Engine control device and vehicle

Abstract

To provide an engine control device that can rapidly raise the temperature of the catalyst and maintain an appropriate temperature. [Solution] An engine control device for controlling an engine, wherein when the catalyst temperature of a catalyst that purifies the exhaust gas of the engine is below a first threshold temperature, it performs compression release control to stop fuel injection from the injector in selected cylinders, which are some of the cylinders among a plurality of cylinders of the engine, and increase the amount of fuel injected in non-selected cylinders different from the selected cylinders, and when the catalyst temperature is above the first threshold temperature, it performs Miller cycle control to operate the intake valve to reduce the amount of intake air in all of the plurality of cylinders compared to when the temperature is below the first threshold temperature, and to control the amount of fuel injected.

Description

Technical Field

[0001] The present disclosure relates to an engine control device and a vehicle having the engine control device.

Background Art

[0002] In an engine that operates by burning a mixture of fuel and air, substances such as HC, CO, and NOx are generated in the combustion chamber. In order to purify these substances, a purification catalyst is attached to the exhaust pipe of the engine. In order for the catalyst to fully exhibit its purification ability, it is necessary to warm up the catalyst to a predetermined temperature (catalyst activation temperature).

[0003] The control of the temperature of the catalyst (catalyst temperature) is performed by controlling the temperature of the exhaust gas discharged from the engine. When the catalyst temperature is low immediately after the engine is started, the engine is controlled so that high-temperature exhaust gas flows through the exhaust pipe in order to quickly raise the catalyst temperature. For example, Patent Document 1 describes that when the SCR catalyst temperature falls below the activation lower limit temperature, a compression release brake (also called a power turndown, a Jake brake, or an engine retarder) is operated in a predetermined cylinder. In the power turndown, a negative work amount is generated, and the fuel injection amount of other cylinders is increased and corrected to compensate for the loss of that work amount. Thereby, the total heat generation amount of the engine is increased, and the SCR catalyst is heated up by the rise in the exhaust temperature.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the conventional technology described above, a method was used to increase the amount of fuel injected by the engine in order to rapidly raise the catalyst temperature, but this method had the problem of worsening fuel efficiency. In addition, there was a challenge in controlling the catalyst temperature to maintain an appropriate temperature even after it had reached a predetermined temperature.

[0006] This disclosure aims to solve these problems and provide an engine control device that can rapidly raise the catalyst temperature and maintain an appropriate temperature. [Means for solving the problem]

[0007] The engine control device according to this disclosure is an engine control device for controlling an engine, wherein when the catalyst temperature of a catalyst that purifies the exhaust gas of the engine is below a first threshold temperature, it performs compression release control to stop fuel injection from the injector in selected cylinders, which are some of the cylinders among a plurality of cylinders of the engine, and increase the amount of fuel injected in non-selected cylinders different from the selected cylinders, and when the catalyst temperature is above the first threshold temperature, it performs Miller cycle control to operate the intake valve to reduce the amount of intake air in all of the plurality of cylinders compared to when the temperature is below the first threshold temperature, and to control the amount of fuel injected. [Effects of the Invention]

[0008] According to this disclosure, when the catalyst temperature is lower than the first catalyst temperature indicating the activated state of the catalyst, the exhaust gas temperature is increased by operating the engine while applying a load through compression release control, thereby rapidly heating the catalyst. After the catalyst temperature reaches or exceeds the first catalyst temperature, the exhaust gas temperature is maintained while improving fuel efficiency through Miller cycle control, thereby optimally controlling the catalyst temperature. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic diagram of the vehicle. [Figure 2] This diagram shows the operation of the engine control system. [Figure 3]This is a flowchart of the engine control system. [Figure 4] This diagram shows the relationship between catalyst temperature and purification rate. [Figure 5] This diagram shows the relationship between catalyst temperature, refrigerant temperature, and the switching of operation control. [Figure 6] Here is another example of an engine control system flowchart. [Modes for carrying out the invention]

[0010] The embodiments of this disclosure will be described below with reference to the drawings. The embodiments described below are all specific examples of this disclosure. Therefore, the components, their arrangement positions, and connection configurations shown in the following embodiments are examples and are not intended to limit this disclosure. Furthermore, components in the following embodiments that are not described in an independent claim will be described as optional components.

[0011] Furthermore, each figure is a schematic diagram and not necessarily a strictly accurate representation. Note that in each figure, substantially identical components are denoted by the same reference numerals, and redundant explanations may be omitted or simplified.

[0012] Figure 1 shows an overview of the configuration 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 that controls the operation of the engine 2 based on data acquired from the various sensors 4, 5, 6, 7, and 8.

[0013] Engine 2 generates power by burning and expanding a mixture of fuel and air. Engine 2 is, for example, a diesel engine, but it may also be a gasoline engine. Engine 2 has multiple cylinders (cylinder #1, cylinder #2, ..., cylinder #N). As the mixture of fuel and air burns and expands inside each cylinder, the piston in each cylinder moves up and down. The piston is connected to a crankshaft, and the up and down motion of the piston is converted into the rotational motion of the crankshaft, which powers vehicle 1. Each cylinder is connected to an intake pipe and an exhaust pipe. The intake pipe introduces air into each cylinder. The exhaust pipe discharges the exhaust gas generated in each cylinder by combustion into the atmosphere.

[0014] Each of the cylinders (cylinder #1, cylinder #2, ..., cylinder #N) has an intake valve, an exhaust valve, and an injector. The intake valve is located between each cylinder and the intake manifold and is a valve that can be opened and closed. When the intake valve is open, air is introduced from the intake manifold to each cylinder, and when the intake valve is closed, the introduction of air from the intake manifold to each cylinder is blocked. The exhaust valve is located between each cylinder and the exhaust manifold and is a valve that can be opened and closed. When the exhaust valve is open, exhaust gas is discharged from each cylinder to the exhaust manifold, and when the exhaust valve is closed, the discharge of exhaust gas from each cylinder to 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, cylinders #1, #2, ..., and #N each have an intake valve 11, an intake valve 21, ..., and an intake valve N1, an exhaust valve 12, an exhaust valve 22, ..., and an exhaust valve N2, and each has an injector 13, an injector 23, ..., and an injector N3.

[0015] The catalyst temperature sensor 4 detects the catalyst temperature of a catalyst (not shown). Here, the catalyst is installed in the exhaust pipe and purifies the exhaust gas of the engine 2. If the engine 2 is a diesel engine, the catalyst is, for example, an SCR (Selective Catalytic Reduction) catalyst. The catalyst temperature sensor 4 is installed in the catalyst or the exhaust pipe. The refrigerant temperature sensor 5 detects the refrigerant temperature, which is the temperature of the refrigerant that cools the engine 2. The refrigerant is, for example, coolant. The engine 2 is equipped with a cooling system (not shown) that cools the engine 2. The refrigerant temperature sensor 5 is installed in the refrigerant circuit of the cooling system. The refrigerant temperature sensor 5 detects the refrigerant temperature of the refrigerant circulating inside the refrigerant circuit for cooling the engine 2.

[0016] By detecting the refrigerant temperature using the refrigerant temperature sensor 5, information regarding 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 it has warmed up, the viscosity of the lubricating oil in engine 2 increases, potentially increasing the load on engine 2. Also, if engine 2 is not fully warmed up, cooling losses during fuel combustion increase, potentially reducing fuel efficiency. To prevent these issues, engine 2 is controlled based on the refrigerant temperature to maintain the engine temperature within an appropriate range. Specifically, this may be achieved by controlling the engine 2 to increase the amount of heat generated, thereby maintaining the engine temperature within an appropriate range.

[0017] The intake air volume sensor 6 is located in the intake manifold (not shown) and detects the amount of intake air supplied to the engine 2. Here, the intake air volume refers to the amount of air introduced into each cylinder during fuel injection. The rotational speed sensor 7 is located on the crankshaft (not shown) and detects the rotational speed of the engine 2 (crankshaft). The accelerator pedal position sensor 8 is located on the accelerator pedal (not shown) and detects the amount the accelerator pedal is operated. The driver of vehicle 1 can increase the engine 2's required output by increasing the amount the accelerator pedal is operated, and decrease the engine 2's required output by decreasing the amount the accelerator pedal is operated.

[0018] The control device 3 is a computer provided in the vehicle 1. The control device 3 has an arithmetic device such as a CPU (Central Processing Unit), a storage device such as a memory, a communication interface, etc., and controls the operation of the engine 2 according to an engine control program stored in the storage device. The control device 3 selects any one of a plurality of controls including normal control, mirror cycle control, and compression release control based on the data acquired by various sensors, and controls the engine 2.

[0019] FIG. 2 is a diagram showing the operations of the exhaust valve, intake valve, and fuel injection for each control of the engine 2. The horizontal axis in FIG. 2 represents the passage of time in the combustion cycle, and the vertical axis represents the lift amount of the intake valve or exhaust valve. The top dead center or bottom dead center described as the scale on the horizontal axis of FIG. 2 indicates the time when the position of the piston is at the top dead center or bottom dead center. The lift amount on the vertical axis of FIG. 2 indicates that the intake valve or exhaust valve is opened when it increases, and indicates that the intake valve or exhaust valve is closed when it decreases. FIG. 2(a) is a diagram showing the operation in the combustion cycle of normal control. FIG. 2(b) is a diagram showing the operation in the combustion cycle of mirror cycle control. FIG. 2(c) is a diagram showing the operation in the combustion cycle of compression release control in the selected cylinder, and FIG. 2(d) is a diagram showing the operation in the combustion cycle of compression release control in the non-selected cylinder.

[0020] Here, focusing on one cylinder (cylinder #1), the combustion cycle of normal control will be described. FIG. 2(a) is a diagram showing the operations in the combustion cycle of normal control. As shown in FIG. 2(a), in the combustion cycle of normal control, first, air is introduced into cylinder #1. While the piston descends from the top dead center, only the intake valve 11 is opened, and air is introduced into cylinder #1 (intake stroke). Next, when the piston is located near the bottom dead center, the intake valve 11 is closed. With the intake valve 11 and the exhaust valve 12 closed, the piston rises to the top dead center. As a result, the air introduced into cylinder #1 is compressed (compression stroke). Subsequently, when the piston is located at the top dead center, fuel injection is executed into the cylinder by the injector 13. Thereby, the fuel mixed with the compressed air burns, and the expanded combustion gas pushes the piston down to the bottom dead center (combustion stroke). Then, as the piston rises again to the top dead center due to inertia and the expansion in other cylinders, only the exhaust valve 12 is opened, and the combustion gas is pushed out of cylinder #1 and discharged into the atmosphere as exhaust gas (exhaust stroke). When the piston rises to the top dead center, the intake valve 11 is opened again while the piston descends to the bottom dead center, and air is introduced into cylinder #1. Thus, by repeating the intake stroke, compression stroke, combustion stroke, and exhaust process, the engine 2 generates power.

[0021] In normal control, in all of the plurality of cylinders, when the piston is located near the bottom dead center, the intake valve is closed, and when the piston is located near the top dead center, fuel injection is executed. The calorific value in the case of the combustion cycle of normal control is less than that of the compression release control described later and more than that of the Miller cycle control described later. Therefore, the engine can be warmed up while suppressing the catalyst temperature from becoming too high before the engine is warmed up.

[0022] In Miller cycle control, the intake valves are operated to reduce the amount of intake air in all cylinders compared to normal control or the compression-release control described later, and the amount of fuel injected is also reduced. Figure 2(b) shows the operation of the combustion cycle in Miller cycle control. In Miller cycle control, as with normal control, air is first introduced into cylinder #1. As the piston descends from top dead center, only the intake valve 11 opens, and air is introduced into cylinder #1 (intake stroke). Next, the piston reaches bottom dead center. Here, unlike normal control, in Miller cycle control, the intake valve 11 does not close when the piston descends to bottom dead center, but closes after the piston begins to rise again towards top dead center. For example, the intake valve 11 closes after the piston has passed a position midway between bottom dead center and top dead center. After that, the piston rises to top dead center with the intake valve 11 and exhaust valve 12 closed. This compresses the air introduced into cylinder #1 (compression stroke). Next, when the piston is at top dead center, fuel is injected into the cylinder by the injector 13. This causes the fuel, mixed with compressed air, to burn, and the expanding combustion gases push the piston down to bottom dead center (combustion stroke). Then, due to inertia and expansion in other cylinders, as the piston rises back up to top dead center, only the exhaust valve 12 is opened, pushing the combustion gases out of cylinder #1 and expelled into the atmosphere as exhaust gas (exhaust stroke). Once the piston has risen to top dead center, the intake valve 11 opens as it descends back down to bottom dead center, and air is introduced into cylinder #1.

[0023] In Miller cycle control, the amount of intake air is reduced in multiple cylinders of engine 2 compared to normal control. For example, as shown in Figure 2(b), a "delayed closing" control is performed during the intake stroke, closing the intake valve 11 later than in normal control or compression release control. Alternatively, the intake valve 11 may be closed midway through the intake stroke. In other words, an "early closing" control may be performed, closing the intake valve 11 earlier than in normal control.

[0024] In Miller cycle control, the amount of intake air to cylinder #1 is reduced compared to normal control, and consequently, the amount of fuel injected into each cylinder is also reduced. For example, as shown in Figure 2(b), the period during which fuel injection is performed may be shortened. By reducing the amount of fuel injected, engine 2 generates power with less fuel. That is, vehicle 1 can run on less fuel, resulting in improved fuel efficiency compared to normal control. On the other hand, although the amount of fuel injected is reduced, the heat capacity decreases as the amount of gas in cylinder #1 decreases, making it easier to maintain the temperature of the exhaust gas due to combustion. Therefore, the catalyst temperature is prevented from falling below the activation temperature and can be maintained at an appropriate temperature.

[0025] Next, we will explain the combustion cycle of compression-release control. In compression-release control, some of the cylinders of engine 2 are selected as selected cylinders to execute the compression-release control combustion cycle. The non-selected cylinders, which are different from the selected cylinders, execute the same combustion cycle as in normal control.

[0026] This section describes the combustion cycle of a selected cylinder under compression-release control. Figure 2(c) shows the operation of the combustion cycle under compression-release control in a selected cylinder. In a selected cylinder under compression-release control, as with normal control, air is first introduced into cylinder #1. As the piston descends from top dead center, only the intake valve 11 opens, and air is introduced into cylinder #1 (intake stroke). Next, when the piston descends to bottom dead center, the intake valve 11 closes, and the piston rises to top dead center with both the intake valve 11 and the exhaust valve 12 closed. This compresses the air introduced into cylinder #1 (compression stroke). Here, in a selected cylinder under compression-release control, unlike normal control, the exhaust valve 12 opens when the piston is at top dead center during the compression stroke. Also, unlike normal control, fuel injection is not performed while the piston is at top dead center. Subsequently, after the piston passes top dead center, the exhaust valve 12 closes again. Then, with the intake valve 11 and exhaust valve 12 closed, the piston descends towards bottom dead center (expansion stroke). Then, due to inertia and expansion in other cylinders, as the piston rises again to top dead center, only the exhaust valve 12 opens, pushing the gas inside cylinder #1 out (exhaust stroke). Once the piston has risen to top dead center, it descends again towards bottom dead center, and the intake valve 11 opens, introducing air into cylinder #1.

[0027] On the other hand, in non-selective cylinders under compression-release control, the combustion cycle is executed in the same way as under normal control. Figure 2(d) shows the operation of 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. As the piston descends from top dead center, only the intake valve 11 opens, and air is introduced into cylinder #1 (intake stroke). Next, when the piston descends to bottom dead center, the intake valve 11 closes, and with the intake valve 11 and exhaust valve 12 closed, the piston rises to top dead center. This compresses the air introduced into cylinder #1 (compression stroke). Subsequently, when the piston is at top dead center, fuel is injected into the cylinder by the injector 13. As a result, the fuel mixed with the compressed air burns, and the expanding combustion gas pushes the piston down to bottom dead center (combustion stroke). Then, due to inertia and expansion in other cylinders, as the piston rises again to top dead center, only the exhaust valve 12 opens, pushing the combustion gases out of cylinder #1 and expelled into the atmosphere as exhaust gas (exhaust stroke). Once the piston rises to top dead center, the intake valve 11 opens as it descends again to bottom dead center, and air is introduced into cylinder #1.

[0028] In compression release control, the selected cylinder is appropriately selected according to the displacement, number of cylinders, rotational speed, and required load of the engine 2. For example, in the case of a four-cylinder engine having cylinders #1, #2, #3, and #4, the combustion cycle shown in Figure 2(c) may be executed with cylinders #1 and #4 as selected cylinders, and the combustion cycle shown in Figure 2(d) may be continued with cylinders #2 and #3 as unselected cylinders. Alternatively, the combustion cycle shown in Figure 2(c) may be executed with cylinders #2 and #3 as selected cylinders, and the combustion cycle shown in Figure 2(d) may be continued with cylinders #1 and #4 as unselected cylinders.

[0029] In compression release control, fuel injection from the injector is stopped in selected cylinders (some of the multiple cylinders), while the fuel injection amount is increased in the non-selected cylinders (those not selected). In compression release control, stopping fuel injection in the selected cylinders reduces output, and increasing the fuel injection amount in the non-selected cylinders compensates for this loss of output. For example, as shown in Figure 2(d), the period during which fuel injection is performed may be extended.

[0030] In the selected cylinder, engine braking is applied. During the compression stroke in the selected cylinder, the air inside the cylinder is compressed. This creates a load that resists the rotation of engine 2. Furthermore, the exhaust valve is opened when the piston is near top dead center, and then closed again after the compressed air is expelled. This causes the pressure inside the cylinder to decrease during the expansion stroke, creating a load that resists engine 2. In the non-selected cylinder, it is necessary to obtain power that exceeds these loads, requiring more fuel injection. Therefore, the heat generated in the non-selected cylinder is greater than in the normal control case, and the exhaust gas temperature is also higher than in the normal control case. In addition, the hot air compressed during the compression stroke is expelled from the selected cylinder. This efficiently increases the exhaust gas temperature and allows the catalyst temperature to rise rapidly.

[0031] The control device 3 obtains the catalyst temperature from the catalyst temperature sensor 4 and the refrigerant temperature from the refrigerant temperature sensor 5. Based on this temperature data, 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.

[0032] Furthermore, the control device 3 may acquire the intake air volume from the intake air volume sensor 6, the engine speed from the rotation speed sensor 7, and the accelerator opening from the accelerator opening sensor 8. Based on this data, the control device 3 may control the operation of the intake valves 11, 21, ..., N1, the exhaust valves 12, 22, ..., N2, and the injectors 13, 23, ..., N3.

[0033] Figure 3 is a flowchart showing how the control device 3 controls the operation of the engine 2 according to the engine control program. The control device 3 obtains the refrigerant temperature from the refrigerant temperature sensor 5 (step S1). The control device 3 also obtains the catalyst temperature from the catalyst temperature sensor 4 (step S2). Then, the control device 3 determines whether the refrigerant 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 warmed-up state. If the refrigerant temperature is below the threshold temperature z, the engine 2 is in a cold state with a low temperature, and if the refrigerant temperature is above the threshold temperature z, the engine 2 is in a warmed-up state with a high temperature. The threshold temperature z is, for example, 100°C.

[0034] If the refrigerant 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 refrigerant 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).

[0035] Here, threshold temperature x is the upper limit temperature at which catalyst heating is required, and threshold temperature y is the lower limit temperature at which catalyst heating is not required. Threshold temperature x is lower than threshold temperature y. Figure 4 shows the relationship between catalyst temperature and catalyst purification rate. The catalyst purification rate follows a curve with respect to catalyst temperature. For example, threshold temperature x is the catalyst temperature at which the catalyst purification rate reaches a predetermined target value, the target purification rate. Threshold temperature y is the temperature at which the catalyst is fully activated and the catalyst purification rate is at its maximum. For example, threshold temperature x is 150°C and threshold temperature y is 300°C. Threshold temperatures x and y can be appropriately determined according to the type and degradation state of the catalyst in engine 2, the number of cylinders and displacement of engine 2, etc.

[0036] If the catalyst temperature in step S4 is greater than or equal to the threshold temperature x (step S4 is YES), the control device 3 performs Miller cycle control (step S6). On the other hand, if the catalyst temperature in step S4 is less than the threshold temperature x (step S4 is NO), the control device 3 performs compression release control (step S8).

[0037] Furthermore, if the catalyst temperature in step S5 is greater than or equal to the threshold temperature y (step S5 is YES), the control device 3 performs normal control (step S7). On the other hand, if the catalyst temperature in step S5 is less than the threshold temperature y (step S5 is NO), the control device 3 performs compression release control (step S8).

[0038] The flowchart above is constantly repeated while the vehicle is running. If the refrigerant temperature or catalyst temperature changes and the judgment result in steps S3 to S5 changes, the control content is changed 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. When transitioning from normal control or Miller cycle control to compression release control, fuel injection is stopped for the selected cylinder and the fuel injection amount is increased for the non-selected cylinders before the transition. When transitioning from compression release control to normal control or Miller cycle control, fuel injection is restarted for the selected cylinder and the fuel injection amount is reduced for the non-selected cylinders after the transition. This prevents the exhaust of fuel that was not burned during compression release control and suppresses torque fluctuations caused by sudden changes in fuel injection amount.

[0039] Figure 5 shows the criteria for determining whether to perform Miller cycle control, compression release control, or normal control depending on the refrigerant temperature and catalyst temperature. Miller cycle control is performed when the refrigerant temperature is above the threshold temperature z, which is the lower limit temperature indicating that the engine is warmed up, and the catalyst temperature is above the threshold temperature x, which is the upper limit temperature indicating that the catalyst needs to be heated up. Compression release control is performed when the refrigerant temperature is above the threshold temperature z and the catalyst temperature is below the threshold temperature x.

[0040] When the refrigerant temperature is above the threshold temperature z and the catalyst temperature is above the threshold temperature x, the engine 2 is warmed up and does not need to be heated any further, and the catalyst temperature has reached the threshold temperature x and does not need to be heated any further. Therefore, Miller cycle control suppresses the amount of heat generated by the engine 2 while suppressing the decrease in exhaust gas temperature and appropriately controlling the catalyst temperature.

[0041] When the refrigerant temperature is above the threshold temperature z and the catalyst temperature is below the threshold temperature x, the engine 2 is warmed up, but the catalyst temperature has not reached the threshold temperature x. Therefore, the exhaust gas temperature is increased by compression release control, which generates a large amount of heat, and the catalyst temperature is raised.

[0042] Normal control is performed when the refrigerant temperature is below the threshold temperature z and the catalyst temperature is above the threshold temperature y, which is the lower limit temperature indicating that catalyst heating is unnecessary. Furthermore, compression release control is performed when both the refrigerant temperature is below the threshold temperature z and the catalyst temperature is below the threshold temperature y.

[0043] When the refrigerant temperature is below the threshold temperature z and the catalyst temperature is above the threshold temperature y, it is not necessary to warm up the engine 2 or raise the catalyst temperature. Therefore, by using normal control to generate more heat from the engine 2 than in Miller cycle control but less than in compression release control, the engine 2 is warmed while the exhaust gas temperature is maintained and the catalyst temperature is appropriately controlled.

[0044] When the refrigerant temperature is below the threshold temperature z and the catalyst temperature is below the threshold temperature y, it is necessary to warm up the engine 2 and raise the catalyst temperature. Therefore, the amount of heat generated by the compression release control, which generates a large amount of heat, is increased to warm up the engine 2, while the exhaust gas temperature is raised to raise the catalyst temperature.

[0045] As a result, the operation of engine 2 is controlled based on the refrigerant temperature and catalyst temperature to control the exhaust gas temperature, thereby enabling appropriate control of the catalyst temperature and engine temperature, and allowing for the proper decomposition and removal of harmful substances in the exhaust gas.

[0046] Figure 6 is a flowchart of another example of the operation of the control device 3. The control device 3 obtains the refrigerant temperature from the refrigerant temperature sensor 5 (step S11). The control device 3 also obtains the catalyst temperature from the catalyst temperature sensor 4 (step S12). Then, the control device 3 determines whether the refrigerant temperature is above a predetermined threshold temperature z (step S13). Here, the threshold temperature z is the temperature that indicates the warmed-up state of the engine 2.

[0047] If the refrigerant 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 temperature indicating that the catalyst needs to be heated. On the other hand, if the refrigerant 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 temperature indicating that the catalyst does not need to be heated, and is a higher value than the threshold temperature x.

[0048] If the catalyst temperature is above the threshold temperature x in step S14 (step S14 is YES), the control device 3 obtains the rotational speed of the engine 2 from the rotational speed sensor 7 and calculates the requested output (engine load) based on the accelerator opening obtained from the accelerator opening sensor 8 (step S16). If the rotational speed of the engine 2 and the requested output match the execution conditions for Miller cycle control (step S18 is YES), the control device 3 drives the engine 2 using Miller cycle control (step S19). For example, Miller cycle control is executed when the rotational speed is below a predetermined rotational speed and the requested output is below a predetermined requested output. On the other hand, if the rotational speed of the engine 2 and the requested output do not match the execution conditions for Miller cycle control (step S18 is NO), the control device 3 drives the engine 2 using normal control (step S20).

[0049] In Miller cycle control, the intake air volume is reduced, so there are upper limits on the rotational speed and requested power output. Therefore, in step S18, it is determined whether the rotational speed and requested power output are suitable for Miller cycle control. The specific values ​​of the predetermined rotational speed and predetermined requested power output can be appropriately determined according to the number of cylinders and displacement of engine 2.

[0050] On the other hand, if 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 and the rotational speed of the engine 2 from the rotational speed sensor 7, and calculates the requested output (engine load) based on the accelerator opening obtained from the accelerator opening sensor 8 (step S17). If the intake air volume, the rotational speed of the engine 2, and the requested output meet the execution conditions for compression release control (step S21 is YES), the control device 3 drives the engine 2 by compression release control (step S22). For example, Miller cycle control is executed when the rotational speed is less than a predetermined rotational speed, the requested output is less than a predetermined requested output, and the intake air volume is a predetermined intake air volume. On the other hand, if the intake air volume, the rotational speed of the engine 2, and the requested output do not meet the execution conditions for compression release control (step S21 is NO), the control device 3 drives the engine 2 by normal control (step S20).

[0051] In compression release control, fuel injection is stopped for some cylinders, and fuel injection is performed only for the remaining cylinders. Reducing the number of cylinders that receive fuel injection makes vibrations more likely, so it is not suitable for low-speed operation. Also, if the intake air volume is insufficient, the required power output may not be achieved. Therefore, in step S21, it is determined whether the intake air volume, engine speed 2, and required power output are suitable for compression release control. The specific values ​​for the predetermined intake air volume, predetermined engine speed, and predetermined required power output can be appropriately determined according to the number of cylinders and displacement of engine 2, etc.

[0052] If 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, if 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 and the rotational speed of the engine 2 from the rotational speed sensor 7, and calculates the requested output (engine load) based on the accelerator opening obtained from the accelerator opening sensor 8 (step S17). Then, if the intake air volume, the rotational speed of the engine 2 and the requested output match the execution conditions for compression release control (step S21 is YES), the control device 3 drives the engine 2 by compression release control (step S22), and if they do not match (step S21 is NO), the control device 3 drives the engine 2 by normal control (step S20).

[0053] As a result, in addition to the refrigerant temperature and catalyst temperature, the engine 2 is controlled based on the intake air volume, engine speed 2, and required output (engine load) to control the exhaust gas temperature. This allows Miller cycle control and compression release control to be performed under appropriate conditions, enabling proper control of the catalyst temperature and engine temperature, and allowing for proper decomposition and removal of harmful substances in the exhaust gas. [Industrial applicability]

[0054] The vehicle described herein is widely applicable in the automotive industry. In particular, it is useful in areas where optimal control of catalyst temperature is required in engine exhaust gas purification systems. [Explanation of Symbols]

[0055] 1 vehicle 2 engines 3. Control device 4. Catalyst temperature sensor 5. Refrigerant temperature sensor 6. Intake air volume sensor 7. Rotation speed sensor 8. Accelerator position sensor 11, 21, N1 Intake Valve 12, 22, N2 Exhaust Valve 13, 23, N3 Injector

Claims

1. An engine control device that controls the engine, If the catalyst temperature of the catalyst that purifies the exhaust gas of the engine is below a first threshold temperature, compression release control is performed to stop fuel injection from the injectors in selected cylinders, which are some of the cylinders among the multiple cylinders of the engine, and to increase the fuel injection amount in non-selected cylinders that are different from the selected cylinders. If the catalyst temperature is above the first threshold temperature, Miller cycle control is performed to operate the intake valves to reduce the intake air amount in all of the plurality of cylinders compared to when the temperature is below the first threshold temperature, thereby reducing the fuel injection amount. Engine control device.

2. If the refrigerant temperature of the refrigerant circulating inside the refrigerant circuit that cools the engine is above the second threshold temperature and the catalyst temperature is below the first threshold temperature, the compression release control is executed. If the refrigerant temperature is equal to or greater than the second threshold temperature and the catalyst temperature is equal to or greater than the first threshold temperature, the Miller cycle control is executed. If the refrigerant temperature is less than the second threshold temperature and the catalyst temperature is less than a third threshold temperature greater than the first threshold temperature, the compression release control is executed. If the refrigerant temperature is below the second threshold temperature and the catalyst temperature is above the third threshold temperature, then normal control is performed in all of the plurality of cylinders, closing the intake valve when the piston is near bottom dead center and injecting fuel when the piston is near top dead center. The engine control device according to claim 1.

3. In the compression release control described above, 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. The engine control device according to claim 1 or 2.

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

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

6. In the Miller cycle control described above, during the intake stroke, a control is performed in which the intake valve is closed later than the compression release control. The engine control device according to claim 1 or 2.

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

8. A vehicle having the engine control device described in claim 1 or 2.

9. In the computer that controls the engine, If the catalyst temperature of the catalyst that purifies the exhaust gas of the engine is below a first threshold temperature, a compression release control is performed which stops fuel injection from the injector in selected cylinders, which are some of the cylinders among the multiple cylinders of the engine, and increases the fuel injection amount in non-selected cylinders that are different from the selected cylinders. If the catalyst temperature is above the first threshold temperature, Miller cycle control is performed to operate the intake valves to reduce the intake air amount in all of the multiple cylinders compared to when the temperature is below the first threshold temperature, thereby reducing the fuel injection amount. Engine control program.

10. An engine control method, If the catalyst temperature of the catalyst that purifies the exhaust gas of the engine is below a first threshold temperature, the engine performs compression release control, which involves stopping fuel injection from the injectors in selected cylinders (some of the multiple cylinders of the engine) and increasing the fuel injection amount in non-selected cylinders (other than the selected cylinders). If the catalyst temperature is above the first threshold temperature, the intake valve is operated to reduce the amount of intake air in all of the plurality of cylinders compared to when the temperature is below the first threshold temperature, and Miller cycle control is performed to reduce the amount of fuel injection. An engine control method including...

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