Patent Publication Number: US-8973546-B2

Title: Lash adjuster

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2013-26425 filed on Feb. 14, 2013, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     1. Technical Field 
     The present invention relates to a lash adjuster. 
     2. Related Art 
     A conventional lash adjuster includes a bottomed cylindrical body fixed to a cylinder head of an internal combustion engine and a plunger which is inserted into the body so that the plunger is movable up and down. The plunger has an upper end supporting a rocker arm. The plunger further has a peripheral wall formed with an oil passage hole and a bottom wall formed with a valve hole. Hydraulic fluid, such as oil, supplied through an oil filler hole of the cylinder head is stored in a low-pressure chamber in the plunger through the oil passage hole and also supplied through the valve hole into the body thereby to fill the body. A high-pressure chamber is defined by dividing an interior of the body by the bottom wall of the plunger. The plunger is moved up and down according to oil pressure in the high-pressure chamber. The hydraulic fluid in the low-pressure chamber in the plunger is drawn through the valve hole into the high-pressure chamber when the plunger is moved upward. In this case, there is a possibility that air entrainment may occur in the high-pressure chamber when the hydraulic fluid level is low in the low-pressure chamber. 
     In view of the aforementioned problem, the conventional art provides a lash adjuster provided with a cylindrical partitioning member inserted into the plunger. A space inside the partitioning member serves as a low-pressure chamber. An oil passage is formed between an inner periphery of the plunger and an outer periphery of the partitioning member. An oil passage end is located above the oil passage hole. As a result, a large amount of hydraulic fluid is supplied from the oil passage hole via the oil passage and the oil passage end into the low-pressure chamber. Since the hydraulic fluid level depends upon the oil passage end located above the oil passage hole, air entrainment can be prevented in the high-pressure chamber. 
     The above-described partitioning member is press-fitted into the plunger. In this case, if without execution of treatment such as shrinkage fitting, the dimensional control is required under the condition that there is little press-fit tolerance between an inner diameter of the plunger and an outer diameter of the partitioning member or a press-fit allowance is zero or close to zero. This requires a high machining accuracy. In particular, the partitioning member is provided with a stepped portion located midway in an up-down direction. Accordingly, the partitioning member has a possibility of buckling beginning at the stepped portion when forcedly fitted into the plunger without a suitable control of the press-fit tolerance. 
     SUMMARY 
     Therefore, an object of the invention is to provide a lash adjuster which can relax the machining accuracy of the plunger and the partitioning member thereby to render the machining easier. 
     The invention provides a lash adjuster including a body formed into a bottomed cylindrical shape, a plunger which is inserted into the body so as to be movable up and down and has a bottom wall formed with a valve hole and a peripheral wall standing from an outer periphery of the bottom wall and having an oil passage hole formed therethrough, so that the plunger is formed into a bottomed cylindrical shape, the plunger defining a high-pressure chamber between the bottom wall and the body, a partitioning member formed into a tubular shape and inserted into the plunger, the partitioning member having an oil passage end located above the oil passage hole in a state where the partitioning member is inserted in the plunger, the partitioning member defining an oil passage between itself and the peripheral wall of the plunger outside the partitioning member, the partitioning member having a low-pressure chamber located inside the partitioning member, the low-pressure chamber reserving a hydraulic fluid flowing thereinto through the oil passage hole, the oil passage and the oil passage end, the low-pressure chamber causing the hydraulic fluid reserved therein to flow through the valve hole into the high-pressure chamber, and a spacer interposed between the peripheral wall of the plunger and the partitioning member so that the partitioning member is held in the plunger. 
     The spacer interposed between the peripheral wall of the plunger and the partitioning member causes the partitioning member to be held by the spacer. Accordingly, the dimensional control need not be rendered stricter between the inner diameter of the plunger and the outer diameter of the partitioning member, with the result that the machining of the plunger and the partitioning member can be rendered easier. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIG. 1  schematic sectional view of an internal combustion engine in which a lash adjuster in accordance with one embodiment is incorporated; 
         FIG. 2  is a sectional view of the lash adjuster of embodiment 1; 
         FIG. 3  is a sectional view of the lash adjuster of embodiment 2; 
         FIG. 4  is a sectional view of the lash adjuster of embodiment 3; and 
         FIG. 5  is a sectional view of the lash adjuster of embodiment 4. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiment 1 of the present invention will be described with reference to  FIGS. 1 and 2  of the accompanying drawings. Referring to  FIG. 1 , a lash adjuster  10  in accordance with embodiment 1 is shown. As shown, the lash adjuster  10  is incorporated in a valve gear of an internal combustion engine. The valve gear includes a valve  50 , a rocker arm  60  and a cam  70  in addition to the lash adjuster  10 . 
     The lash adjuster  10  is inserted into a mounting recess  91  of a cylinder head  90  from above. The valve  50  is provided to be capable of opening and closing an intake/exhaust port  80  of the cylinder head  90 . The rocker arm  60  is disposed so as to extend between an upper end (a support portion  25  of a plunger  12  as will be described later) of the lash adjuster  10  and an upper end of the valve  50  in a right-left direction. The cam  70  is disposed above the rocker arm  60  so as to be sidable together with a roller  61  of the rocker arm  60 . Upon rotation of the cam  70 , the rocker arm  60  is swung in an up-down direction with the upper end of the lash adjuster  10  serving as a fulcrum. With swing of the rocker arm  60 , the valve  50  is moved up and down thereby to open and close the intake/exhaust port  80 . 
     The lash adjuster  10  will now be described more concretely. The lash adjuster  10  includes a body  11 , a plunger  12 , a partitioning member  13  and a spacer  100  as shown in  FIG. 2 . The body  11  has a disc-shaped bottom wall  14  and a cylindrical peripheral wall  15  standing from an outer periphery of the bottom wall  14 . The body  11  is formed into a bottomed cylindrical shape as a whole. The body  11  is fittable into the mounting recess  91  of the cylinder head  90 . The peripheral wall  15  of the body  11  has an outer oil passage hole  16  formed therethrough. The outer oil passage hole  16  is disposed in communication with an oil filler hole  92  of the cylinder head  90 . Furthermore, the body  11  has an outer periphery formed with an annular recess  17  which extends over the entire periphery thereof and in which the outer oil passage hole  16  is open. Accordingly, the outer oil passage hole  16  and the oil filler hole  92  are retained in communication via the annular recess  17  even when the body  11  is rotated in the mounting recess  91 . 
     The plunger  12  has a disc-shaped bottom wall  18  and a cylindrical peripheral wall  19  standing from an outer periphery of the bottom wall  18  and is formed into a bottomed cylindrical shape as a whole. The bottom wall  18  includes a central part through which a valve hole  20  is formed. The valve hole  20  communicates between a high-pressure chamber  22  and a low-pressure chamber  23  via a valve element  21  as will be described later. The peripheral wall  19  has an upper end formed with a semispherical support potion  25  which is radially squeezed and has a centrally located through hole  24 . The support potion  25  includes an outer semispherical surface on which a rocker arm  60  is adapted to slide during swinging. 
     The peripheral wall  19  also has an oil passage hole  26  formed therethrough. The peripheral wall  19  has an outer peripheral surface with an annular recess  27  formed over an entire circumference thereof. The oil passage hole  26  is open to the recess  27 . The oil passage hole  26  communicates via the recess  27  with the outer oil passage hole  16  of the body  11 , so that the oil passage hole  26  and the outer oil passage hole  16  are retained in communication even when the plunger  12  is rotated in the body  11 , respectively. 
     A high-pressure chamber  22  is defined between the bottom wall  18  of the plunger  12  and the body  11  in the state where the plunger  12  is inserted in the body  11 , as shown in  FIG. 2 . A spherical valve element  21  is provided in the high-pressure chamber  22 . The valve element  21  is housed in a cage-like retainer  28  and biased by a first spring  29  in a direction such that the valve hole  20  is closed. The high-pressure chamber  22  is also provided with a second spring  30  located between the bottom wall  14  of the body  11  and an upper edge of the retainer  28 . The plunger  12  is biased upward by the second spring  30 . 
     The partitioning member  13  is inserted into the plunger  12 . The partitioning member  13  is a tubular body made of a metal and is formed into a cylindrical shape extending in an up-down direction. In the state where the partitioning member is inserted in the plunger  12 , a lower end of the partitioning member  13  is in abutment with the bottom wall  18  of the plunger  12  and an upper end of the partitioning member  13  is located at a position near the support portion  25  of the plunger  12 , at which position the upper end of the partitioning member  13  is located above the oil passage hole  26 . More specifically, the partitioning member  13  extends in an up-down direction with a uniform diameter has a circular section which is uniform over an entire height thereof. The partitioning member  13  has no stepped portion midway in the up-down direction. The partitioning member  13  has an outer diameter set to be smaller than an inner diameter of the peripheral wall  19  of the plunger  12 . 
     The spacer  100  is interposed between the peripheral wall  19  of the plunger  12  and the partitioning member  13  in the state where the partitioning member  13  is inserted in the plunger  12 . The spacer  100  is formed into an annular elastic ring comprised of a sintered metal having a lower hardness than the plunger  12  and the partitioning member  13 . The spacer  100  has a radial width that is slightly larger than the difference between the inner diameter of the peripheral wall  19  of the plunger  12  and the outer diameter of the partitioning member  13  in a natural state. 
     The spacer  100  is incorporated in an upper position located below the oil passage hole  26  and spaced from the bottom wall  18  of the plunger  12 , so that an oil passage  40  is defined by the spacer  100  between the peripheral wall  19  of the plunger  12  and the partitioning member  13 . The oil passage  40  has a passage width that is equal to a width of the spacer  100  interposed between the plunger  12  and the partitioning member  13 . The oil passage  40  has a lower end liquidtightly sealed by the spacer  100 . The oil passage  40  has a passage side surface defined by an inner periphery of the peripheral wall  19  of the plunger  12  and an outer periphery of the partitioning member  13 . In other words, the passage width of the oil passage  40  is defined by the spacer  100 . Furthermore, the oil passage  40  faces an upper end of the partitioning member  13 . The upper end of the partitioning member  13  serves as an oil passage end  33 . Still furthermore, a space defined inside the partitioning member  13  is constituted as a low-pressure chamber  23 . 
     The partitioning member  13  and the spacer  100  are inserted into the plunger  12  from an upper end opening of the plunger  12  on which the support portion  25  has not been formed. In this case, the partitioning member  13  is inserted inside the spacer  100  which is in a heated state. Thereafter, the spacer  100  is cooled thereby to be binding fitted with the partitioning member  13 . In the state where the partitioning member  13  and the spacer  100  have been inserted into the plunger  12 , the upper end of the plunger  12  is squeezed in a diameter-reducing direction, so that the support portion  25  is formed together with a through hole  24 . 
     The hydraulic fluid flowing through the oil filler hole  92  of the cylinder head  90  is supplied sequentially through the outer oil passage hole  16 , the oil passage hole  26 , the oil passage  40  and the oil passage end  33  to be reserved in the low-pressure chamber  23 . The hydraulic fluid reserved in the low-pressure chamber  23  is further supplied through the valve hole  20  to fill the high-pressure chamber  22 . In this case, since the oil passage end  33  of the partitioning member  13  is located above the oil passage hole  26 , the hydraulic fluid is reserved in the low-pressure chamber  23  to a level above the oil passage hole  26 . 
     The valve element  21  closes the valve hole  20  thereby to close the high-pressure chamber  22  when a downward pressure is applied from the rocker arm  60  side to the plunger  12  in the state where the hydraulic fluid has been introduced into the low-pressure chamber  23  and the high-pressure chamber  22 . As a result, the plunger  12  is stopped lowering by the hydraulic pressure of the high-pressure chamber  22 . On the other hand, when the plunger  12  is raised with decrease in the pressure from the rocker arm  60  side, the capacity of the high-pressure chamber  22  is increased. When the capacity of the high-pressure chamber  22  is increased, the valve element  21  is lowered thereby to open the valve hole  20 . As a result, the hydraulic fluid in the low-pressure chamber  23  flows through the valve hole  20  into the high-pressure chamber  22  thereby to fill the high-pressure chamber  22 . Upon stop of the upward movement of the plunger  12 , the valve element  21  is biased by the first spring  29  thereby to be moved upward and close the valve hole  20 , so that the high-pressure chamber  22  is closed. Thus, the plunger  12  is moved up and down relative to the body  11 , whereby the support position of the plunger  12  relative to the rocker arm  60  fluctuates with the result that a valve clearance is adjusted. 
     In embodiment 1, the partitioning member  13  is held in the plunger  12  by the spacer  100  interposed between the peripheral wall  19  of the plunger  12  and the partitioning member  13  as described above. Accordingly, when differing from the case where the partitioning member is press-fitted into the plunger  12 , the dimensional control of the inner diameter of the peripheral wall  19  of the plunger  12  and the outer diameter of the partitioning member  13  need not be rendered stricter. This can relax the machining accuracy of the plunger  12  and the partitioning member  13 , rendering the machining of the plunger  12  and the partitioning member  13  easier. Furthermore, since the passage width of the oil passage  40  is defined by the spacer  100 , no members or machining dedicated to define the oil passage  40  is required with the result that the construction of the lash adjuster can be simplified. 
     Furthermore, since the spacer  100  has sealing properties of liquidtightly sealing the lower end of the oil passage  40 , the reliability of hydraulic fluid supply through the oil passage  40  can be improved. Still furthermore, since the partitioning member  13  is cylindrical in shape and extends in the up-down direction without any stepped portion, no particularly complicate working is required in the manufacture of partition member  13 , with the result that the manufacture man-hour can be reduced and the manufacturing costs can be suppressed. Furthermore, since an inner capacity of the low-pressure chamber  23  located inside the partitioning member  13  can be increased, the above-described construction is suitably applicable to small-sized lash adjusters. Since the partitioning member  13  has no stepped portion midway in the up-down direction, the partitioning member  13  can be prevented from buckling in the course of insertion into the plunger  12 . Additionally, since the spacer  100  is disposed at the upper position spaced from the bottom wall  18  of the plunger  12 , the lower end of the oil passage  40  can be prevented from being uselessly departed below the oil passage hole  26 . 
     Embodiment 2 
       FIG. 3  illustrates embodiment 2. A plurality of spacers  100  is interposed between the peripheral wall  19  of the plunger  12  and the partitioning member  13  in embodiment 2. More specifically, two spacers  100  are provided vertically in parallel below the oil passage hole  26 . According to embodiment 2, the partitioning member  13  is stably supported by the plural spacers  100  in the plunger  12 . The lash adjuster of embodiment 2 is similar to that of embodiment 1 except for the number of the spacers  100 . Accordingly, identical or similar parts in embodiment 2 are labeled by the same reference symbols as those in embodiment 1. 
     Embodiment 3 
       FIG. 4  illustrates a third embodiment. Embodiment 3 differs from embodiment 1 in the shape of the spacer  100 A. More specifically, the spacer  100 A has lips  110  which elastically adhere closely to the inner periphery of the peripheral wall  19  of the plunger  12  in a collapsed state in the state where the spacer  100 A is interposed between the peripheral wall  19  of the plunger  12  and the partitioning member  13 . Two lips  110  as shown in  FIG. 4  are each formed into a protrusion provided around the outer periphery of the spacer  100 A vertically in parallel. According to embodiment 3, the oil passage  40  can be maintained in a good liquidtight state by the lips  110 . The lips may be provided around the inner periphery of the spacer  100  so as to adhere closely to the outer periphery of the partitioning member  13 , instead. 
     Embodiment 4 
       FIG. 5  illustrates embodiment 4. Embodiment 4 differs from embodiment 1 in the shape and arrangement of the spacer  100 B. Furthermore, the shape of the partitioning member  13  in embodiment 4 slightly differs from that of the partitioning member  13  in embodiment 1. A reverse-tapered guide portion  120  having a diameter upwardly increased is provided on an inner periphery of the upper end of the spacer  100 B. The spacer  100 B is pushed deep into the plunger  12  thereby to be disposed in abutment on the bottom wall  18 . On the other hand, the partitioning member  13 B has a lower end formed with a tapered guided portion  39  having a diameter downwardly reduced. When the spacer  100 B which is in a heated state and the partitioning member  13 B are inserted in turn into the plunger  12 , the guided portion  39  slides on the guide portion  120 , so that the partitioning member  13 B is smoothly guided inside the spacer  100 B. The spacer  100 B is subsequently cooled thereby to be binding fitted with the partitioning member  13 B, with the result that the partitioning member  13 B is stably held in the plunger  12  by the spacer  100 B. 
     Other Embodiments 
     Embodiments 1 to 4 may each be deformed as follows. 
     (1) The oil passage end may be recessed in the upper end of the partitioning member into a cutout shape. 
     (2) The upper end of the partitioning member may radially be squeezed along the semispherical shape of the support portion. 
     (3) The spacer may be comprised of a resin ring which is elastically deformable in the radial direction.