Background and prior art Automotive vehicles are fitted with seat belts. The seat belt assembly is a critical safety item because in the event of collision, the seat belt assembly should restrain the occupant. In addition, it should be able to absorb and withstand the force of impact, without any major deformation or failure.

A secured seatbelt in motor vehicle prevents the occupant from hitting the windshield or steering wheel, greatly reducing the potential for fatal and/or severe injuries.

Seat belts are equipped with webbing, designed to stretch to a desired level to restrain the occupant of the seat, on sudden impact of a vehicle. The inertia locking mechanism of the retractor of a seat belt assembly locks the webbing if the webbing is pulled out suddenly. The webbing of a seat belt is designed to elongate when loaded so that the vehicle impact is translated to the restraint wearer at lower loads and over a longer period of time.

Mainly, the rigid components like sash guide, anchor plate and retractor which are attached to the vehicle body play an important role in load transfer.

The sash guide is provided on the inner body of a vehicle in proximity to the seat assembly to facilitate the passage of webbing through the sash guide and further to permit the webbing to pivot freely.

A conventional seat belt comprises a sash guide that is made of hardened medium carbon steel of about 3mm thick material. The major problem with regard to the sash guide is poor consistency after the heat treatment, wherein the process of heat treatment is a critical step in its development.

A conventional seat belt also comprises an anchor plate with low carbon steel with 4 mm thickness to provide optimum load bearing capacity. The existing sash guide material is hardened medium carbon steel sheet metal subjected to heat treatment to about 42-45 HRC (Rockwell Hardness Scale C) to accomplish tensile load requirement. The process of heat treatment is cumbersome and time consuming.

In order to achieve 42-45 HRC, the component will have to be tempered over and again until the required product is obtained. In the event of increase in the HRC value, there will be a transition in the solid lattice structure of the material giving way to brittleness, which lead to predetermined failure of the product. On the other hand, if the value of HRC is decreased the product starts yielding much before the yield point resulting again in the failure of the product.

On stress analysis of sash guide and anchor plate the following stress points were observed (a) bolt hole; and (b) webbing slot hole.

In view of the above stress analysis, a need was felt to develop a sash guide and anchor plate having fortifications at the desired places wherever the stress points are observed and further to enhance the overall tensile strength of the products. Further, starting materials used for manufacturing the sash guide and anchor plate of the present invention is selected from non-hardened material steel on reduced thickness without compromising the tensile strength of the product.

Objects of the invention The primary object of the present invention is to provide a seat belt device as an occupant restraint system comprising a double layered sash guide and an anchor plate of reduced thickness.

An object of the present invention is to provide a sash guide of reduced thickness starting material but retaining the optimum tensile strength and load characteristics.

Another object of the present invention is to provide an anchor plate that can withstand a high tensile load while in operation even when using a starting material of reduced thickness.

Yet another object of the present invention is to provide sash guide and anchor plate, which are non-heat treated.

Still another object of the present invention is to develop a cost effective sash guide and anchor plate.

Summary of the invention The present invention provides a seat belt device comprising a double layered sash guide having non-hardened steel as a starting material and an anchor plate of reduced thickness. The present invention also provides a sash guide with reduced thickness but retaining the optimum tensile strength and load characteristics by incorporating bolt and webbing slot embossing. Further, the anchor plate of the present invention can withstand a high tensile load while in operation even while using a starting material of reduced thickness. The sash guide and anchor plate of the present invention are non-hardened wherein no heat treatment process is adopted.

Brief description of the accompanying drawings Fig 1 depicts an exploded view of the sash guide assembly.

Fig la depicts a complete seat belt assembly Fig 2 is an exploded view of the anchor plate assembly.

Fig 3 depicts side and front views of a double layered sash guide having primary and secondary base plates.

Fig 4 provides both front and side views of the sash guide to depict double layered sash guide and further to show embossed webbing and bolt slots.

Fig 5 provides both front and side view of an anchor plate of reduced thickness with embossed bolt and webbing slots.

Detailed description of the invention Initially referring to Fig la, wherein a seat belt assembly is disclosed, a seat belt device generally comprises a retractor to provide an'inertia'locking mechanism, by locking the seat belt in the event of sudden impact. As a part of seat belt device, seat belts are made using webbing 2 designed to elongate to provide restraint to the wearer of seat belts at lower loads and over a longer period of time. The sash guide 1 facilitates the webbing 2 to pivot freely and is fastened to the vehicle structure. The tongue and buckle assemblies are used to latch the occupant safely every time the seat belt is used. The seat belts are designed to bear upon the skeletal structure of the body, and worn across the front of pelvis, chest and shoulders. An anchor plate 9 is disposed in the proximity with the retractor to receive webbing. The webbing 2 as received from the sash guide 1 and the anchor plate 9 culminates in a tongue for easy fitment into a buckle whenever the seat belt is used by a user.

Accordingly, the present invention provides a seat belt assembly comprising a sash guide and an anchor plate for restraining occupants in automobiles on sudden impact. Now initially referring to Figures 1-5, wherein a sash guide 1 is normally positioned at or near the roof or supporting pillar positioned just rearward of the occupants. The webbing of the seatbelt 2 is fed through this sash guide 1 from the retractor (not shown in these figures) to the seat belt's tongue (not shown in this figure) and to the anchor plate 9 which will be fastened to the lower part of pillar or floor of the vehicle body and tongue in turn locked to the buckle (not shown in this figure) which is mounted other side of the seat belt system. This routing of belt called 3-point seat belt which restrain the shoulder and lap portion of the occupant. This sash guide 1 is used to both to properly position the shoulder belt across the occupant and to guide the passage of the belt during extraction and retraction.

A seat belt device with a seat belt having a double layered sash guide 1 supported by an anchor plate 9, to provide a restraint to the occupant of seat of a vehicle in the event of a sudden impact. The double layered sash guide 1 is mounted on a bolt 4 by means of an embossed bolt slot 15 to pivot freely. The bolt 4 is suspended to the lateral inner surface of a vehicle in proximity to the upper area of the seatbelt assembly. Now specifically referring to Fig 3 the sash guide having a secondary base plate 10 is sheared out of a sheet made of non-hardened steel, preferably a micro alloy steel of reduced thickness of about 2-2.5 mm. A slot 11 is carved out on the secondary base plate 10 to permit an unhindered passage of the webbing 2 drawn from the retractor assembly (not shown in this Figure). A primary base plate 12 is sheared out of a sheet made of non-hardened steel, preferably a micro alloy steel of thickness of about 2-2.5 mm and a webbing slot 13, which is embossed, is formed in the webbing region of the primary base plate 12 similar to that of secondary base plate 10. Now turning to Fig 4, the primary base plate 12 is curled at one end to act as a locking means for the secondary base plate 10 which is molded on to the primary base plate 12. The secondary base plate 10 mounted on the primary base plate 12 forms an additional layer in surrounding region of webbing slot 13 to provide an additional tensile strength to the sash guide. A plastic over molding 19 (Fig 4) is done in the web slots 11 & 13 regions to provide abrasion free and smooth flow of webbing through the sash guide. The primary base plate 12 is further extended to provide an area for an embossed bolt slot 15 (Fig 3), which provides a passage for the bolt 4 to pass through. The embossing of the bolt slot 15 is done on the side of contact with bolt 4 to withstand the tear strength acting on the sash guide 1 while in use. Now again referring back to Fig 1, an anti rattle bush 5 having a circular passage and is peripherally disposed in the bolt slot 15 through which the bolt 4 passes and further to provide a swiveling effect to the sash guide 1, when the sash guide 1 is in use. A spacer 6 is disposed on the opposite side of the bolt slot 15 along with a set of spring washer 7 and transport washers 8 to provide a fitting arrangement of the sash guide 1 with-that of bolt 4. A sash guide cap 3 is disposed on the side of the bolt head to cover the bolt 4 by means of a pair of slots 14.

The sash guide 1 of the present invention is developed by subjecting a metal sheet selected from low carbon micro alloyed steel of reduced thickness of about 2.5 mm to shearing for converting the metal sheet into desired dimensions to form a secondary base plate 10 for the sash guide 1. Further, a webbing slot 11 is pierced on the secondary base plate 10. A primary base plate 12 is sheared to the desired shape and dimensions from a metal sheet having low carbon alloyed steel of reduced thickness of about 2 to 2.5 mm and a corresponding embossed webbing slot 13 is extruded. An embossed bolt hole 15 is extruded to permit the passage of bolt 4 for fitment to the structure of a vehicle. The secondary base plate 10 is mounted on the primary base plate 12 and locked by means of curvature 17 and bent 18 to avoid webbing of the seat belt rubbing against the body of the vehicle and molded together to form a double layered webbing area in the region of webbing slots 11 and 13. The molded primary and secondary base plates 10 and 12 are further over molded with a plastic material in the area of webbing slots 11 and 13. Further ear shaped grooves 28 are provided on either ends of the webbing slots to provide an unhindered flow of the webbing of the seat belt.

Now by referring to Figure 5 the webbing of the seat belt 2 is allowed to pass through the webbing slot of the sash guide 1 (not shown in this figure) and the webbing is further extended to the assembly where an anchor plate 9 is mounted on the bolt 23. The anchor plate is manufactured from a starting material of non- hardened steel of thickness of about 2-2. 5mm. An embossed bolt slot 20 is disposed on one end of the anchor plate 9 and an embossed webbing slot 21 is disposed on the other end and the anchor plate is suitably bent 22 to provide an unobstructed webbing path. The anchor plate 9 further having a pair of embossed slots 20 and 21 one each for allowing the passage of bolt 23 to pass through and the other for receiving the webbing 2 from sash guide 1. An anti rattle bush 24 having a circular passage and is peripherally disposed in the bolt slot 20 through which the bolt 23 passes and further to provide a swiveling effect to the anchor plate 9, while the anchor plate 9 is in use.

A spacer 25 is disposed on the other side of the bolt slot 20 along with a set of a spring washer 26 and a transport washer 27 to provide a fitting arrangement of the anchor plate 9 with bolt 23.

In the event of impact caused by apparently by a collision or due to any other reason occupant will be restrained by seat belt, in conjunction with sash guide 1, anchor plate 9, and the retractor, (not shown in the figures) which anchors the webbing of the seat belt in holding the occupant to the vehicle seat.

The invention is further illustrated in the form of following examples. However, the following examples should not be construed as limiting the scope of the invention.

Example 1 A Sash Guide with a material composition (non-hardened micro alloyed steel) as provided in the below table are tried and the properties thus achieved are tabulated. Mechanical Properties Composition (wt %) Ultimate tensile strength (N/mm2) 540-% C % Nb % Ti % Mn % S % P % A1 % Si 690 Elongation (%) 18-25 0. 05- 0. 03- 0. 096- 0. 83- 0. 001 0. 012- 0. 046 0.24- 012 0. 09 0. 22 1. 70-0. 30 0. 050 (Max) 0. 50 Example 2 An Anchor plate with a material composition (non-hardened plain carbon steel) as provided in the below table are tried and the properties thus achieved are tabulated. Mechanical Properties Composition (wt%) Ultimate tensile strength 420-510 % Mn % S % P % Al % Si C% Elongation (%) 23-31 0. 226- 0. 012- 0. 012- 0. 046 0.007 0.039- 0.5 0.050 0. 050 (Max) (Max) 0. 1 It is also understood here that the sash guide can also be made of above-stated non- hardened plain carbon steel as provided in Example 2.

Advantages 1. The sash guide and anchor plate of the present invention are free from heat treatment.

2. Consistency of the tensile load is achieved for the sash guide and anchor plate.

3. The raw material used for the sash guide and anchor plate is cheaper.

4. The sash guide and anchor plate of the present invention meets the test requirements of International Regulation Standards.

5. The thickness of the anchor plate of the present invention is lesser than the conventional anchor plates.