HYDRAULIC SYSTEM AND METHOD FOR CONTROLLING THE SPEED AND PRESSURE OF A HYDRAULIC CYLINDER

Abstract

A method for controlling a speed of a hydraulic cylinder (2) in a hydraulic system (1) is provided. The hydraulic system (1) may include a hydraulic cylinder (2) fluidly connected to a load-holding valve arrangement (3) including a first load-holding valve (4) connected to a first end (5) of the hydraulic cylinder (2) and a second load-holding valve (6) connected to a second end (7) of the hydraulic cylinder (2). The hydraulic system (1) may further include a flow-control valve arrangement (8) comprising a directional flow-control valve (9) and at least one hydraulic pump (10).

Claims

1. A method for controlling a speed and a pressure of a hydraulic cylinder (2) in a hydraulic system (1) comprising the hydraulic cylinder (2) fluidly connected to a load-holding valve arrangement (3) comprising a first load-holding valve (4) connected to a first end (5) of the hydraulic cylinder (2) and a second load-holding valve (6) connected to a second end (7) of the hydraulic cylinder (2), a flow-control valve arrangement (8) comprising a directional flow-control valve (9), and at least one hydraulic pump (10), the method comprising: inputting an extension speed or a retraction speed for the hydraulic cylinder (2) by an operator controller; measuring a working pressure within the hydraulic system (1); and measuring a speed of the hydraulic cylinder (2) or measuring a differential pressure over the load-holding valve arrangement (3), wherein responsive to detection of the measured working pressure and one of the speed of the hydraulic cylinder (2) or the differential pressure over the load-holding valve arrangement (3), setting the hydraulic system (1) to operate in a first mode, a second mode, or a third mode, wherein the extension speed or the retraction speed of the hydraulic cylinder (2) is controlled by adjusting a position of the directional flow-control valve (9), the first load-holding valve (4), and the second load-holding valve (6), and wherein the first mode is a pushing/pulling mode, the second mode is a neutral movement mode, and the third mode is a gravity-assisted movement mode.

2. The method of claim 1, wherein when measuring the speed of the hydraulic cylinder (2), the adjusting the position of the directional flow control valve (9), the first load-holding valve (4), and the second load-holding valve (6) comprises: responsive to detection of the measured working pressure within the hydraulic system (1) being lower than a first pressure needed to move the hydraulic cylinder (2) at the desired extension or retraction speed, activating the first mode in which a load from the hydraulic cylinder (2) is identified to determine the first pressure, increasing the working pressure by the at least one hydraulic pump (10), adjusting the position of the directional flow-control valve (9) to control the speed of the hydraulic cylinder (2), setting the position of the first load-holding valve (4) to a closed position and setting the position of the second load-holding valve (6) to a fully open position.

3. The method of claim 1, wherein the measuring of the speed of the hydraulic cylinder (2), the adjusting the position of the directional flow control valve (9), the adjusting the first load-holding valve (4) and the second load-holding valve (6) further comprises: responsive to detection of the measured working pressure decreasing and the speed of the hydraulic cylinder being constant or increasing relative to the desired extension or retraction speed, activating the second mode in which a position of the directional flow-control valve (9) and the first load-holding valve (4) is adjusted to control the speed of the hydraulic cylinder (2) and a position of the second load-holding valve (6) is set to a closed position.

4. The method of claim according to any one of claims 1-3, wherein when measuring the speed of the hydraulic cylinder (2), the adjusting the position of the directional flow control valve (9), the first load-holding valve (4), and the second load-holding valve (6) further comprises: responsive to detection of the measured working pressure and the speed of the hydraulic cylinder (2) indicating that the hydraulic system (1) moves by its own weight, activating the third mode in which the at least one hydraulic pump (10) is shut off, the position of the directional flow-control valve (9) is set to center, the first load-holding valve (4) is adjusted to control the speed of the hydraulic cylinder (2), and the position of the second load-holding valve (6) is set to a fully open position.

5. The method according to any one of the preceding claims, wherein the hydraulic system (1) further comprises a proportional pressure limiter (14), and wherein the method further comprises: in the first mode, adjusting the pressure in the hydraulic system (1) by the proportional pressure limiter (14).

6. The method according to any one of the preceding claims, wherein the method comprises transitioning seamlessly between the modes based on the measured working pressure and the speed of the hydraulic cylinder (2) or a differential pressure over the load-holding valve arrangement (3).

7. The method of claim 1, wherein the measuring of the differential pressure over the load-holding valve arrangement (3) further comprises setting the hydraulic system (1) to operate in the second mode and the third mode simultaneously, wherein the position of the directional flow-control valve (9) and the first load-holding valve (4) is adjusted to control the speed of the hydraulic cylinder (2).

8. A hydraulic system (1) comprising a hydraulic cylinder (2) fluidly connected to a load-holding valve arrangement (3) comprising: a first load-holding valve (4) connected to a first end (5) of the hydraulic cylinder (2) and a second load-holding valve (6) connected to a second end (7) of the hydraulic cylinder (2), a flow-control valve arrangement (8) comprising a directional flow-control valve (9) and at least one hydraulic pump (10), a working pressure sensor (11), and a hydraulic cylinder position and speed sensor or a differential pressure sensor (15) arranged to measure the pressure over the load-holding valve arrangement (3), wherein in each mode, a desired extension or retraction speed of the hydraulic cylinder (2) is controlled by adjusting the position of the directional flow-control valve (9), the first load-holding valve (4) and the second load-holding valve (6) based on a measured working pressure in the hydraulic system (1) and a measured speed of the hydraulic cylinder (2) or a differential pressure over the load-holding valve arrangement (3).

9. The hydraulic system (1) of claim 8, wherein the system further comprises a speed sensor, wherein the system is configured for activating the first mode if the measured working pressure within the hydraulic system (1) is lower than a first pressure needed to move the hydraulic cylinder (2) at the desired extension or retraction speed, wherein a load from the hydraulic cylinder (2) is identified by the hydraulic system (1) to determine a first pressure needed to move the hydraulic cylinder (2) at a desired extension or retraction speed, the working pressure is increased by the at least one hydraulic pump (10), the position of the directional flow-control valve (9) is adjusted to control the speed of the hydraulic cylinder (2), the position of the first load-holding valve (4) is set to a closed position, and the position of the second load-holding valve (6) is set to a fully open position.

10. The hydraulic system (1) of claim 9, wherein the hydraulic system (1) is configured for activating the second mode responsive to detection of the measured working pressure decreasing and detection of the speed of the hydraulic cylinder (2) being constant or increasing relative to the desired extension or retraction speed, and wherein the position of the directional flow-control valve (9) and the first load-holding valve (4) is adjusted to control the speed of the hydraulic cylinder (2) and the position of the second load-holding valve (6) is set to a closed position.

11. The hydraulic system (1) of any of claims 8-10, wherein the hydraulic system (1) is further configured for activating the third mode if the measurement of the hydraulic cylinder (2) indicates that the hydraulic cylinder moves by a weight of the hydraulic cylinder, wherein the at least one hydraulic pump (10) is shut off, the position of the directional flow-control valve (9) is set to center, the first load-holding valve (4) is adjusted to control the speed of the hydraulic cylinder (2), and the position of the second load-holding valve (6) is set to a fully open position.

12. The hydraulic system (1) of any of claims 8-12, wherein the load-holding valve arrangement (3) is separate from or integrated with the flow-control valve arrangement (8).

13. The hydraulic system (1) of any of claims 8-13 further comprising a proportional pressure limiter (14) arranged to adjust the pressure in the hydraulic system (1), when in the first mode.

14. The hydraulic system (1) of claim 8 further comprising a differential pressure sensor (15), wherein the hydraulic system (1) is further configured for activating the second mode and the third mode simultaneously, and wherein the position of the directional flow-control valve (9) and the first load-holding valve (4) is adjusted to control the speed of the hydraulic cylinder (2).

15. The hydraulic system (1) of claim 8, wherein the hydraulic system is configured for use with a vehicle.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Other features, advantages, and details appear, by way of example only, in the following detailed description, the detailed description referring to the drawings in which:

[0022] FIG. 1 is a schematic diagram showing an example of a hydraulic system in an inactive state;

[0023] FIG. 2a is a schematic diagram showing the hydraulic system of FIG. 1 in a first mode;

[0024] FIG. 2b is a schematic diagram showing the hydraulic system of FIG. 1 in a second mode;

[0025] FIG. 2c is a schematic diagram showing the example of the hydraulic system of FIG. 1 in a third mode;

[0026] FIG. 3 is a schematic diagram showing another example of a hydraulic system in an inactive state;

[0027] FIG. 4 is a schematic diagram showing another example of a hydraulic system in an inactive state;

[0028] FIG. 5a is a schematic diagram showing an example of a hydraulic system in a first mode;

[0029] FIG. 5b is a schematic diagram showing the example of the hydraulic system of FIG. 5A in a second mode;

[0030] FIG. 5c is a schematic diagram showing the example of the hydraulic system of FIG. 5A in a third mode; and

[0031] FIG. 6 is a schematic diagram showing yet another example of a hydraulic system in an inactive state.

DETAILED DESCRIPTION

[0032] The hydraulic system and method described herein are suitable for use with hydraulically operated equipment and/or vehicles. Non-limiting examples of the hydraulically operated equipment and/or vehicles include hook lifts, dumpers, stationary cranes, crane vehicles, forklifts, bucket loaders, front loaders, front-end loaders, payloaders, scoops, shovels, skip loaders, wheel loaders or skid loaders.

[0033] FIG. 1 schematically shows a hydraulic system 1 according to a first example with the hydraulic system 1 in an inactive state. The hydraulic system 1 may include a hydraulic cylinder 2 fluidly connected to a load-holding valve arrangement 3. The load-holding valve arrangement 3 comprises a first load-holding valve 4 connected to a first end 5 of the hydraulic cylinder 2 and a second load-holding valve 6 connected to a second end 7 of the hydraulic cylinder 2. The hydraulic system 1 may further include a flow-control valve arrangement 8 fluidly connected to the load-holding valve arrangement 3. The flow-control valve arrangement 8 may include a directional flow-control valve 9. The hydraulic system 1 also may include at least one hydraulic pump 10 fluidly connected to the flow-control valve arrangement 8 that may be arranged to provide hydraulic fluid flow to the hydraulic system 1. A pressure sensor 11 may be attached to a pressure line from the at least one hydraulic pump 10 and may measure the working pressure of the hydraulic system 1. The pressure sensor 11 may for instance be a PT sensor or a PU sensor. The hydraulic system 1 may further include a hydraulic cylinder position and speed sensor (not shown) arranged to measure both position and movement speed of the hydraulic cylinder 2. The cylinder speed sensor may for instance be an angular sensor, a linear potentiometer, or a pulse encoder.

[0034] The first and second load-holding valves 4, 6 of the load-holding valve arrangement 3 may be electronically operated or proportional. Non-limiting example of the valves include a solenoid valve, a 2-way valve, a normally closed valve, a proportional valve, or a poppet-type valve. The first and second load-holding valves 4, 6 may alternatively be a direct-acting, pilot-operated, or servo-operated, normally open and spool-type valve.

[0035] The directional flow-control valve 9 of the flow-control valve arrangement 8 is for example a pilot operated 4/3 valve, normally closed, and proportionally controlled. Alternatively, the directional flow-control valve 9 may be a poppet valve or a spool valve. Another example of a directional flow-control valve 9 is described below. Maximum flow through the directional flow-control valve 9 may be designed for a specific application. The flow-control valve arrangement 8 may further include a hydraulic valve arrangement 13 arranged to protect the hydraulic system 1 and to regulate and operate pilot pressure to the directional flow-control valve 9 with a pilot supply line (EHP) and a pilot tank line (EHT).

[0036] It is contemplated that the directional flow-control valve 9 can be operated in other ways. For example, the directional flow-control valve 9 may be direct-acting, pilot-operated, or servo-operated.

[0037] As mentioned above, the hydraulic system 1 may include the at least one hydraulic pump 10. In this example, the at least one hydraulic pump 10 may be a fixed displacement and pressure-compensated hydraulic pump. The hydraulic system 1 may alternatively be a load-sensing hydraulic system with a variable-displacement hydraulic pump 12 arranged to provide additional hydraulic fluid to the system based on a load sensed. Such a system is illustrated in the figures. The variable-displacement hydraulic pump 12 is indicated in dashed line to indicate that it is optional.

[0038] The hydraulic system 1 may further include a proportional pressure limiter 14 arranged to adjust the pressure in the first mode to maintain a constant force on the hydraulic cylinder 2 on both inward and outward movement of the hydraulic cylinder 2. The proportional pressure limiter 14 may be a solenoid operated two-way pressure relief valve, normally open.

[0039] The following description illustrates examples of functions of the hydraulic system 1 during three different modes. In these examples, it is assumed that the hydraulic cylinder 2 is operating with a load attached to the hydraulic cylinder 2 and that the hydraulic cylinder 2 has a range of motion where the load moves over center.

[0040] A geometry of the hydraulic system 1 may define a maximum pressure for different positions of the hydraulic cylinder 2 and the pressure can be different in outwards or inwards movement. The flowrates into and out from the hydraulic cylinder 2 can be adjusted as well. A number of flowrates is only limited by a resolution of the hydraulic cylinder's position and a speed sensor.

[0041] FIG. 2a schematically shows the hydraulic system 1 according to a first example of a first mode of the hydraulic system 1 activated. The first mode may also be referred to as a pushing/pulling mode. In the first mode, or the pushing/pulling mode, an operator has input a desired extension or retraction speed for the hydraulic cylinder 2 by means of an operator controller (not shown). A working pressure in the hydraulic system 1 is measured by the pressure sensor 11. If the measured working pressure is lower than a first pressure needed to move the hydraulic cylinder 2 at a desired extension or retraction speed with the load attached to it, a load from the hydraulic cylinder 2 is identified to determine the first pressure and a position of the directional flow-control valve 9 is adjusted to provide flow to extend the hydraulic cylinder 2. As the directional flow-control valve 9 is a proportional valve, the directional flow-control valve 9 is used to control the speed of the hydraulic cylinder 2. A position of the first load-holding valve 4 is set to a closed position allowing fluid to pass through to the first end 5 of the hydraulic cylinder 2. The position of the second load-holding valve 6 is set to a fully open position allowing fluid to pass through to tank.

[0042] It is contemplated that the above-described method can be performed in a hydraulic system with or without load-sensing. A system with load-sensing is more energy efficient than a system without, but energy usage may also be reduced in a system without load-sensing.

[0043] FIG. 2b schematically shows the hydraulic system 1 according to a second mode of the hydraulic system 1 activated. The second mode can also be referred to as a neutral movement mode and may be used when the hydraulic cylinder 2 works in light conditions, e.g. with the load close to center after having passed center in a longitudinal motion in either direction. The second mode may be activated if the measured working pressure decreases and if the speed of the hydraulic cylinder 2 is constant or increasing relative the desired extension or retraction speed input by the operator controller. In the second mode, a position of the directional flow-control valve 9 is adjusted to provide fluid to the second end 7 of the hydraulic cylinder 2. The position of the directional flow-control valve 9 and the first load-holding valve 4 are adjusted simultaneously to control the speed of the hydraulic cylinder 2 with the first load-holding valve 4 adjusting the amount of fluid passing to tank and the directional flow-control valve 9 adjusting the amount of fluid passing to the second end 7 of the hydraulic cylinder 2. The position of the second load-holding valve 6 may be set to a closed position allowing fluid to pass through to the second end 7 of the hydraulic cylinder 2.

[0044] FIG. 2c schematically shows the hydraulic system 1 according to a third mode of the hydraulic system 1 activated. The third mode is a gravity-assisted movement mode and may be used when the load accelerates the hydraulic cylinder 2 by means of gravity. When the directional flow-control valve 9 is fully open and the measured working pressure is lower than a predetermined pressure for a desired speed of the hydraulic cylinder 2 input by the operator controller, this indicates that the hydraulic cylinder 2 moves by its own weight or is said to be gravity-assisted. A position of the directional flow-control valve 9 is set to center and the first load-holding valve 4 adjusts an amount of fluid passing to tank from the first end 5 of the hydraulic cylinder 2 to control the speed of the hydraulic cylinder 2. A position of the second load-holding valve 6 is set to a fully open position.

[0045] FIG. 3 schematically shows the hydraulic system 1 according to another example with the hydraulic system 1 in an inactive state. In this example, a differential pressure over the load-holding valve arrangement 3 is measured using a differential pressure sensor 15 or two pressure sensors. A predefined differential pressure can be used instead of the measurements from the hydraulic cylinder 2 position and speed sensor of the first example.

[0046] When the differential pressure over the load-holding valve arrangement 3 is used to control the operation of the hydraulic system 1, a pre-determined differential pressure is set. In this example, the second and third modes may operate simultaneously. The counter pressure experienced by the hydraulic system 1 when the system operates without a load is reduced and when the system operates with a load, the load assists with the movement of the hydraulic cylinder 2.

[0047] FIG. 4 schematically shows the hydraulic system 1 according to a third example embodiment with the hydraulic system 1 in an inactive state. A configuration of the hydraulic system 1 of FIG. 4 differs from the configuration of the hydraulic system 1 shown in FIG. 1 in that the hydraulic system 1 of FIG. 4 includes a combined load-holding and directional flow-control valve arrangement 16. The combined load-holding and directional flow-control valve arrangement 16 includes a load-holding valve arrangement 3 including the first and second load-holding valves 4, 6 and a directional flow-control valve 9 including first and second directional flow-control valves 9a, 9b.

[0048] The first and second load-holding valves 4, 6 of the combined load-holding and directional flow-control valve arrangement 16 may be electronically operated, proportional valves. The first and second directional flow-control valves 9a, 9b of the combined load-holding and directional flow-control valve arrangement 16 may be electronically operated, proportional valves. The first and second load-holding valves 4, 6 and the first and second directional flow-control valves 9a, 9b can be operated in other ways such as direct-acting, pilot-operated, or servo-operated.

[0049] The following description illustrates examples of functions of the hydraulic system 1 during the three different modes described above. In these examples, it is assumed that the hydraulic cylinder 2 is operating with a load attached to the hydraulic cylinder 2 and that the hydraulic cylinder 2 has a range of motion where the load moves over center.

[0050] A geometry of the hydraulic system 1 may define a maximum pressure for each different position of the hydraulic cylinder 2 and the pressure can be different in outwards or inwards movement. The flowrates into and out from the hydraulic cylinder 2 can be adjusted as well. The number of flowrates is only limited by a resolution of the hydraulic cylinder 2 position and speed sensor.

[0051] FIG. 5a schematically shows the hydraulic system 1 according to a third example embodiment with the first mode of the hydraulic system 1 activated. In the first mode, or the pushing/pulling mode, an operator has input a desired extension or retraction speed for the hydraulic cylinder 2 by means of the operator controller. A working pressure in the hydraulic system 1 is measured by the pressure sensor 11. If the measured working pressure is lower than a first pressure needed to move the hydraulic cylinder 2 at the desired extension or retraction speed with the load attached to it, a load from the hydraulic cylinder 2 is identified to determine the first pressure and a position of the first and second directional flow-control valves 9a, 9b is adjusted to provide flow to extend the hydraulic cylinder 2. As the first and second directional flow-control valves 9a, 9b are proportional valves, the first and second directional flow-control valves 9a, 9b may be used to control the speed of the hydraulic cylinder 2. The position of the first load-holding valve 4 is set to a closed position allowing fluid to pass through to the first end 5 of the hydraulic cylinder 2. The position of the second load-holding valve 6 is set to a fully open position allowing fluid to pass through to tank.

[0052] The method described above can be performed in a hydraulic system with or without load-sensing. A system with load-sensing is more energy efficient than a system without, but energy usage is reduced also in a system without load-sensing.

[0053] FIG. 5b schematically shows the hydraulic system 1 according to a third example embodiment with the second mode of the hydraulic system 1 activated. As described above, the second mode can be used when the hydraulic cylinder 2 works in light conditions, e.g. with the load close to center after having passed center in a longitudinal motion in either direction. The second mode may be activated if the measured working pressure decreases, and if a speed of the hydraulic cylinder 2 is constant or increasing relative to the desired extension or retraction speed input by the operator controller. In the second mode, a position of the first and second directional flow-control valves 9a, 9b may be adjusted to provide fluid to the second end 7 of the hydraulic cylinder 2. The position of the first and second directional flow-control valves 9a, 9b and the first load-holding valve 4 may be adjusted simultaneously to control the speed of the hydraulic cylinder 2 with the first load-holding valve 4 adjusting an amount of fluid passing to tank and the first and second directional flow-control valves 9a, 9b adjusting an amount of fluid passing to the second end 7 of the hydraulic cylinder 2. A position of the second load-holding valve 6 may be set to a closed position allowing fluid to pass through to the second end 7 of the hydraulic cylinder 2.

[0054] FIG. 5c schematically shows the hydraulic system 1 according to an embodiment with the third mode of the hydraulic system activated. As described above, the third mode may be a gravity-assisted movement mode and may be used when a load accelerates the hydraulic cylinder 2 by means of gravity. When the first and second directional flow-control valves 9a, 9b are fully open and the measured working pressure is lower than a predetermined pressure for the desired speed of the hydraulic cylinder 2, this indicates that the hydraulic cylinder 2 moves by its own weight or is said to be gravity-assisted. The position of the first and second directional flow-control valve 9a, 9b is set to open center, i.e. ports A and B are connected to tank, and the first load-holding valve 4 adjusts the amount of fluid passing to tank from the first end 5 of the hydraulic cylinder 2 to control the speed of the hydraulic cylinder 2. The position of the second load-holding valve 6 is set to a fully open position.

[0055] FIG. 6 schematically shows the hydraulic system 1 according to another example embodiment with the hydraulic system 1 in an inactive state. In the second example, a differential pressure over the load-holding valve arrangement 3 is measured using a differential pressure sensor 15 or two pressure sensors. A predefined differential pressure can be used instead of the measurements from the hydraulic cylinder 2 position and speed sensor of the first example.

[0056] When the differential pressure over the load-holding valve arrangement 3 is used to control the operation of the hydraulic system 1, a predetermined differential pressure is set. In this example, the second and third modes operate simultaneously. The counter pressure experienced by the hydraulic system 1 when the system operates without a load is reduced and when the system operates with a load, the load assists with movement of the hydraulic cylinder 2.

[0057] 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 the claims easier to understand.

[0058] As will be realized, embodiments of the disclosure are capable of modification in various obvious 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.