EP3045082A1

EP3045082A1 - Counterbalancer for the opening and closing mechanism of a sofa bed as well as method for counterbalancing the opening and closing of a sofa bed

Info

Publication number: EP3045082A1
Application number: EP15184234.1A
Authority: EP
Inventors: Juha Miikkulainen
Original assignee: Taimeka Oy
Current assignee: Taimeka Oy
Priority date: 2014-09-08
Filing date: 2015-09-08
Publication date: 2016-07-20
Also published as: FI10728U1

Abstract

The invention relates to a counterbalancer for the opening and closing mechanism of a sofa bed (10), wherein the sofa bed (10) comprises a frame (1) provided with an armrest (2), as well as a seat portion (20) including a foot section (7) and a middle section (6), which are connected to each other rotatably in a vertical plane by way of a hinge or the like and which are connected to the frame (1) rotatably in a vertical plane by means of the sofa bed opening and closing mechanism, by linking the middle section (6) of the seat portion (20) rotatably to a center of rotation (C) of the armrest (2) of the sofa bed frame (1) in such a way that the seat portion (20) is on the one hand capable of being set in a seating configuration (A), in which its middle section (6) has been folded underneath the foot section (7), and on the other hand to an opened position (B) or a bed configuration, in which the foot section (7) and the middle section (6) are at the same level. In the present invention the sofa bed opening and closing mechanism comprises at least one torsion spring (11), which is arranged in connection with the center of rotation (C) of the armrest (2) of the frame (1) by connecting a first end of the torsion spring to said center of rotation (C1) of the armrest and a second end thereof to a respective center of rotation (C2) of the middle section, such that said torsion spring (11) is in a rest condition once the middle section (6) of the seat portion (20) has pivoted to an upright position and in a stressed condition as the foot section (7) and the middle section (6) are in the seating configuration (A) or in the opened position (B).

Description

The invention relates to a counterbalancer for a sofa bed opening and closing mechanism as defined in the preamble of claim 1.
The invention relates also to a method for counterbalancing the opening and closing of a sofa bed.
Sofa beds obtainable by opening a sofa are commercially available in large variety. There are also a large variety of opening mechanisms for this purpose.
This invention focuses on counterbalancing the opening and closing of one regular sofa bed. In the process of both opening and closing such a sofa bed, the sofa bed's seat portion which is hinged to a sofa frame so as to enable its rotation in a vertical plane, will be pivoted relative to the frame. This type of sofa bed involves folding a middle section of the seat portion inside a sofa frame, into a lower part of the frame, such that a foot section of the seat portion is left on top of the middle section when it is desirable to set the sofa bed in a seating configuration. When the sofa bed is in an opened position, i.e. in a bed configuration, the foot section and the middle section have in turn been folded to a common plane.
The prior known sofa beds of this type are quite heavy to open and close in a manner described above.
Indeed, it has been a principal objective of the invention to provide a counterbalancer for the opening and closing mechanism of such a sofa bed, as well as a method which effectively counterbalances both the opening and closing of a sofa bed.
A further objective of the invention has been to maintain the counterbalancer for a sofa bed opening and closing mechanism compact, because the middle section of a seat portion to be displaced inside the sofa bed frame in a seating configuration leaves a relatively small intermediate space since increasing the frame size with respect to the seat portion is not desirable.
Thus, the invention indeed relates to a counterbalancer according to claim 1 for the opening and closing mechanism of a sofa bed.
More specifically, the invention relates to a counterbalancer for the opening and closing mechanism of a sofa bed, wherein the sofa bed comprises a frame provided with an armrest, as well as a seat portion including a foot section and a middle section, which are connected to each other rotatably in a vertical plane by way of a hinge or the like and which are connected to the frame rotatably in a vertical plane by means of the sofa bed opening and closing mechanism, by linking the middle section of the seat portion rotatably to a center of rotation of the armrest of the sofa bed frame in such a way that the seat portion is on the one hand capable of being set in a seating configuration, in which its middle section has been folded underneath the foot section, and on the other hand to an opened position or a bed configuration, in which the foot section and the middle section are at the same level. In the invention, the sofa bed opening and closing mechanism comprises at least one torsion spring, which is arranged in connection with the center of rotation of the armrest of the frame by connecting a first end of the torsion spring to said center of rotation of the armrest and a second end thereof to a respective center of rotation of the middle section of the seat portion, such that said torsion spring is in a rest condition once the middle section of the seat portion has pivoted to an upright position and in a stressed condition as the foot section and the middle section are in a seating configuration (A) or in an opened position (B).
The invention relates also to a counterbalancer according to claim 2 for the opening and closing mechanism of a sofa bed, wherein the sofa bed comprises a frame provided with an armrest and having two seat portions placed side by side in a lateral direction of the sofa. Thus, each seat portion comprises a foot section and a middle section, which are connected to each other rotatably in a vertical plane by way of a hinge or the like and which are connected to the frame rotatably in a vertical plane by means of the sofa bed opening and closing mechanism by linking the middle section of the seat portion rotatably to a center of rotation of the armrest of the sofa bed frame as well as to a center of rotation between the middle sections of the seat portions in such a way that the seat portion is on the one hand capable of being set in a seating configuration, in which its middle section has been folded underneath the foot section, and on the other hand to an opened position (B) or a bed configuration, in which the foot section and the middle section are at the same level. In this case, the sofa bed opening and closing mechanism comprises at least two torsion springs, one being arranged in connection with a center of rotation (C) of the armrest of the frame and the other at a center of rotation between the middle sections of the seat portions. At least one torsion spring has its first end connected to the center of rotation of the armrest and its second end to a respective center of rotation of the middle section, such that said torsion spring is in a rest condition once the middle section of the seat portion has pivoted to an upright position and in a stressed condition as the foot section and the middle section are in a seating configuration (A) or in an opened position (B).
The invention relates also a method according to claim 9 for counterbalancing the closing of a sofa bed, said sofa bed comprising a frame provided with an armrest, as well as a seat portion including a foot section and a middle section, which are connected to each other rotatably in a vertical plane by way of a hinge or the like and which are connected to the frame rotatably in a vertical plane by means of the sofa bed opening and closing mechanism by linking the middle section of the seat portion rotatably to a center of rotation C of the armrest of the sofa bed frame, in connection with said center of rotation being provided at least one torsion spring, said method comprising at least the following method steps of:

pivoting the middle section with respect to the foot section from an initial condition, in which the middle section and the foot section are at the same level (position B (bed configuration) of the seat portion) in a vertical plane defined by the hinge or the like therebetween as well as by said center of rotation of the armrest, whereby, at the same time, the torsion spring is in a stressed condition until the seat portion's middle section reaches an upright position and the torsion spring has relaxed from its tension and the torsion spring is in a rest condition,
continuing to pivot the seat portion by turning the middle section around the foot section and the center of rotation of the armrest with respect thereto until the middle section has become folded underneath the foot section ((seating) configuration (A) of the seat portion), the torsion spring having become stressed again at the same time.

The invention relates also to a method according to claim 10 for counterbalancing the opening of a sofa bed, said sofa bed comprising a frame provided with an armrest, as well as a seat portion including a foot section and a middle section, which are connected to each other rotatably in a vertical plane by way of a hinge or the like and which are connected to the frame rotatably in a vertical plane by means of the sofa bed opening and closing mechanism by linking the middle section of the seat portion rotatably to a center of rotation C of the armrest of the sofa bed frame, in connection with said center of rotation being provided at least one torsion spring, said method comprising at least the following method steps of:

pivoting the middle section of the seat portion in a vertical plane with respect to the foot section as well as around a center of rotation of the frame's armrest from an initial condition, in which the middle section has been folded underneath the foot section (position (A) of the seat portion, seating configuration), whereby at the same time the torsion spring is in a stressed condition, in a vertical plane defined by the hinge or the like between the armrest's center of rotation as well as the seat portion as well as the foot section as well as by the armrest's center of rotation until the seat portion's middle section has reached an upright position and the torsion spring has relinquished a spring force bound thereto, i.e. the torsion spring is in a rest condition,
continuing to pivot the middle section by turning the middle section with respect to the foot section and around the aforesaid center of rotation of the armrest until the middle section has folded to become coplanar with the foot section (position (B) of the seat portion), the torsion spring becoming stressed again at the same time.

The counterbalancer for the opening and closing mechanism of a sofa bed according to the invention is based on the fact that, in the invention, the sofa bed's opening and closing mechanism has its cylindrical torsion spring fitted in a space between the seat portion and the sofa frame and attached to the frame's center of rotation in such a way that the torsion spring counterbalances the actuation of the sofa's seat portion as the latter is pivoted along its trajectory around the center of rotation.
The number of springs can be one or more in connection with a center of rotation/centers of rotation between the frame and the seat portion.
On the other hand, the method according to the invention is based on the fact that, when the sofa bed presently in a seating configuration is begun to be opened into a bed configuration, the torsion spring is in a stretched condition, thereby counterbalancing the motion of a sofa bed's seat portion along its trajectory around the center of rotation towards an upright position of the seat portion's middle section. When the sofa is being opened from a seating configuration to a bed configuration, the middle section of the sofa's seat portion has its trajectory first directed upwards. When the middle section is halfway across its trajectory and at the same time in a vertical orientation and approximately at the highest point of its trajectory, the torsion spring has relinquished a spring force bound thereto.
When the bed-opening motion of the middle section of a sofa bed's seat portion is continued, its trajectory around the center of rotation will be directed downward and the torsion spring becomes stressed again and counterbalances the turning motion of the middle section of the sofa bed's seat portion on its way down towards a bed configuration of the seat portion.
When a sofa is being closed from bed configuration to seating configuration, the opening and closing mechanism of a sofa bed works in a reverse fashion counterbalancing again the turning motion of the sofa's seat portion.
The sofa bed's seat portion comprises a foot section and a middle section, which are connected to each other by the ends thereof rotatably in a vertical plane by way of a hinge, such as an articulation.
In the invention, the opening and closing mechanism of a sofa bed comprises a center of rotation having coupled therewith a torsion spring capable of being used for regulating a force required for pivoting the seat portion's foot section and middle section around the center of rotation. In case the sofa bed has two seat portions placed side by side, the seat portions thereof can be further connected with a torsion spring to a vertical sub-frame present between the seat portions.
The position B of a seat portion refers to an opened position or a bed configuration of the seat portion, wherein its foot section and middle section (seating section) are in succession and thereby extends a joint horizontal plane.
The position A of a seat portion refers on the other hand to a sitting position of the seat portion, wherein its middle section (seating section) has folded underneath the foot section.
The center of rotation refers here to a center point of rotational motion. In particular, the center of rotation of an armrest body refers here to a location in the armrest body about which a seat portion, and especially the middle section of a seat portion, strives to rotate as the seat portion is displaced with respect to the armrest body.
The solution according to the invention is new, favorable in terms of manufacturing technique and, moreover, the torsion spring enables effectively a reduction of the force required for opening and closing a sofa bed.
By selecting the spring explicitly as a torsion spring which is then mounted on a center of rotation between the armrest and the seat portion of a frame, it will be possible to reduce the size of the frame and the seat portion associated therewith.
In one preferred embodiment of the invention, the torsion spring is a steel wire-coiled cylindrical double torsion spring having its first end connected to the center of rotation of the seat portion's middle section and its second end to the center of rotation of the frame's armrest.
In another preferred embodiment of the invention, the torsion spring is connected by way of an attachment bracket to the armrest of a sofa frame and to the middle section of a seat portion.
The torsion spring can be accommodated between an armrest and the seat portion of a sofa bed. In addition, the torsion spring can be accommodated between two seat portions of a sofa bed as connected to the center of rotation of a sub-frame present therebetween.
The invention will now be described in more detail with reference to the accompanying figures.

Fig. 1 shows a sofa in a lateral section view with the sofa opened into a bed configuration.
Fig. 2 shows a sofa with two side-by-side seat portions in a view from above with a first seat portion of the sofa in a seating configuration and a second seat portion in a bed configuration.
Fig. 3 shows a sofa in a lateral section view with the sofa in a seating configuration.
Fig. 4 shows a section A-A of fig. 1. The position of a torsion spring is depicted between a middle section and a sofa frame.
Fig. 5 shows even more precisely the fitting of a torsion spring between a seat portion's middle section and a sofa frame.
Figs. 6A-6D show schematically stress conditions of a torsion spring as dependent on a turning angle of the seat portion.
Fig. 7 shows schematically a seat portion of the bed in a bed configuration.

As seen particularly from figs. 1 and 2, the sofa bed 10 consists of a sofa frame 1 and a seat portion 20 attached thereto, as well as a backrest cushion 5. The finished sofa bed 10 is upholstered as regards its frame 1, seat portion 20 and backrest cushion 5. The sofa frame 1 comprises a rear frame section 1a, to which are connected two armrests 2 which are parallel to each other in a lateral direction of the rear section and between which is left a certain gap capable of having the seat portion 20 / seat portions fitted therein.
Each seat portion 20 is a two-piece component, consisting of a foot section 7 and a middle section 6. In an assembled (closed) configuration of the sofa, i.e. in a seating configuration A, the seat portion 20 has its foot section 7 functioning as a seat and underneath it is folded the middle section 6 connected to the foot section in a hinged, such as pivoted fashion. In the closed seating configuration A of the sofa, the middle section thus folds down underneath the seat portion's foot section 7 for concealment (cf. figs. 2, 3), being thereby located in a space, in a lower part thereof, defined by the frame's armrests 2 as well as by the frame's rear section 1a extending in a direction transverse to the armrests. In an opened configuration B of the seat portion 20, the foot section 7 and the middle section 6 of the seat portion 20 are in succession with a common horizontal plane T extending thereby (cf. figs. 1, 2, 7).
Mutual coupling and resulting centers of rotation C; C1 as well as C; C2 for the armrest 2 and the seat portion 20 are illustrated with figs. 3-5. The seat portion of a sofa bed comprises a foot section 7 and a middle section 6, which are on the one hand connected rotatably to each other by the ends thereof, i.e. by end sides 65, 75 thereof, by way of a joint 16 and, on the other hand, connected rotatably to the armrest 2 of a sofa bed 10, particularly to an armrest body 21, by a side flank 66 of the middle section 6. Said opening and closing mechanism includes particularly a coupling between the seat section 6 and the armrest body 21, wherein at least one armrest 2 of the sofa bed 10 has the seat portion 20 connected thereto by the center of rotation C; C1, said center of rotation having a torsion spring 11 associated therewith for rotating the seat portion 20 with respect to the body 21 of the armrest 2.
In one preferred embodiment of the invention, the sofa bed opening and closing mechanism further includes a mechanism bar 8 (cf. fig. 1), which is coupled between a body 61 of the middle section 6 and the foot section's 7 legs 9 that are closer to the middle section in such a way that rotating the middle section 6 around the center of rotation C; C1 of the armrest body enables the foot section 7 to trace the rotational motion of the middle section 6 around the frame's armrest and/or a second center of rotation of the middle section in synchronism with the middle section. As the sofa bed 10 is opened by turning the middle section 6 around its attachment point to the armrest 2, i.e. a center of rotation C, the foot section 7 and the middle section 6 are thereby turning concurrently and at the same time the legs 9 included in the foot section 7 open up as a result thereof.
In an opened position or bed configuration of the sofa bed 10, as well as simultaneously in that of the seat portion 20, the seat portion 20 of the sofa bed 10 has its foot section 7, and the middle section 6 rotatably connected to the latter, at the same level (cf. fig. 1).
The backrest cushion 5 is used for supplement the bed as the seat portion 20 is in a seating configuration A, wherein the middle section 6 has been folded underneath the foot section 7 into a lower part of the body of the armrest 2.
The seat portion 20 has its middle section 6 attached by its side flanks 66 on the one hand to the body 21 of a sofa's armrest 2 and on the other hand to a possible sub-frame 3, such as to a fixing plate or to a body 21 of the frame's second armrest 2. The coupling points between the seat portion's middle section 6 and the body 21 of the armrest 2 function as a center of rotation C; C1, C2 serving the middle section and the body and having a torsion spring 11 associated therewith.
Since the middle section 6 and the foot section 7 are connected to each other with a double torsion spring 11, the coupling points of the torsion spring with the armrest body 21 and with the middle section's side flanks 66; 66a, 66b function as centers of rotation. Hence, on the one hand, the coupling points between a first side flank 66a of the middle section 6 and a body 21 of the first armrest 2, as well as, on the other hand, those between a second side flank 6; 66b of the middle section 6 and a body 21 of the second armrest 2, function as a center of rotation C. In addition, in case the bed has two seat sections 6 side by side in a single frame, the coupling points between a sub-frame 3 extending between the seat sections 21 (cf. figs. 1 and 2) and the middle section's second side flank 6; 66b may function as a center of rotation C to which can be connected the ends of a torsion spring 11.
It is possible that the middle section 6 and the body 21 of the armrest 2 be pivoted relative to each other in a vertical plane defined by the centers of rotation C and by the hinging between the middle and foot sections, since the coupling between the seat portion's foot section 7 and middle section 6, on the one hand, and, on the other hand, between the seat portion's middle section 6 and the upright positioned sub-frame 3 such as a fixing plate, and/or between the body 21 of the armrest 2 and the seat portion's middle section 6, is arranged to be rotatable in a vertical plane. By providing the armrest's center of rotation C; C1 and/or the center of rotation C of the sub-frame 3 with a torsion spring, it will be possible to pivot the seat portion 20 of the sofa bed 10 in a controlled manner relative to the armrest body 21 and/or the stationary sub-frame 3 around said center of rotation C.
At the same time, this entails that the foot and middle sections 7, 6 of the seat portion 20, which are coupled to each other with a hinge or the like joint in a manner rotatable in a vertical plane, are capable of being pivoted around the armrest's center of rotation C; C1 along a certain trajectory present in a vertical plane.
The center of rotation C; C2 in the middle section 6 of the seat portion 20, when viewed from a hinge point 16 between said middle section 6 and the foot section 7 connected thereto, is located after a halfway point along the length of the seat portion 20. Preferably, in addition, the seat portion's center of rotation C; C2, in a position B of the seat portion (cf. figs. 1, 5), i.e. when the middle section and the foot section are at the same level, is moreover located slightly below the middle section 6. This is feasible for example in such a way that the torsion spring 11 has its attachment point with a body of the middle section 6 located at an attachment bracket 15 which is present slightly below a body 61 of the middle section 6.
The center of rotation C; C1 of the armrest body 21, on the other hand, when viewed from a lower edge of the armrest body 21, is located at such a height that the middle section 6 fits in its entirety below a horizontal plane extending by way of the center of rotation C; C1 of the body 21 of the armrest 2 in a space defined by the armrest body and the sofa frame's rear section 1a after the seat portion has been folded to a position A, i.e. to a seating configuration. Figs. 1, 5 illustrate the center of rotation C of the armrest body at a location where the torsion spring 11 is fastened with an attachment bracket 14 to the body 21 of the armrest 2.
In case the seat portion has its center of rotation C; C2 located at an attachment bracket 15 present slightly below the middle section 6 of the seat portion 20 as the seat portion is in a position B and as, moreover, the armrest body has its center of rotation C; C1 at a suitable height in the vertical direction of the body 21 of the armrest 2, it will be possible to fold the middle section 6 of the seat portion 20 to a position below a horizontal plane extending by way of the armrest attachment bracket 15. As a result, the middle section 6 fits almost in its entirety below a horizontal plane extending by way of the center of rotation C; C1 of the body 21 of the armrest 2 (cf. fig. 3).
On the other hand, the location for a center of rotation C in the body 21 of the armrest 2, in its lengthwise direction, will be primarily determined on the basis of a length of the middle section 6 and a location of middle section's center of rotation C; C2. The middle section 6 must be able to make a rotation through between the rear frame section 1 a and the frame's armrest 21 around the center of rotation C; C1 in the process of proceeding from the seat portion's position B, i.e. from the seat portion's bed configuration, to the seat portion's position A or vice versa. This is why the distance from the rear frame section 1 a to the center of rotation C; C1 of the body of the armrest 2 is equal to the distance from the center of rotation C; C1 of the body of the armrest 2 to an articulation point 16 between the middle section 6 and the foot section. The rear frame section 1 a extends transversely relative to the frame's armrests 2.
In association with the center of rotation C; C1 of the body 21 of at least one armrest, preferably both armrests 2, is provided a torsion spring 11 counterbalancing the operation of a sofa bed opening and closing mechanism. The torsion spring 11 has its first end fixed by way of a first attachment bracket 15 to a side flank 66 of the middle section 6 of the bed sofa's seat portion 20, to the center of rotation C of said side flank 66. The torsion spring 11 has its second end connected by way of a second attachment bracket 14 to the center of rotation C; C1 of the body 21 of the armrest 2, whereby the spring 11 has its lengthwise direction transverse relative to the lengthwise direction of the seat portion 20. In the exemplary embodiment of the invention presented in the figures, each center of rotation C; C1 of the armrest is fitted with just one spring kit comprising a helical torsion spring 11, but there can be more of those side by side. The spring kit includes an actual torsion spring 11 as well as its assembly rod 13 and a straight end 12 of the spring (figs. 1, 4).
More specifically, the helical torsion spring 11 is connected to the centers of rotation C; C1, C2 of the middle section 6 as well as the armrest body 21 so as to enable its rotation in both directions around its longitudinal axis which is concentric with the center of rotation C1.
As can be seen from figs. 6a-6d, when the seat portion 20 of the sofa bed 10 has its foot and middle sections 7, 6 halfway across its trajectory rotating around the armrest's center of rotation C; C1, at least the middle section 6 is in a vertical position, nor is there any stress in the torsion spring 11. When the foot and middle sections 7, 6 of the seat portion 20 of an opening and closing mechanism are pivoted from this rest position of the spring in either direction around the center of rotation C; C1, the torsion spring 11 becomes stressed. The magnitude of a torque or stress generated in the torsion spring is determined according to Hooke's law on the basis of how much the spring has been twisted from an equilibrium condition in which the torque = 0.
When the sofa bed 10 has been set in a seating configuration A, the seat portion's middle section 6 is in a folded position below a line extending by way of the center of rotation C; C1 of the body of the armrest 2 while the foot section 7 is located on top of the middle section, mostly above said horizontal line. Hence, said torsion spring 11 is in a stressed condition, striving to twist around its longitudinal axis toward its rest condition. At the same time, said torsion spring 11 strives to turn the seat portion's middle section 6 and the seat portion's foot section 7 in engagement therewith around the center of rotation C; C1 in such a way that both of these will end up side by side in an upright position. However, the weight of a sofa bed's seat portion 20 prevents the sections 6, 7 of the seat portion 21 from turning unintentionally to an upright position. The spring tension of the spring 11 nevertheless counterbalances operation of the sofa bed opening and closing mechanism and thereby makes opening and closing the sofa more comfortable.
When the sofa bed's seat portion 20 is being opened into a bed configuration B and as the pivoting motion of the spring 11 around the center of rotation C; C1 crosses a halfway point of the rotational motion at which the spring 11 is in a rest condition, the spring 11 begins to stress and lighten the perceived heaviness of turning the sofa bed's seat portion 20.
In the process of closing the sofa bed into a seating configuration A, all this occurs respectively in a reversed order, thus facilitating the procedure.
The invention is not limited to the foregoing example, but may vary within the scope of the subsequently presented claims.

List of reference numerals

1 Sofa frame
1 a Rear section of the sofa frame
2 Armrest of the sofa
21 Body of the armrest
3 Sub-frame, fixing plate
4 Front board of the sofa
5 Backrest cushion
20 Seat portion
6 Middle section of the seat portion
61 Body of the middle section
65 End side of the middle section
66; 66a, 66b Side flanks of the middle section
7 Foot section of the seat portion
75 End side of the foot section
8 Mechanism bar
9 Legs of the foot section
10 Sofa bed
11 Torsion spring
12 Straight end of the spring
13 Assembly rod
14 Spring attachment bracket for the armrest
15 Spring attachment bracket for the middle section's body
16 Hinge or the like between foot section and middle section
A Seating configuration of the seat portion
B Seat portion opened into a bed
C Center of rotation for the armrest, the middle section, or the fixing plate
C1 Center of rotation for the armrest
C2 Center of rotation for the middle section

Claims

A counterbalancer for the opening and closing mechanism of a sofa bed (10), wherein the sofa bed (10) comprises a frame (1) provided with an armrest (2), as well as a seat portion (20) including a foot section (7) and a middle section (6), which are connected to each other rotatably in a vertical plane by way of a hinge or the like and which are connected to the frame (1) rotatably in a vertical plane by means of the sofa bed opening and closing mechanism, by linking the middle section (6) of the seat portion (20) rotatably to a center of rotation (C) of the armrest (2) of the sofa bed frame (1) in such a way that the seat portion (20) is on the one hand capable of being set in a seating configuration (A), in which its middle section (6) has been folded underneath the foot section (7), and on the other hand to an opened position (B) or a bed configuration, in which the foot section (7) and the middle section (6) are at the same level, characterized in that the sofa bed opening and closing mechanism comprises at least one torsion spring (11), which is arranged in connection with the center of rotation (C) of the armrest (2) of the frame (1) by connecting a first end of the torsion spring to said center of rotation (C1) of the armrest and a second end thereof to a respective center of rotation (C2) of the middle section, such that said torsion spring (11) is in a rest condition once the middle section (6) of the seat portion (20) has pivoted to an upright position and in a stressed condition as the foot section (7) and the middle section (6) are in the seating configuration (A) or in the opened position (B).
A counterbalancer for the opening and closing mechanism of a sofa bed (10), wherein the sofa bed (10) comprises a frame (1) provided with an armrest (2) and having two seat portions (20) placed side by side in a lateral direction of the sofa, each of which comprises a foot section (7) and a middle section (6), which are connected to each other rotatably in a vertical plane by way of a hinge or the like and which are connected to the frame (1) rotatably in a vertical plane by means of the sofa bed opening and closing mechanism by linking the middle section (6) of the seat portion (20) rotatably to a center of rotation (C; C1) of the armrest (2) of the sofa bed frame (1) as well as to a center of rotation (C) between the middle sections of the seat portions in such a way that the seat portion (20) is on the one hand capable of being set in a seating configuration (A), in which its middle section (6) has been folded underneath the foot section (7), and on the other hand to an opened position (B) or a bed configuration, in which the foot section (7) and the middle section (6) are at the same level, characterized in that the sofa bed opening and closing mechanism comprises at least two torsion springs (11) which are arranged in connection with the center of rotation (C; C1) of the armrest (2) of the frame (1) by linking a first end of the torsion spring to said center of rotation (C; C1) of a body of the armrest, and a second end thereof to a respective center of rotation (C; C2) of the middle section (6) in such a way that said torsion spring (11) is in a rest condition once the middle section (6) of the seat portion (20) has pivoted to an upright position and has become stressed as the middle section (6) and the foot section (7) are in the seating configuration (A) or in the opened position (B).
A counterbalancer according to claim 2 for an opening and closing mechanism, characterized in that between the seat portions (20, 20) extends a vertical sub-frame (3) to whose center of rotation (C) the middle section (6) of at least one seat portion (20) is connectible by way of the torsion spring (11).
A counterbalancer according to any of the preceding claims for an opening and closing mechanism, characterized in that the torsion spring (11) is cylindrical double torsion spring coiled from steel wire, said torsion spring (11) having its first end connected to the center of rotation (C1) of the frame's armrest (2) and its second end to the center of rotation (C2) of the middle section (6) of the seat portion (20).
A counterbalancer according to any of the preceding claims for an opening and closing mechanism, characterized in that the spring (11) is connected by way of an attachment bracket (14, 15) to the armrest (2) of the sofa frame and to the middle section (6) of the seat portion (20).
A counterbalancer according to any of the preceding claims for an opening and closing mechanism, characterized in that the center of rotation (C2) of the seat portion's middle section (6), when viewed from a connection point between the seat portion's middle section (6) and the foot section (7) connected thereto with a hinge (16) or the like rotatably in a vertical plane, is located after halfway across the length of the seat portion's middle section (6).
A counterbalancer according to any of the preceding claims for an opening and closing mechanism, characterized in that the seat portion has its center of rotation (C; C2) located at an attachment bracket (15), which is in a lower part of the middle section (6) or below the middle section and attaches to the middle section when the seat portion is in position B, and the armrest has its center of rotation (C; C1) located at a body (21) of the armrest (2) at such a height that the middle section (6) of the seat portion (20) is capable of being pivoted around the armrest's center of rotation (C; C1), ending up mostly below a horizontal plane extending by way of the middle section (6) or the attachment bracket (15) in engagement therewith, said plane extending by way of a second end of said center of rotation in a space confined by the body (21) of the armrest (2) and a rear section (1 a) of the frame.
A counterbalancer according to any of the preceding claims for an opening and closing mechanism, characterized in that the foot section (7) and the middle section (6) are connected to each other by the ends thereof rotatably in a vertical plane by way of a hinge, such as an articulation element, and further by way of a mechanism bar (8) which connects to legs of the foot section (7) and to the side flank of a body (61) of the middle section (6) in such a way that the foot section (7) traces the middle section in synchronism as the middle section (6) pivots in its trajectory around the center of rotation (C; C1) located in the body (21) of the armrest (2).
A method for counterbalancing the closing of a sofa bed (10), said sofa bed comprising a frame (1) provided with an armrest (2), as well as a seat portion (20) including a foot section (7) and a middle section (6), which are connected to each other rotatably in a vertical plane by way of a hinge (16) or the like and which are connected to the frame (1) rotatably in a vertical plane by means of the sofa bed opening and closing mechanism by linking the middle section (6) of the seat portion (20) rotatably to a center of rotation (C) of the armrest (2) of the sofa bed frame (1), in connection with said center of rotation being provided at least one torsion spring (11), said method comprising at least the following method steps of:
- pivoting the middle section (6) with respect to the foot section (7) around a center of rotation (C1) of the armrest from an initial condition, in which the middle section (6) and the foot section (7) are at the same level (position B (bed configuration) of the seat portion) in a vertical plane defined by the hinge (16) or the like therebetween and by the center of rotation (C; C1) of the armrest, whereby, at the same time, the torsion spring (11) is in a stressed condition until the seat portion's middle section (6) reaches an upright position and the torsion spring (11) has relaxed from its tension and said torsion spring is in a rest condition,

- continuing to pivot the seat portion (20) by turning the middle section (6) with respect to the foot section (7) around said center of rotation (C; C1) until the middle section (6) has become folded underneath the foot section (7) ((seating) configuration (A) of the seat portion), the torsion spring (11) having become stressed again at the same time.
A method for counterbalancing the opening of a sofa bed, said sofa bed comprising a frame (1) provided with an armrest (2), as well as a seat portion (20) including a foot section (7) and a middle section (6), which are connected to each other rotatably in a vertical plane by way of a hinge (16) or the like and which are connected to the frame (1) rotatably in a vertical plane by means of the sofa bed opening and closing mechanism by linking the middle section (6) of the seat portion (20) rotatably to a center of rotation (C) of the armrest (2) of the sofa bed frame (1), in connection with said center of rotation being provided at least one torsion spring (11), said method comprising at least the following method steps of:
- pivoting the middle section (6) with respect to the foot section (7) around a center of rotation (C; C1) of the armrest from an initial condition, in which the middle section (6) has been folded underneath the foot section (7) (position (A) of the seat portion, seating configuration), whereby at the same time the torsion spring (11) has become stressed, in a vertical plane defined by the hinge (16) or the like therebetween until the seat portion (20) is in a vertical position in which its middle section (6) has become folded to an upright position and the torsion spring (11) has relinquished a spring force bound thereto, i.e. the torsion spring is in a rest condition,

- continuing to pivot the middle section (6) of the seat portion (20) by turning the middle section (6) further with respect to the foot section (7) around said center of rotation (C; C1) until the middle section (6) has folded to become coplanar with the foot section (7) (position (B) of the seat portion), the torsion spring (11) becoming stressed again at the same time.
A method according to claim 10, characterized in that the torsion spring (11) is in a stretched condition in the seat portion's position A (seating configuration), and it counterbalances the movement of the sofa bed's seat portion along a trajectory around a center of rotation (C; C1) of the armrest body, said trajectory being directed upwards around the center of rotation (C; C1) until the middle section of the seat portion (20) has reached an upright position.
A method according to claim 11, characterized in that, when the movement of the middle section of the sofa bed's seat portion (20) is continued from the upright position of the middle section, the seat portion has its trajectory around the center of rotation (C; C1) of the armrest directed downward and the torsion spring ( C ) becomes stressed again and counterbalances the pivoting motion of the sofa bed's seat portion (20) on its way down towards the seat portion's bed configuration (B).
A method according to any of claims 9-12, characterized in that, in the seating configuration (A) of the seat portion (20), the middle section (6) has become folded underneath the foot section (7) in a space confined by the frame's armrests (2) as well as the frame's rear section (1 a).