Internal combustion engine cooling system

An internal combustion engine cooling system, including: an internal combustion engine; a cooling circuit in which cooling fluid for cooling the internal combustion engine is circulated; a radiator for cooling the cooling fluid; a radiator circuit that branches from the cooling circuit to guide the cooling fluid to the radiator and return the cooling fluid having passed the radiator to the cooling circuit; a thermostat that is provided in a portion where the cooling circuit and the radiator circuit are connected to each other and that opens and closes a path between cooling circuit and the radiator circuit; a heater for heating the thermostat; and a control device for controlling the heater.

TECHNICAL FIELD

The present invention relates to a system for cooling an internal combustion engine.

BACKGROUND ART

In a system for cooling the internal combustion engine provided in a vehicle, an electronically-controlled thermostat including a heater is used as a valve for switching a flow path of cooling water (see Patent Literature 1).

The thermostat is a wax thermostat which opens and closes by utilizing a volume change of wax which occurs with a temperature change. Such a thermostat opens not only when the temperature of the cooling water rises but also when the thermostat is heated by the heater.

In the technique described in Patent Literature 1, the heater is supplied with heater supply power set for each target cooling water temperature and causes the thermostat to open at the target cooling water temperature (see FIGS. 2 and 3 and others in Patent Literature 1).

CITATION LIST

Patent Literature

Patent Literature 1: JP 5152595 B

SUMMARY OF INVENTION

Technical Problem

Patent Literature 1 describes correcting the power to be supplied to the heater after completion of warm-up of the engine depending on a condition such as a deviation between the cooling water temperature and the target cooling water temperature (see FIG. 9 and others in Patent Literature 1) but does not describe timing to start the power supplying to the heater.

In the electronically-controlled wax thermostat, even when the water temperature of the cooling water rises or the heater heats the thermostat, opening response of the thermostat is sometimes delayed by a time required for the volume of wax to change.

For example, when the engine abruptly transitions from a low thermal load range to a high thermal load range during warm-up, the water temperature of the cooling water abruptly rises before the opening of the thermostat, which may impair the performance of cooling engine parts and therefore affect the durability life of the engine.

The present invention has been made in view of the aforementioned points and has an object to provide an internal combustion engine cooling system which can preferably heat a thermostat with a heater.

Solution to Problem

In order to solve the aforementioned problems, an internal combustion engine cooling system of the present invention includes: an internal combustion engine; a cooling circuit in which cooling fluid for cooling the internal combustion engine is circulated; a radiator for cooling the cooling fluid; a radiator circuit which branches from the cooling circuit to guide the cooling fluid to the radiator and return the cooling fluid having passed the radiator to the cooling circuit; a thermostat which is provided in a portion where the cooling circuit and the radiator circuit are connected to each other and which opens and closes a path between cooling circuit and the radiator circuit; a heater for heating the thermostat; and a control device for controlling the heater, wherein the thermostat is in a closed state for blocking the path between the cooling circuit and the radiator circuit below a first predetermined temperature and is in an open state for opening the path between the cooling circuit and the radiator circuit at or above the first predetermined temperature, and the control device starts supplying power to the heater to set the thermostat to the open state, based on rotation speed of the internal combustion engine, engine load of the internal combustion engine, and temperature of the cooling fluid flowing through the thermostat.

In this configuration, the timing of starting the power supplying to the thermostat is determined based on the rotation speed and engine load (air charge ratio) of the internal combustion engine and the water temperature of the cooling fluid flowing through the thermostat. Accordingly, it is possible to preferably heat the thermostat with the heater and prevent abnormal temperature rise of the cooling fluid.

The internal combustion engine cooling system may be configured such that the control device includes a target temperature map in which the rotation speed and the engine load of the internal combustion engine are associated with a target temperature of the cooling fluid flowing through the thermostat, and starts supplying power to the heater to set the thermostat to the open state when the target temperature associated with the rotation speed and the engine load is equal to or lower than a second predetermined temperature lower than the first predetermined temperature and a difference between the target temperature and the temperature of the cooling fluid is larger than a predetermined value.

In this configuration, when the internal combustion engine is in a high thermal load state, it is possible to preferably heat the thermostat with the heater and prevent the abnormal water temperature rise of the cooling water.

The internal combustion engine cooling system may be configured such that the control device performs duty control on the heater such that the larger the difference between the target temperature and the temperature of the cooling fluid is, the higher a duty ratio in the power supplying is.

In this configuration, for example, when the temperature of the cooling fluid exceeds the target temperature, it is possible to increase the duty ratio of the heater and increase the flow rate of the cooling fluid to the radiator.

The internal combustion engine cooling system may be configured such that, when the target temperature of the cooling fluid is higher than the second predetermined temperature and is lower than the first predetermined temperature and the temperature of the cooling fluid is lower than the target temperature or when the target temperature of the cooling fluid is the second predetermined temperature or lower and the difference between the target temperature and the temperature of the cooling fluid is equal to or smaller than the predetermined value, the control device performs standby power supplying to the heater within a range in which the thermostat is maintained in the closed state.

In this configuration, prior to the power supplying (pre-power supplying and main power supplying) to the heater, the standby power supplying to the heater is performed within the range in which the thermostat is maintained in the closed state. Accordingly it is possible to preheat the thermostat and improve opening response.

Furthermore, combining the pre-power supplying and the standby power supplying can increase the predetermined value (target temperature−detected temperature of cooling fluid) which is a threshold for the pre-power supplying (that is bring the predetermined value closer to zero).

The internal combustion engine cooling system may be configured such that the control device performs duty control on the heater such that the higher the temperature of the cooling fluid is, the lower a duty ratio in the standby power supplying is.

In this configuration, the duty control is performed on the heater such that the higher the temperature of the cooling fluid is, the lower the duty ratio in the standby power supplying is. Accordingly, the heater can be preferably preheated within the range in which the thermostat is maintained in the closed state.

Moreover, an internal combustion engine cooling system of the present invention includes: an internal combustion engine; a cooling circuit in which cooling fluid for cooling the internal combustion engine is circulated; a radiator for cooling the cooling fluid; a radiator circuit which branches from the cooling circuit to guide the cooling fluid to the radiator and return the cooling fluid having passed the radiator to the cooling circuit; a thermostat which is provided in a portion where the cooling circuit and the radiator circuit are connected to each other and which opens and closes a path between cooling circuit and the radiator circuit; a heater for heating the thermostat; and a control device for controlling the heater, wherein the thermostat is in a closed state for blocking the path between the cooling circuit and the radiator circuit below a first predetermined temperature and is in an open state for opening the path between the cooling circuit and the radiator circuit at or above the first predetermined temperature, and when a target temperature of the cooling fluid flowing through the thermostat is higher than a second predetermined temperature which is lower than the first predetermined temperature and is lower than the first predetermined temperature and a temperature of the cooling fluid flowing through the thermostat is lower than the target temperature or when the target temperature of the cooling fluid is at or lower than the second predetermined temperature and a difference between the target temperature and the temperature of the cooling fluid is equal to or smaller than a predetermined value, the control device performs standby power supplying to the heater within a range in which the thermostat is maintained in the closed state.

In this configuration, it is possible to preheat the thermostat and improve opening response of the thermostat.

Advantageous Effects of Invention

According to the present invention, the thermostat can be preferably heated with the heater.

DESCRIPTION OF EMBODIMENTS

Next, an embodiment of the present invention is described in detail with reference to the drawings as necessary. As shown inFIGS. 1A and 1B, an internal combustion engine cooling system1according to the embodiment of the present invention is a system for cooling an engine21being an internal combustion engine provided in a vehicle by circulating cooling water being cooling fluid. Arrows inFIGS. 1A and 1Bindicate a flow direction of the cooling water.

The internal combustion engine cooling system1includes a cooling circuit11, a bypass circuit12, a radiator circuit13, and a turbocharger circuit14as circuits through which the cooling water flows.

Moreover, the internal combustion engine cooling system1includes the engine21which is the internal combustion engine, a thermostat22which is an opening-closing valve, a heater core23, a pump24, a radiator25, a turbocharger26, and a gas-liquid separator27on the circuits11to14.

First, the circuits through which the cooling water flows in the internal combustion engine cooling system1are described.

The cooling circuit11is a circuit in which the cooling water for cooling the engine21is circulated.

An upstream end portion of the cooling circuit11is connected to a cooling water outlet21aof the engine21and a downstream end portion of the cooling circuit11is connected to a cooling water inlet21bof the engine21.

The thermostat22, the heater core23, and the pump24are provided on the cooling circuit11in this order from the upstream side (cooling water outlet21aside).

The bypass circuit12is a circuit for causing the cooling water to flow from the thermostat22to a downstream of the heater core23in a closed state of the thermostat22in the cooling circuit11.

An upstream end portion of the bypass circuit12is connected to a portion of the cooling circuit11provided with the thermostat22. A downstream end portion of the bypass circuit12is connected to a portion of the cooling circuit11downstream of the heater core23.

The radiator circuit13is a circuit for returning the cooling water in the cooling circuit11to the cooling circuit11via the radiator25.

An upstream end portion of the radiator circuit13is connected to the portion of the cooling circuit11provided with the thermostat22and a downstream end portion of the radiator circuit13is connected to a portion of the cooling circuit11provided with the pump24.

The radiator25is provided on the radiator circuit13.

The turbocharger circuit14is a circuit for returning the cooling water in the cooling circuit11to the cooling circuit11via the turbocharger26.

An upstream end portion of the turbocharger circuit14is connected to the cooling water outlet21aof the engine21and a downstream end portion of the turbocharger circuit14is connected to the portion of the cooling circuit11provided with the pump24.

The turbocharger26and the gas-liquid separator27are provided on the turbocharger circuit14.

Next, devices provided on the circuits11to14in the internal combustion engine cooling system1are described.

The engine21is a drive source of the vehicle provided with the engine21and includes a cylinder block, a cylinder head, pistons, connecting rods, a crank shaft, and the like which are not shown.

The thermostat22is provided in a connection portion between the cooling circuit11and the radiator circuit13and is a valve which opens and closes a path between the cooling circuit11and the radiator circuit13.

Specifically, the thermostat22is a so-called wax thermostat and opens and closes an inlet from the cooling circuit11to the radiator circuit13by utilizing a volume change of wax which occurs with a temperature change.

In the embodiment, the thermostat22is in a closed state below a first predetermined temperature (for example, 105° C.) to block the flow of cooling water from the cooling circuit11to the radiator circuit13and allow the flow of cooling water from the cooling circuit11to the bypass circuit12. The thermostat22is in an open state at and above the first predetermined temperature to allow the flow of cooling water from the cooling circuit11to the radiator circuit13and block the flow of cooling water from the cooling circuit11to the bypass circuit12.

Moreover, the thermostat22is a so-called electronically-controlled thermostat and integrally includes a heater42to be described later. The heater42generates heat by being controlled by a control device50and the thermostat22can open and close by being heated by thus-generated heat (seeFIG. 2).

The heater core23is provided in the cooling circuit11and is a device which exchanges heat between the cooling water heated by heat exchange in the engine21and air introduced into the heater core23from a vehicle cabin and heats the air by such heat exchange. The air heated by the heater core23is returned into the vehicle cabin.

The pump24is provided at the portion where the cooling circuit11is connected to the radiator circuit13and the turbocharger circuit14and pumps out the cooling water in the cooling circuit11, the radiator circuit13, and the turbocharger circuit14to generate a flow of cooling water toward the cooling water inlet21bof the engine21, based on control of a motor41performed by the control device50to be described later.

The radiator25is provided on the radiator circuit13and is a device which exchanges heat between the cooling water heated by the heat exchange in the engine21and air sent to the radiator25by traveling of the vehicle and cools the cooling water by such heat exchange.

The turbocharger26is provided on the turbocharger circuit14and is a device which compresses air and supplies it to the engine21based on the control of the control device50to be described later. The turbocharger26is cooled by the cooling water flowing through the turbocharger circuit14.

The gas-liquid separator27is provided on the turbocharger circuit14and is a device which separates gas included in the cooling water from the cooling water.

<Sensors, Control Device, and the Like>

As shown inFIG. 2, the internal combustion engine cooling system1includes an intake volume sensor31, a rotation speed sensor32, a water temperature sensor33, the motor41, the heater42, and the control device50.

The intake volume sensor31is a sensor which detects an intake volume of air to be taken in from intake valves of the engine21as a parameter for calculating an intake air volume being an example of an engine load of the engine21and which outputs the detected intake volume to the control device50.

The rotation speed sensor32is a sensor which detects the rotation speed of a crank shaft being an output shaft of the engine21as a parameter for calculating the intake air volume being an example of the engine load of the engine21and which outputs the detected rotation speed to the control device50.

The water temperature sensor33is a sensor which detects the temperature (water temperature) of the cooling water flowing through the portion of the cooling circuit11provided with the thermostat22(that is the cooling water heated by the heat exchange in the engine21) and outputs the detected water temperature to the control device50.

The motor41is made to rotate by the control of the control device50and activates the pump24described above.

The heater42is provided integrally with the thermostat22. Electric power is supplied to the heater42by the control of the control device50and the heater22thereby generates heat to heat the thermostat22.

Duty control can be performed to control the amount of power supplied to the heater42by the control device50.

The control device50is an engine ECU (Electrical Control Unit) for controlling the internal combustion engine cooling system1including the engine21and includes a CPU (Central Processing Unit), a ROM (Read-Only Memory), a RAM (Random Access Memory), an input-output circuit, and the like.

The control device50includes a memory51, an engine load measurement unit52, a target water temperature calculator53, and a heater controller54as function units for controlling the heater42.

A target water temperature map51a, a main power supplying duty ratio map51b, a pre-power supplying duty ratio map51c, a standby power supplying duty ratio map51dare stored in the memory51.

As shown inFIG. 3A, the target water temperature map51ais a map in which an air charge ratio [%], the rotation speed [rpm] of the engine21, and the target water temperature [° C.] of the cooling water are associated with one another.

In the embodiment, the target water temperature in the target water temperature map51ais set such that the higher the air charge ratio of the engine21is, the lower the target water temperature is, and the higher the rotation speed of the engine21is, the lower the target water temperature is.

<<Main Power Supplying Duty Ratio Map>>

As shown inFIG. 3B, the main power supplying duty ratio map51bis a map used to perform main power supplying and the target water temperature [° C.] of the cooling water, a difference [° C.] between the target water temperature of the cooling water and the water temperature detected by the water temperature sensor33, and a duty ratio of the heater42in the main power supplying (main heating of the thermostat22) are associated with one another.

As shown inFIG. 4A, the pre-power supplying duty ratio map51cis a map used to perform pre-power supplying in a warm-up process at a high thermal load and the engine rotation speed [rpm], the air charge ratio [%] of the engine21, and a duty ratio of the heater42in the pre-power supplying (preheating of the thermostat22) are associated with one another.

In the embodiment, in the pre-power supplying duty ratio map51c, a power supplying duty ratio is set to be higher than zero under a high thermal load condition, based on the engine rotation speed and the air charge ratio of the engine21.

Moreover, the pre-power supplying duty ratio map51cis set to be used when the difference between the target water temperature of the cooling water and the water temperature detected by the water temperature sensor33is larger than a predetermined value (for example, −5° C.).

<<Standby Power Supplying Duty Ratio Map>>

As shown inFIG. 4B, the standby power supplying duty ratio map51dis a map in which the water temperature [° C.] detected by the water temperature sensor33and the duty ratio of the heater42in standby power supplying are associated with each other.

In the embodiment, the duty ratio in the standby power supplying duty ratio map51dis set within a range in which the thermostat22is maintained in the closed state, that is a range below the duty ratio at which the thermostat22opens (lower than the thermostat22opening duty ratio inFIG. 4B).

Moreover, the duty ratio in the standby power supplying duty ratio map51dis set such that, in a range equal to or above certain water temperature, the higher the water temperature detected by the water temperature sensor33is, the lower the duty ratio is.

The engine load measurement unit52obtains an engine load calculation parameter outputted from an engine load calculation parameter detector and measures (calculates) the engine load of the engine21based on the obtained engine load calculation parameter.

In the embodiment, the engine load measurement unit52obtains the intake volume of the engine21detected by the intake volume sensor31and the rotation speed of the engine21detected by the rotation speed sensor32, measures (calculates) the air charge ratio as the engine load based on the obtained intake volume and rotation speed, and outputs the measured air charge ratio to the target water temperature calculator53.

The air charge ratio is a ratio of the volume of air taken in by the engine21.

Note that the engine load measurement unit52can also measure the air charge ratio based on an operating condition of the turbocharger26in addition to the intake volume and the rotation speed.

The target water temperature calculator53obtains the engine load (air charge ratio) measured by the engine load measurement unit52and the rotation speed of the engine21detected by the rotation speed sensor32and calculates the target water temperature of the cooling water based on the obtained engine load and rotation speed.

In the embodiment, the target water temperature calculator53calculates the target water temperature by referring to the target water temperature map51abased on the obtained air charge ratio and rotation speed to read the target water temperature corresponding to the obtained air charge ratio and rotation speed, and outputs the calculated target water temperature to the heater controller54.

The heater controller54obtains the target water temperature calculated by the target water temperature calculator53and the water temperature (actual water temperature) of the cooling water detected by the water temperature sensor33and controls the heater42based on the obtained target water temperature and water temperature.

In the embodiment, the heater controller54executes control of performing the pre-power supplying and the main power supplying to the heater42(preheating and main heating of the thermostat22) to cause the thermostat22to open in a warm-up process performed when the engine21is in a high thermal load state, executes control of performing the main power supplying to the heater42(main heating of the thermostat22) to cause the thermostat22to open in a warm-up process performed when the engine21is in an intermediate thermal load state, and executes control of performing the standby power supplying to the heater42(standby heating of the thermostat22) in a warm-up process performed when the engine21is in an intermediate or low thermal load state. Methods of the control are described in detail in operation examples to be described later.

The target water temperature is temperature at which the thermostat22is to be opened. When the target water temperature is lower than the first predetermined temperature, the heater controller54performs the main power supplying to the heater42in the case where the water temperature detected by the water temperature sensor33is the target water temperature or higher.

The first predetermined temperature is a temperature at which the thermostat22opens, and is set as the highest value of the target water temperature in the target water temperature map51a.

A second predetermined temperature is set to be the lowest value of the target water temperature in the target water temperature map51aor higher and lower than the highest value of the target water temperature in the target water temperature map51a(set to be the lowest value in the embodiment).

A predetermined value relating to the difference between the target water temperature and the water temperature is set such that the heater controller54performs the pre-power supplying to the heater42when the temperature difference between the water temperature detected by the water temperature sensor33and the target water temperature is larger than the predetermined value. Specifically, the thermostat22is set such that performing the pre-power supplying causes the thermostat22to open when the water temperature reaches the target water temperature.

Next, a first operation example of the internal combustion engine cooling system1is described. In an example of regions indicating the warm-up process and a period after the warm-up shown inFIG. 5B, the target temperature at the low thermal load is set to be equal to the first predetermined temperature and the target temperature at the high thermal load is set be equal to the second predetermined temperature.

As shown inFIG. 5A, when the rotation speed of the engine21and the torque of the engine21are both low, the thermal load of the engine21is low. When either the rotation speed of the engine21or the torque of the engine21is high, the thermal load of the engine21is high.

<<Warm-Up Process at Low Thermal Load>>

As shown inFIG. 5B, when the water temperature of the engine21is low (the first predetermined temperature (for example, 105° C.) or lower) and the thermal load of the engine21is low (in other words, necessity of cooling the engine21is relatively low and the target water temperature is set high), the heater controller54of the control device50does not supply power to the heater42.

In this case, the internal combustion engine cooling system1is in a state where the thermostat22closes the radiator circuit13as shown inFIG. 1A.

In this state, since the cooling water in the internal combustion engine cooling system1does not flow through the radiator25to be cooled, the engine21is warmed up.

As shown inFIG. 5B, when the water temperature of the cooling water rises in the warm-up process at the low thermal load and the water temperature of the cooling water reaches the first predetermined temperature (105° C., that is the opening temperature of the thermostat22), the internal combustion engine cooling system1is in a state where, as shown inFIG. 1B, the thermostat22opens the radiator circuit13without the heater controller54of the control device50supplying power to the heater42.

In this state, since part of the cooling water in the internal combustion engine cooling system1flows through the radiator25to be cooled, the engine21is cooled.

<<Warm-Up Process at Intermediate Thermal Load>>

As shown inFIG. 5B, when the water temperature of the engine21is low (the first predetermined temperature (105° C.) or lower) and the thermal load of the engine21is low (in other words, necessity of cooling the engine21is relatively low and the target water temperature is set high), the heater controller54of the control device50does not supply power to the heater42.

In this case, the internal combustion engine cooling system1is in a state where the thermostat22closes the radiator circuit13as shown inFIG. 1A.

In this state, since the cooling water in the internal combustion engine cooling system1does not flow through the radiator25to be cooled, the engine21is warmed up.

<<After Warm-Up at Intermediate Thermal Load: Main Heating of Thermostat22>>

As shown inFIG. 5B, when the water temperature of the cooling water rises in the warm-up process at the intermediate thermal load and the water temperature of the cooling water reaches the target water temperature lower than the first predetermined temperature (for example, 95° C.), the heater controller54of the control device50starts to supply power to the heater42(main power supply). In the main power supplying duty ratio map51bofFIG. 3B, the duty ratio in the main power supply is set to be higher as the difference between the target water temperature and the water temperature is larger, in other words, the smaller the difference between the target water temperature and the water temperature is, the lower the duty ratio is. The heater controller54performs the main power supplying to the heater42by referring to such a power supplying duty ratio map.

In this case, the internal combustion engine cooling system1is in a state where the thermostat22opens the radiator circuit13as shown inFIG. 1B.

In this state, since part of the cooling water in the internal combustion engine cooling system1flows through the radiator25to be cooled, the engine21is cooled.

<<Warm-Up Process at High Thermal Load: Preheating of Thermostat22>>

As shown inFIG. 5B, when the water temperature of the engine21is low and the thermal load of the engine21is high (in other words, necessity of cooling the engine21is relatively high and the target water temperature is set low), the heater controller54of the control device50supplies power to the heater42(pre-power supplying) in the case where the difference between the target water temperature and the water temperature of the cooling water is larger than a predetermined value (−5° C.). The duty ratio in the pre-power supplying is 100% at the high thermal load as shown in the pre-power supplying duty ratio map51cofFIG. 4A.

In this case, the internal combustion engine cooling system1is in a state where the thermostat22opens the radiator circuit13and closes the bypass circuit12as shown inFIG. 1B.

In this state, since part of the cooling water in the internal combustion engine cooling system1flows through the radiator25to be cooled, the engine21is cooled.

Here, the heater controller54refers to the pre-power supplying duty ratio map51cbased on the obtained engine rotation speed and air charge ratio to read the duty ratio corresponding to the obtained engine rotation speed and air charge ratio, and performs the duty control on the heater42based on the read duty ratio.

<<After Warm-Up at High Thermal Load: Main Heating of Thermostat22>>

As shown inFIG. 5B, when the water temperature of the cooling water rises in the warm-up process at the high thermal load and the difference between the target water temperature and the detected water temperature of the cooling water is smaller than the predetermined value (−5° C.), in the internal combustion engine cooling system1, as shown inFIG. 1B, the heater controller54of the control device50continuously supplies power to the heater42(main power supplying). In the power supplying duty ratio map51bofFIG. 3B, the duty ratio in the main power supplying is shown in a region where the target water temperature is high and the difference between the target water temperature and the water temperature is equal to or smaller than 0° C.

In this state, since part of the cooling water in the internal combustion engine cooling system1flows through the radiator25to be cooled, the engine21is cooled.

As shown by the dotted line inFIG. 6B, in the internal combustion engine cooling system1, when no pre-power supplying is performed in the warm-up process at the high thermal load, the heater controller54starts supplying power to the heater42at time t3when the water temperature of the cooling water detected by the water temperature sensor33reaches the target water temperature (90° C.) and then causes the thermostat22to open at time t4. In this case, the water temperature of the cooling water at the time when the thermostat22opens is 120° C. which is higher than 90° C. being the target water temperature (seeFIG. 6C).

Meanwhile, as shown by the solid line inFIG. 6B, in the internal combustion engine cooling system1, when the pre-power supplying is performed in the warm-up process at the high thermal load, the heater controller54starts supplying power to the heater42at time t1before the time t3and then causes the thermostat22to open at time t2before the time t4. In this case, the water temperature of the cooling water at the time when the thermostat22opens is 90° C. which is the target water temperature (seeFIG. 6C).

Moreover, as shown by the solid line and the dotted line ofFIG. 6D, an inter-cylinder temperature of the engine21in the case where the pre-power supplying is performed is lower than the inter-cylinder temperature of the engine21in the case where no pre-power supplying is performed.

Accordingly, the internal combustion engine cooling system1can guarantee a certain level of the inter-cylinder temperature of the engine21by performing the pre-power supplying.

Next, a second operation example of the internal combustion engine cooling system1is described while focusing on differences from the first operation example. The second operation example is an operation example in which the standby power supplying to the heater42is performed in the closed state of the thermostat22.

<<Warm-Up Process at Low Thermal Load and Intermediate Thermal Load: Standby Heating of Thermostat22>>

In this operation example, as shown inFIGS. 7A and 7B, in the warm-up process at the low thermal load and the intermediate thermal load, when the target water temperature of the cooling water is higher than the second predetermined temperature (90° C.) and the water temperature of the cooling water is lower than the target temperature at each thermal load (low thermal load: 105° C., intermediate thermal load: 95° C.), the heater controller54of the control device50performs the standby power supplying to the heater42within a range in which the thermostat22is maintained in the closed state. The standby power supplying causes the thermostat22to be heated such that the thermostat22is maintained in the closed state without opening (standby heating).

<<Warm-Up Process at High Thermal Load: Standby Heating of Thermostat22>>

Moreover, as shown inFIG. 7C, in the warm-up process at the high thermal load, when the difference between the target water temperature of the cooling water and the water temperature detected by the water temperature sensor33is equal to or smaller than the predetermined value (−5° C.), the heater controller54of the control device50performs the standby power supplying to the heater42within the range in which the thermostat22is maintained in the closed state. The standby power supplying causes the thermostat22to be heated such that the thermostat22is maintained in the closed state without opening (standby heating).

Specifically, when the target water temperature of the cooling water is higher than the second predetermined temperature and is lower than the first predetermined temperature and the water temperature of the cooling water is lower than the target temperature, that is in the warm-up process at the low thermal load and the intermediate thermal load or when the target water temperature of the cooling water is the second predetermined temperature or lower and the difference between the target water temperature and the water temperature of the cooling water is equal to or smaller than the predetermined value, that is before the pre-power supplying in the warm-up process at the high thermal load, the heater controller54performs the standby power supplying to the heater42within the range in which the thermostat22is maintained in the closed state.

Here, the heater controller54refers to the standby power supplying duty ratio map51dbased on the obtained target water temperature and water temperature to read the duty ratio corresponding to the obtained target water temperature and water temperature, and performs the duty control on the heater42based on the read duty ratio.

In the example shown inFIGS. 8A to 8D, in the warm-up process at the low thermal load before the rise of the rotation speed and torque of the engine21, the standby power supplying is performed prior to the pre-power supplying and the main power supplying as shown inFIGS. 8A to 8D. As shown inFIGS. 8C and 8D, this can reduce the highest value of the water temperature detected by the water temperature sensor33by T1and reduce the highest value of the inter-cylinder temperature of the engine21by T2from those in the case where the pre-power supplying and the main power supplying are performed without performing the standby power supplying.

<Method of Controlling Heater Based on Target Water Temperature and Water Temperature>

Next, the open-closed state of the thermostat and a method of controlling the heater based on the target water temperature and the water temperature detected by the water temperature sensor are described with reference toFIG. 9. The control method described herein is a method corresponding to the second operation example in which the standby power supplying is performed.

In this control example, calculation of the target water temperature by the target water temperature calculator (step S2) and determination of the method of controlling the heater42by the heater controller54(steps S3to S11A, S11B, S11C, and S11D) are repeatedly performed while an ignition switch is ON (YES in step S1).

<<Case of Low Thermal Load>>

When the target water temperature calculated in step S2is the first predetermined temperature (105° C.) or higher (in the embodiment, the target water temperature is equal to the first predetermined temperature) (Yes in step S3), the following operation is performed. When the water temperature detected by the water temperature sensor33is lower than the first predetermined temperature (No in step S4), the heater controller54performs the standby power supplying to the heater42and the thermostat22is in the closed state (step S11A).

Meanwhile, when the water temperature detected by the water temperature sensor33is the first predetermined temperature or higher (Yes in Step S4), the heater controller54does not supply power to the heater42and the thermostat22is in the open state due to the water temperature (step S11D).

<<Case of Intermediate Thermal Load>>

When the target water temperature calculated in step S2is higher than the second predetermined temperature (90° C.) and lower than the first predetermined temperature (105° C.) (No in step S3and YES in step S5), the following operation is performed. When the water temperature is detected by the water temperature sensor33is lower than the target water temperature (No in step S6and No in step S7), the heater controller54performs the standby power supplying to the heater42and the thermostat22is in the closed state (step S11A).

Meanwhile, when the water temperature detected by the water temperature sensor33is the target water temperature or higher (Yes in step S7), the heater controller54performs the main power supplying to the heater42and the thermostat22is in the open state (step S11C). In step S11C, the heater controller54performs the main power supplying to the heater42also when the detected water temperature is higher than the first predetermined temperature to maintain the detected water temperature constantly at the target water temperature.

<<Case of High Thermal Load>>

When the water temperature detected by the water temperature sensor33is “target water temperature—predetermined value” or higher (No in step S8, No in step S9, and Yes in step S10), the heater controller54performs the pre-power supplying to the heater42and the thermostat22is in the open state (step S11B).

Meanwhile, when the water temperature detected by the water temperature sensor33is equal to or higher than the target water temperature (No in step S8and Yes in step S9), the heater controller54performs the main power supplying to the heater42and the thermostat22is in the open state (step S11C).

The aforementioned relationships can be summarized as follows.

TABLE 1target temperature ≥waterlower than first predetermined temperaturefirst predeterminedfirst predetermined temperaturetemperaturetemperature or higherthermostatclosedopenheaterstandby power supplyingno power supplyingsecond predetermined temperature <waterlower than target watertarget water temperature or higherfirst predeterminedtarget water temperature <temperaturetemperatureand lower than first predeterminedtemperature or higherfirst predetermined temperaturetemperaturethermostatclosedopenopenheaterstandby power supplyingmain power supplyingmain power supplyingtarget water temperature ≤water“target water temperature -target water temperature or higherfirst predeterminedsecond predetermined temperaturetemperaturepredetermined value” orand lower than first predeterminedtemperature or higherhighertemperaturethermostatopenopenopenheaterpre-power supplyingmain power supplyingmain power supplying

The internal combustion engine cooling system1according to the embodiment of the present invention determines the timing of stating the power supplying to the heater42based on the rotation speed and the engine load (air charge ratio) of the engine21and the water temperature of the cooling water flowing through the thermostat22. Accordingly, it is possible to preferably heat the thermostat22with the heater42and prevent abnormal water temperature rise of the cooling water before the opening of the thermostat22.

Moreover, when the rotation speed and the engine load (air charge ratio) of the engine21fall under the high thermal load condition and the difference between the target water temperature and the water temperature of the cooling water is larger than the predetermined value, the internal combustion engine cooling system1starts supplying power to the heater42. Accordingly, when the engine21is in the high thermal load state, it is possible to preferably heat the thermostat22with the heater42and prevent the abnormal water temperature rise of the cooling water before the opening of the thermostat22.

Furthermore, the internal combustion engine cooling system1performs duty control on the heater42such that the larger the difference between the target water temperature and the water temperature of the cooling water is, the higher the duty ratio in the power supplying is. Accordingly, when the water temperature of the cooling water exceeds the target temperature, it is possible to increase the duty ratio of the heater42and increase the flow rate of the cooling water to the radiator25.

Moreover, prior to the power supplying (pre-power supplying and main power supplying) to the heater42, the internal combustion engine cooling system1performs the standby power supplying to the heater42within the range in which the thermostat22is maintained in the closed state. Accordingly it is possible to preheat the thermostat22and improve opening response.

Furthermore, combining the pre-power supplying and the standby power supplying can decrease the predetermined value (target water temperature−water temperature) which is a threshold for the pre-power supplying (that is bring the predetermined value closer to zero).

Moreover, the internal combustion engine cooling system1performs the duty control on the heater42such that the higher the water temperature of the cooling water is, the lower the duty ratio in the standby power supplying is. Accordingly, the heater42can be preferably preheated within the range in which the thermostat22is maintained in the closed state.

The embodiment of the present invention has been described above but the present invention is not limited to the aforementioned embodiment and appropriate changes can be made within a scope not departing from the spirit of the present invention.

For example, the method of measuring (calculating) the air charge ratio as the engine load is not limited to that described above. For example, the engine load measurement unit52may measure (calculate) the air charge ratio based on the rotation speed and a throttle opening degree or a boost (intake negative pressure) of the engine21.

Moreover, the engine load measurement unit52may be configured to measure (calculate) an engine load other than the air charge ratio.

Specifically, the engine load measurement unit52only has to be configured to obtain the engine load calculation parameter detected by the engine load calculation parameter detector and measure (calculate) the engine load of the engine21based on the obtained engine load calculation parameter.

Moreover, the predetermined value which is the threshold for the pre-power supplying may be set to vary depending on the target water temperature.

REFERENCE SIGNS LIST