DE102010030496B4 - Direct injection engine control device - Google Patents

Abstract

A control device for a direct injection engine in which a fuel is directly injected into a cylinder, the control device comprising:a variable valve control device (40) which adjusts a valve opening timing of an exhaust valve (38);a PM increase estimation means (30, 103) for estimating, based on a driving state of the engine (11), whether an amount of particulate matter generated in a combustion chamber will increase; andcontrol means (30, 111) for controlling the variable valve control device in such a manner that a valve opening timing of the exhaust valve (38) is retarded when the PM increase estimating means estimates that the amount of particulate matter will increase.

Description

FIELD OF THE INVENTION

The present invention relates to a control device for a direct injection engine in which fuel is directly injected into a cylinder.

BACKGROUND OF THE INVENTION

A direct injection engine is capable of increasing power, reducing fuel consumption, and reducing emissions. However, depending on a driving state of the engine, a discharge amount of particulate matter such as soot is increased. In order to reduce the amount of particulate matter, the following technologies have been proposed.

For example, the JP 2002 - 327 651 A a control system for a direct injection engine. In this control system, a temperature in a combustion chamber is estimated, and when this estimated temperature is lower than a set value, it is determined that soot (impure carbon particles) is contained in the exhaust gas. Then, the amount of internal EGR (Exhaust Gas Recirculation) is increased. When it is determined that the combustion state becomes unstable, the amount of internal EGR is decreased, an ignition timing is advanced and a fuel injection timing is advanced, or an intake air flow rate is increased, so that the soot is reduced and the combustion state becomes stable.

Also shows the JP 2008 - 88 856 A ( U.S. 2009/0 271 092 A1 ) a control system for a direct injection engine. In this control system, a penetrating force (thrusting force) of the injected fuel is changed stepwise in such a manner that the penetrating force of the injected fuel is reduced when a piston is positioned relatively high in a cylinder.

Also show DE 11 2004 001 288 B4 as DE 694 24 868 T2 each describe a direct injection variable valve timing engine capable of retarding a valve opening timing of the exhaust valve.

With each control system described above, the amount of soot generated in the combustion chamber of the engine is reduced. However, depending on engine operating conditions or fuel property, it is likely that the amount of soot cannot be reduced sufficiently. In such a case, since the soot generated in the combustion chamber is not cleaned by a catalyst in an exhaust pipe, the soot is discharged to the atmosphere through a tail pipe.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a control device for a direct injection engine capable of burning the particulate matter generated in a combustion chamber of the engine so that a discharge amount of the particulate matter is reduced.

According to the present invention, a control device for a direct injection engine includes: a variable valve control device that adjusts a valve opening timing of an exhaust valve; PM increase estimating means for estimating, based on a driving state of the engine, whether an amount of particulate matter (PM) generated in a combustion chamber will increase; and a controller for controlling the variable valve timing device in such a manner that a valve opening timing of the exhaust valve is retarded when the PM increase estimating means estimates that the amount of particulate matter will increase.

By retarding the opening timing of the exhaust valve, a period of time that the exhaust gas having a high temperature remains in the combustion chamber is lengthened in response to the delayed period of time. Thereby, a high-temperature period (combustion period) in which the soot generated in the combustion chamber is exposed to the high-temperature exhaust gas is prolonged to promote burning of the PM in the combustion chamber, so that the discharge amount of the PM can be effectively reduced.

In a direct injection engine equipped with a turbocharger and a wastegate, the controller estimates whether an amount of particulate matter emitted from the engine will increase based on a driving state of the engine. When it is estimated that the amount of particulate matter will increase with the wastegate open, the wastegate is closed. All of the exhaust gas flows into an exhaust gas turbine of the turbocharger. An internal pressure of the exhaust passage upstream of the exhaust turbine increases and its internal temperature also increases. The burning of the PM in the exhaust pipe is promoted, so the emission of the PM is effectively reduced.

In addition, in a direct injection engine equipped with a secondary air supply system, when it is estimated that the amount of particulate matters will increase, the secondary air supply system supplies the secondary air to an exhaust pipe. An oxygen concentration in the exhaust pipe is increased, so that the burning (oxidation reaction) of the PM is promoted to effectively reduce the emission of the PM.

character list

• 1 eine schematische Ansicht eines Maschinensteuersystems gemäß einem ersten Ausführungsbeispiel der vorliegenden Erfindung ist;
• 2 ein Ablaufdiagram ist, das einen Ablauf einer PM-Reduktionssteuerungsroutine gemäß dem ersten Ausführungsbeispiel zeigt;
• 3 eine Darstellung zum Erklären einer Abweichung bei einer mittleren Temperatur von Abgas in einem Zylinder ist, wenn ein Ventilöffnungszeitpunkt eines Abgasventils verzögert wird;
• 4 eine Darstellung ist, die eine Beziehung zwischen einer mittleren Temperatur eines Abgases in einem Zylinder und einer PM-Emission zeigt;
• 5 eine schematische Ansicht eines Maschinensteuersystems mit einem Turbolader gemäß einem zweiten Ausführungsbeispiel der vorliegenden Erfindung ist;
• 6 ein Ablaufdiagram ist, das einen Ablauf einer PM-Reduktionssteuerroutine gemäß dem zweiten Ausführungsbeispiel zeigt;
• 7 eine schematische Ansicht eines Maschinensteuersystems mit einem sekundären Luftzufuhrsystem gemäß einem dritten Ausführungsbeispiel der vorliegenden Erfindung ist;
• 8 ein Ablaufdiagram ist, das einen Ablauf einer PM-Reduktionssteuerroutine gemäß dem dritten Ausführungsbeispiel zeigt;
• 9 eine Darstellung ist, die eine Veränderung eines Ventilhubbetrags und eines Ventilöffnungszeitpunkts zeigt; und
• 10 eine Darstellung ist, die eine Veränderung einer Ventilzeitstellungsphase und eines Ventilöffnungszeitpunkts zeigt.

Other objects, features and advantages of the present invention will become clearer from the following description given with reference to the accompanying drawings, in which like parts are denoted by like reference numerals, and in which:

• 1 Fig. 12 is a schematic view of an engine control system according to a first embodiment of the present invention;
• 2 Fig. 12 is a flowchart showing a flow of a PM reduction control routine according to the first embodiment;
• 3 Fig. 14 is an illustration for explaining a deviation in an average temperature of exhaust gas in a cylinder when a valve opening timing of an exhaust valve is retarded;
• 4 Fig. 12 is a graph showing a relationship between an average temperature of an exhaust gas in a cylinder and a PM emission;
• 5 Fig. 12 is a schematic view of an engine control system having a turbocharger according to a second embodiment of the present invention;
• 6 Fig. 12 is a flowchart showing a flow of a PM reduction control routine according to the second embodiment;
• 7 Fig. 12 is a schematic view of an engine control system having a secondary air supply system according to a third embodiment of the present invention;
• 8th 12 is a flowchart showing a flow of a PM reduction control routine according to the third embodiment;
• 9 Fig. 12 is a graph showing a change in a valve lift amount and a valve opening timing; and
• 10 Fig. 14 is an illustration showing a change in a valve timing phase and a valve opening timing.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Embodiments of the present invention are described below.

[first embodiment]

Referring to the 1 until 4 a first exemplary embodiment is described below. A direct injection engine is provided with a variable valve timing device (VVC) for an exhaust valve. A machine control system is based on the 1 schematically explained.

An air cleaner 13 is disposed upstream of an intake pipe 12 of an internal combustion engine 11 which is a direct injection engine. An air flow meter 14 that detects an intake air flow rate is provided downstream of the air cleaner 13 . A throttle valve 16 driven by a DC motor 15 and a throttle position sensor 17 that detects a throttle position (a throttle opening degree) are provided downstream of the air flow meter 14 .

A surge tank 18 having an intake air pressure sensor 19 is provided downstream of the throttle valve 16 . The intake air pressure sensor 19 detects an intake air pressure. An intake manifold 20 that introduces air into each cylinder of the engine 11 is provided downstream of the surge tank 18 . An air flow control valve 31 is disposed on each of the intake manifolds 20 to control an air flow intensity (a swirl flow intensity and a tumble flow intensity) in each cylinder.

A fuel injector 21 is provided at an upper portion of each cylinder of the engine 11 to inject fuel directly into the cylinder. A spark plug 22 is mounted on the cylinder head of the engine 11 corresponding to each cylinder to ignite an air-fuel mixture in each cylinder. In addition, the engine 11 is provided with variable valve timing devices (VVCs) 39,40. The variable valve timing device (VVC) 39 for an intake valve controls a valve lift amount and valve opening timing of an intake valve 37. The variable valve timing device (VVC) 40 for an exhaust valve controls a valve lift amount and valve opening timing of an exhaust valve 38. Each of the variable valve timing devices (VVCs) 39, 40 is hydraulically or electrically driven.

A cylinder block of the engine 11 is equipped with a knock sensor 32 that detects knocking, a coolant temperature sensor 23 that detects a coolant temperature, a crank angle sensor 24 that outputs a crank pulse for each set crank angle, and cam angle sensors (not shown) that correlate to cam pulses output to an intake camshaft and an exhaust camshaft. An engine speed is calculated based on an interval of the crank pulses. A crank angle is calculated based on the crank pulse. In addition, the valve opening timings of the intake valve 37 and the exhaust valve 38 are calculated based on the output pulses from the crank angle sensor 24 and the cam angle sensors.

An exhaust pipe 25 of the engine 11 is provided with an upstream catalyst 26 and a downstream catalyst 27 which purify CO, HC and NOx in the exhaust gas. An exhaust gas sensor 28 such as an air/fuel ratio sensor and an oxygen sensor is disposed upstream of the upstream catalyst 26 for detecting an air/fuel ratio or rich/lean of the exhaust gas. In the present embodiment, the upstream catalyst 26 is a three-way catalyst, and the downstream catalyst 27 is a NOx catalyst (NOx absorption-reduction catalyst). This NOx catalyst 27 performs absorption of NOx in the exhaust gas when the air-fuel ratio of the exhaust gas is lean. When the air-fuel ratio of exhaust gas is a stoichiometric air-fuel ratio or rich, the NOx catalyst 27 performs reduction purification of the absorbed NOx.

An EGR pipe 33 connects the exhaust pipe 25 and the surge tank 18. A part of an exhaust gas is returned to the surge tank 18 through the EGR pipe 33. As shown in FIG. The EGR passage 33 is provided with an EGR valve 34 that controls a flow rate of exhaust gas flowing therethrough.

The outputs from the above sensors are input to an electronic control unit (ECU) 30 . The ECU 30 has a microcomputer that executes an engine control program stored in a read-only memory (ROM) to control a fuel injection amount, fuel injection timing, ignition timing of the spark plug 22, and control outputs of the variable valve timing devices (VVCs) 39, 40 .

The ECU 30 switches a combustion mode between a stratified combustion mode and a homogeneous combustion mode according to an engine driving condition (required torque, engine speed, engine load, etc.). In the stratified combustion mode, a small amount of fuel is injected directly into the cylinder during a compression stroke. A stratified air-fuel mixture is formed in a vicinity of the spark plug 22 to perform stratified combustion (lean combustion) to improve fuel efficiency. In the homogeneous combustion mode, a fuel injection amount is increased and the fuel is directly injected into the cylinder during the intake stroke. A homogeneous air-fuel mixture is formed to perform homogeneous combustion to improve engine performance.

In general, particulate matter (PM) tends to be generated in stratified combustion rather than homogeneous combustion. In addition, even in the homogeneous combustion mode, the PM tends to be generated when the engine is cold started or an engine load is relatively high. Thus, the amount of PM generated in the combustion chamber of the engine 11 is increased during a period of the stratified charge combustion mode, the cold start, or the high engine load.

According to the first embodiment, the ECU 30 executes a PM reduction control routine shown in FIG 2 is shown, whereby the computer estimates whether the amount of PM in the combustion chamber of the engine 11 will be increased based on the engine driving state. When it is determined that the amount of PM will be increased, the variable valve control device (VVC) 40 decreases a valve lift amount of the exhaust valve 38, as shown in FIG 9 is shown to retard an opening timing of the exhaust valve 38 . Like this in the 3 1, by retarding the opening timing of the exhaust valve 38, a period of time that the exhaust gas having a high temperature remains in the combustion chamber is lengthened in response to the delayed period of time. As a result, a high-temperature period (combustion period) in which the soot generated in the combustion chamber is exposed to the high-temperature exhaust gas is prolonged more than usual. Like this in the 4 1, such a high-temperature period is lengthened appropriately to promote burning of the PM in the combustion chamber, so that the discharge amount of the PM can be reduced effectively.

Referring to the 2 the PM reduction control routine is described in detail. This routine runs when a target valve lift amount and/or a target valve opening timing of the exhaust valve 38 can be changed. This routine corresponds to a controller. At step 101, the computer determines a current engine driving condition based on the outputs from the various sensors. At step 102, the computer determines whether a control output of the variable valve timing device (VVC) 40 can be corrected. If the answer is NO, the process ends.

When the answer of step 102 is YES, the process proceeds to step 103, where the computer determines whether the engine is being driven in a PM increasing state in which the amount of PM in the combustion chamber is increasing. In the present embodiment, the PM increasing state corresponds to the stratified combustion mode, the cold start, or the high engine load. The process at step 103 corresponds to PM increase estimating means. If NO in step 103, the process ends.

When the answer of step 103 is YES, the process proceeds to step 104, where the computer estimates the amount of internal EGR based on a valve lift amount and valve opening/closing timings of the intake valve 37 and the exhaust valve 38. Then, the process proceeds to step 105, where the computer determines whether the valve opening timing of the exhaust valve 38 can be retarded. If the answer is NO, the process ends. If the amount of internal EGR becomes excessive, the stability of combustion will deteriorate.

If YES in step 105, the process proceeds to step 106, where a target valve opening timing of the exhaust valve 38 is set. Then, the process proceeds to step 107, where the computer determines whether the amount of internal EGR is in a proper range that ensures stable combustion. If YES in step 107, the process proceeds to step 111, where the valve opening timing of the exhaust valve 38 is corrected (retarded) to the target valve opening timing set in step 106. Thereby, the high-temperature period (combustion period) in which the soot is exposed to the high-temperature exhaust gas is prolonged to promote combustion of the PM, so that the discharge amount of the PM can be reduced effectively.

If NO in step 107, the process proceeds to step 108, where the target valve lift amount of the exhaust valve 38 is corrected to decrease the amount of internal EGR. Then, at step 109, the target valve lift amount of the intake valve 37 is also corrected to decrease the amount of internal EGR. The process then proceeds to step 110 where the computer again determines whether the amount of internal EGR is in the correct range. If YES in step 110, the process proceeds to step 111, where the valve opening timing of the exhaust valve 38 is corrected (retarded) to the target valve opening timing set in step 106.

If NO in step 110, the process goes back to step 106, where the target valve opening timing of the exhaust valve is corrected in such a manner that the amount of internal EGR is reduced. Then, the processes in steps 107 to 110 are repeatedly executed. At this time, the target valve opening timing of the exhaust valve 38 is retarded as much as possible in a range in which the stable combustion is ensured.

According to the first embodiment described above, when it is estimated that the amount of soot in the combustion chamber will increase, the opening timing of the exhaust valve 38 is retarded and the high-temperature period (combustion period) is prolonged to promote the combustion of the PM. Thus, the discharge amount of the PM can be reduced effectively.

Furthermore, since the opening timing of the exhaust valve 38 is retarded based on the estimated amount of internal EGR, the amount of internal EGR can be avoided from becoming excessive to impair the stability of combustion.

In the above first embodiment, the opening timing of the exhaust valve 38 is retarded by reducing a valve lift amount of the exhaust gas 38, as shown in FIG 9 is shown. Alternatively, the opening timing of the exhaust valve 38 can be delayed by switching a valve phase of the exhaust valve 38, as shown in FIG 10 is shown.

[second embodiment]

Referring to the 5 and 6 a second exemplary embodiment is described below. In the second embodiment, the direct injection engine is provided with a turbocharger. A machine control system is based on the 5 schematically clarified. In the second embodiment, the same parts and components as those in the first embodiment ment example are denoted by the same reference numerals and the same descriptions will not be repeated.

A turbocharger 45 has an exhaust gas turbine 46 arranged in the exhaust pipe 25 and a compressor 47 arranged in the intake pipe 12 . This turbocharger 45 has a well-known structure that charges the intake air into the combustion chamber.

Furthermore, an intake bypass passage 48 that bypasses the compressor 47 is connected to the intake pipe 12 .

An air bypass valve (ABV) 49 is arranged in the intake bypass passage 48 to open/close the intake bypass passage 48 . An opening degree of the ABV 49 is controlled by a negative pressure switching valve (VSV) 50 for the ABV. An intercooler 51 that cools the intake air pressurized by the compressor 47 is arranged in the intake pipe 12 between the compressor 47 and the throttle valve 16 .

An exhaust bypass passage 52 bypassing the exhaust turbine 46 is connected to the exhaust pipe 25 . A wastegate valve (WGV) 53 is disposed in the exhaust bypass passage 52 to open/close the exhaust bypass passage 52 . An opening degree of the WGV 53 is controlled by a diaphragm actuator 55 . The diaphragm actuator 55 is controlled by a vacuum switching valve (VSV) 54 for the WGV.

In a driving state where charging is required, the opening degree of the WGV 53 is made small or the WGV 53 is fully closed so that the exhaust gas flows into the exhaust turbine 46 to drive the exhaust turbine 46 . The rotational speed of the compressor 47 is also increased, so that a supercharging effect is improved.

In a driving state where charging is not required, the WGV 53 is fully opened so that the exhaust gas flows into the exhaust bypass passage 52 . The exhaust turbine 46 is stopped and the ABP 49 is opened to introduce the intake air into the intake bypass passage 48 .

According to the second embodiment, the ECU 30 executes a PM reduction control routine shown in FIG 6 is shown. The computer estimates whether the amount of PM in the combustion chamber of the engine 11 will be increased based on the engine driving state. When it is estimated that the amount of PM will increase with the WGV 53 opened, the WGV 53 is fully closed so that all of the exhaust gas flows into the exhaust turbine 46 . The internal pressure of the exhaust pipe 25 upstream of the exhaust turbine 46 increases and its internal temperature also increases. The burning of the PM in the exhaust pipe 25 is promoted, so that the PM emission is effectively reduced.

The above PM reduction control is carried out according to the method in FIG 6 shown PM reduction control routine is executed. This routine is repeatedly executed in a predetermined cycle while the engine is running. This routine corresponds to PM increase estimation means and control means.

At step 201, the computer determines a current engine driving condition based on the outputs from the various sensors. The process then proceeds to step 202 where the computer determines whether the WGV 53 is open. If the answer is NO, the process ends.

If the answer at step 202 is YES, the process proceeds to step 203 where the computer determines whether the WGV 53 can be closed. If the answer is NO, the process ends.

When the answer of step 203 is YES, the process proceeds to step 204, where the computer determines whether the engine is being driven in a PM increasing region in which the amount of PM in the combustion chamber increases. In the present embodiment, the PM increasing state corresponds to the stratified combustion mode, the cold start, or the high engine load. If the answer to step 204 is NO, the process ends.

If the answer of step 204 is YES, the process proceeds to step 205, where the WGV 53 is fully closed. All of the exhaust gas flows into the exhaust turbine 46 to increase the internal pressure of the exhaust pipe 25 upstream of the exhaust turbine 46 . The internal temperature of the exhaust pipe 25 also rises, so the burning of the PM in the exhaust pipe 25 is promoted to effectively reduce the PM emission. In addition, control to increase the temperature of the exhaust gas may be performed while the WGV 53 is closed. The temperature of the exhaust gas can be increased, for example, by retarding the ignition timing.

It should be noted that ABV 49 need not always be provided.

[third embodiment]

Referring to the 7 and 8th a third exemplary embodiment is described below. In the third embodiment, the direct injection engine is provided with a secondary air supply system. A machine control system is based on the 7 schematically explained. In the third embodiment, the same parts and components as those in the first embodiment are denoted by the same reference numerals, and the same descriptions are not repeated here.

A secondary air supply system 60 supplies secondary air to the exhaust pipe 25 upstream of an exhaust gas sensor 28 . Specifically, an air pump 61 driven by an electric motor discharges the secondary air into each exhaust manifold through a secondary air duct 62 and a secondary air supply nozzle 63 . A secondary air control valve 64 is arranged in the secondary air line 62 which opens/closes this secondary air line 62 .

The air pump 61 and the secondary air control valve 64 are controlled by the ECU 30 . According to the second embodiment, the ECU 30 performs an in the 8th shown PM reduction control routine. The computer estimates whether the amount of PM in the combustion chamber of the engine 11 will be increased based on the engine driving state. When it is estimated that the amount of PM will be increased, the air pump 61 is turned on and the secondary air control valve 64 opens the secondary air passage 62. The secondary air is introduced into the exhaust passage 25 so that an oxygen concentration in the exhaust passage 25 is increased. The burning (oxidation reaction) of the PM is promoted to effectively reduce the PM emission.

The above PM reduction control is carried out according to the method described in FIG 8th shown PM reduction control routine is executed. This routine is repeatedly executed in a predetermined cycle while the engine is running. This routine corresponds to PM increase estimation means and control means.

At step 301, the computer determines a current engine driving condition based on the outputs from the various sensors. The process then proceeds to step 302 where the computer determines whether the secondary air is now being introduced into the exhaust pipe 25. If the answer is YES, the process ends.

If the answer at step 302 is NO, the process proceeds to step 303 where the computer determines whether the secondary air can be introduced into the exhaust pipe 25. If the answer is NO, the process ends.

When the answer of step 303 is YES, the process proceeds to step 304, where the computer determines whether the engine is being driven in a PM increasing region in which the amount of PM in the combustion chamber increases. Also in the present embodiment, the PM increasing state corresponds to the stratified combustion mode, the cold start, or the high engine load. If the answer to step 304 is NO, the process ends.

If YES in step 304, the process proceeds to step 305, where the air pump 61 is turned on and the secondary air control valve 64 opens the secondary air line 62. The secondary air is introduced into the exhaust pipe 25 so that an oxygen concentration in the exhaust pipe 25 is increased. The burning (oxidation reaction) of the PM is promoted to effectively reduce the PM emission. In addition, control to increase the temperature of the exhaust gas can be performed while the secondary air is being introduced. The temperature of the exhaust gas can be increased, for example, by retarding the ignition timing.

The air pump 61 can be driven by the engine 11 through an electromagnetic clutch (not shown).

The present invention is not limited to the disclosed embodiments but may be embodied in other forms without departing from the scope of the invention. For example, the above three embodiments can be appropriately combined.

Claims (7)

A control device for a direct injection engine in which a fuel is directly injected into a cylinder, the control device comprising: a variable valve control device (40) which adjusts a valve opening timing of an exhaust valve (38); PM increase estimating means (30, 103) for estimating, based on a driving state of the engine (11), whether an amount of particulate matter generated in a combustion chamber will increase; and control means (30, 111) for controlling the variable valve control device in such a manner that a valve opening timing of the exhaust valve (38) is retarded when the PM increase hung estimator estimates that the amount of particulate matters will increase. Control device for a direct injection engine according to claim 1 wherein the PM increase estimating means estimates that the amount of particulate matter will increase when a driving state of the engine corresponds to stratified combustion, a cold start, or a high load. Control device for a direct injection engine according to claim 1 or 2 , wherein the control means (30) estimates an amount of internal EGR when the PM increase estimating means (30, 103) estimates that the amount of particulate matters will increase, and the variable valve control device (40) estimates the valve opening timing of the exhaust valve (38 ) based on the estimated amount of internal EGR is delayed as long as combustion stability is ensured. Control device for a direct injection engine according to one of Claims 1 until 3 wherein the variable valve control device (40) reduces a valve lift amount of the exhaust valve (38) to retard the valve opening timing of the exhaust valve (38). Control device for a direct injection engine according to one of Claims 1 until 3 wherein the variable valve control device (40) changes a valve phase of the exhaust valve (38) to retard the valve opening timing of the exhaust valve (38). A control device for a direct injection engine in which a fuel is injected directly into a cylinder, the control device comprising: a turbocharger (45) having an exhaust gas turbine (46) and a compressor (47) for charging an intake air; a waste gate valve (53) opening/closing an exhaust bypass passage (52) bypassing the exhaust turbine (46); PM increase estimating means (30, 204) for estimating, based on a driving state of the engine (11), whether an amount of particulate matters emitted from the engine (10) will increase; and control means (30, 205) for closing the wastegate (53) when the PM increase estimating means estimates that the amount of particulate matter will increase with the wastegate being opened. A control device for a direct injection engine in which a fuel is injected directly into a cylinder, the control device comprising: a secondary air supply system (60) supplying a secondary air to an exhaust pipe (25) of the engine (11); PM increase estimating means (30, 304) for estimating, based on a driving state of the engine (11), whether an amount of particulate matter emitted from the engine (10) will increase; and control means (30, 305) for controlling the secondary air supply system such that the secondary air is supplied to the exhaust pipe when the PM increase estimating means estimates that the amount of particulate matters will increase.

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