Patent Publication Number: US-6213075-B1

Title: Roller follower assembly for an internal combustion engine

Description:
TECHNICAL FIELD 
     This invention relates generally to a roller follower assembly for a reciprocating engine and more particularly to an axle pin for use with the roller follower assembly. 
     BACKGROUND ART 
     Engine manufacturers strive to improve performance of internal combustion engines by maximizing the conversion of chemical energy to mechanical energy. The conversion efficiency may be improved when losses of energy used to overcome friction between moving parts in the engine are reduced. Mechanical design along with oil and other lubricants aid in reducing these losses. 
     Roller follower assemblies are mechanical design improvements that reduce friction losses between a cam and a rocker arm. Past systems used a sliding contact between the cam and rocker arm. These systems resulted in large frictional losses. Also, these systems experienced increased wear. Roller follower assemblies reduce friction between the cam and rocker arm by changing the sliding contact to a rolling contact. However, roller follower assemblies may still have a problem with wear. 
     Each roller rotates about an axle pin. Typically, oil reduces sliding friction between a roller and an axle pin. Oil also provides an additional and equally important role of cleaning the engine. Oil along with an oil filter system may remove particles above a particular size. However, the roller and axle pin may ingest smaller particles. At some point these small particles may cause sliding between the roller and axle pin to cease. The interruption in sliding stops the rolling contact between the cam and roller and causes sliding contact between the cam and roller. The sliding contact between the roller and cam may cause a tearing damage at their respective surfaces. 
     The present invention is directed to overcoming one or more of the problems set forth above. 
     DISCLOSURE OF THE INVENTION 
     In one aspect of the present invention a roller follower assembly for an internal combustion engine comprises a roller having a central bore. An axle pin is positioned within the central bore. A hard coating is disposed between the axle pin and the roller. 
     In another aspect of the present invention a method for improving wear of a roller follower assembly on an internal combustion engine includes lubricating an axle pin and a roller. Particles present during the lubricating step are reduced. Remaining particles are pulverized between the axle pin and the roller. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates an internal combustion engine embodying the present invention; and 
     FIG. 2 illustrates a view of one embodiment of an axle pin in accordance with the present invention. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Referring to FIG. 1, the engine assembly  10  includes an engine block  12 , a cylinder head  14  attached to the engine block  12  via a plurality of bolts  16 , and a valve cover  18  attached to the cylinder head  14 . A plurality of cylinders  20  are formed in the engine block  12 , and a piston  22  is disposed for reciprocating movement within each of the cylinders  20 . Each piston  22  is coupled to a crankshaft (not shown) via a connecting rod  24 . A fuel injector  28  is disposed to periodically inject fuel into each cylinder  20 . Each fuel injector  28  includes a body  30 , a nozzle  32 , a vertically reciprocable plunger  34 , and a spring  36  for biasing the plunger  34  upwards. 
     A rocker arm  40  pivotally mounted on a shaft  42  is associated with each fuel injector  28 . Each rocker arm  40  has a first end mechanically coupled to the top of the fuel injector plunger  34  in some conventional manner. The present application shows mechanical coupling via a coupler  44  in the form of a pin  46 . The pin  46  is disposed within a cup-shaped receptacle  48  located in a cylindrical bore formed in the top of the plunger  34 . Each rocker arm  40  has a second end mechanically coupled to a vertically disposed pushrod  50  via a pin  52  having a spherical head  54 . An upper end of the pushrod  50  has a concave surface  56  conformed to the shape of the spherical head  54 . A lower end of the pushrod  50  has a convex surface  58  which is attached to a roller follower assembly  60 . 
     The roller follower assembly  60  has a roller  66  that is generally cylindrical. The roller  66  in this application is made from a high carbon alloy steel such as from about 0.9-1.1% by weight carbon. An axle pin  68  passes through a central bore  70  of the roller  66 . The axle pin  68  is preferably made of a material similar to the roller  66 . Other hard metallic materials may also be used. In this application, the roller follower assembly  60  is supported by a cylindrical shaft  76  passing through a pivot bore on the left end of the roller follower assembly  60 . The cylindrical shaft  76  has a hollow central portion  78 . The roller  66  engages and follows a cam  80 . The cam  80  has a raised portion or cam lobe  82 . A camshaft  86  is disposed within a bore through the cam  80 . Other configurations may have the roller follower assembly  60  attached directly to the rocker arm  40 . Also, the rocker arm  40  may be attached to operate valves (not shown) instead of the fuel injector  28 . 
     FIG.  2 . shows a load bearing surface  87  of the axle pin  68  having a hard coating  88  applied thereto. In this application, the hard coating  88  is applied to a load bearing portion of the axle pin  68 . In the preferred embodiment the hard coating  88  is chromium nitride (CrN). However, other hard coatings may also be used including diamond-like carbons (DLC)like tungsten carbide carbon (WCC). As applied, the hard coating  88  should have a hardness of about 60-100 Rockwell C and preferably about 80-90 Rockwell C. A thickness of the hard coating  88  should be between less than about 5 μm and preferably about 3 μm. The hard coating  88  should have good adhesion to the axle pin  68 . Although not shown, it would be equally advantageous to apply the hard coating  88  to at least the bore of the roller  66 . The hard coating  88  is applied, in this application, using an arc vapor deposition (AVD) process known to those in the industry. However, other conventional methods such as chemical vapor deposition, physical vapor deposition, and other coating methods may be used. 
     INDUSTRIAL APPLICABILITY 
     In operation, during each revolution of the camshaft  72  and the cam lobe  82  forces the roller  66 , the roller follower assembly  60 , and the pushrod  50  upwards. The upwards movement of the upper end of the pushrod  50  causes the rocker arm  40  to rotate in a clockwise direction, causing the right-hand end of the rocker arm  40  to force the fuel injector plunger  34  downwards, causing fuel to be injected from the nozzle  32  into the cylinder  20 . As the cam lobe  82  rotates past the roller  66 , the roller follower body  64  pivots downwardly about the shaft  76 . As the downward movement of the roller follower assembly  60  continues, the pushrod  50  begins to move downwards, the rocker arm  40  pivots in a counter-clockwise direction, and the fuel injector plunger  34  moves upwards under the force of the spring  36 . 
     During this operation, the roller  66  maintains sliding contact with the axle pin  68 . Oil lubricates this contact. Oil may also carry contaminates and particles from other parts of the engine  10 . The hard coating  88  on the axle pin  68  prevents particles from penetrating the surface of the axle pin  68 . Instead, as the particles deposit on the surface of the axle pin, the roller  66  and axle pin  68  provide forces sufficient to pulverize the particles. The hard coating  88  also reduces sliding friction between the axle pin  68  and roller  66 .