Hydraulic system and method for controlling a hydraulic system

Abstract

A hydraulic system and a method comprising a linear actuator 23 for generating discrete sum forces, chambers A-D for generating discrete force components, at least two charging circuits 3,4 configured to maintain predetermined pressure levels of hydraulic fluid, independent control interfaces 9-16 configured to open and close connections of the first and second charging circuits to the chambers, and an electronic control unit 50 for controlling the control interfaces. At least two control interfaces are proportional valves which are used as shut-off valves and are independently switchable to the open and closed positions in a controlled manner. Moreover, non-throttled control and secondary control are implemented in the hydraulic system and the method.

Claims

1. A hydraulic system comprising: a linear actuator configured to generate a plurality of discrete sum forces of different magnitudes; at least four chambers provided in the linear actuator and configured to generate a plurality of discrete force components where combinations of the plurality of discrete force components generate the plurality of sum forces; at least two charging circuits configured to maintain predetermined pressure levels of hydraulic fluid including a first pressure level of a first charging circuit of the at least two charging circuits and a second pressure level of a second charging circuit of the at least two charging circuits, and the at least two charging circuits being configured to supply hydraulic fluid to the linear actuator and to receive hydraulic fluid from the linear actuator; a plurality of independent control interfaces configured to open and close connections of the first and second charging circuits to the at least four chambers, the plurality of control interfaces including at least: a first control interface configured to open and close the connection of the first charging circuit to the first chamber; and a second control interface configured to open and close the connection of the second charging circuit to the first chamber; and an electronic control unit configured to control at least two of the plurality of control interfaces, including the first and the second control interfaces, wherein: at least two of the control interfaces, including the first and the second control interfaces, are proportional valves which are used as shut-off valves and are independently shiftable to the open and closed positions in a controlled manner, and the control unit, the linear actuator, and the proportional valves are configured to couple the first and second pressure levels to the first chamber causing discrete force components to be produced corresponding the first and second pressure levels.

2. The hydraulic system according to claim 1, wherein, for generating discrete force components and switching sum forces, the control unit is configured: to shift the first control interface to either the open or the closed position, and to shift the second control interface to either the open or the closed position, and to synchronize the operations of the first control interface and the second control interface.

3. The hydraulic system according to claim 1, wherein at least one of the proportional valves is an electronically controlled 2-way directional proportional valve with an opening controlled in a stepless manner.

4. The hydraulic system according to claim 1, wherein the control unit, the linear actuator, and the proportional valves are configured to implement non-throttled control.

5. The hydraulic system according to claim 1, wherein each sum force is a combination of at least two force components, and the control unit is configured to control the control interfaces so that force components are generated for forming sum forces and for acting on a state of the linear actuator.

6. The hydraulic system according to claim 1, wherein the control unit is configured to control the control interfaces such that hydraulic fluid is received from the linear actuator by one of the charging circuits, and hydraulic fluid is conveyed from another one of the charging circuits to the linear actuator.

7. The hydraulic system according to claim 1, further comprising: an energy storage unit is connected to one or more charging circuit of the at least two charging circuits configured to convert hydraulic energy to potential or kinetic energy and to return potential or kinetic energy to hydraulic energy; or at least one first pressure accumulator is connected to the first charging circuit, and at least one second pressure accumulator is connected to the second charging circuit.

8. The hydraulic system according to claim 1, further comprising: at least one charging unit configured to provide hydraulic energy to at least one charging circuit of the at least two charging circuits, or the at least one charging unit is configured to transfer hydraulic energy between two or more charging circuits of the at least two charging circuits or to transfer hydraulic energy out of the hydraulic system in the form of kinetic energy or electric energy.

9. The hydraulic system according to claim 8, wherein at least two control interfaces of the plurality of control interfaces are on-off valves which are used as shut-off valves and are independently shiftable to the open and closed positions in a controlled manner.

10. The hydraulic system according to claim 1, wherein ratios of effective areas of the at least four chambers of the linear actuator follow a series N.sup.M, in which N is a number of the charging circuits and M is an integer.

11. A method comprising controlling a hydraulic system, the hydraulic system including: a linear actuator for generating a plurality of discrete sum forces of different magnitudes; at least four chambers provided in the linear actuator and generating a plurality of discrete force components where combinations of the plurality of discrete force components generate the plurality of sum forces; at least two charging circuits maintaining predetermined pressure levels of hydraulic fluid, the predetermined pressure levels of hydraulic fluid including a first pressure level of a first charging circuit of the at least two charging circuits and a second pressure level of a second charging circuit of the at least two charging circuits, the at least two charging circuits supplying hydraulic fluid to the linear actuator and receiving hydraulic fluid from the linear actuator; a plurality of independent control interfaces opening and closing connections of the first and second charging circuits to the at least four chambers, the plurality of control interfaces including at least: a first control interface for opening and closing the connection of the first charging circuit to a first chamber of the at least four chambers, and a second control interface for opening and closing the connection of the second charging circuit to the first chamber; and an electronic control unit controlling at least two of the plurality of control interfaces including the first and the second control interfaces, wherein: the at least two of the plurality of control interfaces including the first and the second control interfaces, are proportional valves which are used as shut-off valves and are independently shiftable to the open and closed positions in a controlled manner, and the control unit, the linear actuator, and the proportional valves are configured to couple the first and second pressure levels to the first chamber causing discrete force components to be produced corresponding the first and second pressure levels.

12. The method according to claim 11, in which method, for generating discrete force components and switching sum forces, the control unit further: shifts the first control interface to either the open or the closed position, and shifts the second control interface to either the open or the closed position, and synchronizes the operation of the first control interface and the second control operation.

13. The method according to claim 11, in which method the operation of the first control interface and the second control interface is synchronized by controlling delays of the first control interface and the second control interface.

14. The method according to claim 11, in which method each sum force is a combination of at least two force components, and the control unit controls the control interfaces such that force components are generated for forming sum forces and for acting on a state of the linear actuator.

15. The method according to claim 14, in which method at least one of the proportional valves is an electrically controlled 2-way directional proportional valve with an opening that is controlled in a stepless manner.

16. The method according to claim 11, in which method at least one of the proportional valves is an electrically controlled 2-way directional proportional valve with an opening that is controlled in a stepless manner.

17. The method according to claim 11, wherein the hydraulic system further includes: an energy storage unit connected to one or more charging circuit of the at least two charging circuits for converting hydraulic energy to potential or kinetic energy and for returning potential or kinetic energy to hydraulic energy; or at least one first pressure accumulator connected to the first charging circuit, and at least one second pressure accumulator is connected to the second charging circuit.

18. The method according to claim 11, wherein: the hydraulic system further includes at least one charging unit for supplying hydraulic energy to at least one charging circuit of the at least two charging circuits, or the charging unit transfers hydraulic energy between two or more charging circuits of the at least two charging circuits or out of the hydraulic system in a form of kinetic energy or electric energy.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The presented solution will be described in more detail by means of some examples and with reference to the appended drawings.

(2) FIG. 1 shows a hydraulic system according to an example of the solution, which utilizes a linear actuator with four chambers.

(3) FIG. 2 shows a hydraulic system according to another example of the solution.

(4) FIG. 3 shows force steps generated by the hydraulic system according to an example of the solution.

(5) FIG. 4 shows a hydraulic system according to a third example of the solution.

MORE DETAILED DESCRIPTION OF THE SOLUTION

(6) FIG. 1 shows an example of the hydraulic system according to the solution, which is based on a secondary controlled linear actuator and non-throttled control implemented by proportional valves.

(7) The hydraulic system may comprise at least two charging circuits 3 and 4, at least one actuator 60 which is a multi-chamber linear actuator 23, and a control circuit 40 with several control interfaces 9 to 16 and lines 5 to 8 for hydraulic fluid, as well as an electronic control circuit 50.

(8) The charging circuit 3 is a high pressure charging circuit 3, so-called HP line, and the charging circuit 4 is a low pressure charging circuit 4, so-called LP line.

(9) Each charging circuit 3, 4 comprises hydraulic fluid lines connected to each other and having the same pressure level. Each charging circuit 3, 4 is capable of supplying hydraulic fluid to e.g. the actuator 60 as well as receiving a volume flow from e.g. the actuator 60 and simultaneously maintaining a stable predetermined pressure level. A filter for hydraulic fluid, a pressure relief valve, or other necessary auxiliary components may be connected to the charging circuit 3, 4.

(10) The linear actuator 23 has at least four chambers 19, 20, 21, 22, which are so-called A, B, C and D chambers. The linear actuator 23 comprises a frame and a piston structure linearly movable with respect to the frame and acting on e.g. a load L, for example directly or via a piston rod. The chambers 19 to 22 are so-called displacement chambers whose volume changes as the piston structure moves and which have an effective area subjected to the pressure of the hydraulic fluid. The linear actuator 23 and the sum force F generated by it act on e.g. the load L.

(11) In this description, the term linear actuator also refers to the actuator unit acting on the load L and comprising multi-chamber linear actuators or, alternatively, a combination of one or two chamber linear actuators.

(12) At least two charging circuits 3, 4 are connected to each chamber 19 to 22 of the linear actuator 23; in the example of FIG. 1 the HP line and the LP line.

(13) A line for hydraulic fluid is connected to each chamber 19 to 22 of the linear actuator 23, and said line is connected to at least two charging circuits 3, 4. Said lines 5 to 8 in combination with the charging circuits 3, 4 enable the flow of hydraulic fluid between the chambers 19 to 22 of the linear actuator 23 and also between the linear actuator 23 and another actuator 60, 90 connected to the system, as shown in the example of FIG. 2. In this way, hydraulic energy may be transferred between different actuators or to the charging circuit 3, 4.

(14) The line 5 is connected to the chamber A of the linear actuator 23, the line 6 is connected to the chamber B, the line 7 is connected to the chamber C, and the line 8 is connected to the chamber D of the actuator 23. In an example, a pressure relief valve or other necessary auxiliary components may be connected to each line 5 to 8.

(15) Each control interface 9 to 16 controls the connection of one chamber 19 to 22 of the linear actuator 23 to one charging circuit 3, 4, for example the connection of chamber A to the HP line or the connection of chamber A to the LP line. The control interfaces 9 to 16 are placed in the lines 5 to 8.

(16) Each control interface 9 to 16 controls the entry of hydraulic fluid into the linear actuator 23 and its returning from the linear actuator 23 independently, that is, separately from the other control interfaces 9 to 16, and individually.

(17) The control interface 9 controls the connection between the HP line and the chamber A; the control interface 10 controls the connection between the LP line and the chamber A; the control interface 11 controls the connection between the HP line and the chamber B; the control interface 12 controls the connection between the LP line and the chamber B; the control interface 13 controls the connection between the HP line and the chamber C; the control interface 14 controls the connection between the LP line and the chamber C; the control interface 15 controls the connection between the HP line and the chamber D; and the control interface 16 controls the connection between the LP line and the chamber D.

(18) In the presented solution, at least two control interfaces 9 to 16 are comprised by a control valve which is a proportional vale of the above presented type, is used as a shut-off valve, and is shifted to the open position and the closed position in a controlled manner. According to an example and FIG. 1, each control interface 9 to 16 or at least eight control interfaces 9 to 16 are comprised by a proportional valve of the above presented type.

(19) According to an example and FIG. 1, said proportional valve is a 2-way directional proportional valve.

(20) Further according to an example, at least two control interfaces 9 to 16 in the hydraulic system according to the present solution may be comprised by a control valve which is a shut-off valve and is shifted in a controlled manner to either the open position or the closed position only. In an example, said shut-off valve is an electrically controlled on-off valve which is preferably quick and has a low pressure loss, for example a 2-way directional valve. Said shut-off valves are also used to implement the above presented non-throttled control and secondary control, if a more comprehensive control of the pressure level of a chamber in the linear actuator and the use of proportional valves are not necessary.

(21) In an example and FIG. 4, at least one control interface 9, 10 alternatively comprises several control valves, for example 2 to 5 valves, coupled in parallel on the same line so that in combination they will define the maximum value of the volume flow of hydraulic fluid in said line 5. The volume flow will depend on the state of each control valve in the control interface 9, 10; in other words, whether the control valve is open or closed. Said control valves are also used to implement the above presented non-throttled control. The control valve is preferably quick and has a low pressure loss. According to the example of FIG. 4, each control valve is a proportional valve of the above presented type. In another example, each control valve is a shut-off valve of the above presented type.

(22) Moreover, the hydraulic system may comprise at least one pressure accumulator 17 connected to the HP line, and at least one pressure accumulator 18 connected to the LP line. The pressure accumulator 17, 18 is used both as an energy storage and a source of hydraulic fluid.

(23) In the example of FIG. 1, the two chambers produce a movement in the same first direction, extending the linear actuator 23, and two working chambers 20, 22 produce a movement in the opposite direction, retracting the linear actuator 23.

(24) In an example and FIG. 1, the linear actuator 23 is also configured, with respect to the effective areas of the chambers 19 to 22, such that the relative values of the effective areas of the chambers 19 to 22 follow weighting coefficients of the binary system, for example 1, 2, 4, 8, so that the linear actuator 23 may also called binary coded (see the series M.sup.N, in which M is 2). The sum forces F generated by the binary coded linear actuator 23 are unequal and are uniformly stepped as force steps.

(25) An example of sum forces F generated by the linear actuator 23 is shown in FIG. 3 which illustrates force steps 1 to 16 when two charging circuits 3, 4 are used and the linear actuator 23 comprises four chambers 19 to 22, the ratios of their effective areas following said binary coding.

(26) In another example, the ratios of the effective areas of the chambers of the linear actuator 23 follow the series M.sup.N, the series 1, 1, 3, 6, 12, 24, the Fibonacci series, or the PNM series.

(27) Each chamber 19 to 22 of the linear actuator 23, connected to at least two charging circuits 3, 4, may generate force components FA, FB, FC, FD which correspond to the pressure levels of said at least two charging circuits 3, 4.

(28) The force components FA, FB, FC, FD produced by the chambers 19 to 22 are illustrated in the example of FIG. 1.

(29) The number of sum forces F generated in the linear actuator 23 is 2.sup.n, n being the number of chambers 19 to 22 of the linear actuator 23, to which two charging circuits 3, 4 are connected. The linear actuator 23 of the example of FIG. 1 provides 16 different combinations of force components FA to FD generated by the chambers 19 to 22 so that 16 sum forces F may be generated by the linear actuator 23, as shown in FIG. 3.

(30) In another example, the number of sum forces F generated in the linear actuator 23 is m.sup.n, n being the number of chambers 19 to 22 of the linear actuator 23, to which m charging circuits 3, 4 are connected.

(31) The force components FA to FD generated by the chambers 19 to 22 of the linear actuator 23 may be effective in the same direction or in the opposite direction. The combined force components FA to FD determine the magnitude and direction of action of each sum force F generated by the linear actuator 23. The generated sum forces F may be effective in the same direction or in opposite directions.

(32) The electronic control unit 50 controls the control interfaces 9 to 16 of the control circuit 40 and the control valves therein, for example by means of electronic control signals. The hydraulic system may comprise various sensors connected to a control unit 50. On the basis of measurement signals from the sensors, the control unit 50 may determine the state of the hydraulic system, the state of the actuators 60, particularly the state of the linear actuator 23, and control the hydraulic system in a predetermined way and to a desired state, for example by means of feedback relating to measurement signals and control. The sensors are, for example, pressure sensors, position sensors, or movement sensors.

(33) The hydraulic system enables and the control unit 50 implements said non-throttled control and secondary control, as well asin an examplethe above described recovery and return of energy to the hydraulic system, by controlling the components and actuators of the hydraulic system. The control unit 50 comprises e.g. a processor that follows desired programmed algorithms. The control unit 50 is configured to implement the predetermined force, moment, acceleration, angular acceleration, speed, angular speed, position, or rotation, relating to the linear actuator 23 or the load L by means of the linear actuator 23.

(34) According to an example of the solution and FIG. 2, the hydraulic system may comprise at least one actuator 90 which is a rotary actuator, for example a hydraulic motor 91 which may be a variable displacement motor. In another example, the hydraulic motor 91 is a variable displacement motor having two directions of flow and rotation. Further, the hydraulic motor 91 may be secondary controlled and connected to the control unit 50. The actuator 90 is coupled to one or more charging circuits 3, 4. With secondary control, the actuator 90 may also return energy to the hydraulic system, as described above. In an example, the operation of the actuator 90 is controlled by a control valve.

(35) According to one example of the solution and FIG. 2, the hydraulic system may comprise one or more energy storage unit 80 which is, for example, a pressure accumulator or a device that utilizes potential energy. An example of the energy storage unit 80 is a pressure accumulator 17, 18. The energy storage unit 80 is connected to the HP line or the LP line. The energy storage unit 80 is capable of converting hydraulic energy of the hydraulic system to potential or kinetic energy, and returning potential or kinetic energy to hydraulic energy to be used by the hydraulic system. The energy storage unit 80 may be used to recover energy generated or returned by the actuator 80, 90 or the linear actuator 23.

(36) The hydraulic system may also comprise one or more charging unit 70 for generating hydraulic energy to one or more charging circuit 3, 4 and maintaining predetermined pressure levels of the charging circuits 3, 4. The charging unit 70 utilizes, for example, kinetic energy and converts it to hydraulic energy. The control unit 50 may control the operation of the charging unit 70.

(37) The operation of the actuator 60, 90, for example the linear actuator 23, may be energy binding (for example lifting of a load L or acceleration) or energy releasing (for example lowering of the load L or deceleration). In an example, the charging unit 70 or an actuator in the charging unit 70 may also transfer energy to the outside of the hydraulic system by utilizing excess energy and hydraulic power of the hydraulic system and by producing kinetic energy or electric energy by means of a motor or a generator.

(38) In an example, the charging unit 70 also transfers energy from one charging unit 3, 4 to another, for example from the HP line to the LP line, or to the outside of the hydraulic system.

(39) In an example and FIG. 2, the charging unit 70 comprises at least one hydraulic pump 72, for example a variable displacement pump. In another example, the hydraulic pump 72 is a variable displacement pump having two directions of flow and rotation. In a third example, said variable displacement pump may also be used as a secondary controlled hydraulic motor, for example for producing kinetic energy.

(40) The hydraulic pump 72 is connected to a motor 100 for producing kinetic energy, which may be an internal combustion engine or an electric motor.

(41) The charging unit 70 may also comprise a coupling unit 71, by which the charging unit 70 is connected to at least one charging circuit 3, 4, for example the HP line, the LP line or both of them, in a controlled manner. The control unit 50 may control the operation of the coupling unit 71. In an example, the coupling unit 71 comprises one or more control valve for controlling the pressure or volume flow of the hydraulic fluid, or for controlling the flow of the hydraulic fluid.

(42) A line 73, 74 of hydraulic fluid may be connected to the hydraulic pump 72. In an example, the function of the coupling unit 71 is to connect lines 73, 74 together or to several charging circuits 3, 4 as desired. The function of the coupling unit 71 may also be to connect the line 73, the line 75 or the charging circuit 3, 4 to the tank of hydraulic fluid as desired.

(43) The present solution is not limited to the above presented figures, alternatives or examples only, but it may be applied within the scope of the appended claims.