DEACTIVATING ROCKER ARM / MECHANICAL LASH ADJUSTMENT SYSTEM

Abstract

A deactivating rocker arm mechanical adjustment system for internal combustion engines is provided wherein a lash adjustment screw which has eccentric cam and a feature by which the screw can be rotated using a tool. The adjustment screw is installed a valve actuation section of a split rocker arm wherein the cam end of the adjustment screw engages a feature of the cam follower section of the split rocker arm. When the lash adjustment screw is rotated, the design of the cam is such that the angular orientation of the valve actuation and cam follower sections is varied and in turn varies the distance or lash between the cam follower section latch pin and the receiving latch pin hole in the valve actuation section. The lash adjustment screw is rotated until a previously specified lash is obtained and then a jam nut is tightened to prevent rotation of the lash adjustment screw. Valvetrain component design may be altered that other than threaded means may be used to control the rotational orientation of the adjustment cam. An additional feature of the invention is that in the preferred embodiment, the lash adjustment screw provides a valve actuation section feature upon which a lost motion spring is mounted.

Description

FIELD OF THE INVENTION

The present invention relates to valve trains for internal combustion engines. More particularly, the present invention relates to a split rocker arm arrangement for use in a valve train for internal combustion engines comprising a lash adjustment screw having a cam at one end which, when rotated, changes the angular orientation of two parts of a split rocker arm.

BACKGROUND OF THE INVENTION

Generally prior art valve deactivating rocker arms such as that described in the Lotus Cars Limited UK Patent Application GB2,333,322A, published Jul. 21, 1999, have been manufactured without a means to adjust the clearance, or mechanical lash, between the latch pin in one rocker arm section and the receiving latch pin bore in the other rocker arm section. As a result there may be insufficient clearance to ensure proper function of the deactivation mechanism, thereby disabling or delaying deactivation and/or re-activation and impairing engine operation. More over there may exist excessive mechanical lash such that the opening and closing ramp portions of the cam lift profile are bypassed, resulting in improper valve motion. A consequence of improper valve motion is undesired noise due to the impact velocity of the engine valve against the valve seat during closing, and to some degree, additional noise due to the impact of the latch pin against the receiving latch pin bore. Engine valve and valve seat durability are also reduced. Accordingly, an arrangement which accurately locates the cam follower section relative to the valve actuator section such that the latch pin is free to move in and out of the receiving latch pin bore without contacting it and avoiding the noise resulting from excessive lateral clearance would be very advantageous. The present invention provides an arrangement that allows the amount of transverse motion of the latch pin within the receiving latch pin bore to be controlled such that it ensures deactivating mechanism function and as well significantly reduces the noise generated by the impact in part of moving parts thereby reducing valve train NVH (noise, vibration, and harshness) and as well improving engine valve durability.

SUMMARY OF THE INVENTION

The present invention is directed to an improved split rocker arm having a valve deactivation device for a valve train which provides for adjustment of mechanical lash. The first section and the second section of the split rocker arm comprise an adjustment system that includes a cam positioned between said sections, said cam which, when rotated, changes the angular orientation of said first section and said second section of said split rocker arm, thereby controlling the lateral clearance between the latch pin in said first section and a receiving latch pin hole in said second section to permit free movement of the latch pin which, when engaged, opens and engine valve in response to the valvetrain camshaft, and which, when disengaged, permits one section of the rocker arm to rotate in response to the valvetrain camshaft without opening the engine valve. The system of the invention locates the cam follower section relative to the valve actuator section such that the latch pin is free to move in and out of the receiving latch pin bore without contacting it while at the same time limiting the amount of transverse movement of the latch pin within the receiving latch pin bore. As so configured, the opening and closing ramp portions of the cam profile are followed, ensuring proper engine valve motion, and thereby reducing the amplitude of the sound of impact of the engine valve against the valve seat, and to a lesser degree, the latch pin against the receiving latch pin bore, thereby improving valve train NVH (noise, vibration and harshness) and improving engine valve durability.

As distinguished from prior art deactivating arms which typically require the use of components which are selected from within the range of manufacturing variability or are manufactured with very high precision, the present invention reduces manufactured cost in that the rocker arm assemblies may be either manually or robotically adjusted to provide a specified amount of lateral clearance, or mechanical lash, between the latch pin and the receiving latch pin bore. As a result the range of variation of mechanical lash is more economically controlled to a tighter tolerance thereby reducing NVH and wear and in addition may optionally be adjusted during the service life of the engine.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a rocker arm assembly that includes a valve deactivation device in accordance with the present invention.

FIG. 2 is a rear perspective view of a rocker arm assembly of FIG. 1.

FIG. 3 is a side view of the rocker arm assembly of FIG. 2.

FIG. 4 is a sectional view taken along line 4-4 of FIG. 3 illustrating the valve deactivation device in accordance with the present invention in a valve activated condition.

FIG. 5 is a detail view within circle 5 of FIG. 4 illustrating the eccentricity of the lash adjustment screw cam and the clearance, or mechanical lash, between the cam follower and valve actuator sections of the rocker arm.

FIG. 6 is a perspective view of the lash adjustment screw illustrating the eccentricity of the cam portion relative to the threaded portion.

FIG. 7 is an end view of the lash adjustment screw illustrating the eccentricity of the cam portion relative to the threaded portion.

DETAILED DESCRIPTION OF THE INVENTION

In the mechanism of the invention, cam follower and valve actuator sections of a valve deactivating rocker arm assembly are mounted on a rocker shaft for free rotation about the shaft.

The invention is devised to locate the cam follower section relative to the valve actuator section such that the latch pin of the rocker arm deactivating mechanism in one section is free to move in and out of the receiving latch pin bore in the other section without contacting the receiving latch pin bore. This construction allows the amount of transverse motion of the latch pin within the receiving latch pin bore to be controlled such that the opening and closing ramp portions of the cam profile are followed, ensuring proper engine valve motion. By so doing the invention significantly reduces the amplitude of the sound of impact of the engine valve against the valve seat, and to a lesser degree, the latch pin against the receiving latch pin bore, thereby reducing valve train NVH (noise, vibration and harshness) and improving engine valve durability.

A lash adjustment pin, preferably a threaded pin, screw having a cam at one end is provided which, when rotated, changes the angular orientation of two sections of the valve deactivating rocker arm assembly. It is necessary to control their rotational orientation to each other to ensure free movement of a latch pin which, when engaged, couples the two parts to open an engine valve in response to the valvetrain camshaft, and when disengaged, permits one part of the rocker arm to rotate in response to the valvetrain camshaft, but without opening the engine valve. Control of the two parts' rotational orientation to each other is essential to controlling lash within the valvetrain system to ensure consistent valvetrain operation.

Again with reference to FIGS. 1-2, rocker arm assembly 10 includes a cam follower section 12 having a valve actuator section 14 journaled therein, a cam follower section retaining clip 16, a spring retaining clip 18, and a lost motion spring 20. Cam follower section 12 includes a tubular cam follower body portion 30 having an arm portion 32 and a deactivation device, or deactivation portion 34 extending therefrom. Arm portion 32 includes a cam spring pin 36 extending therefrom, a bifurcated end 38 having a roller 40 rotatably coupled thereto via a roller axle 42. Roller axle 42 is interposed through both the bifurcated end 38 and the roller 40. Valve actuator section 14 includes a tubular valve body portion 44 having an arm portion 46 extending therefrom. Arm portion 46 includes a proximal end 48 attached to valve body portion 44 and a distal end 50 having a valve contacting portion 52 attached thereto. Arm portion 46 further includes a lash adjustment screw 22 extending therefrom, a latch pin aperture 120 (FIGS. 4 and 5) formed therein, and a latch pin sliding surface 58 (FIG. 2). Cam follower body portion 30 is a hollow elongated cylinder that includes a first annular end 60, a second annular end 62 (FIG. 2), a generally cylindrical cam follower section inner surface (not shown), and a cylindrical cam follower section outer surface 66.

With specific reference to FIGS. 4 and 5, deactivation portion 34 including a latch pin 72 is at least partially housed within body 68 and positioned so as to be in engagement with a return spring 74. Deactivation portion 44 includes a return spring 74 and a cap 76 secured to end 70. Cap 76 closes off body 68 and provides a surface for return spring 74 to react against. Alternately, end 70 may be provided with mounting shoulders for return spring 74 to act against, thereby eliminating the need for cap 76.

Referring to FIGS. 1-2, the valve body portion 44 is a hollow elongated cylinder that includes a first annular end 80 (FIG. 2), a second annular end 82 (FIG. 1), a generally cylindrical valve actuation section inside surface 84, and a generally cylindrical valve actuation section outside surface 86. Valve body portion 44 also includes a pair of annular retaining grooves 88 formed in valve actuation section outside surface 86, adjacent the first annular end 80 and the second annular end 82, respectively. Valve contacting portion 52 includes a surface which slideably contacts the tip of a valve (not shown) for operation thereof.

As shown in FIG. 1, lost motion spring 20 is mounted on second annular end 82 of valve body portion 44. In one embodiment, lost motion spring 20 includes a curved body 98 that defines an arcuate section. Curved body 98 has an open section 100 flanked by lash adjustment screw end 102 and a cam pin end 104. It is apparent that the lost motion spring may comprise a helical form (not shown) whereby lost motion spring hook 102 attaches to surface 28 (FIG. 6) of lash adjustment screw 22 and lost motion spring hook 104 attaches to a pin that would be coaxial with pin 36 but located on the other side of the cam follower section.

Referring again to FIGS. 1-2, lost motion spring 20 is superposed around second annular end 82 (FIG. 2). Lash adjustment screw end 102 of lost motion spring 20 is coupled to surface 28 of lash adjustment screw 22 and cam pin end 104 is coupled to cam spring pin 36. Lost motion spring 20 selectively biases cam spring pin 36 away from surface 28 of lash adjustment screw 22. Preferably, lost motion spring 20 is a partial coil spring with at least a portion thereof curved about valve actuation section outside surface 86. Also preferably, lost motion spring 40 extends less than 360° about valve actuation section outside surface 86. The cam follower section retaining clip 16 is inserted into a retaining groove 88, limiting lateral clearance between valve actuator section 14 and cam follower section 12. The spring retaining clip 18 is inserted into retaining groove 88 to retain lost motion spring 20 on valve body portion 44.

Referring again to FIGS. 4 and 5, latch pin 72 is positioned within tubular body 68 and in alignment with latch pin aperture 120. Latch pin 72 is moveable between an activated position (FIGS. 4 and 5) and a deactivated position (not shown).

To deactivate rocker arm assembly 10 from the activated condition, pressureized oil is introduced into the deactivating mechanism to urge latch pin 72 toward cap 76, against the biasing force of return spring 74. The existence of clearance or mechanical lash (FIG. 5) between cylindrical plunger portion of latch pin 72 and cylindrical pin surface 120 within arm portion 46, ensures that the motion of latch pin 72 will not be impeded by friction between those surfaces, thereby ensuring smooth action. When the latch pin 72 has moved out of engagement with arm portion 46, cam follower section 12 is free to rotate relative to valve actuation section 14, thereby placing rocker arm assembly 10 in a deactivated condition (not shown). As the camshaft rotates further, urging roller 40, cam follower section 12 rotates about the axis of valve body portion 44 and valve actuation section 14 does not rotate. Since valve actuation section 14 does not rotate, the valve is not operated and is effectively shut down. With relative rotation of cam follower section 12 about valve actuation section 14, lost motion spring 20 is deflected, thereby storing energy and inducing a relative torsion between valve actuation section 14 and cam follower section 12. This torsion urges roller 40 to generally stay in contact with the camshaft.

To activate rocker arm assembly 10 from the deactivated condition, pressurized oil is released from the deactivation mechanism, thereby allowing return spring 74 to urge latch pin 72 toward valve actuation section 14. The existence of clearance or mechanical lash (FIG. 5) between the cylindrical plunger portion of latch pin 72 and cylindrical pin surface 120 within arm portion 46 ensures that latch pin 72 may freely enter arm portion 46. Depending upon the relative rotational orientations of valve actuation section 14 and cam follower section 12, the distal end of latch pin 72 will contact either contact latch pin sliding surface 58 (FIGS. 3 and 4) or enter arm portion 46. When latch pin 72 contacts latch pin sliding surface 58, valve actuation section 14 will not rotate and lost motion spring 20 urges cam follower section 12 to rotate as the camshaft rotates. As cam follower section 12 rotates and valve actuation section 14 does not rotate latch pin 72 in contact with latch pin sliding surface 58, it follows a generally circular arc. As the camshaft rotates further, latch pin 72 will align with and engage cylindrical pin surface 120, thereby placing rocker arm assembly 10 in an activated condition. Thus, latch pin 72 is selectively guided into engagement with said cylindrical pin surface 120 within arm portion 46 by the relative rotation of cam follower section 12 and valve actuation section 14.

In a preferred embodiment of the invention, as seen by reference to FIGS. 6 and 7, a lash adjustment screw 22 is provided which has a cam 24 and a feature 54 by which the pin can be rotated using a tool to adjust the lateral clearance or mechanical lash (FIG. 5) between the latch pin 72 and the cylindrical pin surface 120 within arm portion 46. Here the lash adjustment screw 22 is installed into a mating threaded hole in valve actuator section 14 wherein the cam end 24 of the lash adjustment screw 22 engages a stop feature 64 of the cam follower section 12. When the lash adjustment screw 22 is rotated, the eccentricity (FIG. 7) of the cam 24 is such that the rotational orientation of the valve actuator and cam follower sections is varied and in turn varies the lateral clearance or mechanical lash between the cam follower section latch pin 72 and the cylindrical pin surface 120 within arm portion 46. The lash adjustment screw 22 is rotated until a previously specified mechanical lash is obtained. A jam nut 56 is tightened on a portion of the threads 26 of the lash adjustment screw 22 to prevent rotation of the lash adjustment screw 22. In a preferred embodiment, the lash adjustment screw 22 provides the valve actuator section feature 28 upon which the lost motion spring 20 is mounted. It will also be apparent to one skilled in the art of valvetrain component design that other than threaded means may be used to control the rotational orientation of the cam 24 to adjust the mechanical lash of the deactivating rocker arm assembly 10. For example the cam could be mounted on a shaft which, following adjustment, is secured from rotating by welding or bonding or mechanical means. Alternatively the cam could be shouldered within a recess within one rocker arm section and, following adjustment, is secured from rotating by welding or bonding or mechanical means.

Although the invention has been described with respect to the preferred embodiments thereof. Various modifications will become apparent to one skilled in the art from the foregoing description. It is therefore the intention that all such variations and modifications be included within the scope of the appended claims.

Claims

1. In a rocker arm comprising a split rocker arm having a first section and a second section, the improvement comprises an adjustment system including a cam positioned between said sections, said cam which, when rotated, changes the angular orientation of said first section and said second section of said split rocker arm, thereby controlling the lateral clearance between the latch pin in said first section and a receiving latch pin hole in said second section to permit free movement of the latch pin which, when engaged opens an engine valve in response to the valvetrain camshaft, and which, when disengaged, permits one section of the rocker arm to rotate in response to the valvetrain camshaft without opening the engine valve.

2. The rocker arm/mechanical adjustment system of claim 1 which includes a valve actuator section and a cam follower section.

3. The rocker arm/mechanical adjustment system of claim 2 wherein the cam follower section includes the adjustment system.

4. The rocker arm/mechanical adjustment system of claim 2 wherein the valve follower section includes the adjustment system.

5. The rocker arm/mechanical adjustment system of claims 3 and 4 wherein the adjustment system includes a cam at one end of a threaded pin or screw which includes a wrenching feature and a locking feature.

6. The rocker arm/mechanical adjustment system of claims 3 and 4 wherein the adjustment system includes a cam at one end of a pin or shaft which includes a wrenching feature and is locked by bonding, welding, or mechanical means.

7. The rocker arm/mechanical adjustment system of claims 3 and 4 wherein the adjustment system includes a cam which includes a wrenching feature and which is shouldered within a recess or other feature and is locked by bonding, welding, or mechanical means.

8. The rocker arm/mechanical adjustment system of claim 2 wherein the cam follower section includes a tubular cam follower body and a deactivation section.

9. The rocker arm/mechanical adjustment system of claim 2 wherein the latch pin is a threaded pin.

10. The rocker arm/mechanical adjustment system of claim 2 wherein the valve actuator section includes a tubular body and an arm portion attached to said tubular body.

11. The rocker arm/mechanical adjustment system of claim 2 including a lost motion spring that extends less than 360° around the valve actuator section.