US2255560A - Hydraulic power system - Google Patents

Description

Sept. 9, 1941. K. w. FIEBER ET AL HYDRAULIC. POWER SYSTEM Filed Feb. 15, 1938 IN VENTOR.

.2 a I bun 14 ATTORNEY.

Patented Sept. 9, 1941 2,255,560 HYDRAULIC rowan SYSTEM Karl Wilfrid Fieber, Berlin-Charlottenburg, and

Oskar Wiirthner, Berlin-Wannsee,

Germany,

assignors to Siemens Apparate und Maschinen Gesellschaft mit beschrankter Haftung, Berlin, Germany, a corporation of Germany Application February 15, 1938, Serial No. 190,650 In Germany February-20, 1937 Claims.

This invention relates to hydraulic power systems and more particularly to apparatus comprising a plurality of pumping units which, in combination, are adapted to give a wide range of fluid pressures and fluid outputs.

Quite frequently in instances where a servomotor is used to overcome some resistance, said resistance varies in magnitude over a wide range, as, for example, in the actuation by a servomotor of the collapsible landing gear of an airplane. Itis well known that, in order to retract the' carriage of an airplane, it is necessary to apply a relatively low pressure during the greater part of the retraction and a comparatively high pressure at the very end of the retraction, and, if a single pump driven by an electric motor provides the fluid to the servomotor, the pumping unit, including the pump and electro-motor, must be designed to meet the maximum demand of the servo-motor, i. e., the

demand at the end of the retraction. As a result, the pumping unit operates at full load only during a fractional part of the total time that it is used. It is accordingly an object of the present invention to provide a novel hydraulic power unit which is adapted for use with a servo-motor demanding varying fluid pressures and which comprises a plurality of pumps, each of which operates at substantially full load for all pressure outputs'of the unit, thereby saving weight and space over a pumping unit comprising a single pump operating under similar load conditions. The decreased weightand size of the former is due to the difference in capacity'of the electric motors necessary to drive the said power units.

Another object of the invention is to provide a novel power means for procuring either a low fluid pressure with a large fluid output or a greater fluid pressure with a decreased output.

A further object of the invention is to provide novel automatic means for controlling the output of the above power unit in accordance with the pressure demand thereon.

Still another object is to provide a novel hydraulic power unit which is particularly adapted for actuating the retractable landing gear of an .airplane.

A still further object is to provide a novel supplementary feeder in combination with the abovehydraulic power means for the purpose of meeting any excessive demands for fluid pressure or fluid output upon said means.

The above and further objects and novel features of the invention will more fully appear ever, that the drawing is for the purpose of illustration only and is not intended to define the limits of the invention, reference for this latter purpose being had primarily to the appended claims.

In the drawing, wherein like reference characters refer to like parts throughout the several v1ews-- 1 Fig. l is a pressure curve showing the pressure demand upon the servo-motor of a retractable landing gear during the collapsing of' the carriage, and i Fig. 2 is a diagrammatic representation of one embodiment of the present invention.

In the single embodiment of the invention illustratedin the drawing, there is provided a hydraulic power unit comprising a plurality of fluid pumps and .a pressure responsive valve mechanism for controlling the fluid connection between the said pumps. The pumps are connected, depending upon the desired pressure output, either in parallel or in series, 1. e., either as a group of single stage pumps operating between the same pressure range or as a single pump comprising several stages operating be- I tween a greater pressure range. When the power intake upon a predetermined pressure rise, when unit used, as, for example, to feed a servomotor, the pumps initially operate in-parallel,

pumping a large quantity of low pressure fluid,

but when the pressure demand reaches a predetermined value, preferably when-the pumps become slightly overloaded, the valve mechanism controlling the connections between said pumps automatically rearranges said connections to cause the pumps to operate in series and the increased pressure demand is readily met, al-

though the fluid output is proportionately decreased. A supplementary feeder and a valve mechanism controlling the operation/thereof are also. provided and ;are adapted try supply fluid to the motor, upon a drop of pressure when the pumps are operating in either pressure range or inthe alternative to supply fluid to the pump the pumps are connected in series.

The pressure demand upon the novel hydraulic power system of the present invention by the servo-motor of a retractable landing gear unit, as shown in Fig. '1, is typical of the conditions under which said system operates most efllciently. When the carriage is to be retracted,

the pressure during the greater part a of the retraction does not exceed 12. However, after the gear has been movedinto the airplane body, the pressure must necessarily be increased to terminally move the landing gear into full retractedor housed position and during this part b of the retraction, the pressure builds up considerably in excess of p. If the pressure exceeds that of the pumps operating in series and the demand is for a still greater fluid pressure, the valve mechanism controlling the supplementary feeder is automatically operated to introduce the said feeder into the fluid circuit to meet the demand.

In the embodiment illustrated'in 2, the

novel power system comprises a reservoir or source 4, from which fluid is adapted to flow into a conduit Sand through a valve mechanism f into the fluid circuit of the said system. Nor-= mally, conduit 5 is directly connected by valve mechanism 6; with a conduit l and, when the power system is operating in the low pressure range, 1. e., below pressure 10, substantially onehalf of the fluid flows from conduit! to a conduit 8. 5 The latter, as shown, is connected to the suction port of a rotary pump 9, diagrammatically illustrated in the drawing. It will be understood that pumps 9 and H are of the type in which an increase in the input pressure will cause a corresponding increase in its output pressure.

Pump 9 is preferably driven by an electric motor (not shown) and the high pressure fluid discharge therefrom flows into a conduit Ill and from said conduit through a control valve mechanism ll, then through conduits I2 and l3 to a conduit l5.

A conduit l5, by which substantially one-half of the fluid flow through conduit I from source 4. is diverted when the system is operating in the low pressure range, causes the diverted portion ofthe fluid to pass through valve mechanism II and into a conduit l6. Conduit I6 is connected to the suction port of a pump II, which is of a similardesign to pump 9 and which is preferably driven by the same electric motor as pump 9. The discharge from pump ll flows into conduit Hi where it combines with the high pressure discharge of pump 9, and the combined discharge of J the two pumps flows into a servo-motor l8 to drive a piston l9 and operate, forexample, the

. retractable landing gear of an airplane. When operating in this .manner, the combined discharge of the pumps is the sum of the fluid outputs of each of the pumps and the pressure of said discharge is equal to the pressure which a single pump is capable of producing.

When the resistance to the movement 01' piston I9 increases. to the point where the demand upon the pumps is for a fluid pressure equal to or greater than pressure p, the resulting increase in the pressure discharge of the pumps in response to this demand actuates valve mechanism I l' and causes said mechanism to shut ofl conduits Ill and i6 from conduits l2 and I5, respectively, and to connect the two first-named conduits to each other. The rearrangement of connections is preferably eflectedby movement of a piston valve 20 in a casing or valve body 2| of valve mechanism. As shown, said valve is adapted for reciprocal movement in said body and isnormally maintained in a position to permit fluid flow from conduit in toconduit I2 and from conduit l5 to conduit l6 by suitable resilient means in the form of coil spring 22 interposed between said body and the right end of said valve. A chamber 23 between said body and the left end of said piston valve is connected by channel 24 to the conduit l0 and, therefore, to the discharge side of pump! and when the pressure in said chamber becomes great enough to overcome the resistive force of spring 22, valve 20 is moved thereby to the right and simultaneously shuts off the connection between conduit Hi and conduit i2 and between conduit l5 and conduit l6 and opens a connection between conduit is and conduit i6. Coil spring 22 may be suitably chosen so as to have the above movement occur. in response to any predetermined pressure and in the instance where the power system is utilized in combination with a retractable landing gear, the rearrangement of connections between pumps 9 and i1 is made to occur when. the de mand begins to exceed the pressure p. The said rearrangement of connections causes pumps it and Q to operate in series instead of, as initially, in parallel and the discharge fluid of pump 9 now feeds the suction intake of pump Ell providing a two-stage pumping system which has an initial second stage) pressure equal to the final pressure of the pumping unit, when operatingin said feeder is connected to the high pressure or 1 I discharge side of said pumping units by conduits 26 and 21. Conduit 26 is connected at one end to the junction of conduits i2 and i3 and at the I other end to valve mechanism 6, and conduit 2! pumps due perhaps to a greater demand upon,

movement to the right.

is connected from said valve mechanism to said supplementary feeder. piston 28 reciprocable in-a cylinder 29 and means, in the form of coil spring 30, interposed between the right end of said cylinder andthe right face of said piston, tendingto keep said piston from capacity of the left end of said cylinder is a function of the. pressure of the fluid flowingtherein through conduit 21 and when the pressure'o'f the pump discharge fluid in conduit I4 is equal to the pressure of the fluid within said cylinder end, there is no flow into or out of said cylinder through the conduit '27. However, any increase in the discharge pressure causes a flow into cylinder 29 and correspondingly any sudden decrease in pressure in the discharge of the the fluid output thereof causes a flow of fluid out of said cylinder. Therefore, in normal operation, whether in'the high or low pressure range, supplementary feeder 25 may act to offset operation of valve mechanism 6 in conjunction" with supplementary feeder 25. This is accom-.

any sudden demand upon the fluid volume output of pumps 9 and I1.

A further increase of the pressure output of the hydraulic power system during operation in the high pressure range maybe had by suitable plished by charging said feeder as above described and causing the pressure in said feeder to become equal to the discharge pressure of said-pumps. Then, if a further pressure demand is made upon said pumps, valve mechanism 6 may be so designed as to respond to the increased Feeder 25 comprises a.

As a result, the fluid' discharge pressure built up by the pumps to meet this increased demand, and automatically cut off conduits and 26 from conduits I and 21, respectively, and opens conduit 21 to conduit 1,

. thereby feeding the suction side of pump 9 with a fluid of a pressure equal to the discharge 1 pressure of said pumps at the time valve 6 is operated and thereby increasing the operating range of said pumps. 4

Thus, whenoperating to give the greatest possible pressure range, the hydraulic power unit operates with pumps 9 and I! connected in parallel and fed by the fluid from source 4 and with supplementary feeder 25 being charged by the discharge fluid of said pumps. Upon anysudactuated by the increased pressure of the pump to, meet this demand and rearranges the connection between said pumps, connecting the same in series as previously described in detail. As the multi-stage operation of pump units 5 and I1 begins, valve mechanism 6 is so chosen that the fluid circuit is fed by source 4 and supplementary feeder 25 is' charged by the high pressure discharge of pumps I1 and 9 in series and the same will continue to be so charged until a still further pressure demand brings said feeder into the fluid circuit to feed the suction. side of pump 9 and thereby increase the discharge pres sure of pumps I7 and 9 in series. The last step is performed as follows:

Referring to the valve 6 of Fig. 2 and assuming that a pressure slightly above the minimum output of pumps 9 and IT in series is required by servomotor i8. The discharged pressure of the two pumps at this value will be lead by conduit 26 through the port 33 in piston 32 to chamber 34. This pressure will be exerted against piston 32 to move the same to the right against the force of spring 31. The connection between conduits ii and l is not broken, however, until conduits 21 and l are connected bythe shift of the piston 32. At this time the pressure in chamber 34 forces the piston 32 to shut off the communication of conduit 5 so that source 4 no longer feeds the pumps. An initial pressure slightly above the minimum pressure of the pumps in series is then fed from the feeder 25 by way of conduits I and 21 to the inlet of pump 9.

There is thus provided a novel hydraulic power system which is adapted, for example, for actuating the retractable landing gear of an airplane and which, as a complete unit, weighs'less than the' pumping unit, at present employed in airplanes for this purpose. There is, furthermore, provided a novel arrangement of a plurality of pumps, a supplementary feeder, and novel automatic control means therefor, whereby a wide den decrease in output pressure, due to sudden thespirit and scope of the invention. For a definition of thelimits 'of the invention, reference will be had primarily to the appended claims.

What is claimed is:

1. In apparatus of the class described, a servomotor, a plurality of pumps in parallel, a conduit connecting said pumps to said servo-motor, valve mechanism operatively controlled by the discharge pressure of one of said'pumps and adapted to change the fluid connections between said pumps causing a series arrangement of the latter, I

a reservoir of fluid, a second conduit connecting said reservoir to said pumps, valve means controlling the fluid flow through said second-named conduit, and a supplementary feeder normally connected through said valve means to said first-.

named conduit and adapted to be disconnected therefrom by said valve means at a predetermined pressure output of said pumps whereupon said feeder is placed in communication with said second-named conduit.

2. In apparatus ofthe class described, a fluid reservoir, a plurality of pumps fed from said reservoir, conduit means connecting said pumps to act in parallel, a servo-motor fed by said pumps, means in the discharge end of one of 'said pumps operative to cause a series arrangement of said pumps when the pressure in said dischargereaches a predetermined amount, and

means connected in the discharge end of said pumps whereby upon a further increase in presrange of pressure outputs may be obtained during substantially full load operation of the pumps.

Although only a single embodiment of the invention has been illustrated and described in detail, it is to be expressly understood that the sure in the discharge end of said pumps the latter are disconnected from said fluid reservoir and the pressure input at the inlet of said one pump is increased.

3. In apparatus of the class described, a fluid reservoir, a plurality of fluid pumps arranged in parallel and being normally fed from said reservoir, means comprising a valve responsive to the pressure demand upon said pumps for increasin the pressure output thereof by varying the connection of saidpumps to a series arrangement, and means for further increasing the pressure output of said pumps, said last-named means comprising a supplementary feeder normally fed by the output of said pumps and a valve mechanism interposed in the output of said pumps and operative when the pressure in the Pump output reaches a predetermined amount to disconnect said pumps from said fluid reservoir and to connect said feeder with the input of the first of said pumps when the latter are in series arrangement.

4. In apparatus of the class described, a fluid reservoir, a plurality of fluid pumps arranged to operate in parallel and fed from said reservoir means responsive to the pressure demand upon said pumps for increasing the pressure output thereof by varying the. connections of said pumps from a parallel to a series arrangement, a supplementary reservoir in the output side of said pumps normally fed by said pumps, and valve means connecting said last-named reservoir to the output side of said pumps whereby upon a predetermined increase in the pressurein the output side of said pumps said valve means act to cut off said pumps from said first-named reservoir and to place said last-named reservoir in communication'with the input of the first of said pumps when the latter are in series arrangement.

5. In apparatus of the class described, a servomotor, pumpingmeans adapted to operate in parallel, a conduit connecting said pumping means to said servo-motor, a, pressure controiied valve operatively, connected to said pumping means and adapted to change the fluid connections to a series arrangement for said pumping means, a fluid reservoir. asecond conduit connecting said reservoir to said pumping means, valve means controlling the fluid flow from said reservoir, and a supplementary feeder connected to said second-named conduit through said valve means, said valve means operating upon the attaming ot-a predetermined pressure in the second-named conduit to cause said feeder to supplant said reservoir as a fluid source.

KARL WILF'RID FIEBER,

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