Patent Application
20080022974
Supply 12 may constitute a reservoir configured to hold a supply of fluid. One or more hydraulic systems associated with the power source may draw fluid from and return fluid to supply 12. It is contemplated that fluid system 10 may be connected to multiple separate fluid supplies, if desired.
Pumping mechanism 14 may produce a flow of pressurized fluid and may include any suitable source of pressure such as, for example, a variable displacement pump, a fixed displacement pump, a variable flow pump, or any other source known in the art. Pumping mechanism 14 may be dedicated to supplying pressurized fluid to only fluid system 10 or may, alternatively, supply pressurized fluid to multiple separate hydraulic systems.
Each of fuel injectors 16 may be associated with a different combustion chamber (not shown) of the power source. Fuel injectors 16 may be operable to inject an amount of pressurized fuel into the combustion chambers at predetermined timings, fuel pressures, and fuel flow rates. Fuel injectors 16 may be mechanically, electrically, pneumatically, or hydraulically operated.
Common rail 18 may embody a hollow tubular member that distributes fluid from pumping mechanism 14 and returns fluid to supply 12. In particular, common rail 18 may connect pumping mechanism 14 to fuel injectors 16 by way of a main supply line 20 and a plurality of branch lines 22. Common rail 18 may also be connected to supply 12 by way of a main return line 24. In this manner, pumping mechanism 14 may draw fluid from supply 12, pressurize the fluid, direct the pressurized fluid to each fuel injector 16, and return excess fluid to supply 12.
As also illustrated in
Pressure relief valve 26 may include an assembly of components that cooperate to relieve the pressure within common rail 18. Specifically, pressure relief valve 26 may include a first valve element 28, a second valve element 30, a single return spring 32, and a shim element 33. First valve element 28 may be mechanically connected to move with second valve element 30. Return spring 32 may bias both first and second valve elements 28, 30 toward flow blocking positions. Shim element 33 may be used to cost effectively set the bias of return spring 32.
First valve element 28 may be a two position element movable in response to a pressure within common rail 18. In particular, an inlet 34 of pressure relief valve 26 may communicate pressurized fluid from common rail 18 with a hydraulic surface 28a of first valve element 28. Because first valve element 28 may be mechanically connected through second valve element 30 with return spring 32, first valve element 28 may remain in a first of the two positions until a force generated by the common rail pressure acting on hydraulic surface 28a exceeds the spring's biasing force. When the force generated by the pressure of common rail 18 exceeds the biasing force of return spring 32, first valve element 28 may move from the first position at which fluid from common rail 18 is blocked from the second valve element 30, to a second position at which the fluid flows from first valve element 28, through a central bore 36 of pressure relief valve 26, to second valve element 30. In one example, the pressure required to move first valve element 28 away from the first position may be in the range of about 180-240 MPa. To minimize hunting of first valve element 28 between the first and second positions, a restrictive orifice 35 may be located between inlet 34 and central bore 36.
Second valve element 30 may be a proportional valve element movable in response to a pressure of the fluid within central bore 36. In particular, fluid within central bore 36 may act against a hydraulic surface 30a of second valve element 30. Because of the bias of return spring 32 acting directly on second valve element 30, second valve element 30 may remain in a flow-blocking position until a force generated by the pressure of the fluid on hydraulic surface 30a exceeds the biasing force of return spring 32. When the force generated by the pressure of the fluid within central bore 36 exceeds the biasing force of return spring 32, second valve element 30 may move from the flow-blocking position at which fluid from common rail 18 is blocked from supply 12, toward a second position at which the fluid from common rail 18 flows through an outlet 38 of pressure relief valve 26 to supply 12. Second valve element 30 may be movable to any position between the first and second positions in response to the pressure of the fluid within central bore 36 to vary the flow rate of fluid passed to supply 12. In one example, the pressure required to move second valve element 30 away from the first position may be about 6-8 times less than the pressure required to move first valve element 28 away from its first position (e.g., about 35 MPa).
In the embodiment of
As illustrated in
As piston member 46 is moved upward out of central bore 36, fluid may flow in several different paths relative to flange member 48. In particular, flange member 48 may include one or more through holes 54. As shoulder 52 emerges from central bore 36, fluid from recesses 50 may simultaneously pass through holes 54 and around an outer periphery of flange member 48. In this manner, through holes 54 may reduce drag and the likelihood of bounce associated with the movement of piston member 46.
The disclosed fluid system has wide use in a variety of applications including, for example, fuel systems, lubrication systems, work implement actuation systems, transmission systems, and other hydraulic systems, where protection from excessive pressures is desired. The disclosed fluid system may provide the desired protection by implementing a multi-stage pressure relief valve. When the pressure of the fluid within the system exceeds a maximum threshold value, the multi-stage pressure relief valve may drain fluid from the system, thereby lowering the pressure of the fluid within the system. The pressure of the fluid within the system may be lowered just enough to protect the system without creating instability or completely disabling the system. The operation of fluid system 10 will now be explained.
During operation of fluid system 10, pumping mechanism 14 may draw fluid from supply 12, pressurize the fluid, and direct the pressurized fluid to common rail 18. Pressure relief valve 26 may be in communication with the fluid of common rail 18 via inlet 34, and in fluid communication with supply 12 via outlet 38. As the pressure of the fluid within common rail 18 acting on hydraulic surface 28a exceeds the bias of return spring 32, first valve element 28 may move to the second or flow passing position, at which the fluid from common rail 18 is communicated with central bore 36 and hydraulic surface 30a of piston member 46. As the pressure of the fluid within central bore 36 acting on hydraulic surface 30a exceeds the bias of return spring 32, piston member 46 may be moved out of central bore 36 until interrupted shoulder 52 emerges an amount from central bore 36 and fluid passes through recesses 50 to outlet 38. As the fluid drains through outlet 38 back to supply 12, the pressure of the fluid within common rail 18 may reduce.
The amount that interrupted shoulder 52 extends above the rim of central bore 36 may correspond to a pressure of the fluid within common rail 18. That is, although first valve element 28 may be a substantially two-position element, second valve element 30 may be a proportional valve element movable between its first and second positions in response to the pressure within common rail 18. Once first valve element 28 has opened, the resulting pressure within common rail 18 may no longer be controlled by first valve element 28. Instead, the movement of second valve element 30 may regulate the pressure of the fluid within common rail 18 and ensure that it remains low enough for component protection, yet high enough for continued injector operation. For example, once second valve element 30 has opened, an increase in pressure within common rail 18 may push interrupted shoulder 52 further out of central bore 36, thereby increasing a flow area for fluid draining from common rail 18. The increased flow area may result in a greater flow rate of fluid from common rail 18 to supply 12 and, subsequently, a lower pressure within common rail 18. Conversely, as the pressure within common rail 18 decreases, interrupted shoulder 52 may retract back into central bore 36 and reduce the flow area. The reduced flow area may result in a lower flow rate of fluid from common rail 18 and, subsequently, a higher pressure within common rail 18. Once first valve element 28 opens to pass fluid, it may remain open until interrupted shoulder 52 of second valve element 30 is nearly or completely retracted into central bore 36.
The disclosed pressure relief valve may be a low cost alternative to controlling pressure within a common rail. Specifically, because pressure relief valve 26 utilizes only a single conical valve seat, the cost of fluid system 10 may be lower than other systems employing multiple conical valve seats. In addition, because first valve element 28 does not include any internal fluid passageways, the manufacturing cost of pressure relief valve 26 may be small. Further, because first and second valve elements 28, 30 may be combined into a single integral component, the component cost of pressure relief valve 26 may be reduced even more.
It will be apparent to those skilled in the art that various modifications and variations can be made in the fluid system of the present disclosure without departing from the scope of the disclosure. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the fluid system disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.
