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Patent Searching and Data


Title:
A TRANSMISSION SYSTEM
Document Type and Number:
WIPO Patent Application WO/2019/012078
Kind Code:
A1
Abstract:
A planetary roller transmission comprises at least two ring pairs, a first ring pair and a second ring pair, in which each ring pair is aligned to a common axis, each ring pair comprising an outer ring and an inner ring radially spaced apart to accommodate a plurality of rollers, the plurality of rollers being arranged in a pitch circle between said ring pairs to frictionally engage both the outer and the inner rings and connect the ring pairs to each other, the rollers comprising a first portion disposed between the first ring pair and a second portion disposed between the second ring pair, the first and second roller portions having substantially different diameters, wherein either the inner or outer ring of the first ring pair is fixed, the other of the first or second rings of the first ring pair being free to rotate, so that rotation of the freely rotatable ring causes the rollers to rotate about the fixed ring and therefore transfer drive to the outer and inner ring of the second ring pair.

Inventors:
BIKMUKHAMETOV, Alexy (Lakhtinsky prospect 129 lit B, Saint-Petersburg, 19722, RU)
Application Number:
EP2018/069028
Publication Date:
January 17, 2019
Filing Date:
July 12, 2018
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
ARRIVAL LIMITED (Unit 2, Southam Road Banbury, Oxfordshire OX16 2DJ, OX16 2DJ, GB)
International Classes:
F16H3/091; F16H15/56
Domestic Patent References:
WO2005071287A12005-08-04
Foreign References:
JPS5364881U1978-05-31
EP2586694A12013-05-01
EP0713284A11996-05-22
Other References:
None
Attorney, Agent or Firm:
BROWN, Alexander (Venner Shipley LLP, 200 Aldersgate, London EC1A 4HD, EC1A 4HD, GB)
Download PDF:
Claims:
Claims

1. A planetary transmission system comprising at least two ring pairs, a first ring pair and a second ring pair, in which each ring pair is aligned to a common axis, each

5 ring pair comprising an outer ring and an inner ring radially spaced apart to

accommodate a plurality of rollers, the plurality of rollers being arranged in a pitch circle between, and in frictional engagement with, the inner and outer rings of said ring pairs to connect the ring pairs to each other, the rollers comprising a first portion disposed between the first ring pair and a second portion disposed between the secondo ring pair, the first and second roller portions having substantially different diameters, wherein either the inner or outer ring of the first ring pair is fixed, the other of the inner or outer rings of the first ring pair being free to rotate, so that rotation of the freely rotatable ring causes the rollers to rotate about the fixed ring and therefore transfer drive to the outer and inner rings of the second ring pair.

5

2. A planetary transmission system according to claim l, further comprising any number of additional ring pairs aligned to the common axis, the plurality of rollers comprising a corresponding number of additional roller portions to extend between inner and outer rings of the additional ring pairs and connect the ring pairs together soo that rotation of the freely rotatable ring of the first ring pair transfers drive

simultaneously to each of the additional ring pairs.

3. A planetary transmission system according to claim 1 or claim 2, further comprising a layshaft that extends along the common axis within the ring pairs, the5 layshaft being configured to selectively engage the inner ring of the second ring pair and, when dependent on claim 2, the inner rings of the additional ring pairs.

4. A planetary transmission system according to claim 3, wherein the inner ring of the second ring pair and, when dependent on claim 2, additional ring pairs, is provided0 with a serrated inner surface against which the layshaft is selectively engageable.

5. A planetary transmission system according to claim 4, wherein the layshaft comprises a pawl which can be selectively moved into an engaged position in which the pawl engages the serrated inner surface of the inner ring of the second ring pair.

5

6. A planetary transmission system according to claim 5, wherein the layshaft comprises a number of additional pawls corresponding to the number of additional ring pairs, each of the additional pawls being associated with one of the ring pairs and being selectively moveable into an engaged position in which the pawl engages the serrated inner surface of the corresponding inner ring.

7. A planetary transmission system according to any of claims 3 to 6 wherein the outer ring of the first ring pair is fixed and forms part of a transmission housing. 8. A planetary transmission system according to claim 7 wherein the layshaft is rotatably mounted to the transmission housing.

9. A planetary transmission system according to any preceding claim wherein the plurality of rollers is held in a roller cage to maintain the separation of said rollers.

10. A planetary transmission system according to any of claims 3 to 9, wherein the layshaft and/or the inner ring or the outer ring of the first ring pair is provided with a mechanical couple to transfer drive to a further component.

11. A planetary transmission system according to claim any preceding claim, wherein the rollers are provided with teeth which mesh with serrated surfaces of the first pair of rings and the driven rings respectively.

Description:
A Transmission System

Conventional transmission systems use toothed gears to transfer drive between an input and output shaft. The gear ratio is set by the number of teeth of the geared components, allowing the design of the transmission to be adapted to either step up or step down an output rotational velocity and a torque with respect to an input.

Geared transmissions are known to suffer efficiency loses as a result of the meshing action of the teeth. For example, as one tooth slide across another, it generates noise, loses energy to friction and, depending on wear and tolerances, may suffer from play between the teeth which can cause backlash.

In an attempt to mitigate some of these drawbacks, gears are lubricated to ease the sliding action as one tooth engages another. However, this can only reduce loses to a limited extent and does not provide any remedy for backlash. Furthermore, lubricant has a finite life meaning that a maintenance schedule is required.

One type of transmission system is a planetary transmission system. Planetary transmissions comprise an input and an output shaft with a common axis which affords particular packaging advantages. Planetary transmissions usually require a sun gear and an annular gear with planetary gears meshed in a pitch circle between the sun gear and annular gear. Drive is transferred between the sun and annular gear via the planetary gears. This arrangement is quite inefficient due to the number of meshed teeth employed at any one time to transfer drive.

Therefore there is a requirement for an improved transmission system, and more particularly, an improved planetary transmission system.

According to the invention there is provided a planetary roller transmission

comprising: at least two ring pairs, a first ring pair and a second ring pair, in which each ring pair is aligned to a common axis, each ring pair comprising an outer ring and an inner ring radially spaced apart to accommodate a plurality of rollers, the plurality of rollers being arranged in a pitch circle between said ring pairs to frictionally engage both the outer and the inner rings and connect the ring pairs to each other, the rollers comprising a first portion disposed between the first ring pair and a second portion disposed between the second ring pair, the first and second roller portions having substantially different diameters, wherein either the inner or outer ring of the first ring pair is fixed, the other of the first or second rings of the first ring pair being free to rotate, so that rotation of the freely rotatable ring causes the rollers to rotate about the fixed ring and therefore transfer drive to the outer and inner ring of the second ring pair.

The transmission system may further comprise any number of additional ring pairs aligned to the common axis, the plurality of rollers comprising a corresponding number of additional roller portions to extend between inner and outer rings of the additional ring pairs and connect the ring pairs together so that rotation of the freely rotatable ring of the first ring pair transfers drive simultaneously to each of the additional ring pairs.

The transmission may further comprise a layshaft that extends along the common axis within the ring pairs, the layshaft being configured to selectively engage the inner ring of the second ring pair and, when dependent on claim 2, the inner rings of the additional ring pairs.

The inner ring of the second ring pair and, optionally, any additional ring pairs, may be provided with a serrated inner surface against which the layshaft is selectively engageable.

The layshaft may comprise a pawl which can be selectively moved into an engaged position in which the pawl engages the serrated inner surface of the inner ring of the second ring pair.

The layshaft may comprise a number of additional pawls corresponding to the number of additional ring pairs, each of the additional pawls being associated with one of the ring pairs and being selectively moveable into an engaged position in which the pawl engages the serrated inner surface of the corresponding inner ring.

The outer ring of the first ring pair may be fixed and form part of a transmission housing. The layshaft may be rotatably mounted to the transmission housing. The plurality of rollers may be held in a roller cage to maintain the separation of said rollers.

The layshaft and/or the inner ring or the outer ring of the first ring pair may be provided with a mechanical couple to transfer drive to a further component.

The gear ratio of the planetary roller transmission system may be given by:

= -.£ (0.5 -— )

R b r 2 J wherein R a is the radius of the ring of the first ring pair that is rotated, R a being measured from the common axis to the surface of said ring in contact with the plurality of rollers; and R b is the radius of the ring of the second ring pair, or when dependent on claim 2, an additional ring pair for which the gear ratio is to be calculated, R b being measured from the common axis to the surface of said ring in contact with the plurality of rollers.

The rollers may be provided with teeth which mesh with serrated surfaces of the first pair of rings and the driven rings respectively.

Embodiments of the present invention will now be described with reference to the accompanying drawings in which:

Figure l shows a transmission system in section taken along its axis;

Figure 2 shows another transmission system in section taken along its axis;

Figure 3 shows another transmission system in section taken along its axis; and Figure 4 shows another transmission system end on to its axis.

An example of a planetary transmission system 1 is shown in Fig. 1. The transmission system 1 comprises two pairs of rings. A first pair of rings 2, which comprise an outer ring 3 and an inner ring 4, are arranged coaxially and have an inner surface 5 and an outer surface 6 respectively which are spaced apart to accommodate a set of rollers 7. The rollers 7 are spaced evenly about a pitch circle between the outer and inner rings 3, 4 and are tightly pressed thereto so that rotation of one of the outer or the inner ring 3, 4 causes the rollers 7 to rotate about the other of the outer or inner rings 3, 4 which are held stationary. For example, the outer ring 3 may be held stationary and the inner ring 4 rotatable, so that when the inner ring 4 is rotated its rotation drives the rollers 7 about the inner surface 5 of the outer ring 3.

The rollers 7 are each provided with a stepped portion 8 having a reduced diameter which extends along the roller's axis from between the first pair of rings 2 and into engagement with a second pair of rings 9, which are herein referred to as the driven rings. The driven rings 9 comprise an outer driven ring 10 and an inner driven ring 11 which are coaxially aligned and spaced apart to accommodate the stepped portion 8 of the rollers 7. The stepped portion 8 of the rollers 7 are pressed tightly between the outer and inner driven rings 11, 10 so that, as the rollers 7 rotate about the fixed outer 3 or fixed inner ring 4 of the first set of rings 2, the rotation of the rollers 7 drives the inner and outer driven rings 10, 11, rotating them about a common axis A-A.

In particular, if the outer ring 3 of the first set of rings 2 is fixed, rotation of the inner ring 4 drives the rollers 7 about the inner surface 5 of the outer ring 3 which in turn rotate both the inner and outer rings 10, 11 of the driven rings 9 in the same direction to each other and to the inner ring 4 of the first pair of rings 2. The speed of rotation of the driven rings 9 will depend on the relative diameters of the inner and outer ring of each of the pairs of rings 2, 9 as will be explained below. But in all cases, the outer and inner rings 11, 10 of the driven ring pair 9 will rotate more slowly than the inner ring 4 of the first pair of rings 2 due to the reduced diameter of the stepped portion 8 of the rollers 7.

It shall be appreciated that in another unillustrated example the stepped portion 8 may have an increased diameter in order to rotate the inner and outer rings 10, 11 of the driven ring pair 9 more quickly than the inner ring 4 of the first pair of rings 2. Again, if the outer ring 3 of the first set of rings 2 is fixed, rotation of the inner ring 4 drives the rollers 7 about the inner surface 5 of the outer ring 3 which in turn rotates both the inner and outer rings 10, 11 of the driven rings 9 in the same direction to each other and to the inner ring 4 of the first pair of rings 2.

In the example given above in which the inner ring 4 of the first pair of rings 2 is rotated to transfer drive to the driven pair of rings 9, the output rotational velocity of the inner ring 10 of the driven rings 9, for example, can be given by a multiple of the gear ratio k and the input velocity. The gear ratio k can also be used to determine output torque in the same way and is given by: «2 r

k = K 3 ( - 0 - 5 ~ r 2

Where:

R 2 is the radius of the outer surface 6 of the inner ring 4 of the first pair of rings 2; ff 3 is the radius of an outer surface 12 of the inner ring 10 of the driven pair of rings 9; r x is the radius of the stepped portion 8 of the rollers accommodated between the driven rings 9; and

r 2 is the radius of the rollers 7 accommodated between the first pair of rings 2. The general rule for deriving the gear ratio between any two of the rings from the first pair to the second pair can be given by the expression:

R a

k =—(0.5 - -)

Where R a is the radius of the surface in contact with the rollers of the ring of the first pair of rings 2 that is rotated; and R b is the radius of the surface in contact with the rollers of the ring of the driven pair of rings 9 for which the rotational velocity or torque transfer is to be calculated.

Another planetary transmission 1 is shown in Fig. 2 in which like features retain the same reference numbers. Two further ratios are provided. To achieve this, the rollers comprise a further stepped portion 13 which will herein be referred to as a second stepped portion 13, the above mentioned stepped portion 8 being referred to as a first stepped portion 8. The second stepped portion 13 extends from the first stepped portion 8 along the roller's axes into contact with a second pair of driven rings 14. The second stepped portion 13 has a diameter less than the first stepped portion 8 to offer an even lower gear ratio. Though it shall be appreciated that the diameter of the second step portion 13 may be greater than the diameter of the first stepped portion, or the radius of the rollers 7 accommodated between the first pair of rings 2, in order to provide an increased gear ratio.

In order to add further gear ratios, any number of additional stepped portions may be provided. Specifically, additional stepped portions may be added that extend along the roller's axes into contact with a corresponding number of additional pairs of driven rings. An example is shown in Fig.3 which shows a total of three pairs of driven rings. With each additional pair of driven rings two additional ratios are provided; the ratio provided by the outer driven ring and the ratio provided by the inner driven ring, giving the example transmission system of Fig.3 a theoretical total of 6 ratios. However, in the example of Fig. 3 only the inner rings of the additional pairs of driven rings are configured to transfer drive as will be explained below, which limits the illustrated transmission system to three ratios. In the examples of Figs. 2 and 3, the inner ring 4 of the first pair of rings 2 is rotated to transfer drive to the driven rings 9, 14, 15 whilst the outer ring 3 of the first pair of rings 2 is fixed. This causes the rollers 7 to travel about the inner surface 5 of the outer ring 3 and therefore simultaneously drive all of the driven ring pairs 9, 14, 15. Drive can be transferred from any one of the inner or outer rings of the driven ring pairs 9, 14, 15, but in the example described in connection with Fig. 3, drive is transferred from the inner rings 10, 16, 17 to a layshaft 18 as will be explained below. Although the outer rings of the additional ring pairs 9, 14, 15 are not configured to transfer drive in this example, they are still required in order to clamp the rollers 7 tightly against their corresponding inner ring 10, 16, 17 and therefore hold the rollers 7 in frictional engagement with the therewith.

The layshaft 18 is aligned to the common axis A-A of the driven ring pairs 9, 14, 15 and is configured to selectively engage the inner surface of any one of the inner driven rings 10, 16, 17 at any one time. This can be achieved by any conventional means. In the illustrated example, serrated inner surfaces are provided on the inner driven rings 10, 16, 17 which engage corresponding pawls 19 on the layshaft. Each pawl 19 is aligned with a corresponding inner ring 10, 16, 17 and, when engaged with said inner ring, transfers drive from the selected inner ring 10, 16, 17 to the layshaft 18. The pawls 19 are selectively activated depending on the gear ratio desired.

For example, the gear ratio delivered by the inner ring 16 of the second pair of driven rings 14 will be a reduction over the gear ratio of the inner ring 10 of the first pair of driven rings 9. To change from the higher ratio to the lower ratio and deliver an increased torque output, the pawl 19 engaging the inner ring 10 of the first pair of driven rings 9 is disengaged and the pawl 19 corresponding to the inner ring 16 of the second pair of driven rings 14 is engaged. Still referring specifically to the example of Fig. 3, the transmission system 1 may further comprise a housing 20 in which the driven rings 9, 14, 15 and first pair of rings 2 are enclosed. In this example, the outer ring 3 of the first ring pair 2 is integral with the housing 20, that is to say, the housing 20 comprises a cylindrical inner surface 5 which serves as the inner surface 5 of the outer ring 3 of the first pair of rings 2. The inner ring 4 of the first pair of rings 2 is rotatable so that rotation of the inner ring 4 relative to the outer ring 3 causes rotation of the rollers 7 as described above. The housing 20 comprises an end wall portion 21 in which the layshaft 18 may be mounted, a portion of the layshaft 18 extends externally from the end wall portion 21 and can be provided with the necessary mechanical coupling to allow connection to a further driveline component, such as a key way or spline. The end wall portion 21 illustrated is detatchable from the housing 20 to allow the transmission system 1 to be assembled and may be held to the remainder of the housing 20 by bolt, screw or other suitable faster.

The inner ring 4 of the first pair of rings 2 may be connected to an input shaft (not shown) that extends along the common axis A-A from out of the housing opposite to the end wall 21. A facing plate (not shown) may be added to enclose the transmission system 1 within the housing 20 and protect it from dirt. In this example, the input shaft is rotated to transfer drive to the layshaft via the first pair of rings 2 and the driven rings 9, 14, 15 as described above. The input shaft may be connected to the inner ring 4 of the first ring pair 2 by a spline, key way or similar mechanical coupling known to those skilled in the art.

In any of the above examples, the transmission system 1 may be further provided with a roller cage 21 to maintain separation of the rollers 7 as the rollers 7 travel around the respective surfaces of the rings to which they are engaged. For example, in Fig. 4, a modification of the example of Fig. 1 is shown end on to the common axis A-A comprising a roller cage 21. The roller cage 21 maintains separation of the rollers 7 as travel around the inner and outer rings of the ring pairs 2, 9.

In any of the above examples, the rollers 7 can be lightened by removing a central section of each of the rollers to form hollow tubes. It shall be appreciated that an advantage of the above examples is that no lubrication is required and, in fact, is undesirable as the rollers must be frictionally engaged with the ring pairs. This reduces the maintenance schedule of the transmission system compared to conventionally geared transmission systems which require, from time to time, the lubricant to be changed.

In other example planetary transmissions, the rollers 7 of any of the above described examples may be provided with gear teeth, the corresponding surfaces of the rings being serrated to engage the teeth. Therefore drive is transferred by meshing of the teeth and the serrated inner surfaces of the rings.

Although these example transmissions lose the advantage of reduced frictional loses afforded by smooth rollers, as described above, it shall be appreciated that the present examples maintain a key advantage over conventional planetary transmissions in that they do away with gear carriers. Specifically, a conventional planetary gearbox comprises a sun gear; an annular gear; and a gear carrier provided with stub axles on which planetary gears, meshed in a pitch circle between the sun gear and annular gear, are mounted. In operation, it is normally this carrier which is rotated to transfer drive to the sun gear. As the carrier of the present examples is omitted, drive is transferred directly between a ring 3, 4 of the first pair of rings 2 and one of the driven rings.

Therefore no carrier is required and frictional loss associated with the planetary gears and the stub axles is eliminated.

An advantage of providing the rollers with teeth is that greater torque loads can be sustained than by simple frictional engagement of the smooth roller 7 examples described above.

In order to address various issues and advance the art, the entirety of this disclosure shows by way of illustration various embodiments in which the claimed invention(s) may be practiced and provide for a superior electro -hydraulic power steering system. The advantages and features of the disclosure are of a representative sample of embodiments only, and are not exhaustive and/or exclusive. They are presented only to assist in understanding and teach the claimed features. It is to be understood that advantages, embodiments, examples, functions, features, structures, and/or other aspects of the disclosure are not to be considered limitations on the disclosure as defined by the claims or limitations on equivalents to the claims, and that other embodiments may be utilised and modifications may be made without departing from the scope and/or spirit of the disclosure. Various embodiments may suitably comprise, consist of, or consist essentially of, various combinations of the disclosed elements, components, features, parts, steps, means, etc. In addition, the disclosure includes other inventions not presently claimed, but which may be claimed in future.