WO2012043277A1

WO2012043277A1 - Lash adjuster

Info

Publication number: WO2012043277A1
Application number: PCT/JP2011/071225
Authority: WO
Inventors: 将司卜藏; 前野　栄二
Original assignee: Ntn株式会社
Priority date: 2010-09-29
Filing date: 2011-09-16
Publication date: 2012-04-05
Also published as: JP2012072724A

Abstract

Provided is a lash adjuster which enables a thread surface to resistant to wear and ensures a certain level of frictional coefficient between thread surfaces for a long period of time even in a Diesel engine in which a large amount of carbon soot is mixed with an engine oil. The lash adjuster (1) includes a nut member (17) having a female screw thread (16) on the inner circumference; an adjusting screw (19) having a male screw thread (18) on the outer circumference, the male screw thread being brought into screw engagement with the female screw thread (16); and a return spring (20) for exerting a force on the adjusting screw (19). The adjusting screw (19) is axially moved while rotating through the nut member (17), thereby adjusting a gap between component members of a valve actuating device. The lash adjuster (1) is adapted such that the adjusting screw (19) has a scratch-brush finished thread surface (19a) and the thread surface (19a) is provided thereon with a high-hardness carbide layer (27) which has a hardness equal to or greater than Hv1500.

Description

Rush adjuster

This invention relates to a lash adjuster for adjusting a gap between constituent members of a valve operating apparatus in an internal combustion engine.

In a valve operating device that operates an intake valve or an exhaust valve by rotation of a cam, a gap between the components of the valve operating device changes due to a difference in thermal expansion that occurs between the components of the valve operating device during engine operation. There is a risk that abnormal noise or compression leakage may occur due to a change in the gap. Further, even if the sliding portion of the valve operating device is worn, the gap between the constituent members of the valve operating device changes, and there is a possibility that abnormal noise is generated due to the change in the gap.

In order to prevent this abnormal noise and compression leakage, a lash adjuster is incorporated in the valve operating device, and the lash adjuster often absorbs a change in a gap between components of the valve operating device.

As such a lash adjuster, for example, a hydraulic lash adjuster using engine oil as a working fluid is known. However, the hydraulic lash adjuster is susceptible to changes in oil pressure due to engine speed, contamination and bubbles contained in engine oil. In addition, the structure is complicated, requiring a lot of man-hours for manufacturing and assembly, which is disadvantageous in terms of cost.

As a lash adjuster for solving this problem, there is a mechanical lash adjuster as described in

Patent Documents

1 and 2. The mechanical lash adjuster includes a nut member having an internal thread on the inner periphery, an adjustment screw having an external thread that engages with the female thread on the outer periphery, and a return spring that urges the adjustment screw in a direction protruding from the nut member. And when the gap between the components of the valve operating device changes due to thermal expansion of the valve operating device, etc., the adjusting screw moves in the axial direction while rotating in the nut member according to the change in the clearance. Thus, the gap between the constituent members of the valve gear is adjusted.

By the way, when the screw surface of the adjusting screw and the nut member is worn due to the long-term use of the lash adjuster, the surface roughness of the screw surface becomes small and the friction coefficient between the screw surfaces becomes small. In this case, when a load in the pushing direction is applied to the adjusting screw due to the rotation of the cam, excessive slip occurs between the screw surfaces, and the adjusting screw moves greatly in the pushing direction, resulting in the configuration of the valve operating device. There is a possibility that the gap between the members is enlarged and valve lift loss occurs. And if the magnitude | size of a valve lift loss exceeds the lamp height preset in the cam, when a valve closes, there exists a problem that a valve | bulb seats impacting on a valve seat and an abnormal noise arises.

In order to solve this problem, in the lash adjuster described in Patent Document 3, one screw surface of the adjusting screw and the nut member is a matte surface, and the surface of the thread surface that is the matte surface is Hv1000 or more and less than Hv1500. A DLC (diamond-like carbon) film having a hardness of 5 mm is provided, and the wear resistance of the thread surface is improved by this DLC film.

Japanese Utility Model Publication No. 64-34407 Japanese Patent Laid-Open No. 5-10109 Japanese Patent No. 4183598

Incidentally, the screw surfaces of the adjusting screw and the nut member are lubricated with engine oil. In general gasoline engines, carbon suit is hardly mixed in engine oil, so the wear of the thread surfaces is dominated by dual abrasive wear, where the thread surfaces are scraped together. It was possible to ensure sufficient wear resistance.

However, in a diesel engine, a large amount of primary particles made of carbon suit having a diameter of about 15 to 60 nm and secondary particles aggregated in a tuft of grapes are mixed in the engine oil. Therefore, the wear of the thread surface is dominated by ternary abrasive wear in which primary particles act as an abrasive between the thread surface. The primary particle of the carbon suit has a hardness of about Hv1000 to Hv1500, so the wear of the thread surface could not be sufficiently suppressed with the DLC film.

The problem to be solved by the present invention is to provide a lash adjuster capable of securing a friction coefficient between screw surfaces over a long period of time even in a diesel engine in which a large amount of carbon suit is mixed in engine oil. Is to provide.

In order to solve the above-mentioned problems, a nut member having an internal thread on the inner periphery, an adjustment screw having an external thread that engages with the internal thread on the outer periphery, and a return spring that biases the adjustment screw in a direction protruding from the nut member In the lash adjuster that adjusts the gap between the constituent members of the valve gear by rotating the adjusting screw in the axial direction while rotating in the nut member, one of the adjusting screw and the nut member The thread surface was a satin finish, and a high-hardness carbide layer having a hardness of Hv1500 or more was provided on the surface of the thread surface that was the satin finish.

In this way, even in a diesel engine in which a large amount of carbon suit is mixed in the engine oil, the hardness of the surface of the thread surface that is made of satin is equal to or higher than the hardness of the primary particles of carbon suit. Therefore, it is possible to ensure the friction coefficient between the screw surfaces over a long period of time. Therefore, a stable valve lift amount can be obtained over a long period of time.

The high-hardness carbide layer can be formed by a diffusion permeation treatment, and examples of such a high-hardness carbide layer include a chromium carbide layer, a vanadium carbide layer, and a titanium carbide layer.

When the high-hardness carbide layer is provided on the surface of the screw surface of the adjustment screw, in order to form a good high-hardness carbide layer, it is preferable that the carbon content of the base material of the adjustment screw is large. When there is too much, it will become difficult to form an adjustment screw by plastic processing, such as a header and rolling, and a manufacturing cost will rise. Therefore, if carburizing treatment is applied to the adjustment screw in advance and then a high-hardness carbide layer is formed on the surface of the screw surface, it is possible to achieve both good formation of the high-hardness carbide layer and plastic workability of the adjustment screw. It becomes. In this case, the completed adjustment screw has a carburized layer provided under the high-hardness carbide layer. As a base material of the adjusting screw at this time, SCM435 having a carbon content of 0.35 mass% can be employed.

The surface roughness of the threaded surface can be set in the range of Ra 1.6 μm to Ra 12.5 μm. When Ra is 1.6 μm or more, formation of an oil film between the screw surfaces can be suppressed, and a friction coefficient between the screw surfaces can be ensured. When Ra is 12.5 μm or less, it is possible to prevent the screw surfaces from being caught and to ensure the smooth operation of the adjusting screw.

The dimple shape of the thread surface that is the matte surface can have an equivalent circular diameter of φ50 μm to φ500 μm and a depth of 10 to 50 μm, and the load length at a depth of 5 μm from the outermost surface of the matte thread surface When the ratio is 10 to 80%, it is possible to maintain the recess for removing the oil film even after wear at the initial familiarization stage, while suppressing the partner attack of the thread surface.

The lash adjuster of the present invention is provided with a high-hardness carbide layer on the surface of the threaded surface, and the hardness is equal to or higher than the hardness of the primary particles of the carbon suit. The friction coefficient between the thread surfaces can be ensured over a long period of time. Therefore, even in a diesel engine in which a large amount of carbon suit is mixed in the engine oil, a stable valve lift amount can be obtained over a long period of time.

The front view which shows the valve operating apparatus incorporating the lash adjuster of embodiment of this invention 1 is an enlarged cross-sectional view near the lash adjuster in FIG. Sectional view along line III-III in FIG. Sectional view along line IV-IV in FIG. Enlarged view of the screw surface of the adjusting screw and nut member shown in FIG.

FIG. 1 shows a valve gear incorporating a lash adjuster 1 according to an embodiment of the present invention. This valve operating device can swing around a camshaft 2 that is rotationally driven in synchronization with a crankshaft (not shown) of an engine, a tappet 3 that is slidably supported up and down, and a rocker shaft 4. The rocker arm 5 is supported, the push rod 6 transmits power between the tappet 3 and the rocker arm 5, and the valve 9 opens and closes the intake port (or exhaust port) 8 of the cylinder head 7.

The valve 9 is integrally provided with a valve stem 10 that extends upward from the valve 9. The valve stem 10 is supported by a cylindrical valve stem guide 11 fixed to the cylinder head 7 so as to be slidable up and down. An annular spring retainer 12 is fixed to the upper outer periphery of the valve stem 10. A valve spring 13 is incorporated between the lower surface of the spring retainer 12 and the upper surface of the cylinder head 7. The valve spring 13 urges the valve stem 10 upward via the spring retainer 12, and the valve 9 is seated on the valve seat 14 by the urging force.

The cam 15 is formed integrally with the camshaft 2. The cam 15 has a base circle 15b and a cam peak portion 15a raised with respect to the base circle 15b on the outer periphery. The lower end of the tappet 3 is in sliding contact with the outer periphery of the cam 15, and the tappet 3 reciprocates following the contour of the cam 15.

The rocker arm 5 disposed above the tappet 3 is supported by the rocker shaft 4 at the center, and can swing around the rocker shaft 4 as a fulcrum. Further, the lash adjuster 1 is incorporated in one end portion of the rocker arm 5, and the other end portion of the rocker arm 5 is in contact with the upper end of the valve stem 10.

The lower end of the push rod 6 is supported by the upper end of the tappet 3, and when the tappet 3 reciprocates, the lower end of the push rod 6 reciprocates together with the tappet 3. The upper end of the push rod 6 supports one end portion of the rocker arm 5 via the lash adjuster 1, and when the tappet 3 is raised, the push rod 6 transmits the power of the tappet 3 and one end portion of the rocker arm 5. The other end of the rocker arm 5 pushes down the valve stem 10.

As shown in FIG. 2, the lash adjuster 1 includes a cylindrical nut member 17 having an internal thread 16 on the inner periphery, an adjustment screw 19 having an external thread 18 that engages with the internal thread 16 on the outer periphery, and the adjustment screw 19. The return spring 20 is urged in a direction protruding from the nut member 17. The protruding end of the adjusting screw 19 from the nut member 17 is in contact with the upper end of the push rod 6.

The nut member 17 is provided by being inserted through a fitting hole 21 penetrating the end of the rocker arm 5 vertically. A flange 22 that is in contact with the lower surface of the rocker arm 5 is integrally provided at the lower end of the nut member 17. As shown in FIG. 4, a flat surface 22 a is formed on the outer periphery of the flange 22, and this flat surface 22 a engages with a stopper surface 5 a formed on the lower surface of the rocker arm 5 to prevent the nut member 17 from rotating. is doing.

As shown in FIG. 2, a retaining ring 23 that prevents the nut member 17 from coming off from the fitting hole 21 is attached to a protruding portion of the nut member 17 upward from the fitting hole 21. A wave spring 24 is incorporated between the retaining ring 23 and the rocker arm 5 in order to absorb the axial play of the nut member 17.

The return spring 20 is a torsion coil spring. The lower end of the return spring 20 is locked in a locking hole 25 formed on the outer periphery of the nut member 17, and the upper end of the return spring 20 is a locking groove 26 formed on the upper end of the adjusting screw 19 as shown in FIG. 3. Due to the torsional deformation, the adjusting screw 19 is given a rotational force in a direction in which the adjusting screw 19 protrudes downward from the nut member 17.

As shown in FIG. 2, the male screw 18 and the female screw 16 are such that the flank angle of the pressure side flank that receives pressure when a load in the direction of pushing the adjusting screw 19 into the nut member 17 is applied is the flank angle of the play side flank. It is formed in a larger sawtooth shape.

As shown in FIG. 5, the screw surface 19a of the adjusting screw 19 is a matte surface, and the surface roughness is set in the range of Ra 1.6 μm to Ra 12.5 μm. By setting Ra to 1.6 μm or more, formation of an oil film between the screw surface 19 a and 17 a of the adjusting screw 19 and the nut member 17 can be suppressed, and a friction coefficient between the screw surfaces 19 a and 17 a can be ensured. Further, when Ra is set to 12.5 μm or less, the adjustment screw 19 can be prevented from being caught between the screw surfaces 19 a and 17 a of the nut member 17, and the smooth operation of the adjustment screw 19 can be ensured. In consideration of manufacturing variations and the fact that the surface roughness of the screw surface 19a becomes small due to long-term use, the surface roughness of the screw surface 19a of the adjusting screw 19 is in the range of Ra 2.0 μm to Ra 4.0 μm. It is more preferable to set.

Further, the dimple shape of the screw surface 19a of the adjusting screw 19 has an equivalent circular diameter of 50 μm to φ500 μm and a depth of 10 to 50 μm when the area of the dimple is replaced with a circle area, and further from the outermost surface of the screw surface 19a. The load length ratio at a position of 5 μm is 10 to 80%. Accordingly, it is possible to maintain the recess for removing the oil film even after the wear at the initial familiarization stage, while suppressing the opponent attack of the thread surface 19a.

Here, the load length rate is a ratio of the load length of the contour curve element at the cutting level to the evaluation length. Japanese Industrial Standard “Product Geometric Specification (GPS) —Surface Properties: Contour Curve Method—Terminology” It complies with “Definitions and surface texture parameters” (JISB0601: 2001).

When the surface roughness of the threaded surface 17a of the nut member 17 is Ra 1.0 μm or more, such as when the female thread 16 of the nut member 17 is formed by tapping, it is caught between the adjusting screw 19 and the threaded surfaces 19a, 17a of the nut member 17. Is likely to occur. Therefore, in order to prevent this catching and ensure a smooth operation of the adjusting screw 19, the root mean square roughness Rq (JIS B0601: 2001) of the screw surface 19a of the adjusting screw 19 is σ ₁ , and the nut member 17 It is preferable that the root mean square roughness Rq of the thread surface 17a is σ _{2 and} the size of the combined roughness σ (= (σ ₁ ² + σ ₂ ² ) ^1/2 ) is 5.0 μm or less. More preferably, it is 3.0 μm or less.

The adjust screw 19 is formed using a carbon steel or alloy steel (for example, SCM435) having a carbon content of 0.33 to 0.38 mass% as a base material. A high-hardness carbide layer 27 having a hardness of Hv1500 or higher is provided on the surface of the screw surface 19a of the adjusting screw 19. As the high-hardness carbide layer 27, a chromium carbide layer (about Hv1700) formed by chromization treatment that diffuses and permeates chromium on the surface, and a vanadium carbide layer (about Hv2500) formed by vanadium treatment that diffuses and permeates vanadium on the surface. ), A titanium carbide layer (about Hv 3000) formed by a titanizing treatment that diffuses and permeates titanium on the surface can be employed. Under the high-hardness carbide layer 27, a carburized layer (not shown) hardened by quenching and tempering is provided.

Such an adjusting screw 19 can be manufactured as follows, for example. First, the adjusting screw 19 is formed by subjecting a rough shape made of SCM435 (carbon content 0.33 to 0.38 mass%) to header processing and thread rolling. Next, shot blasting is performed on the screw surface 19a of the adjusting screw 19 to form a satin-like unevenness. Thereafter, the top of the textured unevenness of the thread surface 19a is removed by barrel polishing to make it flat. Thereby, it becomes possible to suppress that the screw surface 19a promotes wear of the screw surface 17a of the nut member 17. Next, the adjustment screw 19 is subjected to a carburizing process, and a carburized layer having a carbon concentration of 0.6 to 0.8% is formed on the surface of the screw surface 19 a of the adjusting screw 19. Subsequently, the thread surface 19a of the adjusting screw 19 is subjected to diffusion permeation processing (chromization processing, vanadizing processing, titanizing processing, etc.) to form a high hardness carbide layer 27 on the surface of the thread surface 19a. At this time, the surface temperature of the thread surface 19a rises to around 1000 ° C. Thereafter, quenching and tempering are performed to harden the carburized layer under the high-hardness carbide layer 27. If this quenching and tempering is performed after the diffusion and penetration treatment, the adhesion of the high-hardness carbide layer 27 can be enhanced.

Next, an operation example of the above-described lash adjuster 1 will be described.

When the camshaft 2 is rotated by the operation of the engine and the cam crest 15a of the cam 15 pushes up the tappet 3, the valve 9 is separated from the valve seat 14 and the intake port 8 is opened. At this time, although the axial load in the pushing direction is applied to the adjusting screw 19, the screw surface 19a of the adjusting screw 19 is received by the screw surface 17a of the nut member 17, and the axial position of the adjusting screw 19 is fixed. .

When the cam 15 further rotates and the cam crest 15 a passes the position of the tappet 3, the valve stem 10 is raised by the urging force of the valve spring 13, the valve 9 is seated on the valve seat 14, and the intake port 8 is close.

Strictly speaking, when the cam crest 15a of the cam 15 pushes up the tappet 3, a slight slip occurs between the adjusting screw 19 and the screw surfaces 19a and 17a of the nut member 17, and the adjusting screw 19 is pushed in the pushing direction by the slip. Although it moves slightly, when the cam crest 15a passes the position of the tappet 3 and the load in the pushing direction is released, the adjustment screw 19 moves in the protruding direction by the load applied from the return spring 20, Return to the original position.

Immediately after the start of the engine when the engine is cold, the valve (especially the exhaust valve) 9 and the valve stem 10 among the components of the valve operating device first rise in temperature and thermally expand, so the difference in thermal expansion from the other components May cause a gap between the valve 9 and the valve seat 14. However, at this time, even when the base circle 15b of the cam 15 is in the position of the tappet 3, the urging force of the valve spring 13 acts on the adjustment screw 19, so that the cam peak portion 15a of the cam 15 pushes up the tappet 3. The amount of protrusion of the adjusting screw 19 when the cam 15 further rotates and the load in the pushing direction is released is smaller than the amount of pushing of the adjusting screw 19. As a result, each time the cam 15 rotates, the adjustment screw 19 gradually moves in the pushing direction, and no gap is generated between the valve 9 and the valve seat 14.

Also, when the contact portion between the valve stem 10 and the rocker arm 5, the contact portion between the adjustment screw 19 and the push rod 6, the contact portion between the push rod 6 and the tappet 3, the contact portion between the tappet 3 and the cam 15, etc. As a result of the wear, a gap is generated between the components of the valve operating device, and the valve lift amount of the valve 9 may be insufficient. However, at this time, the protrusion of the adjusting screw 19 when the cam 15 rotates and the load in the pressing direction is released is larger than the pressing amount of the adjusting screw 19 when the cam crest 15a of the cam 15 pushes up the tappet 3. The amount increases. As a result, each time the cam 15 rotates, the adjusting screw 19 gradually moves in the protruding direction, so that the gap between the constituent members of the valve operating device is kept at zero, and the valve lift loss of the valve 9 does not occur.

Incidentally, during operation of the engine, the space between the screw 19a and 17a of the adjusting screw 19 and the nut member 17 is lubricated with engine oil splashed on the rocker arm 5. When the lash adjuster 1 is incorporated in a diesel engine, a large amount of primary particles of carbon suit of about Hv1000 to Hv1500 are mixed in the engine oil, so that the wear of the thread surfaces 19a and 17a is accelerated by the primary particles. There is a fear.

However, in the lash adjuster 1, the high hardness carbide layer 27 is provided on the surface of the thread surface 19 a which is a satin finish, and the hardness is equal to or higher than the hardness of the primary particles of the carbon suit, so the finish is finished. The threaded surface 19a is not easily worn, and the friction coefficient between the threaded surfaces 19a and 17a can be ensured over a long period of time. Therefore, even in a diesel engine in which a large amount of carbon suit is mixed in the engine oil, an excessive slip between the thread surfaces 19a and 17a hardly occurs, and a stable valve lift amount can be obtained over a long period of time. As a result, the engine output is stabilized and the engine burns completely, so that the exhaust gas can be kept clean. Moreover, since the behavior of the valve 9 is a faithful reproduction of the designed valve lift curve, the seating of the valve 9 is smooth, and excellent quietness can be obtained.

In the above embodiment, the male screw 18 and the female screw 16 of the lash adjuster 1 are sawtooth screws in order to suppress the amount of movement of the adjusting screw 19 in the pushing direction and stabilize the valve lift, but the male screw 18 and the female screw 16 are It is also possible to employ vertically symmetrical triangular screws and trapezoidal screws.

Moreover, in the said embodiment, although the screw surface 19a of the adjusting screw 19 is used as a satin surface among the adjusting screw 19 and the nut member 17, the high-hardness carbide layer 27 which has the hardness of Hv1500 or more was provided in the surface of the screw surface 19a. Instead of the threaded surface 19a, the threaded surface 17a of the nut member 17 may be a satin finish, and a high-hardness carbide layer 27 having a hardness of Hv1500 or more may be provided on the surface of the threaded surface 17a.

In the above embodiment, the torsion coil spring is used as the torsion spring that applies the rotational force in the direction protruding from the nut member 17 to the adjustment screw 19. However, instead of the torsion coil spring, another torsion spring such as a mainspring spring is used. May be adopted. Further, instead of the torsion spring, a compression coil spring that applies an axial force in a direction protruding from the nut member 17 to the adjustment screw 19 may be employed.

1 Rush Adjuster 16 Female Thread 17 Nut Member 17a Threaded Surface 18 Male Thread 19 Adjusting Screw 19a Threaded Surface 20 Return Spring 27 High Hardness Carbide Layer

Claims

A nut member (17) having an internal thread (16) on the inner periphery, an adjustment screw (19) having an external thread (18) threadedly engaged with the female thread (16) on the outer periphery, and the adjustment screw (19) as a nut member A return spring (20) that urges in a direction protruding from (17), and the adjustment screw (19) moves in the axial direction while rotating in the nut member (17), thereby In the lash adjuster that adjusts the gap between components,
Of the adjusting screw (19) and the nut member (17), one thread surface (19a) is a matte surface, and the surface of the mated thread surface (19a) is a high-hardness carbide layer (27 A lash adjuster characterized in that
The lash adjuster according to claim 1, wherein the high-hardness carbide layer (27) is formed by a diffusion permeation treatment.
The lash adjuster according to claim 1 or 2, wherein the high-hardness carbide layer (27) is a chromium carbide layer.
The lash adjuster according to claim 1 or 2, wherein the high-hardness carbide layer (27) is a vanadium carbide layer.
The lash adjuster according to claim 1 or 2, wherein the high-hardness carbide layer (27) is a carbide layer of titanium.
The high-hardness carbide layer (27) is provided on the surface of the screw surface (19a) of the adjustment screw (19), and a carburized layer is provided under the high-hardness carbide layer (27). The lash adjuster according to any one of the above.
The lash adjuster according to claim 6, wherein a base material of the adjusting screw (19) is SCM435.
The lash adjuster according to any one of claims 1 to 7, wherein a surface roughness of the thread surface (19a), which is the matte surface, is set in a range of Ra 1.6 µm to Ra 12.5 µm.
The lash adjuster according to any one of claims 1 to 8, wherein a dimple shape of the thread surface (19a), which is the matte surface, has an equivalent circular diameter of 50 µm to 500 µm and a depth of 10 to 50 µm.
The lash adjuster according to any one of claims 1 to 9, wherein a load length ratio at a depth of 5 µm from the outermost surface of the thread surface (19a), which is the matte surface, is 10 to 80%.