This invention relates to a resin pulley that guides movements of a timing belt or an engine accessory drive belt of a vehicle engine.
As an idler pulley that guides movements of a timing belt or an engine accessory drive belt or a tension pulley for adjusting the tension of the belt, to reduce the weights and costs, a resin pulley is widely used which includes a rolling bearing, and a pulley body molded on the radially outer surface of the outer race of the rolling bearing using a synthetic resin.
Since the pulley body of such a resin pulley is made from a material different in linear expansion coefficient from the material of the outer race of the rolling bearing, when the temperature rises, the outer race and the pulley body are expanded to a different degree. This lowers the force with which the pulley body retains the outer race, and could result in relative slippage (creep) between the outer race and the pulley body.
To reduce emissions of carbon dioxide, an increasing number of today's vehicle engines are configured to be stopped when the vehicle stops, and provided with an integrated starter generator (ISG) capable of starting the engine as soon as the driver depresses the accelerator pedal to start the vehicle.
In an automobile including the above described ISG, the idler pulley and the tension pulley are accelerated and decelerated extremely frequently, and thus a simple slip stop arrangement including an eccentric groove or a helical groove formed in the radially outer surface of the outer race cannot prevent creep between the outer race and the pulley body.
A resin pulley is proposed in which straight knurling is provided by rolling on the radially outer surface of the outer race, molten resin for molding the pulley body is filled in groove-shaped recesses of the straight knurling, and is cooled and solidified to form protrusions, and through engagement between the protrusions and the recesses of the straight knurl, creep between the outer race and the pulley body is prevented (see Patent Documents 1 and 2 below).
When one wishes to prevent creep between the outer race and the pulley body through straight knurling, if the depths of the groove-shaped recesses of the straight knurling are small, it is difficult to effectively prevent creep, and thus, relatively deep groove-shaped recesses are necessary.
In the resin pulley described in Patent Documents 1 and 2, an engaging groove is formed in the radially outer surface of the outer race, and straight knurling is applied to the bottom of the engaging groove to form groove-shaped recesses and projections disposed circumferentially alternating with the groove-shaped recesses. Accordingly, if the depths of the groove-shaped recesses are large, the load applied to the outer race is large and the outer race deforms. The deformation of the outer race may cause noise during rotation of the rolling bearing, and also result in a decrease in a rotation accuracy due to whirling, and thus, functions of the bearing are lowered. Accordingly, it is not possible to form a groove recesses having a depth large enough to prevent the creep.
An object of the present invention is to provide a resin pulley that can reliably prevent creep while reducing deformation of the outer race of the rolling bearing.
To achieve the above object, the present invention provides a resin pulley comprising: a rolling bearing including an outer race; and a pulley body that is integrally resin-molded on a radially outer surface of the outer race of the rolling bearing; wherein the outer race has, on the radially outer surface of the outer race, a pair of annular grooves axially spaced apart from each other and each having a circular bottom, and an annular protrusion between the pair of annular grooves; the annular protrusion has, on a radially outer surface of the annular protrusion, straight knurling formed by rolling, the straight knurling comprising groove-shaped recesses and projections disposed circumferentially alternating with the groove-shaped recesses, each of the groove-shaped recesses and the projections having two ends that extend to the respective pair of annular grooves; the diameter of a circle that contacts, from radially inwardly, bottoms of the groove-shaped recesses is larger than the diameter of the circular bottom of each of the pair of annular grooves; and the pulley body includes protrusions formed by solidification of a molten resin filling the groove-shaped recesses.
As described above, knurling by rolling is applied to the radially outer surface of the annular protrusion formed axially between the pair of annular grooves, and thus, a load applied to the annular protrusion when the annular protrusion plastically deforms is partially axially applied to and absorbed by the pair of annular grooves.
Since the diameter of the circle that contacts, from radially inwardly, the bottoms of the groove-shaped recesses formed by the knurling is larger than the diameter of the circular bottom of each annular groove, the load applied to the annular protrusion when the annular protrusion plastically deforms is effectively absorbed by the pair of annular grooves, so that a radial load is very small, and the straight knurling can be applied without deforming the outer race. Further, deep groove-shaped recesses can be formed, and through the engagement between the protrusions formed in the groove-shaped recesses and the projections, creep between the outer race and the pulley body can be reliably prevented.
The axial sectional shape of the annular protrusion may be a circular arc or a trapezoid. Alternatively, the axial sectional shape of the annular protrusion may be a combination of a trapezoid and a circular arc. By having such sectional shapes, the axial width of the annular protrusion is smallest at the radially outer surface and gradually and radially inwardly increases, so that when teeth a knurling tool are pushed into the annular protrusion, the contact area between the teeth of the knurling tool and the annular protrusion gradually increases, thus preventing a sudden increase in load applied to the annular protrusion. This makes it easier to provide straight knurling by rolling on the annular protrusion.
Since the outer race of the rolling bearing is made from a material different in linear expansion coefficient from the material of the pulley body, when the temperature rises, the outer race and the pulley body are expanded to a different degree. If the height of the protrusions that circumferentially engage the projections of the straight knurling is less than 0.3 mm, the circumferential engaging force therebetween may become so weak that creep may occur between the outer race and the pulley body when the outer race and the pulley body are expanded to a different degree, Thus, the depths of the groove-shaped recesses in which the protrusions are formed is preferably 0.3 mm or over.
As described above, in the present invention, the pair of annular grooves provided at axial both sides of the annular protrusion to which knurling is applied can effectively absorb the load applied to the annular protrusion when the annular protrusion plastically deforms. Accordingly, a radial load applied to the outer race is very small, so that deep groove-shaped recesses can be formed, and through engagement between the protrusions formed in the groove-shaped recesses and the projections, creep between the outer race and the pulley body can be reliably prevented.
A resin pulley embodying the present invention is now described with reference to the drawings. As illustrated in
The rolling bearing 10 is a deep groove ball bearing including an outer race 11 having a raceway groove 12 in the radially inner surface thereof, an inner race 13 having a raceway groove 14 in the radially outer surface thereof, and balls 15 disposed between the raceway groove 12 of the outer race 11 and the raceway groove 14 of the inner race 13, the balls 15 being retained by a retainer 16. The rolling bearing 10 further includes seal members 18 each closing the respective open ends of the bearing space 17 defined between the outer race 11 and the inner race 13.
The rolling bearing 10 is not limited to a sealed deep groove ball bearing. For example, the rolling bearing 10 may be a cylindrical roller bearing.
As illustrated in
The knurling is straight knurling such that each recess 21 has a V-shaped section taken along a plane perpendicular to the center axis of the rolling bearing 10, and a depth h (see
As illustrated in
As illustrated in
As illustrated in
The pulley body 30 is molded on the radially outer surface of the outer race 11 by injection molding. During molding, as illustrated in
The annular ribs 35 axially engage the outer side surfaces of the respective annular grooves 19, thus preventing relative axial movement between the outer race 11 and the pulley body 30. The protrusions 36 circumferentially engage the projections 22 to prevent creep between the outer race 11 and the pulley body 30.
In the embodiment, since the pair of annular grooves 19 are formed in the radially outer surface of the outer race 11, and knurling by rolling is applied to the radially outer surface of the annular protrusion 20 formed between the pair of annular grooves 19, when teeth of a knurling tool are pushed into the annular protrusion 20 during the knurling, the annular protrusion 20 is plastically deformed such that it is partially moved into the pair of annular grooves 19, and a load applied to the annular protrusion 20 during knurling is also partially axially applied to and absorbed by the pair of annular grooves 19.
Since the annular protrusion 20 has a trapezoidal sectional shape such that its axial width is smallest at the radially outer surface and gradually and radially inwardly increases, when the teeth of the knurling tool are pushed into the annular protrusion 20, the contact area between the teeth of the knurling tool and the annular protrusion 20 gradually increases, thus preventing a sudden increase in load applied to the protrusion 20. This makes it easier to provide straight knurling by rolling on the annular protrusion 20.
Since the diameter B of the circle that contacts, from radially inwardly, the bottoms of the groove-shaped recesses 21, which are formed by knurling, is larger than the diameter A of the circular bottom of each annular groove 19, the load applied to the annular protrusion 20 when the annular protrusion 20 is plastically deformed is effectively absorbed by the pair of annular grooves 19. Thus, a radial load applied to the outer race 11 is very small, and thus, straight knurling can be formed without deforming the outer race 11. Accordingly, deep groove-shaped recesses 21 can be formed, and by the engagement between the protrusions 36 formed in the recesses 21 and the projections 22 by the straight knurling, it is possible to reliably prevent creep between the outer race 11 and the pulley body 30.
In
In
Since any of the annular protrusions 20 illustrated in
Number | Date | Country | Kind |
---|---|---|---|
2015-154104 | Aug 2015 | JP | national |
Filing Document | Filing Date | Country | Kind |
---|---|---|---|
PCT/JP2016/071124 | 7/19/2016 | WO | 00 |