GB2185714A

GB2185714A - Vehicle bumper assembly with mounting bracket connecting strap

Info

Publication number: GB2185714A
Application number: GB08601850A
Authority: GB
Inventors: Kevin O'neill; Idris Lewis
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1986-01-25
Filing date: 1986-01-25
Publication date: 1987-07-29
Also published as: GB8601850D0; GB2185714B

Abstract

A vehicle bumper assembly comprises a channel-section outer shell (12) of injection moulded plastics material extending transversely across the front or rear of a motor vehicle and having spaced apart brackets (32) for mounting the bumper on the motor vehicle. The brackets are fixed to a flat sheet metal strap (30). The strap (30) is moulded into an energy absorbing foam filling (24) adhered to the inside of the outer shell (12). In the event of impact the center portion of the bumper is supported by tension in the strap (30). <IMAGE>

Description

SPECIFICATION Vehicle bumper assembly with mounting bracket connecting strap This invention relates to a bumperassemblyof plastics material four a motor vehicle.

A known form of vehicle bumper of plastics material is shown from GB-A-2 118489 A. This comprises a box structure formed from an injection moulded channel section outer memberfriction welded to a backing plate injection moulded from the same material. This structure has been used on the Ford Sierra vehicle and allows considerable styling freedom together with sufficient strength and energy absorbing characteristics to meet the applicable European regulations. However, a sufficient thickness of material must be used to avoid droop when a vehicle fitted with the bumper is putthrough a paint oven and to provide adequate strength forthe bumperto survive low speed collisions without damage.

An improved bumper structure which allows a reduced thickness of plastics shell and obviates the needforan injection moulded backing member without loss of energy absorbing anddamagability characteristics is described in UK Patent Application No.8511191. By reducing the amount of shell material required,the cost and weight ofthe bumper is reduced.

The vehicle bumper assembly described in UK Patent Application No. 851 1 191 includesa channel-section outer shell of injection moulded plastics material for extending transversely across the front or rear of a motor vehicle and spaced apart brackets for mounting the bumper on the motor vehicle.

The outer shell is substantially filled with an energy absorbing foam adhered to the inside of the outer shell and the mounting brackets have arm portions moulded into the foam filling.

This kind of bumper makes effective use ofthe energy absorbing properties of the foam when used on vehicles which have a cross-member immediately behind the bumper because, in the eventofan impactthefoamfilling is crushed between the vehicle cross-member and the outer shell. The bumper need not have great beam strength because the main run is supported against bending in the event of an impact between the supporting brackets by contact of the foam filling with the vehicle cross-member. Another foam filled plastics bumper described in GB-A-2 151 993 uses a beam-like backing member to give the structure sufficient beam strength.

The present invention relates to an improvement ofthe bumper structure described in Appln. No.

8511191 which is suitable for use in vehicles that have no cross member immediately behind the bumper.

According to the present invention, there is provided a vehicle bumper assembly comprising a channel-section outer shell of injection moulded plastics material for extending transversely across the front of rear of a motorvehicle and having integral end portions for extending along the sides of the motor vehicle, and spaced apart brackets for mounting the bumper on the motor vehicle, the transversely extending portion of the outer shell being substantially filled with an energy absorbing foam adhered to the inside ofthe outer shell, characterised in that the mounting brackets are fixed one at each end of a substantially straight, sheet metal strap, the assembly of mounting brackets and strap being mouldedintothefoamfilling.

In use, the strap interconnects the ends of two longitudinal frame members of a vehicle so that impact in the centre region of the bumper produces tension in the strap which is transferred to the vehicle frame members. Because the strap operates in tension ratherthan as a beam it need only be of flexible, lightweight construction.

The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective diagrammaticviewfrom above of a motor vehicle front bumper embodying the invention; Figure2 is a section along the line Il-Il of Figure 1 showing the bumper mounted on the vehicle; Figure 3 is a section along the line Ill-Ill ofFigure2; and Figure 4 is a view of one end of the strap and mounting bracket assembly looking in the direction ofthe arrow IV in Figure 2.

Avehicle front bumper assembly 10 embodying the invention comprises an outer shell 12 of injection moulded polycarbonate plastics material. The shell 12 is of generally channel section with a transversely extending main run 14with integally moulded end portions 16 and 18 each of which extends along a respective side of the vehicle (of which only the front ends of longitudinal frame members 20 and 22 are shown in Figure 2).

The outer shell 12 is supported and strengthened by a foam filling 24 formed in situ in the main run 14 of the shell 12 with rearwardly extending runners 16 which underlie and supportthe upper surfaces of end portions 16 and 18.

Two sheet metal mounting brackets 32 are welded one at each end of a flat elongate, flexible sheet metal strap 30. The assembly of strap 30 and mounting brackets 32 is moulded into the foam filling 24. Apertures 28 in this assembly allowthe foam to flow through during the foam moulding process.

Each bracket 32 comprises a mounting area 34 lying substantially parallel to the strap 30 and four flanges 36 welded to the strap to form a box structure. Adhesion of the foam to the brackets 32 and the key provided by their shape ensures good retention ofthe brackets in the foam filling overthe lifetime ofthe bumper.

Bolts 40 fixed to each mounting area 34 enable fastening of the mounting brackets 32 to the forward ends of longitudinal frame members 20 and 22 as shown in Figure 2. The rear ends of the end portions 16 and 18 are supported on the vehicle frontfenders by fastening means 46 described fully in GB-A-2 118 489.

Impact absorption requirements for the end portions 16 and 18 can be met without a full foam filling. The filling is carried round the corners ofthe bumper up to surfaces 54. The runners 26 and 28 line onlythe upper part of the end portions 16 and 18 to supportthe uppersurfaces against any tendency to sag when the vehicle is putthrough a paint oven.

The bumper may be made by the method described and claimed in our UK Patent Application No.8511191. The outer shell is placed in one partofa moulding tool. Avacuum formed polypropylene liner is held in place on the other partofthe moulding tool by vacuum. The liner and contacting face ofthetool have the shape required for the outer surface ofthe foam filling 24. The tool is closed with the mounting bracket and strap assembly in its required position relative to the outer shell 12.

Atwo component polyurethane foam material made by mixing a polyol and isocyanate is introduced into the mould and allowed to reactand foam to fill the mould cavity. After partial curing the bumper is removed from the mould and left to finish curing with the liner over the outer surface of the foam. When the foam is sufficiently stable the liner is removed and reused in subsequentfoaming operations.

The foam material is selected for energy absorbing properties and for good adhesion to the polycarbonate shell and to the metal of the mounting bracket and strap assembly. The polypropylene liner prevents adhesion of the foam to the mould without requiring the use of liquid release agents which have to be cleaned off the finished bumper and can cause paint adhesion problems during laterfinishing processes.

In the event of a frontal impact both the outer shell 12 and the foam filling 24 contribute to the energy absorbing characteristics ofthe bumper. The beam strength of the bumper is not significantly increased bythe strap 30 but by acting in tension and thereby transferring frontal impact forces to the frame members 20 and 22, the strap greatly improves the energy absorbing capacity of the overall assembly in conditions of impact againstthe central region of the bumper.

The same structure may be used also for a vehicle rear bumper.

Claims

1. A vehicle bumper assem bly comprising a channel-section outershell (12) of injection moulded plastics material for extending transversely across the front of rear (20) of a motor vehicle and having integral end portions (16 and 18) for extending along the sides ofthe motor vehicle, and spaced apart brackets (32) for mounting the bumper on the motor vehicle, the transversely extending portion (14) of the outer shell (12) being substantiallyfilled with an energy absorbing foam (24) adhered to the inside of the outer shell (12), characterised in that the mounting brackets (32) are fixed one at each end of a substantially straight, sheet metal strap (30),the assembly of mounting brackets (32) and strap (30) being moulded into the foam filling (24).

2. Avehicle bumper assembly as claimed in Claim 1 ,wherein the strap (30) is a flat relatively thin and flexible elongate member.

3. A vehicle bumper assembly as claimed in any one of the preceding claims, wherein that each mounting bracket (32) is formed from sheet metal with a mounting area (34) forthreaded fastening means (40) and flange portions (36) integral with the mounting area and welded to the strap (30).

4. Avehicle bumper assembly as claimed in Claim 3, wherein each mounting bracket (32) forms with its respective end ofthe strap (30) a rigid box structure so that any loads applied along the strap (30) are transferred to the mounting area (34).

5. Avehicle bumper assembly as claimed in any one ofthe preceding claimswhereintheoutershell (12) is injection moulded from a polycarbonate plastics material and thefilling (24) is made from a two component polyurethane foam material.

6. A vehicle bumper assembly substantially as hereinbefore described with reference and as illustrated in the accompanying drawings.

7. A motor vehicle having a end structure which includes spaced apart longitudinal frame members (20 and 22) and a bumper assembly (10) as claimed in any one of Claims 1 to 6, wherein inthattheframe members (20 and 22) are connected bythe strap (30) so that in the eventofimpactagainstthe bumper(10) between the mounting brackets (32, the area ofthe bumper between the mounting brackets (32) is supported against bending by tension in the strap (30).