Dynamic Stability Analysis of High-Speed Traction Drive CVT for Aircraft Power Generation

The traction-drive integrated drive generator (T-IDG®) has been developed since 1999 to replace current hydrostatic transmission drive generators mounted on Japanese military aircraft. The T-IDG® consists of a generator and a half-toroidal traction-drive continuously variable transmission (CVT), which maintains a constant output speed of 24000 rpm, that is, a 400 Hz AC power supply. To cope with recent trends of more electric aircraft (MEA) and the need for weight reduction, a high-speed traction-drive CVT is advantageous over other transmissions. The torque on the half-toroidal variator is transmitted through multiple power rollers. The equal load sharing among power rollers is typically controlled by a mechanical hydraulic feedback system, whose stability is one of the main issues for the high-speed traction-drive CVT. Previous studies have shown that insufficient damping and stiffness of the mechanical hydraulic feedback system cause self-induced vibration. We found that the support stiffness of the variator also affects the stability of the feedback system when it is driven at a high speed. This paper describes the theoretical criteria to maintain the stability of the load-sharing system of the power rollers of the high-speed CVT. A test to validate the theory is also conducted with a prototype traction-drive CVT at speeds of up to 20000 rpm with a peripheral speed of the traction contact of 70 m/s. The test results show that the vibration is excited at high rotational speeds when the variator is supported with a low-stiffness bearing support. We conclude that a high-stiffness support is necessary to transmit the power stably with a high-speed traction-drive CVT.