GB2122688A - Fuel supply device for internal combustion engines - Google Patents

Abstract

The device comprises fuel metering nozzle 11 with needle 7 and pump 14 for generating a secondary air stream in duct 13, 8 drawn from the atmosphere in duct 1. The secondary air stream conveys the fuel through pipes 15, 16, 17 into the intake pipe of the engine. Differential pressure control valve 18 controls the pressure PT of the air at fuel-outlet point 11 and thus controls the differential pressure PO-PT which governs the fuel metering. To provide a change in the differential pressure for adapting the mixture composition for cold starting, warming-up and for acceleration phases, for the stabilization of idling, for balancing changing air densities, or for compensating the viscosity changes of the fuel with temperature changes, valve 18 is provided with electromagnet 19 which acts upon membrane 20. The force provided by electromagnet 19 to provide required changes in differential pressure may be controlled by a micro-computer. Electromagnet 19 may be replaced with bi-metallic springs and the pressure Pv in the valve may be reduced using a valve controlled connection between passage 8 and the corresponding chamber, Fig. 2 (not shown). <IMAGE>

Description

SPECIFICATION Fuel supply device for internal combustion engines This invention relates to a fuel supply device for a mixture-compressing internal combustion engine, the device comprising a main air duct having a throttle valve, a carrier air duct branching from the main air duct, a pump for drawing air through the air carrier duct to entrain fuel in the air from the fuel metering nozzle, at least one distribution duct leading from the carrier air duct downstream of the pump and arranged to lead to an intake pipe of an engine upstream of inlet valves of the engine, and a differential pressure valve for controlling the flow of air through the carrier air duct, the differential pressure valve being upstream of the fuel metering nozzle.

A device such as this is disclosed in published British Patent Application No. 2 103 291 A. Even with such a device, adaptation of the composition of the mixture to the requirements of the engine for cold starting, warming-up and overrunning, and for correcting for the density of the air, or for correcting for the fuel calorific value or the fuel density, is necessary. The above device is capable to only a limited extent, however, of enriching the mixture by increasing the differential pressure which brings about metering of the fuel.

The object of the present invention is to construct a fuel supply device as initially described in such a way that adaptation of the composition of the mixture to various operating states of the engine that occur is possible. In particular in a preferred construction complete shutting-off of the fuel or a reduction in the metering differential pressure, which is proportional to the density of the air supplied to the device, is effected by the differential pressure valve.

To this end, according to this invention, a fuel supply device as initially described is characterized in that the carrier air duct opens at its upstream end into a space at substantially ambient pressure; the differential pressure valve has a flow aperture which is controlled by an adjusting member, an active surface of which is acted upon in one direction by a pressure which is dependent upon the pressure upstream of the throttle valve which is conveyed to the valve by a duct, and in an opposite direction by the pressure in the carrier air duct downstream of its flow aperture.

Preferably, the adjusting member is additionally acted upon by a device which produces a force which, in operation, is controlled as a function of operating parameters of an engine to which the fuel supply device is fitted.

Preferably also, means are provided for varying the pressure which acts upon the active surface in the one direction independently of variations in the pressure upstream of the throttle valve.

With the device in accordance with the invention, the metering differential pressure can be controlled in such a way that the mixture is enriched or is made lean and, in the extreme case, no fuel supply to the air flow at all takes place.

This result is achieved by the feature that the carrier air stream flows into the carrier air duct directly from the atmosphere at ambient pressure and thus the pressure at the metering point can be set at ambient level by means of the differential pressure valve in the carrier air duct.

The differential pressure valve controls the free cross-section of the carrier air duct and thus controls the magnitude of the differential pressure of the air at the fuel nozzle which effects the fuel metering. The differential pressure is the pressure drop between the air pressure acting on the fuel in, for example, a float chamber at the upstream side of the nozzle and the pressure of the air in the region of the metering valve in the carrier air duct, that is the pressure on the downstream side of the nozzle. By varying this differential pressure of the air, it is possible in a simple and advantageous manner to determine the quantity of the fuel to be taken from the fuel nozzle and thus the composition of the mixture.For a warming-up phase it is sufficient to provide only a differential pressure valve, the active surface of which is additionally acted upon by a force produced by an electrically heated temperature element, so that during progressive heating-up the air duct is continually further opened. A further loading of the active surface as a function of other engine operating parameters or of external influencing variables, such as the nature of the fuel, air temperature, or air pressure, is directly possible by applying a force of an appropriate magnitude from an electromagnet or a moving coil system. One engine operating parameter which may, for example, be used is exhaust gas composition, which can be measured as usual by an oxygen probe. For processing the engine operating parameters, a microprocessor may be used.This then governs an electrical correction element, for example a linear motor. Regulation of the mixture during non-steady operating conditions, such as in acceleration phases, is also possible.

Two examples of devices in accordance with the invention will now be described with reference to the accompanying diagrammatic drawings in which: Figure 1 is a vertical section through one example of the device; Figure 2 is a similar view of a second example with an altitude corrector; and Figures 3 and 4 are graphs showing the air flow rate M, through the devices plotted against the differential metering pressure PD and the fuel flow proportion % Vs respectively.

Referring to Figures 1 and 2, in operation, combustion air drawn in by an engine flows downwards through a principal air duct 1 past a throttle valve 2 and then through an intake pipe 3.

Upstream of the throttle valve 2, an asymmetrical choke or air flow metering valve 5, which opens against the action of a spring 4, is provided. The angle of opening of the valve 5 provides a measure of the air flow rate. A fuel metering needle 7 is fixed to a lever 6 on the valve 5, and forms with its ground profile 10 a metering cross section in the nozzle 1 The size of the metering cross-section is varied as a function of the axial position of the needle. Through the metering cross-section, the pressure difference P, -- P, sucks fuel out of a float chamber 12.The fuel is sucked, together with a carrier air stream, through a carrier air duct 8, 13 by a pump 14 and is fed by this pump through a line 1 5 to a distributor 1 6 and thence is supplied via injection lines 1 7 into a portion of the engine intake pipe directly upstream of inlet valves of the engine.

A differential pressure valve 1 8 is disposed in the carrier air duct 8, 1 3. If no force is exerted by an electromagnet system 1 9, then, if the control area of a flow aperture 21, which is very small compared with the active area of a membrane 20, is ignored, the metering differential pressure PD is given by the equation:- PD PO PT where PT= P,, i.e. the metering differential pressure is equal to the pressure difference across the air flow metering valve 5.

In the following description, symbols having the following meanings are used:- PD= = Metering differential pressure; P0 = Ambient pressure; PT = Pressure in carrier air duct; Pv = Pressure in a venturi in the duct 1 and serves as a control pressure; PVK = Corrected control pressure in the differential pressure valve 18; AM = Active area of the membrane 20; FMa = Force produced by the electromagnet 19; Over one side of the active area of the membrane 20 in the differential pressure valve, there acts, via the carrier air duct portion 1 3 the pressure in the carrier air duct downstream of the flow aperture 21.Over the other side acts, via a line 9, the control pressure Pv which is obtained from the venturi downstream of the air flow metering valve 5.

If the electromagnet 1 9 exerts a force in the one or the other direction, then the pressure PT must adjust to FMa PT PV + AM in order that force equilibrium shall exist. The pressure PT can, for example, be increased by a magnetic force acting in the direction of opening of the flow aperture 21 up to a value of P0, so that the metering differential pressure P0 = 0 and no fuel is metered. On the other hand, a magnetic force acting in the closure direction of the aperture 21 causes the pressure PT to decrease, so that an increase in the metering differential pressure PD takes place.

In Figure 2 a differential pressure valve is shown, where, in addition to forces on the membrane from bimetallic springs 22 and 23 which are the equivalent of the action of the electromagnet system 1 9 of Figure 1, and where one force serves for compensating for air temperature and the other for warming-up mixture enrichment by heating up of a heating element 28, the control pressure Pv can be modified to PVK.

This is achieved in that the control pressure PVK is modified by two throttle points 24 and 25. The pressure PVK resulting from the throttling areas A24 and A25 is given by the equation:- P0. + A225 + PV A224 PVK A224 + A225 If one of the two throttles is made variable in area, then the pressure PVK can also be varied and thus the metering differential pressure PD can be varied.

In the example of Figure 2, this change in throttling area is effected by means of a cone 26, which is moved by an aneroid cell 27. Thus, as the atmospheric pressure decreases at higher altitudes, an increase in the throttling area A25 is produced and this produces a reduction in the pressure PVK; this in turn causes a reduction in the metering differential pressure PD and thus in the metered quantity of fuel.

For constant throttling areas A24 and A25, the ratio of Pv to PVK is also constant, and thus also the depletion factor is constant over the entire operating range, which is very important, for instance, for an altitude correction.

Figure 4 shows some typical curves of fuel flow proportion plotted against air flow rate and Figure 3 shows the corresponding metering differential pressure plotted against air flow rate.

The lines a show the air flow rate and fuel flow rate for a heated-up engine without any magnetic or other interventions at the control valve 1 8. The lines b are typical for warming-up enrichment, because a slightly rising air flow rate leads to decreasing enrichment. This is achieved by a force in the closure direction of the flow aperture 21. If the enrichment is to be constant over the entire operating range (e.g. for alternative fuels), as shown by lines c, then it is necessary for the pressure difference to rise proportionally to the basic pressure difference according to line a, and therefore when the basic pressure difference a is not constant, it is necessary for the correction force also to rise. This can be achieved by the electromagnet system 19, with the electromagnet controlled for example by a microcomputer.

If, according to the lines d, a uniform depletion of fuel flow is to be achieved, for instance for altitude correction, then the basic pressure difference P0 must be lowered proportionally. This can be achieved by the control valve shown in Figure 2 or, where a microcomputer is used, by the electromagnet system 1 9 of Figure 1. If the electromagnet system fails, the basic differential pressure PoPv hunts, and the fuel metering takes place according to the lines a.

Claims (5)

1. A fuel supply device for a mixturecompressing internal combustion engine, the device comprising a main air duct having a throttle valve, a carrier air duct branching from the main air duct, a fuel metering nozzle which leads into the carrier air duct, a pump for drawing air through the air carrier duct to entrain fuel in the air from the fuel metering nozzle, at least one distribution duct leading from the carrier air duct downstream of the pump and arranged to lead to an intake pipe of an engine upstream of inlet valves of the engine, and a differential pressure valve for controlling the flow of air through the carrier air duct, the differential pressure valve being upstream of the fuel metering nozzle, characterized in that the carrier air duct opens at its upstream end into a space at substantially ambient pressure; the differential pressure valve has a flow aperture which is controlled by an adjusting member, an active surface of which is acted upon in one direction by a pressure which is dependent upon the pressure upstream of the throttle valve which is conveyed to the valve by a duct, and in an opposite direction by the pressure in the carrier air duct downstream of its flow aperture.

2. A fuel supply device according to Claim 1, characterized in that the adjusting member is additionally acted upon by a device which produces a force which, in operation, is controlled as a function of operating parameters of an engine to which the fuel supply device is fitted.

3. A fuel supply device according to Claim 1 or Claim 2, characterized in that means are provided for varying the pressure which acts upon the active surface in the one direction independently of variations in the pressure upstream of the throttle valve.

4. A fuel supply device according to Claim 2, in which the device which produces the force is an electromagnet,

5. A fuel supply device according to Claim 1, substantially as described with reference to Figure 1 or Figure 2 of the accompanying drawings.