JPH0120286B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a hydraulic latch adjusting tappet for use in a direct-acting valve gear for an internal combustion engine.

[Conventional technology]

In valve gear designs for internal combustion engines operating at speeds above 5000 rpm, the use of cam-over-valve style valve gears has been deemed desirable. This type of valve gear is known as a direct acting valve gear and uses a tappet that is in direct contact with the engine camshaft at one end and the end of the combustion chamber valve stem at the other end. Directly actuated valve gears have the advantage of lower mass, fewer moving parts, and higher stiffness due to the elimination of rocker arms and/or push rods. Low mass and high stiffness result in high natural frequencies, which
Allows the valve gear to reach higher rpm before valve mismotion occurs. Direct-acting valve gear also allows the use of lighter valve spring loads for a given valve movement and engine speed compared to those used in other valve gear systems. The lower mass and higher stiffness of the system increases the area under the valve lift curve and therefore increases engine power.
Allows for increased valve lift speed and acceleration. Other overhead cam configurations can provide similar lift speeds and accelerations, but direct valve gearing has the added benefit of allowing the cam contact surface to rotate as the lifter rotates. This provides significant advantages that are not possible with rocker-arm valve gear systems. Therefore, with a direct-acting valve gear device,
Higher allowable cam contact stresses are possible.

In addition, the cam profile for other overhead cam valve gear systems with high lift accelerations and speeds is more complex than that required for direct acting valve gears. The simpler cam profile required for direct acting valve gears reduces the manufacturing difficulty and cost of gear valves used when high speeds and accelerations are desired.

However, direct-acting valve gears cannot be provided in engine applications where the engine height is kept to a minimum so that the camshaft must be located in close proximity to the end of the combustion chamber valve stem. was proving difficult. In addition, if it is desired to fit a hydraulic latch adjusting tappet (hydraulic L/A tappet) into the direct-acting valve gear of a production engine, the space provided between the camshaft and one end of the valve stem may be Providing hydraulic L/A tappets is often difficult. Since the tappet must be guided into a hole in the engine, it is necessary to provide a structure intermediate the end of the camshaft and valve stem to provide the tappet guide hole.
And in doing so the height of the engine increases somewhat.

[Problem that the invention seeks to solve]

A compact profile for use in engines with direct-acting valve gears, where the distance between the camshaft and one end of the valve stem is therefore minimal, in order to minimize the mass of the engine structure required to accommodate the tapepet guide. It would have been desirable to invent a hydraulic L/A tappet with high pressure. Furthermore, in designing the tappet for a direct-acting valve gear to minimize unbalanced loads in the guide to minimize wear, the reaction force of the valve stem is directed through the tappet to the cam surface as much as possible. It is desirable to concentrate on points close to . Also, by placing the point of action of the reaction near the cam surface, the tappet can be designed to have a minimum mass, which in turn reduces inertia.

Well-known fluid tappets for direct-acting valve gears use a body or tappet formed as an integral unit, as shown and described in U.S. Pat. No. 3,509,858 to Schieb et al.
The unit has a generally tubular outer wall, means for providing a camming surface at one end of the outer wall, and a guide hole spaced within the outer wall for slidably receiving a plunger assembly. The plunger assembly includes a plunger having an end face adapted to contact a valve stem, a piston slidably mounted within the plunger to form a fluid pressure chamber with the plunger, and a piston for supplying fluid to the chamber. and a one-way valve means for controlling. A fluid reservoir is provided by an undercut in the guide hole of the plunger. The undercut requirement requires a relatively large plunger guide hole in the body, which in turn reduces the upper hydraulic pressure limit. This lowering of the upper operating limit of hydraulic pressure is caused by the force of the supply hydraulic pressure acting on a large piston area and tending to extend the plunger. Furthermore, if the diameter of the plunger guide hole is reduced, the undercut reservoir will have a reduced volume and the mass of the tappet will increase, resulting in an increased inertia.

A similar construction is also shown and described in U.S. Pat. No. 3,658,038, except that the tappet includes a reduced tappet body and separate guide members attached to the body and providing a generally tubular outer wall.
In this case, the tapepet body includes a hub spaced on the inside of the outer wall to provide a guide hole for the plunger assembly, and means for providing a camming surface at one end of the hub with a diameter smaller than the diameter of the guide member. have. The guide hole is integral with the hub. As previously mentioned, the reservoir is provided by an undercut within the plunger guide hole.

Another problem encountered in the design of hydraulic L/A tappets for direct-acting valve gears is providing a means for retaining the hydraulic L/A plunger assembly in the tappet bucket prior to installation in the engine. Ta.

Additionally, a problem encountered in the design of such hydraulic bucket tappets has been the need to provide precision sliding surfaces on the outside diameter of the plunger and on the inside circumference of the plunger guide hole formed in the bucket. Such a precision surface is necessary to control leakage from the high pressure fluid chamber in the tappet, in which case this sliding inner surface is suitable for example as described in the German patent
Used as a leak control surface, such as in tapepets as described in 1914693. In tappets of this latter known construction, the high pressure liquid chamber for effecting lash adjustment is located at or near the upper liquid level of the fluid reservoir and is, as a result, sensitive to the retention of trapped air. This requirement for leakage control has heretofore required extremely tight tolerances on the dimensions of the bucket hole and plunger diameter. The need to form plunger guide holes in the bucket to tight tolerances created scrap losses if such procedures were performed imperfectly.

[Means for solving problems]

The present invention provides a hydraulic L/A tappet of the type used in direct-acting valve gears for internal combustion engines operating at high rotational speeds. The hydraulic tappet of the present invention is of the general shape known as a "bucket" in which the diameter of the tappet body is substantially larger than the hydraulic plunger housed therein. The present tappet configuration provides a low profile height to minimize the required distance between the engine cam and the end of the combustion chamber valve stem. Furthermore, the present tappet uses a unique construction whereby the natural leakage surface from the high pressure chamber is formed not between the tappet body and the plunger, but between the plunger and another piston housed therein. This configuration allows the control of the gap between the natural leakage surfaces to be performed on smaller diameter sections and eliminates the need for machining or grinding precise hole diameters into the tapepet body.
Scrap losses related to surfaces used for leakage control are therefore limited to the plunger piston subassembly.

The hydraulic tappet of the present invention provides a relatively small L/A plunger that reduces the load transferred to the cam and valve at high engine lubrication operating pressures. The tappet of the present invention has a high-pressure L/A hydraulic chamber at a vertical level close to or below the level of the lowest part of the liquid reservoir, and the highest part of the air sealed therein is provided. Equipped with a device that provides a convenient escape route.

The hydraulic tappet for a direct-acting valve gear according to the invention has the features set out in the features of the claims.

The body of the tapepet generally has a tubular outer wall construction, with a radially inwardly extending web located intermediate the ends thereof, the web being centrally located in the body and integrally formed with the web. It has an axially extending tubular hub.
The tappet surface is generally provided by joining the peripheral edge of the disc-shaped member to one end of the tubular outer wall section. The hydraulic plunger and piston assembly are housed in the inner hub, and a fluid reservoir is formed within the annular chamber between the inner surface of the cam face member, the outer tubular wall, the web, the inner tubular hub, and the plunger. This unique configuration provides a relatively large volume fluid reservoir intermediate the hydraulic plunger and the inner periphery of the outer wall portion without the need for undercutting material in forming the tapepet body. The final assembly of the tappet of the present invention provides a very low profile height for the hydraulic L/A tappet, yet allows for relatively easy control in the manufacture of the leakage surface, and also for the hydraulic L/A mechanism. , providing a suitable reservoir of fluid. The tappet of the present invention also provides a means for escaping trapped air and allows operation at high engine lubricant operating pressures. The tappet of the present invention provides a unique means for retaining the in-body hydraulic L/A subassembly.

〔Example〕 Next, examples of the present invention will be described.

Referring now to FIG. 1, a bucket tappet, generally indicated at 10, is slidably received within a guide hole 12 provided in a cylinder head H of the engine structure. A camshaft 14 having a cam lobe 16 abuts the upper end or cam surface 18 of the tappet. A typical combustion chamber valve 20 is shown mounted to a valve seat surface formed in the cylinder head H, with the valve 20 extending substantially vertically through a valve guide 24 formed in the cylinder head H. The upper end 2 of the valve stem, with the valve stem portion 22 extending upwardly.
6 contacts the lower end of the tapepet. The valve 20 is biased to a closed position by a valve spring 28;
The spring 28 has its lower end aligned outside the upper position of the valve guide 24, and its upper end abuts a retainer 30 which is fixed to the valve stem 22 near its upper end and is fixed to the valve stem 22, for example in a known manner. It is held in place by the use of a split keeper 32.

2, 3 and 4, a presently preferred embodiment of the tapepet 10 is shown, in which:
The body, indicated generally at 40, is preferably formed integrally with the outer tubular wall 42 and has a transverse web 44 extending generally radially from the inner periphery of the outer tubular wall portion at a location intermediate the ends thereof. The web 44 integrally forms therewith a tubular hub portion 46 formed about its inner periphery, with the hub 46 extending axially from the web in a downward direction with respect to FIG. The inner circumference of hub 46 extends in generally parallel relation to the outer circumference of tubular wall portion 42 . The outer circumference of tubular wall portion 42 is generally dimensioned to be received within tappet guide hole 12 (see FIG. 1) in a snug relationship. Although it has been stated that the outer wall, web and hub are preferably integral, such parts may be formed in sections and the body may be formed by joining these parts, e.g. by melting or brazing. It will be appreciated that it may also be formed by welding.

In the presently preferred implementation of the invention, the cam surface portion 18, which has a relatively thin disk-like configuration, is connected at its outer periphery to the upper end of the tubular body portion 42 by any suitable method, such as laser welding. A fluid bypass recess 43 is formed in the lower surface of member 18, the function of which will be described hereinafter. In the presently preferred implementation, the tappet cam face member is formed from a suitable alloy steel, such as, for example, an alloy containing a desirable amount of chromium, and is moderately hardened for wear resistance. In the presently preferred implementation, the tubular body portion is formed of a suitable iron-based material, such as steel or cast iron. In a preferred implementation, the cam face member is formed of steel with a hardened surface;
Other metals, such as nickel alloys, may be used;
Hardened cast iron or ceramic materials or, if desired, cermets are used.

The inner circumference 48 of the hub 46 has a plunger 49 therein.
The outer circumference of the plunger is the inner circumference 4 of the hub.
It has a sliding and tight fitting relationship with 8.
The plunger 49 has a cross section 52 or lower surface in FIG. 3, which surface is adapted for driving engagement with the end 26 of the combustion chamber valve stem (see FIG. 1).

In the presently preferred implementation, the plunger 49
is constructed of steel with a suitably hardened surface 52 for wear resistance. The outer peripheral surface 50 of the plunger has an annular shoulder 54 formed thereon at the line of intersection with the lower surface 52. The annular retainer 56 is attached to the hub 46
and preferably within a groove 58 formed in the outer periphery of the hub 46.
The inner circumference 60 of the retainer 56 has a diameter intermediate the diameter of the hub interior 48 and the inner diameter of the shoulder 54 to allow the retainer 56 to limit downward movement of the plunger 49.

Plunger 49 has a precision cylindrical bore 62 formed in its upper end, the lower end of which terminates in a shouldered flat bottom 65. Precision hole 6
2 slidably receives therein a piston portion 64 in a very tight fitting relationship;
The outer periphery 66 of the piston portion has a precise, smooth diameter to control leakage or flow of pressurized engine lubricant therebetween. In the actual preferred implementation, piston 64 is formed of a suitable steel material.

Piston 64 has a fluid passageway 68 extending vertically and preferably through its center and having a counterbore 70 formed therein. The bottom end of the passage 68 has a counter hole 71 provided at the lower end of the piston 64, the counter hole 71 of the piston 64 having a flat bottom 7
3 and an annular valve seat surface 74 is formed where passageway 68 traverses flat bottom 73 . A one-way valve member in the form of a check ball 72 is placed against the annular valve seat surface 74 and is mounted in accordance with the known techniques and techniques of John J. Krieg, Ser. No. 093782 1979, 11.
As stated in the application for registration (now abandoned and assigned to the assignee of this invention) dated May 13th:
It is biased by a suitable element, such as a conical check ball spring 76. The check ball 72 is located in the counter hole 7.
1 and held by a cage 78 having an outwardly extending flange 80 and by any suitable means, such as a press fit. In the actual preferred implementation, the cage has a central hole into which the check ball 72 is partially encased in the fully open position of the valve, as described in FIG. 4 and in the aforementioned J. Krieg patent application. ing. The check ball, cage, and piston subassembly is biased upwardly by a plunger spring 82, the upper end of which lies in mate with the flange 80 of the check ball gauge, and the lower end of which mates with the bottom 65 of the plunger. be in contact with

The area surrounding the plunger 49 in the upper part of the web 44 and bounded by the lower surface of the camming surface member 18 contains an annular chamber whose reservoir is connected to the outer area around the body 42 and the outer tubular wall of the tapepet body and the web 4
4 through a passageway 84 provided therethrough. The bypass recess 43 has a chamber 83 and a piston 64 surrounded by the piston bore 70 and the portion 18.
It functions to provide continuous flow to and from the reservoir 85 within. The piston is moved by the spring 82 and the hydraulic pressure in the chamber 86 as illustrated in the third and fourth examples.
It will be appreciated that in the uppermost position, the underside of member 18 is held pressed.

In the presently preferred implementation, if fluid evacuates from chamber 83 during periods of engine rest, the fluid held in fluid reservoir 85 is supplied to one-way valve 72 upon engine start-up. To ensure that sufficient fluid is available under various conditions, chamber 83 is at least equal to the volume of reservoir 85.

The area 86 surrounded by the plunger bottom 64 and the plunger hole under the piston check ball and seat 74 is opened to the passage 6 by the opening of the check ball 72.
Encloses a high pressure fluid chamber for retaining therein fluid entering through 8.

In operation, valve 72 is biased to the closed position by spring 76 and lobe 16 is rotated when the camshaft rotates to the position shown in solid outline in FIG.
is oriented out of contact with the cam surface of the tappet, and the upper surface of the tappet matches the basic circular portion of the cam. Rotation of the camshaft 14 to the position shown in phantom in FIG. 1 causes the cam load to contact the upper surface 18 of the tappet and move the tappet downwardly to the position shown in phantom, thereby opening the combustion chamber valve. When the camshaft returns to the solid line position in Figure 1 with the next rotation, one cycle of valve operation is completed.
The valve is placed back on the valve seat.

In operation, when engine cam lobe 16 is in the position shown in FIG. The plunger 49 is forced downwardly until it contacts the upper surface 26 of the valve stem 22, thereby disengaging the valve gear. This inflates chamber 86 and causes check ball 72 to become inflated.
is pulled open to the position shown in FIG.
allow for inflow into the country. The cessation of expansion of chamber 86 causes check ball 72 to close under biasing spring 76. The next rotation of the cam lobe 16 causes the ramp of the cam lobe to force the piston 64 into the hole 62 in the plunger.
Start exerting downward force on the upper surface 18 of the tapepet,
The compression is resisted by the fluid confined within chamber 86. The fluid confined in chamber 86 prevents substantial movement of piston 64 relative to plunger 49 and transmits movement through the bottom of plunger 49 onto the top of valve stem 26 . It will be appreciated by those skilled in the art that a small movement of the plunger relative to the piston occurs, the magnitude of which is controlled by the amount of fluid that can pass through the leakage surfaces 62 and 66. Piston 64 and plunger 49 thus act as steel members that further lift cam lobe 16 to open the valve to the position shown in FIG. 1 by dashed lines.

Referring now to FIG. 5, another embodiment of the tapepet, indicated generally at 100, includes a tubular outer wall 1.
02 and extends inwardly.
4 and a central tubular hub portion 106 integrally formed with a web 104. Plunger 108 is slidably received within hub 106.
Plunger 108 has a hydraulic piston and one-way valve means similar to the embodiment of FIG. Plunger 108 of the embodiment of FIG.
has a circumferential groove 110 formed around it;
It contains a radially compressible-expandable C-shaped snap spring 112.

When assembling the embodiment of FIG.
The plunger assembly housing the hub 10
6, the ring 112 is then compressed such that the outer circumference is smaller than the inner circumference of the hub. The plunger is then moved upwardly with respect to FIG. 5 until the snap ring 112 passes the hub 106 and is then free expanded slightly to prevent the plunger assembly from disengaging from the hub. It will be appreciated that the embodiment of FIG. 5 eliminates the need for forming grooves, such as groove 58, in the wall of hub 46 (see FIG. 3). Forming such grooves presents a difficult manufacturing operation, especially when the outer diameter of the body is less than 35 mm. However, the embodiment of FIG. 5 may result in a tappet assembly where the plunger subassembly is more difficult to remove.

Referring now to FIG. 6, a further modified embodiment of the present invention is shown, in which a portion of the tappet designated generally at 120 is shown. The tapepet body of FIG. 6 includes a transverse web 1 integral with a central tubular hub 126 extending axially downwardly from an outer tubular wall portion 122 and a web 124.
It has 24. The inner circumference of the hub 126 has a circumferential groove 128 formed near its lower end and has retaining means in the form of a snap spring 130 housed therein for retaining the plunger in the hub. There is.

Referring now to FIG. 7, a modified embodiment of the tapepet 140 is shown, which includes the transverse web 14.
2, the web 142 has a hardened upper surface for contacting the cam. Web 142 is integrally formed with outer wall 140 and is preferably a suitable iron-based material, such as easily formable and hardenable steel. The outer wall 140 has an annular rib 144 extending from the inner surface in the middle of its end, and a circumferential groove formed on the inner periphery of the outer wall 140 and spaced vertically downward from the annular rib 144 in FIG. It is desirable to have 147. An annular member 146 formed of a suitable iron-based material, such as unhardened carbon steel, is inserted into the inner periphery of the wall 141 and mated with the upper surface of the annular member 146 facing the lower surface of the annular rib. . Annular member 146
has a centrally disposed and downwardly extending annular hub portion 148 formed integrally therewith, the hub portion 148 housing a suitable hydraulic L/A assembly, generally indicated at 150, which assembly are similar to those described above with respect to FIGS. 3, 4, and 5. Hydraulic L/A assembly 150 has lip 15
2 is retained on the inner circumference of hub 148 by deforming the lower end of the hub to form 2.

The outer periphery of the annular portion 146 has an annular wall portion 154 extending downwardly with respect to FIG. 7 from the outer periphery of the annular portion 146 along the inner surface of the tapepet body wall portion 141. The lower edge of wall 154 is deformed outward into groove 147;
This holds the annular portion 146 in alignment with the lower surface of the rib 144 and prevents the annular portion 146 from coming off the tapepet body. Annular portion 146 thus defines an outer annular portion 146 of a liquid reservoir similar to portion 83 of the embodiment of FIG. The function of the hydraulic L/A mechanism 150 in the tappet 140 is otherwise the same as described above with respect to the embodiment of FIGS. 2-5. The embodiment of FIG. 7 provides a simplified construction of a bucket or tappet body, but separate inserts must be provided for the outer portion of the fluid reservoir and the supporting hub of the L/A mechanism. In addition, in Figures 2 to 5,
In an embodiment in which the head members 18, 107 are separate from the outer walls 42, 102, the hub 46 and web 44 (hub 106 and web 104) are separated from the outer walls 42, 102 as in the embodiment of FIG. It goes without saying that a separate structure may be used.

〔Effect of the invention〕

As described and illustrated in the foregoing embodiments, the present invention provides a unique bucket tappet for use in direct-acting valve gears of internal combustion engines, which is particularly suitable for drive speeds of 5000 rpm and above. The tappet uses a hardened steel disk connected to one end of the tubular body to provide the camming surface of the tappet. The tubular body is integrally formed with inwardly extending webs disposed intermediate the ends of the tubular walls, the webs integrally forming a centrally disposed tubular hub for housing the hydraulic L/A mechanism. Preferably, the plunger mechanism is retained by retaining means engaging the wall of the tubular hub, or alternatively by a snap ring provided on the outer periphery of the plunger. The novel configuration of the present tappet provides lash adjustment by precision fit of the piston within a hole formed in a plunger slidably housed in the hub, thus providing a leakage control surface between the tappet and plunger. Eliminates the need for precise fitting. The area around the plunger between the web and the tubular wall of the body and the cam surface member provides a first portion of the reservoir, and the cavity of the piston supplies fluid to a one-way check valve for the hydraulic L/A means. A second partial reservoir is provided for. External retention means in the preferred embodiment facilitate manufacturing and quick removal of the hydraulic plunger assembly for cleaning and/or parts replacement.

In addition, as the prior art of this application, Japanese Patent Application Laid-Open No. 47-14526
This tappet is equipped with an inexpensive metal intermediate guide member between the guide hole drilled in the cylinder head and the valve lifter housed therein, and the intermediate guide member is fixed to the valve lifter. The lash adjustment plunger has a structure in which it slides in direct contact with the inner surface of the valve lifter. It is also an object of the invention to reduce costs by reducing the number of high quality metal parts in the tapepet. Therefore, the structure is fundamentally different from that of the present application, which has a structure in which the plunger is accommodated in and slides in the hub, and the hub is fixed to the outer tubular wall only by the web. The features resulting from the differences, such as the liquid flow path means, are also clearly different. The purpose of the invention is also completely different.

Although the invention has been described and illustrated in the presently preferred embodiment, it is understood that modifications and variations of the invention may be made in the form disclosed herein, and that the invention is limited only by the scope of the claims. The limitations will be apparent to those skilled in the art.

[Brief explanation of drawings]

1 is a sectional view of a direct-acting valve gear of an internal combustion engine, illustrating a tappet installed in the engine; FIG. 2 is a view of the end of the plunger of the hydraulic tappet of the present invention; and FIG. FIG. 4 is a view similar to FIG. 3 showing the one-way valve means in the fully open position; FIG. 3 is a view similar to FIG. 3 showing parts of another embodiment of the tappet using alternative retention means for the plunger, and FIG. 6 shows an additional embodiment of the tappet using a third plunger retention means. FIG. 5 is a view similar to FIG. 5, and FIG. 7 is a view similar to FIG. 3 showing another embodiment of the tapepet with an alternative description of the body. 10: Bucket tapet, 12: Guide hole, 1
4: Camshaft, 16: Cam lobe, 18: Cam surface, 20: Valve, 24: Valve guide, 40:
Body, 42: Tubular wall portion, 44: Web, 4
6: Hub, 48: Hub inner circumference, 50: Plunger.

Claims (1)

[Claims] 1. A bucket tappet 10 used in a direct-acting valve gear of an internal combustion engine, in which one end of the tappet 10 is in contact with an engine cam 16 and the other end is in direct contact with a stem 22 of a combustion chamber valve 20. the generally tubular outer wall 42 ; 102 ; 122 and the outer wall 42 ; 102 ;
2; 102; 122 and in contact with the engine cam 16, the outer wall 42; 102;
a continuous head member 18, 107 comprising a cam surface equal to the diameter of 22;
generally cylindrical hub 46; 10 generally parallel thereto;
6; 126; and a plunger 49, 108 slidably received in said hub 46; 106; 126 and having at its lower end a bottom wall for contacting the valve stem 22.
and a piston 64 which is not fixed to the head member 18, 107 and is slidably received within said plunger 49, 108 and cooperates with said plunger 49, 108 to define a liquid pressure chamber 86; and a biasing means 82 disposed between the plunger 49 and the piston 64 to bias the plunger 49 and the piston 64 away from each other, into the liquid pressure chamber 86 when the piston 64 moves in a direction in which the volume of the liquid pressure chamber 86 increases. one-way valves 72, 74 operable to allow liquid to flow in and prevent liquid from flowing back out of the liquid pressure chamber 86 when the piston 64 moves in a direction that reduces the volume of the liquid pressure chamber 86; and the inside of the piston 64 and the piston 64 for supplying liquid to the one-way valves 72 and 74.
a liquid reservoir 85 located between and between said head members 18, 107;
2, an annular chamber 83 located between the piston 64 and the plunger 49; a first passage means 84 for supplying liquid to the annular chamber 83; and a flow path between the annular chamber 83 and the reservoir 85. a second passage means 43 forming a hub 46; 106; 126 and a tubular outer wall 42;
Spread between 02; 122, hub 46; 10
6; 126 with the tubular outer wall 4 so as to form the only structural support member of the hub 46;
Web 44; 10 connected to 2; 102; 122
4;124 by hub 46;106;126
The upper end is separated from the head member 18,107 in the axial direction so that the hub 46;106;126
07, such that said annular chamber 83 is axially aligned with the web 4.
4; 104; 124 and the head member 18, 107, the radial extent of the annular chamber 83 is substantially equal to that of the web 44; 104; Forming the only open flow path to or from the tappet structure, said annular chamber 83 is connected to said first passage means 84 and between said hub 46; 106; 126 and said plunger 49, 108. A hydraulic tappet for a direct-acting valve gear that is effectively sealed except for leaks. 2. A generally tubular bucket tappet 10 used in direct-acting valve gears of internal combustion engines, with one end of the tappet 10 in contact with the engine cam 16 and the other end in direct contact with the stem 22 of the combustion chamber valve 20. an outer wall 141; a continuous head member 142 integral with the outer wall 141 and including a cam surface having a diameter equal to the diameter of the outer wall 141 and in contact with the engine cam 16; a cylindrical hub 148; slidably accommodated in the hub 148;
a plunger having a bottom wall at its lower end for contacting the valve stem 22; and a plunger not fixed to the head member 142, slidably received within said plunger and cooperating with said plunger to define a liquid pressure chamber. piston,
a biasing means disposed between the plunger and the piston to bias the plunger and the piston away from each other, and a biasing means configured to cause liquid to flow into the liquid pressure chamber when the piston moves in a direction in which the volume of the liquid pressure chamber increases; a one-way valve operable to allow and prevent liquid from flowing back from the liquid pressure chamber when the piston moves in a direction in which the volume of the liquid pressure chamber decreases; and for supplying liquid to the one-way valve. , the interior of the piston, and the piston and the head member 14
a liquid reservoir located between 2 and axially below said head member 142;
an annular chamber 156 located radially between the tubular outer wall 141 and said piston and plunger; first passage means for supplying liquid to said annular chamber 156; and a first passage means between said annular chamber 156 and said reservoir. extending between the hub 148 and the tubular outer wall 141 and having second passage means defining a flow path;
A web 146 connecting hub 148 to tubular outer wall 141 to form the only structural support member for hub 148 causes the upper end of hub 148 to be spaced axially from head member 142 so that hub 148 is held in a fixed relationship with respect to member 142;
Said annular chamber 156 is thereby located axially between the web 146 and the head member 142, the radial extent of the annular chamber 156 substantially extending beyond the web 14.
6, said first passage means forming the only open flow path to or from said tappet structure, and said annular chamber 156 connecting said first passage means and said hub 148. A hydraulic tappet for a direct-acting valve gear, characterized in that the tappet is effectively sealed except for leakage between the plunger and the plunger.