Abstract:
A dry-plate clutch (single or dual) of inverted construction for a vehicle transmission includes a clutch structure with a connecting device arranged to be connected to a prime mover; a pressure plate rotationally fixed and axially displaceable relative to the clutch structure, and a driven disc connected to a driven shaft and located between the clutch structure and the pressure plate. An actuator is arranged to displace the pressure plate between an engaged state, where the driven disc is clamped between the clutch structure and the pressure plate, and a disengaged state, where the disc is rotatable relative to the clutch structure. The connecting device has hollow sections at a number of angular locations extending into a radial surface facing the pressure plate. The pressure plate has corresponding axially extending protrusions in a radial surface facing the connecting device; and the protrusions at least partially extend axially into the hollow sections in the disengaged state.

Description:
BACKGROUND AND SUMMARY 
     The present invention relates to vehicle powertrains, more particularly to a dry-plate clutch for a vehicle transmission having an improved combination of stiffness, strength and thermal capacity without increasing the installation space requirements for said dry plate clutch. 
     Dry plate clutches are used in manual and automated vehicle transmissions to facilitate start-off from rest and disengage the transmission from the engine at shifts. Particularly when starting off, beat will be generated in the sliding surfaces in contact as torque is being transferred during the transition from disengaged to fully engaged state. This heat is absorbed as a temperature increase of the parts in contact. The heat is then, in a rather slow way, conducted and radiated to the surrounding. Due to this slow heat dissipation, quite a large mass is required for absorbing the heat generated while keeping the temperature increase limited. Thus, dry plate clutches are relatively heavy. That requires a stiff and strong suspension in order to carry a dry plate clutch. Moreover, dry plate clutches are bulky, which may lead to conflicts with available installation space, especially in axial direction. 
     Dry plate clutches comprise a primary side, also referred to as the driving or input side, rotationally connected to an engine, and a secondary side also referred to as the driven or output side, that is rotationally connected to a transmission input shaft. In order to facilitate gear shifting, the secondary side, also referred to as the driven disc, has low inertia. 
     Therefore, the thermal mass is allocated to the primary side of the clutch. The primary side has an axially moveable clutch plate, referred to as the pressure plate that selectably can clamp and release the driven disc for engaging and disengaging the clutch. 
     In general, the primary side is fixed to a prime mover, such as an engine flywheel. There are two basic types of construction of the primary side with respect to how the flywheel is used. 
     Most common is the construction where the engine flywheel has a friction surface facing the driven disc, and hence is a functional pan of the clutch. The pressure plate is located on the other side of the driven disc. An example of such an arrangement is shown in DE10304502A1. The mass of the flywheel is not only used for levelling out engine torque i0 fluctuations, but can also absorb heat generated in the clutch. 
     Less common, but still frequent, is the primary side construction where the engine flywheel has no other use for the clutch than to suspend it to, and transfer torque from, the engine crankshaft. Instead, the pressure plate faces the flywheel and crankshaft end. This will be referred to as “inverted construction” in the subsequent text. An example of a clutch with an inverted construction can be found in DE10220205A1. Inverted construction clutches are often used when the connection to the engine crankshaft is a sheet metal part. It is also common in dry plate clutches for dual clutch transmissions, e.g. as shown in DE10018646A1. 
     Normally, more axial space is needed when there is no clutch friction surface on the flywheel. That can lead to compromises between conflicting requirements. On one hand, there must be sufficient thermal mass for the pressure plate. On the other hand, sufficient strength and stiffness is required for the flywheel or the corresponding part that carries the clutch. 
     Consequently, there is a need for an axially compact dry plate clutch of inverted construction that enables high thermal mass of the pressure plate as well as high strength and stiffness of the device that connects the primary side of the clutch to the engine crankshaft. It is desirable to provide an improved dry plate clutch of inverted construction that solves the above problems. 
     According to a preferred embodiment, an aspect of the invention relates to a dry-plate clutch of inverted construction in a vehicle transmission. The dry-plate clutch will be referred to as “the clutch” in the subsequent text. The clutch comprises a clutch structure with a connecting device drivingly connected to a prime mover. A pressure plate is rotationally fixed and axially displaceable relative to the clutch structure. A driven disc is connected to a driven shaft and is located between the clutch structure and the pressure plate. The clutch further comprises an actuator means arranged to displace the pressure plate between an engaged state, where the driven disc is clamped between the clutch structure and the pressure plate, and a disengaged state, where the disc is rotatable relative to the clutch structure. The actuator means can comprise any suitable device for actuating the clutch, such as a hydraulic or pneumatic cylinder or an electric motor. 
     The connecting device is provided with hollow sections, or recesses, at a number of angular locations extending into a radial surface facing the pressure plate. The pressure plate has corresponding axially extending protrusions in a radial surface facing the connecting device, which protrusions at least partially extend axially into the hollow sections in the disengaged state. The corresponding hollow sections and protrusions are located so that the rotational balance of the component parts is retained. For individual hollow sections and protrusions this requires two or more such features in the respective component. 
     According, to one example, the hollow sections can extend axially at least partially through the connecting device. Alternatively, the hollow sections can extend axially fully through the connecting device. 
     The protrusions have a circular or oval cross-section and can be equally distributed around the radial surface of the pressure plate. Alternatively, the protrusions have a rectangular, triangular or trapezoidal cross-section. The protrusions can be arranged as two identical protrusions at opposite sides of the rotational axis and at the same radius from this axis. Alternatively, multiple protrusions can be equally distributed around the face of the pressure plate. The protrusions can have the same or different sizes and be arranged on the same or at different radii. 
     The protrusions can also have a honeycomb cross-section, wherein they can be provided as a pattern over an annular section of the pressure plate where it faces the connecting device. 
     According to a further example, the protrusions can comprise two or more ring segments. Such ring segments can have an intermittent annular cross-section, wherein the interrupted sections allow for radial reinforced portions between adjacent recesses in the connecting device. The protrusions can be arranged as a single ring or as concentric rings. 
     The connecting device with its hollow sections can comprise a cast component. Manufacturing the connecting device as a cast part with the hollow sections formed in the casting process, enables cost-effective production. Alternatively it can comprise a metal sheet component with cut-out sections, e.g. by blanking. Manufacturing the connecting device as a sheet metal part were the hollow sections are cut out also enables cost-effective production. 
     Alternatively, the invention relates to a dual dry plate clutch in a vehicle transmission. The dual clutch transmission comprises a clutch structure with a connecting device arranged to be drivingly connected to a prime mover. The prime mover can be an internal combustion engine or an electric motor. A first and a second pressure plate are rotationally fixed and axially displaceable relative to the clutch structure. A first and a second driven disc are connected to a first and a second driven shaft, respectively, and are located between the clutch structure and their respective pressure plate. A first and a second actuator means is arranged to displace their respective pressure plates alternately between a disengaged state and an engaged state, wherein one driven disc is clamped between the clutch structure and one pressure plate white the other driven disc is rotatable relative to the clutch structure and other pressure plate. The operation of dual clutch transmissions is well known in the art and will not be described in further detail. The dual clutch transmission comprises one dry-plate clutch according to the invention adjacent the connecting device, which clutch has been described above. 
     The invention further relates to a vehicle provided with a transmission comprising a dry-plate clutch as described above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following text, the invention will be described in detail with reference to the attached drawings. These schematic drawings are used for illustration only and do not in any way limit the scope of the invention. In the drawings: 
         FIG. 1  shows a longitudinal section of a prior art dry plate clutch with inverted construction primary side; 
         FIG. 2  shows a modified variant of the prior art clutch in  FIG. 1  with increased pressure plate thickness but reduced thickness of the connecting device; 
         FIG. 3 a    shows a longitudinal section of a dry plate clutch with primary side of inverted construction having a hollowed connecting device according to the invention; 
         FIG. 3 b    shows an axial view of the clutch of  FIG. 3   b;    
         FIG. 4 a    shows a variant of the clutch in  FIG. 3 a    where the hollow sections do not extend fully through the connecting device according to a preferred embodiment of the invention; 
         FIG. 4 b    shows an axial view of the clutch of  FIG. 4   a;    
         FIG. 5  shows a dry plate dual clutch where one clutch has inverted, construction primary side. 
         FIG. 6  shows a dry plate dual clutch where alternative examples of protrusions and their location is indicated; and 
         FIG. 7  shows a vehicle provided with a transmission according, to the invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a schematic longitudinal section of a prior art single-disc dry plate clutch  110  of inverted construction. There, a clutch structure  111  is fastened to a connecting device  119 , e.g., a flywheel, by means of screws  120 . The connecting device  119  is rotationally connected to an engine crankshaft (not shown) A pressure plate  112  is rotationally connected to but axially moveable relative to the clutch structure  111 . A driven disc  130  is arranged axially between the clutch structure  111  and pressure plate  112 . The driven disc  130  is composed of a friction lining part  131 , a damper unit  132 , and a hub part  133  that is rotationally connected to and slidably arranged on a transmission input shaft  113 . A diaphragm spring  114  is arranged at the right end of the clutch structure  111 . A number of pull rods  115  are arranged around the circumference form an axial connection between the pressure plate  112  and diaphragm spring  114 . In a not actuated state, the diaphragm spring  114  pulls the pressure plate  112  via pull rods  115  to the right, thus clamping the driven disc  130  to the clutch structure  111 . Torque can then be transferred between the engine and transmission input shaft  118 . The disengagement and engagement of the clutch  110  is performed by a clutch actuator  116 . Therein, a piston  117  pushes, when energized, the innermost part of the diaphragm spring  114  to the left via a release bearing  118 . That will release the pull rods  115  and pressure plate  112 . The driven disc  130  is no longer clamped. This corresponds to disengaged state; the engine and transmission input shall  113  can rotate independent of each other. 
     In  FIGS. 2-4   b  different modifications of the clutch  10  in  FIG. 1  are shown. Several parts could be identical to parts in  FIG. 1 . Those parts are referred to by similar numbers. Corresponding parts have initial digits that correspond to the number of the  FIG. 2, 3   a ,  4   a , etc.), but the second and third digits are the same as in  FIG. 1 . 
     Consequently,  FIG. 2  shows a schematic longitudinal section of a further prior art single-disc dry plate clutch  210  of inverted construction. There, a clutch structure  211  is fastened to a connecting device  219 , e.g., a flywheel, by means of screws  220 . The connecting device  219  is rotationally connected to an engine crankshaft (not shown). A pressure plate  212  is rotationally connected to but axially moveable relative to the clutch structure  211 . A driven disc  230  is arranged axially between the clutch structure  211  and pressure plate  212 . The driven disc  230  is composed of a friction lining part  231 , a damper unit  232 , and a hub part  233  that is rotationally connected to and slidably arranged on a transmission input shaft  213 . A diaphragm spring  214  is arranged at the right end of the clutch structure  211 . A number of pull rods  215  are arranged around the circumference form an axial connection between the pressure plate  212  and diaphragm spring  214 . In a not actuated state, the diaphragm spring  214  pulls the pressure plate  212  via pull rods  215  to the right, thus clamping the driven disc  230  to the clutch structure  211 . Torque can then be transferred between the engine and transmission input shaft  218 . The disengagement and engagement of the clutch  210  is performed by a clutch actuator  216 . Therein, a piston  217  pushes, when energized, the innermost part of the diaphragm spring  214  to the left via a release bearing  218 . That will release the pull rods  215  and pressure plate  212 . The driven disc  230  is no longer clamped. This corresponds to disengaged state; the engine and transmission input shaft  213  can rotate independent of each other. 
     In the clutch  110  in  FIG. 1 , the pressure plate  112  has a considerably lower mass than the clutch structure  111 . The heat absorption capacity is correspondingly lower. If the axial space available is limited, an increase of the pressure plate mass could be embodied in a straightforward way by reducing the connecting device thickness around the whole circumference of the connecting device. This is shown in a modified clutch  210  in  FIG. 2 . A modified pressure plate  210  with increased thickness has required a modified connecting device  219  that has a correspondingly reduced thickness. A problem with this solution is that the reduction of thickness has a negative impact on the strength and stiffness of the connecting device  219 . 
     The mass of an element is proportional to the width (circumference) and thickness. From solid mechanics it is well-known that bending strength is proportional to the width and to the square of the thickness. Moreover, bending stiffness is proportional to the width and to the third power of the thickness. Hence, a reduction in thickness has a larger impact on the strength and stiffness compared to the impact on weight. A width reduction has the same impact on weight as on strength and stiffness. So, with respect to strength and stiffness, it is more favourable to obtain a weight reduction by reduced width. For the connecting part  119  and  219  this can be interpreted as a dimension in circumferential direction. One advantageous way to embody this is to have hollow sections between solid sections with original or increased thickness. 
       FIGS. 3 a  and 3 b    show a modified clutch  310  according to the invention.  FIG. 3 a    shows a schematic longitudinal section of a single-disc dry plate clutch  310  of inverted construction. A clutch structure  311  is fastened to a connecting device  319 , such as a flywheel, by means of screws  320 . The connecting device  119  is rotationally connected to an engine crankshaft (not shown). A pressure plate  312  is rotationally connected to but axially moveable relative to the clutch structure  311 . A driven disc  330  is arranged axially between the clutch structure  311  and pressure plate  312 . The driven disc  330  is composed of a friction lining part  331 , a damper unit  332 , and a hub part  333  that is rotationally connected to and slidably arranged on a transmission input shaft  313 . A diaphragm spring  314  is arranged at the right end of the clutch structure  311 . A number of pull rods  315  are arranged around, the circumference form an axial connection between the pressure plate  312  and diaphragm spring  314 . In a not actuated state, the diaphragm spring  314  pulls the pressure plate  312  via pull rods  315  to the right, towards the driven disc  330 , thus clamping the driven disc  330  to the clutch structure  311 . Torque can then be transferred between the engine and transmission input shaft  318 . The disengagement and engagement of the clutch  310  is performed by a clutch actuator  316 . Therein, a piston  317  pushes, when energized, the innermost part of the diaphragm spring  314  to the left via a release bearing  318 . That will release the pull rods  315  and pressure plate  312 . The driven disc  330  is no longer clamped. This corresponds to disengaged state; the engine and transmission input shaft  313  can rotate independent of each other. 
     The connecting device  319  has been modified in that it comprises hollow sections  321  at a number of angular locations. Furthermore, the pressure plate  312  has been modified to comprise protrusions  322  that extend, at least partly, into the hollow sections  321 . Thereby, the thermal mass of the pressure plate  312  has been increased compared to the prior art clutch  110  in  FIG. 1 . This has been achieved in combination with less impact, on strength and stiffness of the connecting device  319  compared to the clutch  210  in  FIG. 2 . 
       FIG. 3 b    shows an axial view of the clutch  310  and connecting device  319  in the direction of the arrow “B” in  FIG. 3 a   . It can be seen that there are hollow sections  321  and protrusions  322  at a number of angular locations. The solid sections between hollow sections  321  act as big spokes. 
     The hollow sections  321  extend through the connecting device  319 . This can maximize the mass of the pressure plate  312 . The ventilation around the pressure plate  312  can also be improved, which will improve the cooling of the clutch  310  and the ability to withstand repeated start-offs from rest. Utile connecting device  319  is embodied as a sheet metal part, hollow sections  32  can be cut out in a simple way by e.g. a blanking or stamping operation. 
     Blanking, is a specialized form of stamping, where there is no fracture zone when shearing. This is achieved by compressing the whole part and then an upper and a lower punch extract the blank. This allows the process to hold very tight tolerances, and perhaps eliminate secondary operations. Materials that can be blanked include aluminium, brass, copper, as well as carbon, alloy and stainless steels. 
     Blanking presses are similar to other metal stamping presses, but they have a few critical additional parts. A typical compound blanking press includes a hardened die punch (male), the hardened blanking die (female), and a guide plate of similar shape/size to the blanking die. The guide plate is the first applied to the material, impinging the material with a sharp protrusion or stinger around the perimeter of the die opening. Next a counter pressure is applied opposite the punch, and finally the die punch forces the material through the die opening. Since the guide plate holds the material so tightly, and since the counter pressure is applied, the material is cut in a manner more like extrusion than typical punching. Mechanical properties of the cut benefit similarly with a hardened layer at the cut edge of the part. Because the material is so tightly held and controlled in this setup, part flatness remains very true, distortion is nearly eliminated, and edge burr is minimal. Clearances between the die and punch are generally around 1% of the cut material thickness, which typically varies between 0.5-13 mm (0.020-0.51 in). Currently parts as thick as 19 mm (0.75 in) can be cut using blanking. Tolerances between ±0.0003-0.002 in (0.0076-0.051 mm) are possible based on material thickness and tensile strength, and part layout. 
     For some reasons it might sometimes be undesirable to have hollow sections extending, fully through the connecting device. Casting of the connecting device can be facilitated, and dust can be contained within the clutch.  FIGS. 4 a  and 4 b    show an alternative modified clutch  410  according to the invention.  FIG. 4 a    shows it schematic longitudinal section of a single-disc dry plate clutch  410  of inverted construction. A clutch structure  411  is fastened to a connecting device  419 , such as a flywheel, by means of screws  420 . The connecting device  419  is rotationally connected to an engine crankshaft (not shown). A pressure plate  412  is rotationally connected to but axially moveable relative to the clutch structure  411 . A driven disc  430  is arranged axially between the clutch structure  411  and pressure plate  412 . The driven disc  430  is composed of a friction lining part  431 , a damper unit  432 , and a hub part  433  that is rotationally connected to and slidably arranged on a transmission input shaft  413 . A diaphragm spring  414  is arranged at the right end of the clutch structure  411 . A number of pull rods  415  are arrange around the circumference form an axial connection between the pressure plate  412  and diaphragm spring  414 . In a not actuated state, the diaphragm spring  414  pulls the pressure plate  412  via pull rods  415  to the right, towards the driven disc,  430 , thus clamping the driven disc  430  to the clutch structure  411 . Torque can then be transferred between the engine and transmission input shaft  418 . The disengagement and engagement of the clutch  4   0  is performed by a clutch actuator  416 . Therein, a piston  417  pushes, when energized, the innermost part of the diaphragm spring  414  to the left via a release bearing  418 . That will release the pull rods  415  and pressure plate  412 . The driven disc  430  is no longer clamped. This corresponds to disengaged state; the engine and transmission input shaft  413  can rotate independent of each other. 
     In this alternative modified clutch  410  the hollow sections  421  do not extend fully through the connecting device  419 . Correspondingly, the protrusions  422  of the pressure plate  412  are smaller in height in order to avoid axial interference with the connecting device  419 . 
     Dry plate clutches for dual clutch transmissions, e.g., as shown in DE10018646A1, tend to have relatively large overall axial extension. Hence, the invention should be particularly suited to such clutches.  FIG. 5  shows a dry dual clutch  510  according to the invention. It comprises two clutches  510   a  and  510   b  with a common clutch structure  511 . There are pressure plates  512   a  and  512   b , driven discs  531   a  and  531   b , diaphragm springs  514   a  and  514   b , pull rod  515 , and actuators  516   a  and  516   b . The driven discs  531   a  and  531   b  are connected to transmission input shafts  513   a  and  513   b  respectively. The clutch structure  511  is fixed by means of screws  520  to connecting device  519  that has hollow sections  521 . The pressure plate  512   a  has protrusions  522  that axially extend partially into the hollow sections  521 . Said protrusions and hollow section are arranged at a number of angular locations. This makes the dual clutch  510  compact in axial direction. In one embodiment the hollow sections do not extend fully through the connecting device  519 . In an alternative embodiment of the dry plate clutches for dual clutch transmissions shown in  FIG. 5  the hollow sections  521  can extend fully through the connecting device. 
       FIG. 6  shows a dry plate dual clutch or single clutch where alternative examples of protrusions and their location are indicated. In the above  FIGS. 3 b  and 4 b   , the connecting devices and the pressure plates have been describes as comprising cooperating circular protrusions. However, several variations and modifications are possible within what is covered by the claims, as will be apparent to persons skilled in the art. For instance, as indicated in  FIG. 6 , the hollow sections  321 ,  421 ,  521  and the corresponding protrusions  322 ,  422 ,  522  may have any suitable shape or pattern, e.g., circular as shown in  FIGS. 3 b  and 4 b   ), oval  611 , rectangular  612 , triangular  613 , trapezoidal  614 , honeycomb  615 , or as multiple ring segments  616 . The clutch structures  311 ,  411 ,  511  as well as the connecting devices  319 ,  419 ,  519  may be composed of several parts each. 
       FIG. 7  shows a schematically indicated vehicle  71  provided with a transmission comprising a dry-plate clutch according, to the invention. The vehicle  71  is provided with an internal combustion engine (ICE)  72  connected to a transmission  73 , such as an automated manual transmission (AMT), fix transmitting torque to a vehicle drive axle (not shown). The AMT can comprise either a single ( FIG. 3 a    or  4   a ) or a dual clutch ( FIG. 5 ) arrangement (not shown). The ICE  72  is connected to a radiator arrangement  74  for cooling engine coolant and oil from the ICE  72 . The transmission  11  is controlled by the driver or automatically via an electronic control unit (ECU)  75 . The transmission is controlled to select a gear ratio between the engine  72  and a pair of driven wheels  76 . 
     The invention should not be deemed to be limited to the embodiments described above, but rather a number of further variants and modifications are conceivable within the scope of the following patent claims. The connecting devices  319 ,  419 ,  519  may be drivingly connected upstream to the shaft of an electric motor or a gas turbine. Moreover, the clutch structures  311 ,  411 ,  511  as well as the connecting devices  319 ,  419 ,  519  may each comprise several component parts. Especially the single dry-plate clutch embodiments can be manually (via clutch pedal) or automatically (via an electronic control unit) controlled.