Abstract:
A hydraulic system for a tire curing press includes at least one tire press operated by a hydraulic cylinder and a hydraulic control valve; a hydraulic unit for supplying pressure oil of a fixed pressure; an accumulator circuit for accumulating pressure oil from said hydraulic unit to supply the accumulated pressure oil to the hydraulic cylinder and the hydraulic control valve; and a check valve provided on every tire press. The check valve cuts off pressure oil from the hydraulic unit and the accumulator circuit during vulcanization of the tire press. Thereby, it is possible to limit the operation of the hydraulic unit during the vulcanization which results in energy saving operation.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a hydraulic actuator used for various mechanisms of a hydraulic type tire press, and a hydraulic system for a tire curing press for supplying pressure oil to a hydraulic control valve. 
     2. Description of the Related Art 
     A press frame of a tire vulcanizer (a tire press) comprises, as shown in FIG. 3, an upper frame  31 , a lower frame  32 , and a side frame  33 , and a metal mold  35  is secured to the lower frame  32  through a lower mold mounting member  34 . An upper metal mold  36  is secured to an upper mold mounting member  37 , and is closable with respect to the lower metal mold  35 . A piston rod  38  is secured to the mounting member  37 , the mounting member  37  being moved up and down along a vertically elevating guide  39  by operation of an elevating cylinder  26 . A pressurizing and transmitting rod  40  is stood upright on the mounting member  37 , and a clamping cylinder  27  for transmitting a pressurizing force to the pressurizing and transmitting rod  40  is fixedly mounted on the upper frame  31 . 
     The tire vulcanizer repeats the inserting step for inserting a green tire prior to vulcanization between the upper and lower metal molds  35  and  36  to close the upper and lower metal molds  35  and  36 , the vulcanizing step for loading the clamping force to the upper and lower metal molds  35  and  36  so that the tire is not forced out during vulcanization to vulcanize the tire, and the taking out step for opening the mold in order to take out the vulcanized tire to vulcanize the tires sequentially. As shown in FIG. 5, the inserting step and the taking out step are referred to as “dry cycle”, and the step for loading the clamping force to vulcanize the tire is referred to as “vulcanizing cycle”. That is, the operating cycle of the tire vulcanizer is divided broadly into the dry cycle and the vulcanizing cycle. 
     The conventional hydraulic unit in the tire curing press is generally designed so that as shown in FIG. 4, a large capacity, 100 l/min, variable capacity pump  43  with cut-off pressure set to 125 kgf/cm 2 , and a large capacity, 170 l/min, fixed capacity pump  44  are respectively driven by a 22 kw motor to supply pressure oil to five presses  48  to  52 . An unload valve  45  having 140 kgf/cm 2  of set pressure is connected to the variable pump  43 , and an unload valve  46  having 100 kgf/cm 2  of set pressure is connected to the fixed pump  44 . These unload valves  45  and  46  have a relief function for protecting line pressure, and a role for compensating for operating pressure of the press, and are designed so that pressure oil discharged from the pumps is switched to the press sides  48  to  52  and the tank side  53 . In the conventional hydraulic unit  47 , in the press closing operation during the dry cycle, pressure oil is supplied to the press sides  48  to  52  by the variable pump  43  and the fixed pump  44 ; and during the vulcanization, necessary flow rate is supplied to the presses  48  to  52  sides merely by the variable pump  43  to compensate for pressure. The dry cycle in the presses is approximately 1/10 of the vulcanizing cycle, and the variable pump  43  is continuously operated in order to compensate for pressure. 
     The variable pump  43  is always in the on-load state during the dry cycle and during the vulcanization as well, and pressure oil discharged from the pump  43  is supplied to the presses  48  to  52  sides. However, during the vulcanization, pressure oil is merely necessary for the clamping cylinder and a part of actuators such as a clamp portion, and the flow rate necessary for the presses  48  to  52  sides is lessened as a whole. Therefore, the discharge flow rate of the variable pump  43  is automatically adjusted to the minimum discharge flow rate to supply pressure oil. 
     However, since the variable pump always supplies pressure oil to the press sides, pressure is always applied to hydraulic lines on the press sides after the hydraulic pump to cause a leakage of the about 5 to 10 l/min mark from the hydraulic valve. Further, the flow rate necessary for the presses is variable as shown in FIG. 5, and the constant flow rate is not always necessary, and therefore, the fixed pump is in the unload state during the vulcanization, and the discharged pressure oil is thrown into the tank. As described above, in the conventional hydraulic system, the motor of the hydraulic unit is continuously operated despite the fact that the most machineries stop during the vulcanization so that two pumps are being operated without stopping. Further, since the leakage from the hydraulic valve is incontinent, there poses a problem in that power (energy) is used wastefully so that consuming electric power of the hydraulic unit is wasted. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a hydraulic system for a tire curing press for limiting operation of a hydraulic unit during vulcanization by which machineries are stopped. 
     The present invention provides a hydraulic system for a tire vulcanizer in which various hydraulic cylinders of a tire vulcanizer for vulcanizing and molding tires and a hydraulic unit for supplying pressure oil having a fixed pressure are connected by hydraulic lines, comprising the one or more tire vulcanizers operated by said various hydraulic cylinders, a hydraulic unit for supplying pressure oil of fixed pressure, an accumulator circuit for supplying the accumulated pressure oil to said various hydraulic cylinders, and check means provided every said tire vulcanizer so that during vulcanization of said tire vulcanizer, pressure oil of said hydraulic unit and said accumulator circuit is cut off, and in the operation of said tire vulcanizer, the cutting off is released to cause the pressure oil of said hydraulic unit and said accumulator circuit to pass. 
     In this case, during the dry cycle, pressure oil is supplied from the hydraulic unit and the accumulator; and during the vulcanization, a master valve constituting the check means is closed to cut off a supply of pressure oil from the accumulator and the hydraulic unit to the various hydraulic cylinders. The hydraulic unit supplies pressure oil to the accumulator to accumulate it during the time pressure oil is cut of a supply to the various hydraulic cylinders. Thereby, pressure oil can be supplied at a stretch from the hydraulic unit and the accumulator to the various cylinders during the dry cycle, and a pump having a smaller capacity than that of conventional pumps without delaying the dry cycle time for about 1 to 2 minutes. When a supply of pressure oil from the hydraulic unit and the accumulator is cut off by the master valve constituting the check means, it is not necessary to always supply pressure oil of fixed quantity in order to compensate for a leakage from the hydraulic valve in each vulcanizer but a supply quantity of pressure oil during the vulcanization can be reduced, thus enabling reduction of consuming electric power of the hydraulic unit. 
     The present invention further provides, in addition to the above-described constitution, a hydraulic system in which every said tire vulcanizer is provided an auxiliary accumulator for accumulating the remainder of the discharged flow rate of said hydraulic unit, if the discharged flow rate of said hydraulic unit and said main accumulator exceeds the necessary flow rate of said tire vulcanizer, to compensate for pressure of said various hydraulic cylinders during the vulcanization. 
     In this case, since pressure oil can be supplied to clamps or the like requiring pressure oil during vulcanization by the auxiliary accumulator without throwing out the remainder of the discharged flow rate of the hydraulic unit as in prior art, and therefore, the effective utilization of pressure oil can be achieved, and the consuming electric power of the hydraulic unit can be further reduced. 
     Further, according to the present invention, in addition to the above-described constitution, the hydraulic unit turns on and off a supply of pressure oil with fixed pressure of the hydraulic line being a reference. 
     In this case, when the hydraulic line reaches fixed pressure, the hydraulic unit is stopped, and pressure oil can be supplied merely by the main accumulator, whereby the hydraulic unit need not be operated always during the vulcanization, and the consuming power of the hydraulic unit can be further reduced. 
     Furthermore, according to the present invention, in addition to the above-described constitution, a supply of pressure oil and the operation of the pump are turned on and off with whether or not the tire vulcanizer is in the vulcanizing operation state being a reference, whereby pressure oil more than as needed is not supplied, and the consuming power of the hydraulic unit can be further reduced. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a view for explaining a hydraulic system for a tire curing press according to the present embodiment; 
     FIG. 2 is a view for explaining various actuators for a tire vulcanizer according to the present embodiment; 
     FIG. 3 is a view for explaining a tire vulcanizer according to the present embodiment; 
     FIG. 4 is a view for explaining a conventional hydraulic system for a tire curing press; and 
     FIG. 5 is a view for explaining operating cycles of a tire vulcanizer according to the present embodiment. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The embodiments of the present invention will be described with reference to the drawings. Since the tire vulcanizer is similar to that described in the related art, a description thereof will be omitted. As shown in FIG. 1, a hydraulic system  1  for a tire curing press is divided broadly into a hydraulic unit  2 , a main accumulator circuit  3 , and a hydraulic circuit  25  on the vulcanizer side from master valves  4  to  8  constituting check means (see FIG.  2 ). The hydraulic unit  2  comprises two small capacity variable pumps  14  and  15 , a hydraulic tank  24 , and a pressure switch  18  so as to supply pressure oil to vulcanizers  9  to  13 . The small capacity variable pumps  14  and  15  are driven by a small motor of approximately 15 kw so as to supply oil to a hydraulic tank  24 . Check valves  16  and  17  are connected to the vulcanizers  9  to  13  sides of the variable pumps  14  and  15  so as to prevent the back flow to the variable pumps  14  and  15 . Further, a hydraulic line is joined after the check valves  16  and  17 , and the pressure switch  18  is connected to the junction. The pressure switch  18  is designed so as to provide a signal by which the hydraulic unit  2  side and the vulcanizer side are cut off when pressure oil from the variable pumps  14  and  15  assumes 135 kgf/cm 2 . When they are cut off, the variable pumps  14  and  15  stop their operation. 
     The main accumulator circuit  3  is connected to the hydraulic lines after the hydraulic unit  2  so as to accumulate pressure oil from the hydraulic unit and supply pressure oil to the vulcanizers  9  to  13  sides. In the accumulator circuit  3 , four accumulators  19  to  22  are connected in parallel through a sequence valve  23  from the hydraulic line. The main accumulator circuit  3  supplies, when pressure oil of fixed capacity is accumulated, pressure oil to the vulcanizers  9  to  13  sides from the accumulated portion. 
     When the dry cycle ends, the master valves  4  to  8  cuts off pressure oil from the main accumulator circuit  3  and the hydraulic unit  2 . When pilot check valves are used for the master valves  4  to  8 , the check function can be released by fixed pilot pressure caused by pressure oil of the hydraulic unit  2  and the main accumulator circuit  3 . To the hydraulic line after the master valves  4  to  8  are connected, as shown in FIG. 2, various actuators such as a press closing cylinder  26  of the vulcanizers  9  to  13 , a press clamping cylinder  27 , a bladder clamp  29  (always generating a clamping force) and so on. The press closing cylinder  26  is used here to clamp a green tire prior to vulcanization, and to elevate an upper mold  36  when the tire after vulcanized is removed. That is, pressure oil from the main accumulators  19  to  22  and the small capacity variable pumps  14  and  15  is supplied to order to actuate various actuators during the dry cycle. 
     On the other hand, a pneumatic pressure hydraulic booster  28  constituting an amplifying circuit is connected to the press clamping cylinder  27 , and even if the master valves  4  to  8  are closed to cut off pressure oil from the main accumulators  19  to  22  and the small capacity variable pumps  14  and  15 , clamping of the upper and lower metal molds  36  and  35  can be done by pressure oil from the pneumatic pressure hydraulic booster  25 . Further, an auxiliary accumulator  30  is connected to the bladder clamp  29 , and even if the master valves  4  to  8  are closed to cut off pressure oil from the main accumulators  19  to  22  and the small capacity variable pumps  14  and  15 , the bladder end can be clamped and held by pressure compensation of pressure oil from the auxiliary accumulator  30 . When the discharged flow rate of the small capacity variable pumps  14  and  15  exceeds necessary flow rate of the vulcanizers  9  to  13  during the dry cycle, the remainder thereof is accumulated in the auxiliary accumulator  30 . To other accumulators for which compensation of holding pressure of the hydraulic line is necessary during vulcanization are supplied pressure oil from the main accumulator circuit  3  opening the master valves  4  to  8  as necessary. 
     In the following, the operation of the hydraulic system for a tire curing press  1  will be described on the basis of the above-described constitution. As shown in FIG. 5, during the dry cycle (T 0  to T 1 ), pressure oil is supplied to various press actuators on the vulcanizers  9  to  13  side by the two small capacity variable pumps  14  and  15  and the main accumulator circuit  3 . When the necessary flow rate of press exceeds its peak, the discharged flow rate of the two small capacity variable pumps  14  and  15  exceeds the necessary flow rate of press, and therefore, the remainder thereof is accumulated in the main accumulator and the auxiliary accumulator  30 . In this manner, when a fixed quantity of pressure oil is supplied to the press, the upper metal mold  36  moves toward the lower metal mold  35  so that both the upper and lower metal molds  36  and  35  are closed to clamp the green tire. Then, the master valves  4  to  8  are closed to cut off a supply of pressure oil from the main accumulator circuit  3  and the hydraulic unit  2  and start the vulcanization of the green tire (T 1 ). 
     Since the accumulated portion of the main accumulators  19  to  22  is lessened by the supply of pressure oil during the dry cycle, and pressure lowers, the small capacity variable pumps  14  and  15  supply pressure oil to the main accumulators  19  to  22  (T 1 ). When oil is accumulated in the four accumulators  19  to  22  (T 1  to T 2 ), and pressure of the hydraulic line assumes 135 kgf/cm 2 , pressure oil from the two variable pumps  14  and  15  is cut off by the check valves  16  and  17  of the hydraulic unit  2 , and the variable pumps  14  and  15  stop their operation (T 2 ). During the vulcanization (T 1  to T 5 ), pressure oil is supplied from the pneumatic pressure hydraulic booster  28  to the press clamping cylinder  27  to clamp the upper and lower metal molds and clamp the green tire. Further, pressure oil is supplied to the bladder clamp  29  in order to compensate for leakage of the pilot check valve from the auxiliary accumulator  30 . Where other actuators are operated, the master valves  4  to  8  are opened (T 3 ) to supply pressure oil from the main accumulator circuit  3  (T 3  to T 4 ). Since at that time, the check valves  16  and  17  of the hydraulic unit  2  are in the closed state, pressure oil of the main accumulator circuit  3  does not flow toward the variable pups  14  and  15  and the hydraulic tank  24 . 
     As described above, when the master valves  4  to  8  are closed during the vulcanization, pressure of the hydraulic line after the master valves  4  to  8  lowers so that pressure oil does not leak from the hydraulic circuit of each oppress as in prior art, thus not making it necessary to compensate for the leakage. That is, since as in the prior art, the hydraulic unit  2  need not be always operated in order to compensate for leakage during the vulcanization, the energy saving operation can be accomplished. Further, since necessary flow rate of the press closing cylinder  26  can be compensated for by the main accumulator circuit  3 , even if small pumps  14  and  15  are used for the hydraulic unit  2  as compared with prior art, the press closing can be accomplished within a fixed period of time (within the dry cycle for about one minute). 
     When two variable pumps of 135 kgf/cm 2 , 55 l/min, and 15 kw are used for the small capacity variable pumps  14  and  15  of the hydraulic unit  2 , the consuming power of the conventional hydraulic unit using the variable pump of 125 kgf/cm 2 , 100 l/min, and 22 kw and the fixed pump of 170 l/min and 22 kw can be reduced by approximately 30%. In this case, the initial investment cost imposed on the unit is about double, but the initial investment cost can be recovered in about two years by the energy saving effect.