With the development of new energy applications as new energy development the earlier wind energy accounted for an increasingly large proportion of the power grid. At the same time, more and more manufacturers have developed various wind turbines host from the drive chain design improvements to various parts of different features to consider in order to enhance the competitive strength of its product on the market, have become improved design of wind turbines host of different considerations.

As the main components of the wind turbine, the selection of the bearing has been the greatest concern of the host manufacturer, whether bearing design, bearing configuration choices, determine the operating performance and service life of the wind turbines host.

Wind turbine complex operating conditions, the host maintenance costs higher to ensure the reliability of its operation, the service life of the wind turbine, has always been troubled by a host of manufacturers important problem. Wherein the bearings of the impact of the application of the host efficiency is extremely important. Therefore, based on the complexity of the wind turbine, SKF specifically for the development of a special bearing, namely, the "Nautilus" - a special bearing contact angle double row tapered roller bearings (Figure 1).

 
R & D in Figure 1 SKF Nautilus bearing

Wind turbine host bearings configuration

Traditional wind turbine bearings double bearing support. According to the working principle of the wind generator, the drive chain is usually designed as follows: main shaft, gearbox (growth rate boxes), and generators. Take double bearing spindle configuration is more traditional and more common form of bearing types vary depending on the design requirements, but usually more traditional configuration bearing configuration for spherical roller bearings or tapered roller bearings configuration.

Double bearing configuration advantage spindle bearings to withstand the most complex wind loads, in addition to torque, basically no other loads will be passed to the gear box drive chain, has brought great convenience to the design of the gearbox. However, this configuration also has its own drawbacks, such as the drive chain is longer, in addition to the major axis length, also consider the length of the coupling of the spindle and the gear box is connected. Accordingly, in a small power of the wind generator, this configuration is more common. In the high-power of a wind generator, the long drive chain means a larger volume, and higher manufacturing costs.

Spindle bearing configuration is the latest solutions for single-bearing support. With the development of wind turbines, high-power wind turbines become the development trend of the market, higher energy density has also become the target of each host manufacturers competing to catch up, and posed a great challenge to the bearing design.

High power wind turbines, to ensure that there is sufficient load capacity to withstand greater wind loads. Therefore, the spindle, including the size of the bearing is bound to be increased, and this will cause the host the overall increase in the weight of the attendant is the host related components, including the increase in the cost of the tower and other parts manufacturing. Improve wind turbine power can reduce weight and reduce the manufacturing cost of the entire wind turbine? This became the host manufacturers and parts manufacturers are facing an increasingly urgent problem, because of the decline in the cost, which means the improvement of the competitiveness of products. For these purposes, SKF specifically developed for high-power wind turbines with a large contact angle cone roller bearings (Figure 2).

Nautilus bearing prominent features

The bearings for the back-to-back configuration of tapered roller bearings, has a large contact angle (45). Not only allow a single bearing spindle configuration possible, while greatly reducing the length of the transmission chain in the traditional design, compact wind turbine designs are possible. Of course, a special design to ensure the same bearing or all the features of the transmission system.

A larger contact angle

Traditional pairing (or double row) tapered roller bearings, the contact angle of the ability to have some restrictions generally only 20 or so, other than to ensure that its large radial load capacity, bearing axial bearing capacity and withstand the overturning moment. Accordingly, in a spindle to ensure that the design to meet the requirements of the application, must have a bearing as the second fulcrum to withstand the additional radial force, and the configuration of the two bearings, in order to meet the entire shaft by overturning moments , are not deformed.

Nautilus bearings to break through the traditional design of the contact angle, the contact angle of each single row bearings enlarged to 45. Compared with conventional dual-bearing arrangement, the distance between the Nautilus bearing two separate bearing contact point of connection is much higher than the generally conical roller bearings, and the intersection of the connection of two contact points can be used as two of the entire shafting a focus, the role of point supported shafting running.

2 segmented engineering plastic holder

In addition to the large contact angle, the bearing another notable feature is the use of a segmented plastic cage. The rolling body is important for the interior of the bearing member, the bearing member, the holder in addition to maintaining the operating state rolling, there is separated by rolling bodies to avoid their mutual friction generated between the function. The holder is not a force element, can not be exposed to any form of external force. Therefore, it often use lighter materials to produce, while maintaining the frame material to meet another requirement, namely sufficient strength. Are provided by the rolling body and, therefore, the cage material requires a certain amount of strength to ensure its normal operation due to the holding of the power required by the rotation of the frame in the bearing running.

SKF Nautilus bearing contact angle connection enough to withstand the force, the size of the bearing system often is used more often on the market for 2 ~ 2.5 m in diameter bearing products. Therefore, the need to overcome technical problems in its design to reduce the weight of the bearing itself. As the inner and outer rings and rolling elements of the bearing member to ensure the carrying capacity of the bearing, the selection can not have the slightest careless. SKF Nautilus bearings used in engineering plastics, can not only ensure adequate strength, and lighter weight, to ensure the rotation of the bearing performance, while reducing the internal friction of the bearing.

The segmented design SKF Nautilus bearing another feature (Figure 3). Four or five of the bearing rolling elements share a common cage assembly, while each holding no other links between the frame assembly. Using traditional integrated in the bearing holder, because the size is too large, to maintain the weight of the frame itself, so that it will be deformed, in the bearing during operation, this deformation will lead to the additional contact of the rolling body and the retainer, generate additional friction. This not only increases the operating temperature of the bearing, and the friction on the holding frame and the wear of the rolling material will cause the holder and even the deformation of the rolling body, and ultimately affect the carrying capacity of the bearing or even life.

Segmented cage, each of the individual components is very small, even though many components together, it will not be deformed. The same time, due to the rolling bodies of each component is only four to five, and therefore, the friction generated by the holder will also be reduced to the minimum range.

3 Application Features

Nautilus bearing is now widely used in high-power wind power generator, a substituted bis bearing design, reducing the size of the drive chain. This application in the end what benefit, which will be produced in the application?

The force of the design of the conventional wind generator shaft, its bearing division Usually the fixed end of the bearing to withstand all of the axial load and radial load, and the other bearing to bear as a floating end portion of the radial load. The wind farm of wind load size determines the desired size of the bearing, the bearing size determines the distance between the two bearings, and also determines the length of the entire transmission chain.

The single bearing (Nautilus) is designed to guarantee the same bearing load conditions, by a bearing to withstand all of the axial and radial loads, and reducing the size of the entire transmission chain. Single bearing design in addition to the need to consider internal preload, bearing in terms of the application, without distinction of any kind, and double bearing. And single bearing cage design, to have very good operating performance in the grease and oil lubrication conditions.

Only one spindle bearings, have two bearings, bearing stiffness on the key factors that must be considered in the bearing design. The Nautilus the inner race of the bearing as two separate parts, by checking for wind turbine applications, the internal clearance in the production of the bearing is designed to the ideal range can achieve optimal preload in the bearing after installation and simplify the installation process of the bearing, and need to meet the normal operation of the bearing at the same time.

The tapered roller bearing design

In the early market, in order to meet the design requirements for single bearing, usually bearing three cylindrical roller bearings. The bearing design is similar to the slewing ring, a rolling element (similar to cylindrical roller bearings) withstand all radial force, two rolling element (similar to roller thrust bearings) bear bidirectional axial force. The bearing seem to meet some of the features of the single-bearing arrangement, but was found through the analysis of the bearings run to do the whole ring is rotated, the two end faces of the rolling bodies can not achieve the same linear velocity as a thrust bearing function of the two rolling bodies in the bearing, which means there are a large number of sliding friction in the bearing during operation. And as rolling bearings, sliding friction to its utmost to avoid, because it will not only bring more bearing heating at the same time to sliding friction lubrication bearing lubrication is very difficult a problem. Due to some of the problems in the design of the bearing is now can not meet the demand for more towards the high power of the wind-power generator.

Comparison of different design holder

In addition to the SKF Nautilus bearing cage design, market several different cage design. Is respectively compare several advantages and disadvantages of the cage.

Figure 4 is a metal integrally wear pin type cage. The name implies, the rolling bodies of the bearing design of the through-hole, a pin in the middle of the rolling bodies are respectively connected at both ends of the ring in the holder side. In the design, this bearing rolling body size than the other bearings of the same size is much greater, since not only to meet the sufficient bearing capacity, but also in the inside of the rolling bodies to open a through hole in order to wear the installation of the pin type cage. Further, the lubrication of the sliding member is a very important problem, which have been mentioned above. The body bore of the bearing rolling and keep shelf wear off all the sliding friction between not only the poor lubrication problem solved, the bearing heating it is necessary to pay attention.

Another typical design is not holding the rack is full roller bearing design. Of course, from the lower speed of spindle bearings, the decline is not enough to become a full rotation of the roller bearings ability obstruction of the bearing application. However, the friction between the rolling body is a key that can not be ignored.

Reason to design the holder bearing, and an important feature is that the adjacent two separate rolling bodies in the bearing running to avoid the internal friction of the bearing rolling elements to reduce friction and noise. Therefore, full roller bearings with high load carrying capacity, but in the spindle bearings, rolling friction inside its still not the ideal choice.

Further, the above-mentioned another cage design, i.e. similar to the conventional bearing integrated holder. SKF Nautilus bearing no choice in integrated holder, mainly because of its size is too large, its own weight will cause the deformation of the holder to bring more rolling body and to maintain the friction between the holder. In addition, as a device to generate energy, an important issue in the wind turbine design is to improve the energy density, to maximize the reduction of the energy loss of its components. From this perspective, the integrated holder also has limitations.

Wind turbines, because of its special application conditions, the critical choice of parts. According to the research report shows that by 2012, the installed capacity of wind power will be 90000 MW in 2007 rose to 290000MW. Wind turbine manufacturers and operators are increasingly inclined to the high reliability of wind turbines host, in order to achieve the balance of economic and ecological benefits.