  has a stepped axial bore having a relatively large diameter inner end  460  and a small diameter outer end  462 . The inner end  460  of the stepped bore threads onto an externally threaded neck  464  on the outermost end portion of the ram  392 . The innermost end of the body  450  seats against a shoulder  466  on the ram  392  and is sealed to the neck  464  of the ram  392  by an O-ring seal  468 . The outermost end  462  of the stepped bore seals against the O-ring seal  431  on the outer end of the tube  426 . 
     Still referring to  FIGS. 6 and 7 , a rocker assembly  470  and a control valve assembly  472 ,  474  are housed in a cavity  475  of the interior of the actuator body  450 . The control valve assembly includes two valves  472  and  474  that are located on opposite sides of the longitudinal axis of the ram  392  and that thus are readily actable by the rocker assembly  470 , which rocks about that axis. Each valve  472 ,  474  is housed in a respective cavity  526 ,  524 . The rocker assembly  470  is mounted on a bolt  473  that is received in a through bore  476  in the body  450  ( FIG. 7 ) and held in place by a nut  478 . Assembly  470  includes an annular yoke  480  and first and second rocker arms  482  and  484  that extend laterally outwardly from a center of the yoke  480 . The yoke  480  is fastened to a sleeve  486  by a set screw  488  extending through the center of the yoke. As best seen in  FIG. 8 , the sleeve  486  surrounds the bolt  473  and is kept centered in the bore  476  by bushings  490 ,  492 . O-ring seals  494  and  496  are provided at the ends of the bushings  490  and  492 . The outer end of the sleeve  486  is connected to an inner end of the actuating lever  452 . The sleeve  486  thus is rotatable with the bolt  473  upon pivoting movement of the actuating lever  452 , hence causing the rocker assembly  470  to rock. 
     Still referring especially to  FIG. 7 , each rocker arm  482  and  484  has a tapped bore  500 ,  502  that receives an externally-threaded adjustment screw  504 ,  506  that extends through the bore  500 ,  502  of the respective rocker arm  482 ,  484 . Each screw  504 ,  506  acts as a valve actuator that imparts actuating forces to an associated valve  472  or  474  through a corresponding pin  514 ,  516 . The effective length of each screw  504 ,  506 , i.e. the distance it extends inboard of the associated rocker arm  482 ,  484 , can be adjusted by threading it into or out the bore  500 ,  502 , and the screw  504 ,  506  can then be locked in place using a lock nut  510 ,  512 . Due to this construction, pivotal movement of the rocker assembly  470  due to translation of the actuating lever  452  causes the rocker assembly  470  to pivot or rock about the central axis of the bolt  473 . This movement causes one or the other of the adjustment screws  504  or  506  to engage an associated actuator pin  514  or  516  to open an associated valve  472  or  474  as detailed below. Each actuator pin is slidably guided in a corresponding guide block  518  or  519 . 
     Referring particularly to  FIG. 8 , a control chamber  520  is formed in the body  450  outbound of the end of the tube  426 . Control chamber  520  has an inlet in fluid communication with a first chamber containing an extend valve  472 , an outlet in fluid communication with a second chamber containing the retract valve  474 , and a control port opening into the outboard end of the hollow tube  426 . The extend valve  472  selectively connects the control chamber  520  to the high pressure chamber  526  housing the valve  472 . Chamber  526  is in fluid communication with the annular passage  432  in the ram  392  via a cross passage  528 . The retract valve  474  selectively connects the control chamber  520  and the chamber  524  that houses the valve  474  to a low pressure chamber  530 . Chamber  530  is in fluid communication with the outlet port leading to the reservoir. 
     Each of the extend and retract valves  472  and  474  is of identical construction. The extend valve  472  therefore will be described in detail, it being understood that the description applies equally to the retract valve  474 . 
     The extend valve  472  is a ball-type check valve having a ball  540  that is normally sealed against a seat  542  separating the control chamber  520  from the high-pressure chamber  526 . The ball  540  is urged against the seat  542  by a spring assembly including a coil spring  544  and a spring guide  546  that has a head that engages the ball  540 . The seat  542  is hollow so as to define a central through-passage that receives the actuator pin  514 . Movement of the actuator pin  514  upon engagement of the associated adjustment screw  504  therewith due to rocker assembly motion drives the ball  540  off the seat  542  to allow fluid in the high pressure chamber  526  to flow past the ball  540 , through the hollow seat  542 , into an intermediate chamber  522 , and into the control chamber  520 . The fluid can then flow through the tube  426  and into chamber  422 . Similarly, movement of the ball  540  of the retract valve  474  off the seat by motion of the actuator pin  516  causes fluid to flow from control chamber  520 , into chamber  524 , past the ball  540 , through the hollow seat  542 , and into the low pressure chamber  530  before flowing out of the actuator assembly  352  and to the reservoir. 
     In operation, the actuating lever  452  and the remaining components of the system  352  assume the position illustrated in  FIGS. 6 and 7  in the absence of the imposition of steering forces on the steering ram  68 . At this time, both the extend and retract valves  472  and  474  are closed, and fluid flow into or out of the cylinder assembly  372  is prohibited, locking the ram  392  in place relative to the barrel  390 . 
     To steer the boat, actuation of the wheel or other input in a desired direction translates the steering ram  68  to cause the actuator lever  452  to swing in one direction or the other about the bolt  473 . Hence, referring to  FIG. 8 , movement of the actuator ram  68  in the direction of arrow  560  causes the rocker assembly  470  to pivot clockwise. This pivoting motion causes the actuating screw  504  to drive the actuator pin  514  to the left as viewed in  FIG. 8 , driving the ball  540  of the extend valve  472  off its seat  542  against the biasing force of the spring  544 . Pressurized fluid thereafter flows into the inlet passage  427  and into high pressure chamber  424 . Fluid in the high pressure chamber  424  then flows through passages  429  and  430  and into annular chamber  432 . Fluid in chamber  432  then flows through the cross passage  528 , through the high-pressure chamber  526 , past the extend check valve  472 , through the seat  542  and the chamber  522 , and into the control chamber  520 . The pressurized fluid then flows inwardly through the hollow tube  426  and into the chamber  422 , forcing the piston  400  to the right to extend the ram  392 . When the manual input is stopped to relieve the actuating force from the actuating lever  452 , the system continues to move a brief time until the check ball  540  of valve  472  is reseated, whereupon further ram movement is prevented. 
     When the actuating lever  452  is moved in the opposite direction or counterclockwise as seen in the drawings, the rocker assembly  470  will pivot counterclockwise, causing the adjustment screw  506  to engage the actuator pin  516  and drive the ball  540  of the retract valve  474  from the seat  542 . Fluid in chamber  422  now flows through the internal passage  428  in the tube  426 , into the control chamber  520 , through chamber  524 , past the retract valve  474 , into the low pressure chamber  530 , and out to the reservoir. Pressurized fluid then flows into the chamber  424  from the pressure source and the passage  427 , driving the piston  400  to the left and causing the ram  392  to retract. When movement of the actuating lever  452  stops due to the release of manual forces, the system will continue to move for a brief time until the check ball  540  of valve  474  reseats on the seat  542 . 
     The actuator assembly of  FIGS. 6-8  has several advantages over prior known assemblies. Because the valving is located in a common port in the actuator body, the valving can be easily assembled or accessed for repair without having to completely disassemble the piston and cylinder assembly  372 . The valves  472  and  474  also need not be constructed to close tolerances, and valve clearance can be easily adjusted using the adjusting screws. The check valves also provide a simple, reliable sealing system. Finally, if desired, the pressure source line could be routed to the chamber  526  on the actuator block, making for a simpler cylinder endcap. 
     Although the best mode contemplated by the inventor of carrying out the present invention is disclosed above, practice of the present invention is not limited thereto. It will be manifest that various additions, modifications and rearrangements of the aspects and features of the present invention may be made in addition to those described above without deviating from the spirit and scope of the underlying inventive concept. The scope of some of these changes is discussed above. The scope of other changes to the described embodiments that fall within the present invention but that are not specifically discussed above will become apparent from the appended claims and other attachments.