Abstract:
A variable tensioner according to an exemplary embodiment of the present invention may include: a base, an arm including a boss and a mounting portion, wherein the boss is co-axially and rotatably coupled to the base and a pulley is coaxially and rotatably mounted to the mounting portion, the arm forming an elastic member insert recess with the base, an elastic member mounted in the elastic member insert recess, one end of the elastic member fixed to the base and the other end of the elastic member fixed to the boss, and a tension actuator deforming a portion of the elastic member according to signal of an engine control unit.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to and the benefit of Korean Patent Application No. 10-2007-0131560 filed in the Korean Intellectual Property Office on Dec. 14, 2007, the entire contents of which are incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    (a) Field of the Invention 
         [0003]    The present invention relates to a variable tensioner. More particularly, the present invention relates to a variable tensioner that reduces friction loss and improves fuel mileage and durability of a pulley and a belt as a consequence of controlling tension of the belt according to an engine speed. 
         [0004]    (b) Description of the Related Art 
         [0005]    Generally, auxiliary machines such as a camshaft, an alternator, a power steering pump, and an air conditioner compressor are connected to a crankshaft of an engine by a belt. Therefore, power of the crankshaft is transmitted to the auxiliary machines by frictional force of the belt. 
         [0006]    In a case that tension of the belt is too strong, the frictional force of the belt may increase and friction loss may also increase. On the contrary, in a case that the tension of the belt is too weak, slip of the belt may occur and power delivery efficiency may be deteriorated. 
         [0007]    Particularly, an integrated starter-generator is used in a hybrid vehicle in order to drive the hybrid vehicle at a starting or low engine speed. Since load of the integrated starter-generator is very high, there is high possibility for slip of the belt to occur, and accordingly it is required that the tension of the belt is more heightened. 
         [0008]    However, the friction loss is very high and fuel mileage is very low because of high tension of the belt. 
         [0009]    To solve such problems, two tensioners are generally mounted in the hybrid vehicle so as to control the tension of the belt. However, since two tensioners are used, the mounting structure of the belt may be complex and manufacturing cost of the hybrid vehicle may rise. 
         [0010]    The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. 
       SUMMARY OF THE INVENTION 
       [0011]    Embodiments of the present invention provide a variable tensioner having advantages of reducing friction loss and improving fuel mileage and durability of a pulley and a belt as a consequence of controlling tension of the belt according to an engine speed. 
         [0012]    A variable tensioner according to an exemplary embodiment of the present invention may include a base, an arm including a boss and a mounting portion, wherein the boss is co-axially and rotatably coupled to the base and a pulley is coaxially and rotatably mounted to the mounting portion, the arm forming an elastic member insert recess with the base, an elastic member mounted in the elastic member insert recess, one end of the elastic member fixed to the base and the other end of the elastic member fixed to the boss, and a tension actuator deforming a portion of the elastic member according to signal of an engine control unit. The elastic member insert recess may be enclosed by the base and the boss. 
         [0013]    In an exemplary embodiment of the present invention, the boss and the mounting portion of the arm may be integrally formed of a single body. The base and the boss may be coupled by a first connecting member, the base is fixed so that the boss is rotatable relative to the base, and the mounting portion and the pulley are coupled by a second connecting member. The first connecting member and the second connecting member may be offset with a predetermined distance. The first connecting member may be a shaft and the second connecting member may be a bolt. The elastic member may be wound substantially around the first connecting member. 
         [0014]    The base may comprise an interior circumference, an exterior circumference, and a protruding portion configured to be disposed between the interior circumference and exterior circumference thereof, and the boss comprises an interior circumference and an exterior circumference wherein the exterior circumference of the boss protrudes downwardly and contacts the exterior circumference of the base and the interior circumference of the boss protrudes downwardly and a lower portion of the interior circumference of the boss is slidably inserted in a boss insert groove of the base formed between the interior circumference and protruding portion of the base. The elastic member insert recess may be disposed between the interior circumference and exterior circumference of the base and the interior circumference and exterior circumference of the boss. The elastic member may be wound substantially around the interior circumference of the base and the interior circumference of the boss in the elastic member insert recess. 
         [0015]    In another exemplary embodiment of the present invention, the tension actuator may be provided with one end fixed to the base and the other end disposed in close proximity to a portion of the elastic member. The tension actuator may deform rotationally the portion of the elastic member so as to enforce torsion moment when the tension actuator is activated. The tension actuator may be a piezoelectric element. 
         [0016]    The engine control unit may control the tension actuator in a case that the engine speed is less than or equal to a predetermined speed so as to extend the tension actuator. A crank shaft position sensor may detect the phase angle of a crankshaft and send the detected phase angle to the engine control unit to calculate the engine speed. The predetermined engine speed may be 2000 RPM. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a cross-sectional view of a variable tensioner according to an exemplary embodiment of the present invention. 
           [0018]      FIG. 2  is a cross-sectional view taken along the line II-II in  FIG. 1 . 
           [0019]      FIG. 3  is a graph showing a rotational vibration according to an engine speed. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0020]    An exemplary embodiment of the present invention will hereinafter be described in detail with reference to the accompanying drawings. 
         [0021]    As shown in  FIG. 1  and  FIG. 2 , a variable tensioner according to an exemplary embodiment of the present invention includes a base  16 , an arm  10 , an elastic member  34 , an engine control unit  50 , and a crankshaft position sensor  60 . 
         [0022]    The base  16  has a cylindrical shape, an upper end thereof is open, and a lower end thereof is closed. The base  16  is fixed. In addition, the base  16  includes an interior circumference  30  and an exterior circumference  26 , and a protruding portion  46  that protrudes upwardly from the lower end thereof is formed between the interior circumference  30  and the exterior circumference  26 . 
         [0023]    The interior circumference  30  protrudes upwardly, and a first shaft insert hole  48  is formed substantially at a middle portion and in the longitudinal direction thereof. A boss insert groove  36  is formed between the interior circumference  30  and the protruding portion  46 , and an elastic member insert recess  32  is disposed between the interior circumference  30  and the exterior circumference  26 . In addition, an elastic member fixing groove  38  is formed at a lower portion of the elastic member insert recess  32 , and one end  40  of the elastic member  34  is fixed to the elastic member fixing groove  38  of the base  16 . 
         [0024]    As shown in  FIG. 2 , a tension actuator insert groove  42  is formed in the elastic member fixing groove  38 , and a tension actuator  44  is mounted in the tension actuator insert groove  42 . 
         [0025]    The tension actuator  44  controls tension of a belt by controlling elastic force of an elastic member  34 . The tension actuator  44  is provided with two ends, wherein one end thereof is fixed to the tension actuator insert groove  42  of the base  16  and the other end thereof is disposed in close proximity to the elastic member  34 . In addition, the tension actuator  44  is electrically connected to and is controlled by the engine control unit  50 . The tension actuator  44  may be a piezoelectric element, and the engine control unit  50  controls operation of the tension actuator  44  by applying current to the tension actuator  44 . Therefore, in an exemplary embodiment of the present invention, if the engine control unit  50  applies the current to the tension actuator  44 , the tension actuator  44  is extended and pushes substantially the one end of the elastic member  34  so as to strengthen the elastic force and thus pull the elastic member  34  thereof as explained later in detail. 
         [0026]    Referring to  FIG. 1 , the arm  10  includes a boss  14  and a mounting portion  12 , and the boss  14  and the mounting portion  12  are integrally formed with each other. 
         [0027]    The boss  14  has a cylindrical shape, an upper portion thereof is closed, and a lower portion thereof is open. In addition, the boss  14  includes an interior circumference  28  and an exterior circumference  24 , and the elastic member insert recess  32  is formed between the interior circumference  28  and the exterior circumference  24 . A second shaft insert hole  47  corresponding to the first shaft insert hole  48  is formed substantially at a middle portion of the boss  14  in the longitudinal direction thereof, and a shaft  49  is inserted through the first and second shaft insert holes  48  and  47  such that the boss  14  is rotatably connected to the base  16 . 
         [0028]    The exterior circumference  24  of the boss  14  protrudes downwardly and contacts the exterior circumference  26  of the base  16 . The interior circumference  28  of the boss  14  protrudes downwardly and a lower portion of the interior circumference  28  is inserted in the boss insert groove  36  of the base  16 . The interior circumference  28  of the boss  14  is slidably coupled to the boss insert groove  36  of the base  16 . 
         [0029]    A pulley  18  is coupled to the mounting portion  12  by a bolt  20 , and a bearing  22  is interposed between the pulley  18  and the mounting portion  12 . Therefore, the pulley  18  can rotate relative to the mounting portion  12 . The belt is mounted on the pulley  18  such that the pulley  18  rotates together with a crankshaft (not shown). Furthermore the bolt  20  is offset from the shaft  49  with a predetermined distance. 
         [0030]    However, in a case that tension of the belt is too strong, the frictional force of the belt may increase and friction loss may also increase and if the tension of the belt is too weak, slip of the belt may occur and power delivery efficiency may be deteriorated. To solve such problems, the position of the pulley  18  can be regulated so as to control the tension of the belt as explained hereinafter. 
         [0031]    In an exemplary embodiment of the present invention, the elastic member  34  is wound around the interior circumference  28  of the boss  14  and the protruding portion  46  of the base  16  in the elastic member insert recess  32  formed by the boss  14  and the base  16 . The one end  40  of the elastic member  34  is fixed to the base  16  in the elastic member fixing groove  38 , and the other end  41  thereof is fixed to the boss  14  of the arm  10 . Since the base  16  is fixed but the boss  14  can rotate relative to the base  16  around the shaft  49 , the elastic member  34  elastically supports rotation of the arm  10  with torsion moment when the elastic member  34  is deformed by the torsion actuator  44 . 
         [0032]    The crankshaft position sensor  60  is mounted at the crankshaft (not shown), and detects phase angle of the crankshaft and transmits a signal corresponding thereto to the engine control unit  50 . The engine control unit  50  calculates an engine speed from a change in the phase angle of the crankshaft detected by the crankshaft position sensor  60 . Based on the calculated engine speed, the engine control unit  50  electrically connected to the tension actuator  44  applies the current thereto to control the position of the pulley  18 . 
         [0033]    The position of the pulley  18  can be controlled by rotation of the boss  14  since the bolt  20  is offset from the shaft  49  with a predetermined distance and the boss  44  and the mounting portion  12  is integrally formed. 
         [0034]    Operation of the variable tensioner according to an exemplary embodiment of the present invention will be described in detail. 
         [0035]      FIG. 3  is a graph showing a rotational vibration according to an engine speed. 
         [0036]    As shown in  FIG. 3 , it can be known that rotational vibration generated at the engine is large in a case in which the engine speed is less than or equal to 2000 RPM. Therefore, it can be also known that the tension of the belt must be strong in a case in which the engine speed is less than or equal to 2000 RPM. 
         [0037]    The engine control unit  50  receiving the signal corresponding to the phase angle of the crankshaft from the crankshaft position sensor  60  calculates the engine speed from the change in the phase angle of the crankshaft. 
         [0038]    If the engine speed is less than or equal to a predetermined speed (e.g., 2000 RPM), the engine control unit  50  applies the current to the tension actuator  44  so as to extend it. In this case, the extended tension actuator  44  pushes a portion of the one end  40  of the elastic member  34  such that the elastic force of the elastic member  34  increases. Further since the base  16  is fixed but the boss  14  can rotate relative to the base  16  around the shaft  49 , the elastic member  34  rotates clockwise in  FIG. 2  as the elastic member  34  is deformed by the tension actuator  44 . The rotation of the boss  14  is converted into a pivotal rotation of the pulley  18  since the bolt  20  is offset from the shaft  49  with a predetermined distance and the boss  44  and the mounting portion  12  is integrally formed. As a result, the pivotal rotation of the pulley  18  pulls the belt (not shown) and thus the tension of the belt increases. 
         [0039]    If the engine speed is greater than the predetermined rotation speed, the engine control unit  50  does not apply the current to the tension actuator  44  and thereby the tension actuator  44  is restored to an original length thereof. Therefore, the elastic member  34  also is restored to the home position by the elastic force and torsion moment thereof stored as it was deformed. As a result the tension of the belt decreases due to the restoration of the elastic member  34 . 
         [0040]    As described above, the engine control unit  50  controls the tension of the belt by controlling the current applied to the tension actuator  44  according to the engine speed. 
         [0041]    According to the present invention, friction loss may be reduced and fuel mileage may improve as a consequence of the tension of a belt being increased in a case of low engine speed where rotational vibration is strong and the tension of the belt being decreased in a case of high engine speed where the rotational vibration is weak. 
         [0042]    While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.