Development of Next-generation Tilting Train by Hybrid Tilt System A.Shikimura1, T. Inaba1, H.Kakinuma1, I.Sato1, Y.Sato1, K.Sasaki2, M.Hirayama3 1Hokkaido Railway Company, Sapporo, Japan; 2Railway Technical Research Institute, Kokubunji, Japan; 3Kawasaki Heavy Industries, Ltd., Kobe, Japan [Abstract] To shorten train arrival time in existing railway lines (with a gauge of 1067mm), JR Hokkaido has improved running speed and acceleration and deceleration performance by solving Hokkaido’s regional problems of heavy snowfall and extremely severe cold and developed the capability to run on a curve section by our specific tilt-controlled vehicle system. Furthermore, to improve curving performance, this operating company developed “hybrid tilt system,” which can achieve a car body tilt angle of 8 degrees, by introducing the conventional “tilt system (curve guide type, tilt angle of 6 degrees)” and an “air spring car body tilt system (tilt angle of 2 degrees)” combined in cooperative control. This system is characterized by the reduction in tilt angel to 6 degrees on a curve in the conventional tilt-controlled system and another tilt angle of 2 degrees in a new tilting mechanism comprising the air spring on the outer rail side, thereby reducing the centrifugal force on a passenger. Meanwhile, since the motion of the center of gravity toward the outer rail side can be reduced by 25%, passenger’s riding comfort can be improved, which cannot be achieved in a single natural tilting vehicle with the same tilt angle. This paper outlines “hybrid tilt system” in this development project and provides cooperative control method for the 2 systems and the results of a stationary test. [1. Introduction] In existing railway lines accounting for 92% of Japan’s total length of railways lines operated (1067mm-gauge is mainly used for non-Shinkansen (bullet train) lines), the reduction in train arrival time has been achieved by the improvement in maximum running speed, acceleration and deceleration performance and curving performance. Being geographically located at latitude 41 to 45 degrees north and prone to heavy snowfall and extremely severe cold, Hokkaido suffers from the resultant serious drawbacks to achieve industrial and technological advantages. Under these circumstances, JR Hokkaido, the regional leading railway operating company with railway networks extending about 2,500km in an area of 83 thousand square kilometers, has been dedicated to developing brake system capable of train operation at a speed of 130km/h and specific tilt system to improve the curve running speed. In the process of further reduction in arrival time, the increase in maximum running speed seems relatively difficult, because it needs building or improving ground facilities and measures to prevent collisions with a car at many railroad crossings in Japan’s existing railway lines with the maximum running speed normally set at 130km/h. In addition, no substitute technologies of the tilt system fail to improve curving performance. In the following tests, which are characterized by no improvement in maximum speed in a straight section but in curving performance, we developed “hybrid tilt system” consisting of conventional tilt-controlled system and air spring-tilting approach with improved curving performance and cooperative control method. A stationary test, shown in the following detailed descriptions, was performed with an experimentally produced bogie to validate its technological functions and performance. [2. Progress of the development of hybrid tilt system] The running of a railway vehicle at a higher speed on a curve requires the reduction in centrifugal force applied on the outer rail side or unbalanced centrifugal acceleration. However, since this force cannot be sufficiently reduced even by cant adjustment, JR Hokkaido developed a combination of “tilt-controlled system” and “car body tilt system” which can tilt a vehicle toward the inside of the curve. The outline will be given as follows. 2.1 Conventional technologies for curve running speed improvement 2.1.1 Tilt-controlled system (curve guide type) For increasing a train speed in a Hokkaido’s main railway line (318.7km between Sapporo and Hakodate), JR Hokkaido introduced a tilt-controlled system that can achieve the operation with the maximum running speed of 130km/h, and a curve running speed of basic speed+30km/h for about half the total operating lines. The conventional car body tilt device in a tilt-controlled vehicle employs “roller,” but this system allows snow to pass through small gaps in the vehicle and it to freeze inside in a winter running test, resulting in failure in the entire tilt system. Consequently, we launched the development of tilt-controlled system, using a bearing curve guide which can completely seal the tilt-controlled vehicle by protecting it from such weather condition, and then manufactured a 281-series limited railway train (for Super Hokuto) with this onboard bogie. The operation started in 1994. The tilt angle was set at 5 degrees, and the curve running speed was determined at basic speed+30km/h (R>600m, cant deficiency: 120mm). 2.1.2 Self-steering tilt system (curve guide type) As a next step, JR Hokkaido developed a tilt system for another main railway line (348.5km between Sapporo and Kushiro). Based on the curve guide type of the 281-series train system, however, this tilt system is in operation near wetland with soft roadbeds and many gentile curves, therefore we significantly improved functions of the basic tilt system. First of all, to reduce lateral pressure on a train running on a curve, we introduced “link-type self-steering structure” to make each of two axles face toward the curve center using lever and linkage. This system can reduce the lateral pressure by up to 15% to lower the force on the rail and increase the curve running speed on a soft roadbed. In addition, aimed at improving the running speed and riding comfort, car body tilt angle was raised by 1 degree to 6 degrees to gain the speed limit. Furthermore, by installing the equipment primarily in the lower part after a full review of its arrangement, the center of gravity for a vehicle was lowered by 116mm and the tilting roll center was lowered by 400mm compared with the 281-series train vehicle. To maintain running stability on a steep curve, the interval between bogie air springs was raised by 150mm and the center of gravity and the height of the tilting roll center were reduced. In addition, the accommodating of the bearing curve guide within a tilting beam was able to completely seal the equipment in more cold-resistant and snow-proof structure. Then, JR Hokkaido manufactured 283-series limited railway train carrying this system and started the operation in 1997. The tilt angle was set at 6 degrees, and the curve running speed was given as basic speed+30km/h (R>600m, cant deficiency: 120mm). 2.1.3 Car body tilt system (air spring height control system) While the tilt-controlled system had a significant effect on the improvement in the curving performance, car body tilt by this system required a dedicated and highly complex bogie and thus expensive vehicles and ground facilities. On the other hand, we developed low-cost “car body tilt system” by air spring height control for a section with a lower transportation density. With no tilt-controlled vehicle, this system can reduce unbalanced centrifugal acceleration. This is because two air springs in the bogie, one on the outer rail side and the other on the inner rail side, serve as actuators when air supply makes the outer air spring height larger than the counterpart to tilt the car body. For curve detection, a yaw rate gyroscope is used in an autonomous control system independent of ground facilities. Although the performance seems insufficient (tilt angle: 2 degrees, curve running speed: basic speed+25km/h (R>600m)), this tilt system gives a competitive cost advantage over the above-mentioned tilt-controlled vehicle. JR Hokkaido started the operation of 201-series commuter train with this system in 1997 and 261-series limited railway train in 2000. 281series DMU 283 series DMU 261 series DMU Figure 1 Tilt-controlled Train (281and283) and Car Body Tilt Train (261) of JR Hokkaido 2.2 Problems toward improving curving performance We have examined various technological problems to increase curve running speed and thus improve curving performance. First of all, to determine the tilt angle at 6 degrees (current angle) or higher in the tilt-controlled system, there are three major problems to be solved. Firstly, lateral motion is particularly high. Since the tilting beam on the vehicle is designed to swing laterally, the higher the tilt angle the noticeable the vehicle’s lateral motion or floor shift in the passenger compartment, resulting in unfavorable riding comfort and motion sickness. Secondly, a high tilt angle, leading to the shifting of vehicle’ center of gravity toward the outer rail side, might cause wheel unloading on the inner rail side. Thirdly, if the tilt angle is higher, the section of a car body must be smaller due to rolling stock gauge or other conditions, thus presenting difficult problems such as reduction in the passenger compartment capacity and underfloor equipment space. Meanwhile, since car body tilt system is designed to raise the air spring on the outer rail side, it generates no lateral motion, thereby overcoming the above problems with the tilt-controlled system. However, to obtain the tilt angle at 6 degrees using car body tilt by air springs, the spring displacement must be given at least 200mm, which is unlikely to be achieved due to its structure. A comparison of these two distinct systems found no common technological problems and the possibility of overcoming each of the disadvantages.