The present invention relates to a high pressure fuel pump and more particularly to a dilation arrangement of the piston of the pump.
High pressure fuel pumps known in the art have a housing provided with a bore defining a compression chamber and, a cylindrical piston reciprocally translating within the bore so that fuel in the compression chamber is pressurized. While the majority of the pressurized fuel exits via an outlet orifice, a small quantity of pressurized fuel leaks through the functional clearance that is between the bore and the piston. In operation, when fuel is under high pressure, the clearance increases allowing more important fuel leak.
Accordingly, it is an object of the present invention to solve the above mentioned problem in providing a fuel pump of a fuel injection equipment of an internal combustion engine. The pump has a housing provided with an axial bore defining a compression chamber and a cylindrical piston slidably arranged in the bore. The piston extends from a top extremity inside the bore, defining a high pressure extremity, to a lower extremity, defining a low pressure extremity. The piston is able to reciprocally slide between a lower position where fuel at low pressure enters the compression chamber via an inlet and, a top position where fuel present in the compression chamber is pressurized before being expelled via an outlet.
The piston is further provided with dilation mean arranged on its high pressure extremity, said mean enabling the piston to expand radially when fuel in the compression chamber is pressurized. This dilation mean advantageously limits the clearance between the piston and the bore.
In an embodiment, the dilation mean is a recess provided on the top face of the piston and surrounded by a peripheral wall integral to the piston.
More specifically, the recess defines a cylindrical volume.
In an alternative embodiment, the dilation mean is a circular groove extending from the top face of the piston, the circular groove being surrounded by a peripheral wall integral to the piston.
The dilation mean further comprises a pressure drop feature enabling pressurized fuel to drop in pressure and to flow toward a low pressure circuit. The location of said feature limits the portion of the piston that expands under fuel pressure.
The pressure drop feature comprises a groove ring arranged on the outer cylindrical face of the peripheral wall and a fuel path extending from said groove ring toward the low pressure circuit. The fuel path may comprise a flat arranged on the outer cylindrical face of the piston, said flat axially extending to the lower end of the piston.
In another alternative, the diameter of the piston is larger above the groove ring than below the groove ring so that the clearance between the piston and the bore is largely increased below the groove. This difference in diameter creates an annular volume that is the fuel path wherein pressurized fuel in the groove flows toward the low pressure circuit.
The present invention is now described by way of example with reference to the accompanying drawings in which:
In the following description, similar elements will be designated with the same reference numbers. Also, to ease and clarify the description a top-down orientation will be followed in reference to the orientation of the figures. Therefore, words and expressions such as “top, upper, lower, over, under” . . . may be utilized without any intention to limit the scope of the invention.
A main embodiment is now described in reference to
In the main embodiment of
In operation the piston 18 is actuated by a non-represented rotating cam that reciprocally displaces the piston 18 between a top position PT,
The deformation of the peripheral wall 22 is a consequence of the outwardly oriented forces F1 and of the inwardly oriented F2. The skilled person will understand that the barrel-type expansion of the peripheral 22, as represented on
An alternative to the main embodiment is now described in reference to
In operation, the pressure inside the groove 24 generates on the peripheral wall 22 the same outwardly oriented radial forces FR generating similar expansion as in the main embodiment and also, generates inwardly oriented radial forces on the inner cylindrical core, said inward forces not generating any noticeable deformation of the inner core.
In this alternative, the opening of the functional clearance C is compensated by the deformation of the peripheral wall 22 without important increase of the volume of the compression chamber 16.
In non-represented further alternatives, the inner core 26 could be non-integral to the piston 18 and fixed inside the recess 20. Also, the recess 20 of the main embodiment is described as a cylindrical volume but, other shapes such as a conical recess or, two or more adjacent cylindrical volumes on the top of each other are possible alternatives.
In
The fuel path 30, as represented on
An alternative to the passage 30 is represented on
The following references have been utilized in this description:
Number | Date | Country | Kind |
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1402528.2 | Feb 2014 | GB | national |
This application is a national stage application under 35 USC 371 of PCT Application No. PCT/EP2015/050444 having an international filing date of Jan. 13, 2015, which is designated in the United States and which claimed the benefit of GB Patent Application No. 1402528.2 filed on Feb. 13, 2014 the entire disclosures of each are hereby incorporated by reference in their entirety.
Filing Document | Filing Date | Country | Kind |
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PCT/EP2015/050444 | 1/13/2015 | WO | 00 |