Hydraulic system, mining machine and method of controlling hydraulic actuator

Abstract

A hydraulic system, mining machine and method of controlling a hydraulic actuator. The hydraulic system (HS) is provided with a control valve (23) for controlling movement direction and speed of a hydraulic actuator (HA) connected to the system. Generated force of the hydraulic actuator is controlled independently relative to the control valve by means of counterbalance valves (Cb1, Cb2) and servo valves (Sv1, Sv2) controlling their opening pressure. The counterbalance valves and the servo valves operate as a meter-out control assembly which controls flow of hydraulic fluid discharged from working pressure spaces (16a, 16b) of the hydraulic actuator. The disclosed system may be implemented to control a mining boom (3) of a mining machine (1).

Claims

1. A hydraulic system for a mining machine comprising: a pump for producing hydraulic pressure and flow to the system; a tank for storing and receiving hydraulic fluid; a hydraulic actuator including a first working pressure space and a second working pressure space; a first pressure conduit being in fluid connection with the first working pressure space and a second pressure conduit being in fluid connection with the second working pressure space; a first counterbalance valve connected to the first pressure conduit and configured to restrict discharged fluid flow out of the first working pressure space and allowing free input flow into an opposite direction; a second counterbalance valve connected to the second pressure conduit and configured to restrict discharged fluid flow out of the second working pressure space and allowing free input flow into an opposite direction; a control valve arranged for controlling feeding and discharging of hydraulic fluid to and from the first and second working pressure spaces in order to control direction and speed of movement generated by the hydraulic actuator; and a first solenoid valve arranged for controlling opening pressure of the first counterbalance valve and a second solenoid valve arranged for controlling opening pressure of the second counterbalance valve, whereby pressure of the hydraulic fluid discharging from the working pressure spaces of the hydraulic actuator is independently controllable.

2. The hydraulic system as claimed in claim 1, wherein the control valve is configured to control the hydraulic fluid flow affecting to generated movement speed of the hydraulic actuator and the counterbalance valves are configured to control the hydraulic pressure affecting to generated force of the hydraulic actuator whereby the hydraulic system is provided with independent control of force and speed of the hydraulic actuator.

3. The hydraulic system as claimed in claim 1, wherein the first and second solenoid valves are electrically controlled valves and the first and second solenoid valves are controlled by means of at least one control unit.

4. The hydraulic system as claimed in claim 3, further comprising a first pressure sensor for sensing the pressure acting in the first pressure space, a second pressure sensor for sensing the pressure acting in the second pressure space, wherein sensing data of the pressure sensors is transmitted to the control unit for controlling the first and second solenoid valves in response to the sensed pressures.

5. The hydraulic system as claimed in claim 1, wherein the control valve is a proportional directional valve, and wherein a third solenoid valve is configured to control movement of the control valve in a first operational direction and a fourth solenoid valve is configured to control the movement in an opposite second operational direction.

6. The hydraulic system as claimed in claim 1, wherein the hydraulic actuator connected to the hydraulic system is a hydraulic cylinder.

7. The hydraulic system as claimed in claim 1, wherein the hydraulic pump is a variable displacement pump.

8. The hydraulic system as claimed in claim 1, further comprising a third counterbalance valve connected to a first control pressure line between the first solenoid valve and the first counterbalance valve, and a fourth counterbalance valve connected to a second control pressure line between the second solenoid valve and the second counterbalance valve, wherein nominal flow directions of the third and fourth counterbalance valves is opposite to nominal flow directions of the first and second counterbalance valves.

9. The hydraulic system as claimed in claim 1, further comprising a control mode wherein the first and second solenoid valves are inoperative and the first and second counterbalance valves are controlled by pressure acting in the first and second pressure conduits.

10. A mining machine comprising: a movable carrier; at least one mining boom connected movably to the carrier; a mining unit mounted at a distal end of the mining boom; at least one hydraulic boom actuator for moving the mining boom relative to the carrier and being connected to the hydraulic system; and a hydraulic system as claimed in claim 1 arranged for providing hydraulic power and for controlling the boom actuator.

11. The mining machine as claimed in claim 10, wherein the hydraulic boom actuator is a hydraulic cylinder configured to turn the mining boom relative to the carrier.

12. The mining machine as claimed in claim 10, wherein the mining machine is an undercutting mining machine provided with a cutting boom, and the mining unit mounted to the cutting boom includes at least one rotatable cutting head provided with several cutting tools.

13. A method of controlling a hydraulic actuator, the method comprising: generating hydraulic pressure and flow by means of a hydraulic pump to a hydraulic system; directing selectively hydraulic fluid flow from the pump to working pressure spaces of the hydraulic actuator and correspondingly discharging the hydraulic fluid from the working spaces to a tank by means of a control valve; restricting the fluid flow discharged from the working pressure spaces by means of dedicated counterbalance valves; and adjusting opening pressure of the counterbalance valves by means of separate solenoid valves and thereby providing the hydraulic actuator with adjustable force control being independently controllable relative to the control valve.

14. The method as claimed in claim 13, further comprising adjusting hydraulic fluid flow and pressure affecting in the working pressure spaces independently relative to each other, whereby movement speed and generated force are also independently controlled.

15. The method as claimed in claim 13, further comprising controlling the solenoid valves by means of electrical control signals generated by means of a control unit, and generating hydraulic control signals by means of the solenoid valves for hydraulically controlling the counterbalance valves.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) Some embodiments are described in more detail in the accompanying drawings, in which

(2) FIG. 1 is a schematic side view of a mining machine intended for undercutting process;

(3) FIG. 2 is a schematic top view of a hydraulic double piston cylinder arranged to turn a boom in a horizontal direction;

(4) FIG. 3 is a schematic top view of an alternative solution which utilizes a hydraulic motor for turning a boom;

(5) FIG. 4 is a schematic view of a first hydraulic circuit configured to provide needed hydraulic power to a hydraulic actuator and for controlling its operation;

(6) FIG. 5 is a schematic view of a second hydraulic circuit wherein pressure prevailing inside a hydraulic actuator is detected;

(7) FIG. 6 is a schematic view of a third hydraulic circuit wherein additional counterbalance valves are utilized;

(8) FIG. 7 is a schematic view of a fourth hydraulic circuit wherein additional features of previous FIGS. 5 and 6 are combined with the basic system of FIG. 4; and

(9) FIG. 8 is a diagram showing some principles and features relating to the disclosed method.

(10) For the sake of clarity, the figures show some embodiments of the disclosed solution in a simplified manner. In the figures, like reference numerals identify like elements.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

(11) FIG. 1 shows a mining machine 1 intended for undercutting. The mining machine 1 comprises a movable carrier 2 and a mining boom 3 connected to the carrier 2 by means of a turret or turning table 4. The mining boom 3 comprises a mining unit 5 at a distal end of the boom 2. The mining unit 5 comprises one or more rotatable C cutting heads 6 each provided with several cutting tools, which are not shown in detail. The mining boom 2 may be moved horizontally H by turning the turning table 4 around vertical turning axis 7. The mining boom 3 may also be moved vertically V relative to a joint 8. The horizontal movement H may be executed by means of a first boom actuator 9 and the vertical movement may be executed by means of a second boom actuator 10. The boom actuators 9 and 10 may be hydraulic cylinders which are powered by means of a hydraulic power pack PP. The mining machine 1 can be moved forwards A and can be reversed B. At a front end of the mining machine 1 may be a collecting device 11 for receiving material 12 excavated by means of the cutting unit 5. The mining machine 1 comprises at least one on-board control unit CU which may be is data communication with one or more external control unit CU. On the carrier 2 may or may not be a control cabin CC for an operator.

(12) FIG. 2 is a highly simplified figure showing a system for turning a mining boom 3 horizontally H. The boom 2 is mounted to connecting flanges 13 of a turning table 4 shown in broken lines for clarity reasons. The turning table 4 is turned relative to a support element 14 provided with a toothed rim 15. A hydraulic boom actuator 9 is a cylinder mounted horizontally and comprising two pistons and working pressure spaces 16a, 16b whereby a piston rod 17 is located between the working pressure spaces 16a, 16b. The piston rod 17 is provided with a toothed outer surface 18 matching with the toothed rim 15. When the piston rod 17 is moved the turning table and the connected mining boom 3 turn horizontally H. The boom cylinder 9 is connected to a hydraulic circuit HS by means of pressure conduits 19a and 19b. Further, the hydraulic circuit HS may communicate with one or more control units CU. An operator O may communicate with the control unit CU via a user interface. The operator O may make selections, feed control parameters and make control commands for influencing control of the boom 3.

(13) FIG. 3 discloses another solution for turning a turning table 4 and a mining boom 3. The solution differs from the one shown in FIG. 2 in that the hydraulic cylinder is substituted by a hydraulic motor. So in this case the hydraulic boom actuator 9 is a hydraulic motor which is arranged to cause horizontal boom movement. The hydraulic motor may be connected to a gear or other transmission element 20 in order to transmit generated rotation movement to a toothed outer rim 15 of a support element 14. Working pressure space of the hydraulic motor are connected to a hydraulic circuit HS by means of pressure conduits 19a and 19b.

(14) The hydraulic cylinders and motors 9, 10 shown in FIGS. 1 and 2 are hydraulic actuators HA which may be controlled in accordance to principles disclosed in this document.

(15) FIG. 4 discloses a hydraulic circuit HC of a hydraulic system HS. The system comprises a hydraulic actuator HA, a pump 21, a tank 22, a control valve 23 and needed pressure conduits. The hydraulic actuator HA may be a hydraulic cylinder having a double piston configuration whereby it has two pistons 24 and a piston rod 17 between them. The cylinder also has two working pressure spaces, namely a first working pressure space 16a with a first pressure conduit 19a, and a second working pressure space 16b with a second pressure conduit 19b. The cylinder may correspond to the one shown in FIG. 2. A first counterbalance valve Cb1 is connected to the first pressure conduit 19a for controlling pressure fluid discharged from the first working pressure space 16a, and a second counterbalance valve Cb2 is connected to the second pressure conduit 19b for controlling pressure fluid discharged from the second working pressure space 16b. The counterbalance valves Cb1 and Cb2 allow pressure fluid to flow freely towards the working pressure spaces 16a, 16b but they restrict flow out of the working pressure spaces 16a, 16b. The counterbalance valves Cb1, Cb2 are provided with basic opening pressure setting, for example 400 bar, and their opening pressure setting may be adjusted to be lower than the basic setting by means of solenoid valves Sv1 and Sv2. A first solenoid valve Sv1 provides pressure control for the first counter balance valve Cb1 and a second solenoid valve Sv2 provides pressure control for the second counterbalance valve Cb2. By adjusting the opening pressure of the counterbalance valves Cb1 and Cb2 pressure prevailing in the working pressure spaces may be adjusted allowing thereby controlling force generated by the hydraulic actuator HA. The solenoid valves Sv1 and Sv2 are electrically controlled valves and can be controlled by means of electrical control signals generated by means of a control unit CU. An operator may feed control data and commands by means of a user interface UI for the control unit CU. The solenoid valves Sv1 and Sv2 can be controlled independently by means of the control unit CU.

(16) The control valve 23 is configured to control movement direction of the hydraulic actuator HA. The control valve 23 may be a proportional directional valve as shown in FIG. 1. When the control valve 23 moves from its middle position to left direction, then pressure fluid flow generated by the pump 21 is directed through the control valve 23 to the first working pressure space 16a of the hydraulic actuator HA and correspondingly fluid is discharged from the second working pressure space 16b. Then the piston rod 17 moves to left. When the control valve 23 moves from the middle position to right direction then the fluid flow is directed to the second working pressure space and the first working pressure space is discharged causing the piston rod to move to right. Since the control valve is a proportional valve, magnitude of the movement in either direction adjust magnitude of fluid flow passing through the control valve whereby the control valve adjusts fluid and also generated speed of movement of the hydraulic actuator HA. As can be noted, the control valve 23 may be hydraulically pilot controlled, or directly solenoid controlled. An electrically controlled third solenoid valve SV3 produces pressure control for moving the control valve 23 to right and an electrically controlled fourth solenoid valve SV4 produces pressure control for moving the control valve 23 to left. The solenoid valves Sv3 and Sv4 may provide electrical control signals 25 from the control unit CU.

(17) FIG. 4 further disclose that the pump 21 may be a variable displacement pump and may be controlled by a load sense signal Lss.

(18) FIG. 5 discloses a hydraulic system HS which substantially corresponds to the one shown in FIG. 4. However, pressures prevailing in the working pressure spaces 16a, 16b are sensed by means of a first pressure sensor S1 and a second pressure sensor S2. The produced sensing data is transmitted to a control unit CU via data transmission paths 26a and 26b. Then the control unit CU is able to take the received pressure data into account and send control signals via a data transmission path 27 to servo valves Sv1 and Sv2.

(19) FIG. 6 discloses a hydraulic system HS basic configuration of which corresponds to the system disclosed in FIG. 4. The present solution differs from the basic solution in that there are two additional counterbalance valves Cb3 and Cb4 series corrected with main counterbalance valves Cb1 and Cb2. Then a first additional counterbalance valve Cb3 is mounted between a first counterbalance valve Cb1 and a first solenoid valve Sv1, and correspondingly, a second additional counterbalance valve Cb4 is mounted between a second counterbalance valve Cb2 and a second solenoid valve Sv2. As can be noted, nominal operating direction of the additional counterbalance valves Cb3 and Cb4 is opposite to nominal operating direction of the main counterbalance valves Cb1 and Cb2. Further, pressure setting of the additional counterbalance valves Cb3, Cb4 is significantly lower as pressure setting of the main counterbalance valves Cb1, Cb2. As it is disclosed earlier in this document, the additional counterbalance valves Cb3 and Cb4 are used for special use cases wherein external pulling forces may be directed to the hydraulic actuator. The pulling may hamper proper controlling of the system and the use of the additional counterbalance valves Cb3, Cb4 eliminates the undesired effects of the pulling.

(20) FIG. 7 discloses a hydraulic system HS which comprises a combination of features disclosed in connection with FIGS. 4 to 6. Therefore, there is no need to provide detailed disclosure of the system shown in FIG. 7. The disclosed control features may be selective activated whereby a versatile and well adjustable system is provided.

(21) Let it be mentioned that the hydraulic systems and circuits presented in FIGS. 4-7 are suitable also for controlling normal hydraulic cylinders with one single piston, and also for controlling hydraulic motors. The disclosed solution suits well for controlling different boom actuators but may also be used for controlling other mechanical arms and structures of different kind of excavating and tunnelling machines.

(22) The basic pressure setting values disclosed in connection with the counterbalance valves are only examples and can be selected case by case.

(23) FIG. 8 discloses features that have already been discussed above in this document.

(24) The drawings and the related description are only intended to illustrate the idea of the invention. In its details, the invention may vary within the scope of the claims.