JPH10167006A - Seatbelt retractor using ultrasonic motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a retractor operated by an ultrasonic motor and in which the extraction of a seatbelt is obstructed when the electrification to the ultrasonic motor is stopped. SOLUTION: A shaft 30 is inserted in a reel 20 and both are connected by a tension spring 37. The projection part 104 of the shaft 30 is connected to an ultrasonic motor 24. A lock mechanism 22 consisting of a ratchet wheel 38, a pawl 58, a lock ring 44, a hook retainer 72, a hook 74 and a flywheel 90 are installed on the reel 20. When a seatbelt 18 is extracted in a state in which the electrification to the ultrasonic motor 24 is stopped, a lock mechanism 22 is operated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention is installed in a vehicle,
The present invention relates to a seat belt retractor for protecting an occupant, and more particularly to a seat belt retractor using an ultrasonic motor.

[0002]

2. Description of the Related Art Conventionally, in the case of a retractor in which a seat belt is wound by a motor, the rotation speed of the motor is reduced by using a gear. For example, 50-102
No. 017 and British Patent No. 1393505 disclose an apparatus in which a winding shaft of a seat belt and a rotating shaft of a motor are connected via a planetary gear. Japanese Patent Laid-Open No. 58-101
No. 855 and JP-A-58-101857, a winding shaft of a seat belt and a rotating shaft of a motor are connected via a worm gear. A retractor using these motors detects a seat belt feeding position to determine an optimal belt position for an occupant and adjusts a tension according to a vehicle speed as disclosed in U.S. Pat. No. 4,489,804. can do. Further, as disclosed in Japanese Patent Application Laid-Open No. 58-101855, the belt can be extended in accordance with the posture of the occupant of the vehicle to adjust the amount of slug (looseness).

[0003]

The seat belt retractor connecting the rotation shaft of the motor and the winding shaft of the seat belt through the above-described winding planetary gear is more than the one connected through the worm gear. Although it can be manufactured in a small size, the power to wind up the seat belt is weak. Therefore, when the seat belt is extended, slugs are taken, and the seat belt is wrapped when not in use, it can function sufficiently. Can not do.

A DC motor that drives a winding shaft of a belt via a worm gear has a drawback that although the winding force in an emergency is large to some extent, rapid winding is difficult.

SUMMARY OF THE INVENTION It is a first object of the present invention to provide a seat belt retractor in which an ultrasonic motor is used as a motor so that a seat belt can be rapidly wound.

By the way, in such a seat belt retractor driven by a motor, it is preferable that when the power supply from the electric system of the vehicle is stopped, the retractor is locked so that the seat belt cannot be pulled out. A second object of the present invention is to provide a seat belt retractor in which a lock mechanism is activated when such energization is stopped to prevent the seat belt from being pulled out.

As described above, the seat belt retractor that connects the rotation shaft of the motor and the take-up shaft of the seat belt through the worm gear has a strong force to wind up the seat belt as described above, A clutch is necessary to allow the belt to be freely pulled out when the occupant wears or when the occupant moves forward after wearing.

Even when using a planetary gear or the like, when the seat belt is smoothly worn or when the occupant changes his or her posture after wearing, the clutch must also be used to freely pull out or wind up the belt. It is more convenient to prepare.

However, if a clutch is used, it is necessary to apply tension to the belt when the clutch is not in a connected state. Therefore, a spring is attached to the winding shaft of the belt so that the belt is always wound in the direction in which the belt is wound. We need to keep up. Therefore, the longer the belt withdrawal length,
The spring is tightened, increasing the force required to pull out the seat belt. In addition, the seat belt fits the occupant strongly.

A third object of the present invention is to provide a seat belt retractor which operates an ultrasonic motor following pulling out of a seat belt, whereby the seat belt can always be pulled out lightly.

[0011]

According to the present invention, there is provided a seat belt retractor comprising: a reel for winding a seat belt;
In a seat belt retractor having a frame that supports the reel, a motor that drives the reel to rotate, and a lock mechanism that locks the rotation of the reel and prevents the seat belt from being pulled out, the motor is an ultrasonic motor. The locking mechanism is characterized in that the locking mechanism is operated when the phase difference between the rotation axis of the ultrasonic motor and the reel in the circumferential direction of rotation becomes equal to or larger than a predetermined angle.

In such a seat belt retractor, an ultrasonic motor is used as a motor for driving the reel, so that the reel can be rapidly rotated, and the seat belt can be quickly wound up.

Further, since the holding torque of the ultrasonic motor is large, the ultrasonic motor does not rotate even when the seat belt pulling output is applied during the stop of energization. Therefore, if the seat belt is pulled out while the power is stopped, the phase difference between the seat belt and the rotary shaft of the ultrasonic motor becomes a predetermined angle or more, the lock mechanism operates, and further pulling out of the seat belt is prevented.

The lock mechanism is provided on a reel and has a ratchet wheel having a tooth surface on the outer peripheral surface, and a rear end side rotatably supported by the frame and a front end side of the ratchet wheel. A pawl capable of locking the reel by engaging with the tooth surface, separating the pawl from the ratchet wheel when the phase difference is smaller than a predetermined value, and engaging the pawl with the ratchet wheel when the phase difference is equal to or more than the predetermined value. A mechanism comprising a pawl operating mechanism to be combined can be used.

The seat belt retractor of the present invention controls the ultrasonic motor so that when the rotation speed of the reel is lower than a predetermined speed, the phase difference detected by the phase difference detecting means becomes smaller than a predetermined angle. Is preferably provided.

In such a seat belt retractor, when the seat belt is pulled, the reel rotates. When the reel is pulled out in a normal use mode, the rotation speed of the reel is not so high. Therefore, the lock mechanism does not operate, and the reel rotates smoothly. The rotation phase difference between the reel and the ultrasonic motor increases due to the rotation of the reel. The ultrasonic motor rotates so that the rotation phase difference falls within a predetermined range. This allows the reel to rotate with little or no resistance and allows the seat belt to be pulled out with very little force.

The means for detecting the rotational phase difference is preferably a variable resistor provided so that the operation piece is moved by the phase difference.

In the lock mechanism used in the present invention, when the collision detecting means of the vehicle detects a collision, the power supply to the ultrasonic motor is stopped, and after the ultrasonic motor power supply is stopped, the reel is further rotated so that the reel is connected to the ultrasonic wave. It is preferable that the phase difference with the motor becomes equal to or larger than a predetermined angle, and thereby the lock operation is performed.

[0019]

1 to 4 are exploded perspective views of the whole or a part of a seat belt retractor according to an embodiment of the present invention, and FIG. 5 is a sectional view of the seat belt retractor. FIGS. 6 and 7 are lines VI-VI and VII-VII of FIG.
FIG. 8 and FIG. 9 are views for explaining the operation of the portion along the line. FIG. 2 is an enlarged view of the lock mechanism shown in FIG.

The frame 10 has a pair of parallel side walls 12,
14 and a back plate portion 16 connecting these side wall portions 12 and 14 to each other.
And In this frame 10, the seat belt 1
The reel 20 for winding the reel 8 is provided.
An emergency lock mechanism 22 for the reel 20 is provided outside the reel. An ultrasonic motor 24 for rotating the reel 20 is provided outside the side wall 12.

First, the structure of the reel lock mechanism 22 will be described mainly with reference to FIG.

The support holes 2 are coaxially formed on both side walls 12 and 14.
6, 28 are formed. A shaft 30 for rotatably supporting the reel 20 is inserted into the support holes 26 and 28. The shaft 30 is inserted through a through hole at the center of the reel 20. A flange 34 is provided integrally with the shaft 30 at one end of the shaft 30. A flange 32 is also provided on one end side of the reel 20, and these flanges 32 and 34 face each other. A variable resistor 36 for detecting a rotational phase difference between the shaft 30 and the reel 20 is provided between the flanges 32 and 34.

In this embodiment, the variable resistor 36 has a main body 36a fixed to the flange 32 and an operating piece 36.
b engages with a long groove 34 a provided in the flange 34. The long groove 34a extends in the radial direction of the flange 34. The main body 36a extends in the chord direction of the flange 32. When a rotational phase difference occurs between the flanges 32 and 34, the operation piece 36b moves in the longitudinal direction of the main body 36, and the resistance value of the variable resistor 36 changes. The lead wire (not shown) connected to the variable resistor 36 is drawn into the shaft 30 through an opening 30 </ b> H provided in the shaft 30, and further passes through the convex shaft 104 having a hollow polygonal shape. Current collecting member 105 (fifth
(Fig.) The resistance value of the variable resistor 36 is input to the control device via a current collecting brush (not shown) sliding on the current collecting member 105.

When the seat belt 18 is pulled out, the reel 20 and the reel shaft 30 are indicated by arrows A.
Rotates in _one direction, when winding the seat belt 18 which are rotated in the arrow A ₂ direction.

A tension spring 37 composed of a torsion spring is interposed between the flanges 32 and 34 to transmit a rotational force between the reel 20 and the shaft 30. The tension spring 37 has ends 37a and 37b projecting in the diametrical direction. As shown in FIG. 3, one end 37a is in contact with the projection 34b of the flange 34, and the other end 37b is a flange. 32 is engaged with the recess 32b.

As shown in FIG. 3, the flange 32 of the reel 20
Are provided with steps 32c and 32d which are spaced apart from each other in the circumferential direction, and the protrusion 34b is arranged between the steps 32c and 32d. The end portion 37 of the tension spring 37
a is in contact with and locked by the convex portion 34b, and the tension spring end 37a is also connected to these step portions 32c, 32c.
d. Therefore, this end 37a
A partial range θ between the step portions 32c and 32d (the step portion 32
c, 32d, the side surface of the convex portion 34b and the step portion 3
2d).

The flange 32 is further provided with a step 32e, and the projection 34c of the flange 34 is
e can be contacted. When the motor 24 is stopped and no external force is applied to the reel 20,
The projection 34c is in contact with the step 32e by the tension spring 37 (the state shown in FIG. 8A), and this state is an initial state in which there is no phase difference between the reel 20 and the shaft 30.

At the other end of the shaft 30, a ratchet wheel 38 is provided integrally with the shaft 30. On the outer side of the ratchet wheel 38, a protruding portion 40 concentric with the rotation axis of the shaft 30 is formed. This projection 4
The opening 43 of the tie plate 42 is fitted to 0.
The center hole 48 of the lock ring 44 is loosely fitted in the protruding portion 40.

The tie plate 42 supports one end of a C-shaped spring 50 described below. The opening 43 is provided on the tip side of the tie plate 42, and an opening 64 described later is provided on the other end side. The rear end of the tie plate 42 is supported by the frame side wall portion 14 by the shaft pin 60 inserted into the opening 64. That is, the tie plate 42 is provided between the projecting portion 40 and the shaft pin 60.

One end 50a of the C-shaped spring 50 is locked in a locking hole (spring hanger) 52 provided substantially in the center of the tie plate 42, and the other end is locked in a locking ring 44 (spring hanger). 54. The spring hanger 5 extends around the shaft 30.
A biasing force is applied to the lock ring 44 in the direction of the arrow A2 by the spring 50 provided between the _{second and the second} 54.

The lock ring 44 is provided with internal teeth 56.

The pawl 5 is provided on the side wall 14 of the frame 10.
8 is pivotally connected to a shaft pin 60 inserted through the opening 58. The tip of the pawl 58 is engageable with the ratchet wheel 38. A protruding pin 62 protrudes from a middle portion of the pawl 58. As described above, the shaft pin 60 has the opening 6 on the distal end side of the tie plate 42.
4 is also fitted. This shaft pin 60 is attached to a hole 65 of the frame side wall portion 14.

The lock ring 44 is integrally provided with a projecting portion 66 projecting radially. This overhang 66
Wherein the pawl 58 is intended for turning in the C ₁ direction, the overhung portion 66, arcuate long hole 70 extending in the constant radius position with respect to the central hole 48 is provided, the length The protruding pin 62 of the pawl 58 is inserted into the hole 70.

The square hole 72a at the center of the hook retainer 72 is fitted into the rectangular cylindrical reel protrusion 40 which penetrates through the center hole 48 of the lock ring 44 and projects outward.
Protrusions 76 and 78 for supporting the hook 74 are provided on the periphery of the hook retainer 72 so as to face each other in the diametrical direction. The holes 8 of the hooks 74 are provided in the projections 76 and 78.
0, 82 are inserted, so that the hook 74 connects the projections 76, 78 to the hook retainer 72 in the direction (B
₁ and B ₂ directions).

The spring locking portion 72b with the hook retainer 72 and the hook 74, between 74b are compression coil spring 84 is interposed, the hook 74 is biased in the arrow B ₁ direction. A hook 86 is provided at a part of the outer peripheral edge of the hook 74 so as to be able to engage with the internal teeth 56 of the lock ring 44. A connecting pin 88 is provided on the outer surface of the hook 74.

The hook 74 is, in the normal state, takes the position shifted in the arrow B ₁ direction by being biased in the compression coil spring 84, as a result, the pawl 86 is disengaged from the internal teeth 56 I have.

The connecting pin 88 is fitted with a locking hole 92 provided in the vicinity of the outer peripheral edge of the disk-shaped flywheel 90. A flywheel cap 96 is fitted on the flywheel 90. The center hole 96 a of the flywheel cap 96 is loosely fitted to the tip of the shaft 30. The flywheel cap 96 includes a disk portion 96b and a peripheral wall portion 96c that stands upright from the periphery of the disk portion 96b. The flywheel 90 is fitted inside the peripheral wall portion 96c. Flywheel 90
A bent end 98a of an arcuate spring 98 is mounted in a notch 90a on the outer peripheral edge of the spring 98.
Are slidably pressed against the inner peripheral surface of the peripheral wall portion 96 c of the flywheel cap 96, whereby the flywheel cap 96 is slidably rotated while receiving a frictional force against the flywheel 90. A cover 100 covers the lock mechanism 22.

A hollow polygonal projection 104 projects from one end of the shaft 30, and is engaged with a polygonal center hole of a rotor 114 of the ultrasonic motor 24, which will be described later.

As shown in FIG. 5, the ultrasonic motor 24 includes a piezoelectric element array 110 and a piezoelectric element array 11 arranged in a circle.
Annular stator 112 installed in a state of being substantially in contact with zero
And a circular rotor 114 whose center is fitted to the convex portion 104 of the shaft 30.

The convex portion 104 at the tip of the shaft 30 penetrates through the hollow center portions of the annular piezoelectric element row 110 and the annular stator 112. The rotor 114 is pressed against the annular stator 112 by the urging force of the dish-shaped annular spring 116.

When the piezoelectric element array 110 is not energized, the circular rotor 114 is strongly pressed against the annular stator 112 by the spring 116, and the shaft 30 is moved via the circular rotor 114 to the annular stator 112.
Then, the rotation is stopped. That is, the piezoelectric element row 11
If the current is not supplied to 0, the reel 20 cannot rotate, and the seat belt 18 cannot be pulled out from the retractor. The rotation preventing torque of the reel 20 by the annular stator 112 is extremely large, and is usually 30 kg-c.
Even if a torque of m is applied, the reel 20 does not rotate.

When an ultrasonic signal is applied to the annular piezoelectric element array 110, the annular piezoelectric element array 110 is distorted in a wave shape in accordance with the ultrasonic signal, and the rotor 11
4 is rotated.

The seat belt retractor is controlled by an ultrasonic motor 24 by a control device to which a variable resistor 36 is connected.
Is configured to be controlled.

In the seat belt retractor thus configured, when the seat belt 18 is not pulled out, the phase difference between the reel 20 and the shaft 30 is zero as shown in FIG. The 36 operation pieces 36b are located at an initial position (for example, zero resistance).

The speed of the seat belt 18 is lower than a predetermined speed (normal seat belt pull-out speed, for example, 60 cm / sec or less).
When the reel 20 is pulled out, the reel 20 rotates accordingly, but when the reel 20 starts rotating, the shaft 30 remains stopped, and between the reel 20 and the shaft 30 (that is, between the flanges 32 and 34). ) Produces a phase difference,
The operation piece 36b of the variable resistor 36 moves as shown in FIG. 8B, and the resistance value of the variable resistor 36 changes. The resistance value of the variable resistor 36 increases as the phase difference between the reel 20 and the shaft 30 increases. The control device controls the ultrasonic motor so that the resistance value of the variable resistor 36 is equal to or less than a predetermined value, that is, the phase difference between the reel 20 and the shaft 30 is within a predetermined angle (eg, θ / 2 or less). 24
Activate

That is, when the reel 20 rotates with the seat belt 18 being pulled out at a predetermined speed or less, the shaft 30 is also rotated by the ultrasonic motor 24, and the phase difference between the reel 20 and the shaft 30 always becomes a predetermined angle. Within.

Thus, the vehicle occupant can pull out the seat belt 18 very lightly without any or little resistance when pulling out the seat belt 18 from the seat belt retractor.

When the occupant stops pulling out the seat belt 18, the phase difference between the reel 20 and the shaft 30 falls within a predetermined range, and the ultrasonic motor 24 stops. After this,
The reel 20 returns to the position where the phase difference is zero by the urging force of the tension spring 37. When the ultrasonic motor 24 stops, the reel 20 is stopped from rotating by the ultrasonic motor 24. Then, the seat belt 18 is in a state of being pulled out.

The control device starts a timer when the seat belt 18 is pulled out. If the buckle switch does not turn on within a predetermined time, the occupant determines that the seat belt is not used, and turns the ultrasonic motor 24 in reverse to wind up the seat belt 18. If the buckle switch is turned on within a predetermined time, the timer is reset. And then, the buckle switch is turned off
When it becomes F, the seat belt 18 is wound up by the ultrasonic motor 24.

In the lock mechanism 22, when the seat belt 18 is pulled out by the occupant at a speed lower than a predetermined speed, the ratchet wheel 38 and the pawl 58 are disengaged as shown in FIGS. 9 (a) and 9 (b). State, reel 2
0 and the shaft 30 rotate freely. Seat belt 18
Can be obtained, for example, by differentiating the resistance value of the variable resistor 36 with respect to time.

When the pulling-out speed of the seat belt 18 is higher than a predetermined speed, the energization of the ultrasonic wave 24 is stopped and the lock mechanism 22 is locked. Note that an upper limit is set for the rotation speed of the ultrasonic wave 24 following the pulling out of the seat belt 18, and the lock mechanism 22 is operated by this.

The operation of the lock mechanism 22 when the power supply to the ultrasonic wave 24 is stopped is as follows.

That is, in a state where the power supply to the ultrasonic wave 24 is stopped, the shaft 30 does not rotate, and only the reel 20 rotates as shown in FIG. 9 (c). When the reel 20 rotates, the hook retainer 72 engaged with the triangular protrusion 40 of the reel 20 is rotated in A ₁ direction of Figure 1. At this time, projections 76 and 78 of the hook retainer 72 to rotate in the arrow A ₁ direction together with the hooks 74 also hook retainer 72 engaging the holes 80 and 82. However, since the rotation of the flywheel 90 to the pin 88 of the hook 74 is engaged is stopped, the hook 74 can not rotate as it is, an amount corresponding to the hook retainer 72 is rotated in the A ₁ direction hook 74 slides in the arrow B ₂ direction, FIG. 9 (c)
The hook 86 engages with the internal teeth 56 of the lock ring 44 as shown in FIG.

As a result, the lock ring 44 is also
To to rotated in the arrow A ₁ direction to be dragged in rotation. Then, the projecting portion 66 of the lock ring 44 also becomes A
Rotates in _one direction, pawl 58 having a pin 62 engaged with the long hole 70 of the overhung portion 66 is rotated in the arrow C ₁ direction.
As a result, the tip of the pawl 58 is engaged with the ratchet wheel 38 of the reel 20 as shown in FIG.
0 is firmly locked. At this time, as shown in FIG. 8D, the phase difference between the shaft 30 and the reel 20 is maximum.

Thereafter, when pulling out of the seat belt 18 is stopped, the reel 20 returns to the position where the phase difference between the reel 20 and the shaft 30 is zero due to the urging force of the tension spring 37. Then, the hook 74 is also returned to B ₂ direction by the urging force of the spring 84, the engagement between the internal teeth 56 and pawl 86, also the engagement between the pawl 58 and the ratchet wheel 38 is released, the reel 20 is rotatable again Become.

When the vehicle collides or a sudden brake is applied, the control device stops the power supply to the ultrasonic motor 24 in response to a signal from the vehicle acceleration sensor.

As a result, the shaft 30 does not rotate and only the reel 20 can rotate, so that when the occupant's body moves forward, the seat belt 18 is pulled out.
As described above, the lock mechanism 22 operates, and the seat belt 1
Further withdrawal of 8 is prevented.

When the occupant's body returns to the original posture and the tension of the seat belt 18 is lost, the reel 20 is moved by the urging force of the tension spring 37 to the reel 20 and the shaft 30.
And returns to the position where the phase difference is zero. Then, the hook 74 is also returned to B ₂ direction by the urging force of the spring 84, the engagement between the internal teeth 56 and pawl 86, also the engagement between the pawl 58 and the ratchet wheel 38 is released, the reel 20 is rotatable again Become.

A failure occurs in the electric system of the vehicle, and the ultrasonic wave 24
When power is not supplied to the ultrasonic wave 24, the ultrasonic wave 24 does not rotate at all. Therefore, when the seat belt 18 is slightly pulled out, the lock mechanism 22 operates in the same manner as described above, and further pulling out of the seat belt 18 is prevented.

In the above embodiment, the frame 10
The pawl 58 is pivotally supported on the reel 20 and the pawl 58 is engaged with the ratchet wheel 38 provided on the reel 20. In the present invention, the pawl 58 is pivotally supported on the reel 20 side and the ratchet is provided on the inner peripheral surface of the hole 28. Teeth may be provided so that the pawl engages the ratchet teeth.

[0061]

As described above, the present invention uses an ultrasonic motor as a motor in a motor-driven retractor, and can rapidly wind up a seat belt. In this seat belt retractor, the lock mechanism operates when the phase difference between the reel and the ultrasonic motor exceeds a predetermined angle, so that when the power to the ultrasonic motor is stopped, the seat belt is pulled out from the retractor. Will be blocked. Further, when the seat belt is pulled out extremely rapidly, the locking mechanism can be operated to prevent the seat belt from being pulled out.

In the present invention, the seat belt can be pulled out from the retractor with extremely small force by rotating the ultrasonic motor following the pulling out of the seat belt.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view of a seat belt retractor according to the present invention.

FIG. 2 is an enlarged view of the lock mechanism of FIG.

FIG. 3 is an exploded perspective view of a main part of the seat belt retractor according to the present invention.

FIG. 4 is a perspective view of the seat belt retractor according to the present invention.

FIG. 5 is a sectional view of the seat belt retractor according to the present invention.

FIG. 6 is a side view for explaining the present invention, taken along the line VI-VI of FIG. 4;

FIG. 7 is a side view taken along the line VII-VII of FIG. 4 for explaining the present invention.

FIG. 8 is an operation explanatory view of the present invention.

FIG. 9 is an operation explanatory view of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Frame 12,14 Side wall part 20 Reel 24 Ultrasonic motor 26,28 hole 30 Shaft 32,34 Flange 36 Variable resistor 36a Body part 36b Operation piece 37 Tension spring 38 Ratchet wheel 40 Projection part 42 Tie plate 44 Lock ring 58 Paul 66 Overhanging portion 72 Hook retainer 74 Hook 76, 78 Projection 80, 82 Hole 90 Flywheel 104 Projection 110 Piezoelectric element row 112 Annular stator

Claims (5)

[Claims] 1. A reel for winding up a seat belt, a frame supporting the reel, a motor for rotating the reel, and a lock mechanism for locking the rotation of the reel to prevent the seat belt from being pulled out. Wherein the motor is an ultrasonic motor, and the lock mechanism performs a lock operation when a phase difference between the rotation axis of the ultrasonic motor and the reel in the circumferential direction of rotation becomes equal to or greater than a predetermined angle. A seat belt retractor characterized by the following. 2. The device according to claim 1, wherein the lock mechanism comprises:
A ratchet wheel provided on the reel and having a tooth surface on an outer peripheral surface; a reel having a rear end side rotatably supported by the frame and a front end side engaging with the tooth surface of the ratchet wheel; And a pawl actuating mechanism that separates the pawl from the ratchet wheel when the phase difference is smaller than a predetermined value, and engages the pawl with the ratchet wheel when the phase difference is equal to or more than a predetermined value. A seat belt retractor comprising: a seat belt retractor; 3. The ultrasonic motor according to claim 1, wherein when the rotation speed of the reel is lower than a predetermined speed, the phase difference detected by the phase difference detection means is smaller than a predetermined angle. Control means for preventing the lock operation of the lock mechanism, and setting the phase difference to be equal to or more than a predetermined angle when the rotation speed of the reel becomes equal to or more than a predetermined speed, thereby locking the lock mechanism. A seat belt retractor characterized by the following. 4. A seat belt retractor according to claim 1, wherein said phase difference detecting means is a variable resistor provided so that an operation piece is moved by a phase difference. . 5. The vehicle according to claim 1, further comprising collision detection means for detecting a collision of the vehicle, and when the collision detection means detects a collision, power supply to the ultrasonic motor is stopped. The seat belt retractor according to claim 1, wherein the phase difference becomes equal to or more than a predetermined angle when the reel further rotates after the power supply to the ultrasonic motor is stopped, and the lock mechanism is operated.