Title: PLANETARY REDUCTION GEAR WITH BELT

DESCRIPTION

Field of application

The present invention refers to a planetary reduction gear with belt, i.e. a reduction gear in which the wheels of a planetary gearing are connected together with a belt and that, by the particular arrangement of the wheels, manages to develop very high transmission ratios.

Prior art

In the state of the art reduction gears, even planetary ones, are known in which the inner gear wheel of the gearing consists of a chain arranged at a predetermined radius from the rotation axis of the planetary mechanism or even arrangements of pins that form a chain in the aforementioned position with a constant radius, whereas mechanisms in which belts are used are not known.

The reduction in the transmission is obtained by using, in the known reduction gear, a divided satellite that engages on a first planetary mechanism with the solar gear of the input shaft, rotating the satellites on the fixed outer wheel, and collecting the rotation motion of the satellites on a second wheel with inner toothing, or crown, aligned in the second planetary mechanism, moreover without a solar gear, with a different radius, generally slightly smaller than the crown of the first planetary mechanism. The reduction ratio is obtained due to the difference between the diameters of the two inner crown wheels: the second is connected in rotation with the output shaft from the reduction gear.

Moreover, the reduction gear thus constituted can only be made with

chain or gear toothings, whereas the use of belts, which would make manufacturing very cost-effective, is not possible due to the small winding angles of the belts if replaced at the wheels and due to the lack of the possibility of tensioning the same belts inside the planetary mechanism.

Indeed, known planetary mechanisms have the fixed position of the engaging wheels thus preventing the small radial adjustments that the pulleys notoriously require to place the belts in tension in the transmissions, be they flat, trapezoidal or toothed. Moreover, inside the planetary mechanism it is not easy to obtain reciprocal movements in order to achieve the necessary tensioning of the belt possibly used.

Finally, the size of the transmission ratios that can be obtained is, generally, limited by the presence of fixed ratios between the teeth of the wheels.

The technical problem forming the basis of the present invention is to make a planetary reduction gear that uses belts instead of gear wheels, also constructed similar to chains with fixed radius, known in the field.

Another purpose of the invention is to make a planetary reduction gear that allows production in large quantities and with low costs and allows production with substantially different transmission ratios without significantly affecting the cost.

Another and not least substantial purpose of the invention is to make a planetary reduction gear that allows transmission of minimal torques, but also significantly higher torques with a precise transmission ratio or, possibly, with a transmission ratio very close to the desired value, even if not extremely precise. This last purpose, moreover, can be achieved without particular differences in cost in the various versions in

which the reduction gear can be made. In conclusion, the reduction gear made can be built modularly to meet the most varied requirements, of torque and consequently power transmission

Summary of the invention

This problem is solved, according to the present invention, by a planetary reduction gear with belts, comprising: a planetary mechanism in which there is a fixed wheel at the gearbox; characterised in that it has said fixed wheel divided into two halves between which a satellite wheel is inserted that is in contact for a wide arc with a belt, said belt, in turn, being in contact with the fixed wheel on a different arc to the previous one, but still wide; the shaft of the input rotation motion is equipped with an eccentric cam that determines the eccentricity of the satellite wheel with respect to the rotation axis and the axis of the fixed wheel coinciding with it; the motion of the output rotation is obtained by the satellite wheel so as to transmit the precession motion or orbital delay in the rotation of the satellite wheel on the belt; the two fixed and satellite wheels have slightly different diameters, and thus the transmission ratio is a function of the difference between said diameters; moreover, it has a mechanism for adjusting the eccentricity of the eccentric cam for the tensioning of the belt; finally, it has a synchronising front joint mechanism to compensate for the radial adjustment in tension of the belt with the shaft of the output motion.

In a preferred embodiment the reduction gear also has the belt equipped with a toothing in the inner surface and the fixed and satellite wheels correspondingly toothed.

In a preferred embodiment the reduction gear has, furthermore, the belt equipped with a toothing in the outer surface and the fixed and satellite wheels are smooth in correspondence to the inner surface of the belt.

In a preferred embodiment the reduction gear also has the belt equipped with small transversal reinforcing pins against the transversal bending stress present in the coupling with the fixed wheel and, in a different arc, with the satellite wheel.

In a preferred embodiment the reduction gear has, furthermore, the mechanism for adjusting the tension of the belt consisting of a frustoconical bushing, adjusted with axial position to the assembly of the reduction gear; the bushing is in contact with a ball that in turn radially pushes the eccentric cam on which the satellite wheel of the planetary mechanism is fitted so that it can rotate.

In a preferred embodiment the reduction gear also has the front joint synchronising mechanism with a ring with axial pins, opposite one another and engaged in guides at a right angle to each other, one of which is fixedly connected with the satellite wheel and the other with a flange fitted and rotating with the output shaft from the reduction gear.

In a further preferred embodiment the reduction gear also has two twin planetary mechanisms; the angular position of the eccentric cams determines the phasing of the mechanisms, advantageously at half a full revolution.

In a further preferred embodiment the reduction gear has, furthermore, more than two twin planetary mechanisms; the angular position of the eccentric cams is angularly adjusted with the equal division of the full revolution.

In a preferred embodiment the belt for the reduction gear with belts has, in the thickness of the belt, small pins or transversal reinforcements housed here to stiffen the belt in bending in the transversal direction.

In a preferred embodiment the belt for the reduction gear with belts, finally, has said small pins or transversal reinforcements preferably arranged in the inner or outer toothing present on the belt.

The characteristics and advantages of the present invention, in making a planetary reduction gear with belts, shall become clearer from the following description of an example embodiment, given for indicative and non limitative purposes, with reference to the five attached tables of drawings.

Brief description of the drawings

- Figure 1 represents a section along a plane intersecting the rotation axis, of a planetary reduction gear, in the figure with a belt that is flat and toothed on the outer surface, where there are two planetary mechanisms connected in parallel according to the invention;

- Figure 2 is a schematised view on an axial plane of the synchronising mechanism between the satellite wheel of a planetary transmission mechanism with belt and the output shaft;

- Figure 3 represents a view in a plane normal to the rotation axis of the mechanism of Figure 2, for synchronising between the satellite wheel and the output shaft to allow the tensioning of the belt;

- Figures 4, 5 and 6 represent, respectively, a view on an axial plane, a view on a plane normal to the rotation axis and an analogous section indicated D-D of just the planetary mechanism with toothed belt having inner toothing, according to the invention;

- Figures 7, 8 and 9 represent, respectively, a view on an axial plane, a view on a plane normal to the rotation axis and an analogous section indicated PR- PR of just the planetary mechanism with a belt that is flat

and toothed on the outer surface, as well as each individual tooth being equipped with a small pin, to reinforce it, according to the invention;

- Figures 10 and 11 represent, respectively, a view on a plane normal to the axis and an analogous section indicated DR-DR of just the planetary mechanism with a belt that is flat and toothed on the inner surface, as well as each individual tooth being equipped with a small pin, to reinforce it, according to the invention;

- Figure 12 represents a perspective view of the schematic section of Figure 11;

- Figure 13 represents a perspective view of the planetary mechanism according to the invention with the belt toothed on the inside, as well as each individual tooth being equipped with a small pin for reinforcement;

- Figure 13 represents a perspective view of the planetary mechanism according to the invention with a belt that is flat and toothed on the outer surface, as well as each individual tooth being equipped with a small pin for reinforcement.

Detailed description of a preferred embodiment

The planetary reduction gear with belt 1 consists of at least a planetary mechanism 2 in which an outer wheel 3 is fixedly connected with the outer box 4 of the reduction gear. Said outer wheel is divided into two halves 5 and 6 on a plane normal to the rotation axis A of both the fast input shaft 7 and the slow output shaft 8. The two halves 5 and 6 are spaced to receive just one satellite wheel 9 with its rotation axis eccentric with respect to the axis A; said satellite wheel 9 is coupled in rotation with an eccentric cam 10 made to rotate with the fast input shaft 7. Figure 1 represents two planetary mechanisms with two different eccentric cams 10 180 degrees apart, in order to balance the

mechanisms also in the presence of eccentricity and of the orbital motion of the satellite wheels 9; a belt 1 1 is stretched and adheres on a substantial winding arc to said wheels 9. The orbital motion of the satellite wheel 9 takes place by action of the eccentric 10 that pushes the satellite 9 from a withdrawn position to a position eccentric to the aforementioned fixed wheel 3. The difference in diameter between the fixed wheel 3 and the satellite wheel 9, as well as for the friction of both of the wheels on the belt 11 , makes it perform an orbital rotation with rotary translation of the satellite 9, which is collected by the output shaft 8 by means of a front synchronising joint 12, between the satellite 9 and the shaft 8, and a rotary flange 13 with which the shaft 8 is equipped.

Figure 1 also shows the command mechanism 14 of the eccentric cam 10, advantageously consisting of frustoconical bushings 15 for thrusting balls 16 in a radial direction, under the adjustment action of an axial screw 17, rotating in a bushing and engaged with the threaded portion 18 in the other frustoconical bushing.

In Figure 2 the synchronising mechanism has pins 19 for coupling with guides 20 in one direction, on said rotary flange 13, on a side of the front joint 12, whereas on the opposite side it has pins 21 for coupling with guides 22 in a direction normal to the previous one, on the satellite wheel 9.

In Figures 4, 5 and 6, due to the use of a toothed belt 25 and relative fixed wheel 33 and satellite wheel 39, instead of a flat one, and correspondingly in Figures 7, 8 and 9, due to the use of a belt that is flat and toothed on the outside 30, but each tooth 32 being reinforced with a small pin 31, it is possible to appreciate the compactness of the planetary mechanism with a single satellite 9, as well as the simplicity of construction also in the presence of substantial reduction ratios.

Figures 10 and 11, similar to Figures 4, 5 and 6, show the planetary mechanism with a single satellite 39 using a toothed belt 45 with inner toothing, but each tooth 42 being reinforced with a small pin 41.

In Figures 12, 13 and 14, it is possible to see in perspective the planetary mechanisms with a single satellite 9, 39, according to the invention, with belt having inner toothing 45, Figures 12 and 13, and outer toothing 30, Figure 14, but all with the small reinforcement pins 41, 31 in each tooth 42, 32.

The transmission of torque between the fixed and satellite wheels of the planetary mechanism takes place by friction in the internally flat belt or by meshing in the internally toothed belt; moreover, the contact occurs only centrally on the satellite wheel 9, 39 and only at the sides on the fixed wheel 3, 33, i.e. the two halves 5 and 6 or 35 and 36. The belt is, therefore, biased to bend in both cases, thus to substantially increase the tension of the belt, and consequently the torque than can be transmitted, the small pins 31 or 41 are present in the belt, advantageously housed in the inner functional teeth 42, of a known toothed belt, or of outer strengthening 32, in a flat belt 30, toothed on the outside, according to the present invention. Thus, the greater tension that can be applied allows the transmission of much higher torques of the belt without small reinforcement pins 31, 41.

The increase in transmissible torque, being linked to the tension of the belt, to the type of belt and to the friction between the wheels and the belt, is obtained, as can be seen in Figure 1, by adopting a twin planetary mechanism, coupled with the planetary mechanism with one satellite according to the invention, through a series or connection rods of a further flange in turn coupled, through a front synchronising joint 12, with the satellite wheel 9 of the twin planetary mechanism. Each satellite wheel is equipped with axial holes to allow the passage of said

connection rods.

The coupling of two twin planetary mechanisms is advantageous for easily balanced adjustment of the tension of the belts and for the balancing that can be obtained by positioning the eccentric cams in angular opposition relative to the two planetary mechanisms.

However, it is also possible to adopt more than two planetary mechanisms with one satellite, compatibly with the bulk of the resulting reduction gear.

In addition to what has been illustrated in the figures, i.e. the flat belt reinforced on the outside with a toothing, also further reinforced with a small pin in each tooth, the adoption of the internally toothed belt allows the transmission ratio to be precisely and constantly determined, even if the use of gear wheels does not allow variation of the transmission ratio, which depends upon the diameters of the fixed wheel 3, 33 and of the satellite wheel 9, 39, in a very free manner. As a matter of fact, with externally toothed wheels the variation can be by one tooth and not less; whereas with smooth wheels, i.e. with the belt flat on the inside, the variation in diameter can be minimal so as to obtain at minimal cost a series of transmission ratios that can be determined almost continuously during manufacturing.

The planetary reduction gear with belts can, advantageously, be built with fixed wheels 3, 33 and satellite wheels 9, 39 with small differences in diameter or also with the number of teeth different by one tooth; moreover, it is possible to have the diameter of the fixed wheel greater than the diameter of the satellite wheel or even vice-versa. In fact, since the output rotation is obtained from the precessional or delay motion, of evolution of the satellite wheel, the reduction ratio only depends upon the ratio between the diameters, whereas the greater diameter of a

wheel on the other determines the direction of rotation on the output shaft 8 in accordance with or opposing the direction of rotation on the input shaft 7.

As stated above with belts having inner toothing 45 ratios are obtained that are definite, but that can only be differentiated by single tooth, i.e. discretely; whereas, by using belts in the construction of the transmission, it is possible with small corrections of the diameters of the fixed wheels 3, 33 and satellite wheels 9, 39 involved to vary the transmission ratio with continuity when manufacturing it.

Finally, the reduction gear with belt of the present invention can work without lubricant since belts must work dry, while the rolling friction bearings used can be of the type with airtight seal, i.e. pre-lubricated.

Of course, a person skilled in the art can make numerous modifications to the planetary reduction gear with belts, described above in its various embodiments, in order to satisfy specific and contingent requirements, all of which are, moreover, covered by the scope of protection of the present invention as defined by the following claims. Thus, although less advantageously, the belt can be flat, which, to withstand the bending induced by the planetary gearing of the invention can be equipped with small pins or transversal reinforcement elements similar to the small pins 31 and 41 described above.