Ibuki – The Next Mazda MX-5

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    Mazda officials describe it as a ‘near future concept roadster’ but the Mazda Ibuki which was unveiled at the Tokyo Motorshow last week is widely known to be the basis for the next Mazda MX-5/Miata that will debut in 2005. This will be the true successor to the Mazda which, when launched in 1989, re-established for enthusiasts around the world the concept of the lightweight open-top sportscar, in the process becoming the best-selling, lightweight open-top two-seater sportscar of all time (as recorded in the Guinness Book of Records).

    The Mazda Ibuki concept (‘ibuki’ comes from a Japanese word that refers to “breathing new energy into” and “adding vigor”) clearly showcases Mazda’s current efforts in both design and technology as the development team works to further refine the company’s famous lightweight, open-top sportscar.

    The overall aim with this concept was to further refine the fun-to-drive spirit that can be derived from a lightweight, open-top sportscar. At the same time, the design team has worked to advance the true roadster identity and further refine the levels of comfort and safety in a vehicle with the top down.

    In an effort to more fully realize ‘oneness’ between car and driver – a oneness that was the overall intent of the original MX-5 – the Ibuki design team has borrowed from the advanced front-midship engine layout of Mazda RX-8, although in this case employing an inline 4-cylinder engine.

    Overall vehicle proportions have been defined by extremely short front and rear overhangs that confidently signify the extreme fun-to-drive spirit achieved by the innovative engine layout. The overall shape is clean and simple, reminiscent of the original MX-5, with a wide and stable stance, pronounced fenders and the elegant use of oval shapes throughout the design.

    Isao Tohda, a key member of the Ibuki development team who also played an important role in the development of the Mazda RX-8 says: “We aimed for a sportscar that offers the sort of fun felt from being in firm control of one’s own driving. With Mazda Ibuki, our primary theme was to minimize the car’s yaw inertia moment, and to take Mazda’s own sports car values to the absolute extreme. Mazda Ibuki is not simply a concept of what the future has in store. It is an ultimate statement of the kind of roadster Mazda could be building before very long.”

    Essential to the success of Ibuki concept is the super front-midship layout that places all critical powertrain and accessory components within the wheelbase. The power unit, including the engine, radiator and key parts of the cooling system, is located towards the rear of the engine compartment, well behind the front axle. Compared to the MX-5, the engine is located about 400 mm more rearward and 40 mm lower. To achieve this position, Mazda’s design team moved the air conditioner unit behind the seats: an innovative idea that creates space within the dash section for part of the engine.

    At the back of the car, the rear-mounted air conditioner unit, fuel tank and main exhaust muffler are located ahead of the rear axle. The super front-midship layout allows substantial weight reduction in the front and rear overhangs, enabling a 15% decrease in yaw inertia moment compared with the MX-5. This decrease in the yaw inertia moment can be felt in the natural and linear handling, and superior control at the limit of tyre grip. The ultra-low yaw inertia moment in itself is said to promote the kind of driving fun expected of a lightweight sportscar.

    This layout also assures an adequate crushable zone, making a significant contribution to safety including the protection of pedestrians in accidents, according to a Mazda engineer.
    For the Ibuki, the engineers developed a twin backbone body structure. Based on the high-mount backbone frame concept employed for the RX-8, the structure comprises an open body frame with extensive reinforcements and a rigid lower backbone frame located beneath the transmission tunnel.

    This unique construction featuring upper and lower backbone frames helps the Ibuki achieve extremely high rigidity, a level of stiffness comparable to that of a closed body structure, while maintaining the extremely low weight demanded of a sportscar.

    In addition to the lightweight, high-rigidity body structure, the Ibuki employs lightweight materials at key strategic points. Reinforced plastic is used for the fenders, bonnet, rear floor panel and door outer panels. Brake discs and door inner panels are made of aluminum. The propeller shaft and power plant frame are of carbonfibre, while the wheels are of magnesium alloy. This judicious use of lightweight materials keeps overall vehicle weight down (though the kerb weight of the concept car has not been revealed)

    In addition to carefully choosing lightweight materials, the design team has also employed recyclable materials such as fibre-reinforced plant-based plastic wherever possible.

    The Ibuki has an overall length of 3640 mm, is 1720 mm in width, 1230mm in height and rides on a wheelbase of 2330 mm. The overall length is 315 mm shorter than that of the current MX-5 and a key design feature is a 380-mm reduction in the combined front and rear overhang lengths, as compared to the MX-5.

    With the exterior, Mazda capitalizes on these compact dimensions and the benefits of the twin backbone frame to give concrete support to driving functions. The oval body shape evokes a look of tension in repose, and the 18-inch wheels and run-flat tyres accentuate the car’s well-planted stance. Incidentally, double wishbone suspension is used at the front while a multi-link layout has been designed for the rear.

    Front and rear views inherit the familiar look of the first-generation Roadster/MX-5 married to a more futuristic design. The radically curved windscreen conceals the front pillars and gives occupants of the Ibuki a wide field of view as well as a distinctive character.

    “Sportscar design is a question of expressing the car’s frame, and begins by supporting driving functions,” explains Moray Callum, general manager of Mazda Design Division. “With the Ibuki concept, we aimed to visualize, as simply as possible, the car’s compact size and the undeniable excellence of its super front-midship layout. The results can be seen in a contemporary design that also manages to evoke the familiarity of past Roadster/MX-5. As we worked to develop the future direction of the Roadster, it was very important for the Mazda design team to fully understand and appreciate the original. The purity of the original design is particularly interesting to us.”

    The high-mount backbone frame presents an axis that integrates interior and exterior design. The interior expresses the strength inherent in the backbone structure that extends forward beyond the dashboard towards the bonnet and rearward to the cowl aft of the seats. This smooth continuity of interior and exterior is further emphasized in the smooth joining of the rear cowl and interior, and the way the passenger seat integrates with the body and creates a sense of unity between interior and exterior.

    Locating the air conditioning unit behind the seats confers two major advantages. First, it allows the engine to be mounted much further to the rear. Second, it helps enable improved independent left/right zoning so that occupants can obtain comfortably warm or cool air according to their individual needs, even when driving with the top down.

    Spot-cooling zones provide cool air for the neck, the back and the pelvis, and thighs, three areas of the body particularly sensitive to temperature change. Louvres are installed in the rear cowl section (for the neck), within the seatbacks (back and pelvis) and upper part of the centre console (thighs).

    For cold weather driving, a heating zone traps warm air between the occupants’ waist and lower extremities. Warm air is directed to the thighs from a louver in the top of the centre console. In this way, occupants enjoy a comfortable cabin environment during open-top driving, irrespective of the season or weather.

    The Ibuki’s proposed powerplant is a new, lightweight and compact 16-valve MZR 1.6-liter inline 4-cylinder engine equipped with sequential valve timing and lift for both intake and exhaust valves (dual S-VTL). Maximum power is expected to be 132 kW (180 ps) at 7500 rpm with the target peak torque as 180 Nm at 6000 rpm.

    The engine also features an integrated electric hybrid motor that improves acceleration and partly serves to control engine vibration, allowing the use of a lighter flywheel for heightened response.

    At low engine speeds, the electric hybrid motor provides torque assistance to boost acceleration from a standing start. Additionally, when the car is stationary, the hybrid motor automatically stops the engine from idling to save fuel and reduce emissions. The motor then restarts the engine automatically when the driver is ready to accelerate. Also, during deceleration the hybrid motor functions as a generator, using regenerative braking energy to recharge the battery.

    There is a 6-speed manual transmission which weighs less than the MX-5 gearbox and has reinforced synchronizers to give a decisive yet smooth shift feel – a hallmark of the MX-5-with its extremely short, precise throws.

    In an effort to advance safety in open-top vehicles, the Ibuki design team has installed a 4-point active roll bar into the front pillars and rear cowl section that instantly lifts up under impact sensor control to reduce occupants’ injuries in the event of a rollover.

    Powerful LED headlamps give improved visibility, and a keyless entry by ID card is provided. Other innovations include a unique side-parting boot offering a wider opening and easier access. In addition, a new audio system that combines the seat air conditioner ducts and speaker in one, delivers much clearer sounds. This feature enhances the open-top driving.


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