JPS61200364A - Intake secondary air supply device of internal-combustion engine - Google Patents

Abstract

PURPOSE:To promote the stable combustion condition of an engine, by providing an opening and closing valve in an intake secondary air supply passage while a control means closing the opening and closing valve when the engine is in low loaded operation. CONSTITUTION:An intake manifold 4 communicates with a part in the vicinity of the air delivery port of an air cleaner 2 through an intake secondary air supply passage 8. Said passage 8 provides a solenoid opening and closing valve 9. An absolute pressure sensor 10 generates an output of the level corresponding to the absolute pressure in the intake manifold 4. A control circuit 20 stops the supply of intake secondary air by closing the opening and closing valve 9 when an engine is in low loaded operation. In this way, the stable combustion condition of the engine can be promoted by preventing air-fuel ratio from becoming overlean.

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 an air-fuel ratio control device, an on-off valve is provided in the intake secondary air supply passage that communicates downstream of the carburetor throttle valve, and the on-off valve opens and closes according to the output level of the oxygen concentration sensor, that is, the amount of intake secondary air is determined. There is a feedback control intake secondary air supply device that performs T-control (for example, Japanese Patent Publication No. 55-3533).

In such conventional intake secondary air supply devices, an oxygen concentration sensor that is not proportional to the oxygen concentration in the exhaust gas is used. However, recently, a lean oxygen concentration sensor has been developed that generates an output proportional to the oxygen concentration in exhaust gas when the air-fuel ratio of the mixture supplied to the engine is leaner than the stoichiometric air-fuel ratio. There is also already known an air-fuel ratio control method in which the air-fuel ratio is precisely controlled to a target air-fuel ratio in the lean region (for example, Japanese Patent Laid-Open No. 58-59330).

When such a lean oxygen concentration sensor is applied to an intake secondary air supply device, the air-fuel ratio tends to become over-lean when the engine is under low load by controlling the target air-fuel ratio in the lean region. That is, when the load is low, such as during deceleration, the throttle valve is fully closed, and the amount of intake air-fuel mixture decreases rapidly. At the same time, the negative pressure inside the intake manifold increases, so a large amount of intake secondary air flows into the engine, resulting in an over-lean condition. If the air-fuel ratio becomes over-lean in this way, the combustion state of the engine becomes unstable, so it is desirable to take measures against over-lean during low loads.

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 using a lean oxygen concentration sensor that can prevent overleaning at low loads and stabilize the combustion state. be.

The intake secondary air supply device for an internal combustion engine according to the present invention is characterized in that when the load is low, the on-off valve is closed and the supply of intake secondary air is stopped regardless of the output level of the oxygen concentration sensor.

Example 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 9α.

On the other hand, 10 is an absolute pressure sensor that is installed in the intake manifold 4 and generates an output at a level corresponding to the absolute pressure inside the intake manifold 4. 1 is an absolute pressure sensor that generates a pulse according to the rotation of the crankshaft (not shown) of the engine 5. The crank angle sensor 12 is a coolant temperature sensor that generates an output at a level corresponding to the coolant temperature of the engine 5. Further, reference numeral 13 is an intake air temperature sensor that is installed near the air intake port 1 and generates an output at a level corresponding to the intake air temperature, and 14 is an air intake air temperature sensor that is installed on the exhaust manifold 15 of the engine 5 and that is connected to a fuel ratio that is theoretically proportional to the oxygen concentration in the exhaust gas. It has a characteristic that the output level increases proportionally as the air-fuel ratio becomes leaner than (1-4, 7).

A catalytic converter 33 is provided in the exhaust manifold 15 downstream of the oxygen concentration sensor 14 in order to promote reduction of harmful components in the exhaust gas. Electromagnetic on-off valve 9, absolute pressure sensor lO, crank angle sensor 11, water temperature sensor 12, intake temperature sensor 13, and oxygen concentration sensor 14
is connected to the control circuit 20.

The control circuit 20 further includes a vehicle speed sensor 16 that generates an output at a level corresponding to the speed of the vehicle, and a clutch switch 17 that is turned on when the vehicle clutch is released and outputs a predetermined voltage.
A 2-1-1 tral switch 18 that is turned on and outputs a predetermined voltage when the gear shift lever of the 5-speed manual transmission is in the 2-toral position, and an atmospheric pressure sensor 19 that generates an output at a level corresponding to atmospheric pressure. is connected.

As shown in FIG. 3, the control circuit 20 includes an absolute pressure sensor 10,
Water temperature sensor 12, intake temperature sensor 13, oxygen concentration sensor 1
4. Level conversion circuit 21 that converts each output level of vehicle speed sensor 16 and atmospheric pressure sensor 19, and level conversion circuit 2
1, an A/D converter 23 that converts the signal output from the multiplexer 22 into a digital signal, and an A/D converter 23 that converts the output signal of the crank angle sensor 11 into a waveform. A waveform shaping circuit 24 for shaping, and a counter 25 for measuring the generation interval of the TDC signal output as a pulse from the waveform shaping circuit 24.
, clutch switch 17 and neutral switch 1
a level conversion circuit 26 that converts each output level of 8; a digital human power module and rotor 27 that uses each switch output via the level conversion circuit 26 as digital data; and a drive circuit 28 that drives the electromagnetic on-off valve 9 to open. , a CPU (central processing circuit) 29 that performs digital calculations according to programs, a ROM 30 in which various processing programs and data are written in advance, and a RAM 31.

Multiplexer 22, A, /D converter 23, counter 2
5. Digital human power module, rater 27, drive circuit 28
, CPU 29, ROM 30, and RAM 3] are connected to each other by an input/output port 32.

In such a configuration, the information of the absolute pressure PBA% in the intake manifold 4, the cooling water temperature Tw, the intake temperature TA1, the oxygen concentration in the exhaust gas, the vehicle speed, and the atmospheric pressure PA are alternatively transmitted from the A/D converter 23 to the counter 25. Information representing the engine speed N is obtained from the clutch switch 17 and neutral switch 18 from the Dinotarian camosulator 27.
On/off information is supplied to the CPU 29 via the input/output bus 32. CPU U29 has 1 data cycle T8
An internal interrupt signal is generated every oL (for example, ]-(JOm, sec), and in response to this interrupt signal, the intake secondary air supply is controlled as described later. Perform the action for the purpose.

Next, the operation of the intake secondary air supply device according to the present invention will be explained according to the operation flowchart of C P TJ'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 to prevent malfunction of the electromagnetic on-off valve 9 during the calculation operation of the CPU 29. Next, the closing period TAF of the electromagnetic on-off valve 9 is made equal to one data period Tsot (
Step 52), and the opening period T of the electromagnetic on-off valve 9. U
In order to calculate T, the A/F routine shown in FIG. 5 is executed (step 53).

In the "A/F" routine, first, the operating state of the vehicle (including the operating state of the engine) is determined by the air-fuel ratio feedback CF/B.
) It is determined whether or not the control conditions are satisfied (Stenoa '531). If it is determined that the air-fuel ratio feedback control conditions are not satisfied, the valve opening period T. UT is II
It is designated as O71 (Stella f532).

On the other hand, if it is determined that the air-fuel ratio feed puncture control conditions are satisfied, the secondary air supply for l date period TsoL, that is, the reference date ratio C period for opening of the electromagnetic on-off valve 9) DBAsE is set. (Stenoa °53
3). As shown in Fig. 6, the standard data ratio DBASE, which is determined from the intake manifold internal pressure PBA and the engine speed Ne, is pre-written in the ROM 30 as DBASP, a data map, so the CPU 2Q is able to read the absolute pressure. Read PBA and engine speed Ng, and DB the standard data ratio DFIA8° corresponding to each read.
Search from the ASg data map. Next, it is determined whether the count time of the internal timer counter (not shown) A of the CPU 29 has elapsed by a predetermined time Δt1 (step 5
34). The predetermined time Δt1 corresponds to a response delay time from when the intake secondary air is supplied until the result is detected by the oxygen concentration sensor 14 as a change in the oxygen concentration in the exhaust gas. 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). In other words, after the time counter A starts counting from the initial value by executing step 535, it is determined in step 534 whether or not a predetermined time Δt1 has elapsed.

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).

A DB is stored in the ROM 30 to set this target air-fuel ratio.

. Similar to the data map, the absolute pressure in the intake manifold PBA
The reference level Lref corresponding to the target air-fuel ratio determined from
BASB data map (pre-written separately. Therefore, the CPU 29 sets the reference level Lref according to !, EEP, & Enson rotation speed NeL to A, /
Search from F data map. Next, the output level L of the oxygen concentration sensor 14 is determined from the oxygen concentration information. 2 is larger than the reference level Lref determined in step 536 (step 7' 537). That is, 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. Lo2〉
If Lr and f, the air-fuel ratio is leaner than the target air-fuel ratio, so the subtraction value ■ is calculated (Step 7'538). Subtraction value ■1 is 1 for the constant, engine speed N, and absolute pressure P
It is obtained by multiplying BA by each other (K1, N, PBA), and depends on the intake air amount of the engine 5. After calculating the subtraction value ■1, the correction value I which has already been calculated by executing the A/l'i'' routine with is read out from the memory location α1 of the RAM 31, and the read correction value ■. The subtraction value ■1 is subtracted from UT, and the calculated value becomes the new correction value ■.It is set as UT and written to storage location a1 of the RAM 31 (step 539).On the other hand, in step 0537, if 2≦Lref,
Since the air-fuel ratio is richer than the target air-fuel ratio, an additional value ■□ is calculated (step 5310). The additional value IR is a constant of 2 (NK, ), the engine speed N, and the absolute pressure PBA.
are obtained by multiplying each other (K2.Ne-PBA), and are made to depend on the intake air amount of the engine 5. After calculating the additional value ■□, the correction value ■ has already been calculated by executing the A/F routine. UT is read out from the memory location α1 of RAM3], and the read correction value ■.

An additional value ■ is added to UT, and the calculated value is set as a new correction value ■oUT and written to storage location a of the R, AM 31 (step 5311). In this way, the correction value 1
When °UT is calculated in step 539 or 5311, its correction value ■. UT and the reference date ratio DBAsF set in the STETSUNO 533 are added, and the addition result is the valve opening time T. UT (Step 5)
312).

Note that if it is determined in step 534 that the predetermined time Δt1 has not elapsed after the time counter A is reset in the Stella f535 and counting starts from the initial value, step 5312 is immediately executed; , correction value■. In the UT, the value obtained by the previous execution of the A/F routine is read from the storage location α1 of the RAM 31.

When the execution of the A/F routine is completed, the valve opening time T starts from the data period T8oL. The valve closing time TAP is obtained by subtracting UT (Stella f54).

Next, a value corresponding to the valve closing time TAF is set in the internal time counter (not shown) B of the CPU 29, and down counting of the time counter B is started (step f55
). Then, it is determined whether the count value of time counter B has reached to On (step 56), and if the count value of time counter B has reached II OII, a valve opening drive command is issued to the drive circuit 28. generated (step 57
). In response to this valve opening driving command, the driving circuit 28 drives the electromagnetic on-off valve 9 to open, and this valve opening driving state is then changed to step 5.
This continues until 1 is executed. If the count value of time counter B does not reach "0" in step 56,
Step 56 is executed repeatedly.

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 cut off. In addition, the closing time TAF of the electromagnetic on-off valve 9 in one duty period T8oL 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 sent to the ennon 5. Secondary air is supplied via the intake secondary air supply passage 8.

Because this operation is repeated, the intake secondary air is subjected to data control. 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. Also intake 2
The responsiveness to the next air supply command and the accuracy of air-fuel ratio control can be improved. Further, by determining the reference duty ratio DBA8° according to the operating state of the engine, it is possible to compensate for control delays based on changes in the operating state.

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

Next, the determination of sufficiency of the air-fuel ratio feedbank control condition in step 531 will be described with reference to the flowchart shown in FIG. In this sufficiency determination, it is first determined whether the clutch switch 17 is on or not (steno: 7
'61 If the clutch switch I7 is on, the clutch is released, so it is assumed that the gear is being changed, and the valve opening period T is set to stop the air-fuel ratio pump control. UT is I
I O+7 (step '532). If the clutch switch 17 is off, the clutch is engaged, so it is determined whether or not the 211 torque switch 18 is on (
Stetsuno 62).

If the neutral switch 18 is on, the gear shift lever of the transmission is in the neutral position, so it is determined that the gear is being changed, and step 532 is executed. If the neutral switch 18 is off, the gear shift lever of the transmission is in any of the first to fifth speed positions, so it is determined whether the oxygen concentration sensor 14 is activated (Stella f63).

If the oxygen concentration sensor 14 is not activated because its temperature is low, step 532 is executed. If the oxygen concentration sensor 14 has already been activated, it is determined whether the intake air temperature TA is equal to or higher than a predetermined temperature T1 (for example, 15° C.) (step 64), and if TA≦T1, the intake air temperature is low. Therefore, step 532 is executed. If TA>T1, vehicle speed S. is a predetermined speed S1 (for example, 8 km/
h) It is determined whether or not it is greater than or equal to (step 65)
. If Sc≦81, the vehicle speed is low, so step 7' 532 is executed to stop the air-fuel ratio feedback control. S,) If S1h, the cooling water temperature Tw is the predetermined temperature T.
2 (for example, 70° C.) or higher (step 66), and when Tw≦T2, the cooling water temperature is low, so step 532 is executed. When Tw>T2, the engine rotation speed N becomes the first predetermined rotation speed N1 (for example,
6507.7), m, ) or less is determined (step 67). If Ne<N1, the engine speed is low, so step 532 is executed and the supply of intake secondary air is stopped.

If Ne≧N1, the engine speed is the first predetermined speed N
A second predetermined rotation speed N2 greater than 1 (for example, 2500
γ, p, m) or more is determined (step 6
8), N,)N2, the engine speed is high, so step 532 is executed. When N, ≦N2, it is determined whether the absolute pressure PBA inside the intake manifold 4 is greater than the first predetermined absolute pressure PBA1 (for example, 210 mmHg) (step 69). If PBA≦PRAI, the load on the engine 5 is low, so step 532 is executed to stop the air-fuel ratio feedback control, and if PBA>PBAl, the absolute pressure PBA is greater than the first predetermined absolute pressure PBA1. 2. It is determined whether the absolute pressure is greater than a predetermined absolute pressure PBA2 (for example, 460 mmH!l) (step 70). If PBA>PBA2, the load on the engine 5 is high, so step 532 is executed. If PBA≦PBA2, it is determined whether the gear shift lever of the transmission is in any one of the third to fifth speeds (step 71). In this determination, engine rotation speed N and vehicle speed S are used. The gear shift position is determined from the ratio.

If it is determined that the speed change lever is in either the first or second speed, this is the low speed shift position, so step 532 is executed. If it is determined that the gear shift lever is in one of the third to fifth gears, the atmospheric pressure PA is set to a predetermined pressure PA1 to detect high-altitude driving.
(For example, it is determined whether or not it is larger than 650 mml (g) (step 72).

If PA≦PA, it is assumed that the engine 5 is being operated at a high altitude, and step 532 is executed to stop the air-fuel ratio feedback control. If PA>PA1, step 533 is executed assuming that the vehicle is operating on level ground and that the air-fuel ratio feedback control conditions are satisfied.

The valve opening period T is within the duty cycle T8oL in which Stella f532 is executed. Since UT is set to ``0'''', the electromagnetic on-off valve 9 is closed and the supply of intake secondary air is subsequently stopped. Therefore, the air-fuel ratio of the supplied air-fuel mixture is enriched.

In the embodiment of the present invention described above, it is detected that either the engine rotation speed is low, the vehicle speed is low, or the absolute pressure of the negative pressure in the intake manifold is low. The low load state is defined as the time when this occurs, but the present invention is not limited to this, and for example, the low load state may be defined as the throttle valve opening being less than or equal to a predetermined value.

Summary of the Invention As described above, in the intake secondary air supply device for an internal combustion engine of the present invention, the supply of intake secondary air is stopped by closing the on-off valve when the engine is under low load. By fully closing the throttle valve, even if the amount of air-fuel mixture supplied is suddenly reduced, the air-fuel ratio is prevented from becoming over lean, and the combustion state of the engine can be stabilized.

[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, 5, and 8 are flowcharts showing the operation of the CPU, FIG. 6 is a diagram showing a data map written to the ROM, and FIG. 7 is a diagram similar to that shown in FIG. 1. FIG. 3 is a diagram showing the operation timing of the device. Explanation of symbols for main parts 2... Air cleaner 3... Carburetor 4... Intake manifold 6... Throttle valve 7... Bench stiffness 8... Intake secondary air supply passage 9... Electromagnetic Opening/closing valve 10...Pressure sensor 1
1...Crank angle sensor 12...Cooling water temperature sensor 14...Oxygen concentration sensor 15...Exhaust manifold 33...Catalytic converter.

Claims (2)

[Claims] (1) An intake secondary air supply passage communicating downstream of the carburetor throttle valve of the internal combustion engine, an on-off valve provided in the intake secondary air supply passage, and an exhaust gas passage provided in the engine exhaust gas passage to supply air to the engine. Comparing an oxygen concentration sensor that generates an output proportional to the oxygen concentration of exhaust gas when the air-fuel ratio of the air-fuel mixture is at least leaner than the stoichiometric air-fuel ratio, and the output level of the oxygen concentration sensor and a level corresponding to the target air-fuel ratio. and a control means for duty-controlling the opening and closing of the on-off valve based on the comparison result, and a detection means for detecting that the engine is in a low load state, and the control means detects that the low load state is detected by the detection means. An intake secondary air supply device characterized in that as long as the oxygen concentration sensor is detected, the on-off valve is closed regardless of the output level of the oxygen concentration sensor. (2) The detection means detects that the engine speed is below a predetermined speed, that the vehicle speed is below a predetermined speed, or that the intake absolute pressure downstream of the throttle valve is below a predetermined absolute pressure. 2. The intake secondary air supply device according to claim 1, wherein the intake secondary air supply device is set to the low load state.