- Extensive use of high strength steels throughout for strong safety performance
- More than 55 percent of body structure features high-strength and ultra-high-strength steel
- Body structure lighter than predecessor, improving fuel economy and CO2 emissions
- Array of pedestrian protection features
October 2008 – Under the stylish exterior of the new Ford Fiesta is a robust body structure, crafted from high-strength and ultra-high strength steels to protect occupants in the event of a collision.
The new Fiesta uses an exceptionally high level of cold- and hot-formed high-strength steels in its body structure for a car in this segment. More than 55 percent of the body structure is high-strength steel, including grades of very-high-strength, dual-phase steel and ultra-high-strength aluminised Boron steel.
Ingredients like these make the new Fiesta stronger and stiffer than ever. The Fiesta’s new shape is approximately 10 percent stiffer torsionally than its predecessor, providing its occupants with a robust safety cell.
Yet despite its advances in strength, the Fiesta’s body structure overall is lighter than before. This means advancements in safety have not been compromised at the expense of key attributes, like fuel economy and CO2 emissions.
Structural Strength for Safety
Under Ford’s safety strategy, high-strength steels are used in areas of the vehicle where structural strength and reinforcement are essential for crashworthiness. This includes the floor structure, front rails and beams and the ultra-rigid, integrated bodyside reinforcement ring to protect against side impact.
High strength materials were used to create a very stiff B-pillar section and stiff rocker section fore and aft. Impact loads are also transferred laterally to the opposite side of the car via chassis cross-members, to maximise dissipation of side impact forces.
This integrated bodyside reinforcement ring resists side intrusion in the unlikely event of a collision and helps the body structure manage the energy of other impacts effectively – be they frontal, offset or rear.
To create the bodyside reinforcement ring, high-strength-steel elements were welded into an ultra-stiff structure whose crash performance was carefully developed using advanced computer simulation technology, long before its first real crash tests.
Elements of the bodyside reinforcement ring include:
- A-pillar – The slim A-pillar forms the forward part of the vehicle’s stylish roof arch. It is fashioned from ultra-high-strength aluminised Boron steel. The A-pillar delivers the strength and rigidity required for crashworthiness while remaining fashionably slim, as a key element in the Fiesta’s dynamic design, and to minimise its potential to obscure driver visibility.
- B-pillar – Another Boron steel component, the B-pillar reinforcement is shaped for ultra-high strength. Its job is to resist intrusion and retain structural rigidity in the case of side impacts, while providing the strength to help the vehicle safety cell retain its shape in other crash modes.
- Rocker panels – The rocker panels are crafted from very-high-strength, dual-phase steels renowned for their energy absorption properties.
- Rocker baffles – To optimise the side-impact performance of the vehicle, uniquely shaped, twin-sheer baffles are welded to the inner rocker panel. These stabilise the rocker section to ensure that it performs optimally in the event of a side impact. This is designed to make the rocker panel and B-pillar act as a system, with the B-pillar retaining its shape and its connectivity to the rocker panel in a side impact.
- Side Roof Arch – Another dual-phase steel component – the side roof arch – joins with the A-Pillar to form the Fiesta’s strong roof profile and provide a robust top attachment point for the B-pillar.
- Lower A-Pillar – The lower A-pillar is formed of very-high-strength, dual-phase 600-grade steel.
These individual, high-strength elements are formed into an integrated subassembly during manufacture before they are joined to the vehicle on the production line. This new process ensures better joint strength and even better precision build for the overall body structure. It is also more weight efficient.
Even More High-Strength Steel
More high-strength steel can be found in other key areas of the new Fiesta’s body structure.
The dual-phase steel front frame rails and side rails feature structural actuation points – called trigger points – to initiate predictable collapse in crush zones. This is a key energy absorption feature. Forming the ‘triggers’ hardens the dual-phase material, giving it unique twin characteristics of energy absorption and energy resistance.
The underfloor structural beams or sled runners are formed from dual-phase steel, as are the lateral floor reinforcements, which help the structure manage side impact forces.
Such extensive use of dual-phase steel inspired the Ford body engineering team to develop new engineering techniques. Because dual-phase steels acquire greater strength after stamping, the team worked to quantify how much this added strength contributed to the overall body structure. Defining the ultimate strength of the assembly would help Ford’s sophisticated crash simulation computers model crash performance with a very high degree of accuracy.
The new Fiesta team created a new computer map of the strength of the body structure taking into account the components’ ‘forming history’.
Reinforcements in the roof, doors and floors of the vehicle are made from other gauges of high-strength steel, including a Boron steel door beam on three-door models. To support extensive use of high-strength steels, further manufacturing investment was required for new robotic welding heads equipped for mid-frequency welding to deliver optimal weld quality with the new materials, and replacing heads calibrated for normal 50Hz welding used milder steel grades.
Advanced passive safety features
The Intelligent Protection System (IPS) links the Fiesta’s restraints and passive safety technologies to perform as a single system designed to protect occupants in the event of a collision.
The impressive suite of restraint technologies found in the Fiesta’s IPS, includes the following:
- Dual front airbags for driver and passenger
- Three-point safety belts with dual-stage digressive load-limiting pretensioners for the front seat occupant positions
- Anti-submarining front seat design
- Whiplash-optimised front seats
- Beltminder safety belt reminder system for the front seat occupants
There are three-point safety belts in place for all five occupant positions, retractor pretensioner safety belts for the front seating positions and anti-submarining front seats.
The retractors pull the safety belts tightly to position the occupant ideally for airbag effectiveness, with a ‘dual-stage digressive load limiting’ feature that allows a slight reduction in belt tension to reduce risk of chest injury. The Ford Beltminder system encourages occupants to use their safety belts.
More Safety then Meets the Eye
The Fiesta’s safety features extended beyond those you can see from the cabin. A new front seatback design has been developed to give excellent whiplash protection. The design exceeded crash test requirements without requiring the use of active head-restraint technology.
The new Fiesta also has an additional safety feature located under the carpet in the front driver’s footwell. This is a special carpet underlay – called a ‘crash pad’ – situated between the floor panel and carpet, to minimise loading to the lower leg during an impact.
Looking Out for Pedestrians
The Fiesta’s kinetic design-inspired styling incorporates an array of features designed to protect pedestrians. From major design elements – like its distinctive clamshell bonnet and sporty windscreen rake – to small details like the breakaway spindles of its new aero windscreen wiper blades or the finely shaped headlamps, the Fiesta has been crafted around pedestrian protection.
The Fiesta’s clamshell bonnet helps protect pedestrians from impacting hard surface and sharp edges. Its rear corners are a particular pedestrian safety improvement, while its unique four-bar hinge – which allows the bonnet to open outward and upward – also plays a role in distancing the bonnet from the engine underneath.
The clamshell’s interior structure is as important as its curvy exterior. The pedestrian protection design target was to minimise an underlying structure with hard points that could cause head injuries. The bonnet therefore incorporates an innovative ‘hexagenous’ architecture – a term coined by Ford engineers to describe the reinforcement that comprises joined –up hexagon shapes which create space between the bonnet and engine.
Hard elements like the windscreen wiper motor have also been relocated to the outboard side of the engine compartment to remove other potential hard points of contact.
The front bumper design is another pedestrian-friendly design element. Its shape, known as a ‘tri-plane curvature’, comprises three curves, or planes, rather than being continuous curve. This limits the exposure of a pedestrian to the most damaging perpendicular impacts with the bumper.
The bumper also includes an integrated energy absorbing grille insert which acts as another key pedestrian safety element. It has been engineered with specific deformation properties to avoid causing pedestrian lower leg injuries. The Fiesta also incorporates a lower leg stiffener behind the fascia in the area of the lower spoiler. Its function is to ensure the pedestrian’s lower leg remains vertical and is not allowed to rotate below the vehicle.
Safety engineers and designers worked hand in hand to shape the fine detail of the new Fiesta’s distinctive headlamps to protect pedestrians, particularly children. The location and dimensions of the headlamps – a key design element of the front end – were carefully designed to minimise exposure for direct contact with the head in an impact. This is matched to the steeply raked ‘pedestrian-friendly’ windscreen.