Endless belt power transmission systems or components – Means for adjusting belt tension or for shifting belt,... – Tension adjuster has surface in sliding contact with belt
Reexamination Certificate
2001-07-03
2003-04-15
Bucci, David A. (Department: 3682)
Endless belt power transmission systems or components
Means for adjusting belt tension or for shifting belt,...
Tension adjuster has surface in sliding contact with belt
C474S109000, C074S57700S
Reexamination Certificate
active
06547684
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a ratchet tensioner used for applying an appropriate tension to a timing belt or a timing chain of a vehicle engine, and more particularly to a ratchet tensioner equipped with a plunger releasing mechanism operative to turn a ratchet pawl in a direction to disengage a locking pawl of the ratchet pawl from rack teeth formed on a plunger.
2. Description of the Related Art
In a drive system having a timing belt or chain stretched for power transmission between an engine crankshaft and a camshaft, a ratchet tensioner is widely used for suppressing vibration generated during travel of the timing belt or chain as well as for maintaining a proper tension in the timing belt or chain. The ratchet tensioner has a spring-loaded plunger projecting outward from a tensioner housing to urge a back surface in the vicinity of the distal or free end of a tensioner lever in a direction, so that a shoe surface of the tensioner lever is held in slide contact with the slack side of a timing chain to thereby apply a tension to the timing chain. Prior examples of the ratchet tensioner are disclosed in Japanese Patent Publication No. HEI-3-8414 and Japanese Patent Laid-open Publication Nos. HEI-10-2386 and HEI-11-344086.
FIGS. 13 and 14
hereof illustrate a typical example of the conventional ratchet tensioner. This tensioner
31
includes a plunger
33
slidaby received in a plunger accommodating hole (not designated) of the housing
32
with its outer end
33
A (
FIG. 13
) projecting outward from a front surface of the housing
32
by the force of a plunger spring
36
(
FIG. 14
) received inside the housing
32
, and a ratchet pawl
34
pivotally mounted by a pivot shaft or pin
34
A to the housing
32
. The ratchet pawl
34
is accommodated in a cutout recess or groove
32
E defined by two opposed side walls
32
C,
32
D. The ratchet pawl
34
is urged by a ratchet spring
38
to turn about the pivot pin
34
A in one direction to keep meshing engagement between a locking prong
34
B (
FIG. 14
) and one of a series of rack teeth
33
B formed on an outer circumferential surface of the plunger along the axis thereof, so that the plunger
33
is prevented from moving backward.
The illustrated ratchet tensioner
31
has a built-in hydraulic shock absorbing mechanism using the flow resistance of oil. The rack teeth
33
B and the locking prong
34
B are designed to provide a backlash therebetween. The oil (not shown) supplied from an external oil pump operating in synchronism with an engine is introduced into a hollow interior space (not designated) of the plunger
33
via a check valve mechanism
35
provided at the bottom of the plunger accommodating hole of the housing
32
. When the plunger
33
is subjected to a shock or impact force from a tensioner lever (now shown), the plunger
33
moves backward within the range of the backlash against the force of the plunger spring
36
while the prong
34
B and the rack teeth
33
B are kept in mesh with each other. In his instance, the check valve mechanism
35
is closed so that the oil within the hollow interior space of the plunger
33
is forced to leak out from a clearance between the outer circumferential surface of the plunger
33
and an inner peripheral surface of the plunger accommodating hole of the housing
32
to thereby absorb the impact force. Reference character
32
B shown in
FIGS. 13 and 14
denotes holes used for mounting the ratchet tensioner
31
to the engine body.
The ratchet tensioner
31
further has a lever
37
(
FIG. 13
) firmly connected at one end to an end of the pivot pin
34
A and projecting outward from the housing
32
. By turning the lever
37
, the ratchet pawl
34
is turned about the pivot pin
34
A in the direction of arrows shown in
FIGS. 13 and 14
with the result the engagement between the ratchet prong
34
B and the rack teeth
33
B is released.
When the engine is to be repaired or when the chain is to be removed, the plunger
33
of the ratchet tensioner needs to be displaced in a fully retracted position. In the conventional ratchet tensioner
31
, the plunger
33
, which is operating as a one-way mechanism, can be released by turning the ratchet pawl
34
in the direction of arrows against the force of the ratchet spring
38
. However, the conventional ratchet tensioner
31
has no means or mechanism for maintaining the plunger
33
in the released state. It is, therefore, difficult to keep the locking prong
34
B of the ratchet pawl
34
separated from the rack teeth
33
B of the plunger
33
. This makes it difficult to achieve the chain replacement operation with ease. In addition, the lever
37
cannot be easily turned or manipulated by a screwdriver which is inserted in a hole
37
A in the lever
37
through a small service hole provided in the engine. Even when the lever
37
is turned by using such screwdriver, a difficulty still arise in maintaining the lever in an angularly displaced condition. As a consequence, it is practically impossible for the plunger
33
to be maintained in a released condition with the locking prong
34
B disengaged from the rack teeth
33
B. Another problem is that the lever
37
attached as a separate part to the pivot shaft
34
A of the ratchet pawl
34
increases the number of part of the tensioner
31
, which will incur an additional cost.
SUMMARY OF THE INVENTION
Accordingly, a general object of the present invention is to solve the aforementioned problems associated with the conventional ratchet tensioners.
A more specific object of the present invention is to provide a ratchet tensioner having a plunger releasing mechanism which can readily turn a ratchet pawl against the force of a ratchet spring in a direction to disengage prongs of ratchet pawl from rack teeth on a plunger, thereby keeping the plunger in a released condition.
To achieve the objects, according to the present invention, there is provided a ratchet tensioner comprising: a housing; a plunger reciprocally mounted in the housing and urged by a plunger spring received inside the housing so that one end of the plunger projects outward from the housing; a ratchet pawl pivotally mounted by a pivot shaft to the housing within a recessed groove formed in the housing, the ratchet pawl having a locking prong at one end thereof located on one side of the pivot shaft; and a ratchet spring urging the ratchet pawl to turn about the axis of the pivot shaft in one direction so that the locking prong of the ratchet pawl is held in mesh with one of a series of rack teeth
3
B formed on an outer circumferential surface of the plunger along the axis thereof. The ratchet tensioner further includes a plunger releasing mechanism for turning the ratchet pawl about the axis of the ratchet shaft in the opposite direction against the force of the plunger spring to disengage the locking prong of the ratchet pawl from the rack tooth of the plunger. The plunger releasing mechanism has a pin insertion hole formed in the housing transversely across the recessed groove for permitting insertion of a pin from the exterior of the housing, the pin insertion hole being located on the opposite side from the locking prong with respect to the pivot shaft, and a sloped surface formed on the ratchet pawl and normally extending obliquely across the axis of the pin insertion hole. The sloped surface, upon abutment with a tip end of the pin which is inserted in the pin insertion hole, is capable of causing the ratchet pawl to turn in the opposite direction against the force of the ratchet spring to thereby disengage the locking prong of the ratchet pawl from the rack tooth of the plunger for releasing the plunger.
In one preferred form of the present invention, the ratchet pawl has a pin accommodating hole formed therein with the axis normally offset from the axis of the pin insertion hole of the housing. The pin accommodating hole has an inner circumferential surface portion extending at an angle to the axis of the pin accommodating hole and forming th
Bucci David A.
Dann Dorfman Herrell and Skillman
McAnulty Timothy
Skillman Henry H.
Tsubakimoto Chain Co.
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