Hydraulic rotary actuator

A hydraulic torque motor comprising a cylindrical housing (1), a piston (30) which can only be moved axially in the housing (1) and a rotor (20) which can only be rotated and which extends through the piston (39). The rotor (20) has a spiral groove (21) and the piston (30) has an engagement element (39) which extends radially inward in the groove (21). The piston (30) has a cylindrical section (31), each end of which has a circular end flange (34, 35), which abuts sealingly and slidingly against the housing's (1) boring. The housing (1) has a center flange (5) which projects radially inwards between the end flanges (34, 35) and is arranged to abut slidingly against the cylindrical piston section (31). The end flanges (34, 35) and the center flange (5) and those sections of the housing's (1) boring which are located between the flanged (5, 34, 35) define two cylinder spaces (37, 38).

BACKGROUND OF THE INVENTION 
The invention relates to a hydraulic torque motor comprising a housing with 
a central boring, an annular piston, which can be moved axially in the 
housing's boring, but which is prevented from rotating about its 
longitudinal axis in this boring and a substantially cylindrical rotor 
which extends axially through the piston, and which can rotate about its 
longitudinal axis in the housing, but cannot be moved axially in relation 
thereto, there being provided in the rotor's outer surface at least one 
spiral groove and the piston has at least one engagement element which 
extends radially into the groove, the housing's boring together with one 
end section of the piston partially defines a first cylinder space and 
together with the piston's second end section partially defines a second 
cylinder space, the cylinder spaces are arranged for alternate connection 
with a source and a reservoir for a pressure fluid for movement of the 
piston axially between two end positions in the housing and thereby 
rotation of the rotor between two associated angle positions via the 
engagement element, at each end of the piston there is a radially 
outwardly projecting end flange which is arranged for sealing and sliding 
abutment against the housing's boring, and the housing has a centre flange 
which at the central area of the housing's boring, considered in the axial 
direction, projects radially inwards, and which works in conjunction with 
a section of the piston between the end flanges. 
DESCRIPTION OF THE PRIOR ART 
In torque motors of this kind the housing can be connected to a stationary 
part such as a valve body and the rotor is connected to the valve element, 
the valve element being rotatable for opening or closing of the valve. 
A torque motor of the above-mentioned type is known, e.g. from DE 39 18 
400. In this torque motor the cylinder spaces are defined by the rotor, 
which causes the hydraulic fluid to come into direct contact with the 
spiral groove and the engagement element inserted therein, i.e. those 
sections or components of the torque motor which are particularly prone to 
wear, with the result that the hydraulic fluid can easily become polluted 
by particles which have been worn off these parts, and which can 
contribute to a reduction in the working life of the motor and increase 
the need for its maintenance. 
Since the rotor is instrumental in defining the cylinder spaces, i.e. it 
comes into contact with the hydraulic fluid, and the groove is not open at 
the ends of the rotor, the rotor cannot simply be replaced with a rotor 
with a differently shaped groove, e.g. with a different pitch in order to 
obtain a rotary distance of a different length. Thus this torque motor 
cannot easily be adapted to, e.g., valves with different strokes. 
Furthermore from EP application no. 34069 there is known a torque motor 
with a housing which has a centre part with coarse, internal screw 
threads. The cylinders are screwed fast to each side of the centre part. 
In the cylinders' heads there are mounted bearings for a spindle. A piston 
with coarse, external threads is screwed into the centre part and has 
internal, axially extending splines which engage with corresponding, 
external splines of the spindle. The piston can rotate about its own 
longitudinal axis. The pitch of the threads together with the pistons' 
axial movement in the cylinder determine the spindle's rotation. 
With this torque motor none of the components can be replaced for 
alteration of the torque motor's characteristics such as the required 
torque, rotary strokes and the like, without the hydraulic system being 
opened. Even though no alteration can be obtained of the motor's 
characteristics by replacing a spindle, even a replacement of this kind 
cannot be carried out without the hydraulic system being opened. The only 
alternative is replacement of the entire torque motor. Nor can the spindle 
be secured to the torque motor's housing in order to prevent rotation of 
the spindle and the bodies which are operated thereby when the pistons 
have been moved axially to a desired position. Moreover no device is 
described whereby an indication can be obtained when the end of the torque 
motor's stroke has been reached. 
SUMMARY OF THE INVENTION 
The object of the invention is to provide a torque motor of the type 
mentioned in the introduction which is not encumbered by the 
above-mentioned disadvantages. 
The characteristics of the torque motor according to the invention are 
indicated by the characteristic features presented in the claims.

DETAILED DESCRIPTION OF THE INVENTION 
In the following, the expressions "upper" and "lower" with reference to 
FIG. 2 will imply the relative location of sections and the like closer to 
the edge of the page of the drawing which faces away from and towards the 
reader respectively. 
As indicated in the figures the torque motor according to the invention has 
a cylindrical housing 1 which comprises a cylindrical lateral wall 2 and a 
lower and an upper end wall 3 and 4 respectively. Radially inwards from 
the section of the cylindrical lateral wall which is located substantially 
halfway between the ends, thereof, there extends a circular centre flange 
5 with a circular, central boring 6. 
In opposite recesses which extend coaxially in relation to the housing's 
lateral wall 2, in the housing's lower and upper end walls 3 and 4 
respectively there are radially secured axial bearings 7,8, whereby there 
is mounted a rotor 20. The rotor's end sections have a reduced diameter 
and project into an axially extending, through-going, central boring 14,15 
in the respective end walls 3,4. 
The bearings 7,8 are located with one side abutting against respective, 
axial shoulders at the rotor's end sections and with their other side 
against opposite surface sections of the recesses in the end walls 3,4. 
Through each of a number of axial borings 9 which extend through the upper 
end wall 4, there extends a screw 10, whose lower end section is screwed 
into threaded blind borings 11 in the lower end wall 3. On the upper end 
section of the screw 10 which projects above the upper end wall 4, there 
is passed a disc 12 and thereafter a nut 13 is screwed on, thus securing 
the end walls 3,4 via the disc 12 and to some extent pressing them against 
each other, and the rotor 20 can be turned, but not moved axially in 
relation to the housing 1. 
In the rotor's cylindrical outer surface there is provided a spiral groove 
21, whose ends 22 at the respective ends of the rotor 20 however extend 
substantially axially and are connected to the spiral section of the 
groove via a curved groove section 23. 
The rotor 20 has an axially through-going, central boring 24. In its lower 
section there is attached a sleeve or adaptor 25 which is arranged for 
attachment to a rotor of a valve (not shown), with the possibility of 
providing in the adaptor's inner wall an axially extending groove, which 
is adapted to axially extending teeth of the valve rotor's shaft. The 
valve body can be arranged for attachment to the torque motor's housing 1, 
e.g. via screws (not shown) which can be screwed into threaded borings 26 
in the housing's lower end wall 3. 
Between the housing's cylindrical lateral wall and the rotor's cylindrical 
outer surface there is provided a substantially cylindrical piston 30. 
This comprises a cylindrical connecting section 31 which extends coaxially 
with the rotor 20 and the housing 1. To the connecting section's lower end 
section there is attached by means of screws 32 a lower or first circular 
end flange 34, and to its upper end section there is attached by means of 
screws 33 an upper or second circular end flange 35. The end flanges 34,35 
project radially outward from the piston's cylindrical connecting section 
31 to close to the radially inner surface of the housing's cylindrical 
lateral wall 2. The piston 30 is provided in the housing 1 in such a 
manner that the end flanges 34,35 extend on each side of the housing's 
centre flange 5, considered in the housing's axial direction. The 
housing's lateral wall 2 and the centre flange 5 together with the 
piston's cylindrical connecting section 31 and the lower together with the 
upper end flange 34,35 define a lower and an upper annular cylinder space 
37 and 38 respectively. 
In the piston there are provided through-going, axial borings 36 
corresponding to the borings 9 in the upper end wall, the screws 20 with 
clearance also extending through the borings 36. Thus the piston can be 
moved axially, but cannot rotate in the housing 1. 
There extends radially inwards from the piston 30 at least one engagement 
element 39 which can be in the form of a cylindrical pin or the like, 
which projects into the groove 21 of the rotor, as there can be only a 
small clearance between the pin 39 and the lateral walls of the groove. 
In an annular groove in the radially inwardly facing, cylindrical surface 
of the boring 6 of the housing's centre flange 5, there is provided a ring 
joint, e.g. an O-ring 50 which provides a seal between the centre flange 5 
and the opposite cylindrical connecting section 31 of the piston 30. 
Furthermore in radially outwardly open grooves formed in the radially 
outwardly facing, cylindrical surfaces of the lower and the upper end 
flange 34,35, there is provided a ring joint, e.g. an O-ring 51 and 52 
respectively, which provides a seal between the end flanges 34,35 and the 
lateral wall 2 of the housing 1. 
In the housing 1, e.g. in its centre flange 5, there extend channels 53,54 
which lead into the respective lower and upper cylinder spaces 37,38, and 
which can be connected to a source and a reservoir and vice versa (not 
shown) for a pressure fluid, thus enabling the piston to be moved upward 
or downward in the housing 1. By means of the pin 39, the rotor 20 is 
hereby forcibly rotated in relation to the housing 1. 
In radially outwardly open, circumferential grooves which are provided in 
the rotor's end sections, there are fitted packings, e.g. O-rings 55 and 
56 respectively which abut against opposite, radially inwardly facing 
surfaces of the borings 14,15 in the end walls 3,4, thus preventing dirt 
from the space outside the torque motor from reaching the axial bearings 
7,8. 
Since the cylinder spaces 37,38 are not defined by the radially outer 
surface of the rotor in which the spiral groove 21 is provided, hydraulic 
fluid does not come into contact with this groove during the operation of 
the torque motor. 
Due to the axially extending groove section 22 of the groove 21, rotation 
of the rotor 20 can be prevented, i.e. the rotor is locked when the piston 
is located in the upper or lower end position in the housing and a torque 
is exerted on the rotor from outside, i.e. not from the motor's piston 30, 
whereby a valve spindle which may be connected to the rotor will also be 
locked. 
The upper bearing 8 can be easily removed by first removing the nuts 13 and 
the discs 12 and then the upper end wall 4 from the housing 1. The rotor 
can then be removed from the piston and the pin 39 by gripping the upper 
section of the rotor 20 and rotating the rotor in relation to the housing, 
thus causing it to be moved axially up and out of it until the pin 39 can 
finally be removed from the groove via the groove's open end. Thereafter a 
rotor, e.g., with a groove with a different pitch can be inserted into the 
housing, the pin 39 first being inserted into the groove's open end, 
whereupon the axial bearing 8 is put into position and the upper end wall 
4 is attached to the housing by screwing the nuts 13 on to the screws 10. 
The replacement of rotor and bearings can therefore be performed without 
the necessity of emptying hydraulic fluid from the cylinder spaces. 
The ease with which the rotors are replaced also permits easy replacement 
of the torque motor's hydraulic components while the rotor is still used, 
e.g. changing to a larger housing and piston which, e.g., provide a 
greater torque than the original housing and piston. 
It is stated above that the rotor 20 extends coaxially through the piston 
30, but it will be understood that it only requires to extend axially in 
relation thereto, i.e. in the piston's direction of movement. 
Even though a double-acting torque motor has been described above, it will 
be understood that it can be single-acting by providing a return spring 
for the piston. 
By providing additional axially extending groove sections, a locking can be 
achieved of the rotor and of a device driven thereby, e.g. a valve stem, 
in positions between the completely open and the completely closed 
positions of the valve. 
In order to give the operator of the torque motor an indication as to 
whether the piston has reached an end position in the housing 1, e.g. in 
order to denote that a valve which is connected to the torque motor has 
reached the completely closed position, an axial leakage boring 58 with a 
small diameter can be provided in the housing's centre flange 5, as 
indicated by a dotted line in FIG. 2. Moreover there can be provided on 
sides of the end flanges 34,35 which face each other, closing or seat 
areas 59,60, which are arranged to abut against respective openings of the 
boring 58 and seal it when the piston 30 is located in an end position and 
one of the end flanges 34,35 is located close to the centre flange 5. 
The boring 58 is so small that a leakage of fluid to the reservoir through 
it does not noticeably affect the function of the torque motor when a 
pressure fluid is added to one of the cylinder spaces from a pressure 
fluid source for operation of the torque motor. By measuring the pressure 
of the fluid in the return pipe to the fluid reservoir, however, it can be 
established thereby that the pressure of the return fluid is greater than 
the pressure in the reservoir. 
After the piston has reached the desired end position and the valve has 
consequently been closed, one of the closing areas 59,60 has abutted 
against the opening of the boring 58. The leakage of fluid has thereby 
been stopped and the pressure of the fluid in the return pipe has been 
reduced to the pressure of the fluid in the reservoir due to the missing 
small supply of pressure fluid. This pressure reduction which can be 
established by means of a pressure gauge, thus informs the operator that 
the valve is located in the closed position.