DEVICE FOR MONITORING INJECTION OF FUEL

Abstract: An arrangement for monitoring injection of fuel in an internal combustion engine, especially a compression ignition engine, in which fuel is injected into the or each cylinder via a fuel injector, comprises a polymeric piezoelectric pressure sensor (17), preferably in the form of a coaxial cable that is immersed in fuel that is in or in communication with a fuel injector (1) to sense pressure changes in the fuel. The sensor may be located in the high pressure line or in the low pressure return fuel line. In one specific embodiment, a coaxial cable pressure sensor is located in the excess fuel drain pipe (16) of a fuel injector (1). The arrangement has the advantage that it is mechanically very simple, thereby reducing expense of manufacture and maintenance, and yet is able to detect the beginning of fuel injection accurately due to good acoustic impedance matching of the pressure sensor and the fuel.

Description: DEVICE FOR MONITORING INJECTION OF FUEL This invention relates to injection of fuel in internal combustion engines and especially in compression ignition internal combustion engines. It has been proposed, for example as described in German Specification No. 3,131,541, to incorporate a piezoceramic sensor in a fuel injector in order to monitor the start of injection of the fuel into the engine cylinder. However such arrangements suffer from a number of disadvantages. For example, the design of the mechanical coupling between the sensor and the injector value assembly is relatively complex and therefore expensive, and maintenance and repair of the device can be time consuming. According to one aspect, the present invention provides an arrangement for monitoring injection of fuel in an internal combustion engine in which fuel is injected into the or each cylinder via a fuel injector, which comprises a polymeric piezoelectric pressure sen¬ sor that is immersed, or arranged to be immersed, in fuel that is in, or in communication with, a fuel injector, thereby to sense pressure variations in the fuel. The arrangement according to the invention has the advantage that, because the piezoelectric sensor is arranged to detect pressure changes in the fuel, it is possible to dispense with much of the mechanical coupling arrangement between the sensor and the mecha¬ nical parts of the injector such as the valve assembly, thereby reducing the cost of the arrangement. Also, the reliability of the arrangement can be improved due to the removal of the mechanical coupling arrangement, and maintenance of the injector can be facilitated since the piezoelectric element is relatively accessible and the number of mechanical parts is reduced. It is not necessary for the pressure sensing element to be located within the fuel injector, and it may be located in one of the fuel lines, either in the high pressure line that conveys fuel to the injector or in the low pressure line that returns excess fuel from the injector, provided that the fuel line communicates directly with the injector. If the sensor is not located in the fuel injector, it is preferably located in the high pressure line, i.e. the line that conveys fuel to the injector since the signal to noise ratio that can be obtained in the high pressure line is greater than that in the low pressure line. Whether it is appropriate to incorporate the sensor in one of the fuel lines or in the fuel injector itself will depend on a number of considerations including whether the sensor is a permanent installation or whether it is used simply for an initial adjustment of the engine, whether the sensor is being incorporated into a new or an existing engine, the maximum temperature that the sensor is intended to experience and whether or not any modification of the injector is warranted for other reasons. According to a preferred aspect of the invention, in which the sensor is located at least partly in the fuel injector, there is provided an arrangement for monitoring injection of fuel in an internal combustion engine, which comprises a fuel injector comprising an injector housing having an injection orifice through which fuel is injected, a valve element for controlling flow of fuel through the injection orifice, and a drainage passage for removal of excess fuel from the valve element, the arrangement including an elongate polymeric piezoelectric pressure sensing element that is arranged to be immersed in the excess fuel and to sense pressure variations in the excess fuel. Preferably the drainage passage for removal of excess fuel is removably connected to an excess fuel recovery line and the pressure sensing element extends from the fuel recovery line, or at least the end thereof, into the drainage passage in the injector. The piezoelectric pressure sensor may have any of a number of configurations. Preferably it is elongate in form, for example it may be in the form of a thin ribbon or a coaxal cable, and it may be used either in a discrete length or in a continuous, indefinite length. Where the sensor is located wholly in one of the fuel lines, it may if desired be positioned within the main body of the line although it is preferred for it to be positioned in a blind side extension of the line so that flow of fuel along the line is unhindered. In the case where the sensor is located in the fuel injector it may be entirely located within the drainage passage and optionally also the fuel recovery line, and at least one electrode or current carrying line asso¬ ciated therewith extends through the wall of the fuel recovery line to the exterior thereof, the other electrode or current carrying line either also extending through the wall of the recovery line or being earthed to the injector housing. Where the sensing element is used as a continuous length the sensing element itself may extend through the wall of the fuel recovery line to the exterior thereof. Preferably the piezoelectric sensing element is in the form of a coaxial cable having a piezoelectric dielectric. A number of such cables have been pro¬ posed, and the preferred cables for use in the arrange¬ ment according to the invention are as described in British Patent Applications Nos. 2,150,345A and 2,150,346A, the disclosures of which are incorporated herein by reference. These cables preferably have a central conductor that is formed from a low melting point metal, by which is meant a metal having a melting point below, or at substantially the same temperature as, the melting or softening point of the piezoelectric polymer, to enable the dielectric to be oriented when the cable is manufactured. The preferred polymers for forming the piezoelectric sensing element include viny- lidine fluoride homo and copolymers, and especially polyvinylidine fluoride (PVF2). Such piezoelectric pressure sensing elements have the advantage that they can be supported by the fuel recovery line, e.g. at the end of the recovery line that joins the drainage passage in the injector or by a coupling element bet¬ ween the drainage passage and the recovery line, thereby allowing easy access to, and removal of, the sensing element, and yet the element can extend a significant distance along the drainage channel into the injector housing. In the most usual form of injector, the drainage passage comprises a chamber in the injector housing and a fuel recovery conduit leading from the chamber, the chamber enclosing a spring for biassing the valve assembly in its closed state. In this form of injec¬ tor, the pressure sensing element is preferably located in the recovery conduit for ease of maintenance, but preferably extends as far as possible toward the valve assembly. Usually the sensing element will extend substantially as far as the chamber, but it is possible, if appropriate modifications are made to the housing, for the sensing element to extend into the chamber. In contrast with the previously proposed injec¬ tors, for example as described in German Specification No. 3,131,541 and Motortechnische Zeitschrift 43 (1982) 10, it has been found that accurate deter¬ mination of the start and duration of fuel injection can be made by monitoring the pressure fluctuations in the fuel, thereby obviating the necessity of mechani¬ cally coupling the sensing element to the valve assembly, and considerably reducing the complexity of the arrangement. It is believed that the ability to monitor the fuel injection in this way is due partly to the improved sensitivity of the polymeric pressure sen¬ sors as compared with piezoceramics, and partly because of the fact that polymeric piezoelectric materials exhibit considerably better acoustic impedance matching with the fuel, whereas piezoceramic materials will exhibit poor acoustic impedance matching with the fuel and thereby cause a reflection of the acoustic signal at the sensor/fuel interface. In order to improve the signal obtained by the sensing element and reduce the level of noise transmitted via the injector housing, it is preferred that, at most, only a minor part of the element, and especially substantially none of the ele¬ ment, is in contact with the injector housing. Thus, although in the broadest aspect of the invention, the sensing element may be freely suspended within the drainage passage, it is preferably positioned in the drainage passage by means of a support member. The support member may take any suitable form, i.e. one that spaces the sensing element from the housing and allows the fuel to contact the sensing element. The preferred form of support member comprises a hollow metal tube or pin within which the pressure sensing element, or a part thereof, is located, the metal tube or pin preferably having at least one aperture therein to allow communication of the excess fuel with the sensing element. Although such polymeric piezoelectric materials are considerably more sensitive to high temperatures than piezoceramic materials, and will suffer from depo¬ larizing at temperatures normally associated with the running of internal combustion engines, it is observed that the temperature rise of the pressure sensor can be kept within acceptable limits due to the cooling effect of the fuel. The number of piezoelectric sensors that are employed will depend on various factors including the particular nature of the data processing unit and feed¬ back control. Sometimes it may be desirable to employ a sensor for each fuel injector in the engine although in many cases only a single fuel injector will need to be monitored. Also it is possible to employ sensors in the excess fuel line in addition to sensors in the high pressure fuel line in order to obtain information regarding the duration of injector needle lift as well as determining the point at which needle lift occurs. Several embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a side sectional elevation through a fuel injector according to the present invention; Figure 2 is a view of a support member for the sensing element used in the fuel injector of figure 1; Figure 3 shows an alternative form of injector accord¬ ing to the invention; and Figure 4 shows a sensor and associated mounting that is inserted in a high pressure fuel line. Referring to the accompanying drawings, a fuel injector 1 comprises a housing 2 having a coupling 3 to a fuel line 4. The housing has an injection fuel passage 5 leading from the fuel line 4 to an injection orifice 6. The injection orifice 6 is normally closed by means of a valve assembly comprising a needle 7 that is slidably mounted within the housing. The needle 7 has an upper shoulder 8 that abuts collar 9 in the housing to limit upward movement of the needle, and a seating shoulder 10 that abuts a corresponding internal seat 11 in the housing to limit downward movement of the needle (the needle being shown in the drawing at an intermediate position between its two extremes of position). The needle 7 is biassed to its downward position in which it closes the injection orifice 6 by means of a helical spring 12, one end of which bears on a valve disc 13 connected to the needle 7 and the other end of which bears on an internal surface in the injec¬ tor housing or on a further disc 14 which may be pre¬ sent in order to adjust the biass of the spring 12 on the needle 7. The spring 12 is located in a chamber 19 in the injector housing which receives excess fuel that leaks past the needle 7 and which communicates with a fuel recovery conduit 15 leading to a fuel recovery line 16. A piezoelectric sensing element 17 in the form of a cut length of coaxial cable having a piezoelectric polyvinylidine fluoride dielectric is located in the fuel recovery conduit 15 and extends from a connection piece 18 between the conduit and the recovery line 16 substantially to the chamber 19, the connection piece 18 also functioning as a feedthrough to allow wires 20 connected to the inner and outer conductors of the pressure sensing element 17 to pass through the wall of the recovery line 16. The sensing element is seated within the recovery conduit 15 by means of a steel pin support member 21 as shown in figure 2. The steel pin preferably has a length of about 40.5mm, an outside diameter of 1.9mm, a wall thickness of 0.2mm, and is provided with at least two apertures 30 in its wall of 3mm length and 1mm width. In operation, fuel is transmitted to the fuel injector 1 by a fuel pump (not shown) via the fuel line 4. The fuel pressure in the fuel line 4 is varied cyclically to correspond with the intended injection timing, in such a way that when the fuel pressure is increased, it overcomes the bias of the spring 12 on the needle 7, causing the needle 7 to lift and open the injection orifice 6. The movement of the needle 7 and disc 13 causes the pressure of the excess fuel in the chamber and recovery conduit to vary, and the variation in fuel pressure is monitored by the piezoelectric sensing element 7 which sends the signals to a pro¬ cessing unit (not shown). An alternative form of fuel injector is shown in figure 3. This form of fuel injector is as shown in figure 1 with the exception that the pressure sensing element 17 is located within a blind tube 23 which com¬ municates with the chamber 9 in the injector housing. In this arrangement excess fuel is recovered via a separate conduit 24. Figure 4 shows an alternative arrangement in which a blind side extension 41 is formed in a high pressure fuel line 42 that takes fuel from a distributor pump to a fuel injector. The side extension is formed by means of a "T" piece 43 and extension pipe 44 and is closed at its end by means of a metal plug 45. A length of piezoelectric coaxial cable 46 having a low melting point central conductor, polyvinylidine fluoride dielectric and silver paint outer conductor is located in the extension pipe 44 and extends up to the main fuel line 42. The central and peripheral electrode of the coaxial cable are connected to a pair of terminals 47 and 48 by means of a crimp connector as described in European Patent Application No. 86305571.1 and which is encapsulated in a mass of resin 52 a pair of solder joints 49 and 50, the end of the crimp connector abutting the plug 45 in order to relieve any strains acting on the solder joints 49 and 50 due to the pressure pulses in the fuel. The terminals 47 and 48 extend through the plug 45 and are insulated from it by means of glass or cured resin insulators 51.

Claims: CLAIMS : 1. An arrangement for monitoring injection of fuel in an internal combustion engine in which fuel is injected into the or each cylinder via a fuel injector, which comprises a polymeric piezoelectric pressure sen¬ sor that is immersed, or arranged to be immersed, in fuel that is in, or in communication with, a fuel injector, thereby to sense pressure variations in the fuel. 2. An arrangement as claimed in claim 1, wherein the piezoelectric pressure sensor is an elongate pressure sensor. 3. An arrangement as claimed in claim 1 or claim 2, wherein the pressure sensor is immersed, or arranged to be immersed in fuel that flows toward the fuel injec¬ tor. 4. An arrangement as claimed in any one of claims 1 to 3, wherein the pressure sensor is located in a blind side extension of a fuel line so that flow of fuel along the line is not hindered. 5. An arrangement as claimed in claim 1 or claim 2, wherein the pressure sensor is located within a fuel injector. 6. An arrangement as claimed in claim 5, wherein the pressure sensor is arranged to be immersed in the excess fuel. 7. An arrangement for monitoring injection of fuel in an internal combustion engine, which comprises a fuel injector comprising an injector housing having an injection orifice through which fuel is injected, a valve element for controlling flow of fuel through the injection orifice, and a drainage passage for removal of excess fuel from the valve element, the arrangement including an elongate polymeric piezoelectric pressure sensing element that is arranged to be immersed in the excess fuel and to sense pressure variations in the excess fuel. 8. An arrangement as claimed in claim 7, wherein the pressure sensing element is located within the drainage passage. 9. An arrangement as claimed in claim 8, wherein the drainage passage for removal of excess fuel is removably connected to an excess fuel recovery line, and the pressure sensing element extends from the fuel recovery line into the drainage passage in the injec¬ tor. 10. An arrangement as claimed in claim 9, wherein at least one electrode associated with the pressure sensing element extends through the wall of the fuel recovery line to the exterior thereof. 11. An arrangement as claimed in claim 9, wherein the pressure sensing element extends through the wall of the fuel recovery line to the exterior thereof. 12. An arrangement as claimed in any one of claims 7 to 11, wherein the drainage passage in the injector comprises a chamber in the housing and a fuel recovery conduit leading from the chamber, and the pressure sensing element, or at least part of the pressure sensing element, is located within the recovery con¬ duit. 13. An arrangement as claimed in claim 12, wherein the pressure sensing element extends along the conduit substantially up to the chamber. 14. An arrangement as claimed in any one of claims 7 to 13, wherein the pressure sensing element is so arranged that substantially none of the element is in contact with the injector housing. 15. An arrangement as claimed in any one of claims 7 to 14, wherein the pressure sensing element is posi¬ tioned in the drainage passage by means of a support member. 16. An arrangement as claimed in claim 15, wherein the support member is in the form of a hollow metal pin or tube within which the pressure sensing element, or at least a part thereof, is inserted. 17. An arrangement as claimed in claim 16 wherein the support member has at least one aperture in the wall thereof to allow communication of the excess fuel with the pressure sensing element. 18. An arrangement as claimed in any one of claims 1 to 17, wherein the pressure sensing element is in the form of a coaxial cable having a piezoelectric dielectric. 19. An arrangement as claimed in claim 18, wherein the coaxial cable has a central conductor formed from a low melting point metal. 20. An arrangement as claimed in any one of claims 1 to 19, wherein the pressure sensing element comprises a vinylidine fluoride homo- or copolymer. 21. An arrangement as claimed in claim 20, wherein the pressure sensing element comprises polyvinylidine fluoride. ******

Inventors: LIESS HANS-DIETER, STERN MARIO, SUDWORTH KEITH, LIESS, HANS-DIETER, STERN, MARIO, SUDWORTH, KEITH
Applicants: RAYCHEM GMBH, RAYCHEM LTD, RAYCHEM LIMITED
Application year: 1986
Main classification: F02M65
IPC codes: F02M65, G01L23