Abstract:
An actuator is used for controlling an intake valve lift of an automotive engine. A control shaft is joined with a transmission device on its one end side, and is joined with a valve lift controller on the other end side. The control shaft is arranged perpendicularly to a spindle of a motor. Besides, the transmission device includes a drive cam internally. Thus, the actuator is reduced in size in a longitudinal direction of the control shaft regardless the length of the motor. When the motor rotates, the control shaft reciprocates in accordance with a cam profile of the drive cam. The intake valve lift can be precisely controlled by defining the cam profile, especially in a rotation range of the drive cam corresponding to the idling operation of the engine.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application is based on Japanese Patent Application No. 2002-315588 filed on Oct. 30, 2002 the disclosure of which is incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   The present invention is related to an actuator for manipulating a controlled object in accordance with an axial position of a control shaft while transferring a rotation of a motor to a reciprocating motion of the control shaft, and a valve lift control system using the actuator.
     1. Related Art   

   In an automotive engine, an actuator is used for manipulating a controlled object in accordance with an axial position of a control shaft. 
   According to a variable valve mechanism for an internal combustion engine in U.S. Pat. No. 6,425,357 (JP-A-2001-263015), an intermediate driving mechanism is movably supported on its axis independent of the axis of a valve cam. The intermediate driving mechanism includes a control shaft, a valve cam related part and intake valve related parts. The intermediate driving mechanism is provided for transmitting a driving force of the valve cam to an intake valve. A reciprocating motion of the control shaft is transferred into a rotation motion of the valve cam related part and a rotation motion of the intake valve related parts. Accordingly, the relative lift-difference of the valve cam related part with the intake valve related parts are controlled based on the axial position of the control shaft. Here, controlled object can be an exhaust valve instead of the intake valve. 
   However, the axial position of the control shaft is controlled by adjusting oil pressure in a pressure chamber. The pressure chamber is provided on one end side of the control shaft for reciprocating the control shaft. In this structure, a piston for receiving oil pressure from the pressure chamber and a housing for forming a pressure chamber are provided so as to control differential pressure between the front side of the piston and the rear side of the piston. Accordingly, controllability of a position and response is inferior. 
   Here, an electric actuator can be used instead of a hydraulic actuator. However, a length of the electric actuator may be elongated in the axial direction of the control shaft depending on an arrangement of a motor and the control shaft. 
   SUMMARY OF THE INVENTION 
   In view of the foregoing problems, it is an object of the present invention to propose an actuator having a small-sized body in the axial direction of the control shaft, and a valve lift controller using the actuator. 
   A spindle of a motor for rotating a drive cam is arranged perpendicularly to a control shaft in the actuator. Therefore, the length of the motor does not directly affect the length of the actuator in the axial direction of the control shaft. Thus, the length of the actuator can be shortened. 
   A spur gear is coaxially provided with the drive cam for rotating the drive cam. Two tabs are formed on both flat surfaces of the spur gear. Stoppers are separately provided on both sides of the spur gear corresponding to the positions of the convexities for locking the spur gear. Therefore, interference between the stoppers and convexities is avoided. 
   A transmission device including the drive cam is joined with the control shaft for transferring a rotation of the inner drive cam into a reciprocating motion of the control shaft. The transmission device is arranged so that the axis of the inner drive cam is perpendicular to the axis of the control shaft while the transmission device and the control shaft overlap each other. Therefore, a length of a joining section between the control shaft and the transmission device is shortened in the axial direction of the control shaft. 
   The rotation angle of the drive cam is detected by an angular sensor using a Hall element. The detection is performed without contacting, so that reliability of the angular sensor is enhanced and a life of the angular sensor can be extended. 
   An electromagnetic clutch is included in the actuator so as to prohibit rotation of the motor for fixing a position of the control shaft when the electromagnetic clutch is de-energized. Therefore, power consumption of the motor can be reduced if the electromagnetic clutch is used for an actuator in which a total stopping period of the controlled object is longer than a total moving period during its operation. 
   When an engine is idling, the angle of the drive cam is defined to be in an angle range around one end of its rotation range. Here, the rotation of the drive cam is equivalent to the lift of the intake valve. 
   A rate of change of the lift (lift change rate) of the intake valve while the drive cam rotates around the end of the rotation range is defined to be smaller than a lift change rate of the intake valve while the drive cam rotates in a range different from the range around the end of the rotation range. Accordingly, cam lift change rate of the drive cam decreases with respect to a rotation degree of the drive cam. Subsequently, a displacement amount of the control shaft in its reciprocating direction is reduced with respect to the rotation degree of the drive cam. Here, a displacement of the control shaft (i.e., lift of the intake valve) is detected by sensing the rotation angle of the drive cam. 
   Accordingly, the detection accuracy of a displacement of the control shaft is enhanced when the engine is idling. Thus, axial position of the control shaft can be precisely controlled, so that the lift of the intake valve can be precisely controlled. Here, the controlled object can be the exhaust valve instead of the intake valve. 
   The control shaft receives reactive force from a controlled object such as the intake valve or the exhaust valve when the control shaft controls the lift of the intake valve or the exhaust valve. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings, in which: 
       FIG. 1  is a partially cross-sectional perspective view showing an actuator according to a first embodiment of the present invention; 
       FIG. 2  is a perspective view showing a joint section between a control shaft and a transmission device according to the first embodiment; 
       FIG. 3  is a side view from the arrow III in  FIG. 2  showing the transmission device; 
       FIG. 4  is a partially cross-sectional perspective view showing convexities formed on a cam gear; 
       FIG. 5  is a waveform chart showing a load applied to a drive cam from a lift controller; 
       FIG. 6  is a graph showing a relation among a cam angle, a cam lift of a drive cam and torque applied to the drive cam; 
       FIG. 7  is a schematic side view showing a direction of a load applied to the drive cam and arm length of the drive cam; and 
       FIG. 8  is a graph showing a relation between a cam angle and a cam lift of a drive cam; 
       FIG. 9  is a partially cross-sectional perspective view showing an actuator according to a second embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   (First Embodiment) 
   As shown in  FIG. 1 , an actuator  10  is used for actuating a valve lift controller  38  for an internal combustion engine, for example. Here, the valve lift controller  38  controls relative lift-difference between an intake valve  35  and a valve cam  36  of the engine in accordance with an axial position of a control shaft  30 . The valve cam  36  opens and closes the intake valve  35 . 
   The actuator  10  includes a motor  20 , the control shaft  30 , a transmission device  40 , a drive cam  52  (shown in  FIG. 3 ), an angular sensor  60 , an electronic control unit (ECU)  80 , and an electronic drive unit (EDU)  82 . The motor  20  is a DC motor including a rotor  22  having a winding coil and magnet  26  surrounding an outer periphery of the rotor  22 . A motor gear  28  is provided on the axial end of a spindle  24  of the motor  20 . The spindle  24  rotates with the rotor  22 . 
   The control shaft  30  is joined with a supporting frame  41  of the transmission device  40  on its one end, and is joined with the valve lift controller  38  on the other end. The axis of the control shaft  30  is perpendicular to the axis of the spindle  24  of the motor  20 . 
   As shown in  FIG. 2  and  FIG. 3 , a coupling  32  is formed at one end of the control shaft  30 , and is fitted with a joint  42 . The coupling  32  is joined with the joint  42  of the supporting frame  41  so that the coupling  32  and the joint  42  fit and overlap each other. A joint section between the coupling  32  and the joint  42  is coupled by a clip  46  so as to be fixed each other. 
   The transmission device  40  includes the box-shaped supporting frame  41  and a roller  44 . A cam shaft  50  and the drive cam  52  are rotatably accommodated in the supporting frame  41 . The roller  44  is rotatably supported by the supporting frame  41  on the opposite side of the control shaft  30  with respect to the drive cam  52 . The drive cam  52  is rotated with the cam shaft  50 , and contacts the roller  44  sliding each other. The structure of the transmission device  40  is reduced in size in the axial direction of the control shaft  30  compared with a structure in which the roller  44  and the drive cam  52  are provided outside of the transmission device  40 . 
   Referring back to  FIG. 1 , cam gears  54 ,  56  are provided on both ends of the cam shaft  50 . The cam gear  54  engages with the motor gear  28 . The motor gear  28  and the cam gear  54  are spur gears, and are used as reduction gears. 
   As shown in  FIG. 4 , a tab  54   a  is formed on one end face of the cam gear  54 . A shaft  70  is provided on the housing of the motor  20 , and is used as a stopper. A rotation of the motor  20  stops when the tab  54   a  is received by the shaft  70 . Another tab  54   b  is formed at the second end face of the cam gear  54  on the opposite side of the tab  54   a  with respect to an axial direction of the cam gear  54 . Another shaft  72  is provided on the housing of the motor  20 , and is used as a stopper as well as the shaft  70 . A rotation of the motor  20  stops when the tab  54   b  is received by the shaft  72 . Here, the two shafts  70 ,  72  are separately provided so that interference between the shafts  70 ,  72  is avoided. 
   Both tabs  54   a ,  54   b  are locked by both shafts  70 ,  72  respectively, so that a rotation range of the drive cam  52  is defined within approximately 300°. First end of the rotation range of the drive cam  52  substantially corresponds to a lift of the intake valve  35  when the engine is idling. 
   Referring to  FIG. 1  again, an angular sensor  60  has a sensing gear  62  engaging with the cam gear  56 . A sensor object (not shown) is coaxially provided with the sensing gear  62 . The angular sensor  60  detects the rotation angle of the sensor object using a non-contacting Hall element so as to detect a rotation angle of the cam shaft  50 . Here, an angular sensor  60  does not contact any object, so that reliability of the angular sensor  60  is enhanced and a life of the angular sensor can be extended. A range of the rotation angle of the sensor object is restricted within 90° by setting gear ratio between the cam gear  56  and the sensing gear  62 . Therefore, the range of the rotation angle of the sensor object is in a range where the Hall element can detect the rotation angle of the rotation member. 
   The ECU  80  inputs detection signal of the angular sensor  60 , accelerator position signal and so on, and outputs control signals to the EDU  82  so as to rotate the motor  20 . 
   Next, operation of the actuator will be now described. 
   When the motor  20  rotates, torque of the motor  20  is transmitted to the cam shaft  50  and the drive cam  52  (shown in  FIG. 3 ) via the motor gear  28  and the cam gear  54 . 
   As shown in  FIG. 3 , when the drive cam  52  rotates, the supporting frame  41  linearly reciprocates in the axial direction of the control shaft  30 . The roller  44  supported by the supporting frame  41  rolls while sliding on the surface of the drive cam  52  so that the supporting frame  41  can move smoothly. The valve lift controller  38  controls relative lift-difference of the intake valve  35  with respect to the valve cam  36  in accordance with an axial position of the control shaft  30  which is reciprocated corresponding to a cam profile of a cam face  53  of the drive cam  52 . 
   When the control shaft  30  controls relative lift-difference of the intake valve  35  with respect to the valve cam  36 , the control shaft  30  receives a reactive force from the intake valve  35 . The reactive force is shown as a load  200  in  FIG. 5 . The reactive force (load) changes while the drive cam  52  is rotated from the one end (first end) of its rotation range toward the other end (second end) of its rotation range, and the drive cam is stopped on the second end after approximately 0.6 sec. Each peak of the load  200  corresponds to each lift of one intake valve  35  of each of four cylinders. The load applied to the control shaft  30  from the valve lift controller  38  increases as the drive cam  52  rotates from the first end of its rotation range to the second end of its rotation range. The load decreases when the drive cam  52  is rotated to the second end of its rotation range, because the drive cam  52  does not receive reactive force from the intake valves  35  while the drive cam  52  is rotating. 
   When the drive cam  52  is stopped at the second end of its rotation range, the drive cam  52  receives a load higher than a load when the angle of the drive cam  52  is at the first end of its rotation range. 
   As shown by a straight line  210  in  FIG. 6 , a cam profile of the drive cam  52  is defined so that the cam lift linearly changes with respect to the cam angle of the drive cam  52 . As shown in  FIG. 7 , an arm length δ of the drive cam  52  is defined as the distance between a normal line  102  of the drive cam  52  and the center of the cam shaft  50 . In the profile shown with the straight line  210  in  FIG. 6 , an arm length δ of the drive cam  52  is substantially constant while the drive cam  52  rotates from the first end toward the second end of its rotation range. When the drive cam  52  receives a load that increases while the drive cam  52  rotates from the first end toward the second end of its rotation range, torque applied to the drive cam  52  from the valve lift controller  38  linearly increases as shown by a straight line  212  in  FIG. 6 . 
   On the other hand, when the drive cam  52  has another cam profile as shown by a curved line  214  in  FIG. 6  where the curved line  214  is parabolic and is convex on its upper side, a rate of change of the lift (lift change rate) of the drive cam  52  once increases, subsequently decreases while the drive cam  52  rotates from the first end toward the second end of its rotation range. Referring back to  FIG. 7 , the normal line  102  approaches the axis of the drive cam  52  while the drive cam  52  is rotated from the first end of the rotation range toward the second end, and accordingly, the arm length of the drive cam  52  is shortened. 
   The load F works along a normal line  102  with respect to a tangent line  100  of the cam face  53  where the load F works. Here, the load F increases while the drive cam  52  rotates from the first end toward the second end of its rotation range. That is, the arm length δ of the drive cam  52  decreases simultaneously the load F applied to the drive cam  52  increases. 
   The torque applied from the valve lift controller  38  to the drive cam  52  is calculated as a product Fδ which is the product of the load F applied to the drive cam  52  and the arm length δ of the drive cam  52 . 
   Here, the load F decreases while the arm length δ increases, Therefore, the product of the load F and the arm length δ (i.e., the torque applied to the control shaft  30  from the intake valve  35 ) can be substantially constant over the rotation range of the drive cam  52 . 
   Therefore, the maximum torque applied to the drive cam  52  can be reduced. Here, torque required for the motor  20  is determined based on the maximum torque which the drive cam  52  receives from the valve lift controller  38 . Therefore, the torque needed to the motor  20  can be reduced. Thus, the motor can be sized small. 
   The rotation angle of the drive cam  52  is equivalent to the lift of the intake valve  35 . The angle of the drive cam  52  when the engine is idling is in a range where around the first end of the rotation range. 
   As shown by a line  216  in  FIG. 8 , a cam lift change rate can be defined to be small in the range around the first end of the rotation range, subsequently the cam lift change rate becomes large in a rotation range beginning at the end of the range around the first end and progressing toward the second end. In this case, a cam lift change rate of the drive cam  52  is reduced with respect to a rotation degree of the drive cam  52  around the first end of the rotation range. Accordingly, displacement amount of the control shaft  30  in its reciprocating direction is reduced while the drive cam  52  rotates around the first end. Therefore, lift change rate of the intake valve  35  is reduced with respect to the rotation degree of the drive cam  52 . 
   The sensor  60  detects the lift change rate of the intake valve  35  by detecting the rotation degree of the drive cam  52 , and the sensitivity of the angular sensor  60  is enhanced when the angle of the drive cam  52  is in the range around the first end of the rotation range. Therefore, the lift of the intake valve  35  can be precisely controlled when the engine is idling in that the rotation speed of the engine is low. 
   The drive cam  52  may have another cam profile as shown by a curved line  218  in  FIG. 8 , where the curved line  218  is parabolic and is convex on its upper side, the lift change rate is small around the first end of the rotation range compared with that in the rotation range different from around the first end. In this case, the lift of the intake valve  35  can be precisely controlled when the engine is idling. Further, a maximum torque applied to the drive cam  52  can be reduced. 
   (Second Embodiment) 
   As shown in  FIG. 9 , an electromagnetic clutch  90  is provided on the motor  80  on the opposite end side of the motor gear  28  with respect to the spindle  24 . The electromagnetic clutch  90  includes a rotating plate  91 , a stator  92 , a coil  94 , an armature  96  and a blade spring  97 . The rotating plate  91  is press-inserted onto the spindle  24  so as to be rotated with the spindle  24 . The armature  96  is pressed onto the rotating plate  91  by the blade spring  97  when the coil  94  is de-energized. The blade spring  97  is partly locked by the stator  92 . The rotation of the spindle  24  is restricted by friction between the armature  96  and the rotating plate  91  when the armature  96  is pressed onto the rotating plate  91  by the blade spring  97 . That is, a rotation of the motor  80  is stopped when the coil  94  is de-energized. The armature  96  is pulled toward the stator  91  against pressing force of the blade spring  97  when the coil  94  is energized, so that the armature  96  is departed from the rotating plate  91 . Thus, the spindle  24  is released from the restricted condition. 
   When the actuator  10  is used for actuating a valve lift controller, a period while the control shaft  30  is stopped is longer than a period while the control shaft  30  is reciprocating. That is, a period while the lift of the intake valve  35  is fixed is longer than a period while the lift of the intake valve  35  is being changed. When the coil  94  of the electromagnetic clutch  90  is de-energized, a rotation of the motor  80  is stopped so that reciprocating motion of the control shaft  30  is stopped, subsequently the lift of the intake valve  35  is fixed. While the lift of the intake valve  35  is fixed, electrical power supply is not needed. Therefore, electrical power supply for controlling the lift of the intake valve  35  can be reduced. 
   A one way clutch and a friction plate can be used for a clutch mechanism of the electromagnetic clutch. Here, the one way clutch is rotatable in its both rotation directions while it is energized. On the other hand, the one way clutch is rotatable in one direction, where such as opposite direction of reactive force of a lift control shaft of the air intake valve, while it is de-energized. The friction plate is rotatable in its both directions while it is energized. On the other hand, friction plates are connected for generating friction, which is less than driving power of the motor  80  in its both directions, while it is de-energized. In this case, the driving power of the motor  80  can rotate even if the clutch is connected, while decreasing power supply to the motor  80  when the lift control shaft of the air intake valve is fixed. If this friction plate is used, the friction plate can be constantly connected without using the electromagnetic clutch. 
   The drive cam  52  can directly manipulate the supporting frame  41  for reciprocating the control shaft  30  without using the roller  44 . Additionally, the drive cam  52  can directly manipulate the control shaft  30  while sliding each other. 
   The actuator  10  can be used for a valve lift control apparatus for controlling a lift of an exhaust valve instead of a lift of an intake valve  35 . 
   The actuator  10  can be used for any other structures, in that manipulation amount is controlled in accordance with an axial position of the control shaft of the actuator according to the present invention. 
   Other various changes and modifications are to be understood as being within the scope of the present invention as defined by the appended claims.