JP2015059560A - Egr device and exhaust gas recirculation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an EGR device and an exhaust gas recirculation method which can prevent an exhaust gas from generating HC during early warm-up control thereof and under a low load by changing use of an EGR cooler depending on whether or not the exhaust gas is under early warm-up control and an operation state of the engine in a manner that introduces a high-temperature EGR gas, when cooling the EGR gas is not required, directly into a cylinder without letting the EGR gas pass through the EGR cooler.SOLUTION: The EGR device recirculates an exhaust gas Ge using an EGR bypass passage 24 which circumvents an EGR cooler 22 when early warm-up control to increase a temperature of the exhaust gas Ge is not executed and an operation region of an engine 10 is in a first low load region Ra or when the early warm-up control is executed and the operation region of the engine 10 is in the first low load region Ra or a second low load region Rb having a load larger than the first low load region Ra.

Description

  The present invention relates to an EGR device that recirculates exhaust gas of an engine and an exhaust gas recirculation method. More specifically, the present invention relates to EGR that can suppress the generation of hydrocarbons (HC) during early temperature rise control for raising the temperature of exhaust gas. The present invention relates to an apparatus and an exhaust gas recirculation method.

  In recent years, it has been necessary to comply with strict regulations on exhaust gas emitted from internal combustion engines such as diesel engines, and as a method of reducing exhaust gas components on the engine body side, EGR which is part of exhaust gas emitted from the engine EGR devices that recirculate gas to the intake passage or intake manifold are used. In this EGR device, in order to increase the intake efficiency of the intake air (fresh air) into the cylinder, an EGR cooler is provided in the EGR passage to cool the EGR gas, reduce its volume, and merge with the intake air.

  With regard to this EGR device, in addition to the EGR passage provided with the EGR cooler, a bypass passage that bypasses the EGR cooler is provided, and these passages are switched according to the operating state of the engine, or the bypass valve provided in the bypass passage is opened. By adjusting the degree, the flow rate of the EGR gas flowing through the EGR cooler is adjusted, the EGR gas temperature is adjusted, and the temperature of the exhaust gas discharged to the exhaust passage is adjusted via the temperature of the EGR gas. EGR devices have been proposed (see, for example, Patent Documents 1 and 2).

  On the other hand, when the temperature of the exhaust gas at the start of the engine is low, or when the temperature of the exhaust gas decreases due to running in an urban area, etc., in order to make the exhaust gas purification device arranged in the exhaust passage work effectively, It is necessary to raise the temperature of the exhaust gas discharged from the engine to the exhaust passage so that the temperature of the catalyst of the exhaust gas purification device becomes higher than the activation temperature and improve the exhaust gas purification performance at an early stage.

  However, in the prior art, once it is determined that the warm-up has been completed, the EGR gas is controlled so as to always pass through the EGR cooler. Therefore, when the engine operating state is in the low load region, Since the EGR gas having a low temperature flows into the cylinder and the temperature in the cylinder decreases, there is a problem that the combustion in the cylinder deteriorates and the amount of hydrocarbon (HC) generated increases.

  In addition, when early warming control is performed to warm the exhaust gas when the engine is warmed up or when the exhaust gas temperature decreases, the injection timing in the cylinder fuel injection, the ratio change between the main injection amount and the sub injection amount, etc. Therefore, there is a problem that HC is more likely to be generated than when the engine operating region is in a low load region during normal operation.

Japanese Patent Laid-Open No. 11-200955 JP 2010-163938 A

  The present invention has been made in order to solve the above-described problems, and an object of the present invention is to cool the EGR gas by properly using the EGR cooler depending on whether or not the early temperature increase control is being performed and the operating state of the engine. Is not required to pass through the EGR cooler, the EGR gas having a high temperature is introduced into the cylinder to prevent HC from being generated during the early temperature rise control of the exhaust gas or at a low load. To provide an EGR device and an exhaust gas recirculation method.

  An EGR device for achieving the above object includes an EGR passage for recirculating engine exhaust gas, an EGR cooler provided in the EGR passage, an EGR bypass passage for bypassing the EGR cooler, and the EGR passage. And an EGR device having a switching valve for switching the flow path of the EGR bypass passage, when the engine operating range is the first low load range when the early temperature increase control for increasing the exhaust gas temperature is not being performed. The exhaust gas is recirculated using a passage, and the engine operating region is in the first low load region or the second low load region where the load is larger than the first low load region in the case of the early temperature increase control. There is provided switching valve control means for controlling the switching valve so as to recirculate the exhaust gas using the EGR bypass passage. Constructed.

  According to this configuration, it is determined whether or not the early temperature increase control is being performed, and whether the engine operating region is the first low load region, the second low load region, or any other region. Since the passage with the EGR cooler and the EGR bypass passage that bypasses the EGR cooler are properly used, when cooling of the EGR gas is unnecessary, the EGR gas is not allowed to pass through the EGR cooler, and the high temperature EGR gas is in-cylinder ( Can be introduced into the cylinder).

  Further, the engine operating range when using the EGR bypass passage is the first low load region or the second low load region in which the load is larger during the early temperature increase control than during the early temperature increase control. By using the low load range, the engine load range when using the EGR bypass passage in the early temperature rise control is expanded to the second low load range, so HC is generated during the early temperature rise control of the exhaust gas. It is possible to raise the temperature of the exhaust gas at an earlier stage while preventing this from occurring more effectively. That is, HC generation under a low load condition can be suppressed by the early temperature rise control.

  In the above EGR apparatus, the switching valve control means uses the EGR cooler when the engine operating region is a region where the load is larger than the first low load region when the early temperature raising control is not being performed. The exhaust gas is recirculated using the EGR cooler when the gas is cooled and the exhaust gas is recirculated and the engine operating region is a region where the load is larger than the second low-load region in the case of the early temperature rise control. When the exhaust gas is recirculated and the exhaust gas is recirculated, when the EGR gas needs to be cooled in order to increase the EGR efficiency, the EGR gas is cooled by passing through the EGR cooler, and the temperature is lowered. Can be introduced into the cylinder.

  An exhaust gas recirculation method for achieving the above object is an exhaust gas recirculation method for recirculating the exhaust gas of the engine, in the case where the early temperature increase control for raising the temperature of the exhaust gas of the engine is not in progress. When the operating region is the first low load region, the first step of recirculating exhaust gas without cooling is performed, and the engine operating region is the first low load region when the early temperature increase control is being performed. Alternatively, in the second low load region where the load is larger than that of the first low load region, the second step of recirculating the exhaust gas without cooling is performed.

  Further, in the above exhaust gas recirculation method, when the early temperature increase control is not being performed and the engine operating region is a region where the load is larger than the first low load region, the exhaust gas is cooled to exhaust gas When the early temperature rise control is being performed and the engine operating region is a region where the load is larger than the second low load region, the exhaust gas is cooled to recirculate the exhaust gas. The fourth step is performed.

  According to these exhaust gas recirculation methods, the same effects as those of the above EGR device can be obtained.

  According to the EGR device and the exhaust gas recirculation method according to the present invention, whether or not the early temperature increase control is being performed and whether the engine operating region is the first low load region, the second low load region, or any other region. The EGR cooler and the EGR bypass passage that bypasses the EGR cooler are selectively used according to the determination result. Therefore, when cooling of the EGR gas is unnecessary, the EGR gas is not allowed to pass through the EGR cooler. High temperature EGR gas can be introduced into the cylinder.

  Furthermore, since the engine load range when using the EGR bypass passage in the early temperature rise control is expanded to the second low load range, it is more effective that HC is generated during the early temperature rise control of the exhaust gas. It is possible to raise the temperature of the exhaust gas at an earlier stage while preventing it.

It is a figure showing composition of an engine provided with an EGR device of an embodiment concerning the present invention. It is a figure which shows typically the 1st low load area | region and the 2nd low load area | region in the exhaust-gas recirculation method which concerns on this invention. It is a figure which shows the flow of control of the exhaust-gas recirculation method which concerns on this invention.

  Hereinafter, an EGR device and an exhaust gas recirculation method according to embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a configuration of an engine (internal combustion engine) 10 including an EGR device 20 according to an embodiment of the present invention. The engine 10 includes an engine body 11, an intake passage 12, an exhaust passage 16, and an EGR passage 21 that connects the exhaust passage 16 and the intake passage 12.

  In the intake passage 12 through which the intake air A passes, an intake air amount sensor (MAF: not shown), a compressor 13a of the turbo-type supercharger 13, an intercooler 14, an intake valve 15 and the like are arranged in order from the upstream side. In addition, in the exhaust passage 16 through which the exhaust gas Go passes, a turbine 13b of the turbocharger 13, an exhaust throttle valve 17, an exhaust gas purification system 30 and the like are arranged in order from the upstream side.

  The exhaust gas purification system 30 includes a DPD system 31 having a pre-stage oxidation catalyst device (DOC) 31a and a filter with catalyst (CSF) 31b, an SCR (selective reduction catalyst) device 32a, an ammonia slip prevention catalyst 32b, and a reducing agent. An SCR system 32 having a supply device 32c, an exhaust gas temperature sensor, a filter front-rear differential pressure sensor, a NOx concentration sensor, and the like are used to purify PM, NOx and the like in the exhaust gas Go, and the purified exhaust gas Gc is It is discharged into the atmosphere from a tail pipe (not shown).

  Further, an EGR device 20 is disposed. In the configuration shown in FIG. 1, the EGR device 20 connects the exhaust passage 16 upstream of the turbine 13b and the intake passage 12 downstream of the compressor 13a, thereby connecting the exhaust gas. The EGR passage 21 through which the EGR gas Ge that is a part of Go passes, and the EGR cooler 22 and the EGR valve 23 that are sequentially disposed in the EGR passage 21 from the upstream side are configured. At the same time, an EGR bypass passage 24 that bypasses the EGR cooler 22 is provided, and a switching valve 25 is provided in the EGR bypass passage 24. The switching valve 25 is configured as an ON / OFF valve that performs an alternative of passing the flow of the exhaust gas (EGR gas) Ge through the EGR cooler 22 or the EGR bypass passage 24.

  In addition, a control device 40 called an engine control module (ECM) that performs overall engine control is provided. The control device 40 inputs a rotational speed Ne indicating the operating state of the engine 10 and a fuel injection amount q (or load Q), and also detects a cooling water temperature Tw and an intake air temperature detected by a cooling water temperature sensor (not shown). The intake air temperature Ta detected by the sensor, the EGR cooler outlet temperature To detected by the outlet exhaust gas temperature sensor of the EGR cooler 22, etc. are input to control the EGR valve 23 and the switching valve 25, Control fuel injection. Further, exhaust gas purification is efficiently performed based on the temperature detected by the exhaust gas temperature sensor, the differential pressure sensor before and after the filter, the NOx concentration sensor, etc., the differential pressure before and after the filter, the NOx concentration, and the like. Therefore, the exhaust gas purification system 30 is controlled.

  On the other hand, when the temperature of the exhaust gas Go in the warm-up at the start of the engine 10 is low, or when the temperature of the exhaust gas Go decreases due to running in an urban area, the exhaust gas purification system 30 disposed in the exhaust passage 16 is used. In order to make the engine work effectively, the temperature of the exhaust gas Go discharged to the exhaust passage 16 of the engine 10 is raised so that the temperature of the catalyst of the device of the exhaust gas purification system 30 is higher than the activation temperature. It is necessary to perform early temperature rise control that improves the temperature at an early stage. In this early temperature raising control, the injection timing in the cylinder fuel injection, the ratio change between the main injection amount and the sub injection amount, and the like are performed.

  In the present invention, the control device 40 includes the switching valve control means 41 that controls the switching valve 25. Further, as shown in FIG. 2, the operating range of the engine 10 (engine speed Ne and fuel injection amount q (or load Q)) is divided into a first low load region Ra and a load from the first low load region Ra. Dividing into a large second low load region Rb and other load regions Rc, the ranges of these regions are set in advance. The range of each region is set by previously determining whether or not the exhaust gas Ge used for EGR needs to be cooled by experiments or the like, and stored in the switching valve control means 41 in advance.

  For example, for each engine speed Ne, a first fuel injection amount qa (Ne) and a second fuel injection amount qb (Ne) are set and stored in the form of map data, functions, etc. The fuel injection amount q is equal to or less than the first fuel injection amount qa (Ne) in the first low load region Ra, the fuel injection amount q is larger than the first fuel injection amount qa (Ne), and the fuel injection amount q is the first fuel injection amount q. 2 The fuel injection amount qb (Ne) or less is set in the second low load region Rb, and when the fuel injection amount q is larger than the second fuel injection amount qb (Ne), it is set in the other load region Rc. Instead of the fuel injection amount q, the first fuel injection amount qa (Ne), and the second fuel injection amount qb (Ne), the load Q, the first load Qa (Ne), and the second load Qb (Ne) are used. May be.

  The determination of the first low load region Ra and the second low load region Rb may be performed using the fuel injection amount q (load Q), the coolant temperature Tw, the outlet gas temperature To of the EGR cooler 22, and the like. . When the cooling water temperature Tw is used, the threshold value of the cooling water temperature Tw is set to about 60 ° C. during the normal control, and is used for the inside / outside determination of the first low load region Ra. This is because the switching valve 25 is always closed and the exhaust gas Ge flows to the EGR cooler 22 side after warming up when the cooling water temperature Tw becomes higher than about 60 ° C.

  Further, during the early temperature rise control, the threshold value of the cooling water temperature Tw is invalidated by setting it to a large value that does not substantially exceed the cooling water. This is because the coolant temperature Tw may increase during traveling during the early temperature rise control, and the internal / external determination of the second low load region Rb is made except for the coolant temperature Tw (for example, fuel injection amount, load, EGR). (Cooler outlet temperature). As a result, it is possible to reliably prevent the generation of HC without closing the switching valve 25 in the second low load region Rb.

  Then, the switching valve control means 41 uses the EGR bypass passage 24 to exhaust gas (EGR) when the operating region of the engine 10 is the first low load region Ra when the early temperature raising control for increasing the exhaust gas temperature is not being performed. Gas) Ge is refluxed. At the same time, when the operating range of the engine 10 is the first low load region Ra or the second low load region Rb in the case of the early temperature rise control, switching is performed so that the exhaust gas Ge is recirculated using the EGR bypass passage 24. It is configured to control the valve 25.

  Further, the switching valve control means 41 uses the EGR cooler 22 when the operating range of the engine 10 is the regions Rb and Rc where the load is larger than the first low load region Ra when the early temperature raising control is not being performed. The exhaust gas Ge is refluxed by cooling Ge. In addition, the exhaust gas Ge is recirculated using the EGR cooler 22 when the operating region of the engine 10 is in the other region Rc where the load is larger than the second low load region Rb in the case of the early temperature rise control. Is done.

  Next, the exhaust gas recirculation method in the EGR device 20 will be described with reference to the control flow illustrated in FIG. The control flow shown in FIG. 3 starts when the engine 10 is started, is called from the advanced control flow, is executed from the start to the return, returns to the advanced control flow, and is called from the advanced control flow. The control flow is repeatedly executed.

  When the control flow of FIG. 3 is called from the advanced control flow and starts, it is determined in step S11 whether or not the engine 10 is in the early temperature raising control. If it is determined in step S11 that early temperature increase control is not being performed (NO), the process proceeds to step S12.

  In step S12, it is determined whether or not the operating region of the engine 10 is in the first low load region Ra. Whether or not the vehicle is in the first low load region Ra is input by inputting the current engine speed Ne and the fuel injection quantity q, and the fuel injection quantity q is equal to the first fuel injection quantity qa (Ne with respect to the engine speed Ne). ) If it is equal to or less than the first low load region Ra (YES), and if the fuel injection amount q is larger than the first fuel injection amount qa (Ne), it is not in the first low load region Ra and the first It is assumed that the area is larger than the low load area Ra (NO).

If it is determined in step S12 that the operating region of the engine 10 is in the first low load region Ra (YES), control is passed to step S14 to open the switching valve 25, and If the valve is being opened, control is performed to maintain the valve opening, and the exhaust gas Ge is guided to the EGR bypass passage 24 to bypass the EGR cooler 22 (first step).
If it is determined in step S12 that the operating region of the engine 10 is not in the first low load region Ra (NO), the process goes to step S15 to perform control for closing the switching valve 25. If the valve is closed, control is performed to keep the valve closed, and the exhaust gas Ge is guided to the EGR cooler 22 (third step).

  If it is determined in step S11 that early temperature increase control is being performed (YES), the process goes to step S13.

  In step S13, it is determined whether or not the operating region of the engine 10 is in the first low load region Ra or the second low load region Rb. Whether or not the vehicle is in the first low load region Ra or the second low load region Rb is determined by inputting the current engine speed Ne and the fuel injection amount q, and the fuel injection amount q is a second value with respect to the engine speed Ne. If it is equal to or less than the fuel injection amount qb (Ne), it is in the first low load region Ra or the second low load region Rb (YES), and if the fuel injection amount q is larger than the second fuel injection amount qb (Ne). , It is not in the first low load region Ra or the second low load region Rb, but is assumed to be another load region Rc (NO).

  If it is determined in step S13 that the operation region of the engine 10 is in the first low load region Ra or the second low load region Rb (YES), the process goes to step S14 and the switching valve 25 is opened. If the valve is open, control is performed to maintain the valve open, and the exhaust gas Ge is guided to the EGR bypass passage 24 to bypass the EGR cooler 22 (second step).

  If it is determined in step S13 that the operating region of the engine 10 is not in the first low load region Ra or the second low load region Rb (NO), the process goes to step S15 and the switching valve 25 is turned on. Control is performed to close the valve, and if the valve is closed, control to maintain the valve close is performed to guide the exhaust gas Ge to the EGR cooler 22 (fourth step).

  That is, the first step of recirculating using the EGR bypass passage 24 when the operating region of the engine 10 is the first low load region Ra when the temperature of the exhaust gas Go of the engine 10 is not under early temperature increase control is being performed. If the operating range of the engine 10 is the first low load region Ra or the second low load region Rb where the load is larger than the first low load region Ra, the EGR bypass passage 24 is performed. Is used to perform a second step of recirculating the exhaust gas Ge.

  Further, when the early temperature rise control is not being performed and the operating region of the engine 10 is the regions Rb and Rc where the load is larger than the first low load region Ra, the exhaust gas Ge is cooled using the EGR cooler 22 and exhausted. The third step of recirculating the gas Ge is performed, and when the operating region of the engine 10 is the region Rc where the load is larger than the second low load region Rb in the case of the early temperature increase control, the exhaust gas is exhausted using the EGR cooler 22 A fourth step of cooling the Ge and refluxing the exhaust gas Ge is performed.

  When a predetermined time (time related to the control interval of the switching valve) elapses in step S14 or step S15, the process goes to return and returns to the advanced control flow.

  According to the EGR device 20 and the exhaust gas recirculation method described above, whether or not the early temperature increase control is being performed, whether the operating region of the engine 10 is the first low load region Ra, the second low load region Rb, or the other region Rc. Since the EGR cooler 22 and the EGR bypass passage 24 are selectively used according to the determination result, the EGR gas Ge is allowed to pass through the EGR cooler 22 when cooling of the EGR gas Ge is unnecessary. In addition, the EGR gas Ge having a high temperature can be introduced into the cylinder.

  Further, the operating range of the engine 10 when the EGR bypass passage 24 is used is the second low load region where the load is larger during the early temperature increase control than the first low load region Ra when the early temperature increase control is not being performed. Since it has expanded to Rb, it is possible to raise the temperature of the exhaust gas Go earlier while more effectively preventing the generation of HC during the early temperature rise control of the exhaust gas Go.

10 Engine (Internal combustion engine)
11 Engine body 12 Intake passage 16 Exhaust passage 20 EGR device 21 EGR passage 22 EGR cooler 23 EGR valve 24 EGR bypass passage 25 Switching valve 21 EGR passage 30 Exhaust gas purification system 40 Control device 41 Switching valve control means A Intake Gc Purified Exhaust gas Ge Exhaust gas (EGR gas)
Go Exhaust gas Ne Rotational speed q Fuel injection amount qa First fuel injection amount qb Second fuel injection amount Q Load Ra First low load region Rb Second low load region Rc Other load regions Ta Inlet temperature To EGR cooler outlet temperature Tw Cooling water temperature

Claims (4)

An EGR passage for recirculating the exhaust gas of the engine, an EGR cooler provided in the EGR passage, an EGR bypass passage for bypassing the EGR cooler, and a switching valve for switching between the EGR passage and the EGR bypass passage. In the EGR device,
When the engine operating region is the first low load region when the early temperature raising control for increasing the exhaust gas temperature is not being performed, the exhaust gas is recirculated using the EGR bypass passage,
When the early temperature rise control is being performed and the engine operating region is the first low load region or the second low load region where the load is greater than the first low load region, exhaust is performed using the EGR bypass passage. An EGR device comprising switching valve control means for controlling the switching valve so as to recirculate gas. The switching valve control means includes
When the engine operating region is a region where the load is larger than the first low load region when the early temperature raising control is not being performed, the exhaust gas is cooled using the EGR cooler to recirculate the exhaust gas, and
The exhaust gas is cooled by using the EGR cooler to recirculate the exhaust gas when the early temperature raising control is being performed and the engine operating region is a region where the load is larger than the second low load region. The EGR device according to claim 1. In an exhaust gas recirculation method for recirculating engine exhaust gas,
When the temperature of the exhaust gas of the engine is not in the early temperature increase control and the engine operating region is the first low load region, the first step of recirculating the exhaust gas without cooling is performed.
When the early temperature increase control is being performed, the exhaust gas is not cooled when the operating range of the engine is the first low load range or the second low load range where the load is larger than the first low load range. An exhaust gas recirculation method for performing a second step of recirculating the exhaust gas. When the early temperature raising control is not being performed and the engine operating region is a region where the load is larger than the first low load region, a third step of recirculating the exhaust gas by cooling the exhaust gas is performed,
When the early temperature raising control is being performed and the engine operating region is a region where the load is larger than that of the second low load region, the fourth step is performed to cool the exhaust gas and recirculate the exhaust gas. The exhaust gas recirculation method according to claim 3.

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