Field of the invention
[0001] This invention relates to a fuel relief passage used in combination
with a high pressure fuel pump.
Background of the invention
[0002] U.S. Patent Application Number 2055580 A describes a piston of a
high pressure pump which is operated by an elastic fluid that moves the injection valve into its closed position during the injection stroke through the agency of cushioning- means interposed between the piston and the valve. The cushioning-means may comprise either a spring or a fluid medium. As shown in Fig. 1, fuel is supplied by a low-pressure pump through a pipe, past a non-return valve, into a pump chamber, and is forced by a differential piston past the fuel valve and through bores into the cylinder. A fuel accumulator is arranged in the pipe and is formed by a spring-pressed piston operating in a cylinder provided with a port which is uncovered if the pressure in the pipe is excessive. The piston is driven by compressed air or gas which enters the casing through an inlet and is admitted to the cylinder by a mechanically operated valve, which first closes an outlet in a valve and then opens the valve. The upward pressure of the gas in the cylinder on the valves is balanced by the downward pressure of the gas on a piston mounted in the casing and connected to the cylinder by a passage. After a spring carried by the piston contacts with a flange on the valve, further movement of the piston forces the valve on to a seat and terminates the injection. When the spring raises the valve to open the outlet the compressed gas in the cylinder escapes through an opening. In a modified construction, Fig. 2, the injection valve carries a piston which is exposed on its upper side to the pressure in the pipe, and on the lower side to the pressure in the pump chamber. The valve opens by fluid pressure pressing the piston against a spindle, and is closed when a spring-pressed abutment on the piston contacts with the spindle. The pump is driven by gases taken from the working cylinder through pipes the total volume of which is at least as great as the maximum volume swept out by the piston during its stroke. A vacuum relief valve is included in the pipe. In a further

modification, the movement of the piston is transmitted to the piston of the injection valve through a column of fuel, and the increase in pressure, when the piston covers an escape port, closes the valve.
Brief description of the accompanying drawings
[0003] Different modes of the invention are disclosed in detail in the
description and illustrated in the accompanying drawings:
[0004] Figure 1 illustrates a high pressure fuel pump in one embodiment of
the invention.
[0005] Figure 2 illustrates a dual lobe cam for the high pressure fuel pump
in one embodiment of the invention.
Detailed description of the embodiments
[0006] A high pressure fuel pump 10 is described. The high pressure fuel
pump 10 comprises a housing 12 and a fuel inlet flow path 14 defined in the
housing 12. A cam 16 is coupled to a drive shaft of the high pressure fuel pump
10. A roller tappet 18 is secured to the cam 16, the roller tappet 18 adapted to be
translated due to a rotational motion of the cam 16. A piston 20 is secured to the
roller tappet 18, wherein a translation of the roller tappet 18 causes a translation
of the piston 20 within a pumping chamber 21 of the high pressure fuel pump 10
to deliver fuel to a fuel injector via a fuel pipe. One of a groove and a bore 26 is
defined through the piston 20, one of the groove and the bore 26 adapted to be
aligned with the fuel inlet flow path 14 to channel fuel from the pumping
chamber 21 of the high pressure fuel pump 10 to the fuel inlet flow path 14.
[0007] In addition, a high pressure fuel pump 10 is described. The high
pressure fuel pump 10 comprises a housing 12 and a fuel inlet flow path 14 defined in the housing 12. A cam 16 is coupled to a drive shaft of the high pressure fuel pump 10, the cam 16 comprising a first lobe 28, a dwell 29 defined adjacent the first lobe 28, and a second lobe 30 defined adjacent the dwell 29, the second lobe 30 having a higher lift than the first lobe 28.

[0008] Figure 1 illustrates a high pressure fuel pump 10 in one embodiment
of the invention. The high pressure fuel pump 10 comprises a housing 12. The housing 12 of the high pressure fuel pump 10 comprises a fuel inlet flow path 14 that is defined within the housing 12. The fuel inlet flow path 14 permits the flow of fuel from out of the pump housing 12 to a pumping chamber 21 of the high pressure fuel pump 10. In addition, the fuel inlet flow path 14 also permits a flow of fuel out of the pumping chamber 21 of the high pressure fuel pump 10 when the pressure of fuel within the pumping chamber 21 is higher than the pressure of fuel in the fuel inlet flow path 14.
[0009] A cam 16 is coupled to a drive shaft of the high pressure fuel pump
10 and is rotated by the drive shaft of the high pressure fuel pump 10. The cam 16 comprises a first lobe 28, a second lobe 30, and a dwell 29 located between the first lobe 28 and the second lobe 30. The second lobe 30 of the cam 16 is positioned adjacent to the dwell 29.
[0010] In between the first lobe 28 and the second lobe 30, the dwell 29 is
a flat shaped portion. The second lobe 30 of the cam 16 has a higher lift as compared to the first lobe 28 such that the roller of the roller tappet 18 of the high pressure fuel pump 10 is lifted upwardly to a greater extent when it comes in contact with the second lobe 30. The roller tappet 18 is positioned above the cam 16 and translates due to the rotational motion of the cam 16. More specifically, when the cam 16 is rotating in the clockwise direction, the roller tappet 18 rides on the surface of the cam 16 and is lifted upwardly when it comes in contact with the first lobe 28 and the second lobe 30.
[0011] A piston 20 is in contact with the roller tappet 18. When the roller
tappet 18 translates, the piston 20 that is within the pumping chamber 21 of the high pressure fuel pump 10 also translates. Therefore, fuel is delivered to the fuel injector via the fuel pipe. When the piston 20 translates in the downward direction thereby opening the fuel inlet flow path 14, fresh fuel is channeled within the pumping chamber 21 of the high pressure fuel pump 10 via the fuel inlet flow path 14.

[0012] A vertical groove or bore and a horizontal groove or bore 26 are
defined through the piston 20. In an exemplary embodiment, one of the bore and the groove 26 further comprises at least one of an L-shaped bore and an L-shaped groove. A first end of at least one of the L-shaped bore and the L-shaped groove culminates at a piston head of the piston 20 of the high pressure fuel pump 10. A second end of at least one of the L-shaped bore and the L-shaped groove culminates at the fuel inlet flow path 14. In an alternate exemplary embodiment, one of the bore and the groove 26 further comprises at least one of a straight bore and a straight groove. In yet another alternate exemplary embodiment, one of the bore and the groove 26 comprises any other shaped bore and groove that permits the passage of fuel from the pumping chamber 21 of the high pressure fuel pump 10 to the fuel inlet flow path 14.
[0013] The high pressure fuel pump 10 comprises a bi-directional flow
control valve 32 that is defined downstream from the pumping chamber 21. In an exemplary embodiment, the bi-directional flow control valve 32 permits the flow of fuel from the pumping chamber 21 of the high pressure fuel pump 10 to a fuel injector when it is required to inject fuel from the fuel injector to an engine cylinder. The bi-directional flow control valve 32 is further adapted to permit a flow of fuel from the fuel pipe to the pumping chamber 21 of the high pressure fuel pump 10 after the pumping stroke of the piston 20 of the high pressure fuel pump 10.
[0014] Figure 2 illustrates a dual lobe cam 16 for the high pressure fuel
pump 10. The cam 16 is coupled to a drive shaft of the high pressure fuel pump 10 and is rotated by means of the drive shaft of the high pressure fuel pump 10. The cam 16 comprises a first lobe 28 and a second lobe 30. The second lobe 30 of the cam 16 is positioned adjacent to the first lobe 28 and a dwell 29 located between the first lobe 28 and the second lobe 30. The second lobe 30 of the cam 16 has a higher lift as compared to the first lobe 28 such that the roller of the roller tappet 18 is lifted upwardly to a greater extent when it comes in contact with the second lobe 30 as compared to the first lobe 28. The roller tappet 18 is positioned above the cam 16 and translates due to the rotational motion of the

cam 16. More specifically, when the cam 16 is rotating in the clockwise direction, the roller tappet 18 rides on the surface of the cam 16 and is lifted upwardly when it comes in contact with the first lobe 28. Therein, a period of dwell 29 exists on the cam 16, wherein the roller tappet 18 dues not lift but merely the pumping chamber 21 delivers pressurized fuel from the high pressure fuel pump 10. After the period of dwell 29 is complete, the roller tappet 18 rides over the second lobe 30 that is higher than the first lobe 28, thereby causing the pumping chamber 21 of the high pressure fuel pump 10 to come in contact with the fuel inlet flow path 14 via one of the bore and the groove 26 of the piston 20. This occurs due to the rise of the piston 20 when the roller tappet 18 rides over the second lobe 30 of the cam 16.
[0015] A working of the high pressure fuel pump 10 is described as an
example. Fuel is supplied to the pumping chamber 21 of the high pressure fuel pump 10 via the fuel inlet flow path 14. The cam 16 is rotated in the clockwise direction by means of a drive shaft. When the roller tappet 18 rides over the first lobe 28 of the cam 16 until it reaches a first top dead center, the piston 20 is translated, thereby pressurizing fuel and delivering pressurized fuel from the pumping chamber 21 of the high pressure fuel pump 10. The dwell 29 provided after the first lobe 28 of the cam 16 facilitates delivering a constant supply of pressurized fuel from the pumping chamber 21 of the high pressure fuel pump 10. The pressurized fuel that is delivered from the pumping chamber 21 lifts the bi-directional valve 32 in the upward direction. Therein, the pressurized fuel flows through the space defined between the bi-directional valve 32 and the housing 12 and out of the high pressure fuel pump 10. From the high pressure fuel pump 10, the pressurized fuel is channeled to the fuel injector via the fuel inlet pipe, wherein the pressurized fuel is delivered from the fuel injector to an engine cylinder. After the period of dwell 29, the cam 16 is rotated thereby causing the roller tappet 18 to ride over the second lobe 30 of the cam 16 until it reaches a second top dead center. When the roller tappet 18 rides over the second lobe 30 of the cam 16, the piston 20 is translated, thereby causing the fuel inlet flow path 14 from coming in contact with the pumping chamber 21 of the high

pressure fuel pump 10 via one of the bore and the groove 26. After the pressurized fuel is delivered from the fuel injector to the engine cylinder, the excess pressurized fuel from the fuel inlet pipe flows to the bi-directional valve 32 as the roller tappet 18 begins receding from the second top dead center of the cam 16. A ball of the bi-directional valve 32 is translated against a force of a spring member, thereby causing the fuel to flow through the bi-directional valve 32 and back to the pumping chamber 21 of the high pressure fuel pump 10. As the pumping chamber 21 is at a higher pressure relative to the fuel inlet flow path 14, the pressurized fuel from the pumping chamber 21 is channeled to the fuel inlet flow path 14. During the next working cycle of the high pressure fuel pump 10, the pressurized fuel is supplied from the fuel inlet flow path 14 to the pumping chamber 21 of the high pressure fuel pump 10 for delivery to the fuel injector.
[0016] It must be understood that the embodiments explained in the above
detailed description is only illustrative and does not limit the scope of this invention. The scope of this invention is limited only by the scope of the claims. Many modification and changes in the embodiments aforementioned are envisaged and are within the scope of this invention.

We Claim:
1. A high pressure fuel pump (10), said high pressure fuel pump (10)
comprising:
a housing (12);
a fuel inlet flow path (14) defined in said housing (12);
a cam (16) coupled to a drive shaft of said high pressure fuel pump (10);
a roller tappet (18) secured to said cam (16), said roller tappet (18) adapted to be
translated due to a rotational motion of said cam (16);
a piston (20) secured to said roller tappet (18), wherein a translation of said roller
tappet (18) causes a translation of said piston (20) within a pumping chamber
(21) of said high pressure fuel pump (10) to deliver fuel to a fuel injector via a
fuel pipe; characterized in that
one of a bore and a groove (26) defined through said piston (20), said one of the
bore and the groove (26) adapted to be aligned with said fuel inlet flow path (14)
to channel fuel from said pumping chamber (21) of said high pressure fuel pump
(10) to the fuel inlet flow path (14).
2. The high pressure fuel pump (10) in accordance with Claim 1 wherein said
cam (16) comprises a first lobe (28), a dwell (29) defined adjacent said first lobe
(28), and a second lobe (30) defined adjacent said dwell (29), said second lobe
(30) having a higher lift than said first lobe (28).
3. The high pressure fuel pump (10) in accordance with Claim 1 wherein said
at least one of the bore and the groove (26) further comprises at least one of an
L-shaped bore and an L-shaped groove, a first end of at least one of the L-shaped
bore and the L-shaped groove culminating at a piston head of said piston (20) of
said high pressure fuel pump (10), a second end of at least one of the L-shaped
bore and the L-shaped groove culminating at the fuel inlet flow path (14).

4. The high pressure fuel pump (10) in accordance with Claim 1 further
comprising a bi-directional flow control valve (32) defined downstream from
said pumping chamber (21), said bi-directional flow control valve (32) adapted
to permit a flow of fuel from said fuel pipe to the pumping chamber (21) of said
high pressure fuel pump (10).
5. A high pressure fuel pump (10), said high pressure fuel pump (10)
comprising:
a housing (12);
a fuel inlet flow path (14) defined in said housing (12); characterized in that
a cam (16) coupled to a drive shaft of said high pressure fuel pump (10), said
cam (16) comprising a first lobe (28), a dwell (29) defined adjacent said first
lobe (28), and a second lobe (30) defined adjacent said dwell (29), said second
lobe (30) having a higher lift than said first lobe (28).
6. The high pressure fuel pump (10) in accordance with Claim 5 further
comprising a roller tappet (18) secured to said cam (16), said roller tappet (18)
adapted to be translated due to a rotation of said cam (16);
a piston (20) secured to said roller tappet (18), wherein a translation of said roller tappet (18) causes a translation of said piston (20) within a pumping chamber (21) of said high pressure fuel pump (10) to deliver fuel to a fuel injector via a fuel pipe; and
one of a bore and a groove (26) defined through said piston (20), said one of the bore and the groove (26) adapted to be aligned with said fuel inlet flow path (14) to channel fuel from said pumping chamber (21) of said high pressure fuel pump (10) to the fuel inlet flow path (14).
7. The high pressure fuel pump (10) in accordance with Claim 6 wherein said
at least one of said at least one of the bore and the groove (26) further comprises
at least one of an L-shaped bore and an L-shaped groove, a first end of at least

one of the L-shaped bore and the L-shaped groove culminating at a piston head of said piston (20) of said high pressure fuel pump (10), a second end of at least one of the L-shaped bore and the L-shaped groove culminating at the fuel inlet flow path (14).
8. The high pressure fuel pump (10) in accordance with Claim 6 further comprising a bi-directional flow control valve (32) defined downstream from said piston (20), said bi-directional flow control valve (32) adapted to permit a flow of fuel from said fuel pipe to said pumping chamber (21) of said high pressure fuel pump (10).