Abstract:
A V-shaped belt transmission system includes a small pulley ( 2 ) and a large pulley ( 1 ). A V-shaped belt ( 3 ) winds around the large pulley ( 1 ) and the small pulley ( 2 ). The V-shaped belt ( 3 ) is in friction transmission with the large pulley ( 1 ). The transmission between the V-shaped belt ( 3 ) and the small pulley ( 2 ) is a transmission including the friction transmission with the mesh transmission. The invention provides a V-shaped belt transmission system which can effectively avoid the occurrence of slippage, improve the transmission efficiency, reduce the distortion of the belts, and prolong the service life of the belts, thus addressing the problem of the slippage and idle rotation of the existing belt transmissions.

Description:
[0001]    This application is a continuation-in-part of PCT/CN2010/074345, filed Jun. 23, 2010, which claims priority to Chinese Application No. 200910303564.1, filed Jun. 23, 2009, and Chinese Application No. 200910303563.7, filed Jun. 23, 2009. The PCT/CN2010/074345 application is incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The invention relates to a transmission system, in particular to a V-shaped belt transmission system for preventing slippage and idle rotation of pulleys in belt transmissions with high power, heavy load and high transmission ratio. 
       BACKGROUND 
       [0003]    There are a lot of transmission modes in mechanical field, including gear transmission, chain transmission, belt transmission, etc., in which the gear mesh transmission has accurate transmission ratio and can realize high transmission ratio and large loading power, but is only used in the condition that two transmission shafts are positioned in a short distance, when two transmission shafts are set in a long distance, the chain transmission or the belt transmission is usually employed. The chain transmission is mainly realized by engagement between a chain and a sprocket wheel, but its inherent defect of instantaneous impact load causes low driving velocity and is only used for low-speed transmission and in condition without impact load. The engagement or contact between a chain and a sprocket wheel is realized between two rigid members, while the engagement between a belt and a pulley is realized between a rigid member and a flexible (soft) member, and there is an essential difference between the two types of engagements. In the engagement of two rigid members, the meshing characteristics of the two members must be in specific fit, and any slight error will cause clearance meshing and interference meshing. However, when a rigid member is meshed with a flexible member, even interference meshing of the flexible member with the rigid member can satisfy the meshing requirements owing to the flexibility of the flexible member, namely the rigid member can press the flexible member into a desired size to realize engagement. Presently, the belt transmission primarily involves friction transmission (triangle belt or V-shaped belt) and mesh transmission (synchronous belt), wherein the friction transmission is generally suitable for transmissions with large power, heavy load and overload protection requirement and mainly employs members made of rubber or elastic material, and elastic slip and elastic deformation occur inevitably in transmission, thus causing unavoidable slippage and idle rotation in transmission. Synchronous belt transmission designed based on the principle of mesh transmission has accurate transmission ratio and no slippage or idle rotation because of the meshing relationship between a belt and a pulley, but because the synchronous belt is usually thin to keep normal meshing station, it is only suitable for transmission with light load, so that the flexibility of the belt body can be insured, and belt teeth cannot distort. Such structure of the belt body causes it cannot bear a heavy load. If the synchronous belt bears a heavy load, belt teeth will be scraped off by pulley teeth, or the belt body is broken. In the condition of high transmission ratio, the manufacturing difficulty of a large synchronous pulley is very high, and the manufacture process is complex, thereby causing high cost and diseconomy. 
         [0004]    The Chinese Patent Publication No. CN1183338 entitled a V-shaped belt System. In the system, the surface of a V-shaped belt is provided with tooth profiles meshed with a synchronous pulley, a large pulley used is a V-shaped grooved pulley, and a small pulley is a synchronous pulley purely driven by mesh transmission. When the system is started, the V-shaped belt slips slightly in the V-shaped grooved pulley to reduce initial starting impact to the system. Therefore, the slippage between the V-shaped belt and the small pulley is overcome because of synchronous engagement. But experiments show that above invention is merely suitable for a belt transmission system with low power and light load. In the conditions of large power and heavy load, tooth gnawing will occur to the transmission belt, namely belt teeth (flexible teeth) are gnawed off by gear teeth (rigid teeth) of the small pulley used for mesh transmission, causing failure of the mesh transmission. Therefore, the system does not solve the problem of slippage and idle rotation in the conditions of large power, heavy load and high transmission ratio and has no practical significance. That is why the above invention cannot be applied as yet. Especially, the patent violates the basic precondition of belt design, that is to say the torsion bearer of a belt should be a core layer or other strong layer of the belt instead of a rubber layer of the belt, thus, the problem of tooth gnawing of the invention cannot be solved resulting from wrong design principle, the situation of tooth gnawing is very serious, and the service life of the belt is too short to work normally. 
         [0005]    The Chinese Patent Publication No. CN201187558Y entitled “an oil pumping machine jointed tooth-shaped cog V-shaped belt transmission device”, wherein trapezoidal dummy clubs especially configured on a belt correspond to trapezoidal grooves of a belt pulley to prevent slippage. Without design of eliminating interference, in practical application, the trapezoidal dummy clubs on the belt cannot actually correspond to and be meshed with the trapezoidal grooves of the belt pulley due to elastic slip and elastic deformation of the belt, so interference occurs between the trapezoidal dummy clubs on the belt and the trapezoidal grooves of the belt pulley. The trapezoidal dummy clubs on the flexible (soft) belt is gnawed off by the trapezoidal grooves on the rigid (hard) belt pulley, namely tooth gnawing. Such situation of tooth gnawing will keep going, and the trapezoidal grooves on the rigid (hard) belt pulley keeps gnawing the trapezoidal dummy clubs on the belt until all trapezoidal dummy clubs on the belt are gnawed off. This gnawing has collapse effect, and the belt teeth will be gnawed off within very short time. That all trapezoidal dummy clubs on the belt are gnawed off foreshows the objective of anti-slip by means of the trapezoidal dummy clubs on the belt corresponding to the trapezoidal grooves on the belt pulley cannot be realized. 
       SUMMARY 
       [0006]    The disclosure relates to a novel V-shaped belt composite transmission system for overcoming defects of various transmission modes in transmission field. The invention provides a V-shaped belt composite transmission system which can effectively prevent slippage, improve the transmission efficiency, reduce the distortion of belts, and prolong the service life of the belts, solving the problems of easy slippage and idle rotation of conventional belts of the prior art. 
         [0007]    The V-shaped belt transmission system comprises a small pulley acting as a driving pulley and a large pulley acting as a driven pulley, the small pulley drives the large pulley to rotate through V-shaped belt, and the large pulley is the working pulley. The large pulley is provided with a belt groove fitted with a V-shaped belt, both side surfaces of the belt groove are fitted with both side surfaces of the V-shaped belt to transmit rotational movement by friction between the side surfaces of the belt groove and the V-shaped belt; the small pulley is provided with a belt groove fitted with the V-shaped belt, both side surfaces of the belt groove are fitted with both side surfaces of the V-shaped belt to transmit rotational movement by friction between the side surfaces of the belt groove of the small pulley and the V-shaped belt; the bottom surface of the belt groove of the small pulley is provided with continuously distributed concave-convex teeth; each concave tooth on the bottom surface of the belt groove of the small pulley comprises a meshing section at the bottom, and a belt tooth rolling-in section and a belt tooth rolling-out section symmetrically designed at both sides of the meshing section, and the belt tooth rolling-in section and the belt tooth rolling-out section are connected with convex teeth positioned at both sides of the concave teeth of the small pulley; the internal bottom surface of the V-shaped belt is provided with continuously distributed concave-convex teeth, the convex teeth on the internal bottom surface of the V-shaped belt and the meshing section on the bottom surface of the belt groove of the small pulley are engaged to transmit rotational movement, the concave teeth on the internal bottom surface of the V-shaped belt and the convex teeth on the internal bottom surface of the V-shaped belt have corresponding contours, the convex tooth is designed smaller than the concave tooth of the small pulley so as to remain a clearance with the bottom of the concave tooth of the V-shaped belt, thereby insuring heat dissipation of the belt and the pulley and reducing flex restriction to the belt. 
         [0008]    The invention employs a transmission including sliding friction transmission of the large pulley acting as the driven pulley, sliding friction transmission and mesh transmission of the small pulley acting as the driving pulley and rolling friction transmission in overload. In belt transmission, the large pulley and the small pulley have same linear velocity and different angular velocities and contact angles due to different diameters, the contact angle of the large pulley is greater than 180 degrees, and the contact angel of the small pulley is smaller than 180 degrees. As a result of large contact angle and diameter, the length of the V-shaped belt contacting with the large pulley is far longer than the length of the V-shaped belt contacting with the small pulley, the contact area between the V-shaped belt and the large pulley is far larger than the contact area between the V-shaped belt and the small pulley, so slippage concentrates on the small pulley, and idle rotation occurs to the large pulley. The large pulley is the driven pulley, namely working pulley, and thus idle rotation of the large pulley indicates power decrease and work waste. In order to improve the efficiency, the problem of idle rotation must be solved, and accordingly, slippage of the small pulley must be prevented. The meshing section is arranged at the bottom of the belt groove of the small pulley to prevent slippage through mesh transmission between the meshing section and the convex teeth of the V-shaped belt. The V-shaped belt is only in mesh transmission with the small pulley at the meshing section, and among the concave-convex teeth on the small pulley, only the meshing section is designed based on the meshing theory. In the invention, the belt body and the belt teeth of the V-shaped belt are lengthened and enlarged under the action of tension and flex in transmission area except the meshing area of the small pulley, and when entering the meshing area, the enlarged teeth become identical to the gear teeth of the small pulley in shape and size under press of the rigid gear teeth of the small pulley to realize normal engagement. Because only the bottom section of the small pulley is designed based on the meshing theory, and both sides of the meshing section are of the belt tooth rolling-in section and belt tooth rolling-out section, the possibility of the gear teeth of small pulley locking the belt teeth of the V-shaped belt is reduced, thereby preventing the occurrence of tooth gnawing, reducing abrasion of the V-shaped belt and prolonging the service life of the V-shaped belt. The design of tooth shape of the small pulley is totally different from the mesh transmission of a synchronous belt, and because the V-shaped belt composite transmission system of the invention will be applied to equipment with high power, heavy load and high transmission ratio, the meshing principle of the synchronous belt is entirely unsuitable. Meanwhile, the meshing section can be adjusted. The lengthening of the transmission belt caused by elastic deformation of the V-shaped belt can be restored in the meshing section. In normal operation, the convex teeth of the V-shaped belt are in meshing motion with the meshing section of the small pulley, such meshing engagement is not fully engagement between the belt teeth and the gear teeth, the meshing depth is designed smaller than the radius of the belt teeth, and in the condition of shocking load or overload, the belt teeth are permitted to conveniently withdraw from meshing engagement in the belt tooth rolling-in section and the belt tooth rolling-out section of the concave teeth of the small pulley and turn into rolling friction transmission, and such rolling friction transmission is carried out under the restriction of the curve designed between the meshing section of the small pulley and the convex teeth of the V-shaped belt. Therefore, the design insures the accuracy of mesh transmission as well as protects the belt in shocking load or overload. That is the innovation of the invention. In operation of the invention, both side surfaces of the belt and the both side surfaces of the pulleys are in sliding friction transmission, the convex teeth of the V-shaped belt and the meshing section of the pulley are in mesh transmission, the V-shaped belt and the small pulley are in rolling friction transmission when transmission is overloaded or load suddenly changes, and even the belt teeth can upmost climb over the convex teeth of the gear teeth to be in mesh transmission with the meshing section again through the belt tooth rolling-in section. The transmission system combining sliding friction transmission, mesh transmission and rolling friction transmission and skillfully solves the problem of slippage and the problem of overload protection requirement by meshing transmission. Because the belt teeth and the gear teeth are in rolling motion, the conventional sliding friction turns into rolling friction, thereby greatly reducing friction coefficient, significantly prolonging the service life of the belt, and decreasing the friction energy consumption to endow the belt with energy-saving effect. The convex teeth of the pulley are designed to be smaller than the concave teeth on the V-shaped belt such that the convex teeth on the pulley remain a clearance with the bottom of the concave teeth of the V-shaped belt, thereby improving the heat dissipation performance and flex restriction of the belt in operation, and further prolonging the service life of the belt. The convex teeth of the V-shaped belt are designed according to the principle of meshing engagement with the meshing section on the bottom of the belt groove of the pulley, and the concave teeth and the convex teeth of the V-shaped belt having corresponding contours facilitates molding and manufacture. 
         [0009]    Preferably, the belt tooth rolling-in section and the belt tooth rolling-out section are in the same shape which is one of circular arc, parabola, involute, elliptical line and cycloid, the curvature radius of the belt tooth rolling-in section and the belt tooth rolling-out section is greater than that of the meshing section, and the curvature radius of the convex teeth of the small pulley is smaller than that of the meshing section. The shape of the belt tooth rolling-in section and the belt tooth rolling-out section insures rolling friction with the V-shaped belt, and the curvature radiuses of the convex teeth, the meshing section, the belt tooth rolling-in section and the belt tooth rolling-out section are sequentially increased. The meshing section is designed based on meshing theory, the curvature radius of the convex teeth of the small pulley is smaller that of the meshing section such that a clearance is remained between the convex teeth of the small pulley and the concave teeth on the V-shaped belt to dissipate heat and reduce the flex restriction of the belt, the belt tooth rolling-in section and the belt tooth rolling-out section have maximum curvature radius and thus can insure that when the small pulley contacts with the V-shaped belt, the convex teeth of the V-shaped belt with elastic deformation can enter the concave teeth of the small pulley to generate mesh transmission without tearing the belt teeth. 
         [0010]    Preferably, the belt tooth rolling-in section and the belt tooth rolling-out section are symmetrically distributed at both sides of the meshing section, and the belt tooth rolling-in section and belt tooth rolling-out section are in rolling friction motion with the convex teeth of the V-shaped belt. The belt tooth rolling-in section and the belt tooth rolling-out section are different from the convex teeth of the V-shaped belt in curvature radius so as to insure point contact between them, the belt tooth rolling-in section and the belt tooth rolling-out section and the convex teeth of the V-shaped belt are in rolling friction, and because the rolling friction force is the smallest, so the belt and the small pulley are worn least. 
         [0011]    Preferably, the meshing section is in arc transition connection with the belt tooth rolling-in section and the belt tooth rolling-out section, and the belt tooth rolling-in section and the belt tooth rolling-out section are in arc transition connection with the convex teeth of the small pulley. All sections are in arc transition, and thus have good stationarity and improvement of transmission efficiency. 
         [0012]    Preferably, the belt groove of the small pulley can be divided into 1 to 100 parallel sub belt grooves in the axial direction of the pulley, the internal bottom surface of the V-shaped belt is axially divided into sub V-shaped belts equal to the sub belt grooves in number, the side surfaces of the sub belt grooves and the side surfaces of the sub V-shaped belts are in sliding friction transmission, and the bottom surfaces of the sub belt grooves and the internal bottom surfaces of the sub V-shaped belts move in transmission combing mesh transmission and rolling friction transmission. Simultaneous transmissions of a plurality of groups improve the transmission efficiency and the transmission torque. 
         [0013]    Preferably, the belt structure of the V-shaped belt comprises a cord layer; above the cord layer, a buffer rubber layer, a cord fabric layer, a buffer rubber layer, a wide-angel fabric layer, a buffer layer and a wide-angel fabric layer are sequentially bonded; under the cord layer, a buffer rubber layer, a fiber rubber layer, a buffer rubber layer, a cord fabric layer, a buffer rubber layer, a fiber rubber layer and a buffer rubber layer are sequentially bonded; and the surface of the concave-convex teeth of the V-shaped belt  1  is provided with an elastic fabric layer. The design can increase the rigidity of the transmission belt and prevent break of the transmission belt. 
         [0014]    Preferably, a clearance h is remained between the top of the convex teeth of the small pulley and the bottom of the concave teeth of the V-shaped belt, the radius of the convex teeth of the V-shaped belt is expressed as R, 0.2 mm≦h&lt;R, the clearance can be adjusted according to the size of the pulley to insure enough space for dissipating heat to improve the heat dissipation performance. 
         [0015]    Preferably, the diameter ratio of the large pulley to the small pulley is 1:1.5 to 1:50, the rotating shaft center distance between the large pulley and the small pulley is larger than the sum of the radiuses of the large pulley and the small pulley, the contact angle of the large pulley is α, the contact angle of the small pulley is β, and α:β=1.1˜3. Synchronous belt transmission cannot be used due to long distance between two pulleys and large torque and load to be transferred. 
         [0016]    Therefore, the V-shaped belt transmission system of the invention has the following advantages: because the contact angle of the large pulley is large, and the ratio of the large pulley to the small pulley is large, slippage has little effect on the large pulley, so the large pulley is in sliding friction transmission with the V-shaped belt to increase the pulling force; the contact angle of the small pulley acting as the driving pulley is smaller than 180 degrees, the small pulley is provided with concave-convex teeth, and correspondingly, the V-shaped belt is provided with the same concave-convex teeth, wherein the bottom of each concave-convex tooth of the small pulley is the meshing section, the concave-convex teeth of the V-shaped belt are designed according to the meshing relationship with the meshing section to prevent slippage through mesh transmission, and meanwhile, the belt tooth rolling-in section and the belt tooth rolling-out section are positioned at both sides of the meshing section to prevent tooth gnawing, and the convex teeth of the V-shaped belt can easily roll into the meshing section through rolling friction to realize mesh transmission. The combination of sliding friction transmission between the side surfaces of the V-shaped belt and the small pulley, the rolling friction transmission of the belt tooth rolling-in section and the belt tooth rolling-out section, and the mesh transmission of the meshing section improves the transmission torque and transmission power, prevents the occurrence of tooth gnawing and prolongs the service life of the V-shaped belt. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  a perspective view of the V-shaped belt transmission system of the invention at an angle; 
           [0018]      FIG. 2  is a perspective view of the V-shaped belt transmission system of the invention at another angle; 
           [0019]      FIG. 3  is a front enlargement view of the V-shaped belt winding around the small pulley of the invention; 
           [0020]      FIG. 4  is a front enlargement view of D position of  FIG. 3 ; 
           [0021]      FIG. 5  is a front enlargement view of D position of the small pulley of  FIG. 3 ; 
           [0022]      FIG. 6  is a sectional view of the V-shaped belt of  FIG. 1 ; and 
           [0023]      FIG. 7  is a sectional view of the small pulley of  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0024]    The technical scheme of the invention is further described by combining the following embodiments and figures. 
       Embodiments 
       [0025]    Referring to  FIGS. 1 ,  2  and  3 , a V-shaped belt transmission system comprises a large pulley  1  with diameter of 990 mm and a small pulley  2  with diameter of 280 mm, the rotating shaft center distance between the large pulley  1  and the small pulley  2  is 1807.57 mm, the contact angle α of the large pulley  1  is 202.65 degrees, and the contact angle β of the small pulley  2  is 157.35 degrees. The small pulley  2  is the driving pulley, the large pulley  1  is the driven pulley, a V-shaped belt  3  winds around the large pulley  1  and the small pulley  2 , and the small pulley  2  drives the large pulley  2  to rotate through the V-shaped belt  3 . The large pulley  1  is provided with a belt groove  23 , both side surfaces  31  of the V-shaped belt  3  contact with both side surfaces  111  of the belt groove  112  of the large pulley, and the V-shaped belt  3  drives the large pulley  1  to rotate. The outer circumferential surface of the small pulley  2  is provided with a belt groove  23  as well, both side surfaces  211  of the small pulley belt groove  23  contact with and are in friction transmission with both side surfaces  31  of the V-shaped belt  3 . In order to prevent slippage, concave-convex teeth are configured on the bottom surface of the belt groove of the small pulley  2  as well as on the internal bottom surface of the V-shaped belt  3 . As shown in  FIG. 4 , a concave tooth  4  of the small pulley comprises a meshing section  20  positioned on the bottom, both sides of the meshing section are connected with a belt tooth rolling-in section  221  and a belt tooth rolling-out section  21  via transition arcs, the belt tooth rolling-in section  221  and the belt tooth rolling-out section  21  have corresponding contours, and the belt tooth rolling-in section  221  and the belt tooth rolling-out section  21  are connected with convex teeth  41  on the bottom surface of the belt groove of the small pulley  2 , wherein the height ratio of the meshing section  20  of the small pulley  2  to the belt tooth rolling-in section  221  and the belt tooth rolling-out section  21  is 1:2.5; a convex tooth  32  on the internal bottom surface of the V-shaped belt  3  and the meshing section  20  on the bottom of the concave tooth of the small pulley  2  are in mesh transmission, the concave tooth  22  on the internal bottom surface of the V-shaped belt  3  and the convex tooth  32  on the internal bottom surface of the V-shaped belt  3  are in the same shape, a clearance is remained between the top end of a convex tooth  41  of the small pulley  2  and the bottom of the concave tooth  22  of the V-shaped belt, the distance h of the clearance is 0.72 mm, the height of the meshing section  20  on the small pulley is 1.4 mm, and the radius R of the convex tooth of the V-shaped belt is 2.95 mm. Referring to  FIG. 5 , a broken circle E in  FIG. 5  is an imaginary circle of the meshing section  20 , a broken circle F is an imaginary circle on the convex tooth  41  of the small pulley, the belt tooth rolling-in section  221  and the belt tooth rolling-out section  21  are involutes, the belt tooth rolling-in section  21  and the belt tooth rolling-out section  221  are symmetrically arranged at both sides of the meshing section  20 , the curvature radius of the convex tooth  41  of the small pulley (which is the radius of circle F) is 1.69 mm, the curvature radius of the meshing section  20  (which is the radius of circle E) of the small pulley is 2.95 mm, the curvature radius of the belt rolling-in section  221  and the belt tooth rolling-out section  21  is greater than that of the meshing section  20 , the curvature radius of the convex tooth  41  of the small pulley is smaller than that of the meshing section  20 , and because the curvature radius of the belt tooth rolling-in section  221  and the belt tooth rolling out  21  is different from that of the meshing section  21 , that is to say, the curvature radius of the belt tooth rolling section  221  and the belt tooth rolling-out section  21  is different from that of the convex tooth  32  of the V-shaped belt  3  as well, rolling friction is generated between the belt tooth rolling-in section  221  and the belt tooth rolling-out section  21  and the convex tooth  32  of the V-shaped belt  3 . As shown in  FIG. 6 , the belt structure of the V-shaped belt  3  comprises a cord layer  11 ; above the cord layer  11 , a buffer rubber layer  10 , a cord fabric layer  9 , a buffer rubber layer  8 , a wide-angel fabric layer  7 , a buffer layer  6  and a wide-angel fabric layer  5  are sequentially bonded; under the cord layer  11 , a buffer rubber layer  12 , a fiber rubber layer  13 , a buffer rubber layer  14 , a cord fabric layer  15 , a buffer rubber layer  16 , a fiber rubber layer  17  and a buffer rubber layer  18  are sequentially bonded; and the surfaces of the concave-convex teeth of the transmission belt  1  are provided with elastic fabric layer  19 . In order to bear heavier load, a plurality of the large pulleys, the small pulleys and the V-shaped belts can be connected in series in parallel rows. In the invention, the belt groove of either the large pulley or the small pulley is divided into two parallel V-shaped belt grooves  23 , and correspondingly, the V-shaped belt is provided with two belt bodies matched with the belt grooves. As shown in  FIG. 7 , five belt grooves are connected in series to form a joint group, the small pulley is provided with five belt grooves  23 , and the side surfaces  31  of the belt grooves  23  and the V-shaped belts are in friction transmission. 
         [0026]    When the invention is applied to an oil pumping unit, the torque required by the transmission system is 1200 NM to 2000 NM; because the small pulley  2  is the driving pulley, and the large pulley  1  is the driven pulley, the large pulley  1  rotates merely under the action of sliding friction of the V-shaped belt  3 , and the V-shaped belt  3  generating greater friction force can provide a larger traction force, thereby being suitable for situations with heavy load and large torque. Because the contact angle of the small pulley  2  is smaller, the V-shaped belt  3  tends to generate elastic deformation and elastic slide easily in operation, resulting in slippage and thus reducing the service life of the V-shaped belt  3 . In order to prevent slippage and reduce the elastic deformation and elastic slide of the V-shaped belt  3 , the small pulley  2  as well as the V-shaped belt  3  is provided with a meshing section  20 ; the belt tooth rolling-in section  221  and the belt tooth rolling-out section  21  are configured at both sides of the meshing section to smooth the entry and the exit of the V-shaped belt through the mesh transmission of the meshing section  20 ; and the transmission between the small pulley and the V-shaped belt is realized by the cooperation of the friction between the V-shaped belt  3  and the side surfaces  111  of the small pulley, the rolling friction between the belt tooth rolling-in section and the belt tooth rolling-out section  21  and the mesh transmission of the meshing section such that the phenomenon of tooth gnawing cannot occur when insuring large transmission torque, and the service life of the belt is prolonged. 
         [0027]    With reference to  FIGS. 1-5 , the large pulley  1  is provided with a belt groove  23  fitted with a V-shaped belt, both side surfaces  111  of the belt groove  23  are fitted with both side surfaces of the V-shaped belt  3  to transmit rotational movement by friction between the side surfaces  111  of the belt groove  23  and the V-shaped belt  2 ; the small pulley  2  is provided with a belt groove  23  fitted with the V-shaped belt  3 , both side surfaces  211  of the belt groove  23  are fitted with both side surfaces of the V-shaped belt  3  to transmit rotational movement by friction between the side surfaces  211  of the belt groove  23  of the small pulley  2  and the V-shaped belt  3 ; the bottom surface of the belt groove  23  of the small pulley  2  is provided with continuously distributed concave-convex teeth  41 ; each concave tooth  41  on the bottom surface of the belt groove  23  of the small pulley  2  comprises a meshing section  20  at the bottom, and a belt tooth rolling-in section  221  and a belt tooth rolling-out section  21  symmetrically designed at both sides of the meshing section, and the belt tooth rolling-in section  221  and the belt tooth rolling-out section  21  are connected with convex teeth positioned at both sides of the concave teeth of the small pulley  2 ; the internal bottom surface of the V-shaped belt  3  is provided with continuously distributed concave-convex teeth, the convex teeth on the internal bottom surface of the V-shaped belt  3  and the meshing section  20  on the bottom surface of the belt groove  23  of the small pulley  3  are engaged to transmit rotational movement, the concave teeth on the internal bottom surface of the V-shaped belt  3  and the convex teeth on the internal bottom surface of the V-shaped belt  3  have corresponding contours, the convex tooth is designed smaller than the concave tooth of the small pulley  2  so as to remain a clearance with the bottom of the concave tooth of the V-shaped belt  3 , thereby insuring heat dissipation of the belt  3  and the pulley  2  and reducing flex restriction to the belt  3 . 
         [0028]    With reference to  FIGS. 1-5 , the invention employs a transmission including sliding friction transmission of the large pulley  1  acting as the driven pulley, sliding friction transmission and mesh transmission of the small pulley  2  acting as the driving pulley and rolling friction transmission in overload. Sliding friction transmission utilizes the friction created when two surfaces contact each other. For example, the side surfaces of the V-shaped belt and the side surfaces of the grooves of the large pulley contact each other, and the movement of the V-shaped belt is transmitted to the large pulley by friction created by the contact between the belt and the pulley. The meshing transmission is created between two geared surfaces. The geared surfaces include teeth and grooves. The shape of the teeth is generally complementary to the shape of the grooves. The movement of one geared surface can be transmitted to the movement of the other geared surface when the teeth and grooves of one surface match the complementary grooves and teeth of the other surface. The rolling friction transmission happens when the shape of one surface is not complementary to the shape of the other surface, and therefore the contact between the two surfaces is merely lines or spots. For example, if the teeth and grooves are not complementary to each other in the meshing transmission, the only contacts between the teeth of one surface and the corresponding grooves on the other surface are just the rolling-in and rolling-out sections. Since this is only spot contact, it does not create a meshing transmission, but a rolling friction transmission. In belt transmission, the large pulley  1  and the small pulley  2  have same linear velocity and different angular velocities and contact angles due to different diameters, the contact angle of the large pulley  1  is greater than 180 degrees, and the contact angel of the small pulley  2  is smaller than 180 degrees. As a result of large contact angle and diameter, the length of the V-shaped belt  3  contacting with the large pulley  1  is far longer than the length of the V-shaped belt  3  contacting with the small pulley  2 , the contact area between the V-shaped belt  3  and the large pulley  1  is far larger than the contact area between the V-shaped belt  3  and the small pulley  2 , so slippage concentrates on the small pulley  2 , and idle rotation occurs to the large pulley  1 . The large pulley  1  is the driven pulley, namely working pulley, and thus idle rotation of the large pulley  1  indicates power decrease and work waste. In order to improve the efficiency, the problem of idle rotation must be solved, and accordingly, slippage of the small pulley  2  must be prevented. The meshing section  20  is arranged at the bottom of the belt groove  23  of the small pulley  2  to prevent slippage through mesh transmission between the meshing section  20  and the convex teeth of the V-shaped belt  3 . The V-shaped belt  3  is only in mesh transmission with the small pulley  2  at the meshing section  20 , and among the concave-convex teeth  41  on the small pulley  2 , only the meshing section  20  is designed based on the meshing theory. In the invention, the belt body and the belt teeth of the V-shaped belt  3  are lengthened and enlarged under the action of tension and flex in transmission area except the meshing area of the small pulley  2 , and when entering the meshing area, the enlarged teeth become identical to the gear teeth of the small pulley  2  in shape and size under press of the rigid gear teeth of the small pulley  2  to realize normal engagement. Because only the bottom section of the small pulley  2  is designed based on the meshing theory, and both sides of the meshing section  20  are of the belt tooth rolling-in section  221  and belt tooth rolling-out section  21 , the possibility of the gear teeth  41  of small pulley  2  locking the belt teeth of the V-shaped belt  3  is reduced, thereby preventing the occurrence of tooth gnawing, reducing abrasion of the V-shaped belt and prolonging the service life of the V-shaped belt  3 . The design of tooth shape of the small pulley  2  is totally different from the mesh transmission of a synchronous belt, and because the V-shaped belt  3  composite transmission system of the invention will be applied to equipment with high power, heavy load and high transmission ratio, the meshing principle of the synchronous belt is entirely unsuitable. Meanwhile, the meshing section  20  can be adjusted. The lengthening of the transmission belt caused by elastic deformation of the V-shaped belt  3  can be restored in the meshing section  20 . In normal operation, the convex teeth of the V-shaped belt  3  are in meshing motion with the meshing section  20  of the small pulley  2 , such meshing engagement is not fully engagement between the belt teeth and the gear teeth  41 , the meshing depth is designed smaller than the radius of the belt teeth, and in the condition of shocking load or overload, the belt teeth are permitted to conveniently withdraw from meshing engagement in the belt tooth rolling-in section  221  and the belt tooth rolling-out section  21  of the concave teeth of the small pulley  2  and turn into rolling friction transmission, and such rolling friction transmission is carried out under the restriction of the curve designed between the meshing section  20  of the small pulley  2  and the convex teeth of the V-shaped belt  3 . Therefore, the design insures the accuracy of mesh transmission as well as protects the belt in shocking load or overload. In operation of the invention, both side surfaces of the belt  3  and the both side surfaces of the pulleys  1 ,  2  are in sliding friction transmission, the convex teeth of the V-shaped belt  3  and the meshing section  20  of the pulley are in mesh transmission, the V-shaped belt  20  and the small pulley  2  are in rolling friction transmission when transmission is overloaded or load suddenly changes, and even the belt teeth can upmost climb over the convex teeth of the gear teeth  41  to be in mesh transmission with the meshing section  20  again through the belt tooth rolling-in section  221 . The transmission system combining sliding friction transmission, mesh transmission and rolling friction transmission and skillfully solves the problem of slippage and the problem of overload protection requirement by meshing transmission. Because the belt teeth and the gear teeth  41  are in rolling motion, the conventional sliding friction turns into rolling friction, thereby greatly reducing friction coefficient, significantly prolonging the service life of the belt, and decreasing the friction energy consumption to endow the belt with energy-saving effect. The convex teeth of the pulley  2  are designed to be smaller than the concave teeth on the V-shaped belt  3  such that the convex teeth on the pulley  2  remain a clearance with the bottom of the concave teeth of the V-shaped belt  3 , thereby improving the heat dissipation performance and flex restriction of the belt in operation, and further prolonging the service life of the belt. The convex teeth of the V-shaped belt  3  are designed according to the principle of meshing engagement with the meshing section  20  on the bottom of the belt groove  23  of the pulley  2 , and the concave teeth and the convex teeth of the V-shaped belt  3  having corresponding contours facilitates molding and manufacture. 
         [0029]    With reference to  FIGS. 1-5 , the belt tooth rolling-in section  221  and the belt tooth rolling-out section  21  are in the same shape which is one of circular arc, parabola, involute, elliptical line and cycloid, the curvature radius of the belt tooth rolling-in section  221  and the belt tooth rolling-out section  21  is greater than that of the meshing section  20 , and the curvature radius of the convex teeth of the small pulley  2  is smaller than that of the meshing section  20 . The shape of the belt tooth rolling-in section  221  and the belt tooth rolling-out section  21  insures rolling friction with the V-shaped belt, and the curvature radiuses of the convex teeth, the meshing section  20 , the belt tooth rolling-in section  221  and the belt tooth rolling-out section  21  are sequentially increased. The meshing section  20  is designed based on meshing theory, the curvature radius of the convex teeth of the small pulley  2  is smaller that of the meshing section  20  such that a clearance is remained between the convex teeth of the small pulley  2  and the concave teeth on the V-shaped belt  3  to dissipate heat and reduce the flex restriction of the belt, the belt tooth rolling-in section  221  and the belt tooth rolling-out section  21  have maximum curvature radius and thus can insure that when the small pulley  2  contacts with the V-shaped belt  3 , the convex teeth of the V-shaped belt  3  with elastic deformation can enter the concave teeth of the small pulley  2  to generate mesh transmission without tearing the belt teeth. 
         [0030]    With reference to  FIGS. 1-5 , the belt tooth rolling-in section  221  and the belt tooth rolling-out section  21  are symmetrically distributed at both sides of the meshing section  20 , and the belt tooth rolling-in section  221  and belt tooth rolling-out section  21  are in rolling friction motion with the convex teeth of the V-shaped belt  3 . The belt tooth rolling-in section  221  and the belt tooth rolling-out section  21  are different from the convex teeth of the V-shaped belt  3  in curvature radius so as to insure point contact between them, the belt tooth rolling-in section  221  and the belt tooth rolling-out section  21  and the convex teeth of the V-shaped belt  3  are in rolling friction, and because the rolling friction force is the smallest, so the belt and the small pulley are worn least. 
         [0031]    With reference to  FIGS. 1-5 , the meshing section  20  is in arc transition connection with the belt tooth rolling-in section  221  and the belt tooth rolling-out section  21 , and the belt tooth rolling-in section  221  and the belt tooth rolling-out section  21  are in arc transition connection with the convex teeth of the small pulley  1 . All sections are in arc transition, and thus have good stationarity and improvement of transmission efficiency. 
         [0032]    With reference to  FIG. 7 , the belt groove  23  of the small pulley  2  can be divided into 1 to 100 parallel sub belt grooves  23  in the axial direction of the pulley  2 , the internal bottom surface of the V-shaped belt  3  is axially divided into sub V-shaped belts equal to the sub belt grooves in number, the side surfaces of the sub belt grooves and the side surfaces of the sub V-shaped belts are in sliding friction transmission, and the bottom surfaces of the sub belt grooves and the internal bottom surfaces of the sub V-shaped belts move in transmission combing mesh transmission and rolling friction transmission. Simultaneous transmissions of a plurality of groups improve the transmission efficiency and the transmission torque. 
         [0033]    With reference to  FIG. 6 , the surface of the concave-convex teeth of the V-shaped belt  3  is provided with an elastic fabric layer. The design can increase the rigidity of the transmission belt and prevent break of the transmission belt. 
         [0034]    With references to  FIGS. 1-5 , a clearance h is remained between the top of the convex teeth of the small pulley  2  and the bottom of the concave teeth of the V-shaped belt  3 , the radius of the convex teeth of the V-shaped belt  3  is expressed as R, 0.2 mm≦h&lt;R, the clearance can be adjusted according to the size of the pulley  2  to insure enough space for dissipating heat to improve the heat dissipation performance. 
         [0035]    With reference to  FIGS. 1-5 , the diameter ratio of the large pulley  1  to the small pulley  2  is 1:1.5 to 1:50, the rotating shaft center distance between the large pulley  1  and the small pulley  2  is larger than the sum of the radiuses of the large pulley  1  and the small pulley  2 , the contact angle of the large pulley  1  is α, the contact angle of the small pulley  2  is β, and α:β=1.1˜3. Synchronous belt transmission cannot be used due to long distance between two pulleys and large torque and load to be transferred. 
         [0036]    Because the contact angle of the large pulley  1  is large, and the ratio of the large pulley  1  to the small pulley  2  is large, slippage has little effect on the large pulley  1 , so the large pulley  1  is in sliding friction transmission with the V-shaped belt  3  to increase the pulling force; the contact angle of the small pulley  2  acting as the driving pulley is smaller than 180 degrees, the small pulley  2  is provided with concave-convex teeth  41 , and correspondingly, the V-shaped belt  3  is provided with the same concave-convex teeth, wherein the bottom of each concave-convex tooth of the small pulley  2  is the meshing section  20 , the concave-convex teeth of the V-shaped belt  3  are designed according to the meshing relationship with the meshing section  20  to prevent slippage through mesh transmission, and meanwhile, the belt tooth rolling-in section  221  and the belt tooth rolling-out section  21  are positioned at both sides of the meshing section  20  to prevent tooth gnawing, and the convex teeth of the V-shaped belt  3  can easily roll into the meshing section  20  through rolling friction to realize mesh transmission. The combination of sliding friction transmission between the side surfaces of the V-shaped belt and the small pulley, the rolling friction transmission of the belt tooth rolling-in section  221  and the belt tooth rolling-out section  21 , and the mesh transmission of the meshing section  20  improves the transmission torque and transmission power, prevents the occurrence of tooth gnawing and prolongs the service life of the V-shaped belt. 
         [0037]    The above-mentioned is merely preferred embodiment of the invention and does not limit the invention in any shape or form. The foregoing preferred embodiment is merely illustrative of the invention and is not to be construed in a limiting sense. Various changes and modifications, or equal replacements based on the above-mentioned methods and technical contents will become apparent to those of ordinary skill in the art without departing from the scope of the invention. Therefore, any simple change, equal replacement and modification of the above embodiment based on the technical essence of the invention are seen to fall within the scope of the invention.