Development of Next-Generation Tilting Train by Hybrid Tilt System A

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. JR Hokkaido planned to develop a new train tilting system with a combination of these systems.

[3. Structure and features of hybrid tilt system] Figure 2 illustrates the layout of the hybrid tilt system bogie that we developed. This bogie can tilt a car body with the maximum angle of 8 degrees, comprising a conventional tilt-controlled system capable of obtaining a tilt angle of 6 degrees and air springs which can further tilt the vehicle at an angle of 2 degrees. Table 1 provides performance comparison between this system and the conventional system. In this new system, the shift in the vehicle’s center of gravity to the outer rail side can be lowered by approx. 30% (32mm smaller) in comparison to 8-degree tilting merely by the tilt-controlled system, and this shift is identical to that at an angle of 6 degrees in the tilt-controlled vehicle. Consequently, since unbalanced centrifugal acceleration corresponding to the 8-degree tilting can be reduced, this new vehicle can maintain a conventional level of riding comfort performance, even if the hybrid tilt system adopts basic speed+50km/h (R>600m, cant deficiency: 180mm) exceeding the speed of a conventional tilting vehicle. The tilt-operating actuator was changed from a conventional air cylinder to electro-hydraulic actuator (EHA). This is because later-described hybrid car body tilt control requires more rapid response and higher positioning accuracy. Also, adopting such a natural tilting actuator, which acts as a tilting damper by diaphragm, provides remarkable technological advantages such as unwanted conventional tilting damper and more simplified vehicle structure. To maintain running stability in accordance with increased tilt angle, wheel diameter was determined at 760mm (50mm smaller than a conventional wheel diameter), and compared with a conventional (283-series) tilt bogie, the height of the center of gravity was reduced by 20mm and the tilting roll center height was lowered by 117mm. The miniaturization of this bogie can achieve the production of low-floor and barrier-free passenger compartment (The air spring surface became lower by 170mm than a conventional type). (see Figure 2)

Tilt-controlled system Car body tilt system Hybrid tilt system (Curve guide type) Natural tilting by tilt Cooperative control by tilt- Type of tilt cylinder and centrifugal Forced tilting by air springs controlled system and car force body tilt system Tilt Angle ６° ２° ８° ８° ２° ８°

Air spring raised Problems by 64mm with

8°tilting

Using the tilt-controlled system and air springs ・The increase in floor shift Worsens combined, the floor shift is identical to that of the tilt- riding comfort. ３°maximum only by raising air spring. controlled system to gain 8° tilting (riding comfort is ・Obtaining clearance for rolling stock (A tilt angle of 8 is currently impossible) favorable) The floor width is the same as currently to gain 8° gauge requires narrower floor width tilting. ８°by tilt ２°by air spring ° ° 100mm toward the outer rail side (4mm toward the inner rail side) 6 by tilt-controlled and 2 by air spring (68mm toward the outer rail side) Motion of ６°by tilt 75mm toward the outer rail side center of gravity Raised32mm by Raised by 32mm

Raised by 14mm

Curve running 90km/h → 120km/h 90km/h → 115km/h 90km/h → 140km/h speed （＋３０km/h）（＋２５km/h）（＋５０km/h）

Table 1 Performance comparison of car body tilt system

Air spring Tilting beam (Tilt angle of 2) (Tilt angle of 6)

EHA cylinder

Hybrid tilt bogie Wheel diameter

760mm Figure 2 Layout and features of bogie for hybrid tilt system

[4. Optimization of hybrid tilt system control method] Figure 3 shows the control configuration for the hybrid tilt system. This chapter describes vehicle’s position detection, algorithm for car body tilt target angle, and hybrid tilt cooperative control method.

GPS

Yaw rate gyroscope Center of gravity Air spring Lateral damper Detection of vehicle height

Tachometer generator Tilt beam EHA

Compressor

Solenoid valve device

Position Tilt angle Hybrid tilt EHA command value detection device operation control controller

Pneumatic Serial Electric signal piping communication Figure 3 Hybrid tilt system configuration diagram

4.1 Position detection for curve running and algorithm for car body tilt target angle The running position is detected by GPS signal, yaw angular velocity and running speed in real time. The conventional system is characterize by on-board position database on the origin station and collation ATS ground unit, in which the interval between the origin station and collation ATS is obtained from accumulated distance travelled by the cumulative pulse signals in the vehicle’s tachometer generator (60 pulse per wheel revolution) for position detection. However, wheel’s idling or gliding might cause errors in position detection, and no modification in the database on the collation ATS ground unit upon relocation results in positioning errors and abnormal tilting control. In fact, this system employs no ground facilities like ATS ground unit for position detection, but the database on a premeasured curvature (reciprocal number of curve radius which is obtained from yaw angular velocity and running speed) is on-board. By searching a position in which curvature data obtained in real time while travelling corresponds to this premeasured curvature, the current position can be identified. The car body tilt target angle for a vehicle running on a curve is calculated so that vehicle vibration after current vehicle position (lateral vibration acceleration (yp), maximum lateral jerk (yj), rolling angular velocity (θp) and roll angular acceleration (θj)) is predicted from the premeasured curvature data and vehicle’s running velocity and resulting riding comfort evaluation index is the most favorable.

(JT pattern: Judgment function with TCT)

This riding comfort evaluation index is expressed as follows, using an index (TCT) in the transition curve and weighting compound value of the above 4 car body vibration components.

TCT = a*max (yp) + b*max (yj) + C*max (θp) + d*max (θj) +e

4.2 Cooperative control for hybrid tilt system The car body tilt control part in the Figure 3 gives a tilt command to the tilting actuator and air springs after receiving the car body tilt target angle command as mentioned above. Subsequently, however, air spring tilting approach is characterized by the delay in response compared with the (electro-hydraulic) tilting actuator, resulting in delayed motion and thus inaccurate control by JT pattern. Therefore, JR Hokkaido developed a system to improve the response of car body tilt by cooperative control comprising air springs and tilting actuator. Figure 4 shows the control flow diagram.

The tilt target angle is determined by predicting the tilt angle which minimizes TCT in subsequent seconds, using railway data and current running speed (1). To compensate for the delay in response of the air spring, the use of this predicted value generates a signal with an advanced phase corresponding to such delayed motion (2). In accordance with a sharing rate of tilt angle with the tilting actuator, 25% thereof is feedback controlled (4) as a tilt target value of air spring tilting (3). Since the tilting actuator provides a favorable response property, optimal tilt angle for a current time is given as a tilt target angle. By feedback controlling the tilting actuator using car body tilt angle (tilt angle by tilting beam + tilt angle by air spring) (5), the error in air spring tilting is corrected and the final tilt angle is set as the optimal tilt angle for a current time. From the above cooperative control approaches, the system including the air spring car body tilt was found to gain a high response performance. LPF (Low Pass Filter) with regard to air spring output will be described later.

Figure 4 Hybrid tilt control logic

[5. Results of stationary test] After experimentally manufacturing a bogie for the hybrid tilt system, JR Hokkaido conducted a stationary test using a single bogie unit to examine cooperative control system comprising the tilt-controlled system and air spring car body tilt and evaluate the performance.

5.1 Test equipment and description Figure 5 shows the layout of test equipment. The equipment comprises one experimental bogie, air spring controller and hybrid tilt controller. A load frame, equivalent to 0.5 vehicle weight (13t), was installed on air springs of the experimental bogie (1 unit). For simulating curve running, another device was attached to generate simulated centrifugal force ranging from the position of the center of gravity to the outer rail side (to the left in the Figure 5) using EHA. The distance between the center of gravity of car body and the center of gravity of tilt was given as 720mm. The tests are described as follows. ① Basic performance test Confirmations of each car body tilt control performance by the tilt and air springs ② Cooperative control test Confirmation of functions in cooperative control system (Confirmation of concurrency control and operation for car body tilt by the tilt and air springs) Optimization of control parameters (Adjustment for LPF threshold frequency and JT pattern advanced time) Confirmation of hybrid tilt control functions with centrifugal force Confirmation of restored operations after the system has failed From the results of these tests, the optimization of control parameters in a cooperative control test and a test of hybrid tilt functions with centrifugal force are described as follows.

Figure 5 Layout of test equipment

5.2 Optimization of control parameters 5.2.1 Optimization of LPF frequency This tilt system is feedback controlled, using car body tilt angle after adding tilt angles by the tilting beam and by the air spring. The air spring installed on the tilting beam generates some vibration affected by the motion of the tilting beam. Therefore, when the tilting beam actuator is operated with a frequency exceeding rolling resonant frequency by the air spring and car body, coupled feedback from the air spring vibration and tilting actuator was found to cause oscillation. To prevent this problem, an LPF should be inserted into a feedback loop of the tilt cylinder from the air spring to reduce loop gain over the rolling resonant frequency. However, LPF, with a delayed response property, was inserted into the moving air spring to avoid the delay in the target-value path. It shows the relationship between the amplification ratio of rolling vibration traveling from the tilting beam to the car body and the inserted LPF. The insertion of FIR-type LPF with a cutoff of 0.4Hz into a rolling resonant frequency of 0.6 to 0.7Hz decouples air spring vibration and tilting actuator and eliminates oscillation.

5.2.2 Optimization of JT pattern advanced time To optimize the advanced time to compensate for the delay in air spring motion shown in the Figure 4, the advanced time of air spring tilt target value to the tilt target value of the tilting actuator was set ranging from 0.0 to 3.0 seconds in a response test. The evaluation function is shown in the expression (1). This expression indicates the motion of the tilting actuator which compensates for error in air spring, and the smaller the more favorable. The Figure 6 demonstrates that 2.0-second time is the most appropriate advanced time. t2 θr −θb dt ∫t J = 1 (1) t2 − t1

θr : target tilt angle, θb : car body tilt angle, t1 : tilt start time, t2 : tilt finish time

Advanced time (sec)

Figure 6 Relationship between advanced time and evaluation function

5.3 Hybrid car body tilt control test with simulated centrifugal force JR Hokkaido performed hybrid car body tilt control test with simulated single curve running and simulated centrifugal force. The cooperative control found favorable test results by parameter adjustment as shown in Figure 7. From this observation, air spring tilting raises the height of the 1st rank air spring to tilt the car body. The car body tilt angle properly accords with the target tilt angle, indicating advantageous tilting control. Since the air spring is given an advanced target value of 2 seconds preceding a titling target value of the tilting actuator, the air spring and tilting actuator starts tilting at the same time. In addition, while the air spring tilt angle is insufficient for the target value at the start of tilting, it exceeds slightly after the tilt finishes. Despite such imbalance, the tilt angle data of the air spring is feedback controlled in the tilting actuator and the difference is compensated. The motion of the tilting actuator and car body tilt angle is observed smooth and no sign of resonance due to the vibration of the air spring is found. This observation presents an LPF’s effect of removing signals in a resonant band by the air spring.

Figure 7 Test result of hybrid car body tilt control with simulated centrifugal force [Conclusion] In this experiment, JR Hokkaido developed “hybrid tilt system” which performs complex control of the tilt-controlled system and air spring car body tilt with the aim of improving curving performance, by means of experimentally manufactured bogie and tilt controllers. In cooperative control comprising the tilt-controlled system and air spring car body tilt with distinct response properties, we formulated specific control logic by combining the feedback control of actual tilt angle with control command signal in consideration of air spring response time. In a stationary test, favorable tilting control results were obtained. Currently, two units of this hybrid tilt system bogie are being manufactured and running tests of a tilt-controlled vehicle with this on-board bogie will be planned. In such running tests, we will confirm curving performance by means of hybrid tilt control, collect and analyze data, aimed at improving running stability and riding comfort, and achieve advanced vehicle designs.

[References] [1] Enomoto, Kamoshita, Kamiyama, Sasaki, Hamada, Kazato: “Development of Tilt Control System Using Electro-Hydraulic Actuators”: QR of RTRI, Vol.46, No.4, pp.219-214, Nov. 2005 [2] Maki, Enomoto, Sasaki, Tsujino: “A System to detect the Train Position using GPS and a Track Geometry Database”: RTRI Report Vol.17, No.4, pp11-16, April 2003 [3] Hirayama, Ide, Nakagaki, Kouno, Ozaki: “It make running curve at high speed agreeable – Tilting Control System by Use of Air Spring – for Rolling Stock”: KHI Technical Report No.160, Jan. 2006