A STEERING WHEEL ASSEMBLY

Abstract: A steering wheel comprises a main body part defining an outer ring (1) and a component (6) movable relative to the main body. A projection (19) carried by a platform (5) associated with the main body co-operates with a switch formed on the under-side of a housing (7) that forms part of the movable component. The switch forms part of a laminated element (21) which has an insulating substrate (23) secured to the housing (7) which carries a conductive metal foil (24). A further insulating layer (25) spaces this foil from a further foil (26) carried by an insulating layer (27). In the region of the projection (16) the intermediate insulating layer (24) is removed and the dimension of the insulating layer (27) and the metal foil (26) is enlarged to form a "bubble". The pressure that must be applied to move the movable component (6) downwardly rises to a maximum during initial movement, and then the "bubble" collapses, causing the applied pressure to reduce to a minimum and subsequently to climb again towards a fresh maximum with continued movement. As the "bubble" collapses a circuit is completed which incorparates a horn.

Description: "A STEERING WHEEL ASSEMBLY" THE PRESENT INVENTION relates to a steering wheel assembly, and more particularly the invention relates to a steering wheel assembly incorporating a component which is movable relative to the rest of the steering wheel, the said movable component being movable to close an electric switch to complete a horn actuating circuit. It has been proposed previously to provide a steering wheel comprising a fixed part and a movable component, the movable component being movable, relative to the fixed part, to complete an electric circuit incorporating a horn. Reference may be made, for example, to EP-A-0,330,306. In this Specification, the movable part comprises a housing which contains an air-bag. The movable component can be moved against a resilient force provided by a plurality of helical compression springs. The resistance to movement of the movable component provided by the helical springs is progressive. Consequently, the further the movable component moves, the greater the force resisting further movement of the movable component. Consequently, it is not easy to determine when sufficient pressure has been applied to the movable part to actuate the horn. It is to be noted that in the arrangement disclosed in EP-A-0,330,306, the outer casing of the air-bag unit itself is used as an electrical conductor that forms part of the completed horn circuit. This may prove to be undesirable in that spurious electric currents may be generated within the air-bag unit which may activate the gas generator that forms part of the air-bag unit. The present invention seeks to provide an improved steering wheel assembly. According to this invention there is provided a steering wheel arrangement comprising a main body part defining an outer ring that forms the steering wheel and a component comprising an air-bag module, said component being mounted on the main body, so as to be movable over a permitted range of movement relative to the main body, there being at least three resilient elements located between the movable component and the main body, providing a resilient resisting force which resists movement of the movable component relative to the main body, each resilient element being associated with an electric switch adapted to be incorporated in an electric circuit in a motor vehicle, which circuit also incorporates a horn, the resilient elements each being such that when the movable component is initially moved, the resisting force will rise to a maximum over an initial distance of movement, will then decline, over a subsequent distance of movement, to a second force which is above zero, and will finally rise again over a further distance of movement as the movable component approaches the end of the permitted range of movement of the movable component relative to the main body part. Conveniently the said maximum is between 12 and 18 Newtons and is preferably 15 Newtons. Conveniently the second force is between 2 and 10 Newtons and is preferably substantially 7 Newtons. Conveniently the said range of movement is between 0.5 and 2 millimetres and is preferably 1.2 millimetres. In a preferred embodiment each resilient part comprises a dome or bubble-shaped sheet of resilient material. In one embodiment the resilient material comprises plastic, but alternatively the said sheet of resilient material comprises a sheet of metal. Conveniently at least the inside of the dome or bubble-shaped sheet of material has an electrically conducting surface, the dome or bubble-shaped sheet initially being spaced from a further conducting surface, the inside of the dome or bubble-shaped sheet being adapted to be brought into engagement with the further conductive surface as the movable component moves towards a position in which the resisting force declines to the said second force. Conveniently the metal surface on the inside of each dome or bubble-shaped sheet comprises a conductive foil and the said further conductive surface comprises a further conductive foil. Preferably the conductive foils extend from switch to switch, being separated by insulating layers. Conveniently all of the resilient elements are integrated into a single unit having two contacts, all of the switches being connected in parallel between the two contacts. Advantageously the single unit is mounted on the lower surface of the movable component. Conveniently the single unit has a substantially rectangular shape, a resilient element being located in each corner of the rectangle. In order that the invention may be more readily understood, and so that further features thereof may be appreciated, the invention will now be described, by way of example, with reference to the accompanying drawings in which: FIGURE 1 is a diagrammatic top view of a steering wheel assembly following removal of a cover, air-bag and gas generator which ordinarily are carried by the steering wheel assembly, FIGURE 2 is a cross-sectional view taken on the line B-B of Figure 1 with the cover and the gas generator in place, but omitting the air-bag for the sake of clarity of illustration, FIGURE 3 is a cross-sectional view taken on the line D-D of Figure 1 with the cover and the gas generator in place, but omitting the air-bag omitted for the sake of clarity of illustration, FIGURE 4 is an enlarged view of part of Figure 3, FIGURE 5 is a view corresponding to Figure 4 illustrating the same part of the arrangement of Figure 3 when in an alternate condition, FIGURE 6 is an illustrated view of a sub-assembly forming part of the steering wheel arrangement, with parts cut away for the sake of clarity of illustration, FIGURE 7 is a diagrammatic view illustrating the counter-compression force of each "dome-switch" which forms part of the illustrated steering wheel assembly, as a function of compression, and FIGURE 8 is a circuit diagram. Referring initially to Figures l to 3 of the accompanying drawings, a steering wheel assembly comprises a main body or fixed part which has an outer ring 1, formed of a metal tube, associated with substantially radially inwardly directed spokes 2, at least the outer ring and the terminal ends of the spokes being covered with a foamed, substantially rigid plastics material 3. The inner end of each spoke 2 is connected to a boss 4 by means of which the steering wheel may be mounted on a steering column. Mounted on the spokes 2 is a support platform 5. The support platform 5 supports a component 6 which is movable relative to the main body defined by the ring 1, the spokes 2, the boss 4 and the platform 5. In this embodiment, the movable component 6 comprises a housing 7 which supports a gas generator 8 which is adapted to supply gas to an air-bag (not shown) . A cover 9 is provided which is connected to the housing 7 by means of snap fasteners, such as the snap fastener 10 shown in Figure 2. A space 11 is defined between the cover 9 and the housing 7 which is provided to contain an air- bag. A casing 12 may be provided located beneath the spokes 2 of the steering wheel and connected to the boss 4, at least in the region of the spokes 2, in order to provide a smooth under-surface for the steering wheel. As will become clear from the following description, the component 6 is movable against a resilient force in order to complete an electric circuit which incorporates a horn, so that the horn is actuated. Figure 2 illustrates one of a pair of guide pins provided to guide the relative movement of the movable component 6 with regard to the main body of the steering wheel assembly. Referring to Figure 2, it can be seen that the platform 5 is provided with a relatively large aperture 13. The aperture 13 is dimensioned to receive, as a sliding fit, a cylindrical body 14 that forms a guide pin. The cylindrical body 14 terminates with an enlarged radius flange 15 at a position beneath a platform 5. The cylindrical body 14 is provided with a threaded stud 16 which extends upwardly into a threaded aperture 17 provided in the base of the housing 7. It is to be appreciated that the movable component 6 may move, in a vertical direction, relative to the platform 5, with its movement being guided by the cylindrical body 14. Two guide pins of this nature are provided, one on each side of the central axis of the steering wheel. Of course, a greater number of guide pins may be provided if desired in alternate embodiments of the invention. Figure 3, and Figures 4 and 5 which are enlargements of part of Figure 3, illustrate a switch arrangement 18. At least three such switch arrangements are provided. In this embodiment four of the switch arrangements 18 are provided, at substantially evenly spaced positions around the periphery of the movable component 6, as illustrated in Figure 1. Referring now to Figure 4, part of the platform 5 is illustrated, that part of the platform carrying an upwardly extending projection 19. Also visible in Figure 4 is part of the base 20 of the housing 7 and a laminated element 21 secured to the under-surface of the base 20 of the housing 7. Also visible is part of a flange 22 that forms part of the gas generator 8. The laminated element 21 comprises an insulating substrate 23 on which is mounted an electrically conductive layer 24. A further insulating layer 25 separates the conductive layer 24 from a further conductive layer 26, the conductive layer 25 being carried by a further insulating layer 27. The electrically conductive layers comprise metal foils within the laminate. The insulating substrate 23 is connected to the lower part of the housing 7. Even if this lower housing part is made of metal, it is electrically insulated from the electrically conductive layers. In the region adjacent the projection 19, the insulating layer 24 is cut away in a circular region, and the dimension of the insulating layer 27 is increased, so that the insulating layer 27 and the electrically conductive layer 26 carried thereby, form a "bubble" or do e. The bubble or dome is arched away from the insulating layer 23 and the conductive layer 24. As can be seen in Figure 4, in the initial condition of the steering wheel arrangement, the electrically conductive layer 26 is totally separated from the electrically conductive layer 24. As will be explained in greater detail below, as the movable component moves downwardly the bubble or dome collapses, to have the condition illustrated in Figure 5, and the conductive layer 26 contacts the layer 24, closing the switch and completing a circuit. Referring now to Figure 6, the laminated element 21 is illustrated. It is to be observed that the laminated element 21 has a configuration such that it can be readily mounted on the under-surface of the housing 7. Thus the outer periphery 28 is of a substantially rectangular form in conformance with the outer periphery of the housing 7 and the inner periphery 29 is substantially circular, in conformance with the gas generator 8, there being a radially, inwardly directed strip 30 extending across the central aperture 29. The position of the four switches 18 is clearly visible located substantially at four corners of the substantially rectangular laminated element 21, and the conductive laser 25 with the insulating overlay 26 can be clearly seen in connecting the four switches 18. On the strip 30 the conductive laser 26 extends across the upper surface of the tongue (in the position orientated) , and the conductive laser 23, which is in alignment with the laser 26 over the major part of the laminate 21, extends across the tongue at an off-set position. The conductive laser 23 and the conductive laser 26 are connected into a circuit incorporating the hooter or horn of the motor vehicle, as will be described. It is to be noted that in the described embodiment, the dome or bubble formed by the insulating layer 26 and the associated electrically conducting layer 27 is resilient and provides a force which resists downward movement of the movable component 6 and which biases the movable component 6 back upwardly to its initial position. When a downward pressure is applied to the movable component 6, tending to cause the movable component to move downwardly as indicated by the double-headed arrow in Figure 3, a relatively high force has to be applied to compress the dome or bubble constituted by the insulating layer 26 and the conductive layer 25 carried thereby. This is shown in region 31 of the graph shown in Figure 7. When a certain predetermined force has been applied, which force is preferably between 12 and 18 Newtons, typically about 15 Newtons, after a predetermined distance of movement of the movable component, as indicated at point 32 on the graph, the dome or bubble suddenly "collapses" and a force which defines with continued movement, as indicated at region 33 of the graph, subsequently has to be applied in order to move the arrangement to the condition illustrated in Figure 5. This relatively low force is between 2 and 10 Newtons, preferably being about 7 Newtons. It can be seen that on the collapse of the dome or bubble, the switch 18 has moved to a situation in which the two electrically conductive layers, namely the layers 24 and 26, are brought into contact with each other. This, as will be described below, completes an electric circuit incorporating a horn. If subsequent pressure is applied, an increasingly high force has to be applied to move the movable component further in the downward direction, as indicated in region 34 of the graph. This increasingly high force is thus applied as the movable component approaches the end of the permitted range of movement of the movable component 6 relative to the support platform 5. The movable component 6 thus moves to the end of its range of permitted movement. The maximum movement of the movable component may be between 0.5 and 2.0 mm, but is preferably about 1.2 mm. Should the movable component be released, an upward force exerted by the resilient dome or bubble will move the movable component back up to its initial position, as indicated by the lower line 35 present in the graph. The lower line of the graph is of the same general form as the upper line. there is a certain amount of hysteresis. It is to be noted that even at point 36 of the graph, which corresponds to a point at which the movable component is moving upwardly under a force applied thereto when the "bubble" is in the condition that it occupies immediately after collapse, there is still an upward force applied by the "bubble", causing the movable component to return to its initial condition. Thus, during the return of the movable component to its initial condition, there is always a restoring force that is greater than zero. Referring now to Figure 8, it can be seen that the switches 18 are connected in parallel in a circuit which incorporates a vehicle battery 37 and a horn 38. Should any one of the switches 18 be closed, the horn will be activated. -li¬ lt is to be appreciated that in the described embodiments, the "dome" or "bubble" has been described as being fabricated of an insulating layer carrying a metal layer. The insulating layer may be a layer of plastic material, but it is to be appreciated that in an alternative embodiment of the invention, the dome may be made solely of a layer of resilient metal, but in such an arrangement the projection 19 carried by the platform 5 should preferably be made of an electrically insulating material. Because the substrate 23 is insulating and is connected to the housing 7, none of the current flowing in the conductive layers 24 and 26 can flow through the housing 7 to cause unintended deployment of the air-bag. As the movable component is depressed, once the initial resistance to movement is overcome, the movable element subsequently moves relatively easily, thus providing a recognisable effect that confirms that the movable component has been pressed firmly enough to activate the horn.

Claims: CLAIMS : 1. A steering wheel arrangement comprising a main body part defining an outer ring that forms the steering wheel and a component comprising an air-bag module, said component being mounted on the main body, so as to be movable over a permitted range of movement relative to the main body, there being at least three resilient elements located between the movable component and the main body, providing a resilient resisting force which resists movement of the movable component relative to the main body, each resilient element being associated with an electric switch adapted to be incorporated in an electric circuit in a motor vehicle, which circuit also incorporates a horn, the resilient elements each being such that when the movable component is initially moved, the resisting force will rise to a maximum over an initial distance of movement, will then decline, over a subsequent distance of movement, to a second force which is above zero, and will finally rise again over a further distance of movement as the movable component approaches the end of the permitted range of movement of the movable component relative to the main body part. 2. A steering wheel arrangement according to Claim 1 wherein the said maximum is between 12 and 18 Newtons. 3. A steering wheel arrangement according to Claim 2 wherein said maximum is substantially 15 Newtons. 4. A steering wheel arrangement according to any one of the preceding Claims wherein the second force is between 2 and 10 Newtons. 5. A steering wheel arrangement according to Claim 4, wherein the second force is substantially 7 Newtons. 6. A steering wheel arrangement according to any one of the preceding Claims wherein the said range of movement is between 0.5 and 2 millimetres. 7. A steering wheel arrangement according to Claim 6 wherein the said range is substantially 1.2 millimetres. 8. A steering wheel arrangement according to any one of the preceding Claims wherein each resilient part comprises a dome or bubble-shaped sheet of resilient material. 9. A steering wheel arrangement according to Claim 8 wherein the resilient material comprises plastic. 10. A steering wheel arrangement according to Claim 8 wherein the said sheet of resilient material comprises a sheet of metal. 11. A steering wheel arrangement according to any one of Claims 8 to 10 wherein at least the inside of the dome or bubble-shaped sheet of material has an electrically conducting surface, the dome or bubble-shaped sheet initially being spaced from a further conducting surface, the inside of the dome or bubble-shaped sheet being adapted to be brought into engagement with the further conductive surface as the movable component moves towards a position in which the resisting force declines to the said second force. 12. A steering wheel arrangement according to Claim 11, wherein the metal surface on the inside of each dome or bubble-shaped sheet comprises a conductive foil and the said further conductive surface comprises a further conductive foil. 13. A steering wheel arrangement according to Claim 12 wherein the conductive foils extend from switch to switch, being separated by insulating layers. 14. A steering wheel arrangement according to any one of the preceding Claims wherein all of the resilient elements are integrated into a single unit having two contacts, all of the switches being connected in parallel between the two contacts. 15. A steering wheel arrangement according to Claim 14, wherein the single unit is mounted on the lower surface of the movable component. 16. A steering wheel arrangement according to Claim 15, wherein the single unit has a substantially rectangular shape, a resilient element being located in each corner of the rectangle.

Inventors: AHLKVIST MIKAEL, MALMENSTAM JONAS, AHLKVIST, MIKAEL, MALMENSTAM, JONAS
Applicants: AHLKVIST MIKAEL, AUTOLIV DEV, MALMENSTAM JONAS, AHLKVIST, MIKAEL, AUTOLIV DEVELOPMENT AB, MALMENSTAM, JONAS
Application year: 1997
Main classification: B60R21
IPC codes: B60Q5, B60R21, H01H13