The road transport sector is responsible for 22% of the generation of greenhouse gasses in Europe[1]. Therefore, the transport sector is forced to change at a high pace towards electric mobility. Zero and low emission zones are introduced all over Europe which challenges fleet owners to make their vehicles more sustainable and compliant with the new emission regulations. Light commercial vehicles (LCV) with a traditional internal combustion engine (ICE) are affected by this and are banned from city centers like Amsterdam, London and Berlin. However, they still make up a large part of the current transport fleet.

For fleet owners it can be hard to comply with the new regulations, especially because viable fully electric LCVs alternatives are not always available for their use case. The range, payload, charging time and price are not attractive. A hybrid LCV would smoothen this transition, enabling users to drive purely electric within the environmental zones and use the traditional ICE for longer distances.  XYZ Dynamics develops such a retrofit add-on electric powertrain for LCVs, the AxLectric®.  TNO supports XYZ dynamics during their development of the AxLectric­­® specifically on the dimensioning and specifications of their battery system. A geofence-based energy management system will then take care of what drive mode needs to be active in which area, e.g. full electric driving in zero emission zones. Retrofitting an add-on electric drivetrain is a cost effective solution for fleet owners to make their vehicle fleet comply with the new emissions standards. In that way they can keep performing their work in the future.

3D animation of the geofence-based energy management system

Battery requirements and constraints

As the maximum payload of the vehicle should remain as high as possible, the battery choice is of high importance. The size and weight constraints are therefore of great influence with respect to the payload and available space. Furthermore, the requirements of the battery pack for a hybrid LCV differs from the existing hybrid passenger vehicles (HEV), as LCVs are typically much heavier. When accelerating the electric motor would demand a larger current from the battery cells. This in turn asks for more powerful cells. In order to guarantee high safety and reliability of the AxLectric® a reliable battery cell is of high importance. Lastly, in the commercial market it all comes down to cost. Therefore, cost plays a big role as well. All these constraints and design requirements influence the optimal battery cell choice. As TNO has a lot of experience conducting battery cell tests, it was for XYZ Dynamics the logical choice to start collaborating with them in this project. They are a very good partner to collaborate with as they have great expertise in the battery field and have good battery testing facilities at their disposal which can be used to find the optimal battery cell choice.

Collaboration with TNO

TNO helped evaluating the battery cells on various factors such as safety, specific energy density, specific power density, costs and durability. The properties differ per cell chemistry and therefore not every type is suitable to the AxLectric® retrofit kit. An overall assessment of the different chemistries was done, before selecting a particular cell.
Moreover, the drivetrain components such as the electric motor sets new requirements for the cells, as the arrangement of cells needs to meet the demanded power supply of the motor. In addition to the practical and economical requirements, the rated voltage and capacity of a cell needs to be selected optimally. For the tested configuration a Lithium Iron Phosphate (LFP), Lithium Nickel Manganese Cobalt Oxide (NMC) and Lithium Titanate (LTO) cell were chosen. LTO was selected for research due to its durability, safety and high C-rate capabilities. The C-rate of a cell defines the rate at which a battery is being able to discharge, a higher C-rate means more power can be drawn and cells can be charged faster. NMC was selected for research as a cell with a high specific energy in order to make the battery pack as light as possible. The option of LFP was selected because of its considerable durability and specific energy. The different cells were tested under the so called US City II driving cycle. Such a driving cycle simulates the power demand in areas of high population density, thus inner city use.

The future

Erik Hoedemaekers (Scientist Integrator at the Powertrains research group TNO Unit Traffic & Transport) and Annekoos Schaap (TU/e Bachelor student Electrical Engineering) have worked together to select a battery cell for the AxLectric® series product. The battery research project combined the expertise and facilities of TNO and the vision of XYZ Dynamics which resulted in the ideal cell choice for the battery pack designed for the AxLectric® powertrain. XYZ Dynamics is thankful for the support of TNO and hopes to smoothen the transition to fully electric driving. The research outcomes are positive and we are looking forward to the next step in having our first vehicles on the road.

[1] Agency, E. E. (2017). Greenhouse gas emissions from transport in Europe. Retrieved from https://www.eea.europa.eu/data-and-maps/indicators/transport-emissions-of-greenhouse-gases/transport-emissions-of-greenhouse-gases-12

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