JPS61187569A - Intake secondary air feeder of internal-combustion engine - Google Patents

Abstract

PURPOSE:To control the air-fuel ratio at high precision by increasing or decreasing the open period of a switching valve controlling the air-fuel ratio of the air-fuel mixture by predetermined values respectively depending on whether the air-fuel ratio is rich or lean against the target air-fuel ratio. CONSTITUTION:A solenoid switching valve 9 is provided on an intake air secondary air feed passage 8 communicating an intake air manifold 4 on the downstream side of the throttle valve 6 of a carburetor 3 and the vicinity of the air exhaust port of an air cleaner 2, and the solenoid 9a of the said valve 9 is duty-controlled by a control circuit 20 based on the output of an O2 sensor 14. In this case, whether the air-fuel ratio of the air-fuel mixture is lean or rich against the target air-fuel ratio is judged based on the output of the O2 sensor 14 at every predetermined time. If it is judged to be lean, the open period of the switching valve 9 in one duty cycle is decreased by the first predetermined value, and on the other hand, if it is judged to be rich, the said open period is increased by the second predetermined value.

Description

TECHNICAL FIELD The present invention relates to an intake secondary air supply system for an internal combustion engine.

Background technology In order to purify the exhaust gas of internal combustion engines and improve fuel efficiency, the oxygen concentration in the exhaust gas is detected by an oxygen concentration sensor, and the air-fuel ratio of the mixture supplied to the engine is fed back according to the output level of this oxygen concentration sensor. Air-fuel ratio control devices are known. As this air-fuel ratio control device, an on-off valve is provided in the intake secondary air supply passage communicating with the downstream side of the carburetor throttle valve, and the opening/closing of the on-off valve, that is, the intake secondary air supply is duty controlled according to the output level of the oxygen concentration sensor. There is an intake secondary air supply device for feedback control (
For example, Special Publication No. 55-3533).

In such conventional intake secondary air supply devices, it is determined from the output level of the oxygen concentration sensor whether the air-fuel ratio of the supplied air-fuel mixture is lean or rich with respect to the target air-fuel ratio, and the determination result is lean or rich. When , the opening period of the on-off valve in one duty cycle is reduced by a predetermined value, and when the determination result is rich, the opening period of the on-off valve in one duty cycle is increased by a predetermined value. There is.

However, in general, the response speed of the oxygen concentration sensor when the air-fuel ratio of the supplied air-fuel mixture changes from ridge to lean is slower than the response speed when the air-fuel ratio of the supplied air-fuel mixture changes from lean to rich. Therefore, even if the air-fuel ratio determination result is lean or rich as described above, there is a problem in that the air-fuel ratio cannot be accurately controlled to the target air-fuel ratio by changing the valve opening period by the same value.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an intake secondary air supply device for an internal combustion engine that can accurately control the air-fuel ratio to a target air-fuel ratio even if the response speed of an oxygen concentration sensor varies depending on the direction of change in the air-fuel ratio. be.

The intake secondary air supply device of the present invention determines whether the air-fuel ratio of the supplied air-fuel mixture is lean or rich with respect to the target air-fuel ratio from the output level of the oxygen concentration sensor at predetermined time intervals, and determines whether the air-fuel ratio of the supplied air-fuel mixture is lean or rich with respect to the target air-fuel ratio. In this case, the opening period of the on-off valve within one duty period is decreased by a first predetermined value, and when the determination result is rich, the opening period of the on-off valve within one duty period is ゛.

is increased by a second predetermined value different from the first predetermined value.

M f! I.J. Embodiments of the present invention will be described below with reference to the drawings.

In the intake secondary air supply system for an on-vehicle internal combustion engine, which is an embodiment of the present invention shown in FIG. supplied to vaporizer 3
A throttle valve 6 is provided, and a venturi 7 is formed upstream of the throttle valve 6.

The intake manifold 4 and the vicinity of the air discharge port of the air cleaner 2 are communicated through an intake secondary air supply passage 8.

An electromagnetic on-off valve 9 is provided in the intake secondary air supply passage 8 . The electromagnetic on-off valve 9 is opened by energizing the solenoid 9a.

On the other hand, 10 is an absolute pressure sensor installed in the intake manifold 4 and generates an output at a level corresponding to the absolute pressure inside the intake manifold 4, and 11 generates a pulse in accordance with the rotation of the crankshaft (not shown) of the engine 5. A crank angle sensor 12 generates an output at a level corresponding to the cooling water temperature of the engine 5. A cooling water gt sensor 14 is installed in the exhaust manifold 15 of the engine 5 and generates an output proportional to the oxygen concentration in the exhaust gas. It is an oxygen concentration sensor. As shown in FIG. 2, the oxygen concentration sensor 14 has a characteristic that the output level increases proportionally as the air-fuel ratio of the air-fuel mixture supplied to the engine 5 becomes leaner than the stoichiometric air-fuel ratio (14,7>. A catalytic converter 33 is provided in the exhaust manifold 15 downstream of the concentration sensor 14 in order to promote reduction of harmful components in the exhaust gas.

Electromagnetic on-off valve 9, absolute pressure sensor 10, crank angle sensor 1
1. The water temperature sensor 12 and the oxygen concentration sensor 14 are connected to a control circuit 20. Further connected to the control circuit 20 is a vehicle speed sensor 16 that generates an output at a level corresponding to the speed of the vehicle.

As shown in FIG. 3, the control circuit 20 includes an absolute pressure sensor 10,
Water temperature sensor 12, oxygen concentration sensor 14, and vehicle speed sensor 1
6, a multiplexer 22 that selectively outputs one of the sensor outputs that have passed through the level conversion circuit 21;
A/2 converts the signal output from 2 into a digital signal.
A waveform shaping circuit 24 that shapes the waveform of the output signal of the D converter 23 and the crank angle sensor 11, a counter 25 that measures the generation interval of the TDC signal output as a pulse from the waveform shaping circuit 24, and an electromagnetic switch. A drive circuit 28 that drives the valve 9 to open, a CPU (central processing circuit) 29 that performs digital calculations according to a program, a ROM 30 that is pre-loaded with various processing programs and data, and an RA.
It consists of M31. Multiplexer 22, A/D
Converter 23, counter 25, drive circuit 28, CP, U
29, ROM 30 and RAM 31 are connected to each other by an input/output bus 32.

In this configuration, the A/D converter 23 selectively provides information on the absolute pressure in the intake manifold 4, the cooling water temperature, the oxygen concentration in the exhaust gas, and the vehicle speed, and the counter 25 provides information representing the engine speed. Input/output bus 3 to CPU29
2, respectively. The CPU 29 is configured to generate an internal interrupt signal every duty cycle TsOL (for example, 100 m5ec), and in response to this interrupt signal, performs an operation for duty-controlling the intake secondary air supply as described later. Let's do it.

Next, the operation of the intake secondary air supply device according to the present invention will be explained according to the operation flowchart of the CPLI 29 shown in FIGS. 4 and 5.

In the CPU 29, first, a valve opening drive stop command is issued to the drive circuit 28 to close the electromagnetic on-off valve 9 every time an interrupt signal is generated (step 51). This is a CPU
This is to prevent malfunction of the electromagnetic on-off valve 9 during the calculation operation of step 29. Next, the closing period TAF of the electromagnetic on-off valve 9 is made equal to one duty cycle TsOL (step 52).
Then, the A/F routine shown in FIG. 5 is executed to calculate the opening period TOLJT of the electromagnetic on-off valve 9 (step 53).

In the A/F routine, first, check the driving condition of the vehicle! ? ! (including engine operating status) is air-fuel ratio feedback (F/B)
) It is determined whether the control conditions are satisfied (step 531). This determination is made based on the absolute pressure in the intake manifold, cooling water temperature, heavy speed, and engine speed. For example, it is determined that the air-fuel ratio feedback control conditions are not satisfied at low vehicle speeds and low cold W water temperatures. Here, if it is determined that the air-fuel ratio feedback control ms is not satisfied, the valve opening period T is set to stop the air-fuel ratio feedback control.
o u r is set to "0" (step 532). On the other hand, if it is determined that the air-fuel ratio feedback control conditions are satisfied, the reference duty ratio (period>DBAsF for the secondary air supply for one duty period TSQL, that is, the opening of the electromagnetic on-off valve 9) is set ( Step 533
). As shown in FIG. 6, the reference duty ratio D8A SE SDe A s E data map determined from the intake manifold internal absolute pressure PEA and the engine speed Ne is pre-written in the ROM 30, so the CPU 2
9 reads the absolute pressure PEA and engine speed Ne,
M9 duty ratio D8ASE corresponding to each read value
Search from the DaASE data map. next,
It is determined whether the count time of the internal timer counter A (not shown) of the CPU 29 has elapsed by a predetermined time Δ1+ (step 534).

The predetermined time Δ[1 is the oxygen concentration sensor 1 whose result is a change in the oxygen concentration in the exhaust gas after the intake secondary air is supplied.
4 corresponds to the response delay time until detection.

When a predetermined time Δt1 has elapsed since the time counter A was reset and started counting, the time counter A is reset and counting starts from the initial value (step 535). That is, even though the time counter A starts counting from the initial value by executing step 535, it is determined in step 5 whether or not the predetermined time Δ[1 has elapsed.
This was done in 34.

When the time counter A starts counting the predetermined time Δt1, a target air-fuel ratio leaner than the stoichiometric air-fuel ratio is set (step 536). To set this target air-fuel ratio, the ROM 30 contains a reference level l ref corresponding to the target air-fuel ratio determined from the intake manifold absolute pressure PBA and engine speed Ne, as well as the D8ASE data map, as an A/F data map and a DBASE data map. is written separately in advance. Therefore, C
The PU 29 searches the A/F data map for a reference level lrcf corresponding to the absolute pressure P8A and the engine speed Ne. Next, from the oxygen concentration information, oxygen 11a IJI
It is determined whether the output level 102 of the sensor 14 is greater than the reference level 1 - - rer determined in step 536 (step 537).

In other words, it is determined whether the air-fuel ratio of the air-fuel mixture supplied to the engine 5 is leaner than the target air-fuel ratio. L
If oz>1rer, the air-fuel ratio is leaner than the target air-fuel ratio, so a subtraction value IL is calculated (step 538).
. The subtraction value IL is determined by multiplying a constant by 1, the engine speed Nc, and the absolute pressure PBA by i (Kl·Ne-PeA), and is made to depend on the intake air m of the engine 5. After calculating the subtraction value IL, this A/F
Correction value I already calculated by executing the routine
o uT is read from storage location a1 of RAM 31,
b) The read correction value ■OU is subtracted from the subtraction value ILA as the first predetermined value, and the calculated value becomes the new correction value fo.
uT and written to storage location a1 of the RAM 31 (step 539). On the other hand, if LO2≦l ref in step 537, the air-fuel ratio is richer than the target air-fuel ratio, so the additional value IR is calculated (step 53
10). The additional value IR is calculated by multiplying the constant by 2 (<Kl), the engine speed Ne, and the absolute pressure PEA (K2
・KO・PBA), engine 5
depends on the amount of intake air. Added value IR
After the calculation of , the correction value four that has already been calculated by executing the A/F routine is read from the storage location a1 of the RAM 31, and the added value IR is added to the read correction value l0UT.
is added as a second predetermined value, and the calculated value is set as a new correction value 10LJT and written to the storage location @a+ of the RAM 31 (step 5311). In this way, the correction value is 10L.
When JT is calculated in step 539 or 5311, the correction value Tout and the reference duty ratio DBASε set in step 533 are added, and the addition result is set as OUT under the valve opening time (step 531
2).

Note that if it is determined in step 534 that the predetermined time Δ[blindness has not elapsed after the time counter A is reset in step 535 and starts counting from the initial value, step 5312 is immediately executed; In this case, the correction value IourIfi obtained by the previous execution of the Δ/F routine is read out.

When the execution of the A/F routine is completed, the valve closing time TAF is determined by subtracting the valve opening time TOU from one duty cycle TSOL (step 54). Next, ffj corresponding to the valve closing time T'AF is set in the internal time counter B (not shown) of the CPU 29, and down counting of the time counter B is started (step 55).
). Then, it is determined whether the count value of time counter B has reached "O" (step 56), and time counter B
When the count value reaches °O'', a valve opening drive command is issued to the drive circuit 28 (step 57).

In response to this valve opening driving command, the driving circuit 28 operates the electromagnetic opening/closing valve 9.
The valve is driven to open, and the valve driving state continues until step 51 is executed next. If the count value of time counter B does not reach 0'' in step 56, step 56 is repeatedly executed.

Therefore, in the intake secondary air supply device according to the present invention, the electromagnetic on-off valve 9 is immediately closed in response to the generation of the interrupt signal INT, as shown in FIG. Supply is stopped. In addition, the closing time TAF of the electric on-off valve 9 in one duty period Ts OL is calculated, and when the closing time TAF has elapsed from the time when the interrupt signal was generated, the electromagnetic on-off valve 9 is opened and the intake 2 is supplied to the engine 5.
Secondary air is supplied via the intake secondary air supply passage 8.

Because this operation is repeated, the intake secondary air supply is duty-controlled. By controlling the intake secondary air in this manner, the air-fuel ratio of the air-fuel mixture supplied to the engine 5 is controlled to the target air-fuel ratio.

In the intake secondary air supply device according to the present invention,
Since the air-fuel ratio is controlled by setting the target air-fuel ratio leaner than the stoichiometric air-fuel ratio using the oxygen concentration sensor 14 having the characteristics shown in FIG. 2, it is possible to improve fuel efficiency without deteriorating drivability. .

In addition, in the intake secondary air supply device according to the present invention, the subtraction value IL and the addition value IR are set according to the intake air amount, and because they become large when the intake air amount is high, the intake secondary air supply at the high intake air amount is It is possible to compensate for the time delay between supply and detection of oxygen concentration in exhaust gas.

In the embodiment of the present invention described above, a case is shown in which the response speed of the oxygen concentration sensor 14 is faster when changing in the rich direction than when changing in the lean direction. The present invention can also be applied when the response speed is faster when changing to the lean direction.

1 ri 1] υ As mentioned above, in the intake secondary air supply device for an internal combustion engine of the present invention, when the air-fuel ratio of the supplied air-fuel mixture is determined to be leaner than the target air-fuel ratio from the output level of the oxygen concentration sensor, The opening period of the on-off valve in the duty period is decreased by a first predetermined value, and when it is determined that the valve is rich, the valve opening period is increased by a second predetermined value different from the first predetermined value.

Therefore, even if the response speed of the oxygen concentration sensor is different when the air-fuel ratio of the supplied air-fuel mixture changes in the lean direction and in the rich direction, the intake air 2 per predetermined time will change depending on whether the air-fuel ratio is controlled in the rich or lean direction. Since the amount of change in the secondary air is made different, it is possible to compensate for the difference in time delay from the secondary supply of intake air to the detection of the oxygen concentration in the exhaust gas due to the difference in the response speed of the oxygen concentration sensor depending on the direction of change in the air-fuel ratio. Therefore, the air-fuel ratio of the supplied air-fuel mixture can be controlled to the target air-fuel ratio with high accuracy.

In addition, in the intake secondary air supply system using a lean oxygen concentration sensor, an output that follows changes in the air-fuel ratio of the supplied mixture is obtained from the oxygen concentration sensor, so the output is not proportional to the oxygen concentration. The difference in the response speed of the oxygen concentration sensor in the rich direction and the lean direction tends to have a negative effect on the air-fuel ratio control accuracy, but the device of the present invention avoids such a negative effect. This allows for more accurate air-fuel ratio control.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing the output characteristics of the oxygen concentration sensor in the device shown in FIG. 1, and FIG. 3 is a specific diagram of the control circuit in the device shown in FIG. 4 and 5 are flowcharts showing the operation of the CPU, FIG. 6 is a diagram showing a data map written in the ROM, and FIG. 7 is a diagram showing the operation timing of the device in FIG. 1. FIG. Explanation of symbols of main parts 2... Air cleaner 3... Carburetor 4... Intake manifold 6... Throttle valve 7... Venturi 8 ...Intake secondary air supply passage 9 ...Solenoid on-off valve 10 ...Absolute pressure sensor

Claims (4)

[Claims] (1) An intake secondary air supply passage communicating with the downstream side of the carburetor throttle valve of the internal combustion engine, an on-off valve provided in the intake secondary air supply passage, and an oxygen concentration sensor provided in the exhaust gas passage of the engine. , control means for duty-controlling the opening and closing of the opening/closing valve based on the output level of the oxygen concentration sensor, and the control means determines whether the air-fuel ratio of the supplied air-fuel mixture is the target air-fuel ratio based on the output level of the oxygen concentration sensor at predetermined time intervals. Determine whether the fuel ratio is lean or rich, and if the determination result is lean, reduce the opening period of the on-off valve within one duty cycle by a first predetermined value, and if the determination result is rich, the above-mentioned 1. An intake secondary air supply device characterized in that the opening period of the on-off valve within a duty cycle is increased by a second predetermined value different from the first predetermined value. (2) The intake secondary air supply device according to claim 1, wherein the second predetermined value is set smaller than the first predetermined value. (3) The oxygen concentration sensor generates an output proportional to the oxygen concentration in the exhaust gas when the air-fuel ratio of the supplied air-fuel mixture is at least leaner than the stoichiometric air-fuel ratio. intake secondary air supply device. (4) The intake secondary air supply device according to claim 3, wherein the first and second predetermined values are set according to the amount of intake air.