JP2557517B2 - Air-fuel ratio control device for vaporizer - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control device for a carburetor mainly applied to an automobile.

[Prior Art] A three-way catalyst, which is widely used as one of exhaust gas purification means, contains CO contained in exhaust gas unless the air-fuel ratio of the air-fuel mixture is maintained near the stoichiometric air-fuel ratio. It cannot purify all of HC and NO _x efficiently. Therefore, in an engine equipped with a carburetor, a flow control valve that opens and closes an air bleed passage, an oxygen sensor that detects the oxygen concentration in exhaust gas, and the flow control valve based on the output voltage of this oxygen sensor are installed. It is usual to provide an air-fuel ratio control device having feedback control means for opening and closing. The air-fuel ratio is maintained near the stoichiometric air-fuel ratio by adjusting the opening of the flow control valve based on the output voltage of the oxygen sensor and increasing or decreasing the amount of air supplied through the air bleed passage. I have to.

However, when the engine shifts to the high speed region and the amount of exhaust gas becomes large, unburned gas and residual oxygen increase accordingly, and the three-way catalyst overheats. for that reason,
Utilizing the property that the temperature of the exhaust gas decreases as the air-fuel ratio shifts to the rich side, if the temperature of the exhaust gas exceeds a certain value at high engine load and high engine speed, the flow control valve should be turned on. There is one that is fixedly held to temporarily stop the feedback control of the air-fuel ratio and adjusts the air-fuel ratio to the rich side to prevent overheating of the catalyst (for example,
JP-A-61-283742).

Further, as the prior art of the present invention, for example, Japanese Patent Application No. 63-12
As shown in No. 2862, when the engine exceeds the set value set in the high rotation range, the fixed holding position of the flow control valve is moved to the low opening side every predetermined engine rotation exceeding this set value. The air-fuel ratio is adjusted to the rich side according to the amount of exhaust gas by changing it stepwise. Therefore, in this device, the control position of the flow control valve is learned in the region immediately before the engine shifts to the predetermined high rotation region, and the fixed holding position of the flow control valve at the time of high rotation is determined based on it. ing.

[Problems to be Solved by the Invention] However, in a case where the air-fuel ratio is indirectly adjusted to the rich side by the temperature of the exhaust gas, there is a high possibility that the air-fuel ratio is adjusted to the overrich side. May generate unburned gas.

Further, in the system in which the control position of the flow control valve is learned and the fixed holding position of the flow control valve in the high rotation range is determined based on the learned value, the learning range also limits input / output signals. Therefore, it is determined by the engine rotation regardless of the load condition of the engine. Therefore, based on the value learned at high engine load,
When the flow control valve is held fixed in the light load / high rotation range, the air-fuel ratio may shift to the lean side contrary to the original purpose due to variations in the basic air-fuel ratio of the carburetor.

The present invention aims to solve such a problem.

[Means for Solving the Problems] In order to achieve the above-mentioned object, the present invention adjusts the air-fuel ratio of an air-fuel mixture supplied to an engine by an air-fuel ratio control device of a carburetor, as shown in FIG. In order to adjust the air-fuel ratio to a constant value, a flow control valve (8) that opens and closes the air bleed passage (7) of the carburetor (1), an oxygen sensor (15) that detects the oxygen concentration in the exhaust gas, Feedback control means (20) for opening and closing the flow control valve (8) based on the output voltage of the oxygen sensor (15), and the feedback control means (20) when the engine speed exceeds a predetermined value.
The flow control valve (8) is fixedly held and the fixed holding position is set to the oxygen sensor (15).
And a valve holding means (21) for gradually changing the output voltage to a low opening side until the output voltage is switched to the air-fuel ratio rich voltage.

[Operation] According to such a configuration, when the engine speed is lower than the predetermined value, the feedback control means (20) controls the engine based on the output voltage of the oxygen sensor (15). The air-fuel ratio of the supplied air-fuel mixture is maintained near the stoichiometric air-fuel ratio.

On the other hand, when the engine speed exceeds the predetermined value, the control by the feedback control means (20) is temporarily stopped and the flow rate control valve (8) by the valve holding means (21).
Is fixedly held on the low opening side, and the amount of air supplied through the air bleed passage (7) is reduced. Despite such an operation, when the output voltage of the oxygen sensor (15) indicates the lean state of the air-fuel ratio, the fixed holding position of the flow control valve (8) is moved toward the lower opening side. be changed.
Then, the above-described scanning is repeated until the output voltage of the oxygen sensor (15) is switched to the air-fuel ratio rich voltage, and when the air-fuel ratio becomes rich, the flow control valve (8) is fixedly held at that position.

Embodiment An embodiment of the present invention will be described below with reference to FIGS.

In the drawing, reference numeral 1 denotes a carburetor mounted on an intake manifold of an engine, 2 denotes a mixing chamber, 3 denotes a main jet, 4 denotes a throttle valve, 5 denotes a float chamber, and 6 denotes an air bleed.
A flow control valve ABCV8 is provided in the air bleed passage 7, which is a starting end of the air bleed 6, and the flow control valve A
The inlet 8a of the BCV 8 is open to the atmosphere. Flow control valve ABCV
Numeral 8 advances and retracts the pointed valve body 9 with respect to the valve seat 10 to change the opening area of the air passage formed between the valve body 9 and the valve seat 10, thereby changing the flow rate of air. The valve body 9 is replaced with the tip of the operating rod 12 of the stepper motor 11. Then, the stepper motor 11 is controlled by an electronic control unit 13 described later to move the valve body 9 from the fully closed position (0 step) to the fully opened position (100 step).
Among the steps), during feedback control of the air-fuel ratio,
It is set to move forward and backward before and after the control position corresponding to the vicinity of the theoretical air-fuel ratio.

On the other hand, an oxygen sensor 15 is arranged upstream of the three-way catalytic converter 14 provided in the exhaust system. This oxygen sensor 15
Generates a low voltage when the air-fuel ratio of the air-fuel mixture is leaner than the conversion point existing near the stoichiometric air-fuel ratio and the oxygen concentration in the exhaust gas is high. When the oxygen concentration in the exhaust gas is lower than the rich side, the high-voltage air-fuel ratio rich voltage can be generated.

The electronic control unit 13 comprises a microcomputer unit having a central processing unit 16, a memory 17, an input interface 18 and an output interface 19, and the feedback control means 20 and valve holding means.
It plays the role of 21. Then, the signal a from the oxygen sensor 15 is input to the input interface 18 at least.
And a signal b from the rotation speed sensor 22 for detecting the engine speed, a signal from an idle switch (not shown) for detecting whether or not the throttle valve 4 is in the open position, and so on. It has become. On the other hand, the output interface 19 outputs a feedback control signal c, a valve holding signal d, etc. toward the flow rate control valve ABCV8.

Then, in the electronic control unit 13, the region immediately before the engine shifts to a predetermined high rotation range (for example, 3000 to 3500RP
In M), in order to learn the control position of the flow control valve ABCV8, a program as schematically shown in FIG. 3 is set. First, in step 31, 1 is set to the address n as the initial value, which is the control position on the high opening side or the control position on the low opening side of the flow rate control valve ABCV8 at the start of the feedback control, and the process proceeds to step 32. In step 32, as shown in FIG. 4, the high opening side (or the low opening side) of the flow control valve ABCV8.
Flow control valve ABCV8 with the average value ( _Pn + _{Pn + 1} ) / 2 of the control position _{Pn of Pn} and the control position _{Pn + 1} of the low opening side (or high opening side)
Compare with the learning value of HLDNEX. Then, the average value (P _n
When it is determined that + P _{n + 1} ) / 2 is large, the process proceeds to step 33, and when it is determined that the learning value HLDNEX is large, the step is performed.
Proceed to 34. In step 33, it is judged whether the difference between the average value (P _n + P _{n + 1} ) / 2 and the learning value HLDNEX is 5 steps or more, and 5
If it is determined that the number of steps is greater than or equal to the step, the process proceeds to step 35.
Proceed to 37.

In step 34, the average value (P _n + P _{n + 1} ) / 2 and the learning value HLDN
It is determined whether or not the difference from EX is 5 steps or more. If it is determined that it is 5 steps or more, the process proceeds to step 36, and if it is determined that it is not 5 steps or more, the process proceeds to step 37. In step 35, a value obtained by adding 1 to the learning value HLDNEX is set in the address HLDNEX, and the process proceeds to step 37. Step 36
Then, the value obtained by subtracting 1 from the learning value HLDNEX is set in the address HLDNEX, and the process proceeds to step 37. At step 37, the value n indicating the number of times of control of the flow control valve ABCV8 is updated and step 32 is performed.
Return to.

In addition to the learning function as described above, the electronic control unit 13 also contains a program as schematically shown in FIG. First, in step 41, the engine speed NEHI
Is within a certain range (for example, 3000 to 3500 RPM), and if it is within the certain range, the process proceeds to step 42, and if it is not within the certain range, the process proceeds to step 44. At step 42, feedback control of the air-fuel ratio is performed by the feedback control means 20 and the routine proceeds to step 43. In step 43,
As described above, the control position of the flow rate control valve ABCV8 is learned and the process returns to step 41. In step 44, the engine speed NE
It is determined whether HI exceeds a predetermined value (for example, 3500 RPM), and if it is determined that it does not exceed step 45, step 45
And the feedback control of the air-fuel ratio is continued, and when it is determined that the air-fuel ratio is over, the routine proceeds to step 46.

In step 46, as schematically shown in FIG. 6, the feedback control of the air-fuel ratio is stopped, and the position HL obtained by subtracting a fixed value from the learning value HLDNEX immediately before the stop.
Flow control valve ABCV8 is moved to DNEX-S1 at normal feedback speed TI, and flow control valve is moved to that position HL DNEX-S1.
Hold ABCV8 fixed and proceed to step 47. In step 47, after changing the holding position of the flow control valve ABCV8, a certain time T
It is determined whether or not DHI1 has elapsed, and if it has elapsed, the process proceeds to step 48. In step 48, the signal a from the oxygen sensor 15 is read and the process proceeds to step 49. In step 49, it is judged whether or not the signal a indicates the lean state of the air-fuel ratio. If the air-fuel ratio is not lean, the routine proceeds to step 50, where it is indicated that the air-fuel ratio is lean. Go to step 51.

In step 50, the flow control valve ABCV8 is fixedly held at the position where the air-fuel ratio changes to rich, and the process returns to step 41. In step 51, after changing the fixed holding position of the flow control valve ABCV8, it is judged whether or not the lean state of the air-fuel ratio has continued for a certain period of time TDHI2-TDHI1, and if it has not continued, step 49
Return to step 52, and if it continues, proceed to step 52. In step 52, as schematically shown in FIG. 6 (see formulas below), the fixed holding position of the flow rate control valve ABCV8 is changed to the lower opening side by the set value from the previous fixed holding position. , Return to step 47.

HLDNEX-S1 HLDNEX-S1-SA HLDNEX-S1-SA × 2 HLDNEX S1-SA × m HLDNEX-S2-SA × m HLDNEX-S2-SA × (m + 1) (m is positive) In addition, when there is a shift to the low opening side as described above,
The fixed holding position of the flow control valve ABCV8 at a certain engine speed NEHIn is changed from the fixed holding position HLDNEX-Sn at that engine speed NEHIn to each engine speed NE before that.
It is set to a value obtained by subtracting the total number of steps transferred by the control to transfer to the low step side by HI (n is a positive number from 1 to 5). Also,
As shown in FIG. 7, the throttle amounts S1 to S5 of the flow control valve ABCV8 are set to increase as the engine speed NEHI shifts to the high speed region NEHI1 to NEHI5.

The above control is repeatedly performed after the engine is started.

According to such a configuration, the predetermined time has elapsed since the engine was started, the throttle valve 4 is in the open state,
When the engine speed NEHI is lower than the predetermined value, feedback control of the air-fuel ratio is performed based on the signal a from the oxygen sensor 15, that is, the oxygen sensor 15
When the output voltage of is on the lean side of the conversion point and the oxygen concentration in the exhaust gas is high, as shown in FIG. 4, the opening of the flow control valve ABCV8 is throttled by a certain value in a skip shape,
After that, it is rapidly decreased in small values at a constant speed TI. Therefore, the amount of air supplied through the air bleed passage 7 is rapidly reduced, and the air-fuel ratio is rapidly changed to near the stoichiometric air-fuel ratio.

When the signal a from the oxygen sensor 15 is on the rich side of the conversion point and the oxygen concentration in the exhaust gas is low, the opening degree of the flow control valve ABCV8 is increased in a skip manner by a constant value, and then It is rapidly increased by small values. Therefore, the amount of air supplied through the air bleed passage 7 is rapidly increased, and the air-fuel ratio is rapidly changed to near the stoichiometric air-fuel ratio. By repeatedly performing such control during the feedback control, the air-fuel ratio of the air-fuel mixture is maintained near the stoichiometric air-fuel ratio, and when the engine speed NEHI is in the predetermined region, the flow rate control in that region is controlled. The control position of valve ABCV8 is learned (steps 31-3).
7).

On the other hand, when the engine speed NEHI exceeds the predetermined value,
Since the feedback control of the air-fuel ratio is stopped, the flow control valve ABCV8 is fixedly held at the position on the air-fuel ratio rich side based on the learning value HLDNEX of the flow control valve ABCV8 immediately before the stop (step 41 → 44 → 46). ), The amount of air supplied through the air bleed passage 7 is throttled. Despite this operation, when the output voltage of the oxygen sensor 15 continues to show the lean state of the air-fuel ratio for a certain period of time TDHI2-TDHI1, the fixed holding position of the flow control valve ABCV8 is further lowered. Since the opening degree is changed, the amount of air supplied from the air bleed passage 7 is further reduced. The above-described scanning is repeated until the output voltage of the oxygen sensor 15 indicates the rich state of the air-fuel ratio, so that the amount of air supplied from the air bleed passage 7 is gradually reduced in the high engine speed region. At the same time (steps 47 to 52), the throttle amount also increases as it shifts to the high rotation range.

Therefore, according to the above configuration, when the feedback control is stopped in the high engine speed range,
When the output voltage of the oxygen sensor 15 indicates the lean state of the air-fuel ratio, the fixed holding position of the flow control valve ABCV8 gradually shifts to the low opening side until it indicates the rich state, and the air bleed passage 7 is passed through. The amount of supplied air is gradually reduced. Therefore, in the high engine speed range, the air-fuel ratio can be reliably changed to the rich state regardless of the load, so that the temperature rise of the exhaust gas can be suppressed and the overheating of the three-way catalyst can be effectively prevented.

Moreover, when the output voltage of the oxygen sensor 15 is switched to the signal indicating the rich state of the air-fuel ratio, the flow control valve AB
Since the CV8 is fixedly held, it is possible to reliably maintain the air-fuel ratio rich state in response to the air-fuel mixture amount in the high rotation range, and it is possible to prevent the air-fuel ratio from becoming excessively rich, which is effective. Air-fuel ratio control can be performed.

Then, as in this embodiment, the control position of the flow control valve ABCV8 is learned in the region immediately before the feedback control is stopped, and the flow control valve ABCV8 is fixedly held on the low opening side based on the learned value HLDNEX. With this setting, it is possible to prevent a sudden change in the air-fuel ratio during control switching.

Although one embodiment of the present invention has been described above, it goes without saying that the present invention is not limited to the above embodiment. For example, the fixed holding position of the flow control valve may be set more finely.

[Advantages of the Invention] As described in detail above, in the present invention, when the feedback control is stopped in the high engine speed region, the amount of air supplied through the air bleed passage while confirming the output voltage of the oxygen sensor. Is adjusted. Therefore, the air-fuel ratio in the high engine speed range can be reliably changed to the rich state regardless of the load, and the rich state at the time of the change can be maintained corresponding to the air-fuel mixture amount. It is possible to effectively suppress the overheating of the three-way catalyst due to the temperature rise, etc., and to perform the effective air-fuel ratio control without the air-fuel ratio becoming excessively rich.

[Brief description of drawings]

FIG. 1 is a configuration explanatory view for clarifying the present invention, FIGS. 2 to 8 show an embodiment of the present invention, FIG. 2 is a schematic overall configuration diagram, and FIG. 3 shows a control procedure. Flowchart diagram, FIG. 4 is a timing chart diagram showing the control mode of the flow control valve, FIG. 5 is a flowchart diagram showing the control procedure, FIG. 6 is a timing chart diagram schematically showing the control mode, and FIG.
FIG. 8 is a diagram showing an example of control setting conditions, and FIG. 8 is a timing chart diagram schematically showing a control mode. DESCRIPTION OF SYMBOLS 1 ... Vaporizer 7 ... Air bleed passage 8 ... Flow control valve 13 ... Electronic control device 14 ... Three-way catalytic converter 15 ... Oxygen sensor 20 ... Feedback control means 21 ... Valve holding means

Claims (1)

(57) [Claims] 1. A flow control valve for opening and closing an air bleed passage of a carburetor for adjusting the air-fuel ratio of an air-fuel mixture supplied to an engine, an oxygen sensor for detecting an oxygen concentration in exhaust gas, and a constant air-fuel ratio. Feedback control means for opening and closing the flow rate control valve based on the output voltage of the oxygen sensor to adjust the flow rate, and the flow rate control by releasing the control by the feedback control means when the engine speed exceeds a predetermined value. And a valve holding means for holding the valve fixedly and gradually changing the fixed holding position toward the low opening side until the output voltage of the oxygen sensor is switched to the air-fuel ratio rich voltage. Air-fuel ratio controller for carburetor.