|
Powershift Clutches
Operated exclusively in oil-cooled environments, powershift clutches are used in automatic and semi-automatic transmissions to change gear ranges and are usually engaged under full engine power. Powershift clutches may be range clutches which typically require high friction coefficients, or direction clutches, which require good durability and high power absorption characteristics.
Lock-up Clutches
Used with a torque converter on a powershift transmission, Lock-up clutches bypass the torque converter to transmit power directly from the transmission to the powershift drive line. This is a low-speed, high-torque application.
PTO (Power Take-Off) Clutches
Used to supply power from the vehicle engine to auxiliary devices such as implement pumps for loaders, refrigeration units, etc. Material requirements typically include good engagement characteristics and the ability to absorb high energy without wear.
Differential Lock Clutches
Locks the differential to insure that both rear wheels turn at the same speed when operating on different surfaces. A differential lock clutch must be disengaged for turns and re-engaged on demand. Material requirements often include a very high static friction coefficient and many designs use high apply pressures.
Wheel Brakes
These are fade-resistant, high capacity brake systems used in heavy duty applications. Rotating friction discs, similar in design to clutch discs, are packed alternately with fixed steel separator plates in an oil filled compartment. Material requirements include a low static-dynamic ratio (in order to eliminate chatter), good durability and thermal stability.
Automotive Automatic Transmission Clutches
Friction elements to drive or hold components of the planetary gear system are usually categorized as either “shifting” or “static.” For shifting elements, timing and smoothness are facilitated by selecting a material with a dynamic friction coefficient which is both uniform and generally high. The static coefficient must be relatively low to prevent a torque peak at lockup. In addition, engagement characteristics are usually controlled to help minimize extended, abrupt and/or “jerky” operation. Applications characterized as static (i.e. neutral to drive or reverse) will engage at low speed where capacity must be sufficient to meet engine stall requirements: therefore, a high static coefficient of friction is desirable. These elements are often subjected to high apply pressures so material strength is also an important consideration.
|
