Abstract
A brake system, method for controlling the brake system and a mine vehicle having the same are provided. The brake system of the mine vehicle includes spring activated and hydraulically released brake assemblies in connection with wheels of the vehicle. The brake assemblies have hydraulic release actuators, which are pressurized for releasing the brakes. During normal operation, the release actuators are pressurized by a main brake circuit and are controlled by a brake controller. A separate release circuit and pressure source may be activated for releasing the brakes when the vehicle is disabled. The system further includes an override device for selectively depressurizing the release actuators during towing.
Claims
1. A brake system of a mine vehicle comprising: a plurality of spring applied hydraulically released brake assemblies, wherein the brake assemblies include springs arranged to apply brakes and hydraulically operable release actuators arranged to release the brakes; a hydraulic main brake circuit connected to a first pressure source and to the release actuators and including at least one brake controller having a first control position to pressurize the release actuators for releasing the brakes, and a second control position to depressurize the release actuators for applying the brakes; a hydraulic release circuit including at least one second pressure source for pressurizing the release actuators, and thereby activating the release circuit, independently relative to the main brake circuit; and at least one override device, which is selectively operable for depressurizing the release circuit for applying the brakes, whereby the brakes are operable by means of the override device despite the activation of the release circuit.
2. The brake system as claimed in claim 1, wherein the override device includes at least one override valve connected to the release circuit, the override valve being switchable from a first control position to a second control position for depressurizing the release circuit and to thereby activate the brakes.
3. The brake system as claimed in claim 2, further comprising a brake pedal arranged to control operation of the brake controller of the main brake circuit, the override valve being located so as to also be actuated by the brake pedal.
4. The brake system as claimed in claim 3, further comprising a brake pedal unit including a frame, the brake pedal, the brake controller and the override valve, wherein the brake pedal is connected to the frame by means of a turning joint arranged to allow the brake pedal to swing relative to the frame, the brake controller and the override valve being located at opposite sides of the turning joint, whereby the swinging movement of the brake pedal in one direction is configured to move the brake controller and the override valve in opposite directions.
5. The brake system as claimed in claim 1, wherein the release circuit is separated from the main brake circuit by means of at least one pressure controlled separation valve; and the at least one separation valve is configured to open a fluid connection from the release circuit to the brake assemblies when the pressure of the release circuit exceeds a preset pressure limit.
6. A mine vehicle comprising: a carrier provided with several wheels; at least one mine work device arranged on the carrier for executing mine work tasks; and a brake system including a plurality of spring applied and hydraulically released brake assemblies at the wheels, the brake assemblies being provided with hydraulic release actuators, wherein the brake system includes a hydraulic main brake circuit and a separate hydraulic release circuit for actuating the release actuators, and wherein the main brake circuit includes a first pressure source and a brake controller for directing hydraulic pressure to the release actuators for releasing the brakes during normal use of the mine vehicle, the release circuit including a second pressure source and at least one control element for directing hydraulic pressure independently to the release actuators when the main brake circuit is depressurized, and the brake system including at least one tow element allowing towing of the mine vehicle when being disabled, wherein the brake system is in accordance with claim 1 and includes the disclosed override device for depressurizing the release circuit to allow breaking during towing.
7. The mine vehicle as claimed in claim 6, wherein the tow element is arranged movably relative to the carrier and has an idle normal position and an activated towing position, the movable tow element being connected to a hydraulic pump configured to generate hydraulic pressure for the release circuit when the tow element is moved from the idle normal position to the activated towing position.
8. The mine vehicle as claimed in claim 6, wherein the control element of the release circuit is a pressure controlled separation valve configured to separate the main brake circuit and the release circuit from each other when pressure of the release circuit is under a preset pressure limit.
9. A method of controlling spring activated and hydraulically releasable brake assemblies of a mine vehicle, the method comprising: generating hydraulic pressure to a main brake circuit by means of a first hydraulic source; controlling feeding of the hydraulic pressure to release actuators of the brake assemblies by means of a brake controller connected to the main brake circuit; directing the hydraulic pressure fluid in the main brake circuit to the release actuators for releasing the spring activated brakes; directing the hydraulic pressure fluid in the main brake circuit away from the release actuators for depressurizing the release actuators and applying the brakes by means of the springs of the brake assemblies; directing selectively hydraulic pressure fluid from a second pressure source via a separate release circuit to the release actuators, and thereby activating the release circuit, for releasing the brakes independently when the main brake circuit is depressurized; and depressurizing the release circuit selectively by means of an override device connected to the release circuit and activating the brakes despite of the activated release circuit.
10. The method as claimed in claim 9, further comprising disconnecting the release circuit from the second pressure source and discharging the release circuit selectively by means of an override valve connected to the release circuit.
11. The method as claimed in claim 9, comprising activating the operation of the override device by means of a brake pedal arranged to control the brake controller of the main brake circuit.
12. The method as claimed in claim 9, comprising providing control for the brake system by means of the override device only after the release circuit has been pressurized.
13. The method as claimed in claim 9, comprising pressurizing the release circuit automatically in response to towing of the mine vehicle.
Description
BRIEF DESCRIPTION OF THE FIGURES
[0037] Some embodiments are described in more detail in the accompanying drawings, in which
[0038] FIG. 1 is a schematic side view of a wheel loader,
[0039] FIG. 2 is a schematic view of a brake system of a mine vehicle,
[0040] FIG. 3 is a schematic view of a part of a brake system comprising an override device,
[0041] FIG. 4 is a schematic view of a part of a brake system comprising an alternative override system for allowing braking despite of the activated release circuit,
[0042] FIG. 5 is a schematic view of a part of a brake system wherein an override valve and a brake controller are both actuated by means of a brake pedal,
[0043] FIG. 6 is a schematic view of a part of a brake system wherein a brake controller and an override valve have dedicated manual actuation elements,
[0044] FIG. 7 is a schematic diagram showing some alternative pressure sources for generating needed release pressure for a release circuit of a brake system, and
[0045] FIG. 8 is a schematic view of brake pedal unit.
[0046] 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
[0047] FIG. 1 shows a wheel loader 1 as an example of a mine vehicle 2. Also hauling trucks and rock drilling rigs are mine vehicles 2 comprising at least one mine work device 3. The disclosed method and solution may be applied in all type mine vehicles and especially for those intended for underground mines.
[0048] The wheel loader 1 shown in FIG. 1 comprises a carrier 4 and a bucket 5 connected movably to the carrier 4. The carrier 4 comprises a front axle 6 provided with front wheels 7a and a rear axle 8 provided rear wheels 7b. The wheels 7 are provided with spring activated and hydraulically released brakes (SAHR-brakes), which are connected to a hydraulic brake circuit. The carrier also comprises a main power unit 9 in connection of which may be a main hydraulic pump 10 for generating hydraulic pressure for a hydraulic system of the wheel loader 1. During normal operation of the wheel loader the hydraulic pressure generated by the main hydraulic pump 10 may be conveyed to the brake system too. FIG. 1 further discloses that a rear end of the carrier 4 may be provided with a towing element 11, such as towing hook, for towing the wheel loader when it has become disabled. The towing element 11 may be connected movably to the carrier 4. At a front end portion of the carrier 4 is a control cabin 12 provided with brake and other control means.
[0049] In FIG. 2 a brake system 13 of the wheel loader 1 of FIG. 1 is shown. In connection with the front wheels 7a and the rear wheels 7b are brake assemblies 14 each of which comprise at least one spring S for connecting brakes 15 and at least one release actuator RA for disconnecting the brakes 15. The brakes 15 may comprise disc-like braking elements for generating braking forces, or alternatively, the brakes may comprise brake shoes, for example. The brake assemblies 14 are connected to a hydraulic main brake circuit 16, which comprises at least one first pressure source Ps1 and at least one brake controller BC. The first pressure source Ps1 may comprise a connection to a main hydraulic system of the wheel loader, or it may comprise a dedicated hydraulic pump. The brake controller BC may be located in the control cabin whereby an operator may control operation of the release actuators RA. Further, the brake system 13 comprises a hydraulic release circuit 17 provided with a second pressure source Ps2. The second pressure source Ps2 may be operated independently relative to the first pressure source Ps1, whereby the release actuators RA may be pressurized also in situations when the main brake system is failed. Both brake circuits 16, 17 comprise dedicated pressure channels 18, 19, which are separated from each other at the front and rear axles 6, 8 by means of separating valves 20a, 20b or corresponding control elements. The separating valves 20a, 20b may control feeding of pressure fluid selectively to the brake assemblies 14.
[0050] FIG. 3 discloses a brake system 13, which is provided with an override device 21 configured to depressurize the release circuit 17 in response to control measures. The override device 21 may comprise a control element 22 for generating manual control movements or signals for controlling operation of a control member 23, which is arranged in fluid connection with the release circuit 17. The control element 22 may be a push button or a control lever arranged to affect operation of the control member 23, which may be a valve, for example. The control member 23 may close connection to the second pressure source Ps2 and may connect the release circuit 17 to a discharge line, whereby the release circuit may be depressurized in response to control measures executed by the control element 22.
[0051] In normal situation a pressure controlled separating valve 20 is in a first control position 24a since a first pressure control line 25 is pressurized by means of pressure of the main brake circuit 16. The separating valve 20 is also pushed towards the first control position 24a by means of a spring 26. When the main brake circuit 16 is disabled and the release circuit 17 is pressurized, a second pressure control line 27 of the separating valve 20 is pressurized and the valve 20 moves against force of the spring 26 towards a second control position 24b. The spring force may be adjusted so that the change of the control positions occurs only in response to exceed of a predetermined pressure limit, which may be 10 bars, for example. The release actuator RA may be a hydraulic cylinder, or alternatively, it may be a hydraulic motor connected to a gear device for transforming generated turning movement into linear movement.
[0052] In the first control position 24a the main brake circuit 16 is connected to the release actuators RA and the release circuit 17 is disconnected. In the second control position 24b the main brake circuit 16 is disconnected and the release circuit 17 is connected. However, operation of the connected release circuit 17 may be cancelled by means of the override device 21.
[0053] In FIG. 3 only one release actuator RA is shown for the shake of clarity. However, the separating valve 20 may control pressure fluid to one or more release actuators on the same axle through a pressure channel 28. Further, the main brake circuit 16 may be connected to one or more other separating valves by means of a pressure channel 29, and the release circuit 17 may have a corresponding connection to them through a pressure channel 30. Operation principle of the brake system 13 is the same despite of number of the axles of the mine vehicle and number of the controlled brake assemblies. Thus, FIGS. 4-6 are simplified in the same manner for improving clarity.
[0054] The brake system disclosed in FIG. 4 is substantially the same as in FIG. 3, except the override device 21, which is in FIG. 4 arranged to a pressure line connecting the separating valve 20 and the release actuator RA. Then, the override device 21 may comprise an electrically controlled override valve 31 serving as a control member 23. The control valve 31 may be controlled remotely by means of a manual control element 22, such as a control button, which may be located in the control cabin. The override valve 31 is in FIG. 4 in a first control position 32a wherein connection between the separating valve 20 and the release actuator RA is connected. When the control element 22 is actuated, the valve switches to a second control position 32b, wherein connection to the separating valve 20 is closed and connection to a tank 33 is opened. Thus, the release actuator RA is depressurized and the brakes are actuated. Similar override device 21 may be arranged to other axles and wheels of the mine vehicle.
[0055] FIG. 5 discloses an alternative system for controlling the brake controller BC and the override device 21 by utilizing a normal brake pedal 34. The brake controller BC and an override valve 36 of the override device 21 may be located on opposite sides of a turning joint 35. Thereby the brake controller BC and the override valve 36 are moved in opposite directions when the brake pedal 34 is pressed. The brake controller BC may be a directional valve having three control positions 37a-37b. In a first control position 37a the main brake circuit 16 is pressurized since connection to the first pressure source Ps1 is open. In a second control position 37c the main brake circuit 16 is connected to a tank line T and the brakes are actuated. In a third control position 37b all connections are closed. Actuation of the brake pedal 34 lifts the control valve of the brake controller BC upwards and the brake pedal 34 and the brake controller BC may be returned to the normal lower position by means of a spring element. The override valve 36 may also be a directional valve and it comprises a normal first control position 38a wherein the release circuit 17 is connected to the second pressure source Ps2 and connection to the tank line T is closed. The override valve is kept in the normal first control position 38a by means of a spring 39, for example. When the brake pedal is pressed, then a roller element 40 or corresponding force transmitting element or plunger transmits mechanical movement of the brake pedal 34 to the override valve 36 and moves it in down ward direction. Then a second control position 38b is actuated and the release circuit 17 is connected to a tank line T and connection to the second pressure source Ps2 is closed. The structure and operation of the separating valves 20 and the brake assemblies 14 may be the same as disclosed in connection with the previous Figures.
[0056] FIG. 6 discloses a solution that differs from the solution of FIG. 5 in that the override valve 36 is not actuated by the brake pedal but instead it may be actuated by a control lever 41. The control lever 41 may be located in the control cabin or elsewhere.
[0057] FIG. 7 discloses some feasible second pressure sources Ps2 for pressurizing the release circuit. The needed pressure may be generated by means of a pressure pump unit 42 arranged in connection with the towing element 11. Then the towing element 11, such as towing hook, is arranged to move a piston rod 43 of a cylinder 44, whereby a piston 45 moves inside the cylinder 44 and generates pressure in a pressure space 46. The generated pressure may be conveyed through a pressure port 47 to the release circuit. When towing force is removed a spring 48 may return the towing element 11 and the piston 45 to their initial normal positions. Thus, the cylinder 44 acts as a pumping device when the towing element 11 is pulled for initiating the towing. Alternatively, the release circuit may comprise a dedicated hydraulic power pack 49 comprising a hydraulic pump 50 and a power device 51 for actuating the pump 50. The power device may be an electrical motor M and the power pack 49 may comprise an energy storage for driving the motor. Alternatively, the power device may be a manually operable lever or corresponding element. A further alternative is to use a pressure storage or pressure accumulator 52 for pressurizing the release circuit. The pressure accumulator 52 comprises a gas space 53, a hydraulic fluid space 54 and a separating element 55, such as a piston or membrane, between the spaces 53, 54. Hydraulic fluid may be stored inside the space 54 and the gas space 53 may be pre-charged with pressurized gas. Operational condition of the accumulator 52 may be monitored in order to ensure that the accumulator is continuously operable to provide the needed pressure for the release circuit.
[0058] FIG. 8 discloses a brake pedal unit 56 comprising a frame 57, a brake pedal 34, a turning joint 35, a brake controller BC and an override device 21. The frame 56 may comprise fastening means for mounting the brake pedal unit 56 in one single piece to a mine vehicle. The brake controller BC may be a directional valve which is connected by means of a lifting lever 58 and a joint 59 to the brake pedal 34. The override device 21 comprises an override valve 36 fastened to the frame 57 and comprising a plunger 60 facing towards the brake pedal 34. The brake pedal 34 may comprise a rotating roller 40 configured to push the plunger 60 when the brake pedal 34 is actuated.
[0059] In an alternative brake pedal unit may the brake controller and the override valve may be arranged on the same side relative to the turning joint, or their location may be opposite to that shown in FIGS. 5 and 8.
[0060] 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.
