DE2753452A1 - Air fuel mixt. control system with exhaust oxygen sensor - keeps control range for mixt. constant independently of operating conditions - Google Patents

Abstract

An oxygen sensor (10) is mounted in the exhaust gas stream of the motor. The output signal of this sensor is integrated and used to control the oxygen content of this gas. The control arrangement (12) incorporates a transducer which converts at least one of the following parameters: engine speed, suction vacuum, control valve opening, amount of inlet air and exhaust gas speed, into a time delay parameter. The control arrangement further incorporates an integrator which integrates the signal from the transducer, and a modulator to compare the integrator with a second integration signal which is obtained by integrating the output of the oxygen sensor. The pulse modulator generates a signal, the frequency of which increases with increase of the time delay parameter, while the pulse width is modulated according to the second integration signal. The oxygen content of the exhaust gasses is controlled at a speed which corresponds with the delay parameter.

Description

The invention relates to an air-fuel ratio control system, that is able to adjust the control fluctuation range of the air-fuel ratio regardless of changes to keep the operating conditions of a Prennkraftmaschine constant.

In general, it has been difficult to determine the air-fuel ratio that is processed in the carburetor of an internal combustion engine Mixtures or the gases flowing into a catalytic converter of the machine must always be kept constant. Uir. overcoming this difficulty is an aspiration system feedback control device has been proposed in an air-fuel ratio detector for detecting the air-fuel ratio of the mixture of the oxygen content of the exhaust gases, which is closely related to the air-fuel ratio is in use and the air-fuel ratio is controlled with feedback by an electronic control unit, thereby reducing the air-fuel ratio of the mixture to one

809830/0598

VII / 8

-4- B 8546

to hold a predetermined value. It is also an exhaust system feedback control device has been proposed in which lift air is supplied to the exhaust system to increase the air-fuel ratio to control the exhaust gases with feedback and thereby keep the air-fuel ratio at the value that is required for a Exhaust gas purification device such as a catalytic converter is required.

In these feedback control systems having a feedback path, the mean air-fuel ratio becomes by keeping the feedback control speed constant in accordance with the output of the air-fuel ratio detector kept constant.

With these tax systems, however, it is impossible to allow for control fluctuations or after-run effects in the air-fuel ratio to avoid the delay time of the System. This delay time depends on such delay factors as the engine speed, the suction negative pressure, the amount of intake air, the exhaust gas flow rate, etc .; as a result of an increase and / or decrease in the delay factors is the control fluctuation range of the air-fuel ratio subject to considerable fluctuations, as is the case with the intake system feedback control devices leads to disadvantageous unstable engine operation and in the case of the exhaust system feedback control devices disadvantageously deteriorates the efficiency of the exhaust gas purification device.

The object of the invention is to provide an improved air-fuel ratio control system in order to eliminate the above disadvantages, in which a pulse signal having a frequency which changes depending on a delay factor corresponding to the delay time and the output signal of an air-fuel ratio detector and an air-fuel ratio correcting electromagnetic

809830/0598

-5- B 8546

Valve is controlled by pulse signals derived from the resulting integration signals and having a pulse width rate of change which varies according to the Delay time changes, which increases the fluctuation range of the Air-fuel ratio within a tight predetermined Area is held.

An advantage of the system according to the invention is that that the opening time (the on-off duty cycle) of the electromagnetic valve controlled by the pulse signal obtained from the integrated output of the air-fuel ratio detector and the integrated output of a delay detector and has the pulse width rate of change which changes according to the delay changes so that consequently the control speed (changing speed of the air-fuel ratio) is controlled so that the control speed is increased, when the delay time becomes shorter while the control speed is decreased, as the delay time becomes longer, whereby the fluctuation range of the air-fuel ratio, even during the low-speed, light load operation, can be kept within a predetermined narrow range, and this ensures a greater purification efficiency of an exhaust gas purification device that uses a triple catalytic converter used. Another advantage is that, in the case of an intake air-fuel ratio feedback system, the Occurrence of a vibration phenomenon due to an increase in the fluctuation range of the air-fuel ratio can be prevented, thereby making the engine operation stable results.

The invention is described below with reference to the in Exemplary embodiments shown in the drawing are described in more detail.

Fig. 1 is a schematic representation of a Implementation of the invention.

809830/0598

- ⁶ - 2753A52 ^B

FIG. 2 is a circuit diagram of that shown in FIG

electronic control unit.

Figs. 3A and 3B are waveform diagrams showing the conditions during high-speed and low-speed During machine operation in the circuits of the electronic control unit of FIG. 2, output signal waveforms generated demonstrate.

Figs. 4 and 5 are sectional views showing the main parts of other embodiments of the present invention Show embodiments.

According to Fig. 1, as an embodiment

Air-fuel ratio control system with feedback to the As an intake system shows, an internal combustion engine 1 is an ordinary one Four-stroke piston engine. The mixture prepared in a carburetor 2 is fed to the engine 1 through a suction pipe 3, while the exhaust gases resulting from the combustion of the mixture through an exhaust pipe 4, an exhaust pipe 5 and a triple catalytic converter 6 released into the atmosphere will.

The basic mixture formed in the carburetor 2 is on

a richer air-fuel ratio than the desired air-fuel ratio adjusted; the air-fuel ratio of the mixtures is adjusted by additional air flowing through an air intake pipe 8 is supplied, which bridges the carburetor 2 and opens in the downstream section of a throttle valve 7. The additional amount of air is appropriately set according to the on-off duty cycle of an electromagnetic valve 9, see above that the mixture is adjusted to the desired air-fuel ratio by means of additional air.

809830/0598

-7- B 8546

In this embodiment, the triple catalytic converter 6 is used for the exhaust gas purification device and the mixture is adjusted to the stoichiometric air-fuel ratio by additional air, since the triple catalytic converter 6 is able to process Ν0 _χ , CO and HC most effectively, when the mixture is supplied at the stoichiometric air-fuel ratio.

An air-fuel ratio detector 10 is mounted in the exhaust pipe 5 in order to detect the composition of the exhaust gases, in particular the oxygen content, and to generate an electrical signal in accordance with the air-fuel ratio, which is closely related to the oxygen content. The detector 10 uses a detector element, the main component of which is a solid electrolyte that conducts oxygen ions such as zirconium earth (ZrO) or a semiconducting metal oxide such as titanium oxide (TiO ₂ ). For example, when zirconia is used, the detector 10 generates an electromotive force of 10000 mV to 800 mV when the air-fuel ratio is richer than the stoichiometric ratio, whereas an electromotive force of 200 to 0 mV is generated when the air-fuel ratio is leaner than the stoichiometric ratio.

A speed detector 11 generates electrical signals corresponding to the speed of the crankshaft of the engine 1 and has, for example, an ignition interrupter, the electrical signals with a corresponding to the engine speed Frequency generated. In this case, there is a time lag between the timing of a change in the air-fuel ratio of the mixture in the intake system of the engine 1 and the time when this change is detected by the air-fuel ratio detector in the exhaust system of the engine 1; this delay time depends in an inversely proportional relationship on the speed of the machine 1; the speed detector represents a deceleration detector.

809830/0598

-8- B 8546

The output signals of the air-fuel ratio detector 10 and the speed detector 11 receives an electronic control unit 12 as input signals, whereby the input and off duty cycle of the electromagnetic valve 9 is feedback controlled so that the deviation from the predetermined Air-fuel ratio is corrected. the Electronic control unit 12 is connected to a DC voltage source 14 by an ignition key switch 13 of the machine 1 connected, which can for example be an Eatterie.

Next, the electronic control unit 12

described in more detail with reference to FIG. The electronic control unit 12 has a comparison circuit 12a, a first integrating circuit 12b, a converting circuit 12c, a second integrating circuit 12d, a pulse width modulator circuit 12e and a constant voltage circuit 12f on

The comparison circuit 12a receives the output of the air-fuel ratio detector 10 and discriminates whether the detector output is lower or higher than a predetermined value. The comparison circuit has an input resistor 101, voltage dividing resistors 102 and 103 for generating a predetermined air-fuel ratio corresponding voltage and a comparator 104. As shown at (X) in Figures 3Λ and 3B, takes the output of a terminal A becomes "1" when the air-fuel ratio is richer (smaller) than the predetermined one Ratio is, and the level "0" when the air-fuel ratio is leaner (greater) than the predetermined ratio.

The first integration circuit 12b receives the output signal of the comparison circuit 12a in order to generate an integration signal with a predetermined time constant in accordance with this output signal of the comparison circuit 12a. This integrating circuit has an inverter 105, resistors

809830/0598

-9- B 8546

and 107 for setting the time constant of the integration signal, a capacitor 112, analog switches 108 and 109 for making and breaking connection of the resistors 106 and 109, respectively. 107, an arithmetic amplifier 113 and voltage divider resistors 110 and 111 for setting the mean operating point of the Integration signal. In the exemplary embodiment, the resistance values are set so that the resistance 106 is the same resistor 107 and resistor 110 is equal to resistor 111. When the output of the comparison circuit 12a

IQ assumes the level "1", the analog switch 108 is turned on and the analog switch 109 is turned off, so that the arithmetic logic amplifier 113 operates with the predetermined time constant from the resistor 106 and the capacitor 112 and the output signal at the terminal B gradually decreases, as by the broken lines B ₁ and B ₂ at (Y) in Figs. 3A and 3B. On the other hand, when the output of the comparison circuit 12a changes from "1" level to "0" level, the analog switch 109 is turned on and the analog switch 108 is turned off, and the output signal at the terminal B increases gradually, as indicated by the kinked lines B. and B. at (Y) shown in Figures 3A and 3B.

The conversion circuit 12c receives pulse signals from the speed detector 11 and generates pulse signals having one of the applied pulse signals corresponding frequency. The conversion circuit comprises a pulse shaping circuit composed of resistors 114, 115 and 119, capacitors 116 and 117, and a Transistor 118 and a frequency divider 120 with a binary counter. The electrical signals from the speed detector 11 are formed into square-wave signals by the pulse shaping circuit, which in turn are formed by the frequency divider 120 divided to the desired frequency and adjusted so that they have a duty cycle of 120 by the frequency divider about 50% received.

809830/0598

-10- B 8546

The second integrating circuit 12d is similar to the first integrating circuit 12b and receives the output signal of the converting circuit 12c and generates an integration signal having a predetermined time constant in accordance with the received signal. The second integrating circuit has an inverter 121, resistors 122 and 123 for setting the time constant of the integration signal, a capacitor 128, analog switches 124 and 125 for making and breaking the connection of resistors 122 and 123, an arithmetic amplifier 129 and voltage divider resistors 126 and 127 for setting the mean working point of the integration signal. In this exemplary embodiment, the resistance values are specified in such a way that the resistance is equal to the resistor 123 and the resistor 126 is equal to the resistor 127. When the output of the conversion circuit 12c becomes "1" level, the analog switch 124 is turned on and the analog switch 125 is turned off, which causes the arithmetic amplifier 129 to operate with the predetermined time constant of the resistor 122 and the capacitor 128, and the output signal am Terminal C gradually decreases as shown by broken lines C ₁ and C ₂ at (Y) in Figures 3A and 3B. In contrast, when the output of the conversion circuit 12c changes from the "1" level to the "0" level, the analog switch 125 is turned on and the analog switch 124 is turned off, causing the operational amplifier 129 to be disconnected from the resistor 123 with the predetermined time constant and capacitor 128 operates, and the output at terminal C _{gradually increases as shown by broken lines C 1} and C ₂ at (Y) in Figs. 3A and 3B. As a result, a sawtooth wave or triangular wave is generated at the terminal C, the frequency and amplitude of which are changed according to the engine speed, which is one of the deceleration factors of the engine 1.

The pulse width modulator circuit 12e subjects the output signals of the first and second integrating circuits 12b and 12d of a pulse modulation and controls the on and off duty cycle with the resulting modulated signals

809 83 0/0598

of the electromagnetic valve 9. The circuit 12e has Input resistors 130 and 131, a comparator 132, diodes 133, 134 and 136, a resistor 135 and a transistor on. The comparator 132 receives the output of the first

Integrating circuit 12b at its inverting input terminal

circuit and the output of the second integrating circuit 12d at its non-inverting input terminal and generates at its output D those shown at (Z) in FIGS. 3A and 3B Pulse signals. When the output signal at the output terminal D of the comparator 132 goes to "1" level, the transistor becomes 137 turned on and the electromagnetic valve 9 opened, whereas when the output signal goes to the "0" level, the transistor 137 turned off and the electromagnetic

Valve 9 is closed. 15th

The constant voltage circuit 1'2 £ has a constant voltage regulator 138 and capacitors 139 and 140, whereby the voltage from the DC voltage source 14 is regulated to a predetermined value and applied to the individual circuits.

With the arrangement described above, if the air-fuel ratio detector 10 determines from the oxygen content of the exhaust gases that the air-fuel ratio is richer (smaller) is than the predetermined air-fuel ratio (the stoichiometric ratio), the output of the comparison circuit goes 12a to the level "1" and the first integrating circuit 12b supplies an electrical signal at its output which integrates and decreases with the predetermined time constant. If in In contrast, the detector 10 determines that the air-fuel ratio is leaner (greater) than the predetermined air-fuel ratio, the output of the comparison circuit goes 12a to level "0" and the first integrating circuit 12b generates a voltage at its output that is integrated and increases with the same time constant. The output signal of the first integrating circuit 12b thus has the form of a

809830/0598

-12- B 8546

Triangular wave, which has a similar period, shown at (Y) in Figs. 3Λ and 3B by waveforms B ₁ and B-, as the period of the output signal of the comparison circuit 12a, which is indicated by waveforms Λ. and A- at (X) in Figs.

3A and 3B.

On the other hand, the converting circuit 12c generates pulse signals having a frequency corresponding to the speed of the engine 1 and the duty ratio of 50%, and the second Iq integrating circuit 12d integrates the pulse signals to generate a triangular wave having a relatively short period as indicated by the waveforms C. and C- shown at (Y) in Figures 3A and 3E.

The output signals of the first and second integrating circuits 12b and 12d are applied to the pulse width modulator circuit 12e and modulated by the comparator 132, whereby the pulse width (duty cycle) and the pulse width correction speed are controlled and thereby pulse signals are generated at the terminal D as they are are shown by waveforms D ₁ and D_ at (Z) in Figures 3A and 3B. While the air-fuel ratio detector 10 generates a richer air-fuel ratio indicative signal so that the comparison circuit 12a generates a "1" signal, the pulse width (duty cycle) of the pulse _{signals shown by waveforms D 1} and D_ gradually increases, see above that the opening duration of the electromagnetic valve controlling the additional air increases with the passage of time, and the air-fuel ratio is controlled so that it becomes leaner by the increasing additional air.

In contrast, while the air-fuel ratio detector 10 generates a signal indicative of the lean air-fuel ratio, so that the comparison circuit 12a generates a signal "0", the pulse width (duty cycle) of the

809830/0598

-13- B 8546

2753A52

Pulse signals shown by the waveforms Dj and D ₂ , gradually decreased, so that the opening duration of the electromagnetic valve 9 decreases with the passage of time and the air-fuel ratio is controlled so that it is richer or decreased by means of the reduced additional amount of air .

Waveforms A ₁ , B, C ₁ and D in Fig. 3A correspond to high speed operation of engine 1, and waveforms A-, B ₂ , C- and D- in Fig. 3B correspond to low speed operation of machine 1, which can be seen from a comparison between waveforms D ₁ and D ₂ . When the engine speed is high and the system delay time is short, the pulse width (duty cycle) is quickly regulated, thereby increasing the control speed for controlling the air-fuel ratio. if in contrast, the engine speed is low and the system delay time is long, the pulse width (duty cycle) is changed at a low speed, thereby the control speed for controlling the air-fuel ratio decreases. Ratio is always kept within a predetermined range, regardless of the size of the system delay time, and consequently, the harmful components in the exhaust gases emitted from the engine 1 become through the catalytic Triple converter 6 eliminated with high efficiency.

In addition, the occurrence of a load fluctuation may result an increase in the control fluctuation range can be prevented, thereby ensuring stable operation of the engine 1.

While in the embodiment described above, the air-fuel ratio is controlled by the additional air supplied to the portion downstream of the throttle valve 7 is supplied, it is possible to design the embodiment so that the amount of air supplied to an air port 15 of the carburetor 2 through the electromagnetic valve 9 as in 4 or that of a fuel path 16

809830/0598

- ■ 14- B 8546

The amount of fuel supplied to the carburetor 2 is controlled by the electromagnetic valve 9 as shown in FIG. In the arrangement shown in Fig. 5 is to be noted that the electromagnetic valve 9 must be opened in a reverse manner to that shown in Figures 1 and 4 arrangement and closed.

In addition to feedback control in the intake system, the invention can be effectively used in applications XO will be there where additional air is added to the exhaust system a time delay is caused if the air-fuel ratio detector is mounted in a place that is away from the place where the secondary air is supplied.

While in the embodiment described above, the engine speed as a deceleration factor and a speed detector is used as a delay detector, similar effects can be achieved by a detector for detecting the intake manifold vacuum, the throttle opening, the amount of intake air, the exhaust gas flow rate or the like obtained.

While also the waveforms of the ignition signals through the conversion circuit can be changed and the frequency divider generates frequency-divided signals and sends them to the second integrating circuit it is only necessary to specify that the degree of modulation of the amplitude and the frequency of the triangular wave correspond to the delay time characteristic of the machine, and it is possible, by replacing the frequency divider with a smoothing circuit, a V-f converter circuit or the like feed required signals to the second integrating circuit to achieve greater accuracy.

In summary, in the present invention, a detection signal from an engine speed detector and a detection signal from an air-fuel ratio detector located in the Exhaust pipe of a machine is arranged, fed to an electromagnetic valve control unit. According to the supplied

809830/0598

The electromagnetic valve control unit generates detection signals an output signal supplied to an electromagnetic valve. The additional amount of air created by bridging of the machine carburetor flows through the opening and closing the electromagnetic valve is controlled to thereby control fluctuation of the air-fuel ratio to avoid, which is caused by the delay time, which varies according to the operating conditions of the Machine changes.

809830/0598

e e r e i t e

Claims (4)

TlEDTKE "Bühling - KlNNH - group Dipl.-Chem. G. Bühling Dipl.-Ing. R. Kinne Dipl.-Ing. P. Grupe 2 1 O 3 H 5 2, Bavariaring 4, P.O. Box 20 24 8000 Munich 2 Tel .: (0 89) 53 96 53 Telex: 5-24845 tipat cable: Germania patent, Munich November 30, 1977 B 8546 case A2564-O2 Soken Claims tj ^, a control system for an engine in which an oxygen sensor detects the oxygen concentration in the exhaust gases generated by the engine and the output signal of the oxygen sensor is integrated to control the oxygen concentration in the exhaust gases which is in a downstream of the Engine-arranged catalytic converter flow, characterized by a conversion device (12c) for converting at least one of the variables such as engine speed, intake negative pressure, throttle opening, intake air quantity and exhaust gas flow rate as a time delay parameter into a pulse signal, an integration device (12d) for integrating the pulse signal of the conversion device and a pulse Modulation device (12e) for comparing the integration signal of the integration device with a second integration signal which is formed by integrating the output signal of the oxygen sensor (10), the pulse modulation device being a pulse lssignal generated, whose frequency increases with increasing delay parameter and its pulse width corresponding to ^m second de integration signal modulated v / ill, whereby the oxygen concentration in the exhaust gases with a velocity corresponding to said delay parameter controlled v / ill. 809830/0598 VII / 8 Dr ** dnar Bank (Munich) Account 3Θ38Μ4 Postal check (MCnChWi) Account 670-43-804 ORIGINAL INSPECTED - ² 2753A52 2. The air-fuel ratio control system according to claim 1, characterized in that a speed detection device an ignition detector (11) for detecting the ignition of the engine (1) and a "frequency divider (120) connected to the ignition detector for dividing the frequency of the output signal thereof to thereby generate the pulse signal which the Integration device (12d) is supplied. 3. Air-fuel ratio control system according to claim 2, characterized by an electromagnetic valve (9) arranged in the fuel flow path of the carburetor (2) of the engine for controlling the amount of fuel flowing therethrough in proportion to the pulse width of the pulse signal of the pulse modulation device.
15th 4. Air-fuel ratio control system according to Claim 2, characterized by an air supply path (8) connected to the carburetor (2) of the machine as a bridge, the supplies additional air downstream at the throttle valve (7) of the carburetor, and an electromagnetic one arranged in the air supply path Valve (9) for controlling the additional amount of air proportional to the pulse width of the pulse signal of the pulse modulation device .