Patent Description:
Drive assemblies are used in many applications where a driving force is provided by an actuator such as a manual lever or a motor and the torque from the actuator is transmitted to a movable part along a drive line. For example, a valve may include a valve closure that is rotated by an actuator, either manually by means of a lever or handle or by means of a motor. The drive force from the motor is transmitted to the valve closure along a shaft arrangement, the shaft configured to transfer torque from the actuator to the valve closure. Particularly where the actuator is an electric motor, there is often a need to provide dielectric separation between the electrics and the moveable part especially if the movable part is in e.g. a wet environment, to avoid damage to the 'dry' motor end. On the other hand, it is necessary to maintain torque transmission along the entire drive line.

Ball valves are valves for controlling flow of a fluid e.g. water. The valve includes a ball shaft having a hole therethrough. The ball shaft is rotatable relative to the fluid flow channel such that when the hole is aligned with the channel, the valve allows fluid flow. To stop flow, the ball shaft is rotated so that the hole is not aligned with the flow. Ball valves can be operated manually e.g. by means of a handle for rotating the ball. Actuated ball valves are operated by a motor, which moves the ball shaft between the open and closed positions. Ball valves find use in e.g. sanitation or water systems. One application of a valve moved by an electric motor is in an aircraft water supply system. Aircraft commonly have a water supply system for providing potable water to various outlets e.g. to sinks or wash basins, coffee machines, toilets, etc..

One or more valve assemblies is provided in the system for the various outlets and at least some of these are driven by an electric motor so that they can be operated remotely or automatically. Such a system is described e.g. in <CIT>. The use of actuated ball valves is, however, not limited to aircraft water systems and there are many other fields of application for such systems.

Actuated ball valves comprise the motor and drive part, also known as the 'dry' part, and the ball shaft part, which comes into contact with the water, also known as the `wet' part. Seals need to be provided between the wet part and the dry part to avoid damage to the assembly by water getting to the electric motor.

In aircraft systems and in other water systems, the valve ball shaft often has to be made of metal to satisfy durability and safety standards. Problems may occur with the valve if a fault in the electric motor transmits to the ball shaft due to the conductive path between the various metal parts.

<CIT> discloses a torque transfer assembly according to the preamble of independent claim <NUM>.

The inventors have identified a need for a dielectric barrier to be provided between the two ends of a drive train e.g. between the ball shaft and the electric drive part of a ball valve assembly. The design should be capable of transmitting torque from the actuator end of the drive to the moveable part even in the event that the moveable part experiences some resistance e.g. becomes jammed or frozen such that a short torque peak is experienced.

According to the disclosure, there is provided a torque transfer assembly as defined by claim <NUM>.

The sleeve may be formed as a single piece. Alternatively, the sleeve may be shaped to define a plurality of sleeve sections each configured to fit around a corresponding one of a corresponding plurality of protrusions forming the second engagement feature and to fit into a corresponding one of a corresponding plurality of recesses forming the first engagement feature, the sleeve sections together defining a cross-shape.

The insert and the mating interfaces may be configured such that an air gap is defined between the drive shaft and the driven shaft when the shafts and the insert are assembled together.

The insert may be incorporated in a ball shaft assembly comprising a ball shaft as the driven shaft. A motor may be arranged to drive the ball shaft via a cam shaft, as the drive shaft, the insert being located between and in torque transfer engagement with the ball shaft and the cam shaft.

The ball shaft may be part of a water supply system e.g. an aircraft water supply system.

Preferred embodiments will now be described by way of example only, with reference to the drawings.

<FIG> is a perspective view of a motorised ball valve assembly including a dielectric insulation component according to the present disclosure.

The operational part of the valve comprises a ball shaft <NUM> having a head part 11a defining a hole <NUM> therethrough defining a flow passage, and a shaft part 11b extending from the head for engagement with a drive part of the assembly. In use, the valve is arranged in a water or fluid pipe system such that in a first rotational position of the ball shaft <NUM>, the hole is aligned with a fluid pipe to form a flow passage from the pipe and through the hole <NUM>. To switch off the flow, the ball shaft is rotated e.g. by one quarter turn, so that the hole is no longer aligned with the pipe and, instead, flow from the pipe is blocked by the body <NUM> of the ball shaft. Valves with several positions and several input/output ports are known.

In a motorised ball valve, the ball shaft is rotated by means of an electric motor <NUM>. The electric motor <NUM> drives a cam shaft <NUM> which engages with the ball shaft <NUM>. In the example shown (see <FIG>) the cam shaft <NUM> is provided with a key feature <NUM> that engages with a D-shaft <NUM> - i.e. a D-shaped shaft component extending from the motor. Rotation of the motor <NUM> causes rotation of the D-shaft <NUM> which, in turn, rotates the cam shaft <NUM> which rotates the ball shaft <NUM>. Seals e.g. O-rings (not shown) are provided around the ball shaft <NUM> to prevent water passing into the electric part of the assembly. The cam shaft may be provided with indicators such as microswitches (not shown) which can be mounted in recesses or races on the cam shaft <NUM>, or other forms of sensors or indicators, to provide an indication of the angular position of the shaft. These components are standard for a motorised ball valve such as described in <CIT>.

In the event that the motor fails, there is not only the risk of an electrical fault being transmitted to the wet end of the assembly, but there is also the problem that a motor failure will mean that the ball shaft cannot be rotated. In the event of failure of the motor, it may be necessary to change the position of the ball shaft to switch flow on or off. To address this, a manual handle <NUM> may be provided in close fitting arrangement around the ball shaft so that manual operation of the handle can rotate the ball shaft <NUM>. The handle can be fitted to the ball shaft such that there is a form fitting or frictional engagement between them. Alternatively, a fixing element e.g. a locking pin (not shown) may be provided to secure the handle to the shaft.

As mentioned above, to provide the required strength and to satisfy other standards such as safety, life and hygiene standards, the various shafts and the key feature will often be made of metal e.g. steel. If there is a problem with the electrics at the motor end of the assembly, these would be transmitted directly to the ball shaft and can cause problems such as electric shocks or arcing. To avoid this problem, the assembly of the present disclosure includes a dielectric insulator insert <NUM> to be fitted between the ball shaft <NUM> (or, more generally, driven end) and the electric motor <NUM> (or, more generally, drive end).

The dielectric insulation insert is structured to have dielectric properties and is shaped to provide torque transmission from the electric motor <NUM> to the ball shaft <NUM>. The shape of the insert should be such as to be able to withstand a short torque peak if the ball shaft end is fixed or blocked. To achieve the torque transfer property, the insert is shaped to define alternating flanges and recesses that engage with corresponding engagement features provided at the ball shaft and the electric motor. The important thing is that the insert has a shape that can engage with the shafts between which it is located in a manner that torque applied to one of the shafts is transferred to the other shaft via the insert.

The insert according to the disclosure may have different forms, as will be described further below, but it is a discrete component made from a body of dielectric material and has a shape arranged to mate with a corresponding shape on the cam shaft and/or the ball shaft or a bushing provided on the ball shaft <NUM>. The mating structure should be such that any misalignment can be accommodated. The insert is a simple, re-usable component easily manufactured from a readily available starting material which can be appropriately shaped and then easily slotted and secured between the cam shaft (or, more generally drive end) and the ball shaft (or, more generally, driven end) to ensure reliable torque transfer between the ends. In an example, particularly for use in wet or harsh environments, all of the components required for torque transfer are made of steel, particularly stainless steel expect for the dielectric insert <NUM> which functions as a dielectric barrier between the steel parts.

Whilst the insert may have different shapes, as described below, ideally, to ensure reliable torque transmission, the shape should be such as to define multiple points of engagement, as such a structure has been found to transfer the required torque optimally. The camshaft pushes the insert, and the insert pushes the ball shaft. Multiple forces act on distances to the centre of moment. In all examples, the insert and the mating parts of the drive end and the driven end should form a tight fit to reduce the effects of backlash and to ensure coaxiality. The inserts can be e.g. machined to shape from tubing or can be moulded to shape.

In one example, as shown in <FIG> the insert may be formed as a cross-shaped sleeve <NUM> of dielectric material that is arranged to be fitted between the cam shaft <NUM> and the ball shaft <NUM> to form a dielectric barrier. In this example, the insert <NUM> is mated with the cam shaft by an interface of the cam shaft <NUM> having a corresponding cross-shaped blind bore <NUM> formed therein that matches the outer shape of the insert <NUM>; the ball shaft <NUM> is provided with an interface that is formed as a protrusion <NUM> having a corresponding cross shape matching the inner shape of the insert <NUM>. Thus, in use, the insert <NUM> is fitted over the protrusion <NUM> at the interface to the ball shaft. The cam shaft <NUM> is then fitted to the ball shaft such that the blind bore <NUM> fits over the protrusion <NUM> sandwiching the sleeve <NUM>, in a tight fit, between the cam shaft and the ball shaft. The cam shaft and ball shaft are therefore tightly fitted together via the insert sleeve <NUM> such that rotation of the cam shaft causes rotation of the ball shaft by torque being transmitted through the joint with the insert.

In more detail, with reference to <FIG>, the dielectric insert <NUM> is in the form of a hollow cross having four arms <NUM>. The blind bore <NUM> in the cam shaft is a recess defining four portions <NUM> that match the shape of, and are arranged to closely receive the four arms of the insert <NUM>. The open, hollowed side of the insert fits over corresponding arms <NUM> of the cross-shaped protrusion <NUM> on the ball shaft <NUM>, again with a close fit.

As shown in <FIG>, the cross-shaped insert can be formed in various ways. The insert can be manufactured as a single piece as shown in <FIG> e.g. by moulding or additive manufacture. Alternatively, the insert can be formed from several individual pieces that are then placed with respect to each other to form the cross. As shown in <FIG>, each of the arms <NUM> of the cross could be formed as an individual segment <NUM> which combined form the cross shape. It may be simpler and more efficient to manufacture a large number of such simple shapes, rather than a ready-made cross-shaped insert. Further, using individual segments allows larger dimensional tolerances to be accommodated.

As shown in <FIG>, as the motor <NUM> rotates the cam shaft <NUM>, the resulting torque <NUM> from the rotating blind bore <NUM> engaging with the insert <NUM>, which is held in position on the protrusion <NUM> of the ball shaft, causes pressure loading <NUM> on the insert <NUM> which compresses and the torque is transferred to the ball shaft <NUM>. Engineering plastics such as PEEK, G10 or rubber (EPDM) such as used for the dielectric barrier show superior strength in compression compared to strength in the tension or shear directions.

The dimensions of the protrusion <NUM>, insert <NUM> and blind bore <NUM> in the axial direction may be designed, as shown in <FIG>, such that an air gap <NUM> is created between the cam shaft and the ball shaft to provide additional dielectric isolation at the perimeters of the shafts.

In another example, not forming part of the claimed invention, described with reference to <FIG> and <FIG>, the insert <NUM> may be formed as a cross-piece defined by two opposing essentially triangular cross-section flanges or wedges separated by similarly shaped recesses - this is in effect similar to the cross-shape described above but with the space between two of the four arms 'filled' as shown in <FIG> and <FIG>. The principle, however, is similar to that described in relation to the first example. The insert <NUM>' is fitted over the ball shaft protrusions <NUM>' such that the cam shaft is then fitted to the ball shaft whereby the protrusions <NUM>' fit into the recesses such that the dielectric insert forms a tightly fitted lining between the protrusions and the recesses and is able to transfer torque and provide a dielectric barrier in essentially the same way as the insert <NUM> described above.

In more detail, with reference to <FIG>, in this embodiment, rather than having four distinct arms defining a cross, as in the previously described example, the insert <NUM>' has two opposing hollow arcuate segments <NUM>' separate by two opposing recesses <NUM>' closed by a respective flange <NUM>'. The result is that the insert <NUM>' has a top surface defined by the arcuate segments <NUM>' separated by recesses <NUM>' and a bottom surface defined by the flanges <NUM>' separate by the hollow spaces beneath the arcuate segments.

The blind bore <NUM>' is shaped to have a corresponding shape of opposing arcuate recesses <NUM>'. The ball shaft protrusion <NUM>' comprises two upstanding correspondingly shaped arcuate protrusions <NUM>, <NUM> shaped to closely fit in the arcuate recesses <NUM>', between the flanges <NUM>' of the insert <NUM>. The top surface of the insert <NUM>' is arranged with the arcuate segments <NUM>' closely fitted into the arcuate recesses <NUM>' of the blind bore <NUM>'.

Variations on the shape of the cross-piece are shown in <FIG> shows the cross-piece just described. In an alternative design, as shown in <FIG>, the flanges <NUM>' on the bottom surface of the inert may be joined by a flange <NUM> extending around the full circumference of the insert. This provides a dielectric barrier without air gaps and allows a much higher insulation resistance. The alternative shown in <FIG> essentially splits the arcuate segments into two separate arms <NUM>', <NUM>' but retains the bottom flanges <NUM>' which results in a lighter, simpler insert, although one having less strength and stiffness. The revers arrangement would be to separate the bottom flanges into two separate arms and retain the arcuate segments (not shown). The variation shown in <FIG> separates both the bottom flanges <NUM>' and the arcuate segments <NUM>' into two separate arms forming a four-armed cross shape as described above.

According to the claimed invention, the contact surfaces of the insert which are configured to engage with the blind bore and the protrusions are not straight but, rather, have a convex or bowed shape. Such a shape maintains the contact area between the parts as explained with reference to <FIG>. The torque <NUM>' generated by the motor <NUM> is transferred through the parts by means of pressure loading <NUM>'. Because of the bowed shape of the engagement surfaces of the cross arms <NUM>, <NUM>' the contact points can be controlled. This is in contrast to two flat contacting surfaces. Two flat surfaces are never in perfect surface contact due to e.g. geometrical inaccuracies or imperfections. Here the engagement points are around the centre of the cross arms, thus contact is maintained. Different shapes can be formed to shift the contact point as required.

<FIG> illustrate the effectiveness of the resulting dielectric barrier. In one dimension (<FIG><NUM> being a section through the protrusions <NUM>' of the ball shaft <NUM>, an air gap <NUM>' is created as described for the first example which adds to the dielectric barrier effect. <FIG> shows the resulting structure as a section through the arms of the cross piece insert <NUM>'. <FIG> is a cross-section through the engaging parts of the blind bore in the cam shaft.

The dielectric insulation assembly provides electrical insulation between the dry and wet parts of the motorised ball valve assembly whilst ensuring torque transfer between the shafts of the respective parts. The insert must therefore have dielectric properties. Various dielectric materials are known and can be used, for example, but not exclusively, plastic, e.g. PEEK, G10, FR4, G11, FR5 etc., rubber (EPDM), ceramic or aluminium with an oxidized layer on the entire outer surface as a dielectric barrier. The material selected should have superior strength in terms of compression rather than in the tension or shear directions, as the torque is transferred in the compression direction as shown in <FIG> and <FIG>. Plastic and rubber materials allow the sleeve to buffer vibration or shocks sent by the motor through the system.

The insert can be quickly and easily fitted and does not require precise alignment, since it will naturally slot into the right shape even if initially located slightly out of alignment. It is therefore impossible to assemble the insert incorrectly. The tight fitting between the parts reduces the effect of any backlash and ensures reliable torque transfer. The shape is also such that coaxiality between the parts is ensured.

Claim 1:
A torque transfer assembly comprising a drive shaft (<NUM>) and a driven shaft (<NUM>) and a dielectric insert (<NUM>) arranged to be positioned between the drive shaft and the driven shaft, the insert assembly comprising a body of dielectric material shaped to form an insulating layer and configured to engage, respectively, with a first shaped engagement feature (<NUM>) on the drive shaft and a second shaped engagement feature (<NUM>) on the driven shaft, in torque transfer engagement, the insulating layer providing a dielectric barrier between the drive shaft and the driven shaft; and
wherein the dielectric insert defines four opposing arms (<NUM>), defining a cross, separated by recesses, each arm defining two opposing contact surfaces to respectively contact corresponding surfaces of the first or the second engagement feature, and a hollow space within the arms (<NUM>), the dielectric insert thus being in the form of a hollow cross; and
wherein the first or the second engagement feature comprises a cross-shaped blind bore (<NUM>) shaped to receive the arms, the blind bore defining surfaces arranged to contact the contact surfaces of the arms, and wherein the other of the first or the second engagement feature comprises a protruding cross (<NUM>) configured to engage within the hollow spaces of the arms of the dielectric insert; and
characterised in that
the contact surfaces have a convex or bowed profile.