GB2188109A - Continuously variable ratio epicyclic gearbox controlled by the applied load - Google Patents

Abstract

A continuously variable ratio gearbox comprises an assembly of first and second epicyclic gear units (11, 13) and a differential gear unit (15) arranged such that, in use, in response to the load conditions on the gearbox a portion of the power to an input shaft (12) of the gearbox is transmitted directly between the epicyclic gear units (11, 13) to an output shaft (14) and another portion is transmitted therebetween by a path the rotation of which is under the control of the differential gear unit (15), the input and output gears (26, 27) of which are arranged for rotation respectively with said input and output shafts. The first epicyclic gear unit serves to divide input drive between two paths through the gearbox and the second epicyclic gear unit serves to combine drive through the two paths into a single output drive at the output shaft. The carrier of the first epicyclic gear unit (11) is preferably integral with the carrier of the differential and a ring gear (20) of the second epicyclic gear unit (13). The carrier of the second epicyclic gear unit (13) is preferably integral with the ring gear of the first (11). <IMAGE>

Description

SPECIFICATION Continuouslyvariable ratio gearbox This invention rel ates to a conti n uously variabl e ratio gearbox and in particular, though not exclusively, to a continuously variable ratio gearbox for use in the drive system of a vehicle.

One known kind of continuously variable ratio gearboxemploysabeltand pulleywheelsto transmit drive forces from an in put shaft to an output shaft ofthe gearbox. The pulley wheels each have a variable effective diameter for engagement with a beltandarearrangedtoworkasa pairwherebyas the effective diameter of one pulley wheel decreases the effective diameter of the other pulley wheel increases. The gearbox ratio is determined by the relative effective diameters of the pulley wheels.

The disadvantages of known kinds of gearboxes includethe existence of a response time lag between a change in demand on the gearbox and a resulting change in the gear ratio. Also there is a limit to the power capacity of the gearbox without an undue risk of slippage orbreakage ofthe belt.

The present invention seeks to provide a continuously variable ratio gearbox in which the afore-described disadvantages are mitigated or overcome.

In accordance with one of its aspects the present invention provides a continuously variable ratio gearboxcomprising an assembly offirstand second epicyclic gear units and a differential gear unit arranged such that, in use, in response to the load conditions on the gearbox a portion ofthe powerto an input shaft of the gearbox is transmitted directly between the epicyclic gear units to an output shaft and another portion is transmitted therebetween by a path the rotation of which is underthe control of the differential gear unit the input and output gears of which are arranged for rotation respectively with said input and output shafts.

In the preferred construction of a gearbox in accordance with the present invention it is provided that: a) the input shaft drive to the gearbox is applied two the sun gear of the first epicyclic gear unit, b) the planet gear carriage ofthefirst epicyclic gear unit is connected to the annular, i.e. outer, gear ofthe second epicyclic gear unit, c) the annular, i.e. outer,gearofthefirstepicyclic gear unit is connected to the planet gear carriage of the second epicyclic gear unit, d) the output shaft drive of the gearbox is taken from the sun gear ofthe second epicyclic gear unit, e) the input and output shafts are connected respectively to input and output gears of the differential gear unit, f) the pinion gearofthedifferential gearunit provided to transmit power between said input and output gears is supported by a pinion cage arranged to rotate in unison with the planet gear carriage of the first epicyclic gear unit and thus also with the annular gear of the second epicyclic gear unit, g)thesun and planet gears ofthefirst epicyclic gear unit are of the same diameter, and h)the sun gear ofthe second epicyclic gear unit has a diameter twice the diameterofthe planetgear of said unit.

Afurtherfeature of the preferred construction is thatthe input and output shafts are coaxial.

In the afore-described construction there are two pathsforthetransmission of drive between input and output shafts. One path, to be referred to hereinafter as an inner path, is from the planet gear carriage ofthefirst epicyclic gear unit to the annular gearofthe second epicyclic gear unit. The other path, to be referred to hereinafter as the outer path, is from the annular gear ofthe first epicyclic gear unit to the planet gear carriage ofthe second epicyclic gear unit.

The first epicyclic gear unit serves to dividethe input shaft between the inner and outer paths and the second epicyclic gear unitservesto combinethe inner and outer path drives into a single output drive atthe output shaft.

The rotation ofthe inner path, to which the pinion cage of the differential gear unit is connected, is determined by the rotations ofthe input and output gears of said differential gear unit.

The rotation ofthe outer path is determined indirectly by the rotations of the input and output shafts and the inner path.

The rotations ofthe inner and outer paths determine the overall ratio of the gearbox and that ratio is continuously variable in accordance with input drive conditions.

One embodiment ofthe invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, wherein Figure 1 is an axial cross-section of palt of a continuously variable ratio gearbox in accordance with the present invention, Figure 2 is an axial cross-section of the gearbox of Figure 1 from which the differential gear unit has been omitted, Figure3isa sectional view on the lineA-Aof Figure 2, Figure4is a sectional viewonthe line B-B of Figure 2, Figures 5, 7,9and llareschematicviewssimilarto Figure 2 and showing the first epicyclic gear unit in successive positions, and Figures 6,8,10 and 12 are schematic views similar to Figure 3 and showing the second epicyclic gear unit in successive positions.

Acontinuouslyvariable ratio gearbox 10, as shown in Figure 1, comprises a first or input side epicyclic gear unit 11 connected to an input shaft 12, a second oroutput side epicyclic gear unit 13 connected to an output shaft 14 and interposed between said gear units a differential gear unit 15.

The assembly ofthe gear units 11,13 and 15 is housed within a casing (not shown) in a conventional manner whereby adequate lubrication of moving components may be ensured.

Each epicyclicgearunit 11,13,comprisesthe customary sun gear, planet gear and outer or annular gear.

Theinputshaftl2isconnectedtothesungearl6 of the first epicyclic gear unit 1 1 .The planet gear 1 7 of gear unit 11 has the same diameter as the sun gear 16 and is rotatably mounted on a planet gear carriage 18which is connected via the pinion cage 19 ofthe differential gear unit 15to the annular gear 20 ofthe second epicyclic gear unit 13.

Theannulargear21 ofthefirstepicyclicgearunit is connected by a cylindrical shaped tubular outer member22 to the planet gear carriage 23 ofthe second epicyclic gear unit 13. The pla netgear 24 of thesecond unit13 is rotatably mounted ontheplanet gear carriage 23 and has a diameter halfthat ofthe sun gear25 ofthe second epicyclic gear unit. The sun gear 25 is secured to the output shaft 14.

The differential gear unit 15 comprises input and output gears 26,27, of the same diameter and secured respectively to the input and output shafts 12,14, for rotation therewith. The two gears 26,27, are interconnected by a pinion gear 28 rotatably mounted on the pinion cage 19.

The pinion cage 19 is rotatably supported relative to the input and output shafts by means of conventional ball-bearing units (not shown).

The operation of the epicyclic gear units 11,13, of the gearbox 10 will now be described with reference toFigures2and5to12.

Two drive transmission conditions will be considered. Afirst condition is that in which drive is transmitted solely through an outer path comprised by the cylindrical outer member 22, with no rotation of an inner path comprised by the pinion cage 19 (not shown in Figure 2), first planetgearcarriage 18and annulargear20 ofthe second epicyclic gear unit The second drive condition is that in which drive is transmitted solelythrough the inner path with no rotation of the outer path. For each condition the effect of a single clockwise rotation will be considered.

Firstcondition- Drive transmitted solely through the outer path.

Referring to Figure 5, which is a simplified form of Figure3,foran inputofasingle clockwise rotation the sun gear 16will rotate the planet gear 17to cause the annular gear 21 andthustheouterpathtorotate through one third of a rotation in an anti-clockwise direction.

Referring to Figure 6 which shows the second epicyclic gear unit in a simplified form. the onethird of a rotation anti-clockwise of the carriage ofthe planetgear24 results in a complete rotation ofthe sun gear 25 in an anti-clockwise direction.

Accordinglythe overall ratio of the gearbox in the firstcondition is 1 :1,thoughthereisa reversal of direction of rotation.

Secondcondftion- Drive transmitted solely through the inner path.

Referring to Figure 7, a single clockwise input to sun gear16will causethe planetgear 17and its carriage 18to movethrough onequarterofarotation about the sun gear in a clockwise direction.

Referring to Figure 8, the one quarter clockwise rotation ofthe carriage 18 and thus oftheannular gear20 results in a one half of a rotation ofthesun gear 25 in an anti-clockwise direction.

Accordinglythe overall ratio of the gearbox in the second condition is 2:1, though again there is a reversal of the direction of rotation.

Having discussed the overall gear ratios for said first and second conditions consideration will now be given to the differential gear unit 15 which controls the overall gear ratio ofthe gearbox by determining the rotation of the inner drive path. The differential gear unit has its input and output gears 26,27, connected respectively to the input and output shafts 12,14, as described above and its pinion cage 19 forms a part of the inner drive path.

The relative ratios of the sun and planet gears in each ofthe first and second epicyclic gear units have been chosen such that all times during operation of the gearboxthe rotation of the inner path and thus of the pinion cage is exactly one half of the sum of rotations of the input and outputs shafts. This is of significance insofar as in a conventional differential gear unit having input and output gears of equal effective diameter the rotation ofthe pinion cage is exactly half the sum of the rotation of the input and output shafts.

Consideration will now be given to the manner in which the three gear units 11,13,15, ofthe gearbox interact when the gearbox is operating in each ofthe afore-described first and second conditions. In this consideration the convention is adopted that clockwise rotations are positive and anti-clockwise rotations are negative.

In the first condition a rotation of+1 on the input shaft 12 causes a rotation of - 1 at the output shaft 14.

The rotation ofthe pinion cage 19 and thus ofthe inner drive path isO. Thus drive is transmitted through only the outer drive path.

In the second condition a rotation of + 1 on the input shaft 12 causes a rotation of -0.5 at the output shaft 14. This results in a rotation of the pinion cage 19 and thus the inner drive path of +0.25. In this condition the combination of the rotations ofthe input and output drive shafts and the rotation ofthe inner drive path prevents the outer drive path from rotating. Thus drive is transmitted through onlythe inner drive path.

The above-described first and second conditions are special conditions in which in each case drive passes through a single drive path. However, the gearbox is of a construction which will allow drive to be transmitted th roug h the i n ner and outer paths simultaneously in continuously variable proportions thereby to result in an overall gearbox ratio which is continuously variable over the range from 1 :0 through a ratio of 1 :1 to a limit ratio of 0:1.

To describe the operation of the gearboxwhen drive is being transmitted through the inner and outer paths simultaneously consideration will now be given to two further conditions, referred to as third and fourth conditions, in which the gearbox has overall ratios of 1:0.75 and 1:0.25 respectively.

When considering operation ofthefirstepicyclic gear unit 11 it can be stated that: Rotation of input shaft = 4 x (Rotation of inner path) + (-3) x (Rotation of outer path) When considering operation ofthe second epicyclic gear unit 13 it can be stated that:- Rotation of output shaft = 3 x (Rotation of outer path) + (-2) x (Rotation of inner path) Third condition - The drive is transmitted through both of the inner and outer paths and the overall gear ratio is the sum of the individual gear ratios ofthe two paths. The condition described here is only one of a range of gear ratios extending continuously from the 1:1 ratio ofthefirstcondition to the 2:1 ratio ofthe second condition.

The overall gear ratio of the third condition is 4:3 and thus ifthe input shaft 12 has a rotation of +1 the outputshaftwill have a rotation of -0.75. Hencethe rotation of the inner path and thus also the pinion cagewill be +0.125.

The effect of this rotation on the first epicyclic gear unit is shown in Figure 9. A rotation of +0.5 ofthe input shaft andthus sun gear 16will cause a rotation ofthe inner path of 0.125. Thus only halfthe rotation oftheinputshaftistransmittedthroughtheinner path, the remainderofthe rotation ofthe input shaft must be transmitted through the outer drive path. A rotation of +0.5 ofthe input shaft will result in a rotation of-0.166... ofthe outer path and thus of the first annular gear 21.

The effect of the rotation on the second epicyclic gear unit 13 is shown in Figure 10. A rotation of +0.125 of the inner path will result in a rotation of -0.25ofthesun gear 25 and output shaft 14. A rotation of -0.166. . . ofthe outer path will result in a rotation of -0.5 of the output shaft. The sum of the two rotations gives a total rotation of the output shaft of -0.75.

Fourth condition - The drive is transmitted through both of the inner and outer paths and the overall gear ratio isthe difference between the overall gear ratios of the two paths. The condition described herein is only one ofthe a range of gear ratios which, staring at the 2:1 ratio ofthe second condition extends through a ratio of 100:1 to a limit of1 :0.

The overall gear ratio in the fourth condition is 4:1 and thus if the input shaft 12 has a rotation of + 1 the outputshaftwill have a rotation of -0.25. This results in the inner path and thus also the pinion cage having a rotation of +0.375.

The effect of this rotation on the first epicyclic gear unit is shown in Figure 11. A rotation of + 1.0 ofthe input shaft and thus the sun gear 16 and a +0.375 rotation ofthe inner path will result in a +0.166. . .

rotation of the outer path. Note that the rotation of the outer path is now in a clockwise direction and oppositetothat ofthethird condition. The drive passing through the outer path is subtracted from the drive passing through the inner path.

The effect of the rotation on the second epicyclic gear unit is shown in Figure 12. Entering the second epicyclic gear unit is a rotation of +0.375 ofthe inner path and a rotation of ......... ofthe outer path.

This results in a rotation of -0.25 of the sun gear25 and thus the output shaft.

A gearbox in accordance with the present invention is of particular potential valuefor use ion a wide range ofvehicles including bicycles, tanks and motor cars. It provides a continuouslyvariable ratio gearbox which is able to adjust its ratio smoothly and without any undesirable time lag.

In the afore-described construction the input and output gears ofthe differential gear unlit have equal effective diametersforengagementwith the simple pinion gear, correspondingly to result in equal gear ratios with the pinion gear, and in consequence the rotation of the pinion cage is exactly half the sum of the rotations of the input and output shafts. This is not an essential requirement ofthe invention and input and output differential gears which give non-equal ratios with a suitable pinion gear may be employed provided that the relative ratios ofthe sun and planet gears in each ofthe first and second epicyclic gear units are chosen such that during operation of the gearbox the rotation of the inner path as determined by the movements ofthefirst planet gear carriage and annular gear of the second epicyclicgearunitexactlyequalstherotation ofthe pinion cage as determined by the rotations ofthe input and output differential gears.

The afore-described gearbox may be operated in a reverse manner in which power is applied to the output shaft 14 and taken from the input shaft 12.

Claims (15)

1. Acontinuouslyvariable ratio gearbox comprising an assembly offirst and second epicyclic gear units and a differential gear unit arranged such that, in use, in response to the load conditions onthe gearbox a portion of the power to an input shaft of the gearbox is transmitted directly between the epicyclicgearunitstoan output shaft and another portion is transmitted therebetween by a path the rotation of which is underthecontrol of the differential gear unit the in put and output gears of which are arranged for rotation respectively with said input and output shafts.

2. Acontinuouslyvariable ratio gearbox according to claim 1, wherein the input shaft drive is applied to a su n gear or sun gearofthefirstepicyclicgearunit.

3. Acontinuouslyvariable ratio gearbox according to claim 1 or claim 2, wherein a planetgear carriage ofthefirst epicyclic gear unit is connected to an annular, outer gear ofthe second epicyclic gear unit.

4. Acontinuouslyvariable ratio gearbox according to any one of the preceding claims, wherein an annular, outer gear of the first epicyclic gear unit is connected to a planet gear carriage of the second epicyclic gear unit.

5. Acontinuouslyvariable ratio gearbox according to any one of the preceding claims, wherein the output shaft drive is taken from a sun gear of the second epicyclic gear unit.

6. Acontinuouslyvariable ratio gearbox according to any one ofthe preceding claims, wherein said input and output shafts are connected respectively to input and output gears ofthe differential gear unit.

7. Acontinuouslyvariable ratio gearbox according to any one ofthe preceding claims, wherein the differential gear unit comprises a pinion gearto transmit power between said input and output gears.

8. Acontinuouslyvariableratiogearbox according to claim 7, wherein the pinion gear is supported by a pinion cage arranged for rotation in unisonwiththeplanetgearcarriageofthefirst epicyclic gear unit.

9. Acontinuouslyvariable ratio gearbox according to any one ofthe preceding claims, wherein the sun and planet gears ofthe first epicyclic gear unit are of the same diameter.

10. Acontinuouslyvariable ratio gearbox according to any one of the preceding claims, wherein the sun gear ofthe second epicyclic gear unit has a diameter twice the diameter of the planet gear of said unit.

11. Acontinuouslyvariable ratio gearbox according to any one of the preceding claims, wherein the input and output shafts are coaxial.

12. Acontinuouslyvariable ratio gearbox according to any one ofthe preceding claims, wherein the differential gear unit comprises input and output gears of equal effective diameter.

13. A continuously variable ratio gearbox according to claim 12, wherein the relative ratios of the sun and planet gears in each of the first and second epicyclic gear units are such that at all times during operation of the gearbox the rotation ofthe pinion cage is exactly one halfthe sum ofthe rotations of the input and output shafts.

14. Acontinuouslyvariable ratio gearbox according to any one of claims 1 to 1 wherein the differential gearunitcomprises input and output gears of different effective diameters and the relative ratios ofthe sun and planet gears in each ofthefirst and second epicyclic gear units is such that during operation ofthe gearbox the rotation of the first planet gear carriage and annular gear of the second epicyclic gear unit exactly equals the rotation of the pinion cage as determined by the rotations of the input and output differential gears.

15. Acontinuouslyvariable ratio gearbox constructed and arranged substantially as hereinbefore described, with reference to the accompanying drawings.