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.

Systems, apparatus, and methods for tensioning systems of a drive belt are disclosed. Particularly, tensioning systems for a drive belt of a rotary screen of a harvester combine are disclosed. The tensioning system provides for avoiding over-tensioning the drive belt when the drive belt is disengaged from a drive shaft. The tensioning system may also provide for maintaining continuous operation of the drive shaft as the drive belt is moved between engagement and disengagement with the drive shaft.

Systems, apparatus, and methods for tensioning systems of a drive belt are disclosed. Particularly, tensioning systems for a drive belt of a rotary screen of a harvester combine are disclosed. The tensioning system provides for avoiding over-tensioning the drive belt when the drive belt is disengaged from a drive shaft. The tensioning system may also provide for maintaining continuous operation of the drive shaft as the drive belt is moved between engagement and disengagement with the drive shaft.

In a pulley apparatus, belt supporting portions of belt support pieces, which support a belt from a radially inside thereof, are arranged along a circumferential direction of a power shaft and each have a predetermined circumferential length. In a pulley driven mode, the belt support pieces rotate about corresponding first supporting members in a direction making the belt supporting portions become closer to the power shaft with second supporting members being relatively moved in corresponding elongated holes toward radially outer ends thereof, causing the belt supporting portions to be reduced in radius. In a pulley driving mode, the belt support pieces rotate about the corresponding first supporting members in a direction making the belt supporting portions become further from the power shaft with the second supporting members being relatively moved in the corresponding elongated holes toward radially inner ends thereof, causing the belt supporting portions to be increased in radius.

A variable transmission system for a vehicle is configured such that, when a magnitude of a hydraulic pressure detected by an hydraulic pressure sensor is a first predetermined value or more, a chord portion of a chain belt is pressed such that a raceway length of the chain belt is extended by at least a circumferential extension amount of the chain belt at the time when the magnitude of the hydraulic pressure is the first predetermined value. Hereby, it is possible to restrain the chain belt from coming off from a sheave even in a low vehicle speed range, at a low cost, without causing a fuel efficiency decrease and a driving torque decrease of the vehicle.

In a pulley apparatus, belt supporting portions of belt support pieces, which support a belt from a radially inside thereof, are arranged along a circumferential direction of a power shaft and each have a predetermined circumferential length. In a pulley driven mode, the belt support pieces rotate about corresponding first supporting members in a direction making the belt supporting portions become closer to the power shaft with second supporting members being relatively moved in corresponding elongated holes toward radially outer ends thereof, causing the belt supporting portions to be reduced in radius. In a pulley driving mode, the belt support pieces rotate about the corresponding first supporting members in a direction making the belt supporting portions become further from the power shaft with the second supporting members being relatively moved in the corresponding elongated holes toward radially inner ends thereof, causing the belt supporting portions to be increased in radius.

A belt-type continuously variable transmission capable of continuously changing a speed reduction ratio of a driven pulley to a drive pulley, has a speed reduction ratio regulation mechanism that regulates a minimum speed reduction ratio of the driven pulley to the drive pulley. The driven pulley includes a fixed sheave, a movable sheave displaceable in an axial direction with respect to the fixed sheave, and a coil spring that urges the movable sheave toward the fixed sheave. The speed reduction ratio regulation mechanism has a swing arm that adjusts an allowable range in which moving away in an axial direction of the movable sheave with respect to the fixed sheave is possible, and a regulation drive section that drives the swing distal end portion of the swing arm to swing continuously.

A variable transmission system for a vehicle is configured such that, when a magnitude of a hydraulic pressure detected by an hydraulic pressure sensor is a first predetermined value or more, a chord portion of a chain belt is pressed such that a raceway length of the chain belt is extended by at least a circumferential extension amount of the chain belt at the time when the magnitude of the hydraulic pressure is the first predetermined value. Hereby, it is possible to restrain the chain belt from coming off from a sheave even in a low vehicle speed range, at a low cost, without causing a fuel efficiency decrease and a driving torque decrease of the vehicle.

A belt-type continuously variable transmission capable of continuously changing a speed reduction ratio of a driven pulley to a drive pulley, has a speed reduction ratio regulation mechanism that regulates a minimum speed reduction ratio of the driven pulley to the drive pulley. The driven pulley includes a fixed sheave, a movable sheave displaceable in an axial direction with respect to the fixed sheave, and a coil spring that urges the movable sheave toward the fixed sheave. The speed reduction ratio regulation mechanism has a swing arm that adjusts an allowable range in which moving away in an axial direction of the movable sheave with respect to the fixed sheave is possible, and a regulation drive section that drives the swing distal end portion of the swing arm to swing continuously.