Hydraulic lash adjuster

Abstract

 A hydraulic lash adjuster for a valve train of an internal combustion engine comprises a body (18) having a plunger chamber (19); a hollow plunger (20) reciprocally mounted in the plunger chamber (19) of the body (18), the plunger (20) having an upper part (22) with an oil bore (24) that protrudes out of the plunger chamber (19) for engaging a socket (164) of a rocker arm (16) of a valve train; and a high-pressure chamber (28). A partition wall (32) divides the interior of the hollow plunger into two chambers.

Description

FIELD OF THE INVENTION

[0001] The present invention generally relates to a hydraulic lash adjuster, in particular the one used as fixedly mounted pivot point in a valve train using rocker arm assemblies with integrated switching function.

BACKGROUND OF THE INVENTION

[0002] In an engine valve train equipped with rocker arm assemblies with integrated switching device, hydraulic lash adjusters are mainly used to take up clearance within the valve train and to control the actuation of the rocker arms switching function.

[0003] Such a hydraulic lash adjuster (HLA) is e.g. described in US 5,509,385. The HLA comprises a cylindrical body with a plunger chamber and a hollow plunger cap which is reciprocally mounted within this plunger chamber in the body. The upper part of the plunger cap protrudes out of the body and there is an oil bore in this upper part to communicate with the hollow interior of the plunger cap. Oil ports are arranged in side walls of the cap and body to supply oil from the engine to the hollow interior of the plunger cap. The HLA further comprises a high-pressure chamber between the lower end of the plunger cap and the bottom of the plunger chamber. This high-pressure chamber is connected to the hollow interior of the plunger chamber via an oil passage provided with a check valve to prevent the return flow of oil into the hollow plunger cap.

[0004] Basically, the end of the plunger cap engages into a socket in the rocker arm. The lash adjuster will receive pressurized oil from the engine lubricating pump through an oil gallery and this oil will pass through the oil ports in the body and plunger cap to reach the hollow plunger interior.

[0005] Actuation of the rocker arm switching function is conducted by raising the oil pressure high enough in the oil feed gallery to still maintain lash adjustment but also to actuate the two-step rocker arm by moving a lock mechanism (switching device) within the rocker arm. A problem with such an HLA is linked to the fact that high oil pressure in the engine is limited, especially under hot idle conditions. Therefore, current control schemes only dispose of small pressure variations for the actuating function of the HLA, making the actuation slow, insecure and with lots of variations.

OBJECT OF THE INVENTION

[0006] The object of the present invention is to provide an improved hydraulic lash adjuster. This object is achieved by a hydraulic lash adjuster as claimed in claim 1.

SUMMARY OF THE INVENTION

[0007] According to the present invention, a hydraulic lash adjuster for a valve train of an internal combustion engine comprises a body having a plunger chamber, in which a hollow plunger is reciprocally mounted. The plunger has an upper part with an oil bore that protrudes out of the plunger chamber for engaging a socket of a rocker arm of the valve train. A high-pressure chamber is arranged between the lower end of the plunger and the bottom of the plunger chamber. According to an important aspect of the invention, a partition wall divides the interior of the hollow plunger into two chambers. A first chamber has a first oil port and is in fluid communication with the oil bore in the protruding upper part of the hollow plunger. A second chamber has a second oil port and is connected to the high-pressure chamber via an oil passage.

[0008] The HLA of the invention allows a separate and independent control of the lash adjustment function and the actuating/switching function. On the one hand, the lash adjustment is achieved by supplying oil to the second chamber in order to fill the high-pressure chamber and thereby move the hollow plunger to adjust the valve lash. On the other hand, controlled oil pressure is fed to the first chamber in order to supply oil at controlled pressure to an associated rocker arm with integrated switching device via the oil bore in the protruding upper plunger part.

[0009] The pressure in the second chamber may thus typically be that of the engine lubrication circuit, which is susceptible to uncontrolled variations e.g. due to engine temperature, ambient temperature, engine speed, etc. On the other hand, the oil pressure in the first chamber is preferably controlled to vary between predetermined pressures in order to permit switching of the latch (switching device) in the rocker arm assembly. Due to the use of two separate chambers, the oil pressure in the first chamber can be controlled independently from the second chamber, which is typically fed from the engine lubrication circuit. As a result, the present HLA permits an enhanced switching control, that globally leads to improved valve timing control and engine operation.

[0010] Preferably, the partition wall is formed by an element that is press-fitted inside the hollow plunger. This is a simple way of dividing the interior of the hollow plunger into two chambers. It will however be understood that there are many different ways to design such a partition wall dividing the plunger interior into two chambers. The partition wall could e.g. be integrally formed with the hollow plunger. The partition wall may also be inserted in the plunger and secured therein by any suitable means. The hollow plunger could also consist of two separate parts, the partition wall being formed by a wall of at least one of these elements.

[0011] In a preferred embodiment, the plunger is made from a generally cylindrical tube and the upper part ends by a semi-spherical nose in which the oil bore is provided. The semi-spherical nose may be obtained by roll-forming. In such a case, the partition wall advantageously is a cup-shaped element that is press-fitted into the hollow plunger interior before roll-forming of the plunger nose.

[0012] Advantageously, plunger biasing means are provided to bias the hollow plunger in the outward direction for an improved lash adjustment. The plunger biasing means preferably comprise a spring arranged in the high-pressure chamber. Furthermore, a check valve is preferably provided to prevent the return flow of oil from the high-pressure chamber into the second chamber. This check valve may comprise a spring loaded ball in the high-pressure chamber that cooperates with a valve seat in the oil passage leading from the high-pressure chamber to the second chamber.

[0013] Preferably, the first and second oil ports are arranged in the lateral walls of the hollow plunger. In such a case, the body is provided for each oil port in the plunger with a respective oil bore in the lateral sides of the body. These cooperating body bores and plunger ports are designed so as to overlap in any position of the plunger.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The present invention will now be described, by way of example, with reference to the accompanying drawing, in which:

FIG. 1: is a partial section view through a preferred HLA arranged in a cylinder head and engaging a two step finger follower rocker arm.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0015] Fig. 1 shows a preferred embodiment of a hydraulic lash adjuster 10 in accordance with the invention that is located in a cylinder head 12 of an internal combustion engine. Such a HLA 10 is typically provided as a complete assembly ready to be mounted in the cylinder head 12. The HLA's 10 function is to take up clearance within the engine valve train and to control the actuation of switching device of the rocker arms of the valve train. Accordingly, the HLA 10 engages a socket 164 in a rocker arm assembly generally indicated 16, comprising inner and outer arms 162 and 163. Briefly, the rocker arm assembly 16 typically has an oil channel 161 that is supplied with pressurized oil from the HLA 10 and that leads from the socket 164 to a piston assembly (not shown) in order to actuate a latch (not shown) fixedly connected to the piston assembly. The latch is moveable between two positions, which enables the rocker arm assembly 16 to be operated in a first and a second valve lift capability position.

[0016] The present HLA 10 comprises a body 18 of preferably cylindrical shape having a plunger chamber 19, in which a hollow plunger 20 is reciprocally mounted. This hollow plunger 20 has an upper part 22 (i.e. the part directed towards the rocker arm assembly 16) that protrudes out of the cylindrical body 18 and that preferably ends by a semi-spherical nose shape. The plunger nose 22 engages the socket 164 in the rocker arm assembly 16 and is provided with an oil bore 24. The plunger 20 is preferably spring loaded by a cylindrical spring 26, which urges the hollow plunger 20 towards the rocker arm assembly 16. The cylindrical spring 26 is located in a high-pressure chamber 28 in the lower part (away from the rocker arm assembly 16) of the HLA 10. The high-pressure chamber 28 is actually defined by the lower end of the hollow plunger 20 and the closed bottom 30 of the cylindrical body 18. To limit the displacement of the hollow plunger 20, a crimped flange 28 is advantageously arranged at the open end of the cylindrical body 18, this crimped flange 28 being typically put in place after the complete HLA has been assembled. This flange 28 also avoids any accidental dismounting of the HLA during handling.

[0017] It will be appreciated that the HLA 10 further comprises a partition wall 32 dividing the interior of the hollow plunger 20 into two chambers 34 and 36. The first chamber 34 has a first oil port 38 and is in fluid communication with the oil bore 24 in the protruding plunger nose 22. The second chamber 36 has a second oil port 40 and is connected to the high-pressure chamber via an oil passage 42.

[0018] Such a structure of the HLA 10 allows to separate the control of the lash adjusting function and the actuating function. Indeed, since the partition wall 32 divides the hollow plunger 20 into two chambers 34 and 36 hydraulically sealed from each other, the pressures in the two chambers 34, 36 can be controlled independently.

[0019] Therefore, the body 18 has in its lateral side a first oil bore 44 that coincides with the first oil port 38 in the plunger 20 and is in fluid communication with a first oil gallery 46 in the cylinder head 12. The body 18 further includes in its lateral side a second oil bore 48 that coincides with the second oil port 40 in the plunger 20 and is in fluid communication with a second oil gallery 50 in the cylinder head 12. The coinciding oil ports and bores in plunger 22 and body 18 are designed so as to overlap in any axial position of the plunger 22. Furthermore, as can be seen, each oil bore 44, 48 in the body 18 is in fluid communication with its respective oil gallery 46, resp. 50, via an annular groove 52, resp. 54, on the body's external surface. These annular grooves 52 and 54 ensure that at tolerance stack-up, the oil feed bores can still be supplied with oil.

[0020] The lash adjusting function of the HLA 10 is controlled by supplying pressurized oil to the second chamber 36 from the second oil gallery 50. Basically, the hollow plunger 20 is urged towards the assembly 16 by the cylindrical spring 26 thereby suppressing any lash between the protruding upper part or nose 22 of the hollow plunger 20 and the assembly 16. The second chamber 36 and the high-pressure chamber 28 are initially filled with pressurized oil from the second gallery 50. A check-valve 56 is preferably provided in the oil passage 42 between the second chamber 36 and the high-pressure chamber 28 to prevent the return flow of oil into the second chamber 36. The check valve 56 comprises a ball 58 urged by a spring (not shown) against an annular seat 60 formed at the beginning of the oil passage 42 when seen from the high-pressure chamber 28. During a valve lift, an effort is exerted from the assembly 16 on the hollow plunger 20. This effort will put the oil contained in the high-pressure chamber 28 under pressure and force the check-valve 26 onto its seat so that the high-pressure chamber 28 is sealed. Due to oil incompressibility, the HLA 10 will form a rigid stud on which the assembly 16 can be supported. If the lash in a valve train region increases over time (due e.g. to wear of valve train parts), the spring 26 will urge the hollow plunger 20 so as to absorb the gap and as a result, the high-pressure chamber 28 will fill up with oil via the oil passage 42 when no effort is exerted on the HLA 10, typically when the valve is not lifted. A decrease in valve train lash will cause the plunger to seek in the housing, which is allowed by emptying of the high-pressure chamber due to a small oil leakage between housing and plunger (due to a design clearance), as is conventional in the art.

[0021] Referring now to actuating function of the HLA 10, this is achieved through the first chamber 34. Oil is supplied to the first chamber 34 at different pressures from the oil gallery 46 in order to move the latch 163 between its two positions, thereby allowing switching between the first and second valve lift modes. Also, the oil exiting the plunger nose 22 at the interface with the socket 164 permits to lubricate this contact.

[0022] In the present embodiment, engine oil is fed to the second chamber 36 at standard pressures from the second oil gallery 50, as with conventional HLA, for the purpose of lash adjustment.

[0023] In order to control the switching function of the HLA 10, the oil delivered by the first oil gallery 46 is preferably controlled by means of a control solenoid. The switching of the rocker arm would be performed by varying the pressure in this gallery 46 between a high pressure (e.g. engine oil pressure) and a low pressure (e.g. zero or very low controlled pressure). Furthermore, to avoid the first gallery and the first chamber to bleed empty, the control solenoid could either have a calibrated leak into this gallery or maintain some very low pressure level (e.g. 20kPa).

[0024] It remains to be noted that the hollow plunger is typically formed from a tubular body, the end of which is roll-formed so that it ends by the semi-spherical nose. Therefore, the partition wall 32 preferably is a cup-shaped element that is press-fitted into the hollow plunger 20 before the extremity of the latter is roll formed. This is a simple and cost efficient way to arrange the partition wall inside the plunger 20.

LIST OF REFERENCE SIGNS

[0025] 

10

hydraulic lash adjuster

12

cylinder head

16

rocker arm assembly

161

oil channel

162

inner arm

163

outer arm

164

socket

18

body

19

plunger chamber

20

hollow plunger

22

plunger nose

24

oil bore

25

abutment ring

26

cylindrical spring

28

high-pressure chamber

30

closed bottom

32

partition wall

34

first chamber

36

second chamber

38

first plunger oil port

40

second plunger oil port

42

oil passage

44

first body oil bore

46

first oil gallery

48

second body oil bore

50

second oil gallery

52

first annular groove

54

second annular groove

56

check valve

58

ball

60

valve seat

Claims

1. A hydraulic lash adjuster for a valve train of an internal combustion engine comprising:

a body having a plunger chamber;

a hollow plunger reciprocally mounted in said plunger chamber of said body, said plunger having an upper part with an oil bore that protrudes out of said plunger chamber for engaging a socket of a rocker arm of a valve train;

a high-pressure chamber arranged between the lower end of said plunger and the bottom of said plunger chamber;

characterised by

a partition wall dividing the interior of said hollow plunger into two chambers:

a first chamber having a first oil port and being in fluid communication with said oil bore in said protruding upper part of said hollow plunger;

a second chamber having a second oil port and being connected to said high-pressure chamber via an oil passage.

2. The hydraulic lash adjuster according to claim 1, characterised in that said partition wall is formed by an element that is press-fitted inside said hollow plunger.

3. The hydraulic lash adjuster according to claim 1 or 2, characterised in that said plunger is made from a generally cylindrical tube and said upper part ends by a semi-spherical nose in which said oil bore is provided.

4. The hydraulic lash adjuster according to claim 3, characterised in that said semi-spherical nose is formed by roll-forming of an extremity of said tube.

5. The hydraulic lash adjuster according to any one of the preceding claims, characterised by plunger biasing means to bias said hollow plunger in the outward direction.

6. The hydraulic lash adjuster according to claim 5, characterised in that said plunger biasing means comprise a spring arranged in said high-pressure chamber.

7. The hydraulic lash adjuster according to any one of the preceding claims, characterised by a check valve in said oil passage between said second chamber and said high-pressure chamber to avoid return flow of oil in said second chamber.

8. The hydraulic lash adjuster according to claim 7, characterised in that said check valve comprises a ball biased against a valve seat by means of a spring.

9. The hydraulic lash adjuster according to any one of the preceding claims, characterised in that said body has a first oil feed bore associated with said first oil port of said hollow plunger; and
   said body has a second oil feed bore associated with said second oil port of said hollow plunger.

Drawing