Hydraulic control device for two pumps and several actuators, hydraulic drive system and mobile work machine

Abstract

Hydraulic control device (20) for use with a first and a second pump (11; 12), at least one first actuator (13) and a second actuator (14), wherein the control device (20) has a continuously adjustable first orifice (21) through which pressure fluid can be supplied from the first and second pumps (11; 12) to an associated first actuator (13), wherein at least one continuously adjustable second orifice (22) is provided through which pressure fluid can be supplied from the second pump (12) to an associated second actuator (14), wherein a pressure balance (26) with a continuously adjustable third orifice (28) is provided through which pressure fluid can be supplied from the first pump (11) to a tank (15), wherein the pressure balance (26) is acted upon by a first spring (27) in a closing direction of the third orifice (28), wherein the preload of the first spring (27) defines a first pressure difference,characterized in that a first check valve (25) is connected between the first pump (11) and the at least one first orifice (21), which allows only a fluid flow from the first pump (11) to the at least one first orifice (21), wherein the third orifice (28) is connected between the first pump (11) and the check valve (25), and wherein the second pump (12) is fluidically connected between the check valve (25) and the at least one first orifice (21).

Description

[0001] The invention relates to a hydraulic control device according to the preamble of claim 1, a hydraulic drive system with such a control device and a mobile working machine with such a hydraulic drive system.

[0002] From DE 10 2012 208 938 A1, a hydraulic drive system with a control device is known, which can be used, for example, in a wheel loader. Several first actuators and a second actuator are provided. Furthermore, a first and a second pump are provided, the first pump having a constant displacement volume and the second pump having an adjustable displacement volume. As long as the actuators draw only a small amount of pressurized fluid, they are supplied exclusively by the second pump, which is very energy-efficient. The cost-effective first pump delivers fluid to the tank with low back pressure. Only when the first actuators require a large amount of pressurized fluid does the first pump deliver fluid at high pressure.

[0003] WO 2011 / 068 441 A1 discloses a method for controlling a hydraulic system of a working machine. The corresponding hydraulic drive system comprises two separate pumps and at least one actuator.

[0004] US Patent 6,176,083 B1 discloses a device and a method for controlling the displacement volume of a steering pump of a mobile working machine. The corresponding hydraulic drive system comprises at least two separate pumps and at least one actuator.

[0005] US Patent 8,756,930 B2 discloses a hydraulic system for a mobile work machine in which the flow rate of a pump is split between an attachment and a steering system. The corresponding hydraulic drive system comprises two separate pumps and at least one actuator.

[0006] An advantage of the present invention is that the volume flow rate diverted into the tank via the pressure compensator is small. In particular, closed-center directional control valves can be used. Furthermore, the control device is particularly cost-effective. In addition, the actuators offer excellent fine control.

[0007] According to the independent claim, it is proposed that a first check valve be connected between the first pump and the at least one first orifice, which allows only a fluid flow from the first pump to the at least one first orifice, wherein the third orifice is connected between the first pump and the check valve, and wherein the second pump is fluidically connected between the check valve and the at least one first orifice. Preferably, all first orifices are fluidically connected in parallel to a common branch point, wherein a single first check valve is fluidically connected between the branch point and the first pump.

[0008] The speed of movement of the associated first or second actuator can be adjusted by changing the continuously adjustable first or second orifice. Each first or second actuator can be associated with a first or second directional control valve, which allows the direction of movement of the respective actuator to be adjusted. The continuously adjustable first or second orifice and the associated first or second directional control valve are preferably actuated together, most preferably by a common valve spool. Preferably, only a single second orifice is present.

[0009] Preferably, the hydraulic control device has a first and a second pump connection point, at least one tank connection point, and a first and a second working connection point for each first and second actuator, respectively, which are most preferably part of a fluid line system. The first pump preferably has a constant displacement volume. For reasons of energy efficiency, the second pump preferably has a continuously variable displacement volume, although it can also have a constant displacement volume.

[0010] The dependent claims specify advantageous further developments and improvements of the invention.

[0011] It can be provided that each first orifice is assigned a first load pressure, which depends on the pressure downstream of the respective first orifice, wherein a second load pressure depends on the pressure downstream of the second orifice, wherein a pump controller is provided with which the delivery pressure of the second pump can be adjusted by changing the displacement volume of the second pump to a value which lies above the highest pressure from a group of pressures formed by the at least one first load pressure and the second load pressure by a predetermined second pressure differential. Thus, the delivery pressure of the second pump is sufficient to supply all first and second actuators with pressure fluid. The first and second load pressures are preferably connected on the inlet side to a changeover valve cascade, wherein one outlet of the changeover valve cascade is connected to the pump controller. The first and second load pressures are then...The second load pressure is preferably equal to the pressure downstream of the associated first or second orifice, provided the associated fluid flow path is not blocked. If the fluid flow path is blocked, the relevant load pressure is preferably equal to the pressure in the tank. This saves energy when at least one of the actuators is stationary.

[0012] It can be designed so that the second pressure differential is greater than the first. This means the delivery pressure of the second pump is higher than that of the first pump, as long as the maximum flow rate of the second pump is sufficient to supply all actuators with pressurized fluid. In this operating state, the first check valve is forced into the closed position by the delivery pressure of the second pump, with the entire flow rate of the first pump passing through the pressure equalizer into the tank with minimal back pressure. Thus, all actuators are supplied with pressurized fluid by the adjustable second pump in an energy-efficient manner.

[0013] It can be provided that the pressure balance, in a closing direction of the third orifice, is subjected to the highest pressure from a group of pressures formed by the at least one first load pressure. The second load pressure of the second actuator is therefore not included in this group of pressures, since the second actuator is supplied with pressure fluid exclusively from the second pump. A particularly high second load pressure thus does not lead to energy losses at the first pump. The aforementioned highest pressure is preferably tapped at the aforementioned changeover valve cascade, specifically at the first control point.

[0014] It can be provided that the pressure compensator, in the opening direction of the third orifice, is subjected to a pressure that exists between the check valve and the at least one first orifice. Preferably, this pressure is the pressure at the aforementioned branch point. The pressure compensator thus does not directly regulate the delivery pressure of the first pump, but rather the pressure downstream of the first check valve. This pressure, however, is equal to the delivery pressure of the second pump as long as its delivery capacity is sufficient to supply all actuators with pressurized fluid. As long as the first check valve is closed, the pressure compensator is forced by this pressure into the fully open position, so that the first pump delivers into the tank via the pressure compensator with particularly low back pressure.

[0015] A priority valve can be provided with a continuously adjustable fourth orifice and a continuously adjustable fifth orifice, which are adjustable together, wherein the fourth orifice is open in every position of the priority valve, and the fifth orifice is only open when the pressure downstream of the fourth orifice exceeds a predetermined value. The second pump is fluidically connected to the second orifice via the fourth orifice, and the second pump is fluidically connected to at least one second orifice via the fifth orifice. Preferably, the second pump is connected to the branch point via the fifth orifice. If the flow rate of the second pump is no longer sufficient to supply all actuators with pressurized fluid, the fifth orifice closes, so that only the second actuator is supplied with pressurized fluid by the second pump.This ensures that the second actuator is adequately supplied with pressurized fluid in every operating state, regardless of how the first actuators are controlled.

[0016] It can be provided that the priority valve is actuated in a closing direction of the fifth orifice by a second spring and by the second load pressure, while in an opening direction of the fifth orifice it is actuated by the pressure downstream of the fourth orifice. This allows the priority valve to be easily actuated by the pressure downstream of the first orifice. The second load pressure is preferably connected to the tank when the second actuator is not moving, and otherwise connected to the pressure downstream of the second orifice. This allows the flow from the second pump to be used to supply the first actuators even when the first actuator is stationary and a large external force is acting upon it.

[0017] Protection is also sought for a hydraulic drive system with a first and a second pump and at least a first actuator and a second actuator, which are fluidically connected to each other via a hydraulic control device according to the invention, wherein the first pump has a constant displacement volume, and wherein the second pump has a continuously adjustable displacement volume.

[0018] It can be provided that the first and second pumps are connected to a common motor via a rotary drive. The motor is preferably an internal combustion engine, most preferably a diesel engine.

[0019] Protection is also sought for a mobile working machine with a hydraulic drive system according to the invention, wherein the second actuator and the second orifice are part of a steering system of the mobile working machine, and wherein the at least one first orifice with the associated first actuator are part of a working hydraulic system of the mobile working machine. The mobile working machine can be, for example, an excavator, a wheel loader, an agricultural tractor, or a municipal vehicle.

[0020] It is understood that the features mentioned above and those to be explained below can be used not only in the combinations specified, but also in other combinations or on their own, without leaving the scope of the present invention.

[0021] The invention is explained in more detail below with reference to the accompanying drawings. They show: Fig. 1 a hydraulic drive system with a control device according to the invention.

[0022] Fig. Figure 1 shows a hydraulic drive system 10 with a control device 20 according to the invention. The control device 20 has a first pump connection point 70 to which a first pump 11 with a constant displacement volume is connected. The first pump 11 draws pressure fluid from a tank 15 and delivers it via the first pump connection point 70 in parallel to several first orifices 21. The pressure fluid is preferably a liquid, most preferably hydraulic oil. The in Fig. The tank symbols shown in 1 all refer to the same tank 15.

[0023] The distribution of the pressurized fluid to the various first orifices 22 occurs at the branch point 75 of the corresponding fluid line system. A first check valve 25 is installed between the first pump connection point 70 and the branch point 75, which allows fluid flow exclusively from the first pump 11 to the first orifices 21.

[0024] Furthermore, a pressure compensator 26 with a continuously adjustable third orifice 28 is provided. The third orifice 28 is fluidically connected between the first pump connection point 70 and the first check valve 25, so that pressurized fluid from the first pump 11 can be directed through the third orifice 28 into the tank 15. For this purpose, the pressure compensator 26 is connected to a tank connection point 72 of the control device 20, to which the tank 15 is fluidically connected. In the closing direction of the third orifice 28, the pressure compensator 26 is subjected to a first spring 27 and the pressure at a first control point 76. The preload of the first spring 27 defines a first pressure differential, which is, for example, 5 bar. In the opening direction, the pressure compensator 26 is subjected to the pressure at the branch point 75.Accordingly, the pressure balance 26 regulates the pressure at the branch point 75 to a value that is higher than the pressure at the first control point 76 by the first pressure difference. The pressure at the first control point 76 is the highest load pressure on the first actuators 13, insofar as they are moved.

[0025] The first actuators 13 are, for example, hydraulic cylinders or hydraulic motors, which are preferably installed in the working hydraulics of a mobile machine, such as an excavator, a wheel loader, an agricultural tractor, or a municipal vehicle. The first actuators 13 are each fluidically connected to the control device 20 via a first and a second working connection point 73; 74. Each first actuator 13 is associated with a continuously adjustable first orifice 21 and a first directional control valve 23. The first orifice 21 sets the speed of movement of the associated first actuator 13, while the first directional control valve 23 sets its direction of movement.

[0026] In the first operating position of the first directional control valve 23, pressurized fluid is directed from the branch point 75 via the first orifice 21 to the associated first working port 72, with pressurized fluid being directed from the corresponding second working port 74 into the tank 15. The first working port 73 is fluidically connected to a load sensing point 45 on the first directional control valve 23. In the second operating position of the first directional control valve 23, pressurized fluid is directed from the branch point 75 via the first orifice 21 to the associated second working port 74, with pressurized fluid being directed from the corresponding first working port 73 into the tank 15. The second working port 74 is fluidically connected to the load sensing point 45 on the first directional control valve 23. In the middle closed position, the load sensing point 45 is connected to the tank 15, with all other fluid flow paths being closed.Thus, the pressure downstream of the first orifice 21 is present at the load sensing point 45 when the respective first actuator 13 is moving; when it is stationary, the pressure in the tank 15, which is essentially zero, is present at the load sensing point 45. The first directional control valves 23 are preferably pressed towards the closed position by means of at least one spring. The first orifice 21 and the first directional control valve 23 are preferably adjustable together, most preferably being formed by a common valve spool. The same applies to the second orifice 22 and the second directional control valve 24.

[0027] Each first orifice 21 is preferably assigned a second check valve 29, which allows only a fluid flow from the branch point 75 to the first orifice 21.

[0028] The load sensing points 45 of the first directional control valves 23 are each connected on the input side to an associated first changeover valve 41, which is part of a changeover valve cascade 40. The aforementioned first control point 76 forms the output of the changeover valve cascade 40, which comprises all first changeover valves 41. The highest load pressure of all first actuators 13 is therefore present there, as long as they are moving. The free input of the first changeover valve 41, which is located at the first position in the changeover valve cascade 40, is preferably connected to the tank 15. However, it can also be connected to a load sensing point 45, so that this first changeover valve 41 is associated with two load sensing points 45.

[0029] The second directional control valve 24, which is assigned to the second actuator 14, is identical in construction to the first directional control valve 23, so reference is made to the above descriptions in this regard. The same applies to the first and second orifices 21; 22. The second actuator 14 is preferably a hydraulic cylinder, which is most preferably part of a steering system of the aforementioned mobile working machine. The second actuator 14 is in turn connected to the control device 20 by means of a first and a second working connection point 73; 74.

[0030] The second directional control valve 24 is assigned a second changeover valve 42, to which the first control point 76 and the load sensing point 45 of the second directional control valve 24 are connected on the input side. Accordingly, all first and second changeover valves 41; 42 are connected together to form a changeover valve cascade 40. The output of the second changeover valve 42 forms a second control point 77, at which the highest load pressure of all first and second actuators 13; 14 is applied, as long as they are moving.

[0031] The second pump 12 has an adjustable displacement volume and is fluidically connected to a second pump connection point 71 of the control device 20. The second pump 12 can also have a constant displacement volume, in which case the pump controller 60 is designed as a pressure compensator that directs excess flow into the tank 15. The second pump 12, together with the first pump 11, is driven by a common motor 16, preferably an internal combustion engine, most preferably a diesel engine. It draws pressurized fluid from the tank 15 and delivers it under pressure to a priority valve 50. The priority valve 50 ensures that the second actuator 14 is primarily supplied with pressurized fluid from the second pump 12. Only if the second pump 12 delivers more pressurized fluid than is drawn off at the second actuator 14 does pressurized fluid flow via the branch point 75 to the first actuators 13.

[0032] The priority valve 50 has a fourth and a separate fifth orifice 51; 52, which are continuously adjustable together. The fourth orifice 51 is at least partially open over the entire adjustment range of the priority valve 50. The fifth orifice 52, on the other hand, has a fully closed end position. Pressure fluid can flow from the second pump 12 via the fourth orifice 51, then via the continuously adjustable second orifice 22, and further via the second directional control valve 24 to the second actuator 14. In addition, pressure fluid can flow from the second pump 12 via the fifth orifice 52 to the branch point 75. In the closing direction of the fifth orifice 52, the priority valve 50 is acted upon by the pressure at the load sensing point 45 of the second directional control valve 24 and a second spring 53. In the opening direction of the fifth orifice 52, the priority valve 50 is subjected to the pressure upstream of the second orifice 22.The priority valve thus regulates the pressure drop at the second orifice 22 to the pressure equivalent of the second spring 53. If the flow rate of the second pump 12 is insufficient to maintain this pressure differential, the fifth orifice 52 closes completely, so that only the second actuator 14 is supplied with pressurized fluid.

[0033] A pump controller 60 is assigned to the second pump 12, which regulates the delivery pressure 62 of the second pump 12 by adjusting the displacement volume of the second pump to a value that is a predetermined second pressure differential above the pressure at the second control point 77. The second pressure differential is, for example, 15 bar, which is greater than the first pressure differential defined by the first spring 27 on the pressure balance 26. Thus, the delivery pressure of the second pump 12 is higher than the delivery pressure of the first pump 11, as long as the maximum flow rate of the second pump 12 is sufficient to supply all actuators 13 and 14 with pressurized fluid.

[0034] The delivery pressure 62 of the second pump 12 thus forces the first check valve 25 into the closed position, whereby the entire delivery flow of the first pump 12 flows through the third orifice 28 of the pressure compensator 26 into the tank 15. The pressure compensator 26 is thereby moved by the pressure at the branch point 75 into the fully open position, so that only a small pressure drop occurs at the third orifice 28, resulting in only a small energy loss. This operating condition exists when one or more first actuators 13 are moved slowly, i.e., when they are operated in the fine control range.

[0035] If more pressurized fluid is drawn from actuators 13 and 14 than the second pump 12 can deliver, the fifth orifice 52 on the priority valve 50 closes. This allows the pressure compensator 26 to regulate the delivery pressure of the first pump 11, or the pressure at the branch point 75, to a value that is a first pressure differential above the pressure at the first control point 76, i.e., the maximum load pressure of all first actuators 13. The first pressure differential is defined by the pressure equivalent of the first spring 27, which is, for example, 5 bar. In this operating state, the second pump 12 delivers exclusively to the second actuator 14.

[0036] It should also be noted that the pressure relief valve 61 is connected to the branch point 75. If the pressure there exceeds a predetermined limit, pressurized fluid flows from the branch point 75 into the tank 15, thus reducing the pressure at the branch point 75.

[0037] It should be noted that the first and / or the second directional valve 23; 24 can also be designed as open-center valves. Instead of the closed position, a bypass position is then present, which forms a bypass channel in which only a small volume flow passes, which is used to adjust the second pump 12. Reference sign 10 hydraulic drive system 11 first pump 12 second pump 13 first actuator 14 second actuator 15 Tank 16 engine 20 hydraulic control devices 21 first aperture 22 second aperture 23 first directional valve 24 second-way valve 25 first check valve 26 Pressure scale 27 first spring 28 third aperture (of the pressure balance) 29 second check valve 40 changeover valve cascade 41 first changeover valve 42 second changeover valve 43 first load pressure 44 second load pressure 45 Load reporting point 50 priority valve 51 fourth aperture 52 fifth aperture 53 second spring 60 pump controllers 61 Pressure relief valve 62 Delivery pressure of the second pump 70 first pump connection point 71 second pump connection point 72 Fuel connection point 73 first work connection point 74 second work connection point 75 Junction 76 first tax office 77 second tax office

Claims

[1] Hydraulic control device (20) for use with a first and a second pump (11; 12), at least one first actuator (13) and a second actuator (14), wherein the control device (20) has a continuously adjustable first orifice (21) through which pressure fluid can be supplied from the first and second pumps (11; 12) to an associated first actuator (13), wherein at least one continuously adjustable second orifice (22) is provided through which pressure fluid can be supplied from the second pump (12) to an associated second actuator (14), wherein a pressure balance (26) with a continuously adjustable third orifice (28) is provided through which pressure fluid can be supplied from the first pump (11) to a tank (15), wherein the pressure balance (26) is acted upon by a first spring (27) in a closing direction of the third orifice (28), wherein the preload of the first spring (27) defines a first pressure difference characterized by, that a first check valve (25) is connected between the first pump (11) and the at least one first orifice (21), which allows exclusively a fluid flow from the first pump (11) to the at least one first orifice (21), wherein the third orifice (28) is connected between the first pump (11) and the check valve (25), wherein the second pump (12) is fluidically connected between the check valve (25) and the at least one first orifice (21). [2] Hydraulic control device according to claim 1, wherein each first orifice (21) is assigned a first load pressure (43) which depends on the pressure downstream of the first orifice (21) in question, wherein a second load pressure (44) depends on the pressure downstream of the second orifice (22), wherein a pump controller (60) is provided with which the delivery pressure (62) of the second pump (12) can be adjusted to a value by adjusting the displacement volume of the second pump (12) which is a predetermined second pressure difference above the highest pressure from a group of pressures formed by the at least one first load pressure (43) and the second load pressure (44). [3] Hydraulic control device according to claim 2, wherein the second pressure difference is greater than the first pressure difference. [4] Hydraulic control device according to claim 2 or 3, wherein the pressure balance (26) is subjected in a closing direction of the third orifice (28) by the highest pressure from a group of pressures formed by the at least one first load pressure (43). [5] Hydraulic control device according to one of the preceding claims, wherein the pressure balance (26) in the opening direction of the third orifice (28) is subjected to a pressure which is located between the check valve (25) and the at least one first orifice (21). [6] Hydraulic control device according to one of the preceding claims, wherein a priority valve (50) is provided with a continuously adjustable fourth orifice (51) and a continuously adjustable fifth orifice (52), which are jointly adjustable, wherein the fourth orifice (51) is open in every position of the priority valve (50), wherein the fifth orifice (52) is open only when the pressure downstream of the fourth orifice (51) exceeds a predetermined value, wherein the second pump (12) is fluidically connected to the second orifice (22) via the fourth orifice (51), and wherein the second pump (12) is fluidically connected to the at least one second orifice (22) via the fifth orifice (52). [7] Hydraulic control device according to claim 6, wherein the priority valve (50) is acted upon in a closing direction of the fifth orifice (52) by a second spring (53) and by the second load pressure (44), wherein it is acted upon in an opening direction of the fifth orifice (52) by the pressure downstream of the fourth orifice (51). [8] Hydraulic drive system with a first and a second pump (11; 12) and at least a first actuator (13) and a second actuator (14), which are fluidically connected to each other via a hydraulic control device (20) according to one of the preceding claims, wherein the first pump (11) has a constant displacement volume, wherein the second pump (12) has a continuously adjustable displacement volume. [9] Hydraulic drive system according to claim 8, wherein the first and the second pump (11; 12) are in rotary drive connection with a common motor (16). [10] Mobile working machine with a hydraulic drive system according to claim 8 or 9, wherein the second actuator (14) and the second aperture (22) are part of a steering system of the mobile working machine, wherein the at least one first aperture (21) with the associated first actuator (13) are part of a working hydraulic system of the mobile working machine.

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