HYDRAULIC ADJUSTMENT DEVICE

Description

[0001] The present invention relates to a hydraulic adjustment device, in particular for the transverse adjustment of the lower links of a three-point power lift on an agricultural machine with two optionally controllable hydraulic cylinders and a hydraulic control circuit for controlling the hydraulic cylinders.

[0002] On agricultural machines such as tractors, tow tractors, or the like, implements such as mowers, plows, harvesters, and the like are attached to the front or rear via a so-called three-point linkage. A three-point linkage is described, for example, in EP 1 116 430 A1. Together with a hydraulic system for raising and lowering the implement, such a three-point linkage is also referred to as a three-point linkage.

[0003] A three-point linkage typically has two lower links pivoted at corresponding pivot points on the work machine, as well as a pivoting top link. The lower links must be capable of transverse adjustment in order to adapt the distance between the lower links to the width of the attachment. Solutions using chains or toggle bolts are available for this type of width adjustment. However, hydraulic transverse adjustment of the lower links is advantageous. In this case, the two lower links are each connected to a hydraulic cylinder that runs diagonally in the laterally direction. By simultaneously extending or retracting the hydraulic cylinders and moving the two lower links accordingly in the transverse direction, the distance between them can be increased or decreased in order to adapt it to the width of the attachment mount.

[0004] EP 1 175 817 A1 describes a hydraulic control system for the lower links of a three-point linkage. It is used to adjust the lower links to defined standard widths and easily center an attached implement relative to the tractor's longitudinal axis. The travel direction of the corresponding hydraulic cylinders is adjusted via electrically switched solenoid valves. A total of five electrical control signals are required for the adjustment device shown to extend or retract the hydraulic cylinders either simultaneously or in opposite directions.

[0005] DE 197 37 318 A1 describes a device for hydraulically controlling the lower links of a three-point linkage, allowing the lower links to be hydraulically locked and unlocked at the push of a button. This allows for convenient switching between safe transport of the implement on the road and towing operations, where the implement is typically intended to be mobile.

[0006] WO 2021 / 004888 A1 describes a device that can adjust the position of a tractor-mounted towing device transversely to the direction of travel, allowing the device to precisely follow the desired path. The adjustment occurs during operation in response to GPS or other sensor data.

[0007] AT 272 721 B describes a device that allows the lower links of a three-point linkage to be moved hydraulically from the tractor seat and optionally stabilized.

[0008] EP 3 479 668 A1 describes a device that can be attached to devices intended for coupling to a three-point coupling.

[0009] It is an object of the present invention to provide a hydraulic actuating device and an associated hydraulic control circuit that enables the selective control of two hydraulic cylinders in a simple manner. In particular, the actuating device and its hydraulic control circuit should require as few electrical control signals as possible.

[0010] The problem is solved by the features of claim 1. Advantageous embodiments can be found in the dependent claims.

[0011] In an adjustment device of the type mentioned at the outset, the invention provides that the control circuit has a pressure control device for generating an adjustable control pressure as a function of an electrical control signal and a pressure-controlled switching valve connected to the pressure control device, which valve assumes a first switching position when a first control pressure value is applied, in which a first of the hydraulic cylinders is connected to a pressure sink and the second hydraulic cylinder is connected to a pressure source, and when a second control pressure value is applied, which is higher than the first control pressure value, assumes a second switching position in which the first hydraulic cylinder is connected to the pressure source and the second hydraulic cylinder is connected to the pressure sink.

[0012] If one of the hydraulic cylinders is pressurized while the second is connected to the pressure sink and can thus retract, in the case of a three-point hitch, both lower links are adjusted transversely in the same direction, thus adjusting an attachment transversely via the three-point hitch. The locking circuit according to the invention thus makes it possible to perform a transverse adjustment in either direction with a single electrical control signal, depending on the switching position to which the pressure-controlled changeover valve is switched by adjusting the switching pressure. Thus, the present invention makes it easy to perform a transverse adjustment of an attachment on an agricultural machine.

[0013] In an advantageous further development, it can additionally be provided that the pressure-controlled changeover valve assumes a third switching position when a third control pressure value is applied, which is different from the first and second control pressure values. In this third switching position, both hydraulic cylinders are connected to the pressure source or to the pressure sink. In this third switching position, both hydraulic cylinders can thus be extended or retracted simultaneously. This enables a width adjustment of the lower links in a three-point suspension. Thus, the invention makes it possible to carry out both a transverse adjustment and a width adjustment of the lower links in a three-point suspension of an agricultural work machine with a single control signal. The third control pressure value is preferably selected such that it is lower than the first or the second control pressure value.Since the width adjustment of the lower links of a three-point linkage is usually performed without load, it can be performed at the lowest control pressure value. In this case, the control pressure can be used simultaneously not only to switch the switching valve but also to extend the hydraulic cylinders, meaning the hydraulic cylinders are only subjected to the control pressure and not to the full working pressure of the pressure source.

[0014] A further advantage arises if the control circuit additionally has an electrically switched switching valve which, either directly or via pressure-controlled valves, interrupts a connection to the pressure source or the pressure sink switched via the pressure-controlled switching valve in a first switching position and switches it through in a second switching position.

[0015] On the one hand, a safety function such as an emergency stop can be implemented by interrupting the connection to the pressure source and pressure sink, preventing adjustment of the hydraulic cylinders and thus securely holding their position. Furthermore, interrupting the switched connection in the third switching position enables the direction of the width adjustment to be reversed, i.e., either simultaneous retraction or simultaneous extension of the hydraulic cylinders for width adjustment. As already mentioned, extension can be achieved using the control pressure, which, due to the pressure control device, is below the working pressure supplied by the pressure source.

[0016] In order to be able to adjust the hydraulic cylinders using the control pressure, the control pressure from the pressure control device is conveniently connected directly to both hydraulic cylinders via check valves, at least in the third switching position. The check valves serve, in particular, to prevent the working pressure from flowing back to the outlet of the pressure control device when the full pressure of the pressure source is applied to one of the hydraulic cylinders during operation of the attachment.

[0017] In a further development of the invention, it can also be provided that the control pressure from the pressure control device is connected directly to one of the two hydraulic cylinders via check valves and a further, electrically switchable changeover valve, at least in the third switching position. Thus, in the third switching position, i.e., for adjusting the width of the lower links, the latter can be adjusted laterally separately from one another. This can be helpful for adjusting the position of the lower links to the position of their pivot points for coupling an attachment. This avoids complex, precise maneuvering of the work machine.

[0018] The pressure control device can expediently be formed by a pressure control valve or by an adjustable pressure relief valve with a flow resistance.

[0019] Furthermore, it can be expedient to provide load sensing lines branching off from the pressure lines leading to the hydraulic cylinders, which are connected to a load flow sensing system of the pressure source, and for the pressure source to be designed as a volume-flow-adjustable hydraulic pump. Many agricultural machines today are equipped with a corresponding load pressure sensing system (LS system). In this way, the pressure or volume flow of the hydraulic pump can be adapted to the conditions required by the consumer. The pump therefore only has to deliver the volume flow that is currently required for all active consumers. This avoids power losses that would occur if the hydraulic pump always delivered at maximum power, even with a throttled volume flow.

[0020] If the pressure-controlled switching valve is designed as a proportional valve, such that a switching movement from the first switching position to the second switching position is proportional to the control pressure, the adjustment speed of the respective lower link can be changed via the control pressure.

[0021] The hydraulic actuating device specified by the present invention can be used for all types of applications in which two hydraulic cylinders are to be deflected in different directions, either in the same direction or in opposite directions. However, a preferred application concerns a so-called three-point linkage of an agricultural machine. This has two laterally pivoting lower links, each of which is transversely adjustable via a hydraulic cylinder, as well as a hydraulic control circuit for controlling the hydraulic cylinders.According to the invention, it is provided that the control circuit has a pressure control device for generating an adjustable control pressure as a function of an electrical control signal and a pressure-controlled switching valve connected to the pressure control device, which valve, when a first control pressure value is applied, assumes a first switching position in which a first of the hydraulic cylinders is connected to a pressure source and the second hydraulic cylinder is connected to a pressure sink, and when a second control pressure value is applied, which is higher than the first control pressure value, assumes a second switching position in which the first hydraulic cylinder is connected to the pressure sink and the second hydraulic cylinder is connected to the pressure source.

[0022] Preferably, the three-point linkage can be equipped with a hydraulic adjustment device according to one of claims 2 to 7. The hydraulic cylinders of the three-point linkage are expediently designed as single-acting cylinder / piston units with spring return. Instead of a return spring, the return can also be achieved by gas pressure, for example.

[0023] Further advantages and features of the present invention will become apparent from the following description of exemplary embodiments with reference to the figures. It shows: Figure 1 shows the hydraulic diagram of a hydraulic adjustment device in a first embodiment, Figure 2 shows the hydraulic diagram of a hydraulic adjustment device in a second embodiment, Figure 3 shows the hydraulic diagram of a hydraulic adjustment device in a third embodiment, Figure 4 shows a hydraulically controlled switching valve with additional pressure relief function, which can be used in the embodiments 1 to 3, Figures 5A and 5B show alternative embodiments of a pressure control device by means of a pressure control valve ( Fig. 5A ) or by an adjustable pressure relief valve ( Fig. 5B ), and Figure 6 a schematic drawing of the lower links of a three-point linkage with laterally arranged hydraulic cylinders for transverse adjustment of the lower links.

[0024] The Figure 1The hydraulic circuit shown comprises two single-acting hydraulic cylinders 1, 2 with spring return, which can be selectively controlled. The circuit includes a pressure supply line 3, to which a pressure source, such as the hydraulic pump of an agricultural machine, is connected. A tank 4 forms the pressure sink of the hydraulic circuit.

[0025] The heart of the circuit is a pressure control valve 5, which serves as a pressure control device for generating an adjustable control pressure depending on an electrical input signal. The pressure control valve has a first port A1 connected to the pressure supply line 3, a second port A2 to which the adjustable control pressure is applied, and a third port A3 connected to the tank 4 via a tank return line. Port A2 is connected to the control port of a pressure-controlled changeover valve 6, which functions as a 4 / 3-way valve. The four ports of the changeover valve 6 are connected to the pressure line 3, to a tank return line 7, and each via a pressure-controlled closing valve 8, 9 to one of the two hydraulic cylinders 1, 2.In the tank return line 7 between the switching valve 6 and the tank 4, there is a pressure compensator (differential pressure valve) 10, whose control input is connected to port A2 of the pressure control valve 5. Furthermore, port A2 of the pressure control valve 5 is directly connected to the two hydraulic cylinders 1, 2 via a check valve 11, 12.

[0026] In addition, the circuit also includes an electrically switched changeover valve 13 in the form of a 3 / 2-way valve, via which the control connections of the two pressure-controlled closing valves 8, 9 can be connected either to the pressure line 3 or to the tank 4 in order to either open the closing valves 8, 9 or to close them in a spring-return manner when the control line to the tank 4 is depressurized.

[0027] Load sensing lines 14, 15, and 16 branch off from the pressure lines 8', 9' leading from the pressure-controlled switching valve 6 to the hydraulic cylinders 1, 2 and from the control pressure line connected to port A2 of the pressure control valve 5, respectively, upstream of the two pressure-controlled closing valves 8, 9. They are connected to the LS system of the pressure source to adapt the delivered volume flow to the load demand. To prevent pressure feedback between the load sensing lines or with other connected load sensing lines, each of the load sensing lines 14, 15, and 16 is equipped with a check valve 14', 15', and 16'.

[0028] The hydraulic circuit shown therefore requires only two electrical control signals, namely for the pressure control valve 5 and the switching valve 13, to selectively control the hydraulic cylinders 1, 2. Depending on the control pressure value p set by the pressure control valve 5, the pressure-controlled switching valve 6 assumes one of the three switching states shown. Up to a lower control pressure value p1, the switching valve 6 remains in the left switching position (S1) held by a return spring, in which the two pressure lines 8', 9' leading to the pressure-controlled closing valves 8, 9 are connected to the tank 4 via the pressure compensator 10. The pressure compensator only opens at a switching pressure p0 that is below the control pressure value p1. As long as the control pressure p < p0, the tank return line 7 is closed and, regardless of the switching position of the closing valves 8, 9, no hydraulic fluid can flow from the hydraulic cylinders 1, 2 to the tank.

[0029] At a control pressure value p0 < p < p1, the pressure compensator 10 opens, so that the hydraulic cylinders 1, 2 are connected to the tank 4 when the closing valves 8, 9 are open, i.e., when the switching valve 13 is energized. In this switching state, the piston rods of both hydraulic cylinders 1, 2 can retract due to the force of their respective return springs. If, however, the switching valve 13 is de-energized and the closing valves 8, 9 are thus closed, the control pressure p applied to the hydraulic cylinders 1, 2 via the check valves 11, 12 causes the piston rods of both hydraulic cylinders 1, 2 to extend.

[0030] If the control pressure is increased to a value above the control pressure value p1, the switching valve 6 initially switches to the middle switching state (S2), in which the pressure line 8' leading to the hydraulic cylinder 1 is connected to the tank 4 and the pressure line 9' leading to the hydraulic cylinder 2 is connected to the pressure supply line 3. From a control pressure above an upper control pressure value p2, the switching valve 6 switches to the right switching state (S3), in which the pressure line 8' leading to the hydraulic cylinder 1 is connected to the pressure supply line 3 and the pressure line 9' leading to the hydraulic cylinder 2 is connected to the tank 4. With a control pressure value p1 < p < p2 and energized switching valve 13, the piston rod of the hydraulic cylinder 1 will extend and the piston rod of the hydraulic cylinder 2 will retract. With a control pressure value p > p2 and energized switching valve 13, the direction of movement is reversed, i.e.The piston rod of hydraulic cylinder 1 can retract and the piston rod of hydraulic cylinder 2 can extend. When the switching valve 13 is de-energized, however, the closing valves 8, 9 are closed and the pressure lines 8', 9' leading from the switching valve 6 to the hydraulic cylinders 1, 2 are blocked, so that the piston position of the hydraulic cylinders 1, 2 is blocked. In this way, an emergency stop function can be implemented using the switching valve 13.

[0031] The hydraulic cylinders 1, 2 can be used in particular as a hydraulic adjustment device for the transverse adjustment of the lower links 21, 22 of a three-point power lift on an agricultural machine, as shown schematically in Figure 6. Shown here in a highly simplified manner are the two lower links 21, 22 of a three-point power lift, which are pivotably attached to corresponding mounting points, e.g. a hitch of the agricultural machine. The two hydraulic cylinders 1, 2 are each connected diagonally in the lateral direction to one of the two lower links 21, 22. By moving in the same direction, i.e. extending or retracting the piston rod of the hydraulic cylinders 1, 2 on both sides, the width between the two lower links 21, 22 can be reduced or increased. This takes place in the left switching position (S1) of the changeover valve 6, i.e.at a control pressure value p0 < p < p1, whereby the width is increased by energizing the changeover valve 13 (retraction movement of the piston rods) and reduced when the changeover valve 13 is de-energized (extension movement of the piston rods). At a control pressure value p1 < p < p2 and an energized changeover valve 13, an implement coupled to the three-point linkage can be adjusted to the right (switching position S2) and at a control pressure value p > p2 to the left (switching position S3). In one embodiment, the switching position S1 is assumed at a pressure of 0 to 5 bar; the switching position S2 is assumed at a pressure between 10 and 15 bar and the switching position S3 at a pressure between 15 and 20 bar. Of course, higher or lower pressure values ​​for the individual switching positions are also conceivable. In general, the required pressure level depends on the friction values ​​of the mechanical components, in particular the friction in the hydraulic cylinder.Preferably, the pressures are selected, as in the aforementioned embodiment, so that an adjustment can be carried out with the operating pressure of a power-controlled hydraulic pump of a tractor (LS system) in idle mode. The switching position from S2 to S3 can be controlled seamlessly, i.e., from 10 to 15 and then from 15 to 20 bar.

[0032] The hydraulic circuit thus enables both width adjustment of the three-point linkage and lateral movement of the attached implement via the lateral adjustment of the lower links. Such lateral movement of the entire implement or parts of the implement, for example, during work in the field, can be used to protect the crop in the field from damage caused by the implement, for example, during hoeing or similar work between crop rows.

[0033] Furthermore, the control circuit according to the invention allows the lower links to be braced against each other when the attachment is mounted, thus stiffening them against lateral movement. This enables safe operation of the work machine on public roads as well as in the field. Bracing occurs in the left switching position (S1) of the changeover valve 6, i.e., at a control pressure value p0 < p < p1, by extending both hydraulic cylinders 1, 2 against each other.

[0034] By preloading the return line to tank 4 via line 7 using the pressure compensator 10, the risk of a vacuum occurring in the hydraulic cylinders 1, 2 is reduced if lateral acceleration causes the load to overtake the hydraulic pressure. The preload essentially functions as a lowering brake with a low opening pressure. If higher preload pressures are required, the pressure compensator 10 could alternatively be replaced by two lowering brakes connected in parallel. In this case, the pressure from lines 15 and 14 could be tapped to open the respective lowering brake.

[0035] Since the opening pressure p0, at which the pressure compensator 10 opens, is below the lower switching pressure p1 of the switching valve 6, the two valves are switched sequentially. This sequential control ensures that functional overlaps cannot occur.

[0036] The pressure-controlled switching valve 6 can additionally incorporate a proportional function, meaning that the connections switched by the valve are opened more or less depending on the pressure, thus creating a pressure-dependent throttling function. This allows cylinders 1 and 2 to be moved dynamically in the field proportionally to the pump pressure (preferably of an LS system). The maximum pump power of the hydraulic system is then available, even if the adjustment device according to the invention typically requires only a small amount of pump power.

[0037] A further development of the hydraulic circuit from Figure 1 is in Figure 2shown. There, an additional electric 3 / 2-way switching valve is installed in the control pressure line coming from port A2 of the pressure control valve 5. This valve allows the control pressure p in the left switching position (S1) of the switching valve 6 (p0 < p < p1) to be applied to only one of the two hydraulic cylinders 1, 2 instead of to both hydraulic cylinders 1, 2 simultaneously. This enables independent positioning of the lower links when coupling an attachment.

[0038] In Figure 3 is a further modification of the hydraulic circuit from Figure 1 This refers to the Figure 1 The existing load signal line 16, which branches off from the control pressure line connected to port A2 of the pressure control valve 5, is omitted. This allows for width adjustment or tensioning of the lower links 21, 22 without a pressure signal being sent to the LS system of the working machine.

[0039] In Figure 4A pressure-controlled shut-off valve 18 with an additional control line for pressure relief is shown, which can be installed instead of the pressure-controlled shut-off valves 8, 9. This allows the pressure in the hydraulic cylinders 1, 2 to be limited to a permissible maximum pressure. If this is exceeded, for example due to external forces acting on a connected attachment, the valves 8, 9 open and excess pressure can be released via the tank return line 7.

[0040] The Figures 5a and 5b show a comparison of a pressure control valve 5 as in the Figures 1 to 3 used, with a pressure relief valve 5' with additional flow resistance 5" (throttle), which can be used alternatively as a pressure control device. The connections A1, A2, and A3 are connected according to their functionally correct wiring in the hydraulic circuits of the Figures 1 to 3 designated.

Claims

1. Hydraulic adjustment device for transverse adjustment of lower links (21, 22) of a three-point power lift on an agricultural machine, with two selectively actuatable hydraulic cylinders (1, 2) and a hydraulic control circuit for actuating the hydraulic cylinders (1, 2), characterized in that the control circuit has a pressure control apparatus (5) for generating an adjustable control pressure depending on an electrical control signal, and a pressure-controlled changeover valve (6) which is connected to the pressure control apparatus (5) and which, when a first control pressure value is applied, assumes a first switching position (S2) in which a first of the hydraulic cylinders (1) is connected to a pressure sink (4) and the second of the hydraulic cylinders (2) is connected to a pressure source (3), and, when a second control pressure value is applied which is higher than the first control pressure value, assumes a second switching position (S3) in which the first hydraulic cylinder (1) is connected to the pressure source (3) and the second hydraulic cylinder is connected to the pressure sink (4).

2. Hydraulic adjustment device according to claim 1, wherein the pressure-controlled changeover valve (6), when a third control pressure value is applied that differs from the first and the second values, assumes a third switching position (S1) in which both of the hydraulic cylinders (1, 2) are connected to the pressure source (3) or to the pressure sink (4).

3. Hydraulic adjustment device according to claim 2, wherein the control circuit additionally has an electrically switched changeover valve (13) which, either directly or via pressure-controlled valves (8, 9), in a first switching position interrupts a connection to the pressure source (3) or the pressure sink (4), which connection is switched via the pressure-controlled changeover valve (6), and in a second switching position connects through.

4. Hydraulic adjustment device according to claim 2 or 3, wherein the control pressure from the pressure control apparatus (5) is connected directly to both hydraulic cylinders (1, 2) via check valves (11, 12) at least in the third switching position (51).

5. Hydraulic adjustment device according to claim 2 or 3, wherein the control pressure from the pressure control apparatus (5) is connected directly to one of the two hydraulic cylinders (1, 2) selectively via at least one check valve (11, 12) and a further electrically switchable changeover valve (17) at least in the third switching position (S1).

6. Hydraulic adjustment device according to any one of the preceding claims, wherein the pressure control apparatus (5) is formed by a pressure control valve (5) or by an adjustable pressure-limiting valve (5') with a flow resistor (5").

7. Hydraulic adjustment device according to any one of the preceding claims, wherein load signal lines (14, 15) branch off from pressure lines (8', 9') leading to the hydraulic cylinders (1, 2) and are connected to a load pressure signal system (LS) of the pressure source (3), and the pressure source (3) is designed as a volume-flow-controllable hydraulic pump.

8. Hydraulic adjustment device according to any one of the preceding claims, wherein the pressure-controlled changeover valve (6) is configured such that a changeover movement from the first switching position (S2) into the second switching position (S3) is proportional to the control pressure.

9. Three-point power lift of an agricultural machine, with two laterally pivotable lower links (21, 22), each of which is hydraulically transversely adjustable via a hydraulic cylinder (1, 2), and with a hydraulic control circuit for actuating the hydraulic cylinders (1, 2), characterized in that the control circuit has a pressure control apparatus (5) for generating an adjustable control pressure depending on an electrical control signal, and a pressure-controlled changeover valve (6) which is connected to the pressure control apparatus (5) and which, when a first control pressure value is applied, assumes a first switching position (S2) in which a first of the hydraulic cylinders (1) is connected to a pressure sink (4) and the second of the hydraulic cylinders (2) is connected to a pressure source (3), and, when a second control pressure value is applied which is higher than the first control pressure value, assumes a second switching position (S3) in which the first hydraulic cylinder (1) is connected to the pressure source (3) and the second hydraulic cylinder (2) is connected to the pressure sink (4).

10. Three-point power lift according to claim 9, with a hydraulic adjustment device for the lower links (21, 22) according to any one of claims 2 to 8.

11. Three-point power lift according to claim 9 or 10, wherein the hydraulic cylinders (1, 2) are configured as single-acting cylinder-piston units with spring or gas pressure return.