In a tappet with a built-in lash adjuster, hydraulic oil is prevented from leaking from a low pressure chamber during a long-period stop.A tappet (10) includes a hydraulic lash adjuster (11) which supports a lower end portion of a push rod (96) and a tappet case (12) to which the lash adjuster (11) is internally fitted and which is reciprocally displaced in a vertical direction according to a rotating cam (85). An inner peripheral surface of the tappet case (12) is provided with an air-vent passage (34) through which air existing between the tappet case (12) and the lash adjuster (11) can be discharged upward when the lash adjuster (11) is being assembled.

TECHNICAL FIELD

The present invention relates to a tappet.

BACKGROUND ART

Patent Literature 1 discloses a tappet configured as a valve lifter. The tappet has a cup-like shape, and a lower end portion of a push rod abuts and is supported on an inner bottom portion of the tappet. An upper end portion of the push rod supports one end of a rocker arm. The other end of the rocker arm abuts on an upper end portion of an exhaust valve.

A lower surface of the tappet is a flat sliding contact surface and is in contact with a cam. When the cam rotates, the tappet is raised and lowered in a cylinder bore together with the push rod, and accordingly, the rocker arm swings to open and close the valve.

CITATIONS LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problems

There has been known a configuration in which the tappet does not directly support the push rod but a hydraulic lash adjuster is incorporated in the tappet and a top portion of the lash adjuster abuts against the lower end portion of the push rod so that the tappet indirectly supports the push rod via the lash adjuster. According to this configuration, a position of a swing fulcrum of the rocker arm can be properly adjusted by the hydraulic pressure of the lash adjuster, so that valve clearance can be eliminated.

When the lash adjuster is incorporated into the tappet, it is necessary to remove the air enclosed between the lash adjuster and the tappet. In this case, if an air-vent passage is provided in a lower end portion of a peripheral wall of the tappet so as to be opened laterally, hydraulic oil stored in a low pressure chamber of the lash adjuster may be discharged to the outside through the air-vent passage when an internal combustion engine is stopped for a long period of time, so that an amount of the hydraulic oil in the low pressure chamber may be significantly reduced. As a result, so-called air entrainment where the air in the low pressure chamber transfers to a high pressure chamber may occur at the time of restart of engine, so that a countermeasure therefor is desired.

The present invention has been completed based on the above circumstances, and its purpose is to provide a tappet with a built-in lash adjuster, in which hydraulic oil is prevented from leaking from a low pressure chamber during a long-period stop.

Solutions to Problems

A tappet of the present invention includes a hydraulic lash adjuster which supports a lower end portion of a push rod and a tappet case to which the lash adjuster is internally fitted and which is reciprocally displaced in a vertical direction according to a rotating can. In the tappet, an inner peripheral surface of the tappet case is provided with an air-vent passage through which air existing between the tappet case and the lash adjuster is discharged upward when the lash adjuster is being assembled.

Advantageous Effects of Invention

When the hydraulic lash adjuster is incorporated into the tappet case, the air existing between the tappet case and the lash adjuster is discharged upward through the air-vent passage. Since the air-vent passage is opened upward (including obliquely upward), the hydraulic oil stored in the low pressure chamber (reservoir chamber) of the lash adjuster can be prevented from leaking through the air-vent passage when the internal combustion engine is stopped for a long period of time. As a result, it is possible to avoid air entrainment to the high pressure chamber at the time of restart.

DESCRIPTION OF EMBODIMENTS

Preferred embodiments of the present invention are shown below.

The lash adjuster includes: a body which has a body oil hole; and a plunger which has a plunger oil hole and is inserted into the body so as to be reciprocally slidable in the vertical direction, the body oil hole communicating with a low pressure chamber in the plunger through the plunger oil hole. An oil level of the hydraulic oil in the low pressure chamber is located above the body oil hole when the internal combustion engine is stopped. According to such a configuration, air entrainment to a high pressure chamber can be reliably avoided. In the case of the present invention, the lash adjuster is internally fitted to a tappet case, and an air-vent passage is opened upward. Therefore, a sufficient amount of hydraulic oil can be secured in the low pressure chamber as described above.

The tappet case is provided with an oil passage which guides downward hydraulic oil overflowing from the tappet case. According to this, it is possible to secure a predetermined amount of hydraulic oil in the tappet case without trouble.

A lower end of the oil passage is opened at a position where hydraulic oil falling from the oil passage is adherable to a cam surface of the cam. According to this, the cam surface of the cam can be efficiently lubricated by the hydraulic oil having overflowed from an upper portion of the tappet case.

The tappet case includes an inner case having the air-vent passage and an outer case in which the inner case is housed, and the oil passage is formed between the inner case and the outer case. According to this, the tappet case is not unnecessarily thickened, so that weight of a valve gear mechanism can be reduced.

The inner case includes large-diameter portions provided at an interval in the vertical direction, each of the large-diameter portions protruding outward in a radial direction and having a distal end surface in a protruding direction which is capable of abutting against the inner peripheral surface of the outer case. The outer case includes an opening which is provided penetrating therethrough at a height position corresponding to the large-diameter portion and which a part of the large-diameter portion in a circumferential direction faces. According to this, since a small-diameter portion located between the upper and lower large-diameter portions of an outer peripheral surface of the inner case and the opening of the outer case are used as the oil passage, there is no need to form a longitudinal groove structure extending long over the entire length in the vertical direction as the oil passage, so that manufacturing cost can be reduced. Furthermore, when centerless machining is performed, the upper and lower large-diameter portions can be rotatably supported between a grindstone, an adjustment grindstone and a support blade without trouble, so that grinding of the outer peripheral surface of the inner case can be performed smoothly.

The tappet case is provided with a thin portion which is recessed in a direction retracting from an inner peripheral surface of a tappet guide over an entire circumference of the tappet case to define a part of the oil passage in the vertical direction between the inner peripheral surface of the tappet guide and the thin portion. Since the thin portion is provided over the entire circumference of the tappet case, the weight of the valve gear mechanism can be reduced. Furthermore, since a part of the oil passage in the vertical direction is constituted by the thin portion, there is no need to form a longitudinal groove structure extending long over the entire length in the vertical direction as the oil passage, so that manufacturing cost can be reduced.

The lash adjuster has a cylindrical body having a body peripheral wall through which the body oil hole penetrates and the plunger having a plunger peripheral wall through which the plunger oil hole penetrates and which is inserted in the body so as to be reciprocally slidable in a vertical direction, the plunger including the low pressure chamber, the body including a high pressure chamber defined between a lower portion of the body and a bottom wall portion of the plunger, the body oil hole and the plunger oil hole communicating with the low pressure chamber and also communicating, though a gap between the body peripheral wall and the plunger peripheral wall, with the high pressure chamber. The inner peripheral surface of the tappet case has a seal surface formed in a region above the body oil hole and except the air-vent passage, the seal surface being configured to contact the body peripheral wall.

For example, immediately after assembly of the lash adjuster, the hydraulic oil may be stored in the lash adjuster only up to the height of the body oil hole. Thus, if an upper side of the body oil hole is opened to the outside, there is a concern that the hydraulic oil may flow out to the outside by the reciprocating sliding of the plunger relative to the body, and in addition, air may enter the high pressure chamber, so that malfunction of the lash adjuster may be caused.

Thus, according to the above configuration, the seal surface of the tappet case contacts the body peripheral wall above the body oil hole, so that it is maintained in the state where the body oil hole does not communicate with the outside except for the air-vent passage. As a result, at the time of start-up immediately after the lash adjuster is assembled, the hydraulic oil is prevented from flowing out to the outside and air entrainment to the high pressure chamber can be avoided.

The air-vent passage has a concave groove which extends spirally in the vertical direction on the inner peripheral surface of the tappet case. There is a concern that the hydraulic oil in the lash adjuster flows out to the outside through the air-vent passage, but according to the above configuration, the concave groove of the air-vent passage extends spirally on the inner peripheral surface of the tappet case. As a result, the hydraulic oil is less likely to flow in the concave groove and prevented from flowing out to the outside.

Embodiment 1 of the present invention will be described with reference toFIGS. 1 to 4. A tappet10according to Embodiment 1 is provided in a valve gear90of an internal combustion engine, and illustrates a valve lifter of an OHV type engine.

As shown inFIG. 1, the valve gear90includes: a valve93which is incorporated so as to be able to open and close an intake or exhaust port92of a cylinder head91and has an upper end portion disposed protruding above the cylinder head91; a rocker arm94having one lengthwise end portion which abuts against the upper end portion of the valve93; a push rod96having an upper end portion which abuts against the other lengthwise end portion of the rocker arm94via an adjusting screw95; a hydraulic lash adjuster11against which a lower end portion of the push rod96abuts; and a tappet case12housing the lash adjuster11. Among these, the tappet10is constituted of the lash adjuster11and the tappet case12.

The valve93is inserted through a valve guide97so as to be vertically slidable, and is biased in a valve closing direction (a direction for lifting one end portion of the rocker arm94) by a biasing member98such as a coil spring.

The rocker arm94is swung with a rocker shaft99, which penetrates a lengthwise middle portion of the rocker arm94, serving as a fulcrum, thereby opening and closing the valve93based on the swing displacement. The adjusting screw95penetrates the other end portion of the rocker arm94and is screwed to a nut89, and an amount of downward protrusion thereof from the other end portion of the rocker arm94is adjustable according to screwing into the nut89.

The push rod96has a rod-like shape elongated vertically, and is housed in a rod housing portion (not shown) so as to be vertically displaceable. The upper end portion of the push rod96is a hemispherical upper end recess88spread outward and upward. A lower end portion of the adjusting screw95is slidably supported on the upper end recess88. The lower end portion of the push rod96is a hemispherical lower end recess87spread outward and downward. As shown inFIG. 2, the lower end recess87is slidably supported on a top portion16of a plunger14, which will be described later, of the lash adjuster11.

The push rod96is provided with an axial hole86which extends to be elongated in the axial direction and has an upper end opened at a central portion of the upper end recess88and a lower end opened at a central portion of the lower end recess87. When hydraulic oil (lubricating oil) is supplied to the rocker arm94, the supplied hydraulic oil mainly flows from an oil passage100in the rocker arm94and in the adjusting screw95to enter the axial hole86through a sliding region of the adjusting screw95and the upper end recess88, descends along the axial hole86to reach the lower end recess87, and is stored in a low pressure chamber22through a top hole17which will be described later. Furthermore, a part of the hydraulic oil flows down along an outer surface of the push rod96from the rocker arm94side and enters inside the tappet case12.

Next, the tappet10will be described. First, the lash adjuster11constituting the tappet10will be described. As shown inFIG. 2, the lash adjuster11includes a bottomed cylindrical body13and the bottomed cylindrical plunger14inserted therein so as to be slidable in the vertical direction of the body13. The plunger14has a valve hole15in a bottom wall portion thereof and has the hemispherical top portion16at an upper end portion of a peripheral wall portion thereof (plunger peripheral wall59). The center of the top portion16is provided with a top hole17penetrating therethrough vertically. In a peripheral wall portion of the body13(body peripheral wall58), upper and lower abutment portions18which abut against an inner peripheral surface of an inner case28which will be described later are provided over the entire circumference, and a body oil hole19penetrating the body peripheral wall58is provided so as to be opened at a recessed portion between the abutment portions18. In the plunger peripheral wall59of the plunger14, a plunger oil hole21which communicates with the body oil hole19is provided penetrating therethrough.

The inside of the plunger14is constituted as the low pressure chamber22. Inside the body13, a high pressure chamber23is defined between a lower end portion of the body13and the bottom wall portion of the plunger14. Here, the hydraulic oil flows into the low pressure chamber22from the axial hole86of the push rod96through the top hole17and also flows into the low pressure chamber22from the inside of the inner case28which will be described later through an air-vent passage34, the body oil hole19and the plunger oil hole21, and is stored in the low pressure chamber22. The hydraulic oil in the high pressure chamber23ascends through a gap between the body peripheral wall58and the plunger peripheral wall59, and can enter the recessed portion between the abutment portions18from the body oil hole19, and also can return to the low pressure chamber22through the plunger oil hole21.

The hydraulic oil stored in the low pressure chamber22is filled into the high pressure chamber23through the valve hole15. The high pressure chamber23houses a spherical valve body24, a cage-shaped retainer25, a first spring26and a second spring27. The valve body24and the first spring26are arranged inside the retainer25, and the valve body24is biased by the first spring26in a direction to close the valve hole15. The retainer25is press-fitted into the plunger14and abuts against the bottom wall portion of the plunger14.

The tappet case12includes an inner case28having bottomed a cylindrical shape and an outer case29having a bottomed cylindrical shape which is separated from the inner case28and in which the inner case28is housed. The peripheral wall of the inner case28is formed thin as a whole and has annular rib-shaped large-diameter portions31provided at two places spaced from each other in the middle of the vertical direction and protruding radially outward over the entire circumference. A radially outer end surface of the large-diameter portion31has a circumferential shape capable of abutting against an inner peripheral surface of the outer case29along the circumferential direction. A region excluding the upper and lower large-diameter portions31in the outer peripheral surface of the inner case28is retracted in a direction away from the inner peripheral surface of the outer case29(inward direction). In this region, a region lower than the lower large-diameter portion31and a region between the upper and lower large-diameter portions31are largely retracted inward due to an inclined portion32which will be described later.

In the peripheral wall of the inner case28, the inclined portion32having a diameter reduced downward is provided at a portion of a height position corresponding to the upper large-diameter portion31. As shown inFIG. 4, in upper and lower regions of the inner peripheral surface of the inner case28bordering the inclined portion32, the lower region has a smaller diameter than the upper region. Inside the inner case28, the lash adjuster11is inserted from above in a closely fitted state. In the lower region of the inner peripheral surface of the inner case28, a pair of upper and lower inner annular portions33capable of abutting against the abutment portions18of the body13is provided over the entire circumference.

The air-vent passage34is provided on the inner peripheral surface of the inner case28. Specifically, the air-vent passage34is constituted by: a concave groove35which is engraved in the upper and lower inner annular portions33in the inner peripheral surface of the inner case28and extends so as to be spirally wound in the vertical direction in the lower region as a whole; and a recess36having a form retracted over the entire circumference in a direction away from the outer peripheral surface of the body peripheral wall58of the body13. In the air-vent passage34, an upper end of the concave groove35is opened at a slope portion of the inclined portion32, whereas lower end is closed by a bottom wall of the inner case28. Since the concave groove35has a form wound spirally, an inner peripheral surface of the inner case28can be polished smoothly.

As shown inFIG. 2, a bottom wall of the outer case29has a flat lower surface portion which slidingly contacts a cam surface84of a rotating cam85. A peripheral wall of the outer case29is in a thin-walled form in which inner and outer peripheral surfaces are both arranged almost along the vertical direction, and the upper end of the peripheral wall is located above an upper end of the inner case28to be inserted therein. The outer peripheral surface of the outer case29is configured to slidingly contact along an inner peripheral surface of a tappet guide83.

As shown inFIGS. 2 and 3, in the peripheral wall of the outer case29, a pair of upper and lower circular openings37are provided penetrating therethrough at a height position corresponding to the upper and lower large-diameter portions31of the inner case28to be inserted therein. The upper and lower large-diameter portions31are each arranged such that a part thereof in the circumferential direction faces the opening37.

Here, the hydraulic oil falls from the rocker arm94side and is stored inside the inner case28. As shown inFIG. 2, an oil passage38for guiding downward the hydraulic oil overflowing from the upper end of the inner case28is formed between the inner case28and the outer case29. The oil passage38is constituted by: an inter-wall passage39having a passage width or diameter determined by the large-diameter portion31between an outer peripheral wall of the inner case28and an inner peripheral wall of the outer case29; and a bypass passage41located in the upper and lower openings37and between the tappet guide83and the large-diameter portions31. An outlet of the oil passage38is constituted by an opening portion of the lower bypass passage41and disposed at a position facing the cam surface84of the cam85from above.

Next, the operation of the tappet10according to Embodiment 1 will be described.

At the time of assembly, the lash adjuster11is inserted into the inner case28of the tappet case12from above. At this time, there is a concern that the abutment portion18of the body13and the inner annular portion33of the inner case28abut against each other so that air between the body13and a lower end portion of the inner case28is enclosed. However, the air ascends in the air-vent passage34and is discharged upward, whereby the lash adjuster11is housed in the tappet case12without trouble. In a state where the lash adjuster11is properly housed in the inner case28, the upper end of the inner case28is located above an upper end of the plunger14.

Next, a valve gear mechanism will be described. When the cam85rotates, the outer case29in contact with the cam85is slidingly displaced in the tappet guide83in the vertical direction. In accordance therewith, the push rod96is raised and lowered in the rod housing portion via the lash adjuster11. The rising and lowering operation of the push rod96is transmitted to the rocker arm94via the adjusting screw95, whereby the rocker arm94is swung and displaced with the upper end recess88of the push rod96serving as an approximate fulcrum, so that the valve93is opened and closed.

By the way, when downward pressure is applied to the plunger14from the push rod96side according to the driving of the cam85, the valve body24closes the valve hole15, and the plunger14and the body13are turned into a rigid body, so that lowering of the plunger14is restricted. When the pressure applied to the plunger14is reduced, the plunger14is biased by the second spring27and the valve body24opens the valve hole15, so that the hydraulic oil in the low pressure chamber22is transferred to the high pressure chamber23. Thus, lift force of the cam85is attenuated and transmitted to the push rod96and the rocker arm94via the lash adjuster11. While the tappet case12moved vertically, the lower bypass passage41is located below the tappet guide83, and the hydraulic oil overflowing from the upper end of the inner case28passes through the oil passage38and is discharged from the lower bypass passage41to the cam85side.

The low pressure chamber22of the lash adjuster11communicates with the inside of the inner case28via the plunger oil hole21and the body oil hole19. Though the air-vent passage34is provided on the inner peripheral surface of the inner case28, the air-vent passage34is opened at the slope portion of the inclined portion32and the inside of the inner case28is opened only upward as a whole. Therefore, when an internal combustion engine is stopped for a long period of time, the hydraulic oil is stored in the inner case28substantially up to the upper end of the inner case28, and via the inner case28, the hydraulic oil is also stored in the lash adjuster11in almost the entire low pressure chamber22.

As described above, while the internal combustion engine is stopped, the hydraulic oil is not discharged from the low pressure chamber22to the outside through the air-vent passage34of the tappet case12, and the state where the hydraulic oil is stored in the low pressure chamber22is maintained. Therefore, when the valve hole15is opened at the time of restart later, substantially only the hydraulic oil is transferred from the low pressure chamber22to the high pressure chamber23, so that air entrainment in the high pressure chamber23can be avoided.

Furthermore, as the tappet case12moves vertically at the time of restart, the hydraulic oil stored in the inner case28overflows from the upper end of the inner case28and enters the oil passage38. The hydraulic oil having entered the oil passage38falls downward through the inter-wall passage39and the bypass passage41, and adheres to the cam surface84of the cam85to lubricate a sliding region between the cam85and the tappet case12. Since the hydraulic oil in the inner case28is used as a lubricating means for the cam85, the sliding region between the cam85and the tappet case12can be quickly lubricated after restart.

As described above, according to Embodiment 1, when the lash adjuster11is incorporated into the tappet case12, the air existing between the tappet case12and the lash adjuster11is discharged upward through the air-vent passage34, so that assembling performance of the lash adjuster11can be improved.

Furthermore, since the air-vent passage34is opened upward (in detail, obliquely upward), the hydraulic oil stored in the low pressure chamber22of the lash adjuster11can be prevented from leaking through the air-vent passage34when the internal combustion engine is stopped for a long period of time. As a result, it is possible to avoid air entrainment to the high pressure chamber23at the time of restart, and the function of the lash adjuster11can be properly exhibited. In particular, since the oil level of the hydraulic oil in the low pressure chamber22of the lash adjuster11is located above at least the body oil hole19when the internal combustion engine is stopped for a long period of time, the air entrainment to the high pressure chamber23can be reliably avoided.

Furthermore, since the tappet case12is provided with the oil passage38which guides downward the hydraulic oil overflowing from the tappet case12, it is possible to secure a predetermined amount of hydraulic oil in the tappet case12without trouble. In addition, since a lower end of the oil passage38is opened at a position where the hydraulic oil falling from the oil passage38is adherable to the cam surface84of the cam85, the cam surface84of the cam85can be efficiently and quickly lubricated.

Furthermore, the tappet case12includes the inner case28having the air-vent passage34and the outer case29in which the inner case28is housed, and the oil passage38is formed between the inner case28and the outer case29. Therefore, the tappet case12is not unnecessarily thickened, so that the weight of the valve gear mechanism can be reduced.

Furthermore, the inner case28includes the pair of large-diameter portions31provided at an interval in the vertical direction, each of the large-diameter portions31protruding outward in the radial direction and having a distal end surface in the protruding direction which is capable of abutting against the inner peripheral surface of the outer case29. The outer case29includes the opening37which is provided penetrating therethrough at the height position corresponding to the large-diameter portion31and which a part of the large-diameter portion31in the circumferential direction faces. Therefore, when centerless machining is performed for the inner case28, the upper and lower large-diameter portions31can be rotatably supported between a grindstone, an adjustment grindstone and a support blade without trouble, so that grinding of the outer peripheral surface of the inner case28can be performed smoothly. In addition, since the small-diameter portion located between the upper and lower large-diameter portions31of the outer peripheral surface of the inner case28and the openings37of the outer case29are used as the oil passage38, there is no need to form a longitudinal groove extending long over the entire length in the vertical direction as the oil passage38, so that manufacturing cost can be reduced.

FIGS. 5 to 7show a tappet10A according to Embodiment 2 of the present invention. In the tappet10A of Embodiment 2, a tappet case12A is integrally formed in its entirety, and the form thereof is different from that of Embodiment 1. However, a lash adjuster11is internally fitted to the tappet case12A, and the structure other than the tappet case12A is the same as that of Embodiment 1. Therefore, in Embodiment 2, the components similar to those of Embodiment 1 are labeled by the same reference symbols as those in Embodiment 1, and duplicate explanations will be omitted.

The tappet case12A includes a relatively thick disk-like bottom wall portion43and a cylindrical peripheral wall portion44rising from an outer periphery of the bottom wall portion43. The bottom wall portion43has a flat lower surface portion which slidingly contacts a cam surface84of a rotating cam85. An outer peripheral edge portion of the bottom wall portion43is formed as an expanded portion45which protrudes radially outward over the entire circumference. An outer peripheral surface of the expanded portion45is constituted by a circulating plane46in a circumferential shape and a lower end inclined surface47in a tapered shape having a diameter reduced upward from an upper end of the circulating plane46.

The peripheral wall portion44has a lower sliding contact portion48in the middle in the vertical direction, and the lower sliding contact portion48is formed thicker than regions on both upper and lower sides thereof. An outer peripheral surface of the lower sliding contact portion48is constituted by: a lower sliding contact surface49having a circumferential shape and capable of slidingly contacting an inner peripheral surface of a tappet guide83; and upper and lower inclined surfaces51in a tapered shape having the respective diameters reduced toward upper and lower sides from the lower sliding contact surface49. The lower sliding contact surface49of the lower sliding contact portion48is provided with a recessed groove52formed in a cut-out shape which extends vertically and has both upper and lower ends opened at the upper and lower inclined surfaces51.

The region above the lower sliding contact portion48in the peripheral wall portion44is a thin portion53which is recessed over the entire circumference in a direction retracting from the inner peripheral surface of the tappet guide83. The thin portion53is formed along the vertical direction and is formed the thinnest in the tappet case12A together with an upper sliding contact portion55which will be described later.

An upper end portion of the peripheral wall portion44includes: an enlarged diameter portion54in a tapered shape having a diameter increased upward from an upper end of the thin portion53; and the cylindrical upper sliding contact portion55rising substantially upright from an upper end of the enlarged diameter portion54, and is provided continuously with the thin portion53with almost the same thickness as the thin portion53.

An outer peripheral surface of the upper sliding contact portion55is an upper sliding contact surface56in a circumferential shape which is capable of slidingly contacting the inner peripheral surface of the tappet guide83. The upper sliding contact surface56is disposed at substantially the same position as the sliding contact surface49of the lower sliding contact portion48and the circulating plane46of the expanded portion45with respect to the radial direction. When centerless machining is performed for the tappet case12A, since the upper sliding contact portion55and the expanded portion45can be rotationally supported between a grindstone, an adjustment grindstone and a support blade, grinding of the outer peripheral surface of the tappet case12A can be performed smoothly.

In the enlarged diameter portion54, a circular through hole57is provided penetrating therethrough in the thickness direction at almost the same position as the recessed groove52in the circumferential direction. Here, hydraulic oil stored inside the tappet case12A is discharged downward through an oil passage38A. The oil passage38A is constituted by the through hole57, an inter-wall passage39A defined between an outer peripheral surface of the thin portion53and the inner peripheral surface of the tappet guide83, and the recessed groove52. A part of the hydraulic oil descends from the through hole57along the oil passage38A, then is temporarily received by a lower end inclined surface47, and then falls from the lower end inclined surface47toward the cam surface84side of the cam85.

The lash adjuster11is inserted into the tappet case12A from above in a closely fitted state. A pair of upper and lower inner annular portions33A capable of abutting against the abutment portions18of the body13of the lash adjuster11is provided on an inner peripheral surface of the tappet case12A over the entire circumference.

An air-vent passage34A is provided on the inner peripheral surface of the tappet case12A. Specifically, the air-vent passage34A is constituted by: a concave groove35A which is engraved in the upper and lower inner annular portions33A in the inner peripheral surface of the tappet case12A and extends so as to be spirally wound in the vertical direction as a whole; and a recess36A having a form retracted over the entire circumference between the upper and lower inner annular portions33A in a direction away from the outer peripheral surface of the body peripheral wall58of the body13. The upper end of the air-vent passage34A is opened at a slope portion of the inclined portion32A, whereas the lower end thereof is closed by a bottom portion of the tappet case12A. Accordingly, the inner peripheral surface of the tappet case12A has substantially the same structure as the inner peripheral surface of the inner case28of Embodiment 1.

Furthermore, the upper inner annular portion33A in the inner peripheral surface of the tappet case12A is provided with a seal surface61. In a state where the lash adjuster11is assembled to the tappet case12A, the seal surface61is located above a body oil hole19of the lash adjuster11and is in contact with the abutment portion18of the body peripheral wall58along the circumferential direction. The seal surface61is provided over the entire area of the upper inner annular portion33A except the air-vent passage34A. The seal surface61is similarly provided on the upper inner annular portion33in the inner case28of the tappet case12of Embodiment 1 (seeFIG. 2).

As shown inFIG. 7, immediately after the lash adjuster11is assembled to the tappet case12A, there are some cases where the top portion16side of the plunger14largely projects above the body13and the hydraulic oil is not supplied in the tappet case12A and is stored only up to the height of a plunger oil hole21.

In that state, when the push rod96is supported by the top portion16of the plunger14and the plunger14is lowered to rotate the cam85, the plunger14may reciprocally slide vertically with respect to the body13even though the hydraulic oil is not supplied from an axial hole86of the push rod96to a low pressure chamber22.

For example, when the plunger14is lowered relative to the body13, the hydraulic oil in the high pressure chamber23may ascends through a gap between the body peripheral wall58and the plunger peripheral wall59and may enter a recessed portion between the abutment portions18through the body oil hole19. At this time, if the upper side of the body oil hole19is largely opened to the outside, there is a concern that the hydraulic oil which has entered the recessed portion between the abutment portions18may flow out to the outside.

However, according to the above configuration, since a gap between an upper portion of the tappet case12A (upper inner annular portion33A) and the body peripheral wall58is closed in a fluid-tight manner by the seal surface61except for the air-vent passage34A, the hydraulic oil is returned from the recessed portion between the abutment portions18to the low pressure chamber22through the plunger oil hole21, or maintained staying in the low pressure chamber22and the high pressure chamber23. Accordingly, at the time of start-up immediately after the lash adjuster11is assembled, the hydraulic oil is prevented from flowing out to the outside of the lash adjuster11by the seal surface61, and consequently, air entrainment to the high pressure chamber23is avoided.

Furthermore, since the air-vent passage34A provided in the upper and lower inner annular portions33A is the concave groove35A extending spirally, the hydraulic oil is less likely to move in the concave groove35A and can suitably stay in the low pressure chamber22and the high pressure chamber23. In particular, above the body oil hole19, since the spiral concave groove35A is disposed together with the seal surface61, the hydraulic oil is less likely to flow above the body oil hole19and preferentially returned from the body oil hole19side toward the low pressure chamber22side through the plunger oil hole21. As a result, a predetermined amount of the hydraulic oil can be stored in the low pressure chamber22of the lash adjuster11, so that the air entrainment to the high pressure chamber23can be more reliably avoided.

Furthermore, according to Embodiment 2, since the air-vent passage34A is opened upward as in Embodiment 1, the hydraulic oil stored in the low pressure chamber22of the lash adjuster11can be prevented from leaking to the outside through the air-vent passage34when an internal combustion engine is stopped for a long period of time.

Furthermore, when the internal combustion engine is stopped for a long period of time, the hydraulic oil is stored in the tappet case12A up to a height position regulated by the through hole57and the hydraulic oil is stored in the entire low pressure chamber22of the lash adjuster11. Therefore, the air entrainment to the high pressure chamber23can be reliably avoided.

Furthermore, the tappet case12A is provided with the thin portion53which is recessed in the direction retracting from the inner peripheral surface of the tappet guide83over the entire circumference to define the inter-wall passage39A of the oil passage38A between the inner peripheral surface of the tappet guide83and the thin portion53. Therefore, there is no need to form a longitudinal groove structure extending long over the entire length in the vertical direction of the tappet case12A as the oil passage38A, so that cost can be reduced.

OTHER EMBODIMENTS

Other embodiments will be briefly described below.

(1) An air-vent passage may extend on an inner peripheral surface of a tappet case almost along the vertical direction.

(2) The air-vent passage may extend on the inner peripheral surface of the tappet case continuously without interruption in the vertical direction.

(3) A plurality of the air-vent passages may be provided on the inner peripheral surface of the tappet case at intervals in the circumferential direction.

(4) Almost the entire outer peripheral surface of the tappet case may be formed to be slidable on the inner peripheral surface of a tappet guide.

(5) An oil passage may be a longitudinal groove extending on the outer peripheral surface of the tappet case over the entire length in the vertical direction.

REFERENCE SIGNS LIST