FUEL INJECTOR WITH A FLOW LIMITER FOR A FUEL INJECTION SYSTEM

Description

[0001] The present invention relates to a fuel injector with a flow restrictor for a fuel injection system and to a fuel injection system with such a flow restrictor.

[0002] To understand the invention, it is helpful to understand the basic functionality of an injector (fuel injection nozzle), which will be examined in more detail below. An injector has a nozzle needle (also called an injector needle) that allows fuel under high pressure to escape when an outlet orifice of the injector is opened. This nozzle needle, in conjunction with this outlet orifice, acts like a plug that, when lifted, allows the fuel to escape. Therefore, it is necessary to lift this needle at relatively short intervals and then allow it to slide back into the outlet orifice after a short time. Hydraulic servo valves (also called pilot valves), controlled by solenoid valves, are used to trigger the movement of this nozzle needle. The servo valves are necessary for the controlled opening and closing of the nozzle needle.This makes it possible to determine the start of injection, the injection duration and the end of injection.

[0003] Due to the high injection pressures exceeding 2500 bar, it is not possible to directly control (move) the nozzle needle using a solenoid valve. The forces required to open and close the nozzle needle would be too great, making such a method feasible only with very large electromagnets. However, such a design is impractical due to the limited installation space available in an engine.

[0004] Typically, instead of direct actuation, so-called pilot valves, usually in the form of a servo valve, are used. These control the nozzle needle and are themselves controlled by a solenoid valve. In a control chamber that interacts with the nozzle needle, a pressure level is built up using the high-pressure fuel. This pressure acts on the nozzle needle in the closing direction. This control chamber is typically connected to the high-pressure fuel supply via an inlet restrictor. Furthermore, this control chamber has a small, closable outlet restrictor from which the fuel can escape. When the fuel escapes, the pressure in the control chamber and the closing force acting on the nozzle needle are reduced. This causes the nozzle needle to move, opening the outlet at the injector tip. The pilot valve comprises the inlet restrictor, the control chamber, and the outlet restrictor.To control the movement of the nozzle needle, the outlet throttle of the control chamber is selectively opened or closed using a solenoid valve or another suitable valve. The controlled opening of this outlet throttle, in combination with the inlet throttle, determines the pressure in the valve's control chamber. This pressure, as briefly explained above, is then responsible for opening and closing the nozzle needle.

[0005] To terminate injection and keep the valve's drain gate closed between injections, a specific spring force is required. This force presses a locking element (also known as an armature) against the drain gate, preventing fuel from leaking out and thus preventing a reduction in pressure within the control chamber. To open the valve, the set spring force pressing the locking element against the sealing surface of the drain gate must be overcome so that the locking element releases the drain gate as quickly as possible. Typical required activation times, i.e., the time from the start of energization until the locking element reaches the upper stroke limit of such solenoid valves, are in the range of approximately 200 microseconds.

[0006] However, for an engine with this type of fuel injection, excessive or continuous fuel injection is particularly damaging. In the event of such an injector malfunction, for example, incomplete injector closure by the needle, incomplete closure of the armature element, or a leak in the injector housing, the continuous flow of fuel into the combustion chamber can cause serious damage.

[0007] A fuel injector of the same type with a flow limiter is already known from DE 10 2015 220 028 A1.

[0008] Therefore, in the event of a defective fuel injection process, it is advantageous to limit the total amount of fuel that can be introduced into the combustion chamber in order to avoid damage as much as possible.

[0009] This problem is solved according to the invention by means of a fuel injector with a flow restrictor according to claim 1. Further advantageous embodiments of the invention are set forth in the dependent claims.

[0010] A fuel injector according to the invention with a flow restrictor for a fuel injection system comprises a throttle bushing with a through-hole, a throttle insert movably mounted in a first section of the through-hole, a sealing section in a second section of the through-hole, the cross-section of which is reduced compared to the first section of the through-hole, and a spring element mounted in the through-hole that pushes the throttle insert away from the sealing section. Furthermore, the flow restrictor is characterized in that the throttle insert has a sealing surface at its end facing the sealing section, which closes the through-hole upon contact with the sealing section.

[0011] If a fuel injector located downstream of the flow restrictor does not close correctly, resulting in the undesired condition of continuous fuel flow into the combustion chamber, the shut-off mechanism of the flow restrictor will engage.

[0012] In a resting state, fuel is present at high pressure on both sides of the throttle insert. The high-pressure fuel reservoir, typically the rail, is connected to the flow restrictor on the side of the throttle insert facing away from the sealing section. Since fuel is now present at identical pressure on both sides of the throttle insert, the spring element located between the throttle insert and the sealing section acts, pushing the throttle insert away from the sealing section. The resulting space forms a fuel reservoir that can flow completely into the combustion chamber even in the event of a malfunction. When the injector opens, fuel flows from this reservoir, causing a pressure drop. The constant high pressure on the side of the throttle insert facing the rail then causes the throttle insert, which slides within the throttle bushing, to move towards the sealing section.The amount of fuel flowing from the rail (high-pressure side) through the throttle insert cannot quickly replace the amount of fuel flowing out of the injector and injected into the combustion chamber. Therefore, if the injection process is faulty and lasts longer than normal, the throttle insert's sealing surface will contact the sealing section, interrupting the fuel supply to the injector. This prevents a continuous, damaging injection of fuel into the combustion chamber of a cylinder.

[0013] In normal operation, however, fuel injection is stopped before the sealing surface of the throttle insert contacts the sealing section, allowing the fuel flowing through the throttle insert to fill, or rather increase, the reservoir defined between the sealing surface of the throttle insert and the sealing section of the bushing. If fuel under high pressure is present on both sides of the throttle insert, which slides within the bushing, the spring element pushes the throttle insert away from the sealing section, thus increasing the reservoir.

[0014] According to an optional modification of the invention, it can be provided that the throttle insert with its outer cross-section interacts sealingly with the inner cross-section of the through-hole and prevents the flow of a fluid between the outer cross-section of the throttle insert and the inner cross-section of the through-hole.

[0015] This restricts the flow of high-pressure fuel into the reservoir (the space between the sealing section and the sealing surface of the throttle insert) to a line running through the throttle insert. This line can be a bore in the body of the throttle insert and runs from the side facing the sealing section to the opposite side of the throttle section.

[0016] Furthermore, according to the invention, the throttle insert has or generates a throttle line that provides a fluid connection along the through-hole from the side of the throttle insert facing away from the sealing surface to the side of the throttle insert facing the sealing surface.

[0017] This allows for the implementation of a throttle line that is not implemented through a bore in the throttle insert, but rather runs along the edge of the throttle insert and the inner wall of the throttle bushing. To implement the throttle line, it is only important to limit the flow of high-pressure fuel so that the flow restrictor functions correctly and prevents fuel from flowing in the event of a continuous fuel leak.

[0018] According to a modification of the invention, the throttle line can have a bore in the throttle insert that is parallel to the longitudinal direction of the throttle bushing and preferably has at least one further bore that is not parallel to the longitudinal direction of the throttle bushing. Typically, the throttle line is inserted centrally along the longitudinal direction from above (coming from the rail) into the approximately cylindrical throttle insert and then extends laterally to the outer surface of the throttle insert. The shape of the throttle line can therefore, for example, be an inverted "T". Care must be taken in the design of the throttle line to ensure that it does not form a fluidic connection downstream when the throttle insert's sealing surface contacts the sealing section of the throttle bushing.

[0019] Preferably, the second section of the through-hole is provided for adjacent to the first section of the through-hole.

[0020] By merging the two sections, it is ensured that no other sections can be located in between.

[0021] According to an advantageous embodiment of the invention, the spring element is supported by the cross-sectional reduction of the second section and projects into the first section of the through-hole. This ensures that the throttle insert is always pressed towards the rail when fuel under high pressure is present on both sides.

[0022] Furthermore, according to an advantageous modification of the invention, a stop element can be provided which limits the stroke of the throttle piece away from the sealing section, wherein the stop element is preferably pressed into the through-hole or attached to the end of the through-hole.

[0023] To limit the reservoir between the sealing section and the throttle insert to a defined maximum size, the stroke of the throttle insert is limited not only by the sealing section but also by a stop element on the opposite side. The spring element then presses the throttle insert against this stop element, creating a space of defined size proportional to the maximum amount of fuel that can flow out. This amount, or rather the stroke of the throttle insert, is chosen so that even if the fuel inside is completely emptied, and even if fuel flows in through the throttle line until sealing occurs, no serious damage will be caused.

[0024] According to the invention, a filter element for filtering fuel is provided, which is arranged on the side of the through-hole facing the sealing surface and is preferably attached to the through-hole by means of an interference fit.

[0025] The filter element can be pressed or inserted into the sealing section, which has a narrowed cross-section, and protrudes downstream, i.e., away from the throttle insert. Fluid flowing downstream from the throttle insert must therefore pass through the filter element, so that larger particles present in the fuel are filtered out.

[0026] The invention further comprises a fuel injector with a flow restrictor according to one of the aspects discussed above, wherein the flow restrictor is arranged between a fuel supply line, the so-called rail, and the fuel injector.

[0027] This arrangement ensures that the amount of fuel that can be dispensed by the injector is limited, so that even in the event of a malfunction in the injector, fuel cannot flow continuously.

[0028] It may be provided that the flow restrictor is pressed into the fuel supply line by inserting the throttle bushing into the fuel supply line with its outer surface in a sealing manner.

[0029] Press-fitting is a particularly simple and economical way to attach the flow restrictor.

[0030] Preferably, the flow restrictor is arranged outside the injector and attached to the injector housing. The flow restrictor can be attached by means of a union nut. This union nut engages with an external thread on the injector housing and presses the flow restrictor against the injector.

[0031] Furthermore, according to a further development of the invention, it can be provided that the fuel supply line opens into the union nut. In this way, the fuel supply line can have a collar-like expansion at its end provided at the flow restrictor, which is pressed against the flow restrictor by means of the union nut.

[0032] It can be provided that the flow restrictor is arranged inside the injector by inserting the throttle bushing with its outer surface sealingly into a housing of the injector, preferably into a supply line of the injector.

[0033] Further advantages, details and features of the invention will become apparent from the following description of the figures. These show: Fig. 1a-c: various representations of a flow restrictor which can be arranged outside an injector, and Fig. 2a-d: various representations of a flow restrictor which is arranged inside an injector. Fig. 1a Figure 1 shows a flow restrictor 1 in a sectional view, which can be mounted outside an injector. This restrictor has a throttle bushing 2 in which a through-hole 3 is arranged longitudinally. This through-hole 3 has a first section which is located in the Fig. 1a The opening 3 comprises approximately the upper 75% of the through-hole and contains a movably mounted throttle insert 4. This throttle insert 4 can be moved slidably within the through-hole 3, depending on the prevailing pressure conditions. The diagram shows a position of the throttle insert 4 in which it is in its maximum position away from a sealing section 5. The movement of the throttle insert 4 is facilitated, among other things, by a spring element 6, which bears against the reduced cross-section of the sealing section 5 and pushes the throttle insert 4 away. The stroke of the throttle insert 4 is limited by the stop element 12, which defines the maximum deflection of the throttle insert 4 away from the sealing section 5.

[0034] This stop element 12 is attached to the throttle bushing 2 by means of a union nut 11. Furthermore, it can be provided that this union nut 11, via an internal thread or an alternative fastening option, brings a fuel supply line 10 (typically the rail) to the flow restrictor 1, so that fuel is permanently present at high pressure on the side of the throttle insert 4 facing away from the sealing section 5.

[0035] The fuel, under high pressure, flows downstream through the throttle line 8 towards the outlet side of the flow restrictor 1. If a downstream fuel injector is in a closed state, fuel will be present at the same high pressure on both sides of the throttle insert once the downstream passages are full. The pressure force of the spring element 6 then causes the throttle insert 4 to be forced towards the stop element 12.

[0036] The fuel supply is maintained via a throttle line 8, which is located in the Fig. 1a through the throttle insert 4 and then runs outwards perpendicular to the longitudinal direction of the throttle insert 4.

[0037] It is clear to those skilled in the art that the exact design of the throttling line 8 for the present invention may also be subject to certain variations. It merely needs to be ensured that, in a sealing state of the flow restrictor 1, where the throttling insert 4 is in contact with the sealing section 5, the throttling line 8 must not have any fluidic connection to a section located downstream of the sealing section 5.

[0038] Fig. 1b shows a view rotated by 90° of the Fig. 1a . This illustration shows the components of the throttle line 8 extending outwards to the left and right.

[0039] Fig. 1c Figure 1 shows a possible side view of the flow restrictor 1. It can be seen that the union nut 11 is chamfered so that it can be tightened with a wrench in the external thread of the throttle bushing 2. The throttle bushing 2 itself also has corresponding chamfers on its outer circumference so that it can be secured when the union nut 11 is tightened.

[0040] Fig. 2a Figure 1 shows a flow restrictor 1 in a sectional view, which can be installed inside an injector. The basic structure of the flow restrictor 1 is the same as the previously considered model.

[0041] One difference is, for example, the stop element 12, which is now located inside the throttle bushing 2 and fixed there. This fixing can be achieved by pressing it in, gluing it, or similar means.

[0042] In addition, the outer contour of the throttle bushing 2 has also been changed, as it is now essentially cylindrical, with the outer circumference increasing slightly in the lower area near the sealing section 5.

[0043] A filter element 9 is also present, which is pressed into the reduced-cross-section sealing section 5. Fuel flowing through the throttle bushing 2 is thus inevitably filtered, so that unwanted foreign particles are filtered out.

[0044] Fig. 2b shows a 90° rotated view of the flow restrictor 1, in which the course of the throttle line 8 can also be seen very well.

[0045] Fig. 2c This is a possible external view of the flow restrictor 1, from which the two cylindrical surfaces with different radii can be seen.

[0046] Fig. 2d shows a flow restrictor in a state recorded inside a fuel injector.

[0047] The flow restrictor 1 is pressed into a pressure piece 13 of the injector with its radially larger part and extends with its slimmer part into the fuel pipe, which supplies fuel at high pressure.

[0048] The expert understands that, alternatively or additionally, the flow restrictor 1 can also be pressed into the fuel pipe.

Claims

1. Fuel injector with a flow limiter (1), wherein the flow limiter (1) for a fuel injection system comprises: a throttle sleeve (2) with a through hole (3), a throttle insert (4) movably received in a first section of the through hole (3), a sealing section (5) in a second section of the through hole (3), the cross-section of which is reduced relative to the first section of the through hole (3), and a spring element (6) received in the through hole (3) and urging the throttle insert (4) away from the sealing section (5), wherein the throttle insert (4) has, at its end facing the sealing section (5), a sealing surface (7) which closes the through hole (3) when in contact with the sealing section (5), wherein the flow limiter (1) is arranged within the injector by the throttle sleeve (2) being sealingly inserted with its outer side into a housing of the injector, and further a filter element (9) for filtering fuel is provided, which is arranged on a side of the through hole (3) facing the sealing surface and is fastened in the through hole (3) with a press fit, characterized in that the throttle insert (4) comprises or forms a throttle passage (8) which provides a fluid connection along the through hole (3) from the side of the throttle insert (4) facing away from the sealing surface to the side of the throttle insert (4) facing the sealing surface.

2. Fuel injector according to the preceding claim, wherein the throttle insert (4) sealingly cooperates with its outer cross-section with the inner cross-section of the through hole (3) and prevents a flow of a fluid between the outer cross-section of the throttle insert (4) and the inner cross-section of the through hole (3).

3. Fuel injector according to one of the preceding claims, wherein the throttle passage (8) comprises a bore extending parallel to the longitudinal direction of the throttle sleeve (2) in the throttle insert (4), and preferably comprises at least one further bore extending not parallel to the longitudinal direction of the throttle sleeve (2).

4. Fuel injector according to one of the preceding claims, wherein the second section of the through hole (3) adjoins the first section of the through hole (3).

5. Fuel injector according to one of the preceding claims, wherein the spring element (6) is supported on the cross-sectional reduction of the second section and protrudes into the first section of the through hole (3).

6. Fuel injector according to one of the preceding claims, wherein a stop element (12) is further provided which limits a stroke of the throttle insert away from the sealing section (5), wherein preferably the stop element (12) is press-fitted into the through hole (3) or is fastened at the end of the through hole (3).