JP2018119406A - Engine control method, and engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform purge at desired timing.SOLUTION: An engine comprises a supercharger, an EGR passage, a canister, a purge passage for purging evaporated fuel collected in the canister into the EGR passage, an admission valve, an EGR valve, and a PCV valve. A control method for the engine, when EGR is determined to be executed, executes the EGR by reducing the opening of the admission valve smaller than that before execution of the EGR and by opening the EGR valve, and when purge is determined to be executed during the execution of the EGR, performs purge by reducing the opening of the EGR valve smaller than the opening when the EGR is determined to be executed and by opening the PCV valve.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an engine control method and an engine.

  An engine that performs exhaust gas recirculation (EGR) is configured such that a part of the exhaust gas is circulated to the intake air to the engine (Patent Document 1). In such an engine, since the intake temperature of the engine can be lowered by the recirculation of the EGR gas, the fuel consumption can be improved.

JP 2012-241608 A

  In general, a fuel tank is provided with a canister for collecting vaporized fuel in order to suppress release of vaporized gasoline fuel (vaporized fuel) into the atmosphere. The vaporized fuel collected by the canister must be purged to the intake system of the engine before the amount of collection in the canister reaches the upper limit. Here, since the purge of the vaporized fuel collected by the canister needs to be performed under a negative pressure, for example, the purge is performed in a low load operation state where the intake pressure is low.

  Some engines that perform EGR are further provided with a supercharger. In such an engine, when the supercharger is operating during the execution of EGR, there is a problem that it is difficult to purge the EGR passage because the pressure in the EGR passage is further increased by the supercharger.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide an EGR for the vaporized fuel collected by a canister at a desired timing in an engine equipped with a supercharger and executing EGR. It is to provide a method for controlling an engine that can be purged into a passage.

  The engine control method according to the present invention includes a turbocharger including a turbine and a compressor, an EGR passage that branches from a downstream side of the turbine in the exhaust passage and merges upstream of the compressor in the intake passage, and vaporization in the fuel tank. A canister that collects fuel, a purge passage that purges vaporized fuel collected by the canister to the EGR passage, and an admission valve that is provided on the upstream side of the junction with the EGR passage in the intake passage; An engine comprising: an EGR valve provided upstream of a junction with the purge passage in the EGR passage; and a PCV valve provided between the canister and a place where the purge to the EGR passage is performed in the purge passage. It is a control method. When it is determined that EGR is to be executed, the engine control method is such that the opening of the admission valve is made smaller than before the EGR is performed, and the EGR valve is opened to execute the EGR. If it is determined that purging is to be performed, the opening of the EGR valve is made smaller than that when it is determined that EGR is to be performed, and purging is performed by opening the PCV valve.

  According to the present invention, purge can be performed at a desired timing.

FIG. 1 is a schematic configuration diagram of an engine system of the present embodiment. FIG. 2 is a flowchart showing purge control.

  Hereinafter, an engine system according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic configuration diagram of an engine system 100 according to the present embodiment. The engine system 100 is mounted on a vehicle. The engine system 100 is provided with an intake passage 10 for sending intake air to the engine (internal combustion engine) 1 and an exhaust passage 20 through which exhaust from the engine 1 passes.

  In the intake passage 10, an air flow meter 11, an admission valve 12, a compressor 2 </ b> A of a turbocharger 2, a pressure sensor 13, a throttle valve 14, and a water-cooled type are sequentially installed from the upstream side of the intake flow. An intercooler (WCAC) 15 is disposed. Intake air is supplied to the engine 1 through the intake passage 10.

  The intake passage 10 is provided with a bypass passage that branches at a downstream position of the compressor 2A and joins the upstream position of the compressor 2A. A recirculation valve 16 is provided in the bypass passage. When the intake pressure measured by the pressure sensor 13 is higher than a predetermined value, the controller 50 opens the recirculation valve 16 to recirculate the intake air via the bypass path. If it does in this way, since supercharging by compressor 2A is controlled, intake pressure can be lowered.

  The throttle valve 14 is driven and controlled by the controller 50. The intake air whose intake pressure is adjusted by the throttle valve 14 is cooled by the intercooler 15 and then introduced into the engine 1. The intercooler 15 is a water-cooled type, and the strength of cooling can be controlled by controlling the flow rate of water.

  The engine 1 is provided with a fuel injection device 17. By controlling the fuel injection device 17 at a predetermined timing, fuel is injected into a cylinder of the engine 1, and a mixture of fuel and air in the cylinder. Is formed. A spark plug 18 is provided in the cylinder, and the air-fuel mixture is combusted using the spark plug 18.

  The combustion gas of the engine 1 is discharged to the exhaust passage 20. In the exhaust passage 20, in order from the upstream side of the exhaust flow, the turbine 2 </ b> B of the supercharger 2, an air-fuel ratio sensor 21, a three-way catalyst (hereinafter also simply referred to as “catalyst”) 22 for purifying exhaust, A silencer 23 is arranged to reduce the sound generated by the exhaust. The catalyst 22 is not limited to a three-way catalyst, and may be an oxidation catalyst.

  The turbine 2B of the supercharger 2 is rotated by exhaust energy. Along with the rotation of the turbine 2B, the compressor 2A provided coaxially with the turbine 2B rotates. Then, the intake air introduced into the cylinder of the engine 1 is supercharged by the rotation of the compressor 2A.

  The exhaust passage 20 is provided with a bypass passage that bypasses the turbine 2B. The bypass path is configured to be openable and closable by a waste gate valve 24. When the exhaust pressure becomes too high, the exhaust pressure can be lowered by opening the waste gate valve 24.

  Although this embodiment demonstrates the case where the turbocharger 2 of an exhaust turbine system is used, it is not necessarily limited to this. For example, a mechanical supercharger may be used.

  The engine system 100 further includes an exhaust gas recirculation passage (hereinafter also referred to as an “EGR passage”) 30 that communicates the downstream side of the turbine 2B in the exhaust passage 20 and the upstream side of the compressor 2A in the intake passage 10. . Specifically, the EGR passage 30 branches in the exhaust passage 20 at the downstream side of the air-fuel ratio sensor 21 and at the upstream side of the three-way catalyst 22, and in the intake passage 10, the admission valve 12 and the upstream side of the branch point of the bypass passage.

  In the EGR passage 30, an EGR valve 31 that controls the amount of exhaust gas (EGR gas) flowing through the EGR passage 30 and an EGR cooler 32 that cools the EGR gas are arranged. The EGR valve 31 is controlled by the controller 50. The EGR passage 30, the EGR valve 31, and the EGR cooler 32 are sometimes referred to as an “EGR device”.

  The EGR device of the present embodiment corresponds to a so-called low pressure / EGR device in which the EGR passage 30 connects the downstream of the turbine 2B in the exhaust passage 20 and the upstream of the compressor 2A in the intake passage 10.

  The engine system 100 further includes a purge passage 40. The purge passage 40 is a fuel passage in which vaporized fuel in the fuel tank 41 is collected by the canister 42 and then purged. In the present embodiment, the vaporized fuel is purged to the EGR passage 30. The fuel tank 41 stores fuel supplied to the engine 1 via the fuel injection device 17.

  Further, a canister 42 is provided so as to communicate with the fuel tank 41, and vaporized fuel evaporated in the fuel tank 41 is collected by the canister 42. The purge passage 40 joins the EGR passage 30 downstream of the EGR valve 31 and the EGR cooler 32, and the vaporized fuel collected by the canister 42 is purged at this joining point. The purge passage 40 is provided with a PCV (Positive Crankcase Ventilation) valve 43 at a stage preceding the point where vaporized fuel is purged into the EGR passage 30. When the controller 50 controls the opening and closing of the PCV valve 43, the vaporized fuel purge can be turned on / off.

  The controller 50 includes a crank angle sensor (not shown), an accelerator opening sensor (not shown), in addition to the intake air flow rate measured by the air flow meter 11 and the air-fuel ratio in the exhaust gas measured by the air-fuel ratio sensor 21. ) Is also input. Based on these detected values, the controller 50 controls the opening of the throttle valve 14, the fuel injection control using the fuel injection device 17, the ignition timing control using the ignition plug 18, and the opening control of the EGR valve 31. And so on. The controller 50 includes a microcomputer that includes a central processing unit (CPU), a read-only memory (ROM), a random access memory (RAM), and an input / output interface (I / O interface). The controller 50 can be composed of a plurality of microcomputers.

  When the operating condition of the engine 1 satisfies a predetermined EGR execution condition, the controller 50 executes EGR and recirculates EGR gas. In general, EGR is performed when the required load of the engine 1 corresponding to the accelerator opening is low and the combustion is stably performed such that the opening of the throttle valve 14 is small.

  Note that the controller 50 controls the opening degree of the EGR valve 31 after the start of EGR. Specifically, the controller 50 uses a table or the like to calculate the EGR rate during intake air from the oxygen concentration detected by an intake oxygen concentration sensor (not shown) provided in the intake passage 10 after the EGR gas has merged. calculate. Then, the controller 50 feedback-controls the opening degree of the EGR valve 31 so that the calculated EGR rate coincides with the target EGR rate that is uniquely determined according to the operating conditions.

  When the EGR gas is recirculated to the intake passage 10, it is necessary to increase the opening of the throttle valve 14 by an amount corresponding to the increased amount of intake air by the EGR gas. It is known to do. In addition, when EGR gas is recirculated to the intake passage 10, the combustion temperature of the air-fuel mixture in the cylinder of the engine 1 is lowered and the knocking resistance is improved. Therefore, the retard amount of the ignition timing for avoiding knocking is reduced. It is also known that fuel consumption performance is improved by making it smaller (advancing the lead angle).

  Further, the controller 50 calculates the air-fuel ratio feedback correction coefficient based on the output of the air-fuel ratio sensor 21 so that the air-fuel ratio of the exhaust matches the target air-fuel ratio. Further, the controller 50 corrects the air-fuel ratio feedback correction coefficient based on a detection value of an exhaust oxygen concentration sensor (not shown) provided in the exhaust passage 20. Then, the controller 50 feedback-controls the amount of fuel supplied from the fuel injection device 17 using the corrected air-fuel ratio feedback correction coefficient.

  Here, in order to purge the vaporized fuel collected by the canister 42 into the EGR passage 30, the EGR passage 30 needs to have a negative pressure. Therefore, in the present embodiment, the purge can be performed by generating a negative pressure in the EGR passage 30 by making the opening degree of the EGR valve 31 smaller than the opening degree during normal EGR execution. In addition, when performing EGR, by reducing the opening degree of the admission valve 12, the intake pressure is lowered and it becomes easier to execute EGR.

  Note that when EGR is executed, the temperature of the intake air to the engine 1 decreases and knocking is less likely to occur. Therefore, the ignition timing can be advanced to ignite at the optimal ignition timing. In the present embodiment, when purging is performed, the flow rate of the EGR gas is decreased by the amount by which the opening degree of the EGR valve 31 is decreased. Therefore, by reducing (retarding) the advance amount, Occurrence can be suppressed. Further, if the fuel injected from the fuel injection device 17 is the same regardless of the presence or absence of purge, opening the PCV valve 43 causes more fuel to be supplied to the engine 1 by the purge amount, so that torque fluctuation is likely to occur. . Therefore, torque fluctuation can be suppressed by retarding the ignition timing.

  FIG. 2 is a diagram illustrating a flowchart of purge control performed by the controller 50. The purge control is programmed in the ROM of the controller 50 and is repeatedly performed during operation.

  In step S1, the controller 50 determines whether or not the required load of the engine 1 corresponding to the accelerator opening or the like is smaller than a threshold load Tp that is a threshold for performing EGR. In general, it is preferable to perform EGR when the required load is low. Therefore, when the required load is smaller than the threshold load Tp (S1: Yes), the controller 50 next executes step S2 in order to determine a further execution condition of EGR. When the required load is equal to or greater than the threshold load Tp (S1: No), the controller 50 executes Step S1 again.

  In step S2, the controller 50 determines whether or not the opening degree of the throttle valve 14 (throttle opening degree) is smaller than the opening degree X that is a threshold value for performing EGR. In general, EGR is preferably performed when the throttle opening is small. Therefore, when the throttle opening is smaller than the threshold opening X (S2: Yes), the controller 50 next executes step S3 in order to perform EGR. If the throttle opening is equal to or greater than the threshold opening X (S2: No), the controller 50 executes Step S1 again.

  In step S3, the controller 50 makes the opening of the admission valve 12 smaller than the opening during normal operation without EGR in order to perform EGR by reducing the pressure in the intake passage 10. And the controller 50 performs the process of step S4 next.

  In step S4, the controller 50 opens the EGR valve 31 and performs EGR. And the controller 50 performs the process of step S4 next. In this case, the opening degree of the EGR valve 31 is set to the opening degree θn at the time of normal EGR execution without purging.

  In step S <b> 5, the controller 50 determines whether it is time to purge the vaporized fuel collected by the canister 42. The purging may be repeated at a predetermined period calculated in advance, or at a timing when the fuel pressure in the canister 42 exceeds a predetermined threshold, or at a timing when the travel distance from the previous purge exceeds the threshold. May be. If it is the purge timing (S5: Yes), the controller 50 next executes the process of step S6. If it is not the purge timing (S5: No), the controller 50 ends the purge control.

  When purging is performed during execution of EGR, the process of step S6 is executed. In the process of step S6, the controller 50 makes the opening degree of the EGR valve 31 smaller than the opening degree θn at the time of normal EGR execution without purging in S4. By doing in this way, the pressure of the EGR passage 30 can be reduced. Then, the controller 50 next executes the process of step S7.

  In step S7, the controller 50 opens the PCV valve 43. Since the pressure decreases in the EGR passage 30 and the negative pressure is generated, the vaporized fuel collected by the canister 42 is supplied from the purge passage 40 to the EGR passage 30 through the PCV valve 43. The

  In step S7, the PCV valve 43 may not be kept open for a certain period, but may be opened and closed intermittently. By doing in this way, since it is suppressed that the fuel collected by the canister 42 is purged in large quantities at once, the driving | operation of the engine 1 can be stabilized more.

  In step S8, the controller 50 determines whether it is time to end the purge. If it is time to end the purge (S8: Yes), the controller 50 ends the purge process. If it is not time to end the purge (S8: No), the controller 50 returns to the process of step S4. Generally, the purge is ended after the PCV valve 43 is opened for a predetermined time from the start of the purge (S5: Yes).

  According to the present embodiment, the following effects can be obtained.

  According to the present embodiment, the engine system 100 includes the supercharger 2, branches from the downstream side of the turbine 2 </ b> B in the exhaust passage 20, and joins the upstream side of the compressor 2 </ b> A in the intake passage 10. It has. In the engine system 100 capable of executing such low pressure EGR, the opening of the admission valve 12 is reduced and the intake pressure in the intake passage 10 is reduced (S3). And EGR is performed by setting the opening degree of the EGR valve 31 to the opening degree θn at the time of normal EGR before performing the purge (S4).

  The vaporized fuel vaporized in the fuel tank 41 is collected by the canister 42. The collected vaporized fuel must be purged before the collected amount of the canister 42 reaches the upper limit. In order to purge the vaporized fuel collected by the canister 42, it is necessary to generate a negative pressure at the purge destination. Therefore, in this embodiment, since it is determined that it is time to execute the purge in order to perform the purge in the EGR passage 30 (S5: Yes), the opening degree of the EGR valve 31 is set to the opening at the normal EGR before the purge is performed. By making it smaller than degree θn, a negative pressure is generated in the EGR passage 30 (S6).

  In this state, when the PCV valve 43 provided in the purge passage 40 at a stage before the connection point with the EGR passage 30 is opened, the vaporized fuel collected by the canister 42 passes through the purge passage 40 and the EGR passage 30. (S7).

  Thus, in the engine system 100 that includes the supercharger 2 and performs the low pressure EGR, the purge can be executed even when the EGR is being executed. Further, by purging the EGR passage 30 during EGR, the vaporized fuel to be purged can be used for traveling more efficiently than in the case of purging in the idle state, so that fuel efficiency can be improved.

  According to the present embodiment, the ignition timing of the engine 1 is retarded when performing the purge. When EGR is executed, since the intake air temperature to the engine 1 is lowered, knocking is less likely to occur. Therefore, the ignition timing is advanced to ignite at the optimal ignition timing. In the present embodiment, when purging is performed, the flow rate of the EGR gas is reduced by the amount by which the opening degree of the EGR valve 31 is reduced, so that knocking is likely to occur. Therefore, the occurrence of knocking can be suppressed by reducing (retarding) the advance amount.

  Further, if the fuel injected from the fuel injection device 17 is the same regardless of whether or not the purge is performed, when the PCV valve 43 is opened, the fuel is supplied to the engine 1 as much as the engine 1 is purged. Fluctuation is likely to occur. Therefore, the occurrence of torque fluctuation can be suppressed by retarding the ignition timing.

  According to the present embodiment, when purging, the PCV valve 43 is opened and closed intermittently. Here, if control is performed such that the PCV valve 43 is kept open for a certain period of time, the vaporized fuel is purged at a time, so that the energy of the purged vaporized fuel becomes unnecessary thermal energy other than rotational drive in the engine 1. There is a high risk of becoming. However, by intermittently opening and closing the PCV valve 43 and purging the vaporized fuel over a longer period of time, the energy of the purged vaporized fuel can be used for the rotational drive of the engine 1, thereby improving fuel efficiency. be able to.

  The embodiment of the present invention has been described above. However, the above embodiment only shows a part of application examples of the present invention, and the technical scope of the present invention is limited to the specific configuration of the above embodiment. Absent.

DESCRIPTION OF SYMBOLS 1 Engine 2 Supercharger 10 Intake passage 12 Admission valve 20 Exhaust passage 30 EGR passage 31 EGR valve 40 Purge passage 41 Fuel tank 42 Canister 43 PCV valve 50 Controller

Claims (4)

A turbocharger comprising a turbine and a compressor;
An EGR passage that branches from the downstream side of the turbine in the exhaust passage and merges upstream of the compressor in the intake passage;
A canister that collects vaporized fuel in the fuel tank;
A purge passage for purging the vaporized fuel collected by the canister to the EGR passage;
In the intake passage, an admission valve provided on the upstream side of the junction with the EGR passage;
An EGR valve provided upstream of a junction with the purge passage in the EGR passage;
In the purge passage, an engine control method comprising: the canister and a PCV valve provided between the place where the purge to the EGR passage is performed,
When it is determined that EGR is to be executed, the opening of the admission valve is made smaller than before the EGR is performed, and the EGR valve is opened to execute the EGR.
When it is determined that purging is performed during the execution of the EGR, the opening degree of the EGR valve is made smaller than the opening degree when it is determined that the EGR is executed, and the PCV valve is opened. , Purge, engine control method. The engine control method according to claim 1,
An engine control method that retards the ignition timing of the engine when it is determined to execute the purge. An engine control method according to claim 1 or 2,
An engine control method for intermittently opening and closing the PCV valve when it is determined that the purge is to be executed. A turbocharger comprising a turbine and a compressor;
An EGR passage that branches from the downstream side of the turbine in the exhaust passage and merges upstream of the compressor in the intake passage;
A canister that collects vaporized fuel in the fuel tank;
A purge passage for purging the vaporized fuel collected by the canister to the EGR passage;
In the intake passage, an admission valve provided on the upstream side of the junction with the EGR passage;
An EGR valve provided upstream of a junction with the purge passage in the EGR passage;
In the purge passage, a PCV valve provided on the upstream side of the place where the purge to the EGR passage is performed;
A controller that controls the admission valve, the EGR valve, and the PCV valve;
The controller is
When it is determined that EGR is to be executed, the opening of the admission valve is made smaller than before the EGR is performed, and the EGR valve is opened to execute the EGR.
When it is determined that purging is performed during the execution of the EGR, the opening degree of the EGR valve is made smaller than the opening degree when it is determined that the EGR is executed, and the PCV valve is opened. , Purge, engine.

Images