Abstract:
A rotary device comprising two elements ( 12, 20/22 ) supported for rotation about an axis ( 11 ) and movable relative to one another along said axis, and diaphragm spring means ( 33 ) urging said elements axially relative to one another, said diaphragm spring means having radially inner and outer portions connected respectively to said elements and arranged such that said elements are constrained to movement in opposite directions by the same or substantially the same distance as one another about an axially fixed position.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a rotary device, which preferably is a pulley for use with an endless flexible drive element such as a belt, and whose effective diameter is variable in order to achieve a variable transmission ratio between the pulley and another pulley or pulleys with which the flexible drive element cooperates. 
     The invention has been devised in relation to such a pulley which comprises a pair of sheave members rotatable about an axis and supported for movement relative to one another in the direction along said axis, the sheave members having generally frusto-conical driving surfaces facing one another to define a generally V-section annular groove therebetween; and a drive ring disposed between the sheave members and having an external circumferential surface engagable by the drive belt and side surfaces engaging said facing generally frusto-conical driving surfaces of the sheave members, the drive ring being constrained between the sheave members and being able to assume an eccentric position relative thereto when permitted by the dimensions of the groove defined between the sheave members in accordance with the relative axial position thereof. Such a pulley will hereafter be referred to as a pulley of the kind specified. 
     In a pulley of the kind specified, as the distance between the driving surfaces of the sheave members increases (i.e. the V-section groove there between becomes wider) the drive ring is able to assume an increasingly eccentric position relative to tie sheave members and is caused to do so by the tension of the belt entrained around it. It may be the tension in the belt which causes the drive ring to assume an eccentric position and increase the distance between the sheave members. As the speed at which the drive ring is driven by the sheave members is dependent on the effective diameter at which they are engaged by the drive ring, the effective diameter of the pulley is decreased. 
     A pulley of the kind specified may be required to be used in the auxiliary drive system of an internal combustion engine for a motor vehicle. It is usual to arrange for the auxiliaries, which may comprise one or more of the following, namely an alternator, a water pump, a cooling fan, a power steering pump, an air conditioning pump, and so on, to be driven from the engine crank shaft by a belt. If a pulley of the kind specified is provided on the engine crank shaft, a variable transmission ratio may be provided between the crank shaft and the auxiliaries, so that the latter can be driven at a reasonably high speed when the engine is running slowly and yet not be over-speeded when the engine is being operated at its maximum speed. A means for maintaining the required tension in the drive belt or for causing a speed-dependent increase in belt tension, is, of course, additionally required when a pulley of the kind specified is thus used. 
     When a pulley of the kind specified is in use, it is a requirement that the drive ring should remain in a constant or substantially constant axial position, to maintain its alignment with the other pulley or pulleys with which the drive belt cooperates. It is the object of the present invention to provide a pulley of the kind specified with a convenient construction which enables this requirement to be met. In fulfilling this object, however, it will be appreciated as pointed out hereafter that the present invention is applicable to devices other than a pulley of the kind specified. 
     BRIEF SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, we provide a rotary device comprising two elements supported for rotation about an axis and movable relative to one another along said axis, and diaphragm spring means urging said elements axially relative to one another, said diaphragm spring means having radially inner and outer portions connected respectively to said elements and being arranged so that said relative movement between said elements comprises movement thereof in opposite directions by the same or substantially the same distance as one another. 
     According to another aspect of the invention, we provide a rotary device comprising two elements supported for rotation about an axis and movable relative to one another along said axis, and diaphragm spring means urging said elements axially relative to one another, said diaphragm spring, means having a torque transmitting connection with each of said elements whereby torque can be transmitted therebetween. 
     Preferably, both aspects of the invention are provided together, and further preferably the diaphragm spring means provides for torque transmission between said axially movable elements and a driving component such as a shaft element on which they are supported. 
     The diaphragm spring means preferably comprises a diaphragm spring element having an annular portion and a plurality of fingers extending radially from the annular portion and circumferentially spaced thereabout. Preferably the fingers extend radially inwardly from the annular portion of the spring element, and are connected at or adjacent their free ends to one of the two axially movable elements of the device, whilst the other of the axially movable elements of the device is connected at or adjacent the outer periphery of the annular portion of the spring element. 
     To ensure that the two elements of the device undergo their relative axial movement about a reference position which is axially stationary or substantially stationary, the spring element of the device requires to be supported against axial movement about a part thereof which, in use, has an unchanged axial position when the inner and outer parts of the spring element move relative to one another. 
     Preferably the rotary device is a pulley, and the two elements comprise sheave members with generally frusto-conical surfaces facing one another to define a generally V-section annular groove therebetween. 
     The pulley may be one which cooperates directly with an endless flexible drive element whose cross-sectional shape includes portions which engage the generally frusto-conical surfaces of the sheave members directly, the effective diameter of tie pulley depending on the axial distance between the sheave members so that the drive element engages the sheave members at a greater or lesser radius depending on the axial position thereof. 
     Preferably, however, the pulley is a pulley of the kind specified, with a drive ring disposed between the sheave members and which is engaged by the drive element. 
     A rotary device, such as a pulley, according to the first aspect of the invention has the advantage that the spring means constituted by a diaphragm spring element serves the two purposes of urging the axially movable elements towards one another and controlling their relative movement so that they move by the same distance as one another in opposite directions. It is not necessary to provide, in addition to the spring means, a separate mechanism for the latter purpose. 
     If the spring element also provides for torque transmission between the sheave members of the pulley and a driving component, yet a further relative simplification in construction and manufacture can be achieved. 
     In the case where the diaphragm spring element does not provide for torque transmission between the sheave members of the pulley and a driving component such as a shaft element on which they are supported, there is required to be provided an alternative torque transmission means for such purpose. Such an alternative torque transmitting means may be arranged to provide, in the normal direction of torque transmission in use, an axial force which assists the diaphragm spring means in urging said elements axially towards one another. 
     Such an alternative torque transmission means may comprise cam and follower means associated with the shaft element or other driving component and with one of the axially movable elements. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described by way of example with reference to the accompanying drawings, of which: 
     FIG. 1 is a section through a pulley according to the invention, in a first operative position; 
     FIG. 2 is a section through the pulley of FIG. 1 in a second operative position; 
     FIG. 3 illustrates the diaphragm spring element of the pulley, in different operative positions; 
     FIG. 4 shows diagrammatically how a pulley according to the invention may be incorporated in an auxiliary drive system of an internal combustion engine for a motor vehicle; 
     FIG. 5 is a section through a further embodiment of pulley according to the invention in a first operative position; 
     FIG. 6 is a section through the pulley of FIG. 5 in a second operative position. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring firstly to FIGS. 1 and 2 of the drawings, the illustrated pulley comprises a shaft  10  whose rotational axis is indicated at  11 . All references to “radially” and “axially” are with reference to this axis  11 . A first sheave element indicated generally at  12  comprises a portion  13  which affords a frusto-conical driving, surface  14 , and a tubular portion  15  extending from the radially innermost part of the portion  13 , closely surrounding the shaft  10  and being slidable axially thereon with interposed bearing bushes  16 . At the end of the tubular portion  15  remote from that at which the portion  13  extends there is a radially outwardly extending portion  17  followed by a further tubular portion  18  which defines an annular gap  19  between it and the portion  15 . 
     A second sheave member comprises a tubular portion  20  which is slidable axially on the outside of the portion  15  of the first sheave member, with interposed bearing bushes  21 , and a portion  22  extending outwardly from the portion  20  and affording a frusto-conical driving surface  23  facing the driving surface  14  of the first sheave member 
     Between the driving surfaces  14 ,  23  of tie two sheave members there is disposed a drive ring  24  which is somewhat wedge-shaped in cross-sectional shape having inclined side surfaces  25 ,  26  for cooperation respectively with the driving surfaces  14 ,  23  of the sheave members. The drive ring further comprises a peripheral surface  27  whose shape is adapted for cooperation with a drive belt of so-called poly-vee configuration, having a ridged surface on its face which cooperates with the drive ring. 
     At the end of tie shaft  10  adjacent the portion  17  of the first sheave member there is fixed a carrier member which is indicated generally at  28  and which comprises an annular portion  29  extending radially outwardly from the shaft  10  followed by a tubular portion  30 , a further radially outwardly extending annular portion  31 , and a number of circumferentially spaced axially extending inclined fingers  32 . 
     A diaphragm spring element comprises an annular portion  33  from the radially innermost periphery of which extend a plurality of circumferentially spaced fingers  34 . The fingers  32  of the carrier member  28  extend through the gaps between the fingers  34 , and the diaphragm spring element is held captive to the carrier member  28  by a spring ring  35  engaging annular groove portions provided within the fingers  32  adjacent the free ends thereof. The radially innermost free ends of the fingers  34  engage the end of the portion  18  of the first sheave element  12 , whilst the outer periphery of the annular portion  33  of the diaphragm spring element abuts an abutment ring  36  provided within an outward extension  37  of the portion  22  of the second sheave element. The diaphragm spring element has a number of circumferentially spaced outwardly extending projections at its outer periphery, engaging recesses in the extension  37  of the sheave member for torque transmission between the sheave member and the diaphragm spring. The innermost ends of the fingers  34  of the diaphragm spring engage recesses in the end of the portion  18  for torque transmission with this and thus with the sheave member  12 , and the engagement of the diaphragm spring with the portion  32  provides for torque transmission between the spring and the shaft  10 . 
     The diaphragm spring, in addition to providing for torque transmission between the two sheave members and the shaft  10 , also biases the sheave members axially relative to one another so that the driving surfaces of the sheave member are urged towards one another. The V-section groove defined between the sheave members always attempts to reach its narrowest value as shown in FIG. 1 in which the drive ring runs concentrically with the sheaves. If, however, the tension in the belt engaging the drive ring is such that an axial component of force is exerted between the sheaves exceeding the force exerted by the spring urging the sheaves together, the sheave members move apart and the drive ring can run eccentrically, as shown in FIG.  2 . The drive ring runs stably in such eccentric position, because of the tension in the belt entrained around it. 
     FIG. 3 of the drawings shows diagrammatically the configuration of the diaphragm spring of the pulley in various conditions. FIG. 3A shows the spring in its free state, in which the fingers  34  are each straight and in line with the annular portion  33 . As installed, as shown in FIG. 1 of the drawings, the spring is of the configuration shown in FIG. 3B, in which the annular portion  33  is of slightly less dished configuration than in the free state of the spring while the fingers are each curved, under axial load. When the pulley is in the condition shown in FIG. 2, the spring is in the condition shown in FIG. 3C, in which the annular portion  33  of the spring is of a dished configuration in the opposite sense to that in its free state, whilst the fingers  34  remain curved since they are still under load. When the annular portion of the diaphragm spring changes the sense of its dished configuration as between the conditions of FIG.  3 B and FIG. 3C, the axial force exerted between the innermost and outermost parts of the annular portion of the spring varies comparatively little, so the curvature of the fingers in FIG. 3C is substantially the same as that in FFIG.  3 B. The support of the spring by the ring  35 , as indicated by arrow  35   a  in FIG. 3, which is generally midway between the outer periphery of the annular portion  33  of the spring and the inner ends of the fingers  34  thereof, is such that the radially inner and outer extremities of the spring move equal distances in opposite directions relative to the support  35   a  of the spring. The result of this is that when the pulley changes its operative condition between that of FIG.  1  and that of FIG. 2, the drive ring  24  does not move axially relative to the shaft  10 , and remains in alignment with the other pulleys with which the belt entrained around the drive ring cooperates. 
     FIG. 4 of the drawings shows how the pulley as above described may be utilised in the auxiliary drive system of an internal combustion engine of a motor vehicle. In FIG. 4, the pulley of variable effective diameter is indicated at  50 , with a belt  51  entrained around the drive ring of the pulley. The belt is also entrained around a number of other pulleys, in a serpentine path, which other pulleys are: 
     an air pump for an exhaust gas treatment device  52   
     water pump and fan  53   
     power steering pump  54   
     air conditioning compressor  55   
     idler pulley  56   
     alternator  57 . 
     Belt tension is maintained by a tensioner pulley  58  controlled by an actuator  59 . The actuator  59  is responsive to engine speed in such a way that when engine speed is slow the tension in the belt is slightly reduced, so that the pulley  50  assumes its condition of maximum effective diameter, thereby to drive the auxiliaries relatively quickly. When engine speed increases, the belt tension is increased so that the drive ring of the pulley  50  is caused to run eccentrically, decreasing the effective diameter of the pulley as shown in FIG.  2 . Thus the auxiliaries driven by the engine are not overspeeded at high engine speeds. 
     A pulley as described above uses a diaphragm spring element for three purposes, namely torque transmission, spring biasing and centering of the sheave members. It would be possible for the diaphragm spring element to provide only the latter two functions, and to include some other mechanism or expedient, e.g. co-operating, splines or the mechanism described hereafter, for torque transmission between the sheave members and shaft of the pulley. 
     Referring now to FIGS. 5 and 6 of the drawings, these show, in operative conditions corresponding to those of FIGS. 1 and 2, a further embodiment of pulley in accordance with the invention. The majority of the components of the pulley shown in FIGS. 5 and 6 correspond in function to components previously described with reference to FIGS. 1 and 2, and accordingly these aspects of the pulley of FIGS. 5 and 6 will not hereafter be described in detail. Components corresponding, to those appearing in FIGS. 1 and 2 are identified by like reference numerals with the addition of  100 . 
     The principal components shown in FIGS. 5 and 6 are a shaft  110  and first and second sheave elements which afford driving surfaces  114 ,  123  respectively. A drive ring  124  is received between tie surfaces  114 ,  123  of the sheave elements. There is a diaphragm spring element comprising an annular portion  133  and radially inwardly extending fingers  134 , the innermost ends of which engage respective recesses in a portion  118  connected to the sheave element ( 112 ) having the surface  114 . The outer periphery of the annular portion  133  of the diaphragm spring has a number of circumferentially spaced projections engaging respective recesses in a formation  137  of the sheave element having the surface  123 . Thus the two sheave elements are connected to one another by the diaphragm spring element for torque transmission, in addition to having their surfaces  114 ,  123  urged towards one another. 
     The pulley further comprises a carrier member  128  with a portion  132  which is of annular form instead of comprising fingers as in the embodiment of FIGS. 1 and 2, and thus simply abuts the diaphragm spring element near the outermost ends of its fingers  134 . The carrier member  128  is not rotationally fast with the shaft  110  but is held captive thereon by a head  150  on the end of the shaft with an interposed thrust bearing  151 . 
     The diaphragm spring element provides for torque transmission between the sheave elements of the pulley and urges the sheave elements axially relative to one another. Torque transmission between the sheave elements and the A shaft  110  is provided by at least two circumferentially spaced pegs, one of which is shown at  152 , extending radially outwardly from the shaft and carrying respective rollers as  153  engaging in arcuate cam slots  154  in a boss part  155  of the sheave elements  112 . The orientation of the cam slot  154  is such that in the normal direction of torque transmission with the shaft the sheave element  112  is urged axially towards the other sheave element. The reaction force is carried by portion  132  of the carrier member  128 . This augments tile force exerted by the diaphragm spring element urging the sheave elements towards one another, with an increasing force as the torque increases. 
     By relieving the diaphragm spring element of the function of transmitting torque with the shaft  110  and by having the above described “servo action”, which reduces the axial force required to be exerted by the diaphragm spring alone, the size of the diaphragm spring can be reduced and durability should be improved. 
     It is to be appreciated that there are other ways of achieving the servo action effect provided by the roller  153  engaging cam slot  154 : for example a screw-threaded engagement between a sheave element and shaft or a part connected thereto could be provided. 
     The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately or in any combination of such features, be utilised for realising the invention in diverse forms thereof.