Differential assembly provided with an adjustment device, in particular for motor vehicles

A differential assembly, in particular for motor vehicles, transmits the motion from an input shaft to a pair of reciprocally counterposed coaxial output shafts and is provided with a ring gear rotably fed in use by the input shaft about a rotation shaft; the assembly being further provided with a gear set transmitting the motion from the ring gear to the output shafts and having a satellite gear carrier pin, whose axis is orthogonal to the axis of rotation of the ring gear; a single leaf spring is abuttingly coupled to two satellite gears to automatically adjust the position of the satellite gears themselves.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 USC 371 as a National Phase in the UNITED STATES of International Application No. PCT/EP2006/070208, filed on Dec. 23, 2006.

TECHNICAL FIELD

The present invention relates to a differential assembly provided with an adjustment device, in particular for motor vehicles.

BACKGROUND ART

As known, in motor vehicles the differential assembly transmits motion from a propeller shaft to a pair of reciprocally counterposed, coaxial drive axles which rotably feed the drive wheels.

Specifically, the differential assembly is arranged in an oil bath inside a fixed casing and comprises a supporting box, usually of cast iron, having two reciprocally opposite openings crossed by the ends of the two drive axles and carrying an outer ring gear in a relative fixed position.

The ring gear has a toothing meshing with the pinion integral with the propeller shaft, thus defining a speed reduction ratio, for rotably feeding the supporting box about the axis defined by the two drive axles.

The supporting box accommodates a planetary gear set comprising a pair of satellite gears, a pair of planetary gears meshing with the satellite gears and a satellite gear carrier pin, whose ends are coupled to respective anchoring portions of the supporting box.

The satellite gear carrier pin extends in the direction orthogonal to the drive axles, turns along with the supporting box, while each of the planetary gears is mounted, in a fixed angular position, onto the end of a respective drive axle to rotationally feed it.

The position of the satellite gears and/or the planetary gears is normally adjusted during assembly by appropriately mounted spacer members, whose thickness may be selected to compensate for possible clearance due to machining or coupling tolerance with respect to the supporting box and/or the other gears.

The differentials of the known type described above are poorly satisfactory, because they have a relatively high number of components and require relatively long times for choosing and mounting the aforesaid spacer members.

Furthermore, the solutions described above are not capable of adjusting the position of the gears automatically to compensate for possible clearance due to wear occurring during operation, and of constantly maintaining the satellite gears and the planetary gears correctly reciprocally meshed.

DISCLOSURE OF INVENTION

It is the object of the present invention to achieve a differential assembly provided with an adjustment device, in particular for motor vehicles, which allows to simply and cost-effectively compensate for the problems explained above and, preferably, allows to facilitate the assembly of the differential assembly itself.

According to the present invention, a differential assembly, in particular for motor vehicles, adapted to transmit the motion from an input shaft to a pair of reciprocally counterpoised, coaxial output shafts is obtained; the assembly comprising:a ring gear adapted to be rotably fed by said input shaft about its axis;a gear set to transmit the motion from said ring gear to said output shafts; the gear set comprising two reciprocally coaxial satellite gears, turning along with said ring gear about said rotation axis, and turning with respect to said ring gear about a further axis orthogonal to said rotation axis;adjustment means of the position of said satellite gears for compensating clearance;
characterised in that said adjustment means comprise a single spring coupled to both said satellite gears.

Preferably, said spring is a leaf spring having a C-shaped about the rotation axis of said ring gear, for example a circular shape, open along a segment of its circumference.

Conveniently, said spring comprises two diametrically and reciprocally opposite end portions on which said satellite gears are abuttingly arranged and has a concave surface complementary to a base surface of said satellite gears, for abutting said satellite gears.

Specifically, said end portions have respective reciprocally openings which are coaxial along said further axis of said satellite gears and are engaged by the ends of a satellite gear carrier pin.

Preferably, said spring carries at least two reference teeth reciprocally defining a seat in a direction parallel to said axis of rotation, in particular for engaging an inner portion of said ring gear.

BEST MODE FOR CARRYING OUT THE INVENTION

InFIG. 1, it is indicated by1a differential assembly constituting part of a transmission assembly2of a motor vehicle (partially shown). Specifically, the transmission assembly2comprises a gearbox3, whose output shaft4carries a pinion5splined at its end.

The assembly1transmit the motion from the pinion5to a pair of counterpoised drive axles7(schematically shown by a broken line inFIG. 3), which extend coaxially together along an axis8.

The assembly1is accommodated in a supporting casing (not shown) and comprises a ring gear11which is made of steel and has, on its outer periphery, a toothing12meshing with the pinion5and defined, in the particular example described, by a cylindrical straight toothing.

The ring gear11is turnable about its axis13coinciding with axis8, as will be better explained in detail below, and has respective circular axial centring ridges15on its side faces14.

With reference toFIG. 2, the ridges15radially delimit an inner annular portion17, having a plurality of holes18parallel to the axis13and angularly reciprocally distanced for fastening a protection box19, preferably made of aluminium.

Some of the holes18may eventually be engaged by a protruding reference dowel18afor angularly positioning the box19.

The box19comprises two half shells20, each fastened to the holes18of a respective face14by means of screws or other fastening members (not shown).

Each half shell20comprises a housing21, having a plurality of openings22for the passage of oil and radially outwardly ending with an annular flange23abuttingly arranged against the portion17.

The flange23has, in turn, a plurality of holes24aligned with the holes18for fastening said fastening members, and an outer circular edge25surrounded by the ridge15.

Each half shell20further comprises a respective cylindrical shank30, extending from the respective housing21along the axis13in a direction opposite to the ring gear11and is axially hollow to allow the passage with clearance of the end31of a respective drive axle7(FIG. 3).

The outer cylindrical surfaces of the shanks30carry respective bearings32, which maintain the assembly1coupled to said supporting casing and allow the ring gear11and the box19to turn about the axis13.

With reference toFIGS. 2 and 3, the box19accommodates a planetary gear set33comprising a pair of satellite gears34, whose toothing is not shown inFIG. 2. The satellite gears34are carried by a pin36, whose axis37is orthogonal to axis13.

The satellite gears34are coaxial to each other and to the pin36itself so as to turn with respect to the ring gear11about axis37.

With reference toFIG. 3, the gear set33further comprises a pair of planetary gears38, which are reciprocally coaxial along axis8, are interposed between the satellite gears34, mesh with the satellite gears34themselves, and are each splined in fixed angular position onto a respective end31.

Specifically, the planetary gears38comprise respective bases39, which rotationally engage, about axis8, respective centring and guiding seats40made in the half shell20.

The ring gear11comprises a coupling device41for the pin36, so as to transmit the motive torque to the pin36itself without the motive torque being transferred to the box19.

The device41comprises two seats42made along the axis37in the portion17in reciprocally diametrically opposite positions with respect to the axis13and each engaged by a respective end43of the pin36.

Specifically, the pin36may be rotationally coupled to the portion17about axis37, for example by radial clearance or by interposing sleeve or ball bearings (not shown); alternatively, it may be fixedly coupled thus leaving only the satellite gears34free to rotate about the axis37.

In the particular example described above, the seats42cross portion17in a direction parallel to axis13and are delimited and closed, along such direction, by the flanges23. Therefore, fins23act as shoulder for withholding the ends43of the pin37in engagement with the seats42in direction parallel to the axis13(FIG. 3).

In the particular example described, the pin36is coupled to the ring gear11so as to have a clearance, for example equal to a tenth of a millimeter, in a direction parallel to the axis13: in such way, the position of the pin36may settle or adjust itself automatically with respect to the ring gear11in use and compensate for possible machining inaccuracies in couplings and/or alignments.

According to the invention, the position of the satellite gears24is adjusted, in use, automatically by a single elastic leaf member50having a C-shape in front view along the axis13.

The elastic member50is essentially coaxial to the ring gear11and comprises two end portions51interposed between the satellite gears34and the portion17of the ring gear11.

The portions51are joined together by an intermediate portion52and are provided with respective slots53crossed by the pin36, with clearance in the circumferential direction with respect to the axis13, have an inner surface54abuttingly arranged against the base surfaces55of the satellite gears34. Specifically, the elastic member50has a C-shaped cross section: in other words, the inner surface54is concave towards the axis13, so that the surfaces54and55are essentially and reciprocally complementary.

The elastic element50has an outer surface56, which is outwardly convex and faces portion17in a radial direction with respect to axis13. Two pairs of teeth57protrude in a direction opposite to the axis13from surface56. The teeth57are arranged at the ends of the elastic member50, considering the circumferential direction with respect to axis13, and therefore the C-shaped section of the elastic member50is constant along such circumferential direction up to its ends.

The teeth57define therebetween, in a direction parallel to axis13, a seat58which is engaged by the portion17. Specifically, the coupling between the teeth57and the edges of the portion17allows to position and withhold the elastic member50during the assembly of the assembly1, along with the pin36and the satellite gears34, in a fixed axial position.

Specifically, the pin36, the satellite gears34and the elastic member50define a set60which can be pre-assembled before being coupled to the ring gear11during assembly.

To assemble the assembly60it is sufficient to abuttingly arrange the bases of the satellite gears34on the inner surface54, aligning the holes of the satellites34(not shown in the attached figures) with the respective slots53, and then inserting the pin36along the axis37through the slots53and such holes.

After being pre-assembled, the assembly60is coupled to the portion17of the ring gear11, by inserting the ends43of the pin36into the seats42in a direction parallel to axis13and by inserting portion17in the seat58defined by the elastic member50, making the two teeth57snap on opposite sides of the portion17itself. In this condition, the assembly60remains temporality stationary with respect to the ring gear11.

Then, the planetary gears38are coupled to the satellite gears34and the half shells20are fastened to the faces14of the ring gear11, so as to enclose the gear set33and stably maintain the pin36engaged in the seats42and the planetary gears38meshed to the satellite gears34.

In use, the elastic member50exerts an elastic thrust pressure on both satellite gears34radially towards axis13and then towards the planetary gears38, both to compensate for the clearance due to machining and coupling tolerance of the various components of the gear set and to compensate for clearance due to wear arising inside the box19during operation.

The meshing of the planetary gears38and the satellite gears34is therefore optimal, shock-free, with consequent silentness of the system, also in time.

It is evident that the adjustment is automatic, being caused by the bias of an inner elastic member, and not by rigid spacers, does not require interventions from the outside after assembly, and is extremely simple because it envisages the use of a single component for both satellite gears34.

Advantageously, the automatic adjustment is then performed, not only by the elastic member50, but also by the clearance between the pin36and the seats43, to allow the pin36to arrange itself automatically with respect to the ring gear11.

The features of the elastic member50also make assembly extremely simple because they allow to form the assembly60from the ring gear11. Specifically, the teeth57facilitate the coupling of the ring gear11and maintain the assembly60stationary before fastening the flanges23.

Then, the assembly of the assembly1is also simple because a portion of the box19, i.e. the flanges23, stably maintains the pin36in a fixed position, without the need for additional components.

It is finally apparent that changes and variations can be made to the assembly1here described and illustrated without however departing from the scope of protection of the present invention, as defined in the accompanying claims.

Specifically, different materials may be used for the various components with respect to those shown by way of example and/or the device41may be different from that described with reference to the attached drawings.

Furthermore, the half shells of the box19may be fixed to the ring gear in a different way with respect to coupling by screws, for example by welding, and/or the elastic member50may be coupled to a cast iron supporting box of the traditional type, instead of being directly coupled to the ring gear11as in the solution shown.