Mazda SKYACTIV transmission, body and chassis technology

The new SKYACTIV-Drive automatic transmission features full range direct drive. Click to enlarge.

In addition to the new gasoline and diesel engines (earlier post), Mazda’s SKYACTIV technology portfolio includes new transmissions (automatic and manual), body and chassis technology. At a media workshop last week in Vancouver, Canada, Mazda engineers stepped through the highlights of the new SKYACTIV systems. (Mazda hosted Green Car Congress at the event.)

SKYACTIV-Drive six-speed automatic transmission. The new six-speed automatic (which is being applied in the Mazda3/Axela commencing production in Japan, earlier post) combines the advantages of continuously variable (CVT), dual clutch and conventional automatic transmissions.

SKYACTIV-Drive automatic transmission. Click to enlarge.

The heart of SKYACTIV-Drive is a newly-developed six-speed torque converter with a full range lock-up clutch for all six gears that Mazda calls “full range direct drive”. The lock-up clutch ratio has been raised from 64% from the current five-speed automatic to 88% during vehicle operation.

The early lock-up between engine and transmission by the torque converter (which enables engine output to be sent directly to the drive wheels) inhibits the characteristic loss of power during acceleration, delivering a more direct driving feel. Preventing engine output loss also improves fuel economy; Mazda calculates that the new transmission improves fuel economy by up to 7%.

High-precision hydraulics are required to support such a design. In order to make the necessarily fast and accurate oil pressure modulation possible in the first place and improve reliability, Mazda furnished SKYACTIV-Drive with a new mechatronics module.

The mechatronics control module is integrated into the transmission case, and features new software and new direct linear solenoids. Benefits include improved shift response and quality, higher precision, and less hydraulic fluctuation.

While maximizing the lock-up range is necessary to improve the driving feel and fuel economy, a negative effect is an increase in NVH (noise, vibration and harshness) because there is nothing to absorb the difference in the rotational speeds of the engine and transmission. Mazda developed a new torque converter to resolve this conflict. The expanded lock-up meant the role of the torus piece was confined to very low speeds. Therefore, it became smaller and thus creating space for an improved damper as well as a multi-disk lock-up clutch and its piston, which improve clutch durability and control.

SKYACTIV-Drive is available in two versions—a mid-sized version for up to 200 lb-ft (271 N·m) of torque, and a large version for up to 340 lb-ft (461 N·m) of torque—making the automatic transmission compatible with both SKYACTIV gasoline and diesel engines.

Newly introduced technologies in the SKYACTIV manual transmission. Click to enlarge.

SKYACTIV-MT six-speed manual transmission. Like the automatic transmission, the SKYACTIV-MT six-speed manual transmission will be launched in two versions to meet different engine torque requirements. The goal was to reduce weight by between 7 to 16% (depending on the model) relative to the current manual transmissions.

Optimized for front-engine, front-wheel-drive vehicles, the transmission features a new architecture with a shortened countershaft and no separate reverse idling shaft in the larger model; a common input gear is used for 1^st gear and reverse. A common input gear is used for 2^nd and 3^rd gear, and the length of the secondary shaft is reduced by 20%.

The SKYACTIV-MT features a light and compact layout. Click to enlarge.

With the shift knob having a 1.8-inch (4.57-centimeter) stroke from neutral to the in-gear position, the SKYACTIV-MT’s tight-shifting is reminiscent of the MX-5. To add precision and crispness, the shifter was designed to feel moderately heavy at the start of a gear shift and gradually became lighter, as if simply sliding into the next gear.

Mazda also reengineered the transmission case with a thinner metal, resulting in a 30% weight reduction compared to the current 6-speed manual transmission.

SKYACTIV-Body. The new SKYACTIV-Body weighs 8% less than its predecessor while the SKYACTIV-Chassis is 14% lighter. Mazda has set the goal of making all its next-generation models 220.5 pounds (100 kilograms) lighter than their predecessors.

To efficiently transmit forces, Mazda said, a lightweight yet strong body structure requires as many straight sections as possible. The layout also needs to be optimized so that forces are dispersed throughout the structure and not concentrated at localized sections. Mazda engineers created a design featuring continuous straight lines from front to rear, and curves were removed from the underbody to as great an extent as possible.

The suspension mounting positions at the rear, for example, are bonded directly to the underbody framework as a dual brace. Additionally, the four vertically-positioned ring structures used for the upper body are bonded to the reinforcement area of the underbody, further enhancing overall rigidity. Redeveloped suspension cross members not only enhance body rigidity locally but also improve it overall since the body mount positions were optimized in the process.

SKYACTIV-Body reduces weight by 8% while increasing rigidity by 30%. Click to enlarge.

Mazda engineers enhanced passive safety performance by re-engineering crash zones using multi-load paths. This structure efficiently absorbs the load at the time of a collision by dispersing it into multiple directions. For example, during a frontal collision, crash energy is dispersed from the front (and thus absorbed) along three continuous routes or upwards to the A-pillar, downwards through the underbody and via a middle path to the sides of the car body. The upper branch frame plays a multifunctional role. It not only diverts energy to the A-pillar but also works to counter any upward motion of the front frame since this would negatively affect the desired distribution of energy.

On the manufacturing side, weld bonding is used for the roof-rail section to create a circular ring-like reinforcing structure. Previously, the body assembly process meant that this structure was separate from the C-pillar section. With weld bonding, parts are attached in advance and sent to the assembly line as a unit. This same method was used in creating the wheel housing. The number of spot weld points also was greatly increased, contributing significantly to the body’s increased rigidity.

Additional advantages were generated by greatly increasing the use of high-tensile steels in the SKYACTIV-Body, and engineering efforts have paid off. Utilization of high-tensile steels has grown from 40 to 60%, thus reducing the weight of the car body while increasing its strength and rigidity at the same time.

High tensile steel usage rate. Click to enlarge.

SKYACTIV-Chassis. The SKYACTIV-Chassis achieves increased rigidity along with a 14% reduction in chassis weight thanks to newly developed suspension with front struts and a multi-link rear axle. The new chassis improves driving quality at all speeds (low- and mid-range agility as well as high-speed stability) following a complete re-engineering of rear suspension mountings, trailing arm position, steering components and set-ups (among other things).

SKYACTIV-Chassis technologies. Click to enlarge.

Mazda also developed a new electric power steering system that enhances the driving experience by providing an immediate response to the driver right from very low starting speeds. To prevent overreaction at higher speeds, Mazda optimized suspension links and enhanced rear-wheel grip to reduce yaw gain (or ease of turning). Meanwhile, a higher steering gear ratio (for more direct steering) was adopted, increasing yaw gain to maintain nimble steering at lower speeds. As a result, the vehicle is both agile and stable.

The firmer high-speed steering feel was reinforced by increasing the caster angle — and subsequent caster trail — on the front wheels, which enhances the steering’s self-aligning torque. Power steering assistance was then increased at lower speeds to ease steering and give it the desirably lighter feeling at such velocities.

To enhance the operational efficiency of the dampers in the rear suspension, the mounts were set at a position enabling a greater lever ratio. The damping force and rigidity of the top mount rubber were thus reinforced, reducing their impact on ride comfort. The position of the rear suspension trailing link attachment was also shifted upwards, thereby adjusting the direction of movement of the trailing links to more easily absorb longitudinal impact shocks from the road. This improves ride comfort while at the same time preventing the rear of the vehicle from rising. The result is increased stability when braking, which helps reduce stopping distance.

Source: Green Car Congress