FIELD OF THE INVENTION 
       [0001]    The present invention relates to an oven that has an adjustable effective heating space and particularly to an oven heating mechanism that provides external and manual stepless adjustment of the relative position of a heating tube assembly and foodstuff such that an effective heating space can be set according to foodstuff characteristics. 
       BACKGROUND OF THE INVENTION 
       [0002]    Baking and roasting food with a conventional oven to get satisfactory results usually is more difficult. This is caused by a number of constraints and drawbacks, notably: 
         [0003]    1. The heating space of the conventional oven is fixed. The oven with a smaller heating space can heat quickly but unevenly, and cannot roast foodstuff of a greater size. On the other hand, the oven with a larger heating space heats slower and results in wasting a great amount of electric power. 
         [0004]    2. The conventional oven often has a heating means consisting of one or more sets of fixed heating tubes. Adjustment stages and distances are greater, thus cannot fully meet cooking requirements of most people. 
         [0005]    3. In principle, the foodstuff of different characteristics requires different types of ovens. Trying to do this has to procure and prepare a number of different ovens. It incurs wastes of money and space. 
         [0006]    4. The conventional oven cannot be adjusted instantly according to different conditions of the foodstuff. It makes cooking with the oven less appealing and results in user&#39;s frustration. 
       SUMMARY OF THE INVENTION 
       [0007]    The primary object of the present invention is to overcome the problems and constraints of the conventional oven such as a limited heating area, fixed distance and limited heating modes by providing an oven with an adjustable effective heating space to offer multifunctional baking and roasting environments. 
         [0008]    In order to achieve the foregoing object, the invention adopts techniques as follow: an oven body with an adjustable effective heating space including a space control knob to provide external and manual control in a stepless fashion and control the position of an effective heating tube assembly located in the heating space relative to another fixed heating tube so that the adjustable effective heating space is formed. Users can directly adjust the effective heating space from outside whenever desired according to requirements and their judgments. Such a design also can save energy and meet a wide variety of baking and roasting requirements with a single product. 
         [0009]    The foregoing, as well as additional objects, features and advantages of the invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a perspective view of the invention. 
           [0011]      FIG. 2  is a front view of the space control knob. 
           [0012]      FIG. 3  is a schematic view of a rear space according to the invention, partly cut away. 
           [0013]      FIG. 4  is an exploded view of the effective heating tube assembly of the invention. 
           [0014]      FIG. 5  is a perspective view of the effective heating tube assembly of the invention. 
           [0015]      FIG. 6  is a fragmentary sectional view of the invention showing the relative position of the movable dock and the sliding track. 
           [0016]      FIG. 7  is a fragmentary sectional view of the invention showing the relative position of the movable detent plate and the sliding track. 
           [0017]      FIG. 8  is a schematic view of the invention in a condition of adjusting the heating assembly. 
           [0018]      FIG. 9  is a schematic view of the invention for adjusting the effective heating space. 
           [0019]      FIG. 10  is another schematic view of the invention for adjusting the effective heating space. 
           [0020]      FIG. 11  is a perspective view of the invention equipped with a hotdog rack. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]    Please refer to  FIGS. 1 ,  2  and  3 , an oven having an adjustable effective heating space according to the invention includes an oven body  1  and an effective heating tube assembly  2 . 
         [0022]    The oven body  1  has a case  13  on the surface, a space control knob  30  hinged on the case  13  and a scale  130  formed on the surface of the case  13  corresponding to the space control knob  30 . 
         [0023]    Also referring to  FIGS. 3 ,  6  and  7 , the case  13  has a side board  12  with a slot  120  formed in the center and a sliding track  121  at a lower side. The side board  12  divides the interior of the oven body  1  into a heating chamber  14  and a facility chamber  15 . The heating chamber  14  has a first heating tube  50   a  at one end. 
         [0024]    Referring to  FIGS. 4 and 5 , the effective heating tube assembly  2  includes a transmission assembly  3  and a lever assembly  4  located in the facility chamber  15 , and a heating assembly  5  located in the heating chamber  14 . 
         [0025]    The transmission assembly  3  includes the space control knob  30 , an axle  31 , a helical sleeve  32  and a movable dock  33 . The axle  31  has one end  311  run through the case  13  to couple with the space control knob  30  and another end  312  coupled with the helical sleeve  32 , and is clipped respectively by a fastening element  34  such as a latch clip close to two distal ends thereof inside the facility chamber  15  to form a fixed positioning. The helical sleeve  32  has a through hole  320  run through by the another end  312  of the axle  31  and positioned at another side of the facility chamber  15  through another fastening element  34 . The helical sleeve  32  has an external thread  321  on the outer side. The movable dock  33  has a lug  330  at an upper side with an aperture  331  formed thereon and an internal thread  332  at a lower side engageable with the external thread  321  of the helical sleeve  32 , and movable latch tenons  333  at another side corresponding to each other to be coupled with the sliding track  121  of the side board  12  (referring to  FIG. 6 ) and slidable thereon to prevent shaking during sliding of the movable dock  33 . 
         [0026]    The lever assembly  4  includes a main lever  40 , two secondary levers  41  and a linkage transverse rod  42 . The main lever  40  has a first screw hole  400  and a second screw hole  401  at two ends. The first screw hole  400  can be fastened to the aperture  331  of the lug  330  of the movable dock  33  through a fastening element  43  such as a screw. The two secondary levers  41  are coupled with two ends of the linkage transverse rod  42 , each has a screw hole  411  corresponding to the second screw hole  401  of the main lever  40  to be hinged together through another fastening element  43  such as a screw. Each of the secondary levers  41  also has a fastening hole  410  at an inner side close to the screw hole  411  and a sliding slot  412  at another end thereof. The linkage transverse rod  42  has a fastening groove  421  close to each of the two ends thereof to be wedged in by a fastening element  422  such as a latch clip at two sides of the fastening hole  410  after each end has run through the fastening hole  410  of the secondary lever  41  to form a secured positioning. 
         [0027]    The heating assembly  5  includes a second heating tube  50 , a tube seat  51 , a bracing rack assembly  52 , a first movable detent plate  53  and a second movable detent plate  54 . The second heating tube  50  is corresponding to the first heating tube  50   a  at one end of the heating chamber  14 . The second heating tube  50  has one side fastened to one side of the tube seat  51 . The tube seat  51  has a bolt  511  at another side coupling with a tube seat cap  510 . The second heating tube  50  has other side anchored on the bracing rack assembly  52 . The bracing rack assembly  52  includes a first rack  520  with a fastening hole  522  formed thereon and a second rack  521  with a plurality of other fastening holes  523  and a first sliding rod orifice  524  formed thereon. The first rack  520  has two ends forming respectively a bend plate  5201  opposing to each other. Each bend plate  5201  has a latch slot  5200  at one end to latch the other side of the second heating tube  50 . The first movable detent plate  53  has a fastening hole  531  at a lower side to be run through by the another side of the tube seat  51 , such that the bolt  511  on the tube seat  51  also runs through the sliding slot  412  of the secondary lever  41  and is fastened to the tube seat cap  510 . The second movable detent plate  54  has a second sliding rod orifice  541  and a fastening hole  542  at a lower side corresponding to each other. The second sliding rod orifice  541  and the first sliding rod orifice  524  of the second rack  521  and the sliding slot  412  of the secondary lever  41  are run through by another bolt  525 , and fastened by a nut  526 . The fastening hole  522  of the first rack  520 , the fastening hole  523  of the second rack  521  and the fastening hole  542  of the second movable detent plate  54  are run through by another fastening element  527  such as a screw and fastened by another nut  528 . 
         [0028]    Referring to  FIGS. 5 and 8 , when the invention is in use, an user turns the space control knob  30  to drive the axle  31  and the helical sleeve  32  to rotate; the movable dock  33  also is moved on the sliding track  121  due to mutual engaging of the external thread  321  and internal thread  330 ; the main lever  40  also is moved by the movable dock  33  to drive one secondary lever  41  which has one end coupled with the linkage transverse rod  42  through the fastening hole  410  serving as a fulcrum; hence the movement is transmitted to another secondary lever  41  to sway about the linkage transverse rod  42 ; the bolts  525  and  511  fastened to the two secondary levers  41  and held in the sliding slots  412  are moved along the sliding slot  120  to move the heating assembly  5  up and down. 
         [0029]    Referring to  FIGS. 7 and 8 , when the space control knob  30  is adjusted, the bolts  525  and  511  are driven, and the entire heat assembly  5  is moved up and down along the sliding slot  120  on the side board  12 . While an effective heating space  11  is formed in such a movement, the sliding slot  120  forms a crevice of the effective heating space  11 . The first movable detent plate  53  can close the crevice to prevent heated air from leaking outwards. Thus the heated air can be trapped in the effective heating space  11  to serve its purpose. 
         [0030]    Referring to  FIG. 9 , when the space control knob  30  is turned, the movable dock  33  is driven to move the lever assembly  4  so that the heating assembly  5  in the heating chamber  14  also is moved up and down to change the size of the effective heating space  11 . When the heating assembly  5  is moved closer to a lower side of the heating chamber  14 , the effective heating space  11  between the first and second heating tubes  50   a  and  50  is larger and can evenly roast foodstuff A. When the heating assembly  5  is adjusted and moved to an upper side of the heating chamber  14 , referring to  FIG. 10 , the effective heating space  11  between the two heating tubes  50   a  and  50  is smaller, thus can roast the foodstuff A at a selected portion. 
         [0031]    Referring to  FIG. 11 , the oven body  1  may include an upper lid  64  and a hotdog rack  6  beneath thereof. The hotdog rack  6  has a plurality of hotdog rollers  63 . A driving means  62  is provided at one end of the hotdog rack  6  to rotate the hotdog rollers  63 . A driving motor  60  also may be provided at the outer side of the side board  12  of the facilitate chamber  15  to drive the driving means  62  through a chain  61  so that the hotdog rollers  63  can be rotated automatically on the hotdog rack  6 .
An oven having an adjustable effective heating space includes an oven body with a scale and a space control knob on the outside to allow manual adjustment of the heating space. Through a transmission assembly and a lever assembly, the position of a heating assembly located in a heating chamber can be adjusted to form an effective heating space with another heating tube in the heating chamber. The size of the effective heating space can be adjusted in a stepless fashion according to user's requirements so that baking and roasting condition can be fine-tuned whenever desired without moving foodstuff or the oven. The oven thus formed provides multiple functions to heat the foodstuff effectively. Roasting can be done simpler and safer with less energy consumption.