You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to hinges and more particularly, to a hinge, which uses a split retaining tube in a barrel to secure a pivot shaft, for allowing the pivot shaft to be rotated relative to the barrel and quickly positioned in the desired angle. 
     2. Description of the Related Art 
     A consumer electronic product with a lifting cover such as mobile computer, electronic dictionary, mobile video player, cell phone, etc., commonly uses a hinge to coupled the cover to the base member so that the cover can be opened from or closed on the base member. Therefore, the hinge also determines the quality level of the product. A good hinge allows positive positioning and does not cause noises during operation. 
     There is known a socket type hinge, which enables the pivot shaft to be positively positioned in the adjusted angular position. According to this design, the hinge comprises a female hinge member, which defines therein an axle hole, a male hinge member, which has a split shaft body positioned in the axle hole. The split shaft body of the male hinge member has two friction portions disposed in friction engagement with the peripheral wall of the axle hole of the female hinge member. However, this design of socket type hinge is not durable in use because the friction portions wear quickly with use. 
     Taiwan patent publication no. 313274, issued to the present inventor, discloses an improved structure of hinge for computer. According to this design, a springy adapter is provided between the male hinge member and the female hinge member to impart a friction resistance to the male hinge member, holding the male hinge member positively in the adjusted position. According to this design, the female hinge member must be processed to provide an inside annular step for securing the male hinge member in place. The processing of such an inside annular step is complicated, increasing the manufacturing time of the hinge. 
     SUMMARY OF THE INVENTION 
     The present invention has been accomplished under the circumstances in view. According to one aspect of the present invention, the hinge comprises a pivot shaft, a retaining split tube, and a barrel. The pivot shaft has a mounting portion for mounting, a shaft body, and a collar connected between the mounting portion and the shaft body. The shaft body has at least one annular locating groove extending around the periphery thereof. The barrel is capped on the shaft body of the pivot shaft and stopped against the collar of the pivot shaft, having an inside wall, a receiving open chamber surrounded by the inside wall for receiving the shaft body of the pivot shaft, and a mounting portion extended from one end thereof for mounting. The resilient retaining split tube is mounted in the receiving open chamber around the shaft body of the pivot shaft and forced by the inside wall of the barrel into friction with the periphery of the shaft body of the pivot shaft. The resilient retaining split tube has a plurality of angles respectively disposed in contact with the inside wall of the barrel, a plurality of planes respectively separated by the angles and disposed in contact with the periphery of the shaft body of the pivot shaft, a longitudinal crevice defined between two adjacent planes, and at least one retaining strip respectively protruded from the planes and engaged with the at least one annular locating groove of the shaft body of the pivot shaft to secure the pivot shaft to the retaining split tube and the barrel. 
     According to another aspect of the present invention, the mounting portion of the pivot shaft and the mounting portion of the barrel each have at least one mounting hole for mounting. 
     According to still another aspect of the present invention, the mounting portion of the pivot shaft and the mounting portion of the barrel each have at least one longitudinally extending plane. 
     According to still another aspect of the present invention, the number of the at least one annular locating groove of the pivot shaft is 1; the number of the at least one retaining strip of the split retaining tube is 2, and the two retaining strips are disposed at two sides relative to the longitudinal crevice and respectively engaged into the annular locating groove of the pivot shaft. 
     According to still another aspect of the present invention, the shaft body of the pivot shaft has a spiral grease groove extending around the periphery thereof for accommodating lubricating grease, and a chamfered end edge at the distal end remote from the collar. 
     According to still another aspect of the present invention, the split retaining tube has a relatively higher hardness than the barrel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded view of a hinge according to the present invention. 
         FIG. 2  is a sectional assembly view of the hinge according to the present invention. 
         FIG. 3  is a cross-sectional view taken along line A-A of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to  FIGS. 1˜3 , a hinge in accordance with the present invention is shown comprised of a pivot shaft  1 , a retaining split tube  2 , and a barrel  3 . 
     The pivot shaft  1  has a mounting portion  11  disposed at one side for fastening to a body, for example, the cover member of a mobile electronic device, a shaft body  13  disposed at the other side for coupling to the retaining split tube  2 , a collar  12  connected between the mounting portion  11  and the shaft body  13  for stopping against the barrel  3 . The mounting portion  11  can be made in the shape of a flat bar, triangular prism, rectangular bar, or polygonal bar. Further, the mounting portion  11  can be made having mounting through holes for fastening to the cover member of a mobile electronic device with fastening members, for example, screws. The shaft body  13  has a chamfered front end  16  convenient for insertion into the retaining split tube  2 , an annular locating groove  14  extending around the periphery adjacent to the chamfered front end  16 , and a spiral grease groove  15  for receiving lubricating grease. 
     The retaining split tube  2  is a polygonal, for example, pentagonal split tube made of a metal spring plate, having a plurality of angles  21  and planes  22  alternatively arranged around the periphery, a longitudinal crevice  23  defined between two adjacent planes  22  and extending through two distal ends, and two retaining strips  24  respectively protruded from the two planes  22  at two sides of the longitudinal crevice  23  for engaging the annular locating groove  14  of the shaft body  13  of the pivot shaft  1  to secure the pivot shaft b 1   b  to the inside of the retaining split tube  2 . 
     The barrel  3  has a barrel body  32 , a receiving open chamber  33  defined in the barrel body  32  and extending to one end of the barrel body  32  in communication with the atmosphere, and a mounting portion  31  extended from the other end of the barrel body  32  for fastening to, for example, the base member of the aforesaid mobile electronic device. The mounting portion  31  of the barrel  3  can be made in the shape of a flat bar, triangular prism, rectangular bar, or polygonal bar. Further, the mounting portion  31  can be made having mounting through holes for fastening to the base member of the mobile electronic device with fastening member, for example, screws. Further, the hardness of the retaining split tube  2  is relatively higher than the barrel  3 . 
     During installation, the retaining split tube  2  is attached to the shaft body  13  of the pivot shaft  1  to force the locating groove  14  of the pivot shaft  13  into engagement with the two retaining strips  24  of the retaining split tube  2 . Thereafter, the retaining split tube  2  is inserted with the pivot shaft  1  into the receiving open chamber  33  of the barrel  3 . At this time, the inside wall of the barrel  3  compresses the retaining split tube  2  radially inwards (because the diameter of the retaining split tube  2  is slightly greater than the inner diameter of the barrel body  32  of the barrel  3 , thereby keeping the retaining strips  24  in engagement with the annular locating groove  14  of the shaft body  13  of the pivot shaft  1 . When rotating the pivot shaft  1 , the inside wall of the barrel body  32  imparts a pressure to the angles  21  of the retaining split tube  2 , forcing the planes  22  in friction with the periphery of the shaft body  13  of the pivot shaft  1 . Therefore, the pivot shaft  1  is quickly positioned in position after disappearance of the external biasing force. 
     As indicated above, the invention provides a hinge, which is comprised of a pivot shaft, a retaining split tube, and a barrel. The retaining split tube is radially inwardly forced by the inside wall of the barrel against the periphery of the shaft body of the pivot shaft, thereby producing a friction resistance to hold the pivot shaft in position. Further, the split retaining tube has retaining strips engaged with the annular locating groove of the pivot shaft, preventing disconnection of the pivot shaft from the barrel. Further, the pivot shaft has a spiral grease groove spirally extending around the periphery of the shaft body of the pivot shaft for accommodating lubricating grease to lubricate the contact area between the pivot shaft and the split retaining tube. 
     Although a particular embodiment of the invention has been described in detail for purposes of illustration, various modifications and enhancements may be made without departing from the spirit and scope of the invention.

Summary:
A hinge includes a pivot shaft affixed to a first member, a barrel affixed to a second member, a polygonal retaining split tube mounted in the barrel around the shaft body of the pivot shaft and hooked on an annular locating groove at the shaft body of the pivot shaft and forced by the inside wall of the barrel in friction engagement with the periphery of the shaft body of the pivot shaft.