More than one hundred years ago, a kind
of disc brake, which was called spot-type disc brakes was developed by
Frederick William Lanchester, a British engineer. However, the American
inventor Elmer Ambrose Sperry had designed the earliest disc brake in the
1890s. And during the Second World War, benefited from to the development of
the aviation industry, aircraft disc were also used on automobile. That kind of
brakes was improved from Sperry's and called clutch-type disc brakes.
Spot-type disc brake improvements can be
traced back to the 1950s.Today, this kind of brakes used in automobile today is
similar to the one in 1950s. Because of superior water resistance and fade
performance, disc brake has become more popular than drum brakes in the United
States since 1970s. (Harper, 1998)
A modern spot-type disc brake includes some
major components: the rotor or disc, caliper, brake pad assemblies and a
hydraulic actuation system. The rotor is firmly fitted on the axle hub. So it
will rotate with the automobile wheel. The pair of brake pad assemblies, the
main friction component, and the other components has to be pressed against the
rotor, in order to provide the friction torque to slow down the rotation speed
of the wheel. The hydraulic pistons, with the caliper cover, drive the pad
assemblies. All of these components are known as the master cylinder. When the
brake pedal is depressed, the hydraulic pressure in the pistons housed inside
the caliper will increase. That means the master cylinder transforms the brake
pedal's motion to hydraulic pressure, which is attached by brake lines and
hoses to the caliper.
The
figure about the automotive brake system
The brake pad assemblies consist of a
friction material, mounted to a rigid pad. And friction materials are always
considered as composite materials. Bergman and Jacko state that more than 25
components of a brake pad are termed the friction material. These can be
divided into five types: a matrix, fibres, friction modifiers, mineral fillers,
and solid lubricants. (Kinkaid, 2003)
In 1978, After Felske’s experimental
work, he believed that the coupled vibration of the disc brake assembly lead to
brake squeal. He found that "the greater the coefficient of friction of
the rubbing surface, the more the likelihood of squeal". Nishiwaki who was
working for the Toyota Motor Corporation, found that brake squeal could be
eliminated by improving the rotor (or disc). His group eliminated a lot of
cooling fins in the vented brake rotor. And Saad's experimental results in a
recent also emphasized the importance of brake pad resonance in squeal.
(Kinkaid, 2003)
Rhee, working at Allied-Signal Inc.,
observed the formation and destruction of friction films on the rotor in a
series of dynamometer tests. And then he recorded effects on brake squeal. Rhee
reported that brake squeal did not occur from an initial state to a stable
state when the coefficient of friction was stable in the temperature range of
100– 300 degrees Celsius. High temperature eliminated squeal. However, this
process also severely damaged the rotor and the pads. (Rhee, 1990)
No comments:
Post a Comment