The object of the invention is a self-regulating, continuously variable gear drive, more particularly a gear drive that is capable of load-dependent stepless, self-regulating gear ratio adjustment with the application of three differential gear systems, through positive (shape-fit) mechanical connections.

Several known types of transmission are capable of stepless gear ratio adjustment. Continuously variable gear drive transmissions can be grouped into hydraulic and mechanically operated transmissions. In transmissions based on hydraulic principles stepless gear ratio adjustment is achieved by the modification of flow characteristics of a fluid medium. A widely known group of mechanically operated transmissions provide the steering of the energy flow and stepless gear ratio adjustment by means of non-positive mechanical connections, utilizing frictional force. Some two-degree-of-freedom drives apply positive (shape-fit) mechanical connections, in most cases, gears, for energy flow transmission, in such a way that there is no fixed mechanical connection between the input and the output of the drive. Transmissions having two degrees of freedom can be configured such that the rotational speed ratio of the drive decreases, with the torque transfer ratio increasing, while the load at the drive's output is raised. Several transmissions disclosed in patent literature achieve stepless gear ratio adjustment by means of epicyclic gear trains. United States patent No. 6, 213, 908 discloses a solution which utilizes three differential gear systems to provide for continuously variable gear ratio adjustment. This solution applies a differential gear system as main drive unit, with two or four additional differential gear systems being connected to the main drive as feedback amplifier. Control is performed by the gear ratio changing unit disposed in the smaller branch of the energy flow.

The aim of our invention has been to provide a drive that has no control unit, reacts to loads presented to its output by changing the gear ratio in a wide range and in a self-regulating manner, is not self-locking in case of back-action arising from reaction forces of the bodies moved by it, and its output can be loaded at zero angular velocity while the input angular velocity remains nearly constant.

Our invention is therefore a self-regulating stepless gear drive comprising three interconnected differential gear systems, where each differential gear system contains sun gears and/or ring gears and planet gears, with the planet gears being connected through bearings to a planet carrier. The planet carriers and the two sun gears and/or ring gears of two differential gear systems are connected to each other, and the two not interconnected sun gears and/or ring gears of said two differential gear systems are connected to the sun gear and/or ring gear of the third

differential gear system, with at least one of the sun gears and/or ring gears of said two differential gear systems being connected to the planet gears with a rolling circle diameter different from the rolling circle diameter of the other sun gears and/or ring gears of said two differential gear systems or the interconnected sun gears and/or ring gears and the interconnected planet carriers of the two differential gear systems are connected by means of drive gears having different gear ratios.

The invention will now be explained in detail with reference to the attached drawings, where

Fig. 1 shows the schematic diagram of the inventive gear drive,

Fig. 2 shows the kinematic diagram of the drive comprising bevel gear differential gear systems,

Fig. 3 is the kinematic diagram of the drive comprising cylindrical gear differential gear systems,

Fig. 4 shows a possible connection scheme of the inventive drive implemented with coaxial input and output,

Fig. 5 shows an alternative connection scheme of the inventive drive with coaxial input and output,

Fig. 6 shows the connection scheme of the drive implemented with coaxial input and output and intermediary drive gears,

Fig. 7 shows the measured characteristics of an actually built drive,

Fig. 8 shows the measured characteristics of another actually built drive,

Fig. 9 shows the measured characteristics of a further actually built drive,

Fig. 10 shows the measured characteristics of a still further actually built drive, and

Fig. 11 shows the measured characteristics of a fifth actually built drive.

The connection scheme of the inventive gear drive is explained referring to Fig. 1. The drive is implemented as a gear drive comprising three interconnected differential gear systems Dl, D2, D3 containing sun gears or ring gears, and planet gears, the latter being connected through bearings to planet carriers 14, 15, 16. The sun gears or ring gears are provided with outlets from differential gear systems Dl, D2, D3 by means of shafts 11, 12, 13, 17, 18, 19. The planet carriers 14, 15 of two of the three differential gear systems Dl, D2, D3 are interconnected through a drive gear H2, with the sun gears or ring gears of these two differential gear systems Dl, D2 being interconnected through shafts 11, 12 and a drive gear Hl. The two not interconnected sun gears or ring gears of the differential gear systems Dl, D2 are connected through drive gears H3, H4 by means of shafts 17, 19 and through shafts 13, 18 to the two sun

gears and/or ring gears of the third differential gear system D3. Drive gears to., tiz, Hj, Ji4 can be a pair of gears, a gear drive, an epicyclical gear set, a chain drive or any other intermediary drive that provides transmission with given gear ratios in the desired direction of rotation.

The gear drive consisting of differential gear systems Dl, D2, D3 provides the load- dependent self-regulating, continuously variable adjustment of the gear ratio by the application of gears, that is, by positive (shape-fit) mechanical connections. This means that the drive unit automatically produces the gear ratio characteristic of an input/output torque ratio as a function of load torque at the drive's output. Thus, no control unit is needed for the inventive drive to be operated as an automatic torque converter. If necessary, any one of the sun gears or ring gears, or planet carriers of the differential gear systems Dl, D2, D3 can be furnished with a mode shift switch that provides for fixing /immobilizing certain components or prohibiting certain specific directions of rotation or angular velocity differences, or allowing these specific directions of rotation or angular velocity differences in a switch-controllable way; thereby influencing permanently or in a user-selectable manner the operating mode, degrees of freedom, and characteristics of the drive. Mode shift switches can be comprised of free-wheel mechanisms, fixing brakes, and disengaging clutches well known in the field of epicyclic gear drives. Freewheel mechanisms, disposed properly, do not alter the degrees of freedom of the drive but restrict the direction of the energy flow and thus affect drive characteristics. Fixing brakes and disengaging clutches reduce the DOF of the drive, so it can be set to function at a chosen gear ratio or perform a fixing role.

The drive gear made up by connecting the differential gear systems Dl, D2, D3 has two degrees of freedom. It thus follows that, in spite of the positive mechanical connections (geared connections) there is no direct mechanical connection between the input and the output of the drive. The drive has states of motion where the input is rotating and the output is stopped, while the transformed value of the input torque is fed to the drive's output.

A further condition for the self-regulating operation of the drive is that at least one sun gear or ring gear of each of the two differential gear systems Dl, D2 must be connected to its planet gears with a rolling circle diameter that is different from the rolling circle diameter of the other sun gears or ring gears of the same differential gear system Dl, D2; or that in case the two differential gears systems Dl, D2 have the same configuration or the same internal gear ratio, the interconnected sun gears or ring gears (being interconnected through drive gear Hl) and the interconnected planet carriers 14, 15 (being interconnected through drive gear H2) of the two differential gear systems Dl, D2 must be connected at different gear ratios. The difference of the internal gear ratios of the differential gear systems Dl, D2 or the difference of the gear ratios of

drive gears Hl (responsible for interconnecting the sun- or ring gears) and H2 (interconnecting the planet carriers) result in an asymmetry of the drive's internal force conditions that is necessary for self-regulating operation.

Differential gear systems Dl, D2, D3 of the drive, or in certain cases only one or two of the three differential gear systems, are configured such that in case the planet carrier of the differential gear system is immobilised and one sun gear or ring gear is rotated in a given direction, the other sun gear or ring gear will undergo reverse-direction rotation.

The input and output of the drive unit can be disposed on the planet carriers 14, 15, 16 of differential gear systems Dl, D2, D3, or on the shafts 11, 12 of the interconnected sun gears or ring gears of differential gear systems Dl, D2 (being interconnected through drive gear Hl) ₅ or on shafts 13, 17, 18, 19. The planet carrier 16 of differential gear system D3 is, however, always used as an input or output location. By selecting the configuration of the differential gear systems Dl, D2, D3 and drive gears Hl, H2, H3, H4, and also the locations of the input and output of the drive, the power transmission, torque conversion and rpm ranges and maximum rated torque can be chosen so as to match the needs of various applications.

Fig. 2 shows the configuration of a gear drive consisting of bevel gear differential gear systems and interconnecting drive gears. In the embodiment shown in the figure all three differential gear systems D21, D22, D23 are of the same bevel-gear configuration. The internal gear ratio of all three differential gear systems D21, D22, D23 is -1. This means that in case the planet carrier of any of these differential gear systems is immobilised and one sun gear is rotated in a given direction by a given amount, the other sun gear will be rotated in the reverse direction by the same amount. For instance, if the planet carrier 24 of differential gear system D21 is immobilised and sun gear 213 is rotated in a given direction, the other sun gear, fixed on shaft 21, will be rotated (through the rotation of planet gear 212) in the reverse direction by the same amount. Planet carriers 24, 25 of differential gear systems D21, D22 are interconnected through drive gear H22, with two of the sun gears thereof being interconnected through shafts 21, 22 by means of drive gear H21. Drive gears H21 and H22 have different gear ratios. The two not interconnected sun gears of differential gear systems D21, D22 are connected through shafts 27, 23 and shafts 28, 29, respectively, by means of drive gears H23, H24 to the two sun gears of differential gear system D23. Drive gears H23, H24 may have identical or different, speed- increasing or reducing gear ratios. In this particular case, because differential gear systems D21, D22, D23, D24 all have an internal gear ratio of -1, the rpm conversion and torque conversion ratio of the drive (showing the ratio of output/input rpm and torque) can be modified in a given speed range by the adjustment of the gear ratios of drive gears H21, H22, H23, H24 and by

adjusting the relative loss torque values of differential gear systems D21, D22, D23, D24 and drive gears H21, H22, H23, H24. The planet carrier 26 of differential gear system D23 can be utilized as the input or output of the drive, similarly to shafts 21, 22 and planet carriers 24, 25 of differential gear systems D21, D22, but the planet carrier 26 is always applied as an input or output.

Fig. 3 shows the connection scheme of a gear drive comprising cylindrical-gear differential gear systems. The operation of the differential gear systems indicated by reference numerals D31, D32, D33 in the figure is explained referring to differential gear system D31 as an example. Planet gears 315 and 312 of differential gear system D31 are connected to ring gears 311 and 313, respectively. Planet gears 315, 312 are also connected to each other, and both are connected through bearings to a planet carrier 314. In case the planet carrier 314 is immobilised by fixing shaft 34 and ring gear 311 is rotated, the planet gear 315 is also rotated, causing planet gear 312 to rotate in the reverse direction, with ring gear 313 being rotated in turn by planet gear 312. Thus, if the planet carrier 314 is immobilised, ring gears 311 and 312 will be rotated in opposite directions together with shafts 31, 37.

Differential gear system D31 has an asymmetric configuration and an internal gear ratio different from -1. This follows from the fact that ring gears 313 and 311 have different rolling circle diameters, meaning also that in case the planet carrier 314 is fixed, ring gears 311 and 313 are rotated by different amounts in opposite directions.

Because the internal force conditions required for self-regulating operation of the drive are provided by the asymmetrical configuration of differential gear system D31, drive gears H31, H32, H33, H34 of the gear drive shown in Fig. 3 may have a uniform gear ratio of -1 (implemented e.g. by a gear pair with identical diameter). To match the requirements of particular applications, the gear drive may of course be configured such that one or more of the drive gears H31, H32, H33, H34 have a gear ratio different from -1.

The input and output of the drive may be located at the shafts 34, 35 of the planet carriers of differential gear systems D31, D32, or at the shafts 31, 32 of the ring gears thereof, or at the shaft 36 of the planet carrier of the differential gear system D33, the only requirement being that shaft 36 should always be utilized as an input or an output.

Fig. 4 shows the schematic connection of the coaxial configuration of the inventive drive. The relative sizes of individual components vary according to the operating requirements the drive has to fulfill. In the gear drive shown in the figure the differential gear systems D41, D42, D43 are implemented as cylindrical gear sets. Ring gears of differential gear systems D41, D42 (playing, respectively, the role of differential gear systems Dl, D2 of Fig. 1) are connected with

a direct connection that functions as drive gear H41. This means that ring gears of differential gear systems D41 and D42 rotate in the same direction with the same angular velocity. Drive gear H42, disposed between the planet carriers of differential gear systems D41, D42, is implemented as a single, common planet carrier for both differentials. The sun gear of differential gear system D41 and the ring gear of differential gear system D43 (performing the role of differential gear system D3 of Fig. 1) are in direct connection to form drive gear H43. The direct connection can be established by fastening together the sun gear and the ring gear with screws or by implementing the sun- and ring gears as a single piece having both external and internal gearing. Sun gears of differential gear systems D42, D43 are fixed to a common shaft, which provides direct transmission functioning as drive gear H44. The input or output of the drive can be located at the planet carrier 46 of differential gear system D43 or at the ring gears of differential gear systems D41 and D42 (where said ring gears are interconnected by means of drive gear H41) and at the common planet carrier functioning as drive gear H42, or at the shaft functioning as drive gear H44 and at the combined sun/ring gear functioning as drive gear H43; but planet carrier 46 is always utilized as an input or output. This embodiment requires fewer components and implements the inventive gear drive in a coaxial configuration.

Fig. 5 shows the connection scheme of another coaxial configuration of the inventive gear drive. In this case as well, relative sizes of individual components may vary according to the operating requirements the drive has to fulfill. Compared to the embodiment shown in Fig. 4 the differential gear systems are disposed in different order. The function of differential gear systems Dl, D2, D3 of Fig. 1 is performed, respectively, by differential gear systems D51, D52, D53, with the role of drive gears Hl, H2, H3, H4 being played by drive gears H51, H52, H53, H54, respectively, with the special constraint that the gear ratio of drive gears H51, H52, H53, H54 is uniformly 1 according to the configuration shown in Fig. 5. The sun gear of differential gear system D51 is connected with the sun gear of differential gear system D52 through a shaft functioning as drive gear H51. Planet gears of differential gear systems D51 and D52 are connected through bearings to a common planet carrier, thereby forming drive gear H52. Similarly, the interconnection of the ring gears of differential gear systems D52 and D53 forms drive gear H54. Drive gear H53 is implemented by the provision of the ring gear of differential gear system D51 and the sun gear of differential gear system D53 as a single component having both internal and external gearing. The input and output of the drive can be located at the planet carrier 56 of differential gear system D53 or at the common shaft of the sun gears of differential gear systems D51, D52 (said shaft implementing drive gear H51) as well as at the common shaft of drive gear H54, but planet carrier 56 is always applied as an input or output location. This

configuration of the inventive drive provides coaxial transmission and automatic torque control.

Fig. 6 shows a coaxial configuration of the inventive gear drive, with torque modifying drive gears. The only difference between this configuration and the one shown in Fig. 5 is in the drive gears that are disposed between the differential gear systems. Some practical applications may pose requirements that render unfeasible the configuration where the gear ratio of every intermediary drive gear is 1. In that case, when either direction-reversing or gear ratio modification is needed, drive gears H61, H62, H63, H64 should be disposed between the differentials of the drive. These drive gears H61, H62, H63, H64 are adapted for interconnecting each particular pair of differentials with the gear ratio required for the orderly operation of the gear drive.

Figs. 7-11 show measurement records for experiments carried out on an engineering sample of the drive shown in Fig. 1, with different input-output configurations and different gear ratio values for drive gears Hl, H2, H3. Differential gear systems of the engineering sample had a configuration corresponding to that of the cylindrical-gear differential gear systems D32, D33 shown in Fig. 3, with the rolling circle diameter of ring gears being uniformly 60 mm and the distance between centre lines of differentials being 84 mm. Differential gear systems D2, D3 were disposed along a single axis line, with the gear ratio of the drive gear disposed between them being uniformly 1. Gears of differential gears systems Dl, D2, D3 and drive gears Hl, H2, H3 had a module of 2 mm, being produced using a gear cutter with no after-machining. With the application of three gears, drive gear H3 provided that the shafts 17, 13 were rotated in the same direction. The drive unit was disposed in a closed casing that was filled up with gear oil to the necessary level. To the input of the drive a 4 kW, two-pole asynchronous motor and a device adapted for measuring input torque were connected, with a disc brake and an electronic load cell being connected to the output. During our experiments we measured the input rpm, input torque, and output rpm as a function of load torque. On charts shown in Figs. 7-11, data for the output rpm (scaled down using appropriate constants, n2/10, n2/100), the input torque (Ml) and the torque transfer ratio (M2/M1) are plotted.

During the recording of the chart shown in Fig. 7 the motor was connected to the planet carrier 15 of differential gear system D2. Gear ratios of drive gears Hl, H2 and H3 were 1.3333, 1.47058, and 0.9285, respectively. As the chart shows, output rpm varied between 627 and 222 1/min, with input torque varying between 2.2 and 7.5 Nm and the torque transfer ratio varying in the range 0-2.8. At a load torque value of 11 Nm (M2=l l) zero rpm was detected on shafts of drive gear H3 disposed between Dl and D3.

For the measurements recorded on the chart shown in Fig. 8 only the location of the input was modified with respect to the previous experiment, the motor being disconnected from the planet carrier 15 of differential gear system D2 and connected to shaft 12 rotating the ring gear of differential gear system D2. It can be discerned from the chart that output rpm varied in the range 150-0 1/min, with the input torque varying in the range 1.05-2.75 and torque transfer ratio being in the range 0-5.37. At a load torque value M2=8 Nm zero rpm was detected on every shaft of drive gear H4 disposed between differential gear systems D2, D3.

Fig. 9 shows measurement data recorded with the motor connected to the planet carrier 15 of differential gear system D2, with the gear ratio of drive gears Hl, H2, H3 being, respectively, 2.5, 2.652, and 1.0769. Output rpm varied between 911 and 0 1/min, with input torque varying in the range 1.575-3.1 Nm and torque transfer ratio varying between 0 and 2.32. At a load torque value M2= 2.5 Nm zero rpm was detected on shafts of drive gear H3 disposed between differential gear systems Dl, D3, and at a load torque M2=6.5 Nm we detected zero rpm on shafts of drive gear H4 disposed between differential gear systems D2 and D3. It can be observed that above load torque value M2=6.5 Nm the torque transfer ratio shows a slightly descending tendency, with the input torque (Ml) increasing at the same time.

Measurement data shown in Fig. 10 are from an experiment where only one parameter, the gear ratio of drive gear H3, was modified (to 1.0385) from the previous setup. As the chart shows, output rpm was in the range 938-0 1/min, while input torque varied between 1.6-3.05 Nm and the torque transfer ratio varied in the range 0-2.62. At a load torque value M2=3 Nm zero rpm was detected on shafts of drive gear H3 disposed between differential gear systems Dl, D3, and at a load torque M2=7 Nm we detected zero rpm on shafts of drive gear H4 disposed between differential gear systems D2 and D3. It can be observed that for load torque values above M2=7 Nm there is a growing tendency in the torque transfer ratio (M2/M1), while the input torque (Ml) remains nearly constant.

For the recording of data shown in the chart of Fig. 11 only one parameter, the gear ratio of drive gear H3, was modified (to 0.9643) from the setup of the previous experiment. Output rpm varied in the range 960-0 1/min, while input torque was between 1.35-2.75 Nm, with the torque transfer ratio varying in the range 0-2.901. At a load torque value M2=3 Nm zero rpm was detected on shafts of drive gear H3 disposed between differential gear systems Dl, D3, with zero rpm being detected at a load torque M2=8 Nm on shafts of drive gear H4 disposed between differential gear systems D2 and D3. Looking at the chart it can be observed that in case the load torque is slightly raised the output rpm drops down to zero while the input torque remains at a near constant value.

Characteristics of the inventive drive recorded in Fig. 7-11 may be different from those shown in the figures in case a motor having a torque-speed characteristics different from the motor used for our experiments (two-pole asynchronous motor) is applied for testing.

As it is shown by the results of our measurements, the inventive gear drive can be utilized for a wide range of applications in case the differential gear systems and intermediary drive gears are dimensioned appropriately. By way of example only, the application fields of vehicles (with mode shift switches: buses and cars, without mode swift switches: scooters and light vehicles), heavy machines, chemical-industry mixers, household machinery, mixers, power generating or water pumping windmills could be mentioned. An important field of application may be the actuation of automatic gates and sliding doors, because with the application of the inventive drive it can be provided that the gate is opened faster when there is smaller drag and slower when more significant drag is present (e.g. due to snow or mud), without overloading the motor- gear drive assembly; and also that the gate is stopped in case of an obstacle when a well defined and safe maximum force is reached, while the drive still remains turning. Such a configuration of an automatic gate or door may help prevent drawing-in accidents, injuries and equipment damage.

List of reference numerals

shaft shaft shaft planet carrier planet carrier planet carrier shaft shaft shaft shaft shaft shaft planet carrier planet carrier planet carrier shaft shaft shaft shaft shaft shaft shaft shaft shaft planet carrier planet carrier planet gear sun gear ring gear planet gear ring gear planet carrier

315 planet gear

Dl differential gear system

D2 differential gear system

D3 differential gear system

D21 differential gear system

D22 differential gear system

D23 differential gear system

D31 differential gear system

D32 differential gear system

D33 differential gear system

D41 differential gear system

D42 differential gear system

D43 differential gear system

D51 differential gear system

D52 differential gear system

D53 differential gear system

Hl drive gear

H2 drive gear

H3 drive gear

H4 drive gear

H21 drive gear

H22 drive gear

H23 drive gear

H24 drive gear

H31 drive gear

H32 drive gear

H33 drive gear

H34 drive gear

H41 drive gear

H42 drive gear

H43 drive gear

H44 drive gear

H51 drive gear

H52 drive gear

H53 drive gear

H54 drive gear

H61 drive gear

H62 drive gear

H63 drive gear

H64 drive gear