EP0879374A2

EP0879374A2 - Directional valve

Info

Publication number: EP0879374A2
Application number: EP97919246A
Authority: EP
Inventors: Georg Rausch
Original assignee: Mannesmann Rexroth AG
Current assignee: Bosch Rexroth AG
Priority date: 1996-02-16
Filing date: 1997-02-06
Publication date: 1998-11-25
Anticipated expiration: 2017-02-06
Also published as: DE19605862A1; WO1997030306A3; EP0879374B1; US6068021A; CA2246709A1; JP2000505864A; DE59700719D1; WO1997030306A2

Abstract

The invention relates to a 2-port directional fitted valve (2) with a main piston (6) through which hydraulic fluid can flow, guided in a valve bushing (4) and via which an inlet connection (B) is connected to an outlet connection (A). An operative surface (D-d) is provided in the region of a throttle point (8) of the main piston (6) with the result that when the pressure drops at the throttle point (8) a pressure force acts on the main piston (6) which pushes it back into its starting position.

Description

Description directional valve

The invention relates to a directional valve according to the preamble of claim 1 and pressure reducing and flow control valves provided with such a directional valve.

1 shows an embodiment of such a directional control valve, which is designed as a 2-way cartridge valve 2. This has a valve sleeve 4, in which a main piston 6 is guided axially. The valve bushing 4 can be fastened in a known manner in a control block and can thus be part of a hydraulic circuit, which will be discussed in more detail below.

The valve bushing 4 has two connections A and B, the connection B usually being the input connection and being designed as a radial or branching connection. The output port A is arranged coaxially with the main piston 6. Radial bores 8 are provided on the peripheral wall of the main piston 6, via which the connection B can be connected to the connection A when the main piston 6 flows through. In the embodiment shown, the connection B and the radial bores 8 are each designed as a star. In the starting position shown in FIG. 1, the main piston 6 is biased by a spring 10 against a stop position in which the connection of B via the main piston 6 to the outlet port A is opened. That is, in the starting position of the main piston 6, the hydraulic fluid flows in the radial direction through the connection B, enters the interior of the main piston 6 through the radial bores 8 and is deflected by approximately 90 ° to the connection A.

By means of a suitable design of the control block and the valve cover (not shown), a control pressure can be supplied to the spring side of the main piston 6, via which this is biased towards its starting position. This control pressure can be applied, for example, via a control pressure line branching off the output connection A.

Such valve arrangements in a 2/2-way valve construction belong to the group of so-called logic elements which are used as a main stage, for example for pressure limiting, pressure regulating, pressure switching valves, etc. In this case, pilot valves can be assigned to the main stage, which can be integrated, for example, on the valve cover, in the valve cover or at another location on a control block.

3 shows a circuit example in which the built-in valve 2 is a component of a pilot-controlled pressure reducing valve 12. This consists essentially of the built-in valve 2 and a directly controlled pilot valve 14 which is designed as a pressure relief valve. The direction of volumetric flow at the built-in valve 2 is from port B to port A, a free volumetric flow being ensured in the starting position as shown in FIG. 1.

The pressure at the outlet connection A is tapped off via a control line 16 and led to the spring side of the main piston 8 via two nozzles 18 and 20 connected in series. The desired outlet pressure at outlet port A can be set via the spring of pilot valve 14. This output pressure acts on the piston underside of the main piston 6 and is guided to the spring side of the main piston 6 via the control line 16 and the nozzles 18 and 20. As long as the pressure at the outlet connection A is lower than the inlet pressure set at the pilot valve 14, the main piston 6 remains in its initial position by the spring 10, in which the connection between A and B is completely opened. If the pressure at the outlet connection A - and thus that between the two nozzles 18 and 20 - exceeds the preset value, the pilot valve 14 is opened so that control fluid flows via the pilot valve 14 to a tank T. By the resulting _^ control liquid flow 18, a pressure gradient so that fluid pressure difference due to control the side between the piston base and the Fe¬, the main piston 6 against the bias of spring 10 from its initial position to the top (view of FIG. 1 formed on the nozzle ) is moved and the connection from B to A is controlled until a pressure equilibrium is established. In this state, only enough hydraulic fluid can then flow from port B through main piston 6 to port A that the pressure set at A via pilot valve 14 is not exceeded. If a consumer connected to the output connection A does not take off any hydraulic fluid, the main piston 6 is brought into its closed position in which the connection between B and A is closed to such an extent that only the required control oil volume flow reaches the connection A. During the control function, control fluid constantly flows through the pilot valve 14 to the tank T. In the exemplary embodiment shown in FIG. 3, the two nozzles 18 and 20 and the pilot valve 14 are formed in or on the valve cover 22.

When the built-in valve 2 flows through, a flow pulse acts on the bottom 24 of the main piston 6, so that the latter is subjected to an impulse force F _j which acts counter to the spring force F ^ applied by the spring 10 (see FIG. 1). At high volume flows, it can happen that the momentum force F _{j is} greater than the spring force Fι_, so that the main piston is moved into its closed position solely by the momentum of the flowing hydraulic fluid. In this case, the performance limit of the built-in valve 2 is reached, which limits the maximum throughput volume flow. This means that the volume flow cannot be increased further if the power limit is exceeded.

2 shows the outlet pressure at the outlet connection A above the volume flow which has passed through, the vertical lines drawn in dashed lines representing the performance limits which arise when different springs 10 are used. In the embodiment shown in FIG. 2 is the performance limit. when using a 4bar spring at about 120 L / min, so that a stronger spring must be used for higher volume throughputs.

However, a stronger spring 10 harbors a number of disadvantages, such as, for example, a lack of response and a lack of fine control, which are particularly important in the case of low volume flows and are not acceptable. The minimum adjustable pressure at port A increases disadvantageously through the use of stronger springs.

In contrast, the invention has for its object to provide a directional control valve and pressure reducing / flow control valves provided with such a directional control valve, which have an increased performance limit with minimal expenditure on device technology and also show sufficient response behavior at low volume flows.

This object is achieved with respect to the directional valve by the features of patent claim 1, with regard to the pressure reducing valve by the features of patent claim 8 and with regard to the flow control valve by the features of patent claim 10.

The measure of forming a surface difference upstream of a throttle point of the main piston, via which a force component acts on the main piston during the flow and acts on the main piston in the direction of its starting position, the impulse force Fj acting on the main piston can be at least partially compensated, so that the performance limit compared to conventional solutions is raised without the need to use a stronger spring. This additional force, which acts on the area difference effective area in the opening direction, arises due to the pressure drop occurring in the flowing hydraulic fluid as it flows through the radial bores. It is particularly preferred if the active surface is designed as a radial shoulder on the outer circumference of the main piston, so that the main piston is expanded formally. At. This design of the active surface is of course also followed by a corresponding configuration of the bore of the valve bushing.

If the main piston is designed with a radial bore star, the radial shoulder is preferably arranged in the area between the radial bore star and the underside of the piston.

Extensive preliminary tests have shown that an area difference of 3-10% based on the smaller main piston diameter guarantees optimal results.

For reasons of manufacturing technology, it is preferred if the radial shoulder (area difference) is formed by means of an annular groove, the radial shoulder being an end face of the

Ring groove forms. The other end face is then preferably designed as an inclined shoulder.

The manufacture, in particular grinding, of the valve bore is facilitated if the corresponding step-like expansion of the valve bushing is also formed via a circumferential groove, one end face of which forms the step-like expansion.

Particularly advantageous applications of the directional control valve according to the invention result in a pilot-controlled pressure reducing valve according to claim 8 or a flow control valve according to claim 10.

Further advantageous embodiments of the invention are the subject of the other subclaims.

Preferred exemplary embodiments of the invention are explained in more detail below with the aid of schematic drawings. Show it: 1 shows a section through a built-in valve known from the prior art;

FIG. 2 shows a diagram from which the performance limit of the cartridge valve from FIG. 1 is shown as a function of a valve spring used;

3 shows a circuit in which the cartridge valve from FIG. 1 is the main stage of a pressure reducing valve;

Fig. 4 shows a cartridge valve according to the invention, as can be used in a circuit according to FIG. 3 and

Fig. 5 shows another embodiment in which the cartridge valve of FIG. 4 is used in a flow control valve.

4 shows a partial section of a built-in valve 2 according to the invention, the same reference numerals as in FIG. 1 being used in the following representations for corresponding components.

The built-in valve 2 according to the invention can be used, for example, in a pilot-controlled pressure reducing valve according to FIG. 3 or a flow control valve according to FIG. 5, which will be discussed below.

4, the built-in valve 2 according to the invention has a valve bushing 4, in the valve bore 28 of which a main piston 6 is guided axially displaceably. This is biased by a spring 10 into its initial position, in which a stop ring 30 attached to the outer circumference of the main piston 6 bears against a stop surface of the valve bushing 4. The valve bushing 4 is fastened in a control block 26 by means of a fastening bushing 32 and closed with a valve cover, not shown, in or on which the further components indicated in FIGS. 3 and 5 can be arranged. The fastening bushing 32 has an inner bore which is coaxial to the valve bore 28 is arranged, and which has such a diameter that the spring-side part (at the top in FIG. 4) of the main piston 6 can dip into it without colliding.

The valve bushing 4 could be constructed in accordance with FIG. 1.

An input connection B is formed on the valve bushing 4 as a bore star, that is to say as a plurality of radial bores 36. In addition, several, preferably two smaller bores 38 are provided offset.

Via the smaller bores 38, fine control takes place at low volume flows when the connection from B to A is opened.

As can further be seen from FIG. 4, the main piston 6 is designed as a hollow piston, a piston crown 40 being formed approximately in the central region. The spring 10 acts on this piston crown 40 in order to bias the main piston 6 into its open position (FIG. 4).

Below the piston crown 40, that is to say in the part of the piston jacket facing away from the spring 10, radial bores 8 are formed through which the hydraulic fluid can enter the interior of the piston from the connection B (bores 36, 38). These radial bores 8 are designed in the same way as shown in FIG. 1 as a star which penetrates the jacket of the main piston 6.

In the initial position of the main piston 6 shown in FIG. 4, the bores 36, 38 of the connection B and the radial bores 8 overlap, so that the connection between the connections B and A is completely opened.

Below the radial bores 8 (view according to FIG. 4), the main piston 6 is moved via a radial shoulder 42 from a spring-side main piston diameter d to a main piston diameter. knife D expanded. The radial shoulder 42 is formed by means of an annular groove 44, in the base of which the radial bores 8 open and the other end face of which is designed as an inclined shoulder 46.

The valve bore 28 of the valve bushing 4 is expanded radially above (view according to FIG. 4) of the connection B in accordance with the diameter ratio d / D, a circumferential groove 48 being formed in the region of the radial expansion, via which the lower, expanded part of the valve bore (Diameter D) is separated from the upper, narrowed part of the valve bore 28 (diameter d).

The circumferential groove 48 and the annular groove 44 are provided for manufacturing reasons, since the surfaces adjoining the two grooves (circumferential surface of the main piston 6; inner circumferential surface of the valve bore 28) are finely machined by grinding and are avoided by the grooves that the grinding wheel must be guided up to the radial shoulders when grinding the smaller piston diameter or the larger valve bore diameter.

In the starting position shown in Fig. 4 is the

Oblique shoulder 46 of the annular groove 44 is arranged at an axial distance from the adjacent end face of the circumferential groove 48, so that the two grooves 44, 48 do not overlap one another in the starting position.

In the area between the two grooves 44, 48, an annular gap 50 is formed between the main piston 6 and the valve bush 4.

When hydraulic fluid flows through the built-in valve 2, a pressure drop occurs along the radial bores 8, which leads to a resultant pressure force acting on the differential surface, which is characterized by the difference in diameter Dd, on the radial shoulder 42, which pushes the main piston 6 in the direction the starting position. That is, this Compressive force acts in addition to the force of the spring 10 in the opening direction, so that the performance limit is increased.

The magnitude of the force F depends on the one hand on the diameter ratio d / D and on the other hand on the pressure drop in the radial bores 8. For this reason, efforts will be made to make the depth of the annular groove 44 as small as possible, since the pressure drop also depends on the remaining wall thickness of the main piston 6. The same applies to the depth of the circumferential groove 48 and for the annular gap 50, which should also be made as small as possible, so that the hydraulic fluid cannot flow through the annular gap 50 into the circumferential groove 48 to a significant extent when flowing through the installation valve 2, so that It is ensured that a suitable pressure is present on the outer circumference of the main piston 6 and thus the pressure drop along the radial bores also has the required size arrangement.

3, the built-in valve 2 installed in a control block is provided with a valve cover 22 in which the components described above, such as, for example, the nozzles 18, 20 and the pilot valve 14, can be provided.

In the starting position shown (FIG. 4), the built-in valve 2 is flowed through, the effect of the spring 10 being reinforced by the force acting on the area difference, which is present in the radial bores 8 due to the pressure drop. The power limit is then shifted upwards in accordance with the additional pressure force applied, so that a larger volume flow can be achieved. When the preset pressure on the spring side of the main piston 6 is reached, the pilot valve 14 opens so that the control fluid flows to the tank T and a pressure drop occurs at the throttle 18, which leads to a closing movement of the main piston (upwards in FIG. 4) leads. The bores 36 and 38 are controlled by this closing movement, so that the connection from B to A is throttled accordingly and a pressure is established at the outlet connection A which corresponds to the pilot valve setting. As already mentioned at the beginning, the installation valve 2 is in its closed position when the consumer connected to the connection A does not take off any hydraulic fluid. When hydraulic fluid is consumed, the pressure at the outlet connection A then drops, so that the pilot valve 14 controls the connection to the tank T and the main piston 6 is moved back towards its starting position due to the control pressure building up on the spring side. Initially, the smaller bores 38 are opened, which thus become effective at low volume flows and enable the consumer to be finely controlled with good response behavior.

In the case of larger volume flows, the bores 36 with a larger diameter are also opened until the main piston 6 is moved back into its starting position (FIG. 4) and the maximum volume flow that can be achieved is reached, which is limited by the performance limit described above.

5 schematically shows another application example of a cartridge valve according to FIG. 4. The built-in valve 2 is used in a 2-way flow control, a throttle body for load compensation being assigned a pressure compensator which is formed by the built-in valve 2. The throttle point is designed as an adjustable throttle valve 52, which is provided downstream of the built-in valve 2.

A control line 54 branches off downstream of the throttle valve 52 and is led via a throttle 18 to the spring side of the main piston. The pressure at the outlet connection A of the installation valve 2 is - as in the embodiment described above - on the underside of the piston (outlet connection side). In this embodiment, the built-in valve 2 is thus used as a pressure compensator with a pressure reducing function. In this variant, the built-in valve 2 is open in the starting position, so that the hydraulic fluid from the connection B via the built-in valve 2 to A and from there via the throttle valve 52 to the consumer, for example a Hydraulic cylinder or a hydraulic motor (not shown) flows. The pressure at the outlet of the throttle valve 52 is influenced by the axial displacement of the main piston 6 and the associated change in the volume flow cross section so that the pressure drop across the throttle valve 52 always remains constant. This pressure drop depends on the strength of the spring on the piston.

If the pressure at the outlet of the throttle valve 52 drops due to a change in load, the pressure in the control line 54, which is guided to the spring side of the main piston 6 via the nozzle 18 acting as a damping element, decreases accordingly. The pressure drop on the spring side of the main piston moves it against the bias of the spring in the direction of its closed position, so that the volume flow cross section, that is to say the effective cross section of the radial bores 36, is controlled. This also reduces the volume flow of the hydraulic fluid which is led to the throttle valve 52 via the built-in valve 2. The movement of the main piston 6 continues until the pressure at the outlet connection A and thus also at the inlet of the throttle valve 52 has decreased by the same amount as the pressure at the outlet of the throttle valve 52 (control line 54). The pressure drop across the throttle valve 52 is thus always kept at a constant value.

In this exemplary embodiment, too, the maximum volume flow that can be passed through the built-in valve 2 is considerably increased by pushing the performance limit further than conventional solutions.

The solution according to the invention therefore enables the performance limit to be pushed upward with a minimal outlay on device technology, so that the installation valve according to the invention can be used in a further volume flow range without changing the spring 10.

Claims

Expectations

1. 2-way valve with a main piston (6) guided in a valve bushing (4) and through which hydraulic fluid can flow, via which an input port (B) can be connected to an output port (A) and which is connected by means of a spring (10) its initial position is biased, characterized in that the main piston (6) upstream of a throttle point (8) is provided with an area difference effective area (42, Dd), via which a pressure force component acts on the main piston (6) during the flow, which applies this in the direction of its starting position.

2-way valve according to claim 1, characterized gekennzeich¬ net that the effective surface is designed as a radial shoulder (42) on the outer circumference of the main piston (6) and the valve bushing (4) is correspondingly expanded stepwise.

3. 2-way valve according to claim 2, characterized in that the main piston (6) has radial bores (8) as Drossel¬ point through which the hydraulic fluid can flow from the inlet port (B) to the outlet port (A), the radial shoulder (42) is formed in the area between the radial bores (8) and the piston underside facing the outlet connection (A).

4. 2-way valve according to claim 2 or 3, characterized in that the diameter of the main piston through the

Radial shoulder (42) is expanded by 3-10%.

5. 2-way valve according to one of claims 3 or 4, da¬ characterized in that the radial shoulder (42) is formed by an annular groove (44) into which the radial bores (44) of the main piston (6) open.

6. 2-way valve according to claim 5, characterized in that - that of the radial shoulder (42) removed end face is designed as an inclined shoulder (46).

7. 2-way valve according to one of the claims 2 to 6, characterized by the fact that the valve bushing (4) has a circumferential groove (48) in the region of the step-like extension.

8. Pilot-operated pressure reducing valve with a 2-way valve according to one of the preceding claims, wherein the

Pressure at the outlet connection (A) is guided via a nozzle (18) to the spring side of the main piston (6) and the pressure on the spring side can be limited via a pilot valve (14).

9. Pilot-operated pressure reducing valve according to claim (8), characterized in that the pilot valve is a direct or pilot-operated pressure relief valve (14).

10. Flow control valve with an adjustable throttle valve (52) which is connected upstream of a 2-way valve (2) according to one of the claims 1 to 7 as a pressure compensator, the pressure downstream of the throttle valve (52) towards the spring side of the main piston (6) 2-way valve (2) is guided.