Basic knowledge of couplings (2)

Flexible coupling

Types of rigid movable couplings (non-elastic couplings): cross slide couplings, universal joints and crown gear couplings.

1. Gear coupling

A. Composition: Two outer sleeves with internal teeth and flanges, two inner sleeves with external teeth.

B. Working principle: The two inner sleeves are respectively connected with the two shafts by a key, and the two outer sleeves are by bolt, and torque and movement are transmitted by engagement of the inner and outer teeth.

C. Characteristics: In order to compensate the relative displacement of the two shafts, the teeth of the outer ring gear are made into drum-shaped teeth, and the tooth top is made into a spherical surface with a center line on the axis, and a large gap is left between the tooth top and the tooth side.

The top clearance and backlash between the meshing teeth provide radial, axial and angular comprehensive displacement compensation between the two shafts; high speed (up to 3500r/min), which can transmit a large torque (up to 106N·m) ), and can compensate for the large comprehensive displacement, the installation accuracy is not high, to be lubricated.

D. Disadvantages: The quality is large, the manufacturing is difficult, and the cost is high.

E. Application: Widely used in large heavy machinery such as automobiles.

2. Cross slider coupling

A. Structural features: Coupled together by the semi-couplings 1, 3 (left and right sleeves) and the floating disc 2 (cross slide), the two shafts rotate together; The tenon of the floating disc can slide in the groove of the semi-coupling; the friction is large and needs to be lubricated.

B. Advantages: Small radial size, a simple structure.

C. Disadvantage: Poor impact resistance, easy to wear between the slider and groove, need to be lubricated; cross slide will generate a large centrifugal inertia force due to the radial displacement, and bring additional load to the shaft and bearing.

D. Applications: It is often used in applications with high rigidity, low speed and low impact.

3. Universal coupling

A. Structure: Consists of a cross shaft, two universal joint forks, and four needle bearings; The center of rotation (axis) of all the rotating pairs is at a point O, and the angle between the two axes is α; It is a device (coupling) for transmitting motion between intersecting two axes of varying angles.

B. Working principle: When the axis I rotates one turn, the axis II will also turn one turn, that is, the average gear ratio of the two axes is 1; However, the instantaneous transmission ratio of the two axes is not constant, it is periodically changed. This characteristic of the universal joint is called the non-uniformity of the instantaneous gear ratio. In the case of a single universal joint, when there is an angle between the input shaft and output shaft, the angular velocities of the two shafts are not equal, that is, the universal joint has a non-equal speed; The larger the angle α between the two axes, the more obvious the fluctuation of the driven shaft speed; Therefore, α should be between 35° and 45°. In order to prevent the angular velocities of the main and driven shafts from being not equal, the disadvantages of the above-mentioned driven shaft shifting transmission are completely eliminated, the universal joints are often used in pairs.

C. Advantage: It has large angular compensation capability, compact structure and high transmission efficiency.

D. Disadvantages: Additional dynamic loads will be generated in the transmission, and the rotational speed should not be too high.

E. Applications: Mainly used for transmissions where two axes intersect. It is used in medium and low speed applications such as heavy load, medium load and light load, for example, machine tools and automobiles.

F. Double universal joints should meet the conditions:

In order for the mechanism to obtain a constant gear ratio, the mechanism must meet the following three conditions:

(1) The three axes of the drive shaft, the driven shaft and the intermediate shaft should be in the same plane.

(2) The angle between the axis of the master shaft, the driven shaft and the intermediate shaft should be equal.

(3) The fork faces at both ends of the intermediate shaft should be in the same plane.

Commonly used elastic couplings are divided into two types: elastic sleeve pin coupling and elastic pin coupling.

1. Elastic sleeve pin coupling (standard number GB4323-2002)

A. Structure: It is similar to the flange coupling in structure, except that the bolt is replaced by a logout with a rubber elastic sleeve.

B. Principle: Using the elastic deformation of the elastic sleeve to compensate the relative displacement of the two shafts.

C. Features: The elastic sleeve pin coupling is easy to manufacture, convenient to assemble and disassemble, and low in cost, but the elastic sleeve is easy to wear and has a short life.

D. Applications: It is suitable for two-axis connection with stable load, frequent reversal or starting, high speed and medium and small torque.

2. Elastic pin coupling

A. Structure: A plurality of non-metallic materials are placed in the flange holes of the coupling halves to realize the connection of the two coupling halves. The pin material is usually nylon, and other non-metallic materials with elasticity can also be used.

B. Principle: The elastic deformation of the elastic pin is used to compensate the axial displacement of the two shafts.