JPH11117751A - Egr device for supercharging engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To sufficiently ensure an air rate intaked to a cylinder, and prevent generation of smoke and deterioration of fuel consumption by arranging an EGR gas compressor driven by a turbine of a supercharger in an EGR passage, and arranging an intake passage for leading new air into the EGR passage arranged on an upstream side of the EGR gas compressor. SOLUTION: An EGR passage 9 is arranged to connect the exhaust passage 12 and an intake passage 11 of a supercharging engine 1, and an EGR gas compressor 5 is arranged in the EGR passage 9, and EGR gas G2 is boosted up so as to recirculate to the intake passage 11. An intake passage 13 for leading new air A2 is arranged in the EGR passage 9 arranged on an upstream side of the EGR gas compressor 5, a control valve 8 is arranged on a part for connecting the passages 9, 13 to each other, and the rate of EGR gas G2 and the rate of new air A2 are controlled by the control valve 8. In an ECU 20, outputs of a rotating speed sensor 14 and a load sensor 15 are inputted, the control valve 8 is controlled in compliance with an EGR map 30 which is inputted beforehand, and EGR control is carried out with an EGR rate which is set beforehand.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an EGR device for a supercharged engine in which a part of exhaust gas is recirculated to an intake side in order to reduce a NOx emission in a turbocharged diesel engine or the like. It is.

[0002]

2. Description of the Related Art In exhaust gas countermeasures for diesel engines and the like, in order to reduce the amount of NOx emitted from exhaust gas, the combustion temperature is reduced by recirculating a part of the exhaust gas, which is an inert gas, to the intake side. It is known that EGR (exhaust gas recirculation), which suppresses NOx generation while keeping it low, is effective and widely used.

[0003] This EGR device is also applied to a supercharged engine, and as shown in FIG. 3, an exhaust gas G2 is taken out from an exhaust manifold 12a and an EG provided with an EGR cooler 7 is provided.
The EGR is performed by mixing the fresh air A in the intake passage 11 through the R passage 9 and recirculating the mixture to the intake manifold 11a.
However, in the supercharged engine, as the engine load increases, the intake pressure (boot pressure) increases and becomes higher than the exhaust pressure, so that the EGR gas G2 cannot be recirculated to the intake passage 11. .

Therefore, the exhaust pressure is reduced by opening the waste gate 12b communicating with the exhaust passage 12 and the exhaust gas G3 is caused to flow out, thereby reducing the rotational speed of the turbine 2 and thereby reducing the intake pressure, thereby reducing the EGR gas. There is a method of returning G2 to the intake passage 11. However, this method reduces the amount of fresh air A and causes an increase in smoke. Therefore, the region where EGR can be performed is, as shown in FIG. There is a problem that it is limited to E.

In a variable capacity turbocharger (VG turbo) in which the cross-sectional area of the inlet of the turbine 2 is variable,
By controlling the cross-sectional area of the inlet and changing the turbine speed, the exhaust pressure and the intake pressure are controlled to expand the EGR-capable region. In this case, FIG.
Up to the engine operating range indicated by E with medium load as shown in
Although GR becomes possible, there is a demand for enabling EGR even in a high-load operation region of the engine in order to further reduce NOx and purify exhaust gas.

[0006] Regarding this request, Japanese Patent Laid-Open Publication No.
5, JP-A-5-180089, JP-A-5-8985
No. 9 proposes an EGR device that expands the EGR region by compressing the EGR gas by a compressor to increase the pressure and recirculating the increased EGR gas to the intake passage side.

[0007]

However, in the device disclosed in Japanese Patent Application Laid-Open No. 3-117665, since the EGR gas is compressed by a compressor driven by the engine and stored in an accumulator tank, the EGR gas is supplied. Is used for this compressor, so that the loss of engine output increases accordingly. This loss increases as the engine speed increases and the load increases. Therefore, there is a problem that the loss increases when high output is required.
Further, there is a problem that a compressor and an accumulator having a large capacity are required to perform the EGR in a high rotation speed and a high load region.

In the apparatus disclosed in Japanese Patent Application Laid-Open No. H5-180089, a turbine driven by exhaust gas is provided in an exhaust passage, and an EGR gas compressor connected to the turbine is used for EG.
The R gas is pressurized and returned to the intake passage. However, in this device, since three turbines including a power turbine for recovering the power of the exhaust gas are provided in series in the exhaust passage, the exhaust pressure of the exhaust manifold rises significantly during the EGR operation, so that pumping loss is reduced. There is a problem that the fuel efficiency is deteriorated due to the increase in size, and there is a problem that a region where the EGR can be performed due to the generation of black smoke due to a decrease in fresh air during high load operation is limited.

The apparatus disclosed in Japanese Patent Application Laid-Open No. Hei 5-89859 divides the compressed air obtained by the first turbocharger to drive the second turbocharger, and the EGR gas is compressed by the compressor of the second turbocharger. , And at the same time, the compressed air is released from the compressor to lower the intake pressure to perform EGR. However, in this device, since the compressed air is branched, the amount of compressed intake air supplied to the cylinder is reduced, so that there is a problem that the amount of intake air with respect to the amount of EGR gas is reduced and smoke is generated.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and an object of the present invention is to make it possible to perform EGR even during high-load operation of an engine and to secure a sufficient amount of intake air to a cylinder. The generation of smoke and the deterioration of fuel consumption can be prevented.
It is an object of the present invention to provide an EGR device for a supercharged engine capable of efficiently performing EGR by increasing the pressure of GR gas and reducing the emission amount of NOx in exhaust gas in the entire operation range of the engine.

[0011]

SUMMARY OF THE INVENTION In order to achieve the above object, a supercharged EGR system for a supercharged engine drives a compressor provided in an intake passage by a turbine provided in an exhaust passage of the engine. In the engine, an EGR gas compressor driven by the turbine and pressurizing EGR gas and returning to the intake passage is provided in an EGR passage connecting the exhaust passage and the intake passage. A second intake passage for introducing fresh air into the upstream EGR passage;
A control valve is provided at a connection portion between the second intake passage and the EGR passage, and the control valve is controlled so that EGR gas,
A mixed gas of EGR gas and fresh air,
It is configured so that it can be supplied to the R gas compressor.

Then, without providing a clutch mechanism, E
By driving the GR gas compressor and controlling the control valve, fresh air is supplied from the second intake passage provided in the EGR passage according to the operation state of the engine, and only the EGR gas (first intake state) is supplied. An intake state in which both gas and fresh air (second intake state) and only fresh air (third intake state) can be selected and sent to the EGR cooler side.

For this reason, in the low load / low rotation range of the engine or the like, the EGR gas is supplied partially or entirely to the EGR gas.
E by increasing the amount of gas or supplying only EGR gas
GR can be performed. When the load increases, E
The GR gas and fresh air can be supplied at a ratio so as to have a required EGR rate. Then, in the high load operation region, the amount of fresh air can be increased or only fresh air can be supplied. Furthermore, at the time of the acceleration operation, generation of smoke can be suppressed by supplying only fresh air.

Further, since it is not necessary to newly provide a turbine for the EGR gas compressor, it is possible to prevent an increase in exhaust pressure and to prevent deterioration of fuel consumption. In addition, since there is no decrease in the intake air amount due to branching and release of the intake air, the intake air amount supplied to the cylinder can be sufficiently ensured, and EGR can be performed while preventing generation of smoke.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a supercharged engine EGR device according to the present invention will be described with reference to the drawings. As shown in FIG. 1, in this supercharged engine 1, a turbine 2 is provided in an exhaust passage 12 and an exhaust gas G1 + G
2, the rotation is transmitted by a shaft 2a, and the compressor 3 provided in the intake passage 11 is driven to generate fresh air A1.
The fresh air A1 is supplied to the intake manifold 11a via the intercooler 6.

An EGR passage 9 for connecting the exhaust passage 12 and the intake passage 11 of the supercharged engine 1 is provided, and an EGR gas compressor 5 directly driven by the turbine 2 without a clutch mechanism in the EGR passage 9. Is provided so that the EGR gas G2 is pressurized and recirculated to the intake passage 11. The EGR gas compressor 5 has a higher supercharging degree than the air-only compressor 3 so that the EGR gas G2 and A2 can be reliably supplied to the intake passage 11 side, and a sufficient EGR gas G2 at the maximum EGR. With the ability to supply

Further, a second intake passage for introducing fresh air A2 into the EGR passage 9 upstream of the EGR gas compressor 5.
A control valve 8 is provided at a connection between the EGR passage 9 and the second intake passage 13, and the control valve 8 controls the amount of the EGR gas G2 flowing into the EGR gas compressor 5 and the fresh air A2. It is configured so that the amount can be adjusted and controlled. Further, a rotation speed sensor 14 for detecting the rotation speed of the engine 1, a load sensor 15 for detecting the load of the engine 1, and a controller (E
CU) 20. The controller 20 receives the output of the rotation speed sensor 14 and the output of the load sensor 15 and determines the valve opening of the control valve 8 according to the load and speed of the engine in accordance with the data of the EGR map 30 previously input. Control is performed so that EGR can be performed at a preset EGR rate.

The details of the EGR map 30 differ depending on the size of the engine 1, the operating conditions, and the like, and the details also differ depending on the exhaust gas limit value of the country of use.
To briefly describe this configuration, two compressors 3 driven by the turbine 2 in the exhaust passage 12 at the same rotation,
5, one compressor 3 is dedicated to air, and the other EGR gas compressor 5 is
The EGR device is configured to selectively suck only the GR gas G2, the fresh air A2 and the EGR gas G2, or only the fresh air A2.

In the EGR device having the above-described configuration, by controlling the control valve 8, the operating state of the engine is detected based on the number of revolutions, load, and the like, and the EGR is performed at the optimum EGR rate for the operating state. it can. That is,
By performing the first intake state in which the control valve 8 is adjusted to supply only the EGR gas G2 to the EGR gas compressor 5, the EGR can be performed in the low-load / low-speed operation region.
Since a large amount of EGR gas is required in the low-load / low-speed operation region, the control valve 8 performs adjustment so that only the EGR gas G2 is supplied to the EGR gas compressor 5.

Then, by adjusting the opening of the control valve 8 and introducing fresh air, the second intake state in which a mixed gas of the EGR gas G2 and the fresh air A2 is supplied, the low-load / low-rotation range is achieved. It is possible to cope with a shortage of intake air due to excessive EGR gas. In the second intake state, the opening degree of the control valve 8 is adjusted to supply the EGR gas G2 and the fresh air A2 to the EGR gas compressor 5 at a ratio such that the required EGR rate is obtained. Load increases and EGR
It is possible to perform EGR corresponding to a medium / high load operation region in which it is necessary to reduce the rate.

As the load increases, the intake pressure is compressed by the compressor 3 of the supercharger.
Although the state becomes the intake pressure (boost pressure), the EGR gas G is compressed by the EGR gas compressor 5 provided in the EGR passage 9.
2 and the fresh air A2 are compressed and pressurized.
The pressure of the gas G2 and the fresh air A2 can be made higher than the intake pressure of the fresh air A1, and EGR can be performed smoothly.

Further, in the third intake state in which only fresh air is supplied, it is possible to supply sufficient fresh air at the time of acceleration operation in which the amount of fresh air tends to be insufficient without requiring any EGR, thereby suppressing generation of smoke. be able to. Therefore, by adjusting and controlling the control valve 8 in accordance with the operating state of the engine, only the fresh air A2, a mixed gas of the fresh air A2 and the EGR gas G2,
The EGR gas can be supplied to the EGR gas compressor 5 side by selecting only the EGR gas G2 and changing the mixing ratio of the mixed gas, so that the EGR can be efficiently performed at the optimum EGR rate. Therefore, the emission amount of NOx in the exhaust gas can be reduced in the entire operating region of the supercharged engine.

Further, since the EGR gas G2 is compressed and pressurized by the EGR gas compressor 5, it is possible to smoothly perform the EGR even during the high load operation of the supercharged engine having a high intake pressure, thereby reducing NOx. Can be planned.
Further, if necessary, the fresh air A2 can also be compressed and pressurized by the EGR gas compressor 5 and supplied, so that a sufficient amount of intake air to the cylinder can be secured, and generation of smoke and deterioration of fuel consumption can be prevented.

In addition, the control valve 8 is controlled to
By changing the flow rates of the gas G2 and A2, the load on the turbo 2 can be changed, and the compressors 3 and 5 can be operated at an efficient operating point with respect to the rotation speed of the turbo 2, thereby improving fuel efficiency. Can be done. According to the EGR device having this configuration, an EGR gas compressor for clutch control is provided to drive the EGR gas compressor only when the pressure of the EGR gas needs to be increased.
Since a clutch mechanism is not required, the size is reduced, and the cost and reliability are improved. In addition, fresh air A2 is EG
Since it can also be supplied from the R gas compressor 5, a sufficient amount of fresh air A1 + A2 can be supplied at the time of acceleration or the like where fresh air tends to be insufficient. Further, power for driving the compressor other than the energy of the exhaust gas is not required, and the control target is also a control valve, so that the control mechanism is simplified.

[0025]

As described above, according to the EGR device for a supercharged engine of the present invention, an EGR gas compressor coaxial with an intake compressor is provided in an EGR passage, and the EGR gas compressor upstream of the EGR gas compressor is provided. EGR
A second intake passage for introducing fresh air into the passage is provided.
A control valve is provided at a connection between the intake passage and the EGR passage,
This control valve is controlled so that only EGR gas, EGR gas, fresh air, and fresh air alone are selectively boosted and supplied to the intake passage side.
GR gas and fresh air can be supplied, and at the time of EGR, EGR can be efficiently performed at an optimum EGR rate, and when fresh air needs to be increased, sufficient fresh air can be supplied.

Since the EGR gas is pressurized by the EGR gas compressor and supplied to the intake passage, the EGR can be performed smoothly even in the high intake pressure state in the high load operation range. It can be extended over the entire operating area. Therefore, it is possible to reduce the emission amount of NOx in the exhaust gas in the entire operation range of the supercharged engine, and also reduce the amount of smoke generated.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an EGR device for a supercharged engine according to the present invention.

FIG. 2 is a schematic view showing an EGR region according to the related art, and FIG.
Is the EGR range of the EGR device of the supercharged engine,
(B) EG of the EGR device in the VG turbo engine
The R region is shown.

FIG. 3 is a configuration diagram of a conventional EGR device for a supercharged engine.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Engine 2 Turbocharger turbine 3 Supercharger compressor 5 EGR gas compressor 6 Intercooler 7 EGR cooler 9 EGR passage 11 Intake passage 11a Intake manifold 12 Exhaust passage 12a Exhaust manifold 13 Second intake passage 14 Speed sensor 15 Load Sensor 20 Controller (ECU) 30 EGR map

Claims (1)

[Claims] 1. A supercharged engine in which a compressor (3) provided in an intake passage (11) is driven by a turbine (2) provided in an exhaust passage (12) of the engine (1).
An EGR passage (9) connected to the exhaust passage (12) and the intake passage (11) is driven by the turbine (2) and pressurizes EGR gas (G2) to increase the pressure of the intake passage (11). And a second air inlet (A2) for introducing fresh air (A2) into the EGR passage (9) upstream of the EGR gas compressor (5).
An intake passage (13) is provided, and a control valve (8) is disposed at a connection between the second intake passage (13) and the EGR passage (9).
By controlling the control valve (8), the EGR gas (G
2) a mixed gas of EGR gas (G2) and fresh air (A2),
E of a supercharged engine configured to selectively supply fresh air (A2) to the EGR gas compressor (5).
GR device.