This invention relates generally to pumps and more particularly to variable flow rate pumps for hydraulic systems.
Aircraft gas turbine engines often incorporate various high pressure hydraulic actuators to operate components such as variable geometry exhaust nozzles, vectoring exhaust nozzles, bypass doors, variable stator vanes, and the like.
Depending on which actuators are being used, the flow requirements vary greatly, and it is desirable to match pumping capacity to the demand. Variable displacement high-pressure piston pumps are therefore commonly used in engine and aircraft hydraulic systems. However, prior art variable displacement piston pumps can be complex, heavy, costly and can lack desired reliability.
These and other shortcomings of the prior art are addressed by the present invention, which provides a high pressure, variable flow rate pump with low weight and high reliability.
According to one aspect of the invention, a variable flow pump includes: (a) a housing including an inlet chamber and an outlet chamber interconnected by a main bore; (b) a non-rotating cylinder block with first and second ends disposed in the main bore, the cylinder block including:(i) a central bore disposed in fluid communication with the inlet chamber; (ii) a plurality of cylinder bores arrayed around the central bore; (iii) a plurality of first feed passages interconnecting the inlet chamber and the cylinder bores, the first feed passages defining a bypass flowpath between the cylinder bores; and (iv) at least one check valve disposed at the second end which permits fluid flow from the cylinder bores to the discharge chamber but prevents flow in the opposite direction; (d) a plurality of pistons disposed in the bores; (e) a shaft mechanically coupled to the pistons so as to cause the pistons to reciprocate through an axial pump stroke between predetermined fill and discharge positions, when the shaft is rotated; and (f) a mechanism coupled to the cylinder block which is adapted to selectively axially position the cylinder block within the housing, so as to vary the size of the bypass flowpath.
According to another aspect of the invention, a method of operating a variable flow pump includes: (a) receiving fluid into an inlet chamber of a housing of the pump, wherein the pump includes an inlet chamber and an outlet chamber interconnected by a main bore; and (b) using a piston which reciprocates through an axial pump stroke between predetermined fill and discharge positions: (i) drawing fluid from the inlet chamber into a cylinder bore in a non-rotating cylinder block with first and second ends disposed in the main bore; (ii) discharging fluid through the cylinder bore; and (iii) during discharge, selectively bypassing a portion of the fluid from the cylinder bore through a first feed passage into the inlet chamber, the proportion of bypass being controlled by modulating the axial position of the cylinder block within the housing.
The invention may be best understood by reference to the following description taken in conjunction with the accompanying drawing figures in which:
Referring to the drawings wherein identical reference numerals denote the same elements throughout the various views,
The housing 12 includes a main bore 24. An inlet chamber 26 is disposed at one end of the main bore 24 and a discharge chamber 28 is disposed at the opposite end. An inlet 30 connects to the inlet chamber 26, and an outlet 32 connects to the discharge chamber 28.
The cylinder block 14 is received in the main bore 24. It is free to move axially, between a maximum flow position (seen in
The shaft 16 passes through appropriate bearings and seals 54 in the housing 12. A first end of the shaft 16 extends outside the housing 12 and incorporates one or more mechanical features (not shown) such as a keyway, splines, or a driven gear, allowing the shaft to be connected to a driving element.
The opposite end of the shaft 16 is formed into an enlarged plug 55 having a cylindrical outer surface 56 which fits closely in the central bore 38. A bleed port 57 is provided in the shaft 16 which lets working fluid pass freely between the inlet chamber 26 and the interior of the central bore 38. This allows the cylinder block 14 to translate axially relative to the shaft 16 without causing excessive loads or hydraulic lock. A rotating port 58 is incorporated near the second end to pass working fluid from the inlet chamber 26 to the second feed passages 46. As seen in
As seen in
Means are provided for selectively moving the cylinder block 14 to a desired axial position relative to the housing 12. Any type of actuator capable of moving the cylinder block 14 (e.g. electrical, hydraulic) may be used. In the illustrated example, the cylinder block 14 is moved by an electrohydraulic servo valve (EHSV) 72 of a known type in which a small pilot valve (not illustrated) is used to port working fluid pressure to either side of a primary cylinder (shown schematically at 74). As shown, discharge pressure may be ported to a pressure regulator 76 which in turn feeds regulated fluid pressure to the EHSV 72 through a line 78. The pressure drop across the EHSV 72 is thus nearly constant over a wide range of pump output pressures, which simplifies control programming. A controller 80 including one or more processors, such as a programmable logic controller (PLC) or computer, is coupled to the EHSV 72. The controller 80 responds to a flow demand signal and in turn drives the EHSV 72 to an appropriate position. A suitable transducer (not shown), such as a linear variable differential transformer (LVDT), may be used to provide cylinder block axial position feedback information to the controller 80.
The pump 10 operates as follows. Working fluid enters the inlet 30 and floods the inlet chamber 26 volume on the left side of the pump 10. The fluid is at a relatively low inlet pressure, which may be supplied by a suitable boost pump of a known type (not shown). Meanwhile the shaft 16 is rotating, causing the pistons 20 to reciprocate as described above. When a piston 20 is in the retracted or fill position, (the upper piston 20 in
Discharge flow is varied by altering the percentage of piston stroke delivering fluid to the discharge chamber 28 versus bypass flow back to the inlet chamber 26. This is achieved by modulation of the axial position of the cylinder block 14.
The pump may also include a balance piston 82. In operation, discharge pressure is ported to the balance piston 82 through a line 84. This pressure tends to drive the cylinder block 14 towards the right, in opposition to the force applied by discharge pressure on the second end of the cylinder block 14. The area of the balance piston 82 may be selected such that the net axial force on the cylinder block 14 is zero or very small, thereby reducing bearing loads. With the balance piston 82, the EHSV 72 need only have enough capacity to overcome seal friction and allows the EHSV 72 to be much smaller than it would have to be otherwise.
If desired, the pump 10 can include a pressure relief valve 86. If the discharge pressure exceeds the relief valve's set point, flow is bypassed to the inlet chamber 26.
The foregoing has described a variable flow pump. While specific embodiments of the present invention have been described, it will be apparent to those skilled in the art that various modifications thereto can be made without departing from the spirit and scope of the invention. Accordingly, the foregoing description of the preferred embodiment of the invention and the best mode for practicing the invention are provided for the purpose of illustration only and not for the purpose of limitation.