Retractor for seat belt

A seat belt retractor provides a base, a ratchet plate attached to a winding shaft for winding a webbing, a ratchet member rotatable with the winding shaft in a webbing draw-out direction for locking a rotation of the winding shaft in the webbing draw-out direction by engaging a pawl with the ratchet plate, a lock arm rotatable at a first position where the lock arm engages with the ratchet plate and a second position where the lock arm does not engage with the ratchet plate, a control plate rotated corresponding to the rotation of the winding shaft, and an operation mode switching lever having a guide pin projected at a swing end portion for rotating the lock arm to the first position and the second position, the guide pin being guided by a guide groove of the control plate, in which the guide groove includes first and second cam grooves for guiding the guide pin of the operation mode switching lever so as to rotate the lock arm to the second and first position, respectively, and a switching area provided so as to connect an end point of the first cam groove to a start point of the second cam groove, and operated to deliver the guide pin to the second cam groove for switching the lock arm from the second position to the first position.

BACKGROUND OF THE INVENTION 
The present invention relates to a retractor (winding device) for a seat 
belt, and particularly to the improvement of a seat belt retractor having 
an emergency lock function and an automatic lock function. 
Conventionally, a seat belt for keeping an occupant of a vehicle or the 
like on his or her seat safely is constituted by a webbing (or belt), a 
buckle, a mounting bracket and a retractor (winding device). 
The retractor is a winding device for retracting a webbing automatically at 
the time of no use of the seat belt so as to prevent the webbing from 
being injured, and for changing the draw-out length of the webbing 
desirably at the time of use of the seat belt. 
In an example of such a conventional retractor, at a normal time a webbing 
for restraining an occupant is allowed to be drawn out and wound 
desirably, so as to avoid such a problem that excessive restraining of the 
occupant gives an oppressive feeling to the occupant. On the other hand, 
an inertia detecting device responding to sudden acceleration or 
deceleration of the vehicle is provided to add an emergency lock function 
for locking a winding shaft of the webbing so that the webbing is 
prevented from being drawn out by use of the reaction of the inertia 
detecting device at the time of sudden acceleration or deceleration of the 
vehicle to thereby ensure the safety of the occupant. Hereinafter, the 
term "ELR" means an emergency locking retractor. 
However, in the case of such an emergency lock function, it is impossible 
to prevent the webbing from being drawn out at a normal time. Accordingly, 
when a baggage, an auxiliary child seat (child seat), or the like, is set 
on a seat by use of the webbing, the webbing is gradually drawn out of the 
retractor by vibration or the like during the running of the vehicle, so 
that there is a fear that the attachment of the child seat or the like 
becomes loose. 
Therefore, as disclosed in U.S. Pat. No. 4,811,912, Unexamined Japanese 
Utility Model Publication No. Hei. 3-126745, Unexamined Japanese Utility 
Model Publication No. Hei. 5-72612, and so on, independently of such an 
emergency lock function, an automatic lock function is provided for 
preventing a webbing from being drawn out after the setting of the webbing 
regardless of normal time or a case where sudden acceleration or 
deceleration of the vehicle occurs. Hereinafter, the term "ALR" means an 
automatic locking retractor. Then the automatic lock function is operated 
when a baggage, a child seat, or the like, is set on a seat, and the 
emergency lock function is operated when an occupant is restrained. 
A seat belt retractor disclosed in those publications has the 
above-mentioned emergency lock function, and is designed so that the 
automatic lock function can be switched between its active state and its 
inactive state by proper operation of the state where the retractor winds 
a webbing. 
A seat belt retractor disclosed in Unexamined Japanese Utility Model 
Publication No. Hei. 5-72612 provides a rotation lock device for engaging 
with a winding shaft of the retractor winding a webbing so as to lock the 
rotation of the winding shaft in the webbing draw-out direction; and a 
lock device driving mechanism for controlling the operation of the 
rotation lock device to form a lock state where the rotation lock device 
is engaged with the winding shaft to thereby prevent the winding shaft 
from rotating in the webbing draw-out direction, or a non-lock state where 
the rotation lock device is kept not so as to engage with the winding 
shaft so that the winding shaft is allowed to rotate in the webbing 
draw-out direction. The seat belt retractor further provides an operation 
mode switching device for setting and switching the operation mode of the 
lock device driving mechanism so as to be switchable between an ELR mode 
(emergency lock mode) where the lock device driving mechanism is operated 
as an emergency lock mechanism to bring the rotation lock device into the 
lock state in an emergency of sudden acceleration or deceleration of the 
vehicle or the like, and an ALR mode (automatic lock mode) where the lock 
device driving mechanism is operated as an automatic lock mechanism to 
bring the rotation lock device into the lock state whether in an emergency 
or not. 
The operation mode switching device has an operation mode switching lever 
attached pivotably between an ELR mode position for setting the ELR mode 
and an ALR mode position for setting the ALR mode; a control plate which 
rotates in interlocking with the winding shaft to thereby reflect the 
state of the webbing wound on the winding shaft; and a guide groove 
provided on the control plate and guiding a guide pin provided and 
projecting on the operation mode switching lever, so as to control the 
swing of the operation mode switching lever in accordance with the state 
of the webbing wound on the winding shaft. 
In the conventional seat belt retractor, which has such a configuration, 
the automatic lock function can be actuated selectively by the operation 
of the state of the wound webbing. 
Further, in the above-mentioned Publication, the guide groove has an outer 
cam groove for receiving the guide pin of the operation mode switching 
lever, and holding the operation mode switching lever in the ELR mode 
position in a period from the time when the quantity of the webbing wound 
is the maximum to the time when a constant amount of the webbing is drawn 
out; a narrow groove portion (cam groove) formed to be connected to the 
end point of the outer cam groove, and for receiving the guide pin and 
holding the operation mode switching lever in the ELR mode position until 
the webbing is further drawn out up to the minimum winding quantity after 
the constant amount of the webbing is drawn out; and a wide groove portion 
(inner cam groove) formed so as to connect the start point of the narrow 
groove portion onto the way of the outer cam groove, and for receiving the 
guide pin returned, by the winding of the webbing, to the start point of 
the narrow groove portion, and holding the operation mode switching lever 
in the ALR mode position until the webbing is further wound up to a 
predetermined quantity. Further, in order to prevent the operation mode 
switching lever from being moved to an opposite mode position unexpectedly 
by the vibration of a vehicle or the like, there is provide such a 
technique that an urging force is given to the operation mode switching 
lever by a snap action spring or the like by which the urging direction is 
changed by use of the central, neutral position between the ELR mode 
position and the ALR mode position as a border. 
A seat belt retractor disclosed in U.S. Pat. No. 4,811,912, Unexamined 
Japanese Utility Model Publication No. Hei. 3-126745 has a well-known 
emergency lock mechanism having a rotation lock device for engaging with a 
winding shaft to thereby lock the rotation of the winding shaft in the 
webbing draw-out direction, and an inertia detecting device for actuating 
the rotation lock device in an emergency of a vehicle; and an operation 
mode switching device for operating the inertia detecting device in 
accordance with the state of the wound webbing to thereby suitably move 
the rotation lock device to an engagement position or a disengagement 
position with the winding shaft. If the operation mode switching device 
makes the rotation lock device engage with the winding shaft, the rotation 
of the winding shaft in the webbing draw-out direction is locked so as to 
actuate an automatic lock mechanism. 
Further, as an operation mode switching device used in such a seat belt 
retractor, for example, an operation mode switching lever (operating 
lever) which is movable between a position where the inertia detecting 
device is operated and a position where it is not operated, and a control 
plate (operating member) displaced relatively to the operation mode 
switching lever in accordance with the rotation of the winding shaft, are 
provided for bringing the rotation lock device to the engagement position 
or the disengagement position with the winding shaft. Since the operation 
mode switching lever is moved by the control plate, the operation mode 
switching lever swings between a position where the inertia detecting 
device is operated and a position where it is not operated, in accordance 
with the state in which the webbing is wound on the winding shaft. As a 
result, the rotation lock device is taken to the engagement position or 
the disengagement position. 
Such an operation mode switching lever as disclosed in U.S. Pat. No. 
4,811,912, Unexamined Japanese Utility Model Publication No. Hei. 3-126745 
is urged to the position where the inertia detecting device is operated or 
the position where not operated, by an urging device (for example, a 
so-called snap action spring) designed to change the urging direction in 
the border of a neutral position by use of an over center spring, a 
compression spring, or the like, in accordance with necessity. 
When the automatic lock mechanism is in operation, the operation mode 
switching lever keeps the inertia detecting device in operation by the 
urging force of the urging device in order to dispose the rotation lock 
device in the engagement position. However, if the urging device is moved 
beyond the neutral position by the effect of vibration, shock, or the 
like, which acts on the operation mode switching lever during the running 
of a vehicle, the urging direction of the urging device is changed over, 
so that the operation mode switching lever is urged in the direction in 
which the inertia detecting device can not be kept in operation. Then the 
operation mode switching lever cannot dispose the rotation lock device in 
the engagement position. Accordingly there is a possibility that the 
retractor is released from the automatic lock state. 
Therefore, when a baggage, a child seat or the like is set on a seat by use 
of the webbing, there is a fear that the seat belt retractor is released 
from the automatic lock state by vibration, shock or the like during the 
running of a vehicle so as to return to its emergency lock state, and the 
webbing is therefore drawn out of the retractor gradually during the 
running of the vehicle to thereby loosen the attachment of the baggage, 
the child seat or the like. 
In the case of a seat belt retractor disclosed in Unexamined Japanese 
Utility Model Publication No. Hei. 5-72612, in order to solve the 
foregoing problem, a guide groove for controlling the swing of an 
operation mode switching lever has a cam groove for guiding a guide pin of 
the operation mode switching lever. A cam surface, which is a side surface 
of the cam groove, contacts with the guide pin so that the operation mode 
switching lever is prevented from swinging to an improper mode position. 
However, in the case of this seat belt retractor disclosed in Unexamined 
Japanese Utility Model Publication No. Hei. 5-72612, a narrow groove 
portion guides the guide pin until a predetermined length of the webbing 
is completely wound after the webbing is drawn out up to the maximum. In 
the position where this narrow groove portion guides the guide pin, the 
operation mode switching lever moves slightly toward the ALR mode position 
beyond the neutral position, so that the urging device changes its urging 
direction toward the ALR mode position. However, near the neutral 
position, the urging force of the urging device is so weak, and the 
section where the narrow groove portion guides the guide pin is 
comparatively so long, that the movement toward the ALR mode position is 
continuously prevented on the way during the guide of the narrow groove 
portion. Even if the guide pin reaches a wide groove portion, the 
operation of moving to the ALR mode position is delayed or so, so that 
there is a fear that the operation of the automatic lock function goes 
wrong. 
SUMMARY OF THE INVENTION 
An object of the present invention is to solve the foregoing problems in a 
conventional retractor. 
It is another object of the present invention to provide a seat belt 
retractor by which the mode position of an operation mode switching lever 
can be switched at a stroke without stopping the switching operation on 
the way, and therefore by which it is possible to prevent the production 
of operation faults of an automatic lock function caused by the stoppage 
of the operation mode switching lever near a neutral position. 
In order to attain the above objects, according to an aspect of the present 
invention, a seat belt retractor provides: a base; a ratchet plate 
attached to a winding shaft for winding a webbing; a ratchet member 
rotatable with the winding shaft in a webbing draw-out direction for 
locking a rotation of the winding shaft in the webbing draw-out direction 
by engaging a pawl with the ratchet plate; a lock arm rotatable at a first 
position where the lock arm engages with the ratchet plate and a second 
position where the lock arm does not engage with the ratchet plate; a 
control plate rotated corresponding to the rotation of the winding shaft; 
and an operation mode switching lever having a guide pin projected at a 
swing end portion for rotating the lock arm to the first position and the 
second position, the guide pin being guided by a guide groove of the 
control plate, and the guide groove including: a first cam groove for 
guiding the guide pin of the operation mode switching lever so as to 
rotate the lock arm to the second position; a second cam groove for 
guiding the guide pin of the operation mode switching lever so as to 
rotate the lock arm to the first position; and a switching area provided 
so as to connect an end point of the first cam groove to a start point of 
the second cam groove, and operated to deliver the guide pin to the second 
cam groove for switching the lock arm from the second position to the 
first position. 
According to another aspect of the present invention, a seat belt retractor 
provides: a base; a ratchet plate attached to a winding shaft for winding 
a webbing; a ratchet member rotatable with the winding shaft in a webbing 
draw-out direction for locking a rotation of the winding shaft in the 
webbing draw-out direction by engaging a pawl with the ratchet plate; a 
lock arm rotatable at a first position where the lock arm engages with the 
ratchet plate and a second position where the lock arm does not engage 
with the ratchet plate; a control plate rotated corresponding to the 
rotation of the winding shaft; an operation mode switching lever having a 
guide pin projected at a swing end portion for rotating the lock arm to 
the first position and the second position, the guide pin being guided by 
a guide groove of the control plate; an emergency lock mechanism for 
preventing the webbing from being drawn out in an emergency; and an 
automatic lock mechanism for preventing the webbing from being drawn out 
in accordance with a winding state of the webbing wound on the winding 
shaft regardless of whether it is in the emergency or not, in which the 
guide groove includes: a first cam groove for guiding the guide pin of the 
operation mode switching lever so as to rotate the lock arm to the second 
position; a second cam groove for guiding the guide pin of the operation 
mode switching lever so as to rotate the lock arm to the first position; 
and a switching area provided so as to connect an end point of the first 
cam groove to a start point of the second cam groove, and operated to 
deliver the guide pin to the second cam groove for switching the lock arm 
from the second position to the first position. 
According to a still further aspect of the present invention, the seat belt 
retractor provides: a base; a rotation lock device for locking in a 
webbing draw-out direction a rotation of a winding shaft for winding a 
webbing; a lock device driving mechanism for controlling the rotation lock 
device so as to form a lock state where the rotation in the webbing 
draw-out direction is prevented and an anti-lock state where the rotation 
in the webbing draw-out direction is allowed, selectively; and an 
operation mode switching device for switching an operation mode of the 
lock device driving mechanism between an emergency lock mode where the 
rotation lock device is set to the lock state in an emergency of a vehicle 
and an automatic lock mode where the rotation lock device is set to the 
lock state regardless of whether it is in the emergency or not; in which 
the operation mode switching device includes: an operation mode switching 
lever attached pivotably between an emergency lock mode position for 
setting the emergency lock mode and an automatic lock mode position for 
setting the automatic lock mode; a control plate rotated in interlocking 
with the winding shaft for controlling the swing of the operation mode 
switching lever, the control plate including a guide groove for receiving 
a guide pin projected on the operation mode switching lever; and a lock 
arm for bringing the operation mode of the lock device driving mechanism 
into the automatic lock mode, and in which the guide groove includes: a 
first cam groove for guiding the guide pin so as to maintain the operation 
mode switching lever in the emergency lock mode position; a second cam 
groove for guiding the guide pin so as to maintain the operation mode 
switching lever in the automatic lock mode position; and a switching area 
provided so as to connect an end point of the first cam groove to a start 
point of the second cam groove, and operated to deliver the guide pin to 
the second cam groove for switching the mode position of the operation 
mode switching lever from the emergency lock mode position to the 
automatic lock mode position. 
According to the above-mentioned structure of the present invention, the 
mode position of the operation mode switching lever is switched from the 
ELR position to the ALR mode position by the switching area following the 
end point of the first cam groove of the guide groove of the control 
plate, so that the guide pin of the operation mode switching lever cannot 
return to the first cam groove on the ELR mode side by the function of the 
step portion at the beginning of winding or immediately after winding 
after the webbing is drawn out up to the maximum. As a result, the 
switching from the ELR mode to the ALR mode becomes sure. After switching 
to the ALR mode position completely, the ALR mode position is maintained 
by the second cam groove. 
The mode position of the operation mode switching lever is switched from 
the ALR mode position to the ELR mode position by the cam surface provided 
at the end point of the second cam groove when the quantity of the wound 
webbing reaches to a predetermined value after the whole amount of the 
webbing is drawn out. Therefore, it is possible to avoid the operation 
faults of the automatic lock function caused by the operation mode 
switching lever stopping near the neutral position. 
In addition, according to the above-mentioned structure, when the swinging 
end portion of the operation mode switching lever engages with the first 
cam groove of the control plate, the operation mode switching lever is 
urged to a position where the operation mode switching lever does not 
actuate the inertia detecting device to operate by the urging device. On 
the other hand, when the swinging end portion of the operation mode 
switching lever is moved to a side of the second cam groove of the control 
plate, the operation mode switching lever is urged to a position where the 
operation mode switching lever actuates the inertia detecting device to 
operate by the urging device. 
That is, the operation mode switching lever is urged by the urging device 
to the position where it actuates the inertia device to operate or to the 
position where it does not actuate the inertia device to operate. At the 
same time, the swinging end portion of the operation mode switching lever 
engages with the first or second cam groove of the control plate so that 
the operation mode switching lever is prevented from swinging 
unexpectedly. Accordingly, there is no fear that the urging direction of 
the urging device for urging the operation mode switching lever is changed 
unexpectedly by vibration, shock or the like.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Embodiments of the present invention will be described below with reference 
to the accompanying drawings. 
First, a schematic structure of a seat belt retractor according to a first 
embodiment of the present invention will be described with reference to 
FIGS. 6 to 8. 
In the exploded perspective view of the seat belt retractor of this 
embodiment shown in FIGS. 6 and 7, a base 1 has an substantially U-shaped 
section in most of its portions. Through holes 1b are provided in 
opposition to each other in opposite side plates 1a, respectively. A 
winding shaft 4 on which a bobbin 2 for winding a webbing thereon is fixed 
is laid rotatably through right and left plastic bushes 3 so as to bridge 
the through holes 1b. A well-known winding spring device 5 is disposed at 
one end of the winding shaft 4 so as to always urge the winding shaft 4 in 
the direction to wind the webbing. 
On the other hand, at the other end of the winding shaft 4, there is 
provided a lock mechanism having a function, as an emergency lock 
mechanism, for preventing the webbing from being drawn out in case of 
emergency, and a function, as an automatic lock mechanism, for preventing 
the webbing from being drawn out in accordance with the webbing winding 
state on the winding shaft 4 regardless of the fact it is in case of 
emergency or not. This lock mechanism has a rotation lock device 
constituted by a ratchet plate 4a which is a ratchet wheel fixed to the 
other end portion of the winding shaft 4, and a pawl 11 which is a ratchet 
member for engaging with the teeth of the ratchet plate 4a and thereby 
restricting the rotation of the ratchet plate 4a in the webbing draw-out 
direction (in the direction of the arrow X.sub.1). The lock mechanism also 
has an inertia detecting device 31 having a function as a lock device 
driving mechanism for controlling the operation of the rotation lock 
device so as to form a lock state where the rotation lock device engages 
with the winding shaft 4 to prevent the winding shaft 4 from rotating in 
the webbing draw-out direction or a non-lock state where the rotation lock 
device is kept not to engage with the winding shaft 4 to allow the winding 
shaft 4 to rotate in the webbing draw-out direction. 
An end portion of the winding shaft 4 projects outside the ratchet plate 
4a. A tension plate 9 and a ratchet cup 13 which is a ratchet member are 
loose fitted to the projecting end portion of the winding shaft 4 in order 
to constitute the inertia detecting device 31. A return spring 12 is 
attached to spring hangers 13b and 9a formed in the ratchet cup 13 and the 
tension plate 9 respectively so that an urging force is given to the 
ratchet cup 13 to rotate the ratchet cup 13 in the direction of the arrow 
X.sub.2 in FIG. 7. A flange 14 constituting the lock device together with 
a lock member 15 having a lock portion 15a for engaging with inner teeth 
13d of the ratchet cup 13, and a sensor spring 16 are fixed to the end 
portion of the winding shaft 4 projecting outside the ratchet cup 13. 
Further, a ratchet wheel 17 which is an inertia member loosely fitted to a 
tapping screw 20 screwed down to the end portion of the winding shaft 4 
through a plane washer 33 is provided outside the lock member 15. On the 
outer circumference of the ratchet wheel 17, a plurality of teeth 17a 
looking toward the belt draw-out direction are provided for engaging with 
a sensor arm 28 of a vehicle acceleration detecting device 32 which will 
be described later. In a mounting portion provided inside the ratchet 
wheel 17, a friction spring 19 is mounted slidably. Since the friction 
spring 19 is engaged with the lock member 15, the ratchet wheel 17 can 
rotate together with the winding shaft 4 and be displaced relatively to 
the winding shaft 4. 
On the other hand, the pawl 11 for restricting the rotation of the ratchet 
plate 4a in the webbing draw-out direction (in the direction of the arrow 
X.sub.1 in FIG. 6) by engaging an engagement portion 11a with the ratchet 
plate 4a is pivoted through a pawl pin 10 outside the side plate 1a so as 
to be engagable with and detachable from the ratchet plate 4a. One end 
portion of this pawl pin 10 is inserted to a through hole 35 formed in the 
side plate 1a while the other end portion is inserted to a through hole 9b 
of the tension plate 9, so as to prevent the pawl pin 10 from falling down 
by the load of the engagement between the pawl 11 and the ratchet plate 
4a. Therefore, the pawl 11 can swing about the pawl pin 10. A pawl guide 
projection 11b projects over the pawl 11, and the pawl guide projection 
11b is inserted to a pawl guide hole 13c formed to project over the outer 
circumferential portion of the ratchet cup 13. 
Further, a sensor case 27 constituting the vehicle acceleration detecting 
device 32 is fixed to the lower portion of the side plate 1a. A ball 
weight 29 which is a sensor is mounted inside a hollow portion of the 
sensor case 27, and the sensor arm 28 having a projection 28a is pivotably 
attached into the hollow portion. A sensor cover 30 covering the lock 
mechanism constituted by those parts is disposed outside the side plate 
1a. 
As shown in FIG. 8, an idle gear 21 gearing with a main gear 18 fixed to 
the tapping screw 20 (refer to FIG. 7), and a control plate 22 as a 
control disk for gearing with a pinion 21a of the idle gear 21 to rotate 
in a reduced rate are rotatably supported on sub-shafts 30a and 30b 
provided and projecting on the inner wall of the sensor cover 30 
respectively. The control plate 22 is formed of synthetic resin. In the 
inner surface of the control plate 22, there is formed a guide groove 40 
(which device the whole guide groove) which is a guide portion 
constituting an operation mode switching device together with an operation 
mode switching lever 23 and a lock arm 24, which will be described later. 
Here, the operation mode switching device is defined to be a mechanism for 
setting and switching the operation mode of the inertia detecting device 
31 having a function as a lock device driving mechanism, so as to bring 
the inertia detecting device 31 into an ELR mode where the inertia 
detecting device 31 is operated as an emergency lock mechanism for 
bringing the rotation lock device into a lock state in an emergency such 
as at the time of sudden deceleration of a vehicle, and an ALR mode where 
the inertia detecting device 31 is operated as an automatic lock mechanism 
for bringing the rotation lock device into a lock state regardless of the 
fact as to whether system is in case of emergency or not. 
Further, the operation mode switching lever 23, which is a lever member 
made of synthetic resin, is pivotably supported on a pivot 25 projectingly 
provided on the inner wall of the sensor cover 30. The operation mode 
switching lever 23 is constituted by a cylindrical portion 23b loose 
fitted to the pivot 25, a cam arm 23c extended from the cylindrical 
portion 23b toward the outside in the radial direction, and a flexible arm 
portion 23e extended toward the outside in the radial direction oppositely 
to the cam arm portion 23c. A guide pin 23a, which is an engagement 
portion provided so as to project on a swinging end portion of the cam arm 
portion 23c, engages with the guide groove 40 of the control plate 22 so 
that the operation mode switching lever 23 can swing along the guide 
groove 40 between an ELR mode position for setting the ELR mode and an ALR 
mode position for setting the ALR mode. 
In this embodiment, an operation mode switching device is constituted by 
the idle gear 21, the control plate 22, the operation mode switching lever 
23, the sensor cover 30 and so on, and each structure of these parts will 
be described in detail with reference to FIGS. 1 to 5. 
The control plate 22 rotates together with the winding shaft 4 through the 
main gear 18, the idle gear 21 and so on, so as to reflect the state where 
the webbing is wound on the winding shaft 4. On this control plate 22, 
formed is the guide groove 40 for guiding the guide pin 23a projecting 
over the operation mode switching lever 23 to thereby control the swing of 
the operation mode switching lever 23 in accordance with the state where 
the webbing is wound on the winding shaft 4. 
As shown in FIG. 4, in the control plate 22, the guide groove 40 is 
constituted by an outer cam groove 55 which is a first cam groove formed 
in an outer-sided position close to a gear portion of the outer periphery 
of the control plate 22, an inner cam groove 56 which is a second cam 
groove formed on the inner side of the outer cam groove 55 so as to be 
half as long as the cam groove 55, and a switching area 52 formed so as to 
connect the cam grooves 55 and 56 to each other. 
A side wall 50 (a side wall which is outer-sided in the radial direction of 
the control plate 22) of the outer cam groove 55 has a function to guide 
the guide pin 23a slidably, and becomes a guide surface for guiding the 
guide pin 23a so that the operation mode switching lever 23 is kept in the 
ELR mode position in a period from the time when the quantity of the wound 
webbing becomes the maximum to the time a little before the quantity of 
the wound webbing becomes the minimum. The position A shown in the outer 
cam groove 55 designates the place where the guide pin 23a is located when 
the quantity of the wound webbing becomes the maximum (that is, the place 
on the start point side of the guide groove in the ELR mode), and on the 
other hand, the position B designates the place where the guide pin 23a is 
located a little before the quantity of the wound webbing becomes the 
minimum (that is, the place on the end point side of the guide groove in 
the ELR mode). The length (circumferential length) of the outer cam groove 
55 depends on the maximum drawn-out length of the webbing and the 
reduction ratio of the idle gear 21, and is designed to have a length 
substantially as long as one round of the outer circumferential portion of 
the disc-like control plate 22. 
The inner cam groove 56 is a groove for guiding the guide pin 23a so that 
the operation mode switching lever 23 is kept in the ALR mode position in 
a period from the time when the quantity of the wound webbing becomes the 
minimum to the time when the webbing is wound completely. The inner cam 
groove 56 is disposed on the inner side of the outer cam groove 55, and 
separated therefrom with a constant distance by a partition 70. 
The partition 70 prevents such a trouble that the guide pin 23a jumps to 
the outer cam groove 55 due to the swing of the operation mode switching 
lever 23 or the like caused by the vibration of a vehicle or the like. The 
side wall of the inner cam groove 56 on the outer cam groove 55 side is 
made to be an inclined surface 51. In the inner cam groove 56 on its end 
point side and on a side wall opposite to the inclined surface 51, there 
is provided a cam surface 53 which is bent so as to urge the guide pin 23a 
in the radial and outward direction of the control plate 22 when the guide 
pin 23a moves to the outer cam groove 55. 
This cam surface 53 is a guide surface by which the guide pin 23a reaching 
the end point of the inner cam groove 56 is guided (returned) onto the way 
of the outer cam groove 55, so that the mode position of the operation 
mode switching lever 23 is switched from the ALR mode position to the ELR 
mode position at a stroke. 
The switching area 52 is a guide area which is provided to connect the end 
point of the outer cam groove 55 and the start point of the inner cam 
groove 56, and by which the mode position of the operation mode switching 
lever 23 is switched from the ELR mode position to the ALR mode position 
so as to deliver the guide pin 23a to the inner guide groove 56 at the 
beginning of winding after the quantity of the wound webbing becomes the 
minimum. 
As shown in FIG. 5, on the border between the switching area 52 and the 
outer cam groove 55, there is provided a step portion 57 constituted by an 
inclined surface 58 for allowing the guide pin 23a to move from the outer 
cam groove 55 to the switching area 52, and a step surface 59 for 
preventing the guide pin 23a from returning from the switching area 52 to 
the outer cam groove 55. That is, by this step portion 57, the guide pin 
23a can climb over the inclined surface 58 easily in the case of the 
movement from the outer cam groove 55 to the switching area 52 while the 
guide pin 23a is prevented from moving by the step surface 59 standing 
substantially upright in the case of the relative movement from the 
switching area 52 side to the outer cam groove 55 side. The step surface 
59 is connected with the inclined surface 51 of the inner cam groove 56 
through a cam surface 60, so as to be operated as a guide surface for 
taking the guide pin 23a to the inner cam groove 56 at the beginning of 
winding the webbing. 
In the innermost portion of the switching area 52, there is provided a cam 
surface 61 by which the guide pin 23a can be guided to the inside of the 
control plate 22 when the guide pin 23a is drawn in largely. 
As shown in FIGS. 2 and 8, the cylindrical portion 23b is loosely fitted 
onto the pivot 25 of the sensor cover 30, and a coil spring 64 and a 
detachment prevention clip 65 are attached to the top end of the pivot 25 
inserted into the cylindrical portion 23b, so that the operation mode 
switching lever 23 is urged to the sensor cover 30 by a predetermined 
elastic force, and at the same time is made rotatable about the pivot 25. 
As shown in FIGS. 2 and 3, a first lock convex portion 34 having a 
triangular section is projected on the inner wall of the sensor cover 30 
by the urging force of the coil spring 64. A second lock convex portion 
23f having a triangular section is formed at the swinging end portion of 
the flexible arm portion 23e. The second lock convex portion 23f is 
engaged with the first lock convex portion 34. The first and second lock 
convex portions 34 and 23f constitute an urging device which can urge the 
operation mode switching lever 23 so that the direction of the urging 
force is changed between the ELR mode position side and the ALR mode 
position side with the neutral position (position of the apex of the 
triangle) as a border, by the effect of the elastic force of the flexible 
arm portion 23e in the direction of a rotating axis, and the drag of the 
inclined surfaces opposingly pressed to each other. Accordingly, the 
operation mode switching lever 23 is swingable about the pivot 25 and is 
urged to each of the swinging ends. 
Further, an engagement projection 24b of the lock arm 24 swingably pivoted 
on the side plate 1a of the base 1 through a guide member 67 (refer to 
FIGS. 2 and 6) attached to the side plate 1a of the base 1 can be made to 
engage, through the outer circumferential neighborhood of the ratchet cup 
13, with a cam groove 23d formed into a long hole through the cam arm 
portion 23c. 
This lock arm 24 is fitted at its lower end engagement pin 68 into a long 
hole 69 of the guide member 67 so as to be rotatable with the engagement 
pin 68 as a center of rotation. A swinging end of the lock arm 24 is urged 
in a direction separating from a rotational center of the winding shaft 4. 
As the operation mode switching lever 23 swings, an engagement portion 
(latch) 24a of the lock arm 24 is engaged with the teeth of the ratchet 
plate 4a, so that the lock arm 24 constituting the above-mentioned 
operation mode switching device together with the operation mode switching 
lever 23 can bring the operation mode of the inertia detecting device 31, 
which is a lock device driving mechanism, into the ALR mode. When the 
engagement portion 24a is not engaged with the teeth of the ratchet plate 
4a, the lock arm 24 can bring the operation mode of the inertia detecting 
device 31 into the ELR mode. Thus the lock arm 24 can take two first and 
second positions, for engaging and not-engaging with the ratchet plate 4a, 
respectively. 
Next, the operation of the above-mentioned seat belt retractor will be 
described. 
First, in the state where the whole amount of the webbing is wound up, as 
shown in FIG. 9, the guide pin 23a of the operation mode switching lever 
23 is disposed in the position A on the start point of the outer cam 
groove 55 of the control plate 22, and at the same time, the guide pin 23a 
is pressed onto the side wall 50 of the outer cam groove 55 by the 
repulsion between the first lock convex portion 34 and the second lock 
convex portion 23f. As shown in FIGS. 2 and 15, the lock arm 24 is held 
between the operation mode switching lever 23 and the guide member 67, and 
kept away from the ratchet plate 4a, so that the ratchet cup 13 can rotate 
relatively to the winding shaft 4. In this case, the inertia detecting 
device 31 is in the ELR operation mode. 
Next, if the webbing begins to be drawn out of the retractor, the winding 
shaft 4 begins to rotate in the direction of the arrow X.sub.1 in FIGS. 6 
and 9, and the main gear 18 fixed to the tapping screw 20 rotated by the 
rotation of the winding shaft 4 also begins to rotate in the same 
direction. Therefore, the control plate 22 is decelerated by the idle gear 
21, and begins to rotate in the direction of the arrow Y1 as shown in FIG. 
9, and the guide pin 23a of the operation mode switching lever 23 runs 
along the side wall 50 of the outer cam groove 55. 
Even if the webbing is further still drawn out so that the guide pin 23a 
closes to the outlet portion of the inner cam groove 56 on the way of the 
outer cam groove 55, then the guide pin 23a is urged to contact with the 
side wall 50, so that there is no fear that the guide pin 23a enters the 
inner cam groove 56. 
Thus, while the guide pin 23a is being guided by the outer cam groove 55 of 
the control plate 22, there is no case that the engagement portion 24a of 
the lock arm 24 engages with the teeth of the ratchet plate 4a to thereby 
switch the operation mode of the inertia detecting device 31 to the ALR 
mode. Accordingly, the ELR mode is kept so that the inertia detecting 
device 31 is operated as a normal emergency lock mechanism (that is, the 
automatic lock function is kept inactive). 
That is, in a normal use, as shown in FIG. 18, the ratchet cup 13 is urged 
in the webbing winding direction (the direction of the arrow X.sub.2) by 
the urging force of the return spring 12 attached to the spring hanger 13b 
and the spring hanger 9a of the tension plate 9, and the pawl 11 having 
the pawl guide projection 11b engaging with the pawl guide hole 13c is 
urged in the direction where the pawl 11 does not engage with the ratchet 
plate 4a. In addition, the lock portion 15a of the lock member 15 is urged 
to the position not to engage with the inner teeth 13d of the ratchet cup 
13 by the urging force of the sensor spring 16. Consequently, the webbing 
can be drawn out freely. 
If tension is given to the webbing (not shown) in case of emergency such as 
a collision or the like so that an impacting rotating force exceeding a 
predetermined value in the webbing draw-out direction (in the direction of 
the arrow X.sub.1) is exerted on the winding shaft 4 as shown in FIG. 19, 
then the ratchet wheel 17 receives an inertia force so as to produce delay 
in rotation of the winding shaft 4 in the webbing drawout direction (the 
direction of the arrow X.sub.1). Then, if the force with which the 
engagement portion of the friction spring 19 mounted on the mounting 
portion of the ratchet wheel 17 pushes the lock member 15 in the direction 
of the engagement of the lock portion 15a with the inner teeth 13d is 
stronger than the urging force of the sensor spring 16, then the lock 
member 15 is moved in the direction of the engagement of the lock portion 
15a with the inner teeth 13d. Then, the lock portion 15a of the lock 
member 15 engages with the inner teeth 13d of the ratchet cup 13, so that 
the rotation force of the flange 14 is transmitted to the ratchet cup 13 
and the inertia detecting device 31 is actuated to rotate the ratchet cup 
13 in the direction of the arrow X.sub.1 against the urging force of the 
return spring 12. 
At this time, the pawl guide hole 13c engaging with the pawl guide 
projection 11b rotates the pawl 11 in the direction of the arrow Z.sub.1 
(refer to FIG. 6) through the pawl guide projection 11b so as to engage 
the pawl 11 with the ratchet plate 4a. As a result, the lock state is 
produced so as to prevent the rotation of the winding shaft 4 in the 
direction of the arrow X.sub.1, that is, to prevent the draw-out of the 
webbing. When the ratchet cup 13 is rotated in the direction of the arrow 
X.sub.1, the lock arm 24 remains being held between the inner cam groove 
23d of the operation mode switching lever 23 and the guide member 67, so 
that the lock arm 24 is left not engaging with the ratchet plate 4a. 
If a vehicle receives a change of speed more than a predetermined value in 
an emergency, the ball weight 29 rolls to swing the sensor arm 28, so as 
to engage the top end 28a thereof with the teeth 17a of the ratchet wheel 
17. Accordingly, the ratchet wheel 17 is prevented from rotating in the 
belt draw-out direction. If the webbing is further drawn out in the state 
where the ratchet wheel 17 is prevented from rotating, the ratchet wheel 
17 has rotation delay relative to the rotation of the winding shaft 4 in 
the webbing draw-out direction, so that the rotation lock device is 
operated to lock the draw-out of the webbing as mentioned above. 
When the tension acting on the webbing is released, the ratchet cup 13 is 
rotated in the direction of the arrow X.sub.2 through the urging force of 
the return spring 12 so as to make the pawl 11 swing in the direction 
opposite to the direction of the arrow Z.sub.1 in FIG. 6. Accordingly, the 
ratchet plate 4a is released from being locked, so as to allow the webbing 
to be drawn out desirably. 
Such an ELR mode state continues until the webbing is further drawn out so 
that the guide pin 23a of the operation mode switching lever 23 enters the 
switching area 52 of the guide groove 40 to thereby switch the operation 
mode. FIGS. 10 and 11 respectively show the state where the quantity of 
the drawn-out webbing closes near almost the whole amount thereof so that 
the guide pin 23a is beyond the position B on the end point side of the 
outer cam groove 55. That is, a little before the quantity of the 
drawn-out webbing reaches the maximum (whole amount), as shown in FIGS. 
10(a) and 10(b), the guide pin 23a is beyond the end position B and on the 
inclined surface 58 of the step portion 57. FIG. 10(a) shows an exploded 
plan view of the state where the guide pin 23a has run onto the step 
portion 57, and FIG. 10(b) shows a sectional view of the portion taken on 
X--X line in the same drawing. 
If the webbing is further drawn out, as shown in FIGS. 11(a) and 11(b), the 
guide pin 23a goes beyond the step portion 57, and enters the switching 
area 52. If the webbing is intended to be further drawn out thereafter, 
the guide pin 23a moves along the cam surface 61 constituting the side 
wall of the switching area 52. In this state, the webbing can be still 
drawn out. 
After substantially the whole amount of the webbing is drawn out, if 
winding is started in the state where the guide pin 23a is located in the 
switching area 52, the control plate 22 begins to rotate in the direction 
(Y.sub.2 direction) opposite to the direction of the rotation performed 
till then. Then, the guide pin 23a contacts with the step surface 59 or 
with the cam surface 60 continuously extended from the step surface 59 to 
the inner cam groove 56 so that the guide pin 23a is guided to the inner 
cam groove 56 (refer to FIG. 12). 
When the guide pin 23a moves to the cam surface 60, the second lock convex 
portion 23f of the operation mode switching lever 23 is made to go over 
the first lock convex portion 34 of the sensor cover 30 by the repulsion 
between the first lock convex portion 34 and the second lock convex 
portion 23f, so that the guide pin 23a enters the inner cam groove 56. At 
this time, the inner cam groove 23d of the operation mode switching lever 
23 pushes the engagement projection 24b of the lock arm 24, so that the 
engagement portion 24a of the lock arm 24 engages with the teeth of the 
ratchet plate 4a as shown in FIGS. 12 to 16, and the operation mode of the 
inertia detecting device 31 is switched from the ELR mode to the ALR mode. 
FIGS. 12 and 13 show the state where winding the webbing is advanced in the 
ALR mode. That is, the ALR mode is continued while the guide pin 23a of 
the operation mode switching lever 23 is being guided by the inner cam 
groove 56. 
If the webbing is started to be wound on the winding shaft 4 in this ALR 
mode, as shown also in FIG. 20, the winding shaft 4 begins to rotate in 
the direction of the arrow X.sub.2, and the ratchet plate 4a also rotates 
in the same direction. However, the engagement portion 24a of the lock arm 
24 engaging with the teeth of the ratchet plate 4a is pivoted to go beyond 
the teeth of the ratchet plate 4a, so that there is no fear that the lock 
arm 24 prevents the winding shaft 4 from rotating. When the engagement 
portion 24a goes beyond the ratchet plate 4a, as shown in FIGS. 13 and 17, 
the guide pin 23a of the operation mode switching lever 23 is moved, 
together with the lock arm 24, in the inner cam groove 56 toward the outer 
cam groove 55 (in the outward radial direction of the control plate 22). 
However, since the side wall of the inner cam groove 56 is constituted by 
the suitably inclined surface 51, it is possible to give an urging to the 
guide pin 23a to thereby restrict the guide pin 23a from moving in the 
outward radial direction of the control plate 22. When the engagement 
portion 24a of the lock arm 24 goes beyond the ratchet plate 4a, the lock 
arm 24 is urged in the direction of engagement with the ratchet plate 4a 
by the urging force in the direction of the arrow W.sub.2 acting on the 
operation mode switching lever 23 by the repulsion between the first lock 
convex portion 34 and the second lock convex portion 23f. As a result, the 
engagement between the teeth of the ratchet plate 4a and the engagement 
portion 24a is maintained, so that there is no fear that the ALR mode is 
released. 
On the other hand, if the webbing is drawn out of the retractor in the 
operation state of the ALR mode so that the winding shaft 4 begins to 
rotate in the direction of the arrow X.sub.1 as shown in FIGS. 12 and 21, 
the lock arm 24 engaging with the ratchet plate 4a is urged 
counterclockwise in FIG. 21. Therefore, the lock arm 24 slides in the long 
hole 69 of the guide member 67 by use of the engagement pin 68 thereof as 
a fulcrum. At that time, the lock arm 24 pushes the ratchet cup 13 by an 
expanded portion 24c on the base side of the engagement projection 24b 
thereof so that, at the same time the ratchet cup 13 also rotates in the 
direction of the arrow X.sub.1 (that is, the direction of rotation of the 
winding shaft 4) against the urging force of the return spring 12. When 
the ratchet cup 13 rotates in the direction of the arrow X.sub.1, the 
rotation in the direction of the arrow Z.sub.1 (refer to FIG. 6) is 
produced in the pawl 11 through the pawl guide projection 11b engaging 
with the pawl guide hole 13c of the ratchet cup 13. Consequently, the pawl 
11 engages with the ratchet plate 4a so as to enter the lock state where 
the webbing is prevented from being drawn out. 
If the webbing is further wound in the state of FIG. 13 in the ALR mode, 
the control plate 22 further rotates in the direction of the arrow 
Y.sub.2, so that the guide pin 23a of the operation mode switching lever 
23 is guided by the inner cam groove 56 to thereby move onto the cam 
surface 53 at the end point of the inner cam groove 56. If the webbing is 
further wound, the guide pin 23a contacts with the cam surface 53 as shown 
in FIG. 14, and is returned to the outer cam groove 55 by the cam surface 
53. 
At this time, the second lock convex portion 23f formed in the swinging end 
portion of the flexible arm portion 23e of the operation mode switching 
lever 23 goes beyond the top of the first lock convex portion 34, so that 
the direction of the repulsion between the first lock convex portion 34 
and the second lock convex portion 23f is changed. Accordingly, the 
direction of the urging force acting on the operation mode switching lever 
23 is switched to the direction where the guide pin 23a is pushed onto the 
side wall 50 of the outer cam groove 55. The urging force makes the lock 
arm 24 swing away from the ratchet plate 4a through the engagement 
projection 24b engaging with the inner cam groove 23d so that the 
engagement portion 24a of the lock arm 24 is released from engaging with 
the ratchet plate 4a. As a result, the operation mode is switched from the 
ALR mode to the ELR mode. If the webbing is further wound in this state, 
and the whole amount of the webbing is wound up, the state returns to the 
above-mentioned initial state shown in FIG. 9. 
After the whole amount of the webbing is drawn out again, until the guide 
pin 23a of the operation mode switching lever 23 enters the switching area 
52 or immediately after the guide pin 23a enters the switching area 52, 
the ELR mode is maintained. After that, if the guide pin 23a contacts with 
the cam surface 60 by the succeeding winding, as mentioned above, the 
operation mode is switched from the ELR mode to the ALR mode. This ALR 
mode is continued until the guide pin 23a is moved to the outer cam groove 
55 by the cam surface 53 of the inner cam groove 56. 
Thus, in the seat belt retractor according to the first embodiment, with 
respect to the switching of the operation mode switching lever 23 from the 
ELR mode position to the ALR mode position, the guide pin 23a is located 
in the switching area 52 when the quantity of winding reaches a 
predetermined value after almost the whole amount of the webbing is drawn 
out so that the guide pin 23a can move only to the ALR mode (by the effect 
of the structure of the step surface 59 and so on), and it is therefore 
extremely sure to perform the switching of the operation mode from the ELR 
mode to the ALR mode. In addition, when this seat belt retractor is 
assembled, the above-mentioned switching of the operation mode can be 
performed if the guide pin 23a can be disposed in the switching area 52 
which is comparatively large so that it is possible to improve the 
performance of the assembling. 
In addition, it is possible to prevent the production of operation faults 
of an automatic lock function caused by a conventional operation mode 
switching lever 23 stopping near a neutral position. Therefore, when the 
webbing is used for attaching a baggage, a child seat or the like onto a 
seat, there is no fear that the seat belt retractor is released from the 
automatic lock state and returns to the emergency lock state by vibration, 
shock or the like during the running of a vehicle. Accordingly, it is 
possible to surely prevent the webbing from being gradually drawn out of 
the retractor during the running of the vehicle to thereby loosen the 
attachment of the baggage, the child seat or the like. 
FIGS. 22 to 24 are exploded perspective views of a seat belt retractor 
according to a second embodiment of the present invention. The detailed 
description of the constituent parts the same as those in the first 
embodiment will be omitted here. 
As shown in FIG. 24, an operation mode switching lever 123 which is a lever 
member made of synthetic resin is swingably pivoted on a pivot 125 
projectingly provided on the inner wall of a sensor cover 130. The 
operation mode switching lever 123 is constituted by a cylindrical portion 
123b loosely fitted to the pivot 125, a cam arm 123c extended from the 
cylindrical potion 123b toward the outside in the radial direction, and a 
flexible arm portion 123e extended toward the outside in the radial 
direction oppositely to the cam arm portion 123c. A guide pin 123a which 
is an engage portion projectingly provided on a swinging end portion of 
the cam arm portion 123c engages with a guide groove 140 of a control 
plate 122 so that the operation mode switching lever 123 can swing along 
the cam surface of the guide groove 140. As shown in FIG. 25, a second 
lock convex portion 123f having a triangular section and formed in the 
swinging end portion of the flexible arm portion 123e engages with a first 
lock convex portion 134 having a triangular section and projecting on the 
inner wall of the sensor cover 130 so as to constitute an urging device by 
which an urging force can be given to the operation mode switching lever 
123 so that the direction of the urging force is changed properly with a 
neutral position as a border by the effect of the elastic force of the 
flexible arm portion 123e in the direction of axis of rotation, and the 
drag of the inclined surfaces pressed to each other in opposition to each 
other. Thus, the operation mode switching lever 123 is swingable with a 
pivot 125 as a center and is urged to each end of the swinging. 
Further, an engagement projection 124b of the lock arm 124 swingably 
pivoted on the pivot 113a provided so as to project toward the inside of a 
ratchet cup 113 is made engageable through an opening 113f of the ratchet 
cup 113, with an inner cam surface 123d of the cam arm portion 123c. The 
swinging end of the lock arm 124 is urged away from the rotation center of 
the winding shaft 4 by a torsion coil spring 138 one end portion of which 
is engaged with a lock piece 113e projectingly provided on the ratchet cup 
113. The lock arm 124 is moved with the pivoting of the operation mode 
switching lever 123 at the position where an engagement portion 124a 
thereof engages with the teeth of the ratchet plate 4a so that an inertia 
detecting device 131 is started up as a lock device driving mechanism, or 
at the position where the engagement portion 124a does not engage with the 
teeth of the ratchet plate 4a so that the inertia detecting device 131 is 
not started up as a lock device driving mechanism (refer to FIG. 26). 
Thus, the lock arm 124 can take the two first and second positions where 
the lock arm 124 engages or does not engage with the ratchet plate 4a, 
respectively. The swing region of the lock arm 124 is restricted by the 
opening 113f of the ratchet cup 113. 
As shown in FIG. 27, the guide groove 140 of the control plate 122 is 
constituted by an outer cam groove 122a which is a first cam groove for 
positioning a guide pin 123a of the operation mode switching lever 123 
near the outer circumference of the control plate 122 so as to hold the 
lock arm 124 in the position where the lock arm 124 does not engage with 
the ratchet plate 4a; an inner cam groove 122b which is a second cam 
groove for positioning a guide pin 123a near the inner circumference of 
the control plate 122 so as to hold the lock arm 124 in the position where 
the lock arm 124 engages with the ratchet plate 4a; a notch portion 122c 
which is a switching area for introducing the guide pin 123a from the 
outer cam groove 122a to the inner cam groove 122b when a webbing is drawn 
out by the quantity equal or more than a predetermined value; and a notch 
portion 122d which is a connection portion for moving the guide pin 123a 
from the inner cam groove 122b to the outer cam groove 122a when the 
webbing is wound by a predetermined quantity after that. 
The outer cam groove 122a is extended almost all over the circumference in 
the vicinity of the outer circumference of the control plate 122, and the 
inner cam groove 122b is extended almost over a half of the circumference 
in the inner side than the outer cam groove 122a. When the guide pin 123a 
of the operation mode switching lever 123 is located in the outer cam 
groove 122a, the second lock convex portion 123f of the operation mode 
switching lever 123 disposed in the position shown by the continuous line 
in FIG. 128 has a repulsion for the first lock convex portion 134 of the 
sensor cover 130 so as to urge the operation mode switching lever 123 
counterclockwise (in the direction of the arrow W.sub.1) in FIG. 27. When 
the guide pin 123a is located in the inner cam groove 122b, the second 
lock convex portion 123f is moved beyond a top S of the first lock convex 
portion 134 which is a neutral position so as to be disposed in the 
position shown by the two-dots chain line in FIG. 28. Accordingly, the 
second lock convex portion 123f has a repulsion against the first lock 
convex portion 134 of the sensor cover 130 so as to urge the operation 
mode switching lever 123 clockwise (in the direction of the arrow W.sub.2) 
in FIG. 27. 
That is, these inner and outer cam grooves 122b and 122a are separated by a 
partition 143, so that there is no fear that the guide pin 123a disposed 
in either one of the cam grooves goes beyond the partition 143 and moves 
to the other cam groove unexpectedly. 
Next, the operation of the seat belt retractor according to the second 
embodiment will be described. 
In the same manner as in the first embodiment, while the guide pin 123a of 
the operation mode switching lever 123 is guided by the outer cam groove 
122a of the control plate 122, the inertia detecting device 131 is not 
operated, and the ELR mode is maintained. That is, the webbing can be 
drawn out freely. 
If tension is given to the webbing (not shown) in case of emergency such as 
a collision or the like so that an impacting rotation force in the webbing 
draw-out direction (the direction of the arrow X.sub.1) stronger than a 
predetermined value acts on the winding shaft 4, then the inertia 
detecting device 131 is operated in the same manner as in the first 
embodiment so that the pawl 11 engages with the ratchet plate 4a, and as a 
result, the lock state is produced so as to prevent the rotation of the 
winding shaft 4 in the direction of the arrow X.sub.1, that is, to prevent 
the draw-out of the webbing. When the ratchet cup 13 is rotated in the 
direction of the arrow X.sub.1, the lock arm 124 pivoted on the pivot 13a 
of the ratchet cup 13 is also rotated together with the ratchet cup 13. 
However, the lock arm 124 is urged away from the rotation center of the 
winding shaft 4 by the torsion coil spring 138 so that the lock arm 124 
does not engage with the ratchet plate 4a. 
Next, if the whole amount of the webbing is drawn out, as shown in FIG. 
30(b), the guide pin 123a of the operation mode switching lever 123 is 
pushed by a cam surface 141 of the notch portion 122c so as to enter the 
inner cam groove 122b. At the same time, the operation mode switching 
lever 123 is made to swing clockwise (in the direction of the arrow 
W.sub.2) in FIGS. 30(a) and 30(b). At this time, since the second lock 
convex portion 123f formed in the swinging end portion of the flexible arm 
portion 123e goes beyond the top S of the first lock convex portion 134, 
the direction of the repulsion between these first lock convex portion 134 
and second lock convex portion 123f is changed so that the cam arm portion 
123c urges the lock arm 124 in the direction where the lock arm 124 
engages with the ratchet pate 4a. Consequently, in FIG. 30(a) where the 
repulsion between the second lock convex portion 123f and the first lock 
convex portion 134 acts on the operation mode switching lever 123, the 
engagement portion 124a is engaged with the teeth of the ratchet plate 4a 
by the urging force added clockwise (in the direction of the arrow 
W.sub.2). 
If the webbing begins to be wound by the retractor, as shown in FIG. 31(a), 
then the winding shaft 4 begins to rotate in the direction of the arrow 
X.sub.2, and the ratchet plate 4a also rotates in the same direction. 
However, the engagement portion 124a of the lock arm 124 engaging with the 
teeth of the ratchet plate 4a is pivoted to go over the teeth of the 
ratchet plate 4, so that there is no fear that the lock arm 124 prevents 
the winding shaft 4 from rotating. At this time, the lock arm 124 is urged 
in the direction to engage with the ratchet plate 4a by the urging force 
in the clockwise direction (the direction of the arrow W.sub.2) in FIGS. 
31(a) and 31(b) which acts on the operation mode switching lever 123 by 
the repulsion between the first lock convex portion 134 and the second 
lock convex portion 123f. Accordingly, the engagement between the teeth of 
the ratchet plate 4a and the engagement portion 124a is maintained. 
Further, at this time, the cam arm portion 123c of the operation mode 
switching lever 123 is also pivoted by the teeth of the ratchet plate 4a 
through the engagement projection 124b of the lock arm 124. However, as 
shown in FIG. 31(b), the guide pin 123a of the pivoted cam arm portion 
123c is restricted by the outer side wall of the inner cam groove 122b so 
that the guide pin 123a cannot go over the partition 143. Accordingly, 
there is no fear that the urging force acting clockwise (in the direction 
of the arrow W.sub.2) onto the operation mode switching lever 123 is 
released. 
On the other hand, if the webbing is drawn out of the retractor so that the 
winding shaft 4 begins to rotate in the direction of the arrow X.sub.1, 
then the rotation force of the winding shaft 4 is transmitted to the 
ratchet cup 113 through the lock arm 124 engaging with the ratchet plate 
4a as shown in FIG. 32. Accordingly, the inertia detecting device 131 is 
operated to rotate the ratchet cup 113 in the direction of the arrow 
X.sub.1 against the urging force of the return spring 12. At this time, a 
pawl guide hole 113c engaging with the pawl guide projection 11b rotates 
the pawl 11 in the direction of the arrow Z.sub.1 through the pawl guide 
projection 11b so as to make the pawl 11 engage with the ratchet plate 4a 
(refer to FIG. 33). As a result, the rotation in the direction of the 
arrow X.sub.1 of the winding shaft 4, that is, the draw-out of the webbing 
is prevented and locked. 
Thus, while the guide pin 123a is located in the inner cam groove 122b of 
the control plate 122, the engagement portion 124a of the lock arm 124 
always engages with the teeth of the ratchet plate 4a so that the 
automatic lock mechanism is being in the operating state. 
If the webbing is further wound in this state, the control plate 122 begins 
to rotate in the direction of the arrow Y.sub.2, so that the guide pin 
123a of the operation mode switching lever 123 moves in the inner cam 
groove 122b. If the webbing is further wound, as shown in FIG. 34(a), the 
guide pin 123a is pushed by a cam surface 142 of the notch portion 122d to 
thereby enter the outer cam groove 122a. At the same time, the operation 
mode switching lever 123 is made to swing counterclockwise (in the 
direction of the arrow W.sub.1) in FIGS. 34(a) and 34(b). At this time, 
since the second lock convex portion 123f formed in the swinging end 
portion of the flexible arm portion 123e goes beyond the top S of the 
first lock convex portion 134, the direction of the repulsion between 
these first lock convex portion 134 and second lock convex portion 123f is 
changed so as to release the urging force of the operation mode switching 
lever 123 which acts the lock arm 124 in the direction where the lock arm 
124 is engaged with the ratchet plate 4a. 
The urging force of the torsion coil spring 138 makes the lock arm 124 
swing in the direction where the engagement between the engagement portion 
124a and the teeth of the ratchet plate 4a is released. Accordingly, only 
the emergency lock mechanism is left operated in the retractor, and the 
whole amount of the webbing is wound up. Thus, only the emergency lock 
mechanism is operated until the whole amount of the webbing is drawn out 
again and the guide pin 123a of the operation mode switching lever 123 is 
introduced into the inner cam groove 122b of the control plate 122. It is 
therefore possible to switch the operation mode from the emergency lock 
function to the automatic lock function by such an extremely simple 
operation that the whole amount of the webbing is drawn out. 
That is, by the repulsion between the second lock convex portion 123f of 
the flexible arm portion 123e and the first lock convex portion 134 of the 
sensor cover 130, the operation mode switching lever 123 of the seat belt 
retractor urges the lock arm 124 in the direction where the lock arm 124 
is engaged or is not engaged with the ratchet plate 4a. At the same time, 
the guide pin 123a of the operation mode switching lever 123 is engaged 
with the outer or inner cam groove 122a or 122b of the control plate 122 
so as to be prevented from swinging unexpectedly. 
For example, even if vibration, impact or the like acts on the operation 
mode switching lever 123 when the automatic lock mechanism is operated so 
that the second lock convex portion 123f would like to go over the top S 
of the first lock convex portion 134 unexpectedly, there is no fear that 
the direction of the urging force of the operation mode switching lever 
123 does not change since the guide pin 123a engages with the inner cam 
groove 122b, and further there is no fear that the automatic lock state of 
the retractor is released. 
Therefore, when a baggage, a child seat or the like is set on a seat by use 
of the webbing, there is no fear that the automatic lock state of the seat 
belt retractor is released by vibration, shock or the like so that the 
operation mode returns to the emergency lock state during the running of a 
vehicle. It is therefore possible to surely prevent the webbing from being 
gradually drawn out of the retractor during the running of the vehicle to 
thereby loosen the attachment of the baggage, the child seat or the like. 
The members constituting the lock device driving mechanism or the operation 
mode switching device according to the present invention are not limited 
to those structures in the above-mentioned embodiments, and, but it is a 
matter of course that various modifications can be given to them. For 
example, although the repulsion between a first lock convex portion and a 
second lock convex portion is used for an urging device for urging the 
operation mode switching lever in the respective swinging directions, it 
is possible to use any other urging device having a structure using a 
spring member such as an over center spring, a compression spring or the 
like in which the direction of the urging force thereof changes suitably 
with a neutral position as a border. 
Although an inertia detecting device is started up by the engagement of a 
lock arm with a ratchet plate in the present invention, it is, for 
example, possible to use such a configuration in which the lock arm is 
made to engage with a ratchet wheel so as to start up the inertia 
detecting device in accordance with the winding state of a webbing. 
According to the seal belt retractor of the present invention, when almost 
the whole amount of a webbing has been drawn out, a guide pin of an 
operation mode switching lever is located in a switching area of a guide 
groove, so that the mode position of the operation mode switching lever 
can be switched only in one direction from the ELR mode side to the ALR 
mode side. Accordingly, there is no room to produce such an event that the 
operation mode returns unexpectedly, so that it is possible to switch the 
operation mode extremely accurately. In addition, in the seat belt 
retractor of the present invention, if the guide pin is set to be disposed 
in such a comparatively large switching area when the retractor is 
assembled, switching the operation mode can be ensured, so that it is also 
possible to improve the assembling property. 
As described above, in the seat belt retractor according to the present 
invention, when a swinging end portion of an operation mode switching 
lever which is swingable between positions where an inertia detecting 
device is started up and not started respectively, engages with a first 
cam groove of a control plate, the operation mode switching lever is urged 
by an urging device to a position where the inertia detecting device is 
not started up. If the swinging end portion of the operation mode 
switching lever is moved to a second cam groove side of the control plate, 
the operation mode switching lever is urged by the urging device to a 
position where the inertia detecting device is started up. 
That is, the inertia detecting device is operated in accordance with the 
winding state of a webbing. The operation mode switching lever of an 
operation mode switching device for moving a rotation lock device to a 
position where the rotation lock device engages with a winding shaft or a 
position where it does not engage with the same, is urged by the urging 
device to the position where the inertia detecting device is started up or 
the position where it is not started. At the same time, the swinging end 
portion of the operation mode switching lever engages with the first or 
second cam groove of the control plate so as to be prevented from swinging 
unexpectedly. Accordingly, there is no fear that the urging direction of 
the urging device for urging the operation mode switching lever is changed 
by vibration, impact, or the like, unexpectedly. 
Therefore, for example, when the automatic lock mechanism is being 
operated, there is no fear that the urging direction of the urging device 
is changed unexpectedly by the effect of vibration, impact, or the like to 
thereby release the automatic lock state of the retractor. 
It is therefore possible to provide a seat belt retractor superior in 
practical use in which an automatic lock mechanism is incorporated in an 
emergency lock retractor, and in which an operation mode switching device 
capable of switching its operation mode from the emergency lock function 
to the automatic lock function through a simple operation does not release 
the automatic lock function unexpectedly.