WO1994004840A1

WO1994004840A1 - Fabrication of friction elements

Info

Publication number: WO1994004840A1
Application number: PCT/GB1993/001731
Authority: WO
Inventors: Terfel Jones; Adrian Howard Watkins
Original assignee: Ferodo Caernarfon Limited
Priority date: 1992-08-22
Filing date: 1993-08-16
Publication date: 1994-03-03
Also published as: GB2269799B; GB9217906D0; GB2269799A

Abstract

An annular preform (18) for a clutch friction facing is wound from an impregnated filament (11) on a rotating face plate (17) and held and consolidated by a non-rotating tailstock pressure plate (20) through which the filament passes to the face plate. To ensure the leading end of the filament is properly attached to the rotating plate and laid down in the proper (lobed) pattern, the rotation rate is relatively slow and tailstock pressure relatively high. Thereafter, and with the filament properly anchored, the rotation rate is increased significantly to shorten the overall winding time and/or the tailstock pressure is reduced to prevent disturbance or damage to filament layers deposited on other filament layers. A sequence of rotation rates and pressures may be matched to different patterns of winding in the same preform. The pressure plate may be temperature controlled (30) to optimise filament adhesion characteristics.

Description

Fabrication of Friction Elements

This invention relates to the fabrication of a friction element by winding a filament or tape impregnated or coated with a suitable friction material into a generally disc-shaped preform suitable for curing to form the friction element.

For convenience of description herein the term "filament" is used irrespective of its structure, that is, whether it is a single filament, bundle of filaments or woven combination. Also, the term "impregnated" is used whether the filament is fully impregnated or coated or both with the friction material, and accordingly the term "impregnant" is intended to encompass a coating.

Disc-shaped friction elements, for example, annular disc-shaped elements are employed inter alia as the facings for clutches and patent specification GB-A-2242883 describes a method of, and apparatus for, winding a preform of such an element, the preform being wound by depositing filament onto a rotating headstock face plate and consolidated into the preform by pressure from a non- rotating tailstock having a cooperating pressure plate.

The apparatus disclosed therein differs from previously known preform winding apparatus by controlling instantaneously variably as a function of winding position the radial position of the impregnated filament added thereto so as to be able to wind the preform to one or more predetermined patterns rather than randomly and/or confining it within a dimensionally limited die.

SUBSTITUTE SHEET It is a feature of such apparatus that specifying the radial position with respect to the face plate at which the filament is deposited by controllable filament guide means should produce a definite winding pattern, usually having a characteristically lobed form, which provides in the cured friction element a predictable and reproducible combination of axial, circumferential and radial strengths.

Hitherto, in such winding apparatus as described and in other winding machines, in order to produce preforms at an economic unit rate it has been necessary to wind a preform on a headstock face plate rotating at a maximum angular speed consistent with satisfying the different circumstances encountered in the initial part of the winding process, when the filament is being deposited onto the face plate directly, and in the later part of the winding process, when the filament is being laid onto previously applied and consolidated filament material.

In the initial part of the winding process it is necessary both to deliver the leading end and adjacent part of the filament (conveniently called the leading end portion) to, and deposit it on, the face plate with radial positional accuracy such that it not only engages and effects attachment to the face plate with resistance to shear forces, for example, due to drawing in more filament, but also engages the rotating face plate with the correct radial pattern to define the basis for the remainder of the preform.

To this end it is necessary to ensure that the face plate is not rotating above an angular speed at which the filament of the leading end portion delivered thereto is thrown off or disturbed from its point of deposition before effective engagement is established between the impregnated filament and the surface of the face plate by axial consolidating pressure of the tailstock pressure plate.

Thus the angular speed of the face plate, and thus the time taken to wind each preform, has essentially been defined by the initial

SUBSTΠ-UTE SHEET winding conditions. The precise maximum face plate angular speed at which engagement of the leading end of the filament can be effected is dependent also upon the properties of the filament impregnant in forming a suitable attachment, upon both the "stickiness" and/or plasticity of the part-cured impregnant per se, upon the resistance to slippage or shear provided by the surface profile of the face plate and upon the level of tailstock pressure applied.

Thus the tailstock pressure applied during the winding of the preform has also largely been based upon satisfying the initial conditions. As it is the essence of producing a preform at all that the conditions necessary to establish the leading end portion attached to the face plate are satisfied, any relatively large tailstock pressure necessary to effect such engagement and attachment is unavoidable, even where it may be found to inflict damage on the structure of the filament of the leading end portion and cause similar damage in, and/or disturb pattern uniformity of, the remainder of the preform, and result in preforms and subseguently cured elements whose structures and strengths may vary unpredictably.

Thus notwithstanding any deleterious effects caused throughout the winding of the majority of the preform by such initial conditions the consequences of satisfying initial conditions on the remainder of the preform have hitherto been considered as unavoidable.

To some extent, it may be considered that the perceived need to accept a degree of non-uniformity in winding later layers of the preform because of the effects of tailstock pressure teaches tolerance of such non-uniformity in the initial layers formed from the leading end portion directly on the face plate, insofar as it results from rotating the face plate at a rate higher than optimum, if it permits a greater preform production rate.

It is an object of the present invention to provide a method of, and apparatus for, winding a filament into a generally disc-

SUBSTITUTE SHEET shaped preform suitable to be cured to form a friction element, which provides more efficient and effective winding than hitherto.

According to a first aspect of the present invention apparatus for winding a filament impregnated with friction material into a generally disc-shaped preform suitable to be cured to form a friction element, comprises a rotatable headstock including a face plate having a surface profiled to engage with filament pressed against the surface, a non-rotatable tailstock including a pressure plate, aligned coaxially in facing disposition with respect to the face plate, said pressure plate having a through- aperture extending radially by way of which said filament is fed to the face plate and consolidated on the face plate by axial tailstock pressure, a movable guide operable to move the filament radially with respect to the aperture to vary the radial point of the face plate at which the filament is deposited, guide control means responsive to the rotational position of the face plate and a predetermined winding pattern to position the guide as a function of the rotational position of the face plate to produce said wound preform, and winding control means operable to define initial deposition conditions of a first tailstock pressure and rotation of the face plate below a limiting angular speed whilst a leading end portion of the filament is fed to the face plate and caused to engage with the surface of the face plate by tailstock pressure, and thereafter operable to change at least one of said initial deposition conditions for deposition of further filament on the filament engaging the face plate.

Preferably, and subject to limitations placed by the filament, temperature and winding pattern, the winding control means is arranged to effect rotation rate change that increases the angular speed of the face plate above said limiting angular speed and/or to effect tailstock pressure change that reduces the tailstock pressure below said first tailstock pressure.

Preferably the winding control means is operable to effect changes to both the angular speed and the tailstock pressure.

SUBSTITUTE SHEET According to a second aspect of the present invention a method of winding a filament impregnated with friction material into a generally disc-shaped preform suitable to be cured to form a friction element, on a rotating face plate under tailstock consolidation pressure, comprises depositing a leading end portion of the filament directly onto the face plate under initial deposition conditions defined by a rotation rate below a first angular speed and by a first tailstock pressure and thereafter changing at least one said initial deposition conditions.

Preferably a change of rotation rate increases it above said limiting angular speed whilst a change of tailstock pressure reduces it below said first tailstock pressure.

The method defined in the two preceding paragraphs may include changing both the angular speed of the face plate and the tailstock pressure.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which:-

Figure 1 is a schematic perspective view of a part of preform winding apparatus in accordance with the present invention illustrating the principal components involved in winding of a preform on a rotating headstock face plate, including associated non-rotating tailstock pressure plate showing temperature controlled pressure means in the form of a sliding pad thereon containing heat exchange means and control means for changing the face plate angular speed and tailstock pressure,

Figure 2 is a sectional elevation through the tailstock of Figure 1 along the line II-II illustrating the form of the sliding pad and heat exchange means within it and, schematically, means for controlling the temperature at regions of the sliding pad,

Figure 3 is an end-on view of a tailstock pressure plate in accordance with the invention and corresponding to the pressure

SUBSTITUTE SHEET plate of Figures 1 and 2 except for showing heat exchange means in the form of fluid ducts arranged to receive gas or liquid,

Figure 4 is a schematic flow diagram illustrating a winding method in accordance with the present invention as performed by the apparatus of Figure 1,

Figure 5(a) is a representation of the rotation rate of the face plate as a function of time in relation to winding a first and subsequent preforms to illustrate the relationship between the steps of the flow diagram,

Figure 5(b) is a representation of tailstock pressure as a function of time on the same time scale for the winding sequence of Figure 5(a), and

Figure 6 shows similarly to Figure 5(a) representation of different face plate rotation schemes normalised to the same time scale.

Referring to Figure 1 there is shown schematically the elements of preform winding apparatus 10 necessary for an understanding of apparatus in accordance with the present invention described hereinafter. Many of the parts, and the underlying basis of the preform winding, are described in the aforementioned GB-A-2242883.

A filament impregnated with a curable friction material, in accordance with the definitions given hereinbefore and conveniently hereinafter referred to simply as a filament 11, is temporarily stored in a container or bin 12, the container comprising part of a load cell at which a length of filament required to wind a preform is defined by weight.

The container may be refilled between preforms or a plurality of containers circulated for refilling whilst winding from another is in progress.

SUBSTITUTE SHEET The machine includes a headstock shown generally at 13, mounted on shaft 14 for rotation about horizontal axis 15 by motor and gearbox 16, the headstock including a vertically disposed face plate 17 on which filament, withdrawn from the container, may be deposited in a radially oscillating manner that combines with the rotation of the face plate to give a characteristically lobed winding pattern, as shown by broken lines 18.

The face plate surface is profiled to provide engagement points for the filament that assist in retaining the filament, and the preform built up thereon, on the face plate against lateral or shear forces caused by the winding. Conveniently such profiling is provided primarily by an array of shallow recesses or dimples in the face plate into which friction material carried by the initially deposited filament is depressed by axial pressure from a tailstock 19.

The tailstock 19 is non-rotatable and has a pressure plate 20 aligned coaxially in facing disposition with respect to the face plate. It is supported for controlled movement along the common axis 15, between a forward position adjacent the face plate and a rearward position that is distanced therefrom, by tailstock ram means 21 including piston and cylinder means 22 and 23 respectively. The tailstock, when disposed in operation in its forward position, is urged by the ram means towards the face plate in order to apply pressure to filament material on the face plate 17 and effect its adherence thereto to fix the lobed pattern and to cause subsequently added filament to be consolidated into the preform wound by such filament addition. When distanced therefrom in its rearward position it permits a wound preform to be detached from the face plate and removed.

The tailstock pressure plate 20 has a radially extending through- aperture 24 by way of which filament 11 is fed to the face plate, and movable filament guide means 25, disposed between the pressure plate and the container 12, is operable to move the filament radially with respect to the aperture to vary the radial

SUBSTITUTE SHEET point at which the filament is deposited on the face plate in accordance with the desired winding pattern.

Feed rollers 26 are disposed adjacent the lip of the container 12 to grip a tail of filament weighed into the container and deliver it to a transport or feed tube 27 along which it is propelled by a stream of gas to the guide means 25 and therethrough to the pressure plate aperture 24. At least one proximity detector 28 associated with tube 27 is operable to provide signals indicative of the presence or absence of filament, in particular the approach of the leading ends and trailing towards the face plate.

The tailstock pressure plate carries radially extending consolidation rollers 29,, 29₂, 29₃ , separated from each other in a circumferential direction by small sliding pads 29' that prevent filament from lifting or becoming stuck to the rollers, by which the axial tailstock pressure is applied to the filament on the face plate, the use of rollers and their circumferential distribution serving to retain the preform and to apply consolidating pressure axially with minimal lateral forces on the filament to disturb the winding pattern.

The rollers 29, etc. are tapered to reduced radius towards the tailstock axis 15 and the axis of rotation of each roller has components both radially with respect to, and along, axis 15, being inclined towards the face plate 17 such that the surface of each roller closest to the face plate is parallel to it. The rolling radius of each roller thus increases with distance from axis 15 such that for a constant angular velocity the linear or tangential surface speed increases with distance from axis 15 in approximate correspondence with the linear speed of any preform on the face plate rotating at constant angular velocity. That is, for all radial distances from axis 15 each roller rolls over the preform surface with little or no significant dragging forces caused by speed mis-match.

In respect of filament 11 employed with such apparatus it is

SUBSTITUTE SHEET known to provide a so-called dry filament wherein the friction material impregnating the filament is a curable resin in a part- cured state in which it exhibits thermoplastic properties, at normal ambient temperatures being dry to touch and able to contact itself without flowing plastically and fusing.

Adhesion between the filament impregnant and itself and the profiled face plate may, at its simplest, be effected by working of the impregnant by way the tailstock pressure which causes it to flow into engagement and develop a tacky nature by which an adhesive bond is formed that helps hold it in position on the face plate and maintain the relative dispositions of successive layers of the preform that gives its stability for removal and handling prior to final curing. However, it will be understood that the precise impregnant conditions cannot always be guaranteed, depending upon the precise formulation of the impregnant, its manufacture conditions and indeed the ambient and machine temperature at which used and that such pressure can only be employed at moderate levels before deleterious effects on filament and pattern disturbance or dis-arrangement results.

Although such a so-called dry filament is the norm and requires to be given more desirable properties by some degree of tailstock pressure, a situation must also be considered in which it is possible for a filament impregnant to be too tacky or plastic at particular operating temperature whereby adhesion to itself and/or engagement with the face plate is impaired and making the preform susceptible to damage by the various forces exerted on it during and after winding.

Thus the combination of the face plate rotation rate and tailstock pressure required to maximise the speed at which the leading end portion of the filament can be deposited on and engage with the face plate to form the basis of a desired winding pattern may be further dependant upon the properties of the filament at the point of use and divergence of the filament properties from any of those for which the relationship between face plate rotation rate and tailstock pressure has been

SUBSTITUTESHEET optimised serving only to magnify the differences existing between the requirements of the initial and later stages of preform winding.

To mitigate the effects of filament variations the winding apparatus 10 is further distinguished from that in the aforementioned publication by the provision of temperature controlled pressure means 30 defined by the tailstock pressure plate.

Referring also to Figure 2, in accordance with a first embodiment of the temperature controlled pressure means 30, it is defined in part by the pressure plate 20 and by heat exchanging means 31. The heat exchanging means comprises a sliding or rubbing pad 32 carried by the surface of pressure plate 20, separated from the plate by a layer of thermal insulation material 33 and extending both in radial and circumferential directions at a part of the face plate spaced from the aperture 24 in the circumferential direction of rotation of the face plate and filament deposited thereon by at least a quarter of a revolution. The surface of the sliding pad is raised with respect to the surface of the pressure plate almost to the level of roller 29, etc. such that axial consolidation pressure is provided principally by the rollers but any recovery of the preform after such consolidation is acted on by the sliding pad in applying a degree of pressure that prevents the deposited filament from delaminating from the preform or face plate.

The heat exchanging means 31 also comprises one or more heat exchange elements or cartridges 34 formed in or under the sliding pad and temperature control means 35 operable to define and maintain the temperature or temperatures associated with various points of the sliding pad in said radial and circumferential directions.

A single heat exchange element may extend throughout a substantial part of the sliding pad in order to define a substantially uniform temperature over the surface pad, or a

_SUBSTITUTESHEET plurality of smaller heat exchange elements may be confine individually to one or more regions of the pad with th temperature defined for such regions and/or confined thereto b thermal barriers. Insofar as a plurality of heat exchang elements may be associated individually with separate regions of the pad, such elements may be addressed individually to provide a temperature profile which varies over the pad surface in circumferential, and possibly radial directions.

It will be appreciated that in general the establishment and maintenance of a desired temperature, and particularly different temperatures to give a temperature profile across the pad surface, is best served by the temperature control means 35 including a temperature sensor 36 associated with each heat exchange element or separate region of the sliding pad to enable the control means to maintain the temperature of such element at a desired level to influence heat flow between the heat exchange elements or elements and the sliding pad and ultimately the preform in contact therewith.

It is to be expected that such a sliding pad 32 intended to make sliding contact with the rotating preform containing a friction material will generate heat thereby and the heat exchanging means may therefore take such heat as is generated with prolonged use into account in determining and controlling the desired temperature of the sliding pad and, as a consequence of such sliding, the temperature of the surface of the preform.

Where because of the nature of the filament impregnant it is required only to raise the temperature of the sliding pad to achieve the desired properties each heat exchange element may comprise a simple heater, such as an electrical resistance heating element, whereas if it is desired to lower the temperature of the sliding pad, possibly in addition to raising the temperature, a fluid carrying heat exchange element, as indicated at 34' in Figure 3 with fluid control valve 34", is preferred.

SUBSTITUTESHEET The temperature control means shown at 35 may be a discrete arrangement linked to general or winding control means, shown at 38, of the winding machine, the latter being able to correlate any desired temperature with achieving optimum filament conditions, such as tackiness, in relation to any predetermined winding speed and tailstock pressure to define, and cause operation of the motor 16 at, a particular angular speed and to define, and cause operation of the tailstock ram to effect, a particular tailstock pressure. The temperature control means may alternatively be incorporated within such general control means of the machine and the temperature controlled with related variables such as winding rate and tailstock pressure that are separately applied to the winding control means.

In addition to providing direct or indirect control of the temperature of the temperature controlled pressure means 30, the winding control means 38 also provides speed control of the headstock motor 16 and of the positioning of, and pressure exerted by, tailstock ram means 21.

The headstock motor is part of a closed servo loop which receives signals representative of angular position of shaft 14 from sensor 16', and possibly signals representative directly of angular speed, and controls the rotational speed of the face plate in accordance with speed demand signals derived by, or fed manually to, the winding control means. The motor control servo loop may also include an acceleration control loop by which any change to a new speed demanded is effected at a controlled rate, or the winding control means 38 may implicitly include such controlled acceleration by providing a succession of demanded speeds.

The provision of motor speed and acceleration control per se in response to speed demands is considered conventional and does not require detailed further description.

The tailstock ram means 21 is also arranged such that when in its forward position it is able to exert an axial pressure towards

SUBSTITUTE SHEET the face plate that is controllable between a higher value and lower one by controlled venting of ram pressure in response to pressure demands derived by, or fed manually to, the winding control means 38.

The tailstock ram means 21 is conveniently pneumatic in operation, including a cylinder containing a double acting piston (or equivalent pair of single acting piston/cylinder arrangements) the cylinder at one side of the piston receiving compressed air whilst the cylinder at the other side is vented to displace the piston and pressure plate between forward and rearward positions defined by abutments. The source of compressed air to the appropriate cylinder part is regulated by the winding control means to satisfy the initial deposition conditions and subsequent winding conditions, maintaining pressure in opposition to displacement of the pressure plate and ram piston as the preform builds up, including venting, at a controlled rate if appropriate, of the pressured cylinder in providing the reduction in tailstock pressures.

The provision of tailstock ram displacement and axial pressure control^ per se in response to position and pressure demands respectively is considered conventional and does not require detailed further description.

The winding control means 38 also conveniently serves to provide guide control means for the filament guide means 25, the latter being positioned both as a function of a stored winding pattern and instantaneous face plate rotational position from a datum, as monitored by 16'. It may be noted that such a rotational position may involve a total or cumulative angular displacement from a datum position in excess of 360°. Most conveniently said control means comprises digital computer means responsive to both stored parameters and stored program steps with the measured parameters to perform the control means functions.

Considering operation of apparatus 10 in winding a preform from a dry filament, reference is also made to Figure 4 and Figures

SUBSTITUTE SHEET 5(a) and 5(b). Figure 4 summarises the steps of the winding method in a schematic flow diagram, the individual steps, as represented by the blocks and decision points of the flow diagram, being identified by Roman numerals and correlated with the description by incorporation of such reference numerals.

Figures 5(a) and 5(b) illustrate respectively the face plate rotation rate and tailstock pressure as a function of time in winding an initial and successive preforms, relevant functional steps of the operation being marked on the time axes by the corresponding reference numerals of Figure 4.

Initially, before any preforms have been wound and notwithstanding that the temperature of the filament to be employed is not optimum for the conditions anticipated for later in operation, a compromise is arrived at with or by the winding control means 38 for the particular filament properties that relate the face plate rotation rate, tailstock pressure and deposited filament temperature that will provide optimal deposition and engagement of the leading end portion of the filament; that is, defines initial deposition conditions that permit a rotation rate consistent with accurate and strong deposition of the filament in a particular pattern in said anticipated conditions.

The leading end portion of the filament essentially comprises that part of the preform filament considered to be primarily deposited on the face plate that is required to establish the winding pattern and necessary to give adhesion of the preform against shearing forces caused for example by its rotation or by resistance to pulling subsequent filament from the container. The length of the leading end portion may, for a particular winding pattern, be measured directly or be more indirectly defined by the time taken to deposit at a fixed angular speed of the face plate, but most conveniently it is defined in terms of the extent of total angular movement of the face plate from the deposition of the leading end of the filament. In general, to define any pattern the leading end portion is expected to be at

SUBSTITUTESHEET least that length of filament deposited in one revolution of the face plate and in this example is taken as that deposited in two revolutions, 720° rotation from a datum position defined by its (arbitrary) position at the instant the leading edge is deemed deposited.

The maximum face plate rotation rate acceptable for initial deposition of the leading end portion of the filament, that is, above which rotation rate such deposition cannot be effected adequately, may be referred to as a limiting angular speed for the face plate.

The winding control means thus defines initial deposition conditions of a first tailstock pressure and rotation of the face plate below said limiting angular speed.

After such definitions, which may be considered as part of the start of a preform winding sequence (I) , the temperature controlled pressure means 30 on the tailstock pressure plate is operated to bring the sliding pad 32 of the heat exchanging means to the desired temperature for the particular filament impregnant in order to optimise the filament's ability to be moulded into engagement with the face plate and adhere to itself (II) .

It will be appreciated that when in due course the leading end portion of the filament is first deposited on the face plate and consolidated by the tailstock pressure exerted through the rollers 29,, etc it will not at that time have been influenced by the temperature controlling effects of direct contact with the sliding pad 32, as a consequence of which it may be desirable to have the temperature of the face plate itself preconditioned by arranging for the pressure plate to spend some time in its forward position prior to operation in order to exchange heat between the sliding pad and the slowly rotating face plate or for the face plate to be heated or cooled directly before, or during, rotation (III) .

SUBSTITUTESHEET When such optional pre-heating or pre-cooling of the face plate has been effected, and typically under manual initiation, the winding control means 38 in accordance with the initial deposition conditions causes the motor 16 to rotate at a first angular speed, below said limiting angular speed, determined as optimum for causing the filament to engage with and adhere to the face plate for the properties of the filament at the controlled temperature (IV) .

The winding control means effects the provision of a length of filament for the preform by ensuring that the container or bin 12 is filled, or that a filled container is positioned for filament extraction (V) . The presence of filament in container 12 is determined by monitoring the weight of the container (VI) and assuming this is correct, the winding control means issues an instruction to rollers 26 to propel the filament along the transport, or feed, tube 27 and by way of guide means 25 and aperture 28 to the face plate (VII) .

The winding control means simultaneously issues the instructions to the tailstock ram means to displace the tailstock to its forward position (VIII) and to apply a first tailstock pressure (IX).

The finite time interval required for the tailstock to assume operation at the forward position is arranged to coincide substantially with the time taken for the leading end of the filament to pass along the transport tube to the face plate. The passage of filament along the tube is monitored in the vicinity of the feed rollers 26 by proximity detector 28 (X) and the winding control means responds to this presence to flag that the filament has indeed begun to feed (XI) . After a short delay (XII) corresponding to the time taken for the leading end of the filament to pass from the proximity detector to the face plate, the instantaneous angular position of the rotating face plate is sampled as the angular position datum for the winding operation (XIII) .

SUBSTITUTE SHEET The winding means then monitors the angular or rotational position of the face plate (XIV) to check when the pre-defined 720° from the datum has been reached and that the filament continues to be fed (loop to X) .

The leading end of filament deposited on the face plate is pressed by the rollers under said first tailstock pressure against the face plate, the filament deforming under maximum pressure exerted as it passes under each roller and impregnant is caused to engage with, and adhere to, the face plate but tending to recover somewhat in between.

After the filament has been pressed by rollers 29, 29₂, 29₃ etc. , it bears against the sliding pad 32 which applies a degree of consolidation pressure (although less than the rollers) and also defines the temperature of the filament on the face plate that forms the preform, supplying heat thereto if necessary to induce the filament properties that might be anticipated in later operation when friction between the filament and sliding pad has raised the overall operating temperature within the apparatus and for which conditions the first angular speed and first tailstock pressure have been optimised.

When the winding control means detects that said 720° of angular rotation (or two revolutions) of the face plate have occurred, it causes a change to both of the initial deposition conditions, that is, to the angular speed of the face plate and the tailstock pressure (XV) . The motor 16 is caused to increase its angular speed, changing to a second controlled value above said limiting speed that is demanded by the control means and which may be of the order of five times the first angular speed. Furthermore the acceleration of the motor between the two speeds is controlled also so that the change occurs over an interval, which may be of the order of one revolution, such that the preform, and its engagement, is not subjected to jerking by the change. Such acceleration phase therefore may be arranged to provide a slight lengthening of the time at which the filament at or near the leading end position is deposited at a relatively slow rate for

SUBSTITUTE SHEET better engagement with the face plate and a smooth transition to accommodate external speed-related forces acting on the preform and filament.

In addition to the increase in rotation rate of the face plate, and contemporaneously therewith, preferably starting simultaneously with the increase in rotation rate, the winding control means also causes the ram means 21 to reduce the tailstock pressure from that required by initial conditions. Preferably the pressure is reduced to a second controlled pressure and one that is of the order of half of the first pressure, such pressure change being effected quickly by venting the ram means and typically achieved before the face plate has achieved its second angular speed.

Whilst causing the second angular speed of the face plate and the second tailstock pressure to be established, and subsequently thereto, the winding control means monitors the presence of filament by way of proximity detector 28 (loop to X) . When the proximity detector senses that the trailing end of the filament has left the container, the winding control means, knowing that a leading end had previously been detected (XI, XVI) increases the speed of rotation of the face plate (XVIII) .

After an optional delay (XIX) , which may be introduced to ensure the face plate rotation is established at a higher speed and/or to ensure that the trailing end of filament in the transport tube at the time increase is instigated has been deposited and consolidated into the preform, the winding control means determines that the preform winding has been completed and causes the tailstock to be displaced to its rearward position (XX) followed by detachment of the preform by any convenient means to be thrown and/or roll clear of the rotating face plate of the apparatus (XXI) .

In anticipation of winding another preform, the winding control means causes the face plate rotation rate to be reduced to said first rotation rate and the filament container 12 to be

SUBSTITUTE SHEET replenished or replaced with a new one (loop to IV) , and the proceeds to repeat the above described procedure.

Operation has been described above in its simplest terms to assist understanding but makes no provisions for bringing the procedure to a halt other than manually, which may be the preferred method of operation.

Alternatively, a simple batch counting step (XXII) may be introduced after detachment of each preform to end the looping if an appropriate number of preforms have been wound.

Furthermore, if in response to checking at VI that filament is available in the container to be wound the control means detects that no filament is present, it may loop back to V to replace or refill the container before trying to continue. An attempt counter XXIII may be included to end the operation of filament is not available after a number of attempts.

Similarly, if after an instruction is given to feed filament none is detected by the proximity detector (at X) as present in the transport tube, then in the accompanying absence of leading end detection (XI) the decision at XVI is negative and the cycle loops to VII to attempt to feed filament again. If filament begins to feed, the operation continues as normal but if not, an attempt counter XXIV may be incorporated to end cycling after a number of attempts.

Insofar as the above described method of operation results in a wound preform, the increase in face plate rotation rate beyond that limiting speed dictated by the initial deposition conditions clearly permits a preform to be wound from a given length of filament in shorter time than hitherto, with an increase in overall production rate.

The reduction in tailstock pressure from that required and defined for initial deposition serves to mitigate disarrangement of the pattern of the growing preform and even damage to the

SUBSTITUTESHEET filament itself at crossover points by direct axial pressure. Such reduction in tailstock pressure may also mitigate any tendency for frictional drag on the preform by rubbing contact with the sliding pad of the temperature controlled pressure means at the higher rotation rate to disarrange the preform pattern or induce overheating of the preform, notwithstanding a desire to supply a controlled degree of heat to the preform by way of such frictional drag, and may assist in minimising or negating altogether heating resulting from friction contact with the sliding pad that contains cooling means.

The apparatus described and the method followed is comprehensive in giving control over three variables influencing the quality of the preform and speed of production rate that gives some independence from variability between the properties or behaviour of different lengths of impregnated filament used.

The method of winding and apparatus described above has assumed implicitly that the radial component of the winding which gives rise to the lobed pattern and which forms part of the definition of the leading end portion and the initial deposition conditions is maintained throughout the whole preform.

It will be appreciated that in apparatus, such as 10, having continuous control over the filament guide means 25, a winding pattern may be varied throughout the winding.

Although the preform is wound continuously and built up helically, it is conceptually convenient to consider the preform as formed by a succession of layers which may be wound with the same or different radial components. A conventional uniform lobed pattern may be conceived as a plurality of layers offset circumferentially from each other. Thus in the apparatus 10, after the leading end portion has been deposited, the radial winding pattern may be changed continuously, or more conveniently at intervals, throughout the remainder of the winding operation to give the effect of preform layers exhibiting different winding patterns. Changes between winding patterns, that is, in motion

SUBSTITUTE SHEET of the guide means, are made by the winding control means in response to a predetermined pattern and a relationship between filament disposition and the measured cumulative face plate rotation.

It will be appreciated that in accordance with the present invention, the winding control means may establish particular face plate rotation speeds and/or tailstock pressures to accommodate optimum filament deformation for particular winding patterns. For example, it may be desired to introduce one or more "layers" that have no lobes, being simple spiral layers, that are known to contribute to increased radial burst strength to a cured preform rotated at high speed. Because of the slow radial movement of the guide means and the deposition of filament in line with the direction of rotation, it is possible to wind such a layer at a higher face plate rotation rate than lobed patterns.

Accordingly, the winding control means may be adapted to respond not only to the completion of deposition of the leading end portion but also to respond to completion of each subsequent winding pattern to control the face plate rotation rate and/or the tailstock pressure.

Referring again to Figure 4, when deposition of the leading end portion has been completed and detected by the angular position of the face plate at XIV, a store within the winding control means that relates pattern changes to cumulative angular position of the face plate and the desired rotation rate/tailstock pressure is triggered by the detection (XXV) to set a new angular limit to XIV and a new angular speed/tailstock pressure to XV for when the new angle is reached. Clearly this may be repeated several times during winding of the preform.

It will be appreciated that in winding some patterns, and in view of the strong dependence of winding speed or filament properties, that it may be necessary, subsequently to depositing the leading end portion below the angular face plate limiting speed, to

SUBSTITUTESHEET decrease the rotation rate below the first rotation rate or even to increase tailstock pressure above the first pressure.

It will be appreciated that an apparatus in accordance with the present invention, or in the method of performance, changes may be made with a view to enhancing the apparatus and product made thereby or with a view to simplifying the apparatus and operation notwithstanding the possibility of compromising product quality.

For example, after the leading end portion of the filament has been deposited under said initial deposition conditions it is possible for the winding control means to change one only of the initial deposition conditions (at XV) .

The winding control means may change the tailstock pressure alone, operating with the face plate rotating at below said limiting angular speed throughout the winding operation. As indicated above, where such a first tailstock pressure has been necessary to effect engagement of the leading end portion that pressure damage to filament structure and/or winding pattern disarrangement of the preform would result from continuance of such pressure, then such change and/or disarrangement would be reduced by such reduction in tailstock pressure alone and produce a better quality preform, notwithstanding no increase in production rate.

Analogously, the winding control means may change only the rotation rate of the face plate, operating with only said first tailstock pressure throughout the winding of each preform. Where the filament properties can be provided consistently and/or particularly favourable to the winding of a preform between headstock face plate and non-rotating tailstock pressure plate, with or without the optimising of such properties by the provision of temperature controlled pressure means, it may be possible to effect suitable engagement of a leading end portion of the filament with the face plate (both strength of attachment and layout accuracy) at a relatively low first tailstock pressure that beneficially causes little damage to the filament structure

^SUBSTITUTESHEET of the leading end portion and for such tailstock pressure to be retained unaltered in winding the remainder of the preform without causing damage to the filament structure and/or disarrangement of the winding pattern by axial or drag forces. Absent such filament properties, changing of the first tailstock pressure may be omitted where possible disarrangement of the winding pattern and/or filament damage is not considered to detract from the required quality of preform to the extent of justifying apparatus complexity over a non-changeable tailstock pressure arrangement.

Notwithstanding any change of tailstock pressure, although the winding control means has been described as causing the face plate to accelerate and decelerate between first and second angular speeds at which the plate speed is maintained, it will be appreciated that provided the critical limiting angular speed of the face plate is not exceeded as the leading end portion of the filament is deposited, the first angular speed may be any one speed up to the limiting value or indeed may be a continuously varying speed as illustrated in Figure 6 by the full line relationship. Similarly, the face plate rotation rate, when increased above the limiting angular speed may not settle at a quickly attained second angular speed (assuming no intervening sequence of programmed speeds) but may continue to increase until the trailing end of the filament is detected and the preform ejected, before being reduced for engagement of the leading end of the next preform, as illustrated in Figure 6 by the broken line relationship.

The relationships shown in Figure 6 are schematic only, it being understood that for any fixed length of filament weighed to define a preform the winding time until the trailing end is detected (XVI) will vary with the different face plate rotation schemes.

It will be appreciated also that if a production run involves producing many identical parts the repetitive speed cycling of the face plate seen from Figures 5(a) or 6 may be built in to the

^SUBSTITUTESHEET winding control means 38, the only effective difference from that shown in those Figures being that deceleration is effected upon a timed instruction or a counting of face plate revolutions corresponding to the time anticipated for winding a particular length or weight of filament rather than in response to detection of the filament end of each preform wound.

In an analogous manner, in relation to repetitive operation based upon a supply of filament having unchanging properties, where first and second pressures are demanded repetitively at what are substantially fixed intervals, the winding control means 38 may cause positioning of the tailstock pressure plate and changing of tailstock pressure at timed intervals rather than in response to other conditions such as the face plate position or speed change or end of filament.

As indicated above, the leading end portion of the filament defined for any particular preform has a length that is dependant on filament properties, tailstock pressure and the face plate rotation rate so that deposition of this length is conveniently measurable in terms of the rotation undergone by the face plate from deposition of the leading end. It will be seen that such length is readily ascertained irrespective of whether the face plate is rotating at a constant speed or accelerating, but if the face plate is caused to rotate at a constant first speed at that time then such deposition may be determined by the winding control means as passage of a time interval or result from monitoring the supply of a fixed length of filament to the face plate.

As described above, the selection of first tailstock pressure and limiting angular speed of the face plate for initial deposition conditions and change to either or both is dependant upon the filament properties which may themselves be altered to the benefit of other parameters or so as to be less influential, by the temperature controlled pressure means. Clearly, if the filament has suitable properties then temperature controlled pressure means as such may be omitted altogether, the pressure

SUBSTITUTESHEET plate comprising rollers, such as 29,; 29₂ etc., arranged about the whole face of the plate and interspersed with small sliding pads 29' to maintain the preform.

If temperature control of the deposited filament of the preform is required then it may take form other than the sliding pad 32 shown in Figures 1 to 3. It may for example be incorporated with such an array of rollers as described above, heat exchanging means being incorporated into the sliding pads 29' between rollers or in some of the rollers themselves.

Temperature control means 35 may have its temperature maintained by other than a temperature sensor 36 associated with a part of large thermal capacity and inherently slow to change. Furthermore, as it is the temperature of the preform itself which is of primary interest, the temperature sensor may be of a remote, non-contact making type arranged to respond to the surface of the preform visible by way of the filament supply aperture in the tailstock plate and at the point of filament deposition.

To the extent that over a long operating period conditions remain substantially constant and heat provided by such pressure means is balanced by convected or conducted losses or in finished preforms, the heat exchanging means may be arranged to produce heat at a fixed rate without a closed loop temperature control including a sensor 36 (Figure 2) but rely upon such long term variations to effect temperature control. Similarly if heat is produced undesirably by frictional contact or the like that requires extraction at a constant rate, such temperature control may be effected simply by a constant flow of cooling fluid in heat exchange means.

The temperature controlled pressure means insofar as it can affect operation of the winding apparatus and method independently of changes in face plate rotations rate and tailstock pressure forms the subject of co-pending application No 9217908.4 (Case Ref JH/23/92) .

SUBSTITUTESHEET It will be appreciated that numerous changes may be made to the above described embodiment of ejection means, either alone or in combination, without departing from the present invention.

Other changes to the apparatus described above, and not instrumental to the invention are mentioned for completeness. For instance, the surface of the face plate may be profiled with projections rather than recesses or with a mixture of both. Also, the filament guide means 25 may be controlled as a function of the face plate rotational position other than by digital control means that effects the remainder of winding control. Such filament guide control may be effected by or with a mechanical linkage between guide position and the face plate position, such as by an eccentric or cam that defines a fixed winding pattern.

If the temperature of the face plate is to be controlled this may be achieved directly by heat exchange means associated with the face plate or indirectly, as indicted above.

The face plate may be considered to be particularly suited to heating by eddy current induction by rotating it within a magnetic field provided for the purpose. The ability to rotate the face plate at a high speed of several hundred revolutions per minute permits rapid heating.

SUBSTITUTE SHEET

Claims

1. Apparatus (10) for winding a filament (11) impregnated with friction material into a generally disc-shaped preform (18) suitable to be cured to form a friction element, comprising a rotatable headstock (13) including a face plate (17) having a surface profiled to engage with filament pressed against the surface, a non-rotatable tailstock (19) including a pressure plate (20) , aligned coaxially in facing disposition with respect to the face plate, said pressure plate having a through-aperture (24) extending radially by way of which said filament is fed to the face plate and consolidated on the face plate by axial tailstock pressure, a movable guide (25) operable to move the filament radially with respect to the aperture to vary the radial point of the face plate at which the filament is deposited, guide control means responsive to the rotational position of the face plate and a predetermined winding pattern to position the guide as a function of the rotational position of the face plate to produce said wound preform, and characterised by winding control means (38) operable to define initial deposition conditions of a first tailstock pressure (IX) and rotation of the face plate below a limiting angular speed (IV) whilst a leading end portion of the filament is fed to the face plate and caused to engage with the surface of the face plate by tailstock pressure, and thereafter (XV) operable to change at least one of said initial deposition conditions for deposition of further filament on the filament engaging the face plate.

2. Apparatus as claimed in claim 1 characterised in that the winding control means is operable to change said at least one of the initial deposition conditions after a predetermined rotation of the face plate (X-XIV) .

3. Apparatus as claimed in any claim 1 or claim 2 characterised in that the winding control means is responsive to subsequently reached, predefined angular positions of the face plate to effect further change to at

SU^BSTITUT least one of the face plate rotation rate and tailstock pressure for each predefined angular position (XXV) .

4. Apparatus as claimed in any one of claims 1 to 3 characterised in that the winding control means is operable to define initial deposition conditions in which the face plate is rotated below said limiting angular speed at a first angular speed (IV) .

5. Apparatus as claimed in any one of claims 1 to 4 characterised in that the winding control means is operable to change the rotation rate of the face plate to, and maintain it at, a second angular speed for at least part of the remainder of the winding operation (XXV, XV) .

6. Apparatus as claimed in any one of the preceding claims characterised in that the winding control means is responsive to the trailing end of the filament defining the preform (X) to maximise the rotation rate of the face plate (XVIII) and cause detachment of the preform from the face plate (XX, XXI) . v

7. Apparatus as claimed in any one of the preceding claims characterised in that the winding control means is operable to change the initial deposition conditions by reducing the tailstock pressure contemporaneously with increasing the rotation rate of the face plate (XV) .

8. Apparatus as claimed in claim 7 characterised in that the tailstock pressure is reduced to a second pressure maintained for deposition of the remainder of the filament (XXV, XV) .

9. Apparatus as claimed in any one of the preceding claims characterised by temperature controlled pressure means (30) associated with the tailstock pressure plate operable to contact, and define the temperature of, filament deposited between the face plate and the tailstock pressure plate.

SUBSTITUTESHEET

10. Apparatus as claimed in claim 9 characterised in that the temperature controlled pressure means is spaced from the point of filament deposition in the direction of rotation of the face plate.

11. Apparatus as claimed in claim 10 characterised in that the temperature controlled pressure means comprises heat exchanging means (31) carried by the tailstock pressure plate extending in radial and circumferential directions and displaced circumferentially from the point of deposition of the filament by at least one quarter of a revolution of the face plate in the direction of rotation.

12. Apparatus as claimed in claim 11 characterised in that the heat exchanging means comprises at least one sliding pad (32) having a surface raised with respect to the surface of the pressure plate and adapted to make sliding contact with a rotating preform on the face plate and enclosing between the sliding surface and the pressure plate at least one heat exchange element (34) .

13. Apparatus as claimed in any one of the preceding claims characterised in that the winding control means and said guide control means comprises digital computer means responsive to both stored parameters and stored program steps to perform the function of said control means.

14. A method of winding a filament impregnated with friction material into a generally disc-shaped preform (18) suitable to be cured to form a friction element, on a rotating face plate (17) under tailstock consolidation pressure, characterised by depositing a leading end portion of the filament directly onto of the face plate under initial deposition conditions defined by a rotation rate below a first angular speed and by a first tailstock pressure and thereafter changing at least one said initial deposition conditions.

SUBSTITUTE SHEET

15. A method as claimed in claim 14 characterised by changing at least one of the new plate rotation rate and tailstock pressure for each of subsequently reached predefined angular positions of the face plate.

16. A method as claimed in any one of claims 14 or 15 characterised by causing the face plate rotation rate to increase to a maximum when depositing a trailing end portion of the filament between the face plate and tailstock pressure plate and detaching the preform at said maximum rotation rate.

17. A method as claimed in any one of claims 14 to 16 comprising effecting any reduction in said tailstock pressure from said first pressure to a second pressure and maintaining said second tailstock pressure for depositing the remaining filament.

18. A method as claimed in any one of claims 14 to 17 comprising defining a temperature at the tailstock pressure plate to assist in engagement of the leading end portion of the filament with the face plate and transferring heat between said tailstock pressure plate and the filament deposited between the face plate and the tailstock pressure plate by conduction resulting from tailstock pressure.

19. A method as claimed in claim 18 comprising heating the filament of the preform carried by the face plate above ambient temperature by way of temperature controlled pressure means (30) carried by the tailstock pressure plate.

SUBSTITUTESHEET