Winding – tensioning – or guiding – Reeling device – With particular drive
Reexamination Certificate
2002-06-24
2004-12-07
Walsh, Donald P. (Department: 3653)
Winding, tensioning, or guiding
Reeling device
With particular drive
C180S268000, C280S825000
Reexamination Certificate
active
06827308
ABSTRACT:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
The present invention relates to a controlling method of a seat belt retractor, i.e. motorized seat belt retractor, which can change its operating condition to correspond to the state of an occupant wearing a seat belt or to external signals.
In a seat belt retractor provided in an automobile, it is preferable to retract an excess amount of a seat belt after the seat belt is pulled and a tongue is engaged with a buckle device, without applying too much stress to the chest or other portions of an occupant normally wearing the seat belt.
Normally used for winding up a seat belt in a seat belt retractor is a biasing force of a single return spring. When a spring providing a small biasing force is employed in order to reduce stress applied to the chest of an occupant, the force for winding or retracting the seat belt becomes weak, thus lowering its operation and its accommodation to the retracted state.
To the contrary, when a spring for providing a large biasing force is employed in order to provide an enough winding force for its retraction, the stress to be applied to the chest of the occupant normally wearing the seat belt is increased.
Since a single return spring is employed, a conventional seat belt retractor has a problem that the biasing force of the return spring increases as the amount of withdrawal of the webbing (hereinafter, the term “webbing” is used for referring to the belt itself in this specification) is increased because the return spring is repeatedly wound.
As one of means for solving the problem with regard to the winding of a webbing caused by using a single return spring, the applicant has developed a tension reducing mechanism for reducing the retraction force, which comprises two rope pulleys of truncated cone shape with a helical guide groove (see Japanese Patent No. 2711428).
On the other hand, the applicant also has developed a seat belt retractor in which a tension control for a seat belt is performed by a built-in electric motor to improve comfortableness as one of functions when an occupant normally wears, and to correspond to a distance from another vehicle running in front of or behind its own vehicle (see Japanese Unexamined Patent Publication No. H09-132113).
In the seat belt retractor disclosed in the aforementioned publication No. H09-132113, an ultrasonic motor is employed as a driving unit for the tension control and a spring mechanism is provided as a main winding mechanism. The motor is employed for controlling the tension on the seat belt when the occupant wears the seat belt, and for controlling the winding and unwinding of the seat belt to correspond to external signals inputted during running of the vehicle. Therefore, it is required to rotate the motor in reverse. This makes the control circuit complex. Since the operation of winding up the seat belt is performed by two circuits, there is also a problem that it is hard to smoothly switch the operation of winding up the seat belt according to the inputted external signals.
When the external signals from sensors mounted on the vehicle are set to function as the trigger of the motor, a speed-reduction gear to be driven by the motor employed in the seat belt retractor can not cope with a wide range of a winding mode because the reduction range allowed by the speed-reduction gear is limited.
Therefore, it is an object of the present invention to solve the problems of the prior art and to provide a seat belt retractor in which a seat belt can be wound by only a motor with a simple control circuit and a driving mechanism, and the winding mode can be set widely to correspond to external signals inputted when an occupant wears the seat belt and a vehicle runs, and to provide a control method for the seat belt retractor.
Further objects and advantages of the invention will be apparent from the following description of the invention.
SUMMARY OF THE INVENTION
To solve the aforementioned problems, the present invention provides a seat belt retractor comprising: a base frame; a spool journalled at a spool shaft to the base frame; a speed-reduction mechanism; and a motor for rotating the spool via the speed-reduction mechanism for winding up a webbing onto the outer periphery of the spool. The speed-reduction mechanism has two transmission trains with different reduction gear ratios, switching means for switching the transmission trains to one of the trains corresponding to a driving signal obtained from external units, and resistant torque means having a preset value so that a transmission element common to the two trains transmits rotation of the motor when the torque of the rotation is smaller than the preset value.
The driving signal is preferably set according to a state signal obtained by movement of an occupant wearing the seat belt and an external signal obtained from detecting means installed in a vehicle during the running of the vehicle.
It is preferable that when the state signal is received, the rotational torque is reduced at a small reduction gear ratio to be smaller than the preset value of the resistant torque means, and the spool shaft is rotated with the reduced rotational torque for winding up the webbing.
It is preferable that when the external signal is received, the switching means switches the transmission trains so that the rotational torque is increased at a large reduction gear ratio to exceed the preset value of the resistant torque means to wind the webbing.
It is preferable in the above that the resistant torque means is a slip mechanism comprising a viscosity resistant element disposed on the trains of the speed-reduction mechanism.
It is also preferable that the switching between the trains is achieved by actuating the switching means according to the driving signal when the external signal is received and securing a part of the transmission element disposed in the speed-reduction mechanism.
It is preferable that the switching means comprises a pawl mechanism which engages one of ratchet teeth formed on the outer periphery of an internal gear in a planetary gear unit to stop the rotation of the internal gear.
It is also preferable that the switching means comprises a pawl mechanism having two pawls journalled by shafts, which cooperate to engage ratchet teeth of the internal gear to stop rotation of the internal gear.
In this case, it is preferable that the two pawls are a first pawl and a second pawl, and the first pawl pivots about the shaft by excitation of a solenoid to engage one of the ratchet teeth and, after that, the first pawl makes the second pawl to engage another of the ratchet teeth.
It is preferable that a spring connected to the first pawl biases the first pawl after cancelling the excitation of the solenoid with the result that the second pawl disengages from the ratchet teeth.
It is preferable that the rotation of the spool is reduced through a reduction gear train, and the spool shaft is provided with a spool rotation detecting unit for detecting a rotational direction and a stopping state of the spool.
It is preferable that the withdrawal of the webbing is detected by the start of rotation of the spool and acts as a trigger for turning ON a power source of a control circuit for driving the motor.
The present invention also provides, as another invention, a seat belt retractor comprising a base frame, a spool journalled at a spool shaft to the base frame, around which a webbing is wound, a return spring for winding up the webbing by its return force, and a motor with a speed-reduction mechanism for switching the winding of the webbing, wherein the speed-reduction mechanism has a transmission train with a predetermined reduction gear ratio and switching means for connecting the transmission train to the spool shaft corresponding to a driving signal obtained from an external unit.
The driving signal is preferably set according to a state signal obtained by movement of an occupant wearing the seat belt and/or an external signal obtained from detecting means installed in the vehicle during running
Fujii Hiroaki
Fujita Hitoshi
Furukawa Koichi
Tanaka Koji
Beauchaine Mark J.
Kanesaka Manabu
Takata Corporation
Walsh Donald P.
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