Control system for a hydraulic circuit including a plurality of parallel variable-delivery pumps

Abstract

 A hydraulic circuit includes a plurality of parallel variable-delivery pumps (11-14) for supplying pressure fluid to an appliance such as an extrusion press (60). A control system is provided to optimize the operation of the pumps. This system utilizes a sensor which senses the quantity of fluid demanded by the appliance and a controller provides control signals which vary in accordance with the sensor function. These control signals in turn control solenoid valves (41-44) and regulators (31-34) which control the individual pumps in accordance with the demanded fluid.

Description

BACKGROUND OF THE INVENTION

Field of the Art;

[0001] This invention relates to a control system for use in a hydraulic circuit supplying pressurized oil or fluid from a plurality of parallel-connected variable-delivery pumps to a hydraulic appliance.

SUMMARY OF THE INVENTION

[0002] According to the invention there is provided a control system for use in a hydraulic circuit including a plurality of parallel variable-delivery pumps; said control system comprising means for bringing one of said pumps into a loaded state for delivering a required volume of pressure fluid and the other pumps into an unloaded state when the required volume of pressure fluid is less than the maximum volume of pressure fluid deliverable from one of said pumps, and for bringing one or more of said pumps into a loaded scate under its substantially maximum delivery state, one of the other pumps into some intermediate delivery state and the remaining pumps into an unloaded state when the required volume of pressure fluid exceeds the maximum deliverable from one or more pumps.

[0003] The invention also provides a control system for use in a hydraulic circuit including a plurality of parallel variable-delivery pumps; said control system comprising a sensor for sensing a demanded quantity of pressure fluid, means for developing control signals in dependence on the operation of the sensor and control valves and regulators for controlling the operation of the pumps in dependence on said control signals whereby when the demanded quantity of pressure fluid is less than the maximum quantity deliverable from one of the pumps, one of the pumps is brought into a loaded state to deliver the demanded quantity of pressure fluid and the other pumps are brought in an unloaded state and when the demanded quantity exceeds the maximum quantity deliverable from one of the pumps at least one of the pumps is brought into a loaded state to deliver its maximum deliverable quantity of fluid, another pump is brought into an intermediate state to deliver a quantity of fluid less than its maximum deliverable quantity of fluid and the remaining pumps are brought into an unloaded state.

[0004] In general the quantity of fluid delivered from each of the pump is controlled by the control system dynamically and according to the demanded quantity required by the appliance which may be an extrusion press. The system ensures the pumps operate i.n an optimum manner to reduce energy loses and power consumption.

[0005] The invention may be understood more readily, and various other features of the invention may become apparent from consideration of the following description.

[0006] A specific embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, wherein :

Figure 1 is a schematic circuit diagram of a hydraulic circuit for an extrusion press control system constructed in accordance with the present invention;

Figure 2 is a schematic electric circuit diagram showing an example of means for developing _control signals;

Figure 3 is a table for explaining the relationship between press extrusion speed and the loaded state of the pumps;

Figure 4 is a table for explaining the relationship between press extrusion speed and the inclinations of the pumps ;

Figure 5 is a characteristic graph showing the volume efficiency of one of the variable-delivery pumps ;

Figure 6 is a characteristic graph showing the overall efiiciency of one of the variable-delivery pumps; and

Figure 7 is a graph representing the energy-saving effect of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0007] Figure 1 shows a hydraulic circuit of an extrusion press, which comprises variable -delivery pumps (11,12,13 and 14), pump driving motors (21,22,23 and 24), delivery regulators (31, 32, 33 and 34) one for each of the pumps, loading control valves (41, 42, 43 and 44) for loading and unloading the respective pumps, relief valves (45, 46, 47 and 48), direction switching solenoid valves (51, 52, 53, 54, 55 and 56), a full oil valve (57), relief valves ( 58 and 59), an extrusion press (60) having a main cylinder (61), side cylinders (62 and 63) and a stem (64), and pilot pumps (71 and 72). These hydraulic component parts are interconnected as shown in Figure 1.

[0008] In the illustrative embodiment, only the four variable-delivery pumps (11, 12, 13 and 14) are connected in parallel and the volume of pressure fluid, e.g. oil, delivered from each of the pumps is supplied to a respective cylinders (61, 62 and 63) of the extrusion press (6) to actuate the stem (64). When this occurs, programmed electric signals are fed from a control panel not shown to actuate one or more of the solenoid valves (51, 52, 53, 54, 55 and 56), thus establishing flow paths between the respective cylinders (61, 62 and 63) and the pumps or an oil reservoir and actuating the respective cylinders (61, 62 and 63)according to the control program.

[0009] The operation speed of the stem (64,) that is, the volume of oil supplied to each of the cylinders (61, 62 and 63) is controlled by switching on and off the loading control valves (41, 42, 43 and 44) which in turn govern the delivery of each of the respective pumps (11, 12, 13 and 14). As best shown in Figure 2, the operation speed of the stem (64) (this is referred to as "extrusion speed" hereinafter) is monitored with a sensor (81) operatively associated with a stem speed setting (80) installed on the extrusion press (6). The function of the sensor is to detect the actual extrusion speed in terms of percentage wherein rated maximum speed is denoted as 100%. The output of the sensor (81) is converted into an AC or DC signal and supplied to a controller (82) which in turn provides individual signals (C1, C2, C3 and C4) for the delivery regulators (31, 32, 33 and 34) and individual signals (Cl', C2', C3' and C4') for the loading control solenoid valves (41, 42, 43 and 44 in response to a previously programmed extrusion start signal. It is noted that the delivery regulators (31, 32, 33 and 34) are supplied with a given pilot pressure (Pa) from the pilot pump (71).

[0010] In order that the inclinations of the respective pumps (11, 12, 13 and 14) may control its delivery as depicted in Figure 4, the respective solenoid valves (41, 42, 43 and 44) are switched on and off to load and unload the respective pumps (11, 12, 13 and 14) according to the extrusion speed or the required volume of oil for each of the cylinders (61, 62 and 63) as seen from Figure 3.

[0011] In particular, when the extrusion speed is within the range from 0% to 25% of the rated maximum speed or when the volume of oil necessary for the cylinder is within the range from 0% to 25% of the total of the maximum delivery volumes of the respective pumps (11, 12, 13 and 14) (i.e., the rated maximum flow rate), the solenoid valve (41) is energized to load only the one pump (11) of which the inclination is varied by the delivery regulator (31) to control its delivery output within the range of 0-100%. Ps a result, the only pump which supplies the required volume of oil and actuates the stem (64) is the pump (11). Under these circumstances the remaining solenoid valves (42, 43 and 44) are disenergized to place the corresponding pumps (12, 13 and 14) into no-load state.

[0012] With the extrusion speed within the range of 25 to 50% of the rated maximum speed or the required volume of oil within the range of 25 to 50% of the total of the rated maximum delivery volumes, the solenoid valves (41 and 42) are energizea to load the two pumps (11 and 12). The delivery regulator (31) increases the inclination of one of the two pumps (11) to its maximum (100%) and the delivery of that pump (11) to its maximum (100%). The delivery regulator (32), on the other hand, controls the inclination of the other pump (12) and regulates its delivery within the range of 0-100%. Accordingly, the 100% delivery pump (11;, combined with the other pump (12) which supplies the deficiency of oil, provides exactly the required volume of oil for actuation of the stem (64). In this instance, the solenoid valves (43 and 44) are disenergized to to unload the remaining pumps (13 and 14) and place the same into no-load state.

[0013] Similarly, with the extrusion speed within the range of 50-75% of the rated maximum speed, two of the pumps (11 and 12) are loaded with 100% delivery and one of the remaining pumps (13) is placed into half-load state with its delivery within the range of 0-100% so as to compensate for the deficiency of oil, thus exactly the required volume of oil. The remaining one pump (14) is unloaded under these circumstances. When the extrusion speed is within the range of 75-100% of the rated maximum speed, there are three of the pumps (11,12 and 13) loaded with 100% delivery and the remaining one of the pumps (14) whose delivery is controlled within the range of 0-100% under half-load state so as to compensate for deficient oil.

[0014] With an increase in the required volume of oil the pumps (11, 12, 13 and 14) are loaded in the numerical order in this manner (the reverse of order with a decrease in oil requirement). One or more 100% delivery pumps and one supplemental pump under half-load state satisfy exactly the oil requirement, while the remaining pump or pumps are maintained under no-load state with no delivery. This control method ensures up to 40% power ^; saving as compared with the conventional method wherein all of the pumps are loaded at one time.

[0015] In Figure 4, a particular pump is adapted to start inclining after 100% inclination of the preceding pump. However, in the case where speed should vary during one operation stroke, the particular pump may start inclining subsequent to 95% inclination of the preceding pump, for example, in order to provide smooth and continuous operation as a whole, In this case, the relationship between the extrusion speed and the inclination speed is controlled to be one half of that with only one pump.

[0016] For the variable-delivery pump the volume efficiency and the overall efficiency vary in dependence on the inclination (α) or the delivery volume of oil delivered as shown in Figure 5 and 6. The characteristic of the variable-delivery pump is that its volume efficiency amount to maximum values when it operates with its rated maximum delivery (maximum inclination).

[0017] As discussed with regard to the illustrative embodiment, the operation speed of the stem within the extrusion press is varied frequently and within a wide range so that the volume of oil supplied and the delivery of the pump are varied frequently and within a wide range. As a result, the respective pumps operate less frequently with its rated maximum speed (the required volume of oil is equal to the total of the maximum deliveries of the overall pumps).

[0018] In the past, all of the pumps were loaded at one time according to the extrusion speed (the required volume of oil) to supply constantly the same volume of pressurized oil so as to supply exactly the required volume of oil while the inclinations of all of the pumps in the extrusion press were controlled to the same extent. All of the pumps were therefore held in half-load state with poor volume efficiency a.nd poor overall efficiency at all times. In other words, all of the pu.nps operated with low efficiency and consumed wastefully power or energy.

[0019] According to the present invention, only a minimum number of the pumps are loaded depending upon oil requirement and the remaining pumps are unloaded, thus reducing power consumption. Moreover, only one of the loaded pumps is held in half-load state while all of the remaining pumps operate with full or 100% delivery. This leads to a substantial increase in the total efficiency of the pumps and remarkable energy-saving characteristics.

[0020] Further energy-saving effected is ensured if the hydraulic circuit is unloaded in conjunction with the unloaded pumps and the drive motors (21, 22, 23 and 24) are disenergized. Under the circumstance it is easy to incorporate an automatic sequence as follows : For example, the motor (24) is disenergized when the pump (11) is in 100% delivery state and the pump (12) is in half-load state. The motor (23) is disenergized when the delivery control signal (C2) for the pump (12) is less than 70% and energized when the same exceeds 70%. The pump (13) is maintained in ro-load state.

[0021] Assume now that the four main pumps are used and the extrusion speed is selected at 25% and 50% of the rated speed. Power-saving effect can be evaluated and compared as follows . In the conventional pump uniform control method all of the pumps are loaded with 25% delivery and 50% delivery, respectively, whereas according to the present invention only one of the pumps is energized with 100% delivery and the remaining three pumps are unloaded when the extrusion speed is desired to be 25% of the rated speed. Moreover, when the extrusion is 50% of the rated speed, two of the pumps are loaded under 100% delivery state and the remaining two pumps are unloaded. Under these circumstances the present invention exhibits outstanding energy-effects as depicted in Figure 7. Figure 7 shows estimated ratios of percentages of power saving by the present invention wherein power saving by the conventional method is 100%. The line (a) depicts power saving when the extrusion speed is 25% of the rated value, while the line (b) power saving when the extrusion speed is 50% of the rated speed. It is clear from Figure 7, that the present invention ensures 20-40% power saving in the case of the line (a) and 8-18% power saving in the case of the line (b). The lower the extrusion pressure (remarkable especially with less than 50 kg/cm )and the extrusion speed, the greater the power saving effect.

[0022] As noted earlier, the present invention provides effective and power-saving actuation of the pumps.

[0023] Whereas in the above illustrated embodiment of the present invention the power-saving effect is ensured in the extrusion press wherein the extrusion speed (the required volume of oil) is varied frequently and within a wide range, it is obvious that the concept of the present invention is equally applicable to any hydraulic actuators including an extrusion press.

Claims

1. A control system for use in a hydraulic circuit including a plurality of parallel variable-delivery pumps; said control system comprising means for bringing one of said pumps into a loaded state for delivering a required volume of pressure fluid and the other pumps into an unloaded state when the required volume of pressure fluid is less than the maximum volume of pressure fluid deliverable from one of said pumps, and for bringing one or more of said pumps into a loaded state under its substantially maximum delivery state, one of the other pumps into some intermediate delivery state and the remaining pumps into an unloaded state when the required volume of pressure fluid exceeds the maximum volume deliverable from one or more pumps.

2. A control system for use in a hydraulic circuit including _P plurality of parallel variable-delivery pumps; said control system comprising a sensor for sensing a demanded quantity of pressure fluid, means for developing control signals in dependence on the operation of the sensor and control valves and regulators for controlling the operation of the pumps in dependence on said control signals whereby when the demanded quantity of pressure fluid is less than the maximum quantity deliverable from one of the pumps , one of the pumps is brought into a loaded state to deliver the demanded quantity of pressure fluid and the other pumps are brought in an unloaded state and when the demanded quantity exceeds the maximum quantify deliverable from one of the pumps at least one of the pumps is brought into a loaded state to deliver its maxin.um deliverable quantity of fluid, another pump is brought into an intermediate state to deliver a quantity of fluid less than its maximum deliverable quantity of fluid and the remaining pumps are brought into an unloaded state.

Drawing