JP2019105190A - Engine with supercharger - Google Patents

Abstract

To prevent degradation of emission performance in a cold state and a low load area.SOLUTION: An engine with a supercharger includes an engine main body 10, an electrically-driven supercharger 18, a turbo-supercharger 56, a high-pressure EGR passage 80, a waste gate valve 65 guiding an exhaust gas to bypass a turbine 56b in an exhaust passage 60, an oxidation catalyst 61 disposed in the exhaust passage 60, and a control portion (PCM100) for opening the high-pressure EGR valve 82 and the waste gate valve when the engine main body is in a cold state and in a prescribed low load area, and outputs a control signal to the electrically-driven supercharger to increase a supercharging pressure by the electrically-driven supercharger.SELECTED DRAWING: 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 is a diesel equipped with a turbocharger for supercharging using exhaust energy and an electric turbocharger for supercharging without using exhaust energy. It is configured as an engine.

JP, 2010-180719, A

  In a diesel engine, a part of exhaust gas is recirculated to the intake passage in order to suppress the generation of RawNOx by lowering the combustion rate 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 communicating the exhaust passage upstream of the turbine of the turbocharger with the intake passage downstream of the compressor of the turbocharger. The low pressure EGR system comprises a low pressure EGR passage communicating the exhaust passage downstream of the turbocharger turbine with the intake passage upstream of the compressor of the turbocharger, and an EGR for cooling the exhaust gas flowing through the low pressure EGR passage. And a cooler.

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

  In addition, when managing engine emissions, it is necessary to pay attention not only to the generation of RawNOx but also to the generation of HC (hydrocarbons) 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 area, such as immediately after starting from a stopped state, the amount of exhaust gas becomes small and low temperature, and the oxidation catalyst may not be warmed up promptly. This is not preferable for securing the purification performance of HC.

  Therefore, in order to warm up the oxidation catalyst as early as possible, it is conceivable to guide the 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 is reduced 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 decreases, and the EGR gas recirculation by the high pressure EGR system is also insufficient. Could be In order to suppress the generation of RawHC, it is required to secure a sufficient compression end temperature. In order to meet such requirements, it is required to properly supply fresh air, EGR gas, etc. into the cylinder.

  The technique disclosed herein has been made in view of the above point, and its object is to prevent a decrease in emission performance in a cold state and a low load region in a supercharged engine. .

  The technology disclosed herein is characterized by operating the turbine bypass means while raising the supercharging pressure via the electric supercharger at least in a cold state and a low load region in the over-payment engine. I assume.

  Specifically, the supercharged engine disclosed herein is provided in an engine main body mounted on a vehicle, an intake passage and an exhaust passage connected to the engine main body, and the intake passage, and is overheated by an electric motor. An electric supercharger for feeding, a turbine disposed in the exhaust passage, and a compressor disposed upstream of the electrically driven turbocharger in the intake passage, using exhaust energy An EGR that connects a supercharger turbocharger, the exhaust passage upstream of the turbine, and the intake passage downstream of the electric turbocharger, and recirculates part of exhaust gas to the intake passage A passage, turbine bypass means provided in the exhaust passage for guiding at least a portion of the exhaust gas so as to bypass the turbine, and disposed downstream of the turbine in the exhaust passage The control unit includes: a catalyst; and a control unit that determines whether 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. When the engine body is in a cold state and in a predetermined low load area, the EGR passage is opened and the exhaust gas is guided to bypass the turbine via the turbine bypass means, and the motorized type A catalyst warm-up control is performed to output a control signal to the electric supercharger so as to raise the supercharging pressure via the supercharger.

  According to this configuration, when the engine body is in the cold state and in the predetermined low load region, the control unit opens the EGR passage and at least a portion of the exhaust gas to bypass the turbine through the turbine bypass means. Distribute. By diverting the turbine to the exhaust gas, a sufficient amount of heat can be given to the catalyst, so that the catalyst can be heated as quickly as possible. As a result, the catalyst can be activated at an early stage, and it is possible to secure the purification performance of HC.

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

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

  In addition, the flow of fresh air generated by the operation of the electric supercharger can rotate the compressor of the turbocharger. Since the turbine also rotates in conjunction with the rotation of the compressor, the turbine does not become resistant in the exhaust passage. Since it is possible to provide a sufficient amount of heat to the catalyst as the turbine does not become resistant, it is advantageous in activating the catalyst early. Further, since the exhaust pressure is reduced by the rotation of the turbine, the effect of scavenging by the electric supercharger is also increased, and it is also possible to reduce the pump loss.

  In this way, a decrease in emission performance in the cold state and low load region is prevented.

  The supercharger-equipped engine communicates with the exhaust passage downstream of the turbine and the intake passage upstream of the compressor, and a second EGR passage for recirculating part of the exhaust gas to the intake passage. The control unit may open the second EGR passage when it is determined that the temperature of the catalyst has risen to a predetermined temperature or higher after the catalyst warm-up control.

  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 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 speed and the combustion temperature can be reduced, and the generation of RawNOx is suppressed. In addition, by opening the second EGR passage after the temperature of the catalyst has risen to a predetermined temperature or higher, the purification performance of HC can be secured at the time of catalyst warm-up, while the generation of RawNOx can be suppressed after the completion of warm-up. .

  In addition, the control unit may execute the catalyst warm-up control when the vehicle starts moving from a stopped state.

  Generally, at the initial stage of acceleration when starting from a stopped state, the engine body is in a cold state. Therefore, if the catalyst warm-up control is performed at the time of start of the vehicle, it is possible to appropriately prevent the emission performance from being degraded.

  Further, the supercharged engine includes idle stop means for putting the engine body into an idle stop state, and the control unit performs automatic restart of the engine body brought into the idle stop state by the idle stop means, The catalyst warm-up control may be performed.

  Generally, at the time of the automatic restart of the engine body, the exhaust gas becomes relatively low temperature. Therefore, if the catalyst warm-up control is performed at the time of automatic restart of the engine body, it is possible to appropriately prevent the emission performance from being degraded.

  Further, the control unit may operate the electric supercharger in a partial state. Here, "operating the electric supercharger in the partial state" means operating the electric supercharger so that the electric motor has a torque lower than the maximum torque, and / or the compressor wheel has a limit It may mean that the electric supercharger is operated so as to have a rotational speed lower than the rotational speed. When the electric supercharger is operated in the partial state, the power consumption of the electric motor decreases and the efficiency of the compressor wheel increases. Then, in the supercharged engine provided with both the turbocharger and the electric supercharger, the power consumption can be reduced by operating the electric supercharger auxiliary.

  Further, 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 by the exhaust gas by the turbine bypass means, the exhaust pressure decreases, so the amount of EGR gas recirculated by the EGR passage decreases, and the temperature in the cylinder before the start of compression 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 EGR gas reflux decreases as described above, the specific heat ratio of the gas in the cylinder is increased. Even if the temperature is low, the compression end temperature is high. Therefore, the supercharged engine of the above configuration is advantageous in securing the ignitability of the mixture in a low compression ratio diesel engine.

  In addition, diesel engines are superior in thermal efficiency to general gasoline engines in the first place. However, since the exhaust gas temperature is low because the thermal efficiency is excellent, the delay in the warm-up of the catalyst as described above becomes a further problem. 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 outside the low load range. .

  In general, when the engine speed is low, the gas leakage from the combustion chamber (particularly, the gas leakage through the piston ring) is relatively large as compared with the high engine speed. Therefore, when the engine speed is low, the pressure of the gas in the combustion chamber is reduced, which causes the reduction of the compression end temperature. This is inconvenient in suppressing the generation of RawHC.

  On the other hand, according to the above configuration, the control unit executes the catalyst warm-up control described above when the engine body is in a cold state and the engine rotational speed is lower than the predetermined rotational speed. By performing the catalyst warm-up control, it is possible to effectively purify the generated RawHC.

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

FIG. 1 is a schematic view showing a supercharged engine. 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 drawing of FIG. 5 is a performance curve graph showing the specification of the compressor of the electric supercharger, and the lower drawing of FIG. 5 is a graph 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 the gas composition in the cylinder in the comparative example in which the catalyst warm-up control is not performed and the embodiment in which the catalyst warm-up control is performed. It is a figure shown comparing. FIG. 8 is a schematic view illustrating the fuel injection mode in the diffusion combustion mode and the history of the heat release 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 release rate associated therewith. FIG. 10 is a flowchart showing processing operation of engine control by the PCM.

  Hereinafter, embodiments 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 the embodiment. An engine main body 10 of the engine 1 is a diesel engine which is mounted on a vehicle and to which a fuel mainly composed of light oil is supplied.

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

  A piston 32 (see FIG. 2) is inserted in each cylinder 30a of the cylinder block 30 so as to be reciprocatively slidable, and the combustion chamber 33 (the cylinder 32, the cylinder block 30, and the cylinder head 31) See Figure 2).

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

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

  As shown in FIG. 2, an intake port 34 and an exhaust port 35 are formed in each cylinder 30 a in the cylinder head 31, and the intake port 34 and the exhaust port 35 have openings at the combustion chamber 33 side. The intake valve 36 and the exhaust valve 37 which open and close are each arrange | positioned.

  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 rotationally driven in conjunction with the rotation of the crankshaft. Although not shown, in order to adjust the open / close timing and open / close period of the intake valve 36 and the exhaust valve 37, for example, a hydraulically operated valve variable mechanism is provided.

  Further, an injector (i.e., a fuel supply unit) 38 which 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 such that its injection 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, into the combustion chamber 33, fuel of an amount according to the operating condition of the engine 1 at an injection timing set according to the operating condition 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 is in communication with the intake port 34 of each cylinder 30 a and supplies intake air to each cylinder 30 a 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 is in communication with the exhaust port 35 of each cylinder 30a, and exhausts burned gas (that is, exhaust gas) 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 performing supercharging of intake air.

  An air cleaner 54 for filtering intake air is disposed at the upstream end of the intake passage 50. On the other hand, a surge tank 51 is disposed in the vicinity of the downstream end of the intake passage 50. The intake passage 50 downstream of the surge tank 51 is an independent intake passage branched for each cylinder 30a, and the downstream end of each independent intake passage is connected to the intake port 34 of each cylinder 30a.

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

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

  The electric supercharger 18 includes a compressor wheel 18a provided in the intake passage 50 and an electric motor 18b for driving the compressor wheel 18a. By driving the electric motor 18b, the compressor wheel 18a is rotationally driven to perform intake supercharging. That is, the electric supercharger 18 is a supercharger that does not use exhaust energy. The supercharging pressure capacity 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. Although the details will be described later, the electric supercharger 18 is operated in a partial state while the engine 1 is in operation.

  The electric motor 18b is driven by the 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 the power supplied to the electric motor 18b. In the battery 19, for example, power generated by an alternator (not shown) mounted on a vehicle is accumulated. The battery 19 may be, for example, a 48V battery. The electric motor 18 b may be driven by being supplied with a 48 V 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 a refrigerant discharged to the supply passage 91 by the water pump 93 passes through the supply passage 91, the intercooler 57, the return passage 92, and the radiator 90, and is returned to the water pump 93 again to the supply passage 91 again. It is discharged and supplied to the intercooler 57. Then, 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 risen by the intercooler 57 is cooled by heat exchange with, for example, the atmosphere by the radiator 90.

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

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

  The turbocharger 56 is rotationally driven by receiving energy of exhaust gas (ie, exhaust energy). Specifically, when the turbine 56b of the turbocharger 56 receives exhaust energy and is rotationally driven, the compressor 56a is rotationally driven via the connection shaft 56c to perform intake supercharging.

  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 housed in a turbine case (not shown). The wastegate valve 65 exemplifies “turbine bypass means” that allows at least a portion of the exhaust gas to flow so as to bypass the turbine 56 b.

  The turbocharger 56 may be a variable displacement turbocharger in which movable vanes are disposed in a turbine case. If it is possible to flow the exhaust gas substantially bypassing the turbine 56b by adjusting the opening degree of the movable vane, the exhaust side bypass passage 63 and the waste gate valve 65 can be omitted. In that case, the movable vanes become "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 above a predetermined temperature. As described above, the oxidation catalyst 61 is disposed downstream of the turbine 56 b in the exhaust passage 60. The oxidation catalyst 61 is an example of the “catalyst”.

  The DPF 62 is disposed downstream of the oxidation catalyst 61 in the exhaust passage 60 and is configured to collect particulates 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 the exhaust gas flowing through the exhaust passage 60 is recirculated to the intake passage 50 by the low pressure EGR passage 70 described later. May be

  The engine 1 does not have a catalyst for purifying NOx. However, the technology 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 which are connected to the intake passage 50 and the exhaust passage 60 and can return part of the exhaust gas flowing through the exhaust passage 60 to the intake passage 50 are provided.

  The high pressure EGR passage 80 is a portion of the intake passage 50 between the intercooler 57 and the surge tank 51 (that is, a portion on the downstream side of the electric supercharger 18), the exhaust manifold 60 and the turbo exhaust passage 60. It is connected to a portion between the feeder 56 and the turbine 56 b (that is, a portion on the upstream side of the turbine 56 b of the turbocharger 56). In the high pressure EGR passage 80, an electromagnetic high pressure EGR valve 82 for adjusting the flow rate of exhaust gas (hereinafter referred to as high pressure EGR gas) returned 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 the “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 56 a of the turbocharger 56 (that is, a portion on the upstream side of the compressor 56 a of the turbocharger 56) The passage 60 is connected to a portion between the DPF 62 and the exhaust shutter valve 64. In the low pressure EGR passage 70, an EGR cooler 71 for cooling exhaust gas (hereinafter referred to as low pressure EGR gas) returned to the intake passage 50 through the low pressure EGR passage 70, and an electromagnetic type for adjusting the flow rate of low pressure EGR gas And a low pressure EGR valve 72 are provided. Like 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 the opening degree thereof. The low pressure EGR passage 70 is an example of the “second EGR passage”.

  Hereinafter, a system including the high pressure EGR passage 80 and the high pressure EGR valve 82 will be 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 will be 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 or more and 16 or less, thereby improving emission performance and combustion efficiency. ing. In this engine 1, the reduction of the geometric compression ratio is compensated by the adjustment of the amount of fresh air by the turbocharger 56 and the electric turbocharger 18 and the adjustment of the low pressure EGR gas and the high pressure EGR gas. ing.

(Configuration of engine control system)
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 is composed of a microprocessor having a CPU 101, a memory 102, a counter timer group 103, an interface 104, and a bus 105 connecting these units. The PCM 100 is an example of the “control unit”.

  The PCM 100 includes a water temperature sensor SW1 for detecting a temperature of engine cooling water, a boost pressure sensor SW2 for detecting a boost pressure, an intake temperature sensor SW3 for detecting an intake air temperature, an exhaust temperature sensor SW4 for detecting an exhaust temperature, A crank angle sensor SW5 for detecting a rotational angle of a 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 a vehicle speed of the vehicle, A detection signal from a turbine rotational speed sensor SW8 that detects the rotational speed of the turbine 56b of the turbocharger 56 is input.

  The PCM 100 performs various calculations based on the detection signals of the sensors SW1 to SW8 to estimate or determine the state of the engine 1 or the vehicle, and the control signal generated in response to the determination makes the engine 1 Control the operation.

  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.

  When the temperature detected by 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 opening degree sensor SW6 detects the accelerator 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 area” refers to the operation on the low load side when the operating area of the engine 1 is divided into a high load area, a medium load area, and a low load area according to the load level. It may be a region. The boundary of each area changes according to the engine speed. In this configuration example, the low load area is included in an operation area 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 actuators of the injector 38, the electric motor 18b, and the various valves 55, 58, 64, 65, 72, 82. The PCM 100 also outputs a control signal to the variable valve mechanism of the intake valve 36 and the exhaust valve 37.

(Outline of Control of Electric Turbocharger)
Next, control of the electric supercharger 18 by the PCM 100 will be described. FIG. 4 shows an aspect of control of the electric supercharger 18. The PCM 100 basically keeps the electric supercharger 18 constantly rotating during operation of the engine body 10, but the temperature of the engine coolant detected by the water temperature sensor SW1 and the crank angle sensor SW5 Based on the detected rotational speed of the engine 1, the number of revolutions of the electric supercharger 18 (that is, the supercharging pressure) is controlled. Specifically, control is performed so as to decrease the rotational speed as the high water temperature or the engine speed becomes higher from the region of low water temperature to low engine speed where the rotation speed is the highest.

  In the present embodiment, the engine rotation is such that the pressure ratio of the compressor 56 a of the turbocharger 56 becomes 1.2 or more when the water temperature becomes 80 ° C. or more, or the engine speed exceeds r1. In the range of the number, the electric supercharger 18 is brought into an idle rotation state, and the intake side bypass valve 58 is fully opened so that supercharging by the electric supercharger 18 is not substantially performed. Do. In this way, the turbo supercharger 56 does not stop the rotation of the electric supercharger 18 in the region of the engine rotation where the water temperature becomes 80 ° C. or more or the pressure ratio becomes 1.2 or more. It can only be supercharged.

  As described above, when the charging pressure is increased by the electric supercharger 18 as described later by always rotating the electric supercharger 18, the electric supercharger 18 is temporarily stopped. The motorized supercharger 18 (strictly, the electric motor 18b for operating the motorized supercharger 18) is more efficient than performing on-off control to make it drive in a necessary scene. Can be activated.

  FIG. 5 shows a performance curve that represents the characteristics of the electric supercharger 18. The upper part of FIG. 5 is a performance curve graph showing the characteristics of the compressor wheel 18a of the electric supercharger 18, the vertical axis is the pressure ratio of the electric supercharger 18 (ie, the upstream pressure with respect to the downstream pressure) Ratio), the horizontal axis is 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. The area surrounded by these lines is the operable area of the electric turbocharger 18. The operating efficiency of the electric supercharger 18 becomes higher as it is located on the center side of this region.

  The electric supercharger 18 assists the turbocharger 56 and is used for the purpose of adjusting the amount of fresh air introduced into the cylinder 30a, so the rotation limit as shown by the mesh in the upper diagram of FIG. Depending on the temperature of the engine coolant and the engine speed, the engine is operated at an appropriate speed in an area remote from the line. In other words, the electric supercharger 18 is operated in a partial state largely separated from the limit rotational speed.

  The lower part of FIG. 5 exemplifies the characteristics of the electric motor 18b of the electric turbocharger 18. The vertical axis represents the torque of the electric motor 18b, and the horizontal axis represents the number of rotations of the electric motor 18b. The one-dot chain line in the lower part of FIG. 5 indicates a line for equal power consumption, the higher the power consumption at the upper right of the figure and the lower the power consumption at the lower left. The electric supercharger 18 is operated in the area shown by the mesh in the upper view of FIG. 5, while the electric motor 18b is operated in the area shown by the mesh in the lower view of FIG. The power consumption of the electric motor 18b is relatively low, and the efficiency of the electric motor 18b is relatively high. A state in which the electric motor 18 b is operating at a torque lower than the maximum torque may be referred to as operating in a partial state of the electric supercharger 18. As described above, although the electric supercharger 18 is always rotating during operation of the engine body 10, the power consumption can be reduced by operating the electric supercharger 18 in the partial state. It is.

  In the idle rotation region shown in FIG. 4, the electric supercharger 18 may be stopped.

(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 degree, and the amount of fresh air and high pressure introduced into the cylinder 30a so that the corresponding combustion state is realized. The EGR gas amount and the low pressure EGR gas amount are adjusted, and the injection amount of fuel, the injection timing, and the like are realized by controlling the operation of the injector 38.

  FIG. 6 illustrates the φ-T map of the engine 1. The φ-T map is a map showing a region in which unburned components CO / HC, soot and NOx are generated on a plane consisting of the combustion temperature (T) and the equivalence ratio (φ) of the air-fuel mixture. When the combustion temperature is high, it enters the region of NOx, and when the equivalence ratio is high, it enters the region of soot. In addition, if the combustion temperature is too low, it will enter the CO / HC region. 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 adjusts the injection amount of fuel, the injection timing, and the like to obtain CO / HC, soot and Achieve combustion that does not enter the area where NOx is generated.

  Specifically, during partial load operation (that is, operation at a load other than full open load), the engine 1 operates the turbocharger 56 to introduce an amount of fresh air corresponding to the fuel supply amount into the cylinder 30a. While introducing the EGR gas, the equivalence ratio of the air-fuel mixture is adjusted so as not to be too high, and by introducing the EGR gas into the cylinder 30a, the combustion speed and the combustion temperature are prevented from becoming too high, thereby generating RawNOx. Suppress. The EGR gas introduced into the cylinder 30a is mainly a low temperature low pressure EGR gas when the engine 1 is warm, and a high temperature high pressure EGR gas may be introduced into the cylinder 30a as required.

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

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

  The pre-combustion in the diffusion combustion mode can increase the compression end temperature and the compression end pressure. As a result, 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, the diffusion combustion using the pre-stage combustion as the fire type) can be stably generated near the compression top dead center, the work amount of the engine 1 can be increased, and the fuel consumption can be increased. It can improve. Further, the improvement of the ignitability makes it possible to suppress the generation of soot and to prevent the rapid increase of heat generation in the main combustion, that is, the extremely short combustion period, and the generation of NOx. Can be suppressed.

  Further, by performing after injection within the expansion stroke period in which the in-cylinder pressure decreases, the soot can be burned, and the discharge of the soot from the combustion chamber 33 can be suppressed.

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

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

  However, with such a configuration, the amount of work by the compressor a of the turbocharger 56 is reduced according to the flow rate of the exhaust gas bypassing the turbine 56b, and supply of fresh air into the cylinder 30a is 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 generation of RawHC, it is required to appropriately supply fresh air, EGR gas, and the like.

  On the other hand, when the engine body 10 is in a cold state and in a low load region, the engine 1 raises the supercharging pressure via the electric supercharger 18 and opens the waste gate valve 65 to exhaust gas. Bypass the turbine 56.

  Concretely, taking the case where the vehicle starts from the stopped state as an example, the PCM 100 generates the high pressure EGR valve 82 and the waist when the driver requests acceleration of the vehicle by stepping on the accelerator pedal. While the gate valve 65 is opened, catalyst warm-up control is performed to drive the electric supercharger 18 to increase the supercharging pressure.

  By opening the waste gate valve 65, the exhaust gas can bypass the turbine 56b. Since this makes it possible to provide a sufficient amount of heat to the oxidation catalyst 61, the temperature of the oxidation catalyst 61 can be raised as quickly as possible. As a result, it becomes possible to activate the oxidation catalyst 61 by scavenging and to secure the purification performance of HC.

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

  Further, as described above, when activation of the oxidation catalyst 61 is intended by opening the waste gate valve 65, the PCM 100 operates the electric supercharger 18 so that the supercharging pressure increases. Although the amount of work by the compressor 56 a is reduced because the exhaust gas bypasses the turbine 56 b, the reduction can be compensated for by the electric supercharger 18. Thus, the amount of fresh air introduced into the cylinder 30a can be increased even if the turbocharger pressure does not increase in the turbocharger 56. As a result, it is possible to reduce unburned fuel and to suppress the generation of RawHC. In addition, the equivalence ratio of the air-fuel mixture is lowered by the amount of increase of the fresh air amount, and the generation of soot can also be suppressed.

  In addition, the flow of the fresh air generated with the operation of the electric supercharger 18 makes it possible to rotate the compressor 56a of the turbocharger 56. The turbine 56b also rotates in conjunction with the rotation of the compressor 56a, so the turbine 56b does not become a resistance in the exhaust passage 60. Since it is possible to provide a sufficient amount of heat to the oxidation catalyst 61 by the exhaust gas passing through the turbine 56b, for example, because the turbine 56b does not become resistant, it is advantageous in activating the oxidation catalyst 61 early. Furthermore, since the exhaust pressure is reduced by the rotation of the turbine 56b, the effect of scavenging by the electric supercharger 18 is also increased, and it is also possible to reduce the pump loss.

  In this way, a decrease in emission performance in the cold state and low load region is prevented.

  For example, in the upper view of FIG. 7, the electric supercharger 18 is not driven when the vehicle is started and the waste gate valve 65 is not opened (comparative example in which the catalyst warm-up control is not performed). The ratio of the air density to the fresh air volume in the cylinder 30a immediately after the start of the vehicle is shown by comparing the ratio of the air volume in the cylinder 30a immediately after the start of the vehicle when operating the engine 18 and opening the waste gate valve FIG. In the upper part of FIG. 7, the vertical axis represents the ratio of the air density.

  On the other hand, the lower diagram of FIG. 7 is a diagram showing the difference in the gas composition in the cylinder 30a immediately after the start of the vehicle in the comparative example and the example. In the lower diagram of FIG. 7, the vertical axis represents the compression end temperature, and in the 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 embodiment. . The area of a square indicating “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 filled in the cylinder 30a. Therefore, in the lower part of FIG. 7, the magnitude relation between the area of each gas component in the gas composition on the left side as a comparative example and the area of each gas component in the gas composition on the right side as an example is the filling amount of each gas component Does not necessarily indicate the magnitude relationship of

  First, in the comparative example in which the waste gate valve 65 is not opened without operating the electric supercharger 18, the high pressure EGR valve 82 is opened at the start of the vehicle. Thus, 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. As a result, although the ignitability of the mixture can be enhanced and the generation of RawHC can be suppressed, the warm-up of the oxidation catalyst 61 may be delayed by merely 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 is started. This makes it possible to lead the oxidation catalyst 61 to an active state at an early stage. However, when the waste gate 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 boost pressure by the electric supercharger 18 is increased when the waste gate valve 65 is opened. As a result, the amount of fresh air introduced into the cylinder 30a can be increased. Further, as shown in the upper drawing of FIG. 7, the temperature of the air-fuel mixture in the cylinder 30 a is reduced because the amount of introduction of the high pressure EGR gas is reduced. Together with the fact that the introduction amount of fresh air is increased by the electric supercharger 18, the air density is increased 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. Therefore, the unburned fuel can be reduced, and hence the generation of RawNOx can be suppressed.

  Further, 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 more after executing the catalyst warm-up control. Here, the “predetermined temperature” may be set, for example, in the vicinity of the activation temperature of the oxidation catalyst 61. Also, this determination may be made indirectly based on, for example, the exhaust gas temperature detected by the exhaust gas 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 via the low pressure EGR passage 70 is via the high pressure EGR passage 80. It is lower than the temperature of the EGR gas to be recirculated. Therefore, 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 speed and the combustion temperature can be reduced, and the generation of RawNOx is suppressed. Also, by opening the low pressure EGR passage 70 after the oxidation catalyst 61 is heated up 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 completion of warmup. It can be suppressed. In addition, after completion of the warm-up, the waste gate valve 65 may be closed.

  Here, when catalyst warm-up control is performed, as shown in FIG. 9, the fuel injection start timing may be retarded as compared to that during steady operation of the vehicle.

  Specifically, the pilot injection in the pre-stage injection is stopped and the after injection is stopped, and the injection start timing of the pre-injection and the main injection is retarded. Further, in the example of FIG. 9, the main injection is performed twice. Hereinafter, such an injection form is referred to as a retarded combustion mode. 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 an example, and the injection timing of the pre-injection and the main injection in the retarded combustion mode and the fuel injection amount 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 air and fuel is reduced, so that the pre-combustion does not occur before the compression top dead center as shown in the upper diagram of FIG. The specific heat ratio of the gas in the cylinder 30a is increased by increasing the intake density by introducing supercharge by the electric supercharger 18, and introducing as much fresh air as possible into the cylinder 30a. Since the end temperature is sufficiently high, pre-combustion and main combustion occur after compression top dead center.

  With the retarded combustion mode, stable main combustion can be performed even if the compression ratio is low, so it is possible to prevent the combustion temperature from becoming excessively high and to suppress the generation of NOx. Further, if the amount of fresh air increases, the intake air temperature decreases, so that the increase in the combustion temperature can also be suppressed, and the generation of NOx can be suppressed. In the retarded combustion mode, the combustion temperature is higher than in the diffusion combustion mode shown in FIG. 8 even in the late stage of combustion, and soot can be burned without performing after injection. By omitting the after injection, the fuel consumption performance is improved.

  In addition to driving the electric supercharger 18 to increase the supercharging pressure when starting the vehicle, Pmax can be increased more quickly by performing the retarded combustion mode. Therefore, during acceleration of the vehicle, based on the change history of Pmax, specifically, when the slope of the rising edge 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, while when the slope of the rise of Pmax is small, the electric supercharger 18 is driven to increase the supercharging pressure, while the retard combustion mode is performed. You may not do this.

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

  In the 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 rotation number of the electric supercharger 18 to a high rotation number, a middle rotation number, or a low rotation number according to the water temperature of the engine 1 and the engine rotation number.

  In step S103 following step S102, the PCM 100 determines whether the driver has requested acceleration. The PCM 100 determines the presence or absence of the driver's acceleration request based on the detection value of the accelerator opening sensor SW6. When an acceleration request is made, 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 a diffusion combustion mode.

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

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

  In step S107 following step S106, the PCM 100 executes turbine bypass processing. The turbine bypass process is a process that constitutes 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 raises the supercharging pressure of the electric supercharger 18. Thus, catalyst warm-up control is performed.

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

  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 the driving of the electric supercharger 18 is necessary based on the difference between the target boost pressure determined in step S110 and the actual boost pressure based on the detection signal of the sensor. Determine When it is necessary to drive the electric supercharger 18, the control process proceeds to step S108, and the PCM 100 raises the supercharging pressure by supplying power to the electric supercharger 18, as described above. On the other hand, when the PCM 100 determines that the driving of the electric supercharger 18 is unnecessary in step S111, the control process proceeds to step S109 without proceeding to step S108. Then, as in the case where catalyst warm-up control is performed, fuel injection is performed to realize the retarded combustion mode.

  Further, 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. Then, in step S114, the PCM 100 outputs a control signal to each actuator to execute the fuel injection to realize the diffusion combustion mode.

  The control process then returns to step S101. Even when the boost pressure of the electric supercharger 18 is increased in the early stage of acceleration of the vehicle, if the drive of the electric supercharger 18 becomes unnecessary in the late stage of acceleration, the boost pressure by the electric supercharger 18 is descend.

  As described above, this engine 1 can prevent the reduction of the emission performance in the cold state and the low load area.

  Also, generally, at the time of vehicle start from a stop state, the engine 1 is in a cold state. Therefore, by performing the catalyst warm-up control when the vehicle is started, it is possible to appropriately prevent the emission performance from being degraded.

  Further, as illustrated in the lower diagram of FIG. 7 by raising the supercharging pressure of the electric supercharger 18, when the ratio of the fresh air amount in the cylinder 30a is increased, the specific heat ratio of the gas in the cylinder 30a is Even if it rises and the temperature in the cylinder 30a before the start of compression is low, the compression end temperature will be high. Therefore, in a low compression ratio diesel engine in which the geometric compression ratio is set to 16 or less, it is advantageous in securing the ignitability of the mixture.

  In addition, since the electric supercharger 18 operates in the partial state as shown in FIG. 5, it is possible to prevent the rush electric power from being supplied to the electric motor 18 b of the electric supercharger 18 at each acceleration. Can. As a result, it is possible to suppress the power consumption when raising the supercharging pressure by the electric supercharger 18, and also to improve the reliability of the electric supercharger 18.

  In addition, diesel engines are superior in thermal efficiency to general gasoline engines in the first place. However, since the exhaust gas temperature is low because the thermal efficiency is excellent, the delay in the warm-up of the oxidation catalyst 61 as described above becomes a further problem. Therefore, the catalyst warm-up control is particularly effective in such a diesel engine.

Other Embodiments
The present invention is not limited to the above embodiment, and can be substituted without departing from the scope of the claims.

  For example, the technology disclosed herein is not limited to the application to a diesel engine, but may be applied to an engine using fuel including gasoline and naphtha.

  Further, the catalyst warm-up control described above may be performed not only at the start of the vehicle but, for example, at the time of automatic restart from the idle stop state.

  That is, the engine 1 includes idle stop means 110 (shown only in FIG. 3) for putting the engine body 10 in the idle stop state, and the PCM 100 automatically restarts the engine body 10 put in the idle stop state by the idle stop means 1110 Sometimes, the catalyst warm-up control may be performed.

  Generally, at the time of the automatic restart of the engine body 10, the exhaust gas becomes relatively low temperature. Therefore, if the catalyst warm-up control as described above is executed at the time of the automatic restart of the engine body 10, it is possible to appropriately prevent the emission performance from being degraded. In this case, the PCM 100 executes the processes shown in steps S106 to S108 of FIG. 10 in order.

  Furthermore, the catalyst warm-up control described above may be performed not only at the time of start of the vehicle or at the time of automatic restart but also when the engine rotational speed is low.

  That is, the PCM 100 may execute the catalyst warm-up control even when the engine main body 10 is in a cold state and the engine speed is lower than the predetermined engine speed, even 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 (in particular, gas leakage through the piston ring) is relatively large compared to when the engine speed is high. Therefore, when the engine rotational speed is low, the pressure of the gas in the combustion chamber 33 is reduced, which causes the reduction of the compression end sound pressure. This is inconvenient in suppressing the generation 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 lower than the predetermined speed. Specifically, the PCM 100 sequentially executes the processes shown in steps S106 to S108 of FIG. This makes it possible to purify the generated HC effectively.

DESCRIPTION OF SYMBOLS 1 Engine 10 Engine main body 18 Electric supercharger 18b Electric motor 50 Intake passage 56 Turbo turbocharger 56a Compressor 56b Turbine 60 Exhaust passage 61 Oxidation catalyst (catalyst)
65 West gate 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 a 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 turbocharger in the intake passage, the turbocharger being supercharged using exhaust energy;
An EGR passage that connects the exhaust passage upstream of the turbine and the intake passage downstream of the electric turbocharger, and recirculates part of the exhaust gas to the intake passage;
Turbine bypass means provided in the exhaust passage for guiding at least a portion of the exhaust gas so as to bypass the turbine;
A catalyst disposed downstream of the turbine in the exhaust passage;
A control unit that determines whether 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 opens the EGR passage and guides the exhaust gas so as to 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 executes catalyst warm-up control that outputs a control signal to the electric supercharger so as to raise the supercharging pressure by the electric supercharger. In the supercharged engine according to claim 1,
A second EGR passage communicating the exhaust passage downstream of the turbine and the intake passage upstream of the compressor and recirculating part of the exhaust gas to the intake passage;
The supercharger-equipped 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 an engine with a supercharger that executes the catalyst warm-up control when the vehicle starts moving from a stopped state. In the supercharged engine according to any one of claims 1 to 3,
An idle stop means for putting the engine body into an idle stop state,
The control unit is an engine with a supercharger, which executes the catalyst warm-up control at the time of the automatic restart of the engine main body which is put into the idle stop state by the idle stop means. In the supercharged engine according to any one of claims 1 to 4,
The control unit is an engine with a supercharger that operates the electric supercharger in a partial state. The supercharged engine according to any one of claims 1 to 5, wherein
The engine body is a supercharged engine, which is a diesel engine having a geometric compression ratio of 16 or less. The supercharged engine according to any one of claims 1 to 6,
The control unit executes the catalyst warm-up control even when the engine main body is in a cold state and the engine speed is lower than a predetermined engine speed, even outside the low load range.

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