Patent Publication Number: US-7913490-B2

Title: Hydraulic circuit for construction machine

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based on and claims priority from Korean Patent Application No. 10-2007-24030, filed on Mar. 12, 2007 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a hydraulic circuit for a construction machine, which can implement an auto idle function by automatically reducing revolution of an engine when a working device of the construction machine such as an excavator is not driven. 
     More particularly, the present invention relates to a hydraulic circuit for a construction machine, which can minimize an energy loss of a hydraulic system by automatically reducing revolution of an engine when a working device such as a boom is not driven. 
     Hereinafter, in the accompanying drawings, only the construction of pilot signal lines related to an auto idle function is illustrated. When corresponding switching valves are switched over, the pilot signal lines are intercepted. The spool switching state of the switching valves and flow paths formed between the switching valves and working devices are not separately illustrated. 
     2. Description of the Prior Art 
     Referring to  FIG. 1 , a conventional hydraulic circuit for a construction machine having an auto idle function includes first to third hydraulic pumps P 1 , P 2 , and P 3 ; a first switching valve A composed of valves installed in a flow path of the first hydraulic pump P 1  and shifted to control hydraulic fluid fed to working devices, such as arm, boom, bucket, and the like; a second switching valve B composed of valves installed in a flow path of the second hydraulic pump P 2  and shifted to control hydraulic fluid fed to working devices, such as arm, boom, option device, and the like; a third switching valve C composed of valves installed in a flow path of the third hydraulic pump P 3  and shifted to control hydraulic fluid fed to a swing device and so on; a fourth switching valve D composed of valves installed on upstream sides of the flow paths of the first and second hydraulic pumps P 1  and P 2 , respectively, and shifted to control hydraulic fluid fed to left and right traveling devices; and a confluence switching valve  8  installed on a downstream side of the flow path of the third hydraulic pump P 3  and shifted to selectively supply the hydraulic fluid from the third hydraulic pump P 3  to the working devices on the first hydraulic pump side P 1  or the working devices on the second hydraulic pump side P 2 , in response to a pilot signal pressure Pi 1  applied thereto. 
     In a small-sized excavator, the hydraulic fluid fed from the first hydraulic pump P 1  is supplied to a right traveling motor and the hydraulic fluid fed from the second hydraulic pump P 2  is supplied to a left traveling motor to drive the traveling motors. In the case of driving other working devices such as boom and so on, the confluence switching valve  8  is used to supply the hydraulic fluid fed from the third hydraulic pump P 3  to the working devices. 
     The confluence switching valve  8  is shifted, in response to the pilot signal pressure Pi 1  being supplied from a pilot pump to a signal line  3 , to supply the hydraulic fluid fed from the third hydraulic pump P 3  to the working devices on the first hydraulic pump side P 1  or to the working devices on the second hydraulic pump side P 2 . 
     A signal line  4  connected to a signal line  3  includes a signal line  5  passing through the first and second switching valves A and B for the working devices and a signal line  6  passing through the fourth switching valve D for traveling devices. In the case where only either the first and second switching valves A and B or the fourth switching valve D is shifted to operate, no signal pressure is formed in the signal line  3 . 
     In the case where the first and second switching valves A and B for the working devices and the fourth switching valve D for the traveling devices are simultaneously shifted to operate, the confluence switching valve  8  is shifted in response to the pilot signal pressure Pi 1  formed in the signal line  3 . Accordingly, the hydraulic fluid fed from the third hydraulic pump P 3  is supplied to the working devices of the first hydraulic pump side P 1  or the working devices of the second hydraulic pump side P 2 . 
     In the case of simultaneously implementing the above-described confluence function and the auto idle function, it is required to separately provide a signal line that can detect the shifting of the first and second switching valves A and B and the fourth switching valve D. 
     That is, if either the first and second switching valves A and B or the fourth switching valve D is shifted, no signal pressure is formed in the signal line  3 . Accordingly, the pressure in the signal line  3  cannot be used as an auto idle signal pressure. 
     Accordingly, in the case of shifting the first and second switching valves A and B or the fourth switching valve D, a separate signal line  7  that can detect the shifting is required. The signal line  7  is connected to the signal line  3 , and is connected to a flow path in which a second throttling part  2  is installed. In addition, the signal line  7  is constructed to pass through the first to third switching valves A, B, and C for the working devices and the fourth switching valve D for the traveling devices. 
     In a neutral state of the first to fourth switching valves A, B, C, and D, no signal pressure is formed in the signal line  7 . Accordingly, it is judged that the working devices do not operate, and thus the engine revolution of the equipment is automatically reduced. 
     In the case of shifting any one of the first to fourth switching valves A, B, C, and D, the signal pressure is formed in the signal line  7 , and thus the engine revolution can be accelerated by the signal pressure. 
     Referring to  FIG. 2 , another conventional hydraulic circuit for a construction machine having an auto idle function includes a confluence switching valve  8  shifted by a signal pressure Pi 1  fed from a pilot pump (not illustrated) to a signal line  13  to supply hydraulic fluid fed from a third hydraulic pump P 3  to working devices on a first hydraulic pump side P 1  or working device on a second hydraulic pump P 2 ; a signal line  16  which is connected to the signal line  13  and in which a signal pressure is formed when a fourth switching valve D for traveling devices is shifted; a signal line  15  which is connected to a signal line  16  and in which a signal pressure is formed when first and second switching valves A and B for working devices are shifted; and a signal line  17  in which a fourth throttling part  12  is installed, which is connected to a signal line to which a pilot signal pressure Pi 2  is supplied, and in which a signal pressure is formed when the first to third switching valves A, B, and C for the working devices and the fourth switching valve D for the traveling devices are shifted. 
     The conventional hydraulic circuit of  FIG. 2  further includes first to third hydraulic pumps P 1 , P 2 , and P 3 ; a first switching valve A installed in a flow path of the first hydraulic pump P 1 ; a second switching valve B installed in a flow path of the second hydraulic pump P 2 ; and a third switching valve C installed in a flow path of the third hydraulic pump P 3 . However, since these constituent elements are substantially the same as those of the circuit as illustrated in  FIG. 1 , the detailed description thereof will be omitted. The same drawing reference numerals are used for the same elements across various figures. 
     As illustrated in  FIGS. 1 and 2 , the conventional hydraulic circuits having an auto idle function requires a confluence circuit including the confluence switching valve  8  and separate auto idle signal lines  7  and  17 , and this causes the construction of the signal lines to be complicated. Particularly, the hydraulic circuit as illustrated in  FIG. 2  has very complicated signal lines. 
     In addition, since the signal lines  7  and  17  pass through spools of the first to third switching valve A, B, and C for the working devices and the fourth switching valve D for the traveling devices, the hydraulic fluid may leak through joint surfaces of the first to fourth switching valves A, B, C, and D. Particularly, in a high-temperature working environment, the formed auto-idle pressure may become unstable due to the leakage of the hydraulic fluid. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art while advantages achieved by the prior art are maintained intact. 
     One object of the present invention is to provide a hydraulic circuit for a construction machine, which can simplify the construction of signal lines in a hydraulic circuit having a confluence circuit and auto idle signal lines. 
     Another object of the present invention is to provide a hydraulic circuit for a construction machine, which can stably maintain the formed auto-idle pressure by minimizing the leakage of hydraulic fluid through joint surfaces of switching valves for working devices and traveling devices. 
     In order to accomplish these objects, there is provided a hydraulic circuit for a construction machine, according to an embodiment of the present invention, which includes first to third hydraulic pumps; a first switching valve composed of valves installed in a flow path of the first hydraulic pump and shifted to control hydraulic fluid fed to working devices; a second switching valve composed of valves installed in a flow path of the second hydraulic pump and shifted to control hydraulic fluid fed to working devices; a third switching valve composed of valves installed in a flow path of the third hydraulic pump and shifted to control hydraulic fluid fed to working devices; a fourth switching valve composed of valves installed on upstream sides of the flow paths of the first and second hydraulic pumps, respectively, and shifted to control hydraulic fluid fed to left and right traveling devices; a confluence switching valve installed on a downstream side of the flow path of the third hydraulic pump and shifted by a signal pressure fed to a signal line to selectively supply the hydraulic fluid from the third hydraulic pump to either the working devices on the first hydraulic pump side or the working devices on the second hydraulic pump side; a signal line for traveling devices which is connected to the signal line for the confluence switching valve and in which a signal pressure is formed when the fourth switching valve is shifted; signal lines for working devices which are connected to the signal line for the confluence switching valve and in which a signal pressure is formed when any one of the first to third switching valves is shifted; and a shuttle valve, installed at an intersection of a flow path that is connected to a signal line connected to the signal line for the traveling devices and the signal line for the confluence switching valve and a flow path that is branched and connected to the signal line for the confluence switching valve and the signal line for the working devices, for selecting any one of the signal pressure formed in the signal line for the traveling devices and the signal pressure formed in the signal lines for the working devices. 
     The hydraulic circuit for a construction machine according to an embodiment of the present invention may further include a signal pressure output port installed in the signal line for the traveling devices so that the signal pressure formed in the signal line for the traveling devices can be used as the signal pressure for travel boosting or travel alarming. 
     The hydraulic circuit for a construction machine according to an embodiment of the present invention may further include a check valve installed in a signal line branched and connected to the signal line for the traveling devices and the signal line for the confluence switching valve so that the signal pressure is formed in the signal line for the traveling devices when the fourth switching valve is shifted. 
     The hydraulic circuit for a construction machine according to an embodiment of the present invention may further include a check valve installed in a flow path connected to the signal line for the confluence switching valve and the signal line for working devices so that the signal pressure is formed in the signal line for working devices when either of the first and second switching valves is shifted. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a circuit diagram of a conventional hydraulic circuit having an auto idle function; 
         FIG. 2  is a circuit diagram of another conventional hydraulic circuit having an auto idle function; and 
         FIG. 3  is a circuit diagram of a hydraulic circuit for a construction machine having an auto idle function according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. The matters defined in the description, such as the detailed construction and elements, are nothing but specific details provided to assist those of ordinary skill in the art in a comprehensive understanding of the invention, and thus the present invention is not limited thereto. 
       FIG. 3  is a circuit diagram of a hydraulic circuit for a construction machine having an auto idle function according to an embodiment of the present invention. 
     Referring to  FIG. 3 , the hydraulic circuit for a construction machine according to an embodiment of the present invention includes first to third hydraulic pumps P 1 , P 2 , and P 3 ; a first switching valve A composed of valves installed in a flow path of the first hydraulic pump P 1  and shifted to control hydraulic fluid fed to working devices such as arm, boom, bucket, and the like; a second switching valve B composed of valves installed in a flow path of the second hydraulic pump P 2  and shifted to control hydraulic fluid fed to working devices such as arm, boom, option device, and the like; a third switching valve C composed of valves installed in a flow path of the third hydraulic pump P 3  and shifted to control hydraulic fluid fed to working devices such as swing device and the like; a fourth switching valve D composed of valves installed on upstream sides of the flow paths of the first and second hydraulic pumps P 1  and P 2 , respectively, and shifted to control hydraulic fluid fed to left and right traveling devices; a confluence switching valve  8  installed on a downstream side of the flow path of the third hydraulic pump P 3  and shifted by a signal pressure Pi 1  fed to a signal line  31  to selectively supply the hydraulic fluid from the third hydraulic pump P 3  to either the working devices on the first hydraulic pump side P 1  or the working devices on the second hydraulic pump side P 2 ; a signal line  34  for traveling devices which is connected to the signal line  31  for the confluence switching valve and in which a signal pressure is formed when the fourth switching valve D is shifted; signal lines  32  and  33  for working devices which are connected to the signal line  31  for the confluence switching valve and in which a signal pressure is formed when any one of the first to third switching valves A, B, and C is shifted; and a shuttle valve  41 , installed at an intersection of a flow path  50  that is connected to a signal line  35  connected to the signal line  34  for the traveling devices and the signal line  31  for the confluence switching valve and a flow path  60  that is branched and connected to the signal line  31  for the confluence switching valve and the signal line  32  for the working devices, for selecting any one of the signal pressure formed in the signal line  34  for the traveling devices and the signal pressure formed in the signal lines  32  and  34  for the working devices. 
     The hydraulic circuit for a construction machine according to an embodiment of the present invention may further include a signal pressure output port  70  installed in the signal line  34  for the traveling devices so that the signal pressure formed in the signal line  34  for the traveling devices can be used as the signal pressure for travel boosting or travel alarming. 
     The hydraulic circuit for a construction machine according to an embodiment of the present invention may further include a check valve  43  installed in a signal line  35  branched and connected to the signal line  34  for the traveling devices and the signal line  31  for the confluence switching valve so that the signal pressure is formed in the signal line  34  for the traveling devices when the fourth switching valve D is shifted. 
     The hydraulic circuit for a construction machine according to an embodiment of the present invention may further include a check valve  42  installed in a flow path connected to the signal line  31  for the confluence switching valve and the signal line  33  for working devices so that the signal pressure is formed in the signal line  33  for working devices when either of the first and second switching valves A and B is shifted. 
     Second and third throttling parts  22  and  23  are installed in the signal line  31  for the confluence switching valve. 
     The signal line  34  for the traveling devices is connected to an upstream side of the second throttling part  22  installed in the signal line  31  for the confluence switching valve, and the signal pressure is supplied to a spool of the fourth switching valve D through a first throttling part  21 . 
     The signal lines  32  and  33  for the working devices are connected to the signal line  31  for the confluence switching valve interposed between the second and third throttling parts  22  and  23 . The signal pressure is supplied to a spool of the third switching valve C through the second throttling part  22  and the signal line  32 , and then is supplied to the second switching valve B and the first switching valve A along the signal line  33 . 
     The hydraulic circuit, which includes the first to third hydraulic pumps P 1 , P 2 , and P 3 , the first switching valve A installed in the flow path of the first hydraulic pump P 1 , the second switching valve B installed in the flow path of the second hydraulic pump P 2 , the third switching valve C installed in the flow path of the third hydraulic pump P 3 , the fourth switching valve D installed in the flow path of the first and second hydraulic pumps P 1  and P 2 , and the confluence switching valve  8  installed on the downstream side of the flow path of the third hydraulic pump P 3 , is substantially the same as the hydraulic circuit as illustrated in  FIG. 1 , and thus the detailed description thereof will be omitted. The same drawing reference numerals are used for the same elements across various figures. 
     Hereinafter, the operation of the hydraulic circuit for a construction machine according to an embodiment of the present invention will be described with reference to the accompanying drawings. 
     As illustrated in  FIG. 3 , the hydraulic fluid fed from the first hydraulic pump P 1  is supplied to the right traveling motor and the hydraulic fluid fed from the second hydraulic pump P 2  is supplied to the left traveling motor to drive the traveling motors. In the case of driving the working devices such as arm and so on, the confluence switching valve  8  is used to supply the hydraulic fluid fed from the third hydraulic pump P 3  to the working devices. 
     The confluence switching valve  8  is shifted, in response to the pilot signal pressure Pi 1  applied thereto through the second and third throttling parts  22  and  23  installed in the signal line  31  for the confluence switching valve. When the confluence switching valve  8  is shifted, the hydraulic fluid fed from the third hydraulic pump P 3  is supplied to either the working devices on the first hydraulic pump side P 1  or the working devices on the second hydraulic pump side P 2 . 
     In the case of shifting the fourth switching valve D for the traveling devices, a signal pressure is formed in the signal line  34  for the traveling devices by the check valve  43  installed in the signal line  35 . Accordingly, it is possible to use the signal pressure for implementing an auto idle function through the shuttle valve  41  installed in the flow path  50  branched and connected to the signal line  34 . 
     In the case of shifting the third switching valve C connected to the third hydraulic pump P 3 , a signal pressure is formed in the signal line  32  by the third throttling part  23 . Accordingly, it is possible to use the signal pressure for implementing an auto idle function through the shuttle valve  41  installed in the flow path  60  branched and connected to the signal line  32 . 
     The signal line  31  for the confluence switching valve is connected to the signal line  33  for the working devices through the check valve  42 . That is, in the case where the first switching valve A or the second switching valve B is not shifted, no signal pressure is formed in the signal line  31 . In this case, the confluence switching valve  8  is not shifted. 
     In the case of shifting the first switching valve A or the second switching valve B, a signal pressure is formed in the signal lines  32  and  33 . Accordingly, it is possible to use the signal pressure for implementing an auto idle function through the shuttle valve  41  installed in the flow path  60  branched and connected to the signal line  32 . 
     The signal line  35  connected to the signal line  31  for the confluence switching valve is connected to the signal line  34  for the traveling devices. If the fourth switching valve D is not shifted, no signal pressure is formed in the signal line  31 . In this case, the confluence switching valve  8  is not shifted. 
     On the other hand, in the case of simultaneously shifting the fourth switching valve D for the traveling devices and the first and second switching valves A and B for the working devices, the signal pressure is formed in the signal line  31  and in the signal lines  32 ,  33 , and  34 , and thus the confluence switching valve  8  is shifted. 
     Accordingly, the hydraulic fluid fed from the third hydraulic pump P 3  is supplied to the working devices on the first hydraulic pump side P 1  or to the working devices on the second hydraulic pump side P 2  to drive the working devices. 
     In the case of shifting the first to third switching valves A, B, and C connected to the first to third hydraulic pumps P 1 , P 2 , and P 3 , respectively, the signal pressure for implementing the auto idle function can be secured. 
     That is, in the case of simultaneously shifting the fourth switching valve D for the traveling devices and the first and second switching valves A and B for the working devices, the confluence switching valve  8  is shifted by the signal pressure formed in the signal line  31 . Accordingly, signal lines are formed so that the hydraulic fluid on the third hydraulic pump side P 3  joins the working devices on the first and second hydraulic pumps P 1  and P 2 . 
     As described above, in the case of implementing the confluence circuit and auto idle function in the hydraulic circuit for a construction machine according to an embodiment of the present invention, it is not necessary to form a separate signal line for passing through the first to third switching valves A, B, and C for all the working devices corresponding to the first to third hydraulic pumps P 1 , P 2 , and P 3   a  in order to form the auto idle signal pressure line. 
     In other words, the signal line  32  passing through the third switching valve C for the working devices is connected to the signal line  33  passing through the first and second switching valves A and B for the working devices. 
     In addition, the signal line  34  for the traveling devices that is connected to the fourth switching valve D for the traveling devices is independently formed. Accordingly, the signal pressure being outputted through the signal pressure output port  70  formed in the signal line  34  can be used as the signal pressure for travel boosting or travel alarming. 
     As described above, the hydraulic circuit for a construction machine according to the present invention has the following advantages. 
     The construction of the signal lines in the hydraulic circuit having the confluence circuit and the auto idle signal lines can be simplified and thus the manufacturing cost thereof can be reduced. 
     The leakage of the hydraulic fluid through the joint surfaces of the respective switching valves for the working devices and the traveling devices can be minimized, and thus the formed auto idle pressure can be stably maintained. 
     Although preferred embodiment of the present invention has been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.