GB2341353A

GB2341353A - Bulkhead assembly

Info

Publication number: GB2341353A
Application number: GB9819739A
Authority: GB
Inventors: Bhagat Nagra; Michael Mellor
Original assignee: MG Rover Group Ltd
Current assignee: MG Rover Group Ltd
Priority date: 1998-09-11
Filing date: 1998-09-11
Publication date: 2000-03-15
Also published as: GB9819739D0

Abstract

A bulkhead assembly for separating an engine compartment from a passenger cell of a motor vehicle comprises an inner wall 11 and an outer wall 12, at least one of the walls being provided with at least one region defining a cavity 60, 62 which acts as an acoustic resonator for the engine compartment or the passenger cell.

Description

2341353 - 1 Bulkhead Assemblv The present invention relates to an improved

bulkhead assembly for use in a motor vehicle or the like. In particular, the improved bulkhead assembly has advantageous acoustic attenuation properties.

It is known to provide a single firewall or bulkhead assembly between an engine compartment and a passenger cell of a motor vehicle. Such a bulkhead assembly is usually fastened to a structure of the motor vehicle.

In order to provide sound or noise insulation from the engine compartment to the passenger cell it is necessary to provide a sound insulating material in the bulkhead assembly. However, at certain resonant frequencies, typically between 200 Hz and 300 Hz, transmission loss through such current firewalls may not be adequate.

It is an advantage of the present invention that it addresses this problem and provides an improved bulkhead assembly.

According to a first aspect of the present invention, there is provided a bulkhead assembly for a motor-vehicle, the motorvehicle having an engine compartment and a passenger cell separated by thh bulkhead assembly, the bulkhead assembly comprising an inner wall and an outer wall, characterised in that at least one of the walls is provided with at least one region defining a cavity.

This has the advantage that it provides a measure of sound attenuation.

Preferably the or each cavity has dimensions such that the or each cavity acts as an acoustic resonator for the engine compartment or the passenger cell. Conveniently, the or each cavity has a depth corresponding to an integral multiple of a quarter wavelength of a dominant frequency in the region of the bulkhead assembly.

Preferably the or each cavity is provided with an opening.

Preferably, a noise and sound adsorbing material is disposed between the inner wall and the outer wall of the bulkhead assembly.

The invention will now be described, by way of example only, with reference to the accompanying drawing in which: - Figure 1 shows an exploded pictorial representation of a bulkhead assembly according to the invention; and Figure 2 shows a cross-sectional view of a bulkhead assembly according to the invention.

With reference to Figures 1 and 2 there is shown an inner bulkhead 11, an outer bulkhead 12 and a number of components of a motor vehicle in the form of a blower fan 13, an electronic control unit housing 14, an air conditioning evaporator 15, and a heater unit 16 all of which are supported by the inner and outer bulkheads 11, 12. The bulkhead assembly formed by the inner and outer bulkheads 11, 12 therefore provides a support for a number of components of the motor vehicle that can be attached to one or other of the inner and outer bulkheads 11, 12 before the bulkhead assembly is fitted to a structure of the motor vehicle to provide a separator between an engine compartment of the motor vehicle and a passenger cell of the motor vehicle.

At least one and preferably both of the inner and outer bulkheads 11, 12 are made from an impact resistant and flame retardant material and are covered in use by an aesthetically pleasing dashboard moulding 6.

The inner and outer bulkheads 11, 12 when fitted and secured together define an internal cavity. A noise and vibration absorbing material 27 is bonded, sprayed or moulded to the outer bulkhead 12 during manufacture of the outer bulkhead 12.

The inner bulkhead 11 is contoured to define the electronic control unit housing 14, a easing 19 for the blower unit 13, a casing 18 for an interior air temperature unit of the motor vehicle in the form of the evaporator 15 and the heater 16, a receptacle for a combined temperature control and air 5 distribution unit 51 and an integral pedal box support 22.

The inner and outer bulkheads 11, 12 when fastened together define a number of air supply ducts 34, 35, 36 that extend from the combined temperature control and distribution unit 51 to various outlets 32, 37 in the interior of the passenger cell of the motor vehicle.

A face vent duct 34 is formed by a first wall member 31 formed as part of the inner bulkhead 11 and a second wall member 33 formed as part of the outer bulkhead 12. The second wall member 33 also forms a side wall to a demist duct arranged to supply air to a number of demist outlets 38 which are located in close proximity to a windscreen 10 of the motor vehicle. A footwell duct 36 is arranged to supply air to a number of floor outlets 37 and extends around the periphery of the bulkhead assembly. The footwell duct 36 forms a box section which strengthens the bulkhead assembly and enables the outlets 37 to be positioned where required.

The contour of the inner bulkhead 11 is such as to form a casing 18 for an interior air temperature unit of the motor vehicle. The interior air temperature unit comprising of an evaporator unit 15 forming part of an air conditioning circuit and a heater unit 16 forming part of a heater circuit of the motor vehicle.

The inner and outer bulkheads 11, 12 are joined together at a number of points by welding and then the complete bulkhead assembly is fastened to structural members of the motor vehicle in the form of upper and lower box sections 25 and 26 by means of bolts 20.

In addition to provide improved sound attenuation in the inner wall and the outer wall forming the bulkhead assembly at least one of the walls is provided with at least one region defining a cavity or well 60,62,70. The dimensions of the or each cavity 60,62,70 are such that the or each cavity acts as an acoustic resonator for the engine compartment or the passenger cell.

In Figure 1, there are shown two such wells or cavities 60,62 formed in the inner bulkhead 11. A first cavity 60 is shown formed in the footwell ducting at one side of the first wall me mber 31.

A second cavity 62 is shown formed on the face vent duct 34. An example of such a cavity 62 is shown more clearly in section in Figure 2. The cavity 62 is formed in the first waR member 31. The cavity 62 may conveniently be formed by stamping, drawing or any other suitable method. The cavity 62 is defined by a side wall 66 extending from the first wall member away from the face vent duct 34. The side wall 66 of the cavity 62 terminates at an end face 68.

The length of the side wall 66 and hence the depth of the cavity 62 is chosen as an integral multiple of a quarter wavelength of a dominant frequency in that region of the bulkhead. This will provide the best sound attenuation at that location.

A third cavity 70 is shown in Figure 2 as part of the footwell duct 36 an in particular in the casing 18. The third cavity 70 is defined by a side wall 72 extending from the casing 18 away from the footwell duct 36. The side wall 72 of the third cavity 70 terminates at an end face 74. Again, the length of the side wall 72 and hence the depth of the cavity 70 is chosen as an integral multiple of a quarter wavelength of a dominant frequency in that region of the bulkhead. This will provide the best sound attenuation at that location.

The location of each of the first, second and third cavities 60,62,70 are shown for illustrative purposes only. It will be understood that the location of such cavities in other locations on the bulkhead panels is possible.

Each cavity or well, as well as other selected regions on at least one of the walls, may additionally be provided with an opening 80, for example as shown in Figure 1. Such openings allow for the attenuation of sound waves, in particular in regions of the walls which have a tendency to propagate 5 sound waves.

Claims

-8CLAIMS

1. A bulkhead assembly for a motor vehicle, the motor vehicle having an engine compartment and a passenger cell separated by the bulkhead assembly, the bulkhead assembly comprising an inner wall and an outer wall, characterised in that at least one of the walls is provided with at least one region defining a cavity.

2. A bulkhead assembly according to claim 1, characterised in that the or each cavity has dimensions such that the or each cavity acts as an acoustic resonator for the engine compartment or the passenger cell.

3. A bulkhead assembly according to claim 2, characterised in that the or each cavity has a depth corresponding to an integral multiple of a quarter wavelength of a dominant frequency in the region of the bulkhead assembly.

4. A bulkhead assembly according to any previous claim, characterised in that the or each cavity is provided with an opening.

5. A bulkhead assembly according to any previous claim, characterised in that a noise and sound adsorbing material is disposed between the inner wall and the outer wall of the bulkhead assembly.

6. A bulkhead assembly for a motor vehicle substantially as described herein with reference to and as illustrated in the accompanying drawings.