Abstract:
A control system for a heavy duty hydraulic hammer reduces blank firing of the hammer. The control system provides a reduced flow of hydraulic fluid to the hammer for a selected period of time upon actuation of the hammer and then provides full hydraulic flow increasing the frequency of impacts to full rated values.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a control system for use with heavy duty hydraulic hammers of the type mountable on the boom of construction equipment. More particularly, the present invention provides a control system allowing one to start a heavy duty hydraulic hammer at a reduced impact frequency which is automatically increased to full power after a preselected delay. 
     Heavy duty hydraulic hammers are well known and used frequently in demolition, mining and construction tasks. These hammers are often mounted at the end of the stick or boom of an excavator. They are supplied with hydraulic fluid under pressure which causes a piston within the hammer to reciprocate, striking a tool, such as a chisel point, which impacts against a workpiece. The piston is forced up by hydraulic fluid with its end compressing gas in a gas chamber. When the piston completes its upward movement, the high pressure fluid is exhausted and the compressed gas drives the piston into the tool. A set amount of hydraulic fluid is required for each upward stroke of the piston. 
     Heavy duty hydraulic hammers come in various sizes. Smaller units weigh several hundred pounds while larger units can weigh more than 15,000 pounds. These hammers use tool sizes commensurate with their own size and have a rated power capacity commensurate with their size. Hydraulic hammers are used to break up concrete, rock, ore, and the like. 
     Hydraulic hammers are available from a number of sources commercially. Their design and operation are described in numerous patents including U.S. Pat. No. 3,872,934 to Terada; U.S. Pat. No. 4,034,817 to Okada; U.S. Pat. No. 4,852,664 to Terada; and, U.S. Pat. No. 4,945,998 to Yamanaka. 
     One type of hydraulic hammer generally comprises a housing containing a piston, a cylinder and a gas chamber at the top of the cylinder. The piston is driven upwardly by hydraulic fluid compressing gas in the gas chamber. When the piston reaches the top of its stroke, the fluid is exhausted and high gas pressure in the gas chamber forcefully moves the piston downwardly. The piston strikes a tool held in the hammer which in turn strikes a workpiece. The power supplied by the high pressure hydraulic fluid is expended in impacting on the workpiece. The impact frequency, the number of impacts per minute, of a hydraulic hammer can be several hundred or several thousand impacts per minute. Each impact involves significant amounts of energy. 
     While hydraulic hammers generally operate well, problems still exist. When a hammer is operated with the tool not in contact with a workpiece, significant amounts of energy must be absorbed by the hammer itself. Energy is being supplied by the high pressure hydraulic fluid but is not being absorbed by the workpiece. Therefore, significant amounts of energy are absorbed within the hammer, heating it and potentially damaging it. Similar problems occur when the hammer tool is only lightly in contact with a workpiece or in glancing contact with a workpiece. In such situations, the tool is not fully impacting upon a workpiece capable of absorbing energy. Energy is absorbed in the hammer to its detriment. This situation is so common it has a name. Hammers operating when not engaged against a workpiece are often said to be blank firing. 
     SUMMARY OF THE INVENTION 
     Applicant has found that a significant portion of blank firing occurs within the first several seconds of hammer actuation. Thus, blank firing often occurs when a hammer is first positioned on a workpiece and the hammer either slides off resulting in blank firing or quickly breaks the workpiece resulting in blank firing. Often, several impact in a glancing or lightly engaged mode are required before the hammer tool can dig into and grip a workpiece sufficient to supply adequate back pressure to load a hammer. If done at full frequency, the hammer is hard to control and will bounce of a workpiece before it can engage it and grip it. 
     In accordance with the present invention, a control system for a heavy duty hydraulic hammer is provided in which the hammer may be operated in a low frequency, or slow mode, for a selected initial period whenever the hammer is actuated. 
     Yet further in accordance with the invention, the initial period of low frequency operation is selectable by an operator in an excavator cab by means of a hand operated control. 
     Still further in accordance with the invention, a mode switch is provided in the control system allowing an operator to select the low frequency start feature or a constant low frequency operation setting. 
     Yet further in accordance with the invention, a control system is provided which selectively provides hydraulic fluid flow to a heavy duty hydraulic hammer at a rate considerably reduced from its normal operating rate whereby low frequency operation is achieved. 
     Still further in accordance with the invention, an electro-hydraulic hammer control system is provided which allows a user to select from the cab of an excavator between an initial low frequency operation for a selected period of time, constant low frequency operation, full power start operation, and no operation at all. 
     It is a principal object of the present invention to provide a control system for a heavy duty hydraulic hammer which minimizes blank firing. 
     It is another object of the present invention to provide a control system for a heavy duty hydraulic hammer which allows an operator to establish a workpiece grip point at low frequency when working on larger, difficult workpieces. 
     It is yet another object of the present invention to provide a control system for a heavy duty hydraulic hammer allowing an operator to select a period of initial low frequency operation prior to automatic full power operation with simple controls and a cab. 
     It is still another object of the present invention to provide a versatile control system for a heavy duty hydraulic hammer which is robust, easy to use, and easy to install into existing excavators. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing objects, and others, will in part be obvious and in part pointed out more fully hereinafter in conjunction with the written description of the preferred embodiments of the invention illustrated in the accompanying drawings in which: 
     FIG. 1 is a schematic drawing of a hydraulic control system in accordance with the present invention; 
     FIG. 2 is a schematic block drawing of the electrical components of the control system, the hydraulic components of which are shown in FIG. 1; 
     FIG. 3 is a schematic block diagram showing a prior art control system; 
     FIG. 4 is a schematic block drawing of an alternate hydraulic control system; and, 
     FIG. 5 is a schematic block drawing of the electrical components of a control system, the hydraulic components of which are shown in FIG.  4 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now in greater detail to the drawings, wherein the showings are made for the purposes of illustrating preferred embodiments of the invention and not for the purposes of limiting the invention, FIG. 3 illustrates a prior art control system  10  for a heavy duty hydraulic hammer  12 . 
     The control system  10  uses components which are specific to controlling a hydraulic hammer  12  and components which are part of the standard equipment of the heavy duty excavator available from companies including Caterpillar and others. 
     An electrical switch  14  is positioned in the operator cab. The switch  14  is normally a momentary contact switch which must be held closed to operate the hammer. It can be a button or lever operated by hand or a foot switch. When the switch  14  is closed by the operator, current is provided to a solenoid  16  forming part of a solenoid operated pressure regulating valve  18 . The valve  18  receives high pressure hydraulic fluid from a pilot pump  22 . The valve  18  has two outputs,  18 B which is unregulated and  18 D which is regulated. Hydraulic fluid is provided at both the unregulated output  18 B and the regulated output  18 D when the switch  14  is closed. The regulated pressure fluid from output  18 D is provided through fluid line  24  to a shuttle he output of the shuttle valve  26  is provided through a fluid line  28  to a variable output main pump  30  at its control input  30 C. The main pump  30  provides working volumes of hydraulic fluid through hydraulic fluid line  32  to an auxiliary valve  36 . The auxiliary valve  36  also has a control input  36   a . The auxiliary valve control input  36   a  is in fluid communication with the output  18 B of the solenoid operated pressure regulating valve  18  through hydraulic fluid line  38 . When the solenoid operated pressure regulating valve  18  is actuated, fluid is provided through the line  38  to the auxiliary valve input  36   a  which causes the valve to allow flow of hydraulic fluid from the working fluid line  32  through the valve  36  through a fluid line  40  to the hammer  12 . 
     The auxiliary valve  36  also has a fluid flow regulating function. The auxiliary valve  36  senses the flow of fluid being delivered through the working fluid line  32  and provides fluid at a pressure indicative of the working fluid flow at an auxiliary valve control output  36 H. The auxiliary valve control output  36 H is connected through a fluid line an input of the shuttle valve  26 . Shuttle valve  26  is thus provided with two control inputs. One from the solenoid operated pressure regulating valve  18  and the second from the auxiliary valve  36 . As is conventional, the shuttle valve allows fluid flow only from the input having a higher pressure to the output to line  28  and to the pump control  30 C. 
     The controls within the auxiliary valve  36  and the connection through the shuttle valve  26  assures that the hammer  12  is provided with hydraulic fluid at rated flow when the switch  14  is closed. 
     The above-described control system is conventional. The auxiliary valves and pumps are commercially available products often forming part of an excavator. The control system provides hydraulic fluid to the hammer  12  at rated pressure and desired flow whenever the switch  14  is closed. 
     Referring now to FIGS. 1 and 2, a control system in accordance with the present invention is illustrated. FIG. 2 illustrates schematically the electrical components of the control system while FIG. 1 illustrates schematically the hydraulic components of the control system. With reference to FIG. 2, a momentary contact hammer control switch  114  connects a source of  24  volt control power to a variable timer  152 , a mode switch  154  and a circuit switch  156 . The momentary contact switch  114  is in the operator&#39;s cab and is actuated by the operator when he wishes to energize the hammer  12 . The variable timer  152 , mode switch  154  and the circuit switch  156  are all contained in a small housing mounted conveniently for operator control. The circuit switch  156  is a three position rocker switch which is manually switched between three positions. The first position (illustrated) is the “slow start on” position and makes use of the present invention. The second or center position is the off position and prevents hammer operation. The third position connects control power directly to the normal hammer solenoid and operates in a manner identical to the prior art control system illustrated in FIG.  3 . 
     When the circuit switch is in the first, slow start on position, electric power is supplied through the momentary contact switch  114  through the main power line  158  through the contacts of a relay  160 , to the circuit switch  156 , to the slow start solenoid  166 . This will cause operation of the hydraulic control system seen in FIG. 1 in the slow start mode to be described herein below. 
     Closing of the momentary contact switch  114  also supplies power to the variable time delay circuit  152 . The variable time delay circuit  152  waits a selected period of time and then closes switch  168 . In the preferred embodiment, switch  168  is a solid state switch such as a transistor and is mounted integrally with the variable time delay circuit  152 . Closing of the switch  160  completes a circuit from the main power line  158  through the set-up switch (in the normal mode), the relay  160  to ground. This energizes the relay  160  disconnecting the main power line  158  from the slow start solenoid  166  and connecting the main power line  158  to the normal hammer solenoid  166 . Thus, in the normal mode, the circuit described sequentially energizes first the slow start solenoid  166 , de-energizes the slow start solenoid  166 , and energizes the normal hammer solenoid  116 . The period for which the slow start solenoid  166  is energized is selected with a variable resistor delay knob  170 . In the preferred embodiment, the delay can be selected to be a period from 1 to 16 seconds. 
     The mode switch  154  is a two position rocker switch. In the normal position, the mode switch allows operation of the solenoid  160  thereby enabling the rest of the circuit. In the “set-up” position, the mode switch  154  disconnects the solenoid  160  from the main power line  158 . As the solenoid  160  cannot be energized, the main power line  158  will stay connected to the slow start solenoid  166  and the normal hammer solenoid  116  will never be energized. The hammer will operate in the slow start mode for as long as the momentary contact switch  114  is actuated. 
     Referring now to FIG. 1, the slow start solenoid  166 , when energized, opens the slow start solenoid operated pressure regulating valve  172 . The slow start valve  172  receives high pressure hydraulic fluid from a pilot pump  122 . It has a regulated output  172 D which is provided with hydraulic fluid at an adjustably regulated pressure significantly reduced from the pilot pump output pressure. The hydraulic fluid from the output  172 D is applied through a fluid line  174  to a shuttle valve  176 . The output of the shuttle valve  176  is applied through a fluid line  178  to a control input  136   a  of the auxiliary valve  136 . The reduced control pressure applied at the auxiliary valve input  136   a  partially opens the auxiliary valve  136 . This allows high pressure hydraulic fluid to flow from the main pump  130  through the main power hydraulic fluid line  132  through the auxiliary valve  136 , through fluid line  140  to the hammer  12 . However, since the auxiliary valve  136  is only partially open, flow through line  140  is at a low rate. A portion of the flow through the auxiliary valve  136  flows through a control output  136 H to a shuttle valve  126  and to the control input  130 C of the main pump  130  causing the pump to operate at reduced capacity. The delivery of hydraulic fluid to the hammer  12  is significantly less than full rated flow. The hammer  12  will therefore operate at a frequency significantly less than its rated frequency. The impacts are full power impacts. However, the impact frequency is significantly reduced. 
     After the variable time delay circuit  152  (FIG. 2) has timed out and closed the switch  168 , the slow start valve  172  will close preventing flow to output  172 D and the normal hammer solenoid  116  will cause the normal hammer solenoid operated pressure regulating valve  118  to open. High pressure fluid is received from the pilot pump  122 . Regulated pressure fluid is provided to output  118 D and unregulated fluid is provided at output I  18 B. Output  118 D provides fluid at an adjustable regulated pressure greater than that seen at the slow start valve output  172 D through a fluid line  124  to a shuttle valve  126 . The regulated pressure hydraulic fluid is applied through a fluid line  128  to the controlling port  130   c  of the main pump  130 . This causes the main pump  130  to provide rated flow for the hammer  12 . 
     High pressure hydraulic fluid is also provided from the normal hammer valve output  118 B through the shuttle valve  176  and the fluid line  178  to the auxiliary valve input  136   a . This flow causes the auxiliary valve  136  to open sufficiently to provide full rated flow from the pump  130  through the fluid line  140  to the hammer  12 . In this configuration, rated flow is provided independent of pressure and temperature variations in the hydraulic fluid delivered by the main pump  130 . 
     A second embodiment of the invention is illustrated in FIGS. 4 and 5. 
     Not all excavators are equipped with an auxiliary valve such as that used in the embodiment of the invention shown in FIGS. 1 and 2. When a hammer is used in some of the excavators not having an auxiliary valve, a separate flow control valve is installed. FIG. 4 schematically illustrates hydraulic components implementing the present invention in such machines. FIG. 5 schematically illustrates the electrical components used with the hydraulic components of FIG.  4 . 
     Referring to FIG. 5, the electrical control components are similar to those used in the first embodiment and illustrated in FIG.  2 . The difference is that the normal hammer solenoid  216  is wired directly to the switch terminal of the momentary contact hammer control switch  214 . Thus, whenever the momentary control switch  214  is closed, the normal hammer solenoid  216  is energized. 
     The main power line  258  also receives  24  volt power when the momentary contact switch  214  is activated and supplies current to the variable time delay circuit  252 , the mode switch  254  and a supply contact of the solenoid  260 . With the mode switch  254  in the normal position, the circuit operates as follows. When the momentary contact switch  214  is actuated, the normal hammer solenoid  216  is energized. The variable time delay circuit  252  is also energized and starts to time. As the variable time delay circuit  252  has not yet timed out, switch  268  remains open. Thus the relay  260  is not energized and current flows from the main power line  258  through the solenoid  260  and the circuit switch  256  to the slow start solenoid  266 . Thus, both the normal hammer solenoid  216  and the slow start solenoid  266  are energized during the interval from actuation of the momentary contact switch  214  and the timing out of the variable time delay  252 . 
     A time delay is selected with the variable resistor  270 . This time delay starts timing out when the switch  214  is closed. When the time delay is completed, the variable time delay circuit  252  closes the switch  268 . When the switch  268  is closed, current may flow from the main power line  258  through the set-up switch  254 , the coil of the relay  260  and the switch  268  to ground. The relay  260  is energized and current is no longer supplied to the lower set of contact of the circuit switch  256 . Thus, current is no longer supplied to the slow-start solenoid  266 . Current continues to be applied to the normal hammer solenoid  216  through the bypass electrical line  220 . The hammer thus operates normally after the variable time delay switch has timed out. 
     The circuit switch  256  operates somewhat differently in this embodiment when compared to the first embodiment. In the first embodiment, the three positions of the circuit switch were: slow start enabled, system off, and slow start disabled. In the current embodiment, the three positions of the circuit switch are: slow start enabled, slow start disabled, and slow start disabled. This difference in function is the result of use of the bypass electrical line  220  to energize the normal hammer solenoid  216  and the non-use of the second set of contacts in a circuit switch  256 . However, this arrangement allows use of the single circuit design contained in an identical housing for both embodiments of the invention. 
     Referring now to FIG. 4 wherein the hydraulic components of the control system are disclosed, one sees a main hydraulic pump  230 , control valves, and a heavy duty hydraulic hammer  12 . Hydraulic fluid flows from the pump  230  through the main fluid line  232  to a multi-valve  280 . The multi-valve  280  contains several components including a pressure relief  282 , a solenoid actuated valve  284 , and a flow regulating three position valve  286 . 
     The main hydraulic line  232  is connected to the multi-valve input  290 . The input  290  of the multi-valve is also the input of the flow regulating three position valve  286 . The output of the flow regulating valve  286  is connected to a first control input  292  of the flow regulating valve  286  and also to the upstream side of an orifice  294 . The downstream side of the orifice  294  is connected to the output  296  of the multi-valve  280  and also to a first hydraulic connection  298  of the solenoid operated valve  284 . A second hydraulic connection  300  of the solenoid operated valve  284  is connected to a second control input  302  of the flow regulating valve  286 . A spring bias  304  is provided assisting the second control input  302 . When the solenoid actuated valve  284  is actuated by the normal hammer solenoid  216 , the first hydraulic connection  298  is placed in fluid communication with the second hydraulic connection  300 . The downstream side of the orifice  294  is therefore in fluid communication with the second input  302  of the flow control valve  286 . The upstream side of the orifice  294  is in fluid communication with the first input  292  of the flow control valve  286 . Thus, the flow control valve  286  is provided with the pressure on the upstream side of the orifice  294  and the downstream side of the orifice  294  and therefore regulates flow from the input  290  to the output  296  operating as a flow control valve. Excess flow is vented through the excess flow output  306  to the hydraulic reservoir  308 . This control arrangement provides regulated constant rated power flow from the pump  230  through the main hydraulic line  232 , the flow control valve  286 , hydraulic line  140  to the hammer  12 . The hammer operates at rated capacity. 
     In accordance with the present invention, the second control input  302  of the flow control valve  286  is also connected to a variable orifice  310  which is in turn connected to a solenoid actuated pilot valve  312  which is in turn vented to the hydraulic reservoir  308 . The pilot valve  312  is actuated by the slow start solenoid  266 . When the slow start solenoid  266  is de-energized, the valve  312  is open and no flow through the variable orifice  310  occurs. When the slow start solenoid  266  is energized, the valve  312  is actuated and flow through the variable orifice  310  is allowed. This bleeds off a portion of the fluid which would normally flow to the second control input  302  of the flow control valve  286 . Pressure at the second control input  304  is lowered. The pressure of the first control input  292 , which has not been altered, therefore exerts greater control over the spool in the flow control valve  286  and flow through the flow control valve  286  is reduced. This mimics a larger pressure differential across the orifice  294 . By either analysis, flow is reduced. The amount of flow reduction is selected by adjusting the variable orifice  310 . 
     Thus, during the interval in which the time delay circuit  252  has not timed out, both the normal hammer solenoid  216  and the slow start solenoid  266  are energized. Flow from the pump  230  to the hammer  12  is significantly reduced in accordance with the setting at the variable orifice  310 . The hammer  12  operates with full impact energy but at a significantly reduced impact rate. When the variable time delay circuit  252  has timed out, the slow start solenoid  266  is de-energized, the pilot valve  312  opens and the flow control valve  286  again operates as a regulated control flow valve providing full rated flow to the hammer. 
     When both the slow start solenoid  266  in the normal hammer solenoid  216  are de-energized, the second control input of the flow control valve  286  is vented to the hydraulic fluid tank, and the flow control valve  286  provides no flow to the output  296  deactivating hammer  12 . 
     While considerable emphasis has been placed herein on the structures of the preferred embodiments and on the structural interrelationship between the component parts thereof, it will be appreciated that many embodiments of the invention can be made and that many changes can be made in the embodiments herein illustrated and described without departing from the principles of the invention. Accordingly, it is to be understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the preferred invention and not as a limitation.