In-train Dynamics Of Heavy Haul Freght Locomotives With Radial Bogies

Heavy haul transportation plays a decisive role for improving the efficiency of our transportation and coordination with the speed of economic development. With the development of heavy haul transportation, high power freight locomotives have been widely applied. Traction power of AC locomotives has reached 1600kW per axle and gearboxes generally use bearing box with simply supported pinion gear. Locomotive with the C₀-C₀ bogies is a conventional configuration, whose axle load is also raised from 25t to 30～33t. But the traditional bogies with high axle load and long wheelbase reduce the performance of locomotive curve negotiation, resulting in the serious wheel rail wear and restricting the development of heavy haul transportation in china. Radial bogies have been widely used overseas, which has achieved considerable benefits in mitigating wheel/rail wear, and improving traction on curve, Even though China has achieved exporting radial bogie locomotive, but the current total number of domestic radial bogie locomotive is small and heavy haul freight electric locomotives with radial bogies are not used. With the increased axle load, the study on wheel-rail contact characteristics of freight locomotives with radial bogies can provide the basis for the future development of heavy haul freight electric locomotives with radial bogies in our country, which is important for further exploit the potential of heavy transport.Firstly, some characteristics of the freight locomotive are summarized such as the freight locomotive traction and braking characteristics, axle load transfer and axle load compensation measures, motor torque and suspension mode, axle-box positioning and curve negotiating, the coupler force effect under the condition of heavy haul traction etc. The influence is focused on locomotive dynamic performance under service states, to illustrate advantages of radial steering bogies for high adhesion heavy haul locomotives. Application of radial bogies can effectively reduce locomotive curve adhesion drop by reducing the angle of attack and improve locomotive traction on the curve, and significantly reduce wheel flange wear of large wheelbase three-axle bogie.In this paper, the theoretical analysis of the steering mechanism for free wheelset and bogie, and the typical structure of the radial bogie are carried out. Some outstanding dynamic problems of radial steering are analyzed, such as stability, influence between creep slide traction and steering characteristics. In particular, the implications for decreasing wheel wear is theoretically demonstrated by reducing the angle of attack when locomotive curve negotiating and the specific numerical is obtained by using typical wheelset parameters, which theoretically explains that the locomotives with radial bogies have important advantages. Subsequently, substructure models based on bogie, single locomotive, draft gears and so on are described, and comprehensive dynamic analysis model is established, this model has considered two kinds of mode of organization and can switch between the traditional bogie and self-steering radial bogie and forced steering radial bogie for heavy haul locomotive traction train. The effect is investigated with coupler force, traction and brake on wheel/rail creep sliding guide of self-steering radial bogie under service of locomotive drawing heavy haul train, braking, curve negotiating, and the situations are compared with the traditional bogie. The heavy-haul freight transportation is marked by improving the axle load and train length. With the increase of the compositions of the train, train impulse has doubled increase and effect of coupler force on locomotive dynamics also is increasing. Now the commonly used 13A coupler in the locomotive is analyzed as an example in the thesis. Coupler structure and stabilizing coupler deflection process are analyzed on locomotive dynamics in detail. At the same time, the effect of train configurations and in-train forces are studied on locomotive dynamics. Because traditional self-steering radial bogies provide guidance using wheel/rail creep force; especially longitudinal creep force, so locomotive traction forces will weak guide performance. Freight locomotives usually need to offer a larger pulling force, which will weak the curving negotiation performance of the self-steering radial bogie.Finally, the advantages and disadvantages of radial steering locomotive bogie are summarized. An improved forced steering radial steering bogie is proposed, whose dynamics performance are simulated, and the structure is compared with the traditional bogie and self-steering radial bogie. The traditional forced-steering bogie can improve the curving negotiation performance in traction states, but the wheelset motion is related directly with the bogie and carbody movement, which makes the bogie parameters selection and maintenance more difficult, such as the stability of bogie is sensitive to wheel tread wear, lateral wheelset force offsetting is difficult to remove etc. Therefore, an improved structure is proposed, which combines with the existing advantages of two kinds of radial bogie, i.e., the curve negotiation performance of self-steering radial bogie is enhanced under the action of the large traction force on small radius curves, simultaneously the disadvantage of sensitive parameters is overcame for the forced-steering radial bogie. Some main conclusions are as follows in the paper:1. Co-Co shaft type high power AC locomotives have high adhesion utilization and more severe longitudinal impacts. Radial bogies by significantly decreasing angle of attack of wheelset on curve negotiating can significantly improve the Co-Co locomotive curve negotiating performance and reduce the wheel/rail wear and curve adhesion drop. Axle box positioning mode has a decisive effect on the locomotive dynamic performance, but some measures are taken usually such as increasing the cross positioning stiffness of the wheelset, adding primary longitudinal damper and so on to increase operation stability of the self-steering radial bogie and the creep sliding ability is heavy impacted for locomotive with self-steering radial bogie under the situation of high adhesion.2. Lateral components of coupler forces by swing angle of the coupler have a greater effect on the safe operation of locomotive. Draft gears dynamic submodel with the friction force element can better reproduce the hysteretic characteristics of the buffer and the important effect of the coupler tail friction pair on the stability of the coupler.3. When locomotive is located at train head, coupler forces has a minimum effect on locomotive dynamic. When the locomotive locates train center, because the coupler pressure and swing angle are larger under the act of longitudinal impact force, the safety of locomotive is the worst. The coupler force main affects the safety of locomotive near the coupler. When the locomotive is through the curve, at same time, the front of the vehicle body bears larger lateral coupler forces in the outside curve direction, the axle lateral force of leading wheelset is easy to exceed the standard. When swing angle of the coupler is larger and coupler bears over 800kN pressure, coupler force and the running speed will have a greater effect on the lateral dynamic of locomotive. Calculation shows that improved forced steering bogie has a larger advantage between the traditional bogie, self-steering and improved forced radial bogie.4. The main difference between traditional bogie with radial bogie is analyzed from the equivalent stiffness point of view. The wheelset of radial bogie is through the radial mechanism to realize function separation of the steering and transferring traction force or braking force to the frame. Coupling yaw motion of end wheelset in the same bogie can realize the change of bogie instability mode and improve the bogie stability and curve negotiation performance.5. Under the action of additional lateral stiffness, the self-steering radial bogie can maintain the traditional bogie about good straight dynamic performance. Compared with the traditional bogie, self-steering radial bogie can improve angle of attack and wheel\rail wear on tigh （less than 400 m） curves, especially for the leading wheelset. The self-steering radial bogie can achieve through the over medium radius curve without the flange contact and the centrifugal force has a same effect on the both end wheelset, so that the wheelset in the same bogie is under the similar force. The traction force will reduce the curve negotiation performance of the self-steering radial bogie. When the traction force exceeds 450kN, the curve negotiation performance of self-steering radial bogie is close to the traditional bogie. When the curve radius is larger than 500 m, the curve negotiation performance of self-steering radial bogie is superior to that of traditional bogie, in this case self-steering bogies can reduce wheel/rail wear and improve the safety of locomotive. But when the radius of the curve is lower than 500m, the creep steering ability is poor.6. Improved forced steering radial bogie has high nonlinear critical speed and keeps the same straight running performance with self-steering radial bogie. At same time it can further significantly reduce angle of attack and guidance force on tight radius curves. Improved forced steering radial bogie has the biggest advantage that the effect can be reduced on the locomotive guidance performance by traction force. When 400 kN traction force is offered, the locomotive with improved forced steering bogie still can achieve without flange contact through over than 500 m radius curve and maintain a small angle of attack and wear.7. Even under the action of the coupler forces, forced steering radial bogie can still reduce the guidance force for each wheelset, especially for the rear wheelset, but it cannot reduce the coupler lateral force influence on the lateral wheelset force. If considering effects of irregularity, at same time under the action of coupler forces, lateral wheelset forces will exceed the standard. So improving coupler and reducing free swing angle of the coupler only can improve curving negotiation security of the locomotive.