Balanced-reaction variable-ratio transmission

Variable-ratio transmission configurations are derived from a basic balanced-reaction configuration which is known to operate with inherently lower power flow in the reactive path for a given ratio range than the more common split-input or split-output configurations. A pair of planetary gear sets having different base speed ratios, are configured to each provide a power transmission path from the input shaft to the output shaft while the reaction gear elements are cross-coupled to each other through an auxiliary variable ratio power-transfer device. A particular two-planetary-set configuration uses the ring gear elements as the reactors, one mounted to rotate around the input shaft and the other mounted to rotate around the output shaft. The ring gears are thus readily coupled to an auxiliary variable ratio power-transfer device, which may be a pair of hydraulic pump/motors. For extended ratio range, three or more (n) differential gear sets are configured in parallel input/output power paths, to be selected in pairs in (n-1) different ratio ranges for connection through automatic hydraulic or clutch-type range-switching means acting in the reaction power paths. In a "nested" configuration for superior overall power efficiency resulting from reduced reaction path power losses, a first, high power two-differential-set balanced-reaction transmission utilizes in its reaction path a second, medium power two-differential-set balanced reaction transmission, so that the power-handling requirements of the second transmission's variable ratio power-transfer device may be made very low.

What is claimed is:

1. A variable-ratio transmission comprising:

a rotary input shaft;

a rotary output shaft;

a first planetary differential gear set having a sun gear element rotationally coupled to said input shaft, a planet-carrier gear element rotationally coupled to said output shaft, and a ring reaction gear element, referred to henceforth as a reactor, rotatably disposed in concentric relation around said input shaft,

a second planetary differential gear set having a sun gear element rotationally coupled to said input shaft, a planet-carrier gear element rotationally coupled to said output shaft, and a ring gear reactor rotatably disposed in concentric relation around said output shaft; and

an auxiliary variable-ratio power-transfer device having a first driveshaft rotationally coupled to one of said reactors, a second driveshaft rotationally coupled to the other of said reactors, and control means adapted to enable said auxiliary power-transfer device to regulate bilateral power exchange and rotational speed ratio between said first driveshaft and said second driveshaft,

wherein the base ratio, being the locked-reactor input/output rotational speed ratio, of said first differential gear set is made different than the base ratio of said second differential gear set,

whereby said control means is enabled to vary the operating ratio of said transmission over a continuous working range extending at least between the base ratio of said first differential gear set and the base ratio of said second differential gear set.

2. The invention as in claim 1 wherein said auxiliary variable-ratio power-transfer device comprises:

a pair of variable-displacement hydrostatic motor-pumps interconnected with each other through closed hydrostatic conduit means, each of said motor-pumps having one of said two rotary driveshafts; and

displacement control means associated with said motor-pumps, whereby one of said motor-pumps, operating as a pump, is enabled to receive power through its driveshaft from one of said reactors, at rotational speed and torque within a designated range, and to transmit substantially all of the received power hydrostatically to the other of said motor-pumps, which, operating as a motor, is enabled to transfer the power through its driveshaft to the other of said reactors, at a required rotational speed and torque, as regulated by said control means,

whereby said transmission is enabled to operate at a desired overall transmission ratio, which may be varied by said control means.

3. A variable-ratio transmission comprising:

a rotary input shaft;

a rotary output shaft;

three or more differential gear units each having an input gear element rotationally coupled to said input shaft, an output gear element rotationally coupled to said output shaft, and a reactor, wherein said differential gear units are made to each have a different base ratio;

auxiliary variable-ratio power-transfer means, adapted to transfer power from a first selected one of said reactors to a second selected one of said reactors; and

range selection means adapted to select that pair of differential gear units, containing said first and second reactors, whose base ratios are closest above and below a required transmission ratio;

whereby power may be transferred between said first and second reactors through said auxiliary power-transfer means, allowing all other reactors to rotate freely,

whereby a balanced power exchange between a pair of said reactors, thus selected for each range, is enabled to vary the operating ratio of the transmission within a range between the base ratios of the corresponding two differential units having said pair of reactors, thus providing a total variable transmission range extending at least from the lowest to the highest base ratio amongst said differential gear units.

4. The invention as in claim 3 wherein said auxiliary variable-ratio power-transfer means comprises:

a plurality of power transducers, each one associated with a corresponding one of said differential gear units, and each power transducer having (a) first power-port means comprising a rotary shaft rotationally coupled to the reactor of the corresponding differential gear set, and (b) second power-port means associated in bilateral input-output power transfer relation with said first power-port means; and

device-ratio control means, having a device-ratio command input port, adapted to regulate power flow at each of said first power-port means;

and wherein said range selection means comprises a master ratio command input port and command distribution means connected to each of said device-ratio command input ports and to said power-flow interconnection means, programmed to activate, in response to a ratio command, a cross-coupled power flow path through a selected interacting pair of said power transducers.

whereby said transmission is enabled to operate at high power efficiency, without range-clutches or brake-type dissipative loading, over a wide total range of operating ratios, encompassing the lowest and the highest of all of said base ratios, by routing a major portion of available power through the pair of differential gear sets selected as optimally efficient power paths for obtaining a desired working transmission ratio as commanded, while minimizing the power-flow level in said auxiliary variable-ratio power-transfer means.

5. The invention as in claim 4 wherein each of said power transducers comprises a variable-stroke hydrostatic motor-pump having a rotary shaft as its first power-port, an input/exhaust pair of hydraulic fluid passages forming its second power-port, and adjustable-angle swashplate means, coupled to said shaft, adapted to regulate the stroke of said motor-pump and thus regulate its fluid displacement in accordance with a device-ratio input command,

and wherein said power flow interconnection means comprises a hydraulic fluid system of routing valves and conduit interconnecting said hydraulic fluid passages of a pair of said power transducers, as selected by said routing valves under control of said range selection means, thus forming a closed bilateral hydraulic power drive between said pair of power transducers.

6. The invention as in claim 3 wherein said range selection means comprises clutch means adapted to (a) rotationally couple a first rotary shaft of said power-transfer device to said first selected reactor, and (b) concurrently rotationally couple said second rotary shaft of said power-transfer device to said second selected reactor, while allowing all others of said reactors to rotate freely;

whereby a balanced power exchange between the pair of said reactors thus selected by said range selection means may be controlled so as to vary the operating ratio of the transmission within a range between the base ratios of the two corresponding differential units thus selected, and

whereby said transmission is enabled to operate at high power efficiency over a wide continuous range of ratios, encompassing the lowest and the highest of said base ratios, by routing a major portion of the power through the pair of differential gear sets selected as optimally efficient power paths for a commanded transmission ratio, while minimizing the level of power flow through said auxiliary variable-ratio power-transfer means.

7. The invention as in claim 6 wherein said auxiliary variable-ratio power-transfer means comprise:

a pair of variable-displacement hydrostatic motor-pumps interconnected with each other through closed hydrostatic conduit means, each of said motor-pumps having one of said two rotary driveshafts; and

displacement control means associated with said motor-pumps, whereby one of said motor-pumps, operating as a pump, is enabled to receive power through its driveshaft from one of said reactors, at rotational speed and torque within a designated range, and to transmit substantially all of the received power hydrostaticly to the other of said motor-pumps, which, operating as a motor, is enabled to transfer the power through its driveshaft to the other of said reactors, at a required rotational speed and torque, as regulated by said control means, so as to cause said transmission to operate at a desired overall transmission ratio, which may thus be varied by said control means.

8. The invention as in claim 3 comprising three differential gear units, wherein the first differential unit, having said first selected reactor, is made to have a base ratio falling between the base ratio of the second differential unit and the base ratio of the third differential unit, and wherein said variable-ratio power-transfer means has a first shaft rotationally coupled to said first selected reactor, and a second shaft rotationally coupled through clutch means selectably engaging either the reactor of said second or the reactor of said third differential gear unit, as selected by control means.

9. A continuously-variable transmission comprising:

a rotary input shaft;

a rotary output shaft;

a first and a second differential gear set each having an input gear element rotationally coupled to said input shaft, an output gear element rotationally coupled to said output shaft, and a reactor;

a third and a fourth differential gear set each having a first gear element rotationally coupled to said reactor of said first differential gear set, a second gear element rotationally coupled to said reactor of said second differential gear set, and a reactor;

an auxiliary variable-ratio power-transfer device having two rotary driveshafts, one of said driveshafts being rotationally coupled to said reactor of said third differential gear set, and the other of said driveshafts being rotationally coupled to said reactor of said fourth differential gear set;

whereby the input/output rotational speed ratio of said transmission may be varied by regulating power flow through said auxiliary variable-ratio power-transfer device in a power flow path between said reactor of said third differential gear set and said reactor of said fourth differential gear set.

10. The invention as in claim 9 wherein said auxiliary variable-ratio device comprises:

a pair of variable-displacement hydrostatic motor-pumps interconnected with each other through closed hydrostatic conduit means, each of said motor-pumps having one of said two rotary driveshafts; and

displacement control means associated with said motor-pumps, whereby one of said motor-pumps, operating as a pump, is enabled to receive power through its driveshaft from one of said reactors, at a particular rotational speed and torque, and to transmit substantially all of the received power hydrostaticly to the other of said motor-pumps, which, operating as a motor, is enabled to transfer the power through its driveshaft to the other of said reactors, at a required rotational speed and torque, as regulated by said control means, so as to cause said transmission to operate at a desired overall transmission ratio, which may thus be varied by said control means.

11. The invention as in claim 9 wherein said variable control transmission means comprises:

a pair of variable-drive-diameter pulleys, each having a driveshaft;

belt means coupling said pulleys with each other; and

control means enabling the effective belt drive diameter of said variable-drive-diameter pulleys to be varied in inverse relation to each other, thereby providing a range of variable ratio between the rotational speeds of said driveshafts, as regulated by said control means.