Patent Application
20150218982
The present disclosure relates to a rocker arm assembly having a cam roller assembly, and more particularly to a bearing component of the cam roller assembly and method of manufacturing the bearing component.
Generally, in an engine having a cam actuated valve operation, a rocker arm assembly is used for opening and closing of the valves. The operation of the rocker arm assembly is one of the critical parameters for achieving optimal performance of the valves, in a way directly impacting engine performance. A cam roller assembly disposed at one end of the rocker arm assembly is subjected to continuous rotation during the engine operation. The continuous rotation requires an effective lubrication between a bearing surface and a bearing component in the cam roller assembly. The lubrication is achieved by supplying oil through one or more oil holes provided on the bearing component. Presence of sharp edges at the openings of the oil holes causes wear at the bearing surface and also hinders lubrication and eventually leads to the overheating the cam roller.
Japanese patent application No. JP2001208165 discloses a cam follower having a roller rotatably mounted on a spindle and positioned between a pair of supports through a floating ring. A through hole is provided on the floating ring to allow oil for the lubrication purpose between the bearing surface of roller and floating ring. Also, a hollow portion is formed on an outer surface of the floating ring for holding the lubricant. The hollow portion helps in prevention of an opening edge of the through hole coming in contact with the roller during the operation of the cam follower and thereby maintaining the lubrication.
In one aspect, the present disclosure discloses a rocker arm assembly for a valve operation in an engine. The rocker arm assembly includes a rocker arm main body extending between a first end and a second end. The first end of the rocker arm main body is configured to receive a valve actuation button and the second end of the rocker arm main body is configured to receive a cam roller assembly. The cam roller assembly includes a cam roller and a bushing is disposed in the cam roller forming a bearing surface. Further, the cam roller assembly includes a bearing component which is disposed in the bushing forming a bearing surface. The bearing component includes an oil hole and an oil delivery pocket of the oil hole is curved to form a rounded edge. Further, a transitional opening is formed extending from the rounded edge.
In another aspect, the present disclosure provides a method of manufacturing an oil hole in a bearing component of a cam roller assembly. The oil hole with a countersunk oil delivery pocket on an outer surface of the bearing component is formed. The bearing component is positioned on an anvil and a spherical punch ball of a press tool is advanced towards the oil hole to transform an edge of countersunk oil delivery pocket to a rounded edge. Further, the spherical punch ball is advanced to form an transitional opening which extends from the rounded edge.
Other features and aspects of this disclosure will be apparent from the following description and the accompanying drawings.
In an aspect of the present disclosure, the engine 100 may be a compression ignition internal combustion engine, such as a diesel engine. For clarity, the following description refers to a single cylinder engine, but the principle of the present disclosure can be applied to a multi-cylinder engine. The engine 100 includes a cylinder block 102, and a cylinder head 104 attached to the cylinder block 102. In the exemplary embodiment shown in
The valve train 114 further includes a valve actuation assembly 118. In an exemplary embodiment, the valve actuation assembly 118 includes a camshaft 120 suitably journalled within the cylinder head 104 in a conventional manner. The camshaft 120 has a lobe 122 and operatively coupled to a rocker arm assembly 124. The valve actuation assembly 118 is configured to transfer a rotary motion of the camshaft 120 into a linear motion of the valves 116 via the rocker arm assembly 124 and a valve bridge 126. In the illustrated embodiment, the rocker arm assembly 124 is pivotally mounted on the cylinder head 104 about a pivot point A and operatively engaged with the valve bridge 126. In another embodiment, the rocker arm assembly 124 may be directly engaged with the valves 116 without using a valve bridge.
A cam roller assembly 140 is disposed at the second end 132 of the main body 128. The main body 128 has a pair of spaced apart arms 142 (only one is shown in
The support pin 146 is rigidly attached to the arms 142 of the main body 128 and locked in a position by a locking pin 164 received through at least one of the arms 142. The support pin 146 has a cut out portion 166 partly extending along an axial direction on an outer annular surface 167 of the support pin 146. The cut out portion 166 may be a concave portion formed by cutting out a part of the support pin 146 in a plane starting from an end of the support pin 146. Alternatively, the cut out portion 166 may be formed as an axially extending recess or channel. Further, an annular groove 169 originating from the cut out portion 166 is provided on the outer annular surface 167 of the support pin 146. The cut out portion 166 and the annular groove 169 are fluidically connected to a lubrication oil passage 168 provided in the main body 128 and configured to receive lubrication oil. The lubrication oil may be supplied from a lubricating system of the engine pumped up from an oil pan in the lubrication oil passage 168.
According to an aspect of the present disclosure, the bearing component 158 may include multiple oil holes 170 uniformly disposed on the bearing component 158 and fluidically connected to the cut out portion 166 and the annular groove 169 on the support pin 146. The oil holes 170 open between the bearing surface 156 of the bushing 154 and the outer surface 160 of the bearing component 158 to lubricate the sliding surfaces. The lubricating oil supplied from the oil holes 170 form a lubricating oil film between the bearing surface 156 and the outer surface 160 of the bearing component 158.
Additionally, the lubrication oil passage 168 may provide the lubrication oil to the rocker arm support shaft.
According to an aspect of the present disclosure, a method for manufacturing and/or modifying a pre-formed oil holes on the bearing component 158 is provided. In an embodiment, a portable service tool, such as a ‘C’ frame hydraulic press, or a mechanical press of crank, knuckle joint, or eccentric type, may be used to modify the pre-formed oil hole having a countersunk oil delivery pocket. The countersunk oil delivery pocket of the pre-formed oil hole may have a substantially corner edge defining an elliptical or round opening of the oil hole at the outer surface 160 of the bearing component 158. The portable service tool may include a hardened spherical punch ball having a centrally located punch extending to a length substantially equal to a length of the pilot hole portion 180 of the oil hole 170. In an embodiment, a diameter of the spherical punch ball is more than the twice of a diameter of the centrally located punch. To begin with the modification of the oil hole having the countersunk oil delivery pocket, firstly, a hardened anvil is inserted into the bearing component 158. The hardened anvil may have a diameter substantially equal to the inner diameter D1 of the bearing component 158. Following that, a tonnage of the portable service tool is gradually increased from a pre-determined level to advance the hardened spherical punch ball towards the oil hole. The centrally located punch extending from the spherical punch ball may aid in the aligning the spherical punch ball and the oil hole during pressing. Eventually, the spherical punch ball displaces the corner edge of the countersunk oil hole downwards slightly below the outer surface 160 of the bearing component 158. Thus, it transform the corner edge of the countersunk oil delivery pocket of the oil hole to the rounded edge 176 and also creating the depressed concave transitional opening 178.
The industrial applicability of the bearing component 158 in an overhead cam configuration will be readily understood from the foregoing discussion. According to an aspect of the present disclosure, the oil holes 170 provided on the bearing component 158 includes the oil delivery pocket 174 having the rounded edge 176. The rounded edge 176 prevents a direct surface contact of the rounded edge 176 of the oil delivery pocket 174 with the bearing surface 156. Thus, it prevents any wear and damage to the soft ductile of the bushing 154 and improves the overall service life of the rocker arm assembly 124.
Moreover, the supply of the lubricating oil is not hindered or obstructed by the rounded edge 176 and the transitional opening 178 acts a reservoir to maintain a continuous oil film between the bearing surface 156 and the outer surface 160 of the bearing component 158. This causes the frictional forces between the bearing surface 156 and the outer surface 160 of the bearing component 158 to substantially reduce. Thereby, there is an inherent advantage of overheat prevention of the cam roller 152. An effective lubrication also helps to reduce an axial movement of the bushing 154 which otherwise, would be detrimental and can lead to the cam roller 152 assembly and/or the cam lobe 122 failure.
Further, the formation of the transitional opening 178 extending from the rounded edge 176 provides an increased surface area for storing more amount of the lubricating oil when compared with the conventional countersunk oil holes. The formation of the rounded edge 176 in combination with the transitional opening 178 provides an improved lubrication at the bearing surface 156 between the bearing component 158 and thereby enabling the cam roller assembly 140 to roll without any sliding effect during the rotation of the camshaft 120 and thus preventing excessive frictional forces when the cam roller assembly 140 makes contact with the camshaft. Thus, the rocker arm assembly 124 has an improved reliability.
From the foregoing it will be appreciated that, although specific embodiments have been described herein for purposes of illustration, various modifications or variations may be made without deviating from the spirit or scope of inventive features claimed herein. Other embodiments will be apparent to those skilled in the art from consideration of the specification and figures and practice of the arrangements disclosed herein. It is intended that the specification and disclosed examples be considered as exemplary only, with a true inventive scope and spirit being indicated by the following claims and their equivalents.
