GB2083657A

GB2083657A - Control of exhaust gas recirculation

Info

Publication number: GB2083657A
Application number: GB8126244A
Authority: GB
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1980-09-12
Filing date: 1981-08-27
Publication date: 1982-03-24

Abstract

A compression ignition engine is provided with an exhaust gas recirculation valve 16 and a fuel pump 12. The valve position is controlled in response to the outputs of air flow sensor 27, fuel flow sensor 23 and engine speed sensor 20 which signals are used in look-up table 19 and comparator 18 to command actuator 17. The speed sensor 20 also supplies device 26, which provides timing signals for the fuel supply, and a maximum fuel device 24. The maximum fuel at any time is made dependent on the intake air flow by means of modifying circuit 25. <IMAGE>

Description

SPECIFICATION Engine systems This invention relates to engine systems of the kind comprising a reciprocating piston internal combustion engine having an air inlet manifold and an exhaust manifold, a conduit connecting the manifolds and a valve in the conduit which can be adjusted to control the flow of exhaust gas into the inlet manifold, and fuel supply means for supplying fuel to the engine.

The main purpose of exhaust gas re-circulation is to reduce the level of noxious gases in the engine exhaust and in general, as the rate of fuel supply to the engine increases so the rate of supply of exhaust gas to the air inlet manifold should decrease for a given engine speed.

Systems are known in which the setting of the valve is determined by a fluid pressure operable device which is responsive either directly or indirectly to a fluid pressure within the fuel supply means and which varies as the rate of fuel supply to the engine varies. The disadvantage of such a system is the delay which occurs in the adjustment of the valve following an increase in the rate of fuel supply to the engine. This leads to poor combustion of fuel.

The object of the present invention is to provide an engine system of the kind specified in a simple and convenient form.

According to the invention an engine system comprises a reciprocating piston internal combustion engine having an air inlet manifold and an exhaust manifold, a conduit connecting the manifolds and a valve in the conduit, an electrical control for controlling the setting of said valve thereby to control the flow of exhaust gas into the inlet manifold, fuel supply means for supplying fuel to the engine, electrical control means for controlling the operation of said control means for providing an electrical signal representative of the air flow to the engine, said electrical control means being responsive to said signal and to signals representative of the engine speed and the amount of fuel being supplied to the engine to determine the setting of said valve, further means for controlling the amount of fuel supplied by said fuel supply means to the engine, said further means being responsive to said signal whereby the maximum amount of fuel which can be supplied to the engine depends on the air flow to the engine.

Examples of systems in accordance with the invention will now be described with reference to the accompanying drawings: Figure lisa diagrammatic view of the engine and associated components, Figure 2 is a block diagram of part of one example of the engine system, Figure 3 is a block diagram of part of another example of the engine system and Figure 4 is a block diagram of part of the system shown in Figure 2.

Referring to Figure 1 of the drawings the engine system comprises a compression ignition engine 10 having injection nozzles 11 which are connected to the outlets respectively of a fuel injection pump 12 driven in timed relationship with the engine 10. The nozzles direct fuel into the combustion spaces respectively of the engine. In addition, the engine has an air inlet manifold 13 and an exhause manifold 14, the two manifolds being interconnected by use of a conduit 15 in which is incorporated a valve 16 the setting of which is controlled by an actuator 17. In operation, opening of the valve 16 allows exhaust gas to flow from the manifold into the air inlet manifold in a known manner, for the purpose of controlling the production of noxious gases during operation of the engine.

Turning now to Figure 2, valve 16 and its actuator 17 are shown together with the fuel pump 12. The actuator 17 is controlled by a signal provided at the output of a comparator 18 which receives a signal from a "map" represented by the block 19. The "map" receives two inputs to provide an appropriate signal to the comparator indicative of the desired position of the valve 16 and for this purpose an engine speed signal is provided from a transducer 20 and in addition an actual engine fuel signal which is indicated at 21. The map contains stored information relative to the particular engine.

The fuel signal 21 is a signal representing the actual amount of fuel being supplied to the engine and is derived from a transducer and decode circuit (not shown) the transducer being carried by the pump. A fuel control signal 31 is supplied to the pump from a governor circuit which includes a circuit block 22 to be described and to which is supplied an operator originating demand signal from a transducer 23 and also the engine speed signal from the transducer 20. The action of the circuit block 22 is to generate an appropriate fuel control signal 31 in accordance with the demand and engine speed and in order that the maximum amount of fuel which is supplied to the engine should not exceed a given value, a maximum fuel map 24 is provided which receives the engine speed signal and which provides a maximum fuel signal or limit signal to the block 22.This limit signal can be modified by means of a further block 25 which will be discussed later in the specification. The fuel control signal 31 is utilized to determine the setting of the fuel control member of the fuel pump 12. In addition the block 22 serves to control the maximum speed of the associated engine and also the idling speed. The fuel signal 21 and also the engine speed signal obtained from the transducer 20 are supplied to a further map indicated by the block 26, and this block from stored information, provides a signal to the pump which determines the timing of delivery of fuel to the associated engine.

The other input to the comparator 18 in the exampie of Figure 2, is a correction signal which is obtained from a transducer 27 which provides a signal indicative of the fresh air flow to the engine.

This transducer is therefore positioned in the manifold 13 upstream of the junction of the conduit 15 therewith. Interposed between the transducer 27 and the comparator 18 is a circuit block 28 which modifies the signal in accordance with the density of the air. The signal indicative of air flow is also supplied to the circuit block 25 and the effect of this is that the maximum amount of fuel which can be supplied to the engine and which is provided by the map 24, is modified by the actual air flow to the engine.As a result even though the operator of the engine may suddenly increase the demand on the engine, the fuel flow to the engine will be controlled in accordance with the air flow to the engine and as the air flow increases so also will the rate of fuel supply to the engine, a limit being imposed by the map 24to ensure that no morethanthe permitted maximum amount of fuel is supplied to the engine depending upon the engine speed.

The block 22 as shown in Figure 4 includes a comparator 32 from the output of which is obtained the fuel control signal one input of which is the actual fuel signal derived from the decode circuit associated with the transducer which is carried by the pump. The other input of the comparator is connected to the output of a limiting circuit 33 which receives the signal from the circuit block 25 and has its input connected to the output of a fuel demand calculating circuit 34 which receives the engine speed signal from the transducer 20 and the operator demand signal from the transducer 23. The fuel demand calculating circuit 34 takes into account the engine speed to perform a governing function to limit the maximum engine speed.

In the arrangement shown in Figure 3, parts which have the same duty are provided with the same reference numbers. In this case it will be noted that the transducer 27 is omitted and in its place, there is provided a transducer 29 which provides an indication of the position of the valve 16. The output of the transducer 29 is passed through a block 30 which ensures that the signal supplied to the comparator 18 will be representative of the air flow to the engine.

The arrangement of Figure 3 is possible with a compression ignition engine because for a given engine speed, the total volume of air and exhaust gas mixture drawn into the engine is substantially constant so that the volume of fresh air drawn into the engine can be determined by inspecting the position of the valve 16.

The system as shown in Figures 2 and 3 can be modified by modifying the output of the comparator 18 in accordance with the differential of the signal provided by the transducer 23. Thus when a rapid change in the demand is effected, there will be a rapid change in the position of the valve 16.

Analogue or digital or both, techniques may be employed in the systems described whichever is the more convenient.

Claims

1. An engine system comprising a reciprocating piston internal combustion engine having an air inlet manifold and an exhaust manifold, a conduit connecting the manifolds and a valve in the conduit, an electrical control for controlling the setting of said valve thereby to control the flow of exhaust gas into the inlet manifold, fuel supply means for supplying fuel to the engine, electrical control means for controlling the operation of said control, means for providing an electrical signal representative of the air flow to the engine, said electrical control means being responsive to said signal and to signals representative of the engine speed and the amount of fuel being supplied to the engine to determine the setting of said valve, further means for controlling the amount of fuel supplied by said fuel supply means to the engine, said further means being responsive to said signal whereby the maximum amount of fuel which can be supplied to the engine depends on the air flow to the engine.

2. An engine system according to Claim 1 in which said further means comprises a governor circuit including first circuit means responsive to an operator demand signal and an engine speed signal for providing a demanded fuel signal to said fuel supply means, the governor circuit including second circuit means for providing a fuel limit signal to said first circuit means said fuel limit signal depending upon the engine speed, whereby the maximum amount of fuel which can be supplied to the engine depends on the engine speed and third circuit means responsive to said electrical signal for varying said limit signal so that the maximum amount of fuel which can be supplied to said engine is also dependent upon the air flow to the engine.

3. An engine system according to Claim 1 or Claim 2 in which said electrical control means comprises an electrical comparator having its output connected to the control, a first input to the comparator connected to receive said electrical signal and further circuit means connected to a second input of the comparator, said further circuit means receiving signals indicative of engine speed and the actual amount of fuel being supplied to the engine and on the basis of these signals providing a signal to said second input of the comparator indicative of the desired setting of said valve.

4. An engine system according to Claim 1 including a transducer for providing a signal representative of the air flow to the engine, and means for modifying said signal in accordance with the density of the air, said transducer being positioned in the air inlet manifold upstream of said conduit, the output of said means being said electrical signal.

5. A system according to Claim 1 in which the engine is a compression ignition engine and includes a transducer for providing a signal indicative of the setting of said valve, means for modifying said signal at least in response to an engine speed signal so that the output of said means is indicative of the air flow to the engine and constitutes said electrical signal.

6. An engine system comprising the combination and arrangement of parts substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.

7. An engine system comprising the combination and arrangement of parts substantially as hereinbefore described with reference to Figures 1 and 3 of the accompanying drawings.