Patent Application
20120227695
This invention relates to an arm type valve lifter used in an internal combustion engine.
Valve lifters are used to open and close an intake valve or an exhaust valve (hereinafter simply referred to as “valve”), and include an arm type valve lifter having an arm pivotally supported on a rocker shaft. When a cam rotates, one end of the arm is pushed up by the cam, so that the arm pivots about the rocker shaft, thereby pushing down a valve stem with its other end portion. The valve thus opens.
Such arm type valve lifters include a mechanical lash adjuster as disclosed in Patent document 1 or 2, which is mounted in one end of the arm for automatically adjusting the valve clearance.
Either of the lash adjusters disclosed in Patent documents 1 and 2 includes a cylindrical body having an internal thread formed on its radially inner surface, an adjusting screw having an external thread formed on its radially outer surface and in threaded engagement with the internal thread, and a torsion coil spring mounted between respective opposed surfaces of the body and the adjusting screw such that the torsion coil spring applies a rotational moment to the adjusting screw which tends to axially move the adjusting screw while rotating it, thereby eliminating the valve clearance.
Before such a conventional lash adjuster is mounted on an engine, its adjusting screw is protruded from the body to a large extent. If the lash adjuster is mounted to the engine in this state, pressure leakage may occur during cranking of the engine, which could lead to incomplete combustion, or the intake and exhaust valves may be damaged due to interference with each other. Thus it is necessary to push the adjusting screw into the body against the force of the torsion coil spring, and mount the lash adjuster to the engine with the adjusting screw retracted in the body. Thus, it is extremely troublesome to mount such a lash adjuster to the engine.
One extremely effective solution to this problem is to insert a set pin in radial pin holes in the body and the adjusting screw to retain the adjusting screw in its initial set position in which the adjusting screw is fully retracted in the body. But this solution has a problem that an operator could forget to pull out the set pin after assembling the lash adjuster, or after pulling out the set pin, the operator could inadvertently drop the set pin into the engine. Another disadvantage is that an additional cost is necessary to form the pin holes.
An object of the present invention is to provide a lash adjuster which can be easily assembled and mounted in an arm type valve mounted and in an engine.
In order to achieve this object, the present invention provides an arm type valve lifter comprising an arm pivotally mounted on a rocker shaft, a cam configured to rotate and push up one end portion of the arm, thereby pivoting the arm about the rocker shaft, a valve stem carrying a valve and configured to be pushed down by a second end portion of the arm when the first end portion of the arm is pushed up by the cam, and a lash adjuster mounted in a fitting hole vertically extending through the arm at one of the first and second end portions of the arm for automatically adjusting a valve clearance, wherein the lash adjuster comprises a cylindrical body mounted in the fitting hole and fixed to the arm with an upper portion of the body protruding upwardly from a top surface of the arm, the cylindrical body having an internal thread formed on a radially inner surface of the body, an adjusting screw having an external thread formed on a radially outer surface of the adjusting screw and in threaded engagement with the internal thread, a torsion coil spring for applying a rotational moment to the adjusting screw that tends to move the adjusting screw downwardly, the torsion coil spring having a lower end portion fitted on an upper end portion of the body and in engagement with the body, and an upper end portion located over the body, the torsion coil spring having at the upper end portion thereof a first engaging portion which can be brought into engagement with a second engaging portion formed at the upper portion of the adjusting screw.
The lash adjuster of this arm type valve lifter is mounted to the valve lifter as follows. With the external thread of the adjusting screw in threaded engagement with the internal thread of the body, the adjusting screw is screwed into the body until the adjusting screw is retracted into the body. In this state, the body is inserted into the fitting hole of the arm from under the arm until the upper end portion of the body protrudes upwardly from the top surface of the arm. The body is fixed to the arm.
After fixing the body in position, the bottom end portion of the coil spring is fitted on the upper portion of the body and brought into engagement with the body. In this sate, after mounting the arm to the engine, the upper end portion of the torsion coil spring is turned to twist the torsion coil spring. The first engaging portion of the thus twisted torsion coil spring is brought into engagement with the second engaging portion of the adjusting screw, thereby applying from the torsion coil spring to the adjusting screw a rotational moment that tends to move the adjusting screw downwardly while rotating, thereby adjusting valve clearance.
With this arrangement, since the torsion coil spring is twisted after mounting the arm to the engine, and the first engaging portion of the thus twisted torsion coil spring is brought into engagement with the second engaging portion of the adjusting screw, thereby moving the adjusting screw to the position for automatically adjusting the valve clearance, it is not necessary to keep applying a force to the adjusting screw to keep the adjusting screw retracted in the body. The lash adjuster can thus be easily mounted to the engine.
In a preferred arrangement, the body has at a lower end portion thereof a flange which is in abutment with a bottom surface of the arm at the end portion of the arm, the flange having a flat surface formed on an outer periphery of the flange and in abutment with a vertical shoulder surface formed on the bottom surface of the arm at its end portion, thereby rotationally fixing the body to the arm, the lash adjuster further comprising a snap ring mounted to a radially outer surface of the upper portion of the body, and a wave spring disposed between the snap ring and the top surface of the arm at the end portion thereof, whereby the body is fixed to the arm by the flange, the vertical shoulder surface, the snap ring and the wave spring. Alternatively, the body may be adhesively fixed to the arm, or may be fixed to the arm by welding.
Each of the external thread of the body and the internal thread of the adjusting screw may be any one of a serration-shaped thread having a pressure flank for receiving a force that tends push up the adjusting screw and a clearance flank having a smaller flank angle than the pressure flank, a triangular thread, and a trapezoidal thread. Each of the internal thread and the external thread may comprise multiple threads. With this arrangement, it is possible to support axial force applied to the adjusting screw at a plurality of circumferentially equidistantly spaced apart thread engagement portions. This prevents inclination of the adjusting screw relative to the axis of the body, and thus allows smooth axial movement of the adjusting screw.
The second engaging portion may comprise a diametrically extending groove formed in a top surface of the adjusting screw, or a shaft portion having opposed flat surfaces on an outer periphery of the shaft portion. If the second engaging portion comprises the diametrically extending groove, the first engaging portion comprises a engaging piece formed by radially inwardly bending a top end portion of the torsion coil spring. If the second engaging portion comprises the shaft portion, the first engaging portion comprises a helical winding portion having an oblong shape as viewed from top and having opposed inner surfaces that can engage the respective opposed flat surfaces of the shaft portion.
The second engaging portion may comprises a plurality of the above-mentioned diametrically extending grooves which form a cross or a radial pattern. The cross-forming grooves or the radially extending grooves make it possible to adjust the degree of twisting of the torsion coil spring by selecting a suitable groove or grooves in which the first engaging portion is engaged.
An upwardly extending grip portion may be integrally formed at a distal end of the first engaging portion so that the torsion coil spring can be easily twisted manually without using a tool.
According to the present invention, since the torsion coil spring is twisted after mounting the arm to the engine, and the first engaging portion of the thus twisted torsion coil spring is brought into engagement with the second engaging portion of the adjusting screw, thereby moving the adjusting screw to the position for automatically adjusting the valve clearance, it is not necessary to keep applying a force to the adjusting screw to keep the adjusting screw retracted in the body. The lash adjuster can thus be easily mounted to the engine.
The embodiment of the present invention is described with reference to the drawings.
The valve stem 5 carries a spring retainer 7 at its upper end portion. A valve spring 8 is pressed against the spring retainer 7, thereby biasing the valve stem 5 in a direction in which the valve 6 is pressed against a valve seat 9.
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The adjusting screw 23 has a flange 40 at its lower end portion which serves to restrict the amount of retraction of the lash adjuster 20 to a minimum by abutting the bottom surface of the flange 25 of the body 21.
Description is now made of how the lash adjuster of the arm type valve lifter of this embodiment is assembled. The adjusting screw 20 is threaded into the body 21 with the external thread 24 of the adjusting screw 23 in threaded engagement with the internal thread 22 of the body 21 until its flange 40 abuts the bottom surface of the flange 25. In this state, the body 21 is inserted into the fitting hole 12 from under the arm 3 until the top end portion of the body 21 protrudes upwardly from the top surface of the arm 3 at its first end portion, and the body 21 is fixed to the arm 3.
To fix the body 21 to the arm 3, the wave spring 30 is fitted on the upper end portion of the body 21, and the snap ring 29 is fitted in the ring groove 29. By fitting the wave spring 30, the wave spring 30 biases the body 21 upwardly, thus bringing the flange 25 into abutment with the bottom surface of the arm 3 at its first end portion. The body 21 is thus axially immovably supported by the arm 3. The body 21 is also rotationally fixed to the arm 3 due to engagement between one of the flat surface portions 26 and the vertical shoulder 27 formed on the bottom surface of the arm 3 at its first end portion.
After the body 21 is fixed to the arm 3, the bottom end portion of the torsion coil spring 31 is fitted around the upper portion of the body 21, and the engaging piece 32 provided at the bottom end of the torsion coil spring 31 is engaged in the engaging hole 33 formed in the radially outer surface of the body 21 at its upper portion.
With the bottom end of the torsion coil spring 31 engaged and the arm mounted to the engine, the torsion coil spring 31, which is located over the body 21, is twisted by turning its upper portion in such a direction that the adjusting screw 23 is turned in such a direction that the screw 23 is also moved downwardly under the elastic restoring force due to the twisting of the torsion coil spring 31.
With the torsion coil spring 31 twisted in the above manner, the engaging piece 34 is engaged in the engaging groove 35 formed in the top surface of the adjusting screw 23, thereby applying a rotational moment to the adjusting screw 23 due to the elastic restoring force of the torsion coil spring 31. The adjusting screw 23 thus moves downwardly while rotating and thus its spherical bottom surface 36 is pressed against the top spherical seat 37 of the pushrod 11. The thus assembled lash adjuster serves the purpose of adjusting valve clearance.
As described above, to assemble the lash adjuster 20, the arm is first mounted to the engine, and then with the torsion coil spring 31 twisted, the engaging piece 34 of the torsion coil spring 31 is engaged in the engaging groove 35 of the adjusting screw 23 to allow the adjusting screw 23 to be moved to a position where the valve clearance is automatically adjusted. Thus while assembling the lash adjuster 20, it is not necessary to retain the adjusting screw 23 in the retracted position. The lash adjuster 20 can thus be easily mounted to the engine.
With the lash adjuster 20 mounted in position, when the engine is started and the valve 6 is repeatedly opened and closed by the rotating cam 4, if a valve clearance forms between the valve stem 5 and the second end portion of the arm 3, the adjusting screw 23 rotates, under the rotational moment applied from the torsion coil spring 31 to the adjusting screw 23, with its clearance flank 39 sliding along the clearance flank 39 of the body 21, in the direction in which the adjusting screw 23 is moved downwardly relative to the arm 3.
But since the adjusting screw 23 is in abutment with the pushrod 11 and thus immovable when the adjusting screw 23 rotates in the above direction, the first end portion of the arm 3 is moved upward instead. That is, the arm 3 pivots about the rocker shaft 2 in the direction to eliminate the valve clearance.
When force is applied to the adjusting screw 23 from the valve stem 5 through the arm 3 that tends to push the adjusting screw 23 into the body 21, the pressure flanks 38 are pressed against each other and support this force, thus preventing the adjusting screw 23 from being pushed into the body 21 while turning.
If the distance between the axis of the cam 4 and the bottom end of the adjusting screw 23 decreases due e.g. to wear of the valve seat 9, the adjusting screw 23 is gradually moved upward and pushed into the body 21 while rotating under fluctuating axial loads applied from the pushrod 11. This prevents incomplete closure of the valve 6 when the valve 6 is supposed to be completely closed, i.e. when the base circle 4a of the cam 4 is in contact with the tappet 10. At this time, the adjusting screw 23 is pushed into the body 21 until the minimum value of the fluctuating axial loads decreases to zero and is never pushed in any further.
In the embodiment, the lash adjuster 20 is fitted in the fitting hole 12, which is formed in the first end portion of the arm 3. But the fitting hole may be formed in the second end portion of the arm 3 and the lash adjuster 20 may be fitted in this fitting hole.
In the embodiment, to fix the body 21 in position, the wave spring 30 is mounted between the snap ring 29, which is fitted to the upper portion of the body 21, and the first end portion of the arm 3. But instead, the body 21 may be bonded to the arm 3 by means of an adhesive for metal parts, such as “Locktite”, or may be welded to the arm 3.
In the embodiment, the internal thread 22 of the body 21 and the external thread 24 of the adjusting screw 23 are serration-shaped threads. But instead, they may be triangular threads or trapezoidal threads. Instead of the single internal thread and the single external thread, multiple internal threads and multiple external threads may be used. With this arrangement, it is possible to support axial force applied to the adjusting screw 23 at a plurality of circumferentially equidistantly spaced apart thread engagement portions. This prevents inclination of the adjusting screw 23 relative to the axis of the body 21, and thus allows smooth axial movement of the adjusting screw 23.
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The second engaging portion is not limited to a groove or grooves 35. For example, as shown in
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| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-287780 | Dec 2009 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2010/072461 | 12/14/2010 | WO | 00 | 5/2/2012 |
