Locking device for securing objects which are moveable relatively to one another

A system for fluid exchange between two working chambers, comprising:

• a fluid conducting member in series between said two working chambers and containing a through flow chamber;
• a movable sealing piston sealingly confining said through flow chamber adjacent one end thereof;
• a first connection for connecting said through flow chamber to one of said working chambers;
• a second connection for connecting said through flow chamber to the other of said working chambers;
• sealing piston pretensioning means for pretensioning a first connection side end face of the sealing piston adjacent said one end of said through flow chamber into a closed position against the first connection;
• the first connection side end face, when in the closed position, (i) presenting a smaller fluid-exposed cross section to a fluid pressure acting on it through the first connection and (ii) having a larger fluid-exposable cross section not always exposed to said fluid pressure acting through the first connection;
• said second connection communicating with the other working chamber via a pressure drop path;
• said through flow chamber permitting the establishment of a flow path therethrough extending from said one working chamber to said other working chamber, said flow path through said through flow chamber being the sole flow path permitting fluid flow between said working chambers in the fluid exchange direction from-said one chamber to said other working chamber so that, at a predetermined minimum pressure acting on the smaller fluid-exposed cross section of the first connection side end face, the first connection is opened, and subsequently the larger fluid-exposable cross section within the through flow chamber is exposed to a pressure which is dependent upon the rate of flow (mass per time unit) through the through flow chamber and maintains the first connection open until the through flow rate falls below a predetermined minimum;
• and
• means for normally preventing fluid flow in the direction from said other working chamber to said one working chamber and being responsive to the occurrence of a predetermined pressure differential between said other working chamber and said one working chamber to allow fluid flow from said other working chamber to said one working chamber.

A structural sub-assembly comprising, as a basic structure, a motor vehicle construction and, as a movable structural element, one of a flap or hood which is adapted for a movement guided by guide means against the force of gravity between an extreme lower position and an extreme upper position in relation to the basic structure, whereby to facilitate movement of the movable structural element between the extreme lower position and the extreme upper position and in order to arrest the movable structural element in intermediate positions, at least one cylinder-piston unit filled with a pressurized fluid is provided, whereby furthermore the cylinder-piston unit is constructed with a cylindrical tube, a tubular cavity constructed inside the cylindrical tube, a guiding and sealing unit at one end of the tubular cavity, a sealing-tight closure at the other end of the tubular cavity, a piston rod inserted through the guiding and sealing unit, a separating piston unit connected to the piston rod inside the tubular cavity, a rod chamber on the piston rod side of the separating piston unit, an end chamber on the side of the separating piston unit which is remote from the piston rod, and a filling of pressurized fluid in the rod chamber and in the end chamber, whereby furthermore means are provided for compensating for variations in the displacement volume of the piston rod inside the tubular cavity upon displacement of the piston rod in relation to the tubular cavity which generates a push-out force on the piston rod, whereby, furthermore, a fluid exchange system is provided between the rod chamber and the end chamber, whereby, furthermore, of the cylindrical tube and the piston rod, one is connected to the basic structure while the other is connected to the movable structural element and whereby the weight and the guide means of the movable structural element, the points of attack between the cylinder-piston unit, the basic structure and the movable structural element, the cross-section (Q1) of the tubular cavity, the cross-section (Q3) of the piston rod, the fluid filling in the tubular cavity and the fluid exchange system are so constructed and dimensioned that the following conditions are satisfied:

• (a) when the movable structural element is in a midway position, at rest, the end chamber and the rod chamber are separated from each other and the movable structural element is secured against sinking by an end chamber fluid contained in the end chamber and against rising by a rod chamber fluid contained in the rod chamber, in that
• aa) a pressure (P1) of the end chamber fluid bearing on a full cross-section (Q1) of the separating piston unit exerts a push-out effect on the separating piston unit,
• ab) by this push-out effect in the rod chamber a pressure (P2) of the rod chamber fluid is generated which exerts on a differential cross-section (Q2) between the full cross-section (Q1) of the separating piston unit and a rod cross-section (Q3) of the piston rod a push-in effect on the separating unit,
• ac) the push-in effect generated by said pressure (P2) of the rod chamber fluid, together with an additional push-in effect (FG) emanating from the weight of the movable structural element maintains equilibrium with the push-out effect, the pressure (P2) in the rod chamber being greater than the pressure (P1) in the end chamber,
• ad) a lifting-purpose non-return valve system opening from the rod chamber to the end chamber is exposed to the pressure in the rod chamber with a smaller fluid exposed cross-section and is so adjusted that in a state of equilibrium it cannot be opened by the pressure in the rod chamber,
• ae) a lowering-purpose non-return valve system opening from the end chamber to the rod chamber is exposed to the pressure in the end chamber and is so adjusted that in a state of equilibrium it cannot be opened by the pressure in the end chamber;
• b) a brief slight application of an external lifting Force (FH) on the movable structural element results in an increase in the pressure in the rod chamber which acts on the smaller fluid exposed cross-section of the lifting-purpose non-return valve system, thus effecting an opening of the lifting-purpose non-return valve system;
• ba) once the lifting-purpose non-return valve system is opened, there is a flow of fluid from the rod chamber to the end chamber;
• bb) the flow from the rod chamber to the end chamber suffers a drop in pressure in a pressure drop path situated between the lifting-purpose non-return valve system and the end chamber,
• bc) as a result of this pressure drop, there is established at the lifting-purpose non-return valve system an intermediate pressure (PZ) which is greater than the pressure in the end chamber;
• this intermediate pressure (PZ) acts on a larger fluid-exposed cross-section of the lifting-purpose non-return valve system in an opening sense as to the lifting-purpose non-return valve system;
• as a result of the fluid flow from the rod chamber through the lifting-purpose non-return valve system to the end chamber, the pressure in the rod chamber drops;
• the balance is modified and the piston rod is pushed out of the cylindrical tube;
• bd) the pushing of the piston rod out of the cylindrical tube brings about a continued flow from the rod chamber to the end chamber;
• this continued flow continues to ensure maintenance of an intermediate pressure (PZ) at the lifting-purpose non-return valve system;
• this intermediate pressure (PZ) furthermore acts on the larger fluid-exposed cross-section of the lifting-purpose non-return valve system and holds it open, even when the exertion of external lifting force (FH) ceases;
• the pushing-out movement of the piston rod and thus the raising of the movable structural element are therefore continued by the action of the cylinder piston unit, without the need for the continued application of an external lifting force (FH);
• be) if during the continued push-out movement of the piston rod a depressing force (FN) is briefly applied to the movable structural element, then the rate of flow (mass per time unit) through the lifting-purpose non-return valve system drops;
• the intermediate pressure (PZ) acting on the larger fluid-exposed cross-section of the lifting-purpose non-return valve system drops;
• the lifting-purpose non-return valve system is closed again;
• the movable structural element comes to a standstill and remains stationary even if the depressing force (FN) ceases again;
• c) when the movable structural element is in an intermediate position and at rest, it can be moved by a minor lowering force (FS) in the direction of the extreme lower position in that
• ca) firstly there is an increase in the pressure (P1) in the end chamber, a slight increase in the pressure (P1) in the end chamber being sufficient for opening the lowering-purpose non-return valve system,
• cb) consequently there is an approximation of pressures between the end chamber and the rod chamber, and
• cc) the pressure acting on the piston rod cross-section (Q3) and prevailing in the rod chamber and the end chamber once this approximation of pressure is established between the two chambers produces a force to push the piston rod out which only slightly exceeds the gravity-induced piston rod push-in effect of the movable structural element on the piston rod, so that it can be overcome by said minor lowering force (FS) to be permanently applied until a desired lower position of the movable structural member has been reached.