The present invention relates to a clutch assembly for connecting a shaft to a rotary member, such as an idle gear, mounted on said shaft in a rotationally fixed manner, wherein the clutch assembly comprises: a sliding sleeve which is rotationally fixed to the shaft, is axially slidably mounted on said shaft and is provided with a first gearing, a clutch body which is rotationally fixed to the rotary member and provided with a second gearing which can mesh with the first gearing to connect the shaft and the rotary member in a rotationally fixed manner, and a locking synchronisation unit having a synchroniser ring with a friction surface, said ring permitting the speeds of the shaft and the rotary member to be synchronised before the meshing of the first and second gearings, wherein the locking synchronisation unit further comprises a locking member which is coupled to the sliding sleeve by means of a detent groove and to the synchroniser ring in the rotational direction by means of a pair of locking surfaces.
Such a clutch assembly is known from DE 10 2005 025 569 A1.
Clutch assemblies of the generic type are used in countershaft transmissions of motor vehicles. The countershaft transmissions are herein formed as stepped transmissions with a plurality of gear ratios. Each gear ratio is associated with a set of wheels comprising a fixed wheel and an idle gear. The idle gears are respectively supported at one of the shafts of the transmission and can be connected to the shaft by means of a clutch (to shift into gear) and released therefrom (to disengage the gear).
Clutches are nowadays usually formed as synchroniser clutches, in which the speeds of shaft and rotary member are synchronised before establishing a positive locking therebetween. Further, synchroniser clutches are nowadays mainly formed as locking synchroniser clutches in which a locking mechanism provides that the engagement of the gearings of sliding sleeve and clutch body is only enabled when the speeds of the shaft and the rotary member are synchronised.
The locking mechanism most used today comprises a locking gearing at the outer periphery of the synchroniser ring. The synchroniser ring is supported at the shaft (or a guiding sleeve attached thereto, which is also referred to as a synchroniser body) to be movable in a restricted range. In a release position, the sliding sleeve gearing can be passed through the locking gearing of the synchroniser ring in order to establish the positive locking with the clutch body. In the locked position, the synchroniser ring is twisted such that the sliding sleeve is prevented to be moved in the axial direction toward the clutch body. The locked position of the synchronizer ring is obtained by frictionally engaging the synchroniser ring with the associated clutch body (or any other associated friction surface) due to the applied axial shifting force. Consequently, the synchroniser ring is driven in the rotational direction and thus into the locked position. Only after synchronisation of the speeds, the friction force is reduced so far that a turning back of the synchroniser ring due to the shifting force is possible, such that the sliding sleeve can be pushed through the gearing of the synchroniser ring, which gearing was turned back into the release position.
In this kind of synchronisation, the synchroniser ring has to be produced in a comparatively complex manner.
The aforementioned DE 10 2005 025 569 A1 proposes a locking mechanism which is realized by using a pressure piece.
Such a pressure piece or stone is often used in synchroniser clutch assemblies to lock the sliding sleeve in a neutral position. In DE 10 2005 025 569 A1, it is now proposed to form the synchroniser ring without a locking gearing at its outer periphery. Contrary thereto, a plurality of wedged surfaces is provided at the inner periphery of the synchroniser ring, which are assigned to corresponding wedged surfaces of the pressure pieces.
When applying a shifting force, the sliding sleeve tries to move the pressure piece in the radial direction away from the detent groove, and simultaneously pushes the synchroniser ring in the axial direction against a friction surface (starting synchronisation). Hereby, the synchroniser ring is twisted until the pairs of wedged surfaces engage, such that the wedged surfaces counter-effect a radial pushing away of the pressure piece. Accordingly, the sliding sleeve can no longer be displaced axially and is locked in this way. Only after synchronising the speeds of the shaft and the idle gear, the synchroniser ring can be turned back by the shifting force applied to the sliding sleeve, due to the then decreased friction force, such that the pressure piece can be pushed away in the radial inward direction. Consequently, the sliding sleeve can be further displaced in the axial direction in order to engage with the clutch body.
A similar locking mechanism for a synchroniser clutch is known from DE 29 15 965 C2.
Also in this kind of synchroniser clutch assembly, however, the synchroniser ring has to be produced in a comparatively complex manner.