GB2306008A - Method and apparatus for transferring data to and from a reciprocating member of running machinery - Google Patents

Abstract

A method and apparatus for transferring data from a reciprocating member of running machinery to outside the machinery determines, at the reciprocating member, data relevant to at least one condition of interest in the interior of the running machinery, converts the data into electric signals, electrically couples the signals to the rotating part of the machinery, transfers the electrical signals from the rotating part to outside the machinery, and derives from the signals information corresponding to the determined data. As shown data relating e.g. to the temperature and/or lubrication of an i.c. engine piston 7, especially in the area of rings 7a, are transferred to the crankshaft 2 via the connecting rod 8 and the little and large end bearing capacitances, and taken from the crankshaft via a brush 9. Control data may be transferred in the reverse direction.

Description

A METHOD AND APPARATUS FOR TRANSFERRING DATA BETWEEN A RECIPROCATING MEMBER OF RUNNING RECIPROCATING MACHINERY AND OUTSIDE THE SAID RECIPROCATING MACHINERY The present invention relates to a method and apparatus for transferring data between a reciprocating member of running reciprocating machinery and outside the said reciprocating machinery.

In the development of lubricants for reciprocating machinery, such as internal combustion (I.C.) engines, the performance of the lubricant is of critical importance in the piston ring-pack region. The environment is hostile where the lubricant must perform, with e.g. high tempereatures and pressures. The design of lubricants for engines, especially new engines, requires knowledge of the prevailing conditions (e.g. temperature) in this region. Other parameters of interest are for example, ring lift, pressure, piston secondary motion, oil film thickness and acceleration.

Measurements must therefore be made in the ring-pack region whilst the engine is running and it is important to communicate the information from the reciprocating piston assembly to outside the engine.

Traditionally an articulated mechanical linkage, connecting the reciprocating assembly to a stationary part of the engine, is used to carry signal leads from sensors installed in the piston and ring-pack. Normally the linkage consists of two links joined together with hollow hinge pins. The signal leads pass through the hollow pins and here their life is relatively short due to fatigue; typically from 10 to 200 hours, depending upon the number of leads and engine speed.

A linkage is unique to each engine and requires relevant design expertise together with proper working drawings of the engine. Hence it has a high cost plus a long lead time from inception to actually having a linkage in place.

Further, a mechanical device such as a linkage can effect the operation of the engine.

Therefore, there is a need of a cheap and relatively easy method for transferring data in reciprocating machinery which does not require the use of a linkage.

It is an object of the invention to provide such a method.

The invention therefore provides a method for transferring data between a reciprocating member of running reciprocating machinery and outside the said reciprocating machinery, comprising the steps of a) determining, at the reciprocating member, data relevant to the conditions of interest in the interior of the running reciprocating machinery, and converting these data into electrical signals; b) electrically coupling these electrical signals to the rotating part of the reciprocating machinery; c) transferring these electrical signals from the said rotating part; and d) deriving from the said signals information on the data determined in step a).

The invention also provides an apparatus for carrying out the said method for transferring data between a reciprocating member of running reciprocating machinery and outside the reciprocating machinery, comprising means for determining, at the reciprocating member, data relevant to the conditions of interest in the interior of the running reciprocating machinery, and means for converting these data into electrical signals; means for electrically coupling these electrical signals to the rotating part of the reciprocating machinery; means for transferring these electrical signals from the said rotating part; and means for deriving from the said signals information on the data determined at the reciprocating member.

US-A-4,443,754 discloses a method for determining minimum lubricating oil-film thickness under operating engine conditions using electrical capacitance and considers an individual bearing as a capacitance sensor for measuring oil film thickness. Here the bearing is isolated from the other crankshaft bearings by using glass fibre plastic laminate between the bearing back and the bearing housing.

Further, ATA Review January 1978: "A system for assessing the general conditions of lubricating crankshafts", C. Bassoli, G. Cornetti and M. Bilei considers the condition of crankshaft lubrication where all the crankshaft bearings are monitored. The oil films here are considered to behave as resistors.

However, there is no data transfer from and to the piston.

The invention is based upon the idea of using the journal bearings of a running reciprocating machinery for example the crankshaft and connecting rod bearings as an electrical circuit for data transfer. Such an electrical circuit can be resistive or capacitive.

The crankshaft and connecting rod journal bearings, both main, little-end and large-end, operate in the hydrodynamic regime of lubrication, where an oil film separates the journal and bearing surfaces. The journal and bearing can be considered as the electrodes of a capacitor, with the oil as the dielectric medium.

Conventional engine oil is a sufficiently good dielectric for such capacitance measurements to be made readily. The relationship of each bearing capacitor capacitance C, to the bearing eccentricity ratio is described by: EoErA C = ... (1) S ( 1 -e2 ) M where A = bearing area S = radial clearance e = eccentricity ratio of the bearing = = permittivity of free space Er = relative permittivity of the oil The eccentricity ratio is zero when the bearing and journal are concentric, unity when the surfaces are touching. Equation (1) assumes that the capacitor is cylindrical, completely filled with oil and operating with no cavitation.

The invention can be used to communicate between, for example, the reciprocating piston assembly and the stationary parts of an I.C. engine via the rotating crankshaft. The communication can be bi-directional, i.e.

it is possible to send information to the piston, for instance to instruct a circuit to switch on and then to collect data from the piston. The crankshaft is assumed to be isolated from the stationary parts of the engine (crankcase, cylinder block, etc.) when the engine is operating and if not, it must be suitably modified.

The invention will now be described by way of example in more detail with reference to the accompanying drawings in which: Fig. 1 represents schematically the principle of the invention; Fig. 2 represents the simplified equivalent capacitance circuit of Fig. 1 together with additional instrumentation for data transfer.

Referring now to Fig. 1 a simple single cylinder I.C.

engine and the pertinent bearings (little end, large end, main) together with the piston assembly that contribute significantly to the capacitances (little endl Clarge end, Cmain 1 Cmain 2 Cpiston) between the crankshaft 2 and the stationary parts (crankcase 6, cylinder block 1 etc.) of the engine are shown schematically. Reference numeral 3 represents a spark plug. The camshaft (not shown for reasons of clarity) is assumed to be driven by an insulating drive (not shown for reasons of clarity), effectively isolating the valve train capacitances from the crankshaft. Reference numerals 4 and 5 represent a flywheel and an electrical insulator respectively.

Reference numerals 7, 7a and 8 represent the piston, piston rings and connecting rod respectively. Signal transfer from the piston 7 to outside the engine can e.g.

take place by applying an ac signal which contains the information of interest across Clittleend. This signal is ac-coupled to the crankshaft 2 via Clarge-end and loaded by the main bearing capacitances. An electrical brush 9 provides ohmic contact to the crankshaft 2 and is used to pick up the signal which is measured in a measuring system 10 and can be processed further in any suitable manner.

Fig. 2 shows the simplified equivalent circuit for the crankshaft capacitance of Fig. 1. The same reference numerals as in Fig. 1 have been used. The two main bearing capacitances are in parallel. For each individual cylinder assembly of an I.C. engine, the respective connecting-rod to large-end, connecting-rod to little-end and piston/rings to cylinder wall capacitances are in series: 1 1 1 1 = ~~~~~~~ + ~~~~~~~~ + ~~~~~ Cseries Clarge-end Clittle-end Piston.

The dimensions and actual operating oil film thickness of each bearing determine its capacitance.

Hence the instantaneous crankshaft capacitance (Ctotal(B)) is due to contributions from each of the bearings: Ctotal (0) =Cmainl (0)+Cmain2 (0)+Cseries (0) . . . (2) where o is the crankangle.

A simple modification to the engine, isolating the engine crankshaft from the dynamometer brake (not shown for reasons of clarity), ensures that main bearing capacitance are not shorted and hence the signal can be taken from the rotating crankshaft. The isolation can be achieved e.g. by insulating the flywheel from the crankshaft with e.g. glass reinforced plastic laminate.

A typical example illustrating the use of the invention is the real-time measurement of piston temperature (behind the top ring groove) in a running I.C. engine. Knowledge of piston temperatures in operating I.C. engines are of importance in the design of new lubricants and components. In fig. 2 reference character A represents piston-mounted parts.

A temperature sensor 11 such as a thermistor or temperature sensitive capacitor is installed in the piston. The sensor output is conditioned and the temperature signal is converted by an electronic circuit 12 into, for example, a frequency proportional to temperature. The circuit is mounted on the inside of the piston skirt. This signal with suitable interfacing is applied across the little-end bearing capacitance. This is accomplished by making a connection to the connecting rod, for example by utilising a wire or a spring loaded contact, and a return connection from the piston body.

The signal can be picked up externally from the crankshaft by means of an electrical brush or (rotating) capacitance. The frequency is measured by a suitable meter and by using the known frequency to temperature transfer function, the temperature can be obtained.

Advantageously, the piston temperature is sensed by a thermistor, which e.g. is a negative temperature coefficient resistor (i.e. the resistance falls with increasing temperature). A constant current passed through the thermistor produces a voltage drop across the device; this voltage is proportional to the resistance.

This temperature dependent voltage is applied to a voltage to frequency converter (VFC). (A VFC is an oscillator whose frequency output is proportional to the magnitude of the input voltage.) The circuit is calibrated to determine the temperature to frequency transform. Advantageously, the circuit is powered by a battery and both are mounted on the inside of the piston skirt. The skirt runs at a lower temperature (typically 120 OC) than the upper parts of the piston and is therefore a less hostile environment for mounting the circuitry. The thermistor is mounted in a pocket in any manner suitable for the purpose and is fixed in position using e.g. high temperature epoxy resin. The sensor connecting wires are led to the circuit by attaching them to the inside surfaces of the piston and are again attached using epoxy resin.The VFC output is applied across the piston to connecting rod capacitance, Little end Various methods of making this connection to the connecting rod are known to those skilled in the art e.g.

by utilising a wire or a spring loaded contact, and a return connection from the piston body. The signal is taken-off externally from the engine, by for example an electrical brush or (rotating) capacitance, and comprises an amplitude modulated carrier frequency. The temperature information is contained in the carrier whose frequency changes with piston temperature. The amplitude modulation of the signal is due to the varying crankshaft capacitance occurring during normal engine operation. The nominal oscillator frequency is chosen such that it is much higher than the frequency of the amplitude modulation. If the temperature variations are slow, in the order of many seconds, the received signal can be fed directly into a frequency meter, the reading noted and the temperature obtained from the temperature to frequency transform.

Other methods can be used to recover the temperature information, for example, the signal can be amplified to remove the amplitude modulation content and be then applied to a frequency to voltage converter (FVC). This method can be used where the temperature is changing rapidly and the data needs to be stored in for example a personal computer using a suitable data acquisition card.

The transform of the FVC is required to obtain the temperature data.

Multiple channels can be accommodated by serially multiplexing the signals to the piston/little-end capacitance or alternatively by mixing the frequencies from each sensor (each must cover a separate frequency range) and transferring all the information simultaneously.

This latter method involves separating the received signal into the original constituent frequencies by frequency selective circuits. The temperatures are determined from knowledge of the relevant channel frequency to temperature transfer functions.

It will be appreciated by those skilled in the art that various other sensors can be installed on the piston to measure other parameters of interest, for example, ring motion, second land pressure, piston displacement, oil film thickness etc.

As already indicated in the foregoing, modifications to the engine may be required, e.g.

1) Isolation of the crankshaft: For a normally operating I.C. engine the two main causes of the crankshaft not being isolated from the stationary parts of the engine are due to the sub-systems connected downstream of the flywheel and to chain driven valve trains. The electrical impedance of the valve train can be small, effectively swamping the impedance of the bearings and this may also be the case for the components fitted downstream of the flywheel.

Isolation of the crankshaft from the flywheel can be achieved using glass reinforced plastic laminate of suitable mechanical and electrical properties, for example, by ensuring that the flywheel bolts do not electrically come into contact with the flywheel. In an automobile the clutch assembly may provide sufficient isolation.

If the camshaft is operated via an insulating drive, for example a rubber and fibre toothed belt, no further isolation is necessary. However, a chain driven camshaft may require a sprocket to be isolated in a similar way to that suggested above for the flywheel. The characteristics of each engine need to be considered to decide if isolation is necessary; some chain driven camshafts already use fibre sprockets for quiet running and normally these provide the necessary isolation.

2) Connection of the signal from the piston mounted circuit to the connecting rod: An electrical connection is required between the circuit and the connecting rod. This can be accomplished by using flexible wire. A guide made from a tension spring, e.g. the outer of a Bowden cable can be utilized to hold and restrict the movement of the wire and hence increase the wire life. One end of the spring is connected to the piston and the other end to the connecting rod, remembering that at least one end must be isolated from either the piston or the connecting rod to ensure that the little end capacitance is not shorted.

The signal wire is fed through the inside of the spring and connected to the connecting rod. A suitable connection can be made by drilling and tapping a small hole in the connecting rod and securing the wire by using a screw.

A more robust alternative method is an insulated spring loaded contact which bears on the side of the rod.

Another method is a leaf spring, fastened to the connecting rod, which bears on an insulated contact attached to the inside of the piston bearing. The circuit return is connected to the piston body.

3) Signal transfer from the engine: One simple method used is an electrical brush which provides an ohmic contact to the nose-end of the crankshaft. An extension to the shaft may be needed to provide sufficient length of clear area for the brush. In its simplest form the brush can be copper earthing braid, spring-loaded on to the crankshaft and treated with contact lubricant. This system is a primitive slip-ring, which in measurements of large-end bearing capacitance has been found to be more reliable than proprietary devices, in the research environment, at speeds greater than 2500 rpm. Another more robust and longer life method is the use of a rotating take-off capacitor. This effectively is a concentric capacitor with a rotating inner electrode. This device can be made mechanically and electrically robust for a long maintenance-free life.

It will be appreciated by those skilled in the art that the technique of the invention could be applied in the field of condition monitoring, e.g. in large stationary engines and reciprocating compressors. Also if suitably developed the method could provide the communication link from piston located sensors for use by engine management systems. As the control of engines becomes more sophisticated, diagnostics will have an increasingly important part to play in the management of engines.

Knowledge of the historical operating conditions that have prevailed during engine operation will be stored and may be accessed later.

Further, an experiment has been carried out with a diesel engine.

The crankshaft of this engine was not isolated but connected to earth, however, as the engine had a linkage the opportunity was taken to apply the output of an oscillator across the large- end and across the piston capacitors. The results confirmed that this diesel engine behaved similarly to a gasoline engine as regards to the crankshaft capacitance.

Various modifications of the invention will become apparent to those skilled in the art from the foregoing description and accompanying drawings.

Such modifications are intended to fall within the scope of the appended claims.

Claims (11)

1. A method for transferring data between a reciprocating member of running reciprocating machinery, and outside the reciprocating machinery, comprising the steps of a) determining, at the reciprocating member, data relevant to the conditions of interest in the interior of the running reciprocating machinery, and converting these data into electrical signals; b) electrically coupling these electric signals to the rotating part of the reciprocating machinery; c) transferring these electrical signals from the said rotating part; and d) deriving from the said signals information on the data determined in step (a).

2. The method as claimed in claim 1, wherein the reciprocating machinery is an I.C. engine.

3. The method as claimed in claim 1 or 2, wherein said data relevant to the said conditions of interest are temperature and/or displacement and/or pressure and/or acceleration and/or lubricant film thickness.

4. The method as claimed in claim 2 or 3, wherein the electrical signals are coupled to the rotating crankshaft via the large-end bearing.

5. The method as claimed in claim 3, wherein the electrical coupling of the signals to the connecting-rod is via a wire or spring-loaded contact and a return connection from the piston body.

6. The method as claimed in any one of claims 1-5, wherein the electrical signals are picked-up externally by an electrical brush or (rotating) capacitance and processed in a signal measuring system.

7. The method as claimed in any one of claims 1-6 comprising the step of serially multiplexing the signals determined in step (a).

8. The method as claimed in any one of claims 1-6, comprising the step of transferring the signals obtained in step (a) simultaneously.

9. The method as claimed in any one of claims 1-8, comprising the step of communicating bi-directionally between the reciprocating member and stationary parts of the reciprocating machinery via the said rotating part.

10. An apparatus for carrying out the method as claimed in any one of claims 1-9, comprising means for determining, at the reciprocating member, data relevant to the conditions of interest in the interior of the running reciprocating machinery, and means for converting these data into electrical signals; means for electrically coupling these electrical signals to the rotating part of the reciprocating machinery; means for taking off these electrical signals from the said rotating part; and means for deriving from the said signals information on the data determined at the reciprocating member.

11. The apparatus as claimed in claim 10, comprising means for communicating bi-directionally between the reciprocating member and stationary parts of the reciprocating machinery via the said rotating part.