WO2005075853A1

WO2005075853A1 - Eccentric gearbox

Info

Publication number: WO2005075853A1
Application number: PCT/IN2004/000039
Authority: WO
Inventors: Vishvas Vishvas Ambardekar AMBARDEKAR
Original assignee: Individual
Current assignee: Individual
Priority date: 2004-02-03
Filing date: 2004-02-03
Publication date: 2005-08-18
Anticipated expiration: 2006-08-03

Abstract

In this gearbox many eccentric gear pairs (1, 4), (2, 5) and (3, 6) are assembled in parallel, and are connected to a common input shaft (15) and a common output shaft (14). In every gear pair, one gear (1, 2, 3) keeps its orientation fixed is called as fixed gear (1, 2, 3) and another gear (4, 5, 6) that rotates about its own axis is called as moving gear (4, 5, 6). Difference in number of teeth on the two gears of an eccentric gear pair is kept to one tooth or more. Through proper selection of a particular gear pair any speed ratio can be selected. In this way, it is possible to make a compact gearbox, with multiple large speed ratios. Such a gear box can be used in automobiles, robot manipulators, earth moving equipments, space applications, toys, hand held tools and in many other applications.

Description

Title Of Invention Eccentric Gearbox

Technical Field

This invention deals with selectable large speed ratio eccentric gearbox and is a modification of the international patent application number PCT/IN02/00143, filed by Ambardekar, Vishvas P., bearing international filing date as 02/07/2002. In this gearbox many eccentric gear pairs are assembled in parallel, and are connected to a common input shaft and a common output shaft. In every meshing eccentric gear pair, one gear, called fixed gear, keeps its orientation fixed with respect to a fixed body and another gear, called moving gear, rotates about its own axis. The point of contact is moved on to the pitch circle of the fixed gear through some mechanism and the moving gear is connected to an output shaft. Difference in the number of teeth on the two meshing gears of an eccentric gear pair is kept to one or more. Through proper selection of a particular eccentric gear pair any speed ratio from the available speed ratios can be selected. In this way, it is possible to make a compact gearbox, with multiple (two or more) large speed ratios between input and output shafts. These types of gearboxes are useful mainly in automobiles, and in many other applicatiojns-wrιeτ-e ιigfFspeed engines like turbines are used. Such a gear box can also be used in robot manipulators, earth moving equipments, space applications, toys, hand held tools and in many other applications.

Background Art

Few existing patents:

• United States Patent No. 3996816, dated Dec. 14, 1976, titled "Harmonic Drive".

• United States Patent No. 3546972, dated Dec. 15, 1970, titled "Profile shifted involute internal gearing".

• United States Patent No. 5324240, dated Jun. 28, 1994, titled "Eccentric Gear System". All the afore-mentioned inventions deal with single speed ratio gear drives. In all these inventions it is difficult to have multiple speed ratio gearbox, from which a specific speed ratio can be selected. By using existing eccentric gear drives with turbines as a prime mover, it may be necessary to use a conventional gearbox in series with the eccentric drive to obtain selectable speed ratios.

Using the following description, it is possible to make an eccentric gearbox to have multiple (two or more) high speed ratios, any of the available speed ratios can be selected between input and output shaft by employing suitable gear engagement mechanisms. Though eccentric gearbox with any number of speed ratios can be made with following methodology, only three speed ratio gearboxes are explained here for easy understanding.

Definitions and Abbreviations:

Internal gear - A circular gear with internal teeth.

External gear - A circular gear with external teeth. Moving gear - The gear that rotates about its own axis, this axis is fixed with respect to a fixed body reference.

Fixed gear - The gear that does not change its orientation with respect to the fixed body. The axis of this gear revolves around the rotational axis of meshing moving gear. Eccentric - This is a part with two parallel axes. This part itself rotates about one of the axes and the other axis that guides some other part revolves around the first axis. To maintain the orientation of fixed gears, every fixed gear is mounted on two or more eccentrics that have preferably same eccentricity with their respective axes parallel. The eccentrics are free to rotate with respect to the respective fixed gear.

Eccentricity - The difference between the pitch circle radii of the two meshing gears forming an EGP. It is also the distance between the two parallel axes of an eccentric. The eccentricity should preferably be the same for all eccentrics associated to same EGP. EGP - This is abbreviated form of "eccentric gear pair", which is a gear pair with one internal gear and other meshing external gear. One of the gears is a fixed gear and the other one is the moving gear. Plural form of EGP is EGPs.

Identical EGP - The EGPs that have the same ratio of number of teeth on moving gear to that on fixed gear. The eccentricity for different identical EGPs need not be the same.

WRT - This is abbreviated form of "with respect to".

Common shaft - An assembly on which not more than one eccentric for any EGP, are mounted. Eccentrics are free to rotate WRT the respective common shaft except for the common shaft that is used as input shaft. In few cases few of the eccentrics may be fixed to the respective common shaft provided that the common shat is free to rotate WRT the fixed body. The common shafts are either fixed or free to rotate WRT the fixed body. A common shaft can have any number of eccentrics, not more than the number of EGPs in the gearbox, mounted on it for maintaining the orientation of the fixed gears.

Input shaft - A common shaft that is free to rotate WRT the fixed body and have at least one eccentric that is fixed to it or that can be engaged to it, mounted on it. The input shaft can have eccentrics that are fixed to it or that can be engaged to it or that are free to rotate WRT it. This assembly is used to get input from motion source to the gearbox.

Pitch circle - A reference circle on the plane normal to the rotational axis of a gear. The diameter of the pitch circle is used for calculations.

Pitch Cylinder - A reference cylinder, co-axial to the rotational axis of the gear, that passes through the pitch circle of the gear. Point of contact - A point common to pitch circles of the two meshing gears. The two pitch circles are tangential to each other at this point.

Line of contact - A line parallel to the axes of the two meshing gears and passes through the point of contact. This line is common to pitch cylinders of the two meshing gears. The two pitch cylinders are tangential to each other at this, line. Introduction:

This type of gearbox uses EGPs that makes it very compact in size for obtaining large speed ratio. With an eccentric gearbox, it may be possible to use a turbine without use of conventional gearbox connected to it, as a prime mover for automobiles and for many other applications. Use of such a gearbox can make very compact turbine-gearbox units that can replace the conventional reciprocating piston engine-gearbox units in future.

The working of such an eccentric gearbox is explained with the help of three drawings. These three drawings as listed below, give details of three different configurations of such a gearbox. The only joints where the adjacent parts are having relative motion are shown in the following drawings. Fixed joints and rigid joints are not shown in the following drawings instead the components that are rigidly connected are shown as a single component.

FIG 1 - Schematic sectional view, to explain a three speed eccentric gearbox, with external gears as fixed gears and internal gears as moving gears. Input shaft is connected to the eccentrics and output shaft is directly connected to the internal gears.

FIG 2 - Schematic sectional view, to explain a three speed eccentric gearbox, with external gears as fixed gears and internal gears as moving gears. Input shaft is connected to the eccentrics and output shaft is connected to the internal gears through an additional gear.

FIG 3 - Schematic sectional view, to explain a three speed eccentric gearbox, with external gears as moving gears and internal gears as fixed gears. Input shaft is connected to the eccentrics and output shaft is connected to the external gears. Principle of operation:

In FIG 1 , the external gears 1 , 2 and 3 are the fixed gears and the internal gears 4, 5 and 6 are the moving gears; gear pairs (1, 4), (2, 5) and (3, 6) are the EGPs. Two or more of each eccentrics 7, 8 and 9 in FIG 1 , are used to maintain the orientation of external gears 1 , 2 and 3 respectively. Individual common shafts 10 are used to mount one or more of these eccentrics on it. Thus two or more common shafts are to be used. These common shafts are supported at one end by the fixed body 11. A disk 12, which is free to rotate WRT the output assembly 13 and also supported by 13, is used to support other end of the common shafts. The internal gears 4, 5, 6 and output shaft 14 are coaxially connected to the output assembly 13. One of the common shafts 10, which has one eccentric for each EGP mounted on it, is used as input shaft 15 and is free to rotate WRT the fixed body 11. Eccentrics 7, 8 and 9, which are mounted on common shaft 10, are renumbered as 16, 17 and 18 as mounted on input shaft 15 respectively. This input shaft can also be made coaxial to the output shaft 14. An engagement mechanism 19 is employed to engage the input shaft 15 to any one of the eccentrics 16, 17 and 18 mounted on the input shaft. Theoretical lines of contact for EGPs (1 , 4), (2, 5) and (3, 6) are shown by 20, 21 and 22 respectively.

As shown in FIG 1 , when eccentric 17 is engaged with the input shaft, EGP (2, 5) get engaged between input and output shafts. If external gear 2 has N teeth and internal gear 5 has M teeth, where M > N, then the speed ratio obtained between the input and output shafts is M:(M - N). Thus by engaging different EGP, different speed ratios can be obtained.

FIG 2 is a schematic representation of the gearbox in FIG 1 that is made without the disk 12 and without connecting the output shaft directly to the output assembly 23. Only the components in FIG 2 that either have some obvious changes as compared to the corresponding components in FIG 1 or not shown in FIG , are provided with new numbers and explained further. Output shaft 24 is supported by fixed body 11 and is connected to the output assembly 23 through an external gear 25 that is coaxially fixed to 24. The output shaft is free to rotate WRT the fixed body 11. The output assembly 23, which is free to rotate WRT the fixed body 11 , has external gear 26 coaxially fixed to it and meshing with 25. All the common shafts 10 including the input shaft 15, in FIG 2, can be supported by the fixed body 11 at their both ends for providing better support to the eccentrics. Similar to the arrangement shown in FIG 1 , the arrangement shown in FIG 2 also has common shafts 10, one of the common shafts 10 working as an input shaft and numbered as 15, eccentrics, engagement mechanism, EGPs, etc., included in it. The internal gears i.e. the moving gears are coaxially mounted on an output assembly 23. The motion transfer from output assembly 23 to output shaft 26 can also be achieved by any other suitable mechanism instead of gear 25.

Another arrangement can be made in which the gear 26 is an internal gear instead of external gear as shown in FIG 2, and is coaxially fixed to the output assembly 23. Gear 26 is in mesh with an external gear 25. Gear 25 is coaxially fixed to the output shaft 24 that is free to rotate WRT fixed body. This arrangement can help bringing the axis of the output shaft closer to the axis of rotation of the output assembly 23. Appropriate design of all the components is must any arrangement.

As shown in FIG 2, when eccentric 17 is engaged with the input shaft, EGP (2, 5) get engaged between input and output shafts. If external gear 2 has N teeth and internal gear 5 has M teeth, where M > N, then the speed ratio obtained between the input shaft 15 and the output assembly 23 is M:(M - N). Thus by engaging different EGPs, different speed ratio can be obtained. The speed ratio between the input shaft 15 and the output shaft 24 is the product of the speed ratio between the input shaft 15 to output assembly 23 and the speed ratio between gear 26 and output shaft 24. In FIG 1 and FIG 2, the direction of rotation of the output assembly 13 and 23 is same as that of the input shaft 15 respectively.

It is also possible in the arrangements shown in FIG 1 and FIG 2 that the common shafts are supported only at one of its ends by fixed body 11 , in such a case disk 12 for arrangement in FIG 1 may not be necessary and can be avoided, the output shaft can also be made coaxial to the input shaft and can also be designed as to give additional support to the input shaft at its other end. In FIG 3, the internal gears 27, 28 and 29 are the fixed gears and the external gears 30, 31 , and 32 are the moving gears. Gear pairs (27, 30), (28, 31) and (29, 32) are the EGPs in FIG 3. Two or more numbers of each eccentric 33, 34 and 35 are used in FIG 3, to maintain the orientation of the internal gears 27, 28 and 29 respectively. Individual common shafts 36 are used to mount one or more of these eccentrics on it. Thus two or more common shafts are to be used. These common shafts are either fixed to or are free to rotate WRT the fixed body 37. One of the common shafts 36, which has one eccentric for each EGP mounted on it and is free to rotate WRT the fixed body 37, is used as input shaft. The eccentrics on the input shaft are fixed to the input shaft. The external gears 30, 31 and 32 are mounted on the output shaft 38 and are free to rotate WRT the output shaft. An engagement mechanism 39 is employed to engage the output shaft to any one of the external gears 30, 31 and 32. Theoretical lines of contact for EGP (27, 30), (28, 31) and (29, 32) are shown by 40, 41 and 42 respectively.

As shown in FIG 3, when external gear 32 gets engaged with the output shaft, the EGP (29, 32) get engaged between the input shaft and the output shaft. If external gear 32 has N teeth and internal gear 29 has M teeth, where M > N, then the speed ratio obtained between the input shaft and the output shaft is N:(M - N). The direction of rotation of output shaft is opposite to that of the input shaft.

Following different arrangements with appropriate use of common shaft are possible to make an eccentric gearbox:

• From the EGPs internal gears are used as fixed gears and meshing external gears as moving gears or external gears are used as fixed gears and meshing internal gears as moving gears.

• One eccentric for each of the fixed gears is mounted on the input shaft. These eccentrics are free to rotate WRT the input shaft. Moving gears are connected directly or coupled through output assembly to the output shaft. An engagement mechanism is employed to engage one of the eccentrics on the input shaft to the input shaft, thus engaging a particular EGP between the input shaft and the output shaft to select desired sped ratio.

• One eccentric for each of the fixed gears is fixed to the input shaft. Moving gears are free to rotate WRT output assembly. Output assembly is directly fixed or through some mechanism coupled to the output shaft. An engagement mechanism is employed to engage one of the moving gears to the output assembly, thus engaging a particular EGP between the input shaft and the output shaft to select desired speed ratio.

• One eccentric for each of the fixed gears is mounted on the input shaft. These eccentrics are free to rotate WRT the input shaft. Moving gears are free to rotate WRT output assembly. Output assembly is directly fixed or through some mechanism coupled to the output shaft. An engagement mechanism is employed to engage one of the moving gears to output assembly and associated eccentric, mounted on the input shaft, to the input shaft simultaneously, such that a particular EGP is engaged between the input shaft and the output assembly to select desired sped ratio.

• Moving gears are fixed to the output assembly. Output assembly is directly fixed or through some mechanism coupled to the output shaft. More than one input shafts are used; each input shaft is fixed with one eccentric, for different fixed gears. Thus number of input shafts used is equal to the number of EGPs used. A suitable engagement mechanism is used to connect one of the input shafts to the motion source, thus engaging any one of the EGPs between input and output shafts; thus selecting desired speed ratio.

• Moving gears are fixed to the output assembly. Output assembly is directly fixed or through some mechanism coupled to the output shaft. More than one input shafts are used; each input shaft is mounted with one or more eccentrics, for different fixed gears. These eccentrics are either free to rotate WRT the input shaft or fixed to the input shaft, accordingly a suitable engagement mechanism is used to engage a particular eccentric to the input shaft. Another gear engagement mechanism is used to connect appropriate input shaft to the motion source, thus connecting one of the EGPs between input and output shafts, to select desired speed ratio.

• Any other method, that can ensure that at a time only one EGP from the available EGPs of the gearbox is engaged between the input and output shafts for power and motion transfer, can be employed for proper functioning of the gearbox. Thus a particular speed ratio can be selected between the input and the output shaft. When only one EGP is connected between input and output shafts and other EGPs are totally out of engagement, the efficiency and life of the gearbox may increase; this may introduce high impact at the time of changing the engagement from one EGP to other EGP.

• More than one eccentric for any fixed gear are coupled together. If any of the coupled eccentrics is given input, other coupled eccentrics share the load simultaneously and keep only associated EGP engaged. This type of arrangement is applicable for all above-mentioned arrangements with appropriate modification.

In all the above-described gearboxes only one EGP is connected between the input and the output shafts. It is also possible to simultaneously connect and engage more identical EGPs, at appropriate phase difference between input and output shafts instead of single EGP, for any speed ratio. Appropriate modifications for select mechanisms, number of simultaneously engaged eccentrics, number of simultaneously engaged moving gears, number of eccentrics, number of common shafts, number of eccentrics on the input shafts, etc. are to be worked out based on the above description for using multiple identical EGPs simultaneously. These identical EGPs give same speed ratio and thus can be used simultaneously. Use of multiple identical EGPs instead of a single EGP may reduce vibration and increase balancing in the gearbox. For better load distribution few or all the eccentrics maintaining the orientation of a fixed gear can be coupled together.

For the parts, which are free to rotate, for reducing friction appropriate bearings and lubrication systems are to be used. In above description gear teeth and different joints of various components are not shown for simplicity of understanding. Proper lubrication scheme has to be worked out as per the specific application. Unless required for the engagement mechanism, it may be necessary to restrict axial movement of the rotating parts to ensure proper engagement of the gears within EGP, proper engagement of parts that are engaged through engagement mechanism and proper functioning of the gearbox. Individual common shafts within a gearbox can have different designs with different shapes and sizes. Similarly individual eccentrics used for maintaining the orientation of a fixed gear within a single EGP can have different sizes but should have same eccentricity.

Advantages of the eccentric gearbox:

• It is very compact as compared to the conventional multistage gearbox for the same speed ratios.

• As many teeth are interlocked, the operation of the gearbox is smooth. • Can be directly connected to a turbine to give practically useful low speed output.

• Turbine-eccentric gearbox units can replace existing reciprocating piston engine-gearbox, thus the benefits of turbine over conventional reciprocating piston engine can be utilized. • Such a gearbox can be designed for any number of speed ratios.

• More number of common shafts can be used for better load distribution.

• Multiple identical EGPs can be used simultaneously.

• Coupling of the eccentrics for the same EGP is possible.

• Being a gearbox with all metal parts, wide range of materials can be used for its components and thus such a gearbox can be used for speed reduction and also for torque multiplication.

• Being a positive drive such a gearbox can also be used as a speed multiplier and torque reducer just by using the above explained input shaft as output shaft and vice versa.

Disadvantages:

• As many eccentrics are used and high input speed is involved, balancing of the gearbox has to be carried out very carefully.

• Unconventional gear teeth form may have to be used.

Claims

1. An eccentric gearbox that uses more than one EGPs for its operation; each EGP has either one moving gear with external teeth and meshing one fixed gear with internal teeth or one moving gear with internal teeth and one meshing fixed gear with external teeth; every fixed gear is mounted on two or more eccentrics to maintain its orientation; all the eccentrics associated with any EGP have approximately same eccentricity and their respective axes are parallel; one or more of the eccentrics are mounted on individual common shafts such that not more than one eccentric for any EGP is mounted on a single common shaft; these common shafts are appropriately supported and are either free to rotate or fixed WRT a fixed body; the eccentrics are free to rotate WRT the respective fixed gear; these individual eccentrics are either free to rotate WRT the common shaft or are fixed to the common shaft on which they are mounted; one or more common shafts that are free to rotate WRT fixed body are used as input shafts for motion input to the gearbox; the eccentrics, which are being given input motion, are either fixed or able to be engaged to the respective input shafts, other eccentrics are free to rotate WRT the respective input shafts; at a time input motion is given simultaneously to one or more eccentrics associated with an EGP; moving gears are connected directly or coupled through some additional gear or through some other mechanism to the output shaft; one of the EGPs is engaged between the input and output shafts through some engagement mechanism, to select a desired speed ratio from the speed ratios available through the gearbox.

2. An eccentric gearbox as claimed in claim 1 in which the moving gears are connected to or coupled with the output shaft, such that the moving gears and the output shaft can not rotate independent of each other; only one input shaft is used that has one eccentric for every EGP mounted on it; these eccentrics are free to rotate on the input shaft; one engagement mechanism is employed to engage one of the eccentrics to the input shaft, to engage one of the available EGPs between the input and output shaft to select desired speed ratio between the input and output shafts.

3. An eccentric gearbox as claimed in claim 1 that has moving gears that are free to rotate WRT the output shaft; one input shafts is used that has one eccentric for every EGP rigidly mounted on it; an engagement mechanism is employed to engage one of the moving gears to the output shaft, to engage one of the available EGPs between the input shaft and the output shaft, to select desired speed ratio between the input and output shafts.

4. An eccentric gearbox as claimed in claim 1 that has moving gears that are free to rotate WRT the output shaft; one input shaft is used that has one eccentric for every EGP mounted on it; these eccentrics are free to rotate WRT the input shaft; one engagement mechanism is employed to simultaneously engage one of the eccentrics to the input shaft and one moving gear that are associated with the same EGP, to the output shaft, as to engage only one of the available EGPs between the input and output shafts as to select desired speed ratio between the input and output shafts.

5. An eccentric gearbox as claimed in claim 1 in which the moving gears are connected to or coupled with the output shaft, such that the moving gears and the output shaft can not rotate independent of each other; it has multiple input shafts; these each individual input shafts have one eccentric fixed to it, other eccentrics mounted on the input shafts are free to rotate WRT the respective shaft; the eccentric fixed to the individual input shafts give input to individual EGPs; an engagement mechanism is employed to connect one of the input shafts to the source of motion to engage one EGP between the input and the output shaft to select a desired speed ratio.

6. An eccentric gearbox as claimed in claim 1 that has moving gears that are free to rotate WRT the output shaft and has multiple input shafts that has at least one eccentric fixed to individual input shafts, rest of the eccentrics mounted on the input shafts are free to rotate WRT the respective input shaft; an engagement mechanism is used to simultaneously engage one of the input shafts to the motion input source and one of the moving gears to the output shaft as to engage only one EGP between the motion input source to the output shaft to select a desired speed ratio.

7. An eccentric gearbox as claimed in claims 1 to 6, in which more than one eccentrics associated with same EGP are coupled together as to synchronize their motion or to simultaneously give input to these eccentrics associated with the EGP that is engaged in between the input shaft and the output shaft.

8. An eccentric gearbox as claimed in claims 1 to 7, in which more than one identical EGPs are used and are engaged simultaneously instead of engaging one EGP in between the input and output shafts; any suitable engagement mechanism is used to engage these identical EGPs between the input and the output shafts; in this case the eccentrics and moving gears associated with one EGP in the fore said claims are to be considered appropriately as the eccentrics and moving gears associated with simultaneously engaged identical EGPs respectively and accordingly other components of the gearbox are to be considered appropriately.

9. An eccentric gearbox as claimed in claims 1 to 8, in which the regular input shaft works as output shaft and the regular output shafts works as input shaft to make the gearbox work as selectable speed ratio speed multiplier.

10. An eccentric gearbox as claimed in the claims 1 to 9 in which suitable lubrication scheme and bearings are used appropriately for reducing friction.

11. An eccentric gearbox as claimed in the claims 1 to 17; which is used for obtaining multiple speed ratios between input and output shaft so that any one of the speed ratios can be selected for use.