Abstract:
A clutch including two rotary shafts, one of which is connected to one or more first clutch plates which cooperate with a second set of clutch plates, the clutch plates acted on by an actuating piston positioned within a two chamber hydraulic cylinder. A torque control valve comprising a cylindrical inner valve member rotatably and linearly movably received in a cylindrical opening in an outer valve member. Each valve member having elongate recesses positioned such that longitudinal movement of the inner valve member within the outer valve member will vary the degree of communication between the first and second elongate recesses connected to two hydraulic fluid sources of differing pressures. The second clutch plates are connected to one side of a spring of predetermined spring rate, which is also connected to one of the valve members, and the other side of the spring is connected to the other of the valve members and to the other rotary shaft.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims priority to International Application No. PCT/GB2004/002064 filed 13 May 2004, which claims priority to British application No. 0310969.1 filed 13 May 2003, the entire disclosure of which is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to clutches, particularly for automotive use, and is concerned with that type of clutch which may be controlled so that the torque which it transmits is at a predetermined level or alters in accordance with a predetermined pattern. The invention is particularly concerned with such clutches for use in connection with so-called manual automatic gearboxes. 
     Clutches for use with manual automotive gearboxes are inherently of torque controlled type but the torque control is effected by the user. Thus when the user releases the clutch to reconnect the engine output shaft to the gearbox after changing gear, he does so gradually so that the torque transmitted to the gearbox increases progressively to its maximum value. Gear changing is thus rendered smooth, whereas if the clutch were released suddenly gear changing would be accompanied by unacceptably jerky movement of the vehicle. 
     However, manual automotive gearboxes are gradually losing favour and being replaced by either automatic gearboxes or manual automatic gearboxes. Automatic gearboxes typically do not incorporate meshing pairs of gears, as are used in manual gearboxes, and their operation is generally inherently smooth. Manual automatic gearboxes, however, are generally similar to manual gearboxes and incorporate meshing pairs of gearwheels. When a gear change is to be effected, the clutch is automatically disengaged, e.g. hydraulically, and the gear selector fork moved, e.g. again hydraulically, and the clutch is then reengaged. As discussed above, in order to avoid unacceptable jerkiness, it is necessary for the clutch to be re-engaged progressively and in known torque controlled clutches this is effected by applying a progressively increasing hydraulic pressure to the hydraulic actuating piston associated with the clutch plates. However, progressive hydraulic pressure control valves are very expensive. A complex feedback system is commonly used in an attempt to achieve a predetermined profile of the rate of increase of the torque transmitted by the clutch but these systems suffer from a lack of sophistication which results in practice in the gear change being unacceptably jerky. 
     It is therefore the object of the invention to provide a torque-control clutch, particularly for use with a manual automatic automotive gearbox which overcomes the problems referred to above and, in particular, does not incorporate a progressive hydraulic valve and enables smooth gear changes. 
     BRIEF SUMMARY OF THE INVENTION 
     According to the present invention, a clutch includes two rotary shafts, one of which is connected to one or more first clutch plates cooperating with one or more second clutch plates, the clutch plates being acted on by an actuating piston having a portion exposed on two opposite sides to first and second chambers in a hydraulic cylinder, a torque control valve comprising a cylindrical inner valve member rotatably and linearly movably received in a cylindrical opening in an outer valve member, the inner and outer valve members affording cooperating cylindrical surfaces, in one of which an elongate first recess is formed, which communicates with one of the said chambers, and in the other of which two circumferentially spaced elongate second recesses are formed communicating with a source of pressurised hydraulic fluid and a substantially unpressurised hydraulic reservoir, respectively, the elongate recesses extending in the longitudinal direction and in the same circumferential direction in the cylindrical surface in which they are formed and being positioned such that longitudinal movement of the inner valve member within the outer valve member will vary the degree of communication between the first and second elongate recesses, the second clutch plates being connected to one side of a spring of predetermined spring rate, which is connected also to one of the valve members, the other side of the spring being. connected to the other of the valve members and to the other rotary shaft. 
     The actuating piston for the clutch plates may be of either single-acting or double-acting type. If it is of single-acting type, one of the cooperating cylindrical surfaces in the valve will have a recess communicating with that chamber in the hydraulic cylinder which will act to force the piston in the direction to press the first and second clutch plates into engagement with one another. The other of the cooperating surfaces will have two recesses, one connected to the source of pressurised hydraulic fluid and the other connected to the unpressurised hydraulic reservoir. If it is desired to cause the clutch to engage, the inner valve member is moved linearly within the outer valve member so as to cause the recess communicating with the said hydraulic chamber to move progressively into communication with the recess in the other surface communicating with the source of pressurised hydraulic fluid. As the area of communication increases, the pressure in the hydraulic chamber will progressively increase and the clutch plates will be forced smoothly into engagement with one another. If the clutch plates should “snatch”, that is to say suddenly come into hard engagement with one another, the torque transmitted by the clutch will abruptly increase substantially. This torque increase or “spike” will result in the spring yielding and since the two sides of the spring are connected to the valve members, this will result in relative rotation of the two valve members. This rotation is in the sense which will reduce the area of communication between the two said recesses and act to reduce the engagement pressure of the clutch plates and thus also the torque transmitted by the clutch. Since the spring is a mechanical component situated in the torque path, this feedback is both efficient and effectively instantaneous, whereby the torque “spike” is suppressed almost immediately after it commences. As the excessive torque reduces, the two valve members rotate in the opposite sense relative to one another and the progressive smooth engagement of the clutch plate continues, thereby ensuring a smooth gear change. When it is desired to disengage the clutch, the inner valve member is moved linearly in the opposite direction so as to bring the recess communicating with the previously pressurised hydraulic chamber into communication with the recess in the opposite surface communicating with the unpressurised hydraulic reservoir. The clutch plates then move apart and thus out of engagement, e.g. under the action of their natural resilience or the action of a return spring or the like. 
     If the actuating piston is of double-acting type, two elongate first recesses are formed in the said one cylindrical surface, which communicate with respective chambers, and three spaced elongate recesses are formed in the said other cylindrical surface, the central one of which is connected to the source of pressurised fluid and the other two of which are connected to the hydraulic reservoir. Operation of the valve to cause engagement of the clutch is essentially as described above. However, when the clutch is to be disengaged, the inner valve member is moved linearly so that the previously pressurised hydraulic chamber is connected to the unpressurised hydraulic reservoir and the previously unpressurised hydraulic chamber is connected to the source of pressurised hydraulic fluid, whereby the actuating piston is positively retracted and the clutch is thus positively disengaged as opposed to relying on resilience or a spring or the like, as in the single-acting construction. 
     Thus in the single-acting version there are three recesses and in the doubleacting version there are five recesses in the cooperating surfaces of the valve. It will, however, be appreciated that in each case the number of recesses could be larger than that mentioned, e.g. a multiple of that mentioned, for instance if the single valve is used to control two or more cooperating sets of clutch plates or if it is desired, for some reason, to duplicate the hydraulic supply and return passages. 
     In the preferred embodiment, the first recess(es) are formed in the outer valve member and the second recess(es) are formed in the inner valve member. 
     In a practical embodiment, the second clutch plates are connected to a hub or clutch body which is connected to the output shaft. 
     It is preferred that the torque control valve is received in an opening in the. clutch body and rotates with it. It is preferred also. that the source of pressurised hydraulic fluid comprises a pump which is mounted to rotate with the clutch body and includes a piston adapted to cooperate with a stationary track to be reciprocated thereby. The source of pressurised hydraulic fluid preferably communicates with the associated recess(es) via a passage which includes a hydraulic accumulator, e.g. of spring-loaded type. 
     The spring, which essentially constitutes a mechanical feedback element, may take a variety of forms but in the preferred embodiment it comprises one or more plate springs or corneal springs engaged on opposite sides by members connected to the inner and outer valve members, respectively, whereby a sudden increase in the torque transmitted through the engaging first and second clutch plates will result in yielding of the spring and thus relative rotation of the first and second valve members in a sense which reduces the hydraulic pressure acting to urge on the first and second clutch plates into engagement. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features and details of the invention will be apparent from the following description of one specific embodiment of torque control clutch in accordance with the invention which is given by way of example with reference to the accompanying drawings, in which: 
         FIG. 1  is an axial sectional view of one half of the clutch; 
         FIG. 2  is a plan view of the spool valve rotor; 
         FIG. 3  is a perspective view of the spool valve rotor; 
         FIG. 4  is an end view of the spool valve; 
         FIG. 5  is a diagrammatic view showing the relative positions of the cooperating ports in the spool valve, when in the neutral position; 
         FIG. 6  is a view in the direction of the arrow  5  in  FIG. 1  of the feedback connection between the output shaft and the spool valve; and 
         FIG. 7  is a scrap view of the output hub. 
     
    
    
     DETAILED DESCRIPTION 
     Referring firstly to  FIG. 1 , the clutch comprises an input shaft  2  and a coaxial output shaft  4 . Meshing with a splined hub  6  carried by the input shaft  2  is a first set of annular clutch plates  8 , which cooperate with a second set of annular clutch plates  10 , which are connected to rotate with a clutch body  24 . Cooperating with the outermost clutch plate  10  is a clutch piston  12 , of which a portion  14  is received in a clutch cylinder, whose interior is divided into two chambers  16 ,  18  separated by the piston portion  14 . The chambers  16 ,  18  communicate with respective hydraulic fluid supply passages  20 ,  22  extending within the clutch body  24 . Also accommodated within the clutch body  24  is a high pressure hydraulic fluid pump  26 , whose inlet  28  communicates via a non-return valve with an unpressurised tank or reservoir  30  of hydraulic fluid and whose outlet  32  communicates with a further hydraulic fluid supply line  34 , which also extends within the clutch body  24  and includes a spring-loaded hydraulic accumulator  36 . The pump  26  includes a piston  27  biased outwardly, e.g. by a spring, into sliding contact with an annular undulating stationary track  29 . Also extending within the clutch body is a further hydraulic passage  38 , which is connected to the tank  30 . The clutch body  24  is connected via a feedback coupling  40 , which will be described below, to the output shaft  4 . 
     Formed in the clutch body  24  is a circular section cylindrical hole  42  with an internal surface  44 . Located within the hole so as to rotate with the clutch body  24  is a hollow cylindrical spool  46 , which forms the outer member of a spool valve. The hydraulic passages  20 ,  22 ,  34  and  38  all extend to the surface  44  and communicate with corresponding passages  20 ′,  22 ′,  34 ′ and  38 ′ formed in the spool  46 . Rotatably and longitudinally slidably received in the outer spool  46  is an inner spool  48  which forms the inner member of the spool valve. 
     Formed at one end of the outer and inner spools  46 ,  48  and extending parallel to the axes of the spools are respective substantially diametrically opposed pairs of coupling members  50  and  52 , whose function will be described below. The inner spool  48  extends out of the outer spool  46  and at the other end and at this end carries a spaced pair of circumferential flanges, which constitute an engagement area  49  for a linear actuator (not shown). 
     Formed in the outer surface of the inner spool  48  are three elongate, generally rectangular ports or recesses  54 ,  56 ,  58 , which are spaced apart in the peripheral direction by a distance which is only slightly greater than their own width. The central recess  56  communicates with the passage  34 ′ which is connected to the outlet of the pump  26 . The two other recesses  54 ,  58  communicate via similar holes and passages with a circumferential groove  60  in the external surface of the inner spool  48 , which in turn communicates with the passage  38 ′ connected to the unpressurised tank  30 . All three recesses  54 ,  56 ,  58  extend in the longitudinal direction and in the circumferential direction of the inner spool  48  and may thus be regarded as short helical ports. Formed in the inner surface of the outer spool  46  are two further similar short helical recesses  62 ,  64  which communicate with the hydraulic chambers  16 ,  18 , respectively, via the passages  22 ′,  20 ′ and  22 ,  20 , respectively. In the rest or neutral position of the spool valve, the various recesses are in the relative positions shown in  FIG. 4  in which none of them communicate with one another. 
     Connected by a splined connection  66  to the output shaft  4  is a generally circular output hub  68 , in whose outer periphery two diametrically opposed cut-outs  70  are formed. Connected to the outer surfaces of the hubs  68  by rivets or the like  72  are two. spaced parallel circular plates  74 , whose outer edges are connected by further rivets or the like  76  to an inwardly extending flange  78  integral with the clutch body. Formed in the plates  74  are two holes  80 , whose size and position correspond generally with those of the cut-outs  70  in the hubs  68 . Extending through each hole  80  in one of the plates  74  into a respective cut-out  70  are one coupling member  50  and one coupling member  52 , connected to the outer and inner spools, respectively. Each associated pair of coupling members  50 , 52  is spaced apart slightly in the radial direction and also in the circumferential direction. Sandwiched between them is a respective resilient Belleville washer  82 . Each pair of coupling members  50 ,  52  is a close fit within the associated cut-out  70  in the hub  68 . The inner and outer spool members  46 ,  48  are thus substantially constrained to rotate together by virtue of the forces transmitted between them through the coupling members  50 ,  52  via the interposed Belleville washers. Very slight relative rotation of the spool members  46 ,  48 , i.e. of the order of a few degrees, is however possible if the torque applied between the clutch body  24  and the output shaft  4  through the hub  68  is sufficient to cause resilient yielding of the Belleville washers, thereby permitting slight relative temporary displacement of the associated coupling members  50 ,  52 . 
     In use, when the clutch plates are in engagement, rotation is transmitted from the input shaft  2 , through the clutch plates  8 ,  10  to the clutch body  24 . The clutch body  24  and the spool valve thus rotate, carrying with them the hydraulic pump  26 . The piston  27  on the pump thus moves along the stationary undulating track  29  causing it to oscillate radially and thus to produce pressurised hydraulic fluid, which is stored in part in the hydraulic accumulator  36 . For this purpose, hydraulic fluid is drawn into the pump through its inlet  28  from the tank  30 , which is stationary. All the numbered components shown in  FIG. 1  thus rotate, with the exception of those numbered  29  and  30 . The rotation of the clutch body  24  is transmitted via the flange  78  into the plates  74  and then to the hub  68  to the output shaft  4 . Rotation, of the hub  68  is transmitted to the coupling members  50  or  52 , depending on the direction of rotation of the hub  68 , by virtue of their engagement with the surfaces of the cut-outs  70  and thence to the coupling members  52  or  50  through the Belleville washers. Under relatively low torque conditions, the Belleville washers remain substantially undeformed and the pairs of coupling members  50 ,  52  and thus the inner and outer spool valve members remain in their normal relative positions. 
     The clutch plates are engaged by the supply of pressurised hydraulic fluid to the chamber  18  which urges the piston  14 ,  12  to the right, as seen in  FIG. 1 , and thus squeezes the clutch plates  8 ,  10  together with sufficient contact pressure that torque is transmitted between them. Hydraulic pressure is applied to the chamber  18  by actuating the linear actuator to move the inner spool  48  linearly into the outer spool  46 . This will result in the recesses in the cooperating surfaces of the spool valve members moving from the relative positions shown in  FIG. 4  into a position in which the recess  56  will overlap with the recess  62  and the recess  54  will overlap with the recess  64 . The hydraulic chambers  18  and  16  will thus be connected to high pressure and low pressure respectively and the piston  14 ,  12  will be urged to the right, as seen in  FIG. 1 . The linear actuator will move the inner spool inwards at a steady rate and this will result in a progressively increasing area of communication between the recesses  56  and  62  and thus, in the ideal case, in a smooth build up of pressure in the chamber  18  and thus a smooth engagement of the clutch plates, that is to say with no jerkiness. However, it can in practice not infrequently happen that the clutch plates do not move smoothly into engagement but “snatch” or “grab”, that is to say suddenly engage. This results in a “spike” or sudden increase in the torque transmitted and it is such spikes which produce a jerky gear change. However, if such a torque spike should occur, the Belleville washers  82  in the feedback coupling will yield, thus causing relative rotation of the inner and outer spool members. This rotation is in the direction which reduces the degree of overlap of the recesses  62  and  56  and the rate of increase of pressure or the absolute value of the pressure in the chamber  16  is immediately reduced, thereby counteracting or suppressing the torque spike. Since the feedback is mechanical and effected by an element forming a part of the torque path, its effect is immediate and smooth engagement and disengagement of the clutch, whereby jerkiness or changing gear is eliminated. 
     When the clutch is to be released in order to permit a further gear change, the inner spool is moved outwardly until the recesses  62  and  58  come into registry and the recesses  64  and  56  come into registry also. The chambers  16  and  18  are then subjected to high and low pressure, respectively, and the piston is positively moved a short distance to the left, as seen in  FIG. 1 , and the clutch plates are disengaged. 
     It will be appreciated that numerous alterations may be made to the specific embodiment described above. It will be appreciated also that the clutch in accordance with the invention may have many applications other than merely in conjunction with a gearbox to facilitate gear changes. Thus it may be used e.g. to transmit a controllable amount of torque to an axle in a vehicle with an on-demand four wheel drive system or to transmit a controllable amount of torque between two wheels on a single axle. The clutch in accordance with the invention may thus be considered to be a variable torque transmission device or coupling.