Authored by:
Stephen J. Mraz
Senior Editor
stephen.mraz@penton.com

Resources:
Chevrolet, www.chevrolet.com
Ford Motor Co., www.ford.com
Video of air shutters of Chevy Cruze: tiny.cc/kyubg
Video of Curve Control in action: tinyurl.com/26ovyu3

Automotive designers and engineers have a long history of developing new features. Some, like tail fins and vinyl tops, are purely stylistic. But others, such as seat belts, air bags, and antilock brakes, prevent accidents and save lives. And then there are those such as hybrid drives and direct injection that save fuel. Here’s a look at a handful of brand new features — more evolutionary than revolutionary — that aim to make drivers safer and cars more fuel efficient.

Inflatable seat belts
Engineers at Ford Motor Co. took a look at the back seat, where small children and older adults most often ride, and determined they could do better at keeping those passengers safe. After all, front seats already have front and side air bags, seat belts, and padded dashboards. So they developed a hybrid safety device, the inflatable seat belt.

It looks more or less like a normal shoulder harness and lap belt that users buckle into. But beneath the seat, a steel cylinder about 4.5-in. long and 1 in. in diameter carries air compressed to 10 psig that fills the shoulder-to-lap portion of the belt when a side-impact crash is detected. The belt’s accordion-folded bag breaks through the belt fabric as it fills with air, expanding sideways across the occupant’s body in about the same amount of time it takes a car traveling at highway speed to travel 3 ft.

The inflatable belt uses the same accelerometers used to pick up the first signs of front and rear crashes, as well as side-mounted accelerometers and pressure sensors. The pressure sensors mount inside rear passenger doors and senses when pressure inside a door cavity increases as the door is being crushed.

When the sensor readings match those of a side crash, as determined by Ford’s exhaustive testing, the cylinder releases cold gas into the shoulder/torso section of the belt, inflating it within 40 msec of a side crash being detected. The pressurized gas travels up through the shorter portion of the belt and the female connector. A port in the female half of the buckle connects to a matching one in the male part of the buckle, letting the compressed air inflate the air bag tucked into the seat belt. (Seat belts will not inflate if a pressure sensor in the seat indicates no one is sitting in that seat.)

“We use cold gas because we don’t want to put hot gases, such as those created by chemical reactions to inflate front air bags, next to the passenger’s body,” says Saeed Barbat, manager of the Passive Safety Research Team at Ford.

Once inflated, the section of the belt stretching over the torso and up past the neck becomes five times as wide as the uninflated belt. This spreads the restraining force over a greater area to reduce bruising and better keep passengers in a safe position during crashes. The inflated belt also holds the neck and head in place and the inflation creates hoop stresses that pretension the seat belt.

The new air-bag-in-a-belt should reduce head, neck, and chest injuries, which children and older adults can be more susceptible to. The belts also function as traditional seat belts during front and rear impacts and are compatible with infant and child safety and booster seats. And like conventional seat belts, the inflatable version, along with its inflation equipment, will need to be replaced after a crash, assuming the car isn’t totaled.

Ford plans to offer the inflatable seat belts as an option on 2011 Explorers. The option, which should cost about $400, will be on the two outboard seats in the Explorer’s back seat. It won’t be in the middle seat because Ford reasons that the middle position is already the safest seat, the outside seats are more vulnerable to side impacts, and the middle seat is the one used the least.

Ford will monitor customer acceptance of the inflatable belt, says Barbat, and then firm up plans for rolling it out in other vehicles and other seating positions. Early testing already shows that 90% of people who tested the uninflated belts found them to be similar or more comfortable than conventional belts because they seem padded and feel softer. Ford engineers hope the improved comfort could entice more rear-seat passengers to buckle up. Currently, only 61% of rear seaters put on seat belts, compared to 82% of front seaters, according to the National Highway Traffic Safety Administration.

Curve control
Ford engineers also took a look at what causes accidents. One study revealed that 50,000 crashes just in the U. S. and over just one year were caused by drivers taking turns too fast. To drastically reduce that number, those engineers developed Curve Control, a safety subsystem that takes advantage of sensors and features already used for other subsystems. These include sensors for traction and roll control, as well as sensors for antilock brakes and engine controls. In fact, Curve Control (CC) required no new hardware, according to Tony Rendi, manager of Brake Control and Development at Ford.

In general, CC determines when a vehicle enters a turn too fast. It uses sensors that detect yaw and roll, longitudinal and lateral acceleration, vertical acceleration, wheel speed at each corner, direction the front wheels are pointing, and the direction the steering wheel is pointed. This last one is also taken as a measure of driver intent.

“CC engages when the vehicle is undergoing sustained understeer or plowing,” says Rendi. In understeer situations, the driver tries to apply more of a steering angle than the vehicle can respond to. In other words, the car doesn’t turn as quickly as the driver wants. Instead, the car’s momentum pushes the front of the car, forcing it to continue in a direction the driver does not want to go. In many cases, this results in the vehicle careening off the road.

To correct the situation, CC reduces engine torque, which is often enough to do get vehicle to follow the driver’s intended path through the turn. But if the situation is more dire, CC differentially engages all four wheels’ brakes, varying the braking force, and monitoring what effect braking is having. In some cases, CC can slow the vehicle by up to 10 mph in under a second. In the meantime, the car once again obeys driver’s steering commands. The gas pedal does not vibrate as it does in some cars when antilock brakes go into action, even as engine torque is reduced, but drivers will likely feel the deceleration, and appreciate it, according to Rendi. If braking is severe enough, the vehicles brake lights will illuminate.

Although road surface and tire condition play a role in CC, there are no separate sensors measuring these parameters. Instead, wheel slippage sensors, courtesy of traction control, take into account the tire-road interface and the coefficient of friction between them.

Sporty drivers need not worry that CC will cramp their driving style, says Rendi. “CC has been calibrated so that it does not intervene if drivers keep within the limits of the road and their tires, and grip is maintained. It will only take action during sustained understeer. We did quite a bit of testing and development on a wide variety of road types to ensure CC didn’t degrade the normal performance feel we want in our vehicles.”

CC will first appear in next year’s Explorer. On front-wheel-driver versions, CC will always be on. But in four-wheel-drive Explorers, a new feature called Terrain Management will adapt the drivetrain and suspension to various road surfaces or conditions. CC will be switched off in the Sand and Mud/Rut modes. “When driving in sand or mud, off-road drivers want to retain speed and momentum. So we didn’t want CC to throw in a torque reduction and bog the vehicle down, possibly getting it stuck or in a position that it loses traction.”

Curve Control will be standard on 90% of Ford’s pick-ups, crossovers, SUVs, and vans by 2015. The patented safety feature is expected to reduce the number of accidents, especially those that happen on freeway on and off-ramps.

Adaptable air inlet
At Chevrolet, aerodynamic engineers saw an opportunity to make next year’s Cruze Eco even more fuel efficient by giving it adjustable air shutters behind the front grille which open or close in response to vehicle speed and temperature. Signals from the power-management-control module supply vehicle speed, a proxy for engine performance, and a sensor measuring coolant temperature is used to monitor engine temperature. This makes the shutters part of the car’s cooling system.

The shutters are plastic, including the hinges, and a small dc motor powers a linear actuator that opens and closes the shutters. The front grille protects the shutters from road debris. The entire shutter assembly and motor weigh in at about 2 lb, according to Chevy.

On most trips, the shutters would never open. So Chevy engineers made sure to design in some flow even with the shutter closed, says Greg Fadler, manager of the Aerodynamics Group at Chevrolet. And if the shutters aren’t open, the radiator fan doesn’t spin. But if the engine does heat up, the first response is to open the shutters, not start the fan.

“Automobiles are more efficient, from a fuel-economy perspective, if you cool the engine with ram power rather than fan power,” says Fadler.

And if the engine continues to heat up, the radiator fan is eventually called on to provide the extra cooling. Chevrolet engineers have taken pains to ensure the Cruze’s cooling subsystem can handle the worst-case scenarios, including towing a heavy load through desert conditions.

Compared to most conventional vehicles, the big change aerodynamically is that the area behind the Cruze’s grille is not always open. When it is open, it creates drag. Being able to keep this area closed at times let Chevy engineers cut the Cruze’s coefficient of drag by 0.016 in many instances, which translates into an additional 0.5 mpg on average. But at highway speeds, the reduced drag adds another 1 mpg, according to Fadler.

“From the driver’s perspective, they don’t care what state the shutter is in, they just want the engine and cooling subsystem to stay within their normal operating ranges, and this feature gives the subsystem more options and improves gas mileage.”

Though the shutters were designed and tested to ensure they would last the life of the Cruze, accidents and failures are always possible. And because the shutters are part of the engine-control and emission subsystems, federal regulations mandate they be monitored by onboard diagnostics. So if the shutters are stuck in the full open or closed position, drivers will get a “Check Engine” light. If the shutters are open, the driver will only suffer slightly higher gas millage. And if they fail in the closed position, the cooling subsystem would use the radiator fan more often to keep the engine cool. In either case, a failure should not leave a driver stranded.

Chevy and GM are likely to put the feature in other vehicles if market research shows consumers like it. And odds are that the first group of vehicles to get the shutter assembly would be trucks and other vehicles likely to tow or carry loads because their engines see the biggest swings in cooling needs.

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