EQUIPMENT

TECHNICAL FIELD

The present invention relates to a hydraulic fuel circuit of a diesel injection equipment of an internal combustion engine and, more particularly to a low pressure regulator arrangement adapted to regulate the flow returning toward a main low pressure tank.

BACKGROUND OF THE INVENTION

A diesel fuel injection equipment of an internal combustion engine typically comprises a low pressure system and a high pressure system.

In the low pressure system, fuel drawn from a low pressure tank by a transfer pump is filtered prior to enter a metering valve which sends part of said fuel to a high pressure pump, the remaining part being returned to the tank.

In the HP pump, fuel lubricates and cools a rotating camshaft that urges a piston to slide within a bore to perform a pumping cycle. Said fuel exits the pump via the bearings of the camshaft and also returns to the tank. Furthermore, some fuel leaks between the piston and the bore and also returns to the tank.

Fuel pressurized by the piston is delivered to a HP reservoir, well known as a common rail where from fuel injectors connected to the rail spray said pressurized fuel into combustion chambers of the engine and, return the fuel in excess toward the tank.

The return line in which merge the fuel flows coming from the HP pump, the metering valve or the injectors is provided with a venturi vacuum pump enabling evacuation toward the tank and, with a low pressure regulator damping pressure spikes propagating within the return flows. Whether arranged in parallel or in series, said venturi and pressure regulator do not meet the efficiency level required.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to resolve the above mentioned problems in providing a hydraulic fuel circuit of a fuel injection equipment of an diesel internal combustion engine, said fluid circuit comprising a low pressure tank, a high pressure pump, at least one fuel injector and, a return flow circuit comprising a first return line for collecting fuel flows returning to the low pressure main tank, a second return line for collecting pump cooling fuel flow returning to said main tank and,a third return inlet line for collecting injector excess fuel flow not injected and returning to said main tank.

Advantageously, the hydraulic fuel circuit further comprises a low pressure regulator arrangement defining a first fluid path comprising a first chamber for the injector excess fuel flow, a second fluid path comprising a second chamber for the pump cooling fuel flow, the respective volumes of said first and second chambers adjusting to the pressure difference between said chambers so that, the low pressure regulator arrangement operates as a vacuum pump wherein the flow of the third return line is drawn, and wherefrom said flows are expelled toward the first return line.

Also, said low pressure regulator arrangement comprises a pressure regulator defining said first and second chambers, the first chamber having a first inlet port and a first outlet port and, the second chamber having a second inlet port and a second outlet port.

Also, the low pressure regulator arrangement further comprises a first non-return check valve controlling the first inlet port and, a second non-return check valve controlling the first outlet port.

The invention further extends to a low pressure regulator arrangement comprising a pressure regulator, a first non-return check valve and a second nonreturn check valve, said low pressure regulator arrangement being adapted to be arranged in the hydraulic fuel circuit as described above.

The low pressure regulator arrangement has a body with a peripheral wall defining a bore divided by a piston in a first chamber and a second chamber, and wherein the first inlet port and the first outlet port open in the first chamber and, the second inlet port and the second outlet port open in the second chamber, the piston moving as a function of the pressure difference between said first and second chambers.

Furthermore, the low pressure regulator arrangement comprises a main spring urging the piston to maximize the volume of the first chamber. Also, the first non-return check valve controls the first inlet port and prevents, in use, exit of fuel from the first chamber and, the second non-return check valve controls the first outlet port preventing, in use, re-entry of fuel into the first chamber.

Also, said bore extends along a main axis and is partially closed at a first end by a transverse wall in which opens the first inlet port.

Also, the second inlet port is defined at a second end of the bore, opposed to the first end.

Also, the first outlet port and the second outlet port are both radial holes provided in the peripheral wall.

Also, the first non-return check valve is arranged inside the first chamber to control the first inlet port and, the second non-return check valve is arranged outside the peripheral wall to control the first outlet port.

Also, the first non-return check valve comprises a first closing member urged by a first spring against a first seating face provided in the transverse wall around the opening of the first inlet port.

Also, the second non-return check valve comprises a second spring member partially surrounding the body and provided at an end with an index engaged in a recess of the body in order to form a hook fixing said second spring to the body of the regulator and, at a distant moving end with a second closing member urged by the second spring against a second seating face provided on the outer face of the body around the first outlet port.

The invention further extends to a high pressure fuel pump adapted to be arranged in a fuel injection equipment of a diesel internal combustion engine, the pump having a body defining an internal volume in which is arranged a camshaft adapted to rotate about a camshaft axis between two coaxially aligned bearings, and urging a piston to perform a pumping cycle by translating in a bore along a pumping axis. The pump further comprises a low pressure regulator arrangement as described above, said low pressure regulator arrangement enabling to regulate the flow of fuel returning toward a main low pressure tank. 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 diagram of a hydraulic fuel circuit, as per the invention.

Figure 2 is a section of a low pressure regulator comprising a pressure regulator and two check valves as used in the circuit of figure 1.

Figure 3 is the circuit of figure 1 where is arranged the low pressure regulator of figure 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In reference to figure 1 is now described a fuel injection equipment 10 of an internal diesel combustion engine 8, not represented. The equipment 10 comprises a low pressure system 12 and a high pressure system 14. In the low pressure system 12 fuel contained in a main tank 16 is sucked by a transfer pump 18 and filtered 20 prior to enter the high pressure system 14. In the tank 16 also arrives a return line 22. Fuel entering the high pressure system 14 enters a high pressure pump 24 in which the fuel in pressurized in a compression chamber 26 prior to be delivered to a high pressure manifold 28, well known as a common rail 28, which distributes said pressurized fuel to fuel injectors 30 that spray said fuel into compression chambers of the engine 8.

The high pressure pump 24 has a body 32 defining a cambox inner space in which a camshaft 34 rotates between aligned bearings 36, 38 about a camshaft axis Y. A piston 40, urged by a cam of the camshaft reciprocally slides within a bore 42 along a pumping axis X and therein performs a pumping cycle during which the volume of the compression chamber 26 is varied, said chamber 26 being partly defined by an end of the piston.

Part of the fuel entering the high pressure pump 24 is not pressurized and delivered to the common rail 28 but returns toward the main tank 16 after having lubricated the bearings 36, 38, or cooled the pump or, leaked between the piston 40 and the bore 42. Also, as well known the pressurized fuel delivered to the common rail 28 flows to the injectors 30 which spray part of said pressurized fuel, and part in excess being returned toward the main tank 16.

Piston-to-bore leaks return to the cambox inner space, the bearing lubrication fuel returns to the main tank via a first return line 44, the pump cooling fuel returns via a second return line 46 and, the injector excess fuel returns via a third return line 48.

The fuel injection equipment 10 further comprises a low pressure regulator arrangement 50 provided with a first non-return check valve 52, a pressure regulator 54 and a second non-return check valve 56.

With reference to figure 2, the pressure regulator 54 further comprises a return flow regulation means having a first path with first inlet port 58 and first outlet port 60 for regulating the flow coming from the third return line 48 and going toward the first return line 44, and also a second path with second inlet port 62 and second outlet port 64 for regulating the flow flowing coming from the second return line 46 and going toward the first return line 44.

The first path is controlled by the first non-return check valve 52 arranged upstream the first inlet port 58 and also by, the second non-return check valve 56 arranged downstream the first outlet port 60.

The first non-return check valve 52 enables fuel to enter the pressure regulator 54 with almost no resistance, but forbids a counter flow and, the second non-return check valve 56 enables fuel to exit the pressure regulator 54 with almost no resistance, but also forbids counter flow.

Thanks to this low pressure regulator arrangement 50 the return flow is regulated and propagating pressure spikes are damped and do not disrupt the performances of the fuel equipment 10.

The three components of the low pressure regulator arrangement 50 can be separately arranged in the fuel equipment 10 either independently from the pump or within the body 32 of the high pressure pump.

The action of the integrated low pressure regulator arrangement 50 represented on figure 2 is now described. Said low pressure regulator arrangement 50 combines the pressure regulator 54 with the first 52 and the second 56 nonreturn check valves. The pressure regulator 54 has an elongated body 66 extending along a main axis A and comprising a main portion 68, left of the figure, and a narrower connection extension 70, right of the figure.

The main portion 68 has a peripheral wall 72, substantially cylindrical and provided with an inner bore 74 extending from an unrestricted open-end defining the second inlet port 62, left of figure 2, to a transverse bottom wall 76 defining an internal bottom end of the bore. The second inlet port 62 is adapted to be fluidly connected to the second return line 46 and, said bottom end of the bore is indeed limited to an annular shoulder face 78 surrounding the opening 80 of a communication channel 82, narrower than the bore 74 and, axially extending through all the length of the connection extension 70. Externally, said connection extension 70 has a profile adapted to be inserted in a flexible hose forming the third return line 48. Alternatively, should the third line differ from such flexible hose, the connection extension would also differ and be adapted to the new shape of the third line.

The peripheral wall 72 of the main portion of the regulator is further provided with a first radial through hole forming the first outlet port 60 and also with, a second radial hole forming the second outlet port 64, said second outlet port 64 being of larger section than the first outlet port 60.

Inside the bore 74 is slidably arranged a piston 84. The outer cylindrical face 86 of the piston is adjusted to slide against the inner cylindrical face of the bore 74 and, said outer cylindrical face 86 of the piston extends from a first face 88 that faces the first inlet port 58, to a second face 90 facing the second inlet port 62. As it is visible on figure 2, the piston 84 divides the cylindrical space of the bore 74 into a first chamber 96 at the bottom of the bore and, a second chamber 98 by the open end. The first inlet port 58 opens in the first chamber 96 and, the second inlet port 62 opens in the second chamber 98. Furthermore, in the first chamber 96, a main spring 100 is compressed between the shoulder face 78 and the first face 88 of the piston, said main spring 100 urging the piston 84 away from the bottom of the bore.

Also, as visible on figure 2 the axial length of the outer face 86 of the piston is substantially equal to the distance between the first 60 and the second 64 outlet ports and, the second outlet port 64 comprises four radial openings each being of rather large section. Although said openings are partially closed by the piston 84, the remaining opened portion is sufficiently important for said second outlet port 64 not to be fluidly restricted. On the opposite side the first outlet port 60, which is much smaller in section, is not covered by the piston and, in use, the amplitude of the movements of the piston is such that said first outlet port 60 is never covered.

The first non-return check valve 52 in arranged inside the first chamber 96 and it comprises a valve spring 102 urging a ball 104 in sealing abutment against a seating face 106 surrounding the opening 80 of the communication channel at the bottom of the bore. The valve spring 102 is a coil spring 102 compressed between the ball 104 and the bottom of an axial recess provided in the first face 88 of the piston. In an alternative embodiment, another closing member such as a flat plate or a tapered member could replace the ball 104.

The second non-return check valve 56 as a half-ring shape, substantially superior to 180°, having resilient properties and being arranged around the outer face of the peripheral wall 72 of the regulator. Said half-ring is provided at one end with an index inwardly radially oriented, said index being complementary engaged in a small recess provided in the outer face of the peripheral wall 72 of the regulator, said engagement of the index in the recess forming a retaining hook 108 preventing rotation of the half-ring around the regulator. At the other end, opposed to the index, said half-ring is provided with a closing member 110 adapted to close the second outlet port 64. In the embodiment presented, the closing member 100 is a simple widened flat portion. In an alternative a ball, or half a ball, or a tapered shape member could be arranged between the end of the half-ring and the outer face of the regulator.

The low pressure regulator arrangement 50 described operates as a vacuum pump since the reciprocating action of the piston alternately creates a vacuum in the first chamber 96 drawing fuel through the first non-return check valve 52 creating a necessary vacuum at the injectors then, the drawn fuel is expelled through the second non-return check valve 56.

Both non-return check valves 52, 56 must have very low opening pressures. Typically the ball 104 of the first valve or the closing member 110 of the second valve may be of less than 2 mm diameter or section. Also, the spring 102 of the first valve and the resiliency of the half-ring of the second valve generate minimal force, almost negligible, the object of said check valves being ease the flow in one direction without creating any difficulty and, prevent the flow in the opposite way. Also, said valves have a very small lift, for instance smaller than 0.5 mm, controlled by a lift stop.

It may also be necessary that the physical orientation, with respect to gravity, ensures that the seals of both check valves 60, 64 remain "wet" so that they seal the gaseous components of the working fluid.

Figure 3 is similar to figure 1, representing the complete fuel injection equipment 10, the low pressure regulator arrangement 50 being replaced by an integral low pressure regulator as represented on figure 2, the low pressure regulator arrangement 50 integrating the regulator 54 and the two check-valves 52, 54 all arranged in the body 32 of the high pressure pump 24.

The operation of the equipment 10, highlighting in particular the operation of the low pressure regulator arrangement 50 is now described.

The bearing lubrication fuel returns to the main tank 16 via a first return line 44 which bypasses the regulator 54. The action of the actuator 34 and piston 40 in the chamber 34 cause the pressure in the chamber 34 to vary in a cyclic manner. The regulator 54 responds to the cyclic pressure in a well-known fashion and the piston 84 responds in a cyclic fashion. The pump cooling fuel returns via the second return line 46 and enters the second inlet port 62 of the regulator, fills the second chamber 98 and pushes the piston 84 toward the bottom of the bore, widening the section of the second outlet port 64 through which said cooling fuel exits and merges into the first return line 44. The injector excess fuel returns via a third return line 48 and flows in the communication channel 8. As the piston 84 moves into the chamber 98, the pressure in the chamber 96 is reduced below atmospheric pressure and below the pressure in the connection 82 enabling flow from the connection 80 through the first valve 52 into the chamber 96. Provided the valve 56 has a low opening pressure as described the pressure in the connection 82 will also be below atmospheric. At the same time the pressure in the chamber 96 is lower than the pressure in the connection 44 so the valve 56 is closed. As the piston 84 moves into the chamber 96, the pressure in the chamber 96 is increased above the pressure in the connection 44 enabling flow from the chamber 96 through the second valve 56 into the connection 44. At the same time the pressure in the chamber 96 is higher than the pressure in the connection 82 so the valve 52 is closed. LIST OF REFERENCES

X pumping axis

Y camshaft axis

A main axis of the regulator

8 internal combustion engine

10 fuel injection equipment

12 low pressure system

14 high pressure system

16 main tank

18 transfer pump

20 filter

22 return line

24 high pressure pump

26 compression chamber

28 common rail

30 injectors

32 body of the high pressure pump

34 camshaft

36 bearing

38 bearing

40 piston

42 bore

44 first return line

46 second return line

48 third return line

50 low pressure regulator arrangement

52 first non-return check valve

54 pressure regulator

56 second non-return check valve

58 first inlet port

60 first outlet port

62 second inlet port

64 second outlet port

66 body of the regulator

68 main portion of the body

70 connection extension peripheral wall

bore

transverse bottom wall

shoulder face

opening of the communication channel communication channel

piston

outer face of the piston

first face

second face

first chamber

second chamber

main spring

valve spring of the first check valve ball

seating face

hook of the second check valve closing member