Patent Publication Number: US-6988564-B2

Title: Diesel hammer systems and methods

Description:
RELATED APPLICATIONS 
   This is a continuation of U.S. patent application Ser. No. 10/124,201 filed Apr. 16, 2002, now U.S. Pat. No. 6,736,218, which claims priority of U.S. Provisional Patent Application Ser. No. 60/284,180, which was filed on Apr. 16, 2001. 

   TECHNICAL FIELD 
   The present invention relates to methods and apparatus for inserting elongate members into the earth and, more particularly, to diesel hammers that create pile driving forces by combusting diesel fuel. 
   BACKGROUND OF THE INVENTION 
   For certain construction projects, elongate members such as piles, anchor members, caissons, and mandrels for inserting wick drain material must be placed into the earth. It is well-known that such rigid members may often be driven into the earth without prior excavation. The term “piles” will be used herein to refer to the elongate rigid members typically driven into the earth. 
   One system for driving piles is conventionally referred to as a diesel ram for driving the pile and as a piston for compressing diesel fuel. Diesel fuel is injected into a combustion chamber below the ram member as the ram member drops. The dropping ram member engages an anvil member that transfers the load of the ram member to the pile to drive the pile. At the same time, the diesel fuel ignites, forcing the ram member and the anvil member in opposite directions. The anvil member further drives the pile, while the ram member begins a new combustion cycle. 
   An important factor in the operation of a diesel hammer is the quantity of diesel fuel injected into the combustion chamber because the ignition of the diesel fuel directly determines the driving forces applied to the pile. In particular, the quantity of diesel fuel determines both the forces on the anvil member both at the point of ignition and, because it affects how high the ram member goes, when the ram member impacts the anvil member on the compression stroke prior to ignition. 
   Conventional diesel hammers employ a variable fuel pump having a fuel chamber, a control pulley, and a control rope. The fuel chamber stores the fuel to be delivered to the combustion chamber. The angular orientation of the control pulley determines the effective volume of the fuel chamber. The control rope extends partly around the control pulley such that pulling on either end of the control rope causes the control pulley to rotate and change its angular orientation. Conventional variable fuel pumps require an operator to stand on the ground adjacent to the diesel hammer and pull the control rope to adjust the effective volume of the fuel chamber. The process of adjusting the amount of fuel delivered to the combustion chamber is thus cumbersome and conventional variable fuel pumps are typically placed in one setting and left there during the driving process. 
   The need thus exists for improved variable fuel pumps for diesel hammers. 
   RELATED ART 
   Submitted herewith are portions of operations manuals for diesel hammers depicting the basic operation of diesel hammers and the fuel pumps used by commercially available diesel hammers. These references employ a control rope and control pulley to change the amount of fuel delivered to the combustion chamber as generally described in the BACKGROUND section of this application. 
   SUMMARY OF THE INVENTION 
   The present invention may be embodied as a diesel hammer system for driving a pile. The diesel hammer system comprises a housing, an anvil member supported by the housing, a clamp assembly adapted to connect the anvil member to the pile, and a ram member disposed within the housing. A fuel pump system injects fuel into a combustion chamber defined by the housing, anvil member, and the ram member. A coupling system detachably engages the ram member to raise the ram member from an impact position to an upper position, the coupling system comprising a trigger member that, when engaged, causes the coupling system to release, the ram member. A trigger projection mounted is on the housing to engage the trigger member to cause the coupling system to release the ram member at the upper position. 
   The diesel hammer further comprises a pre-trigger system comprising a pre-trigger member movable between an extended position and a retracted position. When the pre-trigger member is in the extended position, the pre-trigger member engages the trigger member as the ram member moves from the impact position towards the upper position to cause the coupling system to release the ram member at a pre-trigger position. When the pre-trigger member is in the retracted position, the pre-trigger member does not engage the trigger member as the ram member moves from the impact position to the upper position. 
   When the pre-trigger member is in the retracted position, the ram member moves from the impact position to the upper position and back to the impact position such that the ram member acts on the pump piston through the pump lever to force fuel out of the fuel chamber and into the combustion chamber. When the pre-trigger member is in the extended position, movement of the ram member from the impact position to the pre-trigger position and back to the impact position does not cause fuel to be forced out of the fuel chamber and into the combustion chamber. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIGS. 1A–1E  are somewhat schematic sectional views of a diesel hammer depicting the basic combustion/drive cycle thereof; 
       FIGS. 2–4  are part sectional/part schematic views depicting the operation of prior art variable fuel pumps employed by conventional diesel hammers; 
       FIGS. 5 and 6  are part sectional/part schematic views depicting the operation of a variable fuel pump constructed in accordance with the principles of the present invention; and 
       FIGS. 7–9  are part sectional/part schematic views depicting the operation of exemplary control systems used by the variable fuel pump of  FIGS. 5 and 6 ; 
       FIG. 10  is a part sectional/part schematic view depicting yet another prior art variable fuel pump system; 
       FIG. 11  is a somewhat schematic front elevation view of the prior art fuel pump of  FIGS. 2–4 ; 
       FIG. 12  is a somewhat schematic front elevation view of an exemplary housing that may be used with a fuel pump of the present invention; 
       FIGS. 13A–F  are somewhat schematic section views of yet another exemplary diesel hammer of the present invention; and 
       FIG. 14  is a somewhat schematic section view of still another exemplary diesel hammer of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The first section of the following discussion will describe the basic construction and operation of diesel hammer pile driving systems. The next section will contain will be a more detailed discussion of prior art variable fuel pumps. The following section will contain a discussion of the variable fuel pump of the present invention. 
   I. Construction and Operation of Conventional Diesel Hammer 
   Turning to the drawing, depicted at  20  in  FIGS. 1A–1E  is a diesel hammer system that may use a variable fuel pump constructed in accordance with, and embodying, the principles of the present invention. The diesel hammer system  20  is designed to insert a pile  22  into the ground. The diesel hammer system  20  will include a spotter, crane, or other equipment as necessary to hold the hammer system  20  in a desired orientation with respect to the ground. Such structural components of the hammer system  20  are conventional and will not be described herein. 
   The diesel hammer system  20  comprises a ram member  30 , an anvil member  32 , a housing member  34 , a clamp assembly  36 , and a fuel pump system  38 . The ram member  30  is guided by the housing member  34  for movement between a lower position ( FIG. 1B ) and an upper position ( FIG. 1D ). The anvil member  32  is guided by the housing member  34  for movement between a rest position ( FIG. 1A ) and an impact position ( FIG. 1B ). The anvil member  32  is rigidly connected to the clamp assembly  36 . The clamp assembly  36  is detachably fixed relative to the pile  22 . 
   A combustion chamber  40  is formed within the housing member  34  between a lower surface  42  of the ram member  30  and an upper surface  44  of the anvil member  32 . Seals  50  and  52  are arranged in gaps  54  and  56  between an inner surface  46  of the housing member  34  and the ram and anvil members  30  and  32 , respectively. When the seals  50  and  52  function properly, fluid is substantially prevented from flowing out of the combustion chamber  40  through these gaps  54  and  56 . 
   A fuel port  60  and an exhaust port  62  are formed in the housing member  34 . The fuel port  60  is arranged to allow the fuel pump system  38  to inject fuel into the combustion chamber  40 . The exhaust port  62  is arranged to allow exhaust gasses to be expelled from the combustion chamber  40  and to allow air to be drawn into the chamber  40 . 
   The fuel pump system  38  comprises a pump lever  70 . The pump lever  70  is biased into a ready position in which at least a portion of the pump lever  70  is within the housing member  34  ( FIGS. 1D and 1E ). When the ram member  30  drops below a trigger point A, the ram member  30  engages the pump lever  70  and moves the pump lever  70  from the ready position into a pump position ( FIGS. 1A–1C ). Forcing the pump lever  70  from the ready position into the pump position causes diesel fuel to be injected into the combustion chamber  40  through the fuel port  60 . 
   The diesel hammer system  20  operates in a combustion cycle that will now be described with reference to  FIG. 1 . Referring initially to  FIG. 1A , the hammer system  20  is shown in a pump state in which the ram member  30  is dropping and has forced the pump lever  70  from the ready position ( FIGS. 1D and 1F ) into the pump position ( FIGS. 1A–1C ). When the pump lever is forced from the ready position into the pump position, diesel fuel is injected as shown at  72  through the fuel port  60  into the combustion chamber  40  where it is mixed with air. 
   As the combustion cycle continues, the ram member  30  drops to a level where both the fuel port  60  and exhaust port  62  are covered by the ram member  30 . At this point, the combustion chamber  40  is effectively sealed, and continued dropping of the ram member  30  compresses the air/fuel mixture within the combustion chamber  40 . 
   Referring now to  FIG. 1B , the hammer system  20  is shown in an impact state in which the lower surface  42  of the ram member  30  contacts the upper surface  44  of the anvil member  32 . In the impact state, the ram member  30  drives the anvil member  32  towards the pile  22  relative to the housing member  34  as shown by a comparison of  FIGS. 1A and 1B . The anvil member  32  thus drives the pile  22  downward through the clamp assembly  36 . In addition, the housing member  34  will immediately fall onto the anvil member  32 , thereby applying additional driving forces onto the pile member  22 . 
   When the system  20  is in the impact state, the diesel fuel within the combustion chamber  40  ignites in the highly compressed air. The explosion resulting from the ignition of the air/fuel mixture forces the ram member  30  up and the anvil member  32  down. This explosion thus further drives the pile member  22  into the ground. 
   After the ignition occurs, the anvil member  32  is raised to an upper position as shown in  FIG. 1C . As the anvil member  32  moves into the upper position, the lower end of the ram member  30  passes the fuel and exhaust ports  60  and  62 . Expanding exhaust gasses are thus forced out of the combustion chamber  40  through the exhaust port  62 . 
   As the ram member continues on to its upper position, fresh air is drawn into the combustion chamber  40  through the exhaust port  62 . In addition, the ram member  30  disengages from the pump lever  70 . As soon as the ram member  30  disengages from the pump lever, the bias on the pump lever  70  returns the pump lever  70  to the ready position from the pump position and the fuel system  38  readies another quantity of fuel for the next cycle. 
   After the ram member  30  reaches the upper position as shown in  FIG. 1D , the ram member  30  is allowed to drop again. The system  20  then enters a pre-injection state as shown in  FIG. 1E . In the pre-injection state, the combustion chamber  40  is filled with fresh air and the fuel pump system  38  is primed to deliver another quantity of fuel. As the ram member  30  continues to drop, the system  20  enters the pump state as described with reference to  FIG. 1A  and the cycle begins again. 
   Referring now to  FIGS. 2–4 , depicted at  120  therein is a prior art variable fuel pump system that may be used as the fuel pump system  38  described above. In particular, the fuel pump system  120  comprises a source  122  of fuel, a fuel pump cylinder assembly  124 , a fuel pump lever  126 , and a travel limiting assembly  128 . The pump lever  126  is used as the pump lever  70  described above. 
   The fuel pump cylinder assembly  124  comprises a fuel pump housing  130 , a piston  132 , and a pump spring  134 . The fuel pump housing  130  defines a longitudinal axis B. The piston  132  comprises a piston head  140  and a piston shaft  142 . The axis of the piston shaft  142  is aligned with the housing axis B such that the piston  132  moves along the housing axis B. 
   The fuel pump housing  130  defines a fuel pump chamber  150 , and the piston head  140  divides the fuel pump chamber  150  into a fuel portion  152  and a reserve portion  154 . A seal (not shown) prevents the flow of fluid between the fuel portion  152  and reserve portion  154 . 
   The fuel source  122  is connected through a first conduit  160  to the fuel portion  152  of the fuel pump chamber  150 . A first check valve  162  arranged in the first conduit  160  allows fluid to flow only from the source  122  to the fuel pump chamber  150 . The fuel portion  152  of the fuel pump chamber  150  is also connected by a second conduit  164  to the fuel port  60  in the housing member  34 . A second check valve  166  arranged in the second conduit  164  allows fluid to flow only from the fuel pump chamber  150  to the fuel port  60 . 
   A spring landing  170  is formed on the fuel pump housing  130 , and a spring retainer  172  is formed on the piston shaft  142 . The pump spring  134  is a compression spring arranged between the spring landing  170  and the spring retainer  172 . The pump spring  134  thus biases the spring retainer  172  away from the spring landing  170 . 
   The fuel pump lever  126  is pivotably connected at one end to a pivot point  174  on the housing member  34 . The pump lever  126  thus rotates between the ready ( FIGS. 2 and 3 ) and pump ( FIG. 3 ) positions relative to the housing member  34 . The other end of the fuel pump lever  126  held against the piston shaft  142  by the travel limiting assembly  128  as will be described in detail below. 
   Accordingly, rotational movement of the fuel pump lever  126  about the pivot point  174  is translated into displacement of the piston  132  along the housing axis B. In particular, clockwise rotation of the fuel pump lever  126  causes the pump head  140  to move within the pump chamber  150  to decrease the volume of the fuel portion  152  thereof, while counter-clockwise rotation of the fuel pump lever  126  allows the pump spring  134  to move the pump head  140  in the opposite direction, thereby increasing the volume of the fuel portion  152  of the pump chamber  150 . The pump spring  134  thus assists movement of the fuel pump lever  126  in the clockwise direction and opposes movement of the fuel pump lever  126  in the counter-clockwise direction. 
   A comparison of  FIGS. 2 and 3  shows that the descending ram member  30  engages the pump lever  126  to rotate this lever in the counter-clockwise direction against the force of the pump spring  134 . As shown in  FIG. 2 , the descending ram member  30  thus indirectly forces any fluid within the fuel portion  152  of the pump chamber  150  out of the pump chamber  150  and into the combustion chamber  40  through the fuel port  60 . 
   Further, as shown in  FIG. 3 , when the ram member  30  moves above the pump lever  126 , the pump lever  126  returns to the ready position under the force of the pump spring  134 . The movement of the piston head  140  as the pump lever  134  returns to the ready position draws fuel from the fuel source  122  to refill the fuel portion  152  of the pump chamber  150 . 
   The amount of fuel delivered by the variable fuel pump system  120  is determined by the volume of the fuel portion  152  of the pump chamber  150 . The travel limiting assembly  128  is used to adjust the angular position of the pump lever  126  when the lever  126  is in the ready position. Because the pump lever  126  is connected to the piston  132  as described above, the travel limiting assembly  128  thus determines the volume of the fuel portion  152 . 
   The travel limiting assembly  128  comprises a link arm  180 , a link spring  182 , a cam member  184 , a cam roller  186 , a control pulley  188 , and a control rope  190 . The cam member  184  rotates about a cam axis C. The control pulley  188  is attached to the cam member  184  such that rotation of the pulley  188  causes rotation of the cam member  184  about the cam axis C. The control rope  190  engages the control pulley  188  such that pulling on either end of the control rope  190  causes the control pulley  188  to rotate, which in turn causes the cam member  184  to rotate about the cam axis C. 
   The cam member  184  is eccentric such that the distance between a cam surface  192  and the cam axis C varies from a first location  194  to a second location  196  on the cam surface  192 . The cam roller  186  rides on the cam surface  192  such that the distance between the cam roller  186  and the cam axis C varies with angular rotation of the cam member  184 . The cam axis C is fixed relative to the housing member  34 ; therefor, rotation of the cam member  184  causes the cam roller  186  to move relative to the housing member  34 . 
   The link arm  180  is rigidly connected to the pump lever  126  such that the link arm  180  also rotates about the pivot point  174 . The link arm  180  is arranged to apply a force on the cam roller  186  that holds the cam roller  186  against the cam surface  192 , with the link spring  182  in compression between the link arm  180  and the cam roller  186 . 
   A comparison of  FIGS. 2 and 4  shows that the angular orientation of the cam member  184  determines the angular location of the pump lever  126 . With the cam member  184  in a first angular orientation as shown in  FIG. 2 , the cam roller  186  engages the first location  194  on the cam surface  192 . With the cam member  184  in a second angular orientation as shown in  FIG. 4 , the cam roller  186  engages the second location  196  on the cam surface  192 . 
   The cam roller  186  in turn acts through the link spring  182  and link arm  180  to place the pump lever  126  in a first angular location ( FIG. 2 ) or a second angular location ( FIG. 4 ). As described above, the angular location of the pump lever  126  determines the location of the piston head  142  within the pump chamber  150  and thus the volume of the fuel portion  152  thereof. 
   The angular position of the cam member  184  thus determines the volume of the fuel portion  152  of the pump chamber  150  when the pump lever  126  is in the ready position; this relationship can be seen by comparing  FIGS. 2 and 4 . 
   As described above, pulling the ends of the control rope  190  determines the angular position of the cam member  184 ; the control rope  190  can thus be used to set the volume of the fuel portion  152  of the pump chamber  150 . 
   Referring now to  FIG. 11 , depicted therein is a schematic view of a housing  200  of the conventional variable fuel pump system  120  described above. The housing  200  has a face  202  on which is formed indicia  204  corresponding to angular positions of the cam member  184 . An indicator  206  is rigidly fixed in a predetermined relationship to the cam member  184 . The indicator  206  is located outside of the housing  200 . As the cam member  184  rotates, the indicator  206  also rotates; the position of the indicator  206  can thus be compared with the indicia on the housing face  202  to determine the location of the cam member  184 . The operator can thus determine the location of the cam member  184 , and thus the amount of fuel to be injected by the fuel pump system  120 , by comparing the location of the indicator  206  with the indicia  204 . 
   Referring now to  FIG. 10 , depicted at  210  therein is a modification to the variable fuel pump system  120  described above. The modification  210  eliminates the cam member  184 , cam roller  186 , control pulley  188 , and control rope  190  of the travel limiting assembly  128  described above. Instead, the modification  210  comprises an actuator assembly  212  that is connected to the link arm  180  through the link spring  182 . The actuator assembly  212  comprises a fixed housing  214  and a shaft member  216 . The actuator assembly  212  is operated to extend the shaft member  216  out of or retract the shaft member  216  into the housing  214 . Operation of the actuator assembly  212  thus can change the effective volume of fuel pump chamber  150 . However, the operator on the ground is provided with no visual feedback indicating the volume of the fuel pump chamber  150 . Accordingly, while some commercial diesel hammers incorporate the modification  210 , this modification  210  has thus not been generally adopted for use on variable fuel pump systems for diesel hammers. 
   II. Remote Controlled Variable Fuel Pump 
   Referring now to  FIGS. 4–8 ; depicted at  220  therein is a variable fuel pump system constructed in accordance with, and embodying, the principles of the present invention. The variable fuel pump system  220  may be used as the fuel pump system  38  described above. 
   The fuel pump system  220  comprises a source  222  of fuel, a fuel pump cylinder assembly  224 , a fuel pump lever  226 , and a travel limiting assembly  228 . The pump lever  126  is used as the pump lever  70  described above. The fuel pump cylinder assembly  224  comprises a fuel pump housing  230 , a piston  232 , and a pump spring  234 . The fuel pump housing  230  defines a longitudinal axis B. The piston  232  comprises a piston head  240  and a piston shaft  242 . The axis of the piston shaft  242  is aligned with the housing axis B such that the piston  232  moves along the housing axis B. 
   The fuel pump housing  230  defines a fuel pump chamber  250 , and the piston head  240  divides the fuel pump chamber  250  into a fuel portion  252  and a reserve portion  254 . A seal (not shown) prevents the flow of fluid between the fuel portion  252  and reserve portion  254 . 
   The fuel source  222  is connected through a first conduit  260  to the fuel portion  252  of the fuel pump chamber  250 . A first check valve  262  arranged in the first conduit  260  allows fluid to flow only from the source  222  to the fuel pump chamber  250 . The fuel portion  252  of the fuel pump chamber  250  is also connected by a second conduit  264  to the fuel port  60  in the housing member  34 . A second check valve  266  arranged in the second conduit  264  allows fluid to flow only from the fuel pump chamber  250  to the fuel port  60 . 
   A spring landing  270  is formed on the fuel pump housing  230 , and a spring retainer  272  is formed on the piston shaft  242 . The pump spring  234  is a compression spring arranged between the spring landing  270  and the spring retainer  272 . The pump spring  234  thus biases the spring retainer  272  away from the spring landing  270 . 
   The fuel pump lever  226  is pivotably connected at one end to a pivot point  274  on the housing member  34 . The pump lever  226  thus rotates between the ready ( FIGS. 2 and 3 ) and pump ( FIG. 3 ) positions relative to the housing member  34 . The other end of the fuel pump lever  226  held against the piston shaft  242  by the travel limiting assembly  228  as will be described in detail below. 
   Accordingly, rotational movement of the fuel pump lever  226  about the pivot point  274  is translated into displacement of the piston  232  along the housing axis B. In particular, clockwise rotation of the fuel pump lever  226  causes the pump head  240  to move within the pump chamber  250  to decrease the volume of the fuel portion  252  thereof, while counter-clockwise rotation of the fuel pump lever  226  allows the pump spring  234  to move the pump head  240  in the opposite direction, thereby increasing the volume of the fuel portion  252  of the pump chamber  250 . The pump spring  234  thus assists movement of the fuel pump lever  226  in the clockwise direction and opposes movement of the fuel pump lever  226  in the counter-clockwise direction. 
   A comparison of  FIGS. 2 and 3  shows that the descending ram member  30  engages the pump lever  226  to rotate this lever in the counter-clockwise direction against the force of the pump spring  234 . As shown in  FIG. 2 , the descending ram member  30  thus indirectly forces any fluid within the fuel portion  252  of the pump chamber  250  out of the pump chamber  250  and into the combustion chamber  40  through the fuel port  60 . 
   Further, as shown in  FIG. 3 , when the ram member  30  moves above the pump lever  226 , the pump lever  226  returns to the ready position under the force of the pump spring  234 . The movement of the piston head  240  as the pump lever  234  returns to the ready position draws fuel from the fuel source  222  to refill the fuel portion  252  of the pump chamber  250 . 
   The amount of fuel delivered by the variable fuel pump system  220  is determined by the volume of the fuel portion  252  of the pump chamber  250 . The travel limiting assembly  228  is used to adjust the angular position of the pump lever  226  when the lever  226  is in the ready position. Because the pump lever  226  is connected to the piston  232  as described above, the travel limiting assembly  228  thus determines the volume of the fuel portion  252 . 
   The travel limiting assembly  228  comprises a link arm  280 , a link spring  282 , a cam member  284 , a cam roller  286 , a control pinion  288 , and a control rack assembly  290 . The cam member  284  rotates about a cam axis C. The control pinion  288  is attached to the cam member  284  such that rotation of the pulley  288  causes rotation of the cam member  284  about the cam axis C. The control rack assembly  290  engages the control pinion  288  to cause the control pinion  288  to rotate, which in turn causes the cam member  284  to rotate about the cam axis C. 
   The cam member  284  is eccentric such that the distance between a cam surface  292  and the cam axis C varies from a first location  294  to a second location  296  on the cam surface  292 . The cam roller  286  rides on the cam surface  292  such that the distance between the cam roller  286  and the cam axis C varies with angular rotation of the cam member  284 . The cam axis C is fixed relative to the housing member  34 ; therefor, rotation of the cam member  284  causes the cam roller  286  to move relative to the housing member  34 . 
   The link arm  280  is rigidly connected to the pump lever  226  such that the link arm  280  also rotates about the pivot point  274 . The link arm  280  is arranged to apply a force on the cam roller  286  that holds the cam roller  286  against the cam surface  292 , with the link spring  282  in compression between the link arm  280  and the cam roller  286 . 
   A comparison of  FIGS. 2 and 4  shows that the angular orientation of the cam member  284  determines the angular location of the pump lever  226 . With the cam member  284  in a first angular orientation as shown in  FIG. 2 , the cam roller  286  engages the first location  294  on the cam surface  292 . With the cam member  284  in a second angular orientation as shown in  FIG. 4 , the cam roller  286  engages the second location  296  on the cam surface  292 . 
   The cam roller  286  in turn acts through the link spring  282  and link arm  280  to place the pump lever  226  in a first angular location ( FIG. 2 ) or a second angular location ( FIG. 4 ). As described above, the angular location of the pump lever  226  determines the location of the piston head  242  within the pump chamber  250  and thus the volume of the fuel portion  252  thereof. 
   The angular position of the cam member  284  thus determines the volume of the fuel portion  252  of the pump chamber  250  when the pump lever  226  is in the ready position; this relationship can be seen by comparing  FIGS. 2 and 4 . 
   The control rack assembly  290  comprises a control rack  320  and a control cylinder assembly  322 . 
   The control cylinder assembly  322  comprises a control cylinder housing  330  and a control piston  332  having a control piston head  334  and a control piston shaft  336 . The control piston head  334  is arranged within the cylinder housing  330  to divide a control chamber  338  defined by the housing  330  into first and second portions  340  and  342 . The application of hydraulic fluid to one or both of the control chamber portions  340  and  342  causes linear displacement of the control rack  320  along a path D. 
   The control rack  320  comprises a toothed surface portion  344 , and the control pinion  288  comprises a toothed surface portion  346 . The teeth on the surface portions  344  and  346  are designed to mate with each other. In addition, the control rack  320  is supported adjacent to the control pinion  288  such that these surfaces portions  340  and  342  engage each other. Accordingly, linear displacement of the control rack  320  along the path D causes rotation of the control pinion  288  about the cam axis C. Because the control pinion  288  is attached to the cam member  284 , the rotation of the control pinion  288  causes rotation of the cam member  284 . 
   Accordingly, the travel limiting assembly  228  allows the volume of the fuel portion  252  of the pump chamber  250  to be changed remotely by the appropriate application of hydraulic fluid to the cylinder assembly  322 . A comparison of  FIGS. 5 and 6  illustrates that the location of the control piston  332  corresponds to different volumes of the pump chamber fuel portion  252 . 
   Referring now to  FIG. 7 , depicted at  350  therein is a first embodiment of a control cylinder assembly that may be used as the control cylinder assembly  322  of the travel limiting assembly  228  of the present invention. 
   The control cylinder assembly  350  comprises first and second ports  352  and  354  that allow hydraulic fluid to be introduced into the first and second control chamber portions  340  and  342 , respectively. In particular, introducing fluid into the first control chamber portion  340  while allowing fluid to flow out of the second control chamber portion  342  causes the control piston  332  to move in a first direction along the axis D. Introducing fluid into the second control chamber portion  342  while allowing fluid to flow out of the first control chamber portion  340  causes the control piston  332  to move in a second (opposite) direction along the axis D. The conduits and hydraulic controls required to apply fluid to the first and second ports  352  and  354  are conventional and will not be described herein in detail. 
   Referring now to  FIG. 8 , depicted at  360  therein is a second embodiment of a control cylinder assembly that may be used as the control cylinder assembly  322  of the travel limiting assembly  228  of the present invention. 
   The control cylinder assembly  360  comprises a port  362  that allows hydraulic fluid to be introduced into the first control chamber portion  340 . In addition, a return spring  364  is arranged in the second control chamber portion  342  to oppose movement of the control piston  332  in a first direction along the axis D. Hydraulic fluid is introduced into the first control chamber portion  340  to cause the control piston  332  to move in the first direction along the axis D to a desired position. As long as a predetermined level of hydraulic pressure is maintained in the first control chamber portion  340 , the control piston  332  will remain in the desired position. Releasing pressure within the first control chamber portion  340  allows the return spring  364  to move the control piston in a second (opposite) direction along the axis D. The conduits and hydraulic controls required to apply fluid to the first port  362  are conventional and will not be described herein in detail. 
   Referring now to  FIG. 9 , depicted at  370  therein is a second embodiment of a control cylinder assembly that may be used as the control cylinder assembly  322  of the travel limiting assembly  228  of the present invention. 
   The control cylinder assembly  370  comprises a port  372  that allows hydraulic fluid to be introduced into the first control chamber portion  340 . In addition, a return spring  374  is arranged to engage the control rack  322  to oppose movement of the control piston  332  in a first direction along the axis D. Hydraulic fluid is introduced into the first control chamber portion  340  to cause the control piston  332  to move against the force of the spring  374  in the first direction along the axis D to a desired position. As long as a predetermined level of hydraulic pressure is maintained in the first control chamber portion  340 , the control piston  332  will remain in the desired position. Releasing pressure within the first control chamber portion  340  allows the return spring  374  to move the control piston in a second (opposite) direction along the axis D. The conduits and hydraulic controls required to apply fluid to the first port  372  are conventional and will not be described herein in detail. 
   In any of the control cylinder assemblies  350 ,  360 , and  370 , the hydraulic fluid may be applied to the control ports from a location remote from the location of the hammer system  20 . For example, an operator of the crane or other equipment that supports the hammer system  20  may be provided with a lever or button that may be pulled or depressed to apply hydraulic fluid to these control ports as described above. The operator need not be physically adjacent to the hammer system  20  to vary the amount of fuel required, so the operator is more likely to adjust the fuel setting as required by a particular situation. Referring now to  FIG. 12 , depicted therein is a schematic view of an exemplary housing  420  that may be used to enclose the variable fuel pump system  220  described above. The housing  420  comprises a face  422  on which is formed indicia  424  corresponding to angular positions of the cam member  284 . In one form of the invention, an indicator  426  is rigidly fixed in a predetermined relationship to the cam member  284 . The indicator  426  is located outside of the housing  420 . As the cam member  284  rotates, the indicator  426  also rotates; the position of the indicator  426  can thus be compared with the indicia on the housing face  422  to determine the location of the cam member  284 . The operator can thus determine the location of the cam member  284 , and thus the amount of fuel to be injected by the fuel pump system  220 , by comparing the location of the indicator  426  with the indicia  424 . 
   Referring now to  FIG. 11 , depicted therein is a schematic view of a housing  200  of the conventional variable fuel pump system  120  described above. The housing  200  has a face  202  on which are formed indicia  204  corresponding to angular positions of the cam member  184 . An indicator  206  is rigidly fixed in a predetermined relationship to the cam member  184 . The indicator  206  is located outside of the housing  200 . As the cam member  184  rotates, the indicator  206  also rotates; the position of the indicator  206  can thus be compared with the indicia on the housing face  202  to determine the location of the cam member  184 . The operator can thus determine the location of the cam member  184 , and thus the amount of fuel to be injected by the fuel pump system  120 , by comparing the location of the indicator  206  with the indicia  204 . 
   III. Pre-trigger System 
   Referring now to  FIGS. 13A–F , these figures illustrate that the diesel hammer system  20  conventionally comprises a line  430  from which is suspended a coupling assembly  432 . The coupling assembly  432  is detachably attached to an upper end of the ram member  30 . Accordingly, lifting the line  430  lifts the ram member  30 . In addition, the coupling assembly  434  conventionally comprises a trigger member  434  that, when properly displaced, detaches the coupling assembly  432  from the ram member  30 . The coupling assembly  432  comprises a trigger projection  436  that extends from the housing member  34  to engage the trigger member  434  and release the ram member  30  from the coupling assembly  434 . The coupling assembly  432  is conventional and will not be described herein in detail. 
   Conventionally, the trigger projection  436  is located to engage the trigger member  434  and cause the coupling assembly  434  to release the ram member  30  after the ram member  30  has disengaged from the pump lever  70  and allowed the pump lever  70  to return to its ready position. In this case, the location of the trigger projection  436  ensures that fuel is injected into the fuel chamber  40  each time the line  430  is raised and the ram member  30  dropped. 
   In some situations, however, it is desirable to use the diesel hammer system  20  in a mode in which energy is applied to the pile  22  solely from the weight of the ram member  30  and not from the ignition of the fuel in the combustion chamber  40 . 
   As shown in  FIGS. 13A–F , the diesel hammer system  20  depicted therein comprises a pre-trigger system  450  that allows the diesel hammer system  20  to operate in a conventional ignition mode and in a ram mode. The pre-trigger system  450  comprises a pre-trigger member  452  mounted on the housing member  34 . The pre-trigger member  452  is movable relative to the housing member  34  between a retracted position ( FIGS. 13D–F ) and an extended position ( FIGS. 13A–C ). 
   When the pre-trigger member  452  is in the retracted position, the diesel hammer system  20  incorporating the pre-trigger system  450  operates in a conventional ignition mode. As shown in  FIG. 13D , the ram member  30  starts in the impact state; the ram member  30  is subsequently raised to an upper position as shown in  FIG. 13E  in which the pump lever  70  is in the ready position. Then, as shown in  FIG. 13F , the trigger projection  436  engages the trigger member  434  to cause the coupling assembly  434  to release the ram member  30 , thereby allowing the ram member  30  to drop back into the impact position. Fuel is injected into the fuel chamber  40  when the ram member  30  engages the pump lever  70  as the ram member  30  moves towards into the impact position. In the ignition mode, both the impact of the ram member  30  and the ignition of the fuel drive the anvil member  32 . 
   When the pre-trigger member  452  is in the extended position as shown in  FIGS. 13A–C , the pre-trigger member  452  engages the trigger member  434  before the trigger member  434  reaches the trigger projection  436 . More specifically, the pre-trigger member  452  is arranged such that, as shown in  FIG. 13B , the pre-trigger member  452  engages the trigger member  434  to release ram member  30  before the pump lever  70  has a chance to move into the ready position. Because the pump lever  70  never reaches the ready position, no fuel is injected into the combustion chamber before the ram member  30  strikes the anvil member  32  as shown at  FIG. 13C . Accordingly, when the pre-trigger member  452  is in the extended position, the forces applied to the anvil member  32  are primarily due to the weight of the ram member  30  and not to the combustion of fuel within the combustion chamber  40 . 
   The pre-trigger member  452  may be hand operated or, more conveniently, may be remotely operated by a hydraulic, pneumatic, or electrical actuator. 
   A diesel hammer system incorporating the pre-trigger system  450  may thus operate as a diesel hammer and as a conventional drop hammer. The user of such a diesel hammer system thus has more options when driving the piles  22  than with either a conventional diesel hammer system or a conventional drop hammer system. 
   Referring now to  FIG. 14 , depicted at  460  therein is a housing extension member that may be used in connection with the diesel hammer system  20  described above. The housing extension member  460  extends from the housing member  34  of the system  20 . The ram member  30  extends at least partly into the extension member  460  when the ram member  30  is in its upper position. The extension member  460  inhibits entry of dirt and other debris into the housing  34 . Preferably, one or more slots such as slots  464  and  466  are formed in the extension member  460  to allow the user on the ground to see the travel of the ram member  34  as it is raised and lowered. 
   From the foregoing, it should be clear that the present invention may be embodied in forms other than those described above. The above-described systems are therefore to be considered in all respects illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than the foregoing description. All changes that come within the meaning and scope of the claims are intended to be embraced therein.