Engineering expertise from SKF is helping the UK’s largest bus and coach manufacturer build vehicles for challenging operating environments, in terms of extreme temperatures, above all. SKF Explorer bearings reduce friction by around 50 percent, leading to lower levels of heat and noise.
by Elena Magistretti
Alexander Dennis Limited (ADL) is the UK’s leading bus and coach manufacturer, with facilities in the UK, continental Asia and North America. ADL produces a wide range of innovative and fuel-efficient, low-floor single- and double-deck buses, plus a full portfolio of coaches and mini vehicles.
When ADL received an order for 250 buses from GO Transit in Toronto, Canada, its engineers faced a challenge: in order to keep passengers comfortable year-round in a city where temperatures can vary from -25 ºC in the winter and more than 35 ºC during summer hot spells, the customer specified an uprated heating and air conditioning system. ADL had designed a suitable system. However, to transfer power from the engine to the compressors and alternators, a shaft and intermediate bearings were needed. The company’s engine supplier had quoted a lead time of 18 months to supply an appropriate unit. In need of a quicker solution, ADL called on SKF, which dispatched a team of application engineers to the bus manufacturer’s headquarters to discuss possible solutions. Taking into account the loads, speeds, operating conditions and required life expectancy, the SKF team applied its proprietary engineering tools, including the Bearing Beacon 3D modelling system, to create a suitable system design and select appropriate components. The full design was then modelled using industry-leading Creo CAD software and handed to ADL for approval.
Deep groove ball bearings to satisfy the application requirements
To meet the client’s need for quiet, efficient operation and a long service life, SKF based the design on its SKF Explorer deep groove ball bearings. These bearings feature an innovative design of advanced, high-purity steel, with a homogenized structure and superior finish on all contact faces. This is combined with an optimized design of the ball and cage assembly. As a result, SKF Explorer bearings reduce friction by around 50 percent, leading to lower levels of heat and noise to give a basic rating life that is 15 percent better than standard designs.
Seals and lubrification are optimized for heavy-duty conditions
Each bearing is protected from contaminants by SKF’s V-ring seals. These are easy to install, with a simple interference fit on the shaft, sealing axially against the bearing outer ring side face. The seals provide high levels of abrasion resistance, plus excellent compatibility with a range of oils and chemicals. Bearings are lubricated with SKF heavy-load, extreme-pressure, wide-temperature-range bearing grease LGWA 2. This premium-quality mineral oil-based, lithium complex grease is specifically designed for industrial and automotive applications where loads or temperatures may exceed the capabilities of general-purpose greases. LWGA 2 grease can handle temperatures of up to 220 ºC for short periods; in addition, it offers excellent water and corrosion resistance with effective lubrication in wet conditions and has superior performance at heavy loads and low speeds.
ADL asked SKF to assemble and supply complete bearing units for its Canadian contract, including pulleys and other secondary components. Making use of its UK workshop, SKF was able to assemble all the units for the original order, beating a tight delivery deadline by two weeks.
A tricky engineering challenge was thus won in a short time. The company is now working with SKF to develop a 25 percent lighter version for future vehicles, helping us to achieve challenging emissions reduction objectives.