JP5688959B2 - Control device for internal combustion engine - Google Patents

Description

  The present invention relates to a control device for an internal combustion engine having a high-pressure exhaust gas recirculation passage and a low-pressure exhaust gas recirculation passage.

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.

  As an internal combustion engine having such an EGR device, a high-pressure loop EGR device that recirculates high-temperature and high-pressure exhaust gas immediately after being discharged from a cylinder to an intake passage, a turbine of an exhaust turbocharger, and an exhaust gas purification catalyst A low-pressure loop EGR device that recirculates low-temperature and low-pressure exhaust gas that has passed through the intake passage, and switches between the high-pressure loop EGR device and the low-pressure loop EGR device depending on the operating state such as rotational speed and load. Things are known.

  More specifically, in the low-speed and high-load region, the intake pipe pressure is higher than the gas pressure entering the turbine, and the exhaust gas recirculation using the high-pressure loop EGR device cannot be performed, so the low-pressure loop EGR device is used. However, since it is difficult for knocking to occur in the low, middle and low load regions, a high-pressure loop EGR device with a short path is used to recirculate more exhaust gas by increasing the temperature of the EGR gas and stabilizing the combustion. (For example, refer to Patent Document 1).

  Here, when the accelerator operation amount is rapidly reduced to shift to low load operation to decelerate the vehicle during high load operation, use of the low pressure loop type EGR device is stopped and use of the high pressure loop type EGR device is stopped. Control to start is performed.

  Thus, during the use of the low-pressure loop EGR device at the time of high load, since the entire amount of EGR gas and burned gas passes through the turbine of the turbocharger, the pressure upstream of the turbine is high. When the EGR device to be used is switched from this state to the high-pressure loop EGR device, the upstream pressure of the turbine is increased, so the opening degree of the EGR valve in the high-pressure loop EGR device is set in the same manner as during steady operation. In such a case, there is a concern that the amount of EGR gas introduced into the cylinder is too large, resulting in a problem of misfire.

JP 2008-19730 A

  The present invention pays attention to the above points and aims to prevent misfire at the time of deceleration in an internal combustion engine that includes a high-pressure loop exhaust gas recirculation device and a low-pressure loop exhaust gas recirculation device and uses them by switching them. And

  That is, the control device for an internal combustion engine according to the present invention includes a turbocharger including a turbine provided in an exhaust passage and a compressor of an intake passage driven by the turbine, and 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, and a portion 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 low-pressure loop EGR device having a low-pressure exhaust gas recirculation passage for recirculation and a low-pressure exhaust gas recirculation control valve for controlling the amount of exhaust gas flowing through the low-pressure exhaust gas recirculation passage; and an upstream of the turbine in the exhaust passage Part of the exhaust gas is circulated from the location to the location downstream of the compressor in the intake passage And a high-pressure loop EGR device having a high-pressure exhaust gas recirculation control valve for controlling the amount of exhaust gas flowing through the high-pressure exhaust gas recirculation passage. The exhaust gas is circulated through the low-pressure exhaust gas recirculation passage in the high load region, and the exhaust gas is circulated through the high-pressure exhaust gas recirculation passage in the low load region. The low pressure exhaust gas recirculation control valve closes more rapidly and the high pressure exhaust gas recirculation control valve performs control to open more slowly as the rate of decrease in the required load increases. .

  If this is the case, the increase in the amount of EGR gas introduced into the cylinder can be moderated by gently opening the high-pressure exhaust gas recirculation control valve. The occurrence of misfire due to the excessive amount of EGR gas can be prevented.

  In the present invention, the “required load” corresponds to the output of the internal combustion engine requested by the driver, such as the accelerator operation amount, the throttle valve opening, the intake air amount of fresh air, the intake pipe pressure, and the like. It is a concept showing the whole quantity.

  According to the control device for an internal combustion engine of the present invention, a high-pressure loop exhaust gas recirculation device and a low-pressure loop exhaust gas recirculation device are provided. Can do.

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. Action | operation explanatory drawing which concerns on the same 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. 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, a low-pressure loop EGR device 25 for mixing exhaust gas with fresh air flowing into the intake passage 2 via the air cleaner 7 is communicated between the intake passage 2 and the exhaust passage 3. Provided. That is, the low-pressure loop EGR device 25 is provided in a low-pressure exhaust gas recirculation passage (hereinafter referred to as a low-pressure EGR passage 26) in which the intake passage 2 and the exhaust passage 3 are selectively communicated, and the low-pressure EGR passage 26. A low pressure exhaust gas recirculation control valve (hereinafter referred to as a low pressure EGR valve 27) that controls the amount of exhaust gas (EGR gas) that passes through or is recirculated through the low pressure EGR passage 26, and the low pressure EGR valve 27. And an EGR cooler 28 that cools the EGR gas with water. The low pressure EGR passage 26 has a location downstream of the turbine 5 in the exhaust passage 3, more precisely a location downstream of 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. The low pressure EGR valve 27 is controlled by the ECU 33.

  In the present embodiment, a high-pressure loop EGR device 42 for mixing exhaust gas into fresh air flowing into the intake passage 2 via the air cleaner 7 is also connected between the intake passage 2 and the exhaust passage 3. Provided. The high-pressure loop EGR device 42 includes a high-pressure exhaust gas recirculation passage (hereinafter referred to as a high-pressure EGR passage 43 and a high-pressure exhaust gas recirculation passage) that connects a location upstream of the turbine 5 in the exhaust passage 3 and a location downstream of the compressor 6 in the intake passage 2. And a high-pressure EGR valve 44 for controlling the amount of exhaust gas flowing through the high-pressure EGR passage 43. The high pressure EGR valve 44 is also 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 accelerator, the accelerator operation amount signal h output from the accelerator operation amount sensor 41 for detecting the operation amount of the accelerator pedal, the air-fuel ratio The air-fuel ratio signal i output from the capacitors 21, the voltage signal j or the like to be output from the rear 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 open / close signal r for the fresh air bypass valve 12b, a low pressure An on-off valve signal s is output to the EGR valve 27, and an on-off valve signal t is output to the high pressure EGR valve 44. 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. Various control signals p, q, r, s, and t corresponding to the calculation result are applied through the I / O interface 33e.

  Thus, in the present embodiment, the ECU 33 opens the low pressure EGR valve 27 and closes the high pressure EGR valve 44 so as to use the low pressure loop EGR device 25 in the low speed and high load region, and closes the high pressure EGR valve 44 in the low speed, medium and low load region. Control is performed so that the low pressure EGR valve 27 is closed and the high pressure EGR valve 44 is opened to use the EGR device 42.

  Further, when a decrease in the required load is detected in the high load region, the low pressure EGR valve 27 is closed more rapidly and the high pressure EGR valve 44 is controlled to open more gradually as the decrease rate of the required load increases. . In the present embodiment, an accelerator pedal operation amount (hereinafter referred to as an accelerator operation amount) indicated by an accelerator operation amount signal h is adopted as an amount indicating a required load. That is, it is assumed that a decrease in the required load is detected when a decrease in the accelerator operation amount is detected. More specifically, an opening / closing valve speed map storing the reduction speed of the accelerator operation amount and the valve opening amounts per unit time of the low pressure EGR valve 27 and the high pressure EGR valve 44 is stored in the ROM 33c or the flash memory 33d of the ECU 33, The valve closing amount per unit time of the low pressure EGR valve 27 and the valve opening amount per unit time of the high pressure EGR valve 44 are respectively calculated by interpolation based on the detected decrease rate of the accelerator operation amount, and the valve is opened and closed based on the calculation result. Take control. The valve closing amount per unit time increases as the decrease rate increases, and the valve opening amount per unit time decreases as the decrease rate increases. Here, in this embodiment, the rate of decrease in the accelerator operation amount is detected as a change amount per predetermined time by detecting the accelerator operation amount indicated by the accelerator operation amount signal h every predetermined time, for example, every 0.1 second. I am doing so.

  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 has shifted from the low speed / high load area to the low speed / low / medium load area (S1). Is detected (S2), and the valve closing amount per unit time of the low pressure EGR valve 27 and the valve opening amount per unit time of the high pressure EGR valve 44 are determined based on the detected decrease rate of the accelerator operation amount (S3). The low pressure EGR valve 27 is closed by the closed valve amount and the high pressure EGR valve 44 is opened by the determined valve opening amount (S4).

That is, when the accelerator operation amount decreases at time t ₁ in FIG. 4, the low pressure EGR valve 27 closes at a speed corresponding to the decrease speed of the accelerator operation amount, and the high pressure EGR at a speed corresponding to the decrease speed of the accelerator operation amount. The valve 44 opens as shown by the solid line in FIG. The valve opening speed of the high pressure EGR valve 44 is gentle as compared with the case where the conventional control as shown by the broken line in FIG. 4 is performed. Then, by making the valve opening speed of the high pressure EGR valve 44 gentler than in the conventional case, the change in the air flow rate to the cylinder 1 is compared with the case where the conventional control shown by the broken line in FIG. 4 is performed. Therefore, unlike the case where the conventional control indicated by the broken line in FIG. 4 is performed, the EGR rate does not increase rapidly. Furthermore, as shown by the two-dot chain line in FIG. 4, when the accelerator operation amount decreases more rapidly, the low pressure EGR valve 27 is closed more rapidly and the high pressure EGR valve 44 is opened more gradually. Also at this time, the change in the air flow rate to the cylinder 1 becomes gradual compared to the case where the conventional control indicated by the broken line in FIG. 4 is performed, and accordingly, the case where the conventional control indicated by the broken line in FIG. Unlikely, the EGR rate does not increase rapidly.

  As described above, when the control according to the present invention is performed, the high pressure EGR valve 44 is gradually opened as compared with the case where the conventional control is performed as described above. The increase in the amount of EGR gas can be made moderate. Accordingly, it is possible to prevent the occurrence of misfire due to a sudden increase in the amount of EGR gas introduced into the cylinder 1, and to further improve fuel efficiency by using the high-pressure loop EGR device 25 and the low-pressure loop EGR device 51 together. be able to.

  In addition, this embodiment is not restricted to embodiment mentioned above.

  For example, in the above-described embodiment, the accelerator operation amount is adopted as the amount indicating the required load, and the decrease rate of the accelerator operation amount is associated with the valve closing speed of the low pressure EGR valve and the valve opening speed of the high pressure EGR valve. In addition, other amounts indicating the required load, such as the opening degree of the throttle valve, the fresh air flow rate, the intake pipe pressure, and the valve closing speed of the low pressure EGR valve and the valve opening speed of the high pressure EGR valve are associated with each other. You may do it.

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

2 ... Intake passage 3 ... Exhaust passage 4 ... Turbocharger 5 ... Turbine 6 ... Compressor 8 ... Intake throttle valve 10 ... Throttle valve 25 ... Low pressure loop EGR device 26 ... Low pressure EGR passage (low pressure exhaust gas recirculation passage)
27 ... Low pressure EGR valve (Low pressure exhaust gas recirculation control valve)
42 ... High-pressure loop EGR device 43 ... High-pressure EGR passage (high-pressure exhaust gas recirculation passage)
44 ... High pressure EGR valve (High pressure exhaust gas recirculation control valve)

Claims (1)

A turbocharger comprising a turbine provided in an exhaust passage and 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 low pressure exhaust gas recirculation passage for recirculating 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, and the low pressure exhaust gas recirculation passage; A low-pressure loop EGR device having a low-pressure exhaust gas recirculation control valve for controlling the amount of exhaust gas flowing;
A high-pressure exhaust gas recirculation passage for recirculating a part of the exhaust gas from a location upstream of the turbine in the exhaust passage to a location downstream of the compressor in the intake passage, and an amount of exhaust gas flowing through the high-pressure exhaust gas recirculation passage. Used in a turbocharged internal combustion engine comprising a high-pressure loop EGR device having a high-pressure exhaust gas recirculation control valve to control,
In the high load region, exhaust gas is circulated through the low pressure exhaust gas recirculation passage,
In the low load region, the exhaust gas is circulated through the high-pressure exhaust gas recirculation passage,
When a decrease in the required load is detected in the high load region,
The low pressure exhaust gas recirculation control valve closes more rapidly;
The control apparatus for an internal combustion engine, wherein the high-pressure exhaust gas recirculation control valve performs control to open more gently.

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