WO1997022799A1

WO1997022799A1 - Fuel injection device for an internal combustion engine

Info

Publication number: WO1997022799A1
Application number: PCT/DE1996/001360
Authority: WO
Inventors: Christof Vogel; Christian Preussner
Original assignee: Robert Bosch Gmbh
Priority date: 1995-12-15
Filing date: 1996-07-24
Publication date: 1997-06-26
Also published as: DE19546851A1

Abstract

The present invention relates to a fuel injection device for an internal combustion engine with an injection valve (10) with a spinner (16) allocated to its outlet aperture (21), so that fuel particles in an injected stream of fuel emerge from the outlet aperture (12) with a peripheral velocity component, and with a fuel vaporiser allocated to the outlet aperture (12) of the injection valve (10). In order to obtain effective fuel vaporisation in the warming-up stage of the engine while preventing the fuel vaporiser (20) from hindering the injection of the fuel or its preparation when it is switched off during normal running, the fuel vaporiser takes the form of a vaporiser attachment (20), the heating area (22, 23) of which surrounds an injection chamber (19) in front of the outlet aperture (12) of the injection valve and thus radially restricts it, and the injection chamber (19) widens conically in the direction of injection of the stream of fuel.

Description

KRr \ FTSTOFF INJECTOR FOR A COMBUSTION ENGINE

The invention relates to a fuel injection device for an internal combustion engine according to the preamble of claim 1.

STATE OF THE ART

In the case of fuel injection devices, the use of fuel vaporizers has largely proven itself in order to extremely reduce the pollutant emissions after starting during the warm-up phase until the effective catalytic converter operation begins and in order to be able to comply with the exhaust gas limit values which will become ever stricter in the future.

Since fuel vaporizers have a relatively high power consumption, they are switched off during normal operation of the internal combustion engine as soon as the catalyst operation is effective uses and a pre-evaporation of the fuel is no longer required. In this way, an unnecessary load on the electrical system of a vehicle can be avoided.

In a known fuel injection device (DE 28 43 534 AI), an injection valve is assigned a heating element which surrounds an injection region in the form of a sleeve in front of the injection opening of the injection valve. The heating element has a frustoconical evaporator surface which tapers in the fuel jet direction. During operation, the fuel is sprayed off from the injection valve without swirl with a jet angle which ensures that the sprayed fuel hits the evaporator surface.

In another fuel injection device known from DE 28 43 534 A1, a heating element is arranged at a distance from the injection opening of an injection valve. An air nozzle opens into the spray area of the injection valve between the spray opening and the heating element. The heating element here has a honeycomb structure with a plurality of channels running parallel to one another in the longitudinal direction or a truncated cone-shaped structure which tapers in the direction of the fuel jet.

When this fuel injection device is in operation, the fuel is injected from the injection valve into the spray region with swirl and is additionally atomized by the air entering through the air nozzle. The atomized fuel then goes to the heating element, where it is heated and vaporized.

Such a honeycomb-shaped heating element or conically tapering in the spray direction in the spray region of the Injection valve, however, represents a relatively large obstacle to the sprayed-off fuel jet if it is not heated during normal engine operation, so that it disrupts the fuel preparation for the mixture formation in the unheated state.

Another fuel injection device is known from SAE article 930710, "Cold start performance of an automotive engine using prevaporized gasoline", in which an electrically heatable, tubular fuel evaporator is arranged in front of an injection valve. A first air nozzle opens radially into the spray region between the spray opening and the fuel evaporator in order to deflect the emerging fuel jet. Second air nozzles flow tangentially into the spray area in order to set the deflected fuel jet in rotation and thus to bring it into contact with the inner wall of the fuel evaporator.

If such a fuel evaporator is switched off during normal engine operation, the fuel jet emerging from the injection valve does pass through the tubular fuel evaporator if it is narrow enough. However, there is hardly any fuel preparation to improve the mixture formation.

A known injection valve (EP 0 057 407) has a swirl body upstream of the spray opening, which widens conically from its measuring cross-section to the spray-side end face of the injection valve, which gives the fuel to be sprayed a circumferential speed component. The escaping fuel is atomized and forms a cone-shaped or cone-shaped fuel jet, which due to the circumferential speed speed component is very wide. This very wide fuel jet leads, however, to a wall film in the intake pipe which increases the pollutant emissions when the internal combustion engine is cold.

In order to improve the atomization of fuel in this known fuel injection device, an air gap in the form of a gap is provided, which surrounds the spray opening. A conically tapering, essentially cone-shaped air jet emerges from the air nozzle, which has a swirl that opposes the circumferential velocity component of the emerging fuel jet

ADVANTAGES OF THE INVENTION

The fuel injection device according to the invention with the characterizing features of claim 1 has the advantage that the fuel metered by the injection valve evaporates partially or completely and thus prevents wall wetting in the intake manifold during the start and warm-up phase of an internal combustion engine, or at least reduces it as much, without the fuel evaporator designed as an evaporator attachment, when it is switched off, hindering the fuel preparation during normal operation. In this way, the emission of pollutants can be reduced in such a way that increasingly strict exhaust gas limit values can be maintained.

In particular, seen in the spray direction, there is no heating surface in the way of the fuel jet. Rather, to form the fuel film on the heating surfaces, centrifugal force exploited. This means that the fuel flow can be conducted over the heating surfaces almost unhindered even when the evaporator attachment is switched off.

A major advantage of the fuel injection device according to the invention is that the fuel metering and the fuel evaporation or fuel conditioning are independent of one another. The evaporator attachment can thus be optimized in accordance with the injection valve used in each case for the desired fuel evaporation or preparation, without this affecting the metering function of the injection valve.

The measures listed in the subclaims allow advantageous refinements and improvements to the fuel injection device specified in claim 1.

It is particularly advantageous if a spraying edge on the evaporator attachment is formed by a cylindrical inner surface, since this improves the spraying off of an unevaporated fuel film in such a way that good fuel processing for the mixture formation is achieved. Truncated-cone-shaped or trumpet-shaped heating surfaces offer a continuously increasing heating surface, which ensures good heat transfer to the fuel film, which becomes thinner with increasing distance from the injection valve, and thus ensures the desired fuel evaporation.

The use of PTC resistance heating elements makes it possible to keep the temperature of the heating surfaces at a value suitable for effective fuel evaporation in a simple manner without an own temperature control. DRAWING

Exemplary embodiments of the invention are shown in simplified form in the drawing and are explained in more detail in the following description. Show it:

1 shows a partially sectioned schematic illustration of a fuel injection device according to the invention,

2 shows a schematic section through another evaporator attachment for the fuel injection device according to the invention and

3 shows a schematic section through a further evaporator attachment for the fuel injection device according to the invention.

Corresponding parts in the various figures of the drawing are provided with the same reference numerals.

As shown in FIG. 1, a fuel injection device for an internal combustion engine has an injection valve 10 which, in the usual way, in its outlet-side end face 11 has an outlet opening 12 for fuel, which is associated with a valve seat 14 which cooperates with a valve needle 13. In order to give the fuel exiting through the outlet opening 12 a swirl, that is to say to give the fuel particles of the fuel flow a circumferential speed component, there is a receiving space 15 in which the fuel needle flows and which accommodates and guides the valve needle 13. in front of the valve seat 14, ie upstream there arranged, a swirl element 16, in which helical grooves are machined.

An insert with oblique bores can also be inserted into the receiving space 15 as the swirl element 15. It is also possible to form the swirl element 15 directly on the valve needle 13 or in the wall guiding the valve needle 13 in the region of the valve seat 14 in the form of grooves or webs.

On the end face 11 of the injection valve 10, an electrically heatable evaporator attachment 20 is arranged in front of the outlet opening 12 as a fuel evaporator, which circumferentially surrounds a spray region for fuel lying downstream in front of the outlet opening 12 and thus radially delimits a spray chamber 19.

The evaporator attachment 20, the electrical connections of which are not shown, comprises a heating element 21, to which a circular cylindrical heating surface 22 is assigned on the inside in the inlet area, to which a frustoconical heating surface 23 adjoins, which widens to the outlet area hm and up to a spraying edge 24 extends.

The injection valve 10 and the evaporator attachment 20 are to be designed in such a way that the fuel jet sprayed out of the injection valve 10 forms as thin a fuel film as possible on the heating surface 22, 23 which radially delimits the spray chamber 19 due to its circumferential speed component. The opening angle of the sprayed fuel jet and the swirl generated by the injection valve 10 and the shape of the heating surface 22, 23, that is to say the opening angle of the spray chamber 19 delimited by it, must therefore be in contact with one another. be fitted. Furthermore, the evaporator attachment 20 must be designed in such a way that there is a sufficiently large heating surface 22, 23 for the heat transfer to the fuel, which, however, does not slow down the fuel flow too much in the switched-off state, but only a desired narrowing of the angle for the opening angle of the sprayed fuel jet.

The largest possible heating area can be z. B. realize that the evaporator attachment 20 or its heating element 21 is designed as a cone with a subsequent tube.

2 shows, for example, another evaporator attachment 20 'for the fuel injection device according to the invention, which has a tubular heating element 21' with an inner circular cylindrical heating surface 22 which extends from the end face 11 to the spraying edge 24.

According to FIG. 3, in a further evaporator attachment 20 ", a heating element 21" which widens in the shape of a trumpet is provided, the expanding, inner heating surface 25 of which extends into the outlet area and merges into a circular-cylindrical inner surface 26 there. The circular cylindrical inner surface 26 has only a short axial length and ends in the spraying edge 24.

The evaporator attachment 20, 20 ', 20 "can be formed integrally with the injection valve 10. However, the evaporator attachment 20, 20', 20" is advantageously constructed as a separate assembly which is held on the injection valve 10. It is in particular possible to thermally isolate the evaporator attachment 20, 20 ′, 20 ″ from the injection valve 10, where by the operation of the injection valve 10 is not impaired when the evaporator attachment 20, 20 ', 20 "is switched on.

Instead of the illustrated one-piece heating elements 21, 21 ', 21 ", two- or multiple-divided heating elements can also be used. It is possible to subdivide the heating elements axially or circumferentially. In order to provide an undivided heating surface 22, 23; 22 or To create 25 for impinging fuel, a coating, for example a correspondingly shaped contact sleeve with good thermal conductivity, is to be provided.

The heating element 21 preferably consists of a PTC resistance material, that is to say of a resistance material with a positive temperature coefficient. However, it is also possible to use an NTC resistance material, that is to say a resistance material with negative temperature coefficients. In this case, it is advisable to provide external temperature control. The use of a heating element 21 made of an NTC resistance material is particularly advantageous if, due to different fuel throughputs, a temperature control for the heating element 21 is required anyway.

During operation of the internal combustion engine, the required amount of fuel is injected from the injection valve 10 into an essentially conical area, the opening angle of this area increasing with increasing distance from the outlet opening 12 as a result of the circumferential speed component of the injected fuel, if the injection chamber does not is radially limited. The spraying area for fuel is, however, limited radially to the spraying space 19 by the evaporator attachment 20, 20 'or 20 ", so that the individual fuel particles are directed towards the spraying chamber 19 Heating surface 22, 23; 22 and 25, respectively, and form a thin fuel film there, the individual particles of which are screw-shaped on the heating surface 22, 23; 22 or 25 to the spraying edge 24.

When the heating is switched on during the warm-up phase of the internal combustion engine, the fuel particles of the thin fuel film, which are spread over the heating surface 22, 23; 22 or 25 of the evaporator attachment 20, 20 'or 20 "move, heated and evaporate. Since the fuel particles lying directly on the heating surface 22, 23; 22 or 25 due to the swirl, ie because of the centrifugal force acting on them ¬ are pressed against the heating surface 22, 23; 22 or 25 and are exposed to a greater pressure than the fuel particles further inside in the fuel film, they are in good thermal contact with the heating element 21, 21 ', 21 "and ensure good Heat transfer to the fuel film, which gradually evaporates towards the center of the evaporator attachment 20, 20 ', 20 ".

Since the individual fuel particles are helical over the heating surface 22, 23; 22 or 25 move, there is a relatively long way on the heating surface 22, 23; 22 or 25 are available for heating the fuel. The portions of the fuel film that reach the spraying edge 24 of the evaporator attachment 20 without being evaporated are broken up into many small droplets by the centrifugal force when spraying and are thus well prepared for the mixture formation.

During normal continuous operation of the internal combustion engine, the heating element 21, 21 'or 21 "is switched off and the fuel film which forms on the heating surface 22, 23; 22 or 25 is practically no longer heated. The fuel film thus moves up to Spray edge 24 from which it is injected. The fuel film, like the unevaporated residual fuel when the evaporator attachment 20, 20 'or 20 "is switched on, is torn into many small droplets as a result of the centrifugal force, so that a good preparation for mixture formation is ensured.

When moving the fuel film over the unheated heating surface 22, 23; 22 and 25, part of its circumferential speed component is lost as a result of the friction, so that an opening angle for the cone-shaped spray region is obtained which is reduced compared to an injection valve 10 which produces a swirl without an evaporator attachment. However, the remaining swirl is sufficient for good fuel processing during normal continuous operation.

Claims

PATENT CLAIMS

1. Fuel injection device for an internal combustion engine with an injection valve, which has a swirl element assigned to its outlet opening, so that fuel particles of a sprayed-off fuel jet emerge from the outlet opening with a speed component in the circumferential direction, and with a fuel evaporator assigned to the outlet opening of the injection valve, characterized in that that the fuel evaporator is designed as an evaporator attachment (20, 20 ', 20 "), the heating surface (22, 23, 25) of which surrounds a spray chamber (19) in front of the outlet opening (12) of the injection valve (10) and limits it radially, that the spray chamber (19) is cylindrical in the spray direction of the fuel jet and / or widens.

2. Fuel injection device according to claim 1, characterized in that the tubular evaporator attachment (20 ') has a circular cylindrical heating surface (22) which extends from the outlet opening (12) of the injection valve (10) to an injection edge (24) extends.

3. A fuel injection device according to claim 1, characterized in that the evaporator attachment (20) has an adjacent cylindrical heating surface (22) to the outlet opening (12) of the injection valve (10), to which the heating surface in the spray direction connects a heating surface (23) which widens in the shape of a truncated cone.

Fuel injection device according to claim 1, characterized in that the evaporator attachment (20 ") has a trumpet-shaped heating surface (25) in the spray direction of the fuel jet, so that the spray chamber (19) expands increasingly in the spray direction of the fuel jet.

Fuel injection device according to Claim 3 or 4, characterized in that a cylindrical inner surface (26) adjoins the truncated or trumpet-shaped heating surface (23 or 25), which extends to an injection edge (24).

Fuel injection device according to Claim 5, characterized in that the cylindrical inner surface (26) is narrow in the spray direction of the fuel jet.

Fuel injection device according to one of the preceding claims, characterized in that the heating surfaces (22, 23, 25) on one or more heating elements (21, 21 ', 21) made of a PTC resistance material, ie of a resistance material with positive temperature coefficients ¬ th are formed.