Continuously variable transmission

A continuously variable transmission comprising:

• a speed change input part for receiving power from a prime mover;
• a speed change output part;
• a hydraulic continuously variable transmission mechanism interposed between said speed change input part and said speed change output part;
• a hydraulic pump and a hydraulic motor fluidly connected with each other so as to constitute said hydraulic continuously variable transmission mechanism;
• a mechanical speed change mechanism interposed between said speed change input part and said speed change output part;
• a differential part included by said mechanical speed change mechanism;
• a group of planetary gears constituting said differential part;
• a first differential input part constituting said differential part, wherein a rotational force of said speed change input part is transmitted into both said first differential input part and said hydraulic pump;
• a second differential input part constituting said differential part, said second differential input part receiving a rotational force of said hydraulic motor;
• a first drive train constituting said mechanical speed change mechanism from said hydraulic motor to said second differential input part;
• a second drive train constituting said mechanical speed change mechanism for transmitting a rotation of said group of planetary gears generated by a difference in rotation between said first differential input part and said second differential input part to said speed output part;
• and
• a third drive train constituting said mechanical speed change mechanism for transmitting a rotation of said hydraulic motor to said speed change output part without passing said differential part,
• wherein a transmission mode of said continuously variable transmission is selectively placed into either a first transmission mode for transmitting the rotation of said hydraulic motor to said speed change output part through said third drive train while said third drive train being isolated or a second transmission mode for transmitting said speed change output part through said first drive train, said differential part and said second drive train while said third drive train being isolated;
• wherein, referring to a rotational speed ratio of said speed change output part to said speed change input part as a speed ratio, said speed ratio is changed by regulating a discharge of said hydraulic pump or said hydraulic motor, and
• wherein, during an operation for varying said speed ratio, said transmission mode is changed at a timing when a rotational speed of said group of planetary gears which, if said first transmission mode being set, run idle through said second drive train by the rotation of said speed change output part substantially coincides with a rotational speed of said group of planetary gears if said second transmission mode being set.

A continuously variable transmission comprising:

• a hydraulic continuously variable transmission mechanism including a variable displacement hydraulic pump and a variable displacement hydraulic motor fluidly connected with each other;
• a speed ratio setting means manipulated by an operator, referring to an output/input ratio in rotational speed as a speed ratio, and referring to a speed ratio set by said speed ratio setting means as a target speed ratio, wherein said hydraulic pump or said hydraulic motor is controlled in its discharge so as to make an actual speed ratio agree with said target speed ratio;
• a range of said speed ratio to be set by said speed ratio setting means;
• a pump control zone provided in said range of said speed ratio for controlling only the discharge of said hydraulic pump;
• and
• a motor control zone provided in said range of said speed ratio for controlling only the discharge of said hydraulic motor, said motor control zone being continuous to said pump control zone,
• wherein when a boundary between said pump control zone and said motor control zone is between an actual speed ratio and said target speed ratio, both said hydraulic pump and said hydraulic motor are simultaneously varied in their discharge.

A continuously variable transmission comprising:

• a speed change input part for receiving power from a prime mover;
• a speed change output part;
• a hydraulic continuously variable transmission mechanism interposed between said speed change input part and said speed change output part;
• a hydraulic pump and a hydraulic motor fluidly connected with each other so as to constitute said hydraulic continuously variable transmission mechanism;
• a mechanical speed change mechanism interposed between said speed change input part and said speed change output part;
• a differential part included by said mechanical speed change mechanism;
• a group of planetary gears constituting said differential part;
• a first differential input part constituting said differential part, wherein a rotational force of said speed change input part is transmitted into both said first differential input part and said hydraulic pump;
• a second differential input part constituting said differential part, said second differential input part receiving a rotational force of said hydraulic motor, wherein a rotation of said group of planetary gears generated by a rotational difference between said first differential input part and said second differential input part can be transmitted to said speed output part, wherein said continuously variable transmission is placed in either a first transmission mode for transmitting a rotational power of said hydraulic motor to said speed change output part without passing said differential part or a second transmission mode for transmitting a rotational power of said group of planetary gears to said speed change output part, wherein, when a certain speed ratio is set, said first and second transmission modes are exchanged for each other;
• and
• a speed ratio setting means manipulated by an operator so as to set a speed ratio referred to as a target speed ratio, said continuously variable transmission being controlled so as to adjust an actual speed ratio to said target speed ratio,
• wherein said transmission modes are exchanged only when said actual speed ratio is varied across said speed ratio corresponding to exchanging said transmission modes and this variation of said actual speed ratio is established really by manipulating said speed ratio setting means.

A continuously variable transmission comprising:

• a hydraulic pump;
• a hydraulic motor fluidly connected with said hydraulic pump;
• a hydraulic continuously variable transmission mechanism constituted by said hydraulic pump and said hydraulic motor;
• and
• a speed ratio setting means manually shifted by an operator,
• wherein referring to an output/input rotational speed ratio of said continuously variable transmission as a speed ratio, and defining said speed ratio determined by detecting a position of said speed ratio setting means as a target speed ratio, said hydraulic pump or said hydraulic motor is controlled in its discharge so as to adjust an actual speed ratio to said target speed ratio, wherein a shift speed of said speed ratio setting means is computed,
• wherein an actual speed ratio corresponding to a detected real position of said speed ratio setting means is amended correspondingly to said actual speed ratio and said shift speed so as to be defined as a provisional speed ratio, and
• wherein said hydraulic pump or said hydraulic motor is controlled in discharge so as to adjust said actual speed ratio to said provisional speed ratio.

A continuously variable transmission comprising:

• a hydraulic pump;
• a hydraulic motor fluidly connected with said hydraulic pump;
• a hydraulic continuously variable transmission mechanism constituted by said hydraulic pump and said hydraulic motor;
• and
• a speed ratio setting means manually shifted by an operator,
• wherein referring to an output/input rotational speed ratio of said continuously variable transmission as a speed ratio, and defining said speed ratio determined by detecting a position of said speed ratio setting means as a target speed ratio, said hydraulic pump or said hydraulic motor is controlled in its discharge so as to adjust an actual speed ratio to said target speed ratio,
• wherein if an actual speed ratio belongs to an extremely low speed range in whether forward traveling or rearward traveling while said target speed ratio set by said speed ratio setting means is 0, said target speed ratio is amended so as to reverse the actual rotational direction of said hydraulic motor into the opposite direction.

A continuously variable transmission comprising:

• a speed change input part of said continuously variable transmission, output power of a prime mover being transmitted to said speed change input part;
• a hydraulic pump;
• a hydraulic motor fluidly connected with said hydraulic pump;
• a hydraulic continuously variable transmission mechanism constituted by said hydraulic pump and said hydraulic motor;
• and
• a speed ratio setting means manually shifted by an operator,
• wherein referring to an output/input rotational speed ratio of said continuously variable transmission as a speed ratio, and defining said speed ratio determined by detecting a position of said speed ratio setting means as a target speed ratio, said hydraulic pump or said hydraulic motor is controlled in its discharge so as to adjust an actual speed ratio to said target speed ratio,
• wherein said continuously variable transmission is interlockingly connected with a prime mover rotation control means for controlling said output power of said prime mover, which can be placed into a load control mode for varying an output rotational speed of said prime mover in correspondence to a detected magnitude of load applied on said prime mover, so that, when the rotational speed of said prime mover is varied in correspondence to the load on said prime mover by said prime mover rotation control means placed in said load control mode, an actual speed ratio is controlled by said continuously variable transmission so as to achieve a set traveling speed.

A continuously variable transmission comprising:

• a speed change output part;
• a hydraulic continuously variable transmission mechanism;
• a hydraulic pump and a hydraulic motor fluidly connected with said hydraulic pump so as to constitute said hydraulic continuously variable transmission mechanism;
• and
• a speed ratio setting means manually shifted by an operator,
• wherein referring to an output/input rotational speed ratio of said continuously variable transmission as a speed ratio, and defining said speed ratio determined by detecting a position of said speed ratio setting means as a target speed ratio, said hydraulic pump or said hydraulic motor is controlled in its discharge so as to adjust an actual speed ratio to said target speed ratio,
• wherein said continuously variable transmission is mounted on a vehicle provided with a pair of drive axles, an axle differential unit differentially connecting said drive axles, a steering operation means, and a rotary means which is varied in its rotational speed in its normal and reverse directions in correspondence to the operational direction and degree of said steering operation means, so that the rotation of said speed change output part and the rotation of said rotary means are transmitted into said axle differential unit so as to differentially drive said pair of drive axles thereby making said vehicle turn left and right,
• wherein said speed ratio established in said continuously variable transmission is controlled so as to be reduced according to increase of operational degree of said steering operation means, and
• wherein when said steering operation means is operated adjacent to its maximum operational degree, the rotation of said speed change output part is stopped.

A continuously variable transmission comprising:

• a speed change input part for receiving power from a prime mover;
• a speed change output part, wherein a speed ratio is defined as a ratio of said speed change output part to said speed change input part;
• a hydraulic continuously variable transmission mechanism interposed between said speed change input part and said speed change output part;
• a hydraulic pump and a hydraulic motor fluidly connected with each other so as to constitute said hydraulic continuously variable transmission mechanism;
• a mechanical speed change mechanism interposed between said speed change input part and said speed change output part;
• a differential part included by said mechanical speed change mechanism;
• a group of planetary gears constituting said differential part;
• a first differential input part constituting said differential part, wherein a rotational force of said speed change input part is transmitted into both said first differential input part and said hydraulic pump;
• a second differential input part constituting said differential part, said second differential input part receiving a rotational force of said hydraulic motor, wherein a rotation of said group of planetary gears generated by a rotational difference between said first differential input part and said second differential input part can be transmitted to said speed output part;
• an additional drive train for transmitting said rotation of said speed change input part to said speed change output part without passing said hydraulic pump and said differential part;
• a speed ratio setting means for setting a target speed ratio, wherein an actual speed ratio is adjusted to said target speed ratio by controlling said hydraulic pump or said hydraulic motor in its discharge, and
• wherein, when the maximum allowable speed ratio to be set or a speed ratio value adjacent to the maximum is set by said speed ratio setting means, power is transmitted with said additional drive train;
• a detection means for detecting a rotational speed of said prime mover,
• wherein a transmission mode using said additional drive train is selected only when the rotational speed of said prime mover detected by said detection means at a timing for selecting said transmission mode using said additional drive train is within or adjacent to a range between that of said prime mover corresponding to the maximum torque of said prime mover and that of said prime mover corresponding to the maximum output power of said prime mover, and
• wherein unless it is a timing for choosing the transmission with said additional drive train comes and then said detection means detects that said rotational speed of said prime mover is within or in the vicinity of a range between a value corresponding to the maximum torque of said prime mover and a value corresponding to the maximum output power of said prime mover, said additional drive train cannot be chosen.