Bucket tappet guide

In a bucket tappet guide structure for a valve tappet of an internal combustion engine having a bucket tappet slideably disposed in a tappet receiving bore, wherein the tappet has a chamfered front end providing for a tappet front face having a smaller diameter than the tappet body, a guide bore is disposed in front of the tappet bore and concentric therewith, the guide bore having a diameter which is larger than the diameter of the tappet bore, however by less than the difference between the diameter of the tappet body and the tappet front face so as to facilitate insertion of the bucket tappet into the tappet bore.

BACKGROUND OF THE INVENTION 
The invention relates to a bucket tappet guide for the bucket tappet of the 
lifting valve of a valve-controlled reciprocating-pistons internal 
combustion engine. 
A conventional bucket tappet guide (see, for example, DE C 38 02 659) 
consists of a reception bore in the cylinder head or in the camshaft 
housing sized to guide the bucket tappet in the reception bore essentially 
free of play. In order to make it easier to slip the bucket tappet into 
the reception bore in an automated assembly line, both the lower edge of 
the bucket tappet and the upper edge of the reception bore are chamfered. 
It nevertheless happens repeatedly that the bucket tappets become tilted 
and jammed when they are being slipped into the reception bore. The 
automated operation is thereby interrupted, and it is necessary to carry 
out additional manual work which is costly and, in view of the short cycle 
times of the assembly line, presents big problems. 
The object of the invention is to provide a bucket tappet guide which 
ensures that the bucket tappet is reliably slipped into the reception 
bore. 
SUMMARY OF THE INVENTION 
In a bucket tappet guide structure for a valve tappet of an internal 
combustion engine having a bucket tappet slideably disposed in a tappet 
receiving bore, wherein the tappet has a chamfered front end providing for 
a tappet front face having a smaller diameter than the tappet body, a 
guide bore is disposed in front of the tappet bore and concentric 
therewith, the guide bore having a diameter which is larger than the 
diameter of the tappet bore, however by less than the difference between 
the diameter of the tappet body and the tappet front face so as to 
facilitate insertion of the bucket tappet into the tappet bore. 
With the arrangement according to the invention, the bucket tappet is first 
slipped into the guide bore, this being easily possible because its 
diameter is somewhat larger than the diameter of the tappet bore. In the 
guide bore, the bucket tappet is pre-centered, so that it can then slide 
guided by the chamfered end of the tappet into the tappet bore without 
tilting. 
It is advantageous to provide the edge of the guide bore with a chamfer 
which, together with the chamfer on the lower edge of the bucket tappet, 
insures that the bucket tappet is reliably inserted into the guide bore. 
If a relatively long guidance of the bucket tappet in the guide bore is 
desired, the wall surrounding the guide bore extends upwardly so that it 
projects above the bucket tappet when the tappet is actuated for opening 
an associated valve. In this case, this wall is provided with two 
diametrically opposite recesses extending in the direction of rotation of 
a cam actuating the bucket tappet allowing the cam to move through the 
recesses for operating the bucket tappet.

DESCRIPTION OF A PREFERRED EMBODIMENT 
The numeral 1 denotes a cylinder head (or a camshaft housing) of a 
valve-controlled reciprocating piston internal combustion engine. The 
cylinder head 1 includes a bucket tappet guide for each valve (not shown) 
actuated by a cam via a bucket tappet 2. The bucket tappet guide consists 
of a tappet bore 3 slideably receiving the bucket tappet 2 with a close 
fit. A guide bore portion 4 is arranged in front of the tappet bore 3 and 
is concentric relative to the latter. It has a diameter which is slightly 
larger than the diameter of the tappet bore 3, for example, by 0.04 mm. 
For clarification, this difference in diameter is greatly exaggerated in 
the drawing. The guide bore 4 is provided at the upper edge with a chamfer 
5. Because of the somewhat larger diameter of the guide bore 4 and the 
chamfer 5, insertion of the bucket tappet 2 into the tappet bore 3 by 
automatic manufacturing equipment without cogging and jamming is greatly 
facilitated. The tappet is generally provided with a chamfer 6 formed at 
its lower edge so that the front face of the tappet has a diameter smaller 
than the body of the tappet by a certain length. The guide bore 4 has a 
diameter somewhat larger than that of the tappet bore 3 by an amount which 
is smaller than the certain length by which the diameter of the tappet 
body exceeds the diameter of the tappet front face. In the guide bore 4, 
the bucket tappet 2 is pre-centered relative to the tappet bore 3 so that 
it can then be easily inserted into the tappet bore 3. In order to insure 
good pre-centering of the tappet bucket the guide bore 4 may be so long 
that, when an associated valve is opened, that is to say, when the bucket 
tappet 2 is pushed fully into the tappet bore by a cam operating the 
tappet, the surrounding wall 7 projects above the bucket tappet. In order 
to allow the cam to operate the tappet, this wall is provided, in the 
direction of rotation of the cam, with two diametrically opposite recesses 
8 which are shaped so as to accommodate the cam.