Patent Publication Number: US-9840000-B2

Title: Hydraulic hammer having variable stroke control

Description:
TECHNICAL FIELD 
     The present disclosure is directed to a hydraulic hammer and, more particularly, to a hydraulic hammer having variable stroke control. 
     BACKGROUND 
     Hydraulic hammers can be attached to various machines such as excavators, backhoes, tool carriers, or other like machines for the purpose of milling stone, concrete, and other construction materials. The hydraulic hammer is mounted to a boom of the machine and connected to a hydraulic system. High pressure fluid in the hydraulic system is supplied to the hammer to drive a reciprocating piston in contact with a work tool, which in turn causes the work tool to reciprocate while in contact with the construction material. 
     Typical hydraulic hammers drive the reciprocating piston to contact the work tool with the same continuous stroke. In other words, a stroke length of the reciprocating piston does not change during operation of the hammer. However, some hydraulic hammers are capable of changing the stroke length (e.g., between shorter and longer strokes), which can provide more efficiency in some hammer operations. 
     An exemplary system for changing the stroke length of a hydraulic hammer is disclosed in U.S. Pat. No. 5,669,281 (the &#39;281 patent) that issued to Comarmond on Sep. 23, 1997. Specifically, the &#39;281 patent discloses a percussive machine having a piston that slides in a cylinder and strikes a tool during each cycle. The percussive machine also has a top chamber and a bottom chamber which are fed sequentially with fluid through a distributor controlled by a control device. The percussive machine further includes a selector piston mounted in the cylinder. The selector piston may be controlled by the control device with pressurized fluid to shift the selector piston in and out of a position that lengthens the stroke of the piston. 
     Although the percussive machine of the &#39;281 patent may be adequate for some applications, it may still be less than optimal. In particular, the percussive machine of the &#39;281 patent may be overly complex and require many additional parts. As a result, retrofitting existing hydraulic hammers with one continuous stroke to have an adjustable stroke would be difficult to achieve with the percussive machine of the &#39;281 patent. In addition, the percussive machine of the &#39;281 patent operates initially in a short stroke mode and is later switched to long stroke mode after a period of operation. In some instances, however, it may be desirable to start in the long stroke mode initially to increase the efficiency of the hammer operation. 
     The disclosed system is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art. 
     SUMMARY 
     In one aspect, the present disclosure is directed to a variable stroke control system for a hydraulic hammer. The variable stroke control system may include an inlet groove formed around a piston associated with the hydraulic hammer and configured to receive pressurized fluid, and an outlet groove formed around the piston associated with the hydraulic hammer and configured to discharge the pressurized fluid. The variable stroke control system may further include a valve in fluid communication with the inlet groove and the outlet groove, and configured to selectively adjust a stroke length of the piston based on a change in pressure differential between the inlet groove and the outlet groove. 
     In another aspect, the present disclosure is directed to a variable stroke control system for a hydraulic hammer. The variable stroke control system may include an inlet groove formed around a piston associated with the hydraulic hammer and configured to receive pressurized fluid, and an outlet groove formed around the piston associated with the hydraulic hammer and configured to discharge the pressurized fluid. The variable stroke control system may further include a valve in fluid communication with the inlet groove and the outlet groove, and configured to selectively adjust a stroke length of the piston based on a hardness of a material impacted by a work tool of the hydraulic hammer. An initial stroke of the piston may be longer than a subsequent stroke of the piston. 
     In yet another aspect, the present disclosure is directed to a hydraulic hammer system. The hydraulic hammer system may include a piston, and a sleeve disposed external and co-axial to the piston. The hydraulic hammer system may also include an inlet groove formed at a first internal surface of the sleeve and configured to receive pressurized fluid from a pump, and an outlet groove formed at a second internal surface of the sleeve and configured to direct pressurized fluid to a return tank. The outlet groove may be fluidly connected to the inlet groove. The hydraulic hammer system may further include a first valve configured to control a transition timing between upward and downward movements of the piston, and a second valve in fluid communication with the inlet groove and the outlet groove, and configured to selectively adjust a stroke length of the piston by delaying a transition timing of the first valve. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a pictorial illustration of an exemplary disclosed machine; 
         FIG. 2  is an exploded view of an exemplary disclosed hydraulic hammer assembly that may be used with the machine of  FIG. 1 ; and 
         FIG. 3  is a schematic illustration of an exemplary disclosed variable stroke control system that may be used with the hydraulic hammer of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates an exemplary disclosed machine  10  having a hammer  12 . Machine  10  may be configured to perform work associated with a particular industry such as, for example, mining or construction. Machine  10  may be a backhoe loader (shown in  FIG. 1 ), an excavator, a skid steer loader, or any other machine. Hammer  12  may be pivotally connected to machine  10  through a boom  14  and a stick  16 . However, it is contemplated that another linkage arrangement may alternatively be utilized, if desired. 
     In the disclosed embodiment, one or more hydraulic cylinders  18  may raise, lower, and/or swing boom  14  and stick  16  to correspondingly raise, lower, and/or swing hammer  12 . The hydraulic cylinders  18  may be connected to a hydraulic supply system (not shown) within machine  10 . Specifically, machine  10  may include a pump (not shown) connected to hydraulic cylinders  18  and to hammer  12  through one or more hydraulic supply lines (not shown). The hydraulic supply system may introduce pressurized fluid, for example oil, from the pump into the hydraulic cylinders  18  and hammer  12 . Operator controls for movement of hydraulic cylinders  18  and/or hammer  12  may be located within a cabin  20  of machine  10 . 
     As shown in  FIGS. 1 and 2 , hammer  12  may include an outer shell  22  and an actuator assembly  26  located within outer shell  22 . Outer shell  22  may connect actuator assembly  26  to stick  16  and provide protection for actuator assembly  26 . A work tool  24  may be operatively connected to an end of actuator assembly  26  opposite stick  16 . It is contemplated that work tool  24  may include any known tool capable of interacting with hammer  12 . In one embodiment, work tool  24  includes a chisel bit. 
     As shown in  FIG. 2 , actuator assembly  26  may include a subhousing  28 , a bushing  30 , and an impact system  32 . Subhousing  28  may include, among other things, a frame  34  and a head  36 . Frame  34  may be a hollow cylindrical body having one or more flanges or steps along its axial length. Head  36  may cap off one end of frame  34 . Specifically, one or more flanges on head  36  may couple with one or more flanges on frame  34  to provide a sealing engagement. One or more fastening mechanisms  38  may rigidly attach head  36  to frame  34 . In some embodiments, fastening mechanisms  38  may include, for example, screws, nuts, bolts, or any other means capable of securing the two components. Additionally, frame  34  and head  36  may each include holes to receive fastening mechanisms  38 . 
     Bushing  30  may be disposed within a tool end of subhousing  28  and may be configured to connect work tool  24  to impact system  32 . A pin  40  may connect bushing  30  to work tool  24 . When displaced by hammer  12 , work tool  24  may be configured to move a predetermined axial distance within bushing  30 . 
     Impact system  32  may be disposed within an actuator end of subhousing  28  and be configured to move work tool  24  when supplied with pressurized fluid. As shown by the dotted lines in  FIG. 2 , impact system  32  may be an assembly including a piston  42 , an accumulator membrane  44 , a sleeve  46 , a sleeve liner  48 , a valve  50 , and a seal carrier  52 . Sleeve liner  48  may be assembled within accumulator membrane  44 , sleeve  46  may be assembled within sleeve liner  48 , and piston  42  may be assembled within sleeve  46 . All of these components may be generally co-axial with each other. In addition, piston  42 , sleeve  46 , valve  50 , and seal carrier  52  may all be held together as a sub-assembly by way of slip-fit radial tolerances. For example, slip-fit radial tolerances may be formed between sleeve  46  and piston  42 , and between seal carrier  52  and piston  42 . Sleeve  46  may apply an inward radial pressure on piston  42 , and seal carrier  52  may apply an inward radial pressure on piston  42 . Such a configuration may hold sleeve  46 , seal carrier  52 , and piston  42  together as a sub-assembly. 
     Accumulator membrane  44  may form a cylindrical tube configured to hold a sufficient amount of pressurized fluid for hammer  12  to drive piston  42  through at least one stroke. Accumulator membrane  44  may be radially spaced apart from sleeve  46  when accumulator membrane  44  is in a relaxed state (i.e. not under pressure from pressurized gas). However, when accumulator membrane  44  is under pressure from the pressurized gas, no spacing may exist between accumulator membrane  44  and sleeve  46 , and fluid flow therebetween may be inhibited. 
     Valve  50  may be assembled over an end of piston  42  and located radially inward of both sleeve  46  and seal carrier  52 . A portion of seal carrier  52  may axially overlap with sleeve  46 . Additionally, valve  50  may be disposed axially external to accumulator membrane  44 . Valve  50  and seal carrier  52  may be located entirely within head  36 . Accumulator membrane  44 , sleeve  46 , and sleeve liner  48  may be located within frame  34 . Head  36  may be configured to close off an end of sleeve  46  when connected to frame  34 . 
     Piston  42  may be configured to slide within both frame  34  and head  36 . For example, piston  42  may be configured to reciprocate within frame  34  and contact an end of work tool  24 . Specifically, a compressible gas (e.g., nitrogen gas) may be disposed in a gas chamber (not shown) located within head  36  at an end of piston  42  opposite bushing  30 . Piston  42  may be slideably moveable within the gas chamber to increase and decrease the size of the gas chamber. A decrease in size of the gas chamber may increase the gas pressure within the gas chamber, thereby driving piston  42  downward to contact work tool  24 . 
     Piston  42  may comprise varying diameters along its length, for example one or more narrow diameter sections disposed axially between wider diameter sections. In the disclosed embodiment, piston  42  includes three narrow diameter sections  54 ,  56 ,  58 , separated by two wide diameter sections  60 ,  62 . Narrow diameter sections  54 ,  56 ,  58  may cooperate with sleeve  46  to selectively open and close fluid pathways within sleeve  46 . Piston  42  may further include an impact end  64  having a smaller diameter than any of narrow diameter sections  54 ,  56 ,  58 . Impact end  64  may be configured to contact work tool  24  within bushing  30 . 
     As shown in  FIG. 3 , hammer  12  may be equipped with a variable stroke control system  70 . Variable stroke control system  70  may include one or more components configured to direct pressurized fluid within hammer  12  to selectively adjust a stroke length of piston  42 . For example, variable stroke control system  70  may include a pump  66 , an annular lift groove  68 , an annular switch groove  72 , an annular tank groove  74 , an annular outlet groove  76 , an accumulator  78 , a pressure control valve  80 , a return tank  82 , and a main control valve  84 . 
     Pump  66  may be configured to pressurize and direct fluid to lift groove  68  and accumulator  78 . Lift groove  68  may be configured to direct fluid to contact a shoulder at wide diameter section  60  in order to force piston  42  in an upward direction. Switch groove  72  may be configured to fluidly communicate with main control valve  84  to switch a valve position of main control valve  84 . Tank groove  74  and outlet groove  76  may be configured to direct the pressurized fluid to tank  82 . Lift groove  68 , switch groove  72 , tank groove  74 , and outlet groove  76  may all be formed as concentrically arranged passages around piston  42 . Movement of piston  42  (i.e., of narrow diameter sections  54 ,  56 ,  58  and wide diameter sections  60 ,  62 ) may selectively open or close the grooves to cause movement of piston  42 . 
     Accumulator  78  may be fluidly connected to pump  66  and configured to accumulate pressurized fluid and control pulsations of the fluid within the hydraulic circuit. Pressure control valve  80  may be fluidly connected to tank  82  and configured to regulate a flow rate of fluid that is returned to tank  82 , such that a pressure within the hydraulic circuit is controlled to a desired level. Accumulator  78  and pressure control valve  80  may work together to control pulsations and pressures within the hydraulic circuit. In some embodiments, pressure control valve  80  may also cause piston  42  to return to an uppermost position within sleeve  46  when a hammer operation has stopped. In particular, pressure control valve may cause a pressure at outlet groove  76  to decrease, such that a pressure at lift groove  68  is greater than a pressure at outlet groove  76 , causing piston  42  to move to the uppermost position. As a result, piston  42  may always start a new hammer operation with a longer initial stroke of piston  42 . Without pressure control valve  80 , the piston  42  would return to a position lower than the uppermost position, which would result in a smaller initial stroke of piston  42 . 
     Main control valve  84  may be disposed between pump  66  and tank  82 , and configured to control transition timing between movements of piston  42 . In particular, main control valve  84  may control when piston  42  transitions between upward and downward movements. Main control valve  84  may include a valve element movable between two distinct positions. When the valve element is in the first position (right-most position shown in  FIG. 3 ), outlet groove  76  may be fluidly connected to tank  82 . When the valve element is in the second position (left-most position shown in  FIG. 3 ), outlet groove  76  may be fluidly connected to pump  66 . The valve element may move between the first and second positions depending on a pressure level within the switch groove  72 . Specifically, when the pressure level within the switch groove  72  is below a threshold amount, the valve element may be forced to the first position. Alternatively, when the pressure level within the switch groove  72  is greater than the threshold amount, the valve element may be forced to the second position. 
     As shown in  FIG. 3 , variable stroke control system  70  may also include a stroke control valve  86  configured to selectively adjust a stroke length of piston  42  based on a pressure differential between lift groove  68  and outlet groove  76 . Stroke control valve  86  may be disposed in a switching passage fluidly connecting main control valve  84  and tank  82 . Stroke control valve  86  may include a movable valve element  88  and a spring  90 . Valve element  88  may be configured to move between a flow blocking position (e.g., closed position) and a flow passing position (e.g., open position) in response to the pressure differential between lift groove  68  and outlet groove  76 . Specifically, when the pressure differential is below a threshold amount, valve element  88  may be forced to the flow passing position. Alternatively, when the pressure differential is greater than the threshold amount, valve element  88  may be forced to the flow blocking position. Spring  90  may bias valve element  88  to the flow blocking position. The threshold pressure differential may be indicative of a hardness of a construction material impacted by work tool  24 . 
     In some embodiments, variable stroke control system  70  may further include a first orifice  92 , a first check valve  94 , a second orifice  98 , and a second check valve  97 . Orifice  92  may be disposed in a passage between outlet groove  76  and tank  82 , and configured to reduce a mass flow rate of fluid flowing therethrough. Check valve  94  may be disposed in a passage between outlet groove  76  and orifice  92 , and configured to provide a unidirectional flow from outlet groove  76  to orifice  92 . Orifice  98  may be disposed in a passage between check valve  94  and main control valve  84 , and configured to reduce a mass flow rate of fluid flowing therethrough. Check valve  97  may also be disposed in the passage between check valve  94  and main control valve  84 , and configured to provide a unidirectional flow from check valve  94  to main control valve  84 . It is contemplated that hydraulic hammer  12  may include other orifices, valves, grooves, and/or other components in addition to those included in variable stroke control system  70 , as desired. 
     INDUSTRIAL APPLICABILITY 
     The disclosed variable stroke control system may be used in any hydraulic hammer application. In particular, the disclosed variable stroke control system may automatically adjust a stroke length of a piston of the hydraulic hammer based on a pressure differential between a pressurized fluid inlet and a pressurized fluid outlet. More specifically, the stroke length of the piston may be adjusted based on a hardness of a construction material impacted by the hydraulic hammer. Operation of hammer  12  will now be described in detail. 
     Referring to  FIG. 3 , an operator request may be made to begin operation of hammer  12  via, for example, an operator valve  96 . After the request is made, pump  66  may direct pressurized fluid, for example pressurized oil, into lift groove  68  and accumulator  78 . A sufficient amount of oil within lift groove  68  may apply an upward pressure on piston  42 . Specifically, the oil within lift groove  68  may apply pressure to the shoulder of wide diameter section  60  and bias piston  42  upward. 
     Movement of piston  42  upward may open switch groove  72 . Specifically, movement of piston  42  upward may correspondingly move narrow diameter section  54  to a location adjacent to switch groove  72 . While switch groove  72  is uncovered, pressurized fluid may flow from inlet groove  68  into switch groove  72 , thereby increasing the pressure level at switch groove  72  and causing main control valve  84  to be switched from the first position (right-most position shown in  FIG. 3 ) to the second position (left-most position shown in  FIG. 3 ). Subsequently, pressurized fluid from pump  66  may be allowed to flow through main control valve  84  and towards outlet groove  76 . 
     As pressurized fluid flows from pump  66  through main control valve  84  and towards outlet groove  76 , movement of piston  42  upwards may also cause narrow diameter section  58  to reduce the size of the gas chamber. This reduction in size may further pressurize nitrogen gas within the gas chamber, thereby biasing piston  42  downward. Such biasing may increase the pressure downward on piston  42 , causing piston  42  to accelerate downward and contact work tool  24 , which in turn causes work tool  24  to accelerate downward and impact a construction material. 
     At an impacting position (as shown in  FIG. 3 ), switch groove  72  may be in fluid communication with tank groove  74 , which decreases the pressure level at switch groove  72  and causes main control valve  84  to be switched back to the first position (right-most position shown in  FIG. 3 ). The impact with the construction material may then cause piston  42  to accelerate upwards. The acceleration of piston  42  may vary depending on a hardness of the construction material. For example, impacting a harder construction material may cause piston  42  to have a higher acceleration upwards, while impacting a softer construction material may cause piston  42  to have a lower acceleration upwards. This acceleration of piston  42  may result in a change in pressure differential between lift groove  68  and outlet groove  76 . The pressure differential may also be indicative of the hardness of the construction material. For example, impacting a harder construction material may result in a greater pressure differential between lift groove  68  and outlet groove  76 , while impacting a softer construction material may result in a smaller pressure differential between lift groove  68  and outlet groove  76 . In one embodiment, work tool  24  may penetrate through a surface of a harder construction material by only about 0.5 to 1.0 mm, while work tool  24  may penetrate through a surface of a softer construction material by about 10 mm. 
     When work tool  24  contacts a harder construction material, the pressure differential threshold may be exceeded, and valve element  88  of stroke control valve  86  may be forced to the flow blocking position. In this position, flow through the switching passage between main control valve  84  and tank  82  may be blocked. As a result, this may delay a switching operation of main control valve  84 . In particular, as piston  42  accelerates upwards, main control valve  84  may take longer to switch from the first position (right-most position shown in  FIG. 3 ) to the second position (left-most position shown in  FIG. 3 ). This may allow piston  42  to move further upwards than normal operation, resulting in a longer stroke of piston  42  that provides higher impact energy and lower frequency. 
     When work tool  24  contacts a softer construction material, the pressure differential threshold may not be exceeded, and valve element  88  of stroke control valve  86  may remain in the flow passing position. In this position, flow through the switching passage between main control valve  84  and tank  82  may be allow, and the switching operation of main control valve  84  operates normally. When main control valve  84  switches from the first position (right-most position shown in  FIG. 3 ) to the second position (left-most position shown in  FIG. 3 ), this may result in a shorter stroke of piston  42  than when work tool  24  contacts a harder construction material. The shorter stroke may provide lower impact energy and higher frequency. It is contemplated that the impact energy may also be varied with a pressure regulated by pressure control valve  80 . In some embodiments, pressure control valve  80  may cause the hydraulic circuit to have higher pressure when operating with shorter strokes of piston  42 . 
     Piston  42  may continue to reciprocate up and down in shorter or longer strokes in response to the hardness of the construction material impacted. Because of the simplified operation of stroke control valve  86 , piston  42  can easily switch between longer and shorter strokes. After operation of hammer  12  has stopped (i.e., operator control valve  96  is no longer engaged), piston control valve  80  may cause a pressure at outlet groove  76  to decrease, such that a pressure at lift groove  68  is greater than a pressure at outlet groove  76 , causing piston  42  to move to the uppermost position within sleeve  46 . As a result, any new operation of hammer  12  will start with a longer initial stroke of piston  42 . 
     The present disclosure may provide an variable stroke control for a hydraulic hammer that includes a stroke control valve that selectively delays a transition timing of a main control valve to allow the hydraulic hammer to switch between shorter and longer strokes. The use of the stroke control valve may simplify a variable stroke control operation and be suitable for retrofitting hydraulic hammers having non-variable stroke control. In addition, by utilizing a pressure control valve, the stroke control valve may be capable of starting the hammer operation with a long stroke. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the system of the present disclosure. Other embodiments of the system will be apparent to those skilled in the art from consideration of the specification and practice of the method and system disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents.