US3900012A

US3900012A - Fuel-air mixture proportioning control system for internal combustion engines

Info

Publication number: US3900012A
Application number: US444486A
Authority: US
Inventors: Josef Wahl; Peter-Jurgen Schmidt
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1973-04-28
Filing date: 1974-02-21
Publication date: 1975-08-19
Anticipated expiration: 1992-08-19
Also published as: DE2321721A1; DE2321721C2

Abstract

An electrical signal representative of engine speed is derived; a sensor senses the composition of the exhaust gases and provides an electrical signal to an integrating controller which is connected to adjust the air-fuel ratio applied to the internal combustion engine. In accordance with the invention, a switching circuit is connected to the integral controller which is controlled to switch in synchronism with rotation of the engine to command the integrator to integrate in steps dependent on engine speed so that, as the engine speed changes, the integration rate changes.

Description

United States Patent 11 1 Wahl et a1.

[ Aug. 19, 1975 FUEL-AIR MIXTURE PROPORTIONING CONTROL SYSTEM FOR INTERNAL COMBUSTION ENGINES [731 Assignee: Robert Bosch G.m.b.H.,

Gerlingen-Schillerhohe, Germany 22 Filed: Feb. 21, 1974 211 App]. No.: 444,486

3,745,768 7/1973 Zechnall et a1 123/32 EA 3.782347 1/1974 Schmidt et a1. 123/32 EA 3,831,564 8/1974 Schmidt et al 123/32 EA Primary ExaminerCharles .1. Myhre Assistant Examiner-Joseph A. Cangelosi Attorney, Agent, or Firm-Flynn & Frishauf [5 7] ABSTRACT An electrical signal representative of engine speed is derived; a sensor senses the composition of the exhaust gases and provides an electrical signal to an inte- 1 1 Foreign Application Priority Data grating controller which is connected to adjust the air- Apr. 28, 1973 Germany 2321721 fuel ratio applied to the internal combustion engine In accordance with the invention, a switching circuit is [52] US. Cl. 123/32 EA connected to the integral controller which is con- [51] Int. Cl. F02D 35/00 trolled to switch in synchronism with rotation of the [58] Field of Search 123/32 EA engine to command the integrator to integrate in steps dependent on engine speed so that, as the engine [56] References Cited speed changes, the integration rate changes.

UNITED STATES PATENTS 3,483,851 12/1969 Reichardt 123 32 EA l1 Clams 3 Drawmg F'gures (l3 (l2 coNTkoL.

LER A Ifdndt 11 EXHAUST .L SENSOR l i l I ZLIJREL & FUEL-Age INTERNAL I MIXING 2 COMBUSTION PROPORLION ENGlNE EXAUST FUEL-AIR MIXTURE PROPORTIONING CONTROL SYSTEM FOR INTERNAL COMBUSTION ENGINES Cross reference to related applications and patents US. Pat. Nos. 3,483,851; 3,782,347 3,831,564

The present invention relates to a device to proportion the fuel and air of the fuel and air composition applied to internal combustion engines in such a manner that the noxious exhaust emission is reduced to a minimum.

The mass ratio of air-fuel, applied to the internal combustion engine can be influenced by the composition of the exhaust gases. This is done, as known, by means of a sensing device located to be exposed to the exhaust gases from the internal combustion engine. A controller is provided, controlled in dependence of the sensing signal derived from the sensing device, and connected to change the mass ratio of the air-fuel mixture applied to the internal combustion engine, for example by suitably increasing or decreasing the amount of fuel instantaneously added to a predetermined air quantity. Changing the mass ratio of the air-fuel mixture applied to internal combustion engines can be done with engines having carburetors, as well as fuel injection systems. The controller which influences the mass ratio of the air-fuel mixture applied to the engine preferably is an integral controller so that, if the composition of the exhaust gases deviates for a substantial period of time from a predetermined composition, the correction of the mass ratio of the air-fuel mixture applied to the internal combustion engine, at the inlet side, becomes greater and greater. Known integral controllers have the disadvantage that the time constant of integration is independent of engine speed. The main delay within the control loop, which includes the exhaust sensor, the integral controller, and the adjustment mechanism controlling the actual air-fuel mixture is given by the time which the mixture takes to pass from the carburetor, or injection system, through the internal combustion engine. The air-fuel mixture which may already have a changed composition must first pass through the internal combustion engine, and be delayed by the various strokes of the combustion engine, before the integral controller, sensitive to the exhaust gases, can determine a change in the composition of the exhaust gases. If the integration time constant is matched to an average, median speed of the engine, then, when the speed of the engine is low, the longer time of passage of the air-fuel mixture through the engine causes integration of the integral controller to be too rapid. Correction of the mass ratio of the air-fuel mixture applied to the internal combustion engine will thus be excessive, and a deviation from command value in the opposite direction will result. Conversely, at higher than the speeds for which the integral controller operates at optimum value, the control effect is too slow, and the desired command value is reached only slowly.

It is an object of the present invention to provide a control system to decrease the noxious components in the exhaust emission from internal combustion engines, in which the mass ratio of the fuel-air mixture applied to the internal combustion engine is properly controlled, rapidly, under many different engine operating conditions. The control of this ratio should be accurate, over the speed range of the engine. Further, and in accordance with a desirable feature of the invention, the apparatus or system should utilize already existing components and transducers providing electrical signals, so that the apparatus or system is inexpensive and can be simple constructed.

SUBJECT MATTER OF THE PRESENT INVENTION Briefly, the controller is so arranged that it integrates, in steps, the stepping of integration being controlled by a signal depending on the rotation of the internal combustion engine, and hence on the speed of the internal combustion engine.

The invention will be described by way of example with reference to the accompanying drawings, wherein:

FIG. 1 is a schematic block circuit diagram of a system in accordance with the present invention;

FIG. 2 is a detailed circuit diagram of a speedcontrolled integral controllerjand FIG. 3 is a timing diagram, showing the timing relationship of pulses and signals arising in the circuit of FIG. 2.

An internal combustion engine, schematically shown at 10 (FIG. 1) has its inlet side connected to a fuel-air mixing and proportioning device 11. The device 11 may, for example, be a carburetor, or a fuel injection system, for example of the type described in crossreferenced US. Pat. No. 3,483,851. The proportioning device 11 provides a predetermined quantity of air and fuel to the internal combustion engine 10. An exhaust sensor 12 is located to be exposed to the exhaust gases from the internal combustion engine. Sensor 12 provides an electrical output signal which depends on the composition of the gases in the exhaust from the internal combustion engine 10. The output signal from sensor 12 is applied to a controller 13. The controller 13 is an integral controller which, over a line schematically shown at 13', provides an output to the fuel-air mixing and proportioning device 11 to so control the mass ratio of the air and fuel of the mixture that the exhaust from the internal combustion engine will contain a minimum of noxious components. The details of such a system are seen, for example, in cross-reference US. Pat. No. 3,782,347. Controller 13 is an integral controller and influences the air-fuel proportioning device 11 in steps. The repetition of these steps is determined by a speed signal, as schematically shown by line n, from the internal combustion engine. This speed signal u may be derived, for example, from the ignition system of the internal combustion engine; if the fuel-air proportioning device 11 is a fuel injection system, an electrical signal which controls the injection of fuel may also be used, derived directly from the fuel injection system 11, as schematically shown by dashed line 11 The integration, in steps, has this result: the controller will command a change in the proportioning device 11 for each working stroke of the engine, independent of the speed thereof. Thus, the integration time constant of the controller changes automatically with change in engine speed and is matched to the instantaneous speed of the internal combustion engine I0, practically without delay. The amplitude of the control swing will thus remain constant approximately over the entire speed range of the engine 10, so that the entire control loop can readily be optimized.

The details of the circuit are illustrated in FIG. 2: A threshold switch 14, controlled from sensor 12, is connected to a switching stage which, in turn, is connected to an integrating control amplifier. Threshold switch 14 includes an operational amplifier 17, having one input connected to a command threshold voltage, generated by a voltage divider formed by a potentiometer connected between a positive and negative bus 18, 19. The position of the slider or tap on the potentiometer 20 of the voltage divider determines a reference level. The second connection to the operational amplifier 17 is connected to the sensor 12. FIG. 3, graph a, illustrates an example of the output voltage of the sensor 12 with respect to time t. The broken line 20 in graph 11 of FIG. 3 is representative of the threshold level as set by the setting of the slider of potentiometer 20. If the output voltage of the sensor 12, as shown by the curve 12, FIG. 3, exceeds the threshold level 20', then the output voltage of the operational amplifier, indicated in graph b of FIG. 3,jumps to the value 21; if the output voltage of the sensor 12 is below the threshold level, then the operational amplifier has an output level indicated by 22 in graph b FIG. 3.

The output of the operational amplifier 17 in threshold switch 14 is coupled by resistor 23 to the bases of two

transistors

24, 25. The

transistors

24, 25 are part of the switching stage 15. Switching stage 15 further includes a switching transistor 26. The control electrode of switching transistor 26 is connected to the tap point of the voltage divider formed by resistors 27, 28 connected across buses 18, 19. The output electrode of switching transistor 26 is connected to the bases of the two

transistors

24, 25. The emitters of the

transistors

24, 25 are each connected to the tap point of the voltage divider formed of

resistors

29, 30, 31, and connected across the buss 18, 19. The emitter of transistor 24 is connected to the junction between

resistors

29, 30; the emitter of transistor 25 is connected to the junction between

emitters

30, 31. The collectors of the two

transistors

24, 25 are connected together and then over a resistor 32 to one input, for example the inverting input of an operational amplifier 33, which forms the integrating element of the integrating control amplifier 16. The operational amplifier 33 has its output connected back to the input to which resistor 32 is connected by means of a capacitor 34, to provide the integrating control effect thereof, and giving the control amplifier 16 the integrating characteristics. The second input of operational amplifier 33 is connected to the tap point of the voltage divider formed of resistors 27, 28.

The output A of the operational amplifier 33 provides a correction voltage which is used to control the fuel-air mixing and porportioning device 11, and can be connected, for example, to line 13. This voltage may, for example, control the setting of a flap valve which changes the air flow through, or bypassing a carburetor; or changes the position of a needle valve in the carburetor; or, the setting element in the proportioning device 11 may be a simple resistor which is included in the electronic circuitry of an electronic fuel injection system. By changing the output voltage of operational amplifier 33, the opening time of fuel injection valves can be influenced, thus controlling the relative proportion of fuel and air applied to the internal combustion engine 10.

Switching transistor 26 of the circuit 15 is controlled from a resistor 35 which, in turn, is connected to the output of a monostable flip-flop (FF) 36. The FF 36 is triggered by a signal occurring in synchronism with engine rotation. Such a signal may be derived, for example, from the ignition system of the engine 10; it may also be derived from injection pulses of a fuel injection system, if used, of the proportioning device 11. The speed pulses which are applied to the FF 36 are schematically shown in FIG. 2 and also in graph C of FIG. 3. The output pulses from FF 36 are shown at graph d, and also in FIG. 2. The output signal at the output of the operational amplifier 33, which leads to the stepped correction of the mass ratio of the internal combustion engine is shown in graph e of FIG. 2.

The engine speed signal is a pulse signal which has a predetermined pulse time, as determined by the unstable time of the FF 36. The switching stage 15 is connected to the integrator 16 to command the integrator to integrate, in steps, during these predetermined pulse times.

Operation: Let it be assumed that the transistor 26 is blocked, since the output voltage from the FF 36 is less than the voltage applied by the voltage divider 27,28, and taken off the tap thereof. If the output signal of the operational amplifier 17 is at the level of 21 (FIG. 3 graph b), that is, is positive, then the transistor 24 is conductive over the collector-base diode. Resistor 32 will have a current flowing to the first input of operational amplifier 33. Due to feedback of the output signal of operational amplifier 33 by capacitor 34 to the same input of the operational amplifier, the output voltage of amplifier 33 will change linearly. Upon receipt of a switching pulse by the FF 36, however, the output voltage transmitted over resistor 35 will change and switching transistor 26 in the switching stage will become conductive. The base voltages of the

transistors

24, 25 will be clamped to a value which is intermediate between that of the two emitter voltages. The two

transistors

24, 25 will block. Thus, resistor 32, connected to the integrating control amplifier, will no longer have current flowing thereover to the operational amplifer 33. This interrupts the integration, so that the output voltage of the operational amplifier 33 will remain at the previously existing level until, due to blocking of the switching transistor 26, one or the other of the two

transistors

24, 25 will become conductive. Then integration will proceed, in the one or the other direction, so that the correction signal at the output of the operational amplifier 33 will either increase, or decrease as the case may be. Switching transistor 26 is controlled to conductive, or blocked condition, by change of state of the monostable FF 36 which, in turn, is controlled by a speed signal from the internal combustion engine 10. Each pulse at terminal n, for example an ignition pulse, or a fuel injection control pulse, triggers FF 36. FF 36 then provides a pulse of a predetermined duration which is coupled by resistor 35 to the base of transistor 26. The integration cycle will, therefore, occur in the desired stepped form. The output voltage of control amplifier 16, that is, the output voltage from operational amplifier 33 then provides a signal which can be used to control the mass ratio of the air-fuel mixture being applied to the engine, for example by proportional prolongation, or shortening of fuel injection pulses in electronically controlled fuel injection systems, by proportional change of a nozzle diameter in carburetors, or control of additional, or bypass air in carburetor systems having air bypass ducts.

In accordance with a feature of the invention, aresistor 40 can be provided which is coupled. between the resistor 23 and the input to the operational amplifier 33 which forms part of the integrating circuit, for example the inverting input. This resistor 40 is not necessary and, therefore, the connection thereto is shown in dashed lines. The resistor 40 is preferably large with respect to the resistor 32.

In most applications, the system functions satisfacto rily without the resistor 40. In some applications, however, the situation may arise that the integration time of the control system depends too greatly on the influence of speed and/or load on the engine. This is partic ularly the case if the speed and/or the load on the engine varies over very wide ranges.

The resistor 40 provides an override, or bypass, to a limited extent, around the switching stage 15. As a result, the amplifier 16 will continue to integrate even in the gaps between pulses from FF 36. The correction signal will, therefore, also further increase, or decrease during the pulse gaps between succeeding pulses. The resistance of resistor 40, being large with respect to that of resistor 32, provides for a difference in integration rate during the pulses from FF 36, and during the pulse gaps. Since the resistor 40 is large with respect to resistor 32, the output signal of the operational amplifier 33 will change much more slowly, that is, integration will be carried out with a much larger time constant than during the pulses. This has the additional advantage that change-over of the threshold switch 14 during a pulse gap changes the direction of integration of the control amplifier 16 immediately, rather than when a new pulse is received. This further decreases the dead time, or lag in the control loop. Graph e, FIG. 3, illustrates the output voltage from the integrating amplifier 33 without the resistor 40 in circuit; graph f illustrates the control output from operational amplifier 33 with the resistor 40 connected, in which the resistor 40 has a value which is high with respect to that of the resistor 32. This diagram, graph f of FIG. 3, clearly shows that the output signal of the operational amplifier 33 changes to a much greater extend during the pulses from FF 36 than during the pulse gaps when the change signal is much less, that is, occurs with a much longer time constant.

The output pulses derived from an electrical fuel ignition control system, for example of the type shown in the cross-referenced US. Pat. No. 3,483,851 are of a width which depends on engine operating parameters, such as load on the engine, engine speed and, possibly other additional parameters such as starting conditions, ambient air pressure, and engine temperature, and the like. These pulse have a finite width, and occur in synchronism with engine rotation. In some systems, these pulses may, therefore, be directly used to control conduction of the transistor 26, as schematically indicated by the dashed connection 11 to the coupling resistor 35; the monostable FF 36 may then be omitted, integration occurring during the occurrence of the pulses from the fuel injection system (or their complement, or inverse). These pulses will have different pulse widths so that the integration at the rate determined by the coupling resistor 32 and the voltage levels at the taps of the

voltage dividers

29, 30, 31 not only will occur in steps, but the length, that is, the time duration of these steps, themselves, will vary in accordance with variation of the length of the fuel injection pulses.

Various changes and modifications may be made within the scope of the inventive concept.

We claim:

1. Proportioning control of fuel-air mixture composition applied to an internal combustion engine having means (12) sensing the composition of exhaust gases and providing an electrical signal;

controllable means (11) applying fuel and air to the engine and controlling the relative proportion of fuel and air components of the resulting mixture;

an integral controller (13) having an integrator (16) connected to and controlled by the sensor (12) and being connected to and controlling said controllable means (11) to process the electrical signal and controlling operation of said controllable means to provide a mixture resulting in minimum noxious components in the exhaust of the engine,

wherein the improvement comprises means (36) providing an electrical pulse signal having a pulse repetition rate representative of engine speed, the pulses being of a predetermined pulse time duration, switching means (15) connected to the integrator (16) and controlled by said engine speed signal to command the integrator to integrate in steps in synchronism with engine speed during the pulse time;

and wherein the integration rate of said integration steps occurring during said predetermined pulse time is high with respect to the integration rate during pulse gaps.

2. Control according to claim 1, further comprising a threshold switch (14) connected to and controlled by the sensor (12) and changing its switching level in dependence on output of the sensor.

3. Control according to claim 1, further comprising means (40) controlling the integrator to integrate in a direction dependent on the nature of the signal from the sensor (12) and determining the integration rate during the pulse gaps.

4. Control according to claim 3, further comprising a threshold switch (14) connected to and controlled by the sensor (12) and changing its switching level in dependence on the output of the sensor;

and wherein said integration rate control means comprises resistance means (40) connected between the threshold switch and the integrator (16) and determining the integration rate during pulse gaps.

5. Control according to claim 1, wherein the means providing the engine speed signals comprises a moonostable flip-flop (36) controlled by signals representative of engine rotation, the period of instability of said flip-flop determining the pulse time.

6. Control according to claim 5, wherein the controllable means applying fuel and air to the engine comprises a fuel injection system including means generating pulses occurring in accordance with engine rotation, said pulse generating means being connected to and controlling the monostable flip-flop (36).

7. Control according to claim 1, wherein the controllable means applying fuel and air to the engine comprises a fuel injection system in which the injection duration is controlled in dependence on engine operating parameters and in which fuel injection pulses are generated having a pulse width representative of engine operating parameter characteristics including engine speed;

wherein said pulses are connected to the switching means to command the integrator to integrate v during the occurence of said pulses.

8. Control according to claim 1, wherein the switching means comprises a monostable flip-flop (36) controlled by signals representative of engine rotation; a control transistor (26) connected to be conductive during pulses from said monostable flip-flop (36) and a pair of connection transistors (24, 25) rendered alternately, selectively conductive in dependence on a characteristic of the signal from said sensing means (12) and having their emitter-collector paths connected to said integrator (16), conduction of said transistors, under control of said sensing means (12) being additionally controlled by conduction of said control transistor (26) including a connection of the emittercollector path of said control transistor (26) to the bases of said connection transistors (24, 25).

9. Control according to claim 8, further comprising a two-tap voltage divider (29, 30, 31), the emitters of the connection transistors (24, 25) being connected to a respective tap, each, of said voltage divider, and the collectors being connected to the integrator (16) to effect integration, either in positive, or negative direction, depending on conduction of either one, or the other of said connection transistors (24, 25) and interrupting control of integration by said connection transistors (24, 25) upon blocking of said transistors.

10. Control according to claim 1, wherein the integrator (16) comprises an operational amplifier;

a threshold switch (14) is provided connected to and controlled by the sensor (12) and changing its switching level in dependence on the output of the sensor (12);

and a coupling resistor (40) connected to the integrating control amplifier and to the output of the threshold switch and shunting said connection transistors (24, 25) to control the operational amplifier to integrate in the direction as determined by the polarity of the output from the threshold switch and at a rate as commanded by said coupling resistor (40).

l 1. Control according to claim 10, wherein the transfer transistors (24, 25) and the switching transistor (26) comprise a switching stage;

coupling means (32) coupling the switching stage to the operational amplifier (33), said coupling means having a coupling transfer characteristic which is high with respect to the signal coupled by said coupling resistor (40) to provide for a higher rate of integration when either of said transfer transistors in conductive, than when both of said transfer transistors are blocked and only the signal through said coupling resistor (40) is applied to said operational amplifier (33).

Claims

1. Proportioning control of fuel-air mixture composition applied to an internal combustion engine having means (12) sensing the composition of exhaust gases and providing an electrical signal; controllable means (11) applying fuel and air to the engine and controlling the relative proportion of fuel and air components of the resulting mixture; an integral controller (13) having an integrator (16) connected to and controlled by the sensor (12) and being connected to and controlling said controllable means (11) to process the electrical signal and controlling operation of said controllable means to provide a mixture resulting in minimum noxious components in the exhaust of the engine, wherein the improvement comprises means (36) providing an electrical pulse signal having a pulse repetition rate representative of engine speed, the pulses being of a predetermined pulse time duration, switching means (15) connected to the integrator (16) and controlled by said engine speed signal to command the integrator to iNtegrate in steps in synchronism with engine speed during the pulse time; and wherein the integration rate of said integration steps occurring during said predetermined pulse time is high with respect to the integration rate during pulse gaps.

4. Control according to claim 3, further comprising a threshold switch (14) connected to and controlled by the sensor (12) and changing its switching level in dependence on the output of the sensor; and wherein said integration rate control means comprises resistance means (40) connected between the threshold switch and the integrator (16) and determining the integration rate during pulse gaps.

7. Control according to claim 1, wherein the controllable means applying fuel and air to the engine comprises a fuel injection system in which the injection duration is controlled in dependence on engine operating parameters and in which fuel injection pulses are generated having a pulse width representative of engine operating parameter characteristics including engine speed; wherein said pulses are connected to the switching means (15) to command the integrator to integrate during the occurence of said pulses.

8. Control according to claim 1, wherein the switching means comprises a monostable flip-flop (36) controlled by signals representative of engine rotation; a control transistor (26) connected to be conductive during pulses from said monostable flip-flop (36) and a pair of connection transistors (24, 25) rendered alternately, selectively conductive in dependence on a characteristic of the signal from said sensing means (12) and having their emitter-collector paths connected to said integrator (16), conduction of said transistors, under control of said sensing means (12) being additionally controlled by conduction of said control transistor (26) including a connection of the emitter-collector path of said control transistor (26) to the bases of said connection transistors (24, 25).

10. Control according to claim 1, wherein the integrator (16) comprises an operational amplifier; a threshold switch (14) is provided connected to and controlled by the sensor (12) and changing its switching level in dependence on the output of the sensor (12); and a coupling resistor (40) connected to the integrating control amplifier and to the output of the threshold switch and shunting said connection transistors (24, 25) to control the operational amplifier to integrate in the direction as deTermined by the polarity of the output from the threshold switch and at a rate as commanded by said coupling resistor (40).

11. Control according to claim 10, wherein the transfer transistors (24, 25) and the switching transistor (26) comprise a switching stage; coupling means (32) coupling the switching stage to the operational amplifier (33), said coupling means having a coupling transfer characteristic which is high with respect to the signal coupled by said coupling resistor (40) to provide for a higher rate of integration when either of said transfer transistors in conductive, than when both of said transfer transistors are blocked and only the signal through said coupling resistor (40) is applied to said operational amplifier (33).