Distributor for hydraulic motors

A distributor for hydraulic motors, particularly radial-piston hydraulic motors, wherein an excellent hydraulic seal is provided in the area between the motor housing and the fluid distribution plate by the utilization of a tubular sleeve located in front of the distribution plate. At least two annular steps located on said sleeve which engage with corresponding annular steps on the housing provide such seal.

The present invention refers to a distributor for hydraulic motors, in 
particular for radial-piston hydraulic motors, of the type disclosed in 
U.S. Pat. No. 3,696,710. 
According to the prior art, distributors for hydraulic motors of the above 
mentioned type consist of a hollow housing co-axially secured to one side 
of the casing at one end of the driving shaft, which extends inside said 
housing, a distribution plate connected to said end of driving shaft and 
rotating therewith inside the hollow housing, and a plurality of ducts 
obtained in said plate and cyclically communicating on their one end with 
the feed and drain ducts of the radial pistons of the motor and on their 
other end with corresponding ducts on the walls of said fixed housing for 
the feeding and discharge of the hydraulic fluid. 
According to said prior art there have been serious troubles in separating 
the feeding flow from the discharge flow and vice versa in those areas 
where the ducts on said plate rotating inside the hollow housing and the 
fixed feeding and discharge ducts on the walls of the housing itself are 
connected. 
In fact, according to the prior art, the cavity of the fixed housing is 
divided into two sections being respectively connected with the discharge 
and/or feeding flows through an annular element placed between the 
distribution plate and the front wall opposite to the end of the driving 
shaft, said annular element being secured to said housing wall, for 
example, by means of pins, with the interposition of toroidal washers 
which, besides providing a sealing action in the contact area, also 
provide an elastic thrust, especially when the motor is started, to press 
the distribution plate against the motor casing when this thrust action is 
not yet provided by the pressure of the hydraulic fluid, thus preventing 
leakage between the contact surfaces of said annular piece and said plate. 
In order to allow the toroidal washers to carry out the above listed 
functions, it is necessary to make use of elements as much as possible 
devoid of end floats, i.e. to work with considerably close tolerances. 
However, when the motor is running and due to said close tolerances, 
seizures of the moving parts have been so frequent as to make this 
distributor unsuitable. 
The present invention is therefore based on the problem of providing an 
excellent hydraulic seal in the contact area of feeding and discharge 
between the ducts of the fixed housing and those of the distribution plate 
rotating in the cavity of said housing, thus providing a sharp separation 
between the feeding and the discharge flow as well as suitable thrust of 
the plate against the motor casing at the starting of the motor, when no 
hydraulic pressure is present as yet, without the risk of seizures between 
the moving parts. 
This problem is solved according to the invention, by a sleeve like tubular 
element inserted between said distribution plate and the housing wall 
perpendicular to the rotation axis of the driving shaft, the external 
periphery of said sleeve like tubular element having at least two annular 
steps thereon which are in engagement with corresponding annular steps on 
said fixed housing wall, with the interposition of respective toroidal 
seals, said sleeve like tubular element being secured to said housing by 
locking means which prevent it from rotating while allowing its axial 
displacement and being also provided with a plurality of holes in the area 
between said two steps, said holes communicating, at the one side, with a 
first feeding and/or discharge duct on the fixed housing wall and, at the 
other side, with an annular groove on said distribution plate, the axial 
cavity of said sleeve like tubular element communicating, at one end, with 
a second feeding and/or discharge duct on the housing wall and, at the 
other end, with a cavity on the opposite surface of the distribution 
plate, an elastic means for pressing said sleeve like tubular element 
against said distribution plate being also provided. 
In a preferred embodiment of the invention, said two annular steps on the 
external periphery of said sleeve like tubular element are radially spaced 
between each other by an annular shoulder whose surface area is 
substantially equal to the hydraulically active surface area of the 
central part of the sleeve like tubular element. 
The distributor according to the invention provides the advantage of 
sharply separating the feeding flow from the discharge flow in the passage 
between the rotating distribution plate and the adjacent fixed housing 
wall, and thus assures an excellent seal without risk of seizure between 
the moving parts, since the toroidal seals, by acting radially between 
opposite cylindrical and not flat surfaces, allow the construction of the 
pieces with sufficiently large tolerances. 
There is a further advantage, in that the same toroidal seals do not have 
to carry out any biasing action against the distribution plate, as this 
biasing action is carried out by separate elastic means, when the device 
is still not running. 
Finally, especially in the preferred embodiment of the invention, in which 
the annular surface area of the annular shoulder between the peripheral 
steps on the sleeve like tubular element is equal to the hydraulically 
active surface area of the central part of said sleeve like tubular 
element, there is the further advantage that the hydraulic thrust on the 
distribution plate does not change when the motor is running, whichever is 
the direction of rotation of the motor and therefore whichever duct in the 
fixed housing is used for feeding or discharge.

With reference to the above figures, 1 is the side wall of the casing of an 
hydraulic motor, whose rotor 2 is rotated by a plurality of hydraulic 
cylinders 3 having pistons 3a spaced along the periphery of the rotor and 
fed with hydraulic fluid through corresponding channels 4. Rotor 2 is 
mounted on driving shaft 5, having a power take-off 6 projecting at one 
end from the casing and a section 7 extending at the opposite end inside 
the distributor, by interposing a joint 9, if necessary, said distributor 
being indicated by 8 as a whole. A more detailed example of said motor may 
drawn from Italian Pat. No. 812059 by the same Applicant. 
With particular reference to FIG. 2, section 7 of the driving shaft passes 
through a flat body 10 secured to the casing wall 1 and provided with 
passages for the fluid, like the one indicated by 11, which are connected 
with duct 4 for the feeding cylinders 3. 
Said flat body is locked by pins 12 against rotation with respect to casing 
wall 1. 
On the free end of section 7 of shaft 5 is mounted a distribution plate 13 
which rotates with shaft 5 and is timed with the desired hydraulic 
distribution on cylinders 3. Body 10 and plate 13 are both lodged in 
cavity 14 of box-type housing 15 of distributor 8. 
Distribution plate 13 has, on its surface facing body 10, a first pair of 
arcuate grooves 16 and 17 and a second pair of arcuate grooves 18 and 19 
having reduced transverse size with respect to said first grooves. Further 
details concerning these grooves may be seen in FIG. 4, which is a plan 
view thereof. While grooves 18 and 19 are provided for balancing the 
hydraulic thrust in conventional way, adjacent grooves 16 and 17 are 
provided for cyclically connecting ducts 4 for feeding and/or discharge of 
hydraulic cylinders 3. 
In fact, groove 16 is in communication with a duct 20 which leads though 
the whole thickness of distribution plate 13 to an annular open groove 21 
on the surface opposite to the one which is contact with body 10. Groove 
17, on the other hand, is in communication with a further duct 22 leading 
through the whole thickness of plate 13 to an open cavity 23 in the center 
of plate 13 inside annular groove 21. 
Between plate 13 and vertical wall 24 of casing 15 there is a sleeve like 
tubular element 25 having two annular steps 26 and 27 radially spaced by 
an annular shoulder 28. Said sleeve like tubular element 25 is inserted in 
a corresponding cavity of wall 24 having corresponding steps 29 and 30. 
Between steps 26 and 27 of the sleeve like tubular element 25 and the 
corresponding steps 29 and 30 of wall 24 of the fixed housing 15, there 
are toroidal washers 31 and 32 lodged in annular grooves 33 and 34 
respectively, the first washer being located, for instance, on the sleeve 
like tubular element 25 and the second on the wall of fixed housing 15. 
The same sleeve like tubular element 25 is also provided with a flange 35 
to secure said tubular element 25 to casing 15 through pin 36, which 
prevents rotation while allowing a limited axial displacement with respect 
to wall 24. 
Corresponding to annular shoulder 28 there are holes 37 which communicate 
on one side with annular groove 21 and on the other side with annular 
cavity 38 formed by shoulder 28 and wall 24. 
Ducts 39 end inside said cavity 38 and are reciprocally connected by a 
toroidal cavity 40 communicating with the feeding and/or discharge hole 41 
through wall 24. 
The central part of the sleeve like tubular element 25 forms an axial 
cavity 42 which communicates on one side with feeding/or discharge hole 43 
through wall 24, and on the other side with open cavity 23 provided on the 
opposite surface of distribution plate 13. 
In the same axial cavity 42 lodges a helicoidal spring 44 baised on one 
side against wall 24 and on the other side against annular edge 45 on the 
sleeve like tubular element 25. 
With reference to the modified embodiment of FIG. 3, the sleeve like 
tubular element consists of two pieces 25a and 25b telescopically jointed 
by a cylindrical portion 25c with the further interposition of a toroidal 
washer 46. 
This modified embodiment offers the advantage of making the enlargement of 
the annular thrust surface possible without need to increase the external 
diameter of the distributor. 
In fact, according to this embodiment, the annular thrust surface extends 
between external washer 32 and internal washer 46, being radially 
displaced towards the distributor axis. 
With reference to FIGS. 5 and 6, it is finally observed that the thrust, 
indicated by A and A' as a whole, applied to the hydraulically active 
surface area of the central part of sleeve like tubular elements 25 and 
25b equals the thrust applied to annular shoulder 28, indicated by B and 
B' respectively. These thrusts A-A' or B-B' have to balance those deriving 
from distribution plate 13 in the opposite direction. 
This means that, when the motor is running, whichever of holes 41 or 43 is 
used for feeding the fluid under pressure and whichever is the direction 
of rotation of the motor, the sleeve like tubular elements 25 or 25a, 25b 
are pressed against the distribution plate 13 always with the same force. 
As to the hydraulic feeding and the discharge of cylinders 3, this 
operation is carried out in a conventional way as may be understood from 
the accompanying drawings and from the preceding description. 
As to the function the sleeve like tubular elements 25 or 25a, 25b, it 
should be pointed out that, when the motor is started and there is no 
pressure yet in cavity 42 or in cavity 38, the thrust against distribution 
plate 13 is exerted by spring 44 which thus assures a sealing connection 
between the sleeve like tubular element and the rotating distributor plate 
13 as well as between the latter and fixed body 10. 
When the motor is running, to the above thrust the one of forces A-A' or 
B-B' is added according to the direction of feeding of the fluid under 
pressure; both thrusts are counter-balanced by those exerted in opposite 
direction by distribution plate 13. 
As to the sealing connection between feeding passages and discharge 
passages in the connecting section between distribution plate 13 and wall 
24 of the fixed housing 15, this is assured by toroidal washers 31 and 32, 
as well as 46, which are in their best operating conditions since their 
action is exerted radially between opposite cylindrical surfaces and not 
between flat surfaces as in the prior art. Moreover, these washers allow 
an axial displacement of the pieces, for example in case of sudden 
temperature changes, without impairing the sealing functions and without 
risk of seizure.