# US 5,348,378 A · Pressure balanced torsion system for a backrest and the like

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- Number: US 5,348,378 A
- Document ID: US5348378A
- Status: Granted
- Kind: A
- Application number: 07/820,338
- Filed: 1992-01-14
- Granted: 1994-09-20
- Earliest claimed: 1991-08-20
- Inventors: Yun H. Zhang
- Web page: https://patentgrep.com/patent/US5348378A

## CPC

- A47C 7/40: for the back
- A47C 7/025: {Springs not otherwise provided for in A47C7/22 - A47C7/35}
- A47C 7/405: {with double backrests}
- A47C 23/02: using leaf springs, e.g. metal strips (wooden springs A47C23/06)
- A47C: CHAIRS; SOFAS; BEDS

## Abstract

The pressure balanced torsion system is for use in a backrest and the like. The system has a plurality of torsion action assemblies. Each assembly consists of a pair of pressure bearing plates mounted at the free ends of a torsion spring. The torsion spring is pivotally mounted to a rigid support plate which forms the back plate of the backrest. When a body rests against the backrest, the counter reactive force generated by the assembly causes both pressure bearing plates to push back against the body until the torsion is balanced, thus providing a uniform support to the body.

## Claims

### Claim 1

A pressure balanced torsion system for use in a backrest and the like, comprising
a first pressure bearing plate means and a second pressure bearing plate means, each of said first pressure bearing plate means and second pressure bearing plate means having a front surface and a rear surface opposite to said front surface,
an elongated torsion spring means including a first arm portion having a free end mounted to said rear surface of said first pressure bearing plate means, and a second end mounted to one side of a rocker member, said torsion spring means including a second arm portion having a free end mounted to said rear surface of said second pressure bearing plate means, and a second end mounted to a second side of said rocker member, said second side of said rocker member being directly located opposite to said one side,
said rocker member being pivotally mounted on a support plate.

### Claim 2 (depends on 1)

A pressure balanced torsion system according to claim 1 wherein said torsion spring means has a coil configuration formed at a middle portion therein, and said rocker member is a round disc secured at said middle portion.

### Claim 3 (depends on 1)

A pressure balanced torsion system according to claim 1 including a first sleeve means disposed on said rear surface of said first pressure bearing plate means, and said free end of said first arm portion of said torsion spring means being mounted to said first sleeve means,
a second sleeve means disposed on said rear surface of said second pressure bearing plate means, and said free end of said second arm portion of said torsion spring means being mounted to said second sleeve means.

### Claim 4 (depends on 3)

A pressure balanced torsion system according to claim 3 including a flexible retaining sheet means covering over and secured to the front surface of said first pressure bearing plate means and said second pressure bearing plate means.

### Claim 5 (depends on 1)

A pressure balanced torsion system according to claim 1 including a bracket member mounted between said rocker member and said support plate, and said torsion spring means is a flat spring having two flat surfaces.

### Claim 6 (depends on 5)

A pressure balanced torsion system according to claim 5 wherein said bracket member is a U-shaped bracket mounted fixedly to said support plate.

### Claim 7

A pressure balanced torsion system for use in a backrest and the like, comprising
a plurality of torsion balanced means located between a flexible retaining sheet means and a rigid support plate,
each of said torsion balanced means including a first pressure bearing plate means and a second pressure bearing plate means, each of said first pressure bearing plate means and second pressure bearing plate means having a front surface and a rear surface located behind said front surface, an elongated torsion spring means including a first arm portion having a free end mounted to said rear surface of said first pressure bearing plate means, and a second end mounted to one side of a rocker member, said torsion spring means including a second end mounted to a second side of said rocker member, said second side of said rocker member being directly located opposite to said one side, and said rocker member being pivotally mounted on said rigid support plate.

### Claim 8 (depends on 7)

A pressure balanced torsion system according to claim 7 wherein the front surfaces of said first pressure plate means and said second pressure bearing plate means are secured to said flexible retaining sheet means by adhesion.

### Claim 9 (depends on 8)

A pressure balanced torsion system according to claim 8 wherein said flexible retaining sheet means is a foam sheet material, and said rigid support plate is a rigid board.