JP2006207413A - Secondary air supply device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To quickly activate an exhaust purifying catalyst 12 immediately after the start, by efficiently supplying secondary air to an exhaust passage 11 in supplying the secondary air to the exhaust passage 11 and to thereby increase an exhaust temperature of an inlet of a catalyst 12. <P>SOLUTION: A discharge side (an outlet side of a shutoff valve 14) of an air pump 13 is branched into two secondary air supply passages 16, 17 through a distributing valve 15. A secondary air supply port 16a of one secondary air supply passage 16 is opened to a relatively upstream (exhaust port 18) of the exhaust passage 11. A secondary air supply port 17a of the other secondary air supply passage 17 is opened to relatively downstream of the exhaust passage 11. The secondary air supply parts 16a, 17a to the exhaust passage 11 are disposed to a plurality of portions in an exhaust flow direction, and the secondary air is supplied from the plurality of portions at the same time. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a secondary air supply device for an internal combustion engine that supplies secondary air to an exhaust passage in order to increase the exhaust temperature in order to quickly activate an exhaust purification catalyst immediately after startup.

In Patent Document 1, in order to promote the oxidation reaction in the exhaust system, when supplying secondary air to the exhaust passage upstream of the catalyst, two secondary air supply ports to the exhaust passage are provided in the exhaust flow direction. Secondary air is selectively supplied from either of them. This is because when air-fuel ratio feedback control is performed by the oxygen sensor, secondary air is supplied from the secondary air supply port downstream of the oxygen sensor to prevent erroneous recognition of the air-fuel ratio. This is because when the feedback control is not performed, the secondary air is supplied from the secondary air supply port upstream of the oxygen sensor to promote the oxidation reaction at a higher exhaust temperature position.
Japanese Utility Model Publication No. 5-007920

However, in the technique described in Patent Document 1, although secondary air supply ports to the exhaust passage are provided in the exhaust flow direction, secondary air is selectively supplied from any one of the secondary air supply ports. Therefore, like the conventional ones, since the entire amount of secondary air is supplied from one secondary air supply port, there are the following problems.
When the entire amount of secondary air is supplied from one secondary air supply port, it burns at a short downstream from the supply position, and the exhaust temperature reaches a peak. Therefore, the ambient temperature (for example, the temperature of the inner wall of the exhaust passage) Since the temperature difference is large and the amount of heat released is proportional to the temperature difference, the exhaust temperature subsequently decreases greatly, and the exhaust temperature at the catalyst inlet decreases.

  In view of such a situation, an object of the present invention is to efficiently supply secondary air to increase the exhaust temperature of the catalyst inlet.

  Therefore, in the present invention, the secondary air supply ports to the exhaust passage are provided at a plurality of locations in the exhaust flow direction, and the secondary air is supplied simultaneously from the plurality of secondary air supply ports.

  According to the present invention, the secondary air is divided and supplied from each of the plurality of locations in the exhaust flow direction by the secondary air supply ports, so that the combustion is continuously performed and the increase in the heat radiation amount is suppressed, and the exhaust temperature is reduced. The decrease can be prevented, and the exhaust temperature at the catalyst inlet can be increased.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is an engine system diagram showing an embodiment of the present invention.
In the intake passage 2 of the engine 1, an electrically controlled throttle valve 4 that is positioned on the inlet side of the intake manifold 3 and controls the amount of intake air is installed. The opening degree of the electric throttle valve 4 is controlled by a step motor or the like that is operated by a signal from an engine control unit (hereinafter referred to as ECU) 20. However, a mechanical throttle valve connected to the accelerator pedal by a wire or the like may be used.

A fuel injection valve 6 for injecting fuel into the intake port 5 of each cylinder is attached to the branch portion on the outlet side of the intake manifold 3. The fuel injection valve 6 is opened by energizing the solenoid for a time determined by the pulse width based on the injection pulse signal output from the ECU 20 in synchronization with the engine rotation, and injects the fuel adjusted to a predetermined pressure. .
The air controlled by the electric throttle valve 4 and the fuel injected from the fuel injection valve 6 are sucked into the combustion chamber 8 of the engine 1 when the intake valve 7 is opened.

The air and fuel sucked into the combustion chamber 8 form an air-fuel mixture, and are ignited and burned by the spark plug 9 at the ignition timing controlled by the ECU 20. Exhaust gas after combustion is discharged to the exhaust passage 11 via the exhaust valve 10. An exhaust purification catalyst 12 is provided at a collecting portion of the exhaust passage 11.
Here, in order to supply secondary air to the exhaust passage 11 upstream of the exhaust purification catalyst 12, an electric air pump 13 is provided, and a shutoff valve 14 is provided on the discharge side thereof. The outlet side of the shut-off valve 14 is branched into two secondary air supply passages 16 and 17 via a distribution valve 15 capable of adjusting the flow rate ratio.

One secondary air supply passage 16 supplies secondary air to the relatively upstream side of the exhaust passage 11, branches from the gallery portion on the upstream side, and is formed for each cylinder in the cylinder head. A secondary air supply port (injection port) 16 a on the outlet side of the secondary air supply passage 16 of each cylinder opens to the inner wall of the exhaust port 18 of each cylinder in the cylinder head and faces the umbrella portion of the exhaust valve 10. Yes.
The other secondary air supply passage 17 supplies secondary air to the relatively downstream side of the exhaust passage 11, and the exhaust gas is exhausted at a position after the exhaust passages of the cylinders are gathered (collection portion of the exhaust manifold). A secondary air supply port (jet port) 17 a on the outlet side projects into a pipe shape in the passage 11 and opens at the center of the exhaust passage 11.

  The ECU 20 includes an accelerator opening APO detected by an accelerator pedal sensor 21, an engine speed Ne detected by a crank angle sensor 22, an intake air amount Qa detected by an air flow meter 23, and an engine detected by a water temperature sensor 24. The coolant temperature Tw, the exhaust temperature Te detected by the exhaust temperature sensor 25, the catalyst temperature Tc detected by the catalyst temperature sensor 26, and the like are input as necessary. In addition, although not shown, a signal is also input from an engine key switch having an ignition switch and a start switch.

  The ECU 20 controls the opening degree of the electric throttle valve 4, the fuel injection timing and fuel injection amount of the fuel injection valve 6, the ignition timing of the spark plug 9, and the like based on the engine operating conditions detected from these input signals. . Further, the operation of the air pump 13, the shutoff valve 14, and the distribution valve 15 is controlled. The shut-off valve 14 is opened when the air pump 13 is turned on and closed when the air pump 13 is turned off, and can be omitted when the air pump 13 itself has a shut-off function when turned off. B in FIG. 1 indicates a battery serving as a power source for the air pump 13.

Next, control for early activation (warming-up) of the exhaust purification catalyst 12 immediately after startup will be described with reference to the flowchart of FIG.
In S1, it is determined whether there is a catalyst temperature increase request immediately after startup or the like. Specifically, the catalyst temperature sensor 26 detects the catalyst temperature Tc and determines whether it is lower than a predetermined activation temperature. The activity / inactivity may be determined by predicting the catalyst temperature from the operating conditions. When there is a catalyst temperature increase request immediately after startup, that is, when the catalyst 12 is inactive, the process proceeds to S2 to S8.

In S2, the engine side air-fuel ratio is set to be rich. This is because the exhaust temperature is increased by discharging a large amount of unburned fuel into the exhaust passage and reburning it by supplying secondary air, and the air-fuel ratio is enriched in a range that does not cause rich misfire.
In S3, the driving power Pp of the air pump 13 is calculated. This is to adjust the total amount of secondary air (upstream air amount + downstream air amount) to the exhaust passage so that the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst 12 becomes stoichiometric or slightly lean. In addition, the driving power Pp of the air pump 13 is set.

  In S4, the exhaust temperature Te detected by the exhaust temperature sensor 25 is read. When the exhaust gas temperature Te is detected by the exhaust gas temperature sensor 25, the exhaust gas temperature Te is detected immediately upstream of the catalyst 12, and between the upstream secondary air supply port 16 a and the downstream secondary air supply port 17 a, or the exhaust port 18. You may detect by. When the exhaust temperature sensor is not provided, the engine coolant temperature Tw detected by the water temperature sensor 24 is read.

  In S5, with reference to a table as shown in FIG. 3, the supply air amount ratio K is calculated based on the exhaust temperature Te (or the cooling water temperature Tw). For example, K = upstream air amount / (upstream air amount + downstream air amount). In this case, the supply air amount ratio of the upstream secondary air supply port 16a is K, and the supply air amount ratio of the downstream secondary air supply port 17a is 1-K. The range in which unburned fuel remains in the exhaust gas even when the secondary air oxygen from the upstream secondary air supply port 16a is completely consumed upstream of the downstream secondary air supply port 17a position. The supply air amount ratio is determined in the inside.

Here, when the exhaust temperature Te is low, the ratio of the upstream air amount is increased, and the ratio of the downstream air amount is decreased. On the contrary, when the exhaust temperature Te is high, the ratio of the upstream air amount is decreased and the ratio of the downstream air amount is increased.
The same applies to the cooling water temperature Tw. When the cooling water temperature Tw is low, the ratio of the upstream air amount is increased and the ratio of the downstream air amount is decreased. On the contrary, when the cooling water temperature Tw is high, the ratio of the upstream air amount is decreased and the ratio of the downstream air amount is increased.

In S6, the shutoff valve 14 is opened.
In S7, the distribution valve 15 is controlled based on the supply air amount ratio K calculated in S5.
In S8, drive control of the air pump 13 is performed based on the drive power Pp calculated in S3.
If it is determined in S1 that there is no catalyst temperature increase request, that is, if the catalyst 12 has been warmed up, the process proceeds to S9 to S12.

In S9, the air-fuel ratio on the engine side is returned to the normal setting.
In S10, the shutoff valve 14 is closed. In S11, the distribution valve 15 is fixed at the initial position. The initial position is a position where K = 0% or K = 100%. K = 0% is the upstream side closed position, and K = 100% is the downstream side closed position. By setting either, the secondary air supply passages 16 and 17 remain in communication with each other, and an exhaust flow is generated. The distribution valve 15 can be prevented from being exposed to high-temperature exhaust gas. In S12, the air pump 13 is stopped.

According to the present embodiment, the secondary air supply ports to the exhaust passage are provided at a plurality of locations separated in the exhaust flow direction, and the secondary air is supplied from the plurality of secondary air supply ports 16a and 17a at the same time. The increase in the amount of heat release can be suppressed, the exhaust temperature can be prevented from decreasing, and the exhaust temperature at the catalyst inlet can be increased. The reason will be described below.
4 (A) and 4 (B) both show the change in the exhaust temperature in the exhaust passage, where the horizontal axis is the position in the exhaust flow direction from the engine to the catalyst (distance from the exhaust valve) and the vertical axis is the exhaust temperature. It is shown.

  In FIG. 4A, the characteristic when there is no secondary air is indicated by a dotted line, and the characteristic when secondary air is supplied from one location (position a) relatively upstream of the exhaust passage is indicated by a solid line. When the total amount of secondary air is supplied from one location (a position) relatively upstream of the exhaust passage, the exhaust temperature rise effect can be obtained as compared with the case without secondary air, but slightly downstream from the supply position. After the exhaust gas temperature reaches a peak on the side, the temperature suddenly decreases, indicating that the unburnt fuel is combusted by the catalyst at a temperature T1 that can be combusted.

  FIG. 4B shows the characteristics when secondary air is divided and supplied relatively upstream (a position) and relatively downstream (b position) of the exhaust passage as in the present invention. It shows that a decrease in exhaust temperature at the inlet can be suppressed. If the amount of unburned fuel is the same and the total amount of secondary air is the same, the calorific value is theoretically the same, so the characteristic of FIG. This is because the amount of heat radiation is reduced.

That is, as shown in FIG. 4 (A), when the entire amount of secondary air is supplied from one secondary air supply port, it burns all at once downstream from the supply position, and the exhaust temperature reaches a peak. Since the temperature difference from the temperature (for example, the temperature of the inner wall of the exhaust passage) becomes large and the heat radiation amount is proportional to the temperature difference, the exhaust temperature subsequently decreases greatly, and the exhaust temperature at the catalyst inlet decreases.
On the other hand, as shown in FIG. 4B, when the secondary air is divided and supplied from the two secondary air supply ports, the secondary air is first supplied at the position a on the upstream side. Although it burns and this raises the exhaust temperature, since the temperature difference from the ambient temperature is small, the amount of heat release can be suppressed, and the subsequent decrease in the exhaust temperature can be suppressed. Next, the secondary air is supplied at the position b on the downstream side and combusted, so that the exhaust temperature rises again. In this case, the amount of heat released can also be suppressed, and the subsequent decrease in exhaust temperature can be suppressed. The exhaust temperature at can be set to a temperature T1 or higher at which the unburned fuel can be combusted. In other words, a flat exhaust temperature with a suppressed peak can be realized, and high temperature exhaust gas can be supplied to the catalyst.

In addition, in the case of a configuration in which secondary air is supplied simultaneously from a plurality of locations in the exhaust flow direction, there is a possibility that the mixing of exhaust gas and secondary air will be good, combustion efficiency will be improved, and the heat generation amount itself can be increased. is there. This is because in the case of the configuration in which the secondary air is supplied from one place, the mixing of the exhaust gas and the secondary air may not be successful, and the combustion efficiency may be reduced.
Further, in the case of a configuration in which secondary air is supplied simultaneously from a plurality of locations in the exhaust flow direction, the air supply amount at one location can be reduced, so that the diameters of the secondary air supply ports 16a and 17a can be reduced. Thus, the influence on the output performance can be reduced. The secondary air supply port on the upstream side, particularly the secondary air supply port 16a that opens to the exhaust port 18, is connected to the exhaust passage (exhaust port 18) of each cylinder to attenuate exhaust pulsation when the diameter is large. However, this may be a factor that degrades the output performance, but this can be avoided. Therefore, as shown in FIG. 1, it is desirable that the upstream secondary air supply port 16a has a smaller diameter than the downstream secondary air supply port 17a.

In addition, in the case of a configuration in which secondary air is supplied simultaneously from a plurality of locations in the exhaust flow direction, a large amount of air can be supplied without degrading the output performance, and the air-fuel ratio setting on the engine side is strong within a range that does not cause rich misfire It becomes possible to set to rich, and it becomes possible to increase the exhaust temperature by increasing the amount of unburned fuel discharged to the exhaust passage.
In addition, according to the present embodiment, by providing the distribution valve 15 that adjusts the supply air amount ratio by the secondary air supply ports 16a and 17a at a plurality of locations, the supply air amount ratio is optimized in accordance with the temperature conditions and the like. It becomes possible to adjust to.

Further, according to the present embodiment, the exhaust air temperature is detected, and the supply air amount ratio is adjusted accordingly, thereby adjusting the supply air amount ratio when the exhaust temperature is low or too high, An optimum temperature can be achieved.
Further, according to the present embodiment, the temperature of the cooling water is detected, and the proportion of the supply air amount is adjusted accordingly. It is possible to adjust to obtain the exhaust temperature.

Further, according to the present embodiment, the supply air amount ratio of the upstream secondary air supply port 16a is increased at a low temperature, and the supply air amount ratio of the downstream secondary air supply port 17a is increased at a high temperature. This makes it possible to achieve a flat exhaust temperature even if the exhaust temperature or the cooling water temperature changes.
Further, according to this embodiment, the secondary air supply port 16a on the upstream side is opened in the inner wall of the exhaust passage, and the secondary air supply port 17a on the downstream side is opened in the center of the exhaust passage. On the upstream side, the protrusion of the pipe-like member is eliminated to prevent exhaust resistance and the deterioration of the output performance can be prevented.On the downstream side, the influence on the output performance is reduced. The secondary air can be supplied to the central portion of the exhaust passage to improve the mixing of the exhaust gas and the secondary air, and the unburned HC reduction and the exhaust temperature increase effect can be further improved.

Next, another embodiment of the present invention will be described with reference to FIGS.
In the above-described embodiment, the secondary air supply passage 16 and the secondary air supply port 16a on the upstream side and the secondary air supply passage 17 and the secondary air supply port 17a on the downstream side are provided. As shown in the example, additional secondary air supply passages 31 and 32 and secondary air supply ports 31a and 32a may be provided so as to supply secondary air simultaneously from a larger number of locations in the exhaust flow direction.

  Further, in the above-described embodiment, the upstream secondary air supply port 16a is provided for each cylinder before the exhaust passages of the respective cylinders gather, and the downstream secondary air supply ports 17a, 31a, and 32a are Although it is provided in common for all cylinders after the exhaust passages of each cylinder are gathered, this is not restrictive. In the example of FIG. 6, an intermediate secondary air supply passage 33 and a secondary air supply port 33a are provided, and this intermediate secondary air supply port 33a is provided before the exhaust passages of the cylinders are gathered (the branch portion of the exhaust manifold). ) For each cylinder.

Engine system diagram showing one embodiment of the present invention Flow chart of control for early activation of catalyst immediately after start-up The figure which shows the relationship between exhaust temperature (or cooling water temperature) and supply air quantity ratio The figure explaining the effect of this invention Exhaust system layout showing another embodiment Exhaust system layout showing another embodiment

Explanation of symbols

1 engine
2 Intake passage
3 Intake manifold
4 Electric throttle valve
5 Intake port
6 Fuel injection valve
7 Intake valve
8 Combustion chamber
9 Spark plug
10 Exhaust valve
11 Exhaust passage
12 Exhaust gas purification catalyst
13 Electric air pump
14 Shut-off valve
15 Distributing valve
16 Secondary air supply passage
16a Secondary air supply port
17 Secondary air supply passage
17a Secondary air supply port
18 Exhaust port
20 ECU
21 Accelerator pedal sensor
22 Crank angle sensor
23 Air Flow Meter
24 Water temperature sensor
25 Exhaust temperature sensor
26 Catalyst temperature sensor
31, 32, 33 Additional secondary air supply passage
31a, 32a, 33a Additional secondary air supply port

Claims (7)

In a secondary air supply device for an internal combustion engine that supplies secondary air to an exhaust passage,
Provide secondary air supply ports to the exhaust passage at multiple locations in the exhaust flow direction,
A secondary air supply device for an internal combustion engine, wherein secondary air is supplied simultaneously from the plurality of secondary air supply ports.   2. The secondary air supply device for an internal combustion engine according to claim 1, further comprising a distribution valve that adjusts a supply air amount ratio by the secondary air supply ports at the plurality of locations.   The secondary air supply device for an internal combustion engine according to claim 2, wherein an exhaust gas temperature is detected and the supply air amount ratio is adjusted in accordance with the detected exhaust gas temperature.   3. The secondary air supply device for an internal combustion engine according to claim 2, wherein a coolant temperature is detected and the supply air amount ratio is adjusted according to the detected coolant temperature.   The ratio of the supply air quantity of the secondary air supply port on the upstream side is increased at a low temperature, and the ratio of the supply air quantity of the secondary air supply port on the downstream side is increased at a high temperature. The secondary air supply device for an internal combustion engine according to claim 4.   The upstream secondary air supply port is opened at the inner wall of the exhaust passage, and the downstream secondary air supply port is opened at the center of the exhaust passage. The secondary air supply device for an internal combustion engine according to claim 1.   The upstream secondary air supply port is provided for each cylinder before the exhaust passages of the respective cylinders are gathered, and the downstream secondary air supply port is provided for all the cylinders after the exhaust passages of the respective cylinders are gathered. The secondary air supply device for an internal combustion engine according to any one of claims 1 to 6.

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