Control valve, especially for flow control of an axial piston pump

Abstract

Control valve with a front port (P), a tank port (T), an intermediate control port (A), and a control pressure chamber (17) opposite the port (P), wherein a control piston (8) has a first control collar (10) that controls a connection between the front port (P) and the control port (A), and wherein the control piston (8) has a second control collar (12) that controls a connection between the control port (A) and the tank port (T), wherein a control spring (16) is accommodated in the control pressure chamber (17), wherein the control valve is intended for use with an adjustable hydrostatic piston pump, wherein the front port (P) can be pressurized with the pump pressure, wherein the control port (A) can be connected to an adjustment device of the piston pump, and wherein the control pressure chamber (17) can be pressurized with a load-sensing control pressure.which corresponds to or is derived from the highest load pressure of the consumers supplied by the piston pump, characterized in that the control piston (8) has a guide collar (28) in the region of the end-face connection (P), wherein the control piston (8) has at least one recess in the region of the guide collar (28) via which the end-face connection (P) is connected to the first control collar (10), wherein the recess is a concentric bore (30) in the control piston (8) which is connected to at least one radial bore (32).

Description

The invention relates to a control valve, in particular for controlling the flow rate of an axial piston pump, according to the preamble of claim 1. Documents DE 10 2010 048 068 A1 and DE 10 2012 010 217 A1 each disclose such a flow control valve, which is arranged axially parallel to a pressure control valve in a common screw-in cartridge. Each of these control valves has a control piston guided in a valve bore, and via which a pressure medium connection between a front-facing port pressurized by the pump pressure (system pressure) and a tank port on the one hand, and a control port on the other, can be opened or closed, so that pressure medium flows into a pressure chamber of an actuator cylinder of the axial piston pump or flows out of the pressure chamber to the tank.The control pistons of the flow control valve and the pressure control valve are each actuated by a control spring in one direction of a rest position in which the pressure chamber of the actuating cylinder is connected to the tank and the pressure medium connection between the control port and the end-face port carrying the system pressure is shut off. A disadvantage of such flow control valves is that their control piston can jam and that wear occurs, particularly in the area of ​​the control collar, which controls the connection from the end face connection to the control port. German patent DE 10 2014 202 412 A1 discloses an electrically controlled pressure regulating valve for an adjustable hydrostatic pump. The corresponding regulating piston has three frets. DE 199 27 965 A1 shows a seat valve. The corresponding valve body is elongated and guided in a linear manner. In contrast, the invention is based on the objective of creating a flow control valve whose control piston is less prone to jamming or tilting and therefore experiences less wear. This problem is solved by a control valve having the features of claim 1. Further advantageous embodiments of the invention are described in the dependent patent claims. The claimed control valve, of spool design, has a front-end port, a tank port, and a control port located between the front-end port and the tank port, which can be selectively connected to the front-end port or relieved to the tank. For this purpose, the control valve has a control piston with a first control collar that controls a connection between the front-end port and the control port, and with a second control collar that controls a connection between the control port and the tank port. To regulate the position of the control piston, a front-end control pressure chamber is provided opposite the front-end port, the control pressure of which counteracts the pressure of the front-end port. According to the invention, the control piston has a guide collar in the region of the front-end port.This third support point provides additional support for the control piston, effectively preventing jamming or tilting. The wear of the control valve according to the invention is significantly reduced. The support is further optimized if the guide collar is located on a first end face and thus on the end section of the control piston. In order for the pressure medium to flow from the end-face connection to the first control collar associated with it when the connection from the end-face connection to the control connection is to be opened, the invention provides that the control piston in the area of ​​the end-face connection or the guide collar has at least one radial recess via which the end-face connection is connected to the first control collar. According to the invention, the radial recess is configured as a bore concentrically integrated into the first end face of the control piston, which is connected to at least one radial bore, for example, a through transverse bore. This allows the first end face to be connected to a neck of the control piston formed between the guide collar and the first control collar. Alternatively, the connection can also be formed by several axial grooves arranged on the circumference of the guide collar. This also allows the first end face to be connected to the neck. According to the invention, a control spring is incorporated in the control pressure chamber, which, together with the control pressure, acts against the pressure of the end-face connection on the control piston. Thus, during normal operation of the control valve, the control pressure can be lower than the pressure of the end-face connection. In one application according to the invention, the control valve is a flow control valve for an adjustable hydrostatic piston pump. The end-face port is then pressurized with the pump pressure, while the control port is connected to an adjusting device of the piston pump, for example, an actuating cylinder. According to the invention, the control pressure chamber can be pressurized with a load-sensing control pressure that corresponds to or is derived from the highest load pressure of the consumers supplied by the piston pump. In a particularly preferred further development of the flow control valve as a pressure flow controller, a pressure control valve is also included in a common housing. If the housing is a screw-in cartridge, and if the control port and the tank port are formed by openings on the circumference of the screw-in cartridge, the control valve according to the invention can be screwed into a housing of the piston pump. It is particularly preferred if the control port has four openings around the circumference of the screw-in cartridge. This allows the through-holes of the control port to be arranged in such a way that the transverse forces acting on the control piston of the control valve compensate for each other. This further reduces the wear of the control piston and its guide collar according to the invention. Furthermore, the "dead zone" that occurs in the common control pressure channel between the two regulators in pressure-flow regulators according to the prior art is avoided. According to an initial, manufacturing-optimized version, the four openings are evenly distributed around the circumference of the screw-in cartridge and radially aligned. For this purpose, two through-holes for the control connection are provided inside the screw-in cartridge, intersecting at approximately 90 degrees in the center. One of these through-holes intersects the respective valve bores of the flow control valve and the pressure control valve. The other through-hole intersects the first through-hole at a 90-degree angle in the center of the screw-in cartridge. According to a second variant, the control port has two separate, approximately parallel through-holes, one of which intersects the valve bore of the flow control valve and the other of which intersects the valve bore of the pressure control valve. This minimizes the mutual interference between the two controllers. From a fluid dynamics perspective, it is optimal if the two sections of the through-bores on both sides of the respective valve bore are of the same length. Several embodiments of a control valve according to the invention are shown in the drawings. The invention will now be explained in more detail with reference to the figures in these drawings. Fig. 1 shows a longitudinal section through the first embodiment and Fig. 2 shows a cross-section through a second embodiment. Fig. 1 shows a longitudinal section through a control valve arrangement 1, which in the illustrated first embodiment serves for pressure and flow control of an axial piston pump. This type of flow control is also called load-sensing control or LS control, whereby the axial piston pump is controlled such that the pump pressure is higher by a certain pressure differential than a control pressure applied to the control valve arrangement 1, which is usually the highest load pressure of all hydraulic consumers simultaneously actuated and supplied with hydraulic fluid by the axial piston pump. A housing 2 of the control valve arrangement 1 is designed as a cartridge housing in which a pressure control valve 4 and a flow control valve 6 according to the invention are accommodated. Two end-face connections P are provided on the housing 2, to which the system pressure prevailing at the pressure port of the axial piston pump is applied. The housing 2 further has a control port A extending completely around the cartridge housing, which is in contact with a pressure chamber of an actuating cylinder mentioned at the beginning of the description of the prior art, via which a pivoting cradle of the axial piston pump can be adjusted. The basic design of such an axial piston machine is generally known, so for the sake of simplicity, the corresponding details are omitted. According to the prior art, the control connection A has two radially oriented, opposing openings 7 of a common through-bore 9. According to the invention, the control connection A has two further radially oriented openings (located above and below the plane of the drawing in Fig. 1) of a common further through-bore 13, which are explained in more detail below. As shown in Fig. 1, the housing 2 also has a tank connection T and a connection LS, at which the highest load pressure of all consumers supplied by the pump is applied. This LS connection is associated with the flow control valve 6 according to the invention. The flow control valve 6 has a control piston 8, which is designed with two radially projecting control flanges 10, 12, and which is guided axially displaceably in a valve bore 14. This bore widens in steps to the right (view according to Fig. 1) to a control pressure chamber 17, in which a control spring 16 designed as a helical compression spring is located. This spring acts on the control piston 8 via a spring plate 15 abutting the control piston 8 and biases it in a starting position against a hardened stop pin 18, which is inserted into the housing 2 transversely to the valve bores 14, 22 in the area of ​​the two pressure ports P. The housing 2 also includes a connecting bore 24, which runs between the two valve bores 14 and 22 and is designed as a section of a blind bore that is closed externally by a threaded stud 25. The flow cross-section between the connecting bore 24 and the tank connection T is controlled by the pressure regulating valve 4. In its rest position, the flow cross-section is open to its maximum extent. In the illustrated basic position of the control piston 8 of the inventive flow control valve 6, the two control collars 10, 12 are arranged such that the through-bores 9 and indirectly also the through-bore 13 are in contact with the connecting bore 24, while the connection to the associated pressure port P is blocked. Consequently, the control port A and thus the pressure chamber of the actuating cylinder is connected to the tank – for example, a pivoting cradle of the axial piston machine is then fully pivoted out. The load pressure tapped via port LS acts in the control pressure chamber 17 against the pressure at port P on the control piston 8, whereby the end faces subjected to the respective pressures are of equal size. The control piston 8 is thus moved into its control position when the pressure at pressure port P (pump pressure) is greater than the load pressure by the pressure equivalent of the control spring 16. In the illustrated embodiment, the control spring 16 is supported on a spring seat designed as an adjusting screw 26, which engages in the threads of the enlarged part of the valve bore 14. By screwing this adjusting screw 26 in or out, the preload of the control spring 16 is increased or decreased, respectively. A hardened pin 19 is provided coaxially inside the control spring 16. This pin is integrally formed with the adjusting screw 26 and limits the maximum stroke of the control piston 8, thus preventing the control spring 16 from bottoming out or being overloaded. The circumferential control port A is separated from the end-face port P and the equally circumferential tank port T by a sealing ring each. The control port A has the aforementioned common through-bore 9 with the two openings 7 shown in Fig. 1 and the further through-bore 13 with the two additional radially oriented openings (located above and below the plane of the drawing in Fig. 1). The two through-bores 9, 13 intersect at right angles to each other and centrally in the housing 2, which is designed as a screw-in cartridge. The further through-bore 13 increases the flow through a section of the first through-bore 9, which is located between the two control valves 4, 6 and connects them, thus preventing a "dead zone" and consequently back pressure.Furthermore, the additional through-bore 13 provides two additional passages from the valve bore 14 to the circumferential control port A, the opening cross-sections of which are independent of the pressure regulating valve 4. Transverse forces that can cause wear on the flow control valve 6 and lead to jamming of its control piston 8 are reduced or compensate for each other – depending on the operating state of the flow control valve 6 – because uniform control pressures prevail on both sides of the control piston 8. Furthermore, the control piston 8 of the flow control valve 6 according to the invention has additional support formed by a guide collar 28, which is arranged on the end section of the control piston 8 in the region of the end-face connection P. The guide collar 28 also reduces the wear of the flow control valve 6 and prevents its control piston 8 from jamming. If pressure medium is to reach the first control collar 10 from port P, it must pass through the guide collar 28. For this purpose, a concentric bore 30 is provided inside the guide collar 28, which is connected to a radial bore 32. The radial bore 32 is located in the region of a neck in the control piston 8, which is formed between the guide collar 28 and the first control collar 10. Fig. 2 shows a cross-section through a housing 102 of a control valve arrangement 101 according to a second embodiment of the invention. Only the differences from the first embodiment are explained below. The circumferential control port A has two parallel through-bores 109, 113, each with two openings 7. The through-bore 109 (upper in Fig. 2) is connected only to the valve bore 22 of the pressure control valve 4, while the through-bore 113 (lower in Fig. 2) is connected only to the valve bore 14 of the flow control valve 6. This minimizes the mutual influence of the two control valves 4, 6. The two through-holes 109, 113 are angled at 45 degrees to a connecting plane 134, which connects the two valve bores 14, 22 and intersects them at right angles. The two sections of each through-hole 109, 113 resulting from the intersection with the respective valve bore 14, 22 are of different lengths. This is due to the requirement that a tool used to machine the through-holes can be positioned as radially as possible on the screw-in cartridge. In contrast to the embodiment shown in Fig. 2, the two parallel through-bores can also be arranged perpendicular to the connecting plane 134. In this case, the two sections of each through-bore resulting from the intersection with the respective valve bore 14, 22 are of equal length. Compared to the second embodiment, this results in a more oblique angle of application of the tool, but is optimal from a fluid dynamics perspective. The design reveals a flow regulator for an axial piston pump whose risk of jamming and wear are minimized by an additional guide collar on the control piston. Furthermore, radial forces on the control piston are compensated by a channel for the flow regulator's output pressure, open to the housing's outer wall on both sides of the control piston. Reference symbol list 1; 101 Control valve assembly 2; 102 Housing 4 Pressure control valve 6 Flow control valve 7 Opening 8 Control piston 9; 109 Through-hole 10 Control collar 12 Control collar 13; 113 Through-hole 14 Valve bore 15 Spring retainer 16 Control spring 18 Stop pin 17 Control pressure chamber 19 Pin 22 Valve bore 24 Connecting bore 25 Threaded pin 26 Adjusting screw 28 Guide collar 30 Concentric bore 32 Radial bore 134 Connecting plane

Claims

Control valve with a front port (P), a tank port (T), an intermediate control port (A), and a control pressure chamber (17) opposite the port (P), wherein a control piston (8) has a first control collar (10) that controls a connection between the front port (P) and the control port (A), and wherein the control piston (8) has a second control collar (12) that controls a connection between the control port (A) and the tank port (T), wherein a control spring (16) is accommodated in the control pressure chamber (17), wherein the control valve is intended for use with an adjustable hydrostatic piston pump, wherein the front port (P) can be pressurized with the pump pressure, wherein the control port (A) can be connected to an adjustment device of the piston pump, and wherein the control pressure chamber (17) can be pressurized with a load-sensing control pressure.which corresponds to or is derived from the highest load pressure of the consumers supplied by the piston pump, characterized in that the control piston (8) has a guide collar (28) in the region of the end-face connection (P), wherein the control piston (8) has at least one recess in the region of the guide collar (28) via which the end-face connection (P) is connected to the first control collar (10), wherein the recess is a concentric bore (30) in the control piston (8) which is connected to at least one radial bore (32). Control valve according to one of the preceding claims, in the housing (2;102) of which a pressure control valve (4) is additionally accommodated. Control valve according to claim 2, wherein the housing (2; 102) is a screw-in cartridge, and wherein the control port (A) and the tank port (T) are formed by openings (7) on the circumference of the screw-in cartridge (2; 102). Control valve according to claim 3, wherein the control port (A) is formed by four openings (7) on the circumference of the screw-in cartridge (2; 102). Control valve according to claim 4, wherein the four openings (7) are evenly distributed around the circumference of the screw-in cartridge (2), and wherein the control port (A) has two through bores (9, 13) intersecting each other at approximately 90 degrees, one of which through bores (9) intersects the respective valve bores (14, 22) of the flow control valve (6) and the pressure control valve (4). Control valve according to claim 5, wherein the control port (A) has two approximately parallel through-bores (109, 113), one through-bore (109) intersecting a valve bore (22) of the pressure control valve (4) and one through-bore (113) intersecting a valve bore (14) of the flow control valve (6). Control valve according to claim 6, wherein two sections of the through-bore (109, 113) on both sides of the flow control valve (6) are of equal length, and wherein two sections of the through-bore (109, 113) on both sides of the pressure control valve (4) are of equal length.

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