PASSIVE VIBRATION DAMPER, IN PARTICULAR FOR CONNECTING AN ENGINE TO A VEHICLE BODY

Abstract: A passive vibration damper (3a) is described which utilises the hysteresis of an elastic gasket and the energy dispersion produced by the passage of a gas, in this case air, through small-diameter bores; it consists of a cylinder (6) connected to the vehicle body and housing slidably in a fluid-tight manner a piston (12) which divides the cylinder into two variable-volume chambers; there being rigid with the piston a rod (13) connected to the engine, and in the chambers there being housed respective elastomer gaskets (35) which cooperate with the piston; when this latter moves due to relative movement between the engine and vehicle body, it transfers air contained in the diminishing-volume chamber into the increasing-volume chamber through a plurality of axial bores (30) provided in the piston, and squeezes the elastomer element located in the diminishing-volume chamber, so that it progressively closes said bores.

Description: The present invention relates to a passive vibration damper, particularly suitable for interposing as a connection element between a vehicle body and its power unit to prevent vibration produced by the engine being transmitted to the vehicle body. In automobiles with high-power engines such as grand touring automobiles, the engine is fixed to the vehicle body not only at the floor but also at other points such as at the upper cross-member. As the engine vibrates strongly when in use, ie undergoes small rapid random movements relative to the vehicle body, it is necessary to use devices for connecting the engine to the body which on the one hand are able to allow these movements to take place so as not to induce stresses in the body, and on the other hand are able to rapidly damp vibrations so as to prevent triggering of possible resonance phenomena and/or to prevent or reduce their transmission to the vehicle body, which would cause discomfort to the vehicle users. For this purpose, known vehicles use passive devices consisting of hangers provided with elastomer bearings, but the results obtainable with such devices are not completely satisfactory. In this respect, although they limit the transmission of stresses to the vehicle body and the triggering of resonance phenomena, vibration transmission to the vehicle body remains too high to provide proper comfort for the user, even though the transmitted vibration is damped in terms of amplitude and frequency. From FR-A-2 349 767 is known a passive damper having the function of shock-absorber and of gas-spring, comprising a cylinder full of pressurized gas in which a piston provided with through axial holes travels. Such a system is however not efficient for the aforementioned purpose, because has poor vibration damping capacity. From EP-A-160 277 is also known an active damper, wherein a fluid under pressure is fed inside a cylinder in which a piston travels. This system is more efficient than that of FR-A-2 349 767 but depends on energy produced on board the vehicle. An object of the invention is to provide a damper device which is able to connect two mechanical members together in such a manner as to allow them to undergo relative movement, has high vibration damping capacity and is able to connect an engine to a vehicle body so as to ensure considerable comfort for the vehicle users. A further object of the invention is to provide a passive damper device which is able to provide the required damping by virtue only of its own structure and does not depend on the absorption of the produced energy on board the vehicle. Said object is attained according to the invention by a passive vibration damper for mechanically connecting together two members between which there is the possibility of relative movement, as defined in claim 1. The invention will be more apparent from the non-limiting description of one embodiment thereof given hereinafter with reference to the accompanying drawings in which: Figure 1 is a diagrammatic view of a vehicle provided with the damper according to the invention; Figure 2 is a longitudinal side sectional view of a damper according to the invention; Figure 3 is a front view of a detail of the damper of Figure 2; Figures 4 and 5 show two different working positions of the damper of Figure 2. In Figures 1 to 3, the reference numeral 1 indicates a vehicle which in this case is an automobile, comprising a known body 2 and engine 3 which are connected together in such a manner as to be able to undergo small relative movements by one or more passive dampers 3a, and in this particular case by two dampers 3a which secure the engine 3 to the front upper part of the body 2. In Figure 2 a damper 3a is shown in section in its rest position, whereas in Figures 4 and 5 the same damper is shown in two opposite working positions. With reference to these latter figures, the damper 3a comprises a first element to be rigidly fixed to the vehicle body 2 in known manner by a ring 5, the element 4 consisting of a hollow cylinder at least partly closed in a fluid-tight manner and filled with a gaseous fluid such as air, it comprising a cup-shaped cylindrical member 6 provided with an open mouth end 7 and an end wall 8 distant from the mouth 7, and a tubular end portion 9 projecting outwardly and axially from the wall 8. The damper 3a also comprises a second element 10 for rigidly fixing to the engine 3 in known manner, such as by a fork 11, and consisting of a piston 12 housed slidably in a fluid-tight manner in the cylinder 4 and a rod 13 mounted slidably in a fluid-tight manner in the cylinder 4 and preferably constructed integrally with the piston 12 and rigidly supporting it at its centre. One end 14 of the rod 13 is guided to slide within the tubular portion 9, whereas its opposite symmetrical end 15 projects through the mouth 7 and is rigidly connected by a known screw adjustment mechanism 16 to the fork 11. The mouth 7 which in one possible embodiment of the invention, not shown for simplicity, can be closed in a fluid-tight manner by a simple fixed cover rigid with the cylinder 4, is closed in the non-limitative illustrated embodiment of the invention by an annular element or block 18 which is slidingly traversed by the rod 13 and is disposed so that it can slide axially in a fluid-tight manner in the cup-shaped member 6 at the end distant from the wall 8. A protection bellows 20 is disposed to give protection to the rod 13 and/or partial or total sealing between this and the block 18. The block 18 is halted rigidly with the member 6 by a split ring 21 mounted just inside the mouth 7 to act as a stop shoulder and against which the block 18 comes to rest. The piston 12 slidably engages the inner cylindrical surface 22 of the member 6 and divides its interior into two chambers 24 and 25, the volume of which varies in accordance with the axial position of the piston 12 in the cylinder 4, in that the chambers 24 and 25 are located on opposite sides of the piston 12, with the chamber 24 defined axially in length between the piston 12 and the end 24, and the chamber 25 between the piston 12 and block 18. When the piston 12 moves towards the wall 8, the chamber 24 which is traversed centrally and axially over its entire length by the end 14 of the rod 13 reduces in volume whereas the chamber 25 increases in volume by an equal amount as it is also traversed centrally and axially by the rod 13 and consequently has a cross-section of identical size to that of the chamber 24. In contrast, when the piston 12 moves towards the mouth 7, the volume of the chamber 25 reduces and that of the chamber 24 increases by an equal amount, as the variation in the axial position of the piston 12 induces an equal variation in the axial length of both of the chambers 24 and 25, which thus produces a volume variation of equal amount but opposite sign therein. According to the invention, the piston 12 is provided with a plurality of axial through bores 30 located in different radial positions (Figure 3) and connecting the chambers 24 and 25 together. Specifically, the bores 30 are of small diameter such as to offer considerably resistance to the passage of a gaseous fluid through them, ie are able to determine a very high pressure drop in a gaseous fluid in passing between the chambers 24 and 25. The bores 30 open into the respective opposing front faces 31 and 32 of the piston 12 and are distributed at a constant circumferential pitch along different diameter circles, or alternatively, as shown in Figure 3, are distributed along a spiral linear path. According to the invention, the chambers 24 and 25 each house at least one respective deformable seal element 35 inserted into them by pressing and cooperating with the piston 12 to isolate from the outside in a fluid-tight manner that radially outer portion of the chambers which faces the bores 30 and lies between the surface 22, the faces 31 and 32 of the piston 12 and the elements 35 themselves, so as to progressively close the bores 30 in accordance with the axial position of the piston 12. Specifically, each chamber 24 and 25 houses internally, coaxially with the piston 12, a corresponding annular elastomer element 35, for example of heat-resistant rubber, disposed against a travel stop member located opposite the piston 12 and defined in the chamber 24 by the wall 8, and in the chamber 25 by the ring 21, and against which the corresponding element 35 rests by way of the block 18. Each element 35 is provided with a deformable annular front lip 36 formed as a curved sleeve tapering towards its free end and shaped overall as a barrel, and projecting axially towards the piston 12 to operate by contact with a respective front face 31 or 32 thereof, against which each lip 36 presses preferably with a predetermined equal pressure when the piston 12 is in its rest position of Figure 2, ie substantially in the middle of the cylindrical member 6, the lips being constructed so that when in their undeformed state they are of equal axial length, this length being greater than the maximum length which each chamber 24 and 25 can attain during the movement of the piston 12. When in use, the elements 35 are mounted on the rod 13 and inserted together with this into the cylinder 4 and tightened down under predetermined pressure by inserting and locking in position the block 18 to close the mouth 7 so as to elastically deform the lips 36, which then rest with predetermined equal pressure against the piston 12 in a position radially more inwards than the most inner of the bores 30, to retain the piston in the position shown in Figure 2. With reference to Figures 4 and 5, when the vibration induced by the engine 4 causes the fork 11 to move in the direction of the arrow (Figure 4), the piston 12 moves towards the wall 8 to reduce the volume of the chamber 24 and increase that of the chamber 25. The air or other gaseous fluid contained in that portion of the chamber 24 isolated under fluid-tight conditions by the respective element 35 is therefore compressed and as soon as its pressure is sufficient to overcome the pressure drop through the bores 30 it begins to flow into the chamber 25 to compensate its increases in volume. This pressurisation of the air in the chamber 24 however produces a thrust on the piston 12 which tends to oppose its movement towards the wall 8 so that the piston 12 is firstly slowed down until it stops after which its movement is reversed. The action of the air pressure in the chamber 24 is augmented by the elastic thrust of the gasket 35 situated in this chamber. In this respect the gasket 35 is squeezed against the wall 8 by the movement of the piston 12, and therefore deforms elastically to exert in the manner of a spring an elastic resistance which is a function of its own elastic constant and is greater the greater the extent to which it is squeezed, ie the closer the piston 12 approaches the wall 8. Finally, the force resulting from the pressurisation of the air in the chamber 24 produced by the movement of the piston 12 is accentuated by the fact that as the lips 36 are curved, the lip 36 of that element 35 in the chamber 24 increases its curvature as the element 35 is squeezed and consequently positions itself with its extrados parallel to the face 31 of the piston 12 and against this latter to close part of the bores 30, and specifically firstly the radially more inner bores and then progressively, as the deformation of the element 35 increases, the radially more outer bores until all the bores 30 are closed. Consequently the cross-sectional area available for the air expelled by the reduction in volume of the chamber 24 to pass to the chamber 25 is progressively reduced until completely nullified, to produce a progressive increase in the pressure drop of the air in the chamber 24. When the air trapped between the piston 12, wall 8, element 35 and surface 22 can no longer pass into the chamber 25, its pressure increases until it becomes so high that it exceeds the thrust on the fork 11 and moves the piston 12 backwards, with consequent progressive reopening of the bores 30 and reduction in the deformation of the element 35, so that the pressure in the chamber 24 and the total thrust on the piston 12 are reduced, with the result that under all conditions the damper 3a rapidly and easily attains an equilibrium position which completely nullifies the consequences of the vibration of the engine 3. If this vibration is such as to produce a stress in the opposite direction of the fork 11 (Figure 5), the damper 3a behaves exactly as heretofore described, the only difference being that it is now the chamber 25 which reduces in volume so that the air trapped in a fluid-tight manner in that portion thereof between the relative element 35, the surface 22, the block 18 and the piston 12 is compressed and passes into the chamber 24 through the bores 30, which are progressively closed by the curving of the lip 36 of the element 35 housed in the chamber 25, as a result of it being squeezed against the block 18 retained by the ring 21. The advantages of the invention are apparent from the aforegoing description. The described damper requires no active control systems, is of simple and economical construction, has very high efficiency and is completely self-adjusting, the described structure forming an intrinsically balanced pneumatic system. The assembly of the damper according to the invention is also simple and it is not necessary to ensure that a seal exists between the rod 13, the block 18 and the member 6, the seal in the working portion of the chambers 24 and 25 being in all cases ensured by the sealing action of the lips 36 against the piston 12.

Claims: A passive vibration damper (3a) for mechanically connecting together two members (2,3) between which there is the possibility of relative movement, comprising a first and a second element (4,10) which are coupled together in a manner axially slidable relative to each other and are each arranged to be rigidly fixed to one of said members (2,3), said first element consisting of a hollow cylinder (4) filled with a gaseous fluid, and said second element consisting of a rod (13) connected rigidly to a piston (12) housed slidably in a fluid-tight manner in said cylinder (4) in such a manner as to define within this latter a first (24) and a second (25) variable-volume chamber disposed on opposite sides of the piston (12); said piston (12) being provided with a plurality of through axial bores (30) located in different radial positions and arranged to provide communication between said chambers (24,25); characterized in that the chambers (24,25), each housing at least one respective deformable seal element (35) of annular shape cooperating with a surface (31,32) of said piston (12) and a surface (8,18) of the chamber (24,25) to isolate in a fluid-tight manner a radially outer annular portion of said chambers (24,25) which faces said bores (30), and to progressively close said bores (30), by deformation of said seal element (35) in accordance with the axial position of said piston (12). A damper (30) as claimed in claim 1, characterised in that said through axial bores (30) are of such a diameter as to offer appreciable resistance to the passage of gaseous fluid between said chambers (24,25), and are distributed on respective opposing faces (31,32) of said piston (12) along a spiral linear path. A damper (30) as claimed in claim 1, characterised in that said through axial bores (30) are of such a diameter as to offer appreciable resistance to the passage of gaseous fluid between said chambers (24,25), and are distributed on respective opposing faces (31,32) of said piston (12) along circles of different diameter. A damper (30) as claimed in claim 1, 2 or 3, characterised in that said variable volume chambers (24,25) each house in their interior, coaxially to said piston (12), one annular elastomer element (35) disposed against a travel stop (8,21) opposite said piston (12); said elastomer element (35) being provided with a curved deformable annular front lip (36) extending axially towards said piston (12) and cooperating by contact with a respective front face (31,32) thereof. A damper (30) as claimed in any one of the preceding claims, characterised in that the cross-sections of said variable volume chambers (24,25) are of equal size so that the volume variations in these latter induced by axial movements of the piston (12) within the cylinder (4) are always of equal value but of opposite sign. A damper (30) as claimed in any one of the preceding claims, characterised in that said rod (13) extends axially towards both said chambers (24,25) and at its centre rigidly carries said piston (12); said cylinder (4) comprising a cup-shaped member (6) defining said chambers and slidably engaged by said piston (12), and a tubular smaller-diameter end portion (9) projecting outwards from an end wall (8) of said cup-shaped member (6) and in which a corresponding first end of said rod (13) is guided. A damper (30) as claimed in claim 6, characterised in that said first chamber (24) is defined between said piston (12) and said end wall (8) of the cup-shaped member (6), and said second chamber is defined between said piston (12) and an annular block (18) traversed by the second end of said rod (13) and slidably engaged in said cup-shaped member (6) at the end distant from said end wall (8) so as to close the mouth end of said cup-shaped member (6); this latter being provided with a split ring (21) acting as a stop against which said annular block (18) cooperates by contact. A vehicle (1) comprising a body (2) an engine (3) and at least one damper (30) as claimed in one of claims 1 to 7, and which connects said engine (3) to said body (2).

Inventors: MAGGIONI, VIRGINIO, TITOLO, ANDREA
Applicants: FIAT AUTO S.P.A.
Application year: 1989
Main classification: F16F9
IPC codes: F16F9, B60K5