Exhaust gas recirculation device and exhaust gas recirculation method for internal combustion engine

Abstract

The invention provides an exhaust gas recirculation device and an exhaust gas recirculation method for an internal combustion engine. The EGR cooler exchanges heat between cooling water of an internal combustion engine and EGR gas. The EGR valve is provided in the EGR passage between the intake passage and the EGR cooler. The EGR valve is provided with a temperature sensing part into which EGR gas comes into contact. The EGR gas temperature is the temperature of the EGR gas in contact with the temperature sensing part. The valve body opens the EGR valve when the EGR gas temperature is higher than a predetermined temperature, thereby allowing flow of the EGR gas.

Description

[0001] Cross - reference to related applications

[0002] This application claims priority to Japanese Patent Application No. 2023 - 214839, filed on December 20, 2023, the entire disclosure of which is incorporated herein by reference. Technical field

[0003] The present disclosure relates to an exhaust gas recirculation device for an internal combustion engine. Further, it relates to an exhaust gas recirculation method for an internal combustion engine. Background art

[0004] Japanese Patent Application Laid - Open No. 2007 - 92597 discloses an exhaust gas recirculation device. The exhaust gas recirculation device has an EGR passage, an EGR cooler, and an EGR valve. The EGR passage introduces a part of the exhaust gas of the internal combustion engine into the intake passage as EGR gas. The EGR cooler is provided in the EGR passage and exchanges heat between the cooling water of the internal combustion engine and the EGR gas. The EGR valve opens and closes the EGR passage. Summary of the invention

[0005] According to one aspect of the present disclosure, there is provided an exhaust gas recirculation device for an internal combustion engine. The exhaust gas recirculation device includes an EGR passage that introduces a part of the exhaust gas of the internal combustion engine into the intake passage of the internal combustion engine as EGR gas. An EGR cooler is provided in the EGR passage. The EGR cooler exchanges heat between the cooling water of the internal combustion engine and the EGR gas. The EGR valve is provided in the EGR passage between the intake passage and the EGR cooler. The EGR valve has a temperature - sensing portion with which the EGR gas comes into contact. The EGR gas temperature is the temperature of the EGR gas that comes into contact with the temperature - sensing portion. The valve body opens the EGR valve when the EGR gas temperature is higher than a predetermined temperature, thereby allowing the flow of the EGR gas.

[0006] According to another aspect of the present disclosure, there is provided an exhaust gas recirculation method for an internal combustion engine having the same features in the exhaust gas recirculation device of the internal combustion engine.

[0007] Even when the temperature of the cooling water is low, the exhaust gas recirculation device and the exhaust gas recirculation method of the internal combustion engine can introduce the EGR gas into the intake passage while suppressing the generation of condensed water.

[0008] The EGR valve may have a valve actuator and a valve body that deform according to the temperature of the cooling water. If the temperature of the cooling water is equal to or higher than a predetermined value, the valve actuator deforms. As a result, the valve body opens the EGR valve. Then, the EGR gas is introduced into the intake passage. When the EGR gas is introduced into the intake passage through the exhaust gas recirculation device, the combustion temperature of the air - fuel mixture decreases. Therefore, the amount of NOx generated in the internal combustion engine decreases.

[0009] When the temperature of the EGR gas passing through the EGR cooler drops below the dew point temperature, condensed water is generated in the EGR gas. In a state where the temperature of the EGR gas drops below the dew point temperature, the EGR valve is usually closed.

[0010] The greater the flow rate of the EGR gas in the EGR passage, the lower the cooling efficiency of the EGR cooler. In this case, it is difficult for the temperature of the EGR gas to drop when passing through the EGR cooler. As a result, the temperature of the EGR gas sometimes exceeds the dew point temperature. In a state where the temperature of the EGR gas is high, it is difficult to generate condensed water, so the EGR gas can be introduced into the intake passage. However, in the prior art, when the coolant temperature of the internal combustion engine is low, the EGR valve does not open. Therefore, even in a state where it is difficult to generate condensed water, the EGR gas cannot be introduced into the intake passage. The above structure improves this. Description of the Drawings

[0011] Figure 1 It is a schematic diagram showing the structure of an exhaust gas recirculation device of an internal combustion engine according to an embodiment.

[0012] Figure 2 is Figure 1 A cross-sectional view of the EGR valve shown.

[0013] Figure 3 is for explaining Figure 2 the operation of the EGR valve. Figure 3 Part (A) of... shows Figure 1 the changes in the temperature of the EGR gas and the coolant temperature of the EGR cooler. Figure 3 Part (B) of... shows Figure 1 the changes in the pressure loss of the EGR passage.

[0014] Figure 4 It is a flowchart showing the steps of the process executed by the control device in the modification example.

[0015] Figure 5 It is a cross-sectional view of the EGR valve in another modification example. Detailed Description of the Invention

[0016] It should be understood that the description "at least one of A and B" herein means "only A" or "only B" or "both A and B".

[0017] Hereinafter, an embodiment for embodying an exhaust gas recirculation device and an exhaust gas recirculation method of an internal combustion engine will be described with reference to Figures 1 to 3 ...

[0018] <Structure of the Internal Combustion Engine>

[0019] Figure 1An internal combustion engine 1 provided with the exhaust gas recirculation device in the present embodiment is shown. The internal combustion engine 1 uses hydrogen as fuel.

[0020] The internal combustion engine 1 includes a fuel injection valve 5 that supplies hydrogen, which is the fuel of the internal combustion engine, to the combustion chamber.

[0021] An intake passage 4 is connected to the internal combustion engine 1. A surge tank 2 is provided in the intake passage 4. A throttle valve 3 for adjusting the intake air amount is provided in the upstream portion of the intake passage 4 with respect to the surge tank 2. The direction along the intake passage 4 toward the internal combustion engine 1 is referred to as the downstream direction of the intake passage 4.

[0022] An exhaust passage 6 is connected to the internal combustion engine 1. A supercharger 13 that supercharges the intake air by using the exhaust pressure is provided in the exhaust passage 6. The supercharger 13 is a known variable capacity type supercharger and can adjust the supercharging pressure. The direction along the exhaust passage 6 away from the internal combustion engine 1 is referred to as the downstream direction of the exhaust passage 6.

[0023] The supercharger 13 includes a compressor housing 13a and a turbine housing 13b. The compressor housing 13a houses a compressor impeller 13c. The turbine housing 13b houses a turbine impeller 13t. The turbine housing 13b is provided in the exhaust passage 6. A catalyst 7 for purifying the exhaust gas is provided in the exhaust passage 6 at a downstream portion with respect to the turbine housing 13b.

[0024] The compressor housing 13a is provided at an upstream portion with respect to the throttle valve 3 of the intake passage 4. An intercooler 14 is provided in the intake passage 4 between the compressor housing 13a and the throttle valve 3. The intercooler 14 cools the intake air whose temperature has risen due to supercharging.

[0025] The internal combustion engine 1 includes an exhaust gas recirculation device (hereinafter referred to as an EGR (Exhaust Gas Recirculation) device) that introduces a part of the exhaust gas as EGR gas into the intake passage 4.

[0026] The EGR device 200 has an EGR passage 10 that introduces EGR gas into the intake passage 4. When the EGR gas is introduced into the intake passage 4 through the EGR passage 10, a part of the exhaust gas in the exhaust passage 6 flows through the EGR passage 10 from the exhaust passage 6 toward the intake passage 4. That is, the flow direction of the EGR passage 10 is the direction along the EGR passage 10 from the exhaust passage 6 toward the intake passage 4. The direction along the EGR passage 10 toward the exhaust passage 6 is referred to as the upstream direction of the EGR passage 10. The direction along the EGR passage 10 toward the intake passage 4 is referred to as the downstream direction of the EGR passage 10.

[0027] The inlet of the EGR passage 10 branches from the exhaust passage 6 at a downstream portion with respect to the turbine housing 13b. The outlet of the EGR passage 10 is connected to the intake passage 4 at an upstream portion with respect to the compressor housing 13a.

[0028] An EGR cooler 12 for performing heat exchange between the cooling water of the internal combustion engine 1 and the EGR gas is provided in the EGR passage 10. The EGR cooler 12 is connected to a cooling water circuit 300 for circulating the cooling water of the internal combustion engine 1.

[0029] An EGR valve 230 for opening and closing the EGR passage 10 is provided in the EGR passage 10 between the intake passage 4 and the EGR cooler 12. The structure of the EGR valve 230 will be described later.

[0030] When the EGR valve 230 is opened, a part of the exhaust gas passing through the exhaust passage 6 flows into the EGR passage 10 as EGR gas. The EGR gas flowing into the EGR passage 10 undergoes heat exchange in the EGR cooler 12 and is then introduced into the intake passage 4. Therefore, the EGR gas flowing into the EGR passage 10 and the fresh air are introduced into the combustion chamber of the internal combustion engine 1 again. When the EGR gas is introduced into the combustion chamber, the combustion temperature of the air-fuel mixture decreases. Therefore, the generation of NOx in the internal combustion engine 1 is suppressed.

[0031] The operating state of the internal combustion engine 1 and the like are detected by various sensors. For example, a crank angle sensor 60 detects the rotation angle of the crankshaft of the internal combustion engine 1, that is, the crank angle NE. An air flow meter 61 detects the amount of air inhaled into the internal combustion engine 1, that is, the intake air amount GA. A water temperature sensor 64 detects the temperature of the cooling water of the internal combustion engine 1, that is, the water temperature THW. An air-fuel ratio sensor 65 is provided in the exhaust passage 6 at an upstream portion with respect to the catalyst 7. The air-fuel ratio sensor 65 detects the air-fuel ratio AF. An accelerator sensor 67 detects the amount of depression of the accelerator pedal, that is, the accelerator operation amount ACCP. A throttle sensor 68 detects the opening degree of the throttle valve 3, that is, the throttle opening TA.

[0032] The control device 100 takes the internal combustion engine 1 as the control object. That is, the control device 100 operates various operation target devices such as the throttle valve 3, the fuel injection valve 5, the spark plug of the internal combustion engine 1, and the supercharger 13.

[0033] The control device 100 includes a CPU 110 that performs arithmetic processing, a memory 120 that stores control programs and data, and the like. The control device 100 executes processes related to various controls by the CPU 110 executing the programs or program products stored in the memory 120. The CPU 110 is a processing circuit or a processing device.

[0034] The detection signals of the above various sensors are input to the control device 100.

[0035] Hydrogen is the fuel of the internal combustion engine 1. The range of the combustible mixture of hydrogen is wider than that of gasoline. Therefore, even if the mixture of hydrogen is leaner than that of gasoline, it can burn. Therefore, the control device 100 adjusts the output of the internal combustion engine 1 through the following combustion control.

[0036] The control device 100 calculates a required output Pe based on the accelerator operation amount ACCP, etc. The required output Pe is the required value of the output of the internal combustion engine 1. The control device 100 sets a required injection amount Qd based on the required output Pe. The required injection amount Qd is the target value of the fuel injection amount injected by the fuel injection valve 5. The control device 100 calculates a required air amount GAd based on the target air-fuel ratio AFt and the required injection amount Qd. The required air amount GAd is the target value of the intake air amount required to obtain the target air-fuel ratio AFt. The target air-fuel ratio AFt in the present embodiment is a lean air-fuel ratio, for example, the air excess ratio λ = 2.5 to 3.0. The air excess ratio is, for example, the value obtained by dividing the actual air-fuel ratio by the theoretical air-fuel ratio. The control device 100 controls the fuel injection valve 5 to obtain the required injection amount Qd. The control device 100 controls the opening degree of the throttle valve 3 and the supercharging pressure of the supercharger 13 to obtain the required air amount GAd. By adjusting the fuel injection amount and the intake air amount to change the air-fuel ratio of the mixture, the output of the internal combustion engine 1 is adjusted.

[0037] <Structure of the EGR valve>

[0038] Figure 2 Shows the cross-sectional structure of the EGR valve 230.

[0039] As Figure 2 shown, the EGR valve 230 includes an EGR valve housing 220 that divides a part of the EGR passage 10. The EGR valve housing 220 is formed in a tubular shape, for example. The EGR valve housing 220 has an EGR inlet 221 as the upstream end of the pipe and an EGR outlet 222 as the downstream end of the pipe. The upstream direction of the EGR valve housing 220 is the direction toward the exhaust passage 6. The downstream direction of the EGR valve housing 220 is the direction toward the intake passage 4. The EGR gas that has passed through the EGR cooler 12 flows into the EGR inlet 221. The EGR gas flows out from the EGR outlet 222 toward the part of the EGR passage 10 connected to the intake passage 4.

[0040] Inside the EGR valve housing 220, a displaceable valve body 223 is provided. The valve body 223 has a valve body through-hole 229. The valve body through-hole 229 is provided such that a minute amount of EGR gas can pass through the valve body 223. Therefore, even when the valve body 223 closes the EGR valve 230, the EGR gas that has passed through the EGR cooler 12 can contact a temperature sensing portion 227 described later through the valve body through-hole 229. That is, the valve body through-hole 229 penetrates the valve body 223 from the upstream side to the downstream side of the EGR gas. The diameter of the valve body through-hole 229 is set such that the following aperture condition is satisfied. Assume that the EGR gas passing through the valve body through-hole 229 when the valve body 223 closes the EGR valve 230 contains condensed water. The aperture condition is satisfied when the amount of condensed water contained in the EGR gas is less than the minimum amount of condensed water that has an adverse effect on the internal combustion engine 1. Examples of the adverse effects of condensed water on the internal combustion engine 1 include corrosion of parts and peripheral parts of the internal combustion engine 1, occurrence of misfires, and corrosion of the compressor impeller 13c.

[0041] On the inner wall of the EGR valve housing 220, an EGR valve seat 224 against which the valve body 223 can abut is provided. When the valve body 223 is in an abutting position against the EGR valve seat 224, the EGR valve 230 is closed. The closed EGR valve 230 blocks most of the flow of EGR gas from the EGR inlet 221 to the EGR outlet 222. When the valve body 223 is at a position away from the EGR valve seat 224, the EGR valve 230 is in an open state. The open EGR valve 230 allows EGR gas to flow from the EGR inlet 221 to the EGR outlet 222. That is, by opening the EGR valve 230, the EGR gas is officially introduced into the intake passage 4.

[0042] Inside the EGR valve housing 220, a spring seat 225 is provided at a portion closer to the EGR outlet 222 than the valve body 223. That is, the spring seat 225 is located downstream of the EGR valve seat 224. A plurality of seat holes including a central hole 225a penetrate the spring seat 225. Here, illustration of seat holes other than the central hole 225a is omitted. These seat holes allow EGR gas to flow from the upstream side to the downstream side with respect to the spring seat 225 located inside the EGR valve housing 220. As an addition or alternative, a gap may be provided between the spring seat 225 and the inner surface of the EGR valve housing 220. This gap may also allow EGR gas to flow from the upstream side to the downstream side with respect to the spring seat 225 located inside the EGR valve housing 220.

[0043] A valve spring 226 is interposed between the valve body 223 and the spring seat 225. The valve spring 226 biases the valve body 223 toward the EGR valve seat 224.

[0044] Inside the EGR valve housing 220, a temperature-sensitive portion 227 is accommodated between the valve body 223 and the spring seat 225. The temperature-sensitive portion 227 is disposed at a downstream position with respect to the valve body 223 in the flow direction of the EGR gas. The temperature-sensitive portion 227 is fixed to the valve body 223. The temperature-sensitive portion 227 is inserted into the central hole 225a of the spring seat 225 so as to be able to move relative to the spring seat 225. In Figure 2 , the temperature-sensitive portion 227 extends in a rod shape from the valve body 223 toward the central hole 225a of the spring seat 225. The downstream end of the temperature-sensitive portion 227 is inserted into the central hole 225a of the spring seat 225.

[0045] Wax as a temperature-sensitive material is sealed inside the temperature-sensitive portion 227. On the inner surface of the EGR valve housing 220, a guide rod 228 is fixed at an upstream position with respect to the EGR valve seat 224. The guide rod 228 extends, for example, from the inner surface of the EGR valve housing 220 in a direction toward the center of the valve body 223 and is thus inserted into the temperature-sensitive portion 227. The temperature-sensitive portion 227 has an insertion recess into which the downstream end of the guide rod 228 is inserted. The EGR gas contacts the temperature-sensitive portion 227. Therefore, when the temperature of the EGR gas contacting the temperature-sensitive portion 227 is relatively low, the wax sealed inside the temperature-sensitive portion 227 solidifies / contracts. The wax inside the temperature-sensitive portion 227 melts / expands when the temperature of the EGR gas contacting the temperature-sensitive portion 227 is relatively high.

[0046] According to the volume change of the wax inside the temperature-sensitive portion 227, the insertion amount of the guide rod 228 into the temperature-sensitive portion 227 changes. When the insertion amount of the guide rod 228 into the temperature-sensitive portion 227 changes, both the temperature-sensitive portion 227 and the valve body 223 are displaced with respect to the EGR valve seat 224. By the displacement of the valve body 223, the valve body 223 opens and closes the EGR valve 230. More specifically, when the temperature of the EGR gas rises and reaches a predetermined valve opening temperature Tref, the wax of the temperature-sensitive portion 227 melts and expands. Therefore, the valve body 223 overcomes the biasing force of the valve spring 226 and opens the EGR valve 230. The valve opening temperature Tref is, for example, the lowest temperature of the EGR gas at which the generation of condensed water can be suppressed.

[0047] That is, when the temperature of the EGR gas contacting the temperature-sensitive portion 227 is higher than the valve opening temperature Tref as a predetermined temperature, the valve body 223 opens the EGR valve 230. Therefore, the flow of the EGR gas is allowed.

[0048] <Function of the present embodiment>

[0049] Figure 3Represents the transition of each value of the internal combustion engine 1 starting from the start of the start of the internal combustion engine 1. A state where the EGR gas flow rate flowing in the EGR passage 10 and directed toward the EGR valve 230 is large is referred to as, for example, when the EGR flow rate is high. When the EGR flow rate is high, for example, the pressure of the EGR gas directed toward the EGR valve 230 is high. A state where the EGR gas flow rate is large includes a state where the exhaust gas flow rate is large. A state where the exhaust gas flow rate is large includes, for example, a state where the internal combustion engine 1 operates at a high rotational speed and a state where it operates at a high load. A state where the EGR gas flow rate flowing through the EGR passage 10 is less than when the EGR flow rate is high is referred to as, for example, when the EGR flow rate is low.

[0050] Figure 3 The first line L1 shown in part (A) of [] represents the transition of the water temperature of the cooling water supplied to the EGR cooler 12. Figure 3 The second line L2 shown in part (A) of [] represents the transition of the gas temperature of the EGR gas when the EGR flow rate is high and has passed through the EGR cooler 12. Figure 3 The third line L3 shown in part (A) of [] represents the transition of the gas temperature of the EGR gas when the EGR flow rate is low and has passed through the EGR cooler 12. Figure 3 The fourth line L4 shown in part (B) of [] represents the transition of the pressure loss when the EGR flow rate in the EGR passage 10 is high. Figure 3 The fifth line L5 shown in part (B) of [] represents the transition of the pressure loss when the EGR flow rate in the EGR passage 10 is low.

[0051] As Figure 3 shown, when the internal combustion engine 1 starts at time t0, the temperature of the cooling water of the internal combustion engine 1 rises. Similarly, the water temperature of the EGR cooler 12 shown by the first line L1 also rises. If the rise in the temperature of the cooling water subsides soon, that is, the rate of temperature rise is small, the rise in the water temperature of the EGR cooler 12 also subsides.

[0052] In response to the increase in the water temperature of the EGR cooler 12, the gas temperature of the EGR gas shown by the third line L3 also increases. Here, at low EGR flow rates, the cooling efficiency of the EGR cooler 12 is high. In this case, the difference between the water temperature of the EGR cooler 12 shown by the first line L1 and the gas temperature of the EGR gas shown by the third line L3 is relatively small. When the gas temperature reaches the above-mentioned valve opening temperature Tref at the second time t2, the EGR valve 230 starts to open. Therefore, as shown by the fifth line L5, at the second time t2, the pressure loss of the EGR passage 10 starts to decrease. That is, the formal introduction of the EGR gas into the EGR valve 230 starts. After that, when the EGR valve 230 is in the fully open state, the decrease in the pressure loss of the EGR passage 10 converges. That is, the pressure loss of the EGR passage 10 is a constant value. Here, in the first comparative example, for example, cooling water rather than EGR gas touches the temperature sensing part of the EGR valve. At low EGR flow rates, the difference between the water temperature (L1) of the EGR cooler 12 and the gas temperature (L3) of the EGR gas is relatively small. At low EGR flow rates, the opening timing of the EGR valve 230 is substantially the same as the opening timing of the EGR valve in the first comparative example.

[0053] On the other hand, at high EGR flow rates, the cooling efficiency of the EGR cooler 12 decreases. Therefore, the difference between the water temperature of the EGR cooler 12 shown by the first line L1 and the gas temperature of the EGR gas shown by the second line L2 is relatively large. As a result, when the EGR gas passes through the EGR cooler 12, it is difficult for the EGR gas temperature to drop. For example, the EGR gas temperature is in a state exceeding the dew point temperature. In a state where the EGR gas temperature is higher than the dew point temperature, it is difficult to generate condensed water. In this case, the EGR gas can be formally introduced into the EGR valve 230. The gas temperature of the EGR gas at high EGR flow rates is higher than the gas temperature of the EGR gas at low EGR flow rates. Therefore, at the first time t1 earlier than the second time t2, the EGR gas temperature reaches the valve opening temperature Tref. When the EGR gas temperature reaches the above-mentioned valve opening temperature Tref, the EGR valve 230 starts to open. Therefore, from the first time t1, as shown by the fourth line L4, the pressure loss of the EGR passage 10 starts to decrease. That is, the formal introduction of the EGR gas into the EGR valve 230 starts from the first time t1. That is, the introduction timing (t1) of the EGR gas at high EGR flow rates is earlier than the introduction timing (t2) of the EGR gas at low EGR flow rates. In the fully open state of the EGR valve 230, the decrease in the pressure loss of the EGR passage 10 converges. Therefore, the pressure loss of the EGR passage 10 is a constant value.

[0054] <Effects of the present embodiment>

[0055] When the temperature of the EGR gas in contact with the temperature sensing part 227 is higher than a predetermined temperature, the valve body 223 opens the EGR valve 230. Therefore, even when the cooling water temperature is low, the EGR gas can be introduced into the intake passage 4 in a state where the generation of condensed water is suppressed.

[0056] (2)At high EGR flow rates, the EGR gas flow rate toward the EGR valve 230 is relatively large. On the other hand, at low EGR flow rates, the EGR gas flow rate is relatively small. At high EGR flow rates, the timing of introducing the EGR gas into the intake passage 4 is earlier than at low EGR flow rates. Therefore, a large amount of EGR gas can be introduced into the intake passage 4 earlier.

[0057] (3)The valve body 223 has a valve body through-hole 229. Therefore, even when the valve body 223 closes the EGR valve 230, the EGR gas can pass through the valve body through-hole 229. That is, the EGR gas can flow through the EGR valve 230. In other words, a flow of the EGR gas is generated within the EGR valve 230. Therefore, even when the valve body 223 is closed, the EGR gas easily comes into contact with the temperature sensing part 227. As a result, the valve body 223 can open and close the EGR valve 230 according to the EGR gas temperature.

[0058] (4)The temperature sensing part 227 drives the valve body 223 to open and close the EGR valve 230. Specifically, the temperature sensing part 227 drives the valve body 223 through a mechanical / physical reaction based on the EGR gas temperature. The second comparative example includes an EGR valve having a structure that controls the drive of the valve body by using, for example, an electromagnetic valve. The present embodiment is less expensive than the second comparative example. Here, in the structure that utilizes a mechanical / physical reaction for driving the valve body 223, there may be a disadvantage in terms of the controllability of the gas amount when introducing the EGR gas.

[0059] Studying this point, the fuel of the internal combustion engine 1 of the present embodiment is hydrogen. In the internal combustion engine 1 using hydrogen as fuel, the range of the air-fuel mixture that can be burned is wider than that of an internal combustion engine using gasoline as fuel. That is, in the present embodiment, the tolerance to misfire is high. Therefore, in the present embodiment, fine controllability of the EGR gas amount when introducing the EGR gas is not required. In the present embodiment, even if the EGR device 200 of the internal combustion engine 1 using hydrogen as fuel includes the EGR valve 230 having the above-described temperature sensing part 227, there are few obstacles to controllability. Therefore, the occurrence of misfire can be suppressed, and an inexpensive EGR valve can be adopted.

[0060] (5) As a second comparative example, a structure for controlling the operation of the valve body of the EGR valve by using a solenoid valve or the like is studied. The second comparative example requires the development man-hours for the program for controlling the solenoid valve, the man-hours for obtaining the appropriate value during control, and the drive circuit for driving the solenoid valve. The second comparative example incurs costs. In this regard, the EGR valve 230 of the present embodiment includes a temperature-sensitive portion 227 that operates the valve body 223. Therefore, the present embodiment can eliminate the need for a program and a drive circuit, and thus can suppress an increase in cost.

[0061] <Modified Example>

[0062] The present embodiment can be implemented with the following modifications. The present embodiment and the following modified examples can be implemented in combination with each other within a range where there is no technical contradiction.

[0063] · The internal combustion engine 1 may also perform combustion of a mixture having an air excess ratio of 1 or less when the EGR valve 230 is open. An air excess ratio of 1 or less corresponds to, for example, rich combustion.

[0064] Figure 4 Steps representing the processing executed by the control device 100 to implement this modified example are shown. Figure 4 The processing shown is realized by the CPU 110 executing a program or a program product stored in the memory 120 of the control device 100 at every predetermined cycle. Hereinafter, the step numbers of each processing are represented by numbers preceded by "S".

[0065] In Figure 4 In the series of processing shown, the control device 100 determines whether the EGR valve 230 is open (S100). In the processing of S100, a method for determining whether the EGR valve 230 is open can be appropriately adopted. For example, when EGR gas is introduced into the intake passage 4 by the opening of the EGR valve 230, the air-fuel ratio AF detected by the air-fuel ratio sensor 65 changes. Therefore, when the control device 100 determines that a change in the air-fuel ratio AF has been detected, it determines that the EGR valve 230 is open.

[0066] When it is determined in the processing of S100 that the EGR valve 230 is open (S100: YES), the control device 100 performs stoichiometric combustion (S110). Stoichiometric combustion is an example of combustion based on a mixture having an air excess ratio of 1 or less. The control device 100 performs stoichiometric combustion by adjusting the opening degree of the throttle valve 3 and the amount of fuel injected from the fuel injection valve 5. Alternatively, the processing of S110 may perform rich combustion, which is an example of combustion based on a mixture having an air excess ratio of 1 or less.

[0067] On the other hand, when the process in S100 does not determine that the EGR valve 230 is open (S100: No), that is, when the EGR valve 230 is closed, the control device 100 performs lean combustion (S120). Lean combustion is the combustion of a mixture with an air excess ratio exceeding 1. In the present embodiment, as the lean combustion based on the process in S120, the combustion of a mixture with an air excess ratio significantly exceeding 1 is performed. The control device 100 performs lean combustion by adjusting the opening degree of the throttle valve 3 and the amount of fuel injected from the fuel injection valve 5.

[0068] After the control device 100 executes the process in S110 or the process in S120, this process is temporarily terminated.

[0069] In Figure 4 In the modification shown, when the EGR valve 230 is open, the combustion of a mixture with an air excess ratio of 1 or less is performed. That is, stoichiometric combustion or rich combustion is performed. The output of the internal combustion engine 1 in stoichiometric combustion or rich combustion is relatively high compared to the output of lean combustion of a mixture with an air excess ratio significantly exceeding 1. On the other hand, in stoichiometric combustion or rich combustion, there is a tendency for the generation amount of NOx to increase. Here, in Figure 4 In the modification shown, when the formal introduction of EGR gas into the intake passage 4 is performed by opening the EGR valve 230, the combustion of a mixture with an air excess ratio of 1 or less is performed. Therefore, it is possible to suppress the generation of NOx while increasing the output of the internal combustion engine 1.

[0070] · In the above embodiment, a valve body through-hole 229 is provided in the valve body 223. As an alternative or addition to the valve body through-hole 229, the EGR valve 230 may also have a bypass passage through which the EGR gas flows around the valve body 223.

[0071] Figure 5 The cross-sectional structure of the EGR valve 230 showing the modification is shown. As Figure 5 shown, the valve body 223 in this modification does not have Figure 2 the valve body through-hole 229 shown. On the other hand, in Figure 5 the EGR valve housing 220 of

[0072] In Figure 5In the modified example, even when the valve body 223 closes the EGR valve 230, the EGR gas flows inside the EGR valve 230 through the bypass passage 240. Therefore, the flow of the EGR gas is generated inside the EGR valve 230. Therefore, even when the valve body 223 closes the EGR valve 230, the EGR gas easily contacts the temperature sensing portion 227. As a result, the temperature sensing portion 227 can operate the valve body 223 according to the EGR gas temperature.

[0073] From Figure 5 Further modifying the modified example, the valve body 223 may also have Figure 2 the valve body through hole 229 of Figure 5 and both the bypass passage 240 of

[0074] · The above internal combustion engine 1 uses hydrogen as fuel, but other fuels can also be used. In this case, effects other than the above (4) can also be obtained.

[0075] · The temperature sensing material of the temperature sensing portion 227 is wax, but other temperature sensing materials can also be used. Examples of other temperature sensing materials for the temperature sensing portion 227 include shape memory alloys and bimetals.

[0076] · Figure 1 The EGR device 200 of is a low-pressure type. That is, the EGR passage 10 branches from the exhaust passage 6 at a downstream portion of the exhaust passage 6 with respect to the turbine housing 13b. The EGR passage 10 is connected to the intake passage 4 at an upstream portion of the intake passage 4 with respect to the compressor housing 13a. In addition, the EGR device 200 may also be a high-pressure type. The high-pressure type EGR device branches from the exhaust passage 6 at an upstream portion of the exhaust passage 6 with respect to the turbine housing 13b. The EGR passage 10 may also be connected to the intake passage 4 and the surge tank 2 at a downstream portion of the intake passage 4 with respect to the throttle valve 3.

[0077] The above control device 100 includes a CPU 110 and a memory 120, and executes software processing. However, this is merely an example. The control device 100 may also include, for example, a dedicated hardware circuit (such as an ASIC, etc.) that processes at least a part of the software processing executed in the above-described embodiment. That is, the control device 100 may have any of the following structures (a) to (c). (a) It includes a processing device that executes all of the above-described processing according to a program or a program product, and a program storage device such as a memory that stores the program. (b) It includes a processing device that executes a part of the above-described processing according to a program, a program storage device, and a dedicated hardware circuit that executes the remaining processing. (c) It includes a dedicated hardware circuit that executes all of the above-described processing. Here, the software circuit and the dedicated hardware circuit that include the processing device and the program storage device may be plural. That is, the above-described processing may be executed by a processing circuit that includes at least one of one or more software circuits and one or more dedicated hardware circuits. The program storage device, that is, the non-transitory computer-readable storage medium, includes all available media that can be accessed by a general-purpose or dedicated computer.

Claims

1. An exhaust gas recirculation device for an internal combustion engine, the exhaust gas recirculation device comprising: an EGR passage for introducing a portion of the exhaust gas of the internal combustion engine as EGR gas into an intake passage of the internal combustion engine; an EGR cooler provided in the EGR passage and performing heat exchange between cooling water of the internal combustion engine and the EGR gas; and An EGR valve is provided in the EGR passage between the intake passage and the EGR cooler, The EGR valve has: a temperature sensing portion in contact with the EGR gas, wherein the EGR gas temperature is the temperature of the EGR gas in contact with the temperature sensing portion; and The valve body opens the EGR valve when the temperature of the EGR gas is higher than a predetermined temperature, thereby allowing the flow of the EGR gas.

2. The exhaust gas recirculation device for an internal combustion engine according to claim 1, wherein: The temperature sensing portion is arranged at a downstream position relative to the valve body in the flow direction of the EGR gas. The valve body has a through hole.

3. The exhaust gas recirculation device for an internal combustion engine according to claim 1 or 2, wherein: The temperature sensing portion is arranged at a downstream position relative to the valve body in the flow direction of the EGR gas. The EGR valve has a bypass passage, and the EGR gas bypasses the valve body by flowing in the bypass passage.

4. The exhaust gas recirculation device for an internal combustion engine according to any one of claims 1 to 3, wherein: The fuel of the internal combustion engine is hydrogen.

5. The exhaust gas recirculation device for an internal combustion engine according to any one of claims 1 to 4, wherein: When the EGR valve is open, the air-fuel mixture combusted in the internal combustion engine has an excess air ratio of 1 or less.

6. An exhaust gas recirculation method for an internal combustion engine, the exhaust gas recirculation method comprising the following steps through a processing circuit: allowing a portion of the exhaust gas of the internal combustion engine to pass through an EGR passage, thereby introducing the portion of the exhaust gas into an intake passage of the internal combustion engine as EGR gas; and By using an EGR cooler provided in the EGR passage, heat exchange is performed between cooling water of the internal combustion engine and the EGR gas. The EGR valve provided in the EGR passage between the intake passage and the EGR cooler is opened when an EGR gas temperature is higher than a predetermined temperature, which is a temperature of the EGR gas in contact with a temperature sensing portion of the EGR valve.

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