Half-toroidal variators are core components in Infinitely variable transmissions (IVT). These variators realize smoother and more rapid ratio change than other shift mechanisms. However, the effect of ratio control methods on these characteristics is not necessarily clear. Research was therefore conducted to examine these effects. Using an existing half-toroidal variator analysis model, behavioral analyses were conducted by substituting only the ratio control method. Three control methods were studied: A mechanical control mass-produced by a competitor, direct ratio control that feeds back only input and output revolutions, and observer control that adds shift mechanism state estimation to direct control. With regard to responsiveness in relation to the desired ratio, the direct control provided the best performance from the perspective of accurately realizing the desired ratio. On the other hand, under conditions in which external disturbance cannot be ignored (full closure of the throttle from acceleration at wide-open throttle), the mechanical control displayed the greatest ratio stability. Because control gain in mechanical control can only take a fixed value due to the lead angle of the precise cam, it is not possible to obtain the optimum gain for each ratio. Observer control is based on direct ratio control, but supplements the function of the precise cam with state estimation, and makes it possible to optimize control gain. The research discussed in this paper investigated the ability of the internal behavior of the variator to track target values calculated based on state estimation using simulations, and verified the validity of the state estimation equations. The results obtained indicated that observer control is a control method that balances the ability to track the desired ratio with ratio stability.

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