WO2003019042A1

WO2003019042A1 - Eccentric planetary gear drive

Info

Publication number: WO2003019042A1
Application number: PCT/IN2001/000150
Authority: WO
Inventors: Vishvas Ambardekar
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-08-29
Filing date: 2001-08-29
Publication date: 2003-03-06
Anticipated expiration: 2004-02-29

Abstract

The patent deals with a gear drive, which gives a large gear ratio in a single stage speed reduction using circular gears. An unlimited gear drive comprising of a circular internal gear (1) in mesh with a circular external gear (2) with their axes parallel to each other; one of the said gears that is fixed gear maintains its orientation unchanged throughout with respect to a fixed part; the other said gear i.e. moving gear rotates about its own axis and is connected directly or through some linkage to the output shaft; the input shaft directly or through an input link forces the point of contact to move on pitch circle of one of the said gears. Such a drive can be used in automobiles, robot manupulators, earth moving equipments, space applications, toys, hand-held tools and in many other such applications.

Description

TITLE OF INVENTION Unlimited Gear Drive TECHNICAL FIELD

This patent deals with a gear drive, which can give a large gear ratio in a single stage speed reduction using circular gears. In this unlimited gear drive a gear pair is used with one internal gear and one external gear. In this drive, axis of one gear revolves around the axis of the other gear. One of the gears maintains its orientation and other gear rotates about its own axis. The output shaft is connected directly or through a linkage to the gear, which rotates about its own axis. The input link moves the point of contact on the pitch circle of the gear, which has the fixed axis. The drive can be made very suitable for high torque application by using suitable materials for the gears and the gear teeth. For a specific application the gear tooth profile may have to be designed carefully. In final output stage the drive may use linkage to transfer motion between two parallel shafts for driving output shaft. Input shaft and final output shafts can be but not necessarily be aligned for better performance. The gear ratio obtained is the ratio between the difference in the number of teeth on both the gears and the number of teeth on one of the gears (internal OR external as per the specific case may be). The gear with external teeth should have at least one tooth less than the number of teeth on the gear with internal teeth. Such a drive can be used in automobiles, robot manipulators, earth moving equipments, space applications, toys, hand held tools and in many other applications. Background Art:

Existing patent: United States Patent No. 3996816, dated Dec. 14, 1976, titled "Harmonic Drive". Below are listed few points for comparison and improvements achieved in the present invention over the above-mentioned existing patent.

1. The harmonic drive uses a flexible "flexspline" for its operation. In the present invention "Unlimited gear drive" no flexspline is used, but only rigid circular gears are used.

2. In "Harmonic drive" the difference in the number of teeth on the internal spline and the flexspline can be two or a multiple thereof.

In present invention "unlimited gear drive" the difference in the number of teeth on internal gear and the external gear can be one or more. Thus higher gear ratio is possible in "unlimited gear drive" for comparatively small size.

3. In "Harmonic Drive" only few teeth are in contact, thus the pressure on the meshing teeth is very high. In the present invention "unlimited gear drive" more number of teeth are in contact and thus reduces the pressure on the individual tooth. Every tooth gets into full contact gradually. This distributes pressure among many teeth and also it reduces the pressure gradient on a single tooth in the present invention. More number of teeth in contact and rigid gears in the present invention gives longer life to the present invention. 4. In the present invention "unlimited gear drive", use of rigid gear teeth makes it more suitable for high torque application. Definitions:

Internal gear - A circular gear with internal teeth. External gear - A circular gear with external teeth. Fixed gear - The gear with fixed orientation.

Moving gear - The gear that rotates about its own axis.

Pitch circle - A reference circle on the plane normal to the rotational axis of the gear, the diameter of the pitch circle is used for calculations. Pitch cylinder - A cylinder, co-axial to the rotational axis of the gear, that passes through the pitch circle of the gear. As most of the time the gear cross section is referred, only pitch circle is referred in the explanation that follows. Point of contact - Theoretical common point on the pitch circles of the two meshing gears. The two pitch circles are tangential to each other on this point.

Line of contact - Theoretical common line on the pitch cylinders of the two meshing gears. The two pitch cylinders are tangential to each other on this line. This line is always parallel to the axes of the two gears and passes through the point of contact. As most of the time the gear cross section is referred, only point of contact is referred in the explanation that follows.

Eccentricity - Half the difference between the pitch circle diameters of the two meshing gears-forming gear pair as in Fig. 1 , Fig. 2 and Fig. 3. The eccentricity should preferably be same for all the parts in a particular configuration of the unlimited gear drive.

Dj - Pitch circle diameter of the internal gear with more number of teeth.

D_e - Pitch circle diameter of the external gear with less number of teeth. ε - Eccentricity.

NOMENCLATURE FOR DRAWING SHEETS 1 TO 6

1. - Internal Gear ( Fig. 1 , Fig. 2 & Fig. 3)

2. - External Gear ( Fig. 1, Fig. 2 & Fig. 3)

3. - Eccentricity 14.24 mm ( Fig. 1 ) 4. - Eccentricity 4.75 mm ( Fig. 2)

5. - Eccentricity 2.37 mm ( Fig. 3)

6. - Difference between pitch circle radius and root radius 0.2 mm (Fig. 1A, Fig. 2A).

7. - Tooth profile radius 2.5 mm ( Fig. 1 A, Fig. 2A & Fig. 3A)

8. - Tooth height 5 mm ( Fig. 1 A, Fig. 1 B)

9. - Tooth profile radius 5 mm ( Fig. 1 A, Fig. 2A) 10. - Tooth profile radius 2 mm ( Fig. 1 B, Fig. 2B)

11.- Tooth profile radius 5.1 mm ( Fig. 1 B, Fig. 2B)

12.- Pitch Circle Radius 159 mm (Fig. 1A)

13.- Pitch Circle Radius 144.76 mm (Fig. 1 B)

14.- Pitch Circle Radius 159 mm (Fig. 2A) 15.- Pitch Circle Radius 154.25 mm (Fig. 2B)

16.- Pitch Circle Radius 159 mm (Fig. 3A)

17.- Pitch Circle Radius 156.63 mm (Fig. 3A)

18.- Tooth profile root radius 159.2 mm (Fig. 2A, Fig. 3A)

19.- Tooth profile tip radius 154 mm (Fig. 2A) 20. - Tooth profile radius 2.4 mm (Fig. 3A)

21.- Tooth profile radius 4.4 mm (Fig. 3A)

22.- Tooth profile radius 4.5 mm (Fig. 3A)

23.- Tooth height 4.4 mm (Fig 3A)

Introduction: A gear drive with large gear ratio is very useful. Such a gear drive can allow us to use a gas turbine to drive an automobile. Without such a gear drive use of gas turbine for driving an automobile is very difficult and may not be efficient.

The working of the unlimited gear drive is explained with the help of figures, as listed below:

FIG. 1 - A typical gear pair with 67 internal teeth on the gear (1 ) and 61 external teeth on the gear (2). The eccentricity is 14.24 mm. FIG. 1A - The details of the area marked with FIG. 1A in FIG. 1 , to show the tooth profile for the gear (1). In this case the pitch circle radius of gear

(1 ) is 159 mm (12)

FIG. 1B - The details of the area marked with FIG. 1 B in FIG. 1 , to show the tooth profile for the gear (2). In this case the pitch circle radius of gear

(2) is 144.76 mm (13).

FIG. 2 - A typical gear pair with 67 internal teeth on the gear (1) and 65 external teeth on the gear (2). The eccentricity is 4.75 mm. FIG. 2A - The details of the area marked with FIG. 2A in FIG. 2, to show the tooth profile for the gear (1). In this case the pitch circle radius of gear

(1 ) is 159 mm (14).

FIG. 2B - The details of the area marked with FIG. 2B in FIG. 2, to show the tooth profile for the gear (2). In this case the pitch circle radius of gear

(2) is 154.25 mm (15). FIG. 3 - A typical gear pair with 67 internal teeth on the gear (1) and 66 external teeth on the gear (2). The eccentricity is 2.37 mm. FIG. 3A - The details of the area marked with FIG. 3A in FIG. 3, to show the tooth profile for the gear (1) and gear (2). In this case the pitch circle radius of gear (1 ) is 159 mm (16) and that of gear (2) is 156.63 mm (17). FIG. 4 - The schematic arrangement of the gear pair for configuration-1. (10) represent the toothed portion of the gear with internal teeth (more number of teeth) and (9) represent the toothed portion of the gear with external teeth (less number of teeth). (11) represent the mid span of the meshing zone between the two gears. Fig. 5 - View from input shaft side for schematic arrangement of configuration-2, showing the three eccentric parts (4). FIG. 5A - Shows the approximate section at A-A in FIG. 5, to show the schematic arrangement of the gear pair for configuration-2. (10) represent the toothed portion of the gear with internal teeth (more number of teeth) and (9) represent the toothed portion of the gear with external teeth (less number of teeth). (11) represent the mid span of the meshing zone between the two gears. FIG. 6 - The schematic arrangement of the gear pair for configuration-3. (10) represent the toothed portion of the gear with internal teeth (more number of teeth) and (9) represent the toothed portion of the gear with external teeth (less number of teeth). (11 ) represent the mid span of the meshing zone between the two gears. FIG. 7 - The schematic arrangement of the gear pair for configuration-4. (9) represent the toothed portion of the gear with internal teeth (more number of teeth) and (8) represent the toothed portion of the gear with external teeth (less number of teeth). (10) represent the mid span of the meshing zone between the two gears. Principle of operation:

In the gear arrangement shown in fig. 1 , one internal gear (1) (with more number of teeth) and one external gear (2) (with less number of teeth) are in mesh. If one of the gear is fixed and the (theoretical) point of contact (or the line of contact) is moved by some input link (not shown in the fig.1 ), on the pitch circle (or on the pitch cylinder) of the fixed gear, the other gear (the moving gear) rotates about its own axis while its axis revolves around the axis of the fixed gear. Total rotation of the moving gear about its own axis for one complete revolution of the point of contact on the pitch circle of the fixed gear equals to the difference in the number of teeth on the two meshing gears. If an output shaft is connected to the said moving gear as to have the same rotational speed as that of the moving gear, very large gear ratio in the rotational speed of the input link (rotational speed of the point of contact on the pitch circle) to rotational speed of the output shaft can be obtained.

Similarly, in Fig. 1, if the orientation of one of the gears (fixed gear) is fixed and axis of the other gear (moving gear) is fixed and these two gears are in mesh. If the point of contact is moved on the pitch circle of the moving gear, for one revolution of the point of contact, the moving gear rotates about its own axis by the difference in number of teeth on the two gears. If the input shaft is connected to a link which rotates the point of contact on the pitch circle of the moving gear, and the output shaft is connected to the moving gear in a way to have the same rotational speed as that of the moving gear. Large gear ratio between the input link and output shaft can be obtained.

For example (refer Fig. 1 ) internal gear (1) has N number of teeth and external gear (2) has M number of teeth (where N>M, and (N-M) >1), following two cases are explained: Case (a) Internal Gear (1) is fixed.

Point of contact is moved on the pitch circle of gear (1) for one revolution, keeping gear (2) always in mesh with gear (1). Gear (2) rotates about its own axis by (N-M) teeth for one revolution of the point of contact, which is equal to one revolution of the input link. One revolution of the point of contact on the pitch circle of gear (1) is equivalent to rotation by N teeth. Thus the speed ratio between the rotations of the input link to that of external gear (2) is N/(N-M). In other words the speed ratio is the ratio between the pitch circle diameter of the internal gear and twice the eccentricity of the unlimited gear drive. In this case the direction of angular motion of the input link and that of external gear (2) are opposite. Speed ratio =(π * Dj) / (π * (Di - D_e)) = Di / (D_s - D_e) = Di / (2 * ε) = N/(N-M) Case (b)

External Gear (2) is fixed.

Point of contact is moved on the pitch circle of gear (2) for one revolution, keeping gear (1 ) always in mesh with gear (2). Gear (1) rotates about its own axis by (N-M) teeth for one revolution of the point of contact, which is equal to one revolution of the input link. One revolution of the point of contact on the gear (2) pitch circle is equivalent to rotation by M teeth. Thus the speed ratio between the rotations of the input link to that of internal gear (1) is M/(N-M). In other words the speed ratio is the ratio between the pitch circle diameter of the external gear and twice the eccentricity of the unlimited gear drive. In this case the external gear (2) and point of contact (input link) rotates in the same angular direction. Speed ratio =(π ^* D_e) / (π ^* (Di - D_e)) = D_e / (Di - D_e) = D_e / (2 ^* ε) = M/(N- M) Calculation for the gear ratio:

From the above two cases it can be understood that by selecting appropriate number of teeth on the either gears, large gear ratio can be obtained in a single stage reduction. For ease of understanding, few typical combinations of gears and gear tooth profiles are shown in fig.1 , fig.2 and fig.3.

Fig.1 shows a gear pair with N=67 and M=61. Pitch circle diameter of internal gear (1) = 318 mm, and that of external gear (2) = 318*61/67= 289.52mm. For case (a), the gear ratio obtained is 67/6 = 11.17 and for case (b) the gear ratio obtained is 61/6 = 10.17. Fig.2 shows a gear pair with N=67 and M=65. Pitch circle diameter of internal gear (1) = 318 mm, and that of external gear (2) = 318^*65/67= 308.51mm. For case (a), the gear ratio obtained is 67/2 = 33.5 and for case (b) the gear ratio obtained is 65/2 = 32.5. Fig.3 shows a gear pair with N=67 and M=66. Pitch circle diameter of internal gear (1) = 318 mm, and that of external gear (2) = 318^*66/67= 313.25mm. For case (a), the gear ratio obtained is 67/1 = 67 and for case (b) the gear ratio obtained is 66/1 = 66. For the fig.1 , fig.2 and fig.3 the pitch circle diameter of the internal gear (1 ) is kept at 318mm, this diameter can suitably be changed to any suitable value for a particular (unlimited gear drive) gear drive. Selecting appropriate number of teeth on the two gears decides the gear ratio. The tooth profile for both the gears may have to be designed appropriately. Maximum tooth height from the pitch circle is limited to the difference in the pitch circle diameters of the two gears. Eccentricity is equal to half the difference between the pitch circle diameters of the two gears.

Using the above approach four different configurations of unlimited gear drive can be made to give large gear ratio in a single stage reduction. Details of the four configurations of the unlimited gear drives are given below: Configuration-1 (Fig.4).

In this arrangement part (1 ) is the external gear mounted on a circular rim (7) with joint (J2). This rim, with appropriate eccentricity, has the input shaft (2) rigidly connected to it. Input shaft (2) is connected to the fixed part (3) through joint (J1). This fixed part (3) has the internal gear (10) rigidly connected to it. The gear (10) is the fixed gear. The part (1 ) also has external gear (9) rigidly connected to it, which rotates about its own axis. Part (1 ) has a concentric shaft (8) rigidly connected to it. This shaft (8) is connected to the output shaft (5) through a coupling (6). This coupling rotates the output shaft at the same angular speed of that of the external gear (9), even though the axes of the two gears are not aligned. Here, for the simplicity of understanding, Oldham's coupling is used. The Coupling to be used can be of any type, which ideally can give instantaneous velocity ratio of unity and is capable of transferring motion between two non-aligned parallel shafts. For example instead of Oldham's coupling one can use double universal coupling or two constant velocity ball socket joints in series, or any other coupling that has the above mentioned characteristics.

Part (4) is a circular disk with an eccentric hole to support the shaft (8) of part (1) through joint (J4). Part (4) forces the axis A1 of part (1 ) to revolve around axis A2 of the internal gear (10) and also allows part (1 ) to rotate about its own axis A1. Input link (circular rim (7)), forces the point of contact (11 ) to shift on the pitch circle diameter of the internal gear (10).

All the joints J1 , J2, J3, J4 and J5 are shown as journal bearings and each can conveniently be replaced by any other suitable bearing like ball bearing, roller bearing, needle bearing, etc. to reduce friction and to achieve compactness in the product. All the parts with eccentricity have the same eccentricity. Velocity ratio between input shaft (2) to output shaft (5) depends on the number of teeth on either gears (9) and (10) and can be determined in a way as explained in the case (a). The direction of rotations of input shaft and output shaft are opposite to each other. Configuration - 2 (Fig.5 and Fig. 5A)

In this configuration the output shaft (1) is concentric and rigidly connected to the external gear (7), which is in mesh with revolving internal gear (10). Internal gear (10) is rigidly connected to revolving part (3). Part (2) is a disk connected to part (3) through joint (J2) and has an eccentric hole to support output shaft (1 ) through joint (J1 ). In this configuration part (6) is fixed and is mounted with minimum three number (for easy operation) of part (4) through joint (J6). Part (4) has an eccentric shaft, which is connected to part (3) through joint (J5). These three parts (4) restrict the axis A2 of Gear (10) to revolve around axis A1 of Gear (9) and keep its orientation fixed with respect to the fixed part (6). External gear (7) has a fixed axis and rotates about its own axis. Input shaft (5) has an eccentric disk (8) rigidly connected to it, this disk is connected to part (3) through joint (J3). Disk (8) forces the point of contact (11) to shift on the pitch circle diameter of external gear (7) with external teeth (9). Joint (J4) is provided just to support the part (1 ).

All the joints J1 , J2, J3, J4, J5, J6 and J7 are shown as journal bearings and each can conveniently be replaced by any other suitable bearing like ball bearing, roller bearing, needle bearing, etc. to reduce friction and to achieve compactness in the product. All the parts with eccentricity have the same eccentricity. Velocity ratio between input shaft (5) to output shaft (1 ) depends on the number of teeth on either gears (9) and (10) and can be determined in a way as explained in the case (a). The direction of rotation of input shaft and output shaft is opposite to each other. Configuration - 3 (Fig.6)

In this configuration the rim (7) is rigidly connected to fixed part (1) and external gear (9). The input shaft (2) is rigidly connected to the eccentric disk (8). The input shaft (2) is concentric and connected to the external (fixed) gear (9) through joint (J5). Internal gear (10) is rigidly connected to part (3), which is connected to the disk (8) through joint (J3). Part (3) is rigidly connected to the intermediate shaft (12). Shaft (12) is concentric to Gear (10). Shaft (12) is connected to output shaft (5) through Oldham's coupling (6). As explained in the configuration-1 , this Oldham's coupling can conveniently be replaced by any other coupling e.g. double universal coupling or two constant velocity ball socket joints in series, or any other coupling which has the characteristics as mentioned in configuration-1.

As the input shaft (2) rotates, the point of contact (11 ) determined by the disk (8) between the two meshing gears moves on the pitch circle of gear (9) and thus the axis A2 of gear (10) revolves around axis A1 of the gear (9). Also the part (3) and internal gear (10) rotates about its own axis A2. Part (4), is a disk with an eccentric hole in it, and is used to give support to the part (3). All the joints J1 , J2, J3, J4 and J5 are shown as journal bearings and can suitably be replaced by other types of bearings for reducing the friction, as per the specific requirements. In this configuration the direction of the input and the output shaft is same. The gear ratio can be calculated as in case (b). Configuration - 4 (Fig. 7)

In this configuration shaft (1 ) is the output shaft and is rigidly connected to part (3). The output shaft (1) is also concentric to the gear (9). The internal gear (9) is rigidly connected to the part (3). Axis of gear (9) is fixed. Input shaft (5) is rigidly connected to the eccentric rim (6). The eccentric rim (6) is connected to the part (7) through joint (J4). External gear (8) is rigidly connected to part (7). Three eccentric parts (4) are mounted on the fixed part (2) through joint (J2). These eccentric parts (4) are connected to part (7) through joint (J3). These three eccentric parts (4) keep the orientation of the external gear (8) fixed, with respect to the fixed part (2). Parts (4) also constrain the axis A1 of gear (8) to revolve around the axis A2 of the gear (9). Gear (9) is connected to fixed part (2) through joint (J6). Joint (J7) is used to support the eccentric input link (6).

When the input shaft rotates, the input link (6) forces the point of contact (10) to move on the pitch circle of the gear (9). The axis A1 of the gear (8) revolves around the axis A2 of the gear (9), without changing the orientation of the gear (8). Internal gear (9) rotates about its own axis A2. Axis A2 is fixed. The rotation of the gear (9) is available on the shaft (1) as it is rigidly connected to the gear (9). The ratio of the speed of the input shaft to that of the output shaft can be found in a way as explained in the case (b). The direction of rotation of the input shaft and the output shaft is same. All the joints J1 , J2, J3, J4, J5, J6 and J7 are shown as journal bearings and can suitably be replaced by other types of bearings for reducing the friction, as per the specific requirements. The eccentricity of the part (4) and that of part (6) must be same. For all the above configurations (Configurations - 1 to 4) all the parts are restricted to move along the axes A1 and A2 and are free to rotate while transferring the motion from input to output shaft. All the configurations (Fig.4, Fig.5, Fig.6 and Fig.7) show only the schematic kinematics for various configurations of the unlimited gear drives. For actual product proper lubrication scheme, proper tolerances, and other manufacturing details are to be worked out appropriately. Advantages of the Unlimited gear drive:

1. The unlimited gear drive uses rigid circular gears for its operation.

2. All configurations of the unlimited gear drive are positive drives. 3. Large gear ratio is obtainable in a single stage reduction.

4. By changing the number of teeth on the two meshing gears, almost any gear ratio can be obtained in a single stage reduction. Theoretically a gear ratio of infinity: 1 can be obtained by such a drive. For example if internal gear has 120 teeth and external gear has 119 teeth, the gear ratio obtained for different configurations can be 120: 1 OR 119: 1.

5. As many teeth are in contact, teeth height can be reduced and teeth pitch can also be reduced to have more number of teeth for same pitch diameter. For same pitch circle diameter of internal gear, reducing height of teeth can allow to accommodate larger external gear. Less difference in the pitch circle diameter of the two gears means higher gear ratio.

6. This drive can be used for high torque application by using stronger material for the gears. Similarly for higher torque, gear width can also be

5 increased. The tooth profile has to be designed appropriately.

7. All configurations as explained before are of reversible in nature.

8. Friction can be reduced in all the joints by using appropriate types of bearings and thus the efficiency can be improved.

9. Helical gears can also be used instead of straight gears. 10 10. The eccentricity reduces for higher gear ratios.

11. For getting highest ratio, difference between the numbers of teeth on the two gears can be kept at minimum of one tooth.

12. The difference between the number of teeth on the internal gear and on external gear can be one tooth or more.

15 13. The configurations, which use a coupling to connect the final output shaft to the gear, which rotates about its own axis, are flexible to use any suitable coupling. Disadvantages:

1. For different gear ratios gear tooth profile may have to be carefully 0 designed.

2. Gear tooth profile may pose a limitation on the obtainable gear ratio.

3. The load on the gear is not balanced which can be balanced by using two internal gears meshing simultaneously with one external gear or two external gears meshing simultaneously with one internal gear, keeping 5 the two points of contacts diametrically opposite to each other.

4. In few configurations of unlimited gear drive, some coupling has to be used for driving the output shaft.

Claims

1. An unlimited gear drive comprising of a circular internal gear in mesh with a circular external gear with their axes parallel to each other; one of the said gears that is fixed gear maintains its orientation unchanged throughout with respect to a fixed part; the other said gear i.e. moving gear rotates about its own axis and is connected directly or through some linkage to the output shaft; the input shaft directly or through an input link forces the point of contact to move on pitch circle of one of the said gears.

2. An unlimited gear drive as claimed in claim 1 , has the axis of moving gear revolving around the axis of the fixed gear.

3. An unlimited gear drive as claimed in claim 1 , has the axis of fixed gear revolving around the axis of the moving gear.

4. An unlimited gear drive as claimed in claims 1 ,2 and 3, has internal gear as fixed gear and external gear as moving gear; the axis of the said internal gear revolves around the axis of the said external gear.

5. An unlimited gear drive as claimed in claim 1 , 2 and 3, has internal gear as fixed gear and external gear as moving gear; the axis of the said external gear revolves around the axis of the said internal gear.

6. An unlimited gear drive as claimed in claim 1 , 2 and 3, has external gear as fixed gear and internal gear as moving gear; the axis of the internal gear revolves around the axis of the external gear.

7. An unlimited gear drive as claimed in claim 1 , 2 and 3, has external gear as fixed gear and internal gear as moving gear; the axis of the external gear revolves around the axis of the internal gear.

8. An unlimited gear drive as claimed in claims 1 to 7, has the output shaft speed equal to the rotational speed of the moving gear about its own axis.

9. An unlimited gear drive as claimed in claims 1 to 7, which gives a speed ratio of number of teeth on one of the meshing gear to the difference in the number of teeth on the two gears.

10. An unlimited gear drive as claimed in claims 1 to 7, with gear tooth profile designed appropriately for the two gears separately.

11. An unlimited gear drive as claimed in claims 1 to 7, which uses helical gears for the fixed gear and moving gear.

12. An unlimited gear drive as claimed in claims 1 to 7, in which the input shaft axis and output shaft axis are parallel to each other; these two axes may or may not be aligned.

13. An unlimited gear drive as claimed in claims 1 to 7, with input and output shafts interchanged; this can also give gear ratio of less than unity.

14. An unlimited gear drive as claimed in claims 1 to 13, in which the output shaft is co-axial to the moving gear and is rigidly connected to the moving gear.

15. An unlimited gear drive as claimed in claims 1 to 13, in which the output shaft is co-axial to the moving gear and is connected to the moving gear, through some linkage.

16. An unlimited gear drive as claimed in claims 1 to 13, in which the axis of the output shaft is parallel to the axis of the moving gear and the output shaft is connected to the moving gear through a linkage capable of transferring motion from one shaft to another parallel shaft.

17. An unlimited gear drive as claimed in claims 1 to 16, for any combination of the number of teeth on fixed gear and on moving gear.

18. An unlimited gear drive as claimed in claims 1 to 17, in which the moving gear and the fixed gear may have any tooth profile.

19. An unlimited gear drive as claimed in claims 1 to 18, that uses any configuration of the kinematic linkage as explained in configuration 1 to 4 of the drawing of the accompanying specification.

20. An unlimited gear drive as claimed in claims 1 to 19, which uses any type of bearing for reducing friction in joints.

21. An unlimited gear drive as claimed in claims 1 to 20 and herein illustrated and described with reference to the accompanying drawings and the specification.