Hydraulic system for a cyclically working molding machine and method for operation of such a hydraulic system

Abstract

A hydraulic system for a cyclically operating shaping machine includes at least one hydraulic drive unit for cyclically driving a component of the shaping machine at a start time; at least one pump; and at least one hydraulic accumulator which can be discharged for driving the at least one hydraulic drive unit and which can be charged up by operation of the at least one pump. An open-loop or closed-loop control unit is also provided for control of the at least one pump. The open-loop or closed-loop control unit is adapted to operate the at least one pump continuously until the start time of the at least one hydraulic drive unit to charge up the at least one hydraulic accumulator until the start time of the hydraulic drive unit.

Claims

1. A hydraulic system for a cyclically operating shaping machine, the hydraulic system including: a hydraulic drive unit for cyclically driving a component of the shaping machine at a start time; a pump; a hydraulic accumulator to be discharged for driving the hydraulic drive unit and to be charged up by operation of the pump; and an open-loop or closed-loop control unit for open-loop or closed-loop control of the pump, wherein the open-loop or closed-loop control unit is adapted to operate the pump continuously until the start time of the hydraulic drive unit to charge up the hydraulic accumulator until the start time of the hydraulic drive unit, wherein the open-loop or closed-loop control unit is configured to calculate, based on a delivery volume and/or a hydraulic pressure of the hydraulic system, a rotary speed of the pump to generate an average delivery output of the pump, and to charge the hydraulic accumulator with the required delivery volume and/or the required hydraulic pressure by the pump.

2. The hydraulic system as set forth in claim 1, wherein the open-loop or closed-loop control unit is configured to vary a delivery output of the pump.

3. The hydraulic system as set forth in claim 2, wherein the open-loop or closed-loop control unit is configured to vary a delivery output of the pump by varying the rotary speed of the pump.

4. The hydraulic system as set forth in claim 1, wherein the open-loop or closed-loop control unit is adapted to continuously operate the pump during an entire cycle time of the cyclically operated shaping machine.

5. The hydraulic system as set forth in claim 1, wherein the open-loop or closed-loop control unit is configured to calculate, based on a hydraulic pressure of the hydraulic system and/or a delivery volume required during an entire cycle time of the cyclically operating shaping machine, an average delivery output, and to provide for open-loop or closed-loop control of the pump with regard to the average delivery output.

6. The hydraulic system as set forth in claim 1, wherein the open-loop or closed-loop control unit is configured to adjust a rotary speed of the pump to an operating condition of the hydraulic drive unit.

7. The hydraulic system as set forth in claim 6, wherein the open-loop or closed-loop control unit is configured to: increase the delivery output of the pump during a movement of the hydraulic drive unit, and/or reduce the delivery output of the pump during a stoppage in the movement of the hydraulic drive unit.

8. The hydraulic system as set forth in claim 1, wherein the hydraulic drive unit is connected to the pump by a hydraulic line.

9. The hydraulic system as set forth in claim 8, wherein the hydraulic accumulator is connected to the pump with the hydraulic line connecting the hydraulic drive unit.

10. The hydraulic system as set forth in claim 1, wherein the pump is driven by an electric motor.

11. The hydraulic system as set forth in claim 10, wherein the electric motor is a synchronous motor.

12. The hydraulic system as set forth in claim 1, wherein: the hydraulic accumulator has a bladder accumulator, the drive unit is configured to produce a linear drive and/or a rotational drive of a closing unit and/or an injection unit of the shaping machine, the open-loop or closed-loop control unit is formed by a central machine control of the shaping machine, and/or the hydraulic system further comprises a hydraulic valve for open-loop or close-loop control of the hydraulic drive unit.

13. A shaping machine comprising the hydraulic system as set forth in claim 1.

14. A method of operating the hydraulic system as set forth in claim 1, wherein the method comprises continuously operating the pump until the start time of the hydraulic drive unit to charge up the hydraulic accumulator until the start time of the hydraulic drive unit.

15. A computer program embodied on a non-transitory computer-readable medium, the computer program comprising commands to allow a computer to perform the method as set forth in claim 14.

16. The hydraulic system as set forth in claim 1, wherein the hydraulic drive unit is a piston-cylinder unit.

17. The hydraulic system as set forth in claim 1, wherein the open-loop or closed-loop control unit is configured to charge the hydraulic accumulator at substantially precisely the start time.

18. A hydraulic system for a cyclically operating shaping machine, the hydraulic system including: a hydraulic drive unit for cyclically driving a component of the shaping machine at a start time; a pump; a hydraulic accumulator to be discharged for driving the hydraulic drive unit and to be charged up by operation of the pump; and an open-loop or closed-loop control unit for open-loop or closed-loop control of the pump, wherein the open-loop or closed-loop control unit is adapted to operate the pump continuously until the start time of the hydraulic drive unit to charge up the hydraulic accumulator until the start time of the hydraulic drive unit, wherein the open-loop or closed-loop control unit is configured to calculate, based on a hydraulic pressure of the hydraulic system and/or a delivery volume ascertained during a preceding cycle of the shaping machine, an average delivery output of the pump, and to provide for open-loop or closed-loop control of the pump with regard to the average delivery output.

19. A hydraulic system for a cyclically operating shaping machine, the hydraulic system including: a hydraulic drive unit for cyclically driving a component of the shaping machine at a start time; a pump; a hydraulic accumulator to be discharged for driving the hydraulic drive unit and to be charged up by operation of the pump; and an open-loop or closed-loop control unit for open-loop or closed-loop control of the pump, wherein the open-loop or closed-loop control unit is adapted to operate the pump continuously until the start time of the hydraulic drive unit to charge up the hydraulic accumulator until the start time of the hydraulic drive unit, wherein the open-loop or closed-loop control unit is configured to calculate, based on a hydraulic pressure of the hydraulic system and/or a delivery volume ascertained during a preceding cycle of the shaping machine, a hydraulic pressure and/or delivery volume required at the start time of the at least one hydraulic drive unit and to charge the hydraulic accumulator with the required delivery volume and/or hydraulic pressure by the pump.

20. The hydraulic system as set forth in claim 19, wherein the open-loop or closed-loop control unit is further configured to charge the hydraulic accumulator substantially precisely at the start time with the required delivery volume and/or hydraulic pressure by the pump.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further advantages by way of example and details of the invention are illustrated in the Figures and set forth in the specific description hereinafter, in which:

(2) FIG. 1 shows a hydraulic system according to an embodiment of the invention, and

(3) FIG. 2 shows an embodiment of a method according to the invention in comparison with the state of the art by means of a diagram.

DETAILED DESCRIPTION OF THE INVENTION

(4) FIG. 1 shows a first embodiment of a hydraulic system 1 for a shaping machine.

(5) That hydraulic system 1 has a hydraulic drive unit 2 adapted to drive a component (not shown for the sake of better clarity of the drawing) of a shaping machine at a start time.

(6) The hydraulic drive unit 2 of the hydraulic system 1 is in the form of a double-acting piston-cylinder unit 3 which is actuated in known manner by way of a hydraulic valve 9 (more precisely: an electrically actuated 4/3-way valve).

(7) In addition, the hydraulic system 1 has a hydraulic accumulator 5 which can be charged up by a pump 4 and a (first) hydraulic line 7. A hydraulic valve 11 is provided for changing the hydraulic accumulator 5 between a charging position and a discharging position.

(8) The pump 4 is driven by an electric motor 8 and is in the form of a fixed displacement pump, wherein a delivery output of the pump 4 can be adjusted by variation in the rotary speed of the electric motor 8.

(9) The pump 4 is connected to the hydraulic accumulator 5 by the hydraulic line 7, wherein a further (second) hydraulic line 7 for supplying the hydraulic drive unit 2 branches off between the pump 4 and the hydraulic accumulator 5.

(10) In addition, between the branch connection and the pump 4 is a non-return valve which prevents an uncontrolled backflow because of pressure fluctuations from the hydraulic system 1 to the pump 4.

(11) The hydraulic system 1 further comprises an open-loop or closed-loop control unit 6 which is connected in signal-conducting relationship to the electric motor 8, the hydraulic valve 9 and the hydraulic valve 11 (the signal-conducting connections are shown in this view by the dashed lines).

(12) A (first) hydraulic sensor 12 is further provided between the hydraulic valve 11 and the hydraulic accumulator 5. A further (second) hydraulic sensor 13 is provided between the pump 4 and the non-return valve 10. Those hydraulic sensors 12, 13 are adapted to provide a signal which is representative of the pressure and a through-flow amount and which can also be provided by a signal-conducting connection for an open-loop or closed-loop control unit 6.

(13) A representative signal for a pump output of the pump 4 can be established by the sensor 13 and the delivery flow.

(14) A representative signal for a charging state or a discharging state of the hydraulic accumulator 5 can be established by the hydraulic sensor 12.

(15) The open-loop or closed-loop control unit 6 is adapted to continuously operate the pump 4, wherein hydraulic fluid is continuously conveyed into the hydraulic system 1 by the pump 4 and the hydraulic accumulator 5 is charged up.

(16) As soon as actuation of the hydraulic valve 9 occurs and thus a movement of the hydraulic drive unit 2 is produced by the open-loop or closed-loop control unit 6, the hydraulic valve 11 is also actuated so that the stored hydraulic energy in the hydraulic accumulator 5 can escape and serves to drive the hydraulic drive unit 2.

(17) As the pump 4 runs continuously, upon a movement of the hydraulic drive unit 2, the hydraulic drive unit 2 is also driven to a small extent by the pump 4 (in addition to the communicated hydraulic energy of the hydraulic accumulator 5).

(18) FIG. 2 shows a comparison of a method according to the invention of operating a hydraulic system with a method known from the state of the art.

(19) Thus, in a method of operating a hydraulic system 1 according to the state of the art, firstly the rotary speed of the pump 4 is increased from the stopped condition to a maximum value, as shown by the dashed line A.

(20) The pump 4 is kept at its maximum rotary speed until a desired pressure is reached in the hydraulic system 1 and thus in the hydraulic accumulator 5.

(21) That pressure in the hydraulic accumulator 5 and in the hydraulic system 1 is shown by the line B (in the method according to the state of the art). When that desired pressure is reached, the pump 4 is shut down, which again is to be seen by the line A.

(22) That pressure in the hydraulic accumulator 5, however, falls slightly due to leakage losses, as can be seen from the line B. That slight loss in pressure due to leakage represents an energy loss in the system.

(23) At the start time 14, the hydraulic drive unit 2 is driven by the hydraulic system 1 whereby the pressure in the hydraulic system 1 abruptly drops as the hydraulic energy which is stored in the hydraulic system 1 and the hydraulic accumulator 5 is required by the hydraulic drive unit for moving a component of the shaping machine.

(24) When the pressure in the hydraulic system 1 and thus in the hydraulic accumulator 5 falls to a lower pressure threshold value, the rotary speed of the pump 4 is again increased to its maximum to build up a desired pressure in the hydraulic accumulator 5.

(25) As can be clearly seen from the dashed line in the state of the art, however, it is always necessary to build up a higher pressure by means of the pump 4 than is necessary at the start time 14 of the hydraulic drive unit as leakage losses have to be taken into account.

(26) The lines C and D show a method according to an embodiment of the present invention, wherein the line C represents the rotary speed of the pump 4 and the line D represents a pressure in the hydraulic system 1.

(27) It is to be noted that, in the embodiment of the invention, the pump 4 is operated continuously (with a slight variation in the rotary speed, shown on an exaggerated scale in the Figure).

(28) The line D shows how the pressure in the hydraulic accumulator 5 rises continuously until the start time 14 at which the desired hydraulic pressure is reached.

(29) Shortly before actuation of the hydraulic drive 2, the rotary speed of the pump 4 is increased again so that, during actuation of the hydraulic drive unit 2, additional hydraulic power is provided by the pump 4 for the hydraulic drive unit 2, which can be used in addition to the hydraulic energy delivered by the hydraulic accumulator 5.

(30) After actuation of the hydraulic drive unit 2, the rotary speed of the pump 4 can again be reduced as indicated by the line C in order to charge the hydraulic accumulator 5.

(31) It can be seen how the rotary speed of the pump 4 in the embodiment of the invention (which is shown by the lines C and D in FIG. 2) swings about an average rotary speed.

(32) An example of the calculation of a pilot control of the rotary speed of the pump 4 as indicated by line C is to be described in greater detail hereinafter.

(33) In a first step, the required rotary speed n for continuous charging of the hydraulic accumulator 5 is calculated from the displacement volume V.sub.p (according to manufacturer details) of the pump 4 and a volume flow Q.sub.p. The volume flow Q.sub.P is in that case ascertained in a preceding cycle of the shaping machine and used for the calculation as a benchmark.
Q.sub.P=n*V.sub.P

(34) From that, it is possible to calculate the power output P.sub.p of the pump by way of the pressure difference Δp.sub.p (results from the desired pressure in the hydraulic system) at the pump 4. The differential pressure Δp.sub.p (the desired pressure in the hydraulic system) in that case also arises from a preceding cycle of the shaping machine.
P.sub.P=Δp.sub.p*Q.sub.P

(35) The required rotary speed of the pump 4 can now be calculated by the time variation of the pressure of cycles considered in the hydraulic accumulator 5 of the hydraulic system 1.

(36) In that case, firstly by way of the calculation formula in respect of the pump output P.sub.PM which (as can be seen hereinafter) arises out of a prevailing pressure in the hydraulic accumulator p.sub.Akku and the already previously mentioned desired volume flow Q.sub.p which originates by measurement from a preceding cycle of the shaping machine will be converted to the desired volume flow Q.sub.p.

(37) By means of the knowledge that the volume flow arises out of the multiplicands rotary speed of the pump n.sub.CAC,des and the displacement volume of the pump V.sub.p (Q=n*V) the desired rotary speed of the pump n.sub.CAC,des can now be calculated.

(38) $P_{\mathrm{PM}}=p_{\mathrm{Akku}}*Q_{P,\mathrm{des}}$$Q_{P,\mathrm{des}}=\frac{P_{\mathrm{PM}}}{p_{\mathrm{Akku}}}$$n_{\mathrm{CAC},\mathrm{des}}=\frac{P_{\mathrm{PM}}}{p_{\mathrm{Akku}}*V_P}$

(39) That rotary speed is then also averaged over the range being considered (for example a plurality of cycles). In that way, a constant rotary speed is achieved.

(40) That constant rotary speed, however, can have the result that on the one hand the hydraulic accumulator is overcharged or on the other hand it is not completely charged.

(41) Therefore, that rotary speed presetting also has to be overwritten by a control action (as described hereinafter).

(42) By way of cycle time analysis, it is possible to ascertain the time t.sub.cycle which is available for charging the hydraulic accumulator. The charging volume ΔV can be calculated from that time t.sub.cycle, the calculated rotary speed n.sub.CAC,des and the displacement volume V.sub.p of the pump 4.
ΔV=n.sub.CAC,des*V.sub.p*t.sub.cycle

(43) The accumulator pressure p.sub.2,e which can potentially be reached is calculated therefrom, being reached by way of the charging volume ΔV:

(44) $p_{2,e}=\frac{p_0}{{\left({\left(\frac{p_0}{p_1}\right)}^{\frac{1}{\kappa }}-\frac{\Delta V}{V_0*x}\right)}^{\kappa }}$

(45) The difference between the attainable accumulation pressure p.sub.2,e over the constant rotary speed and the set maximum pressure value for the hydraulic accumulator is used as a control variable. In the final effect then, rotary speed presetting is effected for example by way of the following condition:
n.sub.real=n.sub.CAC,des+k.sub.P*(p.sub.2−p.sub.2,e)+k.sub.l*(p.sub.2−p.sub.2,e)

(46) The two parameters k.sub.P and k.sub.l represent in that case the parameters for example a PI controller which is known from the state of the art and which can be a component part of the open-loop or closed-loop control unit 6.

(47) In principle, however, any other known variant of a controller can be used as part of the open-loop or closed-loop control unit 6 for controlling the rotary speed of the pump 4 by way of the electric motor 8.

(48) In addition, a factor f.sub.V can be introduced in order to store the ascertained parameter p.sub.2,e over a certain number of cycles and if necessary to permanently adapt the pilot control, that is to say with the rotary speed n.sub.CAC,des of the pump 4.

LIST OF REFERENCES

(49) 1 hydraulic system 2 hydraulic drive unit 3 piston-cylinder unit 4 pump 5 hydraulic accumulator 6 open-loop or closed-loop control unit 7 hydraulic line 8 electric motor 9 hydraulic valve 10 non-return valve 11 hydraulic valve 12 hydraulic sensor 13 hydraulic sensor 14 start time A rotary speed of the pump according to the state of the art B pressure in the hydraulic accumulator according to the state of the art C rotary speed of the pump according to the embodiment D pressure in the hydraulic accumulator according to the embodiment Q.sub.p volume flow of the pump n rotary speed of the pump Δp.sub.p pressure difference V.sub.P displacement volume of the pump P.sub.P output of the pump Δp.sub.p differential pressure at the pump P.sub.Akku pressure in the hydraulic accumulator Q.sub.P,des required volume flow of the pump T.sub.P,des required rotary speed of the pump t.sub.cycle time for charging the hydraulic accumulator x.sub.Akku number of the hydraulic accumulators P.sub.0 gas filling pressure of the hydraulic accumulator P.sub.1 min. working pressure of the hydraulic accumulator p.sub.2 max. working pressure of the hydraulic accumulator κ polytropic exponent ΔV.sub.x removal amount per cycle n.sub.CAC,des calculated rotary speed of the pump n.sub.real rotary speed specification by the PI controller p.sub.2,e differential pressure of the achievable hydraulic pressure