(Old)
The clutch is a component that connects a driving and driven part in a mechanism. When the clutch is engaged, the power produced by the engine is transmitted through the clutch to the transmission. When the clutch is disengaged, the power flow stops at the flywheel. The clutch is generally made up of the clutch housing, the flywheel, the clutch disc (or discs), the pressure plate, the release assembly, and the controls. The clutch forces plate surfaces together under pressure. The disk clutch is a clutch which consists of a series of flat friction plates or discs (which enable power transmission) held together by a spring.
(Mike Byrnes, Bumper to bumper: the complete guide to tractor-trailer operations, p.92)
(New)
A multi-disk clutch, as shown in Fig. 11.7, consist of two sets of disks --- A and B. Disks of set A are usually made of hardened steel, while those of set B are made of bronze. Disks of set A are connected to the driven shaft by means of splines. Because of splines, they are free to move in an axial direction on the splined sleeve.
(Design Of Machine Elements, 3rd Ed., By V. B. BHANDARI, p.457)
2 - Uni-Directional Roller Clutches: (Mechanical Component)
(Old)
Roller Clutches are less noisy than toothed clutches. There is lesser engaging shock during engagement. Roller clutches can be operated at much higher speeds (up to 4 m/sec) than toothed clutches (0.7 m/s). Their simple design and ease in manufacture make them convenient for use in uni-directional operation, despite a bigger size and rapid wear. The wear is minimized by using hardened inserts at the contact faces.
(Joshi P.H., Machine Tools Handbook: Design and Operation, pg.332, Kayra Ermutlu)
(New)
This type uses a number of parallel rollers, which are sandwiched between the inner member and the inclined cam faces of a cylindrical outer member. The type shown uses a series of concertina-shaped strip springs to wedge the rollers between the two faces.
The unidirectional clutch application shown in Figure 3.54 is a torque converter. The hub of the unidirectional clutch is mounted on the casing so as to control the direction of movement of the converter stator.
The inner member is rigidly secured to a component casing. An anticlockwise movement of the outer member releases the rollers from the inclined cam faces of the outer member, and the outer member rotates freely.
If the direction of the outer track is reversed, the rollers are forced between the inner member and the outer inclined cam faces of the outer member. The rollers are wedged and prevent any slip taking place.
(Hillier's Fundamentals of Motor Vehicle Technology, V.A.W. Hillier, p.297)
3 - Bayonet-type clamping (Type of Fastening a Workpiece)
(Old)
In this system, a bayonet disk is used.The disk is provided with holes, slightly bigger than the heads of the fixing screws. The clear holes are connected with slots, slightly (0,5) bigger than the threaded diameter. The bayonet disk acts like a special washer. Rotating the disk to align the bigger holes with screw centers, allow allows removal (or insertion) of the plate without removing entire screws (or Nuts). Rotation of the disk in the opposite direction brings the smaller slots to the screw centers. Tightening the screws in this position, secures the work holder to spindle nose. Thus, we only have to loosen screws/nuts by a quarter turn, to remove the bayonet disk and the work holder. Similarly, securing work holder requires the rotation of the bayonet disk through small angle (15 degree), and turning the clamping screws/nuts through a small angle, to tighten them.
(P. H. Joshi, Machine tools handbook: design and operation, p.374)
(New)
This is a cylindrical cam with a part thread serving as a cam (Fig. 3.28). The motion of the bayonet is guided by the spherical-ended screw mating in the groove in the bayonet. A part of the bayonet groove is straight. The bayonet can be pulled back straight axially through the straight slot to provide ample clearance during loading and unloading of workpiece. for clamping the workpiece, the bayonet is first pushed forward through the straight groove to close the distance between the workpiece and the bayonet face. At the end of its straight portion, the bayonet is turned clockwise. The inclined groove in the bayonet acts like a part of a thread. the spherical-end screw pushes the rotating bayonet towards the workpiece to clamp it. To prevent the clamp from loosening due to vibrations the thread of helix angle of the inclined groove should be between 1 to 7 degrees.
(Jigs and Fixtures By P. H. Joshi, p. 65)
4 - Hydro-dynamic bearings (Bearings, Mechanical Component)
(Old)
Hydro-dynamic bearings or fluid film bearings provide for high precision anf a long
life span due to their inherent good damping and heat dissipation properties, and the
absence of any metal to metal contact. The journal (spindle) acts like a pump, delivering
oil into the clearance between the shaft and the bearing. However, the narrowing clearance
in the direction of rotation, causes pressure rise till the hydro-dynamic force counter-balances
the load on the bearing
(P. H. Joshi,Machine tools handbook: design and operation, p.388)
(New)
Fluid film bearings commonly used in heavy rotating machines play a significant role in the dynamic behavior of rotors. Of particular interest are the hydrodynamic bearings, which self acting and capable if carrying heavy loads. Because the thin film that separates the moving surfaces supports the rotor load, these bearings act like a spring and provide damping due to squeeze film effect. The stiffness and damping properties of the oil film significantly alter the critical speeds and out-of-balance response of a rotor. In addition, rotor instability occurs, which is a self excited vibration arising out of the bearing fluid film effects and this is an important factor to be considered in the rotor design. Similar to the bearings are fluid film seals which also can effect the dynamic behavior of rotors in pumps. Further, squeeze film bearings can be employed to limit the whirl amplitudes of rotors.
The subject of fluid film lubrication is very wide concerning hydrodynamic, hydrostatic or hybrid bearings with the fluid medium as gas which is compressible or liquid which can be considered as incompressible operating in laminar or turbulent regimes. Moreover, the geometry of the bearing, e.g., plain cylindrical, four axial grooved, elliptical, multilobe and tilting pad type is to be considered while evaluating the steady state dynamic characteristics of the bearing.
(Rotor Dynamics By J. S. Rao, p. 155)
No comments:
Post a Comment