Patent Description:
The known epicyclic reduction gearings have a sun gear, a planet carrier and an internal toothing outer gear. These elements transmit motion by means of a plurality of planet gears which are rotatably fixed to the planet carrier and which rotate with a fixed distance between centres.

Generally, to obtain a reduction ratio of the number of revolutions between the input shaft and the output shaft, the motion input is applied to the sun gear shaft and it is transmitted, by means of the plurality of planet gear, to the planet carrier provided with the output shaft.

Vice versa, when the epicyclic gearing is used to multiply the revolution numbers, the input motion is applied to the planet carrier shaft and the output motion is taken from the sun gear shaft.

Document <CIT> discloses an epicyclic gear with an input shaft kinematically connected to two planet gears supported by a planet carrier wherein each planet gear is made on a relative shaft supporting a relative pulley engaged by a first annular belt or chain which is engaged with a pinion keyed on the input shaft. The rotation of the input shaft is transmitted, through the belt or chain, to each pulley which set in rotation the relative shaft supporting the relative planetary gear driving into rotation the planet carrier having the axis coaxial with the input shaft axis. The torque support for the epicyclic gear is realized with a second chain on a sprocket of the planet gear, which is meshing with a sprocket that is fixed to the casing.

The document <CIT> discloses a speed reducer in which a reaction sun is held stationary relative to a frame and an output sun is coaxial with the reaction sun. An idler carrier assembly, rotatable relative to the frame about the common axis of the two suns, carries a planet shaft supporting a reaction planet and an output planet for conjoint rotation and in radial alignment, respectively, with the reaction sun and the output sun. Rotation of the idler carrier assembly effects orbiting of the planet shaft and its planets about the common axis of the suns. Endless loop force-transmitting elements connect corresponding suns and planets. Rotary input power is applied to the planet shaft effecting conjoint rotation of planets and orbiting of the planets about the suns' axis. The epicyclic motion of the output planet effects rotation of the output sun.

In the document <CIT> is disclosed an articulated gearing comprising drive outer tooth sprocket and driven sprocket and two-row roller chain to transfer first power flow. Two gears fitted on one axle with equal number of teeth engage with said drive and driven sprockets to make the second power flow. Said first power flow comprises two extra rollers fitted on parallel axles and bus supporting aforesaid roller chain. Driven sprocket has inner teeth for engagement with one of gears and roller chain. Drive and driven sprockets are fitted at equal axle base equal to or approximating to zero and feature different number of teeth. Said bus is arranged with clearance to driven sprocket inner surface for passage of roller chain. The transmission of torque from drive shaft to driven shaft at axle base is equal to or approximating to zero.

European Patent Application <CIT> discloses a solution referring to a common kinematic relationships of planetary gear trains using a sun gear, a planet gear and an outer gear which is internal to the case. In particular it provides an internal ring gear, a driving assembly having the internal ring gear, and an application device employing the driving assembly. The internal ring gear includes at least two ring gears integrally arranged in parallel at an inner surface of a single housing.

Document <CIT> discloses a compact epicyclic gearing falling within the wording of the pre-characterizing portion of claim <NUM>.

Document <CIT> discloses a precision joint type secondary speed reducer comprising a driving motor, a mounting base, three planetary gears, three linkage shafts, three driven synchronous wheels, a driving synchronous wheel, a double cogged synchronous belt, a central shaft disc and a speed reduction output flange. An inner gear ring is arranged in the middle of the mounting base. The central shaft disc is mounted to the front face of the mounting base through a crossed roller bearing. A middle through hole is formed in the middle of the central shaft disc. The driving motor is mounted to the rear face of the mounting base. The three linkage shafts are evenly distributed on the central shaft disc around the middle through hole. The three planetary gears are mounted to the rear ends of the three linkage shafts correspondingly and engaged with the inner gear ring. The three driven synchronous wheels are mounted at the front ends of the three linkage shafts correspondingly. The driving synchronous wheel is mounted to the front end of an output shaft of the driving motor. The double cogged synchronous belt is connected with the three driven synchronous wheels and the driving synchronous wheel simultaneously. The speed reduction output flange is mounted to the front face of the central shaft disc. In brief, the invention disclosed in document <CIT> does not have at least one pair of two intermeshing planet gears, one driven by the respective at least one pulley and the other one meshing with the first outer gear.

The main drawback of known epicyclic reduction gears lies in the fact that the gears are multiple with several gearings in motion and therefore noisy as well as bulky when the diameters, for example of the satellites, are wide.

The known epicyclic gears also have the drawback of having limited contact between the teeth of the mutually meshed gearings and therefore without allowing a considerable size reduction.

The main object of the present invention is to propose a compact epicyclic gearing by virtue of the considerable increase of the mutually meshed portions so as to reduce the axial overall dimensions of the meshed gearings.

Another object is to propose a gearing with multiple gearings having increased stability and reduced noise.

A further object is to propose a gearing having a high reduction ratio.

The features of the invention are highlighted hereinafter, with specific reference to the accompanying drawings, in which:.

With reference to <FIG>, numeral <NUM> indicates an epicyclic gearing having a first stage <NUM> essentially comprising an input shaft <NUM>, a pinion <NUM>, three input planet gears <NUM>, a belt or chain <NUM>, three pulleys <NUM>, three first planet gears <NUM>, a first planet carrier <NUM>, a first outer gear <NUM> and a case <NUM>.

The pinion <NUM> is keyed on the input shaft <NUM> on whose teeth the belt or chain <NUM> engages, constituting a flexible annular gearing <NUM> which transmits the motion of the pinion <NUM> to the three pulleys <NUM> on which the annular gearing <NUM> is wound. The belt <NUM> is kept taut by a tightener <NUM>.

Each pulley <NUM> is keyed by conical sleeves <NUM> to the end of a respective input planet gear shaft <NUM> which is rotatably supported by the first planet carrier <NUM> by means of a first bearing <NUM> and a second bearing <NUM>.

At the free end of each input planet gear shaft <NUM> there are toothings which constitute the respective input planet gear <NUM>.

The three pulleys <NUM> are angularly spaced at <NUM>° with the respective axes on the same circumference. Likewise, the three input planet gears <NUM> are angularly spaced at <NUM>° and are coaxial with the corresponding pulleys <NUM>.

The first planet carrier <NUM> supports the three first planet gears <NUM> by means of a respective pin <NUM> with the interposition of a bearing <NUM> and is held in place by means of a shoulder <NUM> cooperating with a stiffening <NUM>.

Each input planet gear <NUM> meshes simultaneously with two adjacent first planet gears <NUM>.

Each first planet gear <NUM> also engages with the first fixed outer gear <NUM> obtained on the inner wall of the case <NUM>.

The operation of the preferred embodiment of the epicyclic gearing <NUM> provides that the rotary motion of the input shaft <NUM> is transferred to each pulley <NUM> through the synchronous transmission of belt <NUM>, with motion reversal and a first speed reduction.

Then each pulley <NUM> rotates the input planet gear shaft <NUM> of the respective input planet gear <NUM>.

The input planet gear shaft <NUM> axis is parallel to the axis of the input shaft <NUM> and is assigned to travel along a circumference, dragging in rotation, by means of the respective first planet gear <NUM>, the first planet carrier <NUM> whose rotation axis is coaxial to the axis of the input shaft <NUM> and from which it is possible to take a reduced rotary motion with respect to the motion of the input shaft <NUM>.

It should be noted that the rotation of the annular gearing <NUM> constitutes an important flywheel with a positive impact on the efficiency of the epicyclic gearing <NUM>.

A second embodiment of the epicyclic gearing <NUM> provides a second stage <NUM> placed in cascade to the first stage <NUM> in order to increase the reduction ratio of the rotary motion applied to the input shaft <NUM>.

A sun gear <NUM>, coaxial to the input shaft <NUM> and meshing with four second planet gears <NUM>, is coupled to the first planet carrier <NUM> by means of a spline <NUM>. Each of these four second planet gears <NUM> is rotatably supported by a corresponding rod <NUM> constrained to a second planet carrier <NUM>.

Each of the four second planet gears <NUM> is meshed with a second outer gear <NUM> made on the internal portion of the case <NUM>.

The second planet carrier <NUM> is coupled with an output shaft <NUM> coaxial with the input shaft <NUM> and carrying a reduced tail shaft <NUM> which rotatably supports the sun gear <NUM> through two bushes or slides <NUM>.

The shaft <NUM> is axially controlled and tightly supported at the output by a single double-gears taper roller bearing <NUM> and by the same output flange <NUM>.

The case <NUM> is provided with an input flange <NUM> and an output flange <NUM> so creating a chamber having a first and a second compartment.

The first compartment is comprised between the input flange <NUM> and the first planet carrier <NUM> and encloses the annular gearing <NUM> so as to keep it isolated by means of a lip seal <NUM> interposed between the inner portion <NUM> of the case <NUM> and the shoulder <NUM> for supporting the first planet carrier <NUM>.

The second compartment is comprised between the first compartment, the case <NUM>, the output shaft <NUM> and the output flange <NUM>. The second compartment contains the first stage <NUM> and the second stage <NUM> of the epicyclic gearing <NUM> so keeping them into a lubricant bath by virtue of the sealing of the lip seal <NUM> and of a front seal <NUM>, interposed between the output shaft <NUM> and the output flange <NUM>, and by an o-ring <NUM>, interposed between the output flange <NUM> and the inner portion <NUM> of the case <NUM>.

The plurality of meshing points between the input planet gears <NUM> and the respective first planet gears <NUM> does not have hyperstatic problems due to the right relationship between the tensioning of the belt <NUM> by the tightener <NUM> and the appropriate freedom degree of the bearings, first <NUM> and second <NUM>, in the respective housing.

In a stage of a known epicyclic gearing, the sun gear is positioned at the gearing centre and is engaged in only three points with the respective planets arranged at <NUM>° around it.

In the first stage <NUM> of the epicyclic gearing <NUM>, the three input planet gears <NUM> are radially decentralized and are each interposed between two respective first planet gears <NUM> with a doubling of the grip points with respect to the corresponding stage of the known gearing.

Each of the gripping points consists of two teeth of the input planet gear <NUM> which are always conjugated with two teeth of the respective first planet gear <NUM> due to the gear ratio always higher than <NUM>, i.e. εα><NUM> according to UNI <NUM> standard.

This arrangement is made possible by the flexible annular gearing <NUM> which, starting from the pinion <NUM> keyed onto the input shaft <NUM>, distributes the drive torque to the three pulleys <NUM> and, with a first speed reduction, to the integral input planet gears <NUM>. These latter engage externally with the respective first planet gears <NUM> and with the contribution of the first fixed outer gear <NUM> put the first planet carrier <NUM> into rotary motion, reinforced by the flywheel effect impressed by the pulleys <NUM>, with the impact of the reduction process onto the first planet carrier <NUM> and transmission to the second stage <NUM>.

The axes of the three input planet gears <NUM> and the axes of the three pulleys <NUM> trace the same circumference and therefore travel at the same angular speed ω corresponding to a peripheral speed of less than one meter per second.

This particular conformation of the first stage <NUM>, compared to the known three-stage epicyclic gearing, reduces the acoustic impact by over <NUM>% and improves the efficiency by about <NUM>% compared to the efficiency of <NUM>% of the known epicyclic gearings.

In known epicyclic gearings, the dynamic stress is calculated as σFLim <NUM> Nmm<NUM> * <NUM>,<NUM> = <NUM> Nmm<NUM> with reference to case hardening steel <NUM> NI CR MO <NUM>-<NUM> - DIN <NUM>, while the dynamic bending stress of the epicyclic gearing <NUM> is <NUM>% reduced since σFLim <NUM> Nmm<NUM> * <NUM>,<NUM> = <NUM> Nmm<NUM> due to the effect of the grip in two points at <NUM>° on each first planet gear <NUM>, considered idler gear, of two input planet gears <NUM>.

The tangential force, in the known epicyclic gearings with three planet gears and one sun gear, taken in a single point is Ft/<NUM>, while in the first stage <NUM> the tangential force is Ft/<NUM> as there are six grip points between the input planet gears <NUM> and the first planet gears <NUM>.

Known single-sun epicyclic gearings reach a reduction ratio of at most <NUM>:<NUM>, while in the first stage <NUM> the reduction ratio is <NUM>:<NUM> or <NUM>:<NUM>,<NUM> by virtue of the <NUM> teeth engaged between the input planet gears <NUM> and the first planet gears <NUM> maintaining the character of torque reducer.

The overall stabilization of the epicyclic gearing <NUM>, in the radial and axial direction, is guaranteed by the reduced tail shaft <NUM> of the output shaft <NUM> and by the perfect alignment with the input shaft <NUM>.

The controlled flotation of the entire epicyclic gearing <NUM> is controlled by the bushes <NUM> mounted inside the sun gear <NUM> and contained downstream in an anti-sliding function with respect to the input flange <NUM>, by the supporting balls <NUM> mounted on the fixing pins <NUM> of the closed curved rolling bearings <NUM>.

These rolling bearings <NUM> are placed at an equal radial distance from the axis of the input shaft <NUM> and are mounted on the shoulder <NUM> of the first planet carrier <NUM>. During the operation of the epicyclic gearing <NUM>, the rolling bearings <NUM> also move with rototranslatory motion at already reduced speed along the internal circumference of the case <NUM> thus contributing to the radial equilibrium of the epicyclic gearing <NUM> in the operating phase.

The two embodiments of the gearing <NUM> just described provide for the use of the gearing as a reducer in which the driving force (rotary motion) is applied to the input shaft <NUM> and the reduced motion is available at the output shaft <NUM>.

A variant of use of the two embodiments of the epicyclic gearing <NUM> provides that it is used as a multiplier in which the input rotary motion is applied to the output shaft <NUM> and the multiplied motion is taken from the input shaft <NUM>.

It is known that a three-stage epicyclic or reduction gearing, with a reduction ratio of <NUM>:<NUM> using a three-phase motor with <NUM>,<NUM> kw at <NUM> rpm and a torque of <NUM>, has an axial overall dimension of <NUM> between the input and the output face of the gear train itself.

The overall dimensions of the epicyclic gearing <NUM>, object of the present invention, have an axial overall dimension of <NUM> between an inner face <NUM> of the input flange <NUM> and an outer face <NUM> of the output flange <NUM>. Therefore, the axial overall dimensions between the gearing <NUM> and the known one is reduced by about <NUM>%.

It should also be noted that the output flange <NUM> can be square or round shaped based on the type of installation required.

<FIG> illustrate a third embodiment of the compact epicyclic gearing <NUM> which is single-stage and comprises the same annular gearing <NUM> of the first and second embodiments.

The first planet carrier <NUM> is essentially connected by means of three stiffenings <NUM> to the shoulder <NUM> which has on its peripheral edge a track wheel <NUM> on which, for example, a track <NUM> engages.

Between the shoulder <NUM> and the case <NUM> there is the leap seal <NUM> which avoids the flow communication between the inside and outside of the case <NUM> and vice versa.

In this third embodiment, the motion output from the gearing <NUM> is from the shoulder <NUM> to which the track wheel <NUM> is constrained, for example of a not showed but known tracked vehicle.

The main advantage of the present invention is to provide a compact epicyclic gearing obtained thanks to the considerable increase in the number and surfaces of the mutually meshed portions so as to reduce the axial development of the meshed gearings.

In particular, a first axial compression is obtained as a result of the particular configuration of the first stage of the epicyclic gearing with the multiple sun gears off-cantered with respect to the axis of the input shaft and which are moved by a flexible annular gearing acting within the axial overall dimensions of the input shaft itself.

Another advantage consists in providing a gearing with multiple gearings having increased stability and reduced noise.

Claim 1:
Compact epicyclic gearing having a first stage (<NUM>) comprising at least one input shaft (<NUM>) kinematically connected to at least one input planet gear (<NUM>) engaged with at least one first planet gear (<NUM>) rotatably supported by a first planet carrier (<NUM>) and meshed with a first outer gear (<NUM>) internal to a case (<NUM>) of the epicyclic gearing (<NUM>), the latter (<NUM>) being characterized in that the at least one input planet gear (<NUM>) is joined to a respective input planet gear shaft (<NUM>), at one end thereof a respective pulley (<NUM>) is keyed on which is engaged an annular belt or chain (<NUM>) of an annular gearing (<NUM>) which is engaged to a pinion (<NUM>) keyed on the input shaft (<NUM>) whose rotation is transmitted by means of the belt or chain (<NUM>) to the at least one pulley (<NUM>) which sets in rotation the relative input planet gear shaft (<NUM>) of the at least one input planet gear (<NUM>), with the input planet gear shaft (<NUM>) axis parallel to the axis of the input shaft (<NUM>) and rotating along a circumference, dragging in rotation, by means of the at least one first planet gear (<NUM>), the first planet carrier (<NUM>) whose rotation axis is coaxial to the input shaft (<NUM>) axis.