Abstract:
A clutch actuator is configured to change operational force applied to a clutch in cases that a worm wheel is rotated by a motor. The clutch actuator may include a motor provided with a rotatable worm shaft, a screw thread formed along an exterior circumference of the worm shaft, a worm wheel provided with a worm gear engaging the screw thread, and a cam recess, an operation rod mounted to the worm wheel, the operation rod configured to engage or release a clutch, and a rotatable operation unit disposed within the cam recess, and configured to apply elastic force to the worm wheel. Methods of using the clutch actuator are also described.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to, and the benefit of, Korean Patent Application No. 10-2008-0022906, filed in the Korean Intellectual Property Office on Mar. 12, 2008, the entire contents of which are incorporated herein for all purposes by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a clutch actuator. More particularly, the present invention relates to a clutch actuator that changes operation force applied to a clutch by a worm wheel rotated by a motor. 
     2. Description of Related Art 
     Generally, a clutch actuator for a manual transmission uses hydraulic pressure to control engaging and releasing of a clutch. A conventional clutch actuator generally includes a clutch disk, a clutch cover, a clutch fork, an operation cylinder, a master cylinder, and a clutch pedal. 
     A clutch fork engages or releases a clutch cover to a clutch disk by contacting or releasing the cover and disk. The clutch disk and the clutch cover are thus frictionally engaged such that torque applied to the clutch cover is transmitted to the clutch disk. That is, in a case in which the clutch disk and the clutch cover are closely contacted, the torque of the clutch cover is transmitted to the clutch disk by the frictional force. When the clutch disk is separated from the clutch cover, the clutch disk and the clutch cover rotate separately. 
     The clutch fork closely contacts the clutch cover to the clutch disk or separates the clutch cover from the clutch disk so as to engage or release the clutch. The clutch fork is operated by the operation cylinder. The master cylinder generates hydraulic pressure that is supplied to the operation cylinder and is mounted between the clutch pedal and the operation cylinder. Therefore, when the driver pushes the clutch pedal, the master cylinder generates hydraulic pressure and supplies the hydraulic pressure to the operation cylinder to engage the disk and cover. 
     Such actuators are used mainly for manual transmissions. However, the use of manual transmissions is decreasing because of control difficulties thereof. On the contrary, use of double clutch transmissions (DCTs) or automated manual transmissions (AMTs) are on the rise. In double clutch and automated manual transmissions, the clutch is controlled by an electrical signal. Therefore, a pressure-operated clutch actuator is difficult to apply in these cases. 
     The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art. 
     BRIEF SUMMARY OF THE INVENTION 
     Various aspects of the present invention are directed to a clutch actuator including a motor provided with a rotatable worm shaft, a screw thread formed along an exterior circumference of the worm shaft, a worm wheel provided with a worm gear engaging the screw thread, and a cam recess, an operation rod mounted to the worm wheel, the operation rod configured to engage or release a clutch, and/or a rotatable operation unit disposed within the cam recess, and configured to apply elastic force to the worm wheel. 
     The cam recess may be configured such that elastic force applied to the worm wheel by the operation unit is maintained within a predetermined range when the worm wheel rotates. 
     The operation unit may include at least two supporting rods disposed substantially parallel to each other, at least two elastic members applying the elastic force along a predetermined direction of the supporting rods, a rotatable connecting portion connected to first ends of the supporting rods, at least two seats mounted at respective second ends of the supporting rods receiving the elastic force from the elastic members, and/or a first roller connecting at least two seats, disposed in the cam recess, and configured to apply the elastic force of the elastic members to the worm wheel. 
     The operation unit may further include at least two supporting rods disposed substantially parallel with each other, at least two elastic members applying the elastic force in a predetermined direction by the supporting rods, a rotatable connecting portion connected to ends of the supporting rods, at least two seats mounted at respective second ends of the supporting rods and receiving the elastic force from the elastic members, a first roller connecting at least two seats, disposed in the cam recess, and configured to apply the elastic force of the elastic member to the worm wheel, and/or a rail extending from the connecting portion to the first roller. 
     The elastic members may be coil springs, and each may be coiled around one of the supporting rods. The cam recess may be configured such that the length of the coil springs is maintained within a predetermined length range when the worm wheel rotates. The elastic members may be coil springs, and each may be coiled around one of the supporting rods. The cam recess may be configured such that the length of the coil springs is maintained within a predetermined length range when the worm wheel rotates. 
     A second roller for guiding the operation unit on the rail may be mounted at a surface of the cam recess. Any of the above-mentioned supporting rods may be a telescoping cylinder such that the length thereof can be changed. Any of the above-mentioned supporting rod may include an inner rod slidably disposed in an outer rod. 
     The methods and apparatuses of the present invention have other features and advantages which will be apparent from or are set forth in more detail in the accompanying drawings, which are incorporated herein, and the following Detailed Description of the Invention, which together serve to explain certain principles of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of the interior of an exemplary clutch actuator in accordance with various aspects of the present invention. 
         FIG. 2  is a perspective view of an operation unit used in the clutch actuator of  FIG. 1 . 
         FIG. 3  is a perspective view of a worm wheel used in a the clutch actuator of  FIG. 1 . 
         FIG. 4  is a perspective view of another exemplary clutch actuator according to various aspects of the present invention. 
         FIG. 5  is a perspective view of a worm wheel used in a the clutch actuator of  FIG. 4 . 
         FIG. 6  is a perspective view of an operation unit used in the clutch actuator of  FIG. 4 . 
         FIG. 7  is a schematic diagram illustrating the operation of the clutch actuators of  FIGS. 1 and 4  in accordance with various aspects of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made in detail to various embodiments of the present invention(s), examples of which are illustrated in the accompanying drawings and described below. While the invention(s) will be described in conjunction with exemplary embodiments, it will be understood that present description is not intended to limit the invention(s) to those exemplary embodiments. On the contrary, the invention(s) is/are intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the invention as defined by the appended claims. 
     As shown in  FIG. 1 , a clutch actuator according to an exemplary embodiment of the present invention includes a housing  10  and a motor  20 . Mounted in the housing  10  are a worm wheel  30 , an operation rod  70 , and an operation unit  50 . 
     The motor  20  receives an electric signal from a control unit  22  and rotates a worm shaft  40 . A screw thread  42  (see, e.g.,  FIG. 4 ) is provided along an exterior circumference of the worm shaft  40 . The control unit generates a electric signal for controlling an operation of a clutch based on driving conditions such as vehicle speed and engine speed. The control unit  22  transmits the electric signal to the motor  20  as a control signal of the motor  20 . The motor may be a DC motor or a step motor. In addition, the motor  20 , and may be installed in the housing  10  or at an exterior of the housing  10 . In various embodiments in which the motor  20  is mounted at the exterior of the housing  10 , the worm shaft  40  penetrates the housing  10 . The worm shaft  40  engages with the worm wheel  30 . 
     As shown in  FIG. 3 , the worm wheel  30  has a fan shape and is rotatably mounted to the housing  10  by a shaft  38 . A worm gear  36  is provided along an exterior circumference of the worm wheel  30  and engages with the screw thread  42  of the worm shaft  40 . When the motor  20  rotates, the worm wheel  30  rotates about the shaft  38 , which may be substantially perpendicular to the worm shaft  40 . In addition, a receiving portion  32  is provided on an opposite side of the worm gear  36  and the operation rod  70  is mounted in the receiving portion  32 . A cam recess  34  is provided along a radial direction of the worm wheel  30 . The shape of the cam recess  34  will be described in more detail below. 
     The operation rod  70  is mounted in the receiving portion  32  of the worm wheel  30 , and one end of the operation rod  70  penetrates the housing  10  and is connected to an otherwise conventional clutch cover  72 , either directly or via a clutch fork  74 . 
     As shown in  FIG. 2 , the operation unit  50  includes supporting rods  56 , elastic members  54 , a connecting portion  60 , seats  52 , and a first roller  58 . 
     In various embodiments, at least two supporting rods  56  may be provided for mounting the first roller  58 , and in various embodiments, the at least two supporting rods  56  are substantially parallel to one another. The first roller  58  is mounted between the two parallel supporting rods  56 . Each supporting rod  56  may be formed as a double or telescoping cylinder such that length thereof can be changed. Each rod may include an inner cylinder is inserted slidably disposed within an outer cylinder, penetrates the outer cylinder, and moves along a length direction thereof such that the length of the supporting rod  56  is changeable. 
     The elastic member  54  applies elastic force in a predetermined direction, for example, in a direction parallel with the length direction or longitudinal axis of the supporting rod  56 . The elastic member  54  may be a coil spring, and the coil spring may be coiled around the supporting rod  56 . 
     The connecting portion  60  is connected to one end of the supporting rod  56 , for example, the outer cylinder, and is rotatably mounted at the housing  10 . 
     The seat  52  is mounted at the other end of the supporting rod  56 , for example, the inner cylinder. The elastic member  54  applies elastic force to the seat  52 , which is mounted between the seat  52  and the connecting portion  60 . Because the diameter of the seat  52  is larger than that of the elastic member  54 , the elastic member  54  applies elastic force to the seat  52  and the seat  52  can be moved or slid along the length of the supporting rod  56  by the elastic force of the elastic member  54 . 
     The first roller  58  connects at least two seats  52  with each other. The first roller  58  is rotatably supported by a pressure pin  59 , and respectively ends of the pressure pin  59  are fixed to the seats  52 . Therefore, the elastic force of the elastic member  54  is transmitted to the first roller  58  through the seats  52 . 
     In addition, the first roller  58  is mounted in the cam recess  34  and is guided by the cam recess  34 . That is, when the worm wheel  30  rotates, the operation unit  50  rotates about the connecting portion  60 . The first roller  58  is guided by the cam recess  34  and applies the elastic force of the elastic member  54  to the worm wheel  30 . The lengths of the springs  54  and cam recess  34  may be selected such that an elastic force of a predetermined range, that is, a desired selected force is applied to the worm wheel  30  when the worm wheel  30  rotates. In various embodiments in which the elastic member  54  is a coil spring, the cam recess  34  may be configured such that length of the coil spring is maintained within a predetermined length range when the worm wheel  30  rotates. When the length of the coil spring is within the predetermined length range, a clutch may be engaged by the elastic force of the coil spring. One will appreciate that the predetermined length range can be readily determined based upon various parameters. 
     Referring to  FIG. 4  to  FIG. 6 , a clutch actuator according to another exemplary embodiment of the present invention will hereinafter be described. The structure of the clutch actuator according to other various embodiments of the present invention is similar to that of the clutch actuator described above, and various components may be identical to those of the actuator shown in  FIGS. 1-3 . Therefore, the same reference numerals are used for the same constituent elements, and detailed descriptions thereof will be omitted. 
     As shown in  FIG. 4  to  FIG. 6  an alternative exemplary clutch actuator according to the various aspects of the present invention includes a housing  10 , a motor  20 , a worm wheel  30 ′, an operation rod  70 , and an operation unit  50 ′. As the housing  10 , the motor  20 , and the operation rod  70  of this exemplary embodiment are the similar as the housing  10 , the motor  20 , and the operation rod  70  described above, detailed descriptions thereof will be omitted. 
     The worm wheel  30 ′ has a fan shape and is rotatably mounted to the housing  10  by a shaft  38 . A worm gear  36  is provided along an exterior circumference of the worm wheel  30 ′ and engages with the screw thread  42  of a worm shaft  40 . In addition, a receiving portion  32  is formed on the opposite side of the worm gear  36 , and the operation rod  70  is mounted in the receiving portion  32 . In addition, a cam recess  34 ′ is provided along the radial direction of the worm wheel  30 ′, and a second roller  33  is provided at one surface of the cam recess  34 ′. The second roller  33  is rotatably mounted to the housing  10 . 
     The operation unit  50 ′ includes supporting rods  56  (see, e.g.  FIG. 2 ), elastic members  54 , a connecting portion  60 ′, seats  52 ′, a first roller  58 , and a rail  62 . The supporting rods  56  and elastic members  54  may be similar or identical to those described above. 
     Connecting portion  60 ′ may be connected to one end of the supporting rods  56 , for example, the outer cylinders, and is rotatably mounted at the housing  10 . 
     The seats  52 ′ may be disposed substantially parallel with each other, and may be formed as a double or telescopic cylinder such that the length thereof can be changed. 
     The elastic member  54  applies elastic force in a predetermined direction, for example, a direction substantially parallel with the length direction or longitudinal axis of the supporting rod  56 . The elastic member  54  may be a coil spring, and the coil spring coils around the supporting rod  56 . 
     The connecting portion  60 ′ is connected to one end of the supporting rod  56 , for example, the outer cylinder, and is rotatably mounted at the housing  10 . 
     The seat  52 ′ is mounted at the other end of the supporting rod  56 , for example, the inner cylinder, and the seat  52 ′ can be moved along the length of the supporting rod  56  by elastic force of the elastic member. The seat may have various shapes, for example, a spherical or a cylindrical shape. 
     The first roller  58  connects at least two seats  52 ′ with each other. The first roller  58  is rotatably supported by a pressure pin  59 , whose ends are fixed to the seats  52 ′. 
     In addition, the first roller  58  is mounted in the cam recess  34 ′ and is guided by the cam recess  34 ′. When the worm wheel  30 ′ rotates, the operation unit  50  also rotates about the connecting portion  60 ′. At this time, the first roller  58  is guided by the cam recess  34 ′ and applies the elastic force of the elastic member  54  to the worm wheel  30 ′. In this case, the cam recess  34 ′ is configured such that the elastic force of a predetermined range is applied to the worm wheel  30  in a case that the worm wheel  30 ′ rotates. If the elastic member  54  is the coil spring, the cam recess  34 ′ is configured such that the length of the coil spring is maintained within a predetermined length range when the worm wheel  30 ′ rotates. The second roller  33  provided in the cam recess  34 ′ of operation unit  50 ′ according to various embodiments of the present invention, the other. The surface of the cam recess  34 ′ opposite the second roller  33  is arc-shaped and contacts the first roller  58 . Therefore, the coil spring may be maintained to have a constant length even when the operation unit  50 ′ rotates. 
     The rail  62  extends from the connecting portion  60 ′ to the first roller  58 . When the operation unit  50 ′ is mounted in the cam recess  34 ′, the second roller  33  slides on the rail  62  and guides the operation unit  50 ′. 
     Referring to  FIG. 7 , operation of the above-described clutch actuators according to the exemplary embodiments of the present invention will hereinafter be described. 
       FIG. 7  is a schematic diagram for explaining an operation of a clutch actuator according to exemplary embodiments of the present invention. 
     As shown in  FIG. 7 , assuming that a distance from the shaft  38  to the seat  52  is represented as R 1 , the elastic force of the elastic member  54  is represented as L 2 , an angle between directions L 2  and R 1  is represented as θ 1 , and a distance from the shaft  38  to the operation rod  70  is represented as x at an initial state, force L 1  of the operation rod is represented as in Equation 1. If it is assumed that an angle between directions L 1  and x is a right angle.
 
 L 1 =L 2 *R 1*sin θ1 /x   Equation (1)
 
     At this state, if the motor  20  is operated and the worm wheel  30 ,  30 ′ is rotated, the operation unit  50 ,  50 ′ rotates along the cam recess  34 ,  34 ′. In addition, the cam recess  34 ,  34 ′ is configured such that the elastic force L 2  of the elastic member  54  is maintained within the predetermined range when the worm wheel  30 ,  30 ′ rotates. Assuming a distance from the shaft  38  to the seat  52  is represented as R 2  and an angle between directions of L 2  and R 2  is represented as θ 2  at a state that the worm wheel  30 ,  30 ′ rotates to the limit, the force L 1  of the operation rod is represented as in Equation 2. Here, it is assumed that θ 2  is 90°.
 
 L 1 =L 2 *R 2*sin θ2 /x=L 2 *R 2 /x   Equation (2)
 
     Comparing Equation 2 with Equation 1, the force L 1  of the operation rod  70  applied to the fork or the clutch cover is increased because R 2  is larger than R 1 *sin θ 1 . Accordingly, the clutch is engaged. 
     When the motor  20  rotates in the opposite direction, the force L 1  of the operation rod  70  applied to the fork or the clutch cover decreases and thus the clutch is released. 
     Meanwhile, means for supplying an elastic force in the direction opposite to the L 1  direction may be mounted on the clutch cover or the fork. 
     As described above, because operation of a clutch is controlled by a motor, a clutch actuator of this invention can be easily applied to a double clutch transmission or an automated manual transmission. It should be noted that although, in the equations above, the angle between directions L 1  and x, as well as θ 2 , were somewhat arbitrarily set as 90° for the sake of simplicity, the scope of the invention is of course not limited to any specific angles. 
     As described above, because operation of a clutch is controlled by a motor, the exemplary clutch actuators can be used for a variety of transmission, including double clutch and automated manual transmissions. 
     In addition, because power of a motor is used in order to rotate a worm wheel, and a clutch is operated by elastic force of an elastic member, a motor with a low capacity can be used for a clutch actuator of this invention. 
     For convenience in explanation and accurate definition in the appended claims, the terms “interior”, “longitudinal”, and etc. are used to describe features of the exemplary embodiments with reference to the positions of such features as displayed in the figures. 
     The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teachings. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and their practical application, to thereby enable others skilled in the art to make and utilize various exemplary embodiments of the present invention, as well as various alternatives and modifications thereof It is intended that the scope of the invention be defined by the Claims appended hereto and their equivalents.