Converting kinetic energy into thermal energy when slowing down a vehicle: this is the role of brakes. In a disc brake, a disc rotor (referred to below as a “rotor”) rotating in conjunction with the wheels is pinched by a brake pad (referred to below as a “pad”), converting kinetic energy into frictional heat to generate braking force.
A caliper is one of the components of the disc brake, and performs the task of pressing the pad against the rotor. The relatively inexpensive type called the "floating type" or "cantilever type", in which one or two pistons are positioned only on one side of the caliper gripping the rotor, is widely adopted and in general use.
On the other hand, large and high-performance vehicles utilize the "opposed type" or "fixed type" caliper in which a total of 4 to 6 pistons per wheel are positioned on both sides of the rotor and press the pad. Because it has a fixed frame structure, unlike the floating type, it has the advantage of weight reduction and high rigidity that achieves stable braking force at limit performance.
Differences in the structure of the two calipers
To absorb a higher thermal energy load for braking, it is necessary to enlarge the area of the rotor and the pad, and the caliper also inevitably gets larger. The opposed type caliper is particularly suitable for large brakes for high-performance and large-sized vehicles because it can press the pads more efficiently and uniformly with multiple pistons.
ADVICS, which within the Aisin Group is responsible for the development and production of brake systems, has been delivering 4-pot caliper (four pistons per wheel) for large luxury vehicles such as Lexus and Mercedes-Benz, as well as floating calipers for general passenger vehicles. However, the field of premium sports cars with top-class power performance exceeding 500ps output was new to ADVICS in the first half of 2010. The development of 6-pot fixed calipers, which unites the company's various technologies, has begun.
It is recognized as technically difficult, with a conventional structure, to produce 6-pot fixed calipers with smooth, quiet performance and braking power suitable for a premium sports car. However, our development team members had a secret strategy: the world's first “center pin torque receiving structure.”
With conventional opposed type calipers, the pad is suspended from the caliper body with a pin. During braking, the pad moves slightly in the tangential direction of the rotor to abut the caliper body and receive the braking force. More specifically, the pad has a movement allowance of 100μm during braking, and because the pad instantaneously abuts the caliper at the rotational speed of the wheel, the larger in area and heavier the pad becomes, the greater the energy that produces a percussive sound. The developers concluded that "for 6-pot fixed calipers, there are limits in a conventional structureto eliminate this noise.”
In order to overcome these issues, the development team held repeated discussions and worked through trial and error to devise a center pin torque receiving mechanism. The center pin torque receiving mechanism has the world's first structure in which the pad is held by the inner peripheral pin (of the two peripheral pins, inner and outer, arranged in the center of the caliper) and the pad rotates around the inner peripheral pin. As a result, the momentum of the pad is mechanically reduced by about 25% compared to the conventional structure for more silent performance.