Tension reducer

A tension reducer used in a webbing retractor is provided with a weak coil spring, a strong coil spring, and a connecting member all connected in series, the rotation of the connecting member in the webbing winding direction being stopped at a predetermined time after the webbing has been pulled out from the winding shaft when a passenger puts on the webbing. The inner end of the weak coil spring is connected to the connecting member so that, after the rotation of the connecting member has stopped, the urging force of the spring is released as the spring unwinds from its outer end.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention concerns a tension reducer, and in particular, a tension 
reducer used in a webbing retractor for use in a seat belt system with 
which an automobile vehicle is equipped. 
2. Related Art 
This type of tension reducer (webbing retractor) comprises two types of 
flat coil springs, i.e. a strong (large) flat coil springs and a weak 
(small) flat coil spring. One end of the weak coil spring is attached to a 
winding shaft, and the other end is attached to one end of the strong coil 
spring via a gear spring. The other end of the strong coil spring is 
fastened to a case (cover). The winding shaft, weak coil spring, gear 
spring and strong coil spring are therefore connected in series, and the 
winding shaft is urged in the webbing winding direction by these flat coil 
springs. A pawl lever is disposed in the vicinity of the gear spring so as 
to interlock with the gear spring and thereby prevent its rotation. This 
pawl lever acts in synchronism with a solenoid or with the opening and 
closing of a car door. 
After a passenger has put on the webbing, the pawl lever is operated by the 
aforesaid mechanism so as to prevent rotation of the gear spring. The 
urging force of the strong coil spring in the webbing winding direction 
therefore ceases to act on the winding shaft, the webbing is pulled only 
by the weak coil spring. Accordingly, the passenger does not feel 
constrained when he is wearing the webbing. When the passenger releases 
the webbing, the pawl lever no longer prevents the gear spring from 
rotating. The urging force of the strong coil spring in the webbing 
winding direction then acts on the winding shaft, which rapidly winds up 
the webbing. 
In a webbing retractor provided with such a tension reducer, however, when 
all the webbing is wound, the coils of the weak coil spring 60 are in 
close contact with one another as shown in schematically in FIG. 5. After 
the webbing is drawn out and the tension reducer is operating, i.e. when 
the rotation of the gear spring connected to the outer end portion 62 of 
this weak coil spring 60 is prevented by means of the pawl lever, the 
urging force of the weak coil spring 60 in the webbing winding direction 
acts on the winding shaft when the coils of the spring are tightly wound, 
this urging force being released by the rotation of the shaft. 
In this case, as the urging force of the weak coil spring 60 is released 
while an inner end 64 of the spring 60 connected to the winding shaft is 
winding out in the direction X shown in FIG. 5, adjacent side wall parts 
66 in the vicinity of this inner end 64 rub against each other causing 
noise and impairment of operating performance due to friction. 
SUMMARY OF THE INVENTION 
In view of the aforesaid situation, it is an object of the present 
invention to provide a tension reducer wherein noise and friction are 
prevented and operating performance is improved when the tension reducer 
operates. 
The tension reducer according to the present invention is used in a webbing 
retractor which winds a webbing in layers around a shaft. The tension 
reducer comprises a weak flat coil spring connected to this shaft, a 
strong flat coil spring exerting a larger urging force than the weak flat 
coil spring, and a connecting member connected in series with the weak 
coil spring and strong coil spring, the member being rotatable. The 
rotation of the tension reducer in the webbing winding direction is 
stopped at a predetermined time after the webbing has been pulled out from 
the winding shaft when a passenger puts the webbing on, and is 
characterized in that the outer end of the week coil spring is connected 
to the winding shaft, and the inner end of the weak coil spring is 
connected to the connecting member. 
When a passenger has pulled out the webbing against the urging force of the 
strong and weak coil springs in order to put the webbing on, and the 
tension reducer having the aforesaid construction operates, the rotation 
of the connecting member in the webbing winding direction stops. The 
urging force of the strong coil spring in the webbing winding direction 
therefore ceases to act on the winding shaft, and the webbing is pulled 
back only by the weak coil spring. The passenger therefore does not feel 
constrained when he is wearing the webbing. 
In the aforesaid case, when the tension reducer operates and the rotation 
of the connecting member in the webbing winding direction is stopped, the 
urging force in the webbing winding direction of the weak coil spring 
which has been wound by pulling out the webbing, acts on the winding 
shaft. The urging force is released by the rotation of the shaft. 
As the outer end of the weak coil spring is connected to the winding shaft 
which is rotatable, and the inner end of the weak coil spring is connected 
to the connecting member whose rotation is stopped, the urging force of 
the weak coil spring is released as it unwinds from its outer end. 
Adjacent side walls of the weak coil spring therefore do not rub against 
each other, noise and friction are prevented, and operating performance is 
improved. 
When the passenger releases the webbing and the tension reducer is 
released, the connecting member is again free to rotate in the webbing 
winding direction. The urging force of the strong coil spring in the 
webbing winding direction therefore again acts on the winding shaft via 
the connecting member and weak coil spring, and the webbing is rapidly 
wound by the strong coil spring.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows a perspective view of the component parts of a tension reducer 
10 according to this invention. FIG. 2 is a section view of the main parts 
of the tension reducer 10. FIG. 3 shows a schematic representation of the 
component parts of the tension reducer 10. 
In the tension reducer 10, a plate 12 is attached to the frame of a webbing 
retractor, not shown, to which the tension reducer 10 is applied. A hole 
14 is formed in the plate 12 coaxially with the webbing winding shaft 
(having an axis CL), this hole 14 supporting an adaptor 16. 
The adaptor 16 is substantially circular, and has an axle portion 17 facing 
the plate 12. This axle portion 17 is inserted into the hole 14 of the 
plate 12 and is thereby supported such that it can rotate. The axle 
portion 17 is connected to the webbing winding shaft. The adaptor 16 
therefore rotates together with the webbing winding shaft. 
The adaptor 16 has a notch 18 in its inner wall circumference. An outer end 
20A of a weak flat coil spring 20 engages the notch 18. An inner end 20B 
of the weak coil spring 20 engages a gear spring 32 which serves as a 
connecting member. 
The gear spring 32 is in the form of a circular plate, and has ratchet 
teeth 34 formed on its outer circumference. An axle part 33 in a central 
portion of the gear spring 32 projects along the axis CL towards the 
adaptor 16. A notch 35 is cut in the shaft part 33 in the axial direction. 
The inner end 20B of the weak coil spring 20 engages this notch. 
Another axle portion 36 is formed in a central portion of the gear spring 
32 on the opposite side of the axle portion 33 along the axis CL. A notch 
38 is cut in the axle portion 36 in the axial direction, and an inner end 
40A of a strong flat coil spring 40 engages with this notch 38. An outer 
end 40B of the strong coil spring 40 is attached to a cover 42. 
As shown in FIG. 3, the adapter 16, weak coil spring 20, gear spring 32 and 
strong coil spring 40 are connected in series. The adaptor 16 and a 
webbing winding shaft connected to the adaptor are urged in the webbing 
winding direction (direction B in FIG. 1) by these strong and weak coil 
springs. 
A pawl lever 50, which acts as a means for stopping the rotation of the 
gear spring 32, is disposed such that it is free to pivot beneath the gear 
spring 32. A hook 52 is provided on the pawl lever 50 such that it can 
engage the ratchet teeth 34 of the gear spring 32. When the hook 52 
engages the ratchet teeth 34, the rotation of the gear spring 32 in the 
webbing winding direction (direction B in FIG. 1) is prevented. 
A return spring 54 is disposed near the pawl lever 50. This spring 54 urges 
the hook 52 of the pawl lever 50 to separate from the ratchet teeth 34. A 
solenoid 56 is also disposed near the pawl lever 50. An actuator 58 of the 
solenoid 56 is connected to the pawl lever 50. During operation, the pawl 
lever 50 pivots in opposition to the urging force of a return spring 54 so 
that the hook 52 engages the ratchet teeth 34. This solenoid 56 operates 
when a passenger puts on the webbing. 
Next, the operation of the invention according to this embodiment will be 
described. 
In a tension reducer 10 having the aforesaid construction, before the 
passenger puts on the webbing, i.e. when the webbing is fully wound, the 
weak coil spring 20 is tightly wound and the strong coil spring 40 is 
unwound to the maximum as shown in FIG. 4A. The webbing can therefore be 
freely pulled out by rotating the adaptor 16 (winding shaft) in opposition 
to the urging force of the strong coil spring 40. 
When the passenger puts on the webbing which has been pulled out, the 
solenoid 56 operates. When the solenoid 56 operates, the pawl lever 50 is 
pivoted by the movement of the actuator 58, the hook 52 engages with the 
ratchet teeth 34 of the gear spring 32, and the rotation of the gear 
spring 32 in the webbing winding direction is prevented. The strong coil 
spring 40 is thus held tightly wound as shown in FIG. 4C, the urging force 
of the strong coil spring 40 in the webbing winding direction no longer 
acts on the adaptor 16 and the webbing winding shaft connected to the 
adaptor 16, and the webbing is pulled only by the weak coil spring 20. The 
passenger can therefore wear the webbing without feeling constrained. 
When the tension reducer is operated and the rotation of the gear spring 32 
in the webbing winding direction is stopped, the urging force of the weak 
coil spring 20 which was tightly wound in the webbing winding direction 
acts on the adaptor 16 (winding shaft). When the winding shaft rotates, 
the urging force of the spring 20 is released. 
As the outer end 20A of the weak coil spring 20 is connected to the adaptor 
16 (winding shaft), i.e. the rotating side, and the inner end 20B of the 
weak coil spring 20 is connected to the gear spring 32, i.e. the side 
which was stopped from rotating, the urging force of the weak coil spring 
20 is released as the spring is unwinding from its outer end 20A, as shown 
in FIG. 4C. Adjacent side walls of the weak coil spring 20 therefore do 
not rub against each other, noise and friction are prevented, and 
operating performance is improved. 
When the tension reducer is operating, the webbing may also be pulled out 
against the urging force of the weak coil spring 20 alone. In this case 
the situation will alternate between that of FIG. 4B and FIG. 4C, and as 
the webbing winding shaft connected to the adaptor 16 can rotate freely, 
there is no interference with the pulling out of the webbing or with 
operating performance. 
When the passenger releases the webbing and the solenoid 56 is turned off 
(release), the pawl lever 50 is pivoted by the urging force of the return 
spring 54, the hook 52 disengages from the ratchet teeth 34, and the gear 
spring 32 is again allowed to rotate. The urging force of the strong coil 
spring 40 in the webbing winding direction therefore acts on the webbing 
winding shaft via the gear spring 32, weak coil spring 30 and adaptor 16, 
and the webbing is wound rapidly by the large urging force of the strong 
coil spring 40. The strong coil spring 40 also returns to its maximum 
extension. 
The tension reducer of this invention as described hereintofore therefore 
has the excellent features of no noise or friction, and improved operating 
performance.