WO2007010566A1

WO2007010566A1 - Pulley assembly for a continuously variable transmission

Info

Publication number: WO2007010566A1
Application number: PCT/IT2005/000415
Authority: WO
Inventors: Alessio Galletti; Paolo Seta
Original assignee: Dayco Europe S.R.L. Con Unico Socio
Priority date: 2005-07-19
Filing date: 2005-07-19
Publication date: 2007-01-25
Also published as: WO2007010566A8

Abstract

Pulley assembly (1) for a continuously variable transmission of a vehicle, including a shaft (2) having an axis (A), a support element (7) revolving around the axis (A), a first half-pulley (9) rotationally connected to the support element (7), a second half-pulley (11) facing the first half-pulley (9) to define a seat (13a) adapted to house a belt (13) of the transmission, at least one of the first and second half-pulleys (9, 11) being longitudinally mobile in relation to the support element (7), and a clutch (8) to selectively couple rotationally the shaft (2) to the support element (7). The pulley assembly (1) includes in addition unidirectional coupling means (23) interposed between the support element (7) and the shaft (2) to allow the driving of the shaft (2) when the angular velocity of the support element (7) tends to exceed that of the shaft (2).

Description

"PULLEY ASSEMBLY FOR A CONTINUOUSLY VARIABLE TRANSMISSION"

TECHNICAL FIELD

The present invention concerns a pulley assembly for a continuously variable transmission.

BACKGROUND ART

A continuously variable transmission includes a first pulley assembly connected to an .internal combustion engine, a second pulley assembly connected to the wheels of the vehicle and a belt wound between the two pulley assemblies.

Each assembly generally includes a shaft connected to the engine or to the wheels, a support element driven by the shaft, and a pair of half-pulleys rotationally connected in a rigid manner to the support element and mobile with regard to each other along the rotatable support element to define the transmission ratio.

According to the different configurations of the transmission, one of the two pulley assemblies further includes a clutch to selectively couple the shaft to the support element to allow the drive of the half-pulleys.

Continuously variable transmissions are used on board scooters and, thanks to the increase in the transmittable power, also on board other vehicles such as three or four-wheel vehicles or on snowmobiles.

However, the driving methods for a four-wheel vehicle are different to those of a scooter and, in particular, the need is felt to be able to fully exploit "he engine brake.

DISCLOSURE OF INVENTION The aim¹ of the present invention is therefore to allow effective utilization of the engine brake in continuously ■variable transmissions.

The aim of the present invention is achieved by a pulley assembly for a continuously variable transmission as defined in claim 1.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention a preferred embodiment is now described, by way of an illustrative and non-limiting example, with reference to the enclosed design in which:

- figure 1 is an axial section of a pulley assembly according to the present invention; and

- figure 2 is a left lateral view of figure 1 (not to scale) .

BEST MODE FOR CARRYING OUT THE INVENTION

In figure 1 a pulley assembly for a continuously variable transmission is denoted by 1.

The assembly 1 includes a coupling shaft 2 rotating around an axis A and having an end portion 5 adapted to be rigidly connected to a driving shaft of an internal combustion engine

(not shown) , a ball bearing 3 and a freewheel support • 4 disposed on the coupling shaft 2 and a sleeve 7 supported coaxially on the coupling shaft 2 by the ball bearing 3 and the freewheel support 4.

In addition, the pulley assembly 1 includes on the opposite side of the end portion 5, a centrifugal clutch 8 to rotationalIy connect an end portion 6 of the coupling shaft 2 to the sleeve 7, a fixed half-pulley 9 rigidly connected to an end portion 10 of the sleeve 7 axially opposite to the centrifugal clutch 8, and a mobile half-pulley 11 slidable on the sleeve 7 between the fixed half-pulley 9 and the centrifugal clutch 8. The fixed and mobile half-pulleys 9, 11 define a seat 13a which houses a belt 13 to transfer the power from the engine to a driven pulley assembly (not illustrated) connected to the wheels, and the axial position of the mobile half-pulley 11 is automatically set by a centrifugal control device 14 depending on the angular velocity of the sleeve 7 to vary the transmission ratio according to known methods.

In greater detail, the coupling shaft 2 has a longitudinal through hole 15 and defines, at the end portion 5, a conical seat 16 coaxial to the axis A and housing a corresponding coupling portion of a flange 17 adapted to be connected to the internal combustion engine and locked to the coupling shaft 2 by a screw 18 housed in the through hole 15.

Adjacent to the end portion 5 towards the centrifugal clutch 8, the coupling shaft 2 defines a support surface 19 for the freewheel support 4 which includes a cylindrical casing 20 rigidly connected to the sleeve 7 and two roller cages 22 housed inside the casing 20.

The freewheel support 4 besides includes, integrated within the casing 20, a freewheel coupling 23 axially interposed between the roller cages 22. The freewheel joint 23 defines a unidirectional locking device and allows relative rotation when the coupling shaft 2 rotates faster than the sleeve 7, and the locking of the relative rotation when the speed of the sleeve 7 exceeds that of the coupling shaft 2, considering the rotation direction C indicated in figure 2 which coincides with the rotation direction of the engine and identifies a forward gear condition of the vehicle.

On the opposite side to the flange 17, the ball bearing 3 is fitted to the end portion 6 of the driven shaft 2 and is locked in an axial direction against a shoulder 24 of the coupling shaft 2 by the screw 18. The ball bearing 3 is housed inside a detachable portion 25 of the sleeve 7, for example a nut of suitable size, and defines together with the freewheel support 4 a radial support for the sleeve 7 on the coupling shaft 2.

The sleeve 7 is connected to the coupling shaft 2, in a rotationally decouplable manner, by the centrifugal clutch 8 which includes a disc support 27, a plurality of shoes 28 peripherally hinged to the disc support 27, a plurality of springs 50 to connect two adjacent shoes 28 with each other, and a drum 29 rigidly locked on the sleeve 7 by the nut 25 and housing the disc support 27.

In particular, the disc support 27 integrally includes a hub 30 which houses the end portion 6 of the coupling shaft 2 and is axially packed against the ball bearing 3 by the screw 18.

In addition, the disc support 27 defines a plurality of circumferentially equidistant holes 31, which house respective pins 32 parallel to the axis A and defining respective hinge axes B about which the shoes 28 rotate to selectively cooperate with the drum 29.

Each shoe 28 has a friction surface 33 having a curvature radius which is suitable to cooperate, under the effect of centrifugal acceleration, with an internal cylindrical surface 34 defined by the drum 29 and disposed coaxially to the axis A.

In particular, each shoe 28 has a center of gravity G in which are concentrated the inertial forces generated by the centrifugal acceleration and such center of gravity G precedes the respective pin 32, considering the direction C defining a forward ^'gear condition of the vehicle, and directed in the rotation direction of the engine. For example, in the event in which the crankshaft rotates in an anticlockwise direction, viewing from the pulley assembly towards the engine and the crankshaft is rigidly connected to the shaft 2 of the pulley assembly 1, the direction C is anticlockwise and matches the rotation direction of the crankshaft .

Reference hereafter will be made to such assembly of the shoes 28, in the description and in the claims, as to an assembly "in the leading direction".

In addition, the curvature of the friction surfaces 33 and the position of the axes B are preferably devised in a way that a line of action of the friction forces between the shoe 28 and the drum 29 is interposed between the relative axis B and the internal cylindrical surface 34, thus obtaining an effect which will be better described as follows.

When set in rotation by the shoes 28, the drum 29 drives the centrifugal control device 14 which includes a guide element 35 rigidly connected to the drum 29 and a plurality of mobile rollers 36 housed^' inside a space 37 delimited on one side by the guide element 35 itself and on the other by the mobile half-pulley 11.

The mobile rollers 36 are housed in special radial slots (not illustrated) carried by both the guide element 35 and by the mobile half-pulley 11 and thus make the sleeve 7 circumferentially integral with the mobile half-pulley 11.

In addition, the pulley unit 1 is provided with a spring 38 cooperating axially with the guide element 35 and a detachable support 39 connected to the mobile half-pulley 11 and cooperating with the spring 38 to distance the half-pulley 11 from the fixed half-pulley 9.

In particular, the detachable support 39 includes a cylindrical wall 40 having an axial end portion rigidly connected to a peripheral portion 41 of the mobile half-pulley 11. The detachable support 39 extends towards the centrifugal clutch 8 and houses the guide element 35 and has a radial rim 42 disposed at an opposite end with respect to the mobile half-pulley 11 and defining a stop facing the axis A for the spring 38, which is housed inside the cylindrical wall 40 between the radial rim 42 and a ring-shaped seat 43 facing the centrifugal clutch 8 of the guide element 35.

The operation of the pulley assembly 1 is as follows.

When the internal combustion engine is stationary or idling, the pulley assembly 1 is in an opening position in which the spring 38 keeps the half-pulleys 9, 11 apart thus defining a transmission ratio of maximum reduction which proves suitable for the pickup.

Following the acceleration of the engine, the coupling shaft 2 is rotationally driven and rotates inside the sleeve 7 which still remains stationary.

The coupling shaft 2 continues to accelerate exceeding a clutch threshold beyond which the shoes 28 open against the action of springs 50 and come into contact with the internal cylindrical surfaces 34 of the drum 29 while pushed by an approach force generated by the centrifugal acceleration.

The sleeve 7 and the half-pulleys 9, 11 are therefore friction driven and, during running, the transmission ratio is varied by the rollers 36 which are operated by the centrifugal acceleration and move radially on the guide element 35 pushing the mobile half-pulley 11 towards the fixed half-pulley 9 against the action of the spring 38.

During running, an engine brake condition can also occur, in which the half-pulleys 9, 11 exert a driving torque on the coupling shaft 2 and the internal combustion engine resists such torque by slowing the vehicle.

During the engine brake condition, the rotation direction does not change but the torque is inverted and initially the half- pulleys 9, 11 tend to surpass the angular velocity of the coupling shaft 2.

Such effect is however prevented by the freewheel joint 23 of the freewheel support 4 which acts essentially instantaneously, thus stopping the relative rotation between the driven shaft 2 and the half-pulleys 9, 11 and continuing to pull the pulley assembly 1 at an angular .velocity determined by the speed of the vehicle and the transmission ratio.

In this way the pulley assembly 1 allows continuous spanning of the transient state towards the engine brake state, thus avoiding annoying acceleration which would be produced if the half-pulleys 9, 11 were able to surpass the speed of the engine .

In addition, the centrifugal clutch 8 is kept at high angular velocities which allow the drum 29 to be driven by the shoes 28 at least during an initial phase of the engine brake condition.

In order to keep the centrifugal clutch 8 engaged as long as possible during the engine brake condition, the spring 38 contributes in rapidly distancing the fixed and mobile half- pulleys 9, 11 to reaching the minimum transmission ratio. Such ratio multiplies the number of revolutions of the half-pulleys 9, 11 in relation to the wheels of the vehicle thus keeping the pulley assembly 1 at a high angular velocity also at a relatively low vehicle speed and thus increasing the centrifugal acceleration. In order to keep the centrifugal clutch 8 engaged as long as possible, besides, the shoes 28 are assembled on the disc support 27 in a leading direction. In fact, during the engine brake condition, the resultant of the friction forces acting on each shoe 28 is directed towards the relative axis B and therefore generates a torque which tends to keep the shoe 28 against the drum 29, since the line of action lies between the axis B and the internal cylindrical surfaces 34. Such torque is added to the centrifugal force acting on the shoe 28 thus defining an approach force which is less sensitive to the angular velocity of the coupling shaft 2. In this way, the centrifugal clutch 8 remains engaged for a greater range of speed compared to that attainable by a clutch whose shoes are assembled in the opposite or trailing direction, as occurs for example in scooters.

During a pickup phase, however, the resultant of the friction forces is directed from the opposite side of the relative axis B compared to the center of gravity G and influences in a negligible way the approach force which, in the pickup phase, is mainly generated by the centrifugal acceleration. In this way, the centrifugal clutch 8 engages with initial slippage and the pickup is more gentle and suitable for the driving of a four-wheel vehicle, particularly during parking manoeuvres.

Finally, should the engine brake condition be prolonged with an angular velocity being reached which is less than the disengagement threshold, the centrifugal clutch 8 opens under the action of the springs 50.

As a result of the centrifugal clutch 8 being opened, the half-pulleys 9, 11 still remain connected to the driven shaft 2 by the freewheel support 4 and the speed of the vehicle can still be reduced until the driver, by accelerating, brings the number of revolutions of the coupling shaft 2 to a value that exceeds that of engagement of the centrifugal clutch 8.

In theory, the half-pulleys 9, 11 can remain drivingly connected with the coupling shaft 2 until the engine has arrived at its minimum rpm number. Nevertheless such condition corresponds to a vehicle speed that is too low and which is not achieved in practice.

An additional aspect of the functioning of the pulley assembly 1 is illustrated considering the entire transmission assembly which connects the engine to the wheels.

In particular, the pulley assembly 1 is directly constrained through the flange 17 to the internal combustion engine and drives, by the driven pulley assembly, a case including a differential gear to directly drive the wheels and a gearbox interposed between the driven pulley assembly and the differential gear and having a neurral gear, a forward gear and a reverse gear.

In this case, it is important to note how the rotation direction of the pulley assembly 1 is the same both in conditions of forward running as well as in reverse since the engine is directly connected to the shaft 2.

In neutral gear, the wheels are disconnected from the engine and it may happen that the accelerator is accidentally pressed, thus engaging the centrifugal clutch 8 and setting in rotation both the pulley assembly 1 as well as the driven pulley assembly.

As soon as the accelerator is released, the engine immediately returns to its idling state, while the pulley assemblies tend to surpass the coupling shaft 2 due to the inertia acquired and cause gear grating resulting in damage. However, the presence of the freewheel support 4 allows a concurrent deceleration, with the engine, of all of the variable ratio transmission and a subsequent smooth engagement of the forward gear .

The advantages which may be obtained with the present pulley assembly 1 are as follows.

The use of the freewheel support element 4 between ■ the coupling shaft 2 and the half-pulleys 9, 11 enables the engine brake to be used on board a vehicle endowed with the pulley assembly 1, thus preventing the occurrence of sudden and annoying acceleration during the transient state towards the engine brake condition or gearbox damage after accidental acceleration with the neutral gear.

Similarly, the assembly cf the shoes 28 in the leading direction allows the shoes 28 to remain longer against the internal cylindrical surfaces 34 of the drum 29, thereby stressing less the service brakes.

In addition, during the pickup phase, the assembly in leading direction of the shoes 28 makes the pickup softer allowing more precise manoeuvring, without sudden jerks, example while parking.

In addition, the spring 38 allows the opening position of the half-pulleys 9, 11 to be reached more rapidly thus reducing the response times of the pulley assembly during the engine brake condition.

Finally it proves evident that modifications and variations can be made to the pulley assembly 1 described and illustrated herein without departing from the scope of protection of the present invention, as defined in the enclosed claims.

In particular, it is possible that the freewheel support replaces the ball bearing 3 and that the support surface 19 guides a simple roller cage.

In addition, it is possible to envisage that the shape of the friction surface 33 is of a size so that the axis B is interposed between the internal cylindrical surfaces 34 and the line of action of the resultant of the friction forces. In this case it is possible to maintain a gentle pickup, but the interval of speed is reduced within which the freewheel support 4 and the centrifugal clutch 8 jointly transfer to the coupling shaft 2 the driving torque received from the half- pulleys 9, 11 since the centrifugal clutch tends to disengage at a higher number of revolutions.

Continuously variable transmissions have various configurations, and by way of an additional variation it is possible to envisage a configuration in which both the clutch 8 as well as the freewheel support 4 are disposed on the driven pulley assembly.

In addition, both the clutch 8 as well as the control device 14 can be of a different type to that described, for example it can be operated automatically by actuators controlled by an electronic unit.

Also the half-pulleys can be connected in various ways to the sleeve 7; in general, it is in ar.y case necessary that at least one of the two half-pulleys 9, 11 is rotationally connected to the sleeve 7.

The unidirectional locking device 23 can be made up for example of an electronically operated clutch.

In the embodiment example described herein, the forward gear condition of the vehicle corresponds to an anticlockwise rotation of the coupling shaft 2, as shown in figure 2. However, it is possible that the rotation direction of the coupling shaft 2 is clockwise in the forward running condition of the vehicle, for example since a gear reduction unit is interposed between the internal combustion engine and the pulley assembly 1. In this case, the assembly of the shoes 28 would mirror that shown, in figure 2.

Claims

1. Pulley assembly (1) for a continuously variable transmission of a vehicle, including a shaft (2) having an axis (A), a support element (7) rotatable about said axis (A), a first half-pulley (9) rotationally connected to said support element (7), a second half-pulley (11) facing said first half- pulley (9) to define a seat (13a) adapted to house a belt (13) of said transmission, at least one of said first and second half-pulleys (9, 11) being longitudinally mobile in relation to said support element (7), and a clutch (8) to selectively connect rotationally said shaft (2) to said support element (7), said pulley assembly (1) being characterized by including unidirectional coupling means (23) interposed between said support element (7) and said shaft (2) to allow the driving of said shaft (2) when the angular velocity of said support element (7) tends to exceed that of said shaft (2) .

2. Pulley assembly as in claim 1, characterized in that said support element (7) is a sleeve housing at least partially said shaft (2) and by including rotating support means (3, 4) radially interposed between said shaft (2) and said sleeve (7) .

3. Pulley assembly as in claim 2, characterized in that said unidirectional coupling means (23) are integrated in said rotating support means (4) .

4. Pulley assembly as in claim 3, characterized in that said rotating support means (3, 4) include a first and a second ball bearing (3, 4) and in that said unidirectional coupling means (23) are integrated on at least one of said first and a second ball bearing (3, 4) .

5. Pulley assembly as in any one of the previous claims, characterized in that said unidirectional coupling means (23) include at least one freewheel joint.

6. Pulley assembly as in claim 5, characterized in that said at least one of said first and second ball bearing (3, 4) includes a roller cage.

7. Pulley assembly as in any one of the previous clains, characterized in that it includes a spring element (38) cooperating with at least one of said first and second half- pulleys (9, 11) to distance said second half-pulley (11) from said first half-pulley (9)

8. Pulley assembly as in claim 1, characterized in that said spring element (38) cooperates with a fixed element (35) rigidly connected to said support element (7) and with a stop member (42) rigidly connected to a peripheral portion (41) of said second half-pulley (11) , said fixed element (35) being interposed between said stop member (42) and said second half- pulley (11) .

9. Pulley assembly as in any one of the previous claims, characterized in that said clutch (8)^' includes a second support element (27) rigidly connected to said shaft (2) and a drum (29) rigidly connected to said support element (7) and housing said second support element (27), and a plurality of friction elements (28) hinged on said second support element

(27) around respective hinge axes (B) to selectively cooperate with said drum (29) , and^' in that respective centers of gravity

(G) of said friction elements (28) precede the respective hinge axes (B) in a rotation direction of said shaft (2) which defines at least a forward gear condition of said vehicle.

10. Pulley assembly as in any one of the previous claims, characterized by including control means (14) for controlling the longitudinal position of said second half-pxαlley (11) and in that said shaft (2) includes a coupling element (17) adapted to be connected to a driving shaft of an internal combustion engine.

11. Pulley assembly as claimed in claim 10, characterized in that said control means (14) include a guide element (35) rigidly connected to said support element (7), a plurality of centrifugal elements (36) mobile on said guide element (35) and cooperating with said second half-pulley (11) to define the position of said second half-pulley (11).