WO1995025601A1

WO1995025601A1 - Fluid dosing and spraying device

Info

Publication number: WO1995025601A1
Application number: PCT/DE1995/000369
Authority: WO
Inventors: Randolf Mock; Andreas Kappel; Hans Meixner
Original assignee: Siemens Aktiengesellschaft
Priority date: 1994-03-22
Filing date: 1995-03-16
Publication date: 1995-09-28

Abstract

Several fuel spraying units arranged in a row in a housing are linked by a detachable connecting element (SV) to the corresponding dosing units (V) which determine the amount of fuel. Electronic elements (E) for controlling the spraying units are further arranged in the housing. This device allows fuel dosage to be regulated independently from spraying. Production costs of the electric connections are reduced.

Description

Device for metering and atomizing fluids

The invention relates to a device for metering and atomizing fuel for use in internal combustion engines.

From OS-DE 38 33 093 AI a fuel injector for a combustion engine with controllable characteristics of the fuel jet is known. A valve element is moved by means of a piezo element and acts on the nozzle of the fuel injection valve in an opening or closing manner. A fuel atomization is superimposed on this fuel metering. A second piezo element excites the nozzle to oscillate, which leads to accelerated jet decay. If a change in the decay characteristics of the fuel jet is to be brought about, a new injection valve with a modified nozzle must be built, since this cannot be separated from the metering unit. Furthermore, a change in the nozzle geometry has a direct effect on the metering quantity. Thus, two interdependent parameters have to be taken into account when choosing the geometry, which increases the requirements for the development of the nozzle enormously.

The object of the invention is to create a device in which the atomization of the fuel jet can be set independently of the fuel metering.

The object is achieved by a device according to patent claim 1.

A training designed according to claim 2 has the advantage of a ready-to-install installation unit.

The development according to claim 3 has the advantage that the atomizer units are encapsulated by dirt and liquids are and the electrical connection of the piezo elements with the control electronics can be made easily.

A development designed according to claim 4 has the advantage that the atomizer unit can actively influence the jet atomization.

A drive element chosen according to claim 5 is particularly well suited because of its short reaction time.

According to claim 6, it is advantageous to determine the flow rate by means of an orifice.

In order to achieve a simple detachable connection between metering unit and atomizer unit, the device can be developed according to claim 7. The invention is explained in more detail below with reference to the figures.

It shows:

FIG. 1 shows an injection module in cross section,

FIG. 2 shows the enlarged support plate of the atomizer unit,

FIG. 3 shows an assembly consisting of a plurality of metering units, a corresponding number of atomizing units and control electronics,

4a to 41 show a selection of possible nozzle plates with different nozzle holes,

FIG. 5 shows the jet decay in the case of a round nozzle hole compared to that in the case of a rectangular nozzle hole,

FIG. 6 shows a possible combination of different nozzle hole diameters in a nozzle plate, 7a to 7c the basic galvanoplastic production process for a nozzle plate,

Figure 8a, 8b a nozzle with a square nozzle hole in plan view and in cross section in the anisotropic

Etching process, and

9a, b show a conventional nozzle in comparison to several novel nozzles in plan view and in cross section.

The device, as shown in Fig ^• 1, is suitable for metering and atomizing fuel for internal combustion engines. A valve needle VN is movably mounted in a valve housing V. It can be driven by means of the mechanism described in patent application P 43 06 073.0. The fuel flows through a channel K in the direction of the sealing seat DS. If the valve needle VN presses on the sealing seat DS, the fuel flow is inhibited. If the valve needle VN is lifted from the sealing seat DS, the fuel flows out through the metering opening ZMO in the sealing seat DS, the atomizer opening ZSO in the nozzle plate DP and through the bore in the cover plate D. The screws provided in the threaded holes S press the cover plate D, the leaf spring BF and the earring OR against the carrier plate TP, which is supported on a piezo actuator P. The piezo actuator P is mounted in a housing G. The piezo actuator P is held under static pressure by the pressure exerted on the leaf spring BF and the carrier plates TP by the screw connection. A nozzle plate DP is embedded in the carrier plate TP. The path between the metering opening ZMO and nozzle plate DP should be kept as short as possible.

The carrier plate TP shown enlarged in FIG. 2 is drawn in cross section. The nozzle plate DP with its atomizer opening ZSO is arranged on its outside. Each the smaller the height h of the carrier plate TP can be kept, the smaller the dead volume.

For ease of installation, it is advantageous to combine several measuring units with a corresponding number of atomizing units in a common housing (FIG. 3). The atomizer units are arranged on the mounting plate MP. The control electronics E are also located there in connection with the contact pins KS. Since the piezo actuators P are freely accessible, the electrical connections V between the control electronics E and the piezo actuators P can be easily established. The plug otherwise required for each atomizer unit can thus be omitted. Only a single plug with the KS contact pins is required to control the electronics E and thus all atomizer units. The electronics are supplied via the on-board voltage network. The control signal ST is used to control the electronics and thus the piezo actuators P. The piezo actuators are supported on the housing cover GD. In addition, threaded holes are provided in the housing cover GD, so that the metering units can each be detachably connected to the atomizing units by means of a screw connection SV. This means that a complete range of injection modules is available.

FIG. 4 shows a thin sheet metal membrane DP (orifice disk), also referred to as a nozzle plate or atomizing plate, which has a circular opening ZSO in the center with a very narrowly tolerated geometry and is arranged on the outside of the carrier plate TP. The hole diameter d of the metering opening ZSO has a tolerance in the range of 1 μm and a precisely defined corner rounding of the hole edge. The membrane DP with the atomizer opening ZSO is placed on a carrier plate TP. The nozzle plate DP can be connected to the carrier plate TP by welding, for example. This rests on a drive element P, a piezoceramic. If a periodic voltage, for example a sinusoidal voltage, is applied to the piezoceramic P, the carrier plate TP and the membrane DP are forced to oscillate, ie not resonantly. According to a theory developed by Lord Rayleigh of the vibration-induced generation of liquid droplets, this forced movement of the membrane DP leads to the decay of the fuel jet into small drops. In the case of the arrangement according to FIG. 1, the optimal excitation frequency is approximately 5 kHz, but an effective excitation of the nozzle plate DP for jet decay can also be achieved with other frequencies.

The membrane DP can be shaped in the form of a dome in the manufacture to determine the radiation direction.

The invention relates in particular to a low-pressure injection with approximately 1 to 10 bar.

The field of application of the invention is not limited to the metering and atomization of fuel for internal combustion engines, but can be used wherever a fluid has to be metered exactly and the possibility of atomization must be given.

The excitation frequency F of the control signal, with which the piezo element P is driven and which in turn sets the atomizing plate ZP in vibration, is to be matched to the atomizing hole diameter d of the atomizing plate DP. The higher the excitation frequency F, the smaller the depth of penetration into the liquid. The following relationship results between the excitation frequency F and the atomizer hole diameter d:

F ² With d = diameter of the nozzle hole and F = excitation frequency of the piezoelectric element, which sets the nozzle hole ZSO or the nozzle plate DP in vibration.

FIGS. 4a-1 show various nozzle plates DP which are suitable for supporting the jet decay. The nozzle plate DP, as shown in FIG. 4a, has several round openings, the diameter d of which is less than 10 μm. In the nozzle plates DP, as shown in Figures 4a to 1, the aspect ratio is approximately 1.5 to 5, i.e. the length of the nozzle hole D ^ (FIG. 9) is many times larger than the nozzle hole diameter d. Further particularly suitable hole shapes are shown in FIGS. 4g and 41. The nozzle plate holes can have almost any shape. The asymmetry of the flow and surface tension forces induced in the case of a non-circular cross-sectional area of the emerging fuel jet leads, as shown in FIG. 5, to an increase in the periodic swellings of the jet cross-section, as a result of which the accelerated decay of the liquid into very small amounts Drop is caused. In the case of laminar nozzle flow, the following relationships apply in a first approximation between the drop distance λ, the drop diameter Dp and the nozzle hole diameter d (in the case of a non-circular nozzle cross-sectional area, the replacement diameter of one of the nozzle cross-sectional areas is equivalent to the equivalent circular nozzle instead of the nozzle hole diameter d use):

λ = 4.5 • d D _τ s 1.9 • d

In contrast to the almost constant droplet size in a laminal flow, turbulent flow processes lead to a characteristic droplet size distribution, ie in addition to the frequent occurrence of an average droplet size, considerable proportions of small and large-volume droplets are also contained in the aerosol. This often used for atomization The effect can be enhanced by particularly extreme cross-sectional profiles with sharp tips and edges, as shown in FIG. 4f, g, h, i, j, k, 1. In this case, the nozzles function as turbulators.

As shown in FIG. 5, a nozzle cross-sectional shape that deviates from the circular shape causes the liquid jet to disintegrate into individual drops earlier. The liquid emerging from a round nozzle hole disintegrates into individual drops at a distance l_, whereas a liquid passing through a rectangular cross-sectional shape already disintegrates into individual drops at a distance I2, I2 <I3 _. ,

In addition to the shape of the nozzle hole, the arrangement and size of the nozzle holes on the nozzle plate can also be changed within wide limits, as shown in FIG. 6. The nozzle plate DP has a large nozzle hole in the center, which is surrounded by many small nozzle holes in the shape of a hexagon. By combining different nozzle hole sizes, nozzle hole shapes and the nozzle hole arrangement on a nozzle plate DP, the jet properties can be adapted to the different requirements. This makes it easier to cover different operating conditions of the engine, since on the one hand the fine aerosol jacket creates a homogeneous fuel / air mixture, which means that the wall wetting and pollutant emissions are reduced during a cold start and on the other hand good filling when the engine is warm ( Power output) can be achieved by the compact central beam. In addition, the risk of clogging of the nozzle is reduced.

Such nozzle plates DP can be manufactured using the galvanoplastic process using Siemens microstructure technology (MS). As shown in FIGS. 7a-c, in the case of Siemens microstructure technology, a negative resist NR laminated onto a substrate S is formed by a very thin mask M which was previously connected to the substrate S by photostructuring irradiated with UV light UVL. Synchrotron radiation can also be used to expose the photoresist. The unexposed portion of the photo layer is then washed out in the developer. The former mask M can be galvanically reinforced at the exposed points, the photoresist (negative resist) NR can be molded to almost its full height and the additively produced metal layer GP can be chemically or mechanically separated from NI, CU, AU or AG as the desired flat part . With special exposure techniques and photoresists, the creation of double nozzles is also possible

Inlet and two nozzle outlets, inclined nozzles and nozzles with conical or exponential inlet funnels possible. This is described in Trausch Günter: "Novel photolithographic structure generation for the production of precision flat parts in the electroplating process", Siemens Research and Development Report Volume 8, 1979, No. 6. Figure 7c shows the finished electroplating GP in cross section.

Another possibility for producing the nozzle plates DP is to use the anisotropic etching technique. The etching rate, which varies greatly according to the crystallographic orientation, is used for certain single-crystal materials, such as silicon and gallium, in certain etching solutions, such as EDP (ethylenediamine) or KOH. For this purpose, as shown in FIG. 8, for example a (100) oriented Si substrate is first provided with an etching stop layer on both sides, for example in the form of SiO 2 or Si 3 4, into which one-sided square openings of length Wg are etched, the edges of the exposed ones Areas must be aligned parallel to the crystallographic (110) directions of the substrate. In the subsequent self-stopping wet etching process in EDP or KOH, pyramid-shaped depressions with (101) oriented side walls are formed at an inclination of φ = 54.74 °. If the etching window Wg is suitably dimensioned, square openings with an edge length WQ of

where tgi is the thickness of the Si substrate. The nozzles are finally exposed by etching off the SiO 2 or Si3N4 etch stop layer. The production of rectangular nozzle cross-sectional shapes is also possible using this method.

FIG. 9a, b shows a comparison of a conventional nozzle in the top view and in cross section (FIG. 9a) in comparison to several hexagonal arranged nozzles as described in the previous one (FIG. 9b). Previously usual nozzle hole diameters d were in the range from approx. D = 0.3 mm to d = 0.6 mm with typical thicknesses of the nozzle plate DP of approx. Dj_.p = 0.05 to 0.15 mm. As an aspect ratio, this results in approximately η = 1.5 - 5. With the help of photostructuring techniques in conjunction with galvanic impression techniques or anisotropic etching techniques, nozzle holes with aspect ratios of η> 0.5 can be produced, cf. Figure 9b. When using synchrotron radiation to coat the photoresist, even aspect ratios η> 100 are possible. The

Nozzle hole diameter d of each nozzle is approx. 20 μm. The thickness of the nozzle plate DP is approximately D ^ p = 100 μm.

Claims

claims

1. Device for metering and atomizing fluid,

- in which a metering unit is provided,

- in which an atomizer unit is provided, - in which the atomizer unit has a nozzle plate (DP) and a drive element (P) which can set the nozzle plate (DP) in vibration,

- In which the metering unit is detachably connected to the atomizer unit.

2. Device according to claim 1, in which a carrier plate (TP) is provided which connects the nozzle plate (DP) with the drive element (P).

3. Device according to claim 1 or 2, wherein the drive element (P) is a piezo element.

4. The device according to claim 1, 2 or 3, wherein the nozzle plate (DP) has at least one hole with an aspect ratio η> 0.5.

5. The device according to claim 4, wherein the shape of the hole is round, oval, triangular, square, polygonal or star-shaped.

6. Device according to one of claims 1-5, wherein the metering unit has a flow-determining metering opening (ZMO) and a closing element (VN) which selectively closes or opens the metering opening (ZMO).

7. Device according to one of claims 1-6, wherein the connection between the metering unit and the atomizer unit is designed as a screw connection.

8. Device according to one of claims 1-7, for fuel metering and atomization for internal combustion engines.