JP2019210872A - Internal combustion system - Google Patents

Abstract

To suppress temperature drop of a cylinder of an internal combustion engine during a fuel-cut operation.SOLUTION: An internal combustion engine system includes an external EGR flow channel, an EGR valve, an EGR cooler and a control device. The EGR valve is disposed on the external EGR flow channel, and the EGR cooler is disposed on a downstream side with respect to the EGR valve on the external EGR flow channel. The EGR cooler exchanges heat between a passing EGR gas and a refrigerant. The control device controls opening/closing of a throttle, and opening/closing of the EGR valve. Further the control device acquires a cylinder temperature as a temperature in each cylinder of the internal combustion and a refrigerant temperature as a temperature of the refrigerant, fully closes the throttle when the cylinder temperature is lower than a prescribed threshold value during the fuel cut operation of the internal combustion engine, and controls the opening of the EGR valve so that the temperature of the EGR gas flowing into the EGR cooler (that is, the temperature of the EGR gas on the downstream side of the EGR valve) becomes lower than the refrigerant temperature.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an internal combustion engine system.

  Patent Document 1 discloses a hybrid vehicle that can select between fuel supply stop control for stopping fuel supply to an internal combustion engine and regenerative braking by a motor when the vehicle decelerates.

Japanese Unexamined Patent Publication No. 2018-043678

  While the fuel cut operation for stopping the fuel supply to the internal combustion engine is being performed, the temperature in the cylinder decreases. When fuel injection is resumed in a state where the temperature in the cylinder is lowered, it is conceivable that the fuel cannot be sufficiently atomized and becomes droplets and adheres to the cylinder wall surface or the like.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an internal combustion engine system that can suppress a temperature drop of a cylinder of the internal combustion engine during a fuel cut operation.

  An internal combustion engine system according to the present invention includes an external EGR flow path, an EGR valve, an EGR cooler, and a control device. The external EGR flow path is a flow path for allowing a part of the exhaust gas from the exhaust passage to flow into the intake passage as EGR gas, and a portion between the throttle and the intake port in the intake passage of the internal combustion engine, The exhaust passage communicates with a portion between the exhaust port and the exhaust catalyst. The EGR valve is disposed in the external EGR flow path. The EGR cooler is disposed in the external EGR flow path on the downstream side of the EGR valve in the flow of EGR gas in the external EGR flow path. The EGR cooler performs heat exchange between the passing EGR gas and the refrigerant.

  The control device controls opening / closing of the throttle and opening / closing of the EGR valve. Further, the control device is configured to acquire a cylinder temperature that is a temperature in each cylinder of the internal combustion engine and a refrigerant temperature that is a refrigerant temperature. In addition, when the fuel cut operation of the internal combustion engine is being performed and the cylinder temperature is lower than a predetermined threshold value, the control device fully closes the throttle and the temperature of the EGR gas flowing into the EGR cooler (that is, , The opening degree of the EGR valve is controlled such that the temperature of the EGR gas downstream of the EGR valve becomes lower than the refrigerant temperature.

  According to the present invention, during the fuel cut operation of the internal combustion engine, the throttle is fully closed, and the opening degree of the EGR valve is set so that the temperature in the external EGR channel downstream of the EGR valve is lower than the refrigerant. Be controlled. As a result, the temperature of the EGR gas rises due to heat received from the refrigerant when passing through the EGR cooler. Thereafter, the EGR gas flows into the cylinder again. Thereby, the temperature fall in the cylinder during fuel cut operation can be suppressed.

1 is a diagram schematically showing an internal combustion engine system according to an embodiment of the present invention. It is the figure which represented the control routine which the control apparatus of embodiment of this invention performs with the flowchart. It is a figure showing the change of the temperature and pressure of the gas in an absorption period passage and an exhaust passage of an embodiment of the invention, and an external EGR channel.

  FIG. 1 is a diagram schematically showing an internal combustion engine system 100 according to the present embodiment. The internal combustion engine system 100 includes an internal combustion engine 2, a variable valve timing mechanism 4, an intake passage 6, a throttle 8, an intercooler 9, an exhaust passage 10, an exhaust catalyst 12, an external EGR flow path 14, and an EGR. A valve 16, an EGR cooler 18, and a control device 20 are provided. Although not shown, the internal combustion engine 2 is provided with a piston built into the cylinder of the cylinder block, a fuel injection valve for supplying fuel into the cylinder, an intake valve provided at the intake port, and an exhaust port. Provided with an exhaust valve. The variable valve timing mechanism 4 has a function of adjusting the opening / closing timing of the intake valve and the exhaust valve.

  The intake passage 6 includes an intake manifold connected to the intake port of the internal combustion engine 2. The throttle 8 is installed in the intake passage 6. The intercooler 9 is disposed in the intake passage 6 on the downstream side of the intake air flow from the throttle 8. The exhaust passage 10 includes an exhaust manifold connected to the exhaust port of the internal combustion engine 2. The exhaust catalyst 12 is installed in the exhaust passage 10.

  The external EGR channel 14 is a channel for taking a part of the exhaust gas from the exhaust passage 10 as EGR gas and recirculating it to the intake passage 6 side. The external EGR flow path 14 includes a portion 6a downstream of the intake air flow from the throttle 8 and the intercooler 9 in the intake passage 6 and a portion 10a upstream of the exhaust flow from the exhaust catalyst 12 in the exhaust passage 10. Communicate.

  The EGR valve 16 and the EGR cooler 18 are disposed in the external EGR flow path 14. The EGR valve 16 is installed on the upstream side of the EGR gas flow with respect to the EGR cooler 18 (that is, on the side closer to the portion 10 a where the exhaust passage and the external EGR passage 14 communicate with each other), and is introduced into the intake passage 6. Used to adjust the amount. The EGR cooler 18 is a heat exchanger that cools the EGR gas by exchanging heat between the EGR gas and the refrigerant. In the EGR cooler 18 of the present embodiment, cooling water is used as the refrigerant, but the refrigerant of the EGR cooler 18 may not be water.

  The control device 20 is an ECU (Electronic Control Unit). Various sensors and actuators included in the internal combustion engine system 100 are electrically connected to the control device 20. The control device 20 controls the entire internal combustion engine system 100, and is mainly composed of a computer including a CPU, a ROM, and a RAM. Various control routines including routines described later are stored in the ROM.

  In the present embodiment, the control device 20 is configured to execute temperature decrease suppression control for suppressing the temperature in the cylinder from decreasing during the fuel cut operation of the internal combustion engine 2.

  FIG. 2 is a flowchart showing a control routine executed by the control device 20. In the routine of FIG. 2, first, it is detected whether or not the engine brake is being generated (step S101). The control device 20 performs a fuel cut operation for stopping fuel injection when a deceleration request is made. As a result, engine braking occurs. When the engine brake is generated, the determination result in step S101 is YES. Further, when the internal combustion engine 2 is mounted on a hybrid vehicle, there is a configuration in which the determination result in step S101 is YES when there is a request for deceleration of the driver during operation and the motor cannot be regenerated because the battery is fully charged. Also good. If the determination result of step S101 is NO, the current routine ends.

  If the determination result of step S101 is YES, the process proceeds to step S102, and the cylinder temperature is acquired. Specifically, the control device 20 acquires the cylinder temperature by taking the output of a temperature sensor installed in the cylinder of the internal combustion engine 2.

  The cylinder temperature acquisition means is not limited to that acquired by the temperature sensor. For example, when a temperature sensor is not installed in the cylinder, the temperature change of the cylinder is estimated from an estimation map with the stop time of the internal combustion engine 2 and the engine coolant temperature as axes, and the estimated temperature change is integrated. In this case, the current estimated cylinder temperature may be calculated.

  Next, the process proceeds to step S103, and it is determined whether or not the cylinder temperature acquired in step S102 is higher than a predetermined control start threshold value. The control start threshold is a value determined in advance as a reference value for determining whether or not to start the following temperature drop suppression control of the cylinder. If the determination result of step S103 is NO, the process returns to step S101.

  If the determination result of step S103 is YES, the process then proceeds to step S104, and the EGR valve upstream temperature is acquired. Here, the EGR valve upstream temperature is the temperature of the EGR gas on the inlet side of the EGR valve 16, and the control device 20, for example, outputs the output of the temperature sensor installed on the upstream side of the EGR gas flow from the EGR valve 16. By taking in, the EGR valve upstream temperature is acquired.

  In addition, the acquisition means of EGR valve upstream temperature is not restricted to what is acquired with a temperature sensor. For example, the EGR valve upstream temperature may be an estimated value calculated as follows. That is, the estimated value of the exhaust manifold temperature is calculated in accordance with a map having the intake manifold temperature and the cylinder temperature as axes. Here, as the temperature in the intake manifold, for example, a sensor value may be used, or the intake gas temperature may be used instead of the temperature in the intake manifold. Further, as the cylinder temperature, the cylinder temperature acquired in step S102 is used. Then, an estimated value of the temperature decrease amount from the exhaust manifold to the EGR valve 16 is calculated according to a map with the engine rotational speed of the internal combustion engine 2 as an axis. The estimated value of the EGR valve upstream temperature is calculated from the estimated value of the temperature in the exhaust manifold and the estimated value of the temperature decrease amount.

  Next, the process proceeds to step S105, and the required EGR valve opening degree is calculated so that the EGR valve downstream temperature is lower than the refrigerant temperature of the EGR cooler 18. Here, as the refrigerant temperature, an output value of a temperature sensor that measures the temperature of the cooling water or an output value of an outside air temperature sensor is used. However, instead of the output value of the temperature sensor, the refrigerant temperature may be estimated according to the vehicle speed and the operating condition of the cooling water pump.

  By the way, the EGR valve downstream temperature is the temperature on the outlet side of the EGR valve 16, that is, the temperature of the EGR gas between the EGR valve 16 and the EGR cooler 18. If it is considered that the expansion of the EGR gas in the EGR valve 16 is adiabatic expansion, if the EGR valve upstream temperature is known, the EGR valve downstream temperature can be estimated using the gas flow rate and the expansion rate of the EGR valve 16. That is, the EGR valve downstream temperature is estimated by using a map expressing a phenomenon in which the EGR gas temperature decreases due to the expansion of the EGR gas due to the restriction of the EGR valve 16. Here, the expansion rate of the EGR gas is determined by the gas flow rate and the EGR valve opening. The gas flow rate of the EGR valve 16 is determined by the engine speed. Therefore, the estimated value of the EGR valve downstream temperature can be calculated from a map with the EGR valve upstream temperature, the EGR valve opening degree, and the engine rotation speed as axes.

  In the process of step S105, the EGR valve downstream temperature is the refrigerant of the EGR cooler 18 using the map that defines the relationship between the EGR valve downstream temperature, the EGR valve opening degree, the EGR valve gas flow rate, and the engine rotation speed. The opening degree of the EGR valve 16 is calculated backward so as to be lower than the temperature. The phrase “becomes lower than the refrigerant temperature” may be a little lower than the refrigerant temperature, but may be configured to be lower than the refrigerant temperature by a certain rate or a certain temperature.

  Next, in step S106, the throttle 8 is adjusted to be fully closed, and the required EGR valve opening calculated in step S105 is output to the actuator of the EGR valve 16. Thus, the required EGR valve opening is set to an opening at which the temperature of the EGR gas in the EGR cooler 18 becomes lower than the refrigerant temperature.

  FIG. 3 is a diagram for explaining changes in gas temperature and pressure in the intake passage 6, the exhaust passage 10, and the external EGR passage 14 when the above-described cylinder temperature decrease suppression control is executed. In FIG. 3, the broken line a indicates pressure, and the solid line b indicates temperature.

  As shown in FIG. 3, during the fuel cut operation of the internal combustion engine 2, when the exhaust of the exhaust manifold (indicated as “exhaust manifold” in FIG. 3) exhausted from the internal combustion engine 2 reaches the EGR valve 16, the EGR valve 16 Due to the adiabatic expansion caused by the restriction, the temperature and pressure of the EGR gas rapidly decrease. On the downstream side of the EGR valve 16, the temperature of the EGR gas is lowered to the refrigerant temperature or lower, and the pressure is also lowered.

  In the present embodiment, the EGR gas is set to a temperature lower than the refrigerant temperature of the EGR cooler 18 by the temperature drop suppression control of the cylinder. As a result, the temperature of the EGR gas rises to the refrigerant temperature and the pressure rises on the downstream side of the EGR cooler 18. Thereafter, when gas is introduced into the cylinder through the intake manifold (indicated as “intake manifold” in FIG. 3), the gas is compressed in the cylinder, and the pressure and temperature rise. The gas temperature in the cylinder is higher than the temperature one cycle before by the amount of heat absorbed by the EGR cooler 18. Accordingly, the inside of the cylinder is warmed up.

  In this way, while the fuel cut operation is executed and the engine brake is generated, the throttle 8 is closed and the EGR valve 16 is throttled to the closed side, thereby preventing a temperature drop in the cylinder. it can. Therefore, when the internal combustion engine 2 is restarted, it is possible to prevent the fuel from being vaporized and sticking to the cylinder.

  In the cylinder temperature drop suppression control described in the present embodiment, the larger the pressure difference between before and after the EGR valve 16 (that is, the upstream side and the downstream side of the EGR valve 16), the greater the cylinder warm-up effect. Therefore, it is desirable that the EGR valve 16 be closed as much as possible from the viewpoint of warming up the cylinder. However, since the negative pressure on the intake passage 6 side is changed by closing the EGR valve 16, it is conceivable that the strength of the engine brake is reduced. Further, in a hybrid vehicle, a step may be generated in the deceleration force during regenerative braking by a motor.

  On the other hand, it is good also as a structure which performs the following processes with adjustment of the EGR valve opening degree in step S106 of FIG. If the deceleration force becomes excessive, torque is generated on the drive side by the motor to adjust the deceleration force. Further, when the deceleration force is small, the deceleration force by the hydraulic brake is added and adjusted. When a step is generated in the deceleration force, the EGR valve 16 is gradually changed.

  Further, when the variable valve timing mechanism 4 for the intake and exhaust valves is provided, the following processing may be added. Simultaneously with the closing process of the EGR valve 16, the overlap of the intake and exhaust valves is eliminated. As a result, it is possible to prevent gas from flowing from the exhaust side to the intake side during the overlap. As a result, the intake side is maintained at a negative pressure and the exhaust side is maintained at an atmospheric pressure or higher.

  In this case, the closing timing of the intake valve may be further adjusted to be before the bottom dead center. Thereby, the blowback from the cylinder can be reduced, and a high negative pressure can be maintained in the intake system. Further, in this case, the opening timing of the exhaust valve may be delayed. Thereby, the compressed gas can be retained in the cylinder for a longer time, and the inside of the cylinder can be warmed up.

  In the present embodiment, the configuration in which the external EGR flow path 14 communicates with the portion 6a downstream of the intercooler 9 of the intake passage 6 in the intake air flow has been described. However, the external EGR flow path 14 may be configured to communicate with a portion between the throttle 8 and the intercooler 9.

2 Internal combustion engine 4 Variable valve timing mechanism 6 Intake passage 6a Part 8 Throttle 10 Exhaust passage 10a Part 12 Exhaust catalyst 14 External EGR passage 16 EGR valve 18 EGR cooler 20 Control device 100 Internal combustion engine system

Claims (1)

A portion between the throttle and the intake port in the intake passage of the internal combustion engine and a portion between the exhaust port and the exhaust catalyst in the exhaust passage of the internal combustion engine communicate with each other, and a part of the exhaust from the exhaust passage is EGR An external EGR channel for flowing into the intake passage as a gas;
An EGR valve disposed in the external EGR flow path;
An EGR cooler that is arranged in the external EGR flow path downstream of the EGR valve in the flow of EGR gas in the external EGR flow path and performs heat exchange between the EGR gas passing through and the refrigerant;
A control device for controlling opening and closing of the throttle and opening and closing of the EGR valve;
With
The control device includes:
Obtaining a cylinder temperature that is a temperature in each cylinder of the internal combustion engine and a refrigerant temperature that is a temperature of the refrigerant;
When the fuel cut operation of the internal combustion engine is in progress and the cylinder temperature is lower than a predetermined threshold value, the throttle is fully closed and the temperature of the EGR gas flowing into the EGR cooler is the refrigerant temperature. Controlling the opening of the EGR valve to be lower,
An internal combustion engine system configured as described above.

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