WO1999065740A1

WO1999065740A1 - Unitary plastic steering wheel with air bag

Info

Publication number: WO1999065740A1
Application number: PCT/US1999/013192
Authority: WO
Inventors: Larry J. Winget
Original assignee: Winget Larry J
Priority date: 1998-06-16
Filing date: 1999-06-10
Publication date: 1999-12-23
Also published as: AU4232899A

Abstract

A composite steering wheel and air bag cover (10) includes a one-piece plastic body (14) including a circular first rim portion (20) and an air bag cover (18) and a one-piece, plastic skeletal frame structure (28). The structure (20) is formed by either co-injecting the frame structure (28) with the plastic body (20) or by first introducing pressurized gas and then injecting the more rigid plastic of the frame structure (28).

Description

UNITARY PLASΗC STEERING WHEEL WITH AIR BAG

Technical Field

This invention relates to steering wheels and air bag cover assemblies and, in particular, to plastic steering wheels and air bag cover assemblies.

Background Art

Supplemental occupant restraint systems for motor vehicles (i.e., air bags) typically require covers which allow an air bag to exit the air bag cover when deployed. One type of air bag cover includes a front panel which has a predetermined tear seam design formed therein to allow the air bag to exit the air bag cover when deployed.

Not only must the air bag cover perform the utilitarian function of breaking apart along its predetermined tear seam design, but it should also match the vehicle interior decor and trim materials such as the instrument panel, seats, door panels, steering wheel and posts.

Also, not only must the air bag cover allow the air bag to exit the air bag cover when deployed, but also the air bag cover must stay together to the extent that it does not break apart so as to present projectile(s) which may injure an occupant of the motor vehicle. One-piece steering wheel assemblies typically have an inner metal core or frame structure to support an outer plastic layer. However, such steering wheels are costly and difficult to make.

The U.S. patent to Loren 5,447,762 discloses a plastic garbage can having a hollow rim formed by pressurized fluid.

The U.S. patent to Eckardt et al. 5,047,183 discloses a method and system for manufacturing hollow plastic articles from one or more plastics by combining co-injection with gas-assist injection molding.

The U.S. patent to Goetz et al. , 3,984,126 discloses a unitary steering wheel and air bag cover assembly made from plastic.

The U.S. patent to Onishi et al., 5,358,273 also discloses a unitary steering wheel and air bag cover assembly.

The U.S. patent to Cuevas, 5,277,442 discloses an air bag system including a vehicle steering wheel having a structural frame which includes a integral retainer. The system also includes a cover which, together with the retainer forms a container.

The U.S. patent to Chen et al., 5,228,362 discloses a vehicle steering wheel having an armature which defines a structural circular steering wheel.

The U.S. patents to Margetak et al. 5,615,910, Humphreys et al.,

5,348,340, Breed et al., 5,419,585, and Proos et al. , 5,335,935 all disclose conventional steering wheel assemblies having an air bag subassembly. The U.S. patent to Williams 5,470,099 discloses continuous molded material over a diecast magnesium insert on the driver side to provide a continuous molded appearance.

The U.S. patent to Cherry 5,536,037 discloses a thermoplastic material of a second layer which melts and chemically bonds with a thermoplastic material used in a first layer so that a physical bond is formed between an inner interconnecting portion and a projecting portion to hold the second layer to the first layer. This interconnection is used to hold a deployment door along a U- shaped brake line.

The U.S. patent to Hirsch 4,849, 145 discloses a process for forming an article having a flexible layer and a layer of synthetic resin.

The U.S. patent to Jogan et al. 5,429,786 discloses a process for forming an article using a pair of mold halves which define a pair of adjacent cavity sections into which first and second thermoplastic resins are injected, respectively.

Japanese patent document 6-206548 discloses a steering wheel having a synthetic resin formed over a metal frame structure which is subsequently melted to remove it from the resulting steering wheel.

The U.S. patent to Kobayashi 4,811 ,472 discloses a steering wheel having a metal core. Summary of the Invention

It is an object of the present invention to provide a unitary composite steering wheel and air bag cover assembly which is relatively easy to make and which includes a one-piece soft plastic body including a circular first rim portion which encloses a circular second rim portion of a more rigid plastic, skeletal frame structure, thereby eliminating the need for a metal frame structure.

Another object of the present invention is to provide a unitary composite steering wheel and air bag cover assembly wherein an air bag cover portion perfectly matches a rim of the assembly in color and other physical characteristics yet eliminates the need for a more costly metal, skeletal frame structure.

In carrying out the above objects and other objects of the present invention, a unitary composite steering wheel and air bag cover assembly is provided. The assembly cover includes a one-piece, plastic body including a circular first rim portion having a perimeter and an air bag cover portion with a predetermined tear seam design formed therein. The air bag cover portion is adapted to overlie an inflatable air bag system. The assembly also includes a one- piece plastic skeletal frame structure including a circular second rim portion enclosed within the first rim portion. The frame structure has an aperture aligned with the air bag cover portion to allow an air bag of the air bag system to exit the air bag cover portion when deployed.

Preferably, the plastic of the frame structure is more rigid than the plastic of the body and the plastic of the body is softer than the plastic of the frame structure . The plastic of the frame structure may be glass-filled nylon whereas the plastic of the body may be TPO, TPU, DYM or santoprene. The two different plastics may be co-injected or the plastic of the body may be utilized in a gas-assist injection molding process to hollow out the body and then the more rigid plastic of the frame structure can be injected into the hollowed-out body.

The above objects and other objects , features , and advantages of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.

Brief Description of the Drawings

FIGURE 1 is a perspective view showing a unitary composite assembly steering wheel and air bag cover assembly constructed in accordance with the present invention;

FIGURE 2 is an exploded view of the assembly with the front and rear sections of a circular first rim portion separated from each other to show a circular second rim portion, together with other parts including mounting parts of an air bag system adapted to be mounted at an end of a steering wheel post;

FIGURE 3 is a view, partially broken away and in cross-section of an injection molding system which may be utilized to make the assembly of the present invention;

FIGURE 4 is a block diagram flow chart illustrating the various method steps taken to practice a first method to make the assembly; and FIGURE 5 is a block diagram flow chart of a second method to make the assembly.

Best Mode For Carrying Out The Invention

Referring now to the drawing figures, there is illustrated in Figure l a perspective view showing an embodiment of a unitary composite steering wheel and air bag cover assembly, generally indicated at 10, constructed in accordance with the present invention. The assembly 10 preferably is installed over an inflatable air bag system, a support structure of which is generally shown at 12 in Figure 2, mounted at the end of a steering wheel post (not shown). The occupant restraint air bag system is typically mounted at the interior end of the steering wheel post adjacent the assembly 10 so that the air bag may deploy between the vehicle driver and the steering wheel post to prevent injury during an accident or other period of sudden deceleration.

Referring specifically now to Figure 2, there is illustrated in detail an embodiment of the assembly 10 constructed in accordance with the present invention. The assembly 10 includes a one-piece injection molded plastic body, generally indicated at 14, which is preferably injection molded in a mold 15

(Figure 3) and has a predetermined tear seam design as indicated at 16 formed in an air bag cover portion 18. The air bag cover portion 18 is adapted to overlie an inflatable air bag system. The plastic body 14 also includes a circular first rim portion 20. The first rim portion 20 has been separated into front and rear sections and from a second rim portion 28 of a plastic skeletal frame structure, generally indicated at 26, to illustrate the second rim portion 28. However, it is to be understood that the two sections of the first rim portion are integrally formed with the second rim portion 28 within the mold 15. The second plastic of the frame structure 26 is compatible with the plastic of the body 14 so that the second rim portion 28 of the frame structure 26 bonds with the first rim portion 20 of the body 14 by diffusion between the immediately adjacent surfaces thereof in the mold 15 to prevent the body 14 from separating from the frame structure 26 during use of the assembly 10.

As previously mentioned, the frame structure 26 is made from a second plastic also injection molded in the mold 15. The second plastic is more rigid and not as soft as the plastic of the plastic body 14. Preferably, the plastic of the body 14 is a thermoplastic such as TPO, TPU, DYM, santoprene, etc., whereas the plastic of the frame structure 26 is more rigid but not as soft plastic such as glass-filled nylon.

The frame structure 26 also includes a central support portion 29 having a plurality of apertures 30, 32 and 34 formed therethrough. One aperture 30 is aligned with the cover portion 18. An air bag of the air bag system exits through the aperture 30 and through the cover portion 18 when deployed.

The support portion 29 preferably has a plurality of holes 36 formed about the aperture 30 to receive and retain a like plurality of fasteners 38. The fasteners 38 secure a steel inflator assembly collar 40 of the support structure 12 to the frame structure 26 at holes 42.

Typically, if the plastic of the body 14 is a thermoplastic, the durometer of the body 14 will be in the range of about 37 Shore D to 52 Shore D, while the flexural modulus will be in the range of about 30,000 to 70,000 psi. If a RIM plastic is used, the modulus could be lower. The support structure 12 also typically includes a plastic trim plate 44, a metal mounting rim 46 with attachment flanges 48 and a steering column cowl 50 having a close-out seal 52.

Referring now to Figure 3, there is illustrated the mold 15 and an extruder head or nozzle 54 of an injection molding system for making the unitary composite steering wheel and air bag cover assembly 10 of the present invention. However, it is to be understood that other methods and systems may be utilized to make a unitary composite steering wheel and air bag cover assembly 10 of the prevent invention.

The mold 15 includes a first mold half 62 and a second mold half

64. The first and second mold halves 62 and 64, respectively, are movable relative to each other between an open position and a closed position, wherein the first and second mold halves 62 and 64, respectively, define an article-defining cavity 66.

The second mold half 64 includes a gas passageway 68 which extends from an exterior surface (not shown) of the second mold half 64 to an inner interior surface 70 of the second mold half 64 in fluid communication with the article-defining cavity 66.

The second or stationary mold half 64 includes a sprue 72 for communicating thermoplastic material to a runner 74 which, in turn, communicates with the article-defining cavity 66 via a gate 76. A thermoplastic flow path is defined by the sprue 72, the runner 74 and the gate 76. Article ejector pins 78 can extend through the first or movable mold half 62 to eject a completed part. As previously mentioned, the injection molding system includes an extruder or nozzle 54 for injecting predetermined amounts or shots of first and second types of molten resin into the mold 15. The nozzle 54 may be generally of the type disclosed in U.S. Patent No. 5,047,183 which is capable of co- injecting two types of plastics as well as pressurized gas into the mold 15.

Instead of injecting pressurized gas from the nozzle 54, the system 56 may include a gas pin assembly, generally indicated at 80, for injecting the pressurized gas. The gas pin assembly 80 includes a one-piece housing, generally indicated at 82. As shown in Figure 3, a base portion 84 of the housing 82 is threadedly secured to the second mold half 64 at the interior surface 70 of the second mold half 64 so that the gas pin assembly 80 can be readily removed from the second mold half 64 in the open position of the mold 15. A rubber O-ring 86 is provided about the base portion 84 to seal the housing 82 within the second mold half 64.

The housing 82 also includes a hexagonal head portion 88 so that the assembly 80 can be readily removed from the second mold half 64 in the open position of the mold 15 by a conventional tool (not shown). Details of the assembly 80 can be found in the above-noted application entitled "Mold For Use In A Gas-Assisted Injection Molding System And Gas Pin Assembly For Use Therein".

Referring now to Figure 4, there is illustrated the various process steps of a co-injection method for forming the assembly 10 with further reference to Figure 3. This method does not need nor require the gas pin assembly 80.

At block 400, initially the first molten plastic is injected into the mold cavity 66 of the mold 15 through its injection nozzle 54. At block 402, before the first plastic has solidified, the second molten plastic is injected into the mold 15 through the nozzle 54 at a temperature and pressure sufficient to "core-out" or hollow out the first plastic.

At block 404, the resulting steering wheel and air bag cover assembly 10 is cooled to a temperature beneath the softening point of both plastics.

Finally, at block 406, the completed steering wheel and air bag cover assembly 10 is removed from the mold 15.

Referring now to Figure 5, there is disclosed in block diagram flow chart form a gas-assist method for forming the unitary composite steering wheel and air bag cover assembly 10 of the present invention. This method utilizes the gas pin assembly 80 unless the nozzle 54 also has the capability of injecting pressurized gas into the mold 15 as illustrated in U.S. Patent No. 5,047,183.

At block 500, the first molten resin is injected into the mold 15 through its injection aperture.

At block 501, pressurized gas is inserted into the mold 15 to distribute the molten resin over the interior surfaces 66 of the mold 15.

At block 502, the resulting body 14 is cooled to a temperature beneath the softening point of the first molten resin.

At block 503, the pressure within the curved first rim portion 20 of the body 14 is relieved. At block 504, a second molten plastic is injected from the nozzle 54 into the hollowed-out first rim portion 20.

At block 505, the resulting steering wheel and air bag cover assembly 10 is cooled to a temperature beneath the softening point of both resins.

Finally, at block 506, the mold 15 is open and the completed steering wheel and air bag cover assembly 10 is removed from the mold 15.

In this way, the assembly 10 is formed with the second rim portion 28 of the skeletal frame structure 26 within the first rim portion 20 of a one-piece body 14 and an integral air bag cover portion 18 with a predetermined tear seam design 16 formed therein in a single mold cavity. The air bag cover portion 18 with the predetermined tear seam design 16 and the aligned aperture 30 allow an air bag to exit the cover portion 18 when deployed.

While the best mode for carrying out the invention has been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention as defined by the following claims.

Claims

What Is Claimed Is:

1. A unitary composite steering wheel and air bag cover assembly comprising: a one-piece, plastic body including a circular first rim portion having a perimeter and an air bag cover portion with a predetermined tear seam design formed therein, the air bag cover portion being adapted to overlie an inflatable air bag system; and a one-piece, plastic skeletal frame structure including a circular second rim portion enclosed within the first rim portion and having an aperture aligned with the air bag cover portion to allow an air bag of the air bag system to exit the air bag cover portion when deployed.

2. The assembly as claimed in claim 1 wherein the frame structure includes a central support portion having the aperture and adapted to be connected to the air bag system about the aperture.

3. The assembly as claimed in claim 1 wherein the plastic of the frame structure is more rigid relative to the plastic of the body and the plastic of the body is softer relative to the plastic of the frame structure.

4. The assembly as claimed in claim 1 wherein the plastic of the frame structure is co-injected with the plastic of the body.

5. The assembly as claimed in claim 1 wherein the first rim portion is formed by a pressurized fluid to define a closed seamless interior surface which extends at least partially about the perimeter of the first rim portion.

6. The assembly as claimed in claim 1 wherein the plastic of the frame structure is glass-filled nylon.

7. The assembly as claimed in claim 1 wherein the plastic of the body is one of DYM, TPO, TPU and santoprene.