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 an EGR passage (51) connecting an exhaust passage (40) on a downstream side of exhaust gas purification apparatuses (42, 43) with an intake passage (30) and returns EGR gas as a part of exhaust gas to the intake passage. When a purification apparatus temperature is lower than a predetermined reference temperature, an upper limit value of the engine output or the engine torque is set to be lower than a maximum value, and restriction control is carried out which is for controlling the adjustment apparatus such that the engine output or the engine torque becomes the upper limit value or lower. When an outside air temperature is low, the upper limit value is set to a lower value than a value when the outside air temperature is high.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 engines with an EGR passage in which a portion of the exhaust gas is recirculated to the intake passage, simply reducing the intake air volume when the temperature of the catalytic converter is low makes it difficult to achieve sufficient exhaust performance when the outside temperature is low. Specifically, when the outside temperature is low, moisture in the exhaust gas may freeze in the EGR passage. If icing occurs in the EGR passage, the amount of exhaust gas recirculated to the intake passage through the EGR passage becomes insufficient, which can lead to a deterioration in exhaust performance. Thus, the engine described in Patent Document 1 has the problem that exhaust performance is more likely to deteriorate when the outside temperature is low than when the outside temperature is high, even when the temperature of the catalytic converter is similarly low. This leaves room for improvement in this regard.

[0006] 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]

[0007] In order to solve the above problem, the present invention provides an engine comprising an engine body, an intake passage through which intake air introduced into the engine body flows, an exhaust passage through which exhaust gas discharged from the engine body flows, an adjustment device for adjusting engine output or engine torque, an exhaust purification device arranged in the exhaust passage for purifying exhaust gas, an EGR passage connecting the exhaust passage downstream of the exhaust purification device to the intake passage and for recirculating EGR gas, which is a part of the exhaust gas, to the intake passage, an EGR valve for opening and closing the EGR passage, an outside air temperature acquisition device for acquiring an outside air temperature, a purification device temperature acquisition device for acquiring a purification device temperature, which is the temperature of the exhaust purification device, and a control device for controlling the adjustment device and the EGR valve, wherein when the purification device temperature acquired by the purification device temperature acquisition device is below a predetermined reference temperature, the control device sets an upper limit value of the engine output or engine torque lower than a maximum value and 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 outside air temperature acquired by the outside air temperature acquisition device is low, sets the upper limit value to a value smaller than when the outside air temperature acquired by the outside air temperature acquisition device is high.

[0008] In the present invention, when the temperature of the exhaust purification device is below a predetermined reference temperature, the engine output or engine torque is suppressed to an upper limit value that is lower than the maximum value, thereby preventing the generation of a large amount of exhaust gas when the purification capacity of the exhaust purification device is low, and improving exhaust performance.

[0009] In a configuration in which the EGR passage is connected downstream of an exhaust gas purification device, the temperature of the exhaust gas flowing into the EGR passage is relatively low, which can lead to the risk of moisture in the exhaust gas freezing in the EGR passage when the ambient temperature is low. If moisture freezes in the EGR passage, sufficient exhaust gas (i.e., inert gas) cannot be recirculated to the intake passage through the EGR passage, resulting in increased NOx emissions from the engine and other adverse effects on exhaust performance. Thus, even under the same conditions (i.e., the temperature of the exhaust gas purification device is below a reference temperature), exhaust performance is more likely to deteriorate when the ambient temperature is low. In contrast, in the present invention, when limiting engine power or engine torque to a lower upper limit, the upper limit is set to a lower value when the ambient temperature is low than when the ambient temperature is high. Therefore, the upper limit is set to a higher value when the ambient temperature is high, preventing an excessive decrease in engine power or engine torque. At the same time, when the ambient temperature is low, the amount of exhaust gas and harmful substances contained therein, such as NOx, can be reduced, resulting in improved exhaust performance.

[0010] In the above configuration, preferably, the control device prohibits the EGR valve from opening when the outside air temperature is lower than a predetermined judgment temperature (claim 2).

[0011] In this configuration, when the outside air temperature is below a threshold temperature, the EGR valve is prohibited from opening and the flow of exhaust gas through the EGR passage is stopped, thereby preventing moisture contained in the exhaust gas from freezing inside the EGR passage.

[0012] However, if the flow of exhaust gas through the EGR passage, and therefore the recirculation of exhaust gas through the EGR passage to the intake passage, is stopped, there is a risk that the amount of NOx emitted from the engine body will become excessive. In contrast, in the present invention, as described above, when the outside air temperature is low, such as when the outside air temperature is below the threshold temperature, the upper limit is reduced, thereby keeping the amount of exhaust gas low. Therefore, an increase in NOx emissions can be suppressed.

[0013] In the above configuration, preferably, the system further includes a high-pressure EGR passage connecting the exhaust passage upstream of the exhaust purification device to the intake passage, and a high-pressure EGR valve for opening and closing the high-pressure EGR passage, and when the restriction control is performed, the control device sets the upper limit value to a value smaller than when the outside air temperature is equal to or higher than a predetermined judgment temperature, and when the outside air temperature is equal to or higher than the judgment temperature, permits the EGR valve and the high-pressure EGR valve to open, and when the outside air temperature is lower than the judgment temperature, permits the high-pressure EGR valve to open but prohibits the EGR valve from opening (claim 3).

[0014] In this configuration, the EGR valve is prohibited from opening when the outside air temperature is below the threshold temperature, thereby preventing moisture contained in the exhaust gas from freezing in the EGR passage. Furthermore, in this configuration, when the EGR valve is prohibited from opening because the outside air temperature is below the threshold temperature, the upper limit is set to a small value and exhaust gas is allowed to recirculate to the intake passage via the high-pressure EGR passage. Therefore, an increase in NOx emissions, which is likely to occur when the EGR valve is prohibited from opening, can be suppressed by reducing exhaust gas emissions and introducing exhaust gas via the high-pressure EGR passage.

[0015] In the above configuration, preferably, the control device sets a target EGR amount, which is a target value for the amount of exhaust gas to be recirculated to the intake passage, sets a high-pressure EGR gas upper limit amount, which is an upper limit value for the amount of high-pressure EGR gas to be recirculated to the intake passage via the high-pressure EGR passage, and controls the high-pressure EGR valve so that the high-pressure EGR gas amount is equal to or less than the upper limit value, and when the restriction control is performed, if the outside air temperature is below the judgment temperature but the target EGR amount is equal to or less than the high-pressure EGR gas upper limit amount, sets the upper limit value to the same value as when the outside air temperature is above the judgment temperature, and if the outside air temperature is below the judgment temperature and the target EGR amount is greater than the high-pressure EGR gas upper limit amount, sets the upper limit value to a value smaller than when the outside air temperature is above the judgment temperature (claim 4).

[0016] In this configuration, if the target EGR amount can be achieved by recirculating exhaust gas to the intake passage via the high-pressure EGR passage even when the outside air temperature is below the threshold temperature, the upper limit is set to the same relatively high value as when the outside air temperature is above the threshold temperature. Therefore, by achieving the target EGR amount, it is possible to keep NOx emissions low while ensuring engine output or engine torque. On the other hand, if the outside air temperature is below the threshold temperature and the target EGR amount cannot be achieved, the upper limit is set to a small value, reducing exhaust gas emissions. Therefore, even in this case, excessive NOx emissions can be prevented.

[0017] In the above configuration, it is preferable that an exhaust temperature detection device is provided that detects the temperature of the exhaust gas, and the control device sets the high-pressure EGR gas upper limit amount to a smaller value as the temperature of the exhaust gas detected by the exhaust temperature detection device increases (claim 5).

[0018] This configuration prevents a large amount of exhaust gas from passing through the high-pressure EGR passage when the exhaust gas temperature is high. This reduces heat damage to components around the high-pressure EGR passage from the exhaust gas. Furthermore, when the exhaust gas temperature is low and heat damage to the components is unlikely to occur, the amount of exhaust gas returned to the intake passage is ensured, thereby reliably reducing NOx emissions.

[0019] In the above configuration, preferably, when the outside air temperature is lower than the judgment temperature and the target EGR amount is greater than the high-pressure EGR gas upper limit amount, the upper limit value is set so that the lower the purification device temperature is, the smaller the upper limit value becomes, and the greater the shortfall of the high-pressure EGR gas upper limit amount relative to the target EGR amount is, the smaller the upper limit value becomes (claim 6).

[0020] According to this configuration, when the outside air temperature is lower than the determination temperature, the upper limit value can be set to an appropriate value according to the outside air temperature and the purifier temperature. [Effects of the Invention]

[0021] As described above, the engine system of the present invention can improve exhaust performance. [Brief explanation of the drawings]

[0022] [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] 1 is a map showing a control region of an EGR device provided in an engine. [Figure 5] 1 is a map for explaining a prohibited region of LP-EGR. [Figure 6] 10 is a graph showing the relationship between engine water temperature and a determination temperature. [Figure 7] 1 is a graph showing the relationship between engine speed, SCR catalyst temperature, and normal upper limit torque. [Figure 8] 4 is a graph showing the relationship between exhaust gas temperature and HP-EGR upper limit amount. [Figure 9] 10 is a graph showing the relationship between the EGR shortage amount and the reduction amount of the upper limit torque. [Figure 10] 10 is a graph showing a comparison between a normal upper limit torque and a low-temperature upper limit torque; DETAILED DESCRIPTION OF THE INVENTION

[0023] (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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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."

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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).

[0036] 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.

[0037] 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 SCRF 42 and SCR catalytic device 43 correspond to the "exhaust gas purification device" of the present invention.

[0038] 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.

[0039] 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 exhaust temperature sensor SN5 corresponds to the "exhaust gas temperature detection device" of the present invention.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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. The LP-EGR passage 71 corresponds to the "EGR passage" of the present invention, and the LP-EGR valve 73 corresponds to the "EGR valve" of the present invention. The HP-EGR passage 51 corresponds to the "high-pressure EGR passage" of the present invention, and the HP-EGR valve 53 corresponds to the "high-pressure EGR valve" of the present invention. The amount of HP-EGR gas corresponds to the "high-pressure EGR gas amount" of the present invention.

[0044] (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.

[0045] 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.

[0046] 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 information detected by these accelerator sensor SN6, outside air temperature sensor SN7, and vehicle speed sensor SN8 is also sequentially input to the controller 100. The outside air temperature sensor SN7 is a device that acquires the outside air temperature by detection, and corresponds to the "outside air temperature acquisition device" of the present invention.

[0047] 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 injector 9, throttle valve 33, urea injector 45, HP-EGR valve 53, LP-EGR valve 73, etc., and outputs control signals to these devices based on the results of the above-mentioned calculations, etc.

[0048] The control performed by the controller 100 will be described with reference to the flowchart of Fig. 3. The flowchart shown in Fig. 3 is repeatedly performed at predetermined calculation cycles while the engine is running.

[0049] 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.

[0050] The controller 100 also calculates a target EGR amount, which is a target value for the amount of EGR gas introduced into the cylinder 2a, that is, a target value for the amount of exhaust gas recirculated to the intake passage 30 (step S1). The controller 100 sets the target EGR amount based on the required torque calculated in step S2, etc. In this embodiment, the higher the required torque, the larger the target EGR amount is set to.

[0051] 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 "purifier temperature" of the present invention.

[0052] 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 against 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. In this way, in this embodiment, the SCR catalyst temperature is estimated by the controller 100, and this controller 100 corresponds to the "purifier temperature acquisition device" of the present invention.

[0053] After step S2, the controller 100 determines whether the estimated SCR catalyst temperature is less than a judgment catalyst temperature (step S3). The judgment catalyst temperature is the temperature of the SCR catalyst when the NOx purification rate by the SCR catalyst becomes equal to or greater than a predetermined value, i.e., the temperature of the SCFR 42. The judgment catalyst temperature is set in advance and stored in the controller 100. The judgment catalyst temperature corresponds to the "reference temperature" of the present invention.

[0054] If the determination in step S3 is NO and the SCR catalyst temperature is equal to or higher than the determination catalyst temperature, the controller 100 performs normal control (step S30) and ends the process (return to step S1).

[0055] When normal control is performed, 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, if 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 its maximum value.

[0056] Furthermore, during normal control, the controller 100 controls the openings of the throttle valve 33, the HP-EGR valve 53, and the LP-EGR valve 73 so as to achieve the target EGR amount calculated in step S3. FIG. 4 is a map showing the control regions of the HP-EGR device 50 and the LP-EGR device 70 during normal control. As shown in FIG. 4, the engine operating region is divided into a low load region A1, where the fuel injection amount is equal to or less than a predetermined switching injection amount Q1, and a high load region A2, where the fuel injection amount is greater than the switching injection amount Q1, with respect to EGR device control. In the low load region A1, exhaust gas is recirculated by both the HP-EGR device 50 and the LP-EGR device 70. That is, during normal control, the controller 100 determines whether the engine is operating in the low load region A1 or the high load region A2. If the engine is operating in the low load region A1, the controller 100 opens both the HP-EGR valve 53 and the LP-EGR valve 73. On the other hand, when the engine is operated in the high load range A2, the controller 100 closes the HP-EGR valve 53 and opens only the LP-EGR valve 73. The controller 100 makes the above determination based on the fuel injection amount determined based on the required torque.

[0057] Returning to step S3, if the determination in step S3 is YES and the SCR catalyst temperature is determined to be lower than the determination catalyst temperature, the controller 100 determines whether the condition for prohibiting LP-EGR is met. FIG. 5 is a map with the horizontal axis representing the outside air temperature and the vertical axis representing the engine water temperature. In the map of FIG. 5, the region where the engine water temperature is equal to or higher than a predetermined determination water temperature TW1 is defined as a first region A11, the region where the engine water temperature is lower than the determination water temperature TW1 and the outside air temperature is equal to or higher than a predetermined determination temperature Ta is defined as a second region A12, and the region where the engine water temperature is lower than the determination water temperature TW1 and the outside air temperature is lower than the determination temperature Ta is defined as a third region A13. In this embodiment, LP-EGR is prohibited when the engine water temperature and the outside air temperature are both within the third region. The determination water temperature TW1 is preset and stored in the controller 100. The determination water temperature TW1 is set to a temperature approximately equal to the engine water temperature when the engine warm-up operation is completed. The determination temperature Ta is preset and stored in the controller 100. Fig. 6 is a graph showing the relationship between engine water temperature and the threshold temperature Ta. As shown in Fig. 5 and Fig. 6, the threshold temperature Ta is set so that the higher the engine water temperature, the smaller its value. Details of the threshold temperature will be described later.

[0058] If the determination in step S3 is YES, the controller 100 first determines whether or not the engine water temperature detected by the water temperature sensor SN2 is lower than the determination water temperature TW1, that is, whether or not the temperature is within the first region A11 (step S4).

[0059] If the determination in step S4 is NO and the engine water temperature is equal to or higher than the determination water temperature TW1, the controller 100 does not prohibit LP-EGR and performs normal EGR control. That is, the controller 100 controls the HP-EGR device 50 and the LP-EGR device 70 in the same manner as during normal control (step S20). Specifically, as described above, the controller 100 determines whether to use the HP-EGR device 50 or the LP-EGR device 70 depending on the engine operating range (low load range A1, high load range A2), and controls the opening degrees of the throttle valve 33, the HP-EGR valve 53, and the LP-EGR valve 73 so as to achieve the target EGR amount calculated in step S3.

[0060] If the determination in step S4 is NO, the controller 100 implements normal torque limitation (step S21).

[0061] When the normal torque limit is implemented, the controller 100 first sets a normal upper limit torque, which is the upper limit of the engine torque. The controller 100 sets a normal upper limit torque that is smaller than the maximum value of the engine torque, based on the engine speed and the SCR catalyst temperature. FIG. 7 is a graph that schematically illustrates 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. 7 illustrate 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 higher 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 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.

[0062] When the normal torque limit is implemented, after setting the normal upper limit torque, the controller 100 compares the required torque calculated in step S1 with the normal upper limit torque. If the required torque is equal to or less than the normal upper limit torque, the controller 100 determines the 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 normal upper limit torque, the controller 100 determines the fuel injection amount, which is the amount of fuel injected from the injector 9, so that the normal upper limit torque, which is lower than the required torque, is realized, and controls the injector 9 in accordance with the determination.

[0063] In this way, when the SCR catalyst temperature is lower than the determination catalyst temperature (YES in step S3) and the engine water temperature is equal to or higher than the determination water temperature TW1 (NO in step S4), the normal torque limit is implemented and the engine torque is suppressed to be equal to or lower than the normal upper limit torque. After the normal torque limit is implemented, the controller 100 ends the processing (returns to step S1).

[0064] 3, if the determination in step S4 is YES and the engine water temperature is lower than the determination water temperature TW1, the controller 100 further determines whether the outside air temperature is lower than the determination temperature Ta (step S5). That is, in step S5, the controller 100 determines whether the outside air temperature and the engine water temperature are each within the third region A13.

[0065] If the determination in step S5 is NO and the outside air temperature is equal to or higher than the determination temperature, the controller 100 proceeds to step S20, does not prohibit LP-EGR, and performs normal EGR control. After that, the controller 100 proceeds to step S21, and performs normal torque limitation.

[0066] On the other hand, if the determination in step S5 is YES and the outside air temperature is lower than the determination temperature, the controller 100 prohibits LP-EGR. That is, the controller 100 closes the LP-EGR valve 73 and prohibits it from opening (step S6). Note that if the LP-EGR valve 73 is already closed, the controller 100 keeps the LP-EGR valve 73 closed.

[0067] As described above, the LP-EGR passage 71 is connected to a portion of the exhaust passage 40 downstream of the SCR catalytic device 43, and the temperature of the exhaust gas flowing into the LP-EGR passage 71 is relatively low. Therefore, if the exhaust gas is allowed to flow into the LP-EGR passage 71 when the outside air temperature is low, moisture contained in the exhaust gas may freeze inside the LP-EGR passage 71. In particular, in this embodiment, the EGR cooler 72 is provided in the LP-EGR passage 71 to cool the exhaust gas, making icing more likely to occur inside the LP-EGR passage 71. If icing occurs inside the LP-EGR passage 71, problems such as the LP-EGR valve 73 being unable to open and close properly may occur. Therefore, in this embodiment, when the outside air temperature is low (below a threshold temperature) and it is estimated that icing will occur inside the LP-EGR passage 71, LP-EGR is prohibited. That is, in step S5, it is determined whether or not freezing will occur in the LP-EGR passage 71, and the determination temperature is the highest temperature at which freezing is estimated to occur in the LP-EGR passage 71.

[0068] Here, when the engine water temperature is high, the maximum outside air temperature at which freezing occurs decreases due to the high exhaust gas temperature. Accordingly, in this embodiment, as described above, the threshold temperature is set to a smaller value as the engine water temperature increases. Specifically, as shown in FIG. 6 , when the engine water temperature is below a predetermined water temperature TW2, the threshold temperature decreases as the engine water temperature decreases. However, when the engine water temperature is equal to or higher than the water temperature TW2, the threshold temperature is set to a constant value regardless of the engine water temperature. The water temperature TW2 is lower than the threshold water temperature TW1. The relationship between the engine water temperature and the threshold temperature shown in FIG. 6 is preset through experiments or the like, and this relationship is stored in the controller 100 as a map. The controller 100 extracts from this map a threshold temperature corresponding to the engine water temperature detected by the water temperature sensor SN2, and uses the extracted threshold temperature to make the determination in step S5.

[0069] After step S6, the controller 100 calculates the HP-EGR upper limit amount (step S7). The HP-EGR upper limit amount is the upper limit of the HP-EGR gas amount, which is the amount of HP-EGR gas recirculated. By performing step S6, LP-EGR is prohibited. Therefore, when step S7 is performed, exhaust gas needs to be recirculated only by the HP-EGR device 50. However, the HP-EGR passage 51 is connected to a portion of the exhaust passage 40 upstream of the turbine 62, and the temperature of the exhaust gas flowing through the HP-EGR passage 51 is relatively high. Therefore, if a large amount of exhaust gas flows through the HP-EGR passage 51, there is a risk of thermal damage to devices around the HP-EGR passage 51. The HP-EGR upper limit amount is the minimum value of the HP-EGR gas amount that can prevent thermal damage. Here, when the exhaust gas temperature is high, the thermal damage is likely to occur. Accordingly, as shown in FIG. 8, the HP-EGR upper limit amount is set to a smaller value as the exhaust gas temperature increases. The relationship between the exhaust gas temperature and the HP-EGR upper limit amount shown in Figure 8 is set in advance through experiments or the like, and this relationship is stored in the controller 100 as a map. In step S9, the controller 100 extracts from this map a value corresponding to the exhaust gas temperature detected by the exhaust temperature sensor SN5, and sets this value as the HP-EGR upper limit amount. Note that the above HP-EGR upper limit amount corresponds to the "high-pressure EGR gas upper limit amount" of the present invention.

[0070] After calculating the HP-EGR upper limit amount, the controller 100 determines whether or not the target EGR amount calculated in step S1 is larger than the HP-EGR upper limit amount (step S8).

[0071] If the determination in step S8 is NO and the target EGR amount is equal to or less than the HP-EGR upper limit amount, the controller 100 controls the HP-EGR device 50 so that the target EGR amount is achieved. That is, the controller 100 controls the opening degrees of the HP-EGR valve 53 and the throttle valve 33 so that the HP-EGR gas amount becomes the target EGR amount. The controller 100 also implements normal torque limitation (step S21) to suppress the engine torque to be equal to or less than the normal upper limit torque. After implementing the normal torque limitation, the controller 100 ends the processing (returns to step S1).

[0072] On the other hand, if the determination in step S8 is YES and the target EGR amount is greater than the HP-EGR upper limit amount, the controller 100 controls the opening degrees of the HP-EGR valve 53 and the throttle valve 33 so that the HP-EGR gas amount becomes the HP-EGR upper limit amount (step S12). In other words, the EGR gas amount is limited.

[0073] If the determination in step S8 is YES, the controller 100 implements low-temperature torque limiting (step S11). Low-temperature torque limiting is a control that limits engine torque more strongly than the normal torque limiting, and the upper limit value of the engine torque is set to low-temperature normal torque, which is smaller than the normal upper limit torque, and the engine torque is controlled so as not to exceed this upper limit value (low-temperature normal torque).

[0074] Specifically, the controller 100 first sets the normal upper limit torque in the same manner as during normal torque limitation. Next, the controller 100 sets a reduction amount M of the upper limit torque. In this embodiment, as shown in FIG. 9, the reduction amount M is set to a larger value as the EGR shortage amount increases. The EGR shortage amount is the amount of shortage of the HP-EGR upper limit amount relative to the target EGR amount, and is the difference between the target EGR amount and the HP-EGR upper limit amount. The controller 100 calculates the EGR shortage amount based on the target EGR amount set in step S1 and the HP-EGR upper limit amount calculated in step S7. Thereafter, the controller 100 sets a value smaller than the normal upper limit torque by the reduction amount M as the low-temperature upper limit torque.

[0075] FIG. 10 is a graph comparing the normal upper limit torque and the low-temperature upper limit torque. In FIG. 10, the solid line represents the normal upper limit torque, and the dashed line represents the low-temperature upper limit torque. In FIG. 19, dashed lines L11 to L14 represent the normal 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 low-temperature 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 larger value as the EGR shortage amount increases. Thus, the low-temperature upper limit torque is set to a smaller value as the SCR catalyst temperature decreases and as the EGR shortage amount increases.

[0076] After setting the low-temperature upper limit torque, the controller 100 compares the required torque calculated in step S1 with the low-temperature upper limit torque. If the required torque is equal to or less than the low-temperature upper limit torque, the controller 100 determines the 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 low-temperature upper limit torque, the controller 100 determines the fuel injection amount, which is the amount of fuel injected from the injector 9, so that the low-temperature upper limit torque, which is smaller than the maximum value of the engine torque and the normal upper limit torque, is realized, and controls the injector 9 in accordance with the determination. After implementing the low-temperature torque limit, the controller 100 ends the processing (returns to step S1).

[0077] In both cases where normal control is performed and where torque limitation is performed, the controller 100 determines the injection amount of urea water based on the SCR catalyst temperature estimated in step S4, and controls the urea injector 45 in accordance with the determination.

[0078] As described above, when the SCR catalyst temperature is below the judgment catalyst temperature (when the determination in step S3 is YES), the normal torque limit or low-temperature torque limit is implemented to limit the engine torque. Furthermore, when the SCR catalyst temperature is below the judgment catalyst temperature, if the engine water temperature is equal to or higher than the judgment water temperature (when the determination in step S4 is NO) or the outside air temperature is equal to or higher than the judgment temperature (when the determination in step S5 is NO), the normal torque limit is also implemented. Furthermore, when the SCR catalyst temperature is below the judgment catalyst temperature (when the determination in step S3 is YES), the normal torque limit is also implemented when the engine water temperature is below the judgment water temperature (when the determination in step S4 is YES) and the outside air temperature is below the judgment temperature (when the determination in step S5 is YES) but the target EGR amount is less than the HP-EGR upper limit amount. On the other hand, when the SCR catalyst temperature is below the judgment catalyst temperature (when the judgment in step S3 is YES), the engine water temperature is below the judgment water temperature (when the judgment in step S4 is YES), the outside air temperature is below the judgment temperature (when the judgment in step S5 is YES), and the target EGR amount is equal to or greater than the HP-EGR upper limit amount, low-temperature torque limiting is implemented, and a stronger restriction than the normal torque limiting is imposed on the engine torque. Note that this control, which combines the normal torque limiting and the low-temperature torque limiting and which imposes a restriction on the engine torque, corresponds to the "limiting control" of the present invention.

[0079] (action) As described above, in the engine system 1 according to this embodiment, when the SCR catalyst temperature is below the determination catalyst temperature, normal torque limitation or low-temperature torque limitation is implemented, and the injector 9 is controlled so that the engine torque is equal to or less than the normal upper limit torque or low-temperature upper limit torque, which are lower than the maximum values. This prevents the generation of large amounts of combustion gas and, ultimately, exhaust gas, when the purification capability of the SCR catalyst is low due to the SCR catalyst temperature being below the determination catalyst temperature. This prevents NOx that cannot be purified by the SCR catalyst from being emitted from the engine body 2. This reduces NOx emissions, improving exhaust performance.

[0080] Furthermore, when the outside air temperature is lower than the threshold temperature, the LP-EGR device 70 is prohibited from operating. This prevents moisture in the exhaust gas from freezing inside the LP-EGR passage 71 due to low outside air temperature, as described above, and avoids problems such as the LP-EGR valve 73 being unable to open and close properly.

[0081] Furthermore, when the outside air temperature is lower than the threshold temperature, the flow through the LP-EGR device 70 is prohibited as described above, while the HP-EGR is permitted. This prevents freezing inside the LP-EGR passage 71, while allowing exhaust gas, i.e., inert gas, to be introduced into the intake passage 30 and the cylinder 2a, thereby minimizing the generation of NOx in the cylinder 2a and the amount of NOx emitted from the engine body 2.

[0082] However, as described above, if a large amount of exhaust gas is allowed to flow through the HP-EGR passage 51, there is a risk that devices around the HP-EGR passage 51 may be thermally damaged. In contrast, in this embodiment, when the outside air temperature is below the threshold temperature, the HP-EGR gas amount is kept below the HP-EGR upper limit amount, preventing excessive high-temperature HP-EGR gas from flowing through the HP-EGR passage 51. This makes it possible to prevent the above-mentioned thermal damage while suppressing the generation and emission of NOx through the HP-EGR. In particular, by setting the HP-EGR upper limit amount to a smaller value as the exhaust gas temperature increases, it is possible to effectively prevent thermal damage and suppress the generation and emission of NOx.

[0083] When torque is limited because the SCR catalyst temperature is below the critical catalyst temperature, if the following conditions are met: the ambient temperature is below the critical temperature and the target EGR amount is equal to or greater than the HP-EGR upper limit amount; i.e., when the purification capacity of the SCR catalyst is low, LP-EGR is not possible to prevent icing, and sufficient exhaust gas cannot be recirculated by the HP-EGR device 50 to prevent thermal damage, the upper limit of engine torque is set to a value (low-temperature upper limit torque) lower than the value (normal upper limit torque) when these conditions are not met. This allows the insufficient exhaust gas recirculation to be compensated for by reducing the amount of combustion gas, thereby suppressing an increase in NOx generation and emission. Thus, this embodiment prevents icing in the LP-EGR passage 71, thereby ensuring proper operation of the LP-EGR device 70, and preventing thermal damage to components surrounding the HP-EGR device 50, thereby ensuring proper operation of the HP-EGR device 50, and thereby improving exhaust performance.

[0084] In this embodiment, the low-temperature upper limit torque is set to decrease as the SCR catalyst temperature decreases and as the EGR gas shortage increases. This allows the low-temperature upper limit torque to be set to an appropriate value depending on the NOx purification capacity of the SCR catalyst and the EGR gas shortage. This allows for improved exhaust performance without excessively reducing engine torque.

[0085] (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 flow rate 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.

[0086] 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.

[0087] In the above embodiment, the determination in step S4, i.e., the determination as to whether the engine water temperature is lower than the threshold water temperature, may be omitted. Also, steps S7, S8, S9, and S10 may be omitted. That is, if the determination in step S5 is YES and the outside air temperature is lower than the threshold temperature, low-temperature torque limitation may be implemented regardless of the target EGR amount. Also, the HP-EGR device 50 itself may be omitted.

[0088] Furthermore, in the above embodiment, step S6, i.e., the control to prohibit LP-EGR, may be omitted. That is, LP-EGR may be permitted even when the outside air temperature is below the threshold temperature. In this case, although there is a risk of icing in the LP-EGR passage 71, the same torque limitation as in the above embodiment can be implemented to improve exhaust performance. Specifically, when LP-EGR is permitted, there is a risk of icing in the LP-EGR passage 71 when the outside air temperature is below the threshold temperature. As a result, exhaust gas may not be sufficiently recirculated through the LP-EGR passage 71, which may increase the generation and emission of NOx. In contrast, by implementing the torque limitation described above and tightening the engine torque limit when the outside air temperature is below the threshold temperature, it is possible to reliably reduce the generation and emission of NOx and improve exhaust performance.

[0089] In the above embodiment, the SCR catalyst temperature is estimated, but the SCR catalyst temperature may be detected by a sensor. Similarly, the outside air temperature may be estimated instead of being detected by the outside air temperature sensor SN7.

[0090] Furthermore, the specific device for purifying exhaust gas is not limited to the above. Furthermore, the engine is not limited to a diesel engine and may be a gasoline engine. Furthermore, the specific structure of the device for purifying exhaust gas provided in exhaust passage 40 is not limited to the above. [Explanation of symbols]

[0091] 2 Engine body 9 Fuel injector (adjusting device) 30 Intake passage 40 Exhaust passage 42 SCRF (exhaust gas purification system) 43 SCR catalytic converter (exhaust gas purification device) 51 HP-EGR passage (high pressure EGR passage) 53 HP-EGR valve (high pressure EGR valve) 71 LP-EGR passage (EGR passage) 73 LP-EGR valve (EGR valve) 100 Controller (control device, purifier temperature acquisition unit) SN5 Exhaust temperature sensor (exhaust temperature detection device) SN7 Outside air temperature sensor (outside air temperature acquisition device)

Claims

1. The engine body and an intake passage through which intake air introduced into the engine body flows; an exhaust passage through which exhaust gas discharged from the engine body flows; an adjusting device for adjusting the engine output or engine torque; an exhaust purification device disposed in the exhaust passage for purifying exhaust gas; an EGR passage that connects the exhaust passage downstream of the exhaust purification device and the intake passage and recirculates EGR gas, which is a part of the exhaust gas, to the intake passage; an EGR valve that opens and closes the EGR passage; an outside air temperature acquisition device for acquiring an outside air temperature; a purification device temperature acquisition device that acquires a purification device temperature, which is the temperature of the exhaust purification device; a control device that controls the adjusting device and the EGR valve, The control device When the purifier temperature acquired by the purifier temperature acquisition device is lower than a predetermined reference temperature, an upper limit value of the engine output or engine torque is set lower than a maximum value, and a limit control is performed to control the adjustment device so that the engine output or engine torque is equal to or lower than the upper limit value; An engine system characterized in that when the outside air temperature acquired by the outside air temperature acquisition device is low, the upper limit value is set to a smaller value than when the outside air temperature is high.

2. 2. The engine system according to claim 1, The engine system is characterized in that the control device prohibits the EGR valve from opening when the outside air temperature is lower than a predetermined judgment temperature.

3. 2. The engine system according to claim 1, a high-pressure EGR passage connecting the exhaust passage upstream of the exhaust purification device and the intake passage; and a high-pressure EGR valve opening and closing the high-pressure EGR passage, When the limit control is performed, the control device When the outside air temperature is below a predetermined judgment temperature, the upper limit value is set to a value smaller than when the outside air temperature is equal to or higher than the judgment temperature; When the outside air temperature is equal to or higher than the judgment temperature, the EGR valve and the high-pressure EGR valve are permitted to open; When the outside air temperature is lower than the threshold temperature, the engine system permits the high-pressure EGR valve to open, but prohibits the EGR valve from opening.

4. 4. The engine system according to claim 3, The control device a target EGR amount, which is a target value of the amount of exhaust gas recirculated to the intake passage; setting a high-pressure EGR gas upper limit amount, which is an upper limit value of the amount of high-pressure EGR gas recirculated to the intake passage via the high-pressure EGR passage, and controlling the high-pressure EGR valve so that the high-pressure EGR gas amount is equal to or less than the upper limit value; When the restriction control is performed, if the outside air temperature is below the judgment temperature but the target EGR amount is below the high-pressure EGR gas upper limit amount, the upper limit value is set to the same value as when the outside air temperature is above the judgment temperature, and if the outside air temperature is below the judgment temperature and the target EGR amount is greater than the high-pressure EGR gas upper limit amount, the upper limit value is set to a value smaller than when the outside air temperature is above the judgment temperature.

5. 5. The engine system according to claim 4, An exhaust gas temperature detection device is provided to detect the temperature of the exhaust gas, The engine system is characterized in that the control device sets the high-pressure EGR gas upper limit amount to a smaller value as the temperature of the exhaust gas detected by the exhaust gas temperature detection device increases.

6. 5. The engine system according to claim 4, The control device an upper limit value set so that, when the outside air temperature is lower than the judgment temperature and the target EGR amount is greater than the high-pressure EGR gas upper limit amount, the lower the purification device temperature, the smaller the upper limit value, and the greater the shortfall of the high-pressure EGR gas upper limit amount relative to the target EGR amount, the smaller the upper limit value.

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