GB2202000A - I.C. engine fuel injection systems using electro fluidic injectors - Google Patents

Abstract

An electronic control unit 13 provides pulsed switching of the fluidic device 1 having the injector nozzle 18 by means of the solenoid valve 12 which opens and closes the port 14. A single two-stage device (1, 21, Fig. 2) may have a nozzle 18 located either upstream or downstream of a throttle valve (30, Fig. 3). For multi-point injection each inlet tract of the engine manifold has an injector nozzle (37, Fig. 4) located near to the associated inlet valve and is supplied by a two-stage device. In order to make the output stage insensitive to sub-atmospheric pressure variations in the manifold one output of the first stage (39, Fig. 5) provides a supply for an ejector (40, 41, 42) which creates a sub-atmospheric pressure in one output 5 of the second-stage 1 to prevent premature switching. <IMAGE>

Description

IMPROVEMENTS IN ENGINE FUEL INJECTION SYSTEMS USING ELECTRO FLUIDIC INJECTORS The invention relates to a fuel injector used for the supply of fuel to spark ignition internal combustion engines and is intended to provide improved performance and cost reduction in comparison with prior art devices.

' Digital fuel injection systems are used to provide improved efficiency coupled with reduced emissions compared to carburettor systems. Injection is provided conventionally by electro mechanically activated devices that respond to commands from a digital electronic controller and are in the form of pulses that vary in width dependent upon the fuel demand for an engine operating condition.

Fuel injection systems can either be described as being single or multi point. Single point injection utilises a single injector to introduce fuel either upstream or downstream of the throttle with the air/fuel mixture being shared between the engine cylinders. Multi point injector systems assign an injector to each cylinder that is activated to meet the fuelling requirements of that cylinder only.

Conventional fuel injection systems are complex and costly and attempts have been made to provide an alternative solution based upon Fluidics technology. Fluidics uses the pressure and flow characteristics of fluid streams to control other fluid streams without the use of moving parts. Such devices may be configured in either digital or analogue form and can provide signal amplification.

As digital devices, a range of logic functions may be provided, such as AND, OR, EXCLUSIVE OR, ADDER, SUBTRACTOR, etc. In analogue form they maybe used as integrators, differentiators, push-pull amplifiers, etc.

Within the context of a fuel injection system, various engine parameters are measured and supplied as input to a control system to determine the appropriate fuel injection quantity. Such functions implemented with fluidics technology involve a large number of devices and the resulting circuitry exhibits considerable complexity.

Prototype fluidic systems for single point fuel injection have been produced, examples of which are to be found in the U.K. patents 1403259 and 1470961. Fluidic systems involving a large number of devices in integrated circuit form exhibit a considerable sensitivity to variations in manufacture. The emergence of electronic integrated circuit technology resulted in such systems being abandoned, since the functions would be more readily implemented with electronics at a lower cost and with improved reliability.

While the case for discarding fluidic devices in favour of electronics for control circuit implementation is clear cut, they offer considerable potential as fuel injector stages driven by a modern digital electronic controller. Within this context, the simple no moving parts configuration offers considerable improvement in cost and performance in comparison with conventional units that utilise complex and expensive solenoid activated valves.

The object of the invention is to provide a fluidic injector stage for use in single or multi point applications that is readily interfaced with a conventional electronic engine controller. Such a device offers significant benefits with regard to lower injector drive power, lower production costs and faster response.

The injector is required to respond to the output of an interface that is switched by the electrical pulse output of the digital controller. Dependent upon the engine application, the injector may be in the form of a single stage fluidic amplifier or as a two stage device for improved amplification.

A particular characteristic required by the fluidic injector stage is that of load insensitivity. Particularly in the case of multi point injector systems, the injector can be subjected to powerful vacuum conditions that could cause premature switching of conventional fluidic devices. The fluidic injectors incorporate features to provide the necessary load insensitivity.

Features of the invention will be described with reference to accompanying drawings, in which: Figures 1 and 2 illustrate two proposed configurations for the invention.

Figure 3 illustrates the use of the invention in a single point fuel injection system.

Figure 4 illustrates the use of the invention in a multi point fuel injection system.

Figure 5 illustrates a third embodiment of the invention with enhanced load insensitivity.

Figure 1 shows the first embodiment of the invention in which a monostable wall re-attachment fluidic device (1) is controlled to switch at a controlled rate to generate fuel pulses for input to the engine. Such a device is supplied continuously with fuel from the engine fuel pump (2) at a pressure set by a regulator (3). The device has a supply nozzle (4) sized to provide the required pressure and flow characteristic required by the engine. The device may be produced by machining, photo etching or moulding in a metal, ceramic or plastic material and has a two dimensional planar form.

In the normally stable state, the jet issuing from the supply nozzle passes to one outlet (5) and fuel is returned over a line (6) to the fuel tank (7). In this state, the jet is attached to the side wall (8) of the device due to the so-called Coanda effect and no flow takes place through the other output channel (9).

The device may be switched from one output to the other by either applying a positive pressure signal to one control nozzle (10) or by inducing a negative pressure in the other control nozzle (11). Both control nozzles are set at right angles to the main supply nozzle and have a smaller cross-sectional area. The angle of inclination (e1) of the normally stable outlet -(5) is l & s than that (02 ) of the switched outlet (9) to ensure that in the absence of control signals the jet always attaches to one wall (8) and ensures that the switched condition is only maintained while a differential pressure is applied between the control nozzles.

In the normally stable mode, the conditions in both control nozzles are slightly sub atmospheric due to the ejector effect generated by the main jet across the control nozzles resulting in entrainment of air.

For use as a fuel injector, the control port (11) on the switched side of the device is closed by a small solenoid interface device (12) that responds to pulses generated by a conventional digital controller (13). The closure of the nozzle port (14) reduces the air entrained into the main jet flow and the pressure reduces causing a pressure difference to be applied across the jet. The difference is sufficient to cause the jet to separate from the wall (8) and flow is rapidly diverted into the switched output channel (9). The jet remains in this state for as long as the control port is closed. When the port is opened by solenoid de-energisation, the pressure balance across the supply jet is re-established and the jet returns to the normally stable condition.

The solenoid interface consists of a stator with a coil (15) and an armature (16) that is subjected to very small dynamic forces and is required to move a very short distance. Accordingly, the armature has low mass and is produced with a low friction coating that enables a fast response to be obtained.

The outlet (17) of the amplifier terminates in a nozzle (18) that injects fuel into the engine inlet. Depending upon the point of injection, the inlet pressures can be well below atmospheric conditions and when the amplifier is in the normally stable state in which fuel is not being supplied to the engine, the negative pressure condition in the outlet channel (9) could result in premature switching of the jet.

To counteract this effect, the switched outlet channel has atmospheric vents (19) shaped to generate a stabilising effect. Such vents provide ameans of raising the pressure in the outlet channel (9) to reduce load sensitivity. In the switched condition minor flow will take place through the vents and these are coupled via a return line (20) to the tank.

Figure 2 illustrates a second embodiment of the invention in which a two stage amplifier is used. Both stages are monostable wall reattachment devices of the type used in the embodiment of Figure 1. In this version the outlets (5, 9) of the first stage (1) are used to cause switching of the second stage (21) and are directly coupled to the inlet ports (22, 23). The second stage supply jet is normally attached to the side wall (24) associated with an outlet that discharges flow back to the fuel tank (7) through a return line (25).

As the first stage (1) is switched by opening and closing of the control port by the solenoid actuator (12) the outputs switch to cause operation of the output stage (21). In this way the second stage operates to provide fuel pulses to the injector nozzle (18) and is switched on and off by the first stage operating as a pre-amplifier.

Since wall re-attachment fluidic devices provide pressure and flow amplification, the first stage can be physically smaller than the second stage and can be operated at a reduced pressure supply.

The arrangement offers improved benefits with regard to load insensitivity in comparison to the version of Figure 1. While the vent arrangement (26) still provides load insensitivity, this is further enhanced by the second stage being continuously subjected to a pressure difference between the control ports (22, 23) to maintain the supply jet in required state.

Figure 3 illustrates the way in which the injector stages of Figures 1 or 2 may be used for the single point injection of fuel. The injector amplifier (1) has the output channel (27) connected to a nozzle located either upstream (28) or downstream (29) of the throttle (30) located in the duct (31) leading to the induction manifold (32) of the multi cylinder engine (33). With single point injection, the fuel is atomised and is mixed with the induced air flow in the manifold duct to be delivered to the cylinders of the engine dependent upon inlet valve opening.

When the fuel is introduced upstream of the throttle conditions only differ marginally from atmospheric. When the injection point is located downstream of the throttle conditions are sub atmospheric and the load insensitivity characteristic of the fluidic injector is fully utilised.

The vents and unused output of the injector amplifier (34) are coupled back to the fuel tank.

Figure 4 illustrates the use of injector stages of the type shown in Figures 1 and 2 to perform multi point injection. Here an injector (1) is assigned to each cylinder (36) of the engine with the fuel injection nozzle (37) being located in the inlet tract directly adjacent to the inlet valve (38). Again pressure conditions are substantially below atmospheric and the injector amplifier is required to exhibit adequate insensitivity to load conditions.

While multi point injection offers improved performance and efficiency in comparison with single point injection, it is more expensive since one injector stage per engine cylinder is required.

In this respect, the low cost fluidic injector possesses considerable advantage over conventional devices.

Figure 5 illustrates a third embodiment of the invention in which an enhanced load insensitivity injector is provided for single or multi point systems. Here the output of the solenoid interface (12) is used to control the port of a monostable wall re-attachment preamplifier (39) that has the stable output channel coupled to the supply nozzle (40) of a fluid ejector stage of known design. Located at right angle to the supply nozzle is an ejector port (41). The main jet flow passes through an exhaust duct and is returned to the fuel tank. In doing so air is entrained in the ejector port (41) causing sub atmospheric pressure conditions.

The ejector port is connected to the vent in the outlet channel (5) of the injector amplifier of Figure 1. The induced suction condition provides jet stabilisation against the imposed depression in the injector nozzle supply channel (17), when fuel is not being supplied to the engine.

The device operates as follows: when fuel is not being supplied to the injector nozzle (18) the pressure condition in the supply line (17) is below atmospheric and attempts to cause the attached jet to switch from one outlet (5) to the other (9). In this condition, the ejector is supplied by the pre-amplifier and suction is induced in the injection amplifier vents (19). This counter balances the sub atmospheric pressure caused by engine inlet conditions and maintains stability of the injection amplifier supply jet.

When the digital controller generates a command pulse the solenoid (12) closes the port of the pre-amplifier (39) which switches to cut off the supply to the ejector and the control port (10) of the injection amplifier (1) receives a positive pressure signal to cause switching.

The embodiments of the invention illustrated in Figures 1, 2 and 5 are intended to provide improvements in cost and performance in the injection of fuel into spark ignition internal combustion engines.

The injector system is compatible in operation with conventional digital electronic fuel injection controllers.

Claims (7)

1. A fuel injection system for IC engines in which a fluidic injector is controlled by an electronic control unit via an electro mechanical interface.

2. A fuel injection system as claimed in Claim 1 where the fluidic injector is in the form of a single stage pure fluid device operating on the wall reattachment effect that is supplied by the engine fuel pump as shown in Fig. 1.

3. A fuel injection system as claimed in Claims 1 and 2 in which the outlet vents are shaped to provide insensitivity to load changes.

4. A fuel injection system as claimed in Claim 1 where the fluidic injector is in the form of two stages of pure fluid wall reattachment devices with the second stage acting as a fuel injector as shown in Fig. 2.

5. A fuel inj ection system as claimed in Claims 1 to 4 in which a single unit is used for single point fuel injection into the engine upstream or downstream of the throttle as shown in Fig. 3.

6. A fuel injection system as claimed in Claims 1 to 4 in which each engine inlet tract leading to an inlet valve has an injector nozzle supplied by a separate fluidic injector unit to constitute multi point injection as shown in Fig. 4.

7. A fuel injection system as claimed in Claims 4 to 6 in which a pure fluid ejector is located between the pure fluid wall reattachement devices to lower the pressure on one side of the fuel injector jet to provide insensitivity to sub atmospheric pressure in the engine manifold as shown in Fig. 5.