Stepless speed change structure

A stepless speed change structure including a hydrostatic transmission and a speed change operating member, wherein the hydrostatic transmission includes a variable displacement hydraulic pump so configured that a volume of a pump body changes in accordance with an operation of a pump volume adjusting member, and a variable displacement hydraulic motor so configured that a volume of a motor body changes in accordance with an operation of a motor volume adjusting member, and wherein the speed change operating member is configured to change a speed change state of the hydrostatic transmission, the stepless speed change structure comprising:

• a pump operation connecting mechanism that operates the pump volume adjusting member from a neutral position in first and second operating directions;
• a motor operation connecting mechanism that operates the motor volume adjusting member in a smaller volume direction and a larger volume direction,
• wherein the pump operation connecting mechanism includes a pump spool that is operatively connected to the speed change operating member in such a manner as that pump spool takes a pump spool neutral position in accordance with the operation of the speed change operating member to the neutral position, and moves from the pump spool neutral position in a first slide direction on one side and a second slide direction on the other side in an axial direction, respectively, in accordance with the operations of the speed change operating member from the neutral position in the first and second operating directions,
• wherein the motor operation connecting mechanism includes a motor spool that is placed coaxially in series on one side of the pump spool in the axial direction and that is movable bidirectionally in a smaller volume direction on one side and a larger volume direction on the other side in an axial direction, and a larger volume operation spring that biases the motor spool in the larger volume direction, the motor operation connecting mechanism so configured as to operate the motor volume adjusting member in the smaller volume direction and the larger volume direction, respectively, in accordance with the movements of the motor spool in the smaller volume direction and larger volume direction,
• wherein there is provided a flexible portion between the pump spool in a state of being positioned at the pump spool neutral position and the motor spool in a state of being positioned at a larger volume direction movement end, the flexible portion allowing the pump spool to move by a predetermined distance in the first slide direction with the motor spool held at the larger volume direction movement end, and
• wherein only the pump spool moves in the first slide direction with the motor spool held at the larger volume direction movement end when the pump spool is moved to an end of the flexible portion in accordance with the operation of the speed change operating member, and the pump spool presses and moves the motor spool in the smaller volume direction when the pump spool is moved in the first slide direction beyond the flexible portion.

A stepless speed change structure including a hydrostatic transmission and a speed change operating member, wherein the hydrostatic transmission includes a variable displacement hydraulic pump so configured that a volume of a pump body changes in accordance with an operation of a pump volume adjusting member, and a variable displacement hydraulic motor so configured that a volume of a motor body changes in accordance with an operation of a motor volume adjusting member, and is configured so that an output rotational speed becomes zero speed when the pump volume adjusting member is positioned at a neutral position and an output rotational direction becomes forward and reverse directions, respectively, when the pump volume adjusting member is moved from the neutral position to forward and reverse areas, and wherein the speed change operating member is configured to change the rotational direction and the rotational speed of the output of the hydrostatic transmission, the stepless speed change structure comprising:

• a pump operation piston that is movable bidirectionally in first and second slide directions on one side and the other side in an axial direction, and that is directly or indirectly engaged with an operation end portion of the pump volume adjusting member such that movements of the pump operation piston in the first and second slide directions cause the pump volume adjusting member to be operated in first and second operating directions, respectively;
• a neutral spring mechanism that holds the pump operation piston at a neutral position when no external force is added to the pump operation piston and generates a biasing force toward the neutral position when the pump operation piston is moved in the first and second slide directions from the neutral position;
• first and second slide oil chambers that is so configured that pressure oil, which has been supplied thereinto, presses and moves the pump operation piston in the first and second slide directions, respectively, against the biasing force of the neutral spring mechanism;
• a motor operation piston that is movable bidirectionally in a smaller volume direction on one side and a larger volume direction on the other side in an axial direction, and that is directly or indirectly engaged with an operation end portion of the motor volume adjusting member such that movements of the motor operation piston in the smaller volume direction and the larger volume direction cause the motor volume adjusting member to be operated in a smaller volume direction and a larger volume direction, respectively;
• a larger volume operation spring that biases the motor operation piston in the larger volume direction;
• a smaller volume operating oil chamber that is so configured that pressure oil, which has been supplied thereinto, presses and moves the motor operation piston in the smaller volume direction against the biasing force of the larger volume operation spring;
• a first pressure control valve that supplies and discharges pressure oil to and from the first slide oil chamber, respectively, in accordance with the operation of the speed change operating member that operates the pump volume adjusting member in the first and second operating directions,
• a second pressure control valve that supplies and discharges pressure oil to and from the second slide oil chamber, respectively, in accordance with the operation of the speed change operating member that operates the pump volume adjusting member in the first and second operating directions, and
• a flow path switching valve that introduces pressure oil of the first and second slide oil chambers into the smaller volume operating oil chamber, respectively, when the speed change operating member is positioned in forward and reverse operation areas,
• wherein biasing forces of the neutral spring mechanism and the larger volume operation spring are so set that, after pressure oil within the first slide oil chamber causes the pump operation piston to move in the corresponding slide direction so that the neutral spring mechanism is brought into a predetermined retained-elastic state, pressure oil within the smaller volume operating oil chamber causes the motor operation piston to start moving in the smaller volume direction while compressing the larger volume operation spring.

A stepless speed change structure including a hydrostatic transmission, a planetary gear mechanism and a speed change operating member, wherein the hydrostatic transmission includes a variable displacement hydraulic pump so configured that a volume of a pump body changes between a first operating direction movement end and a second operating direction movement end in accordance with an operation of a pump volume adjusting member, and a variable displacement hydraulic motor so configured that a volume of a motor body changes in accordance with an operation of a motor volume adjusting member, wherein planetary gear mechanism so configured to receive rotational powers from a drive source and the hydrostatic transmission at first and second elements, respectively, and output a combined rotational power, which has been formed by combining these rotational powers, from a third element, and wherein the speed change operating member is configured to change a speed change state of the hydrostatic transmission, the stepless speed change structure comprising:

• a pump operation piston that is movable bidirectionally in first and second slide directions on one side and the other side in an axial direction, and that is directly or indirectly engaged with an operation end portion of the pump volume adjusting member such that movements of the pump operation piston in the first and second slide directions cause the pump volume adjusting member to be operated in first and second operating directions, respectively;
• a second slide spring that biases the pump operation piston in the second slide direction;
• a first slide oil chamber that is so configured that pressure oil, which has been supplied thereinto, presses and moves the pump operation piston in the first slide direction against the biasing force of the second slide spring;
• a motor operation piston that is movable bidirectionally in a smaller volume direction on one side and a larger volume direction on the other side in an axial direction, and that is directly or indirectly engaged with an operation end portion of the motor volume adjusting member such that movements of the motor operation piston in the smaller volume direction and the larger volume direction cause the motor volume adjusting member to be operated in a smaller volume direction and a larger volume direction, respectively;
• a larger volume operation spring that biases the motor operation piston in the larger volume direction;
• a smaller volume operating oil chamber that is so configured that pressure oil, which has been supplied thereinto, presses and moves the motor operation piston in the smaller volume direction against the biasing force of the larger volume operation spring;
• and
• a first pressure control valve that commonly switches supplying and discharging of pressure oil to and from the first slide oil chamber and the smaller volume operating oil chamber in accordance with the operation of the speed change operating member;
• wherein a gear ratio of the planetary gear mechanism is so set that the rotational speed of the combined rotational power becomes zero speed when the pump volume adjusting member is positioned at the second operating direction movement end, and is accelerated in one rotational direction as the pump volume adjusting member is operated from the second operating direction movement end to the first operating direction movement end, and
• wherein biasing forces of the second slide spring and the larger volume operation spring are so set that, after pressure oil within the first slide oil chamber causes the pump operation piston to move in the first slide direction so that the second slide spring is brought into a predetermined retained-elastic state, pressure oil within the smaller volume operating oil chamber causes the motor operation piston to start moving in the smaller volume direction while compressing the larger volume operation spring.