GB2037403A - Fuel metering valve for a fuel injection system - Google Patents

Abstract

The valve has a piston valve (3) mounted within a piston valve cylinder (4) by two spaced apart bearing regions (13, 14) so that the piston valve (3), can rotate and/or move axially relative to the piston valve cylinder (4) under the control of an air quantity measuring device. Fuel under pressure is introduced in the cylinder space between the bearing regions (13, 14) and low pressure prevails outside the bearing regions. The bearing regions (13, 14) of piston valve (3) are provided with circumferentially disposed grooves (27). The pressurised fuel migrates into those grooves (27) and tend to equalise the pressure on the circumferential surfaces of the bearing regions (13, 14) so that the piston (3) does not tend to adopt an eccentric attitude and bear against the side wall of the cylinder (4). <IMAGE>

Description

SPECIFICATION Fuel metering valve for a fuel injection system In one type of fuel metering valve of a fuel injection system the piston valve is made to move relative to the piston valve cylinder by a measuring device which is located in the intake pipe and moves so as to meter accurately a quantity of fuel which is in a certain ratio to the quantity of air flowing through the intake pipe of the engine. This movement varies the throttle cross-section defined by a control or guide edge which is located on the piston valve moving past a passthrough aperture in the piston valve cylinder, and via which throttle cross-section the metered fuel passes to the injection nozzle.In order alwavs to obtain exact metering of the fuel under all operating conditions, but more especially with throttle positions of the metering valve with a small or minimum flow cross-section, the piston valve is movably fitted to the piston valve cylinderwith very high precision and surface finish, whereby an exceptionally narrow gap is formed at its bearing or support regions in the piston valve cylinder, Although the piston valve is surrounded by å film of fuel at its support regions, which are designed to fit exactly in the piston valve cylinder, it has been shown that the piston valve has its support regions seated eccentrically in relation to the inside wall of the piston valve cylinder as a result of its temporary state seating in the piston valve cylinder owing to marginal conditions, such as, for example, interfence or influence of the measuring device, or dimensional variations in permitted manufacturing tolerances. In the event of a predetermined fall in pressure in the fuel which is introduced under pressure between the support regions as compared with the area outside the support regions, a variable reduction in pressure occurs, however, via the eccentric seating. This variable reduction in pressure inside the support regions leads to a lateral force which presses the piston valve against the inside wall of the piston valve cylinder in such a way that a frictional moment, occurring as a result of this, considerably impairs the relative movement between the piston valve and the piston valve cylinder.The metering error in the fuel metering valve caused by the greater friction have a disadvantageous effect, especially during idling and in the lower partial load range, and eventually lead to an increase in detrimental ingredients in the exhaust gas.

It is therefore an object of the invention to produce a fuel metering valve wherein the disadvantages which have been described above are reduced or eliminated to ensure good metering accuracy of the fuel in all running conditions.

Accordingly, this invention provides a fuel metering valve for a fuel injection system of a mixture-compressing spark-ignition internal combustion engine with continuous injection, which valve has a piston valve which is mounted in a piston valve cylinder by two cylindrical bearing regions spaced from each other and which is rotatable and/or axially displaceable relative to the piston valve cylinder by an air quantity measuring device wherein an inlet for pressurised fuel into the cylinder space between the bearing regions is provided and wherein circumferentially disposed grooves are provided on the circumferential surfaces of the bearing regions of the piston valve.

As a result of the arrangement of grooves which is proposed, an equalization of pressure between the piston valve and the piston valve cylinder takes place over the entire circumferential surface of the support regions, as a result of which a unilateral placing of the piston valve against the piston valve cylinder can be avoided and the frictional moment is considerably reduced, so that accurate fuel metering becomes possible.

The invention may be performed in various ways and preferred embodiments thereof will now be described with reference to the accompanying drawings, in which: Figure lisa diagrammatic sectional illustration of a first embodiment of a fuel metering valve and air measuring device of a fuel injection system, Figure 2 is a longitudinal section through the fuel metering valve of Figure 1 showing a piston valve and a piston valve cylinder on an enlarged scale, together with diagrams from which the variation of the pressure at the support regions can be seen; Figure 3 shows a cross-section through one support region on line Ill-Ill in Figure 2;; Figure 4 shows a longitudinal section through the fuel metering valve of Figure 2, modified in accordance with the invention, Figure 5 shows a cross-section through one support region on line V-V in Figure 4, Figure 6 is a diagrammatic sectional illustration of a second embodiment of a fuel metering valve of an air measuring device of a fuel injection system; and Figure 7 is a longitudinal section on an enlarged scale through the fuel metering valve of Figure 6 as modified in accordance with the inventiqn.

Figure 1 illustrates a fuel metering valve 1 of a fuel injection system, which valve is located on an intake pipe 2 of a mixture-compressing internal combustion engine which is not shown. This fuel metering valve 1 essentially comprises a piston valve 3, which is rotatably mounted in the cylinder space of a piston valve cylinder 4, which in turn is tightly and firmly inserted in a corresponding bore in a housing 5 and also in a lateral shoulder 6 of the intake pipe 2. The top of the housing 5 is closed by a cover 7, which is connected to the intake pipe 2 by screws 8 which are indicated by dashed lines. The intake pipe 2 contains a measuring device 9, which is designed as a baffle plate and can be swivelled according to the quantity of air flowing through.An extension 10 of the device 9 extends into the lateral shoulder 6 of the intake pipe 2 to provide a lateral seating for the device 9. The extension 10 has a bore 11, into which the bottom end 12 of the piston valve 3 projects from the piston valve cylinder 4. This end 1 2 serves as an actuating pin and consequently forms a non-rotating connection for the measuring device 9. The rotatable seating of the piston valve 3 is formed from a bottom support region 13 and an upper support region 14, whilst these support regions within the piston valve cylinder 4 provide at the same time the swivellable seating of the measuring device 9.The axial seating of the piston valve 3 and the measuring device 9 connected to the latter is effected by means of an axial ball-bearing 1 5, which is located between the top end of the piston valve cylinder 4 and a disc 16 which at the top end 17 is rigidly connected to the piston valve 3 by a screw 1 8. The upper front face of the piston valve cylinder 4 which forms the track of the ballbearing 1 5, and the lower front face of the disc 1 6 are suitably tempered.

The piston valve 3 carries between its two support regions 13 and 14 a helically grooved portion 19, which forms a control edge 20 with the outer wall of the piston valve. The groove 1 9 is in communication, via an annular groove 21, with a fuel inflow port 22, and via an annular groove 23 is in communication with a return port 24. In the inside wall of the piston valve cylinder 4 are provided flow orifices 25, the number of which corresponds to the number of injection nozzles. In this exemplified embodiment, however, only two orifices 25 are illustrated. The flow orifices 25 cooperate with the control edge 20 which runs spirally round the piston valve 3 and in each case constitute a variable throttle cross-section.To each flow orifice 25 there connects an oufflow port 26, each of which is connected to an injection nozzle via a diaphragm valve which is not shown.

The fuel being metered, in the case of this arrangement, is conveyed under pressure by a pump from a fuel tank (not shown) through the inflow port 22 and the annular groove 21 into the grove 19 of the piston valve 3. The quantity of air flowihg through the intake pipe 2, determines the rotation of the piston valve 3 by the measuring device 9 to which it is connected via the actuating pin 12, whereby a small or larger throttle is defined by the control edge 20 of the groove relative to the flow orifices 25, and an appropriate quantity of fuel is delivered via the flow orifices 25 and the outflow ports 26. The excess fuel flows from the groove 19 via the return port 24 back into the fuel tank.

In the enlarged scale drawing of Figure 2, the piston valve 3 and the piston valve cylinder 4 are only partly illustrated. By way of better illustration, the gaps produced by high precision between the piston valve cylinder4 and the piston valve 3 which are several thousands of a millimetre wide are shown on an exceptionally large scale.By this means, it can be recognised that the piston valve 3 can no longer completely float on the fuel penetrating into these gaps from the annular grooves 21 and 23, both because of the engagement of the measuring device 9 which is located laterally on the actuating pin 12 and also, when the valve is at a temporary standstill or carries out a slight rotating movement with respect to the piston valve cylinder 4, because the valve 3 is pressed with its support regions 1 3 and 14 to one side against the inside wall of the piston valve cylinder 4 in the direction of the arrows, and an eccentric gap is formed - as can also be seen in Figure 3.As a result of this eccentric gap, the pressure of the fuel which is introduced into the annular grooves 21 and 23 and penetrates into the gaps is more sharply reduced in the narrow gap than in the wide gap across the support regions 13 and 14 towards the area outside the support regions. The variation of the pressure resulting from this can be seen from the diagrams shown beside the respective gaps, where the fuel pressure is indicated with P and the length of the support regions 13 and 14 is indicated with L.This drop in pressure, which varies in the respective transverse planes of the support regions 13 and 14 and which emanates from the annular grooves 21 and 23 at a pressure of, for example, 4.7 bars and drops roughly 0.4 bars residual pressure, results in a hydraulic auxiliary lateral force also becoming effective in the direction of the arrow, which force produces a high frictional moment in the left hand narrower gap which impairs the rotating movement of the piston valve 3 in the piston valve cylinder 4 and causes metering errors in the throttle cross- section.

In Figure 4 is shown the fuel metering valve of Figure 2 modified in accordance with invention, in which the modification is embodied by the fact that the support regions 13 and 14 are provided on their circumferential wall with grooves 27 running in circumferential directions. The effect of these grooves 27 is that the fuel, which is introduced under pressure into the annular grooves 21 and 23 and penetrates into the gaps, is divided uniformly at the respective transverse planes of the support regions 1 3 and 14 and consequently there occurs an equalization of pressure on the circumferential surface of the support regions which results in the piston valve 3 floating at the support regions and thereby prevents the piston valve 3 from being displaced to one side against the piston valve cylinder 4 as can also be seen from Figure 5. As can be understood from the diagrams shown beside the gaps, there occurs between the annular grooves 21 and 23 and the areas outside the support regions 13 and 14 a drop in pressure which is orientated in a similar way, and where a pressure of 4.7 bars, for example, is reduced to a residual pressure. As a result of the more uniform gap between the piston valve 3 and the piston valve cylinder 4 which is formed in this way, the frictional moment is largely reduced, so that satisfactory operation of the fuel metering valve is ensured.

Figure 6 shows, in section, a second exemplified embodiment of a fuel metering valve 30 of a fuel injecting system, which is located on the intake pipe 31 of a mixture-compressing internal combustion engine which is not shown. In this exemplified embodiment, the fuel metering valve essentially comprises a piston valve 32 which is movably mounted by means of an upper support region 33 and a lower support region 34 in the cylindrical space of a piston valve cylinder 35 which is tightly and rigidly inserted in a housing 36. The intake pipe 31 contains, in a conical section 37, a measuring device 38, which is designed as a baffle plate and is moved in the direction of the arrow according to the quantity of airflowing through.The measuring device 38 is mounted about a pivot 40 via a lever arm 39 and acts, via a cam 41, on the movable piston valve 32, which to this end, has a rounding 42 as a means of engagement. The piston valve 32 carries between its support regions 33 and 34 an annular groove portion 43, which forms a control edge 44 with the outer wall of the piston valve 32. The annular groove 43 is in communication with a fuel inlet port 45 which opens in the inner wall of the piston valve cylinder 35, and with a number of flow orifices which are designed as control slits 46 and emanate from the inner wall and correspond to the number of injection nozzles (indicated by arrows 51). The control edge 44 of the piston valve 32 cooperates with the control slits 46 and forms in each case a variable throttle crosssection.To each control slit 46 is connected a chamber 47 of a diaphragm valve 50 which has two chambers 47 and 48 separated from each other by a diaphragm 49, and which is in communication via a valve aperture 52 controlled by the diaphragm 49, with the respective injection nozzle 51.

The fuel which is being metered is conveyed by a pump (not shown) under pressure from a fuel tank (not shown), through the inlet port 45 into the annular groove 43 of the piston valve 32. The piston valve 32 is moved by the measuring device 48, in accordance with its deflection created by the quantity of air flowing through the intake pipe 31, counter to a readjusting force which is created by a spring 53 in the exemplified embodiment, whereby a smaller or larger throttle cross-section is released by the control edge 44 and the control slits 46 in proportion to the deflection of the measuring device 38, and an appropriate quantity of fuel is delivered to the injection nozzles 51.In this exemplified embodiment also, the piston valve 32 may be pressed to one side against the inside wall of the piston valve cylinder 35 by the transmission movement and deflection of the measuring device 38 via the lever arm 39 and the cam 41 acting on the rounding 42, so that the same disadvantageous effects occur as have been described in connection with the arrangement of Figures 2 and 3.

The longitudinal section illustrated in Figure 7 shows the fuel metering valve of Figure 6 modified in accordance with the invention, on an enlarged scale, in which the piston valve cylinder 35 is only partly shown This modification is in the fact that the support regions 33 and 34 are provided on their circumferential walls with grooves 54 running in circumferential directions. As a result of these grooves, the fuel which is introduced under pressure into the annular groove 43 penetrates into the gaps and is distributed uniformly over the support regions in each transverse plane. A pressure equalization thereby occurs on the circumferential surfaces of the support regions which causes the piston valve 32 to float and prevents the piston valve being placed to one side, so that the operation of this fuel metering valve is also ensured.

The invention is not limited merely to the exemplified embodiments which have been illustrated. The proposed grooves can also be used with those fuel metering valves having a piston valve seated in the cylindrical space of the piston valve cylinder, where the throttle cross-section is formed by control edges and flow apertures of other known designs.

Claims (2)

1. A fuel metering valve for a fuel injection system of a mixture-compressing spark-ignition internal combustion engine with continuous injection, which valve has a piston valve which is mounted in a piston valve cylinder by two cylindrical bearing regions spaced from each other and which is rotatable and/or axially displaceable relative to the piston valve cylinder by an air quantity measuring device and having an inlet for pressurised fuel into the cylinder space between the bearing regions and wherein circumferentially disposed grooves are provided on the circumferential surfaces of thebearing regions of the piston valve.

2. A fuel metering valve for a fuel injection system of a mixture-compressing spark-ignition internal combustion engine substantially as herein described with reference to Figure 4 or Figure 7 of the accompanying drawings.