Air/fuel ratio control for an internal combustion engine using an exhaust gas sensor

What is claimed is:

1. In an internal combustion engine wherein a combustible air/fuel mixture is introduced into combustion chambers of the engine and combusted therein and products of combustion are exhausted from the combustion chambers, and the air/fuel ratio of the mixture is controlled by a closed-loop regulated air/fuel ratio control having a sensor sensing predetermined compositions of the products of combustion and exhibiting a change from one state to another correlated with a predetermined change in the composition of the products of combustion, means adjusting the air/fuel ratio of the combustible mixture and control means closed-loop coupling said sensor and said adjusting means, the improvement in said control means comprising: means responsive to each change in state of said sensor for always immediately effecting a predetermined increment of change in the setting of said adjusting means to a setting calculated to return said sensor, under reasonably steady state operation of the engine, to the sensor's immediately preceding state upon elapse of the transport time required for the effect of the change in the setting to be detected by said sensor and for holding the setting of said adjusting means substantially at its incremented value for a time interval essentially equal to that of the transport time, and means effective at the conclusion of said time interval if said sensor has not yet returned to its immediately preceding state for progressively increasing the setting of said adjusting means beyond that established by said predetermined increment of change until said sensor does return to its immediately preceding state.

2. In an internal combustion engine wherein a combustible air/fuel mixture is introduced into combustion chambers of the engine and combusted therein and products of combustion are exhausted from the combustion chambers, the method of closed-loop regulating the air/fuel ratio by an air/fuel ratio control having a sensor sensing predetermined compositions of the products of combustion and exhibiting a change from one state to another in response to a predetermined change in composition of the products of combustion, and means adjusting the air/fuel ratio of the combustible mixture in accordance with the state of said sensor, said method comprising: always immediately effecting a predetermined increment of change in the setting of said adjusting means to a setting calculated to return said sensor, under reasonably steady state operation of the engine, to the sensor's immediately preceding state upon elapse of the transport time required for the effect of the change in the setting to be detected by said sensor, holding the setting of said adjustment means substantially at its incremented value for a time interval essentially equal to the transport time, and at the conclusion of said time interval progressively increasing the setting of said adjusting means beyond that established by said predetermined increment of change if said sensor has not yet returned to its immediately preceding state and continuing to progressively increase the setting of said adjusting means until said sensor does return to its immediately preceding state.

3. In an internal combustion engine wherein a combustible air/fuel mixture is introduced into combustion chambers of the engine and combusted therein and products of combustion are exhausted from the combustion chambers, and the air/fuel ratio of the combustible mixture is controlled by a closed-loop regulated air/fuel ratio control having sensing means sensing predetermined compositions of the products of combustion for providing a rectangular waveform signal in accordance therewith, means adjusting the air/fuel ratio of the combustible mixture, and control means closed-loop coupling said sensing means and said adjusting means, said control means including an integrator controlled by said sensing means providing an integrator signal which ramps in one direction when said rectangular waveform signal is high and which ramps in the opposite direction when said rectangular waveform signal is low, and means controlling the rate of the integrator with engine speed, the improvement comprising: stability circuit means coupled with said sensing means comprising means always responsive to each transition of said rectangular waveform signal for always immediately providing a corresponding pulse whose polarity corresponds to the direction of the corresponding transition and which comprises an initial increment and ensuing transient decay thereof, and means summing the pulses of said stability circuit means and said integrator signal together algebraically to form a command signal, and means controlling the setting of said adjusting means in accordance with said command signal, said stability circuit means and said integrator being so constructed that when their respective outputs are summed together by said summing means the command signal exhibits a characteristic effective to cause the setting of said adjusting means to be changed in response to each transition in said rectangular waveform signal by a predetermined amount calculated to return said rectangular waveform signal, under reasonably steady state operation of the engine, to the level existing immediately prior to the transition upon elapse of a time interval essentially equal to the transport time required for the effect of the transition to be detected by said sensing means, and hold the setting of said adjusting means substantially at its changed setting for said time interval, and then at the conclusion of said time interval, if said rectangular waveform signal has not yet returned to the level existing immediately prior to the transition, progressively increase the setting of said adjustment means beyond that established by said predetermined amount until said rectangular waveform signal does return to the level existing immediately prior to the transition.

4. In an internal combustion engine wherein a combustible air/fuel mixture is introduced into combustion chambers of the engine and combusted therein and the products of combustion are exhausted from the combustion chambers, and the air/fuel ratio of the mixture is controlled by a closed-loop regulated air/fuel ratio control having means sensing predetermined compositions of the products of combustion, means adjusting the air/fuel ratio of the combustible mixture and control means closed-loop coupling said sensing means and said adjusting means, the improvement in said control means comprising: means providing a command signal representative of a desired setting of said adjusting means to create a corresponding desired air/fuel ratio of the combustible mixture, a duty cycle control circuit receiving said command signal and developing a corresponding duty cycle control signal, a solenoid coil which is duty-cycle operated to control the setting of said adjusting means, and means coupling said duty cycle circuit and said solenoid coil comprising a transistor driver circuit including a driving transistor having base, emitter and collector electrodes, means serially connecting the emitter-collector circuit of said transistor and said solenoid coil across a source of energizing potential, means coupling the base-emitter circuit of said transistor to said duty cycle circuit to cause the duty cycle signal to be applied across said base and emitter electrodes and thereby subject said transistor to duty cycle operation to similarly duty cycle said solenoid coil, a zener diode, means connecting the anode of said zener diode to said base electrode, and means connecting the cathode of said zener diode to the junction at which said solenoid coil and the emitter-collector circuit of said transistor are serially connected.

5. In an internal combustion engine wherein a combustible air/fuel mixture is introduced into combustion chambers of the engine and combusted therein and products of combustion are exhausted from the combustion chambers and the air/fuel ratio of the combustible mixture is controlled by a closed-loop regulated air/fuel ratio control having means sensing predetermined compositions of the products of combustion, means adjusting the air/fuel ratio of the combustible mixture and control means, including control circuitry on a circuit board, closed-loop coupling said sensing means and said adjusting means, the improvement in said control means comprising: a programming device which establishes that air/fuel ratio about which the air/fuel ratio of the mixture is closed-loop regulated, said programming device comprising a first element having a plurality of terminals which are hard-wired onto said circuit board into that portion of the control circuitry which establishes the air/fuel ratio about which the air/fuel ratio of the mixture is closed-loop regulated, a first set of said terminals being inputs and a second set of said terminals being outputs, and a second element which is removably engaged with said first element, said second element comprising a first set of terminals mated with the first set of terminals of said first element and a second set of terminals mated with the second set of terminals of said first element, said second element comprising a plurality of direct conductive paths from selected ones of said first set of terminals thereof to selected ones of said second set of terminals thereof whereby the conductive paths establish selected circuits from selected input terminals of said first element to selected output terminals of said first element and thereby program that air/fuel ratio about which the air/fuel ratio of the mixture is closed-loop regulated.

6. In an internal combustion engine wherein a combustible air/fuel mixture is introduced into combustion chambers of the engine and combusted therein and the products of combustion are exhausted from the combustion chambers, and the air/fuel ratio of the combustible mixture is controlled by a closed-loop regulated air/fuel ratio control having means sensing predetermined compositions of the products of combustion, means adjusting the air/fuel ratio of the combustible mixture, control means closed-loop coupling said sensing means and said adjusting means, means for interrupting the closed-loop control of said adjusting means by said sensing means in favor of an open-loop mode of control of said adjusting means in response to a predetermined condition, and means for detecting failure of said sensing means, the improvement in said means for detecting failure of said sensing means comprising: means for determining (1) that the closed-loop control of said adjusting means by said sensing means has not been interrupted in favor of an open-loop mode of control, (2) that said sensing means is giving an indication of a selected predetermined composition, (3) that the temperature of the products of combustion is above a selected temperature, (4) that the engine is running in a non-idle condition, and (5) that the control is commanding a mixture which would cause said sensing means to give an indication different from that which it is in fact giving and means for giving a fault indication in response to the determination of the concurrence of the foregoing five conditions for a predetermined time period.

7. In an internal combustion engine wherein a combustible air/fuel mixture is introduced into combustion chambers of the engine and combusted therein and products of combustion are exhausted from the combustion chambers, and the air/fuel ratio of the combustible mixture is controlled by a closed-loop regulated air/fuel ratio control having means sensing predetermined compositions of the products of combustion for providing a rectangular waveform signal in accordance therewith, means adjusting the air/fuel ratio of the combustible mixture, and control means closed-loop coupling said sensing means and said adjusting means, said control means including an integrator controlled by said sensing means providing an integrator signal which ramps in one direction when said rectangular waveform signal is high and which ramps in the opposite direction when said rectangular waveform signal is low and means controlling the rate of said integrator with engine speed, the improvement comprising:

said integrator comprising a multi-bit binary up/down counter circuit;

clock input, up/down control, output, and clock inhibit terminals associated with said counter circuit;

said counter circuit comprising means for algebraically summing clock pulses applied to the clock input in accordance with an up/down control signal applied to the up/down control and developing at the output an output signal representing the integrator signal;

said counter circuit further comprising means preventing clock pulses at the clock input from being algebraically summed whenever a clock inhibit signal is being applied to the clock inhibit and causing the count to be thereby held at the value existing just prior to the application of the clock inhibit signal to the clock inhibit;

means supplying clock pulses to the clock input at a rate correlated with engine speed;

means coupling said sensing means with the up/down control such that the rectangular waveform signal forms an up/down control signal which controls algebraic summation of clock pulses by said counter circuit;

and means for selectively interrupting closed-loop operation of the control in favor of an open-loop mode of operation comprising means providing an open-loop command signal in response to a predetermined condition for which closed-loop operation is to be interrupted and means responsive to said open-loop command signal causing a clock inhibit signal to be applied to the clock inhibit which in turn causes the count in the counter circuit, and hence the integrator signal, to be held at the value existing just prior to the occurrence of the open-loop command signal.

Description Submit all comments and votes

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention pertains to an air/fuel ratio control for an internal combustion engine using an exhaust gas sensor, and in the preferred embodiment disclosed herein is concerned with an electronic feedback carburetor system including an oxygen sensor.

Although the basic concepts relating to air/fuel ratio control systems for automotive internal combustion engines using exhaust gas sensors have been long known, in recent years there have been a number of patents issued relating to improvements in such systems. Generally, the improvements are a result of the application of electronic technology to the problem of reducing exhaust emissions output of the engine while improving the engine fuel economy and obtaining satisfactory driveability of the vehicle. Some of these improvements are relatively crude and unsophisticated. Others are more elaborate and complicated.

In addressing the problem of designing an electronic feedback carburetor system applicants have made new discoveries and have developed a new and unique system which achieves new and unique modes of operation resulting in significant improvements in a number of different respects over other systems of which applicants are aware. As a result, an electronic feedback carburetor system embodying principles of the invention attains heretofore unachieved results and exhibits advantages which are not provided by other systems. Moreover, the invention, in its preferred embodiment, makes use of the latest electronic technology to provide a system wherein the electronics can be conveniently and economically packaged for mass production usage, yet is capable of being readily programmed to meet specific engine requirements. While details of the invention will be explained later in the description of the preferred embodiment, the more impressive improvements which are believed new and unique in applicants' system may be generally set forth as follows.

One feature of the present invention relates to the development of a control signal which provides for more precise regulation of the air/fuel ratio when the system is operating in the closed-loop mode. One problem in obtaining precision control arises from the limitations of commercially available oxygen sensors which are suitable for use in an automotive vehicle. These sensors present an impediment because they only possess a switching characteristic at stoichiometry and can therefore indicate only a rich mixture or a lean mixture condition. Applicants have overcome this impediment through the provision of an integrator circuit and a stability circuit which both receive a rectangular waveform signal derived from the oxygen sensor. The two circuits in turn develop respective output signals which cooperate to produce a composite signal which controls the air/fuel ratio. The integrator by itself develops a ramp type signal which ramps in one direction when the oxygen sensor is in one state and in the opposite direction when the oxygen sensor is in the other state. The stability circuit is responsive to transitions of the oxygen sensor from one state to the other and develops a signal which may be generally described as being the derivative of the oxygen sensor signal. This composite signal referred to above is developed by algebraically summing the integrator and stability circuit signals. In response to a change in state in the oxygen sensor, this composite signal commands a predetermined amount of correction of the air/fuel ratio which is maintained at essentially a constant level for a time interval essentially equal to the transport time of the mixture from the carburetor through the engine to the oxygen sensor. With the engine operating at a reasonably steady state condition, the amount of correction is such that by the conclusion of the transport time interval, the oxygen sensor will have switched back to its original state. In this way, the air/fuel ratio is closely regulated to be within a narrow window about the desired operating point which may be at or in the vicinity of stoichiometry. This enables a more precise and accurate control of the air/fuel ratio to be obtained which is advantageous in securing the best performance of certain types of catalysts which subsequently treat the exhaust gases after they have passed by the oxygen sensor. While the disclosed embodiment utilizes analog circuits, it will be appreciated that the principles of this aspect of the invention may be applied to other embodiments using digital circuits or microprocessors. Where the engine is operating under a more dynamic condition and the amount of correction is insufficient to change the state of the oxygen sensor, additional correction is performed.

Another feature of the invention is that there are additional circuits which are responsive to more extreme transient conditions, such as substantial changes in engine load, engine deceleration, etc., and are operative to interrupt the closed-loop mode of operation in favor of an open-loop mode of operation.

A further feature of the invention is that when the closed-loop mode of operation is interrupted, the output signal of the integrator circuit is locked (or held in memory) so that when the closed-loop mode of operation resumes, the integrator output signal is at a level which will enable the system to quickly return to the window about the desired operating point.

Still another feature of the invention relates to the provision of a programming device in the circuit whereby the closed-loop operating point may be programmed without having to make changes in the layout of the circuit board containing the circuit electronics. According to this aspect of the invention a programming circuit section which is associated with the integrator contains a socket which is hard-wired onto the circuit board. Another element, called a header, is inserted into the socket to perform the programming function. The header contains circuit paths which connect certain of the terminal pins on the socket with certain other terminal pins in such a way that a selected characteristic is programmed into the circuit depending upon the particular header which is used. This is of significant advantage in the application of the invention to the mass production of automotive engines since it means that changes in the calibration of the system can be made expeditiously and without requiring substantial tooling changes. Thus, rather than having to change components on the circuit board and the circuit board layout, all that is necessary is to make a new header which can be done expediently and without any substantial amount of tooling change. Circuitry on the board coacts with the programming device to shift the operating point under certain conditions of engine operation, and this constitutes a further feature of the invention.

The system also includes circuits responsive to initial operating conditions of the engine whereby the closed-loop mode of operation is prevented until both the engine is warmed up and a certain "after start" timing interval has elapsed after the engine has started. During this initial open-loop mode of operation, an analog coolant temperature signal related to engine temperature is utilized to control the air/fuel mixture to the exclusion of the composite signal from the integrator and stability circuits.

Another aspect of the invention provides for detection of certain system faults or failures. For example, the disclosed embodiment has a fault detection circuit which is particularly useful in connection with detection of a failed oxygen sensor. When such a failure is detected, a fault signal is given to both provide an alarm via an alarm circuit and is also utilized to control the air/fuel ratio to the exclusion of the other signals which usually control the air/fuel ratio.

Additional features are also disclosed and may be seen with reference to the ensuing disclosure and accompanying drawings. Naturally, the recitation of the inventive features set forth above is merely to acquaint the reader with the disclosure and should not be construed as limiting the scope of the invention or its various aspects because it is the set of claims at the conclusion of this specification which define the invention in its various aspects.

The invention is disclosed in connection with a preferred embodiment thereof according to the best mode presently contemplated in carrying out the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic illustration of the general organization of an example of a closed-loop engine control system embodying principles of the present invention.

FIG. 2 is a schematic diagram in block diagram form illustrating further detail of a portion of the system shown in FIG. 1.

FIGS. 3 through 19 are individual electronic schematic circuit diagrams, each illustrating circuit details of a corresponding one of the blocks of the system shown in FIG. 2.

FIGS. 20 and 20A illustrate details of the vacuum regulator shown in FIG. 1.

FIG. 21 illustrates detail of the carburetor shown in FIG. 1.

FIG. 22 is a diagram disclosing illustrative idealized waveforms useful in explaining the operation of the system in one particular operating mode.

FIG. 23 illustrates additional explanatory waveforms useful in explaining operation of a portion of the system.

FIG. 24 illustrates a comparison of two idealized waveforms to demonstrate the benefit of the invention in providing more precise control of the air/fuel ratio.

FIG. 25 is an illustrative idealized waveform useful in explaining system operation in response to transients.

FIG. 26 is an illustrative waveform of a portion of the waveform of FIG. 25 illustrating more realistic detail.

FIG. 27 is an idealized waveform useful in further explaining the operation of the system.

FIG. 28 is an electronic schematic diagram illustrating details of an alternate circuit construction which may be used in one of the blocks shown in FIG. 2.

FIG. 29 is a series of illustrative idealized waveforms useful in explaining the operation of the circuit of FIG. 28.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Description of FIG. 1

By way of introduction, FIG. 1 illustrates the general organization of an example of a closed-loop control system embodying principles of the present invention. Briefly, the Figure schematically portrays an internal combustion engine 200 including a carburetor 202 which supplies a combustible air/fuel charge for combustion in the cylinders of the engine. Engine power is developed by ignition of the charge. The products of combustion are exhausted via a conventional exhaust system 204. Exhaust system 204 conducts the combustion products to a 3-way catalyst 206 whose purpose is to oxidize and reduce the usual noxious products of combustion, namely, hydrocarbons, carbon monoxide, and oxides of nitrogen, before discharge to atmosphere. In order to most efficiently utilize the capabilities of catalyst 206, a closed-loop control system 208 is provided to control the air/fuel ratio of the charge mixture supplied by carburetor 202 to engine 200 as a function of the oxygen concentration present in the combustion products passing through exhaust system 204 prior to entering catalyst 206. An oxygen sensor (O.sub.2 sensor) 210 mounts at a suitable location on exhaust system 204 to communicate with the exhaust products passing therethrough and sense the oxygen concentration present therein. Oxygen sensor 210 is electrically connected with an ECU (electronic control unit) 212 to supply thereto an input signal representative of the oxygen concentration. Other input signals (to be hereinafter explained in greater detail) are also supplied as inputs to ECU 212. In turn ECU 212 develops a command control signal which is supplied to an electropneumatic vacuum regulator 214. This command signal represents the desired air/fuel ratio of the charge which carburetor 202 should be supplying to the engine. The vacuum regulator in turn supplies a control vacuum signal to carburetor 202 which causes the carburetor to adjust the air/fuel ratio of the charge to the commanded value. An air pump system 216 including an engine driven air pump 216a may be employed to pump air into the exhaust system. The disclosed system contains a temperature controlled diverter valve 216b which is selectively operable to cause the pumped air to be introduced either upstream or downstream of catalyst 206. Generally, pressurized air is fed upstream of the catalyst before the engine has fully warmed up and downstream with the engine warmed-up. For this purpose, valve 216b may be made responsive to engine coolant temperature so that when the sensed coolant temperature is less than a selected temperature, for example 98.degree. F., air is fed upstream and when the sensed coolant temperature is above the selected temperature, the air is fed downstream. As will be seen later, the closed-loop mode of operation does not occur until the coolant temperature is somewhat above that at which valve 216b diverts so that when the closed-loop mode of operation does occur the oxygen sensor is exposed essentially only to the products of combustion which emanate from the engine cylinders. An electrically actuated dump valve 216c is located in the downstream path from diverter valve 216b and is selectively operable to divert downstream air to atmosphere when a dump signal is given by ECU 212. The conditions under which the dump signal is given will be explained later in the description.

Briefly, the system of FIG. 1 operates in the following manner during the closed-loop mode of operation. Oxygen sensor 210 supplies to ECU 212 a signal which indicates one of either two conditions: (1) either a certain oxygen concentration in the combustion products (indicative of a leaner than stoichiometric ratio being supplied to the engine by the carburetor); or (2) a lack of oxygen therein (indicative of a richer than stoichiometric ratio). The ECU command signal supplied to the vacuum regulator causes the air/fuel ratio supplied by carburetor 202 to progressively richen when a leaner than stoichiometric condition is indicated by the oxygen sensor; correspondingly, it causes the ratio to progressively lean when a richer than stoichiometric condition is indicated. In this way, the air/fuel ratio is caused to vary about the stoichiometric ratio (air/fuel ratio equal 14.7) between a slightly richer than stoichiometric ratio and a slightly leaner than stoichiometric ratio. As will be seen from the later description, features of the present invention provide variations in the command signal during closed-loop operation such that new and improved modes of operation are achieved. As will also be more fully explained in the ensuing description, other features of the invention relate to the newly found desirability of interrupting the closed-loop mode of operation under certain conditions and instead having the system operate in an open-loop mode. These likewise create new and improved modes of operation.

Description of FIG. 2

Features of the present invention are disclosed in greater detail in FIG. 2 which is a block diagram illustrating the arrangement and construction of ECU 212 in its presently preferred embodiment. Before proceeding with the description of FIG. 2, it should be appreciated by the reader that the FIG. 2 illustration is intended to facilitate his comprehension of the principles of the present invention and that no inference of limitation of the invention's scope should be drawn by virtue of the specific designations given to the blocks or to the specific selection of and inter-relationship between the blocks shown, because the scope of the invention is defined by the appended claims at the conclusion of this specification.

It is deemed desirable to first follow the closed-loop path between the O.sub.2 sensor input signal and the command output to the vacuum regulator, called the vacuum regulator control signal. ECU 212 comprises an oxygen sensor circuit 218 to an input of which the oxygen sensor 210 is connected to supply the oxygen concentration signal also referred to as the O.sub.2 sensor input signal. The oxygen sensor circuit in turn produces a corresponding output signal (called the O.sub.2 sensor circuit output signal) which is supplied to an integrator circuit 220, to a stability circuit 222, to an integrator rate control and programming circuit 224, and to a fault detection circuit 226. The four circuits 218, 220, 222 and 224 form a portion of the closed-loop path. Integrator circuit 220 and stability circuit 222 develop respective output signals which are supplied as inputs to a summing circuit 225. Summing circuit 225 develops a resultant signal which is representative of the desired air/fuel ratio which is to be commanded by the ECU. This resultant signal from the summing circuit is supplied to a duty cycle circuit 228 which develops a duty cycle signal that is supplied to a regulator driver circuit 230. The regulator driver circuit 230 produces the vacuum regulator control signal, which is the command signal supplied to the vacuum regulator for causing adjustment of the carburetor so that the charge inducted by the engine possesses the desired air/fuel ratio.

ECU