1. Field of the Invention
The present invention relates to a webbing take-up device which restrains a vehicle occupant by a webbing belt.
2. Description of the Related Art
A webbing take-up device forms a main portion of a seat belt device which restrains the body of a vehicle occupant by an elongated webbing belt. In the webbing take-up device, a take-up shaft which takes up the webbing belt is urged by an urging device such as a spiral spring in a direction of taking up the webbing belt. (Hereinafter, for convenience of explanation, the rotating direction in the direction of taking up the webbing belt will be called the xe2x80x9ctake-up directionxe2x80x9d, and the rotating direction in the direction opposite to the take-up direction will be called the xe2x80x9cpull-out directionxe2x80x9d.) When a vehicle occupant cancels the state in which the webbing belt is applied to him or her, due to the urging force of the urging device such as that described above, the webbing belt is taken up onto the take-up shaft and is accommodated.
Further, the urging force of an urging device such as a spiral spring increases in accordance with the amount of the webbing belt which is pulled out. Thus, when the webbing belt is applied, a compressing sensation caused by the urging force of the urging device is applied to the vehicle occupant to which the webbing belt is applied. As a result, in recent years, webbing take-up devices have been proposed which are provided with a so-called tension reducer mechanism which, in a state in which the webbing belt is pulled out to a predetermined amount, reduces the urging force of the urging device such that the aforementioned constricting sensation is mitigated.
There are tension reducer mechanisms of a type utilizing a structure in which the rotational force of a shaft member, which rotates coaxially and integrally with the take-up shaft, which rotational force is due to the urging force of the urging device is lessened by the frictional force at the time when a torsion coil spring, which is wound in a spiral shape around the shaft member, is fit closely to the outer peripheral portion of the shaft member. Hereinafter, this type of tension reducer mechanism will be briefly explained.
This type of tension reducer mechanism includes a ratchet wheel which is provided so as to be able to rotate coaxially with and relative to the take-up shaft. One end of the torsion coil spring is anchored on the ratchet wheel. The take-up shaft passes through the inner side of the torsion coil spring, and the other end of the torsion coil spring is anchored on the take-up shaft. When the ratchet wheel rotates relatively with respect to the take-up shaft in the pull-out direction, the torsion coil spring is wound tighter, and is ultimately set in close contact with the outer peripheral portion of the take-up shaft.
The ratchet wheel is generally rotatable. However, when an engagement pawl, which is formed at a plunger for locking which is provided next to the ratchet wheel, engages with the outer peripheral portion of the ratchet wheel, the ratchet wheel can rotate in the pull-out direction, but rotation thereof in the take-up direction is restricted.
Namely, when the webbing belt is applied to an occupant, and the rotation of the ratchet wheel is restricted by the engagement pawl of the plunger, the rotation of the take-up shaft in the take-up direction due to the urging force of the spiral spring becomes relative rotation in the take-up direction with respect to the ratchet wheel. At this time, the ratchet wheel rotates in the pull-out direction when viewed from the standpoint of the take-up shaft. Therefore, when the take-up shaft rotates to a certain extent, the torsion coil spring is wound tighter, and begins to fit closely to the outer peripheral portion of the take-up shaft. The torsion coil spring, one end of which is anchored to the ratchet wheel, cannot rotate integrally with the take-up shaft. Thus, a frictional force is generated between the outer peripheral portion of the take-up shaft and the torsion coil spring. This frictional force acts to prevent rotation of the take-up shaft in the take-up direction. Thus, a force, which is of a magnitude equal to the urging force of the spiral spring minus the frictional force, is the restraining force of the webbing belt. Accordingly, the restraining force is less than a case in which the urging force of the spiral spring is directly applied to the vehicle occupant and thus, the compressive sensation can be mitigated.
In a state in which a vehicle is traveling normally, when the body of a vehicle occupant sways due to slight movements of the vehicle or the like, the body of the vehicle occupant (in particular, the shoulders or the like of the vehicle occupant) may pull the webbing belt. However, in this case, in the tension reducer mechanism of the above-described type, the urging force of the spiral spring applied to the webbing belt cannot be reduced from a structural standpoint. When the body of the vehicle occupant attempts to pull the webbing belt out, the full urging force of the spiral spring is applied to the body of the vehicle occupant.
In view of the aforementioned, an object of the present invention is to provide a webbing take-up device in which, when a webbing belt is pulled out, the urging force applied in the direction of taking up the webbing belt can be reduced.
A first aspect of the present invention is a webbing take-up device for taking up an elongated webbing belt for restraining a body of a vehicle occupant, the webbing take-up device comprising: (a) a take-up shaft to which one longitudinal direction end of the webbing belt is anchored, and which takes up the webbing belt by rotating in a take-up direction which is one direction around an axis of the take-up shaft; (b) a shaft member provided so as to be rotatable coaxially with and relatively to the take-up shaft; (c) a first urging device connected to the shaft member, the first urging device urging the shaft member in the take-up direction by urging force of a magnitude corresponding to an amount of rotation of the shaft member in a pull-out direction which is opposite to the take-up direction; and (d) a second urging device connecting the take-up shaft and the shaft member such that the take-up shaft and the shaft member are able to rotate relatively over a predetermined angle, and when an angle of rotation in the pull-out direction of the shaft member with respect to the take-up shaft exceeds a predetermined angle, the second urging device connects the shaft member and the take-up shaft integrally such that the shaft member and the take-up shaft are able to rotate in the pull-out direction.
A second aspect of the present invention is a webbing take-up device used in a seat belt device of a vehicle, the webbing take-up device comprising: (a) a take-up shaft to which one end of a webbing is anchored, and which is able to rotate in a webbing take-up direction and in a webbing pull-out direction which is opposite to the webbing take-up direction; (b) a first urging device which urges the take-up shaft in the webbing take-up direction; and (c) a second urging device which, while rotation of the take-up shaft in the webbing pull-out direction is within a predetermined angle, urges the take-up shaft in the webbing pull-out direction by an urging force which is less than an urging force of the first urging device.
In accordance with the webbing take-up devices having the above-described structures, when the webbing belt is pulled out, the take-up shaft rotates in the pull-out direction. At this time, the second urging device attempts to rotate, by the urging force thereof, the shaft member to follow the rotation of the take-up shaft. However, because the urging force of the first urging device is greater than the urging force of the second urging device, the shaft member cannot rotate in the same direction as the rotating direction of the take-up shaft. Accordingly, the take-up shaft rotates in the pull-out direction relatively to the shaft member. In a state in which the take-up shaft has rotated a predetermined angle in the pull-out direction relative to the shaft member, when the webbing belt is pulled out further, the shaft member rotates in the pull-out direction integrally with the take-up shaft, and the first urging device urges the take-up shaft in the take-up direction via the shaft member.
Next, in the case where pulling out of the webbing belt has been completed and the other end of the webbing belt is fixed, the first urging device attempts to rotate, by the urging force thereof, the shaft member in the take-up direction. Here, if the restriction of rotation of the shaft member in the take-up direction by the shaft member rotation restricting mechanism is canceled, the second urging device makes the shaft member and the take-up shaft integral at the time the webbing belt is pulled out. Thus, the urging force of the first urging device is transferred as is to the take-up shaft. The urging force of the first urging device, as is, is the restraining force for restraining the body of the vehicle occupant by the webbing belt.
On the other hand, when rotation of the shaft member in the take-up direction is restricted by the shaft member rotation restricting mechanism, the restricting force at this time acts against the urging force of the first urging device. Thus, the rotational force of the shaft member in the take-up direction is reduced.
Further, the resultant force of the restricting force of the shaft member rotation restricting mechanism and the urging force of the second urging device in the state in which the take-up shaft is rotated a predetermined angle in the pull-out direction relative to the shaft member, is greater than the urging force of the first urging device. Thus, until this resultant force is in balance with the urging force of the first urging device, the second urging device rotates, by its urging force, the take-up shaft in the take-up direction relatively to the shaft member. In this way, the integral connection of the take-up shaft and the shaft member by the second urging device is canceled (i.e., although the take-up shaft and the shaft member are mechanically connected, relative rotation thereof is possible.)
In this state, some or all of the urging force of the first urging device is offset by the restricting force of the shaft member rotation restricting mechanism. Thus, the restraining force is lower than in a case in which the urging force of the first urging device is, as is, the restraining force. Therefore, the compressing sensation when the webbing belt is applied is alleviated.
Due to the urging force of the second urging device rotating the take-up shaft in the take-up direction and relative rotation of the shaft member with respect to the take-up shaft being enabled, even if the webbing belt is pulled out when applied, the urging force of the first urging device, which does not rotate the take-up shaft a predetermined angle in the pull-out direction with respect to the take-up shaft, is not applied to the shaft member. Accordingly, in this state, due to the application of a tensile force of an extent which resists the urging force of the second urging device, the webbing belt can be pulled out by a predetermined amount. The compressive sensation of the webbing belt at the time when the body of the vehicle occupant attempts to pull out the webbing belt due to slight vibrations or the like while the vehicle is traveling, can be mitigated.
In accordance with the webbing take-up devices having the above-described structures, when the webbing belt is pulled out and the take-up shaft is rotated in the pull-out direction and the take-up shaft rotates a predetermined angle in the pull-out direction with respect to the shaft member and the take-up shaft and the shaft member become integral and the shaft member rotates in the pull-out direction, the rotating body connected to the shaft member via the third urging device rotates in the pull-out direction, following the rotation of the shaft member.
Next, in the webbing belt applied state in which pulling out of the webbing belt is completed and one end of the webbing belt is fixed, the first urging device attempts to rotate, by the urging force thereof, the shaft member in the take-up direction.
At this time, when the rotation body restricting device, which, together with the rotating body and the third urging device, forms the shaft member rotation restricting mechanism, restricts rotation of the rotating body in the take-up direction, even if the shaft member rotates in the take-up direction by the urging force of the first urging device, the rotating body cannot follow this rotation. As a result, the shaft member rotates in the take-up direction relative to the rotating body. When the shaft member rotates a predetermined angle relatively to the rotating body, the third urging device is fit tightly to the outer peripheral portion of the shaft member. At this time, rotation of the shaft member in the take-up direction is restricted due to the frictional force arising between the third urging device and the shaft member.