Abstract:
A clutch actuator assembly is disclosed that includes, but is not limited to an electric motor with a gear arrangement. The gear arrangement includes, but is not limited to a worm gear with a threaded worm rod and a worm wheel with an actuator section. The worm wheel is actuated by the worm rod and the worm rod is actuated by the electric motor. The worm wheel further includes, but is not limited to an advance gear section with an advance thread. A stationary thread of the clutch actuator assembly engages with the advance thread. The gear arrangement includes, but is not limited to a self-locking feature that at least inhibits, and preferably prevents the actuator section from moving when the electric motor is not actuated.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to British Patent Application No. 1001027.0, filed Jan. 22, 2010, which is incorporated herein by reference in its entirety. 
       TECHNICAL FIELD 
       [0002]    The technical field relates to a clutch actuator assembly, and more particularly to an electro-mechanical clutch actuator assembly. 
       BACKGROUND 
       [0003]    The operation of a launch clutch via an electromechanical clutch actuator provides an alternative to hydraulic or pneumatic clutch actuation. Electromechanical clutch actuators are used for example in automatic manual transmission and double clutch transmissions. Several types of electromechanical clutch actuators are known. One type of clutch actuator comprises a movable slide. The motion of the slide is driven by a worm gear that is attached to an electric motor. The slide acts as a pivot point of a lever arm such that the force of a spring onto the lever arm is translated into an output force that varies with the position of the slide. According to a further type, one end of a Bowden wire is connected to a spindle drive of an electric motor. The other end of the Bowden wire is connected to a disk with a ramp that translates the rotational motion of the disk into a throw-out motion of a clutch release bearing. 
         [0004]    In view of the foregoing, at least one object is to provide an improved clutch actuator assembly for actuating a single clutch and at least another object is to provide an arrangement of two electromechanical clutch actuator assemblies for actuating a double clutch. The clutch actuator assembly will also be referred to as electromechanical clutch actuator. In addition, other objects, desirable features and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background. 
       SUMMARY 
       [0005]    A clutch actuator assembly is disclosed that comprises an electric motor with a gear arrangement. The gear arrangement comprises a worm gear with a threaded worm rod and a worm wheel. An actuator section, for example a clutch release bearing, is attached to the worm wheel for actuating a clutch. The worm wheel is actuated by the worm rod and the worm rod is actuated by the electric motor. The worm wheel further comprises an advance gear section with an advance thread. A stationary thread of the clutch actuator assembly engages with the advance thread. The gear arrangement comprises a self-locking feature that prevents the actuator section from moving when the electric motor is not actuated. More specifically, the self-locking feature is provided by the form of one or more of the threads such as the inclination or the form of the flanks of the threads. 
         [0006]    In embodiments, the worm wheel is provided by a first cylindrical and a second cylindrical part. A second thread of the worm wheel that meshes with a thread of the worm rod is provided on the circumference of the first cylindrical part. The advance gear section of the worm wheel is provided by the second cylindrical part. The stationary thread is provided by a thread on an inner surface of a cup shaped part. In the embodiments, the first and the second cylindrical parts are parts of a second portion of the clutch actuator assembly that is rotatable around an axis of rotation. The axis of rotation coincides with a symmetry axis of an output shaft. The worm rod and the cup shaped part are parts of a first and a third portion of the clutch actuator assembly, respectively. 
         [0007]    In an embodiment of the application, the stationary thread is provided on a surface of a cup shaped part that is attached to a clutch casing. In a further embodiment, the stationary thread is provided by a thread of a clutch casing. The stationary thread is formed as internal thread or also as external thread. 
         [0008]    In an embodiment, a thread of the worm wheel is provided by a female thread on a circumference of a first cylindrical part and an advance thread of the worm wheel is provided by a male thread on a circumference of a second cylindrical part. Thereby, an engaging thread on a rod can be realized as male thread and an engaging stationary internal thread can be realized as female thread, which is easy to machine. 
         [0009]    In an embodiment, the motor and the threaded worm rod are movable along an axis of movement. A guiding means for moving the motor and the worm rod along the axis of movement is provided which is connected to the motor. The guiding means engages with an engaging section that is connected to the worm wheel. The engaging section is provided at a second portion of the clutch actuator assembly. 
         [0010]    In an embodiment, the stationary thread is provided on a surface of a cup shaped part and the cup shaped part is attached to a clutch casing. 
         [0011]    Furthermore, an arrangement is disclosed for two clutch actuator assemblies for actuating a double clutch. The arrangement comprises a first clutch actuator assembly according to one of the application for actuating a first clutch of the double clutch and a second clutch actuator assembly according to the application for actuating a second clutch of the double clutch. The clutch actuator assemblies are nested within each other such that the advance thread of the first electromechanical clutch actuator partially encloses the advance thread of the second electromechanical clutch actuator. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and: 
           [0013]      FIG. 1  illustrates a side view of a first embodiment of an electromechanical clutch actuator; 
           [0014]      FIG. 2  illustrates a cross section of a clutch in an open position and the electromechanical clutch actuator of  FIG. 1 ; 
           [0015]      FIG. 3  illustrates a cross section of a clutch in a closed position and the electromechanical clutch actuator of  FIG. 1 ; 
           [0016]      FIG. 4  illustrates a side view of a second embodiment of an electromechanical clutch actuator with a guiding means; 
           [0017]      FIG. 5  illustrates a cross section of the first cylindrical part and of the guiding means of the electromechanical clutch actuator of  FIG. 4 ; and 
           [0018]      FIG. 6  illustrates a cross section of a double clutch with two electromechanical clutch actuators according to a third embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    The following detailed description is merely exemplary in nature and is not intended to limit application and uses. Furthermore, there is no intention to be bound by any theory presented in the preceding background or summary or the following detailed description. 
         [0020]      FIG. 1  shows a schematic side view of an electromechanical clutch actuator  10 . The electromechanical clutch actuator  10  comprises a first portion  11 , a second portion  12  and a stationary third portion  13 . The first portion  11  is oriented perpendicular to an axis  8  of an output shaft, which is not shown in  FIG. 1 , while the second portion  12  and the stationary third portion  13  are arranged concentrically to the axis  8 . 
         [0021]    The first portion  11  comprises an electric motor  9  and a rod  15  or shaft that is attached to an axis of the electric motor  9 . The rod  15  comprises a thread  14  at the end of the rod  15 . The rotation of the rod  15  around the axis of the electric motor  9  is indicated by an arrow  16 . 
         [0022]    The second portion  12  comprises a first threaded cylindrical part  17 . A thread  18  on the circumference of the first threaded cylindrical part  17  meshes with the thread  14  on the rod  15 . A clutch release bearing  19  is in contact with one side of the first threaded cylindrical part  17 . A second threaded cylindrical part  20  with a thread  21  is attached to the opposite side of the first threaded cylindrical part  17 . 
         [0023]    The stationary third portion  13  comprises a cup shaped part  22  that is attached to a clutch housing. The clutch housing is not shown in  FIG. 1 . An internal thread  23  is provided at the inside of the cup shaped part  22 . The internal thread  23  meshes with the thread  21  of the second threaded cylindrical part  20 . A circular opening for taking up the output shaft is provided at the bottom of the cup shaped part  22 . The opening can be seen in the cross sections of  FIG. 2  and  FIG. 3 . 
         [0024]    The threads of the rod  15 , the first threaded cylindrical part  17 , the second threaded cylindrical part  20  and the cup shaped part  22  are threads of low inclination. Low inclination means that the inclination angle of the thread is substantially smaller than approximately 45° relative to a surface that is perpendicular to a rotation axis. The rotation axis is defined by the symmetry axis of the respective thread. The inclination angle of a thread is also known as the lead angle. In particular, the inclination of the threads of the rod  15 , the first cylindrical part  17 , the second threaded cylindrical part  20 , and the cup shaped part are such that the electromechanical clutch actuator  10  provides a self-locking feature. Therefore, the second portion  12  of the electromechanical clutch actuator  10  is prevented from moving if the electric motor  9  is not actuated. 
         [0025]    In the embodiment of  FIG. 1 , the dimensions of the parts are related as follows. The diameter of the clutch release bearing  19  is greater than the diameter of the first threaded cylindrical part  17  that is in turn greater than the diameter of the second threaded cylindrical part  20 . The thickness, measured along the axis  8 , of the clutch release bearing  19  is smaller than the thickness of the first threaded cylindrical part  17  that is in turn smaller than the thickness of the second threaded cylindrical part  20 . 
         [0026]    The width of the thread  18  of the first threaded cylindrical part  17  along the  8  is dimensioned such that the thread  18  of the first cylindrical part  17  and the thread  14  of the rod  15  mesh over a range of movement of the first cylindrical part  17 , which is sufficient to open and to close a clutch via the clutch release bearing  19 . 
         [0027]      FIG. 2  and  FIG. 3  show cross sections of a naturally closed clutch  25  with an electromechanical clutch actuator  10  according to  FIG. 1 . The clutch release bearing  19  and a spline shaft are shown in side view.  FIG. 2  shows the clutch  25  in an open position and  FIG. 3  shows the clutch  25  in a closed position. In the following, right-handed threads are assumed. The sense of rotation of the rod  15  is described as seen from the electric motor  9  and the sense of rotation of the first threaded cylindrical part  17  is described as seen from the clutch  25 . 
         [0028]    As indicated in  FIG. 2  and  FIG. 3 , the cylindrical parts  17  and  20  are hollow and the bottom of the cup shaped part  22  has a circular opening. An output shaft  32  is arranged concentrically within the cylindrical parts  17  and  20  and within the circular opening of the cup shaped part  22 . The output shaft  32  is supported by a bearing  33  that is located between the output shaft  32  and the circular opening of the cup shaped part  22  and by a further bearing that is located between the output shaft  32  and a clutch casing of the clutch  25 . The clutch casing is connected to a flywheel and the flywheel is connected to an output shaft of an engine in a known way. The flywheel and the engine are not shown. 
         [0029]    To close the clutch  25  that is shown in an open position in  FIG. 2 , the electric motor  9  is supplied with a current such that the electric motor  9  turns the rod  15  in an anti-clockwise direction, as indicated by arrow  26 . The anticlockwise rotation of the thread  14  of the rod  15  turns the first threaded cylindrical part  17  via the engagement of the thread  14  with the thread  18  of the first threaded cylindrical part  17 . The clockwise rotation of the first threaded cylindrical part  17  is indicated by an arrow  27 . The first threaded cylindrical part  17  transmits its clockwise rotation to the second threaded cylindrical part  20 . The second threaded cylindrical part  20  moves into the cup shaped part  22  via the engagement of the internal thread  23  of the second threaded cylindrical part  20  with the internal thread  23  at the inside of the cup shaped part  22 . The second portion  11  of the electromechanical clutch actuator  10  moves inwards towards the cup shaped part  22  and away from the clutch  25 . The inward movement of the second portion  11  is indicated by an arrow  28 . 
         [0030]    A spring  30  of the clutch  25  presses the clutch release bearing  19  against the first threaded cylindrical part  17 . The clutch release bearing  19  moves away from a clutch disk  31 . The outward movement of the spring  30  is translated into a pressure against a friction disk via a pivot mounting of the spring  30 . The friction disk is pressed against the clutch disk and the rotation of the friction disk is transmitted to the clutch disk that is connected to the output shaft  32 . 
         [0031]    To open the clutch  25 , which is shown in a closed position in  FIG. 3 , the electric motor  9  is supplied with a current such that the electric motor  9  turns the rod  15  in a clock-wise direction, as indicated by arrow  35 . The rod  15  turns the first threaded cylindrical part  17  in an anticlockwise direction via the engagement of the thread  14 , as indicated by an arrow  27 . The first threaded cylindrical part  17  transmits its rotation to the second threaded cylindrical part  20 . The second threaded cylindrical part  20  moves out of the cup shaped part  22  and towards the clutch  25 . The outward movement of the second threaded cylindrical part  20  is indicated by an arrow  37 . 
         [0032]    The outward movement of the second threaded cylindrical part  20  is transmitted to the first threaded cylindrical part  17  and to the clutch release bearing  19 . The clutch release bearing presses the spring  30  inwards towards the clutch  25 . The inward movement of the spring  30  is translated into an outward movement of the friction disk via the pivot mounting of the spring  30 . The friction disk is released from the clutch disk. 
         [0033]      FIG. 4  and  FIG. 5  show a second embodiment of an electromechanical clutch actuator in which the electric motor  9  is supported in such a way that it is movable parallel to the axis  8 , but such that the movement of the electric motor  9  is constrained to a plane which contains the axis  8 . A guiding means connects the first portion  11  to the second portion  11  such that the movement of the first portion  11  follows the movement of the second portion  11 . 
         [0034]      FIG. 4  shows a side view of a second embodiment electromechanical clutch actuator  10 ′. Identical parts have the same reference number, similar parts have a primed reference number. Different from the previous embodiment, the thread  18  on the circumference of the first cylindrical part  17  has essentially the same width as the thread  14  at the end of the rod  15 . 
         [0035]    In addition to the features shown in  FIG. 1 , the electromechanical clutch actuator  10 ′ of  FIG. 4  comprises a guiding means  40  that is attached to the electric motor  9 ′. The guiding means comprises a finger portion  41  and a fork portion  42 . The finger portion is fixed to an attachment at the casing of the electric motor  9 ′ at one end. The fork portion  42 , which is provided at the other end of the finger portion, is shaped in the form of a half circle. The fork portion  42  engages with a circular groove  43  at the outside of the first cylindrical part  17 ′. 
         [0036]    If the first cylindrical part  17 ′ moves towards or away from the cup shaped part  22 , the side walls of the guiding groove  43  move the guiding means  40  and the attached electric motor  9 ′ in the direction of movement of the first cylindrical part  17 ′. 
         [0037]      FIG. 5  shows a cross section of the guiding means  40 , the first cylindrical part  17 ′ and the output shaft  32 . In the lower part of  FIG. 5 , a sidewall of the circular groove  43  is shown. 
         [0038]      FIG. 6  shows a cross section of a double clutch  25 ′ that comprises two naturally open clutches. The clutches of the double clutch  25 ′ are actuated from a first electromechanical clutch actuator  10 ″ and a second electromechanical clutch actuator  10 ′″ according to a third embodiment. In  FIG. 6 , the electric motors of the actuators  10 ″ and  10 ′″ are outside the cross section and are therefore not shown. Only the features of the electromechanical clutch actuators  10 ″,  10 ′″ that are different from the electromechanical clutch actuator  10  of  FIG. 1  will be explained below. 
         [0039]    An inner output shaft  32 ′ is arranged concentrically within a hollow output shaft  45 . A first and a second clutch disk are mounted on splined sections of the hollow output shaft  45  and the output shaft  32 ′, respectively. A first and a second friction disk are actuated by the electromechanical clutch actuators  10 ″ and  10 ′″, respectively. 
         [0040]    A second threaded cylindrical part  20 ′″ of the electromechanical clutch actuator  10 ′″ is arranged concentrically within a second threaded cylindrical part  20 ″ of the electromechanical clutch actuator  10 ″. 
         [0041]    A first threaded cylindrical part  17 ″ of the electromechanical clutch actuator  10 ″, which is formed as a gearwheel, is mounted on the second threaded cylindrical part  20 ″ of the electromechanical clutch actuator  10 ″. A thread  18 ″ of the first threaded cylindrical part  17 ″, which is formed as teeth of the first threaded cylindrical part  17 ″, engages with a thread  14 ″ of a rod  15 ″, which is connected to an electrical motor. An internal thread  23 ″ on the inside of a first threaded circular opening of a clutch casing  22 ′ engages with a thread  21 ″ on the outside of the second threaded cylindrical part  20 ″. 
         [0042]    Likewise, a first threaded cylindrical part  17 ′″ of the electromechanical clutch actuator  10 ′″, which is formed as a gearwheel, is mounted on the second threaded cylindrical part  20 ′″ of the electromechanical clutch actuator  10 ′″. A thread  18 ′″ of the first threaded cylindrical part  17 ′″, which is formed as teeth of the first cylindrical part  17 ′″, engages with a thread  14 ′″ of a rod  15 ′″, which is connected to an electrical motor. An internal thread  23 ′″ on the inside of a second threaded circular opening of a clutch casing  22 ′ engages with a thread  21 ′″ on the outside of the second threaded cylindrical part  20 ′″. 
         [0043]    A roller bearing, which is not shown in  FIG. 6 , is provided between the second cylindrical part  20 ″ of the electromechanical clutch actuator  10 ″ and the second cylindrical part  20 ′″ of the electromechanical clutch actuator  10 ′″, such that the second cylindrical part  20 ′″ is free to rotate within the second cylindrical part  20 ″ and the second cylindrical part  20 ′″ is supported within the second cylindrical part  20 ″. A dual mass flywheel of the double clutch  25 ′ is connected to an output shaft of an engine, as shown on the left hand side of  FIG. 6 . 
         [0044]    Due to the self-locking feature, an electromechanical clutch according to the application requires no additional energy to keep a naturally open clutch in a closed position. This is especially advantageous in double clutch transmissions in which at least one of the clutches is realized as naturally open clutch. Due to the energy savings, the emissions of a combustion engine are reduced as well. 
         [0045]    The electromechanical clutch actuator according to the application can be used with both naturally open and naturally closed clutches, however. Furthermore, it can be used with advantage in double clutch transmissions (DCT) and in automated manual transmissions (AMT). The electromechanical clutch actuator can be realized with very few parts only. No hydraulic lines and no sealing against leakage are required, no refilling of hydraulic fluid is necessary. 
         [0046]    With a low inclination of the threads, a relatively low output torque of a fast turning electric motor can be transformed in a relatively high actuation force. Moreover, a low inclination of the threads provides a self-locking feature that prevents the actuator from sliding out of position when the electric motor is turned off, even when no additional means such as brake mechanisms are provided. The thread may have a special form to enhance the self-locking feature, for example a certain inclination of the thread flanks. The threads may be formed, for example, in a saw-shape or a trapezoidal shape such as in Buttress, V-shaped and Acme threads. The Acme and Buttress threads have the advantage of supporting high loads whilst the V-thread can provide a larger friction surface for the self-locking feature. The threads may furthermore have multiple start threads to increase linear motion for faster clutch actuation. 
         [0047]    The threaded parts of the electromechanical clutch actuator may be produced out of standard parts with standard machine tools. Therefore, a car that is equipped with clutch actuators according to the application is more service friendly. This advantage applies especially, but not exclusively, for vehicles that are intended to be used in less developed areas. 
         [0048]    Moreover, the parts an electromechanical clutch actuator according to the application can be made sturdy as compared to other electromechanical mechanisms that comprise levers, springs, rolls and the like. Therefore, the electromechanical clutch actuator according to the application can also be used for operation in harsh environments and for military vehicles. 
         [0049]    The use of a stationary internal thread for both actuators of a double clutch makes it possible that the second cylindrical parts can be placed close to the output axis. Therefore, the lever arms of the clutch can be made large for achieving a large pressure force. Although the above description contains much specificity, these should not be construed as limiting the scope of the embodiments but merely providing illustration of the foreseeable embodiments. Especially the above stated advantages of the embodiments should not be construed as limiting the scope of the embodiments, but merely to explain possible achievements if the described embodiments are put into practise. Thus, the scope of the embodiments should be determined by the claims and their equivalents, rather than by the examples given. 
         [0050]    Several modifications are possible. For example, the second and the first cylindrical parts of the second portion may be realized as one single part that has two outer threads or as a single part with one outer thread and teeth. The first cylindrical part may be realized as a cogwheel with teeth. The threads of the parts may also be left handed. The position of the motor and the rod may be swapped by approximately 180 degrees relative to the position shown in the drawings. 
         [0051]    An arrangement of two electromechanical clutch actuators may also be used to actuate a double clutch of a type in which the clutches are actuated from different sides. In this arrangement, the second cylindrical parts are not nested within each other and the electromechanical clutch actuators may be constructed identically. 
         [0052]    Instead of a cup shaped part, an internal threading may be used which is formed out of another part such as the clutch casing. The positions of the first and second cylindrical parts may also be swapped, which means that the internal thread and the second cylindrical part may be next to the clutch release bearing while the rod and the first cylindrical part are located further away from the clutch release bearing. 
         [0053]    While at least one exemplary embodiment has been presented in the foregoing summary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents.