Design scheme of elements MA
The invention relates to mechanical engineering. Mechanical continuously variable transmission includes driving and driven shafts mounted on the drive shaft eccentric converter mechanism (16) adjustment of eccentricity, hosted a star-freewheel (MoA) and coaxial with them gears (10), engaging with the sun gear (11), mounted on the driven shaft (18). Leading elements (7) MA joined with converter and slave (8) through torsion bars (9) with a toothed wheel (10). The crank drive is formed on the intermediate shaft (2), installed inside the drive shaft with an eccentricity equal to the radius of the crank and being rotatable around its axis by the eccentricity adjusting mechanism. This allows you to perform a neck crank sufficiently small diameter in order to connect it with the rocker arms pivot elements (7) Ministry of Agriculture via the crank mechanism. The present invention allows better control, allowing to obtain any desired engine load in a wide range of transmission ratio, a potential increase reliability of the converter.
The angle between the tangents drawn through the point of contact between the roller and cage assembly and an asterisk is called a wedge angle.
To reduce the influence of errors of manufacture and wear and tear on the angle of jamming the rollers work surfaces with an asterisk are not recommended to perform flat and cylindrical with guides in the form of a circle, Archimedes or logarithmic spiral.
Wedging and wedged state Ministry of Agriculture
By wedging MA refers to the process of rolling rollers in the tapered portion of the wedge of space between the sprocket and the ring as a result of the friction forces caused by the movement of the driving member relative to the driven in the direction of torque transmission. This process is characterized by the growth and strength of the normal pressure friction force between the clutch yoke and the sprocket, the energy loss due to friction of rollers rolling on the working surfaces, loss of energy to break the oil film and the accumulation of strain energy.
The process is preceded by jamming the time corresponding to the end of the period of free running when the angular velocity of the cage from the 1 and 2 with an asterisk are equal.
It has assumed that all of the rollers, placed in the separator, the same force and effect wedging rollers occurs simultaneously.
Method of calculation and diagram of the forces acting on the roller during the seizure MA, shown in . At the present time it has not yet adopted any unified theory of jamming USDA.
Period wedging MAU characterized by a decrease of the transmitted clutch torque from a value corresponding to a jammed state to zero. With decreasing torque main elements are released from strain.
Under the action of the elastic roller are moved into the wider part of the wedge space. Simultaneously, the driving and driven members are rotated relative to each other.
Free wheeling MA
Under the period of freewheel USDA understand the movement of the mechanism in which the driven member moves at a higher angular velocity than the master. Rasklineny the rollers and by the forces of friction in contact with the yoke rotate in cage windows. Free running is continued after the end of the process of propping USDA before the start of a period of jamming.
Selection of the main design parameters of the Ministry of Agriculture
The main criteria of efficiency USDA are:
- - coupling the ability to jam without slipping;
- - Contact fatigue strength and endurance of the most loaded elements;
- - The absence of increased wear of the working surfaces of parts at high relative angular velocities of links between the freewheel.
Reliable jamming USDA possible under the conditions:
- - Contact roller and cage assembly and an asterisk at the initial moment of jamming;
- - Self-jamming rollers in the initial stage of the period of their seizure;
- - But slipping clutch in the presence of the strain of loaded elements.
Implementation of the first and second conditions is provided mainly by the action of the pressure forces on the rollers, the value of which is selected based on the dynamics of movement of the main units of the Ministry of Agriculture and the properties of the lubricating oil.
Selecting a wedge angle
The choice of the angle of wedge roller in designing roller MOA usually decided on the basis of experimental data of their design and operation. For selfwedging MA
corners sticking selected within 3 ° <a <5 ° 30 ', and admission to the angle of jamming is ± 15'.
Requirements for the construction of parts MA
To reduce the dimensions of the Ministry of Agriculture is necessary to use the maximum possible number of rollers and ensure a more uniform contact with the yoke of an asterisk. The uniformity of the pressure distribution along the length of the rollers can be achieved by making the rollers is slightly convex (with Bombino) or rollers are slightly tapered at the ends.
Great influence on the uniformity of distribution of the load between the rollers and the length of each of them has a precision manufacturing separator and asterisks, and in the process of long-term operation - wear of the separator material. The use of separators made of aluminum alloys show that they have an unsatisfactory durability. Higher rates provide a bronze and steel separators. Operating experience and research results of high-speed helicopter USDA indicate the appropriateness of lightweight steel separators and the need to improve the quality of their dynamic balancing.
Particular attention in the design of the Ministry of Agriculture should be paid to the accuracy of centering stars, cage and cage. In eccentric disposition relative to the cage sprocket rollers wedged at different angles and that can lead to considerable overloading of some clips, while others may not transmit torque.
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