JP5545654B2 - Turbocharged internal combustion engine - Google Patents

Description

  The present invention relates to a turbocharged internal combustion engine equipped with an exhaust gas recirculation device.

Lowering the combustion temperature in the cylinders, than Te to reduce the emissions of the NO _x which is a harmful substance exhaust gas recirculation (Exhaust Gas Recirculation) system has been known. The EGR device mixes a part of exhaust gas generated by combustion into intake air.

  For the high-pressure loop EGR that recirculates the high-temperature and high-pressure exhaust gas immediately after being discharged from the cylinder to the intake passage, the low-temperature and low-pressure exhaust gas that has passed through the exhaust turbocharger turbine and the exhaust gas purification catalyst is taken into the intake passage. The low-pressure loop EGR (see, for example, Patent Document 1 below) is advantageous in that a large amount of EGR gas can be mixed into the intake air and fuel efficiency can be improved more effectively.

  By the way, when the low pressure loop type EGR is employed, the exhaust gas is recirculated upstream of the compressor in the intake passage. This is because when the confluence of the EGR passage and the intake passage is set downstream of the compressor, the exhaust gas is not recirculated to the intake passage particularly during the operation of the compressor. Therefore, even when control is performed so that the EGR valve is fully closed when the required EGR rate is reduced, the low-pressure loop EGR is compared with the case where the high-pressure loop EGR is used. A large amount of EGR gas remains in the intake passage. That is, even if the EGR valve is fully closed, the residual EGR gas is mixed with the intake air, so that the decrease in the EGR rate is delayed. As a result, the EGR rate of the intake air filled in the cylinder becomes excessive as compared with the required EGR rate, which may cause misfire and an unstable combustion state. Misfires and unstable combustion conditions cause torque shocks and an increase in the amount of hydrocarbons in exhaust gas, so it is necessary to suppress the occurrence.

  Therefore, when the conventional low-pressure loop EGR is used, the upper limit of the EGR rate is set low to prevent the occurrence of misfire or combustion instability. However, when the upper limit of the EGR rate is set low, the effect of performing the low-pressure loop type EGR control as described above, that is, the effect that the fuel consumption can be improved by mixing a large amount of EGR gas into the intake air is preferable. A new problem occurs that cannot be obtained.

JP 2008-248729 A

  An object of the present invention is to avoid the problem that combustion becomes unstable due to a delay in control of the EGR rate during acceleration / deceleration.

That is, an internal combustion engine with a turbocharger according to the present invention is an internal combustion engine with a turbocharger provided with a turbine provided in an exhaust passage and an intake passage compressor driven by the turbine. A throttle valve provided; an intake throttle valve provided upstream of the compressor in the intake passage; a fresh air bypass passage communicating the upstream of the intake throttle valve and the downstream of the throttle valve in the intake passage; and the fresh air bypass A fresh air bypass valve for fresh air metering provided in the middle of the passage, and a part of the exhaust gas from a location downstream of the turbine in the exhaust passage to a location upstream of the compressor and downstream of the intake throttle valve in the intake passage comprising an exhaust gas recirculation system for recirculating, and a control device for controlling the fresh-air bypass valve , Wherein the controller, the absolute value of the time differential value of the accelerator operation amount exceeds the first threshold value, performs control to open the fresh air bypass valve when below a larger second threshold value than the first threshold value It is characterized by that.

  With such a configuration, immediately after the EGR control is finished, the EGR concentration in the air-fuel mixture introduced into the cylinder can be reduced by introducing fresh air into the cylinder through the fresh air bypass passage. . Therefore, it is possible to suppress the occurrence of problems due to a large amount of EGR gas remaining in the intake passage as described above.

And a control device that controls the fresh air bypass valve, wherein the control device has a second threshold value that is greater than the first threshold value and whose absolute value of the time differential value of the accelerator operation amount exceeds the first threshold value. since the control for opening the fresh air bypass valve when below, in particular, and when performing a gentle acceleration to the extent that the supercharging by the turbo charger is not carried out sufficiently, gentle deceleration to the extent that the fuel cut is not performed The effect of opening the fresh air bypass valve when performing the operation can be suitably obtained.

Furthermore, before Symbol controller, as long as it performs control in the surge tank is opened a fresh air bypass valve only when a negative pressure, fresh air bypass valve when the surge tank is a positive pressure By closing the valve, it is possible to suppress the occurrence of a problem that the EGR gas flows backward to the upstream side of the intake throttle valve.

  According to the present invention, it is possible to obtain an effect that it is possible to avoid a problem that combustion becomes unstable due to a delay in control of the EGR rate during acceleration / deceleration.

BRIEF DESCRIPTION OF THE DRAWINGS Schematic structure explanatory drawing of the engine which concerns on one Embodiment of this invention. FIG. 3 is a schematic configuration explanatory diagram of the electronic control device of the embodiment. The flowchart which shows the control procedure of the embodiment.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  An engine 100 which is an internal combustion engine schematically shown in FIG. 1 has two cylinders 1, an intake passage 2 for supplying intake air to each cylinder 1, and an exhaust gas for discharging exhaust gas. It comprises at least an exhaust passage 3 and a turbocharger 4 having a turbine 5 disposed on the exhaust passage 3 and a compressor 6 disposed on the intake passage 2. In the intake passage 2, an air cleaner 7, an intake throttle valve 8, a compressor 6, an intercooler 9, and an electronically controlled throttle valve (hereinafter referred to as a throttle valve 10) are arranged in this order from the upstream. In the present embodiment, a surge tank 11 is provided between the throttle valve 10 and the cylinder 1. In addition, in the present embodiment, a fresh air bypass passage 12a that communicates between a location upstream of the intake throttle valve 8 and a location downstream of the throttle valve 10, specifically, the surge tank 11, and the fresh air bypass. A fresh air bypass mechanism 12 having a fresh air bypass valve 12b provided in the passage 12a is disposed. The fresh air bypass valve 12b is a valve capable of continuously changing the opening degree between a fully closed state and a fully open state. In particular, during moderate acceleration / deceleration, as described later, fresh air is introduced from the fresh air bypass passage 12a to prevent misfire due to excessive EGR. The throttle valve 10 opens and closes according to an operation amount of an accelerator pedal (not shown). The fuel evaporative gas generated in a fuel tank (not shown) is adsorbed by the canister 13 and is introduced into the intake passage 2 via the purge vacuum switching valve 14 (purge VSV) after the engine 100 is started. It is.

  Each cylinder 1 is provided with a spark plug 15 and a fuel injection valve 16. The fuel injection valve 16 is connected to a high-pressure fuel pump 18 via a delivery pipe 17.

On the exhaust passage 3, a turbine 5, a three-way catalyst 20, and an exhaust muffler (not shown) are arranged in this order from the upstream. On the upstream side of the three-way catalyst 20, an air-fuel ratio sensor 21 is provided that outputs an output signal corresponding to the air-fuel ratio or oxygen concentration upstream of the three-way catalyst 20 to an electronic control unit (hereinafter referred to as ECU 33). On the other hand, a rear O ₂ sensor 22 that outputs a signal corresponding to the oxygen concentration in the three-way catalyst 20 to the ECU 33 is provided downstream of the three-way catalyst 20.

  The turbocharger 4 can use a well-known one in this field, and includes an exhaust bypass passage 23a that enables communication between the upstream and downstream of the turbine 5 in order to control the supercharging pressure. A waste gate valve 23b for opening and closing the exhaust bypass passage 23a is provided. The waste gate valve 23b is closed so as to supercharge more fresh air into the cylinder 1 by introducing more exhaust gas to the turbine 5 during low-speed traveling, and supercharging during medium-high speed traveling. Opened to prevent knocking from occurring. A turbocharging pressure bypass mechanism 24 that bypasses the compressor 6 is provided on the compressor 6 side of the turbocharger 4. The supercharging pressure bypass mechanism 24 includes an intake bypass passage 24a that enables communication between the upstream and downstream of the compressor 6, and an ABV 24b (air bypass valve) that is an intake bypass valve that opens and closes the intake bypass passage 24a. . During deceleration, the boost pressure is reduced.

  In the present embodiment, an EGR device 25 for mixing exhaust gas with fresh air flowing into the intake passage 2 via the air cleaner 7 is provided in communication between the intake passage 2 and the exhaust passage 3. . That is, the EGR device 25 is provided in the exhaust gas recirculation pipeline (hereinafter referred to as the EGR pipeline 26) in which the intake passage 2 and the exhaust passage 3 are selectively communicated with each other and the EGR pipeline 26. An exhaust gas recirculation control valve (hereinafter referred to as an EGR valve 27) that controls the amount of exhaust gas (EGR gas) that passes through or is recirculated through the pipe line 26, and an EGR provided upstream of the EGR valve 27 An EGR cooler 28 that cools the gas with water is provided. The EGR pipe line 26 has a location downstream of the turbine 5 in the exhaust passage 3, more precisely a location downstream from the three-way catalyst 20, and a location downstream of the intake throttle valve 8 and upstream of the compressor 6 in the intake passage 2. Communicate. That is, the EGR device 25 is of a low pressure loop type. The EGR valve 27 is controlled by the ECU 33.

  Furthermore, in this embodiment, a continuously variable valve timing mechanism (hereinafter referred to as VVT 29) is provided. The VVT 29 changes the valve timing of the intake valve while constantly opening and closing the exhaust valve with respect to the rotation of the crankshaft (not shown), so that the relative position between the valve timing of the exhaust valve and the valve timing of the intake valve is changed. The phase difference can be freely changed within a predetermined angle range. The ECU 33 controls the VVT 29.

  In addition, in this embodiment, a blow-by gas recirculation device 30 for sending blow-by gas generated in the crank chamber in the crank case of the engine 100 and the cam chamber in the cylinder head cover to the intake passage 2 is also provided. The blow-by gas recirculation device 30 includes a PCV passage 31 and a blow-by passage 32 as elements. The PCV passage 31 allows the crank chamber in the crankcase to communicate with the intake passage 2. In the present embodiment, one end of the PCV passage 31 is connected to a portion of the intake passage 2 downstream from the throttle valve 10. The blow-by passage 32 allows the cam chamber in the cylinder head cover to communicate with the intake passage 2. Although not shown, the cam chamber is connected to the crank chamber via an internal passage, and blow-by gas and fresh air can be exchanged with each other. In the present embodiment, one end of the blow-by passage 32 is connected to a predetermined location on the upstream side of the compressor 6 in the intake passage 2, more precisely on the upstream side of the intake throttle valve 8.

As schematically shown in FIG. 2, the ECU 33 is a microcomputer system including a CPU 33a, a RAM 33b, a ROM 33c, a flash memory 33d, an I / O interface 33e, and the like. The I / O interface 33e includes an air flow rate signal a output from the air flow meter 34 for detecting the air flow rate, a vehicle speed signal b output from the vehicle speed sensor 35 for detecting the vehicle speed, and a rotational speed for detecting the engine speed. The rotation speed signal c output from the sensor 36, the throttle opening signal d output from the throttle position sensor 37 for detecting the throttle valve opening, the intake pressure in the intake passage 2, more specifically in the surge tank 11 ( The intake pressure signal e output from the pressure sensor 38 for detecting the supercharging pressure), the intake air temperature signal f output from the intake air temperature sensor 39 for detecting the intake air temperature in the intake passage 2, and the water temperature sensor 40 for detecting the cooling water temperature. The water temperature signal g output from the fuel pressure signal h output from the fuel pressure sensor 41 that detects the fuel pressure, the air-fuel ratio signal i output from the air-fuel ratio sensor 21, Voltage signal j or the like which is output from the A O ₂ sensor 22 are inputted. Further, from the I / O interface 33e, a fuel injection signal p for the fuel injection valve 16, an ignition signal q for the ignition plug 15 (ignition coil thereof), an opening / closing signal r for the fresh air bypass valve 12b, and the like. Output. The ECU 33 functions as a control device in the claims.

  Various control programs are stored in the ROM 33c or the flash memory 33d, and the programs are read into the RAM 33b and decoded by the CPU 33a. The CPU 33a acquires various signals a, b, c, d, e, f, g, h, i, j necessary for operation control of the engine 100 via the I / O interface 33e, and uses the information indicated by these signals. Based on this, the intake air amount, the required fuel injection amount, the ignition timing, the opening / closing valve timing, the opening degree of the EGR valve 25b, and the like are calculated. Then, various control signals p, q, r corresponding to the calculation result are applied via the I / O interface 33e.

  Thus, in the present embodiment, the ECU 33 performs control to open the fresh air bypass valve 12b when a predetermined acceleration / deceleration condition indicating gradual acceleration or gradual deceleration is satisfied.

  Specifically, the absolute value of the time differential value of the accelerator operation amount exceeds the first threshold (acceleration or deceleration is performed), and falls below a second threshold greater than the first threshold (acceleration or When the inside of the surge tank 11 has a negative pressure, control is performed to open the fresh air bypass valve 12b. Further, when there is a sudden change in the operating state, specifically when the fuel cut is started or when the accelerator operation amount increases, control is performed to close the fresh air bypass valve 12b. Note that the second threshold value is a value such that the supercharging pressure becomes sufficiently large due to sudden acceleration and the amount of fresh air supplied is sufficiently large compared to the EGR gas in the intake passage, or a fuel cut is performed. Of the values indicating the degree of sudden deceleration, a larger value is determined based on experiments and adopted.

  Hereinafter, the procedure of processing executed by the ECU 33 according to the program will be described with reference to the flowchart shown in FIG.

  First, it is determined whether or not the operating state satisfies a predetermined acceleration / deceleration condition (S1). Specifically, it is determined whether or not the absolute value of the time differential value of the accelerator operation amount is above the first threshold value and below the second threshold value. If the operating condition satisfies a predetermined acceleration / deceleration condition, it is then determined whether or not the surge tank is under negative pressure (S2). Further, when the surge tank has a negative pressure, the opening degree θ of the fresh air bypass valve 12b is determined using the engine speed and the intake pressure as parameters (S3), and then the time differential value of the accelerator operation amount is used as a parameter. The valve opening time t of the air bypass valve 12b is determined (S4). Then, the fresh air bypass valve 12b is opened (S5), and it is determined whether or not the valve opening time t has elapsed since the start of the fresh air bypass valve 12b (S6). If the valve opening time t has not elapsed since the start of the fresh air bypass valve 12b, whether or not there has been a sudden change in the operating state, specifically, whether fuel cut has started or the accelerator It is determined whether or not the operation amount has increased (S7). Here, when there is no sudden change in the operation state, the fresh air bypass valve 12b is continuously opened (S5). On the other hand, when the valve opening time t has elapsed from the start of opening of the fresh air bypass valve 12b, or when there is a sudden change in the operating state, control is performed to close the fresh air bypass valve 12b (S8). . Further, even when the operating state does not satisfy the predetermined acceleration / deceleration conditions and when the surge tank is at a positive pressure, control is performed to close the fresh air bypass valve 12b (S8). Here, the opening degree θ of the fresh air bypass valve 12b is determined in the ROM 33c or the flash memory 33d that stores the typical engine speed and intake pressure and the corresponding opening degree θ of the fresh air bypass valve 12b in association with each other. The interpolation is calculated by referring to the stored opening degree map. In addition, the determination of the valve opening time t of the fresh air bypass valve 12b is performed by the ROM 33c or flash memory in which the time differential value of the representative accelerator operation amount and the valve opening time t of the corresponding fresh air bypass valve 12b are stored in association with each other. This is performed by interpolation calculation with reference to the valve opening time map stored in 33d.

  In addition, the ECU 33 performs control for bringing the EGR valve 27 into a fully closed state in parallel with the above-described control when it is detected that the absolute value of the time differential value exceeds the first threshold value and falls below the second threshold value. And do it.

  When such control is performed, when gradual acceleration / deceleration is performed, the fresh air bypass valve 12b is opened and fresh air is introduced into the surge tank 11 while the EGR valve 27 is fully closed. The EGR concentration in the air-fuel mixture introduced into the cylinder 1 can be reduced. Therefore, it is possible to suppress problems caused by a large amount of EGR gas remaining in the intake passage 2, that is, the occurrence of misfires and unstable combustion states. And this makes it possible to introduce a large amount of EGR gas into the cylinder by setting the upper limit of the EGR rate at the time of performing EGR control to be high, so that an improvement in fuel consumption can be effectively obtained. .

  In addition, since the ECU 33 performs control to open the fresh air bypass valve 12b when the operating condition satisfies a predetermined acceleration / deceleration condition, the acceleration is particularly moderate to such an extent that supercharging by the turbocharger 4 is not sufficiently performed. Thus, the effect of opening the fresh air bypass valve can be suitably obtained when performing slow deceleration to such an extent that fuel cut is not performed.

  Furthermore, since the ECU 33 performs control to open the fresh air bypass valve 12b only when the inside of the surge tank 11 is negative pressure, the fresh air bypass valve 12b is closed when the inside of the surge tank 11 is positive pressure. By performing the valve operation, it is possible to suppress the occurrence of a problem that the EGR gas flows backward upstream of the intake throttle valve.

  The present invention is not limited to the embodiment described above.

  For example, in the above-described embodiment, the detection of the driving state is performed based on the time differential value of the accelerator pedal operation amount, but may be performed based on the time differential value of the throttle valve opening.

  Further, when the operation state satisfies a predetermined acceleration / deceleration condition, control may be performed to open the fresh air bypass valve regardless of the pressure in the surge tank. On the other hand, when the pressure in the surge tank is negative, control may be performed to open the fresh air bypass valve regardless of the operation amount of the accelerator pedal or the time differential value of the opening of the throttle valve.

Furthermore, the purge vacuum switching valve, the continuously variable bulk timing mechanism, the rear O ₂ sensor, and the blow-by gas recirculation device in the above-described embodiment are not necessarily provided.

  In addition, although the electronically controlled throttle valve is used in the above-described embodiment, the present invention may be applied to an internal combustion engine having a throttle valve that is mechanically connected to an accelerator pedal.

  The present invention may be applied to an internal combustion engine that injects fuel into the intake port.

  In addition, various modifications may be made without departing from the spirit of the present invention.

2 ... Intake passage 3 ... Exhaust passage 5 ... Turbine 6 ... Compressor 8 ... Intake throttle valve 10 ... Throttle valve 12a ... Fresh air bypass passage 12b ... Fresh air bypass valve 25 ... EGR device (exhaust gas recirculation device)
33 ... ECU

Claims (2)

A turbine provided in the exhaust passage;
In an internal combustion engine with a turbocharger provided with a compressor of an intake passage driven by the turbine,
A throttle valve provided downstream of the compressor in the intake passage;
An intake throttle valve provided upstream of the compressor in the intake passage;
A fresh air bypass passage communicating the upstream of the intake throttle valve and the downstream of the throttle valve in the intake passage;
A fresh air bypass valve for fresh air metering provided in the middle of the fresh air bypass passage;
An exhaust gas recirculation device that recirculates part of the exhaust gas from a location downstream of the turbine in the exhaust passage to a location upstream of the compressor and downstream of the intake throttle valve in the intake passage ;
A control device for controlling the fresh air bypass valve;
The control device performs control to open the fresh air bypass valve when the absolute value of the time differential value of the accelerator operation amount exceeds a first threshold value and falls below a second threshold value that is larger than the first threshold value. An internal combustion engine equipped with a turbocharger. Wherein the controller, turbocharged internal combustion engine according to claim 1 for performing control in the surge tank is opened a fresh air bypass valve only when a negative pressure.

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