Control method for cooling system

A control method for a cooling system is provided. The method includes determining whether the output signals of a first coolant temperature sensor and a second coolant temperature sensor satisfy a predetermined coolant overheating condition. A coolant control valve unit is operated to move the cam to a maximum position when the predetermined coolant overheating condition is satisfied. Additionally, a control temperature is determined according to an output signal of the first coolant temperature sensor and the second coolant temperature sensor and an operation of the injector is limited according to the determined control temperature.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean Patent Application No. 10-2018-0098122 filed on Aug. 22, 2018, the entire contents of which are incorporated herein by reference.

BACKGROUND

(a) Field of the Invention

The present invention relates to a cooling system control, and more particularly, to a method for controlling a cooling system that prevents coolant boiling and the like.

(b) Description of the Related Art

One developed the integrated heat management technologies is a separation cooling technique which improves the fuel efficiency by independently adjusting a coolant temperature of a cylinder head and an engine block. Mainly, a temperature of the cylinder head is maintained in low temperature to reduce NOx generation and knocking, and a temperature of the engine block is maintained in high temperature and thus, fuel efficiency may be improved.

Even when separate cooling is applied, the coolant boiling point is the same since the cooling system uses one loop. Therefore, the temperature of the coolant of the engine block may increase thus causing boiling to occur which may damage the heat exchange element or the engine.

SUMMARY

The present invention provides a control method of a cooling system capable of preventing coolant boiling and the like. In particular, the present invention provides a control method for preventing coolant boiling in an engine block of a cooling system that independently adjusts coolant of a cylinder head and an engine block.

A control method according to an exemplary embodiment of the present invention may be applied to a cooling system including a coolant control valve unit having a cam which adjusts opening rates of a first coolant passage through which the coolant distributed to a heater flows, a second coolant passage through which the coolant distributed to a radiator flows and a third coolant passage through which the coolant discharged from a cylinder block flows, a vehicle operation state detecting portion having a first coolant temperature sensor configured to measure the temperature of the coolant flowing through the cylinder head and output a corresponding signal, a second coolant temperature sensor configured to measure the temperature of the coolant flowing through the cylinder block, a position sensor configured to sense a rotation of the cam and outputting a corresponding signal, an injector and a controller configured to operate the coolant control valve unit and the injector based on output signals of the vehicle operation state detecting portion.

The control method may include determining, by the controller, whether the output signals of the first coolant temperature sensor and the second coolant temperature sensor satisfy a predetermined coolant overheating condition, operating the coolant control valve unit to move the cam to a maximum position when the predetermined coolant overheating condition is satisfied, determining a control temperature based on an output signal of the first coolant temperature sensor and the second coolant temperature sensor and limiting an operation of the injector based on the determined control temperature.

The maximum position may be a position where the first coolant passage and the third coolant passage are fully opened. The controller may be configured to determine a first correction temperature and a second correction temperature by subtracting a first and second offset values from the output signals of the first coolant temperature sensor and the second coolant temperature sensor respectively and then compare the first and second correction temperatures and set a greater correction temperature to the control temperature.

The operation limitation of the injector may be performed by applying the control temperature to a predetermined table. The coolant control valve unit may be equipped with a fail-safe thermostat for selectively discharging coolant to the radiator. The fail-safe thermostat may be an electrical thermostat and the control method may further include opening the fail-safe thermostat by operating the fail-safe thermostat when the coolant overheating condition is satisfied.

The moving of the cam to the maximum position may be performed by the controller configured to output the movement signal of the cam for a predetermined period of time. The control method of the cooling system according to the exemplary embodiment of the present invention may prevent the coolant boiling of the cooling system to which the engine for independently adjusting the coolant temperature of the cylinder head and the engine block is applied.

DESCRIPTION OF SYMBOLS

DETAILED DESCRIPTION

Hereinafter, an exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings. However, the size and thickness of each component illustrated in the drawings are arbitrarily shown for ease of description and the present invention is not limited thereto, and the thicknesses of portions and regions are exaggerated for clarity.

In addition, parts that are irrelevant to the description are omitted to clearly describe the exemplary embodiments of the present invention, and like reference numerals designate like elements throughout the specification. In the following description, dividing names of components into first, second, and the like is to divide the names because the names of the components are the same, and an order thereof is not particularly limited.

FIG. 1is a block diagram of a control system applicable to a control method according to an exemplary embodiment of the present invention andFIG. 2is a schematic diagram of a control system applicable to a control method according to an exemplary embodiment of the present invention. Referring toFIG. 1andFIG. 2, a cooling system according to an exemplary embodiment of the present invention may include a controller300configured to operate a coolant control valve unit125and an injector340based on an output signal of the vehicle operation state detecting portion10.

The vehicle operation state detecting portion10may include a first coolant temperature sensor12, a second coolant temperature sensor14, an oil temperature sensor16configured to detect engine oil temperature and output a corresponding signal, an ambient temperature sensor18configured to detect ambient air temperature and output a corresponding signal, an accelerator pedal sensor20configured to detect an operation angle of an accelerator pedal and output a corresponding signal, a vehicle speed sensor22configured to detect a speed of a vehicle and output a corresponding signal and a position sensor24.

The controller300may be implemented as one or more microprocessors operating by a predetermined program, and the predetermined program may include a series of commands for performing the exemplary embodiment of the present invention. The cooling system which may be applied to a control system according to an exemplary embodiment of the present invention may include an engine90having an engine block100and a cylinder head105, an low pressure-exhaust gas recirculation (LP-EGR) cooler110, a heater115, a radiator130, an oil cooler135, an oil control valve140, a high pressure-exhaust gas recirculation (HP-EGR) valve145and a coolant pump155.

The coolant pump155may be configured to pump the coolant to a coolant inlet side of the engine block100and the pumped coolant may be distributed to the engine block100and the cylinder head105. The coolant control valve unit125may be configured to receive the coolant from the cylinder head105and adjust an opening rate of a coolant outlet side coolant passage of the engine block100. The first coolant temperature sensor12configured to sense the temperature of the coolant exhausted from the cylinder head105may be disposed on the coolant control valve unit125. The second coolant temperature sensor14configured to sense the temperature of the coolant exhausted from the engine block100may be disposed on the engine block100.

The coolant control valve unit125may be configured to respectively adjust the coolant flow distributed to the heater115and the radiator130. In particular, the coolant may pass through the low pressure EGR cooler110before passing through the heater115, and the heater115and the low pressure EGR cooler110may be disposed in series or in parallel. The heater115may not be limited to an element for heating inside of a vehicle. In other words, the heater115in detailed description and claims may be a heater, an air conditioner, or a heating, ventilation and air conditioning (HVAC) and so on. The coolant control valve unit125may be configured to always supply the coolant to the HP-EGR valve145and the oil cooler135.

Additionally, a part of engine oil circulated along the engine block100and the cylinder head105may be cooled while circulating the oil cooler or oil coolant heat exchanger135, and the oil control valve140may be disposed between the engine90and the oil cooler or oil coolant heat exchanger135to adjust the flow of the oil. The coolant control valve unit125may further include a fail-safe thermostat330for selectively discharging coolant to the radiator130. The fail-safe thermostat330may be an electric thermostat, and the controller300may be configured to operate the fail safe thermostat330. The structure and function of the components according to the exemplary embodiment of the present invention are well known in the art, and detailed description thereof will be omitted.

FIG. 3is a partial detailed perspective view of a coolant control valve unit of a control system applicable to a control method according to an exemplary embodiment of the present invention. Referring toFIG. 3, the coolant control valve unit125may include a cam210, tracks formed to the cam210, rods that contact the tracks, valves connected with the rods and elastic members biasing the valves and the valves may close coolant passages.

A plurality of tracks, for example, a first track320a, a second track320b, and a third track320c, each having a predetermined inclination and height, and a plurality of rods, for example, a first rod215a, a second rod215b, and a third rod215c, may be disposed in a lower portion of the cam210such that the first, second, and third rods215a,215b, and215cthat respectively contact the first, second, and third tracks320a,320b, and320cmay move downward based on a rotation position of the cam210. In addition, the elastic member may include three elastic members, i.e., a first elastic member225a, a second elastic member225b, and a third elastic member225cto respectively elastically support the first, second, and third rods215a,215b, and215c.

While the first, second, and third elastic members225a,225b, and225care compressed based on the rotation position of the cam210, a first valve220a, a second valve220b, and a third valve220crespectively mounted to the first, second, and third rods215a,215b, and215cmay open and close a first coolant passage230a, a second coolant passage230b, and a third coolant passage230c. In particular, opening rates of each passage230a,230b, and230cmay be adjusted according to the rotation position of the cam210.

The controller300may be configured to receive vehicle operation conditions, (e.g., a coolant temperature, an ambient air temperature, a rotation position signal of the position sensor24configured to detect a rotation position of the cam210and so on) and may be configured to operate a motor305and the motor305may change the rotation position of the cam210through a gear box310. The position sensor24may be a sensor configured to directly detect a rotation position of the cam210, or the controller300may be configured to indirectly calculate the rotation position of the cam210by detecting a rotation portion of the motor305using a resolver (not shown). The first coolant path230amay be in fluid communication with the heater115, the second coolant path230bmay be in fluid communication with the radiator130, and the third coolant path230cmay be in fluid communication with the engine block100.

FIG. 4is a graph of control modes of a control system applicable to a control method according to an exemplary embodiment of the present invention. InFIG. 4, the horizontal axis denotes a rotation position of the cam210, and the vertical axis denotes valve lifts (or moving distance) of the respective valves220a,220b, and220c. In particular, lifts of each valve220a,220band220cis proportional to the opening rates of the each coolant passage230a,230b, and230c.

In the first mode, the first, second, and third coolant passages230a,230b, and230ccorresponding to the heater115, the radiator130and the cylinder block100may be blocked and the valve lift is zero. In the second mode, the second and third coolant passages230band230ccorresponding to the radiator130and the engine block100may be closed, and the opening rate of the first coolant passage230acorresponding to the heater115and the LP-EGR cooler110may be adjusted. In the third mode, the third coolant passage230ccorresponding to the engine block100is closed, the opening rate of the second coolant passage230bcorresponding to the radiator130may be adjusted, and the opening rate of the first coolant passage230acorresponding to the heater115and the LP-EGR cooler110may be maximized.

In the fourth mode, the opening rate of the third coolant passage230ccorresponding to the engine block100may be adjusted, the opening rate of the second coolant passage230bcorresponding to the radiator130may be maximized, and the opening rate of the first coolant passage230acorresponding to the heater115and the LP-EGR cooler110may be maximized. In the fifth mode, the opening rate of the third coolant passage230ccorresponding to the engine block100may be maximized, the opening rate of the second coolant passage230bcorresponding to the radiator130may be maximized, and the opening rate of the first coolant passage230acorresponding to the heater115and the LP-EGR cooler110may be maximized. In the sixth mode, the opening rate of the third coolant passage230ccorresponding to the engine block100may be maximized, the opening rate of the second coolant passage230bcorresponding to the radiator130may be adjusted, and the opening rate of the first coolant passage230acorresponding to the heater115and the LP-EGR cooler110may be maximized.

In the seventh mode, the opening rate of the third coolant passage230ccorresponding to the engine block100may be maximized, the second coolant passage230bcorresponding to the radiator130may be blocked, and the opening rate of the first coolant passage230ccorresponding to the heater115and the LP-EGR cooler110may be maximized Additionally, in the first mode, as the flow of the coolant is minimized, the temperature of the engine oil and the coolant rapidly increases in the low temperature state. The second mode is a section that is operated using the heater or the LP-EGR cooler110and a warm-up may be executed.

Further, the third mode is a section in which a target coolant temperature is adjusted by adjusting a cooling amount based on a driving region of the engine as a radiator cooling section. The fourth mode adjusts the temperature of the engine block100as a cylinder block cooling section. The fifth mode is a section used in a driving condition in which an engine heating amount is high and it may be difficult to secure the cooling amount as a maximum cooling section. In the fifth mode, a separation cooling may be released to thus secure a cooling performance of the block. The sixth mode may separately adjust a target coolant temperature of the cylinder head and the block as a cylinder block and radiator cooling section.

FIG. 5is a flowchart showing a control method according to an exemplary embodiment of the present invention. Referring toFIG. 5, the controller300may be configured to receive the output signal of the vehicle operation state detecting portion10including the first coolant temperature sensor12and the second coolant temperature sensor14at step S10.

In step S20, the controller300may be configured to determine whether the output signals of the first coolant temperature sensor12and the second coolant temperature sensor14satisfy a predetermined coolant overheating condition. The cooling system to which the control method according to the exemplary embodiment of the present invention may be applied may independently adjust the coolant temperature of the engine block100and the cylinder head105. Even when separate cooling is applied, the coolant boiling point is the same since the cooling system uses one loop. Therefore, the temperature of the coolant of the engine block100may increase thus causing boiling to occur, and the heat exchange element or the engine90may be damaged. Thus, the controller300may be configured to determine whether the coolant is in a condition in which a risk of boiling occurs in accordance with the output signals of the first and second coolant temperature sensors12and14, and the coolant overheating condition may be set by experiment.

When the coolant overheating condition is satisfied, the controller300may be configured to operate the coolant control valve unit125to move the cam210to the maximum position in operation S30. The moving the cam210to the maximum position may be performed by the controller300configured to output the movement signal of the cam210for a predetermined period of time. The set time may be set to a time required for the cam210to move to the maximum position according to an output signal of the controller300.

The overheating of the cooling system may occur due to various causes. For example, the cause may be a broken or shorted line of the position sensor24, a short circuit or short circuit of the motor305, a damage to the motor305, the cam210may be stuck, or the like. When the position sensor24malfunctions, an error may occur with respect to the current position of the cam210. Accordingly, the controller300may be configured to operate the coolant control valve unit125to move the cam210to the maximum position.

Referring toFIG. 4, the maximum position may be a position where the first coolant passage230aand the third coolant passage230care fully opened, that is the seventh mode. When the coolant control valve unit125operates in the seventh mode, the third coolant passage230cin communication with the engine block100may be opened and coolant may be supplied to the engine block100and the cylinder head105. At this time, the fail-safe thermostat330may be opened by the high temperature coolant.

In particular, the fail-safe thermostat330may be an electrical thermostat and the controller300may be configured to operate the fail safe thermostat330when the coolant overheating condition is satisfied (S40). When the fail safe thermostat330is opened, coolant may be cooled through the radiator130. When the controller300transmits an operation signal to the motor305, the motor305may be unable to be operated due to a failure of the motor305or a foreign substance in the rotation direction of the cam210. Accordingly, the third coolant passage230cmay not open and the engine90, particularly the engine block100, may be overheated.

Additionally, even when the fail-safe thermostat330is opened, the engine90may be overheated. Accordingly, the controller300may be configured to determine the control temperature T_max based on the output signals of the first and second coolant temperature sensors12and14(S50), and output the determined control temperature T_max for the operation of the injector340to be restricted (S60). The torque of the engine may be limited or restricted based on the operation restriction of the injector340, and thus, the engine90may continue to be operated and the engine90may be prevented from overheating.

Furthermore, the controller300may be configured to operate the coolant control valve unit125according to the first mode to the seventh mode described above, that is, the general operation control logic may be performed (S70). The controller300may be configured to determine whether the coolant overheating condition is satisfied based on an output signal of the vehicle operation state detecting portion10while operating the coolant control valve unit125according to general operation control logic. When the coolant overheating condition is satisfied, the control method according to the example may be performed repeatedly.

FIG. 6is a block diagram illustrating a comparison of coolant temperature in a control method according to an exemplary embodiment of the present invention. Referring toFIG. 6, the controller300may be configured to receive the present output signals T_h1and T_h2of the first coolant temperature sensor12and the second coolant temperature sensor14. Additionally, the controller300may be configured to determine a first correction temperature T_off1and a second correction temperature T_off2by subtracting a first and second offset values from the output signals T_h1and T_h2of the first coolant temperature sensor12and the second coolant temperature sensor14respectively.

The cooling system to which the control method according to the exemplary embodiment of the present invention may be applied, may independently adjust the coolant temperature of the engine block100and the cylinder head105and adjust the temperature of the engine block100and the cylinder head105with a difference of approximately 10° C. Since the cylinder head105and the engine block100have different control temperatures, the offset values may be applied differently to the coolant temperature that enters the maximum torque limit to maintain the engine protection and the appropriate engine torque.

For example, the first offset value may be about 0° C. and the second offset value may be about 10° C. The controller300may be configured to compare the first and second correction temperatures T_off1and T_off2and set a greater correction temperature to the control temperature T_max to operate the injector340. The operation limitation of the injector340may be performed by applying the control temperature T_max to a predetermined table.

FIG. 7is a torque limiting table that may be applied to a control method according to the exemplary embodiment of the present invention. For example, when the control temperature T_max is about 120° C., the limit torque is set to 100%, and when the control temperature T_max is about 125° C., the limit torque may be set to 80%. Particularly, limit torque may be defined as a limit value for the maximum torque of the engine90. The control temperature and the proposed torque shown in the table are shown for the sake of understanding, but are not limited thereto.

As described above, when the over-temperature of the coolant is detected during operation of the vehicle, the cooling system control method according to the exemplary embodiment of the present invention may be performed. When the abnormality of the cooling system is detected by performing the general error diagnosis control logic, the abnormality may be determined to correspond to the coolant overheating condition, and the cooling system control method according to the exemplary embodiment of the present invention may be performed to execute engine protection and the engine torque may properly be limited. In addition, even when the second coolant temperature sensor14is affected by the vibration of the engine and is exposed to a relatively high temperature, the cooling system control method according to the exemplary embodiment of the present invention may be performed to protect the engine and maintain proper engine torque may be possible.