GB2093912A - A fuel injection nozzle - Google Patents

Abstract

A valve needle 6 is biased in the closing direction by a permanent magnet 10 or an electromagnet (not shown) such that an increasing closing force acts on the valve needle 6 as it approaches its seat (not shown). The needle is also biased in its closing direction by a spring 5. A holding plate is located on the valve needle and is acted on by the permanent magnet or electromagnet and is so arranged at a distance from the magnet that a predetermined force acts in the closing direction and prevents needle bouncing. The valve needle may be provided with damping pistons (19), (28), Fig. 3 (not shown). <IMAGE>

Description

SPECIFICATION A fuel injection nozzle State of the Art The invention originates from a fuel injection nozzle according to the preamble to the main chain.

Fuel injection nozzles are normally so designed that the valve needle is radially guided in a nozzle body and is mounted for axial movement wherein it can either open outwardly in the direction of flow (A-valve) or inwards against the direction of flow (I-valve). Moreover, it is desirable to influence the valve needle movements and to control these as far as possible. Thus, a fuel injection nozzle is known from British specification 720 011 in which a valve needle pin abuts against a spring loaded additional mass in the opening direction so that, as regards the opening movement, a kind of impact damping braking effect and a corresponding control on the latter is produced. Moreover, the additional mass displaces fuel from a damping chamber through a calibrated opening and through the same calibrated opening back into the damping chamber between the opening strokes of the valve needle.The known fuel injection nozzle opens inwardly and due to the axial stratification of the valve needle and the additional mass, it has a considerable constructional length. There is a further disadvantage that an attempted matching and adjustment of the sequences of movement of the valve needle cannot be undertaken completely. A particular disadvantage is the absence of any influence on disadvantageous rebounds at the injection end.

In a further known fuel injection nozzle for combustion engines (German AS 20 52 311) the valve needle co-operates with a spring loaded annular piston but not for damping purposes but in order to form an accumulator which is variable in volume so that a substantial pressure rise of the fuel at the instant of injection is prevented. In so doing, the annular piston acts against the force of its helical spring and gives way under the increase of the volume under pressure of the quantity of liquids supplied.

Advantages are, of course, provided with fuel injection valves provided with valve needles opening in the direction of flow of the fuel (Avalve) especially very small dimensions and leakage free operation. However, on the other hand, the fitting of such valves to engines involves difficulties since a rebound free injection end cannot be realised or only with difficulty due to the slight damping of the valve needle. As a result of such rebounds, the hydrocarbon values in the exhaust gas are worsened and furthermore, due to the low needle damping, overshoot of the latter is produced which is undesirable particularly during the closing operation. Such overshooting valve needle movements permit combustion gases to blow through into the interior of the valve whereupon the narrow metering cross-section and the injection pins can become choked.An increased combustion noise and a widening of the jet angle occurs as a result of such coking.

Furthermore, due to the widening of the jet angle, a worsening of the mixture formation is produced and with it the consumption values and smoke values.

It is desirable to attempt to influence the opening and closing movements for matching and optimising in both injection valves opening in the direction of flow and valves opening against the direction of flow since the injection procedure in co-operation with the coupled emission crosssection from the injection openings is formed by these movements. Apart from the general trend towards miniturisation which also exists with conventional inwardly opening injection nozzles (Ivalves) especially small injection pins for the nozzle needles (with A-valves) have become necessary for the simultaneously developed jet preparation which then leads to very small valve needle diameters compared with conventional nozzles.Such small valve needles permit a tuning of the natural frequency and the optimal damping only over narrow operating ranges whereby a matching of these injection valves to the entire characteristic field of the engine is not possible.

Thus, a need exists for a fuel injection nozzle which is of small size and has variable and required influenceable opening and closing movements.

Advantages of the Invention The fuel injection nozzle in accordance with the invention comprising the characterising features of the main claim has the advantage that, due to the magnetic additional force produced over the range of the smallest needles strokes, the inclination of the valve needle to bounce is reduced or is completely eliminated whereby the injection characteristic of the valve and with it the kinetic vaues may be improved. Moreover, it is of advantage for the effective magnetic force to fall as rapidly as possible during the opening movement as a result of the increase in air gap, so that no further influence occurs due to the magnet system available and the completion of the opening movement is then purely a function of the closure spring always acting in the closing direction of the valve needle.On the other hand, during the valve needle closing movement, the effect of the magnetic force is reversed so that as the valve needle approaches its seat the acting holding force increases extremely rapidly up to a predetermined maximum value. Thus, it is not necessary to produce the damping of rebounds during the closing movement of the valve spring purely by a particularly large return force of the closure spring, since this increase in closing force recycled to the spring characteristic not only occurs during the damping of rebounds but is permanently available and would limit the design possibilities too strongly.

The invention facilitates the substantially desired formation of the behaviour of the forces acting on the valve needle both in the opening and in the closing direction whereby the possibility of adaptation of the fuel injection nozzles generally is increased and indeed of inwardly as well as outwardly opening nozzles and particularly those of small needle diameter.

Advantageous further developments and improvements of the fuel injection nozzle in accordance with the invention set forth in the main claim are made possible by the measures set forth in the sub claims. In this case, there is the advantage of achieving an additional mass and velocity dependent damping by further additional masses in the form of pistons which engage the valve needle.

Drawing Embodiments of the invention are illustrated in the drawing and are described in detail in the following specification. Figure-la shows a section through a first comparativeiy simple form of outwardly opening fuel injection valve (A-valve) in accordance with the invention and Figure 1 b is a section along the line 1 b-1 b in Figure 1 a whereas in Figure 3 a further form of a fuel injection valve is illustrated in which damping forces act on the valve needle movement both in the closing and in the opening direction in addition to the effective magnetic force.

Description of the Embodiments With the relatively simple form of a fuel injection nozzle shown in Figure 1 the valve region together with the valve needle opening in the direction of flow, thus opening outwards, is referenced 1 but is not illustrated in detail since it is not the subject of the present invention. The valve region 1 consisting of the valve needle guided radially and mounted for axial movement in a nozzle body and the nozzle body is clamped by means of a cap nut 2 to the nozzle holder 3 which, by means of a cylindrical annular wall 3a extending downwardly forms the spring chamber 4 in which, apart from the closure spring 5, the nozzle needle 6 and an upper spring plate 7 is provided against which the closure spring 5 is supported. The fuel is supplied under pressure through a duct 8 whereby the pressure wave arriving from the injection pump opens the valve needle.In the closed condition, the valve needle is forced against its sealing seat in the nozzle body and is also returned to the seat under the influence of the valve spring when the pressure in the valve chamber collapses at the end of the injection. In order to prevent the valve needle when striking the sealing seat from performing any rebounding movements the amplitude of which can as a rule be approximatley 0.01 mm, a further return force additional to the return force applied by the closure spring is introduced by the present inVention, if necessary also exceeding the spring force, and indeed on a magnetic basis.

For this purpose, the spring plate 7 of the valve needle is first of all supplemented by a further holding plate 9 or the upper end of the valve needle has a counterpart which provides a large magnetic effective area and effective mass, itself non-magnetic, but reacts on the action of magnetic lines of force thus having magnetic properties and can consist of soft iron for example or the like. Above the magnetic holding plate 9, referred to in the following simply as the magnetic valve member, a permanent magnetic system 10 is located which fits tightly in the base of the bore in the nozzle body 3 or is held stationary and is fixed in some other manner.It is to be understood that an electromagnet can also be used instead of a permanent magnet system with the additional possibility of developing correspondingly much larger magnetic holding forces at desired instances according to the control of the electromagnet; this will be further discussed below.

In the embodiment shown in Figure 1 a the permanent magnet system is made rotationally symmetrical and provides a throughly homogeneous field distribution. In the closed condition of the valve needle, that is to say in the position illstrated in Figure 1 a, the air gap A in the form of a magnetic working air gap formed between the holding plate 9 of the valve needle and the permanent magnet system is minimal but is predetermined in accordance with the desired effective magnetic force and indeed by the abutment of the valve needle on its seat in the nozzle body whereupon the holding plate 9, which in this case serves as a holding plate for the magnet 10 can only approach the permanent magnet system 10 up to the predetermined distance A.In designing the holding member for the magnet on the valve needle, that is to say for the holding plate 9, an effective magnetic area as large as possible is sought and with it a large magnetic effective force; a magnetic effective force has a return force on the valve needle which may still be enlarged, improved and made more accurate by an appropriate minimising and adjustment of the gap between the permanent magnet system 10 and the holding plate 9.

As shown in Figure 1 a, the permanent magnet system can be rotationally symmetrical formed as a hollow bush closed at the top and provided in the wall region with axial iongitudinal grooves 1 Oa for the passage of the fuel.

Then, the following function is provided. In the closed condition of the valve needle, the air gap between the opposite parts of the permanent magnet system 10 acting as pole plates and the holding plate 9 is minimal so that the maximum magnetic force for supporting the spring force acts on the valve needle. During an opening movement of the valve needle due too the fuel pressure wave, the air gap then increases and the magnetic force falls rapidly over proportionally so that already after an initial opening movement of about 25% of the total needle stroke, the magnetic force can drop to a quarter of its original value and thus need no longer be taken into account during the most extreme needle opening movement, uriless that is desired.In this connection, reference is made to the diagram in Figure 2 from which it can be seen that the magnetic forces behave practically exponentially with respect to the needle stroke (see magnetic force curve I) so that only the spring force corresponding to the curves II and II' need to be considered the further opening movement of the needle up to the end of the needle stroke. According to the design of the spring, the spring force can increase linearly with the needle stroke or, if a very soft spring characteristic is selected, the spring force can behave practically horizontally according to II' whereby from substantially half of the needle stroke the entire return force acting on the valve needle approaches the spring force curve asymptotically.However, it can be appreciated from the illustration of Figure 2 that with very small needle strokes or when the needle is located on its seat, the acting magnetic force still exceeds the effect of the spring force since on the basis of the data the return force on the valve needle attributable to the spring is lowest in the seat region where it should really be maximum for preventing rebounds.

As regards the closing movement of the valve needle the effect is then reversed; as soon as the valve needle the effect is then reversed; as soon as the valve needle arrives in the region of magnetic influence of the permanent magnet system 10, the latter draws the valve needle with a practically stronger and stronger acting force on to its seat whilst supporting the spring return force. Thus, the additional magnetic force achieved in the range of the smallest needle strokes appreciably reduces the inclination for the valve needle to bounce, if necessary completely eliminates the latter and efficiently improves the injection characteristic of the valve and with it the kinetic values.

Moreover, the large attainable magnetic forces and the condition that these forces proceed inversely exponentially with respect to the needles stroke are of importance for the described function so that more favourable injection procedures and increases closing efficiency can be achieved.

Under some circumstances with particularly large magnetically acting forces, an additional damping can turn out to be necessary, a damping which, in one form of the invention as illustrated in Figure 3, can exert an influence in a correspondingly desired manner both on the opening and on the closing movement of the valve needle.

An A-valve with a valve needle opening outwardly in the direction of flow of the active fuel is likewise illustrated in Figure 3 wherein a cap nut 12 rigidly clamps a spring chamber and damping piston system to the nozzle holder 1 3. The valve region is illustrated at 1 it comprises the nozzle body 21 gripped by the cap nut through an annularflange 20 and the rear end region of the valve needle which is illustrated at 1 6.

At least one, preferably two, damping pistons are provided within the spring chamber and damping piston system and are so fixed by various abutments to the valve needle or to its rear end that a damping for the valve needle of the desired type is provided both in the opening and in the closing direction because the valve needle must entrain the respective damping pistons during its movement. The damping can be a pure mass damping by increasing the mass of the valve needle as a result of the damping pistons and/or a velocity dependent damping in that in addition to the entrained movement, a resistance to flow within the spring chamber is opposed to the damping pistons and indeed by the fuel permanently located within the spring chamber.

Finally, the fuel injection nozzle of Figure 3 is provided with the same or similar magnetic return force system as the injection nozzle of Figure 1 a.

Specifically, a hollow cylinder 14 forming an inner cavity and serving for the bearing of the remaining parts is provided inside the bore in the cap nut 12 and the cylinder 14 is tightly fitted in a shouldered portion 14' of the nozzle holder 13 and abuts at the bottom agains the annular flange 20 on the nozzle body 21. In an annular groove, the end of the valve pin referenced 1 6a retains an abutment plate 1 5 which changes downwardly into a contact plate 1 spa. The valve needle closure spring 17 which is supported on a lower annular surface 18 on the nozzle body 21 is supported by the said contact plate 1 spa.

A first damping piston 19 for a needle opening movement is provided which is axially displaceable and if necessary is guided at intervals in the hollow cylinder 14. Its own pretension spring 22 retains the needle opening damping piston 19 in an upper abutting position, arrested by the thickened pin head 23 of the valve needle which is located moreover on its seat. The valve needle also opens in this embodiment in the direction of flow, thus outwardly.

Beyond this, the damping piston 1 9 for the needle opening movement supports the magnetic counter-holding plate 24 at its upper end region and which itself is located at a predetermined distance from the magnet system 25 corresponding to the working air gap of the magnet system. As in Figure 1 a, the magnet system 25 can be a permanent magnet system or an electro-magnet and the magnetic interaction with the holding plate 24 can take place through an extended pole piece 25a as illustrated in the embodiment of Figure 3 or directly.The magnet system 25 together with the pole piece 25a is situated in a corresponding recess in the nozzle holder 1 3 wherein axial grooves and bores are provided in all the necessary parts so that the fuel can be forced from the fuel supply duct 26 into the spring chamber and then to the seat region of the valve needle. In this case, the engagement between the contact plate 1 5a at the needle end of the valve and the outer damping piston 19 for the needle opening, takes place through inwardly directed lug-like projecting edges 27 at the lower end of the damping piston 1 9 which engage behind the contact plate 1 5a of the valve needle.

It is appreciated with regard to the function of the system so far described that on the occurrence of the fuel pressure wave and after overcoming the considerable magnetic holding force which is developed between the pole piece 25a and the holding plate 24, the valve needle 1 6 begins its downwardly directed opening movement whereby as a result of the increase in the air gap the magnetic force falls progressively rapidly.At the same time however, the valve needle must entrain the outer damping piston 19 during its opening movement as a result of the abutment between the contact plate 1 spa and the supporting lugs 27 whereupon a smoothing and damping of the dynamic procedure is produced either only by the additional mass of the damping piston to be moved and/or supplemented as a result of the liquid displacement which the damping piston 1 9 must perform during its downwards movement.

This corresponds to a velocity dependent damping wherein the displacement takes place through a corresponding clearance at the bearing or by a calibrated bore.

In this connection, reference is made to the fact that on the lefthand side separated by the central line of the fuel injection nozzle shown in Figure 3 the particular distances and the co-operation between the parts is illustrated as if the nozzle needle is performing its downwards movement or has arrived at the end of its opening stroke whereas to the right of the central line, the nozzle needle is performing or has finished its closing movement.

During the closing movement, the valve needle is separated from the damping piston 19 by the closing pressure of its closure spring 17 since the contact plate 1 spa can rise from the supporting lugs 27 on the damping piston 19; simultaneously, an abutment is provided between the abutment plate 15 of the valve needle 16 and an inner damping piston 28 for the needle closing movement. This abutment is shown in Figure 3 on the right-hand side at 29; it corresponds to the gap 30 on the opposite side which is produced with the needle open between the abutment plate 1 5 and the inner damping piston 28 for the needle closing movement. The inner damping piston 28 is guided by the outer damping piston; in other words the inner damping piston slides independently in the outer damping piston.

Moreover, an annular flange 31 on the inner damping piston engages in an inner shoulder 32 on the outer damping piston and with the latter forms an abutment. This abutment fixed the lowermost position of the inner damping piston for the needle closing movement. The inner damping piston 28 is prestressed downwardly by its own prestressing spring 33 so that, for the closing stroke of the valve needle, the inner damping piston is located with its inner annular projection 34 in a predetermined position also directly engaging the abutment plate 1 5 of the valve needle.Thus, during the closing movement, the valve needle must push the inner damping piston 28 upwards, indeed released from the outer damping piston 19, whereby a rapid and desired correspondingly damped closing movement is produced, damped by the mass of the inner damping piston 28 through the pretension spring 33 and by the hydraulic effect of the liquid displacement by the inner damping piston. It is understood that the outer damping piston follows or imitates the said closing movement of the valve needle directly so that on reaching the valve seat the outer damping piston 1 9 together with the holding plate 24 has reached its upper abutment position once again and certainly prevents the valve needle itself from performing a rebounding movement Moreover, with an appropriate control of the dynamic effects and movements, a possible inclination of the valve needle to bounce can certainly be inhibited by the increasing acceleration of the outer damping piston 19 on approaching the magnet system 25 or its pole piece 25a, since the outer damping piston 1 9 can strike the contact plate 1 spa in the fraction of a second at which the valve needle would like to perform a downwardly directed first rebound movement.

Claims (9)

1. A fuel injection nozzle for combustion engines, comprising a valve needle loaded in the closing direction, radially guided in a nozzle body and axially displaceably mounted, characterised in that, a stationary magnetic part is provided at a distance from a counterpart movable with the valve needle defining a predetermined holding force so that as the valve needle approaches its seat a progressively increasing holding force is developed on the needle in the closing direction.

2. A fuel injection nozzle according to claim 1, characterised in that, the distance between the counter-part formed by a holding plate on the valve needle and the magnet system determines the working air gap of the magnet system as a value for the magnetic return force portion in addition to the value determined by the magnetically effective area.

3. A fuel injection nozzle according to claim 1 or 2, characterised, in that, opening and/or closing movements of the valve needle are additionally influenced by damping members wherein at least one of the damping pistons is connected to the holding plate which is under magnetic influence.

4. A fuel injection nozzle according to claim 1 or 2, characterised in that, a holding plate consisting of ferromagnetic material of predetermined permeability is arranged on the rear valve needle pin and is arranged opposite a permanent magnet system fixed in the nozzle holder at a distance.

5. A fuel injection nozzle according to claim 4, characterised in that, the permament magnet system is a socket spanner-like permanent magnet with a completely homogeneous field distribution.

6. A fuel injection nozzle according to one or more of claims 1 to 3, characterised in that, the magnet system in the nozzle holder is an electromagnet.

7. A fuel injection nozzle according to one or more of claims 1 to 6, characterised in that, the holding plate which is under magnetic influence is arranged on an outer damping piston for the needle opening, which slides within a hollow cylinder under the pretension of a spring associated therewith.

8. A fuel injection nozzle according to claim 7, characterised in that, the outer damping piston for the needle opening retains an abutment on the valve needle pin by means of inwardly directed holding lugs or an inner annular projection.

9. A fuel injection nozzle according to claim 7 or 8, characterised in that, within the outer damping piston, a further damping piston is slidingly mounted for the damping of the needle closing movement, which, together with the valve needle forms an abutment and has its own pretension spring which tensions it away from the needle closing direction.

1 0. A fuel injection nozzle according to one or more of claims 1 to 9, characterised in that, apart from the mass damping, the damping pistons have an hydraulic damping through displacement of the fuel located in the spring chamber.

1 A fuel injection nozzle substantially as herein described with reference to Figures 1 a and 1b or Figure 3 of the accompanying drawings.