JP2008196419A - Egr device for engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an EGR device for an engine capable of executing EGR even in a heavy load region. <P>SOLUTION: The EGR device for the engine 1 provided with a turbocharger 4 is provided with an air cooled EGR cooler 37 cooling EGR gas, a bypass passage 40 leading part of intake air from a compressor 5 of the turbocharger 4 to the air cooled EGR cooler 37 as cooling medium, and a control means (control unit 14) controlling opening/closing of a bypass valve 50 according to an operation condition, and is constructed to make EGR gas passing through the EGR passage 33 radiate heat to intake air passing through the bypass passage 40 under an operation condition where the bypass valve 5 opens. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an improvement of an EGR (Exhaust Gas Recirculation) device provided in an engine having a turbocharger.

In general, an EGR device that recirculates a part of exhaust gas (EGR gas) from an exhaust passage of an engine to an intake passage is provided with a water-cooled EGR cooler that cools the EGR gas so as to increase the EGR rate in a partial load region or the like. (See Patent Document 1).
JP 20059404 A

  However, in an EGR device for an engine having such a turbocharger, the exhaust gas temperature and the intake air temperature become higher in the high load region, and if EGR is performed, the intake air temperature further rises and knocking occurs. There was a problem that the EGR could not be performed in the region, and the engine output could not be sufficiently increased.

  The present invention has been made in view of the above problems, and an object thereof is to provide an EGR device for an engine that can perform EGR even in a high load range.

  In the present invention, an EGR device for an engine having a turbocharger that supercharges intake air by exhaust energy, an EGR passage that communicates an exhaust passage and an intake passage, and an air-cooling type that cools EGR gas that passes through the EGR passage The EGR cooler, a bypass passage for leading a part of the intake air discharged from the compressor of the turbocharger to the air-cooled EGR cooler as a cooling medium, a bypass valve for opening and closing the bypass passage, and opening and closing of the bypass valve according to operating conditions In the operation state in which the bypass valve is opened, the EGR gas passing through the EGR passage is radiated to the intake air passing through the bypass passage in the operation state in which the bypass valve is opened.

  According to the present invention, surplus intake air discharged from the compressor of the turbocharger is used to cool the EGR gas, and knocking of the engine can be suppressed by reducing the temperature of the intake air mixed with the EGR gas. For this reason, EGR can be performed even in a high load region, and the engine knock limit can be extended.

  An embodiment in which the present invention is applied to a CNG engine using compressed natural gas as a fuel will be described with reference to the accompanying drawings.

  As shown in FIG. 1, the CNG engine 1 includes an intake passage 2 that guides intake air to each cylinder, an exhaust passage 22 that discharges exhaust from each cylinder, and a part of the exhaust (hereinafter referred to as EGR gas) is recirculated to the intake passage 2. A circulating EGR passage 33, a turbocharger 4 for supercharging intake air by exhaust energy, and the like are provided.

  In the intake passage 2, in order from the upstream side, an air cleaner 3 that removes foreign matters such as dust from the outside air, a compressor 5 that constitutes a turbocharger 4, an intercooler 6 that cools intake air, a fuel injection nozzle 8 that injects fuel, an intake air flow A throttle valve 7 for increasing / decreasing the road cross-sectional area and an intake pressure sensor 9 for detecting intake pressure are provided.

  In order from the upstream side, the exhaust passage 22 is connected via a turbine 25 constituting the turbocharger 4, an exhaust shutter 26 that opens and closes the exhaust passage, an O2 sensor 27 that outputs a signal according to the oxygen concentration in the exhaust, and a catalyst. A catalyst-equipped muffler 28 that cleans the exhaust gas and silences the exhaust noise is provided.

  The EGR passage 33 communicates the exhaust manifold 23 of the exhaust passage 22 and the intake passage 2 downstream of the throttle valve 7. In the EGR passage 33, a water-cooled EGR cooler 34, an EGR valve 35, an EGR gas temperature sensor 36, and an air-cooled EGR cooler 37 are interposed in order from the exhaust manifold 23 toward the intake passage 2.

  The water-cooled EGR cooler 34 is cooled by circulating engine cooling water as indicated by arrows in the drawing, and the EGR gas passing through the EGR passage 33 dissipates heat to the engine cooling water. The engine cooling water circulates through the engine 1 and dissipates heat to the outside air by a radiator (not shown), so that it is maintained at about 80 ° C., for example.

  The EGR valve 35 increases or decreases the cross-sectional area of the EGR passage 33 according to a signal from the control unit 14, and controls the flow rate of EGR gas recirculated to the intake passage 2.

  The control unit 14 calculates the EGR flow rate and controls the opening degree of the EGR valve 35 according to the rotational speed of the engine 1 from the rotational speed sensor 17 and the intake pressure from the intake pressure sensor 9, that is, the load of the engine 1. . FIG. 5 is a characteristic diagram showing the relationship between the load factor of the engine 1 and the EGR rate.

  As a gist of the present invention, a bypass passage 40 is provided that guides a part of the intake air discharged from the compressor 5 of the turbocharger 4 to the air-cooled EGR cooler 37 as a cooling medium.

  In the bypass passage 40, the upstream end (inlet) of the upstream passage 41 from the air-cooled EGR cooler 37 is connected downstream from the intercooler 6 in the intake passage 2, and the downstream end (exit) of the downstream passage 42 from the air-cooled EGR cooler 37. ) Is released to the atmosphere.

  The air-cooled EGR cooler 37 is a heat exchanger having a flow path through which a part of the intake air that has passed through the intercooler 6 circulates and a flow path through which the EGR gas that passes through the EGR passage 33 circulates, as indicated by arrows in the drawing. Yes, the EGR gas flowing through the EGR passage 33 is cooled by releasing heat to the intake air flowing through the bypass passage 40.

  A bypass valve 50 is interposed in the bypass passage 40 upstream of the air-cooled EGR cooler 37. The bypass valve 50 opens and closes the bypass passage 40 according to a signal from the control unit 14, and controls the intake air flow rate that is guided to the air-cooled EGR cooler 37 through the bypass passage 40.

  The control unit 14 inputs the rotational speed of the engine 1 and the intake pressure from the intake pressure sensor 9, closes the bypass valve 50 in the low / medium rotational speed and partial load areas of the engine 1, and bypasses in the high rotational speed and high load areas. The valve 50 is controlled to open.

  The flowchart of FIG. 2 shows the control routine of the bypass valve 50, which is executed by the control unit 14 at regular intervals.

  First, in step 1 (denoted as S1 in the figure, the same applies hereinafter), the rotational speed Ne of the engine 1 is input, and in the subsequent step 2, it is determined whether or not the engine rotational speed Ne is equal to or less than a set value Nes. When the engine speed Ne is equal to or lower than the set value Ne, the process proceeds to step 3 and the bypass valve 50 is closed.

  On the other hand, when the engine speed Ne is higher than the set value Ne, the routine proceeds to step 4 where the intake pressure Pi is input from the intake pressure sensor 9, and in the subsequent step 5, the intake pressure Pi (load of the engine 1) is equal to or less than the set value Pis. It is determined whether or not. When the intake pressure Pi is equal to or lower than the set value Pis, the process proceeds to step 3 and the bypass valve 50 is closed. On the other hand, when the intake pressure Pi is higher than the set value Pis, the process proceeds to step 6 and the bypass valve 50 is opened.

  FIG. 3 is a characteristic diagram showing the relationship between the rotational speed of the engine 1 and the generated torque with respect to the load. The bypass valve 50 is opened in the hatched region in the figure, and the air-cooled EGR cooler 37 is operated.

  In addition, the control unit 14 may input the EGR gas temperature from the EGR gas temperature sensor 36 and perform control to open the bypass valve 50 as the EGR gas temperature increases beyond a predetermined value.

  The flowchart of FIG. 4 shows a control routine for the bypass valve 50, which is executed by the control unit 14 at regular intervals.

  First, in step 11, the EGR gas temperature Ti is input, and in the subsequent step 12, it is determined whether or not the EGR gas temperature Ti is equal to or lower than a set value Tis. When the EGR gas temperature Ti is equal to or lower than the set value Tis, the process proceeds to step 13 and the bypass valve 50 is closed. On the other hand, when the EGR gas temperature Ti is higher than the set value Tis, the process proceeds to step 14 and the bypass valve 50 is opened.

  Next, the operation and effect will be described.

  The outside air sucked into the air cleaner 3 is compressed by the compressor 5 after the foreign matter such as dust is removed by the air cleaner 3 as the intake air of the engine 1. Although this compressed intake air becomes high temperature, it is cooled by passing through the intercooler 6. Thereby, the volume of the intake air is reduced and the intake efficiency of the engine 1 is improved. The intake air cooled by the intercooler 6 is supplied to each cylinder of the engine 1 while its flow rate is adjusted by the throttle valve 7.

  On the other hand, the exhaust discharged from each cylinder of the engine 1 is supplied to the turbine 25, and the turbine 25 is rotated by the pressure energy of the exhaust, and the compressor 5 provided coaxially with the turbine 25 is rotationally driven. Exhaust gas that has passed through the turbine 25 passes through the muffler 28 with catalyst and is released into the atmosphere.

  A part of the exhaust discharged from each cylinder of the engine 1 is not supplied to the turbine 25 but flows into the EGR passage 33 from the exhaust manifold 23 as EGR gas. The EGR gas is cooled by passing through the water-cooled EGR cooler 34 and further recirculated to the intake passage 2 via the air-cooled EGR cooler 37. In this way, the EGR gas having a low temperature is recirculated to the intake passage 2, so that the combustion temperature of the engine 1 is lowered and nitrogen oxides in the exhaust can be reduced.

  By closing the bypass valve 50 in the low / medium rotational speed and partial load range of the engine 1, the entire amount of intake air discharged from the compressor 5 is guided to the intake passage 2. At this time, the EGR gas passing through the air-cooled EGR cooler 37 is hardly cooled, but in this partial load region, the temperature of the EGR gas flowing into the EGR passage 33 from the exhaust manifold 23 is lower than that in the high load region. The EGR gas is sufficiently cooled by passing through the water-cooled EGR cooler 34.

  By opening the bypass valve 50 in the high rotation speed and high load region of the engine 1, surplus intake air discharged from the compressor 5 is guided to the air-cooled EGR cooler 37 through the bypass passage 40, and the water-cooled EGR cooler 34. The EGR gas that has passed through is further cooled by an air-cooled EGR cooler 37. The EGR gas temperature flowing into the EGR passage 33 from the exhaust manifold 23 into the high load region of the engine 1 is about 700 to 800 ° C., for example, and is dissipated to the engine cooling water (for example, about 80 ° C.) by the water-cooled EGR cooler 34. The temperature of the EGR gas that has passed through the water-cooled EGR cooler 34 is, for example, about 120 to 130 ° C., but by dissipating heat to the intake air that has exited from the intercooler 6 in the process of passing through the air-cooled EGR cooler 37, The intake air temperature can be lowered to about 60 to 70 ° C. or less, for example.

  FIG. 6 shows the relationship between the engine load and the pressure in the intake manifold 10, the inlet pressure of the turbine 25, the outlet pressure of the intercooler 6, and the relationship between the engine load and the temperature in the intake manifold 10, and the inlet pressure of the turbine 25. FIG. In FIG. 6, a load region between the C line and the D line is a region where the bypass valve 50 is opened and the air-cooled EGR cooler 37 is operated. The intake air temperature in the intake manifold 10 is lower than the characteristic indicated by the A line when the air-cooled EGR cooler 37 is not used, and the characteristic indicated by the B line when the air-cooled EGR cooler 37 is used. Thus, in the high load range, the air-cooled EGR cooler 37 operates and the intake air temperature supplied to each cylinder decreases, so that knocking of the engine 1 can be suppressed and the knocking limit is extended as shown by the white arrow in FIG. it can.

  As described above, the EGR device of the engine 1 includes the turbocharger 4 that supercharges the intake air by the exhaust energy, the EGR passage 33 communicating the exhaust manifold 23 (exhaust passage 22) and the intake passage 2, and the EGR An air-cooled EGR cooler 37 that cools the EGR gas passing through the passage, a bypass passage 40 that guides a part of the intake air discharged from the compressor 5 of the turbocharger 4 to the air-cooled EGR cooler 37 as a cooling medium, and the bypass passage 40 And a control means (control unit 14) for controlling the opening and closing of the bypass valve 50 according to operating conditions. When the bypass valve 50 is open, the air-cooled EGR cooler 37 is used for the EGR passage. Because the EGR gas that passes through 33 radiates heat to the intake air that passes through the bypass passage 40 The cooled EGR gas by utilizing the intake of excess discharged from the compressor 5 of the turbocharger 4 is suppressed knocking of the engine 1 by reducing the temperature of the intake fresh air and EGR gas are mixed. For this reason, EGR can be performed even in a high load region, and the engine knock limit can be extended.

  The control unit 14 (control means) inputs the engine rotational speed and the intake pressure (load), closes the bypass valve 50 in the low and medium rotational speed and partial load areas of the engine, and in the high rotational speed and high load areas. Since the bypass valve 50 is controlled to open, it is possible to accurately determine the operating conditions that require cooling of the EGR gas, and to effectively operate the air-cooled EGR cooler 37.

  Further, the control unit 14 (control means) inputs the EGR gas temperature and controls the opening of the bypass valve 50 as the EGR gas temperature rises above a predetermined value, so that the EGR gas needs to be cooled. It is possible to accurately determine the conditions and operate the air-cooled EGR cooler 37 effectively.

  Next, another embodiment shown in FIG. 7 will be described. This basically has the same configuration as that of the embodiment of FIG. 1, and only different portions will be described.

  A downstream passage 42 from the air-cooled EGR cooler 37 of the bypass passage 40 is provided in the upstream passage 38 and the exhaust manifold 23 from the water-cooled EGR cooler 34 of the EGR passage 33, and a downstream end (exit) of the downstream passage 42 is provided. Open to the atmosphere.

  Also in this case, when the bypass valve 50 is opened under predetermined operating conditions, surplus intake air discharged from the compressor 5 is guided to the air-cooled EGR cooler 37 through the bypass passage 40, and the water-cooled EGR cooler 34 is The passed EGR gas is cooled by an air-cooled EGR cooler 37. Then, the EGR gas flowing through the upstream passage 38 and the exhaust manifold 23 in the course of the intake air discharged from the air-cooled EGR cooler 37 passing through the upstream passage 38 of the EGR passage 33 and the bypass passage 40 provided in the exhaust manifold 23 is removed. Cooling. Thus, the EGR gas is cooled upstream and downstream of the water-cooled EGR cooler 34 by using surplus intake air discharged from the compressor 5 of the turbocharger 4.

  Furthermore, as another embodiment, as shown in FIG. 8, an enclosure in which the downstream passage 42 from the air-cooled EGR cooler 37 in the bypass passage 40 surrounds the upstream passage 38 from the water-cooled EGR cooler 34 in the EGR passage 33. It may have a portion 42a and a through portion 42b provided in the exhaust manifold 23 so that the downstream end (exit) of the downstream passage 42 is opened to the atmosphere.

  In this case, the intake air discharged from the air-cooled EGR cooler 37 passes through the upstream side passage 38 and the exhaust manifold 23 in the process of passing through the surrounding portion 42a of the upstream side passage 38 of the EGR passage 33 and the through portion 42b inside the exhaust manifold 23. Cool the flowing EGR gas. Thus, the EGR gas is cooled upstream and downstream of the water-cooled EGR cooler 34 by using surplus intake air discharged from the compressor 5 of the turbocharger 4.

  As described above, the EGR passage 33 is provided with the water-cooled EGR cooler 34, the air-cooled EGR cooler 37 is provided downstream of the EGR passage 33 with respect to the water-cooled EGR cooler 34, Since the EGR gas flowing upstream from the 33 water-cooled EGR cooler 34 is cooled, the EGR gas is supplied upstream of the water-cooled EGR cooler 34 by using surplus intake air discharged from the compressor 5 of the turbocharger 4. Cooling is performed on the downstream side, and knocking of the engine 1 can be effectively suppressed.

  The present invention is not limited to the above-described embodiment, and it is obvious that various modifications can be made within the scope of the technical idea.

  The EGR device of the present invention is not limited to a CNG engine, but can be used for a spark ignition type engine using gasoline or other fuel.

  Further, the EGR device of the present invention may be applied to a diesel engine to increase the EGR rate.

The block diagram of the EGR apparatus of the engine which shows embodiment of this invention. The flowchart which similarly shows the control content of a bypass valve. The characteristic view which similarly shows the relationship between the engine speed and the generated torque with respect to the load. The flowchart which similarly shows the control content of a bypass valve. The characteristic view which similarly shows the relationship between an engine load factor and an EGR rate. The characteristic view which similarly shows the relationship between the engine load and the temperature in the intake manifold. The block diagram of the engine EGR apparatus which shows other embodiment. The block diagram of the engine EGR apparatus which shows other embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine 2 Intake passage 4 Turbocharger 5 Compressor 6 Intercooler 9 Intake pressure sensor 14 Control unit 17 Rotation speed sensor 22 Exhaust passage 25 Turbine 33 EGR passage 34 Water-cooled EGR cooler 35 EGR valve 36 EGR gas temperature sensor 37 Air-cooled EGR cooler

Claims (4)

An EGR device for an engine having a turbocharger that supercharges intake air by exhaust energy,
An EGR passage that connects the exhaust passage and the intake passage, an air-cooled EGR cooler that cools EGR gas that passes through the EGR passage, and a part of the intake air discharged from the compressor of the turbocharger to the air-cooled EGR cooler A bypass passage that leads as a cooling medium; a bypass valve that opens and closes the bypass passage; and a control unit that controls opening and closing of the bypass valve according to operating conditions, and the air-cooled EGR cooler is in an operating state in which the bypass valve is open. An EGR device for an engine characterized in that the EGR gas passing through the EGR passage dissipates heat to the intake air passing through the bypass passage.   2. The engine according to claim 1, wherein the control unit inputs a load of the engine, closes the bypass valve in a partial load region of the engine, and opens the bypass valve in a high load region of the engine. EGR device.   3. The engine EGR device according to claim 1, wherein the control unit inputs an EGR gas temperature and opens the bypass valve as the EGR gas temperature rises beyond a predetermined value. 4.   A water-cooled EGR cooler is provided in the EGR passage, the air-cooled EGR cooler is provided on the downstream side of the water-cooled EGR cooler in the EGR passage, and the water-cooled EGR in the EGR passage is provided by intake air discharged from the air-cooled EGR cooler. The EGR device for an engine according to any one of claims 1 to 3, wherein the EGR gas flowing upstream from the cooler is cooled.

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