GB1584932A - Fuel injection systems for internal combustion engines - Google Patents

Description

(54) IMPROVEMENTS RELATING TO FUEL INJECTION SYSTEMS FOR INTERNAL COMBUSTION ENGINES (71) We, ROBERT BOSCH GmbH, a German company of Postfach 50, 7 Stuttgart 1, Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to a fuel injection system for mixture-compressing, spark-ignited internal combustion engines having an injection point into the air intake pipe.

In certain known fuel injection systems unsuitable fuel guidance downstream of the fuel metering valve results in undesirable leakages and spattering of the fuel jet.

According to the present invention there is provided a fuel injection system for mixturecompressing, externally ignited internal combustion engines having an injection point into an air intake pipe, comprising an air flow measuring element and an arbitrarily actuable throttle valve disposed one behind the other in the intake pipe, the measuring element being movable in dependence upon the throughflowing air flow rate, against a restoring force, to thereby displace the movable part of a valve disposed in the fuel line for metering a fuel flow rate proportional to the air flow rate, the fuel metering valve having a control slot which is opened to a greater or lesser extent by a control edge, there being provided downstream of the control slot, between the control slot and an injection line leading to the injection point, a truncated-cone-like portion of line whose smaller cross-section opens out into the injection line, this truncated-cone-like portion of line operatively connecting the control slot to the injection line.

A fuel injection system according to the present invention has by comparison with known systems, the advantage that the fuel jet is guided downstream of the fuel metering valve with the minimum possible resistance and without spattering, to the injection point.

The present invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 shows a section through one embodiment of a fuel injection system according to the present invention, along the line I-I of Fig. 2.

Fig. 2 shows a plan view of the fuel injection system; and Fig. 3 shows a cutout of the fuel injection system with the fuel metering valve, to an enlarged scale.

In the fuel injection system shown in Fig. 1, the combustion air flows in the direction of the arrow into an air intake pipe or manifold 1, which has a portion 2 having disposed therein an air flow measuring element in the form of a flat valve 3, and on through a portion 4 having an arbitrarily actuable throttle valve 5, to one or more cylinders (not shown) of an internal combustion engine.

The measuring element in the form of a flap valve 3 moves in the suitably adapted portion 2 of the air intake pipe 1 according to a substantially linear function of the air quantity flowing through the air intake pipe, the pressure between the measuring element and the throttle valve 5 remaining constant when a constant air pressure prevails before the measuring element. The measuring element 3 is rotatably journalled on a fixed bearing axle 7 disposed transversely to the air intake pipe, and is provided with a damping valve member 8. During an opening movement of the measuring element 3, the damping valve member 8 dips into a damping portion 9 of the air intake pipe.The chamber 10 formed by the damping valve member 8 and the damping portion 9 is connected by a small gap 11 between the end face of the damping valve member 8 and the wall of the damping portion 9, to the air intake pipe downstream of the measuring element 3. The effect of the damping valve 8, 10, 11 is that intake manifold pressure fluctuations caused by intake strokes of the engine have almost no influence upon the angular setting of the measuring element 3.

As Fig. 2shows, fuel is supplied by a fuel pump 14 which is driven by an electric motor 13. The pump 14 draws fuel from a fuel tank 15 and supplies the fuel through a line 16 to a chamber 17 of a differential pressure valve 18. From the chamber 17 the fuel passes through a line 19 into a chamber 20 formed by an end face of the bearing axle 7 and the guide bore 21 in which the bearing axle is located. The chamber 20 is connected by a bore 22 (shown by dashed lines in Fig. 2) to a control groove 23 worked into the surface of the bearing axle 7. The measuring element 3 and the damping valve member 8 are disposed on a bearing hub 24 which is firmly connected to a bush 25 which is rotatable on the bearing axle 7. Worked into the bush 25 is a control slot 26 which opens out into a groove 27 of the bush 25.

The control slot 26 cooperates with a control edge 28 formed by the area of contact of control groove 23 formed in the bearing axle.

By means of the control edge 28, the control slot 26 is opened to a greater or lesser extent depending upon the position of the measuring element 3 so that a fuel quantity proportional to the air quantity drawn in by the engine, may be metered. The control edge 28 and the control slot 26 form a fuel metering valve 29 which is disposed in the bearing axle 7 of the measuring element 3.

The metered fuel passes through the groove 27 into a truncated-cone-like portion of line 30 which leads into a simaller crosssection injection line 33 disposed in the measuring element 3. The injection line 33 leads to the end face of the measuring element 3 and by way of an injection nozzle 34, into the gap 35 between the end face of measuring element 3 and the wall of the air intake pipe portion 2, a high air speed prevailing in this gap 35. The groove 27 is connected by an air opening 36 to the intake manifold portion 1 upstream of the measuring element 3 so that the intake pipe or manifold pressure upstream of the measuring element, prevails as a counterpressure downstream of the fuel metering point.The injection line 33 may alternatively, ,as is not shown, be connected to several injection nozzles 34 disposed in the erid face of the measuring element 3. An injection gap which extends almost over the entire width of the front face of the measuring element 3 may alternatively be used as an injection nozzle 34.

Metering of the fuel at the fuel metering valve 29 is effected with a constant pressure difference prevailing across the metering valve. For this purpose, a chamber 38, which is separated by a diaphragm 39 from the chamber 17 of the differential pressure valve 18, is connected by an air line (shown by dashed lines) 37 to the intake manifold portion 1 upstream of the measuring element 3 so that the same pressure prevails in the chamber 38 as downstream of the control slot 26. The differential pressure valve 18 is acted upon in a closing direction by a spring 40 disposed in the chamber 38. The force of the spring 40 is variable in depence upon operating characteristics of the engine.For this purpose it 'is possible, for example, to use an electromagnet 41 which acts by way of an actuating pin 42 upon the spring 40 or an additional force which is dependent upon operating characteristics may act parallel to the spring 40 directly upon the diaphragm 39. The magnetic force may be, for example, variable in dependence upon the signal of an oxygen probe disposed in the exhaust gas line of the engine.

The differential pressure valve 18 takes the form of a flat seat valve having the diaphragm 39 as a movable valve part and a fixed valve seat 43 through which fuel may pass into a return line 44 which opens out into the fuel tank 15. The differential pressure valve serves simultaneously as a system pressure valve.

The measuring element 3 is deflected against the force of a helical spring 47, one end of which is connected to the bush 25 while the other end is connected to a stop 48 on the air intake line. The basic adjustment of the fuel metering valve 29 is variable by rotating the bearing axle.

As Fig. 1 shows, the groove 27 is connected to an air opening 36 which opens out into the air intake line 1 upstream of the measuring element 3. The application of the intake pipe pressure upstream of the measuring element 3 by way of the air opening 36 as a counterpressure upon the metering point has besides the advantage of preliminary preparation of the metered fuel with air, the additional advantages that on the one hand it is possible to operate with an open injection nozzle and on the other hand regulation of a constant differential pressure at the metering point may be simplified.

The fuel injection system operates as follows :- When the engine is running, fuel is drawn from the fuel tank 15 by the fuel pump 14 driven by the electric motor 13 and is supplied through the line 16 to the fuel metering valve 29. At the same time, the engine draws in air through the air intake pipe 1 so that the measuring element 3 is deflected to some degree from its position of rest. According to the deflection of the measuring element 3, the control slot 26 opens to a greater or lesser extent relative to the control edge 28. The direct control of the fuel metering valve by the measuring element 3 produces a constant ratio of air intake quantity and metered fuel quantity.Metering is effected with a pressure difference held constant by the differential pressure valve 18, the force of the spring 40 and therefore the pressure difference being variable for adaptation to the various working conditions of the engine.

The metered fuel is injected through the injection nozzle 34 at the end face of the measuring element 3 into the gap 35 between the front face of the measuring element 3 and the wall of the portion 2, i.e. at the point of highest flow speed, in order to achieve a fuel-air mixture which is as homogeneous as possible.

The contour of the wall of the portion 2 opposite the front face of the measuring element may be adapted to the desired fuel-air ratio.

Since the geometry of the fuel jet emerging from the control slot 26 varies widely depending upon opening of the control slot, the entrance into the injection line 33 must have a precisely defined shape to avoid undesirable spattering of the fuel jet and to convey the metered fuel with the minimum resistance to the fuel injection point. According to the invention, therefore, there is provided downstream of the control slot 26 between the control slot and the injection line 33 a truncated-cone-like portion of line 30 which leads into the smaller cross-section injection line, the cone preferably having an opening angle of approximately 30".

WHAT WE CLAIM IS:- 1. A fuel injection system for mixturecompressing, externally ignited internal combustion engines having an injection point into an air intake pipe, comprising an air flow measuring element and an arbitrarily actuable throttle valve disposed one behind the other in the intake pipe, the measuring element being movable in dependence upon the throughflowing air flow rate, against a restoring force, to thereby displace the movable part of a valve disposed in a fuel supply line for metering a fuel flow rate proportional to the air flow rate, the fuel metering valve having a control slot which is opened to a greater or lesser extent by a control edge, there being provided downstream of the control slot, between the control slot and an injection line leading to the injection point, a truncated-cone-like portion of line whose smaller cross-section opens out into the injection line, this truncated-cone-like portion of line operatively connecting the control slot to the injection line.

2. A fuel injection system as claimed in claim 1, in which the truncated-cone-like portion of the injection line has an opening angle of approximately 30".

3. A fuel injection system for mixturecompressing, externally ignited internal combustion engines, constructed and arranged substantially as herinbefore described with reference to and as illustrated in the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. ratio of air intake quantity and metered fuel quantity. Metering is effected with a pressure difference held constant by the differential pressure valve 18, the force of the spring 40 and therefore the pressure difference being variable for adaptation to the various working conditions of the engine. The metered fuel is injected through the injection nozzle 34 at the end face of the measuring element 3 into the gap 35 between the front face of the measuring element 3 and the wall of the portion 2, i.e. at the point of highest flow speed, in order to achieve a fuel-air mixture which is as homogeneous as possible. The contour of the wall of the portion 2 opposite the front face of the measuring element may be adapted to the desired fuel-air ratio. Since the geometry of the fuel jet emerging from the control slot 26 varies widely depending upon opening of the control slot, the entrance into the injection line 33 must have a precisely defined shape to avoid undesirable spattering of the fuel jet and to convey the metered fuel with the minimum resistance to the fuel injection point. According to the invention, therefore, there is provided downstream of the control slot 26 between the control slot and the injection line 33 a truncated-cone-like portion of line 30 which leads into the smaller cross-section injection line, the cone preferably having an opening angle of approximately 30". WHAT WE CLAIM IS:-

1. A fuel injection system for mixturecompressing, externally ignited internal combustion engines having an injection point into an air intake pipe, comprising an air flow measuring element and an arbitrarily actuable throttle valve disposed one behind the other in the intake pipe, the measuring element being movable in dependence upon the throughflowing air flow rate, against a restoring force, to thereby displace the movable part of a valve disposed in a fuel supply line for metering a fuel flow rate proportional to the air flow rate, the fuel metering valve having a control slot which is opened to a greater or lesser extent by a control edge, there being provided downstream of the control slot, between the control slot and an injection line leading to the injection point, a truncated-cone-like portion of line whose smaller cross-section opens out into the injection line, this truncated-cone-like portion of line operatively connecting the control slot to the injection line.

2. A fuel injection system as claimed in claim 1, in which the truncated-cone-like portion of the injection line has an opening angle of approximately 30".

3. A fuel injection system for mixturecompressing, externally ignited internal combustion engines, constructed and arranged substantially as herinbefore described with reference to and as illustrated in the accompanying drawings.