Zero-delivery throttle valve

Abstract

The invention relates to a zero-delivery throttle valve (50) for the low-pressure system (63) of a high-pressure injection system (14) for an internal combustion engine, comprising an inlet opening (52) for introducing fuel from the suction side of a high-pressure pump (1) into the zero-delivery throttle valve (50), an outlet opening (53) for discharging fuel out of the zero-delivery throttle valve (50), and a zero-delivery duct (51) for conducting fuel therethrough, wherein the zero-delivery duct (51) connects the inlet opening (52) to the outlet opening (53), and wherein the zero-delivery duct (51) is curved in the flow direction of the fuel.

Description

[0001] Description

[0002] title

[0003] Zero-feed throttle

[0004] The present invention relates to a zero-feed throttle for the low-pressure circuit of a high-pressure injection system according to the preamble of claim 1 and a high-pressure injection system according to the preamble of claim 7.

[0005] State of the art

[0006] In high-pressure injection systems for internal combustion engines, particularly in common-rail injection systems of diesel or gasoline engines, a high-pressure pump continuously maintains the pressure in the high-pressure accumulator of the common-rail injection system. The high-pressure pump can be driven, for example, by a gear drive connected to the crankshaft of the internal combustion engine, by a belt drive, or by a chain. Pre-feed pumps, e.g., a gear pump or rotary vane pump, are used to deliver the fuel to the high-pressure pump. The pre-feed pump delivers the fuel from a fuel tank through a fuel line to the high-pressure pump.

[0007] Piston pumps, among others, are used as high-pressure pumps. A drive shaft is mounted in a housing. Pistons are arranged radially to it in a cylinder. A roller with a roller rolling surface, which is mounted in a roller shoe, rests on the drive shaft with at least one cam. The roller shoe is connected to the piston so that the piston is forced into an oscillating translational movement. A spring applies a force to the roller shoe directed radially towards the drive shaft so that the roller is in constant contact with the drive shaft. The roller is in contact with the drive shaft with the roller rolling surface on a shaft rolling surface as the surface of the drive shaft with the at least one cam. The roller is mounted in the roller shoe by means of a plain bearing.

[0008] The drive shaft with the at least one cam, the idler roller and the roller shoe are arranged within a lubrication chamber of the high-pressure pump. The drive shaft of the high-pressure pump is positively connected to the pre-feed pump, for example by means of a coupling. The delivery rate and the resulting delivery pressure of the pre-feed pump therefore depend on the speed of the high-pressure pump and is often limited by a throttle in the intake area of ​​the pre-feed pump. At high engine speeds and low injection quantities, the pre-feed pump generates an excessive delivery rate and volume flow and, as a result, excessive pressure in the fuel line from the pre-feed pump to the high-pressure pump. This problem is preferably counteracted by the use of a spring-loaded overflow valve. The fuel is guided from the fuel line from the pre-feed pump to the high-pressure pump through the lubrication chamber into the overflow valve.For this reason, a fuel line from the pre-feed pump to the high-pressure pump is fluidly connected to an overflow valve, whereby the overflow valve is fluidly connected to a lubrication chamber of the high-pressure pump. The overflow valve preferably has two outlet openings, whereby the first outlet opening is always open or opens even at low pressure in the fuel line from the pre-feed pump to the high-pressure pump and directs a smaller amount of fuel through a fuel return channel back to the fuel tank for cooling purposes. The second outlet opening opens at a pressure of preferably between 3 bar and 7 bar in the fuel line from the pre-feed pump to the high-pressure pump and directs the fuel directly back into the fuel line to the intake side of the pre-feed pump. The direct return to the intake side of the pre-feed pump allows the vehicle manufacturer to use a smaller fuel filter.

[0009] Fuel delivered from the pre-feed pump to the high-pressure pump is fed through this lubrication chamber of the high-pressure pump in order to lubricate the components within the lubrication chamber and to cool them with the fuel fed through the lubrication chamber. The volume flow of the fuel delivered from the pre-feed pump to the high-pressure pump therefore includes the fuel fed through the lubrication chamber to lubricate and cool the components of the high-pressure pump within the lubrication chamber, as well as the fuel intended for the high-pressure pump to be delivered under high pressure to the high-pressure rail. An essentially constant pressure should be maintained in the fuel line from the pre-feed pump to the high-pressure pump.

[0010] When using a mechanical pre-feed pump without an electric motor, which is driven exclusively by the crankshaft of the combustion engine, the volume flow of fuel delivered by the mechanical pre-feed pump to a fuel suction line of the high-pressure pump is controlled and / or regulated by a metering unit. For example, the pre-feed pump delivers a volume flow of approximately 400 l / h of fuel. Even when fully closed, the metering unit has a leakage volume flow of approximately 0.5 l / h. When the combustion engine is operating without fuel being consumed, this leakage volume flow would be directed into the fuel suction line of the high-pressure pump, then fed by the high-pressure pump to the high-pressure fuel line and the high-pressure rail, and the pressure in the high-pressure rail would be continuously increased. The high-pressure injection system is therefore designed with a zero-feed throttle with a zero-feed channel.The zero-feed throttle directs the leakage flow through the zero-feed channel into a fuel line of the low-pressure circuit. This prevents an increase in fuel pressure in the high-pressure rail when the metering unit is fully closed, with the leakage flow, and the combustion engine operating without fuel demand. The throttle diameter of the zero-feed throttle is preferably designed so that, at maximum pressure in the low-pressure range of the high-pressure pump, which is limited by the overflow valve, the maximum leakage volume from the metering unit can flow through the throttle bore as the zero-feed channel.In the fuel line, which serves as the fuel discharge channel and into which the zero-feed channel of the zero-feed throttle opens, a higher fuel pressure can occur than in the zero-feed channel of the zero-feed throttle, for example due to a small diameter of the fuel line to the fuel tank and / or a long length of this fuel line. This would lead to a backflow of fuel from this fuel line through the zero-feed channel of the zero-feed throttle into the fuel suction line of the high-pressure pump. To prevent a backflow of fuel through the zero-feed channel of the zero-feed throttle in the opposite direction to the desired flow of the zero-feed channel, the pressure at the inlet of the zero-feed channel of the zero-feed throttle is reduced using the Venturi effect. For this purpose, the cross-section of the channel is narrowed downstream of the first outlet opening of the overflow valve, shortly before the inlet of the zero-feed channel.Due to Bernoulli's equation, the flow velocity at the constriction increases and the pressure drops. In the area where the zero-feed channel of the zero-feed throttle opens into this fuel line or channel downstream of the first outlet opening in the direction of fuel flow, this is formed on a straight Venturi section with a smaller flow cross-sectional area than outside the Venturi section of this fuel line. As a result, lower pressure occurs locally only in the Venturi section of this fuel line (Bernoulli's equation), and backflow of fuel from this fuel line into the zero-feed channel of the zero-feed throttle is prevented. In the area of ​​the Venturi section, the fuel line is designed as a throttle tube. The throttle tube is located in a bore in the housing of the high-pressure pump.On the radial outer side of the throttle tube, sealing rings are arranged at the ends in the axial direction between the throttle tube and the bore housing. Furthermore, a small radial bore, straight in the direction of fuel flow, is formed in the throttle tube as the zero-feed channel of the zero-feed throttle. The zero-feed channel opens into the central channel of the throttle tube in the area of ​​the smallest diameter, i.e., the Venturi section of the throttle tube. Disadvantageously, the throttle tube is complex and expensive to manufacture and requires complex assembly processes.

[0011] EP 2 708 728 A2 discloses a low-pressure circuit for a fuel injection system, in particular a common rail injection system of internal combustion engines, comprising a pre-feed pump by means of which fuel can be sucked from a fuel tank and fed via a fuel line to a low-pressure region of a high-pressure pump, wherein a metering unit for quantity regulation is arranged in the low-pressure region, a zero-feed line with a zero-feed throttle branches off downstream of the metering unit and an overflow line with an overflow valve branches off upstream of the metering unit, wherein a shut-off device which can be switched between an open and a closed state for selectively opening or blocking the zero-feed line is arranged in the zero-feed line.

[0012] Disclosure of the invention

[0013] Advantages of the invention

[0014] A zero-feed throttle according to the invention for the low-pressure circuit of a high-pressure injection system for an internal combustion engine, comprising an inlet opening for introducing fuel from the intake side of a high-pressure pump into the zero-feed throttle, an outlet opening for discharging fuel from the zero-feed throttle, a zero-feed channel for conducting fuel, and the zero-feed channel connecting the inlet opening to the outlet opening, wherein the zero-feed channel is preferably curved in the direction of fuel flow. The curvature of the zero-feed channel is preferably substantially constant, in particular with a deviation of less than 30%, 20%, or 10%. The curvature of the zero-feed channel is preferably less than 30 cm, 20 cm, 10 cm, 5 cm, 3 cm, 2 cm, or 1 cm. Preferably, at least 30%, 50%, 70%, 90%, or 95% of the length of the zero-feed channel is curved.A curved design of the zero feed channel is also considered if a curvature of at least 3, 5 or 7 straight sections of the zero feed channel is approximated in the flow direction of the fuel.

[0015] In a further embodiment, the zero-feed channel is formed at least partially, in particular completely, in an annular groove. The cross-section of the annular groove is preferably designed such that, at maximum pressure in the low-pressure range of the high-pressure pump, which is limited by the overflow valve, the maximum leakage quantity of the metering unit can flow through.

[0016] In an additional variant, the zero-feed throttle comprises a throttle ring, preferably in the shape of a cylinder jacket, and the annular groove is formed on the throttle ring, in particular on a radial outer side of the throttle ring. In a supplementary variant, the zero-feed throttle at least partially comprises an overflow valve channel for passing fuel from an overflow valve into the low-pressure circuit of the high-pressure injection system.

[0017] In a further embodiment, the overflow valve channel has a different flow cross-sectional area and a Venturi section of the overflow valve channel is designed with a smaller flow cross-sectional area than outside the Venturi section for a reduced pressure of the fuel flowing through the Venturi section.

[0018] Preferably, the Venturi section of the overflow valve channel is at least partially delimited by the throttle ring, in particular an axial end of the throttle ring.

[0019] A high-pressure injection system according to the invention for an internal combustion engine, comprising a high-pressure pump, a high-pressure rail, a spill valve, a zero-feed throttle with an inlet opening for introducing fuel from the intake side of the high-pressure pump into the zero-feed throttle, an outlet opening for discharging fuel from the zero-feed throttle, and a zero-feed channel for conveying fuel, the zero-feed channel connecting the inlet opening to the outlet opening, a spill valve channel for conveying fuel from the spill valve into a low-pressure circuit of the high-pressure injection system, wherein the spill valve channel has a different flow cross-sectional area, and a Venturi section of the spill valve channel is designed with a smaller flow cross-sectional area than outside the Venturi section for a reduced pressure of the fuel flowing through the Venturi section of the spill valve channel,a pre-feed pump, a metering unit, wherein the zero feed channel is preferably curved in the flow direction of the fuel.

[0020] In a further embodiment, the zero-feed channel is formed in an annular groove.

[0021] In a supplementary embodiment, the zero-feed throttle comprises a throttle ring, preferably in the shape of a cylinder jacket, and preferably the annular groove is formed on the throttle ring, in particular on a radial outer side of the throttle ring.

[0022] The cylinder jacket-shaped throttle ring is expediently arranged in a bore of a housing of at least one pump of the high-pressure injection system.

[0023] In a further embodiment, the zero-feed channel is delimited by two different components; in particular, the zero-feed channel is delimited by the throttle ring, preferably in the shape of a cylinder jacket, and the housing of the at least one pump of the high-pressure injection system. Preferably, the two different components are connected to one another in a form-fitting and / or force-fitting manner, and / or the two different components are not connected to one another in a material-fitting manner. The throttle ring, as a first component, is fastened to the housing of the at least one pump, as a second component, in a form-fitting and preferably force-fitting manner, in particular by means of a press fit in the bore of the housing of the at least one pump.

[0024] In a supplementary embodiment, the Venturi section of the overflow valve channel is delimited by the throttle ring, in particular an axial end of the throttle ring.

[0025] Preferably, the Venturi section of the overflow valve channel is delimited by the housing of the at least one pump of the high-pressure injection system. Preferably, the housing of the at least one pump is the housing of the pre-feed pump and / or the housing of the high-pressure pump.

[0026] In a further embodiment, the zero-feed channel of the zero-feed throttle and the Venturi section of the overflow valve channel open into a common fuel discharge channel. The fuel discharge channel is preferably designed as a fuel line and / or as a fuel bore in a housing of the at least one pump.

[0027] In a supplementary variant, the overflow valve comprises a first stage with a first discharge opening and a second stage with a second discharge opening. The second discharge opening of the overflow valve opens into the overflow valve channel with the Venturi section. In a further embodiment, the zero-discharge channel is delimited by the throttle ring and the pump housing.

[0028] Preferably, the annular groove is formed on the housing of the at least one pump.

[0029] In an additional variant, the zero-feed throttle comprises a cylinder-jacket-shaped throttle ring and the annular groove is formed on a radial inner side of the cylinder-jacket-shaped throttle ring.

[0030] In a further embodiment, the throttle ring is arranged on the bore in the radial direction with respect to a longitudinal axis of the overflow valve and / or the throttle ring between the overflow valve and the housing.

[0031] In an additional embodiment, an axial end of the throttle ring rests on a step of the bore of the housing, in particular completely circumferentially and / or liquid-tight.

[0032] In a further embodiment, the Venturi section of the overflow valve channel is slot-shaped in cross section with a greater extent in a first direction than in a second direction and the first and second directions are perpendicular to one another and preferably the extent of the Venturi section in the first direction is greater than 1.1, 1.5, 2, 3 or 4 times the extent of the Venturi section in the second direction.

[0033] In a further embodiment, the boundary of the Venturi section of the overflow valve channel is at least partially straight and / or at least partially curved. A first partial region of the boundary of the Venturi section is curved, as the end of the fuel discharge channel, and a second partial region of the boundary of the Venturi section is straight, as the axial end of the throttle ring.

[0034] In a supplementary embodiment, the fuel discharge channel is delimited by the throttle ring, in particular a radial inner side of the throttle ring, and the housing, in particular a radial outer side of the housing of the overflow valve.

[0035] In a further variant, the housing of the pump as a high-pressure pump and / or pre-feed pump limits the Venturi section of the overflow valve channel.

[0036] In a supplementary embodiment, a portion of the annular groove of the throttle ring forms the inlet opening of the zero-feed throttle.

[0037] In an additional embodiment, a portion of the annular groove of the throttle ring forms the outlet opening of the zero-feed throttle.

[0038] In a supplementary variant, the flow cross-sectional area of ​​the Venturi section of the overflow valve channel is smaller than 90%, 70%, 50%, 30% or 10% of the flow cross-sectional area of ​​the overflow valve channel outside the Venturi section.

[0039] In an additional embodiment, the flow cross-sectional area of ​​the zero-feed channel of the zero-feed throttle is designed such that the leakage volume flow from the metering unit can be completely passed through during operation of the high-pressure injection system.

[0040] In a supplementary embodiment, the zero-feed channel is designed such that the volume flow of fuel introduced through the inlet opening of the zero-feed throttle is divided into a first partial volume flow and a second partial volume flow, and the first partial volume flow can be conducted through a first partial region of the zero-feed channel and the second partial volume flow can be conducted through a second partial region of the zero-feed channel, and preferably the first and second partial volume flows can be introduced into one, in particular only one, outlet opening of the zero-feed throttle.

[0041] In a further variant, the flow cross-sectional area of ​​the annular groove is designed to allow a larger volume flow of fuel than necessary for discharging the zero-flow rate. Preferably, an additional zero-flow throttle is formed upstream in the flow direction of the fuel passing through the annular groove, preferably pressed in, screwed in, and / or glued in.

[0042] In an additional embodiment, the housing of the overflow valve and / or the throttle ring and / or the housing of the pump are at least partially, in particular completely, made of plastic and / or steel and / or aluminum.

[0043] In a supplementary variant, the volume flow of the fuel delivered from the pre-feed pump to the high-pressure pump can be controlled and / or regulated during operation of the internal combustion engine by using a metering unit to control and / or regulate the flow cross-sectional area of ​​a flow channel from the pre-feed pump to the high-pressure pump.

[0044] In another variant, the pre-feed pump is a gear pump.

[0045] In a supplementary embodiment, the front feed pump is mechanically driven, in particular exclusively, by the internal combustion engine. The front feed pump is mechanically coupled and / or driven, for example, by a transmission and at least one shaft to the crankshaft of the internal combustion engine.

[0046] Preferably, the high-pressure pump comprises a lubrication chamber.

[0047] The pressure that can be generated by the high-pressure pump in the high-pressure rail is, for example, in the range of 100 bar to 3000 bar for diesel engines or between 40 bar and 400 bar for gasoline engines.

[0048] Short description of the drawings

[0049] In the following, embodiments of the invention are described in more detail with reference to the accompanying drawings. Fig. 1 shows a cross-section of a high-pressure pump for conveying a fluid,

[0050] Fig. 2 shows a section AA according to Fig. 1 of a roller with roller shoe and a drive shaft,

[0051] Fig. 3 is a highly schematic view of a high-pressure injection system,

[0052] Fig. 4 is a perspective view of a throttle ring,

[0053] Fig. 5 shows a cross-section of a discharge channel for the zero discharge channel and the overflow valve channel, looking towards one end of the discharge channel with the throttle ring,

[0054] Fig. 6 a cross-section of a bore in the housing of the high-pressure pump with the overflow valve, throttle ring, discharge channel and

[0055] Fig. 7 a longitudinal section of the bore in the housing of the high pressure pump with the overflow valve, throttle ring, discharge channel and

[0056] Fig. 8 an enlarged partial longitudinal section of the bore in the pump housing with the overflow valve, throttle ring, discharge channel and

[0057] Embodiments of the invention

[0058] Fig. 1 shows a cross-section of a high-pressure pump 1 for pumping fuel. The high-pressure pump 1 is used to pump fuel, e.g., gasoline or diesel, to an internal combustion engine (not shown) under high pressure. The pressure that can be generated by the high-pressure pump 1 is, for example, in a range between 40 bar and 3000 bar.

[0059] The high-pressure pump 1 has a drive shaft 2 with two cams 3 which rotate about a rotational axis 26. The rotational axis 26 lies in the plane of the drawing in Fig. 1 and is perpendicular to the plane of the drawing in Fig. 2. A piston 5 is mounted in a cylinder 6 which is formed by a housing 8. A working chamber 29 is delimited by the cylinder 6, the housing 8 and the piston 5. An inlet channel 22 with an inlet valve 19 and an outlet channel 24 with an outlet valve 20 open into the working chamber 29. The fuel flows into the working chamber 29 through the inlet channel 22 with an inlet opening 21 and the fuel flows out of the working chamber 29 again under high pressure through the outlet channel 24 with an outlet opening 23. The inlet valve 19, e.g. B. a check valve, is designed in such a way that only fuel can flow into the working chamber 29 and the outlet valve 20, e.g.A check valve is designed such that only fuel can flow out of the working chamber 29. The volume of the working chamber 29 is changed due to an oscillating stroke of the piston 5. The piston 5 is supported indirectly on the drive shaft 2. At the end of the piston 5 or pump piston 5 is a roller shoe 9 with a roller.

[0060] 10. The roller 10 can perform a rotational movement, the rotational axis 25 of which lies in the plane of the drawing according to Fig. 1 and is perpendicular to the plane of the drawing in Fig. 2. The drive shaft 2 with the at least one cam 3 has a shaft rolling surface 4, and the roller 10 has a roller rolling surface 11.

[0061] The roller running surface 11 of the roller 10 rolls on the shaft rolling surface 4 of the drive shaft 2 at a contact surface 12 with the two cams 3. The roller shoe 9 is mounted as a plain bearing in a roller shoe bearing formed by the housing 8. A spring 27 or spiral spring 27 as an elastic element 28, which is clamped between the housing 8 and the roller shoe 9, applies a compressive force to the roller shoe 9, so that the roller rolling surface

[0062] 11 of the roller 10 is in constant contact with the rolling surface 4 of the drive shaft 2. The roller shoe 9 and the piston 5 thus jointly perform an oscillating stroke movement. The roller 10 is mounted in the roller shoe 9 with a plain bearing 13.

[0063] Fig. 3 shows a highly schematic representation of a high-pressure injection system 14 for a motor vehicle (not shown) with a high-pressure rail 30 or a fuel rail 31. From the high-pressure rail 30 or a fuel rail 31, the fuel is injected through high-pressure fuel lines 44 and by means of valves (not shown) into the combustion chambers (not shown) of the internal combustion engine (not shown). The fuel is supplied to a high-pressure fuel line 44 through the outlet channel 24 and the outlet opening 23 and introduced into the high-pressure rail 30 through the high-pressure fuel line 44.

[0064] A pre-feed pump 15 feeds fuel from a fuel tank 32 through a fuel line 33, a pre-filter 34, a main filter 36, and a metering unit 35 to the high-pressure pump 1. The pre-feed pump 15 is a mechanical pre-feed pump 15 that is mechanically coupled to the crankshaft of the internal combustion engine and feeds a maximum of 400 l / h of fuel depending on the speed of the internal combustion engine. The high-pressure pump 1 is also driven by the crankshaft of the internal combustion engine, so that the high-pressure pump 1 and the pre-feed pump 15 feed the fuel depending on the speed of the internal combustion engine. The pre-feed pump 15 is designed as a gear pump 16, for example an internal gear pump 17 or an external gear pump 18. The high-pressure pump 1 is driven by the drive shaft 2, and the drive shaft 2 is driven by the crankshaft of the internal combustion engine.The metering unit 35 controls and / or regulates the volume of fuel supplied to the high-pressure pump 1 per unit of time. The metering unit 35 is designed, for example, as a slide valve with a linear magnet (not shown). The slide valve is released by the linear magnet into different positions with a different flow cross-section for the fuel, so that the volume flow of fuel supplied through a fuel suction line 45 from the metering unit 35 into the high-pressure pump 1 is controlled and / or regulated depending on the fuel demand in the internal combustion engine.

[0065] The fuel is pumped by the pre-feed pump 15 through the main filter 36 into the metering unit 35. The high-pressure rail 30 serves to inject the fuel into the combustion chamber of the internal combustion engine using injection valves (not shown). The fuel pumped by the high-pressure pump 1 into the high-pressure rail 30 and not required by the internal combustion engine is returned to the fuel tank 32 via a fuel return line 46 after the pressure has been reduced by a pressure control valve (not shown) to a predetermined pressure. This prevents the fuel pressure in the high-pressure rail 30 from being exceeded and ensures that a predetermined fuel pressure is available to the injection valves on the inlet side. The fuel return line 46 is part of a low-pressure circuit 63.

[0066] The fuel sucked from the fuel tank 32 by the pre-feed pump 15 is fed by the pre-feed pump 15 at a pre-feed pressure, e.g., of 4 bar, through the fuel line 33 to the high-pressure pump 1, i.e., to the inlet channel 22 of the high-pressure pump 1. The delivery rate of the pre-feed pump 15 is generally greater than the maximum delivery rate of the high-pressure pump 1, so that in various operating states of the internal combustion engine, a sufficient supply of fuel to the high-pressure pump 1 is always guaranteed and a lubrication chamber 37 of the high-pressure pump 1 is sufficiently flowed through and supplied with fuel as a lubricant.

[0067] The lubrication chamber 37 is formed within the housing 8 of the high-pressure pump 1. The drive shaft 2, the roller 10, the roller shoe 9, and part of the piston 5 are arranged in the lubrication chamber 37. These components 2, 5, 9, and 10 are lubricated by the fuel passed through the lubrication chamber 37. For this purpose, a channel 38 for introducing fuel into the lubrication chamber 37 and a channel 39 for discharging fuel from the lubrication chamber 37 are formed within the housing 8 and as a separate fuel line. The channel 38 for introducing fuel into the lubrication chamber 37 is connected to the fuel line 33 upstream of the metering unit 35, so that the excess fuel from the pre-feed pump 15 that is not passed through the metering unit 35 is passed through the lubrication chamber 37.

[0068] A bore 41 is machined into the housing 8 of the high-pressure pump 1 (Figs. 6, 7 and 8), and an overflow valve 40 is arranged in this bore 41. The overflow valve 40 has the task of diverting the excess fuel that was pumped by the pre-feed pump 15, is not required by the high-pressure pump 1, and was passed through the lubrication chamber 37, into the fuel tank 32 and / or into the fuel line 33 as the suction line of the pre-feed pump 15, and of keeping the pressure of the fuel in the lubrication chamber 37 essentially constant. This excess fuel is introduced through the channel 38, the lubrication chamber 37, and the channel 39 into an inlet opening of the overflow valve 40. The overflow valve 40 is designed as a slide valve with a valve piston 43 and a valve spring 42. The pressure of the fuel at the inlet opening of the overflow valve 40 counteracts the force exerted by the valve spring 42 on the valve piston 43.The overflow valve 40 has a first outlet opening 47 as a first stage and a second outlet opening 48 as a second stage (Figs. 3 and 8). At a low pressure of, for example, 0.5 bar or more at the inlet opening of the overflow valve, fuel is discharged through the first outlet opening 47 with a small flow cross-sectional area due to the movement of the valve piston 43. If the pressure at the inlet opening of the overflow valve 40 continues to rise, the valve piston 43 is moved further against the pressure force applied to the valve piston 43 by the valve spring 42, and the second outlet opening 48 is opened at a pressure of, for example, 4 bar, and a large volume flow of fuel is passed through the second outlet opening 48.

[0069] In addition to the fuel delivery rate for the high-pressure pump 1, the pre-feed pump 35 also delivers an additional amount of fuel for lubricating the high-pressure pump 1, i.e. the fuel that flows through the lubrication chamber 40. In order to avoid an increase in pressure in the fuel line 33 upstream of the overflow valve 41 when the delivery rate of the pre-feed pump 35 is increased, the second outlet opening 48 of the overflow valve 40 preferably also opens when the pressure of the fuel upstream of the overflow valve 40 increases, e.g. from a pressure of 4 bar, i.e. provides a larger flow cross-sectional area of ​​the fuel through the overflow valve 40 until a pressure of less than 4 bar is present upstream of the overflow valve 40 again.As a result, a substantially constant pre-feed pressure of approximately 4 bar can be provided in the channel 39 upstream of the overflow valve 40 during operation of the internal combustion engine 3, even in the event of fluctuations in the delivery capacity of the pre-feed pump 35. The overflow valve 40 has the task of keeping the fuel pressure upstream of the metering unit 35 and in the lubrication chamber 37 almost constant in order to achieve a high control quality of the metering unit 35 and a reliable flow through the bearings of the high-pressure pump 1.

[0070] A further task of the overflow valve 40 is to return a volume flow of fuel passed through a first outlet opening 47 and a fuel return channel 54 back into the fuel tank 32. This fuel quantity is replaced by the pre-feed pump 15 with generally cooler fuel from the fuel tank 32, thereby ensuring cooling of the high-pressure pump 1.

[0071] The metering unit 35 is not completely sealed even when the slide valve is fully closed, so that a leakage volume flow of approximately 0.5 l / h flows through the metering unit 35 into the fuel suction line 45. If the internal combustion engine does not require fuel, this leakage volume flow would cause a constant increase in the pressure in the high-pressure rail 30 due to the introduction into the fuel suction line 45. A zero-feed throttle 50 of the high-pressure injection system 14 prevents the unhindered increase in pressure in the high-pressure rail 30 due to the leakage volume flow of the metering unit 35. A channel 49 as a fuel line and / or channel in the housing 8 directs the leakage volume flow from the fuel suction line 45 through a zero-feed throttle 50 with a zero-feed channel 51 into a fuel discharge channel 56 as a fuel line and / or channel in the housing 8.The fuel from the second outlet opening 48 of the overflow valve 40 is introduced into an overflow valve channel 55 as a second overflow valve channel 55. The zero-feed channel 51 of the zero-feed throttle 50 and the overflow channel 55 open into a common fuel discharge channel 56. The fuel discharge channel 56 opens into the fuel line after the pre-filter 34 and before the pre-feed pump 15. A fuel return channel 54 as a fuel line and / or channel in the housing 8 conducts the fuel from the first outlet opening 47 of the overflow valve 40 through the end region of the fuel return line 46 into the fuel tank 32. The fuel return channel 54 forms a first overflow valve channel 54 because the fuel is discharged from the first outlet opening 47 of the overflow valve 40 through the fuel return channel 54.

[0072] A throttle ring 58 is arranged in the bore 41 concentrically and coaxially with the overflow valve 40 (Figs. 5 to 8). The throttle ring 58 is thus arranged in the radial direction with respect to a longitudinal axis 61 of the overflow valve 40 and the throttle ring 58 between the overflow valve 40 and the housing 8 on the bore 41. A completely circumferential annular groove 59 is formed in the throttle ring 58 on a radial outer side. One axial end of the throttle ring 58 rests on a step 62 of the bore 41, and the other axial end 60 of the throttle ring 58 partially delimits a Venturi section 57 of the overflow valve channel 55 (Fig. 8). The second outlet opening 48 of the overflow valve 40 opens into an annular space 55 as an overflow valve channel 55 between a radial inner side of the throttle ring 58 and the radial outer side of the housing of the overflow valve 40. This annular space 55 as an overflow valve channel 55 has only one opening as the Venturi section 57.The Venturi section.

[0073] 57 (Fig. 7 and 8) is from the upper axial end 60 of the throttle ring in Fig. 8

[0074] 58 and the housing 8 at the end of the fuel discharge channel 56 and has a significantly smaller flow cross-sectional area compared to the remaining overflow valve channel 55. The Venturi section 57 is elongated and slot-shaped in cross-section.

[0075] The annular groove 59 of the throttle ring 58 is aligned with the end of the channel 49 at the bore 41, so that the aligned portion of the annular groove 59 at the channel 49 forms an inlet opening 52 of the zero-feed channel 51. The annular groove 59 of the throttle ring 58 is aligned with the end of the fuel discharge channel 56 at the bore 41, so that the aligned portion of the annular groove 59 at the fuel discharge channel 49 forms an outlet opening 53 of the zero-feed channel 51. Outside the end of the channel 49 and the end of the fuel discharge channel 56, the annular groove 59 is covered by the housing 8 at the bore 41, so that the fuel flows in the annular groove 59 as the curved zero-feed channel 51 with a substantially constant radius of curvature in the flow direction of the fuel from the channel 49 into the fuel discharge channel 56 in order to introduce the leakage volume flow from the metering unit 35 into the fuel discharge channel 56.The volume flow of fuel flowing in through the inlet opening 52 is divided into a first partial volume flow, as shown in Fig. 6, to the left of the inlet opening 52, and a second partial volume flow, as shown in Fig. 6, to the right and below the inlet opening 52. The first and second partial volume flows, which flow through two separate sections of the annular groove 59, are introduced into the outlet opening 53. In the Venturi section 57 of the overflow valve channel 55, the flow cross-sectional area is greatly reduced, so that the pressure of the fuel flowing through the Venturi section 57 drops sharply, and this low pressure also partially occurs at the end of the fuel discharge channel 56 near the outlet opening 53 of the zero-feed channel 51.This prevents a backflow of fuel from the fuel discharge channel 56 through the zero-feed channel 51 into the fuel suction line 45 when the fuel pressure in the fuel discharge channel 56 is higher than in the fuel suction line 45. Fuel lines and fuel channels of the high-pressure injection system 14, excluding the high-pressure fuel line 45, form a low-pressure circuit 63 of the high-pressure injection system 14.

[0076] Overall, the zero-feed throttle 50 according to the invention and the high-pressure injection system 14 according to the invention offer significant advantages. The throttle ring 58 with the annular groove 59 forms the zero-feed throttle 50 in a simple structural manner due to its arrangement in the bore 41 of the housing 8. The throttle ring 58 is simple and inexpensive to manufacture, thus advantageously resulting in low costs for the manufacture of the zero-feed throttle 50 and the high-pressure injection system 14.

Claims

Claims 1. Zero-feed throttle (50) for the low-pressure circuit (63) of a high-pressure injection system (14) for an internal combustion engine, comprising - an inlet opening (52) for introducing fuel from the suction side of a high-pressure pump (1) into the zero-feed throttle (50), - an outlet opening (53) for discharging fuel from the zero-feed throttle (50), - a zero feed channel (51) for passing fuel and the zero feed channel (51) connects the inlet opening (52) to the outlet opening (53), characterized in that the zero feed channel (51) is curved in the flow direction of the fuel.

2. Zero-feed throttle according to claim 1, characterized in that the zero-feed channel (51) is formed at least partially, in particular completely, in an annular groove (59).

3. Zero-feed throttle according to claim 2, characterized in that the zero-feed throttle (50) comprises a throttle ring (58), preferably in the shape of a cylinder jacket, and the annular groove (59) is formed on the throttle ring (58), in particular on a radial outer side of the throttle ring (58).

4. Zero-feed throttle according to claim 3, characterized in that the zero-feed throttle (50) at least partially comprises an overflow valve channel (55) for passing fuel from an overflow valve (40) into the low-pressure circuit (63) of the high-pressure injection system (14).

5. Zero-feed throttle according to claim 4, characterized in that the overflow valve channel (55) has a different flow cross-sectional area and a Venturi section (57) of the overflow valve channel (55) is designed with a smaller flow cross-sectional area than outside the Venturi section (57) for a reduced pressure of the fuel flowing through the Venturi section (57).

6. Zero-feed throttle according to claim 5, characterized in that the Venturi section (57) of the overflow valve channel (55) is at least partially delimited by the throttle ring (58), in particular an axial end (60) of the throttle ring (58).

7. High-pressure injection system (14) for an internal combustion engine, comprising - a high-pressure pump (1), - a high-pressure rail (30), - an overflow valve (40), - a zero-feed throttle (50) with an inlet opening (52) for introducing fuel from the suction side of the high-pressure pump (1) into the zero-feed throttle (50), an outlet opening (53) for discharging Fuel from the zero-feed throttle (50) and with a zero-feed channel (51) for passing fuel and the zero-feed channel (51) connects the inlet opening (52) with the outlet opening (53), - an overflow valve channel (55) for conducting fuel from the overflow valve (40) into a low-pressure circuit (63) of the high-pressure injection system (14), wherein the overflow valve channel (55) has a different flow cross-sectional area and a Venturi section (57) of the overflow valve channel (55) is designed with a smaller flow cross-sectional area than outside the Venturi section (57) for a reduced pressure of the fuel flowing through the Venturi section (57) of the overflow valve channel (55), - a pre-feed pump (15), - a metering unit (35), characterized in that the zero feed channel (51) is curved in the flow direction of the fuel.

8. High-pressure injection system according to claim 7, characterized in that the zero-feed channel (51) is formed in an annular groove (59).

9. High-pressure injection system according to claim 8, characterized in that the zero-feed throttle (50) comprises a throttle ring (58), preferably in the shape of a cylinder jacket, and the annular groove (59) is formed on the throttle ring (58), in particular on a radial outer side of the throttle ring (58).

10. High-pressure injection system according to claim 9, characterized in that the cylinder jacket-shaped throttle ring (58) is arranged in a bore (41) of a housing (8) of at least one pump (1, 15) of the high-pressure injection system (14).

11. High-pressure injection system according to one or more of claims 7 to 10, characterized in that the zero-feed channel (51) is delimited by two different components (8, 58), in particular the zero-feed channel (51) is delimited by the, preferably cylinder-jacket-shaped, throttle ring (58) and the housing (8) of the at least one pump (1, 15) of the high-pressure injection system (14).

12. High-pressure injection system according to one or more of claims 9 to 11, characterized in that the Venturi section (57) of the overflow valve channel (55) is delimited by the throttle ring (58), in particular an axial end (60) of the throttle ring (58).

13. High-pressure injection system according to one or more of claims 7 to 12, characterized in that the Venturi section (57) of the overflow valve channel (55) is housing (8) of the at least one pump (1, 15) of the high-pressure injection system (14).

14. High-pressure injection system according to one or more of claims 7 to 13, characterized in that the zero-feed channel (51) of the zero-feed throttle (50) and the Venturi section (57) of the overflow valve channel (55) open into a common fuel discharge channel (56).

15. High-pressure injection system according to one or more of claims 7 to 14, characterized in that the overflow valve (40) comprises a first stage with a first discharge opening (47) and a second stage with a second discharge opening (48), and the second discharge opening (48) of the overflow valve (40) opens into the overflow valve channel (55) with the Venturi section (57).

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