This invention relates to a seat belt retractor of a type used as part of a seat belt occupant restraint system, particularly adapted for motor vehicle applications.
Seat belt retractors are in common use in motor vehicles around the world as part of an occupant restraint system for providing occupant protection. Seat belt retractors store belt webbing which is deployed across an occupant in the typical so-called “active” type belt system, in which the occupant manually fastens the belt. The seat belt retractor typically incorporates a torsion rewind spring which enables an internal spindle to store a spool of seat belt webbing. The retractor allows extension of the belt during fastening and retraction when it is unfastened. The basic functions of the retractor are to provide convenient storage of belt webbing, enable occupant movement when the belt is fastened, and control the extension of belt webbing upon the occurrence of a crash event.
Significant advances have been made in recent decades in the area of motor vehicle occupant restraints. In addition to passive restraints, such as inflatable air cushion restraint systems, the area of belt restraint systems has also undergone significant advancement. Two areas of advancements in retractor design are particularly noteworthy. Retractor pretensioning devices are often provided which are typically pyrotechnically actuated and forcibly wind up the belt retractor to reduce slack in the webbing upon the detection of a crash event (or prior to). By reducing the slack in the webbing by pretensioning, the belt is able to couple with the occupant early in the crash sequence to provide control of the occupant's displacement relative to the vehicle. Taking up webbing slack and tightening the belt at the initial portion of the crash sequence also enables belt loading to be managed better while restraining the occupant. Pretensioning also helps provide proper positioning of the belt webbing on the occupant's body during a crash event.
Another area of significant development in seat belt retractors is providing seat belt webbing load limiting. Early retractors had spindles which were rigidly locked, typically by an inertia sensitive device which locked the spool to the retractor frame. Upon retractor locking, loads exerted on the belt webbing would result in some stretching of the webbing and deflection of the retractor and other belt system components. However, the extension of the webbing in retractors without load limiting features was not tailored in a precise manner. Accordingly, these retractors could result in high loads applied to the occupant which can lead to less than optimal restraint performance. To improve performance, designers have developed load limiting systems for retractors. Load limiting systems typically use a torsion bar coupled between the webbing spindle and the inertial locking device which provides controlled torsional deflection in response to belt webbing loads. Twisting of the torsion bar will “soften” the restraint characteristics of the belt retractor. In yet a further refinement of belt load limiting systems, multilevel load limiting systems have been implemented. These systems may have one, two, or more sections of torsion bar or other deformable elements which can be activated in a controlled manner, depending on a number of factors. For example, it may be desirable to provide a high belt load limiting characteristic when a high severity crash is occurring, or where a large and heavy occupant is involved. On the other hand, for lower severity impacts, or for lighter weight occupants, less stiff load limiting characteristics are desired. Retractors are presently known which have a pyrotechnic device which can be fired through a controller to select between high and low load limiting conditions, depending on a variety of factors, such as those mentioned previously.
Providing retractors with increasing features has disadvantages, including the cost to provide these features, the complexity of the retractor, and the packaging size in the vehicle required for installation and operation of the retractor. Motor vehicle designers are constantly striving to reduce the mass, cost, and enhance the packaging efficiency of their products, including seat belt retractors.
In a continuous effort to enhance performance, seat belt safety system designers are seeking to increase the amount of belt pay-in capacity during pretensioning operation. Current retractor rotopretensioners provide excellent performance, but have a limitation in the amount of webbing pay-in capability. Moreover, there is a desire to increase the flexibility of the operation of a retractor during pretensioning to accommodate various types of impact scenarios and also perform well for occupants of various structures. Present retractors with pretensioning systems are generally capable of operating in a single impact condition. Although the pretensioning effect is provided following an initial impact, additional pretensioning may be desired to enhance occupant protection during a secondary impact. This is the case since slack is introduced in the system after an initial impact.
In accordance with this invention, a seat belt retractor having a dual stage pretensioning and high pay-in capacity is provided which achieves many enhancements in view of the previously noted desirable characteristics. The seat belt retractor in accordance with an embodiment of this invention includes a pair of separate rotopretensioners which are activated by firing micropyrotechnic gas generators. Preferably the rotopretensioners are positioned at opposite ends of the retractor spool and can be coupled to the spool in various manners. The high pay-in capacity of a dual rotopretensioner system will enable significant amounts of slack to be removed in a system in an impact condition by firing the rotopretensioners in a serial manner. This can be achieved without exceeding desired limits on pretensioning force. In addition, if a single rotopretensioner is fired following an initial impact, the second rotopretensioner can be activated upon the occurrence of a secondary impact or to provide more webbing pay-in in a single impact event. Another capability provided by the dual stage pretensioning retractor in accordance with this invention is the ability to establish load limiting functions based on the activation of the pretensioner. Thus, when one pretensioner is fired, a certain load limiting characteristic can be provided, whereas if only the second pretensioner is fired, a different load limiting characteristic can be provided. This enables optimization for various impact severities, and occupant types.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which the present invention relates from the subsequent description of the preferred embodiment and the appended claims, taken in conjunction with the accompanying drawings.
Frame assembly 12 includes frame 18 which is formed from sheet metal stock and bent in a generally “U” shape and a pretensioner cover 19 that is connected to frame 18 by fasteners. Frame 18 includes means for mounting the retractor to a motor vehicle structure, principally through tab 21 with a bore for a threaded fastener or other fastening means (not shown). Frame 18 forms mounting surfaces for remaining components of retractor 10. Torsion spring cap 20 is affixed to one end of frame 18 and includes an internal torsion spring (not shown) which exerts a torsional compliant force onto spindle assembly 14 for rewinding the belt webbing 11. Mechanism cover 19 is attached to frame 18 and is typically molded of a plastic material. Tread head assembly 22 is mounted to the opposite “leg” of frame 18. Tread head assembly 22 has internal inertia sensitive components (not shown) of conventional design which cause locking of retractor 10 in response to vehicle deceleration above a predetermined magnitude. This operation of tread head assembly 22 is in accordance with well known prior art principles, and is not described in detail here. Tread head assembly 22 operates to provide an emergency locking retractor (ELR) function. This allows webbing 11 to be freely paid out from retractor 10, allowing movement of the occupant and extension of the seat belt webbing except when deceleration forces above a predetermined magnitude are acting on the retractor. The inertia sensors of the seat belt retractor 10 will cause tread head assembly 22 to lock, either in response to acceleration forces exceeding a given magnitude and direction acting on the retractor, as well as in conditions where the motor vehicle is in an inclined condition. In these cases, tread head assembly 22 locks spindle assembly 14 to frame 18. Frame assembly 12 further includes a number of additional elements illustrated such as protective caps and other elements not directly related to the features of the present invention.
Now with specific reference to
Installed coaxially within hollow interior cavity 30 of spindle 26, is a pair of elongated torsion bars, including high level torsion bar 42, and a low level torsion bar 44. Bar 42 has an enlarged head 46 which is splined to engage with spindled spindle bore 36. The opposite end of torsion bar 42 forms an outer perimeter rim 48 which has external splines as well as a splined end bore 50 which receives and meshes with a splined headed end 52 of low level torsion bar 44. Torsion bar 44 further forms splined end 54. End 54 is splined into an internal splined bore 62 of tread head hub 24. Torque transfer tube 56 has an open end 57 with internal splines which engage and mesh with torsion bar rim 48 and an opposite end 59 having external splines 60.
Torque transfer tube end 59 is mounted over hub tube projection 63. This connection is preferably not splined and allows some relative rotation between tread head hub 24 and torque tube 56 during load limiting webbing extension. A degressive bending element 64 is interlocked through bearing disc 40 to torque tube 56 and is coupled to spindle 26 by degressive insert 66.
In some operating circumstances, some relative rotation between torque tube 56 and tread head hub 24 is desirable. However, it may be further desirable to limit such angular rotation until a torque level of given magnitude is exerted between these two components. For example, shear pins (not shown) could be installed between tread head hub 24 and torque tube 56 which would shear when a predetermined torque is applied between them.
As mentioned previously, retractor 10 features a pair of pretensioner assemblies, including first pretensioner assembly 16 and second pretensioner assembly 17. First pretensioner assembly 16 is shown at the left hand side of retractor 10 as illustrated in
Pretensioner tube 76 guides balls 80 to follow a generally circular path when they are driven to move through the pretensioner tube such that they engage with pinion ball grooves 74 for forcibly rotating spindle 26 in a known manner. A cavity 84 is positioned to act as a ball trap, in which balls 80, after traveling the path formed by pretensioner tube 76, are held. Ball separators 86 and 88 are provided to guide balls 80 so that they engage with pinion 68 in a desired, tangent manner, in accordance with conventional rotopretensioner design principles. Upon firing of microgas generator 78, the ball chain formed by balls 80 is driven forcibly through tube 76 until they interact with pinion 68 which causes the pinion and accordingly spindle 26 to rotate in a direction to pretension the associated seat belt webbing. Other types of engagement elements could replace balls 80 such as chain type elements which would drive the pinion when the unit is activated.
Presently designed rotopretensioner units often have provisions for locking rotation of the spindle after actuation, which locking action can be used to engage operation of load limiting elements or to otherwise act as a lock to restrict extraction of webbing from the retractor. In the present invention in which a pair of pretensioning units 16 and 17 are employed, it is desirable that at least one of the pretensioning units does not have a locking function, in other words, acting in an “off clutch” manner (not locked). In the described embodiment, pretensioner 16 does not lock, whereas pretensioner 17 locks after actuation (the reverse characteristic could be provided if desired). This feature means that the rotation of spindle 26 will not be controlled by pretensioning unit 16 after it is activated (gas generator 78 is fired). A further discussion of the operation of pretensioning unit 16 will be provided in the following sections.
Second pretensioning unit 17 is best shown with reference to
Various operational modes for retractor 10 are provided employing the features of the present invention. With reference to
If second pretensioner 17 is not fired, a locking of retractor 10 occurs through the action of tread head assembly 22 resulting from inertial forces acting on the retractor. The loading conditions acting through retractor 10 are illustrated in
Now with reference to
Bending element 64 is fixed to torque tube 56 through bearing disc 40 and degressive insert 66 fits in a pocket 101 in the spindle 26. In the event of activation of high level load limiting, a degressive decrease in belt loading may be provided. Initially, element 64 and insert 66 act with high level torsion bar 42 to control belt webbing loads, since they both couple spindle 26 to pinion 90. If, in a high load limiting mode, deflection of the spool (or loads) exceeds a predetermined level, bending element 64 will be pulled through from bending of insert 66, whereupon the loads are transferred only by high level torsion bar 42, to provide a degressive operation to a lower load limiting (lower than when both elements are acting).
A number of different operating conditions are possible using retractor 10. The action of controller 85 selects these operation conditions. The range of possibilities include at least the following:
In the last mentioned sequence when second pretensioner 17 is fired during or after low load limiting, the load limiting level goes from low to high, as shown in
Retractor 10 provides, in addition to great flexibility for dealing with occupant and impact types, also the ability to adapt retractor 10 to varying automotive safety requirements, vehicle characteristics, and regulations in jurisdictions throughout the world. Moreover, automotive manufacturers often have their own performance specifications which a single retractor design may not be able to accommodate. Retractor 10 provides a high pretensioning pay-in capacity to remove excessive webbing slack without increasing pretensioning force beyond acceptable levels. The system further provides different power levels to adjust belt occupant coupling. As also described, the system can accommodate multiple impacts by serially activating pretensioners. Also, based on which of pretensioners 16 or 17 is activated, a high or low load level load limiting characteristic can be provided, depending on accident severity and occupant type.
While the above description constitutes the preferred embodiment of the present invention, it will be appreciated that the invention is susceptible to modification, variation, and change without departing from the proper scope and fair meaning of the accompanying claims.