How Bogies Work Isao Okamoto

T Technology echnolo Railway Technology Today 5 (Edited by Kanji Wako) How Bogies Work Isao Okamoto Role of Bogie Figure 1 Wheel and Axle Set Railcar bogies usually go unnoticed by rail passengers, but despite their obscurity, Wheel tread Flange they are very important in safe railway Tread operations and perform the following Wheel Axle gradient functions: • Support railcar body firmly Wheel • Run stably on both straight and curved diameter track • Ensure good ride comfort by absorbing vibration generated by track irregulari- Rail ties and minimizing impact of centri- fugal forces when train runs on curves at high speed Gauge • Minimize generation of track irregularities and rail abrasion To help clarify the basic mechanism of gy bogies, this article explains bogies used affect the running performance and and some express trains of the Odakyu on conventional railcars. Bogies used on strength of the bogie frame, so none are Line in suburban Tokyo. Although the shinkansen will be discussed in more de- used for passenger railcars in Japan today. articulated bogie has some disadvantages, tail in the next article in this series. Non-articulated and articulated bogies such as a complex structure, increased Bogies can be classified into non-articu- axle load due to the support of one body lated and articulated types according to by one bogie, and difficult maintenance, Bogie Configurations the suspension. Two non-articulated it offers various advantages including a bogies usually support one railcar body lower centre of gravity, better ride com- Types (Fig. 3a), but one articulated bogie sup- fort because car ends do not overhang Bogies are classified into the various types ports the back end of the forward car and bogies, and less effect of running noise described below according to their con- the front end of the rear car (Fig. 3b) as on passengers because seats are not over figuration in terms of the number of seen in the Spanish Talgo, French TGV, bogies. axles, and the design and structure of the suspension. Number of axles Since bogies run on two steel rails, the Figure 2 Comparison of Effect of Track Irregularity between Single-Axle Bogie and Two-Axle Bogie minimum structural requirement is an axle and two wheels, which are usually pressed onto the axle (Fig. 1). Bogies are Smaller effect of classified into single-axle, two-axle, three- track irregularity axle, etc., based on the number of axles. on car suspension point The two-axle bogie is most common. In addition to its relatively simple structure, Car suspension point it has the advantage of decreasing the Car suspension impact of track irregularities on the rail- point car at the car suspension point, in comparison to the single-axle bogie which transmits the impact to the car directly Single-axle bogie Two-axle bogie (Fig. 2). The three-axle bogie has a more complex structure that tends to adversely 52 Japan Railway & Transport Review 18 • December 1998 Copyright © 1998 EJRCF. All rights reserved. Figure 3 Non-articulated Bogie and Articulated Bogie Figure 4 Swing Hanger and Small Lateral Stiffness (a) Non-articulated cars Bolster Spring Bogies Swing Hanger Bogie Centre pin Non-articulated bogie Upper Side bearer swing (b) Articulated cars bolster Bogie frame Bolster anchor Bolster spring Swing Lower hanger swing bolster Small Lateral Stiffness Bolster Spring Bogie Articulated bogie Centre pin Swing hanger bogie and small lateral Bolster and bolsterless bogies Side bearer Bolster stiffness bolster spring bogie Bolster and bolsterless bogies (Fig. 7) are Bolster Air bolster Based on the structure of the suspension differentiated by their suspension gear. anchor spring Bogie gear, bogies are classified into two types: The bolster bogie was developed first. A frame the swing hanger type, and the small fundamental characteristic of the bogie is lateral stiffness bolster spring bogie type that it must rotate relative to the body on (Fig. 4). To ensure good ride comfort on curves, while retaining high rotational passenger cars, the bogie must absorb the resistance during high-speed running on reducing the number of parts and the rolling motion that passengers are most straight sections in order to prevent bogie weight (the bolsterless bogie for sensitive to. Conventional swing hanger wheelset hunting (Fig. 8) that reduces ride shinkansen was commercialized in the bogie designs support the body by using comfort. To achieve these characteristics, 1990s). In recent years, most narrow- lower swing bolster beams suspended the bolster bogie has a centre pivot that gauge and shinkansen cars use the from the bogie frame by means of a link serves as the centre of rotation, and side bolsterless bogie, which permits rotational consisting of two vertical members that bearers that resist rotation. displacement on curves through the hori- widen toward the bottom, together with In the 1980s, a bolsterless bogie was com- zontal deformation of bolster springs (also bolster springs and upper swing bolster mercialized to improve performance by known as secondary suspension springs) beams (to support vertical movement). Although the swing hanger type (Fig. 5) achieves good ride comfort by minimiz- Figure 5 Swing Hanger Bogie ing horizontal stiffness of the suspension gear, its maintenance is relatively difficult due to the complex structure and large number of wearing parts. In the 1960s, bolster bogie with air spring that absorbs vibration due to its small lateral stiffness, was developed (Fig. 6). It soon replaced the swing hanger type and was used in the first shinkansen in 1964, contributing greatly to their size and weight reduction. Most recent bogies are of the small lateral stiffness bolster spring bogie type Swing hanger because of its simplified suspension (Author) design. Copyright © 1998 EJRCF. All rights reserved. Japan Railway & Transport Review 18 • December 1998 53 Technology Figure 6 Lateral Stiffness Bolster Bogie discussion focuses on the bolsterless DT50 Centre plate type (Fig. 9) which is widely used in commuter passenger railcars of JR companies. The DT50 was first commercialized in 1985 by the former JNR when it was used Bolster Centre pivot for the Series 205 railcars. Centre pivot wearing plate Suspension gear The suspension gear (bolster spring, trac- Bogie frame tion transfer device, anti-yawing damper, and lateral damper) plays an important role in supporting the body, allowing the bogie to rotate relative to the car body on curves, isolating the body from vibration (including high harmonics) generated by the bogie, and transmitting traction force from the bogie to the body. For these Bolster anchor purposes, the bolsterless bogie has air Wheelset Traction motor Air spring under bolster springs that permit large horizontal displacement, as well as a traction transfer Gears Axle spring device (classified into permanent-link type, the Z-link type and laminated- rubber type) at the virtual rotational centre of the bogie for transmitting the on both sides of the bogie. Rotation is tractive force to the car. In addition, the resisted by longitudinal anti-yawing bolsterless bogie used for express trains Figure 7 Bolster and dampers on both sides of the bogie, and shinkansen has anti-yawing dampers Bolsterless Bogies resulting in better rotational resistance (Fig. 7) at the outer side of the side beam Bolster Bogie than conventional side bearers. of the body and bogie frame (parallel to the side beam) to prevent wheelset hunting that reduces ride comfort. Basic Bogie Elements Coil springs were originally used as Air bolster bolster springs to support the body, but in spring This section describes key components the 1960s, air springs were commercial- Bolster anchor and parts of the bogie, including their ized for railcars in Japan and were used Bolster structure and performance. However, it for high-speed trains. Since the 1980s, Side bearer Bogie frame Centre pivot should be noted that the parts vary widely they have been used for commuter and according to the bogie type, and this short-distance trains in order to take Bolsterless Bogie Figure 8 Wheelset Hunting Traction transfer device Air bolster spring Anti-yawing damper Bogie frame 54 Japan Railway & Transport Review 18 • December 1998 Copyright © 1998 EJRCF. All rights reserved. Figure 9 DT50 Bogie for Series 205 EMU advantage of their improved ride comfort and ability to maintain body height. Bogie frame Traction transfer device The bogie frame accommodates various Series 205 EMU (Author) bogie equipment and is generally fabri- cated by welding together two side beams Brake equipment Bolster spring and two cross beams into an H-shaped frame, (Fig. 10). In 1955, compound side Bogie frame (side beam, beams were developed using press weld- cross beam) ing and this structure is used to manufac- ture most bogie frames in Japan. The thickness of the side and cross beams was increased from 6 mm (used in some Lateral damper frames around 1960) to 9 mm. It was increased again to 12 mm in the 1970s, Traction motor when some bogie frames of express trains were found to have minor faults. How- ever, since the DT50, as a result of Axle bearing and axle box simpler construction and improved weld- Axle spring, axle box suspension ing technology, bogie frames use 8 or 9 mm plates to reduce weight. Finally, (Brake disc for trailing bogie) around 1980 (1976 for shinkansen), the Wheelset material of major bogie frame members for narrow-gauge railcars was improved Gear from SS400 (rolled steel for general structures) to SM400B (rolled steel for welded structures). Some bogie frames since the DT50 use Brake disc seamless steel pipes for cross beams to reduce weight and cost. Axle box suspension Figure 10 Bogie H-Frame This device supports the axle via the bear- Cross beam ing from the bogie frame. It is a critical component determining the running performance of the bogie, ride comfort and bogie frame construction, due to the suspension method and support rigidity.

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