Hydraulic Power Supply System

Abstract

An hydraulic power supply system including a pump, an accumulator and a variable flow rate valve connected to by-pass to the reservoir that portion of the pump output which exceeds current system demand. This is accomplished by varying the flow rate of the by-pass valve in accordance with the quantity of fluid stored in the accumulator.

Description

FIELD OF THE INVENTION

This invention relates generally to hydraulic power supply systems and particularly to such systems which automatically make a supply of fluid under pressure available for actuating useful load devices.

BACKGROUND OF THE INVENTION

A typical system of the prior art includes a continuously running pump which delivers fluid from a reservoir through a check valve to an accumulator and to a load line. A by-pass valve is connected between the high pressure side of the pump and the reservoir. At the start of operations, the by-pass valve is closed and the pump supplies the load and charges the accumulator. When the accumulator becomes fully charged, the by-pass valve is automatically opened, diverting the entire flow of the pump to the reservoir while the load is supplied from the accumulator. When the accumulator becomes nearly depleted, the by-pass valve is automatically closed, whereupon the pump again delivers fluid to both the load and the accumulator.

Systems as described above, although widely used, are subject to certain disadvantages. For example, the accumulator is continually being cycled from empty to full, causing rapid wear of the tail rod seals. As another example, the wide and frequent fluctuations in pressure cause rapid deterioration and frequent failure of hoses, pipes; seals and pumps.

It is a general object of the present invention to provide an improved hydraulic power supply system.

Another object is to provide such a system in which the fluctuations in line pressure are minimized.

Another object is to provide such a system in which the cycling of the accumulator is minimized.

SUMMARY OF THE INVENTION

Briefly stated, in a system incorporating the present invention, the by-pass valve is one in which the flow rate is continuously variable in response to the quantity of fluid stored in the accumulator so as to divert continuously to the reservoir substantially that portion of the output of the pump which exceeds the current system demand.

BRIEF DESCRIPTION OF THE DRAWING

For a clearer understanding of the invention, reference may be made to the following detailed description and the accompanying drawing, in which:

FIG. 1 is a schematic diagram illustrating the principles of the invention; and

FIG. 2 is a schematic diagram of a preferred embodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENT

Referring first to FIG. 1, there is shown a continuously operating pump 11 for drawing fluid from a reservoir 12 and furnishing it under pressure to a line 13 which in turn is connected to supply the useful loads, from which it is returned to the reservoir 12 by return lines (not shown). The line 13 is also connected to an accumulator 14, shown schematically as including a piston 15 which divides the accumulator into an upper chamber containing the fluid and a lower chamber connected to a source 16 of a gas, such as nitrogen, under pressure. A by-pass valve 17 has its inlet 18 connected to the line 13 and its outlet 19 connected to the reservoir 12. It is shown schematically and includes a portion 21 which, in response to an increase in applied fluid pressure and working against a spring 22, increases the flow of fluid from inlet 18 to outlet 19.

A variable pressure divider, denoted generally by the reference character 23, comprises a fixed restrictor 24 and a variable restrictor 25 serially connected between the line 13 and the reservoir 12. Preferably a filter 26 is inserted between the line 13 and the restrictors. Each restrictor provides a certain amount of resistance to the flow of fluid so that the pressure at their junction depends upon the pressure in the line 13 and the relative values of the two restrictors. The restrictor 25 is mechanically connected to have its magnitude varied continuously in accordance with the position of the piston 15 which in turn is indicative of the quantity of fluid currently stored in the accumulator 14. In the present example the mechanical connections are such that the magnitude of the restrictor 25 increases as the amount of fluid stored in the accumulator increases. The junction 27 is connected to the pressure responsive portion 21 of the valve 17.

The pump 11 is preferably (but not necessarily) a constant displacement pump which delivers fluid at a constant rate of flow determined by its capacity into the line 13. A portion of this rate of flow, determined by the system demand, is bypassed to the reservoir 12 by the valve 17. The system demand is the sum of the small flow through the pressure divider, the flow through the load and the flow to the accumulator. The latter, of course, may be positive or negative in sign.

In operation, the pump 11 furnishes the fluid required by the pressure divider, the loads, and the accumulator. A portion of the pump output is diverted to the reservoir 12 by the valve 17. If the load should increase, it would tend to draw fluid from the accumulator 14, reducing the quantity of fluid stored therein. Such reduction would decrease the magnitude of the restrictor 25 thus decreasing the pressure drop thereacross and decreasing the pressure at the junction 27. Such decrease would allow the spring 22 to decrease the rate of flow of fluid through the valve 17, thus making a greater rate of flow available to the load and to the accumulator. The system would soon stabilize with the valve 17 diverting to the reservoir 12 that portion of the output of the pump 11 which exceeds the then current system demand. If the load should then decrease, a similar but opposite sequence of events would occur. Flow of fluid into the accumulator would tend to increase, thus increasing the quantity of fluid stored therein, increasing the magnitude of the restrictor 25, increasing the pressure at the junction 27 and increasing the rate of flow through the valve 17 until the system again stabilized with the flow through the valve 17 again substantially equal to the excess of pump output over the new system demand.

Referring now to FIG. 2, a preferred embodiment of the invention shown schematically in more detail. Components identical or comparable to those of FIG. 1 are denoted by the same reference characters. The pump 11 draws fluid from the reservoir 12 and delivers it through a check valve 31 to the line 13 which, as before, is connected to the load and to the accumulator 14. The piston 15 is connected to a tail rod 32 which extends through a seal 33 to the exterior of the accumulator 14. The tail rod 32 actuates a limit switch 36 through any suitable mechanical linkage, shown schematically by the dotted line 37. In the position of the parts shown, the accumulator 14 is full and the movable arm 38 of the switch engages a fixed contact 41. When the accumulator is nearly empty, the arm 38 engages a fixed contact 42. The moveable arm 38 is connected to a terminal 43 which in turn is connected to a conductor X. The contacts 41 and 42 are connected to conductors Y and Z respectively.

The tail rod 32 carries a short arm 44 the end of which is connected to an endless flexible member 45 such as a light chain which drives two sprockets 46 and 47. The sprocket 47 is fastened to a hub 48 to which is also fastened a gear 49 which engages a sector of a gear 51 fastened to a hub 52, to which is also fastened a cam 53. The latter is engaged by a roller 54 pivoted on one end of an arm 55 the other end of which is pivoted at point 56.

Fluid from the line 13 flows through the filter 26 and the conduit 58 to the restrictor 24 which comprises several orifices in series. Fluid then flows through a nozzle 61 and impinges on the closely adjacent flat surface of one end of a member 62 fastened to a resilient spider 63 which holds the member 62 in place radially. The nozzle 61 and the member 62 are comparable to the restrictor 25 of FIG. 1 and are denoted together by this reference character in FIG. 2. The other end of the member 62 bears against a spring seat 65 against which a spring 66 bears which urges the member 62 towards the nozzle 61 in opposition to fluid pressure. The other end of the spring 66 bears against another spring seat 67 which in turn bears against one end of a rod 68 the other end of which engages an intermediate portion of the arm 55.

The valve 17 includes a body formed with a generally cylindrical bore including end spaces 71 and 72 and ports 73, 74, 75 and 76. Within the bore is a spool 77 formed with three lands 78, 79 and 81. The end space 72, to the left as viewed in FIG. 2, is connected by a conduit 82 to the reservoir 12 and contains a spring 83 bearing against spring seats 84 and 85, the former bearing against the body of the valve 17 and the latter bearing against the land 81, urging the spool 77 to the right. The end space 71 is connected by a conduit 86 to the control fluid pressure as will be more fully explained. The ports 74 and 76 may contain a plurality of restrictors 87 and 88, respectively, which may be many small diameter tubes or pipes but which preferably comprise a series of plates formed with baffles on one or both faces as more fully described in the copending application of Paul F. Hayner and Richard J. Brockway, Ser. No. 093,192 filed Nov. 27, 1970 for Fluid Flow Restrictor, now U.S. Pat. No. 3,688,800 issued Sept. 5, 1972, and assigned to the same assignee as is the instant application. The port 73 is connected by a conduit 89 to the high pressure side of the pump 11. Fluid flows from the conduit 89 through the port 73 to the central bore, then through the restrictor 87 in the port 74 to a conduit 91, then into the port 75 to the central bore, then through the restrictors 88 in the port 76 to a conduit 92 and then to the reservoir 12. The spool 77 is shown in an intermediate position in which the lands 79 and 81 occlude some of the restrictors 87 and 88, respectively, allowing flow only through the remainder of them. These restrictors reduce the noise which otherwise would be generated by the throttling action of the lands. It has been found helpful to pass the fluid through two sets of restrictors 87 and 88 although this is not necessary for the purposes of the present invention.

Three solenoid operated valves, denoted generally by the reference characters 94, 95 and 96, are provided to enable the apparatus to operate in either of two modes. The valve 94 includes two lands 97 and 98 and an operating winding 99. In the de-energized position shown, an inlet conduit 101 communicates with an outlet conduit 102 while another inlet conduit 103 is occluded. When the winding 99 is energized, the conduit 101 is occluded while the conduit 103 communicates with the conduit 102. Similarly, the valve 95 includes lands 104 and 105 and an operating winding 106. In the de-energized position shown, a conduit 107 communicates with the conduit 101 while a conduit 108 is occluded. When the winding 106 is energized, the conduit 107 is shut off while the conduit 108 communicates with the conduit 101. The valve 96 includes lands 111 and 112 and an operating winding 113. This valve is shown in its energized position in which a conduit 114 communicates with the conduit 107 while in the de-energized position the conduit 114 is cut off. The remaining conduit 115 of the valve 94 is sealed off and is not used. The conduit 114 is connected to the junction of the restrictors in the pressure divider 23, that is, to a point between the restrictor 24 and the nozzle 61.

One terminal of each of the windings 99, 106 and 113 is grounded. The other terminal of the winding 113 is connected to the lower contact 121 of a single pole double throw switch 122. This switch serves to connect one side of the power line 123 to either the contact 121 (as shown) or a contact 124 which is connected to the conductor X. The conductor X interconnects the contact 124 with the terminal 43. The remaining terminals of the winding 99 and 106 are connected to conductors Z and Y respectively, which, in turn are connected to the contacts 42 and 41, respectively. The intermediate portions of the conductors X, Y and Z have been omited in order to simplify the drawing.

The apparatus of FIG. 2 operates in substantially the same manner, except for details, as has been explained in connection with FIG. 1. It will be assumed at first that the switch 122 is in the position shown where it energizes the winding 113 but not the conductor X with the result that the valves 94, 95 and 96 are in the positions shown in the drawing. The conduit 114 communicates through these valves with the conduit 86 and the end space 71. The position of the spool 77, and the flow rate through the valve 17 are responsive to the pressure in this end space 71.

The pump 11 supplies fluid through the check valve 31 to the loads and to the accumulator 14. In the position shown in FIG. 2, the accumulator is substantially full, that is, it contains substantially the maximum quantity of fluid it is capable of storing. In this position, the tail rod 32 is down and the arm 38 engages the contact 41 but this has no effect at this time because the conductor X is not energized. The arm 44 has operated the chain 45, the sprockets 47 and 48, the gears 49 and 51 and the cam 53 to the positions shown at which the arm 55 is at substantially its most leftward position so that the member 62 is as close as possible to the nozzle 61 and the restrictor 25 has substantially its maximum value. Thus the pressure drop across the restrictor 25 and the pressure in the conduit 114 and the end space 71 are substantially maximum and the valve spool 77 is urged against the spring 83 to the position shown at which the valve 17 is capable of diverting the entire output of the pump 11 to the reservoir 12.

If now the load should increase so as to require a greater rate of fluid flow, it would tend to draw fluid from the accumulator 14. The cam 53 would rotate clockwise, allowing the arm 55 and the member 68 to be urged to the right by the spring 66, thereby decreasing the magnitude of the force on member 62 which in turn decreases the pressure drop across restrictor 25 and decreases the pressure in the end space 71. The spring 83 would then urge the spool 77 to the right, decreasing the portion of the pump output which is diverted to the reservoir 12, making more available to the load and the accumulator. An equilibrium position would soon be reached with the valve 17 passing the excess of pump output over system demand.

With the switch 122 in the upper position, the winding 113 is deenergized so that the valve 96 shuts off the conduit 114. Thus, the pressure divider 23 and its associated apparatus have no effect. With the contact 124 and the conductor X energized, the valves 94 and 95 are controlled by the position of the accumulator tail rod 32. In the position shown, the accumulator is full, the arm 38 engages the contact 41, conductor Y and winding 106 are energized, while conductor Z and winding 99 are de-energized. The end space 71 communicates, through conduits 86 and 102, valves 94 and 95, conduit 108 and filter 26 with the load line 13 with the result that this high pressure overcomes the spring 83 and opens the valve 17 fully so that the entire output of the pump 11 is diverted to the reservoir 12 while the accumulator 14 supplies the entire load. As fluid is first drawn from the accumulator 14, the tail rod 32 rises, disengaging the arm 38 from the contact 41 thereby de-energizing conductors Y and the winding 106. The valve 95 reverts to the position shown in the drawing, closing the connection between the load line 13 and the end space 71. However, the valve 17 remains in its fully open position because the hydraulic lock created by the closure of all connections to the end space 71 maintains the pressure in this space and holds the valve 17 open. When the accumulator 14 is nearly empty, the moveable arm 38 engages the contact 42 thereby energizing the chamber Z and the winding 99. The valve 94 connects the end space 71 to the reservoir 12 thereby closing the valve 17 so that the entire output of the pump 11 goes to the load and the accumulator 14, none being directed to the reservoir 12. Hydraulic lock holds the valve 17 closed when the arm 38 is disengaged from the contact 42. This condition continues until the accumulator is again full as shown in FIG. 2, at which time the arm 38 will again engage the contact 41.

From the above it is apparent that Applicants have provided an hydraulic power supply system with two alternative modes of operation. There are some circumstances in which the "open-closed" mode just described can be used to advantage. However, it is usually preferred to operate the system in the continuously variable mode with the pressure in the end space 71 controlled continuously by the amount of fluid stored in the accumulator 14. In this mode the cyclic changes of pressure in various parts of the apparatus resulting from discontinuous operation are avoided. Likewise, the movements of the piston 15 in the accumulator are minimized.

It will be understood that the drawing is schematic only and that an actual system may include additional apparatus such as safety valves, limit switches and the like. However, such items have been shown because they are well known and do not form a part of the present invention.

Although a preferred embodiment has been described in considerably detail for illustrative purposes, many modifications can be made within the spirit of the invention. Therefore, it is desired that the protection afforded by Letters Patent be limited only by the true scope of the appended claims.

Claims

What is claimed is:

1. An hydraulic power supply system, comprising,

a reservoir containing a supply of fluid,

an accumulator for storing fluid under pressure,

a load line connected to said accumulator,

a continuously running pump including an inlet connected to said reservoir and an outlet connected to said load line and to said accumulator,

a variable flow rate valve including an inlet connected to said outlet of said pump and an outlet connected to said reservoir,

first and second restrictors serially connected between said load line and said reservoir,

means for varying the magnitude of said second restrictor in accordance with the variations in the quantity of fluid in said accumulator whereby the pressure at the junction of said restrictors constitutes a control pressure, and

means responsive to said control pressure for continuously controlling the rate of flow of fluid through said valve.

2. An hydraulic power supply system in accordance with claim 1, in which said second restrictor includes a nozzle through which fluid flows and also includes a member formed with a flat surface positioned adjacent to said nozzle for intercepting the flow of fluid therethrough and in which said means for varying includes means for controlling the position of said member in accordance with the quantity of fluid in said accumulator.