Integrated In-Wheel Motors for Low Power Traction Application
Doktorsavhandling, 2003

This thesis is primarily concerned with the practical limits, imposed by magnetic saturation and thermal considerations, of the force density in low-speed permanent-magnet electric machines. The practical force density values obtainable in integral- and fractional-slot machines are determined. The achievable force density for machines utilizing slot per pole per phase of 0.375, 0.5, 0.75 and 1 are determined. The theoretical investigation covered a large range of machine sizes. For saturation reasons, shallow slots are more favourable for achieving high force densities. However for thermal reasons deeper slots become favourable. An optimum slot depth that maximises the force density for each current density level therefore exists and is determined in this thesis for a range of machines. In particular, the maximum allowable slot depth range for four low-speed applications are identified for a given maximum motor diameter. Plots of the force density against slot depth for various current densities for fixed pole pitches enabled a useful database to be established. These curves would enable one to determine if the demanding specification can be meet within a given restricted space. The slot depth required can be determined instantly for the practical allowable current density. The results presented will help the design engineer to determine if the surface mounted permanent magnet machine configuration is suitable to fulfil one's specification. If the configuration is not suitable, then other topologies must be considered. An experimental in-wheel motor, intended for wheelchair applications, was built and tested, and is shown to meet the design specifications. When assembled into the wheelchair the results were promising and showed a remarkable increase in performance compared to the existing conventional geared drive.

electric golf cart


force density


traction motors

forklift trucks


electric wheelchairs/power wheelchairs

low speed machines



Prakashraj Kasinathan

Chalmers, Institutionen för elteknik


Elektroteknik och elektronik



Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 1950

Technical report - School of Electrical Engineering, Chalmers University of Technology, Göteborg, Sweden: 445