BUMPER BAR FOR A MOTOR VEHICLE

Abstract: A plastics bumper bar for motor vehicle has an outer skin 10, integral mounting brackets 16 by which the bumper can be mounted on a vehicle and a strap 12 stretched between two mounting brackets. The interior of the skin is filled with a plastics foam which is moulded in situ and encapsulates the strap completely. The presence of the strap helps to absorb energy.

Description: This invention relates to a bumper bar for a motor vehicle, and in particular to a bumper bar made largely from plastics materials of the type as specified in the peamble of claim 1, and for example as disclosed in GB-A- 2 151 993. Bumper bars of plastics are now widely used. They have advantages in allowing great styling flexibility, relatively low weight and the ability to absorb minor impacts without any permanent damage. However to allow the bumper to absorb such minor impacts without damage to the bumper itself or without damage to the vehicle bodywork behind the bumper, it has often been necessary to form the bumper so that it projects a substantial distance from the bodywork which it protects, and this is undesirable from the point of view of appearance and because it increases the overall vehicle length. GB-A-2 151 993 describes a bumper construction where a foam core is moulded in situ in a fascia or shell. It is an important part of that construction that the foam has an integral skin, because the integral skin has a functional role to play in the connection between the fascia and the bumper mounting means. According to the invention, there is provided a vehicle bumper comprising a plastics skin, a plastics foam filling moulded in situ within the skin, and a metal strap extending across the bumper inside the skin and encapsulated by the foam, characterised in that internal mounting brackets are moulded integrally with the skin, the brackets being arranged for mounting the bumper on a vehicle and for supporting the ends of the strap. The internal strap is put under tension between the brackets in the event of an impact and thus absorbs the energy of the impact. Supporting the strap between the mounting brackets allows the strap to be close to the front of the bumper and thus allows the dimensions of the bumper to be kept small. Preferably the strap is of metal, although it could be possible to form it of a plastics material. The strap can be simply clipped at each end to a bumper mounting bracket, and in this case assembly is very easy. The bumper preferably has integral wrap-around ends which extend along the side of the vehicle body. The skin of the bumper may be very thin, for example less than 1.5 mm thick, and preferably 1.2 mm. When the skin is so thin, the foam extends over the whole of the inner surface of the skin, to provide reinforcement to all parts of the skin. The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a top view of one corner of a bumper in accordance with the invention; Figure 2 is a section through the bumper of Figure 1 on the line II-II; and Figure 3 is a view of the back (or inside) of the bumper before foaming. The bumper shown in the figures has a skin 10, an internal metal strap 12 and a foam filling 14. A mounting bracket 16 is moulded integrally with the skin. The bumper is shown in position against a part 18 of the vehicle bodywork to which the bumper will be mounted. The skin 10 can be injection moulded from polycarbonate at a thickness of 1.2 mm. The strap 12 can be of steel and the foam 14 can be a polyurethane foam. The form of the mounting bracket 16 can be seen most clearly from Figures 2 and 3. It has a flat top face 20 and three walls 22, 24 and 26 each extending from one of three sides of the face 20. The fourth side 28 of the face 20 has no wall. The walls 22 and 26 are directly connected to the skin 10 (Figure 2). The wall 24 is supported at each end by being connected to the walls 22 and 26. Stiffening ribs 30 brace the wall 24 against the underside of the face 20 and extend parallel to, and to the full depth of the end walls 22 and 26. At the foot of the wall 24, there is a lip 32. This is braced by ribs 34 against the wall 24. The strap 12 has a bifurcated end with two inturned integral clips 36 which clip over the lip 32 as shown in Figure 1, and this engagement of the strap with the bracket supports the strap in the bumper. There are two brackets 16, one adjacent each end of the bumper, and the strap is stretched between the two brackets. The outward facing side of the face 20 also has two integrally moulded plastics threaded bosses 38 which are used to secure the bumper to the part 18 of a vehicle. The bosses are passed through holes in the vehicle bodywork and plastics nuts 40 are screwed on. To stiffen the bosses 38 and to help them to resist shearing forces, the bosses are hollow and are provided with internal metal pins 42 which are a push fit in the hollow bushes. The pins 42 are initially pushed in until they touch the strap 12. Once the strap 12 has been assembled to the brackets 16, the bumper is placed in a foaming box and foam is cast into the interior so that it completely encapsulates the strap and forms a rear exposed surface 44 which is a continuation of the face 20 of the bracket. The strap can have holes formed in it, as at 45, so that the foam can extend all around it. Although the foam may well in practice adhere to the strap, this is not necessary and the bumper would still function correctly if there were no holes 45 and a release agent had been applied to the strap to prevent any adherence. The foam will however bond to the inside surface of the skin. The bumper has wrap-around ends 46 which extend along the side of the car, for example up to the wheel arch. Because the skin 10 is made very thin, the foam filling extends over the whole internal surface to support the skin. In use, an impact occurring between the brackets 16 initially causes elastic deformation of the skin and of the foam filling, which both absorb energy. As the effect of the impact moves further into the bumper, the strap 12 is deflected backwards and is put into tension between its ends 36. As the tension in the strap increases, so does the amount of energy absorbed. When the strap is deflected, the pins 42 are pushed back through the centres of the bosses 38, and this also helps to absorb energy.

Claims: 1. A vehicle bumper comprising a plastics skin (10), a plastics foam filling (14) moulded in situ within the skin, and a metal strap (12) extending across the bumper inside the skin and encapsulated by the foam, characterised in that internal mounting brackets (16) are moulded integrally with the skin (10), the brackets being arranged for mounting the bumper on a vehicle and for supporting the ends of the strap (12). 2. A bumper as claimed in Claim 1, wherein the strap (12) is of metal. 3. A bumper as claimed in Claim 1 or Claim 2, wherein the strap (12) is clipped at each end to one of the brackets. 4. A bumper as claimed in any preceding claim, which has integral wrap-around ends (46) adapted to extend along the side of the vehicle body. 5. A bumper as claimed in any preceding claim, wherein the skin (10) of the bumper is less than 1.5 mm thick. 6. A bumper as claimed in Claim 5, wherein the skin (10) of the bumper is 1.2 mm thick. 7. A bumper as claimed in Claim 5 or Claim 6, wherein the foam (14) extends over the whole of the inner surface of the skin (10), to provide reinforcement to all parts of the skin. 8. A bumper as claimed in any preceding claim, wherein each bracket (16) has a flat top face (20) and walls (22, 24, 26) extending from the top face on three sides, the walls (22, 24, 26) forming the connection between the top face (20) and the skin (10), and the top face (20) carrying an integrally moulded threaded boss (38) by which the bumper can be attached to a vehicle. 9. A bumper as claimed in Claim 8, wherein the boss (38) is hollow and a metal pin (42) is inserted into the cylindrical cavity through the boss, the pin (42) extending through the boss and through the flat top face (20). 10. A bumper as claimed in Claim 8 or Claim 9, wherein the wall (24) on one of the three sides incorporates a lip (32) over which the strap (12) is clipped, and wherein stiffening ribs (34) are moulded in to brace the lip (32) against the wall (24) and to brace the wall (24) against the flat top face (20).

Inventors: CHURCHILL, JOHN, LEWIS, IDRIS
Applicants: FORD FRANCE SOCIETE ANONYME, FORD MOTOR COMPANY, FORD MOTOR COMPANY LIMITED, FORD-WERKE AKTIENGESELLSCHAFT
Application year: 1987
Main classification: B60R19
IPC codes: B60R19