JP2010521605A - Fuel injector for internal combustion engine - Google Patents

Abstract

A fuel injector comprising an injector body (10) having a spray aperture (12); a pintle (14) extending within the injector body for axial movement between a closed position and an open position; said pintle head (16) comprising a tapered portion (18) engageable against the valve seat of the spray aperture and a cylindrical portion (22) upstream of said tapered portion, an annular channel (26) being provided defining a first part of a flow passage upstream of the spray aperture (12), wherein a discontinuity (30, 50) is provided downstream of the annular channel (26) and upstream of the spray aperture to generate cavitation when the pintle stroke exceeds a predetermined limit to thereby generate a virtual channel of constant cross section downstream of the annular channel (26) whereby the flow rate of the fuel flowing through said spray aperture is substantially independent of the stroke of the pintle when the pintle is in its open position.

Description

  The present invention relates to a fuel injector, and more particularly to a fuel injector for directly injecting gasoline into a combustion chamber of an internal combustion engine.

  The exemplary outwardly open fuel injector shown in FIG. 1 includes a valve body having a tip portion 2 defining a spray hole 3 and a shaft within the tip portion 2 between an extended position and a retracted position. A pintle 4 or valve stem extending to move in a direction, with a tapered portion 6 that can engage the valve seat 8 of the spray hole 3 to close the spray hole when in the retracted position A pintle 4, a return spring (not shown) for urging the pintle 4 toward its retracted position, and an actuating means (not shown) such as a solenoid or a piezoelectric stack, And operating means that acts on the pintle 4 to push the pintle 4 to its extended position when electric power is supplied.

Particularly in the case of solenoid operated injectors, the pintle opening is usually limited by an end stop which is one upper surface of the guide.
The flow rate of fuel through the injector is highly dependent on the gap between the pintle head and the valve seat, which gap is determined by the pintle stroke. In a typical fuel injector having a pintle stroke between 30 μm and 40 μm and a fuel supply pressure of 200 bar, the flow rate varies by 3% for every 1 micron change in pintle stroke. As such, the sensitivity to variations in pintle stroke is high, and manufacturing tolerances for end stops, pintles, and associated components must be very tight to achieve the required flow rates. Further, over time, pintle strokes fluctuating due to wear and / or differential thermal expansion can cause undesirable fluctuations in fuel flow.

  According to the present invention, a fuel injector is provided, the fuel injector having an atomizing hole; for moving axially within the injector body between a closed position and an open position. An extending pintle, in the closed position, the pintle head engages the valve seat of the spray hole to seal the spray hole, and in the open position, the pintle head is spaced from the valve seat; A pintle, wherein fuel is allowed to flow through the spray hole, and the actuating means is provided for selectively moving the pintle toward its open position; The pintle head includes a tapered portion that can be pressed and engaged with the valve seat of the spray hole, and a cylindrical portion that is upstream of the tapered portion, and is provided with an annular channel. Upstream A first portion of the flow path is defined, the discontinuity is provided downstream of the annular channel and upstream of the spray hole, and cavitation occurs when the stroke of the pintle exceeds a predetermined limit. A virtual channel is created downstream of the annular channel so that the flow rate of fuel flowing through the spray hole is substantially unaffected by the pintle stroke when the pintle is in its open position. It is like that.

Desirably, the annular channel is defined between a substantially cylindrical portion of the pintle and a concentric portion of the injector body.
The discontinuity may be provided between the cylindrical portion and the tapered portion of the pintle head. Alternatively, the discontinuity may be provided between the concentric part of the injector body and the valve seat. The discontinuity may comprise a chamfered or stepped surface, or may comprise any other suitable structure that serves to draw the flow away from the surface of the annular channel.

  By providing a discontinuity between the cylindrical portion and the tapered portion of the pintle head, a virtual channel with a constant cross section is created between the tapered portion and the valve seat, which is substantially unaffected by the pintle stroke. Since a flow rate is provided, flow deceleration due to stroke variation is prevented and energy loss can be avoided downstream of the annular channel. By generating fuel cavitation upstream of the tapered portion of the pintle head, the maximum flow rate through the spray holes can be substantially unaffected by the maximum pintle stroke. The maximum required flow rate should be calibrated for a particular application by appropriate selection of discontinuities, the gap between the cylindrical part between the pintle head and the valve body, and the relative dimensions of the stroke. Can do.

  Fuel is sent to a first portion of the flow path between the cylindrical portion of the pintle head and the valve body where it is accelerated. The liquid fuel flow leaves the valve body at a discontinuity, creating a low pressure region where the fuel cavitates (ie, the liquid fuel becomes vapor because the local pressure is below the vapor pressure of the fuel). Since cavitation occurs within the flow area that is affected by the pintle stroke, the cavitation zone is self-adjusting and becomes larger as the pintle stroke increases and maintains a constant effective flow area for liquid fuel. Pressure is not restored and fuel flow does not slow down.

  In contrast, in a typical injector nozzle having a cylindrical metering region upstream of the tapered seal portion, the flow area of the seal zone increases as the pintle stroke increases, thus reducing the flow rate and losing energy. This affects the atomization. In the present invention, a self-regulating cavitation bubble is created downstream of the cylindrical portion to create a virtual channel of constant cross section, avoiding fuel flow deceleration and avoiding such energy loss.

  The present invention further provides a method of manufacturing a fuel injector, the fuel injector including an injector body having spray holes; and axially within the injector body between a closed position and an open position. A pintle that is extended to move in the closed position, in the closed position the pintle head engages the valve seat in the spray hole to seal the spray hole and in the open position the pintle head is spaced from the valve seat. The pintle head can be pressed against and engaged with the valve seat of the spray hole, and the tapered part. A pintle comprising an upstream cylindrical portion, the method comprising providing an annular channel defining a first portion of the flow path upstream of the spray hole; and downstream of the annular channel And spray A discontinuity is provided upstream of the pintle so that cavitation occurs when the pintle stroke exceeds a predetermined limit so that a virtual channel of constant cross-section is created downstream of the annular channel, thereby passing through the spray hole. A discontinuous portion is provided so that the flow rate of the flowing fuel is substantially unaffected by the pintle stroke when the pintle is in its open position.

  Conveniently, the relative dimensions of the annular channel, the discontinuity, and the gap between the valve seat and the tapered portion of the pintle head when the pintle is in the fully open position causes the cavitation downstream of the annular channel. To occur, it is selected as a function of one or more physical characteristics of the injected fuel. One or more physical properties of the fuel include one or more of fuel vapor pressure, density, and fuel viscosity.

Figure 2 shows a known injector nozzle as discussed above. 1 shows an injector nozzle of a fuel injector according to a first embodiment of the invention. 3 is a graph of flow rate versus stroke of the known injector of FIG. 1 and the injector nozzle of FIG. FIG. 3 is a detailed cross-sectional view of the injector nozzle of FIG. 2 showing a cavitation zone in the flow of fuel through the nozzle. 7 shows an injector nozzle of a fuel injector according to a second embodiment of the invention.

Certain aspects of the invention will now be described, by way of example, with reference to the accompanying drawings in which:
The fuel injector nozzle has two functions:
1 to feed the correct amount of fuel into the combustion chamber (metering), and 2 to create a spray suitable for combustion.

With known injectors, the dependence of the static flow rate (i.e. the flow rate when the injector is fully open) on the injector stroke is very high.
In known fuel injectors, the flow rate variation is 1 g / s (nominal value 3.3%) per 1 μm stroke. To ensure reliable operation and avoid excessive fuel flow variations caused by manufacturing tolerances, thermal effects and maximum pintle stroke variations due to valve wear, the injector specifications A flow rate variation of 2% or less per 1 μm lift is required. The current nozzle design (FIG. 1) does not meet such requirements, the metering flow area is directly linked to the injector stroke, and the variation is 3.4% per 1 μm stroke variation. .

  The present invention generates cavitation upstream of the tapered portion of the pintle head, creating a constant flow virtual flow channel between the pintle head and the valve seat to prevent fuel flow through the injector nozzle from changing By doing so, the objective of improving weighing accuracy and maintaining good spray characteristics is realized.

  As shown in FIG. 2, the fuel injector includes an injector body including a tip portion 10 having a spray hole 12 at a distal end. The pintle 14 extends in the distal end portion 10, and the head 16 is provided with a tapered seal portion 18, and the seal portion is engaged with a corresponding tapered valve seat 20 surrounding the spray hole 12. When combined, the spray hole 12 can be closed.

  The pintle 14 has a retracted position in which the region of the tapered seal portion 18 of the head 16 engages with the valve seat 20 to close the spray hole 12 in the tip portion 10, and the tapered seal portion 18 of the head 16 has the valve seat 20. It is possible to move in the axial direction between the extended positions arranged at a distance from each other. In order to urge the pintle 14 to its retracted position, a return spring is generally provided.

  In general, an end stop (not shown) defined by the upper end of the tubular sleeve or pintle guide cooperates with the collar of the pintle 14 to limit pintle extension and define the pintle stroke.

A solenoid actuator (not shown) having an electromagnetic coil and a movable armature may be provided to selectively push the pintle 14 to its extended position.
A cylindrical portion 22 is provided upstream of the tapered seal portion 18 of the head 16 of the pintle 14, which cooperates with the concentric inner wall region 24 of the tip portion 10 to fully open the pintle 14. When in position, an annular flow channel 26 is defined between the pintle head 16 and the wall region 24 for accelerating and flowing fuel flow. A discontinuity is formed at the downstream end of the annular flow channel 26 so that the fuel flow is pulled away from the channel walls and cavitation occurs. In the illustrated embodiment, this discontinuity is defined upstream of the valve seat 20 by the chamfered surface 30 of the wall region 24 of the tip portion 10. However, a step or any other shape may be used as long as the flow can be separated to generate cavitation, and the discontinuity is one of the pintle head and the tip of the injector body. Or you may form in both.

  The chamfered surface 30 creates a cavitation zone 40 (FIG. 4) when the pintle stroke exceeds the critical stroke value, causing the fuel to move away from the chamfered edge and create a low pressure region where the liquid fuel evaporates. This has the following two positive effects.

  1. As the pintle stroke increases, the size of the cavitation zone 40 increases so that once the stroke exceeds a critical value, the flow rate through the valve seat remains constant.

  2. Because of the cavitation zone 40, the flow does not slow down downstream of the annular gap. This is important because as the pintle stroke increases, the flow area between the tapered pintle head and the valve seat increases and usually the flow velocity decreases. By providing the cavitation zone 40, the flow area is partially filled with liquid fuel and partially filled with fuel vapor having a much lower density than the liquid fuel. Since the cavitation zone 40 grows as the pintle stroke increases, the flow area occupied by the liquid fuel is substantially constant and the flow velocity remains substantially constant. This allows fuel flow to be metered with minimal energy loss (energy loss only occurs in the gap).

  Although the chamfered surface is described as generating the cavitation zone 40, it is contemplated that other shaped shapes may be used downstream of the gap to create the cavitation zone. For example, the cavitation zone may be formed on the outer shape of the pintle head or valve seat with a step 50 (FIG. 5) or other discontinuous portions. Considering the very small dimensions and tolerances of the tip 10 of the injector body, the step 50 is easy to manufacture.

  FIG. 3 shows an improvement regarding the dependence of flow rate versus stroke variation. In existing nozzle designs, the flow rate increases linearly with stroke, whereas in the proposal according to the invention, there is a stroke value (critical stroke) at which the flow rate is almost unaffected by the stroke when the stroke exceeds a certain value. The required maximum flow rate can be calibrated for a specific application by appropriately selecting the discontinuities, the gap between the cylindrical part between the pintle head and the valve body, and the relative dimensions of the stroke, These dimensions can also vary depending on customer requirements.

  In conclusion, with the proposed nozzle design, the static flow rate is less sensitive to stroke variations (flow rate variation per micron <2%), and the nominal static flow rate does not affect the spray characteristics. By changing the relative dimensions, adjustments can be made based on customer requirements.

  The method of manufacturing the fuel injector includes providing an annular channel 26 defining a first portion of the flow path upstream of the spray hole 12, and a discontinuity 30 downstream of the annular channel 26 and upstream of the spray hole. 50 so that cavitation occurs when the pintle stroke exceeds a predetermined limit so that a constant cross-section virtual channel is created downstream of the annular channel 26, thereby allowing the fuel flowing through the spray hole to flow. Providing a discontinuity that causes the flow rate to be substantially unaffected by the pintle stroke when the pintle is in its open position.

  Conveniently, the relative dimensions of the annular channel 26, the discontinuities 30, 50 and the gap between the valve seat and the tapered portion of the pintle head when the pintle is in its fully open position are To cause the cavitation downstream, it is selected as a function of one or more physical characteristics of the injected fuel. One or more physical properties of the fuel include one or more of fuel vapor pressure, density, and fuel viscosity.

  It will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments described with respect to the present invention without departing from the scope of the invention as defined in the claims. Although the invention has been described in connection with specific preferred embodiments, it is to be understood that the claimed invention is not unduly limited to such specific embodiments.

DESCRIPTION OF SYMBOLS 10 Injector main body 12 Spray hole 14 Pintle 16 Pintle head 18 Tapered part of pintle head 20 Valve seat 22 Cylindrical part of pintle head 24 Concentric part of injector main body 26 Annular channel 30, 50 Discontinuous part

Claims (9)

An injector body (10) having a spray hole (12); a pintle (14) extending in the injector body for axial movement between a closed position and an open position, wherein the closed In the position, the pintle head (16) engages the valve seat (20) of the spray hole to seal the spray hole, and in the open position, the pintle head is spaced from the valve seat. A pintle (14), wherein fuel is allowed to flow through the spray hole and actuating means are provided for selectively moving the pintle toward its open position; The pintle head (16) includes a tapered portion (18) that can be pressed against and engaged with the valve seat of the spray hole, and a circle upstream of the tapered portion. And an annular channel (26) that defines a first portion of the flow path upstream of the spray hole (12), and a discontinuity (30, 50). ) Is provided downstream of the annular channel (26) and upstream of the spray hole, and cavitation occurs when the stroke of the pintle exceeds a predetermined limit. 26) so that the flow rate of fuel flowing through the spray hole is substantially unaffected by the stroke of the pintle when the pintle is in its open position. Has become a fuel injector. The fuel injector of claim 1, wherein the annular channel (26) is defined between a substantially cylindrical portion (22) of the pintle and a concentric portion (24) of the injector body. . The fuel injector according to claim 2, wherein the discontinuity is provided between the cylindrical portion (22) and the tapered portion (18) of the pintle head (16). The fuel injector according to claim 2, wherein the discontinuity (30) is provided between the concentric part (24) of the injector body and the valve seat (20). A fuel injector according to any preceding claim, wherein the discontinuity (30) comprises a chamfered surface. A fuel injector according to any preceding claim, wherein the discontinuity (50) comprises a stepped surface. In a method for manufacturing a fuel injector, the fuel injector moves in an axial direction between a closed position and an open position in an injector body (10) having a spray hole (12); A pintle (14) extending in the closed position, wherein the pintle head (16) engages the valve seat (20) of the spray hole to seal the spray hole and the open position. The pintle head is disposed at a distance from the valve seat so that fuel can flow through the spray hole, and the pintle head (16) is connected to the valve seat of the spray hole. A pintle (14) comprising a tapered portion (18) that can be pressed into engagement with and a cylindrical portion (22) upstream of the tapered portion, the method comprising: ,in front Providing an annular channel (26) defining a first portion of the flow path upstream of the spray hole (12); and discontinuities (30, 50) downstream of the annular channel (26) and upstream of the spray hole. ) To cause cavitation when the pintle stroke exceeds a predetermined limit, so that a virtual channel of constant cross section is created downstream of the annular channel (26), thereby passing through the spray hole. Providing a discontinuity so that the flow rate of the flowing fuel is substantially unaffected by the stroke of the pintle when the pintle is in its open position. The relative dimensions of the annular channel (26), the discontinuities (30, 50), and the gap between the valve seat and the tapered portion of the pintle head when the pintle is in the fully open position are: The method of claim 7, wherein the method is selected as a function of one or more physical characteristics of the injected fuel to cause the cavitation downstream of the annular channel. The method of claim 8, wherein the one or more physical characteristics of the fuel include one or more of fuel vapor pressure, density, and fuel viscosity.

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