This invention relates to an hydraulic linear actuator.

Conventional hydraulic linear actuators, when used in closed loop positional servo control systems, require the use of a positional transducer which is incorporated as a separate device in the mechanism being controlled. The positional transducer provides a feedback which is measured to enable adjustment of the actuator, more especially to adjust the stroke of the piston.

In general, therefore, a positional transducer, must be specifically matched to the particular stroke of the actuator, which is in turn a function of its specific application. Disadvantageously, therefore, even for similar applications differing combinations of transducer and actuator are required. A further disadvantage arises because positional transducers are generally not robust in comparison with the actuator, and are thereby liable to damage.

It is an object of this invention to provide an hydraulic linear actuator capable of minimising or overcoming the above-described disadvantages.

According to the invention, there is provided an hydraulic linear actuator having a linearly driven piston, wherein a mechanism is incorporated within the actuator and coupled to the piston to produce rotation of a member proportional to

incorporated within the actuator to sense the rotation of said member.

Thus , in acc ordance wi th the invent io n , the rotary transducer, which may be of a variety of types such as an opti cal sens or , electr ic ( potentio etr ic ) sen s or or electromagnetic ( inductive) sensor, is provided within the actuator. In addition, the transducer is inherently matched to the piston stroke, thus f aci litating the use of the identical transducer for differing actuator strokes .

In a practical arrangement, the actuator- piston is held against rotation and carr ies a nut formation within which engages a screwthreaded rod which constitutes the said member .

A tens ioned rod may pass through the piston to hold it against rotation. Alternatively, a non-circular piston may move in a matching non-circular bore.

The rotary transducer ( rotational position sensor) may be located at one end of the actuator in an enclosure sealed from the hydraulic chambers of the actuator and into which the rotationally driven rod extends from the ad jacent chamber. However, it is alternatively possible to locate the rotary transducer (if of an appropriate type) in one of the hydraulic fluid chambers. This simplifies sealing require¬ ments, since the rotationally driven rod is not required to pass through a sealed bore into a separate enclosure.

The invention will now be described further, by way of example, with reference to the accompanying drawings, in

•• which:- Figure 1 is an end view ^" of the actuator;

₅ Figure 2 is a longitudinal cross-section on the line 2-

2 of Figure 1; and

Figure 3 is a part longi tudinal cross-section on the line 3-3 of Figure 1.

Referring to the drawings, the hydraulic linear actuator has ₁₀ a hous ing 10 sealed by end closures 12 and 14. W ithin the hous ing 10 is a piston 16 connected to a pi ston rod 18 which emerges th rough the end c lo su re 12. The pi ston 16 i s linearly displaceable along the housing 10 by the passage of oil to or from hydraulic chambers 20 , 22 on oppos ite s ides _{1 5} of the piston 16. Port 24 (Figure 2) connects to the chamber 20 , and port 26 (F igure 3 ) connects through a pas sage 28 in the wall of the hous ing to the chamber 22. The piston 16 i s held against rotation by a tens ioned rod 30 f ixed between the end closures 12 and 14 and passing through said piston.

₂₀ A mechanism is incorporated within the actuator to produce a rotation proportional to piston di splacement, thereby to enable a rotational position sensor also to be incorporated

^ within the actuator body. The mechan i sm compr ises a nut assembly 32 located in a bore in the piston rod 18. This

It

₂₅ bore extends over a part of the length of the piston rod 18 to enable a screwthreaded rod 34, which is in screwthreaded engagement with the nut assembly 32, to extend therefrom out

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of the piston rod bore, through the hydraulic chamber 20 and thence through bearings 36 in the end closure 14 to the exterior of the latter. Two bearings 36 support the rod 34 for rotation under the drive of the nut assembly 32 when the piston 16 is linearly displaced, but hold such rod agains t longitudinal movement.

On the exterior of the end closure 14 an end cap 38 dif ines an enclosure into which extends the end of the rotationally driven rod 34. An 0-ring 40 (Figure 3 ) seals the rod 34 in the bore in the end closure 14 between the bearings 36, thus isolating the end cap enclosure from the adjacent hydraulic chamber 20. Within the end cap enclosure is located a rotational positional sensor 42, which may be a transducer of any of a variety of convenient types such as those previously mentioned.

I n use , the li near di sp lacement of the p i s ton 16 i s proportionately converted into rotational di splacement of the screwthreaded rod 34 , the rotation of which is detected and measured by the transducer 42. Clearly, the rotation sensed is inherently matched to the stroke of the actuator, however the latter changes as a function of the specific application to which the actuator is put.

In addition , the transducer 42 is wholly enclosed and thereby protected within the body of the actuator, whi ch includes the end cap 38 rigidly fixed to the end closure 14. If desired, moreover, the rotational position transducer 42 can a lterna t ively be i ncorpor ated w i th in one of the

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hydraulic chambers 20, 22, thus dispensing with the requirements for the end cap and also for seal 40, since the rod 34 is no longer required to extend beyond its bearings to the exterior of the end closure 14.

In a modified version of the above embodiment, alternative or additional transducers can be employed for measurement of velocity or acceleration.