BACKREST DEVICE FOR A VEHICLE SEAT

Abstract: An arrangement for a backrest (1) of a vehicle seat (2), comprising a frame (3) and a support member (9), flexibly suspended inside the frame by means of compliant members (10), for absorbing, together with the support member, that load from a person sitting in a vehicle seat, which is acting on the backrest. The compliant members comprise resilient spring members and stroke-limiting members arranged for allowing, in co-operation with the spring members, resilient compliance functioning to absorb load from the back during a normal state of use within a first load range. Within a second load range, the stroke of the compliant members is limited. Each spring member and stroke-limiting member is designed, for each individual compliant member (10), as an integrated component having a first fastening element for attachment to the frame (3) and a second fastening element for attachment to the support member (9).

Description: BACKREST DEVICE FOR A VEHICLE SEAT TECHNICAL AREA The present invention relates to an arrangement for a vehicle seat backiest according to the preamble of the appended claim 1. Conventional backrests for vehicle seats are provided with resilient compliant means having only a comfort function, i.e. are functional to provide an even and comfortable support for the back and will adapt to normal back motions during a normal state of use. In case of a rear-end collision, the back will be subjected to an excessive rearwards movement in the backiest, and, furthermore, accumulation of resilient energy will cause the back to recoil forward, creating a risk of so called whiplash injuries. From WO 95/11818 a backiest is known, that has been designed with the aim of reducing whiplash injuries caused by rear-end collisions. According to the known solution, this has been achieved by arranging separate stroke-limiting means, such as for example bands or links having attachment points separate from the fastening points of the springs. The means of attachment and the design of the spring means and the stioke-limiting means are veiy critical with regaid to the total function of the compliance of the backiest, for normal loads as well as extreme loads, such as dur- ing a collision. SUMMARY OF THE INVENTION The object of the present invention is to provide an arrangement for a backrest in which the compliant members can be given accurately specified properties. Said object is achieved by an arrangement according to the invention, the characteristics of which are specified by the accompanying claim 1. By designing the compliant members with each spring member and stroke- limiting member being an integrated component, these components can be produced with well-specified properties as regards their compliance. DESCRIPTION OF THE DRAWINGS In the following, the invention will be described in detail by way of embodiment examples, with reference to the accompanying drawings, in which: Fig. 1 schematically illustrates a partly cut open view of a vehicle seat seen from the front, provided with an arrangement for backrests according to the present invention, Figs. 2-5 illustrate various embodiment examples of compliant members provided with stioke-limiting members, comprised in the arrangement according to the invention, Fig. 6 schematically illustrates, by way of a diagram, the characteristics of the compliant members according to Figs. 2-5, Figs 7 and 8 illustrate further embodiment examples of compliant members, comprised in the arrangement according to the invention, and provided with stroke-limiting members as well as with plastically compliant members, Fig. 9 schematically illustrates, by way of a diagram, the characteristics of the compliant members according to Figs. 7 and 8, Figs. 10-17 illustrate some examples of the plastically compliant members and their function under extreme load. Fig. 1 shows, schematically, the construction of a backiest 1 comprised in a vehicle seat 2 for a motor vehicle. The figure shows that the backiest 1 is generally constructed as a frame 3 having two side members 4, 5 and a top member 6. The backiest extends conventionally upward from the rear edge of a seat member 7 of the vehicle seat and is attached thereto by a lockable joint for adjustment of the inclination of the backiest 1. The frame encloses an area 8, in which a support member 9 is suspended. The support member is arranged to be flexibly suspended in the frame by means of a multitude of resiliently compliant members 10, attached between the support member and the frame. These members comprise the load-car- rying elements of the backrest, which are embedded in a cushion of well-adjusted softness and enclosing upholstery. In Fig. 1, the compliant members 10 are, for the sake of simplicity, shown as simple tension springs, which are, however, according to the invention, integrated with other elements, as will be described in greater detail below. The support member 9 preferably consists of a flexible webbing, so called net webbing or pullmaflex webbing, i.e. a flexible, compliant unit functioning to absorb the load emanating from the back of a person sitting in the vehicle seat. This is performed in co-operation with the compliant members, in the illustrated example being attached between the two side members 4, 5 of the frame and the support member 9. The latter is, in the illustiated example, of rectangular shape having two side edges 11, 12, spaced from the frame side members 4, 5, respectively. The compliant members extend, in the illustrated example, from the respective side member 4, 5 of the frame 3 to the neighbouring side edge 11, 12 of the support member 9. The support member in the illustiated example consists of two rigid wires or rods 13, 14 forming its side edges 11, 12, with a multitude of flexible thieads 15 stretched between the rods. The compliant members 10 are at each end provided with fastening elements, attached to fastening points in the frame 3 and the support member 9, respectively. The fastening elements consist of, for example, hook-shaped elements, hooked into holes in the frame, and around the rods 13, 14, respectively. Through the compliance of the compliant members, a difference s in the distance between the fastening elements is allowed when absorbing, mainly in the longitudinal direction of the compliant members, the load and the movement which generally directed towards the support member, i. e. being directed transversely thereto and thus to the longitudinal direction of the members. Above the backrest there is furthermore a head restraint 17, which may be of conventional design but is of major importance regarding the supporting function during extreme load, such as during a rear-end collision caused by another vehicle. Fig. 2 illustrates a first example of a compliant member, in this example des- ignated 18 and comprising on one hand a spring member 19 and on the other a stroke-limiting member 20, integrated with the spring member. The compliant member exhibits a hook-shaped fastening element 21, 22 at each end, for attachment either to the frame 3 or to the support member 9, or vice versa. The spring member 19 is comprised of a tension type coil spring, for example made of coil wound spring steel wire, continuing at its ends into the fastening elements 21, 22. The stroke-limiting member 20 is at one end 23 fastened to one end 24 of the spring member, extends along the latter with a straight portion 25, being principally of fixed length and having a stop 26 in the form of a hook-like portion, located at a predetermined distance Sj; from the other end 27 of the spring member in its unloaded condition. The stroke limitation is achieved by the end 27 of the spring member being pulled out the distance Si in the excessively loaded condition of the compliant member, whereby the hook-like portion 26 hooks into the winding of the spring member at its end 27. Figs. 3 and 4 illustrate another example of a compliant member, here desig- nated 28. For the sake of clarity, the compliant member is shown in an exploded view in Fig. 3, whereas Fig. 4 shows the assembled member. The comprised spring member 29 is in this case a compression spring in the form of a coil spring, which in the illustrated unloaded condition is expanded. The stroke-limiting member 30 is created indirectly in this example, by two identical parts 31, 32, in the shape of V- bent wire sections, meeting at their tip ends 33, creating fastening elements for the compliant member and being attached to the remote end of said spring member 29. At their opposite ends, two hook-like sections 34, 35 are provided. As is shown in Fig. 4, in the assembled compliant member 24, the two elements 31, 32 are passed through the spring member 29, one from each side, with the tip end 33 leading, until the hook-like sections 34, 35 in practice hook onto the respective ends 36, 37 of the spring member 29. The two tip ends 33, 38 thus each create one fastening element of the assembled component, to be attached to the frame 3 or the support member 9, respectively. Consequently, in this case the two elements 31, 32 as such are no stroke-limiting members, but are creating a stroke limitation by causing an inverted movement of the spring member, i.e. a pulling load between the fastening element . 33, 38 creates a pushing load on the spring member 29, because the hook-like sections 34, 35, by hooking onto the ends 36, 37 of the spring member compresses the latter until it "bottoms out", i. e. reaches a butt contact end position, which creates the stroke limitation. A variant compliant member 39 is illustrated in Fig. 5, in which the spring member 40 is a coil type compression spring, shown in its unloaded condition and exhibiting hook-like fastening elements 41, 42, extending via straight wire sections 43, 44, through the spring member and being equipped also at their opposite ends with hook-like elements 41', 42', which are each hooked onto that end 45, 46, respectively, of the spring member which is located opposite the corresponding fastening element 41, 42. The same function as in the embodiment of Fig. 4 is obtained, i.e. a pulling of the fastening elements 41, 42 entails a compression of the spring element 40 until it "bottoms out", whereby a stroke limitation is achieved. Fig. 6 schematically shows the characteristics of the above discussed compliant members, whereby the compliant movement of the compliant member is designated by s and the load is designated by F. The compliant movement is, in the illustiated example, proportional to the load, but may also be progressive, up to a travelled distance Si, which range of movement is used during normal loads from the person's back, i.e. during normal conditions of vehicle use within a first load range, up to a limit load F.. By extreme load, such as during a rear-end collision, the limit load Fi is exceeded, the maximum movement stroke S! is reached, causing the stroke-limiting member to be activated, so that the distance of movement will not increase in spite of increasing load. Through this action, the compliant members are prevented from yielding further, whereby the support member will not allow the person's back to sink further into the backrest, thereby reducing the risk of a whiplash injury. Fig. 7 illustrates a compliant member 47 constructed from three integrated members influencing the compliance, that is, besides the spring member 40 and the stioke-limiting member, a plastically compliant member 48, in this example being arranged in series with the other two members. In the example shown in Fig. 7, the spring member 40 and the stroke-limiting member is of a design similar to that of Fig. 5, but it may alternatively be of a different design, for example according to the examples illustiated in Figs. 2 and 3. The plastically compliant member 48 is inte- grated into the straight section between the attachment point at the end of the spring member 46 and the attachment point 42 of the compliant member, and is in the illustrated example designed as, in relation to the resilient member 40, a highly shape-resistant, Z-shaped or spiral-shaped loop. Its shape resistance is dimensioned such that the distance between its two end points 49, 50 remains generally constant, on one hand during normal use, i.e. a first load range, and on the other hand during-. a second load range of elevated load, during stroke limitation. If the load strives to increase even further, the plastically compliant member will yield plastically until the distance between the two points 49 and 50 reaches an end position, at which the plastic deformation ceases and a further stroke limitation will occur for still higher loads. Fig. 8 illustrates an alternative example with a spring member 51 in the form of a tension spring and, in parallel thereto, attached both a stroke-limiting member 52 and a plastically compliant member 53 connected in series with each other. One end of the spring member and the corresponding end of the stroke-limiting member exhibit a common fastening member 54, whilst the opposite end of the spring member and the external end of the plastically compliant member also exhibit a common fastening member 55. Fig. 9 shows, schematically by means of a diagram, characteristics of the compliant members of the type illustiated by examples in Figs. 7 and 8, i. e. exhibiting a spring member as well as a stroke-limiting member and a plastically compliant member. During a primary, normal load range, the resilient compliance thus takes place over a distance of movement up to the distance Sj, whereupon the stroke limitation occurs at a load limit Fi. In case of further load inside a range up to the load F 2 no compliance occurs, whereupon the plastically compliant member will be activated up to a predetermined distance s 2 , after which a second stroke limitation will occur in case of further increased load. In the case of Fig. 9, a resilient compliance will however remain also for loads above F 2 , which is indicated by a dot- dashed line. Fig. 10 shows an independent view of the plastically compliant member 48 of Fig. 7. The plastic deformation and absoiption of energy will thus occur at a certain load, at which the bent or spirally wound wire will be straightened out so that the distance between the two points 49, 50 will increase to a maximum value, changing the compliance by a distance s 2 . The example according to Figs. 12 and 13 shows an alternative embodiment of the plastically compliant member, designated by 57. In this example, said member is designed as a wire extending in a tube 58, having a forward portion 59 and a return portion 60. This creates an end portion 61 that can function as a fastening element for attachment either to the frame of the vehicle seat or to the support mem- ber and which may for example consist of an eye 62. The plastic compliance will occur at a certain tension load in the forward portion 59, which is attached to the spring member of the compliant member, forcing the return portion 60 to yield through bending and subsequent straightening. Figs 14 and 15 show a further example of a plastically compliant member 63, consisting of a wire portion 64, which at one end is attached to the spring member, e.g. a tension spring, and at the other end 65 has a lager diameter, which is furthermore larger than a hole 66, through which the wire 64 will stretch and be pulled out at a predetermined excessive load. The plastic compliance is created by the thicker portion of the wire being plastically deformed by passing through the hole 66. Figs 16 and 17 illustrate a further example of the plastically compliant member 67. In this example, one end 69 of a wire portion 68 is attached to the spring member and the other end 70 is fastened to the remote end of a deformable distance element 71 that is attached to a plate 72 having an opening 73 through which the wire extends. The distance element is for example designed as a cylinder, which, at the predetermined overload, will buckle and allow the end 70 to travel in the direction of said plate 72. To summarise, various examples of compliant members, for attachment between the frame 3 and the support member 9 in the backiest of a vehicle seat have been demonstrated and described. Without exception, the compliant members have been designed as integrated components having resilient and stroke-limiting members, and in some cases also plastic members, arranged to have a common point of attachment for each component, to the frame and the support member, respectively, and being ananged either in series or parallel, or in a combination of series and parallel connection. The compliant members are mainly made of a wire material and can be dimensioned for providing specific properties regarding compliant movement and load limits. The compliant members 10 have, during normal use, i.e. normal use of the vehicle, only a comfort function, whereby they provide, together with the support member, in co-operation with stuffing and upholstery of the backiest, an even support for the back, and compliance for normal movement of the back. During extreme loads, such as a rear-end collision, the compliant members 10 provide a load- absorbing function and a recoil-dampening function, on one hand preventing the back from being pressed too far into the backiest 1, and on the other not recoiling forward in a limited movement, which might otherwise entail detrimental loads on the spinal column and the neck vertebrae, when combined with the more limited compliance of the head restraint. The invention is not limited to the embodiment examples shown in the draw- ings and described above. The number of compliant members 10 between the frame 3 and the support member 9, and their location may vaiy from seat to seat. For example, compliant members may be attached also between the top member and the support member 9. The latter may further be constructed in a different way. At the lower portion of the majority of backrests, an adjustable sway-back support is provided, which should have a larger compliance than the compliant members during extreme load, in such a manner that the sway-back support will not prevent the above discussed compliance of the backiest as a whole.

Claims: CLAIMS 1. An arrangement for a backiest ( 1) of a vehicle seat (2), comprising a frame (3) and a support member (9), flexibly suspended inside the frame by means of compliant members (10/18/28/29/47/56) for absorbing, together with the support member, that load from a person sitting in a vehicle seat, which is acting on the backiest, the compliant members comprising resilient spring members (19/29/40/51) and stroke-limiting members ananged for allowing, in co-operation with the spring members (19/29/40/51), resilient compliance functioning to absorb load from the back during a normal state of use within a first load range, and for limiting the stroke of the compliant members within a second load range, characterised in that each spring member (19/29/40/51) and stroke-limiting member is designed, for each individual compliant member (10), as an integrated component having a first fastening element (21/38/41) for attachment to the frame (3) and a second fastening element (26/33/42) for attachment to the support member (9) 2. An arrangement according to claim 1, characterised in that at least some of the individual compliant members comprise a plastically compliant member (48, 57, 63, 67), functioning to provide, at a load exceeding said second load range, a plastic compliance in said compliant member. 3. An anangement according to claim 2, characterised in that the plastically compliant member (48) is ananged in series with the spring member (47). 4. An arrangement according to claim 2, characterised in that the plastically compliant member (53) is ananged in parallel with the spring member (51). 5. An anangement according to claim 4, characterised in that the stroke-limiting member (52) is ananged in series with the plastically compliant member (53). 6. An anangement according to any one of the preceding claims, characterised in that also said plastically compliant members (48, 67) are provided with a stroke limiting device, whereby the compliant members are given a second stroke limitation after a predetermined distance of travel (s 2 ). 7. An anangement according to claim 1, characterised in that said compliant member (10) is comprised of a coil type compression spring (29/39) and two fastening elements (31, 32/41, 42), of which one fastening element has one end (34, 35/41) attached to the frame (3) and the other fastening element has one end attached to the support member (9), and in that the two fastening elements extend through the compression spring and have their respective other ends (33/45, 46) connected to the opposite ends (36, 37), respectively, of the compression spring, whereby a pulling motion of the fastening elements will cause a compression of the compression spring until it is completely compressed, at which point stroke limitation will occur.

Inventors: ANDERSSON TORSTEN, LUNDELL BJOERN, ANDERSSON, TORSTEN, LUNDELL, BJOERN
Applicants: ANDERSSON TORSTEN, LUNDELL BJOERN, VOLVO AB, AB VOLVO, ANDERSSON, TORSTEN, LUNDELL, BJOERN
Application year: 1998
Main classification: B60N2
IPC codes: A47C7, B60N2, F16F1, F16F3, F16F7