JP7354875B2 - supercharged engine - Google Patents

Description

The technology disclosed herein relates to a supercharged engine.

Patent Document 1 describes a supercharged engine. A turbine of an exhaust turbo supercharger is provided in the exhaust passage of this engine. Further, an oxidation catalyst and a DPF are disposed upstream of the turbine in the exhaust passage. A compressor for an exhaust turbo supercharger is provided in the intake passage of the engine.

Japanese Patent Application Publication No. 2013-189900

In the supercharged engine 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 increases. This configuration is advantageous in improving exhaust gas purification performance.

On the other hand, since the turbine is provided downstream of the oxidation catalyst and the DPF, the volume upstream of the turbine is large. If the volume upstream of the turbine is large, the supercharging response of the exhaust turbo supercharger to a driver's acceleration request accompanied by an increase in the accelerator opening decreases.

The technology disclosed herein achieves both improved exhaust purification performance and improved supercharging response in a supercharged engine.

The technology disclosed herein relates to a supercharged engine. This supercharged engine is
A fuel injection valve that supplies fuel to the engine;
an exhaust purification device that is provided in an exhaust passage of the engine and purifies exhaust gas discharged from the engine;
a turbine of an exhaust turbo supercharger provided downstream of the exhaust purification device in the exhaust passage;
A control unit that outputs a control signal to a controlled object,
The control unit causes the fuel injection valve to perform fuel injection during an exhaust stroke after main injection to the engine when the vehicle accelerates due to an increase in accelerator opening.

According to this configuration, the exhaust purification device is provided upstream of the turbine of the exhaust turbo supercharger in the exhaust passage. Since the exhaust purification device is close to the engine, the temperature of the exhaust purification device is kept high.

In particular, when the thermal efficiency of an engine is increased for the purpose of improving fuel efficiency, the temperature of the exhaust gas decreases. When the temperature of the exhaust gas is low, the temperature of the exhaust purification device tends to be low. In the above configuration, since a turbine with a large heat capacity is not interposed between the engine and the exhaust gas purification device, the temperature of the exhaust gas purification device can be increased even when the temperature of the exhaust gas is low. By maintaining the exhaust gas purification device at the activation temperature, the exhaust gas purification device can purify exhaust gas. In addition to improving the fuel efficiency of the engine, the exhaust gas performance of the engine also improves.

Since the turbine of the exhaust turbo supercharger is provided downstream of the exhaust purification device, the supercharging response of the exhaust turbo supercharger is low when the driver requests acceleration of the vehicle. On the other hand, the engine control unit described above causes the fuel injection valve to perform fuel injection during the exhaust stroke after the main injection to the engine when the vehicle is accelerated due to an increase in the accelerator opening. The fuel injected during the exhaust stroke is discharged from the engine in an unburned or almost unburned state and is supplied to the exhaust gas purification device. Fuel reacts in the exhaust gas purification device and reaction heat is generated. The heat of reaction increases the exhaust energy supplied to the turbine. As a result, although the engine with this configuration has a large volume upstream of the turbine, the supercharging response of the exhaust turbo supercharger improves when the vehicle accelerates.

Therefore, this engine achieves both improved exhaust purification performance and improved supercharging response.

The supercharged engine includes:
a compressor for the exhaust turbo supercharger that is provided in the intake passage of the engine and supercharges intake air supplied to the engine;
an electric supercharger provided downstream of the compressor in the intake passage,
The control unit may drive the electric supercharger when the vehicle accelerates.

According to this configuration, the intake passage is provided with an electric supercharger in addition to the compressor of the exhaust turbo supercharger. The control unit drives the electric supercharger when the vehicle accelerates. This improves the engine's supercharging response.

Here, the electric supercharger is provided downstream of the compressor of the exhaust turbo supercharger in the intake passage. The compressor and electric supercharger are arranged in series. The capacity of the compressor of the electric supercharger may be smaller than the capacity of the compressor of the exhaust turbocharger. By doing so, the electric supercharger can efficiently supercharge intake air when the operating state of the engine is within a predetermined low rotation range. The compressor of the exhaust turbo supercharger, which is upstream of the electric supercharger, is substantially not driven when the operating state of the engine is within a predetermined low rotation range. The compressor of the exhaust turbo supercharger can efficiently supercharge intake air when the operating state of the engine is in a high rotation range other than a low rotation range. The combination of two superchargers allows supercharging of the intake air over a wide operating range of the engine.

The control unit drives the electric supercharger when the vehicle accelerates, and when driving the electric supercharger alone is insufficient to provide a required acceleration according to the accelerator opening, the control unit causes the fuel injection valve to: Fuel injection may be performed during the exhaust stroke.

In this way, the supercharging response can be improved by driving the electric supercharger, and the required torque of the engine can be achieved by the combination of driving the electric supercharger and fuel injection during the exhaust stroke.

The control unit may prohibit fuel injection during the exhaust stroke when the temperature of the exhaust purification device exceeds a constraint temperature.

When the temperature of the exhaust gas purification device exceeds the constraint temperature due to reaction heat generated in the exhaust gas purification device, the reliability of the exhaust gas purification device decreases. When the temperature of the exhaust gas purification device exceeds the constraint temperature, the control unit prohibits fuel injection during the exhaust stroke, thereby ensuring reliability of the exhaust gas purification device.

In the technology disclosed here,
The supercharged engine includes:
an EGR passage that connects a portion of the exhaust passage between the exhaust purification device and the turbine and an intake passage of the engine; and an EGR passage that is provided in the EGR passage and cools EGR gas flowing through the EGR passage. an EGR cooler, and an EGR system that recirculates a part of the exhaust gas to the intake passage as EGR gas,
The control unit controls the EGR system when the fuel injection valve executes fuel injection during the exhaust stroke when the vehicle accelerates, and when the temperature of the exhaust purification device exceeds a constraint temperature. , causing the EGR gas to be refluxed.

When EGR gas is recirculated through the EGR passage, the oxygen concentration in the combustion chamber of the engine decreases, thereby lowering the combustion temperature. Furthermore, the combustion temperature can be further lowered by the EGR cooler cooling the EGR gas. As a result, the exhaust temperature decreases.

When the temperature of the exhaust gas purification device exceeds the constraint temperature, lowering the temperature of the exhaust gas from the engine prevents the temperature of the exhaust gas purification device from becoming excessively high.

In another technique disclosed herein,
an EGR passage that connects a portion of the exhaust passage between the exhaust purification device and the turbine and an intake passage of the engine; and an EGR passage that is provided in the EGR passage and cools EGR gas flowing through the EGR passage. A liquid-cooled EGR cooler, and an EGR system that recirculates a part of the exhaust gas to the intake passage as EGR gas,
The control unit causes the EGR system to recirculate the EGR gas when the vehicle accelerates,
The control unit controls the EGR system when the fuel injection valve executes fuel injection during the exhaust stroke when the vehicle accelerates, and when the temperature of the exhaust purification device exceeds a constraint temperature. , increasing the amount of coolant supplied to the EGR cooler .

As described above, when EGR gas is recirculated through the EGR passage, the oxygen concentration in the combustion chamber of the engine decreases, thereby lowering the combustion temperature. Furthermore, the combustion temperature can be further lowered by the EGR cooler cooling the EGR gas. Furthermore, when the amount of coolant supplied to the liquid-cooled EGR cooler is increased, the temperature of the EGR gas flowing back into the intake passage is further reduced. As a result, the temperature of the exhaust gas from the engine decreases.

When the temperature of the exhaust gas purification device exceeds the constraint temperature, lowering the temperature of the exhaust gas from the engine prevents the temperature of the exhaust gas purification device from becoming excessively high.

In yet another technique disclosed herein,
The exhaust purification device includes a catalyst device that reacts harmful substances in the exhaust gas, and a filter device that collects particulate matter in the exhaust gas,
The control unit reduces the amount of injection during the exhaust stroke when the amount of particulate matter deposited in the filter device is large, and increases the amount of injection during the exhaust stroke when the amount of deposited particulate matter is small.

If the amount of particulate matter deposited in the filter device is large, the temperature of the exhaust gas purification device tends to rise when fuel is reacted in the exhaust gas purification device. By reducing the injection amount during the exhaust stroke, the control unit can suppress the temperature of the exhaust gas purification device from rising excessively.

If the amount of particulate matter deposited on the filter device is low, the control unit increases the injection amount during the exhaust stroke. Exhaust energy supplied to the turbine is increased while suppressing the temperature of the exhaust purification device from becoming excessively high. The turbocharging response of the exhaust turbo supercharger improves when the vehicle accelerates.

As explained above, the supercharged engine achieves both improved exhaust purification performance and improved supercharging response.

FIG. 1 is a schematic diagram illustrating the configuration of an engine system. FIG. 2 is a block diagram illustrating the control configuration of the engine. FIG. 3 is a map illustrating the operating range of the engine. FIG. 4 is a diagram illustrating characteristics of a compressor of an electric supercharger. FIG. 5 is an example of a pv diagram of an engine. FIG. 6 is a flowchart illustrating engine control by the ECU. FIG. 7 is a diagram illustrating the relationship between the accelerator opening increase rate and the selection mode of the supercharging means. FIG. 8 is a flowchart illustrating a modification of engine control by the ECU. FIG. 9 is a flowchart illustrating a modification of engine control by the ECU. FIG. 10 is a flowchart illustrating a modification of engine control by the ECU.

Hereinafter, embodiments of a supercharged engine 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 supplied with fuel containing light oil as a main component. Although not shown, the engine 2 has a plurality of cylinders. Each cylinder forms a combustion chamber of the engine 2. The fuel supplied into the combustion chamber is combusted by compression self-ignition.

(Engine system configuration)
A fuel injection valve, that is, an injector 21 is attached to the engine 2. Injector 21 supplies fuel to engine 2 . More specifically, the injector 21 is provided for each cylinder and directly injects fuel into the cylinder. Injector 21 receives a control signal from ECU 100, which will be described later. The injector 21 injects fuel into the combustion chamber at an injection timing set according to the operating state of the engine 2 and in an amount corresponding 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 air includes air or air and EGR gas. An exhaust passage 32 is also connected to the engine 2. The exhaust passage 32 discharges exhaust gas from each cylinder.

In the intake passage 31, a compressor 41 of the exhaust turbo supercharger 4, an electric supercharger 5, and an intercooler 43 are arranged in order from the upstream side to the downstream side. Compressor 41 boosts the pressure of intake air. The electric supercharger 5 also boosts the pressure of intake air. The intercooler 43 cools the pressurized 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 includes a compressor wheel 51 provided in the intake passage 31 and an electric motor 52 that drives the compressor wheel 51. When the electric motor 52 operates, the compressor wheel 51 rotates, and the compressor wheel 51 boosts the pressure of 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 power from a battery 55 mounted on the vehicle. The battery 55 stores electric power generated by, for example, an alternator (not shown).

Here, the capacity of the electric supercharger 5 is set smaller than the capacity of the compressor 41 of the exhaust turbo supercharger 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 range, and is not driven in other cases. The compressor 41 of the large-capacity exhaust turbo supercharger 4 and the small-capacity electric supercharger 5 are provided in series, and only the compressor 41 of the exhaust turbo supercharger 4 is driven, and only the electric supercharger 5 is driven. By switching the drive of both the compressor 41 of the exhaust turbo supercharger 4 and the electric supercharger 5, this engine 2 can supercharge intake air over a wide operating range.

A bypass passage 53 that bypasses the compressor wheel 51 is provided in the intake passage 31 . An upstream end of the bypass passage 53 is connected between the compressor 41 and the compressor wheel 51 in the intake passage 31 . A 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. Bypass valve 54 adjusts the amount of intake air flowing through bypass passage 53. While the electric supercharger 5 is driving, the bypass valve 54 is closed. The bypass valve 54 is open while the electric supercharger 5 is not being driven.

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

The exhaust purification device 6 includes an 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 gas purification device 6, the DOC is arranged upstream of the DPF.

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

This engine system 1 does not include a catalyst for purifying NOx in exhaust gas. However, the technology disclosed herein does not exclude application to an engine equipped with a catalyst that purifies NOx.

The turbine 42 of the exhaust turbocharger 4 is rotated by the energy of the exhaust gas. A connection 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, increasing the pressure of intake air.

Although detailed illustration is omitted, the exhaust turbo supercharger 4 is a variable capacity turbo supercharger. A movable vane is disposed within the turbine case. By adjusting the opening degree of the movable vane, the passage area in the exhaust turbo supercharger 4 changes.

The engine system 1 also includes an EGR (Exhaust Gas Recirculation) system 7. The EGR system 7 recirculates a portion 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. A first EGR valve 73 is provided in the first EGR passage 71 . The first EGR valve 73 is, for example, an electromagnetic opening adjustment valve. The first EGR valve 73 adjusts the flow rate of EGR gas that passes through the first EGR passage 71 and is returned to the intake passage 31.

The first EGR passage 71 is also provided with an EGR cooler 75. In the configuration example shown in FIG. 1, the EGR cooler 75 is provided upstream of the first EGR valve 73 with respect to the direction in which EGR gas flows. The EGR cooler 75 cools 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 EGR gas and cooling water. Note that the configuration of the circulation circuit 8 will be described later.

The second EGR passage 72 branches off from the middle of the first EGR passage 71. More specifically, the second EGR passage 72 branches from the first EGR passage 71 upstream of the EGR cooler 75. 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 adjustment valve. The second EGR valve 74 adjusts the flow rate of EGR gas that passes through the second EGR passage 72 and is returned to the intake passage 31.

The engine system 1 has a cooling water circulation circuit 8. A broken line in FIG. 1 indicates a cooling water flow path that constitutes the circulation circuit 8. Circulation circuit 8 includes a radiator 81, a water pump 82, and an electric thermostatic valve 85.

The circulation circuit 8 has a main flow path 83. The main flow path 83 is a path that returns from the engine 2 to the engine 2 through the radiator 81, the electric thermostatic valve 85, and the water pump 82. The water pump 82 circulates cooling water in the circulation circuit 8 . The water pump 82 is driven by the engine 2, for example. The radiator 81 radiates heat from the cooling water received in the engine 2. The electric thermostatic valve 85 opens and closes the main flow path 83. The electric thermostatic valve 85 electromagnetically switches between opening and closing based on a control signal from the ECU 100, which will be 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 electrothermostat 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 to the engine 2 from the engine 2 through the EGR cooler 75 and the water pump 82. The cooling water flowing through the sub-channel 84 does not pass through the radiator 81.

FIG. 2 is a block diagram illustrating a control configuration of the engine system 1. As shown in FIG. The engine system 1 includes an engine control unit (hereinafter referred to as ECU) 100. The ECU 100 includes a microprocessor having a CPU 101, a memory 102, a counter timer group 103, an interface 104, and a bus 105 connecting these units. ECU 100 controls engine 2 . ECU 100 is an example of a control unit.

The ECU 100 receives signals from a water temperature sensor SW1, a boost pressure sensor SW2, an exhaust temperature sensor SW3, a crank angle sensor SW4, an accelerator opening sensor SW5, a vehicle speed sensor SW6, a DPF differential pressure sensor SW7, and a 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. Crank angle sensor SW4 is attached to engine 2 and outputs a signal corresponding to the rotation angle of the crankshaft of 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. Vehicle speed sensor SW6 is provided, for example, on 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. Catalyst temperature sensor SW8 is attached to exhaust purification device 6 and outputs a signal corresponding to the temperature of DOC.

ECU 100 calculates the engine rotation speed based on the signal from crank angle sensor SW4, and calculates the engine load based on the signal from accelerator opening sensor SW5. Further, the ECU 100 determines whether the engine 2 is in a cold state or a warm state based on a signal from the water temperature sensor SW1. ECU 100 determines whether the driver of the vehicle has requested acceleration and the degree of the acceleration request based on the signal from accelerator opening sensor SW5.

The ECU 100 also determines whether or not DPF regeneration is necessary based on the signal from the DPF differential pressure sensor SW7. Regeneration of the DPF involves burning particulate matter that has accumulated on the DPF. If the ECU 100 determines that DPF regeneration is necessary, it performs DPF regeneration control.

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

Air and EGR gas are introduced into the combustion chamber of the engine 2 in an amount depending on the operating state of the engine 2, and fuel is also supplied. The fuel supplied into the combustion chamber is combusted by compression self-ignition at appropriate timing.

Here, this engine 2 burns fuel in a state with excess air so that thermal efficiency is improved. Furthermore, by introducing EGR gas into the combustion chamber, the amount of air within the combustion chamber is also adjusted. A 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 temperature of the exhaust gas is low, it is disadvantageous for activation of DOC. Conventional engines are generally provided with an exhaust purification device downstream of the turbine of the exhaust turbocharger. In this conventional configuration, since the heat capacity of the turbine is large, there is a problem in that when the temperature of the exhaust gas is low, the temperature of the exhaust gas purification device is even more difficult to rise.

On the other hand, in this engine system 1, the exhaust purification device 6 is provided upstream of the turbine 42 of the exhaust turbo supercharger 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 exhaust gas, and the temperature of the exhaust gas purification device 6 is maintained at a high temperature while the engine 2 is operating. In this engine system 1, the DOC can be maintained in an active state during operation of the engine 2 even if the temperature of the exhaust gas is low, so that the exhaust gas performance is improved.

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

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

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

When the electric supercharger 5 is operating in the second region, the ECU 100 closes the bypass valve 54. 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 operating, the compressor wheel 51 supercharges intake air.

When electric supercharger 5 is stopped in the first region, ECU 100 opens bypass valve 54 . 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, an increase in 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 turbo supercharger 4. The electric supercharger 5 has high efficiency in the low rotation range of the engine 2. The electric supercharger 5 can efficiently supercharge intake air in the second region.

Since the compressor 41 of the exhaust turbo supercharger 4 has a large capacity, it does not substantially supercharge intake air when the operating state of the engine 2 is in the second region. The compressor 41 supercharges intake air when the rotational 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 intake air. Note that near the boundary between the first region and the second region, the compressor 41 may increase the pressure of the intake air, and the electric supercharger 5 may further increase the pressure of the intake air.

Next, a driving scene of a vehicle in which the electric supercharger 5 is driven will be described. The solid line arrow and the broken line arrow in FIG. 3 illustrate changes in the operating state of the engine 2 when the driver depresses the accelerator pedal to request acceleration of the vehicle. The ECU 100 increases the load on the engine 2 from the operating state indicated by the white circle in FIG. 3 based on the signal from the accelerator opening sensor SW5. As a result, the operating state of the engine 2 shifts from the first region to the second region. ECU 10 operates electric supercharger 5. After that, ECU 100 increases the rotation speed of 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 turbo supercharger 4 has a low supercharging response because the volume upstream of the turbine 42 is larger.

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 requested. As a result, the supercharging response of the engine 2 is improved.

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

The electric supercharger 5 operates when the operating state of the engine 2 is in a low rotation region and the vehicle is in an acceleration transition, and when the engine 2 is operating under high load in the low rotation region. Drive in both.

Thereby, the electric supercharger 5 can improve the supercharging response during the acceleration transition of the vehicle, as described above. The electric supercharger 5 can also sufficiently supercharge intake air when the engine 2 is operating at low rotation speeds and high loads, so that sufficient air and EGR gas are 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 used when the operating state of the engine 2 is within a low rotation range and the vehicle is in an acceleration transition, or when the engine 2 is operating under high load within the low rotation range. It may be driven at either time.

(Control of EGR system by ECU)
ECU 100 recirculates EGR gas to intake passage 31 in all operating ranges of 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), by circulating the EGR gas into the intake passage 31, the oxygen concentration in the combustion chamber decreases, and the combustion temperature decreases. 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 low rotation and full load, that is, when the engine 2 is operating in the second region. This makes it possible to introduce it indoors. The electric supercharger 5 improves the exhaust gas performance of the engine 2.

When the electric supercharger 5 is driving, in the intake passage 31, the pressure is low upstream of the electric supercharger 5, and the pressure downstream of the electric supercharger 5 is high. As described above, the electric supercharger 5 is driven in the low rotation range of the engine 2, so 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 recirculate 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 it is impossible to recirculate the EGR gas to the intake passage 31. Can not.

In contrast, 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 driving, the EGR system 7 can recirculate EGR gas to the intake passage 31 via the first EGR passage 71. As shown in FIG. 3, when the operating state of the engine 2 is in the second region, in other words, when the electric supercharger 5 is operating, the ECU 100 opens the first EGR valve 73 and opens the second EGR valve 73. Valve 74 is closed. EGR gas in an amount depending on the operating state of the engine 2 is returned 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 in 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. Performance curve 401 shows the efficiency contours of compressor wheel 51.

As mentioned above, when EGR gas is recirculated to the intake passage 31 via the first EGR passage 71, the amount of gas flowing into the compressor wheel 51 of the electric supercharger 5 is equal to the sum of air and EGR gas. become. Here, the black circles in FIG. 4 illustrate operating points of the compressor wheel 51 when 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 a low rotation range of the engine 2, the flow rate of 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 circles in FIG. 4 illustrate the operating points of the compressor wheel 51 when EGR gas is recirculated upstream of the electric supercharger 5. Air and EGR gas flow into the compressor wheel 51 . That is, the EGR gas is added to the flow rate passing through the compressor wheel 51. Since more flow passes through the compressor wheel 51, the efficiency of the compressor wheel 51 increases.

Therefore, in the second region in which the electric supercharger 5 is driven, the efficiency of the electric supercharger 5 can be improved by circulating 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. EGR cooler 75 cools EGR gas. When the load on the engine 2 is high, the EGR system 7 can recirculate the cooled EGR gas to the intake passage 31. The temperature inside the combustion chamber into which EGR gas is introduced is suppressed from becoming excessively high. The occurrence of abnormal combustion in the engine 2 is suppressed.

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

Here, the second EGR passage 72 bypasses the EGR cooler 75. Furthermore, since the second EGR passage 72 is connected to a portion of the intake passage 31 between the intercooler 43 and the engine 2, the EGR gas is not cooled by the intercooler 43. Furthermore, when the EGR gas is recirculated through the second EGR passage 72, the EGR gas can be recirculated with a shorter passage length than when 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 relatively high temperature EGR gas into the engine 2 through the second EGR passage 72.

When the load on the engine 2 is low, the temperature inside the combustion chamber tends to be low, and the ignitability of the fuel tends to decrease. When the engine 2 is operating at low load or light load in the first region, the EGR system 7 recirculates high-temperature EGR gas to the intake passage 31 via the second EGR passage 72. The ignitability of the fuel can be improved by increasing the temperature of the fuel. This increases the combustion stability of the engine 2.

Further, as shown with hatching in FIG. 3, when the engine 2 is operating at high rotation and full load in the first region, the EGR system 7 intakes EGR gas through the second EGR passage 72. When it flows back into the passage 31, the pumping loss of the engine 2 is reduced. FIG. 5 illustrates a pv diagram 501 of the engine 2. Since the EGR system 7 extracts a portion 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 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, and thus the pumping loss of the engine 2 is reduced.

Furthermore, when the engine 2 is operating in a high rotation and full load range, 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 amount of air passing through the compressor 41 increases too much, resulting in a decrease in the efficiency of the compressor 41. On the other hand, the engine system 1 described above introduces EGR gas downstream of the compressor 41 in the intake passage 31 through the second EGR passage 72 . Thereby, the engine system 1 also has the advantage that the efficiency of the compressor 41 does not decrease.

Conventional engine systems had two paths: a high pressure EGR path and a low pressure EGR path. On the other hand, the EGR passage of this engine system 1 includes a first EGR passage 71 and a second EGR passage 72 branched from the first EGR passage 71. The EGR system 7 is configured by one path. This configuration has the advantage that the configuration of the engine system 1 is simplified.

Further, the first EGR passage 71 is connected downstream of the exhaust purification device 6 in the exhaust passage 32. The EGR system 7 can recirculate the clean exhaust gas purified by the exhaust purification device 6 to the intake passage 31 as EGR gas. Contamination of the constituent members of the intake system with, for example, particulate matter is suppressed.

(Control at the time of acceleration request by ECU)
Next, the control of the engine 2 by the ECU 100 when the driver requests acceleration will be explained. FIG. 6 is a flowchart showing a control procedure for the engine 2 executed by the ECU 100.

As described above, when the driver requests acceleration, the ECU 100 drives the electric supercharger 5. This improves the supercharging response of the engine 2. When the driver's acceleration request is high, the electric supercharger 5 alone may not be able to achieve the required supercharging pressure. This engine system 1 drives the exhaust turbo supercharger 4 when the required supercharging pressure cannot be achieved with the electric supercharger 5 alone.

When driving the exhaust turbo supercharger 4, the engine system 1 utilizes the exhaust purification device 6 to promote the drive of the exhaust turbo supercharger 4. Specifically, the injector 21 is caused to perform fuel injection during the exhaust stroke after main injection to the engine 2 . Note that the injector 21 performs main injection near the compression top dead center. Since fuel injection during the exhaust stroke is an injection performed after main injection, it may be referred to as post injection hereinafter.

The fuel injected during the exhaust stroke is supplied to the exhaust purification device 6 in an unburned or almost unburned state. The fuel reacts in the DOC of the exhaust purification device 6, and reaction heat is generated. The heat of reaction increases the exhaust energy supplied to the turbine 42 downstream of the exhaust gas purification device 6. As a result, the drive of the exhaust turbo supercharger 4 is promoted, and the supercharging pressure increases quickly.

In the flowchart of FIG. 6, the ECU 100 first reads signals from various sensors in step S61, and in the subsequent step S62, the ECU 100 determines whether the accelerator opening increase rate exceeds a predetermined first threshold value. do. The accelerator opening increase rate is detected based on the signal from the accelerator opening sensor SW5. The rate of increase in accelerator opening corresponds to the speed at which the driver presses the accelerator pedal. When the depression speed is high, the accelerator opening increase rate is high, and when the depression speed is slow, the accelerator opening increase rate is low.

FIG. 7 is a diagram illustrating a relationship 701 between the accelerator opening increase rate and the selection mode of the supercharging means. In the relationship 701, if the accelerator opening increase rate is less than or equal to the first threshold value, the ECU 100 turns off the electric supercharger 5. In other words, the electric supercharger 5 is not driven. Since the acceleration requested by the driver is slow acceleration, supercharging using the electric supercharger 5 is not performed. Note that depending on the operating state of the engine 2, the exhaust turbo supercharger 4 supercharges intake air.

In relationship 701, when the accelerator opening increase rate exceeds the first threshold, ECU 100 drives electric supercharger 5.

In relationship 701, when the accelerator opening increase rate exceeds the second threshold, ECU 100 drives electric supercharger 5 and executes the above-described fuel injection during the exhaust stroke, that is, post injection. Note that the second threshold is larger than the first threshold.

Returning to the flowchart of FIG. 6, if the determination in step S62 is YES, the process proceeds to step S63. If the determination in step S62 is NO, the process returns. In this case, ECU 100 performs normal engine control without performing acceleration control in steps S63 to S66.

In step S63, ECU 100 drives electric supercharger 5. The electric supercharger 5 quickly supercharges intake air, improving the supercharging response of the engine 2.

In subsequent step S64, the ECU 100 determines whether the accelerator opening increase rate exceeds a predetermined second threshold. If the determination in step S62 is YES, the process proceeds to step S65. If the determination in step S62 is NO, the process returns. In this case, the ECU 100 continues to drive the electric supercharger 5 or shifts to normal engine control depending on the driver's accelerator pedal operation.

In step S65, the ECU 100 determines whether fuel injection during the exhaust stroke is possible. Specifically, the ECU 100 determines (1) whether the temperature of the DOC exceeds the constraint temperature, and (2) whether the temperature of the turbine 42 exceeds the constraint temperature.

The ECU 100 can determine the temperature of the DOC based on the signal from the catalyst temperature sensor SW8, for example. The constraint temperature may be determined in advance in consideration of the reliability of the DOC.

The ECU 100 may also estimate the temperature of the turbine 42 based on, for example, a signal from the exhaust temperature sensor SW3 and a predetermined temperature prediction model for the exhaust passage 32. The constraint temperature may be determined in advance in consideration of the reliability of the turbine 42.

For example, the memory 102 of the ECU 100 stores information on these temperature constraints and a temperature prediction model.

If the determination in step S65 is YES, the process proceeds to step S66. If the determination in step S65 is NO, the process returns to step S63. By not performing post-injection, reliability of the DOC and/or turbine 42 is ensured.

In step S66, the ECU 100 causes the injector 21 to perform post injection during the exhaust stroke. As described above, the fuel reacts in the DOC of the exhaust gas purification device 6, and reaction heat is generated. The heat of reaction increases the exhaust energy supplied to the turbine 42. As a result, the drive of the exhaust turbo supercharger 4 is promoted. Since the engine system 1 supercharges intake air using both the compressor 41 of the exhaust turbo supercharger 4 and the electric supercharger 5, the required supercharging pressure can be quickly reached.

In this way, the engine system 1 uses the compressor 41 of the exhaust turbo supercharger 4 and the electric supercharger 5 arranged in series to improve the supercharging response and achieve the required torque of the engine 2. realizable.

(First modification of acceleration control)
FIG. 8 is a flowchart showing a modification of the control procedure for the engine 2 executed by the ECU 100. Steps S81 to S84 in this flowchart correspond to steps S61 to S64 in the flowchart of FIG.

After the ECU 100 determines in step S84 that the rate of increase in accelerator opening exceeds the predetermined second threshold, the process proceeds to step S85. In step S85, the ECU 100 causes the injector 21 to perform post injection during the exhaust stroke. As described above, the reaction heat generated in the DOC of the exhaust gas purification device 6 increases the exhaust energy supplied to the turbine 42.

In subsequent step S86, the ECU 100 determines whether the temperature of the DOC exceeds the constraint temperature. This determination is the same as the determination in step S65. If the temperature of the DOC exceeds the constraint temperature, the process proceeds to step S87; if the temperature of the DOC does not exceed the constraint temperature, the process proceeds to step S88. Note that in step S86, the ECU 100 may determine whether the temperature of the turbine 42 exceeds the constraint temperature, or may determine both the catalyst temperature and the turbine temperature.

In step S87, the ECU 100 opens the first EGR valve 73. As a result, the EGR gas is cooled by the EGR cooler 75, and the low-temperature EGR gas flows back into the intake passage 31. The temperature inside the combustion chamber into which EGR gas is introduced decreases. Furthermore, the reflux of the EGR gas reduces the oxygen concentration within the combustion chamber and lowers the combustion temperature.

As a result, the temperature of the exhaust gas discharged from the engine 2 decreases. The temperature of the DOC is suppressed from exceeding the constraint temperature. The engine system 1 can increase exhaust energy and improve supercharging response while ensuring reliability of DOC.

In step S88, the ECU 100 closes the first EGR valve 73. As a result, EGR gas flows back into the intake passage 31 through the second EGR passage 72 . Since the temperature of EGR gas is high, the combustion temperature also increases.

As a result, the exhaust energy supplied to the turbine 42 of the exhaust turbocharger 4 increases, and the supercharging response improves.

(Second modification of acceleration control)
FIG. 9 is a flowchart showing another modification of the control procedure for the engine 2 executed by the ECU 100. Steps S91 to S96 in this flowchart correspond to steps S81 to S86 in the flowchart of FIG.

In the second variant, the water pump 82 of the engine system 1 is not driven by the engine 2 but by an electric motor. By controlling the electric motor by the ECU 100, the water pump 82 can change the circulating flow rate of cooling water.

Further, the EGR system 7 opens the first EGR valve 73 when there is an acceleration request, and causes the EGR gas cooled by the EGR cooler 75 to flow back to the intake passage 31.

After the ECU 100 determines in step S96 of the flowchart of FIG. 9 that the temperature of the DOC exceeds the constraint temperature, the process proceeds to step S97. In step S97, the ECU 100 increases the flow rate of cooling water supplied to the EGR cooler 75 by controlling the water pump 82. This promotes heat exchange in the EGR cooler 75, so that the temperature of the EGR gas returned to the intake passage 31 is further reduced. As a result, the temperature of the exhaust gas discharged from the engine 2 decreases. The temperature of the DOC is suppressed from exceeding the constraint temperature. The engine system 1 can increase exhaust energy and improve supercharging response while ensuring reliability of DOC.

On the other hand, if the determination in step S96 is NO, the process moves to step S98. ECU 100 stops increasing the flow rate of cooling water supplied to EGR cooler 75. Thereby, the temperature of the EGR gas recirculated to the intake passage 31 does not drop too much. As a result, the temperature of the exhaust gas discharged from the engine 2 becomes relatively high, so the temperature of the exhaust gas discharged from the DOC also increases. The exhaust energy supplied to the turbine 42 of the exhaust turbo supercharger 4 increases, and the supercharging response improves.

(Third modification example of acceleration control)
FIG. 10 is a flowchart showing yet another modification of the control procedure for the engine 2 executed by the ECU 100. Steps S101 to S104, S106, and S107 of this flowchart correspond to steps S91 to S94, S95, and S96 of the flowchart of FIG.

After determining the execution of fuel injection during the exhaust stroke, that is, the post injection, the ECU 100 sets the fuel injection amount of the post injection according to the amount of accumulation in the DPF in step S105. As described above, the amount of DPF accumulation is estimated based on the signal from the DPF differential pressure sensor SW8. If the amount of DPF accumulation is large, the ECU 100 reduces the amount of fuel injection for post injection. This is because if too much reaction heat is generated in the exhaust gas purification device 6, the temperature of the exhaust gas purification device 6 may become too high. When the amount of DPF accumulation is small, the ECU 100 increases the amount of fuel injection in the post injection to prevent the temperature of the exhaust purification device 6 from becoming too high.

In subsequent step S106, ECU 100 executes post injection according to the set injection amount. Then, in step S107, it is determined whether the temperature of the DOC exceeds the constraint temperature. If the temperature of the DOC exceeds the constraint temperature, the process proceeds to step S108. ECU 100 cancels post injection. If the temperature of the DOC does not exceed the constraint temperature, the process returns. Thereby, while ensuring the reliability of the DOC, the exhaust energy can be increased to the extent possible and the supercharging response can be improved.

The present invention is not limited to the embodiments described above, and substitutions may be made without departing from the scope of the claims.

For example, at the time of an acceleration request, the ECU 100 may perform post-injection during the exhaust stroke without driving the electric supercharger 5 to promote the drive of the exhaust turbo supercharger 4.

For example, the technology disclosed herein is not limited to application to diesel engines, but can also be applied to engines that use gasoline or fuel containing naphtha.

The above-described embodiments are merely illustrative and should not be construed as limiting the scope of the present invention. The scope of the invention is defined by the claims, and all modifications and changes that come within the range of equivalents of the claims are intended to be within the scope of the invention.

1 Engine system 100 ECU (control unit)
2 Engine 21 Injector (fuel injection valve)
31 Intake passage 4 Exhaust turbo supercharger 41 Compressor 42 Turbine 5 Electric supercharger 53 Bypass passage 6 Exhaust purification device 7 EGR system 71 First EGR passage 72 Second EGR passage 75 EGR cooler

Claims (6)

A fuel injection valve that supplies fuel to the engine;
an exhaust purification device that is installed in an exhaust passage of the engine and purifies exhaust gas discharged from the engine;
a turbine of an exhaust turbo supercharger provided downstream of the exhaust purification device in the exhaust passage;
a control unit that outputs a control signal to a controlled object;
an EGR passage that connects a portion of the exhaust passage between the exhaust purification device and the turbine and an intake passage of the engine; and an EGR passage that is provided in the EGR passage and cools EGR gas flowing through the EGR passage. an EGR cooler, and an EGR system that returns part of the exhaust gas to the intake passage as EGR gas,
The control unit causes the fuel injection valve to perform fuel injection during an exhaust stroke after main injection to the engine when accelerating the vehicle due to an increase in accelerator opening ;
The control unit controls the EGR system when the fuel injection valve executes fuel injection during the exhaust stroke when the vehicle accelerates, and when the temperature of the exhaust purification device exceeds a constraint temperature. , execute the reflux of the EGR gas.
Engine with supercharger. A fuel injection valve that supplies fuel to the engine;
an exhaust purification device that is installed in an exhaust passage of the engine and purifies exhaust gas discharged from the engine;
a turbine of an exhaust turbo supercharger provided downstream of the exhaust purification device in the exhaust passage;
a control unit that outputs a control signal to a controlled object;
an EGR passage that connects a portion of the exhaust passage between the exhaust purification device and the turbine and an intake passage of the engine; and an EGR passage that is provided in the EGR passage and cools EGR gas flowing through the EGR passage. a liquid-cooled EGR cooler, and an EGR system that recirculates part of the exhaust gas to the intake passage as EGR gas,
The control unit causes the fuel injection valve to perform fuel injection during an exhaust stroke after main injection to the engine when accelerating the vehicle due to an increase in accelerator opening ;
The control unit causes the EGR system to recirculate the EGR gas when the vehicle accelerates,
The control unit controls the EGR system when the fuel injection valve executes fuel injection during the exhaust stroke when the vehicle accelerates, and when the temperature of the exhaust purification device exceeds a constraint temperature. , increasing the amount of coolant supplied to the EGR cooler.
Engine with supercharger. A fuel injection valve that supplies fuel to the engine;
an exhaust purification device that is installed in an exhaust passage of the engine and purifies exhaust gas discharged from the engine;
a turbine of an exhaust turbo supercharger provided downstream of the exhaust purification device in the exhaust passage;
A control unit that outputs a control signal to a controlled object,
The exhaust purification device includes a catalyst device that reacts harmful substances in the exhaust gas, and a filter device that collects particulate matter in the exhaust gas,
The control unit causes the fuel injection valve to perform fuel injection during an exhaust stroke after main injection to the engine when accelerating the vehicle due to an increase in accelerator opening ;
The control unit reduces the amount of injection during the exhaust stroke when the amount of deposited particulate matter in the filter device is large, and increases the amount of injection during the exhaust stroke when the amount of deposited particulate matter is small.
Engine with supercharger. The supercharged engine according to any one of claims 1 to 3 ,
a compressor for the exhaust turbo supercharger that is provided in the intake passage of the engine and supercharges intake air supplied to the engine;
an electric supercharger provided downstream of the compressor in the intake passage,
The control unit is a supercharged engine that drives the electric supercharger when the vehicle accelerates. The supercharged engine according to claim 4 ,
The control unit drives the electric supercharger when the vehicle accelerates, and when driving the electric supercharger alone is insufficient to provide a required acceleration according to the accelerator opening, the control unit causes the fuel injection valve to: An engine with a supercharger that performs fuel injection during the exhaust stroke. The supercharged engine according to claim 5 ,
In the supercharged engine, the control unit prohibits fuel injection during the exhaust stroke when the temperature of the exhaust purification device exceeds a restriction temperature.

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