Pulley assembly for belt drive

A variable-speed belt drive pulley assembly includes a plurality of pulley segments, a plurality of sliders, and a rotatable hub. Each segment is adapted to engage a drive belt and is mounted to an outer end of a corresponding slider which is slidably received by the hub. Each slider may be a pair of rods extending from the body in parallel relationship to each other. The hub has a plurality of bores. Each bore slidably receives a corresponding one of the rods. An actuator device moves the segments radially inwardly and outwardly with respect to the hub. A coil spring is mounted on each the rods, and is biased to urge one of the segments radially outwardly.

FIELD

The present disclosure relates to a pulley assembly for a belt drive.

BACKGROUND

Known variable speed drive units include hydrostatic drives, viscous drives, toroidal drives, and Vari-Cool™ and similar variable sheave drives. Variable sheave designs use the side of the belt and axial force to affect different speed ratios. The axial force pinches the belt which must be physically pulled out from the sheave pair. Certain belt drive power transmissions use a ribbed belt which has lengthwise grooves and which engages a pulley with grooves. Typically, the pulleys in such a rib-belt drive have a fixed radius, and thus, have a fixed ratio between the radius of the driving pulley and the radius of the driven pulley. It is desired to provide a variable radius pulley for such a ribbed belt drive which has the efficiency of a typical poly-rib belt drive.

SUMMARY

According to an aspect of the present disclosure, a variable-speed belt drive pulley assembly includes a shaft, a rotatable hub, a plurality of pulley segments, a plurality of sliders and an actuator. Each segment is adapted to engage a drive belt. The segments are moveable via a four-bar linkage. More bars or alternative four-bar elements could be used but the preferred embodiment includes two sliders and a link affixed to a ground element. Each segment has a curved body attached an outer end of a corresponding slider. Each slider is slidably received by the hub. The shaft is the ground member of the four-bar linkage.

Each slider may comprise a pair of rods extending from the body in parallel relationship to each other. The hub has a plurality of bores. Each bore extends inwardly from an outer surface of the hub, and each bore slidably receives a corresponding one of the rods. The plurality of bores form sets of bores which are parallel to each other and which are spaced apart on opposite sides of a line which extends radially outwardly from a central axis of the hub.

The assembly also includes a plurality of resilient members or coil springs. Each spring is mounted to a corresponding one of the rods, and each spring is biased to urge one of the segments radially outwardly. Each bore includes a larger diameter portion and a smaller diameter portion joined together by an annular shoulder. Each shoulder engages an end of a corresponding one of the springs.

An actuator device moves the segments inwardly and outwardly with respect to the hub. The actuator device includes a sleeve which is slidably mounted on the shaft, and a plurality of arms coupled to the sleeve. Each arm has an inner end pivotally coupled to the sleeve and has an outer end pivotally coupled to a corresponding one of the segments. The sleeve forms the second slider in the preferred four-bar embodiment. Each arm forms the link in the four-bar linkage.

This drive pulley assembly can be used in a variable drive for a vehicle to match fan speed with cooling requirements. This design relies on predominantly radial force to create the friction required between belt and pulley to be able to transmit force which is turned into shaft torque.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring toFIGS. 1 and 2, a variable-speed belt drive assembly10includes a drive unit14. The drive unit14includes a hub16mounted to a shaft15. The hub16includes a plurality of sets18of bores20and22. Within each bore set18, bores20and22are parallel to each other, as best seen inFIG. 3. Each bore20and22extends inwardly into the hub16from the outer surface17of the hub16.

The assembly10also includes a plurality of slider devices23and a plurality of pulley segments26. Each segment26is mounted on the outer end of a slider device23which slidably received by the hub16. The slider device23may include two or more rods24. Each rod24is slidably received in a corresponding one of the bores20,22. Each segment26has a curved outer surface28which engages a belt (not shown) which is preferably a poly-rib belt. The rods24and segments26rotate with the hub16. The rods24slide in the bores20,22so that the segments26are radially movable with respect to the hub16. Alternatively, the slider device23may be a generally rectangular bar (not shown) which slidably received in a corresponding slot (not shown) formed in the hub16.

The assembly10also includes a plurality of resilient members or coil springs30. Each resilient member30is mounted to a corresponding one of the rods24. Each resilient member30is biased to urge one of the segments26radially outwardly with respect to the hub16. Each resilient member30is preferably a coil spring which surrounds one of the rods24. The resilient members30spring load the segments26to keep the sheave segments expanded and in contact with the belt (not shown).

The assembly10also includes an actuator device40for moving the segments26radially inwardly and outwardly with respect to the hub16. The actuator device40includes a hollow sleeve42and a plurality of arms44. The sleeve42is slidably mounted on the shaft15. Each arm44has an inner end46pivotally coupled to the sleeve42and having an outer end48pivotally coupled to a corresponding one of the segments26. The sleeve42has tabs50which project outwardly from the sleeve42. Pairs of the tabs50support pivot pins52. The inner end46of each of the arms44is pivotally supported by one of the pins52. Similarly, each segment26has a pair of tabs54which support pivot pins56. The outer end48of each of the arms44is pivotally supported by one of the pins56. As the sleeve42slides towards the hub16, the arms44pivot and move the segments26radially outwardly. As the sleeve42slides away from the hub16, the arms44pivot and move the segments26radially inwardly. The length of element44as coupled to segment26and sleeve42is designed in a manner whereby rods24cannot escape bores20,22should the poly-rib belt break during operation, yet the mechanism can be assembled and disassembled via insertion and removal of pins52and56.

The actuator40device maintains the segments26in synchronization and in a certain radial position to define a speed ratio with another pulley unit (not shown).

The assembly10also includes a hollow bearing60slidably mounted on the shaft15adjacent to the sleeve42. The bearing60is engagable with a non-rotating actuator (not shown) which moves the sleeve42axially on the shaft15. The actuator (not shown) may be a hydraulic actuator, air cylinders, a ramp mechanism or other linear actuator. The actuator could be similar to transmission clutch throw-out bearing axial movement device (not shown). The actuator (not shown) could also include screw-pitch members (not shown) whereby rotation could cause the sleeve42to move axially, or the actuator could act directly on the arms44or the segments26. Alternatively, actuation could be accomplished by balanced weighting and spring forces between drive units wherein increase rotation speed with subsequent centripetal forces drive actuation of the unit.

As best seen inFIG. 3, each bore20and22includes a larger diameter outer portion62and a smaller diameter inner portion64. Portions62and64are joined together by an outwardly facing annular shoulder66. Each shoulder engages an end of a corresponding one of the springs30. Also, as best seen inFIG. 3, the bores20and22form parallel sets of bores, wherein bore20and22are parallel to each other and are spaced apart on opposite sides of a line L which extends radially outwardly from a central axis A of the hub16.

The result is a pulley assembly for a poly-rib belt pulley which has a plurality of pulley segments. These segments are then moved radially away from a central axis of the pulley hub to change the affective pulley diameter. Two or more adjustable pulleys assemblies may be used in a system (not shown) to affect a variable ratio between driver(s) and driven shafts. This pulley assembly may be used in a fan drive, or the pulley assembly may be used for any drive requiring variable speed.

With this pulley assembly, a belt tensioner (not shown) may not be needed if the spring mechanisms can provide the required system dampening. The drive unit14preferably has6pulley segments26, and could be a driven unit driven by a driver pulley unit (not shown) having a different number such as five, pulley segments (not shown). Each drive unit may have the same or different effective diameter. Having a combination of drive units with different numbers of pulley segments can help reduce possible vibration harmonics, as is known in powertrain design. When segments are radially extended, the effective diameter of the mechanism between segments may be slightly smaller than the segment itself. To overcome small fluctuations in speed due to this varied diameter, a damper (not shown) could be used to smooth torsional oscillation, and could be integrated into the assembly connection points of the driver, driven or both.