Such a clutch device is known. It is applied in several fields, for instance in connection with a generator for an internal combustion engine. In case the generator is coupled to the engine through a belt drive, variations in the engine torque cause belt vibrations and hence a reduction in belt life. As a result of the one-way clutch in the clutch device however, the transmission of vibrations from the engine, e, g. due to engine acyclism, is reduced. The reverse torque resulting from such phenomena is limited, which has a favourable effect on belt behaviour.

The prior art device however has the disadvantage that it cannot be applied in combination with a combined starter and generator. The one-way clutch in fact prevents to transmit the starter torque to the engine, as it allows a free relative rotation in the drive direction of the starter. The object of the invention is therefore to provide a clutch device which can also be applied in connection with a combined starter and generator.

Said object is achieved by a means of a locking clutch for providing a fixation between the shaft and the rotation member, said locking clutch preventing mutual rotations between the shaft and the pulley in both relative rotational directions. For engine starting the locking clutch is engaged, effectively disabling the one-way clutch, allowing torque to be transmitted from the starter/generator device acting as a starter to the engine. Once the engine is started, said locking clutch can be disengaged, which then enables operation of the one way clutch, allowing the transmission of torque from the engine to the starter/generator device now acting as generator, but preventing the transmission of torque from the starter/generator device to the engine, thereby preventing belt vibration due to engine acyclism.

Preferably, the locking clutch is of an electromagnetic type. The locking clutch may comprise a first armature which is axially slidably and rotationally fixed to the

shaft or the rotation member, and a second armature which is fixedly connected to the other of said shaft and rotation member. The coupling means of these said armatures may be provided by either friction plates or meshing teeth.

According to a particular embodiment, the clutch device comprises a locking clutch for providing a fixation between the shaft and the rotation member, said locking clutch, when engaged, enabling direct torque transmission from the shaft to the rotation member, the one-way clutch being disabled.

The invention is furthermore related a belt driven starter/generator device, comprising a starter/generator provided with a housing, a stator connected to the housing, and a rotor having a rotor shaft rotatably supported with respect to the housing, as well as a clutch device as described before, said clutch device comprising a rotation member which is rotatably mounted on the rotor shaft, and a one-way clutch for providing a freely rotatable condition when the rotor shaft and the rotation member are rotated with respect to each other in a first relative rotational direction, and for providing a fixation between the rotor shaft and the rotation member when they are rotated with respect to each other in the opposite relative rotational direction, as well as a locking clutch for providing a fixation between the rotor shaft and the rotation member, said locking clutch preventing mutual rotations between the rotor shaft and the rotation member in both relative rotational detections.

Said locking clutch comprises a first armature which is axially slidably and rotationally fixed to the shaft or the rotation member, a second armature which is fixedly connected to the other of said shaft and rotation member, an electromagnetic coil connected to the housing for generating a electromagnetic flux under the influence of which the armatures are attracted towards each other as well as coupling means associated with said armatures, said coupling means engaging each other when the electromagnetic coil is energized.

The rotation member at its side facing the housing carries the second armature, and the electromagnetic coil extending next to said second armature. The electromagnetic coil is comprised of a flux carrying stator that may be U-shaped in radial cross-section, and a radially wound electromagnetic magnetic coil extending into the recess defined by the U-shaped stator.

Furthermore, the first armature and the connecting bridge of the second armature have facing surfaces which may be provided with friction plates or meshing teeth.

The invention will now be described further with reference to an example of a clutch device according to the invention.

The figure shows a clutch device 1 in combination with a starter/generator device 2 only the front cap 3 of which is shown. The clutch device comprises a shaft 4 and a pulley 5 which is rotatable with respect to the shaft 4 in one direction only. This rotation between the shaft 4 and the pulley 5 is obtained by means of the one-way clutch 6 which in the present embodiment is carried out as a wrap spring. Other one- way clutches, such as with spraques, are possible as well. A bearing 19 is used to support the pulley on the shaft and allow rotation as dictated by the operation of the one-way clutch.

The starter/generator device shaft, which is not shown, is to be connected to the shaft 4 of the clutch device 1. For engine starting, torque must be transferred from the starter/generator device to engine. Since the one-way clutch 6 does not pass torque from starter/generator device to the engine, it must be temporarily locked-out to enable engine starting. This temporary lock-out is achieved by enabling the electromagnetic locking clutch 7 so that shaft 4 and pulley 5 are locked with no relative motion between them. Starting torque can then be transferred from the pulley 5 via the belt (not shown) to the internal combustion engine in question. This means that during the brief starting period there may be belt tension reversals.

The locking clutch 7 comprises a first armature 8 which is fixed on a sleeve 9.

The sleeve 9 is axially slidable but non-rotatably fixed to the shaft 4 by means of the key/groove connection 10. A second armature 12 is fixedly connected to the pulley 1.

Furthermore, the locking clutch comprises an electromagnetic actuator having a U- shaped stator 13 fixed through a bracket 18 to the front cap 3, as well as a coil 15 which fits within the recess of said stator 13. When the electromagnetic coil is energized a flux path 14 is created causing the first armature 8 together with sleeve 9 to be attracted towards the second armature 12. The facing surfaces 16 respectively 17 of the first armature 8 and the second armature 12 are provided with coupling means, for example friction plates or engaging teeth and as a result the pulley 5 is rigidly fixed to the shaft 4.

Once the internal combustion engine is started, the coil is de-energized and the first armature 8 is pushed out of contact with second armature 12 by a spring 11. The one-way clutch is thereby enabled and the starter/generator device now operates as a

generator. In this mode, the shaft 4 through the one-way clutch 6 rotates the pulley 5.

The pulley 5 is connected to the internal combution engine in question via a belt (not shown). The one-way clutch allows torque to pass from engine to starter/generator device, but does not let torque pass from starter/generator device to engine. In this way the one-way clutch operates in generator mode to eliminate belt tension reversals and improve belt life. Although the rotation member has been described as a pulley, other embodiments are possible as well such as a tooth gear or a toothed belt gear.