JP6399198B1 - Turbocharged engine - Google Patents

Abstract

A reduction in emission performance in a cold state and in a low load region is prevented.
An engine with a supercharger includes an engine main body 10, an electric supercharger 18, a turbocharger 56, a high-pressure EGR passage 80, and an exhaust gas so as to bypass a turbine 56b in an exhaust passage 60. When the engine body is in a cold state and in a predetermined low load region, the high-pressure EGR valve 82 and the waste gate valve are opened, And a control unit (PCM100) that outputs a control signal to the electric supercharger so as to increase the supercharging pressure by the electric supercharger.
[Selection] Figure 1

Description

  The technology disclosed herein relates to a supercharged engine.

  Patent Document 1 discloses an example of a supercharged engine. Specifically, the engine disclosed in Patent Document 1 includes a diesel turbocharger that supercharges using exhaust energy and an electric supercharger that supercharges without using exhaust energy. It is configured as an engine.

JP 2010-180719 A

  In a diesel engine, a part of the exhaust gas is recirculated to the intake passage in order to suppress the production of RawNOx by lowering the combustion speed and the combustion temperature.

  Therefore, the diesel engine described in Patent Document 1 includes a high-pressure EGR system and a low-pressure EGR system. The high-pressure EGR system has a high-pressure EGR passage that connects an exhaust passage upstream of the turbocharger turbine and an intake passage downstream of the turbocharger compressor. The low-pressure EGR system cools exhaust gas flowing through the low-pressure EGR passage and the low-pressure EGR passage communicating the exhaust passage downstream of the turbocharger turbine and the intake passage upstream of the turbocharger compressor. With cooler.

  When such a diesel engine is operating in a steady state in a partial load region, the EGR gas is recirculated to the intake passage by the low pressure EGR system and the high pressure EGR system, and the supercharging pressure is increased via the turbocharger. As a result, an amount of fresh air corresponding to the amount of fuel is introduced into the cylinder. Thereby, the equivalence ratio of the air-fuel mixture and the temperature in the combustion chamber can be adjusted appropriately, and the generation of RawNOx and the generation of soot (soot) are suppressed.

  Further, in managing the emission of the engine, it is necessary to pay attention not only to the generation of RawNOx, but also to the generation of HC (hydrocarbon) caused by unburned fuel. Therefore, in a general diesel engine, HC in exhaust gas is oxidized and purified by an oxidation catalyst (so-called DOC).

  By the way, when the engine is in a cold state, early activation of the oxidation catalyst is required. However, when the engine is in a cold state and in a low load range, such as immediately after starting from a stopped state, there is a possibility that the exhaust gas becomes a small amount and a low temperature, and the oxidation catalyst cannot be warmed up early. This is not preferable for ensuring HC purification performance.

  Therefore, in order to warm up the oxidation catalyst as early as possible, it is conceivable to introduce exhaust gas so as to bypass the turbine of the turbocharger by using a so-called turbine bypass means such as a waste gate valve or VGT. .

  However, in such a configuration, the amount of work by the compressor of the turbocharger decreases according to the flow rate of the exhaust gas bypassing the turbine, and the supply of fresh air into the cylinder becomes insufficient. there is a possibility. Furthermore, if the exhaust gas bypasses the turbine, the exhaust pressure in the exhaust passage also decreases, so the differential pressure between the exhaust side and the intake side becomes small, and the recirculation of EGR gas by the high pressure EGR system is insufficient. There is a possibility. In order to suppress the production of RawHC, it is required to sufficiently secure the compression end temperature. In order to satisfy such a demand, it is required to supply fresh air, EGR gas, and the like appropriately into the cylinder.

  The technology disclosed herein has been made in view of such a point, and an object thereof is to prevent a decrease in emission performance in a cold state and a low load region in an engine with a supercharger. .

  The technology disclosed herein is characterized in that the turbine bypass means is operated while increasing the supercharging pressure via the electric supercharger at least in a cold state and in a low load region in the super benefit engine. And

  Specifically, an engine with a supercharger disclosed herein includes an engine body mounted on a vehicle, an intake passage and an exhaust passage connected to the engine body, an exhaust passage provided in the intake passage, and an electric motor. An electric supercharger for supplying, a turbine disposed in the exhaust passage, and a compressor disposed upstream of the electric supercharger in the intake passage, and using exhaust energy An EGR that causes a turbocharger to be supercharged, the exhaust passage upstream of the turbine and the intake passage downstream of the electric supercharger to communicate with each other, and a part of the exhaust gas is recirculated to the intake passage A passage, a turbine bypass means provided in the exhaust passage, for guiding at least a part of the exhaust gas so as to bypass the turbine, and disposed downstream of the turbine in the exhaust passage. A control unit that determines whether or not the engine main body is in a cold state and in a predetermined low load region based on a detection signal from a sensor attached to the engine main body, and the control unit When the engine main body is in a cold state and in a predetermined low load region, the EGR passage is opened and exhaust gas is guided to bypass the turbine via the turbine bypass means, and the electric motor The catalyst warm-up control is executed to output a control signal to the electric supercharger so as to increase the supercharging pressure via the supercharger.

  According to this configuration, when the engine body is in a cold state and in a predetermined low load region, the control unit opens at least a part of the exhaust gas so as to open the EGR passage and bypass the turbine via the turbine bypass means. Circulate. By making the exhaust gas bypass the turbine, a sufficient amount of heat can be given to the catalyst, so that the temperature of the catalyst can be raised as quickly as possible. As a result, it becomes possible to activate the catalyst at an early stage and thus to secure the HC purification performance.

  In the above configuration, since the EGR passage is connected upstream of the turbocharger turbine in the exhaust passage, the EGR gas recirculated through the EGR passage has a relatively high temperature. Therefore, the minimum in-cylinder temperature can be ensured even in the cold state. This is effective in suppressing the generation of unburned fuel and, in turn, suppressing the production of RawHC.

  In the above configuration, when the catalyst is activated by the turbine bypass means, the electric supercharger operates to increase the supercharging pressure. Although the amount of work by the compressor is reduced by the amount of exhaust gas bypassing the turbine, the reduction can be compensated by the electric supercharger. Thereby, even if the supercharging pressure does not increase in the turbocharger, the amount of fresh air introduced into the cylinder can be increased. As a result, the air density increases in the cylinder, so that the specific heat ratio of the gas in the cylinder increases and the compression end temperature increases. Thereby, it is also possible to suppress unburned fuel and to suppress the generation of RawHC. Further, the equivalence ratio of the air-fuel mixture is lowered by the amount of increase in the amount of fresh air, and soot generation can be suppressed.

  Further, the compressor of the turbocharger can be rotated by the flow of fresh air that occurs as the electric supercharger operates. Since the turbine also rotates in conjunction with the rotation of the compressor, the turbine does not become a resistance in the exhaust passage. Since the turbine does not become a resistance, a sufficient amount of heat can be given to the catalyst, which is advantageous in activating the catalyst at an early stage. Furthermore, since the exhaust pressure is reduced by the rotation of the turbine, the scavenging effect by the electric supercharger is also increased, and as a result, the pump loss can be reduced.

  In this way, it is possible to prevent a decrease in emission performance in a cold state and in a low load region.

  The supercharged engine has a second EGR passage that communicates the exhaust passage downstream of the turbine and the intake passage upstream of the compressor and recirculates a part of the exhaust gas to the intake passage. The controller may open the second EGR passage when it is determined that the catalyst has been heated to a predetermined temperature or higher after the catalyst warm-up control is executed.

  Since the second EGR passage is connected downstream of the turbine of the turbocharger in the exhaust passage, the temperature of the EGR gas recirculated through the second EGR passage is equal to the temperature of the EGR gas recirculated through the EGR passage. Lower than temperature. Therefore, the specific heat of the gas in the cylinder can be increased by increasing the amount of EGR gas while preventing the in-cylinder temperature from becoming too high. As a result, the combustion rate and the combustion temperature can be kept low, and the production of RawNOx is suppressed. Further, by opening the second EGR passage after the temperature of the catalyst has been raised to a predetermined temperature or higher, it is possible to ensure the HC purification performance when the catalyst is warmed up, while suppressing the generation of RawNOx after the warming up is completed. .

  The control unit may execute the catalyst warm-up control when the vehicle starts from a stopped state.

  In general, the engine body is in a cold state at the beginning of acceleration when starting from a stopped state. For this reason, if the catalyst warm-up control is executed at the time of starting, it is possible to appropriately prevent the emission performance from being lowered.

  Further, the engine with a supercharger includes an idle stop means for bringing the engine body into an idle stop state, and the control unit is configured to automatically restart the engine body that has been brought into an idle stop state by the idle stop means. The catalyst warm-up control may be executed.

  Generally, when the engine body is automatically restarted, the exhaust gas becomes relatively low in temperature. For this reason, if the catalyst warm-up control is executed during the automatic restart of the engine body, it is possible to appropriately prevent the emission performance from being lowered.

  The controller may operate the electric supercharger in a partial state. Here, “activate the electric supercharger in the partial state” means that the electric supercharger is operated so that the electric motor has a torque lower than the maximum torque and / or the compressor wheel is limited. It may mean that the electric supercharger is operated so that the rotational speed is lower than the rotational speed. When the electric supercharger is operated in the partial state, the power consumption of the electric motor is reduced and the efficiency of the compressor wheel is increased. And in an engine with a supercharger provided with both a turbocharger and an electric supercharger, power consumption can be reduced by operating the electric supercharger in an auxiliary manner.

  The engine body may be a diesel engine having a geometric compression ratio of 16 or less.

  A diesel engine having a geometric compression ratio of 16 or less tends to have a low compression end temperature. In particular, when the turbine is bypassed to exhaust gas by the turbine bypass means, the exhaust pressure decreases, so the amount of recirculation of EGR gas through the EGR passage decreases, and the temperature in the cylinder before compression starts may decrease. is there. This also contributes to a decrease in the compression end temperature.

  However, if the amount of fresh air in the cylinder is increased by the electric supercharger as much as the amount of recirculation of the EGR gas as described above, the specific heat ratio of the gas in the cylinder increases, so that Even if the temperature is low, the compression end temperature is high. Therefore, the supercharged engine having the above-described configuration is advantageous in ensuring the ignitability of the air-fuel mixture in a diesel engine having a low compression ratio.

  In the first place, diesel engines are more efficient than general gasoline engines. However, since the exhaust temperature becomes low as much as the thermal efficiency is excellent, the delay in warming up the catalyst as described above becomes even more problematic. Therefore, the catalyst warm-up control is particularly effective in such a diesel engine.

  Further, the control unit may execute the catalyst warm-up control even when the engine body is in a cold state and the engine rotational speed is lower than a predetermined rotational speed, even if it is out of the low load range. .

  In general, when the engine speed is low, gas leakage from the combustion chamber (particularly, gas leakage through the piston ring) is relatively large compared to when the engine speed is high. For this reason, when the engine speed is low, the gas pressure in the combustion chamber decreases, which causes a decrease in the compression end temperature. This is inconvenient in suppressing the production of RawHC.

  On the other hand, according to the above configuration, the control unit performs the above-described catalyst warm-up control when the engine body is in a cold state and the engine speed falls below a predetermined speed. By executing the catalyst warm-up control, the generated RawHC can be effectively purified.

  As described above, the technique disclosed herein can prevent a decrease in emission performance in a cold state and a low load region.

FIG. 1 is a schematic view showing an engine with a supercharger. FIG. 2 is a cross-sectional view showing the inside of the cylinder of the supercharged engine. FIG. 3 is a block diagram showing a control system of the supercharged engine. FIG. 4 is a map showing the operating state of the electric supercharger. The upper diagram of FIG. 5 is a performance curve graph showing the identification of the compressor of the electric supercharger, and the lower diagram of FIG. 5 is a diagram showing the characteristics of the electric motor of the electric supercharger. FIG. 6 is a φ-T map of a diesel engine. FIG. 7 shows the ratio of the air density to the amount of fresh air in the cylinder and the difference in gas composition in the cylinder in the comparative example in which the catalyst warm-up control is not executed and in the example in which the catalyst warm-up control is executed. It is a figure shown in comparison. FIG. 8 is a schematic view illustrating the fuel injection form in the diffusion combustion mode and the history of the heat generation rate associated therewith. FIG. 9 is a schematic view illustrating the fuel injection mode in the retarded combustion mode and the history of the heat generation rate associated therewith. FIG. 10 is a flowchart showing the processing operation of engine control by PCM.

  Hereinafter, an embodiment of a supercharged engine will be described in detail with reference to the drawings. FIG. 1 shows a supercharged engine (hereinafter simply referred to as “engine”) 1 according to an embodiment. The engine body 10 of the engine 1 is a diesel engine that is mounted on a vehicle and supplied with fuel mainly composed of light oil.

(Schematic configuration of the engine)
Specifically, the engine body 10 includes a cylinder block 30 provided with a plurality of cylinders 30a (only one is shown in FIG. 2), a cylinder head 31 disposed on the cylinder block 30, An oil pan 39 is provided below the cylinder block 30 and stores lubricating oil.

  Pistons 32 (see FIG. 2) are fitted into the cylinders 30a of the cylinder block 30 so as to be reciprocally slidable. The pistons 32, the cylinder block 30, and the cylinder head 31 serve as combustion chambers 33 ( 2).

  On the top surface of the piston 32, as enlarged in FIG. 2, a cavity 32a like a reentrant type in a diesel engine is formed. The cavity 32a faces an injector 38 described later when the piston 32 is positioned near the compression top dead center.

  The piston 32 is connected to the crankshaft via a connecting rod. The shape of the combustion chamber 33 is not limited to the shape illustrated. For example, the shape of the cavity 32a, the shape of the top surface of the piston 32, the shape of the ceiling portion of the combustion chamber 33, and the like can be changed as appropriate.

  As shown in FIG. 2, the cylinder head 31 is formed with an intake port 34 and an exhaust port 35 for each cylinder 30a. The intake port 34 and the exhaust port 35 have openings on the combustion chamber 33 side. An intake valve 36 and an exhaust valve 37 that are opened and closed are provided.

  Each intake valve 36 is opened and closed by an intake side cam 40, and each exhaust valve 37 is opened and closed by an exhaust side cam 41. The intake side cam 40 and the exhaust side cam 41 are each driven to rotate in conjunction with the rotation of the crankshaft. Although illustration is omitted, for example, a hydraulically operated variable valve mechanism is provided in order to adjust the open / close timing and open / close period of each of the intake valve 36 and the exhaust valve 37.

  In addition, an injector (that is, a fuel supply unit) 38 that directly injects fuel into the cylinder 30a is attached to the cylinder head 31 for each cylinder 30a. As shown in FIG. 2, the injector 38 is disposed so that its nozzle hole faces the inside of the combustion chamber 33 from the central portion of the ceiling surface of the combustion chamber 33. The injector 38 directly injects an amount of fuel into the combustion chamber 33 at an injection timing set according to the operating state of the engine 1 and according to the operating state of the engine 1.

  As shown in FIG. 1, an intake passage 50 is connected to one side surface of the engine body 10. The intake passage 50 communicates with the intake port 34 of each cylinder 30a, and supplies intake air to each cylinder 30a via the intake port 34.

  On the other hand, an exhaust passage 60 is connected to the other side surface of the engine body 10. The exhaust passage 60 communicates with the exhaust port 35 of each cylinder 30a, and burnt gas (that is, exhaust gas) is discharged from each cylinder 30a via the exhaust port 35.

  As will be described in detail later, the intake passage 50 and the exhaust passage 60 are provided with an electric supercharger 18 and a turbocharger 56 for supercharging intake air.

  An air cleaner 54 that filters intake air is disposed at the upstream end of the intake passage 50. On the other hand, a surge tank 51 is disposed near the downstream end of the intake passage 50. The intake passage 50 on the downstream side of the surge tank 51 is an independent intake passage branched for each cylinder 30a, and the downstream ends of these independent intake passages are connected to the intake ports 34 of the respective cylinders 30a.

  Between the air cleaner 54 and the surge tank 51 in the intake passage 50, the compressor 56 a of the turbocharger 56, the electric supercharger 18, the throttle valve 55, the heat, in order from the upstream side to the downstream side. A water-cooled intercooler 57 as an exchanger is provided. The throttle valve 55 is basically fully opened, but when the engine 1 is stopped, the throttle valve 55 is fully closed so that no shock is generated. The intercooler 57 is provided, for example, in the intake manifold.

  The intake passage 50 is provided with an intake side bypass passage 53 that bypasses the electric supercharger 18. The upstream end of the intake side bypass passage 53 is connected between the compressor 56 a in the intake passage 50 and the electric supercharger 18. On the other hand, the downstream end of the intake side bypass passage 53 is connected between the electric supercharger 18 and the throttle valve 55 in the intake passage 50.

  The intake side bypass passage 53 is provided with an intake side bypass valve 58 for adjusting the amount of air flowing through the intake side bypass passage 53. By adjusting the opening degree of the intake side bypass valve 58, the ratio between the intake air amount supercharged by the electric supercharger 18 and the intake air amount passing through the intake side bypass passage 53 is changed stepwise or continuously. Will be able to.

  The electric supercharger 18 includes a compressor wheel 18a provided in the intake passage 50, and an electric motor 18b that drives the compressor wheel 18a. By driving the electric motor 18b, the compressor wheel 18a is rotationally driven, and the intake air is supercharged. That is, the electric supercharger 18 is a supercharger that does not use exhaust energy. The supercharging pressure capability of the electric supercharger 18 (that is, the supercharging pressure by the electric supercharger 18) is changed by changing the driving force of the electric motor 18b. As will be described in detail later, the electric supercharger 18 is operated in a partial state while the engine 1 is operating.

  The electric motor 18b is driven by the electric power stored in the battery 19 mounted on the vehicle. The magnitude of the driving force of the electric motor 18b is changed according to the magnitude of electric power supplied to the electric motor 18b. The battery 19 stores, for example, electric power generated by an alternator (not shown) mounted on the vehicle. The battery 19 may be a 48V battery, for example. The electric motor 18b may be driven by being supplied with a 48V current.

  The intercooler 57 is water-cooled, and is connected to the radiator 90 via a supply path 91 and a return path 92. A water pump 93 is connected to the supply path 91. Cooling water as refrigerant discharged to the supply path 91 by the water pump 93 returns to the water pump 93 again through the supply path 91, the intercooler 57, the return path 92 and the radiator 90, and again to the supply path 91. It is discharged and supplied to the intercooler 57. When the cooling water passes through the intercooler 57, heat is exchanged between the cooling water and the intake air to cool the intake air. The cooling water whose temperature has been raised by the intercooler 57 is cooled by heat exchange with, for example, the atmosphere by the radiator 90.

  The upstream portion of the exhaust passage 60 is constituted by an exhaust manifold having an independent exhaust passage branched for each cylinder 30a and connected to the outer end of the exhaust port 35, and a collecting portion where the independent exhaust passages gather. ing.

  A turbine 56b of the turbocharger 56, an oxidation catalyst 61, a diesel particulate filter 62 (hereinafter referred to as DPF 62), and an exhaust shutter are disposed downstream of the exhaust manifold in the exhaust passage 60 in order from the upstream side. A valve 64 is provided.

  The turbocharger 56 is driven to rotate by receiving energy of exhaust gas (that is, exhaust energy). Specifically, when the turbine 56b of the turbocharger 56 receives rotational energy and is rotationally driven, the compressor 56a is rotationally driven via the connecting shaft 56c, and the intake air is supercharged.

  The exhaust passage 60 is provided with an exhaust side bypass passage 63 for bypassing the turbocharger 56. The exhaust side bypass passage 63 is provided with a waste gate valve 65 for adjusting the flow rate of the exhaust gas flowing to the exhaust side bypass passage 63. The turbocharger 56 is accommodated in a turbine case (not shown). The wastegate valve 65 exemplifies “turbine bypass means” for circulating at least part of the exhaust gas so as to bypass the turbine 56b.

  The turbocharger 56 may be a variable capacity turbocharger in which a movable vane is disposed in a turbine case. The exhaust side bypass passage 63 and the wastegate valve 65 may be omitted if the opening of the movable vane can be adjusted to allow the exhaust gas to flow substantially bypassing the turbine 56b. In that case, the movable vane becomes the “turbine bypass means”.

  The oxidation catalyst 61 is a so-called diesel oxidation catalyst (DOC), and is configured to promote the oxidation reaction of CO and HC in the exhaust gas by being activated at a predetermined temperature or higher. As described above, the oxidation catalyst 61 is disposed downstream of the turbine 56b in the exhaust passage 60. The oxidation catalyst 61 is an example of a “catalyst”.

  The DPF 62 is disposed downstream of the oxidation catalyst 61 in the exhaust passage 60 and is configured to collect fine particles such as soot contained in the exhaust gas of the engine 1.

  The exhaust shutter valve 64 is a valve capable of adjusting the exhaust pressure in the exhaust passage 60 by adjusting the opening degree thereof. The exhaust shutter valve 64 is used, for example, to increase the exhaust pressure in the exhaust passage 60 when a part of the exhaust gas flowing through the exhaust passage 60 is returned to the intake passage 50 by a low-pressure EGR passage 70 described later. There is a case.

  The engine 1 does not include a catalyst for purifying NOx. However, the technique disclosed herein does not exclude application to an engine equipped with a catalyst for purifying NOx.

  In the present embodiment, a high-pressure EGR passage 80 and a low-pressure EGR passage 70 that are connected to the intake passage 50 and the exhaust passage 60 and are capable of returning a part of the exhaust gas flowing through the exhaust passage 60 to the intake passage 50 are provided.

  The high-pressure EGR passage 80 includes a portion of the intake passage 50 between the intercooler 57 and the surge tank 51 (that is, a portion downstream of the electric supercharger 18), and the exhaust manifold and turbocharger in the exhaust passage 60. The turbocharger 56 is connected to a portion between the turbocharger 56 and the turbine 56b (that is, a portion upstream of the turbine 56b of the turbocharger 56). In the high-pressure EGR passage 80, an electromagnetic high-pressure EGR valve 82 that adjusts the flow rate of exhaust gas (hereinafter referred to as high-pressure EGR gas) recirculated to the intake passage 50 through the high-pressure EGR passage 80 is provided. . The high pressure EGR valve 82 is configured to adjust the flow rate of the high pressure EGR gas by changing its opening degree. The high pressure EGR passage 80 is an example of an “EGR passage”.

  On the other hand, the low-pressure EGR passage 70 is a portion of the intake passage 50 between the air cleaner 54 and the compressor 56a of the turbocharger 56 (that is, a portion upstream of the compressor 56a of the turbocharger 56), and an exhaust gas. The passage 60 is connected to a portion between the DPF 62 and the exhaust shutter valve 64. The low-pressure EGR passage 70 includes an EGR cooler 71 that cools exhaust gas recirculated to the intake passage 50 through the low-pressure EGR passage 70 (hereinafter referred to as low-pressure EGR gas), and an electromagnetic type that adjusts the flow rate of the low-pressure EGR gas. Low pressure EGR valve 72 is provided. As with the high pressure EGR valve 82, the low pressure EGR valve 72 is configured to adjust the flow rate of the low pressure EGR gas by changing its opening degree. The low pressure EGR passage 70 is an example of a “second EGR passage”.

  Hereinafter, a system including the high pressure EGR passage 80 and the high pressure EGR valve 82 is referred to as a high pressure EGR system 8, while a system including the low pressure EGR passage 70, the EGR cooler 71, and the low pressure EGR valve 72 is referred to as a low pressure EGR system 7.

  The engine 1 is configured to have a relatively low compression ratio with a geometric compression ratio of 12 to 16, thereby improving emission performance and combustion efficiency. ing. In this engine 1, the reduction of the geometric compression ratio is compensated by adjusting the amount of fresh air by the turbocharger 56 and the electric supercharger 18 and adjusting the low pressure EGR gas and the high pressure EGR gas. ing.

(Engine control system configuration)
The engine 1 configured as described above is controlled by a powertrain control module (hereinafter referred to as PCM) 100 shown in FIG. The PCM 100 includes a microprocessor having a CPU 101, a memory 102, a counter timer group 103, an interface 104, and a bus 105 for connecting these units. The PCM 100 is an example of a “control unit”.

  The PCM 100 includes a water temperature sensor SW1 that detects the temperature of engine cooling water, a supercharging pressure sensor SW2 that detects supercharging pressure, an intake air temperature sensor SW3 that detects intake air temperature, an exhaust gas temperature sensor SW4 that detects exhaust gas temperature, and the above A crank angle sensor SW5 for detecting the rotation angle of the crankshaft, an accelerator opening sensor SW6 for detecting an accelerator opening corresponding to an operation amount of an accelerator pedal (not shown) of the vehicle, a vehicle speed sensor SW7 for detecting the vehicle speed of the vehicle, and The detection signal from the turbine rotation speed sensor SW8 for detecting the rotation speed of the turbine 56b of the turbocharger 56 is input.

  The PCM 100 estimates or determines the state of the engine 1 and the vehicle by performing various calculations based on the detection signals of these sensors SW1 to SW8, and uses the control signal generated in response to the determination to determine the state of the engine 1. Control driving.

  For example, the PCM 100 estimates the engine speed from the detection result of the crank angle sensor SW5, and calculates the engine load from the detection result of the accelerator opening sensor SW6.

  Further, when the detected temperature of the water temperature sensor SW1 is lower than the predetermined temperature Tc, the PCM 100 determines that the temperature in the cylinder 30a is low and the engine 1 is in a cold state, and the accelerator detected by the accelerator opening sensor SW6. Based on the opening degree, it is determined whether or not the engine body 10 is in a predetermined low load range. Here, the predetermined “low load range” is an operation on the low load side when the operation range of the engine 1 is divided into a high load range, a medium load range, and a low load range according to the load level. It may be an area. The boundary of each region changes according to the engine speed. In this configuration example, the low load region is included in an operation region in which a partial load operation described later is performed.

  The PCM 100 generates a control signal based on the determination result, and outputs the control signal to the injector 38, the electric motor 18b, and the actuators of the various valves 55, 58, 64, 65, 72, and 82. The PCM 100 also outputs control signals to the variable valve mechanisms of the intake valve 36 and the exhaust valve 37.

(Outline of control of electric supercharger)
Next, control of the electric supercharger 18 by the PCM 100 will be described. FIG. 4 shows a control mode of the electric supercharger 18. The PCM 100 basically rotates the electric supercharger 18 during the operation of the engine body 10, but the engine cooling water temperature detected by the water temperature sensor SW1 and the crank angle sensor SW5 are used. Based on the detected rotational speed of the engine 1, the rotational speed (that is, the supercharging pressure) of the electric supercharger 18 is controlled. Specifically, the rotational speed is highest in a region where the water temperature is low or the engine is low, and from there, control is performed so as to decrease the rotational speed as the water temperature increases or the engine speed increases.

  In the present embodiment, the engine speed is such that the pressure ratio of the compressor 56a of the turbocharger 56 becomes 1.2 or more when the water temperature becomes 80 ° C. or higher or the engine speed exceeds r1. In a certain number of regions, the electric supercharger 18 is set in the idle rotation state and the intake side bypass valve 58 is fully opened so that the supercharging by the electric supercharger 18 is not substantially performed. To do. In this way, the turbocharger 56 does not stop the rotation of the electric supercharger 18 in the engine rotation region where the water temperature is 80 ° C. or higher or the pressure ratio is 1.2 or higher. Only supercharging can be done.

  As described above, by constantly rotating the electric supercharger 18, the electric supercharger 18 is temporarily stopped when the supercharging pressure is increased by the electric supercharger 18 as will be described later. Thus, the electric supercharger 18 (strictly, the electric motor 18b for operating the electric supercharger 18) is more efficient than the on-off control which is driven in a necessary scene. Can be operated.

  In FIG. 5, the performance curve showing the characteristic of the electric supercharger 18 is shown. The upper diagram of FIG. 5 is a performance curve graph showing the characteristics of the compressor wheel 18a of the electric supercharger 18, and the vertical axis indicates the pressure ratio of the electric supercharger 18 (that is, the upstream pressure relative to the downstream pressure). The horizontal axis represents the discharge flow rate. In the upper diagram of FIG. 5, a curve LL represents a rotation limit line, a straight line SL represents a surge line, and a straight line CL represents a choke line. A region surrounded by these lines is a region where the electric supercharger 18 can be operated. The operation efficiency of the electric supercharger 18 increases as the position is closer to the center of this region.

  Since the electric supercharger 18 is used for assisting the turbocharger 56 and adjusting the amount of fresh air introduced into the cylinder 30a, the rotation limit as shown by the mesh in the upper diagram of FIG. 5 is used. In an area away from the line, the engine is operated at an appropriate speed according to the engine coolant temperature and the engine speed. That is, the electric supercharger 18 is operated in a partial state far away from the limit rotational speed.

  The lower diagram of FIG. 5 illustrates the characteristics of the electric motor 18b of the electric supercharger 18. The vertical axis represents the torque of the electric motor 18b, and the horizontal axis represents the rotation speed of the electric motor 18b. The one-dot chain line in the lower diagram of FIG. 5 indicates a line that has equal power consumption. The electric supercharger 18 is operated in a region indicated by a mesh in the upper diagram of FIG. 5. At this time, the electric motor 18 b operates in a region indicated by a mesh in the lower diagram of FIG. 5. The electric power consumption of the electric motor 18b is relatively low, and the efficiency of the electric motor 18b is relatively high. The state in which the electric motor 18b is operating at a torque lower than the maximum torque may be called operating in the partial state of the electric supercharger 18. As described above, although the electric supercharger 18 is always rotating during the operation of the engine body 10, it is possible to reduce power consumption by operating the electric supercharger 18 in a partial state. It is.

  Note that the electric supercharger 18 may be stopped in the idle rotation region shown in FIG.

(Engine combustion control)
The basic control of the engine 1 by the PCM 100 mainly determines the required driving force based on the accelerator opening, and the amount of new air introduced into the cylinder 30a and the high pressure so that the corresponding combustion state is realized. The EGR gas amount and the low-pressure EGR gas amount are adjusted, and the fuel injection amount, the injection timing, and the like are realized by the operation control of the injector 38.

  FIG. 6 illustrates a φ-T map of the engine 1. The φ-T map is a map showing a region where CO / HC, soot and NOx, which are unburned components, are generated on a plane composed of the combustion temperature (T) and the equivalence ratio (φ) of the air-fuel mixture. When the combustion temperature is high, the NOx region is entered, and when the equivalence ratio is high, the soot region is entered. Further, if the combustion temperature is too low, the CO / HC region is entered. The engine 1 adjusts the amount of fresh air, the amount of high-pressure EGR gas, and the amount of low-pressure EGR gas, and also adjusts the fuel injection amount, injection timing, etc., so that CO / HC, soot and Combustion that does not enter the region where NOx is generated.

  Specifically, during partial load operation (that is, operation at a load other than a fully open load), the engine 1 operates the turbocharger 56 to generate an amount of fresh air corresponding to the fuel supply amount in the cylinder 30a. By introducing the EGR gas, the mixture ratio is adjusted so that the equivalence ratio of the air-fuel mixture does not become too high. By introducing the EGR gas into the cylinder 30a, it is possible to avoid the combustion speed and the combustion temperature from becoming too high, thereby generating RawNOx. Suppress. The EGR gas introduced into the cylinder 30a is mainly low-temperature low-pressure EGR gas when the engine 1 is warm, and high-temperature high-pressure EGR gas may be introduced into the cylinder 30a as necessary.

  Further, in order to suppress the generation of RawNOx, as illustrated in FIG. 8, the engine 1 performs the front injection that performs at least one fuel injection before the compression top dead center (TDC) during the partial load operation. And the main injection having a fuel injection amount larger than that of the preceding injection after the preceding injection. In the injection example of FIG. 8, two pre-stage injections are executed during the compression stroke before the compression top dead center (TDC), and the main injection having a fuel injection amount larger than the pre-stage injection is performed once near the compression top dead center. In addition, after the main injection, after injection is executed once with the fuel injection amount equivalent to the pre-injection. Hereinafter, such an injection form is referred to as a diffusion combustion mode.

  Of the two pre-stage injections executed in this diffusion combustion mode, the first fuel injection with relatively early injection timing is pilot injection, and the second fuel injection is pre-injection. By performing the pilot injection and the pre-injection before the compression top dead center, the mixing property between the air and the fuel is enhanced, and the chemical reaction of the air-fuel mixture proceeds during the compression stroke. As a result, combustion is possible even if the in-cylinder temperature is relatively low, and as shown in the heat generation history of FIG. Combustion due to compression ignition) occurs.

  The compression end temperature and the compression end pressure can be increased by the pre-stage combustion in the diffusion combustion mode. Thereby, the temperature and pressure in the cylinder at the start of the main injection can be optimized, and the ignitability and combustibility in the main injection can be improved. As a result, since the main combustion (that is, diffusion combustion using the preceding stage combustion as a fire type) can be stably generated in the vicinity of the compression top dead center, the work of the engine 1 can be increased, and the fuel consumption can be improved. Improvements can be made. In addition, by improving the ignitability, it is possible to suppress the generation of soot, and to prevent a rapid increase in heat generation in the main combustion, that is, to prevent the combustion period from becoming extremely short. Can be suppressed.

  Further, by performing after injection within the expansion stroke period during which the in-cylinder pressure is reduced, soot can be combusted and soot discharge from the combustion chamber 33 can be suppressed.

(Engine control when starting the vehicle)
Here, when the engine body 10 is in a cold state and in a low load range, such as when the vehicle starts from a stopped state, the exhaust gas may be relatively low temperature, and the oxidation catalyst 61 may not be sufficiently activated. This is not preferable from the viewpoint of HC purification performance.

  Therefore, it is conceivable that the exhaust gas is guided to bypass the turbine 56b of the turbocharger 56 by opening the waste gate valve 65 in order to raise the temperature of the oxidation catalyst 61 as early as possible.

  However, with such a configuration, the amount of work by the compressor a of the turbocharger 56 decreases according to the flow rate of the exhaust gas bypassing the turbine 56b, and the supply of fresh air into the cylinder 30a is reduced. It may be insufficient. Furthermore, if the exhaust gas bypasses the turbine 56b, the exhaust pressure in the exhaust passage 60 also decreases, so that the EGR gas recirculation by the high-pressure EGR system 80 may be insufficient. In order to suppress the production of RawHC, it is required to supply fresh air, EGR gas, and the like appropriately.

  On the other hand, when the engine body 10 is in a cold state and in a low load region, the engine 1 has an exhaust gas by opening the wastegate valve 65 while increasing the supercharging pressure via the electric supercharger 18. The turbine 56 is bypassed.

  Specifically, the case where the vehicle starts from a stop state will be described as an example. When a driver requests acceleration of the vehicle by depressing the accelerator pedal, the PCM 100 includes the high pressure EGR valve 82 and the waist. While opening the gate valve 65, the catalyst warm-up control which drives the electric supercharger 18 and raises the supercharging pressure is executed.

  By opening the waste gate valve 65, the exhaust gas can bypass the turbine 56b. As a result, a sufficient amount of heat can be applied to the oxidation catalyst 61, so that the temperature of the oxidation catalyst 61 can be raised as quickly as possible. As a result, the oxidation catalyst 61 can be activated by scavenging, and as a result, the HC purification performance can be secured.

  Further, as shown in FIG. 1, since the high-pressure EGR passage 80 is connected upstream of the turbine 56b of the turbocharger 56 in the intake passage 50, the EGR gas recirculated through the high-pressure EGR passage 80 is The temperature becomes higher than that of the EGR gas recirculated through the low pressure EGR passage 70. Therefore, the minimum in-cylinder temperature can be ensured even in the cold state. This is effective in suppressing the production of RawHC.

  Further, as described above, when the activation catalyst 61 is activated by opening the wastegate valve 65, the PCM 100 operates the electric supercharger 18 so that the supercharging pressure increases. Although the amount of work by the compressor 56a is reduced by the amount of exhaust gas bypassing the turbine 56b, the reduction can be compensated by the electric supercharger 18. Thereby, even if the supercharging pressure does not increase in the turbocharger 56, the amount of fresh air introduced into the cylinder 30a can be increased. As a result, unburned fuel can be reduced and the production of RawHC can be suppressed. Further, the equivalence ratio of the air-fuel mixture is lowered by the amount of increase in the amount of fresh air, and soot generation can be suppressed.

  In addition, the compressor 56 a of the turbocharger 56 can be rotated by the flow of fresh air that occurs as the electric supercharger 18 operates. Since the turbine 56b also rotates in conjunction with the rotation of the compressor 56a, the turbine 56b does not become a resistance in the exhaust passage 60. For example, exhaust gas passing through the turbine 56b can provide a sufficient amount of heat to the oxidation catalyst 61 because the turbine 56b does not become a resistance, which is advantageous in activating the oxidation catalyst 61 at an early stage. Further, since the exhaust pressure is reduced by the rotation of the turbine 56b, the scavenging effect by the electric supercharger 18 is also increased, and as a result, the pump loss can be reduced.

  In this way, it is possible to prevent a decrease in emission performance in a cold state and in a low load region.

  For example, the upper diagram of FIG. 7 shows the case where the electric supercharger 18 is not driven when the vehicle starts and the wastegate valve 65 is not opened (comparative example in which catalyst warm-up control is not executed), and the electric supercharger when the vehicle starts The ratio of the air density to the amount of fresh air in the cylinder 30a immediately after the start of the vehicle is shown in comparison with the time when the machine 18 is operated and the waste gate valve 65 is opened (example in which the catalyst warm-up control is executed). FIG. In the upper diagram of FIG. 7, the vertical axis represents the ratio of the air density ratio.

  On the other hand, the lower diagram of FIG. 7 is a diagram showing a comparison of the difference in gas composition in the cylinder 30a immediately after the start of the vehicle between the comparative example and the example. In the lower diagram of FIG. 7, the vertical axis represents the compression end temperature, and in this lower diagram, the gas composition in the cylinder 30a is set so that the compression end temperature is the same in each of the comparative example and the example. . In addition, the square area which shows "new air" and "high pressure EGR gas" shown in the lower part of FIG. 7 represents the ratio (%) of each gas component to the total gas charged in the cylinder 30a. Accordingly, in the lower diagram of FIG. 7, the magnitude relationship between the area of each gas component in the left gas composition shown as a comparative example and the area of each gas component in the right gas composition shown as an example is the filling amount of each gas component. It does not always indicate the magnitude relationship.

  First, in the comparative example in which the electric supercharger 18 is not operated and the wastegate valve 65 is not opened, the high pressure EGR valve 82 is opened when the vehicle starts. Thereby, the high pressure EGR gas is introduced into the cylinder 30a.

  That is, as described above, the EGR gas recirculated through the high-pressure EGR passage 80 has a higher temperature than the EGR gas recirculated through the low-pressure EGR passage 70. Thereby, although the ignitability of the air-fuel mixture can be improved and the generation of RawHC can be suppressed, the warming-up of the oxidation catalyst 61 may be delayed by simply opening the high-pressure EGR passage 80.

  On the other hand, in the embodiment, both the high-pressure EGR valve 82 and the waste gate valve 65 are opened by executing the catalyst warm-up control when the vehicle starts. Thereby, it becomes possible to guide the oxidation catalyst 61 to the active state at an early stage. However, when the wastegate valve 65 is opened, the exhaust pressure decreases, so the differential pressure between the exhaust side and the intake side decreases, the amount of high-pressure EGR gas introduced into the cylinder 30a decreases, and the compression end temperature decreases. there's a possibility that.

  However, in this embodiment, as described above, the supercharging pressure by the electric supercharger 18 is increased when the wastegate valve 65 is opened. Thereby, the amount of fresh air introduced into the cylinder 30a can be increased. Further, as shown in the upper diagram of FIG. 7, the temperature of the air-fuel mixture in the cylinder 30a is lowered by the amount of introduction of the high-pressure EGR gas is reduced. In combination with this, the amount of fresh air introduced by the electric supercharger 18 increases the air density in the cylinder 30a (see the arrow in the upper diagram of FIG. 7). . As a result, the specific heat ratio of the gas in the cylinder 30a is increased and the compression end temperature is increased, so that unburned fuel can be reduced, and generation of RawNOx can be suppressed.

  Further, after executing the catalyst warm-up control, the PCM 100 opens the low pressure EGR passage 70 via the low pressure EGR valve 72 when the temperature of the oxidation catalyst 61 is raised to a predetermined temperature or higher. Here, the “predetermined temperature” may be set near the activation temperature of the oxidation catalyst 61, for example. Further, this determination may be performed indirectly based on, for example, the exhaust temperature detected by the exhaust temperature sensor SW4.

  Since the low-pressure EGR passage 70 is connected downstream of the turbine 56 b of the turbocharger 56 in the exhaust passage 60, the temperature of the EGR gas recirculated through the low-pressure EGR passage 70 passes through the high-pressure EGR passage 80. Lower than the temperature of the refluxed EGR gas. Accordingly, the specific heat of the gas in the cylinder 30a can be increased by increasing the amount of EGR gas while preventing the temperature in the cylinder 30a from becoming too high. As a result, the combustion rate and the combustion temperature can be kept low, and the production of RawNOx is suppressed. In addition, by opening the low pressure EGR passage 70 after the oxidation catalyst 61 has been heated to a predetermined temperature or higher, HC purification performance is ensured when the oxidation catalyst 61 is warmed up, while RawNOx is generated after the warm-up is completed. Can be suppressed. Note that the wastegate valve 65 may be closed after the warm-up is completed.

  Here, when performing the catalyst warm-up control, as illustrated in FIG. 9, the fuel injection start timing may be retarded as compared with the steady operation of the vehicle.

  Specifically, the pilot injection in the front stage injection is stopped and the after injection is stopped, and the injection start timings of the pre-injection and the main injection are retarded. Moreover, in the example of FIG. 9, main injection is performed in two steps. Hereinafter, such an injection form is referred to as a retarded combustion mode. In addition, the total value of the fuel injection amounts of the two main injections is larger than the fuel injection amount in the pre-stage injection (pre-injection). The fuel injection mode shown here is merely an example, and the pre-injection and main injection injection timings and the fuel injection amount in the retarded combustion mode are appropriately changed based on the required driving force of the vehicle.

  When the pilot injection is stopped and the pre-injection is retarded, the mixing property of the air and the fuel is deteriorated. Therefore, as shown in the upper diagram of FIG. 9, the pre-stage combustion does not occur before the compression top dead center. By supercharging with the electric supercharger 18, the intake density is increased, and as much fresh air as possible is introduced into the cylinder 30a, the specific heat ratio of the gas in the cylinder 30a is increased, and compression is performed. Since the end temperature becomes sufficiently high, the pre-stage combustion and the main combustion occur after the compression top dead center.

  Since the retarded combustion mode enables stable main combustion even when the compression ratio is low, the combustion temperature can be prevented from becoming excessively high, and the generation of NOx can be suppressed. Further, since the intake air temperature decreases as the amount of fresh air increases, it is also possible to suppress the increase in combustion temperature and suppress the generation of NOx. In the retarded combustion mode, the combustion temperature is higher even in the later stage of combustion than in the diffusion combustion mode shown in FIG. 8, and soot can be burned without performing after injection. Omitting after-injection is advantageous for improving fuel efficiency.

  When the vehicle starts, in addition to driving the electric supercharger 18 to increase the supercharging pressure, Pmax can be increased more quickly by performing the retard combustion mode. Therefore, during acceleration of the vehicle, based on the change history of Pmax, specifically, when the inclination of the rise of Pmax is small, in addition to driving the electric supercharger 18 to increase the supercharging pressure, the retard By performing the combustion mode, Pmax is increased more quickly. On the other hand, when the rising slope of Pmax is small, the electric supercharger 18 is driven to increase the supercharging pressure, while the retard combustion mode is performed. It may not be possible.

  Next, the engine control processing operation by the PCM 100 will be described based on the flowchart of FIG. In addition, the flowchart shown in FIG. 10 is a flowchart when the engine main body 10 is in a cold state. The determination that the engine body 10 is in the cold state can be made based on, for example, a detection signal from the water temperature sensor SW1. Alternatively, it may be indirectly estimated that the engine body 10 is in a cold state based on a detection signal from the vehicle speed sensor SW7. For example, if it is estimated based on the transition of the vehicle speed that it is immediately after starting from the stop state, the engine body 10 is determined to be in the cold state.

  In first step S101, the PCM 100 reads signals from various sensors and determines the operating state of the engine 1. In the next step S102, the PCM 100 drives the electric supercharger 18 according to the map illustrated in FIG. The PCM 100 sets the rotational speed of the electric supercharger 18 to a high rotational speed, a medium rotational speed, or a low rotational speed in accordance with the water temperature of the engine 1 and the engine rotational speed.

  In step S103 following step S102, the PCM 100 determines whether or not there is a driver acceleration request. The PCM 100 determines whether or not the driver has requested acceleration based on the detected value of the accelerator opening sensor SW6. When there is an acceleration request, the control process proceeds to step S104 to perform the above-described retarded combustion mode, and when there is no acceleration request, the control process proceeds to step S112 to perform the diffusion combustion mode.

  In step S104, the PCM 100 calculates the required driving force of the engine 1 (driving force based on the accelerator opening or the like). In step S105, the PCM 100 determines whether or not the engine body 10 is in a low load range based on the required driving force and the engine speed calculated in step S104. When in the low load range, the process proceeds to step S106 to perform the above-described catalyst warm-up control in addition to the diffusion combustion mode, and when not in the low load range, the process proceeds to step S110. Even when the engine body 10 is in the low load region, as described above, when the temperature of the oxidation catalyst 61 is raised to a predetermined temperature or higher, the process proceeds to step S110 instead of step S106. ing.

  In step S106, the PCM 100 sets target values such as the fuel injection amount, the fuel injection timing, the target EGR rate, and the target boost pressure in order to execute the catalyst warm-up control while realizing the required driving force calculated in step S105. Determine the control amount of each actuator.

  In step S107 following step S106, the PCM 100 executes a turbine bypass process. This turbine bypass process is one process that constitutes the catalyst warm-up control, and is configured to open the waste gate valve 65 and the high-pressure EGR valve 82.

  In step S108 following step S107, the PCM 100 increases the supercharging pressure by the electric supercharger 18. Thus, catalyst warm-up control is executed.

  In subsequent step S109, the PCM 100 outputs a control signal to each actuator based on the control amount determined in step S106. Then, fuel injection that realizes the above-described retarded combustion mode is executed.

  On the other hand, in step S110, the PCM 100 determines the control amount of each actuator as in step S106. In the following step S111, the PCM 100 determines whether or not the electric supercharger 18 needs to be driven based on the difference between the target supercharging pressure determined in step S110 and the actual supercharging pressure based on the sensor detection signal. Determine. When it is necessary to drive the electric supercharger 18, the control process proceeds to step S108, and the PCM 100 increases the supercharging pressure by supplying electric power to the electric supercharger 18, as described above. On the other hand, when the PCM 100 determines in this step S111 that it is not necessary to drive the electric supercharger 18, the control process does not proceed to step S108 but proceeds to step S109. Then, the fuel injection that realizes the retarded combustion mode is executed in the same manner as when the catalyst warm-up control is executed.

  In step S112, the PCM 100 calculates the required driving force of the engine 1 as in step S104. In the subsequent step S113, the PCM 100 determines the control amount of each actuator so as to meet the required driving force. In step S114, the PCM 100 outputs a control signal to each actuator, thereby executing fuel injection that realizes the diffusion combustion mode.

  The control process then returns to step S101. Even when the supercharging pressure of the electric supercharger 18 is increased at the early stage of acceleration of the vehicle, if the driving of the electric supercharger 18 becomes unnecessary in the latter half of the acceleration, the supercharging pressure by the electric supercharger 18 is descend.

  As described above, the engine 1 can prevent a decrease in emission performance in a cold state and in a low load region.

  In general, when the vehicle starts from a stopped state, the engine 1 is in a cold state. For this reason, by performing the catalyst warm-up control when the vehicle starts, it is possible to appropriately prevent a decrease in the emission performance.

  Further, by increasing the supercharging pressure of the electric supercharger 18 and increasing the ratio of the amount of fresh air in the cylinder 30a as illustrated in the lower diagram of FIG. 7, the specific heat ratio of the gas in the cylinder 30a is increased. Even if the temperature in the cylinder 30a before starting the compression is low, the compression end temperature becomes high. Therefore, in a diesel engine having a low compression ratio in which the geometric compression ratio is set to 16 or less, it is advantageous for ensuring the ignitability of the air-fuel mixture.

  In addition, since the electric supercharger 18 operates in a partial state as shown in FIG. 5, it is avoided that rush power is supplied to the electric motor 18 b of the electric supercharger 18 every time acceleration is performed. Can do. Accordingly, it is possible to suppress power consumption when raising the supercharging pressure by the electric supercharger 18, and it is advantageous for improving the reliability of the electric supercharger 18.

  In the first place, diesel engines are more efficient than general gasoline engines. However, since the exhaust temperature becomes low as the heat efficiency is excellent, the above-described delay in warming up of the oxidation catalyst 61 becomes even more problematic. Therefore, the catalyst warm-up control is particularly effective in such a diesel engine.

<< Other embodiments >>
The present invention is not limited to the embodiment described above, and can be substituted without departing from the spirit of the claims.

  For example, the technology disclosed herein is not limited to being applied to a diesel engine, but can also be applied to an engine using gasoline or fuel containing naphtha.

  Further, the above-described catalyst warm-up control may be performed not only when the vehicle is started but also when the vehicle is automatically restarted from the idle stop state, for example.

  That is, the engine 1 includes idle stop means 110 (illustrated only in FIG. 3) that puts the engine body 10 in an idle stop state, and the PCM 100 automatically restarts the engine body 10 that has been placed in the idle stop state by the idle stop means 1110. Sometimes, the catalyst warm-up control may be executed.

  Generally, when the engine body 10 is automatically restarted, the exhaust gas becomes relatively low in temperature. For this reason, if the catalyst warm-up control as described above is executed during the automatic restart of the engine body 10, it is possible to appropriately prevent the emission performance from being lowered. In this case, the PCM 100 sequentially executes the processes shown in steps S106 to S108 in FIG.

  Further, the above-described catalyst warm-up control may be performed not only when the vehicle starts or when the vehicle restarts automatically, but also when the engine speed is slow.

  That is, the PCM 100 may execute the catalyst warm-up control even when the engine body 10 is in a cold state and the engine speed is lower than the predetermined speed, even if it is outside the low load range. Here, the predetermined number of revolutions may be designed according to the configuration around the combustion chamber 33, such as a piston ring.

  Generally, when the engine speed is low, gas leakage from the combustion chamber 33 (particularly, gas leakage through the piston ring) is relatively large as compared to when the engine speed is high. Therefore, when the engine speed is slow, the gas pressure in the combustion chamber 33 is reduced, which causes a reduction in the compression end leading. This is inconvenient in suppressing the production of RawHC.

  On the other hand, according to the above configuration, the PCM 100 executes the catalyst warm-up control as described above when the engine body 10 is in a cold state and the engine speed is below a predetermined speed. Specifically, the PCM 100 sequentially executes the processes shown in steps S106 to S108 in FIG. As a result, the generated HC can be effectively purified.

DESCRIPTION OF SYMBOLS 1 Engine 10 Engine main body 18 Electric supercharger 18b Electric motor 50 Intake passage 56 Turbo supercharger 56a Compressor 56b Turbine 60 Exhaust passage 61 Oxidation catalyst (catalyst)
65 Wastegate valve (turbine bypass means)
70 Low pressure EGR passage (second EGR passage)
80 High pressure EGR passage (EGR passage)
100 PCM (control unit)
SW1 Water temperature sensor (sensor)
SW6 Accelerator opening sensor (sensor)

Claims (7)

An engine body mounted on the vehicle;
An intake passage and an exhaust passage connected to the engine body;
An electric supercharger provided in the intake passage and supercharged by an electric motor;
A turbocharger having a turbine disposed in the exhaust passage and a compressor disposed upstream of the electric supercharger in the intake passage, and supercharging using exhaust energy;
An EGR passage that communicates the exhaust passage upstream of the turbine and the intake passage downstream of the electric supercharger and recirculates part of the exhaust gas to the intake passage;
A turbine bypass means provided in the exhaust passage, for guiding at least a part of the exhaust gas so as to bypass the turbine;
A catalyst disposed downstream of the turbine in the exhaust passage;
A controller that determines whether or not the engine body is in a cold state and in a predetermined low load region based on a detection signal from a sensor attached to the engine body,
The control unit guides the exhaust gas so as to open the EGR passage and bypass the turbine via the turbine bypass means when the engine body is in a cold state and in a predetermined low load region. An engine with a supercharger that performs catalyst warm-up control for outputting a control signal to the electric supercharger so as to increase a supercharging pressure by the electric supercharger. The supercharged engine according to claim 1,
A second EGR passage that communicates the exhaust passage downstream of the turbine and the intake passage upstream of the compressor and recirculates part of the exhaust gas to the intake passage;
The supercharged engine that opens the second EGR passage when the control unit determines that the temperature of the catalyst has risen to a predetermined temperature or higher after performing the catalyst warm-up control. The supercharged engine according to claim 1 or 2,
The control unit is a supercharged engine that performs the catalyst warm-up control when the vehicle starts from a stopped state. The supercharged engine according to any one of claims 1 to 3,
Comprising idle stop means for bringing the engine body into an idle stop state,
The supercharged engine that performs the catalyst warm-up control when the engine is automatically restarted by the idle stop means when the engine body is automatically restarted. The engine with a supercharger according to any one of claims 1 to 4,
The control unit is a supercharged engine that operates the electric supercharger in a partial state. The engine with a supercharger according to any one of claims 1 to 5,
The engine body is a supercharged engine that is a diesel engine having a geometric compression ratio of 16 or less. The engine with a supercharger according to any one of claims 1 to 6,
The supercharged engine that performs the catalyst warm-up control when the engine body is in a cold state and the engine rotational speed is lower than a predetermined rotational speed even when the controller is out of the low load range.

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