1、Transmission System introduced The important position of the wheel gear and shaft cant falter in traditional machine and modern machines. The wheel gear and shafts mainly install the direction that delivers the dint at the principal axis box. The passing to process to make them can is divided into m
2、any model numbers, used for many situations respectively. so we must be the multilayers to the understanding of the wheel gear and shaft in many ways. In the force analysis of spur gears, the forces are assumed to act in a single plane. We shall study gears in which the forces have three dimensions.
3、 The reason for this, in the case of helical gears, is that the teeth are not parallel to the axis of rotation. And in the case of bevel gears, the rotational axes are not parallel to each other. There are also other reasons, as we shall learn. Helical gears are used to transmit motion between paral
4、lel shafts. The helix angle is the same on each gear, but one gear must have a right-hand helix and the other a left-hand helix. The shape of the tooth is an involute helicoid. If a piece of paper cut in the shape of a parallelogram is wrapped around a cylinder, the angular edge of the paper becomes
5、 a helix. If we unwind this paper, each point on the angular edge generates an involute curve. The surface obtained when every point on the edge generates an involute is called an involute helicoids. The initial contact of spur-gear teeth is a line extending all the way across the face of the tooth.
6、 The initial contact of helical gear teeth is a point, which changes into a line as line as the teeth come into more engagement. In spur gears the line of contact is parallel to the axis of the rotation； in helical gears, the line is diagonal across the face of the tooth. It is this gradual of the t
7、eeth and the smooth transfer of load from one tooth to another, which give helical gears the ability to transmit heavy loads at high speeds. Helical gears subject the shaft bearings to both radial and thrust loads. When the thrust loads become high or are objectionable for other reasons, it may be d
8、esirable to use double helical gears. A double helical gear (herringbone) is equivalent to two helical gears of opposite hand, mounted side by side on the same shaft. They develop opposite thrust reactions and thus cancel out the thrust load. When two or more single helical gears are mounted on the
9、same shaft, the hand of the gears should be selected so as to produce the minimum thrust load. Crossed-helical, or spiral, gears are those in which the shaft centerlines are neither parallel nor interesting. The teeth of crossed-helical fears have point contact with each other which changes to line
10、contact as the gears wear in. for this reason they will carry out very small loads and are mainly for instrumental applications, and are definitely not recommended for use in the transmission of power. There is on difference between a crossed helical gear and a helical gear until they are mounted in
11、 mesh with each other. They are manufactured in the same way. A pair of meshed crossed helical gears usually have the same hand； that is, a right-hand driver goes with a right-hand driven. In the design of crossed-helical gears, the minimum sliding velocity is obtained when the helix angle are equal
12、. However, when the helix angle are not equal, the gear with the larger helix angle should be used as the driver if both gears have the same hand. Worm gears are similar to crossed helical gears. The pinion or worm has a small number of teeth, usually one to four, and since they completely wrap arou
13、nd the pitch cylinder they are called threads. Its mating gear is called a worm gear, which is not a true helical gear. A worm and worm gear are used to provide a high angular-velocity reduction between nonintersecting shafts which are usually at right angle. The worm gear is not a helical gear beca
14、use its face is made concave to fit the curvature of the worm in order to provide line contact instead of point contact. However, a disadvantage of worm gearing is the high sliding velocities across the teeth, the same as with crossed helical gears. Worm gearing are either single or double envelopin
15、g. A single-enveloping gearing is one in which the gear wraps around or partially encloses the worm. A gearing in which each element partially encloses the other is, of course, a double-enveloping worm gearing. The important difference between the two is that area contact exists between the teeth of
16、 double-enveloping gears while only line contact between those of single-enveloping gears. The worm and worm gear of a set have the same hand of helix as for crossed helical gears, but the helix angles are usually quite different. The helix angle on the worm is generally quite large, and that on the
17、 gear very small. Because of this, it is usual to specify the lead angle on the worm, which is the complement of the worm helix angle, and the helix angle on the gear； the two angles ate equal for a 90-deg. Shaft angle. When gears are to be used to transmit motion between intersecting shaft, some of
18、 bevel gear is required. Although bevel gear are usually made for a shaft angle of 90 deg. They may be produced for almost any shaft angle. The teeth may be cast, milled, or generated. Only the generated teeth may be classed as accurate. In a typical bevel gear mounting, one of the gear is often mou
19、nted outboard of the bearing this means that shaft deflection can be more pronounced and have a greater effect in the contact of teeth. Another difficulty, which occurs in predicting the stress in bevel-gear teeth, is the fact the teeth are tapered. Straight bevel gears are easy to design and simple
20、 to manufacture and give very good results in service if they are mounted accurately and positively. As in the case of squrgears, however, they become noisy at higher values of the pitch-line velocity. In these cases it is often good design practice to go to the spiral bevel gear, which is the bevel
21、 counterpart of the helical gear. As in the case of helical gears, spiral bevel gears give a much smoother tooth action than straight bevel gears, and hence are useful where high speed are encountered. It is frequently desirable, as in the case of automotive differential applications, to have gearin
22、g similar to bevel gears but with the shaft offset Such gears are called hypoid gears because their pitch surfaces are hyperboloids of revolution The tooth action between such gears is a combination of rolling and has much in common with that of worm gears. A shaft is a rotating or stationary member
23、 usually of circular cross section, having mounted upon it such elementsas gears pulleys flywheels, cranks sprockets and other power-transmission elements Shaft may be subjected to bending tension compression or torsional loads acting singly or in combination with one another .When they are combined
24、 one may expect to find both static and fatigue strength to be important design considerations since a single shaft may be subjected to static stresses completely reversed, and repeated stresses, all acting at the same time The word “shaft” covers numerous wariations, such as axles and spindles. Ana
25、xle is a shaft, wither stationary or rotating nor subjected to torsion load. Ashirt rotating shaft is often called a spindle. When either the lateral or the tosional deflection of shaft must be held to close limits, the shaft must be sized on the basis of deflection before analyzing the stresses The reason
