Development of a WSP System for Freight Trains

Kiyoshi Kawaguchi1

, Nobuo Seko2

, Takashi Nagai3

, Yoshiaki Ookita4

Railway Technical Research Institute, Tokyo, Japan1

, Shinko-Electric CO, Mie, Japan2

,

TACO Company, Saitama, Japan3

, NEC-TOKIN Ceramics Company, Hyogo, Japan4

Abstract The authors have developed a system for wheel-slide prevention (referred to below as WSP) or anti-lock braking (ABS) for use in freight trains that have neither a power source nor a heater on board. This system, controlled through a power -saving method, has an anti -skid valve that can be driven by static electric energy charged in an electric double-layer capacitor (EDLC) with a maintenance -free lifespan of eight years or more. The anti -skid valve features low power consumption of 2.5W or less, and has the capacity to perform the role of two valves with an electromagnetic coil. The newly developed capacitor, which is of the aquatic electrolytic solution type, has a capacity of 5F and works at 24V in a temperature range of -40 to +85°C. Satisfactory results were obtained from bench and field tests on a freight train fitted with the new WSP system, showing that it fulfils the requirements of durability, reliability, freedom from maintenance for eight years or more and low manufacturing costs. These are features that have long been awaited in the field of tran sport by freight train.

Keywords: WSP, wheel-slide prevention, wheel slide preventive device, antilock brake system, air brake, electric double-layer capacitor, anti -skid valve, freight train

1 Introduction Freight trains in Japan are equipped with a simple automatic air brake system that meets the standards of industrialized countries. However, since they run on the same rails as passenger trains, they are required to have a brake system with a response and deceleration performance high er than those of brake systems anywhere else in the world. As a result , freight trains (and especially high-speed container trains) are susceptible to wheel flats in the same way as ordinary passenger trains. It has been found that the maximum incidence o f wheel flat in high-speed container trains is as high as 25% per car per year.Wheel flats cause increases in vehicle noise and vibration as well as a rise in the cost of axle and bearing maintenance. Worse still, the phenomenon can invite complaints from consigners about damaged goods, abrasion of printed surfaces on cardboard boxes, damage to barcodes etc. The eradication of wheel flats was therefore a major challenge in promoting the modal shift to freight railways. As a measure to help promote th is shift, the authors have developed a new anti -lock brake system (WSP) for freight trains using a subsidy from the Ministry of Land, Infrastructure and Transport (see 3.5 for the WSP system configuration).

2 Technical problems involved in WSP for freight trains

In the past 15 years or so, several types of WSP for freight trains have been developed in Japan and overseas. However, since these have all been based on the conventional WSP system for passenger trains with a lead-acid storage battery, they are inadequate in terms of reliability and maintainability , and as a result none of the m has been widely adopted. Key background factors include the exceptionally severe operating environment and conditions unique to freight trains . The technical problems posed by t hese factors are outlined below.

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1) Ordinary freight trains have neither a power supply nor a heater on board, making it necessary to secure an economical power supply for them. It must also be considered that , unlike passenger cars, freight trains are not equipped with high-performance dehumidifier s. The brake control equipment on freight trains is fitted to the bottom of the car body underframe, making it necessary to significantly improve the durability of each individual part to withstand extremes of temperature (from intense cold in winter to intense heat in summer ) as well as dew, wind and rain, ultraviolet rays and soiling.Unlike passenger cars, freight trains undergo frequent coupling/uncoupling and loading/unloading . As they feature neither air springs nor axle springs, this subjects the car body to substantial vibration acceleration. As a result, it is necessary to reinforce the valve body opening/closing power to prevent air leakage due to vibration or shock and reduce friction.The freight train brake cylinder (BC) is a foundation brake gear fitted to each bogie under the car body. The number of BCs is 1/4 as opposed to 1/8 in passenger cars, so along with the large loads applied to freight trains, the capacity of each BC is quite large. The exhaust capacity of the anti-skid valve for freight trains therefore needs to be much greater than that for passenger cars.With an automatic air brake system, the idle running time of the service brake is so long that the actual average deceleration required is c omparatively large. Additionally, the inertial mass of wheel rotation is small, whereas the difference in mass between an empty car and a loaded car is large. The WSP control must therefore be highly responsive.The supply voltage for the WSP of passenger trains is 100V DC, and the output voltage of, say, a lead -acid storage battery is 12V DC. If the electromagnetic valve for the WSP of a freight train is to be driven by a part for use on 100V using the same power, the current capacity of the valve, or the coil cross-section area, must be about 8.3 times that of the WSP of a passenger car. In other words, the coil ’s electrical resistance ratio must be reduced to 1/8.3*2.The compressed air used for braking needs to be properly dehumidified to prevent valve problems. However, with old locomotives that are not equipped with high-performance dehumidifier s, the entry of foreign matter into the brake valves of freight trains from dew formation, drainage, rust, etc. inside the air piping of freight trains hauled by the locomotive tends to occur easily. Therefore, when brake valves designed for passenger cars are to be used for freight trains, it is necessary to provide drastic measures against sticking, air leakage, rust formation and rubber deterioration in the valves.The cost of a freight train is several times l ess than that of a passenger car, and the cost of its brake system is comparatively low. However, since it requires a generator, a storage medium and a charging/discharging control unit for the WSP, the cost of the system actually becomes higher than that of a passenger car.When a chemical storage battery is used for the WSP of a freight train, it is subject to electrode deterioration from charging/discharging. In addition, depending on the temperature at which the chemical reaction takes place, the electrodes deteriorate or decline in function. The provision of measures to prolong battery life or increase battery capacity adds to the costs involved.

10) The power consumption of the WSP increases instantaneousl y with the on/off-type anti-skid valve. Securing the necessary power using a storage battery with low instantaneous power also adds to the costs involved.

3 Newly developed WSP for freight trains 3.1 Anti-skid valve 3.1.1 Energy -saving method of controlling anti -skid valve The power consumption of a representative anti -skid valve for passenger cars is 66W per set. For a freight train with BCs fitted to the car body underframe, the maximum power consumption reaches 132W (2 sets). Thus, if the battery output increases, the total cost will rise. In view of this, the authors studied ways to control anti -skid valves with lower power consumption, and developed the method outlined below.

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In Fig.1, the diagram on the left shows the conventional method of controlling a repre sentative on/off-type anti-skid valve in the WSP of a passenger car, while the diagram on the right shows the newly devised control method. Providing the electromagnetic release valve with a lockout capability has enabled the peak value of power consumptio n to be reduced by half. 3.1.2 Air circuit for the new control method A number of air circuits were studied in implementing the new control method outlined above, and the circuit shown on the right of the diagram in Fig. 2 was devised. The conventional air circuit can be expressed by a main

Initial controlling pressure

Final controlling pressure

Lockout valve

Release valve

Power consumption

Time Time

Fig. 1 Conventional control method (left) and new energy -saving control method (right) used by anti-skid valve

Control mode

Fig. 2 Conventional air circuit (left) and energy -efficient air circuit (right) for anti -skid valve

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valve configuration in which direct -acting two-port valves (normal open and normal close) are arranged in parallel. The high-order electromagnetic valve, known as an air shutoff valve, is a two-port electromagnetic shutoff valve, and the low-order electromagnetic valve is a release valve. When the wheels begin to slide under a conventional air circuit, the two electromagnetic valves are both excited to reduce the BC pressure. Exciting only the release valve is impracticable because it causes the supply-side air and the BC-side air to be exhausted at the same time (see the shaded part in the left-hand diagram of Fig. 2). The newly developed air circuit can be expressed by a main valve configuration in which a direct -acting two-port valve for normal open and a direct -acting three-port valve for normal close are arranged in series. With this arrangement, it is possible to stop the air supply to the high-order valve and exhaust air from the low-order valve at the same time by exciting only the electromagnetic release valve. 3.1.3 Internal structure of anti -skid valve (1) Saving energy while increasing valve capacity The internal structure and operating principle of the newly developed energy-saving anti-skid valve are shown in Fig. 3, and its appearance and principal dimensions are shown in Fig. 4. The four round holes (two on each side of the valve; see Fig. 4) indicate a newly developed dust filter made of non -woven fabric (left: supply side, right: BC side). By employing the valve’s internal structure as shown in Fig. 3, it has become possible to make the electromagnetic air shutoff valve (AV) and the electromagnetic release valve (RV) perform the same function as they do under the ON condition, even when the AV is in an OFF condition and the RV is in an ON condition. To reduce the power consumption of the pilot electromagnetic valve unit, the current -dependent electromagnetic coil was converted to a winding -dependent type by increasing the number of turns. In addition, to reduce valve size and increase its capacity, the flow amplification ratio was increased. In order to reduce sliding friction and improve reliability, the valve was also made free of sliding parts. (2) Prolonging life and reducing maintenance In order to prolong the life of the anti -skid valve and extend the maintenance-free period to eight years, the authors reviewed the mechanism and material of the valve and redesigned the valve body, dust filter and other component parts. The key points in the development are shown below.

1) Designing an energy-saving pilot electromagnetic valve operating on 24V 2) Applying a rustproof alloy material to parts that require high mechanical strength 3) Designing a diaphragm valve with no sliding parts

Fig. 3 Internal structure and operating principle of anti-skid valve

Variable load valve (VLV) side

Brake cylinder (BC) side

port (EXH)

To exhaust

AV: Air shutoff valve → Pilot valve OFF RV: Release valve → Pilot valve ON

Fig. 4 Appearance and dimensions of anti-skid valve

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4) Applying hydrogen-added NB rubber (HNBR) to the valve body and seal 5) Reinforcing the valve seat seal and improving its airtightness 6) Providing the valve openings with a non-woven fabric dust filter 7) Designing a valve case with a drip -proof construction 8) Providing a ventilation port to prevent dew formation 9) Improving the dielectric strength and insulation type (Type H).

3.1.4 Results of characteristic tests and durability test The newly developed anti-skid valve was subjected to a range of characteristic tests and a durability test, with the results outlined below.

1) The maximum power consumption of the anti -skid valve was reduced to 2.2W per bogie, or 1/60 th that of the conventional anti-skid valve.

2) By expanding the effective orifice diameter, the flow rate was increased to more than twice that of the conventional anti-skid valve

3) The cost performance ratio was improved significantly by simplifying the valve configuration, increasing the flow rate, reducing power consumption and cutting the cost of the valve.

4) The results of a bench test on valve durability showed that the valve could be made free of maintenance for eight years.

3.2 Electric double-layer capacitor for rail vehicles Generally speaking, the rated performance of a storage battery is based on a chemical reaction temperature of 25+-15 ºC and the original condition of the electrodes. Under temperatures beyond 25+-30 ºC during the hottest or coldest seasons (e.g. below -20 ºC or above +65 ºC), the battery rapidly declines in function a nd durability. In view of this, the authors developed a 24V-class electric double-layer capacitor (EDLC) that is minimally influenced by chemical reaction temperature and electrode deterioration (Fig. 5). The measures taken to apply the EDLC to freight tra ins and the features of the EDLC are shown below, together with the test results. (1) Measures taken to prolong service life, reduce maintenance and improve reliability

1) A diluted sulfuric acid solution -based (or water-based) electrolyte is used in place o f the organic electrolyte of the conventional EDLC to improve reliability under a range of temperature conditions, cut costs and give an EDLC without a cell balancing circuit (voltage: 24V, electrostatic capacity: 5F) , which is the first of its kind.

2) Organic-based electrodes have a flat laminated construction rather than the twisted construction used for the conventional EDLC. They are hermetically sealed to prevent damage from unusual vibration and to widen the operating temperature range.

3) A thick-walled ceramic vessel (with an aluminum-ceramic vessel) is used in place of the thin -walled metallic vessel of the conventional EDLC to make it rustproof and increase its strength and durability. The EDLC measures 72mm x 148mm x 84mm, and weighs 1.6kg including the vessel.

4) Taking advantage of the diluted sulfuric acid solution -based electrolyte, 28 homogeneous cells are prepared and connected in series to generate 24V. This eliminates the need for a cell balancing circuit, thus reducing the cost of the EDLC.

Fig. 5 Newly-developed EDLC for railway cars

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(2) Bench test results

1) Based on the premise that the EDLC would undergo rapid and frequent charging/discharging , an accelerated durability test was carried out under continuous conduction condition s. From the test results, it was judged that the EDLC would last over 30 years, far longer than the target life of eight years. The test conditions were extremely rigorous: 85 ºC, 10,000 hours, and continuous conduction (equivalent to 50 ºC, 320,000 hours and 10,000,000 cycles or more).

2) The EDLC met all the JIS -specified requirements of railway cars, including temperature conditions in the hottest and coldest seasons and vibration/explosion-proof performance. In particular, the operating temperature range was as wide as -40 ºC to +85 ºC.

3) The unit internal resistance val ue (or ESR value) decreased markedly, to 1/100 that of the conventional organic-based EDLC in the low temperature range (max. 500m 㪐 per 24 V, 5F).

3.3 Speed sensor and generator The speed sensor developed for the freight train WSP and the WSP generator are shown in Fig. 6. The speed sensor is of the magnetic resistance type. The generator employs a permanent magnet -type inner rotor and incorporates a wheel ring for counting pulses. One generator is fitted to each car with four speed sensors on each axle. 3.4 Control and arithmetic unit The low -cost, energy-saving control and arithmetic unit developed for the freight train WSP is shown in Fig. 7. The device on the right (as viewed from front) is an EDLC. A couple of EDLCs arranged one behind the other offer a storage capacity of 2.88 kJ. Since the control channel is formed by the BCs fitted to the car body underframe, a two-channel control system was adopted to cut system cost s and save energy.

3.5 Brake system for freight trains and WSP configuration Fig. 8 shows the freight train WSP made up of newly developed parts, and the general WSP configuration when applied to the automatic air brake of a freight train. The speed generator fitted to the end of an axle is used to store electricity in the EDLC, and power to control the WSP is obtained from both the EDLC and the generator. Storing power in the form of static electricity (which is unaffected by electrode deterioration and chemical reaction temperature ) has enabled correction of errors in the previous development. The meanings of the symbols used in Fig. 8 are shown below.

1) RV: Magnetic release valve (for promoting release com mand) 2) SV: Magnetic service valve (for promoting service command) 3) EV: Emergency magnetic valve (for promoting emergency command) 4) EXT: Exhaust port 5) SG: Speed generator6) SS: Speed sensor

Fig. 6 Speed generator (right) fitted with a speed sensor

Fig. 7 Control and arithmetic unit

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4 Results of running test and long -term operation test on an actual freight train

A running test and a long-term on-site operation test have been implemented using a series Koki -106 freight train equipped with the newly developed parts (Fig. 9). The running test results obtained so far show that, even under test parameters representing the severe conditions unique to freight trains ( i.e. BCs fitted to the car body underframe, independent control of each bogie, a sprinkling of 3% soapy water and BC pressure equivalent to empty and fully-loaded cars), the WSP functions properly, suggesting that it is capable of preventing freight train wheel flats completely. In addition, the results of quarterly inspections of the freight train fitted with the WSP show a complete absence of wheel flats, and, in line with the durability bench test results , overhaul of individual components revealed no deterioration. All these results suggest that it should be possible to attain the initial target of developing a WSP for freight trains that has a maintenance-free period of eight years. Fig. 10 shows examples of the condition of the valve casing interior (top) and the non-woven dust filter interior (bottom) revealed at a breakdown inspection of the WSP after a long-term operation test.

Fig. 8 Example of general configuration of freight train brake system and WSP

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5 Conclusion Incorporating a new electricity storage concept , a new anti-skid valve structure and a new method of valve drive control, the newly developed WSP for freight trains has achieved the development targets of long life and low cost. The degree of perfection of the WSP has also reached the target level. The major results of the present development are summarized below.

1) For the anti-skid valve, a new structure allowing air to be shut off at the top and bottom of the valve body and an efficient method of valve control were developed. As a result, the power consumption of the valve was reduced to 2.2W per set, or 1/60 th that of conventional anti-skid valves. The valve was also fitted with two pairs of dust filters. These moves have enabled the development of an anti-skid valve with a maintenance-free period of eight years. For the storage battery, a new railway car EDLC featuring 24V, 5F (electrostatic capacity), a water-based electrolyte, a ceramic vessel and absence of a cell balancing circuit was developed. This has produced a battery unit with an eight-year maintenance-free period, long life and low cost , even under the extreme temperatures of the hottest and coldest seasons.The combination of the long-life, high-reliability EDLC and the energy-saving, easy-to-maintain anti-skid valve has made it possible to cut the WSP cost to half that of the conventional storage battery-type WSP and significantly reduce the maintenance burden. A range of tests on the newly developed WSP has shown quite satisfactory results . Thus, the requi red degree of perfection has been attained for the first practical WSP to be used on freight trains.Continuation of long -term WSP testing over a period of approximately two years is planned, with a view to its introduc tion in the next generation of contai ner freight cars.

6 Reference

Kiyoshi Kawaguchi, Development of a Low Cost Anti-Lock Brake System for Trailers and Freight Cars (in Japanese), J -Rail 2003 proceeding, pp101 -102, 2003.12

Fig. 10 Examples of conditi ons of valve casing (top) and filter (bottom) after test

Fig. 9 Installed condition of WSP and test car