Abstract:
Disclosed is an auxiliary wheel comprising a wheel hub and a tire. The auxiliary wheel is fixedly mounted on a wheel of an automotive vehicle in a manner that the auxiliary wheel and the wheel have a common rotary axis. The auxiliary wheel may further comprise one or more locking components located on the wheel hub, and the locking component is used to fix the auxiliary wheel on the wheel hub of the wheel, so that the auxiliary wheel is driven by the wheel hub of the wheel. The present invention further relates to an unassisted lifting jack used when the auxiliary wheel is mounted. The unassisted lifting jack comprises a climbing block and a supporting block connected in a rotary way, the climbing block and the supporting block have a common supporting bottom, and the climbing block has a slope provided to the auxiliary wheel for climbing.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a national stage application under 35 U.S.C. 371 and claims the benefit of PCT Application No. PCT/CN2012/070021 having an international filing date of Jan. 4, 2012, which designated the United States, and which PCT application claimed the benefit of Chinese Patent Application 201110020106.4 filed Jan. 6, 2011; Chinese Utility Model Application No. 201120017252.7 filed Jan. 6, 2011; Chinese Utility Model Application No. 201120017247.6 filed Jan. 6, 2011; Chinese Patent Application No. 201110143418.4 filed May 31, 2011; and Chinese Patent Application No. 201110143416.5 filed May 31, 2011, the disclosures of which are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The invention relates to an auxiliary wheel and an unassisted lifting jack for mounting and demounting the auxiliary wheel. 
     BACKGROUND OF THE INVENTION 
     An accident may happen to a travelling vehicle due to, e.g., a gas leakage of a tyre, bad weather, etc. A general measure taken for the existing tyre experiencing the accident may include: replacing the failed tyre with a good tyre, using tyres dedicated for the bad weather, or temporarily processing the tyre. To alleviate the damage caused by tyre burst, for example, special purpose tyres with an internal supporting structure may be adopted to allow the vehicle to travel safely a certain distance after the tyre burst. In the case of traveling on a slippery road, tyres with anti-slip spikes may be used. Again, in the case of traveling on a road with snow, anti-slip chains may be wound on the tyre to improve travel safety of the vehicle. 
     The special purpose tyres are helpful but expensive, and it is not cost-effective to use the special purpose tyres all the time. Further, to replace the failed tyre or vehicle wheel, special tools are required for demounting the tyre or vehicle wheel and mounting again the spare tyre or vehicle wheel, which is time consuming and troublesome and requires for professional skills. Therefore, more cost-effective, quick, easy and convenient measures are needed to deal with any potential accident on the tyre or vehicle wheel. 
     SUMMARY OF THE INVENTION 
     In view of the above problems, the invention provides an auxiliary wheel and an unassisted lifting jack for mounting and demounting the auxiliary wheel. 
     In an aspect, an auxiliary wheel including a hub and a tyre is configured to be fixedly and coaxially mounted on a vehicle wheel of a motor vehicle. 
     Preferably, the auxiliary wheel includes at least one first locking assembly on the hub, which is used to fix the auxiliary wheel onto a hub of the vehicle wheel, so that the auxiliary wheel is driven by the hub of the vehicle wheel. 
     Preferably, the first locking assembly is used to fix the auxiliary wheel onto the hub of the vehicle wheel by means of at least one through hole in the hub of the vehicle wheel; or the first locking assembly is used to connect with a second locking assembly on the hub of the vehicle wheel, to fix the auxiliary wheel on the hub of the vehicle wheel. 
     Preferably, the first locking assembly includes a catch device and a self-locking device with continuous locking positions, and the self-locking device includes: 
     a housing with a cavity that is fixed on or formed integrally with the hub of the auxiliary wheel, where a wall of the cavity includes a first frictional contact face and a fourth frictional contact face; 
     a locking member including a second frictional contact face and a third frictional contact face, which is configured to be at least partially within the cavity so that the second and third frictional contact faces face the first and fourth frictional contact faces, respectively; and 
     a first lock block arranged between and in contact with the first and second frictional contact faces, and a second lock block arranged between and in contact with the third and fourth frictional contact faces, so that the first and second lock blocks allow the locking member to be movable in a first direction relative to the housing, but locked in a second direction opposite to the first direction, and the locking member is allowed to be locked at any of the continuous locking positions; 
     the movement of the locking member in the first direction causes the catch device to abut against the hub of the vehicle wheel, in order to sandwich the hub of the vehicle wheel between the self-locking device and the catch device; and the locking of the locking member in the second direction prevents the catch device from releasing from the hub of the vehicle wheel. 
     Preferably, the first frictional contact face forms an angle α with respect to the second frictional contact face, the fourth frictional contact face forms an angle α′ with respect to the third frictional contact face, and α≦φ 1 +φ 2  and α′≦φ 3 +φ 4 , where φ 1  and φ 2  represent a frictional angle between the first lock block and the first frictional contact face and that between the first lock block and the second frictional contact face, respectively, and φ 3  and φ 4  represent a frictional angle between the second lock block and the third frictional contact face and that between the second lock block and the fourth frictional contact face, respectively. 
     More preferably, 0&lt;α≦17° and 0&lt;α′≦17°, and more preferably a=a′, φ 1 =φ 2 , and φ 3 =φ 4 . 
     Preferably, the self-locking device further includes a holding member, which is used for applying forces on the first and second lock blocks, so that the first lock block is kept in contact with the first and second frictional contact faces and the second lock block is kept in contact with the third and fourth frictional contact faces when the locking member is locked at the locking position. 
     Preferably, the holding member includes at least one spring and a lock block retainer extending through the cavity, the locking member extends through the lock block retainer, and a longitudinal side wall of the lock block retainer includes a first hole for accommodating the first lock block and a second hole for accommodating the second lock block; 
     the at least one spring is arranged within the cavity and applies elastic forces on the first and second lock blocks; or 
     the spring is arranged external to the housing, between the external surface of the housing and a flange at an end of the lock block retainer, and applies an elastic force on the lock block retainer. 
     In another aspect, the first locking assembly includes a catch device and a self-locking device with continuous locking positions, and the self-locking device includes: 
     a housing with a cavity that is fixed on or formed integrally with the hub of the auxiliary wheel, where a wall of the cavity includes a first frictional contact face; 
     a locking member including a second frictional contact face, which is configured to be at least partially within the cavity so that the second frictional contact face faces the first frictional contact face; and 
     a first lock block arranged between and in contact with the first and second frictional contact faces, so that the first lock block allows the locking member to be movable in a first direction relative to the housing, but locked in a second direction opposite to the first direction, and the locking member is allowed to be locked at any of the continuous locking positions; 
     here, the movement of the locking member in the first direction causes the catch device to abut against the hub of the vehicle wheel, in order to sandwich the hub of the vehicle wheel between the self-locking device and the catch device; and the locking of the locking member in the second direction prevents the catch device from releasing from the hub of the vehicle wheel. 
     Preferably, the first frictional contact face forms an angle with respect to the second frictional contact face, and the angle is less than or equal to the sum of a frictional angle between the first lock block and the first frictional contact face and that between the first lock block and the second frictional contact face; preferably, the angle between the first and second frictional contact faces is less than or equal to 17°. 
     Preferably, the self-locking device further includes a holding member, which is used for applying a force on the first lock block, so that the first lock block is kept in contact with the first and second frictional contact faces when the locking member is locked at the locking position. 
     Preferably, the frictional contact faces have a groove complementary with the shape of the lock block. 
     Preferably, the housing, the locking member and the lock block are made of steel. 
     Preferably, the locking member is a disc wheel with is rotatablely connected with the housing and rotatable in the first and second directions; more preferably, a handle for rotating the disc wheel extends radially from the disc wheel. 
     Preferably, the catch device includes a rod mechanism and a catch mechanism hinged to the rod mechanism, the rod mechanism is used to extend through a through hole in the hub of the auxiliary wheel to engage with the locking member, so that the movement of the locking member in the first direction causes the catch mechanism to abut against a side of the vehicle wheel hub that is away from the hub of the vehicle wheel. 
     Preferably, the rod mechanism and the catch mechanism are connected movably or formed integrally, and/or the rod mechanism and the locking member are connected movably or formed integrally; more preferably, if the rod mechanism and the catch mechanism are connected movably, one end of the catch mechanism is rotatablely connected with the hub of the auxiliary wheel, and the other end of the catch mechanism abuts against or releases from the hub of the vehicle wheel under the driving of the rod mechanism; more preferably, the catch device further comprises a member which is used for applying an elastic force on the catch mechanism, to release the catch mechanism from the hub of the vehicle wheel when the catch mechanism is unlocked. 
     Preferably, the first locking assembly further includes an adaptation module which has a shape complementary with that of the through hole in the hub of the vehicle wheel and is embedded into the through hole when the auxiliary wheel is placed onto the hub of the vehicle wheel. 
     Preferably, one end of the catch mechanism is rotatablely connected with the adaptation module, and the other end of the catch mechanism abuts against or releases from the hub of the vehicle wheel under the driving of the locking member. 
     Preferably, the second locking assembly is a stake which is to be locked by the first locking assembly. An annular locking groove is formed on the stake, and the first locking assembly comprises a lock block retainer, at least one lock block, a self-locking cap, an elastic member and a cover; the lock block retainer is fixed onto or formed integrally with the hub of the auxiliary wheel, the stake extends through the lock block retainer, at least one lock block receiving hole is formed in the longitudinal side wall of the lock block retainer, the number and position of the at least one lock block receiving hole correspond to the number of the at least one lock block and the position of the annular locking groove, respectively, the lock block is inserted into the lock block receiving hole, the self-locking cap surrounds the lock block retainer and has a tapered contact face that faces the lock block, the cover is fixedly attached to the lock block retainer, and the elastic member is used to apply an elastic force on the cap, to cause the tapered contact face of the cap to press and drive the lock block into the annular locking groove. 
     Preferably, a contact face of the stake relative to the lock block forms an angle with respect to a contact face of the cap relative to the lock block, and the angle is less than or equal to the sum of a frictional angle between the lock block and the contact face of the stake and that between the lock block and the contact face of the cap. 
     Preferably, the first locking assembly further comprises a cam lever, which includes a cam and a handle attached to the cam, the cam is hinged with the self-locking cap and in contact with the cover, and is switchable between its locking position and unlocking position; when the cam lever is at its locking position, the tapered contact face of the cap presses and drives the lock block into the annular locking groove, and when the cam lever is at its unlocking position, the cap is lifted to cause the releasing of the lock block from the annular groove. 
     Preferably, the tyre includes an external tyre and spikes that are attached to the external tyre and protrude from the external surface of the external tyre; more preferably, the tyre further comprises an isolator arranged between an inner tyre of the tyre and the external tyre. 
     Preferably, the tyre further includes a spike seat attached to the external tyre, and the spikes are formed on a substrate, which is slidable along a pole of the spike seat, with the pole extending through a through hole in the substrate. Thus, the inventive auxiliary wheel, which is easy for manufacturing, has a good anti-flip effect and little damage to the road. 
     In a further aspect, an unassisted lifting jack useful for lifting an auxiliary wheel to be mounted includes a receiving seat and a climbing block which are rotatablely connected, the bottom of the climbing block and that of the receiving seat are in the same plane, and the climbing block has a slope for climbing by a vehicle wheel. 
     The locking assembly of the invention may be easily locked and unlocked with a high efficiency. Further, the auxiliary wheel is very compact relative to the traditional spare wheel, thus has good portability. The inventive lifting jack with a simple structure has good portability and adaptability and easy to use. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which form a part of the application, are intended to provide further understanding of the invention. Illustrative embodiments of the invention are intended to explain, but not to limit, the invention. 
         FIG. 1A  shows a front view of an auxiliary wheel of an embodiment of the invention mounted on a conventional vehicle wheel, where the hub of the auxiliary wheel is fixedly mounted on the hub of the vehicle wheel; 
         FIG. 1B  shows a sectional view along a line A-A of the auxiliary wheel mounted on the vehicle wheel of  FIG. 1A ; 
         FIG. 2A  shows a partial front view of the vehicle wheel hub for illustrating the auxiliary wheel of the embodiment; 
         FIG. 2B  shows a sectional view along a line B-B of the vehicle wheel hub of  FIG. 2A ; 
         FIG. 3A  shows a front view of an example of an adapting module used for the auxiliary wheel of the embodiment; 
         FIG. 3B  shows a sectional view along a line C-C of the adapting module of  FIG. 3A ; 
         FIG. 3C  shows a rear view of the adapting module of  FIG. 3A ; 
         FIG. 4A  shows principles of a first example of a self-locking device used in a locking assembly of the auxiliary wheel of the invention; 
         FIG. 4B  shows a schematic force triangle illustrating the principles of the first example of the self-locking device of the invention; 
         FIGS. 4C-4D  respectively show structures and principles of a second and a third examples of the self-locking device used in a locking assembly of the auxiliary wheel of the invention; 
         FIGS. 5A-5D  show a front view and sectional views along lines A-A, B-B and C-C of the second example of the self-locking device used in a locking assembly of the auxiliary wheel of the invention, respectively; 
         FIGS. 6A-6C  show a front view, a sectional view along a line A-A and a rear view of an example of the locking assembly employing the second example of the self-locking device, respectively; 
         FIG. 6D  shows a radial sectional view of both the vehicle wheel and the auxiliary wheel mounted on the hub of the vehicle wheel, where the locking assembly shown in  FIGS. 6A-6C  is mounted on the auxiliary wheel; 
         FIG. 7  shows a sectional view along a line A-A of a locking assembly, which is similar to the locking assembly of  FIGS. 6A-6C  but includes a catch mechanism of a different form; 
         FIGS. 8A-8D  shows a front view and sectional views along lines C-C, A-A and B-B of a third example of the self-locking device in the locking assembly of the invention, respectively; 
         FIG. 9  shows a sectional view along a line A-A of a variant of the third example of the self-locking device in the locking assembly of the invention, where the lock blocks have a shape of pentagonal prism; 
         FIG. 10  shows a sectional view along a line B-B of a variant of the third example of the self-locking device in the locking assembly of the invention, where the lock blocks have a spherical shape; 
         FIG. 11A  shows a perspective view of a locking and unlocking tool for the self-locking device according to an embodiment; 
         FIG. 11B  shows a perspective view of a locking and unlocking tool for the self-locking device according to another embodiment; 
         FIG. 11C  shows a perspective view of a locking and unlocking tool for the self-locking device according to still another embodiment; 
         FIGS. 12A-12C  show the front view and sectional views along lines A-A and B-B of a stake protruding from the hub of the vehicle wheel and the locking assembly locked on the stake; 
         FIGS. 13A-13C  show the perspective view, top view and sectional view along a line A-A of an unassisted lifting jack of the invention; 
         FIG. 14A  shows a radial sectional view of an anti-slip auxiliary wheel of an embodiment of the invention; 
         FIG. 14B  shows a radial sectional view of an anti-slip auxiliary wheel of another embodiment of the invention; and 
         FIG. 14C  shows a perspective view of anti-slip spikes used in the anti-slip auxiliary wheel shown in  FIG. 14B . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The invention is described below referring to the accompanying drawings and embodiments. The embodiments or features in the embodiments may be combined without conflict. 
     The auxiliary wheels of the invention are fixedly and coaxially mounted on various conventional vehicle wheels, generally at the outer side of the vehicle wheels. Particularly, the auxiliary wheel may be mounted or connected on the hub and/or shaft of the vehicle wheel, for the purpose of anti-slip, preventing the tyre burst, working in place of any failed vehicle wheel, etc. 
     To mount the auxiliary wheel on the shaft of the conventional vehicle wheel, one or more bolts for mounting the vehicle wheel are used to pass through preformed screw holes in the auxiliary wheel, then pass through the screw holes of the vehicle wheel, and be screwed into the shaft of the vehicle wheel to mount the auxiliary wheel on the vehicle wheel. The case where the auxiliary wheel is mounted on the hub of the vehicle wheel is described in detail below. 
     An axial direction refers to a direction along the rotation axis of the vehicle wheel, a radial direction refers to a direction along the diameter of the vehicle wheel, and a radial plane refers to a plane containing the vehicle wheel diameter that is perpendicular to the axial direction. Further, an inner side of vehicle wheel refers to a side of the vehicle wheel that is adjacent to the wheel shaft, while an outer side of vehicle wheel refers to a side of the vehicle wheel that is away from the wheel shaft. The vehicle wheel here may be any type of wheels used for daily travel of the vehicle. A linkage path refers to any through hole used for mounting the auxiliary wheel on the hub of the vehicle wheel, such as lightening holes in the wheel hub. 
       FIGS. 1A-1B  show a front view of a vehicle wheel with the auxiliary wheel of the invention. As shown in  FIG. 1B , the vehicle wheel  2  includes a hub  12  and a tyre  14 . The auxiliary wheel  1  includes a hub  11 , a tyre  13  (as shown in  FIG. 1B ), and one or more locking assemblies  6  fixed on the hub  11 . The locking assemblies  6  function to fix the auxiliary wheel  1  on the hub  12  of the vehicle wheel  2 , so that the auxiliary wheel  1  may be driven by the hub  12 . The locking assemblies  6  are shown as blocks in  FIGS. 1A-1B . The auxiliary wheel  1  is preferably coaxial with the vehicle wheel  2  and at the outer side of the vehicle wheel  2 , and may function in place of the vehicle wheel  2 . 
     The locking assemblies  6  may be received in through holes  16  of the hub  12  of the vehicle wheel  2  to fix the auxiliary wheel  1  on the hub  12 . Alternatively, each of the locking assemblies  6  may be engaged with another matching locking assembly on the hub  12  to fix the auxiliary wheel  1  on the hub  12 . The locking assembly in the invention, which is safe and easy for using, has a simple structure and may be manufactured easily at a low cost, as described below. 
       FIG. 2A  shows an illustrative hub of the vehicle wheel on which the auxiliary wheel of the invention is mounted.  FIG. 2B  shows a sectional view along a line A-A (i.e. a radial sectional view) of the hub of the vehicle wheel. As shown in  FIG. 2A , the hub  12  contains through holes (e.g. lightening holes)  16 , each of which includes side walls  16 A- 16 D that are matching with an adaptation module described below. As shown in  FIG. 2B , the hub  12  also includes internal walls  16 E, against which the catch mechanism described below abuts. 
     The locking assembly  6  of the auxiliary wheel preferably includes the adaptation module  8  that has a shape complementary with that of the through hole  16 , as shown in  FIGS. 3A-3C . When the auxiliary wheel  1  is engaged with the vehicle wheel  2 , the adaptation module  8  is inserted into the through hole  16  of the hub  12 , so that side walls  8 A- 8 D of the adaptation module  8  abut against the side walls  16 A- 16 D, to achieve stable fixing and positioning of the auxiliary wheel on the hub  12 . 
     When the auxiliary wheel  1  is locked on the vehicle wheel  2 , each adaptation module  8  is located in the through hole  16  in the hub  12  of the vehicle wheel  2 . The engagement between the side walls  16 C- 16 D of the through hole  16  and the side walls  8 C- 8 D of the adaptation module  8  allows the torsion transmission between the vehicle wheel  2  and the auxiliary wheel  1 , and the engagement between the side walls  16 A- 16 B of the through hole  16  and the side walls  8 A- 8 B of the adaptation module  8  allows the coaxial positioning of the auxiliary wheel  1  on the vehicle wheel  2 . 
       FIGS. 3A-3C  show an illustrative structure of the adaptation module used in the auxiliary wheel of the invention. The adaptation module  8  has a shape matching with that of the through hole  16  to be placed in and tightly engaged with the through hole  16 . 
     Preferably, the adaptation module  8  includes one or more positioning members  8 G, which match with corresponding positioning members on the hub  11  of the auxiliary wheel  1 , so that the positioning member  8  may be precisely positioned. Alternatively, the positioning member may be positioned and fixed on the hub  11  by screw holes  8 F. The positioning member may be fixed on the hub  11  in various manners, such as a screw connection, a snap-fit connection, adhering, a rivet connection, etc., or formed integrally with the hub  11 . 
     The principles and examples of the locking assembly are described below. 
     The locking assembly  6  includes a self-locking device with continuous locking positions. In a first example of the self-locking device, as shown in  FIG. 4A , the self-locking device includes a housing  101  with a cavity, a locking member  102  that is at least partially within the cavity, and a lock block  103 . The wall of the cavity includes a first frictional contact face (i.e. a locking face) W. A second frictional contact face M, which faces the face W and forms an angle α with the face W, is provided on the locking member  102 . The lock block  103  is arranged between and contacts with the faces W and M, and may have a shape, such as a spherical shape, a cylindrical shape and a polyhedral shape, that may vary as desired. The locking assembly  6  preferably further includes a holding member (not shown), which may be a spring. One end of the spring is arranged on the housing  101 , and the other end of the spring applies a pretightening force on the lock block  103  towards the vertex of the angle α. The locking member  102  may be in contact with the housing  101 , with no or substantially no frictional force between the locking member and the housing. 
     The lock block  103  is in frictional contact with the frictional contact faces W and M within the housing, to lock the locking member  102 , particularly to allow the locking member  102  to be movable in a first direction F 1  with respect to the housing but be locked in a second direction F 2  opposite to the first direction F 1 , so that the locking member  102  may be locked at any continuous locking positions. The first direction F 1  substantially points to the vertex of the angle α. If a force opposite to the direction of the vertex of the angle α is applied to the lock block  103  (against the pretightening force of the spring in the presence of the holding member) to separate the lock block  103  from at least one of the frictional contact faces W and M, the lock block  103  is released and hence the locking member  102  is unlocked. That is, the locking member  102  can be moved along the second direction F 2 . Thus, the locking member  102  can be locked in the second direction F 2  as long as the lock block  103  is in frictional contact with the faces W and M. 
     The theory about self-locking of the first example of the self-locking device is described below. 
     As shown in  FIG. 4A , a force applied to the lock block  103  by the first frictional contact face W is denoted by R 13 , a force applied to the lock block  103  by the second frictional contact face M is denoted by R 23 , the pretightening force P, which is at an angle β with respect to the second frictional contact face M, is applied to the lock block  103  by a spring, the first frictional contact face W is at an angle α with respect to the second frictional contact face M, a frictional angle and a friction factor between the lock block  103  and the first frictional contact face W are denoted by φ 1  and μ 1 , respectively, and a frictional angle and a friction factor between the lock block  103  and the second frictional contact face M are denoted by φ 2  and μ 2 , respectively, where μ 1 =tan φ 1  and μ 2 =tan φ 2 . μ 1  may be the same with or different from μ 2 . The normals of the first and second frictional contact faces are denoted by Y 1  and Y 2 , respectively. 
     According to such a criterion that the generated resistance is less than or equal to zero in the case of reversal of stroke, as shown in  FIG. 4B , a self-locking condition is determined as follows. 
                   R   13       sin   ⁡     (       90   ⁢   °     +     φ   2     -   β     )         =     P     sin   ⁡     (     α   -     φ   1     -     φ   2       )           ,         
that is,
 
               P   =       R   13     ⁢       sin   ⁡     (     α   -     φ   1     -     φ   2       )         cos   ⁡     (       φ   2     -   β     )             ,         
therefore, to prevent the release of the lock block from the first and second frictional contact faces, P shall be less than or equal to 0. Considering −90′&lt;φ 2 −β&lt;90′, then cos(φ 2 −β)&gt;0, and hence α≦φ 1 +φ 2 , i.e. the condition for self-locking.
 
     That is, if the angle α is less than or equal to the sum of the frictional angles φ 1  and φ 2 , i.e. α≦φ 1 +φ 2 , the locking member  102  is allowed to be moved in the first direction F 1  with respect to the housing  101 , but locked in the second direction F 2  opposite to the first direction F 1 , so that the locking member can be continuously locked, i.e. locked at any of continuous locking positions. 
     If the housing, the locking member and the lock block are all made of steel, the frictional angles φ 1 =φ 2 =8.5° since the friction factor of steel is about 0.15, thus the angle α is less than or equal to about 17°. However, the components of the self-locking device may be made of any other suitable material, or the components may be of different material, and even the same component of the device may be made of various materials. 
     Based on the operation principle of the first example of the self-locking device, it is possible to combine multiple, e.g. two, self-locking devices as desired. 
       FIGS. 4C-4D  show the structure and operation principles of the second and third examples of the self-locking device used in the locking assembly of the auxiliary wheel of the invention. 
     As shown in  FIG. 4C , the second or third example of the self-locking device actually is consisted of two first examples of the self-locking device. Particularly, the self-locking device in the second or third example includes a housing  111  with a cavity, a locking member  112  that is at least partially within the cavity, a first lock block  113  and a second lock block  113   a . The wall of the cavity includes a first and a fourth frictional contact faces  111 W,  111 M. A second and a third frictional contact faces  112 M,  112 W are provided on the locking member  112 . The first and second frictional contact faces  111 W and  112 M face each other and form an angle α, and the fourth and third frictional contact faces  111 M and  112 W face each other and form an angle α′. The first lock block  113  is arranged between and contacts with the first and second frictional contact faces, and the second lock block  113   a  is arranged between and contacts with the third and fourth frictional contact faces. The self-locking device may further include holding members (not shown), which apply pretightening forces on the first and second lock blocks  113 - 113   a  towards the vertexes of the angles α and α′, respectively. 
     If the angle α between the first and second frictional contact faces ( 111 W,  112 M) meets α≦φ 1 +φ 2 , and the angle α′ between the third and fourth frictional contact faces ( 112 W,  111 M) meets α′≦φ 3 +φ 4 , where φ 1  and φ 2  denote the frictional angle between the first lock block  113  and the first frictional contact face and that between the first lock block  113  and the second frictional contact face, respectively, and φ 3  and φ 3  denote the frictional angle between the second lock block  113   a  and the third frictional contact face and that between the second lock block  113   a  and the fourth frictional contact face, the locking member  112  may is movable along a first direction F 1  with respect to the housing  111  but is locked in a second direction F 2  opposite to the first direction F 1 , and hence can be locked at any continuous locking position. Further, if the angle between the second and third frictional contact faces ( 112 M,  112 W) is denoted by γ, and the angle between the first and fourth frictional contact faces ( 111 W,  111 M) is denoted by θ, then θ≦φ 1 +φ 2 +φ 3 +φ 4 +γ. The above angles may be designed according to the above principles, so that the locking member can be locked at any of continuous locking positions by the lock blocks. 
     The second example of the self-locking device used in the locking assembly arranged on the hub of the auxiliary wheel is described below. The locking assembly includes a self-locking device with continuous locking positions and a catch device associated with the self-locking device, as shown in  FIGS. 5A-5D . The self-locking device includes a housing  121 , a locking member  122  and two lock blocks ( 123 ,  123   a ), and preferably further includes a holding member (e.g. springs  124 ). 
     As shown in  FIGS. 5A-5D , the housing  121  is fixed on the hub of the auxiliary wheel, alternatively formed integrally with the auxiliary wheel. The housing  121  contains a cavity, the wall of which includes two frictional contact faces  121 W and  121 M (which are equivalent to the first and fourth frictional contact faces  111 W,  111 M shown in  FIG. 4C ). Two frictional contact faces  122 M and  122 W (which are equivalent to the second and third frictional contact faces  112 W,  112 M shown in  FIG. 4C ) are provided on the locking member  122 , which is designed to be at least partially within the cavity of the housing  121 , so that the faces  122 M and  122 W of the locking member  122  face the faces  121 W and  121 M of the housing  121 , respectively. As shown in  FIG. 5C , the locking member  122  is rotatablely connected to the housing  121 , for example, hinged to the housing  121  through a pin  126 . The housing  121  functions to fix its components and/or itself. The rotation of the locking member  122  relative to the housing  121  causes the faces  122 M and  122 W to be moved relative to the faces  121 W and  121 M. For example, the locking member  122  may be a disc wheel, which is rotatablely connected to the housing  121  through a pin  126  perpendicular to the side faces of the disc wheel, and the faces  122 M and  122 W are provided on both side faces of the disc wheel. 
     The two lock blocks  123  and  123   a  are received within the housing  121 , with the lock block  123  being sandwiched between and in contact with the faces  121 W and  122 M, and the lock block  123   a  being sandwiched between and in contact with the faces  121 M and  122 W. The self-locking device including the frictional contact faces  121 W,  122 M,  121 M and  122 W and the lock blocks  123  and  123   a  is equivalent to the self-locking device shown in  FIG. 4C , and the lock blocks  123  and  123   a  allows the locking member  122  to be movable in the first direction F 1  relative to the housing  121  but locked in the second direction F 2  opposite to the first direction F 1 , so that the locking member  122  can be locked at any continuous locking position. Once the lock block  123  or  123   a  is separated from the frictional contact face of the housing or locking member by a force applied to the lock block, the locking member  122  is allowed to be moved in the second direction F 2  and thus is unlocked. Preferably, the angle between the faces  121 W and  122 M is less than or equal to the sum of the frictional angle between the lock block  123  and the face  121 W and that between the lock block  123  and the face  122 M, and the angle between the faces  121 M and  122 W is less than or equal to the sum of the frictional angle between the lock block  123   a  and the face  121 M and that between the lock block  123   a  and the face  122 W. 
     The frictional contact faces  121 W and  121 M within the housing  121  and the lateral frictional contact faces  122 M and  122 W of the locking member  122  may have a partial annular shape (the center of which is located at the center of the pin  126 ). All the frictional contact faces may have a flat shape, or any other shape complementary with the lock blocks  123  or  123   a . Preferably, all the frictional contact faces are shaped to allow for rolling or sliding of the lock blocks  123  and  123   a  on the frictional contact faces and the increased contact area between the lock blocks ( 123 ,  123   a ) and the frictional contact faces. For example, the lock block may have a spherical shape and the corresponding frictional contact faces have a recessed shape. The housing  121  may be fixedly connected to the hub  11  of the auxiliary wheel through screw holes  121 C. 
     Two open grooves  122 B are preferably provided in the two frictional contact faces of the locking member  122 , so that the locking member  122  is unlocked before its use, to facilitate the use and improve the use efficiency of the device. 
     Preferably, the self-locking device further includes spring retainers  125 , springs  124  and screws  128  for fixing the spring retainers. The springs  124 , together with the spring retainers  125 , apply an elastic pretightening force on the lock blocks  123  and  123   a . The spring retainer  125  may be fixed onto the housing  121  through screws  128 , or be formed integrally with the housing  121 . The pin  126 , which functions as the rotation shaft of the locking member  122 , may be further fixed to the housing  121  by nuts  127 . 
     The locking assembly may further include a catch device as described in detail below. An engaging tab  122 D used to engage with the catch device extends from the periphery of the locking member  122 , i.e. the disc wheel. A handle  122 C used for rotating the locking member  122  additionally extends radially from the periphery of the locking member  122 . 
       FIGS. 6A-6C  shows the locking assembly with the second example of the self-locking device. The assembly includes the self-locking device mounted on the hub  11  of the auxiliary wheel and a catch device that is mounted on the adaptation module  8  attached to the hub  11 . The catch device includes a rod mechanism  120  and a catch mechanism  110  rotatablely hinged to the rod mechanism  120 . One end  110 B of the catch mechanism  110  is rotatablely hinged to the adaptation module  8 , while the other end of the catch mechanism  110  that is opposite to the end  110 B is used to abut against the inner wall of the hub of the vehicle wheel. The rod mechanism  120  passes through the through hole in the hub of the auxiliary wheel to be movably engaged with the engaging tab  122 D of the locking member  122 , so that the movement of the locking member  122  in the first direction F 1  causes the catch mechanism  110  to abut against the vehicle wheel hub (particularly the inner wall  16 E of the vehicle wheel hub, i.e. a side of the vehicle wheel hub that is away from the auxiliary wheel, for example), in order to sandwich the vehicle wheel hub between the self-locking device and the catch device (particularly the catch mechanism). However, the locking of the locking member  122  in the second direction F 2  prevents the catch mechanism from releasing from the vehicle wheel hub. Therefore, when the catch mechanism  110  is locked, the auxiliary wheel is fixedly mounted on the vehicle wheel hub, and when the catch mechanism  110  is unlocked, the auxiliary wheel may be released from the vehicle wheel hub. 
     The adaptation module  8  may be fixed on the inner side of the hub  11  of the auxiliary wheel, or formed integrally with the hub  11 . The catch device may further include a seat  130  for the catch mechanism  110  (shown in  FIG. 6B ) fixedly arranged in a recess  8 H (shown in  FIG. 3C ) of the adaptation module  8 . The catch mechanism  110  is hinged to the seat  130  through a pin  126 B, as shown in  FIG. 6B . An intermediate engaging portion  110 A of the catch mechanism  110  is hinged to an end  120 A of the rod mechanism  120 . The seat  130  may be also formed integrally with the adaptation module  8 . Alternatively, the catch mechanism  110  may be directly hinged to the adaptation module  8  without the seat  130 . 
     The rod mechanism  120 , a catch mechanism  110 ′ (see  FIG. 8 ), and/or the locking member  132  (see  FIG. 8A ) may extend through the adaptation module  8  via the opening  8 E (see  FIGS. 3A and 3E ) in the adaptation module  8 . 
     A flexible part may be arranged between the adaptation module  8  and the vehicle wheel hub  12  to prevent any possible damage made to the hub  12  by the adaptation module  8 . The flexible part may be elastic or non-elastic and made of various flexible materials. Further, the adaptation module  8  may be eliminated, in this case, one end of the catch device  110  is directly hinged to the hub  11  of the auxiliary wheel, or to the seat  130  fixed on the hub  11 . 
     The catch device may further include a part, such as a spring  124 A, which applies an elastic force to the catch mechanism  110  to keep the unlocked catch mechanism  110  away from the vehicle wheel hub (i.e. at an open position). As shown in  FIG. 6B , the rod mechanism  120  extends through the spring  124 A, one end of which rests against the adaptation module  8  and the other end of which rests against the catch mechanism  110 . 
     The rod mechanism may be movably connected with or formed integrally with the catch mechanism and/or the disc wheel. 
       FIG. 7  shows the case where the rod mechanism is formed integrally with the catch mechanism, and shows the assembly of the adaptation module  8 , the self-locking device, the catch mechanism  110 ′, the seat  130 ′ for the catch mechanism, a torsion spring  124 B and the hub  11  of the auxiliary wheel. As shown in  FIG. 7 , one end  110 ′A of the catch mechanism  110 ′ (which is equivalent to the rod mechanism  120  and the catch mechanism  110  shown in  FIG. 6B ) is directly hinged to the locking member  122  of the self-locking device of the locking assembly, and the other end of the catch mechanism  110 ′ is an abutting end  110 ′B. An end  130 ′C of the seat  130 ′ may function as a pivot point used for the locking and opening of the abutting end  110 ′B. The torsion spring  124 B is arranged on the seat  130 ′, one end of the torsion spring  124 B is fixed on the seat  130 ′ and the other end is fixed on the abutting end  110 ′B of the catch mechanism  110 ′. In the unlocked state of the self-locking device, the locking member  122  is allowed to rotate freely and thus the abutting end  110 ′B of the catch mechanism  110 ′ is released away from the vehicle wheel hub under the effect of the torsion spring  124 B, in this case, the catch mechanism  110 ′ rests against the end  130 ′C of the seat  130 ′ by its recess  110 ′C. 
       FIG. 7  shows the locked state of the catch mechanism  110 ′, where the abutting end  110 ′B of the catch mechanism  110 ′ rests against the vehicle wheel hub. To put the catch mechanism  110 ′ into its locked state, the locking member  122  is rotated in the locking direction F 1  to pull the catch mechanism  110 ′, and the abutting end  110 ′B of the catch mechanism  110 ′ is supported by the end  130 ′C of the seat  130 ′ and abuts against the inner wall  16 E of the vehicle wheel hub  12 , to lock the hub  11  of the auxiliary wheel on the vehicle wheel. While in the unlocked state of the locking assembly, the locking member  122  may be rotated freely in the unlocking direction F 2 , and the catch mechanism  110 ′ may return to its released state under the effect of the torsion spring  124 B. 
     The catch mechanism may be of any form, as long as it can abut against the vehicle wheel hub when driven by the rod mechanism. 
       FIGS. 8A-8D  show a schematic structural representation of a third example of the self-locking device, which is a variant of the second example of the self-locking device and operates with the same principles as the second example. The self-locking device in the third example includes a housing  131 , a locking member  132 , two lock blocks  133  and  133   a , and a lock block retainer  136  (which is actuated to lock and unlock the device, as described below), and preferably includes a holding member (e.g. springs  134 ). 
     The third example of the self-locking device is generally different from the second example of the self-locking device by adopting a different locking member  132  and introducing a lock block retainer  136 , but these examples operate in the same self-locking principles. The housing  131  in the third example contains a cavity, wall of which includes two frictional contact faces  131 W and  131 M (which are equivalent to the frictional contact faces  121 W and  121 M in  FIG. 5B ), and the locking member  132  includes two frictional contact faces  132 M and  132 M (which are equivalent to the frictional contact faces  122 W and  122 M in  FIG. 5B ) and is arranged at least partially within the cavity of the housing  131 , so that the faces  132 M and  132 W face the faces  131 W and  131 M, respectively. 
     The lock block  133  is arranged between and contacts with the frictional contact faces  131 W and  132 M, and the lock block  133   a  is arranged between and contacts with the frictional contact faces  131 M and  132 W. The self-locking device having the frictional contact faces  131 W,  132 M,  131 M,  132 W and the lock blocks  133 ,  133   a  is equivalent to the one shown in  FIG. 5B , and the lock blocks  133  and  133   a  allow the locking member  132  to be movable in the first direction F 1  relative to the housing  131  but be locked in the second direction F 2  opposite to the first direction F 1 , so that the locking member  132  can be locked at any of continuous locking positions. Once the lock block  133  or  133   a  is separated from the corresponding frictional contact face of the housing or locking member by a force applied to the lock block, the locking member  132  is allowed to be moved in the second direction F 2  and thus is unlocked. Preferably, the angle α between the faces  131 W and  132 M is less than or equal to the sum of the frictional angle φ 1  between the lock block  133  and the face  131 W and the frictional angle φ 2  between the lock block  133  and the face  132 M, and the angle α′ between the faces  131 M and  132 W is less than or equal to the sum of the frictional angle φ 3  between the lock block  133   a  and the face  131 M and the frictional angle φ 4  between the lock block  133   a  and the face  132 W. 
     Preferably, the vertexes of the angles α and α′ substantially point the direction F 2 . Preferably, α=α′, and/or φ 1 =φ 2 , and/or φ 3 =φ 4 . The lock blocks  133  and  133   a  are symmetrical with respect to the locking member  132 . 
     The lock block retainer  136  is extended into the cavity of the housing  131 , and the locking member  132  is extended through the lock block retainer  136 . The lock blocks  133  and  133   a  are arranged in holes in the longitudinal (i.e. in the direction of F 1  or F 2 ) side wall of the lock block retainer  136 , so that the lock block retainer  136  may be used to actuate the lock blocks  133  and  133   a  and prevent irregular movements of the lock blocks  133  and  133   a . In this embodiment, the lock blocks  133  and  133   a  have a column shape which is complementary with that of the hole in the longitudinal side wall of the retainer  136 . 
     The lock block retainer  136  may be used for locking and unlocking the self-locking device. For example, as shown in  FIG. 8A , the lock block retainer  136  has a flange at its one end along its longitudinal direction (i.e. the direction F 1  or F 2 ), and the lock block retainer  136  may be moved in the direction F 2  if a prying face  136 A on the top of the flange is pressed down. Further, a pivot face  132 A facing the prying face  136 A is provided at one end of the locking member  132 , and the locking member  132  may be moved in the direction F 1  by lifting the pivot face  132 A. To lock the self-locking device, a prying rod  7 B or  7 C (shown in  FIGS. 11B-11C ) is inserted between and pries the prying face  136 A and the pivot face  132 A, and the prying face  136 A is pressed down while the pivot face  132 A is lifted by the prying rod through a lever principle, thus the locking member  132  is lifted in the direction F 1  while the lock block retainer  136  is pressed down, and the lock block retainer  136  in turns pulls the two lock blocks  133 - 133   a  down which are then sandwiched tightly between the frictional contact faces  131 W and  132 M and between the frictional contact faces  131 M and  132 W, respectively, in this way, any retracting stroke is prevented during the locking of the self-locking device and any deformation of the locking member and the housing is absorbed. The lock block retainer  136  may also have a pivot face  136 B, which may be lifted to pull up the lock block retainer  136  in the direction F 1 ; further, a prying face  135 B facing the pivot face  136 B may be provided on the housing  131  or any other part (e.g. a spring retainer  135 ) fixed on the housing  131 . To unlock the self-locking device, the prying rod  7 B or  7 C is inserted between and pries the pivot face  136 B and the prying face  135 B, and the pivot face  136 B may be lifted by the prying rod through a lever principle, so that the lock block retainer  136  is lifted to pull up the lock blocks  133 - 133   a  in the direction F 1 ; in this case, one or both of the lock blocks  133 - 13   a  are released from the locking member  132 , which is then may be moved in the direction F 2 . As an alternative to the pivot face  136 B, prying holes  136 D may be formed in the side wall of the lock block retainer  136  and lifted or pressed by a prying rod to lock or unlock the lock block retainer  136 . 
     In the third example of the self-locking member, a spring retainer  135  is preferably fixed on the housing or formed integrally with the housing. The springs  134  rest on the spring retainer  135  and apply elastic forces on the lock blocks  133 - 133   a , to keep the lock blocks  133 - 133   a  to be in contact with both the locking member  132  and the housing  131 . 
     Likewise, the locking member  132  may be used with the catch device and the adaptation module described above with reference to the second example of the self-locking device, so that the movement of the locking member  132  in the first direction F 1  causes the catch device to abut against the hub of the vehicle wheel, while the locking of the locking member  132  in the second direction F 2  prevents the detachment of the catch device from the hub of the vehicle wheel. Preferably, one end of the locking member  132  is provided with a T-shaped head  132 C for hinging with the catch device; alternatively, the locking member  132  has a catch part at its one end and may be used as the catch mechanism to be locked on the hub of the vehicle wheel. 
     If required, the lock blocks may have a shape of pentagonal prism (with a trapeziform cross-section), as shown in  FIG. 9 , the lock blocks  133 ′ and  133   a ′ are in surficial contact with the locking member  132  and the housing  131  to increase the frictional contact areas. Such lock blocks  133 ′ and  133   a ′ are helpful in reducing deformation of the frictional contact faces of the locking member  132  and the housing  131 . The lock blocks may alternatively have a spherical shape, as illustrated by lock blocks  133 ″ and  133   a ″ shown in  FIG. 10 . Of course, the lock blocks may have other shapes with triangular, trapeziform, rhombic, irregular cross-sections, for example. 
     The springs  134 , which may be spring leaves or torsion springs, may be used to apply forces on the lock block retainer  136  and/or the lock blocks  133  and  133   a , and may be fixed between the housing and the lock blocks, or between the housing and the lock block retainer. 
     A hook  136 C protruding from the side wall of the lock block retainer  136  between both longitudinal ends of the retainer  136  (along the direction F 1  or F 2 ), as shown in  FIG. 8C , is used for keeping the retainer  136  at a certain position in the unlocked state of the self-locking device. In use, when the prying face  136 B of the lock block retainer  136  is lifted by a prying tool, and the hook  136 C is raised above the housing  131 , at this time, the lock block retainer  136  is pushed and inclined to the side of the hook  136 C by a spring  134 A arranged within the housing  131 , so that the hook  136 C rests on the top surface of the housing  131  or the spring retainer  135  and the self-locking may be kept in its unlocked state. 
     The housing  131  may be fixedly hinged or threadedly connected, or integrally formed with the vehicle wheel hub. 
     Grooves  132 B may be provided on the surface of the locking member  132  to accommodate the lock blocks  133  and  133   a  in the unlocked state of the self-locking device, to prevent the unintended locking of the locking member  132 . The grooves  132 B may also be pried by the prying tool to pull the locking member  132 . 
     The self-locking device, the hub  11  of the auxiliary wheel, and the adaptation module  8  may be fixed together in sequence by bouts. In the self-locking device shown in  FIGS. 8A-8D , if the locking member  132  is also used as the catch mechanism, in order to lock the auxiliary wheel onto the vehicle wheel, first of all, the vehicle wheel  1  is placed on the vehicle wheel  2 , the adaptation module  8  is inserted into the through hole  16  of the vehicle wheel, and the T-shaped head  132 C of the locking member  132  is extended through both an opening in the adaptation module and the through hole  16 ; when the locking member  132  is moved in the direction F 1  and locked, its T-shaped head  132 C abuts against the inner radial wall  16 E of the vehicle wheel hub  12 , so that the auxiliary wheel  1  is locked on the vehicle wheel  2 . After the self-locking device is unlocked, the T-shaped head  132 C is detached from the inner radial wall  16 E, and thus the auxiliary wheel  1  may be separated from the vehicle wheel  2 . 
     Tools for locking and unlocking the above self-locking device are described below referring to  FIGS. 11A-11C . 
     A prying rod  7 A shown in  FIG. 11A  may be used for locking and unlocking the second example of the self-locking device. The paying rod  7 A has an unlocking end  72  for unlocking the self-locking device and an opposite locking end  74  for locking the self-locking device. Two parallel hooks  78  are respectively arranged at two lateral sides of the unlocking end  72 , and two protrusions  76  are arranged between the hooks  78 . A recess is formed at the locking end  74 . To unlock the self-locking device, the hooks  78  respectively hook the nuts  127  on both sides of the self-locking device (as shown in  FIG. 5A ), so that the prying rod  7 A may be rotated about the nuts; then the lock blocks of the second example of the self-locking device are pressed down by the protrusions  76  of the prying rod  7 A due to the rotation of the prying rod  7 A in the direction F 1 , thus the lock blocks are released and the locking member  122  is unlocked. To lock the self-locking device, the locking end  74  of the prying rod  7 A is engaged with the handle  122 C on the locking member  122  and the prying rod  7 A is rotated in the direction F 1 , so that the self-locking device may be put into its locked state. 
     The prying rods  7 B and  7 C shown in  FIGS. 11B-11C  may be used for locking and unlocking the third example of the self-locking device. 
     Two pairs of pawls  7 B and  7 C are arranged at one end of the prying rod  7 B, one of the two pairs of pawls have prying portions  71  and pivot portions  73 , while the other one of the two pairs of pawls have prying portions  77  and pivot portions  75 . The two pairs of pawls are opposite to each other and form a substantial circle. The gap between one pair of pawls is different from that of the other pair of pawls. Likewise, the gap between a pair of pawls (having two prying portions  71 ′ and two prying portions  73 ′) at one end of the prying rod  7 C is different from that between a pair of pawls (having two prying portions  77 ′ and two prying portions  75 ′) at the other end of the prying rod  7 C. The pawls of the prying rod  7 B or  7 C may be inserted between the prying face  136 A of the lock block retainer  136  and the pivot face  132 A of the locking member  132 , or between the pivot face  136 B of the lock block retainer  136  and the prying face  135 B, to lock and unlock the third example of the self-locking device. 
     The prying rods  7 B and  7 C may have a various shape, as long as the prying rods may be used to press down the lock block retainer  136  while lifting the locking member  132 , and lift the lock block retainer  136  with respect to the housing  131 . 
     In order for the coaxial connection between the auxiliary wheel  1  and the vehicle wheel  2 , a member for matching and fixedly connecting with the locking assembly of the auxiliary wheel is fixedly arranged on the hub  12  of the vehicle wheel, to further facilitate the mounting and demounting of the auxiliary wheel on the vehicle wheel. The member may be a stake. 
     For example, the locking member of the above self-locking device may function as the stake, and locking and unlocking the locking member relative to the housing allows locking and unlocking the auxiliary wheel relative to the vehicle wheel. For example, the locking member  132  is fixed as the stake on the hub  12  of the vehicle wheel, and the housing  131  is fixed on the hub  11  of the auxiliary wheel, so that locking and unlocking the locking member  132  relative to the housing  131  allows locking and unlocking the auxiliary wheel relative to the hub of the vehicle wheel. Preferably, the housing has a cylindrical shape, while the stake has a column shape, the diameter of the cross-section of the root portion of the stake is less than the diameter of the cross-section of the top portion of the stake, and the lock block has a spherical shape. 
     In another example, a stake  12 A fixed on the hub  12  of the vehicle wheel is used as the locking member of an individual locking assembly shown in  FIGS. 12A-12C , and an annular locking groove  12 B is formed on the stake  12 A. This locking assembly includes a lock block retainer  11 A, lock blocks  43 , a self-locking cap  41 , an elastic member  44  and a cover  45 . 
     The lock block retainer  11 A is fixed on or formed integrally with the hub  11  of the auxiliary wheel, and the stake  12 A extends through the retainer  11 A. Lock block receiving holes  11 B are formed in the longitudinal (i.e. in the direction of F 1  or F 2 ) side wall of the lock block retainer  11 A, the number and positions of the lock block receiving holes  11 B correspond to the number of the lock blocks  43  and the positions of the annular locking groove  12 B, respectively. 
     The lock blocks  43  are inserted into the lock block receiving holes  11 B. The self-locking cap  41  surrounds the lock block retainer  11 A, and has a tapered contact face that faces the lock block  43 . Preferably, the cover  45  is fixedly attached to the lock block retainer  11 A, and the elastic member  44  is arranged between the cover  45  and the self-locking cap  41  and used to apply an elastic force on the cap  41 , causing the tapered contact face of the cap  41  to tightly press and drive the lock blocks  43  into the annular locking groove  12 B. 
     The stake  12 A may be also formed integrally with the hub  12  of the vehicle wheel. 
     Preferably, the locking assembly in the example further includes a cam lever  42 , which includes a cam and a handle attached to or formed integrally with the cam. The cam is hinged with the self-locking cap  41  through a pin  46  and in contact with the cover  45 , so that when the cam is rotated about the pin  46  due to the operation of the handle, the self-locking cap  41  may be lifted or moved down (by the elastic member  44 ) relative to the cover  45 , causing the self-locking cap  41  to press on or be released from the lock blocks  43 , as a result, the self-locking cap  41  may be switched between its locking position and unlocking position. 
     In the embodiment, four lock block receiving holes  11 B are formed in the side wall of the lock block retainer  11 A, but more or less lock block receiving holes  11 B and lock blocks  43  may be provided. The diameter of the hole  11 B in the internal surface of the side wall of the retainer  11 A is less than the diameter of the lock block  43  while the diameter of the hole  11 B in the external surface of the side wall of the retainer  11 A is larger than the diameter of the lock block  43 , to prevent the lock block  43  from fully passing through the internal surface of the side wall. 
     The lock block  43  may have a spherical shape, an elliptic shape, etc. 
     Preferably, the internal tapered contact face of the cap  41 , the surface of the locking groove  12 B on the stake  12 A and the lock block  43  form the above first example of the self-locking device. That is, the internal tapered contact face of the cap  41  is equivalent to the first frictional contact face in the first example of the self-locking device, the lock block  43  is equivalent to that in the first example of the self-locking device, and the surface of the locking groove  12 B is equivalent to the second frictional contact face in the first example of the self-locking device. The vertex of an angle formed between the internal tapered contact face of the cap  41  and the surface of the locking groove  12 B substantially points to a direction from the vehicle wheel to the auxiliary wheel, so that the lock block  43  is movable to the vehicle wheel (i.e. in the direction F 2 ) but not in the opposite direction (i.e. the direction F 1 ). Since the lock block  43  is received in the wall of the lock block retainer  11 A and moved together with the retainer  11 A, the retainer  11 A is allowed to move towards the vehicle wheel when the lock block  43  is locked, and hence the vehicle wheel and the auxiliary wheel are held together. During the driving of the vehicle, if a gap is formed between the vehicle wheel and the auxiliary wheel due to vibration, the gap will be absorbed automatically according to the principle of the self-locking device and the effect of the elastic member  44 , so that the auxiliary wheel may be locked more tightly on the vehicle wheel. 
     In the practical use of the locking assembly, in order for locking, the auxiliary wheel is placed closely on the vehicle wheel, with the stake  12 A extending into the lock block retainer  11 A, then the cam lever  42  is rotated to its locking position to press down the cap  41 , thus the lock blocks  43  are moved in the lock block receiving holes  11 B and abut against the locking groove  12 B, so that the stake  12 A are locked in the lock block retainer  11 A and the auxiliary wheel is locked onto the vehicle wheel. In order for unlocking, the cam lever  42  is rotated to its unlocking position to overcome the elastic force of the elastic member  44  and lift the cap  41 , in this situation, the lock block  43  is released by the cap  41  and thus the lock block retainer  11 A and the stake  12 A are unlocked, and the auxiliary wheel may be removed from the vehicle wheel. 
     One or more the above-described locking assemblies may be used to steadily lock the auxiliary wheel on the vehicle wheel. 
     Locking means other than the above-described self-locking device may be used for locking an auxiliary wheel on a special-use vehicle. 
     For example, in a first means, a screw rod with a hook at its one end is adopted, where the hook extends through the through hole  16  and hooks the hub  12  of the vehicle wheel  2 , while the other end of the screw rod extends through the mounting hole of the auxiliary wheel  1  and is fixed, thereby coaxially connecting the auxiliary wheel  1  on the vehicle wheel  2  by the screw rod. 
     In a second means, partial of all of available screws on the hub  12  of the vehicle wheel are used for fixing the auxiliary wheel, by forming screw holes on the hub  11  of the auxiliary wheel  1  which corresponding to the screw holes on the hub  12 , in this case, the screws for fixing the hub  12  may be used to pass through both the hubs  11 - 12  and fix the hub  11  on the hub  12 , thereby fixing the auxiliary wheel  1  on the vehicle wheel  2 . 
     The unassisted lifting jack  5  shown in  FIG. 13A  is useful for lifting the vehicle wheel  2  easily to mount the auxiliary wheel  1  on the vehicle wheel  2 . The unassisted lifting jack  5  includes a receiving seat  52  and a climbing block  51 , which are rotatablely connected through a pin  56 . In use, the climbing block  51  is rotated out of the receiving seat  52 , in this case, the bottom of the climbing block  51  and that of the receiving seat  52  are in the same plane and in contact with the ground, and the climbing block  51  has a slope, over which the vehicle wheel may climb onto the receiving seat  52 . The climbing block  51  may be rotated and received within the receiving seat  52 , to reduce the size of the unassisted lifting jack  5  for easy carrying. The climbing block  51  has a substantive triangular shape, and may be formed by elastic material. The surfaces of the climbing block  51  that are in contact with the vehicle wheel and the ground may be coarse to increase frictional forces. A recess is formed on the top of the receiving seat  52  for supporting the vehicle wheel steadily. 
     The auxiliary wheel  1  may function in place of or to assist the conventional vehicle wheel  2 . For example, the auxiliary wheel  1  may be used as a backup wheel to take the role of a failed vehicle wheel; and an anti-slip auxiliary wheel  1  may be used for driving on a snowy road. The auxiliary wheel  1  may be provided with a solid, vacuum or composite tyre. 
     For example, the structure of an auxiliary wheel with an anti-slip function is described below. 
       FIG. 14A  shows an auxiliary wheel  141  with anti-slip spikes. Particularly, the auxiliary wheel  141  includes a hub and a tyre, and the tyre includes an inner tyre  94 , an external tyre  92 , an isolator  93  and anti-slip spikes  91 . The anti-slip spikes  91  are fixed on the external tyre  92 ; the isolator  93 , which has an annular shape and is arranged between the inner tyre  94  and the external tyre  92 , abuts against the inner wall of the external tyre  92 , and is used for preventing any damage made on the inner tyre by the anti-slip spikes or spike seats. The isolator  93  may be omitted if the anti-slip spikes  91  and the spike seats would not damage the inner tyre. Each anti-slip spike  91  includes a flange at its bottom arranged within the external tyre  92 , and the top of the anti-slop spike  91  protrudes from the external surface of the external tyre  92 . 
     Alternatively, the auxiliary wheel  141  may include a solid tyre, on which the anti-slip spikes are arranged. Or, the auxiliary wheel may include the external tyre but no inner tyre. 
       FIG. 14B  shows an anti-slip means arranged on an anti-slip tyre according to an embodiment.  FIG. 14C  shows the structure of the anti-slip means, which includes a spike seat  98  and anti-slip spikes  91  protruding from a substrate. In the embodiment, a through hole is formed in the substrate. The spike seat  98 , which includes a connecting pole and a base  98 B, is fixed within the external tyre  92  of the auxiliary wheel. The connecting pole is fixed on the base  98 B, and preferably has a smaller diameter than that of the base  98 B. A head  98 A opposite to the base  98 B is arranged on the top of the connecting pole in various ways such as riveting, hinging, threads and snapping. The connecting pole of the spike seat  98  extends through the substrate and then the head  98 A is fixed on the connecting pole. Such spike seat  98  ensures that the anti-slip spikes  91  can be mounted on the tyre and prevents the detaching of the spikes  91  from the tyre, and further allows the substrate for the anti-slip spike  91  to be movable along the connecting rod of the spike seat  98  due to the pressure from the ground. 
       FIGS. 14B-14C  show that four spikes  91  are formed on each substrate, but more or less spikes may be formed. The spikes  91  for an anti-slip function pierce into the snowy or muddy road during the driving of a vehicle with such auxiliary wheels. 
     Each spike may be designed with a cavity in communication with its open free end, the free end preferably has a diameter less than that of the other end of the spike that is connected with the substrate. In this case, when the spike pierces into the road during the driving, snow, mud and so on is entered into the hollow spike from its open end and pushed out from a side opening in communication with the cavity, so that the spike may easily pierce into the snowy or muddy road for an anti-slip effect. 
     To prevent the spikes  91  from damaging the road, the free ends of the spikes  91  on the auxiliary wheel  1  do not exceed the outer diameter of the vehicle wheel  2 . Further, the air pressure in the vehicle wheel  2  or the auxiliary wheel  1  may be adjusted so that the spikes  91  are effectively pressed on the road for anti-slip but will not damage the road. 
     The preferable embodiments of the invention have been described, but the invention is not limited thereto. Various modifications and alterations to the invention may occur to those skilled in the art, and all such modifications and alterations fall into the scope of the invention, without departing from the principle of the invention.