Fuel Injection System For An Internal Combustion Piston Engine

Abstract

The valve needle is held closed under the differential pressure of the fuel acting at the ends of the needle. In order to open the valve, a low pressure is applied to lift the control valve body. This allows the fuel to pass from the rear fuel chamber causing a pressure drop and a pressure differential to occur to unseat the needle valve.

Description

This invention relates to a fuel injection system for an internal combustion piston engine.

It has been known in fuel injection systems in which a cylindrical valve needle closes off the access to the jet bores and is guided in a needle bore to provide a front fuel chamber adjacent the fuel seat and to provide a fuel duct along the needle for connecting the fuel chamber to a fuel storage chamber. Also, it has been known to control the valve needle movements hydraulically. In such cases, a line carrying the fuel pressure and a lower pressure alternately has been used for control purposes. However, such control lines are subjected to high mechanical loads due to the high fuel pressure.

Accordingly, it is an object of the invention to control a fuel injection valve by a low hydraulic pressure.

It is another object of the invention to reduce the load on the pressure lines of a fuel injection system.

Briefly, the invention provides a fuel injection system for an internal combustion piston engine which is controlled by the use of a low-pressure pressure medium. The system includes an injection valve having a front fuel chamber in a housing adjacent a valve seat, a needle valve for seating on the valve seat and a fuel duct extending along the needle valve in communication with the front fuel chamber and a fuel storage chamber. The system further includes a rear fuel chamber formed in the housing at the end of the needle remote from the valve seat. This rear fuel chamber is connected to the duct via a throttle bore, and a hydraulically operated control valve is provided in the region of the valve and is adapted to be operated by a control pressure which is much less than the fuel injection pressure. When the control valve is operated, the rear fuel chamber becomes connected to a chamber at a lower pressure than the fuel pressure.

Preferably, the control valve is provided with a piston which is guided in a cylinder bore so as to be substantially sealtight and divides the bore into a front cylinder chamber and a rear cylinder chamber. The front cylinder chamber is adapted to be connected to the control pressure source, while the rear cylinder chamber is permanently connected to a line at a lower pressure than the control pressure. This gives a simple control valve construction which can be disposed in the housing near the valve needle. This is an important feature for the injection operation, since it eliminates any dynamic processes in the lines.

Advantageously, the line to which the rear cylinder chamber is connected contains a pressure-maintaining valve which maintains a pressure higher than atmospheric pressure in the rear cylinder chamber. This suppresses or obviates any cavitation in the valve and in the injection system. A known control valve, preferably a rotary valve, may be provided to deliver the control pressure. Such a valve connects a control line leading to the valve to a pump delivering the pressure medium at the control pressure.

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:

The FIGURE schematically illustrates a fuel injection system according to the invention.

Referring to the drawing a fuel injection valve 1 of an internal combustion engine which operates on the diesel principle includes a housing part 2 containing a valve needle 3 which is guided in a bore so as to be sealing-tight. The end of the valve needle 3 has a conical seat part cooperating with a valve seat 4 which serves to close the access to a plurality of jet bores 5 in the part 2 as required. A front fuel chamber 6 is located above the valve seat 4 and is connected via a duct 7 to a storage chamber 8 for fuel. The storage chamber 8 is connected by a fuel pipe 10 to a fuel pump 11 which delivers the fuel from a tank 12 at a pressure of the required value for injection, e.g., of the order of 1,000 atmospheres.

At the end of the valve needle 3 remote from the valve seat 4 is a rear fuel chamber 13 which communicates with the duct 7 via a throttle bore 14, i.e., a bore whose diameter is smaller than that of the duct 7.

Adjacent the housing part 2 is a housing part 15 containing a control valve 16 guided in bores 17, 18. The lower bore 17 communicates with the rear fuel chamber 13 via a bore 20. A valve body 16 is slidably mounted in the housing part 15 to constitute a control valve and includes a piston 21 which is movable in the bore 18 and divides the bore 18 into a front cylinder chamber 22 and a rear cylinder chamber 23. The front cylinder chamber 22 communicates with a control line 25 via a duct 24 while the rear cylinder chamber 23 is connected via a duct 26 to an overflow line 27 which leads back to the tank 12 and which contains a pressure-maintaining valve 28. The control valve body 16 has a longitudinal bore 30 the front part of which leads out laterally (or radially) and through which the bore 20 can be connected to the duct 26 when the control valve is open.

The control line 25 contains a control valve 31 which may be constructed as a known rotary valve and is connected via a shaft 32 to the engine crankshaft (not shown). The drive is obtained in known manner either at the same speed as or at half the speed of the crankshaft depending upon whether the engine is a two-stroke or a four-stroke engine. The control valve 31 controls the supply of pressure medium used to actuate the valve 16, the pressure medium being delivered by a control pump 33 under a pressure which is much less than the fuel injection pressure. That is, the control valve 31 is constructed so as to selectively make and break a connection between the lines 25, 34 while simultaneously selectively breaking and making a connection between the lines 25 and 27. In the construction illustrated, the pressure medium used is fuel which is also drawn from the tank 12. The control valve 31 is connected to the control pump 33 via a delivery pipe 34.

In operation, when the rotary valve 31 breaks the connection between the lines 25 and 34 during operation of the engine and connects the line 25 to the outflow line 27, the control valve 16 is closed, since it is forced against its seat by the positive pressure in the line 27, and closes the bore 20. The same pressure is operative in the front fuel chamber 6 and in the rear fuel chamber 13, i.e., the fuel pump pressure supplied via line 10. As a result of the larger cross-sectional area adjacent the chamber 13, the needle valve 3 is pressed against the valve seat 4 and shuts off access of the fuel to the jet bores 5.

As soon as the control valve 31 connects the delivery line 34 of the control pump 33 to the control line 25, the valve body 16 is lifted by the imposed low control pressure on the piston 21 and opens a connection of the rear fuel chamber 13 via the bore 20 and bore 30 of the valve body 16 to the duct 26 and the overflow line 27. As a result, the pressure in the rear fuel chamber drops abruptly and the valve needle 3 is lifted by the pressure operative in the front fuel chamber 6. The fuel is then injected into the engine combustion chamber (not shown) through the jet bores 5 from the line 10 and the storage chamber 8.

When it is required to terminate the injection operation, the control valve 31 again breaks the connection between the lines 34 and 25 and connects line 25 to the overflow line 27. The valve 16 is then closed by the pressure operative in front of the pressure-maintaining valve 28 in the line 27. The pressure in the rear fuel chamber 13 immediately again assumes the value operative in the duct 7 and the needle 3 closes. The closing movement of the valve needle 3 is assisted by the pressure drop in the duct 7 along the valve needle 3, with the result that while the needle 3 is still lifted from the valve seat the pressure in the rear fuel chamber 13 is higher than the pressure in the front fuel chamber 6 despite the small cross section of the throttle bore 4.

The object of the throttle bore 14 is to connect the rear fuel chamber 13 to the duct 7 in such a way that when the valve body 16 is lifted, when the rear fuel chamber 13 is connected to the overflow line 27, the fuel pressure in the duct 7 is prevented from dropping appreciably.

Since the pressure-maintaining valve 28 maintains a higher pressure than atmospheric pressure, e.g., a pressure of some atmospheres, in the line 27 and hence also in the rear cylinder chamber 23, a number of advantages are obtained. For example, cavitation is prevented in the entire valve system. In addition, softer operation of the valve 16 is obtained because it does not open as jerkily. Finally, an important advantage is that in this way it is possible to construct a valve without the use of a single spring. The springs which are subjected to high dynamic loading in such valves are in fact a difficult problem in most cases.

Claims

What is claimed is:

1. A fuel injection system for an internal combustion piston engine comprising:

a fuel storage chamber; and

an injection valve having a plurality of jet bores, a valve seat, a front fuel chamber adjacent said valve seat, a rear fuel chamber remote from said valve seat, a valve needle slidably mounted between said front fuel chamber and said rear fuel chamber for seating on said valve seat, a fuel duct extending along said needle communicating said front fuel chamber with said fuel storage chamber, a throttle bore communicating said fuel duct with said rear fuel chamber, and means for selectively connecting said rear fuel chamber to a chamber remote from said fuel duct and at a lower pressure than the fuel pressure, said means includes a stepped bore in said valve communicating with said rear fuel chamber, a valve body having a piston slidably disposed in said bore in sealtight relation for closing said bore from said rear fuel chamber, said piston dividing said bore into a front cylinder chamber and a rear cylinder chamber, said valve body having a bore communicating said stepped bore adjacent said rear fuel chamber with said rear cylinder chamber, a control means connected to said front cylinder chamber to transmit a control pressure thereto less than the fuel pressure for lifting of said valve body to communicate said rear fuel chamber with said stepped bore, and an overflow line connected to said rear cylinder chamber, said overflow line being at a pressure lower than the control pressure.

2. A fuel injection system as set forth in claim 1 wherein said overflow line includes a pressure-maintaining valve for maintaining a pressure higher than atmospheric pressure in said rear cylinder chamber.

3. A fuel injection system for an internal combustion piston engine comprising:

a fuel storage chamber; and

an injection valve having a plurality of jet bores, a valve seat, a front fuel chamber adjacent said valve seat, a rear fuel chamber remote from said valve seat, a valve needle slidably mounted between said front fuel chamber and said rear fuel chamber for seating on said valve seat, a fuel duct extending along said needle communicating said front fuel chamber with said fuel storage chamber, a throttle bore communicating said fuel duct with said rear fuel chamber, and means for selectively connecting said rear fuel chamber to a chamber remote from said fuel duct and at a lower pressure than the fuel pressure, said means including a control line, a pump for delivering pressure medium through said control line at the control pressure, a control valve in said control line to selectively pass the pressure medium therethrough and a control valve in said injection valve connected to said control line for connecting said rear fuel chamber to said lower pressure chamber.

4. A fuel injection valve for an internal combustion engine comprising:

a valve seat,

a front fuel chamber adjacent said valve seat,

a rear fuel chamber remote from said valve seat,

a valve needle slidably mounted between said first chambers for seating on said valve seat,

a fuel duct connected to said front fuel chamber for supplying fuel thereto,

a low-pressure chamber adjacent said rear fuel chamber and remote from said fuel duct,

valve means selectively sealing said rear fuel chamber from said low-pressure chamber; and

a throttle bore connecting said fuel duct with said rear fuel chamber to permit the occurrence of a lower pressure in said rear fuel chamber than in said front fuel chamber upon removal of fuel from said rear fuel chamber through said valve means to said low-pressure chamber.