Design and performances of high torque ultrasonic motor for application of automobile

We propose an ultrasonic motor of high torque with a new configuration for application in automobiles. The newly designed stator is a two sided vibrator consisting of a toothed metal disk with a piezoelectric ceramic ring bonded on both faces of the disk which generates a flexural traveling wave along the circumference of disk. In this configuration, the displacement on the surface of stator may not be confined. It also produces a large vibrating force and amplitude because the vibrator is sandwiched by two piezoelectric plates. It is possible to increase the torque by improving the vibration characteristics. We used the finite element method to compute the vibration mode of the motor of diameter 48 mm. A sixth mode was chosen as the operation mode with a resonance frequency of about 73 kHz. We fabricated a prototype according to this design and measured its performance. The performance measurement of the prototype motor showed that its stall torque was about 1.8 Nm and efficiency was 37% at 60% of the maximum torque. Compared to a conventional motor which employed a single sided piezoelectric vibrator of the same outer diameter, we obtained, with this prototype, a maximum torque of about twice as great. The motor may be useful to apply as an actuator in a mobile car.