GB2219640A - Drive transmission apparatus - Google Patents

Abstract

A continuously variable transmission comprises an epicyclic gear train preferably composed of bevel gears (15, 16, 17, 24) wherein the carrier (20) is variably braked or restrained. The braking is preferably carried out by a fluid transmission (26), but alternatively by a brake band, magnetic coupling, torque converter, or fluid coupling. Two trains may be combined to provide two inputs and two outputs. Also disclosed is bevel epicyclic reversing gearing where the input is selectively clutchable to the carrier and the carrier is braked. The output bevel gear may also be braked. Also disclosed is a single bevel epicyclic gearing train having two inputs to the carrier, two outputs from the side bevel gears and one way clutches to stop one input driving the other. <IMAGE>

Description

DRIVE TRANSMISSION APPARATUS In transmitting drive from a motive power source such as an internal combustion engine or an electric motor it is frequently required to vary the transmission ratio between the power source and the ultimate drive utiliser.

It is well known that internal combustion engines must have a certain minimum speed before they develop sufficiently high torque to drive, for example, a motor vehicle and that while the vehicle is stationary, with its engine running, it is necessary to disconnect the engine from the drive transmission in order to avoid stalling the engine. Drive transmission apparatus for a motor vehicle must, therefore, be capable of operating over a range of transmission ratios from infinity (namely no drive transmitted) and a fixed minimum ratio, normally referred to as direct drive or 1:1 drive transmission.

Internal combustion engines themselves also require a range of different ratios in order to enable them to be operated within the optimum range of performance criteria in different operating conditions. For example, when accelerating from rest or climbing a steep hill it is necessary to select a relatively low gear (namely a high transmission ratio) whereas in order to reach maximum speed a "high" gear that is a low transmission ratio is required. In order to achieve this convential gear boxes comprising a number of gear wheels rotating at different speeds and interconnected by different transmission ratios are utilised: drive transmission through such a gear box is passed from an input shaft via a selected combination of internal gears, to an output shaft in order to achieve the required transmission ratio.The majority of the gears within a gear box, however, are unused at any one time and must therefore be transported as excess weight to be used only in those conditions or range of conditions for which the engine operating parameters are appropriate.

Conventional gear boxes also offer only a limited range of predetermined transmission ratios which are not entirely optimum for the vehicle but necessarily a compromise between the requirements of the engine and convenience of use for the driver: considerations as to minimising excess weight must also be taken into account.

Although a large number of closely spaced ratios would be most efficient for the engine, this would necessitate changing gear very frequently in order to maintain the engine operating in its optimum performance range and this would be tedious and inconvenient. It would also mean that very many unnecessary and for the most part unwanted gears would be conveyed by the vehicle. This disadvantage is to some extent overcome by so-called "automatic" transmissions which act to change the gears in dependence on the output from sensors detecting the engine operating conditions. "Automatic" gear boxes normally, however, offer a predetermined set of transmission ratios so that nevertheless, a compromise on the engine operating conditions is made in use.Various attempts to produce a continously variable transmission mechanism have been made, these including the use of variable diameter belts and pulleys (the pulleys being formed in two parts and being interlinked in such a way that an increase in the separation of the parts causes a reduction in the effective diameter of the pulleys.

Transmissions utilising oppositely directed interconnected cones have also been tried without finding much favour largely due to the fact that drive is transmitted only by frictional contact between the components rather than the positive intermeshing of gears.

The present invention seeks, therefore, to provide a drive transmission mechanism which, among other things, will be able to offer continuously variable transmission ratios whilst nevertheless employing the direct interconnection of meshing of gears. Other problems associated with conventional drive transmission apparatus, such as its complexity, the necessity for changing the predetermined gear ratios, and the fact that decisions have to be made as to precisely when the gears themselves are changed may be overcome.

According to one aspect of the present invention, therefore, a drive transmission apparatus includes at least one input or drive shaft to which, in use of the apparatus, drive is applied for transmission to at least one output or driven shaft of the apparatus, in which the drive train of the apparatus between the input and output shafts includes a gear mechanism incorporating one or a plurality of planet gears mounted for rotations about its or their respective axis of rotation on a planet carrier which is itself rotatable about an axis aligned with one of the input and/or output shafts, and rotational restraint means for selectively limiting the relative rotation of the planet carrier with respect to the or one of the input shaft or shafts and/or the or one of the output shaft or shafts.

The drive transmission apparatus of the present invention may be used, for example, to transmit motive power, or to control the transmission of motive power; for example it may be used as a control system for a continuously variable drive transmission system. The drive transmission apparatus of the present invention may also be used to provide a so-called "soft start" for an electric motor, to enable the motor to start without load and then gradually start transmitting load as the rotation of the planet carrier is restrained.

In a preferred embodiment of the invention the rotational restraint means acts between the planet carrier and the output shaft of a transmission mechanism for transmitting drive from a single input shaft to a single output shaft.

The rotational restraint means may be of any convenient form and it is envisaged that, among others, the means may comprise one or more brake bands (or Van Doorn belts) surrounding a rotating component, magnetic coupling means interconnecting a rotary member and a static or stator member, and fluid transmission means of any type including those in which one or more sets of vanes are rotated within a fluid medium in such a way as to cause movement of the fluid for the storage and transmission of energy and those employing electrostatic fluids.

In another aspect the present invention provides a drive transmission device having a continously variable transmission ratio, within predetermined limits, comprising an input shaft driving an input or drive pinion, an output shaft fixed for rotation with an output or driven pinion, planet gears meshing with both the said drive pinion and the said driven pinion, a planet carrier on which the planet gears are freely rotatably mounted being itself fixed for rotation with respect to the said input or the said output shaft, and means for controlling or limiting the relative rotation of the said planet carrier and the other of the input or output shaft between a condition in which the planet carrier is free to rotate with respect to the said other shaft and no torque is transmitted thereto from the said other shaft, and a condition in which the planet carrier is fixed in relation to the said other shaft and this latter is thus constrained to rotate at a speed determined by the speed of rotation of the said other shaft.

In this aspect the planet gears may be bevel pinions or alternatively may be helical or spur gears, in which case the planet carrier may be the idler plate of an epicyclic gear mechanism constituting the differential gear. There may further be provided means whereby the output drive from the said output or driven shaft is taken, at least in some operating conditions of the drive transmitting device, via an epicyclic gear mechanism adapted for reversing the direction of rotation of the drive transmitted thereby such that the input and output shafts of the drive transmission device both rotate in the same direction when the device is operated in these conditions.

Of course, if the drive transmission device is used for a motor vehicle, it is convenient to have available an option to reverse the direction of rotation in order to provide a so-called "reverse" gear and this may readily be provided within the ambit of the invention as described above by selectively acting on the epicyclic gear mechanism to cause it to reverse the direction of input drive or to transmit the input drive in the same directional sense.

The drive transmission apparatus of the present invention may, of course, be used in other machinery than motor vehicles. Drive transmission is required in many forms of industrial machinery, boats, and other mechanisms, and in appropriately adapted forms the apparatus of the present invention may find application in any of these.

For example, it is envisaged that the drive transmission of the present invention may be applied with some advantage in a winch to make this torque sensitive so that the transmission ratio changes from a high gear under low loads to a low gear under high loads.

Likewise, a torque-sensing differential may be formed utilising the apparatus of the present invention and appropriate sensors as will be described in more detail hereinbelow.

Various embodiments of the present invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram illustrating a continously variable transmission device incorporating the principles of the present invention; Figure 2 is an alternative transmission device for use with a plurality of inputs and from which a plurality of outputs may be taken; Figure 3 is a simple embodiment of a transmission mechanism for achieving reverse operation, suitable for example for boats; Figure 4 is a more complex embodiment having linked differential mechanisms and control means giving a wider range of control options; and Figure 5 is a schematic axial sectional view through a further embodiment of the present invention.

Referring now to the drawings, and first to Figure 1, the continuously variable transmission mechanism illustrated therein is suitable, for example, for use in a motor vehicle drive transmission from an internal combustion engine to the road wheels. It is envisaged that the variable transmission mechanism of the present invention would replace the conventional gear box and clutch, allowing the vehicle to be accelerated from rest with the engine idling, up to a maximum speed without any discrete changes in the transmission ratio during acceleration.

Output drive from the internal combustion engine (not shown) is applied to an input shaft 11 which is carried by bearings 12 in an opening 13 in a main transmission housing 14 and which has a bevel pinion 15 on its interior end.

The bevel pinion 15 meshes with two planet gears 16, 17 (also formed as bevel pinions) which are borne on bearings 18, 19 in a differential casing 20 through which the input shaft 11 passes and with respect to which it is borne by means of a bearing 21. Appropriate oil seals for all rotating shafts may be provided, but will not be described in detail herein since these constitute no more than a practical engineering necessity and their presence and form do not constitute part of the present invention.

The differential housing 20 is traversed by an output shaft 22 which is borne in a bearing 23 in an axial flange of the housing 20. On the inner end of the output shaft 22 is carried a driven pinion 24 which, like the drive pinion 15 is a bevel pinion matching the bevel pinions 16, 17 which constitute the planet gears. As shown in the drawing all these bevel pinions have the same diameter and number of teeth, but obviously the planet gears 16, 17 could have a greater diameter that the drive and driven gears or a smaller diameter than these as appropriate.

The planet housing 20 is connected, as schematically illustrated in Figure 1, to the driving blades of a fluid transmission, in this case generally indicated with the reference numeral 25. The fluid transmission itself is generally indicated with the reference numeral 26 and has a driven turbine 27 which is connected for rotation with the output shaft 22. The output shaft 22 may further be provided with a brake band 28 for ensuring that the vehicle remains stationary when idling.

The fluid transmission 26 is also provided with control means (not illustrated) by which the degree of resistance offered by the driven blade 27 with respect to the speed of rotation of the drive blade 25 can be varied. In operation, therefore, when the vehicle is stationary and the engine is idling the input shaft 11 rotates slowly and the output shaft 22 is stationary, held by the brake 28 whilst the minimum resistance is offered by the fluid transmission 26 so that the least torque is transmitted thereto.Because the output shaft 22 is stationary the driven pinion 24 of the differential gear 10 is stationary and consequently the bevel pinions 16, 17, driven by the input gear 15 are caused to rotate so that the differential housing 20 is also carried into rotation thereby at a fraction of the speed of rotation of the input shaft 11: because the fluid transmission 26 offers the least resistance there is a minimum amount of torque applied to the output shaft 22 which, in any case, as mentioned above is braked by the brake 28 to ensure that it remains stationary. When it is desired to accelerate the vehicle the brake 28 is released and the speed of rotation of the input shaft 11 increases.

Correspondingly the resistance between the drive blade 25 and the driven blade 27 is increased so that a measure of torque is applied by the differential casing 20 to the output shaft 22. This torque is fed back through the driven pinion 24 to the differential housing itself (via the differential pinions 16, 17) causing progressively greater torque to be applied to the output shaft 22 until the situation is reached that the maximum resistance is offered by the fluid transmission 26 and the driven pinion 24 is effectively locked with respect to the differential casing 20 so that, in effect, a direct transmission on a 1:1 ratio is achieved from the input shaft 11 to the output shaft 22. In this situation there is no slip in the fluid transmission 26 and therefore no generation of heat.

In an alternative configuration illustrated in Figure 2 a drive transmission for two input shafts is shown. These input shafts comprise a first input shaft 29 and a second input shaft 30, these being respectively joined to first and second drive pinions 31, 32 respectively. The input shafts 29, 30 are coaxial with one another and each is borne by uni-directional clutch/brake bearing assemblies 33, 34 in a stationary transmission housing 35.

Within the transmission housing 35 is located a differential gear generally indicated 36 comprising the first and second drive pinions 31, 32, two planet gears 37, 38 mounted for rotation about respective axes X-X in a differential casing 39. The differential casing 39 carries a crown wheel 40 meshing with respective first and second output pinions 41, 42 linked to respective first and second output shafts 43, 44 each borne in a bearing (not shown) in the transmission housing.

The input drive to the transmission, applied by rotation of the shafts 29, 30 causes rotation of the differential casing 39 and thus of both output shafts 43, 44. If one of the input shafts, for example the input shaft 30, is stationary its uni-directional clutch/brake bearing 34 will prevent reverse rotation and thus any reduction in the torque transmitted to the output shafts 43, 44 from the single input shaft 29. Correspondingly, the uni-directional clutch/brake bearing 33 allows the drive shaft 30 to apply all of the torque to the transmission or merely more torque than the shaft 29, whilst the differential gear 36 ensures that the torque applied by both inputs is supplied to both outputs 43, 44.

Turning now to Figure 3 this constitutes a simple reversing gear box suitable for use, for example, in the drive transmission from an internal combustion engine to the propeller of a boat. Here, reduction gearing such as is required for a land vehicle is not necessary, but it is necessary to be able to reverse the thrust for braking and/or reverse movement. An input shaft 45 having a splined section 46 passes through a dog toothed gear 47 having an annular channel 48 around its periphery and a circumferential ring of axially facing teeth 49. The dqg gear 47 is engaged on the splined section 46 of the input shaft 45 so that it can be displaced axially therealong whilst continuing to rotate with the input shaft 45.

At the end of the input shaft 45 is a bevel pinion 50 which constitutes the drive pinion of a differential gear generally indicated 51 having two coaxial planet gears 52, 53 this time mounted on a common shaft 54 borne on a cylindrical differential casing 55 around which is wrapped a brake band 56 for selectively braking the rotation of the differential gear 51 as will be described.

The output pinion of the differential gear is a specially shaped bevel pinion generally indicated 57 having an output drive shaft 58 coaxial with the input shaft 45, a conical face 59 bearing teeth meshing with the planet gears 52, 53 and a radial flange portion 60 bearing a flat cylindrical face 61 engaged by a brake band 62. In operation of the gear box described in relation to Figure 3 drive torque from the input shaft 45 is transmitted both to the dog toothed gear 47 and to the drive pinion 50 of the differential gear 51. If the dog toothed gear 47 is displaced to the left by engagement of a gear selector 63 in the annular peripheral channel 48 there is no transmission of rotation from the dog toothed gear 47 to the differential casing 55. In addition this may be braked by contact with the brake band 56.Accordingly the rotation of the drive pinion 50 causes each of the planet gears 52, 53 to rotate about the axis of the shaft 54 driving the output pinion 57 in the reverse directional sense from that of the input shaft 45.

Conversely, if the selector 63 is moved to displace the dog toothed gear 47 to the right to engage the teeth 49 thereof with corresponding teeth 64 formed in an annular array on the end of the cylindrical differential casing 55 this is caused to rotate at the same speed as the shaft 45 and the bevel drive gear 50 so that torque is transmitted to the output pinion 57 in a direct 1:1 ratio and in the same directional sense as the drive to the input shaft 45.

In order to achieve a "neutral" position the selector 63 is again moved to the left to disengage the teeth 49 from the teeth 64, the brake band 62 is engaged to hold the output pinion 57 stationary, and the brake band 56 is released to allow rotation of the differential casing 55.

In this case rotation of the drive pinion 50 is transmitted to the planets 52, 53 which both rotate freely about the stationary output pinion 57 carrying with them the differential casing 50 which now rotates at one half of the speed of the input shaft 45.

Figure 4 illustrates a multiple differential gear arrangement comprising two sets of differential gears 65, 66 in a common coaxial configuration having respective differential casings 67, 68 which can be braked by respective brake bands 69, 70 and which are driven by respective drive pinions 71, 72 via a drive transmission arrangement which will be described in more detail below.

The differential casings 67, 68 have respective crown wheels 73, 74 driven by an input drive shaft 75 via a bevel drive gear 76 (with an idler 77 being provided to ensure that both crown wheels 73, 74 rotate in the same direction).

Each of the differential gears 65, 66 includes pairs of planet gears 78, 79 and 80, 81 and respective output pinions 82, 83 driving respective output shafts 84, 85.

The two input drive pinions 71, 72 are controlled via a control mechanism generally indicated 87 via a control input 86 which will be of appropriate type dependent on the nature of the control mechanism 87. The crown wheels 73, 74 are linked to the respective differential casings 67, 68 by respective clutches generally indicated 88, 89.

With the clutches engaged and the brake bands 69, 70 released the unit operates as a conventional differential gear. This can be caused to act as a limited slip or locking differential by energisation of the input pinion control mechanism 87. Other control configurations can be achieved, for example, by applying one of the brake bands or the other to modify the output speeds of the output shafts 84, 85 in dependence upon the internal ratios of the differential units 65, 66. Likewise, releasing the clutches 88, 89 which interconnect the respective crown wheels 73, 74 to the respective differential housings 67, 68 can achieve reversal of the drive to one or both output shafts and combined clutch release and brake application can double the speed of rotation of the associated output shaft.Alternatively, if one of the differential housings 67, 68 is braked via a torque converter or the like, the embodiment of Figure 4 may be adapted as a four wheel drive continuously variable transmission. The four wheel drive potential from the torque split may also be achieved using other embodiments of the invention with appropriate adaptations and additions.

Finally, referring to Figure 5, a simple embodiment utilising an epicyclic gear is illustrated. In this embodiment an engine fly wheel 90 is formed as a planet carrier with a plurality of axially extending bearing spindles 91 (only two of which are visible in Figure 5, but any convenient number of which may be provided to support the loads experienced in use) carrying respective planet gears 92 meshing between a sun wheel 93 carried on a drive shaft 94 and a ring gear 95.The ring gear 95 and the output shaft 94 are connected to respective relatively rotatable parts of a fluid transmission generally indicated 96 which may be of any known type, including fluid torque converter, electrostatic fluid transmission or the like having means (not shown) for controlling the degree of slip or transmission between the relatively movable parts (indicated in Figure 5 by the reference numerals 97, 98 of the transmission 96).

In use of the transmission mechanism of Figure 5 the engine fly wheel 90 rotates at the same speed as the engine in a conventional manner, carrying with it the planet gears 92 which, if the output shaft 94 is stationary (for example braked) will result in rotation of the planets 92 about their spindles 91 and consequent rotation of the ring gear 95 at a speed greater than that at which the fly wheel 90 rotates. The component 97 of the fluid transmission mechanism 96 connected to the ring gear 95 will thus also rotate at this speed. If the fluid transmission is controlled to transmit no torque the vehicle will remain stationary with the engine idling. When it is desired to transmit drive to the output shaft the control mechanism (not shown) is energised to start transmitting torque from one part 97 of the fluid transmission 96 to the other part 98 thereof in a conventional manner which, since it is already known, will not be described in detail here. As the shaft 94 begins to rotate, therefore, the relative speed of rotation between the ring gear 95 and the sun wheel 93 will reduce until ultimately the ring gear 95 and sun wheel 93 are rotating at the same speed and torque is transmitted through the planet gears 92 which are now locked with respect to rotation about the spindles 91.

Claims (11)

1. A drive transmission device having a continuously variable transmission ratio, within predetermined limits, comprising an input shaft driving an input or drive pinion, an output shaft fixed for rotation with an output or driven pinion, planet gears meshing with both the said drive pinion and the said driven pinion, a planet carrier on which the planet gears are freely rotatably mounted being itself mounted freely rotatably with respect to the said input and/or output shafts, and means for controlling or limiting the relative rotation of the said planet carrier and the output or driven shaft between a condition in which the planet carrier is free to rotate with respect to the output driven shaft and no torque is transmitted thereto from the input drive shaft, and a condition in which the planet carrier is fixed in relation to the output driven shaft and this latter is thus constrained to rotate at a speed determined by the speed of rotation of the input drive shaft.

2. A drive transmission device as claimed in Claim 1, in which the planet gears are bevel pinions.

3. A drive transmission device as claimed in Claim 1, in which the planet gears are helical gear wheels and the planet carrier is the idler plate of an epicyclic gear mechanism.

4. A drive transmission device as claimed in any of Claims 1 to 3, in which the said means for limiting or controlling the relative rotation between the planet carrier and the output or driven shaft comprises a fluid transmission torque converter.

5. A drive transmission device as claimed in any of Claims 1 to 3, in which the said means for limiting or controlling the relative rotation between the planet carrier and the output or driven shaft is a friction restraining means such as a brake band, pad or disc.

6. A drive transmission device as claimed in any preceding Claim, in which there are provided means whereby the output drive from the said output or driven shaft is taken, at least in some operating conditions of the drive transmission device, via an epicyclic gear mechanism adapted for reversing the direction of rotation of the drive transmitted thereby such that the input and output shafts of the drive transmission device both rotate in the same direction.

7. Drive transmission apparatus including at least one input or drive shaft to which, in use of the apparatus, drive is applied for transmission to at least one output or driven shaft of the apparatus, in which the drive train of the apparatus between the input and output shafts includes a differential gear mechanism incorporating one or a plurality of planet gears mounted for rotation about its or their respective axes of rotation on a planet carrier which is itself rotatable about an axis aligned with one of the input and/or output shafts, and rotational restraint means for selectively limiting the relative rotation of the planet carrier with respect to the or one of the input shaft or shafts and/or the or one of the output shaft or shafts.

8. Drive transmission apparatus as claimed in Claim 7 in which the rotational restraint is a brake band.

9. Drive transmission apparatus as claimed in Claim 7 in which the rotational restraint is a magnetic coupling.

10. Drive transmission apparatus as claimed in Claim 7 in which the rotational restraint is a fluid transmission.

11. A drive transmission device substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.