HYDRAULIC SYSTEM AND METHOD OF CONTROLLING HYDRAULIC ACTUATOR

Abstract

A hydraulic system, a mobile mining machine and to a method of controlling a hydraulic actuator is provided. The hydraulic system includes two hydraulic pumps (P1, P2) for generating hydraulic power for a hydraulic actuator. The pumps are powered by means of a common electric motor. Operation of the actuator is controlled by controlling speed and direction of the motor, whereby hydraulic lines (19a, 19b) may be without actively controlled control valves.

Claims

1. A hydraulic system of a mobile work machine comprising: at least one hydraulic pump arranged to generate hydraulic fluid flow and pressure to a hydraulic circuit; at least one electric motor arranged to rotate the at least one hydraulic pump; at least one hydraulic actuator connected to the hydraulic circuit; and at least one control device for controlling operation of the hydraulic system, the at least one hydraulic pump including a first hydraulic pump and a second hydraulic pump, the first hydraulic pump being connected to a first working pressure space of the hydraulic actuator by a first hydraulic line and the second hydraulic pump being connected to a second working pressure space of the hydraulic actuator by a second hydraulic line, and wherein pressure of the hydraulic fluid prevailing in the first working pressure space and the second pressure space are configured to cause inversely directed forces for a moving element of the hydraulic actuator, the at least one electric motor being one common electric motor configured to rotate the two hydraulic pumps simultaneously, the first and second hydraulic pumps having inverse pumping characteristics so that when the first hydraulic pump generates a pressure the second hydraulic pump generates a suction, and vice versa, and wherein movement speed and direction of the hydraulic actuator are controlled by controlling rotational speed and direction of the common electric motor.

2. The hydraulic system as claimed in claim 1, comprising one single hydraulic actuator, whereby the entire hydraulic system is dedicated to operating the single hydraulic actuator.

3. The hydraulic system as claimed in claim 1, wherein rotation speed and direction of the common electric motor is controlled by a frequency converter whereby the hydraulic actuator is controlled indirectly by means of the frequency controlled electric motor.

4. The hydraulic system as claimed in claim 1, wherein movement speed and direction of the hydraulic actuator are configured to be proportional to rotation speed and direction of the common electric motor.

5. The hydraulic system as claimed in claim 1, wherein the first and second hydraulic pump are connected to a same rotating axle rotated by the common electric motor.

6. The hydraulic system as claimed in claim 1, wherein a nominal size of the first working pressure space of the hydraulic actuator is greater than a nominal size of the second working pressure space, the first hydraulic pump having a first volume flow rate per revolution and the second hydraulic pump having a second volume flow rate per revolution which is less than the first volume flow rate per revolution.

7. The hydraulic system as claimed in claim 1, wherein the hydraulic circuit is an open circuit system, wherein feed ports of the first and second pump are connected to a reservoir.

8. The hydraulic system as claimed in claim 1, further comprising an energy recovery feature arranged to convert kinetic energy into hydraulic energy, to convert the hydraulic energy into kinetic rotational energy, and further for converting to convert the kinetic rotational energy into electric energy wherein at least one of the first and second hydraulic pumps is configured to serve as a hydraulic motor when discharged hydraulic fluid flow is flowing through the at least one of the first and second hydraulic pump to the reservoir, whereby rotation of the at least one of the first and second hydraulic pump is generated, the at least one of the first and second hydraulic pump being configured to rotate the common electric motor, which is configured to serve as a generator when being de-energized, and the rotation of the common electric motor being configured to generate electric energy.

9. The hydraulic system as claimed in claim 1, wherein the first and second hydraulic lines are both without any actively controlled valves.

10. A mobile mining machine, comprising: a movable carrier; at least one mine work device for executing mining work at an underground or surface mine work site; and a hydraulic system in accordance with claim 1 for moving the mine work device, wherein the movement speed and direction of the hydraulic actuator connected to the dedicated hydraulic system is controlled by means of the speed controlled electric motor.

11. The mining machine as claimed in claim 10, wherein the mining machine is a rock drilling rig including at least one drilling boom provided with a drilling unit, the drilling boom having at least one hydraulic boom cylinder for moving the drilling boom, and wherein movement speed and direction of the at least one hydraulic boom cylinder connected to the dedicated hydraulic system is configured to be controlled by means of the speed controlled electric motor.

12. The mining machine as claimed in claim 10 or 11, wherein the mining machine is a frame steered vehicle, selected from a rock drilling rig, wheel loader or hauling truck, including two frame parts and a steering joint between the frame parts, the frame parts being turned during steering relative to each other by at least one hydraulic steering cylinder connected to the dedicated hydraulic system, and wherein movement speed and direction of the at least one steering hydraulic cylinder is configured to be controlled by the speed controlled electric motor.

13. The mining machine as claimed in claim 10, wherein the mining machine is a wheel loader having a bucket which is connected to the carrier by at least one lifting arm, the at least one lifting arm being movable relative to the carrier by at least one hydraulic lifting cylinder connected to the dedicated hydraulic system, and wherein movement speed and direction of the at least one hydraulic lifting cylinder is configured to be controlled by the speed controlled common electric motor.

14. The mining machine as claimed in claim 10, wherein the mining machine is a hauling truck including a dump box for receiving rock material, the dump box being movable relative to the carrier by means of at least one hydraulic dump cylinder connected to the hydraulic system, and wherein movement speed and direction of the at least one hydraulic dump cylinder is configured to be controlled by the speed controlled common electric motor.

15. A method of controlling a hydraulic actuator, the method comprising: generating hydraulic power to a hydraulic circuit by means of at least one hydraulic pump which is actuated by an electric motor (M); and feeding and discharging hydraulic fluid from the hydraulic circuit to a first and second working pressure space of a hydraulic actuator for controlling movement speed and direction of a movement element of the hydraulic actuator; influencing hydraulic power prevailing in the first working pressure space of the actuator by means of a dedicated first hydraulic pump; influencing hydraulic power prevailing in the second working pressure space by means of a dedicated second hydraulic pump; rotating the first and second hydraulic pump by means of one common speed controlled electric motor; and controlling movement speed and direction of the movement element of the hydraulic actuator by controlling rotation of the common electric motor.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0052] Some embodiments are described in more detail in the accompanying drawings, in which:

[0053] FIG. 1 is a schematic side view of a frame steered rock drilling rig for underground drilling and being provided with a movable drilling boom.

[0054] FIG. 2 is a schematic side view of a frame steered wheel loader for mine use and being equipped with a movable bucket.

[0055] FIG. 3 is a schematic side view of a frame steered hauling truck provided with a movable dump box.

[0056] FIG. 4 is a schematic diagram of a hydraulic circuit configured to generate power for a hydraulic actuator operation of which is controlled by an electric motor powering a double pump system.

[0057] FIG. 5 is a schematic diagram of a hydraulic circuit configured to drive a hydraulic cylinder.

[0058] FIG. 6 is a schematic diagram of a more complete hydraulic circuit in a de-pressurized state.

[0059] FIG. 7 is a schematic diagram of a hydraulic circuit configured to operate several hydraulic actuators one at a time, and using the disclosed one motor, two pumps control principle.

[0060] FIG. 8 is a schematic diagram of a hydraulic circuit including two hydraulic cylinders operating in parallel manner.

[0061] FIG. 9 is a schematic diagram of another hydraulic circuit including two hydraulic cylinders operating simultaneously but in opposite directions.

[0062] FIG. 10 is a schematic side view of a mobile work machine including a rotatable upper frame.

[0063] FIG. 11 is a schematic side view of a boom lifting and locking means.

[0064] 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

[0065] FIG. 1 shows a rock drilling rig 1 as a first example of a mobile mining machine 2 including a carrier 3 and a drilling boom 4 provided with a rock drilling unit 5. The machine 2 may be frame steered, whereby it includes a front frame part 6a and a rear frame part 6b, and a turning joint 7 between them. The frame parts 6a, 6b may be turned relative to each other by means of one or two hydraulic steering actuators 8. The boom 4 may be moved by one or more lifting cylinders 9. It should be appreciated that machine 2 may also include other hydraulic actuators. Also, rock bolting rigs, charging rigs and measuring vehicles may include a substantially similar basic carrier and boom structures. Further, the machine 2 may be an electrically operated device and may include a battery 10 or corresponding electric power storage.

[0066] The machine 2 includes at least one hydraulic system 11 or circuit for generating hydraulic power for the hydraulic actuators. For clarity reasons the hydraulic system 11 is shown in a simplified manner. The machine 2 may include one or more improved hydraulic systems disclosed herein for powering and controlling dedicated hydraulic actuators, such as the steering cylinders 7 and the lifting cylinders 9. The above disclosed solutions and embodiments may be applied in all type of rigs being implemented in mine operations. The same applies to both surface and underground machines.

[0067] FIG. 2 discloses a wheel loader 12 provided with a bucket 13, which is movable by means of a lifting cylinder 9. The bucket 13 may be tilted relative to an outer end portion a lifting arm 39 by a tilting cylinder 40. The loader 12 may also be frame steered and may include a steering cylinder 7 for turning the frame parts 6a, 6b.

[0068] FIG. 3 discloses a hauling truck 14 including a dump box 15 for receiving rock material. The dump box 15 is movable relative to a carrier 3 by means of one or two hydraulic dump cylinders 16.

[0069] FIGS. 2 and 3 disclose mining machines 2, which may include dedicated hydraulic systems for powering and controlling their steering cylinders 7, lifting cylinders 9 and dump cylinders 16.

[0070] FIG. 4 discloses a hydraulic system 11 including two hydraulic pumps P1 and P2 driven by a common electric motor M. A control device or unit CU may control rotation speed and direction of the motor M. The motor M may be connected to the pumps P1, P2 by a rotating axle 17, whereby both pumps P1 and P2 are rotated simultaneously. In this case the pumps P1 and P2 may have the same capacity since pressure spaces of a hydraulic actuator HA may have similar size on both sides of a moving element of the actuator. The hydraulic actuator HA may be a hydraulic cylinder HC or a hydraulic motor HM, both having movement directions A and B. In the cylinder the moving member or element may be a piston and in the motor it may be rotating separation element, gear or wheel. The hydraulic actuator HA has pressure ports 18a, 18b which are connected by means of fluid lines 19a, 19b to the pumps P1, P2. The pumps P1, P2 are in fluid connection to a reservoir 20 through fluid lines 21a, 21b.

[0071] As can be noted, operation of the hydraulic actuator HA is controlled by controlling the motor since there are no control valves in the fluid lines 19a, 19b. When the motor M receives speed and direction request from the control unit CU, it begins to rotate in direction R1, whereby the first pump P1 generated pressure P+ to the pressure port 18b of the hydraulic actuator HA. Thereafter, the moving member of the hydraulic actuator initiates its movement in the direction A and hydraulic fluid is discharged from the actuator HA through the pressure port 18b. Simultaneously, the second pump P2 is rotated by the motor M and the pump P2 causes suction P- to the pressure line 19b. When the actuator HA is moved in the opposite direction, then direction of the motor M is changed and rotational speed of the motor M is adjusted in accordance with the desired movement speed of the actuator HA. This way, movement control of the actuator HA is controlled indirectly by the electric motor M without a need for any directional control valves.

[0072] FIG. 5 discloses a hydraulic circuit 11, which corresponds to the one shown in previous FIG. 4. However, in this case the hydraulic actuator HA is a hydraulic cylinder HC having pressure spaces 22a, 22b separated by a piston 23. Pressures space 22b has a smaller cross-sectional area because of a piston rod 24, whereby volume of the space 22b is smaller than volume of the space 22a. Therefore, the second pump P2 connected to the second space 22b may have a smaller displacement capacity compared to the first pump P1. Basic structures and operational principles are the same in the solutions of FIG. 4 and FIG. 5.

[0073] FIG. 6 discloses a hydraulic circuit 11, which differs from the previously presented circuit of FIG. 5 in that the circuit 11 is now provided with two load holding valves 25a, 25b arranged in the pressure lines 19a, 19b. When the circuit 11 is in non-pressurized state, spring loaded load holding valves 25a, 25b are closed as it is disclosed in FIG. 6. When the system is activated, a control pressure line 26 is pressurized and the load holding valves 25a, 25b, which are pressure controlled, change their positions into an open state. Further, the circuit 11 may include an anti-cavitation arrangement 27 for protecting the pumps P1, P2 against possible anti-cavitation situations. Thus, the anti-cavitation system has no effect for the control of the hydraulic actuator HA. The anti-cavitation system may include two passive check valves 28a, 28b and a pressure connection 29 to the reservoir 20. When cavitation appears, then the system allows supplementary hydraulic fluid flow to be directed through the line 29 to the pump before cavitation occurs. The circuit 11 may also include a shuttle valve 30 between the cavitation system 27 and the control pressure line 26 of the load holding valves 25a, 25b. However, all of the disclosed valves 25a, 25b, 28a, 28b and 30 are just passive valves requiring no active control, and further, operation of the valves have no influence to operational control of the hydraulic cylinder HC.

[0074] FIG. 6 further discloses that the system may include a user interface UI, by means of which control commands and parameters may be input to the control unit CU. New software programs may also be fed through the user interface UI to be executed in the control unit CU. The system may further include one or more electrical storages ES, such as a battery pack. The recovered electrical energy of the motor M may be stored to the storage ES, or alternatively used for running other electrical devices.

[0075] FIG. 7 discloses a hydraulic circuit 11, which utilizes the above disclosed control principle, but is in this embodiment it is configured to actuate three hydraulic actuators HA1, HA2, HA3 at separate times. Then one of these actuators HA1-HA3 may be selectively connected to the disclosed hydraulic system one at a time. The system includes a distribution device DD for executing the selection. The distribution device DD may operate using simple ON/OFF principle.

[0076] FIG. 8 discloses a hydraulic circuit 11 wherein two similar hydraulic cylinders HC1 and HC2 are controlled simultaneously by utilizing the disclosed one motor and two pumps control principle. The pressure ports 18a1 and 18a2 are connected to each other by a line 31, and correspondingly the ports 18b1 and 18b2 are connected by a line 32. Then the cylinders HC1, HC2, which may be hydraulic dump cylinders of a hauling truck, for example, operate simultaneously.

[0077] FIG. 9 discloses a hydraulic circuit 11 wherein two similar hydraulic cylinders HC1 and HC2 are controlled simultaneously by utilizing the disclosed one motor and two pumps control principle. The solution differs from the one shown in the previous FIG. 8 in that now a piston-side pressure space of the first hydraulic cylinder HC1 and a rod-side pressure space of the second hydraulic cylinder HC2 are in fluid connection to a common line 41, and correspondingly, a rod-side pressure space of the first hydraulic cylinder HC1 and a piston-side pressure space of the second hydraulic cylinder HC2 are in fluid connection to a common line 42. Further, the pumps P1 and P2 are equally sized. This kind of solution is suitable to be used in the frame steering implementations, for example. The cylinders HC1 and HC2 may be located on opposite sides of the steering joint and when the first cylinder HC1 extends, the second cylinder HC2 retracts, and vice versa. The steering requires the same amount hydraulic fluid for both lines 41, 42, wherefore the pumps P1, P2 may be similar.

[0078] FIG. 10 discloses a mobile work machine MWM in a simplified manner. The machine MWM may include a lower frame 33a and an upper frame 33b provided with a work device 34, such as a boom, bucket, mast or corresponding device. The upper frame 33b may be turned relative to the lower frame 33a by mans of a hydraulic rotation motor 35, which may be controlled by the disclosed control principle utilizing the speed and direction controlled electric motor. For simplicity reasons, the hydraulic circuit is not disclosed. The lower frame 35a includes moving members 36 such as crawler tracks or wheels. The upper frame 33b may be arranged to be turned a limited angle range or it may have rotatable operation.

[0079] FIG. 11 discloses a a boom 4 movable relative to a joint 37 on a carrier 3 of a mobile machine. At a distal end of the boom 4 may be a working device WD, such as a man cage, whereby the mobile machine may be a personal lifter, for example. The boom 4 may be lifted using a lifting cylinder 9 or two lifting cylinders operating in parallel. The lifting cylinder 9, or the doubled cylinders, may be driven by the disclosed one motor, two pumps system. The movement of the boom 4 may be locked for security reasons with a locking cylinder 38, which may be located in connection with the joint 37 or it may be arranged to lock movements of the lifting cylinder 9 mechanically. The locking cylinder 38 or motor may be arranged to operate simultaneously together with the lifting cylinder 9, whereby no separate control valves and control commands are needed for controlling their operation.

[0080] Although the present embodiment(s) has been described in relation to particular aspects thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. It is preferred therefore, that the present embodiment(s) be limited not by the specific disclosure herein, but only by the appended claims.