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SAE TECHNICALPAPER SERIES

and

2000-01-2032

A Digital Electronic Solution to Piston Telemetry

G. D. HorlerUniversity of Leeds

D. J. PickenDeMontfort Univ.

Reprinted From: Topics in Lubricants(SP–1550)

International Spring Fuels & LubricantsMeeting & Exposition

Paris, FranceJune 19-22, 2000

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1

2000-01-2032

A Digital Electronic Solution to Piston Telemetry

G. D. HorlerUniversity of Leeds

D. J. PickenDeMontfort Univ.

Copyright © 2000 CEC and SAE International.

ABSTRACT

This paper describes the design, development andoperation of a digital electronic piston telemetry system.A feature is the multiplicity of operating modes, includingtwo-way communication. The system has beendemonstrated to work with thermocouples andaccelerometers embedded in the piston of a very smallengine at speeds of over 2000rev/m.

The piston-mounted components can be fitted to a pistonas small as 80mm diameter, and the size is reduced withevery modification as smaller more powerful electroniccomponents become available. Typical results are quotedin the paper

INTRODUCTION

The need for more accurate, more localized, moreconvenient and less intrusive measurements of pistonparameters has been realized for many years. Thermaland mechanical loads on pistons continue to increase,and the demands on piston rings to control gas and oiltransport and to minimize friction are continuing asengines are expected to be more efficient and lesspolluting. At the same time, oil condition at high reactionpoints such as at the piston rings must be monitored inorder to improve oil life and hence increase engine lifeand time between oil changes. Small transducers tomeasure temperature, stress, displacement, pressureand acceleration are available, and are being developedto operate in high temperature environments.

The use that can be made of these transducers is oftenlimited by the telemetry system used to convey thesignals from the piston to a receiver outside the enginewhere they can be recorded and processed. Theresearch team, at De Montfort University together withthe authors, set itself the task of developing a telemetry

system which could be applied to the above problems,and could be as versatile as possible when looking at theresponses to particular engine conditions such asacceleration.

CLASSIFICATION OF TRANSDUCER AND SENSOR ELEMENTS

In order to extract data from the piston, it is necessary toconvert the physical signals of interest into electricalsignals using transducers. There are many types oftransducer, each using different methods for signalconversion and each producing various forms of outputsignal. Some telemetry methods rely upon the routing ofsignals to the outside of the engine directly, others usethe transducer signals to modulate the carrier of achosen communication channel. So what types oftransducer are available and what signals do theypresent?

Electro-mechanical transducers may be divided into twobroad categories, active and passive. Active transducersgenerate a signal as a result of some mechanicaldeflection, chemical reaction or illumination; for examplethe Seebeck, photo-electric and piezo-electric effects.Passive or non-generating transducers use the deflectionof a mechanical element to modify (modulate) thecharacteristics of an electrical circuit; such as a variablecapacitance or inductance, resistive strain gauge etc.

In general active transducers produce signals which arenon-linear and which require some form of signalconditioning (amplification and filtering) prior toprocessing or communication. Passive transducers, asindicated, cannot produce signals on their own and musttherefore be connected to an electronic circuit. Modernintegrated circuit technologies now permit conditioningcircuitry to be packaged in a single integrated circuit. Asummary of transducer types is presented in Table 1.

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As indicated in Table 1, there is a considerable choice intransducer availability. It is important that piston telemetrytransducers are optimised in terms of an ability towithstand mechanical and environmental forces and thecapability of providing signals compatible with thecommunications channel to be used, as discussed in thefollowing section.

COMMUNICATIONS CHANNEL

In order to successfully transmit data over a wirelesscommunications channel three areas need to beconsidered, planned and optimised. These are:

• Channel performance in terms of data transmissionrate and its susceptibility to interference and noise.

• The propagation of electromagnetic wavesthrough a medium, attenuation mechanisms and anyassociated constraints.

• Operations protocol or the manor in which thetransmissions are managed.

A brief discussion of these potentially limiting factors isprovided.

CHANNEL PERFORMANCE – Each signal of interest(transducer output), or its sampled version, has abandwidth (signal bandwidth) which may be regarded asthe number of harmonics present in that signal. If thesignal is to be transmitted over a wireless channel withinsufficient bandwidth (channel bandwidth) thenharmonics will be lost and errors will be introduced intothe signal.

All channels, be they copper wire, optical fibre, radiofrequency, infra-red or micro-wave links provide finitebandwidths. The bandwidth limitation in each case is dueto various signal attenuation mechanisms and noise. Inthe case of radio frequency broadcasts, anotherbandwidth limitation is the sub-division of theelectromagnetic spectrum into predefined channels offinite bandwidth centred on a specific frequency, the

carrier frequency; refer to next section onelectromagnetic propagation.

In order to transmit radio frequency data, the signal ofinterest is used to modulate a chosen carrier frequency.There are many modulation schemes, such as thecommon amplitude and frequency modulation techniques(AM and FM respectively) used for radio broadcasts. Thechoice of modulation technique is important for eachsystem has benefits and drawbacks in terms ofbandwidth, noise and implementation circuitry. Thetelemetry systems in the literature have a bias towardanalogue FM, due in part to the improved noise immunityof FM over AM; albeit at the cost of bandwidth. It isanticipated that future piston telemetry systems will adoptdigital frequency modulation techniques such asamplitude, frequency and phase shift keying (ASK, FSKand PSK respectively); this is due to improved bandwidthcapabilities with no compromise in noise immunity,(compared to analogue FM).

ELECTROMAGNETIC PROPAGATION – For enginetelemetry systems a carrier frequency should be chosenwhich minimises signal attenuation. The attenuationmechanisms are due to the crankcase environmentalconditions, physical organisation of the enginecomponents and metal construction. In addition, thecarrier frequency will dictate the type of antenna structureand complexity of transmitter and receiver (transceiver)circuitry. Carrier frequencies used by systems in theliterature include infra-red, microwave, VHF and UHFradio frequencies.

OPERATIONS PROTOCOL – The operational protocolof a telemetry system concerns the flow of data and howthe electronic modules comprising the system aremanaged to effect such a flow. In all of the systemsstudied in the literature this flow is unidirectional, i.e.samples are transmitted from the piston to a receiverpositioned within the crankcase. In several of the systemsreviewed, the multiplexing of transducers onto thecommunication channel gives an impression of flexibility.

Table 1. A Summary of Transducer Types with Examples

Active Passive Integrated

Transducer /Sensor Type K ThermocoupleVariable Capacitance Temperature Sensor

Accelerometer

PhysicalMechanism

Seebeck effect Thermo-dielectric effectProprietaryProbably piezo-electric

Transducer element output signal

C ∝ K/T2 (pF): C= capacitanceK= dielectric constantT= temperature (°C)

Signal Conditioning circuitry

Cold junction compensation and high gain amplifier which can be used as a set pint controller

Blocking Oscillator

Output signalAnalogue10 mV/°C

Analogue, Cyclic waveform.Frequency proportional to Temperature

Analogue

Integrated solution Yes No Yes

Other output signal formats.

DigitalPulse Width ModulatedPWM signals.

No

3

In practice however these systems are rigid and inflexiblein terms of how the samples are gathered i.e. fixedsample rate and fixed sampling order.

In order to achieve the desired flexibility in sampling itwas evident that a more suitable mode of operation wasrequired. To achieve this a bi-directional mode ofoperation was considered. This would allow two-waycommunication of data to and from the piston, enablingre-configurable sampling strategies and alternativemodes of operation.

The aim of this section has been to present in generalterms the extent of the electronic design considerationsnecessary for the implementation of a piston telemetrysystem. A complete treatment of these considerations isbeyond the scope of this paper, however the followingsection considers specific sampling features greatlyextending the capabilities of current telemetry systems.

SAMPLING STRATEGIES

Some of the telemetry systems found in the literatureenable a single sensor to be monitored. In such simplesystems the sensor is usually monitored continually. Ingeneral however most systems employ samplingtechniques. Sampling is performed in order to capturedata in a specific manner or in response to a specificevent or stimulus. However the effects of sampling arealso observed when more than one transducer ismultiplexed onto a communication channel. It is apparenttherefore that the sampling of data is intimately related tothe parametric signals of interest (their dynamic responseand magnitude) and the number and type of parametersof interest.

The purpose of this section is to present theconsiderations associated with the sampling issue,specifically.

• The sampling strategies required for piston andcylinder experimentation.

• The justification for adopting such samplingstrategies into the design.

• The limitations (in terms of sampling flexibility)inherent in the systems found in the literature.

• A proposal of the sampling capabilities required by aflexible telemetry system.

There are four common methods of sampling data frompistons undergoing experimentation. They are brieflydescribed below together with the type of measurementthey allow:

1. Continuous Sampling: In such a system the sensoror transducer is monitored continually i.e. throughoutthe piston cycle and from cycle to cycle. Thus data isavailable for analysis on demand. Such types ofmeasurement were made possible by early pistontelemetry systems where sensor leads were guidedfrom the piston by means of “grass hopper” linkages.

2. Cyclic Sampling: Cyclic monitoring concerns themeasurement and analysis of parameters varying

throughout the course of a piston cycle. This type ofmeasurement has historical origins, such as the‘indicator diagram’, where the piston chamberpressure is plotted as a function of crank angle.

3. Event Sampling: Event monitoring enables thesampling of a signal when a specific condition orevent arises. Cyclic monitoring could be classed asevent monitoring, the event being each degree ofrotation in the cycle. In this instance however theterm is extended to encompass events such assampling a parameter when the piston has reached aspecific temperature or when the piston is at bottomdead centre.

4. Sample on Demand: The sample on demandmonitoring enables a sample to be taken at will. Sucha method could be used for random sampling or tochange the sampling period according to a dynamicengine loading profile. This method is useful for longinterval, regular samples as required in the study ofbore wear or oil degradation.

In terms of operation, the systems found in the literatureenabled continuous monitoring or sampled continuousmonitoring, (temporal multiplexing of transducers directlyto the carrier) only. This is due to the unidirectionaltransmission of data from piston to crankcase receiver,which ensures that the sample rate, sample period andsample order are fixed.

In order to remove this restriction and enable effectivesample on demand, event and cyclic sampling, a bi-directional protocol is necessary. The bi-directionalprotocol introduces the ability to reconfigure the samplingcontrol, thus allowing opportunities such as the ability tomatch the cyclic sample period to engine rev/m in orderto satisfy the Nyquist sampling criteria or the facility tovary the threshold value of an event triggered sampleduring engine run time. Another drawback associatedwith unidirectional battery powered systems is the factthat such systems are continually ‘ON’, consumingpower. A bi-directional protocol could enable the systemto invoke a sleep mode, in order to conserve power.

So far a background and insight into the limitations ofcurrent systems and the possibilities awaiting futuresystems have been presented. In the following section amethod for the classification of piston telemetry systemsis provided, based on these limitations and otherimplementation criteria.

CLASSIFICATION OF TELEMETRY SYSTEMS

Piston parametric data as been acquired using manytypes of devices ranging from simple ‘temperature plugs’to sophisticated electronic methods. There are strengthsand weaknesses associated with all the methods. Thissection examines the general attributes of the variousmethods as found in available systems, Table 2. Toconclude the section an effective means for classifyingtelemetry systems is presented.

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The following is a list of general observationssummarising Table 2.

• Electronic systems offer a greater scope in terms ofdata retrieval.

• Hardwired systems are prone to failure (fatigue) andare unreliable.

• Mechanical linkages are capable of withstandingmany hours of accumulated engine run time,however they are costly and compromise engineintegrity due to the range of engine modificationsrequired for their correct installation and operation.

• Contact point systems introduce sampling andcomplex electronics which are in turn dependent on amechanical make, break action.

• Wireless systems remove the need for a mechanicallink at the cost of a power supply or generator andsignificantly more complicated electronics.

• Radio telemetry requires antennas, a suitable carrierfrequency, modulation scheme, transceiver andcontroller circuitry. Radio waves are capable ofpenetrating various environmental (climactic)conditions as found in engine crankcases.

• Micro-wave telemetry is suspect due to the need forlarger wave-guide structures and susceptibility of

Table 2. Strengths and Weaknesses of Systems found in the Literature.

Strengths WeaknessesMechanical

Temperature plugs

Simple in operation.Easy to fit.No power requirementsNo wiresMinimal alteration to piston

Need to be removed from engine to be tested.Costly test apparatus (metal hardness) and procedure.Sample reports maximum temperature reached.Limited diagnostic information.

PTFE Tube oil sampling

Simple in operation.Easy to fit.No power requirementsNo wiresMinimal alteration to piston/ engine.

Cumbersome.Chemical analysis performed off line.Environmental conditions at point of sample unspecified.

Electronic

HardwireVarious sensors may be used.More than one sensor possible.Continuous data readout

Sensor and power leads prone to fatigue.Sensor lead fatigue may be reduced by using linkages.Linkages compromise engine construction/operation.Expensive to install.

Point Contact Method

Cheaper and not as mechanically complex as linkages.Various sensors may be used.More than one sensor possible.

Modification of piston and crankcase to effect contact.Durability of contact questionable.Power supply.Storage of samples between contacts.Bandwidth limitation imposed by minimum contact time at high rev/m.Unidirectional protocol.Fixed sampling regime.

Low frequency electromagnetic linkage

Non contact.Communication possible throughout cycle.Various sensors may be used.More than one sensor possible.Increased bandwidth.

Modification of piston and crankcase to effect linkage, usually large sump coil.Power supply or generator necessary.Bandwidth limited by physical surroundings. Need modulation and coding.Unidirectional protocol. Fixed sampling regime.

Very High or Ultra High Frequency radio telemetry.

Non contact.Communication possible throughout cycle.Various sensors may be used.More than one sensor possible.Good bandwidthGood noise immunity

Modification of piston and crankcase to effect linkage.Need appropriate antenna structures.Power supply or generator necessary.Bandwidth limited by physical surroundings.Attenuation by engine environment. Need modulation and coding.Unidirectional protocol. Fixed sampling regime.

Micro-wave

Non contact.Various sensors may be used.More than one sensor possible.Good bandwidth

Modification of piston and crankcase to effect linkage.Need complicated antenna structures.Line of sight necessary, multiple receivers necessary.Power supply or generator.Bandwidth limited by physical surroundings.Attenuation by engine environment. Need modulation and coding.Unidirectional protocol. Fixed sampling regime.

Infra red

Non contact.Communication possible throughout cycle.Various sensors may be used.More than one sensor possible.Excellent bandwidth

Modification of piston and crankcase to effect linkage.Need complicated antenna structures.Line of sight necessary, multiple receivers necessary.Power supply or generator.Bandwidth limited by physical surroundings.Attenuation by engine environment. Need modulation and coding.Unidirectional protocol. Fixed sampling regime.

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stray capacitance in circuit design. Line-of-sightcommunication is necessary.

• Infra-red telemetry systems require line of sight andlens technology, attenuation of signals is possible ifoil is present on a lens.

The list of observations presented may be summarisedon a diagram, which to a limited extent may be used toclassify wireless telemetry systems. Two simpleclassifiers are used, the carrier frequency of the system

and the power source. Some systems from the literatureare presented in the classification diagram of Figure 1.

PRELIMINARY SYSTEM BLUE-PRINT

Table 3 presents the features considered necessary for apiston telemetry system with extended capabilities alongwith a justification for each feature.

Figure 1. Telemetry Classification Using Carrier Frequency and Power Generation

Table 3. Feature List for Proposed Piston Telemetry System

Feature Rational

Two-way communication.

• Allow piston functionality to be amended on the fly.

• Allows sampling regime, sampling period and sampling accuracy to be amended.

• Enables on-piston systems to be controlled for power saving etc.License exempt. • Financial burden avoided by removing the need to license data transmission.

UHF radio frequency.

• Remove attenuation problems and line-of-sight criteria associated with visible and infra-red lens based systems.

• Remove need for multiple receivers and line-of-sight required by micro-wave systems.

• Resilient to crankcase atmosphere.

• No line-of-sight criteria.Multiple transducer support • System should be able to sample more than one sensor.

Sampling capability

• Capable of acquiring data from a variety of formats (e.g. analogue, digital and pulse width modulated signals) to the required accuracy.

• Enabled data to be sampled on-demand.

• Enable cyclic data sampling.

• Enable cycle to cycle sampling.

• Enable event triggered sampling.

Digital communications channel.

• Enables the use of micro-controllers for overall system management.

• Enables data storage and sensor addressing.

• Ideal for data fidelity and error checking.

• Compliant with data processing, storage and display.

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DESIGN AND DEVELOPMENT

The development of the telemetry system used aniterative design approach in order to identify anytechnological or physical phenomena preventing practicaloperation. The following examples provide an insight intothe development of the telemetry system in terms of thedifficulties encountered and the experimental approach.

1. Cookie Tin Experiment: The operation of theintended system relies upon digital signals beingtransmitted back and forth between two transceiverunits (piston and crankcase electronic systems)within a metal box (crankcase and cylinder). Inpractice the internal organisation of an enginecrankcase leads to the antennae being sited in closeproximity to one another. This proximity ensures thatconventional models regarding the propagation ofelectromagnetic waves are inappropriate. Thissituation is compounded by the complex geometry ofthe crankcase, the metal crankcase construction andthe presence of metal obstructions such as thecrankshaft, camshaft, connecting rod etc., whichdynamically alter the cavity. Nevertheless the mostappropriate carrier frequency was calculated fromthe internal geometry, and the success oftransmitting and receiving data within the metal tinwas an important result.

2. Electronics into the Piston: A significant challengewas integrating the necessary electronics into asmall piston. The challenges included:

• The integration of all the electronic circuitry(controller, transceiver, transducers and powersupply etc.) into the small volume available withinthe piston; while ensuring minimum modificationto the piston.

• A method of attaching electronic components tothe piston in order to withstand an acceleration of2000g.

• The means for protecting the circuitry fromcrankcase oils and gases.

• The choice of antenna, correct orientation andmounting.

An encapsulation technique using epoxy resin faileddue to the resin interfering with the transceiveroperation. The adopted solution required a suitablehousing to be machined from high temperatureplastic; this was fixed to the piston using conventionalscrew fastenings.

3. Crankcase Electronics: Transmission of data to andreception of data from the piston was achieved by atransceiver and controller unit embedded into analuminium plate which covered an aperturemachined into the crankcase wall, the crankcaseelectronics. An antenna attached to the inner surfaceof this wall penetrated the crankcase volume in order

to create and maintain the communications channel.The crankcase electronics was designed to connectto a personal computer or other monitoring systemby means of an industry standard RS232 channel. Inaddition the crankcase system was extended in orderto accept signals from externally mounted sensors.

4. Static Crankcase Tests: The cookie tin experimentwas repeated using the piston and crankcasesystems designed above. The purpose of these testswere to establish the effects or otherwise of theinternal components of the engine on thetransmission. The testing involved turning the engineby hand so that all orientations of the internalcomponents, piston and crankcase systems wereinvestigated. No adverse effects such as “deadspots” were experienced.

5. Dynamic Crankcase Tests: Successful completionof the static test enabled the dynamic tests to beundertaken. For these tests the engine was driven byan electric motor. The only modifications made to theengine were the machining of the crankcaseaperture, which was then sealed by mounting thecrankcase wall plate, and the removal of a crankcounterweight lobe, to accommodate the pistonelectronics. For dynamic testing the engine was runwith both dry and wet sump conditions. The purposeof the dynamic test established that.

• The communications channel was notsusceptible to Doppler effects.

• The mounting system, electronic circuitry andantenna design was appropriate for the forcesexperienced when driven at up to 1200 rev/m.

• The communication channel was resilient to theforces, motion and environment.

• The battery cell lifetime of one hour.

DESCRIPTION OF FINAL SOLUTION

The final solution is best described by focusing on twoareas, operating protocols and implementationtechnology.

OPERATING PROTOCOLS – The system utilises ahalf-duplex bi-directional protocol, for this allows distinctperiods for data reception and transmission; in thissystem the standby state for all electronic modules(piston or crankcase) is receive. The data transmittedthrough the system consists of packets of data. Eachpacket contains data fields containing informationidentifying the transducer to be sampled, the data sampleitself and other fields which are used for error checkingand synchronisation.

The system permits samples to be taken in a variety ofways; these are tabulated in Table 4.

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IMPLEMENTATION TECHNOLOGY – The technologicalconstraint which had the most impact on the developmentof the system concerned the durability of the componentsand sub-systems, such as the transceiver and powersupply units. Not only were the components subject toextremes in terms of mechanical forces, they were alsosubject to temperature fluctuations and solvent attack.These difficulties were overcome through attention todetail and good design, eg. the use of minimal mass

surface mount components, tight tolerances inmanufacture and the use of silicon fluid for environmentalprotection and vibration damping.

In terms of electronic technology, proprietary circuitswere developed incorporating an off-the-shelf transceiverunit and Microchip PIC micro-controller. A fullspecification is provided in Table 5.

Table 4. Sampling Strategies and Features Supported by the Current System

Type of sample QualifierTransducer location

Description

Sample on Demand

SinglePiston and crankcase.

Data from a specific transducer is sampled and then returned.

MultiplePiston and crankcase.

Data from a specific transducer is sampled and returned and another sample from the same transducer initiated, until instructed to stop.

BatchPiston and crankcase.

On demand, a batch of samples is taken according to a programmable specification including the number of samples and sample period. The samples are stored in memory for subsequent down load.

Triggered Sampling

Internal trigger

Signals from piston mounted accelerometer, temperature etc.

Single Piston onlyData from a specific transducer is sampled under the control of a triggering signal (derived from a piston transducer) and then returned.

Multiple Piston only

Data from a specific transducer is sampled under the control of a triggering signal (derived from a piston transducer) and then returned. On return another sample from the same transducer using the same trigger signal is initiated, until instructed to stop.

Batch Piston only

Under the control of a triggering signal (derived from a piston transducer) a batch of samples is taken according to a programmable specification including the number of samples and sample period. The samples are stored in memory for subsequent down load.

Triggered Sampling

External trigger

Signals from crank timing systems, standard timing systems and temperature sensors etc.

SinglePiston and crankcase.

Data from a specific transducer is sampled under the control of a triggering signal (derived from an external transducer) and then returned.

MultiplePiston and crankcase.

Data from a specific transducer is sampled under the control of a triggering signal (derived from an external transducer) and then returned. On return another sample from the same transducer using the same trigger signal is initiated, until instructed to stop.

BatchPiston and crankcase.

Under the control of a triggering signal (derived from an external transducer) a batch of samples is taken according to a programmable specification including the number of samples and sample period. The samples are stored in memory for subsequent down load.

Pseudo transmit mode Analogue Piston only.

The conditioned analogue output signal from the transducer of interest is used to modulate the carrier directly for a programmed period of time. This allows the system to emulate (for a period of time) unidirectional transmissions.

8

DESCRIPTION OF NORTON VILLIERS ENGINETESTING – The engine used for the telemetry systemdevelopment and testing was a 1962 Norton-Villiers256cc single cylinder air cooled industrial four strokepetrol engine. This engine was chosen for continuity withprevious research work (investigating oil degradation)

coupled with the feature that the cylinder, head, exhaustand carburettor could be removed from the crankcase asa single entity. A single engine formed the basis of thedevelopment rig, (which was powered by electric motor)and the final test engine. Table 6 presents the teststrategy adopted.

Table 5. Telemetry System Specification

Specification

Piston SystemTransceiverCarrier frequencyAntenna typeControllerOscillator frequencySystem sample rate

Transmission protocolError correction

Transducers usedTransducer accessPower packMinimum power requirementsLaboratory MTBFIn engine MTBFPiston borePiston heightPiston strokeMass of instrumented piston

Licence exempt 418 MHz transceiver.416 MHzHelicalArizona Microchip PIC 16C714 MHzSample on demand 15msBatch mode 100 micro-seconds1x1Preamble check algorithmXOR Start algorithmChecksumLJK digital temperature sensor, Type K thermocouple and an accelerometer.Fully controllable, random access.Battery powered, 6V.4.6V, 29mA3 Hours28 minutes70.0 mm66.7 mm66.7 mm270.0g

Crankcase SystemTransceiverCarrier frequencyAntenna typeControllerOscillator frequencySystem sample rate

Transmission protocolError correction

Transducers used

Transducer accessPower packComputer link

Licence exempt 418 MHz transceiver.416 MHzWhipArizona Microchip PIC 16C744 MHzSample on demand 15msBatch mode 100 micro-seconds1x1Preamble check algorithmXOR Start algorithmChecksumLJK digital temperature sensor, Type K thermocouple and a custom made crank timing circuitFully controllable, random access.D.C. regulated mains, 9V, 500mA.RS232

9

RESULTS

During the test procedures outlined in Table 6,experimental data was collected by means of videorecording and the acquisition of test data. Computersoftware was written to store, process and display data.Three significant results are presented demonstrating notonly the satisfactory operation of the hardware but alsoshowing the flexibility of the supporting software.

RESULT 1 – Figure 2 presents a classic 1st order lagsystem. The curves denote cylinder cooling fin and pistontemperature. Heat was applied to the cooling fin and withtime the piston started to heat up. The heat was removedand the combined cooling observed. The transducersused were LJK temperature sensors giving a Pulse WidthModulated signal output which was inversely proportionalto temperature (hence a dip in the graphs). The resultswere captured using a simple (limited) graphicalinterface.

RESULT 2 – Figure 3 shows a repeat of the aboveexperiment using a piston instrumented with a Type Kthermocouple. In this instance the data has beenexported to the Microsoft Excel package.

RESULT 3 – Figure 4 presents a view of the datalogging screen used to set up and control dataacquisition. The window on the right shows a history ofcommunications between the operator and the piston.The left-hand portion of the screen shows how 48samples have been requested from the from the pistonmounted accelerometer. Figure 4b shows a plot of the 48samples.

CONCLUSION

A list of conclusions resulting from the design and use ofthe digital telemetry system are presented in Table 7.Table 8 presents a list of good and bad features of thecurrent version of the telemetry system while Figure 5aand 5b presents two illustrations of instrumented pistons,(early and current models respectively).

Table 6. Piston Telemetry System Testing Matrix

Test Description Type Purpose

1Transceivers in metal cookie tin

StaticEstablish the possibility of close proximity transmission within a metal enclosure.

2Bench test prototype piston and crankcase electronic modules.

StaticVerify design approach, implementation technology and operating methodology.

3Bench test instrumented piston and crankcase wall electronics.

StaticVerify correct operation of system integrated into mechanical components of the engine.

4In situ piston and crankcase test, crankcase aperture left open.

Static Establish correct operation at a distance.

5In situ piston and crankcase test, aperture sealed.

Static/

pseudo static

Establishes correct operation of communication channel and sample on demand facility in sealed engine crankcase. Piston moved throughout cycle to test for dead spots.

6In situ piston and crankcase test, aperture sealed, dry sump.

DynamicInstrumented piston driven through cycle by external electric motor, designed to establish extent of Doppler effect and test robustness of design.

7In situ piston and crankcase test, aperture sealed, wet sump.

Dynamic Ascertain effects of oil splash etc. on circuit performance

8 Vibration table test Dynamic To test and develop the piston triggered sampling facility.

9 Engine tests DynamicMonitor and establish survival rate of the telemetry system and power supply.

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Table 7. List of Conclusions

Conclusions

Communications Channel

1. It has been shown that a 418MHz radio frequency communications channel can be constructed within the crankcase of a small four-stroke petrol engine.

1.1 It has been proven (theoretically and experimentally) that 418MHz is the optimal carrier frequency for engine telemetry due to:

• Minimal attenuation by oil-splash, oil-mist and oil contamination as experienced in infrared systems.• Minimal attenuation due to the wavelength of the carrier frequency exceeding the internal dimensions of the crankcase;

antenna wavelength.• Minimal attenuation due to the moving internals of the engine.• Experimental evidence of transmitting data through air, oil-mist and while submerged in oil.

1.2 It has been shown that a reliable two way digital communication channel may be constructed upon the 418MHz carrier, using the following techniques:

• 1x1 digital data encoding scheme.• Frequency modulation of the 418MHz carrier.

• Half Duplex communications protocol.• Error correction techniques.

1.3 It has been shown that a robust digital piston telemetry system may be constructed using low power license exempt technology.

Engine Construction

2. It has been shown that an instrumented piston may be integrated into and shown to perform within a small four-stroke petrol engine.

2.1 It has been shown through design that minimal modification of the engine components is necessary.

2.2 It has been shown that the antenna structures do not impede, foul or prejudice engine operation.

2.3 The engine has been shown to run without modification to the oil lubrication system, using it’s own wet sump.

Data Sampling Methods

3. It has been shown that the condition monitoring system may be configured, when in use, to sample in a variety of ways.

3.1 It has been proved that the system is capable of sampling data from a number of transducers, outputting various signals.

3.2 The system has been shown to sample on demand a specific transducer using the interface provided, or under the control of a triggering event which may be derived from the piston or from some external source.

3.3 The system has been shown to perform the batch sampling of a specific transducer, in a manner which is programmable, under the control of a triggering event which may be derived from the piston or from some external source.

3.4 It has been demonstrated that the system may be used to continuously output digital data for a specified length of time, Pseudo Transmit mode.

Experimentation

4. The system has been used to measure parameters from the piston of the engine while running.

4.1 Ring groove thermocouple runs 1°C hotter than the land thermocouple above it.

Table 8. List of Features

Good Bad

Multiple transducer capability. Maximum recorded test speed 2200rev./min.

Multiple signal sampling capability. Transceiver drifts out of frequency limits at 74.8°C.

Small size. Insufficient number of micro-controller pins to allow power control of the extra components required to enable trigger sampling and multiplexed transducer connections.

License exempt. The “camera” batteries used do not provide a sufficient power rating.

Low power. Manufacturing quality variable due to fabrication by hand.

Constructed from readily available components.

Withstands engine atmosphere.

Withstands forces when in operation, running at 2200 rev./min.Maximum temperature measured using system, 300°C in oven, 182°C in engine.

Two way communication:- controllable.

A variety of sampling modes supported

11

Figure 2. Static Transducer Test (LJK Pulse Width Modulated Temperature Sensor)

Figure 3. Static Transducer Test (Type K Thermocouple)

12

Figure 4a. Setting Up a Batch Sample of a Piston Mounted Accelerometer

Figure 4b. The 48 Accelerometer Batch Samples Plotted on a Graph

Figure 5a. Early Instrumented Piston

Figure 5b. Current Instrumented Piston

13

REFERENCES

1. Assinis, D. N. and Friedmann, F., “A TelemetryLinkage System for Piston TemperatureMeasurements in a Diesel Engine”, SAE Paper910299, 1991

2. Furuhama, S., Tada, T. and Nakamura, T., “SomeMeasurements of the Piston Temperature in a SmallType Gasoline Engine”, Bulletin of J.S.M.E., 7, 26,pp422-429, 1964.

3. Furuhama, S., and Enomoto, Y., “Piston Temperatureof Automobile Gasoline Engine in Driving on theRoad”, Bulletin of J.S.M.E., 16, 99, pp1385-1400,1964.

4. Alkidas, A. C. and Myers J. P., “Transient Heat FluxMeasurements in the Combustion Chamber of aSpark-Ignition Engine”, J. Heat Transfer, ASMETrans., 104, pp62-67, 1982.

5. Whitehouse N. D., “Heat Transfer in a QuiescentChamber Diesel Engine”, Proc. Inst. Mech. Engrs.,85, 71/72, pp963-975, 1970-71.

6. Dent, J. C. and Suliaman, S. J., “Convective andRadiative Heat Transfer in a High Swirl DirectInjection Diesel Engine"” SAE Paper 770407, 1977.

7. Saraten, A., “Survey of Theoretical and ExperimentalEvaluation of Thermal Loading of Diesel Engines inNorway”, SAE Paper 790819, 1979.

8. Enomoto, T., and Furuhama, S., “Heat Transfer intoCeramic Combustion Chamber Wall of InternalCombustion Engines”, SAE Paper 861276, 1986.

9. Iida, Y., Tanaka, K. and Fuse, S., “Contact PointMethod for Measuring Sliding Face Temperature andits Applications”, SAE Paper 830311, 1983.

10. Barna, G., Brumm, D. and Anderson, C., “An InfraredTelemetry Technique for Making Piston TemperatureMeasurements”, SAE Paper 910051, 1991.

11. Chowanietz, E. and Forman, M., “A Mixed-SignalASIC for Piston Temperature Measurement inInternal Combustion Engines Proceedings of the 7thIEEE International ASIC Conference and Exhibit,pp18-21 1994

12. Campbell, R., Brumm, D., Taylor, T., and Bock, B.,“Modulated Scatterer Microwave Telemetry InsideAutomobile Engines and Transmissions”, AP-S Int.Symp. IEEE Antennas and Propagation, 3, 3,pp1914-1917, 1994.

13. Westbrook, M. H., “A Telemetry System for PistonEngine Research”, Proc. International TelemeteringConference, 1, pp154-161, 1963.

14. Westbrook. M. H. and Munro, R., “ElectronicInstrumentation Techniques in the Development ofPistons and Rings”, Proc. I. Mech. E., 180, 3, G,pp54-69, 1965-66.

15. Munro, R., Laws, A. M. and Rhodes, L. P.,“Techniques de recheche et development concernantles pistons et les segments”, Ingenieurs del’Automobile, 42, pp563-580, 1969. (In French)

16. Allwood, H. I. S., “A Simple Telemetry System ForAcoustic Strain Guages”, Shell Research, 1970.

17. Lawrason, G. C. and Rollwitz, W. L., “A TemperatureTelemetry Technique for Reciprocating Engines”,SAE Paper 670026, 1967.

18. Burrahm, R., Davis, K. J., Perry, W. D. and De losSantos, A., “Development of a Piston TemperatureTelemetry System”, SAE Special Publication onElectronic Controls and Sensors, Int. Con. AndExpo., 898(1-11), 1992.

19. Wiczynski, P., Varo, S. and Galarno, M., “New PistonTelemetry Applied to Spherical Joint PistonDevelopment”, SAE Paper 960056, 1996.

20. Picken, D. J., Thompson, A. L., Fox and Preston, W.H., “Lubricating oil-extraction and chemical analysis”,Experimental Methods in Engine Research andDevelopment, Proc. I. Mech. E. Conference, 1991.

CONTACT

Dr. G. D. HorlerSchool of Electronic and Electrical EngineeringUniversity of LeedsLeedsLS2 9JTUnited Kingdom+44 (0) 113 233 2065+44 (0) 1904 414493ghorler@ee.leeds.ac.ukhttp:\\\www.elec-eng.leeds.ac.uk

Professor D. J. PickenSchool of EngineeringDeMontfort UniversityLeicester.United Kingdom.djp@picken98.freeserve.co.uk