Engine control devices, vehicles, computer program products, and engine control methods

Abstract

This disclosure provides an engine control device, vehicle, computer program product, and engine control method capable of rapidly raising and maintaining the temperature of a catalyst at an appropriate temperature. In this engine control device, vehicle, computer program product, and engine control method, when the catalyst temperature of the catalyst purifying the engine exhaust gas is below a first threshold temperature, the following compression release control is performed: fuel injection from the injector is stopped in a portion of the plurality of cylinders in the engine, i.e., the selected cylinders, and the fuel injection quantity is increased in non-selected cylinders different from the selected cylinders. When the catalyst temperature is above the first threshold temperature, the following Miller cycle control is performed: intake valves in all of the plurality of cylinders are actuated in a manner that reduces the intake air quantity compared to the case where the catalyst temperature is below the first threshold temperature, and the fuel injection quantity is controlled to decrease.

Description

Technical Field

[0001] This disclosure relates to an engine control device, a vehicle, a computer program product, and an engine control method, wherein the vehicle is a vehicle equipped with an engine control device. Background Technology

[0002] In an engine that operates by burning a mixture of fuel and air, substances such as HC, CO, and NOx are produced in the combustion chamber. To purify these substances, a purification catalyst is installed on the engine's exhaust pipe. To ensure the catalyst fully exerts its purification capabilities, it needs to be heated to a specified temperature (catalyst activation temperature).

[0003] Catalyst temperature is controlled by controlling the temperature of the exhaust gas emitted from the engine. When the catalyst temperature is low immediately after engine start-up, the engine is controlled to rapidly increase the catalyst temperature by allowing hot exhaust gas to flow through the exhaust pipe. For example, Patent Document 1 describes a method where, when the SCR catalyst temperature is below its lower activity limit, a compression release brake is activated in a designated cylinder. This compression release brake generates negative work, and to compensate for this work loss, the fuel injection quantity in other cylinders is incrementally corrected. This increases the overall heat generated by the engine, and the SCR catalyst is heated by the increase in exhaust gas temperature.

[0004] Existing technical documents Patent documents Patent document 1: Japanese Patent Application Publication No. 2012-219804. Summary of the Invention

[0005] The problem the invention aims to solve In the aforementioned prior art, increasing the fuel injection quantity of the engine was used to rapidly raise the catalyst temperature, but this method suffers from deterioration in fuel efficiency. Furthermore, maintaining the appropriate temperature after the catalyst reaches the specified temperature is difficult to control technically.

[0006] The purpose of this disclosure is to solve these technical problems and provide an engine control device that can rapidly raise the catalyst temperature and maintain an appropriate temperature.

[0007] Solution to the problem The engine control device disclosed herein controls an engine, wherein, when the catalyst temperature of the catalyst purifying the engine exhaust gas is less than a first threshold temperature, compression release control is performed as follows: fuel injection from the injector is stopped in a portion of the plurality of cylinders, i.e., the selected cylinders, and the fuel injection quantity is increased in the non-selected cylinders, which are different from the selected cylinders; when the catalyst temperature is above the first threshold temperature, Miller cycle control is performed as follows: in all of the plurality of cylinders, the intake valve is actuated in a manner that reduces the intake quantity compared to the case where the catalyst temperature is less than the first threshold temperature, and the fuel injection quantity is reduced.

[0008] Invention Effects According to this disclosure, when the catalyst temperature is below the first catalyst temperature, which indicates the activation state of the catalyst, the engine is operated while being loaded by compression release control, thereby increasing the exhaust gas temperature and rapidly heating the catalyst. After the catalyst temperature reaches above the first catalyst temperature, the exhaust gas temperature is maintained by Miller cycle control while improving fuel efficiency, thereby achieving optimal control of the catalyst temperature. Attached Figure Description

[0009] Figure 1 This is a schematic diagram of the vehicle.

[0010] Figure 2 It is a diagram showing the control actions of the engine.

[0011] Figure 3 This is a flowchart of the engine control unit.

[0012] Figure 4 This is a graph showing the correlation between catalyst temperature and purification rate.

[0013] Figure 5 It is a graph showing the relationship between catalyst temperature, coolant temperature and the switching of operation control.

[0014] Figure 6 This is another example of a flowchart for an engine control unit.

[0015] Explanation of reference numerals in the attached figures 1 vehicle 2 Engines 3. Control device 4. Catalyst temperature sensor 5. Coolant temperature sensor 6. Intake volume sensor 7. Speed ​​sensor 8. Accelerator opening sensor 11, 21, N1 intake valves 12, 22, N2 exhaust valve 13, 23, N3 injectors. Detailed Implementation

[0016] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. It should be noted that the embodiments described below represent only one specific example of the present disclosure. Therefore, the constituent elements, their arrangement positions, and connection methods shown in the following embodiments are merely examples and are not intended to limit the present disclosure. Furthermore, constituent elements not described in the independent claims in the following embodiments will be described as arbitrary constituent elements.

[0017] Furthermore, the figures are schematic diagrams, not rigorous illustrations. Also, in each figure, substantially identical structures are given the same reference numerals, and repetitive descriptions are omitted or simplified.

[0018] Figure 1 This section outlines the structure of a vehicle according to an embodiment of the present disclosure. The vehicle 1 includes: an engine 2; various sensors 4, 5, 6, 7, and 8 for detecting the state of various parts of the vehicle; and a control device 3 for controlling the operation of the engine 2 based on data acquired from the various sensors 4, 5, 6, 7, and 8.

[0019] Engine 2 generates power by burning and expanding a mixture of fuel and air. Engine 2 is, for example, a diesel engine, but it can also be a gasoline engine. Engine 2 has multiple cylinders (cylinder #1, cylinder #2, ..., cylinder #N). The pistons in each cylinder move up and down as the fuel-air mixture burns and expands inside. A crankshaft is connected to the pistons, and the up-and-down movement of the pistons is output as the rotational motion of the crankshaft, thus providing power to vehicle 1. Intake and exhaust pipes are connected to each cylinder. The intake pipes introduce air into each cylinder. The exhaust pipes expel the exhaust gases produced in each cylinder due to combustion into the atmosphere.

[0020] Multiple cylinders (cylinder #1, cylinder #2, ..., cylinder #N) each have an intake valve, an exhaust valve, and an injector. The intake valve is a valve located between each cylinder and the intake manifold and operates in an open-closed manner. If the intake valve is open, air is introduced into each cylinder from the intake manifold; if the intake valve is closed, the introduction of air from the intake manifold into each cylinder is blocked. The exhaust valve is a valve located between each cylinder and the exhaust manifold and operates in an open-closed manner. If the exhaust valve is open, exhaust gas is discharged from each cylinder into the exhaust manifold; if the exhaust valve is closed, the discharge of exhaust gas from each cylinder into the exhaust manifold is blocked. The injector performs fuel injection into the interior of each cylinder. Cylinder #1 has an intake valve 11, an exhaust valve 12, and an injector 13. Similarly, cylinder #2 has an intake valve 21, an exhaust valve 22, and an injector 23, and cylinder #N has an intake valve N1, an exhaust valve N2, and an injector N3. In other words, cylinder #1, cylinder #2, ..., cylinder #N each have an intake valve 11, an intake valve 21, ..., an intake valve N1, an exhaust valve 12, an exhaust valve 22, ..., an exhaust valve N2, and an injector 13, an injector 23, ..., an injector N3.

[0021] Catalyst temperature sensor 4 detects the temperature of a catalyst (not shown). Here, the catalyst is located in the exhaust pipe to purify the exhaust gas from engine 2. In the case of engine 2 being a diesel engine, the catalyst is, for example, an SCR (Selective Catalytic Reduction) catalyst. Catalyst temperature sensor 4 is located on the catalyst or in the exhaust pipe. Coolant temperature sensor 5 detects the temperature of the coolant used to cool engine 2, i.e., the coolant temperature. The coolant is, for example, coolant water. A cooling device (not shown) is provided in engine 2 to cool engine 2. Coolant temperature sensor 5 is located in the coolant circuit of the cooling device. Coolant temperature sensor 5 detects the coolant temperature of the coolant circulating inside the coolant circuit used to cool engine 2.

[0022] By detecting the coolant temperature using the coolant temperature sensor 5, information related to the engine temperature (i.e., the engine temperature) of engine 2 can be obtained. During engine 2 operation, it is desirable to maintain the engine temperature within an appropriate range. For example, immediately after starting engine 2 and before the engine has fully warmed up, the viscosity of the lubricating oil may increase, resulting in a greater load on engine 2. Furthermore, before the engine has fully warmed up, cooling losses during fuel combustion increase, sometimes reducing fuel efficiency. To prevent these issues, engine 2 is controlled based on the coolant temperature to maintain the engine temperature within an appropriate range. Specifically, sometimes, engine 2 is controlled in a way that increases heat generation to maintain the engine temperature within an appropriate range.

[0023] An intake air volume sensor 6 is located in the intake manifold (not shown) and detects the amount of air entering the engine 2. Here, intake air volume represents the amount of air introduced into the cylinders when fuel is injected. A speed sensor 7 is located on the crankshaft (not shown) and detects the rotational speed of the engine 2 (crankshaft). An accelerator pedal (not shown) sensor 8 is located on the accelerator pedal and detects the amount of accelerator pedal operation. The driver of vehicle 1 increases the required output of engine 2 by increasing the amount of accelerator pedal operation and decreases the required output of engine 2 by decreasing the amount of operation.

[0024] The control unit 3 is the computer provided by vehicle 1. The control unit 3 has a CPU (Central Processing Unit) and other computing devices, a memory and other storage devices, a communication interface, etc., and controls the operation of engine 2 according to the engine control program stored in the storage device. Based on data acquired by various sensors, the control unit 3 selects one of several controls, including normal control, Miller cycle control, and compression-release control, to control engine 2.

[0025] Figure 2 It is a diagram showing the operation of the exhaust valve, intake valve, and fuel injection of engine 2 in each control cycle. Figure 2 The horizontal axis represents the time elapsed in the combustion cycle, and the vertical axis represents the lift of the intake or exhaust valve. Figure 2 The top dead center (TDC) and bottom dead center (BDC) marks on the horizontal axis indicate the time the piston is at TDC and BDC, respectively. Figure 2 A larger vertical lift indicates that the intake or exhaust valve is open, while a smaller lift indicates that the intake or exhaust valve is closed. Figure 2 (a) is a diagram showing the action in a normally controlled combustion cycle. Figure 2 (b) is a diagram showing the action in the combustion cycle controlled by the Miller cycle. Figure 2 (c) is a diagram representing the action in the combustion cycle where compression release control is selected in the cylinder. Figure 2 (d) is a diagram representing the action in the combustion cycle with compression release control in a non-selective cylinder.

[0026] Here, we will focus on one cylinder (cylinder #1) to explain the normally controlled combustion cycle. Figure 2 (a) is a diagram showing the actions in a normally controlled combustion cycle. For example... Figure 2As shown in (a), in a normally controlled combustion cycle, air is first introduced into cylinder #1. During the piston's descent from top dead center, only intake valve 11 is open, allowing air to be introduced into cylinder #1 (intake stroke). Next, when the piston is near bottom dead center, intake valve 11 is closed. With both intake valve 11 and exhaust valve 12 closed, the piston rises to top dead center. The air introduced into cylinder #1 is thus compressed (compression stroke). Next, while the piston is at top dead center, fuel is injected into the cylinder via injector 13. The fuel mixed with the compressed air burns, and the piston is pressed to bottom dead center by the expanding combustion gases (combustion stroke). Then, as the piston rises again to top dead center due to inertia or expansion in other cylinders, only exhaust valve 12 is opened, allowing the combustion gases to be expelled from cylinder #1 as exhaust gases into the atmosphere (exhaust stroke). If the piston rises to top dead center, it then descends to bottom dead center. During this descent, intake valve 11 is opened, allowing air to be introduced into cylinder #1. Thus, engine 2 repeatedly performs intake, compression, combustion, and exhaust strokes to generate power.

[0027] In normal control, the intake valves are closed in all cylinders when the piston is near bottom dead center, and fuel injection is performed when the piston is near top dead center. The combustion cycle under normal control generates less heat than under compression-release control (described later) but more than under Miller cycle control (described later). Therefore, it is possible to prevent the catalyst temperature from becoming too high and to warm up the engine simultaneously before engine warm-up.

[0028] In Miller cycle control, the intake valve is operated in such a way that the amount of air entering all cylinders is reduced compared to normal control or compression release control described later, thereby further reducing the amount of fuel injection. Figure 2(b) is a diagram illustrating the operation of the combustion cycle in Miller cycle control. In Miller cycle control, similar to normal control, air is first introduced into cylinder #1. During the piston's descent from top dead center (TDC), only intake valve 11 is open, allowing air to be introduced into cylinder #1 (intake stroke). Next, the piston reaches bottom dead center (BDC). Here, unlike normal control, in Miller cycle control, intake valve 11 does not close when the piston reaches BDC; it closes only after the piston begins to rise again towards BDC. For example, intake valve 11 closes only after the piston has passed the midpoint between BDC and TDC. Then, with intake valve 11 and exhaust valve 12 closed, the piston rises to TDC. The air introduced into cylinder #1 is thus compressed (compression stroke). Next, while the piston is at TDC, fuel is injected into the cylinder via injector 13. Thus, the fuel mixed with compressed air burns, and the piston is pressed to bottom dead center (combustion stroke) by the expanding combustion gases. Then, as the piston rises again to top dead center due to inertia or expansion in other cylinders, only exhaust valve 12 opens, thereby forcing the combustion gases out of cylinder #1 and expelled into the atmosphere as exhaust gas (exhaust stroke). If the piston rises to top dead center, it falls again to bottom dead center, during which intake valve 11 is opened, thereby introducing air into cylinder #1.

[0029] In Miller cycle control, the intake air volume in multiple cylinders of engine 2 is reduced compared to normal control. For example, as... Figure 2 As shown in (b), a "delayed closing" control is performed during the intake stroke, causing the intake valve 11 to close later than normal control or compression release control. Alternatively, the control can be performed to close the intake valve 11 midway through the intake stroke. That is, an "early closing" control can also be performed to close the intake valve 11 earlier than normal control.

[0030] In Miller cycle control, the intake air volume to cylinder #1 is reduced compared to normal control, and consequently, the required fuel injection amount for each cylinder is reduced. For example, it can be done as follows: Figure 2 As shown in (b), the duration of fuel injection is shortened. By reducing the amount of fuel injected, engine 2 generates power with less fuel. That is, vehicle 1 can run with less fuel, thus improving fuel efficiency compared to normal control. On the other hand, although the amount of fuel injected is reduced, the amount of gas in cylinder #1 decreases, resulting in a lower heat capacity, making it easier to maintain the temperature of the exhaust gases from combustion. Therefore, it is possible to prevent the catalyst temperature from falling below the activation temperature and maintain it at an appropriate temperature.

[0031] Next, the combustion cycle for compression release control will be explained. In compression release control, a portion of the cylinders in engine 2 are selected as the selected cylinders to perform the combustion cycle for compression release control. The non-selected cylinders, which are different from the selected cylinders, perform the same combustion cycle as in normal control.

[0032] The combustion cycle of the selected cylinder under compression release control is explained. Figure 2 (c) is a diagram illustrating the operation in the combustion cycle under compression-release control in the selector cylinder. In the selector cylinder under compression-release control, as in normal control, air is first introduced into cylinder #1. During the piston's descent from top dead center, only intake valve 11 is open, thus introducing air into cylinder #1 (intake stroke). Next, when the piston descends to bottom dead center, intake valve 11 closes, and with both intake valve 11 and exhaust valve 12 closed, the piston rises to top dead center. Thus, the air introduced into cylinder #1 is compressed (compression stroke). Here, in the selector cylinder under compression-release control, unlike normal control, exhaust valve 12 is opened when the piston is at top dead center during the compression stroke. Furthermore, unlike normal control, fuel injection is not performed while the piston is at top dead center. Then, after the piston passes top dead center, exhaust valve 12 is closed again. Then, with both intake valve 11 and exhaust valve 12 closed, the piston descends towards bottom dead center (expansion stroke). Then, as the piston rises again to top dead center due to inertia or the expansion of other cylinders, only exhaust valve 12 opens, thereby expelling the gas inside cylinder #1 to the outside (exhaust stroke). If the piston rises to top dead center, it falls again to bottom dead center, during which intake valve 11 is opened, thereby introducing air into cylinder #1.

[0033] On the other hand, in the non-selective cylinder under compression release control, the combustion cycle is performed in the same way as under normal control. Figure 2(d) is a diagram illustrating the operation in the combustion cycle under compression-release control in a non-selective cylinder. In a non-selective cylinder under compression-release control, air is first introduced into cylinder #1. During the piston's descent from top dead center, only intake valve 11 is open, allowing air to be introduced into cylinder #1 (intake stroke). Next, as the piston descends to bottom dead center, intake valve 11 closes, and with both intake and exhaust valves 11 and 12 closed, the piston rises to top dead center. Thus, the air introduced into cylinder #1 is compressed (compression stroke). Next, while the piston is at top dead center, fuel is injected into the cylinder via injector 13. The fuel mixed with the compressed air burns, and the piston is pressed down to bottom dead center by the expanding combustion gases (combustion stroke). Then, due to inertia or expansion in other cylinders, as the piston rises again to top dead center, only exhaust valve 12 opens, allowing the combustion gases to be expelled from cylinder #1 as exhaust gases into the atmosphere (exhaust stroke). If the piston rises to the top dead center, it will fall to the bottom dead center again. During the descent, the intake valve 11 will be open, so that air will be introduced into cylinder #1.

[0034] In compression release control, the selected cylinder is appropriately chosen based on factors such as the engine displacement or number of cylinders, engine speed, and required load. For example, in the case of a 4-cylinder engine with cylinders #1, #2, #3, and #4, cylinders #1 and #4 can be selected as the cylinders for execution. Figure 2 The combustion cycle shown in (c) continues with cylinders #2 and #3 as non-selectable cylinders. Figure 2 The combustion cycle is shown in (d). Alternatively, cylinders #2 and #3 can be used as selector cylinders to perform the operation. Figure 2 The combustion cycle shown in (c) continues with cylinders #1 and #4 as non-selectable cylinders. Figure 2 The combustion cycle is shown in (d).

[0035] In compression release control, fuel injection from the injector is stopped in a cylinder that is part of a selection cylinder, while the fuel injection quantity is increased in a non-selection cylinder, which is different from the selection cylinder. In compression release control, the output decreases in the selection cylinder due to the cessation of fuel injection, while the output is compensated by increasing the fuel injection quantity in the non-selection cylinder. For example, it can be as follows... Figure 2 As shown in (d), the duration of fuel injection is extended.

[0036] The selector cylinder is in a state where engine braking is applied. In the selector cylinder, during the compression stroke, the air inside the cylinder is compressed. This generates a load that reacts to the rotation of engine 2. Furthermore, the exhaust valve opens when the piston is near top dead center, and closes again after expelling the compressed air. This causes the pressure inside the cylinder to drop during the expansion stroke, generating a load that reacts to engine 2. In the non-selector cylinder, output exceeding these loads is required, thus necessitating more fuel injection. Therefore, the non-selector cylinder generates more heat than under normal control, and the exhaust gas temperature is also higher. Additionally, the high-temperature air compressed during the compression stroke is discharged from the selector cylinder. This effectively raises the exhaust gas temperature and rapidly increases the catalyst temperature.

[0037] The control device 3 obtains the catalyst temperature from the catalyst temperature sensor 4 and the coolant temperature from the coolant temperature sensor 5. The control device 3 controls the operation of the intake valves 11, 21, ..., N1, the exhaust valves 12, 22, ..., N2, and the injectors 13, 23, ..., N3 based on these temperature data.

[0038] Furthermore, the control device 3 can obtain the intake air volume from the intake air volume sensor 6, the engine speed from the speed sensor 7, and the accelerator opening from the accelerator opening sensor 8. Based on this data, the control device 3 can control the operation of the intake valves 11, 21, ..., N1, the exhaust valves 12, 22, ..., N2, and the injectors 13, 23, ..., N3.

[0039] Figure 3 This is a flowchart illustrating the operation of the engine 2 controlled by the control device 3 according to the engine control program. The control device 3 obtains the coolant temperature from the coolant temperature sensor 5 (step S1). Furthermore, the control device 3 obtains the catalyst temperature from the catalyst temperature sensor 4 (step S2). Then, the control device 3 determines whether the coolant temperature is above a predetermined threshold temperature z (°C) (second threshold temperature) (step S3). Here, the threshold temperature z is the lower limit temperature indicating that the engine 2 is in a warm-up state. When the coolant temperature is below the threshold temperature z, the engine 2 is in a low-temperature cold state; when the coolant temperature is above the threshold temperature z, the engine 2 is in a high-temperature warm-up state. The threshold temperature z is, for example, 100°C.

[0040] If the coolant temperature is above the threshold temperature z (step S3 is "Yes"), the control device 3 determines whether the catalyst temperature is above the threshold temperature x (°C) (first threshold temperature) (step S4). On the other hand, if the coolant temperature is below the threshold temperature z (step S3 is "No"), the control device 3 determines whether the catalyst temperature is above the threshold temperature y (°C) (third threshold temperature) (step S5).

[0041] Here, threshold temperature x represents the upper limit of the temperature at which the catalyst needs to be heated, and threshold temperature y represents the lower limit of the temperature at which the catalyst does not need to be heated. Threshold temperature x is the temperature below threshold temperature y. Figure 4 The diagram illustrates the relationship between catalyst temperature and catalyst purification rate. The catalyst purification rate exhibits a curve-like relationship with catalyst temperature. For example, the threshold temperature x is the catalyst temperature at which the catalyst purification rate reaches a predetermined target value, i.e., the target purification rate. Furthermore, the threshold temperature y is the temperature at which the catalyst is fully activated, i.e., the temperature at which the catalyst purification rate reaches its maximum, i.e., the maximum purification rate. For example, the threshold temperature x is 150°C, and the threshold temperature y is 300°C. The threshold temperatures x and y can be appropriately set according to the type or degradation state of the catalyst in engine 2, the number of cylinders in engine 2, or the displacement, etc.

[0042] When the catalyst temperature is above the threshold temperature x in step S4 (step S4 is "Yes"), the control device 3 performs Miller cycle control (step S6). On the other hand, when the catalyst temperature is below the threshold temperature x in step S4 (step S4 is "No"), the control device 3 performs compression release control (step S8).

[0043] Furthermore, when the catalyst temperature is above the threshold temperature y in step S5 (step S5 is "Yes"), the control device 3 performs normal control (step S7). On the other hand, when the catalyst temperature is below the threshold temperature y in step S5 (step S5 is "No"), the control device 3 performs compression release control (step S8).

[0044] The process shown in the flowchart above is repeated continuously while the vehicle is in motion. Then, when the coolant temperature or catalyst temperature changes and the determination results of steps S3 to S5 change, the control content changes from compression release control to normal control or Miller cycle control, from normal control to compression release control or Miller cycle control, and from Miller cycle control to normal control or compression release control. At this time, during the transition from normal control or Miller cycle control to compression release control, the transition is implemented after stopping fuel injection in the selected cylinder and increasing the fuel injection quantity in the non-selected cylinder. Furthermore, during the transition from compression release control to normal control or Miller cycle control, fuel injection in the selected cylinder restarts after the transition, and the fuel injection quantity in the non-selected cylinder is reduced. This prevents unburned fuel from being discharged during compression release control and suppresses torque fluctuations caused by abrupt changes in fuel injection quantity.

[0045] Figure 5This diagram illustrates the criteria for determining whether to execute Miller cycle control, compression release control, or normal control based on coolant and catalyst temperatures. Miller cycle control is executed when the coolant temperature is above the lower limit (threshold temperature z) indicating the engine is warmed up and the catalyst temperature is above the upper limit (threshold temperature x) indicating the catalyst needs to heat up further. Furthermore, compression release control is executed when the coolant temperature is above threshold temperature z and the catalyst temperature is below threshold temperature x.

[0046] When the coolant temperature is above the threshold temperature z and the catalyst temperature is above the threshold temperature x, engine 2 is in a warm-up state, so no further heating is required. The catalyst temperature reaches the threshold temperature x, so no further heating is required. Therefore, by using Miller cycle control to suppress the heat generation of engine 2 and suppress the decrease in exhaust gas temperature, the catalyst temperature is appropriately controlled.

[0047] When the coolant temperature is above the threshold temperature z and the catalyst temperature is below the threshold temperature x, engine 2 is in a warm-up state, but the catalyst temperature has not reached the threshold temperature x. Therefore, the exhaust gas temperature is increased by controlling the high-heat-generating compression release, thereby raising the catalyst temperature.

[0048] Normal control is performed when the coolant temperature is below the threshold temperature z and the catalyst temperature is above the threshold temperature y, which indicates the lower limit at which the catalyst does not need to be heated. Furthermore, compression release control is performed when both the coolant temperature is below the threshold temperature z and the catalyst temperature is below the threshold temperature y.

[0049] When the coolant temperature is below the threshold temperature z and the catalyst temperature is above the threshold temperature y, it is not necessary to increase the catalyst temperature while heating the engine 2. Therefore, by normally controlling the heat output of the engine 2 to be greater than that of Miller cycle control and less than that of compression release control, the catalyst temperature is appropriately controlled while maintaining the exhaust gas temperature while heating the engine 2.

[0050] When the coolant temperature is below the threshold temperature z and the catalyst temperature is below the threshold temperature y, it is necessary to increase the catalyst temperature while heating the engine 2. Therefore, the heat generation of the engine 2 is increased by controlling the compression release, which generates more heat, so that the catalyst temperature rises while simultaneously heating the engine 2 and increasing the exhaust gas temperature.

[0051] As described above, by controlling the operation of engine 2 based on coolant temperature and catalyst temperature, the temperature of exhaust gas can be controlled. Therefore, catalyst temperature and engine temperature can be appropriately controlled, and harmful substances in exhaust gas can be appropriately decomposed and removed.

[0052] Figure 6This is a flowchart illustrating another example of the operation of the control device 3. The control device 3 obtains the coolant temperature from the coolant temperature sensor 5 (step S11). Furthermore, the control device 3 obtains the catalyst temperature from the catalyst temperature sensor 4 (step S12). Then, the control device 3 determines whether the coolant temperature is above a predetermined threshold temperature z (step S13). Here, the threshold temperature z represents the temperature indicating the warm-up state of the engine 2.

[0053] If the coolant temperature is above the threshold temperature z (step S13 is "Yes"), the control device 3 determines whether the catalyst temperature is above the threshold temperature x (step S14). Here, the threshold temperature x is the upper limit of the temperature at which the catalyst needs to be heated. On the other hand, if the coolant temperature is below the threshold temperature z (step S13 is "No"), the control device 3 determines whether the catalyst temperature is above the threshold temperature y (step S15). Here, the threshold temperature y is the lower limit of the temperature at which the catalyst does not need to be heated, and is a value higher than the threshold temperature x.

[0054] When the catalyst temperature is above the threshold temperature x in step S14 (step S14 is "Yes"), the control device 3 obtains the engine speed of the engine 2 from the speed sensor 7 and calculates the required output (engine load) based on the accelerator opening obtained from the accelerator opening sensor 8 (step S16). Then, if the engine speed of the engine 2 and the required output meet the execution conditions of Miller cycle control (step S18 is "Yes"), the control device 3 drives the engine 2 through Miller cycle control (step S19). For example, Miller cycle control is executed when the engine speed is less than the specified engine speed and the required output is less than the specified required output. On the other hand, if neither the engine speed of the engine 2 nor the required output meets the execution conditions of Miller cycle control (step S18 is "No"), the control device 3 drives the engine 2 through normal control (step S20).

[0055] In Miller cycle control, the intake air volume decreases, thus limiting the engine speed or required output. Therefore, in step S18, it is determined whether the engine speed or required output is suitable for Miller cycle control. The specific values ​​of the specified engine speed and the specified required output can be appropriately determined based on factors such as the number of cylinders or displacement of engine 2.

[0056] On the other hand, when the catalyst temperature is less than the threshold temperature x in step S14 (step S14 is "No"), the control device 3 obtains the intake air volume from the intake air volume sensor 6, the engine speed of the engine 2 from the speed sensor 7, and calculates the required output (engine load) based on the accelerator opening obtained from the accelerator opening sensor 8 (step S17). Then, if the intake air volume, the engine speed of the engine 2, and the required output meet the execution conditions of the compression release control (step S21 is "Yes"), the control device 3 drives the engine 2 through compression release control (step S22). For example, if the speed is less than the specified speed, the required output is less than the specified required output, and the intake air volume is the specified intake air volume, Miller cycle control is executed. On the other hand, if the intake air volume, the engine speed of the engine 2, and the required output do not all meet the execution conditions of the compression release control (step S21 is "No"), the control device 3 drives the engine 2 through normal control (step S20).

[0057] In compression release control, fuel injection is stopped in a portion of the cylinders, and fuel injection is performed only in the remaining cylinders. If the number of cylinders performing fuel injection decreases, vibration is likely to occur, making it unsuitable for low-speed operation. Furthermore, if the intake air volume is insufficient, the required output may not be achieved. Therefore, in step S21, it is determined whether the intake air volume, engine speed, and required output are suitable for compression release control. The specific values ​​of the specified intake air volume, specified engine speed, and specified required output can be appropriately set based on the number of cylinders or displacement of engine 2, etc.

[0058] When the catalyst temperature is above the threshold temperature y in step S15 (step S15 is "Yes"), the control device 3 drives the engine 2 by normal control (step S20). On the other hand, when the catalyst temperature is below the threshold temperature y in step S15 (step S15 is "No"), the control device 3 obtains the intake air volume from the intake air volume sensor 6, the engine speed of the engine 2 from the speed sensor 7, and calculates the required output (engine load) based on the accelerator opening obtained from the accelerator opening sensor 8 (step S17). Then, if the intake air volume, the engine speed of the engine 2, and the required output meet the execution conditions of the compression release control (step S21 is "Yes"), the control device 3 drives the engine 2 by compression release control (step S22); if not all three conditions are met (step S21 is "No"), the control device 3 drives the engine 2 by normal control (step S20).

[0059] As described above, in addition to coolant temperature and catalyst temperature, exhaust gas temperature is controlled by controlling engine 2 based on intake air volume, engine speed and required output (engine load). Therefore, Miller cycle control and compression release control can be performed under appropriate conditions, catalyst temperature and engine temperature can be appropriately controlled, and harmful substances in exhaust gas can be appropriately decomposed and removed.

[0060] Industrial applicability The vehicle disclosed herein can be widely used in the automotive industry. It is particularly useful in fields where optimal control of catalyst temperature is required in engine exhaust gas purification systems.

Claims

1. An engine control device for controlling an engine, characterized in that, When the catalyst temperature of the catalyst purifying the engine exhaust gas is below a first threshold temperature, compression release control is performed as follows: fuel injection from the injector is stopped in a portion of the multiple cylinders of the engine, i.e., the selected cylinders, and the fuel injection quantity is increased in the non-selected cylinders, which are different from the selected cylinders. When the catalyst temperature is above the first threshold temperature, Miller cycle control is performed such that the intake valves in all of the plurality of cylinders are activated in a manner that reduces the intake volume compared to the case where the catalyst temperature is below the first threshold temperature, and the fuel injection volume is reduced.

2. The engine control device according to claim 1, wherein, The compression release control is executed when the coolant temperature circulating inside the coolant circuit cooling the engine is above a second threshold temperature and the catalyst temperature is below the first threshold temperature. When the coolant temperature is above the second threshold temperature and the catalyst temperature is above the first threshold temperature, the Miller cycle control is executed. The compression release control is executed when the coolant temperature is lower than the second threshold temperature and the catalyst temperature is lower than a third threshold temperature that is higher than the first threshold temperature. When the coolant temperature is less than the second threshold temperature and the catalyst temperature is greater than the third threshold temperature, the following general control is performed in all of the plurality of cylinders: the intake valve is closed when the piston is near bottom dead center and fuel injection is performed when the piston is near top dead center.

3. The engine control device according to claim 1, wherein, In the compression release control, in the selected cylinder, the exhaust valve is opened when the piston is near top dead center during the compression stroke, and the exhaust valve is closed again during the expansion stroke.

4. The engine control device according to claim 2, wherein, If the engine speed, required output, and intake air volume do not all meet the execution conditions of the compression release control, the normal control is executed instead of the compression release control. If the engine speed and the required output do not both meet the execution conditions of the Miller cycle control, the normal control is executed instead of the Miller cycle control.

5. The engine control device according to claim 2, wherein, During the transition from the normal control to the compression release control, the transition is implemented after fuel injection in the selected cylinder is stopped and the fuel injection amount is increased in the non-selected cylinder. When transitioning from the compression release control to the normal control or from the compression release control to the Miller cycle control, fuel injection of the selected cylinder is restarted after the transition, and the fuel injection amount of the non-selected cylinder is reduced.

6. The engine control device according to claim 1, wherein, In the Miller cycle control, the intake valve is closed later during the intake stroke compared to the compression release control.

7. The engine control device according to claim 2, wherein, The first threshold temperature is a temperature lower than the third threshold temperature.

8. A vehicle having the engine control device of claim 1.

9. A computer program product, comprising an engine control program, characterized in that, When the engine control program is executed by the computer controlling the engine, it performs the following processing: When the catalyst temperature of the catalyst purifying the exhaust gas of the engine is below a first threshold temperature, compression release control is performed as follows: fuel injection from the injector is stopped in a portion of the cylinders (selected cylinders) of the engine, and the fuel injection quantity is increased in non-selected cylinders (different from the selected cylinders); and When the catalyst temperature is above the first threshold temperature, Miller cycle control is performed such that the intake valves in all of the plurality of cylinders are activated in a manner that reduces the intake volume compared to the case where the catalyst temperature is below the first threshold temperature, and the fuel injection volume is reduced.

10. An engine control method for controlling an engine, characterized in that, Includes the following steps: When the catalyst temperature of the catalyst purifying the exhaust gas of the engine is below a first threshold temperature, compression release control is performed as follows: fuel injection from the injector is stopped in a portion of the cylinders (selected cylinders) of the engine, and the fuel injection quantity is increased in non-selected cylinders (different from the selected cylinders); and When the catalyst temperature is above the first threshold temperature, Miller cycle control is performed such that the intake valves in all of the plurality of cylinders are activated in a manner that reduces the intake volume compared to the case where the catalyst temperature is below the first threshold temperature, and the fuel injection quantity is reduced.

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