Draftex Industries Limited

Etienne Perrin

Dominique Dony

A gas compression spring comprises a gas-filled cylinder in which a piston carrying a hollow piston rod is slidable and divides the interior of the cylinder into first and second chambers. Over part of the length of the cylinder, a groove is provided in the cylinder wall. Gas pressure within the cylinder causes the piston to drive the piston rod outwards of the cylinder, this being permitted by the groove which allows transfer of gas pressure between the two chambers. When the piston reaches the end of the groove, such gas pressure transfer ceases and movement of the piston rod stops. External manual force applied to a control rod, extending through the hollow interior of the piston rod, unseals an opening at the end of the piston rod which brings the two chambers into communication again. Gas pressure transfer can now take place between the two chambers via the interior of the piston rod. Movement of the piston rod outwardly of the cylinder under the pressure exerted by the gas now re-commences, but can be halted at any desired position by release of the force manually exerted on the control rod.

Gas spring

A gas spring for the hatchback or other closure member of a motor vehicle body automatically stops at an intermediate position between the fully closed and fully opened positions. A piston carrying a piston rod separates the interior of a cylindrical body into first and second chambers. Gas under pressure forces the piston and piston rod towards the extended position to open the closure member, a restricted gas path through a groove in the cylinder wall allowing gas to flow from the second chamber to the first chamber. A third chamber is also defined within the cylinder and has an uninterrupted wall portion and a wall portion incorporating a groove. The third chamber is on the opposite side of the second chamber to the first chamber and has a smaller diameter than the first and second chambers. When the piston rod moves a sealing ring into the third chamber and also into contact with the uninterrupted wall portion, the third chamber is completely closed off; pressure build-up therefore arrests the movement of the piston rod at the intermediate position. Manual movement of the piston rod beyond this intermediate position moves the sealing ring over the groove in the third chamber, whereupon gas pressure acting on the piston now moves the piston rod to the fully extended position, gas flow being permitted from the third chamber to the second chamber through the groove in the third chamber. During closure of the hatchback, frictional engagement between the sealing ring and the smooth wall portion of the third chamber moves the sealing ring sideways into a position in which it allows gas flow between the third and second chambers.

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Pirey, France

Etienne Perrin