Hydraulic fan drives are widely used with diesel engines to reduce fuel consumption, emissions, and noise. Despite the additional cost to OEMs, the high return on investment on hydraulic fan drives has been a major reason for their continuing growth.
However, hydraulic fans drives are also being used in train locomotives — specifically, PMC Servi AS, of Norway, which won a contract to upgrade trains used on Norwegian State Railways. Design engineers decided to retain the existing hydraulic cooling and take advantage of several major benefits, including fully independent fan speed control (fan speed can exceed engine speed) and significant fuel savings due to more efficient use of available engine power.
Assessing the existing system
Hydraulically driven cooling has been used on the German built Duewag NSB Type 92 rolling stock since the mid 1980s, due to the limited space available around the engines, where the radiators would normally have been placed.
The original hydromechanical system used a fixed displacement pump, driven directly from the engine that powers a fixed displacement motor and uses a thermostatically controlled unloading valve to regulate the fan speed. The system was sized to give maximum fan speed at 2100 engine rpm, which was adequate on cool days on level track. However, when ambient temperatures rose, or the train encountered an uphill grade, the engine speed quickly dropped to less than 2100 rpm, directly limiting the fan speed and corresponding air flow.
Compounding the loss of air flow with the extra load demand caused a rise in temperature, which led to the engine’s self-protection system to reduce the output power, further limiting the wheel drive and cooling systems abilities. This heat-driven cascading effect eventually caused the train operator to stop the train on the gradient to allow the engines to cool. Not surprisingly, the delays affected passenger satisfaction, not to mention the additional maintenance required for heat stressed locomotive systems from maintenance crews.
Taking on the project
PMC Servi AS was given a directive as part of the project to ensure that 100% cooling capacity was available regardless of engine speed or ambient temperature. Its technical project team, led by David Thomas and consisting of Kjell Prytz and Morten Freland, soon realized that the only way this could be done was to redesign the system. Part of the redesign was to introduce electronics to give accurate independent fan speed control and also take advantage of the other benefits that come with the system. The result reduces operating costs and increases reliability.
After searching for the right hydraulic components and corresponding electrohydraulic fan system controller, the project team contacted High Country Tek (HCT) Inc., Nevada City, Calif., which has a wide range of standard hydraulic fan system controllers that meet all the globally required legal, electrical, mechanical, and environmental specifications as well as comply fully to the latest CE and SAE J1455 operational standards.
Once the project was explained, HCT recommended using its popular HFS-J controller, which can use discrete temperature sensors and/or interface seamlessly with engine SAE J1939 communications if required. It controls the fan speed based on an optimized configuration profile that the PMC Servi team could develop using the prewritten HCT PC user interface.
The train is fitted with dual Daimler Benz V12 engines that produce a combined 970 hp. Each engine has a separate cooling system to allow for single engine running if required. Each engine also direct-drives an axial-piston pump that is sized to give maximum required flow at only about 800 rpm.
Because of their high efficiency, bent-axis piston motors were specified to drive the fans. HAWE PSV size 3 proportional valves control the direction and speed of each of the two fan motors, regardless of the load on them.
Initial results have been positive, with testing carried out on one of the warmest days on Norwegian record last summer. The train easily managed to climb one of the longest ascents at full power with the engine temperature not exceeding its normal working range. The test train also experienced one of the coldest winters in Norway, with temperatures in some locations dropping to -40°C. The system continued to perform flawlessly and with full reliability through both temperature extremes.
During the testing, an unforeseen benefit was realized when it became obvious that the low-slung location of the train’s radiators made them susceptible to being clogged with pollen in the summer and leaves in the fall. In the past, downtime had to be scheduled to inspect the radiators and clean the debris from them. However, HCT’s HFS-J controller module offers a reverse-purge sequence as a standard feature.
The controller reverses the direction of the fan drive motors and maximizes their speed to quickly and effectively blow debris out of the radiators. As a result, the radiators no longer need to be cleaned manually. The operator simply needs to ensure that the purge cycle is not deployed when the train is at a station. Otherwise, passengers could be subject to dirt and debris blown during the cycle.
PMC Servi AS expects to convert the entire Norwegian State Railways fleet of these trains to the revised cooling system, meaning more up time for the customer, happy passengers through the year, whatever the weather, and reduced loss of earnings and maintenance costs.
This information was provided by Gary Gotting, of High Country Tek. For details on electrohydraulic fan drive controllers from High Country Tek, call (530) 265 3236, visit www.highcountrytek.com or e-mail info@HCTControls.