Patent Publication Number: US-2015068485-A1

Title: Cylinder head having wear resistant laser peened portions

Description:
TECHNICAL FIELD 
     The present disclosure relates to a cylinder head for an internal combustion engine, and more particularly to portions of the cylinder head which undergo laser peening. 
     BACKGROUND 
     Some portions of a cylinder head, such as, for example, valve guides and injector bores of an Internal Combustion (IC) engine are subjected to high tensile stresses during combustion events occurring within cylinders of the IC engine. In order to resist these tensile stresses, the valve guides and injector bores are subjected to surface engineering processes, such as, shot peening, in order to induce compressive stresses in these areas. However, a magnitude of the compressive stresses so induced may not be high enough to resist failures during engine operation. Further, an effective depth to which the compressive stresses are induced within the cylinder head is also limited. Hence, the valve guides and injector bores may not be able to sustain high tensile stresses during the combustion events, and are therefore prone to damage or failure. High costs may be associated with repair or replacement, thereby affecting service life and overall efficiency of the system. 
     U.S. Pat. No. 4,617,070 describes a method of using a laser on a cylinder wall to improve a cylinder liner surface. In order to prevent the formation of fissures or tears in the walls of cylinders of an internal combustion engine (ICE), hardening tracks generated by a carbon dioxide laser, are placed parallel to each other at an angle of inclination with respect to the axis of the wall of the cylinder or cylinder liner, and spaced from each other by a distance which is greater than twice the distance between the maxima of tension resulting in the operation of the ICE from the edges of the hardening track. 
     SUMMARY OF THE DISCLOSURE 
     In one aspect of the present disclosure, a cylinder head for an internal combustion engine system is disclosed. The cylinder head has at least one fuel injector to deliver fuel from the cylinder head. Further, the cylinder head has at least one valve reciprocally moveable with at least one valve guide disposed within the cylinder head. The cylinder head includes a portion. The portion of the cylinder head defines an injector mount surface. The cylinder head also includes at least one injector bore disposed within the cylinder head. The injector bore is structured and arranged to receive the injector therein. The cylinder head also includes a peening area being defined on the injector mount surface of the cylinder head. The peening area defines a region being laser peened, such that a compressive stress of around 300 MPa to 600 MPa is induced in the peening area. The compressive stress is induced to an effective depth of approximately up to 2 mm from the injector mount surface. 
     Other features and aspects of this disclosure will be apparent from the following description and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an exemplary cylinder head of an internal combustion engine including injectors and valves associated therewith, according to one embodiment of the present disclosure; 
         FIG. 2  is an enlarged view of the encircled area of  FIG. 1 ; 
         FIG. 3  is a perspective view of the cylinder head of  FIG. 1  with the valve spring assemblies and injectors removed to illustrate the injector mount surfaces; 
         FIG. 4  is an enlarged view of the encircled area of  FIG. 3 ; and 
         FIG. 5  is a sectional view of a portion of the cylinder head of  FIG. 1 , cross-sectioned along line  5 - 5  of  FIG. 1  illustrating an injector bore of the cylinder head. 
     
    
    
     DETAILED DESCRIPTION 
     Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or the like parts. Referring to  FIG. 1 , a perspective view of an exemplary cylinder head  100  associated with an engine is illustrated. In one embodiment, the engine may include a compression ignition internal combustion engine configured to combust a mixture of air and diesel fuel. In alternative embodiments, the engine may include a spark ignition engine, such as, a natural gas engine, a gasoline engine, or any multi-cylinder reciprocating internal combustion engine known in the art. The primary components of the engine include an engine block (not shown) and the cylinder head  100 . In one example, the engine block and the cylinder head  100  may be made from cast iron. On assembling the cylinder head  100  with the engine block, the cylinder head  100  is aligned and bolted to the engine block as is customary. A gasket (not shown) may be provided between the engine block and the cylinder head  100 , as is customary, to form a seal between the engine block and the cylinder head  100  in preparation for high temperatures and high pressures associated with combustion gases formed in each cylinder during operation of the engine. 
     The engine block includes a plurality of cylinders (not shown) and each cylinder includes a piston (not shown) and a liner (not shown) disposed within the cylinder. An engine may have multiple cylinders for exemplary purposes the present disclosure illustrates an engine block and the cylinder head  100  associated with a six cylinder engine commonly referred to as an inline configuration. Alternatively, the present disclosure cylinder head  100  may include fewer or more valve and injector sets associated with less than 6 cylinders or more than 6 cylinders, such as, for example an 8 cylinder V-configuration engine. The engine may be configured for any suitable application, such as, work machines, locomotives or marine engines, and in stationary applications, such as, electrical power generators. 
     Each of the cylinders (not shown) includes the piston (not shown) and a connecting rod assembly (not shown). During a combustion event of the mixture of air and the fuel, high pressure is generated within the cylinders which cause an increase in the temperature of the mixture resulting in combustion. In turn, combustion acts on the piston head (not shown) and forces the piston to translate within the cylinder. As is customary the connecting rod is configured to convert the translatory motion of the piston to a rotary motion of the crankshaft. 
     Referring now to  FIGS. 1 ,  2 , and  5 , the cylinder head  100  includes an upper deck  102  and a lower deck  104 . Further, a valve train  106  is associated with the engine. Some parts of the valve train  106  are shown in the accompanying figures. The valve train  106  is provided within the cylinder head  100  of the engine. The valve train  106  may include one or more intake valves  108  and exhaust valves  110 . The intake and exhaust valves  108 ,  110  may be configured to open and close an intake port (not shown) and an exhaust port (not shown) of the cylinders respectively, in order to control air, fuel mixture (intake) and exhaust gas flow (exhaust) within the cylinders, thereby facilitating combustion. In an exemplary embodiment, each cylinder is provided with two intake valves  108  and two exhaust valves  110 . The valves  108 ,  110  disclosed herein may embody a known valve such as, for example, a poppet valve. Each valve  108 ,  110  may include a valve stem  112  (see  FIGS. 1 ,  2  and  5 ) and a valve spring  114  (see  FIGS. 1 ,  2  and  5 ). The valve stem  112  of the valves  108 ,  110  is received within a respective valve guide  116  (see  FIGS. 3 and 4 ) provided in the cylinder head  100 , and reciprocate therein during an opening or closing of the valves  108 ,  110 . The valve guides  116  are provided within a portion  118  of the upper deck  102  of the cylinder head  100 . The valves  108 ,  110  are retained in the closed position by means of the valve spring  114 . 
     The valve train  106  also includes a camshaft (not shown), a tappet (not shown), a push-rod (not shown) and a rocker arm (not shown). The camshaft may be disposed within the cylinder head  100  of the engine. Alternatively, the camshaft may be disposed within the engine block of the engine. The camshaft may be configured to operate the tappet of the valve train  106 , followed by the push rod, the rocker arm, the valve stem  112 , and thereafter the valves  108 ,  110 . 
     In order to supply the fuel that the engine combusts during the combustion event, a fuel system (not shown) is operatively associated with the engine. A fuel line (not shown) may be provided as a component of the fuel system to carry the fuel from a tank (not shown) to the engine. A fuel pump (not shown) may be provided in the fuel line to pressurize and force the fuel through the fuel line. 
     Further, in order to introduce the fuel into the cylinders, the fuel system (not shown) may include multiple fuel injectors  122  each being operably connected to an actuator  120  (see  FIGS. 1 ,  2  and  5 ). In an exemplary embodiment, one fuel injector  122  and one actuator  120  is associated with each cylinder. Alternatively, a fewer number of fuel injectors may be employed in any manner known to those with ordinary skill in the art. The fuel injectors  122  are controlled by the electrically operated actuators  120  for selectively introducing a predetermined quantity of the fuel into the cylinder. The fuel injectors  122  are mounted to injector mount surfaces  129  within the cylinder head  100 . More particularly, the fuel injectors  122  are mounted such that a portion of each fuel injector  122  extends within an injector bore  124  (see  FIGS. 3 ,  4 , and  5 ) of the cylinder head  100 . The injector bores  124  extend through the portion  118  of the cylinder head  100 . Further, a threaded bore  126  extends through each injector mount surface  129  to receive a fastener (not shown) therein to thereby mount the fuel injector  122  to the injector mount surface  129  of the cylinder head  100 . 
     As best shown in  FIG. 5 , due to the combustion events occurring within the cylinders of the engine, a significant amount of pressure is imparted on a combustion face  130  of the lower deck  104  within each cylinder interface with the cylinder head  100 . This pressure creates tensile stresses in the cylinder head  100  and such tensile stresses tend to propagate through the cylinder head  100 , along a direction X-X′, such that the upper deck  102 , and more particularly, the portion  118  of the cylinder head  100  provided with the valve guides  116  and the injector bores  124  is subjected to these high tensile stresses. A surface engineering process may be applied to the injector mount surface  129  of the portion  118  of the cylinder head  100 . In an exemplary embodiment of the present disclosure, the surface engineering process may include laser peening. Laser peening is configured to induce compressive stresses within the area of which it is applied to the cylinder head  100  in order to resist the high tensile stresses created during the combustion events. Laser peening an area of the injector mount surface  129 , termed the peening area  128 , acts to introduce compressive stresses to the cylinder head  100  along a direction Y-Y′. A value of the compressive stresses being induced within the portion  118  may be, for example, between 300 to 600 MPa such as 350 to 450 MPa, for example. Alternatively, the compressive stress induced in the cylinder head  100  may be between 400 to 600 MPa, for example. 
     Laser peening may be carried out using known laser peening equipment. Laser peening equipment may include, for example, but not limited to, a laser beam, a target provided over the portion  118 , and a confining media. In one example, the laser beam may include a Neodymium glass (Nd) laser. Further, the high energy pulsed laser beam in association with the target and the confining media may produce an intense shock wave on the portion  118  to induce a strong localized compressive stress within the portion  118 . Different combinations of the parameters, namely, the laser beam, the target, and the confining media may be used based on system requirements. 
     As shown in  FIGS. 3 and 4 , the peening area  128  is defined on the portion  118  of the cylinder head  100 . The peening area  128  defines a region of the cylinder head  100  formed using laser peening, such that the compressive stresses are induced within the peening area  128  to an effective depth “D”, along the direction Y-Y′. More particularly, the peening area  128  surrounds the injector bore  124 , the threaded bore  126 , and the valve guides  116 . The injector bore  124 , the threaded bore  126 , and the valve guides  116  are provided in close proximity to one another, and so the peening area  128  is defined such that the peening area  128  surrounds the injector bore  124 , the threaded bore  126 , and the valve guides  116 . However, a person of ordinary skill in the art would appreciate that the shape and size of the peening area  128  may vary based on the location of the injector bore  124 , the threaded bore  126 , and the valve guides  116  respectively on the portion  118  of the cylinder head  100 , such that the peening area  128  surrounds the injector bore  124 , the threaded bore  126 , and the valve guides  116  within a defined diameter based on a size of the engine. 
     Referring to  FIG. 5 , treating the laser peening area  128  to the effective depth “D” will induce compressive stresses within this peening area  128 . For example, the effective depth, “D” may be approximately 2 mm deep measured in the Y-Y′ direction from the portion  118 . It should be noted that the effective depth “D” is not limited hereto, and may change based on parameters, such as, the material of the cylinder head  100  and the laser peening equipment being used. 
     INDUSTRIAL APPLICABILITY 
     The cylinder head of internal combustion engine are subjected to high tensile stresses on account of the combustion events occurring within the cylinders. In order to resist these tensile stresses, certain surfaces are subjected to laser peening which has the effect of creating deeper compressive stress penetration of the material. The present disclosure describes the laser peening of the peening area  128  in order to induce compressive stresses within the peening area  128  of the portion  118  to the depth, “D” which may be approximately 2 mm. By using laser peening, it is possible to achieve compressive stress levels of up to 2 to 3 times higher than that of shot peening process. In some examples, the compressive stress values induced in the cylinder head  100  may be between 300 to 600 MPa. Also, the compressive stresses may be pushed deeper into the portion  118 , creating a thicker layer of pre-stressed material within the portion  118 , thereby increasing fatigue strength of the portion  118 . 
     Further, the injector bore  124 , the threaded bore  126 , and the valve guides  116  may be less susceptible to stress fractures or cracking caused by the induced tensile stresses. Hence, the cylinder head  100  may not require frequent remanufacturing, thereby reducing a cost associated with the remanufacturing of the cylinder head  100 . The use of laser peening may also provide an improved surface finish on the portion  118  of the cylinder head  100 . Further, no residual shot material may need be cleaned from the peening area  128 , thereby decreasing time associated with manufacturing of the cylinder head  100 . 
     While aspects of the present disclosure have been particularly shown and described with reference to the embodiments above, it will be understood by those skilled in the art that various additional embodiments may be contemplated by the modification of the disclosed machines, systems and methods without departing from the spirit and scope of what is disclosed. Such embodiments should be understood to fall within the scope of the present disclosure as determined based upon the claims and any equivalents thereof.