Patent Publication Number: US-2022232986-A1

Title: Sofa bed iron frame mechanism

Description:
BACKGROUND 
     Technical Field 
     This application relates to a sofa bed, and specifically, to a novel sofa bed iron frame mechanism. 
     Related Art 
     Storage and comfort are more concerned in modern living places. In some densely populated cities and countries, storage and organization are no longer limited to daily utensils. Moreover, there are now not abundant living places, and therefore a living area is very compact. Therefore, people usually need to better arrange their living places in limited space. A bed is one of essential household items in home life of people. However, a bed usually occupies a large area and often occupies a quite considerable amount of living space. 
     To make proper use of the area, people improve use modes of the bed to obtain larger activity space. Therefore, a sofa bed is created. The sofa bed allows people to obtain a larger activity space through conversion between a sofa and a bed, greatly improving space utilization, so that people can enjoy a more comfortable living environment in limited space. 
     An existing sofa bed iron frame mechanism has the following problems in use: 
     1. A booster spring in an existing bed frame is connected to and passes through an entire side plate, which increases abrasion and wear among the spring, the side plate, and a soft decoration part in actual use. In addition, the spring passes through the entire side plate, thereby increasing risks in use. For example, a hand may be squeezed and injured by the booster system when being inserted from the portion of the side plate. 
     2. When a backrest is configured to be unfolded and in a horizontal state and bears a large load, abrasion occurs between the backrest and the booster system (a spring and a connecting rod), resulting in damage or abrasion and wear of the backrest and the booster system (the spring and the connecting rod). 
     An objective of the present invention is especially to alleviate this situation. 
     SUMMARY 
     This application is intended to overcome defects of the prior art and provides a novel sofa bed iron frame mechanism. The function of conversion between a sofa and a bed is achieved through unfolding and folding of two interrelated sofa bed frames and a rotatable backrest. 
     To resolve the foregoing technical problems, this application is implemented as follows: 
     A novel sofa bed iron frame mechanism is provided, including a side plate ( 16 ), a back plate ( 21 ), a first frame ( 1 ), a second frame ( 2 ), front support legs ( 13 ), middle support legs ( 14 ), and connecting members ( 17 ), where the first frame ( 1 ) and the second frame ( 2 ) are hinged to the connecting members ( 17 ), the first frame ( 1 ) is hinged to the front support legs ( 13 ), and the middle support legs ( 14 ) are fixed on the connecting members ( 17 ); and further including a stabilizer rod assembly and an elastic connecting rod assembly, where the first frame ( 1 ) is hinged to the second frame ( 2 ) by the stabilizer rod assembly, the second frame ( 2 ) is connected to the side plate ( 16 ) by the elastic connecting rod assembly, and the back plate ( 21 ) is disposed at a back side of the second frame ( 2 ); and the first frame ( 1 ) and the second frame ( 2 ) are folded or unfolded through the stabilizer rod assembly, and the second frame ( 2 ) switches between a folded state and an unfolded state by a tension of the elastic connecting rod assembly. 
     In the novel sofa bed iron frame mechanism, the stabilizer rod assembly includes a first connecting rod ( 4 ), a second connecting rod ( 5 ), the connecting member ( 17 ), and a mounting plate ( 15 ); the first frame ( 1 ) is hinged to the second frame ( 2 ) by the connecting members ( 17 ), one end of the first connecting rod ( 4 ) is hinged to the front support leg ( 13 ) and then is hinged to the first frame ( 1 ) by the front support leg ( 13 ), an other end of the first connecting rod ( 4 ) and one end of the second connecting rod ( 5 ) are jointly hinged to an extended iron sheet on the connecting member ( 17 ), an other end of the second connecting rod ( 5 ) is hinged to the mounting plate ( 15 ), and the mounting plate ( 15 ) is hinged to the second frame ( 2 ) and is fixed on the side plate ( 16 ); and in this manner, a connecting rod mechanism forms a stable structure and plays a role of guiding and limiting during relative rotation between the first frame ( 1 ) and the second frame ( 2 ). 
     In the novel sofa bed iron frame mechanism, the elastic connecting rod assembly includes a booster rod ( 7 ) and a booster spring ( 8 ); one end of the booster spring ( 8 ) is connected to the second frame ( 2 ), an other end is connected to an end portion of the booster rod ( 7 ), and an other end of the booster rod ( 7 ) is fixed on the side plate ( 16 ); and in this manner, when the second frame ( 2 ) rotates, an additional force is provided by the resilience of the booster spring ( 8 ) for the second frame ( 2 ) to switch between the folded state and the unfolded state. 
     In the novel sofa bed iron frame mechanism, the elastic connecting rod assembly includes a third connecting rod ( 23 ), a booster spring ( 24 ), a booster spring fixing sheet ( 25 ), and a hinge rod assembly ( 26 ); one end of the third connecting rod ( 23 ) is connected to the second frame ( 2 ), an other end of the third connecting rod ( 23 ) is connected to one end of the hinge rod assembly ( 26 ), an other end of the hinge rod assembly ( 26 ) is connected to the booster spring ( 24 ), and the booster spring ( 24 ) is connected to the side plate ( 16 ) by the booster spring fixing sheet ( 25 ); the booster spring fixing sheet ( 25 ) is disposed on an inner side of the side plate ( 16 ) and located below the second frame ( 2 ), and the hinge rod assembly ( 26 ) is disposed on the inner side of the side plate ( 16 ); and in this manner, when the second frame ( 2 ) rotates, the resilience of the booster spring ( 24 ) is transmitted to the second frame through the hinge rod assembly ( 26 ) and the third connecting rod ( 23 ) to provide an additional force for the second frame ( 2 ) to switch between the folded state and the unfolded state. 
     In the novel sofa bed iron frame mechanism, the first frame ( 1 ), the connecting member ( 17 ), and the second frame ( 2 ) are sequentially hinged, so that the first frame ( 1 ) and the second frame ( 2 ) do not interfere with each other in the folded state; and the connecting member ( 17 ) is made of channel steel, having a limiting function to prevent the first frame ( 1 ) and the second frame ( 2 ) from continuing to overturn after reaching the unfolded state. 
     The foregoing novel sofa bed iron frame mechanism further includes a backrest frame ( 3 ) and an overturning mechanism, and the overturning mechanism is connected to the backrest frame ( 3 ) and the side plate ( 16 ) or the back plate ( 21 ), so that the backrest frame ( 3 ) is overturned and is switched between an overlapped state and an independent folded state with the second frame ( 2 ) through the overturning mechanism. 
     In the novel sofa bed iron frame mechanism, the overturning mechanism includes a third connecting rod ( 6 ), a locking spring ( 9 ), a support plate ( 10 ), a first support rod ( 11 ), a second support rod ( 12 ), and a back plate connecting member ( 20 ), the support plate ( 10 ) is fixed on the side plate ( 16 ), one end of the third connecting rod ( 6 ) is hinged to the support plate ( 10 ), an other end of the third connecting rod ( 6 ) is sequentially hinged to the back plate connecting member ( 20 ), the second support rod ( 12 ), and the first support rod ( 11 ), one end of the first support rod ( 11 ) is hinged to the support plate ( 10 ), and in this manner, the backrest frame ( 3 ) is disposed on the back plate connecting member ( 20 ), and the locking spring ( 9 ) is disposed between the first support rod ( 11 ) and the second support rod ( 12 ), so that the backrest frame ( 3 ) is overturned around the support plate ( 10 ) through the first support rod ( 11 ), the second support rod ( 12 ), and the back plate connecting member ( 20 ), and the backrest frame ( 3 ) is enabled to have a tension through the locking spring ( 9 ) during overturning. 
     In the novel sofa bed iron frame mechanism, the overturning mechanism includes hinges ( 22 ), a hinge support plate ( 28 ), and an overturnable backrest ( 29 ), a recess is provided at a lower side of the overturnable backrest ( 29 ) and is fitted with the hinge support plate ( 28 ) to enable surfaces on which the hinges ( 22 ) are mounted to be on the same plane, and the overturnable backrest ( 29 ) rotates around the hinges ( 22 ) to a horizontal position to overlap with the second frame ( 2 ). 
     In the novel sofa bed iron frame mechanism, a limiting structure is provided on an inner side of the support plate ( 10 ), the backrest frame ( 3 ) is overturned around the support plate ( 10 ) through the first support rod ( 11 ), the second support rod ( 12 ), and the back plate connecting member ( 20 ), and the backrest frame ( 3 ) overlaps with the second frame ( 2 ) and the support plate ( 10 ) when the backrest frame ( 3 ) is overturned to a horizontal position. 
     In the novel sofa bed iron frame mechanism, a limiting block ( 30 ) for limiting the third connecting rod ( 6 ) in the folded state is disposed on the support plate ( 10 ), and the limiting block ( 30 ) limits the first support rod ( 11 ) when the backrest frame ( 3 ) is overturned upward from a horizontal position. 
     In the novel sofa bed iron frame mechanism, a limiting plate ( 18 ) is disposed on an end portion of the first support rod ( 11 ) or the second support rod ( 12 ), to limit the first support rod ( 11 ) and the second support rod ( 12 ) and prevent further rotation when the first support rod ( 11 ) and the second support rod ( 12 ) rotate relative to each other to a linear position. 
     In the novel sofa bed iron frame mechanism, the booster spring fixing sheet ( 25 ) and the mounting plate ( 15 ) are the same component. 
     In the novel sofa bed iron frame mechanism, a limiting and supporting groove ( 19 ) is provided on the support plate ( 10 ) and configured to limit and support the backrest frame ( 3 ). 
     The novel sofa bed iron frame mechanism provided in this application has the following advantages: 
     1. The first frame and the second frame are connected by the stabilizer rod assembly, especially the connecting rod in the stabilizer rod assembly, so that no abrasion or interference occurs between the first frame and the second frame during folding. 
     2. The elastic connecting rod assembly is used to assist an overturning action of the second frame, thereby making the process of switching states of the first frame and the second frame more convenient. 
     3. The second frame and the backrest frame are independent, so that the volume of the entire sofa bed iron frame is reduced, and the flexibility of use is increased. For example, the overturning mechanism and the elastic connecting rod mechanism are used in pairs, so that processes of switching states of the second connecting rod mechanism and the backrest frame do not interfere with each other, thereby facilitating operations of different users. 
     4. The backrest frame, the side plate, and the back plate are designed to be relatively independent of the first frame and the second frame. During packaging for shipment, the backrest frame may be directly placed on the first frame and the second frame in the folded state, thereby reducing packaging space, facilitating packaging and shipment, and reducing costs. 
     5. The overturning mechanism of the backrest frame uses a multi-turning point structure, so that the backrest frame is easily overturned and can have smaller distances from other softly decorated components, such as the second frame, the side plate, and the back plate, improving the comfort of users. 
     6. Through coordinated operations of locking spring  9  and the limiting plate  18  for the overturning mechanism of the backrest frame, the entire overturning mechanism is enabled to have a self-locking function in an open state. Specifically, the first support rod and the second support rod, and the third connecting rod and the back plate connecting member are all in a linear state, thereby avoiding accidental actions of the overturning mechanism. For example, accidental overturning caused by stepping on a part of the backrest frame, especially a softly decorated backrest part in a headrest direction, is prevented. It is more comfortable and safe for a user to lie flat. 
     7. The first frame  1  and the second frame  2  are suitable for various soft decoration manners, using webbing, wooden strips, snake springs, bed cloths, and the like. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Specific descriptions of this application are further made in detail below with reference to the accompanying drawings and implementations: 
         FIG. 1  is a schematic diagram of Embodiment 1 in an unfolded state; 
         FIG. 2  is a schematic diagram  1  of an unfolding process of a first frame and a second frame in Embodiment 1; 
         FIG. 3  is a schematic diagram  2  of an unfolding process of a first frame and a second frame in Embodiment 1; 
         FIG. 4  is a schematic diagram  3  of an unfolding process of a first frame and a second frame in Embodiment 1; 
         FIG. 5  is a schematic diagram  4  of an unfolding process of a first frame and a second frame in Embodiment 1; 
         FIG. 6  is a schematic diagram  5  of an unfolding process of a first frame and a second frame in Embodiment 1; 
         FIG. 7  is a schematic diagram  6  of an unfolding process of a first frame and a second frame in Embodiment 1; 
         FIG. 8  is a schematic diagram  7  of an unfolding process of a first frame and a second frame in Embodiment 1; 
         FIG. 9  is a schematic diagram of a connection structure of a backrest frame and an overturning mechanism shown in an embodiment; 
         FIG. 10  is a schematic diagram  1  of an action process of a backrest frame and an overturning mechanism shown in an embodiment; 
         FIG. 11  is a schematic diagram  2  of an action process of a backrest frame and an overturning mechanism shown in an embodiment; 
         FIG. 12  is a schematic diagram of a first frame and a second frame in a folded state shown in an embodiment; and 
         FIG. 13  is a schematic diagram of Embodiment 2 in an unfolded state. 
     
    
    
     In the drawings, the same reference number is used to represent the same element or similar elements. 
     DETAILED DESCRIPTION 
     Embodiment 1 
     As shown in  FIG. 1 , a sofa bed iron frame mechanism includes a side plate ( 16 ), a back plate ( 21 ), a first frame ( 1 ), a second frame ( 2 ), front support legs ( 13 ), middle support legs ( 14 ), and connecting members ( 17 ). The first frame ( 1 ) and the second frame ( 2 ) are hinged to the connecting members ( 17 ). The first frame ( 1 ) is hinged to the front support legs ( 13 ). The middle support legs ( 14 ) are fixed on the connecting members ( 17 ). The sofa bed iron frame mechanism further includes a stabilizer rod assembly and an elastic connecting rod assembly. The first frame ( 1 ) is hinged to the second frame ( 2 ) by the stabilizer rod assembly. The second frame ( 2 ) is connected to the side plate ( 16 ) by the elastic connecting rod assembly. The back plate ( 21 ) is disposed at a back side of the second frame ( 2 ). As shown in  FIG. 2  to  FIG. 8 , the first frame ( 1 ) and the second frame ( 2 ) are folded or unfolded through the stabilizer rod assembly, and the second frame ( 2 ) switches between a folded state and an unfolded state by a tension of the elastic connecting rod assembly. 
     In the foregoing sofa bed iron frame mechanism, the stabilizer rod assembly includes a first connecting rod ( 4 ), a second connecting rod ( 5 ), the connecting member ( 17 ), and a mounting plate ( 15 ). The first frame ( 1 ) is hinged to the second frame ( 2 ) by the connecting members ( 17 ). One end of the first connecting rod ( 4 ) is hinged to the front support leg ( 13 ) and then is hinged to the first frame ( 1 ) by the front support leg ( 13 ). The other end of the first connecting rod ( 4 ) and one end of the second connecting rod ( 5 ) are jointly hinged to an extended iron sheet on the connecting member ( 17 ). An other end of the second connecting rod ( 5 ) is hinged to the mounting plate ( 15 ). The mounting plate ( 15 ) is hinged to the second frame ( 2 ) and is fixed on the side plate ( 16 ). In this manner, a connecting rod mechanism forms a stable structure and plays a role of guiding and limiting during folding or unfolding between the first frame ( 1 ) and the second frame ( 2 ). 
     In the foregoing sofa bed iron frame mechanism, the elastic connecting rod assembly includes a booster rod ( 7 ) and a booster spring ( 8 ). One end of the booster spring ( 8 ) is connected to the second frame ( 2 ). An other end is connected to an end portion of the booster rod ( 7 ). The booster rod ( 7 ) is fixed on the side plate ( 16 ). In this manner, when the second frame ( 2 ) rotates, an additional action force is provided by an elastic force of the booster spring ( 8 ) for the second frame ( 2 ) to switch between the folded state and the unfolded state. 
     The foregoing sofa bed iron frame mechanism further includes a backrest frame ( 3 ) and an overturning mechanism. The overturning mechanism is connected to the backrest frame ( 3 ) and the side plate ( 16 ) or the back plate ( 21 ), so that the backrest frame ( 3 ) is overturned and is switched between an overlapped state and an independent folded state with the second frame ( 2 ) through the overturning mechanism. 
     As shown in  FIG. 1  and  FIG. 9  to  FIG. 11 , in the foregoing sofa bed iron frame mechanism, the overturning mechanism includes a third connecting rod ( 6 ), a locking spring ( 9 ), a support plate ( 10 ), a first support rod ( 11 ), a second support rod ( 12 ), and a back plate connecting member ( 20 ). The support plate ( 10 ) is fixed on the side plate ( 16 ). One end of the third connecting rod ( 6 ) is hinged to the support plate ( 10 ). An other end of the third connecting rod ( 6 ) is sequentially hinged to the back plate connecting member ( 20 ), the second support rod ( 12 ), and the first support rod ( 11 ). One end of the first support rod ( 11 ) is hinged to the support plate ( 10 ). In this manner, the backrest frame ( 3 ) is disposed on the back plate connecting member ( 20 ), and the locking spring ( 9 ) is disposed between the first support rod ( 11 ) and the second support rod ( 12 ), so that the backrest frame ( 3 ) is overturned around the support plate ( 10 ) through the first support rod ( 11 ), the second support rod ( 12 ), and the back plate connecting member ( 20 ), and the backrest frame ( 3 ) is enabled to have a tension through the locking spring ( 9 ) during overturning. 
     In the foregoing overturning mechanism, a limiting structure is provided on an inner side of the support plate ( 10 ). The backrest frame ( 3 ) is overturned around the support plate ( 10 ) through the first support rod ( 11 ), the second support rod ( 12 ), and the back plate connecting member ( 20 ). The backrest frame ( 3 ) overlaps with the second frame ( 2 ) and the support plate ( 10 ) when the backrest frame ( 3 ) is overturned to a horizontal position. 
     In the foregoing overturning mechanism, a limiting block ( 30 ) for limiting the third connecting rod ( 6 ) in the folded state is disposed on the support plate ( 10 ). In addition, the limiting block ( 30 ) limits the first support rod ( 11 ) when the backrest frame ( 3 ) is overturned upward from a horizontal position. 
     In the foregoing overturning mechanism, a limiting plate ( 18 ) is disposed on an end portion of the first support rod ( 11 ) or the second support rod ( 12 ), to limit the first support rod ( 11 ) and the second support rod ( 12 ) and prevent further rotation when the first support rod ( 11 ) and the second support rod ( 12 ) rotate relative to each other to a linear position. 
     In the foregoing overturning mechanism, a limiting and supporting groove ( 19 ) is provided on the support plate ( 10 ) and configured to limit and support the backrest frame ( 3 ). 
     As shown in  FIG. 12 , in the novel sofa bed iron frame mechanism shown in Embodiment 1, the first frame and the second frame are connected by the connecting rod, so that no abrasion or interference occurs between the first frame and the second frame during folding. In addition, the backrest frame, the side plate, and the back plate are designed to be relatively independent of the first frame and the second frame, and during packaging for shipment, the backrest frame may be directly placed on the first frame and the second frame in the folded state, thereby reducing packaging space, facilitating packaging and shipment, and reducing costs (as shown in  FIG. 12 ). 
     Further, in the sofa bed iron frame mechanism shown in Embodiment 1, the elastic connecting rod assembly is used to assist an overturning action of the second frame ( 2 ), thereby making the process of switching states of the first frame and the second frame more convenient. In addition, the overturning mechanism and the elastic connecting rod mechanism are used in pairs, so that processes of switching states of the second connecting rod mechanism and the backrest frame do not interfere with each other, thereby facilitating operations of different users. 
     Further, in the sofa bed iron frame mechanism shown in Embodiment 1, through coordinated operations of the locking spring  9  and the limiting plate  18  for the overturning mechanism of the backrest frame, the entire overturning mechanism is enabled to have a self-locking function in an open state. Specifically, the first support rod and the second support rod, and the third connecting rod and the back plate connecting member are all in a linear state, thereby avoiding accidental actions of the overturning mechanism. For example, accidental overturning caused by stepping on a part of the backrest frame, especially a softly decorated backrest part in a headrest direction, is prevented. It is more comfortable and safe for a user to lie flat. 
     However, it is found in practice that for the elastic connecting rod assembly in Embodiment 1, there are problems such as the elastic connecting rod assembly being poorly stressed, with the spring being apt to deform, and probably causing interference with the side plate or the frame. Therefore, based on Embodiment 1, the elastic connecting rod assembly is improved to form Embodiment 2. 
     Embodiment 2 
     As shown in  FIG. 13 , a sofa bed iron frame mechanism includes a side plate ( 16 ), a back plate ( 21 ), a first frame ( 1 ), a second frame ( 2 ), front support legs ( 13 ), middle support legs ( 14 ), and connecting members ( 17 ). The first frame ( 1 ) and the second frame ( 2 ) are hinged to the connecting members ( 17 ). The first frame ( 1 ) is hinged to the front support legs ( 13 ). The middle support legs ( 14 ) are fixed on the connecting members ( 17 ). The sofa bed iron frame mechanism further includes a stabilizer rod assembly and an elastic connecting rod assembly. The first frame ( 1 ) is hinged to the second frame ( 2 ) by the stabilizer rod assembly. The second frame ( 2 ) is connected to the side plate ( 16 ) by the elastic connecting rod assembly. The back plate ( 21 ) is disposed at a back side of the second frame ( 2 ). The first frame ( 1 ) and the second frame ( 2 ) are folded or unfolded through the stabilizer rod assembly. The second frame ( 2 ) switches between a folded state and an unfolded state by inertia of the elastic connecting rod assembly. 
     In the foregoing sofa bed iron frame mechanism, the stabilizer rod assembly includes a first connecting rod ( 4 ), a second connecting rod ( 5 ), the connecting member ( 17 ), and a mounting plate ( 15 ). The first frame ( 1 ) is hinged to the second frame ( 2 ) by the connecting members ( 17 ). One end of the first connecting rod ( 4 ) is hinged to the front support leg ( 13 ) and then is hinged to the first frame ( 1 ) by the front support leg ( 13 ). An other end of the first connecting rod ( 4 ) and one end of the second connecting rod ( 5 ) are jointly hinged to an extended iron sheet on the connecting member ( 17 ) An other end of the second connecting rod ( 5 ) is hinged to the mounting plate ( 15 ). The mounting plate ( 15 ) is hinged to the second frame ( 2 ) and is fixed on the side plate ( 16 ). In this manner, a connecting rod mechanism forms a stable structure and plays a role of guiding and limiting during folding or unfolding between the first frame ( 1 ) and the second frame ( 2 ). 
     In the foregoing sofa bed iron frame mechanism, the elastic connecting rod assembly includes a third connecting rod ( 23 ), a booster spring ( 24 ), a booster spring fixing sheet ( 25 ), and a hinge rod assembly ( 26 ). One end of the third connecting rod ( 23 ) is connected to the second frame ( 2 ). An other end of the third connecting rod ( 23 ) is connected to one end of the hinge rod assembly ( 26 ). An other end of the hinge rod assembly ( 26 ) is connected to the booster spring ( 24 ). The booster spring ( 24 ) is connected to the side plate ( 16 ) by the booster spring fixing sheet ( 25 ). The booster spring fixing sheet ( 25 ) is disposed on an inner side of the side plate ( 16 ) and located below the second frame ( 2 ). In addition, the hinge rod assembly ( 26 ) is disposed on the inner side of the side plate ( 16 ). In this manner, when the second frame ( 2 ) rotates, the resilience of the booster spring ( 24 ) is transmitted to the second frame through the hinge rod assembly ( 26 ) and the third connecting rod ( 23 ) to provide an additional force for the second frame ( 2 ) to switch between the folded state and the unfolded state. 
     In the foregoing sofa bed iron frame mechanism, the booster spring fixing sheet ( 25 ) and the mounting plate ( 15 ) are the same component. 
     The foregoing sofa bed iron frame mechanism further includes a backrest frame ( 3 ) and an overturning mechanism. The overturning mechanism is connected to the backrest frame ( 3 ) and the side plate ( 16 ) or the back plate ( 21 ), so that the backrest frame ( 3 ) is overturned and is switched between an overlapped state and an independent folded state with the second frame ( 2 ) through the overturning mechanism. 
     In the foregoing sofa bed iron frame mechanism, the overturning mechanism includes a third connecting rod ( 6 ), a locking spring ( 9 ), a support plate ( 10 ), a first support rod ( 11 ), a second support rod ( 12 ), and a back plate connecting member ( 20 ). The support plate ( 10 ) is fixed on the side plate ( 16 ). One end of the third connecting rod ( 6 ) is hinged to the support plate ( 10 ). An other end of the third connecting rod ( 6 ) is sequentially hinged to the back plate connecting member ( 20 ), the second support rod ( 12 ), and the first support rod ( 11 ). One end of the first support rod ( 11 ) is hinged to the support plate ( 10 ). In this manner, the backrest frame ( 3 ) is disposed on the back plate connecting member ( 20 ), and the locking spring ( 9 ) is disposed between the first support rod ( 11 ) and the second support rod ( 12 ), so that the backrest frame ( 3 ) is overturned around the support plate ( 10 ) through the first support rod ( 11 ), the second support rod ( 12 ), and the back plate connecting member ( 20 ), and the backrest frame ( 3 ) is enabled to have a tension through the locking spring ( 9 ) during overturning. 
     In the foregoing overturning mechanism, a limiting structure is provided on an inner side of the support plate ( 10 ), the backrest frame ( 3 ) is overturned around the support plate ( 10 ) through the first support rod ( 11 ), the second support rod ( 12 ), and the back plate connecting member ( 20 ), and the backrest frame ( 3 ) overlaps with the second frame ( 2 ) and the support plate ( 10 ) when the backrest frame ( 3 ) is overturned to a horizontal position. 
     The overturnable backrest is a modified form of the backrest frame, specifically the softly decorated backrest frame. 
     In the foregoing overturning mechanism, a limiting block ( 30 ) for limiting the third connecting rod ( 6 ) in the folded state is disposed on the support plate ( 10 ), and the limiting block ( 30 ) limits the first support rod ( 11 ) when the backrest frame ( 3 ) is overturned upward from a horizontal position. 
     In the foregoing overturning mechanism, a limiting plate ( 18 ) is disposed on an end portion of the first support rod ( 11 ) or the second support rod ( 12 ), to limit the first support rod ( 11 ) and the second support rod ( 12 ) and prevent further rotation when the first support rod ( 11 ) and the second support rod ( 12 ) rotate relative to each other to a linear position. 
     In the foregoing overturning mechanism, a limiting and supporting groove ( 19 ) is provided on the support plate ( 10 ) and configured to limit and support the backrest frame ( 3 ). 
     The foregoing Embodiment 2 is a partial improvement of Embodiment 1, specifically replacing the elastic connecting rod assembly. An original single booster rod is replaced with a plurality of rods, so that there is better flexibility between the rods and a stress state of the elastic connecting rod assembly becomes better, thereby avoiding interference with surrounding components. 
     For Embodiment 1 and Embodiment 2, to save space or reduce production costs, the backrest frame ( 3 ) and the back plate ( 21 ) may use a new mounting method, specifically: the overturning mechanism includes hinges ( 22 ), a hinge support plate ( 28 ), and an overturnable backrest ( 29 ), a recess is provided at a lower side of the overturnable backrest ( 29 ) and is fitted with the hinge support plate ( 28 ) to enable surfaces on which the hinges ( 22 ) are mounted to be on the same plane, and the overturnable backrest ( 29 ) rotates around the hinges ( 22 ) to a horizontal position to overlap with the second frame ( 2 ). 
     For the foregoing embodiments and modifications thereof, this application is not limited to a sofa bed iron frame, but also includes a sofa bed iron frame decorated with soft decorating plates, especially with an end portion and a side portion of a back plate being connected to soft decorating plates.