Clutches: Another Secret to Mazda’s “Jinba-Ittai” Driving Experience
Mazda is a car company that’s committed to delivering pure, “Jinba-Ittai” (horse and rider as one) driving exhilaration. To demonstrate its commitment, Mazda offers automatic and manual gearboxes, both developed under the same product development philosophy, for its sports car MX-5 as well as non-sports cars such as the compact Mazda2 and its SUV sibling CX-3. Because Mazda knows that for MT cars, a clutch plays a critical role in ensuring refreshing and liberating driving.
(Transmission of MX-5/ Clutch is located at the left back)
(Flywheel (left) and clutch disk (right))
(Flywheel in Clutch cover has the spring to be pressed by the clutch disk)
Clutches are one of the key differentiators between AT and MT car; a manual transmission requires driver to operate the clutch for gear shifting, whereas a gear is automatically shifted in automatic transmission. A clutch itself is mounted on a flywheel, a circular disk that spins on a high speed when the engine is running, and is attached to a shaft that connects to the transmission. A clutch disk, one of the major parts of the clutch, transmits drive generated by the spinning flywheel to the transmission. When the clutch disk is hard pressed against the flywheel, the drive is transmitted to the transmission through a shaft, but when the clutch disk is released from the flywheel, the transmission is disconnected. This is what happens when the clutch is “disengaged”. Conversely, the flywheel pressed against the clutch disk “engages the clutch”. When a car is started, the static clutch disk gets suddenly pressed against the fast-spinning flywheel in a manual gearbox. That’s why a driver needs to “ride the clutch” – gradually engaging the clutch to seamlessly accelerate from zero to 100.
A feeling of clutch control, from partially to fully engaging the clutch and how the car responds to the clutch, is referred to as a “clutch feel”, and “tuning” is all about adjusting and refining the clutch feel. Since tuning affects the ease and exhilaration of driving an MT car, Mazda takes tuning very seriously.
Mazda’s ongoing pursuit of “Jinba Ittai” driving experience is probably most critical to its lightweight sports car like MX-5. It means that clutches in the MX-5 MT models need to have a highly sophisticated balance of a feeling of clutch pedal operation, how the clutch affects car’s maneuvers, and operability and reliability of the clutch parts. Masami Masuno (left in picture) and Miyoko Ishikawa (right), both in charge of clutch development in Mazda’s Powertrain Development Division, say that in the fourth-generation MX-5’s clutch development process, they had driven all the past-generation Roadsters to make a comparison, followed by extensive analysis on each model’s clutch feel.
Characteristics of friction material used in a clutch disk and a cushioning plate play an important role in creating a desirable clutch feel. A cushioning plate is a thin, subtly waved metallic plate placed between a clutch disk’s friction materials. When a clutch disk is pressed against a flywheel, the subtle waves work as cushions to ease the rapid drive transmission. The clutch feel can vary depending on the degree of pressure on the cushions when the drive is transmitted. Another important factor to remember is that a friction material is a mixture of different materials; since the characteristics such as smoothness and stability are affected by the “recipe”, tuning starts as early as the friction material. Trials and errors on the friction material are made to improve the clutch feel.
(Cushioning plate are shown in red in between friction materials)
(The area shown works as a spring)
(Friction materials attached to clutch disk)
“We’re assuming that a clutch lasts for 100,000-kilometer driving distance, but its life will also depend on driver’s operation. To give you an extreme example, you can break a clutch in just ten minutes if you want to”, says Masuno. He’s right, because clutches are, in fact, “made to break”; in an unexpected car accident, making a clutch break before anything else will release the force and prevents other parts, such as the engine and transmission, from damage. The force generated by the engine is beyond imagination, I’m told, that passengers may get hurt by broken parts flying into the cabin.
Clutch control that becomes a part of the exhilarating driving is “seamless clutch engagement from low revolution, followed by confident, refreshing acceleration”. For Mazda, ideal clutch control enables a driver to naturally operate the clutch and his/her car responds exactly to the driver’s operation. Regardless of the models and transmissions, Mazda strives to develop cars that put a big smile on a driver’s face the moment he/she starts driving. That, according to a car company that celebrates the emotion of motion, is a beginning of the exhilarating driving experience.
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