Abstract:
A cooling system of an engine may include an engine that has a cylinder block where a cylinder is formed therein and a cylinder head that covers the cylinder block, a radiator that is disposed outside the engine, a first thermostat that is disposed on a coolant line connecting the engine with the radiator in such a way that the coolant passes the radiator or does not pass the radiator, and a second thermostat that is configured to make the coolant selectively pass the coolant line that is formed in the cylinder block.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims priority of Korean Patent Application Number 10-2013-0059838 filed on May 27, 2013, the entire contents of which application is incorporated herein for all purposes by this reference. 
       BACKGROUND OF INVENTION 
       [0002]    1. Field of Invention 
         [0003]    The present invention is related to a cooling system of an engine that accurately controls coolant temperature by controlling coolant passage depending on the temperature of the coolant circulated so as to prevent the overheating. 
         [0004]    2. Description of Related Art 
         [0005]    A thermostat for a vehicle is disposed between an engine and a radiator, is automatically opened/closed by the temperature variation of coolant to adjust the flow rate of the coolant, and therefore the temperature of the coolant is controlled in a predetermined range. 
         [0006]    A mechanical thermostat expands wax depending on the temperature of the coolant, and the expanding force of the wax makes a piston move the valve of the thermostat. 
         [0007]    The mechanical thermostat is operated in a predetermined opening/closing temperature of the coolant to open/close the valve only in a predetermined temperature condition, and therefore the mechanical thermostat does not actively move against changes of the driving circumstances of the vehicle. 
         [0008]    Accordingly, an electrical thermostat has been introduced to complements the drawback of the mechanical thermostat, and the electrical thermostat is operated to sustain the coolant temperature in an optimized range. 
         [0009]    The electrical thermostat actively controls the coolant temperature of the engine according to the driving circumstances such as the load level of the vehicle to sustain the optimized coolant temperature, and the electrical thermostat can improve fuel consumption efficiency and reduce exhaust gas. 
         [0010]    Meanwhile, an electrical thermostat can effectively control the coolant circulating an engine, but cannot control the coolant respectively circulating a cylinder block as a high temperature portion of an engine and a cylinder head as a low temperature portion. Accordingly, because the temperature of the coolant is controlled to be relatively lower rather than a relatively high temperature, fuel consumption is increased. 
         [0011]    The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art. 
       BRIEF SUMMARY 
       [0012]    Various aspects of the present invention have been made in an effort to provide for a cooling system of an engine having advantages of reducing fuel consumption and keeping coolant temperature relatively high by respectively controlling coolant circulating a cylinder block as a high temperature portion and a cylinder head as a low temperature portion. 
         [0013]    Various aspects of the present invention provide for a cooling system of an engine that may include an engine that has a cylinder block where a cylinder is formed therein and a cylinder head that covers the cylinder block, a radiator that is disposed outside the engine, a first thermostat that is disposed on a coolant line connecting the engine with the radiator in such a way that the coolant passes the radiator or does not pass the radiator, and a second thermostat that is configured to make the coolant selectively pass the coolant line that is formed in the cylinder block. 
         [0014]    The first thermostat or the second thermostat may be an electrical thermostat type that opens a valve by heating wax through an electrical energy or a coolant heat. 
         [0015]    A first operating temperature of coolant in which the second thermostat is operated to make the coolant flow a coolant line of the cylinder block may be higher than a second operating temperature of coolant in which the first thermostat is operated to make the coolant flow the radiator. 
         [0016]    The first thermostat may be disposed at an outlet side that coolant is exhausted from the engine and the second thermostat may be disposed at a point that coolant is exhausted from the cylinder block. 
         [0017]    The second thermostat may be disposed at a boundary portion that is connected from the cylinder block to the cylinder head. 
         [0018]    The power that is supplied to the first thermostat may be PWM controlled and the second thermostat may be ON/OFF controlled. 
         [0019]    The second thermostat may be direct connected to a battery and a relay may be disposed between them to turn on/off the second thermostat. 
         [0020]    A control portion may supply power with the second thermostat with a predetermined current for a predetermined time and then may supply power with the second thermostat again after a predetermined time elapses from a point that the power is halted, if the temperature of coolant is higher than the first operating temperature. 
         [0021]    The second thermostat may open/close coolant line in such a way that the coolant temperature of the cylinder block becomes higher than the coolant temperature of the cylinder head. 
         [0022]    Various aspects of the present invention provide for a cooling system of an engine in which a first thermostat controlling coolant exhausted from an engine and a second thermostat controlling coolant flowing a cylinder block are used to keep the temperature of coolant flowing the cylinder head high in such a way that fuel consumption is reduced and overall cooling efficiency is improved. 
         [0023]    That is, the temperature of the cylinder block is kept high and friction loss of lubricant interposed between a piston and a cylinder is reduced, and therefore overall fuel consumption is reduced. 
         [0024]    The methods and apparatuses of the present invention have other features and advantages which will be apparent from or are set forth in more detail in the accompanying drawings, which are incorporated herein, and the following Detailed Description, which together serve to explain certain principles of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]      FIG. 1  is an overall schematic diagram of an exemplary cooling system of an engine according to the present invention. 
           [0026]      FIG. 2  is a flowchart showing an exemplary method for controlling a cooling system of an engine according to the present invention. 
           [0027]      FIG. 3  is a flowchart showing an exemplary method for controlling a second thermostat in a cooling system of an engine according to the present invention. 
           [0028]      FIG. 4  shows an exemplary ON/OFF condition of power that is supplied to a second thermostat in a cooling system of an engine according to the present invention based on time. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    Reference will now be made in detail to various embodiments of the present invention(s), examples of which are illustrated in the accompanying drawings and described below. While the invention(s) will be described in conjunction with exemplary embodiments, it will be understood that present description is not intended to limit the invention(s) to those exemplary embodiments. On the contrary, the invention(s) is/are intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the invention as defined by the appended claims. 
         [0030]      FIG. 1  is an overall schematic diagram of a cooling system of an engine according to various embodiments of the present invention. 
         [0031]    Referring to  FIG. 1 , a cooling system of an engine includes a cylinder head  100 , a cylinder block  110 , a coolant pump  120 , a heater  130 , a throttle body  140 , a first thermostat  150 , a radiator  160 , a second thermostat  170 , and a control portion  180 . Here, the cylinder head  100  and the cylinder block  110  can be called as an engine. 
         [0032]    A cylinder in which a piston moves up and down is formed inside the cylinder block  110  and a water jacket or a coolant passage is formed around the cylinder. 
         [0033]    And, a camshaft is disposed in the cylinder head  100  that is disposed at an upper portion of the cylinder block  110  and coolant circulates the water jacket or the coolant passage of the cylinder head  100 . 
         [0034]    The coolant passing the cylinder block  110  and the cylinder head  100  is supplied to the coolant pump  120  through the first thermostat  150  and the radiator  160 , and the coolant pump  120  pumps the coolant to circulate this. 
         [0035]    Here, the coolant that is exhausted from the cylinder block  110  or the cylinder head  100  is supplied to the heater  130  and the throttle body  140 . 
         [0036]    The first thermostat  150  selectively closes a coolant passage that is connected from the radiator  160  to the coolant pump  120  in such a way that the coolant passes the radiator  160  or the coolant does not pass the radiator  160  to be supplied to the coolant pump  120 . 
         [0037]    In various embodiments of the present invention, the cylinder block  110  is a part in which a piston is disposed and it is necessary that the temperature thereof is controlled to be kept high. That is, the higher the coolant temperature of the cylinder block  110  becomes, the lower the friction loss becomes to reduce fuel consumption. 
         [0038]    And, it is necessary that the temperature of the cylinder head  100  is controlled to be lower than the cylinder block  110 . That is, the coolant temperature passing the cylinder head  100  is controlled to be lower than the coolant temperature passing the cylinder block  110 . 
         [0039]    As shown in the drawings, the coolant flowing the cylinder block  110  joins the coolant that flows the cylinder head  100  through the second thermostat  170  and is supplied to the first thermostat  150  and the radiator  160 . 
         [0040]    In various embodiments of the present invention, the second thermostat  170  can be operated by the temperature of the coolant flowing the inside of the cylinder block  110 , and the first thermostat  150  can be operated by the temperature of the coolant that is exhausted from the engine (the cylinder block and the cylinder head). 
         [0041]    For example, in a condition in which the temperature of coolant that is exhausted from the engine is about 80 Celsius degrees, power is supplied to operate the first thermostat  150 , and in a condition in which the temperature of coolant that flows the cylinder block  110  is about 90 Celsius degrees, power is supplied to operate the second thermostat  170 . 
         [0042]    In various embodiments of the present invention, the first thermostat  150  is pulse width modulation (PWM) controlled by the control portion  180  and the second thermostat  170  is direct connected to a battery in such a way that 22 A (ampere current) can be supplied thereto and a relay is disposed to be controlled by the control portion  180 . 
         [0043]      FIG. 2  is a flowchart showing a method for controlling a cooling system of an engine according to various embodiments of the present invention. 
         [0044]    Referring to  FIG. 2 , a controls starts in step S 205 , operating conditions such as coolant temperature, RPM, load, and speed are detected in step S 210 . Step S 215  is performed to control the first thermostat  150  in step S 210 , and step S 300  is performed to control the second thermostat  170 . 
         [0045]    The second thermostat  170  can be controlled based on the temperature of the coolant flowing the cylinder block  110  and the first thermostat  150  can be controlled based on the temperature of the coolant that is exhausted from the engine (cylinder block and cylinder head). 
         [0046]    A system for controlling the first thermostat  150  is described, and referring to  FIG. 3 , a system for controlling the first thermostat  150  will be described. Further, a part that is not described refers to well-known arts. 
         [0047]    It is determined whether the temperature of coolant that is exhausted from the engine  100  and  110  is larger than a predetermined maximum value in step S 215 . If the coolant temperature is larger than that, step S 260  is performed, wherein the PWM duty that is supplied to the operating heater becomes 100%. 
         [0048]    If the coolant temperature is less than that, step S 220  is performed. It is determined whether the coolant temperature is larger than the operating minimum temperature of the electric thermostat  11  in step S 225 . The operating minimum temperature can be +60 Celsius degrees. 
         [0049]    More particularly, if the temperature of coolant that is exhausted from the engine  100  and  110  is higher than 60 Celsius degrees (minimum operating temperature), step S 230  is performed. 
         [0050]    The coolant temperature, the RPM, and the load of an engine, and the vehicle speed are detected in step S 230 , and the PWM duty that is supplied to the operating heater is controlled according to the detected information. 
         [0051]    A real coolant temperature that is exhausted from the engine is compared to a target temperature in step S 240 , it is determined whether the coolant temperature is higher than the target temperature in step S 245 , and if it is higher that, the PWM duty value % that is supplied to the heater is raised in step S 250 . 
         [0052]    It is determined whether the absolute value between the target temperature and the coolant temperature is larger than an upper side allowance value in step S 255 . 
         [0053]    The upper side allowance value is hysteresis value, if the target temperature value ranges within 100±5, the upper side allowance value is 5 and a lower side allowance value is 5. The upper side allowance value and the lower side allowance value can be varied according to the design specification. 
         [0054]    If it is determined that the coolant temperature that is exhausted from the engine  100  and  110  is less than the target temperature in step S 275 , the PWM duty value that is supplied to the operating heater is decreased in step S 280 . And, it is determined whether the difference between the target temperature and the coolant temperature is less than the lower side allowance value in step S 285 . 
         [0055]    If the condition is not satisfied in step S 255  and step S 285 , step S 245  and step S 275  are respectively performed, if the condition is satisfied in step S 255  and step S 285 , step S 260  and step S 290  are respectively performed. 
         [0056]      FIG. 3  is a flowchart showing a method for controlling a second thermostat in a cooling system of an engine according to various embodiments of the present invention. 
         [0057]    Referring to  FIG. 3 , a control method of the second thermostat  170  is described. 
         [0058]    It is determined whether the coolant temperature (ET) flowing the cylinder block  110  is higher than an operating temperature (OT) of the second thermostat  170 . 
         [0059]    If the coolant temperature (ET) is higher than the operating temperature (OT), a predetermined voltage/current is supplied for a predetermined time so as to open the valve through the second thermostat  170  in step S 304 . 
         [0060]    Thus, the second thermostat  170  opens coolant passage in such a way that the coolant flows the cylinder block  110 , and the temperature of the coolant flowing the cylinder block  110  is lowered. 
         [0061]    And, it is determined whether a predetermined time elapses after the power that is supplied to the second thermostat  170  is halted in a  306 . If a predetermined time elapses after the power supply halt, step S 302  is performed again, and if a predetermined time does not elapses after the power supply halt, step S 308  is performed. And, an engine stops its operating or a system is turned off, step S 295  is performed in  FIG. 2 . 
         [0062]      FIG. 4  shows an ON/OFF condition of power that is supplied to a second thermostat in a cooling system of an engine according to various embodiments of the present invention based on time. 
         [0063]    Referring to  FIG. 4 , a power supply time  400  and a power halt time  410  are predetermined so as to protect the second thermostat  170  from the overheat or the fault. 
         [0064]    Because a predetermined high current is supplied to the second thermostat  170  (e.g., 22 A) so as to quickly and completely open the valve of the second thermostat, the power is not supplied for a relatively long time different from the first thermostat  150 . 
         [0065]    Further, after the power supply to the second thermostat  170  is halted, if a predetermined power halt time does not elapses, the power is not supplied to the second thermostat  170 . 
         [0066]    In various embodiments of the present invention, the first thermostat  150  is an electrical type in which the valve thereof is opened or closed through an expansion of wax, wherein if the wax is heated by a heating element, the wax is expanded to move the valve. 
         [0067]    Further, an electrical thermostat type can be applied to the second thermostat  170  of which the valve is opened or closed by the expansion of the wax like the first thermostat  150 . 
         [0068]    In various embodiments of the present invention, if the temperature of coolant that is exhausted from the engine reaches a first operating temperature, power is supplied to the first thermostat and if the temperature of coolant flowing the cylinder block reaches a second operating temperature, power is supplied to the second thermostat, wherein the second operating temperature is higher than the first operating temperature. 
         [0069]    Accordingly, the temperature of coolant flowing the cylinder block is controlled to be high and the temperature of coolant flowing the cylinder head is controlled to be low. Resultantly, because the temperature of the cylinder block is kept high, friction loss of lubricant that is interposed between a piston and a cylinder is reduced and overall fuel consumption is reduced. 
         [0070]    The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teachings. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and their practical application, to thereby enable others skilled in the art to make and utilize various exemplary embodiments of the present invention, as well as various alternatives and modifications thereof. It is intended that the scope of the invention be defined by the Claims appended hereto and their equivalents.