Turbocharged engine control device

Abstract

To provide a control device of an engine with a supercharger which can suppress the adhesion of a throttle valve.SOLUTION: A control device of an engine with a supercharger comprises: an intercooler arranged at a downstream side rather than a compressor of an intake passage, and cooling intake air; a throttle body arranged at a portion between the compressor of the intake passage and the intercooler, and adjusting a quantity of the intake air which circulates in the intake passage; supercharge amount change means which can change a supercharge amount of a turbosupercharger; and control means for controlling the supercharge amount change means. A throttle valve for opening and closing a portion between the compressor of the intake passage and the intercooler, and a valve case surrounding the throttle valve, and allowing cooling water for cooling an engine main body to circulate therein are arranged at the throttle body, and the supercharge amount change means is controlled so that a temperature difference between the intake air which is supercharged by the turbosupercharger and the cooling water reaches a prescribed reference temperature difference or smaller.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a control device for a supercharged engine including an engine body, an intake passage through which intake air introduced into the engine body flows, an exhaust passage through which exhaust gas discharged from the engine body flows, and a turbocharger that supercharges the intake air, including a compressor provided in the intake passage and a turbine provided in the exhaust passage. [Background technology]

[0002] In an engine that has a throttle valve in the intake passage that can open and close, if the throttle valve cannot be opened or closed, an appropriate amount of intake air cannot be introduced into the engine body. Therefore, in order to prevent the throttle valve from becoming unable to open and close, cooling water for cooling the engine body has been conventionally supplied to a valve case that surrounds the throttle valve.

[0003] For example, Patent Document 1 discloses an engine in which a valve case is provided with a cooling water passage in order to prevent freezing of the throttle valve, and cooling water led out from the cylinder head of the engine body is introduced into the cooling water passage and then returned to the water pump. In such a configuration in which cooling water is supplied to the valve case, the valve case can be warmed by the relatively high-temperature cooling water led out from the engine body, and water vapor contained in the intake air can be prevented from freezing around the throttle valve and impeding the opening and closing of the throttle valve. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2017-31964 A Summary of the Invention [Problem to be solved by the invention]

[0005] In an engine equipped with a turbocharger and an intercooler for cooling the intake air supercharged by the turbocharger, and mounted on a vehicle, the intercooler may be disposed downstream of the throttle valve due to vehicle layout considerations, etc. In this arrangement, the high-temperature, high-pressure intake air supercharged by the turbocharger first passes through the throttle valve and is then cooled by the intercooler. For this reason, in an engine employing this arrangement, simply adopting a configuration in which the valve case is cooled by cooling water as described above may cause the throttle valve to stick.

[0006] Specifically, while the throttle body is cooled by cooling water, the throttle valve is heated by the high-temperature intake air, which causes the throttle valve to expand significantly relative to the valve case, and there is a risk that the throttle valve will become stuck to the valve case.

[0007] The present invention has been made in consideration of the above circumstances, and has an object to provide a control device for a turbocharged engine that is capable of suppressing sticking of the throttle valve. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention provides a control device for a supercharged engine including an engine body, an intake passage through which intake air introduced into the engine body flows, an exhaust passage through which exhaust gas discharged from the engine body flows, and a turbocharger including a compressor provided in the intake passage and a turbine provided in the exhaust passage, and which supercharges the intake air, the control device comprising: an intercooler provided in the intake passage downstream of the compressor for cooling the intake air; the throttle body has a throttle valve that opens and closes a portion of the intake passage between the compressor and the intercooler, and a valve case that surrounds the throttle valve and through which cooling water for cooling the engine body flows, and the control means controls the supercharging amount change means so that a temperature difference between the intake air supercharged by the turbocharger and the cooling water becomes equal to or less than a predetermined reference temperature difference. and a target boost pressure setting unit that sets a target boost pressure, which is a target value of the boost pressure, based on the operating conditions of the engine, and corrects the target boost pressure to the same value as a predetermined upper limit boost pressure when the set target boost pressure is higher than the upper limit boost pressure, and a boost pressure control unit that controls the boost amount changing means so that the boost pressure becomes the target boost pressure set by the target boost pressure setting unit, and the target boost pressure setting unit sets the upper limit boost pressure to a higher value when the temperature of the cooling water is high than when it is low. This is characterized by the above (Claim 1).

[0009] According to the present invention, by adjusting the supercharging amount of the turbocharger, the difference between the temperature of the intake air that reaches the throttle valve and heats it after being heated and pressurized by the turbocharger, and the temperature of the cooling water that cools the valve case is kept below a predetermined reference temperature difference. Therefore, it is possible to prevent the temperature of the throttle valve from becoming excessively high compared to the temperature of the valve case, and the relative expansion of the throttle valve to the valve case is kept small, thereby suppressing sticking of the throttle valve.

[0011] Where: The higher the cooling water temperature and the valve case temperature, the higher the lower limit of the throttle valve temperature and the intake air temperature (the intake air that reaches the throttle valve after being heated and pressurized by the turbocharger) at which the throttle valve may stick, and the lower limit of the intake air pressure, i.e., the boost pressure, at which the throttle valve may stick, becomes higher. Therefore, According to the present inventionWhen the cooling water temperature is high, the upper limit of boost pressure is higher. As well as By controlling the boost pressure to be the target boost pressure set based on the engine operating conditions within a range that does not exceed the upper limit boost pressure, a wide range of achievable boost pressure can be secured while suppressing sticking of the throttle valve, and there are more opportunities to set the boost pressure to an appropriate value according to the engine operating conditions.

[0012] In the above-mentioned configuration, the supercharging amount changing means may include a bypass passage provided in the exhaust passage to bypass the turbine, and a wastegate valve that opens and closes the bypass passage, and changes the supercharging amount by changing the opening degree of the wastegate valve (see claim 2 ). Effect of the Invention

[0013] As described above, according to the control device for a turbocharged engine of the present invention, sticking of the throttle valve can be suppressed. [Brief description of the drawings]

[0014] [Figure 1] 1 is a diagram showing a configuration of an engine according to an embodiment of the present invention; [Diagram 2] FIG. 2 is a schematic diagram of a throttle valve. [Diagram 3] FIG. 2 is a diagram showing a control block of the engine. [Figure 4] 4 is a flowchart showing the control of the supercharging pressure. [Diagram 5] 4 is a graph showing the relationship between engine water temperature and a reference temperature difference. [Figure 6] 4 is a graph showing the relationship between the engine water temperature and the upper limit intake air temperature. [Figure 7] 4 is a graph showing the relationship between an upper limit intake air temperature and an upper limit boost pressure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] (Overall engine configuration) 1 is a schematic system diagram showing a preferred embodiment of an engine to which a control device for a turbocharged engine according to an embodiment of the present invention is applied. The engine includes an engine body 1 that is driven by receiving a supply of fuel, an intake passage 50 through which intake air introduced into the engine body 1 flows, and an exhaust passage 60 through which exhaust gas discharged from the engine body 1 flows. The engine includes a turbocharger 70 that is driven by exhaust gas passing through the exhaust passage 60, a turbine 71 that is provided in the exhaust passage 60 and driven by the exhaust, and a compressor 72 that is provided in the intake passage 50 and driven to rotate by the turbine 71 to supercharge the intake air. This engine is mounted in a vehicle such as an automobile as a power source for driving the vehicle.

[0016] The engine body 1 is an in-line multi-cylinder type having a plurality of cylinders 2a (only one of which is shown in FIG. 1) arranged in a direction perpendicular to the paper surface of FIG. 1. The engine body 1 includes a cylinder block 2 in which the plurality of cylinders 2a are formed, a cylinder head 3 attached to the upper surface of the cylinder block 2 so as to close the upper end opening of each cylinder 2a, and a plurality of pistons 4 housed in each cylinder 2a so as to be capable of reciprocating and sliding. In this embodiment, the side from the cylinder block 2 toward the cylinder head 3 is treated as the top and the opposite side as the bottom, but this is for convenience of explanation and is not intended to limit the installation posture of the engine.

[0017] A combustion chamber 5 is defined above the piston 4 of each cylinder 2a. Fuel is supplied to the combustion chamber 5 by injection from an injector 10, which will be described later. A mixture of the supplied fuel and air is combusted in the combustion chamber 5, and the piston 4 reciprocates in the vertical direction due to the expansion force caused by the combustion.

[0018] A crankshaft 13, which is the output shaft of the engine body 1, is provided at the bottom of the cylinder block 2 (below the pistons 4). The crankshaft 13 is connected to the pistons 4 of each cylinder 2a via connecting rods, and rotates around its central axis in response to the reciprocating motion (up and down movement) of the pistons 4.

[0019] A crank angle sensor SN1 and a water temperature sensor SN2 are attached to the cylinder block 2. The crank angle sensor SN1 detects the crank angle, which is the rotation angle of the crankshaft 13, and the engine speed, which is the rotation speed of the crankshaft 13. The water temperature sensor SN2 detects the temperature of the cooling water that flows through the cylinder block 2 and the cylinder head 3 to cool the engine body 1, that is, the engine water temperature. Specifically, a water jacket through which the cooling water flows is formed on the inside of each of the cylinder block 2 and the cylinder head 3, and the cooling water is circulated between the water jacket and a radiator that is mounted on the vehicle and capable of cooling the cooling water by a water pump (not shown) attached to the cylinder block 2.

[0020] In the cylinder head 3, an intake port 6 and an exhaust port 7 communicating with the combustion chamber 5 are formed for each cylinder 2a. In addition, the cylinder head 3 is equipped with a combination of an intake valve 8, an exhaust valve 9, an injector 10, and an ignition plug 11 for each cylinder 2a. The intake valve 8 is a valve that opens and closes the opening of the intake port 6 on the combustion chamber 5 side. The exhaust valve 9 is a valve that opens and closes the opening of the exhaust port 7 on the combustion chamber 5 side. The injector 10 is an injection valve that injects fuel into the combustion chamber 5. In this embodiment, the injector 10 is attached to the cylinder head 3 so as to inject fuel by a side injection method, and is disposed so that its tip faces the combustion chamber 5 from the inner circumferential surface of the combustion chamber 5.

[0021] The intake passage 50 is connected to one side of the cylinder head 3 so as to communicate with the intake ports 6 of each cylinder 2a. In the intake passage 50, an air cleaner 51, a compressor 72, a throttle body 80, an intercooler 53, and a surge tank 54 are arranged in this order from the upstream side.

[0022] The air cleaner 51 is a filter that removes foreign matter from the intake air. The throttle body 80 adjusts the amount of intake air flowing through the intake passage 50. The throttle body 80 will be described in detail later. The compressor 72 is driven by the turbine 71 as described above to supercharge the intake air, that is, to increase the temperature and pressure of the intake air. The intercooler 53 is a heat exchanger that cools the intake air supercharged by the turbocharger 70 (more specifically, the compressor 72). The surge tank 54 is a tank that provides a space for evenly distributing the intake air to each cylinder 2a.

[0023] FIG. 2 is a schematic diagram showing an enlarged view of the throttle body 80 and its periphery in FIG. 1. As shown in FIG. 2, the throttle body 80 has a throttle valve 81 disposed inside the intake passage 50, i.e., in the intake passage, for opening and closing the intake passage. The throttle valve 81 is a butterfly valve, and opens and closes the intake passage by rotating a rotary shaft 82 extending in a direction intersecting the flow of the intake air about its central axis. In this embodiment, the throttle body 80 is electrically driven and has a motor 83 for rotating the rotary shaft 82, i.e., the throttle valve 81. The throttle body 80 also has a valve case 85 that surrounds the throttle valve 81 and rotatably supports the throttle valve 81. The valve case 85 has a substantially cylindrical shape, and its inner space forms a part of the intake passage. That is, the throttle body 80 is disposed in the intake passage 50 such that the inner space of the valve case 85 forms a part of the intake passage. The throttle valve 81 changes the amount of intake air flowing through the intake passage 50 by opening and closing a portion of the intake passage 50 defined by a valve case 85 .

[0024] The valve case 85 is configured so that the cooling water for cooling the engine body 1 flows through its inside. Specifically, a passage 86 through which the cooling water flows is formed inside the valve case 85, and the valve case 85 is provided with an inlet 87 for introducing the cooling water into the passage 86 and an outlet 88 for discharging the cooling water after it has flowed through the passage 86. The inlet 87 and the outlet 88 are connected to a circulation passage through which the cooling water circulates between the water pump and the radiator, and the cooling water flowing through this circulation passage is supplied to the passage 86 in the valve case 85. With this configuration, in this embodiment, the throttle valve 81 is prevented from being stuck due to freezing around the throttle valve 81. Specifically, when the outside air temperature is very low, moisture in the intake air freezes around the throttle valve 81, which may cause the throttle valve 81 to be stuck. On the other hand, if cooling water whose temperature has become higher than the outside air temperature by passing through the engine body 1 is supplied to the inside of the valve case 85, the ice around the throttle valve 81 can be melted and the ice can be prevented from sticking.

[0025] An airflow sensor SN3 and an intake pressure sensor SN4 are disposed in the intake passage 50. The airflow sensor SN3 is disposed in a portion of the intake passage 50 between the air cleaner 51 and the compressor 72, and detects the intake air volume, which is the flow rate of the intake air passing through this portion. The intake pressure sensor SN4 is disposed in the surge tank 54, and detects the pressure of the intake air passing through the surge tank 54. The intake air passing through the surge tank 54 is intake air that has been supercharged by the turbocharger 70, and the pressure inside the surge tank 54 is the supercharging pressure. Thus, the intake pressure sensor SN4 detects the supercharging pressure.

[0026] The exhaust passage 60 is connected to one side surface of the cylinder head 3 (the surface opposite to the intake passage 50) so as to communicate with the exhaust ports 7 of each cylinder 2a. The exhaust passage 60 is provided with, in order from the upstream side, a turbine 71 and a catalytic converter 61 incorporating a catalyst such as a three-way catalyst.

[0027] Further, the exhaust passage 60 is provided with a bypass passage 62 that bypasses the turbine 71, and by passing through the bypass passage 62, a portion of the exhaust gas in the exhaust passage 60 flows to a portion downstream of the turbine 71 without passing through the turbine 71. The bypass passage 62 is connected to a portion of the exhaust passage 60 upstream of the catalytic converter 61. The bypass passage 62 is provided with a wastegate valve 63 that is driven by a wastegate valve motor 64 to open and close the bypass passage 62.

[0028] The opening of the wastegate valve 63 can be changed to a fully closed state, a fully open state, or any opening state between these states, and the amount of exhaust gas flowing through the bypass passage 62 and the amount of exhaust gas passing through the turbine 71 are changed according to the opening of the wastegate valve 63. When the amount of exhaust gas passing through the turbine 71 changes, the supercharging amount of the turbocharger 70, i.e., the supercharging pressure, increases or decreases. Specifically, when the opening of the wastegate valve 63 is decreased (toward the closing side), the amount of exhaust gas passing through the bypass passage 62 decreases and the amount of exhaust gas passing through the turbine 71 increases, so that the rotational driving force of the compressor 72 by the turbine 71 increases, and the supercharging amount and the supercharging pressure of the turbocharger 70 increase. Conversely, when the opening of the wastegate valve 63 is increased (toward the opening side), the amount of exhaust gas passing through the bypass passage 62 increases and the amount of exhaust gas passing through the turbine 71 decreases, so that the rotational driving force of the compressor 72 by the turbine 71 decreases and the supercharging pressure decreases. In this manner, in this embodiment, the boost amount and boost pressure of the turbocharger 70 are changed in accordance with the opening degree of the wastegate valve 63, and the wastegate valve 63 and the bypass passage 62 in which it is disposed correspond to the “supercharging amount changing means” of the claims.

[0029] (Control system) 3 is a functional block diagram showing the engine control system. The ECU 100 shown in the figure is a device for controlling the engine in an integrated manner, and is composed of a microcomputer including a processor (CPU) for performing various arithmetic operations, memories such as ROM and RAM, and various input / output buses.

[0030] Information detected by each sensor of the engine is input to the ECU 100. For example, the ECU 100 is electrically connected to the crank angle sensor SN1, the water temperature sensor SN2, the air flow sensor SN3, and the intake pressure sensor SN4. Information detected by each of the sensors SN1 to SN4, that is, information such as the crank angle, the engine speed, the engine water temperature, the intake amount, and the boost pressure, is sequentially input to the ECU 100. Information detected by various sensors provided in the vehicle on which the engine is mounted is also input to the ECU 100. In this embodiment, the vehicle is provided with an accelerator sensor SN5 that detects an accelerator opening, which is the opening of an accelerator pedal provided in the vehicle. Information on the accelerator opening detected by the accelerator sensor SN5 is also sequentially input to the ECU 100.

[0031] The ECU 100 controls each part of the engine while executing various judgments and calculations based on the input information from the above-mentioned sensors SN1 to SN5. For example, the ECU 100 is electrically connected to the injector 10, the spark plug 11, the throttle valve 81 (more specifically, the motor 83 that drives the throttle valve 81), and the wastegate valve 63 (more specifically, the wastegate valve motor 64 that drives it), and outputs control signals to each of these devices based on the results of the above-mentioned calculations, etc.

[0032] (Boost pressure control) As described above, in this embodiment, the throttle valve 81 is disposed between the compressor 72 and the intercooler 53. As a result, the intake air whose temperature and pressure are increased by the compressor 72 reaches the throttle valve 81 before being cooled by the intercooler 53. Therefore, the throttle valve 81 is heated by the high-temperature intake air and becomes hot. On the other hand, as described above, cooling water flows inside the valve case 85, and the temperature of the valve case 85 is kept low by being cooled by the cooling water. As a result, even if the valve case 85 does not expand or the amount of expansion of the valve case 85 is kept small, the throttle valve 81 may expand significantly as shown by the chain line in FIG. 2. If the throttle valve 81 expands excessively relative to the valve case 85 in this way, the gap between the throttle valve 81 and the valve case 85 is no longer secured, and the throttle valve 81 cannot rotate, that is, the throttle valve 81 may become stuck. Therefore, in this embodiment, in order to prevent the throttle valve 81 from sticking in this manner, the following control of the supercharging pressure is carried out.

[0033] The ECU 100 functionally includes a target boost pressure setting unit 102 that sets a target boost pressure, which is a target value of the boost pressure, and a boost pressure control unit 101 that controls the wastegate valve 63 so as to realize the target boost pressure. The ECU 100 including the boost pressure control unit 101 and the target boost pressure setting unit 102 corresponds to the "control means" in the claims.

[0034] 4 is a flowchart showing the contents of the control of the supercharging pressure performed by the ECU 100 (the supercharging pressure control unit 101 and the target supercharging pressure setting unit 102). In the following, the intake air that warms the throttle valve 81 and that has been supercharged by the turbocharger 70 and has not yet been cooled by the intercooler 53 will be referred to as the supercharged intake air.

[0035] First, in step S1, the ECU 100 reads various information detected by the sensors SN1 to SN5 etc. In step S1, the ECU 100 reads at least the engine speed, the accelerator opening, the boost pressure, and the engine water temperature.

[0036] Next, in step S2, the ECU 100 sets a target boost pressure based on the information read in step S1. The target boost pressure is the target value of the boost pressure, i.e., the pressure in the surge tank 54, as described above. The ECU 100 sets the target boost pressure based on the engine operating conditions. Specifically, the ECU 100 sets the target boost pressure based on the engine speed and the engine load. The ECU 100 calculates the engine load from the accelerator opening and the engine speed, etc.

[0037] Next, in step S3, the ECU 100 sets an upper limit intake air temperature. The upper limit intake air temperature is the maximum value of the temperature of the supercharged intake air at which the sticking of the throttle valve 81 can be avoided.

[0038] Specifically, as described above, the sticking of the throttle valve 81 occurs when the throttle valve 81 expands excessively relative to the valve case 85. The throttle valve 81 expands excessively relative to the valve case 85 when the temperature of the valve case 85, i.e., the temperature of the supercharged intake air that warms it, becomes excessively high relative to the temperature of the valve case 85, i.e., the engine water temperature, which is the temperature of the cooling water. In other words, when the difference between the temperature of the supercharged intake air and the engine water temperature becomes higher than a predetermined reference temperature difference, the throttle valve 81 expands excessively relative to the valve case 85, causing the throttle valve 81 to stick, and the above-mentioned upper limit intake air temperature is the temperature at which the difference with the engine water temperature becomes this reference temperature difference.

[0039] In this embodiment, the reference temperature difference, that is, the upper limit of the temperature difference between the supercharged intake air temperature and the engine water temperature (the maximum value of the above temperature difference that can avoid the sticking of the throttle valve 81), is set as shown in Fig. 5. Specifically, the reference temperature difference is set to a constant value dT (e.g., 110°C) regardless of the engine water temperature when the engine water temperature is equal to or lower than a predetermined water temperature Tw1 (e.g., 80°C), and is set to a lower value as the engine water temperature increases when the engine water temperature is higher than the predetermined water temperature Tw1. However, even when the engine water temperature is higher than the predetermined water temperature Tw1, the variation range of the reference temperature difference with respect to the engine water temperature is small (e.g., about 10°C), and it can be said that the reference temperature difference is set to an approximately constant value regardless of the engine water temperature.

[0040] Since the reference temperature difference is set as shown in Fig. 5, in this embodiment, the upper limit intake air temperature is set as shown in Fig. 6. That is, the upper limit intake air temperature is the engine water temperature plus the reference temperature difference, so the upper limit intake air temperature is set to a higher value as the engine water temperature is higher. In this embodiment, the relationship between the engine water temperature and the upper limit intake air temperature shown in Fig. 6 is set in advance as a map and stored in ECU 100, and ECU 100 extracts from this map the upper limit intake air temperature corresponding to the engine water temperature read in step S1.

[0041] Returning to FIG. 4, the ECU 100 sets an upper limit supercharging pressure in step S4 following step S3. The upper limit supercharging pressure is the supercharging pressure when the temperature of the supercharged intake air becomes the upper limit intake air temperature. The temperature of the supercharged intake air and the supercharging pressure are proportional to each other. Thus, as shown in FIG. 7, the ECU 100 sets the upper limit supercharging pressure so that the higher the upper limit intake air temperature set in step S3, the higher the upper limit supercharging pressure becomes. Here, as described above, the higher the engine water temperature is, the higher the upper limit intake air temperature is set. Thus, the higher the engine water temperature is, the higher the upper limit supercharging pressure is set. In this embodiment, a map of the upper limit intake air temperature and the upper limit supercharging pressure corresponding to FIG. 6 is set in advance and stored in the ECU 100, and the ECU 100 extracts a value corresponding to the upper limit intake air temperature set in step S3 from this map.

[0042] Next, in step S5, the ECU 100 determines whether or not the target boost pressure set in step S2 is higher than the upper limit boost pressure set in step S4.

[0043] If the determination in step S5 is YES and the target boost pressure set in step S2 is higher than the upper limit boost pressure, the ECU 100 proceeds to step S6 and resets the upper limit boost pressure to the target boost pressure. In other words, the ECU 100 corrects the target boost pressure to the same value as the upper limit boost pressure.

[0044] Next, the ECU 100 proceeds to step S7, and adjusts the opening of the wastegate valve 63 based on the target boost pressure. Specifically, the ECU 100 adjusts the opening of the wastegate valve 63 so that the boost pressure (the pressure of the intake pressure sensor SN4) read in step S1 becomes the target boost pressure.

[0045] On the other hand, if the determination in step S5 is NO and the target boost pressure set in step S2 is equal to or lower than the upper limit boost pressure, the ECU 100 proceeds directly to step S7. That is, the ECU 100 does not correct the target boost pressure, but maintains the target boost pressure at the target boost pressure set in step S2. Then, in step S7, the opening of the wastegate valve 63 is adjusted so that this target boost pressure is realized.

[0046] (effect, etc.) As described above, in this embodiment, the opening degree of the wastegate valve 63 is changed so that the boost pressure becomes the target boost pressure, and when the target boost pressure set based on the engine speed is higher than the upper limit boost pressure, the target boost pressure is corrected to the same value as the upper limit boost pressure. Therefore, the boost pressure can be prevented from becoming higher than the upper limit boost pressure, and thus the temperature of the supercharged intake air can be prevented from becoming higher than the upper limit intake air temperature, and further, the difference between the temperature of the supercharged intake air and the engine water temperature can be prevented from becoming higher than the reference temperature difference. In other words, according to the above embodiment, the difference between the temperature of the supercharged intake air (i.e., the intake air supercharged by the turbocharger 70) and the engine water temperature (i.e., the temperature of the cooling water) is suppressed to be equal to or lower than the reference temperature difference by adjusting the supercharging amount of the turbocharger 70. Therefore, the throttle valve 81 can be prevented from expanding excessively relative to the valve case 85, and the sticking of the throttle valve 81 can be suppressed. Furthermore, when the target supercharging pressure set based on the engine speed is lower than the upper limit supercharging pressure, the supercharging pressure can be set to an appropriate pressure corresponding to the engine speed.

[0047] Also, as described above, in response to the fact that the upper limit intake air temperature is higher when the engine water temperature is high than when it is low, the upper limit supercharging pressure is set to a higher value when the engine water temperature is high than when it is low. Therefore, as described above, it is possible to prevent the temperature of the supercharged intake air from becoming higher than the upper limit intake air temperature and the difference between the temperature of the supercharged intake air and the engine water temperature from becoming higher than the reference temperature difference, thereby suppressing the sticking of the throttle valve 81, while widening the possible range of the supercharging pressure and increasing the opportunities for making the supercharging pressure an appropriate value according to the engine speed.

[0048] (Modification) In the above embodiment, a case has been described in which the boost pressure of the turbocharger 70, i.e., the boost amount of the turbocharger 70, is changed by changing the opening degree of the wastegate valve 63, but a specific means for changing the boost pressure and boost amount of the turbocharger 70 is not limited to this. For example, a turbocharger capable of changing the area of ​​the passage through which exhaust gas passes in the turbine (so-called VGT: Variable Geometry Turbo) may be used, and the boost pressure may be increased or decreased by changing the above-mentioned passage area.

[0049] In the above embodiment, the upper limit intake air temperature is set based on the engine water temperature, and the upper limit boost pressure is set based on the set upper limit intake air temperature. However, the setting of the upper limit intake air temperature may be omitted, and the upper limit boost pressure may be set directly from the engine water temperature.

[0050] In the above embodiment, the opening degree of the wastegate valve 63 is changed based on the detection value of the intake pressure sensor SN4 so that the detection value becomes the target boost pressure, but the opening degree of the wastegate valve 63 may be changed based on the target boost pressure without using the detection value of the intake pressure sensor SN4. For example, the relationship between the opening degree of the wastegate valve 63 and the boost pressure may be obtained in advance by experiment or the like and stored in the ECU 100, and the opening degree of the wastegate valve 63 that realizes the target boost pressure from the stored relationship may be set in the ECU 100, and this opening degree may be used as the set value.

[0051] In the above embodiment, the upper limit supercharging pressure is set based on the upper limit intake air temperature, and the supercharging pressure is compared with the upper limit supercharging pressure to change the opening degree of the wastegate valve 63 so that the supercharging pressure becomes equal to or lower than the upper limit supercharging pressure. However, instead of comparing the supercharging pressure with the upper limit supercharging pressure, the opening degree of the wastegate valve 63 may be changed based on a comparison between the intake air temperature after supercharging and the upper limit intake air temperature to change the intake air temperature after supercharging to equal to or lower than the upper limit intake air temperature. For example, after setting the target supercharging pressure in step S2, the intake air temperature after supercharging when the target supercharging pressure is realized may be estimated, and if the estimated value is higher than the upper limit intake air temperature, the target supercharging pressure may be corrected to a smaller value, and the opening degree of the wastegate valve 63 may be changed to the corrected target supercharging pressure.

[0052] Further, the specific structure of the engine to which the engine control device according to the embodiment is applied, such as the number of cylinders, is not limited to the above. [Explanation of symbols]

[0053] 1 Engine body 80 Throttle body 81 Throttle valve 85 Valve case 50 Intake passage 53 Intercooler 60 Exhaust passage 62 Bypass passage (means for changing the amount of supercharging) 63 Wastegate valve (means for changing the amount of supercharging) 70 Turbocharger 71 Turbine 72 Compressor

Claims

1. A control device for a supercharged engine including an engine body, an intake passage through which intake air introduced into the engine body flows, an exhaust passage through which exhaust gas discharged from the engine body flows, and a turbocharger including a compressor provided in the intake passage and a turbine provided in the exhaust passage, the control device comprising: an intercooler provided in the intake passage downstream of the compressor to cool the intake air; a throttle body provided in a portion of the intake passage between the compressor and the intercooler to adjust the amount of intake air flowing through the intake passage; a supercharging amount changing means capable of changing a supercharging amount of the turbocharger; A control means for controlling the supercharging amount changing means, the throttle body includes a throttle valve that opens and closes a portion of the intake passage between the compressor and the intercooler, and a valve case that surrounds the throttle valve and through which cooling water for cooling the engine body flows, The control means controlling the supercharging amount changing means so that a temperature difference between the intake air supercharged by the turbocharger and the cooling water becomes equal to or less than a predetermined reference temperature difference; a target boost pressure setting unit that sets a target boost pressure, which is a target value of the boost pressure, based on an operating condition of the engine, and corrects the target boost pressure to a value equal to the upper limit boost pressure when the set target boost pressure is higher than a predetermined upper limit boost pressure; a boost pressure control unit that controls the boost amount changing means so that the boost pressure becomes the target boost pressure set by the target boost pressure setting unit, 13. A control device for a supercharged engine, wherein the target supercharging pressure setting unit sets the upper limit supercharging pressure to a higher value when the temperature of the cooling water is high than when the temperature is low.

2. The control device for a turbocharged engine according to claim 1, the supercharging amount changing means has a bypass passage provided in the exhaust passage and bypassing the turbine, and a wastegate valve that opens and closes the bypass passage, and changes the supercharging amount by changing an opening degree of the wastegate valve.

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