Electro-hydraulic control system with fail-safe pilot valves

Abstract

The disclosure relates to an electro-hydraulic control system for directing fluid to at least one hydraulic actuator, the system comprising at least one electronic controller; first and second pilot valves being electrically connected to the at least one electronic controller which is arranged to control the operation of the first and second pilot valves, third and fourth pilot valves being electrically connected to the at least one electronic controller which is arranged to control operation of the third and fourth pilot valves. A pilot operated main valve is configured to control fluid flow to at least one hydraulic actuator. Each of the first and second pilot valves and the third and fourth pilot valves is a fail-safe pilot valve arranged to drain a regulated outlet port to a low pressure reservoir if a spool of the fail-safe pilot valve becomes stuck in an open state.

Claims

1. An electro-hydraulic control system for directing fluid to at least one hydraulic actuator, the electro-hydraulic control system comprising: at least one electronic controller; first and second pilot valves being electrically connected to the at least one electronic controller which is arranged to control the operation of the first and second pilot valves, third and fourth pilot valves being electrically connected to the at least one electronic controller which is arranged to control operation of the third and fourth pilot valves, a pilot operated main valve configured to control fluid flow to the at least one hydraulic actuator, wherein the first and second pilot valves and the third and fourth pilot valves each being fluidly connected to the pilot operated main valve and configured to forward a direction input to the pilot operated main valve to control fluid flow to the at least one hydraulic actuator, wherein the first pilot valve and the third pilot valve are connected in parallel via a first shuttle valve to a first pilot inlet port of the main valve, wherein the second pilot valve and the fourth pilot valve are connected in parallel via a second shuttle valve to a second pilot inlet port of the main valve, wherein each of the first and second pilot valves and the third and fourth pilot valves includes a spool, an inlet port fluidly connected to a high-pressure fluid source, a first regulated outlet port fluidly connected to the first pilot input port or the second pilot inlet port of the main valve, and a second outlet port fluidly connected to a low pressure reservoir, wherein the spool is moved to a first position to enable fluid communication between the first regulated outlet port and the second outlet port when a corresponding one of the first and second pilot valves and the third and fourth pilot valves is in a deactivated state, wherein the spool is moved to a second position to enable fluid communication between the inlet port and the first regulated outlet port when a corresponding one of the first and second pilot valves and the third and fourth pilot is in an activated state in which the direction input is provided to the pilot operated main valve, wherein the first and second pilot valves and the third and fourth pilot valves are fail-safe pilot valves arranged to drain the first regulated outlet port to the low pressure reservoir if the spool of a corresponding one of the fail-safe pilot valves becomes stuck in an open state during which a solenoid actuator of the corresponding one of the of fail-safe pilot valves moves into a non-actuated position corresponding to the deactivated state of the corresponding one of the fail-safe pilot valves while the spool remains in the second position corresponding to the activated state of the corresponding one of the fail-safe pilot valves whereby the solenoid actuator is disconnected from the spool, and wherein when the spool is stuck in the open state, the spool being in the second position enables fluid communication between the inlet port and the second outlet port via a fluid connection between an internal fluid line of the spool and a surrounding cavity in which pressurized fluid is accumulated, the internal fluid line being fluidly connected between the surrounding cavity and the low pressure reservoir whereby fluid flows from the high-pressure fluid source to the low pressure reservoir.

2. The electro-hydraulic control system according to claim 1, wherein the system further comprises a first pressure regulator connected to the first and second pilot valves and a second pressure regulator connected to the third and fourth pilot valves, wherein the pressure provided from the first pressure regulator is higher than the pressure provided from the second pressure regulator.

3. The electro-hydraulic control system according to claim 2, wherein the system is configured to monitor a spool position of the main valve.

4. The electro-hydraulic control system according to claim 3, wherein an input device for providing direction input is electrically connected to the at least one electronic controller.

5. The electro-hydraulic control system according to claim 2, wherein the system comprises a first and second main valve pilot pressure sensors for monitoring the pilot pressure supplied to the first and second pilot inlet ports respectively.

6. The electro-hydraulic control system according to claim 1, wherein the system is configured to monitor a spool position of each of the first, second, third and fourth pilot valves respectively.

7. The electro-hydraulic control system according to claim 6, wherein, when the system determines that the spool of any one of the first, second, third and fourth pilot valves is in a stuck position, direction inputs to the first, second, third or fourth pilot valve that has the spool in the stuck position, are shut off.

8. The electro-hydraulic control system according to claim 1, wherein the system comprises a first, second, third and fourth pressure sensor for monitoring the pilot valve pressure of each of the first, second, third and fourth pilot valves respectively.

9. The electro-hydraulic control system according to claim 8, wherein, when a pressure sensor indicates a pressure error of any one of the first, second, third and fourth pilot valves, direction inputs to the first, second, third or fourth pilot valve that has a stuck spool, is shut off.

10. The electro-hydraulic control system according to claim 1, wherein the at least one electronic controller may be arranged to operate only the first pilot valve and the second pilot valve while the third pilot valve and the fourth pilot valve are idle.

11. The electro-hydraulic control system according to claim 10, wherein the high-pressure fluid source comprises a first pump and a second pump arranged to provide fluid flow to the main valve and the first, second, third and fourth pilot valves.

12. The electro-hydraulic control system according to claim 11, wherein the second pump is arranged to be driven by an electrical motor.

13. The electro-hydraulic control system according to claim 1, wherein the at least one electronic controller is arranged to operate the first pilot valve and the third pilot valve substantially in parallel and the second pilot valve and the fourth pilot valve substantially in parallel.

14. The electro-hydraulic control system according to claim 1, wherein the high-pressure fluid source comprises a first pump arranged to provide fluid flow to the main valve and the first, second, third and fourth pilot valves.

15. The electro-hydraulic control system according to claim 1, wherein the at least one controller comprises a first electronic controller and a second electronic controller where the first and second electronic controllers are electrically connected to each other to provide redundancy.

16. The electro-hydraulic control system according to claim 15, wherein the first and second pilot valves are electrically connected to the first electronic controller, which is arranged to relay the direction inputs from an input device to the first and second pilot valves.

17. The electro-hydraulic control system according to claim 15, wherein the third and fourth pilot valves are electrically connected to the second electronic controller, which is arranged to relay the direction inputs from the input device to the third and fourth pilot valves.

18. The electro-hydraulic control system according to claim 15, wherein an input device for providing direction inputs is electrically connected to both the first electronic controller and the second electronic controller.

19. The electro-hydraulic control system according to claim 18, wherein the input device is a three signal input device.

20. A method for directing fluid to at least one hydraulic actuator in an electro-hydraulic control system, the method comprising: providing at least one electronic controller; providing first and second fail-safe pilot valves being electrically connected to the at least one electronic controller which is arranged to control the operation of the first and second pilot valves, providing third and fourth fail-safe pilot valves being electrically connected to the at least one electronic controller which is arranged to control operation of the third and fourth pilot valves, providing a pilot operated main valve configured to control fluid flow to the at least one hydraulic actuator, fluidly connecting each of the first and second pilot valves and each of the third and fourth pilot valves to the pilot operated main valve and configuring each of said pilot valves to provide control action to the pilot operated main valve to control fluid flow to the at least one hydraulic actuator, connecting the first pilot valve and the third pilot valve in parallel via a first shuttle valve to a first pilot inlet port of the main valve, connecting the second pilot valve and the fourth pilot valve in parallel via a second shuttle valve to a second pilot inlet port of the main valve, wherein each of the first and second pilot valves and the third and fourth pilot valves includes a spool, an inlet port fluidly connected to a high-pressure fluid source, a first regulated outlet port fluidly connected to a first pilot input port or a second pilot inlet port of the main valve, and a second outlet port fluidly connected to a low pressure reservoir, supplying fluid from the high-pressure fluid source to the inlet port of a corresponding one of the first and second pilot valves and the third and fourth pilot valves; moving the spool of the corresponding one of the first and second pilot valves and the third and fourth pilot valves to a first position to enable fluid communication between the first regulated outlet port and the second outlet port of the corresponding one of the first and second pilot valves and the third and fourth pilot valves when the corresponding one of the first and second pilot valves and the third and fourth pilot valves is in a deactivated state, moving the spool to a second position to enable fluid communication between the inlet port and the first regulated outlet port when the corresponding one of the first and second pilot valves and the third and fourth pilot valves is in an activated state in which the direction input is provided to the pilot operated main valve, and if the spool of any of the fail-safe pilot valves becomes stuck in an open state during which a solenoid actuator of the corresponding one of the of fail-safe pilot valves moves into a non-actuated position corresponding to the deactivated state of the corresponding one of the fail-safe pilot valves while the spool remains in the second position corresponding to the activated state of the corresponding one of the fail-safe pilot valves whereby the solenoid actuator is disconnected from the spool, draining the first regulated outlet port of the corresponding one of the fail-safe pilot valves to the low pressure reservoir, wherein when the spool is stuck in the open state, the spool being in the second position enables fluid communication between the inlet port and the second outlet port via a fluid connection between an internal fluid line of the spool and a surrounding cavity in which pressurized fluid is accumulated, the internal fluid line being fluidly connected between the surrounding cavity and the low pressure reservoir whereby fluid flows from the high-pressure fluid source to the low pressure reservoir.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 schematically shows a layout of an electro-hydraulic control system according to a first example of the disclosure,

(2) FIG. 2 schematically shows a layout of an electro-hydraulic control system according to a second example of the disclosure,

(3) FIG. 3 schematically shows a layout of an electro-hydraulic control system for directing fluid to actuators according to a third example of the disclosure.

DETAILED DESCRIPTION

(4) Various aspects of the disclosure will hereinafter be described in conjunction with the appended drawings to illustrate and not to limit the disclosure, wherein like designations denote like elements, and variations of the described aspects are not restricted to the specifically shown embodiments, but are applicable on other variations of the disclosure.

(5) In the figures high pressure hydraulic fluid connections are indicated by solid lines, pilot pressure hydraulic fluid connections are indicated by dashed lines and electrical connections are indicated by dash-dotted lines. It is to be understood that other equipment besides the ones shown in the figures can be part of the electro-hydraulic control system, both hydraulic and electrical. Examples are filters, flow restrictors, pressure regulators, distributor valves, batteries, fuses etc.

(6) The electro-hydraulic steering control system 1 is hereinafter partly described in terms of a vehicle steering application but the electro-hydraulic steering control system 1 is not limited to this specific application and other applications where high level of redundancy is desired are equally possible.

(7) FIG. 1 schematically shows a layout of an electro-hydraulic control system 1 for directing fluid to an hydraulic actuator 10 according to a first example of the disclosure. The system 1 comprises an input device 2 for providing direction inputs. A direction input is in a first example a left or right indication by moving the input device 2 in the desired direction for steering a vehicle. A second example of a direction input is a left or right indication or up or down indication for control of a flight control surface such as rudder, aileron or elevator. A third example of a direction input is to deploy or retract a landing gear. The input device 2 can for instance be a joystick, a steering wheel, an electric or electro-mechanical switch.

(8) In the example embodiment of FIG. 1, the input device 2 may be an output lever, joystick, control wheel, control button, or the like for enabling a driver to control the motion of the hydraulic actuator 10. The input device can for example give a left steering direction input and a right steering direction input. The input device 2 is electrically connected to a first electronic controller 3. A first pilot valve 5, a second pilot valve 6, a third pilot valve 7 and a fourth pilot valve 8 are electrically connected to the first electronic controller 3 relaying the direction inputs from the input device 2 to the first, second, third and fourth pilot valves 5, 6, 7, 8. Each pilot valve 5, 6, 7, 8 has an inlet port connected to a high-pressure fluid source, a first regulated outlet port connected to a pilot input port 22, 23 of the main valve 9, and a second outlet port connected to a low pressure reservoir, such as a tank. The first regulated outlet port and the second outlet port are fluidly connected when the pilot valve 5, 6, 7, 8 is in a deactivated state, and the inlet port and first regulated outlet port are fluidly connected when the pilot valve 5, 6, 7, 8 is in an activated state.

(9) A pilot operated main valve 9 is configured to control fluid flow to the hydraulic actuator 10. The first and second pilot valves 5, 6 and the third and fourth pilot valves 7, 8 are each fluidly connected to the pilot operated main valve 9 and configured to provide a control action to the pilot operated main valve 9 to control fluid to the hydraulic actuator 10. The first pilot valve 5 and the third pilot valve 7 are connected to a first pilot inlet port 22 on the left side of the main valve 9 and may for example be arranged to provide a control action to the pilot operated main valve 9 upon a left steering direction input from the input device 2. The second pilot valve 6 and the fourth pilot valve 8 are connected to a second pilot inlet port 23 on the right side of the main valve and may for example be arranged to provide a control action to the pilot operated main valve 10 upon a right steering direction input from the input device 2.

(10) With control action is meant an action to operate the pilot operated main valve 9 such that it moves to either the left or the right position thereby controlling the flow of hydraulic fluid such that the hydraulic actuator 10 are moved left or right. The first pilot valve 5 and the third pilot valve 7 are connected in parallel through a first shuttle valve 11 to the pilot operated main valve 9. The first shuttle valve 11 is thus located between the first and third pilot valves 5, 7 and the main valve 9. The second pilot valve 6 and the fourth pilot valve 8 are connected in parallel through a second shuttle valve 12 to the pilot operated main valve 9. The second shuttle valve 12 is thus located between the second and fourth pilot valves 6, 8 and the main valve 9.

(11) Each of the first and second pilot valves 5, 6 and the third and fourth pilot valves 7, 8 are fail-safe pilot valves arranged to drain the regulated outlet port to tank when a steering direction input from the input device is removed. With the regulated outlet port means the port of the pilot valve 5, 6, 7, 8 that is connected to the pilot input port of the main valve, and that is pressurized during a steering direction input thereby providing a control action to the pilot operated main valve 9.

(12) A first pump 13 is arranged to provide fluid flow to the pilot operated main valve and to the first, second, third and fourth pilot valves 5, 6, 7, 8. The first pump 13 can be a fixed displacement pump or a variable displacement pump. The first pump 13 is connected to a tank 15. The first pump 13 is preferably the vehicle's main pump being able to supply all parts of the vehicle with hydraulic fluid flow.

(13) The pilot operated main valve 9 may be spring centred. The pilot valves 5, 6, 7, 8 may be spring offset to a position where the hydraulic fluid from the first pump 13 is stopped by the spool of the pilot valve 5, 6, 7, 8 when the pilot valve is deactivated.

(14) One example of how the fail-safe function of the pilot valves 5, 6, 7, 8 can function is to provide the spool of the pilot valves 5, 6, 7, 8 with a relief duct connected to the section of the pressure line which is led to the load, i.e. hydraulic actuators, and to the tank 15. The connection of the relief duct to the tank can be controlled by the pilot valve itself, meaning that the connection of the relief duct to the tank will be closed as long as there is a steering direction input to the specific pilot valve. One example of a fail-safe pilot valve can be found in WO 2007/059898 A1.

(15) Many alternative designs may be used for providing a fail-safe pilot valve. According to one example embodiment shown in FIG. 1, the spool 5a of the first pilot valve 5 gets stuck in an open position shown in the detailed view of FIG. 1, i.e. a position so that a control action is provided to the pilot operated main valve 9 to steer for example to the left. Once the left steering direction input to the first pilot valve 5 has been removed, the actuator 5b of the integrated solenoid of the first pilot valve 5 returns to a nonactuated position. However, when the solenoid actuator 5b moves back to a non-actuated position and the spool 5a remains stuck in the actuated position, the solenoid actuator 5b becomes disconnected from spool 5a (at point 5c). This disconnection results in a fluid connection between an internal fluid line 5d, 5e of the spool and a surrounding cavity, thereby enabling fluid from the high-pressure source supplied to the inlet port 5f of the pilot valve to be drained to the tank 15. This means that even if the spool 5a in pilot valve 5 gets stuck in an open position, once the steering direction input is removed the high-pressure fluid supplied to the pilot valve is drained and the first pilot inlet port 22 of the main valve 9 is depressurized, thereby enabling the spool of the main valve 9 to return to its centre position by means of one 29 of its springs.

(16) Once it is discovered that the spool of the first pilot valve 5 is stuck, further steering direction inputs to the first pilot valve 5 is shut off and the third pilot valve 7 takes over provides future steering actions to the main valve 9. The first shuttle valve 11 will shut the connection to the first pilot valve 5 once the third pilot valve 7 receives a left steering direction input. The vehicle can then be driven back for maintenance using the third pilot valve 7. An operator of the vehicle may also receive a warning that the vehicle is in a failure mode, or the like. The warning may for example be provided on the instrument cluster of the vehicle and/or by an alarm sound.

(17) The system 1 further comprises a first pressure regulator 20 for supplying high-pressure fluid from the first pump 13 to the first, second, third and fourth pilot valves 5, 6; 7, 8 with a predetermined pressure level.

(18) The system further comprises monitoring of the first, second, third and fourth pilot valves. When the monitoring of any one of the first, second, third or fourth pilot valves 5, 6, 7, 8 indicates a failure of a pilot valve 5, 6; 7, 8; the electronic controller 3 connected to the failed pilot valve 5, 6; 7, 8 disables the direction input to the failed pilot valve 5, 6; 7, 8. Monitoring can be done by means of spool position monitoring of each of the first, second, third and fourth pilot valves 5, 6; 7, 8 respectively, or by monitoring of the pilot valve pressure of each of the first, second, third and fourth pilot valves respectively by means of a first, second, third and fourth pressure sensor 16, 17, 18, 19.

(19) When the spool position monitoring indicates a stuck spool of any one of the first, second, third and fourth pilot valves 5, 6; 7, 8, the regulated outlet port of the stuck pilot valve will drain to tank 15 when a direction input to the stuck pilot valve 5, 6; 7, 8 is removed.

(20) When a pressure sensor 16, 17, 18, 19 indicates a pressure error of any one of the first, second, third and fourth pilot valves 5, 6; 7, 8, the regulated outlet port of the stuck pilot valve will drain to tank 15 when a direction input to the pilot valve 5, 6; 7, 8 is removed.

(21) Alternatively, the main valve can be monitored by means of a spool position monitoring or main valve pressure sensors measuring the pressure on each side of the main valve 9. By using different pressures for the first and second pilot valve and the third and fourth pilot valve respectively, the output signal of a spool position sensor or pressure sensor can enable the first electronic controller 3 to determine which of the first or third and second or fourth pilot valve respectively that feeds the main valve.

(22) The first and third pilot valves 5, 7 may define a first pair of pilot valves, and the second and fourth pilot valves 6, 8 may define a second pair of pilot valves. The first pair of pilot valves can be controlled by the first electric controller 3 substantially in parallel, meaning that all control signals from the first electronic controller is fed to both the first and third pilot valves 5, 7 in normal operating mode. If a pilot valve failure is detected the system enters failure mode and the control signals to that pilot valve is stopped. This approach provides smooth transition from the normal operating mode to the failure mode and does not rely on the detection of pilot valve failure for maintained functionality.

(23) Alternatively, the first pair of pilot valves may be controlled sequentially, meaning that only the first pilot valve 5 is fed with control signals from the first electronic controller 3 in normal operating mode while keeping the third pilot valve 7 idle, and upon detection of failure of the first pilot valve feeding only the third pilot valve with control signals from the first electronic controller 3 and keeping the first pilot valve idle. This approach may be more energy-efficient but requires quick and reliable detection of pilot valve failure.

(24) Also the second pair of pilot valves may be controlled in parallel or sequentially.

(25) The system may be designed to operate in normal operating mode as long as no malfunction of the pilot valves is detected. The system may be designed to enter a failure mode after detection of failure of one of the pilot valves. These modes are applicable both when the third and fourth pilot valves 7, 8 are idle in normal operating mode, or when the third and fourth pilot valves 7,8 are activated substantially in parallel with the first and second pilot valves 5, 6.

(26) FIG. 2 schematically shows a layout of an electro-hydraulic control system 1 for directing fluid to an hydraulic actuator according to a second example of the disclosure. The features shared with the system 1 described in FIG. 1 have the same numbers.

(27) System 1 of the second example comprises an input device 2 electrically connected to a first electronic controller 3 and a second electronic controller 4. A first pilot valve 5 and a second pilot valve 6 are electrically connected to the first electronic controller 3 relaying the steering direction inputs from the input device 2 to the first and second pilot valves 5, 6. A third pilot valve 7 and a fourth pilot valve 8 are electrically connected to the second controller 4 relaying the steering direction inputs from the input device 2 to the pilot valves 7, 8.

(28) The use of a second electronic controller 4 provides redundancy to the system. In one example the first and second electronic controller are electrically connected to each other in order to provide additional redundancy.

(29) In the example embodiment of FIG. 2, the input device 2 is a three signal input device in form of a joystick or lever for controlling the motion of the actuator 10. The three signal input device 2 provides further improved redundancy over a two signal input device.

(30) Moreover, for further enhanced redundancy, a first pump 13 and a second pump 14 are arranged to provide fluid flow to the pilot operated main valve and to the pilot valves 5, 6, 7, 8. The first pump 13 and second pump 14 are connected to a tank 15. The first pump 13 is preferably the vehicle's main pump being able to supply all parts of the vehicle with hydraulic fluid flow. The second pump 14 may be a pump used for redundancy if the first pump 13 would fail. In the example of steering a vehicle, the second pump 14 can be a gear pump rotatably connected to one of the vehicle's wheel axes. Thus, if the first pump 13 fails when the vehicle is in motion, the secondary pump can more or less instantaneously provide at least the steering control system 1 with hydraulic fluid flow in order to safely steer the vehicle and let it come to a stop. Alternatively, the second pump 14 can be powered by an electrical machine or the like. Both the first and second pumps 13, 14 can be fixed displacement or variable displacement pumps.

(31) The first and second pair of pilot valves 5, 6; 7, 8 of the system in FIG. 2 can be controlled by electric controllers 3, 4 to be activated either substantially in parallel or sequentially, as described above.

(32) The hydraulic system of FIG. 2 may alternatively include a single hydraulic pump or a single electronic controller.

(33) FIG. 3 schematically shows a layout of an electro-hydraulic control system 1 for directing fluid to a hydraulic actuator according to a third example of the disclosure. The features shared with the system 1 described in FIGS. 1 and 2 have the same numbers.

(34) In FIG. 3, a first and a second pilot inlet port 22, 23 of the main valve is shown to be connected to the first and third pilot valves 5; 7 and second and fourth pilot valves 6; 8 respectively. First and second main valve pilot pressure sensors 24, 25 for monitoring the pilot pressure supplied to the first and second pilot inlet port 22, 23 respectively are located near the inlet ports 22, 23 after the shuttle valves 11, 12.

(35) the first pressure regulator 20 regulates the pressure to the first and second pilot valves 5, 6 which in this example are the primary pilot valves. A second pressure regulator 21 regulates the pressure to the third and fourth pilot valves 7, 8 which in this example are the secondary pilot valves. A primary pilot valve pressure fed to the first and second pilot valves 5, 6 is higher than a secondary pilot valve pressure fed to the third and fourth pilot valves 7, 8 in the cases where pressure or position is measured on the main valve 9 only.

(36) The electro-hydraulic control system is particularly suitable for being used in a steering system for mobile machinery and mobile working machines. For example, the electro-hydraulic control system may be used for steering of a wheel loader, mobile mining vehicles, dumper, and mobile forest vehicles. Reference signs mentioned in the claims should not be seen as limiting the extent of the matter protected by the claims, and their sole function is to make claims easier to understand.

(37) As will be realised, the system and method of the present disclosure may be modified in various respects, all without departing from the scope of the appended claims. Accordingly, the drawings and the description thereto are to be regarded as illustrative in nature, and not restrictive.

REFERENCES

(38) 1. System 2. Input device 3. First electronic controller 4. Second electronic controller 5. First pilot valve 6. Second pilot valve 7. Third pilot valve 8. Fourth pilot valve 9. Pilot operated main valve 10. Actuators 11. First shuttle valve 12. Second shuttle valve 13. First pump 14. Second pump 15. Tank 16. First pressure sensor 17. Second pressure sensor 18. Third pressure sensor 19. Fourth pressure sensor 20. First pressure regulator 21. Second pressure regulator 22. First pilot inlet port 23. Second pilot inlet port 24. First main valve pilot pressure sensor 25. Second main valve pilot pressure sensor 29. Spring