JP2012132423A - Control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device for an internal combustion engine that can certainly prevent an exhaust valve from opening during air intake even in a region where an exhaust pressure exceeds an intake air pressure.SOLUTION: The control device for an internal combustion engine includes: a bypass passage communicating an exhaust passage upstream of a turbine of a turbocharger and an exhaust passage downstream of the turbine of the turbocharger; a bypass valve for opening and closing the bypass passage; an exhaust air pressure obtaining means for obtaining an exhaust air pressure; an intake air pressure obtaining means for obtaining an intake air pressure; a determination means for determining, based on the intake air pressure obtained by the intake air pressure obtaining means and the exhaust air pressure obtained by the exhaust air pressure obtaining means, the possibility that the exhaust valve opens during air intake; and a bypass valve control means for increasing the opening degree of the bypass valve when the possibility is determined.

Description

  The present invention relates to a control device for an internal combustion engine.

  In order to prevent the intake pressure (supercharging pressure) from exceeding a specified value in an internal combustion engine equipped with a turbocharger, a bypass passage that connects the upstream side and the downstream side of the turbine, and a bypass valve that opens and closes the bypass passage And a technique is known in which a bypass valve is opened when the intake pressure exceeds a specified value (see, for example, Patent Document 1).

Japanese Utility Model Publication No. 61-6652 JP 58-214620 A JP 2007-23837 A

  As the exhaust energy increases, the intake pressure due to supercharging also increases. However, there is a region where the exhaust pressure exceeds the intake pressure under a condition where the volume of the exhaust gas is excessive, such as in a high rotation high load region. In this region, during the intake stroke, the exhaust valve may be pushed by the exhaust pressure and open. If the exhaust valve opens during the intake stroke, the exhaust gas mixes into the fresh air in the cylinder, causing a reduction in engine output and drivability.

  As described above, whether or not the exhaust valve opens during the intake stroke cannot be determined only by the intake pressure. For this reason, it is not possible to reliably prevent the exhaust valve from being opened during the intake stroke only by opening the bypass valve when the intake pressure exceeds a specified value as in the conventional technique. Further, if the force of the valve spring of the exhaust valve is increased, the exhaust valve can be prevented from opening during the intake stroke. However, when the force of the valve spring is increased, energy required for driving the camshaft increases, resulting in deterioration of fuel consumption.

  The present invention has been made to solve the above-described problems, and is a control device for an internal combustion engine that can reliably prevent an exhaust valve from opening during an intake stroke even in a region where the exhaust pressure exceeds the intake pressure. The purpose is to provide.

In order to achieve the above object, a first invention is a control device for an internal combustion engine,
A turbocharger having a turbine disposed in an exhaust passage of an internal combustion engine and a compressor disposed in an intake passage;
A bypass passage communicating the upstream exhaust passage and the downstream exhaust passage of the turbine;
A bypass valve for opening and closing the bypass passage;
Exhaust pressure acquisition means for acquiring the exhaust pressure of the internal combustion engine;
Intake pressure acquisition means for acquiring the intake pressure of the internal combustion engine;
A determination unit that determines whether or not the exhaust valve may open during an intake stroke based on the exhaust pressure acquired by the exhaust pressure acquisition unit and the intake pressure acquired by the intake pressure acquisition unit;
A bypass valve control means for increasing the opening of the bypass valve when the determination means determines that the possibility exists;
It is characterized by providing.

The second invention is the first invention, wherein
The determination means determines that the possibility exists when a value obtained by subtracting the intake pressure acquired by the intake pressure acquisition means from the exhaust pressure acquired by the exhaust pressure acquisition means is larger than a predetermined value. It is characterized by.

The third invention is the first or second invention, wherein
The bypass valve control means controls the opening degree of the bypass valve based on a value obtained by subtracting the intake pressure acquired by the intake pressure acquisition means from the exhaust pressure acquired by the exhaust pressure acquisition means. And

Moreover, 4th invention is set in 3rd invention,
The bypass valve control means is configured so that a force in a valve opening direction exerted on the exhaust valve by a differential pressure between an exhaust pressure and an intake pressure is equal to or less than a force of a valve spring that biases the exhaust valve in a valve closing direction. The opening degree of the valve is controlled.

According to a fifth invention, in any one of the first to fourth inventions,
In-cylinder pressure detecting means for detecting the in-cylinder pressure of the internal combustion engine,
The exhaust pressure acquisition means acquires the exhaust pressure based on the pressure detected by the in-cylinder pressure detection means in an exhaust stroke;
The intake pressure acquisition means acquires the intake pressure based on a pressure detected by the in-cylinder pressure detection means in an intake stroke.

  According to the first invention, when there is a possibility that the exhaust valve opens during the intake stroke, the exhaust pressure can be lowered by increasing the opening of the bypass valve. For this reason, even in a region where the exhaust pressure exceeds the intake pressure, it is possible to reliably prevent the exhaust valve from opening during the intake stroke. In particular, the above effect can be obtained without increasing the valve spring force of the exhaust valve. For this reason, energy required to drive the camshaft that operates the exhaust valve can be suppressed, and deterioration of fuel consumption can be prevented. Further, since the bypass valve is opened after determining whether or not the exhaust valve may open during the intake stroke, the bypass valve is not opened more than necessary. For this reason, it is possible to suppress wasteful exhaust energy from the bypass passage.

  According to the second invention, it is possible to accurately determine whether or not the exhaust valve is likely to open during the intake stroke.

  According to 3rd invention, when opening a bypass valve, the opening degree of a bypass valve can be controlled to a more suitable opening degree. For this reason, it can prevent more reliably that an exhaust valve opens at the time of an intake stroke, and can suppress the waste of exhaust energy by opening a bypass valve more than necessary.

  According to 4th invention, when opening a bypass valve, the opening degree of a bypass valve can be controlled to a more suitable opening degree. For this reason, it is possible to more reliably prevent the exhaust valve from being opened during the intake stroke, and it is possible to more reliably suppress waste of exhaust energy caused by opening the bypass valve more than necessary.

  According to the fifth aspect, since both the exhaust pressure and the intake pressure can be measured by the in-cylinder pressure detecting means, the system configuration can be simplified.

It is a figure for demonstrating the system configuration | structure of Embodiment 1 of this invention. It is a flowchart of the routine performed in Embodiment 1 of the present invention. It is a figure which shows typically the relationship between a cylinder pressure and a crank angle. It is a flowchart of the routine performed in Embodiment 1 of the present invention.

  Embodiments of the present invention will be described below with reference to the drawings. In addition, the same code | symbol is attached | subjected to the element which is common in each figure, and the overlapping description is abbreviate | omitted.

Embodiment 1 FIG.
FIG. 1 is a diagram for explaining a system configuration according to the first embodiment of the present invention. As shown in FIG. 1, the system according to the first embodiment of the present invention includes an internal combustion engine 10. Although the internal combustion engine 10 of this embodiment is of a spark ignition type, the present invention can also be applied to a compression ignition type internal combustion engine. The number of cylinders and the cylinder arrangement of the internal combustion engine 10 are not particularly limited. In FIG. 1, only one cylinder is representatively depicted.

  Each cylinder of the internal combustion engine 10 is provided with a piston 12, an intake valve 14, an exhaust valve 16, a spark plug 18, and a fuel injector 20. In addition, an intake passage 22 and an exhaust passage 24 are connected to each cylinder. In the illustrated configuration, the fuel injector 20 is provided so as to inject fuel directly into the cylinder (combustion chamber). However, the present invention can be applied to an internal combustion engine that injects fuel into the intake port or a cylinder. The present invention is also applicable to an internal combustion engine that uses both internal injection and intake port internal injection.

  The internal combustion engine 10 has a turbocharger 26. The turbocharger 26 has a compressor 26a and a turbine 26b. The compressor 26 a is arranged in the middle of the intake passage 22, and the turbine 26 b is arranged in the middle of the exhaust passage 24.

  An air cleaner 28 and an air flow meter 30 for detecting the amount of intake air are installed in the intake passage 22 upstream of the compressor 26a. An intercooler 32 and a throttle valve 34 are provided in the intake passage 22 on the downstream side of the compressor 26a.

  In the vicinity of the turbine 26b, a bypass passage 38 communicating the upstream exhaust passage 24 and the downstream exhaust passage 24 of the turbine 26b, and a bypass valve 40 (a waste gate valve) capable of opening and closing the bypass passage 38 are provided. And are installed. The bypass valve 40 is an electronically controlled valve that is opened and closed by an actuator. When the bypass valve 40 is opened, a part of the exhaust gas flows through the bypass passage 38 without passing through the turbine 26b. A catalyst 42 for purifying exhaust gas is installed in the exhaust passage 24 on the downstream side of the turbine 26b.

  The system of this embodiment includes a crank angle sensor 44 that detects the rotation angle of the crankshaft of the internal combustion engine 10, an in-cylinder pressure sensor 46 that detects in-cylinder pressure, and an ECU (Electronic Control Unit) that controls the operating state of the internal combustion engine 10. ) 50. The ECU 50 is electrically connected to the various sensors and actuators described above.

  The ECU 50 controls the operation of the internal combustion engine 10 by driving each actuator based on information detected by each sensor. For example, the fuel injection amount is calculated based on the engine speed detected by the crank angle sensor 44 and the intake air amount detected by the air flow meter 30, and the fuel injection timing, ignition timing, etc. are determined based on the crank angle. Later, the fuel injector 20 and the spark plug 18 are driven.

  In the operating region of the internal combustion engine 10, there is a region where the exhaust pressure on the upstream side of the turbine 26b exceeds the intake pressure (supercharging pressure) on the downstream side of the compressor 26a (throttle valve 34) (for example, a high rotation high load region). To do. In this region, during the intake stroke, the exhaust valve 16 may be pushed by the exhaust pressure and open. If the exhaust valve 16 is opened during the intake stroke, the exhaust gas is mixed into the fresh air in the cylinder, causing a reduction in engine output and a deterioration in drivability.

  Therefore, in the present embodiment, the following control is performed in order to reliably prevent the exhaust valve 16 from being opened due to the exhaust pressure during the intake stroke. During the intake stroke, the exhaust pressure acts on the surface of the exhaust valve 16 on the exhaust port side, and the intake pressure acts on the surface of the exhaust valve 16 on the combustion chamber side. Therefore, in a region where the exhaust pressure is higher than the intake pressure, a force obtained by multiplying the differential pressure between the exhaust pressure and the intake pressure by the area of the exhaust valve 16 acts in the valve opening direction. When the force in the valve opening direction becomes larger than the force of the valve spring 36 that biases the exhaust valve 16 in the valve closing direction, the exhaust valve 16 opens. Therefore, in the present embodiment, the in-cylinder pressure sensor 46 is used to detect the exhaust pressure and the intake pressure, respectively, thereby estimating the valve opening direction force acting on the exhaust valve 16. When the urging force is larger than 1, the bypass valve 40 is opened. By opening the bypass valve 40, a part of the exhaust gas bypasses the turbine 26b, and the exhaust pressure decreases. For this reason, the force in the valve opening direction acting on the exhaust valve 16 during the intake stroke can be reduced below the force in the valve closing direction by the valve spring 36.

  FIG. 2 is a flowchart of a routine executed by the ECU 50 in the present embodiment in order to realize the above function. This routine is repeatedly executed every predetermined time. According to the routine shown in FIG. 2, first, the exhaust pressure Pex is measured (step 100). In the present embodiment, the exhaust pressure Pex is measured by the in-cylinder pressure sensor 46. FIG. 3 is a diagram schematically showing the relationship between the in-cylinder pressure and the crank angle. As shown in FIG. 3, the in-cylinder pressure changes according to the crank angle. During the exhaust stroke, since the exhaust valve 16 is open, the in-cylinder pressure becomes equal to the exhaust pressure. Therefore, in step 100, the pressure detected by the in-cylinder pressure sensor 46 during the exhaust stroke is acquired as the exhaust pressure Pex. Note that the actual in-cylinder pressure is not completely constant in the exhaust stroke as shown in FIG. 3, but in this case, for example, the in-cylinder pressure in the exhaust stroke at a predetermined crank angle or the average cylinder in a predetermined crank angle range. The internal pressure may be set to the exhaust pressure Pex.

  Subsequently, the intake pressure Pin is measured (step 102). During the intake stroke, since the intake valve 14 is open, the in-cylinder pressure becomes equal to the intake pressure. Therefore, in this step 100, the pressure detected by the in-cylinder pressure sensor 46 during the intake stroke is acquired as the intake pressure Pin. The actual in-cylinder pressure does not become completely constant in the intake stroke as shown in FIG. 3, but in that case, for example, the in-cylinder pressure in the intake stroke at a predetermined crank angle or the average cylinder angle in a predetermined crank angle range. The internal pressure may be the intake pressure Pin.

  Next, a differential pressure ΔP between the exhaust pressure Pex acquired in step 100 and the intake pressure Pin acquired in step 102 is calculated (step 104). That is, ΔP = Pex−Pin. Subsequently, a value F obtained by multiplying the differential pressure ΔP by the area of the exhaust valve 16 is calculated (step 106). The value of F corresponds to the force in the valve opening direction that acts on the exhaust valve 16. The area of the exhaust valve 16 is an effective area (flow passage cross-sectional area) of the exhaust valve 16 and can be obtained from a design value and stored in advance in the ECU 50.

  Subsequently, the value of the force F in the valve opening direction calculated in step 106 is compared with the force in the valve closing direction by the valve spring 36 (step 108). The force in the valve closing direction by the valve spring 36 is a biasing force in the valve closing direction that the valve spring 36 exerts on the exhaust valve 16 in a state in which the exhaust valve 16 is closed, and can be obtained from a design value. Is stored in advance.

  In step 108, when the force F in the valve opening direction exceeds the force in the valve closing direction by the valve spring 36, it can be determined that the exhaust valve 16 may open during the intake stroke. In this case, a process for opening the bypass valve 40 is executed (step 110). As a result, the exhaust pressure decreases, and the force in the valve opening direction acting on the exhaust valve 16 during the intake stroke decreases. For this reason, it is possible to reliably prevent the exhaust valve 16 from opening during the intake stroke.

  On the other hand, in step 108, if the force F in the valve opening direction is equal to or less than the force in the valve closing direction by the valve spring 36, it can be determined that the exhaust valve 16 is not likely to open during the intake stroke. In this case, since the bypass valve 40 does not need to be opened, the bypass valve 40 is closed (step 112).

  According to the control of this embodiment as described above, it is possible to reliably prevent the exhaust valve 16 from opening during the intake stroke. For this reason, adverse effects such as a decrease in engine output and a deterioration in drivability due to the exhaust gas mixed into the fresh air in the cylinder can be reliably avoided. Further, the above effect can be obtained without increasing the valve spring force of the exhaust valve 16. For this reason, the energy required to drive the camshaft that operates the exhaust valve 16 can be suppressed, and deterioration of fuel consumption can be prevented. Further, it is possible to accurately determine whether or not the exhaust valve 16 is likely to open during the intake stroke, and the bypass valve 40 is opened only when there is such a possibility. Therefore, the bypass valve 40 can be opened more than necessary. Absent. For this reason, it is possible to suppress the waste of exhaust energy from the bypass passage 38.

  When the bypass valve 40 is opened in step 110, the bypass valve 40 is opened based on the differential pressure ΔP between the exhaust pressure Pex acquired in step 100 and the intake pressure Pin acquired in step 102. The degree may be controlled as follows. FIG. 4 is a flowchart of a routine showing a method for calculating the opening degree of the bypass valve 40 when the bypass valve 40 is opened in step 110. According to the routine shown in FIG. 4, first, a target differential pressure ΔPtg between the exhaust pressure and the intake pressure is calculated (step 200). This target differential pressure ΔPtg is calculated as a value obtained by dividing the valve closing direction force by the valve spring 36 by the area of the exhaust valve 16. Alternatively, the value of the target differential pressure ΔPtg itself may be stored in the ECU 50 in advance. If the differential pressure between the exhaust pressure and the intake pressure after opening the bypass valve 40 is equal to or less than the target differential pressure ΔPtg, the possibility that the exhaust valve 16 opens during the intake stroke can be eliminated. Therefore, as will be described later, in this routine, the target opening degree WGtg of the bypass valve 40 is calculated so that the differential pressure between the exhaust pressure and the intake pressure after opening the bypass valve 40 becomes equal to the target differential pressure ΔPtg. To do.

Subsequent to the process of step 200, a deviation Pdelta between the differential pressure ΔP between the exhaust pressure Pex and the intake pressure Pin and the target differential pressure ΔPtg is calculated (step 202). That is, Pdelta = ΔP−ΔPtg. If the exhaust pressure is reduced by this Pdelta by opening the bypass valve 40, the differential pressure between the exhaust pressure and the intake pressure can be made equal to the target differential pressure ΔPtg. Therefore, following the processing in step 202, the target exhaust gas mass Mextg that is required to reduce the exhaust pressure by Pdelta and is to be passed through the bypass valve 40 is calculated by the following equation based on the gas equation of state ( Step 204).
Mextg = (Pdelta · V) / (R · Tex) (1)

  In the above equation (1), V is the volume of the exhaust passage 24 on the upstream side of the turbine 26b. R is a gas constant and is determined by the composition of the exhaust gas. V and R are stored in the ECU 50 in advance. Tex is the exhaust gas temperature. As a method for obtaining the exhaust gas temperature Tex, for example, information on the exhaust gas temperature Tex may be stored in the ECU 50 in advance as a map of the engine speed, the engine load, and the like. Alternatively, the exhaust gas temperature Tex may be calculated according to a thermodynamic relational expression based on the internal energy of the exhaust gas calculated from the in-cylinder pressure detected by the in-cylinder pressure sensor 46.

Subsequently, the opening area Stg of the bypass valve 40 necessary for realizing the target passing exhaust gas mass Mextg of the bypass valve 40 calculated in step 204 is calculated (step 206). The relationship between the opening area S of the bypass valve 40 and the mass m of the exhaust gas passing through the bypass valve 40 can be expressed by the following equation.
m = S · φ · ρ (2)

In the above equation (2), ρ is the density of the exhaust gas, and is stored in the ECU 50 in advance. φ is a variable that changes according to the engine speed, the engine load, etc., and is stored in advance in the ECU 50 as a map. In this step 206, the target opening area Stg of the bypass valve 40 is calculated by an equation obtained by substituting the target passing exhaust gas mass Mextg calculated in the above step 204 into the above equation (2), that is, the following equation.
Stg = Mextg / (φ · ρ) (3)

  The relationship between the opening degree of the bypass valve 40 and the opening area is determined geometrically, and is stored in advance in the ECU 50 as a map. Therefore, by comparing the map with the target opening area Stg calculated in step 206, the target opening degree WGtg of the bypass valve 40 necessary for realizing the target passing exhaust gas mass Mextg can be calculated. Yes (step 208). Then, the actual opening degree of the bypass valve 40 is controlled to be the target opening degree WGtg.

  According to the processing of the routine of FIG. 4 described above, when opening the bypass valve 40 in step 110 of FIG. 2, the opening degree of the bypass valve 40 can be controlled to an optimum opening degree that is not excessive or insufficient. For this reason, it is possible to more reliably prevent the exhaust valve 16 from opening during the intake stroke, and it is possible to more reliably suppress waste of exhaust energy caused by opening the bypass valve 40 more than necessary.

  In the system of the present embodiment, as control during normal operation, the opening degree of the bypass valve 40 may be controlled by a map set in advance according to the engine speed, the engine load, and the like. In that case, in step 110 or 112, the bypass valve 40 may be originally opened by the control based on the map. In that case, the following control may be performed. In step 110, if the bypass valve 40 is originally open, the opening degree may be increased from the current opening degree. As a result, the exhaust pressure decreases, so that the exhaust valve 16 can be reliably prevented from opening during the intake stroke. Further, in the above step 112, when the bypass valve 40 is originally open, the current opening degree may be controlled.

  In this embodiment, the exhaust pressure Pex and the intake pressure Pin are detected by the in-cylinder pressure sensor 46. In the present invention, the exhaust pressure Pex and the intake pressure Pin are detected by a method using the in-cylinder pressure sensor 46. It is not limited. For example, a sensor for detecting the intake pressure Pin by an intake pressure sensor (supercharging pressure sensor) provided in the intake passage 22 on the downstream side of the compressor 26 a or a sensor for detecting the rotational speed of the turbocharger 26 is provided to rotate the turbocharger 26. The intake pressure Pin may be estimated from the speed (= the rotational speed of the compressor 26a). As for the exhaust pressure Pex, the exhaust pressure Pex is estimated based on the exhaust temperature detected by the exhaust temperature sensor provided in the exhaust passage 24, the rotational speed of the turbocharger 26 (= the rotational speed of the turbine 26b), and the like. Also good.

  In the first embodiment described above, the value obtained by dividing the valve closing force by the valve spring 36 by the area of the exhaust valve 16 corresponds to the “predetermined value” in the second aspect of the present invention. “The ECU 50 executes the process of step 100, so that the“ exhaust pressure acquisition means ”in the first invention performs the process of step 102, and the“ intake pressure acquisition means ”in the first invention. However, the “determination means” in the first and second inventions by executing the processing of the above steps 104 to 108 and the “bypass valve control means in the first invention by executing the processing of the above step 110. "Bypass valve control means" in the third and fourth aspects of the present invention is realized by executing the routine of FIG.

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 12 Piston 14 Intake valve 16 Exhaust valve 18 Spark plug 20 Fuel injector 22 Intake passage 24 Exhaust passage 26 Turbocharger 26a Compressor 26b Turbine 34 Throttle valve 36 Valve spring 38 Bypass passage 40 Bypass valve 46 In-cylinder pressure sensor 50 ECU

Claims (5)

A turbocharger having a turbine disposed in an exhaust passage of an internal combustion engine and a compressor disposed in an intake passage;
A bypass passage communicating the upstream exhaust passage and the downstream exhaust passage of the turbine;
A bypass valve for opening and closing the bypass passage;
Exhaust pressure acquisition means for acquiring the exhaust pressure of the internal combustion engine;
Intake pressure acquisition means for acquiring the intake pressure of the internal combustion engine;
A determination unit that determines whether or not the exhaust valve may open during an intake stroke based on the exhaust pressure acquired by the exhaust pressure acquisition unit and the intake pressure acquired by the intake pressure acquisition unit;
A bypass valve control means for increasing the opening of the bypass valve when the determination means determines that the possibility exists;
A control device for an internal combustion engine, comprising:   The determination means determines that the possibility exists when a value obtained by subtracting the intake pressure acquired by the intake pressure acquisition means from the exhaust pressure acquired by the exhaust pressure acquisition means is larger than a predetermined value. The control device for an internal combustion engine according to claim 1.   The bypass valve control means controls the opening degree of the bypass valve based on a value obtained by subtracting the intake pressure acquired by the intake pressure acquisition means from the exhaust pressure acquired by the exhaust pressure acquisition means. The control apparatus for an internal combustion engine according to claim 1 or 2.   The bypass valve control means is configured so that a force in a valve opening direction exerted on the exhaust valve by a differential pressure between an exhaust pressure and an intake pressure is equal to or less than a force of a valve spring that biases the exhaust valve in a valve closing direction. 4. The control apparatus for an internal combustion engine according to claim 3, wherein the opening degree of the valve is controlled. In-cylinder pressure detecting means for detecting the in-cylinder pressure of the internal combustion engine,
The exhaust pressure acquisition means acquires the exhaust pressure based on the pressure detected by the in-cylinder pressure detection means in an exhaust stroke;
The control of the internal combustion engine according to any one of claims 1 to 4, wherein the intake pressure acquisition means acquires the intake pressure based on a pressure detected by the in-cylinder pressure detection means in an intake stroke. apparatus.

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