Internal combustion engine

Abstract

To provide an internal combustion engine suppressing preignition at low rotation and high load.SOLUTION: An internal-combustion engine 1 for drive of running of a vehicle, includes: a turbocharger 15 having a compressor 15b provided in an intake passage 5 and driven by an electric motor 17 and a turbine 15a provided in an exhaust passage 11; a waste gate valve 25 opening and closing a bypass passage 24 bypassing the turbine 15a; and a control unit 50 controlling the waste gate valve 25 and the electric motor 17. When the target output of the internal-combustion engine 1 moves into a LSPI region from outside the LSPI region with a predetermined rotation or less and a predetermined load or more, the control unit 50 controls the electric motor 17 to drive the compressor 15b and controls the waste gate valve 25 to open the bypass passage 24.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an internal combustion engine equipped with a motor-driven supercharger.

Background Art

[0002] In a supercharger of an internal combustion engine driven by exhaust, an electric supercharger has been developed that can drive a compressor at an arbitrary timing and rotational speed by a motor or the like. Patent Document 1 discloses an internal combustion engine equipped with an electric supercharger that can drive a compressor by an electric motor. Further, the internal combustion engine described in Patent Document 1 includes a bypass passage and a waste gate valve that bypass a turbine provided in an exhaust passage, and a high-pressure EGR device that recirculates a part of the exhaust to the intake air. Then, when the engine is in a cold state and in a low load region, the waste gate valve and the EGR valve of the high-pressure EGR device are opened, and the supercharging pressure is increased by the electric supercharger, thereby suppressing the exhaust heat from being taken away by the turbine and ensuring a sufficient amount of fresh air.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in a spark ignition internal combustion engine such as a gasoline engine, there is a possibility of generating early ignition (pre-ignition) at low engine speeds and high loads, and measures for protecting the inside of the cylinder and ensuring the output are required. Conventionally, such early ignition has been dealt with by limiting the output of the internal combustion engine. Another possible method to suppress premature ignition is to improve scavenging from inside the cylinder by lengthening the valve overlap period. However, lengthening the valve overlap period reduces the actual compression ratio, so changing the valve overlap period may not be sufficient in some cases. It should be noted that in Patent Document 1, the timing for opening the wastegate valve and increasing the boost pressure with an electric supercharger is when the engine is cold and in a low-load state, and measures to address premature ignition at low rotation and high load conditions have not been considered.

[0005] The present invention was made to solve these problems and aims to provide an internal combustion engine equipped with a motor-driven supercharger that suppresses premature ignition at low rotational speeds and high loads. [Means for solving the problem]

[0006] To achieve the above objective, the internal combustion engine of the present invention includes an intake passage for supplying intake air to the combustion chamber of the internal combustion engine, an exhaust passage for discharging exhaust gas from the combustion chamber, a compressor provided in the intake passage and driven by a motor, a turbocharger having a turbine provided in the exhaust passage, a wastegate valve for opening and closing a bypass passage that bypasses the turbine, and a control unit for controlling the wastegate valve and the motor. A variable valve timing mechanism capable of changing the opening timing of at least one of the intake valve or exhaust valve of the internal combustion engine, Equipped with, A valve overlap period is set during which both the intake valve and the exhaust valve are open. The control unit performs exhaust enhancement control when the target output of the internal combustion engine moves from outside the first region, where the engine speed is below a predetermined rotational speed and the load is above a predetermined load, into the first region, by controlling the motor to drive the compressor and controlling the wastegate valve to open the bypass path. i. When performing the exhaust enhancement control, the variable valve timing mechanism is controlled so that the valve overlap period is shorter than when the exhaust enhancement control is not performed. It is characterized by the following:

[0007] As a result, when the target output of the internal combustion engine moves to a first region of low rotational speed and high load, i.e., when the engine's target output is below a predetermined rotational speed and above a predetermined load, exhaust enhancement control is performed to promote the engine's exhaust. Therefore, pre-ignition is less likely to occur in the first region. Furthermore, when performing exhaust enhancement control, shortening the valve overlap period can retard the closing timing of the intake valve, thereby lowering the effective compression ratio. Consequently, knocking is suppressed, making it possible to improve fuel efficiency by, for example, retarding the ignition timing. Preferably, the internal combustion engine is capable of driving the vehicle's drive wheels, the vehicle has a transmission in the power transmission path between the drive wheels and the internal combustion engine, and the control unit performs the exhaust enhancement control before the target output of the internal combustion engine moves into the first region and the transmission shifts down.

[0008] As a result, when the target output of the internal combustion engine moves into the first region, exhaust enhancement control is performed before downshifting, suppressing premature ignition. Therefore, it is possible to suppress the output reduction control of the internal combustion engine that is used to avoid premature ignition. 。

[0009] good More specifically, when the control unit performs the exhaust enhancement control, it adjusts the rotational speed of the internal combustion engine The valve overlap period should be set based on this.

[0010] This allows the valve overlap period to be appropriately set according to the rotational speed of the internal combustion engine, thereby improving the output of the internal combustion engine. Preferably, when the control unit performs the exhaust enhancement control, it controls the variable valve timing mechanism so that the valve overlap period is shortened when the rotational speed of the internal combustion engine is above a predetermined value, and does not shorten the valve overlap period when the rotational speed of the internal combustion engine is below the predetermined value.

[0011] As a result, when performing exhaust enhancement control, at high engine speeds above a predetermined value, the intake and exhaust flow velocities in the combustion chamber increase, ensuring scavenging. This allows for a shorter valve overlap period to suppress knocking, and for example, the ignition timing can be retarded to improve fuel efficiency. Conversely, when performing exhaust enhancement control, at low engine speeds below a predetermined value, the intake and exhaust flow velocities in the combustion chamber decrease, so the valve overlap period is not shortened, and scavenging is maintained. [Effects of the Invention]

[0012] According to the internal combustion engine of the present invention, when the target output of the internal combustion engine moves to the first region of low rotation and high load, by performing exhaust enhancement control, the exhaust of the internal combustion engine is promoted, and it is possible to make pre-ignition difficult to occur. As a result, in order to prevent pre-ignition at low rotation and high load, there is no need for an output limit to prevent the output of the internal combustion engine from moving to the first region, and it is possible to suppress a reduction in the output of the internal combustion engine. Furthermore, when performing exhaust enhancement control, shortening the valve overlap period can retard the closing timing of the intake valve, thereby lowering the effective compression ratio. Consequently, knocking is suppressed, making it possible to improve fuel efficiency by, for example, retarding the ignition timing.

Brief Description of the Drawings

[0013] [Figure 1] It is a configuration diagram of the intake and exhaust system of the internal combustion engine according to an embodiment of the present invention. [Figure 2] It is a flowchart showing the control procedure of the exhaust enhancement control executed in the exhaust enhancement control unit in the present embodiment. [Figure 3] It is an explanatory diagram showing an example of the transition of the operating state of the internal combustion engine during downshift in an internal combustion engine with a valve overlap mechanism. [Figure 4] It is a time chart showing an example of the transition of various operating states of the internal combustion engine during downshift, and is an explanatory diagram showing the change in the exhaust pressure with or without exhaust enhancement control. [Figure 5] It is a timing diagram showing the valve opening timing of the intake and exhaust valves in an internal combustion engine with a valve overlap mechanism, and is an explanatory diagram showing the difference with or without exhaust enhancement control.

Modes for Carrying Out the Invention

[0014] Hereinafter, embodiments of the present invention will be described based on the drawings. FIG. 1 is a configuration diagram of the intake and exhaust system of the internal combustion engine 1 according to an embodiment of the present invention. As shown in FIG. 1, the internal combustion engine 1 of the present embodiment is a port injection type gasoline engine having an injector 3 that injects gasoline as fuel into the intake port 2. The internal combustion engine 1 of the present embodiment is used as a power source for driving a vehicle equipped with an automatic transmission, and transmits power to the driving wheels of the vehicle via the automatic transmission, enabling the vehicle to be driven.

[0015] In the intake passage 5 of the internal combustion engine 1 of the present embodiment, an air cleaner 6, an intercooler 7, and a throttle valve 8 are provided upstream of the intake port 2 along the intake air flow. In the exhaust passage 11 of the internal combustion engine 1, an upstream exhaust purification catalyst 12 and a downstream exhaust purification catalyst 13 are provided along the exhaust flow from the exhaust port 31. Further, the internal combustion engine 1 is provided with a supercharger 15 and an EGR system 16.

[0016] The supercharger 15 is a turbocharger having a turbine 15a (not shown) rotationally driven by exhaust gas, and a compressor 15b that rotates with the rotation of the turbine 15a and compresses the intake air in the intake passage 5. Further, the supercharger 15 includes an electric motor 17 (motor) that drives the compressor 15b, and has a function of assisting supercharging by driving the electric motor 17. In the present embodiment, the electric motor 17 is provided on the shaft connecting the turbine 15a and the compressor 15b, and supercharging assistance is achieved by rotating this shaft with the electric motor 17.

[0017] The EGR system 16 includes an EGR passage 20 that connects the exhaust passage 11 and the intake passage 5 of the internal combustion engine 1, an EGR valve 21 that changes the flow passage area of the EGR passage 20, and an EGR cooler 22 that cools the exhaust passing through the EGR passage 20. The EGR passage 20 connects the downstream side of the turbine 15a in the exhaust passage 11 and the upstream side of the compressor 15b in the intake passage 5.

[0018] Further, the exhaust passage 11 is provided with a wastegate valve 25 that opens and closes a bypass passage 24 that bypasses the turbine of the supercharger 15. The intake passage 5 is provided with a recirculation valve 26 that opens and closes a passage that bypasses the compressor 15b of the supercharger 15. The internal combustion engine 1 is operated and controlled by a control unit 50 (control unit). The control unit 50 consists of an output device, a memory device (ROM, RAM, non-volatile RAM, etc.), a central processing unit (CPU), etc. The control unit 50 receives input such as crank angle, intake air volume, exhaust temperature, etc., and operates and controls the injectors 3, spark plugs 35, throttle valve 8, EGR valve 21, electric motor 17, wastegate valve 25, recirculation valve 26, etc.

[0019] Furthermore, the control unit 50 includes a transmission control unit 52 that controls the vehicle's automatic transmission. The control unit 50 of the internal combustion engine 1 in this embodiment is equipped with an exhaust enhancement control unit 51 that performs exhaust enhancement control (temporary avoidance control from the LSPI region) to suppress knocking caused by pre-ignition at low rotation and high load. The exhaust enhancement control unit 51 acquires the operating status of the internal combustion engine 1 and controls the operation of the electric motor 17, wastegate valve 25, etc.

[0020] The exhaust enhancement control unit 51 and the transmission control unit 52 may be provided separately from the control unit 50. Figure 2 is a flowchart showing the control procedure for exhaust enhancement control performed in the exhaust enhancement control unit 51. The exhaust enhancement control unit 51 is operated repeatedly at predetermined intervals (for example, several msec) during the operation of the internal combustion engine 1.

[0021] First, in step S10, the required torque T of the internal combustion engine 1 is calculated. The required torque T is calculated from the amount of accelerator operation of the vehicle, engine speed, etc. Note that the value calculated by the control unit 50 should be used for the required torque T. Then, the process proceeds to step S20. In step S20, it is determined whether the requested torque T entered in step S10 is greater than or equal to the maximum torque Tmax. The maximum torque Tmax is the torque regulated based on the LSPI (Low Speed ​​Pre-Ignition) region of the internal combustion engine 1, and is a value that is set in advance according to the engine speed.

[0022] The LSPI region is a low-speed, high-load region where pre-ignition (early ignition) is possible, as shown by the upward-sloping right and left-sloping diagonal lines in Figure 3, for example. It is defined by the rotational speed Ne and load Ec of the internal combustion engine 1. The LSPI region corresponds to the first region of the present invention. In this embodiment, the maximum torque Tmax is the boundary between the LSPI region (upward-sloping right and left-sloping diagonal lines) and other regions (no diagonal lines). The maximum torque Tmax, i.e., the LSPI region, can be mapped based on data acquired in advance through experiments or other means.

[0023] If the required torque T is greater than or equal to the maximum torque Tmax, proceed to step S30. If the required torque T is less than the maximum torque Tmax, proceed to step S80. In step S30, exhaust enhancement control is performed to temporarily avoid the LSPI region. The exhaust enhancement control opens the wastegate valve 25 (W / G valve) and drives (ON) the electric motor 17 of the supercharger 15 to drive the compressor 15b and supercharge the intake air into the cylinder of the internal combustion engine 1. Then, the process proceeds to step S40.

[0024] In step S40, a downshift request is determined based on vehicle speed and accelerator opening. The control unit 50 has a map of target gears for each vehicle speed and accelerator opening stored in advance, and the target gear is determined using this map. Furthermore, when the target output P (load Ec, i.e., target torque T and rotational speed Ne) is in the LSPI region, i.e., the low rotational speed, high load region, the map of the target gear is set so that a downshift request is issued, as this is usually an unsuitable region for higher gears. Then, the process proceeds to step S50.

[0025] In step S50, it is determined whether or not to request a gear change from the vehicle's automatic transmission (transmission control unit 52). The determination of whether or not to request a gear change from the automatic transmission is made, for example, by whether or not supercharging assistance is possible with the electric motor 17. Whether or not supercharging assistance is possible is best determined by considering the continuous operating time (continuous operating time) of the electric motor 17. The continuous operating time of the electric motor 17 is set considering the power consumption, circuit, and the temperature rise of the electric motor 17. When exhaust enhancement control is performed, the electric motor 17 of the supercharger 15 will be near its maximum output because the internal combustion engine 1 is at low speed and high load. The electric motor 17 should be one that has a continuous operating time such that when the automatic transmission is downshifted while the electric motor 17 is not being driven, the electric motor 17 does not stop operating before the downshift is completed.

[0026] If supercharging assist is not possible, proceed to step S60. If supercharging assist is possible, continue exhaust enhancement control and return to this routine. Note that "when supercharging assist is not possible" also includes cases where there is a possibility that supercharging assist will become impossible in the near future. For example, if the time the electric motor 17 has been continuously driven reaches a predetermined time slightly shorter than the continuous operating time, it can be determined that supercharging assist has become impossible.

[0027] In step S60, a request signal is output to the transmission control unit 52, which controls the automatic transmission, to shift down to the target gear determined in step S40, and the downshift is initiated. Then, the process proceeds to step S70. In step S70, the exhaust enhancement control is terminated. When terminating the exhaust enhancement control in step S70, instead of abruptly stopping the exhaust enhancement control, the wastegate valve 25 is gradually closed and the amount of supercharging assist is reduced in accordance with the changes in the rotational speed and required torque of the internal combustion engine 1 until it exits the LSPI region. Then, this routine is returned.

[0028] In step S80, the exhaust enhancement control is stopped. Specifically, the electric motor 17 of the supercharger 15 is stopped (turned OFF), and the wastegate valve 25 (W / G valve) is closed. If the exhaust enhancement control has already been stopped by step S80, it remains stopped. If the amount of supercharging assist has been reduced in step S70, but supercharging assist is still continuing when step S80 is reached, it is best to immediately terminate the exhaust enhancement control, i.e., terminate the supercharging assist. Then, this routine is returned.

[0029] As described above, the internal combustion engine 1 of this embodiment is equipped with a supercharger 15 having a turbine 15a and a compressor 15b, and the supercharger 15 is equipped with an electric motor 17 that can drive the compressor 15b at will. In addition, the exhaust passage 11 is equipped with a wastegate valve 25 that opens and closes a bypass passage 24 that bypasses the turbine 15a. The internal combustion engine 1 has an LSPI region, which is a region where pre-ignition may occur at low rotation speeds and high loads. Conventionally, when the target output P of the internal combustion engine 1 falls within the LSPI region, the target output P is changed to a smaller value so that the operating region of the internal combustion engine 1 does not enter the LSPI region. In Figure 3, the white circle represents the target output P. In Figure 3, as shown by the dotted arrow, the output of the internal combustion engine 1 changes toward the target output P. However, since the target output P is located within the LSPI region, the black circle located outside the LSPI region is designated as the new target output P', and the output of the internal combustion engine 1 is changed toward the target output P' as shown by the solid arrow. Note that since the target output P' is in the low rotation speed and high load region, when the output of the internal combustion engine 1 reaches the target output P', it shifts down and the output of the internal combustion engine 1 changes toward the new target output as shown by the dashed arrow.

[0030] In this embodiment, when the target output (rotational speed and load) of the internal combustion engine 1 moves to the low-speed, high-load LSPI region, exhaust enhancement control is performed by opening the wastegate valve 25 and driving the electric motor 17 to operate the compressor 15b and increase the intake pressure, thereby lowering the exhaust pressure of the internal combustion engine 1 and ensuring intake pressure, as shown in Figure 4. This improves scavenging performance and makes premature ignition less likely. Therefore, it is possible to suppress control that would lower the target output P of the internal combustion engine 1 to deviate from the LSPI region. In Figure 3, the areas shown by the upward-sloping right and left-sloping diagonal lines are the LSPI region before exhaust enhancement control is performed, and the upward-sloping right diagonal line is the LSPI region during the implementation of exhaust enhancement control. The target output P is located within the left-sloping diagonal line, but because the exhaust enhancement control causes the area within the left-sloping diagonal line to move out of the LSPI region, it is possible to escape the LSPI region without changing the target output P.

[0031] In this embodiment, since the electric motor 17 is provided to rotate the shaft connecting the turbine 15a and the compressor 15b, when exhaust enhancement control is performed during supercharging, the compressor 15b is driven by the electric motor 17 while the compressor 15b is already rotating, thus reducing the power consumption of the electric motor 17. The exhaust enhancement control unit 51 of the control unit 50 performs exhaust enhancement control before the downshift when the target output P of the internal combustion engine 1 moves into the LSPI region and just before a downshift occurs, that is, when the target output P of the internal combustion engine 1 moves into the region where a downshift request is made.

[0032] Just before downshifting, internal combustion engine 1 is likely to enter the LSPI region (low rotation, high load). After downshifting, the rotational speed of internal combustion engine 1 increases, so it is necessary to reduce the output of internal combustion engine 1. In this embodiment, exhaust enhancement control is performed before downshifting, which suppresses entry into the LSPI region. Furthermore, the wastegate valve 25 is opened by the exhaust enhancement control before downshifting, which suppresses the rotation of the turbine 15a due to exhaust. Therefore, the influence of exhaust on the rotational speed of the turbine 15a after downshifting can be reduced, making it easier to control engine output during downshifting.

[0033] In the internal combustion engine 1 of the above embodiment, it is preferable that the intake valve 32 also has a variable valve timing mechanism 60 that can change the opening timing. As shown by the dashed line in Figure 1, when the exhaust enhancement control unit 51 performs exhaust enhancement control, it is preferable to correct the variable valve timing mechanism 60 so that the valve overlap period is shortened, as shown in Figure 5, that is, to retard the opening timing of the intake valve 32.

[0034] Conventionally, shortening the valve overlap period could not be done near the LSPI region because it would lead to a decrease in scavenging performance. However, according to this embodiment, scavenging is enhanced by exhaust enhancement control, making it possible to shorten the valve overlap period. As a result, knocking is suppressed by a decrease in the actual compression ratio in the internal combustion engine 1, making it possible to improve fuel efficiency by, for example, retarding the ignition timing.

[0035] Furthermore, when performing exhaust enhancement control, the valve overlap period may be changed according to the rotational speed of the internal combustion engine 1. For example, when the internal combustion engine 1 is rotating at a speed above a predetermined value, the variable valve timing mechanism is corrected to shorten the valve overlap period when exhaust enhancement control is performed. When the rotational speed of the internal combustion engine 1 is below a predetermined value, the corrective control of the variable valve timing mechanism is not performed even when exhaust enhancement control is performed, i.e., the valve overlap period is maintained.

[0036] At high rotational speeds, the intake airflow velocity in the combustion chamber increases, ensuring scavenging. This shortens the valve overlap period, suppresses knocking, and improves fuel efficiency by, for example, retarding the ignition timing. At low engine speeds, the intake airflow velocity in the combustion chamber decreases, so the valve overlap period is not shortened to maintain scavenging performance.

[0037] Furthermore, the valve overlap period may be changed continuously or in stages depending on the rotational speed of the internal combustion engine 1. The variable valve timing mechanism may change the opening timing of the exhaust valve 33, or it may change the opening timing of both the intake valve 32 and the exhaust valve 33. The present invention is not limited to the embodiments described above. For example, in the above embodiment, the electric motor 17 provided in the supercharger 15 may be capable of generating electricity. Furthermore, the detailed configuration of the internal combustion engine 1 and various auxiliary equipment may be changed as appropriate. For example, the supercharger 15 may be configured to have, in addition to a turbine 15a and a compressor 15b connected by a shaft, a separate compressor in the intake passage 5 and an electric motor 17 to drive this compressor. [Explanation of symbols]

[0038] 1. Internal combustion engine 5. Intake passage 11 Exhaust passage 15 Supercharger 15b Compressor 15a Turbine 17 Electric motor (motor) 25 Wastegate Valve 32 Intake valve 33 Exhaust valve 50 Control Unit (Control Section) 51 Exhaust Reinforcement Control Unit (Control Unit) 60 Variable valve timing mechanism

Claims

1. An intake passage that supplies intake air to the combustion chamber of an internal combustion engine, An exhaust passage for discharging exhaust gas from the combustion chamber, A supercharger having a compressor provided in the intake passage and driven by a motor, and a turbine provided in the exhaust passage, A wastegate valve that opens and closes a bypass path that bypasses the turbine, A control unit that controls the wastegate valve and the motor, The engine comprises a variable valve timing mechanism capable of changing the opening timing of at least one of the intake valve or exhaust valve of the internal combustion engine, A valve overlap period is set during which both the intake valve and the exhaust valve are open. The control unit performs exhaust enhancement control when the target output of the internal combustion engine moves from outside the first region, where the rotational speed is below a predetermined value and the load is above a predetermined value, into the first region, and controls the motor to drive the compressor and the wastegate valve to open the bypass path, and when performing the exhaust enhancement control, controls the variable valve timing mechanism so that the valve overlap period is shorter than when the exhaust enhancement control is not performed. An internal combustion engine characterized by the following features.

2. The internal combustion engine is capable of driving the vehicle's drive wheels, The vehicle has a transmission in the power transmission path between the drive wheels and the internal combustion engine. The control unit performs the exhaust enhancement control before the target output of the internal combustion engine moves into the first region and the transmission shifts down. The internal combustion engine according to feature 1.

3. The control unit, When performing the exhaust enhancement control, the valve overlap period is set based on the rotational speed of the internal combustion engine. An internal combustion engine according to claim 1 or 2, characterized by the features described above.

4. The control unit, When performing the exhaust enhancement control, if the rotational speed of the internal combustion engine is above a predetermined value, the variable valve timing mechanism is controlled to shorten the valve overlap period. When performing the exhaust enhancement control, if the rotational speed of the internal combustion engine is below the predetermined value, the valve overlap period is not shortened. The internal combustion engine according to claim 3, characterized by the features described above.

Images