Abstract: The present embodiment generally relates to a mechanical assembly which modifies and enhances the performance of a critical portion of the parts which comprise an air spring assembly. A key element common with an air spring assembly is the precharge chamber. This chamber is filled at the factory with compressed gas and along with a floating piston and a piston rod, creates the basic air spring assembly. Although this is a sealed chamber, the potential for air leakage is well documented. The inability to maintain the design gas pressure in the precharge chamber requires the chamber to initially be overcharged to remain functional even with the slow loss of air charge. The present invention demonstrates how the precharge assembly found in all such air springs can be modified and, with the addition of a few parts, be capable of maintaining the precharge pressure at an optimum level.

Abstract: A soft-in-plane proprotor system for a tiltrotor aircraft having a helicopter mode and an airplane mode. The proprotor system includes a hub, a plurality of proprotor blades and a plurality of blade support assemblies coupling the proprotor blades with the hub. Each blade support assembly includes a flapping bearing coupled to the hub and a yoke having first and second longitudinal sections with outboard grip members and an inboard arcuate section connecting the first and second longitudinal sections and coupled to the flapping bearing. A lead-lag damper is coupled between the hub and an inboard station of the respective proprotor blade. A twist shank is coupled between the outboard grip members of the yoke and an outboard station of the respective the proprotor blade. The twist shank defines a virtual lead-lag hinge outboard of the yoke and coincident with the respective pitch change axis.

Abstract: A hydraulic damper including a high frequency valve assembly for reducing the level of damping force provided by the hydraulic damper during a rebound stroke during high frequency and/or low amplitude events.

Abstract: A damping valve includes a piston with a one-side disk and an other-side disk, a port configured to include through holes, a piston rod, and a nut. A plurality of the through holes of the other-side disk are formed along between the inner peripheral seat surface and the outer peripheral seat surface. Elastic deforming portions are formed between the through holes of the other-side disk. A clearance is formed between the inner peripheral seat surface of the one-side disk and that of the other-side disk in a state where the nut is not tightened and the outer peripheral seat surface of the one-side disk and that of the other-side disk are in contact. The elastic deforming portions of the other-side disk are strained and the respective inner peripheral seat surfaces come into contact in a state where the nut is tightened.

Abstract: A technique capable of suppressing a rise in the temperature of a shock-absorber. A motorcycle includes a swing arm having a front end swingably supported by a body frame. A shock-absorber includes a rear end supported by the swing arm via a link and an upper end supported by the body frame via a support hole. A cylindrical reserve tank is connected to the shock-absorber for reserving the hydraulic operating fluid flowing into the shock-absorber, the reserve tank is arranged such that an axis thereof is positioned above the axis of the support hole provided in the upper end of the shock-absorber and extends in the width direction of a vehicle.

Abstract: The present disclosure provides hydraulic dampening systems wherein the dampening effect may be controlled by rotating a body of the dampener, after the dampening system has been installed and in use. The system includes a piston including a front disk and back disk, wherein the front disk has a reduced diameter with respect to the back disk. A washer is positioned between the two piston disks, wherein the diameter of the washer is greater than the piston back disk, wherein the washer includes at least two protruding tabs. The washer is frictionally engaged with the body of the dampener. As the body is rotated, the washer is rotated such that the washer tabs engage at least a portion of the piston front disk to rotate the piston along a threaded surface of a shaft of the system.

Abstract: A damping mechanism (1) generates a damping force in response to movement of a fluid between a first fluid chamber (R1) and a second fluid chamber (R2) of a fluid pressure shock absorber. The damping mechanism (1) comprises a partition wall member (2) that defines the first fluid chamber (R1) and the second fluid chamber (R2), and a plurality of chokes (4) provided in parallel, which penetrate the partition wall member (2) to connect the first fluid chamber (R1) and the second fluid chamber (R2). A leaf valve (8, 9) having a valve body that is constituted by only a single leaf is preferably provided in an opening portion of the chokes (4). The chokes (4) generate a damping force that is substantially commensurate with a speed of the fluid passing therethrough, and the damping mechanism (1) exhibits a linear damping force characteristic while having a simple and compact constitution.

Abstract: An active suspension system for a vehicle including at least one fluid operated ram having a cylinder and a main piston mounted therein for reciprocating movement, control means for controlling an equilibrium position of the piston in the ram in response to lateral acceleration of the vehicle in order to counter the effects of body roll of the vehicle, and wherein the ram includes shock absorbing means for permitting rapid movement of the piston from the equilibrium position when operating fluid in the ram is subjected to transient increases in pressure.

Abstract: A system and method to isolate vibrations from a vibrating structure. The system includes an adjustable vibration isolator that creates a reacting force matching the vibratory force of the vibrating structure. The method includes continuously monitoring the reacting force and vibratory force with a sensor system operably associated with a control unit having an algorithm to determine if adjustment of the vibration isolator is required. If required, the control unit commands a driver to selectively adjust the vibration isolator.

Abstract: An automobile hydraulic shock absorber includes a cylinder body, a piston, an upper support, a piston rod, a volume adjustment mechanism, first and second communicating passages, and a pressure-applying mechanism. The piston rod is attached to the upper support via a rubber cushion. The volume adjustment mechanism includes a free piston. The first and second communicating passages communicate the first oil chamber and second oil chamber with each other in the cylinder body via a diaphragm. The pressure-applying mechanism is disposed outside the cylinder body, movement thereof is restricted by the upper support, and the pressure-applying mechanism pushes the piston rod downward.

Abstract: A spring fork, in particular for bicycles, with a suspension system and a hydraulic damping system, includes a compression stage damping system (6) for a spring deflection process and a traction stage damping system (5) for a rebound process. At least one piston (3, 16, 27) is provided, which is located in the cylinder (2), and at least one connecting channel (17, 17a) is provided which connects the cylinder chambers located on both sides of the piston and is intended for the overflow of hydraulic oil (21). The compression stage damping system (6), which is activated during the spring deflection process, can be blocked by closing the connecting passage (lockout). At least with the compression stage damping system (6) blocked and, if appropriate, also with the traction stage damping system (5) also blocked, a bypass channel (11, 20, 20a) which has a reduced cross-section in comparison to the connecting channel (17, 17a) is opened.

Abstract: The invention relates to a device for damping compressive forces designed to be reversible also upon dynamic impact load. With the objective of achieving the lowest possible construction volume while simultaneously retaining favorable damping properties both upon static as well as dynamic compression, the device comprises a cylinder having a hydraulic chamber, a hollow piston, a valve arrangement and a separating piston, wherein the valve arrangement divides the hydraulic chamber into a front hydraulic chamber region and a rear hydraulic chamber region and the separating piston separates a head space from the front hydraulic chamber region. The valve arrangement comprises an eccentric hydraulic compartment connected to a transfer-flow area which is sealed by an eccentrically arranged multiplier valve.

Abstract: A real-time continuous damping module includes a flow channel that is configured to allow fluid to flow between a first chamber and a second chamber of a cylindrical tubular member when a pressurizing device exerts a pressure on the fluid within the first chamber. A variable damper assembly is configured to control a flow of fluid through the flow channel. The variable damper assembly includes a damper configured to variably obstruct an opening of the flow channel. A magnetic shape memory element is configured to variably control a position of the damper within the opening of the flow channel. The magnetic shape memory element exhibits changes in shape when exposed to a magnetic field. An electromagnetic device regulates the magnetic field for variably controlling the position of the damper within the flow channel by changing the shape of the magnetic shape memory element.

Abstract: A vibration damping device for hydraulic shock absorbers for vehicles, having two cartridges, each associated with a shock-absorber integrated in a component of a vehicle, and each comprising a tubular body, with a piston that forms two chambers with variable volumes of incompressible fluid, a first compression chamber, and a second extension chamber. Each piston is carried by a stem exiting from an end of the tubular body and associated with part of the shock-absorber. The piston is provided with bleeding orifices for fluid bleeding. Flow control and throttling for the orifices are provided.

Abstract: Damper device for damping relative movements of two elements of a mechanical system. The damper device comprises a damping chamber filled with a hydraulic fluid, a rod (4) having a piston (3) movable in the damping chamber so as to define two hydraulic compartments (1, 2), at least one calibrated orifice (10) provided in the piston (3) for throttling the hydraulic fluid flowing from one hydraulic compartment (1, 2) to another hydraulic compartment, at least one compression peak-limiting valve (11) and a traction peak-limiting valve (12), throttling the hydraulic fluid flowing from one hydraulic compartment (1, 2) to another hydraulic compartment. The damper has additional hydraulic means that are active in compression and in traction when the piston (3) reaches the end of its stroke, so as to constitute a progressive hydraulic abutment damping the end-of-stroke jolts.

Abstract: The present invention relates to an oil damper for preventing a seat and a cover from rapidly rotating. The oil damper includes a shaft unit, a cam, a valve, an elastic member, a housing and a fastening member. The shaft unit has a coupling part which is coupled to the seat and the cover. The cam is rotatably coupled to a rotating shaft of the shaft unit. The valve opens or closes a coupling hole depending on movement of the cam to allow fluid to flow through the coupling hole or prevent the fluid from flowing. The elastic member is provided in the housing and is compressed by the cam. A flow rate control groove is formed in the housing and controls the flow rate of fluid in response to movement of the cam. The fastening member is fitted over the shaft unit and fastened to the housing.

Abstract: A modified mono-tube shock is a lighter shock with less rod pressure, less seal drag, a greater range of valving, and faster heat dissipation. The shock includes an outer body, a shaft piston, a plurality of deflective discs, and a divider piston, wherein the divider piston is installed at a particular location inside the shock to create a gas chamber.

Abstract: A vibration damper, comprising a damping medium-filled cylinder, in which a piston rod is guided with freedom of axial movement, where, inside a working space in the cylinder, a stop spring in the form of a circular ring is located, which, after the piston rod has reached a defined stroke position, is compressed between a stop surface on the piston rod side and an end surface forming an axial boundary of the working space, and where the stop spring also forms a boundary of a radially inner space, which is connected to the working space outside the stop spring by means of at least one radial channel. The stop surface on the piston rod side and/or the axially limiting end surface is formed by a rigid body and is provided with at least one radial channel, which extends from the radially inner space to the radially outer working space, “inner” and “outer” being defined with respect to the stop spring.

Abstract: A shock absorber comprising: a cylinder; a piston partitioning the cylinder into two chambers; a piston rod; a by-pass passage passing through the chambers; and a damping-force adjusting mechanism adjusting a passage area of the by-pass passage, wherein the adjusting mechanism includes: a shutter guide; a shutter movably guided by the shutter guide; and an elastic member elastically retaining the shutter at an initial position, an adjustable passage adjusting the passage area of the by-pass passage as that opening is varied by shift of the shutter is formed, shift of the shutter is not influenced by pressure difference between the chambers, and when the shutter is at the initial position, the adjustable passage is opened with a predetermined degree, and the shutter moves to close the adjustable passage by fluid force that generates by flow of the working fluid of the adjustable passage against elastic force of the elastic member.

Abstract: A damping mechanism (1) that generates a damping force in response to a liquid flow between a first liquid chamber (R1) and a second liquid chamber (R2) comprises a partitioning member (2) separating the first liquid chamber (R1) and the second liquid chamber (R2) and a flow passage (P) formed in the partitioning member (2) to connect the first liquid chamber (R1) and the second liquid chamber (R2). The flow passage (P) comprises an odd number of through-holes (10-14) greater than three which penetrate the partitioning member (2) and are connected in series. A large amount of frictional energy loss due to a long path length occurs in the flow passage (P) and causes the damping mechanism (1) to generate a sufficient damping force.

Abstract: A rotor hub assembly for a rotary-wing aircraft has a central member and a plurality of blade grips adapted for attaching rotor blades to the central member. The blade grips are pivotally attached to the central member and are capable of pivoting about a pivot axis generally normal to a plane of rotation of the blades. The pivoting allows for in-plane motion of the blades relative to the central member. A damper is operably connected to each blade grip for damping the in-plane motion of the associated blade, each damper being selectively switchable between at least two spring rates.

Abstract: A damping device (10) for moveable furniture parts, comprising a piston (14) that is supported in a longitudinally displaceable manner in a housing (12) and on two opposing sides forms two working chambers (24; 26), which are variable in size and filled with a fluid damping medium, allowing a throttled transfer of the damping medium between the two working chambers (24; 26) via at least one overflow connection. A piston rod (28) led out of the housing in a sealed manner is connected to one side of the piston (24). Via the outer end of said rod, the movement of the furniture part to be dampened is transmitted to the piston. On the side of the piston opposite the working chamber (26) on the piston rod side, an elongated adjustment shaft (38) is connected.

Abstract: A vibration damping device for hydraulic shock absorbers for vehicles, having two cartridges, each associated with a shock-absorber integrated in a component of a vehicle, and each comprising a tubular body, with a piston that forms two chambers with variable volumes of incompressible fluid, a first compression chamber, and a second extension chamber. Each piston is carried by a stem exiting from an end of the tubular body and associated with part of the shock-absorber. The piston is provided with bleeding orifices for fluid bleeding. Flow control and throttling means for the orifices are provided.

Abstract: Disclosed herein is a strut assembly that comprises a piston that is in slideable communication with a housing. The piston comprises a piston head having a channel in operative communication with a fluid that is disposed in the housing. An elastic member and an active element are disposed in the channel. The active element is in operative communication with the elastic member and is operative to change the shape of the elastic member.

Abstract: A shock absorber for use in lowering heavy structures to the sea floor comprises a cylinder (1) with a piston (2) having a heavy piston rod (3). A plurality of channels (6) extend from the bottom side of the piston (2) to its top side, where the channels are closable by means of a disk-like valve body (7) which permits fluid movement up through the piston to a cylinder chamber (20) above the piston, but not in the opposite direction. The cylinder chamber (20) is provided with a plurality of exit nozzles (21) having diminishing diameter in the direction towards the bottom (13) of the chamber (20). At the lower end of the cylinder it is provided with a number of inlet openings (19), so that when the shock absorber is lowered in the sea together with the structure, the cylinder chamber (20) will automatically fill with sea water. Due to their weight the piston (2) with the piston rod (3) will be in the lower position.

Abstract: An amplitude sensitive damper apparatus that is provided with an amplitude sensitive valve unit may include a plug coupled to a piston rod to form a spring groove with the piston rod in a predetermined section, a spool member configured and dimensioned to cover the spring groove and slidably coupled to the piston rod to move up and down along the piston rod, wherein the spool member includes a supporting portion that protrudes toward the piston rod from a middle portion of an inner surface of the spool member, upper and lower elastic members that are mounted inside the spring groove to support the supporting portion of the spool member upwards and downwards respectively along the piston rod, and an amplitude sensitive valve that is integrally mounted on an outer surface of the spool member to generate a damping force when the spool member is moving.

Abstract: An object of the present invention is to improve productivity by making manufacturing of a piston easier. A piston 13 is constituted by two piston bodies 15 and 16. An annular valve seat 32 is formed on a non-coupled surface 16B of one of the piston bodies, i.e., the piston body 16, so that extension-side communication passages 36 are located radially inside the annular valve seat and compression-side communication passages 35 are located radially outside the annular valve seat, and an annular valve seat 19 is formed on a non-coupled surface 15B of the other of the piston bodies, i.e., the piston body 15, so that the compression-side communication passages 20 are located radially inside the annular valve seat and the extension-side communication passages 21 are located radially outside the annular valve seat. A sliding member 25 is disposed around one of the pitons bodies, i.e., the piston body 15.

Abstract: A hydraulic damper including a tube filled with working liquid which contains a slidable piston assembly attached to a piston rod. The piston assembly includes a piston having a compression valve arrangement to control the flow of working liquid passing through the piston during the compression stroke of the damper. The compression valve arrangement includes a stack of resilient deflectable disks placed on one axial side of the piston and covering compression flow passages in the piston, a spring, spring seat guide and a spring retainer, the spring mounted between the spring seat and the spring retainer. The spring biases the axially slidable spring seat against the stack of disks to normally close the compression flow passages, and the stack of disks is held by the spring seat. The spring seat guide may also be provided with rebound flow passages linked with flow passages in the piston.

Abstract: A gas shock absorber has a pressure tube which defines a working chamber. A piston divides the working chamber into an upper working chamber and a lower working chamber. A flow path extends through the piston to provide fluid communication between the upper and lower working chambers. A valve body is attached to the pressure tube. The valve body defines a flow path between the working chamber and a fluid chamber. The fluid chamber is in communication with either the upper working chamber or the lower working chamber. The fluid chamber can be defined within the pressure tube, between the pressure tube and a chamber tube or it can be defined by an air spring assembly.

Abstract: A damping device for movable furniture parts, such as doors or drawers, includes a cylinder filled with a free-flowing medium which is compressed by a piston which has a spring applied to it in its extended position. In order to provide a damping device of this type of smaller length, the cylinder includes a telescopic cylinder having at least two stages. A pressure spring is clamped between the bottom of the outer cylinder of the last stage and the piston of the first stage.

Abstract: A magneto-rheological damping device comprises a core element capable of acting as a magnetic circuit which carries a magnetic flux, and a case element surrounding a portion of the core element. A passage exists between the case element and core element, and an amount of magneto-rheological fluid is positioned between the core element and case element to flow within the passage. A magnetic flux generator is positioned adjacent a portion of the core element and is operable to generate a magnetic flux which acts upon the magneto-rheological fluid in the passage to affect the flow of fluid in the passage. The core element comprises a plurality of stacked laminations, which form a series of individual magnetic poles with gaps therebetween. The magnetic flux generator is operable to generate a magnetic flux in the poles and case element and across the gaps to affect the fluid flow in the passage.

Abstract: A vibration damper with variable damping force, includes a cylinder filled with damping medium and in which a piston fastened to a piston rod axially moveably therein. The piston divides the working cylinder into two working spaces. The damping force for the directions of rebound and compression are influenced by nonretum valves acting in the respective directions. A damping valve of variable damping action is additionally provided in series with each of the nonreturn valves so that the damping valve is active in both the rebound and compression directions.

Abstract: An air damper suitably used in the glove box of an automobile comprises a cylinder having a first open end and a second end, a guide cap covering the first open end, and a piston movable in the cylinder. A compression coil spring is inserted in the cylinder between the piston and the guide cap. The coil spring forces the piston toward the second end of the cylinder in the free state. The piston has a hook piece, which is threaded with a spring. At least one end of the spring is taken out of the cylinder via the guide cap, and connected to the glove box. The guide cap has a stopper means projecting inside the coil spring and toward the piston. If the glove box is opened and the string is pulled out of the cylinder, the piston moves toward the guide cap. The piston then strikes the stopper means of the guide cap before the coil spring is fully compressed.

Abstract: A shock absorber has a pressure tube with a piston assembly slidably disposed within the pressure tube and attached to a piston rod. The piston assembly divides the pressure tube into an upper working chamber and a lower working chamber. The piston assembly includes a compression and a rebound valve assembly. The piston assembly also includes a housing attached to the piston rod within which is slidably disposed a piston to define a closed chamber. The closed chamber is in communication with one of the working chambers through a passageway extending through the piston rod. The housing and piston provide two stage damping in rebound and compression with a smooth transition between soft and firm damping.

Abstract: A digressive valve for a vehicle damper provides rebound performance with a relatively high damping rate for low velocity inputs and a relatively low flow restriction operation for high velocity inputs so that a relatively firm ride with reduced impact harshness is achieved. A piston has a set of compression openings and a set of rebound openings extending through the piston from one surface, to another surface having a cavity, with an annular seat formed in the cavity. A compression valve is positioned adjacent the piston and normally substantially closes the set of compression orifices. During compression, fluid flow out from the set of compression orifices is restricted by the compression valve. Positioned in the cavity is a rebound valve with a blow-off valve having an annular surface that tightly seals against the annular seat. A spring is biased against the blow-off valve, forcing the annular surface against the annular seat under a preload.

Abstract: An arrangement for damping movement of a mass with respect to a support to which the mass is connected by a suspension device. The suspension device is provided with one or more springs and a hydraulic damping system through which a hydraulic fluid flows. One or more devices are present for wire-drawing this fluid through a respective aperture. Each wire-drawing device is arranged to continuously vary the damping characteristics by controlling the extent of opening of the aperture(s) and thus regulate the flow of the fluid through the hydraulic damping system.

Abstract: According to an illustrative example of the invention a fluid damper comprises a cylinder and a piston rod axially movable through one axial end of the cylinder. The piston rod is provided with two damping pistons within a cavity inside the cylinder. The two pistons are axially spaced and in sealing engagement with an internal circumferential face of the cylinder. In a middle section of the cylinder there is provided a by-pass by an axial groove in the inner circumferential wall of the cylinder. In each axial position of the piston rod at least one piston is within the axial extent of the by-pass. When one of the pistons moves beyond the axial extent of the by-pass toward an axial cylinder end nearer to this piston, a throttled channel through this piston allows restricted fluid flow through the piston. When this piston moves in the other direction away from the nearer end of the cylinder, liquid can flow through this piston without substantial flow resistance.

Abstract: A device for elastic coupling between two parts, especially the principal transmission box and the fuselage of an aircraft with rotating wings, such as a helicopter, includes first and second inner and outer tubular bodies, and an elastic connection, housed in the annular space existing between the first and second bodies and coupling the first and second bodies in a leaktight fashion. The annular space is separated by the elastic connection into first and second chambers filled with a liquid, the first and second chambers being in communication with the inside of the first body. On the inside of said first body, there is a liquid distributor provided with an elastic damping connection and including two pistons, which are coupled by a piston rod and separated from each other by the distance separating orifices in the first and second chambers.

Abstract: A hydraulic vibration buffer for connection between two members with a case coupled with the first member, a piston rod with its top end coupled with a second member, a piston coupled with a base end of the piston rod and housed within the cylinder case so as to divide the cylinder case into first and second chambers, fluid source, a tank, and a control valve disposed in fluid paths connecting the cylinder case, the fluid source, and the tank with one another. The vibration buffer also includes returning-force application device constituted by a swingable link with its one and other ends coupled with the first member and the housing block through which the fluid paths extend, and a pair of springs disposed between a center portion of the swingable link and the spool of the control valve.

Abstract: An adjustable shock absorber for motor vehicles has a cylinder containing damping fluid, a piston rod arranged to be axially displaceable in the cylinder, and a damping piston secured to the inner end of the piston rod. The damping piston divides the cylinder chamber into two working chamber compartments and is provided with fluid flow passages which produce damping forces, the effective cross-section of these flow passages being controllable by a throttling member and an electromagnetic drive controlling the throttling member, with the electromagnetic drive including a coil winding which is mounted in the damping piston. In order to achieve improved control of the damping force the throttling member is under the influence on the one hand of the fluid pressure difference between the two working chamber compartments and on the other hand of a restoring force which is created by the electromagnetic drive.

Abstract: A thermally efficient shock absorber comprising a strut housing having an open end and a closed end, a piston including a piston housing and a piston head slideable in the strut housing, and a preselected volume of fluid and gas located in the strut and piston housings. A compensating system is provided coupled to the fluid for maintaining a constant fluid-to-gas volume ratio irrespective of thermal variations and a valve is provided for isolating the compensating system from the fluid. In a particular embodiment of the invention, the compensating system includes a gas compensating chamber and a fluid compensating chamber having a movable separator piston therebetween, the fluid compensating chamber being coupled to the fluid in the strut and piston housings. The gas and fluid compensating chambers are contained within the strut housing separate from the gas and fluid in the strut and piston housings.

Abstract: A vehicle suspension system with load-controlled damping for a vehicle having a leveling valve actuated by changes in the distance between the axles and the frame and connected to air springs and to a damper to provide load control of the damper. The damper has two cylinders, an inner one filled with oil and in which a piston moves, and an outer one with an annular space between them mostly filled with oil. A jounce metering valve passes oil from below the piston into the annular space upon downward movement of the piston, the resistance to the fluid flow being varied by pressure applied by the leveling valve in accordance with vehicle load. A high-speed-jounce blow-off valve passes oil in the same manner in larger amount when actuated by high-velocity downward movement of the piston, the actuation speed depending on the pressure applied by the leveling valve.

Abstract: A gas spring for height adjustment of drawing-tables or the like includes an arrangement for hydraulically locking the gas spring against sudden collapse due to overloading or loss of internal gas pressure. The hydraulic locking mechanism includes a pressure responsive valve which operates, in response to an excess pressure differential between the gas spring cavity and the pressurized gas chamber, either to prevent flow of the hydraulic locking medium out of the cylinder cavity or to restrict such flow to a slow, safe rate.

Abstract: A device for damping a perpendicularly oscillating primary mass comprising a perpendicularly oscillatory reference mass supported by a piston in a pressure fluid chamber of an adjusting member. The pressure in the fluid chamber compensates for the weight of the reference mass and varies as a result of reference mass oscillation. Upon reduction of the prevailing pressure the fluid chamber receives fluid from a first pressure line through an automatic inlet valve, and upon increase of the prevailing pressure the fluid chamber emits fluid into a first return line through an automatic outlet valve, so as to impose on the adjusting member an oscillatory movement tending to reduce the vertical movement of the primary mass. The adjusting member forms a second piston in a follow-up cylinder to which the primary oscillating mass is connected.