| Land Rover’s Discovery 3 features an
all-new Integrated Body Frame, a stiff but lightweight frame that has
been constructed using high-technology production techniques such as hydroformed
side-members mated to a resistant body structure that incorporates the
latest high-strength steels. It fulfils a complex series of functions
including providing a stable foundation for the vehicle, enclosing and
protecting vital systems and giving a stable platform for the sophisticated
electronic control systems.
To take the complex shape into production required extensive use of hydroforming,
the Discovery 3 being developed from the concept stage specifically to
incorporate hydroformed components enabling Land Rover engineers to exploit
the full potential of the technique.
The hydroforming process uses fluid pressure in place of the punch in
a conventional tool set to form the part into the desired shape. In the
case of the Discovery 3, the hydroformed side-members begin life as welded
tubes of nominal 3 mm thickness which are bent to the basic shape. The
embryonic frame is placed in a die and a special liquid emulsion –
which includes lubricating and rust-proofing compounds – is forced
in at pressure of up to 1,310 bar. At this pressure, the steel is forced
into the die to take up the shape of the finished component.
Hydroforming allows single large components to be produced to tight tolerances
– components that would otherwise have to be made from multiple
stampings.
This makes the frame of the Discovery 3 structurally more efficient than
a conventional chassis, being lighter in weight and with more precision
that a conventional design.
The hydroformed side-members are incorporated into the frame, which also
features conventional pressed components where appropriate for strength
and function. These components use high-strength, low-alloy steel of between
2 and 5 mm thickness to achieve maximum strength for minimum weight.
The holes required for the mounting of components such as fuel lines and
air suspension pipes are cut by laser into the side rails before assembly
into the frame. This method is also used for the precise location of the
sensors serving the vehicle’s dynamic control systems.
The position of the paint drain holes has been carefully designed to achieve
maximum coverage inside the frame. The painting regime is designed to
prevent corrosion, extending chassis and vehicle life.
Use of hydroformed components has enabled Land Rover to take full advantage
of the latest computer design techniques. The design was subjugated to
a number of ‘virtual’ iterations before any metal was cut,
avoiding lengthy prototype build phases. This also enabled the design
teams to work together with manufacturing engineering to ensure efficient
production. Typifying this approach, the sinuous side-members provide
width and stability where required in the centre section in the centre
section while tapering in at the front to assist in giving the Discovery
3 a respectable turning circle.
The complex form of the frame reflects its contribution to the safety
and crash performance of the Discovery 3. The front structure of the frame
is designed to provide the collision load path with buckle points to control
its collapse. The load path is deliberately designed to be low down in
the structure to take into account differential crash performance. The
front structure design is intended to impact any smaller vehicle low down,
at its strongest point. The rear structure is designed to protect the
fuel tank and its filling system, while the substantial side-members help
protect the vehicle from side impacts.
In order to keep the body weight, which is manufactured like a conventional
monocoque, as light as possible, Land Rover engineers incorporated aluminium
while boron steel, which makes up two per cent of the total body structure
by weight, was used for the integrated A-pillar front cant rail reinforcing
member and for the B-pillar reinforcement, giving high strength for minimum
weight. The material can also be found as the side intrusion beams in
all four doors. Lightweight magnesium alloy is used for part of the front
structure and forms part of the front crush crumple zone. Both the bonnet
and the upper and lower tailgates are made from aluminium.
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