Patent Application
20110052427
An apparatus for pumping fluid is disclosed.
Internal combustion engines having common-rail fuel delivery systems utilize high pressure fuel pumps to ensure adequate fuel pressure inside the rail at low engine speeds and to provide good air and fuel mixture at high engine speeds. To meter and pressurize fuel, a high pressure fuel pump typically has a single-piece pumping plunger reciprocating within a bore of a barrel in the pump's body.
An improved high pressure fuel pumping apparatus for an internal combustion engine exhibiting increased efficiency and reliability is provided by the invention.
More particularly, embodiments consistent with the invention relate to a high pressure pumping apparatus including a pump barrel having a bore with a central axis. A pumping plunger is provided in the bore of the barrel and includes a first pumping plunger part and a second plunger part. The first and second pumping plunger parts are separate from one another and arranged substantially coaxial with the central axis of the bore. A first distal end portion of the first pumping plunger part abuts a first distal end portion of the second pumping plunger part, and a pumping chamber is defined in part by a second distal end portion of the first pumping plunger part. The high pressure pumping apparatus includes and a tappet assembly that is operably coupled to a second distal end portion of the second pumping plunger part for operably engaging a rotating camshaft, which causes the first and second pumping plunger parts to move in reciprocal motion.
In accordance with another aspect consistent with the invention, an embodiments of a high pressure fuel pump comprises a pump barrel including a cylindrically shaped bore, a pumping chamber at one end of the bore, and a first cylindrically shaped plunger part positioned in the bore and including a side surface defining a movable surface of the pumping chamber. A second cylindrically shaped plunger part is positioned in the bore and has a diameter smaller than a diameter of the first plunger part, and is adapted to be reciprocally driven at a first end and to drive the first plunger part in the bore at a second end.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and exemplary only and are not restrictive of the invention, as claimed.
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention that together with the description serve to explain the principles of the invention. In the drawings:
The various aspects are described hereafter in greater detail in connection with a number of exemplary embodiments to facilitate an understanding of the invention. However, the invention should not be construed as being limited to these embodiments. Rather, these embodiments are provided so that the disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.
The pump unit 108 includes a pump barrel 136 having a barrel bore 140 in which a two-piece, or “dual” plunger assembly including a lower pumping plunger part 142a and an upper pumping plunger part 142b are provided substantially coaxial with the barrel bore 140. The lower pumping plunger part 142a and the upper pumping plunger part 142b are provided as separate pieces in the barrel bore 140. “Separate”, as used herein with respect to the upper and lower pumping plunger parts 142a/142b, means the upper pumping plunger part 142b is not integral with or physically connected to the lower pumping plunger part 142a. Thus, the upper pumping plunger part 142b “floats” in the barrel bore 140 and its movement is a result of forces from pressure differential and/or the lower pumping plunger 142a acting on it. During operation of the pump assembly 100, an upper surface of the plunger part 142a can contact a lower surface of the plunger part 142b at an interface 143 as they reciprocate in the barrel bore 140. Further, it is to be understood that the terms “upper” and “lower,” as used herein, refer to the orientation exemplary pump assemblies shown in the figures. In other exemplary embodiments consistent with the invention, the orientation of two-piece plunger parts may be flipped relative to the depicted orientations, or both plunger parts may reside on a same vertical plane, for example.
Returning to
The tappet assembly 130 includes a tappet housing 150 adapted for reciprocal motion along tappet guiding surfaces provided in the pump housing by the bore 104. The tappet assembly 130 includes a cam roller 152 rotatably secured to housing 150 by a pin 153 extending through a bore 154 in tappet housing 150. Tappet housing 150 also includes an annular skirt 155 extending toward pump head 112 to form a recess 138 having an inner support surface 139.
The high pressure fuel pump unit 108 further includes a force transmitting device 156 provided on the support surface 139 between tappet assembly 130 and lower plunger part 142a for transmitting axial loads to lower plunger part 142a. Force transmitting device 156 includes a spring seating surface 158 for receiving the outer end of the spring 146 and a lateral retaining surface 160 that prevents lateral movement of the spring 146. The force transmitting device 156 includes a supporting end 162, which abuts, attaches, or otherwise couples to a distal end portion of the lower plunger part 142a. The lower plunger part 142a can float in the barrel bore 140 such that it is not physically connected to the force transmitting device 156, its movement in the bore resulting from forces acting on it from the force transmitting device 156 and/or the upper pumping plunger 142b.
The high pressure fuel pump assembly 100 can include a lubricating oil circuit that includes various lubricating transfer passages 170, 172, and 174 provided in the components of tappet assembly 130. In addition, lubricating oil circuit can include passages 176, 178 in the force transmitting device 156.
During operation, the spring 146 is positioned in abutment against the force transmitting device 156 at one end and the barrel 136 at its other end. The spring 146 biases tappet assembly 130 via the force transmitting device 156 into engagement with the camshaft 124 at an opposite end. As the camshaft 124 rotates, a lobe 126 of the camshaft 124 displaces the tappet assembly 130 within the bore 104, and thus also displaces the transmitting device 156, the lower plunger part 142a, and the upper plunger part 142b.
To substantially improve pumping efficiency, embodiments include separate pumping plunger to barrel bore clearance requirements for the coaxial pumping plunger parts. Referring to
The two-piece plunger assembly comprising two pumping plungers 142a/142b can be designed to optimally address issues specific to each portion of the seal length of the barrel bore. As shown in
In an exemplary embodiment, a plunger-to-bore clearance d1-d3 of the top pumping plunger part 142b can be one half to one quarter of the clearance d1-d2 of the lower pumping plunger part 142a. Thus, for an exemplary embodiment in which a lower pumping plunger part 142a has a clearance of within a range of about 4 to 6 μm, the upper pumping plunger part 142b can have a clearance between about 2.0 to 3.0 μm, or between about 1.0 to 1.5 μm for more efficient operation. The limit to which a clearance can be set for the upper plunger can be based on, for example, machining limitations, material limitations, cost, and/or pressure required for a particular fuel system application.
The two piece plunger can allow for a tighter clearance on the upper pumping plunger part 142b only, which provides an efficiency lever because of reduced high pressure leakage during pumping. The pressure developed on the upstroke of the two-piece plunger will open (i.e., dilate) an upper portion of the barrel bore 140 during pressurization unlike a lower portion of the barrel bore 140, so a tighter the clearance of the upper plunger part 142b and the barrel bore 140 provides better pumping efficiency. Because dilation is related to the pressure in the bore, above the pumping plunger part 142b would have full dilation because it would have full pressure. The pressure is assumed to drop along the match fit to zero in the drain/leakage low pressure groove 147, and the majority of dilation has been observed in about the first ⅓rd of the match fit clearance. Efficiency improvement can be realized with any upper pumping plunger part match being less than the lower pumping plunger part (or single plunger) clearance. Tight clearances, such as clearances less than 1.0 μm, can be applied with improvements in bore and plunger manufacturing. Hence, the clearance of the pumping plunger part 142b could be anything less than the clearance lower pumping plunger part 142a, and can approach zero clearance with increasing efficiency to an extent allowed by manufacturing capability.
The length L1 of the upper pumping plunger part 142b can be related to an upper bore length L3, which is shown in
Some conventional plunger assembly designs have attempted to reduce leakage and improve efficiency by using a one-piece plunger assembly having a particular profile. For example, one conventional fuel pump includes a single-piece plunger having a gradual taper along the length of the plunger. However, this tapered profile allows a significant amount of fuel leakage compared with the constant tight fit of the upper pumping plunger part 142b of the two-piece plunger assembly 142a/142b. Another conventional one-piece plunger assembly utilizes a profile having an upper pumping section and a lower driving section having different constant diameters. In this type of plunger, the diameter of the lower driving section is often significantly smaller relative to the diameter of the upper pumping section. However, the single-piece two-sectioned plunger is less efficient than the two-piece plunger assembly 142a/142b because the lower driving section typically does not substantially contribute to sealing a pump bore along a seal length of the bore. Additionally, the single-piece plunger more susceptible to sticking within the pump's barrel bore compared with fuel pump embodiments including a two piece plunger. By contrast, the fuel pump assembly embodiments described herein significantly reduce high pressure leakage while maintaining continuous operation.
During a pumping operation, the lower pumping plunger part 142a moves in a pumping stroke as the tappet assembly 130 and the force transmitting part 156 are displaced by the cam lobe 126 in a direction toward the head 112. The upper plunger part 142b can float in the barrel bore 140, but makes contact with or abuts the lower pumping plunger part 142a during the upstroke of the tappet assembly 130 and force transmitting part 156. The upper plunger part 142b compresses the fuel volume in the pumping chamber 144 to a prescribed pressure before being released to a common rail (not shown). For example, when the pressure in the pumping chamber 144 reaches a prescribed pressure level, an outlet check valve (not shown) connected to the pumping chamber 144 can open to provide the pressurized fuel to the common rail.
On the retraction stroke of the tappet assembly 130 and force transmitting part 156, which takes place just after cam lobe 126 has reached maximum lift, low pressure fuel from a fuel reservoir, for example fuel fed from a fuel tank by a low pressure pump (not shown), enters the pumping chamber 144 while the outlet to the high pressure rail is blocked. For example, a check valve of an outlet leading to the common rail (not shown) can remain closed when the pumping chamber 144 is at low pressure while another check valve opens to supply fuel from the low pressure pump. While fuel is entering the pumping chamber 144, the floating upper pumping plunger part 142b is forced downward toward the retreating lower pumping plunger part 142a because pressure in a region between an upper face of lower pumping plunger part 142a and an opposing lower face of upper pumping plunger part 142b is lower than pressure in the pumping chamber 144.
The standard plunger pump had a 5.3 μm plunger-to-bore clearance for its single-piece plunger, and the two-piece plunger pump had a clearance of 5.3 μm for the lower plunger part and a clearance of 2.2 μm for the upper plunger part of the coaxial arrangement. The data of
Greater volumetric efficiencies can be obtained by cooling the two-piece plunger pump, for example, by cooling the barrel of the pump using a cooling fluid or providing a fuel cooling unit upstream from the pump.
It will be appreciated that the embodiments described and shown herein may be modified in a number of ways. For instance, while the exemplary embodiments described above include an in-line arrangement of plural pumping units, other embodiments consistent with the invention can include more or less two-piece plunger pumps and/or arrange two-piece plunger pumps in another way, such as a radial arrangement driven by a ring cam. Additionally, the two-piece plunger pumps may be driven by any shaft driven by an internal combustion engine, such as a drive shaft or camshaft, although other mechanisms commonly employed to drive ancillary equipment in an internal combustion engine can be used, such as a belt drive.
Although a limited number of embodiments is described herein, one of ordinary skill in the art will readily recognize that there could be variations to any of these embodiments and those variations would be within the scope of the appended claims. Thus, it will be apparent to those skilled in the art that various changes and modifications can be made to the high pressure two-piece plunger pump assembly described herein without departing from the scope of the appended claims and their equivalents.
