Engine system

Abstract

To provide an engine system capable of enhancing exhaust performance.SOLUTION: An engine system includes: an adjustment apparatus (9) that adjusts engine output or engine torque; and selective reduction catalysts (42, 43) that adsorb ammonia and reduce NOx in exhaust gas by using the ammonia. When a temperature of the selective reduction catalyst is lower than a predetermined determination catalyst temperature, an upper limit value of the engine output or the engine torque is set to a value lower than a maximum value, and restriction control for controlling the adjustment apparatus is carried out such that the engine output or the engine torque becomes the upper limit value or lower. During execution of the restriction control, the upper limit value is set to a lower value when an initial adsorption amount is small than when the initial adsorption amount is large.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an engine system. [Background technology]

[0002] Conventionally, studies have been conducted to reduce the amount of harmful substances emitted, that is, to improve exhaust performance, in engines mounted on vehicles, etc. For example, Patent Document 1 discloses an engine equipped with a catalytic converter that reduces the amount of intake air to reduce the amount of harmful substances emitted when the temperature of the catalytic converter is low and the catalytic converter's ability to purify exhaust gas is low. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 3000804 Summary of the Invention [Problem to be solved by the invention]

[0004] As described above, by reducing the amount of intake air, the amount of combustion gas generated in the engine body and therefore the amount of exhaust gas can be reduced, thereby reducing the amount of harmful substances emitted.

[0005] However, in a selective reduction catalyst that adsorbs ammonia and reduces NOx with it, the purification capacity changes depending on the ammonia adsorption amount (i.e., the amount of adsorbed ammonia) in addition to the temperature. Therefore, a configuration that simply changes the intake air amount depending on the catalyst temperature may not be able to sufficiently reduce the amount of harmful substances emitted when the engine is started.

[0006] Specifically, a selective reduction catalyst has the property that it is more difficult to adsorb ammonia when its temperature is high than when it is low. Therefore, in the first case where the engine is stopped while the temperature of the selective reduction catalyst is relatively low, the next engine start is performed while the ammonia adsorption amount is relatively large, and as a result, the purification capability of the selective reduction catalyst after engine start is relatively high. In contrast, in the second case where the engine is stopped while the temperature of the selective reduction catalyst is high, even if the temperature of the selective reduction catalyst at engine start is the same as in the first case above, the engine start is performed while the ammonia adsorption amount is small, and as a result, the purification capability of the selective reduction catalyst after engine start is low. Therefore, there is a risk that exhaust performance cannot be improved with a configuration in which the intake air amount is changed only in response to the catalyst temperature.

[0007] The present invention has been made in view of the above circumstances, and has an object to provide an engine system that can improve exhaust performance. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention comprises an adjustment device that adjusts engine output or engine torque, a selective reduction catalyst that adsorbs ammonia and uses the ammonia to reduce NOx in exhaust gas, and a control device that controls the adjustment device, wherein when the temperature of the selective reduction catalyst is below a predetermined judgment catalyst temperature, the control device sets an upper limit value of engine output or engine torque to a value lower than the maximum value, and implements limit control that controls the adjustment device so that the engine output or engine torque is equal to or lower than the upper limit value, and when the limit control is implemented, when the initial adsorption amount, which is the amount of ammonia adsorbed to the selective reduction catalyst at engine start, is small, the upper limit value is set to a smaller value than when it is large.

[0009] In the present invention, when the temperature of the selective reduction catalyst is below a predetermined judgment catalyst temperature, the engine output or engine torque is suppressed to an upper limit value or less that is lower than the maximum value. Therefore, it is possible to avoid a large amount of NOx (nitrogen oxides) being supplied to the selective reduction catalyst that is in a state of low purification capacity due to the low temperature, and it is possible to keep low the amount of NOx that is not purified by the selective reduction catalyst and is emitted to the outside.

[0010] Moreover, when the initial adsorption amount, which is the amount of ammonia adsorbed to the selective reduction catalyst at engine start, is small, the upper limit is set to a smaller value than when it is large. Therefore, after engine start, when the purification performance of the selective reduction catalyst is relatively high because the initial adsorption amount is large, it is possible to avoid an excessive decrease in engine output or engine torque while purifying NOx with the selective reduction catalyst. Also, after engine start, when the purification performance of the selective reduction catalyst is relatively low because the initial adsorption amount is small, it is possible to keep the combustion gas generated in the engine body, and therefore the amount of NOx, low, and improve exhaust performance.

[0011] In the above configuration, preferably, the control device sets a target adsorption amount, which is a target value for the amount of ammonia adsorbed by the selective reduction catalyst, and when the limit control is being performed and the initial adsorption amount is less than the target adsorption amount, sets the upper limit value to a smaller value than when the initial adsorption amount is equal to or greater than the target adsorption amount, and reduces the upper limit value as the initial adsorption amount decreases (claim 2).

[0012] In this configuration, when the initial adsorption amount is large and the target adsorption amount is achieved, and the exhaust purification capacity of the selective reduction catalyst is ensured, the upper limit value is set to a relatively large value. Therefore, it is possible to ensure engine output or engine torque while purifying NOx with the selective reduction catalyst. Furthermore, when the initial adsorption amount is small and the amount of ammonia adsorbed to the selective reduction catalyst is insufficient relative to the target adsorption amount, the upper limit value is set to a relatively small value, and the amount of NOx generated is kept low. Therefore, it is possible to reliably reduce the amount of NOx that passes through the selective reduction catalyst and is emitted to the outside of the engine. Furthermore, under the condition that the initial adsorption amount is less than the target adsorption amount, the smaller the initial adsorption amount, the smaller the upper limit value is set to a smaller value. Therefore, even if the initial adsorption amount varies within a range less than the target adsorption amount, the upper limit value can be set to an appropriate value, making it possible to improve exhaust performance while preventing an excessive decrease in engine output or engine torque.

[0013] In the above configuration, preferably, the control device sets the upper limit value so that the upper limit value is smaller when the temperature of the selective reduction catalyst is low than when the temperature is high (claim 3).

[0014] With this configuration, the upper limit can be set to an appropriate value according to the purification capacity of the selective reduction catalyst, which changes according to the temperature of the selective reduction catalyst. Therefore, it is possible to more reliably prevent the engine output or engine torque from becoming excessively small while improving exhaust performance.

[0015] In the above configuration, a urea injector that injects urea into the exhaust passage upstream of the selective reduction catalyst, and a NOx concentration detection device that is disposed in the exhaust passage upstream of the selective reduction catalyst and detects the NOx concentration in the exhaust gas are provided, and the control device estimates the amount of ammonia adsorbed to the selective reduction catalyst based on the amount of urea injected by the urea injector and the NOx concentration detected by the NOx concentration detection device, and sets the amount of ammonia estimated when the engine is stopped as the initial adsorption amount when the engine is next started (claim 4).

[0016] The amount of ammonia adsorbed to the selective reduction catalyst can be calculated from the difference between the amount of ammonia supplied to the selective reduction catalyst and the amount of ammonia consumed by the selective reduction catalyst to reduce NOx. Therefore, according to this configuration, the initial adsorption amount is estimated based on the amount of urea injected by the urea injector, which has a high correlation with the amount of ammonia supplied, and the NOx concentration detected by the NOx concentration detection device, which has a high correlation with the amount of ammonia consumed by the selective reduction catalyst, so the initial adsorption amount can be estimated with high accuracy. [Effects of the Invention]

[0017] As described above, the engine system of the present invention can improve exhaust performance. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a schematic configuration diagram showing a preferred embodiment of an engine system according to the present invention; [Figure 2] FIG. 2 is a functional block diagram showing a control system of the engine. [Figure 3] 10 is a flowchart showing a control procedure performed by a controller. [Figure 4] FIG. 4 is a diagram for explaining a procedure for calculating the amount of adsorbed ammonia. [Figure 5] 4 is a graph showing the relationship between the SCR catalyst temperature and the target adsorption amount. [Figure 6] 1 is a graph showing the relationship between engine speed, SCR catalyst temperature, and normal upper limit torque. [Figure 7] 10 is a graph showing the relationship between the initial amount of adsorption and the amount of reduction in the upper limit torque. [Figure 8] 10 is a graph showing a comparison between a normal upper limit torque and a low-temperature upper limit torque; [Figure 9] 4 is a time chart showing a schematic diagram of changes over time in the SCR catalyst temperature, the ammonia adsorption amount, and the upper limit torque when the engine is started. DETAILED DESCRIPTION OF THE INVENTION

[0019] (Overall engine configuration) Fig. 1 is a schematic diagram showing a preferred embodiment of an engine system of the present invention. The engine included in the engine system 1 shown in this figure is a four-stroke diesel engine mounted on a vehicle as a power source for running. The engine includes an engine body 2, an intake passage 30 through which intake air introduced into the engine body 2 flows, an exhaust passage 40 through which exhaust gas discharged from the engine body 2 flows, an HP-EGR device 50 and an LP-EGR device 70 that recirculate a portion of the exhaust gas flowing through the exhaust passage 40 back to the intake passage 30, and an exhaust turbo device 60 that supercharges the intake air flowing through the intake passage 30.

[0020] The engine body 2 has a plurality of cylinders 2a (only one cylinder is shown in FIG. 1) lined up in a direction perpendicular to the plane of the paper on which FIG. 1 is drawn. The engine body 2 also includes a cylinder block 3, a cylinder head 4, and a plurality of pistons 5. The cylinders 2a are formed by the cylinder block 3 and the cylinder head 4. That is, a plurality of cylindrical spaces corresponding to the plurality of cylinders 2a are formed inside the cylinder block 3, and the cylinder head 4 is attached to the upper surface of the cylinder block 3 so as to close off the cylindrical spaces from above. A piston 5 is housed in each cylinder 2a so as to be able to slide back and forth.

[0021] A combustion chamber C is formed above the piston 5 of each cylinder 2a. Each combustion chamber C is a space defined by the lower surface of the cylinder head 4, the side circumferential surface (cylinder liner) of the cylinder 2a, and the crown surface of the piston 5. The combustion chamber C is supplied with fuel injected from an injector 9, which will be described later. The piston 5 receives the combustion energy of the fuel supplied to the combustion chamber C and reciprocates up and down.

[0022] A crankshaft 7, which is the output shaft of the engine body 2, is provided below the pistons 5 and in the lower part of the cylinder block 3. The crankshaft 7 is connected to the pistons 5 of each cylinder 2a via connecting rods 8, and rotates around its central axis in response to the reciprocating motion (up and down movement) of the pistons 5.

[0023] A crank angle sensor SN1 and a water temperature sensor SN2 are attached to the cylinder block 3. The crank angle sensor SN1 detects the crank angle, which is the rotation angle of the crankshaft 7, and the engine speed, which is the rotation speed of the crankshaft 7. The water temperature sensor SN2 detects the temperature of the cooling water flowing inside the cylinder block 3 and the cylinder head 4, i.e., the engine water temperature.

[0024] A fuel injector 9 is attached to the cylinder head 4. The fuel injector 9 supplies fuel to the combustion chamber C of each cylinder 2a. The fuel injector 9 is attached to the cylinder head 4 so that its tip is exposed to the combustion chamber C. The tip of the fuel injector 9 is formed with multiple nozzle holes that serve as fuel outlets. The fuel injected from each nozzle hole is burned by self-ignition in the combustion chamber C, which is heated and pressurized by the compression action of the piston 5. In the engine according to this embodiment, the engine torque is changed mainly by the amount of fuel injected from the fuel injector 9. Thus, in this embodiment, the fuel injector 9 corresponds to the "adjusting device" of the present invention. Note that in the following description and in FIG. 2, which will be described later, the fuel injector 9 will be simply referred to as "injector 9."

[0025] The cylinder head 4 is formed with intake ports 11 and exhaust ports 12. The intake ports 11 connect the combustion chambers C of each cylinder 2a to the intake passage 30. The exhaust ports 12 connect the combustion chambers C of each cylinder 2a to the exhaust passage 40. An intake valve 13 is provided in the intake port 11 of each cylinder 2a, and an exhaust valve 14 is provided in the exhaust port 12 of each cylinder 2a.

[0026] The cylinder head 4 is equipped with an intake valve train 15 and an exhaust valve train 16. The intake valve train 15 drives the intake valve 13 of each cylinder 2a to open and close in conjunction with the rotation of the crankshaft 7. The exhaust valve train 16 drives the exhaust valve 14 of each cylinder 2a to open and close in conjunction with the rotation of the crankshaft 7. The intake valve 13 periodically opens and closes the opening of the intake port 11 on the combustion chamber C side in response to the drive of the intake valve train 15. The exhaust valve 14 periodically opens and closes the opening of the exhaust port 12 on the combustion chamber C side in response to the drive of the exhaust valve train 16.

[0027] The intake passage 30 is a passage for introducing intake air into the combustion chamber C of each cylinder 2a. The intake passage 30 has a surge tank 34 in a downstream portion near the engine body 2. The surge tank 34 is a tank that provides an expanded space for equalizing the amount of intake air introduced into each cylinder 2a. An air cleaner 31, a throttle valve 33, and an intercooler 32 are sequentially provided in the intake passage 30 upstream of the surge tank 34. The air cleaner 31 is a filter that removes foreign matter from the intake air. The intercooler 32 is a heat exchanger that cools the intake air compressed by the exhaust turbo device 60. The throttle valve 33 is a valve for adjusting the flow rate of the intake air. An air flow sensor SN3 is attached to the intake passage 30. The air flow sensor SN3 is a sensor that detects the flow rate of the intake air introduced into the engine body 2 and is located in the intake passage 30 downstream of the air cleaner 31.

[0028] The exhaust passage 40 is a passage for discharging exhaust gas emitted from the combustion chamber C of each cylinder 2a to the outside. The exhaust passage 40 is provided with a plurality of catalysts 41-44 for purifying various harmful components contained in the exhaust gas. Specifically, an oxidation catalyst device 41, an SCRF 42, an SCR catalyst device 43, and a slip catalyst device 44 are provided in this order from the upstream side of the exhaust passage 40 (the side closer to the engine body 2). In addition, a urea injector 45 and a mixing plate 47 are provided in the portion of the exhaust passage 40 between the oxidation catalyst device 41 and the SCRF 42.

[0029] The oxidation catalyst device 41 has a catalyst for oxidizing CO and HC in the exhaust gas to make them harmless (converting them into CO and HO). The oxidation catalyst device 41 has, for example, a porous carrier and a catalytic material such as platinum or palladium supported on the carrier.

[0030] The urea injector 45 is an injection valve that injects urea water, which is made by dissolving high-purity urea in pure water. The urea injector 45 injects urea water supplied from a urea water tank (not shown) mounted on the vehicle into the exhaust passage 40. The urea contained in the injected urea water is converted into ammonia (NH3) by hydrolysis at high temperature and is adsorbed by the SCRF 42 and the SCR catalyst included in the SCR catalytic device 43 located downstream.

[0031] The mixing plate 47 is a plate-shaped member for mixing the flow of exhaust gas. The mixing plate 47 plays a role of uniformly dispersing the urea contained in the urea water injected from the urea injector 45 and sending it downstream (to the SCRF 42 and the SCR catalyst device 43).

[0032] The SCRF 42 is a filter with an SCR catalyst. The SCRF 42 is a device in which a catalytic material such as platinum for burning soot and an SCR catalyst are supported on a filter capable of capturing soot in exhaust gas. As described above, the SCRF 42 adsorbs ammonia generated from the urea water injected by the urea injector 45. The SCR catalyst included in the SCRF 42 is a selective reduction type NOx catalyst that reduces and detoxifies NOx in the exhaust gas (converting it into N2 or H2O) through a chemical reaction using ammonia as a reducing agent. For example, vanadium, tungsten, zeolite, etc. are used as the SCR catalyst.

[0033] The SCR catalytic device 43 is a device that includes an SCR catalyst, and has, for example, a porous carrier and an SCR catalyst such as vanadium, tungsten, or zeolite supported on the carrier. The SCR catalytic device 43 reduces NOx that was not reduced by the SCRF 42. The SCRF 42 and the SCR catalytic device 43 share a casing, and the SCR catalytic device 43 is provided immediately downstream of the SCRF 42. The SCR catalyst included in the SCRF 42 and the SCR catalytic device 43 corresponds to the "selective reduction catalyst" of the present invention.

[0034] The slip catalyst device 44 is a device having an oxidation catalyst for oxidizing ammonia that has slipped (i.e., flowed downstream without being used to reduce NOx) from the SCRF 42 and the SCR catalyst device 43. As this slip catalyst device 44, for example, one having the same structure as the oxidation catalyst device 41 can be used.

[0035] A NOx sensor SN4 that detects the concentration of NOx in the exhaust gas is provided in the exhaust passage 40 between the oxidation catalyst device 41 and the urea injector 45. In addition, an exhaust temperature sensor SN5 that detects the temperature of the exhaust gas is provided immediately upstream of the SCRF 42 (the portion between the mixing plate 47 and the SCRF 42). The NOx sensor SN4 corresponds to the "NOx concentration detection device" of the present invention.

[0036] The exhaust turbo device 60 is a supercharging device that uses exhaust gas discharged from the combustion chamber C to supercharge the air supplied to the combustion chamber C. The exhaust turbo device 60 includes a compressor 61 arranged in the intake passage 30, and a turbine 62 that is coaxially connected to the compressor 61 and arranged in the exhaust passage 40. The compressor 61 is arranged in a portion of the intake passage 30 between the air cleaner 31 and the intercooler 32. The turbine 62 is arranged in a portion of the exhaust passage 40 upstream of the oxidation catalyst device 41.

[0037] Exhaust gas discharged from the engine body 2 is introduced into the turbine 62, which is rotationally driven by the exhaust gas. The compressor 61 rotates in conjunction with the turbine 62, thereby compressing and sending the intake air downstream. In other words, the exhaust turbo device 60 achieves supercharging by compressing the intake air in the intake passage 30 and sending it to the engine body 2.

[0038] The HP-EGR device 50 includes an HP-EGR passage 51 and an HP-EGR valve 53. The HP-EGR passage 51 is a passage for recirculating exhaust gas from the exhaust passage 40 to the intake passage 30. The HP-EGR passage 51 connects a portion of the exhaust passage 40 upstream of the turbine 62 with a portion of the intake passage 30 between the throttle valve 33 and the compressor 61. The HP-EGR valve 53 is a valve that adjusts the amount of recirculation of HP-EGR gas, which is exhaust gas that passes through the HP-EGR passage 51 and is recirculated to the intake passage 30.

[0039] The LP-EGR device 70 includes an LP-EGR passage 71, an EGR cooler 72, and an LP-EGR valve 73. The LP-EGR passage 71 is a passage for recirculating exhaust gas that has passed through the SCR catalytic device 43 to the intake passage 30. The LP-EGR passage 71 connects a portion of the exhaust passage 40 between the SCR catalytic device 43 and the slip catalytic device 44 with a portion of the intake passage 30 upstream of the compressor 61. The EGR cooler 72 cools LP-EGR gas, which is exhaust gas recirculated to the intake passage 30 through the LP-EGR passage 71. The LP-EGR valve 73 is a valve that adjusts the amount of recirculation of LP-EGR gas. Hereinafter, the exhaust gas recirculated to the intake passage 30 by the HP-EGR device 50 and the LP-EGR device 70 is referred to as EGR gas. In other words, HP-EGR gas and LP-EGR gas are collectively referred to as EGR gas. Furthermore, recirculating exhaust gas using the LP-EGR device 70 will be referred to as LP-EGR, and recirculating exhaust gas using the HP-EGR device 50 will be referred to as HP-EGR, as appropriate.

[0040] (Control system) 2 is a functional block diagram showing the control system of the engine of this embodiment. The engine system 1 has a controller 100. The controller 100 is a device for comprehensively controlling the engine, and is configured by a microcomputer including a well-known CPU (processor), ROM, RAM, etc. This controller 100 corresponds to the "control device" of the present invention.

[0041] Information detected by various sensors is input to the controller 100. Specifically, the controller 100 is electrically connected to the crank angle sensor SN1, water temperature sensor SN2, air flow sensor SN3, NOx sensor SN4, and exhaust temperature sensor SN5 described above, and various pieces of information detected by these sensors, such as the crank angle, engine speed, engine water temperature, intake air flow rate, and exhaust gas temperature, are sequentially input to the controller 100.

[0042] The vehicle is also provided with an accelerator sensor SN6 that detects the opening of the accelerator pedal (hereinafter referred to as accelerator opening) operated by the driver of the vehicle, an outside air temperature sensor SN7 that detects the outside air temperature, and a vehicle speed sensor SN8 that detects the vehicle speed, and the detection information from these accelerator sensor SN6, outside air temperature sensor SN7 and vehicle speed sensor SN8 is also input sequentially to the controller 100.

[0043] The controller 100 controls each part of the engine while executing various determinations and calculations based on input information from the above-mentioned sensors (SN1 to SN8). That is, the controller 100 is electrically connected to the fuel injector 9, the throttle valve 33, the urea injector 45, the HP-EGR valve 53, the LP-EGR valve 73, etc., and outputs control signals to these devices based on the results of the above-mentioned calculations, etc.

[0044] The control relating to engine torque, which is a characteristic control of the present invention and is performed by the controller 100, will be described using the flowchart of Fig. 3. The flowchart shown in Fig. 3 is repeatedly performed at predetermined calculation cycles while the engine is running.

[0045] First, the controller 100 calculates the engine load, that is, the required torque, which is the engine torque required by the vehicle driver (step S1). The controller 100 calculates the required torque based on the vehicle speed detected by the vehicle speed sensor SN8 and the accelerator opening detected by the accelerator sensor SN6. The required torque is set to the maximum value of the engine torque, within a range equal to or less than the maximum torque that the engine itself can achieve. Note that this maximum value of the engine torque is set in advance based on the maximum combustion pressure, the amount of air, etc.

[0046] Next, the controller 100 estimates the SCR catalyst temperature, which is the temperature of the SCRF 42 (step S2). This SCR catalyst temperature corresponds to the "temperature of the selective reduction catalyst" of the present invention.

[0047] In step S2, the controller 100 estimates the amount of heat input to the SCRF 42 and the amount of heat dissipation from the SCRF 42, and estimates the SCR catalyst temperature based on these. Specifically, the controller 100 estimates the flow rate of the exhaust gas based on the intake air flow rate detected by the air flow sensor SN3, and calculates the amount of heat input to the SCRF 42 based on this exhaust gas flow rate and the temperature of the exhaust gas immediately before the SCRF 42 detected by the exhaust temperature sensor SN5. The controller 100 also calculates the amount of heat dissipation from the SCRF 42 based on the vehicle speed detected by the vehicle speed sensor SN8 and the outside air temperature detected by the outside air temperature sensor SN7. The controller 100 calculates the SCR catalyst temperature based on the calculated amounts of heat input and heat dissipation to the SCRF 42 and the pre-stored heat capacity of the SCRF 42. The SCR catalyst temperature is calculated to be a higher value the greater the amount of heat input or the smaller the amount of heat dissipation, and is calculated to be a lower value the smaller the amount of heat input or the larger the amount of heat dissipation. Here, the amount of heat dissipated from the SCRF 42 can be considered to be greater as the vehicle speed increases. This is because the higher the vehicle speed, the more wind blows onto the SCRF 42, promoting heat dissipation. Conversely, the amount of heat dissipated decreases as the vehicle speed decreases, so the SCR catalyst temperature is estimated to be higher as the vehicle speed decreases.

[0048] Next, the controller 100 estimates the ammonia adsorption amount, which is the amount of ammonia adsorbed in the SCRF 42 and the SCR catalyst included in the SCR catalytic device 43. Hereinafter, the SCRF 42 and the SCR catalyst included in the SCR catalytic device 43 will be collectively referred to as the SCR catalyst.

[0049] The controller 100 estimates the amount of ammonia remaining in the SCR catalyst at each time point based on the difference between the amount of ammonia flowing into the SCR catalyst and the amount of ammonia consumed for the reduction of NOx in the SCR catalyst, and calculates the integrated value as the ammonia adsorption amount. FIG. 4 is a diagram for explaining the procedure for estimating the ammonia adsorption amount. The controller 100 estimates the ammonia supply amount, which is the amount of ammonia supplied to the SCR catalyst at each time point, based on the urea-water injection amount, which is the amount of urea-water injected from the urea injector 45. The controller 100 also estimates the NOx inflow amount, which is the amount of NOx flowing into the SCR catalyst at each time point, based on the NOx concentration in the exhaust gas detected by the NOx sensor SN4 and the flow rate of the exhaust gas. The flow rate of the exhaust gas is calculated from the detection value of the airflow sensor SN3, the opening degrees of the HP-EGR valve 53 and the LP-EGR valve 73, etc. The controller 100 also calculates the ammonia consumption amount, which is the amount of ammonia consumed for the reduction of the NOx at each time point, based on the estimated NOx inflow amount. Then, the controller 100 calculates the remaining amount of ammonia at each time point by subtracting the amount of ammonia consumed from the amount of ammonia supplied, and calculates the value obtained by integrating the remaining amounts of ammonia as the amount of ammonia adsorption.

[0050] Returning to the flowchart of FIG. 3, after estimating the ammonia adsorption amount as described above, the controller 100 calculates a target adsorption amount, which is a target value for the amount of ammonia to be adsorbed by the SCR catalyst (step S4).

[0051] FIG. 5 is a graph showing the relationship between the SCR catalyst temperature and the target adsorption amount. The SCR catalyst has the property of being less able to adsorb ammonia when its temperature is high than when it is low. For this reason, as shown in FIG. 5, the target adsorption amount is set to a smaller value when the SCR catalyst temperature is high. Specifically, the target adsorption amount is set to a smaller value when the SCR catalyst temperature is equal to or higher than a predetermined reference catalyst temperature TSCR than when the SCR catalyst temperature is below the reference catalyst temperature TSCR. Furthermore, when the SCR catalyst temperature is below the reference catalyst temperature TSCR, the target adsorption amount is set to a constant value Qa regardless of the SCR catalyst temperature, but when the SCR catalyst temperature is equal to or higher than the reference catalyst temperature TSCR, the target adsorption amount is set to a smaller value as the SCR catalyst temperature increases.

[0052] Returning to the flowchart of FIG. 3, after setting the target adsorption amount, the controller 100 determines whether the SCR catalyst temperature estimated in step S2 is less than a judgment catalyst temperature (step S5). The judgment catalyst temperature is the temperature of the SCR catalyst at which the NOx purification rate of the SCR catalyst becomes equal to or greater than a predetermined value when a sufficient amount of ammonia is adsorbed on the SCR catalyst. The judgment catalyst temperature is set in advance and stored in the controller 100. Here, when a sufficient amount of time has passed since the engine started, the SCR catalyst is warmed by the exhaust gas, and its temperature becomes equal to or greater than the judgment catalyst temperature. Therefore, it can be said that the determination in step S5 becomes YES when a sufficient amount of time has not passed since the engine started.

[0053] When the determination in step S5 is NO and the SCR catalyst temperature is equal to or higher than the determination catalyst temperature, the controller 100 performs normal control (step S20) and ends the process (returns to step S1). Specifically, the controller 100 determines the fuel injection amount, which is the amount of fuel injected from the injector 9, based on the required torque calculated in step S2 and the intake air flow rate detected by the air flow sensor SN3, and controls the injector 9 in accordance with the determination. As will be described later, when the determination in step S3 is YES, torque limitation is performed to limit the fuel injection amount so that the engine torque does not exceed an upper limit torque that is smaller than the maximum value. In contrast, when normal control is performed, torque limitation is not performed, and the required torque is realized and the fuel injection amount is controlled so that the engine torque does not exceed the maximum value. Note that when normal control is performed, the controller 100 determines the injection amount of urea water that can achieve the target adsorption amount set in step S4, and controls the urea injector 45 in accordance with the determination.

[0054] On the other hand, when the determination in step S5 is YES and the SCR catalyst temperature is lower than the determination catalyst temperature, the controller 100 reads the initial adsorption amount (step S6). The initial adsorption amount is the ammonia adsorption amount at the time of engine start, that is, the amount of ammonia adsorbed on the SCR catalyst at the time of engine start. The ammonia adsorption amount hardly changes during the period from when the engine is stopped to when it is started. Thus, the controller 100 sets the ammonia adsorption amount estimated at the time the engine was stopped immediately before as the initial adsorption amount. In other words, the controller 100 stores the ammonia adsorption amount estimated when the engine is stopped, and at the next engine start, reads the stored ammonia adsorption amount at the time the engine was stopped as the initial adsorption amount.

[0055] Next, the controller 100 determines whether or not the initial amount of adsorption read in step S6 is less than the target amount of adsorption set in step S4 (step S7).

[0056] As described above, the determination in step S5 becomes YES when sufficient time has not yet elapsed since the engine was started. As a result, the target adsorption amount used in step S7, which is performed after the determination in step S5 becomes YES, is equivalent to the target adsorption amount at engine start. Furthermore, the SCR catalyst temperature at engine start is generally lower than the reference catalyst temperature TSCR, and the target adsorption amount at engine start is a constant value Qa (FIG. 5) regardless of whether the engine is stopped or in a stopped state. As a result, the determination in step S7 is substantially the same as determining whether the initial adsorption amount is lower than a predetermined value Qa.

[0057] If the determination in step S7 is NO, that is, if it is determined that the initial amount of adsorption is equal to or greater than the target amount of adsorption, the controller 100 calculates the normal upper limit torque (step S8).

[0058] Specifically, the controller 100 sets the normal upper limit torque to a value smaller than the maximum value of the engine torque based on the engine speed and the SCR catalyst temperature. FIG. 6 is a graph schematically illustrating the relationship between the engine speed, the SCR catalyst temperature, and the normal upper limit torque. Lines L1 to L4 in the graph of FIG. 6 are lines illustrating the relationship between the engine speed and the normal upper limit torque for each SCR catalyst temperature. The SCR catalyst temperatures corresponding to the four lines L1, L2, L3, and L4 increase in this order, and the higher the SCR catalyst temperature, the higher the normal upper limit torque is set to. Furthermore, as can be seen from the lines L1 to L4, under conditions where the SCR catalyst temperature is constant, the higher the engine speed, when the engine speed is below a predetermined speed, the higher the normal upper limit torque is set to. However, when the engine speed is equal to or greater than the predetermined speed, the higher the engine speed, the lower the normal upper limit torque is set to. The relationship between the engine speed, the SCR catalyst temperature, and the normal upper limit torque is stored in the form of a map in the controller 100. The controller 100 extracts from this map a value corresponding to the engine speed detected by the crank angle sensor SN1 and the SCR catalyst temperature estimated in step S2, and sets the extracted value as the normal upper limit torque. As described above, the normal upper limit torque stored in the map is set to a value smaller than the maximum value of the engine torque.

[0059] On the other hand, if the determination in step S7 is YES, that is, if it is determined that the initial amount of adsorption is less than the target amount of adsorption, the controller 100 calculates the initial upper limit torque (step S9).

[0060] Specifically, the controller 100 first calculates the normal upper limit torque based on the engine speed and the SCR catalyst temperature, as in the case of performing step S8. Next, the controller 100 sets a reduction amount M of the upper limit torque. In this embodiment, as shown in FIG. 7, the reduction amount M is set to a smaller value as the initial adsorption amount read in step S6 increases. Next, the controller 100 sets a value that is smaller than the normal upper limit torque by the reduction amount M as the initial upper limit torque.

[0061] FIG. 8 is a graph comparing the normal upper limit torque and the initial upper limit torque. In FIG. 8, the solid line represents the normal upper limit torque, and the dashed line represents the initial upper limit torque. Each of the dashed lines L11 to L14 in FIG. 8 represents the initial upper limit torque corresponding to the normal upper limit torque lines L1 to L4, respectively. As can be seen from these dashed lines L11 to L14, the initial upper limit torque, like the normal upper limit torque, changes depending on the SCR catalyst temperature and engine speed, and is set to a smaller value as the SCR catalyst temperature decreases. Also, as described above, the reduction amount M is set to a smaller value as the initial adsorption amount increases. As a result, the initial upper limit torque is set to a smaller value as the SCR catalyst temperature decreases and as the initial adsorption amount decreases.

[0062] After step S8 or step S9 is performed, the controller 100 performs torque limitation (step S10). Specifically, the controller 100 sets an upper limit torque, which is an upper limit value of the engine torque, and compares this upper limit torque with the required torque calculated in step S1. If the required torque is equal to or less than the upper limit torque, the controller 100 determines a fuel injection amount, which is the amount of fuel injected from the injector 9, so that the required torque is realized, and controls the injector 9 in accordance with the determination. On the other hand, if the required torque is greater than the upper limit torque, the controller 100 determines a fuel injection amount, which is the amount of fuel injected from the injector 9, so that an upper limit torque lower than the required torque is realized, instead of the required torque, and controls the injector 9 in accordance with the determination.

[0063] In step S10 after proceeding to step S8, the controller 100 sets the upper limit torque to the normal upper limit torque set in step S8. On the other hand, in step S10 after proceeding to step S9, the controller 100 sets the upper limit torque to the initial upper limit torque set in step S9. As described above, the initial upper limit torque is set to a value smaller than the normal upper limit torque. As a result, when proceeding to step S9, that is, when the initial adsorption amount is less than the target adsorption amount, the upper limit torque is set to a smaller value than when proceeding to step S8, that is, when the initial adsorption amount is equal to or greater than the target adsorption amount, and the engine torque is restricted more strictly. Furthermore, the smaller the initial adsorption amount, the smaller the initial upper limit torque is set to a value. As a result, in step S10 after proceeding to step S9, the smaller the initial adsorption amount, the stronger the engine torque restriction.

[0064] After the torque limitation is implemented in step S10, the controller 100 ends the processing (returns to step S1).

[0065] When torque restriction is implemented, the controller 100 basically determines the injection amount of urea water that can achieve the target adsorption amount set in step S4, as in the case of normal control, and controls the urea injector 45 in accordance with the determination. However, when the SCR catalyst temperature is below the urea injection prohibition temperature, which is set to a value even lower than the judgment catalyst temperature, the reduction of NOx in the SCR catalyst is hardly performed, so the controller 100 prohibits the injection of urea water from the urea injector 45.

[0066] The above torque control, which includes steps S8, S9, and S10 and sets an upper limit torque and limits the engine torque to an upper limit torque that is smaller than the maximum value, corresponds to the "limit control" of the present invention.

[0067] (action, etc.) FIG. 9 is a time chart that schematically shows the time changes in the SCR catalyst temperature, ammonia adsorption amount, and upper limit torque after engine start. The solid and dashed lines in the graphs of upper limit torque and ammonia adsorption amount in FIG. 9 represent patterns with different initial adsorption amounts, with the first pattern shown by the solid line having a smaller initial adsorption amount than the second pattern shown by the chain line. Note that FIG. 9 shows that the SCR catalyst temperature rises in the same manner in both patterns. Furthermore, as described above, the target adsorption amount at engine start is set to a roughly constant value Qa, and therefore FIG. 9 illustrates a case where the target adsorption amount is the same in both patterns.

[0068] In the example of FIG. 9, the engine starts at time t1. The SCR catalyst temperature at time t1 is lower than the judgment catalyst temperature. Furthermore, in both the first and second patterns, the ammonia adsorption amount at time t1, i.e., the initial adsorption amount, is smaller than the target adsorption amount. As a result, in both patterns, torque limitation is implemented and the upper limit torque is set to an initial upper limit torque that is smaller than the normal upper limit torque indicated by the chain line. However, the initial adsorption amount is smaller in the first pattern than in the second pattern. As a result, the upper limit torque (initial upper limit torque) is set to a smaller value in the first pattern than in the second pattern.

[0069] In the example of FIG. 9, the SCR catalyst temperature reaches the urea injection prohibition temperature at time t2. From this point on, injection of urea water is prohibited and NOx reduction in the SCR catalyst is stopped until time t2, and the ammonia adsorption amount is maintained approximately constant until time t2. Meanwhile, the SCR catalyst temperature gradually increases as the engine starts. Accordingly, the initial upper limit torque gradually increases in both the first and second patterns.

[0070] When the SCR catalyst temperature reaches the urea injection prohibition temperature at time t2, urea water injection is started. As a result, the ammonia adsorption amount gradually increases from time t2, and after time t2, the difference between the ammonia adsorption amount and the target adsorption amount decreases. The SCR catalyst temperature also increases after time t2. As a result, after time t2, the initial upper limit torque increases at a faster speed than before time t2.

[0071] In the example of FIG. 9, in both the first and second patterns, the ammonia adsorption reaches the target adsorption amount at time t3. On the other hand, in the example of FIG. 9, the SCR catalyst temperature has not yet reached the judgment catalyst temperature even at time t3. As a result, in this example, in both patterns, at time t3, the upper limit torque is switched to the normal upper limit torque, which is higher than the initial upper limit torque, and torque limitation is implemented with the normal upper limit torque as the upper limit torque. In the example of FIG. 9, the SCR catalyst temperature reaches the judgment catalyst temperature at time t4, after time t3. As a result, torque limitation is stopped after time t4. Note that after time t4, the target adsorption amount and actual adsorption amount decrease as the SCR catalyst temperature rises.

[0072] As described above, in the engine system 1 according to this embodiment, when the SCR catalyst temperature is below the determination catalyst temperature, torque limitation is implemented, and the injector 9 is controlled so that the engine torque is equal to or lower than an upper limit torque (normal upper limit torque or initial upper limit torque) that is lower than the maximum value. This prevents the generation of a large amount of combustion gas and therefore exhaust gas when the purification capability of the SCR catalyst is low due to the SCR catalyst temperature being below the determination catalyst temperature. In other words, it is possible to prevent NOx that cannot be purified by the SCR catalyst from being emitted from the engine body 2. This improves exhaust performance.

[0073] Furthermore, the upper limit torque (initial upper limit torque) when the initial adsorption amount is less than the target adsorption amount and is therefore smaller is set to a smaller value than the upper limit torque (normal upper limit torque) when the initial adsorption amount is equal to or greater than the target adsorption amount and is therefore relatively large. Therefore, when a sufficient amount of ammonia is not adsorbed on the SCR catalyst and sufficient NOx reduction is difficult, the amount of NOx generated in the engine body can be reliably kept low, thereby improving exhaust performance. Furthermore, when a sufficient amount of ammonia is adsorbed on the SCR catalyst, this ammonia can be used to reduce NOx while relatively increasing engine torque. Therefore, both exhaust performance and driving performance can be improved.

[0074] Furthermore, the smaller the initial adsorption amount, the smaller the initial upper limit torque is set to. In other words, even under the common condition that the initial adsorption amount is less than the target adsorption amount, the smaller the initial adsorption amount, the smaller the upper limit torque is set to. Therefore, when the initial adsorption amount is less than the target adsorption amount, it is possible to reliably keep the amount of NOx emitted to the outside of the engine low while preventing an excessive decrease in engine output or engine torque.

[0075] Furthermore, both the normal upper limit torque and the initial upper limit torque are set to smaller values ​​as the SCR catalyst temperature decreases, so these torques can be set to appropriate values ​​according to the purification capacity of the SCR catalyst, improving exhaust performance while preventing excessive reductions in engine output or engine torque.

[0076] Furthermore, the amount of ammonia adsorbed to the SCR catalyst can be calculated by integrating the difference between the amount of ammonia supplied to the SCR catalyst and the amount of ammonia consumed by the SCR catalyst to reduce NOx. Correspondingly, in this embodiment, the initial adsorption amount is estimated based on the amount of urea injected by the urea injector, which has a high correlation with the amount of ammonia supplied to the SCR catalyst, and the NOx concentration detected by the NOx sensor SN4, which has a high correlation with the amount of ammonia consumed by the SCR catalyst. This allows the initial adsorption amount to be estimated with high accuracy.

[0077] (Variation) In the above embodiment, the case where engine torque is changed by changing the amount of fuel injected from the injector 9 has been described, but the device for changing engine torque is not limited to the injector 9. For example, the intake amount may be changed by changing the opening of the throttle valve 33, thereby changing engine torque. However, the engine according to the above embodiment is a diesel engine, and engine torque is changed mainly by the amount of fuel injected.

[0078] In the above embodiment, an upper limit value is set for the engine torque, and the injector 9 is controlled so that the engine torque is equal to or less than this upper limit value. However, an upper limit value may be set for the engine output instead of the engine torque, and the injector 9, etc. may be controlled so that the engine output is equal to or less than this upper limit value.

[0079] In addition, one of the SCRF 42 and the SCR catalyst device 43 may be omitted. [Explanation of symbols]

[0080] 2 Engine body 9 Fuel injector (adjusting device) 30 Intake passage 40 Exhaust passage 42 SCRF (Selective Reduction Catalyst) 43 SCR catalyst device (selective catalytic reduction) 45 Urea Injector 100 Controller (control device) SN4 NOx sensor (NOx concentration detection device)

Claims

1. an adjusting device for adjusting the engine output or engine torque; a selective reduction catalyst that adsorbs ammonia and reduces NOx in exhaust gas using the ammonia; a control device that controls the adjustment device, The control device When the temperature of the selective reduction catalyst is lower than a predetermined judgment catalyst temperature, a limit control is implemented in which an upper limit value of an engine output or an engine torque is set to a value lower than a maximum value, and the adjustment device is controlled so that the engine output or the engine torque is equal to or lower than the upper limit value; and an engine system characterized in that, when the limit control is performed, when an initial adsorption amount, which is the amount of ammonia adsorbed to the selective reduction catalyst at engine start, is small, the upper limit value is set to a smaller value than when it is large.

2. 2. The engine system according to claim 1, The control device A target adsorption amount, which is a target value for the amount of ammonia adsorbed by the selective reduction catalyst, is set; when the limit control is being performed and the initial adsorption amount is less than the target adsorption amount, the upper limit value is set to a smaller value than when the initial adsorption amount is equal to or greater than the target adsorption amount, and the smaller the initial adsorption amount, the smaller the upper limit value is set.

3. 2. The engine system according to claim 1, The control device sets the upper limit value to a smaller value when the temperature of the selective reduction catalyst is low than when the temperature is high.

4. The engine system according to any one of claims 1 to 3, a urea injector that injects urea into the exhaust passage upstream of the selective reduction catalyst; a NOx concentration detection device disposed in the exhaust passage upstream of the selective reduction catalyst and detecting a NOx concentration in the exhaust gas; the control device estimates an amount of ammonia adsorbed to the selective reduction catalyst based on an amount of urea injected by the urea injector and the NOx concentration detected by the NOx concentration detection device, and sets the amount of ammonia estimated when the engine is stopped as the initial adsorption amount when the engine is next started.

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