The present invention relates to a fuel pump integrating a damper to absorb hydraulic waves propagating in the fluid.

BACKGROUND OF THE INVENTION

A fuel circuit feeding a vehicle engine comprises a lift pump that flows fuel from a low pressure tank to a high pressure fuel pump that highly pressurizes the fuel prior to flow it to injectors.

A high pressure pump known in the art comprises a rotating camshaft cooperating with a piston that reciprocally slides within a bore in order to pressurize the fuel in a compression chamber. The camshaft is guided in rotation between two bushings and, in operation a back flow of low pressure fuel wets the camshaft and flows through the bushings, lubricating the surfaces, and returning to the low pressure line. Hydraulic waves propagate in said back flow and generate noise, the pulsations impacting the other components of the low pressure line, such as a filter.

Existing standard solutions are, for instance, low pressure regulators that feed the pulsations back to the back flow but, these regulators are CO ₂ relevant. Another approach is to arrange inlet orifices in the return line but, as they restrict the flow section, the low pressure pump of the fuel circuit has to provide additional flow. SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to solve the above mentioned problems by providing a fuel pump comprising a fixed body in which is received, between rotational guiding means, such as coaxial bushings, a camshaft cooperating with a piston slidably guided within a bore. The camshaft is adapted to rotate and actuates the piston to reciprocally move within the bore in order to pressurize fuel within a compression chamber. The camshaft is provided with an integral fluid damper so that hydraulic waves propagating in a fluid wetting the camshaft and flowing through the rotational guiding means are damped.

The camshaft is partially hollow and the fluid damper is arranged in the hollow part. The camshaft is further provided with a channel extending through the wall of the camshaft and establishing a fluid communication between the external surface of the camshaft and the internal hollow part. The damper in camshaft of the pump is a solution that provides advantages such as to be able to be done with minimum effort and low number of parts.

The damper comprises a deformable partition member arranged in the hollow part. The partition deformations enable to absorb hydraulic waves by varying the volume of a first chamber (50) wherein opens the communication channel (46).

In an embodiment the partition member is arranged inside the hollow part, separating the hollow part into the first chamber and a second chamber.

The second chamber can be open in fluid communication with the fluid flow (FR) or in another embodiment it can be closed.

Furthermore, the partition member can arranged at the extremity of the hollow part, the volume of the first chamber being equal to the volume of the hollow part.

In absence of hydraulic waves, the partition, remains in a rest position and, when hydraulic waves occur, the partition deforms or displaces away from said rest position. To enable such deformations, the partition is a deformable elastic membrane, for instance a metal sheet.

In another embodiment the damper is cylindrical and the partition is a piston slidably guided in said cylindrical shape, a spring soliciting the piston toward a rest position.

In any embodiment, the camshaft is a composite shaft comprising a cylindrical axle shaft over which is fixedly press fitted a cam.

In contrast to known low pressure regulator, there is no flow between inlet and return line, thus there is no impact on CO ₂ . It is only a time wise deflection of a membrane or the displacement of the piston, giving some space for a pressure wave. 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 sketch of a fuel circuit of a vehicle.

Figure 2 is a cross section of a fuel pump according to a first embodiment of the invention.

Figure 3 is a cross section of a fuel pump according to another embodiment of the invention.

Figure 4 is an alternative to the first embodiment of figure 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the following description, similar elements will be designated with the same reference numbers. Also, to ease and clarify the description the orientation of the figures will be followed in reference without any limiting intention. Therefore, words and expressions such as "top, upper, lower, over, under, horizontal or vertical"... may be utilized.

Figure 1 is a non- limiting sketchy representation of a vehicle 8 having an engine 10 in which is arranged simplified fuel equipment 12. This is not limited to any specific type of vehicle, or of fuel, and the teachings of the invention are applicable to diesel as well as to gasoline or any other fuel. In the rear of the vehicle 8 are arranged a fuel tank 14 and a low pressure pump 16 and, in the front, on the vehicle engine 10, are arranged a high pressure pump 18, a manifold 20, also known as a common-rail, distributing high pressure fuel to a plurality of injectors 22. These components are arranged in fluid communication with each other via a low pressure supply line 24 extending from the tank 14 to the high pressure pump 18, a high pressure circuit 26 confined between the high pressure pump 18, the manifold 20 and the injectors 22 and, a return low pressure line 28 extending from the front to the rear of the vehicle 8 to flow some fuel back from the injectors 22 back to the tank 14.

Numerous variants of fuel equipment 12 exist with vehicles 8 having the engine in the front or in the rear and the fuel tank arranged at the other end. Both supply and return low pressure lines 24, 28, are long extending between the front and the rear of the vehicle 10 and, inside said lines, low pressure fuel flows and propagate hydraulic waves generated for instance by the operation of the high pressure pump , or by an injection event.

A first embodiment of the invention is now described in reference to figure 2 where the piloting part of the high pressure fuel pump 18 is sketched. The pump 18 comprises a fixed body 30 having a left member 32 spaced apart from a right member 34.

Between the members 32, 34, is rotationally arranged a camshaft 36, extending along a first axis Al, that cooperates with a piston via a cam follower, not represented. To enable rotation of the camshaft 36, each member 32, 34, is provided with a bushing 38 that are coaxially Al arranged. As visible on the figure the camshaft 36 has one cam 40 arranged between the members 32, 34.

The non-represented part of the pump 18 comprises the piston cooperating with the cam 40 to reciprocally slide along a second axis A2 within a bore wherein it pressurizes fuel in a compression chamber.

As indicated by the arrows, part of the fuel creates a low pressure back flow F that wets the camshaft 36 then divides into a front back flow FF and a rear back flow FR, going through the bushings 38 lubricating the rotating surfaces. Hydraulic waves propagate in said back flows generating undesired pulsations in the low pressure return line.

There are various reasons for pressure oscillations in the low pressure circuit. The main reason is the movement of the camshaft 36 with the associated movement of fluid. This fluid under motion leads to various reflections and wherever the free flow is hindered by geometrical obstacles, pressure spikes appear and are immediately transmitted throughout the low pressure circuit.

To overcome these undesirable effects, the camshaft 36 is provided with a fluid damper 42. The camshaft 36 is manufactured partially hollow, said hollow part 44 axially Al extending inside the camshaft 36 from approximately half the middle of the camshaft 36 to the right extremity of the camshaft 36 where it opens in the rear back flow FR. As visible, the blind end of the hollow cylinder 44 is between the bushings 38 and, the hollow cylinder 44 is in fluid communication with the interior of the pump 10 via a channel 46 extending from the hollow cylinder 44, in the vicinity of said blind end, to the outer surface of the camshaft 36. Inside the hollow cylinder is arranged a transversal elastic membrane 48, for instance a thin sheet of metal laser welded on the shaft, which divides the hollow cylinder 44 into a first chamber 50, where are the blind end and the channel 46, and a second chamber 52 represented on the right of the membrane 48. The membrane 48 is normally plane in a rest position and, should it deform, its elastic properties solicit it permanently to return to said plane rest position.

In operation the inside of the first chamber 50 is filled with fuel. The hydraulic waves propagate along the back flow F enter the channel 46, get in the first chamber 50 and deform the membrane 48 varying the volume and damping the hydraulic pulsations of the flow. The total volume of the two chambers remains constant.

Numerous alternatives to this embodiment can be made. For instance in this first embodiment the right extremity of the hollow cylinder 44 cylinder is open, filled with fuel and when the membrane deforms, fuel is expelled from the second chamber. Alternatively, the membrane can be arranged at the right extremity of the hollow part, as shown in figure 4, the first chamber taking all the volume of the hollow part.

In another embodiment, the right extremity of the hollow part may be closed, and the membrane be installed, as in figure 2, inside the hollow part. The second chamber 52 is then filled with air, or another gas. In operation, the membrane 48 deforms and slightly compresses the gas in the second chamber 52. On figure 2, the first chamber 50 is smaller than the second chamber 52, in other alternatives, the reverse can be made with the first chamber 50 being larger than the second chamber 52, said second chamber 52 being open or closed.

To fixedly arrange the membrane in place, laser welding, as well as other technologies, can be utilized.

Another embodiment is sketched on figure 3. In said embodiment the membrane 48 has been replaced by a sliding piston 54 that is permanently solicited in a rest position by a spring 56 arranged in the second chamber 52. Here again the hydraulic waves displace the piston varying the volume of the chambers 50, 52.

In any embodiment, the camshaft 36 can be mono-bloc, made of one piece, or can be composite, made of a cylindrical axle shaft over which is fixedly arranged, for instance by, a cam. An advantage of the latter construction is to utilize for the axle shaft a lower grade steel than what is used for the cam. In this case manufacturing the hollow cylinder may be easier.

above description the following references have been utilized:

8 vehicle

10 engine

12 fuel equipment

14 fuel tank

16 low pressure pump

18 high pressure pump

20 common rail

22 injectors

24 low pressure supply line

26 high pressure circuit

28 low pressure return line

30 body of the high pressure pump

32 left member of the body

34 right member of the body

36 camshaft

38 bushing

40 cam

42 damper

44 hollow part of the camshaft

46 channel

48 membrane

50 first chamber

52 second chamber

54 piston

56 spring

Al first axis

A2 second axis

F back flow of fuel

FF front back flow

FR rear back flow