In order to obtain a flux density distribution with high magnitude and sinusoidal property, the radio of radial permanent magnet’s arc to pole pitch is designed as 0.62, of which
the fundamental component and the harmonic distortion are 1.01 T and 0.18, respectively. Fig. 5 shows the no-load magnetic flux distribution in the cross section of the machine. It can be observed that the magnetic flux through the barrel is at a low level.It also should be mentioned that an axially segmented structure is applied to the Halbach permanent magnet array to re-
duce the cogging torque produced by the interaction of stator slots and permanent magnets, as shown in Fig. 6. According to the slot number and the pole number, the misalignment angle
Δθ between the segments is designed as 2.5°. The results of time-stepping finite-element calculation indicate that the cogging torque of axially segmented structure is 0.035 Nm while
the original value is 0.19 Nm.The swash plate angle and the piston reference diameter are
coupled with each other as presented from (9) to (12), so it is necessary to determine these two parameters together. Fig. 7 shows the swash plate angle and the nondimensional hoop stress
varying with different piston reference diameter. In general,increasing the piston reference diameter can reduce the swash plate angle as well as the upsetting moment of the barrel, and
too large or too small values will result in high hoop stress.Therefore, the piston reference diameter is set to 60.0 mm and the corresponding swash plate angle is designed as 10°.