JPS60101233A - Air-fuel ratio control device - Google Patents

Abstract

PURPOSE:To make sure the operation of an air-fuel ratio control device with a simple structure, by directly controlling the energization time intervals of a proportional solenoid valve with the use of a CPU while monitoring the current of a drive transistor upon energization. CONSTITUTION:Upon energization of a transistor 4, a voltage between both terminals of a resistor 5 is monitored by means of an AD converter circuit 6, and by changing the energization time ratio of control pulses from the CPU the averaged current of a proportional solenoid valve 3 is made coincide with a desired value. However, dispersion in the resistance of the resistor 5 and so forth, cause the averaged value to be difficult to precisely coincide with the desired value, and therefore, the time rate of rich and lean signals from an air-fuel ratio sensor 1 is monitored so that a compensation is made to the desired current value of the proportional solenoid valve 3. With this arrangement, the structure of the circuit may be simplified to reduce the number of component parts, and as well the characteristics of the control system are made stable and sure.

Description

[Detailed description of the invention] l” Minor work m The present invention relates to an air-fuel ratio control device for an internal combustion engine for an automobile.

Prior Art and Problem 1: The air-fuel ratio is the weight ratio of air to fuel in the air-fuel mixture taken into the engine. , and is also said to be 10 to 17 in consideration of safe driving. In particular, the air-fuel ratio is an important factor that influences the combustion state of fuel, and it has a great influence not only on the output and fuel efficiency of the engine, but also on the composition of exhaust gas. Therefore, it is necessary to control the air-fuel ratio to suit all operating conditions of a gasoline engine, that is, to maintain the desired air-fuel ratio characteristics, and various control methods have been proposed in the past. I am and it is being carried out. In one such prior art, for example, as in Japanese Patent Laid-Open No. 57-69/IQ5, the goal is to receive control commands from a central processing unit (CPU) that includes a microcomputer. 1
A conversion circuit is provided to convert to the τ flow. Here, the control command is, for example, a command value expressed as a pulse width 41, and the conversion circuit includes an oscillator, a current detection circuit, a deviation integration circuit, a comparison circuit, etc.
Since it consists of 1, the entire device requires a fairly large number of circuit elements or components,
However, if these circuit elements or components are 4r,
There is a possibility that variations in the characteristics will occur (1'l has increased), so the f'l of this control system will inevitably have a negative effect on the real III (1f). .

Accordingly, the present invention has been made with the aim of solving the above-mentioned problems in the prior art, and its purpose is to:
During the song! r To provide a new air-fuel ratio control method that can operate reliably and realize extremely good air-fuel ratio control characteristics while absorbing variations in system component parts, etc. be.

In order to achieve the above object, the present invention monitors the current when the driving transistor of the proportional solenoid valve is conductive, that is, the terminal voltage of the load resistor through an AD conversion circuit at a specific timing, and calculates the proportional The energization time width of the solenoid valve is directly controlled by the CPU to obtain a target average current, and the energization time width is further corrected based on the rich/lean time ratio from the air-fuel ratio sensor. do.

An embodiment of the air-fuel ratio control device for an internal combustion engine according to the present invention is not shown in FIG. In FIG. 1, numeral 1 is an air-fuel ratio sensor that is installed in the exhaust pipe of an automobile engine and detects the air-fuel ratio of the exhaust system, 2 is a comparison circuit that compares the signal of the air-fuel ratio sensor 1 with a predetermined voltage, and 3 is a comparison circuit that compares the signal of the air-fuel ratio sensor 1 with a predetermined voltage. Installed in the engine intake system,
A proportional solenoid valve serves as an acticoator for controlling the air-fuel ratio of the air-fuel mixture supplied to the engine, 4 is a transistor that drives the proportional solenoid valve 3, and 5 is a resistor connected to the emitter of the transistor 4. 6 is an analog/digital (hereinafter referred to as 10) converter which receives at least the voltage across the register 5 as an input signal, and 7 is a central processing unit (CI) mainly comprising a microphone and a cork. The memory and Ilo are built-in. 8
is the engine.

The present invention will be described in detail below based on the embodiment shown in No. 11.1. The proportional solenoid valve 3 is of the 0N-OFF controlled type, and of the type in which the average current is controlled by the ON time ratio. Here, the ON time ratio is ON time/9 (
(ON time + OFF time).

In this way, in a proportional solenoid valve, its ON - OFF F
The flrlIm period is generally 200 to 600 Hz. Now, the pulse that drives the proportional voltage VTL valve 3, that is, the control pulse for ON-OFF of the transistor 4, is directly C
PU7,j is outputted and given to transistor 4,
An average current corresponding to the ON II; Y #l state flows through the proportional solenoid valve 3. However, this alone may not be sufficient in terms of reliability or stability of operation, as the average current may not match the target current due to variations in the applied voltage to the proportional solenoid valve 3 or the DC resistance of the proportional solenoid valve 3. do not have. In order to prevent or cover the occurrence of such an undesirable situation, the following measures are adopted. However, in this embodiment, a resistor 5 is connected to the emitter of the transistor 4, and the voltage across the resistor 5 is monitored via the AD conversion circuit 6 as the current when the transistor 4 is turned on. By changing the ON time ratio of the 0N-OFF control pulse, the average current of the proportional solenoid valve 3 is made to match the target current. Note that the average current here is different from the effective value and means the integrated average value of the current within one cycle, and the target current is the current to be targeted. -1 The outline of the two-wheel operation is shown in the flowchart in Figure 3. That is, in FIG. 3, step 4
At step 01, the difference ΔI between the target current and the current actually flowing through the proportional solenoid valve 3, that is, the monitor current is calculated, and at step 402, the difference is compared with predetermined values 11r1 and 1. When the absolute value of the current difference ΔI is smaller than the predetermined value, the ON time ratio is left as it is and the process proceeds to the next step. When the absolute value of Δ■ is larger than a predetermined value, it is determined that the ON time ratio needs to be corrected, and the process proceeds to step 403. In step 403, the magnitude relationship between the target current and the monitor current is determined, and if the monitor current is too high, step 404
Proceed to decrease the ON time. Conversely, when the monitor current is small, the process advances to step 405 and the ON time is increased. Thus, after steps 404 and 405, the procedure continues to the next step. It has been experimentally confirmed that the average current of the proportional solenoid valve 3 almost matches the current value at a specific timing when the drive transistor 4 is turned on. The pattern is shown in Figure 4.η-0 In Figure 4, the king is the proportional electromagnetic Jf'3
The drive cycle is fixed. Now, for example, if the power supply voltage is relatively high, the ON time of the drive transistor 4 is 9, i+ <
When the predetermined average current ia is (q), both resistors 5*2
;The electric current waveform is 11, and the ON time of 1-transistor 4 is T, and the time TI has elapsed, and it is ON1.
) It is assumed that the instantaneous current 11 of the proportional solenoid valve 3 coincides with the average iR flow 1a at the timing. On the other hand, when the power supply voltage is low, the ON time of the 1-heran resistor 4 is approximately 100%. Let us assume that an average current of 1a is obtained, assuming that N2 is used. At this time, the instantaneous current 12 matches the average current 1a at the timing when time T2 has elapsed.

In the above relationship, experimentally T + /T ON 1
It has been confirmed that and T2/King are almost equal, and ON
By monitoring the instantaneous current after the elapse of time N2 multiplied by a certain number, it is possible to estimate the average current ia. By the above-described operation, the average current 1a of the proportional solenoid valve 3 is brought to approximately match the target current. However, with the current monitoring method described above, it is impossible to accurately match the average current of the proportional electric valve 3 to the target current, and the actual current may always be larger or smaller than the target. .

For example, this is caused by variations in the resistance value of the resistor 5.

Therefore, as a solution to this problem, in this invention, we have developed an air fuel
The rich/lean time ratio of the signal is monitored, and the target current of the proportional solenoid valve 3 is corrected based on the rich/lean time ratio. The contents will be explained below. FIG. 2 shows an example of the relationship between the rich/lean time ratio and the target current correction coefficient, and assumes that the optimal control state is when the rich/lean time ratio is 50%. If the time ratio becomes greater than 50%, i.e., if the engine exhaust gas deviates to the rich side, it is necessary to correct the control 211 output to the proportional solenoid valve 3 to the lean side, as shown in Figure 2. In the example, the proportional solenoid valve 3 becomes lean when a large amount of current flows. For example, if you want to supply more air to the engine, the target current should be increased to 4 tons.
La 4r. That is, the correction coefficient shown in FIG. 2 needs to take a value of 1 or more. a5, the lip/lean time ratio for determining the correction coefficient is monitored when the air-fuel ratio return jψ control according to the present invention is executed (the conditions are in this explanation (j is not concerned), and the steady state excluding acceleration/deceleration etc. It won't work if you don't do it while the engine is running.

FIG. 15 is a J-diagram showing a second embodiment of the present invention, in which the current when the proportional solenoid valve 3 is OFF is detected by a resistor 10, The signal is input to the AD conversion circuit 6 via the amplifier circuit.

FIG. 6 shows the voltage across the resistor 10 in FIG.
4 is the timing of the current of the proportional solenoid valve 3 at F time A7-1~, and ■ is the proportional voltage vt as in Figure 4.
This is the drive cycle of ↑3, and 'OFF' is the OFF time of the drive transistor 4. Due to the inductance of the proportional solenoid valve 3, when the transistor 4 is OFF, the current of the proportional solenoid valve 3 flows through a closed circuit consisting of a resistor 10 and a diode 11, and a voltage is generated across the resistor 10, and the voltage waveform is l=, that is, the current waveform becomes i3. In this embodiment, OF F 11. of the proportional solenoid valve 3. The current is the average current i 13 hours before the transistor 4 ON time shown in Figure 6.
a, and the ratio of T3 and ■ oyo is T3/ToF
F is T. It has been experimentally confirmed that it is independent of □ and remains almost constant. Therefore, it is possible to estimate the average current ia by monitoring the current of the proportional solenoid valve 3 at a timing that is equal to the OFF time multiplied by a certain number and before the 0Nvi clock of the transistor. The following operation is the same as in the embodiment shown in FIG.

Effects of the Invention As is clear from the above explanation, according to the present invention, the circuit configuration of the entire system is much simpler than that of the prior art, and the number of circuit elements and components can be reduced. Regardless, the characteristics of the control system, including the air-fuel ratio sensor, are extremely stable and reliable, and the system 4j If
Even if there is some unavoidable variation in characteristics of the component parts, it is possible to absorb the effects of this, perform reliable control operations, and effectively perform the intended air-fuel ratio control function. , a remarkable effect is brought about.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the overall configuration of an embodiment of the air-fuel ratio control device for an internal combustion engine according to the present invention, and FIGS. 1
The origin of the invention in connection with the illustrated embodiments is J! l! 1. Figure 2 is a graph showing the correspondence between the rich/lean time ratio and the energization time correction coefficient, and Figure 3 is a flowchart outlining the control operation in this embodiment. FIG. 4 is a timing chart 1 showing the temporal relationship between the ON-OFF period of the driving transistor 1 and the current of the proportional solenoid valve. Also, the fifth
The figure is a block diagram showing the overall configuration of another embodiment of the present invention, and FIG. 6 is a timing chart showing the temporal relationship between the ON-OFF period of the driving transistor and the current of the proportional solenoid valve in this embodiment. It is. In the diagram: 1... Air-fuel ratio sensor 1, 2... Comparison circuit, 3...
Proportional solenoid valve, 4... Drive transistor, 6... Analog/digital converter, 7... CPU, 8
...Each engine is shown. Agent Asari Koga 1 picture 4 picture

Claims (1)

[Claims] An air-fuel ratio sensor installed in the exhaust pipe of an automobile engine to detect the air-fuel ratio of exhaust gas; a comparison circuit that compares the signal from the air-fuel ratio sensor 1 with a predetermined reference voltage; installed in the intake system of the engine; A proportional solenoid valve that is ON-OFF controlled as an acticoator to control the air-fuel ratio of the air-fuel mixture supplied to the controller, a driving transistor that performs ON-OFF control of the proportional solenoid valve +, and a φ that detects the current of the proportional solenoid valve. a current detection means, an AD conversion circuit that inputs the analog signal of the current detection means and converts it into a digital value, and an 0N-O of the driving transistor connected to the AD conversion circuit;
J3 is in an air-fuel ratio control device consisting of a CPU that outputs an FF control signal; the instantaneous current at a specific timing when the proportional solenoid valve is ON or OFF matches the target average current J: J: The above drive An air-fuel ratio control device for an internal combustion engine, characterized in that the air-fuel ratio control device for an internal combustion engine is configured to control an ON time of a transistor for use in the air-fuel ratio, and to correct a target average current according to a rich/lean time ratio of the air-fuel sensor signal.