SE538038C2

SE538038C2 - Rigid harmonic drive

Info

Publication number: SE538038C2
Application number: SE1450285A
Authority: SE
Inventors: András Kis
Original assignee: Scania Cv Ab
Priority date: 2014-03-13
Filing date: 2014-03-13
Publication date: 2016-02-16
Also published as: DE102015002718A1; SE1450285A1

Abstract

17 SUMARY The invention refers to a gear mechanism (l)(2), inside the internal ring gear comprising aninternal ring gear a planet gear/wheel (3) (2),(9) as well as an input shaft (4) arranged at least one driving pinand an output driver shaft(5). The invention is achieved by that the at least onedriving pin (9) is arranged functionally between the planet gear/wheel (3) and a compensating ring (ll), that the at least one driving pin (9) is arranged non coaxial in relation to the(3), (ll) iS arranged eccentrically in relation to an output drive disc (7) planet gear/wheel and that the compensating ring and adapted to rotate the same, thereby transforming/convert-ing the hypocycloid movement of the at least one driving pin(9) to a regular rotational movement of the output drive disc (7). (Fig 2)

Description

The invention relates in general to gear mechanisms for highspeed reduction of a rotating input shaft and by a certainratio. The invention relates primarily to a planetary gearincluding only rigid parts. The invention is particularlyintended for commercial vehicles such as trucks/buses etc butis also usable in other applications where a more constantrotational speed is needed like industrial generators, inorder to adapt the engine speed to the generators, as well asfor special drive systems on trucks that needs PTO (Power Take OFF), like concrete trucks, tank vehicles with pump systems, crane vehicles etc. The invention also relates to a vehicle equipped with a gear mechanism according to the invention.

BACKGROUND ART Mechanical gears have been known for a long time and their main function is to reduce the speed of a shaft, e.g. an input shaft from an electric motor, an internal combustion engine or similar driving equipment.

A harmonic drive is an example of a compact gear that has ahigh reduction ratio. The harmonic drive uses an elasticplanet gear inside a solid ring gear. An oval rotating partmechanically connected to the input shaft, a “generator”, pushes a part of the elastic gear onto the outer ring gear whereby the elastic gear rotates slowly.

It is desirable to provide a gear mechanism that includes as few parts as possible and that have a high reduction ratio atthe same time as the size of the gear should be kept as smallas possible. Prior art illustrates a number of examples of gear mechanisms.

GB151786 illustrates for example a differential gear with anarrangement of internally geared differential gears where twoeccentrically pinions are so located as to balance each other.The gear includes a fixed internal toothed wheel and the gearratio and the speed reduction results from the diameterdifference on the double geared planet wheel, as well as thetwo different diameters of the ring gears. This is a well-known drive arrangement with a very high output ratio. Themain similarity between the present invention and this priorart technology is the input shaft, which is an eccentric driver.

US2010216585 illustrates a rolling ball type two-stage lowspeed changer device. The only similarity compared with thepresent invention is the eccentric input shaft and the epicyclical movement of the parts. The most important parts are the balls between the driver and the driven discs. Themovement of these balls makes the gear function.GB2357329 illustrates a cycloidal reduction device, or a so called cyclo drive. The cyclo drive is a mechanism for reducing the speed of an input shaft by a certain ratio. Cyclodrives are generally capable of high reduction ratios incompact sizes. The input shaft drives an eccentric bearingthat in turn drives a cycloidal disc in an eccentric,cycloidal motion. The perimeter of the disc is geared to astationary outer ring gear and has a series of output shaft pins or rollers placed through the face of the disc. These output shaft pins directly drive the output shaft as the cycloidal disc rotates. The radial motion of the cycloidal disc is not transferred to the output shaft. The similarity compared to the present invention is the cycloid movement, butthere are no compensation parts between the pins and the hole, and multiple pins are used as well.

DE102004048196 illustrates a conventional double disc cycloiddrive. One difference compared to the present invention is thecompensating ring which in this prior art is situated betweenthe pins of the driver and the holes of the output shaft. Thismechanism needs several driver pins.

Disadvantages for all prior art, are the high number of parts,which makes the manufacturing of the system more expensive.And of course the high number of parts also result in higherrisk of failure of the gear when in use. The present inventionis achieved by designing the gear mechanism with only onedriver pin. Prior art cycloidal drives need at least two pinsfor functioning, but usually several more pins are used.Some drawbacks with known prior art is also that a gearmechanism according to, for instance the cycloidal drive, isnot typically backdriveable and the input and output shafts ofthe mechanism cannot be reversed. Such an operation will havevery poor efficiency of the transmission, leading to premature failure.

Another drawback is that the eccentrically mounted cycloidaldisk will cause vibrations in the mechanism which willpropagate through the drive and shafts. This will also increase wear on the gear teeth of the cycloidal disk.

SUMARY OF THE INVENTION The object of the present invention is to solve the problemsindicated above and to create a gear mechanism with a highreduction ratios and that at the same time is small and compact in size.

A further object of the invention is to create a gearmechanism that is simple in design and that consists of as fewparts as possible and thus being cost effective to manufacture.

A further object of the present invention is that the gear mechanism should be easy to assemble and disassemble.

A further object is to provide a new and efficient mechanicalgear that is backdriveable so that the rotating motion may be reversed.

A further object is to provide a new and efficient mechanicalgear that has fewer gear contacts then normal and therebygenerates less noise.

A further object is to create a light gear mechanism.

The invention relates in general to gears for high speedreducing of a rotating input shaft, and by a certain ratio.The invention relates primarily to planetary gears and its main parts are made of rigid materials.

These and additional objects and advantages are achievedaccording to the invention with a planetary gear having the features according to the characterizing part of claim l.

The present invention consists of an internal ring gear, aplanet gear/wheel, a non-coaxial driving pin located on theoutput side of the planet gear/wheel, a non-coaxial compensating ring and, an input shaft, and an output driver disc with a non-coaxial hole. The invention is achieved bythat the at least one driving pin is arranged functionallybetween the planet gear/wheel and a compensating ring, thatthe at least one driving pin is arranged non coaxial inrelation to the planet gear/wheel, and that the compensatingring is arranged eccentrically in relation to an output drivedisc and adapted to rotate the same, thereby transforming/-converting the hypocycloid movement of the at least onedriving pin to a regular rotational movement of the outputdrive disc.

The internal ring gear is a fixed element, fixed to thesurrounding chassis. The teeth number difference between theplanet gear/wheel and the fixed internal ring gear, isrelatively small, typically one or two, but could be more. Asthe planet gear/wheel is rolling inside the fixed internalring gear, it makes a hypocycloid movement. When the planet gear/wheel rotates and complete one turn, its position issomewhat rotated compared to its starting point. This createsan angle difference and this is dependent on the teethdifference between the planet gear/wheel and the fixedinternal ring gear. This angle difference results in a smallangular turn of the output shaft. The planet gear/wheel isforced to rotate by an input drive shaft. The input driveshaft has a common axel with the internal ring gear, and hasan an eccentric shaft, which has a common axel with the planetgear/wheel. As the drive shaft rotates it forces the planet gear/wheel to rotate inside the fixed internal ring gear.

The planet gear/wheel has in turn an eccentric drive pinlocated on its opposite side in relation to the drive shaft.During the rotating operation the eccentric drive pin rotatesdescribing a hypocyclic movement. If the rotation speed of theplanet gear/wheel is compared to the input drive shaft, thedifference can be great, depending on the teeth numberdifference between the planet gear/wheel and the fixedinternal ring gear. This rotation speed difference is used inorder to increase or decrease the reduction ratio of the gear mechanism.

Since the eccentric driving pins movement path illustrates ahypocycloid in action, its movement cannot be transferreddirectly to the output shaft as a rotation movement. Thereforea "compensating ring" is designed and located between theplanet gear/wheel and the output shaft. A hole is arranged inthis compensating ring and located eccentrically compared tothe center of the compensating ring. The eccentric driving pinconnected with the planet gear/wheel is located inside this hole and rotates therein.

The hypocyclic movement is in this way transferred to acircular movement and could therefore easily be used forpractical purposes.

In the present invention only one driver pin is used. In priorart there are at least two and normally sex or more driverpins used, engaging in corresponding holes of a planet gear.In the present invention the only driving pin is locatedbetween the planet gear/wheel and the compensating ring andoutput shaft, normally fixed to the planet gear/wheel, andinserted in a hole in the compensating ring. But it is ofcourse also possible to locate the driving pin on the compensating ring engaging in a hole in the planet gear/wheel.

A Further difference between the present invention and priorart is that the compensating ring is a rigid disc with aneccentrically located hole. The purpose of this is to trans-form and convert the hypocycloid movement of the planetgear/wheel to a regular rotational movement which is transferred to the output shaft of the gear mechanism.

The invention results in a design that allows a high gearratio in a smaller size compared to prior art solutions.

It is also important that the number of gear contacts (numberof gear connected parts) is as small as possible andpreferably it is only one as is possible in the presentinvention, which results in that the gear mechanism generates low noise.

However one advantage with the present invention is thatmultiple gears are in contact all the time. Compared to normalcylindrical gear contacts, the invention uses an internal ringgear and a relatively large planet gear/wheel. For this reasonthe number of gears which are in contact at each time are greater than in cylindrical gear mechanisms. Of this reason the transferred torque may be higher in the present design.

The present invention could be used at any high ratioapplications that need a compact mechanism. Such examples are wind turbines, satellite dish adjustment, crane cable drums, cement truck chamber rollers, airplane landing gear movements, industrial mixers etc.

Some drawbacks may be identified with the present design,described in the preferred embodiments. The gear mechanism has in its most simple design without bearings relatively high internal friction. This can be reduced/eliminated by using rolling or needle bearings (not shown) in part of or at allsurfaces on the included parts that moves in relation to each other.

Another possible disadvantage is that the gear mechanism couldresult in some unbalance and vibrations. This may be reducedor eliminated by using double planet gears/wheels. In case oftwo planet gear/wheels the centrifugal force caused by the planet gear/wheels is balanced.

The gear mechanism according to the invention could also beassociated with some relative backlash! This could be reduced by tighter tolerances of the gears and other moving parts.

Also the light weight of a gear mechanism according to thepresent invention may be advantageous in all applications where slow movement and/or high torque is required and whereat the same time a requirement of small size mechanisms are desirable.

Further features and advantages of the invention will becomeapparent from the following more detailed description of the invention and the accompanying drawings and dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is described below in some preferred embodiments, in the light of the accompanying drawings.

Figure 1 illustrates in perspective a complete gear mechanism according to the invention.

Figure 2 illustrates in perspective an exploded view of the gear mechanism according to figure l.

Figure 3 illustrates a diagram of the cross section of the gear mechanism including a chassis.

Figure 4 illustrates the movement of a driving pin locatedbetween a planet gear/wheel and a compensating ring. Thehypocycloid movement of the driving pin is transformed in an output drive disc to a rotation movement on the output shaft.

Figure 5 illustrates more in detail a ring gear and the planet wheel/gear for calculation of the gear ratio.

Figure 6 illustrates a front view of the internal parts of the gear mechanism seen from the input side, i.e. from the side where the input drive shaft is located.

Figure 7 illustrates a front view of the internal parts of the gear mechanism seen from the output side, i.e. from the side where the output shaft is located.

DETAILED DESCRIPTION OF PREFFERED EMBODIMENTS The invention relates primarily to a gear mechanism for speedreducing of a rotating input shaft to an output shaft. Theinvention relates especially to a planetary gear mechanism where all rotating parts are rigid.

Figure 1 illustrates in a perspective view a planetary gear laccording to the invention. The gear mechanism l comprises an internal ring gear 2 and a planet gear/wheel 3 with a non- coaxial drive shaft 4 connected to the input side of the planet gear/wheel 3. An output shaft 5 can partly be seen atthe back side of the gear mechanism l. The drive shaft 4 islocated axially with the main parts of the gear mechanism land rotates the planet gear/wheel 3 by an eccentrically shaft 4 located shaft 6 as a part of the drive (not shown in detail). A part of an output drive disc 7 can be seen behind the planet gear/wheel 3.

Figure 2 illustrates an exploded view of the gear mechanism laccording to figure l. The input drive shaft 4 is arranged toengage with its eccentrically located shaft 6 to the planet gear/wheel 3 into its center hole 8. The planet gear/wheel 3is in turn arranged inside the internal ring gear 2 and is provided with an eccentrically located fixed drive pin 9 onthe opposite (back) side. This fixed drive pin 9 is arrangedto engage with a hole lO eccentrically located in a compen- sating ring ll which in turn is arranged in a hole l2 in theoutput drive disc 7. The output shaft 5 is fixed in the centerof the output drive disc 7. All parts are preferably rigid and may be manufactured by metal, plastic or similar material. All parts, except the internal ring gear 2, are rotating coaxially or eccentrically in relation to each other.

Figure 3 illustrates a kinematical model as a cross section ofthe gear mechanism l including a chassis 13. A rotation input,for example from an electric motor or an internal combustion engine, is rotating the drive shaft 4. The input drive shaft 4engages with its eccentrically located shaft 6 into the planetgear/wheel 3 and into its center hole 8. The planet gear/wheel3 is arranged inside the internal ring gear 2. The fixed drivepin 9 engage with the hole lO eccentrically located in the compensating ring ll which in turn is arranged in a hole l2 in 11 the output drive disc 7. The output shaft 5 is fixed in the center of the output drive disc 7.

The kinematical model of the inventive gear mechanism l issimilar to a cycloidal drive. One difference is that thedriving pin 9 is located on the planet gear/wheel 3, and thehole lO is located on the output drive disc 7. This could bereversed like in conventional cyclo drives, but in a preferredcase this arrangement is more advantageous because the size ofthe compensating ring ll can more easily be changed. This isnormally designed the other way around in the cycloidal drive.The compensating ring ll is a separate part in the present invention and makes it possible to transfer the eccentric movement into a rotation movement with only one driving pin 9.

Very important with the invention is that there is acompensating ring ll located between the output shaft 5 andthe planet wheels/gears driving pin 9 which transfers the pins9 hypocycloid movement to rotation on the output shaft 5. Thiscompensating ring ll could be used in any kind of cyclo drive,regardless the number of pins and holes in that system. Innormal case without a compensating ring in cyclo drives justbut if half of the pins are really driving at the same time, compensating ring would be applied to all, all the pins woulddrive all the time. The invention is not dependent of thenumber of driving pins 9, but this is the only known solutionto have a constant gear ratio with only one pin 9. But it could work also with 2, 3...6 or more pins as well. If a normal cyclo drive would be upgraded with this solution, itwould increase its efficiency, and the diameter of the pins 9could be reduced, due to the fact, that the load on each pin 9is half of the original. The gear mechanism l according to the invention could be designed with many driving pins 9, but the 12 described solution is the only way to use only one driving pin 9.

Figure 4 illustrates more in detail the movement pattern ofthe driving pin 9 located between the planet gear/wheel 3 andthe compensating ring ll. In this case the driving pin 9 isfixed to the planet gear/wheel 3 and the hypocycloid movementis transformed in an output drive disc 7 via the compensatingring ll to a rotation movement on the output shaft 5.

Figure 5 illustrates more in detail the input shaft 4, withits eccentrically driving shaft 6, which is driving the planet gear/wheel 3, within the internal ring gear 2 (not shown) for calculation of the gear ratio.

The formula: ~ <1 Z)"z _ 711 ZZ describes the rotation of the output shaft ng (the driving pin9 on the planet gear/wheel 3) compared to the rotation of theinput shaft nl (4) with the number of the teeth on the planetgear/wheel z2(3) and the internal ring gear 23 (2).

The formula: describes the output ratio: i=Z_planetary/(Z_ring-Z_planetary)In verbal form the gear ratio of the system is equal to the teeth number of the planet gear/wheel zg (3) divided by the 13 difference of the gear number of the internal ring gear z3 (2)and the planet gear/wheel 22 (3).is constant during operation of the gear The rotation (wnJo@m) mechanism l. That is possible by using the compensating ringll. Without the compensation ring ll, the ratio would bepulsating and the output speed omm would be dependent on the angular position of the input drive shaft 4.

Figure 6 illustrates a front view of the parts of the gear mechanism l seen from the front side, i.e. from the input side where the rotating drive shaft 4 is located. The drive shaft 4is located coaxially with the center axle Al of the gear mechanism l but has an eccentrically located shaft 6, locatedat an axle A2, engaging in the center of the planet gear/wheel3. The planet gear/wheel 3 rotates inside the internal ringgear 2. The output drive disc 7 also rotates coaxially with the center axle Al of the gear mechanism l.

Figure 7 illustrates a front view of the parts of the gear mechanism l seen from the output side, i.e. from the side where the output shaft 5 is located. The output drive shaft 5is located coaxially with the center axle Al of the gearmechanism l and is fixed to the center of the output drivedisc 7. The output drive disc 7 is provided with an eccentric-ally located hole l2 in which the compensating ring ll isinserted. The driving pin 9 is in turn eccentrically locatedin or on the compensating ring ll. The compensating ring llrotates around its center axle A4. The driving pin 9 has acenter axle A3 but rotates with the planet gear/wheel 3 around(not shown). its center axle A2 The driving pin 9 makes a hypocycloid movement in relation to the axle Al. 14 As indicated above the invention is particularly intended forthe driving systems of commercial vehicles such as trucks/- buses etc but the invention is also usable in other applica- tions where a more constant rotational speed is needed like inindustrial generators, in order to adapt the engine speed tothe generators. The invention is further usable for specialdrive systems mounted on trucks that needs PTO (Power Take OFF), like concrete trucks, tank vehicles with pump systems, crane vehicles etc.

The invention also relates to a vehicle equipped with a gear mechanism according to the invention.

The above description is primarily intended to facilitate theunderstanding of the invention. The invention is of course notlimited to the above embodiments but also other variants of the invention are possible and conceivable within the scope ofthe invention and the appended claims. The invention is ofcourse possible to use in other applications not mentioned here.

Claims

1. l. Gear mechanism (l) comprising an internal ring gear (2), a planet gear/wheel (3) arranged inside the internal ring gear(2), (4) and an output driver shaft at least one driving pin (9) as well as an input shaft (5),characterized by - that the at least one driving pin (9) is arrangedfunctionally between the planet gear/wheel (3) and acompensating ring (ll),is arranged non-(3), is arranged eccentrically in - that the at least one driving pin (9)coaxial in relation to the planet gear/wheel and- that the compensating ring (ll)relation to an output drive disc (7) and adapted to rotate thesame, thereby transforming/converting the hypocycloid movementof the at least one driving pin (9) to a regular rotationalmovement of the output drive disc (7).

2. Gear mechanism (l) according to claim l,characterized by (ll) is (12) that the compensating ring arranged to rotate inside an eccentrically located hole priovided in the output drive disc (7).

3. Gear mechanism (l) according to claim l or 2,characterized by (ll) (12) that the compensating ring is arranged in a hole arranged eccentrically in the output drive disc (7).

4. Gear mechanism (l) according to any preceding claims,characterized bythat the driving pin (9) makes a hypocycloid movement in relation to the axle (Al). 16

5. Gear mechanism (l) according to any preceding claims,characterized bythat the output shaft (5) is fixed at the center of the outputdrive disc (7).

6. Gear mechanism (l) according to any preceding claims,characterized by (ll) that the compensating ring rotates around its center axle

7. (A4).7. Gear mechanism (l) according to any preceding claims,characterized by that the planet gear/wheel is made of rigid material such asmetal, plastic or similar.

8. Gear mechanism (l) according to any preceding claims,characterized by (3,4,5,7,9,ll) that at least all rotating parts of the gear mechanism (l) is made of rigid materials such as metal,plastic or similar.

9. Gear mechanism (l) according to any preceding claims,characterized bythat the teeth number difference between the planet gear/wheel(2), (3) and the internal ring gear is relatively small.

10. Gear mechanism (l) according to any preceding claims,characterized by that the internal ring gear (2)(13). is fixed to the surroundinggear chassissuch as a truck or bus,

11. ll. Commercial vehicle, comprising a gear mechanism (l) according to any preceding claim.