JPH0533633A - Secondary air controller of internal combustion engine - Google Patents

Abstract

PURPOSE:To perform control over the supply and stoppage of secondary air according to a difference in fuel properties. CONSTITUTION:An air pump 28 supplying or stopping secondary air, a water temperature sensor 15 detecting a cooling water temperature, a fuel temperature sensor 32 detecting a fuel temperature, and a vapor flow sensor detecting a vapor flow rate, are all installed in an exhaust passage 6. A central processing unit judges whether fuel is a usual one or a light one or heavy one on the basis of fuel temperature and vapor flow. A supply starting water temperature A at the time of starting a supply of the secondary air, and first - third supply end water temperatures B, C and D at the time of ending the secondary air supply are all stored in a read-only memory (A<D<B<C). The central processing unit starts the supply of the secondary air if a water temperature by the water temperature sensor 15 is more than the supply starting water temperature A. In addition, the central processing unit terminates the secondary air supply at the first supply end water temperature B at the time of using usual fuel, at the second supply end water temperature C at the time of heavy fuel use and at the third supply end water temperature D at the time of light fuel use, respectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary air control device for supplying secondary air to an exhaust system in order to recombust unburned gas (HC, CO) discharged from an internal combustion engine. ..

[0002]

2. Description of the Related Art Conventionally, as one of methods for purifying exhaust gas from an internal combustion engine, secondary air is supplied to an exhaust system. In this method, the exhaust gas discharged from the combustion chamber is subjected to an oxidation reaction with the air supplied by an air pump, whereby hydrocarbon (HC) in the exhaust gas is discharged.
It also reduces carbon monoxide (CO) emissions.

An example of this type of secondary air control device is disclosed in Japanese Patent Laid-Open No. 63-41641. In this technique, secondary air supply means for supplying or stopping secondary air to the exhaust system is provided, and the supply or stop of secondary air by the secondary air supply means is controlled according to the water temperature of the internal combustion engine by the water temperature sensor. There is. That is, the supply start water temperature of the secondary air and the supply end water temperature higher than the supply start water temperature are preset. When the water temperature by the water temperature sensor is lower than the supply start water temperature, the supply of the secondary air by the secondary air supply means is stopped, and when the supply water temperature is higher than the supply start water temperature and lower than the supply end water temperature, the secondary air is supplied and is higher than the supply end water temperature. Then, the supply of secondary air is terminated.

[0004]

By the way, an internal combustion engine,
In particular, various fuels having different fuel properties (mainly distillation characteristics) are appropriately used as fuels used for automobile engines. However, in the above-described conventional secondary air control device, since the supply and stop of the secondary air are controlled regardless of the difference in the above-mentioned fuel properties, there is a problem that the air-fuel ratio is disturbed especially when heavy fuel is used. It was

That is, the fuel is a light fuel having a large amount of low boiling point such that 50% or more of the fuel evaporates at 100 ° C. and less than 50% based on whether or not the fuel evaporates. There is a heavy fuel with a high boiling point content that only evaporates. Therefore, when a heavy fuel is used as the fuel, it is less likely to evaporate than when a light fuel is used. Will increase.

Here, the amount of fuel that actually enters the combustion chamber is
In addition to the amount of fuel injected from the fuel injection valve that did not adhere to the wall surface of the intake passage, the amount of fuel that adhered to the intake passage that flows in as a liquid and the amount of fuel that evaporated from the fuel that adhered to the intake passage Some are inhaled. Therefore, if the amount of fuel adhering to the intake passage is large, such as heavy fuel, the above amounts will not be constantly constant and the amount of fuel entering the combustion chamber will vary from cycle to cycle, resulting in a cycle of air-fuel ratio. The fluctuation of each time becomes large. Then, due to the fluctuation of the air-fuel ratio, the amount of fuel supplied into the cylinder of the engine may be leaner than the lean limit. As a result, misfire occurs, a large amount of unburned HC and CO are discharged, and the exhaust property deteriorates.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an internal combustion engine capable of controlling the supply and stop of secondary air according to the difference in fuel properties.
It is to provide a secondary air control device.

[0008]

In order to achieve the above object, the present invention, as shown in FIG. 1, is a secondary air supply means M2 for supplying or stopping secondary air to the exhaust system of an internal combustion engine M1. An operating state detecting means M3 for detecting an operating state of the internal combustion engine M1, a fuel property detecting means M4 for detecting a property of fuel of the internal combustion engine M1, and an operating state of the internal combustion engine M1 by the operating state detecting means M3. Is a preset supply start operation state, supply start control means M5 for controlling the secondary air supply means M2 to start supply of secondary air to the exhaust system, and supply start by the supply start control means M5 After that, when the fuel property detected by the fuel property detecting means M4 is the normal property, the supply of the secondary air to the exhaust system is terminated in a preset normal supply end operation state, and the fuel property is the normal property. If it is outside, 2 at different supply termination operation state to the normal supply end operating conditions so as to change the supply time of the secondary air from the secondary air supply means M2
Supply end control means M6 for ending the supply of the next air is provided.

[0009]

When the internal combustion engine M1 is operating, its operating state is detected by the operating state detecting means M3 and the fuel property is detected by the fuel property detecting means M4. The supply start control means M5 controls the secondary air supply means M2 to supply the secondary air to the exhaust system when the operating state of the internal combustion engine M1 by the operating state detecting means M3 is a preset supply start operating state. Let it start.

After the supply start control means M5 starts the supply, the supply end control means M6 terminates the supply of the secondary air according to the fuel property detected by the fuel property detection means M4. That is, when the fuel property is the normal property, the supply completion control means M6 terminates the supply of the secondary air to the exhaust system in the preset normal supply completion operation state. Also,
When the fuel property is other than the normal property, the supply end control means M6 ends the supply of the secondary air in a supply end operating state different from the normal supply end operating state. As a result, the supply time of the secondary air from the secondary air supply means M2 differs depending on whether the fuel property is the normal property or the other properties.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment embodying the present invention will now be described with reference to FIGS.
It will be described with reference to FIG. FIG. 2 is a diagram showing a schematic configuration of a multi-cylinder engine 1 for an automobile as an internal combustion engine equipped with a secondary air control device. The engine 1 includes a piston 3 in a cylinder 2, and a combustion chamber 4 formed above the piston 3 has an intake passage 5 forming a part of an intake system and an exhaust gas forming a part of an exhaust system. The passage 6 communicates. A communication portion between the combustion chamber 4 and the intake passage 5 and a communication portion between the combustion chamber 4 and the exhaust passage 6 are opened and closed by an intake valve 7 and an exhaust valve 8.

The engine 1 introduces a mixture of intake air from the intake passage 5 and fuel injected from the fuel injection valve 9 into the combustion chamber 4 via the intake valve 7. An ignition plug 11 is attached to the engine 1, and the ignition voltage distributed by the distributor 12 is applied to the ignition plug 11. The distributor 12 is for distributing the high voltage output from the igniter 13 to each spark plug 11 in synchronization with the crank angle of the engine 1. The ignition timing of each spark plug 11 is the high voltage output from the igniter 13. Determined by timing.
Then, the engine 1 explodes the air-fuel mixture in the combustion chamber 4 by the spark plug 11 to obtain a driving force, and then discharges the exhaust gas to the exhaust passage 6 via the exhaust valve 8.

The distributor 12 includes:
A rotation speed sensor 14 that detects the rotation of the rotor and outputs an engine rotation signal is provided. Further, in the cylinder block 1a of the engine 1, a water temperature sensor 1 as an operating state detecting means for detecting the water temperature of the cooling water of the engine 1 is provided.
5 is attached.

A surge tank 16 for suppressing pulsation of intake air is provided in a part of the intake passage 5, and a diaphragm type pressure sensor 17 is attached to the surge tank 16. A throttle valve 18 that is opened / closed in conjunction with the operation of an accelerator pedal (not shown) is provided on the upstream side of the surge tank 16, and the amount of intake air to the intake passage 5 is adjusted by opening / closing the throttle valve 18. To be done. An idle switch 19 that is turned on when the throttle valve 18 is fully closed is attached near the throttle valve 18.

A throttle valve 1 is provided in the intake passage 5.
A bypass passage 21 is provided that bypasses 8 and connects the upstream side and the downstream side of the throttle valve 18.
An idle speed control valve (ISCV) 22 is attached in the middle of the bypass passage 21. The ISCV22 is a so-called step motor type in which the rotor of the step motor rotates in response to the pulse signal, which changes the lift amount of the valve element and the opening area of the valve, and controls the opening degree of the ISCV22. By adjusting the amount of air flowing through the bypass passage 21, the idle speed is controlled to the target speed. Further, an air cleaner 23 is arranged on the upstream side of the throttle valve 18, and an intake air temperature sensor 24 for detecting the intake air temperature is attached near the air cleaner 23.

On the other hand, in the exhaust passage 6, an oxygen sensor 25 for detecting the oxygen concentration in the exhaust gas and an exhaust gas (H
A three-way catalytic converter 26 for purifying C, CO, NOx) is attached. Further, one end of a secondary air supply passage 27 is connected between the oxygen sensor 25 and the three-way catalytic converter 26 in the exhaust passage 6. This 2
An air pump 28 as a secondary air supply means is connected to the other end of the secondary air supply passage 27 so that secondary air discharged from the air pump 28 is guided to the exhaust passage 6 through the secondary air supply passage 27. It has become. An air switching valve (ASV) 29 is provided in the middle of the secondary air supply passage 27.
When the ASV 29 is turned on, it guides the secondary air from the air pump 28 to the exhaust passage 6, and when it is turned off, the secondary air is discharged to the atmosphere.

In addition, a fuel tank 31 mounted on the vehicle
A fuel temperature sensor 32 for detecting the temperature of the fuel in the fuel tank 31 is attached to the lower part of the. The fuel temperature sensor 32 constitutes a part of the fuel property detecting means. A canister 34 is connected to an upper portion of the fuel tank 31 via a vapor passage 33, and evaporated fuel generated in the fuel tank 31 is guided to the canister 34 through the vapor passage 33. The canister 34 is an adsorption container for the evaporated fuel in which the activated carbon is stored, and the evaporated fuel is once adsorbed by the activated carbon.

A vapor flow meter 35 is provided in the middle of the vapor passage 33. The vapor flow meter 35 includes a rotating part 36 that rotates by the passage of evaporated fuel.
A signal rotor (not shown) is attached to 6. Further, a vapor flow rate sensor 37 is attached to the hausing portion of the vapor flow meter 35, and when the signal rotor of the rotating section 36 crosses the vapor flow rate sensor 37, a high voltage is produced, and when it is separated, a vapor flow rate detection signal is produced. Output. This vapor flow rate sensor 37 is the fuel temperature sensor 3
Together with 2, the fuel property detecting means is configured.

The canister 34 is connected to the intake passage 5 downstream of the surge tank 16 via a purge passage 38 so that the evaporated fuel in the canister 34 is sucked into the engine 1. A purge control valve 39 is provided in the middle of the purge passage 38. The purge control valve 39 is for adjusting the purge amount of the evaporated fuel introduced from the canister 34 to the intake passage 5 by opening and closing the purge passage 38, and the opening degree of the purge control valve 39 is It is adjusted by duty control. The purge passage 38 is provided with an orifice (not shown), and the intake passage 5
The negative pressure of 1 is prevented from directly acting on the fuel tank 31.

The rotation speed sensor 14, the water temperature sensor 15,
The pressure sensor 17, the idle switch 19, the intake air temperature sensor 24, the oxygen sensor 25, the fuel temperature sensor 32, and the vapor flow rate sensor 37 are electrically connected to the input side of an electronic control unit (hereinafter simply referred to as “ECU”) 41. There is. Also,
Each fuel injection valve 9, igniter 13, ISCV22, AS
The V29 and the purge control valve 39 are connected to the ECU 4
1 is electrically connected to the output side. And the ECU
Reference numeral 41 indicates each fuel injection valve 9, igniter 13, ISCV 22, ASV 29 based on detection signals from the various sensors.
And controlling the purge control valve 39.

Next, the configuration of the ECU 41 will be described with reference to FIG.
Will be described with reference to the block diagram of FIG. The ECU 41 includes a central processing unit (CPU) 42 that constitutes a supply start control means and a supply end control means, and a read-only memory (ROM) 43.
, Random access memory (RAM) 44, backup RAM 45, clock generator 46, input ports 48, 49, output ports 51, 52, 53, 54,
55, which are connected to each other by a bus 56. The CPU 42 executes various arithmetic processing according to a preset control program, and the ROM 43 is a CPU.
A control program and initial data necessary for executing the arithmetic processing in 42 are stored in advance. Further, the RAM 44 temporarily stores the calculation result of the CPU 42. Backup R
The AM 45 is backed up by a battery so as to retain various data even after the power is turned off. The clock generator 46 outputs the master clock to the CPU 42.
Supply to.

The fuel temperature signal from the fuel temperature sensor 32 is input to the input port 48 via the buffer 57, the multiplexer 58 and the A / D converter 59. The pressure signal from the pressure sensor 17 is supplied to the filter 61, the buffer 62,
It is input to the input port 48 via the multiplexer 58 and the A / D converter 59. The water temperature signal from the water temperature sensor 15 is supplied to the buffer 63, the multiplexer 58, the A / D converter 5
It is input to the input port 48 via 9. The intake air temperature signal from the intake air temperature sensor 24 is input to the input port 48 via the buffer 64, the multiplexer 58, and the A / D converter 59. The multiplexer 58 selectively outputs the fuel temperature signal, the pressure signal, the water temperature signal, and the intake air temperature signal, and the A / D
The converter 59 converts those signals into digital signals. The filter 61 is for removing the pulsating component of the intake pipe pressure included in the pressure signal of the pressure sensor 17.

The oxygen concentration signal from the oxygen sensor 25 is input to the input port 49 via the buffer 65 and the comparator 66. The engine rotation signal from the rotation speed sensor 14 and the vapor flow rate signal from the vapor flow rate sensor 37 are input to the input port 49 via the shaping circuit 67.
The on / off signal from the idle switch 19 is input to the input port 49 via the buffer 68.

The CPU 42 detects the fuel temperature Ti, the pressure value, the water temperature, the intake air temperature, the rich / lean signal, the engine speed, the vapor flow rate Qi, and the on / off state of the idle switch 19 based on these signals.

On the other hand, the CPU 42 controls the igniter 13 via the output port 51 and the drive circuit 69, and controls the opening and closing of the fuel injection valve 9 via the output port 52 and the drive circuit 70. Further, the CPU 42 controls the opening degree of the ISCV 22 via the output port 53 and the drive circuit 71, and controls the opening / closing of the purge control valve 39 via the output port 54 and the drive circuit 72, thereby controlling the output port 55 and the drive circuit 73. The ASV 29 is controlled to be opened or closed via the.

In the present embodiment, the CPU 42 controls the on / off timing of the ASV 29 according to the water temperature at that time by the water temperature sensor 15, whereby the air pump 2 is operated.
The supply and the end of the supply of the secondary air from 8 to the exhaust passage 6 are performed. Specifically, the supply start water temperature (for example, 0 ° C.) is used as the supply start operation state when starting the supply of the secondary air.
A is stored in the ROM 43.

The ROM 43 stores a first supply end water temperature (for example, 50 ° C.) B for ending the supply of the secondary air when the fuel property is the normal property. The first supply end water temperature B corresponds to a preset normal supply end operation state. Further, the ROM 43 stores the second supply end water temperature C for ending the supply of the secondary air when the fuel property is the heavy property. This second
The end-of-supply water temperature C is set higher than the first end-of-supply water temperature B by a predetermined temperature (for example, 60 ° C.) so that the supply time of the secondary air is longer than when the fuel property is the normal property. ).

Further, the ROM 43 stores a third supply end water temperature D for ending the supply of the secondary air when the fuel property is a light property. The third supply end water temperature D is set lower than the first supply end water temperature B by a predetermined temperature so that the supply time of the secondary air is shorter than that in the case where the fuel property is the normal property. (Eg 40 ° C.). Therefore, the supply start water temperature A, the first supply end water temperature B, the second supply end water temperature C, and the third supply end water temperature D
There is a relationship of A <D <B <C between them. The second supply end water temperature C and the third supply end water temperature D correspond to supply end operation states different from the normal supply end operation state (in this case, the first supply end water temperature B).

When the water temperature measured by the water temperature sensor 15 is lower than the supply start water temperature A, the CPU 42 determines ASV2.
9 is turned off to stop the supply of secondary air. Also, CP
U42 is the first to third supply end water temperatures B, depending on the fuel property.
When one of C and D is selected and the supply start water temperature A or higher and lower than the selected supply end water temperature B, C and D, the ASV 29 is turned on to supply the secondary air. Further, when the water temperature becomes equal to or higher than the selected supply end water temperatures B, C, D, the CPU 42 turns off the ASV 29 and ends the supply of the secondary air.

Next, the operation and effect of the present embodiment constructed as described above will be described. The flowchart of FIG. 4 shows a routine for controlling the end of the supply of the secondary air among the respective processes executed by the CPU 42,
It is activated by a regular interrupt every predetermined time.

When the CPU 42 shifts to this processing routine while supplying the secondary air, the property of the fuel is detected at step 101. That is, the CPU 42 reads the fuel temperature Ti in the fuel tank 31 by the fuel temperature sensor 32 and the vapor flow rate Qi by the vapor flow rate sensor 37.

Next, the CPU 42 executes steps 102 and 10.
In 3, it is determined whether the fuel has a light property, a heavy property, or a normal property. In order to make this determination, the ROM 43 stores in advance a fuel temperature determination value Ta and a vapor flow rate determination value Qa. And CPU
In step 102, 42 compares the fuel temperature Ti measured by the fuel temperature sensor 32 with the determination value Ta, and the vapor flow rate sensor 37
Then, the vapor flow rate Qi at that time is compared with the judgment value Qa. The fuel temperature Ti is lower than the judgment value Ta (Ti <Ta
), And the vapor flow rate Qi is greater than or equal to the judgment value Qa (Qi
≧ Qa), the CPU 42 determines that a large amount of fuel is evaporated despite the low fuel temperature Ti, that is, the fuel used at that time has a large amount of low-boiling components, and the fuel is light. Determined as fuel.

If the CPU 42 determines in step 102 that the fuel is not a light fuel, the CPU 42 proceeds to step 103 to determine the fuel temperature Ti by the fuel temperature sensor 32 and the determination value T.
a is compared, and the vapor flow rate Qi by the vapor flow rate sensor 37 at that time is compared with the determination value Qa. Fuel temperature Ti
Is equal to or larger than the judgment value Ta (Ti ≥Ta) and the vapor flow rate Qi is smaller than the judgment value Qa (Qi <Qa), CP
U42 judges that the fuel is a heavy fuel by judging that only a small amount of fuel has evaporated even though the fuel temperature Ti is high, that is, the low boiling point component is small in the fuel used at that time. To do.

When the CPU 42 determines in step 103 that the fuel is not a heavy fuel, it determines that the fuel used at that time is a normal fuel that is neither a light fuel nor a heavy fuel, and proceeds to step 104. CP at step 104
After setting the first supply end water temperature B as the supply end water temperature of the secondary air, the U 42 determines in step 105 whether or not the supply end condition of the secondary air is satisfied. This determination is whether or not the water temperature by the water temperature sensor 15 is equal to or higher than the first supply end water temperature B, whether the water temperature is lower than the supply start water temperature A, or whether the throttle valve 18 is fully opened. Etc. When the supply end condition in step 105 is not satisfied (when the water temperature is equal to or higher than the supply start water temperature A and is lower than the first supply end water temperature B and the throttle valve 18 is not fully opened), the CPU 42 sets A.
The on state of the SV 29 is maintained and this routine ends.
Therefore, the secondary air from the air pump 28 is continuously supplied to the exhaust passage 6.

When the supply end condition in step 105 is satisfied, that is, whether the water temperature is lower than the supply start water temperature A or the water temperature is equal to or higher than the first supply end water temperature B,
Alternatively, when the throttle valve 18 is fully opened, the CPU 42
Turns off the ASV 29 in step 106 and terminates this routine. Then, the secondary air from the air pump 28 is discharged to the atmosphere without being supplied to the exhaust passage 6.

If the fuel is a light fuel in step 102, the CPU 42 determines in step 107 that the third supply end water temperature D (in this case 4
0 ° C) is set. Then, the CPU 42 performs step 10
Then, the process proceeds to step 8, and it is determined whether or not the secondary air supply termination condition is satisfied, as in step 105. When this condition is not satisfied, the CPU 42 maintains the ASV 29 in the ON state and ends this routine. Therefore, the secondary air from the air pump 28 is continuously supplied to the exhaust passage 6. On the other hand, when the supply end condition is satisfied in step 108, the CPU 42 turns off the ASV 29 in step 109 in the same manner as in step 106, and ends this routine. Then, the secondary air from the air pump 28 is discharged to the atmosphere without being supplied to the exhaust passage 6.

As described above, when the third supply end water temperature D is set as the supply end water temperature of the secondary air when the light fuel is used, this third supply end water temperature D is higher than the first supply end water temperature B. Is also low, the supply time of the secondary air becomes shorter than that when normal fuel is used. Here, since the light fuel has a good evaporation property and a small amount is attached to the wall surface of the intake passage 5, the air-fuel ratio in each cycle is less disturbed, and the unburned HC and CO emissions are smaller than those of the heavy fuel. Quite few. Therefore, even if the supply time of the secondary air is shortened as described above, HC, CO
Can be purified to a sufficiently low level.

When secondary air is supplied to the exhaust passage 6, the air-fuel ratio in the three-way catalytic converter 26 becomes lean due to the stoichiometric air-fuel ratio, and unburned HC and CO can be purified by an oxidation reaction, but NOx is reduced by a reduction reaction. It becomes difficult to be purified. However, in this embodiment, since the supply time of the secondary air is shortened as described above, it is possible to increase the amount of purification of NOx.

If the fuel is a heavy fuel in step 103, the CPU 42 determines in step 110 the second supply end water temperature C as the supply end water temperature of the secondary air.
(60 ° C. in this case) is set. Subsequently, the CPU 42 proceeds to step 111 and determines whether or not the secondary air supply termination condition is satisfied, as in step 105. If this condition is not met, the CPU 42 determines that ASV2
The ON state of 9 is maintained, and this routine ends. Therefore, the secondary air from the air pump 28 is continuously supplied to the exhaust passage 6. On the other hand, when the supply termination condition is satisfied in step 111, the CPU 42 turns off the ASV 29 in step 112 in the same manner as in step 106.
This routine ends. Then, the secondary air from the air pump 28 is discharged to the atmosphere without being supplied to the exhaust passage 6.

As described above, when the second supply end water temperature C is set as the supply end water temperature of the secondary air when the heavy fuel is used, this second supply end water temperature C becomes the first supply end water temperature B. Therefore, the supply time of the secondary air becomes longer than that when normal fuel is used. Therefore, when heavy fuel is used, the amount of fuel adhering to the wall surface of the intake passage 5 is large, and the air-fuel ratio is disturbed between cycles to discharge a large amount of unburned HC and unburned CO. Since the supply time is long, the unburned HC and unburned CO are oxidized with the secondary air to be reliably purified.

As described above, in this embodiment, the fuel temperature sensor 3 is used.
2 detects the fuel temperature Ti and the vapor flow rate sensor 37 detects the vapor flow rate Qi (step 10
1) Based on these fuel temperature Ti and vapor flow rate Qi, it is judged whether the fuel is a normal fuel, a light fuel, or a heavy fuel (steps 102, 103), 2
As the supply end water temperature when terminating the supply of the next air, the first supply end water temperature B is set when the normal fuel is used (step 104), and the third supply end water temperature D is set when the light fuel is used (step 107). ), When the heavy fuel is used, the second supply end water temperature C is set (step 110). Therefore, unlike the prior art in which the supply and stop of the secondary air is controlled regardless of the difference in the fuel property, in the present embodiment, the secondary air supply time is not increased by using the heavy fuel. It is possible to surely purify the burned HC and the unburned CO, and to shorten the supply time of the secondary air when using the light fuel to improve the NOx purification performance.

The present invention is not limited to the configuration of the above-mentioned embodiment, and may be arbitrarily modified within the scope not departing from the spirit of the invention as follows. (1) In the above embodiment, the fuel temperature sensor 32 and the vapor flow rate sensor 37 were used to detect the fuel property, but instead of these, for example, it was determined from the fuel temperature Ti and the rise time of the pressure in the fuel tank 31. Known methods such as a method of detecting the fuel property by the easiness of evaporation of the fuel (lead vapor pressure: RVP), a method of detecting the pressure in the fuel tank 31, a method of learning the air-fuel ratio may be used. (2) Although the air pump 28 is used as the secondary air supply means in the above embodiment, an air suction system may be used instead of the air pump 28. In this air suction system, only the negative pressure portion of the pulsation of the combustion gas generated in the exhaust passage 6 such as the exhaust manifold is taken out by the reed valve, and the negative air is used to introduce the secondary air into the exhaust passage 6. In this case, the same effect as that of the above embodiment can be obtained by controlling the on / off timing of the ASV 29 in this case as well. (3) The supply start water temperature A, the first supply end water temperature B, the second supply end water temperature C, and the third supply end water temperature D are not limited to the values in the above embodiment, and may be changed appropriately. Good. (4) In the above-described embodiment, when the heavy fuel is used, the secondary air supply time is longer than when the normal fuel is used, and when the light fuel is used, the secondary air supply time is shorter than that when the normal fuel is used. However, only one of the supply times may be changed. (5) Generally, when the engine 1 shifts from the steady state or the accelerated state to the decelerated state, the fuel adhering to the wall surface of the intake passage 5 abruptly evaporates, and a temporarily rich air-fuel mixture inside the combustion chamber 4. And a large amount of unburned gas may be discharged. Therefore, if the supply time of the secondary air is increased as in the above embodiment, so-called afterburn, in which the unburned gas explosively burns in the exhaust system, is likely to occur. In order to prevent this, a dashpot is used to temporarily delay the throttle valve from closing to the idle position during deceleration to prevent misfire, or an ISC (idle speed control device) is used to intake air during deceleration. It is possible to introduce it to. Here, dashpot and ISC
Any of these may deteriorate the deceleration characteristics, so it is necessary to set the opening of the dashpot and the inflow air amount by ISC so that the reduction of the deceleration characteristics is small and the occurrence of afterburn is small.

[0043]

As described above in detail, according to the present invention, the supply of the secondary air to the exhaust system is started and the supply of the secondary air is started when the operating state of the internal combustion engine is the preset supply start operating state. After the start, if the fuel property is the normal property, the supply of the secondary air is terminated in a preset normal supply end operation state, and if the fuel property is other than the normal property, the secondary air Since the supply of the secondary air is terminated in the supply end operation state different from the normal supply end operation state so as to change the supply time, the control of the supply and stop of the secondary air is performed depending on the difference in the fuel property. It has an excellent effect that it can be performed by

[Brief description of drawings]

FIG. 1 is a conceptual configuration diagram of the present invention.

FIG. 2 is a schematic configuration diagram showing a secondary air control device for an internal combustion engine according to an embodiment of the present invention.

FIG. 3 is a block diagram showing a configuration of an ECU according to an embodiment.

FIG. 4 is a flowchart for explaining the operation of one embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Engine as an internal combustion engine, 6 ... Exhaust passage forming a part of exhaust system, 15 ... Water temperature sensor as operating state detecting means, 28 ... Air pump as secondary air supplying means,
32 ... Fuel temperature sensor forming part of fuel property detecting means, 37 ... Vapor flow rate sensor forming part of fuel property detecting means, 42 ... CPU forming supply start control means and supply end control means

[Procedure amendment]

[Submission date] August 6, 1991

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Full text

[Correction method] Change

[Correction content]

[Document name] Statement

Title: Secondary air control device for internal combustion engine

[Claims]

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary air control device for supplying secondary air to an exhaust system in order to recombust unburned gas (HC, CO) discharged from an internal combustion engine. ..

[0002]

2. Description of the Related Art Conventionally, as one of methods for purifying exhaust gas from an internal combustion engine, secondary air is supplied to an exhaust system. In this method, the exhaust gas discharged from the combustion chamber is subjected to an oxidation reaction with the air supplied by an air pump, whereby hydrocarbon (HC) in the exhaust gas is discharged.
It also reduces carbon monoxide (CO) emissions.

An example of this type of secondary air control device is disclosed in Japanese Patent Laid-Open No. 63-41641. In this technique, secondary air supply means for supplying or stopping secondary air to the exhaust system is provided, and the supply or stop of secondary air by the secondary air supply means is controlled according to the water temperature of the internal combustion engine by the water temperature sensor. There is. That is, the supply start water temperature of the secondary air and the supply end water temperature higher than the supply start water temperature are preset. When the water temperature by the water temperature sensor is lower than the supply start water temperature, the supply of the secondary air by the secondary air supply means is stopped, and when the supply water temperature is higher than the supply start water temperature and lower than the supply end water temperature, the secondary air is supplied and is higher than the supply end water temperature. Then, the supply of secondary air is terminated.

[0004]

By the way, an internal combustion engine,
In particular, various fuels having different fuel properties (mainly distillation characteristics) are appropriately used as fuels used for automobile engines. However, in the above-described conventional secondary air control device, since the supply and stop of the secondary air are controlled regardless of the difference in the above-mentioned fuel properties, there is a problem that the air-fuel ratio is disturbed especially when heavy fuel is used. It was

That is, the fuel is a light fuel having a large amount of low boiling point such that 50% or more of the fuel evaporates at 100 ° C. and less than 50% based on whether or not the fuel evaporates. There is a heavy fuel with a high boiling point content that only evaporates. Therefore, when a heavy fuel is used as the fuel, it is less likely to evaporate than when a light fuel is used. Will increase.

Here, the amount of fuel that actually enters the combustion chamber is
In addition to the amount of fuel injected from the fuel injection valve that did not adhere to the wall surface of the intake passage, the amount of fuel that adhered to the intake passage that flows in as a liquid and the amount of fuel that evaporated from the fuel that adhered to the intake passage Some are inhaled. Therefore, if the amount of fuel adhering to the intake passage is large, such as heavy fuel, the above amounts will not be constantly constant and the amount of fuel entering the combustion chamber will vary from cycle to cycle, resulting in a cycle of air-fuel ratio. The fluctuation of each time becomes large. Then, due to the fluctuation of the air-fuel ratio, the amount of fuel supplied into the cylinder of the engine may be leaner than the lean limit. As a result, misfire occurs, a large amount of unburned HC and CO are discharged, and the exhaust property deteriorates.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a secondary air control device for an internal combustion engine capable of controlling the supply of secondary air according to the difference in fuel properties. To do.

[0008]

In order to achieve the above object, the present invention, as shown in FIG. 1, supplies and stops secondary air to an exhaust system of an internal combustion engine M1 and supplies the secondary air. A secondary air supply means M2 whose amount can be adjusted, an operation state detection means M3 for detecting an operation state of the internal combustion engine M1, a fuel property detection means M4 for detecting a property of fuel of the internal combustion engine M1, and the operation Internal combustion engine M by state detection means M3
When the operation state of No. 1 is a preset secondary air supply operation state and the fuel property by the fuel property detection means M4 is a normal property within a predetermined range, the secondary air supply means M
When the operating state of the internal combustion engine M1 by the first supply control means M5 that controls 2 to supply a preset amount of secondary air to the exhaust system and the operating state detecting means M3 is the secondary air supply operating state. If the fuel property detected by the fuel property detection means M4 is out of the predetermined range, the secondary air supply means M2 is controlled to make the supply amount of the secondary air different from the supply amount in the normal property. Supply control means M6.

[0009]

When the internal combustion engine M1 is operating, its operating state is detected by the operating state detecting means M3 and the fuel property is detected by the fuel property detecting means M4. When the operating state of the internal combustion engine M1 by the operating state detecting means M3 is a preset secondary air supply operating state and the fuel property by the fuel property detecting means M4 is a normal property within a predetermined range, the first supply control The means M5 controls the secondary air supply means M2 to supply a preset amount of secondary air to the exhaust system.

When the operating state of the internal combustion engine M1 by the operating state detecting means M3 is the secondary air supply operating state and the fuel property by the fuel property detecting means M4 is out of the predetermined range, the second The supply control means M6 controls the secondary air supply means M2 to make the supply amount of the secondary air different from the supply amount in the normal state.

Therefore, the supply amount of the secondary air is controlled according to the difference in the fuel property, and it becomes possible to purify the unburned HC and CO with the optimum amount of the secondary air.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment embodying the present invention will now be described with reference to FIGS.
It will be described with reference to FIG. FIG. 2 is a diagram showing a schematic configuration of a multi-cylinder engine 1 for an automobile as an internal combustion engine equipped with a secondary air control device. The engine 1 includes a piston 3 in a cylinder 2, and a combustion chamber 4 formed above the piston 3 has an intake passage 5 forming a part of an intake system and an exhaust gas forming a part of an exhaust system. The passage 6 communicates. A communication portion between the combustion chamber 4 and the intake passage 5 and a communication portion between the combustion chamber 4 and the exhaust passage 6 are opened and closed by an intake valve 7 and an exhaust valve 8.

The engine 1 introduces a mixture of intake air from the intake passage 5 and fuel injected from the fuel injection valve 9 into the combustion chamber 4 via the intake valve 7. An ignition plug 11 is attached to the engine 1, and the ignition voltage distributed by the distributor 12 is applied to the ignition plug 11. The distributor 12 is for distributing the high voltage output from the igniter 13 to each spark plug 11 in synchronization with the crank angle of the engine 1. The ignition timing of each spark plug 11 is the high voltage output from the igniter 13. Determined by timing.
Then, the engine 1 explodes the air-fuel mixture in the combustion chamber 4 by the spark plug 11 to obtain a driving force, and then discharges the exhaust gas to the exhaust passage 6 via the exhaust valve 8.

The distributor 12 includes:
A rotation speed sensor 14 that detects the rotation of the rotor and outputs an engine rotation signal is provided. Further, in the cylinder block 1a of the engine 1, a water temperature sensor 1 as an operating state detecting means for detecting the water temperature of the cooling water of the engine 1 is provided.
5 is attached.

A surge tank 16 for suppressing pulsation of intake air is provided in a part of the intake passage 5, and a diaphragm type pressure sensor 17 is attached to the surge tank 16. A throttle valve 18 that is opened / closed in conjunction with the operation of an accelerator pedal (not shown) is provided on the upstream side of the surge tank 16, and the amount of intake air to the intake passage 5 is adjusted by opening / closing the throttle valve 18. To be done. An idle switch 19 that is turned on when the throttle valve 18 is fully closed is attached near the throttle valve 18.

Further, the throttle valve 1 is provided in the intake passage 5.
A bypass passage 21 is provided that bypasses 8 and connects the upstream side and the downstream side of the throttle valve 18.
An idle speed control valve (ISCV) 22 is attached in the middle of the bypass passage 21. The ISCV22 is a so-called step motor type in which the rotor of the step motor rotates in response to the pulse signal, which changes the lift amount of the valve element and the opening area of the valve, and controls the opening degree of the ISCV22. By adjusting the amount of air flowing through the bypass passage 21, the idle speed is controlled to the target speed. Further, an air cleaner 23 is arranged on the upstream side of the throttle valve 18, and an intake air temperature sensor 24 for detecting the intake air temperature is attached near the air cleaner 23.

On the other hand, in the exhaust passage 6, an oxygen sensor 25 for detecting the oxygen concentration in the exhaust gas and an exhaust gas (H
A three-way catalytic converter 26 for purifying C, CO, NOx) is attached. Further, one end of a secondary air supply passage 27 is connected between the oxygen sensor 25 and the three-way catalytic converter 26 in the exhaust passage 6. This 2
An air pump 28 as a secondary air supply means is connected to the other end of the secondary air supply passage 27 so that secondary air discharged from the air pump 28 is guided to the exhaust passage 6 through the secondary air supply passage 27. It has become. An air switching valve (ASV) 29 is provided in the middle of the secondary air supply passage 27.
When the ASV 29 is turned on, it guides the secondary air from the air pump 28 to the exhaust passage 6, and when it is turned off, the secondary air is discharged to the atmosphere.

In addition, a fuel tank 31 mounted on the vehicle
A fuel temperature sensor 32 for detecting the temperature of the fuel in the fuel tank 31 is attached to the lower part of the. The fuel temperature sensor 32 constitutes a part of the fuel property detecting means. A canister 34 is connected to an upper portion of the fuel tank 31 via a vapor passage 33, and evaporated fuel generated in the fuel tank 31 is guided to the canister 34 through the vapor passage 33. The canister 34 is an adsorption container for the evaporated fuel in which the activated carbon is stored, and the evaporated fuel is once adsorbed by the activated carbon.

A vapor flow meter 35 is provided in the middle of the vapor passage 33. The vapor flow meter 35 includes a rotating part 36 that rotates by the passage of evaporated fuel.
A signal rotor (not shown) is attached to 6. Further, a vapor flow rate sensor 37 is attached to the hausing portion of the vapor flow meter 35, and when the signal rotor of the rotating section 36 crosses the vapor flow rate sensor 37, a high voltage is produced, and when it is separated, a vapor flow rate detection signal is produced. Output. This vapor flow rate sensor 37 is the fuel temperature sensor 3
Together with 2, the fuel property detecting means is configured.

The canister 34 is connected to the intake passage 5 downstream of the surge tank 16 via a purge passage 38 so that the evaporated fuel in the canister 34 is sucked into the engine 1. A purge control valve 39 is provided in the middle of the purge passage 38. The purge control valve 39 is for adjusting the purge amount of the evaporated fuel introduced from the canister 34 to the intake passage 5 by opening and closing the purge passage 38, and the opening degree of the purge control valve 39 is It is adjusted by duty control. The purge passage 38 is provided with an orifice (not shown), and the intake passage 5
The negative pressure of 1 is prevented from directly acting on the fuel tank 31.

The rotation speed sensor 14, the water temperature sensor 15,
The pressure sensor 17, the idle switch 19, the intake air temperature sensor 24, the oxygen sensor 25, the fuel temperature sensor 32, and the vapor flow rate sensor 37 are electrically connected to the input side of an electronic control unit (hereinafter simply referred to as “ECU”) 41. There is. Also,
Each fuel injection valve 9, igniter 13, ISCV22, AS
The V29 and the purge control valve 39 are connected to the ECU 4
1 is electrically connected to the output side. And the ECU
Reference numeral 41 indicates each fuel injection valve 9, igniter 13, ISCV 22, ASV 29 based on detection signals from the various sensors.
And controlling the purge control valve 39.

Next, the configuration of the ECU 41 will be described with reference to FIG.
Will be described with reference to the block diagram of FIG. The ECU 41 includes a central processing unit (CPU) 42 that constitutes first supply control means and second supply control means, and a read-only memory (ROM).
43, random access memory (RAM) 44, backup RAM 45, clock generator 46, input ports 48, 49, and output ports 51, 52, 53, 5
4 and 55, which are connected to each other by a bus 56. The CPU 42 executes various arithmetic processes according to a preset control program, and the ROM 43 stores C
A control program and initial data necessary for executing arithmetic processing in the PU 42 are stored in advance. In addition, RAM4
Reference numeral 4 temporarily stores the calculation result of the CPU 42. The backup RAM 45 is backed up by a battery so as to retain various data even after the power is turned off.
The clock generator 46 uses the master clock as the CPU.
42.

The fuel temperature signal from the fuel temperature sensor 32 is input to the input port 48 via the buffer 57, the multiplexer 58 and the A / D converter 59. The pressure signal from the pressure sensor 17 is supplied to the filter 61, the buffer 62,
It is input to the input port 48 via the multiplexer 58 and the A / D converter 59. The water temperature signal from the water temperature sensor 15 is supplied to the buffer 63, the multiplexer 58, the A / D converter 5
It is input to the input port 48 via 9. The intake air temperature signal from the intake air temperature sensor 24 is input to the input port 48 via the buffer 64, the multiplexer 58, and the A / D converter 59. The multiplexer 58 selectively outputs the fuel temperature signal, the pressure signal, the water temperature signal, and the intake air temperature signal, and the A / D
The converter 59 converts those signals into digital signals. The filter 61 is for removing the pulsating component of the intake pipe pressure included in the pressure signal of the pressure sensor 17.

The oxygen concentration signal from the oxygen sensor 25 is input to the input port 49 via the buffer 65 and the comparator 66. The engine rotation signal from the rotation speed sensor 14 and the vapor flow rate signal from the vapor flow rate sensor 37 are input to the input port 49 via the shaping circuit 67.
The on / off signal from the idle switch 19 is input to the input port 49 via the buffer 68.

The CPU 42 detects the fuel temperature Ti, the pressure value, the water temperature, the intake air temperature, the rich / lean signal, the engine speed, the vapor flow rate Qi, and the on / off state of the idle switch 19 based on these signals.

On the other hand, the CPU 42 controls the igniter 13 via the output port 51 and the drive circuit 69, and controls the opening and closing of the fuel injection valve 9 via the output port 52 and the drive circuit 70. Further, the CPU 42 controls the opening degree of the ISCV 22 via the output port 53 and the drive circuit 71, and controls the opening / closing of the purge control valve 39 via the output port 54 and the drive circuit 72, thereby controlling the output port 55 and the drive circuit 73. The ASV 29 is controlled to be opened or closed via the.

In the present embodiment, the CPU 42 controls the on / off timing of the ASV 29 according to the water temperature at that time by the water temperature sensor 15, whereby the air pump 2 is operated.
The supply and the end of the supply of the secondary air from 8 to the exhaust passage 6 are performed. Specifically, the supply start water temperature (for example, 0 ° C.) is used as the supply start operation state when starting the supply of the secondary air.
A is stored in the ROM 43.

The ROM 43 stores a first supply end water temperature (for example, 50 ° C.) B for ending the supply of the secondary air when the fuel property is the normal property. The first supply end water temperature B corresponds to a preset normal supply end operation state. Further, the ROM 43 stores the second supply end water temperature C for ending the supply of the secondary air when the fuel property is the heavy property. This second
The end-of-supply water temperature C is set higher than the first end-of-supply water temperature B by a predetermined temperature (for example, 60 ° C.) so that the supply time of the secondary air is longer than when the fuel property is the normal property. ).

Further, the ROM 43 stores the third supply end water temperature D for ending the supply of the secondary air when the fuel property is the light property. The third supply end water temperature D is set lower than the first supply end water temperature B by a predetermined temperature so that the supply time of the secondary air is shorter than that in the case where the fuel property is the normal property. (Eg 40 ° C.). Therefore, the supply start water temperature A, the first supply end water temperature B, the second supply end water temperature C, and the third supply end water temperature D
There is a relationship of A <D <B <C between them. The second supply end water temperature C and the third supply end water temperature D correspond to supply end operation states different from the normal supply end operation state (in this case, the first supply end water temperature B).

When the water temperature measured by the water temperature sensor 15 is lower than the supply start water temperature A, the CPU 42 determines ASV2.
9 is turned off to stop the supply of secondary air. Also, CP
U42 is the first to third supply end water temperatures B, depending on the fuel property.
When one of C and D is selected and the supply start water temperature A or higher and lower than the selected supply end water temperature B, C and D, the ASV 29 is turned on to supply the secondary air. Further, when the water temperature becomes equal to or higher than the selected supply end water temperatures B, C, D, the CPU 42 turns off the ASV 29 and ends the supply of the secondary air.

Next, the operation and effect of the present embodiment constructed as described above will be described. The flowchart of FIG. 4 shows a routine for controlling the end of the supply of the secondary air among the respective processes executed by the CPU 42,
It is activated by a regular interrupt every predetermined time.

When the CPU 42 shifts to this processing routine while the secondary air is being supplied, the property of the fuel is detected in step 101. That is, the CPU 42 reads the fuel temperature Ti in the fuel tank 31 by the fuel temperature sensor 32 and the vapor flow rate Qi by the vapor flow rate sensor 37.

Next, the CPU 42 executes steps 102 and 10.
In 3, it is determined whether the fuel has a light property, a heavy property, or a normal property. In order to make this determination, the ROM 43 stores in advance a fuel temperature determination value Ta and a vapor flow rate determination value Qa. And CPU
In step 102, 42 compares the fuel temperature Ti measured by the fuel temperature sensor 32 with the determination value Ta, and the vapor flow rate sensor 37
Then, the vapor flow rate Qi at that time is compared with the judgment value Qa. The fuel temperature Ti is lower than the judgment value Ta (Ti <Ta
), And the vapor flow rate Qi is greater than or equal to the judgment value Qa (Qi
≧ Qa), the CPU 42 determines that a large amount of fuel is evaporated despite the low fuel temperature Ti, that is, the fuel used at that time has a large amount of low-boiling components, and the fuel is light. Determined as fuel.

If the CPU 42 determines in step 102 that the fuel is not a light fuel, the CPU 42 proceeds to step 103 to determine the fuel temperature Ti by the fuel temperature sensor 32 and the determination value T.
a is compared, and the vapor flow rate Qi by the vapor flow rate sensor 37 at that time is compared with the determination value Qa. Fuel temperature Ti
Is equal to or larger than the judgment value Ta (Ti ≥Ta) and the vapor flow rate Qi is smaller than the judgment value Qa (Qi <Qa), CP
U42 judges that the fuel is a heavy fuel by judging that only a small amount of fuel has evaporated even though the fuel temperature Ti is high, that is, the low boiling point component is small in the fuel used at that time. To do.

When the CPU 42 determines in step 103 that the fuel is not heavy fuel, it determines that the fuel used at that time is normal fuel that is neither light fuel nor heavy fuel, and proceeds to step 104. CP at step 104
After setting the first supply end water temperature B as the supply end water temperature of the secondary air, the U 42 determines in step 105 whether or not the supply end condition of the secondary air is satisfied. This determination is whether or not the water temperature by the water temperature sensor 15 is equal to or higher than the first supply end water temperature B, whether the water temperature is lower than the supply start water temperature A, or whether the throttle valve 18 is fully opened. Etc. When the supply end condition in step 105 is not satisfied (when the water temperature is equal to or higher than the supply start water temperature A and is lower than the first supply end water temperature B and the throttle valve 18 is not fully opened), the CPU 42 sets A.
The on state of the SV 29 is maintained and this routine ends.
Therefore, the secondary air from the air pump 28 is continuously supplied to the exhaust passage 6.

When the supply end condition in step 105 is satisfied, that is, whether the water temperature is lower than the supply start water temperature A or the water temperature is equal to or higher than the first supply end water temperature B,
Alternatively, when the throttle valve 18 is fully opened, the CPU 42
Turns off the ASV 29 in step 106 and terminates this routine. Then, the secondary air from the air pump 28 is discharged to the atmosphere without being supplied to the exhaust passage 6.

If the fuel is a light fuel in step 102, the CPU 42 determines in step 107 that the supply end water temperature of the secondary air is the third supply end water temperature D (4 in this case).
0 ° C) is set. Then, the CPU 42 performs step 10
Then, the process proceeds to step 8, and it is determined whether or not the secondary air supply termination condition is satisfied, as in step 105. When this condition is not satisfied, the CPU 42 maintains the ASV 29 in the ON state and ends this routine. Therefore, the secondary air from the air pump 28 is continuously supplied to the exhaust passage 6. On the other hand, when the supply end condition is satisfied in step 108, the CPU 42 turns off the ASV 29 in step 109 in the same manner as in step 106, and ends this routine. Then, the secondary air from the air pump 28 is discharged to the atmosphere without being supplied to the exhaust passage 6.

As described above, when the third supply end water temperature D is set as the supply end water temperature of the secondary air when the light fuel is used, the third supply end water temperature D is higher than the first supply end water temperature B. Is also low, the supply time of the secondary air becomes shorter than that when normal fuel is used. Here, since the light fuel has a good evaporation property and a small amount is attached to the wall surface of the intake passage 5, the air-fuel ratio in each cycle is less disturbed, and the unburned HC and CO emissions are smaller than those of the heavy fuel. Quite few. Therefore, even if the supply time of the secondary air is shortened as described above, HC, CO
Can be purified to a sufficiently low level.

When secondary air is supplied to the exhaust passage 6, the air-fuel ratio in the three-way catalytic converter 26 becomes lean due to the stoichiometric air-fuel ratio, and unburned HC and CO can be purified by an oxidation reaction, but NOx is reduced by a reduction reaction. It becomes difficult to be purified. However, in this embodiment, since the supply time of the secondary air is shortened as described above, it is possible to increase the amount of purification of NOx.

If the fuel is a heavy fuel in step 103, the CPU 42 determines in step 110 the second supply end water temperature C as the supply end water temperature of the secondary air.
(60 ° C. in this case) is set. Subsequently, the CPU 42 proceeds to step 111 and determines whether or not the secondary air supply termination condition is satisfied, as in step 105. If this condition is not met, the CPU 42 determines that ASV2
The ON state of 9 is maintained, and this routine ends. Therefore, the secondary air from the air pump 28 is continuously supplied to the exhaust passage 6. On the other hand, when the supply termination condition is satisfied in step 111, the CPU 42 turns off the ASV 29 in step 112 in the same manner as in step 106.
This routine ends. Then, the secondary air from the air pump 28 is discharged to the atmosphere without being supplied to the exhaust passage 6.

As described above, when the second supply end water temperature C is set as the supply end water temperature of the secondary air when the heavy fuel is used, the second supply end water temperature C becomes the first supply end water temperature B. Therefore, the supply time of the secondary air becomes longer than that when normal fuel is used. Therefore, when heavy fuel is used, the amount of fuel adhering to the wall surface of the intake passage 5 is large, and the air-fuel ratio is disturbed between cycles to discharge a large amount of unburned HC and unburned CO. Since the supply time is long, the unburned HC and unburned CO are oxidized with the secondary air to be reliably purified.

As described above, in this embodiment, the fuel temperature sensor 3 is used.
2 detects the fuel temperature Ti and the vapor flow rate sensor 37 detects the vapor flow rate Qi (step 10
1) Based on these fuel temperature Ti and vapor flow rate Qi, it is judged whether the fuel is a normal fuel, a light fuel, or a heavy fuel (steps 102, 103), 2
As the supply end water temperature when terminating the supply of the next air, the first supply end water temperature B is set when the normal fuel is used (step 104), and the third supply end water temperature D is set when the light fuel is used (step 107). ), When the heavy fuel is used, the second supply end water temperature C is set (step 110). Therefore, unlike the prior art in which the supply and stop of the secondary air is controlled regardless of the difference in fuel properties, in this embodiment, the amount of secondary air supplied is increased when heavy fuel is used. Unburned HC and unburned CO can be surely purified, and when light fuel is used, the amount of secondary air supplied can be reduced to improve NOx purification performance.

The present invention is not limited to the configuration of the above-mentioned embodiment, and may be arbitrarily modified within the scope not departing from the gist of the invention, for example, as follows. (1) In the above embodiment, the fuel temperature sensor 32 and the vapor flow rate sensor 37 were used to detect the fuel property, but instead of these, for example, it was determined from the fuel temperature Ti and the rise time of the pressure in the fuel tank 31. Known methods such as a method of detecting the fuel property by the easiness of evaporation of the fuel (lead vapor pressure: RVP), a method of detecting the pressure in the fuel tank 31, a method of learning the air-fuel ratio may be used. (2) Although the air pump 28 is used as the secondary air supply means in the above embodiment, an air suction system may be used instead of the air pump 28. In this air suction system, only the negative pressure portion of the pulsation of the combustion gas generated in the exhaust passage 6 such as the exhaust manifold is taken out by the reed valve, and the negative air is used to introduce the secondary air into the exhaust passage 6. This is also a system, and in this case as well, by controlling the on / off timing of the ASV 29, the same effect as that of the above-described embodiment can be obtained. (3) The supply start water temperature A, the first supply end water temperature B, the second supply end water temperature C, and the third supply end water temperature D are not limited to the values in the above embodiment, and may be changed appropriately. Good. (4) In the above-described embodiment, when the heavy fuel is used, the secondary air supply time is longer than when the normal fuel is used, and when the light fuel is used, the secondary air supply time is shorter than that when the normal fuel is used. However, only one of the supply times may be changed. (5) Generally, when the engine 1 shifts from the steady state or the accelerated state to the decelerated state, the fuel adhering to the wall surface of the intake passage 5 abruptly evaporates, and a temporarily rich air-fuel mixture inside the combustion chamber 4. And a large amount of unburned gas may be discharged. Therefore, if the supply time of the secondary air is increased as in the above embodiment, so-called afterburn, in which the unburned gas explosively burns in the exhaust system, is likely to occur. In order to prevent this, a dashpot is used to temporarily delay the throttle valve from closing to the idle position during deceleration to prevent misfire, or an ISC (idle speed control device) is used to intake air during deceleration. It is possible to introduce it in. Where dashpot and ISC
Any of these may deteriorate the deceleration characteristics, so it is necessary to set the opening of the dashpot and the inflow air amount by ISC so that the reduction of the deceleration characteristics is small and the occurrence of afterburn is small.

[0044]

As described in detail above, according to the present invention, when the operating condition of the internal combustion engine is the preset secondary air supply operating condition and the fuel property is the normal property within the predetermined range, the preset condition is set. And supply the required amount of secondary air to the exhaust system,
When the operating state of the internal combustion engine is the secondary air supply operating state and the fuel property is out of the predetermined range, the supply amount of the secondary air is made different from the supply amount in the normal property. This has the excellent effect that the secondary air supply control to the exhaust system by the secondary air supply means can be performed according to the difference in the fuel property.

[Brief description of drawings]

FIG. 1 is a conceptual configuration diagram of the present invention.

FIG. 2 is a schematic configuration diagram showing a secondary air control device for an internal combustion engine according to an embodiment of the present invention.

FIG. 3 is a block diagram showing a configuration of an ECU according to an embodiment.

FIG. 4 is a flowchart for explaining the operation of one embodiment.

[Explanation of Codes] 1 ... Engine as internal combustion engine, 6 ... Exhaust passage forming part of exhaust system, 15 ... Water temperature sensor as operating state detecting means, 28 ... Air pump as secondary air supplying means,
32 ... Fuel temperature sensor forming part of fuel property detecting means, 37 ... Vapor flow rate sensor forming part of fuel property detecting means, 42 ... First supply control means and second supply control means CPU ────────────────────────────────────────────────── ────

[Procedure amendment]

[Submission date] August 6, 1991

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 1

[Correction method] Change

[Correction content]

[Figure 1]

Claims (1)

Claim: What is claimed is: 1. A secondary air supply means for supplying or stopping secondary air to an exhaust system of an internal combustion engine, an operating state detecting means for detecting an operating state of the internal combustion engine, When the fuel property detecting means for detecting the property of the fuel of the internal combustion engine and the operating state of the internal combustion engine by the operating state detecting means is a preset supply start operating state, the secondary air supply means is controlled to the exhaust system. If the fuel property by the fuel property detecting means is the normal property after the supply start control means for starting the supply of the secondary air and the supply start control means starts the supply in the preset normal supply end operation state. When the supply of the secondary air to the exhaust system is terminated and the fuel property is other than the normal property, the normal supply end operation is performed so as to change the supply time of the secondary air from the secondary air supply means. State secondary air control device for an internal combustion engine, characterized in that a supply end control means for terminating the supply of secondary air at different supply termination operation state and.