Abstract:
Modern internal combustion engines produce high temperatures and pressures in the combustion chamber of the engine that place immense stresses on the engine&#39;s pistons. These temperatures and pressures can cause pistons to deform or wear and prematurely fail. One of the primary means of overcoming these detrimental effects on a piston is increasing the efficiency of heat rejection from the piston. One method of increasing the amount of heat drawn away from the piston is increasing the surface area of the inner surface of the piston crown so that a cooling medium, such as oil, can contact the inner surface and draw heat therefrom. Installing or forming an annular fin in the underside of the piston increases the surface area for oil to contact and permits precise targeting of piston locations from which heat is to be evacuated. Such annular fins can be quickly and easily installed or formed for use with any type of pistons, such as forged, cast, composite or mechanically joined pistons.

Description:
TECHNICAL FIELD 
     This invention relates generally to an engine and more particularly to the cooling of a piston by placing a fin within a cooling recess of the piston. 
     BACKGROUND 
     Internal combustion engine manufacturers continually strive to decrease the physical size of engines and increase the power output per cylinder. In doing so, the manufacturer strives to increase fuel economy, efficiency, and service life, while reducing emissions. One way of improving efficiency and reducing size has been to increase temperatures and pressures in the combustion chamber. However, such increased temperatures and pressures in the combustion chamber place higher stresses on the piston that may cause the piston to deform or wear and prematurely fail. 
     One of the primary means of overcoming these detrimental effects on the piston is increasing the efficiency of heat rejection from the piston. For example, many high output engines employ cooling of the underside of the piston by spraying a cooling medium against the underside of the piston. The cooling medium absorbs a portion of the heat from the piston, falls away from the piston to the pan, is cooled and recycled to cool the piston again. To ensure efficient cooling of the underside of the piston, the spray must be precisely directed and retained to best remain in contact with the underside of the piston and absorb heat therefrom. 
     A method of increasing the contact between the oil and the interior of the piston is by increasing the surface area of the interior of the piston, thereby providing more area for the oil to contact and absorb heat. U.S. Pat. No. 2,523,699 issued to G. A. Holt et al. on Sep. 26, 1950 shows a series of ribs projecting inwardly from the interior wall of the piston skirt. These ribs increase the heat dissipating area of the piston that is in contact with the oil as the oil is shaken by the reciprocating motion of the piston. The intricate piston design set forth in Holt, however, is very difficult to produce via forging or machining processes. Therefore, the piston disclosed in Holt is practical for use solely in casting processes. However, the casting process introduces impurities into the cast product. These impurities decrease the density of the product and thus decrease the product&#39;s resistance to deformation at high temperatures and pressures. 
     The present invention is directed to overcoming one or more of the problems as set forth above. 
     SUMMARY OF THE INVENTION 
     In one aspect of the present application, a piston has a top portion having a bowl and a periphery portion. The bowl has an annular bowl that is attached to and extends radially inward from the periphery portion. Each of the annular bowl and the periphery portion has an inner surface. The piston has an outer annular wall that extends axially from the periphery portion of the top portion of the piston. The outer annular wall has an inner surface. The annular bowl inner surface, the periphery portion inner surface, and the outer annular wall inner surface define a cooling gallery. The piston has at least one annular fin that extends from the cooling gallery. 
     In another aspect of the present application, a method of creating a piston includes providing a piston having a top portion and an outer annular wall as described above and introducing to the cooling gallery at least one annular fin. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of an engine; 
     FIG. 2 is a cross sectional view taken along line  2 — 2  of FIG. 1 of the engine; 
     FIG. 3 is an enlarged cross sectional view of a piston within the engine; 
     FIG. 4 is an enlarged sectional view of an annular groove in the piston; 
     FIG. 5 is an enlarged sectional view of an annular fin attached to the piston; 
     FIG. 6 is a sectional view of an annular fin that is integral with the piston; 
     FIG. 7 is a bottom partially sectioned view taken along line A—A of FIG. 3 of the piston without a baffle plate; and 
     FIG. 8 is a bottom partially sectioned view taken along line A—A of FIG. 3 of the piston without a baffle plate and having a plurality of fin sections. 
    
    
     DETAILED DESCRIPTION 
     Referring to the figures, an internal combustion engine  10  is shown. The engine  10  includes a cylinder block  12 , a cylinder head  14  attached to the block  12 , a valve cover  16  attached to the head  14 , and a cooling system (not shown). These components are of a generally conventional design. 
     Referring now to FIG. 1, the block  12  includes a top mounting surface  18 , a bottom mounting surface  20 , and a plurality of cylinder bores  22  located between the top mounting surface  18  and the bottom mounting surface  20 . In the embodiment shown in FIG. 1, six cylinder bores  22  are equally spaced, in-line, and perpendicularly positioned with respect to the top mounting surface  18 . However, the cylinder block  12  may be of any other conventional design, such as “V” or radial, and may have any number of bores  22 . As shown in FIG. 2, each bore  22  defines a cylinder wall  24 . In the engine shown in FIG. 2, a cylinder liner is placed in the bore  22  to form the cylinder wall  24 . However, the apparatus and method described in the present application may be used in engines that do not contain cylinder liners. The cylinder block  12  has a plurality of interconnected passages (not shown) to enable the flow of a lubricating and/or cooling medium, such as oil (not shown). Secured to the block  12  and connected to the cooling passages are a plurality of coolant directing nozzles  26 . The block  12  also has an oil pan  28 , shown in FIG. 1, connected to the block  12 . 
     Referring to FIG. 2, a piston  34  is slidably positioned within the cylinder wall  24  of the cylinder block  12 . The piston  34 , the cylinder wall  24 , and the cylinder head  14  define a combustion zone  36 . The piston  34  is a generally cylindrical structure having a top portion  38  and a pin portion  40 . In FIG. 2, the piston  34  is shown as one piece. However, the piston  34  may be any conventional piston type, including an articulated piston or a composite piston. 
     Referring now to FIG. 3, the top portion  38  is further defined by a bowl  42 , a periphery portion  44 , and an outer annular wall  46 . The bowl  42  is defined by an annular bowl  48  connected with the periphery portion  44 . The annular bowl extends radially inward from the periphery portion  44  and connects to a conical section  50  forming an apex. The annular bowl  48  has an inner surface  52  separated from the combustion zone  36 . In the piston  34  shown in FIG. 3, the periphery portion  44 , the annular bowl  48 , and the conical section  50  are integrally formed. As shown in FIG. 2, the distance from the apex of the conical section  50  to the cylinder head  14  is generally greater than the distance from the periphery portion  44  to the cylinder head  14 . 
     Referring again to FIG. 3, the periphery portion  44  extends radially away from the bowl  42  towards the cylinder wall  24 . The outer annular wall  46  extends axially away from the periphery portion  44  towards the pin portion  40 . The outer annular wall  46  has an inner surface  54  and an outer surface  56 . The periphery portion  44  has an inner surface  58  that is separated from the combustion zone  36 . The periphery portion inner surface  58  is connected to, and integral with, the inner surface  52  of the annular bowl  48  and the inner surface  54  of the outer annular wall  46 . The inner surface  58  of the periphery portion  44 , the inner surface  52  of the annular bowl  48 , and the inner surface  54  of the outer annular wall  46  define a crown interior surface  59 . The outer surface  56  has a sealing portion  60  in which any conventional manner of providing sealing between the piston  34  and the cylinder wall  24 , such as a plurality of piston rings  62 , can be formed. 
     In one embodiment of the piston  34  set forth in the present application, shown in FIG. 4, an annular groove  64  is located in the crown interior surface  59 . The annular groove  64  has an inner wall  66  and an outer wall  68 . One or both of the inner wall  66  and the outer wall  68  may have a thread  70  formed thereon. As shown in FIG. 5, an annular fin  72  is attached to one or both of the inner wall  66  and the outer wall  68  of the annular groove  64 . The annular fin  72  has an inner surface  74 , an outer surface  76 , a first edge  78 , and a second edge  80 . One or both of the outer surface  76  and the inner surface  74  may have a thread  82  formed thereon. The location and dimensions of the annular fin  72 , including diameter, thickness, and length, are predetermined. In another embodiment of the piston  34  of the present application, shown in FIG. 6, the annular fin  72  is integrally formed with the crown interior surface  59 . In other embodiments of the piston, shown in shadow in FIG. 6, a plurality of the annular fins  72  may be attached to, or integral with, the crown interior surface  59 . 
     In one embodiment of the piston  34  of the present application, shown in FIG. 5, a baffle plate  84  is connected between a lip portion  86  on the inner surface  52  of the annular bowl  48  and a lower edge portion  88  of the inner surface  54  of the outer annular wall  46 . The baffle plate  84  has a receiving aperture  90  therethrough and a draining aperture  92 , shown in FIG. 3, therethrough. The baffle plate  84 , the crown interior surface  59 , the inner surface  74  of the annular fin  72 , the first edge  78  of the annular fin  72 , and the outer surface  76  of the annular fin  72  define a cooling gallery  94 . In other embodiments of the apparatus, as shown in FIG. 7, a baffle plate is not present. Although shown in FIG. 7 as one continuous piece, the annular fin  72  may be defined by a plurality of fin segments  96 , as shown in FIG.  8 . 
     INDUSTRIAL APPLICABILITY 
     The location and dimensions of the annular fin  72  are determined by examining various factors. One primary factor is the location in the piston  34  from which heat needs to be dissipated. For example, if the temperature of the annular bowl  48  of the piston  34  needs to be reduced, the diameter of the annular fin  72  may be selected to ensure that the annular fin  72  will contact the area of the inner surface  52  of the annular bowl  48  that will effect the proper heat reduction. Another factor affecting the annular fin  72  dimensions is the magnitude of the heat that is to be evacuated from the piston  34 . An annular fin  72  with a larger surface area will draw more heat from the piston  34 . In addition, a thin annular fin  72  will dissipate more heat than a thick one. The amount of stress placed upon the piston  34  by the introduction of the annular fin  72  is another factor that influences the annular fin&#39;s location and dimensions. The physical dimensions of the piston  34  itself also affect the size and location of the annular fin  72 . If the piston contains the baffle  84 , the optimal dimensions of the annular fin  72  will depend upon the size of the enclosed cooling gallery  94 . The size of the annular fin  72  and the angle at which it protrudes from the crown interior surface  59  may be modified to ensure that the annular fin  72  does not excessively impede the flow of the cooling medium to other portions of the crown interior surface  59  and thereby detrimentally affect the cooling of the piston  34 . 
     One method of attaching the annular fin  72  to the crown interior surface  59  of the piston  34  includes inserting the second edge  80  of the annular fin  72  into the annular groove  64 , creating a press-fit connection between the inner surface  74  and outer surface  76  of the annular fin  72  and the inner wall  66  and outer wall  68  of the annular groove  64 . Another method is used for embodiments of the piston  34  containing thread  82  on the annular fin  72  or thread  70  in the annular groove  64 . In this method, the second edge  80  of the annular fin  72  is placed in the annular groove  64  and the fin  72  is threaded into the groove  64 , thereby connecting the annular fin  72  to the piston  34 . Both of these methods may be used with pistons of any type, including cast, forged, composite, and mechanically joined, as the annular groove  64  may be easily and expeditiously machined into the crown interior surface  59  of any piston  34 . 
     Another method of the present application, shown in FIG. 5, consists of creating the annular fin  72  as an integral part of the piston  34 . In the process of machining the piston  34  and creating the crown interior surface  59 , the annular fin  72 , containing the inner surface  74 , the outer surface  76 , and the first edge  78 , that extends from the crown interior surface  59  and that is integral with the piston  34  is formed. This method may be practiced with forged pistons by simply altering the machining process currently used to create the crown interior surface  59  of forged pistons  34 . 
     The annular fin  72  may also be made integral with the piston  34  via a method that includes inertial welding. In such a method, either the annular fin  72 , the piston  34 , or both, are rotated at high velocity. If both are rotated, they are typically rotated in opposite directions. The annular fin  72  and the piston  34  are then brought together quickly with the annular fin  72  contacting the crown interior surface  59  at the predetermined location. The heat created by the friction between the annular fin  72  and the piston  34  welds them together, making the fin  72  integral with the piston  34 . 
     The addition of the annular fin  72  to the crown interior surface  59  of the piston  34  effects heat attenuation of the portions of the piston  34  that are subject to the highest temperatures and pressures. A cooling medium, such as oil, flows through the cooling passages of the engine  10 . The cooling medium is sprayed by the coolant directing nozzle  26  onto the crown interior surface  59  of the piston  34 . If the piston  34  has the baffle  84 , the cooling medium enters the cooling gallery  94  through the receiving aperture  90  and contacts the crown interior surface  59  and the annular fin  72 . The cooling medium absorbs heat from the crown interior surface  59  and the annular fin  72 . This absorption of heat is greater than that in a piston  34  without an annular fin  72  because the annular fin  72  increases the surface area for the cooling medium to contact the piston  34 . In addition, the annular fin&#39;s  72  position in the crown interior surface  59  allows the annular fin  72  to draw heat from a specific area of the piston  34 . The baffle  84  retains the cooling medium in the cooling gallery  94 , causing the cooling medium to absorb more heat from the crown interior surface  59  as the oil is repeatedly brought into contact with the annular fin  72  and the crown interior surface  59  by the reciprocating motion of the piston  34 . The cooling medium exits the cooling gallery  94  through the draining aperture  92 . After exiting the cooling gallery  94 , the cooling medium enters the oil pan  28  and is recirculated through the engine  10  and cooled by the engine cooling system in a conventional manner. 
     If the piston  34  does not have the baffle plate  84 , the cooling medium is simply sprayed directly onto the crown interior surface  59  and the annular fin  72 . The cooling medium then absorbs heat from the crown interior surface  59  and the annular fin  72  and falls back into the oil pan  28 . The cooling medium is then recirculated through the engine  10  and cooled by the engine cooling system in the conventional manner. 
     The apparatus and method of the present application solves many problems. The apparatus and method may be used in any type of piston, including cast, forged, composite, and mechanically joined. In addition, the apparatus may be quickly and easily installed, decreasing manufacturing costs. The adjustable dimensions and location of the apparatus permit the specific targeting of areas in the piston from which heat is to be removed. 
     Other aspects, objects, and advantages of this invention can be obtained from a study of the drawings, the disclosure, and the appended claims.