JPS638293B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an air-fuel ratio feedback control device for an internal combustion engine, and more particularly to a digital computer that calculates the amount of fuel supplied to the internal combustion engine, and a digital computer that is attached to the exhaust pipe of the engine to detect the oxygen concentration in the exhaust gas. an exhaust sensor, and compares the output signal of the exhaust sensor with a comparison reference potential,
The present invention relates to an air-fuel ratio feedback control device that feedback-controls the air-fuel ratio to a desired value by correcting the calculation result of the digital computer based on the exhaust sensor output signal when it is determined that the exhaust sensor output signal level is in a feedback-controllable state.

There are various proposals for air-fuel ratio feedback control devices of the type described above. However, the exhaust sensor that detects the oxygen concentration of exhaust gas, that is, the O ₂ sensor, has the characteristic that the internal resistance increases significantly and the electromotive force decreases when the temperature becomes low. It becomes impossible to distinguish between “lean” air-fuel mixtures.

For this reason, conventional devices use the following two methods. First, the feedback control region is limited to when the O ₂ sensor temperature is above a predetermined value. The sensor signal input circuit has a basic configuration that detects the voltage of the sensor signal and compares it with a comparison reference potential. Sensor temperature is often not measured directly, but estimated based on cooling water temperature, etc. Second, by flowing a predetermined current into the O ₂ sensor from the outside, changes in the internal resistance of the sensor are monitored, and feedback control is started when the internal resistance falls below a predetermined value.

The disadvantage of the first method described above is that although the input circuit configuration is relatively simple, the predetermined O ₂ sensor temperature must be set to a relatively high temperature, and the feedback control area becomes narrow. Furthermore, there is no unambiguous relationship between the O ₂ sensor temperature and the cooling water temperature, which often causes malfunctions. The disadvantage of the second method is that the feedback control area becomes wider, but the feedback control is not possible by comparing the circuit that supplies current to the exhaust sensor and the output signal level of the exhaust sensor with a comparison reference potential divided by a resistor. A circuit or the like is required to determine whether or not this is the case, and the circuit becomes extremely complicated. In this case, a first comparison reference potential and a second comparison reference potential are set to determine whether the feedback control is possible, and when the exhaust sensor is at a low temperature and has a large internal resistance, the exhaust sensor output signal level is set to the above-mentioned 1 and the second comparison reference potential, but when the internal resistance of the exhaust sensor becomes equal to or less than a predetermined value, the exhaust sensor output signal level becomes the first and second comparison reference potentials.
A method is preferably used in which it is determined that feedback control is possible by deviating from a comparison reference potential of . This is because feedback control can be started quickly regardless of whether the air-fuel mixture is rich or lean. However, if feedback control is started from a rich state, the exhaust sensor Because of the slow response, it takes a relatively long time for the exhaust sensor to detect that the mixture has become "lean" after starting feedback control, and as a result, the engine continues to operate with a lean mixture temporarily. There was also the possibility that the engine speed would drop and the engine would stop.

In recent years, many systems use digital computers to control engines, but air-fuel ratio feedback control devices have a wide controllable range and a simple circuit configuration.
Digital calculation processing method of _O2 sensor output signal is not used.

An object of the present invention is to provide a feedback control device according to the second method described above, in which the signal processing of the O ₂ sensor is performed as a microprocessor program, so that the circuit configuration is simple, the feedback control area is wide, and the air-fuel mixture " Air-fuel ratio feedback control can be started immediately in either the rich or lean state, and appropriate control can be performed without causing a transient drop in engine speed when starting feedback control from the rich state. An object of the present invention is to provide an air-fuel ratio feedback control device.

FIG. 5 is a block diagram showing the functionality of the present invention. In FIG. 5, an exhaust sensor 100 outputs a signal corresponding to the oxygen concentration in the exhaust gas of the internal combustion engine. The current injecting circuit 101 is a circuit that divides a predetermined voltage using a resistor and injects a current from the divided potential point to the connection point with the exhaust sensor through the resistor. It is something like this. In addition, the input circuit 102 amplifies the exhaust sensor output signal from the connection point and outputs the A/D signal.
Convert it to a microprocessor (the part surrounded by the dashed line)
This is what you input. Further, the functions of the microprocessor include the following means. That is, the first comparison reference potential setting means 103 sets a first comparison reference potential (the higher value serving as the reference for the rich state of the air-fuel ratio), and the second comparison reference potential setting means 104 sets the first comparison reference potential (the higher value serving as a reference for the rich air-fuel ratio). A second comparison reference potential (a lower value serving as a reference for the lean state of the air-fuel ratio) is set lower than the comparison reference potential of . In addition, determination means 1
05, the exhaust sensor output signal level is the first,
When the exhaust sensor output signal level deviates from between the second comparison reference level, it is determined that the feedback control is possible, and the air-fuel ratio feedback control means starts the feedback control, and the exhaust sensor output signal level is between the first and second comparison reference levels. The feedback control is stopped by determining that the feedback control exists for a predetermined period of time. Further, the comparison reference potential changing means 106
When the exhaust sensor output signal level exceeds the first comparison reference potential and feedback control is started, the second
The comparison reference potential is shifted to another set value that is higher than the initial set value, and then the set value is lowered at a predetermined rate to change toward the initial set value or another set value. Note that the air-fuel ratio feedback control means feedback-controls the air-fuel ratio to a desired value by correcting the calculation result in the digital computer according to the exhaust sensor output signal, as in the prior art.

As described above, in the present invention, by setting the comparison reference potential, comparing, calculating, etc. using a microprocessor program, the complicated comparison/judgment circuit required in an analog control system or wire logic system can be eliminated. It is unnecessary, the circuit configuration is simple, and at the start of feedback control from the "rich" state, the other comparison reference potential is shifted from the initial setting value to another setting value, and then the above setting value is lowered at a predetermined rate. It is also possible to easily change the value to the initial set value or another set value using a software method, and this allows appropriate control to be performed without causing a drop in engine speed even when starting feedback control from a "rich" state. It can be carried out.

Embodiments and drawings illustrating the present invention will be described.

FIG. 1 shows a block diagram of an internal combustion engine control system using a digital computer suitable for applying the air-fuel ratio feedback control system according to the present invention. Sensor group 1 that detects various states of the vehicle and internal combustion engine, for example, is attached to the exhaust pipe to detect the oxygen concentration in the exhaust gas
Outputs from the O ₂ sensor 11, the crank angle sensor 12 which works with the crank to detect the rotational speed and rotational phase of the engine, and the water temperature sensor 13 which detects the cylinder cooling water temperature are sent via the interface 2. and input it to the arithmetic processing unit (CPU) 4. The interface 2 takes input signals from the sensor group 1, performs A/D conversion, holds data, and the like.
CPU4 takes in this input signal at the required time,
The required calculations are performed to create actuation signal data, and the data is sent to the required actuators of the actuator group 3, such as the fuel injection valve 31, via the interface 2.
The ignition device 32 and exhaust recirculation valve 33 are activated.

The output of the O ₂ sensor that detects the oxygen concentration in the exhaust becomes a signal of "rich" or "lean" mixture compared to the reference value, and the CPU corrects the calculated fuel injection amount based on the intake air amount according to this signal. to maintain the air-fuel ratio at the desired value. This control is called air-fuel ratio feedback control.

FIG. 2 shows an O ₂ sensor signal processing circuit according to the present invention. An internal resistance 111 and an internal superpower 112 are shown as an equivalent circuit of the O ₂ sensor 11. The circuit 5 for supplying current to the O ₂ sensor 11 is connected to the O ₂ sensor 11 and has a configuration in which a predetermined voltage +B is divided into resistors. The output signal of the O ₂ sensor 11 is amplified by a signal amplifier 6. The output of the signal amplifier 6 is supplied to the interface 21, where it is A/D converted and sent to the CPU 4.
Signals are exchanged between the In the current injecting circuit 5, a predetermined voltage +B is divided by resistors 51 and 52, and a current is injected into the O ₂ sensor 11 via the resistor 53. The CPU 4 timely takes in the A/D converted O ₂ sensor output signal and processes the signal and performs calculations for feedback control under the control of a software program according to the present invention.

The operation of the circuit shown in FIG. 2 will be explained. After the engine starts until the exhaust pipe is heated, the O ₂ sensor temperature is low, the internal resistance value is high, and the response is slow. Therefore, feedback control cannot be performed during this period. The terminal potential V _S at this time is the divided voltage potential of the current injecting circuit 5.
The value is almost equal to V _O. Figure 3 shows the change in the value ρ of the internal resistance 111 of the O ₂ sensor 11.
It shows the change in the value of V _S. Part A of FIG. 3 shows the O ₂ sensor low temperature state. The value of ρ is larger on the left side as shown by the arrow.

The temperature of the _O2 sensor 11 rises, and the internal resistance value ρ
If the voltage V S decreases, the internal electromotive force 112 will affect the voltage V _S . If the engine's mixture ratio is richer than the stoichiometric air-fuel ratio, it will generate an internal electromotive force of approximately 0.8V, and if it is lean, it will output a value of approximately 0.1V. Therefore, the terminal potential V _S changes as shown in part B as the internal resistance of the O ₂ sensor decreases. By setting the reference potentials V _REF1 and V _REF2 in the software program, it becomes possible to monitor the internal resistance value of the O ₂ sensor by comparing the reference potential and the terminal potential V _S . That is, when V _S becomes larger than V _REF1 , it is determined that feedback control is possible, and a feedback control start signal is generated. Similarly, in the case of a "lean" mixture, it is determined that feedback control is possible when V _S becomes lower than V _REF2 .

If the temperature of the O ₂ sensor is sufficiently high, feedback control is continued, and the value of the terminal potential V _S is monitored using one of the reference potentials V _REF1 and V _REF2 as a reference signal for air-fuel ratio comparison. It is possible to set another reference potential V _REF3 as the reference signal.

If the engine is left idling, etc.
The temperature of the O ₂ sensor gradually decreases, the internal resistance ρ increases, and the characteristics of the terminal potential V _S change from part B to part A.
Move to. Therefore, the terminal potential V _S is the reference potential V _REF1 ,
Feedback control can be stopped by determining that a predetermined period of time exists between V _REF2 . Comparison of terminal potential and reference potential is performed by a software program.
Performed by CPU4. The above comparison function performed by CPU4,
Discrimination of the starting point of feedback control and discrimination of "rich" and "lean" mixtures can be made very easily, and complex circuits required in analog control systems can be omitted.

The value of the lower limit reference potential V _REF2 is usually a constant value.
As shown in FIG. 4, when feedback control is started in a "rich" state, V _S >V _REF1 , and an operation is performed to control the air-fuel ratio to a "lean" mixture side. As a result of this control, the O ₂ sensor detects a "lean" air-fuel mixture, and the terminal potential V _S outputs a "lean" signal at point C in FIG. It takes a relatively long time from the start of feedback control until the O ₂ sensor issues a "lean" signal, and the engine temporarily continues to operate with a lean mixture, resulting in a drop in engine speed or a stoppage.

In order to prevent this, in the embodiment shown in FIG. 4, the lower limit reference potential V _REF2 is moved to a higher potential V _REF2 ' when starting feedback control with a "rich" mixture.
Thereafter, it is lowered to the original value at a predetermined rate. As a result, the terminal potential V _S reaches the apparent lower limit value at point D earlier than at point C, and a "lean" signal is generated here, which shortens the engine's running time and prevents a drop in rotation. .

Note that when determining the lower limit value of the terminal voltage V _S at point D in FIG. 4, the reference potential is given hysteresis, as is normally done, in order to stabilize the determination output.

As clarified above, according to the present invention, desired air-fuel ratio feedback control can be easily and accurately performed using an extremely simple circuit and a processing program that can be easily created.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an internal combustion engine control device to which the air-fuel ratio feedback control device of the present invention is applied, Fig. 2 is an O ₂ sensor signal processing circuit diagram of the present invention, and Fig. 3 is the sensor output terminal potential of Fig. 2. Figure 4 showing changes in
The figure shows an example of increasing the reference potential at the start of feedback control using a "dark" signal, and FIG. 5 is a block diagram showing the functions of the present invention. 1...Sensor group, 2, 21...Interface,
3... actuator group, 4... central processing unit (CPU), 5... current injecting circuit, 6... amplifier,
11...O ₂ sensor, 111...internal resistance, 112...
Electromotive force.

Claims (1)

[Claims] 1 It has a digital computer that calculates the amount of fuel supplied to the internal combustion engine, and an exhaust sensor that is attached to the exhaust pipe of the engine and detects the oxygen concentration in the exhaust gas, and compares the output signal of the exhaust sensor with a comparison reference potential. , an air-fuel ratio feedback control device that feedback-controls the air-fuel ratio to a desired value by correcting the calculation result of the digital computer based on the exhaust sensor output signal when it is determined that the output signal level of the exhaust sensor is in a feedback control possible state; , a current inflow circuit that divides a predetermined voltage by a resistor and flows a current from the divided potential point to a connection point with the exhaust sensor via the resistor; and A, which amplifies the exhaust sensor output signal from the connection point. a first comparison reference potential setting means for setting a first comparison reference potential as a function of the microprocessor; a second comparison reference potential setting means for setting a second comparison reference potential lower than the potential, and determining that feedback control is possible when the exhaust sensor output signal level deviates from between the first and second comparison reference potentials. to start feedback control,
determining means for determining that the exhaust sensor output signal level exists between the first and second comparison reference levels for a predetermined period of time and stopping the feedback control; When feedback control is started by exceeding the initial setting value, the second comparison reference potential is shifted to another set value that is higher than the initial set value, and then the set value is lowered at a predetermined rate to change to the initial set value or another set value. 1. An air-fuel ratio feedback control device for an internal combustion engine, comprising: comparison reference potential changing means for changing the potential toward a set value.