Abstract:
A linear actuator system including a cylinder, a piston slidably received within the cylinder and defining a piston chamber and a rod chamber in the cylinder, wherein the piston includes a plurality of orifices therethrough that place the piston chamber and the rod chamber in fluid communication, and a sealing member movable between a closed position, wherein the sealing member restricts fluid flow through at least one of the plurality of orifices, and an open position, wherein the sealing member is less restrictive of fluid flow through the orifices. The plurality of orifices may include an always-open orifice that is not blocked by the sealing member when the sealing member is in the closed position.

Description:
This application claims priority to U.S. Provisional Patent App. No. 60/517,000 filed on Nov. 4, 2003, the entire contents of which are hereby incorporated by reference. 
    
    
     BACKGROUND 
     The present invention is directed to hydraulic suspension systems and, more particularly, to linear actuators for hydraulic suspension systems. 
     Automobiles, including trucks and sport utility vehicles, as well as other motor vehicles, incorporate suspension systems designed to minimize the leaning or “rolling” of the vehicle body relative to the frame or wheels that occurs when the vehicle corners or turns at relatively high speeds. 
       FIG. 1 . illustrates a typical suspension system, generally designated  10 , that includes a pump  14  driven by a motor  12  that draws hydraulic fluid from reservoir  16  through supply line  18 . The output of pump  14  is conveyed through line  20  to manifold  22 . Fluid flow is split at  24  and is further conveyed through line  26  to power steering manifold  28  and along lines  30 ,  70  to solenoid valves  32 ,  34 . 
     Lines  36 ,  38  extend from solenoid valve  32  and are in fluid communication with rod chamber  40  and piston chamber  42 , respectively, of front actuator  44 . Lines  46 ,  48  extend from solenoid valve  34  and are in fluid communication with rod chamber  50  and piston chamber  52 , respectively, of rear actuator  54 . Fluid supply lines  64 ,  66  are connected to enable valve  32  to supply fluid to lines  46 ,  48 , respectively, and thereby pressurize rear actuator  54  at the same time as the front actuator  44 . 
     Line  56  is connected to a pressure control valve  58  and a relief valve  60  that, in turn, are connected to line  62 , which returns fluid to the reservoir  16 . Lines  68 ,  70  connect valves  32 ,  34  to return line  62  and supply line  30 , respectively. 
     A controller (not shown) actuates valve  32  to displace its spool from the position shown in  FIG. 1 , thereby opening lines  36 ,  38  to receive pressurized fluid from line  30 , pressurizing rod chamber  40  and piston chamber  42  of front actuator  44  and, through supply lines  64 ,  66  and  46 ,  48 , pressurizing rod chamber  50  and piston chamber  52  of rear actuator  54 . This orientation causes the front and rear actuators  44 ,  54 , respectively, to extend. 
     When valve  32  is actuated such that the spool is in the position shown in  FIG. 1  (i.e., the unopened position), and valve  34  is actuated such that the spool is displaced from the configuration shown in  FIG. 1  (i.e., the open position), pressurized fluid flows through supply lines  30 ,  70 , to valve  34 , and from valve  34  through line  64  and line  36  to the rod chamber  40  of front actuator  44  and through line  46  to the rod chamber  50  of rear actuator  54 . At the same time, fluid in piston chambers  42 ,  52  of front and rear actuators  44 ,  54  flows through lines  38 ,  48 ,  66  to valve  34 , and from valve  34  through return lines  68 ,  62  to the reservoir  16 . Accordingly, the front and rear actuators  44 ,  54  are retracted. 
     Thus, by selectively pressurizing the front and rear actuators  44 ,  54  (which, for example, would both be mounted on one side of a vehicle) by appropriately opening and closing solenoid valves  32 ,  34 , the associated vehicle may be leveled. 
     When the actuators  44 ,  54  receive a shock load, such as by actuator  72  (which schematically shows a test stand associated with the suspension system  10  that is designed to simulate a vehicle associated with the suspension system encountering a bump or bumps), the shock causes the pistons  74 ,  76  to be displaced relative to the cylinders  78 ,  80 . The displacement is facilitated by check valves  82 ,  83  within the pistons  74 ,  76  of actuators  44 ,  54 , respectively. 
     A disadvantage with such systems is that the shock imparted to the actuators  44 ,  54  is, in turn, transmitted to the associated supporting structure, such as a vehicle body, through bushings  84 ,  85  (or other actuator mountings), resulting in discomfort to passengers and possible damage to associated components. 
     In an effort to reduce the transmission of shock, such actuators have been modified as shown in  FIG. 2 . The actuator  86  shown in  FIG. 2  includes a piston  87 , a cylinder  88 , a piston chamber  89 , a rod chamber  90 , an annular disk  91  and a piston rod  92 . The piston  87  includes a plurality of orifices  93  therethrough that interconnect the piston chamber  89  with the rod chamber  90 . The rigid, annular disk  91  extends about the piston rod  92  and is spring-biased (via spring  94 ) to cover the orifices  93  when the pressure in the piston chamber  89  and rod chamber  90  are equal and in conditions when the piston  87  and piston rod  92  are being forced out from the associated cylinder  88  of actuator  86 . However, when a force, indicated by arrow F, is applied to piston rod  92 , as by a shock load imparted to the actuator  86 , thereby forcing piston  87  into cylinder  88 , the flow of fluid from the piston chamber  89  to the rod chamber  90  through orifices  93  displaces the disk  91  away from the piston  87  (i.e., against the bias of spring  94 ), thereby facilitating the flow of fluid from the piston chamber  89  to the rod chamber  90 . The presence of the disk  90  retards the flow of fluid and lessens the shock transmitted to the associated vehicle. 
     Nevertheless, a disadvantage with such actuators and systems is that there is noise associated with the rapid displacement of the piston  87  resulting from the flow of fluid around the annular disk  91  in response to a shock load and the aeration and compression of hydraulic fluid within the actuators. Accordingly, there is a need for an actuator for use in a suspension system in which the noise associated with rapid displacement of the actuator is minimized. 
     SUMMARY 
     One embodiment of the present invention is a linear actuator including a cylinder, a piston slidably received within the cylinder and defining a piston chamber in the cylinder and a rod chamber in the cylinder, a rod connected to the piston, a plurality of orifices defined within the piston, wherein the plurality of orifices interconnect the piston chamber and the rod chamber, and a sealing member mounted on the rod for movement between a closed position, wherein the sealing member generally blocks the flow of fluid through at least one of the plurality of orifices, and an open position, wherein the sealing member generally does not block the flow through the plurality of orifices. The plurality of orifices includes at least one always-open orifice that is not blocked by the sealing member when the sealing member is in the closed position 
     According to a second embodiment of the present invention, the linear actuator includes a cylinder, a piston slidably received within the cylinder and defining a piston chamber in the cylinder and a rod chamber in the cylinder, a rod connected to the piston, a plurality of orifices defined within the piston, wherein the plurality of orifices fluidly couple the piston chamber to the rod chamber, and a sealing member mounted to the rod for movement between an open position, wherein the sealing member forms a gap between the piston and the sealing member to generally allow the flow of fluid between the piston chamber and the rod chamber, and a closed position, wherein the sealing member generally blocks the gap, thereby generally blocking the flow of fluid between the piston chamber and the rod chamber. 
     Accordingly, when the piston is forced into the cylinder, such as when a shock load is applied to the actuator, the flow of fluid from the piston chamber to the rod chamber deflects the sealing member such that the orifices extending through the piston gradually open and reduce sharp pressure increases within the piston and rod chambers. The always-open orifice (which may comprise or include a gap between the piston or rod chamber) provides an initial attenuation of the rate of pressure build-up in the piston chamber. Consequently, pressure spikes in the cylinder resulting from a shock load imparted to the actuator are reduced and the acceleration or shock load transmitted from the actuator to the vehicle or supporting structure is minimized. 
     A third embodiment of the present invention provides a hydraulic actuator system including an actuator having a cylinder, a piston slidably received within the cylinder and defining a piston chamber in the cylinder and a rod chamber in the cylinder, a rod connected to the piston, and a plurality of orifices defined within the piston, wherein the plurality of orifices interconnect the piston chamber and the rod chamber, a valve manifold in fluid communication with the piston chamber by a first fluid line and in fluid communication with the rod chamber by a second fluid line, and at least one restriction positioned on at least one of the first fluid line and the second fluid line. 
     Other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram showing a hydraulic system with prior art actuators; 
         FIG. 2  is a schematic diagram of a prior art actuator having a rigid disk; 
         FIG. 3  is a graph showing pressure versus time and external shock loading versus time for a piston chamber and a rod chamber of the prior art actuator shown in  FIG. 2 ; 
         FIG. 4  is a graph of acceleration magnitude versus time for the prior art actuator shown in  FIG. 2 ; 
         FIG. 5A  is a front elevational view, shown in section, of an actuator according to one embodiment of the present invention; 
         FIG. 5B  is a top plan view of a piston of the actuator of  FIG. 5A ; 
         FIG. 6  is a graph showing pressure versus time and external shock loading versus time for a piston chamber and a rod chamber of the prior art actuator shown in  FIG. 5A ; 
         FIG. 7  is a graph of acceleration magnitude versus time for the actuator shown in  FIG. 5A ; 
         FIG. 8A  is a front elevational view, shown in section, of a piston according to a second embodiment of the present invention; 
         FIG. 8B  is a top plan view of the piston of  FIG. 8A ; 
         FIG. 9A  is a front elevational view, shown in section, of a piston according to a third embodiment of the present invention; 
         FIG. 9B  is a top plan view of the piston of  FIG. 9A ; and 
         FIG. 10  is a front elevational view of the actuator of  FIG. 5A  having two restrictions. 
     
    
    
     DETAILED DESCRIPTION 
     As shown in  FIGS. 5A and 5B , the linear actuator of the present invention, generally designated  100 , is of the type typically used in a dynamic body control system. Such systems typically utilize actuators  100  mounted between the wheel assembly and an associated torsion bar. 
     The actuator  100  includes a tube-shaped cylinder  102 , a piston  104  slidably received within the cylinder  102  and a piston rod  106  connected to the piston  104 . The piston  104  divides the cylinder into a piston chamber  108  and a rod chamber  110 . The piston  104  includes a plurality of orifices  112 ,  118 , each of which provides a passage between the piston chamber  108  and the rod chamber  110 . 
     An annular, flexible, deflective disk  114  is mounted on the rod  106  adjacent to the piston  104 . The disk  114  is shaped to cover the orifices  112  when pressed against the piston  104 . The disk  114  includes an opening  116  that is aligned with one of the orifices  118  of the piston  104  and is urged against the piston  104  by a spring washer  120 . The disk  114  is preferably made of steel, but may also be made of other materials (e.g., plastic, rubber, various metals, various polymeric materials and the like). Alternatively, the disk  114  may include more than one opening  116  such that more than one orifice  118  is aligned with the openings  116  in the disk. 
     The valve manifold  122  (which may be solenoid valves  32 ,  34 , as shown in  FIG. 1 ) connects the actuator  100  to the pump  12  through supply lines  30 ,  36 ,  38 . Lines  36 ,  38  are connected to the rod chamber  110  and piston chamber  108 , respectively. 
     As shown in  FIG. 10 , line  36  may include an orifice or restriction  37  for controlling the flow of hydraulic fluid to and from the rod chamber  110  via line  36 . Line  38  may include an orifice or restriction  39  for controlling the flow of hydraulic fluid to and from the piston chamber  108  via line  38 . According to one embodiment of the present invention, restriction  37  restricts the flow of hydraulic fluid from the rod chamber  110  and restriction  39  opens the flow of hydraulic fluid to the piston chamber  108 . For example, restriction  37  may have an internal diameter of about 2 mm and restriction  39  may have an internal diameter of about 6.2 mm. According to a second embodiment of the present invention, restriction  37  opens the flow of hydraulic fluid to/from the rod chamber  110  and restriction  39  restricts the flow of hydraulic fluid to/from the piston chamber  108 . For example, restriction  37  may have an internal diameter of about 2.5 mm and restriction  39  may have an internal diameter of about 1 mm. Accordingly, by adjusting the internal diameters of the restrictions  37 ,  39 , the noise associated with rapid displacement of the piston  104  may be reduced. 
     The advantage of the actuator  100  of the present invention over prior art actuator  86  (see  FIG. 2 ) is shown graphically in  FIGS. 3 ,  4 ,  6  and  7 . In  FIG. 3 , the cyclical load applied to prior art actuator  86  is shown by line A. This load causes sharp pressure spikes in the piston chamber  89 , shown by line B and in the rod chamber  90 , shown by line C. As shown in  FIG. 4 , the acceleration that the actuator  86  transmits to the associated vehicle is shown by line D. As is apparent from  FIG. 4 , the magnitude of the acceleration, and hence the noise transmitted to the vehicle, is relatively high and coincides with the sharp transition in the pressure increase in the piston and rod chambers  89 ,  90 , respectively. 
     As shown in  FIGS. 6 and 7 , a similar cyclical load, shown by line A′ in  FIG. 6 , is applied to the actuator  100  of the present invention and results in a much reduced pressure spike in the piston chamber  108 , shown by line B′, and in the rod chamber  110 , shown by line C′. Furthermore, the transition from a low pressure state to the maximum pressure state is less sharp as a result of the behavior of the actuator  100  of the present invention, resulting in a reduced acceleration transmitted to the associated vehicle, as shown by line D′ in  FIG. 7 . In fact, the high acceleration transmitted by the prior art actuator  86  to the vehicle, shown at point P in  FIG. 4 , is greatly reduced with the linear actuator  100  of the present invention as shown by point P′ in  FIG. 7 . 
     While not limiting the invention to any particular theory, it is believed that the reason for this improved performance is that the flexible disk  114  (in contrast to the rigid disk  91  of the prior art shown in  FIG. 2 ) effects a gradual opening of the orifices  112 ,  118  between the piston chamber  108  and rod chamber  110  in the actuator  100  in those instances in which the piston  104  is compressed in to the cylinder  102 , since the flexible disk deforms or curls away gradually from the piston  104  in response to fluid flowing through orifices. Furthermore, since orifice  118  is aligned with opening  116 , it is constantly open and is not blocked by disk  114  and thus provides a constant flow between piston chamber  108  and rod chamber  110 , which also acts to reduce sharp transitions of pressure in the piston chamber  108  and reduces the pressure spike in the rod chamber  110  at the beginning of the transmission of a shock load to the actuator  100 . 
     The size of the orifices  112 ,  118  will depend upon the relative sizes of the piston  104  and cylinder  102 . The size of orifices  112 ,  118  should be selected such that the pressure drop across the piston  104  is at or between about  100  bar and about  85  bar during a typical compression movement of actuator  100 . According to one embodiment, the pressure drop should be slightly greater than  100  bar during such a compression movement. Accordingly, while there may be some sacrifice in the performance of the actuator, the slight attenuation in performance is more than compensated by the decrease in noise and shock transmitted from the actuator  100  to the associate vehicle. 
     As shown in  FIGS. 8A and 8B , an alternate embodiment of the present invention includes a piston  104 ′ having a plurality of orifices  112 ′ and an annular ridge  150 ′ extending about the periphery of the piston  104 ′ on the rod side  153 ′ of the piston  104 ′. The deflective disk  114 ′ is mounted on the rod  106 ′ such that it forms a gap  156 ′ with the ridge  150 ′ that is normally open when the pressure differential between the piston chamber  108  and rod chamber  110  is less than a certain threshold pressure (e.g., 4 bar). However, if the pressure differential is greater than the threshold pressure (e.g., greater than about 4 bar), then the disk  114 ′ is deflected against the ridge  150 ′, thereby closing the gap  156 ′. For example, the gap  156 ′ may close when the piston  104 ′ is rapidly forced out of the cylinder  102 . When the piston  104 ′ is rapidly forced into the cylinder  102 , the disk  114 ′ may deflect away from the piston  104 ′, thereby opening the gap  156 ′ from its original position (i.e., expanding the gap  156 ′). 
     As shown in  FIGS. 9A and 9B , an alternate embodiment of the invention includes a piston  104 ″ having a plurality of orifices  112 ″,  118 ″ and an annular ridge  150 ″. A disk  114 ″ is mounted on the rod  106 ″ to form a gap  156 ″ between the disk  114 ″ and the piston  104 ″. The disk  114 ″ has one opening or orifice  160 ″ extending therethrough which acts as a constant bypass to allow fluid to flow across the disk  114 ″ even when the disk is deflected against the ridge  150 ″. The orifice  160 ″ may align with an orifice  118 ″ in the piston  104 ″ to facilitate fluid flow. A disk  114 ″ having more than one orifice  160 ″ is within the scope of the present invention. 
     Although the invention is shown and described with respect to certain embodiments, it is obvious that equivalents and modifications will occur to those skilled in the art upon reading and understanding the specification. The present invention includes all such equivalents and modifications and is limited only by the scope of the claims.