GB2246165A - I.C. engine fuel injection nozzle - Google Patents

Abstract

An atomising nozzle 3 injects fuel into an air intake manifold. Fuel is supplied into the nozzle under pressure through a pressure maintaining valve 15 and flows to a fuel delivery capillary tube 45. The capillary tube 45 extends into an air chamber 49, which has in lets 55 for unthrottled air. The end of the capillary tube 45 is closely surrounded by a convergent nozzle element 51 connecting the air chamber 49 to a throttled portion of the manifold. Air is drawn through the nozzle element 51 by air pressure reduction in the throttled portion of the manifold, the flow of air through the nozzle element 51 reducing the air pressure at the end of the capillary tube 45 and drawing fuel therefrom. The nozzle fuel supply is via a pulse width modulated solenoid valve (106, Figs. 3 and 4) and an analogue metering valve (108). <IMAGE>

Description

Fuel Injection Nozzle The invention relates to a fuel injection nozzle for injecting liquid fuel into a throttled portion of an inlet manifold of an internal combustion engine. The nozzle comprises a capillary fuel delivery tube extending within an air chamber, the air chamber having an inlet for unthrottled air fram the manifold upstream of the throttle of the engine and an outlet convergent around the end of the capillary tube. The outlet leads to the inlet manifold of a working chamber of the engine in a position where the induction of each successive charge of air into the working chamber reduces the static pressure within the manifold and thus draws air fran the nozzle air chamfer.

A nozzle of this type is known fram patent application WO 83/00191 which describes the nozzle as a part of a fuel supply system for an internal combustion engine.

Fuel is supplied by the supply system to the capillary fuel delivery tube within the nozzle. The fuel flow rate is controlled by the system in response to engine speed and throttle opening. The fuel supply pressure is such that, at least at low engine speeds, fuel is drawn from the capillary tube only by the reduction of air pressure at the end of the tube caused by the substantial flow of air through the chamber during each induction phase. The fuel is atamised by the airflow and drawn into the inlet manifold. In the absence of such airflow, the fuel is retained in the capillary fuel delivery tube by its surface tension.

The e fuel supply pressure must therefore be maintained at a pressure insufficient to overcome the surface tension of the fuel in the capillary tube in the absence of airflow past the end of the tube.

In practice, this means that low fuel supply pressures must be used, leading in hot ambient conditions to possible vaporisation of the fuel in the fuel supply system. This is a particular problem with fuels of low vaporisation temperatures, for example petrol or aviation spirit.

The invention provides a nozzle for supplying fuel to a throttled portion of an inlet manifold of an internal combustion engine, comprising a fuel inlet to which fuel is supplied under pressure, a pressure maintaining valve through which the fuel passes from the inlet to a first end of a capillary fuel delivery tube, and an air chamber into which the capillary tube extends, the air chamber having an inlet for unthrottled air and an outlet opening into a throttled portion of the inlet manifold, the outlet comprising a nozzle element convergent around the end of the capillary tube.

The nozzle of the invention therefore permits increased fuel supply pressures to be used compared with previously known high atomisation nozzles, since the fuel pressure is reduced between the supply to the nozzle and the capillary fuel delivery tube. The possibility of fuel vaporisation in the supply system is therefore considerably reduced.

Preferably the nozzle of the invention comprises a pressure maintaining valve having a valve seat and a valve closing element resiliently urged into sealing relationship with the seat, the valve being openable by the application of a pressure difference across the valve greater than a predetermined pressure difference.

Preferably, the chamber around the tube is gradually convergent over a sufficient length to ensure that the air drawn past the end of the tube flows at high velocity under all running conditions, thereby avoiding sudden changes and instabilities in the operation of the nozzle. The chamber may therefore comprise a convergent nozzle element closely spaced from the end of the tube.

Advantageously, the air inlet manifold leading from the throttle towards the combustion chamber is formed with a constriction to reduce the static pressure adjacent the nozzle. This constriction should however not be so narrow as to cause sonic flow conditions under maximum power or engine speed conditions. Accordingly, the constriction design should ensure that the mean flow velocity during intake of a charge of air should not appreciably exceed 125 metres/sec.

when the engine has a plurality of working chambers, the fuel delivery apparatus may have a separate nozzle for each intake manifold branch (which may serve one or more working chambers). The remainder pf the fuel delivery apparatus may be common to all nozzles, the nozzles being connected in parallel. The nozzle of the invention may however be used as a single point injector, in which case a single nozzle is used to supply fuel to all the cylinders (or to a bank of cylinders) of a multi-cylinder engine by injecting fuel into a portion of the inlet manifold common to all the cylinders.

Advantageously, the nozzle of the invention is supplied with fuel by a fuel metering system ocoprising a pulse width modulated (PWM) metering valve and/or an analogue metering valve. These may be connected in series in either order. A fuel pump may be used to feed fuel to the fuel metering system. Preferably a pressure accumulator is used to smooth any pressure pulses introduced into the fuel supply by the?iM valve and/or by the pump.

The nozzle may therefore be supplied with fuel by a fuel supply system comprising an engine management system in which a PEM metering valve is controlled by a microprocessor to meter fuel in response to parameters including for example engine speed and load. Sensors for other engine parameters and for ambient conditions may also be used.

In a preferred embodiment the PEM metering valve may be a solenoid controlled on-off pulser valve and the analogue metering valve a mechanical, variable aperture slot valve.

The pressure accumulator may comprise a chamber in which fuel pressure is maintained by means of a spring-loaded diaphragm.

Alternatively, the pressure accumulator may simply comprise for example compliant fuel piping or fuel rails, or other pressure regulator.

An embodiment of the invention will now be described by way of example with reference to the drawings in which: Figure 1 is a cutaway perspective view of a nozzle according to the invention.

Figure 2 is a flow diagram of a fuel supply system for a four cylinder engine and comprising four nozzles as shown in figure 1; and Figure 3 is a schematic diagram of the fuel supply system of figure 2.

The nozzle 1 shown in figure 1 is for supplying petrol to the throttled portion of an inlet manifold 2 of an internal combustion engine. The nozzle 1 comprises a substantially cylindrical body 3. Fuel is supplied under pressure from a fuel line 5 to the rear end 7 of the nozzle body 3, the line 5 being connected to the body 3 by means of a union nut 9 engaged with a screw thread 11 on the body 3.

A pressure maintaining valve 15 is located within the nozzle body 3 at its rear end. The valve 15 comprises a disc 17, sealed at its outer edge by a seal 19 to prevent flow of fuel between the disc 17 and the inner wall of the body 3. At its centre the disc 17 formed with a frusto-conical valve seat 21 on its downstream side around a central opening.

A valve member 23 has a conical valve head 25 which seats sealingly on the seat 21 and a stem 27 extending through the opening in the disc 17 in the upstream direction. The valve member 23 is urged into contact with the valve seat 21 by a campression spring 29 encircling the stem 27 and acting between the disc and a washer 31 which bears at its centre against an enlargement 33 of the valve stem 27.

The valve 15 opens to permit the flow of fuel only when the pressure difference across the valve exceeds a certain value predetermined by the area of the valve and the rate of the spring 29. The fuel in the fuel line 5 may thus be maintained at sufficient pressure to prevent vaporisation under high ambient temperatures, while the fuel in the nozzle downstream of the valve 15 is maintained at a lower pressure.

Downstream from the valve 15 is a small chamber 41 within the nozzle body 3 between the valve 15 and an annular block 43.

The annular block is sealed at its outer surface against the inner wall of the nozzle body 3 to prevent the flow of fuel therebetween. The central passage of the annular block 43 supports one end of the capillary fuel delivery tube 45, the end of which is flanged outwardly against the upstream end of the block 43 to locate the tube within the block. The tube 45 may alternatively be glued in position within the block 43.

Within the nozzle body 3, downstream of the block 43, is defined an annular air chamber 49 around the capillary tube 45 which extends axially within the body. The downstream end of the air chamber 49 is defined by an annular nozzle element 51 whose outer surface fits within the inner wall of the nozzle body 3 to locate the nozzle element therein. The inner surface of the nozzle element defines a convergent nozzle 53, the fuel delivery tube extending into close proximity with the convergent nozzle 53. Air inlet ports 55 for the admission of air by-passing the throttle of the engine are formed in the wall 57 of the air chamber 49.

In use, as shown in figure 3, the nozzle 1 is located in a passage 60 through the wall 61 of the inlet manifold branch 2 of a working cylinder 63 of an internal combustion engine 65.

The nozzle 1 is sealed by two 0-rings 67 fitted in external grooves 69 of the nozzle body 3 and pressing against the wall of the passage 60. Between the 0-rings 67 the external surface of the nozzle body 3 is of reduced diameter, so that an annular air chamber 71 is formed between the nozzle body 3 and the wall of the passage 60. The annular chamber 71 has an air inlet 73 connected to received unthrottled, filtered air from the manifold 2 between the outlet of a filter 75 at the intake of the manifold 2 and a throttle valve 77 in the manifold 2.

The chamber 71 is connected via the ports 55 to the air chamber 49.

In operation of the nozzle 1, fuel is supplied under pressure from the fuel line 5, through the pressure maintaining valve 15 to the capillary fuel delivery tube 45. The pressure in the capillary tube should be sufficiently low, particularly at low engine speeds and loads, that fuel is retained in the capillary tube 45 by virtue of the surface tension of the fuel. The fuel supply pressure in the line 5 may however be maintained sufficiently high by the valve 15 to prevent fuel vaporisation.

During the induction phase of the working cylinder 63 of the engine 65, a charge of air is drawn into the cylinder 63 through poppet valve seat 75, thus reducing the static air pressure in a venturi 66 in the manifold 2 adjacent the nozzle. Air is thus drawn fram the convergent nozzle 53 out of the air chamber 49. Since the end of the capillary tube 45 is in close proximity to the convergent nozzle 53, very high air flow velocities can be generated past the end of the tube 45, leading to reduced air pressure. Fuel is thus drawn by the reduced pressure from the capillary tube 45 (opening the valve 15), is atanised effectively by the high air flow velocity through the nozzle, and is injected into the manifold 2 for induction into the working cylinder 63 of the engine.

During high speed operation of the engine, an increased fuel supply may be required. The fuel supply pressure may then be increased so as to open the valve 15 and overcome the surface tension of the fuel in the capillary tube and therefore eject fuel continuously fram the capillary tube.

In a four cylinder engine, a separate nozzle 1 may be used for each working cylinder as shown in figure 2. A single fuel supply system may be used to supply all of the nozzles. An embodiment of such a fuel supply is shown schematically in figure 3 and as a flow diagram in figure 2.

Fuel is drawn from a tank 100 by a pump 102, excess fuel being returned to the tank by a regulator 104. Fuel from the pump is then metered through a pulse width modulated (PWM) metering device 106 and an analogue metering valve 108 to a pressure accumulator 110 from which a separate fuel line 5 leads to each of the nozzles 1. The PWM device 106 and analogue metering valve 108 are connected in series but may be in either order.

The PWM device 106 may be a solenoid controlled on/off valve for controlling fuel flow. The PWM device 106 is opened at a frequency proportional to engine speed, the time interval for which it is opened being determined according to engine speed and load by a microprocessor 112 in response to inputs from a throttle opening sensor 114 connected to the throttle linkage 116 from the throttle pedal 118, and an engine speed sensor 120. The time interval rnay then be adjusted in response to inputs from other sensors measuring engine related parameters or ambient conditions.

The PWM device 106 may be a solenoid operated, on-off pulser valve.

The analogue metering valve 108 may be a variable orifice valve, or slot valve, opened in response to throttle opening by means of a mechanical linkage 122.

The pressure accumulator 110 contains a chamber 124 in which a fuel pressure is maintained by means of a spring loaded diaphragrn 126. The pressure is pre-adjustable by means of a threaded rod 128 acting on the end of the spring 130 to alter the compression of the spring 130. The fuel lines 5 connect the pressure chamber 124 to the nozzles 1. The pressure accumulator 110 smoothes pressure pulses caused by the PWM device 106 or the pump 102. These pressure pulses may alternatively be smoothed by for example other pressure regulating devices or the use of compliant piping or fuel rails in the fuel system.

Claims (7)

Claims

1. A nozzle for supplying fuel to a throttled portion of an inlet manifold of an internal combustion engine, comprising a fuel inlet to which fuel is supplied under pressure, a pressure maintaining valve through which the fuel passes from the inlet to a first end of a capillary fuel delivery tube, and an air chamber into which the capillary tube extends, the air chamber having an inlet for unthrottled air and an outlet opening into the throttled portion of the inlet manifold, the outlet comprising a nozzle element convergent around the end of the capillary tube.

2. A nozzle according to claim 1, in which the pressure maintaining valve comprises a valve seat and a valve closing element resiliently urged into sealing relationship with the seat, the valve being openable by the application of a pressure difference across the valve greater than a predetermined pressure difference.

3. A nozzle according to claim 1 or claim 2, comprising a substantially cylindrical nozzle body having at one end the fuel inlet, and within its other end the air chamber, the pressure maintaining valve being housed in the nozzle between the inlet and the air chamber, the air chamber being substantially cylindrical, its radially outer wall being a wall of the nozzle body, and the capillary tube extending axially within the chamber, the chamber inlet passing radially through the wall of the chamber, and the chamber outlet being coaxial with and closely spaced from the capillary tube.

4. A nozzle for supplying fuel to a throttled portion of an inlet manifold of an internal combustion engine substantially as described herein with reference to the drawings.

5. A fuel supply system including a nozzle according to any preceding claim, in which the inlet manifold comprises a constriction to reduce the static pressure adjacent the nozzle during operation of the engine.

6. A fuel supply system including a nozzle according to any preceding claim, in which the fuel is passed, in either order, through a pulse width modulated (PWM) metering device which is cyclically opened at a frequency proportional to engine speed and/or any analogue metering valve which introduces a variable constriction into the fuel flow path.

7. A system according to claim 6, comprising a pressure accumulator connected in series with the PWM device and the analogue metering valve, an output from the pressure accumulator being connected to the fuel inlet of the nozzle.