JP2019105196A - Engine with supercharger - Google Patents

Abstract

To improve acceleration feeling while preventing degradation of emission performance in acceleration.SOLUTION: An engine with a supercharger includes an engine main body 10, an electrically-driven supercharger 18, a turbo-supercharger 56, an EGR passage for communicating an exhaust passage 60 at a downstream side with respect to a turbine 56b of the turbo-supercharger and an intake passage 50 at an upstream side with respect to a compressor 56a of the turbo-supercharger, a parameter calculation portion calculating a magnitude of increase of a rotating speed per a unit time of the engine main body in acceleration of a vehicle on the basis of a detection signal of a sensor mounted on the engine main body, and a control portion (PCM100) for opening the EGR passage in accelerating a vehicle having the increase of the rotating speed calculated by the parameter calculation portion larger than a prescribed value, and outputs a control signal to the electrically-driven supercharger to increase a supercharging pressure of the electrically-driven supercharger.SELECTED DRAWING: Figure 1

Description

  The technology disclosed herein relates to a supercharged engine.

  A supercharged engine is known that includes a turbocharger having a turbine disposed in an exhaust passage and a compressor disposed in an intake passage.

  Further, for example, Patent Document 1 discloses a supercharged diesel engine in which an electric supercharger is provided in an intake passage in addition to a turbocharger.

JP, 2010-180710, A

  In a diesel engine, a part of exhaust gas is recirculated to the intake passage in order to lower the combustion rate and the combustion temperature to suppress the generation of RawNOx. The diesel engine described in Patent Document 1 includes a high pressure EGR system and a low pressure EGR system. The high pressure EGR system has a high pressure EGR passage communicating the exhaust passage upstream of the turbine of the turbocharger with the intake passage downstream of the compressor of the turbocharger. The low pressure EGR system comprises a low pressure EGR passage communicating the exhaust passage downstream of the turbocharger turbine with the intake passage upstream of the compressor of the turbocharger, and an EGR for cooling the exhaust gas flowing through the low pressure EGR passage. It has a low pressure EGR system with a cooler. When the engine is operating in a steady state in a partial load region during engine warm-up, EGR gas is recirculated to the intake passage by a low pressure EGR system and / or a high pressure EGR system, and the turbocharger supercharging pressure Introduces fresh air into the cylinder according to the amount of fuel. As a result, the equivalence ratio of the air-fuel mixture and the temperature in the combustion chamber can be appropriately adjusted, and the generation of RawNOx and the generation of soot (soot) can be suppressed.

  However, when the driver of the vehicle depresses the accelerator pedal to request acceleration in the partial load region, exhaust energy may be increased in order to increase the amount of fresh air introduced into the cylinder in response to the increase in fuel amount. Is relatively low, the boost pressure of the turbocharger is difficult to increase, and the amount of fresh air introduced into the cylinder is insufficient. Lack of fresh air will lead to the occurrence of soot. If the amount of fuel is increased after waiting for the amount of fresh air to avoid the occurrence of soot, the acceleration feeling is reduced.

  In particular, when the transmission is in the low gear, the engine speed increase per unit time (Δrpm / Δt) is much higher than that in the high gear during acceleration of the vehicle. As the Δrpm / Δt increases, the cooling loss of the engine increases, which makes it difficult to increase the exhaust energy supplied to the turbine of the turbocharger. As a result, the supercharging pressure of the turbocharger becomes more difficult to rise, and the acceleration feeling is further reduced.

  The technology disclosed herein improves acceleration feeling while preventing deterioration of emission performance at the time of acceleration.

  The technology disclosed herein is characterized in that in the supercharged engine, at least at the time of acceleration of the vehicle, the equivalence ratio of the air-fuel mixture is actively adjusted using the electric supercharger.

  Specifically, the supercharged engine disclosed herein is provided in an engine main body mounted on a vehicle, an intake passage and an exhaust passage connected to the engine main body, and the intake passage, and is overheated by an electric motor. An electric supercharger for feeding, a turbine disposed in the exhaust passage, and a compressor disposed upstream of the electrically driven turbocharger in the intake passage, using exhaust energy A supercharger turbocharger, an EGR passage communicating the exhaust passage downstream of the turbine with the intake passage upstream of the compressor, and recirculating a portion of the exhaust gas to the intake passage; Parameter calculation for calculating the magnitude of the increase in the number of revolutions per unit time of the engine body at the time of acceleration of the vehicle based on the detection signal of a sensor attached to the engine body And, when the acceleration request signal is received to accelerate the vehicle, the EGR passage is opened when the rotation speed increase calculated by the parameter calculation unit is larger than a predetermined value, and the charge of the electric turbocharger is increased. And a control unit that outputs a control signal to the electric supercharger to increase the pressure.

  According to this configuration, at the time of acceleration of the vehicle, the electric supercharger operates such that the supercharging pressure increases if the magnitude of the increase in the number of revolutions per unit time of the engine body is larger than a predetermined value. Here, the electric supercharger may increase the supercharging pressure by driving from a stopped state, or may increase the supercharging pressure in a driving state. If the magnitude of the increase in the number of revolutions per unit time of the engine body is larger than a predetermined value, the cooling loss of the engine body becomes large, and the exhaust energy supplied to the turbine of the turbocharger becomes difficult to rise. As a result, the supercharging pressure by the turbocharger becomes difficult to rise. In the above configuration, it is possible to quickly increase the amount of fresh air introduced into the cylinder by raising the supercharging pressure by the electric supercharger in a situation where the supercharging pressure by the turbocharger is difficult to increase.

  Further, in the above configuration, when the charging pressure is increased by the electric supercharger, the EGR passage connected upstream of the electric supercharger is opened in the intake passage. Since the EGR gas is sucked into the intake passage through the EGR passage by the operation of the electric supercharger, the amount of EGR gas introduced into the cylinder can also be increased along with the increase of the fresh air amount.

  Since both fresh air and EGR gas introduced into the cylinders increase rapidly when the vehicle accelerates, Pmax of the engine main body can be rapidly increased to improve the acceleration feeling while preventing the generation of RawNOx and soot. be able to.

  The control unit may output a control signal to the electric supercharger so that the supercharging pressure of the electric supercharger is lower than that at the start of acceleration at the late stage of acceleration.

  As described above, when the boost pressure is rapidly increased by the electric supercharger at the start of acceleration, Pmax of the engine main body is rapidly increased, so the exhaust energy is increased. Thereby, the supercharging pressure by the turbocharger is increased. At the late stage of acceleration, the target supercharging pressure can be satisfied by the turbocharger, so power consumption can be reduced by reducing the supercharging pressure of the electric supercharger. Here, the electric supercharger may lower the supercharging pressure by stopping, or may continue driving in a state where the supercharging pressure is reduced.

  The control unit may be configured to operate the electric supercharger in a partial state regardless of the presence or absence of the acceleration request signal.

  In general, a large amount of power is required to drive the electric turbocharger from a stopped state. For this reason, the electric supercharger is driven at the time of acceleration of the vehicle receiving the acceleration request signal, and at the time of acceleration and steady traveling rather than stopping the electric turbocharger at steady traveling of the vehicle not receiving the acceleration request signal Regardless of time, by operating the electric supercharger in the partial state, it is possible to suppress power consumption when raising the supercharging pressure by the electric supercharger.

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

  When the transmission connected to the engine body is in the low gear stage before the acceleration request signal is received, the control unit operates the electric supercharger at a higher rotation speed than in the high gear stage. Good.

  When the transmission is in the low speed stage, the magnitude of the increase in the number of revolutions per unit time of the engine body tends to be larger than a predetermined level when the vehicle accelerates. On the other hand, when the transmission is in the high gear, when the vehicle accelerates, the magnitude of the increase in the number of revolutions per unit time of the engine body is unlikely to be greater than a predetermined value.

  Therefore, when the electric supercharger is operated at a high rotational speed in advance when the transmission is in the low gear stage before receiving the acceleration request signal, the supercharging pressure by the electric supercharger can be swiftly when the vehicle is accelerating. The acceleration feeling can be improved while suppressing the deterioration of the emission performance. On the contrary, when the transmission is in the high gear before receiving the acceleration request signal, the cooling loss of the engine at the time of acceleration of the vehicle is low, and the supercharging pressure by the turbocharger is likely to increase rapidly. There is little need to increase the supercharging pressure by the supercharger. Therefore, power consumption can be reduced by operating the electric supercharger at a low rotational speed in advance.

  The engine body may be a diesel engine having a geometric compression ratio of 16 or less. A diesel engine having a geometric compression ratio of 16 or less tends to have a low compression end temperature. As described above, when the ratio of fresh air in the cylinder is increased by increasing the supercharging pressure by the electric turbocharger at the time of acceleration of the vehicle, the specific heat ratio of the gas in the cylinder is increased, and the pressure before the start of compression is increased. Even if the temperature in the cylinder is low, the compression end temperature is high. Therefore, the supercharged engine of the above configuration is advantageous in securing the ignitability of the mixture in a low compression ratio diesel engine.

  As described above, the technology disclosed herein can improve the acceleration feeling while preventing the decrease in emission performance at the time of acceleration.

FIG. 1 is a schematic view showing a supercharged engine. FIG. 2 is a cross-sectional view showing the inside of the cylinder of the supercharged engine. FIG. 3 is a block diagram showing a control system of the supercharged engine. FIG. 4 is a map showing an operation mode of the electric supercharger. The upper drawing of FIG. 5 is a performance curve graph showing the characteristics of the compressor of the electric supercharger, and the lower drawing of FIG. 5 is a graph showing the characteristics of the electric motor of the electric supercharger. FIG. 6 is a φ-T map of a diesel engine. FIG. 7 is a diagram illustrating changes in Pmax when the vehicle accelerates. FIG. 8 is a diagram illustrating a supercharging region by the electric supercharger and a region in which supercharging by the turbocharger is effective. FIG. 9 is a schematic view showing an example of a fuel injection mode at the time of premixed combustion control and an example of a history of heat release rates associated therewith. FIG. 10 is a schematic view showing an example of a fuel injection mode of retard control and an example of the history of heat release rate associated therewith. FIG. 11 is a flowchart showing processing operation of engine control by the PCM.

  Hereinafter, embodiments of a supercharged engine will be described in detail with reference to the drawings. FIG. 1 shows an engine 1 according to the embodiment. An engine body 10 of the engine 1 is a diesel engine mounted on a vehicle and supplied with fuel mainly composed of light oil, and has a plurality of cylinders 30a (only one is shown in FIG. 2) A cylinder block 30 provided, a cylinder head 31 disposed on the cylinder block 30, and an oil pan 39 disposed below the cylinder block 30 and storing lubricating oil are provided. A piston 32 (see FIG. 2) is inserted in each cylinder 30a of the engine 1 so as to be reciprocatively slidable, and the combustion chamber 33 (the cylinder 32, the cylinder block 30, and the cylinder head 31) See Figure 2). On the top surface of the piston 32, as shown enlarged in FIG. 2, a cavity 32a like a reentrant type in a diesel engine is formed. The cavity 32 a faces the injector 38 described later when the piston 32 is located near the compression top dead center. The piston 32 is also connected to the crankshaft in the cylinder block 30 via a connecting rod. The shape of the combustion chamber 33 is not limited to the illustrated shape. For example, the shape of the cavity 32a, the top surface shape of the piston 32, the shape of the ceiling of the combustion chamber 33, and the like can be changed as appropriate.

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

  Each intake valve 36 is opened and closed by an intake side cam 40, and each exhaust valve 37 is opened and closed by an exhaust side cam 41. The intake side cam 40 and the exhaust side cam 41 are rotationally driven in conjunction with the rotation of the crankshaft. Although not shown, for example, a hydraulically operated valve variable mechanism is provided to adjust the open / close timing and open / close period of each of the intake valve 36 and the exhaust valve 37.

  Further, an injector 38 for directly injecting fuel into the cylinder 30a is attached to the cylinder head 31 for each cylinder 30a. As shown in FIG. 2, the injector 38 is disposed such that its injection hole faces the inside of the combustion chamber 33 from the central portion of the ceiling surface of the combustion chamber 33. The injector 38 directly injects, into the combustion chamber 33, fuel of an amount according to the operating condition of the engine 1 at an injection timing set according to the operating condition of the engine 1.

  As shown in FIG. 1, an intake passage 50 is connected to one side surface of the engine body 10 so as to communicate with the intake port 34 of each cylinder 30 a. On the other hand, an exhaust passage 60 for discharging burned gas (that is, exhaust gas) from each cylinder 30a is connected to the other side surface of the engine body 10. Although described later in detail, the intake passage 50 and the exhaust passage 60 are provided with a turbocharger 56 for performing supercharging of intake air.

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

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

  The intake passage 50 is provided with an intake side bypass passage 53 that bypasses the electric supercharger 18. The intake side bypass passage 53 has its upstream end connected between the compressor 56 a in the intake passage 50 and the electric supercharger 18, while the downstream end thereof has the electric supercharger 18 and the throttle in the intake passage 50. It is connected between the valve 55. An intake side bypass valve 58 for adjusting the amount of air flowing to the intake side bypass passage 53 is disposed in the intake side bypass passage 53. By adjusting the opening degree of the intake side bypass valve 58, the ratio between the intake amount supercharged by the electric supercharger 18 and the intake amount passing through the intake side bypass passage 53 is stepwise or continuously. You will be able to change it.

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

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

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

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

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

  The turbocharger 56 is rotationally driven by receiving energy of exhaust gas (ie, exhaust energy). Specifically, when the turbine 56b of the turbocharger 56 receives exhaust energy and is rotationally driven, the compressor 56a is rotationally driven via the connection shaft 56c to perform intake supercharging. The exhaust passage 60 is provided with an exhaust side bypass passage 63 for bypassing the turbocharger 56. The exhaust side bypass passage 63 is provided with a waste gate valve 65 for adjusting the flow rate of the exhaust gas flowing to the exhaust side bypass passage 63. The turbocharger 56 is housed in a turbine case (not shown).

  The turbocharger 56 may be a variable displacement turbocharger in which movable vanes are disposed in a turbine case. If it is possible to flow the exhaust gas substantially bypassing the turbine 56b by adjusting the opening degree of the movable vane, the exhaust side bypass passage 63 and the waste gate valve 65 can be omitted.

The oxidation catalyst 61 promotes a reaction in which CO and HC in the exhaust gas are oxidized to generate CO ₂ and H ₂ O. Further, the DPF 62 collects particulates such as soot contained in the exhaust gas of the engine 1.

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

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

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

  The high pressure EGR passage 80 is a portion of the intake passage 50 between the intercooler 57 and the surge tank 51 (that is, a portion on the downstream side of the electric supercharger 18), the exhaust manifold 60 and the turbo exhaust passage 60. It is connected to a portion between the feeder 56 and the turbine 56 b (that is, a portion on the upstream side of the turbine 56 b of the turbocharger 56). In the high pressure EGR passage 80, an electromagnetic high pressure EGR valve 82 for adjusting the flow rate of exhaust gas (hereinafter referred to as high pressure EGR gas) returned to the intake passage 50 through the high pressure EGR passage 80 is provided. . The high pressure EGR valve 82 is configured to adjust the flow rate of the high pressure EGR gas by adjusting its opening degree. Hereinafter, a system including the high pressure EGR passage 80 will be referred to as a high pressure EGR system 8.

  On the other hand, the low pressure EGR passage 70 is a portion of the intake passage 50 between the air cleaner 54 and the compressor 56 a of the turbocharger 56 (that is, a portion on the upstream side of the compressor 56 a of the turbocharger 56) The passage 60 is connected to a portion between the DPF 62 and the exhaust shutter valve 64 (that is, a portion on the downstream side of the turbine 56 b of the turbocharger 56). In the low pressure EGR passage 70, an EGR cooler 71 for cooling exhaust gas (hereinafter referred to as low pressure EGR gas) returned to the intake passage 50 through the low pressure EGR passage 70, and an electromagnetic type for adjusting the flow rate of low pressure EGR gas And a low pressure EGR valve 72 are provided. Like the high pressure EGR valve 82, the low pressure EGR valve 72 is configured to adjust the flow rate of the low pressure EGR gas by adjusting its opening degree. Hereinafter, a system including the low pressure EGR passage 70 will be referred to as a low pressure EGR system 7.

  The engine 1 configured as described above is controlled by a powertrain control module (hereinafter referred to as "PCM") 100 as shown in FIG. The PCM 100 is composed of a microprocessor having a CPU 101, a memory 102, a counter timer group 103, an interface 104, and a bus 105 connecting these units. The PCM 100 is an example of a control unit. The PCM 100 includes a water temperature sensor SW1 for detecting a temperature of engine cooling water, a boost pressure sensor SW2 for detecting a boost pressure, an intake temperature sensor SW3 for detecting an intake air temperature, an exhaust temperature sensor SW4 for detecting an exhaust temperature, A crank angle sensor SW5 for detecting a rotational angle of a crankshaft, an accelerator opening sensor SW6 for detecting an accelerator opening corresponding to an operation amount of an accelerator pedal (not shown) of the vehicle, a vehicle speed sensor SW7 for detecting a vehicle speed of the vehicle, A detection signal from a turbine rotational speed sensor SW8 that detects the rotational speed of the turbine 56b of the turbocharger 56 is input.

  The PCM 100 calculates the engine speed of the engine 1 from the detection result of the crank angle sensor SW5, and calculates the engine load from the detection result of the accelerator opening sensor SW6. Further, when the temperature detected by the water temperature sensor SW1 is lower than the predetermined temperature Tc, the PCM 100 determines that the temperature in the cylinder 30a is low and the engine 1 is in a cold state, and is detected by the accelerator opening sensor SW4. Based on the accelerator opening degree, it is determined whether the driver of the vehicle has an acceleration request.

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

  The PCM 100 is also electrically connected to an automatic or manual transmission 106 which is connected to the crankshaft of the engine body 10 and shifts the output of the engine body 10, although not shown. The transmission 106 outputs a signal related to the gear to the PCM 100.

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

(Outline of Control of Electric Turbocharger)
Next, control of the electric supercharger 18 by the PCM 100 will be described. FIG. 4 shows an aspect of control of the electric supercharger 18. The PCM 100 basically keeps the electric supercharger 18 constantly rotating while the engine body 10 is in operation, but the speed of the transmission 106 and the engine 1 detected by the crank angle sensor SW 5 Based on the rotational speed, the rotational speed (i.e., supercharging pressure) of the electric supercharger 18 is controlled. Specifically, in the region where the gear position is the first gear or engine low rotation, the rotational speed of the electric supercharger 18 is the highest, and from there, the gear position becomes higher or the engine rotation becomes higher. Control to reduce the number of revolutions.

  Further, in the present embodiment, the pressure ratio of the compressor 56a of the turbocharger 56 becomes 1.2 or more when the gear position of the transmission 106 becomes a high speed or when the engine speed exceeds r1. In such an area, the electric supercharger 18 is put into an idle rotation state and the intake side bypass valve 58 is fully opened so that supercharging by the electric supercharger 18 is not substantially performed. Do. The “high gear” may be a gear on the high speed side when the highest gear of the transmission 106 is divided into two. In this way, the turbo supercharger 56 is stopped without stopping the rotation of the electric supercharger 18 in the region of the engine rotation where the transmission 106 is in the high speed stage or the pressure ratio is 1.2 or more. It is possible to supercharge only by

  For example, in the transmission 106 with six forward gears, the first, second and third gears may be low, four, five and six may be high. In FIG. 4, when the number of revolutions of the engine is low, if the gear is first gear, the electric supercharger 18 rotates at a high number of revolutions, and if the gear is second gear, the electrically driven supercharger is The machine 18 rotates at a medium rotation speed, and if the gear is third gear, the electric supercharger 18 is rotated at a low rotation number, and if the gear has four, five or six gears, the motor is electrically The supercharger 18 may be in idle rotation.

  As described above, when the supercharging pressure by the electric supercharger 18 is raised as described later by always rotating the electric supercharger 18, the electric supercharger 18 is temporarily stopped. The motorized supercharger 18 (strictly, the electric motor 18b for operating the motorized supercharger 18) is more efficient than performing on-off control to make it drive in a necessary scene. Can be activated. Also, by changing the rotational speed of the electric supercharger 18 according to the gear position of the transmission 106, when raising the supercharging pressure by the electric supercharger 18 as described later, it is possible to swiftly. While the boost pressure can be increased, it is possible to reduce power consumption as much as possible.

  FIG. 5 shows a performance curve that represents the characteristics of the electric supercharger 18. The upper part of FIG. 5 is a performance curve graph showing the characteristics of the compressor wheel 18a of the electric supercharger 18, the vertical axis is the pressure ratio of the electric supercharger 18 (ie, the upstream pressure with respect to the downstream pressure) Ratio), the horizontal axis is the discharge flow rate. In the upper diagram of FIG. 5, a curve LL represents a rotation limit line, a straight line SL represents a surge line, and a straight line CL represents a choke line. The area surrounded by these lines is the operable area of the electric turbocharger 18. The operating efficiency of the electric supercharger 18 becomes higher as it is located on the center side of this region.

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

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

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

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

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

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

  Also, in order to suppress the generation of RawNOx, as illustrated in FIG. 9, the engine 1 performs pre-injection that performs at least one fuel injection before compression top dead center (TDC) during partial load operation, as illustrated in FIG. And, after the pre-stage injection, the main injection having a larger fuel injection amount than the pre-stage injection is executed. In the injection example of FIG. 9, two pre-injections are performed during the compression stroke before compression top dead center (TDC), and main injection with a larger fuel injection amount than the pre-injection is performed once near compression top dead center. After the main injection, the after injection is performed once with a fuel injection amount equivalent to that of the pre-injection. Hereinafter, this injection form is referred to as premixed combustion control.

  Of the two pre-injections performed in this premixed combustion control, the first fuel injection at a relatively early injection timing is pilot injection, and the second fuel injection is pre-injection. By performing the pilot injection and the pre-injection before the compression top dead center, the mixing property of the air and the fuel becomes high, and the chemical reaction of the mixture proceeds during the compression stroke. As a result, combustion becomes possible even if the in-cylinder temperature is relatively low, and as shown in the heat generation history of FIG. 9, pre-combustion by fuel injected by pre-injection occurs before compression top dead center .

  The compression end temperature and the compression end pressure can be increased by the pre-combustion by the above-described premixed combustion control. As a result, the temperature and pressure in the cylinder at the start of the main injection can be optimized, and the ignitability and combustibility in the main injection can be improved. As a result, since the main combustion can be stably generated near the compression top dead center, the amount of work of the engine 1 can be increased, and the fuel consumption can be improved. Further, the improvement of the ignitability makes it possible to suppress the generation of soot and to prevent the rapid increase of heat generation in the main combustion, that is, the extremely short combustion period, and the generation of NOx. Can be suppressed.

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

(Engine control during vehicle acceleration)
Here, when the driver of the vehicle depresses the accelerator pedal and issues an acceleration request while the engine 1 is in partial load operation, the engine 1 is introduced into the cylinder 30a in response to the increase in fuel amount. Even if the amount of fresh air is to be increased, the exhaust energy is relatively low at the time of partial load operation, so the supercharging pressure of the turbocharger 56 is difficult to increase, and the amount of fresh air introduced into the cylinder 30a is insufficient. The lack of fresh air will lead to the generation of soot, so if you wait for the fresh air to increase and then increase the fuel, the feeling of acceleration will deteriorate.

  In particular, when the transmission 106 connected to the engine 1 is in the low speed stage, the increase in the number of revolutions per unit time (Δrpm / Δt) of the engine 1 is more during acceleration of the vehicle than during the high speed stage. It will be much higher. When the Δrpm / Δt becomes high, the cooling loss of the engine 1 increases, so the exhaust energy supplied to the turbine 56 b of the turbocharger 56 hardly increases. As a result, as a result, the boost pressure of the turbocharger 56 becomes harder to raise. FIG. 7 shows an example of the change in Pmax during acceleration of the vehicle, but if boost pressure is to be increased only by the turbocharger 56 during acceleration of the vehicle, as exemplified by the broken line in FIG. It becomes difficult to increase Pmax and the acceleration feeling is reduced.

  Here, the increase in the number of revolutions per unit time (Δ rpm / Δt) of the engine 1 will be described. In the forward six-speed transmission 106 having first to sixth speeds, assuming that the depression amount and depression speed of the accelerator pedal are the same, the number of revolutions per unit time increases, for example, as follows: It may have a relationship. That is, Δrpm / Δt is the largest at the first speed, and decreases in the order of the second speed and the third speed. Further, Δrpm / Δt is greatly reduced at the fourth speed as compared with the third speed, and becomes smaller in the order of the fifth speed and the sixth speed. In this configuration example, with respect to the value of Δrpm / Δt of the engine 1 at the time of acceleration of the vehicle, the first speed, second speed and third speed of the transmission 106 with six forward speeds are low speed where the value of Δrpm / Δt becomes relatively large. The fourth speed, the fifth speed, and the sixth speed are high speed stages in which the value of Δrpm / Δt is relatively small.

  The engine 1 utilizes an electric supercharger 18 to improve acceleration feeling while preventing a decrease in emission performance at the time of acceleration. Specifically, when the driver depresses the accelerator pedal to request acceleration, the PCM 100 determines whether driving of the electric supercharger 18 is necessary, and when it is determined that it is necessary, The electric supercharger 18 is driven to increase the supercharging pressure. As a result, the amount of fresh air introduced into the cylinder 30a can be increased, so the amount of fuel injection can be increased, and the acceleration feeling can be improved while avoiding the occurrence of soot.

  FIG. 8 is a diagram illustrating the relationship between the vehicle speed and the engine speed for each of the first to sixth gear positions of the transmission 106. As shown in FIG. An area surrounded by an alternate long and short dash line in the figure indicates an area where the turbocharger pressure can be increased by the turbocharger 56. The turbocharger 56 is effective when the transmission 106 is at a high speed and the engine 1 is rotating at a relatively high speed with a relatively high speed.

  On the other hand, the electric supercharger 18 is operated in a region surrounded by a two-dot chain line in FIG. That is, in a region where the turbocharger 56 is not effective, that is, when the transmission 106 is at a low speed stage and the engine 1 at a relatively low vehicle speed is low, the electric supercharger 18 is driven to boost the supercharging pressure. Raise.

  If only the amount of fresh air introduced into the cylinder 30a is increased during acceleration of the vehicle, the combustion speed and the combustion temperature become too high, which results in the generation of RawNOx. Therefore, when the electric supercharger 18 is driven to increase the supercharging pressure, the low pressure EGR valve 72 is opened. With the driving of the electric supercharger 18, it becomes possible to suck low temperature low pressure EGR gas into the intake passage 50 through the low pressure EGR passage 70 without closing the exhaust shutter valve 64. As a result, the amount of EGR gas introduced into the cylinder 30a increases with fresh air, so that the combustion rate and the combustion temperature can be prevented from rising, and the generation of RawNOx can be suppressed. In addition, since the exhaust shutter valve 64 is not closed, it is advantageous for improving fuel consumption.

  Thus, Pmax can be rapidly increased as shown by a solid line in FIG. 7 while acceleration performance of the vehicle is prevented, and acceleration feeling can be improved. When Pmax is increased, exhaust energy is increased, and hence the supercharging pressure by the turbocharger 56 is increased. At the later stage of acceleration in which Pmax is increased, the target turbocharger pressure can be satisfied by the turbocharger 56. Therefore, as illustrated in FIG. 7, the turbocharger pressure by the electric turbocharger 18 is reduced. . The electric supercharger 18 may be stopped, or the electric supercharger 18 may be in an idle rotation state. By this, the power consumption of the electric supercharger 18 can be reduced. The timing at which the supercharging pressure of the electric supercharger 18 is reduced may be set to an appropriate timing. For example, the timing at which the supercharging pressure of the electric supercharger 18 is reduced may be set based on the change history of Pmax.

  Here, at the time of acceleration of the vehicle, in addition to driving the electric supercharger 18 described above to increase the supercharging pressure, as illustrated in FIG. 10, the injection start timing of the fuel is before acceleration of the vehicle. It may be retarded in comparison.

  Specifically, the pilot injection in the pre-stage injection is stopped and the after injection is stopped, and the injection timing of the pre-injection and the main injection is retarded. Further, in the example of FIG. 10, the main injection is performed twice. Hereinafter, this injection form is referred to as retarded combustion control. The total value of the fuel injection amounts of the two main injections is larger than that of the pre-injection (pre-injection) in the retarded combustion control. The fuel injection mode shown here is an example, and the injection timing of the pre-injection and the main injection at the time of retarded combustion control and the injection amount of the fuel are appropriately changed based on the required driving force of the vehicle.

  When the pilot injection is stopped and the pre-injection is retarded, the mixing property of the air and the fuel is reduced, so that the pre-combustion does not occur before the compression top dead center as shown in the upper drawing of FIG. The specific heat ratio of the gas in the cylinder 30a is increased by increasing the intake density by introducing supercharge by the electric supercharger 18, and introducing as much fresh air as possible into the cylinder 30a. Since the end temperature is sufficiently high, pre-combustion and main combustion occur after compression top dead center.

  By the above retarded combustion control, stable main combustion can be performed even if the compression ratio is low. Therefore, the combustion temperature can be prevented from becoming excessively high, and generation of NOx can be suppressed. Further, if the amount of fresh air increases, the intake air temperature decreases, so that the increase in the combustion temperature can also be suppressed, and the generation of NOx can be suppressed. In the retarded combustion control, the combustion temperature is higher than in the premixed combustion control shown in FIG. 9 even in the late stage of the combustion, and the soot can be burned without performing the after injection. By omitting the after injection, the fuel consumption performance is improved.

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

  Next, processing operation of engine control by the PCM 100 will be described based on a flowchart of FIG. The flow chart shown in FIG. 11 is a flow chart when the engine body 10 is operating in the warm state and in the partial load region.

  In the first step S101, the PCM 100 reads signals from various sensors to determine the operating state of the engine 1. In the next step S102, the PCM 100 determines, according to the map illustrated in FIG. 4, whether or not the electric supercharger 18 is in an idle rotation state. When the determination in step S102 is NO, the control process proceeds to step S103. In step S103, the PCM 100 drives the electric supercharger 18. The PCM 100 sets the rotation number of the electric supercharger 18 to a high rotation number, a middle rotation number, or a low rotation number according to the gear position of the transmission 106 and the engine rotation number.

  When the determination in step S102 is YES, the control process proceeds to step S104. The electric supercharger 18 is in an idle rotation state.

  In step S104, the PCM 100 determines whether the driver's acceleration request has been made. The PCM 100 determines the presence or absence of the driver's acceleration request based on the detection value of the accelerator opening sensor SW6. When an acceleration request is made, the control process proceeds to step S105, and when there is no acceleration request, the control process proceeds to step S114.

  In the next step S105, the PCM 100 calculates the required driving force (driving force based on the accelerator opening degree etc.) of the engine 1. In step S106, the PCM 100 determines the fuel injection amount and the fuel injection timing to realize the required driving force calculated in the above step S105, and in step S107, the PCM 100 performs the required drive calculated in the above step S105. A target EGR rate is calculated to realize the force, and in step S108, a target boost pressure to realize the required driving force calculated in step S105 is calculated.

  In the following step S109, the PCM 100 calculates an increase in the number of revolutions per unit time (Δrpm / Δt) of the engine 1, and in the step S110, the PCM 100 calculates the difference between the target boost pressure and the actual boost pressure. .

  Then, in step S111, the PCM 100 needs to drive the electric supercharger 18 based on the difference between the Δrpm / Δt calculated in step S109 and the target supercharging pressure and the actual supercharging pressure calculated in step S110. It is determined whether or not. Specifically, when Δrpm / Δt is larger than a predetermined value, the cooling loss of the engine 1 increases, and therefore, the exhaust energy supplied to the turbine 56 b of the turbocharger 56 hardly increases when the vehicle is accelerated. Therefore, the control process proceeds to step S113, and the PCM 100 raises the supercharging pressure by driving the electric supercharger 18, as described above.

  On the other hand, when the PCM 100 determines that the driving of the electric supercharger 18 is unnecessary in step S111, the control process proceeds to step S112 without proceeding to step S113.

  In step S112, the PCM 100 adjusts the opening degree of the low pressure EGR valve 72 and the high pressure EGR valve 82 so as to realize the target EGR rate calculated in step S107, and brings the gas composition in the cylinder 30a into a desired state. , And causes the injector 38 to execute fuel injection in accordance with the fuel injection amount and fuel injection timing determined in step S106.

  The control process then returns to step S101. If the drive of the electric supercharger 18 becomes unnecessary at the late stage of acceleration of the vehicle, the determination in step S111 becomes NO, and the supercharging pressure by the electric supercharger 18 is reduced.

  On the other hand, in step S114, where there is no acceleration request, the PCM 100 calculates the required driving force of the engine 1 as in step S105, and in the subsequent step S115, the PCM 100 performs step S114 in the same manner as step S106. The fuel injection amount and the fuel injection timing are determined in order to realize the required driving force calculated in the above.

  In step S116, the PCM 100 calculates a target EGR rate for realizing the required driving force calculated in step S114, as in step S107. In step S117, the PCM 100 calculates the target EGR rate as in step S108. A target boost pressure is calculated to realize the required driving force calculated in step S105.

  Then, in step S118, the PCM 100 adjusts the opening degree of the low pressure EGR valve 72 and the high pressure EGR valve 82 so as to realize the target EGR rate calculated in step S116, and brings the gas composition in the cylinder 30a into a desired state. Then, the injector 38 is made to execute fuel injection according to the fuel injection amount and fuel injection timing determined in step S115.

  Therefore, since the boost pressure of the PCM 100 is increased by the electric supercharger 18 when the engine speed increase per unit time (Δrpm / Δt) is high during acceleration of the vehicle, the magnitude of the exhaust energy of the engine 1 Regardless of the situation, the boost pressure can be increased quickly. As a result, since the fresh air introduced into the cylinder 30a can be rapidly increased, Pmax of the engine body 10 can be rapidly increased to suppress the occurrence of soot, and the acceleration feeling can be improved.

  In addition, since the low pressure EGR gas can be sucked from the low pressure EGR passage 70 to the intake passage 50 and the EGR gas introduced into the cylinder 30a can be increased with the driving of the electric supercharger 18, the combustion speed and the combustion temperature can be increased. Can be suppressed, and the generation of RawNOx can be suppressed.

  Therefore, the engine 1 can improve the acceleration feeling while preventing the decrease in the emission performance at the time of acceleration.

  In addition, since the exhaust energy is increased by rapidly increasing the supercharging pressure by the electric supercharger 18 at the start of acceleration and swiftly increasing Pmax of the engine body 10, the supercharging pressure by the turbocharger 56 is also It can be raised quickly. If the target supercharging pressure can be satisfied by the turbocharger 56 in the late stage of acceleration, the supercharging pressure of the electric supercharger 18 is reduced to prevent the emission performance from being degraded and to reduce consumption. Power can be reduced.

  In addition, since the electric supercharger 18 operates in the partial state as shown in FIGS. 4 and 5 regardless of the presence or absence of the acceleration request, the charge supercharger 18 raises the supercharging pressure by the electric supercharger 18. Power consumption can be reduced.

  Furthermore, the electric supercharger 18 operates at a higher speed when the transmission gear position is low, as shown in FIG. 4 when there is no acceleration request, than when the transmission gear position is high. The electric supercharger 18 is previously operated at a relatively high rotation speed in a shift stage (first, second or third speed) in which Δrpm / Δt of the engine main body tends to increase during acceleration of the vehicle. Therefore, the supercharging pressure can be rapidly increased, and the acceleration feeling can be improved while suppressing the decrease in emission performance. On the other hand, at the shift speed (fourth, fifth or sixth speed) where the Δrpm / Δt of the engine itself tends to decrease during acceleration of the vehicle, the turbocharger 56 can rapidly increase the supercharging pressure. Because of the high performance, power consumption can be reduced by operating the electric turbocharger 18 at a relatively low rotational speed (for example, in an idle rotational state).

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

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

  The embodiments described above are merely illustrative and should not be construed as limiting the scope of the present invention. The scope of the present invention is defined by the claims, and all variations and modifications that fall within the equivalent scope of the claims fall within the scope of the present invention.

1 Engine 10 Engine Body 18 Electric Turbocharger 50 Intake Passage 56 Turbocharger 56a Compressor 56b Turbine 60 Exhaust Passage 70 Low Pressure EGR Passage (EGR Passage)
100 PCM
106 Transmission SW5 Crank angle sensor (sensor)

Claims (5)

An engine body mounted on a vehicle,
An intake passage and an exhaust passage connected to the engine body;
An electric supercharger provided in the intake passage and supercharged by an electric motor;
A turbocharger having a turbine disposed in the exhaust passage and a compressor disposed upstream of the electric turbocharger in the intake passage, the turbocharger being supercharged using exhaust energy;
An EGR passage communicating the exhaust passage downstream of the turbine and the intake passage upstream of the compressor, and recirculating part of the exhaust gas to the intake passage;
A parameter calculation unit that calculates the magnitude of the increase in the number of revolutions per unit time of the engine body during acceleration of the vehicle based on a detection signal of a sensor attached to the engine body;
When the acceleration request signal is received and the vehicle is accelerated, the EGR passage is opened and the charging pressure of the electric supercharger is increased when the increase in the rotational speed calculated by the parameter calculation unit is larger than a predetermined value. An engine with a supercharger, comprising: a control unit that outputs a control signal to the electric supercharger. In the supercharged engine according to claim 1,
The control unit outputs a control signal to the electric supercharger so that the supercharging pressure of the electric supercharger is lower than that at the start of acceleration at the late stage of acceleration. The supercharged engine according to claim 1 or 2
An engine with a supercharger, wherein the control unit is configured to operate the electric supercharger in a partial state regardless of the presence or absence of the acceleration request signal. In the supercharged engine according to claim 3,
The control unit operates the electric supercharger at a higher revolution when the transmission connected to the engine main body is in the low gear stage before receiving the acceleration request signal, than when the transmission gear is in the high gear stage. Engine. In the supercharged engine according to any one of claims 1 to 4,
The engine body is a supercharged engine, which is a diesel engine having a geometric compression ratio of 16 or less.

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