Patent Publication Number: US-11035392-B2

Title: Hydraulic actuator end stroke stop pressure/load control

Description:
FOREIGN PRIORITY 
     This application claims priority to European Patent Application No. 19290091.8 filed Sep. 12, 2019, the entire contents of which is incorporated herein by reference. 
     TECHNICAL AREA 
     The present application relates to hydraulic actuator systems. In particular, the present application relates to pressure and/or load control at a hydraulic actuator end stroke stop. 
     BACKGROUND 
     Hydraulic actuators usually incorporate end stroke stops between a piston and a cylinder at both ends. In any actuator position, pressure loads in the chamber or chambers is a function of the external load applied to the actuator. Once an actuator piston contacts an end stroke stop, pressure in the chamber that is driving the actuator to the stop usually rises to a maximum system pressure. As an example, an opposite chamber (e.g. in a dual acting actuator system) is usually ported to drain, which means that there is almost no opposite hydraulic pressure load generated by a second actuator chamber. 
     The above, therefore, results in very high loads on actuator components within an actuator system. This has a significant impact on the fatigue of actuator components when actuator stops are contacted at every operating cycle. 
     Further, the size of actuator chamber(s) and system pressure is typically set to meet system performances when the load required to maintain the system against an end stroke stop is much lower than the load developed under full system pressure. This is the case, for example, in propeller pitch change actuators where the load required to maintain the blades in feather position is very small compared to the maximum load generated by blades in flight. This leads to oversizing of actuator components. 
     SUMMARY 
     In one example, there is described a system for providing pressure/load control at an end stroke stop. The system includes an actuator housing having an end stroke stop and a first actuator housing side, an actuator piston provided in the actuator housing, wherein the actuator piston is movable along a longitudinal axis, the actuator piston having a first piston portion perpendicular to the longitudinal axis, and means for regulating the pressure/load control at the end stroke stop provided in the first piston portion, wherein the means for regulating the pressure/load control at the end stroke stop is configured to move from a closed position to an open position when in contact with the first actuator housing side. 
     The first piston portion may have an opening that extends through a first piston portion side to a second piston portion side. The means for regulating the pressure/load control at the end stroke stop may be provided within the opening. 
     The means for regulating the pressure/load control at the end stroke stop may further include a ball bearing, a first biasing spring, a rod, a valve assembly casing. When the valve assembly casing contacts the first actuator housing side, in use, the rod may move to contact the ball bearing such that the means for regulating the pressure/load control at the first actuator housing side provides fluid flow through the opening. 
     The means for regulating the pressure/load control may further include a valve piston and a second biasing spring, wherein, a first force, P 1 ×A 1 , where P 1  is a first pressure and A 1  is the area of the valve piston, is exerted through the opening and on a first side of the valve piston, and wherein a second force, P 2 ×A 2 +S, where P 2  is a second pressure, A 2  is the area of the valve piston and S is the force exerted by the second biasing spring, is exerted on a second side of the valve piston. When P 1 ×A 1  is greater than P 2 ×A 2 +S, the valve piston may move such that pressure can be discharged through at least one passageway provided in the valve piston. 
     In an alternative example to the valve piston, there may be provided an orifice between the ball bearing and the second piston portion side. There may be provided a restriction in the orifice such that the restriction provides a pressure drop to regulate the pressure of the fluid through the opening. 
     In another example, there is described a method for providing pressure/load control at an end stroke stop. The method may include providing an actuator housing having an end stroke stop and a first actuator housing side, providing an actuator piston provided in the actuator housing, wherein the actuator piston is movable along a longitudinal axis, the actuator piston having a first piston portion perpendicular to the longitudinal axis, and providing means for regulating the pressure/load control at the end stroke stop provided in the first piston portion, wherein the means for regulating the pressure/load control at the end stroke stop is configured to move from a closed position to an open position when in contact with the first actuator housing side. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike: 
         FIG. 1  shows an example of an assembly that provides pressure/load control at an end stroke stop; 
         FIG. 2  shows an example of the assembly of  FIG. 1  when the assembly is in an open position; and 
         FIG. 3  shows an alternative example of an assembly that provides pressure/load control at an end stroke stop. 
     
    
    
     DETAILED DESCRIPTION 
     With reference to  FIGS. 1 and 2 , there is shown, generally, an actuator assembly  10 . The actuator assembly  10  may include an actuator housing  110  for housing an actuator piston  100  that can slidably move within the actuator housing  110  along an axis A. The actuator piston  100  may include an end stroke stop valve assembly to control pressure/load when the actuator piston  100  contacts an end stroke stop  115  of the actuator housing  110 . 
     The end stroke stop valve assembly may be provided within and/or on the actuator piston  100 , as shown in  FIG. 1 . The actuator piston  100  may include a first piston portion  122  that extends perpendicular from the axis A to a first inner surface  111  of the actuator housing  110 . As can be seen in  FIG. 1 , there may be provided an opening  130  that extends from a first piston portion side  131  to a second piston portion side  132  through the first piston portion  122  along axis A. Within the opening  130 , there may be provided a first biasing spring  118  and a ball bearing  116 . The ball bearing  116  may be contacted by a rod  114  that may extend out of the opening  130  of the first piston portion  122  and in to a valve assembly casing  113 . The rod  114  may be fixed to the valve assembly casing  113 , and the rod  114  may be slidably received within the opening  130  through the second piston portion side  132  to contact the ball bearing  116 . There may also be provided in the end stroke stop valve assembly a valve piston  134  that may be connected to the valve assembly casing  113  by a second biasing spring  112 . The valve piston  134  may move from a closed position to an open position in response to a pressure differential across the end stroke stop valve assembly. 
     The actuator housing  110  includes a first actuator housing side  120 , as shown in  FIG. 1 . When the actuator piston  100  moves to the first actuator housing side  120 , the valve assembly casing  113  contacts the first actuator housing side  120 . The force exerted on to the valve assembly casing  113  from the first actuator housing side  120  allows the valve assembly casing  113  to move in an opposite direction to the actuator piston  100  such that the rod  114  moves to contact and move the ball bearing  116  into an open position. Opening the ball bearing  116  allows for fluid communication through the end stroke stop valve assembly. When the actuator piston  100  moves away from the first actuator housing side  120 , the first biasing spring  118  acts to restore the position of the rod  114  such that the ball bearing  116  moves to a closed position and prevents any flow communication between a first chamber  11  and a second chamber  12 . Biasing spring  118  force is set to prevent any  116  opening under any delta pressure between the first chamber  11  and the second chamber  12 . 
     When the actuator piston  100  moves to the first actuator housing side  120 , and the ball bearing  116  is in an open position, the valve piston  134  is able to move in response to pressure on either side of the end stroke stop valve assembly. The second biasing spring  112  is provided to the valve piston  134  and a pressure threshold is set in the end stroke stop valve assembly by increasing or decreasing the compressive force of the second biasing spring. The pressure exerted on the left hand side of the valve piston  134  in the first actuator chamber  11 , e.g. fluid flow through the opening  130 , may be denoted as P 1 . When the actuator piston  100  contacts the end stroke stop  115 , P 1  increases over time. The force exerted on the left side of the valve piston  134  may be denoted as P 1 ×A 1 ; A 1  being the area of the valve piston  134  subject to pressure P 1 . The force exerted on the right hand side of the valve piston  134  may be denoted as P 2 ×A 2 +S, where S is the force of the biasing spring, A 2  is the area of the piston  134  subject to pressure P 2  and P 2  is the pressure in the second actuator chamber  12  on the right side of the valve piston  134 . As P 1  increases, and becomes high enough such that P 1 ×A 1 &gt;P 2 ×A 2 +S, the valve piston  134  moves against the second biasing spring  112  to move to open a passage for fluid flow (shown in  FIG. 2 ). The larger the flow, the larger the movement of piston  134  will be. This acts to regulate P 1  pressure to the required range. This range can be adjusted via biasing spring  112  preload and spring rate. 
       FIG. 2  shows an example of the valve piston  134  when in an opened position. As can be seen in this figure, the actuator assembly  10  comprises all the components as described above in relation to  FIG. 1 . When the valve assembly casing  113  contacts the end stroke stop  120 , the valve assembly casing  113  moves in an opposite direction to the actuator piston  100  such that the rod  114  moves to contact and move the ball bearing  116  into an open position. Fluid is then able to flow through the opening  130  and around the ball to exert a pressure (e.g. P 1 ×A 1 ) on the valve piston  134 . As mentioned above, the force exerted on the opposite side of the valve piston  134  is denoted by P 2 ×A 2 +S. As P 1 ×A 1  gradually increases and becomes high enough such that P 1 ×A 1 &gt;P 2 ×A 2 +S, the valve piston  134  may move in a direction against the force exerted from the second biasing spring  112  to move to an open position. At this point, at least one passageway  133  is revealed in the valve piston  134  to provide a fluid communication with the fluid that has moved through opening  130 . The passageway  133  therefore allows fluid to flow in order to bring P 1 ×A 1  to a target level. As shown in  FIG. 2 , the at least one fluid passageway  133  extends through the valve piston  134  in a direction perpendicular to the axis A. It is envisaged that the force P 2 ×A 2 +S can be altered by changing the tensile stress or the biasing spring rate (e.g. stiffness) of the second biasing spring  112 . 
       FIG. 3  shows an alternative example of the actuator assembly  10  of  FIG. 1 . The components in this Figure are denoted by a “ ” to show like-for-like components of  FIGS. 1 and 2 . 
     In  FIG. 3 , the actuator assembly  10 ′ may include an actuator housing  110 ′ for housing an actuator piston  100 ′ that can slidably move within the actuator housing  110 ′ along an axis A′. The actuator piston  100 ′ may include an end stroke stop valve assembly to control pressure/load when the actuator piston  100 ′ contacts an end stroke stop  115 ′ of the actuator housing  110 ′. 
     The end stroke stop valve assembly may be provided within and/or on the actuator piston  100 ′, as shown in  FIG. 3 . The actuator piston  100 ′ may include a first piston portion  122 ′ that extends perpendicular from the axis A′ to a first inner surface  111 ′ of the actuator housing  110 . As can be seen in  FIG. 1 , there may be provided an opening  130 ′ that extends from a first piston portion side  131 ′ to a second piston portion side  132 ′ through the first piston portion  122 ′ along axis A′. Within the opening  130 ′, there may be provided a first biasing spring  118 ′ and a ball bearing  116 ′. The ball bearing  116 ′ may be contacted by a rod  114 ′ that may extend out of the opening  130 ′ of the first piston portion  122 ′ and in to a valve assembly casing  113 ′. The rod  114 ′ may be fixed to the valve assembly casing  113 ′, and the rod  114 ′ may be slidably received within the opening  130 ′ through the second piston portion side  132 ′ to contact the ball bearing  116 ′. 
     In the example shown in  FIG. 3 , there may be provided an orifice  140  that is located in the first piston portion  122 ′ between the ball bearing  116 ′ and the second piston portion side  132 ′. The orifice  140  is shown in  FIG. 3  as extending in a perpendicular direction to axis A′. The orifice  140  may include a restriction  141  that acts to generate a pressure drop—for example, pressure upstream of the restriction  141  may be greater than pressure downstream of the restriction  141 . In this way, the pressure of the fluid flow through the opening  130 ′ may not exceed a target value due to the size of the restriction  141 . The target value may be altered by reducing or increasing the size of the restriction  141 . 
     Although the invention has been described in terms of preferred examples as set forth above, it should be understood that these examples are illustrative only and that the claims are not limited to those examples. Those skilled in the art will be able to make modifications and alternatives in view of the disclosure which are contemplated as falling within the scope of the appended claims. In an example, the system described above can be used at the other actuator end end-stroke stop. Also, it is envisaged that the valve assembly could be installed in the housing with adequate connections via plumbing instead of in the piston  110 .