The present disclosure pertains to hydraulic damping valves, such as a cold start valve used in a gas turbine engine.
Oil valves are used in hydraulic systems to relieve hydraulic pressures. For example, an oil valve known as a cold start valve is used in typical engines to help relieve the oil pressure during cold star conditions. Indeed, when a high-viscosity fluid such as oil is pumped through the engine passages, the pressure builds up and the cold start valve opens to relieve the pressure. The cold start valve will bypass the flow until the system pressure is reduced to a set cracking pressure. The cold start valve may assist in preventing over pressurizing of engine components. During the cold start valve operation, the action of the cold start valve may result in sustained oscillations, defined as valve instability. Valve instability may result in oil pressure fluctuations.
In accordance with a first embodiment of the present disclosure, there is provided a damping valve comprising a tubular body having at least one inlet and at least one outlet, a damping piston in the tubular body, the damping piston moveable between a closed position in which the outlet is substantially blocked, and a bypass position in which fluid flow from the inlet to the outlet is permitted, a damping biasing device biasing the damping piston toward the closed position, the damping piston having a first effective piston area in a first chamber exposed to fluid pressure at the inlet and a second effective piston area in a second chamber, the second effective piston area being smaller than the first effective piston area, at least one fluid passage formed in the damping valve for fluid communication between the first chamber and the second chamber to direct fluid from the inlet to the second chamber, whereby fluid in the second chamber applies a force concurrent to the biasing of the damping biasing device and assists in displacing the damping piston to the closed position.
In accordance with a second embodiment of the present disclosure, there is provided a hydraulic system of a gas turbine engine comprising: a hydraulic circuit configured for receiving a fluid and for feeding the fluid to at least one component of the gas turbine engine; and an oil valve comprising a tubular body having at least one inlet connected to the hydraulic circuit and at least one outlet, a damping piston operatively positioned in the tubular body, the damping piston configured for being exposed to the fluid of the inlet, and for being displaced between a closed position in which the damping piston blocks the outlet, and a bypass position in which the damping piston allows fluid flow from the inlet to the outlet, a damping biasing device to apply a biasing force against the damping piston and toward the closed position, the damping piston having a first side in a first chamber exposed to fluid of the inlet to apply a force against the biasing force of the damping biasing device, the damping piston having a second side in a second chamber and having an effective area smaller than that of the first side, at least one fluid passage formed in the oil valve for fluid communication between the first chamber and the second chamber to expose the second side of the damping piston to the fluid of the inlet, whereby fluid in the second chamber applies a force concurrent to the biasing force of the damping biasing device and assists in displacing the damping piston to the closed position.
In accordance with a third embodiment of the present disclosure, there is provided a method for damping fluid pressure in a hydraulic circuit comprising: exposing a damping valve to a fluid in the hydraulic circuit; biasing a damping piston with a damping biasing force such that the damping piston closes a fluid outlet; allowing the fluid to fill a first chamber and a second chamber on opposite sides of the damping piston of the damping valve; and displacing the damping piston away from closing the fluid outlet when a force resulting from fluid pressure on the damping piston in the first chamber exceeds a combination of a force from fluid pressure on the damping piston in the second chamber and of the damping biasing force.
Reference is now made to the accompanying figures in which:
Referring to
The tubular body 30 defines an inner cavity 30A having a longitudinal axis X and being open at opposed ends, including at an inlet 31. The tubular body 30 is connected to the hydraulic circuit at the inlet 31, so as to expose a portion of its inner cavity 30A to a fluid pressure from the hydraulic circuit. For example, the tubular body 30 may have at the inlet 31 appropriate connection means, such as threading, welding, brazing, for connection to the hydraulic circuit. The tubular body 30 is shown as having a nipple shape, i.e., a straight tube, but may also be shaped as an elbow, a tee (with two inlets), etc. The cross-sectional shape of the inner cavity 30A is not visible, but may be circular, oval, etc.
One or more outlets 32 may be defined in a wall of the tubular body 30. In
One or more relief passages 33 may also be defined in the wall of the tubular body 30. In
The damping piston 40 is operatively received in the tubular body 30, so as to be displaceable between a closed position, as in
The damping piston 40 may have different configurations, one of which is shown in
The damping piston 40 may further include an axial wall 42 radially inwardly of the circumferential wall 41, in such a way that the damping valve 20 is separated in a first chamber A and a second chamber B, namely on opposite sides of the axial wall 42. The axial wall 42 has radially extending surfaces, as does the circumferential wall 41, such that fluid pressure in the first chamber A will result in a force vector F1 in the right direction of
As an alternative configuration, the damping piston 40 may not have the circumferential wall 41, but have instead a thicker version of the axial wall 42, for the axial wall 42 to block the outlet(s) 32 in the closed position of the damping piston 40. As yet another alternative or supplemental configuration, the one or more fluid passages 42A may be formed in the tubular body 30 instead of in the damping piston 40. Tubing and/or pipes may also be used to create the fluid communication between the chambers A and B. The number and the size of the fluid passage(s) 42 to control the flow of fluid between chambers A and B, and takes into account the pressure of operation of the hydraulic system, the set cracking pressure, the desired damping effect, and/or the biasing force, etc.
A plunger 43 extends from the axial wall 42, and extends axially along the longitudinal axis X. The plunger 43 may for instance be hollow, but may also be solid. A plunger extension 44 is connected to an end of the plunger 43, and is the part of the damping piston 40 that is connected to the biasing assembly 60. In an embodiment, the plunger 43 and the plunger extension 44 are a single monoblock piece (resulting in an integral plunger 43), and may also be monoblock with circumferential wall 41 and the axial wall 42. Other arrangements are contemplated as well. The plunger 43 and plunger extension 44 are slidingly received in the relief piston 50, in such a way that the damping piston 40 may translate in the axial direction, i.e., in a direction parallel to the longitudinal axis X. Hence, the relief piston 50 serves as a support for the damping piston 40. A flange 45 may be provided at the end of the plunger extension 44 (or plunger 43 if no extension is present), and serves as interface between the damping piston 40 and the biasing assembly 60. The flange 45 is one possible configuration, with others including a receptacle for spring in the plunger 43 or plunger extension 44. The flange 45 may also act as an abutment coming into contact with the relief piston 50, to set the closed position of the damping piston 40, relative to the tubular body 30.
The effective piston area (a.k.a., effective area) of the damping piston 40 in the first chamber A is greater than the effective piston area of the damping piston 40 in the second chamber B. Stated differently, the total surface of the damping piston 40 that will convert fluid pressure in chamber A to force F1 is greater than the total surface of the damping piston 40 that will convert fluid pressure in chamber B to force F2. Therefore, for an equal fluid pressure in chambers A and B, as leveled out by the fluid passage(s) 42, force F1 will be greater than force F2. A biasing force FB, exerted by the biasing assembly 60 is concurrent with force F2 and will consequently be opposed to force F1.
The relief piston 50 is operatively received in the tubular body 30 and is axially offset from the axial wall 42 of the damping piston 40. The relief piston 50 is displaceable between a closed position, as in
The annular body 51 defines an inner channel 52 in which the plunger 43 and plunger extension 44 of the damping piston 40 are slidingly received, consequently forming a sliding joint. The annular body 51 may also have a flange 53, or similar abutment surface (e.g., tab), to delimit its closed position relative to the tubular body 30. The flange 53 may also be the interface of the relief piston 50 with the basing assembly 60, although other configurations are possible as well.
The biasing assembly 60 is shown as having its own casing 61 that is connected to the tubular body 30 Other arrangements are possible as well, to provide a structure for components of the biasing assembly 60 to exert biasing forces against the damping piston 40 and the relief piston 50. The casing 61 may be equipped with connection means to be connected to a surrounding structure, if necessary. The biasing assembly 60 may have a damping biasing device 64. The damping biasing device 64 may be a compression coil spring, although other types of biasing devices may be used, such as leaf springs, hydraulic/pneumatic cylinders, etc. The damping biasing device 64 exerts force FB on the damping piston 40, to bias the damping piston 40 toward the closed position of
In an embodiment, the current disclosure therefore describes a double-piston valve configuration which allows more gradual damping at various oil viscosity conditions. Damping is achieved by using the chambers A and B, with the calibrated passage(s) 42A, and hence use fluid pressure in the second chamber B to counter the fluid pressure in the first chamber A, to allow the usage of lower spring rate (lb/inch). As a consequence, pressure fluctuations in the hydraulic system employing the valve 20. The relief piston 50 is provided in case the maximum pressure of the system is reached.
The damping valve 20 may be used as a cold start valve. In such a case, in cold conditions and with resulting high oil viscosity, the valve 20 is open as in
The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without departing from the scope of the invention disclosed. For example, while the valve 20 is described as having a pair of pistons 40 and 50, there may be a configuration of the valve 20 with only the damping piston 40, i.e., without the relief piston 50 and associated biasing device 65. In such a case, the damping piston 40 would be slidingly mounted to the tubular body 30, and with the second chamber B axially bound by a wall instead of by the relief piston 50. Still other modifications which fall within the scope of the present invention will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims.