WO2007012168A1

WO2007012168A1 - Pulley with a one-way clutch

Info

Publication number: WO2007012168A1
Application number: PCT/BR2006/000151
Authority: WO
Inventors: Rodrigo Marge Pagnozzi; Hylário ZEN; André Luiz ZEN
Original assignee: Zen S/A Industria Metalúrgica
Priority date: 2005-07-27
Filing date: 2006-07-26
Publication date: 2007-02-01

Abstract

The present free-wheel pulley comprises a shaft (10) externally presenting a cylindrical surface (12) and which is coupled to a load to be rotatively driven, such as a vehicle alternator. An outer ring (20) is mounted around the shaft (10) and defines an outer profile (21) to be operatively coupled, generally through a belt, to an engine, and defining internally, a plurality of cam surfaces (22) which form, with the cylindrical surface (12) of the shaft (22), wedge-like spaces (E). A roller (30) is mounted in each of said spaces (E) and maintained seated on the cylindrical surface (12) of the shaft (10) and on each respective cam surface (22) of the outer ring (20), each roller (30) being forced by a respective spring toward a narrower end of said space (E) so that each roller (30) rotatively couples the outer ring (20) to the shaft (10) when the rotation of the outer ring (20) is superior to the rotation of the shaft (10).

Description

PULLEY WITH A ONE-WAY CLUTCH Field of the Invention

The present invention relates to a pulley provided with a free-wheel system, that is, a one-way clutch, to be used, for example, in alternators operatively coupled to the crankshaft of internal combustion engines through a belt-pulley transmission. The pulley of the present invention is designed to reduce the torsional vibrations and the rotation variations that are transmitted to the alternator. Background of the Invention

The alternator pulley has the function of transmitting the torque of the internal combustion engine to the alternator, by means of a belt, that passes through a pulley affixed to the engine crankshaft. The friction between the belt and the pulleys transmits the torque to the pulley coupled to the rotor shaft of the alternator. The alternator pulleys, which are fixedly coupled (with no free-wheel system) , usually by keys or by friction, to the rotor shaft of the alternator, have had a significant technological progress with the introduction of the free-wheel system (overrunning) in the coupling of the pulley with the rotor shaft of the alternator. The alternator pulley with a free-wheel system allows the torque transmission only in one direction. In the beginning, said system was conceived to avoid vibrations resulting from the acyclic operation of the internal combustion engines of vehicles, thereby minimizing the noise generated by the relative movement (slip) between the belt and the alternator pulley. Moreover, said free-wheel system is designed to prevent the alternator from being re- accelerated every time a deceleration of the engine occurs. Since the alternator rotor has a high inertia, said rotor can be maintained in a rotation above the rotation of the engine when the latter is quickly- decelerated and then re-accelerated. This leads to fuel economy, minimizes the noise, minimizes the abrasive wear of the belt coupled to the pulley and minimizes the forces on the mechanical components coupled to the belt.

There are patent documents with different free-wheel systems, each adopting a different principle. Among the patents that use said system one can mention patent US 6,394,250, which describes a free-wheel system, in which the came surfaces are formed in an inner ring affixed to the pulley shaft of the alternator and which is responsible for the action of coupling and releasing the pulley in relation to the alternator shaft. The system uses rolling bearings to provide the rotation of the shaft in relation to the outer ring of the pulley, and the circumferential drag of the rollers during the disengagement is made by the outer ring of the alternator pulley. Patent US 6,093,991 discloses another system, in which the cam surfaces are also located in the inner ring of the pulley, affixed to the alternator shaft and using ball bearings. The circumferential drag of the rollers during the disengagement is made by the outer ring of the alternator pulley.

The system of US patent 6,083,130 differs from the above described by using springs for locking the pulley outer ring to the alternator shaft. The main focus of the above described patents is to reduce the torque, which is necessary for the system to freewheel because, by minimizing said torque, the alternator is braked with a slower force during the deceleration of the engine. This arrangement makes the alternator remain more time in a high rotation, decoupled from the engine. Furthermore, a lower free- wheel torque makes the pulley more efficient at eliminating noises, as said pulley becomes more sensitive to eliminate vibrations of high frequency and low amplitude. In these pulleys cited above, the static free-wheel torque is equal to or higher than the dynamic torque, i.e., in the whole operative rotation range of the alternator, which is from 0 rpm to 20.000 rpm, the centrifugal force does not alter the torque required for the system to freewheel . As disclosed in patent US 6,394,250, the inner and outer rolling races of the roller are mounted by interference in the pulley with a free-wheel system. Therefore, when the torque is transmitted, a relative movement may occur between the external part of the pulley (in which is located the groove presenting the belt profile) and the outer ring (external race) . The same may occur between the shaft of the free-wheel system (which is affixed to the alternator shaft) and the inner ring (inner race) . Thus, the belt torque will not be fully transmitted to the alternator, since slip will occur between the components.

The alternators are generally located in the front part of the engine, leaving the pulley exposed to dust and mud, which are thrown directly to said pulley. In relation to this, the invention described in the patent publication US 6,394,250 presents deficiency in the sealing of the free-wheel system. In the case the free-wheel system is contaminated by dust or mud, the free-wheel function becomes impaired, locking the pulley.

Summary of the Invention

The pulley object of the present invention has the purpose of improving the free-wheel system provided in the alternator of the automobile engines, solving the above described problems and improving the durability of the free-wheel pulley. The constructive solution of the present invention differs from those of the prior art, by the provision of a free-wheel system that uses a plurality of cam surfaces internally formed in an outer ring which defines a single piece with the outer profile of the pulley, i.e., said outer profile and the cam surfaces constitute a single piece presenting a constructive arrangement such that the centrifugal force actuates minimizing the free-wheel torque as rotation increases. Operating against the cam surfaces, there are provided rollers that are seated against an inner ring incorporated to a pulley shaft. The rollers are responsible for the coupling and disengaging of the pulley in relation to the shaft . The embodiment disclosed herein improves the functionality of the free-wheel system. The cam surfaces incorporated to the outer ring of the pulley and not to the shaft make the dynamic torque in the pulley be lower than the static torque, due to the centrifugal force actuating in the assembly, forcing the rollers against respective positioning springs. The free-wheel torque in high rotation, which is lower than the static torque, optimizes the yield of the alternator, since the lower the free-wheel torque, the lower will be the braking force actuating on the alternator when it is being decelerated, causing the alternator to remain more time in a high rotation and minimizing the vibration resulting from the acyclic operation of the engine. The present pulley can further present a construction using a cage to maintain the rollers joined to the springs, facilitating the assembly of the component parts of the pulley.

The construction proposed by the invention, according to which the cam surfaces, the outer ring and the outer profile of the pulley are formed in a single piece, prevents the free-wheel pulley from being affected by thermal variations of the environment

(since the mounting interference can be impaired with temperature variation) , assuring the engine torque to be fully transmitted to the alternator, i.e., eliminating the relative movement between the outer ring and the outer profile of the alternator pulley.

Furthermore, this construction of the outer ring in a single piece simplifies the manufacture of the pulley, eliminating assembly steps and increasing the strength of the pulley.

Brief Description of the Drawings The invention will be described below, with reference to the enclosed drawings, given by way of example of embodiments of the invention and in which: Figure 1 is a front view of the present pulley illustrating the pulley shaft, the rollers and their respective positioning springs, the outer ring with the cam surfaces and the outer profile of the pulley;

Figure 2 shows a detail of figure I₁ illustrating, schematically, the forces actuating on the rollers and springs of the pulley upon using the free-wheel system; Figure 3 is a front view of the single piece that comprises the outer ring of the pulley with its cam surfaces, and with the outer profile of the pulley further illustrating the travel of one of the rollers; Figure 4 is a view similar to that of figure 3, but further illustrating the provision of a cage for the rollers and the positioning of the springs; Figure 5 is a perspective view of the assembly of figure 3, when provided with the rollers and the respective springs,- Figure 6 is a perspective view similar to that of figure 5, but further illustrating the provision of a cage for containing the rollers and springs; Figure 7 is a perspective view of the present pulley with its component parts already mounted; Figure 8 is a diametral sectional view of the freewheel pulley illustrated in figure 1;

Figure 9 is a diametral sectional view of the freewheel pulley illustrated in figure 8, but provided with a cage for both the rollers and the springs; Figure 10 is an exploded perspective view of the freewheel pulley illustrated in figure 8;

Figure 11 is an exploded perspective view of the freewheel pulley illustrated in figure 9; and Figure 12 is a graph showing the variation of the rotation obtained in a testing bench with a pulley presenting a free-wheel torque of 0,1 N.m and another pulley presenting a free-wheel torque of 0,2 N.m, in relation to the alternator rotation. Detailed Description of the Invention As illustrated in the drawings and as mentioned above, the present free-wheel pulley is particularly appropriate to be mounted to the rotor shaft of an automobile alternator (not illustrated) , so as to permit a one-way coupling, through a belt, between the rotor shaft of the alternator and the driving shaft of an engine, generally the crankshaft of an internal combustion engine of a vehicle.

The present pulley P comprises a generally tubular shaft 10 constructed in any adequate material, such as steel, having one of the ends usually provided with inner splines 11 and presenting, externally and medianly, a cylindrical surface 12, which is smooth and continuous in the axial and circumferential directions. The mechanical coupling of the pulley P with the rotor shaft of the alternator can be executed by providing an inner thread 13 in the shaft 10, so as to engage thereto an outer thread provided in the rotor shaft of the alternator. Since the pulley P transmits torque only in the tightening direction of the thread, this connection becomes simple and reliable. In order to mount and dismount said pulley in relation to the alternator shaft, a tool is connected to the inner splines 11 of the shaft 10. It should be understood that other mounting arrangements could be used for obtaining a coupling to rotationally lock the shaft 10 of the pulley P to the alternator shaft .

The shaft 10 has its cylindrical surface 12 defined in a median portion 10a with a larger diameter and disposed between opposite end portions 10b with a smaller diameter.

Around the shaft 10 is mounted an outer ring 20 also constructed in any adequate material, such as steel, and which is externally and circumferentially configured to define an outer profile 21 for fitting at least one belt (not illustrated) . It should be understood that the design of the outer ring 21 will be determined by the profile and number of belts to be used to provide the torque transmission from the internal combustion engine to the alternator.

The outer ring 20 is defined in a single piece presenting not only the outer ring 21 but also, internally, a plurality of cam surfaces 22, angularly spaced from each other and which form, with the cylindrical surface 12 of the shaft 10, wedge-like spaces E (figure 1) .

In each of the wedge-like spaces E is mounted a roller 30, which is dimensioned to be displaced as a function of the operating regime imposed to the pulley P by the engine, between an inoperative position, in which said roller is seated with reduced friction onto the cylindrical surface 12 of the shaft 10 and onto the respective cam surface 22, and an operative position (illustrated in figure 1) , in which said roller is seated with high friction onto both said cylindrical surface 12 and cam surface 22.

The pulley P further comprises a plurality of generally helical springs 40, each mounted in a respective wedge-like space E, in order to force the respective roller 30 toward a narrower end of said space E, i.e., toward the operative position, for rotatively coupling the outer ring 20 to the shaft 10 when the rotation of the outer ring 20 is superior to the rotation of the shaft 10. As it can be noted, the present constructive solution is of the type in which the torque transmitted from the outer ring 20 of the pulley P to the shaft 10 of the latter is made by the friction of the rollers 30 with said parts of the pulley P. When the rotation of the outer ring 20 is higher than the rotation of the shaft 10, the rollers 30 are displaced through the cam surface 22 toward the narrower end of the respective space E, where the radial distance between the cylindrical surface 12 and the cam surface 22 is shorter, pressing the rollers 30 against said surfaces, rotatively locking the outer ring 20 in the shaft 10.

When the rotation of the vehicle engine is reduced, the rotation of the outer ring 20 of the pulley P is correspondingly reduced, while the rotation of the shaft 10 coupled to the alternator shaft tends to maintain, by inertia, the higher initial rotation. In this condition, the rotation of the shaft 10 is higher than the rotation of the outer ring 20, making the cylindrical surface 12 of the shaft 10 drag the rollers 30, by friction, toward the inoperative position, close to the radially larger end of the spaces E, rotatively disengaging the shaft 10 from the outer ring 20 and allowing the pulley P to free-wheel (overrunning) .

In the inoperative condition, the rollers 30 remain in contact with the cylindrical surface 12 of the shaft 10 and with the respective cam surfaces 22 of the outer ring 20, said contact being made with reduced force insufficient for rotatively locking the two parts of the pulley P, allowing the rollers 30 to slip in relation to the cylindrical surface 12 and the cam surface 22. The contact force results from the friction force of the shaft 10 in relation to the rollers 30 jointly with the centrifugal force Fc. This centrifugal force Fc, which actuates on the rollers 30, actuates in the disengaging direction and against the force of the springs 40. The force of the springs 40 actuates upon the rollers 30 in the disengaging direction, maintaining the rollers 30, the cam surface 22 and the cylindrical surface 12 always in contact, so as to permit the re-coupling to occur as soon as the rotation of the outer ring 20 is equaled to the rotation of the shaft 10, i.e., the elastic constant of the spring is calculated from the maximum rotation in which the alternator is operating, and as follows: V= (n.r.π) (1) 30 and Fc= m.V² (2) r

In which:

V = maximum tangencial velocity of the rollers; n = angular velocity of the rollers; Fc = centrifugal force applied to the roller; m = roller mass; r = radius of displacement of the rollers in relation to the pulley center.

The force actuating on the spring in a given rotation may be defined by decomposing the centrifugal force Fc.

As illustrated in figures 8, 9, 10 and 11, the outer ring 20 has its cam surfaces 22 defined in a median circumferential region 20a, said outer ring 20 presenting, also internally, circumferential end regions 20b opposite to each other and which are configured to be seated around the outer race of the respective rolling bearings 50, whose inner races are seated and retained around respective opposite end portions 10b of the shaft 10.

The pulley P further comprises a pair of thrust washers 60 disposed between each rolling bearing 50 and the adjacent side of the cam surfaces 22 in order to maintain the rollers 30 and the springs 40 correctly positioned in the pulley P and avoid the contact of the ends of the roller 30 with the sealing elements of the rolling bearings 50 and the leak of the lubricant agent . There are further provided 'deflecting washers 70, each mounted to an end of the outer ring 20, to axially retain the adjacent rolling bearing 50 in the pulley P and to prevent debris from directly reaching the sealing elements of the rolling bearings 50, increasing the strength and efficiency of the sealing system of the moving parts. In order to minimize the abrasive wear of the movable components, grease is added to the contact region of the rollers 30 with the cam surfaces 22 of the outer ring 20. During the coupling operation of the components of the pulley P, when the rotation of the outer ring 30 of the pulley P is higher than the rotation of the shaft 10, the rollers 30 are dragged to the coupling operative condition, so that the friction between the cam surfaces 22 and the rollers 30, as well as the friction between the rollers 30 and the cylindrical surface 12 of the shaft 10 are sufficient to avoid the relative movement between the components, resulting in a correct coupling. During the disengagement operation, or when the mechanism begins to operate in free-wheel system, the rotation of the shaft 10 is higher than the rotation of the outer ring 20, making the rollers 30 move along the cam surfaces 22, so as to minimize the friction force existing between the rollers 30 in relation to the shaft 10 and the outer ring 20. The circumferential drag of the rollers during the disengagement is made by the shaft 10. In order to minimize the friction force between the components that effect the coupling, the rollers 30 must overcome the force of the springs 40, which is achieved by the centrifugal force Fc jointly with the drag of the rollers 30 executed by the shaft 10. With the displacement of the rollers 30 along the cam surfaces 22, the shaft 10 rotates freely and the coupling between the outer ring 20 and the shaft 10 ceases to exist, characterizing therefore the freewheel state or overrunning of the pulley. As it can be noted in figure 2, during the disengagement of the pulley, the centrifugal force Fc provided by the rotation of the mechanism, makes the rollers 30 actuate against the spring forces Fm. The higher the rotation of the system, the higher the action of the centrifugal force Fc on the rollers 30 and, consequently, the lower the torque for disengaging the shaft 10 of the outer ring 20, resulting in a free-wheel torque obtained in a high rotation inferior to the static free-wheel torque. The dynamic torque has values around 0,lN.m, while the static torque presents values around 0,2N.m. Figure 12 illustrates the curve of rotation of the outer ring 20 in full lines and the curve of rotation of the shaft 10 in dashed lines, showing the difference of the rotation obtained in a deceleration and acceleration test for an alternator with a pulley- having a constant free-wheel torque 0,2N.m and for another alternator having a pulley according to the present invention, the dynamic torque being 0,lN.m. This allows optimizing the yield of the alternator, since the lower the free-wheel torque, the lower the braking force on the rotor when it is being decelerated, making the rotor remain in a higher rotation. However, it should be emphasized that this free-wheel torque cannot be reduced to zero, as the contact between the rollers 30, the shaft 10 and the cam surfaces 22 should always exist to permit the re- coupling to occur in the instant in which the rotation of the outer ring is superior to the rotation of the shaft 10. As demonstrated above, the spring constant is calculated so as to assure the force of the spring 40 is sufficiently high to maintain the contact between the rollers 30, the shaft 10 and the cam surfaces 22, even in high rotations.

The free-wheel pulley of the present invention can be constructed by seating the springs 40 directly onto the outer ring 20 or by using a cage 80 to facilitate the mounting of the pulley. The cage 80, preferably molded in plastic material, resistant to high temperatures, presenting annular shape and disposed internally to the outer ring 20, allows mounting the springs 40 and the rollers 30 to the outer ring 20 more easily. The sealing -of the pulley, aiming at avoiding the grease leakage, is made through the sealed rolling bearings 50. The outer part of the pulley is electrochemically covered for protection against corrosion. Besides the sealing elements to prevent the grease from leaking as well as the admission of debris from the external environment, an internal sealing is provided between the balls of the rolling bearings 50, by the rolling bearing 50 itself and by the thrust washer 60, in order to prevent the material resulting from the wear of each component from mingling with the grease, causing premature abrasive wear.

The life span of the free-wheel arrangement of the pulley is limited to the travel of displacement C of the roller 30 on the cam surface 22, as it can be seen in figure 3. Aiming at increasing said life span and, consequently, the durability of the pulley, the present invention provides a pulley with the travel C, so that : C = X . D (3]_

Where :

C = roller travel on the cam;

X = factor of proportionality, ranging from 0,12 to 0,15; D = diameter of the cylindrical surface 12 of the shaft 10.

Once defined the diameter D of the cylindrical surface 12 of the shaft 10, the equation presents the value of the travel C of the roller that should be used indicating the length of the cam surface 22 to be used for a given application. The tests carried out indicate that the values of the travel C resulting from the equation significantly increase the life span of the free-wheel. The travel C maintained with these values further helps mounting the shaft 10 to the outer ring 20 .

In order to maintain the shaft 10 mounted in the freewheel system, the cylindrical surface 12 has a diameter which is larger than that of the end portions 10b of the shaft 10, where the rolling bearings 50 are mounted. In order to compensate for alignment errors, at the time the pulley is mounted to the alternator; the shaft 10 is provided with an axial gap generated by the difference between the axial extension of the cylindrical surface 12 and the distance separating the two rolling bearings 50.

It should be understood that the present free-wheel pulley can be applied not only to vehicle alternators, but also to any system using free-wheel and presenting the operational problems described herein.

Claims

1. A pulley with a one-way clutch, characterized in that it comprises: a shaft (10) to be coupled to a load, which is rotatively driven in a certain rotation direction, said shaft externally presenting a smooth and continuous cylindrical surface (12) ; an outer ring

(20) mounted around the shaft (10) and externally defining, in a single piece, an outer profile (21) of the pulley to be operatively coupled to an engine, said outer ring (20) further defining, internally, a plurality of cam surfaces (22) which form, with the cylindrical surface (12) of the shaft (10) , wedge-like spaces (E) ; a plurality of rollers (30) each mounted in one of said wedge-like spaces (E) and maintained seated on the cylindrical surface (12) of the shaft

(10) and on each respective cam surface (22) of the outer ring (20) ; and a plurality of springs (40) , each mounted in a respective wedge-like space (E) , so as to force the respective roller (30) toward a narrower end of said space (E) , said rollers (30) rotatively coupling the outer ring (20) to the shaft (10) when the rotation of the outer ring (20) is superior to the rotation of the shaft (10) in said rotation direction.

2. The pulley, as set forth in claim 1, characterized in that the circumferential extension of each cam surface (22) , which defines the travel ^XΛC" of the respective roller (30) along said cam surface (22), is defined through the equation C = X . D, in which: C = travel of the roller (30) ;

X = proportionality factor, ranging from 0,12 to 0,15; D = diameter of the cylindrical surface (12) of the shaft (10) .

3. The pulley, as set forth in claim 1, characterized in that the springs (40) are dimensioned by determining the centrifugal force (Fc) actuating on each roller (30), according to the equations:

V = (n.r.π)

30 and

Fc= m.V² r In which:

V = maximum tangencial velocity of the rollers; n = angular velocity of the rollers;

Fc = centrifugal force applied to the roller; m = roller mass; r = radius of displacement of the rollers in relation to the pulley center.

4. The pulley, as set forth in claim 1, characterized in that the shaft (10) presents a median portion (10a) with a larger diameter and which defines the cylindrical surface (12), and two opposite end portions (10b) with a smaller diameter.

5. The pulley, as set forth in claim 4, characterized in that it further comprises a pair of rolling bearings (50) , each having its inner race seated and retained around a respective end portion (10b) of the shaft (10) , and an outer race around which is seated a respective region of the outer ring (20) .

6. The pulley, as set forth in claim 5, characterized in that the outer ring (20) has its cam surfaces (22) defined in a median circumferential regions (20a) , disposed between end circumferential regions (20b) opposed to each other and against which are seated the outer races of the respective rolling bearings (50) .

7. The pulley, as set forth in claim 6, characterized in that it further comprises a thrust washer (60) disposed between each rolling bearing (50) and the adjacent side of the cam surfaces (22) , so as to block axial displacements of the rollers (30) .

8. The pulley, as set forth in claim 6, characterized in that it further comprises a deflecting washer (70) mounted to each one of the ends of the outer ring (20), externally and adjacently to a respective rolling bearing (50) , so as to axially retain the latter in the pulley (P) .

9. The pulley, as set forth in claim 1, characterized in that the rollers (30) and the springs (40) are seated directly against the outer ring (20) .

10. The pulley, as set forth in claim 1, characterized in that the rollers (30) and the springs (40) are contained in a cage (80) mounted internally to the outer ring (20) 11. The pulley, as set forth in claim 1, characterized in that the cam surfaces (22) are disposed so as to cause the centrifugal force actuating on the rollers (30) to displace them against the force of the springs (40), reducing the friction of said rollers (30) in relation to the cylindrical surface (12) of the shaft (10) .