Making an impact safely: Ford’s B-pillarless B-Max gets a battering

  • 30-Apr-2012 11:06 EDT
Ford4-12 B-MAX Safety crash c.jpg

Big bang theory becomes reality; Ford's B-pillarless B-Max side-impact test in Germany.

The warning buzzer sounded, a powerful electric motor spooled up, the cable tautened and 950 kg (2090 lb) of safety-test sled accelerated rapidly over 100 m (328 ft) to reach 50 km/h (31 mph) and slam into the side of Ford’s new B-Max to an accompanying cacophony of bending metal and screeching tires.

Being told that the B-Max, with its novel movable B-pillar solution (previously described by AEI here) would meet all necessary safety criteria in a side-impact test is one thing; watching and hearing it happen is convincing.

Confident though it is of the B-Max’s safety capabilities, Ford invited SAE Magazines to its Merkenich, Germany, R&D crash-test center to witness a demonstration involving what the company describes as part of a unique test program “to ensure the B-Max’s Easy Access Door System is as safe as it is innovative.” The test resulted in a maximum 85-mm (3.3-in) intrusion.

The system integrates the B-pillars into the hinged front and sliding rear doors, which allow unimpeded access to the rear seat. The doors, incorporating high-strength steel and boron structures form what is essentially a “movable” B-pillar as they are closed and latched to the body shell.

A possible particular concern for end users might be safety of children travelling in row two, so the test vehicle was equipped not only with a dummy driver but also two highly instrumented dummies representing 18-month-old and 3-year-old children. They easily “survived” to show that a drama had not developed into a crisis. They are the new “Q” generation of dummy, providing both improved kinematics and neck load measurements.

Ford is working on load-spreading inflatable belts for rear seat passengers, which it sees as being particularly effective for children above the age of 12 years, and for the elderly.

The “movable” B-pillar solution was a requirement from the start of the B-Max program, explains Chief Program Engineer Klaus-Peter Tamm. That was five years ago. Since then, some 5000 virtual test collisions have been completed and 40 real-world crashes—plus the one witnessed by SAE Magazines. Each physical test takes four days to set up.

Keeping the doors locked together and attached to the roof and floor—and the movable B-pillar in place—was crucial, and the car uses ultra-high-strength steel (UHSS) brackets that Ford has dubbed “crash catchers” to do the job.

A dedicated rig was built to test the efficacy of the latching. The forces involved in side impacts reached 165 kN (37093 lb); the combined weight of three typical elephants, as Ford drolly put it.

At 752 kN/rad, the B-Max has greater torsional rigidity than the Fiesta on which it is based and a curb weight about 80 kg (176 lb) more, some of that attributable to the extra strengthening in the side doors (they incorporate boron steel in key load bearing areas; high strength and ultra-high strength account for 58% of the body and doors structure) and also to the front seats with their integrated belt system. The front seat structures and mounting points use high-strength steels.

Tom Overington, Ford’s Project Safety Manager, said no auto company had done anything quite like the B-Max before in terms of safety, although there have been some cars with no—or only part—B-pillars, and Nissan had a B-pillarless sliding-door MPV in the 1980s.

“The way in which the front and rear doors of the B-Max are held in place in the event of an impact demonstrates an ingenious solution,” said Overington. This aspect was proved out about halfway through the overall development of the vehicle. “We did lots of simulation work looking at the performance of the latches and the loads they needed to take. And they work.”

The top latch takes a load of up to 11 kN (2473 lb). A “significant” amount of crash loading is through the roof structure, and there is extra structure in the floor to take loads from the door into the rocker. Subtle latch design using pins and cups is used to locate the doors.

The B-Max’s safety performance is “at least” comparable to a similar MPV with regular B-pillars, he states.

Tamm said the production version of the car meets the weight targets of 1200 kg (2645 lb)—1240 kg (2734 lb) established at the project’s conception. As well as the added strengthening for the doors, extra floor structure was also necessary to take loads from the seatbelt system.

In fact, the front seats, with their integrated belting, proved as equally—and possibly more—complex to design as the B-pillar and doors solutions, he says: “We had to integrate the whole seat structure and capture all loads and forces. The force has to flow down through the seats. We also had to ensure that ingress and egress for driver and front passenger was satisfactory. We put engineers from Ford of Europe and North America together with seat supplier Johnson Controls and restraint system supplier TRW to investigate requirements and manage it all. We called it our ‘task force.’ It was the first integrated seat that Ford had created.”

The accent on safety for the B-Max includes a very comprehensive airbag presence, with 3-D thorax side bags, curtain bags running the length of the cabin, and driver’s knee bag. For the first time, Ford provides switchable deactivation of the front passenger airbag to enable a rear-facing child seat to be carried.

To meet pedestrian safety requirements, the B-Max’s cowl area (between hood and windshield) has been designed to minimize hardpoints and a newly created dual-motor wiper system facilitates the motor and wiper mechanism being moved away from the center of the vehicle, a configuration that also enhances pedestrian protection.

The B-Max is offered with Active City Stop, which monitors the road ahead and applies braking automatically if it detects a potential accident situation evolving with a slow moving or stationary car ahead. And the car is the first Ford in Europe to be fitted as standard with emergency assistance, which helps occupants place a call to the emergency services. It requires no subscription and uses Ford’s voice recognition SYNC technology.

Ford is targeting a 5-star EuroNCAP rating for the B-Max.

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