Patent Application
20120006925
The present invention relates generally to seatbelt restraint devices for restraining an occupant of a vehicle, and more particularly, to devices for pretensioning a seatbelt.
Seatbelt restraint systems for restraining an occupant in a vehicle seat play an important role in reducing occupant injury in vehicle crash situations. Seatbelt restraint systems of the conventional so-called “3-point” variety commonly have a lap belt section extending across the seat occupant's pelvis and a shoulder belt section crossing the upper torso, which are fastened together or are formed by a continuous length of seatbelt webbing. The lap and shoulder belt sections are connected to the vehicle structure by anchorages. A belt retractor is typically provided to store belt webbing and may further act to manage belt tension loads in a crash situation. Seatbelt restraint systems which are manually deployed by the occupant (so-called “active” types) also typically include a buckle attached to the vehicle body structure by an anchorage. A latch plate attached to the belt webbing is received by the buckle to allow the belt system to be fastened for enabling restraint, and unfastened to allow entrance and egress from the vehicle. Seatbelt systems, when deployed, effectively restrain the occupant during a collision.
OEM vehicle manufacturers often provide seatbelt restraint systems with pretensioning devices, which tension the seatbelt either prior to impact of the vehicle (also known as a “pre-pretensioner”) or at an early stage of a sensed impact to enhance occupant restraint performance. The pretensioner takes out slack in the webbing and permits the belt restraint system to couple with the occupant early in the crash sequence. One type of pretensioner acts on the webbing retractor to tension the belt. Various designs of retractor pretensioners presently exist, including a type known as a roto-pretensioner that incorporates a gas generator for generating a pyrotechnic charge. Examples of such roto-pretensioners are described in U.S. Pat. No. 5,881,962 and U.S. patent application Ser. No. 11/115,583, which are commonly owned by the assignee of the present application and are hereby incorporated by reference in their entirety for all purposes. Generally, ignition of the pyrotechnic charge or other combustible material creates gas pressure in a chamber having a piston to impart motion upon a driving element such as a piston, rack, or series of balls disposed in a pretensioner tube, which engage with and wind a retractor spool sprocket to retract the webbing.
One issue with pretensioners utilizing gas generators is efficient utilization of the gas volume produced by the generator. For instance, a significant volume of the gas produced by the gas generator can leak through the pretensioner tube or around the piston or balls, thereby decreasing the pressure and force available for pretensioning the seat belt. Therefore, manufacturers use gas generators having sufficient output to compensate for gas leakages.
The present invention provides a pretensioner assembly that substantially reduces gas leakages within a pretensioner tube. The pretensioner assembly includes a pretensioner tube in communication with a gas generator. A driving element in the form of a piston having a generally cylindrical outer surface is disposed within the tube. The piston is operable to impart motion onto driving a element such as a plurality of balls loaded in the tube (or a “ball string”) in reaction to pressurized gas discharged from the gas generator. The piston includes a proximate end spaced from the gas generator so as to define a gas chamber therebetween. The piston further includes a distal end facing the plurality of balls. Portions of the proximate end and the distal end are indented inward to form concave depressions at each end.
The concave depressions include flexible rims that act as pressure-activated seals. More specifically, the flexible rim at the proximate end is configured to expand circumferentially outward in response to forces exerted by the pressurized gas from the gas generator, and the flexible rim at the distal end is configured to expand circumferentially outward due to the application of backpressure from the plurality of balls. The expansion of the flexible rims at the proximate and distal ends create a tight seal between the piston and an inner peripheral wall of the tube, thereby reducing gas leakage beyond the distal end of the piston.
Further objects, features, and advantages of the invention will become apparent to those skilled in the art to which the present invention relates from consideration of the following description and the appended claims, taken in conjunction with the accompanied drawings.
The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.
It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.
The following description is merely exemplary in nature and is not intended to limit the present disclosure or its application or uses.
Referring now to the drawings,
The seat belt webbing 14 is able to pay-out from a retractor 32 assembly (shown in
Now with reference to
As best shown in
During normal operation of the vehicle, the retractor assembly 32 allows pay-out of seat belt webbing 14 to give the occupant a certain amount of freedom of movement. However, if an impact or a potential impact situation is detected, the retractor assembly 32 is locked to prevent pay-out and to secure the occupant in the seat 10. For example, if the vehicle decelerates at a predetermined rate or if the brakes are actuated with a predetermined force, then the retractor assembly 32 is locked. Due in part to the free pay-out of the seat belt webbing 14, the seat belt assembly 12 often develops slack during normal use.
The retractor assembly 32 further incorporates a pretensioner system 44 (shown in
The pretensioner system 44 includes a pretensioner tube 52 in communication with the gas generator 36. The gas generator 36 is used to provide expanding gas in response to a firing signal. As is known in the art, for example, the vehicle includes a sensor sending a signal indicative of an emergency event such as an impact event, crash, or rollover. The vehicle sensor may be a specific impact sensor, or may be a traditional vehicle sensor (e.g. a longitudinal or lateral acceleration sensor) or otherwise part of a control system having a suite of multiple sensors. Any other impact sensor that is or will be known to those skilled in the art may also be readily employed in conjunction with the seat belt assembly 12 of present invention. An electronic control unit such as a central processing unit (CPU) or other controller receives a signal and controls the seat belt assembly 12 to respond by tightening the seatbelt of the vehicle (e.g. via activation of a pretensioner).
Referring now to
As will be discussed in greater detail below, the piston 64 defines a generally elastic structure, and may be composed of various materials known in the art, such as any suitable plastic or polymer (e.g., polyester, rubber, thermoplastic, or other elastic or deformable material). Moreover, the piston 64 may be die cast, forged, or molded from metal, plastic, or other suitable material. In one aspect of the present invention, the piston 64 may be formed using a two-cavity injection molding process.
In operation, the gas generator 36 produces expanding gas that pressurizes the gas chamber 54, thereby enabling the piston 64 to forcibly drive the balls 56 along the actuation path 60. As the balls 56 are driven through tube 52, they engage a spool sprocket assembly 50 that is rotatable about an axis 46. The spool sprocket assembly 50 forms bearing seats 58 that are semi-spherical depressions with an appropriate shape and size to receive the balls 56. Engagement of the balls 56 with the spool sprocket assembly 50 as they are driven by expanding gas in the direction of arrow 60 causes the spool 40 to rotate, which in turn provides pretensioning. Of course, it should be understood that while the pretensioner system 44 employs balls 56 for rotating the spool 40, the pretensioner system 44 may use any suitable driving element known in the art.
Referring now to
In addition, backpressure generated from the balls 56 causes the flexible rim 76 formed by the concave depression 72 at the distal end 68 of the piston 64 to expand circumferentially outward. The expansion of the rims 74 and 76 at the proximal and distal ends 66 and 68 of the piston 64 provide a tightened seal between the outer cylindrical surface of the piston 64 and the inner peripheral wall 78 of the pretensioner tube 52. Accordingly, the piston 64 of the present invention is operable to retain a high seal pressure as well as maintain residual gas pressure within the tube 52.
It should be understood that while the piston 64 includes a generally cylindrical exterior, the piston 64 may include a variety of shapes. For instance, the piston 64 may be shaped so that contact between certain areas of the piston 64 and the inner peripheral wall 78 of the tube is maximized upon expansion of the piston. As shown in
Alternatively, the piston 64 may include a generally flat outer surface having discrete seals 80 formed at specific areas such as the center and outer ends of the piston 64, as shown in
In addition, while the concave depressions 70 and 72 are shown in the drawings as having a semi-spherical shape, it is to be understood that the concave depressions 70 and 72 may be of any suitable shape that enables the rims 74 and 76 to expand outward and form seals with the piston 64. Furthermore, since both rims 74 and 76 are operable to form seals, the piston 64 may be shaped such that only one of the rims 74 or 76 is provided. That is, either the proximate end 66 or the distal end 68 may be indented inward to form a single concave depression 70 or 72 having a rim 74 or 76.
As a person skilled in the art will readily appreciate, the above description is meant as an illustration of the implementation of the principles of this invention. This description is not intended to limit the scope or application of this invention in that the invention is susceptible to modification, variation, and change, without departing from the spirit of this invention as defined in the following claims.
