Patent Publication Number: US-2021180539-A1

Title: Piston for internal combustion engine

Description:
TECHNICAL FIELD 
     The present invention relates to a piston for an internal combustion engine configured to effectively cool a piston by injecting a cooling oil from an oil jet apparatus to a back surface of a top portion of the piston. 
     BACKGROUND ART 
     In the related art, known examples of a piston for an internal combustion engine such as an engine include a configuration having: a piston crown portion including a top portion being subjected to an explosive gas pressure of combustion gas and a land portion having a piston ring groove on the periphery; a pair of pin boss portions coupled to a smaller end portion of a connecting rod via a piston pin; and a pair of skirt portions configured to guide a vertical reciprocal motion of the piston. The top portion of the piston crown portion is inevitably subjected to a high-temperature combustion gas, and thus an increase in temperature of the piston in association with an increase in output of the engine is now an issue. In particular, there is a problem in that high temperature of the piston in an axial direction of front and rear sides (near the pin boss portion of the piston crown portion) may cause a problem such as aluminum adhesion in the piston ring grooves. 
     In Patent Literature 1, therefore, a piston structure having an annular oil channel in an interior of a piston (hereinafter, referred to as a cooling channel) provided for cooling the piston is known. The cooling channel is provided with an oil inlet port and an oil outlet port. The piston is cooled from the interior by an oil supplied from the oil inlet port into the cooling channel. However, as a boss cooling channel that communicates with the oil channel is provided in a pin boss portion, a sufficient thickness for forming the cooling channel is required. Therefore, the piston structure in Patent Literature 1 has a difficulty in achieving a lightweight structure of the piston simultaneously and is complex in shape and costly. 
     For example, in Patent Literature 2, a piston is proposed in which an oil guiding channel is formed to extend between a pair of skirt portions on a back surface of a piston top portion, an oil injected from an oil jet apparatus toward one end side of the oil guiding channel is guided toward the other end side of the oil guiding channel, and thickened portions configured to restrict a flow of the oil flowing toward side wall portions that connect the pair of skirt portions to each other are formed along both sides of the oil guiding channel. However, such a piston can hardly guide a required amount of injected oil to portions that require to be cooled by the guiding channel, and thus does not necessarily provide satisfactory cooling efficiency. 
     CITATION LIST 
     Patent Literature 
     PTL 1: JP-A-2009-520901 
     PTL 2: JP-A-2009-191779 
     SUMMARY OF INVENTION 
     Technical Problem 
     Accordingly, it is an object of the present invention to provide a piston for an internal combustion engine configured to ensure a required amount of cooling oil to be effectively guided to portions that need to be cooled and to achieve a lightweight structure. 
     Solution to Problem 
     A piston for an internal combustion engine of the present invention has been made to solve such problems, the piston for an internal combustion engine comprises a piston crown portion including a top portion and a pair of pin boss portions each having a piston pin hole to allow insertion of a piston pin and configured to be cooled by a cooling oil injected from an oil jet apparatus having a nozzle toward aback surface of the top portion. The top portion comprises a cooling void provided near at least one of the pin boss portions inside the top portion, and an inlet opening provided on the back surface of the top portion and configured to guide the oil injected from the nozzle toward the cooling void. 
     In the piston for an internal combustion engine of the present invention, one each of the cooling voids may be provided near both of the pin boss portions. 
     Also, in the piston for an internal combustion engine of the present invention, the top portion may include a terminal end at one end of the cooling void, and the inlet opening and the terminal end may be provided at ends of each of the cooling voids. 
     Also, in the piston for an internal combustion engine of the present invention, the top portion may include an outlet opening provided in the back surface and configured to let the oil flowed into the cooling void through the inlet opening to be drained, and the inlet opening and the outlet opening are provided respectively at the ends of each of the cooling voids. 
     Also, in the piston for an internal combustion engine of the present invention, the top portion may comprise a side surface opening provided in the back surface and configured to let the oil flowed into the cooling void through the inlet opening be drained from outside of the pin boss portion or the side wall portion. 
     Also, in the piston for an internal combustion engine of the present invention, the top portion may comprise a groove provided on the back surface and configured to guide the oil injected from the nozzle to the inlet opening. 
     Also, in the piston for an internal combustion engine of the present invention, the top portion may comprise a projection at a position in the back surface where the oil injected from the nozzle hits, and the projection may comprise an inclined surface that is lowered toward the inlet opening to guide the hit oil into the cooling void. 
     Also, in the piston for an internal combustion engine of the present invention, the inclined surface may be inclined to guide the oil to the back surface between the pin boss portions. 
     Also, in the piston for an internal combustion engine of the present invention, the nozzle may be arranged near the inlet opening. 
     Also, in the piston for an internal combustion engine of the present invention, the cooling void may have an inner diameter increasing as it goes away from the inlet opening. 
     Also, in the piston for an internal combustion engine of the present invention, the piston may be a piston for a gasoline engine. 
     Advantageous Effects of Invention 
     According to the present invention, the piston can be efficiently cooled to reduce thermal load that the piston bears, and can achieve the lightweight structure of the piston while ensuring the strength of the piston. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a cross-sectional view illustrating a principal portion of an internal combustion engine that a piston of the present invention is applied to. 
         FIG. 2  is a perspective view of the piston of a first embodiment of the present invention viewed from a back surface. 
         FIG. 3  is a lateral cross-sectional view of the piston taken along the line III-III in  FIG. 4 . 
         FIG. 4  is a vertical cross-sectional view of the piston taken along a direction orthogonal to an axial direction of a piston hole. 
         FIG. 5  is a perspective view illustrating a lateral cross section of the piston taken along the line V-V in  FIG. 4 . 
         FIG. 6  is a lateral cross-sectional view of a piston according to a second embodiment of the present invention. 
         FIG. 7  is a lateral cross-sectional view illustrating a modified example of a piston. 
         FIG. 8  is a vertical cross-sectional view of the modified example of the piston taken along a direction orthogonal to an axial direction of a piston hole. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Referring now to attached drawings, a first embodiment and a second embodiment of the present invention will be described. However, the present invention is not limited to the illustrated embodiments. For example, the piston of the present invention is applied to the piston used for a gasoline engine in the description, but may be applied to any engine such as diesel engines, LPG engines, methanol engines, hydrogen engines, etc. 
     First Embodiment 
       FIG. 1  is a cross-sectional view illustrating a principal portion of an internal combustion engine that a piston of the present invention is applied to. A piston  3  is a piston applied to a gasoline engine. The internal combustion engine includes a cylinder block  1 , a cylindrical cylinder bore  2  formed in the cylinder block  1 , and the piston  3  slidably accommodated inside the cylinder bore  2 . An upper end of a connecting rod  5  is coupled to the piston  3  via a piston pin  4 . A lower end of the connecting rod  5  is coupled to a crankshaft  7  via a crank pin  6 . 
     A crank case  8  provided below the cylinder block  1  in the drawing and a lower portion of the cylinder block  1  define a crank chamber  9  in which the crankshaft  7  is accommodated. An oil jet apparatus  11  configured to inject an oil for cooling the piston  3  is provided on a portion near a lower end of the cylinder bore  2 , which is on the crank chamber  9  side. The oil jet apparatus  11  includes a nozzle  12  having a distal end directed upward to inject oil from below in the drawing toward the piston  3 .  
       FIG. 2  is a perspective view of the piston  3  of the first embodiment of the present invention viewed from a back surface. 
     The piston  3  includes a piston crown portion  24 , a pair of skirt portions  25   a  and  25   b , a pair of pin boss portions  26   a  and  26   b , and side wall portions  28   a  and  28   b.    
     The piston crown portion  24  includes a top portion  21  and a land portion  23  having piston ring grooves  22 . The piston crown portion  24  includes cooling voids  29  described later. The skirt portions  25   a  and  25   b  (hereinafter, referred to simply as skirt portions  25  unless otherwise specifically discriminated, the same applies hereinafter) extend upright from an outer peripheral edge of the piston crown portion  24 . The pin boss portions  26   a  and  26   b  (pin boss portions  26 ) are provided on a back surface side of the top portion  21  with the direction of the plane substantially orthogonal to the skirt portions  25   a  and  25   b . Hereinafter, the back surface of the top portion  21  located in a space defined by the skirt portions  25  and the side wall portions  28  is referred to as “back surface  30   a ”, and the back surface of the top portion  21  located outside the above-described space is referred to as “back surface  30   b ”. The pin boss portions  26   a  and  26   b  include piston pin holes  27   a  and  27   b  (piston pin holes  27 ) that allow insertion of the piston pin  4 . The side wall portions  28   a  and  28   b  (side wall portions  28 ) extend in a direction intersecting a direction of center axis of the piston pin holes  27   a  and  27   b  (piston pin  4 ), and couple ends of the pin boss portions  26   a  and  26   b  and the skirt portions  25   a  and  25   b.    
     The cooling voids  29  provided in the piston crown portion  24  will now be described. 
       FIG. 3  is a lateral cross-sectional view of the piston  3  taken along the line III-III in  FIG. 4 .  FIG. 4  is a vertical cross-sectional view of the piston  3  taken along a direction orthogonal to an axial direction of the piston pin holes  27 .  FIG. 5  is a perspective view illustrating a lateral cross section of the piston  3  taken along the line V-V in  FIG. 4 . 
     Cooling voids  29   a  and  29   b  (cooling voids  29 ) are an arcuate-shaped voids formed inside the top portion  21  along the outer peripheral edge of the piston crown portion  24 . The cooling voids  29  are provided near both of the pin boss portions  26  (and the side wall portions  28 ). The cooling voids  29  are formed between the skirt portions  25  (portions where the skirt portions  25   a  and  25   b  are not formed) to surround outer peripheries of the pin boss portions  26 . The cooling voids  29  are formed by using preferably a salt core, but not limited thereto. 
     In the first embodiment, two cooling voids  29   a  and  29   b  are provided along the pin boss portions  26   a , and  26   b , but providing only one of the cooling voids  29   a  and  29   b  is also applicable. 
     The piston crown portion  24  (top portion  21 ) includes, on the back surface  30   a  thereof, inlet openings  35   a  and  35   b , terminal ends  36   a  and  36   b , first to third side surface openings  37   a  to  39   a  and  37   b  to  39   b , and a groove  40 . 
     The inlet openings  35   a  and  35   b  (the inlet openings  35 ) guide an oil to be injected from the nozzle  12  of the oil jet apparatus  11  and let the oil flow into the cooling voids  29 . The inlet openings  35  are provided on the back surface  30   a  of the top portion  21 . Each of the inlet openings  35  corresponds to each ends of the cooling voids  29 , and is provided inside each of the side wall portions  28 . The inlet openings  35   a  and  35   b  are preferably disposed at symmetrical positions with respect to a position where the oil injected from the nozzle  12  hits. The terminal ends  36   a  and  36   b  (terminal ends  36 ) correspond to the other ends of the cooling voids  29  and are provided inside the side wall portions  28 . 
     Inner diameters of the cooling voids  29  increase from the inlet openings  35  toward the terminal ends  36 . Specifically, the cooling voids  29  are formed to increase in inner diameter toward a front surface side of the top portion  21  (to incline toward the front surface side of the top portion  21 ). The increase in diameters of the cooling voids  29  provides oil-flowing surfaces with gradients. This inclination achieves a smooth flow of the oil entirely in the cooling voids  29 . This inclination makes as much oil flow into the cooling voids  29  as possible to make the piston  3  effectively cooled. 
     The first to third side surface openings  37   a  to  39   a  and  37   b  to  39   b  (first to third side surface openings  37  to  39 ) let the oil flowed from the inlet openings  35  into the respective cooling voids  29  drained to outside the pin boss portions  26  or the side wall portions  28 . The first to third side surface openings  37  to  39  are provided in the back surface  30   b.     
     The first side surface openings  37  are provided near the side wall portions  28  on the inlet openings  35  side. The second side surface openings  38  are provided near the pin boss portions  26 . The third side surface openings  39  are provided near the side wall portions  28  on the terminal ends  36  side. The groove  40  is provided in the back surface  30   a , and guides the oil injected form the nozzle  12  to the respective inlet openings  35 . Both ends of the groove  40  are connected to the inlet opening  35   a  and the inlet opening  35   b , respectively. 
     Subsequently, an operation of the piston  3  of the first embodiment will be described. 
     The oil jet apparatus  11  injects a cooling oil from the nozzle  12  toward a substantially center (the back surface  30   a  of the top portion  21 ) of the groove  40  in the longitudinal direction. The oil is injected substantially toward the center as described above in design but may actually be deviated toward one of the inlet openings  35 . The oil hit on the groove  40  is guided by the groove  40 , bifurcates to the inlet openings  35 , and flows into the cooling voids  29 . The oil overflowed from the groove  40  passes over the back surface  30   a  from the skirt portion  25   a  side to the skirt portion  25   b  side to cool the top portion  21  down. 
     The oil flowed into the cooling voids  29  runs along the cooling voids  29  while receiving an inertia force generated by a sliding action of the piston, and efficiently cools over a range from the interior of the piston crown portion  24  to peripheries of the pin boss portions  26 . Part of the oil flows to the terminal ends  36 . The oil flowed to the terminal ends  36  and remaining oil are drained out from the first to third side surface openings  37  to  39  and the inlet openings  35 . Part of the oil drained from the first and third side surface openings  37  and  39  flows along the side wall portions  28  and side walls of the pin boss portions  26  and cools these parts. Part of the oil drained from the second side surface opening  38  flows near the peripheral edge of the piston pin holes  27  and cools these parts. 
     The piston  3  of the first embodiment configured in this manner, being provided with the cooling voids  29  in the piston crown portion  24 , achieves efficient cooling of the periphery of the pin boss portion  26 . In addition, the cooling voids  29  cool a portion near the piston ring groove  22  efficiently, aluminum adhesion in the piston ring groove  22  may be inhibited. The piston  3  of the first embodiment configured in this manner may prevent problems that may occur on the piston  3  in association with improvement of the cooling efficiency and thus may achieve an improvement of engine performances. 
     Even a piston for gasoline engines normally having a thinner piston crown portion  24  (land portion  23 ) than the piston for diesel engines may achieve a lightweight structure with required strength maintained during use with the cooling voids  29  arranged with a high spatial efficiency. In addition, the piston  3  includes three openings; the first to third side surface openings  37  to  39  and thus significant weight reduction is achieved. 
     The piston crown portion  24  may include one, two, three or more side surface openings. The piston crown portion  24  may not have the side surface openings  37  to  39 . In this case, the oil entered through the inlet openings  35  is cooled in the cooling voids  29  and then is drained from the inlet openings  35 . However, considering the oil cooling effect, the side surface openings or an outlet openings  61  described later are preferably provided.  
     Second Embodiment 
     A piston for an internal combustion engine according to a second embodiment of the present invention will be described. 
       FIG. 6  is a lateral cross-sectional view of a piston  50  according to the second embodiment of the present invention and is a drawing corresponding to  FIG. 3 . The piston  50  of the second embodiment is different from the piston  3  of the first embodiment in that a projection  51  is provided on the back surface  30   a  of the top portion  21  instead of the groove  40 . Other configurations of the piston  50  are substantially the same as the piston  3  of the first embodiment, and thus the configurations and parts corresponding to the first embodiment are designated by the same reference signs and overlapped description will be omitted. 
     The top portion  21  of the piston crown portion  24  includes the projection  51  provided on the back surface  30   a  at a position where the oil injected from the nozzle  12  of the oil jet apparatus  11  hits. The projection  51  is the highest substantially at the center between the inlet openings  35   a  and  35   b  and includes inclined surfaces  52   a  and  52   b  (inclined surfaces  52 ) decreasing in height toward the inlet openings  35   a  and  35   b  to guide the hit oil toward the cooling voids  29 . The inclined surfaces  52  incline to be lowered from the skirt portion  25   a  side toward the skirt portion  25   b  to guide the oil to the back surface  30   a  between the pin boss portions  26 . 
     An action of the piston  50  of the second embodiment will be described below. Note that only points different from the first embodiment will be described while omitting the overlapped description. 
     The oil jet apparatus  11  injects oil from the nozzle  12  toward the projection  51 . The oil is guided by the inclined surfaces  52  of the projection  51 , bifurcates to the inlet openings  35 , and flows into the cooling voids  29 . The oil flowed therein runs along the cooling voids  29  while receiving an inertia force generated by a sliding action of the piston, and efficiently cools over a range from the interior of the piston crown portion  24  to the peripheries of the pin boss portion  26 . The oil flows toward the back surface  30   a  between the pin boss portion  26  by being guided by the inclined surfaces  52  to cool the entire top portion  21 . 
     The piston  50  of the second embodiment configured in this manner is allowed to guide the oil suitably into the cooling voids  29  by the inclined surfaces  52  of the projection  51 . The inclined surfaces  52  are further inclined toward the skirt portion  25   b , and thus cooling of the back surface  30   a  between the pin boss portion  26  is also ensured. 
     Although several embodiments of the present invention has been described, these embodiments are intended for illustration only, and are not intended to limit the scope of the invention. These new embodiments may be implemented in other various modes, and various omissions, replacements, and modifications may be made without departing from the gist of the invention. These embodiments and modifications thereof are included in the scope and gist of the disclosure, and are included in the invention described in Claims and a range equivalent thereto. 
     For example, the pistons  3  and  50  of the first and second embodiments may have outlet openings  61   a  and  61   b  instead of the terminal ends  36  of the cooling voids  29 . 
       FIG. 7  is a lateral cross-sectional view illustrating a modified example of a piston  60 , and is a drawing corresponding to  FIG. 3  and  FIG. 6 .  FIG. 8  is a vertical cross section of the piston  60  extending along the direction orthogonal to the axial direction of the piston pin holes  27 . 
     The piston  60  will be described as a modification of the piston  50  of the second embodiment as an example. Configurations and parts corresponding to the pistons and  50  of the first and second embodiments are designated by the same reference signs and overlapped description will be omitted. 
     The outlet openings  61   a  and  61   b  (the outlet openings  61 ) let the oil flowed from the inlet openings  35  into the cooling voids  29  be drained. The outlet openings  61  are provided at positions symmetrical to the inlet openings  35  with respect to an axial direction of the piston pin  4 . In other words, the outlet openings  61  are provided at the other ends of the cooling voids  29  inside the side wall portions  28 . When the outlet openings  61  are provided, the first to third side surface openings  37  to  39  may be omitted. 
     The shape of the cooling voids  29  is not limited to the arcuate shape, and shapes which can effectively cool the piston mainly around the pin boss portion  26  may be employed. 
     In addition, the inlet openings  35  may be provided either on the thrust side or on the counter-thrust side. 
     REFERENCE SIGNS LIST 
       1  cylinder block 
       2  cylinder bore 
       3 , 50 , 60  piston 
       4  piston pin 
       5  connecting rod 
       6  crank pin 
       7  crankshaft 
       8  crank case 
       9  crank chamber 
       11  oil jet apparatus 
       12  nozzle 
       21  top portion 
       22  piston ring groove 
       23  land portion 
       24  piston crown portion 
       25   a ,  25   b  ( 25 ) skirt portion 
       26   a ,  26   b  ( 26 ) pin boss portion 
       27   a ,  27   b  ( 27 ) piston pin hole 
       28   a ,  28   b  ( 28 ) side wall portion 
       29   a ,  29   b  ( 29 ) cooling void 
       30   a ,  30   b  back surface 
       35   a ,  35   b  ( 35 ) inlet opening 
       36   a ,  36   b  ( 36 ) terminal end 
       37   a  to  39   a ,  37   b  to  39   b  ( 37  to  39 ) first to third side surface opening 
       40  groove 
       51  projection 
       52   a ,  52   b  ( 52 ) inclined surface 
       61   a ,  61   b  ( 61 ) outlet opening