JP7486904B2 - Control device for internal combustion engine - Google Patents

Description

The present invention relates to a control device that controls an internal combustion engine equipped with an exhaust turbocharger that is mounted on a vehicle as a power source.

An exhaust turbocharger is known that uses the energy of exhaust gas discharged from the cylinders of an internal combustion engine to rotate an exhaust turbine (turbine wheel), transmits the rotation to a compressor impeller (compressor wheel), and compresses (supercharges) the intake air before sending it to the cylinders (see, for example, the following patent document).

If the pressure of the intake air flowing through the intake passage toward the cylinder, i.e. the boost pressure, becomes excessive, it may cause damage to parts of the internal combustion engine, including the compressor or turbine of the turbocharger. To avoid such damage, the intake air volume and fuel injection volume are generally adjusted so that the boost pressure does not exceed the allowable limit value.

JP 2019-019771 A

When a vehicle is traveling uphill and the gradient is steep, it is desirable to increase the engine torque output by the internal combustion engine to provide sufficient driving force to the vehicle's drive wheels.

Previously, the boost pressure of the intake air filling the cylinders of the internal combustion engine was controlled regardless of whether the vehicle was on a flat road or on a slope. With this, the engine torque on an uphill road was insufficient to provide the driving force necessary for uphill driving, and the vehicle speed or acceleration would decrease, leaving the driver with a feeling of inadequacy and dissatisfaction.

The present invention was developed with the above in mind, and aims to ensure that a vehicle equipped with an internal combustion engine equipped with a turbocharger has adequate power performance when traveling uphill.

In the present invention, a control device for an internal combustion engine equipped with an exhaust turbo supercharger mounted on a vehicle as a power source is configured to control a control device for an internal combustion engine in which, when an accelerator opening operated by a driver of the vehicle is expanded to a predetermined threshold value that is fully open or close to fully open and continues for a certain period of time or more, a correction control is implemented to increase the intake supercharging pressure more than when this state is not the case, and when the correction control is not implemented, a basic amount of a target intake supercharging pressure according to the engine speed and accelerator opening at that time is set, and the intake supercharging pressure is controlled to that target supercharging pressure, while when the correction control is implemented , an increase amount of supercharging pressure to be added to the basic amount is set according to the engine speed at that time and the gradient of the road surface on which the vehicle is located, along with the basic amount of the target supercharging pressure, and if the target supercharging pressure obtained by adding the increase amount to the basic amount does not exceed an allowable limit supercharging pressure, the intake supercharging pressure is increased to the target supercharging pressure, and if the target supercharging pressure obtained by adding the increase amount to the basic amount exceeds the limit supercharging pressure, the intake supercharging pressure is increased to the limit supercharging pressure.

To reliably avoid damage to the internal combustion engine, including the turbocharger, it is preferable to set the limit boost pressure according to the atmospheric pressure or the speed of the exhaust turbocharger at that time.

The present invention makes it possible to ensure proper power performance when a vehicle equipped with an internal combustion engine equipped with a supercharger travels uphill.

1 is a diagram showing a schematic configuration of a vehicle internal combustion engine and a control device according to an embodiment of the present invention; 2 is a block diagram illustrating a method for determining a target boost pressure by the control device for the internal combustion engine according to the embodiment; FIG. FIG. 4 is a flowchart showing an example of a procedure of a process executed by the control device according to the embodiment in accordance with a program. 4 is a diagram for explaining a limit boost pressure in an exhaust turbocharger attached to the internal combustion engine of the embodiment; FIG.

One embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an overview of an internal combustion engine for a vehicle according to this embodiment. The internal combustion engine according to this embodiment is a spark-ignition, four-stroke gasoline engine, and includes a number of cylinders 1 (one of which is shown in FIG. 1). An injector 11 for injecting fuel is provided near the intake port of each cylinder 1. Also, an ignition plug 12 is attached to the ceiling of the combustion chamber of each cylinder 1. The ignition plug 12 generates a spark discharge between a center electrode and a ground electrode when an induced voltage generated by an ignition coil is applied to the ignition plug 12. The ignition coil is integrally built into the coil case together with an igniter, which is a semiconductor switching element.

The intake passage 3 for supplying intake air takes in air from the outside and directs it to the intake port of each cylinder 1. In the intake passage 3, an air cleaner 31, a compressor 51 of the exhaust turbocharger 5, an intercooler 35, an electronic throttle valve 32, a surge tank 33, and an intake manifold 34 are arranged in this order from upstream.

The exhaust passage 4 for discharging exhaust gases guides the exhaust gases generated as a result of burning fuel inside the cylinders 1 from the exhaust ports of each cylinder 1 to the outside. An exhaust manifold 42, an exhaust turbine 52 of the exhaust turbocharger 5, and a three-way catalyst 41 for purifying the exhaust gases are arranged on this exhaust passage 4. In addition, an exhaust bypass passage 43 that bypasses the turbine 52, and a wastegate valve 44 that is a bypass valve that opens and closes the entrance of this bypass passage 43 are also provided.

The exhaust turbocharger 5 is configured so that the exhaust turbine 52 and the compressor impeller 51 are coaxially connected and linked via a shaft 53. The turbine 52 and impeller 51 are rotated using exhaust energy, and the resulting rotational force causes the compressor to perform a pumping action, thereby pressurizing and compressing (supercharging) the intake air and sending it to the cylinder 1.

The wastegate valve 44 plays a role in preventing the boost pressure of the intake air flowing through the intake passage 3 from becoming excessively high by opening the bypass 43 that connects the upstream and downstream sides of the turbine 52 in the exhaust passage 4. In addition, feedback control can be performed to make the boost pressure follow the target boost pressure by opening and closing the wastegate valve 44. The wastegate valve 44 is driven by, for example, a diaphragm-type actuator 6.

The actuator 6 has a diaphragm chamber 61 and a constant pressure chamber 62 separated by a diaphragm 60, and displaces the diaphragm 60 by utilizing the pressure difference between the diaphragm chamber 61 and the constant pressure chamber 62. The diaphragm 60 and the wastegate valve 44 are connected via a valve rod 63. When the pressure difference between the diaphragm chamber 61 and the constant pressure chamber 62 exceeds a predetermined set pressure, the diaphragm 60 and the valve rod 63 displace from the diaphragm chamber 61 side toward the constant pressure chamber 62 side against the elastic force of the spring 64. As a result, the wastegate valve 44 that had been closing the bypass passage 43 is driven, and the bypass passage 43 is opened. On the other hand, when the pressure difference between the diaphragm chamber 61 and the constant pressure chamber 62 is equal to or lower than the set pressure, the diaphragm 60 and the valve rod 63 return to their original positions by the elastic force of the spring 64, the wastegate valve 44 is completely closed, and the bypass passage 43 is closed.

The diaphragm chamber 61 of the actuator 6 is introduced with the pressure of the intake air at the downstream side of the compressor 51 and the upstream side of the throttle valve 32 in the intake passage 3, that is, the boost pressure. To this end, a boost pressure introduction passage 71 that connects the diaphragm chamber 61 with the corresponding part of the intake passage 3, a pressure relief passage 72 that opens the boost pressure introduction passage 71 and the diaphragm chamber 61 to the atmosphere, and an adjustment valve (Vacuum Switching Valve) 73 that opens and closes the pressure relief passage 72 are provided. The VSV 73 is a known flow control valve such as a solenoid valve that changes its opening degree in response to a control signal l. By manipulating the opening degree of the VSV 73, a part of the boost air flowing from the intake passage 3 into the boost pressure introduction passage 71 can be released to the atmosphere via the pressure relief passage 72, thereby controlling the pressure of the diaphragm chamber 61. The constant pressure chamber 62 of the actuator 6 is usually introduced with atmospheric pressure.

Of course, it is also possible to use an electrically operated wastegate valve instead of the wastegate valve 44 that is opened and closed by the diaphragm actuator 6.

The exhaust gas recirculation device 2 includes an external EGR passage 21 that connects the exhaust passage 4 and the intake passage 3, an EGR cooler 22 provided on the EGR passage 21, and an EGR valve 23 that opens and closes the EGR passage 21 to control the flow rate of EGR gas flowing through the EGR passage 21. The inlet of the EGR passage 21 is connected to a predetermined location downstream of the catalyst 41 in the exhaust passage 4. The outlet of the EGR passage 21 is connected to a predetermined location downstream of the throttle valve 32 in the intake passage 3 (in particular, the surge tank 33 or the intake manifold 34).

The variable valve timing mechanism 8, which variably controls the opening and closing timing of the intake valve of each cylinder 1 of the internal combustion engine, is a vane type that uses hydraulic pressure (lubricating oil pressure) to change the rotational phase of the camshaft, which drives the intake valve to open and close, relative to the crankshaft, or an electric type (motor-driven VVT) that uses an electric motor to change it. The VVT mechanism 8 changes the rotational phase of the camshaft relative to the crankshaft by rotating the camshaft relative to the cam sprocket around which the timing chain is wound, thereby changing the opening and closing timing of the intake valve.

The ECU (Electronic Control Unit) 0, which is the control device for the internal combustion engine in this embodiment, is a microcomputer system having a processor, memory, an input interface, an output interface, etc. The ECU 0 may be configured by connecting multiple ECUs or controllers so that they can communicate with each other via an electric communication line such as a CAN (Controller Area Network).

The input interface of the ECU0 receives inputs such as a vehicle speed signal a output from a vehicle speed sensor that detects the actual vehicle speed of the vehicle, a crank angle signal b output from a crank angle sensor that detects the rotation angle of the crankshaft and the engine speed, an accelerator opening signal c output from a sensor that detects the accelerator pedal depression amount or the opening of the throttle valve 32 as the accelerator opening (in other words, the required engine torque or engine load factor for the internal combustion engine), an intake temperature/intake pressure signal d output from an intake temperature/intake pressure sensor that detects the intake temperature and intake pressure (or boost pressure) in the intake passage 3 (particularly the surge tank 33 or the intake manifold 34) connected to the cylinder 1, an atmospheric pressure signal e output from an atmospheric pressure sensor that detects the atmospheric pressure, a cooling water temperature signal f output from a water temperature sensor that detects the temperature of the cooling water for the internal combustion engine, a cam angle signal g output from a cam angle sensor at multiple cam angles of the intake camshaft, and an acceleration signal h output from an acceleration sensor that detects the gradient of the road surface on which the vehicle is located or the acceleration of the vehicle.

The output interface of ECU0 outputs an ignition signal i to the igniter of the spark plug 12, a fuel injection signal j to the injector 11, an opening operation signal k to the throttle valve 32, an opening operation signal l to the EGR valve 23, an opening operation signal m to the VSV 73, and a control signal n for the opening and closing timing of the intake valve to the VVT mechanism 8.

The processor of ECU0 interprets and executes a program stored in memory in advance, and calculates operating parameters to control the operation of the internal combustion engine. ECU0 acquires various information a, b, c, d, e, f, g, and h required for controlling the operation of the internal combustion engine via the input interface, and determines the engine speed and estimates the amount of intake air filled into cylinder 1. Then, it determines various operating parameters such as the required fuel injection amount (necessary to achieve the target air-fuel ratio) corresponding to the intake air amount, the fuel injection timing (including the number of fuel injections per combustion), the fuel injection pressure, the ignition timing (including the number of ignitions per combustion), the target boost pressure, the required EGR rate (or the amount of EGR gas), and the intake valve timing. ECU0 applies various control signals i, j, k, l, m, and n corresponding to the operating parameters via the output interface.

As shown in FIG. 2, the ECU 0 of this embodiment determines the basic amount of the target value of the intake boost pressure to be filled into each cylinder 1 of the internal combustion engine according to the engine speed and the accelerator opening. Map data that defines the relationship between the engine speed and the accelerator opening and the basic amount of the target boost pressure is stored in advance in the memory of the ECU 0. The ECU 0 searches the map using the current engine speed and the accelerator opening as keys to obtain the basic amount of the target boost pressure.

The ECU 0 also determines the opening and closing timing (advance or retard amount) of the intake valve of each cylinder 1 realized via the VVT mechanism 8 according to the engine speed and the intake pressure (boost pressure) in the intake passage 3 (surge tank 33 or intake manifold 34). Map data that defines the relationship between the engine speed and intake pressure and the target intake valve timing is stored in advance in the memory of the ECU 0. The ECU 0 searches the map using the current engine speed and intake pressure as keys to obtain the target intake valve timing.

The ECU 0 controls the operation of the throttle valve 32, wastegate valve 44 (VSV 73), VVT mechanism 8, etc. to realize the target boost pressure and target valve timing. Then, the injector 11 injects an amount of fuel that corresponds to the amount of air drawn into the cylinder 1, and the spark plug 12 sparks and ignites the air-fuel mixture in the combustion chamber of the cylinder 1, causing it to burn and generate the desired engine torque.

When a vehicle is traveling uphill, if the gradient is steep, it is necessary to increase the engine torque and input sufficient driving force to the vehicle's drive wheels. To achieve this, it is necessary to raise the target boost pressure higher and supply a large amount of intake air and fuel to cylinder 1.

As shown in FIG. 3, the ECU0 of this embodiment implements correction control (steps S2 to S6) to increase the intake boost pressure above the normal base amount when the accelerator opening operated by the vehicle driver remains at or near full throttle for a certain period of time (e.g., several seconds (two to five seconds)) (step S1). The fact that the condition of step S1 is met means that the driver is currently requesting a larger engine torque, and it is inferred that the vehicle is currently traveling uphill with a steep gradient.

As shown in FIG. 2, in the correction control, the increase amount to be added to the base amount of the target boost pressure is determined according to the engine speed and the gradient of the road surface on which the vehicle is traveling (step S2). The increase correction amount may be a correction coefficient (a positive number of 1 or more) by which the base amount of the target boost pressure is multiplied, or a correction term (a positive number) by which the base amount of the target boost pressure is added. Map data that specifies the relationship between the engine speed and the gradient of the road surface and the increase amount of the target boost pressure is stored in advance in the memory of the ECU0. The ECU0 searches the map using the current engine speed and gradient of the road surface as keys to obtain the increase amount of the target boost pressure. The gradient of the road surface on which the vehicle is currently located can be known by referring to the output signal a of the vehicle speed sensor and the output signal h of the acceleration sensor.

On the other hand, if the boost pressure exceeds the limit and becomes excessive, it may cause damage to the compressor 51, turbine 52, etc. of the turbocharger 5. Therefore, it is also necessary to ensure that the target boost pressure resulting from adding the increase amount to the basic amount of the target boost pressure does not exceed the allowable limit boost pressure. In order to prevent damage to the compressor 51, turbine 52, etc., the ECU 0 sets a limit boost pressure that is the upper limit of the boost pressure (step S3), and if the target boost pressure resulting from adding the increase amount to the basic amount exceeds the limit boost pressure (step S4), the target boost pressure in the correction control is clipped to the limit boost pressure (step S5). If the target boost pressure resulting from adding the increase amount to the basic amount is equal to or lower than the limit boost pressure, it is used as the target boost pressure in the correction control as is (step S6).

A supplementary note on the limit boost pressure. Figure 4 illustrates the operating characteristics of the exhaust turbocharger 5, the so-called compressor map (adiabatic performance curve). The horizontal axis is the flow rate of the intake air (air) passing through the compressor 51, and the vertical axis is the pressure ratio of the compressor 51, that is, the ratio of the pressure on the downstream (outlet) side of the compressor 51 to the pressure on the upstream (inlet) side (pressure ratio = discharge pressure / suction pressure. Here, suction pressure ≒ atmospheric pressure). The surge line L1 is the limit at which there is no risk of extreme shock being applied to the turbocharger 5 and damaging it. The maximum rotation speed line L2 is an equal rotation speed line at the maximum rotation speed of the compressor 51 and the turbine 52 according to the specifications of the turbocharger 5. The maximum pressure ratio line L3 is the maximum pressure ratio according to the specifications of the turbocharger 5, and is constant regardless of the flow rate of the intake air flowing through the compressor 51. In FIG. 4, the dotted area is the operable range of the turbocharger 5, and the intake air is supercharged at a point within that area depending on the rotation speed of the compressor 51 and the turbine 52 at that time.

The limit boost pressure set in step S3 is set so that the turbocharger 5 does not operate in the region to the left of the surge line L1. Furthermore, it is preferable to set the limit boost pressure so that the turbocharger 5 does not operate in the region above the maximum rotation speed line L2 or the maximum pressure ratio line L3. Map data that defines the relationship between the engine speed and atmospheric pressure and the limit boost pressure is stored in advance in the memory of the ECU 0. In step S3, the ECU 0 searches the map using the current engine speed and atmospheric pressure as keys to obtain the limit boost pressure. The current atmospheric pressure can be known by referring to the output signal e of the atmospheric pressure sensor. However, the current atmospheric pressure may be estimated in accordance with a known method based on the output signal d of the intake pressure sensor without using the atmospheric pressure sensor.

If a sensor is installed to detect the rotation speed of the compressor 51 or turbine 52 of the turbocharger 5, the limit boost pressure can also be determined according to the rotation speed of the turbocharger 5 obtained through the sensor. In this case, map data is stored in the memory of the ECU 0 that defines the relationship between the rotation speed of the turbocharger 5, the amount of intake air flowing through the intake passage 3 toward the cylinder 1 (the flow rate of intake air passing through the compressor 51), and the limit boost pressure. The ECU 0 then searches the map using the current rotation speed and intake air volume of the turbocharger 5 as keys to obtain the limit boost pressure.

During correction control, the throttle valve 32, wastegate valve 44 (VSV 73), VVT mechanism 8, etc. are operated to realize the target boost pressure and target valve timing that take into account the increase amount in addition to the normal basic amount.

On the other hand, during normal control where the condition of step S1 is not met (step S7), the increase added to the base amount of the target boost pressure is 0, and the base amount is used as the target boost pressure as is. In other words, the boost pressure and fuel injection amount are not unnecessarily increased except when driving uphill with a steep upward gradient.

In this embodiment, the control device 0 for an internal combustion engine equipped with an exhaust turbocharger 5 mounted on a vehicle as a power source is configured to control the internal combustion engine, and when the accelerator opening operated by the driver of the vehicle is fully open or close to fully open and continues for a certain period of time or more, a correction control is implemented to increase the intake boost pressure more than when this is not the case. In the correction control, the amount of boost pressure increase is set according to the engine speed at that time and the gradient of the road surface on which the vehicle is located, and if the target boost pressure taking into account the increase amount does not exceed the allowable limit boost pressure, the intake boost pressure is increased to the target boost pressure, and if the target boost pressure taking into account the increase amount exceeds the limit boost pressure, the intake boost pressure is increased to the limit boost pressure.

According to this embodiment, it is possible to output a necessary and sufficient amount of engine torque when the vehicle is traveling uphill without causing damage to the turbocharger 5 or other parts of the internal combustion engine, and the vehicle's power performance is properly ensured, and its drivability or driving feeling is maintained at a high level.

The control method of this embodiment can be implemented without adding new hardware, and does not increase costs.

The present invention is not limited to the embodiment described above. The specific configuration of each part and the processing procedure can be modified in various ways without departing from the spirit of the present invention.

0...Control unit (ECU)
1... cylinder 11... injector 3... intake passage 4... exhaust passage 44... wastegate valve 5... exhaust turbocharger 51... compressor 52... turbine 73... regulating valve (VSV)
a... Vehicle speed signal b... Crank angle signal c... Accelerator opening signal d... Intake pressure signal e... Atmospheric pressure signal h... Acceleration signal j... Fuel injection signal k... Throttle valve opening operation signal m... Adjustment valve opening operation signal

Claims (2)

A system for controlling an internal combustion engine equipped with an exhaust turbocharger that is mounted on a vehicle as a power source,
When the accelerator opening degree operated by the driver of the vehicle is expanded to a predetermined threshold value or more that is fully open or close to fully open and continues for a certain period of time or more, a correction control is implemented to increase the intake supercharging pressure more than when this is not the case,
When the correction control is not performed, a basic amount of a target intake supercharging pressure according to the engine speed and the accelerator opening at that time is set, and the intake supercharging pressure is controlled to the target supercharging pressure.
A control device for an internal combustion engine, when the correction control is performed , sets a basic amount of the target boost pressure, as well as an increase amount of boost pressure to be added to the basic amount depending on the engine speed at the time and the gradient of the road surface on which the vehicle is located, and increases the intake boost pressure to the target boost pressure if the target boost pressure obtained by adding the increase amount to the basic amount does not exceed an allowable limit boost pressure, and increases the intake boost pressure to the limit boost pressure if the target boost pressure obtained by adding the increase amount to the basic amount exceeds the limit boost pressure. The control device for an internal combustion engine according to claim 1, in which the limit boost pressure is set according to the atmospheric pressure or the speed of the exhaust turbocharger at that time.

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