Belt or chain tensioner for power transmitting system

A belt or chain tensioner includes a collar mounted between a bearing and a spring seat. The spring seat includes a externally mounted on a cylinder portion of a rotational cylinder so as to prevent movement of the rotational cylinder in an axial direction and penetration of a torsion spring into a ring groove provided between the cylinder portion and a male threaded portion of the rotational cylinder.

BACKGROUND OF THE INVENTION 
The present invention relates to a belt or chain tensioner for motorcycles 
and automobiles and, more particulary, to a tensioner for tensioning a 
drive a chain or belt for driving camshaft of an engine. 
A conventional tensioner, such as a belt tensioner or a chain tensioner is 
used to apply constant tension on a belt or chain even when the belt or 
chain looses predetermined tension due to elongation or slackening caused 
by wear or friction. For this reason, it is preferable that the tensioner 
be kept advanced at all times in a tensioning direction and that it have 
characteristics of a rigid object against a counterforce in a direction 
opposite the tensioning direction. FIG. 5 shows a vertical section of a 
conventional tensioner. 
The tensioner comprises a casing 1 with a housing 1a formed in an axial 
direction, a rotational cylinder 2 inserted rotatably in said housing, a 
tension rod 3 engaged with a threaded portion of the rotational cylinder 
2, and a torsion spring 4 inserted externally on the rotational cylinder 
2. One end 4a of the spring is inserted in a slit 2a formed on the rear 
end of rotational cylinder 2, and other end 4b is inserted in a long 
groove 1b formed on the front portion of housing 1a for driving the 
rotational cylinder 2. A seal bolt 6 is screwed on the rear end of the 
casing. The top of said tension rod 3 is covered with a cap 8 fixed with a 
spring pin 7, whereby a chain or belt is tensed directly or indirectly to 
keep constant tension. The tension rod 3 is externally round and 
diametrically has two plain surfaces. Tension rod 3 is inserted freely in 
a corresponding slot of same shape formed in the bearing 9 so as not to 
turn, whereby the rotating force of the rotational cylinder 2 can be 
converted into an urging force. 
This type of tensioner can be applied with a predetermined torsional torque 
by using a flat driver inserted through threaded hole on the rear end of 
the tensioner after mounting the component in the housing of casing. The 
threaded hole can then be hermetically closed with an "O" ring and the 
seal bolt. Thus the tensioner may be mounted, for example, on the outer 
wall of equipment, such as engine body, by inserting the front portion of 
the casing so that the cap of tension rod may work to keep constant 
tension on chain or belt by means of the restoring force of the torsion 
spring. 
The tensioner works satisfactorily when mounted. However it is not easy to 
mount components, such as a tension rod, a rotational cylinder and a 
torsion spring in the tensioner housing. Therefore a ring groove of small 
diameter is formed between the cylinder portion and threaded portion so 
that a flat washer 10 may be freely mounted so as to mount a collar 11 
between the bearing 9 and the flat washer 10. In this way, movement of the 
rotational cylinder 2, tension rod 3 and the torsion spring 4 in the axial 
direction can be prevented by the flat washer 10, collar 11, bearing 9 and 
the snap ring 12. 
Hereinafter the problems to be solved by the present invention will be 
explained. In the conventional belt or chain tensioner, when the torsion 
spring 4 is wound to get torsional torque, the wire end 4b used to 
penetrate into the gap between the flat washer 10 and the rotational 
cylinder 2 sometimes impedes the normal function of the torsion spring 4 
or the normal rotation of the rotational cylinder 2. This is because the 
torsion spring 4 extends in an axial direction when wound and, at the same 
time, eccentric movement can occur, causing the problems aforementioned. 
Then, it is effective to make the gap between the collar 11 and the flat 
washer 10 as small as possible, but it is very hard to reduce this gap 
ignoring the diameter of wire material. 
SUMMARY OF THE INVENTION 
The present invention has been developed taking the above situation into 
consideration so as to provide a belt or chain tensioner wherein a hook of 
a torsion spring will not be entangled. 
Now, the means to solve the problems aforementioned will be explained. 
The belt or chain tensioner according to the present invention is a 
tensioner having a rotational cylinder inserted in a torsion spring so as 
to rotate and to engage with a tension rod of which rotation is impeded by 
a bearing sliding in slots of the casing, whereby the rotational force of 
said rotational cylinder can be converted to an urging force for said 
tension rod in an axial direction. A spring seat with a sleeve externally 
inserted on said rotational cylinder to support said torsion spring and to 
stop the movement of said rotational cylinder in the axial direction, and 
a collar mounted between the tension rod side of said spring seat and said 
bearing, are provided.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Hereinafter, an embodiment according to the present invention will be 
explained referring to FIGS. 1 to 3. 
The tensioner comprises a casing or housing 20, a rotational cylinder 30 
screwed in a tension rod 40 both the cylinder and the rod are inserted in 
the casing 20. A torsion spring 50 is provided for driving the rotational 
cylinder 30 and a bearing 60 is mounted on the front end of casing 20 for 
stopping the rotation of tension rod 40. 
The casing 20 is provided with a flange portion 21 extending in radial 
direction, wherein two holes are formed in diametrical positions for 
fixing the casing with bolts on an outer wall of equipment such as engine 
(not illustrated). 
The rotational cylinder 30 comprises a male threaded portion 31 on the 
front end and a cylinder portion 32 on the rear end, between which a ring 
groove 33 is formed. The rear end of cylinder portion 32 of the rotational 
cylinder 30 is supported by a bearing portion 23 formed in the casing 20. 
On the rear end of cylinder portion 32, a slit 34 is formed so as to fix 
rear end of the torsion spring 50 for winding. The male threaded portion 
of rotational cylinder 30 is engaged with female threaded portion of the 
tension rod 40. On the ring groove 33 between the male portion 31 and the 
cylinder portion 32, a spring seat 70, incorporating a sleeve portion 72, 
is mounted. 
On the rear end of tension rod 40, a female threaded portion 41 is provided 
so as to engage with the male threaded portion 31 of the rotational 
cylinder 30. The front end of the tension rod is of tubular form and 
protrudes from the housing of the casing 20. The rotation of the tension 
rod 40 is impeded by the bearing 60 and even when the tension rod 40 is 
driven by the rotational cylinder 30, the tension rod 40 is only urged in 
axial direction so as to apply constant tension on chain or belt, because 
of an urging force converted from rotational force by the bearing 60. In 
addition, the front end of the tension rod 40 is covered with a cap 43 
fixed on the tension rod with a spring pin 42. 
The cylinder portion 32 of the rotational cylinder 30 is inserted in the 
coil portion 51 of the torsion spring 50. The front end 52 of the torsion 
spring 50 is inserted into the long groove 24 formed on the inner wall of 
the housing or casing 20. The rear end 53 of the torsion spring 50 is 
inserted in a slit 34 formed on the rear end of the rotational cylinder 
30. Having this type of construction, when torsional torque is provided on 
the torsion spring by winding the rear end of rotational cylinder 30, the 
rotational cylinder can be driven by the torsion spring 50. The winding 
operation can be done by driving the slit on the rear end of the 
rotational cylinder with tool such as flat driver 80. 
Said bearing 60 is mounted on the front end of the casing 20 and fixed with 
a snap ring 81. The bearing 60 is provided with three protrusions 61 with 
the angular distance of 120.degree., which are inserted in corresponding 
slots formed on the front end of the casing 20 so as not to turn. In other 
words the bearing 60 works to convert the rotational force given on the 
tension rod 40 to an urging force. For this reason, the tension rod 40 is 
externally round and diametrically has two plain surfaces. The mating slot 
62 on the bearing 60 is of the same shape so that the tension rod 40 may 
be inserted freely, into the slot in the axial direction. In FIG. 1, the 
numeral 82 indicates a seal bolt and the numeral 83 indicates an "O" ring 
mounted on the rear end of the tensioner for improving airtightness of the 
seal bolt. 
The spring seat 70 incorporating sleeve portion 72 is freely mounted on the 
ring groove 33. A collar 75 is mounted between the spring seat 70 and said 
bearing 60 as shown in the FIG. 3. The inner flange portion of the sleeve 
side of the spring seat abuts. on the front end of cylinder portion 32 and 
the collar 75 abuts on the front side of flange portion 71 of the spring 
seat 70. 
The sleeve portion 72 is inserted externally on the cylinder portion 32 of 
the rotational cylinder 30. On this sleeve portion 72, a coil portion 51 
of the torsion spring 50 is externally mounted. 
Even though the torsion spring is wound by driving the rotational cylinder 
30 and the front end of coil portion 51 extends, causing eccentric motion, 
the coil portion 51 does not penetrate into the ring groove 33 as happens 
on conventional belt tensioners. Therefore, a normal function of the 
torsion spring 50 for driving the rotational cylinder 30 can be expected 
always. 
From FIG. 3, it can be seen that the sleeve portion 72 is gradually tapered 
to a point so as to facilitate the winding operation. 
The collar 75 is of tube form and is coaxially mounted on the tension rod 
40 engaged with male thread portion of the rotational cylinder 30 and 
between the flange portion 71 of the spring seat 70 and the bearing 60. 
The bearing 60 is fit on the casing 20. 
In this condition, the movement of rotational cylinder 30, due to the 
torsion spring, in the axial direction can be prevented by the spring seat 
70 supported by the collar 75. Consequently there is no movement of the 
rotational cylinder 30 in the axial direction. Also the torsion spring 
will not cause any trouble when mounted. The spring side edge 71a of the 
spring seat is rounded. Therefore, even though there is contact between 
the front end 52 of the torsion spring 50 and said rounded portion, the 
front end 52 will be hardly damaged due to wear. 
FIG. 4 shows another embodiment according to the present invention wherein 
identical components corresponding to the components of the embodiment 
aforementioned are indicated with identical numbers and repetitive 
descriptions are omitted. In this case, the thickness of the sleeve 
portion 72 of the spring seat is formed even. The sleeve portion is 
inserted between the cylinder portion 32 of the rotational cylinder 30 and 
the coil portion 52 of the torsion spring 50 so as to separate the coil 
end from the ring groove 33 of the rotational cylinder 30. In this case, 
the even thickness of sleeve portion 72 does not affect its basic function 
for separating adjacent components. Accordingly it is expected that the 
manufacturing process of spring seat 70 will be simplified. 
The following effect can be obtained through the present invention 
aforementioned. Since the coil end and the cylinder portion are separated 
by inserting the sleeve portion of the spring seat mounted on the 
rotational cylinder, even though the coil end eccentrically extends, it 
will work normally as a torsion spring and not become entangled in the 
ring groove. 
Having this type of construction, the spring seat abuts on the collar and 
the collar abuts on the bearing preventing the movement of the rotational 
cylinder in the axial direction. Accordingly, entanglment of the coil end 
on the rotational cylinder can be eliminated.