BACKGROUND OF THE INVENTION: A typical motor vehicle, for example a passenger car, comprises a chassis of unitary construction. In other words, a large number of individual panels are joined together to form a stress-bearing structure to which i. a. suspension, transmission and drive components can be affixed. An integral part of the chassis is the firewall which typically separates a passenger compartment from an engine compartment. Thus, in a front-engined vehicle, the firewall extends transversely across the vehicle ahead of and below the windscreen.

A firewall serves many purposes. For example, not only does the firewall contribute to the torsional stiffness of the vehicle chassis, it must also protect occupants of the vehicle from intrusion of the engine into the passenger compartment in the event of a collision and resist possible fire-breakthrough. Furthermore, the firewall serves to support various items of ancillary equipment, such as a dashboard, a steering column, a heater unit, a pedal box, a brake servo, etc.

The firewall of a typical vehicle is made from a sheet of pressed steel and is welded to adjacent panels making up the vehicle chassis. Since, in a front-engined vehicle, the firewall separates the engine from the passenger compartment, the steel firewall is normally clad with a layer of sound-insulating material. Since the firewall must be provided with a number of openings to allow components such as a steering column, throttle cable, brake control means and electrical cables, to pass therethrough, the

layer of sound-insulating material must be carefully positioned on the firewall so that it does not affect the operation of these components.

It is a general goal within the automotive industry to reduce the weight of vehicles and to simplify production techniques, whilst still maintaining accepted levels of comfort and refinement.

SUMMARY OF THE INVENTION: It is therefore an object of the present invention to provide a vehicle firewall which, when compared to present day constructions, lends itself to simplified manufacture whilst offering the possibility of reduced weight and fewer number of components.

This object is achieved by the vehicle firewall as claimed in claim 1.

Thanks to the provision of a double-walled firewall, a cavity between the firewalls is defined. This cavity contributes to sound insulation as well as providing a space within which various ancillary components of the vehicle can be housed. In this manner, an integrated assembly can be formed before the firewall is affixed to the remainder of the vehicle chassis. Furthermore, the double-walled structure provides increased protection against engine intrusion into the passenger compartment in the event of a frontal collision.

Preferred embodiments of the firewall according to the present invention are defined in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS:

The invention will be described in the following in greater detail by way of example only, and with reference to the attached drawings, in which Fig. 1 is a simplified schematic perspective view of a vehicle equipped with a vehicle firewall according to the present invention; Fig. 2 is a schematic perspective view of a firewall according to the present invention functionally integrated with a vehicle dashboard construction; Fig. 3 is a schematic sectional view along line III-III of Fig. 2; Fig. 4 is a schematic perspective view of a second embodiment of a firewall according to the present invention functionally integrated with a vehicle dashboard construction, and Fig. 5 is a schematic sectional view along line V-V of Fig. 4.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS: In the drawings, reference numeral 10 generally denotes a firewall according to the present invention. With particular reference to Fig. 1, the firewall 10 is intended to be arranged transversely in a vehicle 12. The firewall comprises a first wall 14 and a second wall 16, with the walls being substantially mutually parallel. Although in the drawings the first and second walls are shown as being substantially coextensive, this is only a preferred embodiment and the invention may be realised with a

firewall having one wall which extends at least 60%, preferably at least 80%, over the surface area of the other wall.

As is apparent from Figs. 1,3 and 5, the first wall 14 and said second wall 16 are spaced by a distance of between 1 cm and 40 cm, preferably between 5 cm and 30 cm, most preferably about 20 cm, to thereby define a cavity 18. In a manner which will be explained later, the provision of a cavity 18 contributes to sound absorption as well as providing a space for housing items of ancillary equipment.

In terms of choice of material for the firewall, it is to be appreciated that, dependent on i. a. weight constraints and manufacturing techniques, any material which offers the required properties as regards strength and fire-resistance may be used. Due to the provision of a double-walled firewall, it is sufficient if only one of the two walls is made of a material which fulfils the above-mentioned requirements. Possible materials may thus be selected from the group consisting of steel, aluminium, magnesium, glass- fibre reinforced polypropylene, ABS, glass-fibre reinforced polyester and talcum-filled polypropylene, or a laminate thereof.

In terms of weight-saving, it is advantageous to produce the firewall from a plastic material. A suitable material is hot-pressed glass-fibre reinforced polypropylene having a 40% glass fibre content. An advantage with this method of production is that relatively intricate shapes can be attained without the need for subsequent finishing steps.

In a further embodiment, one or both of the walls of the firewall may be made from a laminate of sheet metal and plastic, preferably joined together by a polymer foam. Such a laminate provides excellent sound-insulation properties

whilst the metal plate ensures high resistance to fire breakthrough.

Irrespective of the choice of material or materials for the firewall, it is to be understood that the thickness of the first wall and the second wall need not be identical.

Indeed, the thickness of each wall may be varied at different locations on the respective wall to thereby provide regions of increased stiffness, for example at mounting points for ancillary equipment.

In an alternative preferred embodiment, one wall of the firewall may be made from a fire-resistant polymer and the other in a sheet material to which plastic components may be affixed.

Due i. a. to the production techniques which may be employed to manufacture the firewall of the present invention, the firewall may be functionally integrated with other components of the vehicle. By the expression"functionally integrated", it is meant that the firewall of the vehicle is arranged so that it serves at least two distinct functions. Thus, and with particular reference to Figs. 2 and 3, the firewall 10 according to the present invention may also serve as a support for various driving units, this task previously being performed by a separate support member extending between the A-posts of the vehicle. The expression"driving units"hereby denotes any vehicle system or component which is located between the A-pillars of a vehicle. Accordingly, the firewall of the present invention may be adapted to support driving units such as a steering column 20, a passenger airbag 22, an instrument housing 24 and a dashboard panel (not shown).

As is apparent from Fig. 3, the firewall 10 may also be functionally integrated with a vehicle dashboard structure,

generally denoted by reference numeral 26. The expression "vehicle dashboard structure"hereby denotes a generally transversely extending structure which is adapted to support instruments, switches, heater controls, ventilation channels, etc. Thus, in one embodiment of the invention, the second wall 16 of the firewall 10 extends beyond the upper edge of the first wall 14 and constitutes a lower surface of the dashboard structure. The second wall and the dashboard structure may cooperate in such a manner that the second wall 16 partially delimits an air ventilation or heating channel 28 in the dashboard 26 structure.

In a further embodiment of the invention, and as shown in Fig. 3, the firewall 10 may be functionally integrated with a floor section 30 in the vehicle. Thus, the first wall 14 extends beyond the lower extreme of the second wall 16 to constitute a section of the floor 30.

Since the firewall of the present invention may be functionally integrated with e. g. the dashboard structure or floor, fewer components are required and assembly of the vehicle is facilitated.

As previously mentioned, the cavity 18 which is created between the first wall 14 and the second wall 16 of the firewall may be utilized to house items of ancillary equipment. Thus, and as illustrated in Figs. 4 and 5, a vehicle climate unit 32 may be adapted to fit within the cavity. Advantageously, the first and second walls of the firewall may be formed so as to serve as air passageways for the transportation of air to and from the climate unit 32.

In the event that the cavity 18 in the firewall is used to house items of ancillary equipment, then it is advantageous to provide at least one opening in either the first wall 14

or the second wall 16 to allow access to the items. Thus, and as shown in Figs. 1 and 4, one or more openings 34 may be provided in the firewall 10. In order to retain fire and sound insulation properties, the openings are preferably covered by a removable panel.

Before the firewall 10 is installed in the vehicle 12, any items of ancillary equipment may be secured in the cavity 18 between the two walls 14,16. The firewall 10 can then be mounted in the vehicle as a single complete unit. Naturally, should the firewall be functionally integrated with e. g. the dashboard structure of the vehicle, then the dashboard structure will also be included in the single complete unit for mounting in the vehicle.

The invention is not restricted to the embodiments described above and shown in the drawings, but may be varied within the scope of the appended claims.