Cooling water circulation system

Abstract

The present invention comprises: a water flow control valve 12 that is provided to a cooling water passage 10 of an engine 2 and controls the flow rate of cooling water; a pump 11 that circulates the cooling water through the cooling water passage 10; a water temperature sensor 22 that acquires the temperature of the cooling water; and an MCV control unit 20 that predicts the occurrence of air bubbles in the cooling water on the upstream side of the pump 11 in the cooling water passage 10, and controls the opening and closing of the water flow control valve 12. The MCV control unit 20 opens and closes the water flow control valve 12 in accordance with the temperature of the cooling water, and when the occurrence of air bubbles while the water flow control valve 12 is in a closed condition has been predicted, controls the water flow control valve 12 so as to open.

Description

Cooling Water Circulation System

[0001] The present invention relates to a technology for protecting a pump in a cooling water circulation system for cooling an internal combustion engine.

[0002] Coolant circulation systems are widely used in internal combustion engines, circulating coolant to cool the engine. In these systems, the coolant is circulated through a circulation path (coolant passage) by a pump driven by the engine or an electric motor, for example. Furthermore, a technology is known in which a valve is provided to open and close the coolant passage, and the valve is controlled to suppress the flow rate of the coolant during, for example, a cold start, thereby promoting a temperature rise in the internal combustion engine.

[0003] In such a cooling water passage, air bubbles may be generated in the pump when, for example, a valve is closed to change the flow rate of the cooling water. In response to this problem, Patent Document 1 discloses a system in which an electric pump is used to circulate the cooling water, and the generation of air bubbles is detected based on the water pressure of the cooling water and the power consumption of the electric pump. When the generation of air bubbles is detected, the flow rate of the pump is increased to reduce the amount of air bubbles.

[0004] JP 2008-57340 A

[0005] On the other hand, there are cases where it is desirable to quickly increase the engine temperature when the internal combustion engine is cold, such as during a cold start. In such cases, the temperature of the internal combustion engine can be increased by reducing the amount of coolant circulating through the internal combustion engine. However, reducing the amount of coolant circulating can lead to the problem of air bubbles being more likely to form in the coolant. If air bubbles continue to form, the durability of the pump may be reduced.

[0006] The present invention has been made in consideration of these problems, and its object is to provide a cooling water circulation system for an internal combustion engine that can promote warming up of the internal combustion engine when it is cold, while suppressing the generation of bubbles in the cooling water and protecting the pump.

[0007] In order to achieve the above object, the cooling water circulation system of the present invention comprises a valve provided in a cooling water passage of an internal combustion engine and controlling the flow rate of cooling water, a pump that circulates the cooling water through the cooling water passage, a prediction means for predicting the generation of bubbles in the cooling water upstream of the pump in the cooling water passage, a water temperature acquisition unit that acquires the temperature of the cooling water, and a control unit that controls the operation of the valve, wherein the control unit opens and closes the valve according to the temperature of the cooling water, and opens the valve when the generation of bubbles is predicted by the prediction means while the valve is closed.

[0008] This allows the temperature of the internal combustion engine to be appropriately controlled by opening and closing the valve to control the flow rate of the cooling water according to the temperature of the cooling water. Furthermore, by opening the valve when it is predicted that bubbles will be generated when the valve is closed, it is possible to suppress a decrease in the internal pressure of the cooling water passage upstream of the pump and thereby suppress the generation of bubbles.

[0009] Preferably, a pressure acquisition unit that acquires the pressure of the cooling water is provided upstream of the pump in the cooling water passage, and the prediction unit predicts that bubbles will be generated when the pressure of the cooling water acquired by the pressure acquisition unit is equal to or lower than a first pressure. This allows the prediction unit to predict the generation of bubbles with a simple configuration.

[0010] Preferably, the first pressure varies depending on the temperature of the cooling water, thereby enabling the first pressure to be appropriately set in response to the pressure at which bubbles are generated in the cooling water varying depending on the temperature of the cooling water, thereby enabling accurate prediction of bubble generation.

[0011] Preferably, the device includes a rotational speed acquisition unit that acquires the rotational speed of the internal combustion engine, and when the prediction means predicts the generation of bubbles while the valve is closed, the control unit maintains the valve closed if the rotational speed of the internal combustion engine is equal to or lower than a first rotational speed.

[0012] As a result, when the valve is closed according to the temperature of the cooling water and the rotation speed of the internal combustion engine is below a first rotation speed, i.e., when the temperature of the internal combustion engine is low and the rotation speed is also low and warming up of the internal combustion engine is required, such as during a cold start, the valve is kept closed to allow the generation of bubbles, thereby suppressing the cooling effect of the cooling water and promoting warming up of the internal combustion engine.

[0013] Preferably, the apparatus further includes a rotational speed acquisition unit that acquires the rotational speed of the internal combustion engine, and the control unit opens the valve when the prediction means predicts the generation of bubbles while the valve is closed, and then maintains the valve open until the rotational speed of the internal combustion engine becomes equal to or less than a first rotational speed, and closes the valve when the rotational speed becomes equal to or less than the first rotational speed.

[0014] As a result, when the water pressure exceeds a predetermined pressure and the valve is closed, even if the water pressure immediately drops, the valve remains open until the rotation speed of the internal combustion engine falls below the first rotation speed, thereby preventing the valve from being repeatedly opened and closed.

[0015] Preferably, the cooling water passage has a first passage through which the cooling water circulates by passing through a radiator, and a second passage through which the cooling water circulates without passing through the radiator, the valve is provided at the confluence of the first passage and the second passage and is capable of opening and closing the first passage and the second passage, the pump is provided immediately downstream of the valve, and the prediction means predicts the generation of bubbles between the pump and the valve.

[0016] This allows for a simple configuration in which the first and second passages can be opened and closed by the valves, and the cooling water can be circulated through each passage by the pump. Furthermore, by predicting that closing the valve will result in a drop in water pressure between the valve and the pump, and thus generating bubbles, the valve is opened accordingly, thereby effectively suppressing the generation of bubbles upstream of the pump.

[0017] Preferably, the cooling water passage has a first passage through which the cooling water circulates by passing through a radiator, and a second passage through which the cooling water circulates without passing through a radiator, the valve is provided at a junction of the first passage and the second passage and is capable of opening and closing the first passage and the second passage, and the control unit changes which of the first passage and the second passage is opened according to the degree of bubble generation predicted by the prediction means while the valve closes the first passage and the second passage.

[0018] This allows the pressure between the valve and the pump to be appropriately controlled by changing which of the first and second passages is opened depending on the degree of bubble generation, thereby appropriately suppressing the generation of bubbles upstream of the pump.

[0019] Preferably, the cooling water supply system includes an output acquisition unit that acquires the output of the pump, the prediction means predicts the generation of bubbles, and predicts that the greater the output of the pump, the greater the degree of bubble generation, and the control unit, when the prediction means predicts the generation of bubbles while the valves are closing each cooling water passage, opens the second passage if the output of the pump exceeds a first output and is equal to or less than a second output that is greater than the first output, and opens the first passage if the output of the pump exceeds the second output.

[0020] As a result, when the generation of bubbles is predicted and the pump output exceeds the first output but is equal to or less than the second output, simply opening the second passage will sufficiently increase the pressure of the cooling water, thereby promoting warm-up without opening the first passage. Also, when the pump output exceeds the second output, the first passage will be opened to significantly increase the pressure of the cooling water, thereby sufficiently suppressing the generation of bubbles.

[0021] Preferably, the cooling water passage has a first passage through which the cooling water circulates by passing through a radiator, and a second passage through which the cooling water circulates without passing through a radiator, the valve is provided at a junction of the first passage and the second passage and is capable of opening and closing the first passage and the second passage, a pressure acquisition unit that acquires the pressure of the cooling water is provided in the cooling water passage upstream of the pump, the prediction means predicts that bubbles will be generated when the pressure of the cooling water acquired by the pressure acquisition unit is equal to or lower than a first pressure, and the control unit opens the second passage when the pressure becomes equal to or lower than the first pressure while the valve closes the first passage and the second passage, and opens the first passage if the pressure does not exceed the first pressure within a predetermined time thereafter.

[0022] As a result, when the cooling water pressure falls below the first pressure while the valve is closed, the second passage is first opened to suppress a pressure drop while the first passage is kept closed, thereby suppressing a drop in the cooling water temperature and promoting warm-up. Then, if the cooling water pressure does not exceed the first pressure within a predetermined time even after the second passage is opened, the first passage is opened to increase the cooling water pressure and suppress the generation of bubbles.

[0023] Preferably, the cooling water passage has a first passage through which the cooling water circulates by passing through a radiator, and a second passage through which the cooling water circulates without passing through a radiator, the valve is provided at the junction of the first passage and the second passage and is capable of opening and closing the first passage and the second passage, and when the prediction means predicts the generation of bubbles while the valve is closed on the first passage and the second passage, the control unit opens the second passage during series running and opens the first passage during parallel running.

[0024] As a result, during series running, the rotational speed of the internal combustion engine is stabilized at low to medium rotational speeds, and warm-up is promoted without opening the first passage. During parallel running, the rotational speed of the internal combustion engine may become high, so opening the first passage ensures the cooling performance of the internal combustion engine.

[0025] The cooling water circulation system of the present invention appropriately cools the internal combustion engine by opening and closing the valve according to the temperature of the cooling water, and by opening the valve if the generation of bubbles is predicted when the valve is closed according to the temperature of the cooling water, it is possible to prevent a drop in the internal pressure of the pump, suppress the generation of bubbles, and protect the pump.

[0026] 1 is a schematic configuration diagram of an engine cooling water circulation system according to the present embodiment; FIG. 2 is a flowchart showing a control procedure for a water flow control valve of a first embodiment in a cooling water circulation system; FIG. 3 is a graph showing an example of setting the opening degree of a water flow control valve; FIG. 4 is an example of a map for calculating a first threshold value of water pressure; FIG. 5 is a flowchart showing a control procedure for a water flow control valve of a second embodiment in a cooling water circulation system; and FIG. 6 is a flowchart showing a control procedure for a water flow control valve of a third embodiment in a cooling water circulation system.

[0027] An embodiment of a cooling water circulation system embodying the present invention will now be described. Fig. 1 is a schematic diagram of a cooling water circulation system 1 according to this embodiment. In Fig. 1, bold arrows indicate the direction in which cooling water flows.

[0028] The cooling water circulation system 1 of this embodiment is employed in, for example, an engine 2 (internal combustion engine) mounted on a vehicle, and is a system that circulates cooling water to cool the engine 2 and an oil cooler 3 (O / C), and also recovers heat in a heater 4 (heater core) to warm the interior of the vehicle.

[0029] The cooling water circulation system 1 has a cooling water passage 10 that circulates the cooling water. The cooling water passage 10 is provided with a pump 11 that circulates the cooling water. The pump 11 is, for example, a mechanical pump driven by the engine 2, but an electric pump may also be used. The engine 2 is disposed downstream of the pump 11 in the cooling water passage 10, and a water flow control valve (MCV) 12 (the valve of the present invention) is provided upstream of the pump 11.

[0030] The coolant passage 10 branches into a first coolant passage 10a (first passage), a second coolant passage 10b (second passage), and a third coolant passage 10c (second passage) downstream of the engine 2. The first coolant passage 10a passes through a radiator 15 and is connected to a water flow control valve 12. The second coolant passage 10b passes through an oil cooler 3 and is connected to the water flow control valve 12.

[0031] The third coolant passage 10c passes through the heater 4 and is connected to the water flow control valve 12. The radiator 15 cools the coolant that passes through the first coolant passage 10a, out of the coolant whose temperature has increased after passing through the engine 2.

[0032] The oil cooler 3 is a device that cools oil used to drive and control the operation of hydraulic equipment of a vehicle by exchanging heat with cooling water. In the oil cooler 3, the oil is cooled by cooling water passing through the second cooling water passage 10b.

[0033] The heater 4 is a device for heating, for example, the interior of the vehicle, and heats the air supplied to the vehicle compartment by exchanging heat between the coolant passing through the third coolant passage 10c and the air. The first coolant passage 10a is the main passage for cooling the engine 2, and therefore has a larger inner diameter than the second coolant passage 10b and the third coolant passage 10c.

[0034] The water flow control valve 12 is provided at the confluence of the first, second, and third cooling water passages 10a, 10b, and 10c and has the function of controlling the opening of each of the cooling water passages 10a, 10b, and 10c, i.e., the flow rate of cooling water in each of the cooling water passages 10a, 10b, and 10c. The water flow control valve 12 may be provided with, for example, an actuator (not shown), and the relationship between the operation of the actuator and the opening of each of the cooling water passages 10a, 10b, and 10c may be individually set in advance, or an actuator may be provided for each of the cooling water passages 10a, 10b, and 10c so that the opening of each of the cooling water passages 10a, 10b, and 10c can be individually controlled. The operation of the water flow control valve 12 is controlled by the MCV control unit 20 (control unit, prediction means).

[0035] A water pressure sensor 21 (pressure acquisition unit) that detects the pressure of the cooling water in the cooling water passage 10 (water pressure Pw) is provided in the cooling water passage 10 between the water flow control valve 12 and the pump 11, more specifically, in a position close to the cooling water inlet of the pump 11, and a water temperature sensor 22 (water temperature acquisition unit) that detects the temperature of the cooling water (water temperature Tw) is also provided.

[0036] The information detected by the water pressure sensor 21 and the water temperature sensor 22 is input to the MCV control unit 20. The MCV control unit 20 is composed of an input / output device (not shown), a memory device (ROM, RAM, etc.) used to store control programs, control maps, etc., a central processing unit (CPU), a timer counter, etc. The MCV control unit 20 inputs the information detected by the water pressure sensor 21 and the water temperature sensor 22, and information corresponding to the output of the pump 11, such as the engine rotation speed Ne, from a rotation speed sensor 25 (rotation speed acquisition unit, output acquisition unit), and controls the water flow control valve 12.

[0037] The MCV control unit 20 may be provided in a main control unit that is mounted on the vehicle and performs overall control of the vehicle, or may be provided in the vehicle separately from the main control unit.

[0038] 2 is a flowchart showing a control procedure of the first embodiment of the water flow control valve 12, which is executed by the MCV control unit 20. The control of the water flow control valve 12 shown in FIG. 2 is repeatedly executed when the power of the vehicle is turned on.

[0039] First, in step S10, the water temperature Tw is input from the water temperature sensor 22, and it is determined whether or not it is equal to or higher than a predetermined temperature Twa. The predetermined temperature Twa may be set, for example, to the warm-up completion temperature of the engine 2. If the water temperature Tw is equal to or higher than the predetermined temperature Twa, the process proceeds to step S20. If the water temperature Tw is lower than the predetermined temperature Twa, the process proceeds to step S30.

[0040] In step S20, normal control (normal control mode) is executed. Normal control is a control in which the opening of the water flow control valve 12 is increased as the water temperature Tw increases. Specifically, as shown in FIG. 3, for example, when the water temperature Tw is lower than a predetermined temperature (warm-up completion temperature) Twa, the first cooling water passage 10a is closed (opening = 0). When the water temperature Tw becomes higher than the warm-up completion temperature Twa of the engine 2, the water flow control valve 12 is controlled so that the opening of the first cooling water passage 10a increases as the water temperature Tw increases.

[0041] In this embodiment, the second cooling water passage 10b is closed when the water temperature Tw is lower than a temperature Twb, which is lower than the warm-up completion temperature Twa, and is opened when the water temperature Tw reaches or exceeds the temperature Twb. Therefore, when the water temperature Tw is lower than a predetermined temperature Twa but equal to or higher than the temperature Twb, the first cooling water passage 10a is closed and the second cooling water passage 10b is open. However, since the second cooling water passage 10b has a smaller diameter than the first cooling water passage 10a, in this embodiment, the state in which the first cooling water passage 10a is closed and the second cooling water passage 10b is open is also considered to be the state in which the "water flow control valve 12 is closed." Then, this routine ends.

[0042] In step S30, the water flow control valve 12 is controlled to be closed. In this embodiment, the opening degree of the third coolant passage 10c is changed depending on whether the water temperature Tw is equal to or higher than the warm-up completion temperature Tw. However, all of the coolant passages (the first coolant passage 10a, the second coolant passage 10b, and the third coolant passage 10c) may be controlled to be completely closed, or the opening degree of the third coolant passage 10c may be set to be variable. That is, it is sufficient that at least the opening degree of the first coolant passage 10a (the amount of coolant flowing through the first coolant passage 10a) is at a level (zero to very small) that promotes warm-up of the engine 2. Then, the process proceeds to step S50.

[0043] In step S50, the water temperature Tw of the cooling water near the pump inlet is input from the water temperature sensor 22, and a water temperature-water pressure map is used to calculate a first threshold value Pwa (first pressure) of the water pressure for determining whether the valve is open or closed at that water temperature Tw. The water temperature-water pressure map is, for example, a map as shown in FIG. 4, and is set so that the first threshold value Pwa increases as the water temperature Tw increases between 40°C and 100°C. In other words, the higher the water temperature Tw, the more likely it is that air bubbles will be generated, even if the degree of water pressure drop caused by the pump 11 is small. Then, the process proceeds to step S60.

[0044] In step S60, the water pressure Pw at the inlet of the pump 11 is input from the water pressure sensor 21, and it is determined whether the water pressure Pw is lower than the first threshold value Pwa calculated in step S60. If the water pressure Pw is lower than the first threshold value Pwa, the process proceeds to step S80. If the water pressure Pw is equal to or higher than the first threshold value Pwa, the process proceeds to step S160.

[0045] In step S80, all inlet passages (first cooling water passage 10a, second cooling water passage 10b, third cooling water passage 10c) of the water flow control valve 12 are opened (open mode). Note that in this step, not all of the cooling water passages 10a, 10b, and 10c may be completely opened, but any one of the cooling water passages may be opened. In this step, it is preferable to open at least the first cooling water passage 10a, which has the largest diameter. In this step, it is sufficient to control the water pressure upstream of the pump 11 to be higher than when the water flow control valve 12 was closed in step S30. Then, the process proceeds to step 140.

[0046] In step S140, the rotation speed (number of rotations Ne (rpm)) of the engine 2 is input, and it is determined whether the rotation speed Ne is equal to or less than a predetermined first rotation speed Ne. The first rotation speed Ne may be set to a rotation speed that provides an output from the pump 11 at which bubble generation is zero or less than a predetermined level. In this embodiment, the pump 11 is a mechanical pump, and therefore the output of the pump 11 varies depending on the rotation speed of the engine 2. If the pump 11 is an electric pump, the output of the pump 11 may be controlled so that the output of the pump 11 varies depending on the rotation speed of the engine 2. If the rotation speed Ne is equal to or less than the first rotation speed Ne, i.e., if bubbles are unlikely to be generated, the process proceeds to step S150. If the rotation speed Ne is greater than the first rotation speed Ne, the process returns from this routine.

[0047] In step S150, similar to step S30, the water flow control valve 12 is controlled to close all of the inlet passages (the first cooling water passage 10a, the second cooling water passage 10b, and the third cooling water passage 10c). Then, the routine returns. In step S160, the water flow control valve 12 is kept closed as in step S30. Then, the routine returns.

[0048] As described above, in the cooling water circulation system 1 of this embodiment, when the water temperature Tw is lower than the predetermined temperature Twa, which is the warm-up completion temperature, the water flow control valve 12 is closed to promote an increase in the water temperature. This allows the temperature of the engine 2 to be quickly increased during a cold start of the engine 2, thereby improving fuel efficiency and exhaust performance.

[0049] If the water temperature Tw is below the predetermined temperature Twa and the water flow control valve 12 is closed, the water pressure upstream of the pump 11 will decrease, causing air bubbles to form, which may reduce the durability of the pump 11.

[0050] In contrast, the MCV control unit 20 in the coolant circulation system 1 of this embodiment predicts the generation of bubbles based on the water temperature Tw and water pressure Pw when the water temperature Tw is below the predetermined temperature Twa, and opens the water flow control valve 12 when the generation of bubbles is predicted, thereby promoting the circulation of the coolant and suppressing a drop in water pressure upstream of the pump 11, suppressing the generation of bubbles, and protecting the pump 11. When the water temperature Tw is high, equal to or higher than the predetermined temperature Twa, the water flow control valve 12 is not opened or closed based on the prediction of the generation of bubbles, but rather performs normal control to open and close the water flow control valve 12 based on the water temperature Tw, thereby allowing the coolant circulation system 1 to appropriately control the temperature of the engine 2.

[0051] The MCV control unit 20 predicts that bubbles will occur when the water pressure Pw detected by the water pressure sensor 21 located upstream of the pump 11 falls below the first threshold value Pwa, so that it can predict the occurrence of bubbles with a simple configuration.

[0052] The first threshold value Pwa is changed based on the water temperature Tw detected by the water temperature sensor 22 provided upstream of the pump 11. Specifically, the first threshold value Pwa is set to increase as the water temperature Tw increases. Note that as the water temperature Tw increases, the pressure at which bubbles begin to form in the cooling water increases, so by changing the first threshold value Pwa in this way according to the water temperature Tw, it becomes possible to accurately predict the formation of bubbles.

[0053] Furthermore, even if the water pressure Pw is equal to or lower than the first threshold value Pwa while the water flow control valve 12 is closed, the MCV control unit 20 controls the water flow control valve 12 to close if the rotation speed Ne of the engine 2 is equal to or lower than the first rotation speed Ne. The closed state of the water flow control valve 12 indicates a state where warm-up is required. However, when the rotation speed Ne of the engine 2 is low and the output of the pump 11 is low, and the amount of bubbles generated upstream of the pump 11 is small, the durability of the pump 11 is unlikely to deteriorate. Therefore, the water flow control valve 12 is maintained closed to promote warm-up of the engine 2. Furthermore, by closing the water flow control valve 12 and allowing bubbles to be generated, the cooling capacity of the engine 2 by the coolant is reduced, thereby promoting warm-up.

[0054] Furthermore, after the generation of bubbles is predicted and the water flow control valve 12 is opened, even if the water temperature Tw is below the predetermined temperature Twa and the water pressure Pw exceeds the first threshold value Pwa, the water flow control valve 12 will remain open as long as the rotation speed Ne of the engine 2 exceeds the first rotation speed Ne1, thereby preventing the water flow control valve 12 from repeatedly opening and closing even if the water pressure Pw fluctuates around the first threshold value Pwa.

[0055] The coolant passage 10 of the coolant circulation system 1 of this embodiment includes a first coolant passage 10a through which the coolant circulates by passing through a radiator 15, and coolant passages (second coolant passage 10b and third coolant passage 10c) through which the coolant circulates without passing through the radiator 15. A water flow control valve 12 is provided at the junction of the first coolant passage 10a and the other passages (second coolant passage 10b and third coolant passage 10c) to open and close each of the coolant passages 10a, 10b, and 10c. Furthermore, a pump 11 is provided immediately downstream of the water flow control valve 12. The MCV control unit 20 controls the water flow control valve 12 based on the detection values ​​of a water temperature sensor 22 and a water pressure sensor 21, which are disposed in the coolant passage 10 between the pump 11 and the water flow control valve 12, to suppress the generation of air bubbles between the pump 11 and the water flow control valve 12.

[0056] The water flow control valve 12 is efficiently located at the confluence to control the amount of cooling water in each of the first cooling water passage 10a and the other passages (the second cooling water passage 10b and the third cooling water passage 10c). The pump 11 supplies cooling water to each of the first cooling water passage 10a and the other passages (the second cooling water passage 10b and the third cooling water passage 10c), so it is efficient to locate the pump 11 downstream of the confluence. However, in this configuration, the opening and closing of the water flow control valve 12 reduces the water pressure downstream of the water flow control valve 12 and upstream of the pump 11, making it more likely for bubbles to form.

[0057] In contrast, in this embodiment, by controlling the water flow control valve 12 based on the predicted results of bubble generation, it is possible to suppress the generation of bubbles between the pump 11 and the water flow control valve 12 even in a cooling water passage configuration in which bubbles are likely to occur.

[0058] Next, the control of the water flow control valve 12 of the second embodiment will be described with reference to Fig. 5. In this embodiment, the water flow control valve 12 can independently control the opening degree of each of the cooling water passages 10a, 10b, and 10c.

[0059] 5 is a flowchart showing a control procedure for the water flow control valve 12 of the second embodiment in the cooling water circulation system 1. Only the points different from the control of the first embodiment shown in FIG.

[0060] If the water temperature Tw is lower than the predetermined temperature Twa in step S10, the process proceeds to step S40. In step S40, the water flow control valve 12 is controlled to close. In this step, at least the first cooling water passage 10a and the third cooling water passage 10c are controlled to close. The process then proceeds to steps S50 and S60.

[0061] If the water pressure Pw is lower than the first threshold value Pwa in step S60, the process proceeds to step S90. In step S90, the water flow control valve 12 is controlled to open the third coolant passage 10c. The process then proceeds to step S110.

[0062] In step S110, the current water pressure Pw is input from the water pressure sensor 21, and it is determined whether the water pressure Pw is equal to or greater than a second threshold value Pwb. The second threshold value Pwb is greater than the first threshold value Pwa. If the water pressure Pw is equal to or greater than the second threshold value Pwb, the process proceeds to step S140. If the water pressure Pw is less than the second threshold value Pwb, the process proceeds to step S120.

[0063] In step S120, it is determined whether the state in which the water pressure Pw is less than the second threshold value Pwb has continued for a predetermined time ta. The predetermined time ta is, for example, about 30 seconds, which may be a period of time that allows the change in the water pressure Pw to stabilize after the third coolant passage 10c is opened in step S90. If the state in which the water pressure Pw is less than the second threshold value Pwb has continued for the predetermined time ta, the process proceeds to step S130. If the state in which the water pressure Pw is less than the second threshold value Pwb has not continued for the predetermined time ta, the process returns to step S110.

[0064] In step S130, the water flow control valve 12 is controlled to open the first coolant passage 10a for the radiator 15. Then, the process proceeds to step S140. In the second embodiment, the water flow control valve 12 is closed when the coolant temperature (water temperature Tw) is below a predetermined temperature Twa, and then the third coolant passage 10c is first opened if the water pressure Pw is below a first threshold value Pwa. This prevents a drop in water pressure and suppresses the generation of air bubbles, and keeps the first coolant passage 10a closed, thereby promoting warm-up.

[0065] If the water pressure Pw remains lower than the second threshold value Pwb for a predetermined time ta even after the third cooling water passage 10c is opened, i.e., if the possibility of bubble generation continues, the first cooling water passage 10a is opened. In this way, by opening the first cooling water passage 10a, which has a larger diameter (flow path area) (larger flow rate) than the other cooling water passages 10b, 10c, the water pressure Pw is increased, and the generation of bubbles can be further suppressed. In this way, by changing the cooling water passages 10a, 10b, 10c to be opened in accordance with the water pressure Pw, which is related to the degree of bubble generation, the generation of bubbles can be more effectively suppressed while promoting warm-up.

[0066] When the third cooling water passage 10c is opened in step S90, it is preferable to open it gradually in accordance with the water pressure Pw. This makes it possible to more efficiently suppress the generation of air bubbles and promote warm-up. When the first cooling water passage 10a is opened in step S130, it is preferable to open it to full open in a short time. This makes it possible to more effectively suppress the generation of air bubbles.

[0067] In this embodiment, the presence or absence of bubble generation is determined based on the water pressure Pw, but the degree of bubble generation (amount of generation) may also be determined based on the output of the pump 11 (the rotation speed of the pump 11, for example, the rotation speed of the engine 2 that drives the pump 11). Then, the opening operation of the first cooling water passage 10a for the radiator 15 and the other cooling water passages 10b, 10c may be switched based on the degree of bubble generation.

[0068] For example, when the output of the pump 11 exceeds the first output but is equal to or less than the second output, the degree of bubble generation is considered to be small (only a small amount of bubbles will be generated), and therefore bubble generation can be suppressed by simply slightly opening the water flow control valve 12. Therefore, the third cooling water passage 10c is opened to suppress bubble generation, while the first cooling water passage 10a is not opened, thereby promoting warm-up. When the output of the pump 11 is greater than the second output, the degree of bubble generation is considered to be large (a large amount of bubbles will be generated), and therefore the first cooling water passage 10a is opened to strongly suppress bubble generation. In this embodiment, the degree of bubble generation is determined based on the output of the pump 11, but it may also be determined based on the water pressure Pw. For example, it may be determined that the lower the water pressure Pw, the greater the degree of bubble generation.

[0069] Next, control of the water flow control valve 12 in the third embodiment will be described with reference to Figure 6. Note that, like the second embodiment, the water flow control valve 12 in this embodiment can independently control the opening degree of each of the cooling water passages 10a, 10b, and 10c. This embodiment is also applicable to plug-in hybrid vehicles and hybrid vehicles (hybrid vehicles) that can switch between a series running mode in which the engine 2 drives a generator to generate electricity and the electric motor drives the vehicle, and an engine running mode in which the vehicle is mechanically driven by at least the engine 2, as in parallel running.

[0070] 6 is a flowchart showing a control procedure for the water flow control valve 12 of the third embodiment in the cooling water circulation system 1. Only the points different from the water flow control of the second embodiment shown in FIG. 5 will be described below.

[0071] In step S60, if the water pressure Pw is less than the first threshold value Pwa, the process proceeds to step S70. In step S70, it is determined whether the vehicle's driving mode is series driving. If the vehicle is in series driving, the process proceeds to step S90. If the vehicle is not in series driving, for example, in parallel driving, the process proceeds to step S100. In series driving, as described above, the engine 2 generates electricity and the electric motor drives the vehicle, so the rotation speed of the engine 2 is kept approximately constant. In parallel driving, the engine 2 mechanically drives the driving wheels, so the rotation speed of the engine 2 may become high.

[0072] In step S100, the water flow control valve 12 is controlled to open the first coolant passage 10a for the radiator 15. Then, the process proceeds to step S140.

[0073] As described above, in the third embodiment, in addition to the second embodiment, if the water pressure Pw is less than the first threshold value Pwa, it is determined whether or not series running is in progress, and if series running is not in progress, that is, if there is a possibility that the rotation speed of the engine 2 will increase significantly, as in the case of parallel running, the first cooling water passage 10a is opened to suppress the generation of bubbles.

[0074] Furthermore, when the vehicle is in series running mode, i.e., when the rotation speed of the engine 2 is relatively constant, the third cooling water passage 10c is first opened to increase the water pressure and promote warm-up. Even when the vehicle is in series running mode, if the third cooling water passage 10c is opened as in the second embodiment and the water pressure Pw does not increase to or exceed the second threshold value Pwb, the first cooling water passage 10a is opened to promote an increase in water pressure, thereby suppressing the generation of bubbles and protecting the pump 11.

[0075] The present invention is not limited to the above embodiment, and modifications can be made without departing from the spirit and scope of the invention. The cooling water circulation system 1 of the present embodiment can be applied to engines mounted on various vehicles.

[0076] REFERENCE SIGNS LIST 1 Coolant circulation system 2 Engine (internal combustion engine) 10 Coolant passage 10a First coolant passage (first passage) 10b Second coolant passage (second passage) 10c Third coolant passage (second passage) 11 Pump 12 Water flow control valve (valve) 20 MCV control unit (controller, prediction means) 21 Water pressure sensor (pressure acquisition unit) 22 Water temperature sensor (water temperature acquisition unit) 25 Rotational speed sensor (rotational speed acquisition unit, output acquisition unit)

Claims

1. A cooling water circulation system comprising: a valve provided in a cooling water passage of an internal combustion engine for controlling the flow rate of cooling water; a pump for circulating the cooling water through the cooling water passage; a prediction means for predicting the generation of air bubbles in the cooling water upstream of the pump in the cooling water passage; a water temperature acquisition unit for acquiring the temperature of the cooling water; and a control unit for controlling the operation of the valve, wherein the control unit opens and closes the valve in accordance with the temperature of the cooling water, and opens the valve when the prediction means predicts the generation of air bubbles with the valve closed.

2. The cooling water circulation system according to claim 1, characterized in that a pressure acquisition unit that acquires the pressure of the cooling water is provided upstream of the pump in the cooling water passage, and the prediction means predicts the generation of bubbles when the pressure of the cooling water acquired by the pressure acquisition unit is equal to or lower than a first pressure.

3. The cooling water circulation system according to claim 2, characterized in that the first pressure varies according to the temperature of the cooling water.

4. A cooling water circulation system as described in any one of claims 1 to 3, characterized in that it further comprises a rotational speed acquisition unit that acquires the rotational speed of the internal combustion engine, and the control unit maintains the valve in a closed state if the rotational speed of the internal combustion engine is equal to or lower than a first rotational speed when the prediction means predicts the generation of bubbles with the valve closed.

5. A cooling water circulation system as described in claim 4, further comprising a rotational speed acquisition unit which acquires the rotational speed of the internal combustion engine, wherein the control unit opens the valve when the prediction means predicts the generation of bubbles while the valve is closed, and then maintains the valve in an open state until the rotational speed of the internal combustion engine becomes equal to or lower than a first rotational speed, and closes the valve when the rotational speed becomes equal to or lower than the first rotational speed.

6. A cooling water circulation system as described in any one of claims 1 to 3, characterized in that the cooling water passage has a first passage through which the cooling water circulates by passing through a radiator, and a second passage through which the cooling water circulates without passing through the radiator, the valve is provided at the junction of the first passage and the second passage and is capable of opening and closing the first passage and the second passage, the pump is provided immediately downstream of the valve, and the prediction means predicts the generation of bubbles between the pump and the valve.

7. A cooling water circulation system as described in any one of claims 1 to 3, characterized in that the cooling water passage has a first passage through which the cooling water circulates by passing through a radiator, and a second passage through which the cooling water circulates without passing through a radiator, the valve is provided at the junction of the first passage and the second passage and is capable of opening and closing the first passage and the second passage, and the control unit changes which of the first passage and the second passage is opened depending on the degree of bubble generation predicted by the prediction means when the valve closes the first passage and the second passage.

8. A cooling water circulation system as described in claim 7, further comprising an output acquisition unit which acquires the output of the pump, wherein the prediction means predicts the occurrence of bubbles and predicts that the degree of bubble occurrence is greater as the output of the pump is greater, and the control unit opens the second passage when the prediction means predicts the occurrence of bubbles with the valves closing each of the cooling water passages and the output of the pump exceeds a first output and is equal to or less than a second output which is greater than the first output, and opens the first passage when the output of the pump exceeds the second output.

9. A cooling water circulation system as claimed in any one of claims 1 to 3, characterized in that the cooling water passage has a first passage through which the cooling water circulates by passing through a radiator, and a second passage through which the cooling water circulates without passing through a radiator, the valve is provided at the junction of the first passage and the second passage and is capable of opening and closing the first passage and the second passage, a pressure acquisition unit that acquires the pressure of the cooling water is provided upstream of the pump in the cooling water passage, the prediction means predicts that bubbles will be generated when the pressure of the cooling water acquired by the pressure acquisition unit is equal to or lower than a first pressure, and the control unit opens the second passage when the pressure falls to or lower than the first pressure while the valve is closed on the first passage and the second passage, and thereafter opens the first passage if the pressure does not exceed the first pressure within a predetermined time.

10. A cooling water circulation system as described in any one of claims 1 to 3, characterized in that it is mounted on a hybrid vehicle, the cooling water passage having a first passage through which the cooling water circulates by passing through a radiator, and a second passage through which the cooling water circulates without passing through a radiator, the valve being provided at the junction of the first passage and the second passage and capable of opening and closing the first passage and the second passage, and the control unit opening the second passage during series running and opening the first passage during parallel running when the prediction means predicts the generation of bubbles with the valve closing the first passage and the second passage.

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