GB2532964A

GB2532964A - High pressure fuel pump

Info

Publication number: GB2532964A
Application number: GB1421457.1A
Authority: GB
Inventors: T D Mchattie James
Original assignee: Delphi International Operations Luxembourg SARL
Current assignee: Delphi International Operations Luxembourg SARL
Priority date: 2014-12-03
Filing date: 2014-12-03
Publication date: 2016-06-08
Anticipated expiration: 2034-12-03
Also published as: GB2532964B; GB201421457D0

Abstract

A fuel pumping arrangement 10 comprises a fuel pump 102 having a piston 106 which the motions are generated by the rotation of an eccentric cam 12 followed by a roller 110. The pumping arrangement further comprises a bearing assembly adjusted around the peripheral circular face of the eccentric cam, the bearing assembly being adapted to rotate relative to said eccentric cam and the roller being able to roll on said bearing assembly. The use of the bearing assembly and the roller is intended to mitigate against deterioration caused debris and small particles in the lubricating oil. Preferably there are a plurality of pumps uniformly distributed around the eccentric cam.

Description

High pressure fuel pump

TECHNICAL FIELD

The present invention relates to a high pressure fuel pump which motion is generated by the revolution of an eccentric cam

BACKGROUND OF THE INVENTION

Typical high pressure fuel pumps comprise a piston reciprocally moving between a top dead center and a bottom dead center position in order, for the upper extremity of the piston, to compress fuel in a compression chamber.

The piston displacements are generated by the revolutions of an eccentric cam and by a cam follower provided at the lower extremity of the piston. The cam follower comprises a cylindrical roller rotatable in a shoe solidary arranged at the lower end of the piston. The roller is maintained in linear contact against the cam by a spring compressed between the pump head and the shoe, the spring permanently soliciting the roller against the cam.

During a revolution of the eccentric cam the piston reaches once the top dead center position where the fuel is highly compressed and consequently where the contact pressure between the roller and the cam is at its highest level which is more likely to wear the roller.

Unfortunately, in use the oil lubricating the cam carries debris and, small particles may accumulate to the point they can prevent rotation of the roller. In.

this case the outer face of the cam deteriorates rapidly as the roller slides against it.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to resolve or at least mitigate the above mentioned problems in providinga fuel pumping arrangement comprising a fuel pump having a piston adapted to reciprocally move between a top dead centre position TDC, wherein fuel is compressed in a compression chamber and, a bottom dead centre BDC, wherein fuel in said chamber is not compressed. In use the motion of the piston is generated by the rotation of an eccentric cam followed by a roller secured to the piston, the roller following the peripheral circular face of the eccentric cam.

The pumping arrangement further comprises a bearing assembly adjusted around the peripheral circular face of the eccentric cam, the bearing assembly being adapted to rotate relative to said eccentric cam and the roller being able to roll on said bearing assembly. The bearing assembly is able to freely rotate around the eccentric cam.

The bearing assembly specifically comprises a cylindrical tubular outer rider in which is fixedly arranged a plain bushing, said bushing being adjusted with functional clearance J to rotate over the eccentric cam. More precisely the plain bushing is fixedly press fitted in the outer rider.

In another embodiment, the bearing assembly is a roller bearing arranged over the eccentric cam.

Furthermore, the pumping arrangement may comprise a plurality of fuel pump, each having a piston provided with a roller, adapted to roll on the bearing assembly of the eccentric cam.

In this latter case the pumps may be substantially uniformly distributed around the eccentric cam.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is now described by way of example with reference to the accompanying drawings in which: Figure 1 is a schematic arrangement of an eccentric cam and roller as per the invention.

Figures 2 to 5 sketched a pump arrangement as per the invention, each figure being represented after 90° rotation in the clockwise direction.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As per the figures, a pumping arrangement 10 comprises a first pump 102, drawn on the top of the figures 2 to 5, said first pump 102 having a first pumping head 104 symbolized as a rectangle from which outwardly protrudes a first piston 106 extending along a first pumping axis A106. Not detailed on the figures but well known by a person skilled in the art, inside the pumping head 104, the upper end of the piston 106 is in a compression chamber wherein, in use, fuel at low pressure enters and, fuel at high pressure exits. At its lower extremity the piston 106 is provided with the assembly of a shoe 108 and a roller 110, the roller 110 being able to freely rotate about a roller axis A110, relative to the shoe 108.

The roller 110 rolls on the outer circular face 14 of an eccentric cam 12 that rotates about a main axis AO, the roller axis A110 being parallel to said main axis AO. The pumping axis A106 is perpendicular to both the main axis AO and the roller axis A110. As shown on the figures, when the cam 12 rotates about the main axis AO, the centre 0 of the cam describes a circle C, drawn in dotted line, around the main axis AO.

As per detailed on figure 1, the eccentric cam 12 indeed comprises the concentric adjusted arrangement of an outer rider 15, a bearing 18 and an eccentric shaft 16. The outer rider 15 is a cylindrical tubular part made of bearing steel such as 100Cr6. The bearing 18 is a bushing having a metallic outer race with its inner face covered with sliding material such as polytetrafluoroethylene (PTFE) with bronze backing. The bearing 18 is fixedly press fitted inside the outer rider 15 in order to make a rider and bearing assembly. In an alternative embodiment, instead of a press fit arrangement, an integral arrangement can be provided where the inner face of the outer rider 15 is directly covered with PTFE and bronze backing.

The eccentric shaft 16 is cylindrical and receives the rider 15 and bearing 18 assembly in a complementary arrangement freely revolving about the eccentric shaft 16. A radial clearance J of, for instance, 50 to 100 p.m is accommodated between the sliding inner face of the bearing 18 and the outer face of the shaft 16.

Once all components are in place, the eccentric shaft 16 rotates about the main axis AO and the rider 15 and bearing 18 assembly rotates about the shaft 16.

Alternatively, instead of being provided with a plain bearing, the rider 15 and bearing 18 assembly can be a roller bearing having cylindrical roller elements.

In use, the roller 110 is then in linear contact with the outer race of the bearing 18.

As well known, a spring 112 compressed between the pumping head 104 and the shoe 108 permanently biases the shoe 108 and roller 110 against the bearing 18.

The arrangement presented on the figures comprises a second pump 202 which is similar to the first pump 102 and which components are similarly referenced with "2" as hundreds digit.

The second pump 202 is substantially diagonally opposed to the first pump 102, relative to the cam 12. As can be noted, and as known in the art, the pumping axes A106 and A206 are almost radial but do not intersect with the main axis AO creating a small offset d, exaggerated on the figures.

Alternative embodiments comprising three or more pumps can easily be derived from this description. In such alternatives, the pumps are uniformly radially arranged all around the cam 12. For instance in the case of three pumps, an angle of approximately 120° should be kept between each pumping axis and, in the case of four pumps, a right angle should be kept between each consecutive the pumping axis. In any case, said axis should be equidistantly spaced around the cam still maintaining the small offset.

The operation of the pumping arrangement 10 is now described. As known, when the eccentric shaft 16 rotates, for instance in the clockwise direction as shown by the curved arrow Fl on the figures, the piston 106 reciprocally moves in and out of the pumping head 104, arrow F2 on the figures, between a top dead centre TDC position, figure 2 for the first pump 102, and a bottom dead centre BDC position, figure 4 for the first pump 102. When approaching TDC the fuel in the compression chamber is very highly pressurized, up to 2000 bars or 2500 bars or even higher and consequently, the piston 106 generates a very important axial force and the contact linear pressure between the roller 110 and the outer rider 15 is very high.

In a known configuration, without rider 15 and bearing 18 assembly, as the cam rotates clockwise, the roller rotates counter clockwise and, in addition to the high contact pressure, particles and other debris accumulate and may prevent rotation of the roller 110. Consequently sliding occurs damaging the cam outer face or, if the roller continues to roll, debris get under the roller and are pressed between the roller and the cam, also damaging the surfaces.

Thanks to the bearing 18, when the cam rotates clockwise Fl and the contact pressure increases, the bearing freely rotates counter clockwise, arrow F3, maintaining rolling contact with the roller 110, itself rotating clockwise, arrow F4, and enabling and evacuation of particles and debris from the contact region.

In the sequential arrangement presented with first pump 102 and second pump 202, in figure 1 both pumps are in an intermediate position between TDC and BDC. As the cam 12 rotates clockwise, the first pump 102 moves toward TDC and the contact pressure roller 110/cam 12 increases. The clearance J is entirely below the bearing 18. In this phase, the bearing 18 is expected to rotate counter clockwise F3 and the first roller 110 to rotate clockwise F4. To the opposite, the second pump 202 moves toward BDC and the contact pressure decreases. As the roller 106 and the rider 15 and bearing 18 assembly are free to rotate, the rider 15 spins counter clockwise F3 evacuating any debris and particles that may be carried in the oil flow. The contact pressure at the second roller 210 being low, it cannot prevent rotation occurred by the high pressure of the first pump. As the cycle goes on, in figure 3, the first pump 102 moves from TDC to BDC and the contact pressure decreases while the second pump 202 moves from BDC to TDC, the contacting pressure increasing.

REFERENCES UTILIZED IN THE DESCRIPTION

pumping arrangement 12 eccentric cam 14 outer circular face outer rider 16 eccentric shaft 18 bearing first second 102 202 pump 104 204 pumping head 106 206 piston 108 208 shoe 210 roller 112 212 spring A106 A206 pumping axis AO main axis Al 10 A210 roller axis 0 centre of the cam circle described by the centre of the cam offset clearance TDC top dead centre BDC bottom dead centre El direction of rotation of the cam F2 direction of displacement of the piston F3 direction of rotation of the bearing F4 direction of rotation of the roller

Claims

CLAIMSFuel pumping arrangement (10) comprising a fuel pump (102) having a piston (106) adapted to reciprocally move between a top dead centre position (TDC) wherein fuel is compressed in a compression chamber and, a bottom dead centre (BDC) wherein filel in said chamber is not compressed, in use the motion of the piston (106) being generated by the rotation of an eccentric cam (12) followed by a roller (110) secured to the piston (106), the roller (110) following the peripheral circular face of the eccentric cam (12), characterized in that the pumping arrangement (10) further comprises a bearing assembly (15, 18) adjusted around the peripheral circular face of the eccentric cam (12), the bearing assembly (15, 18) being adapted to rotate relative to said eccentric cam (12) and the roller (110) being able to roll on said bearing assembly (15, 18).
2 Pumping arrangement (10) as claimed in the preceding claim wherein the bearing assembly (15, 18) is able to freely rotate around the eccentric cam (12).
3. Pumping arrangement (10) as claimed in any one of the preceding claims wherein the bearing assembly (15, 18) comprises a cylindrical tubular outer rider (15) in which is fixedly arranged a bushing (18), said bushing (18) being adjusted with functional clearance (J) to rotate over the eccentric cam (12).
4. Pumping arrangement (10) as claimed in any one of the claims 1 or 2 wherein the bearing assembly (15, 18) is a roller bearing arranged over the eccentric cam (12).
5. Pumping arrangement (10) as claimed in any one of the preceding claims comprising a plurality of fuel pump (102, 202), each having a piston (106, 206) provided with a roller (110, 210) adapted to roll on the bearing assembly (15, 18) of the eccentric cam (12)
6. Pumping arrangement (10) as claimed in claim 5 wherein the plurality the pumps (102, 202) are substantially uniformly distributed around the eccentric cam (12).