Views: 17 Author: Site Editor Publish Time: 2021-11-26 Origin: Site
The English name of a constant velocity universal joint is constant velocity universal joint. I think this is not more or less, it will be the reason why everyone confuses CVD and universal joint.
(1) Classification of universal joints
According to whether the universal joint has obvious elasticity in the torsion direction, it can be divided into rigid universal joint and flexible universal joint. Rigid universal joints can be divided into unequal velocity universal joints (commonly used as cross shaft type), quasi-constant velocity universal joints (such as double-joint universal joints) and constant velocity universal joints (such as ball cage universal joints). Xiang section) three kinds.
(2) Variable speed universal joint
The cross-shaft rigid universal joint is a variable speed universal joint widely used in automobiles, and the maximum angle of intersection between two adjacent shafts is allowed to be 15゜～20゜. The cross-shaft universal joint shown in the figure below consists of a cross shaft, two universal joint forks and four needle bearings. The holes on the two universal joint forks 1 and 3 are respectively sleeved on the two pairs of journals of the cross shaft 2. In this way, when the driving shaft rotates, the driven shaft can rotate with it, and it can also swing in any direction around the center of the cross shaft, so that the need for simultaneous changes of the included angle and distance can be met. A needle roller bearing 5 is installed between the cross shaft journal and the universal joint fork hole, and the outer ring of the needle roller bearing is axially positioned by the snap ring. In order to lubricate the bearings, oil injection nozzles are generally installed on the cross shaft and an oil path leads to the journal. Lubricating oil can be injected from the grease nozzle to the needle bearing of the cross shaft journal.
The cross-shaft rigid universal joint has the advantages of simple structure and high transmission efficiency. However, when the angle α between the two shafts is not zero, the constant angular velocity rotation cannot be transmitted.
When the following two conditions are met, a constant angular speed transmission from the output shaft of the transmission to the input shaft of the drive axle can be realized:
1) The universal joint forks at both ends of the drive shaft are in the same plane;
2) The angle α1 between the two shafts of the first universal joint is equal to the angle α2 between the two shafts of the second universal joint.
Because when driving, the drive axle has to jump relative to the transmission, it is impossible to have α1=α2 at any time. In fact, it can only achieve approximately constant speed transmission from the transmission to the drive axle.
In the above transmission device, the greater the angle of intersection α between the shafts, the more uneven the rotation of the transmission shaft, the greater the additional alternating load generated, the more unfavorable the service life of the parts, and the reduction of transmission efficiency, so in the overall arrangement The angle of intersection between these axes should be minimized.
(3) Quasi-constant velocity universal joint
Common quasi-constant velocity universal joints have two types, double-joint type and three-pin shaft type. Their working principle is the same as that of double cross-shaft universal joints to realize constant velocity transmission.
The double universal joint is actually a set of double cross-shaft universal joint constant velocity transmission device that reduces the length of the transmission shaft to the minimum. The double fork is equivalent to the universal joint with the transmission shaft and the two ends on the same plane. cross. When the angle of intersection between the output shaft and the input shaft is small, the intersection point of the two shaft axes on the arc is very close to the above-mentioned mid-vertical line, so that the difference between α1 and α2 is small, and the angular velocity of the two shafts is nearly equal, so it is called double The combined universal joint is a quasi-constant velocity universal joint.
(4) Constant velocity universal joint
At present, the commonly used constant velocity universal joints on cars are ball-and-cage universal joints, and there are also ball-fork universal joints or free three-pivot universal joints.
The structure of the ball-cage universal joint is shown in the figure below. The star sleeve 7 is connected with the driving shaft 1 by an inner spline, and six arc-shaped grooves are formed on the outer surface to form an inner raceway. There are corresponding six arc-shaped grooves on the inner surface of the spherical shell 8 to form an outer raceway. The six steel balls 6 are respectively installed in the space opposite to the six sets of inner and outer raceways, and are limited in the same plane by the cage 4. The power is transmitted from the driving shaft 1 (and star sleeve) to the spherical shell 8 through the steel ball 6 for output.