GB2086473A

GB2086473A - Fuel injection valve for compression ignition engines

Info

Publication number: GB2086473A
Application number: GB8132621A
Authority: GB
Original assignee: Daimler Benz AG
Current assignee: Daimler Benz AG
Priority date: 1980-10-31
Filing date: 1981-10-29
Publication date: 1982-05-12
Also published as: FR2493408B1; IT1138675B; IT8124223A0; GB2086473B; FR2493408A1; DE3041018A1; DE3041018C2

Abstract

A pressure chamber 20 located at the back of the valve needle 13 is connected to the spring chamber 10 through a throttle bore (21, 22 or 27), Figs. 3 to 7 (not shown), in the disk 15 between the chambers or between the disc and the stem 17 to limit the rate of needle lift. The chamber 10 is connected to the outlet of a fuel feed pump (2), Fig. 1 (not shown), under the control of a valve 23 responsive to engine speed, load and/or temperature to vary the chamber pressure. <IMAGE>

Description

SPECIFICATION Fuel injection valve for injection systems of air compression injection combustion engines This invention relates to a fuel injection valve for an injection system consisting of a high pressure section and a low pressure section containing a fuel delivery pump, for air compressing fuel injection combustion engines.

It is known for fuel valves, in particular those used for compression ignition internal combustion engines with a pre-combustion chamber, to have a so-called throttle ring gap at the fuel outlet. This ring gap is operative when the load and speed of rotation are low. It ensures that the fuel will be adequately atomized even at the low injection pressure produced in this operating range. It also prolongs injection and hence reduces combustion noise.

After some time in operation, the size of the throttle ring gap is frequently substantially reduced by coke deposits. A higher pressure therefore builds up in front of the construction or cross section so that the needle of the injection valve is pushed out of the range of the throttle. The very much larger main cross section is thereby opened and injection is brief and accompanied by loud combustion noise.

It has already been attempted to overcome this disadvantage by a throttle device disclosed in German Offenlegungsschrift No. 2,801,976, which is arranged in an overflow oil line leading to the fuel tank.

In such an arrangement, the pressure chamber at the rear of the needle nozzle cannot be refilled after the valve stroke. The chamber remains virtually empty and as a result a satisfactory damping of the needle is therefore hardly obtainable.

In the known arrangement described above, damping is too weak and has a delaying effect due to the fuel volume in the spring chamber acting as intermediate spring and due to the length of the overflow oil line to the throttle.

The present invention seeks to provide effective damping of the opening movement of the valve needle by simple measures applied to the injection system and in addition to reduce or even eliminate the damping effect at high speeds and under high loads.

According to the present invention there is provided a fuel injection valve for an injection system consisting of a high pressure section and of a low pressure section containing a fuel delivery pump, for air compressing fuel injection combustion engines, the valve comprising a valve needle guided in a nozzle body, which needle in its opening direction counteracts a closing spring inside a spring chamber by means of a thrust bolt, and further comprising an overflow oil line connected to the injection valve and communicating with the spring chamber, and a throttle device counteracting the opening pressure and situated between the spring chamber and a pressure chamber which is bounded by the back of the valve needle, the injection valve being in the form of a throttle pin nozzle and the overflow line is a low pressure line which communicates with said low pressure section, a valve being arranged in said low pressure line for controlling the pressure therein in dependence upon engine parameters.

This arrangement provides for direct damping of the movement of the needle. It also ensures that fuel is introduced into the pressure chamber by way of the throttle device by the pressure of the low pressure system in the spring chamber before the valve needle is raised.

In a preferred embodiment the throttle device is formed by a throttle disc surrounding the thrust bolt and guided in a recess of the nozzle body, which throttle disc in one direction bears tightly against the undersurface of an intermediate member adjacent to the nozzle body.

In this case, the throttle disc may have a throttle bore connecting the pressure chamber with the spring chamber. Alternatively, a throttle ring gap may be provided connecting the pressure chamber with the spring chamber is provided between the thrust bolt and the throttle disc. In another preferred embodiment, the throttle device is formed by a throttle bore situated in the intermediate member of the fuel injection valve, and the thrust bolt is tightly guided in the intermediate member.

In yet another preferred embodiment the throttle device is formed by a flattened portion on the thrust bolt extending in the longitudinal direction thereof.

In another embodiment, the thrust bolt is stepped and that portion of the thrust bolt which has a smaller diameter faces the valve needle, the larger diameter portion of the thrust bolt being raised out of the central bore of the disc or of the intermediate member when the valve needle is raised by a predetermined amount to thereby increase the cross section of the fluid communication between the pressure chamber and the spring chamber.

The invention will now be described in more detail, by way of example, with reference to embodiments illustrated in the drawings, in which: Fig. 1 is a schematic representation ofthe injection system of a compression ignition combustion engine, Fig. 2 is a longitudinal section through a fuel injection valve with an overflow oil line and a valve controlling the low pressure, Fig. 3 is a sectional view on an enlarged scale through a detail of the fuel injection valve, giving on each side a half view of two different embodiments of the throttle device, Fig. 4 shows the throttle device in the intermediate element of the fuel injection valve, Fig. 5 shows the throttle device formed by flattening on the thrust bolt which forms a unit with the spring plate of the closing spring, Fig. 6 shows the throttle device formed by flattening on the thrust pin which forms a unit with the valve needle, and Fig. 7 shows two different embodiments of the throttle device with switching off means, each side of the Figure showing half of one embodiment.

The injection system shown in Fig. 1 for air compression injection combustion engines includes a tank 1, a fuel delivery pump 2, a filter 3, an injection pump 4, high pressure lines 5 connecting the injection pump 4 with injection valves 6, for each cylinder of the engine, low pressure lines serving as overflow oil lines 7, and supply lines 8.

Fig. 2 shows one of the plurality of identical fuel injection valves 6 each comprising an upper nozzle holder part 9 with spring chamber 10, an intermediate element 11 and a nozzle body 12 with valve needle 13. A throttle device 14 is formed by a throttle disc 15 which is seated with radial and axial clearance in a recess 16 of the nozzle body 12 (Fig. 3). It is lapped on its upper surface and fits tightly against the lapped undersurface of the intermediate element 11.

The valve needle 13 and a thrust pin 17 together form a unit. The thrust pin 17 extends through the central bore 18 of the throttle disc 15. The clearance between the throttle disc 15 and recess 16 is necessary in order to ensure that there is no danger or detriment to acceptable movement of the thrust pin 17 in the central bore 18 (this applies only to the embodiments shown on the left half of Fig. 3 and 7).

The quantity of overflow oil situated in a pressure chamber 20 between the throttle disc 15 and the end face 19 of the valve needle 13 is throttled when the valve needle 13 is raised, either by being displaced through a throttle bore 21 formed in the throttle disc 15 (left half of Fig. 3) or by being displaced through an accurately dimensioned throttle ring gap 22 between the thrust bolt 17 and the central bore 18 (right half of Fig. 3). When a throttle bore 21 is used, the clearance between the thrust bolt 17 and the central bore 18 must be very small so as not to modify the action of the throttle bore 21.

The overflow oil is introduced into the pressure chamber 20 before the valve needle 13 is raised, by being forced eitherthroughthethrottle bore 21 or through the throttle ring gap 22 by the pressure produced in the spring chamber 10 by the fuel delivery pump 2. This pressure is transmitted by way of the overflow oil line 7. As shown in Fig. 2, a valve 23 for switching the pressure on or off or reducing it may be arranged in the overflow oil line 7. Refilling of the pressure chamber 20 with overflow oil and hence the damping effect may thereby be partly or completely eliminated. This may become necessary in cases where damping of the opening movement would be undesirable at high speeds of rotation and under high loads since it could cause unduly prolonged injection and thus impairment of the engine parameters.The switching on and off or reduction of the pressure may be controlled by the speed of rotation andlor the load andlorthetemperature.

Fig. 4 shows an exemplary embodiment in which damping is effected by a throttle bore 24 in the intermediate element 11. The thrust bolt 17 which is in this case separate from the valve needle 13 is tightly guided in the intermediate element 11. The thrust bolt 17 and the spring plate 25 of a closing spring 26 provided in the spring chamber 10 together form one unit.

The throttling cross section for damping may also be formed by a flattened portion 27 (Figs. 5 and 6) formed on the thrust bolt 17 and extending in the longitudinal direction ofthevalve needle 13. Due to the length of this flattened portion, the pressure chamber 20 is in constant communication with the spring chamber 10.

Fig. 7 shows an arrangement in which the throttle device 14 is similar to that of Fig. 3 but the thrust bolt 17 is stepped. That portion 28 of the bolt which has the smaller diameter is directly connected to the valve needle 13 and its length is such that when the valve needle 13 has moved through a certain stroke, the greater cross section is released. This results so to speak in switching off of the damping, i.e. damping is eliminated during part of the injection, and the disadvantages connected with high speeds of rotation and load already mentioned above are avoided.

Damping may be completely switched off by means of a valve 23 provided in the overflow oil line 7. This valve 23 may be adapted to be influenced by engine parameters.

If a throttle disc 15 with throttle bore 21 is used, the smaller portion 28 of the thrust bolt 17 must have guide ribs 29 to ensure trouble free entrance ofthe larger bolt portion 30 in the central bore 18.

Claims

1. A fuel injection valve for an injection system consisting of a high pressure section and of a low pressure section containing a fuel delivery pump, for air compressing fuel injection combustion engines, the valve comprising a valve needle guided in a nozzle body, which needle in its opening direction counteracts a closing spring inside a spring chamber by means of a thrust bolt, and further comprising an overflow oil line connected to the injection valve and communication with the spring chamber, and a throttle device counteracting the opening pressure and situated between the spring chamber and a pressure chamber which is bounded by the back of the valve needle, the injection valve being in the form of a throttle pin nozzle and the overflow line is a low pressure line which communicates with said low pressure section, a valve being arranged in said low pressure line for controlling the pressure therein in dependence upon engine parameters.

2. Afuel injection valve according to claim 1, wherein the throttle device is formed by a throttle disc surrounding the thrust bolt and guided in a recess of the nozzle, which throttle disc in one direction bears tightly against the undersurface of an intermediate member adjacent to the nozzle body.

3. Afuel injectiOn valve according to claim 2, wherein the throttle disc has a throttle bore connecting the pressure chamber with the spring chamber.

4. Afuel injection valve according to claim 2, wherein a throttle ring gap connecting the pressure chamber with the spring chamber is provided between the thrust bolt and the throttle disc.

5. A fuel injection valve according to claim 1, wherein the throttle device is formed by a throttle bore situated in the intermediate member of the fuel injection valve, and the thrust bolt is tightly guided in the intermediate member.

6. Afuel injection valve according to any one of the preceding claims, wherein the thrust bolt is separate from the valve needle and is integral with a spring abutment plate of the closing spring.

7. A fuel injection valve according to any one of the preceding claims, wherein the throttle device is formed by a flattened portion on the thrust bolt extending in the longitudinal direction thereof.

8. A fuel injection valve according to any one of the preceding claims, wherein the thrust bolt is stepped and that portion of the thrust bolt which has the smaller diameter faces the valve needle, the larger diameter portion of the thrust bolt being raised out of the central bore of the disc or of the intermediate member when the valve needle is raised by a predetermined amount to thereby increase the cross section of the fluid connunication between the pressure chamber and spring diameter.

9. Afuel injection valve according to claim 8 wherein the smaller diameter portion of the thrust bolt includes guide means to guide the larger diameter portion into the said central bore.

10. A fuel injection valve for an injection system for air compressing fuel injection combustion engines substantially as described herein with reference to and as illustrated in Figures 1 and 2 or Figures 1 and 2 as modified by any part of Figures 3 to 7 of the accompanying drawings.