EP3253962A1

EP3253962A1 - Method to manufacture a common rail

Info

Publication number: EP3253962A1
Application number: EP16702735.8A
Authority: EP
Inventors: Onur Mehmet Tansug; Ernur Gusav PIHAVA
Original assignee: Delphi International Operations Luxembourg SARL
Current assignee: Delphi International Operations Luxembourg SARL
Priority date: 2015-02-06
Filing date: 2016-02-03
Publication date: 2017-12-13
Also published as: GB201501987D0; WO2016124660A1; CN107223164A

Abstract

A method for manufacturing a common rail (12) adapted to be arranged in a fuel injection system, the common rail (12) having a body (18) provided with a bore (28) defining an internal volume (V), said body (18) extending along a main axis (X) from a first extremity (22) having a first threaded female recess (30) to, a second extremity (26) having a second threaded female recess (44), the bore (28) opening at both ends in one of the recesses (30, 44), the method (100) comprising the steps of a first autofrettage step (130) of said bore (28), an autofrettage fluid (AF) being pressurized to a first pressure (PI) in the bore (28) during this first step (130) and, second autofrettage step (140) for treating the first female threaded recess (30), the autofrettage fluid (AF) being pressurized to a second pressure (P2) in the first recess (30) during this second step (140).

Description

METHOD TO MANUFACTURE A COMMON RAIL TECHNICAL FIELD

The present invention relates generally to a method to manufacture a common rail.

BACKGROUND OF THE FNVENTION

Common rail, as a component of a fuel injection system, are well known to be made of steel and to have an elongated tubular shape. Laterally are provided connection protrusions for complementary engagement of high pressure pipes. At both its extremities, the rail is provided with a recess that is threaded for complementary arrangement, on one side, of a pressure sensor and, on the opposite side, of a pressure regulator device, such as a passive valve or an electromagnetic controlled valve. Manufacturing the rail comprises known stems such as forging a blank, then machining the volume internal to the rail and the threaded recesses. The recesses are typically of a larger diameter than the internal volume, therefore, the wall thickness of the rail reduces suddenly when the internal diameter increases. In use, rail is filled with fuel at high pressure, several thousands of bars and, during operation the fuel pressure rapidly fluctuates over a large range of pressure. This creates varying mechanical stresses in the peripheral wall of the rail. Said stresses, along with tightening stresses concentrate in fragile areas where the wall thickness varies and potentially cracks are generated.

Various reinforcements have been implemented, such as increasing the wall thickness, rounding corners, heat and local surface treatments...

Unfortunately the on-going optimization of the rail goes against these methods that increase mass and cost. SUMMARY OF THE FNVENTION

It is an object of the invention to resolve or at least mitigate the above mentioned problem by a method for manufacturing a common rail adapted to be arranged in a fuel injection system. The common rail has a body provided with a bore defining an internal volume for receiving, in use, high pressure fuel, said body extending along a main axis from a first extremity having a first transverse face wherein centrally opens a first threaded female recess adapted to receive a pressure sensor to, a second extremity having a second transverse face wherein centrally opens a second threaded female recess adapted to receive a fuel pressure regulating valve. The bore opens at both ends in one of the recesses. The method comprises the steps of:

- forging a steel blank of the common rail,

- machining and threading the first and second recesses, in the extremities, of said blank,

- first autofrettage step of said bore, an autofrettage fluid being pressurized to a first pressure in the bore during this first step,

the method further comprises a:

- second autofrettage step for treating the first female threaded recess, the autofrettage fluid being pressurized to a second pressure in the first recess during this second step.

More precisely, the second fluid pressure is inferior to the first fluid pressure.

Also, prior to pressurizing the autofrettage fluid, the second autofrettage step comprises a second sealing step during which are arranged a sealing feature over the first extremity, a plurality of sealing features to close high pressure channels radially provided in the rail and also, an autofrettage machine nozzle arranged over the second extremity.

In a first alternative, the second autofrettage step is performed before the first autofrettage step.

In another alternative, the first and the second autofrettage steps are performed simultaneously.

The method may comprise a third step of autofrettage for treating the second female threaded recess, a third fluid pressure being applied during this third step. The third fluid pressure is inferior to the first fluid pressure.

The invention further extends to a common rail adapted to be arranged in a fuel injection system, the common rail having a body provided with a bore defining an internal volume for receiving, in use, high pressure fuel, said body extending along a main axis from a first extremity having a first transverse face wherein centrally opens a first threaded female recess adapted to receive a pressure sensor to, a second extremity having a second transverse face wherein centrally opens a second threaded female recess adapted to receive a fuel pressure regulating valve, the bore opening at both ends in one of the recesses.

The first threaded recess and/or second threaded recess are/is entirely reinforced by autofrettage.

Furthermore, the autofrettage reinforcement is done by applying a method as previously described.

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 side view of the common rail of a fuel injection equipment, the rail being provided with a pressure sensor and also with a pressure regulating valve.

- Figure 2 is an axial section of a rail similar to the rail of figure 1.

- Figure 3 is a magnified detail of an axial section of an extremity of the rail of figure 2, a sealing feature being arranged on the rail.

- Figure 4 is an alternative to the feature shown on figure 3.

- Figure 5 is a magnified detail of an axial section of an extremity of the rail of figure 2, another sealing feature being arranged on the rail.

- Figure 6 is an alternative embodiment of the feature of figure 4.

- Figure 7 is yet another alternative embodiment of features.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Although the expression "common rail" is often utilized to designate a complete fuel injection system, in the context of this description "common rail" designates a component aiming at being a high pressure reservoir, able to withstand several thousands of fuel bar pressure in a fuel injection system and more specifically in a diesel fuel injection system.

In reference to the figure 1 is presented a rail assembly 10 comprising a common rail 12 provided with a pressure sensor 14 and a pressure limiting valve 16. The common rail 12 is an elongated metallic body 18 extending along a main axis X from a first transverse face 20 defining a first extremity 22, on the left of the figure where is arranged the pressure sensor 14, to a second transverse face 24 defining a second extremity 26, on the right of the figure where is arranged the valve 16.

The body 18 of the rail 12 is provided with an axial bore 28, visible on the axial section of figure 2, defining an internal volume V opening at both extremities 22, 26, of the rail.

In the first transverse face 20 of the first extremity 22, now described, opens a first threaded recess 30 at the bottom face 32 of which centrally opens the bore 28. As is detailed on figure 3, the recess 30 is threaded along its all length from the first transverse face 20 to the first bottom face 32. Externally, the rail body 18 is provided with a first outer cylindrical face 34 axially X extending from the first transverse face 20 to a first shoulder face 36. The bore 28 opening into the bottom face 32 is smoothen with a first inner chamfer 38, the opening of the recess 32 into the first transverse face 20 is smoothen with a first thread-end chamfer 40 and, joining of the first transverse face 20 and of the first outer cylindrical face 34 is smoothen by a first outer chamfer 42.

The second extremity 26 of the rail 12 is similarly arranged. A second threaded recess 44 opens in the second transverse face 24 and, at the bottom face 46 of said second recess centrally opens the small axial channel bore 48 connecting the bore 28 to the second recess 44. Alternatively, the bore 28 can directly open into the second recess 44 without need for any small axial channel 48. As can be seen on the section of figure 2, the threaded portion of the second recess 44 only partially extends along said second recess. Also, the second extremity 26 is provided with a lateral outlet channel 50, adapted to flow low pressure fuel returning to a low pressure tank, said outlet channel 50 radially extending through the body 18, from the non-threaded portion of the second recess to an external opening on the outer face of said body. More particularly, the body is provided with a radial protrusion 52 wherein is centrally provided the lateral channel outlet 50, said channel 50 having an enlarged section portion 54 wherein is arranged a hydraulic nipple 56 outwardly protruding and adapted to complementary sealingly receive a low pressure return hose.

As shown on the figures, the rail body 18 is provided with other protrusions 58 quite regularly spread along the length of the rail between the extremities 22, 26. In each of said protrusions 58 centrally radially extend a high pressure channel 58 adapted to flow high pressure fuel either entering the rail or, exiting the rail toward fuel injectors. Said high pressure protrusions 58 are externally threaded for fixing high pressure pipes.

Finally, the rail body 12 is provided with fixation tabs 60, each having a central hole 62 to enable fixation with bolt screwed, for instance, in an engine block.

The manufacturing method 100 of the common rail 12 starts with a forging step 110 transforming a steel rod into a rail blank. Cooling of the blank is controlled after forging so that the material's mechanical properties are similar to those of tempered steel. Afterward the rail blank is machined 110 to create the bore 28 and all the faces of the first and second extremities 22, 26, previously described: first and second transverse faces 20, 24, threaded recesses 30, 44, first cylindrical face 34, shoulder face 36, chamfers 38, 40, 42, as well as the low pressure outlet channel 50, the high pressure inlet and outlet channels 58 and, the fixation tabs 60 and holes 62.

In order to strengthen the rail 12 steps of autofrettage are implemented. A first autofrettage step 130 enables to treat the bore 28 and the high pressure channels 58. Said first autofrettage step 130 comprises a first sealing step 132 during which, the opening of the bore 28 into the bottom face 32 of the first recess is sealed by a first sealing feature 70 represented on figure 3. The high pressure inlet and outlet channels 58 are sealed by channel sealing features 82 (not shown) and, a machine nozzle 84 (not shown) is applied on the second extremity 26. Afterward, still as part of the first sealing step 132, forces are applied on the sealing features 70, 82 and on the nozzle 84 in order to ensure perfect sealing of the inner space of the rail 12. The axial forces applied to the rail by the first sealing feature 70 and by the nozzle 84 are opposed and balanced and do not generate deformation but, in order to avoid bending or torsion of the rail because of the radial forces generated by the channel sealing features 82, holding features not represented, are arranged opposed to the protrusions 52 in order to generate on the rail opposed and balancing radial forces.

After the first sealing step 132 is performed a first pressurized step 134 during which an autofrettage fluid AF injected in the rail, via the nozzle 84, is pressurized to a first pressure PI that is typically between 6000 bar and 10000 bars. This pressurizing step 134 lasts between 2 seconds and 10 seconds, the fluid pressure and the duration being adjusted as per the rail geometry and required characteristics.

More in details, the first sealing feature 70 comprises an elongated cylindrical body 72 extending along the main axis X and provided with a conical end 80 tapering to a smaller section than the cylindrical section of the protrusion.

Said first sealing feature 70 is designed as a plug so that when it is engaged in the first extremity 22 of the rail, the conical end 80 engages inside the bore 28 until it comes in contact against the first inner chamfer 38. When in place, the first sealing feature 70 contacts the rail only on the chamfer 38. The first transverse face 20 and the first thread-end chamfer 40 are not in contact with the feature 70 and therefore cannot be damaged by the feature 70, especially because of the applying axial forces.

Depending on the variant of the machine process, sealing feature 70 may be provided with an axial drilling 86, as in figure 4, to enable transfer of fluid into the rail.

The channel sealing features 82 are typically balls arranged in the chamfer machined at the outer extremity of the high pressure channels 58 and, when pushed toward the high pressure channel 58 they seal said high pressure channels 58.

The machine nozzle 84 is designed similarly to the first sealing feature 70 to slightly engage in the opening of the bore 28 and to abut against the chamfer at the bottom 46 of the second recess.

The first autofrettage step 130 is followed, or alternatively preceded, by a second autofrettage step 140 for treating the first threaded recess 30.

The second step 140 comprises a second sealing step 142 wherein the first sealing feature 70 is replaced by a second sealing feature 90 represented on figure 5, while the channel sealing features 82 and the nozzle 84 are identical to the ones previously described.

Said second sealing feature 90 comprises a body 92 provided with a recess 94 defining a peripheral wall face 96. In the vicinity of the bottom of said recess 96, the second sealing feature 90 is provided with a shoulder 97. When the second feature 90 is engaged over the first extremity 22 of the rail 12, the peripheral wall face 96 complementary adjusts to the first outer cylindrical face 34 of the rail and, the shoulder 97 comes in sealing contact against the first outer chamfer 42. As shown on figure 5, the second sealing feature is provided with an axial drilling 86 similar to the drilling of the first feature.

In an alternative embodiment represented on figure 6, a similar feature as the first cylindrical feature 70 is utilized in conjunction with the second sealing feature 90 provided with a second drilling 88 through which the fluid can flow and access the volume to be treated of the first recess 30 and therefore manufacturing time may be reduced.

Further alternative embodiments can be designed, for instance replacing the cylindrical protrusion by a spherical portion that would seal the first extremity of the rail.

The first autofrettage 130 step and the second autofrettage 140 step are independent. They can be implemented first before second or, second before first step.

After the second sealing step 142, is performed a second pressurizing step 144 during which an autofrettage fluid AF injected in the rail, via the nozzle 84. While during the first pressurizing step 134, the autofrettage fluid AF was confined inside the bore 28 and the high pressure channels 58, during this second pressurizing step 144 the fluid AF fills the additional volume of the first recess 32.

In this second pressurizing step 144, the autofrettage fluid AF is pressurized at a lesser pressure P2 than during the first step 134. For instance, if during the first step 134 the pressure PI was 7000 bars, during the second step, the pressure P2 may be only 3000 bars, this in order to prevent any damage to the threads. The second pressurizing step 144 similarly lasts between 2 seconds and 10 seconds.

In an alternative to this description, the so-called second autofrettage step 140 can be performed before the first autofrettage step 150.

A third autofrettage step 150 may be performed after the first step 130 or after the second step 140. This third autofrettage step 150 aims at treating the second threaded recess 44. Similarly to the second step 140, this third step 150 comprises a third sealing step 152 followed by a third pressurizing step 154. For the third sealing step 152, a third sealing feature, no represented, is utilized. It is very similar to the second sealing feature 90 but this time it is arranged in sealing abutment against the thread-end chamfer of the second extremity 26. The channel sealing features 82 remain unchanged and the autofrettage machine nozzle 84 is arranged to cover the first extremity 22.

During the third pressurizing step 154 the fluid AF fills the additional volume of the second recess 44 and, similarly to the second step 144, in this third pressurizing step 154, the autofrettage fluid AF is pressurized at a lesser third pressure P3 than during the first step 134, substantially the same pressure as during the second step 144, and for the same duration.

In another alternative using the combination of features shown on figure 7, the autofrettage steps 130, 140, 150, are implemented simultaneously. Indeed, on figure 7 is represented the combination of a first sealing feature 70 provided with an axial drilling 86 with, a second sealing feature 90 provided with a second drilling 88. When in place, as shown on the figure, the volume of the bore 28 and the first threaded recess 30 are isolated from each other and the autofrettage steps 130, 140, can be performed at the same time.

LIST OF REFERENCES

10 assembly

12 common rail

14 pressure sensor

16 pressure limiting valve

18 common rail body

20 first transverse face

22 first extremity of the rail

24 second transverse face

26 second extremity of the rail

28 bore

30 first threaded recess

32 bottom face of the first recess

34 first outer cylindrical face

36 first shoulder face

38 first inner chamfer

40 first thread-end chamfer

42 first outer chamfer

44 second threaded recess 46 bottom face of the second recess

48 small axial channel

50 low pressure outlet channel

52 protrusion of the body

54 enlarged section portion of the LP channel

56 nipple

58 high pressure channel

60 fixation tab

62 hole

70 first sealing feature

72 body of the feature

80 conical end of the protrusion

82 channel sealing feature

84 auto frettage machine nozzle

86 axial drilling

88 second drilling

90 second sealing feature

92 body of the feature

94 recess

96 peripheral wall face of the recess

97 shoulder

100 manufacturing method

110 forging step

120 machining and threading steps

130 first auto frettage step

132 first sealing step

134 first pressurizing step

140 second auto frettage step

142 second sealing step

144 second pressurizing step 150 third auto frettage step

152 third sealing step

154 third pressurizing step

X main axis

V internal volume

autofrettage fluid

first pressure

second pressure P3 third pressure

Claims

CLAIMS:

1. A method (100) for manufacturing a common rail (12) adapted to be arranged in a fuel injection system, the common rail (12) having a body (18) provided with a bore (28) defining an internal volume (V) for receiving, in use, high pressure fuel, said body (18) extending along a main axis (X) from a first extremity (22) having a first transverse face (20) wherein centrally opens a first threaded female recess (30) adapted to receive a pressure sensor (14) to, a second extremity (26) having a second transverse face (24) wherein centrally opens a second threaded female recess (44) adapted to receive a fuel pressure regulating valve (16), the bore (28) opening at both ends in one of the recesses (30, 44), the method (100) comprising the steps of:

- forging (110) a steel blank of the common rail,

- machining and threading (120) the first and second recesses (30, 44) in the extremities (22, 26) of said blank,

- first autofrettage step (130) of said bore (28), an autofrettage fluid (AF) being pressurized to a first pressure (PI) in the bore (28) during this first step (130),

characterized in that, the method (100) further comprises a:

- second autofrettage step (140) for treating the first female threaded recess (30), the autofrettage fluid (AF) being pressurized to a second pressure (P2) in the first recess (30) during this second step (140).

2. Method (100) as claimed in the preceding claim wherein the second fluid pressure (P2) is inferior to the first fluid pressure (PI).

3. Method (100) as claimed in any one of the preceding claims wherein, prior to pressurizing the autofrettage fluid (AF), the second autofrettage step (140) comprises a second sealing step (142) during which are arranged a sealing feature (90) over the first extremity (22), a plurality of sealing features (82) to close high pressure channels (58) radially provided in the rail (12) and also, an autofrettage machine nozzle (84) arranged over the second extremity (26).

4. Method (100) as claimed in any one of the preceding claims wherein the second autofrettage step (140) is performed before the first autofrettage step (130).

5. Method (100) as claimed in claim 1 wherein the first and the second autofrettage steps (130, 140) are performed simultaneously.

6. Method (100) as claimed in any one of the preceding claims further comprising:

- a third step of autofrettage (150) for treating the second female threaded recess (44), a third fluid pressure (P3) being applied during this third step.

7. Method (100) as claimed in the claim 6 wherein the third fluid pressure (P3) is inferior to the first fluid pressure (PI).

8. A common rail (12) adapted to be arranged in a fuel injection system, the common rail (12) having a body (18) provided with a bore (28) defining an internal volume (V) for receiving, in use, high pressure fuel, said body (18) extending along a main axis (X) from a first extremity (22) having a first transverse face (20) wherein centrally opens a first threaded female recess (30) adapted to receive a pressure sensor (14) to, a second extremity (26) having a second transverse face (24) wherein centrally opens a second threaded female recess (44) adapted to receive a fuel pressure regulating valve (16), the bore (28) opening at both ends in one of the recesses (30, 44), characterized in that

the first threaded recess (30) and/or second threaded recess (44) are/is entirely reinforced by autofrettage.

9. A common rail (12) as claimed in claim 8 wherein the autofrettage reinforcement is done by applying a method as claimed in any one of the claims 1 to 7.