A transmission mechanism has a set of two composite sprockets, each having pinion sprockets (210) supported movably in a radial direction with respect to a rotation shaft 1 that inputs or outputs power and a movement mechanism radially moving the pinion sprockets (210) in synchronization with each other while maintaining equidistance of the pinion sprocket (210) from a shaft center (C.sub.1) of the rotation shaft 1, and a chain wound around the two composite sprockets. Transmission ratio is changed by changing a circumcircle radius that is a radius of a circle encircling and circumscribing all the pinion sprockets (210). The pinion sprocket (210) is formed into a sector gear shape having a teeth portion (212) that is arranged along a circumference of a minimum radius circumcircle (A.sub.1) and meshes with the chain. With this configuration, torque can surely be transmitted.

Transmission mechanism has set of two composite sprockets (5, 5), each having pinion sprockets (20) supported movably in radial direction with respect to rotation shaft (1) inputting or outputting power and movement mechanism radially moving pinion sprockets (20) in synchronization with each other while maintaining equidistance of pinion sprocket (20) from shaft center (C.sub.1) of rotation shaft (1), and chain (6) wound around two composite sprockets. Transmission ratio is changed by changing circumcircle radius that is radius of circle encircling and circumscribing all the pinion sprockets (20). Each guide rod (29) has first guide rod (291) guiding chain (6) all the time regardless of circumcircle radius size, and second guide rod (292) guiding chain (6) at least when circumcircle radius is a maximum and positioned at radial direction inner side with respect to first guide rod (291) when circumcircle radius is a minimum. With this, ratio coverage can be expanded.

Disclosed is a continuously variable transmission which can simplify a structure and contribute to miniaturization of a device. A continuously variable transmission including a first disk unit with a first guide slot, a second disk unit with a second guide slot which the first guide slot crosses, and a guide member provided to move along the first guide slot and the second guide slot in response to relative rotation of the second disk unit to the first disk unit, includes: a rotation driving unit rotating any one of the first disk unit and the second disk unit with respect to the other one, wherein the rotation driving unit includes a barrel cam member, a linear movement member linearly moving in response to rotation of the barrel cam member, a driving cam member linearly moving together with the linear movement member, and a driven cam member rotatably connected integrally with any one of the first disk unit and the second disk unit and selectively rotating in response to the linear movement of the driving cam member.

Disclosed is a continuously variable transmission which can simplify a structure and contribute to miniaturization of a device. A continuously variable transmission including a first disk unit with a first guide slot, a second disk unit with a second guide slot which the first guide slot crosses, and a guide member provided to move along the first guide slot and the second guide slot in response to relative rotation of the second disk unit to the first disk unit, includes: a rotation driving unit rotating any one of the first disk unit and the second disk unit with respect to the other one, wherein the rotation driving unit includes a barrel cam member, a linear movement member linearly moving in response to rotation of the barrel cam member, a driving cam member linearly moving together with the linear movement member, and a driven cam member rotatably connected integrally with any one of the first disk unit and the second disk unit and selectively rotating in response to the linear movement of the driving cam member.

A yard maintenance device having a working assembly selectively rotatable based on operation of an engine of the device may include a belt drive system. The belt drive system may include at least one driven pulley operably coupled to the working assembly, a drive shaft operably coupled to the engine, a drive belt configured to selectively couple the drive shaft to the at least one driven pulley, a tension adjustment assembly, and a control unit. The tension adjustment assembly may be configured to operably couple to at least one component of the belt drive system to adjust a position thereof to modify tension of the drive belt. The control unit may be configured to provide electronic control of the tension adjustment assembly.

A yard maintenance device having a working assembly selectively rotatable based on operation of an engine of the device may include a belt drive system. The belt drive system may include at least one driven pulley operably coupled to the working assembly, a drive shaft operably coupled to the engine, a drive belt configured to selectively couple the drive shaft to the at least one driven pulley, a tension adjustment assembly, and a control unit. The tension adjustment assembly may be configured to operably couple to at least one component of the belt drive system to adjust a position thereof to modify tension of the drive belt. The control unit may be configured to provide electronic control of the tension adjustment assembly.

Example gear systems and methods for use are provided herein. An example gear system may include (a) an expandable gear that defines a plurality of circular sectors, (b) a hub disposed in the gear, where the hub includes an expandable portion, and (c) an expander, where the expandable gear has an expanded position when the expander is disposed within the hub and the expandable gear has an unexpanded position when the expander is disposed outside of the hub.

Example gear systems and methods for use are provided herein. An example gear system may include (a) an expandable gear that defines a plurality of circular sectors, (b) a hub disposed in the gear, where the hub includes an expandable portion, and (c) an expander, where the expandable gear has an expanded position when the expander is disposed within the hub and the expandable gear has an unexpanded position when the expander is disposed outside of the hub.

The present invention has a mechanical rotation drive mechanism (50) that drives rotation of at least one rotation pinion sprocket (22; 23) on its axis from among a plurality of pinion sprockets (20). The mechanical rotation drive mechanism (50) drives the rotation of at least one rotation pinion sprocket (22; 23) on its axis in concert with a sprocket movement mechanism (40A) so as to eliminate a phase shift, associated with a radial direction movement of the plurality of pinion sprockets (20) by the sprocket movement mechanism (40A), of the plurality of pinion sprockets (20) with respect to a chain (6).

The present invention has a mechanical rotation drive mechanism (50) that drives rotation of at least one rotation pinion sprocket (22; 23) on its axis from among a plurality of pinion sprockets (20). The mechanical rotation drive mechanism (50) drives the rotation of at least one rotation pinion sprocket (22; 23) on its axis in concert with a sprocket movement mechanism (40A) so as to eliminate a phase shift, associated with a radial direction movement of the plurality of pinion sprockets (20) by the sprocket movement mechanism (40A), of the plurality of pinion sprockets (20) with respect to a chain (6).