JP2012225309A - Secondary air supply system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inhibit a back flow of exhaust to a side of a pump for supplying secondary air.SOLUTION: A system includes: the pump for discharging air; a secondary air supply pipe that connects an outlet of the pump with an exhaust passage of an internal combustion engine; a secondary air pressure detection device for detecting a pressure in the secondary air supply pipe; an exhaust pressure detection device for detecting a pressure in the exhaust passage; and a discharge amount control device for adjusting air amount discharged from the pump such that the pressure in the secondary air supply pipe detected by the secondary air pressure detection device is equal to or higher than the pressure in the exhaust passage detected by the exhaust pressure detection device.

Description

  The present invention relates to a secondary air supply system.

  A technique is known that includes a pump that supplies secondary air upstream of an exhaust purification catalyst provided in an exhaust passage of an internal combustion engine and supplies oxygen to the exhaust purification catalyst (see, for example, Patent Document 1). ).

  In such a system for supplying secondary air, a check valve is provided in the secondary air supply pipe between the pump and the exhaust passage so that the exhaust does not flow backward from the exhaust passage to the pump. For this reason, when supplying secondary air, the extra pump work for opening a check valve is needed, and when a pump is electrically driven, there exists a possibility that power consumption may increase. Further, in the case of a pump driven by a crankshaft of an internal combustion engine, it is necessary to increase the fuel supplied to the internal combustion engine in order to open the check valve. Moreover, there is a possibility that the pump generates heat and deteriorates due to an increase in work of the pump.

JP 2001-303939 A JP 2005-264879 A

  The present invention has been made in view of the above-described problems, and an object thereof is to suppress the backflow of exhaust gas to the pump side supplying the secondary air.

In order to achieve the above object, a secondary air supply system according to the present invention comprises:
A pump that discharges air;
A secondary air supply pipe connecting the outlet of the pump to the exhaust passage of the internal combustion engine;
A secondary air pressure detection device for detecting the pressure in the secondary air supply pipe;
An exhaust pressure detecting device for detecting the pressure in the exhaust passage;
The pressure of the air discharged from the pump is adjusted so that the pressure in the secondary air supply pipe detected by the secondary air pressure detection device is equal to or higher than the pressure in the exhaust passage detected by the exhaust pressure detection device. A discharge amount control device for adjusting the amount;
Is provided.

  By controlling the amount of air discharged from the pump so that the pressure in the secondary air supply pipe is equal to or higher than the pressure in the exhaust passage, the pump can be pumped from the exhaust passage without providing a check valve in the secondary air supply pipe The exhaust can be prevented from flowing backward. And since the work for opening a check valve is not required, it is possible to suppress deterioration in fuel consumption, increase in power consumption, and increase in pump load.

In the present invention, an exhaust purification catalyst is provided in the exhaust passage downstream of the location where the secondary air supply pipe is connected,
The discharge amount control device can increase the amount of air discharged from the pump when it is necessary to increase the temperature of the exhaust purification catalyst than when it is not necessary.

  When it is necessary to raise the temperature of the exhaust purification catalyst, the temperature of the exhaust purification catalyst may be lower than the activation temperature. This may be a case where the engine is operated in an operation region where the temperature of the exhaust purification catalyst decreases because the temperature of the exhaust gas discharged from the internal combustion engine is low. In such an operating region, the combustion state of the internal combustion engine becomes unstable, so that a lot of unburned fuel is contained in the exhaust gas. Such unburned fuel is purified by an exhaust purification catalyst. And since the unburnt fuel generates heat when it is oxidized, the temperature of the exhaust purification catalyst rises. However, if the amount of oxygen is insufficient, unburned fuel will not be purified, and the temperature of the exhaust purification catalyst will decrease. On the other hand, it is possible to suppress the shortage of oxygen by increasing the supply amount of secondary air. Thereby, since the emitted-heat amount can be increased, the temperature of an exhaust purification catalyst can be raised.

  On the other hand, when it is not necessary to raise the temperature of the exhaust purification catalyst, the pressure in the secondary air supply pipe only needs to be equal to or higher than the pressure in the exhaust passage, and the exhaust does not flow back in the secondary air supply pipe. There should be a pressure difference. That is, since it is not necessary to supply air to the exhaust purification catalyst, the air may be discharged to the extent that the exhaust does not flow backward.

  Thus, since the work of the pump is reduced by changing the amount of air discharged from the pump as necessary, it is possible to suppress deterioration in fuel consumption, increase in power consumption, and increase in pump load. In addition, by eliminating the check valve, the check valve is not firmly fixed due to deposit adhesion to the check valve, which is a problem when the check valve is provided, and the check valve is not sufficiently sealed. There is no accumulation of soot in the secondary air supply pipe. In addition, an effect that the responsiveness is improved by the amount not including the check valve as compared with the case including the check valve is also expected.

  ADVANTAGE OF THE INVENTION According to this invention, the backflow of the exhaust_gas | exhaustion to the pump side which supplies secondary air can be suppressed.

It is a figure which shows schematic structure of the secondary air supply system which concerns on an Example. 3 is a flowchart illustrating a control flow of the secondary air supply device according to the first embodiment. It is the figure which showed the relationship between an engine speed, a physical quantity, and the operating area | region of a pump. 6 is a flowchart illustrating a control flow of a secondary air supply device according to a second embodiment.

  Hereinafter, specific embodiments of the secondary air supply system according to the present invention will be described with reference to the drawings.

<Example 1>
FIG. 1 is a diagram illustrating a schematic configuration of a secondary air supply system according to the present embodiment. The internal combustion engine 1 shown in FIG. 1 may be a diesel engine or a gasoline engine.

An exhaust passage 2 is connected to the internal combustion engine 1. An exhaust purification catalyst 3 is provided in the middle of the exhaust passage 2. Examples of the exhaust purification catalyst 3 include an occlusion reduction type NOx catalyst, a selective reduction type NOx catalyst, a three-way catalyst, and an oxidation catalyst. The exhaust purification catalyst 3 may be a catalyst having an oxidation function or a catalyst that generates heat by supplying a reducing agent and air.

A secondary air supply device 4 is provided in the exhaust passage 2 upstream of the exhaust purification catalyst 3. The secondary air supply device 4 includes an opening 41 that opens into the exhaust passage 2, a secondary air supply pipe 42, and a pump 43. The opening 41 is formed so as to have an outer diameter smaller than the inner diameter of the exhaust passage 2 and a cylindrical shape coaxial with the central axis of the exhaust passage 2. The opening 41 is connected to the pump 43 via a secondary air supply pipe 42. The pump 43 includes an electric motor, for example, and discharges air according to the number of rotations. Air is supplied to the exhaust passage 2 by operating the pump 43 to discharge air. The pump 43 may obtain driving force from the crankshaft of the internal combustion engine 1. Further, the pump 43 may control the amount of air discharged by controlling the number of rotations, and controls the amount of air discharged by adjusting the operation time and the stop time. May be.

  The secondary air supply pipe 42 is provided with a secondary air pressure sensor 11 that detects the pressure in the secondary air supply pipe 42. An exhaust pressure sensor 12 that detects the pressure in the exhaust passage 2 is provided in the exhaust passage 2 between the opening 41 and the exhaust purification catalyst 3. An exhaust temperature sensor 13 for detecting the temperature of the exhaust gas flowing through the exhaust passage 2 is attached to the exhaust passage 2 downstream of the exhaust purification catalyst 3. Based on the output signal of the exhaust temperature sensor 13, the temperature of the exhaust purification catalyst 3 is detected. In this embodiment, the secondary air pressure sensor 11 corresponds to the secondary air pressure detection device in the present invention. In this embodiment, the exhaust pressure sensor 12 corresponds to the exhaust pressure detection device in the present invention.

  The internal combustion engine 1 configured as described above is provided with an ECU 10 that is an electronic control unit for controlling the internal combustion engine 1. The ECU 10 is a unit that controls the operation state of the internal combustion engine 1 in accordance with the operation conditions of the internal combustion engine 1 and the request of the driver.

  The ECU 10 is connected to the sensor via an electric wiring, and an output signal of the sensor is input to the ECU 10. On the other hand, a pump 43 is connected to the ECU 10 via electrical wiring, and the pump 43 is controlled by the ECU 10.

  In this embodiment, the ECU 10 controls the pump 43 so that the pressure P1 in the secondary air supply pipe 42 is equal to or higher than the pressure P2 in the exhaust passage 2. That is, the pressure detected by the secondary air pressure sensor 11 is compared with the pressure detected by the exhaust pressure sensor 12, and the pressure detected by the secondary air pressure sensor 11 is detected by the exhaust pressure sensor 12. The pump 43 is controlled so as to be equal to or higher than the pressure to be applied.

  For example, if the pressure P1 in the secondary air supply pipe 42 is lower than the pressure P2 in the exhaust passage 2, the amount of air discharged from the pump 43 is increased or the pump 43 is operated to supply the secondary air. If the pressure P1 in the pipe 42 is equal to or higher than the pressure P2 in the exhaust passage 2, the amount of air discharged from the pump 43 is reduced or the pump 43 is stopped.

  FIG. 2 is a flowchart showing a control flow of the secondary air supply device 4 according to the present embodiment. This routine is repeatedly executed by the ECU 10 every predetermined time. In the present embodiment, the ECU 10 that processes the flow shown in FIG. 2 corresponds to the discharge amount control device according to the present invention.

  In step S101, it is determined whether or not the pressure P1 in the secondary air supply pipe 42 is equal to or higher than the pressure P2 in the exhaust passage 2. That is, it is determined whether or not the exhaust does not flow backward in the secondary air supply pipe 42.

If a positive determination is made in step S101, the process proceeds to step S102. In step S102, the pump 43 is stopped. In this step, the discharge amount of air from the pump 43 may be decreased. That is, since the exhaust does not flow backward in the secondary air supply pipe 42, the work of the pump 43 is reduced by stopping the pump 43 or reducing the discharge amount of air.

  On the other hand, if a negative determination is made in step S101, the process proceeds to step S103. In step S103, the pump 43 is operated. In this step, the amount of air discharged from the pump 43 may be increased. That is, since there is a possibility that the exhaust gas flows backward in the secondary air supply pipe 42, the air is discharged from the pump 43 so that the exhaust gas does not flow backward.

  In this way, by maintaining the pressure P1 in the secondary air supply pipe 42 at or above the pressure P2 in the exhaust passage 2, it is possible to suppress the backflow of exhaust gas through the secondary air supply pipe 42. Thereby, since a check valve can be abolished, fuel consumption can be improved. In addition, power consumption can be reduced. Furthermore, it can suppress that the pump 43 deteriorates.

  In the present embodiment, the secondary air pressure sensor 11 and the exhaust pressure sensor 12 are provided, but instead, the difference between the pressure in the secondary air supply pipe 42 and the pressure in the exhaust passage 2 is provided. You may provide the differential pressure sensor which detects this. Such a differential pressure sensor can also compare the pressure P1 in the secondary air supply pipe 42 with the pressure P2 in the exhaust passage 2, so that the pressure P1 in the secondary air supply pipe 42 is exhausted. The pump 43 can be controlled so as to be equal to or higher than the pressure P2 in the passage 2.

  In the present embodiment, the pump 43 is controlled so that the pressure P1 in the secondary air supply pipe 42 becomes equal to or higher than the pressure P2 in the exhaust passage 2, but instead, the secondary air supply You may control the pump 43 so that the pressure P1 in the pipe | tube 42 may become larger than zero. Further, the pump 43 may be controlled so that the exhaust does not flow backward in the secondary air supply pipe 42. Here, it can be determined whether or not the exhaust gas flows backward in the secondary air supply pipe 42 based on the exhaust gas flow rate, the exhaust gas temperature, the back pressure, and the like. Further, the pump 43 can be controlled using a map obtained in advance through experiments or the like.

<Example 2>
In the present embodiment, the pump 43 is operated while suppressing deterioration of fuel consumption. Since other devices are the same as those of the first embodiment, the description thereof is omitted.

  In this embodiment, when it is not necessary to raise the temperature of the exhaust purification catalyst 3, the minimum amount of air is discharged from the pump 43 so that the exhaust does not flow backward in the secondary air supply pipe. That is, when it is not necessary to supply air to the exhaust purification catalyst 3, the discharge amount of air from the pump 43 is limited. If the exhaust does not flow backward in the secondary air supply pipe 42 even if the pump 43 is stopped, the pump 43 may be stopped.

For example, engine speed NE, engine torque TRQ, fuel injection amount Q, intake air amount Ga, exhaust flow rate Gex (= Ga + Q), accelerator opening ACCP, exhaust pressure P6, change in accelerator opening per unit time (= The pump 43 is controlled using a physical quantity correlated with the exhaust pressure, such as ACCP / sec. The relationship between these physical quantities and the operating state of the pump 43 may be obtained in advance through experiments or the like and mapped. The engine speed NE can be detected by providing a crank position sensor that outputs a signal each time the crankshaft of the internal combustion engine 1 rotates by a predetermined angle. The engine torque TRQ can be calculated based on the fuel injection amount Q or the intake air amount Ga, and the accelerator opening ACCP. As the fuel injection amount Q, a command value calculated by the ECU 10 can be used. The intake air amount Ga can be detected by providing an air flow meter for detecting the flow rate of intake air in the intake passage. The exhaust gas flow rate Gex can be calculated by adding the intake air amount Ga and the fuel injection amount Q. The accelerator opening ACCP can be detected by providing an accelerator opening sensor that detects the opening of the accelerator pedal. The exhaust pressure P6 may be a detection value of the exhaust pressure sensor 12.

  Further, when the amount of unburned fuel (for example, HC) discharged from the internal combustion engine 1 is large and the exhaust purification catalyst 3 is in an active state, the pump 43 may be operated. As a result, unburned fuel can be purified by the exhaust purification catalyst 3, and the activity of the exhaust purification catalyst 3 can be maintained. Whether or not unburned fuel is discharged can be determined based on the operating state of the internal combustion engine 1. Further, whether or not the exhaust purification catalyst 3 is in an active state can be determined by the exhaust temperature sensor 13.

  FIG. 3 is a diagram showing the relationship among the engine speed, the physical quantity, and the operating region of the pump 43. The horizontal axis is the engine speed NE, and the vertical axis is the engine torque TRQ, or the fuel injection amount Q, the intake air amount Ga, the exhaust flow rate Gex, the accelerator opening ACCP, and the exhaust pressure P6.

  A region where the pump 43 is operated is indicated by “actuation”, and a region where the pump 43 is stopped is indicated by “stop”. A region indicated by “operation” in the upper right of FIG. 3 is an operation region where the physical quantity and the engine speed are large, and is an operation region where high rotation and load are high. This region is a region where the pressure of the exhaust becomes relatively high, and for this reason, the exhaust may flow backward through the secondary air supply pipe 42. Therefore, the pump 43 is operated so that the pressure P1 in the secondary air supply pipe 42 becomes equal to or higher than the pressure P2 in the exhaust passage 2.

  Further, in the “stop” region of FIG. 3, since the exhaust pressure is relatively low, there is no possibility that exhaust flows backward through the secondary air supply pipe 42, and unburned fuel may be discharged from the internal combustion engine 1. There is no area. This region is an operation region of a medium rotation and middle load. In this region, the work of the pump 43 can be reduced by stopping the pump 43. The pump 43 may be operated so that the pressure P1 in the secondary air supply pipe 42 is equal to or higher than the pressure P2 in the exhaust passage 2.

  Further, in the region indicated by “actuation” in the lower left of FIG. 3, there is no possibility that the exhaust gas flows backward through the secondary air supply pipe 42 because the pressure of the exhaust gas is relatively low. This is an area where the amount of emissions increases. This region is an operation region of low rotation and low load, and is a region where the temperature of the exhaust purification catalyst 3 may be lowered. That is, this is a region where the temperature of the exhaust purification catalyst 3 needs to be raised. In this region, since a large amount of unburned fuel is contained in the exhaust, if the exhaust purification catalyst 3 is in an active state, the temperature of the exhaust purification catalyst 3 can be increased by supplying secondary air. Therefore, in the lower left region of FIG. 3, the pump 43 is operated only when the exhaust purification catalyst 3 is in an active state. In this case, an amount of air larger than that required to make the pressure P1 in the secondary air supply pipe 42 equal to or higher than the pressure P2 in the exhaust passage 2 is required. For this reason, the discharge amount of the air from the pump 43 is made larger than other regions (regions in which the temperature of the exhaust purification catalyst 3 does not need to be raised).

  FIG. 4 is a flowchart showing a control flow of the secondary air supply device 4 according to the present embodiment. This routine is repeatedly executed by the ECU 10 every predetermined time. In the present embodiment, the ECU 10 that processes the flow shown in FIG. 4 corresponds to the discharge amount control device according to the present invention.

  In step S201, it is determined whether or not it is within the “operation” region of the map shown in FIG. That is, it is determined whether or not the exhaust gas is flowing backward in the secondary air supply pipe 42 or whether or not the unburned fuel can be oxidized by supplying the secondary air.

If an affirmative determination is made in step S201, the process proceeds to step S202. In step S202, the pump 43 is activated. In this step, the amount of air discharged from the pump 43 may be increased as compared with the case where a negative determination is made in step S201. That is, since there is a possibility that the exhaust gas flows backward in the secondary air supply pipe 42, the air is discharged from the pump 43 so that the exhaust gas does not flow backward. Alternatively, by supplying secondary air to the exhaust purification catalyst 3, air is discharged from the pump 43 so that unburned fuel is oxidized. In this step, air is discharged from the pump 43 so that the pressure P1 in the secondary air supply pipe 42 is equal to or higher than the pressure P2 in the exhaust passage 2. Thereafter, the process proceeds to step S204.

  On the other hand, if a negative determination is made in step S201, the process proceeds to step S203. In step S203, the pump 43 is stopped. In this step, the amount of air discharged from the pump 43 may be reduced as compared with the case where an affirmative determination is made in step S201. That is, since the exhaust does not flow back through the secondary air supply pipe 42, the work is reduced by stopping the pump 43 or reducing the discharge amount of air.

  In step S204, it is determined whether or not the temperature of the exhaust purification catalyst 3 needs to be increased. That is, it is determined whether or not the operation region is the “operation” in the lower left of FIG. In addition, it may be determined whether or not the temperature of the exhaust purification catalyst 3 has reached the activation temperature. If an affirmative determination is made in step S204, the process proceeds to step S205, and if a negative determination is made, this routine is terminated.

  In step S205, the amount of air discharged from the pump 43 is increased. At this time, the pump 43 is controlled so that the unburned fuel is oxidized by the exhaust purification catalyst 3. The air discharge amount at this time may be a preset fixed value, or may be increased according to the estimated amount of unburned fuel.

  In this way, when it is necessary to discharge air from the pump 43, the fuel efficiency can be improved and the power consumption can be reduced by operating the pump 43 as necessary. Can be prevented.

  In the present embodiment, when the temperature of the exhaust purification catalyst 3 needs to be raised, the secondary air may be supplied while discharging the unburned fuel from the internal combustion engine 1. Further, when the temperature of the exhaust purification catalyst 3 needs to be raised, the secondary air may be supplied while supplying the reducing agent upstream of the exhaust purification catalyst 3. Since the unburned fuel and the reducing agent supplied in this way generate heat in the exhaust purification catalyst 3 due to air, the temperature of the exhaust purification catalyst 3 can be raised.

1 Internal combustion engine 2 Exhaust passage 3 Exhaust purification catalyst 4 Secondary air supply device 10 ECU
11 Secondary Air Pressure Sensor 12 Exhaust Pressure Sensor 13 Exhaust Temperature Sensor 41 Opening 42 Secondary Air Supply Pipe 43 Pump

Claims (2)

A pump that discharges air;
A secondary air supply pipe connecting the outlet of the pump to the exhaust passage of the internal combustion engine;
A secondary air pressure detection device for detecting the pressure in the secondary air supply pipe;
An exhaust pressure detecting device for detecting the pressure in the exhaust passage;
The pressure of the air discharged from the pump is adjusted so that the pressure in the secondary air supply pipe detected by the secondary air pressure detection device is equal to or higher than the pressure in the exhaust passage detected by the exhaust pressure detection device. A discharge amount control device for adjusting the amount;
A secondary air supply system comprising: An exhaust purification catalyst is provided in the exhaust passage downstream of the location where the secondary air supply pipe is connected,
2. The secondary according to claim 1, wherein the discharge amount control device increases the amount of air discharged from the pump when it is necessary to increase the temperature of the exhaust purification catalyst than when it is not necessary. Air supply system.

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