Toroidal continuously variable transmission control apparatus

A toroidal continuously variable transmission control apparatus for an automotive vehicle comprising:

• a variator unit comprising:
• (i) input and output disks coaxially arranged and opposing each other and having a common rotation axis;
• (ii) a power roller interposed between the input and output disks to transmit torque from the input disk to the output disk via a traction oil film formed between the power roller and each of the input and output disks, using a shearing force in the traction oil film;
• and
• (iii) a trunnion that supports a backface of the power roller so that the power roller is rotatable about a power-roller rotation axis;
• the trunnion being movable in a direction of a trunnion axis perpendicular to the common rotation axis of the input and output disks and the power-roller rotation axis to cause a tilting motion of the power roller and to continuously vary a transmission ratio;
• a ratio control hydraulic system comprising:
• (i) a hydraulic actuator producing a displacement of the trunnion in the trunnion-axis direction from an initial position at which the power-roller rotation axis intersects the common rotation axis of the input and output disks;
• (ii) a control valve hydraulically controlling operation of the hydraulic actuator;
• (iii) a ratio control actuator mechanically linked to the control valve to adjust a valve position of the control valve by changing a displacement of the ratio control actuator;
• and
• (iv) a mechanical feedback device compensating for a difference of a tilt angle of the power roller between forward and reverse operating modes and serving as a positive feedback device in the reverse operating mode and also serving as a negative feedback device in the forward operating mode during which a ratio-control-actuator displacement versus transmission ratio characteristic is relatively stable in comparison with the reverse operating mode;
• and
• a control unit comprising:
• (a) means for setting a desired transmission ratio based on a vehicle speed and an accelerator depression amount;
• (b) means for detecting a transmission ratio based on an input-disk speed and an output-disk speed;
• (c) means for electronically feedback-controlling the transmission ratio based on a deviation of the transmission ratio from the desired transmission ratio so that the transmission ratio is brought closer to the desired transmission ratio, and generating a normal-period command signal to be input to the ratio control actuator for compensating for the deviation;
• (d) means for generating an abnormal-period command signal to be input to the ratio control actuator to realize a ratio-control-actuator displacement capable of shifting the transmission ratio to a speed-reduction side, while keeping the trunnion out of contact with a stopper in the direction of the trunnion axis;
• and
• means for determining whether or not the deviation can be compensated for by the normal-period ratio control section, and for inputting the normal-period command signal to the ratio control actuator when the deviation can be compensated for by the normal-period ratio control section, and for inputting the abnormal-period command signal to the ratio control actuator when the deviation cannot be compensated for by the normal-period ratio control section.

A method of controlling a toroidal continuously variable transmission for an automotive vehicle employing a variator unit including input and output disks coaxially arranged and opposing each other and having a common rotation axis, a power roller interposed between the input and output disks to transmit torque from the input disk to the output disk via a traction oil film formed between the power roller and each of the input and output disks, using a shearing force in the traction oil film, and a trunnion that supports a backface of the power roller so that the power roller is rotatable about a power-roller rotation axis;

• the trunnion being movable in a direction of a trunnion axis perpendicular to the common rotation axis of the input and output disks and the power-roller rotation axis to cause a tilting motion of the power roller and to continuously vary a transmission ratio, and a ratio control hydraulic system including a pressure-differential operated hydraulic servo mechanism producing a displacement of the trunnion in the trunnion-axis direction from an initial position at which the power-roller rotation axis intersects the common rotation axis of the input and output disks, a control valve creating a pressure differential for operating the hydraulic servo mechanism, a step motor mechanically linked to the control valve to adjust a valve position of the control valve by changing a displacement of the step motor, and a mechanical feedback device compensating for a difference of a tilt angle of the power roller between forward and reverse operating modes and serving as a positive feedback device in the reverse operating mode and also serving as a negative feedback device in the forward operating mode during which a ratio-control-actuator displacement versus transmission ratio characteristic is relatively stable in comparison with the reverse operating mode, the method comprising:
• setting a desired transmission ratio based on a vehicle speed and an accelerator depression amount;
• detecting a transmission ratio based on an input-disk speed and an output-disk speed;
• electronically feedback-controlling the transmission ratio based on a deviation of the transmission ratio from the desired transmission ratio so that the transmission ratio is brought closer to the desired transmission ratio, and generating a normal-period command signal to be input to the step motor for compensating for the deviation;
• determining whether or not the deviation can be compensated for by electronically feedback-controlling the transmission ratio based on the deviation;
• and
• generating an abnormal-period command signal to be input to the step motor to realize a step-motor displacement capable of shifting the transmission ratio to a speed-reduction side, while keeping the trunnion out of contact with a stopper in the direction of the trunnion axis, when the deviation cannot be compensated for by electronically feedback-controlling the transmission ratio based on the deviation.