EP1112450A1

EP1112450A1 - Pneumatic or hydraulic operating device

Info

Publication number: EP1112450A1
Application number: EP99969137A
Authority: EP
Inventors: Per Lundqvist
Original assignee: NAF AB
Current assignee: NAF AB
Priority date: 1998-09-10
Filing date: 1999-09-07
Publication date: 2001-07-04
Also published as: AU6015799A; SE9803060D0; WO2000015964A1; SE514794C2; SE9803060L

Abstract

Pneumatic or hydraulic operating control device (10), which has a cylinder (11), which is defined in its longitudinal direction by an end (12) on both sides, thereby defining and enclosing a cylinder chamber (13), a rotary shaft (16) arranged transversely to the longitudinal direction of the cylinder (11) and supported outside the cylinder chamber (13), two pistons (14) running in a longitudinal direction in the cylinder chamber (13) and arranged so that they move towards the rotary shaft (16) when a force is made to act on that side of each piston (14) situated nearest each end (12) respectively, and in the opposite direction when a force is made to act on the opposite side of the pistons (14), the rotary shaft (16) being arranged so that it turns in connection with the said piston movements in the longitudinal direction of the cylinder (11). Each piston (14) is provided with a projecting part, piston rod (14A, 14B), which is designed, as the piston (14) moves longitudinally, to be capable of passing unimpeded outside the rotary shaft (16). A driving pin (17) is articulated at a bearing point (18) in each of the said two piston rods (14A, 14B), and that the two driving pins (17) are arranged at a distance from one another along the rotary shaft (16) in order, through a longitudinally moveable connection (20) with the rotary shaft (16), to translate the reciprocating movement of the pistons (14) in a longitudinal direction into a clockwise or anticlockwise rotational movement of the rotary shaft (16). At least one of the driving pins (17) for the said moveable connection (20) is arranged extending through a cavity in the rotary shaft (16) formed transversely to the direction of the rotary shaft (16) and so that the driving pin (17) is capable of sliding in relation to the rotary shaft (16). One of the driving pins (17) for the said moveable connection (20) may alternatively be arranged so that it can run freely in grooves let into the rotary shaft (16) or arranged on its outside.

Description

PNEUMATIC OR HYDRAULIC OPERATING DEVICE

The present invention relates to a pneumatic or hydraulic operating control device intended, for example, for quarter-turn operating control of valves or the like, the device having a cylinder, which is defined in its longitudinal direction by an end on both sides, thereby defining and enclosing a cylinder chamber, a rotary shaft arranged transversely to the longitudinal direction of the cylinder and supported outside the cylinder chamber, two pistons running in a longitudinal direction in the cylinder chamber and arranged so that they move towards the rotary shaft when a force is made to act on that side of the pistons situated nearest each end respectively, and in the opposite direction when a force is made to act on the opposite side of the pistons, the rotary shaft being arranged so that it turns in connection with the said piston movements in the longitudinal direction of the cylinder.

There are a number of different types of pneumatic or hydraulic operating control devices on the market nowadays, primarily intended for the operating control of quarter-turn valves. Such valves include, for example, ball valves, spherical sector valves and rotary throttle valves. Common to all operating control devices is the fact that they convert a force from one or more pistons into a rotational movement of a shaft in the operating control device. The shaft is then in turn coupled to the spindle of the valve and thereby controls the valve.

Most operating control devices are based on the principle that one or more pistons are acted upon by the pressure from a pressure medium, generally compressed air, water or oil, and then perform a linear movement in one or more cylinders. A corresponding force may also be generated mechanically, for example by pressure from a spring or the like. Such spring-transmitted force may be combined with a pneumatic or hydraulic function and thereby eliminate problems that can occur in the event of accidental failure of the pneumatics or hydraulics, for example in the event of an electrical power failure.

By connecting the piston(s) via a mechanism to a shaft in the operating control device, the force of the piston(s) will be converted to a torque and the linear movement of the piston(s) will thereby be translated into a rotational movement of the rotary shaft. The mechanism connecting the piston(s) to the rotary shaft is based in almost all cases on one of the following principles:

* Rack gearing

* Scotch yoke * Linkages

The rack gearing device comprises one or more pistons, which at one end comprise a spherical segment. The said spherical segments then go towards the shaft, which is in turn designed as a "pinion". When the piston moves along the cylinder the racks will turn the shaft and a torque is generated. The torque will not vary according to the angle of torsion (provided that the drive pressure is constant). There are many disadvantages to this type of device including the fact that the constant operating control torque does not closely match the torque demand of the valves and that the linear contact between the racks gives a very high contact pressure with a strong tendency to loose fitting and fatigue damage as a result.

Scotch-yoke devices are a solution in which a roller (of roller bearing type) is fixed at one end of the piston. A plate having grooves in which the rollers can run is fixed to the shaft of the device. The torque curve in this case produces the highest torque at the extreme positions of the pistons and the lowest torque in the mid-position of the pistons. The advantages of such devices include the fact that the shape of the torque curve often closely matches the torque demand of the valve. A serious disadvantage, however, is that the roller and the groove in which it runs are exposed to a high surface pressure owing to the linear contact with a tendency to loose fitting and fatigue damage.

Linkage devices are principally manufactured by valve manufacturers. In most cases these devices are designed so that one or two pistons are seated on a piston rod, which is in turn coupled to the rotary shaft by means of a linkage mechanism. The advantages include the fact that all forces are absorbed by way of plain bearings, which in turn results in a wide distribution of the force with relatively low surface pressure as a result. The appearance of the torque curve may vary, but as with the Scotch yoke device a torque curve that closely matches the torque demand of the valves can be obtained. The disadvantage with the linkage devices is that they are comparatively expensive to manufacture, due among other things to the many constituent parts. Another basis on which to classify operating control devices of the type described above is the structure of the piston-cylinder function. A first type includes the compact devices in which the rotary shaft is seated directly in the cylinder. In this case it must be sealed so that the pressure in the cylinder is not dissipated. Such compact devices have the advantage of low volumes and the fact that that they are relatively cheap to manufacture. As far as is known, devices of this type on the market are nowadays always constructed as rack gearing devices or Scotch yoke devices, as described, for example, in US-A-3253518 and DE-A-3925887. The disadvantage with the designs of compact device available, rack gearing devices and Scotch yoke devices is, as indicated above, that they are both based on a linear contact between force-transmitting parts and that they are therefore subjected to high surface pressures, which means that the contact surfaces wear out relatively quickly. These types of device are therefore often regarded as unsuitable for use in more demanding applications.

Another type is the device with separate housing and cylinders, and nearly all linkage devices belong to this type. In this "housing and cylinder" type the linkage mechanism is accommodated together with the rotary shaft in a housing separate from the cylinder(s). An important advantage with this type of device is the fact that cylinders with different diameters can be fitted to one and the same housing, thereby compensating for low air pressure, for example. Another advantage is that it is easier to design the rotary shaft as a hollow shaft, into which the spindle from the valve can project. Such a device is described in FR-A-2139731, in which two pistons are connected to a centrally arranged piston rod and to a recess therein, which accommodates the end and the point of attachment for a strong driving pin, which in turn acts upon and turns the rotary shaft. There are essential disadvantages to operating control devices of the "housing and cylinder" type, for example the fact that they are often expensive to manufacture, since they take a comparatively long time to assemble, due among other things to the large number of constituent parts, and the majority of these parts are also expensive to manufacture. In addition, operating control devices of this type are made relatively much longer than corresponding compact devices, which is awkward not least when the space around pipelines in processing industry is often very restricted. Devices of the "housing and cylinder" type are therefore nowadays regarded as expensive, too complicated, too bulky and difficult to find space for.

It is obvious that compact devices present many advantages compared to devices with separate housing and cylinders and, apart from being expensive to manufacture, they are largely standardised with regard to the interface, both with the valve on the underside of the operating control device, and with the valve position adjusters or indicators on the top of the device, and also with connections of solenoid valves. That no compact devices have yet been designed with a power transmission mechanism other than rack gearing or Scotch yoke devices with their known limitations and mechanical disadvantages previously described, despite the fact that these devices have been known for some 20 to 25 years, is presumably due to the fact no such suitable alternative transmission mechanism, such as a simple and practical linkage design, for example, has been forthcoming.

The aim of the invention is therefore to provide an operating control device that combines the advantages of the compact devices with the advantages of linkage devices, producing an operating control device that is cheap to manufacture, easy to fit even into confined spaces, and which is in addition resistant to wear and can therefore be used for more demanding applications, for which known operating control devices of compact type are not regarded as suitable. To this end the operating control device according to the invention has the features set out in the associated claims.

The invention thus relates to a pneumatically or hydraulically acting operating control device, provided with two pistons and a rotary shaft, and of the type defined in the introductory part. Each piston of the device is provided with a projecting part, which is designed, as the piston moves longitudinally, to be capable of passing unimpeded outside the rotary shaft and thereby to serve as piston rod. A driving pin is articulated at a bearing point in each of the said two projecting piston parts and arranged, through a longitudinally moveable connection with the rotary shaft, so as to translate the reciprocating movement of the pistons in a longitudinal direction into a corresponding clockwise or anticlockwise rotational movement of the rotary shaft. One of the driving pins is then arranged above the other, measured along the rotary shaft. Each driving pin is then arranged either extending through a cavity formed in the shaft transversely to the direction of the shaft, or is arranged so that it can run freely in grooves arranged in the rotary shaft or externally on the outside of the shaft, but in both cases so that the pin is capable of sliding in relation to the shaft. Both of the pistons may be provided with arrangements for adjustment of the limit position at one or both of the limit positions in the longitudinal direction of the cylinder. The bearing point of the driving pin in each cylinder is preferably situated in immediate proximity to the inner surface of the cylinder. A bearing or low-friction surface coating can then be suitably arranged between shaft and driving pin. The projecting part of the pistons, the piston rod, can also be arranged so that, with the reciprocating movement of the pistons, lateral forces towards the rotary shaft or cylinder surface are absorbed.

Designing the two pistons in a twin-piston operating control device with projecting parts which at the same time function as separate piston rods, each of which in turn interacts with its driving pin and which in turn is separately connected to the rotary shaft, the one widthways or, viewed along the shaft, above the other, has the- advantage that drivers, piston rods and rotary shaft can be made with such small dimensions or cross-section that it is possible to design a twin piston operating control device in the form of a compact device with the essential advantages that are thereby achieved and which have been discussed above.

The invention will now be described in more detail with reference to the drawing, in which figure 1 is a longitudinal view of an operating control device in a preferred embodiment according to the invention in cross-section, figure 2 shows the same operating control device in cross-section along the line A-A in figure 1, and figure 3 shows a longitudinal view in cross-section of an operating control device provided with limit position adjustment.

Figures 1 and 2 show an operating control device designed according to a preferred embodiment, which is defined by a cylinder 1 1 and ends 12 at each end of the cylinder 11. The cylinder 1 1 and the ends 12 thereby together enclose a closed cylinder chamber 13. In the cylinder chamber 13 there are two pistons 14, opposed to one another and arranged so that they can perform a reciprocating movement in the cylinder chamber 12 whilst forming a seal against the cylinder 1 1. Each piston 14 has a seal 15 bearing tightly against the cylinder 1 1. Each piston 14 has a projecting part, the piston rod 14A,B, in each case pointing away from the nearest end 12. The piston rod 14A,B of each piston 14 is adapted so that, with the reciprocating movement of the piston, it can pass unimpeded by the side of a rotary shaft 16, which is rotatably supported (at position 16 A) through the cylinder chamber 13. The rotary shaft 16 is in turn provided with a bearing 16B, which absorbs the load from the projecting part 14A,B of the piston 14. A driving pin 17, which is articulated in the piston part 14A at a bearing point 18 with a bearing journal 18 A, which passes through a circular hole accommodated in the piston part 14A,B and the driving pin 17, is fixed to the piston rod 14A,B of each piston. The bearing journal 18 A is shown provided with a bearing or smooth surface coating 19, but the reverse can also occur, that is one in which the bearing journal 18A is capable of moving in a bearing located in the actual piston 14. In the embodiment illustrated here the journal 18A is thus firmly seated in the piston and the driving pin 17 has a bearing 19 and turns around the journal 18 A.

The piston rods 14A,B and the driving pins 17 are separately connected to the rotary shaft 16 and, as will be seen from figure 2, to the one pin above the other pin viewed in the longitudinal direction of the shaft. The driving pin 17 has a longitudinally moveable connection 20 to the rotary shaft 16, arranged so that a reciprocating movement of the piston 14 imparts a torque to the to the rotary shaft 16. This condition is illustrated here in that the pin 17 is arranged so that it can run freely through a hole diametrically arranged through the rotary shaft 16. The moveable connection 20 between the driving pin 17 and the rotary shaft 16 can, if so wished, naturally be designed in some other way within the framework of the invention, for example through grooves let into the surface of the shaft or through a connection arranged on the outside of the shaft surface, for example a soldered pipe section with smooth inner surface. The diving pin 17 in this way slides in its longitudinal direction relative to the rotary shaft 16, but consequently at the same time imparts a torque to the rotary shaft 16 when the piston 14 perfomis a reciprocating movement in the cylinder chamber 13, which responds if a force is made to act on one or the other side of the piston 14. Between the driving pin 17 and the rotary shaft 16 there is a bearing 21 in order to facilitate the reciprocating slide movement of the pin 17 through the rotary shaft 16. The piston rods 14A,B of the two pistons 14 are arranged so that the piston rod 14B of the right-hand piston lies on one side of the rotary shaft 16, whilst the piston rod 14A of the left-hand piston lies on the opposite side. The location of the piston rods 14A and 14B respectively shown in figure 1 is naturally just one example of how these parts can be arranged and they can thus change places without changing their function, except that the rotary shaft 16 will in that case be turned in a different direction from that in the example shown.

Figure 3 shows a detail of an operating control device 10 with cylinders 1 1 , ends 12, rotary shaft 16 and the driving pin 17 identical to the embodiment described in figures 1 and 2, but for the sake of clarity only one of the pistons 14 is shown, which is shown provided with a limit position adjusting screw 22, which is fixed in one end 12 and which runs in a recess 22 in the piston rod 14A. In operation, a force is applied, for example in the form of a pneumatically or hydraulically generated pressure, against the pistons in the cylinder chamber 13 of the operating control device, either between the pistons 14 or between each piston 14 and adjacent end 12. If the force is applied between the two pistons 14 these will each move towards the end 12 closest each of them respectively and in the embodiment illustrated here the driving pin 17 will be therefore turned clockwise, thereby also imparting a corresponding clockwise rotation to the rotary shaft 16. If force is applied to the pistons 14 outside these, that is to say between each piston 14 and the end 12 nearest each of them, the driving pin 17 will be turned anticlockwise and will thereby also impart an anticlockwise rotation to the rotary shaft 17. If the projecting parts, that is to say the piston rods 14A and 14B respectively of the pistons are reversed, or in other words change places, the rotary shaft 16, as indicated above, will be turned in opposite directions to those shown and discussed here.

The many advantages of the new operating control device include:

1. All power transmission occurs through a diffused load distribution by way of two pistons with a single linkage system, resulting in both a long service life and small degree of play. ("Normal" plain bearings or surface treatment are used both in the driving pin mounting in each piston and in the driving pin bearing in the rotary shaft).

2. Due to the fact that each driving pin is articulated in the piston, the bearing point can be situated closer to the cylinder surface, thereby maximising the lever arm to the centre of the rotary shaft. This results in a maximum utilisable torque for any given cylinder diameter.

3. The pin is allowed to utilise the full diameter of the rotary shaft at all times.

4. Because the device is designed as a compact device, which is possible due to the specific power transmission to the driving shaft with two separate piston rods and driving pins, this makes it particularly suitable for fitting in confined spaces, for example in processing industry.

Claims

1. Pneumatic or hydraulic operating control device ( 10), which has a cylinder (1 1), which is defined in its longitudinal direction by an end (12) on both sides, thereby defining and enclosing a cylinder chamber (13), a rotary shaft (16) arranged transversely to the longitudinal direction of the cylinder (1 1) and supported outside the cylinder chamber (13), two pistons (14) running in a longitudinal direction in the cylinder chamber (13) and arranged so that they move towards the rotary shaft (16) when a force is made to act on that side of each piston (14) situated nearest each end (12) respectively , and in the opposite direction when a force is made to act on the opposite side of the pistons (14), the rotary shaft (16) being arranged so that it turns in connection with the said piston movements in the longitudinal direction of the cylinder (1 1), characterised in that each piston (14) is provided with a projecting part, piston rod (14A, 14B), which is designed, as the piston (14) moves longitudinally, to be capable of passing unimpeded outside the rotary shaft ( 16), in that a driving pin ( 17) is articulated at a bearing point ( 18) in each of the said two piston rods (14A,14B), and that the two driving pins (17) are arranged at a distance from one another along the rotary shaft (16) in order, through a longitudinally moveable connection (20) with the rotary shaft (16), to translate the reciprocating movement of the pistons (14) in a longitudinal direction into a clockwise or anticlockwise rotational movement of the rotary shaft (16).

2. Operating control device according to claim 1, characterised in that at least one of the driving pins (17) for the said moveable connection (20) is arranged extending through a cavity in the rotary shaft ( 16) formed transversely to the direction of the rotary shaft (16) and so that the driving pin (17) is capable of sliding in relation to the rotary shaft (16)

3. Operating control device according to claim 1, characterised in that at least one of the driving pins (17) for the said moveable connection (20) is arranged so that it can run freely in grooves let into the rotary shaft (16) or arranged on its outside.

4. Operating control device according to any of claims 1 to 3, characterised in that at least one piston (14) is provided with an arrangement (22) for limit position adjustment at one or both limit positions in the longitudinal direction of the cylinder (1 1).

5. Operating control device according to any of claims 1 to 4, characterised in that the bearing point (18) of the driving pin (17) in each piston (14) is situated in immediate proximity to the inner surface of the cylinder (1 1).

6. Operating control device according to claim 2, characterised in that a bearing or a low-friction surface coating (21) is arranged between rotary shaft (16) and driving pin (17).

7. Operating control device according to any of claims 1 to 6, characterised in that the projecting part (14A, 14B) of the piston or the pistons is arranged so that, with the reciprocating movement of the piston or pistons, it absorbs lateral forces towards the rotary shaft (16) or cylinder surface (1 1).