Friction Clutches
Friction clutches are by far the most well-known type of clutches. The purpose of friction clutches is to connect a rotating member to one that is stationary, to bring it up to speed and to transmit power with little slippage.
- Materials
Various materials have been used for the disc friction facings, including asbestos in the past. Modern clutches typically use a compound organic resin with copper wire facing or a ceramic material. A typical coefficient of friction used on a friction disc surface is 0.35 for organic and 0.25 for ceramic. Ceramic materials are typically used in heavy applications such as trucks carrying large loads or racing, though the harder ceramic materials increase flywheel and pressure plate wear.
- Push/Pull
Friction disk clutches generally are classified as push type or pull type depending on the location of the pressure plate fulcrum points. In a pull type clutch, the action of pressing the pedal pulls the release bearing, pulling on the diaphragm spring and disengaging the vehicle drive. The opposite is true with a push type, the release bearing is pushed into the clutch disengaging the vehicle drive. In this instance, the release bearing can be known as a thrust bearing (as per the image above).
- Dampers
In addition to the damped disc centres which reduce driveline vibration, pre-dampers may be used to reduce gear rattle at idle by changing the natural frequency of the disc. These weaker springs are compressed solely by the radial vibrations from an idling engine. They are fully compressed and no longer in use once drive is taken up by the main damper springs.
- Load
Mercedes truck examples: A clamp load of 33 kN is normal for a single plate 430. The 400 Twin application offers a clamp load of a mere 23 kN. Bursts speeds are typically around 5,000 rpm with the weakest point being the facing rivet.
- Manufacturing
Modern clutch development focuses its attention on the simplification of the overall assembly and/or manufacturing method. For example drive straps are now commonly employed to transfer torque as well as lift the pressure plate upon disengagement of vehicle drive. With regard to the manufacture of diaphragm springs, heat treatment is crucial. Laser welding is becoming more common as a method of attaching the drive plate to the disc ring with the laser typically being between 2-3KW and a feed rate 1m/minute.
Read more about this topic: Clutch
Famous quotes containing the words friction and/or clutches:
“We have got onto slippery ice where there is no friction and so in a certain sense the conditions are ideal, but also, just because of that, we are unable to walk. We want to walk so we need friction. Back to the rough ground!”
—Ludwig Wittgenstein (1889–1951)
“Before the birth of the New Woman the country was not an intellectual desert, as she is apt to suppose. There were teachers of the highest grade, and libraries, and countless circles in our towns and villages of scholarly, leisurely folk, who loved books, and music, and Nature, and lived much apart with them. The mad craze for money, which clutches at our souls to-day as la grippe does at our bodies, was hardly known then.”
—Rebecca Harding Davis (1831–1910)