Swash plate mechanism, particularly for a pump drive

A swash plate mechanism, especially for high power swash plate pumps, incorporating, inside a casing (2) bounded by two end walls (21, 22), a driving component (3) mounted so as to rotate about a longitudinal axis (30), an inclined plate (5) bearing upon the driving component (3) and mounted so as to swivel on the latter about an inclined axis (50). The two end walls (21, 22) of the casing are joined at their periphery by additional lateral tie rods (80) parallel to the central tie rod (8), bearing upon the two end walls (21, 22) of the casing (2) and subjected to a preload tension in order to carry the forces developed by the pistons (6) in co-operation with the central tie rod.

FIELD OF THE INVENTION 
The subject of the invention is a swash plate mechanism particularly 
applicable to a pump drive. Such mechanisms, which have been known for a 
long time, incorporate, inside a casing, a driving component mounted so as 
to rotate about a longitudinal axis, on which is arranged an axis of 
swivelling for a swash plate inclined relative to the longitudinal axis 
and bearing against the driving component through the intermediary of an 
axial abutment. The pump incorporates several pistons, spaced about the 
longitudinal axis, and sliding parallel to the latter in cylindrical 
bodies arranged in a frame fixed to one of the end walls of the casing in 
which the mechanism is situated. Each piston is individually joined to the 
inclined plate, for example through the intermediary of a jointed 
connecting rod, and the inclined plate is locked against rotation. In this 
way, when the driving component is driven in rotation, the inclined plate 
moves with an oscillating motion about the point where its axis of 
swivelling intersects the longitudinal axis of rotation, which thus 
constitutes a center of oscillation. As the inclined plate is locked 
against rotation, this oscillating motion causes an alternating 
longitudinal motion of the pistons through the intermediary of jointed 
connecting rods. Longitudinal forces are thus developed by the pistons 
between the frame fixed to the rear end wall of the casing and the 
inclined plate which bears upon the driving component, the latter bearing 
in turn, through the intermediary of an axial abutment, upon the front end 
wall of the casing. Thus the combination of forces must be withstood by 
the casing, more especially by the two end walls of the latter and the 
lateral wall which joins them together. When the pump is of high power, 
the casing must withstand large forces, and this leads to very heavy and 
bulky constructions. 
PRIOR ART 
In order to lighten the pump, U.S. Pat. No. 3,885,444 proposes that the two 
end walls of the casing be joined together by a central tie rod whose ends 
bear upon the outer surfaces of the two end walls and which is put under a 
preload tension capable of balancing the forces developed by the pistons. 
Preferably, the preload force is carried when at rest by a strut column 
interposed between the inner surfaces of the two end walls, its center 
lying on the longitudinal axis of rotation, and through which the 
preloaded tie rod passes. 
The forces, developed by the pistons along their axes of sliding and 
carried by the central tie rod and by the lateral walls, are applied to 
the two end walls of the casing. The latter are thus subjected to 
alternating forces, directed along the axes of the pistons and which 
depend upon the position of the inclined plate. 
SUMMARY OF THE INVENTION 
The aim of the invention is to propose improvements to this arrangement 
which allow the casing to withstand the alternating forces, even in the 
case of a high power pump, while retaining a relatively light 
construction. 
In accordance with the invention, the two end walls of the casing are 
joined at their periphery by a number of additional lateral tie rods 
parallel to the central axis, bearing upon the two end walls of the casing 
and subjected to a preload tension capable of counteracting the forces 
developed by the pistons, in co-operation with the central tie rod, each 
piston corresponding either to a single lateral tie rod, whose center lies 
in the radial plane passing through the central axis and the axis of 
sliding of the piston, or to a pair of lateral tie rods positioned 
symmetrically on each side of the corresponding radial plane. In a 
preferred embodiment, the rotating driving component bears upon the front 
end wall of the casing along a circumference, whose center lies on the 
longitudinal axis, passing through the axes of the pistons, through the 
intermediary of a circular rib arranged on a fixed transverse plate 
positioned at the front end of the central strut column.

DETAILED DESCRIPTION 
FIG. 1 shows the assembly of the pump 1 and of the driving mechanism 
positioned inside a casing 2 and incorporating a driving component 3 
mounted so as to rotate about an axis 30 on a hollow column 4 and on which 
an inclined plate 5 is mounted so as to swivel about an axis 50 inclined 
at an angle (i) relative to the longitudinal axis 30 and intersecting the 
latter at a center of oscillation 0. 
The pump 1 incorporates a number of pistons 6 each mounted so as to slide 
along an axis 60 parallel to the longitudinal axis 30, inside a 
cylindrical body 61 firmly fixed to the frame 11 of the pump. In the 
embodiment shown, each piston 6 is firmly fixed to a slide 62 guided along 
the axis 60 inside a cylindrical body 63. Each slide 62 is joined to the 
inclined plate 5 by a connecting rod 64 provided at its two ends with ball 
joints 65 and 66 for connection to the inclined plate 5 and to the slide 
62, respectively. 
The inclined plate 5 is mounted so as to swivel about the axis 50 on a 
bearing 51 mounted on an inclined bearing surface 31 arranged on the 
driving component 3. The latter is also provided with an inclined bearing 
surface 32 positioned in a plane perpendicular to the axis 50 and upon 
which the inclined plate 5 bears through the intermediary of an axial 
abutment 52. 
In addition, the driving component 3 also bears, through the intermediary 
of an axial abutment 33, upon a transverse plate 41 arranged at the 
opposite end of the column 4 from the pump 1 and perpendicular to the axis 
30, the column 4 also carrying a bearing 34 for the axial guidance of the 
driving component 3. 
The centers of the ball joints 65, connecting the connecting rod 64 to the 
plate 5, are positioned at the intersection points of the axes of sliding 
60 of the pistons 6 with a plane perpendicular to the inclined axis 50 and 
passing through the center of oscillation 0, for the two extreme angular 
positions of the inclined plate for which the axis 50 lies in the radial 
plane passing through the longitudinal axis 30 and the axis 60 of the 
corresponding piston. The centers of the ball joints 66 connecting to the 
slides 62 are, of course, also positioned on the axes of sliding 60. 
It will thus be seen that, when the driving component 3 is driven in 
rotation about its axis 30 by a mechanism 42, the inclined plate 5, which 
is itself locked in rotation by means which are not shown, oscillates 
about the center 0 and causes, through the intermediary of the connecting 
rods 64 and of the slides 62, an alternating motion of the pistons 6 along 
their axes 60. 
The thrust of the pistons 6 is thus contained by the inclined plate 5 and 
transmitted to the driving component 3, and then to the fixed transverse 
plate 41, by the axial abutments 52 and 33, respectively. 
This thrust should thus be carried by the casing 2 which incorporates a 
rear end wall 21, to which the pump 1 is fixed, and a front end wall 22 
upon which the fixed transverse plate 41 bears. 
According to the arrangement which forms the subject of U.S. Pat. No. 
3,885,444 already mentioned, the thrust forces are carried by a tie rod 8 
which passes inside the central tubular column 4 and is provided at its 
two ends with collars 81 and 82 bearing upon the rear end wall 21 and upon 
the front end wall 22, respectively. The latter takes the form of a box at 
whose center an axial column 23 is positioned, which is situated in the 
extension of the strut column 4, and upon which the latter bears on the 
same side as the pump. 
According to the essential characteristic of the invention, the casing 2 is 
also provided with a number of lateral tie rods 80, positioned at its 
periphery, to carry the forces developed by the pistons, each in 
co-operation with the central tie rod, which are spaced, for this purpose, 
symmetrically relative to the radial planes passing through the 
longitudinal axis 30 and through the axes 60 of the pistons 6. Each piston 
6 may thus correspond either to a single lateral tie rod 83 positioned in 
the corresponding radial plane P, or to two lateral tie rods 85 positioned 
symmetrically on each side of the corresponding radial plane. 
In the example shown, which corresponds to a pump with three pistons, the 
two solutions have been combined. In fact, as may be seen in FIG. 2, the 
casing 2 incorporates two upper lateral tie rods 83 whose centers lie in 
the radial planes corresponding to two pistons 6a and 6b, whereas the 
forces developed by the third piston 6c are carried, in co-operation with 
the central tie rod 8, by two other lower tie rods 85 positioned 
symmetrically on each side of the corresponding radial plane P.sub.1. 
The lateral tie rods are subjected, like the central tie rod 8, to a 
preload tension capable of opposing the thrusts of the pistons, and for 
this reason each tie rod 80 is provided at its ends with collars 87 for 
bearing upon the outer surfaces of the two end walls 21, 22 of the casing 
and pass through a strut column 24 constituting part of the casing and 
interposed between the two end walls so as to prevent the latter from 
moving towards one another under the action of the preload tension when 
the thrust of the corresponding piston is not being exerted in the 
opposite direction. 
The preload tensions, and consequently the cross-sections of the tie rods 
are, of course, determined as a function of the forces developed by the 
pistons and of the distances of the axes 60 of the latter relative to the 
lateral tie rods 80 and to the central tie rod 8. 
It will also be seen that the arrangement with two tie rods 85, 86 adopted 
for the piston 6c allows the driving mechanism 42 to be positioned between 
them, which mechanism incorporates, for example, a pinion keyed on a 
driving shaft 43, meshing with a toothed wheel 35 firmly fixed to the 
driving component 3. 
The casing assembly 2 is of welded and built construction and, owing to the 
solutions adopted, can be relatively light. Each end wall takes the form 
of a box consisting of transverse plates joined by struts. The latter are 
formed by the central column 23 and by the lateral columns 24 in the case 
of the rear end wall 21 which forms the fixed base of the installation to 
which are fixed, on one side, the pump 1 and, on the other side, the 
driving mechanism 3, 4, 5. 
The front end wall 22 is formed of a box consisting of two lateral plates 
joined together by bulkhead struts 25 positioned around holes 26 for the 
tie rods 80 to pass through, in the extension of the walls of the columns 
24 of the corresponding tie rod. 
In addition, the frame 1 is advantageously provided with a fixing plate 12 
which is fixed to the outer surface 27 of the rear end wall 21 and upon 
which the collars of the central tie rod 8 and of the lateral tie rods 80 
bear, the tie rods passing through holes arranged in the plate 12. 
This arrangement thus allows simple dismantling of the assembly of the pump 
1, by unscrewing the tie rods. 
The assembly of the casing and the hydraulic body thus forms a rigid 
preloaded unit, easily dismantled, and well capable of withstanding the 
heavy internal thrusts of the pistons. 
Moreover, according to another advantageous arrangement, the axial thrust 
of the driving mechanism upon the front end wall 22 is carried along a 
circumference whose center lies on the longitudinal axis 30 and whose 
radius R equals the distance between the axis 30 and the axes 60 of the 
pistons. For this purpose, the transverse plate 41 is provided, on the 
same side as the end wall 22, with a circular bearing rib 44 having a mean 
radius equal to R. A disk 25 forming a spacer is interposed between the 
bearing rib 44 and the inner surface of the front end wall 22, and the 
central column 4 bears upon the end of the axial column 23 of the front 
end wall 21 through the intermediary of an adjustable abutment, which may 
consist, for example, of a nut 45 screwed on a thread arranged at the end 
of the column 4 facing towards the pump 1. In this way any appreciable 
axial play in the internal mechanical assembly is avoided, adjustment of 
the nut 45 allowing the central column 4 to be pushed back axially so as 
to ensure contact with the end wall 22 along the rib 44. A slight play (e) 
may also be arranged between the central portion of the front end wall 22 
and a circular rib of smaller diameter arranged at the end of the central 
column 4 surrounding the hole through which the central tie rod 8 passes. 
This limits the distortion of the end wall 22 under the action of the 
preload tension applied to the central tie rod 8. 
The invention is, of course, not limited to the details of the embodiment 
which is described above by way of a simple example, and which could be 
modified using equivalent means. This applies particularly to the physical 
construction of the mechanism, of the pump and of the casing. In 
particular, the latter could consist of a simple plate provided on its 
outer surface with reinforcing ribs passing through the longitudinal axis 
and through the axes of the lateral tie rods and of the corresponding 
pistons.