JPH0435606B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a secondary air supply device for an engine that controls the supply amount of secondary air for purifying exhaust gas, and in particular to preventing deterioration of the exhaust gas purifying device. Regarding the improvement of

[Prior art] Secondary air is supplied into the exhaust gas mainly from the viewpoint of exhaust gas purification, and HC, CO, etc. in the exhaust gas are oxidized in a purification device downstream of the engine, and converted into H ₂ O,
It purifies exhaust gas by converting it into _CO2 , etc. Oxidation naturally accompanies heat generation, and the balance between this heat generation and the heat resistance of the purification device becomes a problem. It is said that the upper limit of this heat resistance temperature for catalytic converters is 900°C. Therefore, if the temperature becomes higher than that, there is a risk that the purification device and the like will deteriorate.

In the past, a warning would be issued if the purifier was about to reach a temperature higher than its allowable temperature limit. On the other hand, Tokukai Akira
In systems such as No. 58-119950, which enrich the mixture and introduce secondary air during cold engine operation, the supply of secondary air should be cut off if the engine temperature exceeds a predetermined temperature. ing. However, even with such a system, a rich air-fuel mixture is introduced into the engine during cold operation, resulting in incomplete combustion and, as a result, a large amount of unburned gas is discharged into the purification device. This will cause the temperature of the purifier to rise rapidly, which is likely to lead to deterioration of the purifier.

In view of this point, Utility Model Application No. 53-123315,
No. 51-127918, Special Publication No. 53-9663, Japanese Patent Publication No. 1973-
No. 13820, etc., proposes a technology that attempts to suppress the promotion of reburning when the engine temperature is below a set value when starting the engine, and a technology that uses a diaphragm valve to reduce the amount of secondary air as the temperature decreases. There is.

[Problems to be Solved by the Invention] However, when it comes to deterioration of a purification device, the total amount of unburned gas components is important, but the problem is how much unburned gas is supplied to the purification device per unit time. For example, even if exhaust gas containing only a dilute amount of unburned components is supplied for a long period of time, temperature rise will not be a problem, but dense exhaust gas will be a problem even if it is supplied for a short time. As is well known, once a purification device has deteriorated, it cannot be restored to its original state. In other words, there is a need for more precise control to suppress the temperature rise in the purifier.

The present invention has been made in view of the problems of the prior art described above, and its purpose is to purify exhaust gas at the time of cold start of the engine, and at the same time precisely prevent the temperature of the exhaust gas purification device from rising excessively. The next point is to propose an air supply device.

[Means for Solving the Problems] The configuration of the present invention for achieving the above-mentioned object includes a start detection means for detecting when the engine is started, a temperature detection means for detecting the engine temperature, and an exhaust passage. an exhaust gas purifying means for purifying exhaust gas by means of a combustion engine; a secondary air supply means for supplying secondary air upstream of the exhaust gas purifying device when the start detecting means detects a start; and a secondary air supply means for supplying secondary air upstream of the exhaust gas purifying device; a signal detecting means for detecting a signal representing the secondary air; and a control means for controlling the total amount of secondary air supplied by the total secondary air supply means at the time of cold start, the target value of the total amount of supply being set at the time of starting. The target value is set to a shorter initial value as the engine temperature is lower, and the target value is changed to a smaller value as the signal representing the amount of exhaust gas per unit time becomes larger.

[Function] In the present invention having the above configuration, the total amount of secondary air supplied by the secondary air supply means at the time of cold start determines the degree of temperature rise of the purifier. However, as described above, the temperature rise that causes deterioration of the purification device is dominated by the amount of secondary combustion per unit time. Therefore, the control means first sets the target initial value of the total supply amount to a shorter initial value as the engine temperature at the time of starting is lower. That is, when the engine water temperature is lower because it is estimated that there are more unburned gas components, the initial target value of the total supply amount is set smaller, thereby roughly suppressing the temperature rise of the purifier.

Next, the control means determines that a signal (for example, an engine rotation speed signal or an intake air amount signal) representing the amount of exhaust gas per unit time detected by the signal detection means, which simply represents the amount of unburned gas components, is large. From time to time, the target value of the total supply amount is revised to a smaller value. That is, the deterioration of the purifying device can be precisely prevented by twisting.

[Examples] Examples according to the present invention will be described in detail below with reference to the accompanying drawings.

<Configuration of Embodiment> FIG. 1 shows an embodiment in which the present invention is applied to a so-called reciprocating engine. In the figure, 9 is the engine cylinder, and a water temperature sensor 8 (its output signal is TEMP) is installed in the cooling water passage in this cylinder.
is provided. This water temperature sensor 8 determines whether or not the engine is being operated cold. The catalytic converter 6 is provided in the middle of the exhaust pipe 14, and a catalyst temperature sensor 17 is provided inside to monitor the internal temperature.

The secondary air is supplied so that the air pump 7 sucks purified air led from an air cleaner (not shown) and sends it into the exhaust pipe 14 upstream of the catalytic converter 6. The air pump 7 in this embodiment is, for example, a vane type air pump driven by a belt from the crankshaft of the engine.
The supply of secondary air to the exhaust pipe 14 is controlled by an air control valve (ACV) 3.
The ACV 3 is operated by the intake negative pressure in the intake pipe 13, and is controlled to open and close by the control unit 1 via the ACV solenoid 2. When secondary air is not supplied into the exhaust pipe 14, the ACV 3 is closed by the solenoid 2, and during that time, the secondary air escapes into the relief passage 4. 18 is a fuel injection valve, and its drive signal is
I'm an INJ.

In addition, the information for controlling the secondary air includes a starting signal that means starting the engine, Q _a (output from the air flow meter 16) to know the amount of intake air in the intake system, engine speed rpm, and throttle speed. There are throttle valve opening degrees TVO (output from the throttle valve 15), etc. These signals Q _a ,
TVO is necessary because the amount of unburned gas is the air-fuel ratio,
This air-fuel ratio etc. greatly depends on the engine temperature.
determined by Q _a , TVO, and these quantities
This is because it greatly depends on the INJ, and the main purpose of this embodiment is to take these factors into account and control the secondary air so as not to damage the catalyst while oxidizing and purifying the unburned gas.

FIG. 2 shows the control in this embodiment in the control unit 1 by functional block. The inputs to control unit 1 are engine intake air amount Q _a , rotational speed rpm, and cylinder water temperature.
TEMP, throttle opening TVO. The output is INJ, which is the injection timing of the fuel injection valve 18,
Signal to solenoid 2 that controls opening and closing of ACV3
ACVS.

First, block 30 sets the basic fuel injection amount Q _a ,
Calculate based on rpm. Final fuel injection amount
INJ is determined (block 35) after the fuel increase rate is determined (block 36) by taking into account water temperature correction based on the signal TEMP, throttle opening TVO, etc. The dependence of the fuel ratio on TEMP at this time is such that the air-fuel mixture becomes rich during cold operation. The secondary air control signal ACVS is as follows. In block 32, it is determined whether the operating state is such that the secondary air supply itself is performed, and if it is in such an operating region, in block 33, it is determined how much secondary air is to be supplied and for how long. and operate solenoid 2 with signal ACVS.

FIG. 3 shows an example of the circuit of the control unit 1. 40 is a CPU such as a microcomputer
It is. 41 is a 1/0 boat to which an engine start signal is input. 42 is an interrupt control;
Input the rpm and find out the engine speed from the number of interrupts per unit time. 43 is an AD converter, into which the aforementioned TVO, Q _a , TEMP, etc. are input. 44 stores a control procedure program as shown in FIG.
It is a ROM. The driver 46 is an INJ that drives the fuel injection valve 18 and a signal that drives the solenoid 2.
Activate ACVS. FIG. 4A is a block diagram of a ROM 44 that stores control parameters necessary for control to be described later. FIG. 4B shows the configuration of the RAM 45, in which an area is secured to store an ACVS flag for controlling the output of the signal ACVS.

<Control procedure of the embodiment> FIG. 5 is a flowchart of control according to the embodiment. First, in step S1, the operating state of the engine is read. Information regarding these operating conditions includes, for example, the engine speed rpm and throttle opening as mentioned above.
TVO and intake air volume Q _a . In step S2, a basic fuel injection amount Te ₂ is first calculated based on this information. Here, Te ₂ is calculated according to the following formula.

Te ₂ =k·Q _a /rpm (k is a predetermined coefficient) This Te ₂ may be stored in advance as a map in the ROM 44 as shown in FIG.

Next, in step S3, the water temperature correction amount C _T previously stored in the ROM 44 is set in accordance with the characteristics as shown in FIG. 6A, for example. This characteristic is
It's like the lower the TEMP, the bigger it is. This is because the air-fuel mixture needs to be rich when the temperature is low. In step S4, various correction amounts _CZ are set.
These various corrections are made because it is necessary to enrich the air-fuel mixture under certain operating conditions, such as during light load and idling. Further, in this step S4, as shown in Japanese Patent Application Laid-open No. 58-27844, control is also performed to increase the amount of fuel after startup in accordance with the engine water temperature, and to reduce this increase as time passes.

In step S5, TEMP reaches a predetermined temperature (constant a)
Check the following. The flow is divided into two depending on whether TEMP is smaller than the constant a or not. If step S5
If it is determined that TEMP is lower than a, it is checked in step S6 whether or not the engine has just been started. This determination may be made by determining that the period immediately after starting is within a certain short period of time after the starting signal is input to the control unit 1. If the engine has just been started, the secondary air timer T is set to the initial value X in step S7. Once the secondary air timer T is set, it will no longer be activated immediately after starting, so
After that, the secondary air timer T counts down by the subtraction number y in step S11.

By the way, the value X set in the secondary air timer T becomes shorter as the water temperature becomes lower, as shown in FIG. 6B. That is, the lower the engine temperature, the shorter the secondary air supply time. This is because, as mentioned above, the lower the water temperature, the richer the mixture, and the more unburned gas components there are, the higher the catalyst temperature may rise. Therefore, the secondary air supply time is shortened. This prevents the catalyst temperature from reaching dangerous temperatures.

In step S8, the timeout of the secondary air timer T is checked. If the timeout has not occurred, it is determined in step S9 whether or not the system is in the secondary air supply region based on the signals TVO and rpm. This judgment is the 6th
The area shown in Figure C (this is determined by the secondary air supply area map in the ROM 44 in Figure 4)
This is to check whether the engine is running inside. This is because unburned gas should theoretically be generated in such a region.

After determining whether it is in the secondary air supply region in step S9, the timer T is subtracted regardless of the result of that determination (step S11), but before that, in step S10, the subtraction value y itself is Calculation is performed (step S10). This is because in the control shown in Fig. 5, overheating of the catalytic converter 6 can basically be prevented by making the set time X of the secondary air timer T variable according to TEMP, but the In order to more accurately prevent overheating in areas where there is a large amount of exhaust gas due to the routine, the timeout period is made variable according to the amount of exhaust gas to achieve precise control. That is,
In step S10, the subtraction number y is determined in consideration of Q _a and rpm. At this time, b and c are predetermined coefficients stored in the ROM 44, and when Q _a × rpm is large, the amount of exhaust gas also increases, so in such a case, the secondary air supply time should be made shorter. b and c (increasing the subtrahend y) are set in advance.
In step S11, timer T is subtracted, and step
In S12, it is checked whether the determination in step S9 was in the secondary air supply area (air injection area). If it is such an area, the ACVS flag in the RAM 45 is turned ON in step S13.
If not in the secondary air supply area, step
Turn off the ACVS flag in S14. Regardless of whether it is in the secondary air supply area or not, step S10
The reason why the subtractor y is made to be an amount according to the intake air amount Q _a and the rotation speed rpm is that there is a possibility that there is a lot of unburned gas even if it is not in the secondary air supply area if the timer T has not timed out. This is to prevent the temperature of the purification device from rising due to this.

In step S23, the final fuel injection amount INJ is calculated based on INJ=Te ₂ ×C _T ×C _Z , and in step S24
Driver 4 based on the INJ, ACVS flags in
6 is driven. When this ACVS flag is ON, when the control value is output in step S24, the solenoid 2 is energized via the driver 46.

The above steps are repeated until it is determined in step S8 that timer T has timed out. Once timer T times out, step S5
Solenoid 2 unless it is determined that TEMP≧a.
remains off. This is because the set time X of timer T is set to the maximum time that will significantly reduce the unburned gas components and not destroy the catalytic converter, so even if solenoid 2 is turned off, the exhaust gas purification will be improved. This is because there is no problem.

When TEMP≧a is determined in step S5,
In cases where the engine is already warm before the engine starts and TEMP≧a occurs before timer T times out after the engine starts.
This is when the engine is in a steady temperature state in the normal engine operating range. At times like this, the engine is running at a steady speed and there are few unburned gas components, so the overheating of the catalytic converter is not much of a problem, so secondary air is controlled mainly from the perspective of exhaust gas purification. TVO according to Figure 6c,
Determine whether it is in the secondary air supply area based on rpm,
Based on that judgment (step S21), the step
The flag is turned ON or OFF in S22 or step S11.

<Effects of Example>: After starting the engine when the engine is cold, the lower the temperature of the engine cooling water, the shorter the secondary air supply time to prevent overheating of the catalytic converter, catalyst deterioration, etc. At the same time, it also achieves exhaust gas purification.

:The secondary air supply time after starting the engine is determined by considering the engine speed and intake air amount in addition to the water temperature. This is because when these are large, the amount of exhaust gas increases and the absolute amount of unburned gas components also increases, and the catalyst temperature also rises rapidly, so it is necessary to shorten the secondary air supply time.
By doing so, the catalytic converter can be protected more precisely.

: For the same reason as above, the secondary air supply is controlled during high loads to purify exhaust gas, even when the engine is not starting.

<Other Examples> The present invention can be modified and applied to the following cases.

: When the engine is applied to a rotary engine instead of a reciprocating engine, : When a thermal reactor is used as an exhaust gas purification device, : When secondary air is introduced not by an air pump, but by air suction using a reed valve that uses exhaust pulsation. When this method is applied, : When an electromagnetic solenoid is applied instead of an air control valve, : The secondary air supply amount is determined not by the length of the supply time, but by the
When controlling the supply amount per unit time: When applying to a carburetor engine instead of a fuel injection engine; When detecting engine temperature using engine oil instead of cooling water temperature, etc. . The amount of secondary air supplied per unit time is
For example, the map may be set in advance so that rpm x load x timer T (fixed) x supply amount per unit time = constant.

[Effects of the Invention] As explained above, according to the secondary air supply device of the present invention, it is possible to purify the exhaust gas at the time of cold start of the engine, and at the same time precisely prevent the temperature of the exhaust gas purification device from rising excessively. becomes possible. In other words, the total amount of secondary air supplied by the secondary air supply means at the time of cold start determines the degree of temperature rise of the purifier, but as mentioned above, the temperature rise that causes deterioration of the purifier becomes a problem. Since it is controlled by the amount of secondary combustion per unit time, the control means sets the target initial value of the total supply amount to a shorter initial value as the engine temperature at startup is lower. That is, when the engine water temperature is lower because it is estimated that there are more unburned gas components, the initial target value of the total supply amount is set smaller, thereby roughly suppressing the temperature rise of the purifier.

Furthermore, this control means is capable of detecting a large signal (for example, an engine rotation speed signal or an intake air amount signal) indicating the amount of exhaust gas per unit time by the signal detection means, which directly represents the amount of unburned gas components. As the time increases, the target value of the total supply amount is revised smaller. That is, the deterioration of the purifying device can be prevented more accurately and reliably.

According to a preferred embodiment of the present invention, when the target value of the total supply amount of secondary air is expressed as the product of the supply amount per unit time and the variable total supply time, this total supply time is The lower the engine temperature is, the shorter the initial value is set, and the larger the signal representing the amount of exhaust gas per unit time (e.g. engine speed signal or intake air amount signal) is, the shorter the total supply time is set. Be changed.
That is, the total supply amount of secondary air at the time of cold start of the engine is controlled by changing the total supply time in accordance with the amount of exhaust gas.

According to a preferred embodiment of the present invention, when the target value of the total supply amount of secondary air is expressed as the product of the supply amount per unit time and a constant total supply time,
The initial value of the supply amount per unit time is set to a smaller value as the engine temperature at startup is lower.
Further, as the signal representing the amount of exhaust gas per unit time becomes larger, the amount of gas supplied per unit time is controlled to be changed in a smaller direction. That is, the supply amount of secondary air during a cold start is controlled by changing the supply amount of secondary air per unit time in accordance with the amount of exhaust gas.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a secondary air supply control device according to an embodiment of the present invention, Fig. 2 is a functional block diagram in the control unit, Fig. 3 is a circuit diagram as an example of the control unit, and Fig. 4A. ,B is
FIG. 5 is a block diagram of the ROM 44 and RAM 45, respectively. FIG. 5 is a flow chart of the control procedure of the embodiment.
Figure A is the characteristic of the water correction coefficient, Figure 6B is the timer value T
FIG. 6C is a diagram of the secondary air supply area map. In the figure, 1... Control unit, 2... Solenoid, 3... Air control valve (ACV), 4... Relief passage, 6... Catalytic converter, 7... Air pump, 8... Water temperature sensor, 9... ...Cylinder, 10...Exhaust valve, 11...
Spark plug, 12...Intake valve, 13...Intake pipe,
14...Exhaust pipe, 15...Throttle valve, 1
6...Air flow meter, 17...Catalyst temperature sensor, 18...Fuel injection valve.

Claims (1)

[Scope of Claims] 1. Start detecting means for detecting when the engine is started; Temperature detecting means for detecting engine temperature; Exhaust gas purifying means interposed in the exhaust passage to purify exhaust gas; and the start detecting means. secondary air supply means for supplying secondary air upstream of the exhaust gas purification device when the means detects startup; signal detection means for detecting a signal representing the amount of exhaust gas per unit time; and the secondary air supply means. A control means for controlling the total supply amount of secondary air at the time of cold start by the means, the target value of the total supply amount being set to an initial value that is shorter as the engine temperature at the time of start is lower,
A secondary air supply device for an engine, comprising: control means for changing and controlling the target value in a direction smaller as the signal representing the amount of exhaust gas per unit time becomes larger. 2. The supply amount per unit time by the secondary air supply means is constant, the target value of the total supply amount is expressed as the product of the supply amount per unit time and the variable total supply time, and the control The means sets the total supply time to a shorter initial value as the engine temperature at startup is lower, and changes the total supply time to a shorter value as the signal representing the amount of exhaust gas per unit time increases. The first claim characterized in
A secondary air supply device for the engine described in paragraph. 3. The secondary air supply device for an engine according to claim 1, wherein the signal representing the amount of exhaust gas per unit time is an engine rotational speed. 4. The secondary air supply device for an engine according to claim 1, wherein the signal representing the amount of exhaust gas per unit time is the amount of intake air per unit time. 5. The supply amount per unit time by the secondary air supply means is variable, and the target value of the total supply amount is:
It is expressed as the product of the supply amount per unit time and a constant total supply time, and the control means sets the initial value of the supply amount per unit time to a smaller value as the engine temperature at startup is lower. At the same time, as the signal representing the amount of exhaust gas per unit time becomes larger, the supply amount per unit time is changed in a smaller direction. Next air supply device.