A continuously variable transmission having such pulley sets is known from EP- A-582307. The screw mechanisms of the pulley sets are controlled by means of a common, single motor, which is offset with respect to said screw mechanisms. The motor engages the screw mechanism through a number of intermediate gear wheels and auxiliary shafts.

As a result, this prior art continuously variable transmission unit is complicated, and therefore prone to malfunction. Moreover, its overall dimensions are rather large.

The object of the invention is to provide a pulley set for a continuously variable transmission, which does not have these disadvantages. This object is achieved in that said control means comprises a motor unit, said motor unit comprising a stator and a rotor, one of said stator and rotor engaging the nut of the screw mechanism, and the other of said stator and rotor engaging the screw of the screw mechanism.

The pulley set according to the invention may have its own motor unit. This allows a rapid and independent control of the gap of the pulley set. As a result, the pinching force exerted by the discs on the belt can be regulated as required, in particular in order to avoid slip. Also, a rapid transmission ratio change is made possible.

In case the screw mechanism is static in relation to the nut, the screw mechanism and the nut have the same rotational speed. The transmission ratio is then constant, and the motor keeps the screw mechanism, and thus the discs of the pulley set, in a static position. That is, the discs enclose a gap which remains of constant width.

Upon a relative rotation between the rotor and the stator of each motor, a change in said gap is generated due to the action of the screw mechanism.

The required reduction between the motor and screw mechanism is preferably obtained by means of at least one satellite gear wheel system. For instance, each control means may comprise two linked satellite gear wheel systems, one of which connects

the rotor or the stator to the nut, and the other of which connects the other of said rotor or stator to the screw, said satellite gear wheel systems each comprising a ring gear wheel, a sun gear wheel and satellite gear wheels.

The pulley set having two linked satellite gear wheel systems may be carried out in several ways.

According to a first embodiment, the ring gear wheels are connected to the stator respectively to the rotor, and each satellite gear of one satellite gear wheel system is connected to a satellite gear wheel of the other satellite gear wheel system.

According to a second embodiment, the sun gear wheels are connected to the stator respectively to the rotor, and each satellite gear wheel of one satellite gear wheel system is connected to a satellite gear wheel of the other satellite gear wheel system.

According to a third embodiment, the ring gear wheels are connected to the stator respectively tot he rotor, and the sun gear wheels are connected to each other.

According to a fourth embodiment, the sun gear wheels are connected to the stator respectively to the rotor, and the ring gear wheels are connected to each other.

According to a fifth embodiment, the satellite gear wheels of each satellite gear wheel system are accommodated on a respective carrier, said carriers being connected to the stator respectively to the rotor, and the sun gear wheels are connected to each other.

According to the sixth embodiment, the satellite gear wheels of each satellite gear wheel system are accommodated on a carrier, said carrier being connected to the stator respectively to the rotor, and the ring gear wheels are connected to each other.

The gear ratios of the satellite gear wheel systems should be identical.

Preferably, the satellite gear wheel systems are coaxial and have coaxial ring gear wheels and coaxial sun gear wheels.

The diameters of the ring gear wheels can be identical. Also, the diameters of the sun gear wheels can be identical, and the diameters of the satellite gear wheels can be identical.

The sun gear wheel of a satellite gear wheel system may be connected to the shaft, and the ring gear wheel of a satellite gear wheel system may be connected to the shaft. Also, the carriers for the satellite gear wheels may be connected to the shaft.

Preferably, an electric motor is applied in the control means, which may be concentric with relation to the pulley set.

The invention also relates to a continuously variable transmission comprising two pulley sets according to any of the preceding claims, and an endless belt stretching between said sets and accommodated in the grooves thereof.

The invention will be explained further with reference to the embodiment of the pulley sets shown in the figures.

Figure 1 shows the first embodiment of the pulley set according to the invention.

Figure 2-6 show further embodiments.

The pulley set in figure 1 comprises two discs 1,2, mounted on a shaft 3. In the embodiment shown, disc 1 is fixedly connected to shaft 3, whereas disc 2 is slidably, but non-rotatably through groove/ball connection 4, accommodated on the shaft 3.

The discs 1,2 enclose a V-shaped groove 5, the width of which can be varied upon shifting the slidable disc 2.

To that end, the discs 1,2 are connected to a screw mechanism 6, the action of which is controllable by means of control means 7. In particular, the screw 8 of the screw mechanism 6 is connected to slidable disc 4 by means of a yoke 9. This yoke 9 has legs 10 which protrude through holes 11 which are arranged in the wall 12 of screw mechanism housing 13 which accommodates the screw mechanism 6.

The screw mechanism housing 13 is connected to the support shaft 3 and thereby to the fixed disc 1. Within the screw mechanism housing 13, the nut 14 of the screw mechanism 6 is rotatably fixed in axial direction, supported by means of bearing 15. The nut 14 and the screw 8 engage each other through grooved rollers 16.

Alternatively, balls may be applied instead of grooved rollers.

According to the invention, the nut 14 is accommodated in a sleeve 17, which is connected to a first sun wheel 18.

This first sun wheel 18 forms part of a first satellite gear wheel system 19, which further comprises a number of satellite gear wheels 20 and a ring gear wheel 21. In turn, the ring gear wheel 21 is connected to the rotor of electric motor 23, which electric motor 23 furthermore comprises a stator 24.

The screw mechanism housing 13 is connected to a second sun wheel 25, which forms part of a second satellite gear wheel system 26. This second gear wheel system 26 furthermore comprises a second satellite gear wheel 27, as well as a second ring gear wheel 28. This second ring gear wheel 28 is connected to the stator housing 29, which carries the stator 24 of the motor 23.

The satellite gear wheel 20 and second satellite gear wheel 27 form pairs, which are mutually rotatable and interconnected by means of rods 30.

The stator housing 29 is rotatably supported with respect to the screw mechanism housing 13 by means of a bearing 31. Furthermore, the stator housing 29 is rotatably supported, by means of bearing 32, to the first ring gear wheel 21.

In service of the pulley set in a continuously variable transmission unit, and in the case of a constant width of the V-shaped groove 5, the screw mechanism housing 13 rotates at the same rotational speed as the shaft 3, the motor housing 29 is stationary.

The motor 23 acts to as to keep the nut 14 and the screw 8 in a fixed relative position, by making the rotor 22 stand still.

Upon changing the width of the groove 5 however, the motor 23 is activated in such a way that the rotor 22 is rotated with respect to the stator 24. As a result, the satellite gear wheels 20,27 make the sun gear wheel 18 rotate with respect to the sun gear wheel 25, whereby the nut 14 is rotated with respect to the screw. The screw mechanism 13 thus makes the disc 2 move towards or from fixed disc 1.

The embodiment of figure 2 to some extent corresponds to the embodiment of figure 1. However, the rotor 22 now is connected to the sun wheel 18 of the first satellite gear wheel system 33.

The ring gear wheel 21 of this system 33 is connected to the screw mechanism housing 13 and to the shaft 3.

The ring gear wheel 21 and the sun gear wheel 18 engage each other by means of the first satellite gear wheels 20.

The sun gear wheel 25 of the second satellite gear wheel system 26 is connected to the motor housing 29 through an axle stub 34. The ring gear wheel 28 of this second system 26 is connected to the sleeve 35 which accommodates the nut 14.

The sun gear wheel 34 and the ring gear wheel 28 of the second system 26 engage each other through the second satellite gear wheels 27.

The screw 8 and the nut 14 engage each other through the grooved rollers 16.

By means of bearing 37, motor housing 23 is rotatably supported with respect to screw mechanism housing 13. The sun gear wheel 18 of the first satellite gear wheel system 33 is supported with respect to the axle stub shaft by means of bearing 32.

The satellite gear wheels 20 and 27 of the first and second systems 33,26 are mutually rotatable, but connected to each other through rods 30.

The embodiment of figure 3 also comprises two satellite gear wheels systems 19,26, the sun gear wheels 18,25 of which are interconnected. The rotor 22 of the motor 7 is connected to the ring gear wheel 21 of satellite gear wheel system 19, the stator 24 is connected to the ring gear wheel 28 of satellite gear wheel system 26.

The satellite gear wheels 20 are carried by a carrier 40, which through shaft 41 is connected to the sleeve 14.

Also, satellite gear wheels 27 are carried by carrier 42, which is connected to screw mechanism housing 13.

In the embodiment of figure 4, the outer ring gears 21,25 are interconnected, whereas sun gear wheel 18 is connected to the rotor 24 motor 7, and sun gear wheel 25 through shaft 34 is connected to the stator of said motor. The satellite gear wheels 20, 27 are mounted in respective carriers 40,42, which in turn engage the screw 18 respectively the nut 14 and sleeve 17.

In the embodiment of figure 5 the carrier 40 of the satellite gear wheels is connected to the rotor 24 of the motor 7. The carrier 42 of the satellite gear wheels 27 through shaft 43 is connected to the stator 22 of said motor.

The sun gear wheels 18,25 are interconnected, whereas ring gear wheel 21 engages the screw 18 of the screw mechanism, and sun gear wheel 28 engages the nut 14 with sleeve 17.

In the embodiment of figure 6, the outer rings 21,28 are interconnected. The carriers 40,42 are connected to the rotor 24 respectively to the stator 22.

The sun gear wheels 18,25 are connected to the nut 14 with sleeve 17, respectively to the screw 18.

Although in the embodiments shown one of the pulley discs is fixed and one pulley disc is slidable with relation to the shaft, the invention is also related to pulley sets wherein both pulley discs are slidable with relation to the shaft (symmetrical movement).