The object of this invention is a radial-actuator hydraulic motor,
the cylinder capacity of which may be varied by means of an eccentric ring integral
with the crankshaft, fitted with a hydraulic device having a dual valve to set
and control the variation of eccentricity of such eccentric ring with respect to
the crankshaft, and independent shift actuators mechanically linked to the said
It is known that in hydraulic motors of this type the pistons bring
about the rotation of the crankshaft, supported by bearings located in seats provided
in the housing or integral therewith, acting on its eccentric part. The cylinders
in which the pistons slide may be integral with the housing or hinged thereto.
In some known versions of variable-displacement radial motors, variation of the
cylinder capacity is achieved by varying the eccentricity of the crankshaft by
means of hydraulic jacks operated by valves fitted to the said crankshaft, supplied
via a rotary manifold obtained by utilizing the link between a pin of the said
crankshaft and the housing, with the aid of rotary-shaft gaskets.
Such prior art is disclosed into DE-22 03 054 and is included into
the preamble of claim 1.
The aforesaid variable-displacement radial hydraulic motors have
several disadvantages. For example, they do not stably maintain the cylinder capacity
at all the values comprised within the range of variation; they need to be removed
and detached from the working parts for the maintenance of such rotary-shaft valves
and gaskets (which are severely stressed) and they are subject to significant
losses of energy as a result of friction and discharge. All the foregoing combines
to bring about in such motors inadequate performance, reliability and efficiency
which considerably limit their applications.
Additionally, the control and setting devices of known type provide
for the use of return springs for the movement of the eccentric ring operating
pistons, rendering necessary special equipment and arrangements to achieve the
positioning thereof inside the said eccentric ring.
There is therefore posed the technical problem of providing a variable-displacement
radial-piston hydraulic motor fitted with a control and setting device with a
high rate of response such as to ensure with certainty the implementation of variation
control, and capable of being fitted also to low-capacity motors with reduced housing
Within the context of such problem, a further aim of the invention
is to provide a control device capable of being easily fitted to and/or removed
from fixed-displacement motors for the conversion thereof into variable-displacement
motors by using a small number of moving parts, gaskets and machined surfaces.
Such problem is resolved according to this invention by a variable-displacement
hydraulic motor with radial cylinders supplied by a rotary fluid distributor and
acting on an eccentric ring axially fixed to a crankshaft but capable of moving
radially with respect thereto, such motor being provided with a device for setting
and controlling the variation of eccentricity of the eccentric ring with respect
to the crankshaft, which comprises at least one pair of actuating pistons located
in counterposition to and independent of one another, arranged in a radial sense
between the shaft and the ring, each of which is made mechanically integral with
such eccentric ring via appropriate means of connection, and at least one pair
of alternating-control valves to block the flow of the fluid operating such actuating
According to a preferred form of implementation, provision is made
for such means of mechanical coupling between the actuating pistons and the eccentric
ring to be comprised of T-shaped pins capable of being inserted lengthwise in the
ring and of maintaining the latter secure in the radial direction, and for such
flow of fluid to occur between an inlet and an outlet via a four-way distributor
and ducts provided in a connection unit interposed between the motor housing and
the cover accommodating the rotary distributor supplying the motor cylinders.
Provision is also made for the rotary distributor drive shaft to have
internal axial channels capable of connecting the valves to the radial ducts communicating
with the outlets of the distributor controlling the supply and discharge of fluid.
Furthermore, such control valves may be arranged in a radial sense in relation
to the same section of shaft on which is fitted the eccentric ring or in an axial
sense inside the drive shaft of the rotary distributor supplying the motor cylinders.
Further details may be obtained from the following description with
reference to the attached drawings, which show:
- In figure 1 :
- a schematic cross-section according to a plane perpendicular to the axis of
rotation of the shaft;
- In figure 2 :
- a cross-section according to plotting plane II-II of figure 1;
- In figure 3 :
- a detail of the cylinders which bring about the variation of the cylinder capacity;
- In figure 4 :
- a schematic axial cross-section of one of the two control valves;
- In figure 5 :
- a diagram of the hydraulic circuit supplying the control valve and the actuating
- In figure 6 :
- a detail of the area of coupling of the eccentric ring with the drive shaft,
- In figure 7 :
- an example of an alternative method of implementation with blocking valves
located in an axial sense inside the drive shaft of the rotary oil distributor.
As illustrated in the figures, the variable-displacement hydraulic
motor according to the invention is comprised of a housing 1 in which are located
cylinders 3, each of which is placed in communication with a rotary distributor
4 located in a cover 1a attached to housing 1 by means of screws 1b, operated by
a drive shaft 4d and capable of placing cyclically in a supply or discharge setting
cylinders 3 in phase with the rotation of crankshaft 7.
In cylinders 3, bearing on covers 2, there slide radially pistons
5 which bear against the outer surface of a ring 6 capable of moving eccentrically
in a radial sense with respect to the axis of crankshaft 7, such variation of eccentricity
bringing about the variation of the cylinder capacity of of the motor.
As illustrated in figure 6, shaft 7 has transverse locators 7a, 7b
in relation to its zone of engagement with pistons 5. Such locators are capable
of maintaining ring 6 centred lengthwise and of enabling it to move in a transverse
Inside shaft 7 in relation to the zone of engagement with eccentric
ring 6 are located pistons 8 and 9 in counterposition, the outer end of which
has T-shaped pins, respectively 8a, 9a, capable of being inserted axially in corresponding
seats 6a of eccentric ring 6 with which they become mechanically integral in a
radial sense. Such link enables the pistons to follow the eccentric ring when the
latter moves radially for reasons other than positive and controlled operation
imparted via valves 10 and said pistons 8, 9.
In the said zone of location of the eccentric ring, shaft 7 also has
longitudinal recesses 7c through which ring 6 is made to strike shaft 7, only
in relation to the outer edges of the sliding plane of ring 6, thus making it possible
to unload the resultant of the forces generated by pistons 5, which is substantially
normal to the thrust axis of pistons 8 and 9, spreading the same equally over such
outer edges. This makes it possible to obtain a reduction of stress in relation
to the axes of actuating pistons 8 and 9, which stress could bring about deformations
with consequent hindrance of the sliding movement thereof.
The implementation and control of movement in a transverse sense of
each piston 8 and 9, and therefore of eccentric ring 6, is effected via an appropriate
valve 10 which blocks the fluid to be supplied/discharged to/from pistons 8, 9
and coming from the rotary connection via axial ducts 4a, 4b provided on drive
shaft 4d of distributor 4 which supplies the chambers of cylinders 3.
Such valves are of the alternating-control type in order to obtain
the discharge of one piston when the other is being supplied, and vice versa.
In an initial example of implementation (figs. 2, 3) such valves are
located radially inside the portion of shaft guiding eccentric ring 6 and are
connected to respective pistons 8 and 9 via appropriate ducts 8b, 9b.
Static sealing of the ducts connected to shaft 7 is achieved by means
of gaskets 4c, while dynamic sealing is implemented via gaskets 11 forming the
subject of another patent in the name of the same applicant.
As shown in figure 2, between housing 1 and cover 1a of the motor
is interposed a fixed body 1c in which are provided ducts 12 and 13 for the supply
of fluid which flows via ducts 4a, 4b of drive shaft 4d to blocking valves 10.
Such operating fluid is supplied via an inlet under pressure P and
a duct 12 on which is located a cartridge filter 12a.
The pressurized fluid emerging from filter 12a is fed via ducts 12
and 13 to a distributor 100 from which flow out pressure controls A and B for
the operation of blocking valves 10.
To implement the variation and maintenance of intermediate cylinder
capacities between maximum and minimum, the fluid supplied to and contained in
actuating pistons 8 and 9 should remain intercepted by controllable valves 10 at
In greater detail, such valves 10 are comprised (fig. 4) of a cylindrical
body 10a provided with radial apertures 10b and 10c connected to fluid supply ducts
12 and 13.
Within body 10a is slidingly located a piston 14 capable of acting
against a cone-seated shutter 15 housed in a guide tube with conical sealing seat
16a against which shutter 15 is pressed by a spring 15a.
The valve is closed at the top by a cap 17.
The operation of the variation and control device is as follows:
Supplying fluid under pressure from inlet P communicating with distributor 100
and switching on the latter, brings about the supply of fluid to one of inlets
10b, 10c of valves 10 causing the alternating opening/closure of shutter 15 of
each valve 10 and the consequent supply/discharge of fluid to/from pistons 8 and
9 respectively, which accordingly move in a transverse direction and in one sense
or another, according to whether regulation is aimed at a higher or lower cylinder
capacity. The movement of pistons 8, 9 which are integral with eccentric ring
6 via T-shaped pins 8a, 9a brings about the shifting in a transverse sense of said
ring 6 and therefore the desired variation of cylinder capacity.
The centring of distributor 100 after a preset interval interrupts
the flow of fluid which remains under pressure in the circuit and blocks pistons
8 and 9 in the setting attained corresponding to the desired cylinder capacity.
It is therefore clear that with the cylinder capacity setting and
control device according to the invention it is possible to locate control valves
10 in proximity to actuating pistons 8, 9 to the advantage of the rate of response
of the device, and that the mechanical link between the pistons and the eccentric
ring makes it possible both to obtain a hydraulic braking effect with consequent
increase of stability of positioning and to avoid the use of return springs for
the pistons, which may be made solid with consequent elimination of air bubbles
in the operating circuit which, because of the compressibility of the air, reduce
the accuracy of the setting and control device.
As illustrated in fig. 6, with a motor according to the invention
blocking valves 10 may also be fitted in an axial sense inside shaft 4d driving
rotary distributor 4 while there remains substantially unaltered the previously
described features of setting and control of eccentricity of ring 6.
Provision is also made for the sections of said two pistons 8 and
9 to be capable of differing from one another according to suitable ratios by
reason of the fact that the effort needed to set the eccentricity in order to achieve
an increase of cylinder capacity is greater than the effort needed to achieve a
reduction of the latter.
Many variants may be introduced in the design of the component parts
of the invention without thereby departing from the scope of protection of this
patent as described in the claims which follow.