Oscillating arm suspension unit for vehicles

A suspension unit for vehicles comprises a support fastened to a framework of the vehicle and a longitudinal arm, with a rolling member coupled to the arm, rotating relative to it about a transverse first axis. The arm is coupled to the support and rotates relative to it about a transverse second axis which is parallel to the first axis and offset relative to it in the longitudinal direction. Within the arm is a longitudinal cylinder within which slides a piston. A rod is coupled to the piston and to the support. The rod rotates relative to the support about a third axis parallel to the second axis and offset relative to it transversely. The rod rotates relative to the piston about a transverse fourth axis parallel to the third axis. It is pivoted to the piston by a mechanism comprising a slide member that slides longitudinally within the cylinder and is juxtaposed longitudinally to the piston on the same side as the rod. The rod is pivoted to the slide member for rotation about the fourth axis.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention concerns an oscillating arm suspension unit for 
vehicles. 
To be more precise, it concerns a suspension unit of the type comprising: 
a support adapted to be fastened to a framework of the vehicle, 
a longitudinal arm, 
means coupling a rolling member to the arm defining a transverse first axis 
about which the rolling member rotates relative to the arm, 
means coupling the arm to the support defining a transverse second axis 
about which the arm rotates relative to the support, the second axis being 
parallel to the first axis and offset relative to it in a longitudinal 
direction, 
a longitudinal cylinder within the arm, 
a piston slidable longitudinally within the cylinder and delimiting with it 
a fluid-tight enclosure, 
a compressible fluid in the enclosure serving as spring means, 
a rod linking the piston and the support, 
means pivoting the rod to the support for rotation about a transverse third 
axis parallel to the second axis and offset relative to it transversely, 
and 
means pivoting the rod to the piston for rotation about a transverse fourth 
axis parallel to the third axis. 
2. Description of the Prior Art 
In known suspension units of this type, the means coupling the rod to the 
piston comprise a direct articulation of the rod to the piston about the 
fourth axis. 
Movements of the suspension, that is to say rotation of the arm about the 
second axis relative to the support, necessarily result in an oblique 
disposition of the rod relative to the longitudinal direction of the 
cylinder, in certain angular positions of the arm relative to the support, 
and this oblique disposition results in the application to the piston by 
the rod of forces that are themselves oblique relative to the longitudinal 
direction of the cylinder; the longitudinal component of these forces 
results in longitudinal displacement of the piston relative to the 
cylinder in the manner required, but the transverse component of these 
forces results in increased friction between the piston and the cylinder, 
impeding longitudinal movement of the piston; also, given that the 
transverse forces to which the piston is subjected are transmitted to the 
cylinder through the seals, pivoting movement of the rod relative to the 
piston around the fourth axis results in varying compression of the seals 
between the piston and the cylinder which may lead to premature 
deterioration of the seals and the appearance of leaks between the piston 
and the cylinder. 
These disadvantages are all the more significant in that the suspension arm 
tends to flex between its axis of rotation relative to the support and the 
axis of rotation of the rolling member relative to the arm, which results 
in deformation of the cylinder essentially in a plane perpendicular to the 
various axes of rotation, which is precisely the plane in which are 
developed the transverse components of force when the rod is offset 
angularly relative to the longitudinal direction of the cylinder; 
deformation of the arm then results in the appearance of additional 
transverse components of force between the piston and the cylinder and an 
increased risk of deterioration of the seals and appearance of leaks. 
An object of the present invention is to alleviate these disadvantages. 
SUMMARY OF THE INVENTION 
The present invention consists in a suspension unit for vehicles 
comprising: 
a support adapted to be fastened to a framework of the vehicle, 
a longitudinal arm, 
means coupling a rolling member to the arm defining a transverse first axis 
about which the rolling member rotates relative to the arm, 
means coupling the arm to the support defining a transverse second axis 
about which the arm rotates relative to the support, the second axis being 
parallel to the first axis and offset relative to it in a longitudinal 
direction, 
a longitudinal cylinder within the arm, 
a piston slidable longitudinally within the cylinder and delimiting with it 
a fluid-tight enclosure, 
a compressible fluid in the enclosure serving as spring means, 
a rod linking the piston and the support, 
means pivoting the rod to the support for rotation about a transverse third 
axis parallel to the second axis and offset relative to it transversely, 
and 
means pivoting the rod to the piston for rotation about a transverse fourth 
axis parallel to the third axis and comprising: 
a slide member sliding longitudinally within the cylinder and juxtaposed 
longitudinally to the piston on the same side as the rod, 
means pivoting the rod to the slide member to rotate about the fourth axis, 
and 
means coupling the slide member to the piston and permitting mutual 
transmission of longitudinal forces but not permitting mutual transmission 
of transverse forces. 
In this way only the slide member is subjected to transverse components of 
forces resulting from the oblique disposition of the rod relative to the 
longitudinal direction of the cylinder, whereas the piston is subject only 
to longitudinal forces by the rod; thus the piston may be considered as 
being free in the transverse direction within the cylinder, so that 
movements of the rod and flexing of the arm have virtually no influence on 
the compression of the seals between the piston and the cylinder, that is 
to say on the durability of the seals or on the ease with which the piston 
slides longitudinally within the cylinder. 
The structure in accordance with the invention does not mean that the 
disadvantages manifesting themselves at the level of the piston and the 
seals between it and the cylinder in a conventional structure are merely 
transferred to the level of the slide member, to the degree that it may be 
satisfactory to procure the contact between the slide member and the 
cylinder in a manner just sufficient to ensure guiding of relative 
longitudinal sliding between them without it being necessary to provide 
any seal at this level; to the contrary, in one preferred embodiment of 
the present invention means such as channels passing longitudinally 
through the slide member from one end to the other are provided to feed a 
lubricant between the slide member and the piston in order optimally to 
lubricate both them and their mutual coupling means; these advantageously 
consist in mutual abutment means in the direction in which they move 
towards each other longitudinally, the action of the compressible fluid 
serving as spring means resulting in permanent contact between these 
mutual abutment means; thus the transverse components of force to which 
the slide member may be subjected are transmitted to the piston to only a 
negligible degree. 
The cylinder is advantageously defined by a longitudinal liner within and 
attached to the arm, which also makes it possible to reduce deformation of 
the cylinder resulting from flexing of the arm and the consequences of 
such deformation. 
Other characteristics and advantages of the invention will emerge from the 
following description of one embodiment given by way of non-limiting 
example only and with reference to the appended drawings which form an 
integral part of the description.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The suspension unit 1 is shown in equilibrium positions that it can assume 
when it is mounted on a vehicle, schematically represented by its 
framework 2, with the vehicle resting on a horizontal plane through a 
rolling member schematically represented at 3, such as a road wheel or a 
caterpillar track roller, depending on the type of vehicle in question. 
The unit 1 will be described with reference to these positions and these 
equilibrium states, and it is to be understood that such terms as 
horizontal, vertical, level and direction used in this description have no 
limiting character and are to be interpreted as a simple indication of the 
relative positions of the various component parts of the suspension unit 
1. 
For mounting it on the framework of the vehicle the suspension unit 1 
illustrated comprises a support 4 in the form of a vertical plate 6 which 
may be fastened to the framework of the vehicle, by means of bolts 5, for 
example, and to which is fastened, for example by being formed in one 
piece with it, a shaft 7 a transverse second axis 8 (a transverse first 
axis being described hereinbelow) of which is horizontal, perpendicular to 
the plate 4; when the support 4 is attached to the framework 2 of the 
vehicle the shaft 7 projects externally of the vehicle. 
The shaft 7 carries a crank 9 which is prevented from rotating relative to 
the shaft 7 about its axis 8 by an arrangement of complementary shapes; 
the crank 9 has a bore 10 through which the shaft 7 passes and, 
transversely to the axis 8, the bore 10 and the shaft 7 have respective 
complementary polygonal cross-sections, as shown in FIG. 2; any other 
means of fastening the crank 9 and the shaft together, in particular to 
prevent relative rotation about the axis 8, may be used without departing 
from the scope of the present invention; a conventional keying arrangement 
may be used, for example, or cooperation between the bore 10 and the shaft 
7 by means of complementary splines. 
Above the shaft 7 the crank 9 forms a yoke 11 to which is fastened a 
journal 12 a transverse third axis 13 of which is parallel to, above and 
in a common vertical plane 14 with the axis 8; like the axis 8, this axis 
13 is fixed relative to the support 4; on respective opposite sides of the 
yoke 11 in a direction parallel to the axis 8, the crank 9 defines two 
integral sleeves 20 and 21 respectively situated between the yoke 11 and 
the plate 6 and on the opposite side of the plate 6 relative to the yoke 
11; to each of the sleeves 20 and 21 is fastened the inner cage of a 
respective thrust bearing 16, 17 having an outer cage respectively 
fastened to a casing 18 and a flange 19, these being annular and fastened 
to each other, so as to guide the casing 18 and the flange 19 in rotation 
about the axis 8 relative to the crank 9 and the shaft 7 without any 
possibility of relative translation movement parallel to the axis 8; to 
this end, the inner cages of the bearings 16 and 17 are also respectively 
trapped between the plate 6 and the yoke 4 and between the yoke 11 and an 
abutment plate 93 fastened to the member 7, by means of bolts 92, for 
example, opposite the attachment of the shaft 7 to the plate 6. 
The casing 18 is fluid-tight and surrounds the crank 9 on the same side as 
the plate 6 of the support 4 and in the radial direction away from the 
axis 8; around the bearing 16 and the sleeve 20 the casing 18 has an 
annular ring 23 which is a body of revolution about the axis 8, projecting 
towards the plate 6 and inserted in a complementary groove 24 formed in 
the plate 6 so that it is able to rotate about the axis 8; the plate 6, 
which is itself fluid-tight, and the ring 23, which is also fluid-tight, 
are sealed to each other by sealing means 25, 26 the nature and location 
of which are easy to determine for those skilled in the art. 
The flange 19, which is also fluid-tight, is fastened in fluid-tight manner 
to the casing 18 and covers the crank 9 on the side opposite the casing 
18; it has an orifice in the shape of a body of revolution about the axis 
8 which is shut off in fluid-tight manner by a cover 27 in the general 
shape of a disk perpendicular to the axis 8 and attached to it; similarly, 
an orifice in the casing 18 is shut off in fluid-tight manner by a cover 
28 attached to it, in such a way that the support 4, the casing 18, the 
flange 19, the cover 27 and the cover 28 together define a fluid-tight 
housing 22 enclosing the crank 9, the journal 12 and the two bearings 16 
and 17. 
As will emerge hereinafter, the housing 22 contains a substantially 
incompressible hydraulic fluid, in practise oil, which fills to the 
maximum the housing 22 which may also contain air. 
The casing 18 carries a longitudinal hollow arm 29 projecting relative to 
the housing 22 in a plane 30 perpendicular to the axis 8 and coincident 
with the section plane I--I in FIG. 3; the arm is preferably in one piece 
with the casing 18. 
The arm 29 is shown in a horizontal orientation in FIG. 2 but it is to be 
understood that it can rotate with the housing 22, to which it is 
fastened, about the axis 8 and relative to the support 4; the arm extends 
obliquely downwards from the housing 22 in the position shown in FIGS. 1 
and 4. 
Opposite the end where it is connected to the casing 18 of the housing 22, 
the arm carries a spindle 36 fastened to it, and advantageously in one 
piece with it, to guide rotation of the rolling member 3 relative to it 
about a transverse first axis 37 parallel to the axis 8; in the condition 
shown in FIG. 2, a plane 38 common to the axes 8 and 37 is horizontal but 
it can equally well be oblique provided that variations in the relative 
levels of the framework 2 of the vehicle and the rolling member 3 result 
in rotation of the arm 29 relative to the support 2 about the axis 8. 
The arm 29 is hollow, comprising two tubular cavities 31 and 32 with 
respective rectilinear longitudinal axes 33 and 34 parallel to each other 
and to the plane 38 and situated in the plane 30 so that the cavity 31 is 
above the cavity 32, the axes 33 and 34 are both above the plane 38, and 
the axis 33 of the upper cavity 31 intersects the plane 14 in the 
immediate vicinity of the axis 13. 
At one transverse end, where the arm 29 is fastened to the casing 18, the 
cavities 31 and 32 communicate unrestrictedly with the interior of the 
housing 22 whereas at their other transverse end, constituting the area of 
the arm 29 farthest away from the housing 22, they are closed by 
fluid-tight cover 35 fastened in fluid-tight manner to the arm 29 which is 
itself fluid-tight. 
Approximately halfway between its two transverse ends, the lower cavity 32 
is permanently closed off by a fluid-tight bulkhead 40 attached to the arm 
29 so that the lower cavity 32 comprises, in the immediate vicinity of the 
casing 18, a chamber 41 communicating directly with the interior of the 
housing 22 and, in the immediate vicinity of the cover 35, a chamber 42 
communicating permanently with the cavity 31 through a fluid passage hole 
39 formed between the two cavities 31 and 32 in a direction 43 
perpendicular to the axes 33 and 34. 
As shown, the cavity 31 is preferably lined with a longitudinal tubular 
liner 44 in which are one or more orifices 46 facing the hole 39 and an 
annular groove 45 in the shape of a body of revolution about the axis 33 
of the liner, through which the hole 39 discharges into the cavity 31 in 
the vicinity of the cover 35. 
The liner 44 facilitates guidance of longitudinal sliding within the 
tubular cavity 31 of a fluid-tight piston 47 sealed to the liner 44 by 
appropriate sealing means 48 and coupled by a rod 49 to the journal 12 
attached to the crank 9, so that angular movement of the arm 29 about the 
axis 8 relative to the support 9 result in longitudinal sliding movement 
of the piston 47 within the cavity 31, in one direction or the other. 
To this end the rod 49 has a first end 50 by which it is pivoted to the 
journal 12, preferably through the intermediary of a ball joint device 51, 
so as to be able to pivot about the axis 13 relative to the crank 9; the 
rod 49 also has a second end 51 disposed within the cavity 31 and itself 
in the shape of a part-spherical ball 52 the center of which is maintained 
on the axis 33 by engagement of the ball 52 in a concentric part-spherical 
bearing surface 54 of an annular slide member 55 in the shape of a body of 
revolution about the axis 33, which slide member is mounted in the liner 
44 on the same side of the piston 47 as the axis 13 so as to be able to 
slide longitudinally. 
The piston 47 is fluid-tight and sealed to the liner 44 so as to delimit 
with the tubular cavity 31 a fluid-tight chamber 56 situated on the same 
side as the cover 35 and communicating permanently with the chamber 42 in 
the cavity 32 and a chamber 57 situated on the same side as the housing 
22, with which it communicates, the chamber 57 containing the slide member 
55 and the ball member 52; the slide member 55 is designed to allow the 
hydraulic fluid contained in the housing 22 and in the chamber 57 to pass 
freely into a space 58 between the slide member 55 and the piston 47; to 
this end, longitudinal passages 59 are provided in the slide member 55, 
around the part-spherical bearing surface 54; thus the fluid contained in 
the housing 22 and the chamber 57 can reach the space 58 and lubricate the 
slide member 55 and the piston 47 where they are in contact with the liner 
44 and the ball member 52 where it is contact with the part-spherical 
bearing surface 54, as well as where it is in contact with a buffer 60 
fastened to the piston 47 on the same side as the chamber 57 to serve as 
longitudinal abutment means for the piston 47 against the ball member 52, 
which by virtue of the annular shape of the slide member 55 is totally 
exposed on the side facing towards the piston 47; this preferred 
arrangement makes it possible to procure as direct as possible 
transmission of longitudinal forces between the rod 49 and the piston 47 
with minimum transverse loading of the piston 47 by the rod 49; other 
arrangements could naturally be adopted, for example with the piston 47 
abutting not against the rod 49 but against the slide member 55; the way 
in which the rod 49 is fitted, in particular to the slide member 55, could 
also be different, provided that it defined at least one relative rotation 
axis parallel to the axis 13 and intersecting the plane 50 coincident with 
the center 53 of the ball member 52 said axis coincident with the center 
53 being a transverse fourth axis and the part-spherical bearing surface 
54 of the design as shown. 
The piston 47 is urged longitudinally towards the slide member 55 to 
procure mutual abutting of the buffer 60 and the ball member 52, by means 
of a compressible fluid, in practise a gas, serving as pneumatic spring 
means, accommodated in the communicating chambers 56 and 42 and operative 
directly on the piston 47 in the chamber 56; the hole 39, the groove 45 
and the orifice or orifices 46 are of such sizes as to offer virtually no 
resistance to passage of this fluid from one of the chambers 56 and 42 to 
the other, that is to say in such a way as not to cause any throttling of 
the fluid when the piston 42 slides longitudinally within the liner 44. 
In the chamber 42 the compressible fluid serving as spring means bathes an 
elastically expandable, flexible, fluid-tight material bladder 61 which 
features in the direction towards the bulkhead 40 along the axis 34 an 
orifice 62 advantageously delimited by a termination 67 forming an 
integral part of the bladder 61 and projecting along the axis 34 towards 
the bulkhead 40; by its radially outermost periphery 63 relative to the 
axis 34, the termination 67 is inserted into a bore 66 along the axis 34 
in a fluid-tight wall 64 fastened in fluid-tight manner into the cavity 
32, transversely to the axis 34, so as to cover the bulkhead 40 on the 
side towards the chamber 42 and delimit with the bulkhead 40, in the 
cavity 32, an intermediate volume 65 which is fluid-tight with respect to 
the chamber 41 and the remainder of the chamber 42; all of the outside 
periphery 63 of the termination 67 is in fluid-tight contact with the wall 
64, which defines through the latter a passage 68 connecting the interior 
of the bladder 61 with the volume 65 whilst preserving the fluid-tightness 
of the latter relative to the part of the chamber 42 external to the 
bladder 61, in other words vis-a-vis the compressible fluid filling the 
chamber 42, outside the bladder 61, and 56; the fluid-tight contact 
between the termination 67 and the wall 64 may result from a simple 
interference fit of the termination 67 within the bore 66, for example. 
The bladder 61 thus delimits internally, within the chamber 42, a chamber 
69 which is intended to receive a substantially incompressible hydraulic 
fluid through the intermediary of the volume 65, this fluid serving to 
reduce the space available within the chamber 42 for the compressible 
fluid serving as spring means and, by varying the volume of the chamber 69 
as a result of addition of the substantially incompressible hydraulic 
fluid 2 to or removal of it from this chamber, to oblige a greater or 
lesser quantity of the compressible fluid to remain in the chamber 56 so 
as to vary the longitudinal position of the piston 47 in the liner 44 
corresponding to equilibrium between the weight of the vehicle and the 
reaction force on the rolling member from the ground, in other words to 
vary the ground clearance. 
To achieve this, conduits schematically represented by a chain-dotted line 
70 are formed within the arm 58, the flange 19 and the cover 27, in a 
manner that will be readily apparent to those skilled in the art, so as to 
connect the intermediate volume 65 between the bulkhead 40 and the wall 64 
with a chamber 71 formed in the cover 67 and along the axis 8, as can be 
seen in FIG. 3; the chamber 71 facing the shaft 7 along the axis 8 
accommodates one end of a tube 72 on the axis 8 which is fixedly secured 
and sealed to the cover 27 and which passes through the shaft 7 along the 
axis 8 as far as the plate 6 by means of a bore 73 formed in the shaft 7 
with dimensions such that there remains a peripheral clearance between the 
tube 72 and the shaft 7; at the plate 6 the tube 72 is guided in rotation 
relative to the support 4 and about the axis 8 by a bearing 74 fitted with 
a rotary seal 75 and connects to a fluid-tight chamber 76 formed in the 
plate 6 and itself connected by a conduit 77 to means 78 for adding or 
removing predetermined amounts of the substantially incompressible fluid; 
the means 78, which are known in themselves, may comprise a hydraulic pump 
connected to a hydraulic fluid storage tank within the vehicle, for 
example. 
In an alternative embodiment of the device that has just been described, 
the bladder 61 could be eliminated and replaced with a piston 79, as 
schematically indicated in chain-dotted line in FIG. 2, mounted to slide 
longitudinally within the chamber 42 so as to divide this in fluid-tight 
manner into a part-chamber communicating directly with the chamber 56 
through the hole 39 and a part-chamber corresponding to the chamber 69 in 
fluid communication with the volume 65 through the bore 70 in the wall 64. 
Also, in a manner that is not illustrated and is subject to satisfactory 
conditions for mutual disposition of the components of the suspension unit 
1, the chambers 56 and 42 connected via the hole 39 in the embodiment 
shown could be in non-parallel alignment with each other and/or relative 
to the plane 38, in the plane 30 or offset relative thereto; in 
particular, the chambers 56 and 42 could be aligned with each other along 
the axis 33, for example, in which case there would be aligned with this 
same axis the piston 47, the combined chambers 56 and 42, the bladder 61 
or the piston 79, the chamber 69 and the wall 64, which could then be 
defined by a cover substituted for the cover 35; this embodiment is not 
illustrated but implementing it on the basis of the embodiment illustrated 
and prevously described lies well within the competence of those skilled 
in the art. 
The device that has just been described constitutes a pneumatic spring with 
provision for adjusting the ground clearance and may be used as such on a 
vehicle. 
However, it may also be provided with means for damping rotational movement 
of the arm 29 relative to the support 4 about the axis 8. 
In this instance these damper means consist of brake means operative 
between members respectively fastened to the arm 29 and the support 4, 
resisting relative rotation about the axis 8 with a braking force 
conditioned by the rotation speed of the arm 29 relative to the support 4. 
To this end, in the illustrated embodiment, the crank 9 carries towards the 
bottom, that is to say at the opposite end from the yoke 11, a plurality 
of dovetail-shaped ribs 80 parallel to the axis 8 on which can slide 
parallel to this axis but not rotate about this axis complementary shape 
grooves 81 formed in brake disk sectors 82 which are juxtaposed along the 
axis 8 relative to which they are disposed in respective perpendicular 
planes; there are two brake disk sectors 82 in the example illustrated, 
but one only of the sectors could suffice as likewise could more than two. 
The brake disk sectors 82 are naturally disposed within the housing 22, 
like the crank 9, between the casing 18 and the flange 19. 
Through the intermediary of the cover 28 the housing 22 carries a plurality 
of blade members 83 disposed in respective planes perpendicular to the 
axis 8 and located in the dihedron defined by the planes 38 and 14, 
beneath the plane 38 and on the same side of the plane 14 as the arm 29; 
the number and arrangment of the blade members 83 is such that each disk 
sector 82 is disposed between two such blade members; in other words, in 
the embodiment illustrated three blade members 83 are provided, one of 
which is disposed between the two disk sectors 82 while the other two are 
placed on respective sides of the assembly formed in this way by the two 
disk sectors 82 and the blade member 83 between them. 
Each of the outside blade members 83 carries a known type brake lining 84 
facing towards the immediately adjacent disk whereas the blade member 83 
between the two disk sectors 82, or each such blade member, carries a 
brake lining 84 on either side. 
To bring the brake linings 84 and the brake sectors 82 into contact under 
controled pressure their angular dimension relative to the axis 8 is such 
that contact with the brake linings 84 may be established in all relative 
positions of the arm 29 and the support 4 resulting from relative rotation 
about the axis 8 within the normal operating limits, the blade members 83 
cooperating with conjugate-shaped grooves 127, 128 parallel to the axis 8 
and defined conjointly by the cover 28 and the casing 18; these grooves 
127, 128 guide the blade members 83 so that they slide in the direction 
parallel to the axis 8; the blade member 83 nearest the plate 6 of the 
support 4 bears against the casing 18 parallel to the axis 8, while the 
blade member 83 farthest away from the support 4, that is to say nearest 
the flange 19, is acted on by a hydraulic jack 85 which pushes on the 
blade member 83 so as to apply a predetermined force parallel to the axis 
8 to the blade member 83 and through the blade member 83 to the set of 
disk sectors 82 via the linings 84. 
To this end the flange 19 features at least one blind hole 86 facing 
towards the support 4, that is to say towards the interior of the housing 
22, with its axis 87 parallel to the axis 8, and facing the plate 83 
nearest the flange 19; this blind hole constitutes a cylinder within which 
a piston 88 sealed to the blind hole 86 by sealing means 89 can move in 
the direction of the axis 87, defining a fluid-tight chamber 90 within the 
blind hole 86; a helical compression spring 91 schematically shown in 
chain-dotted line is advantageously accommodated in the chamber 90 to 
provide a minimal contact pressure between the brake linings 84 and the 
disk sectors 82 in the absence of any pressurized fluid in the chamber 90. 
The chamber 90 also contains a fluid the pressure of which is varied 
according to the rotation speed of the arm 29 about the axis 8 relative to 
the support 4, according to predetermined laws of which certain examples 
will be described by way of non-limiting illustration hereinafter. 
For the purposes of achieving such control over the pressure of this fluid 
in the case of the embodiment of the invention shown in FIGS. 3 and 4, the 
shaft 7 carries a cam which is fastened to it, for example by bolts 92, 
within the housing 22 and directly facing the cover 27, the cam lying in a 
plane 100 perpendicular to the axis 8 and advantageously consisting, in 
the embodiment shown, of the abutment plate 93 attached to the shaft 7; 
this cam is seen particularly clearly in FIG. 4. 
Along the axis 8 the cam 93 is pierced by a bore 94 through which the tube 
72 passes with clearance comparable with that of the bore 73; in the 
radial direction away from the axis 8 and in any section plane 
perpendicular to this axis, its outside periphery 95 is of oval shape. 
Above a horizontal plane 96 in which the axis 8 lies and which is fixed 
relative to the support 4 the shape of this periphery is immaterial 
provided that the cam 93 serves as an abutment plate, as previously 
described; below the plane 96 it is of circular shape with an axis 97 
parallel to the axis 8 and situated in the plane 14 under the axis 8, so 
as to define a cam surface 98 featuring, under the axis 8 and in the plane 
14, a point 99 which constitutes the point on the cam surface 98 farthest 
from the axis 8, the distance from the axis progressively decreasing for 
points on the cam surface 98 further and further away from the point 99 in 
one direction of movement of the surface 98 resulting from rotation about 
the axis 8 or in the opposite direction. 
In the plane 100 of the cam 93, taken as the plane of its cam surface 98 
and coincident with the section plane IV--IV in FIG. 3, the flange 19 has 
two cam followers 101 and 102 facing the cam surface 98 each fastened to 
the flange 19 in terms of rotation about the axis 8 but able to slide 
relative to the flange 19 in the radial direction relative to the axis 8 
so as to remain in contact with the cam surface 98 whatever the angular 
position of the arm 29 relative to the support 4, for rotation about the 
axis 8, within the normal operating limits. 
To this end the flange 19 comprises two bores 105 and 106 with respective 
axes 103 and 104 which are radial relative to the axis 8 and situated in 
the plane 100; each of the bores 105 and 106 discharges into the housing 
22, towards the cam surface 98, being shut off at the opposite end by a 
respective plug 107, 108; the axes 103 and 104 are symmetrically 
positioned to each other relative to a plane coincident with the vertical 
plane 14 in the state of static equilibrium shown in FIGS. 1 and 4, with a 
mutual angular offset .alpha. of the axes 103 and 104 relative to the axis 
8; this angular offset .alpha. is at least equal to the range of relative 
angular displacement between the arm 29 and the support 4 about the axis 8 
under normal operating conditions; in the example illustrated this offset 
is in the order of 70.degree.; this figure is given by way of non-limiting 
example only, of course. 
Within each of the bores 105 and 106 is a respective piston 109, 110 
sliding along the axis 103, 104 of the bore with a respective helical 
compression spring 111, 112 disposed between the piston and the plug 
shutting off the corresponding bore urging the pistons 109, 110 
elastically towards the axis 8 so that each projects out of the 
corresponding bore 105, 106 into the housing 22 and bears against the cam 
surface 98 through an end surface that is transverse relative to the axis 
of the corresponding bore, which surface defines the cam follower 101, 
102. 
Thus rotation of the arm 29 and of the axes 103 and 104 with it about the 
axis 8 relative to the support 4 and to the cam 93 results in alternating 
reciprocating movement of the two pistons 109 and 110 in the respective 
bores 105, 106 along the axes 103, 104 of the these bores; the cam is 
shaped according to the relative positions of the axes 103 and 104 so that 
movement of the arm 29 on rotation relative to the support 4 from the 
state of static equilibrium results, irrespective of the direction and 
amplitude of this movement within normal operating limits, in opposed 
movements of pistons 109, 110 in the bores 105, 106; thus in the example 
illustrated where the axes 103 and 104 are at 70.degree. to each other and 
the cam surface 98 subtends an angle of at least 180.degree. (at least 
2.alpha.) at the axis 97, symmetrically distributed to either side of the 
plane 14, and if it is assumed that displacement of the arm 29 on rotation 
of the axis 8 relative to the support 4 from a position of the plane 38 
corresponding to static equilibrium is limited to a maximum of 35.degree. 
(.alpha./2) upwards or downwards, upward rotation of the arm 20 from the 
static equilibrium position results in: 
movement of the point of contact with the cam surface 98 of the follower 
102 defined by the piston 110 accommodated in the bore 106 on the same 
side of the plane 14 as the arm 29 when the plane 38 is horizontal away 
from the point 99, that is to say protrusion of the piston 110, 
movement of the point of contact with the cam surface 98 of the cam 
follower 101 defined by the piston 109 corresponding to the bore 105 
situated on the other side of the plane 14 when the plane 38 is horizontal 
towards the point 99, that is to say retraction of the piston 109 into the 
bore 105. 
Rotation in the opposite direction produces the converse effect. 
Other respective orientations of the cam surface 98 and the bores 
accommodating the pistons 109 and 110 could be chosen without departing 
from the scope of the present invention, provided that there results an 
effect of movement of the pistons in phase opposition on rotation of the 
arm in one direction or the other. 
This effect is employed to pump hydraulic fluid into the housing 22 so as 
to establish by means of this hydraulic fluid a pressure in the chamber 90 
operative on the brake piston 88. 
To this end, as is seen particularly clearly on examining the piston 109 
illustrated in FIG. 4, it being understood that the piston 110 is in all 
respects identical to the piston 109, each of the pistons 109 and 110 is 
hollow and has in the immediate vicinity of the corresponding cam follower 
101, 102 a network of passages 131, 132 arranged so that these passages 
discharge continuously into the housing 22 wherever the cam follower 101, 
102 touches the cam surface 98 within normal operating limits for the 
suspension system; within the respective piston each of the networks of 
passages 131, 132 discharges into an axial passage such as the passage 113 
fitted with a check valve such as the valve 114 of a known design 
permitting passage of fluid from the channels such as 131 into the 
interior of the bores such as 105 through the channels such as 113 and 
preventing flow in the reverse direction; thus protrusion of the piston 
results in the feeding into the bores such as 105 of fluid from the 
housing 22 whereas retraction of the piston into the bore causes discharge 
of the fluid thus introduced through the intermediary of conduits such as 
115 formed in the bores such as 105 in the immediate vicinity of the plugs 
such as 107 closing off the bores. 
The conduit 115 and its counterpart 116 in the bore 106 comprise respective 
check valves 117, 118 of known type permitting fluid to flow in the 
direction out of the bores 105, 106 and preventing flow in the reverse 
direction, and the two conduits 115 and 116 are joined together on the 
output side of the check valves 117 and 118 relative to the permitted 
direction of flow to form a single conduit 119 from which branch the 
conduit 120 connected to the chamber 90 and two conduits 121 and 122 
connected in parallel to a hydraulic fluid storage tank 123 which may 
consist of the housing 22 itself. 
The conduit 121 comprises in series an adjustable relief valve 124 and the 
conduit 122 comprises an adjustable flow restriction used to establish an 
adjustable leakage flow through it; the restriction 125 may advantageously 
be conditioned by the respective downstream and upstream pressures in the 
conduit 122 so as to eliminate the effect of the viscosity of the fluid, 
in other words of temperature, on the leakage flowrate. 
Thus when the arm 29 rotates in one direction or the other about the axis 8 
relative to the support 4, one or other of the pistons 109, 110 feeds the 
conduit 119 with hydraulic fluid from the housing 22 at a flowrate 
dependent on the speed of displacement of the piston in its bore, that is 
to say on the speed of rotation of the arm relative to the support. 
Passing through the restriction 125, this flow produces a pressure which is 
dependent on the head loss in the restriction and which is established 
uniformly in the conduits 119, 120, 121, 122 and consequently in the 
chamber 90, which applies to the brake linings 84 and brake disk sectors 
82 a force directly proportional to the pressure in the conduit 119; by 
virtue of friction between the brake linings 84 and the brake disk sectors 
82, this produces a damping force having about the axis 8 a damping moment 
opposing rotation of the arm 29 in the direction considered and 
proportional to the rotation speed; the head loss in the restriction 125 
follows a substantially parabolic law so that small-amplitude movements of 
the pistons 109 and 110 in their respective bores have no effect on the 
piston 88, that is to say on the damping force due to pressurized contact 
between the friction linings 84 and the brake sectors 83. 
Provided that the pressure in the conduits 119, 120, 121, 122 remains below 
the pressure that opens the relief valve 124, all of the flow of fluid is 
fed via the conduit 122 and the restriction 125 into the storage tank 123. 
If the speed at which the arm 29 rotates about the axis 8 relative to the 
support 4 is sufficiently high for the fluid discharged by one or other of 
the pistons 109 and 110 according to the rotation direction to produce in 
the conduit 119 a pressure exceeding the threshold for opening the relief 
valve 124, which threshold is set according to a required maximum damping 
force, the fluid flows via the conduits 121 and 122 into the storage tank 
123; the pressure in the conduits 119, 120, 121, 122 then remains constant 
and equal to the pressure that opens the relief valve 124; the damping 
force itself then remains constant at its maximum value. 
The damping force substantially proportional to the pressure in the chamber 
90, itself conditioned by the head loss created at 25 by the flow of fluid 
in the conduit 122, tends to be cancelled out as the flowrate reduces, 
that is to say in particular when the arm 29 is stationary relative to the 
support 4 between rotation in one direction and rotation in the opposite 
direction, since the two pistons 109 and 110 are then stationary; to 
maintain a residual flow through the restriction 125 in the conduit 122, 
that is to say to prevent virtually total cancellation of the damping 
force, during transient phases in which the direction of rotation of the 
arm 29 about the axis relative to the support 4 is reversed, there is 
preferably provided a pressure accumulator 130 connected to the conduit 
119 by a conduit 129; the pressure accumulator 130 is dimensioned to have 
a negligible effect on the pressure in the chamber 90 when the arm 29 
rotates about the axis 8 relative to the support 4, at this time possibly 
serving only as a filter to reduce the effects of variations in the 
flowrate due to movements of the pistons 109 and 110 at high frequency in 
their respective bores. 
By varying the slope of the cam surface 98, in other words by assigning 
different values to the angle between tangents to the cam surface 98 at 
various points relative to radii joining these points to the axis 8, it is 
possible not only to condition the force with which the brake linings 85 
are pressed against the brake disk sectors 82 according to the rotation 
speed of the arm 29 about the axis 8 relative to the support 4, but also 
according to the angular position of the arm 29 relative to the support 4 
during such rotation, for example to increase the damping and so harden up 
the suspension when the arm is approaching is permissible limit 
amplitudes, in normal use, relative an an average position defined, for 
example, by the plane 38 being horizontal. 
Also, differing in this respect from what has been described and shown, the 
cam surface 98 may have a shape which is asymmetrical relative to the 
plane 14 with which the plane of symmetry between the respective axes 103, 
104 of the bores 105, 106 is coincident when the arm 29 occupies its 
position of static equilibrium, and/or to use different cross-sections of 
the pistons 109 and 110 so as to obtain different damping forces according 
to the direction of rotation of the arm 29 relative to the support 4. 
By placing the brake disk sectors 82 and the linings 84 in the lower part 
of the housing 22 they are certain to be immersed at all times in the 
hydraulic fluid in the housing 22. 
Thus these components are permanently lubricated and cooled. 
To procure the same effect at the level of the slide member 55, the piston 
47 and the journal 12, means may advantageously be provided to ensure 
that, despite temporary removal of hydraulic fluid from the housing and 
movement of the piston 47 in the liner 44, and whatever the temperature of 
the fluid, the housing 22 is filled to the maximum with hydraulic fluid at 
least in certain angular positions of the arm relative to the support, 
under normal operating conditions. 
To this end there is advantageously provided within the housing 22 an 
elastically expandable, fluid-tight flexible material bladder 126 which 
contains a gas under pressure which, like the compressible fluid 
accommodated in the chambers 56 and 42, may advantageously by nitrogen; in 
a particularly advantageous manner the bladder is placed in the chamber 41 
delimited internally of the cavity 32 by the bulkhead 40 so that, by 
virtue of this position, variations in the volume of the bladder 126 
procure circulation of the hydraulic fluid from the housing 22 in the 
immediate vicinity of the brake linings 84 and brake disk sectors 82. 
In alternative embodiments the bladder 126 could be complemented or 
replaced by accumulator means serving the same function and disposed 
appropriately. 
The embodiments of the invention that have just been described constitute 
non-limiting examples only and numerous variations may be made to the 
arrangements which have just been described without departing from the 
scope of the present invention.