Patent Publication Number: US-11022009-B2

Title: Hydraulic lash adjuster

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to components of an internal combustion engine, and more particularly, to a hydraulic lash adjuster. 
     BACKGROUND 
     Hydraulic lash adjusters are employed in internal combustion engines to reduce clearance between engine components. This clearance, also called lash, can occur between components of a valve train, for example, resulting in the inability of an intake or exhaust valve to open and close fully. Lash can result from the expansion of engine components due to manufacturing tolerances, imperfections, wear, and thermal expansion. A hydraulic lash adjuster located between valve train components may eliminate lash by utilizing a high pressure volume located under a piston. This high pressure volume includes an incompressible fluid, such as oil, that enters via a valve. The volume of fluid maintains the length of the lash adjuster, thereby reducing or eliminating lash. 
     The use of hydraulic fluid allows hydraulic lash adjusters to operate with reduced need for adjustments, in contrast to solid valve lifters, even as engine components age and experience increased wear. However, hydraulic lash adjusters, which employ incompressible fluid, can produce unsatisfactory performance when air is introduced. Air bubbles that enter the high pressure region are especially problematic as they can allow the lash adjuster to compress, brining the lash adjuster out of contact with a component of the valve train. Compression in the lash adjuster can introduce valve lift loss which can result in deficient engine performance and even introduce the possibility of failure. 
     An exemplary valve lash adjuster is disclosed in U.S. Pat. No. 4,917,059 (“the &#39;059 patent”) to Umeda. The &#39;059 patent discloses a hydraulic lash adjuster that includes an elongated generally cylindrical body having an exterior annular oil groove in a side wall thereof. The annular oil groove receives engine oil from an oil gallery connected to the pressure side of an engine oil lubricating system and communicating with the lifter gallery bore. The cylindrical body also includes a central cylindrical bore therein having an open end. A first oil inlet passage extends through the side wall of the body into the bore to allow for flow of oil from the annular oil groove into the bore. 
     While the valve lash adjuster described in the &#39;059 patent may operate adequately under some conditions, there may be other conditions where the lash adjuster does not respond as desired. The disclosed hydraulic lash adjuster may solve one or more of the problems set forth above and/or other problems in the art. The scope of the current disclosure, however, is defined by the attached claims, and not by the ability to solve any specific problem. 
     SUMMARY 
     In one aspect, a hydraulic lash adjuster may include a longitudinally extending pushrod having a proximal end and a distal end, and a cavity located at the distal end and a piston received in the cavity. The piston may include an internal reservoir and a fluid pathway to the internal reservoir. The fluid pathway may include a longitudinal passage and a radial passage. 
     In another aspect, a hydraulic lash adjuster may include a longitudinally extending pushrod having a proximal end and a distal end, and a cavity located at the distal end and a piston received in the cavity. The piston may include an internal reservoir and a fluid pathway to the internal reservoir. The fluid pathway may include a longitudinal passage, a radial passage, and a circumferential recess formed in an outer surface of the piston. 
     In yet another aspect, a hydraulic lash adjuster may include a longitudinally extending pushrod having a proximal end and a distal end, and a cavity located at the distal end, and a piston received in the cavity, the piston including a fluid pathway having at least three turns. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate various exemplary embodiments and together with the description, serve to explain the principles of the disclosed embodiments. 
         FIG. 1  is a sectional view of an internal combustion engine including an hydraulic lash adjuster according to aspects of the disclosure; 
         FIG. 2  is a sectional view of the hydraulic lash adjuster of  FIG. 1 ; and 
         FIG. 3  is a perspective view of a piston of the hydraulic lash adjuster of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the features, as claimed. As used herein, the terms “comprises,” “comprising,” “having,” including,” or other variations thereof, are intended to cover a non-exclusive inclusion such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements, but may include other elements not expressly listed or inherent to such a process, method, article, or apparatus. Moreover, in this disclosure, relative terms, such as, for example, “about,” substantially,” and “approximately” are used to indicate a possible variation of ±10% in the stated value. 
       FIG. 1  illustrates a sectional view of an internal combustion engine  10  that includes a cylinder head  12  having one or more piston cylinders. Cylinder head  12  includes at least one intake valve  14  and a least one exhaust valve for each piston cylinder. Engine power is generated by a combustion reaction in which a piston is driven to reciprocate within each cylinder. Intake air enters each cylinder by one or more intake valves while combustion products are exhausted from each cylinder by one or more exhaust valves. 
     Two valves  14  are illustrated in  FIG. 1 , each valve  14  includes a valve head  16  and a valve stem  18 . Each valve  14  is biased towards a closed position by a valve spring  20  disposed at an upper portion of each valve stem  18 . A bridge  22  is disposed so as to connect the ends of valve stems  18  to a rocker  24 . Rocker  24  includes a shaft  26  disposed at a central portion thereof. Rocker  24  is pivotable about an axis defined by shaft  26 . An end of rocker  24  opposite to bridge  22  contains a threaded through-hole in which an adjusting screw  28  is disposed. Adjusting screw  28  extends from rocker  24  into contact with a hydraulic lash adjuster (HLA)  30 . HLA  30  may extend between adjusting screw  28  and a lifter  74  and camshaft  82  assembly. HLA may and include a piston  32  and a pushrod  34 , with the piston  32  being received within a distal cavity  36  of a pushrod  34 . 
     A hydraulic fluid circuit of the HLA includes a path  80  that provides hydraulic fluid to HLA  30 . In one aspect, the hydraulic fluid flowing through path  80  may be oil. Path  80  may begin in shaft  26  of rocker  24  and form a passage in rocker  24  that connects to a corresponding passage in the interior of adjusting screw  28 . Path  80  may supply hydraulic fluid through adjusting screw  28  to the piston  32 . 
       FIG. 2  illustrates a sectional view of HLA  30 . As noted above, HLA  30  may include piston  32  movable within a distal opening in pushrod  34 . Thus, piston  32  may form a first, distal end  38  of HLA  30 , and a proximal end of pushrod  34  may form a second, proximal end  40  of HLA  30  at a position opposite to first end  38  in a longitudinal direction. In one aspect, a central axis C may form a longitudinal axis of HLA  30  that extends from first end  38  to second end  40 . As can be seen in  FIG. 2 , piston  32  and pushrod  34  may each extend in a longitudinal direction defined by central axis C. 
     Piston  32  may include, from distal to proximal, a recess  42  for receiving an end of adjusting screw  28  and providing a fluid communication with hydraulic fluid path  80 , a widened distal portion from which a neck  48  extends, a central body  88  extending proximally from neck  48 , and proximal end  70  including a check valve  90 . Central body  88  of piston  32  may include a circumferential recess  56  and an internal reservoir  44 . A fluid pathway may extend to internal reservoir  44 . This fluid pathway may include a longitudinal passage  52  and a radial passage  54 . Longitudinal passage  52  may extend from recess  42  through neck  48  and to one or more radial passages  54 , thereby connecting path  80  to the circumferential recess  56  of piston  32 . Circumferential recess  56  may also form part of the fluid pathway, and connects to the internal reservoir  44  via a plurality of radial reservoir passages  62 . Thus, longitudinal passage  52 , radial passage  54 , recess  56 , and reservoir passages  62  may form a fluid pathway to reservoir  44 . As shown in  FIG. 2 , radial passages  54  may be directly connected to longitudinal passage  54  and extend from an end of longitudinal passage  54  to connect to circumferential recess  56  at a location distal of the reservoir passages  62 . Thus, circumferential recess  56  may be in fluid communication with longitudinal passage  52  by radial passages  54 . Proximal end  70  of piston  32  may include a longitudinal passage  76  selectively communicating internal reservoir  44  with cavity  36  of pushrod  34  via check valve  90 . 
     With continued reference to  FIG. 2 , longitudinal passage  52  may extend longitudinally from recess  42  at distal end  38  so as to be approximately aligned with (as shown) or parallel to central axis C. Longitudinal passage  52  may be a narrow passage that has a smaller diameter than recess  42 . In one aspect, longitudinal passage  52  may be an approximately cylindrical passage having a diameter of approximately 1.6 mm. Longitudinal passage  52  may terminate at an intersection with the one or more radial passages  54 , that extend substantially radially within piston  32  in a direction toward diametrically opposite sides of piston  32  within cavity  36 . HLA  30  may include two radial passages  54 , circumferentially separated by 180 degrees  3 , or may include three, four, or more radial passages  54 . As illustrated in  FIG. 2 , radial passage  54  may extend normal to longitudinal passage  52  so that the intersection of longitudinal passage  52  and radial passage  54  forms a first turn  64 . In one aspect, as shown, turn  64  may be a turn of approximately 90 degrees. However, first turn  64  may be a somewhat more gradual turn (extending slightly downward) or a somewhat sharper turn (extending slightly upward). 
     As shown in  FIG. 2 , the one or more radial passages  54  may extend through an axial center of piston  32  represented by central axis C. Like longitudinal passage  52 , the one or more radial passages  54  may be a narrow passage having an approximately cylindrical shape. In one aspect, the one or more radial passages  54  may have a diameter of approximately 1.6 mm. Thus, longitudinal passage  52  and radial passage  54  may have approximately equal diameters. As noted above, radial passages  54  may terminate at the circumferential recess  56 . Thus, recess  56  may extend from the end of one or more radial passages  54  in an outer surface of central body  88 . Thus, longitudinal passage  52  and the one or more radial passages  54  may provide a continuous passage that connects distal recess  42  and circumferential recess  56  with a generally constant diameter pathway. 
     The one or more radial passages  54  and circumferential recess  56  of piston  32  may intersect at one or more locations within HLA  30  to form a plurality of second turns  66 . Like the first turn  64 , the second turns  66  may form a sharp turn of, for example, approximately 90 degrees. However, second turns  66  may be either a somewhat more gradual term or a somewhat sharper turn. Each radial passage  54  may open into recess  56  at a second turn  66 . Thus, longitudinal passage  52  and radial passage  54  may form at least two turns (e.g., first turn  64  and second turn  66 ) in a fluid pathway between distal end  38  and reservoir  44 . 
     Circumferential recess  56  may form a circumferential (360 degree) space between pushrod  34  and piston  32 . In one aspect, recess  56  may be a circumferentially extending recess formed about the annulus, or outer peripheral surface, of piston  32 . However, recess  56  may alternatively be formed as a circumferentially extending recess within the inner peripheral surface of cavity  36  of pushrod  34 . Recess  56  may extend farther proximal than distal along a length of piston  32 . Circumferential recess  56  may also extend distally and proximally beyond the passages  54  and  62  communicating with the recess  56 . In particular, recess  56  includes a first recess end  58  and a second, opposite recess end  60 . First recess end  58  may be located distally with respect to radial passages  54 , reservoir  44 , and reservoir passages  62  (above in  FIG. 2 ). First recess end  58  may terminate at a wall  50  that extends circumferentially between first recess end  58  and a piston retaining member or snap ring  72 . The second recess end  60  may be located proximal of the one or more reservoir passages  62  (below in  FIG. 2 ). Thus, second recess end  60  may allow recess  56  to extend closer to a proximal end of HLA  30  than reservoir passage  62 . 
     As noted above, one or more reservoir passages  62  which may extend from circumferential recess  56  in a radially-inward direction toward reservoir  44 , to fluidly connect recess  56  and reservoir  44 . Each reservoir passage  62  may be a small hole or passage having a diameter of approximately 1.6 mm. Thus, reservoir passage  62  may have a diameter approximately equal to one or both of the diameters of the longitudinal passage  52  and the radial passages  54 . Further, reservoir passage  62  may extend in a radial direction so as to form a third turn  68  of approximately 90 degrees with recess  56 . In one aspect, two reservoir passages  62  may extend through piston  32  from recess  56  to reservoir  44 , each of which forms a third turn  68 . In another aspect, one, three, four or more than four reservoir passages  62  may be provided to connect recess  56  to reservoir  44 . Regardless of the number of reservoir passages  62  provided, each may form a third turn  68  of approximately 90 degrees with recess  56 . Thus, piston  32  may include a fluid pathway having at least three turns, including first turn  64 , second turn  66 , and third turn  68 . Additionally, each of the reservoir passages  62  may be evenly spaced apart about a periphery of reservoir  44 , and may be equal in number and circumferentially aligned with radial passages  54 . However, reservoir passages  62  may also be unevenly distributed with respect to one another and/or radial passages  54 , and HLA  30  may include more or less reservoir passages  62  than radial passages  54 . Each reservoir passage  62  may extend entirely through an outer peripheral surface of piston  32  in which recess  56  is provided ( FIG. 3 ). 
     With continued reference to  FIG. 2 , reservoir  44  may be formed inward of recess  56  within central body  88 . A first end of reservoir  44  may be provided proximal with respect to longitudinal passage  52  and radial passage  54 . An opposite second end of reservoir  44  may be formed by proximal end  70  of piston  32 . Reservoir  44  includes a volume larger than circumferential recess  56 . 
     Check valve  90  may be a one way valve that separates a pressure chamber  46  from the reservoir  44 . In one aspect, check valve  90  is a ball valve having a valve passage  76  and a ball  86 , which is biased by a biasing element (e.g., spring)  92  and longitudinal passage  76 . Ball  86  is urged by biasing element  92  to selectively seal the reservoir  44  from the pressure chamber  46 . Ball  86  may allow passage of hydraulic fluid from reservoir  44  to high pressure chamber  46  via longitudinal passage  76  by moving in a direction toward proximal end  40  and against a biasing force of biasing element  92 . Ball  86  may block a flow of hydraulic fluid from high pressure chamber  46  to reservoir  44 . 
     As mentioned above, HLA  30  may include a retaining member  72  secured within a groove of the cavity  36  of pushrod  34  to stop piston  32  from exiting cavity  36 . In one aspect, retaining member  72  may be a retaining ring such as a snap ring. Thus, piston  32  is movable within cavity  36  between a bottom of cavity and retaining member  72 , with the biasing element  78  urging piston  32  toward retaining member  72 . It is understood that the clearance between the piston  32  and the sidewall of cavity  36  of pushrod  34  is small enough to restrict the free flow of hydraulic fluid, but still allows some quantity of hydraulic fluid to lubricate the outer diameter of piston  32  and the sidewalls of cavity  36  pushrod  34 . Thus, significant friction between piston  32  and the sidewall of cavity  36  may be avoided. It is also recognized that the clearance between piston  32  and the sidewall of cavity  36  may allow for the migration of air from circumferential recess  56  past wall  50  to exit HLA  30 . 
       FIG. 3  illustrates a perspective view of piston  32  isolated from pushrod  34 . As shown, the proximal (lower) portion of piston  32  includes the circumferential recess  56 . Thus, circumferential recess  56  extends farther distal than proximal along a length of piston  32 . As discussed above, recess  56  includes a distal end  58  and a proximal end  60 , and aligned radial passages  54  and reservoir passages  62  (only set shown in  FIG. 3 ). 
     As noted above, circumferential recess  56  may extend along an entire circumference of the outer surface of piston  32  (see  FIG. 3 ). However, recess  56  may instead be formed along only a portion of the outer circumferential surface of piston  32 . When formed along only a portion of the outer surface of piston  32 , a plurality of separate recesses  56  may be provided at different circumferential locations about the outer surface of piston  32 . First recess end  58  and second recess end  60  may similarly extend partially or entirely along the circumference of piston  32 . 
     INDUSTRIAL APPLICABILITY 
     The disclosed aspects of the HLA  30  may be employed in a variety of applications, such as in internal combustion engines. When provided in a valve train of internal combustion engine  10 , HLA  30  may assist in limiting lash in valve train components. Furthermore, HLA  30  may assist in removing air from the hydraulic fluid supplied to the HLA  30 . 
     Returning to  FIG. 1 , during operation of the internal combustion engine  10 , camshaft  82  is brought into rotational motion. As camshaft  82  rotates, lobe  84  regularly presses on lifter  74 , which in turn translationally displaces HLA  30  toward adjustment screw  28  and one end of rocker  24 . 
     Also during operation of the internal combustion engine  10 , a lubrication pump may provide a flow of hydraulic fluid provide fluid to HLA  30 . With reference to  FIG. 1 , the hydraulic fluid from such a lubrication pump may be supplied to shaft  26  of rocker  24 , which may form a beginning of path  80  of hydraulic fluid. Hydraulic fluid may travel along the circumference of shaft  26  to an end of rocker  24  opposite bridge  22 . Hydraulic fluid can then flow to an internal passage of adjusting screw  28 . 
     An end of adjusting screw  28  is received by recess  42  of HLA  30 . Hydraulic fluid may exit an opening provided at an end of adjusting screw  28  to enter recess  42 , and in particular longitudinal passage  52 . Thus, HLA  30  may be provided with a supply of hydraulic fluid via path  80  during the operation of internal combustion engine  10 . 
     Hydraulic fluid may be stored within pressure chamber  46  of HLA  30 . As shown in  FIG. 2 , hydraulic fluid in reservoir  44  is separated from pressure chamber  46  by one way valve  90 . One way valve  90  may allow a relatively small quantity of hydraulic fluid to enter pressure chamber  46  from reservoir  44 . Also, one way valve  90  may prevent hydraulic fluid from passing from the pressure chamber  46  to reservoir  44 . Thus, pressure can be maintained within pressure chamber  46 . 
     The flow of hydraulic fluid from path  80  to recess  42 , may be guided by longitudinal passage  52  to subsequently take first turn  64  at the bottom of longitudinal passage  52  to transition the flow from longitudinal passage  52  to the one or more radial passages  54 . As noted above, the first turn  64  may be a sharp turn of, for example, approximately 90 degrees. After entering turn  64 , the flow of hydraulic fluid flow may proceed in a radially outward direction within the one or more radial passages  54 . Once the flow of hydraulic fluid guided by radial passage  54  reaches an end of radial passage  54 , the flow of hydraulic fluid is drawn into circumferential recess  56  of piston  32  via second turn  66 . Second turn  66 , like first turn  64 , may be a sharp turn and may prevent air from entering recess  56 . Additionally, second turn  66  may allow air contained within the hydraulic fluid to be directed upward in a direction distally toward first end  38  of piston  32 . 
     Hydraulic fluid may flow to reservoir  44  via reservoir passages  62  and third turn  68 . When recess  56  and reservoir  44  are both filled with hydraulic fluid, air in the hydraulic fluid may migrate to first recess end  58  that extends distal of the one or more radial passages  54 . Air may then exit HLA  30  by passing between wall  50  and the sidewall of cavity  36  of pushrod  34 . Furthermore, second recess end  60  provides a further location for collecting air in the hydraulic fluid, thus assisting in preventing air from passing to reservoir  44 . Air captured by second recess end  60  may then migrate distally along circumferential recess  56  and to first recess end  58 . 
     Thus, the various shapes and sizes of passages and recesses of HLA  30  may assist in collecting and allowing air entrained in the hydraulic fluid to escape. For example the longitudinal extent of circumferential recess  56 , the extension of circumferential recess  56  above radial passages  54 , the relatively small size of wall  50 , and the numerous turns of the flow of hydraulic fluid may individually and collectively help to collect and remove air from the HLA  30 . With such an arrangement, air or bubbles contained in hydraulic fluid supplied to HLA  30  may be continuously collected and allowed to migrate out of the HLA  30 . Such a removal of air from the HLA  30  may facilitate a more robust HLA that is less susceptible to inaccuracies caused by a build-up of air in the HLA  30 . 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed HLA  30  without departing from the scope of the disclosure. Other embodiments of the piston  32  and HLA  30  will be apparent to those skilled in the art from consideration of the specification and practice of the system disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents.