US3872887A

US3872887A - Apparatus for selectively establishing a multiplicity of discrete flow rates

Info

Publication number: US3872887A
Application number: US286405A
Authority: US
Inventors: Walter Wohlrab
Original assignee: Krauss Maffei AG
Current assignee: Mannesmann Demag Krauss Maffei GmbH
Priority date: 1971-09-15
Filing date: 1972-09-05
Publication date: 1975-03-25
Anticipated expiration: 1992-03-25
Also published as: DE2146210A1; BR7206421D0; GB1393289A; ZA726249B; FR2153921A5; IT965210B; JPS4838764A

Abstract

For the selective establishment of a multiplicity of discrete flow rates of a liquid, e.g. of oil in a hydraulic system controlling the delivery of plastic material in an injectionmolding machine, two or more pumps (preferably of different capacity) are connected in parallel between a reservoir or sump and a load, the output of at least the higher-capacity pump being also joined to a bypass path with two or more parallel throttles (preferably of different calibration). The throttles can be individually blocked and the pumps can be individually activated by respective solenoid valves which, when operated in different combinations, may establish different flow rates in the load circuit amounting to, say, 10%, 20%, 30%.....100% of a maximum flow rate available with both pumps active and both throttles blocked.

Description

United States Patent [191 Wohlrab 1 Mar. 25, 1975 1 i APPARATUS FOR SELECTIVELY ESTABLISHING A MULTIPLIClTY F DISCRETE FLOW RATES [75] Inventor: Walter Wohlrab,Weissenburg,

Germany [731 Assignee: Krauss-MeffeiAktiengesellschaft,

Munich, Germany 221 Filed: Sept. 5, 1972 211 Appl.No.:286,405

[30] Foreign Application Priority Data Sept. 15, 1971 Germany 2146210 [52] US. Cl. 137/567, 137/597 [51 Int. Cl. Gd 7/03 Field Of Search 137/567, 599, 597; 91/31; 417/28 [56] References Cited UNITED STATES PATENTS 2.999.482 9/1961 Bower 91/31 3,038,449 6/1962 Murphy 1. 91/31 3.072.146 1/1963 Gizeski 137/599 X 3,081,942 3/1963 McClay 91/31 X 11/1966 Schaub 137/567 X 4/1973 Friedland et a1 137/599 Primary E.\'aminer--Wil1iam R. Cline Attorney, Agent, or Firm-Karl F. Ross; Herbert Dubno [57] ABSTRACT For the selective establishment of a multiplicity of discrete flow rates of a liquid, e.g. of oil in a hydraulic system controlling the delivery of plastic material in an injection-molding machine, two or more pumps (preferably of different capacity) are connected in parallel between a reservoir or sump and a load, the output of at least the higher-capacity pump being also joined to a bypass path with two or more parallel throttles (preferably 01 different calibration). The throttles can be individually blocked and the pumps can be individually activated by respective solenoid valves which, when operated in different combinations, may establish different flow rates in the load cir cuit amounting to, say, %....1007r of a maximum flow rate available with both pumps active and both throttles blocked.

10 Claims, 4 Drawing Figures LOAD PATENTEDMAR25|9Y5 3,872,887

SHEET 2 OF 3 F i g 2 PATENTED 2 51975 sumstlfi;

w 2' LL MHEQQaR m N krsnx APPARATUS FOR SELECTIVELY ESTABLISHING A MULTIPLICITY OF DISCRETE FLOW RATES FIELD OF THE INVENTION My present invention relates to a system for the metering of fluids, especially liquids, with selective establishment of a multiplicity of discrete flow rates through a load to be driven, cooled or otherwise treated by the fluid.

BACKGROUND OF THE INVENTION The selective control of the flow rate of a fluid in discrete steps can be conventionally realized with the aid of a fluid source, such as a pump, whose output is diverted from the load to a greater or less extent by means of a multiplicity of parallel fluid sinks, such as calibrated throttles, which are connected to the highpressure side of the pump and can be individually blocked in various combinations. With the crosssections and therefore the fluid-handling capacities of these throttles suitably staggered, e.g. in a binary ratio, the flow rate through the load can be varied by predetermined (e.g. uniform) increments.

A drawback of this system resides in the fact that the pump must be dimensioned to deliver at maximum flow rate and that this rate must be maintained even when only a small fraction of the flow is intended for the load. The constant recirculation of a large volume of fluid through the restricted passages of the throttles is wasteful of energy and therefore undesirable.

. OBJECTS OF THE INVENTION The principal object of my invention is to provide an improved system of the general character referred to which affords greater economy, in terms of both pumping capacity and the number of selectively blockable throttles, in the establishment of a given number of distinct flow rates of a controlled fluid.

A more particular object is to provide a system of this description which can be used with advantage in all instances where (as in many injection-molding machines) a number of not always fully utilized pumps are available. I

SUMMARY OF THE INVENTION The foregoing objects are realized, in accordance with my present invention, by the provision of a plurality of constant-flow fluid sources (such as pumps) connected to the load in parallel, thus replacing the single pump of the conventional system, while a plurality of constant-flow sinks (such as throttles) are connected in parallel to the output of at least one of these fluid sources ahead (i.e., upstream) of the load, preferably to the source or sources of highest capacity; individual control means are used for the selective activation of the several fluid sources and the several fluid sinks. To provide a maximum number of flow rates, the fluid sources and sinks should differ among 'one another in their flow-delivering and flow-reducing capacities.

If each fluid source is designed as a continuously operating pump, it can be activated by the closure of an individual bypass thereof which in its inactive stage discharges the delivered fluid or (especially in the case of hydraulic liquids) returns it to the intake side of 'the pump via a collector or sump; thus, the pump may be activated by the closure of a valve (e. g. of the solenoidoperated type) in its bypass path, a similar valve in cascade with a calibrated throttle serving as a control means for any of the fluid sinks. If the number of fluid sources is n and the number of fluid sinks is m, then the total number of possible combinations of their active states is 2 The number of discrete flow rates is obviously smaller since no flow through the load results if only the sinks are activated or if the diversion flow through the sinks equals or exceeds the supply flow through the active pump or pumps. With suitable selection of the relative numerical values of the capacities of these sources and sinks, to avoid duplications and to make the combined capacity of the sinks less then capacity of the smallest pump, the maximum number N of adjustment steps (i.e., the number of flow rates other than zero) is equal to 2'" 2'" 2"(2 1). Thus, withn =m =2, N= 12; withm =3 andn =2, N=24; and so forth.

If the numerical values of the source and sink capacities are related in a binary ratio, the N l finite flow rates (including zero flow) will be separated from one another by identical increments. With N 12, for example, these increments will equal 100/12 8%%. Increments of 10% can be realized by the binary relationship -1 +2 4 +8, for example, with the minus and plus signs respectively designating the sinks and the sources; a similar result can be achieved with the non- BRIEF DESCRIPTION OF THE DRAWING The above and other objects, features and advantages of the present invention will become more readily apparent from the following detailed description, reference being made to the accompanying drawing in which:

FIG. 1 is a flow diagram of a system embodying my invention;

FIG. 2 is a table showing the various operating conditions of the system of FIG. 1 for establishing any of 10 different flow rates;

FIG. 3 is a circuit diagram illustrating an arrangement for selecting any of the flow rates indicated in FIG. 2; and

FIG. 4 is a table similar to FIG. 2 but illustrating a 12- step arrangement.

DESCRIPTION OF PREFERRED EMBODIMENT In FIG. 1 I have shown a system for selectively supplying liquid at different flow rates to a load 20, e.g. for driving oil through a hydraulic motor operating a feed screw of an injection-molding machine. The system comprises a pair of

pumps

1 and 2 which may be synchronized or provided with a common drive but have different capacities as more fully discussed hereinafter.

The continuously operating

pumps

1 and 2 are connected in parallel to a common supply for the liquid to 20 via a check valve 17 and a conduit 8. A switchover valve 18 is inserted between the check valve 9 in the output line of the small-capacity pump 1 and the conduit 8, this valve being operable to bypass the junction 19 and the check valve 17 in delivering the output of pump 1 directly to the load 20. Check valve 17 is redundant if the bypass through valve 18 is omitted.

Each

pump

1, 2 is provided with a bypass path in the form of a

respective line

21, 22 returning its output to the sump 15 when the pump is inactive, i.e., in the open condition of a solenoid-actuated valve 3 or 4, respectively. A pair of spring-loaded pressure-regulating

valves

5, 6 in

lines

21, 22, ahead of valves 3, 4, respectively, drain off excess fluid from the pump output to the sump 15 to maintain a constant flow through

check valves

9 or 10 whenever the control valve 3 or 4 is closed, i.e., when the

pump

1 or 2 is active, when the control valve is open, low pressure in an

ancillary line

21, 22 throws the corresponding regulating valve wide open as is well known per se.

Junction 19 also feeds a conduit 16, in parallel with conduit 8, which is returned to the sump through a pair of parallel, calibrated

throttles

13, 14 each lying in series with a respective control valve 11, 12 that is electromagnetically operable like the valves 3, 4. With switchover valve 18 in its illustrated position, the combined flow of pumps 1 and 2 (if both are activated) reaches the junction 19 and can be partly diverted from the load 20 through throttles 13 and/or 14 by the selective energization of solenoid valves 11 and/or 12.

Let us now assume that

pumps

1 and 2 are respectively designed to deliver 20% and 80% of the total flow whereas

throttles

13 and 14 can respectively divert 10% and 40% of that flow, i.e., that the capacities of these fluid sources and sinks are related to the aforestated binary ratio of l +2 4 +8. This arrangement enables the selective establishment of ten different flow rates, ranging from 10% to 100% of the total pump output, in uniform increments of 10% as illustrated diagrammatically in FIG. 2. In that Figure, the hatched circles indicate the active condition of any fluid source or sink as brought about by the blocking of

bypass lines

21, 22 and the unblocking of throttles l3, l4.

If the switchover valve 18 were placed in its alternate position, the system would operate in the same manner except that the lowest flow rate of 10% could not be realized.

In FIG. 3 I have shown a set of pushbutton switches 51 60 serving for the selective connection of a battery 50 to operating

coils

3a, 4a, 11a, 12a of solenoid valves 3, 4, ll, 12 to establish any one of the ten flow rates listed in the table of FIG. 2. Thus, depression of pushbutton 51 energizes the

coils

3a and 11a to activate the pump 1 and the throttle 13 for a flow rate of 10% depression of pushbutton 52 energizes only the coil 3a to activate the pump 1; and so on.

FIG. 4 illustrates the selection of twelve distinct flow rates, separated by increments of 8 /a% with a system of two pumps and two throttles as shown in FIG. 1, their capacities having the above-mentioned relationship of-l -.-2 +4 +6. In such a case the control circuit of FIG. 3 is extended to twelve pushbuttons, with suitable modification of the connections for the energization of the several solenoid coils.

It will thus be seen that the system herein disclosed enables the selection of a wide variety of flow rates with relatively simple means and that, in particular, it facili-.

tates the establishment of uniform increments in these flow rates advantageously constituting aliquot fractions (e.g. l/IO or l/l2) of the combined flow from all available fluid sources. The numerical values of the capacities listed in FIG. 2 or in FIG. 4 can be defined as different multiples mq of a basic magnitude corresponding to that aliquot fraction q, the multiplier m being a positive or negative integer.

Naturally, the

conduit system

8, 19 must have a capacity sufficient to handle the aforementioned combined flow, corresponding to a flow rate of so that the capacity of this conduit system (and of the load 20 served thereby) must be greater than that of the larger-capacity pump 2.

I claim:

l. A system for selectively establishing a multiplicity of discrete flow rates of a liquid through a load, comprising:

a first calibrated constant-flow source of liquid having a relatively low capacity;

a second calibrated constant-flow source of liquid having a relatively high capacity;

first control means for individually activating and deactivating said sources;

constant means with a capacity exceeding that of said second source for supplying the combined outputs of said sources to the load, said conduit means including a first and a second branch respectively connected to said first and said second source;

a first and a second calibrated constant-flow fluid sink connected to said second branch for deviating part of the output of said second source from said load upon being placed in an operative condition, said fluid sinks being of different capacity and having a combined capacity less than that of said second source; and

second control means for individually rendering said first and second fluid sinks operative.

2. A system as defined in claim 1 wherein said fluid sinks are in communication with both said branches, the capacity of at least one of said fluid sinks being less than that of said first source.

3. A system as defined in claim 1, further comprising check-valve means between said branches for isolating said first source from said fluid sinks.

4. A system as defined in claim 1 wherein said sources are pumps connected to a supply of liquid, said fluid sinks being restricted passages deverting a part of the pumped liquid from said load.

5. A system as defined in claim 4 wherein said control means comprises a first set of valves in an individual bypass path for each of said pumps and a second set of valves for individually blocking each of said passages.

6. A system as defined in claim 5, further comprising a check valve in the output of each of said pumps at a location downstream of said bypass path.

7. A system as defined in claim 5, further comprising pressure-limiting valve means in said bypass path and in cascade with said passages.

8. A system as defined in claim 1 wherein the capacities of said sources and fluid sinks have relative numerical values which are multiples mg of a basic magnitude q, m being an integer.

9. A system as defined in claim 8 wherein said numerical values bear a binary relationship.

10. A system as defined in claim 8 wherein m is different for all said numerical values.

Claims

1. A system for selectively establishing a multiplicity of discrete flow rates of a liquid through a load, comprising: a first calibrated constant-flow source of liquid having a relatively low capacity; a second calibrated constant-flow source of liquid having a relatively high capacity; first control means for individually activating and deactivating said sources; constant means with a capacity exceeding that of said second source for supplying the combined outputs of said sources to the load, said conduit means including a first and a second branch respectively connected to said first and said second source; a first and a second calibrated constant-flow fluid sink connected to said second branch for deviating part of the output of said second source from said load upon being placed in an operative condition, said fluid sinks being of different capacity and having a combined capacity less than that of said second source; and second control means for individually rendering said first and second fluid sinks operative.

8. A system as defined in claim 1 wherein the capacities of said sources and fluid sinks have relative numerical values which are multiples mq of a basic magnitude q, m being an integer.