Convertible sofa bed

Abstract

A sofa bed traversable between a sofa and bed configurations is disclosed herein. It has a folding mechanism having first and second pairs of link members rotatably attached to a backrest and support members on left and right sides of the back rest. Via the first and second link members, the back rest is transitionable between the sofa configuration and the bed configuration. A seat base is movable up and down at an angle via a sliding mechanism or a five bar parallelogram linkage.

What is claimed is: 
     
         1 . A convertible sofa bed with a rotatable backrest disposable between a sofa configuration and a bed configuration, wherein rotation of the backrest transitions a seat base between an up position and a down position, the sofa bed comprising:
 a frame comprising a left portion and a right portion;   the backrest being disposed between the left and right portions of the frame;   a seat base comprising a left end portion and a right end portion, the seat base being disposed between the left and right portions of the frame;   a folding mechanism which transitions the seat base between the up position and the down position, the folding mechanism comprising:
 a right first linkage rotatably attached to the right portion of the frame and the right end portion of the seat base; 
 a right second linkage rotatably attached to the right portion of the frame and the right end portion of the seat base; 
 a right third linkage rotatably attached to the right portion of the frame and the right end portion of the seat base; and 
 a right fourth linkage rotatably attached to a right end portion of the backrest and the seat base. 
   
     
     
         2 . The convertible sofa bed according to  claim 1 ,
 wherein the right first linkage is rotatably attached to the right portion of the frame at a first pivot joint and to the right end portion of the seat base at a second pivot joint, the right first linkage rotating in a first rotational direction when the convertible sofa bed transitions from a bed configuration to a sofa configuration;   wherein the right fourth linkage is rotatably attached to the right end portion of the backrest at a third pivot joint and to the seat base at a fourth pivot joint;   wherein in the bed configuration, a first linear axis defined by the first pivot joint and the second pivot joint has a positive angle in relation to the first rotational direction relative to a second linear axis defined by the third pivot joint and the second pivot joint; and   wherein in the bed configuration, an upward force on the right fourth linkage results in rotation of the right first linkage in the first rotational direction.   
     
     
         3 . The convertible sofa bed according to  claim 1 , wherein the right first linkage, the right second linkage, and the right third linkage synchronously rotate at a same rate of rotation. 
     
     
         4 . The convertible sofa bed according to  claim 1 , wherein the seat base, the right portion of the frame, the right first linkage, the right second linkage, and the right third linkage define a five bar parallelogram linkage. 
     
     
         5 . The convertible sofa bed according to  claim 1 ,
 wherein the right first linkage is rotatably attached to the right portion of the frame at a first pivot joint and to the right end portion of the seat base a fourth pivot joint;   wherein the right second linkage is rotatably attached to the right portion of the frame at a second pivot joint and to the right end portion of the seat base a fifth pivot joint;   wherein the right third linkage is rotatably attached to the right portion of the frame at a third pivot joint and to the right end portion of the seat base a sixth pivot joint;   wherein the first pivot joint, the second pivot joint, and the third pivot joint are located collinearly along a first axis; and   wherein the fourth pivot joint, the fifth pivot joint, and the sixth pivot joint are located collinearly along a second axis.   
     
     
         6 . The convertible sofa bed according to  claim 5 , wherein in the bed configuration, the fourth, fifth and sixth pivot joints are positioned on first sides of first, second and third vertical planes defined at first, second and third pivot joints, and in the sofa configuration, the fourth, fifth and sixth pivot joints of the first, second and third linkages are positioned on a second opposite sides of first, second and third vertical planes. 
     
     
         7 . The convertible sofa bed according to  claim 5 , wherein a first distance between the first pivot joint and the fourth pivot joint is equal to each of a second distance between the second pivot joint and the fifth pivot joint and a third distance between the third pivot joint and the sixth pivot joint. 
     
     
         8 . The convertible sofa bed according to  claim 5 , wherein the right first linkage is rotatably attached to the right portion of the frame at a first pivot joint, the first pivot joint being fixed in position to the right portion of the frame, and the fourth pivot joint of the right first linkage rotates about the first pivot joint along a circular path. 
     
     
         9 . The convertible sofa bed according to  claim 8 ,
 wherein the right first linkage has a first length from the first pivot joint to a farthest distal end beyond a seventh pivot joint of the right first linkage;   wherein the right second linkage has a second length from the second pivot joint to a farthest distal end;   wherein a distance between the first pivot joint of the right first linkage and the second pivot joint of the right second linkage defines a first distance;   wherein a distance between the second pivot joint of the right second linkage and the third pivot joint of the right third linkage defines a second distance; and   wherein the first length of the right first linkage is less than the first distance between the first pivot joint and the second pivot joint such that the right first linkage clears the right second linkage when pivoting along the circular path;   wherein the second length of the right second linkage is less than the second distance between the second pivot joint and the third pivot joint such that the right second linkage clears the right third linkage when pivoting along the circular path.   
     
     
         10 . The convertible sofa bed according to  claim 1 , wherein a range of rotation of the right first linkage between the up position and the down position of the seat base is from 90 degrees to 270 degrees. 
     
     
         11 . A method of transitioning a convertible sofa bed from a bed configuration to a sofa configuration, the method comprising the step of:
 pulling up on a backrest when the convertible sofa bed is in the bed configuration to transition the convertible sofa bed to the sofa configuration;   transferring a force from the backrest to a seat base through a right fourth linkage attached to the back rest and the seat base;   rotating a right first linkage, a right second linkage, and a right third linkage at a same rate of rotation throughout an entire rotational travel of the seat base as the seat base is transitioned from a down position to an up position.   
     
     
         12 . The method of  claim 11 , wherein the step of rotating further comprises synchronously rotating the right first linkage, the right second linkage and the right third linkage in the same rotational direction. 
     
     
         13 . The method according to  claim 11 , further comprising fixing a first pivot joint which the right first linkage rotates about to the right portion of the frame such that the right first linkage rotates about the first pivot joint along an arcuate portion of a circular path. 
     
     
         14 . The method according to  claim 11 , further comprising rotating the right first linkage between the up position and the down position of the seat base through a range of rotation from 90 degrees to 270 degrees. 
     
     
         15 . The method according to  claim 11 , wherein in the bed configuration, the first, second and third linkages are in a skewed orientation from vertical. 
     
     
         16 . The method according to  claim 11 ,
 wherein the right first linkage is rotatably attached to the right portion of the frame at a first pivot joint and to the right end portion of the seat base a fourth pivot joint;   wherein the right second linkage is rotatably attached to the right portion of the frame at a second pivot joint and to the right end portion of the seat base a fifth pivot joint;   wherein the right third linkage is rotatably attached to the right portion of the frame at a third pivot joint and to the right end portion of the seat base a sixth pivot joint;   wherein the first pivot joint, the second pivot joint, and the third pivot joint are located collinearly along a first axis; and   wherein the fourth pivot joint, the fifth pivot joint, and the sixth pivot joint are located collinearly along a second axis.   
     
     
         17 . The method according to  claim 16 , wherein in the bed configuration, the fourth, fifth and sixth pivot joints are positioned on first sides of first, second and third vertical planes defined at first, second and third pivot joints, and in the sofa configuration, the fourth, fifth and sixth pivot joints of the first, second and third linkages are positioned on a second opposite sides of first, second and third vertical planes. 
     
     
         18 . The method according to  claim 16 , wherein a first distance between the first pivot joint and the fourth pivot joint is equal to each of a second distance between the second pivot joint and the fifth pivot joint and a third distance between the third pivot joint and the sixth pivot joint. 
     
     
         19 . The method according to  claim 11 , wherein the right first, second and third linkages are disposed between the seat base and the right portion of the frame. 
     
     
         20 . The method according to  claim 16 , wherein the seat base, the right portion of the frame, the right first linkage, the right second linkage, and the right third linkage define a five bar parallelogram linkage.