Injection System For Diesel Engines

Abstract

The needle valve is seated against the valve seat by the differential pressure of the fuel. Lifting of the needle valve is caused by transmitting a control pressure sufficient to overcome the differential pressure under the piston. This control pressure is delivered via the control member which selectively opens and closes the control line to the flow of pressure medium.

Description

This invention relates to an injection system. More particularly, this invention relates to a fuel injection system for a diesel engine.

It has been known in fuel injection systems for diesel engines to use hydraulically controlled injection valves. In such instances, the injection operation, i.e. the opening and closing of the valve, is controlled by the fuel at the injection pressure. However, with present day high fuel pressures of 1,000 atmospheres and above, the control line in which the full fuel pressure and a much lower pressure have been operative alternately has been subjected to considerable stress.

Accordingly, it is an object of this invention to provide an injection system which is subjected to a minimum of stress.

It is another object of the invention to provide an efficient high-pressure fuel injection system.

It is another object of the invention to utilize a low pressure to control the injection operation of an injection system.

Briefly, the invention provides an injection system for a diesel engine which relies on the case of a low pressure to operate the system while utilizing a fuel at high pressure. The system includes an injection valve which is constructed with a valve seat, a valve needle for seating on the valve seat and a piston connected to the valve needle, a fuel duct which conveys fuel at a high pressure to a space in front of the valve seat and a space in front of the piston, and a control means which conveys a pressurized control pressure medium of low pressure to a chamber to the rear of the piston.

The piston in the injection valve is guided with a stepped bore located in a first housing part of the valve in a sealtight manner so as to divide the stepped part of the bore into two chambers, one of which communicates with the control means while the other communicates to a low-pressure space, for example, at atmospheric pressure.

The fuel duct also cooperates with a second housing part of the injection valve which has a bore receiving a cylindrical part in slidable sealtight manner. The cylindrical part is disposed to abut against the piston in the first housing part and is pressed against the piston by the fuel pressure which is transmitted to a space in front of the cylindrical part. The diameter of the cylindrical part is greater than the needle valve and thus a differential pressure is imposed on the needle valve by the fuel so as to seat the needle valve on the valve seat. The diameter of the cylindrical part is, however, less than the diameter of the piston such that when the control means transmits a pressure to the chamber to the rear of the piston sufficient to overcome the differential pressure, the piston will move away from the valve seat. At the same time, due to the connection between the needle valve and piston, the needle valve will unseat from the valve seat causing injection of the fuel.

In order to synchronize the transmittal of the pulse of pressure necessary to cause opening of the valve, the control means can utilize a rotary valve which has a duct for the supply of pressure medium and at least one cylindrical control face and a bush which surrounds the control face and contains a duct to receive the pressure medium therefrom. The bush is further adjustably mounted axially and circumferentially of the rotary valve.

These and other objects and advantages of the invention will become more apparent from the following detailed description and appended claims taken in conjunction with the accompanying drawings in which:

FIG. 1 diagrammatically illustrates an injection system according to the invention; and

FIG. 2 illustrates a developed view of the control face of the rotary valve of the control means.

Referring to FIG. 1, a fuel injection valve 1 of a diesel engine is connected to a fuel reservoir 2 which is in turn connected via a fuel pipe 3 to a fuel pump 4 which delivers the fuel from a suitable source, such as a tank, at a pressure required for injection, e.g. 1,000 atmospheres. The injection valve 1 is also connected by a control line 5 to a control valve 6 which receives a hydraulic pressure medium--which is also fuel in this case--via a pipe 8 from a pump 7. The pipe 8 may in this case be connected to the same source of fuel as the pipe 3.

The injection valve 1 comprises a first housing part 10 formed in known manner with jet bores 11. A valve seat 12 is formed in front of the bores 11 and cooperates with a corresponding seat surface of a valve needle 13. The valve needle 13 is guided in sealing-tight relationship in a cylindrical bore 14 of the housing part 10 which communicates with a larger bore 15 in the housing part 10. The bore 15 contains a piston 16 which is also guided in sealing-tight relationship and which is rigidly connected to the valve needle 13 and may, for example, be integral therewith. The bore 15 thus forms a cylinder for the piston 16 which in turn divides the bore into two chambers 17, 18. One cylinder chamber 17 is connected to the control line 5 by a duct 20 formed in the valve 1 while the other cylinder chamber 18 communicates permanently with the external atmosphere via a duct 21 shown in broken lines.

A cylinder part 22 is located above the piston 16 and is guided in sealing-tight relationship in a bore 23 formed in a second housing part 24. The cylindrical part 22 is supported against the piston 16, there being a space 25 above the part 22 in the bore 23. In the valve 1, the space 25 communicates with a duct 26 connected to the fuel pipe 3. The duct 26 also leads into the bottom zone of the valve and into a cavity 27 in front of the valve seat 12.

The control member 6 contains a rotary valve 30 constructed in the form of a shaft and connected via a drive (not shown) to the engine crankshaft which drives the valve 30 accordingly. In a four-stroke engine, the drive occurs, for example, at half the crankshaft speed while in a two-stroke engine the drive occurs at the full engine speed. The rotary valve 30 is provided with an axial bore 31 connected to the delivery line 8 of the pump 7. The pressure in this line 8 may vary, for example, in the region of 200 atmospheres. The rotary valve 30 is also provided with a cylindrical control surface 32 (shown in developed form in FIG. 2). The control surface contains a substantially triangular recess 33 connected by a radial duct 34 to the bore 31 so as to be permanently subjected to the pressure of the pump 7. Adjacent the recess 33 and slightly spaced therefrom as shown, is a recess 35 which extends over the remainder of the periphery of the valve 30 and which is connected to atmosphere via a duct 36.

The control surface 32 forming the control plate of the valve 30 is guided in sealing-tight relationship in a bush 37 provided with a duct 38 leading to the exterior. The bush 37 is disposed in a valve housing 40 having a duct 41 which is connected to the duct 38 and to which the control line 5 is connected. Control members 42 and 43, which comprise gearwheels connected to levers and which mesh with teeth extending circumferentially and longitudinally on the bush 37 allow the bush 37 to be adjusted in these directions upon manipulation of the levers.

The control valve 30 is further mounted in the valve housing 40 in a bearing 44 which is lubricated with the pressure medium via a bore 45.

As will be apparent from the drawing, the diameter D1 of the valve needle 13 is smaller than the diameter D2 of the cylindrical part 22 which is in turn smaller than the diameter D3 of the piston 16. Thus, if the control valve 1 is subjected only to the fuel pressure, the valve needle 13 is pressed against the seat 12 by the difference in the pressures operative on the part 22 in the space 25 and on the valve 13 in the space 27. Access of fuel to the jet bores 11 and thus to the cylinder chamber is closed. As soon as the hydraulic pressure operative in the cylinder chamber 17 is such as to be sufficient to lift the valve needle against this pressure difference, the valve 1 is opened and the fuel is injected from the reservoir 2 into the engine combustion chamber via the jets 11. This injection process continues as long as the control pressure is operative in the cylinder chamber 17.

In order to vary the pressure in the cylinder chamber 17, the valve 30 of the control member 6 is rotated by the drive (not shown) so that the duct 38 of the bush 37 which is in communication with duct 41 is alternatively brought into communication with recess 33 and recess 35. That is, while the duct 38 is in communication with recess 33, the pressure of line 8 is transmitted via control line 5 into the cylinder chamber 17 so that the piston 16 is lifted upon the pressure becoming greater than the pressure differential caused by the fuel pressure. Upon continued rotation of the rotary valve 30, recess 35 comes into communication with the duct 38 so that the line pressure in line 8 is cut off from the control line 5. The pressure in cylinder chamber 17 then drops off and, as the piston 16 moves down, the pressure medium is exhausted through duct 21 as well as duct 36. Depending upon the axial adjustment of the bush 37, the communication between the duct 38 and recess 34 can last for a longer or shorter period, owing to the triangular shape of the recess 33. Thus, the duration of the injection operation and hence the amount of fuel injected can be influenced. Control of the amount of fuel is thus effected by the control member 43. Rotation of the bush 37 with respect to the valve 30 by means of the control member 42 alters the beginning and end of the injection process.

The invention thus provides an injection system which is very simple and very compact in construction and which is made with a minimum number of conduits so that there is a minimum of leakage losses.

It is noted that the control means can be used with injection valves of a number of cylinders. It is only necessary for the rotary valve to be provided with an appropriate number of cylindrical control surfaces and for the appropriate number of bushes to be provided.

Claims

What is claimed is:

1. An injection system for a diesel engine comprising:

an injection valve for injecting fuel and having a valve seat at one end and a bore spaced from said valve seat;

a valve needle in said valve for seating on said valve seat, said valve needle having a piston thereon slidably mounted in said bore in sealtight relation to divide said bore into a pair of chambers;

a duct having pressurized fuel therein for pressing said valve needle against said valve seat under the pressure of the fuel;

first means connecting the chamber of said pair of chambers remote from said valve seat to a low pressure space; and

a single fuel duct in said valve communicating with both a space upstream of said valve seat and a space upstream of said piston for imposing a differential pressure on said needle to seat said needle against said valve seat; and

means connected to said valve communicating with said bore on the side of said piston closest to said valve seat for selectively increasing the pressure therein to an amount greater than said differential pressure to unseat said needle from said valve seat.

2. An injection system as set forth in claim 1 further comprising fuel storage means connected to said injection valve.

3. An injection system as set forth in claim 1 wherein said first means maintains said remote chamber at atmospheric pressure.

4. An injection system as set forth in claim 1 wherein said control member includes a rotary valve having a cylindrical control surface and a duct therein for conveying the control pressure medium therethrough to said control surface and a bush slidably and rotatably mounting said control surface of said valve therein, said bush having a duct therein for selective communication with said rotary valve duct.

5. An injection system as set forth in claim 1 wherein said injection valve includes a first housing part having said bore therein to receive said valve needle and said piston and a second housing part having a bore therein, and wherein said first means includes a cylindrical part slidably mounted in said bore of said second housing part against said piston and a fuel duct connected at one end to a space upstream of said valve seat in said first housing part and to a space in said bore of said second housing part upstream of said cylindrical part.

6. An injection system comprising:

an injection valve for injecting fuel, said valve having a valve seat at one end, a bore therein, and jet bores to one side of said valve seat;

a valve needle in said valve for seating on said valve seat, said valve needle having a piston at one end thereof mounted in said bore in sealtight relation;

second means connecting the chamber of said pair of chambers closest to said valve seat to a source of pressurized control pressure medium of a pressure sufficient to move said piston and said needle valve away from said valve seat, said means including a control member for selectively connecting said closest chamber to the source of pressurized control pressure medium.

7. An injection system as set forth in claim 6 wherein said means includes a rotary valve having a control surface and a duct therein for conveying a control pressure medium therethrough to said control surface, and a bush mounted about said control surface and having a duct therein for conveying the control pressure medium to said bore of said injection valve.

8. An injection system as set forth in claim 7 wherein said control surface includes a triangular recess communicating with said duct in said rotary valve and a peripherally extending recess communicating to the exterior of said rotary valve.

9. An injection system as set forth in claim 7 wherein said bush is adjustably relative to said rotary valve in a circumferential direction and a longitudinal direction.

10. An injection system as set forth in claim 6 wherein said injection valve has a first housing part with a stepped bore respectively receiving said valve needle and said piston, and a second housing part with a bore receiving a cylindrical part therein in slidable sealtight relation, said cylindrical part having a diameter greater than said valve needle and less than said piston.