JP3930228B2 - Unload hydraulic circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an unload hydraulic circuit suitable for use in a hydraulic drive device of an injection molding machine.
[0002]
[Prior art]
FIG. 3 shows a hydraulic drive device for an injection molding machine described in Japanese Patent Laid-Open No. 9-117947. In FIG. 3, an injection ram 2 is fitted in an injection cylinder 1 of an injection molding machine. The position of the injection ram 2 is detected by the position sensor 3 and taken into the control device 4.
[0003]
The fixed discharge flow rate main pump 20 is connected to the injection cylinder 1 via a main hydraulic circuit 61 that is a discharge path. In the main hydraulic circuit 61, the check valve 12 and the proportional flow control valve 23 are interposed, and the proportional electromagnetic relief valve 6 is connected to a portion located between these elements 12 and 23.
[0004]
The fixed discharge flow rate sub pump 11 is connected to the injection cylinder 1 via a sub hydraulic circuit 52 which is a discharge path. In the sub hydraulic circuit 52, the check valve 12 is interposed, and the sub hydraulic circuit pressure adjusting relief valve 9 is connected to a portion located upstream of the check valve 12.
The relief valve 9 has a pilot pressure introduction port connected to the switching valve 21 via a vent circuit 103. The vent circuit 103 includes a shockless valve (one-way valve) 22 on the way, and is selectively connected to the tank and the connection circuit 104 as the switching valve 21 is switched. The other end of the connection circuit 104 is connected between the check valve 12 and the flow control valve 23 in the main hydraulic circuit 61.
[0005]
At the start of the filling process, the control device 4 gives a pressure command value for instructing the proportional electromagnetic relief valve 6 to the injection pressure P1, and a flow rate command value for obtaining the injection speed V1 to the proportional flow control valve 23, respectively. give.
Accordingly, the pressure oil discharged from the fixed discharge flow rate main pump 20 is adjusted to a flow rate corresponding to the flow rate command value by the proportional flow rate control valve 23 and then supplied to the injection cylinder 1. Therefore, the injection ram 2 of the injection cylinder 1 advances to a predetermined position at the speed V1.
[0006]
Here, the control device 4 changes the flow rate command value so that the speed of the injection ram 2 becomes a speed V2 faster than V1, but only with the flow rate of the pressure oil discharged from the fixed discharge flow rate main pump 20, the speed of the ram described above. Cannot be increased to V2.
Therefore, the fixed discharge sub-pump 11 is started, and the pressure oil from the sub-pump 11 is supplied to the injection cylinder 1 through the check valve 12. That is, the discharge pressure oil of the sub pump 11 is joined to the discharge pressure oil of the main pump 20, and the ram 2 is advanced to a predetermined position at the speed V2.
[0007]
At this time, the switching valve 21 is switched by the control device 4. As a result, the main hydraulic circuit 61 is connected to the relief valve 9 via the connection circuit 104 and the switching valve 21, so that the hydraulic pressure of the sub hydraulic circuit 52 is the same as the hydraulic pressure of the main hydraulic circuit 61. The hydraulic pressure of the sub hydraulic circuit 52 is controlled to P 1 by the proportional electromagnetic relief valve 6 together with the hydraulic pressure of the main hydraulic circuit 61.
[0008]
Next, after changing the flow rate command value to reduce the injection speed to V3, the mold is closed and the pressure holding process is started. In this pressure holding step, the pressure command value and the flow rate command value are changed, and the injection pressure and the injection speed are set to P2 (<P1) and V4 (<V3), respectively.
[0009]
When the pressure holding process is completed, the switching valve 21 is switched as shown to open the mold, and the sub hydraulic circuit 52 is brought into an unloaded state. That is, the vent circuit 103 and the connection circuit 104 are interrupted, and the vent circuit 103 is connected to the tank so that the vent pressure of the relief valve 9 is released.
At this time, since the pressure oil of the vent circuit 103 flows to the tank through the shockless valve (one-way valve) 22 provided in the vent circuit 103, the vent pressure of the relief valve 9 is gradually released. As a result, no oil hammer occurs on the line from the relief valve 9 to the tank.
[0010]
[Problems to be solved by the invention]
As described above, the shockless valve 22 provided in the vent circuit 103 causes the relief valve 9 to perform a relief operation so as to prevent the occurrence of oil hammer. If the shockless valve 22 is not provided, the pressure in the hydraulic piping suddenly drops when the hydraulic circuit 52 is unloaded, so an oil hammer is given to the piping from the relief valve 9 to the tank, Generate surging or impact sound.
[0011]
The shockless valve 22 has the oil hammer suppression function as described above. However, when the shockless valve 22 is provided, the following problems occur. That is, because the vent pressure of the relief valve 9 increases due to the throttle action of the shockless valve 22, there is a problem that the relief pressure increases when the relief valve 9 is unloaded, that is, no-load operation energy increases. This causes a problem.
In view of such a situation, an object of the present invention is to provide an unload hydraulic circuit capable of suppressing oil hammer without increasing a relief pressure during unloading.
[0012]
[Means for Solving the Problems]
1st invention is an unload hydraulic circuit provided with the relief valve which carries out an unload operation based on the vent pressure of the vent circuit which has a shockless valve, Comprising: The bypass valve means of a low pressure loss with respect to the said relief valve Are provided in parallel, and the bypass valve means is opened after a delay after the relief valve is unloaded.
According to a second invention, in the first invention, the bypass valve means is opened after the relief pressure of the relief valve is lowered to a minimum value.
According to a third invention, in the first or second invention, a logic valve is used as the bypass valve means.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of an unload hydraulic circuit according to the present invention will be described below. FIG. 1 shows a hydraulic drive device for an injection molding machine to which an unload hydraulic circuit according to the present invention is applied.
In FIG. 1, the same elements as those shown in FIG. In the following, description of the same elements is omitted.
[0014]
The hydraulic drive device for injection molding shown in FIG. 1 is common to the hydraulic drive device shown in FIG. 3 except that a logic valve 201, a switching valve 202 for opening and closing the logic valve 201, and a shuttle valve 203 are added. The configuration is as follows.
The logic valve 201 is a low pressure loss type that has a small passage resistance when hydraulic fluid passes through, and is connected in parallel to the relief valve 9. The shuttle valve 203 has one and other input ports connected to the sub-hydraulic circuit 52 and the connection circuit 104, respectively, and an output port connected to the pilot port of the logic valve 201 via the switching valve 202.
[0015]
The logic valve 201, the switching valve 202, the shuttle valve 203 and the relief valve 9, the shockless valve (one-way valve) 22, and the switching valve 21 constitute an unload hydraulic circuit according to the present invention.
The operation of this unload hydraulic circuit will be described below. The operation of the hydraulic drive device in the filling process for injecting resin from the injection cylinder 1 of the injection molding machine and the subsequent pressure holding process is the same as that of the conventional example shown in FIG. Description is omitted.
[0016]
Here, first, the characteristics of the logic valve 201 and the relief valve 9 will be described with reference to FIG.
FIG. 2A shows the operating characteristics of the logic valve 201. When the logic valve 201 is opened when the internal pressure of the sub hydraulic circuit 52 is in the state of P2, the internal pressure is a relatively low minimum pressure P _RL (for example, 1) along the curve P _L in a short time t _L. The pressure is reduced at ˜3 Kgf / cm ² ). When the internal pressure is suddenly reduced in this way, a large amount of hydraulic fluid flows at once, so surging and impact noise are generated.
[0017]
On the other hand, FIG. 2B shows the operating characteristics of the relief valve 9 during unloading. At the time of unloading, the switching valve 21 is operated as shown in the figure, so that the vent circuit 103 of the relief valve 9 is connected to the tank via the shockless valve 22. For this reason, the pressure oil of the vent circuit 103 flows into the tank. At that time, the pressure of the vent circuit 103 which is the vent pressure of the relief valve 9 gradually decreases due to the action of the shockless valve 22.
[0018]
Thus, the vent pressure of the relief valve 9 is gradually lowered, gradually step down so that the pressure of the working oil of the sub hydraulic circuit 52 that flows to the tank through the relief valve 9 is shown by the curve P _S at time t _S The oil hammer does not occur.
However, in this case, since the relief pressure of the relief valve 9 becomes high, the pressure of the sub hydraulic circuit 52 is reduced only to a relatively high minimum pressure P _RS (for example, 8 to 10 kgf / cm ² ). Load operating energy increases.
[0019]
The unload hydraulic circuit according to the present invention solves the problem that the no-load operation energy increases by using the logic valve 201.
That is, as described above, after the pressure holding process is completed, the sub hydraulic circuit 52 needs to be in an unloaded state. In this case, the control device 4 operates the switching valve 21.
When the switching valve 21 is operated as shown in the figure, the vent circuit 103 of the relief valve 9 is connected to the tank via the shockless valve 22, so that the pressure oil in the sub hydraulic circuit 52 is supplied to the tank via the relief valve 9. Flowing into. Accordingly, the hydraulic pressure of the sub hydraulic circuit 52, as shown in FIG. 2 (c), slowly in along the curve P _S without causing oil hammer step down to P _RS.
[0020]
Where the control device 4, the pressure in the sub hydraulic circuit 52 operates the switching valve 202 at a predetermined small margin time δt from the lowered time point P _RS. As a result, the logic valve 201 is opened, so that the minimum pressure P _RS remaining in the sub hydraulic circuit 52 is _lowered to the minimum pressure _{PR RSL} that is the pressure loss of the logic valve 201 along the curve P _{L + S.}
This minimum pressure P _RSL is sufficiently lower than the relief pressure P _RS when the relief valve 9 combined with the shockless valve 22 is unloaded, so that it is possible to save the no-load operating energy.
[0021]
The time t _S shown in FIG. 2 (b) and (c), that is, from the switching operation time of the switching valve 21 (relief beginning of the relief valve 9) to the point where the relief pressure of the relief valve 9 is reduced to a minimum value The time is set by experiments in advance. Then, the control device 4 switches the switching valve 202 after measuring the time obtained by adding the minute margin time δt to the time t _S from the relief start time.
The unload hydraulic circuit according to the above embodiment is applied to a hydraulic drive device of an injection molding machine, but can also be effectively applied to a hydraulic drive device that drives other hydraulic equipment.
[0022]
【The invention's effect】
The unload hydraulic circuit according to the present invention can reduce the relief pressure during unloading and reduce the energy during no-load operation while maintaining the advantage of being able to unload without oil hammer. Brief description of]
FIG. 1 is a hydraulic circuit diagram showing an embodiment of an unload hydraulic circuit according to the present invention.
FIG. 2 is a graph for explaining the operation of the unload hydraulic circuit according to the present invention.
FIG. 3 is a hydraulic circuit diagram illustrating a conventional unload hydraulic circuit.
[Explanation of symbols]
1 Injection cylinder 9 Relief valve 11 Sub pump 20 Main pump 21, 202 switching valve 22 Shockless valve (one-way valve)
103 Vent circuit 201 Logic valve

Claims (3)

An unload hydraulic circuit including a relief valve that performs an unload operation based on a vent pressure of a vent circuit having a shockless valve, wherein a bypass valve means having a low pressure loss is provided in parallel to the relief valve, An unload hydraulic circuit, wherein the bypass valve means is opened after a delay after the relief valve is unloaded. 2. The unload hydraulic circuit according to claim 1, wherein the bypass valve means is opened after the relief pressure of the relief valve is lowered to a minimum value. The unload hydraulic circuit according to claim 1 or 2, wherein a logic valve is used as the bypass valve means.

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