Suction valve for a high-pressure pump of a fuel injection system

Abstract

Suction valve for a high-pressure pump (20) of a fuel injection system with a valve element (23) which has an actuator piston (23.1) interacting with an actuator (45) and a valve tappet (23.2) connected to a closing element (25), wherein the actuator piston (23.1) and the valve tappet (23.2) are coupled via a coupling device, wherein the coupling device is formed by a hydraulic control chamber (40), characterized in that the hydraulic control chamber (40) is controllable by means of a valve device.

Description

Prior ArtThe invention relates to a suction valve for a high pressure pump of a fuel injection system according to the features of the preamble of claim 1.A fuel injection system having a high-pressure pump, in which metering of the fuel for the high-pressure pump takes place by actuating a suction valve, is known, for example, from DE 10 2010 027 745 A1. The suction valve comprises a valve element with a valve tappet which is guided in an axial bore of a valve plate in a stroke-movable manner. The valve tappet has a valve disk with a sealing surface which interacts with a valve seat formed on the valve plate. The valve tappet is further acted upon by a magnetic actuator, which moves the valve tappet by an axial stroke movement and thereby opens or closes the valve seat. In the open position of the suction valve, the fuel is supplied via the valve seat to a pump working chamber of the high-pressure pump, in which the fuel is compressed to the required high pressure or injection pressure. While the fuel is compressed to high pressure, the valve seat is closed. To open the valve seat, the valve tappet is moved into the open position by means of the magnetic actuator counter to the spring force of a valve spring.DE 10 2012 222 442 A1 discloses a suction valve for a high-pressure pump, in which the valve element is formed in multiple parts from at least two parts, which can be coupled and decoupled via a mechanical coupling device. A permanent magnet or a spring element serves as the coupling device. When the valve seat is opened, the two parts of the valve element are coupled and execute a common lifting movement, while when the valve seat is closed, the two parts of the valve tappet are decoupled, whereby the mass of the valve tappet which can move in a lifting direction is reduced.Document EP 1 642 021 B discloses a fuel injection system for internal combustion engines with several injection nozzles each having a high and a low pressure port, the low pressure ports opening into at least one collecting line. A pressure regulator is located between the collecting line and the unpressurized fuel return line, at least one throttle valve being arranged between each low-pressure connection and the pressure regulator.The high speed of the high-pressure pumps required for the high-pressure injection systems simultaneously necessitates very high closing and opening speeds of the suction valves. In this case, the valve disk of the valve tappet strikes the valve seat at a very high speed. The actuator of the magnetic actuator likewise strikes a stop at the correspondingly high speed. This mechanical impact leads, in addition to the wear of the parts striking one another, to a high noise emission in the form of a nailing noise. The coupling of the two parts of the valve element by means of a mechanical coupling device does not bring about a corresponding noise reduction.It is an object of the present invention to achieve a reduction in the noise emission of the suction valve.Disclosure of the InventionThe object of the present invention is achieved by the characterizing features of claim 1.By means of the hydraulic control chamber, a hydraulic coupling takes place between the actuator piston and the valve tappet of the valve element. The liquid medium in the control chamber has a damping effect, whereby a mechanical contact of the components which can meet at high speed is avoided and thereby the noise emission of the suction valve is reduced.It is particularly advantageous if the hydraulic control chamber can be controlled via a valve device. By means of the valve device, a control quantity flowing out of the control chamber can be controlled. The closing speed of the valve tappet can be influenced by throttling the control quantity flowing off during emptying of the control chamber, so that a smooth closing of the valve seat is made possible, whereby less wear occurs on the valve seat. In addition, this causes a further noise reduction. Expediently, the valve device has a check valve for filling the hydraulic control chamber and an outlet valve for emptying the hydraulic control chamber. Since the outlet valve is electrically activated, it can additionally also be used as an inlet valve. This allows a more rapid filling of the control chamber.Advantageous refinements of the suction valve are possible by the measures of the dependent claims.It is furthermore advantageous if the hydraulic control chamber can be filled via a first hydraulic line connected to a low-pressure circuit and can be emptied via a second hydraulic line connected to the low-pressure circuit, wherein the check valve, which blocks against the filling direction, is arranged in the first hydraulic line for filling the control chamber and the outlet valve is arranged in the second hydraulic line for emptying the control chamber.The outlet valve is formed by a control edge formed on the actuator piston, which opens or closes the second hydraulic line at an inlet to the control chamber.A constructionally and production-relatedally expedient embodiment of the suction valve is achieved by providing a coupler plate with an axial control chamber bore in which end sections of the actuator piston and of the valve tappet are guided in each case in a stroke-movable manner, wherein the end sections are spaced apart from one another, and wherein the hydraulic control chamber is formed between the end sections. Further, the first hydraulic line and the second hydraulic line are disposed in the coupler plate.The first hydraulic line and the second hydraulic line open into the low-pressure chamber which is connected to the low-pressure circuit and is designed to receive a valve plate in a cylinder head of the high-pressure pump, wherein the valve tappet is guided in the valve plate such that it can move in a stroke and the low-pressure chamber is designed as an annular chamber surrounding the valve plate.The suction valve is advantageously open in the case of a normally powered magnetic actuator, wherein the valve tappet is acted upon by a valve spring which holds the valve tappet in a closed position.Exemplary EmbodimentAn exemplary embodiment of the invention is illustrated in the drawing and explained in more detail in the following description.The following are shown: FIG. 1 shows a schematic sectional illustration of a suction valve according to the invention in an open position at the beginning of a suction stroke, FIG. 2 shows a schematic sectional illustration of the suction valve according to the invention in an open position at the end of a suction stroke, FIG. 3 shows a schematic sectional illustration of the suction valve according to the invention in an open position at the beginning of a delivery stroke, and FIG. 4 shows a schematic sectional illustration of the suction valve according to the invention in a closed position during a delivery stroke.FIGS. 1 to 4 show a detail of a high-pressure pump 10 with a pump housing 11. The high-pressure pump 10 is part of a fuel injection system, not shown, of an internal combustion engine, in particular of a common-rail injection system, the high-pressure pump 10 providing the required injection pressure. A cylinder head 12 is inserted in the pump housing 11, in which a pump piston 13 is guided in a stroke-movable manner between a bottom dead point and a top dead point. During a stroke movement from top dead center to bottom dead center, the pump piston 13 performs a suction stroke and during a stroke movement from bottom dead center to top dead center, a delivery stroke. The pump piston 13 moves in a pump working chamber 14 delimited by the cylinder head 12, and an outlet bore 15 hydraulically connected to a high-pressure circuit leads into the pump working chamber 14, and the fuel delivered by the high-pressure pump 10 is fed through the outlet bore 15 via a non-return valve, not shown, to a fuel accumulator, likewise not shown, of the fuel injection system.The pump working chamber 14 is also operatively connected to a suction valve 20. By means of the suction valve 20, the fuel is supplied to the pump working chamber 14 via a draw line 18 connected to a low-pressure circuit from a fuel tank, not shown. By controlling the suction valve 20, the fuel quantity fed into the pump working chamber 14 is metered.The suction valve 20 is inserted into a receptacle 19 formed in the cylinder head 12 and has a valve plate 21 with an axial bore 22, in which a valve element 23 movable in the stroke is guided. The valve element 23 is embodied in two parts and has an actuator piston 23.1 interacting with a magnetic actuator 24, not shown in detail, and a valve plunger 23.2 connected to a closing element 25. The magnetic actuator 24 can be embodied with a flat armature or plunger armature. However, other actuator concepts are also conceivable.The closing element 25 is embodied in the shape of a disk and has a sealing surface 26 which interacts with a valve seat 27 formed on the valve plate 21. Furthermore, a valve spring 28 is provided which is prestressed between the valve plate 21 and a support ring 29 fastened to the valve tappet 23.2. By means of the valve spring 28, the sealing surface 26 is brought into sealing contact with the valve seat 27, so that a closed position of the suction valve 20 is thereby present. In the present exemplary embodiment, the closed position of the suction valve 20 is realized in the non-energized state of the magnetic actuator 24. An open position of the suction valve 20 with the valve seat 27 open is realized by energizing the magnetic actuator 24, as a result of which the valve tappet 23.2 moves downward, as will be described in more detail later.Between the receptacle 19 and the valve plate 21, a low-pressure chamber 31 is formed, which is formed as an annular chamber and into which the aforementioned feed line 18 of the low-pressure circuit opens. In the valve plate 21, a valve chamber 32 is also arranged, which is formed by a section of the axial bore 22 with an enlarged inner diameter. A radial bore 33 leads into the valve chamber 32, via which the valve chamber 32 is hydraulically connected to the low-pressure chamber 31. Thus, the valve chamber 32 is likewise hydraulically connected to the low-pressure circuit. The valve chamber 32 of the suction valve 20 and the adjacent pump working chamber 14 of the high-pressure pump 10 can be hydraulically connected via the valve seat 27, as will be explained in more detail later in connection with the open position and the closed position of the suction valve 20.The coupling of the actuator piston 23.1 and the valve tappet 23.2 is realized by a coupling device in the form of a hydraulic control chamber 40. The hydraulic control chamber 40 can be controlled by a valve device. A coupler plate 41 is used to form the hydraulic control chamber 40, in which a control chamber bore 42 is arranged, which is axially aligned with the axial bore 22. The actuator piston 23.1 is accommodated in the control chamber bore 42 with an end section with an end face 44 and the valve tappet 23.2 with a further end section with a further end face 45 in a stroke-adjustable manner. The two end faces 44 and 45 are spaced apart from one another, so that the control chamber 40 filled with fuel is formed therebetween in the control chamber bore 42.In the present exemplary embodiment, the valve device for controlling the hydraulic control chamber 40 comprises a check valve 49 and an outlet valve 50. the check valve 49 is arranged in a first hydraulic line 47 for filling the control chamber 40, wherein the check valve 49 blocks against the filling direction. The outlet valve 50 is operatively connected to a second hydraulic line 48 for emptying the control chamber 40, wherein the outlet valve 50 opens or closes the second hydraulic line 48. The first hydraulic line 47 for filling the control chamber 40 and the second hydraulic line 48 for emptying the control chamber 40 each connect the control chamber 40 to the low-pressure chamber 31; the outlet valve 50 is formed by the actuator piston 23.1, which opens or closes an inlet of the second hydraulic line 48 that leads into the control chamber 40. For this purpose, the actuator piston 23.1 has a slide edge which is formed by the end face 44, with which the inlet of the second hydraulic line 48 is closed or opened. By means of the outlet valve 50, it is also possible to realize a controlled throttling of the fuel when it drains out of the control chamber 40, as a result of which the closing speed of the valve tappet 23.2 can be controlled.Optionally, for faster filling of the control chamber 40, the outlet valve 50 can additionally be actuated and opened by the magnetic actuator 45. It is also conceivable to control the filling and emptying of the control chamber 40 only by the outlet valve 50. The check valve 49 can then be omitted.To generate the injection pressure in the fuel injection system, the pump working chamber 14 is filled with fuel from the low-pressure circuit via the valve seat 27 of the suction valve 20 by means of the suction stroke of the pump piston 13. After filling of the pump working chamber 14, the required fuel quantity in the pump working chamber 14 is adjusted by means of the suction valve 20. The metered fuel quantity is compressed in the pump working chamber 14 and pumped through the outlet bore 15 via the non-return valve, not shown, into the high-pressure circuit or the high-pressure accumulator in order to provide the injection pressure. The required fuel quantity which is delivered into the high-pressure circuit is controlled by a corresponding actuation of the suction valve 20.The filling of the pump working chamber 14 takes place in that the pump piston 13 moves from the top dead center into the bottom dead center in the suction stroke. Due to the negative pressure that forms in this case, the valve tappet 23.2 according to FIG. 1 is moved against the spring force of the valve spring 28 in the arrow direction into the open position, so that the valve seat 27 is open. As a result, the fuel flows from the low-pressure circuit via the low-pressure chamber 31, the radial bore 33, the valve chamber 32 and via the open valve seat 27 into the pump working chamber 14, and at the same time, the control chamber 40 is filled with fuel via the check valve 49 by the downward movement of the valve tappet 23.2. The outlet valve 50 closes the second hydraulic line 48; in the bottom dead center of the pump piston 13, the control chamber 40 is completely filled with fuel.In the illustration shown in FIG. 2, the pump piston 13 is located in the bottom dead center with the beginning of the delivery stroke in the arrow direction. In this position of the delivery stroke, the valve seat 27 is still open and fuel is forced back into the low-pressure chamber 31 according to the arrows. As a result, the fuel quantity required for the injection process is adjusted in the pump working chamber 14 by the piston stroke of the pump piston 13. The outlet valve 50 is still closed. As a result of the pressure compensation which occurs between the control chamber 40 and the low-pressure chamber 31, the check valve 49 closes the first hydraulic line 47 in the filling direction and the control chamber 40 remains filled with a constant volume.Depending on the fuel quantity required by the fuel injection system, the outlet valve 50 is opened when the required fuel quantity is reached in the pump working chamber 14 according to FIG. 3, in that the actuator piston 23.1 is lifted by the magnetic actuator 24. The end face 44 of the actuator piston 23.1, acting as a control edge, opens up the inlet to the second hydraulic line 48. The fuel thereby flows back from the control chamber 40 into the low-pressure chamber 31 via the second hydraulic line 48. The counterpressure in the control chamber 40 thus decreases and the valve tappet 23.2 is moved in the direction of the closed position by the force of the valve spring (28) and subsequently also by the delivery stroke of the pump piston 14. The closed position is supported by the valve spring 28.As soon as the valve seat 27 is closed and the closed position of the suction valve 20 according to FIG. 4 is present, the required fuel quantity remaining in the pump working chamber 14 is pressed by the further delivery stroke of the pump piston 13 in the arrow direction via the outlet bore 15 into the high-pressure circuit or into the fuel accumulator, wherein the pump piston 13 moves as far as the top dead center.The closing of the suction valve 20 is controlled by the magnetic actuator 24, as already explained, i.e. the time for the closing of the suction valve 20 is freely selectable. As already mentioned, however, the closing speed of the valve tappet 23.2 can also be influenced by a controlled throttling of the fuel when it flows out of the control chamber 40.

Claims

Suction valve for a high-pressure pump (20) of a fuel injection system, having a valve element (23) which has an actuator piston (23.1) which interacts with an actuator (45) and a valve tappet (23.2) which is connected to a closing element (25), wherein the actuator piston (23.1) and the valve tappet (23.2) are coupled via a coupling device, wherein the coupling device is formed by a hydraulic control chamber (40), characterized in that the hydraulic control chamber (40) can be controlled by means of a valve device.Suction valve according to claim 1, characterised in that the valve device comprises a non-return valve (49) and an outlet valve (50).Suction valve according to Claim 1, characterized in that the hydraulic control chamber (40) can be filled via a first hydraulic line (47) connected to a low-pressure circuit and can be drained off via a second hydraulic line (48) connected to the low-pressure circuit.Suction valve according to Claim 3, characterized in that the check valve (49) which blocks against the filling direction is arranged in the first hydraulic line (47) for filling the control chamber (40).Suction valve according to Claim 3, characterized in that the outlet valve (50) is arranged in the second hydraulic line (48) for emptying the control chamber (40).Suction valve according to Claim 5, characterized in that the outlet valve (50) is formed by a control edge (44) which is formed on the actuator piston (23.1) and opens or closes the second hydraulic line (48).Suction valve according to Claim 1, characterized in that a coupler plate (41) having an axial control chamber bore (42) is provided, in which end portions of the actuator piston (23.1) and of the valve tappet (23.2) are guided in each case in a stroke-movable manner, in that the end portions are spaced apart from one another, and in that the hydraulic control chamber (40) is formed between the end portions.Suction valve according to claim 7, characterised in that the first hydraulic line (47) and the second hydraulic line (48) are arranged in the coupler plate (41).Suction valve according to Claim 8, characterized in that the first hydraulic line (47) and the second hydraulic line (48) open into a low-pressure chamber (31) which is designed to accommodate a valve plate (21) in a cylinder head (12) of the high-pressure pump (10), in that the valve tappet (23.1) is guided in the valve plate (21) such that it can move in a stroke, and in that the low-pressure chamber (31) is designed as an annular space which surrounds the valve plate (21).

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