This invention relates to an actuator. More particularly, it relates to an actuator for use in petroleum activities, including a motor which, possibly via a gearing, drives a spindle, the spindle, when rotating, linearly displacing a displacement body.

During the setting and activation of, for example, plugs in boreholes or downhole pipes by means of coiled tubing or a wireline, electrically activated equipment is used increasingly often in order better to control the relevant setting forces.

As it is a question of relatively long supply lines for electrical energy here, and the maximum voltage is given by official regulations, the possible power on an electric motor is relatively limited.

To achieve sufficient power on the equipment which is to be activated, it is therefore necessary to drive the actuator with a relatively high transmission ratio. This results in the displacement proceeding slowly and the setting operation taking a disproportionately long time.

Often, the operation in question has a first phase in which, for example, gnppers are brought, with the motor under insignificant load, from a retracted, passive position into an extended position, for example close to a pipe wall. In a second phase, the grippers are brought under considerable power to grip in the pipe. The same conditions apply also when the grippers are to be released and retracted.

It is obvious that an actuator must be dimensioned for applying the highest power required to the tool.

Ideally, the motor should have had several rotational speeds or the gearing several transmission ratios. However, it has turned out that such solutions either require too much space or complicate equipment or operations too much. The invention has for its object to remedy or reduce at least one of the drawbacks of the prior art or at least provide a useful alternative to the prior art.

The object is achieved, according to the invention, through the features which are specified in the description below and in the claims that follow.

An actuator for use in petroleum activities is provided, the actuator including a motor which, possibly via a gearing, drives a spindle, the spindle, when rotating, linearly displacing a displacement body, and the actuator being characterized by there being an intermediate member arranged between the spindle and the displacement body, a first threaded connection being arranged between the spindle and the intermediate member and a second threaded connection being arranged between the intermediate member and the displacement body, the first and second threaded connections having different pitches, and at least one of the first and second threaded connections having a brake.

The threaded connection may consist of any suitable threaded connection and may be chosen differently for the first and second threaded connections. Examples of relevant threaded connections may be a usual V-thread connection, a trapezoidal-thread connection or a ball- or roller-screw connection, all with a single thread or parallel threads.

In particular cases, it may also be relevant to vary the thread pitch along the first or second threaded connection.

The first and second threaded connections have parallel or approximately parallel centre axes. Often, it is appropriate to arrange the threaded connections concentrically.

The braking may be used to determine which one of the first and second threaded connections is to be activated first, whereby the next threaded connection will be activated only when the braking torque is exceeded. The braking torque may be exceeded, for example, by the actuator encountering resistance or the threaded connection activated first hitting an end stop.

The one of the first and second threaded connections that has the smaller pitch may have a brake. Thereby the threaded connection that has the larger pitch will be activated first so that, for example, taking up slack or a positioning phase may be carried out relatively quickly, whereas the threaded connection with the smaller pitch is activated only when a certain torque has been exceeded, for example when the actual work or activating operation is to be carried out. At least one of the first and second threaded connections may be provided with a torque-releasable coupling for the brake function to be performed. The releasing torque of the coupling may be adjustable.

The coupling is typically rotatably connected to one of the components of a threaded connection and to the corresponding component of the same threaded connection via a releasable element, for example in the form of friction material or a claw coupling.

Normally, the motor of the actuator is electrically operated, but a hydraulically operated motor may be used in special cases.

By means of simple components working automatically, the device according to the invention enables an adjustable transmission in which maximum displacing force is ensured over the entire stroke length of the actuator as well.

In what follows, an example of a preferred embodiment is described, which is visualized in the accompanying drawings, in which :

Figure 1 shows schematically an actuator in accordance with the invention in its retraced starting position;

Figure 2 shows, on a somewhat smaller scale, the actuator in a first phase of the axial displacement; and

Figure 3 shows the same as figure 2, but in a second phase of the displacement.

In the drawings, the reference numeral 1 indicates an actuator which includes an electric motor 2 with a gearing 4, the motor 2 driving a threaded spindle 6 via the gearing 4.

The threaded spindle 6 fits complementariiy in a threaded, through-going bore 8 in an intermediate member 10. The connection between the spindle 6 and the intermediate member 10 constitutes a first threaded connection 12.

The intermediate member 10 is externally threaded and complementariiy fits an internally threaded displacement body 14. The connection between the intermediate member 10 and the displacement body 14 constitutes a second threaded connection 16, the displacement body 14 being prevented, for example by being connected to a plug or the like, not shown, from rotating with the intermediate body 10.

In this preferred embodiment, the first threaded connection 12 has a smaller thread pitch than the second threaded connection 16.

From an end portion facing away from the motor 2, the intermediate member 10 has been bored, with a partially threaded bore 18 extending in to a shoulder 20.

A braking sleeve 22, which is in the bore 18, is axially displaceable on the spindle 6 as it is in engagement in an axial groove 24 in the spindle 6 and thereby rotates together with the spindle 6. A friction disc 26 is placed between the braking sleeve 22 and the shoulder 20.

The braking sleeve 22 is pressed against the friction disc 26 by means of a spring 28 which is clamped between the friction disc 26 and an adjustment sleeve 32 which is axially adjustable by means of threads 30.

The braking sleeve 22, friction disc 26, spring 28 and adjustment sleeve 32, together with the spindle 6 and the intermediate member 10, form a coupling 34.

When, for example, a plug, not shown, connected to the displacement body 14 is to be set, the motor 2 is started. By the friction disc 26 being pressed against the intermediate member 10, the intermediate member 10 is prevented from rotating relative to the spindle 6. The second threaded connection 16 that has the larger thread pitch is thereby activated. The displacement body 14 is thereby moved relatively fast up to a position in which the displacement resistance increases so that the torque on the spindle 6 increases to above the set releasing torque of the coupling 34. As the coupling 34 releases, the first threaded connection 12, which has a smaller pitch, is activated, whereby the displacement body 14 is moved at greater force than what was possible by means of the second threaded connection 16.

Correspondingly, when the plug, not shown, is to be pulled out, the first threaded connection 12 is activated when there is a need for a relatively great release force, whereas the second threaded connection 16 with its relatively larger displacement speed takes over when it is no longer necessary to exert a great displacement force.