Covering structure for covering timing mechanism and timing...

Details Covering structure for covering timing mechanism and timing... Covering structure for covering timing mechanism and timing...

1999-02-04

2001-04-10

Lo, Wellun (Department: 3748)

Internal-combustion engines

Poppet valve operating mechanism

Lubrication

C123S090310, C123S1950HC, C123S19800E

Reexamination Certificate

active

06213073

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a hydraulic tensioner for a timing mechanism included in an internal combustion engine, and a timing mechanism covering structure serving as one of structural members defining a timing mechanism chamber containing a timing mechanism and a lubricating system included in an internal combustion engine. More specifically, the present invention relates to a hydraulic tensioner for a timing mechanism included in an internal combustion engine, having a reduced number of parts, having improved response characteristic and capable of being readily manufactured, and to a timing mechanism covering structure for an internal combustion engine, capable of facilitating maintenance work for the maintenance of a tensioner, of holding the component members of accessories and of preventing support shafts from falling off.
2. Description of the Related Art
As stated in JP-A No. 5-99288, in a conventional internal combustion engine, an open end of the main gallery of the lubricating system of an internal combustion engine on the side of a timing mechanism chamber containing a timing mechanism is stopped with a plug. A tensioning unit included in a hydraulic tensioner for exerting pressure to a timing chain included in a timing mechanism for transmitting the rotation of a crankshaft to a camshaft in a direction substantially perpendicular to the running direction of the timing chain is disposed at a position separate from the main gallery, and working fluid is supplied from the main gallery through a separate oil supply passage to the tensioning unit. Therefore, an additional member, i.e., the plug, is necessary to stop the open end of the main gallery on the side of the timing mechanism chamber, and a wall in which the open end of the main gallery opens must be tapped by a tapping process to close the open end of the main gallery with the plug. Since the tensioning unit is disposed apart from the main gallery, the oil supply passage connecting an oil pump to the tensioning unit is long and it is difficult to raise the working pressure in the tensioning unit quickly immediately after the start of the internal combustion engine. Thus, problems resides in the response characteristic of the tensioner. Since the tensioner is unable to function satisfactorily, the timing chain of the timing mechanism slackens, vibrates and generates noise. Work for forming the long oil supply passage is difficult.
It is difficult to form a narrow bore in a cylinder block owing to the arrangement of an assembly line. Therefore, a pressure regulating constriction cannot be formed and the working fluid of a regulated pressure cannot be supplied to the tensioner.
In an internal combustion engine disclosed in JP-A No. 7-42571, a timing mechanism chamber is formed by covering the respective end walls of a cylinder block and a cylinder head with a timing mechanism cover, and a timing mechanism including a timing chain and a crankshaft sprocket is arranged in the timing mechanism chamber. An end part of the crankshaft penetrates and projects from the timing mechanism cover, and an accessory driving pulley is fixedly mounted on the end part of the crankshaft projecting from the timing mechanism cover. A handhole formed in the timing mechanism cover for the maintenance of an oil pump disposed in the timing mechanism chamber is covered with a cover. The cover is placed on the timing mechanism cover with bolt holes formed therein aligned with threaded holes formed in the timing mechanism cover, and is fastened to the timing mechanism cover with bolts. Since the bolt holes formed in a peripheral part of the cover are concealed behind a crankshaft pulley and an accessory driving belt wound around the crankshaft pulley, the accessory driving belt needs to be removed from the crankshaft pulley and then the crankshaft pulley needs to be removed from the crankshaft before removing the cover for maintenance work, which is very troublesome.
FIG. 24
is a sectional view of a front end part of a V-shape internal combustion engine
01
provided with another prior art timing mechanism cover structure disclosed in JP-A No. 7-42571. Referring to
FIG. 24
, a chain cover (timing mechanism cover)
03
is fastened to the front end of a cylinder block
02
included in the V-shape internal combustion engine
01
to form a timing mechanism chamber
04
. Disposed in the timing mechanism chamber
04
is a timing mechanism comprising a crankshaft sprocket (drive sprocket)
06
mounted on a crankshaft
05
, and a chain
07
wound around the crankshaft sprocket
06
and a camshaft sprocket (driven sprocket), not shown, mounted on a camshaft, not shown. The chain
07
extended between the crankshaft sprocket
06
and the camshaft sprocket is wound round a pump sprocket
09
mounted on the shaft of a water pump
010
. The rotation of the crankshaft
05
is transmitted through the chain to the camshaft to drive the camshaft for rotation and to the shaft of the water pump
010
to drive the water pump
010
.
A pump housing
011
is fastened together with a rear chain cover
012
to the cylinder block
02
with bolts
015
. A handhole for maintenance work is formed in a part of the chain cover
03
facing the water pump
010
and is covered with a cover
016
. Sometimes, the bolts
015
are caused to become loose by vibrations or the like. It is possible that the bolts
015
loosen greatly when the distance between the heads of the bolts
015
and the cover
016
disposed opposite to the bolts
015
is long as shown in FIG.
24
. Consequently, the pump sprocket
09
becomes unsteady, the chain
07
vibrates, and a chain guide and a tensioner arm hit frequently on the chain cover
03
to generate noise. If, by any chance, the bolts
015
should come off the cylinder block
02
, the water pump
010
cannot be held in place and would cause serious damage. If the bolts
015
comes off the cylinder block
02
and need to be recovered, the chain cover
03
needs to be removed, and the crankshaft pulley
017
needs to be removed from the crankshaft
05
to remove the chain cover
03
, which requires very troublesome work.
If the pivot pin of a tensioner is made of a steel, an arm body is made of an aluminum alloy, and the pivot pin is fitted in a mating hole formed in the arm body in a press fit, the interference between the pivot pin and the arm body tends to decrease at a high temperature due to the difference in coefficient of thermal expansion between the pivot pin and the arm body, and it is possible that the pivot pin comes off the arm body.
SUMMARY OF THE INVENTION
The present invention has been made in view of the foregoing problems in the prior art and it is therefore a first object of the present invention to provide a hydraulic tensioner for an internal combustion engine, not requiring a plug for closing an open end of a main gallery on the side of a timing mechanism chamber, requiring a reduced number of parts, having improved response characteristic and capable of being easily manufactured.
A second object of the present invention is to provide a timing mechanism covering structure for an internal combustion engine, capable of solving the foregoing problems in the conventional timing mechanism covering structure for an internal combustion engine, and of facilitating maintenance work for the maintenance of a tensioner unit disposed in a timing mechanism chamber.
A third object of the present invention is to provide a timing mechanism covering structure for an internal combustion engine, capable of solving the foregoing problems in the conventional timing mechanism covering structure for an internal combustion engine, having a simple construction, and capable of preventing fastening parts, such as bolts and nuts, and support parts, such as pivot pins, for fastening and supporting the component parts of a timing mechanism and those of a lubricating system from coming off.
According to a first aspect of the present invention, a hydraulic tensioner for an internal combustion

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