JP2017137830A - Engine control system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an engine control system capable of curbing an excessive increase in cylinder pressure due to a response lag of a turbocharger.SOLUTION: An engine control system, mounted on a vehicle having an engine with a turbocharger, comprises a control section which delays a timing to close an intake valve of the engine by predetermined time for a predetermined period after shifting an operation state of the engine to a low load region when the operation state of the engine is shifted from a high load region to the low load region and actual supercharging pressure by the turbocharger is larger than predetermined target supercharging pressure.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an engine control system for a diesel engine having a turbocharger.

  A diesel engine that injects fuel into air compressed in a cylinder and ignites it is compatible with a turbocharger that compresses intake air by using a flow of exhaust gas. In general, a turbocharger has a turbine that rotates by the flow of exhaust gas and a compressor that rotates in conjunction with the turbine, and compresses intake air by using the flow pressure of the exhaust gas.

  In a turbocharger, even if the flow rate of exhaust gas changes as the engine output changes, the speed of the turbine does not change immediately due to its weight. Response delays that occur late can occur. For example, when the engine changes from a high load state to a low load state, such as when decelerating, if this response delay occurs, even if the engine is in a low load state and the required boost pressure decreases, the rotational speed of the turbine Therefore, the supercharging pressure remains high for a while after the low load state is reached. Thereby, supercharging is performed with a high supercharging pressure, and a situation may occur in which the pressure in the cylinder of the engine excessively increases.

  As a technique for preventing an excessive increase in cylinder pressure caused by such a response delay of the turbocharger, there is a technique disclosed in Patent Document 1, for example.

JP 2013-185540 A

  In Patent Document 1, the calculation means sets the basic injection timing Ta to the advance side when the load is low and the engine load is lower than that when the load is low under the same engine speed. When the engine shifts from a high load to a low load, a diesel engine that executes safety injection control for injecting fuel at a safety injection timing Tb set on the retard side of the basic injection timing Ta only for a predetermined period from the transition A control apparatus is disclosed.

  However, it may not be preferable to inject at the injection timing Tb set in Patent Document 1 as the injection timing. For example, if the injection timing is delayed, the in-cylinder pressure can be reduced, but the exhaust gas temperature may increase, so the turbine rotation speed of the turbocharger increases and the boost pressure increases excessively. Things can happen. In order to avoid such a situation, it is necessary to prevent an excessive increase in the in-cylinder pressure due to the response delay of the turbocharger by a method other than changing the injection timing.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an engine control system that can prevent an excessive increase in cylinder pressure due to a response delay of a turbocharger.

  An engine control system according to the present invention is an engine control system for an engine mounted on a vehicle and provided with a turbocharger, wherein the operating state of the engine transitions from a high load region to a low load region, and a predetermined target supercharging. When the actual supercharging pressure, which is the actual supercharging pressure by the turbocharger, is larger than the pressure, the timing for closing the intake valve of the engine for a predetermined period from the transition to the low load region is predetermined. It has a control unit that delays by time.

  The engine control method of the present invention is an engine control method for controlling an engine mounted on a vehicle and equipped with a turbocharger, and determines whether or not the operating state of the engine has transitioned from a high load region to a low load region. And an actual supercharging pressure that is an actual supercharging pressure by the turbocharger rather than a predetermined target supercharging pressure when it is determined that the operating state of the engine has transitioned from a high load region to a low load region Determining whether or not the engine is larger, and when it is determined that the actual supercharging pressure is larger than the target supercharging pressure, the engine is changed for a predetermined period from the transition to the low load region. Delaying the timing for closing the intake valve by a predetermined time.

  According to the present disclosure, it is possible to prevent an excessive increase in the cylinder pressure due to a response delay of the turbocharger.

The figure which shows an example of a structure of the engine control system which concerns on embodiment of this invention Diagram showing an example of the engine configuration Flow chart for explaining control of ECM The figure which shows an example of the time chart at the time of ECM performing control which retards the valve closing timing of an intake valve Time chart showing the relationship between engine output, supercharging pressure, maximum in-cylinder pressure, and intake valve retardation period in a vehicle in acceleration and deceleration

  Hereinafter, an engine control system according to an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing an example of the configuration of an engine control system 100 according to an embodiment of the present invention. The engine control system 100 is a system for controlling an engine that is mounted on a vehicle such as a passenger car or a truck and supplies power to the vehicle.

  As shown in FIG. 1, the engine control system 100 includes an intake port 11, a compressor 12, a cooler 13, an intake manifold 14, an exhaust manifold 15, a turbine 16, an exhaust port 17, a boost sensor 18, an engine 20, and an ECM 30. .

  Air sucked from the intake port 11, that is, intake air, is compressed by a compressor 12 that operates using the rotational force of the turbine 16 rotated by the flow of exhaust gas as power. The compressor 12 and the turbine 16 constitute a supercharger 19. The supercharger 19 corresponds to the turbocharger of the present invention. The intake air compressed to a high temperature by the supercharger 19 is cooled by a cooler 13 called an intercooler, a charge air cooler or the like, and supplied from the intake manifold 14 to each cylinder of the engine 20.

  Fuel is supplied to each cylinder of the engine 20 from a fuel tank (not shown in FIG. 1), and high-pressure intake air and fuel are mixed and burned in each cylinder. Exhaust gas discharged from each cylinder of the engine 20 is discharged from the exhaust manifold 15 through the exhaust port 17 to the outside of the vehicle. At this time, the turbine 16 is rotated by the flow pressure of the exhaust gas.

  The boost sensor 18 is a sensor that measures the supercharging pressure, that is, the pressure of the intake air compressed by the supercharger 19. The sensor value output from the boost sensor 18 is output to an ECM (Engine Control Module or Electronic Control Module) 30.

  The ECM 30 corresponds to the control unit of the present invention. For example, the ECM 30 includes a CPU, ROM, RAM, backup RAM, etc. (not shown), and the CPU executes arithmetic processing based on various control programs and control maps stored in the ROM. By doing so, various controls of the engine 20 are performed. Note that the RAM is a memory that temporarily stores calculation results in the CPU, data input from each sensor, and the like. The backup RAM stores data to be saved while the engine 20 is stopped.

  Next, an example of the configuration of the engine 20 will be described. FIG. 2 is a diagram illustrating an example of the configuration of the engine 20. As shown in FIG. 2, the engine 20 includes an intake valve 21, an intake variable valve mechanism 22, an exhaust valve 23, an exhaust variable valve mechanism 24, an intake pipe 25, an exhaust pipe 26, and a piston 27. 2 illustrates one of the cylinders of the engine 20, and when the engine 20 is multi-cylinder, the engine 20 has a plurality of cylinders as shown in FIG.

  The intake valve 21 opens and closes when the ECM 30 controls the intake variable valve mechanism 22 and supplies the intake air sent through the intake pipe 25 into the cylinder of the engine 20. After the intake air is compressed in the cylinder of the engine 20 and fuel is injected and combustion occurs, the exhaust valve 23 is opened and closed by controlling the variable valve mechanism 24 for exhaust of the ECM 30, and the cylinder is connected via the exhaust pipe 26. Exhaust the exhaust inside. Along with such an operation, the piston 27 moves up and down to extract power. The detailed structures and operations of the intake variable valve mechanism 22 and the exhaust variable valve mechanism 24 are not particularly limited in the present invention. For example, an electromagnetic solenoid (not shown) operates the operating valve based on the control of the ECM 30. By doing so, the intake valve 21 or the exhaust valve 23 may be opened and closed.

  Next, details of control by the ECM 30 will be described. FIG. 3 is a flowchart for explaining control of the ECM 30. As shown in FIG. 3, in the engine control system 100 of the present embodiment, the ECM 30 controls the closing timing of the intake valve 21 of the engine 20 to the retard side based on the behavior of the engine and the boost pressure. It is.

  In step S1, the ECM 30 acquires a sensor value from an acceleration sensor not shown in FIG. The sensor value output by the acceleration sensor is obtained by measuring the acceleration of the vehicle on which the engine control system 100 is mounted.

  In step S2, the ECM 30 determines whether or not the vehicle is decelerating. This determination may be made based on the acceleration acquired by the acceleration sensor in step S1. That is, the ECM 30 determines that the vehicle is decelerating if the vehicle acceleration is negative, and otherwise determines that the vehicle is not decelerating. If the result of determination in step S <b> 2 is that the vehicle is decelerating, the process proceeds to step S <b> 3; otherwise, the process returns to step S <b> 1.

  In step S3, the ECM 30 acquires a sensor value from the boost sensor 18 shown in FIG. The sensor value output from the boost sensor 18 is obtained by measuring the supercharging pressure of the intake air supplied from the supercharger 19 to the intake manifold 14.

  In step S4, the ECM 30 compares the sensor value (referred to as actual boost pressure) acquired in step S3 with the target boost pressure. As a result of the comparison, if the actual boost pressure is greater than the target boost pressure, the process proceeds to step S5, and if not, the process returns to step S1. The target boost pressure is a value determined by the ECM 30 with reference to a target boost pressure map stored in advance in a memory based on, for example, the accelerator pedal opening of the vehicle, the engine speed, and the like.

  In step S5, the ECM 30 controls the intake variable valve mechanism 22 to control the closing timing of the intake valve 21 to the retard side.

  FIG. 4 is a diagram illustrating an example of a time chart when the ECM 30 performs control for retarding the closing timing of the intake valve 21. In FIG. 4, the vertical axis represents the valve lift amount, and the horizontal axis represents the crank angle of the piston 27 of the engine 20. In FIG. 4, the waveform A shows the operation of the exhaust valve 21, the waveform B shows an example of the operation when the retard control by the ECM 30 is not performed in the engine control system 100 of the present invention, and the waveform B ′ shows the engine control of the present invention. An example of the operation when the retardation control by the ECM 30 in the system 100 is performed is shown.

  As shown in FIG. 4, the ECM 30 determines that the vehicle is decelerating and the actual boost pressure is greater than the target boost pressure in steps S1 to S4 in FIG. In comparison, the intake variable valve mechanism 22 is controlled so as to delay the closing timing of the intake valve 21 by a predetermined time.

  What effect can be obtained by such control of the ECM 30 will be described below. In general, a diesel engine operates by repeating four strokes of an intake stroke, a compression stroke, a combustion stroke, and an exhaust stroke. In the intake stroke, the piston 27 of the engine 20 is lowered and the intake valve 21 is opened, and intake air is supplied into the cylinder through the exhaust pipe 26. In the engine control system 100 according to the embodiment of the present invention, as shown in FIG. 4, the ECM 30 sets the intake variable valve mechanism 22 so as to wait for a predetermined time with the intake valve 21 fully opened. Control.

  While the ECM 30 stands by with the intake valve 21 open, the piston 27 is operating, and the piston 27 that has passed the bottom dead center starts to rise. This shifts from the intake stroke to the compression stroke. In the compression stroke, if the intake valve 21 is closed, the intake air is compressed as the piston 27 rises. In the engine control system 100 according to the embodiment of the present invention, the intake valve 21 is in the open state. No compression is performed during that time.

  When a predetermined time elapses after the intake valve 21 is fully opened, the ECM 30 controls the intake variable valve mechanism 22 to close the intake valve 21. Here, the predetermined time is set to a value less than the time from when the piston 27 starts to rise from the bottom dead center until it reaches the top dead center, that is, a value less than the time required for the compression stroke. By such control, the intake valve 21 is closed while the piston 27 is raised, so that the compression in the cylinder is started from that point. Therefore, the compression start timing is delayed as compared with the case where the above control is not performed.

  Thereby, in the compression stroke, the compression time of the intake air is shortened and the compression ratio is lowered as compared with the case where the above control is not performed. Then, in the combustion stroke following the compression stroke, the combustion pressure is reduced, so that the pressure in the cylinder can be reduced.

  FIG. 5 is a time chart showing the relationship between the engine output, the supercharging pressure, the maximum in-cylinder pressure, and the intake valve retardation period in the vehicle in the acceleration state and the deceleration state.

As shown in FIG. 5, an acceleration state from the time T ₁ to time T _2, the engine output is increasing over time. Further, in a state where the load is large such as an acceleration state, the fuel injection timing is shifted to the retard side by the ECM 30. The reason is to obtain as much combustion energy as possible while preventing the pressure in each cylinder of the engine 20 from excessively rising in a high load region where high torque is required. The control relating to the fuel injection timing by the ECM 30 may be executed with reference to, for example, a fuel injection timing map based on an engine output, an accelerator opening, and the like that is created in advance and stored in a memory.

In the column of the supercharging pressure in FIG. 5, the solid line indicates the actual supercharging pressure, and the dotted line indicates the target supercharging pressure. As shown in FIG. 5, in the acceleration state from time T ₁ to time T ₂ , the target boost pressure is larger than the actual boost pressure that is an actual measurement value by the boost sensor 18. This is because the rotational speed of the turbine 16 of the turbocharger 19 increases and the compressor 12 starts to function even if the flow rate of the exhaust gas increases due to the increase in engine output due to acceleration operation (depressing the accelerator pedal, etc.). This is because it takes some time.

  The column indicating the maximum in-cylinder pressure is a column illustrating the maximum value of pressure in one of the cylinders of the engine 20. If the in-cylinder pressure rises too much, there is a risk of malfunction or failure of the engine 20, so an allowable value for performing safe combustion is determined in advance. In the example shown in FIG. 5, in the acceleration state, the maximum in-cylinder pressure increases to the vicinity of the allowable value.

On the other hand, in the deceleration state from time T ₃ to T _4, the engine output is decreasing over time. Along with this, the fuel injection timing is shifted to the advance side by the ECM 30.

  During deceleration, the actual boost pressure is greater than the target boost pressure. This is because it takes time until the supercharger 19 reflects the operation on the supercharging pressure after the decelerating operation is started, as in acceleration.

  Thus, in the deceleration state of the vehicle, that is, in the state where the engine 20 has made a rapid transition from the high load region to the low load region, the fuel injection timing is suddenly shifted to the advance side, while the supercharging pressure is It remains temporarily high. Here, when control is performed to reduce the fuel injection pressure with the passage of time in the deceleration state, the peak of combustion approaches the compression top dead center due to the shift of the fuel injection timing to the advance side, and a high excess is caused. When a large amount of intake air supplied at the supply pressure is introduced into the cylinder and compressed, and fuel is injected and combustion occurs in the cylinder, the intake air compressed at a high supercharging pressure and the generated combustion pressure The maximum in-cylinder pressure may increase excessively. In such a case, as shown in the waveform A in the maximum in-cylinder pressure column of FIG. 5, a situation may occur in which the maximum in-cylinder pressure exceeds the allowable value.

  The engine control system 100 according to the embodiment of the present invention performs processing as described in association with FIGS. 3 and 4 described above in order to avoid such a situation. That is, in the engine control system 100 according to the embodiment of the present invention, as shown in FIG. 5, the ECM 30 decelerates when the vehicle is in a decelerating state and the actual boost pressure is larger than the target boost pressure. During the predetermined period P from the start of the control, the valve closing timing of the intake valve 21 is retarded. By such control, while the actual boost pressure remains high, the compression start timing in the compression stroke in the cylinder becomes later than usual, so the pressure in the cylinder decreases and the maximum cylinder pressure exceeds The rise can be prevented.

  Note that the length of the predetermined period P during which the ECM 30 retards the closing timing of the intake valve 21 may be determined as follows. That is, for example, the valve closing timing retarding period based on the difference between the target boost pressure and the actual supercharging pressure and the engine speed is obtained in advance by experiments or the like, and the ECM 30 is preliminarily obtained as a valve closing timing retarding period map. Stored in the memory. When the vehicle is in a decelerating state and the actual supercharging pressure is larger than the target supercharging pressure, the ECM 30 calculates the values of the difference between the target supercharging pressure and the actual supercharging pressure and the engine speed. The length of the predetermined period P is determined by referring to the valve closing timing retarding period map. The engine speed may be acquired by a speed sensor or the like not shown in FIG.

  As described above, the engine control system according to the embodiment of the present invention is an engine control system for an engine that is mounted on a vehicle and includes a turbocharger, and the operating state of the engine is changed from a high load region to a low load region. When the actual supercharging pressure, which is the actual supercharging pressure by the turbocharger, is larger than the predetermined target supercharging pressure, the intake valve of the engine for a predetermined period from the transition to the low load region A control unit that delays the timing for closing the valve by a predetermined time.

  The predetermined time is a value less than the time required from the start to the end of the compression stroke of the engine. Further, the predetermined period is determined based on the difference value between the actual boost pressure and the target boost pressure and the engine speed.

  With such a configuration, according to the engine control system according to the embodiment of the present invention, it is possible to suitably prevent an excessive increase in the cylinder pressure caused by the response delay of the turbocharger.

  Further, the engine control system 100 described in the above-described embodiment has one compressor 12 and one turbine 16 to form a single-stage turbocharger, but the present invention is not limited to this. For example, a multistage turbocharger may be configured by a plurality of compressors and turbines.

  The present invention is useful for an engine control system for controlling an engine in which a response delay of a turbocharger may occur.

DESCRIPTION OF SYMBOLS 100 Engine control system 11 Intake port 12 Compressor 13 Cooler 14 Intake manifold 15 Exhaust manifold 16 Turbine 17 Exhaust port 18 Boost sensor 19 Supercharger 20 Engine 21 Intake valve 22 Intake variable valve mechanism 23 Exhaust valve 24 Exhaust possible Variable valve mechanism 25 Intake pipe 26 Exhaust pipe 27 Piston 30 ECM

Claims (4)

An engine control system for an engine mounted on a vehicle and equipped with a turbocharger,
When the engine operating state transitions from a high load region to a low load region and the actual supercharging pressure, which is the actual supercharging pressure by the turbocharger, is larger than the predetermined target supercharging pressure, the low A control unit for delaying a timing for closing the intake valve of the engine by a predetermined time during a predetermined period from the transition to the load region;
Engine control system. The predetermined time is a value less than the time required from the start to the end of the compression stroke of the engine.
The engine control system according to claim 1. The control unit determines the predetermined period based on a difference value between the actual boost pressure and the target boost pressure and the engine speed.
The engine control system according to claim 2. An engine control method for controlling an engine mounted on a vehicle and equipped with a turbocharger,
Determining whether the operating state of the engine has transitioned from a high load region to a low load region;
When it is determined that the operating state of the engine has transitioned from the high load region to the low load region, the actual supercharging pressure that is the actual supercharging pressure by the turbocharger is greater than the predetermined target supercharging pressure. Determining whether or not,
When it is determined that the actual boost pressure is greater than the target boost pressure, the timing for closing the intake valve of the engine is delayed by a predetermined time for a predetermined period from the transition to the low load region. Steps,
An engine control method comprising:

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