The present invention relates to a hydraulic motor with propulsion
members retained against corresponding contact surfaces by resilient means inside
said propulsion members and positioned between the latter and associated means performing
a mechanical retaining action in the radial direction.
It is known in the technical sector relating to the construction of
engines or motors with propulsion members moved by means of a fluid supply and therefore
generally defined as hydraulic that there exists the possibility of forming the
said propulsion members using a cylinder and a piston which are telescopically coupled
together so as to be displaceable relative to each other, upon rotation of a cam
associated with the driving shaft, thus imparting a thrust to the said shaft.
Said propulsion members may be arranged radially or obliquely.
It is also known that, in the case of radial engines or motors, one
of the problems posed by said propulsion members consists in the need to keep the
end edge of the cylinder and the piston sealingly adherent, respectively, to the
said cam and a reaction element consisting of a cap fixed to the engine housing
so as not to cause seepage of fluid during the relative travel movement of piston
One of the solutions commonly used to obtain this sealing effect consists
in the insertion, inside each propulsion member, of a resilient element consisting
of a helical spring arranged coaxially with the propulsion member and able to exert
a thrust against corresponding internal projections of the cylinder and piston so
as to press the latter against the associated bearing surfaces.
An example of this type of actuating system is known from the patent
This solution, however, has certain drawbacks including those consisting
in the dynamic stressing which the spring is subject to during the travel movement
of the piston with respect to the cylinder, resulting in the need to design the
said spring with excessively large dimensions, producing a strong thrust on the
sliding contact surfaces, with consequent greater wear thereof.
In addition to this, the presence of the spring and the associated
projections supporting it inside the cylinder prevents a reduction in the volume
of fluid which cannot flow out of the cylinder at the end of the compression phase
(so-called "dead volume"), increasing the problems of replacement of the said fluid
with new fluid supplied by the delivery ducts.
The technical problem which is posed, therefore, is that of providing
a hydraulic motor provided with means for mechanically retaining each propulsion
member against respective bearing and contact surfaces where the hydraulic seal
preventing seepage of the thrusting fluid must be ensured.
Within the scope of this problem a further requirement is that said
mechanical retaining means should envisage resilient means acting on the propulsion
members with a thrust in a direction parallel to that of their longitudinal axis,
which is independent of the working (compression/discharge) phase of the said propulsion
In addition to this it is required that said resilient retaining means
should be easy and inexpensive to realize and install on motors of the known type
and should allow the motor to be used also as a pump.
These technical problems are solved according to the present invention
by a hydraulic motor with propulsion members positioned between a cam associated
with a shaft and a reaction element, said propulsion members consisting of two elements,
i.e. an internal element and external element, telescopically slidable with respect
to each other in a radial direction and respectively provided with annular bearing
edges kept pressed against corresponding contact surfaces of said reaction element
and said cam via respective resilient means, said resilient means associated with
the external element of the propulsion member being arranged outside the said element
and the resilient means associated with the internal element being arranged inside
the propulsion member and positioned in the radial direction between said internal
element and associated means for mechanically retaining them.
Further details may be obtained from the following description of
a non-limiting example of embodiment of the invention provided with reference to
the accompanying drawings in which:
- Figure 1 shows a partial schematic cross-section through a radial motor according
to the invention along a plane perpendicular to the axis of the driving shaft;
- Figure 2 shows an enlarged detail of a propulsion member of the motor according
to Fig. 1;
- Figure 3 shows a cross-section along the plane indicated by III-III in Fig.
- Figure 4 shows a cross-section along the plane indicated by IV-IV in Fig. 1;
- Figure 5 shows an enlarged detail of the slider for retaining the cylinder against
As shown, the hydraulic motor according to the invention in the version
with radial propulsion members comprises a casing 1 housing internally the shaft
2 mounted on bearings 2a and carrying the cam 3 on which the propulsion members
10 act radially.
Said propulsion members 10 in turn consist of a cylinder 11, one of
the two end edges of which rests on the external surface 3a of the said cam 3, and
of a piston 12 telescopically slidable in a radial direction inside the cylinder
11 and having one of the two end edges bearing against a spherical surface 1a formed
inside the covers 1b constrained to the casing 1 of the motor via suitable fixing
The edge of said cylinder 11 and said piston 12 resting on the respective
contact surfaces 1a and 3a of the cover 1b and the cam 3 (Figure 2) substantially
consists of an annular edge 11a, 12a provided with a contact surface 11b, 12b parallel
to the surface of the cam.
In the zone of contact between the cylinder 11 and the cam 3 said
retaining elements consist of: a slider 13 with a coaxial hole 13a, having a diameter
slightly greater than the external diameter of the cylinder 11 so as to allow the
latter to pass through it as far as an end-of-travel stop consisting of a tooth
11c extending outwards and able to engage with the radial retaining means described
Said slider 13 has, moreover, (Fig. 5) at least one pair of opposite
and parallel depressions 13c with a cylindrical surface 13f able to form an engaging
seat for a ring 15 (Figs. 3 and 4) arranged around each edge of all the sliders
13 retaining each cylinder 11 and having its centre on an axis parallel to that
of the driving shaft 2 and passing through the centre of the spherical cam 3.
In this way the opposite rings 15 radially retain all the sliders
13 which, in turn, keep the associated cylinder 11 in bearing contact against the
cam 3 during rotation thereof.
In order to maintain adherence between the slider 13 and the base
11a of the cylinder 11, a resilient element, in the example consisting of an undulating
spring 16, is positioned between them, said spring being designed to impart a radial
force resulting in relative contact between the contact surfaces 11b and 3a, which
force is constant and independent of the working phases of the propulsion member
As can be seen from Fig. 2, the spring 16 remains inserted inside
a seat formed by the bottom part of the ring 13 which forms in this way an end-of-travel
element for compression of the spring which is prevented from being compressed beyond
its own yield point, with advantages as regards the durability and reliability of
In the zone of contact between piston 12 and cover 1a the retaining
elements consist of a pin 52 provided with a head 53 which has a spherical surface
53a resting on corresponding support elements 54 fixed to the casing 1a so that
the head 53 itself forms a ball joint; the shank of the pin 52 has a cylindrical
body 55 with a diameter such that its side surface 55a makes contact with the side
surface of the piston 12 and an external end surface 55b arranged below an annular
tooth 12c of the cylinder 12 projecting towards the inside thereof.
Resilient means in the form of a spring 16 are arranged between the
cylindrical body 55 and the said annular tooth 12c so as to ensure constant adherence
of the contact surfaces 12b, 1a during the various working phases of the propulsion
member 10; the piston 12 furthermore supports, similar to that occurring in the
bottom part of the ring 13, an end-of-travel element 50 for preventing the spring
16 from being stressed beyond its yield point.
The cylindrical body 55 also has, formed therein, the ducts 56 for
conveying the fluid supplying the motor.
It is therefore obvious how the retaining devices according to the
present invention allow two main advantages to be achieved compared to the known
art; they in fact allow the resilient means to be no longer dependent upon the dynamic
loads resulting from the relative travel movement of the piston and cylinder of
the propulsion member with each rotation of the cam, allowing moreover filling of
the chamber of the cylinder 11 with high-volume and low-weight bodies 55 able to
limit the dynamic imbalance and reduction in the fluid dead volume.
In addition to this, the internal retaining devices according to the
invention allow a larger section of contact to be obtained between the cylinder
11 and the piston 12 in the fully extended condition of the propulsion member 10,
this factor being important for avoiding seizing during the return movement into
the minimum relative extension of the two components.
The solution described above, which envisages engagement of cylinders
and pistons with the associated contact surfaces, also allows the cylinders to perform
a fluid suction function without loss of adherence to the said surfaces, and the
apparatus is therefore able to be operated as a pump instead of as a motor.