Chinese name: linear bearing mbth: linear bearing Usage: Ball or sliding bearing with linear motion includes: plastic cage bearing: hardened steel raceway section for guiding ball rolling Subject: Introduction to mechanical engineering, curve passing analysis of medium and low speed maglev vehicles, design and selection summary of linear bearing, linear bearing is a rolling or sliding bearing for linear motion, with low friction, reliable structure, strong bearing capacity, high long running accuracy and long service life, and is often used in machine tools, punches and so on. The suspension frame of medium and low speed maglev train is composed of several modules with the same basic structure. When a maglev train passes through a curve, the suspension frame module will fit the curve according to the line shape, resulting in different lateral displacements of the module relative to different positions of the car body, in which the lateral displacement of the end module exceeds 300 mm Considering that the air spring commonly used in locomotives and rolling stock cannot provide such a large displacement, a linear bearing with large displacement technology is set between the car body and the suspension frame to meet the curve passing requirements of medium and low speed maglev vehicles. The curve of medium and low speed maglev vehicle is analyzed by the attitude of the suspension frame of medium and low speed maglev vehicle on a straight road: each vehicle suspension frame is equipped with 5 modules, 12 sets of sliding table devices, and 6 sets of left and right modules, among which the sliding tables at positions Ⅱ and ⅴ are fixed sliding tables connected with the vehicle body, the sliding tables at positions Ⅰ and ⅴ are end sliding tables, and the sliding tables at positions Ⅲ and ⅴ are intermediate sliding tables. The linear bearing device is installed on the end slide table and the middle slide table, the linear bearing guide rail is fixed on the bottom plate of the car body, and the slider is fixed on the installation surface of the slide table. When the train passes through the curve, the attitude of the suspension frame: in an ideal state, each module is in the radial position of the curve, and the corresponding curve should be synthesized. Because the sliding table in position ⅱ and ⅴ is fixed with the car body, its position determines the position of the car body on the curve. According to the curve fitting analysis, the lateral displacement of the end slide table relative to the car body is the largest, and the lateral displacement of the middle slide table relative to the car body is about half that of the end slide table. Because the curve radii of the outer rail and the inner rail are slightly different, and the left and right modules of the suspension frame can be decoupled from each other, the lateral displacement of the same slide table relative to the inner and outer rails is also slightly different. The minimum allowable curve radius of the main line of the medium and low speed maglev train can reach 100m, and the minimum curve radius of the storage line can reach 50 m. When the train is located on the curve with a radius of 50m, according to the curve fitting analysis, the lateral displacement of each sliding platform can be preliminarily calculated: the lateral displacement generated by the sliding platform at the end of the inner rail is the largest, with the maximum value of 326 mm, while the maximum lateral displacement of the air spring of the bogie of ordinary wheel-rail vehicles is only/kloc-0. The air spring is small, and its lateral displacement is about 20 mm It is a reasonable choice to set a large displacement linear bearing between the car body and the sliding table to meet the displacement demand of the suspension relative to the car body. The air spring structure is adopted in the design and selection of linear bearing for the secondary suspension device of low-speed maglev vehicle. Linear bearing is one of the key components of air spring suspension device, and its design and selection must meet the performance requirements of connecting suspension and car body, transmitting load and adapting to curve passing of vehicles. The air spring suspension device consists of air spring, end slide table, middle slide table, fixed slide table, linear bearing and other parts. Linear bearing is horizontally installed on the end sliding table and the middle sliding table, and adopts double guide rail sliding mechanism. 1. Selection of linear bearing linear bearing is one of the components of suspension frame with heavy workload and high safety requirements, and its performance directly determines whether the train can run safely and pass the curve smoothly. The vehicle load, safety factor of linear bearing, structural size and maintainability should be considered when selecting. (1) Calculation of linear bearing Load and Safety Factor The linear bearing slider for concentrated low-speed maglev vehicles mainly bears vertical load and lateral load. The vertical load of each slider is related to the supporting force of the air spring on the sliding table and the action center, and the lateral load is related to the inertial force generated by the acceleration of the train during traction or braking. (2) Calculation of linear bearing load of end slide; One guide rail of the end sliding table is supported by a single slider, and the other guide rail is supported by a double slider. According to the design of air spring suspension device, the pressure of all air springs on the train is equal, that is, the supporting force f of each air spring on the sliding table is equal. There is no traction bar on the end slide table, so the lateral direction of linear bearing on it is not affected by the longitudinal force of the vehicle. (3) In the calculation of the linear bearing load of the middle slide table, the slide table has a left-right symmetrical structure, and both guide rails are supported by double sliders, so the vertical forces on the linear bearing sliders are equal to each other. The supporting force of the air spring to the sliding table is the same as that of the end sliding table. When the train is towed or braked, the longitudinal force of the traction rod on each sliding table is equal, and the transverse force on each linear bearing slider on the same sliding table is also approximately considered equal. The calculation object is the middle sliding table with traction rod at the front and rear. When the train is being pulled or braked, the linear bearing slider on this sliding table receives the greatest lateral force. (2) Calculation of Rated Life Although there are no medium and low speed maglev lines officially operating in China at present, according to the experience of rail transit application, it is estimated that the average number of curves per kilometer of maglev lines is 1 line. When designing the entry and exit curves of maglev vehicles, the linear bearing slip corresponding to the minimum curve R 100 m on the main line is calculated as 150 mm, and the linear bearing slip of maglev vehicles is 300 mm each time. According to the calculation that the annual running kilometers of maglev vehicles are 12.5× 104 km, the annual slip of linear bearing is 37.5km.. Therefore, it can be calculated that the minimum rated calculated life of single slider linear bearing on the end slide table is 1392, and that of double slider linear bearing is 23.2 years. The minimum rated calculation life of linear bearing with double sliders on the middle sliding table is 12.4 years. (3) Structural dimension The structural dimension design of linear bearing mainly considers the length dimension of the linear guide rail. When passing through the curve, the slider moves left and right relative to the linear guide rail. Combined with the fitting analysis results of the minimum radius curve in the previous section, the length of the linear guide rail should meet the requirements of the maximum lateral movement of the slider left and right, and a certain safety margin should be left. The safety margins reserved for linear guides are all greater than 30 mm, which meets the safety requirements of linear bearing when sliding left and right. 2. Strength Inspection The following mainly checks and evaluates the strength of linear bearing sliders, guide rails and their connecting parts, which is directly related to the normal operation of linear bearing and the safe operation of trains. (1) Strength check of linear bearing slider and guide rail When calculating the strength of slider, linear bearing slider on the middle slide table with the greatest stress is selected as the calculation object, fixed constraints are imposed on the positioning holes of slider, and loads are imposed on the action surfaces of slider and guide rail. When calculating the strength of the guide rail, the linear bearing guide rail of the middle slide table is selected as the calculation object, a fixed constraint is imposed on the positioning hole of the guide rail, and a load is imposed on the action surfaces of the guide rail and the two sliders. (2) Strength check of connecting parts The connecting parts in linear bearing mainly include M 10 bolts connecting the slider and the sliding table, and M8 bolts connecting the guide rail and the car body floor. By applying pre-tightening force to the bolt, when the connector bears transverse load, the joint surface will not shift. By analyzing the curve of medium and low speed maglev vehicle, it is concluded that it is necessary and feasible to use linear bearing to meet the requirement of large lateral displacement between suspension frame and car body. The working load, safety factor and rated life of linear bearing are calculated and analyzed, and the strength of slider, guide rail and connector in linear bearing is checked. The calculation results show that the selected linear bearing is reasonable, the safety factor meets the relevant regulations, the strength of the slider and guide rail in linear bearing meets the requirements, and the strength of the connecting bolt between the slider and the slide table meets the application requirements. The successful application of linear bearing in medium and low speed maglev vehicles has laid a solid foundation for the development of a new generation of medium and low speed maglev vehicles. The practical application effect of linear bearing, including performance, service life, lubrication cycle, maintenance of vehicle passing curve, etc., has yet to be verified by the long-term running assessment of vehicles in linear bearing.