GB2031995A - Fuel injection system - Google Patents

Abstract

A fuel injection system for a mixture compressing internal combustion engine comprises a fuel injection valve (34) downstream of a throttle (5) in an air induction pipe (1, 7), air being supplied to the injection valve via an air line (55) from upstream of the throttle (5). The injection valve (34) has an injection section (67), which projects into the induction pipe (1, 7) and is furnished with a peripheral groove (69), from which air ducts (70) lead to the injection duct (68) of the injection valve (34), so that the air flowing through the induction pipe is deflected onto the fuel and air flowing through the injection duct to improve atomization. <IMAGE>

Description

SPECIFICATION Fuel injection system The present invention relates to a fuel injection system for a mixture-compression applied ignition internal combustion engine.

According to the present invention there is provided a fuel injection system for a mixturecompression internal combustion engine, comprising an air induction duct, throttle means disposed within the air induction duct, and a fuel injection valve disposed downstream of the throttle means, the fuel injection valve comprises a fuel passage, a valve seat, an air chamber downstream of the valve seat, an air passage leading from the air induction duct upstream of the throttle means to the air chamber, a valve need co-operable with the valve seat to control flow of fuel from the fuel passage to the air chamber to produce an air/fuel mixture, and a valve portion disposed within the air induction duct downstream of the throttle means and defining air duct means arranged to permit air in the air induction duct to flow through the air duct means and to combine with the air/fuel mixture.

An embodiment of the present invention will now be made particularly described by way of example and with reference to the accompanying drawings in which: Fig. 1 shows a fuel injection system and Fig. 2 shows a section through a fuel injection valve.

Referring to the accompanying drawngs, in the fuel injection installation shown in Fig. 1, combustion air flows in the direction of the arrow via an induction pipe portion 1 into an approximately conical portion 2, in which an air flow responsive element 3 is disposed, and then through an induction pipe portion 4, in which is disposed a throttle valve 5 which can be actuated as desired, to an intake manifold 6 and thence via induction pipe portions 7 to one or more cylinders of a mixture-compressing, internal ignition combustion engine.The air flow responsive element 3 comprises a plate 3, disposed transversely to the flow direction and which moves in the portion 2 of the induction pipe according to an approximately linear function of the air flow rate through the induction pipe, whereby, for a constant restoring force acting upon the air flow responsive element 3 and a constant air pressure obtaining upstream of the air flow responsive metering element 3, the pressure between the air flow responsive element 3 and the throttle valve 5 also remains constant. The air flow responsive element 3 regulates a metering and flow dividing valve 10.For transmitting the adjustment movement of the air flow responsive element 3, a pivotable lever 11 connected thereto is used, which lever together with a correcting lever 12 is journaled at a pivot point 13 and, in its pivoting movement, actuates a moveable valve component comprising a valve plunger 14 of the metering and flow dividing valve 10. The desired fuel-air mixture can be adjusted by a mixture regulating screw 1 5. An end face 16, remote from the pivoting lever 11 , of the valve plunger 14 is acted upon by pressurized liquid, the pressure of which on the end face 1 6 produces a restoring force on the air flow responsive element 3.

The fuel supply is provided, for example, through an electric fuel pump 19, which sucks fuel from a fuel tank 20 and delivers it via a fuel reservoir 21, a fuel filter 22 and a fuel supply line 23 to the metering and flow dividing valve 10. A system pressure regulator 24 maintains the system pressure in the fuel injection installation constant.

The fuel supply line 23 leads, via various branches, to chambers 26 of the metering and flow dividing valve 10, so that one face of a diaphragm 27 is subjected to the fuer pressure.

The chambers 26 are also in communication with an annular groove 28 in the valve plunger 14.

Depending upon the position of the valve plunger 14, the annular groove opens to a greater or lesser extent control slits 29, which each lead to a chamber 30, which is separated by the diaphragm 27 from the chamber26. From the chamber 30, the fuel passes via injection lines 33 to individual valves 34, which are disposed for example, in the vicinity of the engine cylinders 8 in the induction pipe portions 7. The diaphragm 27 acts as a moveable part of a flat-seating valve, which is held open by a spring 35 when the fuel injection installation is not operating.The diaphragm spaces each composed of one of each chamber 26 and 30 have the effect that, independently of the overlap existing between the annular groove 28 and the control slits 29, i.e. independently of the fuel flow rate to the injection valves 34, the pressure drop at the metering valves 28, 29 remains largely constant. In this manner it is ensured that the adjustment travel of the valve plunger 14 and the metered fuel flow rate are proportional.

When a pivoting movement of the control lever 11 occurs, the air flow responsive element 3 moves into the portion 2, so that the annular cross section, changing between the air flow responsive element and the cross section of the portion 2, is approximately proportional to the adjustment travel of the flow responsive element 3.

The pressurized liquid producing the constant restoring force on the valve plunger 14 is fuel. For this purpose, a control pressure line 36, which is separated from the fuel supply line 23 by a decoupling throttle 37, branches from the fuel supply line 23. A pressure chamber 39, into which the valve plunger 14 projects by its end face 1 6, is connected via a damping throttle 38 to the control pressure line 36.

In the control pressure line 36, a pressure control valve 42 is disposed, by which the pressurized liquid can pass unpressurized through a return line 43 to the fuel tank 20. By the pressure control valve 42, the pressure of the pressurized liquid producing the restoring force can be varied during warming up of the internal combustion engine in accordance with a temperature and time function. The pressure control valve 42 is in the form of a flat seating valve comprising a fixed valve seating 44 and a diaphragm 45, which is biased in the closure direction of the valve by a spring 46. The spring 46 acts via a spring plate 47 and a transmission pin 48 upon the diaphragm 45.At temperatures below the engine operating temperature, a bimetallic spring 49 acts in opposition to the spring force 46, on which bimetallic spring an electrical heater 50 is mounted, the heating-up of which after the start leads to a reduction in the force of the bimetallicc spring 49 on the spring 46, thus causing the control pressure line 36 to rise.

To enable the system to operate with an electric fuel pump with the least possible power demand and to have as few sealing problems as possible, the objective is to operate with a fuel injection plant with the lowest possible fuel pressure. This however, results in a substantially lower injection pressure at the injection valves 34, which leads to unsatisfactory atomization of the injected fuel. An improvement to the atomization of the injected fuel can be acheved by having an air line 55 leading into the fuel injection valve 34 downstream of the valve seating, which air line is in communication with an induction pipe portion upstream of the throttle valve 5. Air flows through this air line as a result of the pressure difference between the injection point and the induction pipe portion upstream of the throttle valve 5, thus leading to an improved atomization of the injected fuel.In part-load and full-load operation of the internal combustion engine, however, the pressure difference between the injection point and the induction pipe portion upstream of the throttle valve 5 is so slight that satisfactory atomization of the injected fuel no longer occurs. The same is true in the acceleration stage. The fuel injection valve 34 shown in Fig. 2 improves the preparation of the fuel in the part-load and full-load range of the internal combustion engine and during acceleration. The fuel injection valve 34 shown in Fig. 2 comprises a valve needle 56, which is slideably mounted in a bore 57 of a valve body 58. At the end of the valve needle 56 disposed in the direction of flow, the valve needle comprises a conical closure head 59 and at the opposite end it comprises a head 60, which acts as an abutment for a spring plate 61.A closure spring 62, bearing at said opposite end against the valve body 58, acts upon the spring plate 61.

The fuel supplied via the injection line 33 from the fuel flow dividing and metering valve 10 to the injection valve 34 passes into a pressure chamber 63 of the valve casing 64, in which the closure spring 62 is disposed, and thence via the bore 57 to the closure head 59, which co-operates with a valve seat 65 of the valve body 58. When the fuel pressure is sufficient the closure head 59 lifts from the valve seat 65, so that fuel is injected into an air chamber 66 in an injection portion 67 of the fuel injection valve 34 and thence, via an injection duct 68, into the air induction pipe. The injection portion 67 projects into the air induction pipe and is swept by the induction air.The air line 55 leads into the air chamber 66 in such a manner that the fuel entering via the valve seat 65 is surrounded annularly by air, is atomized by this air and is conveyed onwards to the injection duct 68. In the part-load and full-load range of the internal combustion engine, however, the pressure difference between the injection point and the induction pipe section up-stream of the throttle valve 5 is so slight that preparation of the fuel by the air flowing through the line 55 is negligible. In order to assure further preparation of the injected fuel, especially in the part-load and full-load range of the internal combustion engine and during acceleration, the injection portion 67 of the injection valve 34 is furnished with a circumferential groove 69, from which air ducts 70 lead into the injection duct 68. The air ducts 70 guide the air flowing through the induction pipe onto the fuel which is to be injected in the air duct 68, thus causing atomization of the fuel droplets. The injection duct 68 can conically diverge towards the induction pipe, and the injection ducts 70 can have a slope in the direction of flow. The air ducts 70 may also lead tangentially into the injection duct 68, so that as a consequence of the twist produced an intensive turbulence and atomization of the fuel into extremely fine droplets takes place.

The above described embodiment has the advantage that even in part-load or full-load of the internal combustion engine the fuel to be injected is sea prepared with air, that a homogeneous fuelair mixture is assured and the efficiency of the engine is improved and the proportions of toxic constituents in the exhaust gases are reduced.

Claims (5)

1. A fuel injection system for a mixturecompression internal combustion engine, comprising an air induction duct, throttle means disposed within the air induction duct, and a fuel injection valve disposed downstream of the throttle means, the fuel injection valve comprising a fuel passage, a valve seat, an air chamber downstream of the valve seat, an air passage leading from the air induction duct upstream of the throttle means to the air chamber, a valve needle co-operable with the valve seat to control flow of fuel from the fuel passage to the air chamber to produce an air/fuel mixture, and a valve portion disposed within the air induction duct downstream of the throttle means and defining air duct means arranged to permit air in the air induction duct to flow through the air duct means and to combine with the air/fuel mixture.

2. A system as claimed in claim 1, the air duct means being inclined in the down stream direction thereof to converge towards the flow direction of the air/fuel mixture.

3. A system as claimed in either claim 1 or claim 2, the air duct means being defined at least in part by groove means on the outer periphery of said valve portion.

4. A system as claimed in any one of the preceding claims, the air duct means being so arranged as to impart a swirling motion to the air/fuel mixture.

5. A fuel injection system substantially as hereinbefore described with reference to the accompanying drawings.