4.6. The disposal of the first channels 3.6 and the second channels 4.6 helps the transmission component 8 to run through. Further, when the first rail 1 and the second rail 2 are unfolded to be in one straight line, the first channels 3.6 are in communication with the corresponding second channels 4.6 to ensure the transmission component 8 will not be exposed. Moreover, the disposal of the first channels 3.6 and the second channels 4.6 below the first thread holes 3.3 and the second thread holes 4.3 ensures the bending of the transmission component 8 will not be affected by the connection piece 5 when the first rail 1 and the second rail 2 are folded up.

With reference to FIG. 3, the transmission component 8 comprises a wire rope 8.1 and a belt 8.2. The belt 8.2 is disposed in the first rail 1 and connected to the primary transmission box 6 in a winding way. The wire rope 8.1 is disposed in the second rail 2 and connected to the secondary transmission box 7 in a winding way. Furthermore, both ends of the wire rope 8.1 respectively run through the second channels 4.6 and the first channels 3.6 to correspondingly connect with both ends of the belt 8.2 to form a closed loop. The transmission component 8 adopts the structure of the wire rope 8.1 spliced with the belt 8.2 because, on the one hand, the transmission of the belt 8.2 and the primary transmission box 6 is made more stable without any slip, and on the other hand, the wire rope 8.1 is more bendable than the belt 8.2 and can restore with less damage after being bent. As a result, both ends of the wire rope 8.1 respectively run through the second channels 4.6 and the first channels 3.6 to correspondingly connect with both ends of the belt 8.2, such that the belt 8.2 can be entirely located within the first rail 1 without bending when the first rail 1 and the second rail 2 are folded up. The two symmetrical segments of wire ropes 8.1 under the connection piece 5 are bent to facilitate the folding operation and bring little damage.

With reference to FIGS. 3 and 7, two segments of hose 9 are symmetrically sleeved on the wire rope 8.1 at both sides of the connection piece 5. The two segments of hose 9 are located inside the first channels 3.6 and the corresponding second channels 4.6. When the first rail 1 and the second rail 2 are unfolded to be in one straight line, the two segments of hose 9 are shaped like a straight line, and when the first rail 1 and the second rail 2 are folded to be in parallel, the two segments of hose 9 are shaped like “U”. The two segments of hose 9 are sleeved on the bending positions of the wire rope 8.1 such that the wire rope 8.1 can be protected against deformation in a folding process, further reducing the damage to the wire rope 8.1 and extending its service life.

With reference to FIGS. 1, 3, and 5, a first pulley block 10 is disposed in the first rail 1 and a second pulley block 11 is disposed in the second rail 2. The first pulley block 10 and the second pulley block 11 are connected to the transmission component 8 to achieve synchronous movement. The first pulley block 10 and the pulley block 11 move toward each other. The first pulley block 10 is used to connect with a head end of a curtain body in the first rail 1 to open or close the curtain body, and the second pulley block 11 is used to connect with a head end of the curtain body in the second rail 2 to open or close the curtain body. The first pulley block 10 and the second pulley block 11 synchronously move toward the connection piece 5 along with the movement of the transmission component 8 so as to unfold the curtain body or synchronously move in a direction away from the connection piece 5 to close the curtain body. The first pulley block 10 is slidably connected in the first rail 1 and fixedly connected at the connection position of the belt 8.2 and the wire rope 8.1, and the second pulley block 11 is slidably connected in the second rail 2 and moves in synchronization with the wire rope 8.1.

With reference to FIG. 8, at least one adjusting assembly 12 for adjusting a length of the wire rope 8.1 is disposed in the second pulley block 11. The adjusting assembly 12 comprises a spring 12.1 and a push block 12.2. A spring groove 11.1 for accommodating the spring 12.1 and the push block 12.2 is disposed in the second pulley block 11. One end of the spring 12.1 is abutted against an inner wall of the spring groove 11.1 and the other end is abutted against the push block 12.2. The wire rope 8.1 runs through an entry 11.2 of the second pulley block 11 and winds on the push block 12.2 and then runs out of an exit 11.1 of the second pulley block 11. The entry 11.2 and the exit 11.3 of the second pulley block 11 are in a same straight line. The opening direction of the spring groove 11.1 is perpendicular to the direction of the entry 11.2 and the exit 11.3. With the structure, the wire rope 8.1 is wound and squeezed on the push block 12.2 and the push block 12.2 squeezes the spring 12.1 such that the wire rope 8.1 can be maintained in an elastically-adjustable state. Due to cooperation of the push block 12.2 and the spring 12.1, the wire rope 8.1 is run in “S” shape rather than directly straight through and thus the wire rope 8.1 has an elastically-stretching length. When the first rail 1 and the second rail 2 are folded up, the wire rope 8.1 can compensate the extension of the wire rope 8.1 resulting from the bending process by using the elastic stretching of the adjusting assembly 12, further protecting the wire rope 8.1 from damage and extending its service life.

Preferably, an odd number of adjusting assemblies 12, for example, one, or three or five adjusting assemblies, are disposed in the second pulley block 11. A first adjusting assembly is near the entry 11.2, with the push block 12.2 of the first adjusting assembly being at a side away from the entry 11.2; the push blocks 12.2 in adjacent adjusting assemblies 12 are disposed in opposite directions; a last adjusting assembly is near the exit 11.3, with the push block 12.2 in the last adjusting assembly disposed in the same direction as that in the first adjusting assembly. The wire rope 8.1 runs through the entry 11.2 of the second pulley block 11 straightly and winds around the adjusting assemblies 12 in “S” shape and then straightly runs out of the exit