JP2021025493A - Engine system - Google Patents

Abstract

To provide an engine system capable of retaining the state that a catalyst is activated.SOLUTION: The engine system selects a heat insulation mode when a selective reduction type catalyst is in an activated state and the temperature of exhaust gas flowing into the selective reduction type catalyst is lower than a heat insulation possible temperature. In the heat insulation mode, an engine system control device executes heat insulation exhaust operation made by delaying normal intake operation for an intake valve, and executes heat insulation exhaust operation for the exhaust valve, which is composed of first temperature rise exhaust operation made by advancing normal exhaust operation, and second heat insulation exhaust operation having a smaller maximum lift amount and a shorter valve opening period than those of the first heat insulation exhaust operation, while a valve opening period for the second heat insulation exhaust operation overlaps with a valve opening period for the heat insulation intake operation.SELECTED DRAWING: Figure 6

Description

The present invention relates to an engine system.

For example, as in Patent Document 1, an engine system using an engine is equipped with an exhaust purification device having a catalyst that adds a reducing agent to the exhaust gas and reduces NOx of the exhaust gas by using the added reducing agent. Has been done.

Japanese Unexamined Patent Publication No. 2019-007351

In the exhaust gas purification device described above, it is preferable that the catalyst is maintained in an activated state. An object of the present invention is to provide an engine system capable of maintaining an activated state of a catalyst.

The engine system that solves the above problems includes an engine having an exhaust valve and an intake valve that can change the opening / closing timing of opening and closing the combustion chamber separately, an exhaust purification device having a catalyst that purifies the exhaust gas from the engine, and the like. An engine system including a control device for controlling the engine, wherein the control device is an exhaust gas temperature which is a required torque from a driver, a state of the catalyst, and an exhaust gas temperature flowing into the catalyst. A fuel injection amount control unit that controls the fuel injection amount to the engine so that the output torque of the engine becomes the required torque, and a mode selection unit that selects the control mode of the engine system. The mode selection unit includes a valve control unit that controls the opening and closing of the exhaust valve and the opening and closing of the intake valve, and the mode selection unit is such that the catalyst is in an active state and the exhaust gas temperature is equal to or higher than a heat-retainable temperature. Sometimes, the normal mode is selected as the control mode, and when the catalyst is in the active state and the exhaust gas temperature is lower than the heat retention possible temperature, the heat retention mode is selected as the control mode, and in the heat retention mode. The valve control unit executes a heat-retaining intake operation in which the normal intake operation in the normal mode is retarded, a first heat-retaining exhaust operation in which the normal exhaust operation in the normal mode is advanced, and an opening / closing in the suction stroke. The second heat-retaining exhaust operation, which has a smaller maximum lift amount and a shorter valve opening period than the first heat-retaining exhaust operation, is composed of, and at least a part of the valve opening period of the second heat-retaining exhaust operation is the heat-retaining operation. A heat-retaining exhaust operation that overlaps with the valve opening period of the intake operation is performed.

According to the above configuration, in the heat retention mode, the amount of air taken in by the engine is reduced by the heat retention intake operation in which the normal intake operation is retarded. Therefore, the exhaust temperature, which is the temperature of the exhaust gas emitted by the engine, can be raised as compared with the normal mode. In addition, the first heat-retaining exhaust operation can supply exhaust gas having a higher enthalpy than the normal mode to the exhaust purification device. Further, since the heat retention intake operation and the second heat retention exhaust operation overlap, the exhaust gas is sucked into the engine by the second heat retention exhaust operation. Therefore, the discharge temperature can be raised as compared with the normal mode. That is, according to the above configuration, the exhaust energy supplied to the exhaust purification device is increased as compared with the normal mode, and the catalyst can be kept in the active state.

In the engine system having the above configuration, it is preferable that the entire valve opening period of the second heat insulating exhaust operation overlaps with the valve opening period of the heat insulating intake operation. According to the above configuration, the mixing degree of air and exhaust gas can be effectively increased in the engine.

In the engine system having the above configuration, it is preferable that the mode selection unit selects the heat retention mode when the load of the engine is in a light load state.
Since the exhaust gas temperature is the temperature of the exhaust gas flowing into the catalyst, there is a delay in response to changes in engine output. According to the above configuration, even if the exhaust gas temperature is lower than the heat retention temperature, the heat retention mode is selected when the engine load is larger than the light load, that is, when the exhaust gas temperature is expected to rise immediately. It can be avoided.

In the engine system having the above configuration, the heat-retaining intake operation is an opening / closing operation in which the normal intake operation is retarded by 40 ° CA to 75 ° CA, and the first heat-retaining exhaust operation is a 30 ° CA of the normal exhaust operation. It is preferable that the opening / closing operation is advanced by about 40 ° CA. According to the above configuration, it is possible to increase the exhaust energy supplied to the exhaust purification device while effectively suppressing the increase in fuel consumption.

The figure which shows the schematic structure of one Embodiment of an engine system. The figure which shows an example of the cross-sectional structure of an engine in the vicinity of a cylinder schematically. A functional block diagram showing an example of the functional configuration of an engine system. The flowchart which shows an example of a mode selection process. The figure which shows an example of the relationship between the crank angle and a lift amount of a normal exhaust operation and a temperature rise exhaust operation. The figure which shows an example of the relationship between a crank angle and a lift amount for each opening and closing operation in a normal mode and a heat retention mode. (A) A diagram showing an example of the result of a simulation performed on fuel consumption in the heat retention mode, and (b) a diagram showing an example of the result of a simulation performed on the exhaust gas temperature in the heat retention mode. The figure which shows an example of the result of the simulation performed about the temperature raising effect by the 2nd heat insulation exhaust operation. In the modified example, the figure which shows another example of the relationship between a crank angle and a lift amount for each opening and closing operation in a normal mode and a heat retention mode.

An embodiment of the engine system will be described with reference to FIGS. 1 to 8. First, a schematic configuration of the engine system will be described with reference to FIG.
As shown in FIG. 1, the engine system includes a diesel engine 10 (hereinafter referred to as an engine 10). The engine 10 includes an engine block 12 having a plurality of cylinders 11. Fuel is injected into each cylinder 11 from an injector 13 to which fuel of a predetermined pressure is supplied from a common rail. The intake manifold 14 and the exhaust manifold 15 are connected to the engine block 12. An intake passage 16 through which air taken in by the engine 10 flows is connected to the intake manifold 14, and an exhaust passage 17 through which the exhaust gas discharged by the engine 10 flows is connected to the exhaust manifold 15.

As shown in FIG. 2, the engine block 12 has a cylinder block 12A in which the cylinder 11 is formed and a cylinder head 12B connected to the cylinder block 12A. The cylinder head 12B closes the opening of the cylinder 11 formed in the cylinder block 12A. The engine 10 has a piston 20 housed so as to be vertically movable with respect to each cylinder 11. The space surrounded by the cylinder block 12A, the cylinder head 12B, and the piston 20 is a combustion chamber 21 in which the injector 13 injects fuel and the fuel is burned. The piston 20 is connected to the crankshaft 23 shown in FIG. 1 via a connection rod 22. The crankshaft 23 is rotationally driven by the piston 20 moving up and down in the cylinder 11. In the cylinder head 12B, an intake port 25 connected to the intake manifold 14 and an exhaust port 26 connected to the exhaust manifold 15 are formed for each cylinder 11.

The engine 10 has an intake valve 27 and an exhaust valve 28. The intake valve 27 is driven by the intake side valve mechanism 29, and opens and closes the combustion chamber 21 with respect to the intake manifold 14 by opening and closing the intake port 25. The exhaust valve 28 is driven by the exhaust side valve mechanism 30, and opens and closes the exhaust port 26 to open and close the combustion chamber 21 with respect to the exhaust manifold 15. The valve operating mechanisms 29 and 30 are variable valve mechanisms configured so that the lift amount and opening / closing timing of the valve to be driven can be changed. Each valve mechanism 29, 30 may be a cam switching type variable valve mechanism, or may be a variable valve mechanism whose lift amount and opening / closing timing can be changed by an electronically controlled actuator.

As shown in FIG. 1, the engine system includes a turbocharger 35. The turbocharger 35 has a compressor 36, an intercooler 37, and a turbine 38. The compressor 36 and the intercooler 37 are arranged in the intake passage 16. The compressor 36 compresses the air that has passed through the air cleaner 39, and the intercooler 37 cools the air compressed by the compressor 36. The turbine 38 is arranged in the exhaust passage 17. The turbine 38 uses the exhaust energy, which is the energy of the exhaust gas, to rotate the compressor 36.

The engine system includes an EGR (Exhaust Gas Recirculation) device 40. The EGR device 40 is configured to be able to execute an external EGR that recirculates exhaust gas from the exhaust side to the intake side through the EGR passage 41 that connects the exhaust manifold 15 and the intake passage 16. The EGR passage 41 is provided with an EGR cooler 42 and an EGR valve 43. When the EGR valve 43 is in the open state, a mixed gas of EGR gas and intake air is supplied to the cylinder 11 as a working gas. When the EGR valve 43 is in the closed state, intake air is supplied to the cylinder 11 as a working gas. In the cylinder 11, the air-fuel mixture of the working gas and the fuel injected by the injector 13 burns. The exhaust gas from the cylinder 11 flows into the exhaust passage 17 through the exhaust manifold 15 and then flows into the turbine 38. The ratio of EGR gas to the working gas sucked by the engine 10 is called the EGR rate.

The engine system includes an exhaust gas purification device 45. Exhaust gas that has passed through the turbine 38 flows into the exhaust purification device 45. The exhaust gas purification device 45 has an addition unit 46 and a selective reduction catalyst 47. The selective reduction catalyst 47 is housed in the enlarged diameter portion 17A constituting the exhaust passage 17.

The adding unit 46 adds a reducing agent to the exhaust gas flowing into the enlarged diameter portion 17A. The addition unit 46 includes a reducing agent passage 49 connected to a tank 48 for storing the reducing agent. A pump 50 is arranged in the reducing agent passage 49. The pump 50 pumps the reducing agent in the tank 48 to the addition valve 51 at a predetermined pressure. The addition valve 51 is an electronically controlled injection valve having a built-in valve mechanism, and adds a reducing agent to the exhaust gas when the valve mechanism is in the open state.

The selective reduction catalyst 47 reduces NOx contained in the exhaust gas to nitrogen and water by using the reducing agent added by the addition unit 46. The selective reduction catalyst 47 is, for example, a flow-through type monolith carrier made of ceramic or stainless steel having excellent heat resistance, in which various catalyst metals are held. The selective reduction catalyst 47 is in an active state when the catalyst temperature Tc, which is the temperature thereof, is within a predetermined temperature range. The lower limit of this temperature range is the lower limit active temperature TcL.

An example of the selective reduction catalyst 47 is a urea SCR catalyst. In this case, the addition unit 46 adds urea water as a reducing agent, and the selective reduction catalyst 47 reacts ammonia obtained by hydrolyzing urea water with NOx contained in the exhaust gas to reduce NOx to nitrogen or water. .. The selective reduction catalyst 47 is configured by allowing the monolith carrier to hold various catalyst metals such as copper-based, iron-based, and vanadium-based. The selective reduction catalyst 47 has, for example, a temperature range of 150 ° C. to 350 ° C. as an active temperature.

The exhaust purification device 45 has a filter for capturing particulate matter contained in the exhaust gas, a pre-stage oxidation catalyst for oxidizing unburned fuel contained in the exhaust gas, and the like upstream of the addition valve 51 in the exhaust passage 17. You may have. Further, the exhaust purification device 45 may have a post-stage oxidation catalyst or the like that oxidizes ammonia or the like contained in the exhaust gas that has passed through the selective reduction catalyst 47 downstream of the selective reduction catalyst 47 in the exhaust passage 17. .. Further, the exhaust gas purification device 45 may include, as the selective reduction catalyst 47, a catalyst that reduces NOx using light oil as a fuel of the engine 10 as a reducing agent, a so-called HC-SCR catalyst.

The engine system has an exhaust throttle valve 52 between the add-on valve 51 and the turbine 38 of the turbocharger 35. The exhaust throttle valve 52 is configured so that the cross-sectional area of the flow path of the exhaust passage 17 can be changed. The exhaust throttle valve 52 functions as an exhaust brake, which is one of the auxiliary brakes, by reducing the cross-sectional area of the flow path of the exhaust passage 17 and increasing the exhaust resistance. The auxiliary brake is configured to operate when the driver-operable actuation switch S is in the on state. The operation switch S outputs an operation signal indicating an operation status to the control device 60.

The engine system is equipped with various sensors. The engine system includes a crank angle sensor 55, a catalyst temperature sensor 56, an accelerator opening sensor 57, an exhaust gas temperature sensor 58, and a vehicle speed sensor 59. The crank angle sensor 55 detects the crank angle, which is the rotation angle of the crankshaft 23 driven by the engine 10. The catalyst temperature sensor 56 detects the catalyst temperature Tc, which is the temperature of the selective reduction catalyst 47. The accelerator opening sensor 57 detects the accelerator opening ACC based on the amount of depression of the accelerator pedal 57a operated by the driver. The exhaust gas temperature sensor 58 detects the exhaust gas temperature Tex, which is the temperature of the exhaust gas flowing into the selective reduction catalyst 47. The vehicle speed sensor 59 detects the vehicle speed v, which is the speed of the vehicle. The various sensors output signals indicating the detected values to the control device 60 that controls the engine system in an integrated manner.

The control device 60 will be described with reference to FIGS. 3 to 6. The control device 60 can be configured as a circuit including one or more dedicated hardware circuits such as an ASIC, one or more processors operating according to a computer program (software), or a combination thereof. The processor includes a CPU and a memory such as a RAM and a ROM, and the memory stores a program code or an instruction configured to cause the CPU to execute a process. Memory or computer-readable media includes any available medium accessible by a general purpose or dedicated computer.

As shown in FIG. 3, the control device 60 has an acquisition unit 61, a mode selection unit 62, a fuel injection control unit 63, an EGR control unit 64, an addition control unit 65, and a valve as functional units that function by executing various computer programs. It has a control unit 66 and an exhaust brake control unit 70.

The acquisition unit 61 acquires various information through an input interface (not shown). The acquisition unit 61 acquires the crank angle based on the detection signal output by the crank angle sensor 55. The acquisition unit 61 acquires the catalyst temperature Tc as the state of the selective reduction catalyst 47 based on the detection signal output by the catalyst temperature sensor 56. The acquisition unit 61 acquires the accelerator opening ACC based on the detection signal output by the accelerator opening sensor 57. The acquisition unit 61 calculates the engine speed Ne based on the amount of change in the crank angle, and acquires the required torque L from the driver based on the calculated engine speed Ne and the accelerator opening ACC. The acquisition unit 61 acquires the exhaust gas temperature Tex based on the detection signal output by the exhaust gas temperature sensor 58. The acquisition unit 61 acquires the vehicle speed v based on the detection signal output by the vehicle speed sensor 59. The acquisition unit 61 acquires the operation status of the operation switch S based on the operation signal from the operation switch S.

The mode selection unit 62 selects the control mode of the engine system. The mode selection unit 62 describes the fuel injection by the injector 13, the intake operation of the intake valve 27, the exhaust operation of the exhaust valve 28, the operation of the exhaust throttle valve 52, and the like, based on various information acquired by the acquisition unit 61. Executes the mode selection process to select the control mode. The mode selection unit 62 selectively selects the control mode from the temperature rise mode, the heat retention mode, the brake mode, and the normal mode through the mode selection process. The temperature raising mode is a control mode in which the exhaust energy supplied to the exhaust purification device 45 is increased to prioritize the temperature rise of the selective reduction catalyst 47. The heat retention mode is a control mode for holding the catalyst temperature Tc of the selective reduction catalyst 47 at or above the lower limit active temperature TcL. The brake mode is a control mode in which the opening and closing of the intake valve 27 and the exhaust valve 28 are controlled to generate a braking force. The normal mode is a control mode that prioritizes purification of exhaust gas and reduction of fuel consumption.

The mode selection process executed by the mode selection unit 62 will be described with reference to FIG.
As shown in FIG. 4, in the mode selection process, the mode selection unit 62 determines whether or not the catalyst temperature Tc acquired by the acquisition unit 61 is equal to or higher than the lower limit active temperature TcL (step S201).

When the catalyst temperature Tc is less than the lower limit active temperature TcL (step S201: NO), in the mode selection unit 62, for example, the engine load EL based on the required torque L and the engine speed Ne is equal to or less than the temperature rise selection load EL1. Whether or not it is determined (step S202). The temperature rise selective load EL1 is set to a value at which unburned fuel contained in the exhaust gas can be suppressed even if the fuel injection amount is increased, and the torque L required from the driver can be realized. The temperature rise selective load EL1 is set based on the results of experiments and simulations performed in advance. The temperature rise selective load EL1 is preferably set from a value of, for example, 20% or less, and one example thereof is 15%. When the engine load EL is equal to or less than the temperature rise selection load EL1 (step S202: YES), the mode selection unit 62 selects the temperature rise mode (step S203) and temporarily ends a series of processes.

In step S201, when the catalyst temperature Tc is equal to or higher than the lower limit active temperature TcL (step S201: YES), the mode selection unit 62 determines whether or not the exhaust gas temperature Tex acquired by the acquisition unit 61 is the heat retention temperature Tex1 or higher. Is determined (step S204). The heat-retainable temperature Tex1 is a temperature at which it is highly likely that the catalyst temperature Tc will drop to the lower limit active temperature TcL when exhaust gas having a temperature lower than that temperature is supplied to the selective reduction catalyst 47 for a predetermined period. Is. The heat-retainable temperature Tex1 is set to be, for example, a value equal to or higher than the lower limit active temperature TcL, and the lower the detection value of the outside air temperature sensor that detects the outside air temperature as one of the various sensors provided in the engine system, the higher the temperature. You may. As the outside air temperature becomes lower, the heat-retaining temperature Tex1 becomes higher, so that an appropriate heat-retaining temperature Tex1 can be set according to the traveling environment at that time. As a result, it is more reliably suppressed that the catalyst temperature Tc drops to the lower limit active temperature TcL.

When the exhaust gas temperature Tex is less than the heat-retaining temperature Tex1 (step S204: NO), the mode selection unit 62 determines whether or not the engine load EL is the heat-retaining selective load EL2 or less (step S205). The heat retention selective load EL2 is a value at which the engine load EL is determined to be a light load, for example, in an idling state. The heat retention selective load EL2 is set to a value lower than that of the temperature rise selective load EL1. When the engine load EL is equal to or less than the heat retention selective load EL2 (step S205: YES), the mode selection unit 62 selects the heat retention mode (step S206) and temporarily ends a series of processes. That is, in the heat retention mode, the exhaust gas temperature Tex is in a state where the catalyst temperature Tc is likely to reach the lower limit active temperature TcL (step S204: NO), and the engine load EL is in a light load, so that the exhaust gas is exhaust gas. This mode keeps the catalyst temperature Tc at a temperature higher than the lower limit active temperature TcL in a state where the temperature Tex is unlikely to rise (step S205: YES).

On the other hand, when the exhaust gas temperature Tex is the heat-retainable temperature Tex1 or more (step S204: YES), the mode selection unit 62 determines whether or not the accelerator opening ACC acquired by the acquisition unit 61 is 0% or more. (Step S207).

When the accelerator opening ACC is less than 0% (step S207: NO), that is, when the required torque L is at the deceleration required torque requiring deceleration, does the mode selection unit 62 satisfy the operating conditions of the auxiliary brake? It is determined whether or not (step S208). The operating condition is that when the accelerator opening ACC is less than 0%, the operating switch S is in the ON state and the vehicle speed v is equal to or higher than the operating speed v1. The operating speed v1 is set to a vehicle speed v on which the braking force of the auxiliary brake effectively acts. An example of the operating speed v1 is 30 km / h.

When the operating condition is satisfied (step S208: YES), the mode selection unit 62 selects the brake mode (step S209) and temporarily ends a series of processes. In the brake mode, the control device 60 controls the intake side valve mechanism 29 and the exhaust side valve mechanism 30 so that the compression release brake, which is one of the auxiliary brakes, operates. Further, the control device 60 controls the exhaust throttle valve 52 in the closing direction so that the exhaust brake, which is one of the auxiliary brakes, operates.

On the other hand, when the accelerator opening ACC is 0% or more (step S207: YES), the engine load EL is not less than or equal to the temperature rise selection load EL1 (step S202: NO), and the engine load EL is not less than or equal to the heat retention selection value EL2. (Step S205: NO), if the operating condition of the auxiliary brake is not satisfied (step S208: NO), the mode selection unit 62 selects the normal mode (step S210) and temporarily ends a series of processes.

As shown in FIG. 3, the fuel injection control unit 63 controls fuel injection by each injector 13 by outputting a control signal through an output interface (not shown). The fuel injection control unit 63 controls fuel injection by each injector 13 based on the accelerator opening ACC and engine speed Ne acquired by the acquisition unit 61, the control mode selected by the mode selection unit 62, and the like. The fuel injection control unit 63 holds a fuel map in which the fuel injection amount is defined for each accelerator opening degree ACC and engine speed Ne in a predetermined area of the memory. The fuel injection control unit 63 provides a normal map 67 which is a fuel map used in the normal mode, a temperature rise map 68 which is a fuel map used in the temperature rise mode, and a heat retention map 69 which is a fuel map used in the heat retention mode. It is held in a predetermined area of memory. The fuel injection control unit 63 controls the fuel injection amount by using the fuel map corresponding to the control mode selected by the mode selection unit 62. The fuel injection control unit 63 executes fuel cut control for temporarily stopping fuel injection according to the engine speed Ne in the brake mode in which the required torque L is the deceleration required torque.

The EGR control unit 64 controls the opening degree of the EGR device 40, specifically, the EGR valve 43, by outputting a control signal through an output interface (not shown). The EGR control unit 64 controls the EGR valve 43 based on the control mode selected by the mode selection unit 62, and controls the amount of EGR, which is the amount of EGR gas. When the control mode is the normal mode, the EGR control unit 64 controls the opening degree of the EGR valve 43 so that the exhaust gas is recirculated by the amount of EGR suitable for the operating state of the engine 10 at that time. When the control mode is any of the temperature rise mode, the heat retention mode, and the brake mode, the EGR control unit 64 prohibits the external EGR by keeping the EGR valve 43 in the closed state.

The addition control unit 65 controls the opening and closing of the addition unit 46 of the exhaust gas purification device 45, specifically, the addition valve 51, by outputting a control signal through an output interface (not shown). The addition control unit 65 controls the addition amount and addition timing of urea water by the addition valve 51 based on the control mode selected by the mode selection unit 62. When the control mode is one of the normal mode, the heat retention mode, and the brake mode, the addition control unit 65 adds the addition valve 51 so that an amount of urea water suitable for the operating state of the engine 10 at that time is added. Control the opening and closing of. When the control mode is the temperature rise mode, the addition control unit 65 prohibits the addition of urea water by keeping the addition valve 51 in a closed state.

The valve control unit 66 controls the opening / closing operation of the intake valve 27 through the intake side valve mechanism 29 by outputting a control signal through an output interface (not shown), and also controls the opening / closing operation of the exhaust valve 28 through the exhaust side valve mechanism 30. To control. The valve control unit 66 controls the lift amount and the opening / closing timing of each of the intake valve 27 and the exhaust valve 28 based on the control mode selected by the mode selection unit 62.

The valve control unit 66 causes the intake valve 27 to perform a normal intake operation in the normal mode, a temperature rise intake operation in the temperature rise mode, a heat retention intake operation in the heat retention mode, and a brake intake operation in the brake mode. The valve control unit 66 causes the exhaust valve 28 to perform a normal exhaust operation in the normal mode, a temperature rise exhaust operation in the temperature rise mode, a heat retention exhaust operation in the heat retention mode, and a brake exhaust operation in the brake mode.

The exhaust brake control unit 70 controls the exhaust throttle valve 52. The exhaust brake control unit 70 controls the exhaust throttle valve 52 to the operating state when the control mode is in the brake mode, and controls the exhaust throttle valve 52 to the non-operating state when the control mode is different from the brake mode.

The opening / closing operation of the intake valve 27 and the exhaust valve 28 in the normal mode, the temperature rising mode, and the heat retention mode will be described with reference to FIGS. 5 and 6. The crank angles shown in FIGS. 5 and 6 indicate the crank angles based on the compression top dead center (= 0 ° CA), which is the top dead center of the compression stroke. In addition, the description in parentheses shown below indicates the crank angle shown in each figure.

As shown in FIG. 5, in the normal exhaust operation, the valve is opened shortly before reaching the expansion bottom dead center (= 180 ° CA), which is the bottom dead center of the expansion stroke, and the exhaust is on the exhaust, which is the top dead center of the exhaust stroke. It is an opening / closing operation that closes the valve near the dead center (= 360 ° CA). Further, the normal intake operation is an opening / closing operation in which the valve is opened immediately before reaching the exhaust top dead center (= 360 ° CA), which is the top dead center of the exhaust stroke, and is closed in the first half of the compression stroke.

The temperature-increasing exhaust operation is composed of a first temperature-heating exhaust operation that opens the valve during the expansion stroke and a second temperature-heating exhaust operation that opens the valve after a valve closing period that is at least partly included in the exhaust stroke. An example of the temperature raising intake operation is the normal intake operation.

The first temperature-rising exhaust operation is an exhaust operation in which the maximum lift amount is larger and the valve opening period is longer than that of the second temperature-heating exhaust operation. The first temperature rising exhaust operation is an opening / closing operation in which the valve opening time is earlier and the valve opening period is shorter than the normal exhaust operation. For example, the first temperature rising exhaust operation is set to less than half of the normal exhaust operation for each of the maximum lift amount and the valve opening period. The first heating / exhausting operation is an opening / closing operation in which the valve is opened 40 ° CA or later after the compression top dead center and closed in the expansion stroke. The second temperature rising exhaust operation is an opening / closing operation in which the valve is opened in the latter half of the exhaust stroke. For example, each of the maximum lift amount and the valve opening period is set to half or less of the first temperature rising exhaust operation.

As shown in FIG. 6, the heat-retaining exhaust operation is composed of a first heat-retaining exhaust operation in which the normal exhaust operation is advanced and a second heat-retaining exhaust operation that opens and closes in the suction stroke. The first heat-retaining exhaust operation is an opening / closing operation in which a part of the exhaust gas is discharged to the exhaust manifold 15 in the expansion stroke. The first heat-retaining exhaust operation is an opening / closing operation in which the normal exhaust operation is advanced.

The second heat-retaining exhaust operation is an opening / closing operation that opens / closes in the suction stroke, and is an opening / closing operation that introduces a part of the exhaust gas in the exhaust manifold 15 into the cylinder 11, that is, an opening / closing operation that performs internal EGR. The second heat-retaining exhaust operation is an opening / closing operation in which the maximum lift amount is smaller than that of the first heat-retaining exhaust operation and the valve opening period is short. The second heat-retaining exhaust operation is an opening / closing operation in which the valve opening period overlaps with the valve opening period of the heat-retaining intake operation. "The valve opening periods overlap" means that the valves are opened at the same time. In the second heat-retaining exhaust operation, the entire valve opening period overlaps with the valve opening period of the heat-retaining intake operation. The heat-retaining intake operation is an opening / closing operation in which the normal intake operation is retarded. The heat-retaining intake operation is an opening / closing operation in which the valve is opened in the suction stroke and closed in the compression stroke.

The operation of the engine system described above will be described.
Since the exhaust valve 28 has a valve opening period in the expansion stroke, a part of the exhaust gas in the combustion chamber 21 becomes a choked flow and flows out to the exhaust port 26 without pressing the piston 20. Therefore, an output loss (hereinafter referred to as an outflow loss) is generated in the engine 10 by the amount of the exhaust gas flowing out from the combustion chamber 21. Further, the exhaust gas remaining in the combustion chamber 21 at the end of the valve opening period is compressed by the piston 20 in the exhaust stroke. This causes an output loss (hereinafter referred to as a compression loss) in the engine 10. Therefore, in the temperature rise map 68 and the heat retention map 69, the fuel injection amount satisfying the driver's required torque L is obtained in consideration of the above-mentioned outflow loss and compression loss based on the results of experiments and simulations performed in advance. It is stipulated.

In the heat retention mode, the output loss of the engine 10 is small because the compression loss is small although the outflow loss is large under the same conditions as compared with the temperature rise mode. Therefore, the heat retention map 69 defines a value equal to or less than the value specified in the temperature rise map 68 for the same address based on the accelerator opening degree ACC and the engine speed Ne.

In the heat retention mode, the exhaust gas flowing out of the combustion chamber 21 during the execution of the first heat retention exhaust operation is the amount that does not push the piston 20 more than the exhaust gas discharged from the combustion chamber 21 by the normal exhaust operation. Exhaust gas with high enthalpy. Therefore, during the execution of the first heat-retaining exhaust operation, the exhaust gas having a higher enthalpy can be supplied to the exhaust purification device 45.

Further, since the exhaust gas is introduced into the cylinder 11 by the second heat-retaining exhaust operation, a mixed gas of air and exhaust gas is generated in the cylinder 11 as the working gas into which the fuel is injected. The temperature of this mixed gas is raised by the amount that a part of the air is replaced with the exhaust gas, as compared with the case where all of the working gas is air. As a result, when the same amount of fuel is burned, the exhaust temperature can be increased by the temperature increased by the introduction of the exhaust gas. This becomes remarkable when the engine load EL is at a light load.

In the heat retention mode, the amount of air taken in by the cylinder 11 is reduced by the heat retention intake operation in which the normal intake operation is retarded. As a result, the discharge temperature can be increased.
With reference to FIG. 7, the amount of advance of the normal exhaust operation and the amount of retard of the normal intake operation in the heat retention mode will be described. FIG. 7A shows an example of the result of a simulation performed on the fuel consumption in the heat retention mode. FIG. 7B shows an example of the result of a simulation performed on the exhaust gas temperature in the heat retention mode. This simulation was performed under a constant engine speed (for example, 880 rpm) and a constant engine load (for example, 10%) satisfying the selection condition of the heat retention mode.

As shown in FIGS. 7 (a) and 7 (b), when it is comprehensively judged that the exhaust gas temperature Tex can be increased while suppressing the increase in fuel consumption, the normal exhaust operation is 30 ° for the heat-retaining exhaust operation. It was found that it is preferable to advance the angle by about CA to 40 ° CA and delay the normal intake operation by about 40 ° CA to 75 ° CA for the heat retention intake operation.

With reference to FIG. 8, the result of the simulation performed on the temperature rising effect by the second heat-retaining exhaust operation will be described. In FIG. 8, the exhaust temperature when the heat-retaining exhaust operation is composed of the first heat-retaining exhaust operation and the second heat-retaining exhaust operation is A, and the exhaust temperature when the heat-retaining exhaust operation is composed of only the first heat-retaining operation is B. The temperature difference (= AB) is shown when This simulation was performed under the same conditions as the simulation described above. As shown in FIG. 8, it was confirmed that the exhaust gas temperature was raised by the second heat-retaining exhaust operation. Further, a high temperature raising effect was observed at a suitable advance angle amount of the normal exhaust operation and a suitable retard angle amount of the normal intake operation. The parts indicated by dots in the figure are the parts where the effect of reducing fuel consumption was recognized. Specifically, in the second heat retention / exhaust operation, it is preferable to open the valve at 60 ° CA to 90 ° CA, where the descending speed of the piston 20 is large and the rate of decrease in the in-cylinder pressure is large.

The effect of the engine system described above will be described.
(1) High enthalpy exhaust gas is supplied to the exhaust purification device 45 by the first heat-retaining exhaust operation, and the exhaust temperature is raised by the second heat-retaining exhaust operation. In addition, the discharge temperature is also increased by the heat retention intake operation. As a result, the exhaust energy supplied to the exhaust purification device 45 increases when the exhaust gas temperature Tex is lower than the heat-retainable temperature Tex1, so that the selective reduction catalyst 47 can be kept in the active state.

(2) The entire valve opening period of the second heat-retaining exhaust operation overlaps with the valve opening period of the heat-retaining intake operation. Thereby, the mixing degree of the air and the exhaust gas in the cylinder 11 can be effectively increased. As a result, it is possible to raise the operating gas temperature by introducing the exhaust gas while reducing the amount of unburned fuel.

(3) The mode selection unit 62 selects the heat retention mode when the engine load EL is equal to or less than the heat retention selection load EL2. Since the exhaust gas temperature Tex is the temperature of the exhaust gas flowing into the selective reduction catalyst 47, there is a delay in response to a change in the output of the engine 10. According to the above configuration, even if the exhaust gas temperature Tex is less than the heat retention possible temperature Tex1, when the engine load EL is larger than the heat retention selective load EL2, that is, when the exhaust gas temperature Tex is expected to rise immediately. You can avoid selecting the heat retention mode. As a result, it is possible to reduce the frequency of switching the control mode and suppress an increase in fuel consumption due to the selection of the heat retention mode.

(4) The first heat-retaining exhaust operation is an opening / closing operation in which the normal exhaust operation is advanced by 30 ° CA to 40 ° CA, and the heat-retaining intake operation is a retard of the normal intake operation by 40 ° CA to 75 ° CA. It is an opening and closing operation. According to this, it is possible to increase the exhaust energy supplied to the exhaust purification device 45 while effectively suppressing the increase in fuel consumption.

This embodiment can be modified and implemented as follows. The present embodiment and the following modified examples can be implemented in combination with each other within a technically consistent range.
-When the exhaust side valve mechanism 30 is a cam switching type variable valve mechanism, the heat retention exhaust operation may be configured as follows.

That is, the exhaust side valve mechanism 30 has an exhaust cam, which is a normal exhaust operation cam, and a temperature rise cam, which is a temperature rise exhaust operation cam. Further, the exhaust side valve mechanism 30 has an exhaust camshaft and an exhaust camphaser capable of changing the phase of the exhaust camshaft for the exhaust cam, and a temperature rise camshaft and a temperature riser for the temperature rise cam. It has a camphase for raising the temperature that can change the phase of the camshaft. Each cam phaser is configured to be controllable by the control device 60.

Then, as shown in FIG. 9, the heat-retaining exhaust operation is composed of a normal opening / closing operation in which the exhaust cam is advanced by the exhaust cam phaser, and the second heat-retaining exhaust operation is delayed by the temperature-increasing cam phaser. It may be configured by a second temperature rising opening / closing operation that is angled. In this case, it is preferable to configure so that the entire valve opening period of the first warming exhaust operation after the retard angle overlaps with the valve opening period of the first heat retaining exhaust operation. According to such a configuration, since the temperature rising mode and the heat retaining mode can be realized by using the temperature raising cam, it is possible to suppress the complexity of the configuration of the exhaust side valve mechanism 30.

-The first heat-retaining exhaust operation may be an opening / closing operation in which the normal exhaust operation is advanced.
-The heat-retaining intake operation may be an opening / closing operation in which the normal intake operation is retarded.
The mode selection unit 62 may select the heat retention mode when the catalyst temperature Tc is equal to or higher than the lower limit active temperature TcL and the exhaust gas temperature Tex is less than the heat retention temperature Tex1 regardless of the engine load EL. ..

-In the second heat-retaining exhaust operation, the entire valve opening period does not have to overlap with the valve opening period of the heat-retaining intake operation, and a part of the valve opening period may overlap with the valve opening period of the heat-retaining intake operation.
The first heated exhaust operation may be an opening / closing operation in which the maximum lift amount is the same as that of the normal exhaust operation and the valve opening period is short. Further, the first temperature raising exhaust operation may be an opening / closing operation in which the maximum lift amount is smaller than that in the normal exhaust operation and the valve opening period is the same length.

The second temperature rising exhaust operation may be configured such that the exhaust valve 28 closes after the intake valve 27 opens.
The fuel injection control unit 63 may have a configuration in which the fuel injection amount can be increased in the heat retention mode as compared with the normal mode, and is not limited to the configuration in which the normal map 67 and the heat retention map 69 are held as the fuel map. For example, the fuel injection control unit 63 is configured to increase the fuel injection amount by correcting the fuel injection amount specified in the normal map 67 according to the operating state of the engine 10 at that time in the heat retention mode. May be good.

When the exhaust gas purification device 45 has a plurality of catalysts, the determination regarding the catalyst temperature Tc in the mode selection process may be made based on the catalyst temperature located at the uppermost stream. According to such a configuration, at least the catalyst located at the most upstream can act. Further, the determination regarding the catalyst temperature Tc may be made based on the catalyst temperature of the catalyst selected in advance from the plurality of catalysts. According to such a configuration, the catalyst can act on a preselected catalyst.

The engine system may not include at least one of the turbocharger 35 and the EGR device 40.
-The engine 10 is not limited to a diesel engine, and may be a gasoline engine or a gas engine.

10 ... Engine, 11 ... Cylinder, 12 ... Engine block, 12A ... Cylinder block, 12B ... Cylinder head, 13 ... Injector, 14 ... Intake manifold, 15 ... Exhaust manifold, 16 ... Intake passage, 17 ... Exhaust passage, 17A ... Expansion Diameter, 20 ... Piston, 21 ... Combustion chamber, 22 ... Connection rod, 23 ... Crank shaft, 25 ... Intake port, 26 ... Exhaust port, 27 ... Intake valve, 28 ... Exhaust valve, 29 ... Intake side valve mechanism, 30 ... Exhaust side valve mechanism, 35 ... Turbocharger, 36 ... Compressor, 37 ... Intercooler, 38 ... Turbine, 39 ... Air cleaner, 40 ... EGR device, 41 ... EGR passage, 42 ... EGR cooler, 43 ... EGR valve, 45 ... Exhaust gas recirculation device, 46 ... Addition part, 47 ... Selective reduction catalyst, 48 ... Tank, 49 ... Reducing agent passage, 50 ... Pump, 51 ... Addition valve, 52 ... Exhaust throttle valve, 55 ... Crank angle sensor, 56 ... catalyst temperature sensor, 57 ... accelerator opening sensor, 57a ... accelerator pedal, 58 ... exhaust gas temperature sensor, 59 ... vehicle speed sensor, 60 ... control device, 61 ... acquisition unit, 62 ... mode selection unit, 63 ... fuel injection control Unit, 64 ... EGR control unit, 65 ... addition control unit, 66 ... valve control unit, 67 ... normal map, 68 ... temperature rise map, 69 ... heat retention map, 70 ... exhaust brake control unit.

Claims (4)

An engine with an exhaust valve and an intake valve that can change the opening and closing timing of opening and closing the combustion chamber separately.
An exhaust purification device having a catalyst for purifying the exhaust gas from the engine,
An engine system including a control device for controlling the engine.
The control device is
An acquisition unit that acquires the torque required from the driver, the state of the catalyst, and the exhaust gas temperature, which is the temperature of the exhaust gas flowing into the catalyst.
A fuel injection amount control unit that controls the fuel injection amount to the engine so that the output torque of the engine becomes the required torque.
A mode selection unit for selecting the control mode of the engine system and
A valve control unit that controls the opening and closing of the exhaust valve and the opening and closing of the intake valve is provided.
The mode selection unit selects a normal mode as the control mode when the catalyst is in the active state and the exhaust gas temperature is equal to or higher than the heat retention temperature, and the catalyst is in the active state and the mode is described. When the exhaust gas temperature is lower than the heat retention possible temperature, the heat retention mode is selected as the control mode, and the heat retention mode is selected.
In the heat retention mode, the valve control unit executes the heat retention intake operation in which the normal intake operation in the normal mode is retarded, and the first heat retention / exhaust operation in which the normal exhaust operation in the normal mode is advanced. It is composed of a second heat-retaining exhaust operation that opens and closes in the suction stroke and has a smaller maximum lift amount and a shorter valve opening period than the first heat-retaining exhaust operation, and at least one of the valve opening periods of the second heat-retaining exhaust operation. An engine system in which a unit executes a heat-retaining exhaust operation that overlaps with the valve opening period of the heat-retaining intake operation. The engine system according to claim 1, wherein the entire valve opening period of the second heat-retaining exhaust operation overlaps with the valve opening period of the heat-retaining intake operation. The engine system according to claim 1 or 2, wherein the mode selection unit selects the heat retention mode when the load of the engine is in a light load state. The heat-retaining intake operation is an opening / closing operation in which the normal intake operation is retarded by 40 ° CA to 75 ° CA.
The engine system according to any one of claims 1 to 3, wherein the first heat-retaining exhaust operation is an opening / closing operation in which the normal exhaust operation is advanced by 30 ° CA to 40 ° CA.