GB1563698A

GB1563698A - Variable speed-ratio transmissions

Info

Publication number: GB1563698A
Application number: GB2970475A
Authority: GB
Original assignee: Vickers Shipbuilding Group Ltd
Current assignee: Vickers Shipbuilding Group Ltd
Priority date: 1976-10-04
Filing date: 1976-10-04
Publication date: 1980-03-26

Description

(54) VARIABLE SPEED-RATIO TRANSMISSION (71) We, VICKERS SHIPBUILDING GROUP LIMITED, a British company, of Barrow Shipbuilding Works, P.O. Box 6, Barrow-in-Furness, Cumbria LA14 1AB do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particulary described in and by the following statement: This invention relates to variable speedratio tranmissions. A major problem for heavy vehicles having a low power to weight ratio is the need to exert constant engine power over a wide range consistent with obtaining maximum tractive effort together with a high maximum speed. The product of maximum torque at one extreme and maximum speed at the other is known as corner horsepower and dictates the volumetric sizing of the engine and/or tranmission system. An engine that can operate at a constant high speed and low torque can be of small volume and high efficiency provided that the reciprocal increase of torque as speed is reduced is accomplished in a correspondingly small and efficient gearbox.

To obtain these high efficiencies, it is necessary to use a multi-ratio gearbox having as many as, for example, six speeds.

Even with such a multi-ratio gearbox, the engine is still required to produce power over a given speed range. Development of suitable high efficiency engines, has resulted in engines capable of very high power (or torque) outputs, though the characteristic curves of these engines are such that the very high power (or torque) outputs can be realised only over a very limited speed range. Clearly, as the speed range over which the engine can produce very high power (or torque) is decreased, so the number of speeds in the multi-ratio gearbox has to be correspondingly increased to maintain an even, smooth performance over the whole of the engine's speed range.

Alternatively, it is possible to devise a system in which the engine operates at a constant speed either producing its maximum power (or torque, or giving maximum economy), which is passed to an infinitely variable ratio gearbox. However, if such a gearbox having only a single stage were to be used, it can be shown in non-dimensional terms that the corner horse power in the reaction member in relation to the total throughput power would be unacceptably high. A solution is to break up the overall range geometrically into a number of consecutive ranges which collectively give the same overall stepless range, whilst ensuring that the size of the reaction unit can be kept at an acceptable level. In such a gear, the maximum corner horsepower carried by the reaction member is given by the expression

where R is the ratio of maximum to minimum speeds over which constant maximum power is required and n is the number of stages. If, for example, R = 20 and n = 1 (i.e. a single ratio gear), the reaction power is 9.5 times the nominal power, but if n = 6, the reaction power drops to 0.325 the nominal power.

Hereinafter, the terms: 'Constant-speed power source' 'Constant-speed, variable-power source', and 'Constant-speed engine'.

are used to refer to that particular speed which, for a given fuel flow, causes the power source or engine to produce its maximum power, or torque, or operate at its maximum efficiency or economy as required; thus the power source or engine will operate only over a limited portion of its speed range with the particular speed determined by the fuel flow.

According to the present invention there is provided a variable speed-ratio transmission comprising: a shaft provided with a gear wheel rotationally fast therewith; a variable speed mechanism for transmitting a part of the power through the transmission, the variable-speed mechanism having a first terminal member drivingly connected with the shaft, and a second terminal member, the variable-speed mechanism being constructed such that (i) for a constant speed input to the first terminal member a variable speed output can be provided at the second terminal member and (ii) for a variable speed input at the second terminal member a constant speed output can be provided at the first terminal member; and an epicyclic gearing for transmitting the remainder of the power through the transmission, the epicyclic gearing comprising interconnected primary and secondary epicyclic gear arrangements, each of which includes a sun gear, planet gears mounted on a planet carrier, and an annulus gear, the gear wheel on the shaft being in constant driving connection with the annulus gear of the primary epicyclic gear arrangement and the second terminal member of the variablespeed mechanism being adapted for coupling with either the sungear of the primary epicyclic gear arrangement or with the secondary epicyclic gear arrangement so as to accommodate an extended variable speed range, the arrangement being such that, in use, (a) with the shaft serving as an input member driven by a substantially constantspeed power source, a stepless variablespeed power output is obtainable at the planet carrier of the primary epicyclic gear arrangement, and (b) with the planet carrier of the primary epicyclic gear arrangement serving as an input member driven by a variable-speed power source, a constant speed power output is obtainable at the shaft.

The invention also relates to a combination of a variable speed-ratio transmission as hereinbefore defined and an epicyclic gear transmission coupled to the planet carrier of the primary epicyclic gear arrangement. the epicyclic gear transmission comprising low, medium and high speed epicyclic gear arrangements and associated braking mechanism.

In such a combination, the epicyclic gear transmission can be a conventional multistage gearbox. By correctly matching the output speed-range from the transmission with the particular ratios of the conventional multistage gearbox. the drive may be transmitted successively through each stage to give an infinitely variable speed output over the whole range of the conventional gearbox. Thus the constant-speed engine and the transmission combine to produce an output power (from the transmission) over a given speed-range just as a conventional engine might, but the constant-speed engine produces its peak power (or torque, or gives maximum economy), over the whole output speed-range, while the power (torque or economy) output from a conventional engine varies with the engine's speed.

The preferred epicyclic gear arrangement is a development of that disclosed in United Kingdom Patent Specification No.

1,097,253, in which an epicyclic gear consisting of an input member, an output member and a reaction member is used to provide an infinitely variable ratio transmission by driving the reaction member at variable speeds in either direction of rotation.

The variable-speed mechanism (which may also be reversible in direction of rotation) may be of any suitable form, hydraulic mechanisms being preferred.

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the drawing accompanying the Provisional Specification, in which the single figure illustrates schematically one form of variable speed-ratio transmission combined with an epicyclic gear transmission.

In the transmission of the Figure a constant-speed power source is connected, in use, so that there is permanent and simultaneous drive both to the input member of an epicyclic gear arrangement and to the controlling section of a variable-speed mechanism, while the output from the variable-speed mechanism is in permanent driving connection with the reaction member of the epicyclic gear arrangement. It should be noted that although the variablespeed mechanism is connected between the input and reaction members of the epicyclic gear arrangement, it could equally well be connected between the input and output members with the reaction member fixed, or between the reaction and output members of the epicyclic gear arrangement, or between any two members of different epicyclic gear arrangements. It should also be noted that more than one variable-speed mechanism may be used connected between either the same pair or different pairs of members of the epicyclic gear arrangement or arrangements. It should be further noted that one variable-speed mechanism may be used several times (e.g. via clutches or gears etc.), or several variable-speed mechanisms may be used in succession so providing an extended speed range. Thus, if it is desired to use, say, six speeds adequately to cover a given overall speed range, it could be done using a variable-speed mechanism to control the reaction members of a gear-box having six consecutive ratios. In this case the variable-speed mechanism would be used successively six times covering each ratio in turn. It would be preferable, however, to use a two-train infintely-variable gear coupled in series with a conventional threespeed gearbox. This would give 2 x 3 = 6 stages, i.e. effectively six speeds and, therefore, the same reaction member horsepower characteristics as for a six-speed gearbox, but with a simpler mechanical construction.

In a specific form which will now be described, the constant-speed power source permanently drives both the input member of the epicyclic gear arrangement and the controlling section of the variable-speed mechanism, and the output from the variable-speed mechanism is in permanent driving connection with the reaction member of the epicyclic gear arrangement. Such a variable-speed mechanism can be made-up of a first hydrostatic pump (generator) or motor with a variable-stroke swashplate system capable of pumping hydraulic fluid and driving, or being driven by, a second hydrostatic pump (generator) or motor having either variable or constant stroke and acting as the reaction unit. The variablestroke first hydrostatic pump (generator) or motor is permanently driven by the constant-speed power source so forming a control unit which dictates the speed of the variable or constant stroke second hydrostatic pump (generator) or motor reaction unit which is coupled to the reaction member of the epicyclic gear arrangement. The reaction unit is either coupled directly to the reaction member of a single gear arrangement to provide a single speed range, or is coupled indirectly via gearing, gearboxes, clutches etc. to provide a multiple speedrange drive to the reaction members of a plurality of gear arrangements. The maximum speed of any given range of the multiple speed-range drive equals the minimum speed of the next range, i.e. the reaction members are synchronixed at the transition points, so that the drive varies smoothly and steplessly over all the multiple speed ranges. The power is divided and follows boths of two paths which are: (i) direct constant-speed in a mechanical path and (ii) indirect variable-speed power via the two hydrostatic pump (generator) or motor units in a non-mechanical path.

If it is assumed that the input member of a simple epicyclic gear arrangement is driven at a constant A r.p.m. and the variablespeed mechanism is capable of driving the reaction member over a speed range of from -P to +P r.p.m., then the speed of the output member may be varied steplessly between (AX-P) and (AX+P) r.p.m.

where X is the ratio of the epicyclic gear arrangement operating in that configuration.

In this system, power is supplied to the epicyclic gear arrangement through both mechanical and non-mechanical paths when the speed of the output member is AX r.p.m. or greater. If the speed of the output is less than AX r.p.m., power is supplied to the epicyclic gear arrangement through the mechanical path but removed through the non-mechanical path back to the power source; thus a power recirculation loop is set up.

The speed range over which the output member of the epicyclic gear arrangement may be controlled using this method is limited by the speed range available from the hydrostatic pump (generator) or motor units, i.e. -P to +P r.p.m.

However, the speed range over which the output member may be varied is extended when two or more epicyclic gear arrangements are used in succession via a clutching system. In this system, the clutch is used to connect the two hydrostatic pump (generator) or motor units to each epicyclic gear arrangement in turn, with the gearing so arranged that clutching to the first epicyclic gear arrangement provides a low outputspeed range while clutching to the second epicyclic gear arrangement provides the variable-speed input to the first epicyclic gear arrangement and hence a higher output-speed range. In this latter case of the higher output-speed range, the power is divided and flows through each of three paths are as follows: (i) direct constant-speed power into the first epicyclic gear arrangement in a mechanical path, (ii) direct constant-speed power into the second epicyclic gear arrangement, the output of which forms a secondary input into the first epicyclic gear arrangement in a second mechanical path, and (iii) indirect variable-speed power via the two hydrostatic pump (generator) or motor units into the second epicyclic gear arrangement in a non-mechanical path.

As with the two path case described above, and depending on the output speed, power may be supplied along all three paths or supplied only along the two mechanical paths and removed via the non-mechanical path in the power recirculation loop.

Referring now more specifically to the Figure, the drawing shows a speed-ratio transmission and a three stage, constant mesh, epicyclic gearbox. the output of the transmission being coupled to the input of the gearbox. The transmission is used to match a constant-speed, variable-power source driving an input shaft 1 with the input requirements of the gearbox.

The constant-speed, variable-power input on shaft 1 is divided between gearwheels 2 and 4, both fixed on the shaft 1 to rotate therewith, and transmitted to the variablespeed mechanism which will now be described.

The variable-speed mechanism comprises a non-mechanical, reversible, variablespeed generator/motor assembly which comprises a pair of swashplate type hydraulic motor/pump units interconnected by piping (not shown in the figure) so that a rotational drive into either one causes an hydraulic pressure to be developed which causes the other to be driven and give a rotational output. Thus, each unit may be driving or driven. The swashplate motor units comprise a control unit 9, which is coupled to the input shaft 1 by way of the gearwheel 2 meshing with a terminal (in this case input) member constituted by a gearwheel 3 carried on the shaft of the control unit 9 and which has a variable-angle swashplate mechanism, and a reaction unit 10 having a fixed swashplate angle and providing the variable-speed reversible drive. The swashplate angle on the control unit is variable between - 60 and + 60. At the + 60 setting, the control unit pumps a large amount of oil to the reaction unit and drives it at +P r.p.m. (lie. clockwise). As the swashplate angle is reduced, less oil is pumped to the reaction unit and its speed drops proportionately until at 00, no oil is being pumped and the reaction unit cannot rotate. When the swashplate angle is further reduced up to - 60, the reaction unit becomes the pump driving the control unit.

The direction of the oil flow is reversed and the speed of the reaction unit rises uniformly to - P r.p.m. (i.e. anticlockwise). Swashplate motors are preferred for use in the generator/motor assembly because they can transmit high powers in either direction, but other means of varying the speed of rotation of the shaft of the reaction unit 10 may be employed.

As shown in the single figure, the rotary shaft of the unit 10 carries a clutch plate 11 so that the shaft of the unit 10 may be coupled selectively to a primary epicyclic gear 6, to give a low output-speed range by bringing into engagement the clutch plate 11 and a further clutch plate 11L, and to a secondary epicyclic gear 12 to give a high output speed range by bringing into engagement the clutch plate 11 and another clutch plate 11H. Each gear 6 and 12 comprises a sunwheel 6S or 12S constituting one of the rotary members of the epicyclic gear, pluralities of planet gears 6P or 12P, carried by another of the rotary members, and an annular gear 6A or 12A constituting the third rotary member. The clutch plate 11L is coupled to the sunwheels 6S, 12S and the clutch plate 11H is coupled to the annulus gear 12A. A terminal fin this case output) rotary member for the transmission is gearwheel 7 which also serves as the carrier for the planet gears 6P of the primary epicyclic gear 6. The speed of the planet gears 6P, and hence the output speed of gearwheel 7, is determined by the combination of speeds and senses of rotation of the annulus gear 6A and the sunwheel 6S. Through gearwheels 4, 5, the annulus gear 6A is driven at a constant speed in a given direction of rotation. Rotational power to the sunwheel 6S is supplied through the gearwheels 2, 3, to the two hydrostatic pump (generator) or motor units 9, 10, the output from which is taken through clutch plates 11, 11L to the sunwheel 6S.

Changing the swashplate angle on the hydrostatic pump (generator) or motor unit 9, i.e. the control unit, from the maximum negative to the maximum positive angle will cause the speed of rotation of the clutch plate 11 fixed to the shaft of the hydrostatic pump (generator) or motor unit 10 i.e. the reaction unit, to change from - P r.p.m. to + P r.p.m. Thus, the speed of rotation of clutch plate 11 may be changed in an infinitely variable and stepless manner, or held at any desired value, between - P and + P r.p.m. merely by choosing an appropriate, intermediate, value of the swashplate angle, and, as clutch plate 11 may be engaged with either clutch plate 11L or 11H, the speeds of rotation of the sunwheel 6S or the annulus gear 12A, which are integral with clutch plates 11L and 11H respectively, may be controlled in the same manner, i.e.

driven at any speed between -P and + P r.p.m.

When the clutch plates 11, 11L are engaged, there will be a first power input to epicyclic gear 6 giving a constant speed through gearwheel 5 to the annulus gear 6A and a second power input to gear 6 giving a variable speed to the sunwheel 6S. If the swashplate angle of control unit 9 is set to the zero position, there will be no interchange of hydraulic fluid with the reaction unit 10, so that clutch plates 11, 11L are restrained from rotating, causing sunwheel 6S to become a simple reaction member.

Then, the output speed of the gearwheel 7 may be written as AX r.p.m. A r.p.m. is the constant speed of gearwheel 5, and hence of annulus gear 6A, and X is the ratio of epicyclic gear 6 operating in the manner explained. If the swashplate angle of control unit 9 is now changed, there will be interchange of hydraulic fluid with reaction unit 10 causing rotation of clutch plates 11, 11L and hence sunwheel 6S. The speed and direction of rotation of sunwheel 65 may thus be controlled from - P to + P r.p.m.

causing the speed of gear wheel 7 to be steplessly varied from (AS-P) r.p.m. to (AX+P)r.p.m.

It is to be noted that, as sunwheel 12S is fixed to the same shaft as sunwheel 6S and clutchplate 11L, all these members rotate at the same speed. Hence, when the swashplate angle of control unit 9 is set to the maximum positive angle which corresponds to a reaction unit 10 shaft speed of + P r.p.m., both sunwheels 6S, 12S and clutch 11L will be rotating at + P r.p.m. The speed of gearwheel 5 and arrangement and ratio of secondary epicyclic gear 12 is such that A and P are equal to one another so that when the sunwheel 12S is rotating at + P r.p.m.

the planet gears 12P are stationary about their own axes of rotation and the annulus gear 12A is rotating at + P r.p.m. As the annulus 12A is rigidly connected to clutch plate 11H, all three clutch plates 11, 11L and 11H are rotating at + P r.p.m. and so, theoretically, plate 11 could be disengaged from plate 1 1L and re-engaged with plate 11H without any speed change occurring to output gearwheel 7. In practice, this would not happen owing to leakage and other effects in the hydrostatic pump (generator) or motor units 9, 10, which will be referred to later. When clutch plates 11, 11H are engaged, the variable-speed drive will be through the annulus gear 12A and, as the orbital speed of the planet pinions 12P remains constant, sunwheel 12S will become the output member of secondary epicyclic gear 12 which in turn will drive sunwheel 6S of the primary epicyclic gear 6. By reducing the swashplate angle of control unit 9, the speed of annulus gear 12A may be reduced from the + P r.p.m. to - P r.p.m., and this in turn will cause the speed of sunwheel 12S to increase from +P to +3P r.p.m. Thus, the speed of sunwheel 6S will similarly increase from +P to +3P r.p.m. and hence the speed of output gear wheel 7 will increase from (AX + P) to (AX + 3P) r.p.m.

In an alternative arrangement, the values of A and P are not equal. In order that the three clutch plates 11, 11L and 11H should all be rotating at +P r.p.m. at the time that the plates 11, 11L are to be disengaged and the plates 11, 11H re-engaged, the clutch plate 11H is separate from the annulus gear 12A and the rotational coupling between these two components is by way of gearing whose input to output speed-ratio is so chosen that the required speeds for the three clutch plates at disengagement and re-engagement is achieved. However, this arrangement is less advantageous than that illustrated and described above as it requires the use of additional gearing.

It is to be noted that a speed increase of the output gear wheel 7 is effected by increasing the swashplate angle of the control unit 9, i. e. increasing the speed of clutch plate 11, when the plate 11 is engaged with the low speed-range clutch 11L, and by decreasing the swashplate angle, i.e. reducing the speed of clutch plate 11, when this plate is engaged with the high speed-range clutch plate 11H. As a consequence of leakage and other effects in the hydrostatic pump (generator) and motor units 9, 10 the actual maximum output speed of the low range clutch plate 1 1L (theoretically AX + P r.p.m.) will not, in fact, exactly equal the minimum speed of the high range clutch plate 11H. Thus, if clutch plate 11 were simply disengaged from plate 1 1L and reengaged with plate 11H, a small step-wise drop in the speed of gearwheel 7 would occur.

This stepwise drop in speed may be avoided in one of two ways. Either the ratios of spicyclic gears 6 and 12 could be arranged so that the theoretical minimum output speed when driving through the high range clutch plate 11H differs from the maximum output speed when driving through the low range clutch plate 11L by an amount such that the actual values of these speeds are equal. Alternatively, all three clutch plates 11. 11H and 11L could be engaged smultaneously and the swashplate angle of control unit 9 reduced to transfer the drive from clutch plate 11L to clutch plate 11H progressively while the output speed of gearwheel 7 remains constant.

When the drive has been fully transferred to clutch plate 11H, clutch plate 11L is then released. Thus, to summarise, by two complete movements of the swashplate angle of control unit 9, i.e. from maximum negative (corresponding to - P r.p.m. on clutch plate 11) to maximum positive (CORRESPOND ING TO + P r.p.m.) and back to maximum negative (corresponding to - P r.p.m.) with a clutch change from plate 11L to plate 11H, the output speed of gearwheel 7 may be increased in an infinitely variable and stepless manner from (AX-P) to (AX+3P) - 6, where represents the speed loss due to leakage and other effects at the clutch changeover point. Hence, as the transmission is driven by a constant-speed, variablepower source through input shaft 1, the transmission is capable of producing an infinitely-variable stepless-ratio change to convert the constant-speed input with the output speed-range of (AX-P) to (AX+3P) - 6. It should also be noted that the maximum negative swashplate angle of control unit 9. i.e. - P r.p.m. on clutch plate 11, provides both the minimum output speed on gearwheel 7 via clutch plate 11L and the maximum output speed via clutch plate 11H.

The transmission is used to match the constant-speed, variable-power source driving the shaft 1 with a three stage constant mesh epicyclic gearbox consisting of threeepicyclic gear sets 20, 18, 16, together with three respective braking mechanisms 12, 14, 15 giving respectively low speed, medium speed and high speed output ranges. The low, medium and high speed output ranges of this gearbox are so chosen as to be compatible with the output speed range of the transmission, that is to say although the speed of gearwheel 7 drops by [(AX + 3P) 61-(AX - P) = 4P - 6 on disengaging plate 11 from plate 11H and re-engaging plate 11 with plate 11L when the speed of the plate 11 is - P r.p.m., the change in input to output speed ratio of the threestage gearbox on changing from any gear to the next higher gear is such that the overall input to output speed-ratio of the combination remains constant.

Power from the transmission output member, gearwheel 7, is taken via gearwheel 8 into the gearbox via a shaft which carries sunwheel 18S and annulus gear 16A.

Output power is taken from the planetary gears 18P to a terminal member formed by a shaft 22 in this case constituting an output shaft which also carries annulus gear 20A.

Annulus gear 18A is connected to a member 19 which carries the planetary gears 16P and the sunwheel 20S. Brake 13 is operative to act on braking surface 21 connected to the carrier member supporting planetary gears 20P. Brake 14 is operative to act on a braking surface 19A extending from member 19. Brake 15 is operative to act on braking surface 17 which is connected to the sunwheel 16S.

Operation of the combination is as follows. With the transmission at its minimum output speed setting, i.e. (AX -P) r.p.m., the clutch plates 11 and 11L are engaged and then low speed brake 13 is gradually engaged in the manner of a clutch to cause planetary gear 20P to become the reaction member of the gear 20 and initiate an output to shaft 22. After brake 13 has been fully engaged, the output speed of gearwheel 7 ma be increased up to the maximum value of AX + 3P) - 6 by the transmission in the manner previously described. This will cause the output shaft 22 to reach the maximum speed possible in the low speedrange of the gearbox. To change to the medium speed-range of the gearbox, brake 13 is released and, simultaneously, clutch plate 11 is disengaged from plate 11H and re-engaged with plate 11L, which causes all the intermediate gears to change their speeds and, in particular, cause rotation of annulus gear 18A to cease, so that the medium speed-range brake 14 may be engaged without any speed change to output shaft 22. It should be noted that during the speed-range change just described, the swashplate angle of control unit 9 is not altered and the speed of clutch plate 11 remains at -P r.p.m. During the change, the speed of the output shaft 22 and of gearwheels 2, 3, 4 and 5 remains constant but the speeds of all the other intermediate gears changes. However, as these intermediate gears may be of relatively light construction, the rotational inertia to be absorbed by the friction surfaces (those of the clutch plate, and also the braking mechanisms and associated braking surfaces) will be small and hence the change may be effected rapidly.

In a similar way to that of the low speed-range of the gearbox, the speed of output shaft 22 may be increased progressively through the range covered by the medium-speed brake 14, when the annulus gear 18A, sunwheel 20S and planetary gear 16P become reaction members, and then through the range covered by the highspeed brake 15, when sunwheel 16S becomes the reaction member. Thus, the infinitely-variable, stepless-ratio change available from the transmission may be used successively as the input to each gear of a multistage gearbox to give an infinitelyvariable, stepless-ratio change output drive from stationary up to maximum speed available from the gearbox. It should be noted that the transmission just described may be used to match any power source to any type of gearbox, for example a lay-shaft type gearbox, in order to produce an infinitelyvariable, stepless-ratio change output drive.

The operation of the transmission has been described using the example where the speed of the output shaft 22 is being increased, but the syst output member 7 is AX r.p.m. or greater. If the speed of the output is less than AX r.p.m., power is supplied to the primary epicyclic gear through the mechanical path but removed through the non-mechanical path back to the power source. A power recirculation loop would then be set up.

On the other hand, and as already mentioned, in the higher output speed-range of the transmission, the power supplied is divided and flows through each of three paths, as follows: (i) direct constant-speed power into the primary epicyclic gear in a mechanical path, (ii) direct constant-speed power into the secondary epicyclic gear, the output of which forms a secondary input into the primary epicyclic gear in a second mechanical ath, and (iii) indirect variable-speed power via the two hydrostatic pump (generator) or motor units into the secondary epicyclic gear in a non-mechanical path.

As in the case of the lower speed-range of the transmission as described above and depending upon the output speed of the primary epicyclic gear, power may be supplied along all three paths or supplied only along the two mechanical paths and removed via the non-mechanic path in the power recirculation loop.

From the description given for the transmission, it will be observed that power from shaft 1 is divided between gearwheel 2, following the non-mechanical path through the hydrostatic pump (generator) or motor units, 9, 10, and gearwheel 4 following a mechanical path or paths. By careful selection of the ratios of gearwheels 2 and 3, and 4 and 5, the proportions of power taking the non-mechanical and mechanical paths may be optimised so that for a particular set of hydrostatic pump (generator) or motor units, 9, 10, the power transmitted through output shaft is maximised. Use of the clutch plates 11, 11L, llH enables the full range of movement of the swashplate of control unit 9 to be used twice, i.e. maximum negative angle to maximum positive angle, and back again, in developing the necessary speed range of gearwheel 7 to cover each ratio of the output gearbox, so that the particular requirements of the hydrostatic pump (generator) or motor units 9, 10 are also optimised by reducing the duty on these units for a given power transmission.

In the event of failure of either of the hydrostatic pump (generator) or motor units 9, 10, the shaft of reaction unit 10 may be locked by applying a stationary brake 24 to a braking surface fixed relative to the shaft 23.

This would still permit operation of clutch plate 11 which, together with brakes 13, 14 and 15, would enable the combination to be operated as a six-speed fixed-ratio gearbox since for each engagement position of the clutch plate 11 (in which either the plate 11L or 11H is held stationary), three different output-speeds of the shaft 22 may be obtained.

As a possibility it is mentioned that the shaft 22 may be used as an input shaft driven by a variable-speed power source, and the speed of the three-stage gearbox and the swashplate angle may then be selected so as to keep the speed of shaft 1 (which would become the output shaft of the transmission) constant. Another possibility would be to reverse the positions of the transmission and the three-stage gearbox so that the constant-speed, variable-power source drives the gearbox directly and the gearbox, in turn, drives the transmission whose output constitutes the output of the combination. However, the form of transmission /gearbox combination illustrated and described above is to be preferred.

WHAT WE CLAIM IS: 1. A variable speed-ratio transmission comprising: a shaft provided with a gear wheel rotationally fast therewith; a variable speed mechanism for transmit ting a part of the power through the transmission, the variable-speed mechanism having a first terminal member drivingly connected with the shaft, and a second terminal member, the variable-speed mechanism being constructed such that (i) for a constant speed input to the first terminal member a variable speed output can be provided at the second terminal member and (ii) for a variable speed input at the second terminal member a constant speed output can be provided at the first terminal member; and an epicyclic gearing for transmitting the remainder of the power through the transmission, the epicyclic gearing comprising interconnected primary and secondary epicyclic gear arrangements, each of which includes a sun gear, planet gears mounted on a planet carrier, and an annulus gear, the gear wheel on the shaft being in constant driving connection with the annulus gear of the primary epicyclic gear arrangement and the second terminal member of the variablespeed mechanism being adapted for coupling with either the sun gear of the primary epicyclic gear arrangement or with the secondary epicyclic gear arrangement so as to accommodate an extended variable speed range, the arrangement being such that, in use, (a) with the shaft serving as an input member driven by a substantially constantspeed power source, a stepless variablespeed power output is obtainable at the planet carrier of the primary epicyclic gear arrangement and (b) with the planet carrier

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. output member 7 is AX r.p.m. or greater. If the speed of the output is less than AX r.p.m., power is supplied to the primary epicyclic gear through the mechanical path but removed through the non-mechanical path back to the power source. A power recirculation loop would then be set up. On the other hand, and as already mentioned, in the higher output speed-range of the transmission, the power supplied is divided and flows through each of three paths, as follows: (i) direct constant-speed power into the primary epicyclic gear in a mechanical path, (ii) direct constant-speed power into the secondary epicyclic gear, the output of which forms a secondary input into the primary epicyclic gear in a second mechanical ath, and (iii) indirect variable-speed power via the two hydrostatic pump (generator) or motor units into the secondary epicyclic gear in a non-mechanical path. As in the case of the lower speed-range of the transmission as described above and depending upon the output speed of the primary epicyclic gear, power may be supplied along all three paths or supplied only along the two mechanical paths and removed via the non-mechanic path in the power recirculation loop. From the description given for the transmission, it will be observed that power from shaft 1 is divided between gearwheel 2, following the non-mechanical path through the hydrostatic pump (generator) or motor units, 9, 10, and gearwheel 4 following a mechanical path or paths. By careful selection of the ratios of gearwheels 2 and 3, and 4 and 5, the proportions of power taking the non-mechanical and mechanical paths may be optimised so that for a particular set of hydrostatic pump (generator) or motor units, 9, 10, the power transmitted through output shaft is maximised. Use of the clutch plates 11, 11L, llH enables the full range of movement of the swashplate of control unit 9 to be used twice, i.e. maximum negative angle to maximum positive angle, and back again, in developing the necessary speed range of gearwheel 7 to cover each ratio of the output gearbox, so that the particular requirements of the hydrostatic pump (generator) or motor units 9, 10 are also optimised by reducing the duty on these units for a given power transmission. In the event of failure of either of the hydrostatic pump (generator) or motor units 9, 10, the shaft of reaction unit 10 may be locked by applying a stationary brake 24 to a braking surface fixed relative to the shaft 23. This would still permit operation of clutch plate 11 which, together with brakes 13, 14 and 15, would enable the combination to be operated as a six-speed fixed-ratio gearbox since for each engagement position of the clutch plate 11 (in which either the plate 11L or 11H is held stationary), three different output-speeds of the shaft 22 may be obtained. As a possibility it is mentioned that the shaft 22 may be used as an input shaft driven by a variable-speed power source, and the speed of the three-stage gearbox and the swashplate angle may then be selected so as to keep the speed of shaft 1 (which would become the output shaft of the transmission) constant. Another possibility would be to reverse the positions of the transmission and the three-stage gearbox so that the constant-speed, variable-power source drives the gearbox directly and the gearbox, in turn, drives the transmission whose output constitutes the output of the combination. However, the form of transmission /gearbox combination illustrated and described above is to be preferred. WHAT WE CLAIM IS:

1. A variable speed-ratio transmission comprising: a shaft provided with a gear wheel rotationally fast therewith; a variable speed mechanism for transmit ting a part of the power through the transmission, the variable-speed mechanism having a first terminal member drivingly connected with the shaft, and a second terminal member, the variable-speed mechanism being constructed such that (i) for a constant speed input to the first terminal member a variable speed output can be provided at the second terminal member and (ii) for a variable speed input at the second terminal member a constant speed output can be provided at the first terminal member; and an epicyclic gearing for transmitting the remainder of the power through the transmission, the epicyclic gearing comprising interconnected primary and secondary epicyclic gear arrangements, each of which includes a sun gear, planet gears mounted on a planet carrier, and an annulus gear, the gear wheel on the shaft being in constant driving connection with the annulus gear of the primary epicyclic gear arrangement and the second terminal member of the variablespeed mechanism being adapted for coupling with either the sun gear of the primary epicyclic gear arrangement or with the secondary epicyclic gear arrangement so as to accommodate an extended variable speed range, the arrangement being such that, in use, (a) with the shaft serving as an input member driven by a substantially constantspeed power source, a stepless variablespeed power output is obtainable at the planet carrier of the primary epicyclic gear arrangement and (b) with the planet carrier

of the primary epicyclic gear arrangement serving as an input member driven by a variable speed power source, a constant speed power output is obtainable at the shaft.

2. A transmission as claimed in claim 1, wherein the variable-speed mechanism comprises a non-mechanical pump/motor assembly.

3. A transmission as claimed in claim 2, wherein the direction of rotation of the pump/motor assembly is reversibel.

4. A transmission as claimed in claim 2 or 3, wherein the pump/motor assembly comprises a pair of swashplate type hydraulic pump/motor units hydraulically interconnected so that rotational drive into either one causes the other to be driven.

5. A transmission as claimed in claim 4 wherein one of said units has a variableangle swashplate and the other has a fixed angle swashplate.

6. A transmission as claimed in any preceding claim, wherein the second terminal member of the variable speed mechanism is coupled to the primary and secondary epicyclic gear arrangements by way of a coupling which is in permanent driving connection with the sunwheels of the primary and secondary epicyclic gear arrangements and with the annulus of the secondary epicyclic gear arrangements, the coupling including a clutch which serves for placing the second terminal member selectively in driving connection with the sunwheels or with the annulus.

7. A transmission as claimed in claim 6 as appendant to claim 5, wherein the rotary shaft of the fixed-angle swashplate constitutes the second terminal member of the variable-speed mechanism and is rotationally connected with a first clutch plate of the clutch, the clutch further comprising a second clutch plate rotationally connected with the sunwheels of the primary and secondary epicyclic gear arrangements, and a third clutch plate rotationally connected with the annulus of the secondary epicyclic gear arrangement, the first clutch plate being selectively engageable with the second and/or the third clutch plate rotationally to connect said rotary shaft with said sunwheels and/or with said annulus.

8. A transmission as claimed in claim 7, wherein the third clutch plate is rotationally connected with the annulus through gearing.

9. A transmission as claimed in claim 7 or 8, and including a brake for locking against rotation said rotary shaft and the first clutch plate.

10. A transmission as claimed in any one of claims 6 to 9, wherein the sunwheels are rotationally fast on a common shaft.

11. A transmission as claimed in any one of claims 6 to 10, wherein the planet carrier of the secondary epicyclic gear arrangement is rotationally fast with the annulus of the primary epicyclic gear arrangement.

12. A transmission as claimed in claim 11, wherein the gear wheel on the shaft is in constant driving engagement with the planet carrier of the secondary epicyclic gear arrangement.

13. A variable speed-ratio transmission substantially as hereinbefore described with reference to, and as shown in, the drawing accompanying the Provisional Specification.

14. In combination, a variable speedratio transmission as claimed in any preceding claim, and an epicyclic gear transmission coupled to the planet carrier of the primary epicyclic gear arrangement, the epicyclic gear transmission comprising low, medium and high speed epicyclic gear arrangements and associated braking mechanisms.

15. A combination as claimed in claim 14, wherein the planet carrier of the primary epicyclic gear arrangement is rotationally connected with the sunwheel of the medium speed epicyclic gear arrangement and with the annulus of the high speed epicyclic gear arrangement, an input/output member of the epicyclic gear transmission being rotationally connected with the annulus of the low speed epicyclic gear arrangement and with the planet gears of the medium speed epicyclic gear arrangement.

16. A combination of a variable speedratio transmission and an epicyclic gear transmission substantially as hereinbefore described with reference to, and as shown in, the drawing accompanying the Provisional Specification.