JPH078526B2 - Hydraulic system of injection molding machine - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic device for an injection molding machine, which is configured to supply return oil from a hydraulic actuator directly to a hydraulic pump.

[0002]

2. Description of the Related Art Generally, there are an open circuit system and a closed circuit system as a circuit system of a hydraulic system. The open circuit system has an oil tank that stores oil, and the oil in the oil tank is supplied to a hydraulic actuator by a hydraulic pump.
The oil discharged from the hydraulic actuator is returned to the oil tank again. On the other hand, in the closed circuit system (closed hydraulic circuit), oil is supplied to the hydraulic actuator by the hydraulic pump, and the oil discharged from the hydraulic actuator is directly supplied to the hydraulic pump without returning to the oil tank. A hydraulic system using such a closed hydraulic circuit does not require an oil tank or needs a small size, and has an advantage that the entire hydraulic system can be made compact and compact.

FIG. 8 shows a conventional hydraulic device 50 using a closed hydraulic circuit. The hydraulic device 50 includes two hydraulic actuators, that is, a hydraulic cylinder 51 and an oil motor 52, and a discharge port of the hydraulic pump 54 is configured to be connectable to both the hydraulic cylinder 51 and the oil motor 52 via a supply line 53. At the same time, the hydraulic cylinder 51 and the oil motor 52 are connected to each other via the return line 55.
It is configured to be connectable to the suction port of No. 4. As a result, the oil discharged from the hydraulic cylinder 51 and the oil motor 52 is directly returned to the hydraulic pump 54. In addition, the loss of oil, etc.
7 is supplied to the hydraulic pump 54 via the check valve 56. In the figure, 58 is a hydraulic cylinder 51 and a hydraulic pump 54.
Reference numeral 59 denotes a directional control valve connected between the oil motor 52 and the hydraulic pump 54.

The applicant of the present invention has already proposed a hydraulic system having a closed hydraulic circuit of this type, particularly a hydraulic system desirable for an injection molding machine, in Japanese Patent Laid-Open No. 62-177303.

By the way, the hydraulic system which can use such a closed hydraulic circuit is only available when the amount of oil supplied and the amount of oil discharged from the hydraulic actuator are the same and all the oil supplied from the hydraulic pump is returned to the hydraulic pump. For example, there is a problem that it cannot be applied when the amount of supplied oil and the amount of discharged oil do not match, because the piston areas are different on the left and right, such as in a hydraulic cylinder.

Therefore, as a hydraulic device that solves this problem, a hydraulic device 60 as shown in FIG. 9 is also known. The hydraulic device 60 includes two actuators, that is, a hydraulic cylinder 61 and an oil motor 62 capable of rotating in the normal and reverse directions.
Since the left and right areas of the piston 61p in the hydraulic cylinder 61 are different, the supplied oil amount and the discharged oil amount do not match. Therefore, for the oil motor 62, a closed hydraulic circuit 63 similar to that in FIG. 8 is configured, and all the return oil is returned to the hydraulic pump 64, but for the other hydraulic cylinder 61, it is driven by the drive motor 67 shared with the hydraulic pump 64. Is provided with a charge pump 65, and the charge pump 6
The hydraulic circuit 66 of the open circuit type using No. 5 was installed side by side. In addition, 68 is a direction control valve, 69 is a relief valve, 70
Indicate oil tanks, respectively.

However, such a hydraulic system 60 is a combination of a closed circuit system and an open circuit system except that the drive motor 67 is shared, and as a result, a large oil tank (usually,
Hydraulic pump several times the maximum discharge amount)
Since the hydraulic pump is also complicated and large, for example, the installation space of the equipment is extremely limited, and even if it is applied to an injection molding machine that is required to be downsized, it cannot be sufficiently downsized and the cost is high. There was a problem that caused the change.

The present invention solves the problems existing in the prior art as described above, and achieves downsizing and cost reduction of the entire apparatus, and injection capable of performing highly precise control with excellent controllability. An object is to provide a hydraulic system for a molding machine.

[0009]

According to the present invention, as shown in FIG. 1, a plurality of hydraulic actuators Ma and Mb are driven by a single hydraulic pump 2, and the return oil from the hydraulic actuators Ma and Mb is directly hydraulically operated. When constructing the hydraulic device 1 of the injection molding machine adapted to supply to the pump 2, the return line 3 from the hydraulic actuators Ma, Mb
Between the oil tank 4 and the oil tank 4, a bypass circuit 5 using a control valve such as a check valve 5c, a relief valve 5r or a pressure controllable pressure control valve 5s for returning a part of the returned oil to the oil tank 4 is connected and supplied. A basic characteristic is to provide a semi-closed hydraulic circuit 7 in which an interference prevention circuit 6 using a check valve is connected in a return line 3a from a hydraulic actuator Ma having different oil amounts and discharged oil amounts. Further, the hydraulic system 1 according to the present invention includes a cooler 8 connected in series to a return line 3 upstream of a connecting portion of a bypass circuit 5, a return line 3 upstream of the cooler 8 and an oil tank 4 if necessary.
A relief valve 9, which is connected in between to return the return oil to the oil tank 4,
Between the return line 3 and the oil tank 4, or between the supply line 10 and the oil tank 4 downstream of the hydraulic pump 2, a flushing filter 11 that can be selectively connected via a directional control valve, and between the supply line 10 and the oil tank 4. It can be configured by including a temperature raising circuit 12 that can be selectively connected via a directional control valve.

[0010]

According to the hydraulic apparatus 1 of the injection molding machine according to the present invention, oil is supplied from the hydraulic pump 2 to the actuators Ma and Mb respectively, but the hydraulic actuator Ma having different supply oil amount and discharge oil amount is provided in the circuit. In the case of including, the return amount of oil returning to the hydraulic pump 2 decreases or increases with respect to the discharge amount of the hydraulic pump 2. In this case, if the return amount is less than the discharge amount, the shortage is replenished from the oil tank 4, and
If increased, the surplus is returned to the oil tank 4 via the bypass circuit 5.

As described above, since only a part of the return oil, that is, the surplus is returned to the oil tank 4, the oil tank 4
Can be miniaturized. Further, the shortage or excess of oil is replenished or bypassed as necessary, and the amount of oil for the hydraulic pump 2 is adjusted by this, so that only one hydraulic pump 2 is required. On the other hand, if the check valve 5c is used as the control valve used in the bypass circuit 5, the hydraulic actuator Ma,
Even if a high pressure is generated in the return line due to the operating state of Mb, it acts to reduce the pressure, and if a relief valve 5r, a pressure control valve 5s, or the like is used as the control valve, the brake is applied when the speed of the hydraulic actuators Ma, Mb is switched. Since the circuit pressure of the return line 3 can be controlled while exhibiting the action, the pressure can be controlled as a meter-out circuit. That is, since the optimum pressure control for the return oil becomes possible, for example, when the hydraulic actuators Ma and Mb change from high speed to low speed and low pressure, the pressure smoothly shifts and the stop accuracy increases. The accuracy of is improved. Furthermore, since the return oil can be used to assist the inertial force of the oil at the suction port of the hydraulic pump 2, the rising response of the swash plate of the proportional variable discharge pump is dramatically improved, and the injection molding machine is improved. In, it becomes possible to perform more advanced molding.

Further, since the check valve forming the interference prevention circuit 6 is connected to the return line 3a from the hydraulic actuator Ma, the influence of the pressure generated in the return line 3 during the operation of the other hydraulic actuator Mb is affected. It is prevented and interference (malfunction) is prevented.

On the other hand, the return oil is cooled by the cooler 8 and the cooled oil is returned to the oil tank 4 or the hydraulic pump 2, so that the oil temperature is stabilized. In this case, the cooler 8 is inserted into the low-voltage circuit, so that no withstand voltage is required. On the other hand, when the pressure of the return oil exceeds the set value, the return oil is returned to the oil tank 4 via the relief valve 9 to protect the cooler 8 and the like. Moreover, the selectively connectable flushing filter 11 can flush dust and the like in the closed hydraulic circuit, and the temperature raising circuit 12 can raise the temperature of the oil.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, preferred embodiments according to the present invention will be described in detail with reference to the drawings.

First, the structure of the hydraulic system 1 will be described with reference to FIG. Reference numeral 2 is a hydraulic pump using a proportional variable discharge type piston pump, and its suction port is connected to the oil tank 4 via a check valve 21. The check valve 21 allows oil supply from the oil tank 4 to the hydraulic pump 2. The discharge port of the hydraulic pump 2 is connected to the P ports of the direction control valves 22 and 23, respectively.

On the other hand, 24 is a hydraulic cylinder which constitutes a hydraulic actuator Ma, and is provided with oil supply ports 24x, 24 on the left and right.
with y. The hydraulic cylinder 24 has a built-in piston 24p, and its left and right areas are different. Therefore, the supplied oil amount and the discharged oil amount do not match, and when oil is supplied from one of the oil supply ports 24x, the discharged oil amount from the other oil supply port 24y becomes smaller than the supplied oil amount. Further, when the oil is supplied from the other oil supply port 24y, the amount of oil discharged from the one oil supply port 24x becomes larger than the amount of oil supply. Refueling ports 24x and 24y are connected to the A port and B port of the directional control valve 22, respectively, and the T port of the directional control valve 22 is further connected to the return line 3
a (3). An interference prevention circuit 6 using a check valve 6c is connected in the return line 3a to check the check valve 6c.
The downstream side of c is connected to the A port of the directional control valve 25.

On the other hand, 26 is an oil motor which constitutes the hydraulic actuator Mb, and the suction port thereof is the directional control valve 2.
The discharge port is connected to the return port 3 on the downstream side of the check valve 6c and is connected to the A port of the directional control valve 25.

The P port of the directional control valve 25 is connected to the suction port of the cooler 8, and the T port is connected to the oil tank 4 via the flushing filter 11.

On the other hand, the outlet of the cooler 8 is the hydraulic pump 2.
Connect to the intake port of. Further, the downstream side of the cooler 8 is connected to the oil tank 4 via the chuck valve 5c to form a bypass circuit 5. The check valve 5c allows the return oil to flow from the return line 3 into the oil tank 4, and can be a relief valve, or generally a pressure control valve. A suitable pressure control valve in this case is illustrated in FIGS. Figure 3
Is a case where an electromagnetic pressure proportional valve 5s is used instead of the check valve 5c, FIG. 4 is a case where a circuit in which the electromagnetic pressure proportional valve 5s is connected to the vent circuit of the relief valve (pilot valve) 5r is used, and FIG. Direction control valve 4 in the vent circuit of 5r
This is a case in which a circuit is used in which the throttle valve 5m and the relief valves 5ra and 5rb having different pressure settings can be selectively connected via 1.

Therefore, both FIG. 3 and FIG. 4 are capable of continuous pressure control. Further, in the case of FIG. 5, three-stage pressure setting is possible by selecting the throttle valve 5m, the relief valve 5ra, and the relief valve 5rb. In this case, if the direction control valve 41 is in the neutral position, the oil is discharged to the oil tank 4 as the unload pressure of the relief valve 5r. The relief valves 5ra ... Can be arbitrarily changed or added.

On the other hand, a relief valve 9 is connected between the return line 3 on the downstream side of the check valve 6c and the oil tank 4.
A temperature raising circuit 12 is connected between the supply line 10 on the downstream side of the hydraulic pump 2 and the oil tank 4. Temperature raising circuit 12
Is provided with a direction control valve 27, a throttle valve 28, and a flushing filter 29, and the A port of the direction control valve 27 is connected to the supply line 1
The throttle valve 28 is connected to the oil tank 4 via a flushing filter 29, while the T port is connected to the throttle valve 28. The relief valve 9 can be replaced with another control valve.

The case drain of the hydraulic pump 2 is returned to the oil tank 4 via the check valve 30 and returned to the return line 3 via the check valve 31.

The flushing filter 11 (29)
The temperature raising circuit 12 may be connected as shown in FIG.
That is, using the directional control valve 32, the A port of the control valve 32 is connected to the supply line 10 (or the return line 3), and the P port is connected to the oil tank 4 via the cooler 33. Furthermore, B port and T port are throttle valves 2
8 and the T port is connected to the oil tank 4 via the flushing filter 11 (29). As a result, if the directional control valve 32 is in the neutral position, the oil in the supply line 10 is cooled via the cooler 33 and returned to the oil tank 4. Further, if the symbol is switched to the left side, the temperature raising circuit 12 is configured, while if the symbol is switched to the right side, the temperature rise circuit 12 is connected to the flushing filter 11 (29).

Next, the operation of the hydraulic system 1 according to the present invention will be described.

First, the directional control valve will be described. At the neutral position of the directional control valve 22, oil supply to the hydraulic cylinder 24 is shut off. Further, in the figure, switching to the left symbol supplies oil to the oil supply port 24x of the hydraulic cylinder 24, and switching to the right symbol supplies oil to the oil supply port 24y of the hydraulic cylinder 24. On the other hand, if the directional control valve 23 is switched to the left symbol, the oil supply to the oil motor 26 is cut off, and if it is switched to the right symbol, the oil motor 26 is supplied with oil. On the other hand, the directional control valve 2
If 5 is switched to the left side symbol, the return line 3 is in a circulation state, and if switched to the right side symbol, the return line 3 is in a cutoff state, and the return oil is supplied to the flushing filter 11 side. Further, if the directional control valve 27 is switched to the left symbol, the temperature raising circuit 12 and the supply line 10 are cut off, and if it is switched to the right symbol, the temperature raising circuit 12 and the supply line 10 are connected.

Now, while operating the hydraulic pump 2,
When the direction control valve 23 is switched to supply oil to the oil motor 26, the oil motor 26 rotates. On the other hand, if the direction control valve 22 is switched to the symbol on the left side, the oil is supplied to the oil supply port 24x.
Is supplied to the hydraulic cylinder 24, and the piston 24p moves to the right. At this time, since the piston 24p has a large area on the left side, the amount of oil discharged from the oil supply port 24y is smaller than the amount of oil supplied. Therefore, the return oil is the check valve 6
c, through the return lines 3a and 3 and then the cooler 8
And is returned to the suction port of the hydraulic pump 2. The shortage of oil is supplied from the oil tank 4 via the check valve 21.

On the other hand, if the direction control valve 22 is switched to the right symbol, oil is supplied from the oil supply port 24y to the hydraulic cylinder 24, and the piston 24p moves to the left. In this case, the amount of discharge oil discharged from the supply oil 24x becomes larger than the amount of supply oil. Therefore, the return oil passes through the check valve 6c and the return lines 3a and 3 and is cooled by the cooler 8, while a part is supplied to the hydraulic pump 2 and the rest is returned to the oil tank 4 via the check valve 5c. . At this time, if a relief valve 5r, a pressure control valve 5s, or the like is used instead of the check valve 5c, it is possible to perform highly accurate control with excellent controllability as described above.

By the way, the hydraulic cylinder 24 is connected to the piston 2
Since the left and right areas of 4p are different, the hydraulic cylinder 24 side and the return line 3 side may be connected when the directional control valve 22 is in the neutral position. In this case, the pressure on the side of the return line 3 is such that the oil supply ports 24x, 24y of both sides of the hydraulic cylinder 24.
Therefore, the piston 24p moves to one side to cause a malfunction. Therefore, in order to prevent this adverse effect, the check valve 6c prevents the pressure fluctuation of the return line 3 based on another hydraulic actuator or the like from being transmitted to the hydraulic piston 24.

Further, since the return oil cooled by the cooler 8 is returned to both the hydraulic pump 2 and the oil tank 4, the oil temperature is stabilized, especially the oil temperature at the time of confluence at the suction port of the hydraulic pump 2 is stabilized. Is planned. That is, due to the cooling of the return oil by the cooler 8, the variations in the oil temperature in the oil tank 4, the suction port and the discharge port of the hydraulic pump 2 become small as shown in FIG. However, when the cooler 8 is not connected, the cold oil from the oil tank 4 and the warm oil from the return line 3 join the suction port of the hydraulic pump 2, and as shown in FIG. The variation in oil temperature becomes extremely large, and the oil temperature becomes unstable. Since the oil temperature affects the mold temperature and the like, its stabilization is an important factor for the injection molding machine in order to prevent the generation of defective products.

On the other hand, when the return oil has a high pressure, the cooler 8 may be damaged. In this case, the oil is returned to the oil tank 4 through the relief valve 9 to protect the cooler 8 and the like. If the flushing filter 11 is switched if necessary, it is possible to perform initial wear and removal of dust in the pipeline. Also,
If the oil is cold, such as in winter, the temperature raising circuit 12
Is connected to raise the temperature of the oil in the oil tank 4. In this case, the temperature is raised by the pressure difference when the oil passes through the throttle valve 28. When the temperature raising circuit 12 is connected, the directional control valve 22 is switched to the neutral position and the directional control valve 23 is switched to the left symbol. Further, when the temperature is raised, it is flushed by the flushing filter 29 at the same time, but the viscosity can be effectively reduced by raising the temperature. Further, the case drain of the hydraulic pump 2 is cooled by the cooler 8 by passing through the check valves 30 and 31 having a pressure difference. In this case, when there is pressure on the oil tank 4 side, the check valve 30 is closed and the case drain is supplied to the cooler 8 via the check valve 31 to stabilize the oil temperature.

Although the embodiments have been described in detail above, the present invention is not limited to such embodiments, and the detailed configurations, methods and the like can be arbitrarily changed without departing from the gist of the present invention. .

[0032]

According to the present invention, a plurality of hydraulic actuators are driven by a single hydraulic pump, and the return oil from the hydraulic actuator is directly supplied to the hydraulic pump. A bypass circuit that uses a control valve such as a check valve that returns a portion of the return oil to the oil tank is connected between the return line and the oil tank, and the return line from the hydraulic actuator with different supply and discharge oil amounts Since it has a semi-closed hydraulic circuit that is connected to an interference prevention circuit using a check valve, the overall size and cost of the device can be reduced, and the use of return oil makes it possible to achieve high controllability and high accuracy. There is a remarkable effect that the control can be performed.

[Brief description of drawings]

FIG. 1 is a hydraulic circuit diagram of a hydraulic device according to the present invention,

FIG. 2 is a partial hydraulic circuit diagram according to another embodiment of the hydraulic system,

FIG. 3 is a partial hydraulic circuit diagram according to another embodiment of the hydraulic system,

FIG. 4 is a partial hydraulic circuit diagram according to another embodiment of the hydraulic system,

FIG. 5 is a partial hydraulic circuit diagram according to another embodiment of the hydraulic system,

FIG. 6 is a temperature characteristic diagram of oil temperature when a cooler is used in the hydraulic system,

FIG. 7 is a temperature characteristic diagram of oil temperature in the same hydraulic device when a cooler is not used,

FIG. 8 is a hydraulic circuit diagram of a hydraulic device according to the related art;

FIG. 9 is a hydraulic circuit diagram of a hydraulic device according to another example of the related art;

[Explanation of symbols]

 1 hydraulic system 2 hydraulic pump 3 return line 3a return line 4 oil tank 5 bypass circuit 5c check valve 5r relief valve 5s pressure control valve 6 interference prevention circuit 7 semi-closed hydraulic circuit 8 cooler 9 relief valve 10 supply line 11 flushing filter 12 rise Temperature circuit Ma Hydraulic actuator Mb Hydraulic actuator

Claims (8)

[Claims] 1. A return line from a hydraulic actuator in a hydraulic system of an injection molding machine, wherein a plurality of hydraulic actuators are driven by a single hydraulic pump, and return oil from the hydraulic actuator is directly supplied to the hydraulic pump. A bypass circuit using a control valve that returns a part of the return oil to the oil tank is connected between the
A hydraulic system for an injection molding machine, comprising a semi-closed hydraulic circuit in which an interference prevention circuit using a check valve is connected in a return line from a hydraulic actuator having different amounts of supplied oil and discharged oil. 2. The hydraulic system for an injection molding machine according to claim 1, wherein a check valve is used as the control valve. 3. The hydraulic system for an injection molding machine according to claim 1, wherein a relief valve is used as the control valve. 4. The hydraulic system for an injection molding machine according to claim 1, wherein a pressure control valve capable of pressure control is used as the control valve. 5. A hydraulic system for an injection molding machine according to claim 1, wherein a cooler is connected in series to the return line upstream of the connection portion of the bypass circuit. 6. A hydraulic system for an injection molding machine according to claim 5, wherein a relief valve for returning the return oil to the oil tank is connected between the return line upstream of the cooler and the oil tank. 7. A flushing filter selectively connectable via a directional control valve between the return line and the oil tank or between the supply line downstream of the hydraulic pump and the oil tank. Hydraulic system of the injection molding machine described. 8. A hydraulic system for an injection molding machine according to claim 1, further comprising a temperature raising circuit selectively connectable between the supply line and the oil tank via a direction control valve.