Gas strut installation – what you need to know

Crossover

Crossover is the point at which the strut takes over the lifting action (or gravity takes over to close). This will normally be around 10° to 30° from fully closed. In practice, this will vary by several degrees between opening and closing, due to factors such as friction of the internal components of the spring, hinges and end connectors.

Self-Rise & Self-Close

Self-rise is the angle at which the gas spring will lift the lid without any assistance from the operator, similarly Self-close is the angle at which the lid will close without any assistance. In most cases it is undesirable to have the lid open without any operator input (referred to as “instant lift”) because this behaviour is unpredictable to the operator and can allow the lid to open without warning, for example when the P1 force increases above nominal due to elevated ambient temperatures.

Effects of Temperature on Handling

Temperature not only affects the output force, but also the handling forces. The following graphs shows behaviour on an application at 20°C and then again at 65°C. As is seen in the figure below, at 20°C crossover occurs at an opening angle of around 7°, with the handling forces being acceptable in both opening and closing.

Crossover at 20°C.

Crossover at 65°C.

However, when the ambient temperature increases to 65°C (for example, in the case of an engine cover application), lift will occur almost instantaneously. This behaviour is unpredictable to the operator and can in some cases be dangerous. It can also be seen that the handling effort to close the application increases.

For these reasons it is important that the designer understands what the ambient and “normal” operating temperatures of an application will be so that if necessary a suitable compromise can be made in handling performance.