Patent Application
20180087479
The present disclosure relates generally to limiting pump cavitation in a pressurized fluid system, and more particularly to a pump protection device having an active range at medium pressures.
Systems for supplying, distributing and handling pressurized fluids such as pressurized fuel are widespread in the internal combustion engine and machinery fields. For certain engines, notably compression ignition engines, a pressurized fuel system is often used for delivering combustible fuel to individual cylinders by way of fuel injectors. The relatively high pressures of the fuel can assist in atomization of fuel spray to various ends, notably efficiency and reduction of certain emissions. The mechanisms used for pressurizing the fuel, distributing the fuel to individual fuel injectors, and containing fuel throughout the system under relatively high pressures tend to be robust and highly sophisticated. Fuel pressures in some modern systems can exceed 300 MPa.
Decades ago engineers developed so-called common rail fuel systems where a fuel reservoir is maintained at or close to a desired pressure. A plurality of individual fuel injectors fluidly connected to the common rail can be supplied with the fuel at rail pressure and selectively operated to effect fuel injection. Certain variations on the basic common rail design have been developed more recently, including systems where a plurality of separate fuel accumulators are positioned fluidly between a common rail and each of a plurality of fuel injectors. Certain other systems can include variations on these general themes.
As noted above, pressurized fuel system equipment tends to be sophisticated, and components such as pumps, seals, fluid conduits and the like are generally relatively robustly designed. For various reasons, one of which is the tendency for cavitation of the liquid fuel to occur, the high pressure fuel system environment can be relatively harsh, and component service lives are therefore commonly short. Commonly owned U.S. Pat. No. 6,647,966 to Ye Tian teaches a typical common rail fuel injection system.
In one aspect, a fuel system for an internal combustion engine includes a fuel supply having a common rail and a fuel pump. The fuel pump is coupled with the fuel supply and structured to pressurize a fuel from the fuel supply for conveying to the common rail. The fuel system further includes a plurality of fuel injectors coupled with the common rail and structured to inject the fuel into a plurality of cylinders in an internal combustion engine. The fuel system further includes a pump protection device structured to drain pressurized fuel from the common rail to provide a fuel flow through the fuel pump that limits cavitation within the fuel pump. The pump protection device includes a valve body having an inlet fluidly connected with the common rail, a drain outlet, and a valve mechanism positioned within the valve body fluidly between the inlet and the outlet. The valve mechanism further includes a first valve member movable between a closed position inhibiting fluid flow through the inlet, and an open position, and a second valve member movable between a closed position inhibiting fluid flow through the outlet, and an open position. The valve mechanism further includes at least one biaser biasing the first valve member and the second valve member toward the closed position and the open position, respectively.
In another aspect, a pump protection device for limiting cavitation in a pump in a fuel system includes a valve body having an inlet structured to fluidly connect with a common rail in a fuel system, and a drain outlet. The device further includes a valve mechanism positioned within the valve body fluidly between the inlet and the drain outlet. The valve mechanism includes a first valve member movable between a closed position in contact with a first valve seat within the valve body to inhibit fluid flow through the inlet, and an open position. The valve mechanism further includes a second valve member movable between a closed position in contact with a second valve seat within the valve body to inhibit fluid flow through the drain outlet, and an open position. The valve mechanism still further includes at least one biaser biasing the first valve member and the second valve member toward the closed position and the open position, respectively.
In still another aspect, a method of operating a pressurized fluid system includes supplying pressurized fuel at a valve opening pressure to a first valve in a pump cavitation protection device fluidly connected with a common rail, and opening the first valve in response to the supplying of the pressurized fluid at the valve opening pressure, such that the pressurized fluid is drained from the common rail to produce a fluid flow through a pump supplying the pressurized fluid to the common rail that limits cavitation within the pump. The method further includes supplying pressurized fluid at a valve closing pressure greater than the valve opening pressure to a second valve in the pump cavitation protection device, and closing the second valve in response to the supplying of the pressurized fluid at the valve closing pressure such that the draining of the pressurized fluid is stopped.
Referring to
Fuel system 20 may also be equipped with a pump protection device 40 structured to drain pressurized fuel from common rail 30 to provide a fuel flow through fuel pump 28 that limits cavitation within fuel pump 28, details of which are further discussed below. Fuel system 20 is still further equipped, in a practical implementation strategy, with a pressure relief valve 38. The design and functioning of pressure relief valve 38 and pump protection device 40 may be such that valve 38 and device 40 selectively drain or bleed pressurized fuel from common rail 30 to drain inlet 39 of fuel supply 22 under different pressure conditions. In a practical implementation strategy, pump protection device 40 may be active in a range of medium fuel pressures, which have been discovered to be associated with cavitation in pump 28 under at least certain conditions, whereas pressure relief valve 38 may be active at higher pressures, the significance of which will also be further apparent from the following description. Drain lines or conduits 19 and 21 connect pressure relief valve 38 and device 40, respectively, to drain inlet 39 of fuel supply 22. Fuel system 20 may further include a pressure sensor 34 structured to sense a fluid pressure in common rail 30, and an electronic control unit or ECU 36 coupled with pressure sensor 34 and also with pump 28. By sensing rail pressure pump 28 can be operated, such as by varying pump displacement or pump speed or inlet or outlet metering, to provide a desired rail pressure. In a practical implementation strategy pump 28 may include an inlet metered pump, however, the present disclosure is not thereby limited.
Referring also now to
It can also be seen from
In a further practical implementation strategy, first valve member 52 includes an opening hydraulic surface 63 having a first surface area, and second valve member 54 includes a closing hydraulic surface 61 having a second surface area. The first surface area may be smaller than the second surface area, such that pump protection device 40 is active to drain pressurized fuel from common rail 30 in a range of rail pressures. Second valve member 54 may be in contact with first valve member 52 within valve body 42, and transmits a biasing force of biaser 58 to first valve member 52. First valve member 52 and second valve member 54 may be movable in the same travel direction within valve body 42 between the corresponding open or closed positions. In
In
In a practical implementation strategy, the valve opening pressure needed to activate device 40 is defined by device 40 and dependent upon a size of the first surface area and a biasing force of biaser 58. The valve closing pressure is greater than the valve opening pressure as described herein, independent from a size of the second surface area and a biasing force of biaser 58. When device 40 is activated, pressurized fluid fed into device 40 through inlet 46 acts on opening hydraulic surface 63. As first valve member 52 moves away from valve seat 64 pressurized fuel flows through orifices 60 and exerts a force on closing hydraulic surface 61, as well as flowing through orifices 62 and thenceforth out of outlet 50. When the fluid pressure is sufficient, the hydraulic force exerted on closing hydraulic surface 61 will be sufficient to overcome the biasing force of biaser 58 and move second valve member 54 into contact with valve seat 65 to block fluid flow through device 40. It will be appreciated that various factors can bear on the magnitude of the valve opening pressure, the magnitude of the valve closing pressure, the pressure range between those two pressures. For instance, if the first surface area, of opening hydraulic surface 63, is made relatively larger, then device 40 will be activated, other factors being equal, at a relatively lower valve opening pressure. If orifices 62 are made relatively smaller in cross sectional area, for instance, then the valve closing pressure, other factors being equal, may be relatively lower. Accordingly, device 40 can be designed to suit a variety of different applications, such that device 40 is activated to drain pressurized fuel within a pressure range whose size can be selected, and the extremes of which can be set, depending upon engine and fuel system conditions where pump cavitation is expected or known to occur. As further discussed below, it has been observed that pump cavitation can occur where a pump is operating at a relatively high pumping speed but the rate at which fuel is drained from a common rail to feed fuel injectors is relatively small.
As alluded to above, certain engine and pump and fuel system operating conditions have been observed to be associated with cavitation in a fuel pump. Many fuel pumps, and high pressure fuel pump 28, operate at pump speeds that are linked to a speed of the associated engine. Accordingly, as engine speed increases pump speed tends to increase as well. Engine fuel demand, however, can vary independently of engine speed. When an engine is speeding up or otherwise operating to accommodate an increasing engine load, it will generally be desirable to increase fueling amounts, and fuel flow is generally sufficient to avoid cavitation. Likewise, at high power conditions the engine is typically fueled at as high a rate as practicable. In other instances, where the rate of fuel withdrawn from a common rail, and thus a fuel flow through the pump, is relatively low but pump speed is relatively high, cavitation is more apt to occur. It will thus be understood that this combination of relatively low fueling rate and relatively high or at least medium pump speed can occur relatively commonly during operating an internal combustion engine, especially where engine operation is relatively dynamic with respect to engine speed and engine load. The present disclosure contemplates draining fuel through device 40 so as to increase fuel flow through fuel pump 28 in conditions that otherwise might not produce sufficient fuel flow to limit cavitation.
Referring to
Referring also now to
The present description is for illustrative purposes only, and should not be construed to narrow the breadth of the present disclosure in any way. Thus, those skilled in the art will appreciate that various modifications might be made to the presently disclosed embodiments without departing from the full and fair scope and spirit of the present disclosure. Other aspects, features and advantages will be apparent upon an examination of the attached drawings and appended claims.
