JP2009057944A - Supercharging control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a supercharging control device for an internal combustion engine, capable of sufficiently utilizing the supercharging performance of a turbocharger. <P>SOLUTION: This supercharging control device is applied to the internal combustion eigne 1 having the turbocharger 6 and provided with a plurality of exhaust emission control catalysts 10, 11 arranged downstream of a turbine 6a along an exhaust gas flowing direction. The control device is provided with a bypass passage 14 bypassing the turbine 6a and connecting a section 5a upstream of the turbine 6a in the exhaust passage 5 and a section 5b sandwiched between the exhaust emission control catalysts 10, 11, and a bypass valve 15 opening/closing the bypass passage 14. It is determined whether or not supercharging reaches a limit based on a physical quantity correlated with the degree of supercharging by the turbocharger 6. If supercharging has not reach the limit, the bypass valve 15 is closed, and if supercharging reaches the limit, the bypass valve 15 is opened. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a supercharging control device for an internal combustion engine that supercharges intake air using a turbocharger.

  As a supercharging control device applied to an internal combustion engine equipped with a turbocharger, it comprises a bypass passage that bypasses the turbine and connects the upstream and downstream of the turbine, and a wastegate valve that opens and closes the bypass passage, There is known a device that prevents excessive increase of the supercharging pressure or excessive rotation of the turbine by opening the waste gate valve when the supercharging pressure exceeds a predetermined upper limit value (for example, patent document). 1). In addition, there is Patent Document 2 as a prior art document related to the present invention.

JP 2006-299859 A Japanese Utility Model Publication No. 5-32732.

  In conventional supercharging control devices, there is a delay in response until the effect occurs after the wastegate valve is opened, so the upper limit value of the supercharging pressure must be set lower than the original limit value for safety reasons. Absent. Moreover, although the rise of a supercharging pressure can be suppressed by opening a waste gate valve, it is difficult to reduce a supercharging pressure actively. Therefore, the conventional supercharging control device may not fully utilize the performance of the turbocharger.

  Therefore, an object of the present invention is to provide a supercharging control device for an internal combustion engine that can fully utilize the supercharging performance of a turbocharger.

  The present invention has a turbocharger that recovers exhaust energy in a turbine in an exhaust passage and drives a compressor in an intake passage, and a plurality of exhaust purification catalysts are provided downstream of the turbine along the exhaust flow direction. In the supercharging control device applied to the internal combustion engine, the bypass bypasses the turbine and connects a section upstream of the turbine in the exhaust passage and a section sandwiched between the plurality of exhaust purification catalysts. When determining whether or not the supercharging has reached a limit based on a physical quantity that correlates with the degree of supercharging by the passage, the bypass valve that opens and closes the bypass passage, and the turbocharger. Is provided with bypass control means for closing the bypass valve and opening the bypass valve when the limit is reached. (Claim 1).

  According to the supercharging control device of the present invention, the exhaust back pressure generated in the section upstream of the turbine in the exhaust passage can be released to the low-pressure section between the exhaust purification catalysts by opening the bypass valve. it can. Thereby, the exhaust back pressure and the exhaust gas flow rate upstream of the turbine can be quickly reduced. Therefore, the timing for starting the exhaust gas bypass can be made closer to the limit timing of supercharging than before, whereby the turbocharging range by the turbocharger can be expanded and the supercharging performance can be fully exhibited. Since the exhaust gas bypassing the turbine is guided to the exhaust purification catalyst, there is no possibility that the exhaust gas is released into the atmosphere without being purified.

  In one form of the supercharging control device of the present invention, the bypass control means determines that the supercharging has reached a limit when a deviation between an actual value relating to the physical quantity and a target value exceeds a predetermined threshold. (Claim 2). Alternatively, in one form of the supercharging control device of the present invention, the bypass control means performs the supercharging when the temporal change amount of the deviation between the actual value related to the physical quantity and the target value exceeds a predetermined threshold. It may be determined that the limit has been reached (claim 3). Furthermore, in these forms, the physical quantity may be a supercharging pressure or a turbine rotational speed (Claim 4). According to these embodiments, it is possible to determine how much the physical quantity such as the supercharging pressure or the turbine rotational speed has increased with respect to the target rotational speed, and to open the bypass valve near the supercharging limit. Note that when the threshold value is exceeded, the deviation or the temporal change amount thereof decreases beyond the threshold value when the actual value is less than or equal to the target value, or when the actual value exceeds the target value, the deviation or The amount of change over time may be increased beyond a threshold value.

  In one form of the supercharging control device of the present invention, the bypass control means monitors the exhaust back pressure generated in the section upstream of the turbine as the physical quantity, and the exhaust back pressure exceeds a predetermined threshold value. Alternatively, it may be determined that the supercharging has reached a limit (claim 5). If the exhaust back pressure increases, the turbine speed increases accordingly, and the supercharging pressure also increases. Therefore, by monitoring the exhaust back pressure, it is possible to determine how much the boost pressure or the turbine speed has increased, and to open the bypass valve near the limit of the boost.

  As described above, according to the supercharging control device of the present invention, when it is determined that the supercharging has reached the limit, the bypass valve is opened, and is generated in the section upstream of the turbine in the exhaust passage. The exhaust back pressure can be efficiently released to the low pressure section between the exhaust catalysts. As a result, the exhaust back pressure and the exhaust gas flow rate upstream of the turbine can be quickly reduced. Therefore, the timing for starting the bypass of exhaust gas can be made closer to the limit timing of supercharging than before, whereby the turbocharging range by the turbocharger can be expanded and the supercharging performance can be fully exhibited.

  FIG. 1 shows an internal combustion engine (hereinafter sometimes referred to as an engine) to which a supercharging control device according to a first embodiment of the present invention is applied. The engine 1 is mounted on a vehicle as a power source for traveling, and includes an engine main body 2, an intake passage 4 that guides intake air to each of a plurality of (four in the figure) cylinders 3 of the engine main body 2, An exhaust passage 5 through which exhaust from the cylinder 3 is guided, and a turbocharger 6 provided between the intake passage 4 and the exhaust passage 5 are provided. The turbocharger 6 collects exhaust energy by a turbine 6a provided in the exhaust passage 5, and rotates the compressor 6b of the intake passage 4 connected to the turbine 6a so as to rotate integrally with the turbine 6a. In contrast, the intake air is supercharged.

  The intake passage 4 is provided with an intake pressure sensor 7 for detecting the pressure of the intake air supercharged by the compressor 6 b and an intake manifold 8 for distributing the intake air to the cylinder 3. The exhaust passage 5 is provided with an exhaust manifold 9 that joins exhaust from the cylinder 3. The exhaust gas merged in the exhaust manifold 9 is guided to the turbine 6a. A first exhaust purification catalyst 10 and a second exhaust purification catalyst 11 are sequentially provided in the exhaust passage 5 downstream of the turbine 6a along the exhaust flow direction. Hereinafter, these may be abbreviated as the first catalyst 10 and the second catalyst 11.

  An exhaust pressure sensor 12 that detects the exhaust pressure (exhaust back pressure) in the section 5 a is provided in the section 5 a upstream of the turbine 6 a in the exhaust passage 5. The turbine 6a is provided with a turbine rotation sensor 13 that detects the rotational speed (rotational speed) of the turbine 6a. Further, the exhaust passage 5 is provided with a bypass passage 14 that bypasses the turbine 6 a and connects the section 5 a upstream of the turbine 6 a and the section 5 b sandwiched between the catalysts 10 and 11. A bypass valve 15 that opens and closes the bypass passage 14 is provided.

  The opening degree of the bypass valve 15 is controlled by an engine control unit (ECU) 16. The ECU 16 is configured as a computer unit including a microprocessor and peripheral devices such as a ROM and a RAM necessary for its operation, and controls the operating state of the engine 1 according to a program stored in the ROM. As control regarding the opening degree of the bypass valve 15, the ECU 16 repeatedly executes the bypass valve control routine shown in FIG. 2 at a predetermined cycle. Thereby, ECU16 functions as a bypass control means of the present invention.

  In the bypass valve control routine of FIG. 2, the ECU 16 first acquires a physical quantity that correlates with the degree of supercharging by the turbocharger 6 in step S <b> 1, and in the subsequent step S <b> 2, the supercharging reaches a limit based on the acquired physical quantity. It is determined whether or not. The physical quantity correlated with the degree of supercharging includes, for example, the actual supercharging pressure detected by the intake pressure sensor 7, the exhaust back pressure upstream of the turbine 6 a detected by the exhaust pressure sensor 12, and the turbine rotation speed detected by the turbine rotation sensor 13. Etc. Regarding the determination of the limit of supercharging, for example, the limit can be determined when the deviation of the actual supercharging pressure with respect to the target supercharging pressure set according to the operating state of the engine 1 exceeds a predetermined threshold. In this case, it may be determined that the deviation has exceeded a predetermined threshold when the deviation is smaller than the threshold when the actual supercharging pressure is equal to or lower than the target supercharging pressure. It may be determined that the predetermined threshold has been exceeded when the deviation has increased beyond the threshold in the exceeded stage. Alternatively, when the deviation of the deviation of the actual supercharging pressure with respect to the target supercharging pressure, that is, the temporal change amount of the deviation of the actual supercharging pressure with respect to the target supercharging pressure exceeds a predetermined threshold, it is determined that the limit is reached it can. In this case as well, it may be determined that the deviation exceeds a predetermined threshold when the deviation of the deviation decreases below the threshold when the actual supercharging pressure is equal to or lower than the target supercharging pressure, or the actual supercharging pressure may exceed the target supercharging pressure. It may be determined that the predetermined threshold has been exceeded when the deviation of the deviation has increased beyond the threshold at the stage where the supply pressure has been exceeded. When the turbine rotational speed is acquired in step S1 instead of the actual supercharging pressure, whether or not it is the supercharging limit is determined in the same manner by paying attention to the deviation of the turbine rotational speed from the target rotational speed or the deviation of the deviation. be able to. When the exhaust back pressure is acquired in step S1, the exhaust back pressure is monitored, and when the detected value exceeds a predetermined threshold, it is possible to determine that the supercharging is the limit. In this case, supercharging is determined to be a limit when the exhaust back pressure rises above a threshold value.

  If it is determined in step S2 that the supercharging is not the limit, the ECU 16 proceeds to step S3 and closes the bypass valve 15. When in the closed state, the state is maintained. On the other hand, when it is determined in step S2 that the supercharging is the limit, the ECU 16 proceeds to step S4 and opens the bypass valve 15. Thereby, the exhaust back pressure in the section 5a on the upstream side of the turbine 6a is released to the section 5b between the catalysts 10 and 11 through the bypass passage 14, and the rotational speed of the turbine 5a is reduced. After setting the opening degree of the bypass valve 15 in step S3 or step S4, the ECU 16 ends the current routine.

  FIG. 3 shows an example of a correspondence relationship between the opening degree of the bypass valve 15 and the turbine speed when the vehicle is accelerated. The solid line in the figure shows the opening degree and the turbine speed when the routine of FIG. 2 is applied, and the imaginary line shows an example of the control effect by the conventional supercharging control device. When the turbine 6a starts rotating at time t0, the turbine rotational speed starts increasing toward the upper limit rotational speed (target rotational speed) Nmax. In the conventional supercharging control device, processing for limiting supercharging is performed at time t1 in which there is still a margin in the turbine rotation speed in anticipation of response delay. For example, the waste gate valve is opened at time t1. Or if it is a variable nozzle type turbocharger, a variable nozzle will be switched to a full open state at the time t1. Then, after the time t1, the turbine rotational speed reaches a vicinity of the upper limit rotational speed Nmax while gradually increasing as compared to before that time. On the other hand, in this embodiment, by opening the bypass valve 15, the exhaust back pressure upstream of the turbine 6a and the turbine are utilized by utilizing a relatively large pressure difference existing between the sections 5a and 5b of the exhaust passage 5. The amount of exhaust gas flowing into 6a can be instantaneously reduced. Therefore, the bypass valve 15 is kept closed until time t2 when the turbine rotational speed reaches the vicinity of the upper limit rotational speed Nmax, and the turbocharger 6a is opened by determining that supercharging is limited at time t2 and opening the bypass valve 15. Can be prevented from over-rotating. Therefore, it is possible to maintain the turbine rotational speed at a higher rotational speed than before, thereby expanding the supercharging area to the operation area that has been conventionally unusable or difficult and improving the acceleration response. be able to. Further, since the bypass passage 14 is connected to the section 5 b sandwiched between the catalysts 10 and 11, the exhaust gas that has passed through the bypass passage 14 is purified by the second exhaust purification catalyst 11. Therefore, there is no possibility that the exhaust gas bypassing the turbine 6a is discharged without purification.

  The present invention is not limited to the above-described form and can be implemented in various forms. For example, in the above embodiment, supercharging is performed using the detected value of the supercharging pressure by the intake pressure sensor 7, the detected value of the exhaust back pressure by the exhaust pressure sensor 12, or the detected value of the turbine speed by the turbine rotation sensor 13. Although it was determined whether or not it was at the limit, instead of these detected values, physical quantities such as supercharging pressure, turbine speed, and exhaust back pressure were estimated using a map, etc., and the estimated values were regarded as actual values. By comparing with the target value, it may be determined whether or not the supercharging is a limit.

The figure which shows the internal combustion engine to which the supercharging control apparatus which concerns on one form of this invention was applied. The flowchart which shows the bypass control routine which ECU of FIG. 1 performs. The figure which shows an example of the correspondence of the opening degree of a bypass valve at the time of acceleration of a vehicle, and turbine rotation speed.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Engine main body 4 Intake passage 5 Exhaust passage 6 Turbocharger 6a Turbine 6b Compressor 10 First exhaust purification catalyst 11 Second exhaust purification catalyst 14 Bypass passage 15 Bypass valve 16 Engine control unit (bypass control means)

Claims (5)

An internal combustion engine having a turbocharger that recovers exhaust energy in a turbine in an exhaust passage and drives a compressor in an intake passage, and a plurality of exhaust purification catalysts are provided downstream of the turbine along the exhaust flow direction In the applied supercharging control device,
Bypassing the turbine and connecting a section upstream of the turbine in the exhaust passage and a section sandwiched between the plurality of exhaust purification catalysts;
A bypass valve for opening and closing the bypass passage;
Based on a physical quantity that correlates with the degree of supercharging by the turbocharger, it is determined whether or not the supercharging has reached a limit. If the limit has not been reached, the bypass valve is closed and the limit is reached. Bypass control means for opening the bypass valve if
A supercharging control device for an internal combustion engine, comprising:   2. The overcharge according to claim 1, wherein the bypass control unit determines that the supercharging has reached a limit when a deviation between an actual value related to the physical quantity and a target value exceeds a predetermined threshold. Feed control device.   The bypass control means determines that the supercharging has reached a limit when a temporal change amount of a deviation between an actual value and a target value relating to the physical quantity exceeds a predetermined threshold value. Item 2. The supercharging control device according to Item 1.   The supercharging control device according to claim 2 or 3, wherein the physical quantity is a supercharging pressure or a turbine rotational speed.   The bypass control means monitors an exhaust back pressure generated in a section upstream of the turbine as the physical quantity, and determines that the supercharging has reached a limit when the exhaust back pressure exceeds a predetermined threshold. The supercharging control device according to claim 1, wherein

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