How much Do You Know About The Bogies of A Train?

Overview of The Train Bogies

Bogies (called trucks in North America and mostly Bogie in the rest of the world) are important structures that help trains pass the curve, and without bogies, it would be very difficult for trains to pass the curve, as shown in the figure above. Ordinary freight train bogies have “Three big pieces”: Wheelset, Side Frame and Bolster , so this bogie is also called a three-piece Truck.

Structure and Function of the Train Bogies

The wheelset is the part of the train in contact with the rail, which is composed of the Wheel, the Axle and the Journal. The wheel and axle are not cast in one piece but are cast separately and pressed together with strong pressure. Yeah, you read that right, no screws or welds, just straight together. Early wheel sections were straight, but it was found that a curved section helped to spread the stress in the wheel and extend the life of the wheel, so today’s wheel sections are curved.

The part of the axle that protrudes beyond the wheel is called the Journal, to which the Journal Box and the side frame connect. The axle box is divided into two types: Friction/Plain Bearing and Roller Bearing. The early train bogies mostly used plain bearings; that is, the fixed support is directly pressed on the moving journal, the intermediate oil is lubricated, and the sliding friction between the two is complete, as shown in the figure below. Obviously, sliding friction will generate a lot of heat, and the heat will even ignite the lubricant in the axle Box, resulting in a Hot Box accident. Therefore, people have improved the sliding bearing.

The improved train bogie adopts rolling bearings, as shown in the figure below. The rolling Bearing used in railway trains is a kind of Tapered Roller Bearing (Tapered Roller Bearing), compared with Ball Bearings and Cylindrical roller bearings (Cylindrical Roller Bearing); such bearings can provide less resistance while bearing greater radial and normal stresses.

The axle box and side frame of the bus bogie are welded or riveted, while the side frame of the truck bogie is pressed directly on the axle box through the Journal Adapter. If the side frame is lifted, the wheelset can be left on the rail with a small constraint, and it is not lifted with the side frame, which greatly facilitates the operation of the truck wheel change. The following figure shows the wheelset of the truck bogie. The structure wrapped in the journal is the axle box. The axle box of the truck bogie is generally produced with the wheelset. The three screws that can be seen above the axle box are only used to ensure that the axle box cover does not fall off and does not bear any structural load. The wheel, which is not pressed into the axle, can also be seen at the far end of the image.

Like automobiles, railway vehicles also need a damping spring. So, how is the spring connected to the side frame and bolster? The answer is, just shove it in! Yes, there is no screw to fix the spring on the side frame or pillow, but it is directly inserted between the side frame and the bolster, and the gravity of the vehicle itself ensures that no displacement occurs; Moreover, there is no screw fixed between the bolster and the side frame, after the bolster passes through the bottom of the side frame, slide along the slide rail of the side frame to the top of the side frame, and then insert the spring, so that the side frame will not slide out from the low end. Any shock absorption equipment requires damping; otherwise will continue to be vibration. Early railway cars used leaf springs and friction between the blades provided damping. After the spring is used, additional devices must be used to provide damping, and the most widely used is the inclined Wedge Friction Wedge. This device is capable of converting positive pressure into lateral pressure against the side frame, using friction with the side frame to provide damping. The source of positive pressure is some of the vehicle’s weight, and some of it is the pre-loaded spring.