Hydraulic cylinder-piston unit provided with a mechanical safety device, particularly for pantograph type motor vehicle lifts

A hydraulic cylinder-piston unit having a mechanical safety device, particularly for motor vehicle lifts of the pantograph type, comprising

• a cylinder having a first, close, endpiece at one end thereof and a second endpiece at the opposite end thereof, said second endpiece having an aperture therein,
• a piston slidably contained within said cylinder and dividing the same into a rod end chamber and a closed end chamber,
• a hollow rod attached to said piston and extending through the aperture of said second endpiece,
• a toothed rod fixed at one end of said cylinder to the closed endpiece thereof,
• said hollow rod being axially movable with respect to said toothed rod by means of said piston,
• said piston containing a pawl assembly cooperating with said toothed rod, said pawl assembly comprising at least one radially movable stop member and means for biasing said stop member toward said toothed rod, whereby during elongation of the cylinder-piston unit the stop member yields elastically in passing from one tooth to the next, whereas during retraction of the unit said stop member engages within a notch defined between two successive teeth, thereby forming a mechanical safety stop, and further comprising, for each stop member,
• a plunger mounted in said piston for movement parallel to the axis thereof and having an upper surface exposed to the rod end chamber of the cylinder and said plunger further comprising means for retracting the respective stop member into the piston and out of engagement with the toothed rod.