Gasoline cars have the same fuel efficiency as hybrid cars. Mazda's SKYACTIV technology overview (Part 3)

The continuous frame runs straight through

the SKYACTIV-Body. With a body structure that is 8% lighter and 30% more rigid than before, the basic frame is kept straight to the greatest extent possible, and the frame of each part is kept continuous, so that the load is borne by the entire frame as much as possible. The use ratio of high-tensile steel plates above 340MPa has also been increased from 40% to 60%.

Figure 12 shows a comparison between the conventional body structure and the SKYACTIV-Body. For example, the frames on both sides of the floor tunnel of the conventional frame are disconnected in the middle, while the extension of the front side member leading to the underfloor is bent and connected to the rear frame.

Figure 12 The SKYACTIVBody, with its basic skeleton straightened , achieves weight reduction by reducing bends and discontinuities.

In contrast, the newly developed body not only extends the frames on both sides of the floor tunnel to the rear, but also passes the extension of the front longitudinal beam to the underfloor at an inclined angle, so that it can be connected to the rear frame without bending. In addition, in the upper body, a continuous frame passes through the periphery of the door opening, and a ring-shaped frame that is continuous with the roof and floor passes through the center pillar.

As a characteristic structure, there is a large reinforcement material that strengthens the center tunnel (Figure 13). The opening of the center tunnel is reduced and the torsional rigidity of the body is improved.

As mentioned above, as a structure that is faithful to the basic requirements, the body of this time strives to reduce weight while improving rigidity, and the chassis is also taken into consideration in this improvement. One example is that a large hole is opened in the rear frame for the installation of the trailing arm of the rear suspension system (Figure 14).

Mazda said that the SKYACTIV-Chassis consists of a newly developed front strut suspension system (Front Strut Suspension), steering system and rear multi-link suspension system (Rear Multi Link Suspension). It not only reduces the weight by 14% compared to the past, but also improves the lightness in the low and medium speed sections, the stability in the high speed section, and the comfort in all speed sections.

To this end, the rear suspension system sets the mounting point of the trailing arm on the vehicle body at a higher position (Figure 15). In this way, the movement trajectory of the tire when passing over the protrusion can be inclined to the rear, thereby reducing the impact transmitted to the vehicle body and improving the ride comfort. Setting the mounting point of the trailing arm on the vehicle body at a higher position has the effect of suppressing the rear part of the vehicle body from rising when braking.

Figure 13 Large floor tunnel reinforcement material To meet the needs of the larger floor tunnel, the reinforcement material is also larger, which promotes the improvement of torsional rigidity.

Figure 14 Trailing arm mounting part of the rear suspension system A large hole is opened in the frame to raise the mounting position of the trailing arm.

Figure 15 Structure of the rear suspension system The front end of the trailing arm is bent upward

In terms of the front suspension system, the caster angle is increased to improve the sense of stability when driving at high speeds. Mazda said that on this basis, in order to obtain a light and agile control feeling in the medium and low speed range, the boost of the electric power steering system (EPS) is increased, and the sense of stability at high speeds and the lightness in the medium and low speed range are achieved at the same time. In terms of EPS that can achieve the above performance, the newly developed column drive EPS is adopted (Figure 16).

Figure 16 The electric power steering system is switched to column-driven EPS.
The Atenza class models will also change from the previous rack-driven EPS to a column-driven EPS that can more effectively utilize the space inside the engine compartment.

Previously, Mazda only used column-driven EPS in the Demio class. The Atenza class has been using rack-driven EPS, and the Axela class has been using electric hydraulic power steering (EHPS). This is because Mazda previously believed that the performance of column-driven EPS was not enough to be used in high-end models. However, due to its continuous improvement in recent years, column-driven EPS will be uniformly adopted in high-end models in the future. On the other hand, the

improvement in weight reduction is also remarkable. Mazda revealed that the 14% weight reduction of the chassis system is equivalent to about 50kg, which accounts for half of Mazda's 100kg weight reduction target. To achieve this, the chassis also adheres to the design that is faithful to the basic requirements. Specifically, the front and rear distances of the cross members (Members) spanning the left and right on the front and rear subframes are widened, and the distance to the cantilever mounting point is as close as possible so that the force from the cantilever can be received without loss (Figure 17).

Figure 17 Comparison of new and old subframes SKYACTIV-Chassis shortens the distance between the cantilever mounting position and the cross member, thereby achieving load transmission through axial force rather than bending.