JP4108061B2 - EGR system for turbocharged engine - Google Patents

Description

  The present invention relates to an EGR (exhaust gas recirculation) system in a reciprocating internal combustion engine equipped with a turbocharger.

In a reciprocating internal combustion engine, the combustion temperature in the cylinder is high, so that a large amount of NOx, which is a harmful substance, is generated. The turbocharged engine EGR system often uses a high-pressure loop exhaust circulation system (HPL-EGR system) that recirculates part of the exhaust gas upstream of the turbine to the compressor downstream side via an EGR valve and EGR cooler. Has been.
In the case of a turbocharged engine, the engine supply air pressure is sometimes higher than the engine exhaust pressure. In the case of an HPL system, a throttle valve for restricting the supply air is provided upstream from the connection portion of the EGR gas to the supply pipe. Although it is necessary to lower the supply air pressure so that EGR gas can easily enter, there is a problem that the supply air pressure to the engine decreases due to the throttle valve being throttled, and the engine performance deteriorates.

  As a method for solving this problem, there is an LPL-EGR system in which a part of the exhaust gas exiting the turbine is introduced into the compressor inlet and mixed into the intake air. In this LPL system, the exhaust gas passes through the compressor. As a result, the problem of corrosion of the compressor material arises. Even if the EGR gas is cooled through the cooler and sucked into the compressor, when the EGR gas amount is increased, the temperature of the compressor becomes high, and the problem of heat resistance of the compressor material also arises.

The conventional HPL-EGR system is shown in FIG. 5, and the LPL-EGR system is shown in FIG. 5 and 6, 101 is an engine, 102 is a turbocharger, and an exhaust turbine 102a and a compressor 102b are provided on a shaft 102c. 103 is an EGR cooler, 104 is an EGR valve, 105 is a check valve, 106 is an air supply cooler, and 107 is an EGR valve that controls the opening degree of the EGR valve 104 according to the engine speed and load to adjust the EGR rate. It is a controller.
In the case of the HPL-EGR system shown in FIG. 5, as described above, the throttle valve 108 is provided upstream from the joining portion of the EGR gas to the air supply pipe in order to lower the supply air pressure and make it easier for the EGR gas to enter. In the case of the LPL-EGR system of FIG. 6, this throttle valve is not provided.

In the HPL system of FIG. 5, part of the engine exhaust is branched upstream of the turbine 102 a and merges with the engine air supply pipe via the EGR cooler 103, the EGR valve 104, and the check valve 105. On the other hand, the outside air is sucked into the compressor 102 b and compressed, cooled through the supply air cooler 106 and the throttle valve 106, and supplied to the engine 1.
In a turbocharged engine, the engine air pressure is often higher than the engine exhaust pressure. Therefore, the opening of the throttle valve 108 is adjusted to lower the air pressure so that EGR gas is introduced into the air supply pipe. In such a conventional technique, since EGR gas does not pass through the compressor 102b, the conventional compressor can be used as it is. However, when the throttle valve is throttled, the engine supply pressure is lowered and the engine performance is lowered. Therefore, increasing the EGR rate is accompanied by a sacrifice in engine performance.

In the LPL system of FIG. 6, a part of the exhaust gas exiting the exhaust turbine 102a is sucked into the compressor 102b via the EGR cooler 103, the EGR valve 104, and the check valve 105, and the EGR gas is converted into the intake air by the compressor. The mixed air is mixed and cooled through the supply air cooler 106 and supplied to the engine 101.
In such a conventional technique, it is easy to increase the EGR rate, but since EGR gas containing acidic substances such as NOx and SOx passes through the compressor 102b and the charge air cooler 106, the compressor material and the supply air For the air cooler material, it is necessary to pay attention to corrosion.

As an exhaust gas recirculation system for a turbocharged engine, a blade for compressing EGR gas is provided on the back of the compressor impeller, and a part of the engine exhaust is branched upstream of the turbine and led to the EGR gas compression blade. A system is disclosed in which the supplied EGR gas is mixed with the supply air compressed by the compressor and the mixer and introduced into the intake manifold (for example, see Patent Document 1).
According to the system of Patent Document 1, an EGR gas compression blade is provided by minimizing the increase in the axial length of the turbocharger by providing an EGR gas compression blade on the rear surface of the compressor impeller. Further, it is said that the fluctuation of the mixing ratio of the EGR gas for each cylinder can be minimized by effective mixing by the mixer.

  Moreover, in a turbocharged engine, a system is disclosed in which an air turbine is driven by supply air compressed by a compressor, and EGR gas is compressed by a compressor connected to the air turbine shaft (see, for example, Patent Document 2). ). According to the system of Patent Document 2, the supply air is expanded by the air turbine and the temperature is lowered, so that the temperature of the supply air including the EGR gas is lowered, the combustion temperature is lowered, and the NOx emission amount is reduced. It is said.

Further, as an exhaust gas recirculation system in a two-stage turbocharged engine, a system is disclosed in which a part of the exhaust gas between the first-stage exhaust turbine and the second-stage exhaust turbine is guided to the inlet of the first-stage compressor. (For example, see Patent Document 3).
In such a system, in the conventional configuration in which a part of the exhaust gas is branched from the downstream side of the first stage turbine and led to the suction port of the first stage compressor, the system is provided in the downstream side of the branch part. It is possible to delete the throttle valve that has been used, and to control the EGR rate, it is only necessary to control one valve instead of the conventional control of two valves, and the conventional throttle is considerably higher. The engine back pressure can be lowered and the engine can be improved.

Special Table 2002-514285 gazette JP 2000-8963 A Japanese Utility Model Publication No. 5-69364

However, in the system disclosed in Patent Document 1, since the blades for compressing the EGR gas are formed on the back surface of the compressor for compressing the supply air, the life of the compressor is EGR gas compression exposed to the corrosive environment by the EGR gas. It contains problems such as being determined by the blade life.
Further, in the system disclosed in Patent Document 2, since the EGR gas compression compressor is driven by the air turbine, an air turbine for driving the EGR gas compressor is required, and the drive efficiency is low. Inevitable. Furthermore, in the system configuration disclosed in Patent Document 3, EGR gas passes through both the first and second compressors, and both compressors need to take measures against corrosion of acidic substances in the EGR gas.

  Therefore, an object of the present invention is to increase the EGR rate in the entire operating range without providing a throttle valve in the engine air supply pipe or turbine exhaust pipe in a turbocharged engine, and to contain acidic substances such as NOx and SOx. To provide an EGR system capable of limiting compressors and coolers that are components on the supply side through which corrosive exhaust gas passes.

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To achieve the above object, according to the present invention, there is provided a supercharged engine including a turbocharger, wherein the turbocharger includes a low-pressure compressor and a high-pressure compressor on the same axis, and the low-pressure compressor discharge port has an intermediate cooling function. Connected to the suction port of the high-pressure compressor via a compressor, and connected to the high-pressure compressor suction port a branch pipe branching from a pipeline from the exhaust outlet of the engine to the exhaust inlet of the exhaust turbine of the turbocharger, The discharge port of the high pressure compressor is connected to the intake air inlet of the engine via an intake air cooler, a high pressure EGR cooler is disposed in the branch pipe, and an EGR valve is provided downstream of the high pressure EGR cooler. A check valve is disposed on the downstream side of the EGR valve, the EGR valve is disposed between the high pressure EGR cooler and the check valve, and the downstream side of the check valve is disposed on the downstream side of the check valve. High pressure Connected to the inlet of the presser, opening the engine speed of the EGR valve, proposes EGR system turbocharged engine, characterized in that a controller for controlling according to the load.

Such a system is suitable for high Pme (high average effective pressure) engines with increased charge pressure. The turbocharger is configured as a two-stage compression turbocharger in which two low-pressure and high-pressure compressors are provided on the same axis, and an intermediate cooler is installed between the low-pressure and high-pressure compressors to increase the temperature due to compression of the engine air supply. The EGR gas is sucked into the high-pressure compressor, compressed together with the air discharged from the low-pressure compressor, and guided to the engine air supply inlet.
Also in this case, a high-pressure EGR cooler and an EGR valve are arranged in the branch line of the EGR gas. Such an engine is a high-supercharged engine, and an intake air cooler is disposed downstream of the high-pressure compressor. However, since EGR gas flows through the high-pressure compressor and the intake air cooler, it is necessary to consider corrosion. is there. The flow rate adjustment by the EGR valve is controlled by the controller according to the engine speed and load.

Furthermore, in this invention, the low-pressure compressor discharge port is connected to the high-pressure compressor intake port via an intermediate cooler, and branches from a pipe line extending from an engine exhaust outlet to an exhaust inlet of the turbocharger exhaust turbine. The branch pipe is connected to the cooled gas outlet of the intermediate cooler, and the discharge port of the high-pressure compressor is connected to the air supply inlet of the engine. In this case, the EGR gas is cooled by a high pressure EGR cooler provided in the branch pipe and then sucked into the high pressure compressor.

  The EGR rate required for NOx reduction in a turbocharged engine varies depending on the engine speed and load, but the system of the present invention can achieve the EGR rate required over the entire operating range without sacrificing engine performance. In addition, it is possible to limit the functional parts on the air supply side that come into contact with the EGR gas containing a corrosive substance, and there is an effect that only the limited parts need to be considered for corrosion resistance.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, exemplary embodiments of the invention will be described with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention unless otherwise specified, but are merely illustrative examples. Not too much.
(Comparative Example 1)

In FIG. 1, 1 is an engine body, 2 is a turbocharger, and has an arrangement of two compressor wheels in which an exhaust turbine 2a, an intake air compressor 2b, and an EGR gas compressor 2d are connected by a shaft 2c.
A part of the exhaust gas exiting the exhaust turbine 2a is branched and cooled by the low-pressure EGR cooler 3a, passed through the EGR valve 4 and the check valve 5, and sucked into the EGR gas compressor 2d to be compressed and compressed. The EGR gas thus cooled is cooled by the high-pressure EGR cooler 3b and introduced into the engine supply air inlet.

On the other hand, the outside air is sucked into the intake air compressor 2b, compressed, cooled by the intake air cooler 6, and introduced into the engine intake air inlet. The supply air and the EGR gas merge and mix at an engine supply air inlet, for example, an intake manifold, and are sucked into the engine cylinder. Since the amount of EGR gas required to effectively reduce NOx differs depending on the engine speed and load, the opening degree of the EGR valve is controlled according to the speed and load by a program input in advance to the controller 7. . The check valve 5 is designed to prevent backflow even if the pressure on the downstream side of the EGR valve becomes higher than that on the upstream side due to sudden changes in operating conditions, pulsation of the air supply system, or the like. Yes, it is not always necessary.
(Comparative Example 2)

2 is different from Comparative Example 1 (FIG. 1) in Comparative Example 2 shown in FIG. 2 in that the auxiliary air valve 8 is connected to the branch circuit branched from the downstream side of the exhaust turbine 2a and connected to the intake port of the EGR gas compressor 2b. This is because the pipe for introducing the external air is connected via the. Other configurations are the same as those in FIG. 1, and the same components as those in FIG.
With the above configuration, when the required amount of EGR gas is small, the auxiliary air valve 8 is opened so that the outside air can be sucked into the EGR gas compressor 2d. Can be used effectively. The opening degree of the auxiliary air valve 8 may be controlled by the controller 7 according to the engine speed and load together with the opening degree of the EGR valve 4.
1 and 2, the EGR gas compressor 2d is arranged in front of the intake air compressor 2b, but it may be arranged behind the intake air compressor 2b, that is, on the exhaust turbine 2a side. Needless to say.
(Example 1)

In FIG. 3, reference numeral 1 denotes an engine body, and 2 a turbocharger. Unlike the cases shown in FIGS. 1 and 2, the compressor of the turbocharger is composed of a low-pressure compressor 2 e and a high-pressure compressor 2 f. In other words, two low-pressure and high-pressure compressor wheels are coaxially arranged in one turbocharger to form a two-stage compression supercharging, which is suitable for a high Pme (average effective pressure) engine with a high degree of supercharging. .
The discharge port of the low-pressure compressor 2e is connected to the suction port of the high-pressure compressor 2f via an intercooler 9. The EGR gas from which a part of the exhaust gas exiting the engine from the upstream side of the exhaust turbine 2a is branched is led to the intake port of the high-pressure compressor 2f, and is compressed and supplied together with the air from the low-pressure compressor 2e in the high-pressure compressor 2f. It is cooled by the air cooler 6 and sent to the intake port of the engine.
The EGR gas is cooled by the high-pressure EGR cooler 3b , and is guided to the suction port of the high-pressure compressor 2f through the EGR valve 4 and the check valve 5. The opening degree of the EGR valve 4 is controlled by the controller 7 in accordance with the engine speed and the load.
(Comparative Example 3)

The difference between the comparative example 3 shown in FIG. 4 and the first embodiment (FIG. 3) is that EGR gas is introduced into the intermediate cooler 9 instead of the suction port of the high pressure compressor 2f and the high pressure EGR cooler 3b in FIG. The other components are the same as those in FIG. 3, and the same components as those in FIG. 3 are denoted by the same reference numerals.
In FIG. 4, the EGR gas is cooled together with the supply air by the intermediate cooler before being sucked into the high-pressure compressor 2f, and the high-pressure EGR cooler 3b in FIG. 3 and 4, the EGR gas is branched on the upstream side of the exhaust turbine 2a, but may be branched on the downstream side.

  In the first embodiment described above, it is possible to increase the EGR rate in the entire range of low engine operation. In the first embodiment, the compressor through which the EGR gas passes is limited to the high pressure compressor. As described above, by limiting the parts through which the EGR gas passes as much as possible, it is possible to limit the parts to which heat resistance and corrosion resistance measures are to be taken when a large amount of EGR gas is introduced.

  According to the present invention, while exhaust gas regulations for engines are becoming more stringent for environmental protection, NOx in engines that achieve higher output and higher efficiency in a situation where higher output and higher efficiency of the engine are also desired. Therefore, it is possible to provide an EGR system that can secure a necessary and sufficient EGR rate for reducing the amount of exhaust gas discharged, and can limit the functional parts on the supply side through which EGR gas containing corrosive substances passes to a minimum.

It is a schematic block diagram of the EGR system of the turbocharged engine which concerns on the 1st comparative example of this invention. It is a schematic block diagram of the EGR system of the turbocharged engine which concerns on the 2nd comparative example of this invention. 1 is a schematic configuration diagram of an EGR system for a turbocharged engine according to a first embodiment of the present invention. It is a schematic block diagram of the EGR system of the turbocharged engine which concerns on the 3rd comparative example of this invention. It is a schematic block diagram of the HPL-EGR system in the conventional turbocharged engine. It is a schematic block diagram of the LPL-EGR system in the conventional turbocharged engine.

Explanation of symbols

1 Engine 2 Turbocharger 3a Low pressure EGR cooler 3b High pressure EGR cooler 4 EGR valve 5 Check valve 6 Supply cooler 7 Controller 8 Auxiliary air valve 9 Intermediate cooler

Claims (1)

In a supercharged engine having a turbocharger, the turbocharger is coaxially provided with a low-pressure compressor and a high-pressure compressor, and the low-pressure compressor discharge port is connected to an intake port of the high-pressure compressor via an intercooler. A branch pipe branching from a pipe extending from the exhaust outlet of the engine to the exhaust inlet of the exhaust turbine of the turbocharger is connected to the high-pressure compressor inlet, and the discharge outlet of the high-pressure compressor is connected to a supply air cooler. The high-pressure EGR cooler is arranged in the branch pipe, an EGR valve is arranged downstream of the high-pressure EGR cooler, and a check valve is arranged downstream of the EGR valve. and set, the EGR valve is disposed so as to be positioned between the high-pressure EGR cooler and the check valve, the downstream side of the check valve is connected to the inlet of the high pressure compressor, said EG Opening the engine speed of the valve, EGR systems turbocharged engine, characterized in that a controller for controlling according to the load.

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