GB2548317A - System for increasing wheel rail friction in low adhesion conditions - Google Patents

Abstract

A train mounted system for the controlled addition of water to one or more of the wheel rail contact points 3 of a train in conditions of low wheel rail friction characterised in that the addition of water increases the wheel rail traction coefficient to at least 0.1 at speeds below 50kph. The water delivery rate may be constant or may vary, possibly in relation to train speed. The temperature and/or the pH of the water added to the contact point 3 may be controlled. The water added to the contact point 3 may be heated. The system may comprise a water store 7, pump 6, controller and delivery nozzles 5. The system may be activated by a control signal when a low adhesion event is detected or when the train is braked. The water used may be from on-train water resources, waste water, atmospheric water vapour and/or rain water. There may be a control valve 9 and accumulator 10.

Description

Field

The present invention relates to a system and method of improving the traction and braking of a vehicle. In particular, the present invention relates to a friction modification system for trains travelling along rails which are coated with contaminants (e.g. damp compressed fallen leaves) and to a method to improve the friction between a wheel of a train and the railhead when low adhesion conditions are encountered.

Background to the Invention

Adhesion (or traction) between the wheel of a train and the railhead is required to propel the train forward and to enable the train to stop. The traction between the locomotive wheels and the rails is required to start or accelerate the train, to pull loads up gradients, or simply to maintain the required speed.

Rails that are located adjacent to trees and woodland may lose adhesion (or friction) and become slippery due to the fallen leaves. In particular, leaves on tracks may be compacted by passing trains and form a smooth coating.

This coating is hard and reduces traction of the wheels with the rails and significantly reduces the effectiveness of the brakes on the train especially when wetted. The coating of compacted leaves thereby presents major problems for train operating companies and also presents significant safety issues. In particular, trains may not be able to stop in the required stopping distance and may overshoot platforms or the stopping positions for signals. Signals which when passed indicate danger are a significant hazard, and the inability to stop in a reasonable distance increase the chances of a collision. In addition, the acceleration of trains is affected and hindered, since the wheels tend to slip or spin relative to the tracks. Rails may also be contaminated by other matter as well as vegetative matter for example, water, rust, oil, solid particles etc. One cause of low adhesion between locomotive wheels and rails is due to the condition of the rails and, in particular, due to railhead contamination. Such contamination, and reduced adhesion, can result from water (for example, rain, dew, snow, ice or general moisture due to humidity), compacted leaves, rust, solid particles (for example, coal dust), fuel, oil, hydraulic fluid and other chemicals being present on the rails. These conditions can be worsened in certain weather conditions, for example, certain temperatures, humidity and atmospheric pressures.

Another problem connected with stopping trains, in particular when rails are slippery, is the damage caused to the surface of the wheels. Such damage may include the creation of flat areas.

Various methods and systems have been used or proposed for cleaning rails and increasing the adhesion between the railhead and a wheel. For example, the film or coating on the rail can be simply scraped off the rail. Other methods and systems include preventive methods (for example, leaf control), cleaning methods (for example, water jetting, scrubbing, etc.) and/or the use of friction improvers (for example, sand). The present invention relates to a system and method intended to increase wheel to rail friction when conditions of low adhesion are encountered.

For many years it has been known that the presence of water on the rails can have a major effect on train braking. The best adhesion conditions occur with a fully dry rail. While reducing adhesion, a wet rail still provides adequate levels of friction for consistent braking, evidenced by the lack of low adhesion events on very rainy days. A number of rail industry research reports show that train braking performance is greatly reduced when a critical amount of water is present, with contaminants, on the rail. One study [1] showed that as a wetted and contaminated rail dries. initially the friction at the wheel-rail contact drops to a very low level. This is the condition where low adhesion problems typically occur. With further drying, the friction level increases again to a safe level. The conclusion from the research is that both dry and well-wetted rails give good levels of friction, whereas damp contaminated rails lead to low friction. There are therefore two potential routes to recover from a low adhesion situation - drying or wetting the contact point. While drying will ultimately deliver the highest friction levels it has two potential drawbacks. Firstly, it requires a complex additional system to remove water fast enough to give a significant change in friction. Secondly, and more importantly, because the starting condition of the contact point is unknown, drying the rail may well make the situation worse. Our solution avoids these issues by wetting the contact point to return adhesion to the safe level of a wet rail condition. By delivering a sufficient quantity of water we ensure that low adhesion is avoided regardless of the starting condition of the contact point.

Traction coefficient (the term commonly used in the rail industry to quantify friction) determines the maximum possible braking and acceleration rates for a train. For example, a traction coefficient of 0.1 would support a braking rate of 10%g. The normal full service brake rate in the UK is 9%g, which equates to an adhesion demand (or traction coefficient) of approximately 0.09. A fully wetted rail gives a traction coefficient of more than 0.1 at speeds up to SOkph (traction coefficient reduces with speed) [2]. The proposed ERTMS (European Railway Traffic Management System) low adhesion brake rate is 6%g. An objective of our solution is to deliver a traction coefficient of more than 0.1 at speeds up to SOkph in low adhesion conditions.

Water delivery systems are already used in the rail industry to clean contaminants from the rail surface. Currently, water Jetting systems are fitted to special purpose trains which are deployed when the likelihood of rail contamination from fallen leaves is high. In these systems, water is delivered continuously to the rail at extremely high pressures (15,000 psi) and relatively large flow rates to dislodge materials stuck to the surface of the rail. Due to the amount of water required, large water storage tanks are needed on board dedicated trains. WO 00/44992 describes one such system. The large amount of on-train water storage and high cost prevents the use of this solution on normal service trains.

Other trackside water delivery systems have been developed to wet certain sections of track which are known to present low adhesion risk [3]. There a number of issues with this solution including the need to establish and maintain a trackside water delivery infrastructure when the areas of low adhesion risk may not always be in the same place.

The delivery of large quantities of water to the wheel rail interface (either from trackside or on-train spraying) may also give rise to other issues on the rail network such as accelerated degradation of the rails through stress corrosion and erosion of the rail ballast.

As a result of these issues, a key aim of our invention is to minimise the quantity of water needed to deliver the necessary traction coefficient improvement.

Our test results confirm that when water is added to the contact point it can deliver rapid recovery from a low adhesion condition. Moreover, we have been able to demonstrate that the increase in traction coefficient delivered can last long enough to enable an entire train to pass over a previously affected low adhesion track section. Our research also shows that the amount of water needed to deliver significant traction coefficient improvements is far lower than previously assumed.

Previous rail industry research [4, 5] has highlighted that the temperature of water at the wheel-rail interface also affects friction. Higher water temperatures have been found to increase adhesion.

There is also evidence that spraying rails with a high pH solution (alkaline) can reduce leaf adhesion and increase skid resistance of leaf coated rail [6].

Our tests showed that changes in the delivered water temperature and pH value can significantly influence the traction coefficient between wheel and rail but more importantly highlighted optimal settings for both factors to further minimise the amount of water required to achieve a given adhesion level.

Brief summary of the invention

Our proposed concept will increase braking performance by using a train-borne system to supply water in a controlled way to the wheel-rail contact point or points when low adhesion is detected or train braking is initiated. The purpose of adding water in this way is to ensure reliable braking rates that are largely independent of environmental factors and contamination at the wheel/rail interface. The train-borne system we are proposing consists in general of a water reservoir, pump, heater and nozzle arrangement operated either by a dedicated control system or existing train-based control systems - see figure 1.

Test method

The apparatus used to test water addition was a TE54 Mini-Traction Machine made by Phoenix Tribology Limited of Kingsclere, Hampshire, England. Twin disc testing is an established test method for simulating the wheel/rail contact in a small-scale laboratory environment. Factors such as load, slip and speed can be closely controlled and adhesion levels are monitored throughout testing. The test equipment is shown in figure 2.

The MTM can be used in two configurations, either Ball on Disc or Disc on Disc configuration. For the purpose of all of these tests. Disc on Disc was the configuration used, thus giving a line contact.

The program to control each test was prewritten on the software that accompanies the MTM and each test was run at ambient room temperature. The initial pre experimental conditions were decided after consultation with the manufacturer and calculating contact pressures that were similar to testing previously done on another rig. It was decided that for all tests a load of 200N was to be used (333MPa). Different speeds were initially trialled, and it was found that an upper disc speed of 612rpm and a lower disc speed of 300rpm was fast enough to give good results, but slow enough to not consume the surface contaminant before any useful data could be obtained. This configuration gave a slip of 3%.

In order to make the leaf contaminant used during the testing, the following process was applied after the collection of leaves: • Leaves were weighed • Leaves were then torn up, and broken down using an electric hand blender until they passed through a sieve • 10% water and 0.5% thickening agent was added relative to leaf weight • Leaf mulch was then mixed using a pestle and mortar, and then further ground down with the hand blender until a thick runny paste was formed of a consistency that would stick to the discs well

After pre experimentation using the leaf contaminant, leaf mulch was applied to the bottom disc.

The container holding the leaf mulch was weighed before and after with approximately 0.5g applied to the disc. Temperature of the water was measured using a thermometer and for heated tests, the water was heated using a kettle and then applied when the water cooled to the required temperature for each test within +/- 2°. For tests requiring a different pH level (where water was assumed to be pH7) the water was mixed with plain vinegar to achieve pH4 and milk of magnesia to achieve pHlO.

The following four factors were studied for their effect on traction coefficient: • Water addition amount at 0.4ml, 0.8ml and 1.2ml

• Water temperature at 20°C, 45°C and 70°C • Water pH level at 4, 7 and 10 • Rotational speed of the discs at 200rpm, 300pm and 400rpm (larger disc speed)

Test results

Water addition was found to increase traction coefficient consistently across all trials by more than 0.05. Figure 3 shows the averaged traction coefficient against time (in seconds). The traction coefficient rose quickly with a rise time (10% to 90%) of around 5 seconds. It is also notable that an improved level of friction was maintained even 120 seconds after water was added to the contact point.

From the analysis of the results, the most significant factors were found to be water flow (friction increases with flow) and pH (neutral is best). Figure 4 shows the relative effect of each factor on peak traction coefficient.

The results also indicated that increased temperature can compensate, to some extent, for lower water flow rates. Figure 5 shows the effect of the interaction between temperature and water flow rate on resultant peak traction coefficient.

Finally the results revealed an interaction between speed and flow rate. Figure 6 shows this interaction. This graph also suggests that there may be an optimum water delivery rate for a certain rolling speed (note the peak traction coefficient value at 0.8ml flow at 200 rpm).

Given the diameter of the smaller roller was 50mm and the larger roller was 100mm, the water used per metre of contact point ranged from 1.2ml to 7.2ml. Subsequent testing has shown lower levels of water addition down to 0.25ml per metre can still give a significant increase in traction coefficient.

Detailed description of invention

Figure 7 shows the first inventive configuration in which a contact point (3) between a wheel (1) and contaminated rail (2) has water added (4) by a water delivery system consisting of a storage tank (7), pump (6), heater (8) and delivery nozzle (5). When an activation signal is received from the train, the pump (6) and heater (8) are switched on and heated water is delivered to the contact point (3) until the activation signal is removed.

Figure 8 shows the second inventive configuration in which a contact point (3) between a wheel (1) and contaminated rail (2) has water added (4) by a water delivery system consisting of a storage tank (7), pump (6), heater (8) and delivery nozzle (5). In addition to the first configuration, this embodiment includes a control valve (9) and pressure accumulator (10). The pump (6) is used to prime the accumulator (10) with water, retained under pressure by valve (9). When an activation signal is received from the train, the valve (9) releases the pressurised water from the accumulator (10) providing an increased volume of water to the contact point (3). The pump (6) and heater (8) are switched on and heated water continues to be delivered to the contact point (3) until the activation signal is removed.

In a train-borne situation with two rails, there will be a requirement for at least two delivery nozzles (5), however, they could share common water delivery system components as described in the two previous embodiments. A third inventive configuration of water delivery system would make use of existing resources already present on the train. For example, the water storage (7) could be replaced by on-board water storage (e.g. fresh water or waste water tanks), the action of the pump (6) could be provided by on-board air pressure (e.g. from the braking system during activation) and the heating effect of the heater (8) could be provided by waste heat (e.g. from hot exhaust gasses or cooling air). A final inventive configuration of water delivery system (figure 9) replenishes the water storage tank (7) by using Peltier device (11) cooled water collection platforms (9) to capture atmospheric water vapour (10) which is then gravity fed into the water storage tank (7).

The above embodiments have been described by way of example only. Many other embodiments falling within the scope of the accompanying claims will be apparent to the skilled reader.

References 1. A basic study of wheel/rail adhesion laboratory studies of the effects of Water -T.M. Beagley & C Pritchard, Tribology Section, Railway Technical Centre, 1973 2. RSSB Spark database reference T080, Low adhesion risk to ERTMS, 2003 3. The effectiveness of trackside water sprays on leaf affected track at Bearsted Bank 1979, R. K. Taylor, Technical Memorandum TRIB 43, British Railways Board R&D Division. 4. Influential Factors on Adhesion between Wheel and Rail under Wet Conditions, H. Chen, M. Ishida, T. Nakahara Railway Technical Research Institute, Tokyo, Japan; Tokyo Institute of Technology, Tokyo, Japan, 2011 5. H. Chen, T. Ban, M. Ishida, T. Nakahara. "Adhesion between rail/wheel underwater lubricated contact". Wear 253, pp.75-81 (2002). 6. Full Scale Testing to Investigate the Effect of Rail Head Treatments of Differing pH on Railway Rail Leaf Films, P. Hyde, D. Fletcher, A. Kapoor, S. Richardson, NewRail, Newcastle University, Newcastle, U.K.; DeltaRail Group Ltd., Derby, U.K. World Congress on Railway Research (WCRR) 2008, Seoul, Korea.

Claims (15)

What we claim is:

1. A train-mounted system for the controlled addition of water to one or more of the wheel rail contact points of a railway train in conditions of low wheel-rail friction characterised in that the addition of water increases the wheel-rail traction coefficient to at least 0.1 at speeds below 50kph

2. A system according to claim 1 in which the water delivery rate is between 0.25mls/metre of rail and 7.2mls/metre of rail

3. A system according to claims 1 and 2 in which the water delivery rate is constant during the delivery cycle

4. A system according to claims 1 and 2 in which the water delivery rate varies during the delivery cycle

5. A system according to claims 1 and 2 in which the water delivery rate varies in relation to train speed

6. A system according to claim 1 in which the temperature of the water added to the wheel rail contact point is controlled

7. A system according to claim 6 in which the water added to the wheel rail contact point is heated

8. A system according to claim 1 in which the pH level of the water added to the wheel rail contact point is controlled

9. A system according to claim 1 comprising a water store, pump, controller and one or more delivery nozzles

10. A system according to claim 1 which is activated by a control signal when a low adhesion event is detected

11. A system according to claim 1 which is activated by a control signal when the train is braked

12. A system according to claim 1 which makes use of available on-train water resources to replenish its on-board water store

13. A system according to claim 12 which uses waste water from train systems to replenish its on-board water store

14. A system according to claim 12 which collects atmospheric water vapour to replenish its onboard water store

15. A system according to claim 12 which collects rain water to replenish its on-board water store