Abstract:
A feedback air-fuel ratio regulator comprises an air-fuel ratio sensor which determines air-fuel ratio of the combustible gas from the composition of its exhaust gas and produces a sudden change in its output at a preset theoretical air-fuel ratio and an electronic air-fuel ratio controlling circuit. The latter includes voltage detectors for detecting the output voltage of the air-fuel ratio sensor at two or more points corresponding to certain richer and leaner air-fuel ratios than the theoretical one. Switching means are actuated by the output combined by the voltage detectors. An integrating circuits has a time constant which is determined by a condenser and resistance selected by the switching means, whereby the amount of fuel to be injected is regulated by the time constant which is determined by the output of integrating circuit according to said output voltage.

Description:
FIELD OF THE INVENTION 
     The present invention relates to improvements in a feedback air-fuel ratio regulator which comprises an electronic circuit for controlling the amount of injected fuel as well as an air-fuel ratio sensor that determines air-fuel ratio of the combustible gas by detecting the content of oxygen in the exhaust gases of the engine in the exhaust gas cleaning equipment to reduce such toxic substances as hydrocarbons, carbon monoxide and nitrogen oxides which are usually present in the exhaust gases. 
     BACKGROUND OF THE INVENTION 
     The conventional feedback air-fuel ratio regulator of this type is so designed as to transmit a signal that changes with a certain time constant when the air-fuel ratio sensor has detected deviation of the air-fuel ratio from a preset theoretical value. Then, the amount of fuel to be injected is regulated so that the deviated air-fuel ratio is brought back again to the theoretical level by means of a signal transmitted from the electronic fuel injection controlling circuit into which the aforesaid signal and other compensating signals, such as one indicating the amount of sucked gas and one from the distributor for the spark plugs, are inputted. 
     Then, while fuel is injected into the intake air, the air-fuel ratio sensor is installed in a rather limited portion of its exhaust section. This entails a time-lag between the injection of fuel and the detection of air-fuel ratio that is equivalent to the sum of the time during which the sucked mixture is held within the cylinder and the time required for it to pass through the intake and exhaust passages. As a consequence, fuel has to be overinjected by such amount that corresponds to this time-lag, in excess of the amount required for attaining the theoretical air-fuel ratio, which is undesirable for the cleaning of exhaust gas. Said overinjection can be reduced by making the value of said time constant large. Then, however, it will take a considerable time for air-fuel ratio to return to its theoretical value subsequent to sudden change, impairing the response of the engine or the drive performance of the automobile. 
     The primary object of this invention is to provide a feedback air-fuel ratio regulator of the type which assures both a high drive performance and a good exhaust gas cleaning function by rapidly changing the amount of fuel injection with a small time constant until air-fuel ratio reaches the theoretical value, and reducing the amount of oversupply within the time-lag by automatically increasing said time constant after said theoretical air-fuel ratio has been attained. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram showing the overall construction of a conventional feedback air-fuel ratio regulator. 
     FIG. 2 shows a characteristic curve of an air-fuel ratio sensor. 
     FIG. 3 is a block circuit diagram illustrating the principal part of an electronic circuit for controlling the amount of fuel injected in the conventional equipment. 
     FIG. 4 shows changing characteristics of the amount of fuel injected. 
     FIG. 5 is a block circuit diagram showing the principal part of an embodiment of this invention. 
     FIG. 6 shows changing characteristics of the amount of fuel injected in the embodiment of this invention. 
     FIG. 7 is a block circuit diagram of the principal part of another embodiment. 
     FIG. 8 is a diagram of the resistance switching circuits of still another embodiment. 
    
    
     DETAILED DESCRIPTION 
     How fuel injection is regulated in the conventional device will be described more concretely. In FIG. 1, reference numeral 1 designates an engine proper, 2 an intake manifold feeding air to the various cylinders, 3 an air cleaner fitted at the intake port of the intake manifold 2, 4 an air flow detector attached to the intake manifold 2, 5 a throttle valve for regulating the amount of air sucked, 6 a distributor for spark plugs, 7 a fuel injection nozzle, 8 an exhaust manifold, 9 an air-fuel ratio sensor, and 10 an electronic circuit for regulating fuel injection which receives electric input signals from the detector 4, distributor 6 and air-fuel ratio sensor 9 through signal lines 11, 12 and 13, respectively, and transmits instruction signals through a signal line 14 so that the appropriate amount of fuel is injected from the injection nozzle 7. Item 15 is a ternary catalytic converter of the known type that decomposes carbon monoxide, hydrocarbon and nitrogen oxides at the same time. 
     FIG. 2 shown a known characteristic curve of the air-fuel ratio sensor 9, in which air-fuel ratio ρ is plotted along the x-axis and output voltage e of the air-fuel sensor is plotted along the y-axis, representing a characteristic that output voltage changes suddenly, for instance, from 0.2 volt to 0.6 to 0.7 volt in the proximity of the theoretical air-fuel ratio. 
     FIG. 3 is a block circuit diagram of the electronical circuit 10. The output voltage e of the air-fuel ratio sensor 9 is applied on the inversion input terminal of an operational amplifier OP 1 , while a voltage equal to the output voltage of the air-fuel ratio sensor 9 at the theoretical air-fuel ratio (for instance, 0.5 volt in FIG. 2) is applied on the non-inversion input terminal thereof by dividing a constant voltage E with resistances R 1  and R 2 . A resistance R 3  and a diode D 1  are positive feedback elements that impart hysteresis characteristic to the operational amplifier OP 1  so as to stabilize its operation. 
     An integrating circuit I, which is made up of an operational amplifier OP 2 , a resistance R 4  and a condenser C, transmits an output Vo, which is obtained by timeintegrating the output voltage of the operational amplifier OP 1 , to a pluse width correcting circuit 16. 
     Based on the signals from the detector 4 and the distributor 6, a pulse width regulating circuit 17 transmits such injection nozzle controlling pulse as may produce a mixture proportioned to the theoretical air-fuel ratio. In the pulse width correcting circuit 16, the width of said pulse is corrected with the output Vo, and then the corrected pulse actuates a drive solenoid 7a of the injection nozzle 7 through a power transistor Tr 1 . 
     Let us assume that the non-inversion input voltage of the operational amplifier OP 1  is fixed at 0.5 volt so that judgement may be made that air-fuel mixture is rich when the output of the air-fuel ratio sensor 9 in FIG. 2 exceeds 0.5 volt and that it is lean when said output is lower than 0.5 volt. Then, when the aforesaid hysteresis phenomenon is omitted, output Vs of the operational amplifier OP 1  becomes inversed on both sides of e = 0.5 volt. If air-fuel mixture becomes lean and output e falls to 0.1 volt due to some change in operating conditions, the operational amplifier OP 1  produces a high level step output Vs, and the output Vo of the operational amplifier OP 2  changes as expressed by the following equation: ##EQU1## 
     The width of output pulse from the pulse width correcting circuit 16 increases in proportion to the output Vo, while the amount of fuel injected q increases with time t, as represented by a curve A in FIG. 4. If g o  in FIG. 4 is the amount of fuel required for attaining the theoretical air-fuel ratio under a certain steady operating condition, q 1  is the amount of fuel required after a change in the operating condition, and Δt is the aforesaid time-lag, the amount of fuel oversupplied during a period of Δt  is Δq 1 . 
     If the time constant τ is relatively larger as indicated by the curve A, the amount of oversupply Δq 1  becomes small, but it takes a long time t 1  to recover the theoretical air-fuel ratio, thereby impairing the drive performance. In contrast, if the time constant τ is made small to improve the drive performance, the amount of injection q rapidly increases as indicated by a curve B and the time to recover the theoretical air-fuel ratio is reduced to t 2 . However, the amount of oversupply Δq 2  within the time-lag Δt increases, which, in turn, increases the contents of toxic substances in the exhaust gases and, therefore, lowers the cleaning performance of the catalytic converter 15. 
     As may be understood from the above, it is unavoidable that either of the drive performance or the cleanness of the engine exhaust should drop when the amount of fuel injection is change with a given time constant. 
     Now an embodiment of this invention will be described with reference to FIG. 5, in which reference numerals similar to those used in FIG. 3 designate similar parts. According to this invention, voltage detectors are provided for detecting voltages at two or more points that correspond to certain richer and leaner air-fuel ratios on the air-fuel ratio characteristic curve of FIG. 2. So, as illustrated in FIG. 5, voltage detectors K 2  and K 3 , which include operational amplifiers OP 3  and OP 4 , respectively, and possess the same circuit composition as a voltage detector K 1  that includes an operational amplifier OP 1 , are provided. As in the case of FIG. 3, the operational amplifier OP 1  becomes inverted when the output e of the air-fuel ratio sensor 9 reaches 0.5 volt (the hysteresis phenomenon being omitted, and the same for the individual operational amplifiers to be described hereinafter). Also, resistances R 7  to R 10  are so selected that the operational amplifiers OP 3  and OP 4  will be inversed when the output e reaches 0.2 volt and 0.8 volt, respectively. 
     A transistor Tr 2  constitutes a NOT circuit that makes the output of the operational amplifier OP 3  inversed. Diodes D 4  and D 5  and a resistance R 11  constitute an AND circuit that inputs the output of said NOT circuit and the output of the operational amplifier OP 4 . When a transistor Tr 3  conducts an application of the output from said AND circuit, it energizes a switching relay 18. On being energized, the switching relay 18 closes contacts a and c, thereby connecting a resistance R 5  to a condenser C. On being deenergized, contacts b and c are closed to connect a resistance R 6  (&lt;R 5 ) to the condenser C. 
     If the output e of the air-fuel ratio sensor 9 is 0.2 volt&lt; e&lt;0.8 volt, air-fuel ratio almost approximates the theoretical value, then the output of the operational amplifier OP 3  is inverted to negative and the transistor Tr 2  becomes nonconductive. Because its collector potential becomes positive then, and the output of the operational amplifier OP 4  also is positive, said AND circuit produces output, the transistor Tr 3  is caused to become saturated, and the relay 18 is energized to close the contacts a and c. 
     If the output of e&lt;0.2 volt, the operational amplifiers OP 3  and OP 4  are in an non-inversed state, the transistor Tr 2  conducts and its collector potential drops to ground, and the AND circuit produces no output. When the output e &gt;0.8 volt, the operational amplifier OP 4  becomes inversed, and therefore the AND circuit produces no output, similarly. Therefore, when e&lt;0.2 volt and when e&gt;0.8 volt, the transistor Tr 3  does not conduct, and the relay 18 is deenergized to close the contacts b and c. 
     Since R 5  &gt;R 6 , the time constant R 5  C required for the output of an integrating circuit Ia to change is large when 0.2 volt &lt;e&lt;0.8 volt. While the time constant R 6  C for the cases in which e&lt;0.2 volt and e&gt;0.8 volt is small. Accordingly, if air-fuel ratio changes in the proximity of its theoretical value, the amount of fuel injected changes with a large time constant as indicated by the curve A of FIG. 4, thus reducing oversupply. When air-fuel ratio deviates greatly from its theoretical value, the amount of fuel injected first changes rapidly with a small time constant as indicated by the curve B of FIG. 4. Then, when it approaches q 1  that corresponds to the theoretical air-fuel ratio and the output e falls between 0.2 volt and 0.8 volt (0.2 volt &lt;e&lt;0.8 volt), the time constant becomes larger and the amount of fuel injected q changes at the same rate as that of the curve A. That is, the amount of fuel injected q changes as indicated by a solid curve a-b-c in FIG. 6, and the amount of oversupplied fuel Δq 3  within the time-lag Δt is decreased. 
     In the above-described embodiment, the output e of the air-fuel ratio sensor 9 detected for the rich air-fuel ratio and the lean air-fuel ratio is one each, and the output e thus detected is treated with one resistance R 5 . But it is also possible to provide three or more voltage detectors so as to detect a plurality of outputs e for each of the rich and lean air-fuel ratios. By actuating a plurality of switching relays by combining the outputs of these voltage detectors, the time constant of the integrating circuit Ia may be changed in three steps or more. By this means, the curve a-b-c of FIG. 6 may be bent more closely, so that drive performance is improved and the amount of oversupplied fuel Δq 3  is decreased. 
     FIG. 7 exemplifies a circuit in which two each voltage detectors K 2  and K 3 , and K 4  and K 5  are provided for the rich air-fuel ratio and the lean air-fuel ratio, respectively. In this figure, reference numerals similar to those used in FIG. 5 designate similar parts, and the voltage detectors K 4  and K 5  are constructed in the same way as K 2  and K 3 , except that the output of K 4  becomes inversed when, for example, e&lt;0.1 volt and that of K 5  when e&gt;0.9 volt. 
     In this circuit, the contacts b and c are closed as described previously when air-fuel ratio deviates greatly from the theoretical value and the output e becomes lower than 0.1 volt (e&lt;0.1 volt). At the same time, however, the outputs of K 4  and K 5  are not inversed, and a transistor Tr 4  conducts. Consequently a second AND circuit, composed of diodes D 7  and D 8  and a resistance R 12 , does not produce output as described previously. When the output e&gt;0.9 volt, the contacts b and c  are closed as described before, and the output of K 5  is inversed to negative. Therefore, said second AND circuit produces no output this time, too. Therefore, when the output e&lt;0.1 volt and e&gt;0.9 volt, a transistor Ir.sub. 5 does not conduct, a relay 19 is deenergized, and its normally closed contact 19b short-circuits part R 62  of a resistance R 6 . Then, only part R 61  of the resistance R 6  remains effective, and the time constant of the integrating circuit Ia is reduced to R 61  C. 
     As a consequence, the amount of fuel injected q changes rapidly with the time constant R 61  C. Then, if the output e falls between 0.1 volt and 0.2 volt (0.1 volt &lt;e&lt;0.2 volt) or between 0.8 volt and 0.9 volt (0.8 volt&lt;e&lt;0.9 volt), said second AND circuit produces output, the transistor Tr 5  conducts, and the relay 19 becomes energized to open the contact 19b. Then, the time constant of the integrating circuit Ia increases to R 6  C, and the amount of fuel injected is regulated as described previously with reference to FIG. 5. With the output e between 0.2 volt and 0.8 volt (0.2 volt&lt;e&lt;0.8 volt), detectors K 4  and K 5  continue to hold contact 19b open, but as discussed with respect to FIG. 5, detector K 2  inverts, transistor Tr 2  is off, its AND circuit produces output, transistor Tr 3  energizes relay 18 and switch contacts a and c are closed, giving the large time constant R 5  C&gt;R 6  C. A broken curve a-d-e-f of FIG. 6 indicates an increase in the amount of fuel injecteed q that is regulated as described above. 
     FIG. 8 shows a switching circuit for a number of resistances R that are intended for still closer, or more finely divided, regulation of time constant for changing the amount of fuel injected, in a system that provides still greater number of voltage detectors and switching relays for each of the rich air-fuel ratio and the lean air-fuel ratio. The regulating principle of this circuit is the same as that of the circuit shown in FIG. 7. 
     According to this invention that is composed as described hereabove, drive performance of the engine can be maintained satisfactory even when air-fuel ratio of its charge deviates greatly from the theoretical value, by rapidly changing the amount of fuel injected therein. Then, as the air-fuel ratio is brought back to the theoretical value by such regulation, the amount of fuel injection is decreased to hold down oversupply of fuel. By this means, increase of the toxic substances in the exhaust gases can be prevented, and the catalytic converter is allowed to perform its exhaust gas cleaning function to the fullest possible extent.