US2679206A - Hydraulic system with selfpressurized pump inlet - Google Patents

Description

May 25, 1954 Filed Dec. 21-, 1950 M. W. HUBER HYDRAULIC SYSTEM WITH SELF-PRESSURIZED PUMP INLET 2 Shee'ts-Sheet l Enventor Mac'thew W.Hu'ber (Ittomegs Patented May 25, 1954 HYDRAULIC SYSTEM WITH SELF-. PRESSURIZED PUMP INLET Matthew W. Huber, Watertown, N. Y., assignor to The New York Air Brake Company, a corporation of New Jersey Application December 21, 1950, Serial No. 202,110

4 Claims.

This invention relates to hydraulic circuits and particularly to such circuits as are used on airplanes as a source of power for parasite devices.

In this field of use the low barometric pressure at high altitudes makes it important to deliver hydraulic liquid under pressure to the intake of the main pump. According to the invention this is don by a pump submerged in the oil sump. This has the incidental advantage that the sump is operated at atmospheric pressure so'that under high altitude conditions the oil frees itself of most of the air which tends to become dissolved there- In all cases it is desirable, and with certain types of main pump it is necessary, to deliver the oil at substantially constant pressure tothe inlet of the main pump.

The invention meets this requirement, even under the dimcult conditions recently created by the use of jet engines, type reciprocating engines, require no warm-up period. As a consequence in cold climates the hydraulic system must start up in fully operative condition with the hydraulic liquid cold and hence relatively viscous, as compared with its condition after a reasonable period of operation. The invention meets also these conditions, which greatly impair the stability of performance of conventional systems.

At least two types of main hydraulic pump are in common use. One is controlled by'a device which varies pump displacement progressively in response to the discharge pressure developed by the pump. Several such pumps differing in design are known, and one characterized by a remarkably uniform discharge pressure over its entire range of performance from zero to full delivery is shown in the patent to Huber No. 2,433,222 dated December 23, 1947. Another type of installation is characterized by the use of a pump of constant displacement whose efiective output is controlled by a by-passing unloader controlled by pressure in an accumulator. Such an unloader arrangement is shown in the patent to Huber and Huber No. 2,473,953 dated June 21, 1949. v I

While the first type of pump is usually'preferable, the invention is applicable with either, and indeed can be used with any pump Whose effective I output can be varied in someway in response to discharge pressure-so as 'to assure maintenance of approximately constant discharge pressure.

The invention will now be described as embodied with each o1 the two types of pump specifically mentioned above, reference being made to the accompanying drawings, which:

These engines, unlike the old 2 Fig. l is a diagram, part in section and part in elevation, of a hydraulic circuit embodying the invention, and including a positive displacementvariable delivery pump, as the main pump.

Fig. 2 is a similar diagram of a circuit including as the main pump a constant delivery positive displacement pump with a by-pass unloader responsive to discharge pressure.

A sump or tank I I is vented to atmosphere at l 2 and normally is nearly liquid-filled, say to the level A--A. Mounted in the sump II and submerged in the liquid (which is customarily an oil having good lubricating properties) is a hydraulically driven inlet booster pump, whose housin is indicated at 13. In chamber M of housing [3 is the hydraulic pump-driving motor comprising two meshing pinions [5. In chamber iii of the same'housing is the booster pump comprising two larger meshing pinions [1. As shown, the upper pinion l5 and the lower pinion I! are fixed to a common shaft IS. The motor has a tubular inlet connection [9 and a dischargeport 2| which leads to the interior of sump II. The

pump has an inlet port 22 below the surface of liquid in sump H and a tubular discharge connection 23.

If liquid under pressure is delivered through connection I9 to the motor, the pump will discharge liquid through connection 23 in greater volume, but at reduced pressure as compared with the liquid flowing through the motor. In the absence of friction and slip, a simple proportional relation between pressures and volumetric rates would exist but both are present and mustv be allowed for in the design, as will be explained.

Connection 23 leads to the inlet of pump 24, which is a positive displacement variable delivery pump illustrated as of the type shown in Patent 2,433,222, and so having a controller partly shown at 25 responsive to pressure in discharge connection 26, and operating to vary the delivery of pump 24 so as to maintain the pressure in connection 26 substantially constant while the pump runs.

Comaection 26 leads to the body 21 of a selector valve, to which are connected a tubular line 28 leading to the device to be controlled (not shown) and a tubular exhaust line 29 leading to sump H. The plug 3| of valve 27 is turned by handle 32.

In the full line position of handle 32 valve 21 connects lines 26 and 28. When handle 32 is swung to the dotted line position, the valve blanks line 26 and connects together 28 and 29. A check valve 33 is provided to permit pump 24 to draw liquid from sump II at any time when the effective displacement of pump 24 exceeds that of pump l6--l'l. The design is such that when the gear motor-pump is functioning normally, its output tends to exceed slightly the demand of pump 24 for liquid and so normally develops in line 23 a pressure which holds check valve 33 closed. The motive liquid delivered by line [9 to motor l4-l5 is tapped oil from the high pressure discharge line 25 of pump 24.

Assume for discussion that pump 24, running continuously, maintains a pressure of 3000 p. s. i. in line 25 and that a pressure of 100 p. s. i. is to be maintained in line 23. Except for friction and slip, pump l5l'l should have a displacement per revolution 30 times that of motor 14-45, so that the pressure developed by the booster pump would be 19, of the pressure in line 26'or 100 p. s. 1. Actually, a suitable correction factor must be introduced, and it is desirable to over-correct so that pressure in line 25 tends to exceed 100 p. s. i. To assure that pressure in line 23 is maintained constant at the desired value of 100 p. s. i., a regulator is used to control the flow of hydraulic liquid through the motor.

This regulator has a body 34 with an axial bore closed at least at one end and having two annular groove ports, namely port 35 (connected to line [9) and port 35 (connected to line 25). A piston valve 3? is so formed that in its lowermost position it freely connects ports 35 and 36, but as it moves upward it gradually throttles this connection. Valve 3'? is urged to its lowermost position by a coil compression spring 38 whose stress is adjusted by turning thrust screw 35. A branch of line 23 leads to the space within the bore at the end remote from spring 38.

The arrangement is such that as pressure in line as rises above that desired, flow from line 25 to line I9 is progressively thrcttled, with the result that pressure in line 23 is maintained nearly constant despite varying demands of pump 24 for liquid.

The line M is simply an overflow connection which returns to sump I i any liquid leaking past valve 3'1. The line 42 is provided to return to sump ll liquid by-passed by pump 24 for cooling and lubricating purposes.

Modified embodiment, Fig. 2

In Fig. 2, all parts which are identical with parts in Fig. 1 are identified by the same reference numerals.

For the pump 24 are substituted a constant delivery positive displacement pump (which requires no by-pass connection 32), an unload'er 52 interposed between the discharge 53 of pump 5| and high-pressure line 25, and a pressure accumulator 54 connected with line 25.

The pump 5| may be any positive displacement type, and the accumulator 5 1 may be chosen from a wide range of such devices, conveniently one having a pneumatic cushion separated from the hydraulic liquid by a rubber-like diaphragm.

The unloader may be of various types but is shown a conforming to Patent 2,473,953, and is constructed as follows. In the drawing the numeral 52 is applied to the body of the unloader which is generally cylindrical in form and has an axial cylindrical bore closed at one end (the lower end in Fig. 2) Two annular groove ports encircle the bore. The first is a high pressure port 55 which is in free constant communication with pump discharge line 53 and also in communication with high pressure line 25 through a ball check valve 56. A spring clearly shown in 4 the drawing seats valve 56 but does not load it to any significant extent. The second port 51 is connected with drain line 4 l.

A piston valve unit reciprocable in said bore comprises in one piece a piston head 58 which is always below port 51, a valve head 59 which in the lowermost position of the unit obstructs flow between ports 55 and 51, and an upper head 8! which is alway above port 55 and is formed at one side with a restricted port 52. A pilot valve 53 having a restricted port 64 which extends along its side from the lower end to a point below its upper end reacts downward on the valve unit under the urge of coil compression spring 65.

A combined spring seat and closure 56 is threaded into the upper end of housing 52 and may be turned to adjust the stress on spring 85. The space above pilot valve 63 and around spring 55 is vented by passage Bl to the sump via drain line 4|. A port 68 admits pressure fluid from line 26 to the space below piston head 58.

Operation Whether the arrangement of Fig. 1 or Fig. 2 is used, the pump 24 of the former or the pump 5i of the latter runs continuously and maintains in line 25 a high and substantially uniform pres sure here assumed to be 3000 p. s. i. Assuming that it is required that line 23 be maintained at p. s. i., the displacement of pump lt-l? per revolution advisably would be somewhat less than 30 times the displacement of motor i i-l5, the departure from the 30 to 1 ratio bein intended to compensate for the pressure loss caused by friction and slip.

Spring 38 would normally be so adjusted that ports 35 and 35 are in free communication so long as pressure in line 23 does not exceed 100 p. s. i., but if this pressure exceeds this value, this communication is throttl-ed. Other adjustments and proportions may be adopted to meet special conditions.

In any case the regulator 35 gives flexibility of adjustment, and stable control of pump inlet pressure will be established quickly after the pump is put into operation.

Two variable delivery pump systems have been illustrated and others are known and may be used similarly. Other types of motor-driven booster pumps may be substituted, but the one shown is believed to be the simplest available.

Venting of the sump to atmosphere is desirable because it permits the hydraulic liquid to free itself of air, this action being particularly eiiective at high altitudes.

I claim:

1. In a hydraulic system the combination of a sump; ahigh pressure delivery line; a continuously operating high pressure displacement pump provided with regulating means, the pump having an inlet and a connection through which it delivers to the high pressure delivery line under control of said regulating means, the regulating means being responsive to pressure in said delivery line and serving to maintain that pressure substantially constant; a hydraulic motor interposed in a flow path from said delivery line to said sump; a hydraulic booster pump connected to be driven by said motor and arranged to draw liquid from said sump and deliver it under pressure to the inlet of said high pressure pump; a flow regulating valve interposed in the flow path through said motor; and means responsive to the pressure developed by the booster pump and serving to adjust said flow-regulating valve.

2. The combination defined in claim 1 in which the booster pump and the hydraulic motor are each of the positive displacement type and the two are positively connectedwhereby there is a fixed ratio of the volumetric displacement rate of the pump to that of the motor and this ratio is so chosen as to exceed the ratio of the regulated discharge pressure of the high pressure displacement pump to the desired inlet pressure thereof.

3. The combination defined in claim 1 in which the booster pump and the hydraulic motor are each of the positive displacement type and the two are positively connected whereby there is V a fixed ratio of the pressure delivered by the booster pump to the motive pressure effective in the hydraulic motor and the parts are so proportioned that the pressure developed by the booster pump is suificient to close said flow regulating valve slightly, when the viscosity of the hydraulic liquid is normal.

4. In a hydraulic system the combination of a sump; a high pressure delivery line; a continuously operating high pressure displacement pump provided with regulating means, the pump hav ing an inlet and a connection through which it delivers to the high pressure delivery line under control of said regulating means, the regulating means being responsive to pressure in said delivery line and serving to maintain that pressure substantially constant; a pressure reducing hydraulically operated booster pump unit connected to be driven by motive fluid tapped from said high pressure line, and to deliver hydraulic liquid from said sump to said inlet at reduced pressure and increased volume as compared with said motive fluid; and pressure operated valve means responsive to said reduced pressure and serving to regulate the flow of said motive fluid.

Name Date Number V Vickers Oct. 22, 1940

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