In the prior art shift transmissions are described, in which gears are engaged by way of sliding sleeves. Such a sliding sleeve is connected to a shifting device which can comprise a shift fork with slide blocks and a shift rod. The sliding sleeve is connected in a rotationally fixed manner to the transmission shaft by the shifting device. Toothed gearwheels mounted to rotate on the transmission shaft, which mesh with other toothed gear wheels attached solidly on the countershaft. When the sliding sleeve is axially displaced by the shifting device in the direction toward the toothed gear wheel mounted to rotate on the transmission shaft, by virtue of interlocking teeth, a torque-transmitting connection is produced between the transmission shaft and the countershaft. For this the shifting device can be actuated by hand or automatically by way of an actuator. For example in automatic transmissions, shifting is performed by an actuating cylinder which can be controlled pneumatically or hydraulically or by an electric actuator. The disadvantages of such shift mechanisms are wear phenomena of the mechanical components and the large masses that have to be moved during the shift operation.
Likewise in the prior art shift transmissions are described whose clutches and brakes are actuated by the supply of pressure medium from a transmission shaft. From DE 30 13 382 A1, a device is known in which both a clutch and two brakes are actuated by a pressure medium. For this, the pressure medium is delivered to an annular cylinder space via the transmission shaft. In the unpressurized condition, the clutch, which is made as a disk clutch, is disengaged and the brake disks of the brakes form a frictional connection. This initial position is realized by corresponding spring forces. A build-up of pressure in the cylinder space displaces pressure plates, whereby the disk clutch is engaged and the brakes are released. Uniting the movement of the pressure plates reliably prevents simultaneous engagement of the clutch and brakes.
From DE 100 07 847 A1, a shifting device for a transmission is known, which is actuated electromagnetically. Toothed gearwheels are mounted to rotate on a transmission shaft and have internal teeth. A shifter pawl is arranged on the transmission shaft in a rotationally fixed manner, but is able to move axially along an axis of the transmission shaft. The shifting device comprises an electromagnetic device which moves the shifter pawl axially. The electromagnetic device is arranged directly on the shifter pawl and acts directly upon the shifter pawl without the assistance and interposition of a shift fork. A magnetic field is produced at the electromagnetic device by a control unit. This magnetic field moves the shifter pawl axially over the transmission shaft, such that the torque-transmitting connection is produced, between the transmission shaft and the countershaft. Since the action direction of the magnetic field can be reversed, the shifter pawl can be moved axially in both directions along the axis.
A disadvantage of the shifting devices described in the prior art is that at low temperatures large shifting forces have to be applied, since the oil on the shifter pawl becomes very viscous at low temperatures. Furthermore, the known shifting devices need to be improved in terms of component arrangement, the use of the space available and the accessibility of the shift elements.
The purpose of the present invention is to overcome the disadvantages of the prior art.