Bearing structure for a cam shaft in internal combustion engines

A bearing structure for a cam shaft has a first journal-receiving cavity of a semi-circular cross section provided in an upper face of a cylinder head, and a second journal-receiving cavity of a semi-circular section provided in a lower face of a bearing cap. The bearing cap is mounted on the cylinder head with the two faces joining together. A groove is provided in at least one of the two joining faces to extend across that face and to communicate at one end thereof with the internal space of the cylinder head so as to collect or intercept oil leaking out through a clearance left between the two adjacent faces.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a bearing structure for a cam shaft in 
internal combustion engines and, more particularly, a bearing structure 
for a cam shaft which is driven by a timing belt. 
2. Description of the Prior Art 
In overhead cam engines, the cam shaft is conventionally mounted in the 
engine so that its bearing portion is laid in a semi-circular 
journal-receiving cavity in an upper face of the cylinder head. A bearing 
cap, having a second semi-circular journal-receiving cavity provided in a 
lower face thereof, is mounted with the second cavity opposing the first 
mentioned cavity in the cylinder head, thereby enabling the bearing 
portion of the cam shaft to be rotatable in the round bearing cavity 
defined by said first and second semi-circular cavities. The bearing 
surface of this structure is generally formed with an annular oil groove 
which is supplied with oil under a pressure such as 2 Kg/cm.sup.2 -4 
Kg/cm.sup.2 in normal operation and 6 Kg/cm.sup.2 when starting-up at a 
low temperature. The oil is generally supplied through a passage which 
opens into the bearing surface provided by the cylinder head. When the cam 
shaft supported by this bearing structure is driven by gear wheels or an 
endless chain, the driving means are located within the body of the engine 
and no problem arises even if the lubricating oil leaks out either from 
the front or rear of the bearing portion because the oil is positively 
received and collected in an oil pan provided at a lower portion of the 
engine. However, in those engines where the cam shaft is driven by a 
timing belt, the cam shaft has a front end portion which projects forward 
from the body of the engine and supports a pulley on which is mounted a 
timing belt. The latter also runs around another pulley mounted on the 
crank shaft of the engine and, because of this, the oil can no longer be 
collected if it has leaked out forward from the bearing portion. 
To meet this problem, the conventional bearing structure for a cam shaft 
driven by a timing belt generally incorporates oil seal means provided 
between the front end portion of the bearing surface and the journal 
portion of the cam shaft so as to check and collect any oil leaked out 
from the bearing portion and to return the oil to the internal space of a 
cylinder head through an oil return passage which connects the oil seal 
means and said internal space. However, the lubricating oil pumped to the 
bearing under pressure can enter the very small clearance left between the 
upper face of the cylinder head and the lower face of the bearing cap and 
ooze out from the space between the cylinder head and the bearing cap. It 
has been suggested to have the adjacent faces conact each other more 
accurately and closely in order to prevent such an oil leakage. However it 
is practically impossible to finish the joining surfaces to such high 
accuracy as to perfectly exclude any entry of the pressurised lubricating 
oil between adjacent faces. As an alternative measure to meet this 
problem, it has been suggested to provide an oil seal between the joining 
faces. However, this is difficult to accomplish in practice in view of the 
function and structure of the bearing portion. In addition, this would 
result in a higher engine cost. 
SUMMARY OF THE INVENTION 
It is therefore the object of the present invention to solve the 
aforementioned problem of oil leakage in the bearing structure for a cam 
shaft which is driven by a timing belt and to provide an improved bearing 
structure for the cam shaft which is capable of positively eliminating the 
oil leakage therefrom. 
According to the present invention, the above object is achieved by a 
bearing structure for a cam shaft which comprises a cylinder head having a 
first semi-circular journal-receiving cavity provided in an upper face 
thereof, a bearing cap, having a second, semi-circular journal-receiving 
cavity provided in a lower face thereof, said upper face of the cylinder 
head joining said lower face of said bearing cap when said bearing cap is 
mounted on said cylinder head. A groove is provided in at least one of the 
adjoining faces to extend across a face and to communicate at one end 
thereof with the internal space of the cylinder head. 
In the above-mentioned bearing structure, the groove traverses the 
bordering surface defined between the two surfaces which join the cylinder 
head and bearing cap and serves to collect any oil which crosses the 
groove when flowing over the bordering surface from an inside to an 
outside region threof. The oil thus collected is returned through the 
groove to the internal space of the cylinder head, thereby positively 
preventing any oil from leaking out of the cylinder head or the body of 
the engine. 
Since the bearing structure of the aforementioned type further incorporates 
an annular oil seal element provided adjacent the outside edge of the 
bearing surface defined by said journal-receiving cavities, and this 
annular seal slidably contacts an annular surface portion of the cam shaft 
located adjacent its journal portion, it is desirable that the groove 
start from an inside edge portion of the annular seal element and traverse 
the joining border surface toward the other end which opens into the 
internal space of the cylinder head. This groove must, of course, be 
located away from the oil supply port which opens into the bearing surface 
defined by the cavity portions of the cylinder head and the bearing cap.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
In the following the invention will be described in detail with reference 
to the accompanying drawings. Referring to FIGS. 1-6, 1 designates the 
front wall of a cylinder head which has a semi-circular journal-receiving 
cavity 2 provided in its upper face. a cylinder cap 3 also having a 
semi-circular journal-receiving cavity 4 provided in a lower face thereof 
is mounted on the cylinder head in a manner such that the cavity 4 opposes 
the cavity 2, thereby together defining a round cavity rimmed by an 
annular bearing surface in which is received journal portion 9 of cam 
shaft 8. The bearing cap is clamped to the cylinder head by two bolts 7 
which are passed through openings 5 in the bearing cap and are screwed 
into threaded openings 6 in the cylinder head. The cam journal portion 9 
is formed with an annular oil groove 10 at a middle portion thereof, while 
an oil supply port 11 opens into the bearing surface of the cylinder head 
to supply oil directly to the annular space defined by annular groove 10 
and the bearing surface. Adjacent the journal-receiving cavities, the 
cylinder head and the bearing cap are formed with semi-circular cuttings 
of a larger diameter than the cavities, the cuttings together forming an 
annular groove 12 for receiving an annular seal element 13. Annular seal 
13 is in sealing contact with an enlarged forward end portion of the cam 
shaft adjacent its journal portion 9. The bottom portion of the groove 12 
communicates with the internal space of the cylinder head through an oil 
return passage 14 which traverses and extends through the bearing portion 
of the cylinder head, whereby the oil which has leaked out into the 
annular oil seal 13 is returned to the inside of the cylinder head through 
the passage 14. 
The above description, to this point, relates to a conventional bearing 
structure. However, in accordance with the present invention, the 
embodiment shown in FIGS. 1-6 differs from the conventional structure by 
being provided with two grooves 15 which are formed in the upper face of 
the front wall 1 of the cylinder head. In more detail, the grooves 15 
extend from opposite inside corners of the groove 12 toward the internal 
space of the cylinder head. 
By this arrangement, even if the lubricating oil supplied to the bearing 
clearance formed between the bearing surface and the cam journal portion 
leaks out into the clearance space between the adjacent faces of the 
cylinder head and the bearing cap, the oil is intercepted by grooves 15 
and cannot cross these grooves to further leak out through the clearance 
space to the outside of the cylinder. The oil trapped in grooves 15 is 
returned from there into the internal space of the cylinder head. 
Grooves 15 need not necessarily be provided in the upper face of the 
cylinder head. They may, alternatively, be provided in the lower face of 
bearing cap 3, as shown in FIG. 7. Furthermore as a third embodiment the 
grooves may be formed in both the upper face of the cylinder head and the 
lower face of the bearing cap. 
Although the invention has been described with reference to particular 
embodiments thereof, it will be understood by those skilled in the art 
that various modifications can be made in the illustrated embodiments 
without departing from the spirit of the invention.