Overflow valve for a fuel injection system

Abstract

Overflow valve for a fuel injection system, comprising a valve body (1) with an axial bore (2) in which a valve piston (3) is axially displaceable, wherein the valve body (1) has an inlet opening (4) opening into the axial bore (2), which can be connected to at least one outlet opening (6) formed in the valve body (1) by means of an axial displacement of the valve piston (3) against the spring force of a spring (5), and wherein a screen (7) formed in one or more parts for separating harmful particles is positioned upstream of the inlet opening (4), characterized in that at least one bypass opening (8) is formed in the valve body (1) as a further inlet opening, which can be switched on and off.

Description

[0001] The invention relates to an overflow valve for a fuel injection system having the features of the preamble of claim 1. State of the art

[0002] A bypass valve of the type described above can be used in a fuel injection system to limit pressure and / or reduce pressure pulsations in the inlet area of ​​a high-pressure pump. For this purpose, the bypass valve is subjected to inlet pressure on its inlet side. If the inlet pressure rises above a predetermined limit, the bypass valve opens and discharges fuel from the inlet area, causing the inlet pressure to drop again.

[0003] Fuel often contains particles that can damage the bypass valve. To prevent this, a filter is usually installed upstream of the bypass valve on the inlet side. An example of such a bypass valve is disclosed in German patent application DE 10 2013 200 050 A1.

[0004] German patent application DE 10 2005 022 738 A1 discloses a pressure valve for a fuel injection device of an internal combustion engine, wherein the pressure valve is formed in a valve unit and the valve unit comprises a throttle and a fuel filter, which are integrated as a unit into a bypass line of the fuel injection device.

[0005] The patent application DE 10 2012 219 072 A1 discloses a bypass valve for a fuel pump, wherein the bypass valve has a gap filter in the area of ​​an inlet opening to prevent larger particles from entering the bypass valve.

[0006] German patent application DE 10 2015 201 851 A1 discloses a bypass valve for a fuel pump, the bypass valve comprising a valve housing and a valve piston. The valve housing has at least one inlet opening with which the bypass valve can be connected to a fuel supply, wherein a filter is arranged upstream of the inlet opening to prevent the ingress of particles or contaminants into the bypass valve.

[0007] However, sieves or filters can become clogged, especially with gelatinization, so that the function of the bypass valve is no longer guaranteed. The risk of gelatinization is particularly high during a cold start of an internal combustion engine supplied with fuel via the fuel injection system. A malfunctioning bypass valve can, in turn, lead to the fuel supply via a pre-supply pump, especially an electric fuel pump, being interrupted or completely stopped due to the increasing inlet pressure in the fuel injection system. In this case, the internal combustion engine is no longer supplied with a sufficient quantity of fuel.

[0008] The invention is therefore based on the objective of providing an overflow valve for a fuel injection system that has a high level of functional reliability, so that the aforementioned disadvantages do not occur as far as possible.

[0009] To solve the problem, the overflow valve is specified with the features of claim 1. Advantageous embodiments of the invention can be found in the dependent claims. Disclosure of the invention

[0010] The proposed overflow valve for a fuel injection system comprises a valve body with an axial bore in which a valve piston is axially displaceable. The valve body has an inlet opening that opens into the axial bore and can be connected to at least one outlet opening formed in the valve body by means of an axial displacement of the valve piston against the spring force of a spring. A single- or multi-part screen is arranged upstream of the inlet opening to separate harmful particles. According to the invention, at least one bypass opening is formed in the valve body as a further inlet opening, which can be switched on and off.

[0011] The switchable bypass opening increases the operational reliability of the overflow valve. If the strainer upstream of the inlet becomes clogged with gelatin, the bypass opening can be activated, ensuring that the valve piston continues to be subjected to inlet pressure, bypassing the inlet opening which is no longer accessible or only partially accessible. If the inlet pressure rises above a predefined limit, the overflow valve opens and the pressure is reduced, regardless of the degree of gelatinization in the strainer upstream of the actual inlet opening. This also ensures that fuel continues to be delivered via the lift pump.

[0012] The main inlet opening is preferably located on an end face of the valve body. The axial bore formed in the valve body can be connected to an inlet area of ​​the fuel injection system via the inlet opening, so that the valve piston received in the axial bore can be pressurized with inlet pressure.

[0013] The at least one bypass opening is preferably arranged in a circumferential region of the valve body. The axial bore can also be connected to the inlet region via the bypass opening. To ensure this, the valve body is preferably surrounded circumferentially by an annular space when the bypass valve is installed as intended in a fuel injection system, with the annular space being connected to the inlet region.

[0014] The opening and closing of at least one bypass opening can be achieved in various ways. For example, the bypass opening can be switched by a movable closing element.

[0015] According to a preferred embodiment of the invention, the sieve serves as a closing element. For this purpose, the sieve is preferably mounted axially displaceable and / or rotatable on the valve body. The bypass opening can then be opened or closed by moving the sieve or a portion thereof.

[0016] Furthermore, it is proposed that the strainer be designed, at least in part, in a sleeve- or cup-shaped form. In this way, the strainer can be slid onto the valve body, covering the inlet opening, which is preferably located at the front, and—depending on the position of the strainer—also closing the at least one bypass opening. For this purpose, the strainer preferably has a closed section.

[0017] Furthermore, the sieve can have at least one opening that can be brought into contact with the bypass opening. The opening is preferably formed in a circumferential region of the sieve, so that contact between the opening and the bypass opening can be achieved by axial displacement and / or rotation of the sieve.

[0018] Advantageously, an annular shoulder is formed on the outer circumference of the valve body, against which the screen is supported in an end position by a collar extending radially inwards. In this end position, the screen preferably closes the at least one bypass opening. The bypass opening can be released by axially displacing the screen relative to the valve body. In doing so, the collar of the screen lifts away from the shoulder of the valve body. To close the bypass opening, the screen is pushed back against the shoulder.

[0019] To reset the screen, it is preferably axially preloaded against the annular shoulder. This axial preload is preferably achieved by the spring force of a spring. The axial preload of the screen against the shoulder allows the opening and closing of the at least one bypass opening to be controlled based on pressure. For example, if the inlet pressure rises above a certain threshold, the screen is axially displaced against the spring force. The spring force of the spring can be used to define a threshold for the inlet pressure. Therefore, no additional actuators are required to open or close the at least one bypass opening.

[0020] Preferably, the strainer is made of multiple parts. This multi-part design allows the use of a strainer typically employed in a bypass valve. This strainer is generally cup-shaped and features a flanged section for support against the end face of the bypass valve body. The strainer can be inserted into a sleeve-shaped strainer section via this flanged section, which is then slid onto the valve body. Preferably, the multiple strainer sections are rigidly connected to one another, ensuring that the strainer can only be moved or rotated axially as a single unit.

[0021] Furthermore, the opening and closing of the at least one bypass opening can be effected by a screen that has or forms a separate closing element by means of which the bypass opening can be closed or at least partially opened. The screen itself can be fixed in position in this case. The closing element is preferably arranged in the area of ​​the bypass opening and opens upon a pressure increase. For example, the closing element can be designed like a nozzle that opens under pressure.

[0022] According to a further preferred embodiment of the invention, the opening or closing of the bypass opening is effected by a change in the shape of the screen. For this purpose, the screen is made, at least in part, of a material that changes its shape depending on temperature and / or pressure. The material can, for example, be a bimetal or a shape-memory alloy. In this case, too, additional actuators for opening and closing the at least one bypass opening are unnecessary.

[0023] A preferred embodiment of the invention is explained in more detail below with reference to the accompanying drawings. These show: Fig. 1 a schematic longitudinal section through an overflow valve according to the invention in a preferred embodiment and Fig. 2 an enlarged section of the Fig. 1 in the area of ​​an upstream sieve. Detailed description of the drawings

[0024] The one in Fig. The overflow valve for a fuel injection system shown in Figure 1 comprises a valve body 1 with an axial bore 2 in which a valve piston 3 is guided for axial displacement. The axial bore 2 is designed as a through-bore, so that at one end it defines an inlet opening 4 through which the valve piston 3 can be subjected to inlet pressure. At the other end, the valve piston 3 is subjected to the spring force of a spring 5, which is supported by a spring retainer 14 pressed into the axial bore 2. The spring force of the spring 5, and thus the opening force of the overflow valve, can be adjusted by the pressing depth of the spring retainer 14 into the axial bore 2. If the inlet pressure increases, causing the valve piston 3 to be axially displaced against the spring force of the spring 5, a connection can be established between the inlet opening 4 and several outlet openings 6, which are formed in a circumferential region of the valve body 1.The controlled quantity is fed to a return line (not shown) via the drain openings 6. To separate the return line from a fuel injection system inlet, a sealing ring 13 is arranged on the outer circumference of the valve body 1. Another sealing ring 13 seals the return line to the outside when the bypass valve is inserted into a housing bore of a fuel injection system component, for example, a pump housing.

[0025] As in particular the Fig. As can be seen from Figure 2, a screen 7 is positioned upstream of the inlet opening 4. The screen 7 is designed in multiple parts and comprises a pot-shaped first screen section 7.1 and a sleeve-shaped second screen section 7.2, which are firmly connected to each other. The first screen section 7.1 prevents harmful particles contained in the fuel from entering the bypass valve. For this purpose, it is made of a mesh screen. The second screen section 7.2 is closed except for openings 9, which are arranged around its circumference. The openings 9 can be aligned with bypass openings 8 of the valve body 1, thus ensuring the supply of fuel should the first screen section 7.1 become clogged. The screen 7 is mounted axially displaceably on the valve body 1 for this purpose.

[0026] The axial displacement of the screen 7 is pressure-controlled. For this purpose, the screen 7 is axially pre-tensioned against an annular shoulder 10 of the valve body 1 by the spring force of a spring 12. The second screen section 7.2 has a collar 11 for support against the shoulder 10. If the first screen section 7.1 becomes clogged, preventing the overflow valve from opening in the event of an excessively high pressure rise (because no fuel enters the axial bore 2 via the inlet opening 4), the screen 7 is axially displaced against the spring force of the spring 12 (see arrow 15). During this displacement, the circumferential openings 9 in the second screen section 7.2 align with the bypass openings 8 in the valve body 1, ensuring that inlet pressure is applied to the valve piston 3 and that the overflow valve functions correctly.

[0027] An alternative embodiment of an overflow valve according to the invention is described in the Fig. 2 only indicated. Instead of an axial displacement, the openings 9 of the sieve 7 can also be brought into alignment with the bypass openings 8 of the valve body 1 by a rotational movement (see arrow 16). For this purpose, the openings 9 are – unlike the illustration of the Fig. 2 - to be arranged in a common radial plane with the bypass openings 8 of the valve body 1.

Claims

[1] Overflow valve for a fuel injection system, comprising a valve body (1) with an axial bore (2) in which a valve piston (3) is axially displaceable, wherein the valve body (1) has an inlet opening (4) opening into the axial bore (2), which can be connected to at least one outlet opening (6) formed in the valve body (1) by means of an axial displacement of the valve piston (3) against the spring force of a spring (5), and wherein a screen (7) formed in one or more parts for separating harmful particles is positioned upstream of the inlet opening (4), characterized by , that in the valve body (1) at least one bypass opening (8) is designed as a further inlet opening which can be switched on and off. [2] Overflow valve according to claim 1, characterized by , that the inlet opening (4) is arranged on an end face of the valve body (1) and / or that at least one bypass opening (8) is arranged in a circumferential area of ​​the valve body (1). [3] Overflow valve according to claim 1 or 2, characterized by , that the sieve (7) for switching on and off the bypass opening (8) is axially displaceable and / or rotatable on the valve body (1). [4] Overflow valve according to one of the preceding claims, characterized by , that the sieve (7) is at least partly shaped like a tube or a pot. [5] Overflow valve according to one of the preceding claims, characterized by that the sieve (7) has at least one opening (9) which can be brought into overlap with the bypass opening (8). [6] Overflow valve according to one of the preceding claims, characterized by , that an annular shoulder (10) is formed on the outer circumference of the valve body (1), on which the sieve (7) is supported in an end position via a collar (11) extending radially inwards. [7] Overflow valve according to claim 6, characterized bythat the sieve (7) is axially preloaded against the shoulder (10), preferably the axial preload being caused by the spring force of a spring (12). [8] Overflow valve according to one of the preceding claims, characterized by that the sieve (7) has or forms a closing element by means of which the bypass opening (8) can be closed or at least partially opened. [9] Overflow valve according to any one of the preceding claims, characterized by , that the sieve (7) is made at least partially of a material which changes its shape depending on temperature and / or pressure, wherein the material is preferably a bimetal or a shape memory alloy.

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