GB2098756A

GB2098756A - Fibre optic vehicle control arrangements and methods

Info

Publication number: GB2098756A
Application number: GB8115345A
Authority: GB
Original assignee: ITT Industries Ltd
Current assignee: ITT Industries Ltd
Priority date: 1981-05-19
Filing date: 1981-05-19
Publication date: 1982-11-24
Also published as: GB2098756B

Abstract

The optical radiation of a spark produced by a spark plug (1) in a combustion chamber of an internal combustion engine, or the emission radiation spectrum produced upon burning of a fuel/air mixture in the combustion chamber, is collected by one end (3) of an optical fibre (2) directly (or indirectly) coupled to the combustion chamber. The collected radiation is detected via the other end (4) of the optical fibre. Pulses of radiation thus detected when the engine is firing can be counted (8) for use in an electronic tachometer or analysed in a optreal spectrum analyser for use, in determining and/or controlling in a closed loop control system the fuel/air ratio of the mixture being burnt. <IMAGE>

Description

SPECIFICATION Fibre optic vehicle control arrangements and methods This invention relates to the operation and control of internal combustion engines.

Internal combustion engines operating on either the two-stroke or four-stroke principle require accurate control of the fuel air mixture to provide maximum efficiency over a range of operating conditions. At present the fuel air mixture is provided either by a carburettor which mixes the vapourised fuel with air or by a metering pump which injects a measured quantity of fuel into each engine cylinder in each operating cycle. Both these techniques suffer from the disadvantage that it is very difficult if not impossible to provide a sufficient degree of feedback from the engine to control the fuel air mixture to the optimum value for every condition of engine load, speed and power output.

Under conditions where the fuel air mixture is too weak an internal combustion engine loses power, and the relatively high combustion temperatures produced lead to the formation of oxides of nitrogen.

If, however, the mixutre is too rich, excessive carbon is produced and unburnt fuel together with carbon monoxide is emitted from the engine exhaust. In both cases, because the engine is not working at maximum efficiency, energy is wasted and atmospheric pollution is generated.

According to one aspect of the present invention there is provided a method of controlling and/or monitoring the performance of an internal combustion engine comprising the steps of arranging one end of an optical fibre such as to collect optical radiation generated in a combustion chamber of the engine, and detecting the collected radiation via the other end of the optical fibre.

According to another aspect of the invention there is provided a fuel/air mixture control system for an internal combustion engine, the system including means whereby metered quantities of fuel are fed to the engine, and optical feedback means coupled to a combustion chamber of the engine and whereby the fuel metering means is, in use, so controlled that the radiation emission spectrum of the fuel/air mixture during combustion is maintained within a predetermined range.

According to a further aspect of the present invention there is provided an electronic tachometer comprising an optical fibre having one end arranged such as to collect optical radiation generated in a combustion chamber of an internal combustion engine, a photodetector arranged to detect pulses of collected radiation via the other end of the optical fibre, means to count the number of pulses detected in a predetermined time and multiply the counted number by a constant appropriate to the number of combustion chambers of the engine, whereby to produce an output signal proportional to the speed of rotation of the engine, and display means to display the output signal.

Embodiments of the invention will now be described with reference to the accompanying drawings in which Figure 1 shows schematically a spark plug fitted with an optical fibre and a block circuit diagram of equipment for use therewith to form a tachometer, and Figure 2 shows schematically an arrangement of apparatus for use in tuning an engine.

The emission spectrum of burning fuel is determined primarily by the ratio of fuel to air in the burning mixture. It is well known that the optimum mixture for maximum engine efficiency and minimum pollution burns with a distinct blue flame. An over-rich mixture burns with a yeilow flame whilst a lean mixture burns with a white flame. Thus, by continously observing the fuel combustion process within the engine combustion chamber, it is possible to determine and affect what corrective action, if any, is necessary to maintain the engine in its optimum operating state.

A modified sparking plug is already known which can assist in the manual adjustment ofthefuel/air ratio to the optimum value in response to the colour of the fuel burn. The colour is observed via a quartz window which takes the place of the ceramic section of a conventional sparking plug. However the use of such a modified sparking plug is limited to when the vehicle is stationary, and it is solely a visual aid.

We have found that monitoring of an ignition spark or the emission spectrum of the burning fuel may be effected via an optical fibre coupled to the engine combustion chamber. This coupling may be direct or via an optical interface, such as a quartz window, and may involve a single optical fibre, a multiplicity of fibres or a fibre bundle. Conveniently a single fibre may be coupled to a termination mounted on a spark plug or glow plug fitted to the combustion chamber, so that one end of the fibre is arranged in the combustion chamber (direct coupling) and the following description generally assumes such a direct coupling.

In general it is only necessary to employ such an optical fibre with one of the cylinders of an internal combustion engine in order to monitor the emission spectrum, however, in the case of multiple carburettors or multiple choke carburettors, one such optical fibre will be needed for each cylinder or set of cylinders served by each carburettor or choke tube.

Since the optical fibre will actually provide more information than just the radiation emission spectrum, as will be described below, in various arrangements it may also be desirable to employ more than one optical fibre in a cylinder and possibly in all cylinders.

If one or more cylinders are provided with such an optical fibre and the resulting optical pulses, when the engine is operating (stationary or moving), are electronically detected and counted, then with the appropriate multiplying factor applied to account for the number of cylinders there results an electronic tachometer. Such an arrangement is shown, somewhat schematically, in Figure 1. A spark plug 1 has an optical fibre 2 sealingly extending through a bore therein so that its end 3 is positioned to collect light from a spark produced by the plug even if there is no ignition of the fuel/air, i.e. when the engine will not start, for the additional purpose of spark detection as described below. The other end 4 of the optical fibre is arranged adjacent a photodetector 5 which is coupled to an amplifier and comparator 6.Block 7 represents control logic for the amplifier 6 and where more than one plug is fitted with an optical fibre this may comprise a fail-safe arrangement operable to select different plugs to produce a tachometer output. The output of the amplifier 6 is applied to a counter and multiplier 8 which counts the number of optical pulses in a predetermined time and suitably multiplies the count by a factor (a constant) to take into account the total number of cylinders. The output of counter and multiplier 8 can be displayed by means of a digital or analogue display 9; and/or connected to further equipment illustrated schematically as block 10 which may comprise, for example, control for other functions of the vehicle.

The presence of an optical fibre in a combustion chamber, and preferably integral with a sparkplug, means that it can also be employed simply to ascertain whether an ignition spark is present or absent in that particular combustion chamber when the engine will not start, without the necessity for removing the spark plug. Since the spark may be different to see with the naked eye via the optical fibre, it is preferable to detect the presence of the spark by means of an electronic detector coupled to the end of the optical fibre opposite to that in the combustion chamber as shown in Figure 1.A photo-diode is a suitable detector and can be connected in a suitable electronic arrangement with, for example, illuminates a neon lamp if sparking is detected. Additionally, the strength of the spark may be determined by monitoring the optical level or pulse width.

If it is required to tune an engine, that is adjust the fuel/air ratio to the optimum value, optical fibres arranged in the/or each cylinder can be employed in either a visual/manual method, as in the known modified spark plug method, or an electronic method.

In the visual/manual method the fuel/air ratio for the/or each cylinder, fitted with an optical fibre as appropriate to the type of carburettor or fuel injection equipment employed, as described above, can be adjusted while the vehicle is stationary. If, however, the optical fibres are taken through the engine bulkhead and appropriately terminated and positioned, it is possible to check the engine performance dynamically, that is when driving along, and thus detect possible carburation, injector or ignition faults, which can be attended to manually when the vehicle is stationary.

In an electronic method the output from the optical fibre/fibres is detected and interpreted electronically and can be displayed to indicate engine performance to the driver and/or can be used in a closed loop control to automatically control the fuel and air intake of the engine, to maximise the engine performance or economy, accordingly, whilst stationary or driving along.

Various methods of interpretation are possible, which methods rely on the fact that an incandescent gas emits radiation over a wide optical bandwidth, from the ultraviolet to the infrared, that is characteristic of the gas constituents. Thus, basically, the radiation collected by an optical fibre may be applied to a spectrum analyser and a closed loop control system arranged to adjust the fuel/air ratio to maintain the radiation emission spectrum detected within a predetermined range.

Figure 2 illustrates the electronic method as applied to a single spark plug (not shown) for so-called "colour temperature" measurement. The optical fibre from this spark plug is separated into three channels 12 by means of an optical coupler and the light so collected is applied to a respective filter 13, 14, 15 which are prime colour filters e.g. red, yellow and blue, or to alternative spectrum detector means, for example a (swept) spectrometer. The light passed by the filters 13, 14 and 15 is detected by respective photo-diodes 16, 17 or 18, each of which has associated therewith a respective amplifier 19, 20 or 21.The output level of each amplifier is normalised under control of block 28, in a respective block 22, 23 or 24, with respect to the engine revolutionary speed and applied to an analyser 25 which correlates the combined "colourtempera- ture" signals applied thereto with reference signals related to the fuel/air ratio and provides a visual display at 26 of the comparative engine performance, and/or automatically adjusts the fueld/air ratio via line 27 to bring the engine performance within predetermined limits. Thus the engine is controlled via optical feedback means.

Alternatively, specific hydro-carbon lines in the spectrum of radiation collected by the optical fibres can be selected using filters with suitable transmission characterstics and either the light level or ratio of these spectral lines can be correlated with fuel/air ratio, and employed for visual display or automatic control of the fuel/air ratio.

Similary the infrared spectrum, or specific areas thereof, can be correlated with fuel/air ratio, or prime combustion by-product lines such as NO2 or CO, and employed as described above.

The information so derived may thus be used to provide for closed loop control of engine performance and a visual indicator to the driver of control status or as an economy driving monitor. The shape of the spectrum, that is the fuel burn characteristics, can provide information as to the rate of burn and the occurrence of detonation or scavenging within the cylinder. The apparatus may be povided in, for example, a relatively simple form for use in the vehicle for engine control, and in a more sophisticated form for garage use in diagnostic and tuning purposes. Control and monitoring of internal combustion engines via direct monitoring of fuel burn is provided by the present invention rather than the pre- or post-ignition information more normally used previously.

The infrared content of the fuel burn spectrum is related to the engine temperature and can be employed to indicate engine temperature. However, external ciimatic conditions can have adverse influences with the resuit that suitable compensation means are required.

As previously mentioned the spectrum includes lines related to NO2 and CO levels. Therefore, by employing narrow band filters on these spectral lines the amount thereof and thus the degree of pollution of the engine emission can be monitored in a simple manner which is suitable for continuous use. Known sensors, such as the zirconium types, can sufferfrom poisoning and are thus unsuitable for continuous use. Thus the invention can provide optical pollution monitoring in situ.

The ignition timing can also be determined from optical fibre burn detection means as described above in combination with an optical or other monitor of crank shaft position, that is top dead centre (TDC). The time between TDC and the gas ignition of one cylinder (normally cylinder 1 or 4) gives ignition timing information, and by comparison with the engine revolutionary speed the performance of the advance and retard can be determined. Either a visual indication of this can be provided for manual adjustment or an automatic control of the advance and retard can be employed.

In a closed loop control system, ignition timing may be simultaneously controlled, for example via a look-up table, such that both fuel/air ratio and timing are adjusted to the optimum.

Whereas the optical monitoring described above generally refers to optical fibres located in spark plugs, it is applicable to both petrol and diesel engines since optical fibres may be alternatively mounted at suitable places in engines combustion chambers and not necessarily in spark plugs.

Tests have shown that conventional optical fibres such as 250 m core silica/silica fibre are capable of withstanding the operating temperatures involved and remain optically transparent in an engine combustion chamber.

Water and oil leaks in the engine, such that water or oil gets into a combustion chamber being monitored, will affect the colour or spectrum of the burn and can thus be detected. Whereas the invention has been described with respect to petrol or diesel fuel, it is also applicable to water injection, alcohol and other possible future fuel systems.

The present invention threfore provides an optical means of observing the fuel burn within an internal combustion engine cylinder or cylinders. The colour or spectrum of the burn is employed to interpret and control the engine performance and can also be employed to determine prime engine by-products, for example.

Claims

1. A method of controlling and/or monitoring the performance of an internal combustion engine comprising the steps of arranging one end of an optical fibre such as to collect optical radiation generated in a combustion chamber of the engine, and detecting the collected radiation via the other end of the optical fibre.

2. A method as claimed in claim 1, wherein collected pulses of optical radiation are detected electronically by a photo-detector.

3. A method as claimed in claim 2, wherein the pulses are electronically counted and the number of pulses counted in a predetermined time is multiplied by a contant whereby to produce an output signal proportional to the speed of rotation of the engine.

4. A method as claimed in claim 1, wherein selected regions or lines of the spectrum of the collected optical radiation are detected and employed to produce an electronic information signal related to the engine performance or a factor determining the engine performance.

5. A method as claimed in claim 4, wherein an optical fibre having one end thereof arranged in the combustion chamber, is separated into a multiplicity of channels via an optical coupler, wherein the radiation collected by each fibre is passed through a respective prime colour filter or a filter with suitable transmission characterstics prior to detector by a respective photo-detector, wherein the output of the photo-detectors are combined to produce a colour temperature signal, comprising the information signal, which is related to the fuel/air ratio of the mixture burnt in the chamber.

6. A method as claimed in claim 4, wherein there are one or more optical fibres per combustion chamber and the collected optical radiation is passed through a respective filter selective to pass radiation specific to a predetermined hydro-carbon line prior to detection by a respective photodetector, the detected radiation being employed to produce a signal, comprising the information signal, related to the fuel/air ratio of the mixture burnt in the chamber.

7. A method as claimed in claim 4, wherein the optical radiation is passed through a respective filter selective to pass radiation specific to the infrared region of the spectrum or areas thereof prior to detection by a respective photo-detector, the detected radiation being employed to produce a signal, comprising the information signal, related to the fuel/air ratio of the mixture burnt in the chamber or the engine temperature.

8. A method as claimed in claim 4, wherein there are one or more optical fibres per combustion chamber and the collected optical radiation is passed through a respective filter selective to pass radiation specific to a predetermined prime combustion by-product line prior to detection by a respective photo-detector, the detected radiation being employed to produce a signal, comprising the information signal, related to the fuel/air ratio of the mixture burnt in the chamber.

9. A method as claimed in any one of claims 4 to 8, wherein the information signal is displayed on a visual display.

10. A method as claimed in any one of claims 4 to 9, wherein the information signal is employed in a closed loop control system to automatically adjust the fuel/air ratio of the mixture to contol the performance of the engine within predetermined limits.

11. A method as claimed in claim 4, wherein there are one or more optical fibres per combustion chamber and the collected optical radiation is passed through a respective filter selective to pass radiation specific to a predetermined prime combus tion by-product line prior to detection by a respective photo-detector, the detected radiation being employed to produce a signal, comprising the information signal, related to the pollution level of the engine emission.

12. A method as claimed in claim 1, wherein the visually observed colour of the collected radiation is indicative ofthefuel/air ratio of the mixture burnt in the chamber.

13. A method as claimed in claim 12, wherein the engine can be tuned by adjusting the fuel/air ratio to produce a predetermined colourforthe collected radiaion.

14. Afuel/air mixture control system for an internal combustion engine, the system including means whereby metered quantities of fuel are fed to the engine, and optical feedback means coupled to a combustion chamber of the engine and whereby the fuel metering means is, in use, so controlled that the radiation emission spectrum ofthefuel/air mixture during combustion is maintained within a predetermined range.

15. Afuel/air mixture control system as claimed in claim 14 and wherein the optical feedback means is simultaneously employed to adjust the ignition timing.

16. An electronic tachometer comprising an op tical fibre having one end arranged such as to collect optical radiation generated in a combustion chamber of an internal combustion engine, a photodetector arranged to detect pulses of collected radiation, means to count the number of pulses detected in a predetermined time and multiply the counted number by a constant appropriate to the number of combustion chambers of the engine, whereby to produce an output signal proportional to the speed of rotation of the engine, and display means to display the output signal.

17. A method of controlling and/or monitoring the performance of an internal combustion engine substantially as herein described with reference to Figure 1 or Figure 2 of the accompanying drawings.

18. An electronic tachometer substantially as herein described with reference to and as illustrated in Figure 1 of the accompanying drawings.

19. A fuel/air mixture control system for an internal combustion engine substantially as herein described with reference to and as illustrated in Figure 2 of the accompanying drawings.