Patent Publication Number: US-7219653-B2

Title: Electronic control throttle body

Description:
TECHNICAL FIELD 
   This invention relates to an electronically controlled throttle body which is driven by a motor. 
   BACKGROUND ART 
     FIG. 7  is a sectional view showing a structure of a conventional electronically controlled throttle body. The throttle body  1  has a circular bore  2   a  at the center of a main body  2 , and a circular-disc-shaped throttle valve  3  is disposed therein. The throttle valve  3  is fixed with two screws  5 ,  5  to a throttle shaft  4  which pierces the bore  2   a , and is free to rotate from the position to close the bore  2   a  to a full-open position being parallel to the center axis of the bore  2   a . The rotating range is 90 degrees at the maximum, and no more range is needed. 
   A motor  6  is integrally attached to the throttle body  1 , and the shaft of the motor  6  is integral with the throttle shaft  4 . Here, by changing the power supply direction, the throttle shaft  4  turns in the opening direction or the closing direction. 
   A torque motor is adopted as the motor  6 . In general, a torque motor has characteristics of having excellent responsiveness and high reliability since there is no contact. The motor  6  of this kind generally has a rotor to which a ring-shaped magnet is fixed, and controls a rotating position in accordance with changes of magnetic flux distribution formed by a coil and a magnetic path. 
   As mentioned above, with the throttle body  1 , the rotating range of the throttle valve to open and close the bore  2   a  is 90 degrees at the maximum. For example, when an inclination of about 5 degrees is set at idling, the rotating range becomes about 85 degrees. Consequently, the rotating range of the throttle valve  3  is 90 degrees or less. To drive and control within this range, the magnet is not needed over the whole circumference. In addition, the magnet used for the rotor is expensive since the magnetic flux density has to be high. 
   Therefore, a torque motor  10  utilizing segment type magnets was devised, as shown in  FIG. 8 . A rotor  11  of this figure is connected directly to the throttle shaft  4  in  FIG. 7 . About two thirds of the circumference of the rotor  11  is covered by two segment type magnets  12 ,  12 . Since the magnet is downsized by changing from a ring-shape to a segment type, the cost can be reduced. An air-gap is formed between the circumference face of the magnets  12 ,  12  and a yoke  13 . Another air-gap is formed between the circumference face of the magnets  12 ,  12  and a core  14 . A coil  15  is disposed at the core  14 . 
   Parts of the yoke  13  corresponding to the magnet  12 ,  12  are first and second magnetic sides  13   a ,  13   b  whose top end faces are arc-shaped. Similarly, a part of the core  14  corresponding to the magnet  12 ,  12  is a third magnetic side  14   a  whose top end face is arc-shaped. Then, these three magnetic sides  13   a ,  13   b ,  14   a  are located on the same arc. Further, a stator is constructed by the yoke  13 , the core  14  and the coil  15 , and a moving portion is constructed by the rotor  11  and the magnets  12 ,  12 . 
   When electric current is supplied to the coil  15 , the rotor  11  rotates around the axis O, and the throttle valve  3  which is directly connected to the rotor  11  opens and closes. The rotating direction of the rotor  11  changes in accordance with the direction of the electric current which passes through the coil  15 . With the above-mentioned torque motor  10 , the rotating angle of the rotor  11  is about 120 degrees, because the magnets  12 ,  12  cover about two thirds of the circumference of the rotor  11 . 
   However, as mentioned above, since the rotating angle of the throttle shaft  4  is approximately between 85 degrees and 90 degrees, the use of the torque motor  10  in  FIG. 8  is not efficient. 
   Further, the above-mentioned torque motor  10  has a characteristic that the torque generated at both ends is lower than the torque generated at the center of the rotating range. This seems to be caused by magnetic circuit problems, such as the magnetizing angle of the magnet, the magnetic saturation of the magnetic poles, and so on. On the contrary, in a normal usage situation, the throttle valve  3  is operated with approximately equal torque from the full-close position to the full-open position. Therefore, it is desirable to obtain a flat torque characteristic. Further, considering freezing in the winter, it is more desirable that the torque at the full-close position is the maximum torque. 
   For efficiency, adopting a speed reduction mechanism which transmits the rotating angle of the rotor  11  to the throttle shaft  4  via a speed reducer to reduce the angle has been considered. However, having a separate speed reducing mechanism is not desirable since it increases the size of the throttle body. Further, the cost increases because the number of parts increases. 
   On the other hand, as shown in  FIG. 9 , adopting a linear type torque motor  20  to obtain a flat torque characteristic has been considered. The torque motor  20  is disclosed in patent application No. 2000-4107 which was previously submitted by the same applicant as this application. The torque motor  20  shown in  FIG. 9  has a first stator  21  shaped almost like a rectangle, a second stator  22  shaped like three sides of a shallow rectangle which is disposed with a gap  23  to the first stator  21 , an electromagnetic coil  24  which is disposed between the first stator  21  and the second stator  22 , a slider  25 , and two magnetized members  26 ,  27  which are attached to the slider  25 . The magnetized members  26 ,  27  are plate-shaped magnets which have magnetic poles in the thickness direction (the vertical direction in  FIG. 9 ), and disposed so that the magnetic polarities of the magnetized members  26 ,  27  which are adjacent to each other are opposite to each other. 
   The first stator  21  has two magnetic sides  21   a ,  21   b , and the second stator  22  has one magnetic side  22   a . These three magnetic sides are located in a line, and a gap  28  is maintained between the magnetized members  26 ,  27  of the slider  25  and the magnetic sides  21   a ,  21   b ,  22   a.    
   With the linear type torque motor  20 , a stator is structured by the first stator  21 , the second stator  22  and the electromagnetic coil  24 , and a moving portion is structured by the slider  25  and magnetized members  26 ,  27 . Then, in accordance with the direction of electric current to the electromagnetic coil  24 , the slider moves in both directions shown by the arrow. 
   Here, the actuating force applied to the slider  25  is almost constant no matter where the slider  25  is positioned. Therefore, by transmitting the movement of the slider  25  to the throttle shaft  4 , the rotating torque which is applied to the throttle shaft  4  can be almost constant. 
   However, to convert linear motion of the slider  25  to rotating motion of the throttle shaft  4 , separate parts are needed and the structure is complicated. 
   The present invention is devised in consideration of the above-mentioned facts, and the object is to provide an electronically controlled throttle body which can efficiently transmit the motion of a torque motor, including a linear torque motor, to a throttle shaft with a simple structure. 
   SUMMARY OF THE INVENTION 
   In order to achieve the above-mentioned object, the electronically controlled throttle body of the present invention comprises a torque motor which has a stator and a moving portion, and a throttle shaft which is rotated by the torque motor, wherein a plurality of gear teeth is formed at the moving portion, and a gear which mates with the plurality of gear teeth is disposed at the throttle shaft. 
   Further, it is possible to adopt a structure such that the stator has three magnetic sides which are disposed approximately on a same locus, the moving portion is movable in two directions within a specific range having two magnetized members which face the three magnetic sides of the stator, and the plurality of gear teeth of the moving portion is formed at the moving portion where the magnetized portion is not disposed. 
   Here, the moving portion can be formed by laminating a plurality of thin plates of ferromagnetic material. It is also possible to adopt a structure such that the three magnetic sides are located approximately in a line, the moving portion is a slider which reciprocates on a line, and the plurality of gear teeth is a rack which is formed at the slider. It is also possible to adopt a structure such that the three magnetic sides are located approximately on an arc, and the moving portion is a rotor which is rotatable in a range of less than 360 degrees. Here, both the plurality of gear teeth of the rotor and the gear of the throttle shaft can be non-circular gears. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a sectional view of an electronically controlled throttle body structure of the first embodiment of the present invention in which a linear type torque motor is adopted as driving means. 
       FIG. 2  is a view from A in  FIG. 1  showing a stator, a moving portion and its surroundings. 
       FIG. 3  is an exploded perspective view showing around a slider and a magnetized member. 
       FIGS. 4(   a ) and  4 ( b ) show a second embodiment of the present invention utilizing a torque motor which has a rotor as a moving portion.  FIG. 4  ( a ) corresponds to  FIG. 2  of the first embodiment, and  FIG. 4(   b ) corresponds to  FIG. 1  of the first embodiment. 
       FIG. 5  is an exploded perspective view showing a rotor and magnetized members. 
       FIG. 6  explains how to determine pitch curve shapes of a non-circular driving gear and a driven gear. 
       FIG. 7  is a sectional view showing a structure of a conventional electronically controlled throttle body. 
       FIG. 8  shows a structure of a conventional torque motor utilizing segment type magnets. 
       FIG. 9  shows a structure of a conventional linear type torque motor. 
   

   BEST MODE FOR CARRYING OUT THE INVENTION 
     FIG. 1  and  FIG. 2  show the first embodiment of the present invention.  FIG. 1  is a sectional view of an electronically controlled throttle body structure in which a linear type torque motor is adopted as driving means.  FIG. 2  is a view from A in  FIG. 1  showing a stator, a moving portion and their surroundings. 
   With the structure of the linear torque motor  20  in these figures, the same numerical note is given to the same part in  FIG. 9 . A slider  25  of the linear type torque motor  20  has guides  25   a ,  25   a  at both sides which are in rolling contact with rollers  29 ,  29  so as to maintain a gap  28  (see  FIG. 9 ). 
   On the opposite side of magnetized members  26 ,  27  of the slider  25 , a rack  25   b  is formed as a plurality of gear teeth. A gear  30  which mates with the rack  25   b  is fixed to a throttle shaft  4 . 
     FIG. 3  is an exploded perspective view showing around the slider  25  and the magnetized members  26 ,  27 . The slider  25  is constructed by laminating a plurality of plates of ferromagnetic material, such as steel plates. When each thin plate is formed by press working, namely, by being cut out of a base thin plate, the rack  25   b  can be formed simultaneously. Therefore, gear cutting is not needed, and the rack  25   b  can be formed easily. 
   The slider  25  reciprocates within the movable range of the linear type torque motor  20 . Since the rack  25   b  is mated with the gear  30 , the throttle shaft  4  rotates. Here, when the radius of the gear  30  is arranged so that the movable range of the slider  25  fully overlaps the rotating range of the throttle shaft  4 , the whole movable range of the linear type torque motor  20  can be utilized effectively, and waste can be avoided. Since the throttle shaft  4  rotates only up to 90 degrees, the gear  30  can be a sector gear. 
   As explained above, with the aforementioned embodiment, the linear motion of the linear type torque motor  20  can be converted to the rotating motion of the throttle shaft  4  with a very simple structure, and the linear type torque motor capacity can be fully used. 
     FIGS. 4(   a ) and  4 ( b ) show a second embodiment of the present invention utilizing a torque motor  10  which has a rotor as a moving portion.  FIG. 4  ( a ) corresponds to  FIG. 2  of the first embodiment, and  FIG. 4(   b ) corresponds to  FIG. 1  of the first embodiment. The torque motor  10  has the same structure as explained in  FIG. 8 . While the throttle shaft  4  is directly connected to the rotor  11  in the prior art, the throttle shaft  4  is disposed separately from the shaft  32   a  of the rotor  32  in this embodiment. 
     FIG. 5  is an exploded perspective view showing around a rotor  32  and magnetized members  12 ,  12 . The rotor  32  is constructed by laminating a plurality of thin plates of ferromagnetic material such as steel plates, and the shaft  32   a  of the rotor pierces through the center holes thereof. At both sides of the rotor  32 , the two magnetized members  12 ,  12  are bonded and fixed. Then, a plurality of the gear teeth  32   b  is formed at the portion of the rotor where the magnetized members  12 ,  12  are not disposed. When the rotor  32  is cut out of a thin plate, the plurality of the gear teeth  32   b  is simultaneously cut out and formed. Here, in this embodiment, the plurality of the gear teeth  32   b  forms a sector gear being a part of an oval gear whose pitch circle is a vertically oriented oval  32   c.    
   A gear  33  which mates to the plurality of the gear teeth  32   b  is attached to the throttle shaft  4 . The gear  33  is a sector gear being a part of an oval gear whose pitch circle is a horizontally oriented oval  33   a.    
   By adopting these oval gears, the throttle shaft  4  can be rotated with approximately constant rotating torque from the full-close position to the full-open position of the throttle valve  3 . Further, by arranging the gear ratio appropriately, the whole movable rotating range of the torque motor  10  can be efficiently utilized for the range of the throttle valve  3  between the full-close position and the full-open position. Furthermore, the structure is simple because the only modification to the prior structure is the oval gears  32   b  and  33 . Furthermore, the manufacturing cost is low because the plurality of gear teeth  32   b  as one gear can be simultaneously formed when the rotor  32  is formed. 
   Although an oval gear is used in the above-mentioned embodiment, it is not limited to this, and various kinds of non-circular gears can be used. 
     FIG. 6  explains how to determine pitch curve shapes of a non-circular driving gear  41  and a driven gear  42 . As shown in this figure, the center of the driving gear  41  is O2, the center of the driven gear  42  is O1, and both pitch curves of the driving gear  41  and the driven gear  42  are in contact with each other at point P. Then, if the driving gear  41  rotates clockwise (plus direction) by a small angle d θ 2 , and the driven gear  42  rotates counter-clockwise (minus direction) by a small angle d θ 1 , so that point P 1  and point P 2  are to be in contact with each other, the following equations hold.
   r 1 +r 2=α  (1)   r 1 ·dθ 1 =r 2 ·dθ 2  (2) 
   On the condition that α=1, r1 and r2 are given by the equation (1) and equation (2) as follows.
 
 r 1=(− d θ2 /d θ1)/{1−( dθ 2 /dθ 1   )}  (3)
 
 r 2=1/{1−( d θ2/ d θ1)}  (4)
 
   Here, −d θ 2 /d θ 1  represents an angular velocity ratio. Therefore, giving the angular velocity ratio to the equation (3) and equation (4), the radiuses r1, r2 of pitch circles at that angle are determined. 
   Namely, the following equations hold between torque T(θ 2 ) of the torque motor  10  at the rotating angle θ 2 , and torque T(θ 1 ) which is transmitted to the driven gear. 
   
     
       
         
           
             
               
                 
                   
                     
                       
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   Given T(θ 2 ), r1 and r2 can be determined by the equations (3), (4) and (5). 
   Consequently, by drawing a diagram in which desired torque T(θ 1 ) is plotted for every opening θ 1  between full-close position and full-open position of the throttle valve  3 , the pitch curves of the driving gear  41  and the driven gear  42  are obtained in accordance with the diagram. 
   Accordingly, when non-circular gears such as the oval gears are used for the plurality of the gear teeth  32   b  as the driving gear  41 , and the gear  33  as the driven gear  42 , regarding the relations between the throttle shaft opening and the throttle shaft torque, it is possible, for example, that the shaft torque is maintained approximately constant regardless of the shaft opening, or it is also possible that the maximum torque is obtained at the full-close position where the maximum load may be applied. 
   In addition, as a matter of course, it is possible to adopt a circular gear instead of a non-circular gear, and reduce speed merely by the gear ratio. 
   INDUSTRIAL APPLICABILITY 
   As explained above, the electronically controlled throttle body of the present invention comprises a torque motor which has a stator and a moving portion, and a throttle shaft which is rotated by the torque motor, wherein a plurality of gear teeth is formed at the moving portion, and a gear which mates with the plurality of gear teeth is disposed at the throttle shaft. Therefore, by arranging the gear ratio appropriately, the whole operating range of the torque motor can be utilized for the rotating range of the throttle shaft, and the torque motor can be used efficiently. Further, by forming the plurality of the gear teeth at the moving portion, the increase of the number of parts is prevented, and the throttle body can be formed compactly. 
   Further, with the structure that the moving portion is formed by laminating a plurality of thin plates of ferromagnetic material, the plurality of gear teeth is formed simultaneously at the time when the moving portion is formed. Therefore, cost reduction can be achieved by decreasing machining process time. Further, since the thickness of the plurality of the gear teeth can be kept sufficient, the load applied to the gear which mates with the teeth is distributed. Consequently, the durability improves and the gear can be made of low-cost resin material. 
   With the structure having the three magnetic sides located approximately in a line, the moving portion is a slider which reciprocates on a line, and the plurality of gear teeth is a rack which is formed at the slider, the linear motion of the linear type torque motor can be converted to the rotating motion of the throttle shaft with a simple structure. 
   With the structure having the three magnetic sides located on an approximate arc, the moving portion is a rotor which is rotatable within the range of less than 360 degrees, and both the plurality of gear teeth of the rotor and the gear of the throttle shaft are non-circular gears, the desired driving torque can be obtained from the full-close state to the full-open state of the throttle valve.