Abstract: According to the structural characteristics of wind turbine slewing bearings, according to the geometric relationship between the inner and outer rings after the bearing is loaded, the elastic approach value expression between the steel ball and the channel is obtained, and the relative displacement of the ferrule is unknown. The balance equation system of the bearing is established by using variables, and combined with a specific type of bearing, the influence of the change of the bearing clearance, groove curvature radius coefficient, contact angle and other parameters on the bearing capacity is studied. The gap can make the bearing have excellent bearing performance; reducing the groove curvature radius coefficient can improve its bearing capacity; when the relative value of the bearing’s axial load is relatively large, increasing the contact angle can improve its bearing capacity.
For the mechatronics equipment with high reliability requirements such as wind turbines, the importance of bearings is unquestionable. Bearings of different structural forms are installed in the rotating connection or support parts of the pitch system, yaw system, main shaft, gearbox and generator of a wind turbine, among which there are many structural forms of bearings in the pitch system or yaw system It is a single-row four-point contact ball slewing bearing and a double-row four-point contact ball slewing bearing. It needs to bear the combined action of radial, axial load and overturning moment at the same time.
During the working process of the wind turbine, various components of the unit are subjected to aerodynamic loads, inertial loads, gravitational loads, and operating loads. These loads are characterized by static, dynamic, cyclic, and transient loads. , shock and random. Different from the application of slewing bearings in other fields, due to the high maintenance cost of wind turbines, wind turbine bearings must have a lifespan of at least 20 years. For wind power slewing bearings, it is necessary to deeply understand their load conditions, internal mechanical characteristics and relevant laws affecting their performance according to their specific working conditions and use requirements, and on this basis, realize the optimal design and reasonable selection of such bearings. .
1 Static analysis
1.1 Stress condition
Wind energy is the power source of wind turbines, wind is an uncontrollable resource, and the wind speed and direction are constantly changing. Under grid-connected conditions, in addition to the rotational motion of the wind rotor that converts electrical energy, pitch and yaw motions are also required to cope with changes in wind speed and direction, so that the wind turbine can output constant power and ensure the safe operation of the unit. Table 1 shows the main sources of wind turbine slewing bearing loads, which vary with wind speed, rotor speed, blade azimuth, etc.; in addition, the operation control of wind turbines will also have a load on the bearing. Due to the low rotational speed of the wind turbine slewing bearing, it is not necessary to consider the dynamic effects caused by the motion, so only a static analysis is required. The actual bearing load is the result of the combined action of many factors, which can be divided into limit load and fatigue load according to the effect of these loads on the bearing.
1.2 Static modeling In the analysis, it is assumed that the outer ring of the bearing is fixed, and the radial displacement, axial displacement and angular displacement of the inner ring under the combined action of radial load Fr, axial load Fa and overturning moment M are respectively δr , δa and θ, as shown in Figure 1. In the axial plane of the bearing, the channel of the four-point contact ball bearing consists of two arcs; an arc of the steel ball under load and the inner ring channel and a circle on the outer ring channel in the opposite direction The arcs make contact, and the two contact points are called a contact pair. Here, when the bearing only bears the axial load, the contact pair is contact pair 1, as shown in Figure 1, that is, the contact pair generated by the upper half channel of the inner ring, the lower half channel of the outer ring and the steel ball; The other contact pair is contact pair 2. The static model of the bearing is established while considering the forces of contact pair 1 and 2 at the same time.
When the inner ring is displaced, the bearing is loaded and the contact angle changes, and the contact pair is when the steel ball is at the position ψ. Equations 7) to (9) are a nonlinear equation system. When the geometric parameters of the bearing are given, Corresponding to a set of Fr, Fa and M, the values of the unknown variables δr, δa and θ can be obtained by solving, and the load on the steel ball can be further calculated, and finally the contact stress between the steel ball and the channel and the bearing life can be calculated.
1.3 The main parameters of the bearing surface of a certain type of single-row four-point contact ball slewing bearing structure are: Dpw=1900mm, Dw=42.8625mm, α=45°, fi=0.525, fe=0.54, Z=104 . Through the above method, all the combinations of external loads Fr, Fa and M can be calculated when the allowable contact stress between the maximum bearing steel ball and the channel is 4200MPa, using the point (Fr, Fa, M) in the three-dimensional coordinate system The static load bearing surface of the bearing can be drawn; at the same time, all Fr, Fa and M combinations can be calculated when the rated life of the bearing is 30000r, and the dynamic load bearing surface of the bearing can also be drawn, as shown in Figure 2. Show.
2 Influence analysis of bearing parameters
In the process of bearing design, determining the reasonable structural parameters of bearing parts is the primary problem to be solved in the design work. Most structural parameters of wind turbine slewing bearing parts have a clear value basis, such as the inner diameter, outer diameter, height of the bearing, the diameter of the center circle of the mounting hole, the diameter and quantity of the mounting hole, the diameter of the steel ball and the diameter of the pitch circle of the ball group, etc. Most of the standards have been standardized. The value of another part of the structural parameters of the bearing parts is usually based on experience, such as clearance, groove curvature radius coefficient, contact angle, etc. For the slewing bearing, it is very necessary to understand the influence trend and degree of the change of these parameters on the bearing performance, so as to provide a theoretical basis for the value of such parameters in bearing design.
When the structural parameters of the bearing change, the shape and position of the corresponding static load bearing surface and dynamic load bearing surface of the bearing also change, and the bearing capacity also changes. In order to study the bearing clearance and groove curvature , the influence law of contact angle on the bearing capacity, take several sections of the bearing surface corresponding to different radial loads for comparative analysis, and obtain the bearing curves corresponding to different radial loads. The relevant results are shown in Figures 3 to 5. .