Gear box with two pinion shafts

A variable-speed gearbox comprises a main transmission (2) arranged in a housing (30) and a downstream range-change transmission (32), the range-change transmission having power distribution on two countershafts (12, 14). On a main shaft (4) of the main transmission (2), a gear wheel (6) is arranged in a radially movable manner which meshes with respective first gear wheels (8, 10) each on one of the countershafts. In the housing of the variable-speed gearbox, a drive output shaft (22) is radially and axially fixed which is connected a gear wheel (20) that meshes in each case with a second gear wheel (16, 18), respectively, on each of the countershafts. The gear wheel on the main shaft that meshes with the first gear wheels on the countershafts is maintained in its axial position relative to the drive output shaft by way of pressure combs (50, 52, 54, 56).

This application is a national stage completion of PCT/EP2004/009876 filed Sep. 4, 2004 which claims priority from German Application Serial No. 103 46 658.4 filed Oct. 8, 2003.

FIELD OF THE INVENTION

The invention concerns a gearbox with two countershafts for power distribution.

BACKGROUND OF THE INVENTION

Modern, powerful vehicle gearboxes usually comprise a main transmission group with a multi-stage basic gear and an upstream or downstream splitter group and/or a downstream range gear group. In a gearbox housing, they mainly comprise an input shaft as a first shaft and a central or main shaft as a second shaft, which can also be the output shaft, as well as one or more countershafts. The input and main shafts are essentially concentric with one another.

Having regard to the running properties and smooth running, such gearboxes can be designed with helical gearing, at least for the forward driving range. The axial forces from the helical gearing have to be taken up by an axial bearing and transmitted to the housing.

Gearboxes with the structure described can have one or more countershafts.

In gearboxes with power distribution between two countershafts, the main transmission group comprises two shafts arranged essentially one behind the other, one of which, namely either the input shaft or the main shaft of the main transmission, is mounted radially and axially fixed, while the respective other shaft is mounted floating laterally, i.e., able to move radially to allow the necessary load equalization. In this, care should be taken that an easy swivelling motion of the floating shaft is possible.

In gearboxes with two countershafts, the load equalization can preferably be designed such that the input shaft is mounted fixed on the housing, the countershafts are fixed on the housing and the main shaft is mounted floating in the gear wheels involved in the force flow.

The known variable-speed gearboxes for goods vehicles have a three- or four-speed main or basic transmission section and an upstream or downstream splitter transmission as an auxiliary transmission, which doubles the number of gear speeds of the main transmission since it splits the transmission ratio steps of the main transmission. A range-change transmission downstream from the main transmission extends the ratio range of the main transmission. The range-change transmission can be in the form of a planetary gearset or in the form of an arrangement of spur gear wheels.

From EP-A1 0 009 775 a range-change transmission with spur gear wheels downstream from a main transmission with two countershafts for power distribution is known. The range-change transmission has two countershafts which are rotationally independent of the countershafts of the main transmission. A floating gear wheel is arranged on the main shaft of the gearbox, which meshes with a gear wheel on each of the countershafts of the range-change transmission. This gearbox does not have sufficient capacity for absorbing axial forces that result from the gearing.

From DE-A1 196 04 824 by the present Applicant, a variable-speed gearbox with a range-change transmission of planetary design has become known. On the gearing of the planetary transmission pressure combs are provided to take up the axial forces that result from the helical gearing. The content of DE-A1 196 04 824 is intended to be fully incorporated in the present application.

The purpose of the present invention is to improve the axial mounting in a gearbox with two countershafts for power distribution.

SUMMARY OF THE INVENTION

In a range-change transmission with spur gears, the gear wheel arranged on the main shaft, which meshes with gear wheels on the countershafts of the range-change transmission, reaches very high rotation speeds in the disengaged condition in the fast shift position of the range-change transmission. This makes mounting with axial bearings problematic. Accordingly, the invention proposes a variable-speed gearbox with a main transmission arranged in a housing and a downstream range-change transmission, in which the range-change transmission comprises power distribution to two countershafts and in which a gear wheel is arranged in a radially displaceable manner on a main shaft of the main transmission. This gear wheel meshing in each case with a first gear wheel on each respective countershaft and in which a drive output shaft is arranged radially and axially fixed in the housing of the variable-speed gearbox; to that shaft is connected a gear wheel which meshes in each case with a second gear wheel on each respective countershaft. Pressure combs are provided by way of a gear wheel on the main shaft which meshes with the first gear wheels of the countershaft is maintained in its axial position relative to the drive output shaft. More preferably, the countershafts are maintained in their axial position relative to the drive output shaft by way of pressure combs.

In a particularly advantageous embodiment of the invention, the gearwheel on the drive output shaft comprises pressure combs which are in contact with pressure combs formed on the second gear wheels of the countershafts in order to take up axial forces. The gear wheel on the main shaft has pressure combs which are in contact with pressure combs formed on the first gear wheels of the countershafts in order to take up axial forces.

Particularly advantageous is the drive output shaft, held radially and axially in the housing by a double conical-roller bearing arrangement.

In another advantageous embodiment, the countershafts have only one radial mounting in the housing, which preferably comprises roller bearings.

The countershafts and the gear wheel on the main shaft are guided and maintained axially with the help of the pressure combs. The lubrication of the pressure combs can take place from outside and is simple and effective. During the torque transmission by the gear wheels of the countershafts, no axial gear forces have to be taken up by the bearings and transferred to the housing. Thus, the axial mounting of the countershafts can be omitted and the countershafts need only be held in radial-mounting roller bearings. The entire gearset combination of the range-change transmission is fixed axially by the mounting of the drive output shaft.

Exact formation of the pressure combs on the gear wheel of the main shaft ensures that while the axial fixing is maintained, the necessary radial freedom of the movement is secured.

DETAILED DESCRIPTION OF THE INVENTION

InFIG. 1, in a variable-speed gearbox (not illustrated in greater detail), a main transmission2comprises a main shaft4, at the end of which is arranged a gear wheel6with some radial play. For this, the radial mounting of the gear wheel6is provided with its outer teeth engaging only in the outer teeth of two first gear wheels8and10. In each case, the first gear wheels8and10are fixedly arranged on respective countershafts12and14or formed as one piece with the countershafts. Each countershaft12,14has a respective second gearwheel16and18, in each case again fixed on its countershaft12and14or made as one piece with the countershafts12,14.

With their outer teeth, the two second gear wheels16and18mesh with the outer teeth on a gear wheel20arranged fixed on a drive output shaft22of the variable-speed gearbox or made as one piece therewith. To the drive output shaft22is attached a drive output flange24by which the variable-speed gearbox is connected to further elements of a vehicle drive train (not illustrated here).

The drive output shaft22is mounted by two conical-roller bearings26and28in a housing30of the variable-speed gearbox or of a range-change transmission32downstream from the main transmission2. Also mounted in the housing30are the two countershafts12and14, each in two roller bearings34,36and38,40respectively. These roller bearings34,36,38,40only take up radial forces and transfer them to the housing30. All the gear teeth of the gear wheels8,10,16,18,20are of the helical-tooth type from which axial forces result for the absorption and transfer of which the roller bearings34,36,38,40are not suitable.

A gearshift sleeve42is arranged at the end of the main shaft4is which, by virtue of inner teeth, is connected with the main shaft4rotationally fixed but able to be displaced axially. By way of a control mechanism (not shown here), the gearshift sleeve42can be moved axially. When this happens, the gearshift sleeve42with its outer teeth48connects the main shaft4either with inner teeth44on the gear wheel6on the main shaft4or with inner teeth46of the drive output shaft22to form a direct connection between the main shaft4and the drive output shaft22. If desired, the gearshift sleeve42can also adopt a neutral shift position in which there is no connection with either of the inner teeth sets44,46.

The drive output shaft22is mounted axially fixed in the housing30by means of the conical-roller bearings26and28. Laterally on the outer teeth of the gear wheel20on the drive output shaft22respective pressure combs50and52are arranged. The pressure surfaces on the pressure combs50and52react with correspondingly formed pressure surfaces on the gear wheels16and18, thereby fixing the countershafts12and14in the axial direction. Thereby, the gear wheels8and10on the countershafts12and14are also fixed axially.

Laterally on the outer teeth of the gear wheel6on the main shaft4, respective pressure combs54and56are arranged. The pressure surfaces on the pressure combs54and56react with correspondingly formed pressure surfaces on the gear wheels8and10on the countershafts12and14. Since the gear wheels8and10are axially fixed, as described above, the gear wheel6is also axially fixed by virtue of the pressure combs54and56so that the problems associated with axial mounting at high rotation speeds of the gear wheel6are eliminated.

REFERENCE NUMERALS