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Fuel pump assemblyRelated Patent Categories: Pumps, Expansible Chamber Type, Biasing Means Effects Induction Stroke Of Abutment Driven, Vacuum Producing Pumping MemberFuel pump assembly description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070071622, Fuel pump assembly. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] The invention relates to a pump assembly for use in supplying high pressure fuel to the fuel injection system of a compression ignition internal combustion engine. [0002] In a known fuel pump for use in a compression ignition internal combustion engine, a plurality of plungers are reciprocable within respective plunger bores so as to pressurise fuel within respective pumping chambers for delivery to the fuel injection system associated with the engine. It is common to provide three plungers which are equi-angularly spaced around a drive shaft. Each plunger is moveable under the influence of a cam drive arrangement to perform a pumping stroke in which fuel is pressurised within its pumping chamber. A plunger return spring effects a plunger return stroke in which the plunger is retracted from the plunger bore. [0003] The cam drive arrangement includes a common eccentric cam surface, which is co-operable with all three of the plungers to cause reciprocal movement of the plungers within their respective plunger bores in a phased, cyclical manner. Each of the plungers is driven by the cam arrangement via an intermediate drive member. For example, each of the plungers may be coupled to a cylindrical tappet member which serves to drive movement of the associated plunger within its bore. However, pump arrangements of this type can be difficult to assemble. Furthermore, the tappets require a relatively large accommodation space and are relatively expensive components. Parasitic pumping power losses are also an inherent feature of hydraulic tappet operation. [0004] Our co-pending European patent application, EP 1223334A, describes a multi-plunger fuel pump in which the intermediate drive arrangement for each plunger is a roller and show arrangement (a "roller-shoe" drive arrangement), instead of a tappet drive arrangement. The roller is co-operable with the cam surface of the cam arrangement so as to impart reciprocal movement to the shoe upon rotation of the drive shaft. In turn, each shoe is coupled to a plunger which serves to pressurise fuel within a pump chamber as the cam arrangement is driven. The pump includes three pump assemblies housed within a unitary, main pump housing. [0005] A pump housing part in the form of a tubular member is arranged coaxially with the drive shaft and housed within the main pump housing. The tubular member is provided with a plurality of apertures, each of which is shaped to guide reciprocal movement of an associated shoe as the roller rides over the cam surface. The shoe associated with each plunger is of rectangular or square cross section. [0006] There are two phases of pump operation during rotation of the cam. The filling phase occurs as the plunger is retracted within its bore under the return spring force and the fuel enters the pumping chamber, and the pumping phase occurs as the fuel is forced into the injection system at high pressure (at least 1600 bar). Inlet and outlet valves to control fuel flow to and from the pumping chambers, respectively, are provided in flow passages defined within the main pump housing. [0007] Such roller-shoe drive arrangements, although an improvement on the tappet arrangement discussed above, can have unacceptable levels of unreliability especially in the filling phase. [0008] It is an object of the present invention to provide an improved pump assembly for use in supplying high pressure fuel. [0009] The present invention provides a fuel pump assembly for use in an engine, the fuel pump assembly comprising a pumping plunger which is reciprocable, in use, under the influence of an associated drive arrangement so as to cause pressurisation of fuel within a pumping chamber. The drive arrangement includes a shoe and a roller which is cooperable with a driven cam so as to impart reciprocal movement to the shoe as the cam is driven, in use. The pump assembly is characterised in that the roller has a first surface area region having a first surface roughness and a second surface area region having a second surface roughness higher than the first surface roughness. The shoe is adapted so that the static friction between the roller and the cam is larger than the static friction between the roller and the shoe. In this way, the risk of the roller sliding across the cam surface is therefore reduced. Advantageously, the roller can reach its critical speed of rotation quicker compared with a roller having uniform surface roughness. Also, the roller rotation at or above this critical speed is maintained over a range of engine operating conditions, particularly during the filling phase. [0010] Preferably, the first surface area region and the second surface area region are provided on an outer surface of the roller. Advantageously, the shoe has a bearing surface for the roller, the bearing surface being shaped so that, in use, the first surface area region does not contact the bearing surface. This, therefore, minimises wear between the roller and the shoe. Conveniently, the bearing surface is shaped to have a recess that corresponds substantially with the first surface area region of the roller. [0011] Preferably, the size of the recess has a width substantially the same or larger than the width of the first surface area region and the first surface area region is a band extending around the roller. In one embodiment the first surface area region is approximately midway along the length of the roller. [0012] The roller can also have a third surface area region having substantially the same surface roughness as the second surface area region, the second and third surface area regions being positioned either side of the first surface area region, and wherein the surface roughness of the second and third surface area regions is higher than the first surface roughness. [0013] The invention will now be described, by way of example only, with reference to the accompanying drawings in which: [0014] FIG. 1 is a perspective view of a fuel pump assembly in accordance with an embodiment of the present invention, [0015] FIG. 2 is a sectional view of the pump assembly in FIG. 1, [0016] FIG. 3 is a sectional end view of the pump assembly in FIGS. 1 and 2, [0017] FIG. 4 is a sectional end view of a roller and shoe in accordance with the present invention, [0018] FIG. 5 is a side view of the roller and shoe of FIG. 4, with a portion of the shoe cut away for clarity, and [0019] FIG. 6 is a perspective view of part of a main pump assembly housing. [0020] Referring to FIGS. 1 to 3, there is shown a high pressure fuel pump assembly suitable for use in the fuel injection system of a compression ignition internal combustion engine. In particular, the fuel pump assembly is suitable for use in delivering high pressure fuel to the common rail of a common rail fuel injection system. Many aspects of the fuel pump assembly in FIG. 1 are known, and these parts will only be described briefly. The pump assembly includes a main pump housing 10 through which a cam drive shaft 12 of the engine extends along a drive shaft axis extending perpendicularly to the plane of the page. First, second and third pump heads 13a, 13b, 13c respectively are mounted upon the main pump housing 10 at approximately equi-angularly spaced radial locations around the drive shaft axis, with the drive shaft 12 extending through a central through bore 40 provided in the main pump housing 10. Each pump head 13a, 13b, 13c includes a respective pump head housing 18a, 18b, 18c. [0021] The pump heads 13a, 13b, 13c are substantially identical to one another and, as can be seen most clearly in FIGS. 2 and 3, the first pump head 13a includes a pumping plunger 14 which is reciprocal within a blind bore 16 to perform a pumping cycle having a pumping stroke (or forward stroke) and a return stroke. The blind bore 16 is defined partly within the pump head housing 18a and partly within a plunger support tube 20 which extends from a lower surface of the pump head housing 18a. The blind end of the bore 16 defines, together with the pump head housing 18a, a pumping chamber 22. Reciprocating movement of the plunger 14 within the bore 16 causes pressurisation of fuel within the pumping chamber 22 during the pumping stroke. The pumping plunger 14 is driven axially within the bore 16, in use, under the influence of a drive arrangement including a shoe 24 and an associated roller 26. [0022] The roller 26 and shoe 24 are shown in further detail in FIGS. 4 and 5. The roller 26 is substantially cylindrical, having a length extending along a longitudinal axis and having a substantially circular cross-section transverse to its length. The shoe 24 has a length extending along a longitudinal axis which is substantially the same as the length of the roller. The shoe 24 is substantially rectangular in cross-section transverse to its length. In an alternative embodiment, a shoe of square section may also be used. [0023] The shoe 24 has a bearing surface 49 which is recessed and shaped to receive a longitudinal portion of the roller 26 in use. The cross-sectional profile or shape of the bearing surface 49 is substantially semi-circular and has a slightly larger diameter than the diameter of the circular cross-section of the roller 26 so that the roller 26 is rotatable about its longitudinal axis in the bearing surface of the shoe 24. [0024] The roller 26 is also co-operable with a cam surface 27 of a cam member 28 which is carried by the drive shaft 12. As the shaft 12 rotates in use, the roller 26 rides over the cam surface 27 imparting movement to the shoe 24 and, hence, imparting axial movement (i.e. along the main plunger axis) to the pumping plunger 14 to drive the pumping stroke. Continue reading about Fuel pump assembly... Full patent description for Fuel pump assembly Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Fuel pump assembly patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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