GB2094886A

GB2094886A - Fuel injection valve

Info

Publication number: GB2094886A
Application number: GB8206861A
Authority: GB
Original assignee: Daimler Benz AG
Current assignee: Daimler Benz AG
Priority date: 1981-03-14
Filing date: 1982-03-09
Publication date: 1982-09-22
Also published as: IT8247979A0; FR2501792A1; DE3109961A1

Abstract

The upward stroke of fuel pressure actuated needle 5 is counteracted by spring 4 and hydraulic pressure in chamber 15 acting through piston 11. Chamber 15 is connected to fuel inlet bore 13 via throttle 16 which serves to control needle movement at low engine loads and speeds. The return of needle 5 is unhindered. <IMAGE>

Description

SPECIFICATION A fuel injection valve The invention relates to a fuel injection valve especially for air-compressing fuel injection internal combustion engines of the type comprising a fuel inlet bore leading into a pressure chamber in the nozzle body and an injector needle with a thrust member, the said needle opening in the opposite direction to the direction of fuel flow and in opposition to the force of a closing spring, and further comprising a longitudinally displaceable piston which is coaxial with the injector needle, a hydraulic cylinder which is located in the closing spring chamber, and a throttle.

With a fuel injection valve of this kind for example as described in German Offenlegungsschrift 27 42 230, a pressure generated by a fuel pump is delivered through an additional pressure line to the piston by interposing control elements which operate depending on working conditions of the engine, in order that the movement of the injector needle may be varied by this external control.

The present invention seeks to provide particularly simple measures which can influence movement of the injector needle to the extent that the uncontrolled withdrawal of the injector needle from the nozzle opening or gap is prevented at very low loads and engine speeds.

According to the invention there is provided a fuel-injection valve for an air-compressing fuel injection internal combustion engine, comprising a fuel inlet bore leading into a pressure chamber in the nozzle body and an injector needle with a thrust member, the injector needle opening in the opposite direction to the direction of fuel flow and in opposition to the force of a closing spring, the valve further comprising a longitudinally displaceable piston which is coaxial with the injector needle, a hydraulic cylinder which is located in the closing spring chamber and a throttle, the piston being in direct contact with the thrust member and guided in the hydraulic cylinder which is rigidly mounted in the nozzle body, the end face of the piston remote from the injector needle and the hydraulic cylinder forming a pressure chamber which is connected to the fuel inlet bore through the throttle.

By using measures of this kind the existing fuel feed system of the injector arrangement causes a force to be exerted on the piston which is counteracting the needle movement at low loads and speeds of the internal combustion engine right from the beginning of the upward stroke of the injector needle. At the end of the injection cycle the injector needle can close again without difficulty. In this case the piston in the hydraulic cylinder follows the injector needle with a time constant which is determined by the throttle.

In order that the course of the inlet opening in the nozzle holder of conventional injection valves does not have to be changed, there is provided a feed passage which interconnects the throttle and the inlet opening.

A further advantageous embodiment of the invention is achieved in that the hydraulic cylinder is fitted in the nozzle body and one end of the closing spring is supported on the hydraulic cylinder, the other end being supported on the thrust member or bolt.

As a result of this method of securing the hydraulic cylinder and mounting the closing spring, the force of the closing spring can be varied simply by inserting distance or space plates above the hydraulic cylinder.

A further advantageous developement of the invention is obtained in that a disc-shaped plate having a bore which forms the throttle is clamped between the hydraulic cylinder and the body of the injection valve.

An embodiment of the invention will now be described in more detail and by way of example, with reference to the accompanying drawing, which shows the fuel-injection valve in axiai section.

A fuel injection valve 1 for an air-compressing, fuel-injection internal combustion engine consists essentially of a nozzle body 3, which is fitted to a nozzle holder 2, and an injector needle 5, which is controlled by the fuel pressure and opens in opposition to the action of a closing spring 4, and a throttle plug or pin.

The fuel delivered by the injection pump (not shown) passes through a pressure line into a inlet passage 6 in the nozzle holder 2 and an inlet bore 7 in the nozzle body 3 and, finally, into a pressure chamber 8 The fuel pressure generated by the injection pump acts upon a shoulder 9 of the injector needle 5, lifting it off its valve seating in the opposite direction to the direction of flow. At the same time a piston 11, which is longitudinally displaceable in a rigidly mounted hydraulic cylinder 10 and which, at a low engine speed and low load, is resting on the thrust member or bolt 12 as the needle movement commences, is also driven in like manner, the said thrust member or bolt 1 2 being pressed against the injector needle 5 by the pre-load of the closing spring 4.

The piston 11 also acts against the injector needle 5 during the upward stroke since a pressure which corresponds to the fuel pressure delivered by the injection pump to the pressure space in the nozzle body is exerted on the piston 11.

The fuel delivered consequently passes not only into the inlet bores 6, 7, but also into a feed passage 1 3 which branches off the inlet bore 6 in the upper area of the nozzle body 3, into a throttle opening 14 and opens into a pressure space 1 5 which is formed by the hydraulic cylinders 10 and the piston 11.

The throttle opening 14 is located in a discshaped plate 16 which is clamped between the hydraulic cylinder 10, which is screwed in the nozzle body 3, and a stop 1 7 of the nozzle body 3.

The nozzle opening pressure is consequently determined not only by the pre-load of the closing spring 4, which is supported at one end on the pressure bolt 12 and at the other end on a shoulder 18 of the hydraulic cylinder 10, but also by the hydraulic force exerted in the pressure space 15. The volume of fuel in this pressure space 1 5 must be displaced through the throttle during the piston stroke.

After the quantity of fuel delivered by the injection pump has been injected, the closing spring 4 forces the injector needle 5 back on to its seating by way of the thrust member or bolt 12 and, as a result of the build up of fuel pressure, the piston 11 comes to rest again on the thrust member or bolt 12.

Thus, by using the arrangement of an additional piston, the injector needle is prevented, shortly after being lifted off its valve seating, from receiving an undesirable acceleration pulse which has an adverse effect on the noise characteristics of the engine.

At the beginning of the operating cycle the piston has a braking or retarding effect on the injector needle and at the end of the injection cycle the injector needle closes without hindrance.

In this case the piston follows the injector needle with a time delay which is determined by the throttle opening By adjusting this time delay it is possible to prevent a complete return movement of the piston at a relatively high load and speed so that during the injection cycle the injector needle covers a certain distance without being braked.

Also, in the injection valve 1, a fuel leakage pipe connection 20 is connected to the spring chamber 1 9.

Claims

1. A fuel injection valve for an air-compressing fuel injection internal combustion engine, comprising a fuel inlet bore leading into a pressure chamber in the nozzle body and an injector needle with a thrust member, the injector needle opening in the opposite direction to the direction of fuel flow and in opposition to the force of a closing spring, the valve further comprising a longitudinally displaceable piston which is coaxial with the injector needle, a hydraulic cylinder which is located in the closing spring chamber and a throttle, the piston being in direct contact with the thrust member and is guided in the hydraulic cylinder which is rigidly mounted in the nozzle body, the end face of the piston remote from the injector needle and the hydraulic cylinder forming a pressure chamber which is connected to the fuel inlet bore through the throttle.

2. A fuel injection valve according to Claim 1, wherein a fuel feed passage is provided which interconnects the throttle and the inlet bore.

3. A fuel injection valve according to Claim 1 or Claim 2, wherein the hydraulic cylinder is inserted in the nozzle body and the closing spring is supported at one end on the hydraulic cylinder and at the other end is supported on the thrust member

4. A fuel injection valve according to any one of Claims 1 to 3, wherein a disc-shaped plate having a bore which forms the throttle is clamped between the hydraulic cylinder and the nozzle body of the injection valve.

5. A fuel injection valve for an internal combustion engine, substantially as hereinbefore described with reference to the accompanying drawing.