Patent Application
20110146600
This patent disclosure relates generally to reciprocating piston pumps for fluids and, more particularly, to fuel pumps for use with internal combustion engines.
Fluid pumps having pumping elements that include a plunger reciprocating within a bore formed in a barrel are known. The plunger's reciprocating motion is typically accomplished with a mechanism that moves the plunger with a rotating cam. Alternatively, the plunger may contact an outer portion of a rotating angled disk or swash-plate to provide a controlled variable displacement.
A fluid pump might include a plurality of plungers that pressurize a flow of fluid, typically oil or fuel, for use in an internal combustion engine. For example, a fuel injector might use the flow of pressurized fluid, from the pump to inject the fuel or to intensify the pressure of the fuel that is injected into the engine.
Modern fuel systems use progressively higher injection pressures for injecting fuel within the engine increase the efficiency of the engine and, potentially, reduce emissions. Nevertheless, issues are presented when attempting to increase the service pressure of a fluid pump. For example, increased service pressure increases the thermal load imparted to the plunger, bore surfaces, and other pump elements. In the past, various material and design limitations have generally limited pump outlet pressures because of such thermal effects experienced by various pumping elements.
Attempts to reach progressively higher injection pressures and dealing with increasing thermal loads is further constrained by consumer's desires to have smaller pumps. Dealing with thermal loads in smaller pumps is a more difficult task because there is simply less room to apply different cooling solutions. For example, in some midsized and smaller pumps, engineers have observed that as increasing pressures are reached, thermal gradients occur. These temperature gradients may lead to erratic pump behaviors. For example, pumps that have been operable for as little as 40 minutes may see a temperature gradient across a pump bore of 100° C. With one side of the pump bore being significantly hotter than the other, a bowing of the plunger bore may occur. This bowing effect is known as bore deformation. When this happens, the plunger, which moves within the bore in a substantially vertical reciprocating manner, may begin to start rubbing against the bore. Additionally, plunger scuffing may occur because excess heat within the plunger bore may cause the plunger to thermally expand and minimize the annular clearance of the plunger within the bore. The scuffing is caused by the plunger coming into repeated contact with the sides of the plunger bore. Plunger scuffing may lead to pump failure.
In the past, engineers have used alternate pump designs to address the internal cooling issues within pumps. These designs tend to focus on larger clearances between the plunger and the barrel of the pump. However, such clearances can reduce the pumping efficiency of the pump, increase leakage and potentially increase the temperature of the compressed fuel exiting the pump. Alternative cooling designs may utilize excess space around the plunger bore to create an annular reservoir where cooling fluid may pool and work to remove excess heat from plunger and plunger bore. However, as previously mentioned smaller pumps simply do not have the internal space to utilize these more complex cooling solutions. For example, there may be no room for a separate plunger barrel, let alone annular reservoirs therein. The subject matter of the present disclosure address one or more of the aforementioned issues.
In one aspect, a fuel pump including a housing defining a bore having a longitudinal centerline, an inlet port, an outlet port, a return gallery, and an inlet gallery in fluid communication with the inlet port. Also included is a plunger at least partially disposed within the bore, wherein the plunger arranged for reciprocal motion within the bore. The fuel pump further includes pressurization cavity at least partially defined between an end of the plunger and an end portion of the bore, wherein the pressurization cavity is adapted for pressurizing an amount of fuel supplied through the inlet gallery and provided to the outlet port during the pressurization stroke of the plunger. Also included is an annular clearance defined between an outer surface of the plunger and an inner surface of the bore, wherein the annular clearance is in fluid communication with the pressurization cavity. The fuel pump further includes a weep annulus defined around the inner surface of the bore, wherein the weep annulus surrounds a portion of the plunger and is in fluid communication with the annular clearance. A cooling supply passage defined by the housing fluidly coupling the inlet gallery and the weep annulus is also included. The fuel pump further includes a drain passage defined by the housing, wherein the drain passage fluidly couples the fuel return passage and the weep annulus.
In another aspect, an engine system including an internal combustion engine including an engine housing defining a plurality of engine cylinders, and including a plurality of pistons each being movable within a corresponding one of the engine cylinders. Also included is a fuel system including a fuel rail in fluid communication with a plurality of fuel injectors, wherein each fuel injector is associated with each of the plurality of engine cylinders. The fuel system further includes a fuel source, a transfer pump in fluid communication with the fuel source, and a high pressure pump in fluid communication with the transfer pump and the fuel rail. The high pressure pump further includes a housing defining a bore having a longitudinal centerline, an inlet port, an outlet port, a return gallery, and an inlet gallery in fluid communication with the inlet port. Also included is a plunger at least partially disposed within the bore, wherein the plunger arranged for reciprocal motion within the bore. The high pressure pump further includes pressurization cavity at least partially defined between an end of the plunger and an end portion of the bore, wherein the pressurization cavity is adapted for pressurizing an amount of fuel supplied through the inlet gallery and provided to the outlet port during the pressurization stroke of the plunger. Also included is an annular clearance defined between an outer surface of the plunger and an inner surface of the bore, wherein the annular clearance is in fluid communication with the pressurization cavity. The high pressure pump further includes a weep annulus defined around the inner surface of the bore, wherein the weep annulus surrounds a portion of the plunger and is in fluid communication with the annular clearance. A cooling supply passage defined by the housing fluidly coupling the inlet gallery and the weep annulus is also included. The high pressure pump further includes a drain passage defined by the housing, wherein the drain passage fluidly couples the fuel return passage and the weep annulus.
In another aspect, a method of operating a reciprocating plunger fluid pump. The fluid pump including at least one bore. The bore reciprocally accepting a plunger, the reciprocating motion of the plunger including a pressurization stroke and a refill stroke. The method includes a step of admitting an amount of fluid into a pressurization chamber during the refill stroke, wherein the pressurization chamber is at least partially defined between the plunger and the bore. The method further includes the step of pressurizing the fluid during the pressurization stroke. Also included is a step of weeping an amount of fluid out of the pressurization chamber and along an interface between the plunger and the bore. The method includes a step of collecting the weeping amount of fluid into a weep annulus, wherein the weep annulus is defined in the housing around a portion of the plunger adjacent to the bore. A step of admitting an amount of cooling fluid into the weep annulus via a cooling supply passage is also included. The method contemplates mixing the flow of cooling fluid with the fluid that weeps out of the pressurization chamber. A step of routing the mixed fluids out of the weep annulus through via a drain passage is also included. The method further includes a step of conducting heat away from the plunger.
Referring to
The engine system 10 is controlled in its operation in a conventional manner via an electronic control module 52 which is connected to the high pressure pump 18 via a pump communication line 54 and connected to each fuel injector 12 via communication lines (not shown). When in operation, control signals generated by the electronic control module 52 determine how much fuel displaced by the high pressure pump 18 is forced into the high pressure fuel rail 14 and at what time, as well as when and for what duration (indicative of fuel injection quantity) fuel injectors 12 operate. The fuel not delivered to the high pressure fuel rail 14 can be re-circulated back to the fuel tank 28 via the first return line 30.
For the most part, fuel that is provided to the high pressure pump 18 is ultimately either injected via fuel injectors 12 into engine cylinders (not shown) or it is returned to fuel tank 28. Fuel that is injected is routed through the high pressure pump 18 to a pressurization chamber (not shown) where it is pressurized via plunger (not shown) and provided to the high pressure fuel rail 14. The other fuel that is provided to the high pressure pump 18 ultimately ends up back at the fuel tank 28. As discussed in greater detail below, this fuel is either utilized as cooling fluid, whereby it is routed through a cooling circuit within the high pressure pump, or it is collected as excess and/or leakage and then sent back to the fuel tank 28.
Various views of a first embodiment for a fluid pump 100 in accordance with the disclosure are shown in
The pump 100 uses oil for lubrication of various moving parts. Other types of pumps may use fuel for lubrication or, alternatively, be arranged to pump oil instead of fuel for use with intensified or hybrid fuel systems. The pump 100 described herein is presented solely for illustrative purposes and should not be construed as limiting.
The pump 100 includes a base or outer structure or housing, generally denoted in the figures as 102. The housing 102 may include one or more connected components forming a structure that encloses and supports various internal components of the pump. In this exemplary representation, the housing 102 includes a cam or drive shaft 104 having one or more eccentric lobes 106. Each lobe 106 corresponds to an actuator 108 that moves reciprocally along an outer race 110 of each lobe 106 as the shaft 104 rotates. Each actuator 108 contacts a lifter 112. The lifter 112 continuously contacts its respective outer race 110 by action of a resilient element or spring 114. The spring 114 pushes the lifter 112 against the actuator 108 to ensure that the reciprocating motion of the actuator 108 is transferred to the lifter 112 while the shaft 104 is rotating.
A plunger 116 is operatively connected to the lifter 112 such that the plunger 116 can reciprocate as the shaft 104 rotates. The plunger 116 has a cylindrical shape with a centerline 118 extending along its major dimension. During operation of the pump 100, the plunger 116 reciprocates along its centerline 118 within a bore 120 defined by the housing 102. The bore 120 is arranged to have a centerline extending axially or longitudinally along the bore 120. The centerline of the bore substantially coincides with the centerline 118 of the plunger 116. During operation of the pump 100, the plunger 116 moves between an extended position, A, during a pressurization stroke, and a retracted position, B, during a filling stroke.
An inlet port 123 allows fuel from an inlet gallery 124 of the pump 100 to enter a pressurization chamber 126. The pressurization chamber 126 is at least partially defined between a distal end 128 of the plunger 116 (also see
As can be appreciated, a proper clearance is required between the plunger 116 and the bore 120 that can seal the interface there between to promote proper pressurization of the fluid in the pressurization chamber 126, as well as accommodate for thermal expansion of the plunger 116 relative to the housing 102. This annular clearance, generally shown as 138, is defined between an outer surface 140 of the plunger 116 and an inner surface 142 of the bore 120. Smaller clearances, which allow for greater pressurization capability for the pump 100, negatively affect the freedom of motion and thermal expansion of the plunger 116 within the bore 120. On the other hand, while larger clearances cause reductions in the efficiency of the pump.
Further, appreciable heating of the plunger 116 during operation of the pump 100 occurs due to heat transfer from the pressurized fluid within the pressurization chamber 126. A detailed cross section of housing 102 containing the plunger 116 is shown in
The weep annulus 144 is in fluid communication with an fuel in the inlet gallery 124 via a cooling passage 146 that is defined by housing 102. When plunger 116 is retracting during a filling stroke, a localized vacuum may be formed in weep annulus 144. Thus, a portion of the fuel from the inlet port, which is above ambient pressure, flows into the weep annulus 144 via cooling passage 146. In this manner, relatively cool fuel from the inlet gallery 124 mixes with fuel that weeps into the weep annulus 144 from the pressurization chamber 126 via the annular clearance 138. Because the fuel from inlet port 144 is cooler than the fuel from the pressurization chamber 126, the aforementioned temperature gradient between plunger and the housing may be alleviated. During the pressurization stroke of the plunger 116, the pressure within weep annulus is increased. This pressure increase is still lower than the approximately ambient pressure of the fuel in inlet port 144, but it is higher than the pressure within a return gallery 148. Return gallery 148 is in fluid communication with weep annulus 144 via a drain passage 150, which is defined by housing 102. Thus, during the pressurization stroke, fuel within the weep annulus 144 is pumped through the drain passage 150 to return gallery 148. From here, the fuel exits pump 100 and is returned to fuel tank (not shown). Those skilled in the art will recognize that in some embodiments, the fuel that leaves the return gallery 148 may be routed directly back to the inlet gallery 124 without returning to fuel tank (not shown). Such embodiments do not depart from the scope of the present disclosure.
As can be appreciated, a thermal gradient will be present in both the housing 102 and plunger 116 during operation of the pump. This thermal gradient results from heating of the fuel being pressurized in the pressurization chamber 126. Heat transferred from the pressurized fuel tends to heat the portions of the housing 102 and plunger 116 that surround the pressurization chamber 126. Heat conductively travels through the components toward the fuel to oil interface of the pump. The thermal gradients may cause differing degrees of thermal expansion between the plunger 116 and the housing 102, which may in turn cause dimensional clearance issues there between during operation of the pump. These issues become relevant to the operation of the pump when present in the region that lies proximate to the fuel to oil interface and, more specifically, in the portion of the housing 102 extending between the weep annulus 144 and the fuel to oil interface.
A schematic of a fluid pump showing a cross section of two adjacent plungers 416 disposed in respective bores 420 of a fluid pump is shown in
During operation of the pump, a flow of cooling fuel is provided to the pump via the low pressure pump 20. Such flow may be part of a main fuel flow to the pump that is compressed and provided to the fuel injectors (see, for example, the illustration of
The present disclosure is applicable to a fluid pump having one or more reciprocating plungers that can pressurize a fluid to levels that were previously unattainable by use of known pumping systems. The embodiments disclosed herein are advantageously suited for implementation in fluid pumps that are capable of prolonged and reliable operation under high-pressure transient and steady-state conditions. Pumps in accordance with the disclosure are advantageously capable of achieving outlet pressures in the range of 1700 to 2200 bar or higher. This advantageous operation is enabled because of the improved management of heat transferred between the pumping elements.
Moreover, active cooling of elements, for example as shown for the second and third embodiments, further aid in lowering the overall temperatures of the plunger, barrel, and other components of the pump. Further, reduction of the overall mass of the barrels of the three embodiments presented lowers the thermal capacity of each barrel such that the temperature of the barrel tracks the temperature of the plunger, which is especially useful during transient changes in the operation of the pump.
A block diagram for an engine system 500 having a high-pressure (HP) fuel pump 502 operatively associated therewith is shown in
During operation of the engine 504, a work output from the engine 504 operates the HP pump 502. A flow of pressurized fuel (HP Fuel) exits the HP pump 502 and is delivered to the engine 504. For example, the flow of HP fuel may be delivered to a HP fuel rail 514 that is connected to a plurality of fuel injectors 516, which are integrated with the engine 504. A flow of unused fuel from the fuel injectors 516 may return to the reservoir 506. In this exemplary illustration, the HP pump 502 uses lubrication oil from the engine 504 for lubrication of internal moving components, such as, the actuators and lifters (not shown) that contact the drive shaft (not shown) of the HP pump 502. For this purpose, an oil supply line 518 acts in conjunction with an oil return line 520 to circulate a flow of lubrication oil between the engine 504 and the HP pump 502. As can be appreciated, the engine system 500 as described herein is suited for use in a vehicle having the engine 504 arranged to drive and power various systems on the vehicle.
It will be appreciated that the foregoing description provides examples of the disclosed system and technique. However, it is contemplated that other implementations of the disclosure may differ in detail from the foregoing examples. All references to the disclosure or examples thereof are intended to reference the particular example being discussed at that point and are not intended to imply any limitation as to the scope of the disclosure more generally. All language of distinction and disparagement with respect to certain features is intended to indicate a lack of preference for those features, but not to exclude such from the scope of the disclosure entirely unless otherwise indicated.
Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context.
Accordingly, this disclosure includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the disclosure unless otherwise indicated herein or otherwise clearly contradicted by context.
