Cooling system for internal combustion engines

Abstract

The present invention provides a cooling system for an internal combustion engine that allows a cooling pump, which supplies cooling water to an additive valve located in the exhaust path of the internal combustion engine and which adds an additive to the exhaust, to be operated as needed even after the internal combustion engine has stopped operating. [Solution] The cooling system for the internal combustion engine includes a cooling water temperature correlation value acquisition unit (86) that acquires a cooling water temperature correlation value that correlates with the temperature of the cooling water near an additive valve (41) located in the exhaust path (3), an exhaust temperature correlation value acquisition unit (85) that acquires an exhaust temperature correlation value that correlates with the temperature of the exhaust gas near the additive valve in the exhaust path (3), and a control unit (7) that operates a cooling pump (6) that supplies cooling water to the additive valve in response to a cooling request. The control unit determines that a cooling request has occurred when the cooling water temperature correlation value is greater than a first temperature threshold and the exhaust temperature correlation value is greater than a second temperature threshold after the internal combustion engine (1) has stopped operating.

Description

Technical Field

[0001] The present invention relates to a cooling system for an internal combustion engine. Specifically, it relates to a cooling system for an internal combustion engine for cooling an addition valve that adds an additive to the exhaust gas.

Background Art

[0002] In some cases, an addition valve for adding fuel, aqueous urea, or the like is disposed in the exhaust path of an internal combustion engine. In order to suppress the temperature rise of the addition valve, a cooling system including a cooling pump that circulates cooling water has been proposed (for example, see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, even after the operation of the internal combustion engine is stopped, the temperature of the addition valve may rise due to heat received from the exhaust gas that has become high temperature. Therefore, when it is necessary to suppress the temperature rise of the addition valve even after the operation of the internal combustion engine is stopped, it is desirable to operate the cooling pump.

[0005] However, if the cooling pump is operated more than necessary, there is a risk that the consumption of energy related to the drive of the cooling pump (for example, electric power in the case of an electric cooling pump) will increase. The present invention was conceived in view of such points, and one of its purposes is to provide a cooling system for an internal combustion engine that operates a cooling pump related to an addition valve as needed after the operation of the internal combustion engine is stopped.

Means for Solving the Problems

[0006] Therefore, the inventors examined parameters that should be referenced to determine whether or not the additive valve needs to be cooled, and found that the combination of the exhaust temperature near the additive valve and the cooling water temperature near the additive valve correlates with the temperature of the additive valve.

[0007] Therefore, a cooling system for an internal combustion engine to achieve the above objective (the present invention system) comprises: a cooling pump that supplies cooling water to an additive valve disposed in the exhaust path of the internal combustion engine and adds an additive to the exhaust, and circulates the cooling water; a cooling water temperature correlation value acquisition unit that acquires a cooling water temperature correlation value that correlates with the temperature of the cooling water near the additive valve; an exhaust temperature correlation value acquisition unit that acquires an exhaust temperature correlation value that correlates with the temperature of the exhaust near the additive valve in the exhaust path; and a control unit that operates the cooling pump in response to a cooling request. The control unit determines that a cooling request has occurred when, after the operation of the internal combustion engine has stopped, the cooling water temperature correlation value is greater than a first temperature threshold and the exhaust temperature correlation value is greater than a second temperature threshold.

[0008] In the system of the present invention, the necessity of operating the cooling pump after the internal combustion engine has stopped is determined based on the coolant temperature correlation value and the exhaust gas temperature correlation value. Therefore, if the coolant temperature correlation value and / or exhaust gas temperature correlation value decrease due to the operation of the cooling pump, no cooling demand is generated, and consequently, the cooling pump stops operating. Accordingly, according to the system of the present invention, the cooling pump operates according to the necessity of cooling for the additive valve, so it is possible to suppress the increase in energy consumption caused by driving the cooling pump after the internal combustion engine has stopped operating.

[0009] In one embodiment of the present invention, in the combination of the first temperature threshold and the second temperature threshold, a relationship exists where the second temperature threshold decreases as the first temperature threshold increases.

[0010] In this embodiment, if the exhaust gas temperature correlation value is large, it is determined that a cooling requirement exists even if the coolant temperature correlation value is small, compared to when the exhaust gas temperature correlation value is small. Similarly, if the coolant temperature correlation value is large, it is determined that a cooling requirement exists even if the exhaust gas temperature correlation value is small, compared to when the coolant temperature correlation value is small. Therefore, according to this embodiment, it is possible to determine with greater accuracy whether or not cooling is necessary for the additive valve. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic diagram of an internal combustion engine to which the cooling system of the internal combustion engine according to the embodiment is applied. [Figure 2] This is a schematic diagram (cooling system diagram) of the cooling water flow path that supplies cooling water to the fuel additive valve of an internal combustion engine. [Figure 3] This is a schematic diagram showing the relationship between the fuel injection valve and the cooling water flow path. [Figure 4] This diagram shows the relationship between coolant temperature and exhaust temperature, which is referenced when determining whether or not to operate the cooling pump related to the coolant flow path after the internal combustion engine has stopped operating. [Figure 5] This is a time chart showing examples of changes in (A) engine speed, (B) exhaust temperature, (C) coolant temperature, (D) cooling pump operating status, and (E) additive valve temperature after an internal combustion engine has stopped operating. [Figure 6] This flowchart shows the post-engine shutdown cooling routine executed by the control unit related to this system. [Modes for carrying out the invention]

[0012] Embodiments of the present invention will be described with reference to the drawings. The cooling system for an internal combustion engine according to this embodiment is applied to an internal combustion engine 1 shown in Figure 1. The internal combustion engine 1 includes an engine body 11, a supercharger 12, an intake path 2, an exhaust path 3, an exhaust gas purification device 4, an EGR device 5, and a cooling pump 6, and is controlled by an ECU 7.

[0013] The internal combustion engine 1 is a compression-ignition, multi-cylinder diesel engine mounted as a power source in a vehicle (not shown, hereinafter also referred to as the "mounted vehicle"). The engine body 11 includes a plurality of fuel injectors 13. Each of the fuel injectors 13 injects high-pressure fuel supplied from the accumulator chamber of the common rail system into the cylinder (combustion chamber) of the engine body 11 in response to instructions from the ECU 7 (none of which are shown).

[0014] The supercharger 12 includes a turbine 12a and a compressor 12b. The turbine 12a is operated (rotates) by the pressure of the exhaust gas (combustion gas) discharged from each cylinder of the engine body 11. The compressor 12b operates (rotates) in conjunction with the turbine 12a and pressurizes the air (intake) drawn into each cylinder of the engine body 11.

[0015] The intake path 2 includes intake pipes 21a and 21b, an intake manifold 22, a throttle valve 23, and an intercooler 24. Intake pipe 21a introduces intake air (fresh air) drawn in from outside (outside the vehicle) to the compressor 12b. Intake pipe 21b introduces intake air discharged from the compressor 12b to the intake manifold 22. The intake manifold 22 introduces intake air to each cylinder of the engine body 11.

[0016] The throttle valve 23 and intercooler 24 are located in the intake manifold 21b. The throttle valve 23 adjusts the opening of the intake manifold 21b (i.e., the throttle valve opening) in accordance with instructions from the ECU 7. The intercooler 24 cools the intake air, which has been pressurized by the compressor 12b and whose temperature has risen.

[0017] The exhaust path 3 includes an exhaust manifold 31 and exhaust pipes 32a to 32b. The exhaust manifold 31 introduces exhaust gas discharged from each cylinder of the engine body 11 into exhaust pipe 32a. Exhaust pipe 32a introduces the exhaust gas to the turbine 12a. Exhaust pipe 32b discharges the exhaust gas discharged from the turbine 12a to the outside (outside the vehicle). An exhaust gas purification device 4 is installed in exhaust pipe 32b.

[0018] The exhaust gas purification device 4 includes a fuel addition valve 41, a urea addition valve 42, a first oxidation catalyst 43, a DPF 44 (Diesel Particulate Filter), an SCR 45 (Selective Catalytic Reduction), and a second oxidation catalyst 46. The fuel addition valve 41 adds (injects) the fuel supplied from a fuel pump (not shown) in a section upstream of the first oxidation catalyst 43 in the exhaust pipe 32b in accordance with an instruction from the ECU 7 when performing the DPF regeneration process described later. The urea addition valve 42 adds the urea water supplied from a urea water pump (not shown) in a section between the DPF 44 and the SCR 45 in the exhaust pipe 32b in accordance with an instruction from the ECU 7. Note that the fuel added to the exhaust from the fuel addition valve 41 is one of the additives, and the urea water added to the exhaust from the urea addition valve 42 is the other one of the additives.

[0019] The first oxidation catalyst 43 is an oxidation catalyst device (DOC: Diesel Oxidation Catalyst) that oxidizes and purifies carbon monoxide (CO), hydrocarbons (HC), etc. contained in the exhaust gas. The DPF 44 is a particulate matter collection device that collects (captures) particulate matter (PM) contained in the exhaust gas. The SCR 45 reduces and purifies nitrogen oxides (NOx) contained in the exhaust gas using ammonia gas generated by the hydrolysis of the urea water injected from the urea addition valve 42. The second oxidation catalyst 46 oxidizes and purifies the residual ammonia gas discharged from the SCR 45.

[0020] The EGR device 5 includes an EGR pipe 51 and an EGR valve 52. The EGR pipe 51 connects the exhaust pipe 32a and the intake pipe 21b. The EGR valve 52 is installed in the EGR pipe 51. The valve opening state of the EGR valve 52 changes in accordance with an instruction from the ECU 7, and as a result, the amount of EGR gas recirculated from the exhaust pipe 32a to the intake pipe 21b is adjusted.

[0021] The cooling pump 6 is an electric pump, and circulates cooling water (e.g., coolant) in the cooling water flow path 61 in accordance with an instruction from the ECU 7. As schematically shown in FIG. 2, in the cooling water flow path 61, an intercooler 24, a fuel addition valve 41, a urea addition valve 42, and a supercharger 12 (hereinafter also collectively referred to as "cooling target devices"), and an intercooler radiator 62 are disposed. The intercooler radiator 62 is a heat exchanger, and reduces the temperature of the cooling water by heat exchange between the cooling water and the outside air. As the cooling water circulates with the operation of the cooling pump 6, each of the cooling target devices is cooled. That is, when the cooling pump 6 circulates the cooling water, the cooling water is heated by the cooling target devices and dissipates heat at the intercooler radiator 62.

[0022] Note that the internal combustion engine 1 includes an engine water pump that circulates cooling water in a cooling water flow path (different from the cooling water flow path 61) formed in the engine body 11, and an engine radiator that reduces the temperature of the cooling water circulated by the engine water pump. However, illustration and description of the engine water pump and the engine radiator are omitted in this specification.

[0023] More specifically describing the cooling water flow path 61 shown in FIG. 2, the cooling water flow path 61 extending from the cooling pump 6 branches and reaches each of the cooling target devices. The cooling water flow paths 61 extending from each of the cooling target devices merge and reach the intercooler radiator 62. The cooling water flow path 61 extending from the intercooler radiator 62 reaches the cooling pump 6. Therefore, the cooling water discharged from the cooling pump 6 reaches each of the cooling target devices, and then returns to the cooling pump 6 via the intercooler radiator 62. That is, by the operation of the cooling pump 6, the cooling water circulates between the cooling target devices and the intercooler radiator 62.

[0024] A fuel additive valve 41, to which cooling water is supplied from the cooling pump 6, is schematically shown in Figure 3. The fuel additive valve 41 is housed in an additive valve holder 41a. Cooling water is filled into the space between the outside of the fuel additive valve 41 and the inside of the additive valve holder 41a (i.e., the water jacket of the fuel additive valve 41). The space within the additive valve holder 41a, together with the flow path pipes 61a to 61b, constitutes part of the cooling water flow path 61. More specifically, cooling water is supplied to the additive valve holder 41a via the flow path pipe 61a. Cooling water is discharged from the additive valve holder 41a via the flow path pipe 61b.

[0025] The fuel additive valve holder 41a is fixed to the exhaust pipe 32b, thereby fixing the fuel additive valve 41 to the exhaust pipe 32b. The tip of the fuel additive valve 41 is exposed into the exhaust pipe 32b through a through hole formed in the fuel additive valve holder 41a. As a result, the fuel additive valve 41 can add fuel to the exhaust gas flowing through the exhaust pipe 32b (more specifically, the exhaust gas flowing into the first oxidation catalyst 43).

[0026] The ECU7 is an electronic control unit (control device, control unit) that includes a CPU, ROM, RAM, and EEPROM (see Figure 1). The CPU performs data reading, numerical calculations, and output of calculation results by sequentially executing a predetermined program. The ROM stores the program executed by the CPU and maps (lookup tables), etc. The RAM temporarily stores data referenced by the CPU. The EEPROM stores data referenced by the CPU and retains the stored data even when the ECU7 stops operating.

[0027] Furthermore, the ECU7 is connected to the crank angle sensor 81, cam position sensor 82, airflow sensor 83, accelerator opening sensor 84, exhaust temperature sensor 85, coolant temperature sensor 86, and differential pressure sensor 87 (see Figure 1).

[0028] The crank angle sensor 81 outputs a pulse signal to the ECU 7 each time the crankshaft (output shaft) of the internal combustion engine 1 (not shown) rotates by a predetermined angle. The camshaft position sensor 82 outputs a signal to the ECU 7 corresponding to the rotational position of the camshaft (not shown) of the internal combustion engine 1. The ECU 7 obtains the engine speed NE of the internal combustion engine 1 based on the signal input from the crank angle sensor 81. In addition, the ECU 7 obtains the crank angle CA of each cylinder of the engine body 11 based on the signals input from the crank angle sensor 81 and the camshaft position sensor 82.

[0029] The airflow sensor 83 detects the amount of intake air Ga flowing through the intake manifold 21a and outputs a signal representing the amount of air Ga to the ECU 7. The accelerator pedal position sensor 84 detects the accelerator pedal position Ap, which is the opening of the accelerator pedal (not shown) operated by the driver of the vehicle to control acceleration, and outputs a signal representing the accelerator pedal position Ap to the ECU 7. The exhaust temperature sensor 85 detects the exhaust temperature Te, which is the temperature of the exhaust gas flowing out from the turbine 12a, and outputs a signal representing the exhaust temperature Te to the ECU 7.

[0030] The coolant temperature sensor 86 is located in the coolant flow path 61 (see Figures 1-2). The coolant temperature sensor 86 detects the coolant temperature Tw, which is the temperature of the coolant flowing out of the intercooler radiator 62 and into the cooling pump 6, and outputs a signal representing the coolant temperature Tw to the ECU 7. The differential pressure sensor 87 detects the differential pressure Pd, which is the pressure difference between the exhaust pressure flowing into the DPF 44 and the exhaust pressure flowing out of the DPF 44, and outputs a signal representing the differential pressure Pd to the ECU 7.

[0031] As the amount of particulate matter collected in the DPF 44 increases, the differential pressure Pd increases. When the differential pressure Pd exceeds a predetermined threshold, the ECU 7 performs a "DPF regeneration process" in which fuel is injected into the fuel injection valve 41. The fuel added from the fuel injection valve 41 during the DPF regeneration process flows into the first oxidation catalyst 43 and is oxidized. As a result, the temperature of the first oxidation catalyst 43 rises, and consequently, the exhaust gas flowing out of the first oxidation catalyst 43 and into the DPF 44 becomes hot. Therefore, when the DPF regeneration process is performed, the accumulated particulate matter in the DPF 44 is burned off.

[0032] During the operation of the internal combustion engine 1, the ECU 7 obtains the fuel injection amount Qinj by applying the accelerator pedal opening Ap and engine rotation speed NE, etc., to a pre-adjusted map at predetermined intervals. When the crank angle CA of a certain cylinder reaches a predetermined fuel injection angle, the ECU 7 injects fuel corresponding to the fuel injection amount Qinj into the fuel injector 13 of that cylinder in multiple installments.

[0033] In addition, the ECU 7 activates the cooling pump 6 when a "cooling request" occurs. For example, when the temperature of the intercooler 24 and / or supercharger 12 rises as a result of the boost pressure (i.e., the pressure of the intake air pumped from the compressor 12b) remaining relatively high during the operation of the internal combustion engine 1, the ECU 7 determines that a cooling request has occurred and activates the cooling pump 6 accordingly.

[0034] (Cooling process after engine shutdown) Furthermore, the ECU 7 determines that a cooling request has been generated if, after the internal combustion engine 1 has stopped operating, the additive valve temperature Tv related to the fuel additive valve 41 may exceed the upper limit temperature Tmax. This cooling request is also referred to as a "post-stop cooling request." The additive valve temperature Tv is, for example, the temperature of the tip of the fuel additive valve 41. When the additive valve temperature Tv exceeds the upper limit temperature Tmax, there is a high possibility that deposits will adhere to the tip of the fuel additive valve 41 and that the components constituting the fuel additive valve 41 will deteriorate. Note that the internal combustion engine 1 according to this embodiment does not have a device (for example, a temperature sensor) that directly detects the additive valve temperature Tv.

[0035] The ECU7 determines that a post-stop cooling request has occurred when the coolant temperature Tw is greater than the first temperature threshold Tth1 and the exhaust temperature Te is greater than the second temperature threshold Tth2. The condition that is met when the coolant temperature Tw is greater than the first temperature threshold Tth1 and the exhaust temperature Te is greater than the second temperature threshold Tth2 is also referred to as the "post-stop cooling condition".

[0036] The first temperature threshold Tth1 and the second temperature threshold Tth2 will be explained with reference to Figure 4. The combination of coolant temperature Tw and exhaust temperature Te is also called a "temperature state point." Point Pa in Figure 4 is an example of a temperature state point. Point Pa corresponds to a state where the coolant temperature Tw is temperature twa and the exhaust temperature Te is temperature tea.

[0037] The straight line L1 in Figure 4 represents the combination of the first temperature threshold Tth1 and the second temperature threshold Tth2. As exemplified by point Pa, if the temperature state point is located to the right and above the straight line L1, the coolant temperature Tw is greater than the first temperature threshold Tth1 and the exhaust temperature Te is greater than the second temperature threshold Tth2. In this case, the post-stop cooling condition is met, so the ECU 7 determines that a post-stop cooling request has occurred and activates the cooling pump 6.

[0038] If the cooling water temperature Tw and exhaust gas temperature Te decrease due to the operation of the cooling pump 6, resulting in the post-stop cooling conditions no longer being met, the ECU 7 determines that no post-stop cooling request has occurred. Therefore, the ECU 7 will not operate the cooling pump 6 thereafter. However, if a cooling request other than the post-stop cooling request occurs (for example, a cooling request for the intercooler radiator 62), the ECU 7 may operate the cooling pump 6.

[0039] For example, point Pb is a temperature state point on the line L1, corresponding to a state where the coolant temperature Tw is temperature twb and the exhaust temperature Te is temperature teb. In other words, temperatures twb and teb are one combination of the first temperature threshold Tth1 and the second temperature threshold Tth2. Therefore, when the temperature state point moves from point Pa to point Pb due to the operation of the cooling pump 6, the post-stop cooling condition is no longer met, and the ECU 7 determines that no post-stop cooling request has been generated.

[0040] Alternatively, even if the temperature state point moves from point Pa to point Pc due to the operation of the cooling pump 6, the ECU 7 determines that no post-stop cooling request has occurred. Point Pc is another example of a temperature state point on the straight line L1. That is, temperatures twc and tec corresponding to point Pc are another combination of the first temperature threshold Tth1 and the second temperature threshold Tth2.

[0041] As can be seen from the line L1, in combinations of the first temperature threshold Tth1 and the second temperature threshold Tth2, the relationship holds that as the first temperature threshold Tth1 increases, the second temperature threshold Tth2 decreases. For example, points Pb(twb,teb) and Pc(twc,tec) are examples of combinations of the first temperature threshold Tth1 and the second temperature threshold Tth2, where temperature twb is greater than temperature twc and temperature teb is less than temperature tec.

[0042] (Cooling process after engine shutdown - time chart) Figure 5 shows an example of a situation in which the ECU 7 activates the cooling pump 6 after the internal combustion engine 1 has stopped operating, due to the fulfillment of post-stop cooling conditions. At time t0 in Figure 5, as shown by the solid line La, the engine rotational speed NE is greater than "0". That is, at time t0, the internal combustion engine 1 is operating. In addition, as shown by the solid line Ld, the cooling pump 6 is not operating at time t0.

[0043] Subsequently, at time t1, the engine rotational speed NE is "0". That is, the operation of internal combustion engine 1 has stopped at time t1. As shown by the solid lines Lb and Lc1, the exhaust temperature Te at time t1 is temperature tea and the cooling water temperature Tw is temperature tea. That is, the temperature state point at time t1 corresponds to point Pa in Figure 4. In other words, at time t1, when the operation of internal combustion engine 1 has stopped, the post-stop cooling condition has been met.

[0044] Therefore, the ECU 7 operates the cooling pump 6 until the cooling conditions after shutdown are met. More specifically, as shown by the solid line Ld, the ECU 7 operates the cooling pump 6 until the operating duration Tc has elapsed, and then stops the operation of the cooling pump 6. Then, after the waiting time Ts has elapsed, the ECU 7 operates the cooling pump 6 again until the operating duration Tc has elapsed. In other words, the ECU 7 performs intermittent operation of the cooling pump 6. To put it another way, the ECU 7 does not necessarily operate the cooling pump 6 continuously in response to a cooling request after shutdown.

[0045] As shown by the solid line Le, coolant is supplied to the fuel additive valve 41 during the period when the cooling pump 6 is operating, so the additive valve temperature Tv decreases. In addition, during this period, the coolant that has received heat from the fuel additive valve 41 is dissipated by the intercooler radiator 62, so as shown by the solid line Lc1, the coolant temperature Tw decreases.

[0046] On the other hand, during the period when the cooling pump 6 is not operating, the fuel additive valve temperature Tv rises due to heat absorption from the exhaust near the tip of the fuel additive valve 41 and from the exhaust pipe 32b (see solid line Le). Similarly, during this period, the cooling water temperature Tw rises due to heat absorption from the cooling device, including the fuel additive valve 41 (see solid line Lc1).

[0047] In summary, as the cooling pump 6 repeatedly starts and stops, the cooling water temperature Tw and additive valve temperature Tv repeatedly decrease and increase. However, the increase in the cooling water temperature Tw during the cooling pump 6's stop period is greater than the decrease during the cooling pump 6's operation period, so overall, the temperature Tw is increasing (see solid line Lc1).

[0048] On the other hand, the exhaust temperature Te decreases due to heat dissipation from the exhaust to the outside air. Therefore, at time t2, the exhaust temperature Te is at temperature teb (see solid line Lb). At this time, the coolant temperature Tw is at temperature twb (see solid line Lc1). In other words, the temperature state point at time t2 corresponds to point Pb (on the line L1) in Figure 4. In other words, the post-stop cooling condition is no longer met at time t2. Therefore, from time t2 onward, the ECU 7 determines that no post-stop cooling request has occurred and does not operate the cooling pump 6.

[0049] Since the cooling pump 6 is not operating from time t2 onward, the fuel additive valve temperature Tv is rising due to heat absorption from the exhaust pipe 32b and the exhaust gas within the exhaust pipe 32b at the fuel additive valve 41. However, as can be seen from the solid line Le, the fuel additive valve temperature Tv remains below the upper limit temperature Tmax. If the cooling pump 6 were not operating from time t1 onward, as shown by the dashed line Lc2, the coolant temperature Tw would likely rise continuously, and as a result, the fuel additive valve temperature Tv would likely exceed the upper limit temperature Tmax.

[0050] (Cooling process after engine shutdown - specific operation) The specific operation of the ECU7 in controlling the cooling pump 6 after the internal combustion engine 1 has stopped will be explained with reference to the "post-engine shutdown cooling routine" shown in the flowchart in Figure 6. When a predetermined off operation is performed on the ignition switch (not shown) located in the passenger compartment of the vehicle, the CPU of the ECU7 (hereinafter also simply referred to as "CPU") executes an engine shutdown routine (not shown) to stop the operation of the internal combustion engine 1.

[0051] Subsequently, the CPU executes the routine shown in Figure 6 at predetermined processing cycles. If the value of the post-stop cooling process flag Xc is set to "0" in this routine (specifically, step 635 described later), the CPU will not execute this routine thereafter.

[0052] When the appropriate timing is reached, the CPU starts processing from step 600 in Figure 6 and proceeds to step 605 to determine whether the post-stop cooling conditions are met. That is, the CPU determines whether the cooling water temperature Tw is greater than the first temperature threshold Tth1 and the exhaust temperature Te is greater than the second temperature threshold Tth2.

[0053] This routine is executed for the first time after the internal combustion engine 1 has stopped operating, and it is assumed that at the time of shutdown, the post-shutdown cooling conditions are met (similar to the state at time t1 in Figure 5) and the cooling pump 6 is not operating.

[0054] According to this assumption, the post-shutdown cooling condition is met, so the CPU determines "Yes" in step 605 and proceeds to step 610 to determine whether the cooling pump 6 is operating or not.

[0055] According to this assumption, the cooling pump 6 is not operating, so the CPU determines "No" in step 610 and proceeds to step 625 to determine whether a waiting time Ts has elapsed since the cooling pump 6 stopped operating. If a waiting time Ts has elapsed since the cooling pump 6 stopped operating, the CPU determines "Yes" in step 625 and proceeds to step 630 to start the cooling pump 6. Next, the CPU proceeds to step 695 and terminates the processing of this routine.

[0056] The next time this routine is executed, the cooling pump 6 will have started operating, so the CPU determines "Yes" in step 610 and proceeds to step 615. In step 615, the CPU determines whether the operating duration Tc has elapsed since the cooling pump 6 started operating. At this point, the elapsed time since the cooling pump 6 started operating has not yet reached the operating duration Tc, so the CPU determines "No" in step 615 and proceeds directly to step 695. In other words, the state in which the cooling pump 6 is operating is maintained.

[0057] Subsequently, when this routine is executed for the first time after the elapsed time since the cooling pump 6 started operating reaches the operating duration Tc, the CPU determines "Yes" in step 615 and proceeds to step 620. In step 620, the CPU stops the operation of the cooling pump 6. Next, the CPU proceeds to step 695.

[0058] The next time this routine is executed, the cooling pump 6 is not operating, so the CPU determines "No" in step 610 and proceeds to step 625. At this point, the elapsed time since the cooling pump 6 stopped operating has not yet reached the waiting time Ts, so the CPU determines "No" in step 625 and proceeds directly to step 695. In other words, the state in which the cooling pump 6 is stopped is maintained.

[0059] Subsequently, when this routine is executed for the first time after the time elapsed since the cooling pump 6 stopped operating reaches the waiting time Ts, the CPU proceeds from step 625 to step 630 and starts the cooling pump 6. In other words, the processing in step 620 and the processing in step 630 are executed alternately to perform intermittent operation of the cooling pump 6.

[0060] Subsequently, if this routine is executed after the post-stop cooling condition is no longer met as a result of the intermittent operation of the cooling pump 6, the CPU determines "No" in step 605 and proceeds to step 635, setting the value of the post-stop cooling process flag Xc to "0". Next, the CPU proceeds to step 695. Therefore, from this point onward, the CPU does not execute the processing of this routine. In addition, if the cooling pump 6 is operating at the time the CPU proceeds to step 635 due to the processing in step 630, the CPU stops the operation of the cooling pump 6.

[0061] Furthermore, if the post-stop cooling conditions are not met at the time the internal combustion engine 1 stops operating (i.e., if there is no need to cool the fuel additive valve 41), the CPU proceeds from step 605 to step 635 when it first executes this routine. In this case, the value of the post-stop cooling process flag Xc is set to "0" when the internal combustion engine 1 stops operating. Therefore, the cooling pump 6, which is intended to cool the fuel additive valve 41, does not operate after the internal combustion engine 1 stops operating.

[0062] As explained above, when the internal combustion engine 1 stops operating, if the post-stop cooling conditions are met (i.e., if the fuel additive valve 41 needs to be cooled), the cooling pump 6 operates to circulate the coolant, thereby cooling the fuel additive valve 41. Subsequently, when the post-stop cooling conditions are no longer met, the cooling pump 6 stops operating. In other words, when there is no longer a need to cool the fuel additive valve 41 and no cooling request (more specifically, a post-stop cooling request) is generated, the cooling pump 6 stops operating.

[0063] If, when the internal combustion engine 1 stops operating, the ECU 7 determines the operating schedule for the cooling pump 6 (for example, the number of times the cooling pump 6 is intermittently driven) based on the fulfillment of the post-stop cooling conditions, and operates the cooling pump 6 according to the operating schedule, the power consumption of the cooling pump 6 may increase. Specifically, in order to reliably prevent the additive valve temperature Tv from exceeding the upper limit temperature Tmax after the internal combustion engine 1 stops operating, a certain margin will be provided in the operating schedule of the cooling pump 6. As a result, the power consumption of the cooling pump 6 is likely to increase.

[0064] On the other hand, the ECU 7 operates the cooling pump 6 depending on whether the post-stop cooling conditions are met. Therefore, once it is no longer necessary to cool the fuel additive valve 41, the operation of the cooling pump 6 ends. In other words, the possibility of overcooling the fuel additive valve 41 is reduced, and as a result, it is possible to avoid the additive valve temperature Tv exceeding the upper limit temperature Tmax and to suppress an increase in power consumption in the cooling pump 6.

[0065] Incidentally, the coolant temperature Tw is correlated with the temperature of the coolant near the fuel additive valve 41 (more specifically, the coolant in the additive valve holder 41a), and is therefore also referred to as the "coolant temperature correlation value" for convenience. That is, the higher the temperature of the coolant near the fuel additive valve 41, the higher the coolant temperature Tw. Therefore, it can be said that the larger the coolant temperature Tw (i.e., the coolant temperature correlation value), the larger the additive valve temperature Tv. The coolant temperature sensor 86 that detects the coolant temperature Tw is also referred to as the "coolant temperature correlation value acquisition unit" for convenience.

[0066] Similarly, the exhaust temperature Te is correlated with the temperature of the exhaust gas near the fuel additive valve 41 (more specifically, the exhaust gas near the tip of the fuel additive valve 41 in the exhaust pipe 32b), and is therefore also referred to as the "exhaust temperature correlation value" for convenience. That is, the higher the temperature of the exhaust gas near the fuel additive valve 41, the higher the exhaust temperature Te becomes. Therefore, it can be said that the larger the exhaust temperature Te (i.e., the exhaust temperature correlation value), the larger the additive valve temperature Tv. The exhaust temperature sensor 85 that detects the exhaust temperature Te is also referred to as the "exhaust temperature correlation value acquisition unit" for convenience.

[0067] Furthermore, the cooling water in the cooling water passage 61, and the exhaust gas in the exhaust passage 3 and exhaust gas purification device 4, continue to absorb heat from various components that become hot during the operation of the internal combustion engine 1, even after the internal combustion engine 1 has stopped operating. Therefore, if the cooling water temperature Tw and exhaust gas temperature Te are relatively high after the internal combustion engine 1 has stopped operating, it is highly likely that the additive valve temperature Tv will not decrease easily. In other words, the larger the cooling water temperature correlation value and / or exhaust gas temperature correlation value after the internal combustion engine 1 has stopped operating, the greater the amount of heat absorbed by the fuel additive valve 41.

[0068] Therefore, the ECU 7 determines whether the post-stop cooling request is successful based on the coolant temperature Tw and the exhaust temperature Te. This allows the ECU 7 to determine whether cooling is necessary for the fuel additive valve 41 without requiring a new temperature sensor to directly detect the additive valve temperature Tv. In other words, a cooling system that appropriately determines whether cooling is necessary for the fuel additive valve 41 and optimizes the operating time of the cooling pump 6 can be realized with a relatively simple configuration.

[0069] In addition, as shown by the straight line L1 in Figure 4, in the first temperature threshold Tth1 and the second temperature threshold Tth2, which are referenced when determining the success or failure of the post-stop cooling condition, a relationship was observed where the second temperature threshold Tth2 decreased as the first temperature threshold Tth1 increased. Therefore, if the exhaust temperature Te is high, the post-stop cooling condition can be met even if the coolant temperature Tw is low, compared to when the exhaust temperature Te is low. Similarly, if the coolant temperature Tw is high, the post-stop cooling condition can be met even if the exhaust temperature Te is low, compared to when the coolant temperature Tw is low. For this reason, the ECU 7 can accurately determine whether cooling is necessary for the fuel additive valve 41.

[0070] Although embodiments of the present invention have been described above with reference to the above-described structure, many substitutions, improvements, and modifications are possible without departing from the purpose of the present invention. Accordingly, embodiments of the present invention may include all substitutions, improvements, and modifications that do not depart from the spirit and purpose of the appended claims. Embodiments of the present invention are not limited to the above-described special structure, and for example, the following modifications (i.e., variations of the embodiments) are possible.

[0071] In the cooling water passage 61, as shown in Figure 2, the devices to be cooled (i.e., the intercooler 24, fuel additive valve 41, urea additive valve 42, and turbocharger 12) were arranged in parallel with each other. Alternatively, some or all of the devices to be cooled may be arranged in series. Or, if the internal combustion engine 1 has a second turbocharger different from the turbocharger 12 (i.e., if the internal combustion engine 1 is a twin-turbo engine), the second turbocharger may be included in the devices to be cooled in the cooling water passage 61. Furthermore, the cooling water temperature sensor 86, which detects the cooling water temperature Tw, was located at the manifold of the cooling water passage 61 upstream of the intercooler radiator 62, but it may be located in either the additive valve holder 41a and the passage piping 61a to 61b shown in Figure 3. In these configurations as well, the ECU 7 can determine the success or failure of the post-stop cooling conditions based on a cooling water temperature correlation value (e.g., cooling water temperature Tw) that correlates with the temperature of the cooling water near the fuel additive valve 41.

[0072] The exhaust temperature sensor 85, which detects the exhaust temperature Te, was located in the exhaust pipe 32b. Alternatively, the exhaust temperature sensor 85 may be located in the exhaust pipe 32a. In this configuration as well, the ECU 7 can determine whether the post-stop cooling conditions are met based on an exhaust temperature correlation value (e.g., exhaust temperature Te) that correlates with the temperature of the exhaust gas near the fuel additive valve 41.

[0073] In addition, the ECU 7 described above determined whether cooling was necessary for the fuel additive valve 41 after the internal combustion engine 1 stopped operating, and activated the cooling pump 6 according to that determination. Alternatively, or in addition to this, the ECU 7 may also determine whether cooling was necessary for the urea additive valve 42 after the internal combustion engine 1 stopped operating, and activate the cooling pump 6 according to that determination. Furthermore, the ECU 7 may also determine whether cooling was necessary for the intercooler 24 after the internal combustion engine 1 stopped operating, and activate the cooling pump 6 according to that determination. Moreover, the internal combustion engine 1 may be equipped with different combinations of cooling water passages and cooling pumps to supply cooling water to the fuel additive valve 41 and the urea additive valve 42, respectively.

[0074] In addition, the ECU 7 described above would operate the cooling pump 6 if the post-stop cooling conditions were met after the internal combustion engine 1 stopped operating, and would stop operating the cooling pump 6 if the post-stop cooling conditions were no longer met. In other words, the start and end conditions for the cooling pump 6 after the internal combustion engine 1 stopped operating were the same. Alternatively, the start and end conditions for the cooling pump 6 after the internal combustion engine 1 stopped operating may be different from each other. In this configuration, if the start condition is met after the internal combustion engine 1 stops operating, the ECU 7 will determine that a post-stop cooling request has occurred until the end condition is met. In this configuration, the start condition for the cooling pump 6 is, for example, when the coolant temperature Tw is greater than "a temperature slightly greater than the first temperature threshold Tth1" and the exhaust temperature Te is greater than "a temperature slightly greater than the second temperature threshold Tth2".

[0075] In addition, the post-stop cooling conditions related to the straight line L1 in Figure 4 were adapted so that the additive valve temperature Tv would not exceed the upper limit temperature Tmax even during the period after the post-stop cooling conditions were no longer met. The post-stop cooling conditions may be adapted based on a different concept. For example, the post-stop cooling conditions may be adapted so that the additive valve temperature Tv at that point in time, estimated based on the combination of cooling water temperature Tw and exhaust temperature Te, does not exceed a predetermined upper limit.

[0076] In addition, as shown by the solid line Ld in Figure 5, the operating state of the cooling pump 6 was switched between a stopped state (off state) and an operating state (on state). Alternatively, the flow rate of the cooling pump 6 when it is operating (i.e., the amount of cooling water discharged by the cooling pump 6 per unit time) may be variably controlled. In this configuration, the ECU 7 may, for example, control the cooling pump 6 so that the flow rate increases as the distance between the temperature state point and the straight line L1 in the graph of Figure 4 increases.

[0077] In addition, the straight line L1 in Figure 4 represents an example of post-stop cooling conditions adapted for internal combustion engine 1 (specifically, a combination of the first temperature threshold Tth1 and the second temperature threshold Tth2). For post-stop cooling conditions adapted for other internal combustion engines, the result may be a curve, as shown by the dashed line L2 in Figure 4.

[0078] In addition, the fuel additive valve 41 and the cooling pump 6 described above were both controlled by the ECU 7. Alternatively, the fuel additive valve 41 and the cooling pump 6 may each be controlled by different control devices (control units). [Explanation of Symbols]

[0079] 1...Internal combustion engine, 11...Engine body, 12...Supercharger, 12a...Turbine, 12b...Compressor, 13...Fuel injector 2...Intake path, 21a~21b...Intake pipe, 22...Intake manifold, 23...Throttle valve, 24...Intercooler 3...Exhaust path, 31...Exhaust manifold, 32a~32b...Exhaust pipe 4... Exhaust gas purification device, 41... Fuel additive valve, 41a... Additive valve holder, 42... Urea additive valve 43...First oxidation catalyst, 44...DPF, 45...SCR, 46...Second oxidation catalyst 5...EGR device, 51...EGR pipe, 52...EGR valve 6...Cooling pump, 61...Cooling water channel 61a~61b…Flow piping, 62…Intercooler radiator 7…ECU, 81... Crank angle sensor, 82... Cam position sensor 83...Airflow sensor, 84...Accelerator position sensor, 85...Exhaust temperature sensor 86... Coolant temperature sensor, 87... Differential pressure sensor

Claims

1. A cooling system for an internal combustion engine, A cooling pump is provided that supplies cooling water to an additive valve, which is located in the exhaust path of an internal combustion engine and adds an additive to the exhaust, and also circulates the cooling water. A cooling water temperature correlation value acquisition unit acquires a cooling water temperature correlation value that correlates with the temperature of the cooling water located near the additive valve, An exhaust temperature correlation value acquisition unit acquires an exhaust temperature correlation value that correlates with the temperature of the exhaust gas near the additive valve in the exhaust path, It includes a control unit that operates the cooling pump in response to a cooling request, The control unit, A cooling system for an internal combustion engine, which determines that a cooling request has occurred when, after the internal combustion engine has stopped operating, the coolant temperature correlation value is greater than a first temperature threshold and the exhaust gas temperature correlation value is greater than a second temperature threshold.

2. A cooling system for an internal combustion engine according to claim 1, A cooling system for an internal combustion engine, wherein, in the combination of the first temperature threshold and the second temperature threshold, a relationship exists where the second temperature threshold decreases as the first temperature threshold increases.

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