Control device for EGR valve

Abstract

To provide a control device for an EGR valve, which can properly control an EGR rate.SOLUTION: A control device is for an EGR valve that opens and closes an EGR pipe of an engine mounted on a vehicle. The EGR pipe is provided with a water cooling type EGR cooler, and the EGR pipe and EGR cooler are exposed to travel wind passing through a grill shutter of the vehicle. The control device for the EGR valve comprises an acquisition unit that acquires the temperature of cooling water introduced into the EGR cooler, a vehicle speed, and the opening degree of the grill shutter, and a correction unit that corrects the opening degree of the EGR valve on the basis of the cooling water temperature, the vehicle speed, and the opening degree of the grill shutter.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a control device for an EGR valve. [Background technology]

[0002] 2. Description of the Related Art An EGR valve and an EGR cooler are provided in an EGR (Exhaust Gas Recirculation) pipe of an engine mounted on a vehicle (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-178881 A Summary of the Invention [Problem to be solved by the invention]

[0004] The lower the temperature of the EGR gas, the more the EGR rate can be increased to suppress the rise in the temperature of the engine's exhaust gas. Therefore, it is considered that the lower the temperature of the cooling water flowing into the EGR cooler, the greater the EGR opening degree can be controlled. However, if the EGR pipe and the EGR cooler are exposed to wind while the vehicle is running, the temperature of the EGR gas is also affected by this wind. Therefore, if the opening degree of the EGR valve is controlled only by the temperature of the cooling water flowing into the EGR cooler, the EGR rate may not be appropriately controlled.

[0005] SUMMARY OF THE PRESENT EMBODIMENTS Accordingly, an object of the present invention is to provide an EGR valve control device capable of appropriately controlling the EGR rate. [Means for solving the problem]

[0006] The above object can be achieved by an EGR valve control device that opens and closes an EGR pipe of an engine mounted on a vehicle, wherein the EGR pipe is provided with a water-cooled EGR cooler, and the EGR pipe and EGR cooler are exposed to wind passing through a grill shutter of the vehicle, and the EGR valve control device includes an acquisition unit that acquires the temperature of the cooling water introduced into the EGR cooler, the vehicle speed, and the opening degree of the grill shutter, and a correction unit that corrects the opening degree of the EGR valve based on the cooling water temperature, the vehicle speed, and the opening degree of the grill shutter. Effect of the Invention

[0007] According to the present invention, it is possible to provide an EGR valve control device capable of appropriately controlling the EGR rate. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram of an engine mounted on a vehicle. [Diagram 2] FIG. 2 is a flowchart illustrating an example of the EGR valve opening correction control. [Diagram 3] FIG. 3A is an example of a map that defines the ambient flow rate depending on the vehicle speed and the opening degree of the grill shutter, FIG. 3B is an example of a map that defines the ambient temperature depending on the ambient flow rate and the temperature of the cooling water introduced into the EGR cooler, and FIG. 3C is an example of a map that defines a correction coefficient K depending on the ambient temperature and the ambient flow rate. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] [Engine outline] 1 is a schematic diagram of an engine 3 mounted in an engine compartment 2 of a vehicle 1. The engine 3 includes an engine body 10, an intake pipe 12, an exhaust pipe 14, and an EGR pipe 16. The intake pipe 12 and the exhaust pipe 14 are connected to the engine body 10. A catalyst 15 for purifying exhaust gas is provided in the exhaust pipe 14. One end of the EGR pipe 16 is connected to the exhaust pipe 14 downstream of the catalyst 15. The other end of the EGR pipe 16 is connected to the intake pipe 12. Note that one end of the EGR pipe 16 may be connected to the exhaust pipe 14 upstream of the catalyst 15.

[0010] The EGR pipe 16 is provided with a water-cooled EGR cooler 17. The EGR cooler 17 is provided on a cooling water path 27 through which cooling water circulates. The cooling water path 27 is a path provided so that the cooling water circulates between the engine body 10, the radiator, and the EGR cooler 17. The EGR gas is cooled by heat exchange between the EGR gas and the cooling water in the EGR cooler 17. An EGR valve 18 is provided downstream of the EGR cooler 17 in the EGR pipe 16. The EGR rate is adjusted according to the opening degree of the EGR valve 18.

[0011] A grill shutter 20 is provided at the front of the vehicle 1. The grill shutter 20 includes a plurality of loopers 21 and a control motor 22 that adjusts the opening degree of the loopers 21. The wind generated by traveling flows through the engine compartment 2 in accordance with the opening degree of the loopers 21.

[0012] The vehicle 1 is equipped with an ECU (Electronic Control Unit) 50. The ECU 50 is an electronic control unit including a calculation processing circuit that performs various calculation processes related to the driving control of the vehicle 1, and a memory in which control programs and data are stored. The ECU 50 controls the operation of the engine 3 based on various sensor values. The ECU 50 controls the opening degree of the EGR valve 18 based on the operating state of the engine 3. The ECU 50 is an example of a control device for the EGR valve 18. The ECU 50 functionally realizes an acquisition unit and a correction unit, which will be described later. The ECU 50 also controls the stop position of the control motor 22, thereby controlling the attitude of the looper 21. In this manner, the opening degree of the grill shutter 20 is controlled.

[0013] An ignition switch 61, a vehicle speed sensor 62, and a water temperature sensor 63 are connected to the ECU 50. The ignition switch 61 is a switch for starting a system of the vehicle 1. The vehicle speed sensor 62 detects the vehicle speed. The water temperature sensor 63 detects the temperature of the cooling water introduced into the EGR cooler 17.

[0014] The EGR pipe 16 and the EGR cooler 17 are exposed to the wind flowing through the engine compartment 2 via the grill shutter 20. The EGR pipe 16 is made of a metal with high thermal conductivity. Therefore, the EGR gas is cooled not only by heat exchange with the cooling water in the EGR cooler 17, but also by heat exchange with the running wind in the EGR pipe 16. In addition, the temperature around the EGR pipe 16 and the EGR cooler 17 is affected by the temperature of the cooling water introduced into the EGR cooler 17.

[0015] [EGR valve opening correction control] 2 is a flowchart illustrating an example of the opening correction control of the EGR valve 18. This control is repeatedly executed while the ignition is on. First, the ECU 50 acquires the temperature of the catalyst 15 (step S1). The ECU 50 may acquire the temperature of the catalyst 15 by estimating it based on the rotation speed and load factor of the engine 3, for example. The ECU 50 may acquire the temperature of the catalyst 15 by a sensor that detects the temperature of the catalyst 15.

[0016] Next, the ECU 50 acquires the temperature of the cooling water introduced into the EGR cooler 17, the vehicle speed, and the opening degree of the grill shutter 20 (step S2). The ECU 50 acquires the temperature of the cooling water based on the detection value of the water temperature sensor 63. The ECU 50 acquires the vehicle speed based on the detection value of the vehicle speed sensor 62. The ECU 50 may acquire the opening degree of the grill shutter 20 based on the control command value of the control motor 22, or may acquire the opening degree of the grill shutter 20 based on the detection value of a sensor provided in the control motor 22. Step S2 is an example of a process executed by the acquisition unit.

[0017] Next, the ECU 50 calculates the ambient temperature around the EGR pipe 16 and the EGR cooler 17 (step S3). The ambient temperature is calculated based on the flow rate of running air flowing around the EGR pipe 16 and the EGR cooler 17 (hereinafter referred to as ambient flow rate) and the temperature of the cooling water introduced into the EGR cooler 17. Specifically, the ECU 50 calculates the ambient temperature by referring to the maps of Figures 3A and 3B.

[0018] 3A is an example of a map that defines the atmosphere flow rate according to the vehicle speed and the opening degree of the grill shutter 20. In the map of FIG. 3A, the atmosphere flow rate is defined to increase as the vehicle speed increases and as the opening degree of the grill shutter 20 increases. This is because the faster the vehicle speed, the higher the flow rate of the running wind flowing through the engine compartment 2, and as a result, the atmosphere flow rate increases. Also, the larger the opening degree of the grill shutter 20, the more air is introduced into the engine compartment 2, and as a result, the atmosphere flow rate increases. Note that the calculation of the atmosphere flow rate is not limited to being based on the map as described above, and it may be calculated by an arithmetic expression that uses the vehicle speed and the opening degree of the grill shutter 20 as arguments.

[0019] 3B is an example of a map that defines the ambient temperature according to the ambient flow rate and the temperature of the cooling water introduced into the EGR cooler 17. In the map of FIG. 3B, the ambient temperature decreases as the ambient flow rate increases and as the temperature of the cooling water introduced into the EGR cooler 17 decreases. This is because the greater the ambient flow rate, the greater the amount of heat carried away by the running wind from the EGR gas through the EGR pipe 16. Also, the lower the temperature of the cooling water introduced into the EGR cooler 17, the more the running wind flowing around the EGR cooler 17 is cooled, and in particular, the part of the EGR pipe 16 located downwind of the EGR cooler 17 is cooled. The ambient temperature is not limited to being calculated based on the map as described above, and may be calculated by an arithmetic expression that uses the ambient flow rate and the temperature of the cooling water introduced into the EGR cooler 17 as arguments.

[0020] Next, the ECU 50 determines whether or not there is a request to increase the output of the engine 3 and whether or not it is necessary to limit the temperature of the exhaust gas (step S4). The limit on the temperature of the exhaust gas is a limit for suppressing an increase in the temperature of the exhaust gas in order to suppress an excessive increase in the temperature of the catalyst 15. For example, if the temperature of the catalyst 15 acquired in step S1 is close to the upper limit value, it is determined that it is necessary to limit the temperature of the exhaust gas. If the result in step S4 is No, step S1 is executed again.

[0021] If the answer to step S4 is Yes, it means that there is a risk that the temperature of the exhaust gas will rise and exceed the upper limit value of the temperature of the catalyst 15 by increasing the output of the engine 3. In this case, the ECU 50 corrects the opening degree of the EGR valve 18 as follows.

[0022] If the answer is Yes in step S4, the ECU 50 calculates the correction coefficient K (step S5). The correction coefficient K is a variable value ranging from 0.5 to 1.5, for example. FIG. 3C is an example diagram of a map that specifies the correction coefficient K according to the ambient temperature and the ambient flow rate. In the map of FIG. 3C, the correction coefficient K is specified to increase as the ambient temperature decreases and as the ambient flow rate increases. When the correction coefficient K is greater than 1.0, it is considered that the temperature of the EGR gas in the EGR pipe 16 decreases based on the ambient temperature and the ambient flow rate. When the correction coefficient K is less than 1.0, it is considered that the temperature of the EGR gas in the EGR pipe 16 increases based on the ambient temperature and the ambient flow rate. The correction coefficient K is not limited to being calculated based on the map as described above, and may be calculated by an arithmetic expression using the ambient temperature and the ambient flow rate as arguments.

[0023] Next, the ECU 50 corrects the opening of the EGR valve 18 based on the correction coefficient K (step S6). Specifically, the ECU 50 multiplies the target opening A of the EGR valve 18 by the correction coefficient K to calculate a corrected target opening B, and controls the opening of the EGR valve 18 to the corrected target opening B. Note that the target opening A before correction is calculated in advance based on the operating state of the engine 3, etc. Step S6 is an example of a process executed by the correction unit.

[0024] Here, when the correction coefficient K is larger than 1, the corrected target opening degree B is larger than the uncorrected target opening degree A. In this case, it is considered that the temperature of the EGR gas will drop in the EGR pipe 16, and the EGR rate can be increased accordingly. This suppresses the occurrence of knocking in the engine 3 and lowers the temperature of the exhaust gas. Therefore, the demand for increased output of the engine 3 is satisfied while suppressing the overheating of the catalyst 15.

[0025] When the correction coefficient K is less than 1, the corrected target opening degree B is smaller than the uncorrected target opening degree A. In this case, it is considered that the temperature of the EGR gas will rise in the EGR pipe 16, and the EGR rate is reduced accordingly. This makes it possible to suppress knocking in the engine 3 and a rise in the exhaust gas temperature.

[0026] As described above, the opening degree of the EGR valve 18 is controlled based on the temperature of the cooling water introduced into the EGR cooler 17, the vehicle speed, and the opening degree of the grill shutter 20. In this way, the opening degree of the EGR valve 18 is controlled taking into consideration that the EGR pipe 16 and the EGR cooler 17 are exposed to the running wind, and therefore the EGR rate is appropriately controlled.

[0027] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention described in the claims. [Explanation of symbols]

[0028] 1 vehicle 2 Engine Compartment 3 Engine 16 EGR tube 17 EGR cooler 18 EGR valve 20 Grill Shutter 50 ECU (control unit)

Claims

[Claim 1] A control device for an EGR valve that opens and closes an EGR pipe of an engine mounted on a vehicle, The EGR pipe is provided with a water-cooled EGR cooler, The EGR pipe and the EGR cooler are exposed to a traveling wind passing through a grill shutter of the vehicle, an acquisition unit that acquires a temperature of the cooling water introduced into the EGR cooler, a vehicle speed, and an opening degree of the grill shutter; a correction unit that corrects an opening degree of the EGR valve based on the temperature of the cooling water, the vehicle speed, and an opening degree of the grill shutter.

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