JP2021134670A - Engine with supercharger - Google Patents

Abstract

To promote warming of an engine with a supercharger.SOLUTION: An engine 2 with a supercharger comprises: a fuel injection valve (injector 21); an exhaust emission control device 6; a turbine 42 of an exhaust turbocharger 4 provided downstream of the exhaust emission control deice; an EGR system 7 that has an EGR passage (first EGR passage 71) connecting a portion between the exhaust emission control device and the turbine in an exhaust passage and an intake passage to each other, and a water-cooled EGR cooler 75; a circulation circuit 8 that circulates cooling water between the engine and a radiator; and a control unit (ECU100) that outputs a control signal to a control target. The EGR cooler is connected to the circulation circuit and exchanges heat between the cooling water and exhaust. When the engine is cold, the control unit causes the fuel injection valve to perform fuel injection during an exhaust stroke and causes the EGR system to recirculate EGR gas, as warming control for the engine.SELECTED DRAWING: Figure 1

Description

The technology disclosed herein relates to an engine with a supercharger.

Patent Document 1 describes an engine with a supercharger. A turbine of an exhaust turbocharger is provided in the exhaust passage of this engine. Further, an oxidation catalyst and a DPF are arranged upstream of the turbine in the exhaust passage. An exhaust turbocharger compressor is installed in the intake passage of the engine.

Japanese Unexamined Patent Publication No. 2013-189900

In the engine with a supercharger described in Patent Document 1, the oxidation catalyst is provided at a position closer to the engine than the turbine. Therefore, the temperature of the oxidation catalyst can be raised. For example, the oxidation catalyst can be activated early when the engine is started.

However, the engine with a supercharger described in Patent Document 1 does not have a configuration for quickly warming up the engine.

The technology disclosed herein facilitates warming up of supercharged engines.

The technology disclosed herein relates to an engine with a supercharger. This supercharged engine
A fuel injection valve that supplies fuel to the engine and
An exhaust purification device provided in the exhaust passage of the engine and purifying the exhaust gas discharged from the engine.
In the exhaust passage, a turbine of an exhaust turbocharger provided downstream of the exhaust purification device and a turbine of the exhaust turbocharger.
A portion of the exhaust passage between the exhaust purification device and the turbine, an EGR passage that connects the intake passage of the engine to each other, and an EGR gas provided in the EGR passage and flowing through the EGR passage are cooled. An EGR system having a water-cooled EGR cooler and returning a part of the exhaust gas to the intake passage as EGR gas.
A circulation circuit in which cooling water circulates between the engine and a radiator that dissipates heat from the cooling water.
It is equipped with a control unit that outputs a control signal to the control target.
The EGR cooler is connected to the circulation circuit and exchanges heat between the cooling water and the exhaust gas.
The control unit causes the fuel injection valve to perform fuel injection during the exhaust stroke as warm-up control of the engine when the temperature of the engine is lower than a predetermined temperature, and causes the EGR system to perform EGR gas. Perform recirculation.

According to this configuration, the exhaust purification device is provided in the exhaust passage upstream of the turbine of the exhaust turbocharger. Since the exhaust gas purification device is close to the engine, the temperature of the exhaust gas purification device rises rapidly after starting the engine, for example. The exhaust gas purification device is activated at an early stage. Early activation of the exhaust gas purification device is advantageous for improving the exhaust gas performance of the engine.

The engine is equipped with an EGR system. The EGR system has an EGR cooler provided in the EGR passage. The EGR system can supply the cooled EGR gas to the intake passage.

The EGR cooler is connected to the engine cooling water circulation circuit. The EGR cooler exchanges heat between the cooling water of the engine and the exhaust gas. The temperature of the cooling water is low while the engine is warming up. When the EGR system recirculates the EGR gas while the engine is warming up, the heat of the exhaust gas can be applied to the cooling water of the engine, and the temperature rise of the cooling water of the engine is promoted.

The control unit executes warm-up control of the engine when the temperature of the engine is colder than a predetermined temperature. During warm-up control, the control unit causes the fuel injection valve to perform fuel injection during the exhaust stroke. The fuel injected during the exhaust stroke is supplied to the exhaust purification device as unburned or almost unburned. Fuel reacts in the exhaust gas purification device and heat of reaction is generated. The heat of reaction raises the temperature of the exhaust gas.

The control unit causes the EGR system to perform the recirculation of EGR gas through the EGR passage during warm-up control. The high-temperature exhaust discharged from the exhaust purification device is returned as EGR gas to the intake passage through the EGR passage. As described above, in the EGR cooler, heat is supplied from the high temperature EGR gas to the cooling water. Since the temperature of the cooling water rises rapidly, the cooling water circulates in the engine to promote the warm-up of the engine, and the warm-up control is completed promptly. This configuration improves the fuel efficiency of the engine because the engine stays cold for a short period of time.

The control unit may execute the warm-up control after the exhaust gas purification device reaches the active temperature.

After the exhaust purification device reaches the active temperature, the fuel injection valve performs fuel injection during the exhaust stroke. The fuel can react in the activated exhaust gas purification device to generate heat of reaction.

The control unit may bypass the radiator and circulate cooling water between the engine and the EGR cooler in the circulation circuit during the warm-up control.

By doing so, since the cooling water is not dissipated in the radiator during the warm-up control, the warm-up of the engine can be promoted by the cooling water heated by the heat of the exhaust gas. Engine warm-up control can be completed quickly.

The engine with a supercharger
A compressor of the exhaust turbocharger provided in the intake passage of the engine and supercharging the intake air supplied to the engine.
An electric supercharger provided downstream of the compressor in the intake passage and driven when the operating state of the engine is within a predetermined region is provided.
The EGR passage may connect a portion of the intake passage between the compressor and the electric supercharger and a portion of the exhaust passage between the exhaust purification device and the turbine to each other.

When the electric supercharger is driven, the pressure downstream of the electric supercharger is high, but the pressure upstream of the electric supercharger is relatively low. The EGR passage is connected to the upstream of the electric supercharger. The EGR system can supply EGR gas upstream of the electric supercharger in the intake passage when the electric supercharger is driven.

The exhaust gas purification device may include a catalyst device that reacts harmful substances in the exhaust gas and a filter device that collects particulate matter in the exhaust gas.

The catalyst device can react the fuel to generate heat of reaction. Further, the EGR system can supply clean exhaust gas that has passed through the filter device and does not contain particulate matter to the intake passage as EGR gas.

As described above, the engine with a supercharger is warmed up.

FIG. 1 is a schematic view illustrating the configuration of an engine system. FIG. 2 is a block diagram illustrating a control configuration of the engine. FIG. 3 is a map illustrating the operating area of the engine. FIG. 4 is a diagram illustrating the characteristics of the compressor of the electric turbocharger. FIG. 5 is an example of a pf diagram of the engine. FIG. 6 is a flowchart illustrating engine control by the ECU. FIG. 7 is a time chart illustrating changes in each parameter when the engine is started.

Hereinafter, embodiments of the engine with a supercharger will be described in detail with reference to the drawings. FIG. 1 shows an engine system 1 according to an embodiment. This engine system 1 is mounted on a vehicle. The engine 2 of the engine system 1 is a diesel engine to which fuel containing light oil as a main component is supplied. Although not shown, the engine 2 has a plurality of cylinders. Each cylinder forms a combustion chamber of the engine 2. The fuel supplied to the combustion chamber is burned by compression self-ignition.

(Engine system configuration)
A fuel injection valve, that is, an injector 21, is attached to the engine 2. The injector 21 supplies fuel to the engine 2. More specifically, the injector 21 is provided for each cylinder and injects fuel directly into the cylinder. The injector 21 receives a control signal from the ECU 100, which will be described later. The injector 21 injects into the combustion chamber an amount of fuel corresponding to the operating state of the engine 2 at the injection timing set according to the operating state of the engine 2.

An intake passage 31 is connected to the engine 2. The intake passage 31 supplies intake air to each cylinder. Intake includes air or air and EGR gas. An exhaust passage 32 is also connected to the engine 2. The exhaust passage 32 discharges the exhaust gas from each cylinder.

In the intake passage 31, the compressor 41 of the exhaust turbocharger 4, the electric supercharger 5, and the intercooler 43 are arranged in this order from the upstream side to the downstream side. The compressor 41 boosts the intake air. The electric supercharger 5 also boosts the intake air. The intercooler 43 cools the boosted intake air. The intercooler 43 is, for example, a water-cooled heat exchanger. Although not shown, the intercooler 43 is connected to, for example, the cooling water circulation circuit 8 of the engine 2.

The electric supercharger 5 has a compressor wheel 51 provided in the intake passage 31 and an electric motor 52 for driving the compressor wheel 51. When the electric motor 52 operates, the compressor wheel 51 rotates, and the compressor wheel 51 boosts the intake air flowing through the intake passage 31. The electric supercharger 5 is a supercharger that does not utilize exhaust energy. The electric motor 52 receives electric power from the battery 55 mounted on the vehicle. The battery 55 stores, for example, the electric power generated by an alternator (not shown).

Here, the capacity of the electric supercharger 5 is set to be smaller than the capacity of the compressor 41 of the exhaust turbocharger 4. As will be described later, the electric supercharger 5 is driven when the engine 2 is operating in a high load state in a low rotation region, and is not driven in other cases. A large-capacity exhaust turbocharger 4 compressor 41 and a small-capacity electric supercharger 5 are provided in series, and only the compressor 41 of the exhaust turbocharger 4 is driven, only the electric supercharger 5 is driven. By switching the drive of both the compressor 41 of the exhaust turbocharger 4 and the electric supercharger 5, the engine 2 can supercharge the intake air over a wide operating range.

The intake passage 31 is provided with a bypass passage 53 that bypasses the compressor wheel 51. The upstream end of the bypass passage 53 is connected between the compressor 41 and the compressor wheel 51 in the intake passage 31. The downstream end of the bypass passage 53 is connected between the compressor wheel 51 and the intercooler 43 in the intake passage 31. A bypass valve 54 is provided in the bypass passage 53. The bypass valve 54 adjusts the amount of intake air flowing through the bypass passage 53. The bypass valve 54 is closed while the electric supercharger 5 is being driven. The bypass valve 54 opens while the electric supercharger 5 is not driven.

In the exhaust passage 32, an exhaust purification device 6 and a turbine 42 of the exhaust turbocharger 4 are arranged in order from the upstream side to the downstream side.

The exhaust gas purification device 6 includes an oxidation catalyst (Diesel Oxidation Catalyst: DOC) as a catalyst device and a DPF (Diesel Particulate Filter) as a filter device. Although detailed illustration is omitted, in the exhaust purification device 6, the DOC is arranged upstream of the DPF.

DOC promotes a reaction in which CO and HC in the exhaust are oxidized to produce CO ₂ and H _{2 O.} Further, the DPF 62 collects particulate matter such as a suit contained in the exhaust gas of the engine 2.

The engine system 1 does not include a catalyst for purifying NOx in the exhaust gas. However, the techniques disclosed herein do not preclude application to engines equipped with catalysts that purify NOx.

The turbine 42 of the exhaust turbocharger 4 is rotated by the energy of the exhaust gas. A connecting shaft (not shown) connects the turbine 42 and the compressor 41 to each other. When the turbine 42 rotates in the exhaust passage 32, the compressor 41 rotates in the intake passage 31 to boost the intake air.

The exhaust turbocharger 4 is a variable capacity turbocharger, although detailed illustration is omitted. A movable vane is arranged in the turbine case. By adjusting the opening degree of the movable vane, the passage area in the exhaust turbocharger 4 changes.

The engine system 1 also includes an EGR (Exhaust Gas Recirculation) system 7. The EGR system 7 returns a part of the exhaust gas to the intake passage 31 as EGR gas. The EGR system 7 has a first EGR passage 71 and a second EGR passage 72.

The first EGR passage 71 connects a portion of the intake passage 31 between the compressor 41 and the electric supercharger 5 and a portion of the exhaust passage 32 between the exhaust purification device 6 and the turbine 42 to each other. A first EGR valve 73 is provided in the first EGR passage 71. The first EGR valve 73 is, for example, an electromagnetic opening degree adjusting valve. The first EGR valve 73 adjusts the flow rate of the EGR gas returned to the intake passage 31 through the first EGR passage 71.

The first EGR passage 71 is also provided with an EGR cooler 75. In the configuration example of FIG. 1, the EGR cooler 75 is provided upstream of the first EGR valve 73 with reference to the direction in which the EGR gas flows. The EGR cooler 75 cools the EGR gas flowing through the first EGR passage 71. The EGR cooler 75 is, for example, a water-cooled heat exchanger. The EGR cooler 75 is connected to the cooling water circulation circuit 8. The EGR cooler 75 exchanges heat between the EGR gas and the cooling water. The configuration of the circulation circuit 8 will be described later.

The second EGR passage 72 branches from the middle of the first EGR passage 71. More specifically, the second EGR passage 72 branches from the upstream portion of the EGR cooler 75 in the first EGR passage 71. The second EGR passage 72 is also connected downstream of the electric supercharger 5 in the intake passage 31. More specifically, the second EGR passage 72 is connected to a portion of the intake passage 31 between the intercooler 43 and the engine 2.

A second EGR valve 74 is provided in the second EGR passage 72. The second EGR valve 74 is, for example, an electromagnetic opening degree adjusting valve. The second EGR valve 74 adjusts the flow rate of the EGR gas returned to the intake passage 31 through the second EGR passage 72.

The engine system 1 has a cooling water circulation circuit 8. The broken line in FIG. 1 indicates the flow path of the cooling water constituting the circulation circuit 8. The circulation circuit 8 includes a radiator 81, a water pump 82, and an electric thermostat valve 85.

The circulation circuit 8 has a main flow path 83. The main flow path 83 is a passage that returns from the engine 2 to the engine 2 through the radiator 81, the electric thermostat valve 85, and the water pump 82. The water pump 82 circulates the cooling water in the circulation circuit 8. The water pump 82 is driven by, for example, the engine 2. The radiator 81 dissipates heat from the cooling water received by the engine 2. The electric thermostat valve 85 opens and closes the main flow path 83. The electric thermostat valve 85 electromagnetically switches between opening and closing the valve based on a control signal from the ECU 100 described later.

The circulation circuit 8 also has a sub-channel 84. The sub flow path 84 is provided so as to bypass the radiator 81 and the electric thermostat valve 85. The EGR cooler 75 is provided in the sub flow path 84. The cooling water flowing through the sub flow path 84 returns from the engine 2 to the engine 2 through the EGR cooler 75 and the water pump 82. The cooling water flowing through the sub flow path 84 does not pass through the radiator 81.

FIG. 2 is a block diagram illustrating a control configuration of the engine system 1. The engine system 1 includes an engine control unit (hereinafter referred to as an ECU) 100. The ECU 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 ECU 100 controls the engine 2. The ECU 100 is an example of a control unit.

The ECU 100 receives signals from the water temperature sensor SW1, the boost pressure sensor SW2, the exhaust temperature sensor SW3, the crank angle sensor SW4, the accelerator opening sensor SW5, the vehicle speed sensor SW6, the DPF differential pressure sensor SW7, and the catalyst temperature sensor SW8. ..

The water temperature sensor SW1 is provided in the circulation circuit 8 and outputs a signal corresponding to the temperature of the cooling water of the engine 2. The boost pressure sensor SW2 is provided in the intake passage 31 and outputs a signal corresponding to the boost pressure. The exhaust temperature sensor SW3 is provided in the exhaust passage 32 and outputs a signal corresponding to the exhaust temperature. The crank angle sensor SW4 is attached to the engine 2 and outputs a signal corresponding to the rotation angle of the crankshaft of the engine 2. The accelerator opening sensor SW5 is connected to an accelerator pedal (not shown) and outputs a signal corresponding to the amount of operation of the accelerator pedal by the driver. The vehicle speed sensor SW6 is provided on, for example, an axle (not shown) and outputs a signal corresponding to the vehicle speed of the vehicle. The DPF differential pressure sensor SW7 is attached to the exhaust purification device 6 and outputs a signal corresponding to the pressure difference between the inlet pressure and the outlet pressure of the DPF. The catalyst temperature sensor SW8 is attached to the exhaust gas purification device 6 and outputs a signal corresponding to the temperature of the DOC.

The ECU 100 calculates the engine speed based on the signal of the crank angle sensor SW4, and calculates the engine load based on the signal of the accelerator opening sensor SW5. Further, the ECU 100 determines the cold state and the warm state of the engine 2 based on the signal of the water temperature sensor SW1. The ECU 100 determines whether or not the driver of the vehicle has an acceleration request and the degree of the acceleration request based on the signal of the accelerator opening sensor SW5.

The ECU 100 also determines the necessity of regenerating the DPF based on the signal of the DPF differential pressure sensor SW7. Regeneration of the DPF is the burning of particulate matter deposited on the DPF. If the ECU 100 determines that the DPF regeneration is necessary, the ECU 100 controls the regeneration of the DPF.

The ECU 100 determines the operating state of the engine 2 based on the input signal, and the injector 21, the electric motor 52, the bypass valve 54, the vane actuator 44, the first EGR valve 73, and the second EGR correspond to the determined operating state. A control signal is output to the valve 74 and the electric thermostat valve 85. The vane actuator 44 is an actuator that moves the movable vane of the exhaust turbocharger 4.

In the combustion chamber of the engine 2, an amount of air and EGR gas corresponding to the operating state of the engine 2 are introduced, and fuel is supplied. The fuel supplied to the combustion chamber is burned by compression self-ignition at an appropriate timing.

Here, the engine 2 burns fuel in a state of excess air so as to improve thermal efficiency. Further, by introducing the EGR gas into the combustion chamber, the amount of air in the combustion chamber is also adjusted. The vehicle equipped with this engine system 1 has high fuel efficiency.

On the other hand, since the thermal efficiency of the engine 2 is high, the temperature of the exhaust gas discharged from the combustion chamber is low. If the exhaust temperature is low, it is disadvantageous for DOC activation. In a conventional engine, an exhaust purification device is generally provided downstream of the turbine of an exhaust turbocharger. Since the heat capacity of the turbine is large in this conventional configuration, there is a problem that the temperature of the exhaust purification device is more difficult to rise when the exhaust temperature is low.

On the other hand, in the engine system 1, the exhaust purification device 6 is provided upstream of the turbine 42 of the exhaust turbocharger 4. Since there is no turbine between the engine 2 and the exhaust gas purification device 6, the temperature of the exhaust gas purification device 6 tends to rise due to the exhaust gas, and the temperature of the exhaust gas purification device 6 is maintained at a high temperature during the operation of the engine 2. In this engine system 1, even if the exhaust temperature is low, the active state of DOC can be maintained during the operation of the engine 2, so that the exhaust gas performance is improved.

(Control of electric supercharger by ECU)
Next, the control of the engine 2 by the ECU 100 will be described. FIG. 3 illustrates an operating area of the engine 2. The operating area is defined by the engine speed and the torque (that is, the engine load).

FIG. 3 is a map 301 regarding the operation of the electric supercharger 5. The ECU 100 drives the electric supercharger 5 in the second region of the entire operating region of the engine 2, and does not drive the electric supercharger 5 in the first region other than the second region.

The second region corresponds to a high load region in the low rotation region. Here, the low rotation speed region corresponds to a low rotation speed region when the entire operation region of the engine 2 is bisected into a low rotation speed region and a high rotation speed region in the rotation speed direction. Alternatively, the low rotation speed region corresponds to a low rotation speed region when the entire operating region of the engine 2 is divided into three equal parts, a low rotation speed region, a medium rotation speed region, and a high rotation speed region in the rotation speed direction. The high load region corresponds to a high load region when the entire operating region of the engine 2 is bisected into a low load region and a high load region in the load direction. Alternatively, the high load region corresponds to a high load region when the entire operating region of the engine 2 is divided into three equal parts, a low load region, a medium load region, and a high load region in the load direction.

When the electric supercharger 5 is driven in the second region, the ECU 100 closes the bypass valve 54. The intake air passes through the compressor wheel 51 of the electric supercharger 5 and flows to the engine 2. While the electric supercharger 5 is in operation, the compressor wheel 51 supercharges the intake air.

When the electric supercharger 5 is stopped in the first region, the ECU 100 opens the bypass valve 54. The intake air flows to the engine 2 without passing through the compressor wheel 51 of the electric supercharger 5. While the electric supercharger 5 is stopped, the increase in the pump loss of the engine 2 is suppressed.

As described above, the compressor wheel 51 of the electric supercharger 5 has a smaller capacity than the compressor 41 of the exhaust turbocharger 4. The electric supercharger 5 has high efficiency in the low rotation region of the engine 2. The electric supercharger 5 can efficiently supercharge the intake air in the second region.

Since the compressor 41 of the exhaust turbocharger 4 has a large capacity, the intake air is not substantially supercharged when the operating state of the engine 2 is in the second region. The compressor 41 supercharges the intake air when the rotation speed of the engine 2 is high. The compressor 41 is driven when the operating state of the engine 2 is in the first region, and supercharges the intake air. In the vicinity of the boundary between the first region and the second region, the compressor 41 may boost the intake air and the electric supercharger 5 may further boost the intake air.

Next, the driving scene of the vehicle for driving the electric supercharger 5 will be described. The solid line arrow and the broken line arrow in FIG. 3 exemplify a change in the operating state of the engine 2 when the driver depresses the accelerator pedal to request acceleration of the vehicle. Based on the signal of the accelerator opening sensor SW5, the ECU 100 increases the load of the engine 2 from the operating state shown by the white circle in FIG. As a result, the operating state of the engine 2 shifts from the first region to the second region. The ECU 10 operates the electric supercharger 5. After that, the ECU 100 increases the rotation speed of the engine 2. When the operating state of the engine 2 shifts from the second region to the first region, the ECU 100 ends the operation of the electric supercharger 5.

As described above, in this engine system 1, the exhaust purification device 6 is provided upstream of the turbine 42 of the exhaust turbocharger 4. When the driver requests acceleration of the vehicle, the exhaust turbocharger 4 has a low supercharging response because the volume upstream of the turbine 42 is large.

However, the engine system 1 includes an electric supercharger 5, and the ECU 100 can drive the electric supercharger 5 when acceleration of the vehicle is required. As a result, the supercharging response of the engine 2 is improved.

Therefore, in this engine system 1, the exhaust gas purification performance is improved by arranging the exhaust gas purification device 6 upstream of the turbine 42, and the supercharging response is improved by driving the electric supercharger 5 when acceleration is requested. And both are realized.

The electric supercharger 5 is used when the operating state of the engine 2 is in the low rotation region and the vehicle is in the acceleration transient, and when the engine 2 is operating with a high load in the low rotation region. Driven in both.

As a result, the electric supercharger 5 can improve the supercharging response at the time of the acceleration transition of the vehicle, as described above. The electric supercharger 5 can also sufficiently supercharge the intake air when the engine 2 is in low rotation and high load operation, so that air and EGR gas are sufficiently introduced into the combustion chamber. This is advantageous for improving the torque of the engine 2 and improving the exhaust gas performance.

The electric supercharger 5 is operated with a high load when the operating state of the engine 2 is in the low rotation region and the vehicle is in the acceleration transient, or when the engine 2 is in the low rotation region. It may be driven at either time.

(Control of EGR system by ECU)
The ECU 100 recirculates the EGR gas to the intake passage 31 in the entire operating region of the engine 2. That is, the ECU 100 opens the first EGR valve 73 and / or the second EGR valve 74. When the engine 2 is operating at full load (that is, full throttle), the EGR gas is returned to the intake passage 31, so that the oxygen concentration in the combustion chamber is lowered and the combustion temperature is lowered. When the combustion temperature is lowered, the generation of NOx can be suppressed. The electric supercharger 5 burns a large amount of air and a large amount of EGR gas when the engine 2 is operating at a low speed and at full load, that is, when the engine 2 is operating in the second region. Allows introduction into the room. The electric supercharger 5 improves the exhaust gas performance of the engine 2.

When the electric supercharger 5 is driven, the pressure is low upstream of the electric supercharger 5 and high pressure downstream of the electric supercharger 5 in the intake passage 31. Since the electric supercharger 5 is driven in the low rotation region of the engine 2 as described above, when the electric supercharger 5 is driven, the pressure on the exhaust side of the engine 2 is relatively low. Therefore, even if an attempt is made to return the EGR gas to the intake passage 31 through the second EGR passage 72, the pressure on the intake passage 31 side becomes higher than the pressure on the exhaust passage 32 side, so that the EGR gas can be returned to the intake passage 31. Can not.

On the other hand, the engine system 1 has a first EGR passage 71. The first EGR passage 71 is connected to a portion of the intake passage 31 between the compressor 41 and the electric supercharger 5. Therefore, even when the electric supercharger 5 is driven, the EGR system 7 can recirculate the EGR gas to the intake passage 31 via the first EGR passage 71. As shown in FIG. 3, the ECU 100 opens the first EGR valve 73 and opens the second EGR when the operating state of the engine 2 is in the second region, in other words, when the electric supercharger 5 is operating. The valve 74 is closed. An amount of EGR gas corresponding to the operating state of the engine 2 returns to the intake passage 31.

Here, FIG. 4 illustrates a performance curve 401 showing the characteristics of the compressor wheel 51 of the electric supercharger 5. The horizontal axis of FIG. 4 is the flow rate of gas passing through the compressor wheel 51, and the vertical axis is the pressure ratio between the upstream pressure and the downstream pressure of the compressor wheel 51. The performance curve 401 shows the contour lines of the efficiency of the compressor wheel 51.

As described above, when the EGR gas is recirculated to the intake passage 31 through the first EGR passage 71, the amount of gas flowing into the compressor wheel 51 of the electric supercharger 5 is the sum of air and EGR gas. become. Here, the black circle in FIG. 4 illustrates the operating point of the compressor wheel 51 when the EGR gas is not recirculated upstream of the electric supercharger 5. In this case, only air flows into the compressor wheel 51. Since the electric supercharger 5 operates in the low rotation speed region of the engine 2, the flow rate of the intake air passing through the compressor wheel 51 is small. In this case, the efficiency of the compressor wheel 51 is low. On the other hand, the white circle in FIG. 4 illustrates the operating point of the compressor wheel 51 when the EGR gas is recirculated upstream of the electric supercharger 5. Air and EGR gas flow into the compressor wheel 51. That is, EGR gas is added to the passing flow rate of the compressor wheel 51. Since the flow rate passing through the compressor wheel 51 increases, the efficiency of the compressor wheel 51 increases.

Therefore, in the second region for driving the electric supercharger 5, the efficiency of the electric supercharger 5 can be improved by recirculating the EGR gas upstream of the electric supercharger 5 through the first EGR passage 71.

Further, an EGR cooler 75 is interposed in the first EGR passage 71. The EGR cooler 75 cools the EGR gas. When the load of the engine 2 is high, the EGR system 7 can return the cooled EGR gas to the intake passage 31. It is suppressed that the temperature in the combustion chamber into which the EGR gas is introduced becomes excessively high. The occurrence of abnormal combustion is suppressed in the engine 2.

When the electric supercharger 5 is not driven, that is, when the operating state of the engine 2 is within the first region, the ECU 100 opens the second EGR valve 74. As the rotation speed of the engine 2 increases, the flow rate of the exhaust gas increases, so that the pressure on the exhaust side of the engine 2 becomes higher than the pressure on the intake side. Through the second EGR passage 72, the EGR gas returns to the intake passage 31.

Here, the second EGR passage 72 bypasses the EGR cooler 75. Further, since the second EGR passage 72 is connected to a portion between the intercooler 43 and the engine 2 in the intake passage 31, the EGR gas is not cooled by the intercooler 43. Further, when the EGR gas is recirculated through the second EGR passage 72, the EGR gas can be recirculated with a shorter passage length as compared with the case where the EGR gas is recirculated through the first EGR passage 71. In addition, the EGR system 7 extracts EGR gas from upstream of the turbine 42. Due to these factors, the EGR system 7 can introduce a relatively high temperature EGR gas into the engine 2 through the second EGR passage 72.

When the load of the engine 2 is low, the temperature in the combustion chamber tends to be low, and the ignitability of the fuel tends to decrease. When the engine 2 is operating with a low load or a light load in the first region, the EGR system 7 returns the high temperature EGR gas to the intake passage 31 through the second EGR passage 72, thereby causing the combustion chamber to flow. The temperature of the fuel can be increased to improve the ignitability of the fuel. This enhances the combustion stability of the engine 2.

Further, as shown by hatching in FIG. 3, when the engine 2 is operating at high speed and full load in the first region, the EGR system 7 takes in EGR gas through the second EGR passage 72. When the air returns to the passage 31, the pump loss of the engine 2 is reduced. FIG. 5 illustrates a pf diagram 501 of the engine 2. Since the EGR system 7 extracts a part of the exhaust gas flowing through the exhaust passage 32 as EGR gas, the exhaust pressure of the engine 2 decreases. Further, since the EGR system 7 introduces the EGR gas into the intake passage 31, the intake pressure of the engine 2 increases. As the exhaust pressure of the engine 2 decreases and the intake pressure increases, the differential pressure between the exhaust pressure and the intake pressure becomes smaller, so that the pump loss of the engine 2 is reduced.

Further, when the engine 2 is operating in the high rotation full load region, the flow rate of air passing through the compressor 41 is large. Even if EGR gas is introduced upstream of the compressor 41 in the intake passage 31 in a state where the flow rate of air passing through the compressor 41 is large, the passage of the compressor 41 increases too much and the efficiency of the compressor 41 is lowered. On the other hand, the engine system 1 introduces the EGR gas downstream of the compressor 41 in the intake passage 31 through the second EGR passage 72. As a result, the engine system 1 also has an advantage that the efficiency of the compressor 41 does not decrease.

The conventional engine system has two paths, a high pressure EGR passage and a low pressure EGR passage. On the other hand, the EGR passage of the engine system 1 is composed of a first EGR passage 71 and a second EGR passage 72 branched from the first EGR passage 71. The EGR system 7 is composed of one path. This configuration has an advantage that the configuration of the engine system 1 is simplified.

Further, the first EGR passage 71 is connected to the downstream side of the exhaust purification device 6 in the exhaust passage 32. The EGR system 7 can return the clean exhaust purified by the exhaust purification device 6 to the intake passage 31 as EGR gas. It is possible to prevent the components of the intake system from being contaminated with, for example, particulate matter.

(Control at engine start by ECU)
Next, the control of the engine system 1 by the ECU 100 when the engine 2 is started will be described. FIG. 6 is a flowchart showing a control procedure of the engine system 1 executed by the ECU 100. After the catalyst temperature reaches the active temperature, the engine system 1 reacts the fuel in the exhaust gas purification device 6, and utilizes the reaction heat at that time to promote the warm-up of the engine 2.

The flowchart of FIG. 6 starts when the driver starts the engine 2. First, the ECU 100 reads signals from various sensors in step S61. In the following step S62, the ECU 100 operates the engine 2 in the cold start mode. This control is a control using the so-called AWS (Accelerated Warm-up System). By controlling the engine 2 so that the exhaust loss increases, the ECU 100 raises the temperature of the DOC at an early stage and activates the DOC.

At this time, the ECU 100 closes the first EGR valve 73. By not recirculating the cooled EGR gas, the exhaust temperature can be maintained high. The second EGR valve 74 may be opened or closed.

Further, in step S62, the electric thermostat valve 85 of the circulation circuit 8 is closed. The cooling water does not flow through the radiator 81. Since the cooling water does not dissipate heat, it is advantageous for warming up the engine 2.

In step S63, the ECU 100 determines whether or not the catalyst temperature exceeds the active temperature Ta. The ECU 100 can determine the catalyst temperature based on the signal of the catalyst temperature sensor SW8. The memory 102 of the ECU 100 stores the active temperature Ta.

If the catalyst temperature does not exceed the active temperature Ta, the process returns to step S62 to continue warming the catalyst. When the catalyst temperature exceeds the activity temperature Ta, the process proceeds to step S64, and the ECU 100 ends the catalyst activation control.

In step S64, the ECU 100 opens the first EGR valve 73. As a result, the EGR gas that has passed through the EGR cooler 75 returns to the intake passage 31.

In step S65, the ECU 100 determines whether or not the cooling water temperature is lower than the warm temperature Tc. The warm temperature Tc is a threshold value for determining that the engine 2 has transitioned from the cold state to the warm state. The memory 102 stores the warm temperature Tc.

If the determination in step S65 is YES, the process proceeds to step S66. In step S66, the ECU 100 causes the injector 21 to perform fuel injection during the exhaust stroke after the main injection to the engine 2. The injector 21 performs main injection near the compression top dead center. Since the fuel injection during the exhaust stroke is an injection performed after the main injection, it may be referred to as a post injection in the following.

The fuel injected during the exhaust stroke is supplied to the exhaust purification device 6 as unburned or almost unburned. Since the DOC is activated, the fuel reacts in the DOC and heat of reaction is generated. The heat of reaction raises the temperature of the exhaust gas discharged from the exhaust gas purification device 6.

Since the first EGR valve is opened in step S64, a part of the exhaust gas discharged from the exhaust gas purification device 6 returns to the intake passage 31 via the first EGR passage 71. Here, an EGR cooler 75 is interposed in the first EGR passage 71. The heat of the exhaust gas is transferred to the cooling water in the EGR cooler 75, and the temperature of the cooling water rises. Since the cooling water circulates between the engine 2 and the EGR cooler 75 in the sub-flow path 84 of the circulation circuit 8, the warm-up of the engine 2 is promoted by the heated cooling water.

Here, since the electric thermostat valve 85 is closed, the heated cooling water does not dissipate heat in the radiator 81. It is advantageous for promoting warm-up of the engine 2.

After step S66, the process returns to step S63. The process repeats steps S63-S66 until the temperature of the cooling water exceeds the warm temperature Tc, in other words, until the warm-up of the engine 2 is completed.

In step S65, when the temperature of the cooling water exceeds the warm temperature Tc, the process proceeds to step S67. In step S67, the ECU 100 stops post-injection in the exhaust stroke, and in subsequent step S68, opens the electric thermostat valve 85. In the circulation circuit 8, the cooling water flows through each of the main flow path 83 and the sub flow path 84. After the warm-up of the engine 2 is completed, the cooling water dissipates heat in the radiator 81.

Then, in step S69, the ECU 100 shifts the control of the engine 2 to the normal operation mode, and the start control is completed.

FIG. 7 is a time chart illustrating changes in each parameter when the engine is started. The horizontal axis of FIG. 7 is time, and time progresses from left to right in FIG. Time 0 is the time when the driver starts the engine 2. When the engine 2 is started, the first EGR valve 73 is closed (see Graph 706). The electric thermostat valve 85 is also closed (see Graph 705).

As described above, the ECU 100 controls to promote the temperature rise of the catalyst after the engine 2 is started. As illustrated in Graph 703, the temperature of the DOC rises rapidly. In the example of FIG. 7, at time t1, the temperature of the DOC has reached the active temperature Ta.

When the temperature of the DOC reaches the active temperature Ta, the ECU 100 controls to promote the temperature rise of the engine 2. As described above, the ECU 10 causes the injector 21 to perform post injection (see Graph 704). This further raises the temperature of the DOC. The temperature rise rate of the DOC after the time t1 is higher than the temperature rise rate of the DOC before the time t1. The temperature of the EGR gas also rises (see Graph 701).

The ECU 100 also opens the first EGR valve 73 (see Graph 706). As a result, the high-temperature EGR gas and the cooling water exchange heat in the EGR cooler 75, so that the temperature rise of the cooling water is promoted (see Graph 702). The temperature rise rate of the cooling water after the time t1 is higher than the temperature rise rate of the cooling water before the time t1.

In the example of FIG. 7, the temperature of the cooling water reaches the warm temperature Tc at time t2. That is, the warm-up of the engine 2 is completed at time t2. The ECU 100 shifts to the normal operation mode. The ECU 100 ends the post injection. As a result, the temperature of the DOC is lowered, and the temperature of the EGR gas is also lowered (see graphs 701 and 703). The DOC maintains the active temperature or higher. The ECU 100 also opens the electric thermostat valve 85 (see Graph 705). The cooling water maintains a warm temperature of Tc (see Graph 702).

This engine system 1 can quickly warm up the engine 2 after activating the catalyst when the engine 2 is started. The engine system 1 improves fuel efficiency as well as exhaust gas performance.

The present invention is not limited to the above embodiment, and can be substituted within a range that does not deviate from the gist of the claims.

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

The above embodiments are merely examples, and the scope of the present invention should not be construed in a limited manner. The scope of the present invention is defined by the scope of claims, and all modifications and modifications belonging to the equivalent range of the scope of claims are within the scope of the present invention.

1 Engine system 100 ECU (control unit)
2 Engine 21 injector (fuel injection valve)
31 Intake passage 4 Exhaust turbocharger 41 Compressor 42 Turbine 5 Electric supercharger 53 Bypass passage 6 Exhaust purification device 7 EGR system 71 1st EGR passage 72 2nd EGR passage 75 EGR cooler 8 Circulation circuit 81 Radiator

Claims (5)

A fuel injection valve that supplies fuel to the engine and
An exhaust purification device provided in the exhaust passage of the engine and purifying the exhaust gas discharged from the engine.
In the exhaust passage, a turbine of an exhaust turbocharger provided downstream of the exhaust purification device and a turbine of the exhaust turbocharger.
A portion of the exhaust passage between the exhaust purification device and the turbine, an EGR passage that connects the intake passage of the engine to each other, and an EGR gas provided in the EGR passage and flowing through the EGR passage are cooled. An EGR system having a water-cooled EGR cooler and returning a part of the exhaust gas to the intake passage as EGR gas.
A circulation circuit in which cooling water circulates between the engine and a radiator that dissipates heat from the cooling water.
It is equipped with a control unit that outputs a control signal to the control target.
The EGR cooler is connected to the circulation circuit and exchanges heat between the cooling water and the exhaust gas.
The control unit causes the fuel injection valve to perform fuel injection during the exhaust stroke as warm-up control of the engine when the temperature of the engine is lower than a predetermined temperature, and causes the EGR system to perform EGR gas. An engine with a supercharger that performs recirculation. In the engine with a supercharger according to claim 1,
The control unit is an engine with a supercharger that executes the warm-up control after the exhaust gas purification device reaches the active temperature. In the engine with a supercharger according to claim 1 or 2.
The control unit is an engine with a supercharger that circulates cooling water between the engine and the EGR cooler by bypassing the radiator in the circulation circuit during the warm-up control. In the engine with a supercharger according to any one of claims 1 to 3.
A compressor of the exhaust turbocharger provided in the intake passage of the engine and supercharging the intake air supplied to the engine.
An electric supercharger provided downstream of the compressor in the intake passage and driven when the operating state of the engine is within a predetermined region is provided.
The EGR passage is an engine with a supercharger that connects a portion of the intake passage between the compressor and the electric supercharger and a portion of the exhaust passage between the exhaust purification device and the turbine. .. In the engine with a supercharger according to any one of claims 1 to 4.
The exhaust gas purification device is an engine with a supercharger that includes a catalyst device that reacts harmful substances in the exhaust gas and a filter device that collects particulate matter in the exhaust gas.

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