AUSTRALIAN ELECTRONICALLY CONTROLLED PNEUMATIC BRAKE SYSTEM: OZ-ECP

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1 AUSTRALIAN ELECTRONICALLY CONTROLLED PNEUMATIC BRAKE SYSTEM: OZ-ECP Bruce Kuhnell (BE Hons, Dip ME, TTTC, MIE Aust, FI Diag E, MSAE), Mervyn Tan (MEngSc, BE Hons) SUMMARY Rail freight forwarding trends are for: heavier wagon loads; longer train constructs; and faster speeds. However, much of the Australian rail infrastructure and its rolling stock have been inherited from a 19th century legacy. Upcoming changes will create difficult problems for traditional braking systems, which highlight the need for more modern braking systems to cope with changing demands. A low cost Australian electronically controlled pneumatic (OZ-EPC) brake system has been developed for the freight railway industry in Australia and the rest of the world to meet these future needs. The concept involves retrofitting railcars with controller valves to achieve the same response and handling as currently available in electronically controlled pneumatic brakes. Retrofitted wagons will retain the existing pneumatic equipment for automatic backup and will be able to operate with either electronic brakes or revert to conventional pneumatic brakes. This paper will provide a description of the OZ-ECP braking system and the advantages this system has over other electronically controlled pneumatic (ECP) braking systems. 1. INTRODUCTION The ubiquitous train pneumatic brake (PB) based on 1872 and 1889 George Westinghouse inventions suffers several problems. There are commercial pressures that are enticing modern freight forwarders to increase the lengths of freight trains and unit or single commodity trains, to increase wagon loads and to increase speeds (reduce trip times). These trends to longer, heavier and faster freight trains are stretching the performance limits of conventional PB. The most important problem is the slow response time in brake application and release. Delays of up to 120 seconds are common for a 2km long train in the application or release of brakes between the lead locomotive and last railcar. Lack of simultaneous brake application of every wagon can cause excessive in-train forces, can result in coupling failure and can lead to breakaway and/or derailment.braking delays translate into longer trip times leading to revenue losses. Conventional PB systems also lack graduated brake release causing long trains to suffer from poor handling (Kuhnell, B. & Tan, M.). In an over braked train, drivers are unable to partially release the brakes without first performing a full service release followed by a service reapplication to achieve the correct braking pressure. Over braking often causes wheel skid which can result in flat wheels. Flat wheels can generate unwanted vibrations that lead to possible derailments. Furthermore, without partial brake release, train handling suffers when operating on terrain with variable grades. In situations where a train is moving downhill from a steeper to a flatter gradient, the train operator has to release the brakes fully and rely on the dynamic brake (in the locomotive) to provide all of the retardation force downhill. This can force low speed operation that in turn extends trip times. The driver must then wait for the brake pipe (the high pressure pipe that runs the length of the train) and wagon reservoirs to charge up before reapplying the pneumatic brakes, to supplement the dynamic brake if needed, again extending trip times. Many trains worldwide are equipped with conventional pneumatic brakes operating with a single brake pipe system and they lack the ability to continuously recharge the reservoirs. After a service release, the next brake application will not be possible before the brake pipe and the wagon reservoirs are fully recharged. On a long train, recharging the brake pipe and wagon reservoirs can take several minutes, leading to extended trip times. The delay in pumping the system back to full pressure is important in safety critical situations such as travelling downhill where the train has to rely on dynamic brakes while the reservoirs are being recharged. 2. NOTATION AAR CCD ECP EOT ROA UIC Association of American Railroads Car Control Device Electronically Controlled Pneumatic End of Train Railways of Australia International Union of Railways

2 3. AIR BRAKE OPERATION Australia has some 50,000 freight wagons typically fitted with Railways of Australia (ROA) brake systems. Approximately half of the wagons have relayed brake systems and half have non-relayed brake systems. A schematic diagram of a typical ROA relayed brake system is provided in between the auxiliary reservoir and brake pipe triggers the triple valve and allows auxiliary reservoir air to flow into the control volume (chamber B, Figure 1. It consists of a triple valve, reservoirs (dummy, auxiliary, supplementary and accelerated release), accelerated release valve, accelerated application valve, relay valve, VTA changeover valve and brake cylinders. AAR brakes as used in the North American freight wagons, of which there are approximately 1.5 million, are of different design to ROA and UIC brakes but embody similar basic design features and functionality. In steady state (brake release), the brake pipe and the auxiliary reservoir are charged at full system pressure (500 KPa for ROA brakes). During a service application, brake pipe pressure is vented through the lead locomotive and the pressure drop propagates along the brake pipe over the length of the train. When the pressure drop reaches the triple valve on each wagon, pressure imbalance Figure 2) of the relay valve (for relayed brake) or the brake cylinder (non-relayed brake). The amount of auxiliary reservoir air fed into the relay valve or brake cylinder is proportional to the drop in brake pipe pressure. That is, if the brake pipe pressure drops from 500 KPa to 450 KPa, the auxiliary reservoir will exhaust air into the relay valve or brake cylinder until the auxiliary reservoir pressure reaches 450 KPa i.e. the same pressure as in the brake pipe. In a relayed brake, charging the control volume (chamber B) pushes the diaphragm and the spindle upward, thus opening the supply valve to allow supplementary reservoir air to charge the brake cylinder. A portion of pressurised air from the supplementary reservoir is also fed into chamber C through a choke. As the pressures in chamber B and chamber C equalise, the spindle is forced downwards and closes the supply valve. Any leakage in the brake cylinder will be detected by the pressure imbalance between chamber B and chamber C. This will force the spindle upwards opening the supply valve and allow supplementary air to compensate for leakage. Conference On Railway Engineering Melbourne 30 th April 3 rd May 2006

3 Figure 1 Schematic diagram of relayed brake system during brake release. [7]

4 Figure 2 Schematic diagram of a relay valve in (a) release position and (b) applied position. [7] When a railcar is loaded, the changeover valve will redirect a portion of pressurised air feeding into the brake cylinder back into chamber A of the relay valve. In effect, it increases the upward force (the sum of chamber B and chamber A) exerted on the spindle. This keeps the supply valve open for a longer period of time until the pressure in chamber C can overcome the combined pressure of chamber A and chamber B. During a service brake release, compressed air is fed into the brake pipe to increase its pressure back to full pressure. The pressure difference between the auxiliary reservoir and the brake pipe triggers the triple valve into a release position and allows the recharge of the auxiliary reservoir. With the triple valve in the release position, the control volume (chamber B) air on relay valve (relayed brake) or brake cylinder (non-relayed brake) air is exhausted through a vent port on the triple valve. In a relayed brake, venting the control volume (chamber B) air decreases the upward pressure exerted by chamber A and chamber B, thus pushing the spindle downward. The brake cylinder is then allowed to vent through the exhaust port on the relay valve. The changeover valve comes in two forms, manual and automatic (shown in Figure 3). It is widely used on railcars in Australia to prevent over braking. A schematic diagram of a VTA changeover valve is shown in Figure 3. In loaded position, the plunger is pushed upward opening the shutter valve to allow brake cylinder air to feed back into the relay valve thus increasing the amount of air fed into the brake cylinder from the supplementary reservoir.

5 Figure 3 Schematic diagram of VTA changeover valve in (a) empty and (b) loaded position. [7] 4. ELECTRONICALLY CONTROLLED PNEUMATIC BRAKE Electronically Controlled Pneumatic Brakes (ECP) present the most significant change in railway braking technology since the invention of the Westinghouse PB. The basic concept involves installing a microprocessor based controller, a set of solenoid valves and pressure transducers on each wagon to control braking operation on the wagon. For electrical power the, so called, trainline consists of two 8-gauge electric cables, installed throughout the length of the train. The trainline is used to deliver power to the wagon and to charge batteries and to provide two-way data communication using trainline transceivers. Brake commands are broadcast over the trainline to simultaneously apply or release the brakes and to receive status information to monitor train performance. Typical AAR ECP brake systems; replace the service and sometimes the emergency portion with a Car Control Device (CCD) and a vent valve. The AAR ECP system uses an onboard battery to emulate conventional air brake operation during electrical power failure. The AAR ECP system supplies compressed air directly into the brake cylinder from the reservoir/s through full flow control valves. Although in all ROA, UIC and AAR systems the pneumatic signal for braking is replaced by an electrical signal, brake operation is still performed using conventional reservoirs and brake cylinders. ECP brake systems offer a number of advantages over conventional air brakes (Macfarlane, I., Carlson, F.G., Rownd). Most significant are the ability to apply or release the brake simultaneously at every wagon and graduated (partial) brake release capabilities. With simultaneous braking, coupled with graduated release capability, ECP offers greatly improved train handling over PB systems. Train stopping distances are often reduced by half. Strong intrain forces that can cause coupler failures and sometimes costly derailments are also reduced significantly. There is less wear and tear on wheel sets and couplers leading to lower maintenance cost on wagons. ECP equipped trains are able to operate at higher average speed and/or with heavier loads than conventional PB equipped trains and still be able to stop within safe limits (within signalling sectors), thus reducing trip times and consequentially increasing freight forwarding throughputs. ECP equipped trains can generate fuel savings. Drivers of ECP equipped trains do not need to apply wagon brakes as often as on a conventional pneumatic train because of the superior train handling. The drivers can also maintain good speed when going around curves and down grades by using the dynamic brake and modulating the ECP brake to control train speed with good precision. There are less stop-starts and faster restarts from a braked condition due to the reservoir being continuously charged. As ECP brakes do not vent the brake pipe air during braking, the load on the locomotive compressor is lower and this helps to conserve fuel. Results from test trains (McLaughlin, B., Rioux, Y., et. al., Carlson, F.G., Rownd, K.C., Chen, E.D., et. al.) showed that ECP brakes are able to reduce stopping distance by 50% - 70% and achieved on average 4% - 5% fuel saving due to improved train handling, reduced wagon braking and lower compressor duty cycles. Throughput also increased by 10% due to reduced trip times and increased train load. There were significantly less coupler failures, sticking brakes and undesirable emergency brake applications. The effects of ECP equipped trains on wear of brake blocks and wheel sets are unclear. QCM (Quebec Cartier Mining) found a 52% increase in brake block life and a 5% increase in wheel defects (McLaughlin, B., Rioux, Y., et. al.). But data from a joint study conducted by AAR, TSM (Technical Service & Marketing) and Conrail (Chen, E.D., et. al.) indicated a contradictory increase in brake shoe wear and a reduction in wheel defects. 5. SLOW ACCEPTANCE OF ECP Although ECP brakes have been available for over 15 years, implementation of ECP brake technology has been extremely slow. Of the estimated 1.5 million freight wagons in North America only approximately 5,000 are equipped with ECP brakes and less than that are operating in ECP mode. The slow implementation of ECP

6 technology can be attributed to several factors. The cost of refitting a fleet of wagons is an expensive undertaking with a typical per wagon price of $8,000 or more for currently available ECP systems. This requires a huge capital investment and extended sidelining of whole trains. Unless the wagon is refitted with an overlay or emulation system, sidelining whole trains can cause significant disruption to services. The technology is also yet to prove its reliability. Although ECP technology is claimed to benefit the railroads through fuel savings and increases in freight forwarded, cost savings in wheel and brake block maintenance are less clear and currently ECP offers little cost benefit to the car owners. With uncertain cost savings and unproven reliability, private wagon owners have been reluctant to bear the high cost and high risk of implementing the technology. Ironically, even though the development of ECP was initiated by AAR-member railroads, most of the interest in the technology is from operators outside North America (Kuhnell, B. & Tan, M.). South African railroad operator, Spoornet has recently released a tender to convert 6,735 wagons and 230 locomotives to ECP brakes. China Ministry of Railways is currently considering a proposal to convert 8,000 wagons and 200 locomotives to ECP brakes. 6. PROOF OF OZ-ECP DESIGN CONCEPT Because of the problems associated with currently available ECP brake systems Monash University began work on designing OZ-ECP in 2003 as part of a Rail Cooperative Research Centre project. The main objective has been to design a low cost system with the retention of the PB in case of electrical failure. After receiving feedback from industry partners, mainly Queensland Rail (QR), a system with electronic control of the triple and relay valves, with automatic emergency reversion to PB mode was adopted as it allows the railway operators to upgrade their wagon fleet stage by stage to full ECP brakes without causing major disruption to revenue services. The major distinctions between the latest OZ-ECP brake system and current overlay ECP systems are that: OZ-ECP uses non full flow valves; utilises a relay valve for brake control and does not have battery powered emulation but reverts to conventional PB when there is no power. The early design of OZ-ECP used a bread board electronic wagon controller and retained the use of the onboard air brake equipment. Two sets of control valves and pressure transducers were designed to be retrofitted to the existing air brake as illustrated in Figure 4. Solenoid valves installed between the brake pipe and the triple valve controlled the brake application by utilising the triple valve and reservoirs. Solenoid valves installed between the relay valve and the brake cylinder controlled the brake release. Pressure transducers were installed with each set of control valves to provide feedback control.

7 A test to prove the design concept was conducted at the QR Callemondah wagon depot in Original OZ-ECP equipment was fitted onto a stationary tandem coal wagon. The test successfully performed several brake operations followed by graduated releases and reapplication. Further laboratory tests were conducted on a twobrake typical relayed brake system set up in a Monash laboratory. The brakes in the laboratory tests took longer to apply and release compared to the response of conventional PB s after triple valve actuation (not related to brake pipe pressure drop propagation times). This was due to the use of undersized valves. AAR calls for a maximum wagon electrical power consumption of 20 Watts (10 Watts per battery charger and 10 Watts per CCD or EOT device). The valves selected for OZ- ECP were predicated on this power restriction and the poor performance initiated development of a smarter system to avoid full flow solenoid valves. 7. RELAYED ECP BRAKE The original OZ-ECP design went through several refinement processes with again advice from QR. The current OZ-ECP uses only a single set of mini control valves to actuate brake application and release as shown in Figure 5. With small variations and the addition of relay valves to non-relayed brake systems OZ-ECP can be used in most of the worldwide fleet of freight of ROA, AAR and UIC equipped wagons. There are no bulky onboard Figure 4 An illustration of original OZ-ECP design. batteries and power management system; however, it uses a small battery that can be easily replaced for brake initialization and train sequencing. The design is small, compact and lightweight compared to a stand alone ECP system. Onboard power consumption is small because mini control valves are used and there is no need to recharge a large onboard battery. It is also designed to be significantly lower in cost and to require less maintenance due to its simple design. A major advantage of the OZ-ECP is availability of the conventional pneumatic brake as a backup in the event of electrical power failure. Although a stand alone ECP brake is able to run in emulation mode on battery power at low train speed for at least 4 hours, it lacks proven reliability and performance compared with a conventional air brake. Monash University, with responsibility for the mechanical and pneumatic components of the brake system has joined up with Central Queensland University who have developed the OZ-ECP on-wagon controller. At the time of writing this paper, field trials are planned for Static trials are scheduled for February 2006 and they will be followed by field trials on a rolling train. OZ- ECP also provides a ready platform to integrate the Central Queensland University Health Card, an in-train force and derailment detection system, for added functionality. Figure 5 An illustration of current OZ-ECP design.

8 8. STATIC FIELD TEST A static test was conducted in Rockhampton in late March and early April. The test used 20 stationary VAO grain wagons parked on a crossing loop on the Yeppoon line in North Rockhampton. There was no head end loco and the brake pipe was pressurised through an external compressor. Each wagon was equipped with an OZ-ECP module which consists of control valves, pressure transducers and an electronic controller. Each OZ-ECP module had two cables, one connecting the network power line and another connected to National Instruments Compact RIO data acquisition hardware. Train brake commands were sent by the central computer through the network power line to each OZ-ECP module using Echelon LonWorks Communication protocol. Pressure readings from the brake cylinder, brake pipe and relay pilot on each wagons were sent back to the central computer via the NI Compact RIO through an Ethernet cable. The sampling rate for the data was 250Hz and the pressure tolerance for brake control was set at ±3kPa. Figure 6 shows a plot of pressure time history at front end, mid section and rear end of the rack for a full service application then followed by full release. The pressures build up (to full pressure) time is about 5 seconds for full application and 9 seconds for full release. There is a noticeable drop in brake pipe pressure approximately 60kPa due to the brake pipe replenishing the supply reservoir. Pressure build up and discharge time is nearly simultaneous at all positions along the train, although at wagon no. 19 the brake cylinder pressure build up time was slightly behind - possibly due to a small leakage at the relay valve. Figure 7 shows a plot of the time histories of pressure at front end, mid section and rear end of the train for an initial 10% brake application and increase to 20% application then to full service application followed by full release. Pressure build up and discharge time is nearly simultaneous at all positions along the train. There were noticeable drops in brake pipe pressure at 10% and 20% brake application but the pressure drop was most significant at full application (approximately 60kPa drop). There were minor pressure fluctuations at the brake cylinder on wagon no.19 which suggest possible leakage at the relay valve. Wagon No. 1, 11, Pressure (KPa) Time (Sec) BC - Wagon No. 1 BP - Wagon No. 1 BC - Wagon No. 11 BP - Wagon No. 11 BC - Wagon No. 19 BP - Wagon No. 19 Figure 6 Full service and release.

9 Wagon No. 1, 11, Pressure (KPa) Time (Sec) BC - Wagon No. 1 BP - Wagon No. 1 BC - Wagon No. 11 BP - Wagon No. 11 BC - Wagon No. 19 BP - Wagon No. 19 Figure 7 Minimum application, full service and release. Figure 8 shows a plot of the time histories of pressure at front end, mid section and rear end of the train for random brake applications. Pressure build up and discharge times are nearly simultaneous throughout the braking sequences at all position along the train except in the initial application on wagon no.19. On wagon no.19, brake cylinder pressure did not build up to the same pressure as the wagons at the front end and mid section. The cause of this lag was due to Wagon No. 1, 11, 19 leakage at the relay valve when pilot pressure was initially supplied to the relay valve to actuate the brake. As pressure in the relay pilot builds up to a sufficient level, the leakage became insignificant, hence in the later braking sequences pressure build up in the brake cylinder along the train were nearly simultaneous. Similarly, there was a drop in brake pipe pressure during the braking sequences due to the brake pipe replenishing the supply reservoir Pressure (KPa) Time (Sec) BC - Wagon No. 1 BP - Wagon No. 1 BC - Wagon No. 11 BP - Wagon No. 11 BC - Wagon No. 19 BP - Wagon No. 19 Figure 8 Random brake application.

10 9. CONCLUSION The automatic air brakes invented by George Westinghouse have served the railway industry well for more than a century as a safe, fail-safe and reliable brake system. However, on long haul heavy trains, the conventional air brake system is experiencing significant difficulties. Electronically controlled pneumatic brake systems appear to offer a solution that can overcome the limitations of conventional air brakes. Although electronically controlled pneumatic brakes have been available for over 15 years, the take up rate on ECP technology has been slow. The cost of upgrading to electronically controlled pneumatic brakes and the logistical difficulties of implementing the technology coupled with doubts on the reliability of electronically controlled pneumatic technology has deterred railway operators from adopting ECP brakes. Nonetheless, it is thought that electronically controlled pneumatic brakes will inevitably, if reluctantly, be adopted due to market forces in the not too distant future. OZ-ECP can offer the railway industry a low cost, lightweight and compact design that can serve as a logistically convenient alternative to assist the railway industry in the transition to electronically controlled braking. Following expected successful trials early 2006 OZ-ECP could be commercially available in REFERENCES 1. Carlson, F.G., Rownd, K.C., Development and Implementation of Advanced Brakes and Improved Suspension System for the North American Network. 2. Chen, E.D., Tse, Y.H., Myers, L.F., Economics Considerations of Operating a Train with Electronically Controlled Pneumatic Brakes. In Proceedings of the 1998 ASME- IEEE Joint Railroad Conference, 15 th 16 th April 1998, pp Kuhnell, B., Tan, M., Freight Train Braking Past, Present and Future, Conference on Railway Engineering, Melbourne, 30 th April 3 rd May Macfarlane, I., Railway Safety Brakes, Crows Nest, NSW, Engineers Australia Pty Limited, McLaughlin, B., EP-60 ECP: Train Operation Data at Quebec Cartier Mining Company, The Air Brake Association Annual Technical Conference, Chicago, Illinois. 6. Rioux, Y., Truglio, J., McLaughlin, B., ECP Brake s First Stand Alone Test Train, The Air Brake Association Annual Technical Conference, Chicago, Illinois. 7. Brake book of Instructions V/Line and The Met, Volume 1.