7 Design calculation

7.1 Overview

The design calculation for a gas spring generally involves: force, force ratio, stroke and extended length, piston rod diameter, cylinder inner diameter and wall thickness. The design calculation for the gas spring is based on an ambient temperature of 20°C ± 2°C, and the influence of the ambient temperature should also be considered. For every 1°C change in ambient temperature, the change in nominal force F_a will be approximate 0.37%.

7.2 Force

7.2.1 Schematic diagram of force-displacement curve

The force-displacement curve is shown schematically in Figure 9.

a) Force-displacement curve for compression gas spring

b) Force-displacement curve for stretching gas spring

Figure 9 Force-displacement curve for gas spring

7.2.2 Minimum extension force F₁

For compression gas spring, lockable gas spring, and chair height adjustment gas spring, theoretical calculation of F₁ is according to formula (3). The load-based minimum extension force F₁ of a compression gas spring is calculated according to Annex A. See Annex B for calculating F_r.

………………(3)

7.2.3 Maximum extension force F₂

For compression gas spring, lockable gas spring, and chair height adjustment gas spring, F₂ is calculated according to formula (4):

………………(4)

7.2.4 Minimum compression force F₃

For compression gas spring, lockable gas spring, and chair height adjustment gas spring, F₃ is calculated according to formula (5):

………………(5)

7.2.5 Maximum compression force F₄

For compression gas spring, lockable gas spring, and chair height adjustment gas spring, F₄ is calculated according to formula (6):

………………(6)

7.2.6 Minimum tension force F₅

The minimum tension force F₅ of a stretching gas spring is calculated according to formula (7):

………………(7)

7.2.7 Maximum tension force F₆

The maximum tension force F₆ of a stretching gas spring is calculated according to formula (8):

………………(8)

7.2.8 Minimum resilience force F₇

The minimum resilience force F₇ of a stretching gas spring is calculated according to formula (9):

………………(9)

7.2.9 Maximum resilience force F₈

The maximum resilience force F₈ of a stretching gas spring is calculated according to formula (10):

………………(10)

7.2.10 Unlocking force F_K

See Figure 10 for the inner diameter of hollow piston rod of a gas spring d₀ and the effective diameter of the valve pin d₁.

Figure 10 Schematic diagram of the inner diameter of hollow piston rod d₀ and the effective diameter of the valve pin d₁

The unlocking force of valve pin F_k for lockable gas spring, chair height adjustment gas spring and lockable stretching gas spring is calculated according to formula (11):

………………(11)

7.2.11 Gas spring force ratio α

7.2.11.1 The force ratio of gas spring shall be determined by the load, and is generally calculated according to formula (12):

Or α=F_b/F_a ………………(12)

7.2.11.2 The force ratio of an ordinary stretching gas spring is calculated according to formula (13):

Or α=F_b/F_a ………………(13)

Gas spring design calculation (English version of national strandard, initiated by LeiYan Gas Springs), proposed and prepared by SAC/TC 235 (National Technical Committee 235 on Spring of Standardization Administration of China).