US3910358A

US3910358A - Horizontal earth boring machine

Info

Publication number: US3910358A
Application number: US485803A
Authority: US
Inventors: Norman A Martinek
Original assignee: Koehring Co
Current assignee: Koehring Co
Priority date: 1974-07-05
Filing date: 1974-07-05
Publication date: 1975-10-07
Anticipated expiration: 1992-10-07
Also published as: CA1009223A; GB1457493A; JPS516303A; JPS5550556B2

Abstract

A portable, horizontal earth boring machine which employs two or more hydraulic motors to rotate and advance an auger in an earth boring operation in which the motors are supplied with hydraulic fluid from a single variable displacement pump located remotely from the earth boring machine. The pump is controlled to respond to the loads imposed on the motors to limit the horsepower output of the pump up to a predetermined maximum after which the horsepower is maintained constant until a maximum working load is achieved at the motors. The control is so arranged that demands made by an operator of the earth boring machine in excess of the limits of the pump are negated making possible the selection of an engine to drive the pump of sufficient capacity to meet but not greatly exceed the power requirements of the pump.

Description

United States Patent Martinek Oct. 7, 1975 HORIZONTAL EARTH BORING MACHINE [75] Inventor: Norman A. Martinek, Milwaukee,

Wis.

[73] Assignee: Koehring Company, Milwaukee,

Wis.

22 Filed: July 5, 1974 [21] Appl. No.: 485,803

[52] US. Cl. 173/152; 60/452; 173/159;

, 175/122 [51] Int. Cl. E21D 9/10 [58] Field of Search 173/152, 159; 175/122,

175/62, 171; 299/50, 56; 60/452, 391, 445, 487, 488, DIG. 10

[56] References Cited 3,587,755 6/1971 Slusher 173/159 Primary Examiner-Ernest Purser Assistant ExaminerWilliam F. Pate, Ill

Attorney, Agent, or FirmAndrew .1. Beck 57] ABSTRACT A portable, horizontal earth boring machine which employs two or more hydraulic motors to rotate and advance an auger in an earth boring operation in which the motors are supplied with hydraulic fluid from a single variable displacement pump located remotely from the earth boring machine. The pump is controlled to respond to the loads imposed on the motors to limit the horsepower'output of the pump up to a predetermined maximum after which the horsepower is maintained constant until a maximum working load is achieved at the motors. The control is so arranged that demands made by an operator of the earth boring machine in excess of the limits of the pump are negated making possible the selection of an engine to drive the pump of sufficient capacity to meet but not greatly exceed the power requirements of the pump.

15 Claims, 6 Drawing Figures US. Patent Oct. 7,1975 Sheet 1 on 3,910,358

US. Patent Oct. 7,1975 SheetZ 0f3 3,910,358

HORIZONTAL EARTH BORING MACHINE BACKGROUND OF THE INVENTION This invention relates to portable, horizontal earth boring machines and, more particularly, to a hydraulically operated earth boring machine in which the power source for the machine may be disposed remotely in selected positions.

Horizontal earth boring machines are normally mounted in working position on tracks or rails which are positioned in an open ditch so that the machine is advanced as a rotating auger drills a horizontal bore in the earth. To properly control both the advance of the auger and the rotation of the auger, the operator of the machine must be in close proximity to the auger where he can view the operation. Consequently, he is usually positioned in a ditch together with the earth boring machine.

Since horizontal earth boring machines are usually of the portable type, they employ internal combustion engines as the power source. The positioning of such engines in the confines of a ditch results not only in a high noise level, but also can be a health hazard to an operator working adjacent to the engine. To avoid these problems and also to comply with certain government regulations, complex exhaust and engine muffler arrangements have been employed which add to the complexity and size of the earth boring apparatus and make it difficult to properly locate it in a working position.

Another solution to the problem has been to use a pair of hydraulic pumps, one for driving a hydraulic motor which rotates the earth boring auger and the other to supply hydraulic fluid for reciprocating hydraulic actuators which acts to advance or retract the auger as it is rotated in the earth. Both of the pumps are driven by internal combustion engines which can be positioned remotely from the earth boring auger and, as a consequence, can be positioned at ground level above the ditch in which the operator is located.

The operator of the machine remains located in the ditch to regulate the speed and direction of rotation as well as the advance and retraction of the auger. Such operation can subject the pumps to unduly large hydraulic loads which can cause the driving engine to stall. This, of course, requires the operator to leave his work station in the ditch and to restart the engine after which he must return to his work position in proximity to the controls of the machine. Alternatively, the internal combustion engine for driving the pumps can be selected of a size large enough to accommodate the maximum loads. This, of course, requires an excessively large internal combustion engine and adds to the expense of the equipment.

SUMMARY OF THE INVENTION This invention contemplates the use of a single hydraulic pump to furnish pressure fluid to hydraulic motor means to rotate an earth boring auger and to reciprocate the auger using controls which are so arranged that demands in excess of the capacity of the pump to rotate or to advance the auger, or both, are rejected and the capacity of the pump, and therefore the capacity of the internal combustion engine driving the pump, cannot be exceeded. The single hydraulic pump utilizes controls responsive to the higher of the load pressures required to either rotate the auger or to advance the auger which places a limit on the displacement of the pump and, consequently, on its output.

A horizontal earth boring machine has been provided in which the power source may be located remotely from the driven earth boring elements .using the power source. The functions of rotating the auger and of advancing the auger can be conducted independently, simultaneously and efficiently under the control of an operator located in close proximity to the auger where he may observe and control its operation. The hydraulic pump for supplying the hydraulic fluid for the rotating hydraulic motor and for the hydraulic actuators advancing the auger is a single, variable displacement hydraulic pump of the pressure compensated type which responds to the higher of the working pressures existing in the auger rotating motor or in the auger advancing hydraulic actuators to limit the power output up to a predetermined level of pump capacity which determines the size and power capacity of the internal combustion engine required to power the hydraulic pump.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing an earth boring machine embodying the present invention, located in a working position with the power source located remotely from the working position;

FIG. 2 is a side elevation of the horizontal earth boring machine;

FIG. 3 is a top view of the machine shown in FIG. 2;

FIG. 4 is a sectional view taken on line 4-4 in FIG. 3;

FIG. 5 is a schematic diagram of the hydraulic circuit used to control the earth boring machine; and

FIG. 6 is a curve depicting the characteristics of the pump employed to supply power to the earth boring machine.

DETAILED DESCRIPTION Referring to the drawings, and particularly to FIG. 1, a preferred embodiment of the invention includes a horizontal earth boring machine 10 which is operated to rotate an auger 12 and to advance the auger while it is being rotated to form a bore in the earth. The machine can also be used to advance a casing member 14 which forms a lining to the bore formed by the auger l2 and serves to convey the material cut by the auger rearwardly from the bore which is being formed.

The horizontal earth boring machine includes a base structure 16 which is made up of a basic track section 18 and one or more

extension track sections

20 and 22. The basic track section 18 includes a pair of generally channel-

shaped rail members

24 and 26 which are held apart in parallel spaced relationship to each other by a plurality of cross braces 28 which may be rigidly attached to the

rails

24 and 26 as by welding or the like. The cross braces 28 also act to engage the ground and to support the rails generally horizontally and parallel to the axis of rotation of the auger l2 and to the bore which is to be formed in the earth. The cross members 28 at opposite ends of the base structure 18 are provided with lift rings 30 to which lifting equipment may be connected to raise and lower the base track structure relative to the ditch.

The rear or left end of the basic track structure 18, as viewed in FIGS. 2 and 3, is provided with a cross member 32 hich acts as a backstop and the other, or right end of the basic track structure 18, is provided with connecting plates 34 associated with the

tracks

24 and 26 for securing the basic track structure 18 to an extension track structure 20. The extension track structure 20 also includes a pair of

tracks

24 and 26, cross members 28 and lift rings 30 by which the extension section 20 may be raised and lowered relative to the ditch in which the machine is to operate. Similarly connecting plates 34 may be located at the joint between the

extension track sections

20 and 22 to secure them relative to each other.

A carriage structure indicated generally at 36 is disposed on top of the

tracks

24 and 26 for longitudinal sliding movement relative to the latter. The carriage structure 36 includes a pair of anchor plates 38 associated with the track 24 and a similar pair of anchor plates 40 associated with the track 26 which serve to secure the carriage 36 against vertical movement relative to the

tracks

24 and 26.

The carriage 36 supports a reversible hydraulic motor 42 which serves to drive a gear reduction unit 44 which in turn rotates the auger 12.

The carriage structure 36 is moved longitudinally of the

tracks

24 and 26 by means of a pair of hydraulic actuators 48, each of which has a cylinder portion pivotally connected to the carriage 36 and a rod portion 52 pivotally connected to an anchor structure 54. The anchor structure 54 extends transversely to the

tracks

24 and 26. One end of the anchor structure 54 is provided with a pair of pins 56 which are adapted to be inserted and retracted from selected, adjacent pairs of holes 58 in the track 24. Similarly, the other end of the anchor structure 54 is provided with pins 56 adapted to be inserted into selected ones of pairs of openings 58 in the track 26. Pins 56 are rigidly connected to a pin bracket 63 and are adapted to be moved vertically into and out of the openings 58 by means of a lever 64 which serves to raise and lower the pin bracket 63 and the pins 56 through means of links 66.

The hydraulic actuators 48 are of the double-acting type, and the transmission of hydraulic fluid to one end of the actuators 48 causes extension of the rods 52 so that the carriage structure is moved to the right relative to the anchor structure 54 as viewed in FIGS. 2 and 3. Similarly, the transmission of hydraulic fluid to the left end of the hydraulic actuators 48 serves to retract the rods 52 so that the carriage structure 36 moves to the left. Such extension and retraction of the piston rods 52 serves to move the carriage structure 36 relative b the anchor structure 54 to either advance or retract the auger 12.

The carriage structure 36 is also provided with a casing pusher which serves to engage one end of the casing 14 and to hold it nonrotatably relative to the auger 12. Upon advancement of the carriage 36 to the right, as viewed in FIGS. 2 and 3, the casing pusher 70 serves to advance the casing 14 together with the auger 12 so that, as a bore is formed in the earth, the casing 14 lines the bore. The casing 14 also acts to convey the material cut by the auger 12 from the open end of the casing 14 toward the casing pusher from which it is discharged by means of rotating paddles 71.

A pair of generally vertical bar structures 76 are disposed at opposite sides of the carriage 36. The bar members 76 serve as a lift cage by which the carriage member may be lowered into a ditch or raised from a ditch by lifting machinery such as a crane.

Disposed on the bar member 76 are

control levers

78 and 80 operating valve controls to be described. The carriage member 36 also includes an operators platform 82 at which an operator may position himself for operation of the valve control levers. The platform is positioned rearwardly of the direction of auger advance for good visibility of auger operation.

The hydraulic motor 42 and the hydraulic actuators 48 receive hydraulic fluid which is controlled manually by the operator located on the platform by manipulation of a pair of valve operating levers 78 and 80. The Iever 78 is used to control a directional valve mechanism regulating the direction of rotation and speed of the motor 42 and the lever 80 is used to similarly control the operation of the hydraulic actuators 48 to advance or retract carriage 36.

Referring now to FIG. 1, the source of hydraulic fluid pressure for operation of the hydraulic motor 42 and of the hydraulic actuators 48 is incorporated in a power assembly designated generally at 86. The power assembly 86 includes a base frame structure 88 in which an internal combustion engine 90 is mounted to drive a hydraulic pump 92 which is indicated in FIG. 5. The base structure 88 also serves to support a battery 96, a fuel tank 98 and a reservoir 100 for the hydraulic fluid. A lift bar 101 is rigidly secured to the base structure 88 so that all of the components mounted thereon may be lifted and positioned by means of a crane or the like at some point adjacent to the machine 10 but preferably at ground level and out of the ditch in which the machine 10 is being operated.

The hydraulic pump 92 is connected to a control valve 102 manually actuated by lever 78 and a control valve 104 manually actuated by the lever 80 by means of a delivery line 106. A line 108 serves as a return line, and a line 110 serves as a control signal line.

Hydraulic Circuit Referring now to FIG. 5 schematically illustrating the closed-center hydraulic system employed in operating the horizontal earth boring machine 10, the variable displacement pump 92 driven by the internal combustion engine 90 receives hydraulic fluid from the reservoiry100 through a line 112 for delivery by the pump 92 through the line 106 to branch

supply lines

116 and 118. The supply line 116 delivers hydraulic fluid to a control circuit which is utilized to control the doubleacting hydraulic actuators 48 by manual movement of the control lever 80. The supply line 118 delivers hydraulic fluid to a control circuit for controlling the direction and speed of the hydraulic motor 42 which rotates the auger 12.

Referring to the control circuit for controlling the hydraulic actuators 48, movement of the control lever 80 controls the directional four-way control valve 104. Movement of the control lever 80 to the left, as viewed in FIG. 5, is effective to supply hydraulic fluid from the line 116 to a pressure compensating valve 122 and through a line 124 to the directional valve 104. The valve 104 controls the flow of fluid to a line 126 to the head end of both of the actuators 48, forming part of the hydraulic actuators 48. Delivery of hydraulic fluid under pressure in this manner causes the hydraulic actuator rods 52 to move to the left, as seen in FIG. 5 and also in FIG. 2, to advance the carriage 36 to the right in an earth boring direction.

As the rods 52 of the hydraulic actuators 48 move to the left. hydraulic fluid is ejected from the rod ends of the cylinders 50 through line 130 to the control valve 104 from which it passes to the return line 108 and back to the reservoir 100.

Movement of the control lever 80 to the right to move valve 104 from its neutral position shown in FIG. 5 causes hydraulic fluid to be delivered to the valve 104 and through the line 130 to the rod end of the cylinders 50, causing the piston rods 52 to move to the left relative to the cylinders 50. At the same time fluid is ejected through the lines 126 to the control valve 104 and to the return line 108 back to the reservoir 100.

When the control valve 104 is operated by moving the lever 80 to either the left or the right of the neutral position in which the valve is shown in the drawing, the working pressure in either of the

lines

126 or 130 which is being delivered to the hydraulic actuators 48 also is made available in a pilot signal line 134. The pilot control pressure in the line 134 is made available to control the pressure compensating valve 122 through a line 136 and also is made available to a pressure relief valve 138 by way of hydraulic line 140. The pressure relief valve 138 is connected to the return line 108 by way of a line 142. The pressure relief valve 138 serves to relieve the pressure in the working end of the hydraulic actuators 48 when the pressure exceeds some predetermined maximum which, for example, can be to the order of 2,300 psi.

The hydraulic fluid pressure in the pilot signal line 134 from the hydraulic actuator control valve 104 communicates through a one-way check valve 144 to a line 146 which communicates with a signal port 148 associated with the pump 92 and its controls.

Referring now to the control valve circuit associated with the hydraulic motor 42, hydraulic fluid is delivered through the line 118 through a presssure compensating valve 150 which is similar to the pressure compensating valve 122. Hydraulic fluid from the pressure compensating valve 150 is delivered to a control valve 102 through a line 154 and is returned through a line 156 to the return line 108 and to the reservoir 100. The valve 102 is identical to the directional four-way valve 104 and movement of the control lever 78 to the right causes delivery of hydraulic fluid from the line 154 to a line 158 to cause rotation of the motor 42 in one direction. At the same time hydraulic fluid is exhausted from the motor 42 through a return line 160, through the valve 152 and to the line 156 communicating with the return line 132 and the reservoir 100. The movement of the control lever 78 to the left causes delivery of the hydraulic fluid from the line 154 through the valve 102 and to the line 160 causing the motor 42 to rotate in the opposite direction. Fluid from the motor 42 is returned by way of the

lines

158, 156 and 108 to the reservoir 100.

As in the case of the control valve 104, the working pressure delivered through the valve 102 to the motor 42 is made available in a pilot signal line 162 whenever the control valve 102 is moved to the left or to the right of its neutral or center position. Pilot signal pressure from the line 162 is made available to control the pressure compensating valve 150 through a line 164. The pilot signal pressure in the line 162, which is at the working pressure of the motor 42, communicates through a check valve 166 to a line 168 and the signal line 146 to the signal port 148.

A pressure relief valve 170 is disposed between the supply line 118 and the return line 108 to limit the maximum pressure which can be made available to the motor 42, for example, 3000 psi.

The check valve 144 associated with the control circuit for the hydraulic actuators 48 and the check valve 166 associated with the control circuit for the hydraulic motor 42 are so arranged that the higher of the working pressures existing in either the motor 42 or in the'actuators 48 is made available at the signal port 148.

Pump Control Circuit The pump 92 is a pressure compensated variable displacement pump 92 of the axial piston type which includes a swashplate indicated at 174 the angle of which is under the control of a pump servo piston 176. Increase of piston stroke in response to increase of signal pressures results in an increase in the swashplate angle and a corresponding increase ,in displacement of the pump 92. The pump servo piston 176 is under the control of a pressure compensating circuit designated generally at 178 which responds to a differential in pressure at the signal port 148 and in an output pressure signal line 180 communicating with the output line 106 from the pump 92. The circuit 178 operates to maintain the pressure differential at signal port 148 and signal line 180 at some predetermined constant level which could be selected, for example, to be 200 psi. If the working pressure downstream of the

valves

102 and 104 and at the signal port 148 changes, the position of the pump servo piston 176 changes to regulate the displacement of the pump 92 to maintain a constant pressure differential at the signal port 148 and the high pressure signal line 180.

The operator of the earth boring machine 10 can sense only the velocity of flow due to his control of the

valves

102 and 104 but cannot sense the magnitude of the pressure demanded by the load. To prevent a horsepower overload from occurring, the control circuit 178 is provided with a horsepower limiting control indicated at 184 which functions automatically to reject any requirement which is made manifest by operation of the

valves

102 and 104 to require more power than is available in the system. The horsepower limiting device 184 is biased by a spring 186 which is grounded against an arm 188 connected to the swashplate 174. As the pump 92 increases displacement due to an increase in angle of the swashplate the power limiter spring is relaxed requiring less load pressure in the line 180 to overcome the force generated by the spring 186, and the load pressure at which the horsepower limiting device shifts is inversely proportional to the displacement of the pump 92.

The control circuit also includes a valve 192 which is connected to the system so that the pump control differential pressure at the signal port 148 and in the high pressure signal line 180 act across the spool urging it to the right as seen in FIG. 5. Since the control differential is maintained at a constant level during operation, the force on the spool due to the pressure differential remains constant throughout the range of operation. A biasing spring 194 is employed to keep the spool in its normal position. When the

directional control valves

102 and 104 are in their neutral position, the output of the pump 92 is blocked and pressure in the high pressure signal line 180 will rise. This pressure acts on the valve 192 and the rate of the spring 194 can be selected to require an increase in pressure above the normal control differential pressure at the signal part 148 and the high pressure line 180 to overcome the spring load. Once the delivery line pressure meets this pressure requirement, the valve 192 shifts to the left to communicate a fixed bypass orifice 196 with a line 198 to the reservoir 100. The orifice 196 is selected to be only small enough to maintain enough pressure drop across the orifice to keep the valve 192 shifted. Since the valve pressure drop is also the pump control differential, the pump 92 is commanded to a minimum stroke at a low working pressure. By way of example, the pump could be controlled to deliver one or two gallons of fluid per minute at a pressure of 400 to 500 psi.

Operation of the control circuit 178, shown in FIG. 5, can best be understood by reference to FIG. 6 which illustrates the operating characteristics of the pump 92 in terms of hydraulic fluid flow designated by the coordinate Q and the pressure which is designated by the coordinate P. The variable displacement pump is designed and controlled to deliver up to a maximum of 21 gallons per minute and up to a pressure of 2000 psi which is designated by that portion of the characteristic curve between points A and B. Maximum flow to either of the actuators 48 or to the motor 42 is a function of the fluid capacity of the pump 92 and the maximum metering characteristics of

valves

102 and 104 determined by the stroke of the valves from their neutral position.

Beyond the points B to the point C the maximum horsepower output of the pump, which is a product of flow and pressure, is maintained constant by means of the horsepower limiting valve 184 which modifies the displacement of the pump 92 as the working pressure at the signal port 148 increases. The maximum pressure of the system occurs at point C at which point the pressure relief valve 170 in the motor circuit opens. By way of example, the pressure at this point could be 3000 psi with fluid flow to the order of 10 or I 1 gallons per minute.

The point E on the curve denotes the condition in which both of the

directional control valves

102 and 104 are in their neutral position and the pump 92 is restricted to limit flow at a relatively moderate pressure, for example, one to two gallons per minute at 400 to 500 psi.

The maximum torque required to drive the pump 92 is determined by the load occurring at point B at which the maximum flow of the system occurs at its highest pressure. The engine 90 to drive the pump 92 is selected to accommodate this load so that when it occurs the engine will not overload and stall.

Operation The horizontal earth boring operation is begun by placing the machine 10 in a ditch adjacent to the location where the bore is to be formed in the earth and by placing the power assembly 86, preferably to one side of the ditch, in a remote location. The machine 10 and the power assembly 86 are then connected by means of the delivery line 106 the return line 108 and the signal line 110.

With the pump 92 being driven by the internal combustion engine 90 and with the

control valves

102 and 104 in their neutral position, a small quantity of hydraulic fluid is being circulated at a relatively low pressure in the lines between the pump 92 and the

control valves

102 and 104. Movement of the control lever 78 associated with the control valve 102 is effective to deliver hydraulic fluid to the variable hydraulic motor 42 to initiate rotation of the auger 12. Depending on the position of the valve 104 and the resistance to rotation of the auger in the earth, the speed of rotation is controlled. The working load will be made apparent at the control system by an increase in pressure in the signal line 146 and at the signal line port 148. The differential in pressure at the port 148 and in the output line 106 will adjust the pump 92 to deliver hydraulic fluid to the line 106 at a pressure approximately 200 psi higher than the pressure in the signal line 146 which represents the working pressure downstream of the valve 102. With the auger l2 rotating, the control lever 80 may be moved to the right, as seen in FIG. 5, to cause advance of the carriage 36 together with the auger 12. If the carriage 36 is advanced at a speed requiring more than the remaining fluid of the system and at a pressure or load which develops a working pressure less than the working pressure of the motor 42, the flow of fluid to the motor 42 will be restricted and, consequently, the augers rotation will be retarded. Slowing of rotation of the auger 12 will be apparent to the operator, and, if desired, he may retard the demanded speed of operation of the motor 40 or of the actuators 48 to make fluid flow available in the other of these circuits.

If the

valves

102 and 104 are simultaneously stroked to utilize the full flow of the pump and to create a working pressure at one of the functions, for example the motor 42, in excess of 2000 psi, the horsepower control functions to maintain the maximum output or horsepower, which is the product of flow and pressure, at a relatively constant value as depicted in the curve of FIG. 6 between points B and C. As the working pressure increases, the flow decreases. At the point C, for example, the horsepower output of the pump can be equal to or slightly less than the output at point B and the engine driving the variable displacement pump 92 will not be overloaded or stall.

It will be noted that each of the

valves

102 and 104 may be operated independently of each other and the valve 102 is protected by a pressure relief valve and the control valve 104 of the actuator circuit is protected by a pressure relief valve 138.

Although two

valves

102 and 104 have been disclosed to control two different functions of the earth boring machine 10, it should be apparent that additional functions and control circuits can be added and operated independently of the other control circuits.

A horizontal earth boring machine has been provided in which the earth boring functions, such as rotation of an auger and advancing of the auger into a bore which is to be formed, may be conducted at one location, for example in a ditch, and the power source for conducting such functions may be located remotely and to one side and out of the ditch. The functions, such as rotating the auger and advancing the auger or bore casing, can be conducted independently or simultaneously under the control of an operator located close to the boring operation and remote from the power source. The hydraulic pump for supplying the hydraulic fluid for conducting the required operations is provided by a single variable displacement hydraulic pump in which the maximum horsepower is limited by a pump control circuit which permits the operator to operate the earth boring machine without concern for exceeding the capacity of the pump since the control circuit will negate any demands which are made by the operator that exceed the capacity of the system. This makes possible the selection of a power source to drive the hydraulic pump for the earth boring machine of sufficient but not excessive capacity to supply the necessary pump output and at the sametime so that it will not be overloaded and stall.

I claim:

1. A generally horizontal earth boring machine apparatus comprising: a generally horizontally disposed earth boring auger, a hydraulic motor operatively connected to said auger to rotate the latter in opposite directions, hydraulic actuator means operatively connected to said auger to move the latter axially in opposite directions, a variable displacement pump located in a selected position independently of the position of said motor and actuator means and having a discharge for delivering hydraulic fluid to said motor and actuator means, first directional control valve means controlling communication between said pump discharge and said motor, second directional control valve means controlling communication between said pump discharge and said actuator means, hydraulic means responsive to hydraulic pressure to vary the displacement of said pump, control means for delivering hydraulic fluid to said hydraulic means, said control means having a pair of signal ports, one of said signal ports being in communication with said pump discharge, first regulating means between said motor and the other of said signal ports and being responsive to pressure in said motor greater than in said actuator to communicate pressure to said other of said signal ports, second regulating means operatively disposed between said actuator means and said other of said signal ports and being responsive to pressure in said actuator means greater than in said motor to communicate pressure to said other of said signal ports, said hydraulic means being operative to vary the displacement of said pump to maintain a predetermined pressure differential between said pair of signal ports up to a predetermined pressure level at said pump discharge.

2. The combination of claim 1 and further comprising power limiting means communicating with said signal ports and being operative beyond said predetermined pressure level at said output port to deliver hydraulic fluid to said hydraulic means to decrease the displacement of said pump as pressure at said output port increases above said predetermined level.

3. The combination of claim 1 and further comprising power means for driving said variable displacement pump and in which said power means and said variable displacement pump are disposed in selected positions remotely from said earth boring auger.

4. The combination of claim 1 in which said control means includes power limiting means operative beyond said predetermined pressure level to maintain the product of hydraulic fluid flow and hydraulic pressure at a substantially constant value.

5. The combination of claim 1 in which said first and second directional control valve means each include an inlet for receiving fluid from said pump and an outlet for returning fluid to said pump, and further comprising pressure relief valve means between the inlet and the outlet of said first directional control valve means to determine the maximum pressure at said outlet port.

6. The combination of claim 5 further comprising pressure relief valve means between the inlet and the outlet of said second directional control valve means operable to open at a preaaure greater than said maximum pressure at said outlet port.

7. The combination of claim 1 in which said first and second directional control valve means are operable simultaneously and independently of each other.

8. A horizontal earth boring machine comprising:

a carriage supported for horizontal movement, an elongated earth boring auger supported relative to said carriage for rotation relative thereto, a hydraulic motor operatively connected to said auger to rotate the latter in opposite directions, hydraulic actuator means operatively connected to said carriage to move the latter in opposite directions to advance and retract said auger, a pump having a discharge for delivering hydraulic fluid to said motor and said actuator means, first directional control valve means between said pump discharge and said motor for controlling the direction of rotation of said auger, second directional control valve means between said pump discharge and said actuator means for controlling the direction of movement of said carriage, adjusting means movable to vary the displacement of said pump, hydraulic servo piston means connected to said adjusting means and being responsive to hydraulic pressure to move the latter, control means for delivering hydraulic fluid to said servo piston means, said control means having a pair of signal ports, one of said signal ports being in communication with said pump discharge, first regulating means between said motor and the other of said signal ports and being responsive to pressure in said motor greater than said actuator to communicate pressure to said other of said signal ports, second regulating means operatively disposed between said actuator means and said other of said signal ports and being responsive to pressure in said actuator means greater than in said motor to communicate pressure to the other of said signal ports, said control means being operative to deliver hydraulic fluid to said servo piston means to vary the displacement of said pump to maintain a predetermined pressure differential between said pair of signal ports up to a predetermined pressure level at said pump discharge.

9. The combination of claim 8 and further comprising power limiting means communicating with said signal ports and being operative beyond said predetermined pressure level at said pump discharge to deliver hydraulic fluid to said piston means to decrease the displacement of said pump as pressure at said output port increases beyond said predetermined level.

10. The combination of claim 9 in which an adjusting means is moved to decrease displacement of said pump as said pressure increases to maintain the product of displacement and pressure at a substantially constant value.

11. The combination of claim 9 in which said power limiting means is operatively connected to said adjusting means to decrease the displacement of said pump in response to an increase in pressure at said pump discharge and said other of said signal ports.

12. A generally horizontal earth boring machine comprising: a generally horizontal earth boring auger, a hydraulic motor operatively connected to said auger to rotate the latter in opposite directions, hydraulic actuator means operatively connected to said auger to move the latter axially in opposite directions, a variable displacement pump discharge for delivering hydraulic fluid to said motor and actuator means, first and second directional control valve means operatively disposed between said pump discharge and said motor and between said pump discharge and actuator means, respectively, and each being movable from a neutral position to control the delivery of fluid to said motor and to said actuator means in proportion to the amount of movement of said valve means from said neutral position, hydraulic means responsive to hydraulic pressure to vary the displacement of said pump discharge, control means for delivering hydraulic fluid to said hydraulic means, said control means having a pair of signal ports, one of said signal ports being in communication with said pump discharge, means for deliver the highest of the fluid pressures downstream of said first and second control valve means to the other of said signal ports, said hydraulic means being operative to vary the displacement of said pump to maintain a predetermined pressure differential between said pair of signal ports up to a predetermined pressure level of said pump discharge, and power limiting means communicating with said signal ports and being operative beyond said predetermined pressure level at said pump discharge to deliver hydraulic fluid to said hydraulic means to decrease displacement of said pump as the pressure increases above said predetermined pressure level.

13. The combination of claim 12 in which said power limiting means is operative to maintain the flow of hydraulic fluid and the pressure thereof at said output port at a substantially constant value.

14. The combination of claim 12 in which said first and second control valve means are operative in said neutral positions of both of said control valve means to increase the pressure differential between said pair of signal ports to a predetermined amount above said predetermined pressure differential, and regulating means responsive to said last mentioned increase to actuate said hydraulic means to a position decreasing displacement of said pump to a minimum.

15. The combination of claim 12 in which said control valve means are operative in their neutral position to increase pressure at said one of said signal ports to increase pressure differential between said pair of signal ports to a value above said predetermined pressure differential, and regulating means operatively connected to said hydraulic means to actuate the latter to a position decreasing displacement of said pump to a minimum in response to an increase in pressure differential to said level above said predetermined pressure differential.

Claims

8. A horizontal earth boring machine comprising: a carriage supported for horizontal movement, an elongated earth boring auger supported relative to said carriage for rotation relative thereto, a hydraulic motor operatively connected to said auger to rotate the latter in opposite directions, hydraulic actuator means operatively connected to said carriage to move the latter in opposite directions to advance and retract said auger, a pump having a discharge for delivering hydraulic fluid to said motor and said actuator means, first directional control valve means between said pump discharge and said motor for controlling the direction of rotation of said auger, second directional control valve means between said pump discharge and said actuator means for controlling the direction of movement of said carriage, adjusting means movable to vary the displacement of said pump, hydraulic servo piston means connected to said adjusting means and being responsive to hydraulic pressure to move the latter, control means for delivering hydraulic fluid to said servo piston means, said control means having a pair of signal ports, one of said signal ports being in communication with said pump discharge, first regulating means between said motor and the other of said signal ports and being responsive to pressure in said motor greater than said actuator to communicate pressure to said other of said signal ports, second regulating means operatively disposed between said actuator means and said other of said signal ports and being responsive to pressure in said actuator means greater than in said motor to communicate pressure to the other of said signal ports, said control means being operative to deliver hydraulic fluid to said servo piston means to vary the displacement of said pump to maintain a predetermined pressure differential between said pair of signal ports up to a predetermined pressure level at said pump discharge.