Abstract:
A pressure intensifier for generating relatively large output force includes a piston driven in an advancing and a retracting direction. The piston provides a relatively large cross-sectional area for a pressurized fluid to act during the retracting stroke. As such, relatively large, heavy, tools may be returned to an elevated position without the use of external force-producing devices.

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
     The present invention relates generally to a force producing apparatus and, more particularly, to an air to oil pressure intensifier for providing relatively large forces to machines such as clamps, grippers, presses and punches. 
     Many systems utilize the basic principle of inserting a rod into an enclosed oil-filled chamber to produce force. One known system injects a large volume of hydraulic fluid behind a working piston to advance a rod into contact with a work piece. The rod is further inserted into a closed chamber to obtain a force multiplication equal to the ratio of the area of working piston to the area of the end of the rod. 
     Because large forces are generated by air to oil intensifiers, the working piston is often attached to a tool which may weigh several hundred pounds or more. Returning heavy tools to an elevated or beginning position has become a significant design challenge. Some devices accomplish the task of returning the tool by using an additional piston powered by air. The piston must be of sufficient diameter to produce the requisite force to lift the tool. Devices incorporating external additional pistons are very costly, difficult to package within work cells having limited space and require special air circuits and controls to operate the multiple piston arrangement. These systems are typically large in length and may only be shortened by stacking the units side by side. 
     Accordingly, it would be beneficial to provide a compact, lightweight pressure intensifier capable of lifting heavy tooling without the use of an external assist cylinder. 
     A device minimizing the need for external valving and circuit controllers required for operation would also be of benefit. 
     The present invention provides a pressure intensifier for providing relatively large output forces using an air or hydraulic force amplification system. According to one aspect of the present invention, a rod is driven into a sealed chamber of substantially incompressible fluid to generate an output force. 
     According to another aspect of the present invention, a compact, lightweight pressure intensifier capable of lifting heavy tooling with the use of an external assist cylinder is provided. According to another aspect of the present invention, a first piston is selectively driven by a fluid power source to retract the piston from a previously force-intensified position. 
     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
     FIG. 1 is a perspective view of a pressure intensifier according to the principles of the present invention; 
     FIG. 2 is an exploded perspective view of the pressure intensifier shown in FIG. 1; 
     FIG. 3 is an enlarged perspective view of the encircled area of FIG. 2; 
     FIG. 4 is an enlarged perspective view of the encircled area of FIG. 2; 
     FIG. 5 is an enlarged perspective view of the encircled area of FIG. 2; 
     FIG. 6 is a cross-sectional view of the pressure intensifier taken along line  6 — 6  of FIG. 1; 
     FIG. 7 is an end view of the pressure intensifier of the present invention; 
     FIG. 8 is a cross-sectional view of the pressure intensifier taken along line  8 — 8  of FIG. 7; 
     FIG. 9 is a cross-sectional view of the pressure intensifier taken along line  9 — 9  of FIG. 7; 
     FIG. 10 is a cross-sectional view of the pressure intensifier having the first piston positioned in a fully retracted position; 
     FIG. 11 is a cross-sectional view of the pressure intensifier showing the first piston positioned in an intermediate position; and 
     FIG. 12 is a cross-sectional view of the pressure intensifier showing the first piston in an advanced position. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference to FIGS. 1 and 2, an air to oil pressure intensifier constructed in accordance with the teachings of the present invention is identified at reference numeral  10 . Pressure intensifier  10  functions to provide a relatively large output force at a driven end using only compressed air at relatively low pressure (80 to 120 psi) as the power source. Typically, the driven end of the pressure intensifier is coupled to tooling such as a clamp half, a rivet hammer or a punch, collectively identified as a tool  12 . 
     Pressure intensifier  10  operates by extending and retracting a ram  14  to place tool  12  into engagement with a work piece  16 . As will be described in greater detail hereinafter, pressure intensifier  10  operates to rapidly translate tool  12  toward work piece  16  using relatively low force. Once tool  12  contacts work piece  16 , pressure intensifier  10  generates a greatly multiplied force between tool  12  and work piece  16 . On the return stroke, a piston with a relatively large working area within pressure intensifier  10  is pressurized to lift the heaving tooling in preparation for the next work cycle. 
     Pressure intensifier  10  includes a substantially cylindrical hollow front cylinder  18  coupled to a substantially cylindrical hollow rear cylinder  20 . An end cap  22  closes one of the open ends of rear cylinder  20 . 
     As shown in FIGS. 3,  8  and  9 , a divider assembly  24  and a bulkhead assembly  26  divide the interior volume of pressure intensifier  10  into a first cavity  28 , a second cavity  30  and a third cavity  32 . Divider assembly  24  includes a divider  36 , a high pressure seal  38 , a seal retainer  40 , a retaining ring  41 , a front seal  42  and a rear seal  44 . 
     Divider  36  is a generally hollow cylindrical member having a series of stepped cylindrical portions along its outside diameter as well as along its inside diameter. Specifically, divider  36  includes a first external groove  46  and a second external groove  48  for receipt of front seal  42  and rear seal  44 , respectively. As best shown in FIGS. 8 and 9, divider  36  includes a front face  50 , a rear face  52  and a passageway  54  extending therebetween. Passageway  54  includes a series of stepped portions  56  shaped to complement high pressure seal  38 , seal retainer  40  and retaining ring  41 . Accordingly, high pressure seal  38  is captured between divider  36  and retaining ring  41 . Divider  36  is coupled to front cylinder  18  with an external thread  58 . 
     Bulkhead assembly  26  (FIG. 4) includes a bulkhead  60 , a front seal  62 , a rear seal  64 , a front retaining ring  66 , a rear retaining ring  68 , a shaft seal  70  and an oil chamber cushioning seal  72 . Bulkhead  60  is a substantially cylindrical member having a front face  74  and a rear face  76 . Bulkhead  60  includes a passageway  78  extending from front face  74  to rear face  76 . Passageway  78  of bulkhead  60  includes a counterbore  79  having oil chamber cushioning seal  72  positioned therein. Bulkhead  60  includes an outer surface  80 . A first port  82  (FIG. 9) extends through bulkhead  60  from outer surface  80  to counterbore  79 . A first fitting  84  is coupled to first port  82  to allow pressurized fluid to enter and exit first cavity  28 . A passageway  85  interconnects counterbore  79  and first cavity  28 . An orifice  86  is inserted within passageway  85  to restrict air from exiting first cavity  28  at a rapid rate, thereby acting as a damper against impact. 
     A second port  87  (FIG. 8) extends from outer surface  80  through bulkhead  60  and exits at front face  74 . Accordingly, a second fitting  88  is coupled to second port  87  to allow pressurized fluid to enter and exit second cavity  30 . Rear cylinder  20  includes an aperture  90  to allow first fitting  84  and second fitting  88  to access bulkhead  60 . 
     Pressure intensifier  10  includes a first piston assembly  92 , a second piston assembly  94  and a third piston assembly  96 . First piston assembly  92  is positioned within first cavity  28 . First piston assembly  92  is free to move axially within first cavity  28  from a retracted position shown in FIG. 10 to an advanced position shown in FIG.  12 . 
     First piston assembly  92  (FIG. 5) includes a first piston  98 , a seal  100  and a pair of shocks  102 . First piston  98  is a generally cylindrically-shaped member including a body  104 , a front face  106 , a rear face  108  and an outer surface  110 . A front trunion  112  extends from front face  106 . A rear trunion  114  extends axially from rear face  108 . Front trunion  112  includes an outer cylindrical surface  116 . Rear trunion  114  includes an outer cylindrical surface  118 . 
     Front face  106  includes an annular groove  120  sized to receive one of shocks  102 . Similarly, rear face  108  includes an annular groove  122  sized to receive another shock  102 . Shocks  102  dampen the impact forces generated as first piston assembly  92  approaches end cap  22  or bulkhead  60 . Outer surface  110  includes an annular groove  124  for receipt of seal  100 . Seal  100  is positioned between body  104  and rear cylinder  20  to capture fluid within first cavity  28  on either side of seal  100 . 
     Second piston assembly  94  (FIG. 4) includes a generally cylindrically-shaped piston  126  having a front face  128 , a rear face  130  and an outer surface  132 . Outer surface  132  includes a pair of spaced apart circumferential grooves  134  sized for receipt of a pair of seals  136 . Outer surface  132  includes a retention groove  138  positioned between grooves  134  for capturing a ring  140 . Preferably, ring  140  is constructed from a material capable of maintaining a magnetic charge. Piston  126  includes a substantially cylindrical bore  142  extending from front face  128  to rear face  130 . Bore  142  includes a pair of seal grooves  144  for receipt of a pair of shaft seals  146 . 
     Second piston assembly  94  is free to axially move within second cavity  30  to the extent divider assembly  24  and bulkhead assembly  26  allow. It should be appreciated that a portion  148  (FIG. 8) of second cavity  30  defined between rear face  130  of second piston  126  and front face  74  of bulkhead  60  contains a compressible fluid such as air. Second port  87  provides a conduit for supplying compressed air to portion  148  of second cavity  30 . 
     Another portion  150  of second cavity  30  is defined by front face  128  of second piston  126  and rear face  52  of divider  36 . Second portion  150  of second cavity  30  contains an incompressible fluid such as oil. Oil is also contained within the captured volume of third cavity  32  and third piston assembly  96 . 
     Third piston assembly  96  (FIG. 3) includes a third piston  152 , a ram  14 , a cylinder seal  156 , a ram seal  158  and a ram wiper  160 . Third piston  152  is a generally cylindrically-shaped member having a front face  162 , a rear face  164  and a stepped bore  166  extending therethrough. Cylinder seal  156  is positioned within a groove  168  located on an outer surface  170  of third piston  152 . 
     Ram  14  is an elongated cylindrical member having a first end  172  and a second end  174 . A pressure chamber  176  is formed within ram  14  and is shaped as a blind bore entering from second end  174 . Ram seal  158  is positioned between ram  14  and third piston  152  to contain pressurized fluid within pressure chamber  176 . Ram wiper  160  provides a line of defense from contaminants within the work environment. Ram wiper  160  is positioned at a front end  177  of front cylinder  18  in contact with ram  14 . 
     A rod  178  (FIGS. 2 and 4) includes a first end  180  and a second end  182 . First end  180  is coupled to first piston  98  via a fastener  184 . Rod  178  extends through passageway  78  of bulkhead assembly  26 , bore  142  of second piston  126 , passageway  54  of divider  36  and stepped bore  166  of third piston  152 . A washer  186  is positioned within pressure chamber  176  and coupled to the second end  182  of rod  178  with a threaded fastener  188 . 
     Rod  178  includes a generally cylindrical body portion  190  having a first diameter and a generally cylindrical necked portion  192  having a diameter less than the diameter of body portion  190 . Flats  194  are placed along the length of rod  178  to assist with the assembly of components. 
     To assemble pressure intensifier  10 , first piston assembly  92 , second piston assembly  94 , third piston assembly  96 , divider assembly  24  and bulkhead assembly  26  are positioned within front cylinder  18  and rear cylinder  20  as depicted in the Figures. Front cylinder  18  is coupled to rear cylinder  20  using a retention mechanism  196  best depicted in FIGS. 2,  6  and  9 . Retention mechanism  196  includes a pair of lobes  198  radially extending from a cylindrical surface  200  located at a rear end  202  of front cylinder  18 . Cylindrical surface  200  includes a groove  204  for receipt of a housing seal  206 . 
     The complimentary portion of retention mechanism  196  is located at a front end  208  of rear cylinder  20 . Front end  208  includes a lip  210  interrupted by two recesses  212  located 180 degrees apart from one another. Recesses  212  are shaped to compliment the profile of lobes  198 . A slot  214  is positioned rearward of lip  210  and is sized to accept lobes  198  therewithin. 
     To couple front cylinder  18  to rear cylinder  20 , lobes  198  are aligned with recesses  212  and the cylinders are moved toward one another. At this time, lobes  198  are positioned within slot  214 . Front cylinder  18  is then rotated relative to rear cylinder  20  ninety degrees to trap lobes  198  within slot  214 , as shown in FIG. 6. A pair of set screws  216  interconnect front cylinder  18  with rear cylinder  20  and prevent inadvertent rotation of the cylinders relative to one another during operation of pressure intensifier  10 . 
     With reference to FIGS. 5 and 8, end cap  22  includes a generally cylindrical body  218 , a flange  220  and a bore  222  extending into body  218 . Bore  222  is sized for receipt of rear trunion  114  of first piston  98  when first piston  98  is in the fully retracted position. A piston seal  226  is positioned within bore  222  and contacts outer cylindrical surface  118  when first piston assembly  92  is in the retracted position. An inlet port  228  inwardly extends from a rear face  230  in communication with bore  222  and first cavity  28 . Inlet port  228  is also in communication with a passageway  236  extending from bore  222  to a front face  237  of end cap  22 . An orifice screw  238  is positioned within passageway  236  to limit the volumetric flow rate of air attempting to escape first cavity  28  as rear trunion  114  enters bore  222  during retraction of first piston assembly  92 . Therefore, impact loading of first piston  98  against end cap  22  is avoided. 
     End cap  22  is coupled to rear cylinder  20  using a retention mechanism  240  similar to the retention mechanism used to couple front cylinder  18  to rear cylinder  20 . Specifically, end cap  22  includes a pair of lobes  242  extending radially therefrom. Lobes  242  cooperate with a lip  244  to resist axial separation forces generated by pressurized fluid within the cavities. 
     Recesses (not shown) extend through lip  244 . A slot  248  is positioned behind lip  244  to retain lobes  242 . A pair of set screws  250  interconnects end cap  22  and rear cylinder  20  to prevent rotation of lobes  242  within slot  248 . An end cap seal  252  is positioned within a groove  254  of end cap  22  to prevent compressed air from escaping first cavity  28 . 
     With reference to FIGS. 10-12, operation of pressure intensifier  10  will now be described. FIG. 10 depicts first piston assembly  92  in the retracted position. At this time first port  82  is pressurized with compressed air at approximately 80 psi. Second port  87  and inlet port  228  are vented to atmosphere. It should be noted that second piston assembly  94  is in a retracted position having rear face  130  contacting front face  74  of bulkhead  60 . Additionally, third piston assembly  96  is in a fully retracted position having rear face  164  of third piston  152  positioned adjacent front face  50  of divider  36 . 
     To initiate movement of ram  14  in the advanced direction, first port  82  and inlet port  228  are vented to atmosphere during a first phase of actuation. Second port  87  is energized with pressurized air at approximately 80 psi. During the first phase of actuation, ram  14  is extended rapidly using relatively low force to cause tool  12  to contact work piece  16 . The input pressure at second port  87  causes second piston  126  to axially move from right to left as shown in the Figures. As second piston  126  moves, the incompressible fluid located within portion  150  of second cavity  30  passes by necked portion  192  of rod  178  through passageway  54  of divider  36  causing third piston assembly  96  to move axially toward the extended position. Because rod  178  is coupled to third piston  96  via threaded fastener  184 , rod  178  and first piston  98  translate to the position shown in FIG.  11 . 
     At the end of phase one, necked portion  192  of rod  178  has fully traversed the area of divider assembly  24  including high pressure seal  38 . As body portion  190  of rod  178  enters high pressure seal  38 , a high pressure chamber  256  and a low pressure chamber  258  are formed. Hydraulic fluid may no longer freely flow through passageway  54 . 
     A pressure valve  260  senses pressure at second port  87 . Pressure valve  260  is plumbed in communication with a switching valve  262  which controls the condition of first port  82 , second port  87  and inlet port  228 . Each of the ports may be placed in a pressurized condition being supplied with approximately 80 psi or a vented condition allowing pressurized fluid to escape to atmosphere. 
     Once pressure valve  260  senses a pressure indicating that ram  14  has extended to cause tool  12  to contact work piece  16 , switching valve  262  directs pressure intensifier  10  to commence phase two of the actuation. During phase two, pressurized air is supplied to second port  87  and inlet port  228  while first port  82  is instructed to remain vented to atmosphere. Pressure acting on rear face  108  of first piston  98  causes first piston  98  to translate to the advanced position shown in FIG.  12 . Because body portion  190  of rod  178  is engaged with high pressure seal  38 , entry of rod  178  within high pressure chamber  256  causes a very large force amplification due to the incompressibility of the fluid located within the high pressure chamber. A pressure gauge  263  is plumbed in communication with high pressure chamber  256  to provide an operator a visual indication of the hydraulic pressure generated during operation of pressure intensifier  10 . 
     A timer valve  264  is plumbed in communication with switching valve  262 . Timer valve  264  operates to assure that the intensified pressure reaches a maximum before switching valve  262  acts to retract ram  14 . Once a predetermined time has elapsed for maximum pressure to be reached within high pressure chamber  256 , timer valve  264  signals switching valve  262  to retract ram  14 . At this time, second port  87  and inlet port  228  are vented to atmosphere while an 80 psi compressed air source is coupled to first port  82 . 
     Pressurized fluid entering first port  82  acts on front face  106  of first piston  98  to generate a relatively large lifting force during retraction of ram  14 . A large force may be produced because the area on which the pressurized fluid acts includes the entire cross-sectional area of first cavity  28  minus the relatively small cross-sectional area of rod  178 . Accordingly, heavy equipment such as tool  12  may be lifted without assistance from external booster cylinders or other load lifting devices. 
     During retraction of rod  178 , necked portion  192  clears high pressure seal  38  allowing washer  186  and threaded fastener  188  to axially displace third piston assembly  96  in the retracted direction. Oil passes from third cavity  32  to second cavity  30  through passageway  54 . The transfer of fluid causes second piston assembly  94  to move in the retracted direction as well. First piston assembly  92  and rod  178  continue to retract until rear face  108  of first piston  98  contacts end cap  22 . At this time, pressure intensifier  10  is in position to begin another actuation cycle. 
     It should be appreciated that any number of input signals may be used to start a given pressure intensifier sequence. For example, a typical two palm valve anti-repeat circuit  266  including an emergency stop valve may be implemented. An electrical system having an output fluid start-up may also be used. Alternatively, the start signal and control system may include electrically operated solenoid valves. 
     Pressure intensifier  10  includes an oil level detection system  268  including a reed switch  270 , a light emitting diode  272 , a battery  274  and magnetic ring  140 . If the incompressible liquid level within second cavity  30  becomes low, magnetic ring  140  comes within sensing proximity of reed switch  270 . Reed switch  270  closes causing electrical current from battery  274  to power light emitting diode  272 . Accordingly, light emitting diode  272  provides an operator with a visual indication of low liquid level prior to pressure intensifier  10  becoming ineffective.