Problem
The topic of bus trailers is becoming increasingly important both economically and ecologically. This is because the possibility of disconnecting it from the towing vehicle during off-peak periods reduces wear and tear and fuel consumption, important arguments in times of rising energy prices and fine dust regulations. Here, extremely high demands are placed on the safety of the passenger trailers. In the course of the implementation of competition-oriented EU regulations and the energy law reform as well as the increasing cost pressure, all transport companies are required to review their profitability and efficiency in all areas and to base their investment decisions on these framework conditions. At present, exemptions still need to be obtained for the registration of bus trailers. For approval reasons, the trailer is based on a purely mechanical steering system, for which durable and high-quality bearings were sought that would meet the requirements of everyday operation. Safety and comfort, easy handling, problem-free maintenance: these were the most important cornerstones in the development of the trailer, which has four-wheel steering.
Solution
Right from the start, open and closed drylin R linear plain bearings from igus GmbH in Cologne have been used in the bus trailers. The product range is based on highly wear-resistant polymers specially developed for linear technology. The dimensions are compatible with standard ball bearings. Their special geometry guarantees robustness even in extreme environmental conditions. The linear guides with polymer sliding elements for the steering system help to keep the trailer safely on track at all times without grease and oil and in the event of heavy dirt. They are virtually resistant to dirt. They have a very high level of safety even with the coarsest dirt. The omission of lubrication and the special design of the bearing surface using individual slide pads connected by thin film sections, provides special benefits here. Dirt, even when it becomes wet on the shaft, is wiped away by the individual glide pads and is moved into the open areas. The running sections of the bearing then slide on the shaft that has been cleared of all contaminants. A total of fourteen drylin R linear plain bearings are installed in the steering system of each trailer. They transfer the steering movement from the front to the rear wheels. Extra guide systems have been selected which can easily absorb misalignments due to a spherical shape in the middle of the housing in order to take edge loads from the push rod. In addition to their design advantages, linear plain bearings are particularly convincing due to their material features. They are corrosion-free, wear-resistant, have low friction coefficients, quiet operation, are lightweight and cost-effective. An own development would not have paid off in any case. Some time ago the first registered trailer came to Augsburg for a general overhaul. The bearing points in particular were analysed here; no apparent defects were found. Even rust film did not attack the bearings.
The redundant push rod system developed and patented by the company plays an important role in the overall solution. It transmits the steering movements of the front to the rear axis purely mechanically. It consists of several rods and two slewing ring plates at the ends. Depending on the application profile and customer requirements, different steering angles of the rear axis can be specified. By using the trailers, the environment and budget are protected. Calculations show that fleet operation can reduce fuel costs by more than 30% per year. This leads to savings in the clear six-digit range. But the calculations go even further. Since the linear plain bearings are lubrication-free, there is no need for an expensive central lubrication system, which is also very harmful to the environment.
