JP2018178823A - EGR device - Google Patents

Abstract

An object of the present invention is to provide an EGR device that expands the operating range in which EGR gas can be introduced. [Solution] An EGR flow path 81 that introduces a part of the exhaust gas of the engine 1 into the intake pipe as EGR gas, an EGR valve 83 that controls the flow rate of the EGR gas, and an air amount detection means 54 that detects the amount of intake air. , a control means 100 that sets a target EGR rate according to the intake air amount and controls the opening degree of the EGR valve so that the EGR rate approaches the target EGR rate. The upper limit air amount L2 is set so that it becomes the minimum value when it is equal to or higher than a predetermined upper limit air amount. The configuration is set to a large value. [Selection diagram] Figure 3

Description

  The present invention relates to an EGR device for recirculating a part of exhaust gas from an engine to the intake side, and more particularly to an EGR device capable of expanding an operation range in which EGR can be performed.

  For example, in an engine mounted on a car or the like, an exhaust gas recirculation (EGR) device is provided which introduces a part of exhaust gas from an exhaust device to an intake device.

As a prior art related to such an EGR device, for example, in Patent Document 1, in an EGR device provided with an acceleration priority EGR map and a fuel efficiency priority EGR map, the acceleration state is determined based on the accelerator opening, and the acceleration determination result is It is described that the optimum EGR rate according to the acceleration state is set by changing the combining ratio of the two EGR maps in a corresponding manner.
Patent Document 2 describes that a map switching unit for a normal EGR map and a fuel efficiency best EGR map according to acceleration is provided, and the EGR rate is set based on any one of the maps.
Patent Document 3 describes that the target opening degree is corrected according to the change in the operating state of the internal combustion engine in order to suppress the time response delay of the EGR amount control.
Patent Document 4 describes control in which, when it is predicted that the predicted value exceeds a predetermined value, based on the predicted value of EGR, the EGR reduction start time point is advanced earlier than the reference value.

Unexamined-Japanese-Patent No. 2015-7396 JP 2013-72342 A Japanese Patent Application Laid-Open No. 10-9011 JP 2013-32741 A

For example, in a supercharged engine, when the supercharging pressure is high, the intake pipe pressure exceeds the exhaust pipe pressure and it becomes difficult to introduce the EGR gas, so the EGR is stopped.
However, in the case of an engine that performs EGR control that sets a target EGR rate according to the amount of intake air, the EGR valve is introduced together with air when the throttle valve is gradually opened and the amount of intake air tends to increase. On the other hand, when the throttle valve is gradually returned from the supercharged state where the introduction of EGR gas is stopped and the intake air amount tends to decrease, only the air is introduced, so the intake air amount tends to increase In some cases, the intake air amount may be the same but the intake pipe pressure may be different between when and when it tends to decrease.
For this reason, in the existing control, there was a case in which the EGR was stopped even though the intake pipe pressure could actually introduce the EGR gas.
SUMMARY OF THE INVENTION In view of the above-described problems, an object of the present invention is to provide an EGR device in which an operating range in which EGR can be performed is expanded.

The present invention solves the above-mentioned problems by the following solutions.
The invention according to claim 1 comprises an EGR flow path for introducing a part of exhaust gas of the engine into an intake pipe as EGR gas, an EGR valve provided in the EGR flow path and controlling the flow rate of the EGR gas, and the engine The target EGR rate is set according to the intake air amount, and the EGR valve is opened so that the ratio of the flow rate of the EGR gas to the intake air amount approaches the target EGR rate. The target EGR rate is set to a minimum value when the intake air amount is equal to or higher than a predetermined upper limit air amount, and the intake air amount is The upper limit air amount when the intake air amount tends to decrease is set larger than the upper limit air amount when it tends to increase.
According to the present invention, the intake air amount tends to decrease because the upper limit air amount when the intake air amount tends to decrease is set larger than the upper limit air amount when the intake air amount tends to increase When the EGR is started early, it is possible to expand the operating range where the EGR is possible.

  As described above, according to the present invention, it is possible to provide an EGR device in which the operating range in which EGR can be performed is expanded.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows typically the structure of the engine which has embodiment of the EGR apparatus to which this invention is applied. It is a figure which shows typically an example of the correlation of the intake air quantity and the intake pipe pressure in an engine. It is a figure which shows the relationship between the amount of intake air and the target EGR rate in the EGR apparatus of embodiment.

Hereinafter, an embodiment of an EGR device to which the present invention is applied will be described.
The EGR device according to the embodiment is provided, for example, in a horizontally opposed four-cylinder gasoline direct injection turbocharged engine mounted as a driving power source in a car such as a passenger car.

FIG. 1 is a view schematically showing a configuration of an engine having the EGR device of the embodiment.
The engine 1 includes a crankshaft 10, a cylinder block 20, a cylinder head 30, a turbocharger 40, an intake system 50, an exhaust system 60, a canister 70, an EGR device 80, an engine control unit (ECU) 100, etc. There is.

The crankshaft 10 is a rotating shaft that is an output shaft of the engine 1.
A power transmission mechanism such as a transmission (not shown) is connected to one end of the crankshaft 10.
A piston is connected to the crankshaft 10 via a connecting rod (not shown).
At the end of the crankshaft 10, a crank angle sensor 11 for detecting the angular position of the crankshaft is provided.
The output of the crank angle sensor 11 is transmitted to the ECU 100.

The cylinder block 20 is configured as a two-piece so as to sandwich the crankshaft 10 from the left and right direction in vertical mounting on a vehicle body.
At the central portion of the cylinder block 20, there is provided a crankcase portion that accommodates the crankshaft 10 and has a main bearing that rotatably supports the crankshaft 10.
Inside the left and right banks of the cylinder block 20 disposed on the left and right sides of the crankcase portion, for example, a pair of cylinders (in the case of four cylinders) in which pistons are inserted and reciprocated inside are formed.

The cylinder head 30 is provided at each end (left and right end) of the cylinder block 20 opposite to the crankshaft 10.
The cylinder head 30 includes a combustion chamber 31, an ignition plug 32, an intake port 33, an exhaust port 34, an intake valve 35, an exhaust valve 36, an intake camshaft 37, an exhaust camshaft 38, and the like.
The combustion chamber 31 is formed by, for example, indenting a portion facing the piston crown surface of the cylinder head 30 into a pent roof shape.
The spark plug 32 is provided at the center of the combustion chamber 31, generates a spark in response to an ignition signal from the ECU 100, and ignites the air-fuel mixture.

The intake port 33 is a flow path for introducing combustion air (fresh air) into the combustion chamber 31.
The exhaust port 34 is a flow path for discharging the burned gas (exhaust gas) from the combustion chamber 31.
The intake valve 35 and the exhaust valve 36 open and close the intake port 33 and the exhaust valve 34 at predetermined valve timings.
For example, two intake valves 35 and two exhaust valves 36 are provided for each cylinder.
The intake valve 35 and the exhaust valve 36 are opened and closed by an intake camshaft 37 and an exhaust camshaft 38 which rotate in synchronization at a half rotation speed of the crankshaft 10.
The cam sprockets of the intake camshaft 37 and the exhaust camshaft 38 are provided with a variable valve timing mechanism (not shown) that changes the opening timing and closing timing of each valve by advancing and retarding the phase of each camshaft. It is done.

The turbocharger 40 is a supercharger that compresses combustion air (fresh air) using the energy of the exhaust of the engine 1 and supercharges it.
The turbocharger 40 includes a turbine 41, a compressor 42, an air bypass flow path 43, an air bypass valve 44, a waste gate flow path 45, a waste gate valve 46, and the like.
The turbine 41 is rotationally driven by the exhaust gas of the engine 1.
The compressor 42 is coaxially attached to the turbine 41 and rotationally driven by the turbine 41 to compress air.

The air bypass flow path 43 extracts a part of air from the downstream side of the compressor 42 and causes the air to flow back to the upstream side of the compressor 42.
The air bypass valve 44 is provided in the air bypass flow passage 43, and is in a closed state in which the air bypass flow passage 43 is substantially closed in response to a command from the ECU 100, and an open state where air can pass through the air bypass flow passage 43 And in two steps.
The air bypass valve 44 is an electric valve having a valve body that is opened and closed by an electric actuator.
The air bypass valve 44 is opened in order to prevent surging of the turbocharger 40, protect the blades, etc., for example, when the throttle valve 56 is suddenly closed, and the air in the intake pipe downstream of the compressor 42 is opened. Are returned to the upstream side of the compressor 42 to reduce the excess pressure.
Further, the air bypass valve 44 is also used to increase the negative pressure at the inlet of the compressor 42 as an open state at the time of supercharging in order to increase the flow rate of the purge gas from the canister 70 at the time of supercharging.

The west gate channel 45 extracts a part of the exhaust gas from the upstream side of the turbine 41 and bypasses the downstream side of the turbine 41 for the purpose of supercharging pressure control, temperature rise of the catalyst, and the like.
The wastegate channel 45 is integrally formed in the housing of the turbine 41.
The waste gate valve 46 has a valve body provided in the waste gate flow path 45 for opening and closing the flow path, and controls the flow rate of the exhaust gas passing through the waste gate flow path 45.
The waste gate valve 46 is an electric waste gate valve having an electric actuator that opens and closes the valve in accordance with a command from the ECU 100.
The west gate valve 46 can switch between the fully open state and the fully closed state, and can also set an arbitrary degree of opening at these intermediate positions.

The intake system 50 introduces air to the intake port 33.
The intake system 50 includes an intake duct 51, a chamber 52, an air cleaner 53, an air flow meter 54, an intercooler 55, a throttle valve 56, an intake manifold 57, an intake pressure sensor 58, an injector 59, and the like.

The intake duct 51 is a flow path for introducing outside air and introducing it to the intake port 33.
The chamber 52 is a space provided in communication with the vicinity of the inlet of the intake duct 51.
The air cleaner 53 is provided on the downstream side of the communication point of the intake duct 51 with the chamber 52, and filters air to remove dust and the like.
The air flow meter 54 is provided in the vicinity of the outlet of the air cleaner 53 and measures the flow rate of air passing through the intake duct 51.
The air flow meter 54 functions as an air amount detection means in the present invention.
The output of the air flow meter 54 is transmitted to the ECU 100.
The compressor 42 of the turbocharger 40 is provided downstream of the air flow meter 54.

The intercooler 55 is a heat exchanger that is provided on the downstream side of the compressor 42 in the intake duct 51 and that cools the air that has been compressed to a high temperature, for example, by heat exchange with traveling air or the like.
The throttle valve 56 is a butterfly valve which is provided on the downstream side of the intercooler 55 in the intake duct 51 and adjusts the flow rate of air to control the output of the engine 1.
The throttle valve 56 is driven to open and close by a throttle actuator (not shown) in response to an accelerator pedal operation or the like by a driver.
Further, the throttle valve 56 is provided with a throttle sensor for detecting the opening degree, and the output thereof is transmitted to the ECU 100.
The intake manifold 57 is a branch pipe provided downstream of the throttle valve 56 and distributing the air to the intake port 33 of each cylinder.
The intake pressure sensor 58 detects the pressure of the air in the intake manifold 57 (intake pressure).
The output of the intake pressure sensor 58 is transmitted to the ECU 100.
The injector 59 is provided at an end of the intake manifold 57 on the cylinder head 30 side, and injects fuel into the combustion chamber 31 to form an air-fuel mixture according to a valve opening signal issued by the ECU 100.

The exhaust system 60 exhausts the exhaust gas discharged from the exhaust port 34 to the outside.
Exhaust system 60 includes an exhaust manifold 61, exhaust pipe 62, the front catalyst 63, the rear catalyst 64, a silencer 65, the air-fuel ratio sensor 66 is configured to have a rear _{O 2} sensor 67 or the like.
The exhaust manifold 61 is a collecting pipe for collecting the exhaust gas from the exhaust port 34 of each cylinder.
The turbine 41 of the turbocharger 40 is disposed downstream of the exhaust manifold 61.
The exhaust pipe 62 is a pipe line for discharging the exhaust gas from the turbine 41 to the outside.
The front catalyst 63 and the rear catalyst 64 are provided at an intermediate portion of the exhaust pipe 62, and each include a three-way catalyst that purifies HC, NOx, CO and the like in the exhaust gas.
The front catalyst 63 is provided adjacent to the outlet of the turbine 41, and the rear catalyst 64 is provided on the outlet side of the front catalyst.
The silencer 65 is provided in the vicinity of the outlet of the exhaust pipe 62 to reduce the acoustic energy of the exhaust gas.

The air-fuel ratio sensor 66 is provided between the outlet of the turbine 41 and the inlet of the front catalyst 63.
Rear O ₂ sensor 67 is provided between the inlet of the outlet and the rear catalyst 64 of the front catalyst 63.
Air-fuel ratio sensor 66, the rear O ₂ sensor 67 by generating an output voltage corresponding to the oxygen concentration in the exhaust gas together, and detects the amount of oxygen in the exhaust gas.
Air-fuel ratio sensor 66 is more a wide detectable linear output sensor oxygen concentration in the air-fuel ratio with respect to the rear O ₂ sensor 67.
Air-fuel ratio sensor 66, the output of the rear _{O 2} sensor 67 is transmitted together ECU 100.

The canister (charcoal canister) 70 is one in which fuel evaporative gas (evaporative) generated in a fuel tank (not shown) in which gasoline used as fuel for the engine 1 is stored is introduced and temporarily stored.
The canister 70 is configured by housing activated carbon capable of temporarily adsorbing fuel evaporation gas in a canister case which is a resin case.
The canister 70 mainly includes a non-supercharged purge line 71, a purge control valve 72, and a mainly supercharged purge line 73, a purge control valve 74, and the like.

The purge line 71 is a flow path which is connected to the canister 70 and the intake manifold 57 at both ends and which allows the insides to communicate with each other.
The purge line 71 introduces a purge gas composed of the fuel evaporation gas released from the canister 70 into the intake manifold 57 when the internal pressure of the intake manifold 57 is negative and not supercharged.
The purge control valve (PCV) 72 is a duty control solenoid valve provided in the middle of the purge line 71.
The PCV 72 can switch between an open state and a closed state, and set an opening degree in the open state, in accordance with a command from the ECU 100.

The purge line 73 is a flow path which is connected at both ends to the canister 70 and a region adjacent to the inlet of the compressor 42 in the intake duct 51 and allows the insides to communicate with each other.
The purge line 73 introduces the purge gas into the intake duct 51 on the upstream side of the compressor 42 at the time of supercharging in which the inside of the intake manifold 57 has a positive pressure and the introduction of the purge gas by the purge line 71 becomes difficult.
The purge control valve (PCV) 74 is a solenoid valve provided in the middle of the purge line 73.
The PCV 74 can switch between the open state and the closed state in response to a command from the ECU 100.

The EGR device 80 extracts exhaust gas from the exhaust manifold 61 as EGR gas and performs exhaust gas recirculation (EGR) to be introduced into the intake manifold 57.
The EGR device 80 includes an EGR passage 81, an EGR cooler 82, an EGR valve 83, and the like.

The EGR passage 81 is a pipe line for introducing the exhaust gas (EGR gas) from the exhaust manifold 61 to the intake manifold 57.
The EGR cooler 82 is provided in the middle of the EGR passage 81 and cools the EGR gas flowing through the EGR passage 81 by heat exchange with the cooling water of the engine 1.
The EGR valve 83 is provided on the downstream side of the EGR cooler 82 in the EGR flow passage 81, and is a metering valve that adjusts the flow rate of the EGR gas passing through the inside of the EGR flow passage 81.
The EGR valve 83 has a valve body driven by an electric actuator such as a solenoid, and the engine control unit 100 opens the EGR valve so that the actual EGR rate (EGR gas flow rate / new air flow rate) approaches a predetermined target EGR rate. The feedback is controlled.

An engine control unit (ECU) 100 centrally controls the engine 1 and its accessories.
The ECU 100 is configured to include an information processing unit such as a CPU, a storage unit such as a RAM or a ROM, an input / output interface, a bus connecting these, and the like.
Further, the ECU 100 is provided with an accelerator pedal sensor 101 that detects the depression amount of an accelerator pedal (not shown) by the driver.
The ECU 100 has a function of setting the driver request torque based on the output of the accelerator pedal sensor 101 or the like.
The ECU 100 controls the throttle valve opening degree, the supercharging pressure, the fuel injection amount, the fuel injection timing, the ignition timing, the valve timing, and the like so that the torque actually generated by the engine 1 approaches the set driver request torque.
Further, the ECU 100 sets the target EGR rate according to the intake air amount detected by the air flow meter 54, and the EGR valve is set so that the ratio of the flow rate of EGR gas to the intake air amount (actual EGR rate) approaches the target EGR rate. It also functions as control means for controlling the opening degree.

FIG. 2 is a view schematically showing an example of the correlation between the intake air amount and the intake pipe pressure in the engine.
In FIG. 2, the horizontal axis indicates the intake air amount of the engine 1 detected by the air flow meter 54, and the vertical axis indicates the pressure in the intake manifold 57 detected by the intake pressure sensor 58.
In FIG. 2, a solid arrow indicates a correlation when the intake air amount is increasing (accelerator opening increase), and a broken arrow indicates a correlation when the intake air amount is decreasing (accelerator opening decreasing). There is.

Generally, when the intake pressure in intake manifold 57 becomes higher than the exhaust pressure (back pressure) in exhaust manifold 61, the introduction of EGR gas becomes difficult. Therefore, when the intake air amount tends to increase, the intake The EGR valve 83 is fully closed to prevent blow-by of new air and supercharging leakage above the upper limit of the amount of air set in the vicinity of the intake air amount at which the pressure in the manifold 57 and the pressure in the exhaust manifold 61 are balanced. , EGR is not done.
A state where the amount of intake air is larger than this corresponds to a supercharging region in a turbocharged engine, and the pressure in the intake manifold 57 becomes higher than the pressure in the exhaust manifold 61, and the EGR is stopped.
Consider a case where the amount of intake air tends to decrease by gradually returning the accelerator pedal from such a state. In the supercharging region, only the air is introduced substantially to the engine 1 since the EGR is stopped.
Therefore, as shown in FIG. 2, even if the amount of intake air is equal, if the amount of intake air tends to decrease, the intake pressure in the intake manifold 57 will be compared to when the amount of intake air tends to increase. There is a region A where the lowers (the same amount of air, the negative pressure becomes deeper).
In such a region A, when the pressure in the intake manifold 57 is lower than the pressure in the exhaust manifold 61, opening the EGR valve 83 allows EGR gas to be reduced only when the amount of intake air tends to decrease. It becomes possible to introduce.

In the present embodiment, in consideration of the characteristics described above, the setting of the target EGR rate is made different between when the intake air amount is increasing and when it is decreasing.
FIG. 3 is a view showing the relationship between the intake air amount and the target EGR rate in the EGR device of the embodiment.
In FIG. 3, the horizontal axis indicates the intake air amount of the engine 1 detected by the air flow meter 54, and the vertical axis indicates the target EGR rate (EGR gas flow rate / intake air amount) set by the ECU 100.
The target EGR rate when the intake air amount tends to increase is indicated by a white circle and a solid line, and the target EGR rate when the intake air amount tends to decrease is indicated by a black square and a broken line. The minimum value of the target EGR rate in the same figure is the target EGR rate when the EGR is stopped, and is specifically set to zero.
As shown in FIG. 3, when the amount of intake air tends to increase, the amount of intake air tends to decrease with respect to the upper limit air amount L1, which is the amount of air at which the EGR valve 83 is closed (the amount of air to stop EGR). The upper limit air amount L2, which is the amount of air for which the EGR valve 83 is opened (the amount of air for resuming the EGR), is set to a large value.
Therefore, the EGR valve 83 is opened earlier immediately after entering the negative pressure region to start the introduction of the EGR gas than when the same upper limit air amount L1 is used regardless of the increase tendency or the decrease tendency of the intake air amount. can do.

As described above, according to the present embodiment, when the intake air amount tends to decrease with respect to the upper limit air amount L1 when the intake air amount tends to increase (for example, when the accelerator is depressed) (for example, the accelerator By setting the upper limit air amount L2 at the time of return large, it is possible to start EGR early when the amount of intake air tends to decrease and to expand the operation region in which EGR is possible.
As a result, it is possible to improve the thermal efficiency and the fuel consumption by reducing the pump loss.
Further, NOx in exhaust gas can be reduced by suppressing the combustion temperature.

(Modification)
The present invention is not limited to the embodiments described above, and various modifications and changes are possible, which are also within the technical scope of the present invention.
(1) The configurations of the EGR device and the engine are not limited to the above-described embodiment, and can be changed as appropriate.
For example, the cylinder layout of the engine, the number of cylinders, the presence or absence of the supercharger, and the type thereof, the fuel injection method (direct injection, port injection, combination of these, etc.) can be appropriately changed.
Further, the place for extracting the EGR gas in the exhaust system and the place for introducing the EGR gas in the intake system are not particularly limited.
Furthermore, the presence or absence of the EGR cooler, the installation location of the EGR cooler, the cooling method, and the like are not particularly limited.
(2) In the embodiment, the engine is a spark ignition gasoline engine, but the present invention may be applied to a compression ignition engine such as a diesel engine or an HCCI engine or an engine using other fuels it can.
(3) The relationship between the intake air amount and the target EGR rate in the embodiment is an example, and can be changed as appropriate according to engine specifications, individual differences, and the like. Further, it is also possible to set the target EGR rate as in the present invention only in a part of the engine operating range (for example, a predetermined rotational speed range etc.).

Reference Signs List 1 engine 10 crankshaft 11 crank angle sensor 20 cylinder block 30 cylinder head 31 combustion chamber 32 ignition plug 33 intake port 34 exhaust port 35 intake valve 36 exhaust valve 37 intake camshaft 38 exhaust camshaft 40 turbocharger 41 turbine 42 compressor 43 air Bypass flow path 44 Air bypass valve 45 West gate flow path 46 West gate valve 50 Intake system 51 Intake duct 52 Chamber 53 Air cleaner 54 Air flow meter 55 Intercooler 56 Throttle valve 57 Intake manifold 58 Intake pressure sensor 59 Injector 60 Exhaust system 61 Exhaust manifold 62 exhaust pipe 63 front catalyst 4 Rear catalyst 65 silencer 66 air-fuel ratio sensor 67 rear _{O 2} sensor 70 the canister 71 purge line 72 purge control valve 73 purge line 74 purge control valve 80 EGR device 81 EGR passage 82 EGR cooler 83 EGR valve 100 engine control unit (ECU)
101 accelerator pedal sensor

Claims (1)

An EGR flow path for introducing a part of the exhaust gas of the engine as an EGR gas into the intake pipe;
An EGR valve provided in the EGR flow path to control the flow rate of the EGR gas;
Air amount detection means for detecting the intake air amount of the engine;
Control means for setting a target EGR rate according to the intake air amount and controlling the opening degree of the EGR valve such that the ratio of the flow rate of the EGR gas to the intake air amount approaches the target EGR rate There,
The target EGR rate is set to a minimum value when the intake air amount is equal to or higher than a predetermined upper limit air amount.
An EGR apparatus, wherein the upper limit air amount when the intake air amount tends to decrease is set larger than the upper limit air amount when the intake air amount tends to increase.

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