NEW YORK – Volvo Car's upcoming '06 4-seat convertible will bow at the Frankfurt auto show in September.

The C70 successor has an innovative retractable 3-piece hardtop that converts the vehicle into a coupe at the touch of button. Also new is a side inflatable curtain to provide enhanced head protection in side impacts and rollovers.

Volvo C70

The inflatable curtain is embedded in the door and inflates upwards when it deploys. Volvo engineers designed the curtain to be extra stiff when fully inflated so that it can stay upright after it deploys and provide head protection.

Unlike conventional airbags that deflate almost immediately after reaching full inflation, the C70 replacement's air curtain deflates slowly to maintain head protection in the event of a rollover.

About the same size as the current C70, the new model also accommodates four occupants. It uses the same platform architecture as the S40 and V50 models. Pininfarina SpA designed the body, but Volvo engineers gave it extra rigidity and safety to compensate for the topless mode.

“We started with the coupe design,” says Fedde Talsma, design manager for the C70. “When we were satisfied with the result, we made the necessary adjustments to create a convertible out of the coupe lines.”

Volvo says the body has a network of beams that enhance safety and at the same time provide high torsional rigidity. Without the roof, the C70 is twice as stiff as its predecessor. When the roof is up, torsional rigidity increases another 10%-15%, the auto maker says.

The U.S. model will come with only one engine, an inline turbocharged 5-cyl. that generates 218 hp and 236 lb.-ft. (320 Nm) of torque. European buyers also will be offered two 2.4L normally aspirated engines generating either 170 or 140 hp.

Some time after its '06 introduction, Volvo also will offer a 180-hp 5-cyl. in Europe.

The original C70, which was introduced in 1998, enjoyed its best sales year in 2004 when 8,000 units were delivered worldwide. Volvo sold 4,069 of the cars in the U.S. last year. There is no '05 model. (See related story: Volvo C70 Ends Run)

“We expect to more than double our sales compared with the first-generation C70,” says Volvo President and CEO Hans-Olov Olsson.

The car will go on sale in the first half of next year.

Like its predecessor, the new C70 will be built in Volvo's Uddevalla, Sweden, plant.