EP3141738A1

EP3141738A1 - Hydraulic lash adjuster arranged in a servo injector

Info

Publication number: EP3141738A1
Application number: EP16187250.2A
Authority: EP
Inventors: Alexandre TORRESANI; Christophe Tapin
Original assignee: Delphi Technologies Inc
Current assignee: Delphi Technologies Inc
Priority date: 2015-09-08
Filing date: 2016-09-05
Publication date: 2017-03-15
Also published as: GB201515892D0

Abstract

A hydraulic lash adjuster (HLA) (20) adapted to be arranged in a hydraulic volume interposed between the actuator (18) and the control valve assembly (22) of a servo injector, the HLA (20) comprising a cup-like shape lower piston (52) having a cylindrical peripheral wall (54) open at one end and closed by a bottom wall (58) at the other end, an upper piston (46) slidably guided with clearance fit in the cup-like shape lower piston (52), an internal spring (64) compressed between the bottom face (58) of the lower piston and the under face of the upper piston. The HLA (20) is further provided with at least one spill hole (60) provided through the peripheral wall (54) of the lower piston (52).

Description

TECHNICAL FIELD

The present invention relates to a hydraulic lash adjuster that is arranged in a servo injector.

BACKGROUND OF THE INVENTION

Servo injectors provided with piezo or magneto restrictive actuator are provided with hydraulic lash adjuster (HLA) in order to transmit force of displacement from the actuator to a control valve, while compensating for minor dimensional variations due to wear or heat dilation. Therefore, the control valve commutes between an open position where pressure drops in a control chamber enabling injection event and, a closed position where said pressure rises forbidding fuel injection event.
Application GB1420017 filed 11 Novembre 2014 discloses a compact HLA having a cup-like shape lower piston within which is slidably engaged with clearance fit an upper piston. In use the hydraulic volume and the internal volume between the pistons at the bottom of the cup-like shape are filled with fuel, an internal spring being arranged in said volume compressed between the bottom face of the lower piston and the under face of the upper piston.
During the assembly process, the internal spring is positioned at the bottom of the cup-like shape which is filled with fuel prior to engaging the upper piston and, when further engaging the upper piston, the fuel evacuates with difficulty through the small clearance between said two pistons.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to resolve or at least mitigate the above mentioned problems in providing a hydraulic lash adjuster (HLA) adapted to be arranged in a hydraulic volume interposed between the actuator and the control valve assembly of a servo injector, the HLA comprising
a cup-like shape lower piston having a cylindrical peripheral wall open at one end and closed by a bottom wall at the other end, an upper piston slidably guided with clearance fit in the cup-like shape lower piston, an internal spring compressed between the bottom face of the lower piston and the under face of the upper piston. In use the hydraulic volume and the internal space between the pistons at the bottom of the cup-like shape lower piston are filled with fuel F. The HLA is further provided with at least one spill hole provided through the peripheral wall of the lower piston.
The at least one spill hole is at a distance from the bottom wall of the lower piston so that, in use, the hole is closed by the upper piston, said distance being slightly superior to the distance between the bottom wall of the lower piston and the under face of the upper piston.
In an alternative, the lower piston may be further provided with a plurality of spill holes arranged on the peripheral wall, each hole being arranged at a distance superior or equal to said minimized distance.
The spill holes have a diameter comprised between 1µm and 300µm.
The invention further extends to a method to assemble a HLA as described above, the method comprising the steps of:

providing a cup-like shape lower piston having a cylindrical peripheral wall open at one end and closed by a bottom wall at the other end, an upper piston adapted to be slidably guided with clearance fit in the cup-like shape lower piston, and an internal spring adapted to be arranged on the bottom face of the lower piston;
arranging the internal spring at the bottom of the cup-like shape lower piston;
filling the cup-like shape lower piston with fuel;
presenting the upper piston before the opening of the peripheral wall of the lower piston, the inner volume of the cup-like shape lower piston being filled with fuel;
engaging the upper piston to slidably in the lower piston; forcing the fuel to evacuate via the spill hole provided in the peripheral wall.

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 servo fuel injector provided with a hydraulic lash adjuster as per the invention.
Figure 2 is a magnified view of the HLA of figure 1.
Figure 3 is an initial step of the assembly process of the HLA.
Figure 4 is a further engaging step of the HLA.
Figure 5 is the final operational stage of the assembly of the HLA.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

To ease and clarify the following description the top-down orientation of the figures is arbitrarily chosen and, words and expressions such as "above, under, over, below..." may be utilized without any intention to limit the invention. Also, similar features fulfilling similar functions in different embodiments may be identified with same reference numbers.
Figure 1 represents a servo fuel injector 10 which extends generally along a main axis A1 from an injector head 12, arbitrarily drawn at the top of the figure, to an injector nozzle 14, drawn at the bottom of the figure. The injector 10 mainly comprises an injector body 16 constituted of the assembly of several components fixed to each other and, in said body 16 are arranged, from head 12 to nozzle 14, a servo actuator 18, that is either a piezo or a magneto restrictive actuator, a hydraulic lash adjuster (hereafter HLA) 20, a control valve assembly 22 and a needle valve 24. Also, electrical links 26 are provided to energize the servo actuator 18, said electrical links extending from the actuator 18 to a connector 28 arranged on the injector head 12 of the injector 10.
The actuator 18 and the control valve assembly 22 extend along a second axis A2 parallel and offset for the main axis A1 that is also the axis of the needle valve 24.
The persons skilled in the art are invited to learn from GB 1314826 about the detailed operation of the control valve assembly 22.
The injector body 16 further accommodates a high pressure circuit 34, extending from an inlet 36 arranged in the injector head 12 to a plurality of spray holes 38 arranged a the tip of the nozzle 14 and, a low pressure return circuit 40 extending from the control valve 22 to an outlet 42 also arranged in the head 12 of the injector. The high pressure circuit 34 and the low pressure circuit 40 interconnect in the area of the control valve 22.
For illustration purposes and without any intent to limit the present invention, nor to detail the operation of fuel injection equipment's, the "high pressure" is typically superior to 2000 bars, or 2500 bars or even 3000 bars.
As can be seen on the figures, the HLA 20 is arranged in a volume V that, in use, is filled with fuel.
The HLA 20 is now described in reference to figure 2 where it axially extends along the second axis A2 and it comprises an upper piston 46 having a cylindrical body 48 covered by a head cap 50 radially extending beyond the peripheral edges of cylindrical body 48. The upper piston 46 is axially slidably arranged in cup-like lower piston 52.
Said lower piston 52 has a peripheral cylindrical wall 54 defining an internal bore, and a bottom wall 58 forming the cup-like shape. In the peripheral wall 54 is arranged at least one spill hole 60, only one being visible on the figure, creating fluid communication between the inside of the internal bore and the outside of the HLA 20. The spill hole 60 has a diameter D of few tens of micrometers and it is arranged at distance X from the bottom wall 58 of the piston, said distance X being a minimum distance X that will be explained below. In an alternative, the peripheral wall 54 of the lower piston could be provided with a plurality of spill holes 60 arranged from the top of the peripheral wall down to the bottom wall 58. Below the bottom wall 58, the peripheral wall 52 downwardly extends toward a lower rest face. At the centre of the under face of the bottom wall 58 downwardly extends a protrusion that, in use, contacts the upper face of the top of the stem of the control valve 22.
Inside the cup-like lower piston 52, against the bottom wall 58 is arranged a disc spring assembly 64 comprising a lower disc 66, an adjusting shim 68 and an upper disc 70, the leaf-spring assembly 64 being sandwiched between the bottom wall 58 of the lower piston 52 and the under face of the upper piston 46.
The minimum distance X at which the spill hole 60 can be arranged is chosen to be above the under face of the upper piston so that, in operation, when the upper piston 46 is in place and the disc spring 64 is compressed, the spill hole 60 is closed by the upper piston 46.
The HLA 20 further comprises a cylindrical cage spring 72 externally surrounding the peripheral wall 54 of the lower piston 52 and axially compressed between a transversal face of the injector body 16, said face being known by the skilled person as the upper face of the valve body and, the under face of the protruding portion of the upper piston cap-head 50. Cage springs are also known by persons skilled in the art of servo fuel injectors under the name of tubular springs or sleeve springs. A typical cage spring has a tubular body extending along an axis, the cylindrical wall of the body being provided with plurality of elongated transverse apertures. The cage spring 72 has very high compression stiffness, much higher than the stiffness of the disc-spring assembly 64 and, the cage-spring 72 permanently solicits upwardly the upper piston 46 toward the actuator 18.
A quick explanation of the HLA 20 operation is now provided. When the actuator 18 is not energized it retracts. The cage spring 72 axially expands and upwardly displaces the upper piston 46. The low stiffness disc spring assembly 64 downwardly pushes the lower piston 52 so the protrusion comes in contact against the stem of the control valve 22 without exercising sufficient force to open said valve and thus, spray of fuel is forbidden.
When the actuator 18 is energized, it elongates and downwardly solicits the upper piston 46. The downward displacement of the upper piston 46 compresses the cage-spring 72. The fuel captured below the upper piston 46 at the bottom of the lower piston 52 compresses and, consequently the disc spring assembly 64 also compresses to the point that the force generated by the actuator 18 is integrally transmitted to the lower piston 52 which then, opens the valve, and consequently enables fuel spray through the nozzle 14.
In order to minimize mass, and especially mass of moving components so that inertia is reduced and fast displacements is made possible, the upper piston 46 can be made hollow its cylindrical body 48 and its cap head 50 being distinct components are fixed to each other after being machined.
The assembly method 100 of the HLA 20 is now described in relation to figures 3, 4 and 5.
Figure 3 illustrates a presentation step 102 of the assembly method where the cup-like shape lower piston 52 is filled with fuel F and the disc spring 64 is place against the bottom wall 58.
The upper piston 46 is presented above the opening of the opening of the lower piston.
Figure 4 illustrates an engagement step 104 of the assembly method 100 where the upper piston 46 is slidably engaged in the lower piston 52; the fuel is then evacuated through the spill hole 60.
There, is understandable that an alternative where the lower piston would be provided with a plurality of spill holes 60 arranged along the peripheral wall, said plurality of holes 60 enabling evacuation of the fuel F, the engagement of the upper piston 46 closing the holes one by one as the upper piston further moves toward its final position.
Figure 5 illustrates the final stage 106 of the assembly where the upper piston 46 is totally engaged in the lower piston 52, the disc spring 64 being compressed between the two pistons. The spill hole 60 is closed by the upper piston 46 which defines the minimum distance X at which the spill hole 60 is placed. Indeed, the minimum distance X is small enough so that the spill hole 60 is not closed too soon during the engagement of the upper piston 46 and, said minimum distance X is important enough so that the spill hole 60 is indeed closed when the upper piston 46 is finally in place.

LISTS OF REFERENCES

A1: main axis
A2: second axis
V: volume wherein is arranged the lash adjuster
D: diameter of the spill hole
X: minimum distance from the bottom wall to the spill hole
F: fuel

10: injector
12: head of the injector
14: nozzle of the injector
16: injector body
18: actuator
20: hydraulic lash adjuster
22: control valve
24: needle
26: electrical links
28: connector
34: high pressure circuit
36: inlet
38: spray holes
40: low pressure return circuit
42: outlet
46: upper piston
48: cylindrical body
50: head cap
52: lower piston
54: peripheral wall
58: bottom wall
60: spill hole
64: disc-spring
66: lower disc
68: adjusting shim
70: upper disc
72: cage spring

100: Assembly method
102: presentation step
104: engagement step
106: final step

Claims

Hydraulic lash adjuster (HLA) (20) adapted to be arranged in a hydraulic volume (V) interposed between the actuator (18) and the control valve assembly (22) of a servo injector (10), the HLA (20) comprising:
a cup-like shape lower piston (52) having a cylindrical peripheral wall (54) open at one end and closed by a bottom wall (58) at the other end,

an upper piston (46) slidably guided with clearance fit in the cup-like shape lower piston (52),

an internal spring (64) compressed between the bottom face (58) of the lower piston and the under face of the upper piston, and wherein in use,

the hydraulic volume (V) and the internal space between the pistons at the bottom of the cup-like shape lower piston are filled with fuel (F), characterized in that

the HLA (20) is further provided with at least one spill hole (60) provided through the peripheral wall (54) of the lower piston (52).
HLA (20) as claimed in the preceding claim wherein the at least one spill hole (60) is at a distance (X) from the bottom wall (58) of the lower piston (52) so that, in use, the hole (60) is closed by the upper piston (46).
HLA (20) as claimed in claim 2 wherein the distance (X) is slightly superior to the distance between the bottom wall (58) of the lower piston and the under face of the upper piston (46).
HLA (20) as claimed in claim 3 wherein the lower piston (52) is provided with a plurality of spill holes (60) arranged on the peripheral wall (54), each hole (60) being arranged at a distance superior or equal to the minimized distance (X).
HLA (20) as claimed in any one of the preceding claims wherein the spill holes (60) have a diameter comprised between 10µm and 300µm.
Method (100) to assemble a HLA (20) as claimed in any one of the preceding claims, the method (100) comprising the steps of:
- providing a cup-like shape lower piston having a cylindrical peripheral wall open at one end and closed by a bottom wall at the other end, an upper piston adapted to be slidably guided with clearance fit in the cup-like shape lower piston, and an internal spring adapted to be arranged on the bottom face of the lower piston;

- arranging the internal spring at the bottom of the cup-like shape lower piston;

- filling the cup-like shape lower piston with fuel;

- presenting (102) the upper piston before the opening of the peripheral wall of the lower piston, the inner volume of the cup-like shape lower piston being filled with fuel;

- engaging (104) the upper piston to slidably in the lower piston; forcing the fuel to evacuate via the spill hole (60) provided in the peripheral wall.