WO2007036666A1 - High protection rigid electrical connection - Google Patents

Abstract

A plurality of electrical connection cables (12) are directed into a rigid tube (10) having an inner surface in close electrical contact with an inner, highly electrically conductive lining (28) such as aluminium or copper, thereby forming a high-frequency shielding for the electrical connection assembly. Said inner lining (28) may consist of a metal tube coupled to the rigid tube (10) via crimping or brazing, for instance. Said cables (12) are advantageously directed into recesses (24) provided in a profiled part (26) made, for example, of flexible plastic, extending within the rigid tube (10) over the length thereof.

Description

Rigid electrical link with high immunity.

Background of the invention

The invention relates to a rigid electrical connection with high immunity vis-à-vis the electromagnetic radiation comprising a rigid metal tube in which are guided several electrical connection cables.

A particular field of application of the invention is that of multi-channel sensors with several electrical connection cables connected to respective measurement probes housed in a sensor head. The connecting cables convey signals from the probes to circuits for processing and operating these signals. For various reasons, including congestion or difficult or hostile local environment, it may be necessary to have the signal processing and operating circuits at a distance from the measurement probes. A rigid electrical connection with high immunity against electrical radiation may then be required to facilitate assembly and protect the connection cables against possible damage and against electromagnetic disturbances likely to affect the electrical signals conveyed.

In the state of the art, such rigid connections with high immunity are known, for example for multi-speed sensors for rotational speeds of turbine engine shafts, in particular gas turbine engines. Measuring probes are arranged facing an encoder wheel rotatably connected to the low pressure turbine shaft for supplying signals measuring the speed of rotation of the shaft over several measurement channels. In a configuration known and commonly used for gas turbine engine aircraft, the electrical connection cables connected to the measurement probes are housed in a steel metal tube, one end of which is connected to a sensor head positioned in a support near the encoder wheel. The metal tube, which may be several tens of centimeters long, is guided for example along an engine support arm and is subjected to an elastic restoring force to maintain the sensor head and the probes in a desired position. Each connection cable is protected against electromagnetic interference by a low frequency shielding (BF) and shielding high frequency (HF) in the form of concentric layers or metallic braids. At each end of the connection, the RF shielding of the cables must be connected to the electrical ground by connection with the metal tube or a part connected to it. Terminal lugs for the RF shields must be provided, as well as lug fasteners, and welding operations must be performed, which is a sizeable fraction of the cost of the rigid electrical connection.

Obiet and summary of the invention

The object of the invention is to provide a rigid electrical connection with high immunity to electromagnetic radiation of simplified construction and construction and at a cost much lower than that of the known rigid connections mentioned above. This object is achieved by means of a rigid connection comprising a plurality of electrical connection cables guided in a rigid metal tube, a connection in which, according to the invention, the inner surface of the tube is in intimate electrical contact with an internal lining made of a good conducting material. electric to form a high-frequency shield for the entire electrical connection.

This eliminates the need to provide each connecting cable with a respective RF shield and connect the different RF shields to the electrical ground.

The inner liner is advantageously formed by a tube coupled to the rigid metal tube. The coupling of the tubes can be carried out mechanically by crimping or by brazing.

Advantageously, the inner lining is a metal lining formed at least mainly of copper and / or aluminum.

Preferably, the electrical connection cables are guided in housings formed in a profiled piece extending inside the rigid tube along it.

The housings are advantageously distributed around the periphery of the profiled piece and thus also provide a function of holding the electrical connection cables apart from each other. Advantageously, the profiled piece is made of a flexible material, for example a flexible plastic material, and thus ensures also a damping function vis-à-vis vibration undergone by the rigid metal tube.

The flexible material profile may contain metal charges that contribute to immunity to electromagnetic radiation.

The subject of the invention is also a sensor with several measurement channels, in particular a rotational speed sensor of a turbomachine shaft, comprising a plurality of measurement probes housed in a sensor head and a rigid electrical connection as defined above. and connected at one end to the sensor head for guiding electrical connecting cables connected respectively to the measurement probes.

Brief description of the drawings

Other features and advantages of the invention will become apparent from reading the description given below, by way of indication but not limitation, with reference to the accompanying drawings, in which;

- Figure 1 is a very schematic view of a turbomachine shaft speed sensor using a rigid electrical connection; FIG. 2 is a cross-sectional view on an enlarged scale illustrating an embodiment of a rigid electrical connection according to the invention; and

FIG. 3 is a cross-sectional view illustrating an alternative embodiment of the electrical connection of FIG. 2.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The invention finds particular application for multichannel sensors for guiding and protecting electromagnetic radiation from electrical connection cables connected to measurement probes housed in a sensor head. An example of such a sensor used as a rotational speed sensor of a turbomachine shaft is illustrated very schematically in FIG.

Several measurement probes (three in the example shown) are housed in a sensor head 2 which is received in a fixed support (not shown) so as to be positioned opposite a coding wheel 4. The wheel 4 is secured to in rotation of a tree 6 of turbomachine whose rotational speed is to be measured, for example a low-pressure turbine shaft of a gas turbine engine. The sensor is for example of the magnetic type with variable reluctance. In a well-known manner, each probe comprises a pole piece 8 forming, with a permanent magnet and the toothed wheel, a magnetic circuit whose air gap, between pole piece and wheel, varies with the running frequency of the teeth of the wheel in front of the wheel. probe. A coil mounted on the pole piece provides a signal representative of the speed of rotation. Of course, sensors of other type, for example capacitive type, can be used.

The signals collected by the coils of the measurement probes are conveyed by respective electrical connection cables guided in a rigid tube 10, such as a metal tube, and forming therewith a rigid electrical connection. The tube is connected at one end 10a to the sensor head 2. At its other end 10b, the tube 10 can be subjected to an elastic restoring force in order to maintain the sensor head in the desired position on its support, with respect to the control wheel 4. The electrical connection cables 12 leave the tube 10 at the end 10b to be connected to circuits (not shown) for processing and operating the signals of the measurement probes. As a variant, the electrical connection cables could be connected to a connector located at the end 10b of the tube 10. In the case of a low-pressure turbine turbine shaft rotation speed sensor of a gas turbine engine, two measurement channels (including a redundant one) may be for a full authority control circuit (FADEC) of the engine and an additional channel may be for providing flight information to the cockpit.

One embodiment of rigid electrical connection according to the invention is illustrated in FIG.

The electrical connection cables 12 (here three in number) each comprise two conductors 14 forming a two-wire link. The conductors 14 may be traditional commercial BF shielded conductors. They are for example housed in an insulating flexible tubular casing 16 with, optionally, filiform elements 18 wedging arranged parallel to the conductors. A shielding BF 20, for example in the form of a tinned copper or nickel-plated braid or stainless steel is disposed on the insulating casing 16 and is itself covered by an insulating flexible tubular casing 22 forming the outer casing of the connecting cable 12.

The cables 12 are advantageously guided inside the rigid tube 10 being arranged in housings 24 of a section 26 of flexible material such as a plastic material, for example silicone. The profile 26 extends along the tube 10, with the housing 24 formed at its periphery substantially at equal distances. The profile 26 thus provides a function for guiding the cables 12, holding them in spaced apart positions (limiting interference between the measurement channels), and vibration damping, by its flexible nature.

To provide immunity in the HF domain, a lining 28 covers the inner surface of the tube 10, the lining 28 being metallic, typically consisting, at least essentially, of copper and / or aluminum. The tube 10 is preferably metallic, for example steel, and the liner 28 is in intimate electrical contact with the tube 10 to form therewith a low electrical conductivity assembly constituting an efficient RF shield.

The liner 28 may be formed by an inner metal tube which is intimately coupled to the inner surface of the tube 10. The coupling between the two tubes may be made by crimping, for example by insertion of the inner tube 28 into the tube 10 and drawing of this last. Coupling can also be achieved by soldering. One could also consider forming the lining 28 by metal deposition on the inner surface of the tube 10. As shown in Figure 2, the profile 26 occupies virtually the entire internal volume of the tube 10 provided with the lining 28, and the housing 24 s open at the periphery of the profile 26, but with openings 24a of width preferably less than the diameter of the cables 12. These are therefore retained in their housing. The profiled piece 26 made of plastic material can be loaded with metal particles, helping to perfect the shielding of the cables 12.

Although it has been considered above an application to a rotational speed sensor of a turbomachine shaft, a rigid connection with high immunity according to the invention can be used in other applications as soon as a guidance of several connecting cables and their immunization against electromagnetic disturbances are necessary.

Of course, the number of cables 12 may be different from 3. Thus, Figure 3 shows a rigid connection which differs from that of Figure 2 in that it comprises 4 cables 12 guided in housing 24 of a profile flexible 26, inside the tube 10 provided with the inner metal lining 28, the housing being regularly distributed at the periphery of the section 26.

Claims

1. Rigid electrical connection with high immunity to electromagnetic radiation comprising a plurality of electrical connection cables (12) guided in a rigid tube (10), characterized in that the inner surface of the tube (10) is in electrical contact intimate with an internal lining (28) of good electrical conductor material to form a high-frequency shield for the entire electrical connection. 2. Connection according to claim 1, characterized in that the inner lining (28) is formed by a metal tube coupled to the rigid tube (10). 3. Connection according to any one of claims 1 and 2, characterized in that the tubes (10, 28) are coupled by crimping. 4. Connection according to any one of claims 1 and 2, characterized in that the tubes (10, 28) are coupled by brazing. 5. Connection according to any one of claims 1 to 4, characterized in that the inner lining (28) is at least substantially copper and / or aluminum. 6. Connection according to any one of claims 1 to 5, characterized in that the cables (12) are guided in housing (24) formed in a shaped piece (26) extending inside the rigid tube (10) therealong. 7. Connection according to claim 6, characterized in that the profiled piece (26) is of flexible plastic material. 8. Connection according to claim 7, characterized in that the flexible plastic material contains metal charges. 9. Sensor with several measurement channels comprising several probes housed in a sensor head and a rigid electrical connection according to any one of claims 1 to 8, one end of which is connected to the sensor head for guiding electrical connection cables respectively connected to the measurement probes. 10. Rotation speed sensor of a turbomachine shaft with several measurement channels, comprising a plurality of measurement probes housed in a sensor head intended to be placed opposite an encoder wheel coupled in rotation to the shaft of the turbomachine and a rigid electrical connection according to any one of claims 1 to 8, one of which end is connected to the sensor head to guide electrical connection cables respectively connected to the measurement probes.