GB2137693A - Damped fuel injection nozzle for internal-combustion engines - Google Patents

Abstract

Fuel injection nozzle for internal- combustion engines, comprises a valve needle (18) opening outwards and a pressure space (40), limited by two annular shoulders of the valve needle (18) into which opens a fuel channel (30, 34) has a spring chamber (32) designed as a damping chamber into which the fuel can flow only via a throttle channel in valve 54 so as to act on the upstream end face of the valve needle (18) and delay the rate of opening. Valve 54 formed by a wall portion is deflected during the closing stroke to permit rapid closing. Alternatively a piston may be used (Figs. 6-8) to provide no notable resistance to the displacement of the fuel from the spring chamber (32). This arrangement for damping the opening movement of the valve needle (18) is simple and involves only slight wear and allows a conventional design of the valve needle (18) to be used. <IMAGE>

Description

SPECIFICATION Fuel injection nozzle for internal-combustion engines The invention starts from a fuel injection nozzle of the generic type of the main claim. In known injection nozzles of this type, the damping chamber is formed in a cap which is attached on a cylindrical valve-needle extension forming the damping piston and which is supported, during the opening movement of the valve needle, on a shoulder solid with the housing (DE - Al 3,220,398). The cylindrical valve-needle extension carrying the cap projects into a further chamber which is located upstream of the closingspring chamber and is intended for receiving the cap and which is divided towards the closingspring chamber by an inward-directed flange of an annular body which is clamped between a nozzle holder and the nozzle body and which also forms the supporting shoulder for the cap.This design is very reliable in operation, but requires a valveneedle construction which differs from the customary designs.

The arrangement according to the invention, which has the characterising features of the main claim, is simple and involves only slight wear and is also characterised in that the valve-needle design of a conventional injection nozzle can be adopted without any modification.

Advantageous developments of the subject of the main claim are possible as a result of the measures contained in the sub-claims.

The throttle channel leading into the damping chamber can extend in the nozzle body or nozzle holder, and if appropriate its cross-section can be varied by adjusting means. A particularly simple design is obtained when the throttle channel passes through the deflectable wall portion of the damping chamber.

The deflectable wall portion of the damping chamber can be formed by a valve-closing member which is pressed by a spring in the direction of flow of the fuel against a valve seat which surrounds a non-throttling passage crosssection of the connecting bore and which is bridged by the throttle channel leading into the damping chamber. In this case, the throttle channel can be provided in a valve-seat plate inserted into the connecting bore.

It is especially advantageous if, according to the invention, the deflectable wall portion of the damping chamber is formed by a piston mounted displaceably in the connecting bore.

In this arrangement, it is possible to ensure, by means of appropriate dimensions and adjustment of the restoring spring for the piston and of the throttle-channel cross-section, that the damping of the movement of the valve needle begins only after the start of injection, and that the delay in the start of damping in relation to the start of injection is adjusted automatically to a favourable value at various operating points. Such a function is known, in principle, from DE - A - 3,221,442.

During the closing stroke of the valve needle, the piston is deflected counter to the force of its restoring spring, so that the volume of fuel displaced in the damping chamber by the valve needle is absorbed, without notable resistance, by that portion of the connecting bore exposed by the piston which moves back. The restoring spring then pushes the piston back into the initial position, the volume of fuel previously absorbed being displaced via the throttle channel into the fuel throughflow channel. When this process has not yet ended at the start of the next opening stroke of the valve needle, a first part stroke of the next opening stroke of the valve needle takes place without damping. A simple design is obtained when the throttle channel leading into the damping chamber is formed at least partially by the play between the piston and the guide bore.

It is proposed, in a development of the invention, that the piston be provided on the periphery with at least one longitudinal groove which starts from that end face of the piston facing the damping chamber and which is made shorter than the piston.

As a result, the maximum absorption volume of the piston and of its guide bore can be limited to a predetermined value, and the undamped part of the next opening stroke of the valve needle can be restricted to a value which is advantageous in terms of combustion noise.

In some cases, it can be advantageous if the throttle channel is formed by the radial play of the valve needle in the guide bore of the nozzle body in the region of an overlap between the pressure space and the damping chamber.

To limit the damping of the opening movement of the valve needle to a part stroke, it is further proposed that the valve needle be provided with a channel which leads out of the pressure space and which opens out on the cylindrical periphery of the valve needle at a point which, after a predetermined part stroke of the valve needle, coincides with a bore in the nozzle body, which leads into the closing-spring chamber.

The arrangement can also be such that even in the closing position of the valve needle the mouth, located on the cylindrical periphery of the valve needle, of the channel leading out of the pressure space, or the actual annular groove of the valve needle, forming the pressure space, and the bore in the valve body, leading further into the closingspring chamber, overlap one another a little and thus form a throttle channel, so that there is either no need for a throttle bore in the valve-closing member of the damping device or for a specific relatively large radial play of the valve needle in the guide bore of the nozzle body.The advantage of this arrangement is also that, as a result of an appropriate cross-sectional shape of the mouth of the channel in the valve needle and or of the bore in the nozzle body, which leads further, the damping of the valve needle can be limited to a part stroke, and moreover the cross-section of the throttle channel can be made variable above and beyond the stroke or part stroke of the valve needle.

According to a further proposal of the invention, the nozzle-body guide bore located between the damping chamber and the pressure space has a smaller diameter than the valve-needle pressure shoulder assigned to the valve seat.

This measure results in a differential surface on which the unthrottled fuel pressure is exerted in the opening direction of the valve needle. The fuel pressure in the damping chamber now acts as an additional component force on the valve needle, thus ensuring that, even in the high speed ranges of the engine, sufficient force for accelerating the valve needle is already avaiiable, without delay, at the start of injection.

Drawing Six exemplary embodiments of the invention are illustrated in the drawing and explained in more detail in the following description. Figure 1 shows a longitudinal section through the first exemplary embodiment, and Figures 2 and 3 show alternative forms of the damping means according to Figure 1. Figure 4 is an enlarged part section through the second exemplary embodiment, and Figures 5a to 5d show several alternative forms in a section along the line V-V in Figure 4. Figures 6, 7 and 8 illustrate details of the third, fourth and fifth exemplary embodiment. Figure 9 shows a functional diagram of the design according to Figure 8, and Figure 10 illustrates a part section through the sixth exemplary embodiment.

Description of the exemplary embodiments.

The injection nozzle according to Figure 1 has a nozzle body 10 which is clamped firmly on a nozzle holder 14 by means of a union nut 12. A valve seat 1 6 is formed in the nozzle body 10 in which a valve needle 1 8 is mounted displaceably, the sealing cone 20 of the latter being pressed against the valve seat 1 6 by a closing spring 22.

The closing spring 22 is supported on the nozzle body 10 and engages via a flange bush 24 on a spring plate 26 which is supported on a shoulder 28 of the valve needle 18.

The nozzle holder 14 contains a feed bore 30 leading into a chamber 32 which contains the upstream portion of the valve needle 18, the closing spring 22, the flange bush 24 and the spring plate 26. A channel 34 corresponding to an annular groove 36 in the nozzle body 10 branches off from the feed bore 30. The annular groove 36 is connected via a bore 38 to a pressure space 40 which is formed between the wall of the valveneedle bore in the nozzle body 10 and the cylindrical periphery of a portion 42, of reduced diameter, of the valve needle 18 and which extends directly up to a point located in front of the valve seat 1 6. The pressure space 40 is limited upstream by a shoulder 44 of the valve needle 18.

Between the flange bush 24 and the nozzle body 10 there is, in the closing position illustrated, a distance h which corresponds to the stroke of the valve needle 1 8. As described in more detail below, the valve needle 18 is displaced outwards in the opening direction by the fuel pressure counter to the force of the closing spring 22, until the flange bush 24 comes up against the nozzle body 10. When the valve is closed, the closing spring 22 guides the valve needle 18 inwards back into the closing position illustrated.

Downstream of the branch of the channel 34, the feed line 30 has a threaded portion 46, adjacent to which is a bore portion 48 of reduced diameter. This merges at an annular shoulder 50 nto an even narrower bore portion 52 which opens directly into the chamber 32. A valve plate 54 containing a central throttle channel 56 is guided displaceably in the bore portion 48. The valve plate 54 is pressed by a spring 58 against the annular shoulder 50, which, interacting with the valve plate 54, forms a valve seat in the feed bore 30. The spring 58 is supported on a threaded bush 60 which is screwed into the threaded portion 46 of the feed bore 30.

When the injection nozzle is in operation, the fuel conveyed by the injection pump passes via the feed bore 30, the channel 34, the annular groove 36 and the bore 38 into the pressure space 40 and from there directly to the valve seat 1 6.

The resultant force exerted by the fuel in the pressure space 40 on the valve needle 1 8 is zero as long as the valve needle 18 is closed. The chamber 32 is also filled via the throttle channel 56 in the valve plate 54 with fuel, which exerts therein on the valve needle 18 a force determined by the specific fuel pressure multiplied by the cross-sectional area of the valve needle 1 8. As long as this force cannot overcome the prestressing force of the closing spring 22 and the closing force exerted by the combustion-chamber pressure on the valve needle 18, the injection nozzle remains closed.

When the fuel pressure increases at the start of an injection operation and overcomes the closing forces exerted on the valve needle 1 S, the fuel can pass into the chamber 32 only with a delay because of the throttling in the throttle channel 56, so that the valve needle 18 can only open correspondingly slowly. When the valve needle 18 closes, the valve plate 54 is lifted off from the annular shoulder 50, so that the quantity of fuel which entered the chamber 32 during the opening stroke can escape unimpeded back into the feed bore 30 and can close the valve needle 18 correspondingly quickly.

Instead of the valve plate 54, it is also possible to provide a closing body 70 which is designed according to Figure 2 and which likewise interacts with the annular shoulder 50 as a valve seat and is provided with an extension 72 which penetrates into the bore portion 52 and has several longitudinal grooves 74 to allow unthrottled passage of the fuei, when the closing body has been lifted off, and which guides the latter.

In the alternative form according to Figure 3, there is, pressed into the bore portion 48, a valve seat plate 76 which contains in the centre a bore 78 with a non-throttling passage cross-section and next to it a throttle channel 80. The valveclosing member is a ball 82 which is pressed by the spring 58 against the upper mouth edge of the bore 78, designed as a valve seat.

In the exemplary embodiment according to Figure 4, the damping of the opening movement of the valve needle 18 is limited to a part stroke hv.

For this purpose, the valve needle 18 has an oblique bore 84 which leads from the pressure space 40 into an annular groove 86 in the cylindrical periphery of the valve needle 18, this annular groove being located somewhat above the portion 42 of the valve needle 18. The nozzle body 10 has a transverse bore 88 which leads from the guide bore for the valve needle 18 into the chamber 32. The transverse bore 88 is arranged in such a way that, in the closing position of the valve needle 1 8 as illustrated, there is an overlap corresponding to the part stroke hv towards the annular groove 86. The parts of the damping device which are located in the feed bore 30, 48, 52 are identical to those in one of the designs described above and are therefore not illustrated.

After the valve needle 18 has covered the part stroke hv during the opening movement, a connection between the pressure space 40 and the chamber 32 is controlled via the bores 84 and 88, and the fuel finally passes unthrottled into the chamber 32 via this connection. As a result of an appropriate cross-sectional form of the bore 88, this connection can be controlled in accordance with a desired relationship. Figures 5a to Sc show different cross-sectional forms 88a to 88c, in which a linear or more or less progressive relationship between the travel of the valve needle and the control cross-section is obtained.

In the exemplary embodiment according to Figure 4, the throttle channel of the damping device could also be relocated in the radial play, to be calculated accordingly, between the valve needle 18 and the guide bore in the nozzle body 10 in the region of the overlap hv. The throttle channel 56 in the valve plate 54 (Figure 1) or in the closing body 70 (Figure 2) or in the valve-seat plate 76 (Figure 3) could then be omitted. Another possibility is to give the bore 88, according to Figure 5d, a cross-section 88d in which a slot-like extension 90 reaches, in the closing position of the valve needle 18, into the region of the annular groove 86.However, the arrangement could also be such that even in the closing position of the valve needle 1 8 a slight overlap giving the desired throttle effect is present between the bore 88, designed according to Figures 5a to c, and the annular groove 86.

In the exemplary embodiment according to Figure 6, instead of a valve-closing member, a piston 92 is mounted displaceably in the bore portion 52, is pressed by the spring 58 against the annular shoulder 50 solid with the housing, and contains a continuous throttle bore 94. With the exception of the necessary movement play, the piston 92 completely fills the bore portion 52 which thereby acquires the function of a cylinder.

During the opening stroke of the valve needle 18, the fuel passes with a delay into the chamber 32 via the throttle bore 94 in a similar way to the exemplary embodiments according to Figures 1 to 3, as a result of which the opening movement is executed with damping. In contrast to this, the closing stroke of the valve needle 1 8 is practically unimpeded, because the piston 92 deflected upwards allows the volume of fuel displaced out of the chamber 32 by the valve needle 18 to pass into the bore portion 52. After the closing stroke has ended, the piston 92 is guided back by the spring 58 towards the initial position shown in Figure 6.

When the needle strokes are small and/or the injection intervals are longer, the piston 92 has already reached its initial position before the start of the next opening stroke of the valve needle, so that this opening stroke is damped from the outset. The force of the spring 58 and the crosssection of the throttle bore 94 are calculated and coordinated with one another, in such a way that when the needle strokes are longer and/or the injection intervals are shorter the piston 92 has not yet reached its initial position at the start of the next opening stroke. As a result of this, the next opening stroke is undamped over a first part of its distance, because the increasing fuel pressure in the bore portion 48 is transmitted unthrottled via the piston 92 and the fuel cushion in the chamber 32 to the upstream end face of the valve needle 18.Only when the piston 92 has come up against the annular shoulder 50 does the damping effect begin.

In the arrangement described above, the undelayed part of the opening stroke of the valve needle is the greater, the longer the valve-needle stroke and/or the shorter the injection intervals. It is possible to ensure by means of an appropriate design that the delay of the start of damping in relation to the start of injection automatically conforms to requirements at various operating points or over an entire range of the operating characteristics.

Figure 7 illustrates an alternative form of the design according to Figure 6. In this, a piston 96 is provided, and the throttle channel is formed by the appropriately calculated radial play 98 between the piston 96 and the bore portion 52. To connect the radial play 98 to the bore portion 48, a recess 100 is provided in a collar 102, interacting with the annular shoulder 50, of the piston 96.

The exemplary embodiment according to Figure 8 has a piston 104 which likewise possesses a radial play 106 relative to the bore portion 52, this radial play forming the throttle channel. The radial play 106 is connected to the bore portion 48 via bores 1 08 in the piston 104. Furthermore, the piston 104 is provided on the periphery with several longitudinal grooves 110 which extend up to a collar 112 of the piston 104 with the exception of the distance amax.

As a result of the arrangement of the longitudinal grooves 110, the maximum deflection of the piston 104 during the closing stroke of the valve needle 18 is limited to the distance ajax. After this distance has been covered, the piston 104 acts in the same way as a valve-closing member which allows the volume of fuel displaced from the chamber 32 to flow back unimpeded into the bore portion 48. By an appropriate choice of the distance amen, the undamped part stroke of the next opening stroke of the valve needle 1 8 can be restricted to a value which is advantageous in terms of combustion noise.

This advantageous effect is illustrated in the diagram according to Figure 9, in which the valveneedle strokes h are plotted against the time axis t at the top and the deflections a of the piston 104 from the initial position shown in Figure 8 are plotted at the bottom. The curve of the valveneedle strokes is represented by an unbroken line and that of the deflections of the piston 104 by a broken line.

At the point in time t1, the valve needle 18 has executed its complete opening stroke he corresponding to the particular operating point, and the piston 104 is still in the initial position.

During the closing stroke of the valve needle 18 which ends at the point in time t2, the piston 104 is displaced upwards until it has covered the distance ajax. The piston 104 remains in this position until the valve needle 1 8 has reached its closing position at the point in time t2. From this point in time on, the spring 58 pushes the piston 104 back towards the annular shoulder 50, this being represented by the line a1 in Figure 9. At the point in time t3, the next opening stroke begins, and this first takes place without damping, until at the point in time t4 the piston 104 has reached its initial position and the damping means are activated again.

The third line in Figure 9 indicated by dots and dashes represents the stroke curve of the piston 104 if this were not provided with the longitudinal grooves 110. It can be seen that the undamped part of the next opening stroke would extend to the point in time t'4, and that as a result of the arrangement of the longitudinal grooves 110 in the piston 104 the undamped part of the opening stroke of the valve needle is limited.

In the exemplary embodiment according to Figure 10, the valve needle 18' is guided in a bore portion 114 of the nozzle body 10, the diameter D1 of which is somewhat less than the diameter D2 of the pressure shoulder 116 located on the same side as the combustion space and belonging to the valve needle 1 8'. This results in a differential surface at which the unthrottled fuel pressure in the pressure space 40 additionally exerts on the valve needle 18t a force acting in the opening direction. The advantage of this arrangement is that, even in the high speed ranges of the engine, sufficient force to accelerate the valve needle already acts, without delay, on the valve needle at the start of injection. In the lower speed and injection-quantity range, the valve needle can also be damped or delayed effectively up to relatively large needle strokes, without the duration of injection at higher speeds becoming too long.

Claims (11)

1. Fuel injection nozzle for internal-combustion engines, with a nozzle body in which a valve seat is formed and a valve needle is mounted displaceably, the latter being stressed by a closing spring and subjected, opposite to this, to the fuel pressure and moving, during the opening stroke, in the direction of flow of the fuel, also with a fuel throughflow channel which leads from a connecting bore into a pressure space, located in front of the valve seat, in the valve-needle bore of the nozzle body, this pressure space being limited axially by two pressure shoulders of the valve needle which are directed opposite to one another, and furthermore with a damping piston which delays the opening movement of the valve needle and which limits a damping chamber which is filled with fuel and is connected to the throughflow channel via a throttle channel and which has a wall portion deflectable, during the closing stroke of the valve needle, against the force of a restoring spring, characterised in that the damping chamber is formed by the closingspring chamber (32) and the damping piston is formed by that portion of the valve needle (18) projecting into the closing-spring chamber (32), and in that, furthermore, the deflectable wall portion (54, 70, 82, 92, 96, 104) of the damping chamber (32) is located in a connecting bore (48, 52), leading from the throughflow channel (30, 34 38) to the closing-spring chamber (32), and is pressed by the restoring spring (58) against a shoulder (50) solid with the housing.

2. Injection nozzle according to Claim 1, characterised in that the throttle channel (56) passes through the deflectable wall portion (54, 70, 92) of the damping chamber (32).

3. Injection nozzle according to Claim 1 or 2, characterised in that the deflectable wall portion of the damping chamber (32) is formed by a valveclosing member (54, 70, 82) which is pressed by a restoring spring (58) in the direction of flow of the fuel against a valve seat (50, 76) which surrounds a non-throttling passage cross-section (52, 78) of the connecting bore (48, 52) and which is bridged by the throttle channel (56, 80, 90).

4. Injection nozzle according to Claim 3, characterised in that the throttle channel (80) is formed in a valve-seat plate (76) inserted into the connecting bore (48, 52).

5. Injection nozzle according to Claim 1, characterised in that the deflectable wall portion of the damping chamber (32) is formed by a piston (92, 96, 104) mounted displaceably in the connecting bore (48, 52).

6. Injection nozzle according to Claim 5, characterised in that the throttling channel (98, 106) leading into the damping chamber (32) is formed at least partially by the play between the piston (96, 104) and the guide bore (52).

7. Injection nozzle according to Claim 5 or 6, characterised in that the piston (104) is provided on the periphery with at least one longitudinal groove (110) which starts from that end face of the piston (104) facing the damping chamber (32) and which is made shorter than the piston (104).

8. Injection nozzle according to Claim 1, characterised in that the throttle channel is formed by the radial play of the valve needle (1 8) in the guide bore of the nozzle body (10) in the region of an overlap (hv) between the pressure space (40) and the damping chamber (32).

9. Injection nozzle according to one of the preceding claims, characterised in that the valve needle (18) is provided with a channel (84) which leads out of the pressure space (40) and which opens out on the cylindrical periphery of the valve needle (18) at a point which, after a predetermined part stroke (hv) of the valve needle (18), coincides with a bore (88) in the nozzle body (10), which leads into the damping chamber (32).

1 0. Injection nozzle according to one of the preceding claims, characterised in that the guide bore (114), located between the damping chamber (32) and the pressure space (40), of the nozzle body (10) has a smaller diameter (D1) than the pressure shoulder (116) assigned to the valve seat (16) and belonging to the valve needle (18).

11. Any of the fuel injection nozzles substantially as herein described with reference to the accompanying drawings.