Abstract:
The present invention provides a hydraulic circuit for a crane wherein a switching valve is provided between a plurality of motor circuits connected in series within the same actuator group, and at the time of simultaneous operation of the motor circuits, the switching valve is switched from a first position to a second position whereby the series connection between the motor circuits is cut off, and they are driven by each of separate hydraulic sources, thereby enabling prevention of pressure interference at the time of simultaneous operation of the motor circuits within the same actuator group without increasing hydraulic sources.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a hydraulic circuit for a crane in which a boom hoisting motor circuit and a wind-up motor circuit are connected in series to one and the same hydraulic source. 
   2. Description of the Related Art 
   In a case of a normal crawler crane, there are provided winches  1 , 2  and  3  which are a boom hoisting winch, a main winch and an auxiliary winch, respectively, as shown in  FIG. 3. A  main jib (boom)  4  is hoisted by the winch for a boom hoisting  1 . A main hook  5  suspended from the extreme end of the main jib  4  is moved up and down by the main winch  2 . An auxiliary hook  7  suspended from an auxiliary jib  6  mounted on the extreme end of the main jib is moved up and down by the auxiliary winch  3 . 
   In a case of a luffing crane, an auxiliary jib  9  is mounted on the extreme end of a tower type main jib  8 , as shown in  FIG. 4. A  main hook  5  is suspended from the extreme end of the auxiliary jib  9 . The auxiliary jib  9  is hoisted by the auxiliary winch  3 . 
   Operations (rotational operation is omitted in explanation here) including travel motion in these cranes are carried out by a hydraulic motor as a driving source. As hydraulic circuits, there are provided a main winding motor circuit, an auxiliary winding motor circuit, a boom hoisting motor circuit, and left and right traveling motor circuits. 
   A combination of a hydraulic source and an actuator is normally divided, as shown in  FIG. 5 , into a first actuator group A driven by a first hydraulic source  10  such as hydraulic pump and a second actuator group B driven by a second hydraulic source  11 . 
   A left traveling motor circuit  12 , a boom hoisting motor circuit  13 , and an auxiliary winding motor circuit  14  belong to the group A. A right traveling motor circuit  15  and a main winding motor circuit  16  belong to the group B. 
   It is constituted such that in both the groups A and B, the respective motor circuits are connected in series between the hydraulic sources  10 ,  11  and a tank T, and can be operated either individually or simultaneously. 
   According to the hydraulic circuit constitution as described above, in the composite operation in which not less than two motor circuits are operated simultaneously, when both the motor circuits belong to the same group, there occurs the following problem. 
   In a case where the boom hoisting motor circuit  13  and the auxiliary winding motor circuit  14  are operated simultaneously, for example, in a case where a hanging article is moved up and down by the auxiliary hook  7  while hoisting the jib  4  shown in  FIG. 3 , pressure interference occurs between the circuits  13  and  14 . Therefore, the respective operations fail to be carried out smoothly. In a case where the sum of pressure of both the circuits  13 ,  14  is high, a relief valve in the upstream circuit acts to relieve oil, thus resulting in an inconvenience that no operation can be carried out. 
   As shown in  FIG. 6 , a countermeasure is taken into consideration in which the boom hoisting motor circuit  13  is separated from the group A, and a third driving source  17  exclusive use for the circuit  13  is added. In this case, there poses a problem that an increase in cost and an increase in installation space are brought fourth due to further installation of the hydraulic source  17  and the increase in pipes and so on resulting therefrom. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a hydraulic circuit for a crane capable of preventing pressure interference when motor circuits are driven simultaneously within the same actuator group without increasing hydraulic sources. 
   The hydraulic circuit for a crane according to the present invention has the following constitution. 
   First, there is a first actuator group including actuator circuits driven by a first hydraulic source. The actuator circuits include a boom hoisting motor circuit which is a driving circuit for a winch motor for boom hoisting, and a wind-up motor circuit which is a driving circuit for a winch motor for wind-up. Further, the boom hoisting motor circuit and the wind-up motor circuit are selectively connected in series through a control valve for boom hoisting and a control valve for wind-up. 
   Next, there is a second actuator group including actuator circuits driven by a second hydraulic source. 
   There is provided a switching valve provided between the control valve for boom hoisting and the control valve for wind-up in the first actuator group. The switching valve is capable of being switched between a first position and a second position, wherein both the boom hoisting motor circuit and the wind-up motor circuit are connected to the first hydraulic source at the first position of the switching valve, and wherein at the second position of the switching valve, the boom hoisting motor circuit and the wind-up motor circuit are cut off from one another and a downstream one of the boom hoisting motor circuit and the wind-up motor circuit is connected to the second hydraulic source via the switching valve. 
   In this case, when the boom hoisting motor circuit and the wind-up motor circuit connected in series within the same actuator group are operated substantially simultaneously, the switching valve is switched from the first position to the second position, whereby the series connection of both the motor circuits is cut off, and these are driven by separate hydraulic sources, respectively. Therefore, pressure interference therebetween can be prevented. Further, any operation of both the motor circuits can be carried out smoothly. 
   Further, in a case where the hoisting motor circuit has a main motor circuit which is a driving circuit for a winch motor for main hoisting and an auxiliary motor circuit for auxiliary hoisting which is a driving circuit for a winch motor for auxiliary hoisting, employment of the following constitution is preferable. That is, one out of the main motor circuit and the auxiliary motor circuit is arranged in the first actuator group, and the other is arranged in the second actuator group. 
   This is the case of a crane provided with both main and auxiliary motor circuits as a wind-up motor circuit, which is able to exhibit the aforementioned effect. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a hydraulic circuit view showing, in a thick line, a flow of oil in a state that a switching valve is set to a first position in one embodiment of the present invention; 
       FIG. 2  is a hydraulic circuit view showing, in a thick line, a flow of oil in a state that a switching valve is set to a second position in one embodiment of the present invention; 
       FIG. 3  is a schematic view showing the constitution of a jib hoisting and wind-up portion in a crawler crane; 
       FIG. 4  is a schematic view showing the constitution of a jib hoisting and wind-up portion in a luffing crane; 
       FIG. 5  is a block constitution view of a hydraulic circuit in a conventional crane; and 
       FIG. 6  is a block constitution view of a partly modified constitution of the hydraulic circuit in FIG.  5 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Several preferred embodiments of the present invention will be described with reference to  FIGS. 1 and 2 . This is one embodiment of the present invention, and is not limited thereto. 
   In  FIGS. 1 and 2 , C designates a first actuator group provided with a first hydraulic source  21 , and D designates a second actuator group provided with a second hydraulic source  22 . 
   The first actuator group C comprises a left traveling motor circuit  24  for driving a left traveling motor  23 , a boom hoisting motor circuit  26  for driving a boom hoisting and lowering motor  25 , and an auxiliary motor circuit  28  for driving an auxiliary winding motor  27 . The motor circuits  24 ,  26  and  28  are connected in series between the hydraulic source  21  and a tank T through mutual control valves  29 ,  30  and  31 . 
   The second actuator group D comprises a right traveling motor circuit  33  for driving a right traveling motor  32 , and a main motor circuit  35  for driving a main winding motor  34 . Both the circuits  33  and  35  are connected in series through mutual control valves  36  and  37 . 
   Numerals  38  and  39  designate relief valves provided every group C and D. Numerals  40 ,  41  and  42  designate flow control valves provided every motor circuit described above. 
   In the hydraulic circuit, a hydraulic pilot type switching valve  43  is provided between both the control valves  30 ,  31  for boom hoisting and auxiliary winding in the group C. This switching valve  43  is constituted so as to be switched by an electromagnetic operating valve  44 . 
   When a switch  45  is turned on, the operating valve  44  is switched from a block position “a” shown to an open position “b” on the right side in the figure. At the open position “b”, pilot pressure from a pilot hydraulic source  46  is provided to the switching valve  43  through a pilot line  47 . The switching valve  43  is switched from a first position “x” shown to a second position “y” on the upper side in the figure. 
   FIG.  1  and  FIG. 2  show, in a thick line, oil flows in a case where the switching valve  43  is at the position “x”, and in a case where the valve is switched to a position “y”, respectively. At the position “x”, both the control valves  30 ,  31  (both motor circuits  26 ,  28  for boom hoisting and auxiliary winding) are connected in series. 
   In this state, any of the motor circuits for left travel motion, boom hoisting and auxiliary winding  24 ,  26  and  28  can be operated. In a case of  FIG. 1 , in the group C, the auxiliary motor circuit  28  is in the operating state, and in the group D, the main motor circuit  35  is in the operating state. 
   It is noted that in the group D, a flow channel switching valve  48  is provided. In  FIG. 1 , the flow channel switching valve  48  acts as a relief valve. Thereby, oil from a carry-over port  49  in the group D is returned to the tank T. 
   While in the figure, the channel switching valve  48  is illustrated as a sequence valve, it is noted that a hydraulic pilot type switching valve or the like may be used. 
   That is, a hydraulic pilot valve is used as a switching valve, and the switching valve may be constituted so that the valve is switched by an electromagnetic operating valve provided in a pilot circuit of the switching valve. In this case, since the switching valve is operated indirectly by the electromagnetic type operating valve, the operating portion can be installed at a position that is easily operated by an operator or at a position in a sufficient space for operation, as compared with the case where the switching valve is operated to be switched directly. 
   On the other hand, when the jib hoisting operation and the auxiliary winding operation are desired to be carried out simultaneously, the switching valve  43  is switched to the second position “y” through the switch  45  and the operating valve  44 . 
   In this state, both the boom hoisting and auxiliary motor circuits  26 ,  28  are cut off hydraulically as shown in FIG.  2 . Oil from the first hydraulic source  21  is sent to only the left traveling motor circuit  24  and the boom hoisting motor circuit  26 . 
   On the other hand, the switching valve  43  is connected to the carry-over port  49  in the group D through a communication line  50 . Therefore, at the second position “y”, oil from the second hydraulic source  22  is supplied to the auxiliary motor circuit  28  through the communication line  50  and the switching valve  43 . At this time, since the channel switching valve  48  is set to be at high pressure, oil from the carry-over port  49  flows toward the communication line  50 . 
   Accordingly, even if the boom hoisting motor circuit  26  and the auxiliary motor circuit  28  belonging to the same group C are operated simultaneously, no pressure interference likely occurs. 
   Incidentally, the crane is normally equipped with a moment limiter for detecting a jib angle, a suspension load amount or the like to calculate a load and prevent overload. The operating condition of the crane can be grasped by the moment limiter. 
   Thus, the moment limiter  51  may be utilized as simultaneous operation detector as shown in FIG.  2 . In this case, when the jib hoisting operation and the auxiliary or main operation are carried out simultaneously, a signal can be sent from the moment limiter  51  to the operating valve  44  to automatically switch the switching valve  43 . 
   Accordingly, simultaneous operation detector for detecting the simultaneous operation of the boom hoisting motor circuit and the wind-up motor circuit in the first actuator group C is provided so that the switching valve may be switched to the second position on the basis of a signal from the simultaneous operation detector. Thereby, there occurs no escape of operation of the switching valve  43  or no error in operation, and the intended switching action may be carried out definitely. 
   On the other hand, while in the above-described embodiment, the switching valve  43  is operated indirectly by the operating valve  44 , it is noted that the constitution may be employed in which the switching valve  43  is operated directly manually or electromagnetically. 
   Further, while in the above-described embodiment, the boom hoisting motor circuit  26  and the auxiliary motor circuit  28  are arranged in the same group (group C), it is noted that the boom hoisting motor circuit  26  and the main motor circuit  35  may be arranged in the same group. Alternatively, the boom hoisting motor circuit  26  and both the main and auxiliary motor circuits  35  and  28  may be arranged in the same group, and when the boom hoisting operation and the wind-up (main winding or auxiliary winding) works are carried out simultaneously, the hydraulic source may be divided. 
   While one embodiment of the present invention has been disclosed in the foregoing, it is to be noted that the scope of protection of the present invention is not limited thereto.