JP5442581B2 - Hydraulic oil cooling method for injection molding machine - Google Patents

Description

  The present invention relates to a hydraulic fluid cooling method for an injection molding machine having a hybrid configuration in which a hydraulic actuator and an electric actuator are combined.

  In general, a hydraulic injection molding machine includes various hydraulic actuators such as a clamping cylinder, a molded product protruding cylinder, an injection cylinder, and a metering oil motor, and these hydraulic actuators are driven by a hydraulic drive unit including a hydraulic pump. The Moreover, since the temperature of the hydraulic oil used for a hydraulic drive part rises at the time of operation of an injection molding machine, the hydraulic oil which flows into a return oil circuit is normally cooled with the heat exchanger.

  Conventionally, as a cooling circuit for such hydraulic fluid, a cooling circuit provided in a hydraulic device disclosed in Patent Document 1 is known. In the same document 1, a variable discharge pump as a hydraulic source for driving an actuator is known. And a heat exchanger that is connected to the return oil circuit of the actuator that intermittently discharges hydraulic oil, cools the hydraulic oil and discharges it to the oil tank, and a case drain circuit and return oil circuit of the variable discharge pump that constantly discharges hydraulic oil Are connected to the case drain circuit side and opened when the return oil circuit connected to the case drain circuit is used to discharge the return oil of the actuator. A cooling circuit comprising a valve for releasing hydraulic oil into an oil tank is disclosed.

Japanese Unexamined Patent Publication No. 60-26804

  However, the conventional cooling circuit including the above-described hydraulic device of Patent Document 1 has the following problems to be solved.

  First, in order for such a cooling circuit to function, it is necessary that the hydraulic oil sufficiently flows in the return oil circuit, and sufficient cooling cannot be performed when the flow rate of the hydraulic oil is small. . By the way, an injection molding machine having a hybrid configuration in which some hydraulic actuators in a hydraulic injection molding machine are replaced with electric actuators is also known, but an injection cylinder (hydraulic cylinder) is obtained by replacing a metering oil motor with a servo motor. In the hybrid configuration, the metering oil motor has the largest flow rate of hydraulic oil among hydraulic actuators, so the flow rate of hydraulic oil in the return oil circuit is greatly reduced. After all, when such a combination is adopted, it is necessary to improve the capacity of the heat exchanger (size up) or to install a separate cooling device for cooling the hydraulic oil in the oil tank. Inevitable increase in circuit cost and size.

  Secondly, in the conventional cooling circuit in which the hydraulic oil flowing in the return oil circuit is passed through the heat exchanger, the flow resistance of the circuit is increased by the heat exchanger, and the hydraulic oil flowing in the return oil circuit is being driven by the hydraulic actuator. Therefore, it has a considerable influence on the speed control of the hydraulic actuator (oil motor) and the cooling of the hydraulic oil. Therefore, there is a possibility that the stability and accuracy of control in the weighing process may be impaired, and it is easy to cause insufficient cooling of the hydraulic oil and unstable temperature.

  An object of the present invention is to provide a method for cooling hydraulic oil of an injection molding machine that solves the problems existing in the background art.

  In order to solve the above-described problem, the hydraulic fluid cooling method for an injection molding machine according to the present invention drives hydraulic actuators Ao in an injection molding machine M having a hybrid configuration in which hydraulic actuators Ao and electric actuators Ae are combined. A hydraulic fluid cooling method for an injection molding machine that cools hydraulic fluid to be used, and the discharge side of the hydraulic pump 2 that supplies hydraulic fluid to the hydraulic actuators Ao and the oil tank 3 are closed when the hydraulic actuators Ao are driven. Is connected by a series circuit 6 of a cooling on-off valve 4 and a heat exchanger 5 for cooling the hydraulic oil, and the temperature of the hydraulic oil is detected by a hydraulic oil temperature sensor 7, and the detected temperature of the hydraulic oil (temperature detection value) ) Cooling is performed during a period when the hydraulic actuators Ao are not driven so that To becomes a preset appropriate temperature (temperature set value) Ts. Characterized in that to perform the cooling to the working fluid by switching the on-off valve 4 on the open side.

  In this case, according to a preferred aspect of the invention, the temperature set value Ts can be set by a temperature range based on the upper set value Tsu and the lower set value Tsd. Further, after the temperature detection value To reaches the upper set value Tsu, the hydraulic oil can be cooled until it reaches the lower set value Tsd except when the hydraulic actuators Ao. On the other hand, the period when the hydraulic actuators Ao... Are not driven can include the time when the electric actuators Ae are driven. The electric actuator Ae can be a measuring servo motor Aem that rotates the screw 12 built in the heating cylinder 11 of the injection device Mi. Furthermore, the hydraulic pump 2 can be a variable discharge hydraulic pump 2s that can change at least the discharge flow rate according to the rotation speed of the pump motor 13 using a servo motor.

  According to the hydraulic fluid cooling method of the injection molding machine M according to the present invention by such a method, the following remarkable effects are achieved.

  (1) Cooling on-off valve 4 that switches between the discharge side of the hydraulic pump 2 that supplies hydraulic oil to the hydraulic actuators Ao and the oil tank 3 to the closed side when the hydraulic actuators Ao are driven, and heat that cools the hydraulic oil Since the hydraulic fluid is cooled by connecting with the series circuit 6 of the exchanger 5 and switching the cooling on-off valve 4 to the open side, a hybrid configuration combining the hydraulic actuator Ao... And the electric actuator Ae is adopted. Even when a cooling circuit in which a heat exchanger is connected to the flow path of the hydraulic oil is used, sufficient cooling of the hydraulic oil can be performed.

  (2) Since it is sufficient to add a cooling on / off valve 4 to the conventional cooling circuit in terms of structure, the cooling circuit can be implemented at low cost without increasing the size of the cooling circuit, and when the hydraulic actuator Ao is not driven. Since the hydraulic oil is cooled during this period, the cooling process does not affect the drive control of the hydraulic actuators Ao. Therefore, it is possible to contribute to stabilization of control and stabilization of hydraulic oil temperature in the injection molding machine M.

  (3) If the temperature set value Ts is set in a preferred range according to the temperature range of the upper set value Tsu and the lower set value Tsd, chattering during temperature control can be prevented, and stable temperature control can be realized.

  (4) According to a preferred embodiment, after the temperature detection value To reaches the upper set value Tsu, the hydraulic oil is cooled until it reaches the lower set value Tsd except when the hydraulic actuators Ao. Since the problem that the temperature of the hydraulic oil is shifted to the upper set value Tsu side can be avoided, the average temperature of the hydraulic oil can be made close to the original proper temperature.

  (5) According to a preferred aspect, if the period when the electric actuator Ae is driven is included in the period when the hydraulic actuators Ao... Are not driven, it is possible to sufficiently ensure the period of the cooling process for the hydraulic oil.

  (6) According to a preferred embodiment, if the measuring servo motor Aem that rotates the screw 12 built in the heating cylinder 11 of the injection device Mi is applied as the electric actuator Ae, an optimum hybrid configuration of the injection molding machine M is achieved. Thus, a hydraulic oil cooling method matching such a hybrid configuration can be realized.

  (7) According to a preferred embodiment, if a variable discharge hydraulic pump 2s capable of varying at least the discharge flow rate according to the rotation speed of the pump motor 13 using a servo motor is used as the hydraulic pump 2, the variable discharge hydraulic pump 2s is adopted. In addition to the advantages such as improved energy saving, there is almost no case drain amount, so the hydraulic oil can be efficiently cooled without waste.

The flowchart for demonstrating the process sequence of the hydraulic-oil cooling method which concerns on suitable embodiment of this invention, Configuration diagram including a hydraulic drive unit and a control system of an injection molding machine used to implement the hydraulic oil cooling method, Temperature change characteristic diagram of hydraulic oil with respect to time when the hydraulic oil cooling method is carried out, The block diagram which shows the state of the hydraulic drive part at the time of cooling of the hydraulic fluid by the hydraulic fluid cooling method,

  Next, preferred embodiments according to the present invention will be given and described in detail with reference to the drawings.

  First, the configuration of an injection molding machine M that can implement the hydraulic fluid cooling method according to the present embodiment will be described with reference to FIG.

  In FIG. 2, M is an injection molding machine and includes an injection device Mi and a mold clamping device. The mold clamping device is not shown, and only the mold 20 supported by this mold clamping device is shown. The injection device Mi includes a heating cylinder 11 having an injection nozzle 21 at the front end and a hopper 22 at the rear. A screw 12 is inserted into the heating cylinder 11, and a screw is driven at the rear end of the heating cylinder 11. The part 23 is disposed. The screw drive unit 23 includes an injection cylinder (hydraulic cylinder) 24 containing a single rod type injection ram 24p, and a ram rod 24pr protruding forward of the injection ram 24p is coupled to the rear end of the screw 12. The injection cylinder 24 serves as a hydraulic actuator Ao.

  A shaft 25 of a measuring servo motor Aem attached to the rear end surface of the injection cylinder 24 is splined to the rear end of the injection ram 24p. The servo motor Aem is an electric actuator Ae, and a rotary encoder 26 for detecting the rotation speed of the servo motor Aem is provided at the rear end of the servo motor Aem. As described above, when the measuring servo motor Aem for rotating the screw 12 built in the heating cylinder 11 of the injection device Mi is applied as the electric actuator Ae, an optimum hybrid configuration of the injection molding machine M is obtained. A hydraulic oil cooling method matched to the hybrid configuration can be realized. The injection device Mi can touch the injection nozzle 21 to the mold 20 to inject and fill the molten resin into the cavity of the mold 20.

  On the other hand, 31 is a hydraulic drive unit, which includes a hydraulic pump 2 serving as a hydraulic drive source. The hydraulic pump 2 uses a variable discharge hydraulic pump 2 s that can vary the discharge flow rate and the discharge pressure according to the rotation speed of the pump motor 13. The hydraulic pump 2s includes a pump unit 33 and a pump motor 13 using a servo motor such as an AC servo motor that rotationally drives the pump unit 33. Reference numeral 34 denotes a rotary encoder that detects the rotational speed of the pump motor 13. Moreover, the pump part 33 incorporates the pump body 35 comprised with a swash plate type piston pump. Therefore, the pump unit 33 includes the swash plate 36. If the inclination angle (swash plate angle) of the swash plate 36 is increased, the stroke of the pump piston in the pump body 35 increases, the discharge flow rate increases, and the swash plate increases. If the angle is made smaller, the stroke of the pump piston becomes smaller and the discharge flow rate decreases. Therefore, by setting the swash plate angle to a predetermined angle, it is possible to set a fixed discharge flow rate at which the discharge flow rate is fixed to a predetermined size. A control cylinder 37 and a return spring 38 are attached to the swash plate 36, and the control cylinder 37 is connected to a discharge port of the pump unit 33 (pump machine body 35) via a switching valve (electromagnetic valve) 39. Thus, the angle of the swash plate 36 (swash plate angle) can be changed by controlling the control cylinder 37.

  Thus, if the rotational speed of the pump motor (servo motor) 13 is variably controlled, the discharge flow rate and the discharge pressure of the variable discharge hydraulic pump 2s can be varied. Based on this, the above-described injection cylinder 24 and other actuators can be changed. Can be controlled, and each operation process in the molding cycle can be controlled. In particular, since the variable discharge hydraulic pump 2s that can set the fixed discharge flow rate by changing the swash plate angle is used as the hydraulic pump 2, the pump capacity can be set to a fixed discharge flow rate of a predetermined size, and the fixed discharge flow rate is basically used. Since the discharge flow rate and the discharge pressure can be varied, the control can be facilitated and smoothed.

  On the other hand, the suction port of the pump unit 33 is connected to the oil tank 3 via the oil distribution pipe Lp, and the discharge port of the pump unit 33 is connected to the primary side of the switching valve circuit 41. The secondary side is connected to other hydraulic actuators including an injection cylinder 24 in the injection molding machine M, a clamping cylinder, a protruding cylinder, and an injection device moving cylinder. Therefore, the switching valve circuit 41 includes at least switching valves (electromagnetic valves) connected to the injection cylinder 24 and the other hydraulic actuators. Each switching valve is composed of one or two or more valve parts and necessary accessory hydraulic parts, etc., and at least switching related to supply, stop and discharge of hydraulic oil to the injection cylinder 24 and other actuators. It has a function. The oil tank 3 is provided with a hydraulic oil temperature sensor 7 for detecting the temperature To of the hydraulic oil stored in the oil tank 3.

  Further, the oil distribution pipe Lp on the discharge side of the hydraulic pump 2 s and the oil tank 3 are connected by a series circuit 6 of a cooling on-off valve 4 and a heat exchanger 5. In this case, the cooling on-off valve 4 uses an electromagnetic valve. The cooling on-off valve 4 is a normally closed type, and is switched to the closed side at normal times including when the hydraulic actuators Ao. The heat exchanger 5 functions as a cooler for cooling the hydraulic oil, and allows the hydraulic oil to flow through the secondary side flow path, and causes the coolant (cooling water) W to flow through the primary side flow path from the coolant supply unit 100. In addition, between the coolant supply part 100 and the heat exchanger 5, a cooling water flow valve 101 using an electromagnetic valve (open / close valve) is connected in series. This cooling water flow valve 101 is also a normally closed type.

  On the other hand, 51 is a molding machine controller that controls the entire injection molding machine M. The molding machine controller 51 is provided with a setting unit 51s and a display unit 51d. Note that a touch panel type liquid crystal display or the like is used for the setting unit 51s and the display unit 51d. The setting unit 51s sets the upper set value Tsu and the lower set value Tsd as a temperature range with respect to at least the appropriate temperature (temperature set value) Ts of the hydraulic oil, and also detects the abnormal temperature, the upper limit alarm temperature TM and the lower limit alarm. Set the temperature TL. Thus, if the temperature set value Ts is set by the temperature range of the upper set value Tsu and the lower set value Tsd, chattering during temperature control can be prevented, and there is an advantage that stable temperature control can be realized. In the example, the appropriate temperature Ts is 37 [° C.], the upper set value Tsu is 37 + 3 [° C.], the lower set value Tsd is 37-3 [° C.], the upper limit alarm temperature TM is 55 [° C.], and the lower limit alarm temperature TL is 30 [° C.]. The molding machine controller 51 includes hardware such as a CPU and a memory, and includes a computer function having a processing program (software) for executing various arithmetic processes and various control processes (sequence control), and at least relates to the present embodiment. A sequence control program for executing the hydraulic oil cooling method is stored.

  In connection with the present invention, the hydraulic oil temperature sensor 7 is connected to the sensor port of the molding machine controller 51, and the cooling on-off valve 4 and the cooling water flow valve 101 are connected to the output port of the molding machine controller 51. Connecting. Further, the measuring servo motor Aem, the rotary encoder 26, the pump motor 13, and the rotary encoder 34 are connected to a servo circuit incorporated in the molding machine controller 51.

  Next, the hydraulic fluid cooling method according to this embodiment including the operation of the injection molding machine M having such a configuration will be described according to the flowchart shown in FIG. 1 with reference to FIGS.

  Now, it is assumed that the injection molding machine M is operating normally (step S1). The molding machine controller 51 monitors the temperature of the hydraulic oil unless the injection molding machine M stops operating (steps S2 and S3). That is, the temperature of the hydraulic oil is detected by the hydraulic oil temperature sensor 7 and given to the molding machine controller 51 as the temperature detection value To. Since the temperature setting value Ts, that is, the upper setting value Tsu and the lower setting value Tsd, is set in the molding machine controller 51, whether or not the temperature detection value To has reached the upper setting value Tsu or the lower setting value Tsd. Monitor whether or not Note that both the cooling on-off valve 4 and the cooling water flow valve 101 are switched to the closed side in modes other than the cooling mode in which the hydraulic oil is cooled.

  Therefore, the temperature of the hydraulic oil during operation (temperature detection value To) gradually increases. When the temperature detection value To reaches the upper set value Tsu at time t1 shown in FIG. 3, the molding machine controller 51 executes the cooling mode. At this time, first, it is determined whether or not the hydraulic actuators Ao are being driven (steps S4 and S5). Whether or not the drive is in progress can be determined based on whether or not a control command signal for each of the hydraulic actuators Ao. In this case, the hydraulic actuators Ao to be discriminated are preferably all the hydraulic actuators Ao, but are not essential requirements. That is, the protruding hydraulic cylinder or the like that requires a small amount of working oil and does not require a high degree of accuracy may have little influence even when it is being driven. Ao may be set, and the hydraulic actuators Ao to be discriminated can be set in advance.

  When it is determined whether or not the hydraulic actuators Ao are being driven, the molding machine controller 51 performs switching control of the cooling on-off valve 4 and the cooling water flow valve 101 to the open side, respectively, if not being driven. Then, the hydraulic pump 2s is put into an operating state (step S6). As a result, as shown in FIG. 4, the hydraulic oil sucked up from the oil tank 3 by the hydraulic pump 2 s is discharged from the discharge port of the hydraulic pump 2 s and then flows along the route indicated by the dotted arrow Fo. That is, it passes through the cooling on-off valve 4 and then circulates through a path that passes through the heat exchanger 5 and returns to the oil tank 3. The hydraulic oil is cooled by heat exchange with the cooled coolant (cooling water) W when passing through the heat exchanger 5 (step S7). Further, during the cooling process, the molding machine controller 51 monitors whether or not the hydraulic actuators Ao... Start driving, and if the driving does not start, continues the cooling process. Thereby, the hydraulic oil in the oil tank 3 is cooled and gradually decreases. When the temperature detection value To detected by the hydraulic oil temperature sensor 7 reaches the lower set value Tsd at time t2 shown in FIG. 3, the cooling mode is stopped (step S10).

  When the temperature detection value To reaches the upper set value Tsu and it is determined in step S5 described above whether the hydraulic actuators Ao. Step S11). Due to the standby mode, the cooling mode is temporarily suspended until the driving of the hydraulic actuators Ao. In the standby mode, the driving of the hydraulic actuators Ao... Is monitored by the molding machine controller 51. When the driving is completed, the standby mode is canceled and the cooling mode is executed (steps S12, S6...). In this way, the cooling mode is performed only during a period when the hydraulic actuators Ao. In this case, the period when the hydraulic actuators Ao... Are not driven includes the time when the electric actuators Ae are driven. Since the hydraulic actuator Ao is replaced with the electric actuator Ae by the hybrid configuration, the entire driving period of the hydraulic actuators Ao... Is shortened, and the period when the electric actuators Ae are driven is included in the period when the hydraulic actuators Ao. Thereby, the period of the cooling process with respect to hydraulic fluid can be made comparatively long.

  On the other hand, when the hydraulic actuators Ao... Start driving during execution of the cooling mode, the cooling mode is stopped (steps S6 to S8, S13 to S5), and the mode is shifted to the standby mode (step S11). Also in this case, the molding machine controller 51 monitors the hydraulic actuators Ao..., And when driving is completed, the standby mode is canceled and the cooling mode is re-executed (steps S12, S6...).

  FIG. 3 shows a state in which the temperature detection value To reaches the upper set value Tsu at the time t3, the cooling mode is executed, and the driving of the hydraulic actuators Ao ... is started at the time t4 during the cooling. . A symbol Zsa indicates a period during which the hydraulic actuators Ao are being driven, and the driving ends at time t5. Therefore, the cooling mode is stopped during the driving period Zsa and the standby mode is entered. During this period Zsa, the temperature of the hydraulic oil rises, but when the driving of the hydraulic actuators Ao... Is completed at time t5, the cooling mode is executed again, and the cooling process for the hydraulic oil is performed. Furthermore, in the case of the example, the state is shown in which the driving of the hydraulic actuators Ao. In this case, the same processing is performed, the cooling mode is stopped at time t6, the mode is shifted to the standby mode, and the cooling mode is executed again at time t7 after the elapse of the period Zsb. Since the temperature detection value To reaches the lower set value Tsd at time t8, the cooling mode stops thereafter until the temperature detection value To reaches the upper set value Tsu (steps S9, S10, S2...).

  As described above, after the temperature detection value To reaches the upper set value Tsu, the hydraulic oil is cooled until it reaches the lower set value Tsd except when the hydraulic actuators Ao... Are driven. Therefore, it is possible to avoid the problem that the temperature of the hydraulic oil is shifted to the upper set value Tsu side, and the average temperature of the hydraulic oil can be made close to the original proper temperature.

  Therefore, according to the hydraulic fluid cooling method according to this embodiment, the discharge side of the hydraulic pump 2 that supplies the hydraulic fluid to the hydraulic actuators Ao and the oil tank 3 are closed when the hydraulic actuators Ao are driven. The hydraulic actuator is connected by a series circuit 6 of a cooling on / off valve 4 that switches to the side and a heat exchanger 5 that cools the hydraulic oil, and the hydraulic on / off valve 4 is switched to the open side to cool the hydraulic oil. Even when a hybrid configuration in which Ao... And the electric actuator Ae are combined and a cooling circuit in which a heat exchanger is connected to the hydraulic oil flow path is used, sufficient cooling of the hydraulic oil can be performed. In addition, since it is sufficient to add a cooling on / off valve 4 to the conventional cooling circuit in terms of structure, the cooling circuit can be implemented at a low cost without increasing the size of the cooling circuit, and the hydraulic actuator Ao. Since the hydraulic oil is cooled during the period, the cooling process does not affect the drive control of the hydraulic actuators Ao. Therefore, it is possible to contribute to stabilization of control and stabilization of hydraulic oil temperature in the injection molding machine M. In particular, in the present embodiment, since the variable discharge hydraulic pump 2s is used as the hydraulic pump 2, in addition to the advantages such as energy saving improvement by the variable discharge hydraulic pump 2s, the case drain amount hardly occurs, so the hydraulic oil is used. On the other hand, it is possible to perform efficient cooling, that is, efficient cooling.

  The preferred embodiment has been described in detail above. However, the present invention is not limited to such an embodiment, and the detailed configuration, shape, quantity, and the like are arbitrary within the scope of the present invention. Can be changed, added, or deleted. For example, the temperature set value Ts may be set by a single temperature set value Ts without being set by the temperature range of the upper set value Tsu and the lower set value Tsd, and may be combined with other means for preventing chattering. . In addition, the period when the electric actuators Ae are not driven is included in the period when the hydraulic actuators Ao are not driven. However, the cooling mode may be executed using only the operation pause period between the operation steps if necessary. Furthermore, although the electric actuator Ae has been illustrated as being applied only to the measuring servo motor Aem, the application (combination) of the electric actuators Ae... And the hydraulic actuators Ao. On the other hand, although the case where the variable discharge hydraulic pump 2s is used as the hydraulic pump 2 is illustrated, other various hydraulic pumps 2 can be applied, and the coolant W is always flowed without using the illustrated cooling water flow valve 101. There may be.

  The hydraulic fluid cooling method according to the present invention can be used for various injection molding machines having a hybrid configuration in which a hydraulic actuator and an electric actuator are combined.

  2: hydraulic pump, 2s: variable discharge hydraulic pump, 3: oil tank, 4: cooling on-off valve, 5: heat exchanger, 6: series circuit, 7: hydraulic oil temperature sensor, 11: heating cylinder, 12: Screw, 13: Pump motor, Ao ...: Hydraulic actuator, Ae: Electric actuator, Aem: Servo motor for metering, M: Injection molding machine, Mi: Injection device, To: Temperature of hydraulic oil (temperature detection value), Ts: Appropriate temperature (temperature set value), Tsu: upper set value, Tsd: lower set value

Claims (6)

  A hydraulic fluid cooling method for an injection molding machine that cools hydraulic fluid used for driving the hydraulic actuator in an injection molding machine having a hybrid configuration in which a hydraulic actuator and an electric actuator are combined. The hydraulic fluid is supplied to the hydraulic actuator. The discharge side of the hydraulic pump and the oil tank are connected by a series circuit of a cooling on / off valve that switches to a closed side when the hydraulic actuator is driven and a heat exchanger that cools the hydraulic oil, and the hydraulic oil temperature sensor detects the hydraulic oil. And the cooling on / off valve during the non-driving period of the hydraulic actuator so that the detected temperature of the hydraulic oil (temperature detection value) becomes a preset appropriate temperature (temperature setting value). Cooling of hydraulic fluid by switching to open side of hydraulic fluid cooling method for injection molding machine .   2. The method of claim 1, wherein the temperature set value is set according to a temperature range based on an upper set value and a lower set value.   3. The injection molding machine according to claim 2, wherein after the temperature detection value reaches the upper set value, the hydraulic oil is cooled until the lower set value is reached except when the hydraulic actuator is driven. Hydraulic oil cooling method.   4. The hydraulic fluid cooling method for an injection molding machine according to claim 1, wherein the period when the hydraulic actuator is not driven includes the time when the electric actuator is driven.   The method of claim 1, wherein the electric actuator is a measuring servo motor that rotates a screw built in a heating cylinder of an injection device.   The injection molding machine according to any one of claims 1 to 5, wherein the hydraulic pump uses a variable discharge hydraulic pump capable of varying at least a discharge flow rate according to a rotational speed of a pump motor using a servo motor. Hydraulic oil cooling method.

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