JP2005325795A - Exhaust emission control system of engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control system of an engine by which increase in temperature of a HC-trap can be accelerated, while rapidly refluxing HC desorbed from the HC-trap to an intake system. <P>SOLUTION: The exhaust emission control system includes a bypass 15 provided parallel with an exhaust pipe 12 installed in the exhaust system of the engine 1 and the HC trap 16 provided in the bypass. An EGR passage 19 is provided in order to reflux HC desorbed from the HC-trap into the intake system. In order to detect the state of HC desorbed from the HC-trap, a vehicle-speed-sensor, an exhaust-gas temperature sensor 18, a throttle-position sensor 6, etc. are provided. Further, a variable valve timing mechanism 2A capable of changing the EGR amount within the engine, an EGR control valve 20 capable of changing the amount of external EGR refluxed from the EGR passage 19 to the intake system, and an electronic control unit (ECU)8 are provided. If HC desorption from the HC-trap is judged to be insufficient on the basis of detection signals of the vehicle-speed sensor, the exhaust-gas temperature sensor 18, the throttle-position sensor 6, etc., the ECU 8 reduces the amount of internal EGR by the variable valve timing mechanism, and at the same time increases the amount of the exterior EGR by the EGR control valve 20. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an exhaust emission control device for an engine provided with an HC trap that adsorbs unburned hydrocarbon (HC) to an exhaust system of the engine.

  An HC trap that adsorbs HC in the exhaust when the engine is cold started is placed in the exhaust system together with the three-way catalyst, and the HC trap is adsorbed on the HC trap until the three-way catalyst is activated. A technique for reducing the amount of HC emissions at the time has been known.

  Patent Documents 1 and 2 disclose a technique in which the temperature of the HC trap is increased and the HC desorbed therefrom is returned to the intake system. That is, Patent Document 1 discloses a technique for raising the temperature of the HC trap by increasing the ignition retard and the intake air amount to increase the exhaust gas temperature when desorption from the HC trap is insufficient in the bypass HC trap. Patent Document 2 discloses a technique in which a catalyst is provided upstream of the exhaust pipe and a bypass type HC trap is provided downstream thereof, and when the exhaust gas temperature exceeds the HC release temperature, HC is recirculated to the intake system via the EGR passage. Is disclosed.

JP 2002-168169 A Japanese Patent Laid-Open No. 04-17710 (FIG. 1)

  By the way, in the methods of Patent Document 1 and Patent Document 2, HC desorbed by an EGR (exhaust gas recirculation) device is sucked when HC is desorbed from the HC trap (HC desorption start temperature is about 150 ° C.). Reflux to the system.

  Therefore, when the EGR gas temperature is low or the EGR flow rate is low due to operating conditions (for example, low speed operation or low load operation region) during traveling, the temperature of the HC trap is sufficiently raised to the complete desorption temperature (about 400 ° C). Therefore, there is a problem that the HC adsorbed in the HC trap cannot be completely desorbed.

  Therefore, in Patent Document 1, the EGR is recirculated after the ignition timing is retarded to raise the exhaust gas temperature. However, since the recirculation amount of HC desorbed from the HC trap is not taken into consideration, even if the exhaust gas temperature rises, if the engine stop operation is performed while the exhaust gas temperature is being raised, There is a problem that the desorbed HC cannot be returned to the intake system and cannot be completely desorbed from the HC trap.

  On the other hand, if the internal EGR is increased without changing the ignition timing or the like, the exhaust gas temperature increases and the temperature rise of the HC trap is promoted. However, since the amount of EGR that can be supplied to the combustion chamber is limited because combustion is established, if the internal EGR is increased, the external EGR must be decreased, and as a result, desorbed from the HC trap. Since the recirculation amount of HC to the intake system decreases, there is still a problem that HC cannot be completely detached from the HC trap.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an engine exhaust purification device that can accelerate the temperature rise of an HC trap while quickly returning HC desorbed from the HC trap to an intake system.

  The invention according to claim 1 for achieving the above object provides a bypass passage in parallel with an exhaust passage provided in an exhaust system of an engine, and an HC trap is interposed in the bypass passage. An exhaust purification device for an engine having an EGR passage for returning the desorbed HC to the intake system, the desorption state detecting means for detecting a desorption state of HC from the HC trap, and an internal EGR of the engine The internal EGR adjusting means capable of changing the amount, the external EGR adjusting means capable of changing the external EGR amount recirculated from the EGR passage to the intake system, and the detachment of HC from the HC trap by the desorption state detecting means Is determined to be insufficient, the internal EGR adjustment means decreases the internal EGR amount and the external EGR adjustment means increases the external EGR amount. Characterized in that it comprises a an EGR control means for increasing the HC reduction amount of the intake by the.

  According to a second aspect of the present invention, the engine exhaust gas purification device further includes an ignition timing control means for controlling an ignition timing of the engine, and the desorption state detecting means is insufficient in desorbing HC from the HC trap. If it is determined that there is, the ignition timing control means retards the ignition timing of the engine.

The invention according to claim 3 further includes exhaust gas temperature detecting means for detecting the exhaust gas temperature,
The ignition timing control means retards the ignition timing when the exhaust gas temperature detection means has a temperature rise of the exhaust gas smaller than a predetermined value.

  The invention according to claim 4 is provided with an exhaust valve and an intake valve whose opening timing can be changed, and the internal EGR adjusting means is a variable valve timing mechanism for changing the opening timing of the intake valve of the engine. The internal EGR amount is reduced by retarding the opening timing of the intake valve.

  According to a fifth aspect of the present invention, the internal EGR adjustment means and the external EGR adjustment means are arranged so that the internal EGR amount decreased by the internal EGR adjustment means and the external EGR amount increased by the external EGR adjustment means become substantially the same amount. It is characterized by controlling.

  The invention according to claim 6 is characterized in that the control by the EGR control means is stopped when the accumulated time of the EGR control means has passed a first predetermined time.

  The invention according to claim 7 is characterized in that the control by the ignition timing control means is stopped when the integrated time of the ignition timing control means has passed a second predetermined time.

  According to the first aspect of the present invention, the amount of external EGR is reduced while maintaining an appropriate amount of EGR by reducing the amount of internal EGR while securing the amount of HC emission from the HC trap by increasing the amount of external EGR. It can be increased to increase the amount of HC reduction to the intake air, and thus early detachment of the HC trap can be achieved.

  According to the second aspect of the present invention, the HC trap can be heated quickly and the HC desorption timing can be controlled.

  According to the invention of claim 3, the temperature of the exhaust gas can be raised quickly.

  According to the invention of claim 4, fuel consumption can be improved while reducing the internal EGR amount.

  According to the invention of claim 5, the amount of HC reduction to intake air can be increased without deteriorating combustion stability.

  According to the sixth aspect of the present invention, it is prevented that the amount of HC reduction to the intake air becomes insufficient due to this control being cut off halfway.

  According to the invention of claim 7, it is prevented that the amount of HC reduction to intake air becomes insufficient due to the main control being cut off in the middle.

  Hereinafter, an exhaust emission control device for an engine according to the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic configuration diagram of an engine exhaust gas purification apparatus showing an embodiment of the present invention, and FIG. 2 is a flowchart of a control process.

  As shown in FIG. 1, an intake manifold 3, an intake pipe 4, and an air cleaner 5 are connected to an intake port (not shown but opened and closed by an intake valve device 2) of the engine 1 to constitute an intake system. Yes. This intake system is provided with an electronically controlled throttle valve 6, whose opening is detected by a throttle position sensor 7 and input to an electronic control unit (ECU, EGR control means) 8. In addition, an air flow sensor 9 such as a Karman vortex type is interposed in the intake system, and an intake air amount signal is input to an electronic control unit (ECU) 8.

  The intake valve device 2 is provided with a variable valve timing mechanism (VVT, internal EGR adjusting means) 2A for changing the opening timing of the intake valve, and the intake valve and exhaust are controlled by a control signal from an electronic control unit (ECU) 8. The overlap period of the valve can be controlled to increase or decrease.

  An exhaust manifold 11 and an exhaust pipe (exhaust passage) 12 under the floor are connected to an exhaust port (not shown but opened and closed by an exhaust valve device 10) of the engine 1 to constitute an exhaust system. A three-way catalyst 13 for purifying HC, CO, NOx in the exhaust is interposed in the middle of the exhaust pipe 12. The exhaust pipe 12 is provided with a switching valve 14 positioned downstream of the three-way catalyst 13, and a bypass passage 15 that bypasses the switching valve 14 is provided in parallel with the exhaust pipe 12. The bypass passage 15 is provided with an HC trap 16 for adsorbing HC in the exhaust gas, and a pressure regulating valve 17 is provided downstream thereof. The bypass passage 15 upstream of the HC trap 16 is provided with an exhaust temperature sensor (exhaust gas temperature detecting means) 18 for detecting the exhaust gas temperature in the passage, and the detection signal is sent to the electronic control unit (ECU) 8. Have been entered.

  The switching valve 14 is controlled to open and close according to the operating conditions of the engine 1 by an electronic control unit (ECU) 8. That is, it is closed immediately after the engine 1 is started, and then opened when the HC starts to be desorbed from the HC trap 16, or when the three-way catalyst 13 is activated, or when the load of the engine 1 exceeds a predetermined value. is there. The pressure regulating valve 17 is a relief valve that opens when the pressure in the bypass passage 15 increases, and is an on / off type valve that is opened when the switching valve 14 is closed and closed when the switching valve 14 is opened. But it ’s okay.

  The bypass passage 15 downstream of the HC trap 16 and the intake manifold 3 are connected by an EGR (exhaust gas recirculation) passage 19, and an EGR control valve (open / close controlled by an electronic control unit (ECU) 8) is connected to the EGR passage 19. External EGR adjusting means) 20 is interposed.

  The electronic control unit (ECU) 8 receives an engine speed signal from the crank angle sensor 21, an engine coolant temperature (water temperature) signal from the water temperature sensor 22, and a vehicle speed signal from a vehicle speed sensor (not shown). In addition to the input, a fuel injection signal to the injector and an ignition timing signal to the ignition coil are output.

  With this configuration, immediately after the engine 1 is started, the switching valve 14 is closed, exhaust is introduced into the bypass passage 15 and HC is adsorbed to the HC trap 16, and the pressure of the exhaust system is increased by the pressure regulating valve 17. , HC emissions from the engine 1 are suppressed.

  Thereafter, when the temperature of the HC trap 16 is raised to, for example, 150 ° C. (HC desorption start temperature), the switching valve 14 is opened, and the normal EGR control (when the engine coolant temperature becomes high and EGR can be introduced) The normal EGR opening degree map is used), and the adsorbed HC is returned to the intake system and burned.

  At this time, when the electronic control unit (ECU) 8 determines that the HC adsorbed by the HC trap 16 is not completely desorbed, the electronic control unit (ECU) 8 performs the control operation in the forced HC discharge mode as shown in the flowchart of FIG. At the same time, the control operation of the HC trap temperature raising mode is performed as necessary.

  That is, it is determined in step P1 whether the previous HC trap temperature raising mode or forced HC discharge mode is in effect. If yes, the VVT most retarded angle, that is, the valve opening timing of the intake valve by the variable valve timing mechanism 2A is determined in step P2. Is retarded to reduce the overlap period of the intake valve and the exhaust valve, and at step P3, the EGR control valve 20 is controlled by the EGR opening map at the time of the most retarded VVT (a map different from the normal time) to control the EGR. Do. Needless to say, when the exhaust valve device 10 is provided with VVT, the overlap period is reduced by advancing the closing timing of the exhaust valve. However, since retarding the valve closing timing of the exhaust valve may reduce the expansion ratio and reduce fuel consumption, it is preferable to retard the valve opening timing of the intake valve.

  As a result, the amount of exhaust gas blown back into the intake system (internal EGR amount) decreases, and the external EGR amount can be increased accordingly. That is, since the internal EGR amount has a correlation with the opening timing of the intake valve, the HC reduction amount can be increased without changing the total amount of EGR by setting the EGR opening degree according to the VVT operation state. It is. Incidentally, if the total amount of EGR changes in the increasing direction, combustion deteriorates, so the amount of decrease in internal EGR and the amount of increase in external EGR are substantially the same. At this time, since the HC trap 16 exceeds the desorption start temperature, if the external EGR amount is positively increased, the desorbed HC can be quickly returned to the intake system.

  On the other hand, if NO in step P1, it is determined in step P4 whether the low-speed driving has continued for a predetermined time based on a detection signal from the vehicle speed sensor and a timer. If yes, the process proceeds to forced HC discharge mode in step P5. Then, Step P2 and Step P3 described above are executed. On the other hand, if no, the process proceeds to Step P8 described later.

  Next, in step P6, it is determined whether or not the integrated time of the EGR opening control described above has exceeded a predetermined time. If yes, the HC trap 16 can be regarded as having been desorbed, so step P7 To cancel the forced HC discharge mode. Then, in step P8, EGR is performed by controlling the EGR control valve 20 based on the normal EGR opening degree map, and in step P9, the ignition timing of the engine 1 is changed to the normal ignition timing (= basic ignition timing + other temperature depending on the water temperature, etc.). The control operation is terminated by controlling to the correction amount.

  On the other hand, if NO in step P6 and if it is determined in step P10 that the temperature increase of the HC trap 16 is smaller than a predetermined value based on the detection signal from the exhaust temperature sensor 18, the HC trap temperature increase mode is set in step P11. In step P12, the ignition timing of the engine 1 is retarded from the normal ignition timing (ignition timing = basic ignition timing + HC trap temperature increase retard correction amount + other correction amount due to water temperature, etc.). The HC trap temperature increase correction amount at this time is changed according to the load and rotation of the engine 1 because the combustion stability (soundness) varies depending on the operating conditions.

  As a result, the temperature rise of the exhaust gas and the HC trap 16 can be promoted while suppressing the deterioration in drivability accompanying the decrease in the combustion speed, which is a concern when the temperature of the exhaust gas is raised by the above-described EGR opening degree control. Can do.

  Next, in step P13, it is determined whether or not the integration time of the above-described HC trap temperature rise control has exceeded a predetermined time. If yes, the HC trap 16 is completely heated and the HC is completely removed from the HC trap 16. Since it can be considered that the desorption temperature has been reached, the HC trap temperature raising mode is canceled in Step P14, and the process proceeds to Step P8 described above. On the other hand, if NO, the control operation is terminated and the HC trap temperature raising mode is continued as long as Step P10 is established.

  In this way, when the accumulated time of either the EGR opening degree control or the HC trap temperature rise control exceeds a predetermined value, the HC trap 16 can be regarded as completely detached, and the normal control is resumed. The accumulated time of EGR opening control (forced HC discharge mode) is greater than the accumulated time of HC trap temperature raising control (HC trap temperature raising mode). This is the complete removal of HC trap 16 only by EGR opening temperature control. This is because, since the temperature of the exhaust gas is slow when it is going to be performed, the time required to reach the complete desorption of HC becomes longer. The reason that the time that is the key to return to the normal control is not the control continuation time but the accumulated time is that the HC trap temperature increase control and the EGR opening degree control may be cut off halfway due to changes in the operating state. The accumulated time is used. The switching valve 14 remains open except immediately after the cold start, and at that time, the amount of exhaust gas supplied to the HC trap is only as small as the EGR. Therefore, even if the three-way catalyst 13 is located upstream and downstream of the HC trap, the accumulated time is sufficient.

  In this way, according to the present embodiment, the residual HC in the HC trap 16 can be eliminated, the HC reduction capability can be maintained, and the HC during cold start can be reduced.

  As a modification of the present embodiment, a bypass passage 15 may be provided in parallel with the exhaust pipe 12 upstream of the three-way catalyst 13, and the HC trap 16 may be disposed in the bypass passage 15. Further, the three-way catalyst 13 and the HC trap 16 may be integrated. In other words, since the HC trap 16 adsorbs HC at the time of starting, any exhaust gas purification system may be used for purification of exhaust gas components in other operating states. In addition, with the structure as in Patent Document 1, it is also possible to arrange an EGR extraction port upstream of the HC trap.

1 is a schematic configuration diagram of an exhaust emission control device for an engine according to an embodiment of the present invention. It is a flowchart of a control process similarly.

Explanation of symbols

  1 engine, 2 intake valve device, 2A variable valve timing mechanism, 3 intake manifold, 4 intake pipe, 5 air cleaner, 6 throttle valve, 7 throttle position sensor, 8 electronic control unit (ECU), 9 air flow sensor, 10 exhaust Valve device, 11 exhaust manifold, 12 exhaust pipe, 13 three-way catalyst, 14 switching valve, 15 bypass passage, 16 HC trap, 17 pressure regulating valve, 18 exhaust temperature sensor, 19 EGR passage, 20 EGR control valve, 21 crank angle Sensor, 22 Water temperature sensor.

Claims (7)

A bypass passage is provided in parallel with the exhaust passage provided in the engine exhaust system, and an HC trap is provided in the bypass passage, and an EGR passage is provided for returning HC desorbed from the HC trap to the intake system. Engine exhaust gas purification device,
Desorption state detecting means for detecting the desorption state of HC from the HC trap;
An internal EGR adjusting means capable of changing an internal EGR amount of the engine;
An external EGR adjusting means capable of changing an external EGR amount recirculated from the EGR passage to the intake system;
When the desorption state detection means determines that HC desorption from the HC trap is insufficient, the internal EGR adjustment means decreases the internal EGR amount and the external EGR adjustment means increases the external EGR amount. EGR control means for increasing the amount of HC reduction to intake air by
An exhaust emission control device for an engine comprising: In claim 1,
The engine exhaust gas purification device further includes ignition timing control means for controlling the ignition timing of the engine,
An engine exhaust gas purification apparatus that retards the ignition timing of the engine by the ignition timing control means when it is determined by the desorption state detection means that HC is not sufficiently desorbed from the HC trap. . In claim 2,
It further comprises exhaust gas temperature detection means for detecting the exhaust gas temperature,
The engine exhaust gas purification apparatus according to claim 1, wherein the ignition timing control means retards the ignition timing when the exhaust gas temperature rise is less than a predetermined value by the exhaust gas temperature detecting means. In claim 1,
It has an exhaust valve and an intake valve whose valve opening timing can be changed,
The internal EGR adjusting means is a variable valve timing mechanism that changes the opening timing of the intake valve of the engine, and reduces the internal EGR amount by retarding the opening timing of the intake valve. Exhaust purification equipment. In claim 1,
An engine characterized by controlling the internal EGR adjustment means and the external EGR adjustment means so that the internal EGR amount decreased by the internal EGR adjustment means and the external EGR amount increased by the external EGR adjustment means become substantially the same amount. Exhaust purification equipment. In claim 1,
An exhaust emission control device for an engine, characterized in that the control by the EGR control means is stopped when the accumulated time of the EGR control means has passed a first predetermined time. In claim 2,
An exhaust emission control device for an engine, characterized in that the control by the ignition timing control means is stopped when the accumulated time of the ignition timing control means has passed a second predetermined time.

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