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[0001]    This Application is a Section 371 National Stage Application of International Application No. PCT/KR2009/007583, filed Dec. 18, 2009 and published, not in English, as WO2010/071377 on Jun. 24, 2010. 
     
    
     FIELD OF THE DISCLOSURE 
       [0002]    The present disclosure relates to a cooling device for a construction machine, and more particularly, to a cooling device that cools a radiator and an oil cooler of a construction machine by using a cooling fan. 
       BACKGROUND OF THE DISCLOSURE 
       [0003]    In general, a construction machine such as a wheel loader or an excavator cools a radiator and an oil cooler placed in front thereof by forcibly sucking outdoor air through a cooling fan. However, in the case in which a hydraulic motor driving the cooling fan rotates (positively rotates) only in one direction at all times, dust is attached to the radiator and the like, thus, causing an inconvenience to an operator due to requiring periodic cleaning. Therefore, in recent years, a device has been used, which reversibly rotates the cooling fan by switching a rotation direction of the hydraulic motor through a switching valve to blow away dust accumulated by the blowing of the cooling fan. 
         [0004]    In this connection, Korea Patent No. 840044 owned by an applicant discloses a driving control device of a cooling fan of construction heavy equipment. The disclosed driving control device includes a hydraulic pump, a hydraulic motor driven by pressure oil supplied from the hydraulic pump through a hydraulic line, and a cooling fan driven by the hydraulic motor. The hydraulic motor is configured by a hydraulic motor that rotates positively or reversibly. A switching valve that changes a supplying direction of the pressure oil and a switch electrically controlling the switching valve are provided on the hydraulic line connected from the hydraulic pump to the hydraulic motor. 
         [0005]    In the related art, in general, a single cooling fan is adopted. However, in the case in which a plurality of cooling fans are provided in order to improve cooling efficiency, a plurality of switching valves need to be provided so as to change a rotation direction of each of the cooling fans, and as a result, the device becomes complicated and layout efficiency of parts deteriorates. 
         [0006]    Further, when the cooling fan stops instantly in order for the cooling fan rotating positively or reversibly to change its rotation direction to the opposite direction or stop its operation by the switching valve, a sharp pressure drop region, i.e., a “cavity” is generated in the rear of the hydraulic motor, i.e., a point where the pressure oil is inputted into the hydraulic motor on the basis of a flowing direction of the pressure oil due to inertia. The cavity causes a large pressure difference in a mechanism, thereby deteriorating the performance of the hydraulic motor. 
         [0007]    The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter. 
       SUMMARY 
       [0008]    This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
         [0009]    The present disclosure is contrived to solve some or all problems of the related art. An object of the present disclosure is to provide a cooling device for a construction machine in which rotation directions of a plurality of cooling fans can be changed at the same time by a single switching valve. 
         [0010]    Further, another object of the present disclosure is to provide a cooling device for a construction machine in which a pressure is automatically made up to a pressure drop region generated in the rear of a hydraulic motor at the time of changing directions. 
         [0011]    In order to achieve the above-mentioned objects, a cooling device for a construction machine according to the present disclosure includes: two or more hydraulic motors that rotate positively and reversibly to correspond to a supplying direction of pressure oil and drives rotatably cooling fans  20   a  and  20   b  connected thereto, respectively; a switching valve  40  switching rotation directions of the two or more hydraulic motors by switching the supplying direction of the pressure oil supplied to the two or more hydraulic motors from the hydraulic motor  60 ; and flow rate makeup valves  50   a  and  50   b  controlling an additional flow supplied upstream of the two or more hydraulic motors when a pressure drop is generated upstream of the two or more hydraulic motors on the basis of the supplying direction of the pressure oil. 
         [0012]    According to an exemplary embodiment of the present disclosure, the flow rate makeup valves may be constituted by two or more and make up the flow to each pressure drop region of the two or more hydraulic motors. 
         [0013]    Further, the two or more flow rate makeup valves may receive the flow from an oil tank  70 , and at least one of the two or more flow rate makeup valves may be installed on a hydraulic line L 4  connecting a hydraulic line L 1  connecting the switching valve  40  with the hydraulic pump  60  with the oil tank  70 . 
         [0014]    In addition, the cooling device may further include a hydraulic line L 2  guiding the pressure oil drained from the switching valve  40  to the oil tank, and the hydraulic line L 4  on which at least one of the two or more flow rate makeup valves is installed may be the hydraulic line connecting the hydraulic line L 2  connecting the oil tank with the switching valve  40  and the hydraulic line L 1  connecting the switching valve  40  with the hydraulic pump  60 . 
         [0015]    Meanwhile, the two or more flow rate makeup valves may receive the flow from the oil tank  70 , and at least one of the two or more flow rate makeup valves may be installed on a hydraulic line L 5  connecting the two or more hydraulic motors with the oil tank  70 . 
         [0016]    Further, the cooling device may further include the hydraulic line L 2  guiding the pressure oil drained from the switching valve  40  to the oil tank, and the hydraulic line L 5  on which at least one of the two or more flow rate makeup valves is installed may connect the hydraulic line L 2  connecting the oil tank with the switching valve  40  and a hydraulic line L 3  connecting the two or more hydraulic motors to each other. 
         [0017]    According to a controlling device of a construction machine according to the present disclosure, there is an effect that rotation directions of a plurality of cooling fans are changed positively and reversibly at the same time by a single switching valve. 
         [0018]    Further, according to the present disclosure, a pressure is made up by automatically providing makeup oil to a pressure drop region generated in the rear of a hydraulic motor when a direction is changed to prevent a mechanism from being damaged due to a pressure difference in the motor. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  is a hydraulic circuit diagram when a plurality of fans rotates positively in a cooling device of a construction machine according to an exemplary embodiment of the present disclosure. 
           [0020]      FIG. 2  is a hydraulic circuit diagram when a plurality of fans rotates reversibly in a cooling device of a construction machine according to an exemplary embodiment of the present disclosure. 
           [0021]      FIG. 3  is a hydraulic circuit diagram showing the flow of makeup oil when a plurality of fans rotates positively and thereafter, stop in a cooling device of a construction machine according to an exemplary embodiment of the present disclosure. 
           [0022]      FIG. 4  is a hydraulic circuit diagram showing the flow of makeup oil when a plurality of fans rotates reversibly and thereafter, stop in a cooling device of a construction machine according to an exemplary embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    Hereinafter, exemplary embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. 
         [0024]      FIG. 1  is a hydraulic circuit diagram when a plurality of cooling fans rotates positively in a cooling device of a construction machine according to an exemplary embodiment of the present disclosure and  FIG. 2  is a hydraulic circuit diagram when a plurality of cooling fans rotates reversibly. 
         [0025]    A cooling device of a construction machine according to an exemplary embodiment of the present disclosure is basically configured to cool a radiator and an oil cooler  10  by two cooling fans  20   a  and  20   b  as shown in  FIGS. 1 and 2 . The radiator and the oil cooler  10  are arranged on the side and may thus be cooled individually by each of the cooling fans  20   a  and  20   b  and placed in the front and rear, such that they may be cooled at the same time by two cooling fans  20   a  and  20   b.  Two cooling fans  20   a  and  20   b  are driven by two hydraulic motors  30   a  and  30   b,  respectively and two hydraulic motors  30   a  and  30   b  are connected in series by a hydraulic line. 
         [0026]    A single switching valve  40  is provided on the hydraulic line connected from a hydraulic pump  60  to the hydraulic motors  30   a  and  30   b.  The switching valve  40  switches a supplying direction of pressure oil and supplies the pressure oil sequentially to two hydraulic motors  30   a  and  30   b  to change rotation directions of the hydraulic motors  30   a  and  30   b  positively or reversibly. In the exemplary embodiment, the switching valve  40  is a solenoid type and includes a solenoid unit  41  at one side thereof to receive a control signal from a controller  90 . 
         [0027]    A flow is supplied to the switching valve  40  by the hydraulic pump  60  driven by an engine or an electrical motor. The hydraulic pump  60  includes a swash plate  61  and has a configuration in which a discharged flow varies depending on an angle of the swash plate  61 . 
         [0028]    The flow is controlled by the controller  90 . The controller  90  receives temperature signals from temperature sensors mounted on the radiator and the oil cooler  10  and controls the flow by judging rotation speeds of the cooling fans  20   a  and  20   b  required on the basis thereof. The controller  90  also transmits a positive-direction or reverse-direction rotation signal to the switching valve  40  through the solenoid valve  41 . The reverse-direction rotation signal for cleaning may be set so that reverse-direction driving automatically occurs when a contamination level of the radiator  10  is higher than a predetermined level by detecting the contamination level of the radiator  10  or so that the reverse-direction driving occurs periodically at a predetermined time interval. Meanwhile, it may be configured so that the reverse-direction driving occurs manually by an additional external operation switch. 
         [0029]    A regulator  80  is mounted between the controller  90  and the hydraulic pump  60  and adjusts the angle of the swash plate  61  of the hydraulic pump  60  to regulate a supply flow. The controller  80  may be configured to detect an actual flow supplied from the hydraulic pump  60  to feedback-control the pressure of the hydraulic pump  60 . 
         [0030]    Two flow rate makeup valves  50   a  and  50   b  are provided at a front end of the switching valve  40 . Two flow rate makeup valves  50   a  and  50   b  make up the flow to each pressure drop region of two hydraulic motors  30   a  and  30   b  by raising the pressure oil from an oil tank  70 . In the exemplary embodiment, a first flow rate makeup valve  50   a  is mounted between a first hydraulic line L 1  connecting the switching valve  40  with the hydraulic pump  60  and a second hydraulic line L 2  connecting the switching valve  40  with the oil tank  70 . That is, the first flow rate makeup valve  50   a  is installed on a hydraulic line L 4  connecting the first hydraulic line L 1  and the second hydraulic line L 2 . Meanwhile, a second flow rate makeup valve  50   b  is mounted between the second hydraulic line L 2  connecting the switching valve  40  with the oil tank  70  and a third hydraulic line L 3  connecting two hydraulic motors  30   a  and  30   b.  That is, the second flow rate makeup valve  50   b  is installed on a hydraulic line L 5  connecting the second hydraulic line L 2  and the third hydraulic line L 3 . 
         [0031]    Hereinafter, the flow of the pressure oil for each rotational state and the flow of the makeup oil when the rotation direction is changed will be described with reference to the accompanying drawings. 
         [0032]      FIG. 3  is a hydraulic circuit diagram showing the flow of makeup oil when a plurality of cooling fans rotates positively and thereafter, stop in a cooling device of a construction machine according to an exemplary embodiment of the present disclosure and  FIG. 4  is a hydraulic circuit diagram showing the flow of makeup oil when a plurality of cooling fans rotates reversibly and thereafter, stop. 
         [0033]    As shown in  FIG. 1 , in the case in which the cooling fans  20   a  and  20   b  rotate positively to cool the radiator and the oil cooler  10 , the flow supplied from the hydraulic pump  60  passes through the switching valve  40  and a first hydraulic motor  30   a  and thereafter, is supplied to a second hydraulic motor  30   b  and passes through the switching valve  40  again to be discharged to the oil tank  70 . 
         [0034]    In the case in which the cooling fans  20   a  and  20   b  rotating positively stop instantly for reverse rotation or operational stop, the flow of the flow supplied from the hydraulic pump  60  stops and a sharp pressure drop region, i.e., a “cavity” is generated in the rear of the hydraulic motors  30   a  and  30   b,  i.e., a point (a left side of each hydraulic motor in the figure) where the pressure oil is inputted into each of the hydraulic motors  30   a  and  30   b  on the basis of a flowing direction of the pressure oil due to inertia. A pressure difference is generated between each of the hydraulic motors  30   a  and  30   b  and the oil tank  70  due to the generation of the pressure drop region, and as a result, as shown in  FIG. 3 , a part of the flow discharged to the oil tank  70 , that is, the makeup oil is drawn. The makeup oil is distributed to the left and right by the flow rate makeup valves  50   a  and  50   b  in the figure and thus a left flow (--         ) is supplied to the rear of the first hydraulic motor  30   a  through the switching valve  40  and a right flow (--         ) is supplied to the rear of the second hydraulic motor  30   a  through an additional supply line. The supply of the makeup oil to the rear of each of the hydraulic motors  30   a  and  30   b  removes an instant pressure difference in the motor to prevent a mechanism from being damaged. 
         [0035]    Meanwhile, as shown in  FIG. 2 , in the case in which the cooling fans  20   a  and  20   b  rotate reversibly to clean the radiator and the oil cooler  10 , the flow supplied from the hydraulic pump  60  passes through the switching valve  40  and the second hydraulic motor  30   b  and thereafter, is supplied to the second hydraulic motor  30   a  and passes through the switching valve  40  again to be discharged to the oil tank  70 . 
         [0036]    In the case in which the cooling fans  20   a  and  20   b  rotating reversibly stop instantly for positive rotation or operational stop, the flow of the flow supplied from the hydraulic pump  60  stops and a sharp pressure drop region is generated at a point (a right side of each hydraulic motor in the figure) where the pressure oil is inputted into each of the hydraulic motors  30   a  and  30   b  on the basis of the flowing direction of the pressure oil due to inertia. The pressure difference is generated between each of the hydraulic motors  30   a  and  30   b  and the oil tank  70  due to the generation of the pressure drop region, and as a result, as shown in  FIG. 4 , the makeup oil is drawn from the oil tank  70 . The makeup oil is distributed to the left and right by the flow rate makeup valves  50   a  and  50   b  in the figure and thus a left flow (--         ) is supplied to the rear of the second hydraulic motor  30   b  through the switching valve  40  and a right flow (--         ) is supplied to the rear of the first hydraulic motor  30   a  through an additional supply line. The supply of the makeup oil to the rear of each of the hydraulic motors  30   a  and  30   b  removes the instant pressure difference in the motor to prevent the mechanism from being damaged. 
         [0037]    Meanwhile, although the present disclosure has been described with reference to the exemplary embodiments shown in the figures, it is merely exemplary and it is to be understood by those skilled in the art that various modifications and equivalent exemplary embodiments are possible therefrom. Therefore, the scope of the present disclosure will be determined by the appended claims. 
         [0038]    The present disclosure can be applied to all construction machines in which a cooling fan is driven by a hydraulic motor in addition to an excavator or a wheel loader.

Summary:
A cooling device of a construction machine according to the present invention includes: two or more hydraulic motors that rotate positively and reversibly to correspond to a supplying direction of pressure oil and drives rotatably cooling fans connected thereto, respectively; a switching valve switching rotation directions of the two or more hydraulic motors by switching the supplying direction of the pressure oil supplied to the two or more hydraulic motors from the hydraulic motor; and flow rate makeup valves controlling an additional flow supplied upstream of the two or more hydraulic motors when a pressure drop is generated upstream of the two or more hydraulic motors on the basis of the supplying direction of the pressure oil.