GB1594703A - Inductive couplings - Google Patents

Description

(54) IMPROVEMENTS RELATING TO INDUCTIVE COUPLINGS (71) We, FERRANn LIMITED a Company registered under the Laws of Great Britain of Hollinwood in the County of Lancaster do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: THIS INVENTION relates to inductive couplings, and in particular to such couplings for passingsinaIs between a piston and a cylinder block of an internal combustion engine.

The problem of transferring electrical signals between two relatively movable bodies has existed for a long time, and many solutions have been proposed. In the case of linear movement over a limited distance either flexible cables or rubbing contacts have been used. Both of these solutions suffer from the usual mechanical problems; cables will not withstand continuous reciprocating movement indefinitely, and rubbing contacts suffer from the usual problem of wear. In addition, such solutions are not satisfactory under hostile conditions, say in a high temperature and perhaps dirty environment.

It is an object of the invention to provide an inductive coupling for transferring electrical signals between two bodies capable of limited movement relative to one another.

According to the present invention there is provided an inductive coupling for use in an internal combustion engine and capable of transferring electrical signals from a reciprocating piston to an associated cylinder block, which includes a core of magnetic material carried by the cylinder block and having a portion which extends parallel to the direction of linear movement of the piston and of a length greater than the maximum extent of said movement, a first coil carried by the piston for movement therewith and formed around said portion of the core, and a second coil carried by the cylinder block and formed around part of the core other than that over which the first coil is able to move, the arrangement being such that the inductive coupling between the first second coils remains constant regardless of the relative positions of the tow coils.

Preferably the core is shaped to form a closed magnetic circuit.

The invention will now be described with reference to the accompanying drawings, which illustrate its application the testing of internal combustion engines.

In the embodiment to be described, the application relates to the sensing of temperature, and possibly other parameters, inside the cylinder of an internal combustion engine. The temperatures and pressures present may be very high, and the piston on which sensors are carried, moves very rapidly along a linear path. In addition, the environment below the piston is also hostile, due to the presence of hot oil in the crankcase of the engine. These factors have made earlier attempts unsatisfactory to varying extents.

Referring now to the drawing this shows, in schematic form, part of the cylinder block 10 of an internal combustion engine, including a section of one cylinder. A piston 11 is located in the cylinder and moves in a straight line along the axis 12 its upper surface travelling between limits indicated by the dotted lines 13. A connecting rod 14 connects the piston 11 to the rotating crankshaft 15.

A thin rod 16 is attached to one side of the piston 11 so as to extend clear of the cylinder block in all positions of the piston, and a coil 17 is mounted on the end of this rod. The coil may be connected, for example, to a temperature sensor 18 mounted on the crown of the piston.

Supported on the cylinder block 10 is a core 19 of magnetic material, in this example, in this example forming a D-shaped loop. The core has a straight portion 20 extending parallel to the axis of movement 12 of the piston 11. The coil 17 is positioned around this portion 20 of the core, which has a length greater than the stroke of the piston.

A fixed coil 21 is positioned around some other part of the closed-loop core 19. Electrical connectors lead from the coil 21 to the outside of the engine.

In operation, any alternating voltage gen erated by the sensor will be inductively coupled through the core 19 regardless of the position of the piston and hence a measureable voltage will be developed across the coil 21 to provide an external output.

The rod 16 need not be straight as shown, but it must be shaped to clear the block in all positions of the piston. As alreadv stated the shape of the core 19 is not critical so long as there is a straight portion 20 of the necessary length. The core may conveniently be made from a ferrite material.

Since the coupling between coils 17 and 21 is inductive, the output from the sensor must be of alternating form. Some types of sensor, particular temperature sensors such as thermistors will require to be supplied with an alternating supply by some suitable means.

In the particular application described it may be necessary to couple the outputs of a number of sensors. Several devices of the type described may be used, or alternatively suitable multiplexing or scanning arrangements may be employed.

The invention may, of course, be applied in fields other than the testing of internal combustion engines. Any situation presenting limited linear movement in a hostile environment may present a requirement for the technique described.

WHAT WE CLAIM IS: 1. An inductive coupling for use in an internal combustion engine and capable of transferring electrical signals from a reciprocating piston to an associated cylinder block, which includes a core of magnetic material carried by the cylinder block and having a portion which extends parallel to the direction of linear movement of the piston and of a length greater than the maximum extent of said movement, a first coil carried by the piston for movement therewith and formed around said portion of the core, and a second coil carried by the cylinder block in a fixed position relative to the core and formed around part of the core other than that over which the first coil is able to move, the arrangement being such that the inductive coupling between the two coils remains constant regardless of the relative positions of the two coils.

2. A coupling as claimed in Claim 1 in which the core is formed into a closed magnetic circuit.

3. An inductive coupling for use in an internal combustion engine substantially as herein described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. erated by the sensor will be inductively coupled through the core 19 regardless of the position of the piston and hence a measureable voltage will be developed across the coil 21 to provide an external output. The rod 16 need not be straight as shown, but it must be shaped to clear the block in all positions of the piston. As alreadv stated the shape of the core 19 is not critical so long as there is a straight portion 20 of the necessary length. The core may conveniently be made from a ferrite material. Since the coupling between coils 17 and 21 is inductive, the output from the sensor must be of alternating form. Some types of sensor, particular temperature sensors such as thermistors will require to be supplied with an alternating supply by some suitable means. In the particular application described it may be necessary to couple the outputs of a number of sensors. Several devices of the type described may be used, or alternatively suitable multiplexing or scanning arrangements may be employed. The invention may, of course, be applied in fields other than the testing of internal combustion engines. Any situation presenting limited linear movement in a hostile environment may present a requirement for the technique described. WHAT WE CLAIM IS:

1. An inductive coupling for use in an internal combustion engine and capable of transferring electrical signals from a reciprocating piston to an associated cylinder block, which includes a core of magnetic material carried by the cylinder block and having a portion which extends parallel to the direction of linear movement of the piston and of a length greater than the maximum extent of said movement, a first coil carried by the piston for movement therewith and formed around said portion of the core, and a second coil carried by the cylinder block in a fixed position relative to the core and formed around part of the core other than that over which the first coil is able to move, the arrangement being such that the inductive coupling between the two coils remains constant regardless of the relative positions of the two coils.

2. A coupling as claimed in Claim 1 in which the core is formed into a closed magnetic circuit.

3. An inductive coupling for use in an internal combustion engine substantially as herein described with reference to the accompanying drawings.