The UK is one of the leading countries in the world when it comes to the introduction of ultra-low emission diesel-electric hybrid and zero emission electric buses. According to Transport for London (TfL), there are 3,773 diesel-electric hybrid buses and 316 electric buses operating in the capital, out of a total fleet of 9,102 vehicles. Numerous cities across the UK are closely following London’s example with diesel-electric hybrid buses, such as the market-leading Volvo B5LH double-decker, becoming the most common form of low emission PSV powertrain technology.
Hybrid and electric buses
Hybrid and electric buses are equipped with a range of new technologies, which include a new approach to thermal management for batteries on fully electric vehicles and the diesel engines on hybrids, with manufacturers such as ADL, Volvo and Wrightbus introducing electric water pumps to undertake this critical task.
Whereas conventional diesel-powered buses employ the more commonly known engine-driven water pumps that are mounted directly to the engine and driven via the timing gears or belt and rely on the engine speed to govern the flow rate of the water pump, hybrid and electric buses use new technology in the form of electric water pumps to provide thermal management.
High performance electric water pumps use an intelligent Controller Area Network (CAN bus) enabled Electronic Control Unit (ECU) to manage the pump’s speed, unlike conventional water pumps that are engine speed dependent. This provides the unique ability to precisely control the power consumption and performance of the pump, making electric water pumps considerably more efficient than engine-mounted systems.
Electric water pumps are used to boost the circulation of the existing cooling systems, helping to optimise diesel engine heat-up time on hybrid buses, as well as keeping the engine running at a more consistent temperature. They are also used in separate thermal management systems for the battery assemblies on hybrid and electric buses to maintain optimum battery cell temperature.
Electric water pumps typically use robust and efficient brushless DC motors to ensure performance and reliability. Both 12v and 24v DC electric water pumps are available to ensure compatibility with the electrical architecture of specific vehicles. In addition, some electric water pumps have the capability to provide a flow rate in excess of 110 litres per minute, as well as full speed control via a CAN bus connection which enables full diagnostic information via the vehicle manufacturer’s software.
There are currently a few different types of electric water pumps in the bus market. Although they may appear very similar in terms of physical shape, it is critical to ensure that like-for-like replacements are always used. Using an incorrect replacement electric water pump could adversely affect the thermal management system and create faults within the vehicles Onboard Diagnostic (OBD) systems.
Imperial Engineering is an authorised distributor OEM electric water pumps and is pleased to support operators with technical advice and guidance. For further information, please call our sales team on 01992 634255.