Solenoid valve for pressure control and / or pressure limitation

Abstract

Solenoid valve for pressure regulation and / or pressure limitation, comprising a valve piston (1) which interacts with a first valve seat (3) and is accommodated in a valve body (2) for axial displacement, further comprising a valve ring (5) which interacts with a second valve seat (7) and is axially pretensioned against the valve piston (1) in the direction of the second valve seat (7) by the spring force of a spring (6), and an annular magnetic coil (8) for acting on an armature (9) which is connected to the valve piston (1) and which can be moved in the direction of the first valve seat (3) by the magnetic force of the magnetic coil (8) against the spring force of the spring (6), so that a connection between an inlet (10) and an outlet (11) can be established via a first flow path which leads via the first valve seat (3) and the second valve seat (7).

Description

The invention relates to a solenoid valve having a pressure regulating and / or a pressure limiting function. The solenoid valve is intended to be usable in particular for regulating and / or limiting the pressure in a high-pressure accumulator of a fuel injection system, preferably of a common-rail injection system.Prior ArtFor regulating the pressure in a high-pressure accumulator of a fuel injection system, two types of electromagnetically actuatable valves are known in principle from the prior art. Namely, those which are open when electroless and those which are closed when electroless are electroless.Solenoid valves which are open when no current is present have the advantage that in the event of a fault, for example in the event of incorrect actuation of the electromagnet or in the event of a lack of voltage supply, a complete pressure reduction takes place in the high-pressure accumulator. In this way, it is ensured that the pressure in the high-pressure accumulator does not increase above an admissible maximum value. However, it has proven to be disadvantageous that, owing to the complete pressure reduction, no minimum pressure is maintained which ensures an emergency operation function, also called "limp home function".Solenoid valves which are closed when no current is present, on the other hand, permit emergency operation even in the event of a fault, since the spring force of a spring keeps the valve closed, so that no complete pressure reduction takes place.The laid-open specification DE 10 2007 062 176 A1 discloses a pressure control valve for regulating the pressure in a high-pressure fuel accumulator of an internal combustion engine, which is designed as a normally closed valve. This is because it has a valve piston which is loaded against the pressure in the high-pressure fuel accumulator by the spring force of a spring in the closed position. Furthermore, the pressure regulating valve comprises a controllable magnetic device, the force of which acts on the valve piston counter to the spring force of the spring. Furthermore, a second magnetic device is provided, the force of which is in the same direction as the spring force of the spring. The provision of the second solenoid means is intended to allow the use of a weaker spring to ensure that the valve opens before an allowed maximum pressure in the high pressure fuel accumulator is exceeded. The pressure regulating valve thus also performs a pressure limiting function in addition to the pressure regulating function.DE 10 2010 005 411 A1 discloses a valve, in particular a pressure limiting valve, having an electromagnetic coil, by the magnetic force of which an armature is axially displaceable in a pole tube, wherein the armature acts on an actuating element for a valve element, which is guided in a valve housing in an axially displaceable manner.Proceeding from the aforementioned prior art, the object of the present invention is to specify a solenoid valve for pressure regulation and / or pressure limitation, which is of simple construction and can be produced cost-effectively. In particular, a solenoid valve is to be specified which combines the advantages of a normally open and a normally closed valve in one valve without a second magnetic device being required.To achieve the object, the solenoid valve having the features of claim 1 is specified. Advantageous further developments of the invention can be found in the dependent claims.Disclosure of the InventionThe solenoid valve proposed for pressure regulation and / or pressure limitation comprises a valve piston which interacts with a first valve seat and is accommodated in an axially displaceable manner in a valve body. Furthermore, the solenoid valve comprises a valve ring which interacts with a second valve seat and is axially prestressed against the valve piston in the direction of the second valve seat by the spring force of a spring, and an annular solenoid for acting on an armature which is connected to the valve piston and can be moved in the direction of the first valve seat by the magnetic force of the solenoid counter to the spring force of the spring, with the result that it is possible to produce a connection of an inflow to an outflow via a first flow path which leads via the first and the second valve seat.The valve piston and the valve ring each form a valve member interacting with a valve seat, wherein the spring force of the spring acts in the direction of the second valve seat. The connection of an inlet to an outlet via a first flow path requires that both valve seats are released.If the magnet coil is energized, the armature and the valve piston move counter to the spring force of the spring in the direction of the first valve seat. In this case, they carry the valve ring along, so that it is ensured that the second valve seat is released. At the same time, the stroke of the valve piston relative to the first valve seat can be adjusted via the solenoid coil. In this way, a pressure regulating function can be implemented.If the solenoid coil remains non-energized, the spring presses the valve ring against the second valve seat and the valve closes. Since the valve ring is supported on the valve piston, it carries it along and the valve opens via the first valve seat. However, since the first flow path is not released because of the valve ring resting against the second valve seat, an emergency operation function can be implemented-in particular in the event of a fault-as is otherwise inherent only in normally closed valves.The proposed solenoid valve is distinguished by a simple construction and a compact construction arrangement. In favor of a compact construction arrangement, it is proposed that the valve ring and / or the spring surround the valve piston in regions. Alternatively or additionally, the valve piston can be surrounded in regions by the annular magnet coil.In order to be able to additionally represent a pressure limiting function in addition to the pressure regulating function, it is further proposed that, depending on the axial position of the valve piston, a connection of the inlet to the outlet can be established via a second flow path which bypasses the second valve seat. This is because the pressure limiting function is used only when the magnet coil is not energized, that is to say when the first flow path leading via the second valve seat is closed by the valve ring. To implement the pressure limiting function, a second flow path must therefore be releasable, which does not lead via the second valve seat.Preferably, therefore, the valve piston is accommodated in the valve body such that it can move axially beyond the stroke of the valve ring counter to the spring force of a further spring and has a contour in the region of its outer circumference, which contour interacts with a control edge formed in the valve body. The cooperation takes place in such a way that, depending on the axial position of the valve piston with respect to the valve body, a second flow path can be opened, which bypasses the second valve seat, so that a connection of the inlet to the outlet can be produced. The desired limit pressure can be preset by the spring force of the further spring.In order to ensure that the spring force of the further spring loads the valve piston only when a pressure limiting function is to be provided, it is proposed that the spring be mounted so as to float in the axial direction. For example, one end of the spring can be connected to the valve piston for this purpose and the other end can be arranged axially spaced apart from a stop and support surface, which is preferably formed on the housing side.A suitable contour interacting with the control edge is, in particular, a geometry forming a flow channel, such as a groove or a ground surface. The contour is therefore preferably formed by at least one outer-periphery-side groove or at least one outer-periphery-side ground surface of the valve piston.It is further proposed that, for forming the second valve seat and / or the control edge in the valve body, an annular shoulder is formed, the inner diameter of which is preferably adapted to the outer diameter of the valve piston.The shoulder simultaneously guides the valve piston in this manner. The valve body can also be embodied in multiple parts to form the shoulder, which facilitates assembly. The plurality of parts of the valve body can be braced against one another by a union nut.In order to form the second valve seat and / or the control edge, the shoulder is preferably arranged between the inlet and the outlet. To form the first flow path, it is therefore further proposed that the shoulder has at least one throughflow opening which is designed as an inner-periphery-side groove or bore.Furthermore, the valve ring preferably has at least one throughflow opening which is designed as an inner- or outer-periphery-side groove or as a bore. This is because the valve ring can then be guided on the valve piston, since a connection of the inlet to the at least one throughflow opening of the shoulder is ensured via the at least one throughflow opening. In order to disconnect the connection and to close the valve when the valve ring bears against the second valve seat, the throughflow opening of the valve ring is preferably arranged radially offset with respect to the throughflow opening of the shoulder.For support on the valve piston, the valve ring furthermore preferably has an annular collar extending radially inward. The annular collar ensures that the spring force of the spring, by means of which the valve ring is axially prestressed against the valve piston, is uniformly transmitted to the valve piston.To form a supporting surface against which the valve ring is axially prestressed, the design of the valve piston as a stepped piston is proposed. The valve piston can be mechanically coupled to the collar of the valve ring via the step, so that the spring force of the spring provided for axially prestressing the valve ring also acts on the valve piston. Preferably, at least the end of the valve piston facing the first valve seat has a reduced outer diameter. In this way, space is created for the arrangement of the spring.Furthermore, the valve piston is preferably guided through the annular magnet coil and the armature connected to the valve piston comes to lie on the side of the magnet coil which is remote from the valve seats. This results in a compact arrangement.Advantageously, the valve body has an axial bore serving as inlet and / or at least one radial bore serving as outlet. The inflow thus takes place axially, while the discharge quantity is discharged via one or more radial bores. The one or more radial bores are arranged on the side of a shoulder for forming the second valve seat and / or the control edge of the valve housing, which is remote from the inlet.A preferred embodiment of the invention is explained in more detail below with reference to the attached drawings. This shows a schematic longitudinal section through a solenoid valve according to the invention.DETAILED DESCRIPTION OF THE DRAWINGThe solenoid valve shown in the figure comprises a valve body 2 in which a valve chamber 18 is formed, which is divided by a shoulder 14 into a first section 18.1 and a second section 18.2. An axial bore which serves as inlet 10 opens into the first section 18.1. The outlet 11 is formed by a radial bore which opens into the second section 18.2. Since the shoulder 14 simultaneously serves for guiding a valve piston 1, it separates the inlet 10 from the outlet 11, in order to establish a connection between the inlet 10 and the outlet 11 via a first flow path, the shoulder 14 has bores which serve as flow openings 15. A second flow path can be produced via an outer-periphery-side contour 12 in the form of a ground section of the valve piston 1, which for this purpose interacts with a control edge 13 formed on the shoulder 14. If the valve piston 1 assumes an axial position in which the contour 12 is brought into overlap with the shoulder 14, the second flow path is cleared.The valve piston 1 interacts with a first valve seat 3. If the valve piston 1 abuts the first valve seat 3, there is no connection of the inlet 10 to the outlet 11 via the first flow path or via the second flow path. A valve ring 5 is supported on the valve piston 1, which interacts with a second valve seat 7 and is acted upon in the direction of the second valve seat 7 by the spring force of a spring 6. The second valve seat 7 is formed by the shoulder 14.The valve ring 5 is supported via a collar 17 on the valve piston 1, which is designed as a stepped piston for this purpose. Due to the support of the valve ring 5 on the valve piston 1, the spring force of the spring 6 also acts on the valve piston 1. In order to make possible a connection of the inlet 10 to the outlet 11 via the first flow path, flow openings 16 are provided in the valve ring 5, which in the present case are designed as longitudinal grooves on the inner circumference and are arranged radially offset with respect to the flow openings 15 of the shoulder 14.The pressure regulating operation is implemented by means of a magnetic coil 8 which, in the energized state, generates a magnetic field whose magnetic force acts on an armature 9 connected to the valve piston 1, with the result that the armature 9 and the valve piston 1, including the valve ring 5, move in the direction of the first valve seat 3. In this way, a connection of the inlet 10 to the outlet 11 can be established via the first flow path.In the event of a fault, i.e. when the solenoid 8 is not energized, the spring 6 presses the valve ring 5 against the second valve seat 7. due to the support of the valve ring 5 on the valve piston 1, the latter is carried along and opens the first valve seat 3. Consequently, an emergency operation function can be provided by means of the solenoid valve shown-analog to a normally closed valve.If the valve ring 5 abuts the second valve seat 7, there is no connection of the inlet 10 to the outlet 11 via the first flow path. Nevertheless, a connection via the second flow path can be established if the pressure in the inlet 10 exceeds a predeterminable limit pressure.This is because if the pressure in the inlet 10 exceeds a predeterminable limit value, the valve piston 1 disengages from the valve ring 5 and moves together with a further spring 4, which has an end accommodated in the valve piston 1 and a free end, in the direction of a stop and support surface 19 until the free end of the spring 4 comes into contact with the stop and support surface 19. A contour 12 in the form of a ground surface provided on the outer periphery of the valve piston 1 is brought into overlap with the shoulder 14 of the valve body 2, so that a connection of the inlet 10 to the outlet 11 is established via the second flow path. Analogously to a normally open valve, pressure can now be reduced, although the first flow path is closed. The spring 4 thus serves to represent a pressure limiting function.Since the spring 4 is supported in a floating manner in the axial direction, it serves solely for the purpose of providing a pressure limiting function. This is because, in the pressure regulating mode of the solenoid valve, the valve piston 1 is not loaded by the further spring 4. This means that the further spring 4 has no influence on the pressure regulating function of the solenoid valve.

Claims

Solenoid valve for pressure regulation and / or pressure limitation, comprising a valve piston (1) which interacts with a first valve seat (3) and is accommodated in an axially displaceable manner in a valve body (2), further comprising a valve ring (5) which interacts with a second valve seat (7) and is prestressed axially against the valve piston (1) in the direction of the second valve seat (7) by means of the spring force of a spring (6), and an annular solenoid coil (8) for acting on an armature (9) which is connected to the valve piston (1) and can be moved in the direction of the first valve seat (3) by means of the magnetic force of the solenoid coil (8) counter to the spring force of the spring (6), such that a connection of an inlet (10) to an outlet (11) can be produced via a first flow path which leads via the first valve seat (3) and the second valve seat (7).Solenoid valve according to Claim 1, characterized in that, as a function of the axial position of the valve piston (1), a connection of the inlet (10) to the outlet (11) can be produced via a second flow path which bypasses the second valve seat (7).Solenoid valve according to Claim 1 or 2, characterized in that the valve piston (1) is accommodated in the valve body (2) so as to be axially movable counter to the spring force of a further spring (4) beyond the stroke of the valve ring (5) and has a contour (12) in the region of its outer circumference, which contour interacts with a control edge (13) formed in the valve body (2), wherein the contour (12) is preferably formed by at least one outer-circumference-side groove or at least one outer-circumference-side ground section.Solenoid valve according to one of the preceding claims, characterized in that, in order to form the second valve seat (7) and / or the control edge (13) in the valve body (2), an annular shoulder (14) is formed, the inner diameter of which shoulder is preferably matched to the outer diameter of the valve piston (1).Solenoid valve according to Claim 4, characterized in that the shoulder (14) has, for forming the first flow path, at least one throughflow opening (15) which is designed as a groove or bore on the inner periphery side.Solenoid valve according to one of the preceding claims, characterized in that the valve ring (5) has at least one throughflow opening (16) which is designed as a groove on the inner or outer circumference side or as a bore, wherein the throughflow opening (16) is preferably arranged radially offset with respect to the throughflow opening (15) of the shoulder (14).Solenoid valve according to one of the preceding claims, characterized in that the valve ring (5) has an annular collar (17) which extends radially inwards for supporting on the valve piston (1).Solenoid valve according to one of the preceding claims, characterized in that the valve piston (1) is designed as a stepped piston in order to form a supporting surface against which the valve ring (5) is axially prestressed.Solenoid valve according to one of the preceding claims, characterized in that the valve piston (1) is guided through the annular solenoid coil (8) and the armature (9) connected to the valve piston (1) comes to lie on the side of the solenoid coil (8) which is remote from the valve seats (3, 7).Solenoid valve according to one of the preceding claims, characterized in that the valve body (2) has an axial bore serving as inlet (10) and / or at least one radial bore serving as outlet (11).

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